We have, for the first time, provided quantitative data for the EqCr equilibrium and have determined the stoichiometry of adduct formation of [Cp2Ti(III)Cl2]−, [Cp2Ti(III)Cl] and [Cp2Ti(IV)Cl2] and the additives. By studying the structures of the complexes formed by DFT methods, we have established the Gibbs energies and enthalpies of complex formation as well as the adduct structures. The results not only demonstrate the correctness of our use of the EqCr equilibrium as predictor for sustainable catalysis. They are also a design platform for the development of novel additives in particular for enantioselective catalysis.The combination of synthesis, rotating ring‐disk electrode (RRDE) and cyclic voltammetry (CV) measurements, and computational investigations with the aid of DFT methods shows how a thiourea, a squaramide, and a bissulfonamide as additives affect the E What mechanism‐based screening for titanocene catalysis is all about! Combining insights from synthesis and theory with cyclic voltammetry and the rotating ring disk electrode is the deal for understanding not only how but also why condition screening for the titanocene catalyzed radical arylation works. With these mechanistic key features at hand, we can then predict the optimal catalytic reaction condition based on scientific arguments rather than our usual into the blue approach, so that ideally only a few experimental combinations need to be verified. These “predictors” require either the knowledge of the overall mechanism or at least an understanding of the essentials of the catalytic cycle. We chose to illustrate our “predictor” concept with the optimization of electrochemical epoxide arylation. It is only after we exploit widely used and readily available cyclic voltammetry (CV) and DFT techniques to identify the “predictors” of this reaction that we enter the synthesis lab to try our smart guess. For catalysis in single electron stepsqCr equilibrium2TiCl2 in THF (Scheme 2Ti(IV)Cl2] the initial product of electron transfer [Cp2Ti(III)Cl2]− at the electrode must be transformed into arylation catalyst [Cp2Ti(III)Cl], that is—in contrast to [Cp2Ti(III)Cl2]−—easily soluble in THF and can diffuse from the electrode. Increasing the concentration of [Cp2Ti(III)Cl] by halide abstraction from [Cp2Ti(III)Cl2]− will therefore facilitate bulk electrolysis of [Cp2Ti(IV)Cl2]. While [Cp2Ti(III)Cl] constitutes the active catalyst for epoxide arylation, [Cp2Ti(III)Cl2]− provides a catalytic resting state, that prevents undesired catalyst decomposition.Catalysis has shaped our modern society, providing functional molecules, materials, or processes both in the lab and on industrial scale. Substituting stoichiometric reactions by catalytic alternatives offers a conceptionally straightforward approach to a more sustainable, green chemistry.F Scheme .[5] FoqCr equilibrium and therefore bulk electrolysis of [Cp2Ti(IV)Cl2] in THF can be controlled by the addition of supramolecular additives, that bind halides through hydrogen bonding.qCr equilibrium directly translates into the synthetic performance of the catalytic radical arylationAdjusting the relative amounts of both species in a reversible way thus allows a fine‐tuning of the performance of the catalytic system. It turned out that the EqCr equilibrium as predictor for the radical arylation is applicable to bissulfonamides as another class of supramolecular additives. Moreover, it is in accord with quantitative measurements at the rotating ring‐disk electrode (RRDE).qCr equilibrium delivers a complete mechanistic analysis of our predictor. Our study not only leads to a better understanding of the systems already investigated. It also delivers a design platform for the use of supramolecular halide binders in enantioselective catalysis and for their use with complexes of metals other than titanium.Here, we demonstrate that our qualitative analysis of the cyclic voltammograms (CVs) of the EqCr equilibrium includes an electron transfer step and involves species with different redox‐potentials. CV not only allows a characterization of the components of a solution. Relevant data can be obtained in short periods of time and with minor amounts of material (0.02 mmol).A critical aspect for efficient screening is a fast and cost‐efficient technique for a conclusive description of the investigated system. In our case, CVL1L22Ti(IV)Cl2] in THF and the use of the resulting solutions for radical arylation. The CVs Cl2] without additives (black traces), the oxidation waves pertaining to [Cp2Ti(III)Cl2]− have a reduced intensity and that of [Cp2Ti(III)Cl] an increased intensity. This effect is significantly more pronounced for L2 than for L1. We assumed that these effects predict a successful bulk electrolysis and catalytic radical arylation.Our previous studies showed that thiourea L3 (Scheme 2Ti(III)Cl] is visible. This predicts that addition of L3 results in an efficient bulk electrolysis and a successful radical arylation Cl] observed in the CV‐screening, L1 leads to the slowest reaction and lowest yield of 2. L2 and L3 lead to a more active catalytic system giving essentially identical results after 2 h.The performance of the epoxide arylationL1–L3 and the titanocene species. On the reductive sweep (the lower trace) all ligands L form an adduct with [Cp2Ti(IV)Cl2]. This adduct has a more positive reduction potential with L1 and L2 (+160 mV) showing a larger shift than L3 (+80 mV). These differences in the potentials indicate a different strength of the interactions. On the oxidative sweep (the upper trace), for all additives a complex [Cp2Ti(III)Cl2]−*L can be detected. Again, the differences in the shift of the potentials are significant. Interestingly, only L2 and L3 seem to form complexes of the type [Cp2Ti(III)Cl]*L. The shift of the potentials relative to [Cp2Ti(III)Cl] suggest an electron‐donating interaction for L3 (−120 mV) and an electron‐withdrawing interaction for L2 (+110 mV).Besides their usefulness as predictors, the CVs highlight an interesting complexity of interactions between Our CV experiments are an ideal tool for the rapid screening of the additives. For a quantitative analysis, CV merely allows the direct extraction of the redox potentials of the species detected and their diffusion coefficients. More complex information on pre‐equilibria or follow‐up reactions can only be obtained via simulation. One general shortcoming of simulation is that, frequently, several models fit the experimental data. This is especially true for situations involving several steps and a large variety of fitting parameters. We decided to provide quantitative data for our qualitative observations made by CV. To this end, we used the rotating ring‐disk electrode (RRDE).N0. They can be discerned by their individual redox potentials. The currents measured due to their electrochemical reactions are proportional to their concentration at the electrode surfaces and allow quantitative analysis of the composition of the solution. For potentials negative of the equilibrium of a reduction at the disk, the currents reach a plateau representing the diffusion limited current Ilim and can be evaluated by the Levich equation (see Supporting Information).The RRDE set‐up offers major advantages over CV in stagnant solution. In CV, asymmetrically shaped current waves are observed. Therefore, “real” systems cannot be fitted to a physical equation. With a RRDE set‐up this becomes possible as convection results in a time‐independent and well‐defined thickness of the Nernstian diffusion layer. It is composed of a disk and a ring electrode surrounding the disk. Rotation ensures a steady flow of reactants from the bulk solution to the disk. From here, the electrolyte is radially forced out to the ring and the species generated at the disk can be detected with a theoretical collection efficiency 2TiCl2 in THF with 0.2 m NBu4PF6 (TBAPF6). The data are in agreement with results of the Daasbjerg group[2TiCl2. Based on Daasbjerg's work we propose an extended mesh‐scheme for the species present in solutions of Cp2TiCl2 and our additives L (Scheme 2Ti(III)Cl] is not observed in CVs with L and thus not relevant here.We started our RRDE measurements of Cperg group4d, 4eL Scheme . The monL3 and summarize the data for L1–L3 (detailed discussion see Supporting Information).The RRDE measurements will provide the equilibrium constants given in Scheme L3 on [Cp2Ti(III)Cl2]− can be observed directly from the positive shift of the voltammograms detected at the disk iD and the decreasing transfer ratios (IR/ID/N0) for measurements with Cp2TiCl2 and L3 at a rotation frequency f of 25 Hz and a ring potential ER of 0.05 V . A potential of 0.05 V vs. Ag/Ag+ solely allows the oxidation of [Cp2Ti(III)Cl2]− . Thus, only this species is detected at the ring.The stabilizing effect of L3  leads to a positive shift of the reduction potential and a slight decrease of iD in the diffusion limited region at the disk electrode from −1.54 mA cm−2 to −1.46 mA cm−2 Cl2]− in solution  L3.2 Figure  and to a4 Figure . The tran Figure , decreasL3  leads to the formation of a shoulder in the disk current at −0.05V Cl2] with L3 to [Cp2Ti(IV)Cl2]*L3 associated with a change of the diffusion coefficient prior to the electrochemical reaction. If the reaction of L3 occurred after the electrochemical reduction of [Cp2Ti(IV)Cl2], this should not have an impact on the diffusion‐limited current.V Figure , which aD2/3 (D: diffusion coefficient) and to f1/2. Figure iD of [Cp2Ti(IV)Cl2] and with 10 mm of L3 alongside the shoulder current density found for the measurement of L3  as a function of f1/2. The graphical representation of the data yields straight lines. The non‐zero intercept of the line representing the shoulder currents indicates that the current flow is not solely limited by diffusion. Possibly the kinetics of the reduction of the unbound species already play a minor role. We assume that in the solutions with 10 mm of L approximately all [Cp2Ti(IV)Cl2] is bound to L. The different slopes observed for the experiments with base electrolyte and with 10 mmL3 yield the ratio of the diffusion coefficients of [Cp2Ti(IV)Cl2] and [Cp2Ti(IV)Cl2]*L3 according to the Levich equation. The diffusion coefficient D of [Cp2Ti(IV)Cl2] is 1.15 times larger than that of [Cp2Ti(IV)Cl2]*L3 (1.15 with L1 and 1.33 with L2). In the measurement with 1 mmL3 the diffusion‐limited reduction of [Cp2Ti(IV)Cl2]*L3 is observed as a shoulder prior to the reduction of [Cp2Ti(IV)Cl2], as the reaction between [Cp2Ti(IV)Cl2] and L3 is incomplete. From the ratio of this shoulder to the subsequent plateau, the equilibrium constant of association Ka of L3 to [Cp2Ti(IV)Cl2] is accessible. With a value of 1.07 mm−1, L3 lies between L1 (0.69 mm−1) and L2 (1.81 mm−1).According to the Levich equation, the limiting current density at the disk electrode is proportional to III to obtain K1 to K3 Cl2]−, [Cp2Ti(III)Cl2]−*L3, [Cp2Ti(III)Cl] and [Cp2Ti(III)Cl]*L3. These transfer ratios are shown in Figure L3.We studied the composition of the reduced solutions of TiIII species (see Supporting Information for details). The association equilibrium constant K1 of L3 to [Cp2Ti(III)Cl2]− amounts to 0.4 mm−1 . Dissociation of Cl−*L3 from [Cp2Ti(III)Cl2]−*L3 has an equilibrium constant K2 of 3.0 mm . The formation of [Cp2Ti(III)Cl]*L3 has a K3 of 0.7 mm−1 (0.5 mm−1 for L2). This adduct is not observed for L1.The transfer ratios allow the calculation of the equilibrium constants between the TiiD p) with p representing the number of L3 ligands attached to the titanocene.L1 the same slope of 60 mV dec−1 was obtained showing that p is equal to 1. This verifies our initial assumption. The mechanisms of chloride abstraction from the TiIII complexes and activation of the TiIV complexes are likely to be similar for L1 and L3.Therefore, the Nernst equation for this redox system must be linearly dependent on logq) and q = p/2. Thus, we propose the reversible formation of a 2:1 adduct between [Cp2Ti(III)Cl] and L2 in addition to the equilibria shown in Scheme 2Ti(III)Cl] and L2 is considered (in contrast to the 1:1 adduct considered for K1 to K3 given above) a new set of equilibrium constants for the TiIII species has to be calculated . However, it is likely that both adducts are present in the reduced solutions.For d Figure . Thus, tIV (in red) and TiIII species (in green) at concentrations of 2 mm in Ti and L are summarized in Scheme 2Ti(IV)Cl2] is complexed in 40 %–60 % amounts (red numbers) by L1–L3 with L2 being slightly more efficient than the other additives as indicated by the Ka values.The equilibrium constants obtained from the RRDE‐studies together with the relative amounts of the relevant TiL1–L3 have a stronger influence on the equilibria involving [Cp2Ti(III)Cl]. In the presence of L2, essentially no [Cp2Ti(III)Cl2]−*L2 is formed because L2 binds Cl− too strongly. Interestingly, L2 complexes [Cp2Ti(III)Cl] less efficiently than L3 whereas L1 forms no [Cp2Ti(III)Cl]*L1. As a result, the use of L2 results in the highest combined relative amount (77 %) of the catalytically active [Cp2Ti(III)Cl] and [Cp2Ti(III)Cl]*L2. For L1 and L3, the solution contains relatively high proportions of [Cp2Ti(III)Cl2]−*L and [Cp2Ti(III)Cl2]− that constitute the resting state of the active catalyst. This situation may be advantageous when catalyst stability is more important than catalyst activity.The additives qCr equilibrium as predictor for the performance of the bulk electrolysis of Cp2TiCl2 in THF as well as for the titanocene catalyzed radical arylation of epoxides has a sound mechanistic basis. Moreover, the quantitative data obtained allow an accurate prediction of the composition of an electrochemically reduced solution of Cp2TiCl2 containing additives that is essential for a precise control of the reaction conditions. This may be essential for applications on large scale.The RRDE investigations underline that our use of the EqCr equilibrium by DFT methods. The Grimme group has recently developed a powerful multilevel approach to address such situations. It consists of the CREST codemeta‐dynamics (MTD) calculations  populations for a few low‐lying conformers at higher theoretical levels in three steps. First, already relatively accurate B97‐3c[DCOSMO‐RS(THF)]  approximation−1 threshold an even better single point energy is computed at the PW6B95‐D3/def2‐TZVPPAccordingly, we used the xTB, CREST and ENSO programs to determine the structures with the lowest free energy in THF solution for each ligand L and their chloride complexes Cl−*L. As free species, L2 shows higher conformational rigidity than L1 and L3 (for a detailed discussion see Supporting Information). The structures of the most stable conformers were chosen as reference points for the energies of formation of all other complexes. A potential self‐aggregation of L2 in THF is beyond the scope of this study.We started our investigations with the ligands −*L and energies of complexation with respect to the lowest energy conformer of the respective L are depicted in Figure − is bound to both N−H groups of all ligands. The Cl−*L complexes with L1 and L2 show Cv2 symmetry. Cl−*L2 is conformationally rigid in agreement with its X‐ray structure.−*L1 has a second conformer 4.6 kcal mol−1 higher in energy than the one shown with one NHR group rotated by almost 180° and the other bound to Cl−. A second conformer of Cl−*L3 is 2.0 kcal mol−1 higher in energy and has a similar structure to the one shown. In agreement with a previous study on the chloride binding of thioureas, squaramides and sulfonamides,G298.15 for Cl−*L show that L2 binds chloride stronger than L1 and L3. As also pointed out in that study, the strength of chloride binding does not correlate with the pKa values of the different receptors.The structures of the Cl2Ti(III)Cl2]−*L are crucial intermediates in the electrochemical generation of [Cp2Ti(III)Cl] from [Cp2Ti(IV)Cl2]. They provide a mechanism for shifting the EqCr equilibrium to [Cp2Ti(III)Cl] by facilitating chloride abstraction and dissolution of [Cp2Ti(III)Cl2]−*L. Another intriguing aspect is that binding of L to [Cp2Ti(III)Cl] directly impacts the redox properties of [Ti] in the arylation reaction.The supramolecular complexes [Cp2Ti(III)Cl2]−*L together with the corresponding values for ΔG298.15 and ΔH298.15 are depicted in Figure L1 and L2 bind both chloride ligands with the N−H groups, providing complexes that are C2‐symmetric within the limits of accuracy. This is exemplified by the Ti‐Cl bond lengths ([Cp2Ti(III)Cl2]−*L1: 2.545 Å and 2.540 Å, [Cp2Ti(III)Cl2]−*L2: 2.547 Å and 2.550 Å).The structures of −.Curiously, for L1 does not bind to [Cp2Ti(III)Cl] whereas both L2 and L3 do. However, they bind in a different fashion as evident from the shifted oxidation potentials for [Cp2Ti(III)Cl]*L . We analyzed the complex formation starting from [Cp2Ti(III)Cl] and L and included the effect of additional coordination with THF Cl](THF). As for [Cp2Ti(III)Cl2]− both additives bind the chloride ligand with both N−H groups. Adduct formation is disfavored with L1. This is in agreement with the experiment, where no [Cp2Ti(III)Cl]*L1 was observed. The interaction of L2 with the chloride ligand leads to an increase of the Ti−Cl bond length by 0.13 Å. This is in agreement with the experimentally observed positive shift of the redox potential.L3. The favored complexation mode is realized with [Cp2Ti(III)Cl] as starting material. This is due to an intramolecular interaction of one of the sulfonamide groups with Ti that renders an additional complexation of THF superfluous. The coordination of the sulfonamide increases the electron density at Ti in agreement with the experimentally observed negative shift in the redox potential for [Cp2Ti(III)Cl]*L3. Only the adjacent N−H group binds to the chloride ligand.The situation is different for −1 in the RRDE measurements with L2 Cl] and L2 in the adduct formation is possible. The computed structure of the 2:1 complex with one molecule of THF and its ΔG298.15 and ΔH298.15 with respect to the dissociated species are depicted in Figure The slope of 30 mV dec2 Figure  suggestsG298.15 is due to the entropically disadvantageous formation of the complex from four components.Enthalpically, complex formation is strongly favored and the slightly positive ΔL2 binds the second titanocene through one of the carbonyl oxygens. At the same time, the N−H groups each bind to one of the chloride ligands of both titanocenes. This makes L2 a bifunctional ligand and provides an explanation for the broad oxidation wave in the area of Cp2TiCl found in CVs of Cp2TiCl2 and L2. On the oxidative sweep ([Cp2Ti(III)Cl])2*L2 is oxidized first followed by [Cp2Ti(III)Cl] and finally [Cp2Ti(III)Cl]*L2.2Ti(IV)Cl2] and L. This pre‐equilibrium to the EqCr mechanism allows the use of a less negative reduction potential in bulk electrolysis . Figure 2Ti(IV)Cl2] and L1–L3. For L2, the minimum structure of [Cp2Ti(IV)Cl2]*L2 is a van der Waals complex that is 0.3 kcal mol−1 more stable than the complex shown (see Supporting Information for details). It is not discussed here, as it does not suggest a positive shift of the reduction potential.Finally, we investigated the adduct formation between [Cp2Ti(III)Cl2]−*L the formation of the adducts of [Cp2Ti(IV)Cl2]*L is less favorable. The calculated structures show that with the neutral TiIV complex only L2 can interact with both N−H groups. However, they both bind to the same chloride ligand. In the adducts of L1 and L3 only one of the N−H groups is coordinating chloride, the other is pointing away from the complex resulting in a noticeable conformational change of the additive.Compared to the complexes of [CpL2 to [Cp2Ti(IV)Cl2] observed in the RRDE measurements.The computed order of stability of the adducts is in agreement with the stronger binding affinity of 2Ti(IV)Cl2]*L compared to [Cp2Ti(III)Cl2]−*L is most easily rationalized by the negative charge in [Cp2Ti(III)Cl2]− that renders hydrogen bonding more attractive because of the coulomb attraction. We investigated this point by analyzing the exchange reactions shown in Scheme 2Ti(III)Cl2]−*L adducts from their [Cp2Ti(IV)Cl2]*L counterparts.The lower stability of −, [Cp2Ti(III)Cl] and [Cp2Ti(IV)Cl2]. By studying the complexes by DFT methods, we have provided the Gibbs energies and enthalpies of complexation as well as the adduct structures. Our studies show that a balance between activity and stability of the catalyst are vital for reaction efficiency. Changing the inorganic ligand of Cp2TiX2 was not investigated here. Previous investigations2TiBr2 derived catalysts halide abstraction is easier than for complexes derived from Cp2TiCl2. The intricate interactions between the additives and the titanocenes by hydrogen bonding and coordination of polar groups are not only in agreement with the electrochemical data. They also provide a design platform for the development of novel additives for catalysis in single electron stepsWe have introduced bissulfonamides as additives for enabling bulk electrolysis of CpThe authors declare no conflict of interest.As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re‐organized for online delivery, but are not copy‐edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors.SupplementaryClick here for additional data file.


Carbonation of 8,9‐limonene epoxide furnished the 8,9‐limonene carbonate for the first time. Both cyclic carbonates underwent thiol–ene addition reactions to yield linked di‐monocarbonates, which can be used in linear non‐isocyanate polyurethanes synthesis, as shown by their facile ring‐opening with N‐hexylamine. Thus, the selective catalytic route to monofunctional limonene carbonates gives straightforward access to monomers for novel bio‐based polymers.The selective catalytic synthesis of limonene‐derived monofunctional cyclic carbonates and their subsequent functionalisation via thiol–ene addition and amine ring‐opening is reported. A phosphotungstate polyoxometalate catalyst used for limonene epoxidation in the 1,2‐position is shown to also be active in cyclic carbonate synthesis, allowing a two‐step, one‐pot synthesis without intermittent epoxide isolation. When used in conjunction with a classical halide catalyst, the polyoxometalate increased the rate of carbonation in a synergistic double‐activation of both substrates. The  Biopolymers: The selective catalytic synthesis of limonene‐derived monofunctional cyclic carbonates and their subsequent functionalisation via thiol–ene addition and amine ring‐opening is reported. The selective catalytic route to monofunctional limonene carbonates gives straightforward access to monomers for novel bio‐based polymers. Terpenes are a large and diverse class of hydrocarbons naturally occurring in the oils of plants1) and other terpenes have been used in the synthesis of a variety of building blocks,Limonene  and othe2 into the epoxide moieties of 1,2,8,9‐limonene bis‐oxide. A wide range of catalysts for the synthesis of cyclic carbonates from epoxides has been described in literature, including metal complexes, metal organic frameworks, quaternary ammonium salts, imidazolium halide salts and supported ionic liquid phase catalysts.Thus, clean, efficient and scalable routes to these cyclic carbonates are key to sustainable manufacturing of terpene‐based NIPUs. The quaternary ammonium salt used by Mülhaupt is a cheap and relatively efficient catalyst for the insertion of CO2) has previously been investigated  over the cis isomer (cis‐3). Although some catalysts mediate the carbonation reaction at milder temperatures of 75–100 °C and lower pressures in the range of 10–50 bar, these reactions required long reaction times of 16–66 h. Moreover, some systems required the use of organic solvents  yielded 94 % 1,2‐limonene oxide after 1 h reaction time at room temperature using H2O2 as the oxidant.A is highly efficient for limonene epoxidation under these conditions, it was shown to be difficult to recover and lost activity upon recycling. Thus, instead of recycling the catalyst for repeat epoxidation runs, we set out to test whether it could be used in the following carbonation reaction without intermittent epoxide isolation  and the PW4O43− polyotrans‐1,2‐limonene cyclic carbonate (3) and 8,9‐limonene cyclic carbonate (5) using benign oxidants and solvents , a single polyoxometalate catalyst (A) can catalyse both the epoxidation and the CO2 insertion step. Furthermore, we demonstrate effective CO2 insertion to 8,9‐limonene oxide (4) for the first time. Both chiral cyclic carbonates are shown to undergo radical coupling with 1,3‐propanedithiol and react with N‐hexylamine to result in novel hydroxyurethanes as a demonstration of their utility in the synthesis of bio‐based NIPUs.Here, we report the development of such an effective catalytic system that gives access to arbonate  and 8,9‐3[PW4O24] (PTC=methyl tricapryl ammonium) (A) are excellent catalytic systems for the epoxidation of a variety of alkenes, including terpenes.A may take place under solvent‐free conditions and mild temperatures using H2O2 as an oxidant. Moreover, the reaction can be set up in batch or in flow reactor, reaction times are short (10 min residence time in a flow setup), and the selectivity toward epoxides is as high as 90 %.A directly into the synthesis of cyclic carbonates. Silicotungstate polyoxometalates, such as [(n‐C7H15)4N]6[α‐SiW11O39Co] and [(n‐C7H15)4N]6[α‐SiW11O39Mn], have been reported as an efficient nonhalogen anionic catalyst for coupling CO2 and epoxides.2.4N]Br and [(n‐C7H15)4N]5[CrSiW11O39] in carbonation reactions of unsaturated carboxylic acids to give increased reaction rates and improved stereoselectivity.A has not yet been investigated for its ability to catalyse epoxide carbonation.Polyoxometalates such as those originally reported by Ishii and Venturello, [PTC]2 insertion into cyclohexene oxide (10) as a model compound under solvent‐free conditions. At 120 °C [Bu4N]Br showed good activity, providing 53 % of the corresponding cyclic carbonate 11 after 4 hours , with higher pressures of 75 bar improving selectivity to 41 % (entry 2). The addition of 2 mol % A to 3 mol % [Bu4N]Br improved both conversion and selectivity further to give 3 in about 40 % yield after 24 hours (entry 3). An increased loading of [Bu4N]Br alone gave even higher conversion but chemoselectivity to 3 was still below 60 % (entry 4).Following these encouraging results, the same methodology was applied to commercially available ly Table . Initialtrans isomer of 3 with >90 % stereoselectivity. Starting with a 6:4 mixture of trans/cis epoxide isomers in commercial 2, analysis of the 1H NMR spectra of the crude reaction mixture showed predominantly cis‐2 to remain after the reaction. This finding suggested cis‐2 and trans‐2 differ in their reactivity towards CO2 insertion; an observation that has also been reported by Kleij and co‐workers recently.2 insertion  is less favourable than in the case of the more easily accessible trans‐2.cis‐3 and trans‐3 to be very close in energy, and thus propose the observed discrimination between cis‐2 and trans‐2 in the CO2 insertion step to be kinetic in nature.Interestingly, all catalysts and conditions tested predominantly produced the 2 according to previously reported methods.cis isomer of 2 alone did get converted but with very poor chemoselectivity to 3  showed global conversion of the mixture to be lower than for the pure trans isomer due to a lower concentration of the reactive isomer  showed that selectivity was strongly affected by the amount of CO2 added (Table 2 densities between 0.15 and 0.24 g mL−1 (60–70 bar) conversion and selectivity remained high. However, reactions carried out at CO2 densities of 0.06 g mL−1 (30 bar) or below showed significantly lower selectivity whilst retaining the same level of substrate conversion. A reaction carried out under atmospheric pressure of air yielded mostly hydrolysis and rearrangement products 20 and 21 from non‐productive epoxide activation by the halide .When reducing the amount of Br Table , entry 4trans‐3 synthesis we found chloride to be the most active and selective halide co‐catalyst, both on its own and in combination with A  did not result in any significant change in activity  have the highest PMI due to the wasteful workup and non‐selective epoxide production.The overall yield of 4N]4[γHPV2W10O40] (B) as a bulky POM‐based catalyst for the selective epoxidation of limonene to 8,9‐limonene epoxide 4.B proceeded with high regioselectivity to 4 as a 6:4 mixture of two diastereoisomers. Pleasingly, we found CO2 insertion with 4 to be more facile than with the 1,2‐epoxides 2. By using 3 mol % [Bu4N]Br at 140 °C, high conversions were achieved after only 2.5 hours . The attempted use of Mizuno's catalyst B for CO2 insertion yielded no cyclic carbonate but gave the 8,9‐limonene aldehyde 41 as the major product, irrespective of the amount of CO2 added (entries 7 and 8). Thus, unlike the 1,2‐selective epoxidation catalyst A, the 8,9‐selective epoxidation catalyst B does not catalyse carbonate formation and produces antagonistic effects in combination with halide co‐catalysts.Cyclic carbonate formation at the 1,2‐position of limonene is known to be facile due to the ease of selectively epoxidizing the more electron‐rich trisubstituted double bond. However, access to the corresponding 8,9‐epoxide and carbonate would provide an underexplored and potentially useful building block. The 8,9‐selectivity over 1,2‐functionalisation would most easily be achieved on the basis of steric differentiation. Indeed, Mizuno has reported [Bu3 and 5 has remained unexplored so far, although they represent potentially useful building blocks for novel biorenewable NIPUs. Here we demonstrate their utility by linkage through a thiol–ene reaction on their remaining double bond to show that it is possible to create bifunctional carbonate dimers (6 and 7) that may be further ring opened to hydroxyurethanes using n‐hexylamine as a model substrate .Both bifunctional carbonate dimers 9 Figure . Mass sp8 and 9 demonstrates the potential of monofunctionalised terpene‐derived cyclic carbonates for renewable polymer synthesis: whereas the reaction of 6 and 7 with diamines would furnish linear polyurethanes, the reaction of 3 and 5 with polyfunctional amines would give access to pre‐polymers that may be further functionalised on the remaining double bond.The successful synthesis of hydroxyurethanes A and CO2 allowed for a telescoped two‐step synthesis of 1,2‐limonene cyclic carbonate directly from limonene. A different epoxidation catalyst  selectively gave access to 8,9‐limonene oxide that could easily be transformed into its corresponding cyclic carbonate 5, which was fully characterised for the first time. Both cyclic carbonates 3 and 5 have been shown to undergo thiol–ene reactions with 1,3‐propanedithiol to yield di‐monocarbonates 6 and 7 as versatile building blocks for polymer synthesis by nucleophilic ring‐opening with amines. Using combinations of various dithiols and polyamines with these limonene carbonates will give access to a range of novel NIPUs with tuneable properties and consisting of >50 wt % renewables. Application to other terpenes with less stereochemical restraints on the carbonation than limonene will give access to a wide range of bio‐based building blocks in even higher yields.The growing interest in bio‐derived NIPUs and the commitment of the coating industry to improve their sustainabilityThe authors declare no conflict of interest.As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re‐organized for online delivery, but are not copy‐edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors.SupplementaryClick here for additional data file.


We prove that the field generated by the Fourier coefficients of weakly holomorphic Poincaré series of a given level  Let entclass1pt{minimaTaking a basis of Poincaré series, we can invert the above formulas.Let K. Let entclass1pt{minimaWe can always choose ology of ) in term


J. Comput. Chem. 2018, 39, 909). To extend the automatic determination scheme of the buffer region to the DC second‐order Møller–Plesset perturbation (MP2) calculation, a scheme for estimating the subsystem MP2 correlation energy contribution from each atom in the buffer region is proposed. The estimation is based on the atomic orbital Laplace MP2 formalism. Based on this, an automatic buffer determination scheme for the DC‐MP2 calculation is constructed and its performance for several types of systems is assessed.In the linear‐scaling divide‐and‐conquer (DC) electronic structure method, each subsystem is calculated together with the neighboring buffer region, the size of which affects the energy error introduced by the fragmentation in the DC method. The DC self‐consistent field calculation utilizes a scheme to automatically determine the appropriate buffer region that is as compact as possible for reducing the computational time while maintaining acceptable accuracy  electronic structure method, each subsystem is calculated together with the neighboring buffer region, the size of which affects the energy error introduced by the fragmentation. The authors have proposed a scheme to automatically determine the appropriate buffer region for DC Hartree–Fock (HF) calculation that is as compact as possible for reducing the computational time while maintaining acceptable accuracy. They extend the automatic buffer determination scheme to DC second‐order Møller–Plesset perturbation (MP2) calculation. In this scheme, the buffer atoms for DC‐MP2 calculation are selected from those for DC‐HF based on the estimated correlation energy contribution. Therefore, the standard formalisms of electronic structure methods cannot be applied to large‐scale systems. By introducing approximations to the standard formalisms, many low‐scaling electronic structure methodsR‐goodness parameter is used to determine the quality of each fragment.ξ). The cluster‐in‐molecule local correlation method also adopts the distance threshold ξ to control the size of the cluster,By virtue of recent advances in quantum chemical theory as well as the improvements in computer performance, electronic structure calculations of large‐scale systems such as proteins have now become technically feasible. Such theoretical advances include the development of linear‐scaling  electronic structure methods. In the standard formalism of electronic structure methods, the computational time increases cubically [ON3] with rON3] with rON3] with rON3] with rON3] with rON3] with rON3] with rON3] with rON3] with rON3] with rON3] with rON3] with rON3] with rON3] with rON3] with rON3] with rON3] with rON3] with rON3] with rON3] with rON3] with rON3] with rON3] with rON3] with rON3] with rON3] with rON3] with rYang and coworkers introduced a linear‐scaling approach called the divide‐and‐conquer (DC) method.This study attempts to export the idea of the previous automated DC‐HF scheme to the DC‐MP2 calculation. Kobayashi et al.This paper consists of four sections. Section 22.1μ, ν, …. In the DC method, the entire system is divided into several subsystems, each of which consists of the central and buffer regions. Each central region is mutually exclusive with the other central regions. The sets of AOs belonging to the central and buffer regions of subsystem α are referred to as S(α) and B(α), respectively.We first outline the DC‐MP2 electron correlation calculation scheme. The DC‐MP2 method is applicable only with atom‐centered basis functions. Each basis function, α,α, where p refers to an arbitrary MO. The MO coefficients, Cpα, and the MO energies, εpα, of subsystem α are obtained by solving the Roothaan equation for each subsystem:Fα[DSCF] is the subsystem Fock matrix constructed with the density matrix DSCF, and Sα is the subsystem overlap matrix with the element Sμνα=ϕμϕν for DSCF. The density matrix, DSCF, can be constructed from the standard or approximate HF calculation, such as the DC‐HF one. If DSCF is obtained from the DC‐HF calculation, it is constructed with the local density matrices, {β, and In the DC‐MP2 method, the MOs in the subsystem ψiαψjα… and virtual ones ψaαψbα…. This can be accomplished by, for example, using the Fermi level determined in the prior DC‐HF calculations. The MP2 correlation energy for the entire system, ΔEcorr2, can be approximated as the sum of the subsystem MP2 correlation energies, ΔEcorrα2,Before the evaluation of the subsystem correlation energy, the subsystem MOs of Equation ΔEcorrα2 is obtained as the MP2 correlation energy corresponding to the central region of the localization region α by means of energy density analysis (EDA).Because the buffer region in each localization region overlaps with the other localization regions, 2.2α, ΔEcorrα2, can be further divided into contributions from the atoms in the localization region α, ΔEBα2, asBased on EDA, the MP2 correlation energy for subsystem ΔEBα2 rapidly decreases as the distance between atom B and central region α increases. The exponential decay of the MP2 energy contribution with respect to the interatomic distance is discussed in the Appendix. As pointed out by Kobayashi and Nakai,ΔEBα2 is estimated to be smaller than some criterion, the energy change by excluding atom B from the buffer region of subsystem α is expected to be small. By applying the AO‐Laplace MP2 technique to Equation ΔEBα2 can be expressed as.Xα(τ) and Yα(τ) are the energy‐weighted density matrices expressed asAccording to the local correlation philosophy for dynamical electron correlation,Here, the Fermi level, ΔEBα2, its absolute value can be bounded by adopting the Schwarz inequalityAμνα=μνμν. Here, on the analogy to the scaled opposite‐spin MP2 method,AκδαAεγα was omitted owing to its smaller contribution. Because the summation in parentheses in Equation α, the following index can be considered as the magnitude of the contribution from atom B:Assuming that the rhs of Equation eBα index, we propose the following automatic determination scheme for the buffer region in the DC‐MP2 method:Assignment of the initial DC‐MP2 buffer region for each subsystem. This may be determined by prior DC‐HF calculation.eBα from Equation Evaluation of B from the buffer region of subsystem α if eBα is smaller than the energy threshold.The exclusion of atom Cpα and εpα, using Equation Reconstruction of subsystem molecular orbitals ΔEcorrα2, from Equation Evaluation of the subsystem correlation energy, Using the above eBα scales as O(Nm3), where N and m represent the sizes of the entire system and buffer region, respectively, since the evaluation of each eBα of Equation O(m2) owing to the summation over γ and κ and the number of eBα to be evaluated scales with O(Nm).The additional computational cost for the evaluation of all necessary 33.1β, was set to 125 a.u. and the Fermi function cutoff factor (the FTOL option of $DANDC input group in GAMESS program) was set to 20. In addition, the parameters in the automated DC‐HF method were set to ethreshSCF = 0.1 μEh and rext = 3.0 Å, the definitions of which are given in our previous paper.α, llocalSCF,α and llocalcorr,α, respectively, to discuss the size of the localization regions determined by the automated DC method. llocalSCF,α  was defined as half of the maximum atom‐pair distance in the HF (or MP2) localization region for subsystem α. The two‐electron AO integrals, We implemented the above‐mentioned automatically controlled DC‐MP2 method to the GAMESS package3.2−3. Each water molecule was adopted as a central region in the DC calculation. To assess the performance of the automated DC‐MP2 calculation, the entire system was selected as the initial localization region for every subsystem in the DC‐MP2 calculation. Figure B (eBα) with respect to its distance from the O atom in the central region. The blue plot represents the value for B being an H atom, and the red plot that for B being an O atom. The estimated energy contribution decays exponentially as the distance from the central region increases. The slight difference in the slope for H and O atoms in Figure Eh, which are significantly larger than the total MP2 energy of ∼19 Eh. This is because that the estimated energy (eBα) is derived as the upper limit of the atomic MP2 energy contribution. From the following section, the energy threshold in the automated DC‐MP2 method, ethreshcorr, was set to 0.1 μEh unless otherwise noted.We first applied the present automated DC‐MP2 method to a cubic system containing 100 water molecules with weight density of 1.0 g cmeBα on the system size was examined, as shown in Figure rbin=4.5Å and rbout=5.5Å, respectively. The scaling analysis with the double logarithmic plot indicates that the computational time for the evaluation of eBα scales as O(Nwater1.5), which maintains an almost linear‐scaling behavior with respect to the entire system size, as was discussed in Section Next, the dependence of the computational time of 3.3ethreshcorr) dependence of the DC‐MP2 correlation energy. Following Section llocalcorr and σllocalcorr, respectively) are also given in Table ethreshcorr=100μEh, the actual correlation energy error per atom is 18.37 μEh, which is sufficiently smaller than ethreshcorr. It should be noted that the MP2 energy error decreases systematically as ethreshcorr decreases, while the dependence is not proportional but rather logarithmic to ethreshcorr. As with the ethresh parameter in automated DC‐SCF method,ethreshcorr parameter leads to a larger localization region, which can be confirmed from the average of the major axis radii of all localization regions, llocalcorr. Interestingly, the SD of the major axis radii, σllocalcorr, also tends to increase systematically as ethreshcorr decreases, except for ethreshcorr=0.1μEh. This fact suggests that the present scheme can effectively aid the selection of the appropriate buffer region for each subsystem in the DC‐MP2 calculation.The accuracy and the computational time of the automated DC‐MP2 method were investigated for the cubic water system in Section rbin and rbout, the definitions of which are given in our previous paper.llocalHF and llocalcorr) and the SDs  of the major axis radii among all localization regions in the DC‐HF and DC‐MP2 calculations are also shown. Similar to the results in Ref. Eh atom−1). The average radius of the DC‐HF localization region, llocalHF, is 7.0–7.2 Å, which is larger than the average radius, 6.761 Å, of the DC‐MP2 localization region for ethreshcorr=0.1μEh given in Table llocalHF, as was also confirmed in the previous study.llocalcorr becomes smaller than its value when the initial localization region is set to be the entire system. Similarly, σllocalcorr is ∼0.14 Å smaller than σllocalHF.Next, we examined the combination of the present automated DC‐MP2 method with the automated DC‐HF calculation. Table α‐C atoms, and each of the divided systems was treated as a central region. Table ethreshcorr dependence of the DC‐MP2 energy for chignolin. The entire system was selected as the initial localization region for every subsystem in the DC‐MP2 calculation. For ethreshcorr=100μEh, the actual correlation energy error per atom is 2.82 μEh, which is sufficiently smaller than ethreshcorr. As was also confirmed in the case of the water system, the MP2 energy error decreases systematically as ethreshcorr decreases. Again, the dependence of the error on ethreshcorr is rather logarithmic. The smaller ethreshcorr leads to the larger llocalcorr, while it leads to the smaller σllocalcorr, contrary to the case of water system. Comparing Table llocalcorr of chignolin is about 1.0 Å larger than that of the water system for the same ethreshcorr parameter, reflecting the delocalized electronic nature in the covalently bound system.Next, we applied the proposed method to a covalently bound system, namely, the chignolin protein with 10 amino acids. The geometry of chignolin was obtained from the protein data bank (PDBID: 1UAO). Hydrogen atoms were added using the Discovery Studio 2017 R2 software.Eh atom−1). For this small protein system, in contrast to the result in Table β‐strand glycine oligomer (GLY)20, and the result of the calculation are given in Table ethreshcorr were performed to confirm that the present automated DC‐MP2 energy error depends primarily on ethreshcorr and hardly on the initial buffer radii. For this stretched system, the SD of the localization region sizes for the MP2 calculation is smaller than that for the HF calculation, while the energy error is similar to the result in Table ethreshcorr leads to the larger llocalcorr and σllocalcorr.Next, we combined this with the automated DC‐HF calculation. Table n2Hn + 22, shown in Figure 2H2 (or C2H3 for edges) unit divided at the C—C single bond was treated as a central region. Table rbin=5.0Å and rbout=6.5Å, respectively. To avoid division of the localization region at C=C double bond, each C2H2 (or C2H3) unit was treated as one piece, that is, a unit was extracted from the DC‐MP2 localization region only when all the estimated MP2 correlation energies, eBα, for the atoms in the unit were smaller than the threshold, ethreshcorr . The DC‐MP2 energy error per atom is almost constant for Finally, the present method was applied to the conjugated polyacetylene chain CCODE = IMS program$MP2 input group implemented in the GAMESS package was used. The automated DC‐MP2 calculation shows a faster computational time than that of the standard MP2 calculation for O(n2.5), while that for the present automated DC‐MP2 method scales as O(n1.1). It is confirmed that the linear‐scaling behavior of the DC‐MP2 method is preserved even with the present automation scheme.For this conjugated system, the dependence of the computational time on the system size was also examined, as shown in Figure Nwater. The times were measured using a computer node equipped with two Intel Xeon Gold 5118 CPUs , and the average of three measurements was plotted. The initial sizes of the inner and outer buffer regions in the automated DC‐HF calculation were set to rbin=4.5Å and rbout=5.5Å, respectively. The energy threshold in the automated DC‐MP2 method, ethreshcorr, was set to 10 μEh. The scaling analysis with the double logarithmic plot indicates that the computational time for the present automated DC‐MP2 method scales as O(Nwater1.6), which indicates that the present method also achieves near‐linear scaling computational time even for three‐dimensional systems.The scaling analysis was also conducted for three‐dimensional water cluster systems. Figure 4ethreshcorr, decreases. We also confirmed that the linear‐scaling behavior of the DC‐MP2 method is preserved even with the present automation scheme.In this study, we have proposed an automatic determination scheme for the buffer region in the DC‐MP2 calculation. This method is based on a subsystem MP2 correlation energy contribution from each atom in the buffer region, which is estimated with the help of the AO‐Laplace MP2 method and the Schwarz inequality. Because the appropriate size of the buffer region in the DC‐MP2 calculation can be smaller than that in the DC‐HF calculation, as suggested in a previous paper,Since the MP2 amplitude is known to provide a good guess for the CC method in many cases, the proposed automation scheme is straightforwardly applicable to the DC‐CC method.


We observe a preferential enrichment of the fluorinated chain in the topmost layer, relative to the bulk composition, which is most pronounced for the lowest content of [PFBMIm][PF6]. Upon cooling the mixtures stepwise from 95 °C until surface charging effects in XPS indicate solidification, we observe a pronounced increase in surface enrichment of the fluorinated chain with decreasing temperature in the liquid state. In contrast to the mixtures with lower [PFBMIm][PF6] contents, cooling the 75 mol % mixture additionally shows an abrupt decrease of the fluorinated chain signal before complete solidification occurs, which is assigned to partial precipitation effects.Using angle‐resolved X‐ray photoelectron spectroscopy (ARXPS), we investigate the topmost nanometers of various binary ionic liquid (IL) mixtures at different temperatures in the liquid state. The mixtures consist of ILs with the same [PF Mixtures of the ionic liquids [PFBMIm]‐[PF6] and [C4C1Im][PF6] exhibit a very pronounced surface enrichment of the fluorinated chain. This effect is most pronounced at low contents of [PFBMIm][PF6], and increases with decreasing temperature. Ionic liquids (ILs) carrying fluorinated alkyl chains, in the following called fluorinated ILs, represent an interesting class of ILs because they often exhibit unique properties such as high thermal and chemical stability, and high gas solubility. Moreover, they commonly show low surface tension and/or are chemically and biologically inert.While non‐fluorinated ILs are known to form bulk nanostructures consisting of polar and nonpolar domains, fluorinated ILs typically exhibit additional nonpolar fluorous domains, in which the fluorinated chains preferentially agglomerate.Many investigations have been carried out in the last decades on IL mixtures and their composition‐dependent physico‐chemical bulk properties such as viscosity, thermal behavior, density and molar volume, conductivity, solvation abilities, influence on chemical reactivity as well as bulk microscopic structure  with alkyl chain lengths n=2, 4, 6, 8, 10 and 12, and correlated the derived values with MD simulations. The latter revealed that for cations with less than four carbon atoms in the alkyl chain, the outer surface is dominated by the presence of the fluorinated butyl chains of the anion, with the polar head groups preferentially forming a confined sub‐surface layer. Longer alkyl chains (n>4) start to penetrate the fluorinated surface layer pushing the polar head groups of the anion and cation even further away from the outer surface. These findings are in line with the decrease in measured surface tension of the ILs up to n=8, where a maximum number of both fluorinated and alkylated chains (and a minimum number of polar head groups) are present at the outer surface. For even longer alkyl chains (n>8), the surface tension increases again due to the fact that the longer alkyl chains dominate the outer surface, as evidenced by MD simulations.Surface studies of ILs with both alkylated and fluorinated chains are quite rare. In case of neat ILs, Luís et al.8C1Im]x1−[C8C1ImF13]x[Tf2N] mixtures, RAS‐LIF measurements performed by Smoll et al.In the case of [C6] and [C4C1Im][PF6]  anion and similar imidazolium‐based cations. In [C4C1Im]+, the butyl chain is fully hydrogenated, and in [PFBMIm]+ its terminal ethyl moiety is fluorinated. We analyzed the temperature dependence of the surface composition upon cooling from 95 °C, where all mixtures are in their liquid state, until their solidification. We observe a very pronounced surface enrichment of the fluorinated [PFBMIm]+ chains relative to the bulk composition, which increases with decreasing temperature and decreasing mole fraction of [PFBMIm][PF6].In this study, we present a detailed angle‐resolved XPS (ARXPS) study under clean ultra‐high vacuum (UHV) conditions on neat [PFBMIm][PF] and C4CIm[PF6] (4C1Im][PF6] was purchased from Iolitec (purity 99.5 %). The synthesis of [PFBMIm][PF6] has been reported before.Materials: + cation overlaps with the shake‐up of the aromatic system of the cation, the intensity of this peak is set equal to that of the CF2 peak. CasaXPS (version 2.3.16) was used for subtracting the background and for peak fitting (pseudo‐Voigt function with 30 % Lorentzian contribution). In the F 1s, N 1s and P 2p spectra, a two‐point linear background was subtracted, whereas a three‐point linear background was used for the C 1s spectra. The P 2p signal is composed of the spin‐orbit‐split 2p1/2 and 2p3/2 components, which have the same full width at half maximum (FWHM), are separated by 0.9 eV, and have an area ratio of 1:2. The FWHM of the F 1s peaks of the CFx groups (x=2 and 3) and the [PF6]− anions are 1.94±0.1 and 1.47±0.1 eV, respectively. For the C 1s peaks .The sample temperature was measured with a type K thermocouple attached to the molybdenum sample reservoir with an accuracy of ±5 °C, and a stability of ±1 °C.6], and 1‐butyl‐3‐methylimidazolium hexafluorophosphate, [C4C1Im][PF6], imidazolium hexafluorophosphate, [PFBMIm][PF4C1Im][PF6] are depicted, for a temperature of 95 °C. The F 1s spectrum (left panel) shows the FPF6 peak of the [PF6]− anion at 686.6 eV. The single peak in the N 1s region (center panel) at 402.0 eV is assigned to the imidazolium nitrogen atoms, NIm. In the C 1s spectrum (right panel), the Calkyl peak at lowest binding energy of ≈285 eV stems from the three alkyl carbon atoms only bound to hydrogen and carbon atoms, and the peak at higher binding energy consists of two contributions: The smaller C2 peak at 287.5 eV is due to the carbon atom bound to two nitrogen atoms, and the Chetero’ peak at 286.6 eV due to carbon atoms bound to one nitrogen atom. In the P 2p region , the unresolved spin‐orbit peaks of the phosphorus atom of the [PF6]− anion are centered at 136.9 eV. Notably, no signals of possible surface‐active contaminations4C1Im][PF6]. Within the margin of error (±10 %), the quantitative analysis at 0° agrees very well with the nominal composition of [C4C1Im][PF6]  and 0° (black) emission spectra of [C6] are depicted in Figure α X‐ray source in another XP setup.The XP spectra of [PFBMIm][PFCFx atoms (CFx=CF2 and CF3 groups) of the fluorinated chain in the [PFBMIm]+ cation, and the peak at 686.8 eV from the six FPF6 atoms of the [PF6]− anion. In the N 1s region (center panel), a single peak is observed at 402.2 eV, due to the NIm atoms of the imidazolium ring. In the C 1s region (right panel), the peaks at 293.6 and 291.3 eV stem from the CCF3 and CCF2 groups of the fluorinated butyl chain of the [PFBMIm]+ cation. The peak at lower binding energy consists of two peaks due to the C2 atom at 287.8 eV and the Chetero’ atoms at 286.8 eV. The P 2p spectrum  displays the spin‐orbit‐split PPF6 peak of the anion centered at 137.0 eV. Again, the absence of O 1s and Si 2p signals  indicates that [PFBMIm][PF6] is clean.6] (see Table At 0° emission (black spectrum), the F 1s spectrum (left panel) displays two peaks, which arise from the fluorine atoms in two different chemical environments: The peak at 688.9 eV stems from the five FCFx peak of the fluorinated chain at 80° is observed that goes along with a pronounced decrease of the FPF6 signal. This behavior indicates that the fluorinated chain of the cation is enriched at the IL/vacuum interface, while the [PF6]− anion is surface‐depleted. The enrichment of the fluorinated chain is also reflected by the increase of the CCF3 and CCF2 peaks in the C 1s region at 80°. This increase goes along with a decrease of the C2 and Chetero’ peaks and also of the NIm signal in the N 1s region; both observations indicate a surface depletion of the imidazolium ring of the [PFBMIm]+ cation. In the P 2p spectrum, changing the emission angle from 0° to 80° emission leads to a small decrease.Next, we compare the spectra at 80° in Figure 6] and [C4C1Im][PF6] as a function of the composition, we studied four mixtures with molar ratios of 10, 25, 50 and 75 mol % of [PFBMIm][PF6]. The corresponding XP spectra are depicted in Figure To search for preferential enrichment effects of different cations in mixtures of [PFBMIm]+ and the [C4C1Im]+ cations. In the C 1s region (right panel), we find five peaks for all mixtures. The peaks at 293.6 and 291.3 eV are due to the CCF3 and CCF2 atoms of the [PFBMIm]+ cation, respectively. The Calkyl peak of the [C4C1Im]+ cation is observed at 285.1 eV, and the Chetero’ peak with the C2 shoulder is found at 286.7 and 287.7 eV, respectively. The spin‐orbit‐split P 2p peaks of the [PF6]− anion are centered at 137.0 eV . Within the margin of error (±0.2 eV) the peaks in all regions have the same binding energy like in the neat ILs. Again, no signals are detected in the Si 2p and O 1s spectra , verifying that no contaminations are transferred to the mixture by using acetonitrile as a co‐solvent when preparing the mixtures. Within the margin of error, the quantitative analyses are in line with the nominal compositions of the mixtures of [PFBMIm][PF6] and [C4C1Im][PF6], except for a general too high content of FCFx atoms and a too low content of Calkyl atoms, derived from the bulk‐sensitive measurements at 0° (Table We start with the discussion of the F 1s spectra (left panel) at 0°. In addition to the FCFx peak at 688.9 eV indicates a clear surface enrichment of the fluorinated chain, similar to the observation for neat [PFBMIm][PF6]. Interestingly, the increase of the FCFx signal at 80° relative to that at 0° is most pronounced for the mixture with the lowest molar ratio of 10 mol % [PFBMIm][PF6]. With increasing molar ratio, this enhancement continuously decreases. To visualize this behavior, we plotted the normalized FCFx content, that is, the experimentally determined content (mole fraction) divided by the nominal content (see Table CFx content with decreasing molar ratio of [PFBMIm][PF6]. This behavior clearly indicates that the surface enrichment of the fluorinated chain in the outermost layer (relative to the bulk) strongly increases for low molar ratios, that is, the surface of the mixture is preferentially terminated with the fluorinated chain.Next, we analyze the XP spectra at 80°. For all mixtures, a significant increase of the FCF3 and CCF2 peaks. Generally, the effect is less pronounced than in the F 1s region, which is due to the higher kinetic energy of the C 1s photoelectrons of around 1200 eV as compared to around 800 eV for F 1s, which leads to a larger information depth of the former. In contrast to the increase of the CFx signal of the fluorinated chains of [PFBMIm]+, the Calkyl signal of the alkyl chains of [C4C1Im]+ has decreased at 80° for all IL mixtures. This behavior is in contrast to the situation for neat [C4C1Im][PF6] in Figure + cation and the non‐fluorinated side chain of the [C4C1Im]+ cation: The selective enrichment of the [PFBMIm]+ cations is attributed to a  larger surface tension of ILs with an alkyl chain compared to a fluorinated chain.This enrichment of the fluorinated chain is also detected in the C 1s region  as a function of the molar ratio. For both, we find values smaller than 1.0, which reflect the described damping. The data corresponding to the anion and the imidazolium ring are identical, indicating that both are at the same distance from the surface.The analysis of the Fs Figure  a and 2fCFx and FPF6 contents  / , as a function of the molar ratio in Figure + cation. Interestingly, we also find a clear increase of the ratio of the normalized FCFx and FPF6 contents for 0°. This behavior again indicates that strong selective enrichment effects are not only observed at 80° but also at 0° (see above).To visualize the relative enrichment of the fluorinated chain of the cation relative to the anion , we plot the ratio of the normalized FCFx and FPF6 contents at 80° and also at 0° are shown in Figure As a next step, we address the temperature dependence of the XP spectra for the two neat ILs and the IL mixtures, by cooling the ILs from 95 °C down to the temperature, where solidification starts, which is typically indicated by the onset of charging. The F 1s and C 1s spectra of the neat ILs and the IL mixtures are shown in Figures 4C1Im][PF6], we find a slight continuous decrease of the FPF6 signal in Figure hetero’ signal in Figure alkyl continuously increases. At 95 °C, the Calkyl peak is smaller than the Chetero’ peak, but at −55 °C the intensities are reversed. This behavior indicates an increasing surface enrichment of the butyl chain with decreasing temperature. Similar effects have been observed in literature8C1Im]X with X−=Br, [TfO], [Tf2N] and [CnC1Im][TfO] . We assign these effects to the increase in magnitude of the entropic term −TΔS0 with temperature, which favors a more random distribution of the constituents with increasing temperature. This term counteracts the enthalpic driving force favoring surface enrichment of the fluorinated chain at low temperature, due to lowering of the surface tension (see above).For neat CC1Im[PF6]alkyl intensity continues to increase, until at −70 °C charging and peak broadening starts (not shown). This temperature is in accordance with the glass transition temperature of [C4C1Im][PF6] at around −77 °C.Upon further temperature decrease, the C6], we again observe a slow decrease of the FPF6 peak at 80° during cooling from 95 to 25 °C in Figure CFx intensity remains more or less unchanged. The resulting increase of the ratio of the normalized FCFx and FPF6 contents in Figure 6]. Since bulk [PFBMIm][PF6] melts at 66 °C,PF6 signal (not shown), whereas the FCFx signal completely recovers (to within 3 %). A closer look to the other spectra in 80° emission shows that the N 1s XP spectrum shows a shoulder towards lower binding energy, indicating radiation damageFor neat [PFBMIm]PF, we agai6] content. Overall, the ILs with molar ratios of 10, 25 and 50 mol % [PFBMIm][PF6] display the same behavior. Upon cooling from 95 °C to lower temperatures, the FCFx peaks gain intensity and the ratios of the normalized FCFx and FPF6 contents for 80° in Figure CFx intensity , all signals shift towards higher binding energy and peak broadening indicates solidification and therefore charging (note that for a given mixture these temperatures were found to vary by ±5 °C due to the supercooling effects). The corresponding data is not included in Figures 6], we observe a quite different behavior. Initially, the F 1s and C 1s spectra in Figures CFx and FPF6 contents at 80° and also at 0° in Figure + cation in the mixture with decreasing temperature. Between 35 and 20 °C, however, the FCFx intensity decreases by about 40 % while the FPF6 intensity stays constant. This leads to a pronounced decrease of their ratio in Figure 6]‐depleted mixture. The corresponding C 1s spectra of the 75 mol % mixture  to a partial solidification of a [PFBMIm][PF6]‐rich or pure [PFBMIm][PF6] phase, which is depleted from the outer surface beyond the XPS information depth, or even forms a solid precipitate at the buried solid/liquid interface with the support. The remaining liquid mixture is therefore [PFBMIm][PF6]‐depleted and [C4C1Im][PF6]‐rich, which leads to the decrease of the FCFx signal and an increase of the Calkyl signal. The peak broadening at −10 °C then indicates the solidification of this residual mixture. After subsequent heating of the mixture to 95 °C, we find the same peak intensities (within the margin of error) as before the cooling experiment; this behavior signals the re‐dissolution and mixing of [PFBMIm][PF6] and [C4C1Im][PF6] during heating the mixture. Notably, the precipitation of one of the ILs from the mixture was only observed for high [PFBMIm][PF6] content such as 75 mol % , and not in any of the other mixtures . It should be noted that the magnitude of the abrupt decrease of the ratio in Figure 2N] and [PPh4][Tf2N], where the temperature‐dependent depletion of tetraphenylphosphonium, [PPh4]+, from the near‐surface region (information depth) was observed by XPS.For the molar ratio of 75 mol % [PFBMIm]PF, we obse6] and [C4C1Im][PF6], with molar ratios of 10, 25, 50 and 75 mol % [PFBMIm][PF6], along with the two neat ILs, at 95 °C and while cooling to lower temperatures. The two ILs contain the same anion, [PF6]−, but different cations. By performing very surface‐sensitive measurements at an emission angle of 80°, we observe surface enrichment of the fluorinated chain for neat [PFBMIm][PF6] relative to the bulk composition. This effect is in line with the general observation that fluorinated groups in the outermost layer lead to a lower surface tension than alkyl groups.6] in the mixture, the more pronounced is the surface enrichment of the fluorinated chain relative to the bulk composition. Upon cooling the mixtures from their liquid phase at 95 °C to their solidification, we observe a similar behavior for the 10, 25 and 50 mol % mixtures, and also for neat [PFBMIm][PF6]: Decreasing the temperature leads to an increase in surface enrichment of the fluorinated chain of [PFBMIm][PF6] (relative to the bulk composition), which is detected in the F 1s and C 1s spectra. We attribute the observed behavior to entropic reasons, namely a less pronounced enrichment of the fluorinated chains, that is, a lower degree of order, at high temperatures. The 75 mol % mixture shows the same increase in enrichment of the fluorinated chain as the other mixtures when cooling down to 35 °C. Upon further cooling to 20 °C, however, the surface enrichment of the fluorinated chain decreases drastically. This observation is attributed to a  precipitation of the pure [PFBMIm][PF6], which in turn results in a [C4C1Im][PF6]‐rich phase at the topmost layer of the mixture. This change in composition is also reflected by an increase of the Calkyl peak in the C 1s spectrum when comparing the 35 and 20 °C spectra.We used angle‐resolved X‐ray photoelectron spectroscopy to study mixtures of fluorinated and non‐fluorinated ILs, namely [PFBMIm][PFThe authors declare no conflict of interest.As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re‐organized for online delivery, but are not copy‐edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors.SupplementaryClick here for additional data file.


The twists to convert a cube to a square antiprism and a hexagonal prism to a hexagonal antiprism eliminate the need for the highest nodality orbitals in the resulting hybrids. A trigonal twist of an hO octahedron into a Dh3 trigonal prism can involve a gradual change of the pair of d orbitals in the corresponding sp3d2 hybrids. A similar trigonal twist of an hO cuboctahedron into a Dh3 anticuboctahedron can likewise involve a gradual change in the three f orbitals in the corresponding sp3d5f3 hybrids.The combination of atomic orbitals to form hybrid orbitals of special symmetries can be related to the individual orbital polynomials. Using this approach, 8-orbital cubic hybridization can be shown to be sp Such studies included an investigation of distortions from ideal symmetries in relatively symmetrical systems with molecular orbital degeneracies . Th. Th13]. 3, sp3d5, and sp3d5f7 manifolds in hybridization schemes should lead to most nearly spherical polyhedra , synthesized by Ghosh and co-workers [Dh3 tricapped trigonal prism found experimentally in the MH92−  anions [Fully using the complete spolyhedra . For thevertices . The tet-workers . There i) anions .8 metals such as Ni(II), Pd(II), Pt(II), Rh(I), and Ir(I). Since a square is a two-dimensional structure in an xy plane, the polynomials of the atomic orbitals for square hybridization cannot contain a z variable. This limits the p orbital involvement in square hybridization to the p{x} and p{y} orbitals so that a d orbital is required for square hybridization. This d orbital can be either the d{x2 − y2} or d{xy} orbital, depending on whether the x and y axes are chosen to go through the vertices or edge midpoints, respectively, of the square (pd2f) = sp3d3f set for cubic hybridization. This shows that one f orbital, namely the A2u{xyz} orbital with a cube orbital graph } set. Thus, the set of 10 orbitals for the pentagonal prism are sp3d4{x2 − y2,xy,xz,yz} f{xyz,z(x2 − y2)} without involvement of the d{z2} orbital. Capping the pentagonal prism in a way to preserve the Dh5 symmetry adds the d{z2} and f{z3} orbitals to the hybrid leading to an sp3d5f3{z3,xyz,z(x2 − y2)} set for the resulting 12-vertex bicapped pentagonal prism.The 10-vertex pentagonal prism of symmetry  is encou  and f(z3) orbitals to give an sp3d5f3 12-orbital hybridization scheme. This process is exactly analogous to the conversion of the square antiprism to the bicapped square antiprism discussed above.Twisting one pentagonal face of a pentagonal prism 36° around the symmetry . Unlike ndD symmetry of an n-gonal antiprism is preserved by compression or elongation along the major nC axis to give oblate or prolate polyhedra, respective, as illustrated in 5dD symmetry of the bicapped pentagonal antiprism to give the full icosahedral point group hI. This ascent in symmetry combines some of the irreducible representations of the Dh5 point group to give irreducible representations of higher degeneracy. As a result, the A1g + E1g + E2g irreducible representations coalesce into the single five-fold degenerate Hg representation of the icosahedral point group. The five d orbitals belong to this Hg representation in icosahedral symmetry. Similarly, the three f orbitals of the sp3d5f3 icosahedral hybridization belong to the single T2u{x3,y3,z3} irreducible representation of the hI point group considering the cubic set of f orbitals } or the f{y(3x2 − y2)} orbital depending on the {x,y,z} coordinate system chosen.The simplest structure with hexagonal symmetry is the planar hexagon itself. The restriction of the atomic orbitals to those containing no 3d3f set of hybrid orbitals for the hexagonal bipyramid is obtained by supplementing the sp2{x,y}d2{x2 − y2,xy}f{x(x2 − 3y2)} set of orbitals for the equatorial planar hexagon with the p{z} and d{z2} pair for the two additional axial vertices. The hexagonal bipyramid shares with the cube (see above) the feature of not arising from any sp3d4 hybridization scheme but instead requiring an f orbital in a sp3d3f hybridization scheme.The smallest three-dimensional figure with hexagonal symmetry is the 8-vertex hexagonal bipyramid . The sp3x and y in their orbital polynomials with an equal number of orbitals in which the polynomials obtained by multiplying the orbital polynomials for the planar face by the z variable. Thus, the sp2{x,y}d2{x2 − y2,xy}f{x(x2 − 3y2)} orbitals corresponding to the hexagonal face of the hexagonal prism is supplemented by the p{z3}d2{xz,yz}f2{xyz,z(x2 − y2)}g{xz(x2 − 3y2)} set of six orbitals. This leads to the interesting observation that a single g orbital corresponding to the B2g irreducible representation is required to provide a set of 12 hybrid orbitals oriented towards the vertices of a Dh6 hexagonal prism } for the resulting 12-vertex bicapped pentagonal prism.The atomic orbitals required to form a prism combine those for the polygonal face having only al prism . Not surC6 axis leads to the hexagonal antiprism of Dd6 symmetry  to the corresponding antiprisms involves a twist of (180/n)° of an n-fold face around the unique n-fold axis. Analogous processes can be applied to the three-fold axes in the regular octahedron and icosahedron. Such a twist process converts the hO regular octahedron into the D3h trigonal prism and the hO cuboctahedron into the Dh3 anticuboctahedron ,y(z2 − x2),z(x2 − y2)} set of the cubic f orbitals } or the Eu{x(3x2 − y2),y(3x2 − y2)} set. Thus, for the cuboctahedron, like the octahedron under 3dD symmetry, there are two alternative pairs of the required highest l value orbitals in the minimum l value hybrid that can be used in the hybrid. Converting the 3dD cuboctahedron to the 3hD anticuboctahedron eliminates the Eu{x(3x2 − y2),y(3x2 − y2)} pair of f orbitals from the sp3d5f3 hybrid requiring use of the E´{2,yzxz2} pair.The sporbitals . Reducinx and y. Since there are only two orbitals for each non-zero l value and one orbital  for l = 0, square planar hybridization requires one d orbital, pentagonal planar hybridization requires two d orbitals, and hexagonal planar hybridization requires an f orbital as well as two d orbitals. Prismatic configurations with two parallel n-gonal faces and nhD symmetry combine the set of atomic orbitals for the n-gonal face with only the two x and y variables with a set of equal size corresponding to the orbitals having polynomials in which the polynomials of the planar n-gon orbitals are multiplied by a third z variable. As a result, cubic hybridization can be shown to require an f orbital and hexagonal prismatic hybridization can be shown to require a g orbital. For 8-coordinate systems with four-fold symmetry twisting a square face of a cube with sp3d3f hybridization by 45° around a C4 axis to give a square antiprism with sp3d4 hybridization eliminates the need for an f orbital in the resulting sp3d4 hybridization. Similarly, for 12-coordinate systems with six-fold symmetry, twisting a hexagonal face of a hexagonal prism with sp3d5f2g hybridization to a hexagonal antiprism eliminates the need for a g orbital in the resulting sp3d5f3 hybridization. A trigonal twist of an hO octahedron into a Dh3 trigonal prism can involve a gradual change of the pair of d orbitals in the sp3d2 hybrids. A similar trigonal twist of an hO cuboctahedron into a Dh3 cuboctahedron can likewise involve a gradual change in the three f orbitals in the sp3d5f3 hybridization.The combination of atomic orbitals to form hybrid orbitals of special symmetries can be related to the individual orbital polynomials. Thus, planar hybridizations such as the square, pentagon, and hexagon can only use atomic orbitals with only two variables in their polynomials, conventionally designated as


Here, a Li2CO3-affiliative mechanism is proposed for air-accessible interface engineering of garnet electrolyte via facile liquid metal (LM) painting. The natural LM oxide skin enables a superior wettability of LM interlayer towards ceramic electrolyte and Li anode. Therein the removal of Li2CO3 passivation network is not necessary, in view of its delamination and fragmentation by LM penetration. This dissipation effect allows the lithiated LM nanodomains to serve as alternative Li-ion flux carriers at Li-garnet interface. This mechanism leads to an interfacial resistance as small as 5 Ω cm2 even after exposing garnet in air for several days. The ultrastable Li plating and stripping across LM painted garnet can last for 9930 h with a small overpotential.Garnet based solid-state batteries have the advantages of wide electrochemical window and good chemical stability. However, at Li-garnet interface, the poor interfacial wettability due to Li 2CO3 passivation causes large resistance and unstable contact. Here the authors propose a Li2CO3-affiliative mechanism for air-accessible interface engineering of garnet electrolyte with superior wettability via facile liquid metal painting.At Li-garnet interface, the poor interfacial wettability due to Li Uncontrollable lithium dendrite growth would cause serious side reaction with organic liquid electrolyte (LE) and even lead to the dry up of electrolyte. The inferior cycling performance as well as the high safety risk (such as leakage and explosion) severely hinder the development and wide application of LMBs4. The employment of solid-state electrolyte (SSE) is thought to be a promising solution to Li dendrite suppression due to its high Young’s modulus  and chemical stability even at high temperature 6. Besides, many SSEs possess broader electrochemical window which can reach up to 5 V7. Among current SSEs, polymer or hybrid electrolytes provide the advantages of flexibility and deformability but at a cost of relatively low ionic conductivity at room temperature (RT) (<0.1 mS cm−1)9. Inorganic ceramic SSEs not only provide high ionic conductivity (close to 1 mS cm−1), but also are endowed with better nonflammability and moisture-resistance than sulfide/halide SSEs11. The doped garnet-Li7La3Zr2O12 (LLZO) SSE shows the anode stability advantage over other oxide SSEs, such as NASICON-Li1.3Al0.3Ti1.7(PO4)3 and perovskite-Li0.33La0.56TiO3, due to the lacking of redox active elements 14.Lithium metal batteries (LMBs) are attracting more attentions due to their high energy densities, benefitting from lithium metal anode with low redox electrochemical potential and high theoretical specific capacity2CO3, which results in poor wettability of LLZO surface by Li plating and large interfacial resistance16. In order to modify the interface contact, some methods have been attempted to eliminate Li2CO3  or construct lithiophilic interlayer 25. For the alloyable strategy, some expensive installations and refined manipulation for thin film deposition  are usually required in order to achieve compact planar contact27. Although the facile addition of alloyable elements  into molten Li can also improve the wettability of anode on LLZO by tuning the surface tension and viscosity of molten lithium29, a high weight percent of blended alloy  is required for best wetting effect. In this case, the theoretical specific capacity of alloying anode would be significantly reduced compared with pristine Li anode.Nevertheless, the interfacial problem between lithium metal and garnet electrolyte still exists in view of the potential passivation of ceramic grains by naturally formed Li32. Although the high surface tension of pure LM makes it difficult to wet substrates under oxygen-lean condition, the self-formed Ga2O3 skin in an oxygenated environment can lead to the lowering of effective surface tension32. This oxide layer allows LM droplets to wet substrate surfaces and also stabilizes LM by preventing it from further oxidation. The Ga2O3 skin with a thickness of 0.5–3 nm behaves like an elastic membrane that can reform instantaneously when broken, therefore, enabling LM to be structurally self-stabilized under external multivariate conditions33. This particular wetting behavior of LM with intrinsic Ga2O3 skin makes it an available painting material on substrate surface or penetrating material in grain boundaries (GBs)35.Liquid metal (LM) gallium and gallium-based alloys have been widely used in the field of soft microfluidic electronics due to their low viscosity (2 mPa s), low toxicity, and negligible vapor pressure2 in air. In addition, LM can infiltrate into the GBs of garnet to a certain depth, leading to a better interface transition effect. On the other hand, lithiated LM layer can provide extra Li+ transport channels and its high affinity with Li2CO3 enables the bypassing of charge transport from Li2CO3 passivation layer36. With the assistance of LM painting, the area-specific resistance (ASR) values of Li-garnet interface decrease to 5 Ω cm2 at 60 °C. The Li/Li symmetric cells can cycle for at least 9930 h with small overvoltage values.In this work, we propose a lithiophilic layer building strategy by brushing LM with excellent wetting behavior on garnet-based ceramic electrolyte surface to significantly reduce its interfacial resistance and assist the high reversibility of LMBs. This facile method does not require extra deposition equipment and exact (high) alloying content. The conformal oxide layer on LM enables a smooth brushing of LM paint on solid electrolyte surface, which can prevent garnet from further exposure to water and O2O5 as doping agent for cubic garnet electrolyte in view of the structural stabilization and high ionic conductivity of Li6.5La3Zr1.5Ta0.5O12 (LLZT) electrolyte  of Ag/garnet/Ag symmetric configuration were measured to obtain a RT ionic conductivity of LLZT of 4 × 10−4 S cm−1 with an activation energy of 0.36 eV  images of LM@LLZT further certify the wetting behavior of surface-oxidized LM. Note that the Ga2O3 film enables a smooth and continuous coating on garnet grains  at 530.5 eV likely stems from the generation of Ga2Ox3− as a consequence of insufficient surface oxidation. After lithiation, Ga2O3 and Ga components are expected to convert into LixGa and Li2O products42. Therefore the LixGa (19.1 eV) and Li2O (528.5 eV) peaks become dominant in the Ga 3d and O 1s spectra, respectively4. Note that the undecomposed LixGaOy still remains from the appearance of peaks at 20.7 eV for Ga 3d and 531.1 eV for O 1s40. We also compare the corresponding XPS results before and after etching the surface for 10 s  does not remarkably increase with the etching of Ga2O3 skin at outer surface, indicating that the oxidation depth is not very shallow. The increased fraction of Ga2Ox3−  on etched surface agrees with the attenuation or reduction of Ga2O3 during etching process. After lithiation  in the etched sample, indicating the lithiated conversion reaction progresses more sufficiently at the outer region than at the inner region. This phenomenon agrees with the increased fraction of LixGaOy component (compared with LixGa) from Ga 3d spectra. The slight inhomogeneity of lithiation process does not influence the Li-ion transport across LM coating and its oxidation skin. The phase assignment of lithiated LM is further confirmed by X-ray diffraction (XRD) pattern  analysis was performed to characterize the surface components of LM@LLZT before and after lithiation Fig. . For pri2CO3. There is a speculation that alloyable element  may react with Li2CO3 to create more Li vacancies in passivation layer for faster Li-ion transport at the interface zone43. However there is no strong evidence to support this prediction. Herein, we propose a Li2CO3-affiliative mechanism in which Li2CO3 on garnet surface is wetted and downsized by LM drops, and it is torn into Li2CO3 nanodomains by surrounding LM nanoparticles with similar nanoscale. The superior wettability can guarantee a homogeneous mixing of Li2CO3 and LM nanodomains. Therefore the separated Li2CO3 grains cannot form continuous passivation layer to retard Li-ion transport. Instead, the well-dispersed LM grains can serve as ion wires after lithiation to construct the alternative ion channels especially when they penetrate into continuous conductive network. To prove our hypothesis, we ground LM with Li2CO3 or garnet powder  does not display the evident peaks ascribed to LM  also causes the weakening and elimination of LM diffraction peaks  was resorted to. Fig. 2CO3 nanodomains, and there is no serious phase segregation observed. Under high resolution , (020), (−112) planes with d-spacings of 0.187, 0.249, 0.262 nm, respectively  image and corresponding EDS mapping of C, O, Ga , apart from the strong CO32− vibration peak at 1090 cm−1(ref.17). After mixing with LM, the characteristic peaks of garnet are covered, while the Li2CO3 peak is still maintained. This phenomenon indicates a potential interaction between LM (or its oxide skin) and LLTO surface. Compared with the Raman spectrum of LM mixed Li2CO3, we deduce that the broad peak located at 700 cm−1 should stem from the vibration of Ga–O bonding in both the mixture samples45. Note that the blending of LM cannot reduce or decompose the Li2CO3 component, agreeing with the XRD results mentioned above.Raman spectra of garnet pellet, gallium mixed Li4 to 19.5 Ω cm2 at RT, and from 272 to 5 Ω cm2 at 60 °C after LM painting on both the sides of garnet  and capacitance values (C) are listed in Supplementary Table C and τ can be expressed by (Rn1−CPE)n1/ and RC, where n is CPE exponent. The capacitance values referring to interfacial transport are in the range of 10−9–10−7 F cm−2, while those referring to surface reaction are in the range of 10−7–10−5 F cm−2. The discrepancy of capacitance range depending on different process is in accordance with the precious report by Irvine et al.47 After LM painting, the relaxation time is shortened no matter for the interfacial or surface process, also indicating an improved electrochemical kinetics. Both the ASR values of Li|LM@LLZT|Li cell at RT and 60 °C are smaller than most of reported values even if the garnet pellets we used have been intentionally exposed to air for several days  and unmodified garnet (marked as Li|LLZT|Li) as solid electrolytes, respectively. The EIS of Li/Li symmetric cells was performed to evaluate the interfacial situation. The interfacial ASR values of symmetric cells are significantly decreased from 1.75 × 10net Fig. 43. The A−2 based on an areal capacity of 0.2 mAh cm−2  even with the assistance of LE wetting , indicating an excellent defense capability of LM interlayer against Li dendrite growth48. As suggested by Flatscher et al.46, CCD is highly related to the conditions of interface wetting, pressure, and temperature. The obtained high CCD value also confirms the perfect Li wetting and agrees with the significantly reduced ASR values at the fixed conditions without externally applied pressure and high temperature.The symmetric Li|LM@LLZT|Li cells can achieve an ultralong Li plating/stripping cycling for at least 9930 h (4965 cycles) at 60 °C with an ultra-small overpotential from −10 to 10 mV, as well as from −33 to 33 mV at RT at a current density of 0.2 mA cmm−2 Fig. . The symm−2 Fig. , indicatm−2 Fig. . After am−2 Fig. . Before  mV Fig. . This loell Fig. , while ting Fig. . This hi2CO3, the lithiated interphase layer allows a uniform Li+ flux from bulk electrolyte to anode, thus resulting in a high utilization ratio of Li  is used as the nonlithium electrode. The asymmetric cell with solid electrolyte painted by LM is denoted as Li|LM@LLZT|C@Al, while the control cell with extra LE dropped on the anode side of garnet is denoted as Li|LE@LLZT|C@Al. Benefiting from the excellent wettability of LM and its dissipation effect on passive Li Li Fig. . In cont50. The interface is considered as a pseudo-binary structure of lithiated interphase and garnet and the most stable phase equilibria based on thermodynamic driving forces is determined. Lithiated interphase  shows better chemical stability with garnet  with a minor reaction energy more than −15 meV/atom 51. Therefore the side reaction between lithiated LM and LLZT is greatly mitigated. The mutual reaction energy shows the similar trend . Since the wettability of molten lithium on Li2CO3-free garnet is not bad52, the much more negative mutual reaction energy  or trace phase (LiGa5O8) and garnet electrolyte. There is no probable reaction occurring between LiGa or Li2Ga7 and ceramic, while Li5Ga4 has a low reactivity based on its reaction energy of −6 meV/atom with garnet . Therefore the Li-Ga-O interphases would not passivate the interface with LLZT.Interface reactions between lithiated LM components and LLZT were also studied (based on first-principle computations)tom Fig. , which iend Fig.  and this4 cell contains LiFePO4 cathode composited with polyethylene oxide (PEO) and lithium bis-(trifluoromethanesulfonyl) imide (LiTFSI) salt as Li-ion wire  of Li-LM@LLZT interface. This cathode interface resistance (143 Ω cm2) is not high and comparable to those in previous reports based on polymer decorated cathodes53. This solid-state cell enables an ultralong cycling performance with a highly stable capacity around 130 mAh g−1 after 440 cycles at 0.15 mA cm−2 under 60 °C  for Li–Ga alloys has a high value around 10−8–10−6 cm2 s−1 at normal temperature (24–30 °C), which is comparable to those of Li–In and Li–Al alloys54. Both the high Li flux in Li–Ga interlayer and improved interface contact are responsible for the driving of high current density. The high Li flux in Li–Ga alloy stems from the high solubility of Li in Ga metal with the existence of multiply intermetallic phases of Li-rich alloys with kinetically favorable conversion. The intimate interface contact can heal the morphological defects and homogenize the lithium growth55. Therefore the high Li flux path can be well connected from solid electrolyte to electrode. The high CE values and small voltage hysteresis of Li–Ga modified asymmetric cell can act as evidences for the high utilization of Li and fast interfacial kinetics  with certain molar ratio were used as precursors to prepare garnet Li6.5La3Zr1.5Ta0.5O12 (LLZT) by solid-state sintered technology. Fifteen percent excess Li2CO3 was added to offset the volatile loss of lithium in sintering process. La2O3 powder was calcined at 900 °C for 12 h to remove crystal water before sintering. These precursor materials were firstly mixed together with absolute ethyl alcohol and then ball-milled for 12 h at 230 r min−1. The mixed dry powder was sintered at 900 °C for 12 h to achieve tetragonal LLZT. The tetragonal garnet acquired in the previous step was broken into pieces and ball-milled for 24 h. Then the dry powder was pressed into pellet and sintered at 1250 °C for 1 h and 1150 °C for 6 h to obtain the final cubic garnet electrolyte. All of sintered garnet pellets were exposed in air for 7 days before use. The surface area and thickness of ceramic pellets were fixed at about 0.5 cm2 and 0.8 mm, respectively. The density value of used pellets ranges from 90 to 92%.The Li2O3 skin. The excess LM was carefully removed with a brush. This procedure was performed under normal air atmosphere. For interfacial resistance testing, the coin symmetric cell was assembled by melting lithium on LM-painted garnet for 5 min at 230 °C with Ni foam as current collector. During the assembly of asymmetric cell, 10 μL of commercial carbonated electrolyte  was dropped on the non-Li collector  for interface wetting. This C@Al electrode was then attached to garnet electrolyte, which was attached by Li anode at the other side. For the asymmetric cell based on unpainted garnet, the Li anode side was also wetted by 10 μL of LE, apart from the already wetted C@Al electrode side. To fabricate composite cathode, LiFePO4 powder (100 mg) was mixed with carbon black (60 mg), PEO (Aladdin) (246 mg) and LiTFSI (Sigma-Aldrich) salt (80 mg). The electrode slurry was prepared by mixing this mixture powder with acetonitrile for 12 h and then was pasted on clean carbon-coated Al foil and dried at 60 °C under vacuum overnight. The composite cathode has an active species loading of 2 mg cm−2. For polymer electrolyte fabrication, LiTFSI salt was firstly mixed with PEO in acetonitrile solution based on a molar ratio of [EO]:Li+ of 15:1, which was then stirred for 8 h. Then the solvent was evaporated and the polymer film was dried in vacuum.LM  was painted on LLZT surface at 35 °C with a brush until the whole garnet surface is wetted and coated by gallium with a dark Ga+ blocking cell (Ag/LLZT/Ag) was measured by using a Solartron frequency analyzer (1260–1296) in a frequency range from 10−2 to 5 × 106 Hz with an AC amplitude of 10 mV. The EIS spectra of symmetric cells were also measured to estimate the interface ASR with an applied frequency range from 10 MHz to 1 Hz at RT or 60 °C. For the electrochemical performance of symmetric cell, cycling process was performed at a current density of 0.2 or 1 mA cm−2 with a fixed plating/stripping interval of 1 or 0.5 h, respectively. The rate performance was performed under the current densities ranging from 0.05 to 1.2 mA cm−2 with a fixed plating/stripping interval of 0.5 h. For the CCD measurement, the stepped current density test protocol from 0.1 mA cm−2  was employed. The asymmetric cell was discharged at a current density of 0.1 mA cm−2 and then was charged to 1.0 V after 5-h deposition of Li. The solid-state full cells were measured at a current density of 0.15 mA cm−2 or at a changed rate ranging from 0.1 mA cm−2 to 0.4 mA cm−2 in a voltage range of 2.5–3.8 V. All the assembled coin cells were tested on a LAND-CT2001A Battery Test System.To measure the ionic conductivity of sintered LLZT electrolyte, Ag paste which can endure high temperature was coated on ceramics and calcined at 150 °C and then 800 °C for 10 min, respectively, to remove the organic component and ensure a tight contact. Then the EIS of Li2CO3 powder. The sample used in TEM was distributed in ethanol under sonication and then was deposited on a Cu wire mesh. Raman spectra for the garnet powder, LM mixed garnet powder and LM mixed Li2CO3 powder were collected by a thermal dispersive spectrometer excited by a laser with the wavelength of 532 nm and the power of 10 mW. To explore the interface components of LM@LLZT before and after lithiation, XPS measurement (ESCAlab-250) with an Al anode source was also performed. Sample with fresh surface of LM@LLZT was fabricated by simply painting LM on air-exposed garnet surface, while the lithiated sample was firstly lithiated by melting a lithium disc of 0.3 cm2 for 5 min and then the surface-lithiated garnet was peeled from Li disc.SEM  and EDS mapping were used to analyze the morphology and component distribution of garnet electrolyte and its interface. For the morphology observation of electrolyte surface and cross-section, LLZT pellet was smashed to obtain the samples. To prepare the cross-section interface, the Li|LLZT|Li symmetric cell was firstly assembled under a pressure of 50 MPa. Under this pressure, the Li|LLZT|Li trilayer structure was compacted but it is prone to be smashed. Then the smashed cell was disassembled to choose the suitable fragment for cross-section morphology characterization. The prior assembly of symmetric cell guarantees a relatively uniform pressure on the whole interface. Both the pristine and modified interface samples were prepared in this way in order to achieve a comparable result. XRD  was used to characterize the phase constitutions of sintered garnet and LM-painted electrolyte, as well as interface components after lithiation. Air-exposed garnet and LM-painted LLZT pellet were directly tested, while the interface component sample was firstly alloyed with lithium and then the interface was peeled off from garnet for XRD test. All the samples involved with lithium metal were fabricated in Ar-filled glove-box and sealed in a box when transferred to the testing chamber. The TEM with energy dispersive spectroscopy  was operated at 200 kV to characterize the interfacial structure and components of LM mixed LiSupplementary Information