Direct Structure-Performance Comparison of All-Carbon Potassium and Sodium Ion Capacitors.
A hybrid ion capacitor (HIC) based on potassium ions (K+) is a new high-power intermediate energy device that may occupy a unique position on the Ragone chart space. Here, a direct performance comparison of a potassium ion capacitor (KIC) versus the better-known sodium ion capacitor is provided. Tests are performed with an asymmetric architecture based on bulk ion insertion, partially ordered, dense carbon anode (hard carbon, HC) opposing N- and O-rich ion adsorption, high surface area, cathode (activated carbon, AC). A classical symmetric "supercapacitor-like" configuration AC-AC is analyzed in parallel. For asymmetric K-based HC-AC devices, there are significant high-rate limitations associated with ion insertion into the anode, making it much inferior to Na-based HC-AC devices. A much larger charge-discharge hysteresis (overpotential), more than an order of magnitude higher impedance R SEI, and much worse cyclability are observed. However, K-based AC-AC devices obtained on-par energy, power, and cyclability with their Na counterpart. Therefore, while KICs are extremely scientifically interesting, more work is needed to tailor the structure of  "Na-inherited" dense carbon anodes and electrolytes for satisfactory K ion insertion. Conversely, it should be possible to utilize many existing high surface area adsorption carbons for fast rate K application.
['Xu|Ziqiang|Z|', 'Wu|Mengqiang|M|', 'Chen|Zhi|Z|', 'Chen|Cheng|C|', 'Yang|Jian|J|', 'Feng|Tingting|T|', 'Paek|Eunsu|E|', 'Mitlin|David|D|https://orcid.org/0000-0002-7556-3575']
sodium ion capacitors potassium ion capacitors lithium ion capacitors potassium ion batteries sodium ion batteries