Revealing anion chemistry above 3V in Li-ion capacitors

Lithium ion capacitors (LIC) are capable of delivering higher energy densities than supercapacitors due to their hybrid charge storage mechanism in which Li-ions are stored via Faradaic reactions in negative electrodes and anions are adsorbed via non-Faradaic reactions on positive electrodes. Although there have been concerted efforts to increase the energy and power densities of these devices by engineering the electrodes, little attention has been paid to the critical role of the electrolyte. Here, we investigated the influence of electrolytes on LIC performance by exploring Li-salts with different anions. The individual anionic contributions toward the overall electrolyte conductivity and electrochemical performances in half-cell and full-cell configurations highlights the importance of the electrolyte formulation in LIC. We demonstrated that the energy and power densities achievable by LICs are largely influenced (and perhaps determined) by the anion adsorption at the positive electrodes, and by the ion transport within the electrolytes. Our study suggests the electrolyte properties, metrics and structural features that are relevant during the design of new LIC systems.