Effect of fluoroethylene carbonate and vinylene carbonate additives on full-cell optimization of Li-ion capacitors

Lithium-ion capacitors (LICs) operate by two mechanisms, namely a double-layer mechanism based on a capacitor-like positive electrode and the intercalation mechanism of a battery-like negative electrode. Hence, well-designed reaction kinetics between the positive electrode and negative electrode are essential for optimizing LIC full-cell configurations. In this study, we investigated the influences of fluoroethylene carbonate (FEC) or vinylene carbonate (VC) as electrolyte additives on full-cell performance of LICs. We confirmed that the internal resistance of graphite increased with the use of FEC, which degraded the cyclability of the LIC full-cell. Conversely, LICs consisting of the VC additive had good cyclability over 4000 cycles owing to the solid electrolyte interphase (SEI) containing polymeric species. This detailed investigation into the function of SEI compounds derived from VC additives and their effect on cyclability will provide new insights into optimization of LIC full-cell configurations with appropriate electrolyte additives.