Aging processes in high voltage lithium-ion capacitors containing liquid and gel-polymer electrolytes

Lithium-ion capacitors (LICs) are nowadays considered as one of the most interesting high-power devices, and they are used in an increasing number of applications. In the last years, several efforts have been made to increase the energy of these devices, but only a few studies investigated in detail the degradation processes taking place in LICs. In this contribution, we are reporting on a systematic investigation of the aging processes taking place in LIC containing liquid and gel-polymer electrolytes. We show that the use of both electrolytes enables the realization of LICs that operate at 4.5 V and have very good stability. Furthermore, we report that the aging of LICs involves the deterioration of the solid electrolyte interface (SEI) of the graphite electrode, which leads to a decrease of the concentration of LiC6/LiF and to an increase of phosphide (P/LixP) within the electrode. In the activated carbon electrode, the concentration of phosphide (P/LixP) and fluoride (C-Fx) increases, and trapping of Li-ions on the pores of the carbon occurs. These degradation processes are taking place simultaneously and might affect each other.