Cycle Life Evaluation for Lithium-Ion Capacitors

Lithium-ion capacitor (LiC) is a hybrid energy storage device which compounds the energy storage mechanisms of lithium-ion batteries (LIBs) and electric double-layer capacitors (EDLCs). Its structure is composed of a positive electrode with activated carbon as in double-layer capacitor and a negative electrode based on Li-doped carbon like the Li-ion battery. The advantage of the LiC technology compared to the conventional storage device is because of the power density, the nominal voltage, and the energy density is higher than the EDLCs. Due to their inherent long cycle life, it is indispensable to predict the cycle life of this cell type. The objective of this paper is to investigate the capacitance degradation of LiCs by calendar life test and power-cycling test. In the calendar life test, the degradation is measured at different floating voltages and temperatures. In the power cycling test, the degradation corresponding to the current level and the temperature is evaluated. The resulting capacitance retention trends declare a dependency to temperature, SoC, and current levels.