The influence of electrode matching on capacity decaying of hybrid lithium ion capacitor

Hybrid lithium-ion capacitors (HyLICs), combining a battery-type negative electrode and a composite positive electrode, can display a more comprehensive performance than conventional lithium-ion capacitors (LICs), e.g. high energy density. However, owing to the coexisting of non-Faradaic and Faradaic energy storage mechanism in the composite positive electrode, the insufficient cycle stability of device becomes an urgent problem. In this paper, we discussed the influence of electrode matching on the cycling stability of HyLICs with a L30/HC@SLMP structure. The three L30/HC mass ratios were 0.8, 1.0 and 1.2, respectively. Three full cells with above ratios exhibit great difference in cycle stability when charging/discharging at a current density of 1 A g⁻¹. Various methods, including galvanostatic charging/discharging, three-electrodes test and scanning electron microscopy, were used to analyze the performance of difference cells. It turns out that the poor rate performance of HC electrode is the main limited factor in HyLICs' cycling stability. Compared with the composite positive electrode, HC electrode is more sensitive to the current densities. Under high current density, solid electrolyte interface layers on the HC electrode surface accumulated fast, which leads to the increase in the impedance of HC electrode. From the Ragone plot, the best matching strategy of L30/HC electrode was achieved when the mass ratio of L30/HC was 1.0. Finally, the optimal HyLICs with L30/HC mass ratio of 1.0 were assembled and performed an excellent cycle stability of more than 80% retention after 62,000 cycles in 40C, as well as better power and energy density compared with LICs.