Improving anode performances of lithium-ion capacitors employing carbon–Si composites

The lithium-ion capacitor is a promising energy storage system with a higher energy density than traditional supercapacitors. However, its cycling and rate performances, which depend on the electrochemical properties of the anode, are still required to be improved. In this work, soft carbon anodes reinforced using carbon–Si composites of various compositions were fabricated to investigate their beneficial influences on the performance of lithium-ion capacitors. The results showed that the specific capacities of the anodes increased significantly by 16.6 mAh·g−1 with 1.0 wt% carbon–Si composite, while the initial discharge efficiency barely changed. The specific capacity of the anode with a 10.0 wt% carbon–Si composite reached 513.1 mAh·g−1, and the initial discharge efficiency was 83.79%. Furthermore, the anodes with 7.5 wt% or lower amounts of carbon–Si composite demonstrated reduced charge transfer resistances, which caused an improvement in the rate performance of the lithium-ion capacitors. Moreover, the use of the optimized amount (7.5 wt%) of carbon–Si composite in the anode could significantly improve the cycling performance of the lithium-ion capacitor by compensating the consumption of active lithium. The capacity retention of the lithium-ion capacitor reached 95.14% at 20 C after 10,000 cycles, while the anode potential remained below 0.412 V, which is much lower than that of a soft carbon anode.