Improved Cyclability of Lithium-Ion Batteries Using Pyroprotein-Assisted Silicon Anodes

With a 10-fold higher theoretical capacity than that of graphite, silicon has excellent potential for use as an active anode material in lithium-ion (Li-ion) batteries, especially when high capacity and high energy density are required. In this study, we improved the lifetime characteristics of silicon nanoparticles (SINPs) by synthesizing a Si/C composite anode composed of carbonized fibroin (pyroprotein) and SINPs. The pyroprotein matrix effectively accommodates the volume expansion of the SINPs during charging and discharging, thereby suppressing the formation of surface defects on the electrode. This pyroprotein matrix also provides additional storage sites for Li-ion chemisorption and uniformly delivers Li ions to the SINP surfaces through a solid–solution reaction. The Si/C anode exhibits improved rate capability compared to that of the SINPs, with a 30% higher capacity retention over 50 cycles. Furthermore, even in a graphite-silicon (G-Si) composite anode, the G-Si/C anode showed a capacity retention rate of 99.5% over 100 cycles, which is superior to the performance of silicon-based anode materials; hence, it is a potential candidate for use in long-life G-Si composite anodes.