On the Specific Capacity and Cycle Stability of Si@void@C Anode: Effects of Electrolytes

Abstract

Electrolytes play a critical role in the formation of stable solid electrolyte interphase (SEI) for Si anodes. This study investigates the impacts of five different electrolytes on the specific capacity and cycle stability of Si-based anodes and confirms the advantages of the second-generation (Gen2) electrolyte over the first-generation (Gen1) electrolyte in the first 200 cycles, beyond which the advantages of Gen2 electrolyte disappear. Addition of more FEC and VC additives to Gen2 electrolyte does not offer significant advantages in the cycle stability and specific capacities. However, very high FEC electrolytes with 20 wt% FEC and 80% dimethyl carbonate exhibits strong dependance on the lithiation cutoff voltage. This electrolyte results in durable SEI layers when the lithiation cutoff voltage is at 0.01 V vs Li/Li+. Furthermore, lowering the lithiation cutoff voltage from 0.1 V to 0.01 V vs Li/Li+ has raised the specific capacity of Si-based anodes, leading to higher specific capacities than those of graphite anodes at the electrode level for 380 cycles investigated in this study. The understandings developed here provide unambiguous guidelines for selection of electrolytes to achieve long cycle stability and high specific capacity of Si-based cells simultaneously in the future.