Interplay between electrochemical reactions and mechanical responses in silicon–graphite anodes and its impact on degradation

Abstract

Durability of high-energy throughput batteries is a prerequisite for electric vehicles to penetrate the market. Despite remarkable progresses in silicon anodes with high energy densities, rapid capacity fading of full cells with silicon–graphite anodes limits their use. In this work, we unveil degradation mechanisms such as Li⁺ crosstalk between silicon and graphite, consequent Li⁺ accumulation in silicon, and capacity depression of graphite due to silicon expansion. The active material properties, i.e. silicon particle size and graphite hardness, are then modified based on these results to reduce Li⁺ accumulation in silicon and the subsequent degradation of the active materials in the anode. Finally, the cycling performance is tailored by designing electrodes to regulate Li⁺ crosstalk. The resultant full cell with an areal capacity of 6 mAh cm⁻² has a cycle life of >750 cycles the volumetric energy density of 800 Wh L⁻¹ in a commercial cell format.

The degradation in silicon-graphite anodes is originated from Li ion crosstalk between silicon and graphite, and the pressure-induced staging transition of the graphite. Here, the authors demonstrate a prismatic cell with improved volumetric energy density and cycle stability by targeted solving above issues.