Mechanical stress-driven electrochemical thermal model for graphite-silicon blended composite anode in lithium-ion battery

Abstract

The graphite-silicon blended anodes are increasingly employed due to their high power and energy density. The electrochemical and mechanical hysteresis, heat generation rate (HGR) and energy efficiency of the blended anode have not been fully investigated. We propose a mechanical stress-driven composite anode model implemented on an electrochemical-thermal model platform for cylindrical-type lithium-ion batteries, which considers hydrostatic diffusion-induced stress on particle level, biaxial stress on electrode level, stress-induced overpotential and competing Butler-Volmer kinetics between graphite and silicon particles. The model is validated against the experimental terminal voltages and HGRs at different C-rates and temperatures, which enables analysis on the mechanical, electrochemical and thermal behaviors induced by silicon component. The results show that the stress within anode particles is dependent upon not only Li⁺ concentration but also concentration gradient. The hydrostatic stress within silicon particles is notably larger than graphite, which drives a silicon-dominated reaction in low-SOC range, and consequently causes a voltage hysteresis majorly at low SOC. Tuning the graphite-silicon volume ratio as a model parameter, the impacts of the addition of silicon on the voltage and HGR are predicted and investigated. Estimatedly ∼25 % of the cell-level HGR is contributed by the 4 % silicon in low-SOC range at 1C operations.