Probing component contributions and internal polarization in silicon-graphite composite anode for lithium-ion batteries with an electrochemical-mechanical model

Silicon-graphite (Si-Gr) composite anodes are attractive alternatives to replace Gr anodes for lithium-ion batteries (LIBs) owing to their relatively high capacity and mild volume change. However, it is difficult to understand electrochemical interactions of Si and Gr in Si-Gr composite anodes and internal polarization of LIBs with regular experiment methods. Herein, we establish an electrochemical-mechanical coupled model to study the effect of rate and Si content on the electrochemical and stress behavior in a Si-Gr composite anode. The results show that the composites of Si and Gr not only improve the lithiation kinetics of Gr but also alleviate the voltage hysteresis of Si and decrease the risk of lithium plating in the negative electrode. What's more, the Si content is a tradeoff between electrode capacity and electrode volume variation. Further, various internal polarization contributions of cells using Si-Gr composite anodes are quantified by the voltage decomposition method. The results indicate that the electrochemical polarization of electrode materials and the electrolyte ohmic over-potential are dominant factors in the rate performance of cells, which provides theoretical guidance for improving the rate performance of LIBs using Si-Gr composite anodes.