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

Abstract

Silicon-graphite (Si-Gr) composite anode are attractive alternatives to Gr anode for lithiumion batteries (LIBs) owing to relatively high capacity and mild volume change. However, it is difficult to understand the electrochemical interactions of Si and Gr in the Si-Gr composite anode and the 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 the 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, the various internal polarization contributions of the cell using Si-Gr composite anode 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 the cell, which provides theoretical guidance for improving the rate performance of LIBs using Si-Gr composite anode.

Lithium Redistribution Mechanism within Silicon-Graphite Electrodes: Multi-Method Approach and Method Validation

“…The recently applied models for simulations of Si-containing electrodes focus on different scales, electrochemical-mechanical coupling, or higher computational efficiency, but either way show the interaction between Si and graphite by treating them as separate components. 31,[34][35][36] These models reproduce the aforesaid experimental findings by showing, inter alia, the detailed concentration distribution with high spatial resolution which is not easily measurable.…”

“…Qualitative trends are consistent with previous reports. 31,34,42 At 100% SOC, the lithiation state of the graphite component is higher than in the Si component (compare cyan and dark blue solid lines at 100% SOC in Fig. 5a).…”

“…29,30 Physicochemical modeling allowed to unveil the competition of the different components during lithiation at different C-rates and loadings by quantifying the state-of-charge (SOC) in every part of the composite electrode. 31,32 The Li concentration in discretization compartments of the active materials is calculated and normalized by the maximum Li concentration of the respective material yielding a lithiation fraction comparable to the concept of SOC. 32,33 Therefore, modeling enables differentiation not only between the active materials but also between the exact positions within the electrode (e.g.…”