Towards High-Performance Lithium-Ion Batteries via Voltage Modulation of Silicon Anodes

Silicon (Si) is a promising anode material for boosting the energy density of current lithium-ion batteries; however, Si anodes suffer from enormous volume modulations and unstable solid electrolyte interphases (SEI) associated with the voltage window. Nevertheless, the relationship between voltage changes and deterioration of electrochemical performance remains unclear. Through systematic investigation of Si anodes under various cut-off voltages, we reveal that an increased degree of delithiation generates high hoop stress around the particle surface, ultimately leading to SEI thickening, fragmentation, and reformation. Furthermore, residual Li retained within Si particles after delithiation facilitates bidirectional Li⁺ diffusion, from Si core to shell and from electrolyte to shell, during the subsequent lithiation process. This phenomenon reduces the internal Li⁺ concentration gradient, delays the formation of crystalline Li₁₅Si₄, and alters delithiation kinetics. In addition, we observed that maintaining the voltage window within a range that induces high hoop stress and prevents the formation of crystalline Li₁₅Si₄ enables the Si anode to achieve optimized cycling performance and capacity. This voltage modulation criterion is also applicable for nano-sized Si, graphite-Si composite anodes, and solid-state batteries. The practical effectiveness of this approach is demonstrated through the successful operation of 5 Ah LiCoO₂/Si pouch cells, confirming that dynamic voltage control based on polarization can substantially enhance the cycle life of lithium-ion batteries.