Understanding the Kinetic and Mechanical Behavior of Silicon Anodes for Low Stack Pressure All-Solid-State Batteries

Silicon (Si) anodes have attracted significant attention for all-solid-state batteries (ASSBs) due to their high theoretical capacity (~3500 mAh g⁻¹), which is nearly ten times that of conventional graphite (~370 mAh g⁻¹). Additionally, Si is earth-abundant and environmentally benign, making it a highly attractive candidate for sustainable energy storage. However, the practical deployment of Si anodes in ASSBs remains challenging, primarily due to severe volume expansion (>300%) during lithiation/de-lithiation, which leads to particle pulverization, interfacial degradation, and substantial irreversible capacity loss, especially under low stack pressure. In this work, we investigate a Si composite anode architecture that addresses these limitations by embedding Si particles within a Li x PS y Cl z (LPSCl) solid electrolyte (SE) matrix. The SE not only functions as an ion-conducting medium but also serves as a mechanical buffer to mitigate stress-induced degradation. Electrochemical analysis reveals that the Si–LPSCl composite delivers significantly enhanced performance, particularly under low operating pressure. Under high operating pressure (75 MPa), the composite achieves an initial Coulombic efficiency (ICE) of ~95% in a full cell with an NCM811 cathode, approaching the theoretical maximum and far surpassing the 80% ICE observed for a pure Si anode. Notably, the Si composite also retains high performance under low operating pressure (~5 MPa), with an ICE of 81%, compared to only 55% for the pure Si anode. Morphological characterization confirms that the Si–LPSCl anode maintains structural integrity during cycling, exhibiting minimal cracking and allowing for 3D ionic and electronic transport throughout the electrode layer. In contrast, the pure Si anode exhibits pronounced kinetic and mechanical degradation, particularly under low operating pressure, where lithium trapping and poor reversibility dominate. These findings highlight the critical role of kinetic–mechanical coupling in the design of solid-state electrodes and demonstrate that embedding a solid electrolyte matrix within silicon anodes effectively mitigates pressure-induced limitations. This approach enables stable and reversible electrochemical cycling, even under practical low-pressure conditions, thereby advancing the viability of ASSB systems for real-world applications. Figure 1