High‐Performance Sheet‐Type Sulfide All‐Solid‐State Batteries Enabled by Dual‐Function Li4.4Si Alloy‐Modified Nano Silicon Anodes

The silicon-based anodes are one of the promising anodes to achieve the high energy density of all-solid-state batteries (ASSBs). Nano silicon (nSi) is considered as a suitable anode material for assembling sheet-type sulfide ASSBs using thin free-standing Li₆PS₅Cl (LPSC) membrane without causing short circuit. However, nSi anodes face a significant challenge in terms of rapid capacity degradation during cycling. To address this issue, dual-function Li_4.4Si modified nSi anode sheets are developed, in which Li_4.4Si serves a dual role by not only providing additional Li⁺ but also stabilizing the anode structure with its low Young's modulus upon cycling. Sheet-type ASSBs equipped with the Li_4.4Si modified nSi anode, thin LPSC membrane, and LiNi_0.83Co_0.11Mn_0.06O₂ (NCM811) cathode demonstrate exceptional cycle stability, with a capacity retention of 96.16% at 0.5 C (1.18 mA cm^-2) after 100 cycles and maintain stability for 400 cycles. Furthermore, a remarkable cell-level energy density of 303.9 Wh kg^-1 is achieved at a high loading of 5.22 mAh cm^-2, representing a leading level of sulfide ASSBs using electrolyte membranes at room temperature. Consequently, the chemically stable slurry process implemented in the fabrication of Li_4.4Si-modified nSi anode sheet paves the way for scalable applications of high-performance sulfide ASSBs.