High‐Performance Sheet‐Type Sulfide All‐Solid‐State Batteries Enabled by Dual‐Function Li_4.4Si Alloy‐Modified Nano Silicon Anodes

Abstract 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.