Overcoming Kinetic Limitations of Silicon Anodes Toward Fast‐Charging Sulfide‐Based All‐Solid‐State Batteries

All-solid-state batteries (ASSBs) with silicon (Si) anodes offer great potential for high energy density and safety. Although long cycling life can be obtained at a low current density, the fast-charging capability of Si anode is hindered by the short circuit, which reason is unclear. Herein, the kinetic limit leading to the short circuit is probed and identified to be the slow charge transfer rather than the Li⁺ transport in Si anode bulk. The addition of excess conductive carbon can increase the Si anode's electronic conductivity and thus enhance the ASSBs' rate performance but at the expense of reducing the energy density. To resolve this, a micro-size Li-Al alloy is proposed to replace the conductive carbon and construct an all-electrochemical-active Si anode, which demonstrates several merits such as increasing the reaction kinetics (up to 8.1 mA cm^‒2), providing extra capacity, and enhancing mechanical stability during cycling. As a result, the Si||NCM811 ASSBs (N/p = 1.2) achieve a high initial coulombic efficiency of 89.3%, high area capacity of 6.7 mAh cm^‒2, and stable cycling over 850 cycles with capacity retention of 80.5% at 1C. This work figures out the underlying kinetic reason for the Li dendrites growth and guides to achieving high-performance ASSBs.