Li Atomic Diffusivity: A Key Descriptor for Critical Current Density and Cycling Stability in Alloy Anodes for All-Solid-State Lithium Batteries

Alloy anodes hold promise for achieving dendrite-free all-solid-state lithium batteries (ASSLBs) by regulating lithium deposition behavior, leading to enhanced critical current density (CCD) and cycling stability. However, existing alloy anodes in ASSLBs fall short of practical requirements (CCD > 10 mA cm^-2), and key factors determining CCD remain unclear. Here, we propose a diffusion-controlled Li deposition model in which CCD critically depends on the competition between surface attachment and diffusion of incoming atoms. Multimodal characterizations validate that Li atomic diffusivity in the alloy anode is a key descriptor for the CCD and cycling stability of ASSLBs. Leveraging this insight, LiGa is chosen as the optimized alloy anode due to its high Li atomic diffusivity (∼3 × 10^-7 cm² s^-1), which enables a record-high CCD exceeding 50 mA cm^-2 and stable solid electrolyte-anode interface at a high current density of 3 mA cm^-2. ASSLBs pairing the LiGa anode with the LiNi_0.8Co_0.1Mn_0.1O₂ cathode and using Li₆PS₅Cl (LPSCl) solid electrolyte exhibit remarkable long-term cycling stability of 1000 cycles with 80% capacity retention under 25 °C and a stacking pressure of 1 MPa, outperforming state-of-the-art alloy anode-based counterparts. This work establishes a unified descriptor for the control of Li deposition, advancing practical ASSLB development.