Gradient-Engineered Ultra-Thin Lithium Metal Anodes with a Li–Si–N Alloy-Based Lithiophilic Current Collector Interphase

Abstract

Li metal anodes, with high theoretical capacity (3860 mAh g⁻¹) and low redox potential, are promising for high-capacity rechargeable batteries. Especially, ultra-thin Li metal anodes can improve energy density and minimize lithium excess. However, their poor processability leads to non-uniform Li layers and unstable plating/stripping behavior. In this study, we present a current collector interphase (CCI)-based strategy using a Cu foil coated with a lithiophilic Si₃N₄ layer, followed by molten Li dip-coating to form around 20 μm Li layer. Furthermore, the scalable dip-coating method, compatibility with large-area current collectors (up to 100 cm²), and stable cycling in pouch cells demonstrate the practical viability of the proposed SNLMA design for commercial lithium metal batteries. During the process, an in-situ Li–Si–N alloy gradient interphase forms at the interface, enhancing wettability and mechanical integrity. This unique gradient CCI provides synergistic lithiophilicity and structural stability, enabling high-performance Li metal batteries. The resulting Li_xSi_y and Li_xN_y phases reduce nucleation barriers and enable uniform Li deposition. As a result, the Si₃N₄–Li anode paired with a high-loading LCO cathode (22 mg cm⁻²) achieved 83% capacity retention after 100 cycles. This work offers a scalable and practical CCI design for next-generation Li metal batteries.