Stabilizing Lithium Metal Surface in Solid‐State Batteries via Single‐Step Gas‐Phase Synthesis of Li ₃ N Interfacial Layer

The performance of solid‐state Li‐metal batteries (SSLBs) with argyrodite solid electrolytes (SEs) is limited by interfacial side reactions at the Li‐metal/SE interface. In this study, we introduce Li 3 N interfacial layer as a stabilizer at the Li/SE interface based on its good electrochemical and mechanical properties. The Li 3 N is synthesized onto the Li‐metal substrate in micrometer thickness through a straightforward treatment of Li‐metal in a N 2 ‐filled glovebox, as confirmed by plasma focused ion beam analysis. The Li 3 N interfacial layer exhibits outstanding cycling stability in its symmetrical cell for over 5000 cycles, equivalent to 6000 h of operation, while the bare Li symmetrical cell endures only 257 cycles. Multimodal characterization techniques coherently demonstrate that the Li 3 N interfacial layer contributes to reducing mechanical resistance (e.g., voids, microcracks) at the Li/SE interface, as well as charge–transfer resistance during cycling in full‐cells, particularly when paired with LiNbO 3 ‐coated LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622) cathode. Furthermore, the Li 3 N interfacial layer not only enhance specific capacity (178 mAh g −1 ) and Coulombic efficiency (>99% at the 2 nd cycle) but also improve the rate capability of the SSLB full cells. Our study highlights the promising strategy of employing Li 3 N as an interfacial layer for stabilizing the Li/SE interface in SSLBs.