Nitrogen‐Deficient Graphitic Carbon Nitride for Superior All‐Solid‐State Sulfide‐Based Lithium Metal Batteries

All‐solid‐state lithium metal batteries (ASSLMBs) are regarded as the most promising next‐generation energy storage devices due to their high energy density and superior safety. However, sulfide solid electrolytes (SSEs) still suffer from critical challenges, including lithium dendrite propagation, interfacial side reactions, low Coulombic efficiency, and limited cycling stability. Herein, we propose an artificial interlayer of nitrogen‐deficient graphitic carbon nitride (NDGCN) to enhance the interfacial stability between lithium metal and SSEs. The NDGCN layer on the lithium metal surface not only mitigates continuous interfacial reactions but also provides lithiophilic sites to regulate Li + deposition, thereby suppressing dendrite growth. The NDGCN‐Li symmetric cell achieves a significantly enhanced critical current density (CCD) of 3.82 mA cm −2 and maintains stable cycling for over 850 h at 1 mA cm −2 . Moreover, the assembled full cell retains 96.66% capacity retention after 2700 cycles at 2C.