Abstract

The design of functional separators that can simultaneously regulate interfacial stability and safety remains a critical challenge in lithium metal batteries (LMBs). In this work, we introduce an aluminum nitride-based ceramic-coated separator (AlN-CCS) to address these concerns. The AlN-CCS exhibits enhanced ionic conductivity and electrolyte wettability compared to conventional polyethylene separators, while maintaining comparable physical and ion-conductive properties to oxide-based CCSs. Importantly, the conversion reaction between AlN and Li metal induces the in situ formation of a Li3N-rich solid-electrolyte interphase and a lithiophilic LiAl alloy, effectively reducing nucleation overpotential and promoting uniform Li deposition. As a result, Li||LiNi0.6Co0.2Mn0.2O2 (NCM622) full cells with AlN-CCS demonstrate significantly improved cycling stability, achieving 76.6% capacity retention even after 500 cycles, compared to 59.6% for Al2O3-CCS. Furthermore, owing to the intrinsically high thermal conductivity of AlN, the AlN-CCS enables efficient lateral heat dissipation, effectively mitigating localized hotspot formation under abnormal conditions such as internal short circuits. These results demonstrate that nitride-based CCSs can be an effective and easier alternative to simultaneously enhance electrochemical performance and safety, offering a promising pathway toward high-energy-density and reliable LMBs.