Electrode‐Specific Janus Separator Towards High‐Performance Lithium Metal Batteries

ABSTRACT Lithium metal batteries (LMBs) are promising next‐generation rechargeable batteries owing to their exceptional energy densities, especially when paired with layered Ni‐based oxide cathodes. However, the practical realization of LMBs is limited by two asymmetrical degradation pathways at both electrodes: dendritic growth and side reactions at the anode, which pose safety hazards, and transition metal (TM) dissolution at the cathode, which accelerates capacity loss. Herein, a surface‐engineered Janus separator design strategy is proposed that simultaneously suppresses Li dendrite formation and TM dissolution with distinct directionally targeted layers for electrode‐specific challenges in LMBs. On the anode‐facing side, a 315 nm thin conducting hybrid polypyrrole–silicon oxide network (Ppy–SiO 2 ) layer fabricated by vapor‐phase printing enables uniform Li + flux and dendrite suppression while simultaneously providing enhanced thermal and mechanical stability. The cathode‐facing layer, composed of ion‐capturing inorganic particles of polydopamine‐coated boehmite (PDA@BM), acts as a selective barrier, mitigating TM ion migration by over 96%. These dual functionalities yield superior interfacial stability and long‐term cycling performance. The Janus separator design and fabrication strategy enables compositionally distinct, directionally targeted layers to deliver synergistic regulation for anode‐ and cathode‐driven asymmetric failure mechanisms for the practical realization of high‐performance LMBs.