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

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-SiO₂) 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.