Y3+/Zn2+ Codoped LATP/PVDF-HFP Coating Enables Bulk–Interface Regulation for Stable Lithium Metal Batteries

Developing functional separators capable of simultaneously suppressing lithium dendrite growth and enabling compatibility with high-voltage cathodes is critical for realizing long-cycle-life lithium metal batteries. Herein, a synergistic bulk–interface regulation strategy is achieved via a coatable Y3+/Zn2+ codoped LATP/PVDF-HFP composite coating applied onto a commercial polypropylene (PP) separator. Y3+/Zn2+ codoped Li1.3Al0.275Y0.025Ti1.7(PO4)3 (LAYTP-Zn) is synthesized via a solid-state route and uniformly integrated with PVDF-HFP to form a conformal coating with strong interfacial adhesion. Y3+/Zn2+ incorporation induces lattice expansion of LATP, thereby broadening bulk Li+ transport pathways. In addition, Zn2+ regulates interfacial chemistry by enhancing electrolyte dissociation and anchoring anions through Lewis acid interactions, while also promoting the formation of polar β-phase PVDF-HFP, collectively increasing the Li+ transference number to 0.79. In addition, the polymer matrix serves as a physical barrier that mitigates direct interfacial side reactions. The coordinated regulation of bulk ion conduction and interfacial ion distribution enables a more uniform Li+ flux and facilitates the formation of a LiF-enriched and mechanically robust interphase, thereby suppressing dendrite nucleation and growth. As a result, Li||Li symmetric cells exhibit stable cycling for over 3000 h at 1 mA·cm–2 and 1 mAh·cm–2. Furthermore, Li||LFP and Li||NCM811 half-cells deliver capacity retentions of 91.2% after 800 cycles at 1 C and 95.1% after 200 cycles at 0.5 C, respectively, while maintaining stable operation up to 4.73 V. This work provides a scalable separator design that integrates bulk transport optimization with interfacial regulation, offering a practical pathway toward high-performance lithium metal batteries.