Y ³⁺ /Zn ²⁺ 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 Li_1.3Al_0.275Y_0.025Ti_1.7(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.