Facilely Constructing Li ₃ P/Fe Dual-Conductive Interface for High-Performance Garnet-Based Solid-State Lithium Metal Batteries

Garnet-type Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (LLZTO) is recognized as an ideal solid-state electrolyte candidate for high-energy-density solid-state lithium metal batteries (SSLMBs), offering high ionic conductivity and good lithium compatibility. However, poor interfacial wettability with lithium anodes and lithium dendrite formation during cycling hinder its application, causing escalated interfacial resistance and short-circuit risks. To address these challenges, this study proposes an efficient and scalable solution-coating strategy: a uniform FeP coating is deposited on the LLZTO surface, and an in situ chemical reaction between molten lithium and FeP successfully constructs a Li 3 P/Fe composite interfacial layer with mixed ionic/electronic conductivity. This layer significantly reduces interfacial impedance through the synergistic effect of Li 3 P (ionic conductor) and Fe (electronic conductor) while effectively suppressing lithium dendrite nucleation and penetration by leveraging the high interfacial energy of Li 3 P and the uniform lithium deposition guidance effect of Fe. Therefore, the symmetric cell based on the Li 3 P/Fe-modified interface achieves stable cycling for over 2200 h at a current density of 0.1 mA cm –2 . Furthermore, the full cell assembled with a LiFePO 4 (LFP) cathode retains 88.6% capacity retention after 100 cycles at 1 C, demonstrating exceptional long-term cycling stability. This interface engineering strategy provides a novel design approach for developing solid-state lithium metal batteries with high safety, high energy density, and long lifespan, offering significant reference value for advancing the industrialization of solid-state batteries.