In Situ Formation of the Li 3 Bi Alloy Phase Interface for Robust Garnet Solid‐State Lithium Batteries

ABSTRACT Garnet‐type electrolyte Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (LLZTO) is a promising component for commercializing solid‐state batteries owing to its wide electrochemical window, good stability, and high shear modulus. However, poor interface wettability and lithium dendrite growth limit the practical application of the LLZTO electrolyte. In this study, a bismuth metal film was introduced at the electrolyte interface to enhance the performance of lithium metal solid‐state batteries through vacuum thermal evaporation. Through the conversion reaction between bismuth and lithium, an intermediate Li 3 Bi layer was formed in situ at the Li/LLZTO interface. This intermediate layer exhibited excellent lithium affinity and promoted close contact between the solid electrolyte and lithium metal, thereby reducing the interfacial resistance by approximately 6.17 times. Furthermore, the mechanically resilient Li 3 Bi interlayer effectively suppressed stress variations induced by lithium dendrite growth, while its provision of ordered Li + pathways ensured uniform lithium deposition. The lithium symmetric batteries exhibited high critical current densities of 1.1 mA cm −2 . In addition, the corresponding solid‐state LFP/LLZTO@Bi/Li batteries achieved cycling stability over 300 cycles with a retention capacity of 85.67%. This study provides a simple and integrated strategy for developing high‐performance quasi‐solid‐state lithium metal batteries.