Enhancing Ion Transport and Suppressing Electron Conduction: a Hybrid Interlayer for Stable Garnet‐Based Solid‐State Batteries

Abstract Cubic doped Li 7 La 3 Zr 2 O 12 s (LLZOs) are promising solid‐state electrolytes (SSE) for solid‐state lithium batteries due to their excellent lithium‐ion conductivities and electrochemical stability. However, they face the challenge of lithium dendrite growth. Here, a hybrid interlayer–alloy phases (LiZn, Li 22 Sn 5 , Li 5 Sn 2 ) and Li 2 O–is created by an in situ reaction between the modified layer Zn 2 SnO 4 (ZSO) on LLZO and lithium metal anodes. Benefiting from the synergistic effect of the fast lithium‐ion conduction of the Li 5 Sn 2 alloy, the strong affinity between the LiZn alloy and LLZO, and electronic insulator Li 2 O, a super‐conformal structure at the Li/ZSO‐LLZO interface is formed, effectively inhibiting the formation of lithium dendrites in ZSO‐LLZO SSE. Consequently, Li/ZSO‐LLZO/Li symmetric batteries deliver stable cycling (2500 h under 0.3 mA cm −2 at 25 °C and 6000 h under 0.5 mA cm −2 at 60 °C) performances with superhigh critical current densities of 2.5 mA cm −2 at 25 °C and 3.8 mA cm −2 at 60 °C. Moreover, the LiFePO 4 /ZSO‐LLZO/Li battery delivers capacities of 137.45 mAh g −1 under 1 C for 500 cycles and 111.78 mAh g −1 under a high rate of 2 C for 300 cycles. This work with a hybrid interlayer opens a boulevard for designing energy‐dense and long‐life solid‐state batteries.