Interfacial Engineering of Garnet-Type Electrolytes for Solid-State Lithium Metal Batteries

Garnet-type solid electrolytes suffer from severe interfacial issues, notably high interfacial resistance and lithium dendrite propagation. Here, we propose a facile solution-coating strategy to introduce a dual-functional SbI3 buffer layer on the Ta-doped Li6.5La3Zr1.5Ta0.5O12 (LLZTO) surface, where the SbI3 layer reacts with lithium at low temperatures to form a mixed LiI/Li–Sb interphase. This interphase significantly reduces the interfacial resistance from 15 kΩ cm2 to 139 Ω cm2 at room temperature. The symmetric cell demonstrates remarkable cycling stability, maintaining stable operation for over 5000 h at a current density of 0.1 mA cm–2. The modified interface also promotes uniform lithium deposition, effectively suppressing dendrite formation. In a full cell configuration with a LiFePO4 cathode, the SbI3-modified LLZTO delivers a discharge capacity of 145 mA h g–1 at 0.1C, with 98.2% capacity retention after 100 cycles at 60 °C. This work provides a low-temperature interfacial engineering strategy to address key challenges in garnet-based solid-state batteries, paving the way for their practical application.