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 SbI 3 buffer layer on the Ta-doped Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 (LLZTO) surface, where the SbI 3 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 cm 2 to 139 Ω cm 2 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 LiFePO 4 cathode, the SbI 3 -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.