In Situ Fabrication of High Ionic and Electronic Conductivity Interlayers Enabling Long-Life Garnet-Based Solid-State Lithium Batteries

Garnet-type Li6.75La3Zr1.75Ta0.25O12 (LLZTO) is a promising solid-state electrolyte (SSE) because of its fast ionic conduction and notable chemical/electrochemical stability toward the lithium (Li) metal. However, poor interface wettability and large interface resistance between LLZTO and Li anode greatly restrict its practical applications. In this work, we develop an in situ chemical conversion strategy to construct a highly conductive Li2S@C layer on the surface of LLZTO, enabling improved interfacial wettability between LLZTO and the Li anode. The Li/Li2S@C-LLZTO-Li2S@C/Li symmetric cell has a low interface impedance of 78.5 Ω cm2, much lower than the 970 Ω cm2 of a Li/LLZTO/Li cell. Moreover, the Li/Li2S@C-LLZTO-Li2S@C/Li cell exhibits a high critical current density of 1.4 mA cm–2 and an ultralong stability of 3000 h at 0.1 mA cm–2. When used in a LiFePO4 battery, the Li/Li2S@C-LLZTO/LiFePO4 battery exhibits a high initial discharge capacity of 150.8 mA h g–1 at 0.2 C without lithium storage capacity attenuation during 200 cycles. This work provides a novel and feasible strategy to address interface issues of SSEs and achieve lithium-dendrite-free solid-state batteries.