Toward Moisture-Stable and Dendrite-Free Garnet-Type Solid-State Electrolytes

All-solid-state batteries using garnet-type solid-state electrolytes (SSEs) are promising candidates for safe, high energy density batteries due to their wide electrochemical stability window, high lithium-ion conductivity at room temperature, and the use of a lithium metal anode. However, garnet-type SSEs exhibit formidable challenges, including their instability in a moisture-containing atmosphere, high interfacial resistance, and the formation of lithium dendrites. Though several strategies have been deployed to alleviate the issues related to garnet-type SSEs against metallic lithium, most of the approaches fail to solve all the challenges. Herein, we demonstrate a surface modification strategy of the Li6.5La3Zr1.5Ta0.5O12 (LLZT) garnet electrolyte by two-dimensional hexagonal boron nitride (h-BN) nanosheets to solve the interfacial issues. Detailed spectroscopic evidence elucidates that the h-BN interlayer effectively protects the LLZT from moisture-induced chemical degradation and suppresses the formation of adverse carbonate species for over 120 h in an open atmosphere. The h-BN-coated garnet SSE interface has shown a nearly 10-fold reduction in interfacial resistance value compared to the uncoated one and it exhibits stable lithium plating/stripping behavior for over 1400 cycles at 0.2 mA cm–2. Advanced in situ Raman analysis reveals that the h-BN interlayers remain stable during cycling and inhibit the structural transformation of LLZT at the interface.