Stabilizing Solid Electrolyte-Anode Interface in Li-Metal Batteries by Boron Nitride-Based Nanocomposite Coating

Solid-state Li-metal batteries are promising to improve both safety and energy density compared to conventional Li-ion batteries. However, various high-performance and low-cost solid electrolytes are incompatible with Li, which is indispensable for enhancing energy density. Here, we utilize a chemically inert and mechanically robust boron nitride (BN) film as the interfacial protection to preclude the reduction of Li1.3Al0.3Ti1.7(PO4)3 (LATP) solid electrolyte by Li, which is validated by in situ transmission electron microscopy. When combined with ∼1–2 μm PEO polymer electrolyte at the Li/BN interface, Li/Li symmetric cells show a cycle life of over 500 h at 0.3 mA·cm−2. In contrast, the same configuration with bare LATP dies after 81 h. The LiFePO4/LATP/BN/PEO/Li solid-state batteries show high capacity retention of 96.6% after 500 cycles. This study offers a general strategy to protect solid electrolytes that are unstable against Li and opens possibilities for adopting them in solid-state Li-metal batteries. [Display omitted] •Sub-10-nm thin BN film deposited by CVD effectively protects LATP against Li•In situ TEM analyzes the failure mechanism of LATP and the protective effect of BN•Solid-state batteries with LATP/BN show capacity retention of 96.6% over 500 cycles Solid-state Li-metal batteries can improve safety and energy density compared to liquid-electrolyte-based Li-ion batteries; however, various ceramic electrolytes with high conductivities and low cost are not stable against Li metal, and the severe interfacial reaction devastates battery performance in several cycles. To stabilize the solid electrolyte-Li interface, we utilize boron-nitride-based nano-coating as the interfacial layer, which is not only electronically insulating and ionically conductive but also chemically and mechanically robust to preclude the reduction of solid electrolyte by the Li metal. With this strategy, LiFePO4/LATP/BN/PEO/Li solid-state batteries show capacity retention of 96.6% over 500 cycles in 70 days. The development of boron-nitride-based protective film holds great potential to extend the electrochemical window of unstable solid electrolytes and expands the family of applicable solid electrolytes stable against Li metal. Li1.3Al0.3Ti1.7(PO4)3 (LATP) solid electrolyte is inexpensive, light, and highly ionically conductive but unstable against Li metal. To avoid the side reactions between LATP and Li metal, chemically inert and mechanically robust BN nano-coatin