Boron Nitride‐Based Release Agent Coating Stabilizes Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ /Li Interface with Superior Lean‐Lithium Electrochemical Performance and Thermal Stability

Sodium super ionic conductor (NASICON)-type Li1.3Al0.3Ti1.7(PO4)3 (LATP) is one of the most promising solid-state electrolytes (SSEs) owing to its high Li-ion conductivity, high stability with air, and low cost. However, LATP is less widely deployed due to its high incompatibility with lithium metal. Herein, a facile and inexpensive spray-coating approach is proposed to construct a thin 3D organic/inorganic composite layer of a commercial boron nitride-based release agent (BNRA) onto LATP. Apart from protecting LATP, this interfacial BNRA layer enables Li-ion migration through BN defects and affords low resistance at BNRA/Li interface due to in situ formation of Li–N. Compared to bare LATP, which fails to support Li stripping–plating process in a lean-lithium Li/Li symmetric cell (2 µm), BNRA-LATP runs for ≈1800 h. The assembled lean-lithium LiFePO4 (LFP)/BNRA-LATP/Li solid state batteries (SSBs) deliver a specific capacity of 150.9 mA h g–1 at 0.5 C with minor capacity decay after 500 cycles. Besides, the BNRA layer eliminates thermal runaway risks of LATP-based SSBs by fast in-plane thermal dispersion. This work demonstrates a facile LATP-protection strategy regarding Li incompatibility and thermal runway issues, and pinpoints the interfacial formation mechanism, fulfilling the pursuit of high-performance low-cost SSEs.