Highly Thermostable Interphase Enables Boosting High‐Temperature Lifespan for Metallic Lithium Batteries

In consideration of high specific capacity and low redox potential, lithium metal anodes have attracted extensive attention. However, the cycling performance of lithium metal batteries generally deteriorates significantly under the stringent conditions of high temperature due to inferior heat tolerance of the solid electrolyte interphase (SEI). Herein, controllable SEI nanostructures with excellent thermal stability are established by the (trifluoromethyl)trimethylsilane (TMSCF 3 )‐induced interface engineering. First, the TMSCF 3 regulates the electrolyte decomposition, thus generating an SEI with a large amount of LiF, Li 3 N, and Li 2 S nanocrystals incorporated. More importantly, the uniform distributed nanocrystals have endowed the SEI with enhanced thermostability according to the density functional theory simulations. Particularly, the sub‐angstrom visualization on SEI through a conventional transmission electron microscope (TEM) is realized for the first time and the enhanced tolerance to the heat damage originating from TEM imaging demonstrates the ultrahigh thermostability of SEI. As a result, the highly thermostable interphase facilitates a substantially prolonged lifespan of full cells at a high temperature of 70 °C. As such, this work might inspire the universal interphase design for high‐energy alkali‐metal‐based batteries applicated in a high‐temperature environment.