A Silatrane:Molecule‐Based Crystal Composite Solid‐State Electrolyte for All‐Solid‐State Lithium Batteries

All‐solid‐state batteries (ASSBs) are promoted as a promising option towards higher energies and power densities as well as drastically reduced safety risks as compared to conventional lithium‐ion batteries (LIBs). Herein, a composite solid‐state electrolyte (SSE) based on two crystalline materials with two distinctly different ion conduction mechanisms, percolation and ion hopping, is reported. By combining a silatrane (SA; here ethoxysilatrane) with a molecule‐based crystal (MBC; here LiTFSI‐TMEDA) the resulting SA : MBC 2 : 1 crystalline composite shows an appreciable ion conductivity of 10 −5  S cm −1 at room temperature, and low apparent activation energy, 836 K, for the ion transport. Studies of the overall and local structure show that in the composite the Li + and TFSI ions are dissociated, and this seems to be mediated by the SA part of the matrix. As a proof‐of‐concept, an ASSB based on this SSE can operate at 50 °C providing up to 105 mAh g −1 during 20 cycles.