Highly Conductive Networks Encapsulated Borohydride Electrolytes Enabling Superior High Rate Performance for All‐Solid‐State Li‐Ion Batteries

Replacing organic liquid electrolytes with solid‐state electrolytes in all‐solid‐state batteries (ASSBs) is a highly promising strategy to increase the energy density and safety. However, issues with dendrite formation, limited Li‐ion conduction at room temperature, and poor oxidative stability of the solid‐state electrolytes severely retard the practical application of ASSBs. The present work provides a novel LiBH ₄ ‐based electrolyte with a highly lithium‐ion conductive ZrB ₂ network coupling with LiCl on the surface of the LiBH ₄ particles by a facile mechanochemical reaction of LiBH ₄ with ZrCl ₄ , which results in a high ionic conductivity of 1.7 × 10 ⁻⁴  S cm ⁻¹ . This network surface allows an extremely low electron conductivity and functions as a buffer zone for the deposition of metallic Li. A wide electrochemical window up to 7.0 V (vs Li/Li ⁺ ) and a high critical current density (7.2 mA cm ⁻² ) at 30 °C is achieved with the Li electrode. Li|LiCoO ₂ and Li|TiS ₂ full cells coupled with this electrolyte provide high stability at high rates, up to 3 C and 6 C, respectively. In addition, 22LiBH ₄ ZrCl ₄ can improve the interfacial stability against Li metal and the dendrite‐suppression capability of other solid electrolytes that are less stable toward Li or show weaker resistance to dendrite growth, such as LLZTO4LiBH ₄ and Li ₃ InCl ₆ . Moreover, comparative studies of 22LiBH ₄ ZrCl ₄ and ball‐milled products derived from several other metal chlorides further confirm the structure–property relationship between the network morphology in composite solid electrolytes and their high critical current densities.