In‐Situ‐Generated Electron‐Blocking LiH Enabling an Unprecedented Critical Current Density of Over 15 mA cm−2 for Solid‐State Hydride Electrolytes

Abstract LiBH 4 is a promising solid‐state electrolyte (SE) due to its thermodynamic stability to Li. However, poor Li‐ion conductivities at room temperature, low oxidative stabilities, and severe dendrite growth hamper its application. In this work, a partial dehydrogenation strategy is adopted to in situ generate an electronic blocking layer dispersed of LiH, addressing the above three issues simultaneously. The electrically insulated LiH reduces the electronic conductivity by two orders of magnitude, leading to a 32.0‐times higher critical electrical bias for dendrite growth on the particle surfaces than that of the counterpart. Additionally, this layer not only promotes the Li‐ion conductance by stimulating coordinated rotations of BH 4 − and B 12 H 12 2− , contributing to a Li‐ion conductivity of 1.38 × 10 −3 S cm −1 at 25 °C, but also greatly enhances oxidation stability by localizing the electron density on BH 4 − , extending its voltage window to 6.0 V. Consequently, this electrolyte exhibits an unprecedented critical current density (CCD) of 15.12 mA cm −2 at 25 °C, long‐term Li plating and stripping stability for 2700 h, and a wide temperature window for dendrite inhibition from −30 to 150 °C. Its Li‐LiCoO 2 cell displays high reversibility within 3.0–5.0 V. It is believed that this work provides a clear direction for solid‐state hydride electrolytes.