Facile Synthesis of Inorganic Li ₂ B ₁₂ H ₁₂ /LiI Solid Electrolytes for High‐Voltage All‐Solid‐State Lithium Batteries

Hydroborate-based solid electrolytes (SEs), distinguished by their eco-friendliness and non-flammability have emerged as a research hotspot in energy storage research. Despite these advantages, their widespread adoption is constrained by insufficient ionic conductivity and poor high-voltage compatibility. To overcome this challenge, a novel hydroborate SEs, 400-0.6Li₂B₁₂H₁₂-0.4LiI (denoted as 400-0.6B₁₂-0.4I), is engineered through a facile synthesis strategy combining high-temperature processing (400 °C, 2 h, in Ar) and LiI doping. 400-0.6B₁₂-0.4I exhibits an outstanding ionic conductivity up to 0.75 mS cm^-1 at 25 °C, which is the highest level among the reported inorganic Li₂B₁₂H₁₂-based SEs so far. It also improves the cycling stability against lithium metal anodes, limits dendrite growth with a high critical current density of 5.0 mA cm^-2, which enables the Li symmetrical cells to cycle over 1000 h at 25 °C with only 10 mV of overpotential. Moreover, it cycles well in cells using lithium anodes and various high voltage (>4 V vs Li⁺/Li) cathodes materials such as LiCoO₂, NCM811, and LiMn₂O₄. The proposed 400-0.6B₁₂-0.4I SEs offer valuable guidance for designing next-generation lithium-ion solid electrolytes with superior ionic conductivity, enhanced interfacial stability, and exceptional electrode compatibility.