Synergistic Effects of Anion Substitution and Interfacial Modification to Enhance Ionic Conductivity in a Hydride Electrolyte

All-solid-state batteries with a higher energy density and safety promote the development of solid-state electrolytes. LiBH₄, which has extraordinary thermodynamic stability with Li, is considered one of the most promising electrolyte candidates. However, practical application is severely hampered by the issue of low ionic conductivity at room temperature. To overcome the problems, Li₄(BH₄)₃I and amorphous B₂O₃ are combined to attain a composite electrolyte achieving a high ionic conductivity of 1.45 × 10^–4 S cm^–1 at 30 °C, which greatly inhibits lithium dendrite growth for running the Li symmetric battery over 3500 h. The involvement of B₂O₃ strengthens the resistance to lithium dendrites in solid-state electrolytes as a grain boundary filler and generates a highly disordered interface between Li₄(BH₄)₃I and B₂O₃ without the formation of intermediate phase, which is attributed to Li⁺ transfer. The phenomenon strengthens oxidation stability with an extending potential window of 5.0 V. A lithium–sulfur battery was assembled with sulfurized polyacrylonitrile as the cathode material, which exhibits a specific discharge capacity of 1308 mA h g^–1 after 50 cycles at 0.1C. The work will contribute to the further development of low-temperature solid-state ionic conductors.