High ionic conductivities of composites of Li₄(BH₄)₃I with two-dimensional MoS₂ at room temperature

Li₄(BH₄)₃I–MoS₂ composites with high Li-ion conductivity were synthesized by simple ball milling. Owing to the synergic effect of halide substitutions and the formation of the highly disordered interface between the two phases, the composite delivers an ionic conductivity as high as 2.78 × 10⁻⁴ S cm⁻¹ at room temperature, which is over three orders of magnitude higher than that of pristine LiBH₄ and nearly three times higher than our previously studied LiBH₄–MoS₂ (1 × 10⁻⁴ S cm⁻¹). The ionic conductivity of Li₄(BH₄)₃I–MoS₂ at room temperature is also superior over Li₄(BH₄)₃I solid solutions. Additionally, Li₄(BH₄)₃I–MoS₂ exhibits a wide electrochemical stability window of −1 to 5 V and demonstrates an excellent electrochemical stability against Li foil. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) measurements on Li₄(BH₄)₃I–MoS₂ demonstrate that parent phases of these composites were well preserved after ball milling. Field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) reveal a highly dispersed interface between two phases, which acts as a favorable pathway for Li⁺ conduction. This work proposes a new strategy for solid electrolytes, offering a possibility for those two-dimensional materials to be scaffolds for superior solid electrolytes.