Lithium migration pathways at composite interface of LiBH4 and two-dimensional MoS2 enabling superior ionic conductivity at room temperature

LiBH4 is one of the most promising solid electrolyte materials for solid state batteries because its hexagonal structure phase at above 110°C offers a lithium ionic conductivity approaching to 10−2 Scm−1. However, at near room temperature, its orthorhombic phase delivers an ion conductivity of only 10−8 Scm−1, which greatly hampers its further applications. In the present work, a highly disordered interface between LiBH4 and two-dimensional material MoS2 composite was formed, leading to an ionic conductivity of 10−4 Scm−1 at room temperature. LiBH4 and MoS2 are found in close contact without any intermediate phase at the interface. First-principle calculation employing the density functional theory (DFT) and nudged elastic band (NEB) method reveals the migration energy barrier on the three specific pathways which are established on the basis of the microstructure analyses. It was found that the interface between the two phases owns the lowest Li-ion diffusion barrier among all possible Li-ion pathways and that the superior conductivity of the composite is attributed to the highly Li-ion conductive interface. This work proposes a new strategy for designing solid electrolytes, and also provides some possibilities for two-dimensional materials to serve as superior solid electrolytes.