Ab Initio Calculations of Ionic Conductivity in Lithium and Sodium Polyborate Solid Electrolytes

Abstract

A subset of alkali polyborates have recently been identified as highly promising solid electrolytes for next-generation batteries due to their superionic transition temperatures approaching room temperature and ionic conductivities exceeding 0.1 S/cm–1. However, the exact mechanisms driving the transport in these materials remain largely unknown. Here we use large-scale ab initio molecular dynamics calculations to characterize the diffusivity of the Li and Na species in a representative set of B12H12- and B10H10-based closoborane ionic conductors, focusing on the role of stoichiometry, volume, and dopant incorporation in enhancing ionic conductivity. Detailed analysis on representative materials is used to elucidate the specific conduction mechanism, which relies on frustrated competition between longer- and shorter-range interionic interactions. Our results support this class of materials as highly promising solid electrolytes and offer insights that can be used to tailor conductivity and stability for their use in next-generation battery technologies. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.