Superhalogen-based lithium superionic conductors
The development of cheap, durable, and safe inorganic solid electrolytes with superionic conductivity is the key for the next generation of all-solid metal-ion batteries. The recent discovery of antiperovskites with composition Li3OA (A = halogen) shows promise in this regard. Here, we demonstrate the potential of a new class of antiperovskites where halogens are replaced by BH4 superhalogens. In addition to maintaining the high ionic conductivity of Li3OA, Li3O(BH4) is lightweight, mechanically flexible, thermodynamically more stable, and electronically more insulating than Li3OA. By mixing BH4 with Cl to make Li3O(BH4)0.5Cl0.5, we further show that the conductivity will be doubled. The Li+-ion conductivity of the new materials is of the order of 10−4 to over 10−3 S cm−1 at room temperature and will be well above 10−2 S cm−1 at higher temperatures below the melting point. The conduction mechanism of the material is revealed by identifying the relationship between the orientational symmetry of the BH4− rotors and the potential surface felt by the lithium ions.