Superhalogen-based lithium superionic conductors

Abstract

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 Li 3 OA (A = halogen) shows promise in this regard. Here, we demonstrate the potential of a new class of antiperovskites where halogens are replaced by BH 4 superhalogens. In addition to maintaining the high ionic conductivity of Li 3 OA, Li 3 O(BH 4 ) is lightweight, mechanically flexible, thermodynamically more stable, and electronically more insulating than Li 3 OA. By mixing BH 4 with Cl to make Li 3 O(BH 4 ) 0.5 Cl 0.5 , 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 BH 4- rotors and the potential surface felt by the lithium ions.