Li-rich antiperovskite superionic conductors based on cluster ions

Enjoying great safety, high power, and high energy densities, all-solid-state batteries play a key role in the next generation energy storage devices. However, their development is limited by the lack of solid electrolyte materials that can reach the practically useful conductivities of 10(-2) S/cm at room temperature (RT). Here, by exploring a set of lithium-rich antiperovskites composed of cluster ions, we report a lithium superionic conductor, Li3SBF4, that has an estimated 3D RT conductivity of 10-2 S/cm, a low activation energy of 0.210 eV, a giant band gap of 8.5 eV, a small formation energy, a high melting point, and desired mechanical properties. A mixed phase of the material, Li3S(BF4) Cl-0.5(0.5), with the same simple crystal structure exhibits an RT conductivity as high as 10(-1) S/cm and a low activation energy of 0.176 eV. The high ionic conductivity of the crystals is enabled by the thermal-excited vibrational modes of the cluster ions and the large channel size created by mixing the large cluster ion with the small elementary ion.