Unlocking the chemical space in anti-perovskite conductors by incorporating anion rotation dynamics

Anti-perovskite compounds have drawn significant research interest as promising next-generation electrolytes for solid-state batteries, due to the high chemical stability against Li-metal, the negligible electronic conductivity and low cost. However, the low ionic conductivity, and the deficient fundamental understandings of ion transports impede the further optimization of the lithium anti-perovskite electrolytes. Herein, we reveal that exchanging anion lattice sites in the anti-perovskite could promote the structure stabilities and ionic conductivities simultaneously, by incorporating the rotational dynamics of anion clusters and strengthening the coupling between Li migrations and cluster rotations. Based on high-throughput calculations by density functional theory (DFT), twelve new anti-perovskite materials are predicted to exhibit superionic conductivity, among which the highest ionic conductivity of 10.9 mS/cm in Li3BrSO4 can be achieved (hundreds of times higher than the ionic conductivity of typical Li3OCl antiperovskite, 0.021 mS/cm). Furthermore, the local difference frequency center is proposed to quantitatively characterize the coupled degree of Li migration and cluster rotation, revealing the contribution of paddlewheel effect to the ionic conductivity. Our proposed cation-anion dynamics coupling in site-exchanged and cluster-based antiperovskites not only open a new avenue for understanding the key role played by rotational dynamics on fast lithium mobility, but also can be generally applied to develop other fast ionic conductors with cluster dynamics.