Revisiting the Role of Hydrogen in Lithium-Rich Antiperovskite Solid Electrolytes: New Insight in Lithium Ion and Hydrogen Dynamics

Li₂OHX (X = Cl or Br) with an antiperovskite structure possess the advantages of low melting point, low cost, and ease of scaling-up, which show great promise for applications in all-solid-state Li metal batteries (ASSLMBs). However, Li-ion transport mechanisms in Li₂OHX are still debated and the influence of H on the electrochemical performance of Li₂OHX is yet to be explored. Herein, combining the theoretical calculations and experimental measurements, it is found that H affects Li-ion transport, crystal stability, electrochemical stability, and electronic conductivity of Li₂OHX. Compared with H-free Li₃OCl, although H helps to generate vacancy-like defects, the electrostatic repulsive force between H and Li-ion leads to an increase in both the activation energy and the diffusion length (space compensation effect), resulting in special Li ion transport trajectories along the Li-O plane. Decreasing H content reduces the electronic conductivity and enhances the reduction-resistant ability of Li₂OHX, promoting the cycling stability and rate performance of Li∣Li₂OHX∣Li symmetric cells and the ASSLMBs. This work delivers a new insight into the role of H in antiperovskite Li₂OHX and can serve as guidance for solid electrolyte design.