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Li‐rich antiperovskite (LiRAP) hydroxyhalides are emerging as attractive solid electrolyte (SEs) for all‐solid‐state Li metal batteries (ASSLMBs) due to their low melting point, low cost, and ease of scaling‐up. The incorporation of rotational polyanions can reduce the activation energy and thus improve the Li ion conductivity of SEs. Herein, we propose a ternary rotational polyanion coupling strategy to fasten the Li ion conduction in tetrafluoroborate (BF4−) ion doped LiRAP Li2OHCl. Assisted by first‐principles calculation, powder X‐ray diffraction, solid‐state magnetic resonance and electrochemical impedance spectra, it is confirmed that Li ion transport in BF4− ion doped Li2OHCl is strongly associated with the rotational coupling among OH−, BF4− and Li2−O−H octahedrons, which enhances the Li ion conductivity for more than 1.8 times with the activation energy lowering 0.03 eV. This work provides a new perspective to design high‐performance superionic conductors with multi‐polyanions. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Li-rich antiperovskite (LiRAP) hydroxyhalides are emerging as attractive solid electrolyte (SEs) for all-solid-state Li metal batteries (ASSLMBs) due to their low melting point, low cost, and ease of scaling-up. The incorporation of rotational polyanions can reduce the activation energy and thus improve the Li ion conductivity of SEs. Herein, we propose a ternary rotational polyanion coupling strategy to fasten the Li ion conduction in tetrafluoroborate (BF 4 - ) ion doped LiRAP Li 2 OHCl. Assisted by first-principles calculation, powder X-ray diffraction, solid-state magnetic resonance and electrochemical impedance spectra, it is confirmed that Li ion transport in BF 4 - ion doped Li 2 OHCl is strongly associated with the rotational coupling among OH - , BF 4 - and Li 2 -O-H octahedrons, which enhances the Li ion conductivity for more than 1.8 times with the activation energy lowering 0.03 eV. This work provides a new perspective to design high-performance superionic conductors with multi-polyanions., (© 2024 Wiley-VCH GmbH.)