Near-Saturated Coordinated Cations in Oxyhalide Superionic Conductors Boost High-Rate All-Solid-State Batteries

Amorphous oxyhalide solid electrolytes (SEs) have garnered significant attention due to their excellent cathodic stability and favorable mechanical properties. However, the correlations between the structural characteristics in the amorphous phase and Li⁺ transport behavior remain underexplored, limiting further promotion of the ionic conductivities of these SEs. Herein, we establish a correlation between cationic coordination saturation in amorphous oxyhalide SEs and Li⁺ transport. Based on this correlation, near-saturated coordinated cation (NSCC)-incorporated Li_1.5Zr_0.5M_0.5Cl_5.0O_0.5 SEs (M = Nb or Ta, denoted as Nb- or Ta-LZCO) are developed with abundant vacancy concentrations and weakened Li-Cl interaction, thereby significantly enhancing Li⁺ transport. As a result, the Nb-LZCO and Ta-LZCO SEs achieve impressive ionic conductivities of 2.33 and 3.88 mS cm^-1, respectively, at 25 °C. All-solid-state lithium batteries assembled with representative Ta-LZCO and a LiNi_0.8Mn_0.1Co_0.1O₂ cathode demonstrate superior rate performance and long-term cycling stability, delivering a high specific capacity of 120.0 mAh g^-1 at 10.0 C (1 C = 195 mA g^-1) and an outstanding capacity retention of 84.85% after 2000 cycles. This work establishes a generalizable strategy for designing amorphous SEs with high ionic conductivity by modulating the cationic coordination environment.