Superior Li‐Ion Transport in LiNb_0.5Ta_0.5Cl₆

Abstract Halide‐based solid‐state electrolytes have emerged as promising candidates for all‐solid‐state lithium batteries. Among them, amorphous LiTaCl₆ and LiNbCl₆ have shown remarkable conductivities at room temperature, up to 11.0 and 13.5 mS cm⁻¹ at 298.15 K, respectively. Surpassing these values, molecular dynamics simulations based on machine‐learning force fields predict that the Li‐ion conductivity in LiNb_0.5Ta_0.5Cl₆ can reach 15.7 mS cm⁻¹ at 298.15 K with an activation energy of 0.146 eV. Li‐ion mobility is found to correlate with the degree of anharmonic cation‐anion coupling: LiNb_0.5Ta_0.5Cl₆ shows the strongest coupling of low‐frequency Li‐ion modes with Cl‐ion vibration modes. Despite the many similarities between Nb and Ta, this work demonstrates that when both are present, the synergy between Nb and Ta can result in significantly enhanced superionic Li‐ion conductivity in LiNb_0.5Ta_0.5Cl₆, surpassing that observed in both LiTaCl₆ and LiNbCl₆.