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 LiNb0.5Ta0.5Cl6 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: LiNb0.5Ta0.5Cl6 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 LiNb0.5Ta0.5Cl6, surpassing that observed in both LiTaCl6 and LiNbCl6.