Structure, Lithium-Ion Conductivity Coupled with Second-Order Jahn-Teller Effect, and Electrochemical Stability of Sr-Based Perovskite-Type Solid Electrolytes

We synthesized polycrystalline perovskite-typeLi-ion-conductingoxides (general formula: ABO(3)), Sr0.5-x Li0.3+2x Ti0.3Ta0.7O3 (x = 0.030-0.100),and assessed their crystal structure, microstructure, ionic conductivity,and electrochemical stability. Based on first-principles calculations,local structure changes accompanied by Li-ion diffusion were discussed.It was found that the average structure of Sr0.5-x Li0.3+2x Ti0.3Ta0.7O3 (x = 0.030-0.100)is a cubic perovskite-type one, and at x = 0.042,i.e., Sr0.458Li0.384Ti0.3Ta0.7O3, the highest bulk ionic conductivity and the totalionic conductivity at 300 K were observed to be 1.87 x 10(-3) and 1.05 x 10(-3) S cm(-1), respectively, which are greater than those of La2/3-x Li3x TiO3(LLTO).The first-principles calculations suggested that BO6 octahedraare distorted, and the Li-ion diffusion is assisted by the dynamicdistortion of BO6 octahedra coupled with the second-orderJahn-Teller effect. The reduction potential of Sr0.458Li0.384Ti0.3Ta0.7O3 was1.6-1.7 V vs Li/Li+, which is comparable to thatof LLTO. A cell using a Sr0.458Li0.384Ti0.3Ta0.7O3 pellet with a deposited thinfilm LiCoO2 cathode on one side was successfully operatedas a secondary battery at room temperature, indicating that the compoundcan be applied as a solid electrolyte for Li-ion batteries.