Theoretical and Experimental Studies of KLi₆TaO₆ as a Li-Ion Solid Electrolyte

We study a hexagonal oxide KLi₆TaO₆ (KLTO), proposed as a Li-ion solid electrolyte, by using a recently developed screening method. First-principles calculations predict that KLTO presents a good Li-ion conductivity (σ_Li) and a low activation energy (E_a). Li migration is enhanced by the presence of excess Li ions in the interstitial region via a kick-out mechanism. Our experimental results demonstrate that Sn-doped KLTO presents a conductivity of 1 × 10^-5 S cm^-1, a σ_Li of 6 × 10^-6 S cm^-1, and a relatively low E_a of 36 kJ mol^-1, which confirm the validity of the proposed screening method. Conversely, detailed analyses of the microstructure and X-ray diffraction patterns of KLTO samples indicate that a stable Li-excess condition is not achieved, therefore leaving potential improvement of the performance of KLTO as a Li-ion solid electrolyte by optimizing extrinsic doping and fabrication processes.