Realizing fourfold enhancement in conductivity of perovskite Li_0.33La_0.557TiO₃ electrolyte membrane via a Sr and Ta co-doping strategy

Solid-state Li-ion batteries (SSBs) are believed the new future of electrochemical energy storage, while the solid electrolyte membrane is the core part. The development of new electrolyte membrane with easy densification, high stability and high conductivity is crucial for the widespread application of SSBs. In this study, tuning the conductivity and sintering behavior of perovskite-type La_2/3-xLi_3xTiO₃ (LLTO) membranes through a co-doping strategy was proposed and systematically investigated. Specifically, the membranes with the nominal compositions of Li_0.33-y+xLa_0.557-xM_xTi_1-yN_yO₃ (M = Sr, Ba, Ca, N = Ta) were designed and investigated. The results demonstrated that replacement of La³⁺ by smaller Ca²⁺ decreased the bulk Li⁺ conductivity while substitution of La³⁺ by Sr²⁺ or Ba²⁺ with larger ionic radii increased the bulk Li⁺ conductivity. Besides, Ta⁵⁺ and Sr²⁺ co-doped LLTO with optimized Ta/Sr molar ratio could improve the membrane densification involving the relative density and grain size. Accordingly, a high total Li⁺ conductivity (1.4 × 10⁻⁴ S cm⁻¹) with low electronic conductivity (3.2 × 10⁻⁸ S cm⁻¹) could be achieved, and the as-prepared Li_0.33La_0.457Sr_0.1Ti_0.9Ta_0.1O₃ membrane presented prominent electrochemical performance with a high capacity retention (89%) and Coulombic efficiency of 97% for 80 cycles, thus promised co-doping strategy for developing superior perovskite Li-ion conducting membranes for SSBs.