Realizing fourfold enhancement in conductivity of perovskite Li0.33La0.557TiO3 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 La2/3-xLi3xTiO3 (LLTO) membranes through a co-doping strategy was proposed and systematically investigated. Specifically, the membranes with the nominal compositions of Li(0.33-y+x)La(0.557-x)MxTi(1-y)N(y)O(3) (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 x 10(-4) S cm(-1)) with low electronic conductivity (3.2x10(-8) S cm(-1)) could be achieved, and the as-prepared Li0.33La0.457Sr0.1Ti0.9Ta0.1O3 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.