Synthesis of Ta and Ca doped Li7La3Zr2O12 solid-state electrolyte via simple solution method and its application in suppressing shuttle effect of Li-S battery

A modified solution method was applied to synthesize cubic garnet solid-state electrolyte Li7La3Zr2O12 (LLZO) and Li6.45Ca0.05La2.95Ta0.6Zr1.4O12 (LCLTZO). The synergetic doping of Ca and Ta is found to induce the formation of cubic LCLZTO with high ionic conductivity of 4.03 × 10−4 S cm−1 while LLZO without substitution exhibits tetragonal phase with low conductivity. A Li-S cell with sulfur cathode and as-prepared LCLTZO solid electrolyte “separator” was conducted to deliver large initial discharge capacity of 1090 mAh g−1 with high initial Coulombic efficiency up to 92%. Cell with LCLTZO also exhibited better cycling performance at 0.2 C and extremely high Coulombic efficiency (close to 100%) than the cell without solid electrolyte. Better rate performance was also achieved at lower rate (0.2 C, 0.5 C and 1 C) by cell with LCLTZO although it lost advantages at higher rate of 2 C and 5 C due to the limitation of ionic conductivity of LCLTZO. Energy dispersive X-ray spectroscopy (EDS) provided direct evidence that LCLTZO solid electrolyte greatly suppressed the shuttle effect generated by polysulfides. The electrochemical impedance spectroscopy was applied to discuss the difference between cells with and without LCLTZO during the discharge process. Charge transfer reaction referred to soluble polysulfides was found to be slower in cell with LCLTZO than that in cell without solid electrolyte.