Rational design of strontium antimony co-doped Li₇La₃Zr₂O₁₂ electrolyte membrane for solid-state lithium batteries

Considering significant safety advantages, all solid-state LIBs have attracted considerable attentions as alternative power sources for electric vehicles where safety is a big concern, while the development of solid electrolyte membrane with high lithium-ion conductivity, negligible electron conductivity and high stability is the key challenge. Here, Sr and Sb co-doping strategy was applied to further improve the sintering capability and conductivity properties of Li₇La₃Zr₂O₁₂ garnet-type electrolytes. Specifically, Li_6.6+xLa_3-xSr_xZr_1.6Sb_0.4O₁₂ (x = 0–0.2) oxides were designed and the physical and electrochemical performance of the various materials were comparatively studied. The results of X-ray diffraction and Raman spectra revealed Li_6.6+xLa_3-xSr_xZr_1.6Sb_0.4O₁₂ (x = 0–0.2) prepared by conventional solid-state reaction was in cubic structure. The introduction of a small amount of Sr into the La sites is beneficial for membrane densification and lithium-ion mobility, turning out high density of 95.1% and ionic conductivity of 8.83 × 10⁻⁴ S cm⁻¹ at room temperature. The EIS showed the doping of Sr in La sites resulted in improved conductivity at both grain boundary and the oxide bulk. The batteries consisting of lithium film anode, Li_6.66La_2.94Sr_0.06Zr_1.6Sb_0.4O₁₂ solid electrolyte membrane and LiFePO₄ cathode reached the first discharge capacity of 157 mAh g⁻¹ at 0.1 C between 4.2 and 2.0 V (vs. L/Li⁺) with capacity retention of 93% after 100 cycles at ambient temperature. These results displayed that the Sr, Sb co-doped LLZO electrolytes are alternative for all solid-state Li-ion batteries.