Enhanced Air Stability and High Li-Ion Conductivity of Li_6.988P_2.994Nb_0.2S_10.934O_0.6 Glass-Ceramic Electrolyte for All-Solid-State Lithium-Sulfur Batteries

The development of novel sulfide solid-state electrolytes with high Li-ion conductivity, excellent air-stability, and a stable electrode-electrolyte interface is needed for the commercialization of all-solid-state cells. Currently, an ideal solid electrolyte, which can integrate the solid-state batteries, has not been developed. Herein, the Nb and O codoping strategy is excogitated to improve the chemical and electrochemical performance of sulfide electrolytes. The interactive effect of Nb and O in the novel Li_6.988P_2.994Nb_0.2S_10.934O_0.6 glass-ceramic electrolyte results in a superior Li⁺ conductivity of 2.82 mS cm^-1 and remarkable air-stability and electrochemical stability against the Li metal compared to the Li₇P₃S₁₁ counterpart at 25 °C. Solid-state ³¹P MAS-NMR revealed that doping of LiNbO₃ (0 ≤ x ≤ 1) not only enhances the degree of crystallization but also produces P₂OS₆ ^4- units with bridging oxygen atoms in the Li_6.988P_2.994Nb_0.2S_10.934O_0.6 glass-ceramic electrolyte and hence boosts the conductive deportment of glass-ceramics. Impressively, the developed electrolyte exhibits a stable full voltage window of up to 5 V versus Li/Li⁺. Furthermore, electrochemical impedance spectroscopy analysis shows that the interface resistance of the Li₂S/Li_6.988P_2.994Nb_0.2S_10.934O_0.6/Li-In cell is lower than that of the cell with Li₇P₃S₁₁ electrolyte. Besides, the battery of the Li_6.988P_2.994Nb_0.2S_10.934O_0.6 electrolyte delivers initial discharge capacities of 472.7 and 530.9 mAh g^-1 after 50 cycles with 98.88% capacity retention from the second cycle. The Coulombic efficiency of the cell remains at ∼100% after 50 cycles. Thus, the proposed codoped strategy produced a sulfide electrolyte, which addressed the challenging issues of chemical/electrochemical stabilities and showed promising industrial prospects for next-generation all-solid-state batteries.