Realizing Li7La3Zr2O12 garnet with high Li+ conductivity and dense microstructure by Ga/Nb dual substitution for lithium solid-state battery applications
Li7La3Zr2.0O12 (LLZO) garnet has many properties of a suitable solid electrolyte for lithium ion batteries, however, drawbacks like low ionic conductivity and poor interfacial property still hinder its market broadening. Current research have sought to both increase its ionic conductivity and densify its microstructure, which are two important factors for its practical application. This study presents a facile and effective way to obtain compact LLZO with high Li+ conductivity by a one-step multi-elemental doping strategy using Nb5+ and Ga3+ as dopants simultaneously. Garnet-structured oxides with nominal chemical compositions of Li6.8-3xGaxLa3Zr1.8Nb0.2O12 (x=0, 0.1, 0.15, 0.2, 0.25, 0.3) are prepared via conventional solid-state reaction, and the effects of the two dopants on the oxides are investigated based on their phase composition, morphology and Li ion conductivity. Benefitting from the Li+ vacancy generated by the addition of the two elements, the garnet sintered with optimized Ga/Nb dopant amount can exhibit relative densities of 93~95%, and a peak conductivity of 1.42×10-3 S cm-1 at 50 °C. In a symmetric Li/LLZO/Li cell, this dense structured electrolyte shows low overpotential and superior electrochemical stability to Li metal, exhibiting over 200 h under the current density of 100 μA cm-1 upon Li plating/stripping cycles. Besides, this co-doped solid-state electrolyte can exhibit acceptable cycling stability when paired with LiNi0.33Mn0.33Co0.33O2 (NMC111)) cathode, both with the help of liquid electrolyte and assembled as a all-solid-state battery. We believe this research can provide some new insights in developing solid-state electrolyte based lithium ion batteries.