Enhanced Electrochemical Performance of Al- and Nb-Codoped LLZO Ceramic Powder and Its Composite Solid Electrolyte

Using a solid-state method, a Li6.25Al0.2La3Zr1.85Nb0.15O12 (LALZNO) ceramic solid-state electrolyte (SSE) was prepared by codoping with Al and Nb. A PEO-LiTFSI-20%LALZNO composite solid electrolyte (CSE) was prepared by incorporating LALZNO into a poly(ethylene oxide) (PEO) polymer using a solution casting method. Characterization of these materials shows that the lattice distortion caused by the codoping of Al and Nb into Li and Zr sites increases Li+ vacancy concentration and modifies Li+ transmission channels. The ionic conductivity of the LALZNO ceramic SSE at room temperature (RT, 25 °C) can reach 3.04 × 10–4 S/cm. When the LALZNO concentration in the LALZNO/PEO composite is 20 wt %, the PEO-LiTFSI-20%LALZNO CSE exhibits a maximum ionic conductivity (7.64 × 10–5 S/cm at RT), a wide electrochemical window (5.5 V vs Li/ Li+), and a high lithium-ion transport number (0.28). Testing a Li||PEO-LiTFSI-20%LALZNO||Li symmetrical cell shows that this solid electrolyte can be stably cycled for 500 h at 60 °C with a fixed areal capacity of 0.2 mAh/cm2. Furthermore, performance tests of the all-solid-state battery LiFePO4||PEO-LiTFSI-20%LALZNO||Li show that the CSE has excellent cycling and rate performance. This all-solid-state battery can stably cycle for more than 100 cycles under conditions of 60 °C and 0.2C. Furthermore, it retains a specific discharge capacity of 91.6% after 100 cycles, and its Coulombic efficiency is close to 100%.