Stabilization of cubic Li7La3Zr2O12 phase solid electrolyte by gallium doping and its effect on structural and energy storage properties

The garnet-structured Li₇La₃Zr₂O₁₂ has been seen as a potential candidate as solid-state electrolytes (SSEs) for next-generation solid-state batteries (SSBs) due to elevated ionic conductivity, broader electrochemical window, and chemical stability. In this study, the Ga-doped LLZO (LLZGO) SSE was prepared by sol-gel method using heat treatment under ambient conditions. The Li-ion conductivity of the sample was examined with the help of EIS throughout the temperature from +55 °C to −20 °C, followed by material characterization. The phase purity and crystal structure of the sample were confirmed by XRD, TEM, and RAMAN. The crystal structure analysis was further conducted with the help of Rietveld refinement. ICP-OES and EDX confirmed the elemental composition of the sample. The band gap of the sample was calculated (3.9 eV) using the tauc plot of the Kubelka–Munk function, which was confirmed by DFT. At room temperature, the sample exhibits the highest ionic conductivity of 1.05 × 10⁻³ S cm⁻¹, with an activation energy of 0.25 eV. The electronic conductivity of the sample was tested with a chronoamperometry test, which turned out to be ~10⁻⁸ S cm⁻¹. The LLZGO exhibits exceptional ionic conductivity and minimal electrical conduction, making it an exceptional SSE for SSB applications. The critical current density of the sample was measured by fabricating a Li-symmetric cell, which turns out to be 2.99 mA cm⁻². A complete reversible electrochemical reaction was observed in CV, suggesting no additional phase formation on the interface during the electrochemical reaction process. Galvanostatic charge/discharge was used to test the application viability of LLZGO in the full cell against LiNi_0.6Mn_0.2Co_0.2O₂ cathode and Li anode. In the first cycle, the cell delivers a specific capacity of 153.53 mAh g⁻¹ with a capacity retention of 103.84 mAh g⁻¹ and >95 % Coulombic efficiency after 50 cycles.