Synthesis of Garnet Llzo by Aliovalent Co-Doping, and Electrochemical Behavior of Composite Solid Electrolyte for All-Solid Lithium Batteries

Garnet-like Ga-M (M =Ta, Rb, Y) co-doped Li7La3Zr2O12 powders were prepared by the Taylor reaction, including Ga-LLZO (Li6.4Ga0.2La3Zr2O12), Ga-Ta LLZO (Li6.35Ga0.2La3Zr1.95Ta0.05O12), Ga-Rb LLZO (Li6.5Ga0.2La2.95Rb0.05Zr2O12), and Ga-Y LLZO (Li6.4Ga0.2La2.95Y0.05Zr2O12). The lattice constant (12.97 Å) and large crystallite size (866 Å) of Ga-Rb LLZO powder enabled the highest ionic conductivity (2.03×10–3 S cm−1 at 25 °C) in the pellet form, which is the highest conductivity reported to date. Ga-Rb LLZO calcined at different temperatures was utilized in composite solid electrolyte (CSE) sheets consisting of Ga-Rb LLZO, polyethylene oxide (PEO), and salts. The ionic conductivity of the CSE sheets increased in proportion to the calcination temperature in the range of 2.43×10-4 to 8.60×10-4 S cm−1 at 70 °C. The LLZO particle-size and crystallite-size requirements differ for the cathode and CSE sheet. Three types of all-solid-state lithium batteries were designed, among which ASLB-3 employing Ga-Rb LLZO powder calcined at 900 °C and 1100 °C for the positive electrode and CSE sheet, respectively, afforded an initial capacity of ~139 mAh g−1 at 0.1 C and 70 °C, with a capacity retention of ~99% after 50 cycles. In particular, in terms of rate characteristics, 1C compared to 0.1C capacity shows excellent value, maintaining about 88%