Influence of Ga on the Structure and Electrical Properties of Li_7-3xLa₃Ga_xZr₂O₁₂ Garnet-Type Solid Electrolytes

Garnet-type solid-state electrolytes that conduct Li ions are increasingly being considered as very favorable options for all-solid-state lithium-ion batteries due to their stability toward Li metal, their broad electrochemical stability window, and ionic conductivity. Among these electrolytes, lithium lanthanum zirconate is emerging as a potential candidate. Doping these electrolytes with some trivalent elements that help to stabilize the conducting cubic phase can further enhance their performance. So, in this work, samples with different doping concentrations of Ga with Li₇La₃Zr₂O₁₂ have been prepared through the sol–gel technique, and the obtained samples were subjected to heat treatment at two different stages. The structural and electrical properties of the Li_7-3xGa_xLa₃Zr₂O₁₂ (0 ≤ x ≤ 0.6) samples were investigated with different experimental methods. XRD analysis showed that adding Ga to the Li site helped to attain the pure phase cubic structure of LLZO calcined at 1000 °C. Analyzing the samples through scanning electron microscopy revealed the agglomeration of small particles for the formation of larger grains. The Li_7-3xGa_xLa₃Zr₂O₁₂ with x = 0.4 revealed a stabilized cubic garnet-type crystal structure with improved total conductivity from 1.50 × 10⁻⁷ S cm⁻¹ (x = 0.0 mol%) to 0.35 × 10⁻⁵ S cm⁻¹ (x = 0.4 mol%) at 30 °C. The activation energy of the samples decreased with Ga from a value of 0.41 eV for x = 0.0 to 0.28 eV for x = 0.6. The activation energy and pre-exponential factor of total conductivity obeyed the Meyer–Neldel rule. An examination of the isothermal electrical conductivity and modulus spectra was carried out with the use of Jonscher's power law and stretched exponential techniques. The scaling method developed by Summerfield for analyzing AC conductivity spectra demonstrated that the electrical relaxation process of the samples is not affected by the temperatures and concentration of Ga.