Impact of LLZO electrolytes doped with Ta5+ and their structural and electrical characteristics for solid-state energy storage applications

The electrolyte Li₇La₃Zr₂O₁₂ (LLZO) has emerged as a promising contender for solid-state energy storage applications. The present work uses a solid-state reaction technique to synthesize Ta-doped Li₇La₃Zr₂O₁₂ (LLZO: xTa⁵⁺) powder. The powder used to make the pellets is annealed for varying lengths of time. The impact of this process on the structural and electrical characteristics of LLZO: xTa⁵⁺ is thoroughly examined. High-resolution transmission electron microscopy (HRTEM) and selected area of diffracted light (SAED) are used to analyze the microstructural characteristics of the sintered powder, respectively. HRTEM image of LLZO indicates that after sintering, the xTa⁵⁺ powder has uniformly distributed, well-structured grains across the surface. The X-ray photoelectron spectroscopy (XPS) spectra results provide strong evidence for the existence of Ta, O, Zr, Li, and La in the synthesized electrolyte. The cyclic voltammetry results validate that 0.15 M.W.% Ta⁵⁺-doped LLZO gives a higher anodic current density (± 5 mA cm²) than pure (± 2.5 mA cm²) and 0.25 M.W.% (± 3.5 mA cm²) dopant percentage for the same potential levels. The electrochemical impedance spectroscopy (EIS) shows the lower R (resistance), whereas slanting straight line of the Nyquist plot indicates the Warburg impedance, signifying the high conductivity of the electrode. The dielectric constant and its corresponding loss, with respect to change in frequency and different temperature conditions were investigated for 0.15 M.W.% Ta⁵⁺-doped LLZO pellet.