Superionic Solid Electrolyte Li7La3Zr2O12 Synthesis and Thermodynamics for Application in All-Solid-State Lithium-Ion Batteries

Abstract

Solid-state reaction was used for Li₇La₃Zr₂O₁₂ material synthesis from Li₂CO₃, La₂O₃ and ZrO₂ powders. Phase investigation of Li₇La₃Zr₂O₁₂ was carried out by x-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS) methods. The thermodynamic characteristics were investigated by calorimetry measurements. The molar heat capacity (C_p,m), the standard enthalpy of formation from binary compounds (Δ_oxH_LLZO) and from elements (Δ_fH_LLZO), entropy (S⁰₂₉₈), the Gibbs free energy of the Li₇La₃Zr₂O₁₂ formation (∆_f G⁰₂₉₈) and the Gibbs free energy of the LLZO reaction with metallic Li (∆_rG_LLZO/Li) were determined. The corresponding values are C_p,m = 518.135 + 0.599 × T - 8.339 × T^-2, (temperature range is 298-800 K), Δ_oxH_LLZO = -186.4 kJ·mol^-1, Δ_fH_LLZO = -9327.65 ± 7.9 kJ·mol^-1, S⁰₂₉₈ = 362.3 J·mol^-1·K^-1, ∆_f G⁰₂₉₈ = -9435.6 kJ·mol^-1, and ∆_rG_LLZO/Li = 8.2 kJ·mol^-1, respectively. Thermodynamic performance shows the possibility of Li₇La₃Zr₂O₁₂ usage in lithium-ion batteries.

Keywords: lithium-ion battery; lithium-ion thermodynamics; solid-state electrolyte; solid-state synthesis.