Investigation of the Ionic Conduction Mechanism of Polyether/Li₇La₃Zr₂O₁₂ Composite Solid Electrolytes by Electrochemical Impedance Spectroscopy

Polyether-based polymer/cubic Li₇La₃Zr₂O₁₂ (LLZO) composite solid electrolytes were prepared by dispersing LLZO powder in a lithium (Li) conductive polyether-based solid polymer electrolyte. [SUS ∣ electrolyte ∣ SUS] (SUS: stainless steel) and [Li ∣ electrolyte ∣ Li] symmetrical cells were fabricated, and the ionic conductivity, Li/electrolyte interfacial resistance, and Li-cation transport number of the electrolytes were evaluated by electrochemical impedance spectroscopy. The polyether-based polymer/LLZO composite solid electrolytes showed relatively high ionic conductivity of over 10⁻⁴ S cm⁻¹ at 333.15 K, along with high electrochemical stability and low interfacial resistance to Li metal electrodes. Remarkable changes of Cole-Cole plots were observed with the variation of LLZO content, which was attributed to the formation of local percolation pathways between LLZO grains in the polymer matrix. Li-ion conduction was faster in the LLZO phase than in the polymer phase. The Li-cation transport number of the polymer/LLZO composite solid electrolytes was almost constant value regardless of LLZO content because of the rate-limiting ionic transport in the polymer phase with a low Li-cation transport number.