Optimizing Ionic Transport in Polymer (PEO) – Garnet (LLZO) Composite Solid-State Electrolytes*

Composite polymer electrolytes (CPEs) are viable candidates to replace the flammable organic liquid electrolytes in current lithium-ion batteries. The addition of filler particles significantly increments the ionic conductivity of the polymer-anion salt matrix. A comprehensive mechanism for ion transport in CPEs has yet to be developed. This work investigates ionic transport in CPEs comprising Li₆La₃ZrBiO₁₂ (Bi-LLZO) and Li_6.25La₃Zr_1.25Bi_0.75O₁₂ (0.75Bi-LLZO) mesoparticles as fillers embedded in PEO: LiTFSI matrixes. We find that the Bi content of the garnet mesoparticles determines the weight load required to achieve the highest ionic conductivity in these composite materials. Plausible mechanisms of the role of Li-vacancy occupancy, controlled by the Bi-content in the LLZO filler particles, on CPE ionic conductivity will be discussed.