Synergistic Coupling between Li_6.75La₃Zr_1.75Ta_0.25O₁₂ and Poly(vinylidene fluoride) Induces High Ionic Conductivity, Mechanical Strength, and Thermal Stability of Solid Composite Electrolytes

TLDR

Polymer electrolytes are attractive for all‑solid‑state lithium batteries because of their easy processing and flexibility, yet their low room‑temperature conductivity and poor mechanical and thermal properties limit practical use. The authors aim to enhance PVDF polymer electrolytes by incorporating LLZTO ceramics to induce structural modification. LLZTO ceramics trigger La atoms to complex with solvent N atoms and C═O groups, promoting chemical dehydrofluorination of PVDF and activating interactions among the polymer matrix, lithium salt, and fillers. This modification yields a flexible electrolyte membrane with ~5 × 10⁻⁴ S cm⁻¹ ionic conductivity at 25 °C, superior mechanical strength, thermal stability, and delivers satisfactory rate capability and cycling stability in a LiCoO₂|PVDF‑based solid‑state battery, demonstrating its promise for all‑solid‑state lithium batteries.

Abstract

Easy processing and flexibility of polymer electrolytes make them very promising in developing all-solid-state lithium batteries. However, their low room-temperature conductivity and poor mechanical and thermal properties still hinder their applications. Here, we use Li6.75La3Zr1.75Ta0.25O12 (LLZTO) ceramics to trigger structural modification of poly(vinylidene fluoride) (PVDF) polymer electrolyte. By combining experiments and first-principle calculations, we find that La atom of LLZTO could complex with the N atom and C═O group of solvent molecules such as N,N-dimethylformamide along with electrons enriching at the N atom, which behaves like a Lewis base and induces the chemical dehydrofluorination of the PVDF skeleton. Partially modified PVDF chains activate the interactions between the PVDF matrix, lithium salt, and LLZTO fillers, hence leading to significantly improved performance of the flexible electrolyte membrane (e.g., a high ionic conductivity of about 5 × 10-4 S cm-1 at 25 °C, high mechanical strength, and good thermal stability). For further illustration, a solid-state lithium battery of LiCoO2|PVDF-based membrane|Li is fabricated and delivers satisfactory rate capability and cycling stability at room temperature. Our study indicates that the LLZTO modifying PVDF membrane is a promising electrolyte used for all-solid-state lithium batteries.