Enhanced ionic conductivity and interface compatibility of PVDF-LLZTO composite solid electrolytes by interfacial maleic acid modification

Abstract

Improving conductivity and optimizing interface contact are two primary targets to promote the development of solid-state electrolytes. Herein, maleic acid (MA) is introduced into normal PVDF-LLZTO(Li_6.75La₃Zr_1.75Ta_0.25O₁₂) based composite polymer-ceramic electrolytes (CPEs). Benefiting the self-polymerization of MA, a core-shell structure is spontaneously formed with LLZTO as core and MA nano-film as shell, the MA shell builds a bridge to link LLZTO and PVDF. In addition, carboxyl groups in MA provide extra channels for Li⁺ transmission. As a proof, the optimized 25MA-75PVDF-LLZTO CPEs demonstrates an enhanced conductivity as high as 1.15 × 10^-3 S cm^-1 at 30 °C, an extended electrochemical window up to < 5.0 V, a raised Li⁺ transfer number of 0.596, and an improved compatibility with Li metal anode. The as-prepared Li‖25MA-75PVDF-LLZTO CPEs‖LiFePO₄ full cell delivers an initial specific discharge capacity of 170.5 mAh g^-1 at 0.2C, a high rate capability up to 1.0C with 138 mAh g^-1 and an excellent long-term cycling stability of over 180cycles without capacity attenuation. The work provides a new strategy to optimize solid state lithium batteries by introducing unsaturated small organic molecules.

Keywords: Composite polymer-ceramic electrolytes; Conductivity; LLZTO; Maleic acid; PVDF; Solid-state lithium batteries.