One-Pot Green Synthesis of a PEO/TCPP/LiClO4 Solid Polymer Electrolyte with Improvement of Ion Transport

All-solid-state Li-ion batteries (ASSBs) composed of safe and reliable solid electrolyte materials have become increasingly important in energy storage systems. Poly(ethylene oxide) (PEO)-based electrolytes have been rapidly developed for ASSBs over recent years due to their nonflammability, shape flexibility, good interface contact with electrodes, and better electrochemical stability. Nevertheless, their low ionic conductivity remains a serious issue to be addressed urgently. Herein, we report a solid composite polymer electrolyte film with homogeneous network structures, which is composed of a LiClO4-added PEO-based polymer matrix plasticized with an additive meso-tetra (carboxyphenyl) porphyrin (TCPP), a kind of porphyrin covalent organic framework (COF) material, and obtained by a green and easy-to-scale solution-casting technique to improve the ionic conductivity and simplify the synthesis process. To the best of our knowledge, this is the first report on introducing TCPP into the PEO electrolyte. It demonstrates that the blending of PEO with TCPP can effectively suppress the PEO crystallinity and enhance the ion conductivity of the solid polymer electrolytes. As the content of TCPP reaches 8 wt %, it exhibits maximum ionic conductivities of 2.34 × 10–5 and 2.21 × 10–4 S cm–1 at 25 and 65 °C, respectively, which is about five times higher than that of the polymer reference electrolyte. It additionally brings an improved tLi+ value of 0.23 at room temperature with an electrochemical stability window of up to 5 V vs Li+/Li. In addition, when compared to the pure PEO film, a significant improvement in thermal stability is observed. This work may provide a new concept for building a new type of homogeneous COF-PEO-based composite polymer electrolyte film (CPE) that can be utilized as a desirable material in solid electrolytes for lithium-ion battery applications.