Enhanced Electrochemical Properties and Optimized Li+ Transmission Pathways of PEO/LLZTO‐Based Composite Electrolytes Modified by Supramolecular Combination

Abstract

Poly(ethylene oxide) (PEO) and Li6.75La3Zr1.75Ta0.25O12 (LLZTO)‐based composite polymer electrolytes (CPEs) are considered one of the most promising solid electrolyte systems. However, agglomeration of LLZTO within PEO and lack of Li+ channels result in poor electrochemical properties. Herein, a functional supramolecular combination (CD‐TFSI) consisting of active β‐cyclodextrin (CD) supramolecular with self‐assembled LiTFSI salt is selected as an interface modifier to coat LLZTO fillers. Benefiting from vast H‐bonds formed between β‐CD and PEO matrix and/or LLZTO, homogeneous dispersion and tight interface contact are obtained. Moreover, 6Li NMR spectra confirm a new Li+ transmission pathway from PEO matrix to LLZTO ceramic then to PEO matrix in the as‐prepared PEO/LLZTO@CD‐TFSI CPEs due to the typical cavity structure of β‐CD. As a proof, the conductivity is increased from 5.3 × 10−4 S cm−1 to 8.7 × 10−4 S cm−1 at 60 °C, the Li+ transference number is enhanced from 0.38 to 0.48, and the electrochemical stability window is extended to 5.1 V versus Li/Li+. Li‖LiFePO4 CR2032 coin full cells and pouch cells prove the practical application of the as‐prepared PEO/LLZTO@CD‐TFSI CPEs. This work offers a new strategy of interface modifying LLZTO fillers with functional supramolecular combination to optimize PEO/LLZTO CPEs for solid lithium batteries.