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

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 beta-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 beta-CD and PEO matrix and/or LLZTO, homogeneous dispersion and tight interface contact are obtained. Moreover, Li-6 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 beta-CD. As a proof, the conductivity is increased from 5.3 x 10(-4) S cm(-1) to 8.7 x 10(-4) S cm(-1) at 60 degrees 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.

Automated summary

Poly(ethylene oxide) (PEO) and Li6.75La3Zr1.75Ta0.25O12 (LLZTO)-based composite polymer electrolytes (CPEs) are improved by coating LLZTO fillers with a functional supramolecular combination (CD-TFSI). This coating allows for homogeneous dispersion and tight interface contact, resulting in enhanced conductivity, increased Li+ transference number, and extended electrochemical stability window. Practical application of the CPEs is demonstrated in both full cells and pouch cells. This work presents a new strategy for optimizing PEO/LLZTO CPEs for solid lithium batteries.