Surface positive-charged modification of inorganic fillers to optimize lithium ion conductive pathways in composite polymer electrolytes for lithium-metal batteries

The incorporation of inorganic fillers into composite polymer electrolytes (CPEs) is a common strategy to improve ionic conductivity. However, the high surface energy of inorganic fillers typically aggravates poor interfacial contact with polymer chains. Herein, we develop a surface positive-charge modification strategy for enhancing the intermolecular interaction of poly(ethylene oxide) (PEO) electrolytes with inorganic fillers and optimizing lithium ion (Li') conductive pathways in CPEs. The SiO2 nanoparticles are coated with a polydopamine adhesive layer and then functionalized with a branched polyethylenei-mine positively charged functional layer. Such surface modification not only effectively induces more amorphous structure into the PEO matrix but also promotes the dissociation of lithium salts and activates more free Li' in the PEO to accelerate Li' transport. The CPEs achieved a superior ionic conductivity of 6.12 x 10-5 S cm-1 at 30 degrees C. In addition, the modified fillers could induce the formation of a lithium flu-oride (LiF)-rich solid-state interphase and correspondingly achieve excellent compatibility with Li metal. The Li symmetric battery using the as-prepared CPEs delivered stable Li plating/stripping performances over 3960 h under 0.2 mA cm-2. The resulting LiFePO4|Li battery has an excellent capacity retention of 92.8 % after 260 cycles at 0.5C and 60 degrees C.(c) 2022 Elsevier Inc. All rights reserved.

Automated summary

Incorporating inorganic fillers into composite polymer electrolytes (CPEs) is a common strategy to enhance ionic conductivity. However, poor interfacial contact between inorganic fillers and polymer chains is often encountered. In this study, a surface positive-charge modification strategy was developed to improve the intermolecular interaction of poly(ethylene oxide) (PEO) electrolytes with inorganic fillers and optimize lithium ion conductive pathways in CPEs. The modified fillers not only induce more amorphous structure into the PEO matrix but also promote the dissociation of lithium salts, resulting in enhanced Li ion transport.