Lithium-Ion Polymer Batteries Assembled with a Cross-Linked Composite Polymer Electrolyte Using a Vinyl-Functionalized SiO2 Nanoparticles

Abstract

Recently, a safety of lithium-ion batteries has been a critical issue as the demand of high capacity batteries for electric vehicles and energy storage systems has increased. The electrolyte commonly used in current lithium-ion batteries is lithium salts (mostly LiPF6) in a mixture of carbonate-based organic solvents. However, the high flammability of the organic solvents in liquid electrolyte can lead to fires and explosions when short circuits or local overheating accidentally occurs [1]. Furthermore, HF can be generated by thermal decomposition and hydrolysis of LiPF6 by trace moisture in the electrolyte solution, which leads to degradation of the cycling performance of lithium-ion batteries at high temperature [2, 3]. Among the various electrolyte systems for lithium-ion batteries, the cross-linked polymer electrolyte is one of the promising candidates due to its high ionic conductivity, good interfacial properties and thermal safety with no electrolyte leakage. In this work, we synthesized the vinyl-functionalized SiO2 particles and coated them onto the fibrous polymer membrane or the microporous polyolefin separator. The SiO2 particles on polymer participated in free radical polymerization with tri(ethylene glycol) diacrylate in a gel electrolyte precursor to form a cross-linked composite polymer electrolyte. An in-situ cross-linking reaction using these reactive SiO2-coated separators promoted strong interfacial adhesion between electrodes and separator, and allowed effective encapsulation of liquid electrolyte, resulting in low interfacial resistances. In addition, the silica nanoparticles played a role as HF scavengers to reduce HF content in the electrolyte at high temperature. The lithium-ion polymer cells assembled with a SiO2-coated separator exhibited superior cycling performance to cell prepared with a conventional polyethylene separator due to the strong interfacial adhesion between the electrodes and separator, as well as suppression of deleterious reactions during cycling.