Photo-Polymerized Organic Host Network of Ionogels for Lithium Batteries: Effects of Mesh Size and of Ethylene Oxide Content

Abstract

Solid ionogel electrolytes are rather competitive compared to liquid carbonate based electrolyte regarding ionic conductivity but they show much better safety. It is striking that the ionogels presented here are obtained within few minutes by UV curing which triggers the formation of the polymer host network confining N-methyl,N-propylpyrrolidinium bis-(trifluoromethyl)sulfonylimide with lithium bis-(trifluoromethyl)sulfonylimide salt at the concentration of 1M. This fast and easy process allows for obtaining all-solid like micro-batteries. Herein the effect of mesh size and ethylene oxide content of various host networks is deciphered. An optimum balance between mesh size, ethylene oxide and lithium content is identified. The ionogel formed from trimethylolpropane ethoxylate triacrylate and 1,6-hexanediol diacrylate confining 90% wt of ionic liquid shows a mesh size close to 5 nm, with an enhanced fragility of the confined ionic liquid, as referred to that of the bulk one. Along with these last features, its ethylene oxide content allows a very good lithium ion diffusion. At room temperature and at C/5 cycling rate, prototype batteries LiFePO4 | ionogel | Li metal battery can restitute 70% of the initial capacity during up to 1200 cycles.