Comparative Study of Photopolymerized Gel Polymer Electrolytes Obtained via Thiol-Ene Click Reaction for Li Metal Batteries

Abstract

Gel polymer electrolytes (GPEs) present the best compromise between mechanical and electrochemical properties, as well as an improvement of the cell safety in the framework of Li metal batteries production. However, the polymerization mechanism typically employed relies on the presence of an initiator, and is hindered by oxygen, thus impeding the industrial scale-up of the GPEs production. In this work, an UV-mediated thiol-ene polymerization, employing polyethylene glycol diacrylate (PEGDA) as oligomer, was carried out in a liquid electrolyte solution (1 M LiTFSI in EC/DEC) to obtain a self-standing GPE. A comparative study between two different thiol-containing crosslinkers (trimethylolpropane tris(3-mercaptopropionate) - T3 and pentaerythritol tetrakis(3-mercaptopropionate) - T4) was carried out, studying the effects of the crosslinking environment and the GPE production methods on the cell performances. All the produced GPEs present an excellent room temperature ionic conductivity above 1 mS cm⁻¹, as well as a wide electrochemical stability window up to 4.59 V. When cycled at a current density of C/10 for more than 250 cycles, all of the tested cells showed a stable cycling profile and a specific capacity >100 mAh g⁻¹, indicating the suitability of such processes for up-scaling.