UV-curable siloxane-acrylate gel-copolymer electrolytes for lithium-based battery applications

Thermo-set membranes prepared by free-radical photo-polymerisation (UV-curing) could be an interesting alternative to the existing Li-ion battery polymer electrolytes. UV-curing takes place at room temperature and it is based on initiating a chemical polymerisation inside a liquid poly-functional monomer, containing a proper photo-initiator, using direct UV-irradiation to create a highly cross-linked solid film. The present communication illustrates the results obtained from the investigation of a class of polymeric networks prepared by incorporating siloxane-based monomers into a methacrylic-based polymer matrix. The gel-copolymer membranes were obtained in the form of flexible, easy to handle, translucent films by UV-irradiation of a mixture of monomers in the presence of a radical photo-initiator with the in-situ addition of an EC/DEC solution. The polymer electrolyte was prepared by swelling the obtained membrane in a LiTFSI-EC-DEC solution. The chemical and structural properties were characterised by real-time FT-IR, TGA, DSC, and their surface characteristics were assessed by dynamic contact-angle measurements. Electrochemical tests on ionic conductivity, stability and cyclability in lithium cells pointed out the importance of the co-polymerisation in the presence of siloxane acrylates which improved the interfacial properties of the gel-copolymer membranes. Good values of ionic conductivity were obtained even at ambient temperature.