An Environmentally Friendly Crosslinked PMMA Gel Polymer Electrolyte for Li-Ion Battery

摘要

Gel electrolytes for lithium-ion batteries reached commercial success in 1999, when Sony launched its 'LiPo' batteries based on poly(vinylidene fluoride-hexafluoropropylene)(PVDF-HFP), in which the gel is formed in-situ upon introduction of the liquid fraction of the gel and swelling of the porous PVDF-HFP matrix. PVDF-HFP, however, releases HF upon burning (during the smelting recycling process). Poly(methyl methacrylate) (PMMA), on the other hand, is non-fluorinated, cheap, non-toxic, easy to polymerize and modify and can be swollen by carbonate-based electrolytes as well. Here, a crosslinked PMMA gel polymer electrolyte (PGPE) was prepared by radical polymerization from a low viscosity precursor solution incorporating methyl methacrylate, a crosslinker and the liquid fraction (optimized for high temperature and graphite use) to form gels in-situ. Fast polymerization kinetic was confirmed by in-situ Raman spectroscopy. High efficiencies and stable cycling were reached with graphite/NMC111 cells with 2.1 mAh cm[-2] for hundreds of cycles with an optimized PGPE formulation. The thermal properties of the gel electrolytes were characterized as well by DSC and TGA and the mechanical properties of the gel membranes were determined by oscillating rheometry. In addition, ionic transport and dissociation were probed electrochemically and by Raman, PFG-NMR and eNMR spectroscopies, complemented by DFT calculations.