Methacrylated Wood Flour-Reinforced Gelatin-Based Gel Polymer as Green Electrolytes for Li-O₂ Batteries

With its very high theoretical energy density, the Li-O₂ battery could be considered a valid candidate for future advanced energy storage solutions. However, the challenges hindering the practical application of this technology are many, as for example electrolyte degradation under the action of superoxide radicals produced upon cycling. In that frame, a gel polymer electrolyte was developed starting from waste-derived components: gelatin from cold water fish skin, waste from the fishing industry, and wood flour waste from the wood industry. Both were methacrylated and then easily cross-linked through a one-pot ultraviolet (UV)-initiated free radical polymerization, directly in the presence of the liquid electrolyte (0.5 M LiTFSI in DMSO). The wood flour works as cross-linking points, reinforcing the mechanical properties of the obtained gel polymer electrolyte, but it also increases Li-ion transport properties with an ionic conductivity of 3.3 mS cm^-1 and a transference number of 0.65 at room temperature. The Li-O₂ cells assembled with this green gel polymer electrolyte were able to perform 180 cycles at 0.1 mA cm^-2, at a fixed capacity of 0.2 mAh cm^-2, under a constant O₂ flow. Cathodes post-mortem analysis confirmed that this electrolyte was able to slow down solvent degradation, but it also revealed that the higher reversibility of the cells could be explained by the formation of Li₂O₂ in the amorphous phase for a higher number of cycles compared to a purely gelatin-based electrolyte.