Multifunctionality\nand Processability of a Thermoplastic\nBased Gel Electrolyte Cell for the Realization of Structural Batteries

In this work, a battery\nlayup consisting of a poorly\nflammable\nionic liquid electrolyte and a poly(vinylidene fluoride-<i>co</i>-hexafluoropropylene) (PVdF-HFP) thermoplastic has been developed\nalong with composite anode and cathode electrodes. The developed gel\nelectrolyte exhibits feasible ionic conductivity of about 1 mS/cm\nat 30 °C. State-of-the-art active electrode materials, i.e.,\nLiNi<sub>0.8</sub>Mn<sub>0.1</sub>Co<sub>0.1</sub>O<sub>2</sub> (NMC811)\nand graphite, have been employed. Full cells were tested in coin and\npouch cell format, obtaining capacities of about 120 and 100 mA h/g<sub>NMC811</sub>, respectively, at a C-rate of C/10. Thereby, it was\nobserved that good contact between the individual cell layers is crucial.\nRecently, it was shown that the mechanical properties of structural\nbatteries, realized by integrating battery cells into carbon fiber-reinforced\npolymer (CFRP) laminates, depend significantly on the mechanical properties\nof the cell itself. Hence, to promote the realization of such a structural\nbattery concept, tensile tests were carried out to investigate the\nmechanical properties of cells as well as the individual components\ndeveloped in this work. The full cell showed values of 10 GPa and\n49 MPa for the Young’s modulus and tensile strength, respectively.\nThus, feasible multifunctionality could be verified on the cell level.\nHowever, regarding the contributions of the different components,\nit could be shown that mainly the current collector foils contribute\nto the mechanical properties, in contrast to the electrode loadings\nand the gel electrolyte. Additionally, the thermal and chemical stability\nof the developed system was evaluated, highlighting the importance\nof these secondary properties for the fabrication of structural batteries,\ni.e., the integration of cells into load-bearing CFRP laminates. Specifically,\nit was observed that the developed system is thermally stable up to\n150 °C and no HF release was detected upon exposure to ambient\nconditions.