Structural battery composites with solid-state polymer electrolyte produced by slurry coating

Summary:

With the Flightpath 2050 initiative the European union set the goal to drastically reduce the environmental impact of the air transport sector. Amongst others the CO2 and NOX emissions shall be reduced by 65% respectively 90% until 2050 [1]. A goal that can only be achieved by the development of full electric and hybrid electric propulsion technologies. Due to the high power required for the take-off the electrical energy storage is one of the main challenges. State-of-the-art battery technologies do not satisfy the requirements of the commercial air transport sector in terms of specific energy [2]. It is thus necessary to reduce the mass and volume of energy storage as much as possible. The multifunctional use of the energy storage components is one approach to reduce its impact on the overall system [3]. So-called structural battery composites can store electrical energy while bearing mechanical loads.

In this study, the epoxy resin in commonly used load bearing fiber reinforced composites is substituted for the materials of an all-solid-state battery to enable the storage of electrical energy. The focus lies on the electrochemical characterization of carbon fiber-based structural cathodes and a structural separator based on glass fibers. A slurry composed of lithium iron phosphate (LFP), polyethylene oxide (PEO), Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and carbon black was coated on carbon fiber textiles in order to prepare structural cathodes. After coating and drying a compression step was performed to homogenize the coating and to improve the surface quality. For the electrochemical characterization coin cells have been built by laminating the structural cathodes with a polymer film separator and a lithium metal anode. The compression step and the lamination step were found to have a significant influence on the electrochemical performance. With capacities up to 139 mAh g-1AM good utilisation of the active materials in the structural cathodes is demonstrated. Furthermore, the fabrication of a structural battery composite demonstrator is presented. For the demonstrator a structural separator was prepared by slurry coating glass fibers with PEO and LiTFSI. With respect to electrode and separator mass a specific energy of 64 Wh kg-1 was achieved.

References:
[1] Flightpath 2050: Europe’s vision for aviation; Policy / European Commission, Publ. Off. of the Europ. Union: Luxembourg, 2011
[2] Bills, A.; Sripad, S.; Fredericks, W.; Singh, M.; Viswanathan, V. Performance Metrics Required of Next-Generation Batteries to Electrify Commercial Aircraft. ACS Energy Lett. 2020, 5, 2, 663–668. doi:10.1021/acsenergylett.9b02574
[3] Adam, T.; Liao, G.; Petersen, J.; Geier, S.; Finke, B.; Wierach, P.; Kwade, A.; Wiedemann, M. Multifunctional Composites for Future Energy Storage in Aerospace Structures. Energies 2018, 11, 335. doi:10.3390/en11020335.