Structural battery composites for mass-less energy storage

Research Project, 2021 – 2023

Satellites rely on energy storage for their functionality. For this reason, batteries are included in satellites prior to launch. The batteries are pre-charged to power the un-folding of the solar panels and the start of the onboard computer when in orbit. In service, the solar cells keep the battery charged to secure continuous power supply for operation during the frequent, but short, solar eclipses that the satellite experiences. Satellite's battery pack usually weighs a few hundred kilograms. Here, the battery is only providing an electrical energy storage function - adding weight to the system but does not contribute to its structural performance. The proposed
research aims at the development and demonstration of a  multifunctional material that can simultaneously store electrical energy and carry mechanical loads. We have coined this material structural battery composite. Structural battery composite materials will allow radical weight savings for any electrically powered
structural systems, from laptops to cars and, aircraft. Given the extensive use of carbon fibre composites in satellites, and in particular their solar cell panels, we foresee that access to structural batteries would allow to practically remove all weight of the current battery. A 200 kg weight reduction corresponds to a cost reduction
for launch just short of $4 million. C onsequently, access to structural battery composites will provide a competitive advantage for any satellite producer.

For the last decade, C halmers and KTH have performed research to realise structural battery composites. By this work, the Swedish team has established a position as leaders in the field. Current structural battery composites have demonstrated an energy density of 100 Wh/kg at a Young's modulus of 20 GPa. In the proposed project we seek to develop and demonstrate the second-generation structural battery composite with an energy density of at least 180 Wh/kg and a modulus of 70 GPa.

Structural battery composites are made from carbon fibres in a structural battery electrolyte matrix material. Neat carbon fibres are used as a structural negative electrode, exploiting their high mechanical properties, excellent lithium insertion capacity and high electrical conductivity. Lithium iron phosphate coated carbon fibres
are used as the structural positive electrode. Here, the lithium iron phosphate is the electrochemically active substance and the fibres carry mechanical loads and conduct electrons. The surrounding structural battery electrolyte (SBE) is lithium ion conductive and transfers mechanical loads between fibres. With these constituents, structural battery half-cells and full-cells are realised with a variety in device architecture.

The proposed research builds on recent activities funded by EU's Clean Sky II and USAF. During the coming two year period we propose research to realise the second-generation structural battery composite full-cells. The research comprises: Multiphysics models for design and analysis of structural battery devices; ultrathin separators to allow increased charge/discharge rates; highly multifunctional carbon fibre-reinforced positive electrodes; and design and characterisation of multifunctional electrodes/SBE and separator/SBE interfaces. The research is led by the Principal Investigator Prof. Leif Asp and the co-PIs Prof. Dan Zenkert and Dr Johanna Xu. The work will be performed by three doctoral students, in collaboration, during their final years of training.