Manufacture and characterisation of structural battery composite constituents

Licentiate thesis, 2024

Structural battery composites are a promising material that can help improve the efficiency of electric mobility. The possible efficiency gains come from the associated multifunctionality. A structural battery can store electric energy while also playing a structural role. This is made possible thanks to the careful choice of materials, particularly the active materials used for the negative electrode. Here, custom-made carbon fibres are manufactured to improve the multifunctionality in terms of mechanical and electrochemical properties. Different manufacturing processes are considered with three different carbonisation temperature profiles. A significant trade-off is found, with the elastic modulus and strength observed to decrease by up to 7%, while capacity increased by 15%. This suggests that by carefully selecting processing conditions in carbon fibre manufacturing, it is possible to tailor them for specific multifunctional applications within a constrained design space.

Carbon fibres are not the only crucial multifunctional constituent. The structural battery electrolyte also plays a key role, enabling load transfer and ionic transport between the layers. To date, no thorough characterisation of the mechanical properties has been performed. Here, we define a procedure to manufacture bulk samples and extensively characterise the mechanical behaviour of the structural battery electrolyte. The test campaign shows that the material has a very brittle behaviour, with moderate Young's modulus and low tensile strength. A significantly higher compressive strength is measured. Cure shrinkage is also investigated and found to be insignificant. These findings are essential for accurately predicting internal stress states in the structural battery electrolyte and guide future modelling efforts.