On the multifunctional performance of structural batteries

Licentiate thesis, 2019

The structural battery composite is a composite material that can store electrical energy (i.e. work as a battery) while simultaneously provide mechanical integrity in a structural system. Due to its inherent ability to store energy this material offers significant weight savings on a system level. For this reason, this type of material has the potential to revolutionize future design of electric vehicles and devices.
Because of the multifunctional nature of this material novel design frameworks and multiphysics models are needed to predict and evaluate its multifunctional performance. Furthermore, charging and discharging the structural battery will generate heat and alter the volume and elastic properties of the constituents during operation. This will affect the effective properties of the material and generate internal stresses which can cause mechanical and/or electrical failure. For these reasons, it is crucial to be able to predict the multifunctional performance of the material and how it varies during operation.
In this thesis, modelling frameworks to predict and analyse the multifunctional performance of structural batteries is developed. The frameworks are used to estimate the multifunctional performance of different material designs and to study the mechanical consequences from electrochemical cycling. We demonstrate how the material design can be altered to enhance different performances. Furthermore, significant changes in effective elastic properties for the structural battery composite with change in state of charge (SOC) are found. This illustrates the need to consider changes in the elastic properties with SOC when designing structural battery components. Finally, it is shown that the properties of the constituents, charge/discharge current, lamina dimensions and residual stresses have significant effect on the internal stress state and the elastic properties of the composite lamina. The results also show that the heat generated during electrochemical cycling must be accounted for when evaluating the internal stress state in structural batteries.