Carl Larsson, Computational Mechanics and Materials Engineering

As the demand for lightweight energy storage solutions intensifies, structural battery composites have emerged as a promising technology merging electrochemical capacity with mechanical load carrying capability. Unlike conventional systems, where energy storage is typically implemented as battery packs that add mass, structural batteries integrate this function directly into structural elements. The multifunctionality is achieved by utilizing carbon fibres as both the primary structural reinforcement and as active electrode material. To facilitate ion transfer between the electrodes, while maintaining structural integrity, the fibres are embedded in a Structural Battery Electrolyte (SBE)—a bicontinuous material consisting of a porous polymer skeleton and a liquid electrolyte.
The first part of this thesis studies the constitutive modelling and characterization of the structural negative electrode and its constituents. A concentration-dependent constitutive model is developed for the carbon fibres to account for the significant swelling and the evolution of elastic moduli induced by lithium-ion insertion under finite deformations. This is complemented by a continuum porous media representation of the SBE, which utilizes a visco-hyperelastic model for the solid skeleton and incorporates the principle of effective stress to capture the time-dependent coupling between deformation and pore fluid pressure. To accurately analyze the complex internal stress states on the microscale, governed by fibre expansion, SEM micrograph informed microstructures are generated. By integrating the developed constitutive models for both the fibre and the SBE these representative volume elements, the framework resolves the local mechanical interactions between the swelling fibres and the surrounding matrix in the negative electrode during lithiation.
The second part of the thesis develops a coupled computational framework for structural battery full cells. The model is calibrated against experimental charge-rest-discharge voltage profiles, including different charge rates. A sensitivity study is conducted to quantify the contribution of the calibrated parameters to the simulated voltage profiles. The framework is further developed and utilized to characterize the coupled potential-strain response, where an integrated experimental-computational study concludes that the carbon fibres in the negative electrode is the primary contributor to electric potential shifts during mechanical loading. This finding demonstrates an inherent sensing functionality within the structural electrode and validates the multifunctionality of the full cell.