Alternative architectures for structural batteries

Abstract

Structural batteries are multifunctional materials that are simultaneously capable of storing energy and transferring mechanical loads. This allows for mass savings on a systems level when they are used as structural components in electrified transport applications. The key to realising the next generation of structural batteries may be in the development of alternative architectures, which use different materials and assembly strategies to those that are used in the current state-of-the-art laminated architecture. The first part of this thesis involves an in situ synchrotron X-ray diffraction study to characterise the atomic scale changes occurring in carbon fibre anodes during battery cycling. This is carried out in order to gain a better understanding of the lithiation mechanism in carbon fibre anodes, and how this relates to changes in the structure at the fibre scale.

X-ray diffraction measurements showed that the interlayer spacing between the graphene sheets in carbon fibre increase by up to 3.9% during charging, which is caused by the insertion of Li+ ions between the layers. The X-ray diffraction measurements also showed that the spacing between adjacent basal plane carbons in the graphite unit cell of carbon fibre anodes increases by up to 3.6% during charging, which is caused by unfolding of the graphite layers. This work provides valuable insight into the lithiation mechanism of carbon fibre anodes, and the volume changes that this causes at the fi bre scale. These insights are important to structural battery architecture development due to the fact that carbon fibre anodes are a critical material in almost all structural battery architectures.

The second part of this thesis explores materials and assembly strategies that may be used in the realisation of alternative structural battery architectures. The first of these strategies involves using polymerisation-induced phase separation to produce a cathode doped matrix material for the microbattery architecture. A cathode doped matrix produced using this method was found to have a respectable ionic conductivity of 9.16 x 10-3 S cm-1 and a storage modulus of 188 MPa. The second of these strategies is a continuous electropolymerisation process designed to coat a separator material onto carbon fibre anodes for use in the intermingled architecture. Coating of carbon fibres with separator material was demonstrated, but the inconsistent thickness of the coating highlighted the significant challenge associated with coating materials using a continuous process, which was the presence of local concentration gradients of material in the coating solution.

The third and final strategy involves electrospinning of a coaxial cathode material for the electrospun architecture. The coaxial electrospun cathodes consisted of a cathode core, which was insulated by a separator sheath. The separator sheath was successfully able to insulate the cathode core when pressed against a lithium metal anode, and a capacity of 38 mAh g-1 was demonstrated for a coaxial electrospun cathode cycled at a rate of 0.2 C. Overall, all of the materials that have been developed and characterised as part of this thesis create new opportunities for a number of different structural battery architectures, paving the way for the key next step, which is the assembly of full structural battery cells that can compete with the established laminated architecture.

Date of Award	24 Jul 2024
Original language	English
Awarding Institution	University of Bath
Supervisor	Andrew Rhead (Supervisor), Frank Marken (Supervisor), Alexander Lunt (Supervisor) & Steve Parker (Supervisor)