Multiphysics modelling of structural supercapacitors
Topic(s) : Special Sessions
Co-authors :
Shimeng QIAN (UNITED KINGDOM), Sang NGUYEN , Ajit PANESAR (UNITED KINGDOM), Emile GREENHALGH (UNITED KINGDOM)Abstract :
Structural power composites (SPCs) are an emerging class of multifunctional composite materials that can simultaneously fulfil multiple roles such as carrying mechanical loads and storing electrical energy, delivering considerable weight and volume savings for electrically powered structural systems from mobile phones to aircraft. Structural supercapacitor composites (SSCs) are one of the mainstream SPC embodiments alongside structural battery composites. The former offers a trade-off between specific energy and specific power, potentially long cycle life and good environmental tolerance. The SSCs developed by the Structural Power Composites group at Imperial College London have a laminated structure consisting of a pair of carbon aerogel (CAG) modified carbon fibre-reinforced electrodes with metal foil current collectors (CC) attached. These electrodes sandwich an insulating separator and the whole assembly is infused with a two-phase bicontinuous structural electrolyte (SE).
Different scales of multifunctionality are involved in SSCs. At the constituent level, the dual-phase SE consists of one liquid/gel phase for ion conduction and another solid phase for mechanical load-bearing. Another example could be the carbon fibre scaffold of the electrode, providing mechanical support whilst transferring electrons to the CCs. At the device level, electrical energy is stored in the electrical double layers formed at the interface between the CAG in the electrode and the liquid phase of the SE, while mechanical loads are supported by the electrodes, separator and the solid phase of the SE. Due to these inherent multifunctionalities, the interactions between different physical phenomena within the SSCs are pronounced during operation, which could have strong effects on their multifunctional performance. Hence, to gain a profound understanding and make accurate predictions of the coupling behaviours, as well as to guide the optimization and design for the multifunctional constituents of the SSCs, establishing multiphysics models for SSCs is a crucial step.
In this paper, a coupled thermo-electro-chemical-mechanical finite element model of SSCs is proposed. Firstly, a physics-based electrochemical model for SSCs is established based on porous electrode theory. The mechanical and thermal effects are then introduced by defining strain-dependent (e.g. electrical conductivity of carbon fibre fabric, CAG and SE) and temperature-dependent (e.g. diffusion coefficients of the liquid electrolyte) material properties. A parametric study to reveal the effects of the SSC fibre volume fraction and the porosity of the SE on the mechanical and electrochemical performance is conducted. The proposed model is the first endeavour and sets the groundwork for the development of the fully coupled thermo-electro-chemical-mechanical modelling framework of SSCs in a single computational analysis package to accelerate the certification of SPCs for industrial applications.
Different scales of multifunctionality are involved in SSCs. At the constituent level, the dual-phase SE consists of one liquid/gel phase for ion conduction and another solid phase for mechanical load-bearing. Another example could be the carbon fibre scaffold of the electrode, providing mechanical support whilst transferring electrons to the CCs. At the device level, electrical energy is stored in the electrical double layers formed at the interface between the CAG in the electrode and the liquid phase of the SE, while mechanical loads are supported by the electrodes, separator and the solid phase of the SE. Due to these inherent multifunctionalities, the interactions between different physical phenomena within the SSCs are pronounced during operation, which could have strong effects on their multifunctional performance. Hence, to gain a profound understanding and make accurate predictions of the coupling behaviours, as well as to guide the optimization and design for the multifunctional constituents of the SSCs, establishing multiphysics models for SSCs is a crucial step.
In this paper, a coupled thermo-electro-chemical-mechanical finite element model of SSCs is proposed. Firstly, a physics-based electrochemical model for SSCs is established based on porous electrode theory. The mechanical and thermal effects are then introduced by defining strain-dependent (e.g. electrical conductivity of carbon fibre fabric, CAG and SE) and temperature-dependent (e.g. diffusion coefficients of the liquid electrolyte) material properties. A parametric study to reveal the effects of the SSC fibre volume fraction and the porosity of the SE on the mechanical and electrochemical performance is conducted. The proposed model is the first endeavour and sets the groundwork for the development of the fully coupled thermo-electro-chemical-mechanical modelling framework of SSCs in a single computational analysis package to accelerate the certification of SPCs for industrial applications.