Structural Polymer Composites for Energy Storage Devices

Abstract

Multifunctional composites have attracted a great deal of attention as they offer a way to cut down the parasitic weight in vehicles which not only reduces the operational costs but also reduces the fuel consumption in vehicles. Current engineering design is increasingly sophisticated, requiring more efficient material utilisation; sub-system mass and volume are crucial application determinants. This dissertation contributes to the fabrication of composites that can store electrical energy and are known as structural supercapacitors. The key in the fabrication of structural supercapacitors was not simply to bind two disparate components together, but to produce a single coherent material that inherently performed both roles of a structural composite and a supercapacitor. This design approach is at a relatively early stage, and faces significant design and material synthesis challenges. Disparate material requirements, such as structural and electrochemical properties, have to be engineered and optimised simultaneously. This study investigates on structural supercapacitors fabricated by using as-received as well as activated carbon fibre cloths as reinforcement and electrodes; multifunctional resin as electrolyte and matrix; and glass fibre cloths, filter papers or polymer membranes as insulators. Such a system should deliver electrical energy storage capacity as well as bear mechanical loads. Different liquid electrolytes, such as ionic liquids and salts based on Li+ and NH4+, were studied in order to optimise the multifunctionality of polymer electrolyte. Mesoporous silica particles were also introduced into polymer electrolytes in order to enhance the mechanical and electrochemical performance of polymer electrolytes. Nanostructured/ multifunctional resin blends were cured in cylindrical form and were examined by compression testing as well as impedance spectroscopy. An ionic conductivity of 0.8 mS/cm and a compression modulus of 62 MPa have been synthesised for the polymer electrolyte in the current study. By varying the separators, multifunctional resins and the electrodes, different structural supercapacitor configurations were manufactured using a resin infusion under flexible tooling (RIFT) method and were characterised to study the electrochemical performance by using charge/discharge method and mechanical performance by using ±45° laminate shear testing. The improved structural supercapacitors showed an energy density of 0.1 Wh/kg, a power density of 36 W/kg and a shear modulus of 1.7 GPa.