Researchers from Imperial College London and their European partners, including Volvo Car Corporation, are developing a prototype multifunctional structural composite material composed of carbon fibers and a polymer resin which can store and discharge electrical energy and which is also strong and lightweight enough to be used for car parts. Ultimately, they expect that this material could be used in hybrid and electric vehicles to make them lighter, more compact and more energy efficient, enabling drivers to travel for longer distances before needing to recharge their cars. In the new €3.4 mln (US$4.7 mln) project, the scientists are planning to develop the composite material so that it can be used to replace the metal flooring in wheel well, which holds the spare wheel. Volvo is investigating the possibility of fitting this wheel well component into prototype cars for testing purposes. The team says replacing a metal wheel well with a composite one could enable Volvo to reduce the number of batteries needed to power the electric motor. They believe this could lead to a 15% reduction in the car’s overall weight, which should significantly improve the range of future hybrid cars. The potential for such a multifunctional composite material which can simultaneously carry mechanical loads whilst storing (and delivering) electrical energy, writes Dr. Emile Greenhalgh, project coordinator, Department of Aeronautics at Imperial College London, has been demonstrated by researchers at the US Army Research Lab.
In a paper presented at the Materials Research Society Symposium in 2005, Southet al. provided three examples of multifunctional power-generating and energy-storing materials: structural lithium-ion batteries, structural proton exchange membrane (PEM) fuel cells, and structural capacitors. These systems were deliberately designed, so that material elements participating in power or energy processes are also carrying significant structural loads, a necessary condition for achieving mass savings through multifunctional design.
According to Dr Greenhalgh, “Polymer composites have now reached a level of maturity at which such adventurous and novel material configurations can be developed. The laminated architecture of fibre composites mirrors the configuration of many current electrical storage devices. In fact, carbon fibre (CF) composites are attractive as they are commonly used as both electrodes and high performance structural reinforcements; usually, the forms of carbon are different, but there is an opportunity to unify these roles with appropriate tailoring of both the matrix and the reinforcement.
Researchers at the Polymers and Composites Engineering group at Imperial had earlier been investigating development of a carbon fiber reinforced polymer composite which can act as a supercapacitor and show good mechanical properties (Young’s Modulus, Shear stiffness, compression strength, and peel and shear toughness) as a proof-of-concept. The new material under development by the Imperial-led team could be charged by plugging a hybrid car into household power supply. The researchers are also exploring other alternatives for charging it such as recycling energy created when a car brakes. The scientists are planning to further develop their composite material so that it can store more energy. The team will improve the material’s mechanical properties by growing carbon nanotubes on the surface of the carbon fibres, which should also increase the surface area of the material, which would improve its capacity to store more energy. They are also planning to investigate the most effective method for manufacturing the composite material at an industrial level. In addition, the researchers believe the material, which has been patented by Imperial, could potentially be used for the casings of many everyday objects such as mobile phones and computers, so that they would not need a separate battery. This would make such devices smaller, more lightweight and more portable.