Built-in batteries to transform design
Research into integrating batteries within materials could make hybrid vehicles much lighter. Graham Pitcher reports.
Batteries in large scale applications are often heavy and require the product to be designed around them. What if you could integrate the battery into the product itself? That question is being addressed by a research team at Imperial College.
The €3.4million project, which also involves Volvo, is developing a prototype material that can store and discharge electrical energy, but which is light and strong enough to be used for car parts. The researchers say that the composite material they are developing, which is made of carbon fibres and a polymer resin, will store and discharge large amounts of energy much more quickly than conventional batteries. In addition, the material does not use chemical processes, making it quicker to recharge than conventional batteries. And the researchers say this recharging process causes little degradation in the composite material, because it does not involve a chemical reaction, whereas conventional batteries degrade over time.
One of the researchers is Anthony Kucernak, professor of physical chemistry in Imperial's Department of Chemistry. He said: "Today, you have to build products around batteries. Our idea is to develop materials which can replace a structural component, but which can also store power. In an ideal world, these would have the mechanical properties of the material being replaced, along with the electrical properties of a lithium ion battery."
There are two potential applications: battery and supercapacitor. In the latter approach, energy can be stored for use when needed.
Prof Kucernak pointed out that the battery approach requires an electrolyte to be included within the carbon fibre. "We build the battery using an electrolyte," he noted, "but need to modify how we deposit that chemistry on the fibres so that it is integral to the structure. In theory, we could create a device which is smaller and weighs less for a given amount of energy storage. We have demonstrated that the approach works for supercapacitors."
Initially, 7µm carbon fibres were used, but Prof Kucernak said these didn't work very well as capacitors because of their low surface area. "We're now growing carbon nanofibres on their surface, effectively creating 'hairy fibres'. So far, we have achieved a specific capacitance of 14Farad/g and the material maintains good structural performance."
A further avenue of research is hybrid structures – half battery, half supercapacitor. Prof Kucernak said: "This will allow the benefits of both; the energy capacity of batteries and the high charge/discharge rates of supercapacitors."
The researchers believe the composite material could be used to make hybrid vehicles considerably lighter. The research team, in conjunction with Volvo, is planning to develop the composite material so that it can be used to replace the metal flooring of a car's wheel well. This would reduce the number of batteries needed to power the hybrid's electric motor and could reduce vehicle weight by 15%. In addition, the material could potentially be used for the casings of devices such as mobile phones and computers, but the project is targeting large scale applications. "One area is cars," Prof Kucernak explained, "another is planes; both areas where combining mechanical and electrical performance will be better than having a separate battery."
