Why can’t a high-performance laptop be the size of a tablet? Or a smartphone the size of a pager? What is the main hurdle in making an electric vehicle cheap and highly efficient? The answer is its battery.
Despite the many advantages of using a battery as a power source, its size and weight are the two major reasons for not implementing it in high-voltage applications. As the required operating voltage rises, the battery’s volume and mass must also increase, making the final product much bigger and heavier.
Thus using a battery to run a car considerably increases its weight, reducing efficiency and leading to high running costs: in the Tesla Roadster electric car, for example, 37% of its weight is the battery, which means more power is needed to drive the vehicle. Similarly, an increase in volume hinders the miniaturisation of the final product; in the highly compact new iPhone, 54% of its inner space is occupied by the battery alone. That’s a huge percentage of ‘dead’ volume.
Currently, the only way to shrink these products further would be to make the battery more efficient, yet this is limited by its very makeup. The chemical ‘redox’ process that generates electricity is slow, leading to a low power density.
But scientists have come up with a novel idea to tackle this problem – materials that can act as both a structural component and a capacitor. By storing electricity as a potential difference between two insulated plates, capacitors avoid the problem of a slow chemical reaction, while their construction from a sturdy fibre-reinforced polymer composite allows them to form part of the body of the device.
What’s more, the composites are multi-material systems, and so can be tailored to a variety of mechanical and electrical requirements. If individual elements of the device participate both in load-carrying and electrical functions, then the space-wasting, single-function battery could become a thing of the past.
The Polymers and Composites Engineering Group of Imperial College London is currently involved in intensive research into this special class of materials. Of course, there are still challenges to be overcome; in particular the problem that capacitors currently can’t store as much energy as conventional batteries. But these structural power composites have the potential to bring us highly energy-efficient and extremely light products, in technologies as diverse as phones, electric cars, and spacecraft.