Researchers from Chalmers University of Technology have produced a structural battery that performs ten times better than all previous versions.
It contains carbon fibre that serves simultaneously as an electrode, conductor, and load-bearing material. Their latest research breakthrough paves the way for essentially ’massless’ energy storage in vehicles and other technology.
The batteries in today’s electric cars constitute a large part of the vehicles’ weight, without fulfilling any load-bearing function. A structural battery, on the other hand, is one that works as both a power source and as part of the structure – for example, in a car body. This is termed ‘massless’ energy storage, because in essence the battery’s weight vanishes when it becomes part of the load-bearing structure. Calculations show that this type of multifunctional battery could greatly reduce the weight of an electric vehicle.
The development of structural batteries at Chalmers University of Technology has proceeded through many years of research, including previous discoveries involving certain types of carbon fibre. In addition to being stiff and strong, they also have a good ability to store electrical energy chemically. This work was named by Physics World as one of 2018’s ten biggest scientific breakthroughs.
The first attempt to make a structural battery was made as early as 2007, but it has so far proven difficult to manufacture batteries with both good electrical and mechanical properties. But now the development has taken a real step forward, with researchers from Chalmers, in collaboration with KTH Royal Institute of Technology in Stockholm, presenting a structural battery with properties that far exceed anything yet seen, in terms of electrical energy storage, stiffness and strength. Its multifunctional performance is ten times higher than previous structural battery prototypes.
The battery has an energy density of 24 Wh/kg, meaning approximately 20 percent capacity compared to comparable lithium-ion batteries currently available. But since the weight of the vehicles can be greatly reduced, less energy will be required to drive an electric car, for example, and lower energy density also results in increased safety. And with a stiffness of 25 GPa, the structural battery can really compete with many other commonly used construction materials.
The new battery has a negative electrode made of carbon fibre, and a positive electrode made of a lithium iron phosphate-coated aluminium foil. They are separated by a fibreglass fabric, in an electrolyte matrix. Despite their success in creating a structural battery ten times better than all previous ones, the researchers did not choose the materials to try and break records – rather, they wanted to investigate and understand the effects of material architecture and separator thickness.
Now, a new project, financed by the Swedish National Space Agency, is underway, where the performance of the structural battery will be increased yet further. The aluminium foil will be replaced with carbon fibre as a load-bearing material in the positive electrode, providing both increased stiffness and energy density. The fibreglass separator will be replaced with an ultra-thin variant, which will give a much greater effect – as well as faster charging cycles. The new project is expected to be completed within two years.
