Volvo says structural battery is safe

Working with Imperial College London and eight other participants, the team set out to supersede the heavy and expensive batteries found in EVs and hybrid-electric cars with structural batteries that can replace certain metal body parts - door, roof, floor and bonnet - and provide power.

Volvo believes the concept could take 15 per cent off an EV/HEV’s weight and extend its range by around 130km.

The work, part of a European Union research project, has led to the development of a material consisting of a reinforced carbon fibre material that sandwiches the new battery and is formed to fit around the car’s frame. The carbon fibre laminate is first layered, shaped and then cured in an oven to set and harden. Super capacitors are then integrated within the component skin.

Inevitably, such an advance raises questions surrounding the viability of battery/super capacitor life, passenger safety, and the potential for recycling.

Per-Ivar Sellegren, innovation project manager, Volvo Car Corporation explained via email that all batteries have a limited lifetime due to calendar and cycle limitations.

The main factor that most often damages batteries, said Sellegren, is heat created by the battery itself, or from the environment in which it operates.

He said: ‘That’s why EVs and HEVs must have active battery cooling, which…results in added energy and weight. In this new battery concept, we have very low battery-created heat.

‘This is because there are very short distances between the active materials and low resistance for the electrical charges to travel – which generates less heat.

‘In this concept we also have very large cooling areas that keep the temperature within the required range.

‘Thanks to this improved cooling control and lower overall temperature, the lifetime of the battery is calculated to be at least as long as the car itself.

‘For the supercapacitor, there are no practical limitations due to number of cycles. A supercapacitor can be charged and discharged tens of thousands of times.’

Sellegren said the design brief required crash cycles with the new technology to be ‘at least as good as for a regular Volvo vehicle’, adding that the super capacitors and batteries would disconnect in a crash because they’re segmented.

‘By this decentralisation of many lower voltage areas around the car, and by impact disconnectors between these areas, you spread the risk and sensitivity to damage,’ he said. ‘Carbon fibres also work as a protective barrier between passengers and surroundings and are designed to dissipate crash energy. With lighter car components you also get lower energy forces to be absorbed in a crash.’

Car panels developed by the project have so far been incorporated into a Volvo S80 experimental car and a long-term aim is to develop a recyclable system.

‘We have not decided all the details yet,’ said Sellegren. ‘We still have many material formulas to choose between, giving different grades of impact. This is an environmentally sound concept, and…the complete concept chain must give a positive environmental contribution as a whole.’