Conti Begins Series Production of Hybrid Vehicle Batteries

On September 24 Continental’s Powertrain Division held a celebration to mark the start of series production for its lithium-ion batteries for use in hybrid drive cars. The beginning of series production – which takes place following an investment of more than three million euros into developing manufacturing capacity at its factory in Nuremburg, Germany – is, says Conti, a world first.

“This underlines Continental’s claim that, by developing and manufacturing state-of-the-art drive technologies, it can contribute to a significant reduction in fuel consumption by vehicles in future and, consequently, to a reduction in CO2 emissions as well”, said Dr. Karl-Thomas Neumann, CEO of Continental AG and head of the Powertrain Division.

Compared with the nickel-metal hydride battery technology currently in use in hybrid vehicles, lithium-ion batteries offer significantly greater storage capacity. The battery Continental has developed weighs around 25 kilograms and requires an installation volume of some 13 litres. This allows the electric motor to boost the combustion engine by up to 19kW, allowing considerable fuel savings during acceleration or when starting off. The battery is charged when the vehicle brakes or decelerates. This regenerative braking, or recuperation, is controlled by the power electronics.

Working in a similar way to an integral automatic start-stop function that automatically switches off the engine when the vehicle comes to a standstill and switches it on again when starting off, recuperation forms one part of Continental’s hybrid modular system, a system that combines all the company’s hybrid technology expertise in a single package. The lithium-ion battery produced in Nuremberg, including the hybrid technology, will be installed as standard in the new Mercedes S400 BlueHYBRID, available from the middle of 2009. Helped by Conti’s technology, this luxury class six-cylinder petrol engine saloon will achieve a consumption rate of 7.9 litres per 100 kilometres, equating to CO2 emissions of 190 grams per kilometre.

Using lithium-ion technology in vehicles poses particular challenges, says Continental. “The battery has to operate safely and reliably for the whole of the life cycle stipulated by the vehicle manufacturer, and that’s at least ten years”, stresses Jörg Grotendorst, head of the Hybrid Electric Vehicles Business Unit in Continental’s Powertrain Division. This tall order is met through an elaborate battery management system that monitors the battery so that it is always within the optimum working range. The electronics compare the battery’s overall condition, temperature and energy reserves against its age; and safety circuits prevent the energy storage unit from becoming too hot. A Cell Supervision Circuit (CSC) monitors the individual cells and ensures their optimum interaction. To ensure that cells are not permanently subjected to uneven loads, the CSC balances the charge levels of all the cells in the battery. This guarantees that the lithium-ion batteries will last – with unimpaired functionality, power and safety – for the required ten years or 160,000 to 240,000 kilometres. Batteries produced since 2007 as part of Conti’s preproduction series have been artificially aged in the course of exhaustive text cycles in order to simulate their use in vehicles over many years.

It is not just the safety and test engineering which is demanding; assembly poses its own challenges. Since the current inside the battery is not conducted via cables but along copper bus bars, a special welding process has to be used to join the bus bars. Only by using resistance welding which uses 16,000 amps is it possible to join the copper bus bars so that the current can then flow unimpeded past the welding seams and avoid power losses. The lithium-ion batteries are fully enclosed in a laser-welded, stainless steel housing.

These new areas where lithium-ion batteries can be used also pose new disposal and recycling challenges. Continental is conscious of its responsibilities towards the environment and, together with its waste disposal partners, is developing recycling ideas which will allow at least 50 per cent of the content of lithium-ion cells to be recycled.

Continental started pre-series production of lithium-ion batteries last year in Berlin; then, in the space of twelve months, the series production equipment was planned and installed in the Nuremberg plant, at a total investment cost of around 3.3 million euros. Some 15,000 lithium-ion batteries can be produced annually in the 300 square metre production facility, and this capacity can be doubled at short notice.