Traction Batteries on the CO₂ Test Bench

Manufacturing hybrid and battery electric vehicles produces a significant amount of greenhouse gases (GHG) – above all from producing the traction battery. IAV conducts detailed sustainability assessments. Traction batteries are being systematically advanced using the findings gathered.

The holistic comparison of vehicles by using the life cycle assessment can clearly illustrates the benefits and drawbacks. At the moment, conventional powertrains tend to show shortcomings in terms of GHG emissions during usage – i.e. while driving (tank to wheel) and in supplying fuel (well to tank). The emissions generated during production of these vehicles, on the other hand, are relatively low. The picture looks completely different for hybrid and battery electric vehicles. Besides the origin of the electric energy for powering these vehicles, the overall ecological footprint of the cars is essentially determined by production. “A number of powertrain components produce significant emissions”, explains Dr. Ralf Tröger, Head of the Powertrain Configuration department at IAV.

Among the CO₂ drivers from hybrid and battery- electric vehicles are the traction batteries with their active materials that often contain cobalt, manganese, nickel and lithium and are energy-intensive to produce. The rare earths for the e-motors and the high-purity silicon for the power electronics components also have a negative impact on the life cycle assessment results.

As a result, a typical compact-class e-vehicle can already produce 10.8 tons CO₂ equivalents (CO₂e) by the time it reaches the dealership, even before it has driven the first kilometer. Conventional vehicles, in contrast, arrive at a carbon-dioxide footprint of only 5.7 tons. This means that with the present EU power grid mix, an electric car must drive at least 78,000 kilometers before it clears its production-related “CO₂ debt” in comparison to a vehicle with a gasoline powertrain. Until that point, both vehicles will emit 210 grams of CO₂e per kilometer – equating to 16.4 tons of CO₂.

In terms of reducing the emissions from e-vehicles, vehicle production is increasingly moving into the focus of interest. A central driver here is the traction battery which, for a typical compact-class vehicle, accounts for around 40 percent of the carbon-dioxide emissions caused by the manufacturing process. One key impact comes from the active materials used as well as from cell design. By maintaining conventional cell design and using improved active materials, the GHG emissions from producing the traction battery can be reduced by 11 percent. In combination with a planar cell design, which increases the volume of active material utilized, the total reduction can be increased to 46 percent. An intelligent traction battery structure in conjunction with suitable active material can significantly improve an electric vehicle’s life cycle balance. Such findings are also being used, for example, in the EMBATT technology (also refer to the report on page 14 or go to www.embatt.de).

IAV calculations show that in producing a typical compact-class e-vehicle, GHG emissions can be cut by a total of ten percent for a mileage of 200,000 kilometers – around 50 percent can be avoided in producing the battery alone. “We carry out calculations of this type on behalf of our customers, helping them to minimize GHG emissions from battery production”, says Torsten Semper, Manager of the LCA and Benchmark Team at IAV. “Doing so, we determine the influence of battery structure and the materials used, right down to detailed matters of cell chemistry with the electrolytes and collectors.” Parallel to this, IAV’s experts also do cost engineering in order to identify both the CO₂ as well as the cost drivers and keep the specific carbon-dioxide avoidance costs as low as possible.

“In future, life cycle assessment of this type will become increasingly important because relevant legislative requirements are to be expected”, Tröger says. “Even now, we are seeing a growing demand for analyses of entire vehicles and powertrains, but also of hot spots, such as battery, power electronics end e-motor.”