Second-life batteries: Electricity storage systems made from used electric car batteries

Ever more electric cars are taking to the road in Germany and emission-free mobility is growing at a rapid pace. This increases the demand for lithium-ion batteries – as well as the number of used batteries that will need to be replaced in a few years’ time. In conjunction with Audi, EnBW is currently testing whether withdrawn car batteries can be given a new lease of life in stationary electricity storage systems.

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Old car batteries are by no means finished

Accounting for almost 40 percent of the cost, the battery is the most expensive individual component in a modern electric car. Large quantities of valuable resources – such as nickel or lithium – are needed to produce them. Batteries for electric cars generally last for many years and provide reliable performance, clocking up high mileage throughout the entire service life of the vehicle. When the time comes to scrap the vehicle, however, the question arises of whether to recycle the battery or continue using it.

An innovative project launched by Audi and EnBW shows a potential way of sustainably using “second-life batteries”: On the site of EnBW’s combined heat and power plant in Heilbronn, the two partners are installing a reference storage system made of withdrawn electric car batteries and testing various application scenarios here. The batteries come from a test fleet of the Audi “e-tron” electric vehicle and still have high capacity levels.

Several of the electric car batteries are connected to each other in one of the electricity storage system’s containers. The inside of a container resembles a drawer cabinet or a shelf. Each battery has its assigned place here and is lifted into the container by forklift. It can be quickly disconnected and replaced if necessary – for example, when its power capacity is finally exhausted. “When this point is reached, the batteries are returned to the car manufacturer, which then sends them for recycling,” explains Dr. Daniel Bahro, manager of recycling and second-use battery system solutions at EnBW. “With secondary use in stationary storage systems, we are exploiting additional potential in the material life cycle of used electric car batteries. After all, the batteries generally have a much longer service life than the vehicles themselves.”

Still strong together: A retirement home for “old-aged batteries”

At the heart of the storage systems currently being tested in Heilbronn are batteries withdrawn from Audi electric cars. Twelve interconnected “second-life batteries” can fit inside one container.

Internally, the Audi and EnBW project team also humorously refers to the reference storage system in Heilbronn as a “retirement home for car batteries,” says Bahro. At the end of their strenuous “professional life” as a vehicle’s energy source, the batteries here are assured a comparatively relaxed retirement: “The stress levels here are no longer as high as in the mobile setting, where a lot of energy has to flow very quickly when accelerating,” explains the expert. Nonetheless, the used batteries are still powerful – particularly when grouped together: Twelve “old-aged batteries” interconnected in a container are capable of generating a total output of around one megawatt (MW) – enough to supply several hundred households with electricity at the same time, at least in the short term until the batteries are discharged. Many containers connected together deliver even higher performance.

Lower investment costs by using second-life batteries

The reference storage system serves as a technical and process-based model for other plants that EnBW considers to be conceivable for commercial operation. “It may work out very economical for municipal utilities, industrial companies or operators of decentralized generation plants to use storage systems equipped with used battery modules in the future,” says Bahro. “That’s because the secondary use of electric car batteries is expected to cut the investment costs for batteries quite considerably.”

The project is also of great significance to Audi. By giving high-voltage batteries a new lease of life, valuable resources can be used in an economically viable and environmentally sustainable manner. “Audi has set itself the goal of achieving emission-free mobility. Our electric offensive is an important step in this direction,” says Hagen Seifert, head of sustainable product development at Audi. “The idea behind the cooperation with EnBW is to show how the battery can be efficiently repurposed for use by energy suppliers after its use in the car,” says Seifert.

There is huge potential for stationary storage systems made using former electric car batteries: Scientists at the International Energy Agency (IEA) expect that by 2040 electricity storage systems will need capacity to store at least 10 million megawatt-hours (MWh) of energy – as large-scale storage within the power grids, for example – in order to achieve the energy transition’s global climate targets. The supply of “second-life batteries” could increase to such an extent by then that it seems entirely possible to build the required storage systems solely from used batteries. Volkswagen, for example, wants to sell more than one million electric vehicles per year worldwide by 2025, while the German government has set a target of more than ten million electric cars on German roads by 2030. And the EU Commission does not want any new cars with combustion engines to be registered from 2035. Accordingly, the transition to e-mobility is expected to lead to very high battery capacity in the long term. These batteries will then be available for secondary use in applications such as stationary storage systems at the end of their service life in the mobility sector.