Batteries in electric cars Part 4: Refurbishment versus exchange for new part

Inhaltsverzeichnis

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For many decades, the focus in the further development of the powertrain in cars was on the engine. With the switch to battery electric drive, this is shifting, as the battery cell is now the focus of interest. Huge sums are currently being invested globally to achieve progress in this area. Energy density, durability, charging performance and, above all, costs must be optimized if the battery-electric drive is to have a chance anywhere in the world.

In a series of articles, we want to show where we are today and where the development is heading. The European Union has set the political framework: From January 1, 2035, only passenger cars with no direct CO₂ emissions may be newly registered. According to current estimates, this will largely be battery-electric cars. Because the industry cannot simply be switched on and off, there will be a continuous ramp-up in the almost twelve years until the deadline.

The traction battery in an electric car is a wearing part: it ages cyclically and according to the calendar. As a rule, the automotive industry therefore guarantees only 70 percent of the original energy content after eight years and 160,000 kilometers. But eight years is less than the average age of today's existing cars, which is around ten years. We don't really know how good electric cars will be in the long term. The millions of years of experience with combustion engines - blown cylinder-head gaskets, slipping clutches and coked EGR valves - are not yet available with electric cars.

It is plausible that some well-maintained examples will last for many years. For others, aging of the traction battery will lead to unacceptably low range and loss of power. In this case, there is a smarter solution than replacement with a new part: refurbishment, i.e., remanufacturing used batteries with used modules. How can this work?

Cells in modules

In most of today's electric cars, battery systems are made up of modules in which several cells are grouped together. For example, ten modules of twelve cells each. If one or more cells are defective, the current standard procedure is to replace them with a new module. This is expensive, new resources have to be extracted for production, and an additional CO₂ load is incurred.

The startup Heimdalytics has a different approach. When an electric car is out of warranty and has been on the road for perhaps nine, eleven or even more years, replacing one or more modules with a new one can be pointless or ruinous from a business perspective. Pointless because all the parts on the vehicle from the window regulator to the body seam are equally aged. And ruinous because the costs are too high. There is the threat of a total economic loss.

Replace defective module with a suitable used one

Heimdalytics counters this with refurbishment: "The goal is to identify a broken module and replace it not with a brand-new one, but with a congruent used module," says Prof. Christoph Weber, who initiated the startup as a spin-off of Kiel University of Applied Sciences. What Weber means by congruence needs to be explained: If an electric car comes to Heimdalytics with a conspicuous traction battery - for example, with a significantly reduced range, too little power or an illuminated warning lamp - the affected module is removed.

The core of Heimdalytics' method is the subsequent measurement of the impedance spectrum on a self-developed device and a short reference measurement based on load tests on the module: Anomalies can occur when measuring the internal resistance. Professor Weber refers to this as the sound pattern, and discordant tones indicate which specific cell in the module is defective and what state of health the module's intact cells are in. The SOH score (SOH for State Of Health) of the intact cells provides information about which used module is suitable as a congruent solution for repair.

Determination of the SOH score

If the overall system has aged to, for instance, 74 percent, a defective module should be replaced by another with a similar SOH score. This is what Christoph Weber calls congruence. The question now is where such modules come from. The answer is donor vehicles from the inventory. Accident cars, for example. A Renault Zoe with twelve modules could therefore ensure the continued progress of up to twelve aged electric cars.

Even better in this respect are battery systems in which each individual cell can be replaced. In this way, an existing vehicle with hundreds of cells could serve as a donor for many other end-of-life vehicles. The opposite of such ease of repair are battery systems in which the cells are foamed or glued together in such a way that only complete replacement is possible.

Heimdalytics is talking to the auto industry, where the relevance of refurbishment is recognized. The startup is also working with Renault Lüdemann in Norderstedt near Hamburg, one of the French manufacturer's three battery centers in Germany. Lüdemann is enthusiastic about electromobility per se and sees refurbishment as a future business field..

New business segment for car repair shops

Industry circles report that the lower maintenance requirements of electric cars are causing workshop sales to slump by up to two thirds. In addition, new car sales are hardly or no longer lucrative. Car manufacturers are currently trying to take away the last bit of independence from dealers through agency models. Specializing in the workshop business with electric cars and the refurbishment of traction batteries, on the other hand, offers the chance of long-term survival. However, the average car owner has the greatest interest in a traction battery that can be repaired at a reasonable price. The majority of them do not drive new cars in the typical leasing period, but used cars.

(mfz)