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Self-discharge of batteries in electric cars: Researchers find cause of "vampire loss"

2023-05-15T14:47:44.840Z

Highlights: Researchers at Dalhousie University in Halifax, Canada, seem to have tracked down the phenomenon. Redox shuttle molecules form in the battery cells at high temperatures, which transport electrons through the electrolyte liquid. The self-discharge of the battery is therefore caused by a component of a plastic. This, in turn, has come loose from an adhesive tape that holds the electrode layers together. If the PET tape were replaced by another material without DMT, the discharge problem could be solved.



If an electric car is simply parked around for a long time, the battery discharges itself. Researchers have now succeeded in tracking down this phenomenon.

Halifax - Every smartphone owner knows this: If the unused device is not plugged in, the battery discharges by a few percent. If it lies in the drawer for weeks, the battery is even completely empty - nothing works without charging. This effect, called "vampire loss," also affects electric cars. This is not only annoying for little-used vehicles with electric drive, as the range shrinks, it can also cost money, as it has to be recharged. Experts assume a monthly loss of three to five percent for lithium-ion batteries.

Self-discharge of batteries in electric cars: the cause is an adhesive tape

So far, no one has been able to explain why batteries self-discharge occur. But now researchers at Dalhousie University in Halifax, Canada, seem to have tracked down the phenomenon. They published the results of their work in the Journal of The Electrochemical Society. According to this, so-called redox shuttle molecules form in the battery cells at high temperatures, which transport electrons through the electrolyte liquid from the cathode to the anode. These electrons are therefore lacking for the actual supply of energy to the consumers.

An MEB battery system of a Volkswagen ID.3 electric car is on display at the VW plant in Salzgitter. © Julian Stratenschulte/dpa/picture alliance

But where do the redox shuttle molecules come from? The researchers found that a normally colorless electrolyte became more and more discolored as the batteries heated up. At the same time, there were indications of an active redox process. The examination of the electrolyte liquid showed that it contained dimethyl terephthalate (DMT), a raw material for the technical production of polyethylene terephthalate (PET). The self-discharge of the battery is therefore caused by a component of a plastic. This, in turn, has come loose from an adhesive tape that holds the electrode layers together

Self-discharge of batteries in electric cars: adhesive tape could be replaced

The researchers concluded that when the battery is heated, a chemical reaction occurs that decomposes the PET plastic of the tape. In this process, DMT is released into the electrolyte liquid, which becomes an electrochemical shuttle for electrons and discharges the battery.

If the PET tape were replaced by another material without DMT, the discharge problem could be solved. According to Handelsblatt, the scientists from Halifax are already in contact with various battery producers to discuss alternatives. It would therefore be possible to weld the components or use higher-quality film materials.

Discharge of batteries in electric cars: Balancing costs energy

Despite preventing "vampire loss", stationary electric cars will still lose energy, although not as much. On the one hand, the monitoring electronics of the battery regularly switch themselves, which of course costs energy. On the other hand, so-called balancing can consume energy. In this process, battery cells, which have a different state of charge, are adapted to each other. This usually happens by discharging the fuller cells to the level of the weakest cells. The "excess" energy is lost in the process.

Source: merkur

All news articles on 2023-05-15

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