Ingolstadt/Gaimersheim, June 10, 2022 – Electric models must be suitable for everyday use. Purchasing decisions are significantly affected above all by range, but also by the charging performance of the built-in high-voltage batteries. For this reason, Audi designs, develops, and checks battery cells and battery components on its own at its battery testing center in Gaimersheim.
Black, red, gold – these colors indicate the charging status of a battery cell. During charging, lithium ions are deposited in the graphite anode, and the graphite changes its color according to the charging status. When discharged, graphite looks black; charged halfway, it turns red; and when fully charged, graphite appears golden. “This lets us see and assess the charging status,” explains Dr. Bernhard Rieger, cell expert at the Audi battery testing center in Gaimersheim. When electrodes are charged, they don’t do so evenly. An electrode will charge the most quickly where the highest number of lithium ions are present. This results in a charging status gradient. Ideally, everything would be the same color. But that would require an extremely thin electrode that would in turn have a neglectable capacity.
“When it comes to fast charging lithium ion cells, the art lies in precise current control to prevent overcharging the anode in the golden areas. That would result in premature aging,” says Rieger. “This means our task lies in ensuring the ideal operation of lithium-ion cells to achieve the best possible range and charging performance.” For Audi customers, this guarantees a battery electric vehicle with both excellent range and charging performance. “Once the basic need for range has been met, charging capacity becomes more relevant,” adds Rieger.