Graphite, from which batteries are made, takes on different colors depending on the charge when lithium ions are placed on the anode: black, red and gold. In the absence of filling, graphite is black; half charged, it turns red, then gold when it reaches its full charge.
The problem arises because not all cells load at the same speed; they charge faster when more lithium ions are loaded. Different colors make it possible to assess the status of payment.
Avoid premature aging
When the charge is fast, the current must be monitored correctly to avoid overheating of the cells which, in this case, may age prematurely; it is also important to prevent graphite anodes from being overloaded with lithium in areas that are already gold.
There are actually two conflicting goals; it is important to manage to concentrate as much energy as possible in a small space (the battery that fits on the floor of the car) while ensuring fast charging.
Load capacity takes priority
In order to be able to charge a large amount of energy, it is the charge capacity that must be preferred; therefore this is a priority step in the development of the manufacturer’s projects.
The entire battery system and its electronic equipment, thermal management system and high voltage peripheral are calculated for fast charging, as it is difficult to increase the charging capacity later, in order to obtain high efficiency and long life.
Individual cells and the battery system are subjected to many tests: life, fast charging; different loading and application profiles are investigated under temperatures ranging from -30° to + 60° C. These are phases that start 4 years before production to be able to adjust the parameters if necessary.
Temporary test bridges can recreate journeys of up to 300,000 kilometers and include load and crash tests as well as simulations of several driving styles. The pilot plant in Gaimersheim also builds prototype batteries.