Audi develops its own batteries

The graphite, which the batteries are made of, takes on different colors depending on the charge when the lithium ions are deposited on the anode: black, red and gold. In the absence of filler, the graphite is black; half charged, it turns red, then gold when it reaches its full charge.

A problem arises because not all cells load at the same speed; they charge faster when more lithium ions are deposited. The different colors make it possible to assess the state of the charge.


The battery of an Audi e-tron. Audi picture

Avoid premature aging

When the charge is fast, the current must be monitored precisely in order to avoid overheating of the cells which, in this case, would age prematurely; it is also necessary to prevent the graphite anodes from being overloaded with lithium in the parts which are already golden.

There are actually two conflicting goals; it is necessary to manage to concentrate as much energy as possible in a limited space (the battery which fits into the floor of the vehicle) while ensuring rapid charging.

Batteries and cells are tested for four years before entering production, in order to obtain the right match between energy output, load capacity and lifespan.  Audi picture

Batteries and cells are tested for four years before entering production, in order to obtain the right match between energy output, load capacity and lifespan. Audi picture

Load capacity takes priority

In order to be able to charge a large amount of energy, it is the charging capacity that must be privileged; this is therefore the priority point in the development of the manufacturer’s projects.

The entire battery system with its electronics, thermal management system and high-voltage periphery is calculated with fast charging in mind, as it is difficult to subsequently increase the charging capacity, so as to obtain a high efficiency and long life.

The battery center in Gaimersheim tests the batteries of the brand's future electric models and produces prototypes.  Audi picture

The battery center in Gaimersheim tests the batteries of the brand’s future electric models and produces prototypes. Audi picture

Demanding tests

The individual cells and the battery system are subjected to numerous tests: lifetime, rapid charges; different load and use profiles are studied under temperatures ranging from – 30° to + 60° C. These are phases which begin 4 years before production in order to be able to readjust the parameters if necessary.

The duration test benches can reconstruct journeys of up to 300,000 km and incorporate overload and collision tests as well as the simulation of several driving styles. The pilot plant in Gaimersheim also builds prototype batteries.

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