How Audi designed its densest EV battery yet
The new 'stacking technology' makes better use of physical space per cell, leading to increased capacity.
It has been more than two years since former Audi CEO Markus Duesmann announced that after 2026, the automaker will develop only battery-powered models. Audi’s plan is to have more than 20 fully electric models in its portfolio by 2025. The carmaker has already started down this road by investing about 18 billion euros ($19 billion and change) in electrification and hybridization.
In the process, Audi is pursuing battery technology that optimizes energy efficiency. Its primary focus for innovation is solid state batteries, which use solid electrolytes instead of liquid. The brand designs, develops, and checks battery cells and battery components on its own at its battery testing center in Gaimersheim, Germany. It recently transitioned its battery packs from winding to a stacking configuration, where the cells are stacked neatly, like a layer cake, to increase the overall capacity.
More capacity means greater range. And better range makes these vehicles more marketable in a competitive, burgeoning market. Any advantage between today and the sometime-in-the-future implementation of solid state batteries is a coveted position.
Here’s how it works.
Stacking adds density, thus energy
The German brand is known for agile, sleek vehicles that consistently earn high marks for performance and handling. As part of the Volkswagen group along with Porsche and even Lamborghini, Audi is in good company. Audi (along with the other brands in the group) has ratcheted up its EV goals, seeking the best ways to leap ahead of its competitors, and battery stacking is the latest mark of progress.
[Related: Why solid state batteries are the next frontier for EV makers]
In new EVs like the Q8 e-tron, electrodes in lithium-ion cells are thin foils which are traditionally wound into a structure called a jelly roll, Audi explained to PopSci. These jelly rolls can be either round for cylindrical cells or flat for prismatic cells. In prismatic cells, the utilization of the inner volume is limited due to the rounded edges.
By stacking single electrode sheets into larger stacks, more of the cell’s inner volume can be used, increasing the cell’s capacity. This allows Audi’s EVs to make better use of the physical space per cell, as was previously the case with winding technology.
Imagine it this way: in winding, the cell material is wrapped around a roll and squeezed together into a rectangular shell. During stacking, the electrode layers are superimposed to completely fill the rectangular space so that the cell has about 20 percent more active material, which increases the capacity. Cramming more electrons into the space equals overall improved range. A total of 12 battery cells form a module and 36 modules make up a battery system, protected by cube-shaped aluminum housing.
For the Q8 e-tron SUV and Sportback, Audi engineers created a battery pack that delivers about 20 kilowatt hours more gross capacity over 2023 models. Now, the battery offers 114 kWh instead of the 95 kWh on the previous battery tech. And incredibly, it doesn’t take up any more space than the old battery pack. As a result, 2024 Q8 e-tron owners can get 30 percent more range. The Q8 Sportback S-Line e-tron with the ultra package gets 300-plus miles. Even the standard Q8 e-tron SUV is good for 285 miles (296 for the Sportback) so it’s pretty close.
The 2023 model served up a 222-mile EPA-estimated range for the standard SUV and 218 miles in Sportback form. For the 2024 Q8 e-tron, the EPA estimates it’s good for 285 miles for the SUV and 296 miles for the Sportback model. An optional Ultra package, available only with the Sportback, features a smaller wheel and tire package with low-rolling-resistance rubber and retuned suspension that gives it a lower ride height for added efficiency, and this setup delivers the magical 300-mile EPA estimate.
Pros and cons to stacking
Like most new technologies, there are advantages and disadvantages to consider, Audi says. The advantage of this new stacking method allows for more active material to be implemented into lithium-ion cells, resulting in greater capacity, energy, and power. The disadvantage is a slower production process, resulting in higher cost.
Ultimately, Audi opted to prioritize the advantages over the disadvantages, a brand representative shared with PopSci.
Audi cell technicians had a dual goal of packing as much energy as possible into the stack while still having the ability to recharge it as quickly as possible. However, more density requires more time to charge compared to previous, less-dense batteries. This latest achievement also comes with a side of improved battery chemistry that Audi says has a better charge curve, which allows it to hold higher charging rates for longer.
At its battery testing site in Gaimersheim, Audi also runs a construction facility for prototype batteries. Here, employees build the high-voltage batteries from the ground up all the way to pre-series production. The goal for the next iteration will involve greater integration of the cells into the battery pack, reducing overhead, optimizing the battery’s design, and increasing the overall vehicle’s efficiency with the newest cell technologies.
