EV BATTERY SECRETS UNLOCKED
To help engineers better understand electric vehicle batteries and how they’re made, researchers are tearing them apart.
Written by Agam Shah
ELECTRIC VEHICLE manufacturers often have proprietary technology and manufacturing methods, so learning about the ways in which their batteries are made can be difficult. But a team at one German lab has torn down Tesla and BYD Auto batteries with the goal of unearthing their manufacturing mysteries.
The disassembly was an exercise to highlight the challenge of taking exotic battery chemistry from the lab to high-volume manufacturing.
“The biggest challenges in the battery field are scaling up from the lab to a gigafactory and the battery that is built into a car,” said Jonas Gorsch, a research associate at RWTH Aachen University in Germany, who took part in the battery teardown.
Researchers are formulating exotic battery chemistries but ignore the practical challenges of scaling manufacturing at reasonable cost.
“You have to think of the production sequence and process technology,” he added.
Their work is detailed in a study published in the March edition of Cell Reports Physical Science, providing a technical overview of the Tesla and BYD batteries.
The goal wasn’t to rank the better battery but to guide researchers on manufacturing considerations when designing new batteries. Since there is very little material in the public domain on that topic, the researchers wanted to fill that gap.
“We wanted to have a baseline just for reference for future cell designs,” Gorsch said.
If a battery design does achieve scale in manufacturing, more metrics need to be considered when benchmarking.
“Everyone says, ‘Oh, we have this great battery that has increased range or increased charging capability.’ But you can never evaluate the battery if you don’t compare it with at least charging capability, range, or energy density and cost,” he explained.
BUILT DIFFERENT
Acquiring the batteries was the first challenge. Tesla batteries are hard to find and the researchers had to extract one from a Model Y. The BYD battery was available in the open market because batteries are easier to buy in China.
The researchers then reverse engineered the battery during the teardown. They extracted information about mechanical configuration, material compositions, electrode designs, and thermal and performance characteristics.
“It’s very important that if you do cell design, you choose your format and specific design very carefully otherwise it will cause problems in cell assembly,” Gorsch said.
The batteries had different mechanical structures, cell designs, and compositions. Tesla batteries have a cylindrical design and smaller cells, while BYD batteries have a prismatic design and larger cells. Each has distinct advantages and disadvantages.
“Everyone says, ‘Oh, we have this great battery that has increased range or increased charging capability.’ But you can never evaluate the battery if you don’t compare it with at least charging capability, range, or energy density and cost.”
—Jonas Gorsch, research associate at RWTH Aachen University
Tesla’s smaller cells are connected in parallel, so one faulty cell won’t bring down the entire battery. BYD’s larger cells are connected in serial order, which could limit the flow of power.
“If you have one faulty cell in your serial connection, then your whole system is fried. But if you have parallel strings, then you can still have some measures in place so that the customer doesn’t realize, ‘oh, I have some cells that are aging faster,’” Gorsch explained.
But BYD’s large cells also make batteries much cheaper to manufacture as they use significantly less material and space. Tesla’s network of smaller cells can be more expensive as it requires more material volume.
“If you have smaller cells, you have a higher passive component volume because you have more housing, electrodes, sheets, etcetera, per cell,” Gorsch said.
Researchers also found it interesting that “super thin” materials were put together using laser welding. “It’s usually very hard to [laser weld] copper. And it’s even harder to weld very thin sheets because there’s a fine line between laser cutting and laser wedding,” he added.
Tesla and BYD have differing laser welding approaches as well. Tesla laser welded copper and aluminum sheets on each side alongside the electrode edges. BYD combined laser and ultrasonic welding to compact the parts.
REGION-SPECIFIC
The researchers found that the BYD battery used LFP (lithium iron phosphate) material, which is lower cost and a mainstay for batteries made in China. However, LFP batteries provide lower range to electric cars.
Tesla used NMC811 (nickel manganese cobalt) composition, which has higher energy density compared to LFP, and thus offers longer battery life.
The team at Aachen University tore apart batteries from BYD (top) and Tesla (bottom) to see how they differed. BYD batteries have a prismatic design and larger cells, connected in serial order. Tesla batteries are smaller, cylindrical, and connected in parallel, so one faulty cell won’t bring down the entire battery. Photo: Jonas Gorsch
“China is taking more of the LFP approach because you can build cheaper vehicles—people there don’t have as much range and charging anxiety maybe as in Europe and the U.S.,” Gorsch noted.
For the teardown, the researchers first performed electrical characterization on the full battery cells in a climate chamber.
“We measured the internal direct current resistance for different temperatures over the SoC and also for different current,” Gorsch said.
Then came the physical teardown, where the cells were placed at 0 percent charge in an argon environment after which the electrode samples were removed. The electrode samples were sent to partner institutions, which conducted further analysis.
Following that, the researchers weighed and measured the components, examined the connecting parts, and analyzed the material compositions.
The research was funded by the German government, which is also funding the development of the Fraunhofer Research Institution for Battery Cell Production gigafactory in Münster, Germany.
The research could be helpful as electrification goes mainstream. Electric batteries could be used in drones, air taxis, and the military, Gorsch noted, emphasizing that Tesla made their first batteries from cells used in consumer devices.
“These [end-users] will ask for specific battery cell designs that fit their applications,” Gorsch said.
Agam Shah is a business and technology writer in Phoenix and an adjunct faculty member at the Walter Cronkite School of Journalism at Arizona State University.
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