- The Xiaomi SU7 and recently launched YU7 both use the same self-developed Modena platform.
- The brand says the upside-down cells allow for better packaging and improved safety in the event of a crash.
- CATL and Xiaomi came up with a special electrolyte to counteract the effects of gravity since the cells are upside down
The quest for battery safety is an endless endeavor, with many manufacturers working on the problem. Electric battery fires are generally rare, but the phenomenon’s rarity doesn’t mean that manufacturers will throw caution to the wind; no, battery protection and thermal runaway mitigation take many forms. Like BYD’s blade battery, which usually has thin, blade-shaped cells that, in theory, make thermal runaway less likely if a cell becomes punctured.
Xiaomi has its own solution. While in Beijing on a Tour of Xiaomi’s factory, it revealed one of the clever ways it tries to mitigate the phenomenon of thermal runaway and make driving safer:
By mounting its battery cells upside down.
The Xiaomi SU7 comes with a choice of two batteries (not counting the low-volume, super high-performance SU7 Ultra). The base model SU7 standard (single motor, RWD) gets a battery made by BYD subsidiary FinDreams. The real story, however, is the batteries on the mid-level Pro and top-level Max trims. Both packs were built by battery giant CATL and specially designed to meet the needs of the SU7.
Like many new design EVs, the SU7’s Modena chassis is a cell-to-body design. Meaning, the top of the battery pack is actually integral to the structure of the car. Yet, in a cutaway view of the car’s chassis, the floorpan (and top of the battery case) reveals all of the cells against the floor, with no connectors showing. Instead, the cells point downward, with each contact facing the road, not the cabin.
Photo by: Xiaomi
The idea is that in the event of a crash or thermal runaway, any fire or force would be directed downward, not upward, to the occupants.
Xiaomi’s representatives insist that this was more challenging than flipping some off-the-shelf cells from CATL, sticking them underneath the SU7, and calling it a day. It’s more complicated than that because the cells are upside down. The battery electrolyte is affected by gravity in ways a traditional setup would not be. Also, the contacts are facing the road and are now potentially subject to corrosion that standard battery cells would not be. To counter both, CATL and Xiaomi took a few steps. The electrolyte has been specially formulated to work well when upside down, while all of the metal contacts on each cell use anti-corrosive metal to stave off any issues. Add in the aerogel insulation on each cell, and Xiaomi’s cars are fully protected from battery fires, or at least they are in theory. No mitigation is completely foolproof.
Photo by: Kevin Williams/InsideEVs
The upside-down cells along with the structural battery pack is part of the reason why the SU7 is explicitly car-shaped. Integrating the upside-down cells and engineering a “minimalistic wiring system” is how Xiaomi gave the car such a thin floor. The SU7 has the same proportions and dimensions sd a contemporary gas-powered combustion car, avoiding the chunky car-on-top-of-a-battery look inherent to less sophisticated EV designs from other EV manufacturers. Compared to a lot of other EV models, the Xiaomi SU7 looks positively low-slung.
Currently, this tech is on the SU7 sedan, but it will show up in the recently launched YU7 crossover, too which shares the same self-developed Modena platform.
If you’re in China, the SU7 is already on sale, while the YU7 is expected to go on sale this summer. Xiaomi plans on exporting its cars to markets outside of China by 2027.
Contact the author: Kevin.Williams@InsideEVs.com