This week already brought us a camper loaded with solid-state battery power, and now we have a luxury EV putting its own solidified energy storage to work. BMW is road-testing solid-state batteries in the i7 electric sedan. The sulfide-based batteries promise higher energy density, improved safety and more versatile, compact packaging in comparison with traditional lithium-ion batteries.
BMW announced this week that it is testing concept all-solid-state battery (ASSB) cells from Colorado-based battery specialist Solid Power in the i7 electric sedan in and around Munich.
The batteries being tested combine prismatic cells and new, innovative module concepts, it says, and the on-road testing will investigate how the batteries manage cell expansion, operating pressure and temperature conditions.
"Solid Power is extremely proud that our partnership with BMW has resulted in the first demonstration of truly all-solid-state battery cells in a vehicle," said John Van Scoter, Solid Power's president and CEO.
BMW and Solid Power take much care to stress terms like "all-solid-state" and "truly" solid-state throughout the announcement text, so much so we lost count of the number of "ASSB" references. That's likely, at least in part, because BMW's major competitor to the west, Mercedes-Benz announced a similar "first" of its own this past February, beginning testing of solid-state cells in its electric flagship, the EQS.
Unlike the Solid Power cells BMW is testing, though, the Factorial Electrolyte System Technology (FEST) batteries Mercedes has tested use a quasi-solid (or semi-solid) electrolyte and aren't technically "all-solid-state" with no liquid. Factorial describes that electrolyte as a hybrid between liquid and solid that comprises a "solid matrix infused with a liquid or gel-like electrolyte." That combination is said to offer increased thermal stability/reduced flammability in comparison to standard liquid electrolytes with smoother ionic conductivity and easier manufacturability than all-solid-state electrolytes.
Factorial does have its own "Solstice" all-solid-state battery with sulfide-based electrolyte in the works, but that's more of a next-generation solution that was just announced in September, a few months after it had shipped FEST B-samples to Mercedes for advanced testing.
The solid-state achievements we've seen from Chinese automakers like IM have also been of the semi-solid-state variety, so BMW and Solid Power are seemingly spot-on with their declaration of the first integration of all-solid-state batteries in a production vehicle.
Of course, the distinction is purely academic at this point, and the only "first" that will ultimately matter is the automaker that gets solid-state technology to the market. China already has the lead there, but being first to launch semi-solid and all-solid-state battery power in a dealership-ready production vehicle in Western markets like the US will be a laudable feat, too – as will being the first to do so in a convincing car platform available at a reasonable price point.
BMW has been working on solid-state battery development with Solid Power since 2016. Solid Power uses a sulfide-based solid electrolyte in place of the flammable liquid electrolytes that traditional lithium-ion EV batteries use. The thin, solid sulfide-based layer acts as a separator to keep the anode and cathode from touching, as well as serving as the conductive electrolyte that allows ions to move back and forth between the two.
In December 2022, the two companies deepened their working relationship with an expanded joint development agreement under which Solid Power granted the BMW Group a research and development license to its all-solid-state cell design and manufacturing knowledge. The agreement has created synergy in further research, development and manufacturing of the solid-state tech.
As part of this cooperative agreement, BMW will operate a prototype solid-state cell production line at its Cell Manufacturing Competence Center in Parsdorf, Germany. The design of the line will be duplicated from Solid Power's own pilot production lines in Colorado.
BMW did not detail specifics about the cells being tested, but Solid Power advertises energy densities between 390 and 560 Wh/kg, depending on the anode and cathode materials. Volumetric energy densities are estimated at either 785 or 930 Wh/L. Solid Power estimates a 1,000+ cycle life for all chemistries and emphasizes the improved safety of all-solid-state design.
While road tests obviously represent an important step toward eventual solid-state battery launch, BMW admits in this week's announcement that "further development steps are required to implement ASSB technology in a competitive overall storage system." In other words, don't expect to see the solid-state i7 in dealerships in the immediate future.
Source: BMW
