Not long ago, Toyota said it would have presented EVs powered by solid-state batteries at the 2020 Tokyo Olympic Games. That was enough to make people realize that what seemed like a distant future is finally around the corner. But when will we have solid-state batteries (SSB)? According to Solid Power, in 2021, but there’s a catch: automotive validation processes will make cars take more time to present them, according to its CEO, Doug Campbell.
“For non-auto applications, early commercialization can occur out of Solid Power’s existing facility as soon as next year. Solid-state commercialization in EVs is coming in the middle part of this decade. Solid Power is expecting vehicle start-of-production in the 2026-2027 timeframe.”
Solid Power is developing SSB with manufacturers such as BMW and Ford for quite some time already. As the video above shows, it has chosen to use sulfides to create its solid electrolyte. The company is so proud of the results it even calls its battery in a different way: it is an all-solid-state battery – or ASSB.
“Solid Power refers to our cells as ‘all-solid-state’ because we have created an electrolyte that is truly all solid. There are various groups that make the claim of solid-state batteries while using more of a hybrid electrolyte that includes liquid or gel components. We have completely removed the flammable liquid electrolyte and replaced it with our solid ion-conducting sulfide electrolyte. These hybrid solid-liquid electrolytes don’t reap the benefits of added safety at the cell and pack level, which is why we refer to our solution as ASSB to differentiate from a hybrid or semi-solid solution.”
This is one of the benefits of sulfides over oxides or polymers. The video above reveals other aspects that make Solid Power believe its choice for sulfides is the right one, but Solid Power’s CEO also told us more about that.
“There are many different flavors of solid-state technologies which are differentiated first and foremost by which solid ion-conducting materials you use. The most common solid electrolytes are polymers (organic) and sulfides (inorganic). Solid Power works exclusively in sulfide solid-state batteries. Sulfides also have the highest conductivity of any class of solid electrolyte, and furthermore, are relatively soft so they can be processed using traditional roll-to-roll type methods you would find in a lithium-ion gigafactory today. Solid Power is producing a solid sulfide electrolyte that blends high conductivity with excellent compatibility between the anode and the cathode. This allows us to handle electrolyte materials in a dry room while using standard lithium-ion roll-to-roll processes like coating and densification steps. In some cases, sulfide solid electrolytes have been developed that are more conductive than the liquid electrolytes in lithium-ion batteries.”
These properties are what help ASSBs potentially have more energy density than regular Li-ion cells. Solid Power claims a minimum of 50 percent more but says it could double it.
“Battery pack sizes could be significantly reduced while keeping a similar drivable range of a traditional lithium-ion battery pack. The result of how ASSBs are integrated into the final EV will depend on what the OEM, and ultimately, the consumer wants. This could result in a scenario where ASSBs use the maximum footprint for a battery pack to achieve very long range capabilities. Or, conversely, it could also be used to the point where they meet optimal range while lowering weight and increasing vehicle efficiency.”
We asked Campbell about the nature of this solid electrolyte. In other words, what sort of solid it is.
“Solid Power produces a sulfide-based glass-ceramic electrolyte, meaning our material makeup includes ceramic and glass within the overall sulfide structure. The glass or ceramic description would be more of a ‘form,’ whereas sulfides are more specific to the material classification.”
The major challenge an all-solid-state battery can face is anode expansion, which could crack the electrolyte and make the cell lose performance. Campbell says his company has addressed that.
“Solid Power’s battery uses a li-metal anode combined with a sulfide electrolyte specifically developed for its lithium metal stability. Unlike swelling that may occur at the anode with silicon in a liquid Li-ion battery, Li-metal’s challenge is ‘breathing.’ When you plate lithium onto the anode upon charge, you are increasing the volume of the cell. Conversely, when the battery is discharged, lithium is stripped from the anode, reducing the volume of the cell. All batteries, to some degree, breathe upon discharge and charge, but Li-metal is inherently a piston moving back and worth. This can be mitigated at the cell and/or pack level by providing some level of compliance and pressure to allow the Li-metal to move uniformly through the battery. Solid Power has shown very high energy density and close to automotive levels of cycle life, and we expect that pack-level solutions can enable all-solid-state automotive cells that use Li-metal.”
But how far has Solid Power come in what relates to cyclability? What is its current lifespan?
“Long term, we expect solid-state batteries to meet or exceed the best available Li-ion cycle life. Solid Power’s lab-scale cells can currently exceed 1,000 cycles, and we are working to match that performance in larger format cells coming off our Megawatt-hour scale prototype pilot-line.”
Apart from these benefits the ASSB allegedly has, there is one we do not hear much about: a more straightforward thermal control. In fact, Solid Power’s CEO believes it may even not be necessary.
“In traditional lithium-ion cells, heat degrades the battery due to accelerated interactions with the liquid electrolyte. Thus the battery needs to be cooled in order to maintain a safe operating temperature and to maximize lifetime. Because the liquid electrolyte is flammable chemistry, it can catch fire when it reaches high temperatures and tends to be the main initiator of thermal runaway. This is the main safety hazard in lithium-ion cells. A solid-state solution, with the removal of that volatile and flammable liquid, has a much higher upper limit for safe operation, and as such, does not require a cooling system at the pack level. With the removal of the cooling system at the pack level, OEMs can remove a costly safety component and pack cells closer together, resulting in a cheaper and lighter battery pack.”
But how will these batteries work in colder temperatures, for example? Would car manufacturers really get rid of a battery management system with ASSB?
“Solid Power’s all-solid-state batteries are inherently more stable across a broad temperature range. While cooling elimination at the pack level is likely, we do expect ASSB packs to require pack heating, particularly for fast charging. We are currently working to lower our cell’s operational temperatures to match that of Li-ion, and have made significant improvements over the past quarter, which is the direct result of increasing manufacturing maturity and quality. We expect to continue to lower operational temperatures as we make further gains in cell manufacturing quality.”
Campbell’s company mentions its technology can be applied in current battery factories. That led us to wonder if the company will produce ASSB on its own or if it will license its technology to other companies.
“Today, Solid Power is focused on two product lines – the finished all-solid-state battery cell and the solid electrolyte. Once our technology is qualified for automotive requirements, Solid Power will need to significantly increase production in order to produce batteries at scale. Our current facility will allow us to produce cells for automotive sampling up through the cell design freeze for battery pack implementation. Beyond the design freeze, additional production scale is required, and Solid Power will consider both paths of raising growth capital to achieve the necessary production scale or seek a strategic partnership to transfer our technology for production at scale. For our solid electrolyte, Solid Power will scale production to the automotive scale as the technology reaches auto maturity.”
In the pictures Solid Power provided us, we can see pouch cells, but what about cylindrical ones? Can ASSB also have that format?
“Solid-state batteries can be made in various forms. However, Solid Power has decided to manufacture a stacked pouch cell format. As we enter the auto OEM qualification process, it is key to develop in one form factor instead of producing all cell formats in parallel. We decided on a stacked pouch cell as our customers and partners have a preference for this format.”
We know BMW and GM use pouch cells in their EVs. Would any of them be the first to present Solid Power’s ASSBs? Campbell did not give out names.
“Solid Power will be working closely with a handful of auto OEMs as our cells are qualified for automotive use, at which point a battery pack will be designed in conjunction with an OEM partner.”
Whoever this manufacturer is, we would love to see these ASSB in a vehicle as soon as possible. If Sandy Munro is right in his guess, perhaps Tesla will present them before anyone else. With the Tesla Battery Day in September, this would be the news to properly rock the EV world after million-mile batteries became commonplace thanks to SVolt and CATL.