The Fallacy of "Better Battery Chemistries”
How many battery chemistries suitable for electrification applications (e.g., EVs, industrial equipment, etc.) are there? Despite all the new ones you may hear about, the answer is anticlimactic: Only two and a half are ready for prime time.
The two dominant types of battery chemistries are cobalt-based lithium and iron-based lithium. Then, we have the rest.
Cobalt-based chemistries have a nominal cell voltage of 3.7V with a range of 3 to 4.2V and the highest energy density.
Iron-based chemistries tend to operate around 3.3V and range from 2.8 to 3.5V. Lithium Iron Phosphate (LFP or LiFePO4) cells are safer and have a flatter discharge curve.
The most promising candidate in “the rest” category is probably sodium (Na)-ion cells, which have a much steeper discharge curve (1.5V to 4.1V).
Wait. What does a flat or steep discharge curve mean?
A battery discharge curve shows how a battery's voltage changes over time as it discharges, plotting its voltage against the percentage of capacity discharged. It also demonstrates the relationship between the battery's capacity and voltage output during discharge.
Cobalt cells have a 40% higher full charge voltage level than when empty (4.2V vs. 3V), producing a steeper discharge curve than LFP cells’ 25% (3.5V vs. 2.8V).
A sample Li-ion cell discharge curve. Source.
A steeper discharge curve means the host application must accommodate a wider voltage swing, translating into lower charge and discharge circuitry efficiency. The equipment requires more expensive and beefier components to achieve the same power output. As such, it would be heavier and costlier to produce.
In other words, it’s cheaper, easier, and more compact to build a battery using LFP cells with a flatter discharge curve, thanks to the lower variance. Unfortunately, LFP cells have lower energy density than cobalt ones, making them unsuitable for some applications.
A sample LFP cell discharge curve. Source.
Na-ion cells have an even steeper discharge curve than cobalt ones, doubling down on the challenges. The variance ranges from 100% if you play it safe to 200% if you do your damnedest to squeeze out the last drop of juice.
A sample Na-ion cell discharge curve. Source.
The challenges with Na-ion batteries’ steep discharge curves
Let's say you want to put Na-ion batteries into an electric car. Engineers will tell you a 100-cell sodium battery pack provides 400V when full and perhaps 100V when empty — creating a substantial engineering challenge.
The currents at 100V are four times as high as at 400V, requiring massively more complex and expensive semiconductors, magnetics, and assemblies that are much heavier and costlier to integrate than LFP.
You could mitigate this problem by narrowing the state of charge (SoC) window, discharging the cells only down to 2V. However, you would leave 20-25% of the capacity unused. The trade-off means Na-ion batteries are no better, safer, cheaper, or more desirable than the existing options.
But it isn’t just about the discharge curve
Different battery chemistries have different characteristics. Cobalt-based ones aren’t better or worse than iron-based ones. It depends on the use case. For example, a tablet for the consumer market uses cobalt cells to shave weight and volume. A comparable model may use LFP cells in an industrial setting for endurance and longevity.
What about a modular, multi-chemistry, or multi-application product that can mix chemistries? Well, you can’t do that with conventional battery technologies. For instance, replacing a cobalt pack with an LFP one means changing the number of cells, BMS, parameters, cooling system, and more — an engineering and product management nightmare.
Future-proof against shifting battery chemistry trends
One of the biggest challenges for builders of electrified equipment is being locked into one battery chemistry available to them when they design the product. When something more efficient or cheaper comes along, they must go back to the drawing board and reinvest a pretty penny to incorporate the new chemistry.
Moreover, you can’t leverage different characteristics of various chemistries to make the same equipment behave differently to meet specific operational criteria and use cases. You select a battery chemistry, you design a battery pack and a product around it, and you’re locked in.
The initial choice of battery chemistry restricts the equipment’s capabilities.
While everyone is racing to develop better, more efficient, more environmentally responsible battery chemistries, not many talk about what will happen to every electrified vehicle and equipment using Li-ion batteries today —they still require Li-ion batteries with the same environmental and social impacts, and the transition will likely be slow and painful.
Traditional battery technology doesn’t allow you to drop some newfangled-chemistry cells into an existing pack. Introducing new chemistries means redesigning the equipment, maintenance routine, supply chain, and more — creating immense barriers to bringing better battery chemistries from the lab into the commercial world.
Better battery chemistries can’t do much if the adoption hurdle is so high.
Reducing adoption hurdles for new battery chemistries
Software-defined batteries (SDBs) help solve this roadblock to widespread, cost-efficient electrification. SDBs built on the Tanktwo Operating System (TBOS) and Dycromax™️ Architecture allow operators to mix and match cells of different ages, chemistries, or capacities to achieve the desired energy density, output power, and other characteristics.
Here are some examples:
You may replace an LFP pack with a cobalt pack to achieve higher energy density. TBOS will rewire the cells to provide a lower voltage. While fewer cells work at any given moment, the software selects cells to take turns — using all the cells to prolong the pack’s longevity.
You may replace an LFP pack with a Na-ion one for a more environmentally and socially responsible operation. TBOS will automatically wire progressively more cells through the discharge cycle (which has a steeper discharge curve) to keep the input voltage constant, simplifying equipment design and improving efficiency.
You may have a fleet of vehicles with different requirements and use one type of battery pack to streamline product design and supply chain management. Using different cell types in the battery pack will deliver the performance you need for various use cases.
You may use cells from different vendors of various ages or chemistries to mitigate supply chain risks. TBOS will determine the battery pack’s performance and behaviors to meet the operational requirements.
You may retrofit older EVs with chemistries that didn’t exist when they were built to reduce the cost of transitioning to new battery technologies.
You may install cells of specific characteristics into the same product or equipment for different operating conditions. For example, an excavator in Alaska may use a different mix than one in Arizona.
The modular design allows you to perform warranty replacements much faster and cheaper. Moreover, switching battery chemistry can be part of routine maintenance instead of a time-consuming exercise with costly downtime.
You may experiment with different battery chemistries, and if they don’t work as planned, you can switch back to a tried-and-true cell type without changing the equipment design.
SDBs give you more options and flexibility — there’s no chemistry buy-in or vendor lock-in. With more options emerging, the complexity of dealing with today’s two-and-a-half battery chemistries will multiply in every aspect, including product design, supply chain management, maintenance, and more.
TBOS and SDBs allow product builders and operators to support any battery chemistries — whether they exist today — without extra costs or adding complexity to the application.
