StoreDot’s cathode still uses the familiar nickel manganese cobalt chemistry. Do you use an unconventional electrolyte or separator?
For the separator, no, but for the electrolyte, to a degree, yes. You see the chemical reaction is not fully reversible. It creates undesired deposits of electrolyte residue on the anode, releasing gases in the cell and further contributing to swelling. Therefore, to counteract this, we use certain synthesized molecules as an additive in the liquid electrolyte. Moreover, while we do use [nickel manganese cobalt] as the cathode active material, we employ a coating to better protect it, as it, too, can be damaged.
What else is unique about StoreDot’s technology?
We benefit here in Israel from a wealth of scientists who are experts in artificial intelligence. Each battery cycler uploads information into the cloud every two seconds. This includes the cell’s heat, resistance, swelling and coulombic efficiency. With the help of machine learning, these experts analyze the vast amount of data generated from the continuous charge and discharge cycles to determine which formulation gives us the best results. This is then fed back into our rapid R&D prototyping process.
Does the five-minute charge time come with penalties such as reduced range?
The Gen 1 samples we sent to potential customers as proof of concept were based mostly on germanium, which is not cost affordable. Most of our efforts currently are focused on transitioning to silicon and tin. For our Gen 2 extreme fast charging cell, we already have an energy density of 240 watt-hours per kilogram, and by the end of this year, we aim to have a longevity of 1,000 cycles. Our road map then foresees reaching 440 Wh/kg when our Gen 3 cells arrive in 2028.
Will solid-state batteries still be needed?
The most important parameter for drivers is the miles per minute they can get at a charging station. Industry performance is about 3 to 4 miles per minute of charging currently; however, our Gen 2 will show 20 miles per minute. Nevertheless, I see merit in the extreme energy density offered by solid-state batteries. That is why our Gen 3 cells are designed to reach 25 miles per minute while using a hybrid form of the solid-state technology.
Are today’s fast charging stations powerful enough for StoreDot’s cells?
This is an obstacle, as it does not make sense to overdesign for fast speeds when the infrastructure does not allow for it. That is why it was important to us to have strategic backers that cover the entire ecosystem, starting with TDK and Samsung SDI in manufacturing, going through automakers such as Daimler, all the way to infrastructure providers such as BP, our most recent investor. BP’s German subsidiary, Aral, is already installing charge points with 350 kilowatts.
What kind of cell format is the most suitable for your product?
With prismatic cells you gain a hard, outer case that exerts pressure on the chemical reactions going on inside, which can help longevity by mitigating some of the undesirable reactions I spoke about earlier. But you pay the price in terms of lower energy density, both in volumetric and gravimetric terms. Therefore, we opted for a soft pouch cell format. Following Tesla’s Battery Day in September, however, we immediately started developing cylindrical cells in parallel. Tesla’s decision to get rid of the module is smart, as it can reduce costs by 10 to 15 percent. My goal is to put a 4860 [cylindrical] cell that charges in five minutes on Elon Musk’s desk.
Other automakers do not like the cylindrical format because rectangular cells are easier to stack, so more can be packed into a given space. How do you overcome this?
What keeps me up at night is really the problem of cooling. Even if we reduce the electrical resistance in our cells, the fact remains we are conducting 350 kW of energy into the pack. If only 5 percent of this is heat, it is still enough to power five kitchen ovens, and this has to be dissipated from the pack in real time. We still work on the active cooling of the pouches, but it does require us to leave space between our pouch cells. If you take cylindrical cells, by comparison, their arrangement inherently creates gaps, which can be good when it comes to cooling. Tesla uses an epoxy between all the cells that actually acts as a heat dissipation medium.