Building a better battery requires dealing with problems in materials science, chemistry, and manufacturing. We do regular coverage of work going on in the former two categories, but we get a fair number of complaints about our inability to handle the third: figuring out how companies manage to take solutions to the science and convert them into usable products. So, it was exciting to see that a company called StoreDot that was claiming the development of a battery that would allow five-minute charging of electric vehicles was apparently willing to talk to the press.
Unfortunately, the response to our inquiries fell a bit short of our hopes. “Thank you for your interest,” was the reply, “we are still in pure R&D mode and cannot share any information or answer any questions at the moment.” Apparently, the company gave The Guardian an exclusive and wasn’t talking to anyone else.
Undeterred, we’ve since pulled every bit of information we could find from StoreDot’s site to figure out roughly what they were doing, and we went backwards from there to look for research we’ve covered previously that could be related. What follows is an attempt to piece together a picture of the technology and the challenges a company has to tackle to take research concepts and make products out of them.
The need for speed
To an extent, StoreDot is using ideas that have been floating around research labs and startups for years, but it’s taking a bit of a risk by using these ideas in a way that’s different from their apparent promise. The bet that StoreDot is making is that it’s not the absolute charge range of an electric vehicle that matters; it’s how quickly you can extend that range. So, while it’s leveraging research on technologies that allow greater capacity in lithium ion batteries, it’s turning around and sacrificing some of that capacity in order to make charging faster.
Put differently, the bet is that people would rather add 300km to the range of their car in five minutes than have a car with a 600km range that takes an hour to fully charge.
What are the implications of that bet at the hardware level? They’re mostly dictated by heat management. As anyone who’s plugged in a low-charge laptop while it’s sitting on their lap knows, charging a battery produces a lot of heat. Charging it faster produces even more. To deal with this heat, StoreDot is essentially producing a diffuse battery with lots of space in between individual cells, as you can see at the four minute mark of this video (embedded below). The cells have significant gaps between them, and the battery housing has holes that allow airflow between them. It’s charged in a stand with fans that force air through the battery to keep the heat under control.
Anybody could do that with existing battery technology, but there’s a very obvious cost: a much lower energy density, meaning a battery has to be much larger to hold the same amount of charge. StoreDot is compensating by working on technology that allows a much higher charge density, which offsets the lower density of materials. In the end, the battery should hold similar amounts of charge per volume as existing batteries, despite having less battery material present.
You are my density
If you were willing to charge the same battery technology at a much slower rate, you could obviously have a much higher capacity in the same volume. And that’s a problem people have been tackling from a variety of angles for a long time. Fortunately, between the company’s vague technology description and information it gave to The Guardian, it’s possible to get a sense of what’s happening.
All lithium ion batteries need to have electrodes made of materials that can store their eponymous lithium ions when they’re not busy carrying charges from one electrode to the other. One commonly used material is graphite, a form of carbon that’s composed of many layers of graphene sheets, which allow the lithium ions to tuck themselves in between the sheets. But there are other materials, including sulfur and silicon, that can store far more lithium per unit of storage material. Sulfur tends to engage in unfortunate chemical reactions inside the battery, but silicon doesn’t suffer from these problems.
So why isn’t everyone using silicon? Because storing a lot of lithium in silicon causes the silicon to expand. The expansion/contraction cycle that comes with charging and discharging can damage any small structures etched into the silicon or, at larger scales, damage the structural integrity of the battery itself. So, figuring out how to manage the volume changes has been viewed as key to making silicon-based lithium ion batteries work.
StoreDot solves part of this problem as a side product of solving the heat problem. Its individual components are all thinner to allow heat to escape more readily, so even though the expansion is the same as a percentage, its absolute value is a bit smaller.
While that handles the large-scale problems with the battery’s structural integrity, it leaves the small-scale ones that arise as an individual cell’s electrodes expand and contract. Here, the company’s solution seems to overlap with some research we covered back in 2017. Here, the silicon was made into nanoparticles, with the electrode comprised of layers of nanoparticles, similar to what you’d get if you poured a few hundred marbles into a box. This has an added bonus of providing a high surface area, conducive to rapid charging.
As with that earlier research, the nanoparticles are held at the electrode with a flexible mesh that can expand with them. While the paper used graphene, StoreDot indicates it uses a flexible polymer that can also self-heal if breaks occur (we’ve been covering self-healing polymers for at least a decade). It’s not clear whether that polymer is also conductive, which would allow it to move charges into and out of the silicon/lithium mix—graphene is highly conductive. If not, then there’s undoubtedly another material involved that also has to flex as the silicon nanoparticles expand and contract.
Where are we at?
A functional battery also requires a second electrode and an electrolyte to function. Here, the company has not been forthcoming at all; even its barely informative technology Web page refers to the counter electrode as being built with “proprietary compounds.” Mentions of the electrolyte are equally vague, focusing on the functions it performs and not on how it’s made. So it’s impossible to tie anything in the rest of the battery back to earlier research.
But it is possible to know how far the company’s gotten with the technology, as it gave some details to The Guardian. In 2018, StoreDot announced a partnership with a Chinese manufacturer that would ultimately mass produce any hardware once sufficient customers were ready to buy the batteries. The announcement that prompted the news coverage was that the first round of sample batteries had been produced and were ready for testing by hardware manufacturers.
But a key fact mentioned by The Guardian article is that, while the sample batteries are meant to match the performance of the final, mass produced version, they’re not actually chemically identical. To ease the first manufacturing run, StoreDot used the element one row below silicon. Germanium is much easier to work with than silicon and interacts with lithium in the same way, but it suffers from the otherwise crippling feature of being really expensive. There’s no way at this point to determine how much of a challenge it will be to substitute in the far cheaper silicon.
While a lot of the technology and remaining hurdles are a mystery here, a few things should be clear. One is that it’s really hard to track the outcome of developments in materials science, since they often disappear into a black hole of proprietary information somewhere on the way to commercialization.
The other thing is that the road between research and commercialization can be indirect. While we identified a paper that was similar in principle to the solution StoreDot found for working with silicon, there were lots of differences between them. (The team behind that research did not indicate it had patented anything, didn’t list any conflicts of interest, and were based in the US and China, rather than Israel, where StoreDot is based. They seem to be unrelated efforts.) StoreDot also seems to have relied on developments in materials science, like self-healing polymers, that weren’t even studied with the intention of using the results in batteries.
All of which should explain why we can’t always give our readers what they want when it comes to tracking the development of battery technologies once they leave the realm of academic research.