Enlarge /. One of the single-layer, playing card-sized cells that QuantumScape uses for testing.
All modern lithium-ion batteries are in some way a compromise. The original concept was a "lithium metal" battery, which could absorb significantly more energy with the same volume. There was only one small problem: you always self-destruct. But this week a longtime battery technology company announced that it believes it has solved that problem. If what the company is showing is correct, this is a big deal.
First, a brief introduction. Lithium batteries transport lithium ions from the cathode to the anode during charging and gain energy when the ions in the cathode material return to their home. This requires a separator in the middle that only lets lithium ions pass through and a conductive electrolyte. In a lithium metal battery, the oscillating lithium ions on the anode side simply form pure metallic lithium. However, the lithium tends to form branched needle-like structures called dendrites that can penetrate to the cathode, shorting out the battery. And since the liquid electrolytes used in these batteries are flammable, bad things happen if they are shorted out.
The solution was to use a graphite anode. The orderly structure of graphite is a good place for lithium ions to safely check into a room for their stay while charging. This significantly reduces the risk of dendrite formation. However, this graphite can take up almost half of the cell volume without adding additional energy storage. This will make the battery work safely, but will affect performance.
One strategy that has been followed to improve lithium-ion batteries is to create a solid electrolyte material. This is attractive because it replaces the flammable component of the battery and can reduce unwanted chemical reactions between the electrolyte and other battery materials that lead to deterioration over time. QuantumScape has been working on a solid electrolyte for about a decade after the project was spun off from a Stanford laboratory and funded by the US Department of Energy. (Though the company started out with a different technology that didn't catch on.) In addition to these benefits, QuantumScape also prevents dendrite formation, according to QuantumScape.
Make me a solid one
In a press release and video call, QuantumScape revealed a battery cell it had built and presented a fair amount of test data. With the obvious caveat that the tests weren't independently verified, it was enough to get a battery nerd's eyebrows to the forehead.
The test cells aren't exactly what the final product would look like (more on that in a minute), but they are whole cells. These are pouch-style cells with a single layer cathode layer, their solid electrolyte layer and an anode contact foil. You didn't describe the cathode, but based on the answer to a later question, it was likely a nickel-manganese-cobalt cathode material – currently the most common for electric vehicles. However, the solid electrolyte should work with any type of cathode.
Enlarge /. This is what the QuantumScape ceramic solid electrolyte layer looks like.
During charging, lithium ions leave the cathode material, traverse the solid electrolyte layer and plate onto the anode foil to form pure lithium. This causes the thickness of the cell to expand a bit during the charging process. However, according to QuantumScape, this behavior is easy to account for as it only expands in one direction. Some attempts with lithium metal batteries have required an extra layer of lithium on the anode side for better stability, but this battery also skips that fraud.
When the anode material is removed from the equation, these cells check in at around 1,000 watt hours per liter of volume. By comparison, the best lithium-ion batteries available today are at the top in the low 700s.
Some experiments with solid electrolyte materials required elevated temperatures (over 60 ° C) for stability, which is not the case here. Tests showed that the cells worked safely at temperatures from -30 ° C to 45 ° C, although they lost some of their operating capacity at the coldest temperatures.
The cells can also handle remarkable charge rates that go from 0 percent to 80 percent in just 15 minutes. The graphite anode is a major bottleneck for safe, fast charging, and the solid electrolyte layer appears to prevent dendrite formation well enough to drive the charge rate quite far. This also seems to be pretty sustainable, as even that rate of charge could survive 1,000 charge cycles with only about 10 percent of the capacity lost. This means that the service life of the cells should be comparable to today's lithium-ion batteries.
Do it like this
QuantumScape seems to be further than a typical laboratory study. The company identified the ceramic material for its solid electrolyte about five years ago and has been working on the manufacturing process ever since. But there are still hurdles between here and a vehicle that runs on these batteries. While the test cells shown by QuantumScape contained a single battery sandwich layer the size of a playing card, the company says the actual cell unit will look more like a deck of cards with many of those layers stacked up. QuantumScape needs to construct this cell.
From there, the company has to scale the production of its material. It's not just a matter of increasing. QuantumScape has to do a lot more while guaranteeing impeccable quality. While the company's CEO, Jagdeep Singh, was slightly evasive when answering a question about fault tolerance, it is likely that inconsistencies can cause dendrites to form and destroy the cell.
However, QuantumScape has received huge investments. Just a few weeks ago, it went public after a merger with an investment group. (This is a good time to present promising data …) And there is a partnership agreement with Volkswagen that extends to the manufacturing phase, so that the jump to industrial scale is not controlled by itself.
How long that will take, Singh explained that while the company doesn't require any radical manufacturing processes, you can't exactly order these machines for two-day shipping. However, if QuantumScape hits its milestones, a product is expected to hit the electric vehicle market in 2024 or 2025.
In general, caution should be exercised when new battery technologies are promised. However, it is fair to say that this technology appears to be a little more mature than usual. It also seems to tick all the boxes instead of just offering one exciting feature with (downplayed) tradeoffs. This is compelling technology unless the test data was somehow fake or unrepresentative. Perhaps other companies working in this field have something similar and haven't released it yet. But either way, when a battery like this crosses the finish line, it will be a huge leap beyond the gradual advancement of the past few years.