Even though the first real solid-state batteries were originally developed as early as 1970, the technology still hasn’t broken through on a large scale yet. The capacity of the solid-state battery is more than twice as large as that of the ‘wet’ lithium-ion batteries that are found on a massive scale in our devices. This long-promised child prodigy charges more than 65 percent faster than its bigger sibling. Moreover, it is lighter and far safer. No flammable liquid or gel as a conductor. Instead, it is a solid substance that cannot catch fire. For years, this ‘holy grail of battery technology’ has been shifting ever closer to a central position. But why have they still not succeeded in breaking through yet?
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Last week, IO columnist Jan Wouters went even further in that promise, predicting a second electric revolution if the technique can be implemented on a large scale. According to him, the prototypes that Toyota and QuantumScape will bring on the market next year are the first steps in that direction.
And it is not only the automobile world that sees the potential of the solid-state battery. Manufacturers of consumer electronics are also exploring and testing possible uses. For example, researchers at MIT have developed a telephone battery that can last up to three days. They also solved another common problem associated with the new battery technology.
Contracting and expanding
Unlike a ‘traditional’ battery, the anode (minus pole) of a solid-state battery is made entirely of lithium. When charging, this negative pole expands and shrinks again when discharging. This can cause the solid conductive material to break as it expands, or lose contact with the anode as it contracts. To compensate for this effect, the researchers placed tubes in a kind of honeycomb on a small scale that can move with these contraction and expansion.
Researchers at Samsung also came up with something similar. Except instead of tubes in a honeycomb, they used an ultra-thin layer of carbon and silver around the anode to counteract the effects of the contraction and expansion. According to Samsung scientists, inserting this thin layer in a fuel cell results in improved safety, capacity and longevity. The prototype that they built last March was twice as small as a comparable lithium-ion battery.
Nevertheless, 2021 will not be the year that the solid-state battery finally breaks through, Ton van Mol van Holst Centre feels. “I am convinced that the technology will eventually break through,” he points out. According to him, there are four different challenges that need to come together technically within the battery landscape.
“First of all, there’s the capacity. You want to get that as high as you possibly can. Depending on the application, you look at the energy density per volume and per kilo. In a car, for example, you want to be able to use as much energy as possible per kilo of battery so that you can keep the battery compact. But space doesn’t matter as much in a truck. There, it is not so bad if the same amount of energy takes up more space. Then you are looking more at the weight.”
Reducing charging time
Once you have solved this, the next challenge immediately follows, Van Mol adds. “In theory, you have now multiplied your capacity and you can drive 800 kilometers. But the charging time of traditional lithium-ion batteries leads to frustration. A solid-state battery charges much faster and also lasts longer than current batteries.”
This brings him directly to the third challenge which concerns the safety and reliability of a system. “Electric cars with a defective lithium-ion battery are kept in water for a week, otherwise they will catch fire. That’s a real nuisance and we have to get rid of that.” The solid substance systems are not affected by this. “There’s no flammable electrolyzer in there. But things can go wrong there as well, depending on which materials you use in combination with each other. You’ve got to test that too.”
Which brings him to the final challenge that battery systems pose. Sustainability. Van Mol: “You do not want to lose capacity after just a few charging cycles. A lot of money and effort is also being put into optimizing this. There are also parties – for example, Tesla is very active in this – that are working on eliminating cobalt from cathodes.”
Van Mol believes that all these four aspects must be resolved before the great promise of solid-state batteries can be fulfilled. “Certain parties have already come a long way in some areas. You might already be able to find a car with a solid-state battery at innovation trade fairs. But it’s really going to be several years before you and I can buy such a car,” he believes.
The need is great
All the same, developments are going fast and the need is high: “Capacity can increase 2 ½ times over the next few years, that is going to work out. You also see that governments in the US and China are putting a lot of money into development as well as the construction of factories. Especially in China, where air pollution is higher than here, the pressure to electrify is mounting.”
Under the Horizon 2020 program, Europe has invested around half a billion euros in the development of battery technology and the scaling up production in recent years. Van Mol also wants to use the technology developed by the Holst Centre to scale up production. “We are now in the process of demonstrating that our technology works. After that, scaling up will be quite a job; our design is completely different from what is on the market right now. This means we won’t be able to take advantage of existing factories. And we can’t just set up a factory ourselves.”
3D surface provides greater capacity
“We are now working on a tiny battery for use in wearables. Safety is obviously especially important in these. You have a real problem when a battery melts on someone’s skin,” he explains. This battery is different from the solid-state batteries currently under development. “It’s an all-solid-state battery, so it’s intrinsically safe. The layers in the battery are up to 100 times thinner than those in a normal A4 battery, although their capacity is limited,” says Van Mol.
The Holst Centre is using 3D technology to increase the capacity. Van Mol: “We construct billions of these tiny pillars on a micrometric scale between the layers, which creates a 3D surface and compensates for the fact that the layers are so thin. This also ensures that the lithium can cover a shorter distance, which makes the battery extremely fast.”