The future of electric mobility: solid-state batteries

Although it is true that increasingly competitive electric car models are appearing, for electric mobility to become a reality, the autonomy offered by electric vehicles should be even greater.

And that is precisely the fundamental task of solid-state batteries, in addition to offering greater stability and safety.

What are solid-state batteries?

Solid-state battery technology is an evolution of today's lithium-ion (Li-Ion) batteries; not only used in electric vehicles but also in all kinds of electronic devices, such as smartphones.

John B. Goodenough –a German-American scientist and physicist, coinventor of lithium-ion battery– at his 97 years old is also leading the development of the solid-state battery using inorganic crystal electrolytes. And, in fact, he is not alone in this research, since the University of California at San Diego has also been investing in inorganic solids such as ceramic oxides and sulfur glass.

The introduction of solid-state electrolytes into the market will make it possible to provide greater autonomy, greater safety and stability, reduce economic costs and offer much shorter charging periods.

How do solid-state batteries differ from today's lithium-ion batteries?

• Today's lithium-ion batteries

On the one hand, the lithium-ion battery is made up of two electrodes; cathode and anode, which are divided by a separator, embedded in a cell and immersed in the electrolyte, a conductive liquid that chemically reacts the necessary ions between the electrodes. And the combination of multiple cells forms the battery.

Well, when we turn on our vehicle, these chemical reactions are activated and start the ion circulation between electrodes, producing electrons, transferring them to the battery clamps and generating energy. And when we charge the battery, the particles circulate in the opposite direction and the invers process takes place.

As we know, these batteries have a limited lifespan from 8 to 10 years, which is equivalent to about 3,000 complete charging cycles. This is due to the fact that liquid lithium, over time, solidifies and creates small cavities called dendrites, which are guilty of weakening the battery, causing overheating and short circuits.

And not only so, but another problem with liquid electrolyte is that it is flammable, which requires safety and cooling systems to prevent heat build-up and capacity losses. And all this means higher cost, weight and volume for the battery.

• Promising new batteries

On the other hand, the main difference in solid-state battery falls on the electrolyte which, in this case, is a solid rather than a liquid. In other words, the energy storage cells of these batteries do not contain a conductive liquid, but are made up of a solid compound that performs the same function as the liquid electrolyte: it transmits ions between the electrodes to generate energy.

The overall performance is the same, but using an inorganic solid electrolyte facilitates multiple aspects. To be more specific, John B. Goodenough's team, in collaboration with engineer Maria Helena Braga, has already filed its patent for solid glass electrolyte in April 2020. Its version has an alkaline metal anode that allows to increase the energy density and battery life.

Thanks to Spring8 images we can get an idea of how these new batteries work regarding current lithium-ion batteries.

So, which are the advantages of solid electrolyte batteries?

Lower production and sales costs, greater safety, nonflammable, longer lifespan, higher energy density and greater possibilities for recycling. 

• Increased charge density and longer lifespan

Using a solid compound in the cells provides a higher energy density, which means a higher energy storage capacity. In the case of glass, it is capable of storing more energy in less weight.

To be more specific, this type of battery would be capable of storing up to three or even five times more energy than its lithium-ion equivalent. Therefore, this means that they allow much higher autonomy.

In addition, not only do they make it possible to extend charging and discharging cycles (which makes it possible to increase their useful life), but they also reduce passive drainage (the discharging process of the battery when it is not used).

The lithium-glass batteries developed by John B. Goodenough are capable of withstanding more than 20,000 full charging cycles (in laboratory tests they have exceeded 23,000 cycles).

• Reduced charging times

Solid-state electrolytes speed up charging and provide much shorter charging times (just within a few minutes), as these times are reduced by up to six times compared to current lithium-ion batteries.

This is due to the fact that the battery, being made up of a solid inorganic compound (such as glass), allows easier and faster movement between electrodes.

• Greater safety

By preventing dendrites formation and eliminating the possibility of explosion and fire –which current lithium-ion batteries do have (although let's remember that fire risk is four times higher in a gasoline or diesel than in an electric one)– it is possible to further increase the safety provided.

Thus, solid electrolyte batteries, being far less heated, do not need safety or cooling systems to prevent heat build-up. Nor do they need separators between electrodes, or the protective waterproof cover which, after all, add up to the cost, weight and more than half the volume of Li-ion batteries.

And as if that weren't enough, these new batteries work optimally even at extreme temperatures down to -20°C.

• Mass production and cost reduction

Mass production is still at a research stage, but if we talk about a material such as glass, which is easy and quick to manufacture, it would allow the total cost of both the battery itself and the electric vehicle itself to be greatly reduced. It would also make it possible to manufacture the cells from much more sustainable materials than the current lithium-ion ones.

Another very important point to take into account is that these batteries would make it possible to eliminate practically all the cobalt present in the cells; a very expensive, scarce and unsustainable raw material.

When will they land on the market?

Initially, it was not expected that this type of battery would be marketed for at least a decade. However, more than just one manufacturer has already begun to invest in this type of technology and even to develop its own patent, as John B. Goodenough and Samsung have done. Toyota, Porsche, BMW, Fisker, Hyundai, General Motors, Honda, Nissan, Daimler and Volkswagen are examples of brands that are already investing in its development.

Samsung presented in March 2020 its progress in solid electrolyte batteries development, whose prototype promises to produce batteries 50% smaller than the current ones. The company estimates that in a couple of years it could introduce its first smartphone with this new technology.

Toyota, for example, had so far refused to produce all-electric cars because it considered that there were still two very clear limitations: charging periods and electric vehicle range. Well, now, with the solid electrolyte development, Toyota will finally launch its first 100% electric car with solid-state electrolytes battery in 2022.

We are talking about the new C-HR EV which, last April, has already landed at the first Chinese dealers, but in Europe it is supposed to take at least a couple more years to arrive. Under the new company Prime Planet Energy & Solutions, the new joint venture with Panasonic, it was expected that this year the brand would present at Tokyo Olympic Games an electric car powered by batteries with solid electrolyte, but due to the coronavirus we will have to wait a little bit longer!

Which is the future of this technology?

A new study from MIT (Massachusetts Institute of Technology) is also working on the design of a metal anode made of pure lithium.

Prologium (Taiwanese battery manufacturer) has announced at the beginning of this year at CES (world stage where technological innovations are presented) an agreement with different car manufacturers to install the new high voltage solid-state batteries with ceramic electrolyte (based on the MAB, Multi Axis BiPolar+ technique) in their electric cars. Meanwhile, KITECH (The Korea Institute of Industrial Technology) does not want to be left behind with this promising new technology either.

Some point out that the future of the solid-state battery will be using silicon instead of glass, others that the most promising is to use sodium (salt) based glass, as it is a very common material on earth and has a low environmental impact.

However, although both method and implementation time of this technology is somewhat uncertain and must be carried out taking into account reuse and recycling criteria and processes, what is clear is that it will involve a real revolution and not only in electric mobility but in the entire electronics industry.

Can you imagine private transport, heavy shipping, aviation and marine area being powered by sustainable electric batteries? A definitive goodbye to combustion engine and pollution. A dream come true?