One of the most eagerly awaited solutions in the race towards the electric car of the future is solid-state batteries. Everyone wants them, because they have a higher energy density, recharge faster, last longer and are also safer.

The technology is mature and many companies are now producing them in pilot plants or in small volumes. This is precisely the main obstacle to their spread: mass production. If there is one thing that still needs to be worked on, it is production methods. But how are solid-state batteries made?

A question of electrolyte

Let's start with a fundamental concept: solid-state batteries are normal lithium-ion batteries in which the electrolyte, usually liquid, is replaced by a solid electrolyte (hence the name). The cells, otherwise, continue to have two electrodes, anode and cathode, with negative and positive charge, a separator placed between them and - precisely - an electrolyte that allows the lithium ions to move between the two electrodes during charging and discharging.

The battery industry is testing various types of solid electrolyte, usually ceramic or composite. The former is more 'rigid' while the latter, depending on the mixture used, may be more or less elastic. Some researchers are also developing other types of solid electrolytes, but here experimentation is still in its early stages.

Batterie stato solido, BMW, Ford e Solid Power

The Solid Power solid-state battery

Initially thought of as a variant of 'traditional' lithium-ion batteries, solid-state batteries are beginning to differentiate themselves. Thus, there are lithium-metal type solid-state batteries and in the future it is not excluded that we will see other chemists switching to the same technology.

All the advantages of solid state

As mentioned, solid-state batteries are so coveted because they have higher performance. For example, they can reach energy densities as high as 2.5 times that of a lithium-ion battery. Due to the lack of liquids and volatile elements, they are also more resistant to flames. For this reason, they are also safer. They also have greater electrochemical stability, which ensures more consistent performance over time and a longer service life.

Solid-state batteries are also lighter and can be recharged up to 4-6 times faster than a battery with liquid electrolyte. It means that in the future a car will only have to stand at the charging station for a few minutes to fill up with electrons, bridging the gap of 'waiting time' in refuelling that still differentiates it from a combustion engine car.

Mercedes e ProLogium per le batterie allo stato solido

Mercedes and ProLogium: together for solid-state batteries

You have to learn how to produce them

As far as the disadvantages are concerned, for now they are mainly related to the limits still to be overcome in the field of high-volume production and cost management. The processes to make them are still complex, and research has not yet led to the identification of truly effective electrolytes in terms of ionic conductivity. Time is still needed, in short. But how much? A few more years. At least...

Then there is another issue: reliability. Solid-state batteries, like all others, tend to deform during charging and use. The absence of liquids inside the cells can lead to greater stresses that can compromise the proper functioning of the batteries themselves. To remedy, at least partially, these drawbacks, solid-state batteries mainly use pouch-type cells  - or pockets - which by their nature are more flexible.

Where do we stand

As yet, no car manufacturer has marketed an electric car with a solid-state battery. NIO, which is the closest manufacturer to this technology, has presented a semi-solid-state battery with a capacity of 150 kWh and a range of 1,000 km (621 miles), but this is not quite the same thing.

The landscape, however, is evolving fast and soon, 'real' solid-state batteries will arrive on the market. In fact, there are many manufacturers who, by exploiting agreements with specialised companies, will be able to use this technology within a few years.

Toyota, which is undergoing a real technological revolution in the field of batteries, will have them in 2028. Nissan has also set itself this time horizon. But there are those who will do it sooner: Stellantis, which with Factorial has set the goal of commercialisation in 2026, Volkswagen, which is working with QuantumScape, will do more or less the same. And so will Mercedes, which has set its sights on ProLogium (which is negotiating to build a Gigafactory in France). BMW and Ford, which have invested heavily in Solid Power, have already begun testing prototypes. And so have many others.

Tesla Model Y: celle cilindriche tipo 4680 e batteria strutturale (fonte: Paul Kelly)

Tesla's cell-to-pack battery with 4680 cylindrical cells

In all this, there is one manufacturer that is among the benchmarks in electric mobility and is moving against the trend. It is Tesla. Elon Musk, at the moment, seems focused on 4680 cells and is not talking about solid state. He still sees it as a long way off and thinks he can use his new batteries to make a breakthrough over the competition in the near future. But knowing the character, it cannot be ruled out that he will make some shocking statement on the subject sooner or later.

Gallery: Nissan shows how it will build solid-state batteries