The inevitability of solid-state batteries?

The criticism most often levelled against solid-state batteries replacing existing lithium-ion solutions is that the technology is one of those permanently ‘just a few years away’. But Graeme Purdy, CEO of UK solid-state battery developer Ilika, is not fazed by such negativity.

He believes that the key milestone — solid-state batteries proving they can outperform existing current options — has already been reached. Now it is simply a question of building further on that performance advantage and scaling up production.

“There is now lots of evidence, as well as theory, that demonstrates that solid-state batteries can deliver a better performance. We have already overtaken the energy density from a gravimetric perspective that even state-of-the-art traditional lithium-ion batteries can deliver,” he tells EV inFocus.

“So solid-state is already ahead there. And it is just a case of scaling up the technology to the point where it is worthwhile for manufacturers to change horses — because they are not going do that for marginal gains. They need a step change in performance, and they need some immediate benefit from doing that. We are getting close to that switchover point,” Purdy continues.

His confidence is further buoyed by the fact that “some of the faster-moving automotive companies, like Nio for instance, have already deployed some vehicles with solid state in them”. “I think every automotive OEM has got solid state on their roadmap and will be making that switch at some point or another in the next few years,” he predicts.

Lessons from history

Current evolution in the EV battery space is comparable to that seen in other sectors, Purdy suggests. “I think it is the same in many technology areas where you get an improved alternative — the incumbent technology does its very best to squeeze the last bit of performance out of that technology.

“We saw exactly the same transition when we went from copper to fiber in the telecoms industry at the turn of the century, where copper fought back the whole time to get more and more data through copper connections. But eventually, of course, fiber started taking over a significant market share,” Purdy concludes.

And he was happy to share with us some other thoughts on both solid-state battery tech more generally and Ilika’s own ambitions.

Can you tell us, in layman’s terms, what solid-state batteries are and what advantages they promise over liquid electrolyte lithium-ion solutions?

Purdy: Solid state is actually just an analogue for better batteries. Solid state in itself is of no particular benefit to anybody, unless it is wrapped into a better performing battery. The advantages that solid-state technology promises are, first of all, a higher energy density battery — you can get more energy in a given weight of battery — and that then translates into a longer range for the vehicle on a given charge. Secondly, and this is particularly the case with Ilika’s solid-state batteries, it offers a reduction in cost.

Probably the two principal reasons why people who do not already drive an EV are hesitating are, first of all, range anxiety. But, secondly, EVs are still quite expensive relative to their ICE equivalents. So, if you can do some things to reduce the cost by the time it gets engineered into the vehicle, then that is a really big driver for EV adoption.

What about safety advantages?

Purdy: I always think that solid-state batteries being intrinsically safer is something of a nuanced argument, because EVs themselves are very safe. And the reason for that is quite a lot of engineering goes into ensuring that the traditional lithium-ion battery — containing a liquid electrolyte that is intrinsically flammable — is kept safe in the vehicle.

You do that by having a sophisticated control system to manage temperature. Every battery pack has got an associated cooling system, with cooling fluid and pumps and heat exchangers to get rid of that excess and waste energy. It is also mechanically protected by quite large steel girders that run down the side of the vehicle.

So, if you are unlucky enough to stuff the vehicle into a lamppost, the battery pack is protected and the pouches are not punctured. If you have got a ‘safer’ solid-state cell, you do not need quite so much of that protection. And that lightweights the vehicle and gives it a longer range, so the safety argument again translates into a lighter weight vehicle and a longer range. It is cheaper to make as well, as you do not have to put as much stuff into the car in order to keep it safe.

Will a shift towards solid-state batteries affect relative demand for particular battery metals?

Purdy: Not all solid-state batteries are made from the same material; there is actually quite a range of choices for the material on which a solid-state battery developer could focus. The electrolyte itself, for example, which is the solid substitute for the liquid electrolyte that is in a normal battery, can be a variety of different materials. It can be, like in Ilika's case, an oxide-based material, or it can be a sulphide, or it can be a polymer.

There is also a spectrum of how solid a battery is, because a lot of the early movers in the space — in particular Chinese companies making what they call solid-state batteries — contain some liquid to solve some of the challenges that you get with moving to a solid-state electrolyte. Sometimes people refer to a semi-solid-state battery, which is just a slightly drier normal battery.

NMC and LFP are still very much centre stage for a lot of solid-state batteries. People like NMC in vehicles because it is relatively safe, but higher performing relative to LFP; and people like LFP because it is cheap and, although it gives you a lower energy density, that can be okay in some environments, such as if you are just making a small urban run-around. One of the problems is that LFP then adds a lot of weight to the vehicle and starts to erode your range potential.

We claim for our Goliath automotive solid-state battery that we have got NMC performance with the safety of LFP. We use an NMC cathode combined with an oxide electrolyte and a silicon anode.

At what stage is the Goliath project currently?

Purdy: We are at a pilot stage, meaning we can make reproducible P1 two-amp hour (2Ah) prototypes that we share with customers. We will be increasing the capacity of our pilot line using some equipment currently being built by one of our partners — a company called Mpac, which is an automated assembly line — and that will be used to make larger quantities of cells.

Next summer, we will be issuing P1.5 10Ah protypes, again made on the pilot line. We will follow that up at the end of 2025 with P2 50Ah prototypes, which is what the industry might refer to as an A sample — a prototype that performs to an agreed specification but is made on pilot scale.

We would then license the technology at that stage to be sampled, and an OEM partner would make B samples on the next scale-up, perhaps in a facility like the UK Battery Industrialisation Centre, which has got gigafactory-scale equipment, but is not a fully-fledged gigafactory per se. And then that gets transferred for C sample production, as you go into small volume production to larger scale production in a gigafactory.

The next scale of 10Ah prototypes — which we have already made at our facility and we are making larger batches — will be a significant building block. We will be repeating some of the performance tests on safety, cyclability, charge retention and power density over the next few months before they are issued in the summer. And then we will be moving towards 50Ah cells for release at the end of 2025.

What role do Ilika’s partners play in the future roadmap?

Purdy: They are absolutely crucial. It is an asset-light business model in which we develop the technology and we then license it once it is mature enough. We will work with manufacturing partners, who will pick up the technology and manufacture it at scale to get to the cost points required for commercialisation.

Our relationship with Toyota goes back a long way, to the late 2000s, when we did a lot of screening materials to find a shortlist of solid-state electrolytes that could be scaled up. More recently, Agratas has joined one of our projects backed by the Automotive Propulsion Centre (APC), one of the key scale-up agencies for the automotive sector. We have a grant from the APC — we refer to it as our SiSTEM grant — supporting the development of the assembly line that we are building together with Mpac.

Agratas is riding shotgun on that programme with us, learning about assembly technology for solid state with a view to assessing what is required at gigafactory level. And Agratas is the UK’s biggest gigafactory game in town — if it gets as far as building a 40GWh facility, it will have exceeded the size of the Envision AESC gigafactory in northeast England. So we are pretty happy to be working together with them.