Solid-state batteries are safer, cheaper and can be used for longer without a decline in performance, requiring fewer raw materials. 

Countries are looking to accelerate EV uptake to help meet the goals of the Paris Agreement. The transportation sector accounts for 24% of all greenhouse gas emissions, with road transport accounting for three-quarters of that pollution, according to the IEA.

Additional climate urgency has come from the UN's latest IPCC report, which said that limiting global warming to close to 1.5C or even 2C above pre-industrial levels “will be beyond reach” by 2040 without immediate, rapid and large-scale reductions in greenhouse gas emissions.

The next-generation power source, named for the solid electrolytes that replace the flammable liquid solution in current li-ion batteries, can store energy far more densely—meaning they can travel longer distances between charges. The electrolytes also double as the battery’s separator, the barrier between cathode and anode, reducing the fire risk and making them safer. They can be used for longer without a decline in performance, requiring fewer raw materials.

The capacity of conventional lithium-ion batteries has been developed almost as far as it can go, largely unchanged for more than three decades. New kinds of technologies are needed to meet the aggressive energy density requirements

EV sales in Europe more than doubled last year as tougher new emissions targets for new cars were phased in. A swath of countries in the region, from the UK to Germany, have committed to a ban on new petrol and diesel cars from 2030.

In China, a record 1.3m electric cars were sold last year. For the first seven months of this year, China's new energy vehicle production rose to 1.50m, surging 196% on-year, with sales jumping 197% to 1.47m units. Sales could reach 2.4m this year, according to China Association of Automobile Manufacturers (CAAM).

EV optimism is strongly linked to cheaper battery packs—the most expensive component of an EV. Lithium-ion battery prices have fallen nearly 90% over the past decade to around US$110/KWh (around US$12k per car) last year.

EVs on average cost around 30% more than internal combustion engine vehicles. But that gap is closing, and price parity is now roughly three years away. This is fundamental for mass market adoption, and accelerating sales means greater demand for batteries. For automakers, securing the most efficient and cost-effective technology that moves them is key to staying relevant in a rapidly electrifying world.

Lithium-Ion: Benefits & Drawbacks

Li-ion batteries have powered the tech revolution that has brought the world smartphones, tablets and, as the world seeks to lower carbon emissions—electric vehicles. They rely on a liquid electrolyte to ferry lithium ions between an anode (the negative electrode) made of graphite and a cathode (the positive electrode)—such as nickel-cobalt -manganese (NCM).

Compared to lead-acid and nickel-metal hydride batteries, li-ion batteries have longer battery life, better performance in varying temperatures, recyclable components, and higher energy density. Energy density is the amount of energy a battery can store per unit weight.

Despite the many benefits of li-ion batteries, there are drawbacks. Although lighter than older battery technologies, its liquid composition makes it quite heavy—540kg for a Tesla Model S, for example. Their size cuts into legroom and creates other design constraints. The battery, which accounts for up to a third of the total weight, makes EVs heavier than their ICE counterparts. This means they need more power to cover the same mileage, especially in cold weather.

Energy density of li-ion batteries has risen about 4% a year over the past two decades to about 700 watt-hour a litre (Wh/L)—a driving range of about 500km in a passenger car. Further increases have been difficult to achieve given the space that cells and liquid electrolytes take up.

The liquid electrolyte also tends to react faster at high temperatures, which can lead to explosions or fires if damaged or improperly charged. Because of this, most lithium-ion battery packs need to have extra thermal monitoring and management systems, which lead to an increase in the cost and weight of the battery.

Indeed, a fire this month at one of the largest Tesla battery installations in the world has drawn fresh attention to the risks of batteries. It took three days for the blaze to be extinguished at Neoen's "Victorian Big Battery Project". There have been a total of 38 large lithium-ion battery fires since 2018, according to Paul Christensen, a professor at Newcastle University.

The long charging time of around 50 minutes on average for an EV is one of the key concerns for potential buys. “Fast charging does not pair well with liquid electrolytes. The heat generated in the process can damage batteries and absolutely raises the risk of fires,” says Brian Sheldon, professor of engineering at Brown University. “Solid-state batteries could solve that risk.”

Solid-State: Is It the "Holy Grail"?

The promise of a solid-state battery is that you can do away with the liquid electrolyte for a solid one and swap out that graphite anode for one made of pure lithium metal. This would dramatically increase the energy density of the battery—a prospect that has scientists and engineers excited. However, past experiments with lithium-metal batteries have shown them to be extremely unstable, and often exploded. 

Scientists are seeking to address this inherent flaw, known as dendrites. When the anode is made of lithium metal, needle-like structures called dendrites form on the surface. They grow like roots into the electrolyte and pierce the barrier separating the anode and cathode, causing the battery to short or even catch fire.

To overcome this challenge, Harvard University researchers have designed a multilayer battery that sandwiches different materials of varying stabilities between the anode and cathode. This prevents the penetration of lithium dendrites not by stopping them altogether but rather by controlling and containing them. The battery is also self-healing; its chemistry allows it to backfill holes created by the dendrites.

Harvard tested their battery over 10k charge cycles—competitive with the lifetime of a conventional fossil fuel car and a huge step forward. They found their design still held 82% of its charge after 10,000 cycles. This technology could increase the lifetime of EVs to that of ICE cars—10 to 15 years—without the need to replace the battery. With its high current density, the battery could pave the way for electric vehicles that can fully charge within 10 to 20 minutes.

“A lithium-metal battery is considered the holy grail for battery chemistry because of its high capacity and energy density,” said Harvard’s Xin Li in May. "This proof-of-concept design shows that lithium-metal solid-state batteries could be competitive with commercial lithium-ion batteries."

Meanwhile, researchers at Stanford University and SLAC National Accelerator Laboratory have developed a coating to limit dendrites. After 160 cycles, their lithium metal cells still delivered 85% of its power—compared to 30% for regular lithium metal cells, which render them nearly useless even if they don’t explode. The coating prevents dendrites from even forming in the first place by preventing unwanted chemical reactions and reducing chemical build-up on the anode.

Raw Materials Dilemma

Increasing demand for the batteries that drive our modern world has created a fundamental issue, given that supply of the raw materials needed won't be able to scale up as quickly. This has pushed prices higher, which isn't helping automakers in their quest to lower battery pack prices. On average, a passenger EV needs around 20kg of nickel in its battery (a Tesla Model 3 needs 30kg), up to 20kg of cobalt in the cathode, plus around 60kg of lithium compounds.

Battery makers are consistently tweaking raw materials proportions to reduce costs and increase mileage. A more recent trend has been to increase the share of nickel in their cathode chemistries—to around 80%. This is compared to traditional batteries, which had equal amounts of nickel, cobalt and manganese (NCM). Higher use of nickel increases energy density and costs half as much as cobalt. But less cobalt makes batteries more volatile. Lithium iron phosphate (LFP) chemistries are safer, and cheaper, but have a lower energy density.

Tesla's Elon Musk has singled out nickel supply as an area of concern. The California-based EV maker  accounted for more than half of all the nickel used in the European electric car industry last year. It plans to produce batteries storing 3TWh by 2030, which would exhaust most of the world’s nickel production at current levels. Boosting nickel production is tricky, given that less than half of the nickel supplied is suitable for use in batteries.

However, China's Tsingshan plans to process nickel pig iron, or NPI, which is typically used by the stainless-steel sector, into high-grade nickel matte that can be converted into nickel sulphate for use in EV batteries. China's CNGR Advanced Material Co and Australia's Nickel Mines Ltd are also planning to convert NPI into nickel matte for the battery sector. Tsingshan's March announcement turned concerns over not having enough EV nickel supply into concerns about potential oversupply.

Looking at solid-state batteries, there is potential for less copper and aluminium needed. Graphite and cobalt could be eliminated altogether. Meanwhile, recycling solid-state batteries is a simpler and safer process. If a battery uses lightweight lithium instead of heavier graphite, it could hold at least a third more power per pound than a lithium-ion battery and would be significantly lighter and take up less volume.

The Solid-State Race

The company getting the most attention is QuantumScape, a Silicon Valley start-up backed by Volkswagen and Bill Gates. It is aiming to achieve commercial production in 2024. The company is targeting an energy density of close to 400Wh/kg, from roughly 260Wh/kg in today’s EVs. It claims its technology could reduce charging times to under 15 minutes, while also making EVs safer by avoiding the use of flammable liquids.

After listing via a SPAC, its shares rose more than 1,000% in 2020, at one stage reaching a valuation of nearly US$50bn—more than General Motors. Volkswagen, which has invested us$300m in QuantumScape and hopes to deploy its cells in 2025, has also committed an undisclosed sum to help it build a pilot factory. “I have not seen data this good anywhere else,” said Stanley Whittingham, who won the 2019 Nobel Prize in Chemistry for his work on lithium-ion batteries. “So I think it’s a real breakthrough. We just have to make the cells bigger and get them into cars.”

JB Straubel, Tesla co-founder, said that while he was inherently sceptical about battery technologies claims, QuantumScape’s performance data "fundamentally puts the lithium chemistry battery on kind of a different road map for innovation,” He added that: “Seeing these kind of performance numbers is almost unheard of—a 50% improvement, roughly, in energy density volumetric, is incredible.”

Colorado-based start-up Solid Power, which is backed by Ford, said in December it had tested its solid-state cells in 22 layers and recorded an energy density of 330Wh/kg. The firm plans to produce larger cells within a year and have them in cars by 2025.Start-ups will need to scale up their technology in the face of competition from global heavyweights including Samsung, Toyota, Panasonic and France’s Bolloré Group. 

Stellantis will use two battery chemistries by 2024—a high energy-density option and a nickel cobalt-free alternative—with the goal of developing solid-state battery technology by 2026. It is aiming to cut battery pack costs by more than 40% from 2020 to 2024 and by more than an additional 20% by 2030.

Toyota expects to unveil a functional prototype with a solid-state battery as early as this year and allegedly holds the most patents relating to solid-state batteries. The Japanese automaker aims to retain 90% of the battery's performance over a 30-year lifespan. Meanwhile, Samsung has released data showing that its solid-state battery can be charged and discharged 1k times and will provide a range of up to 800km.

Chinese electric car start-up Nio said earlier this year that its electric saloon launching next year would have a solid-state battery with an energy density of 360Wh/kg. It did not reveal its supplier.

Bolloré Group has already deployed its solid-state batteries in a car-sharing service in Paris and in electric buses, although they require high temperatures to work. The company says it can have a battery that can work at room temperature by 2025-2026. 

Ganfeng Lithium, China’s largest lithium producer, says it is testing its solid-state batteries with carmakers, and aims to have a commercial product in the next couple of years. 

Japanese industrial manufacturer Hitachi Zosen has developed a solid-state battery claimed to harness one of the highest capacities in the industry. The Osaka-based company said its solid-state battery can operate under a larger range of temperatures. It will soon be tested in industrial machinery and space.

Reducing the hefty cost of batteries and lessening the failure rate, as well as the weight of the batteries, could create huge savings. This means there is huge incentive to create this next generation power source.

The challenge to making solid-state batteries viable is developing technology commonly used in small devices and applying it to large-scale applications like EVs. Even if the technology development is on track, however, commercialization is a much harder game, given the significant hurdles of price and scalability. “There have been loads of solid-state companies that have come and gone in the past as it’s just really hard to do,” said Billy Wu, a battery expert at Imperial College London. Making something at scale, he said, was a “million miles away from doing it in the lab”.

Given the mammoth interest in battery technology these days and consistent developments being made, the future for solid-state batteries looks promising.