Solid-state batteries vs. silicon anodes: Who will fuel e-cars in the future?

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There is a lot of momentum in the field of battery research. Ultimately, the aim is to find the most powerful and durable energy storage systems possible in order to advance electromobility in particular. It now looks like there is a competition between two approaches.

Solid-state batteries could theoretically end the issue of range anxiety in electric cars once and for all. In practice, however, there have been many promises so far because production is complicated. Now things seem to be moving forward. Many manufacturers are reporting progress on the road to series production.

However, the technology could now be virtually overtaken on the right – by conventional lithium-ion cells with a silicon anode. They offer similarly high energy densities, but are easier to produce. And they reduce dependence on China. Battery development is therefore likely to become even more exciting in the future.

In modern lithium batteries, the anodes are usually made of graphite like pencil leads. The cathodes are usually based on lithium nickel manganese cobalt oxide (NMC) or lithium iron phosphate (LFP). When charging, the lithium ions move from the cathode to the anode, and when discharging, they move back from the anode to the cathode.

Solid-state batteries: "Larger quantities" from 2025

Solid-state cells focus primarily on the metallic component. Instead of metal oxides, they use pure lithium. Their energy density is correspondingly high.

One of the best-known manufacturers is Quantumscape, in which Volkswagen is also involved. According to its own statements, it has now overcome a decisive hurdle to the series production of ceramic separators. "Larger quantities" of sample cells could be delivered as early as 2025. Quantumscape puts their energy density at 844 watt hours per liter. MG, Mercedes, Toyota and CATL have also recently reported progress in solid-state cells.

However, even future solid-state cells will not be able to do without graphite. However, this takes up a lot of space and slows down ion exchange. This is why manufacturers of silicon cells are taking the exact opposite approach: they are not starting with the metal electrode, but with the graphite. An admixture of just five to ten percent silicon can drastically improve charging performance, as demonstrated by the Porsche Taycan, among others. The upcoming Mercedes CLA is also expected to be on the road with a graphite-silicon anode from 2025.

Even better: battery anodes made entirely of silicon

However, anodes made entirely of silicon would be even better. Because while it takes six carbon atoms to accommodate a single lithium ion, two silicon atoms can hold up to seven atoms of lithium. Although silicon is heavier than carbon, the "mass-related advantage" is still said to be "around a factor of ten".

The problem with this is that the silicon shrinks and expands during charging and discharging. This leads to mechanical stresses that affect the service life of a cell. The US companies Sionic Energy and Group14 Technologies now claim to have solved this problem – with an anode that is structured like a sponge on the nanoscale. The tiny silicon particles are surrounded by a framework of other materials. This allows them to expand freely.

These anodes are said to allow a 42 percent higher energy density and reduce the charging time by a third to ten minutes. Specifically, the manufacturers state an energy density of 330 watt hours per kilogram (or 842 watt hours per liter) and a shelf life of up to 1200 cycles for cells up to ten ampere hours. Larger cells with 20 ampere hours achieve an even higher energy density, but with only half the number of cycles. By comparison, the best nickel-rich batteries from Tesla achieve just under 300 Wh/kg or a good 700 Wh/l, according to IEEE Spectrum.

Seamless integration into production

Even more important than these key figures: According to the company, the production of the anodes can be seamlessly integrated into the production of conventional lithium-ion cells. This is crucial, as many promising laboratory concepts fail on the way to mass production. And while over 90 percent of graphite production is in Chinese hands, silicon is much more independent.

Sionic wants to license its technology to other manufacturers. Potential customers should be able to test the first cells as early as 2025. CEO Ed Williams sees the first applications in consumer electronics and aviation, he told IEEE Spectrum. He estimates that anodes with 30 to 100 percent silicon content will penetrate the market in the next three to five years. Rick Luebbe, head of Group14, even believes: "In time, silicon batteries will completely replace conventional lithium-ion batteries."

Research also in Halle

At the beginning of 2025, Group14 plans to open a factory in the USA with an annual capacity of 20 gigawatt hours, enough for 100,000 to 200,000 e-cars. A plant for a further ten gigawatt hours is planned in South Korea. Porsche is also among the investors in Group14 with a share of 100 million US dollars.

The start-up NorcSi from Halle an der Saale is also working on pure silicon anodes. Here too, a nano-structure is intended to prevent volume changes. And here too, the electrodes can be produced using established processes. "Our test cells are already achieving decent values in terms of cycle stability and exceptional values in terms of charging speed and capacity," says the company. "Nevertheless, there are numerous parameters open to us for further optimization."

This article first appeared on t3n.de .

(mma)