As electrical vehicle (EV) sales hit another record, two technologies – silicon anodes and solid-state batteries (SSBs) – are competing for the future of EV batteries. However, silicon anodes appear to be pulling ahead in the race to reach commercialisation for next-generation EV batteries.
Silicon anodes promise improved power and faster charging capabilities, especially lithium-ion, compared to existing battery technology. Indeed, this technology has received a lot of column inches lately, with much interest being shown in it.
On the other hand, its main competitor, solid-state batteries (SSBs), need to catch up with the progress of development and media attention. This is despite several major car manufacturers, such as Mercedes, Porsche and General Motors, all betting on SSBs for the future of EVs.
Yet, despite the hype around silicon anodes, there are some serious concerns about their cycle and shelf life compared to more traditional batteries and SSBs. Their price point is also not yet low enough to make them viable for mass production.
Only five years ago, the best silicon anodes available had a calendar life of around one year. But this has dramatically improved recently, with calendar life extended three-or fourfold.
Silicon anodes or SSBs: which will win the race?!
In case you are unaware, calendar life measures a battery’s degradation over time. This differs from cycle lifetime, which refers to the number of times it can be charged and discharged before becoming unusable.
At present, the calendar life of most batteries refers to the period during which they can function at over 80% of their initial capacity, regardless of usage. However, most SSBs are nowhere near able to achieve this.
Silicon anodes work by forming an alloy (lithium silicide) with lithium ions during the battery charging process. Typically, this amounts to around a 1:4 ratio of silicon to lithium, meaning it has a relatively large lithium ion storage capacity (aka energy density).
In fact, according to some analysts, silicon anodes could offer up to 10 times the energy density of graphite, which is commonly used as an anode in most batteries today. Taiwanese battery maker ProLogium even unveiled the ‘world’s first’ fully silicon anode battery at the 2024 Paris Motor Show.
The company claims its 100% silicon anode battery can charge from 5% to 60% in just 5 minutes and reach 80% in 8.5 minutes, a feat it describes as “unmatched achievement in the competitive EV market”.
How silicon anodes work
When the battery charges, lithium ions move from the cathode to the anode through the electrolyte and are intercalated (inserted) into the anode material. During discharge, the reverse occurs, and lithium ions leave the silicon anode and move back to the cathode, releasing energy.
This process, however, causes the silicon anodes to swell up to 300% or more, which can stress and damage them over several charging cycles. But its impressive energy storage potential promises long-lasting, faster-charging and potentially increased range for things such as EVs.
Silicon is also one of the most abundant elements on Earth (sand is silicon oxide, for example), making it cheap compared to other materials used in batteries.
SSBs, as the name suggests, work using an entirely different technique that replaces the liquid electrolyte with a solid one. For this reason, they are considered significantly safer and stable, meaning they can enable high-energy materials such as silicon and lithium, theoretically.
SSBs must maintain high ionic conductivity while remaining chemically and physically stable to work effectively. This is achieved through materials such as ceramic or polymers, but these materials come with a trade-off…
SSBs: the ‘holy grail’ of future batteries?
As you can imagine, ceramics are very brittle, making them easy to damage. Polymers are more flexible but less effective as electrolytes and can’t operate at higher or lower temperatures like ceramics.
These materials are also very expensive to manufacture, and the process is very time-consuming and complicated. SSBs also need high-purity lithium metals to work effectively, which is more expensive and harder to make than graphite anodes.
To this end, at least right now, silicon anodes are the more promising of the two in reaching the final furlong in the race for the future of EV batteries. But the ultimate winner will depend on which of the two receives the most attention and, more critically, investment for research and development.
“At this stage, silicon anodes are used more as an additive to graphite-based anodes, and in the years to come, we expect to see [an] increase of [the amount of] silicon share in [the] anode, but in combination with graphite. 100% silicon anodes [, on the other hand] will take [a] longer time to enter the mass market,” Georgi Georgiev, battery raw materials analyst at consultancy Fastmarkets, told CNBC.
