Is silicon the answer to modern day battery problems?
Mobile phones losing charge after a day and electric vehicles (EVs) taking hours to charge are modern problems that continue to persist despite constant innovations in battery technology. However, silicon batteries could be the solution to these issues
What are they?
Lithium-silicon batteries are a variant of lithium-ion batteries that utilise silicon as the anode material, rather than graphite.
The next evolution of the silicon battery replaces the conventional liquid electrolyte, through which lithium ions can move, with a solid electrolyte combined with the silicon anode, creating a solid-state silicon battery.
Graphite is like a sturdy bag that only has space for ten books, whereas silicon has room for 100 books, but the straps break easily.
Why silicon?
Silicon is able to store a lot more lithium than graphite. Pure silicon can store 3600mAh/g compared to graphite, which can only hold 372mAh/g, so silicon can hold almost ten times more charge per gram than graphite.
Having a higher energy density enables the potential for smaller, lighter, longer-lasting batteries, which can benefit phones, wearables, EVs, and even grid storage.
Solid-state silicon batteries are also safer than lithium-ion batteries, as they eliminate the need for a liquid electrolyte, which is flammable. Solid electrolytes are also capable of handling higher currents more effectively, theoretically making charging quicker.
The challenges
Silicon swells dramatically when mixed with lithium. This is because the lattice distance between silicon atoms multiplies to accommodate the lithium ions, causing it to reach over 300% of its original volume.
Lithium also causes silicon to overreact. When the battery charges, the silicon surface continues to react with the electrolyte, forming layers that crack and rebuild as the material swells. This reaction wastes energy and consumes lithium, ultimately reducing the battery's capacity.
Solid electrolytes are challenging to manufacture at scale and typically do not conduct lithium ions as efficiently as liquids.
Solutions in progress
One innovation involves incorporating small amounts of silicon into graphite anodes to achieve a slight capacity boost without the full risks.
Another solution involves using silicon compounds instead of pure silicon to reduce swelling and improve stability, such as silicon monoxide, silicon oxycarbide, and silicon nitride.
To tackle the risk of silicon cracking, scientists are redesigning it at the nanoscale. For example, Amprius has built nanowire-based anodes that can bend instead of breaking.
Researchers at Stanford University wrapped silicon microparticles in thin graphene shells, which acted as a flexible exoskeleton, keeping the silicon intact while allowing lithium to flow in and out.
Protective coatings, like a case around silicon, are able to block any unwanted reactions, keeping the battery stable.
Who's working on it?
Various companies and startups are developing silicon-based batteries, for example, Group14, an innovator in silicon battery materials, specialising in its patented silicon-carbon composite SCC55. This material enables batteries to reach an 80% charge in under 10 minutes and offers up to 50% greater density than traditional lithium-ion batteries. Group14 recently received $463 million in funding to help scale the manufacturing of SCC55.
