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Swapping carbon for silicon to improve batteries

Several lithium-ion cell prototypes containing Sila Nanotechnologies’ silicon anode. Image credit: SILANANOTECH

Batteries have kept evolving throughout these last decades however the general perception is that they are not increasing their capacity at all. This is due to that fact that we don’t measure a battery in terms of Power (Ah – Ampere hour) nor in terms of capacity density (how many Ah you can squeeze in a given volume…) but rather in the time that battery would provide power and this time seems basically unchanged (a working day, mostly). Now the reason is that battery are designed with that target of duration in mind: you want to provide a smartphone with sufficient juice to have it run the whole day before recharging it at night.

If you keep this in mind and notice how much more powerful are today’s smartphones and how thinner they are than you realise that batteries have indeed made progress: a smaller battery can power a more power demanding electronics for the same time as before.

Battery engineering is sort of juggling different characteristics, contradicting one.another, aiming for an acceptable tradeoff. You want more capacity, then you need a bigger volume but at the same time you want a smaller volume to have the battery fitting in a thinner device. You want a rapidly charging battery but at the same time you want to keep heating low, you want max charge but you also want long lasting battery life… Modern batteries try to achieve the best compromise through … software. A smart battery controller can embed an intelligent algorithm that learns the way you use that battery and will take care of finely tuning the recharging to fit your needs and yet extend battery life. Similarly, it will regulate the power flow negotiating it with the user (the circuitry) to prolong the battery life and keep performances in an acceptable range (remember the protests on discovering the the iPhone would downgrade its performances over time… there you have it!).

It is, as you would suspect, much more complicated. The chemical structure of a battery is also the result of compromises. You want to have chemicals that can contain a lot of charge and at the same time that are stable over long periods of time. Lithium batteries are the best compromise given the technology available today (although you can see that engineers have already pushed these batteries quite a bit and from time to time some manufacturing defects result in overheating and explosion…).

A lithium battery uses a graphite bar as anode (negative electrode). Silicon would make for a better anode, increasing the capacity of the battery but electrons in the silicon make it swell up to 4 times its original volume when the battery recharges. This swelling destroys the anode structure and may break the barrier separating the anode from the electrolyte, thus killing the battery.

Now scientists are looking for ways to combine carbon with silicon and are focussing on graphene. This is a sort of lattice that can include different types of atoms in the carbon fabric and scientists are looking for a way to include silicon atoms to get all the benefit of silicon and having the graphene lattice shielding the battery form the swelling of silicon nanoparticles. This approach seems to be working and companies like Sila (see the photo) and Advano are ready to introduce carbon silicon anodes in the market. So far the increase in capacity is of the order of 20% but the technology can be pushed to deliver up to 40-50% of increased capacity.

The challenge is no longer in the technology per sé but in finding a way to produce at scale with an affordable price.



About Roberto Saracco

Roberto Saracco fell in love with technology and its implications long time ago. His background is in math and computer science. Until April 2017 he led the EIT Digital Italian Node and then was head of the Industrial Doctoral School of EIT Digital up to September 2018. Previously, up to December 2011 he was the Director of the Telecom Italia Future Centre in Venice, looking at the interplay of technology evolution, economics and society. At the turn of the century he led a World Bank-Infodev project to stimulate entrepreneurship in Latin America. He is a senior member of IEEE where he leads the Industry Advisory Board within the Future Directions Committee and co-chairs the Digital Reality Initiative. He teaches a Master course on Technology Forecasting and Market impact at the University of Trento. He has published over 100 papers in journals and magazines and 14 books.