Crushed silicon more than triples battery capacity in tests

It's been like 30 seconds since we posted about some new trick that'll make batteries less terrible, so it's high time for some updates: researchers at Rice University have found that stuffing piles of crushed silicon into lithium-ion batteries can increase their capacity by a factor of three, but the real news here is that it's both easy to do, and cheap.

A battery anode is designed to do one simple thing: hold on to as many ions as possible. The more ions you can stuff into an anode, the more capacity your battery has. To max out anode capacity, you want to give your anode the maximum amount of surface area in the minimum amount of volume, so a lot of research has gone into finding what material(s) can do this. In lithium-ion batteries, for example, the anode is usually graphite, because it works well and is cheap.

You know what else is cheap? Silicon. The Earth is 28% silicon, making it the second most abundant crustal element by mass after oxygen. And it makes a fantastic battery anode, too: it can hold 10x more lithium ions than graphite. However, if you cram it full of all those ions, it swells in size and will damage itself, which is why batteries tend not to use it.

Researchers at Rice have apparently figured out a way around this by making sponge-like silicon films and then crushing them into a fine powder. Not only does the powered-sponge silicon powder have fifty times more surface area than regular silicon, since it's granular, all of the spaces in between the grains give the silicon a safe place in which to expand without making your battery explode. That's great and all, but here's why we think this is worth paying attention to, according to researcher Madhuri Thakur:

In recent experiments, Thakur designed a half-cell battery with lithium metal as the counter electrode and fixed the capacity of the anode to 1,000 mAh/g. That was only about a third of its theoretical capacity, but three times better than current batteries. The anodes lasted 600 charge-discharge cycles at a C/2 rate (two hours to charge and two hours to discharge). Another anode continues to cycle at a C/5 rate (five-hour charge and five-hour discharge) and is expected to remain at 1,000 mAh/g for more than 700 cycles.

"As a powder, they can be used in large-scale roll-to-roll processing by industry," Thakur says. "The material is very simple to synthesize, cost-effective, and gives high energy capacity over a large number of cycles."

So let's see: this stuff has significantly increased capacity over current technology, seems to have a lifetime on par with current batteries, is simple to make, is cheap, and (perhaps most importantly) is easy to integrate into existing manufacturing processes. All that the researchers will commit to at this point is saying that the next step is to integrate the powder into a full-cell battery and continue tests, but we hope that research partner Lockheed Martin will take some initiative and get this silicon powder into commercial production ASAP.

Rice, via Motherboard

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