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Double-walled silicon nanotube anode for Li-ion batteries shows long cycle life

14 May 2012

Cui
TEM images of an individual DWSiNT before (a) and after (b) lithiation, respectively. They show the tube wall expanded towards the inside, while the outside diameter of the tube remains constant. Wu et al., Supplementary Material. Click to enlarge.

Although silicon has a large charge storage capacity, making it an attractive anode material for advanced Li-ion batteries, the pulverization it experiences during cycling and an unstable solid–electrolyte interphase has limited the cycle life of silicon anodes to the order of hundreds of cycles.

A team of researchers led by Dr. Yi Cui of Stanford University and SLAC National Accelerator Laboratory has now shown that anodes consisting of an active silicon nanotube surrounded by an ion-permeable silicon oxide shell can cycle more than 6,000 times in half cells while retaining more than 85% of their initial capacity. A paper on the double-walled silicon nanotubes (DWSiNT) was published in the journal Nature Nanotechnology.

Over the past five years, Cui’s group has progressively improved the durability of silicon anodes by making them out of nanowires and then hollow silicon nanoparticles. This latest design consists of a double-walled silicon nanotube coated with a thin layer of silicon oxide—a very tough ceramic material.

The outer surface of the silicon nanotube is prevented from expansion by the oxide shell, and the expanding inner surface is not exposed to the electrolyte, resulting in a stable solid–electrolyte interphase. Batteries containing these double-walled silicon nanotube anodes exhibit charge capacities approximately eight times larger than conventional carbon anodes and charging rates of up to 20C (a rate of 1C corresponds to complete charge or discharge in one hour).

—Wu et al.

This strong outer layer keeps the outside wall of the nanotube from expanding, so it stays intact. Instead, the silicon swells harmlessly into the hollow interior, which is also too small for electrolyte molecules to enter.

Cui said future research is aimed at simplifying the process for making the double-wall silicon nanotubes. Others in his group are developing new high-performance cathodes to combine with the new anode to form a battery with five times the performance of today’s lithium-ion technology.

In 2008, Cui founded a company, Amprius, which licensed rights to Stanford’s patents for his silicon nanowire anode technology. Its near-term goal is to produce a battery with double the energy density of today’s lithium-ion batteries.

Resources

  • Hui Wu, Gerentt Chan, Jang Wook Choi, Ill Ryu, Yan Yao, Matthew T. McDowell, Seok Woo Lee, Ariel Jackson, Yuan Yang, Liangbing Hu & Yi Cui (2012) Stable cycling of double-walled silicon nanotube battery anodes through solid–electrolyte interphase control. Nature Nanotechnology 7, 310–315 doi: 10.1038/nnano.2012.35

May 14, 2012 in Batteries | Permalink | Comments (11) | TrackBack (0)

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Impressive numbers. If Amprius could make a battery for the Leaf, with double the energy density and capable of 6,000 charge cycles, that would get over 800,000 miles before needing a battery change. In a cell phone, the battery would last over 16 years if charged every day. Hopefully "near-term" isn't 10 years out.

Yes KR....this may be one of the break through that EVs (plus many other applications) have been waiting for. A battery with 20C charging rate, 8 times the capacity and 6000 cycles would be more than what is required for ICE equivalent highway extended range performances. It could retire all ICEs if the price is right.

Charging rates of 20 C indicate the potential for stellar performance in regenerative braking applications; a 10 kWh battery could absorb 200 kW of braking power; even a 1.5 kWh battery could soak up 30 kW.

That's also more than sufficient to completely charge the battery in the time needed for a brief rest stop.

So many 'eureka' battery announcements - so market them batteries.

Aren't cathodes the present li-ion battery bottleneck?

Does ".. and charging rates of up to 20C (a rate of 1C corresponds to complete charge or discharge in one hour)" imply a 3 minute recharging(w/sufficient power)?

'Cui and his students have used sulfur-coated hollow carbon nanofibers and a special electrolyte additive to improve the other end of the rechargeable lithium ion battery, the cathode.'

http://news.stanford.edu/news/2011/october/sulfur-nanofibers-battery-100411.html

This is the other half of the deal.

"This is the other half of the deal."

"- so market them batteries."

"Cui said future research is aimed at simplifying the process for making the double-wall silicon nanotubes."

In other words, they don't know how to manufacture these things commercially, but they're hoping someone will figure it out in the future.

Aluminum was the same way for quite some time.

Is it just me, or has anyone else noticed that Dr. Cui cranks out new stuff at nearly the same rate as the rest of the industry combined? LOL

The guy, and his team, are apparently freakin sharp!!!

Good observation DaveD. He should partner with the like Warren Buffet and Bill Gates to mass produce his inventions.

It's often easy at lab scale to demonstrate potential in a technology. Here it is mentioned that they need to figure out scaled up manufacturing. I would suggest they need to be able to load the anode current collector densely enough to match a high energy cathode material. Typically with vacumm or vapor grown materials getting the thickness high enough and the porosity high enough for good ionic transport in the electrolyte is difficult. Just one more point, because, I could go on and on, anyway, c-rates are often astounding in very thin materials because there are no issues with ionic conductivity limitations in the porous media. However, those rates often go away when you make an anode that is thick enough to match energy with a decent cathode. You might say "well, why don't they just make thin electrodes", and the answers is because that reduces cell level energy density by making a greater percentage of the cell a none storage material such as separator current collectors and electrolyte.

Don't get me wrong here, this is an interesting result and could potentially be meaningful, but some people are just good at press releases.

There is an unusual phenomenon in the science community in which a certain type of arrogance is seen by some true believers as proof of a superior researcher. Both stanford and MIT have schooled their people in representing this arrogance. They may be good researchers too, but they also manipulate their image very well indeed.

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