New nanostructure for batteries keeps going and going

May 11, 2012 By Mike Ross
The new double-walled silicon nanotube anode is made by a clever four-step process: Polymer nanofibers (green) are made, then heated (with, and then without, air) until they are reduced to carbon (black). Silicon (light blue) is coated over the outside of the carbon fibers. Finally, heating in air drives off the carbon and creates the tube as well as the clamping oxide layer (red). Credit: Hui Wu, Stanford, and Yi Cui

(Phys.org) -- For more than a decade, scientists have tried to improve lithium-based batteries by replacing the graphite in one terminal with silicon, which can store 10 times more charge. But after just a few charge/discharge cycles, the silicon structure would crack and crumble, rendering the battery useless.

Now a team led by materials scientist Yi Cui of Stanford and SLAC has found a solution: a cleverly designed double-walled that lasts more than 6,000 cycles, far more than needed by or mobile electronics.

“This is a very exciting development toward our goal of creating smaller, lighter and longer-lasting batteries than are available today,” Cui said. The results were published March 25 in Nature Nanotechnology.

Lithium-ion batteries are widely used to power devices from electric vehicles to portable electronics because they can store a relatively large amount of energy in a relatively lightweight package. The works by controlling the flow of ions through a fluid electrolyte between its two terminals, called the and cathode.

The promise – and peril – of using as the anode in these batteries comes from the way the lithium ions bond with the anode during the charging cycle. Up to four lithium ions bind to each of the atoms in a silicon anode – compared to just one for every six carbon atoms in today’s anode – which allows it to store much more charge.

However, it also swells the anode to as much as four times its initial volume. What’s more, some of the electrolyte reacts with the silicon, coating it and inhibiting further charging. When lithium flows out of the anode during discharge, the anode shrinks back to its original size and the coating cracks, exposing fresh silicon to the electrolyte.

Within just a few cycles, the strain of expansion and contraction, combined with the electrolyte attack, destroys the anode through a process called "decrepitation."

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. His latest design consists of a double-walled silicon nanotube coated with a thin layer of silicon oxide, a very tough ceramic material.

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. After the first charging cycle, it operates for more than 6,000 cycles with 85 percent capacity remaining.

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.

Explore further: In-situ nanoindentation study of phase transformation in magnetic shape memory alloys

Related Stories

Increasing Electric Car Battery Performance

Sep 23, 2009

(PhysOrg.com) -- Researchers have found that by replacing conventional graphite electrodes with silicon nanotube electrodes, lithium-ion batteries can store 10 times more charge.

Recommended for you

'Exotic' material is like a switch when super thin

10 hours ago

(Phys.org) —Ever-shrinking electronic devices could get down to atomic dimensions with the help of transition metal oxides, a class of materials that seems to have it all: superconductivity, magnetoresistance ...

User comments : 28

Adjust slider to filter visible comments by rank

Display comments: newest first

tpb
not rated yet May 11, 2012
So, can someone explain how this works?
If the outside of the tube is coated with an insulator of SiO2, which I would assume stops any reaction, and the electrolyte can't get into the tube, how can any reaction occur at all?
marox
not rated yet May 11, 2012
The outer wall does not act as an electrical insulator. It's like wrapping a piece of metal in paper, touching a magnet against it will still work.
tpb
not rated yet May 11, 2012
So, are you saying the lithium ions don't react with the SiO2, but somehow go through the SiO2 to the underlying silicon?
dschlink
5 / 5 (1) May 11, 2012
Right, lithium ions are small enough to go through the SiO2 layer, but the electrolyte is too big to do so.
garrigaj
5 / 5 (1) May 11, 2012
The nanotube is hollow. The very small Li cation can easily diffuse into the Si interior and adsorb onto it, while keeping the electrolyte out. The point was to create a scaffold to allow the Si to expand and contract during charging/discharging cycles and not let the electrolyte in (which degrades the Si).
that_guy
5 / 5 (1) May 11, 2012
I was going to ask about cost, but then I thought - a battery with 20 times capacity and 15 year lifespan would justify a steep premium.

because: your cellphone will last a month on a charge.
An electric car will last as long as three tanks of gas on one charge.

You would almost never need to buy a new or replacement battery. (Depending on this concept's environmental durability.)

If price is a significant barrier, even a battery like this at 85% would still have significant value - prompting a resale market.

I'm actually pretty excited about this.

kaasinees
2.3 / 5 (3) May 11, 2012
Very good news i must say. Looks like the real deal.
TAz00
4 / 5 (2) May 11, 2012
A bank in the basement and solar/wind looks quite good
Scottingham
5 / 5 (2) May 11, 2012
Lets hope the fabrication techniques can scale up efficiently.
Tekito
5 / 5 (1) May 11, 2012
Why can't these articles at least get the opinion of a few 3rd party industry experts on this result? Is this really a big deal? Will it be affordable? Estimate of timetable for mass market? I have absolutely no idea how excited I should be feel about this story.
that_guy
5 / 5 (1) May 11, 2012
Why can't these articles at least get the opinion of a few 3rd party industry experts on this result? Is this really a big deal? Will it be affordable? Estimate of timetable for mass market? I have absolutely no idea how excited I should be feel about this story.


This is only a release that indicates that they finally found a whole solution. No one so far, has created a battery that can cycle for over a year (Much less 15 years) that has a significantly higher power potential than current lithium batteries. The end.

They don't have commercialization timetables, because it depends on their refinement of the process.
Cui said future research is aimed at simplifying the process for making the double-wall silicon nanotubes.


This is news, because it is the first breakthrough with a clear practical applicability, even at a very high price.
kaasinees
2.3 / 5 (3) May 11, 2012
If the price increases *1.5 and the efficiency increases by *2.0 or higher, well you do the math.
It might not be a suitable application for cars at start, but think about tank stations and other buildings that want to adopt renewable energy. It just means an invest at start that pays for itself with time.

If we want to apply this to vehicles we should have a little more information about energy density per weight which is more important.
Tekito
not rated yet May 11, 2012
@that_guy - If what you say is true, then it shouldn't be too much trouble to find a couple 3rd party sources to agree this is a potentially big deal.

Point is, we've all read dozens of articles that give the impression of being the next "breakthrough"... then are never heard from again. Much of the time the reader is left with overly optimistic expectations, because the full context is never explained.
that_guy
5 / 5 (1) May 11, 2012
@tekito - Obviously this is still a two birds in the nest situation, but the simple fact they claim is a substantial breakthrough.

Until now, no research has claimed to have tackled all the problems required to overcome to make a practical and usable battery of this type, regardless of price.

The main issue is the durability of the silicon anode, which usually loses a huge amount of potency after less than 100 charges. 6000 charges would constitute a home run.

While some of my conjectures may be far out due to price or manufacturing, just the ability to make what they say they made automatically gives it some applications off the bat, almost regardless of price - Which is something that no one else has achieved yet.

I understand your skepticism, but from my knowledge, this one actually sounds more actionable amid all the pipe dream $hit that gets posted.
fmfbrestel
5 / 5 (2) May 11, 2012
The results were published March 25 in Nature Nanotechnology.


It's not industry review, but it is peer review. Peers who like nothing more than to pick apart someone else's BS -- See Superluminal Neutrinos.

So at the very least we can conclude that there is no "secret sauce" concealing the snake oil.
Midcliff
not rated yet May 11, 2012
@kass They explain the energy density in the article

". Up to four lithium ions bind to each of the atoms in a silicon anode compared to just one for every six carbon atoms in todays graphite anode which allows it to store much more charge."

The breakthrough is in protecting the silicon from the electrolyte allowing it to charge for 6000 cycles.

Four times the charge per anode sounds pretty good. The silicon anode doesn't really add that much to the mass of the battery since it's mostly electrolyte
Sanescience
not rated yet May 11, 2012
"6,000 cycles, far more than needed by electric vehicles or mobile electronics"

I would think the charge-discharge cycles for a car is quite high, every time you press the brake then accelerate, yes?

As for promising articles never heard from again, there are lots of reasons, from "Oops, our bad." to "It looked great on paper, but implementation proved otherwise." Another more sinister reason that I'm sure happens from time to time is it gets bought by the competition and "squashed".
djr
not rated yet May 12, 2012
I would think the charge-discharge cycles for a car is quite high, every time you press the brake then accelerate, yes?
No - each time you plug it in to recharge - is one cycle. If the car has regen braking - that may drop some energy back into the battery - but that is not considered a cycle.
kaasinees
1 / 5 (1) May 12, 2012
I would think the charge-discharge cycles for a car is quite high, every time you press the brake then accelerate, yes?
No - each time you plug it in to recharge - is one cycle. If the car has regen braking - that may drop some energy back into the battery - but that is not considered a cycle.

No, because you have super capacitors that buffer the energy, decreasing cycles.

@Midcliff

Nope, that says nothing about the energy density per weight.
antialias_physorg
5 / 5 (1) May 12, 2012
Why can't these articles at least get the opinion of a few 3rd party industry experts on this result?

Because this site reports on papers as published - it does not do investigative journalism (with the 6 people or so it has it really can't)

Point is, we've all read dozens of articles that give the impression of being the next "breakthrough"... then are never heard from again.

Beacuse what physorg reports on is research and reserach results. Commercialization (if it happens) takes 5-10 years. Often the research reported on isn't even finished (i.e. the project is still ongoing for a couple of years until a decision on commercialization is made and THEN you still have the 5-10 years till it happens)

These things take time. Finding investors, optimizing the process, building factories, finding material suppliers, building machines, hiring people, setting up cooperations with car manufacturers, standardizing product, setting up a distribution net, finding buyers..-
Eikka
not rated yet May 12, 2012
A "cycle" for lithium batteries is measured in the amount of total energy that has gone through the battery. One cycle is a full cycle. If you discharge a little and then recharge a little, only a small number of ions move so the damage done is minimal. When you empty the whole battery, all the ions move.

There are other wear mechanisms though, like heat, and the electric current and the stored charge itself, both of which cause various unwanted chemical reactions that break down the electrolyte and the electrodes because the lithium ions aren't the only ones affected by the potential difference inside the cell. That's why batteries have a cycle life, and a shelf life. For today's lithium batteries it's typically around 1000 cycles or 4-5 years.

The damage done to the battery is cumulative and self-accelerating, which is why the battery is considered dead while it still has capacity left. Beyond some tipping point, 85% or 63% or whatever is used, the battery will break down rapidly.
eachus
not rated yet May 12, 2012
Why can't these articles at least get the opinion of a few 3rd party industry experts on this result? Is this really a big deal? Will it be affordable? Estimate of timetable for mass market? I have absolutely no idea how excited I should be feel about this story.


The reason that many of these breakthroughs are never heard from again is that once the technology makes it to market, specifications for batteries change, but if anyone advertises this product, it will be in the form of advertizing longer life or lighter weight, not the technology that makes it possible.

Personally I am amazed at how much nanotechnology has made it to market without "mature" nanotechnology to manufacture it.
Eikka
not rated yet May 12, 2012
Personally I am amazed at how much nanotechnology has made it to market without "mature" nanotechnology to manufacture it.


There's always many ways to do something. If you want a flint knife, you can either break a rock, or make a rock in the shape of your knife. Guess which one is easier.

I like Feynman's idea of small hands that build small tools to build tiny hands to make even tinier tools etc. but the problem is that you need to make stuff in large volumes which means building them atom by atom is really inefficient.
Tekito
not rated yet May 12, 2012
@antialias et al:
"These things take time. Finding investors, optimizing the process, building factories, finding material suppliers, building machines, hiring people,..."


Exactly my point on why these releases are practically indecipherable to a layperson, who will always lack the perspective or knowledge of whatever other technical or economic hurdles remain. I know a bit about battery research, but not nearly enough to think I can fully parse the ramifications of this, or any other, paper.

I shouldn't have given the impression that Physorg is to blame. I don't pay to visit this site, so I can't have any expectations. I'm just stating the simple fact that for the public to have any decent comprehension of what this really means, you need at least a few industry experts hold your hand and briefly explain "the big picture". No way around that.
MCPtz
not rated yet May 13, 2012
I just wanted to note, hit number two on google for the company "Amprius" was an article published in March 2011, stating the google CEO Kleiner invested $25 million in Amprius.

So they have significant funding from a very rich and influential person. My guess is, this paper is published between 6 months after most of the research was completed. I am excited to see this. It's too bad they are currently located too far away from me, or I'd look into SLAC/Amprius for a job.
eachus
not rated yet May 13, 2012
There's always many ways to do something. If you want a flint knife, you can either break a rock, or make a rock in the shape of your knife. Guess which one is easier.


Guessing accomplishes nothing, even if you get the answer right. If making flint knives was important to the economy, people would examine every possible pathway to making such knives at less cost. It might be the best answer was to create a knife out of some plastic, then use ion-exchange reactions to turn the plastic into flint.

The same sort of thing has been happening in nanotechnology. The "top down" techniques used for making computer chips out of silicon wafers work today, and are used now at 20 nm half-pitch dimensions. The techniques used in making the copper interconnects above the transistor layers employ "bottom up" technology.

But a lot of nanotech products that have hit the market use self-assembly techniques. (Biological life uses self-assembly to make most proteins and genetic material.)
LaraErik
not rated yet May 13, 2012
my co-worker's mom brought home $15378 a month ago. she is making an income on the computer and got a $375200 home. All she did was get fortunate and work up the steps uncovered on this link..CNNMoney2.notlong.com
that_guy
not rated yet May 14, 2012
"6,000 cycles, far more than needed by electric vehicles or mobile electronics"

I would think the charge-discharge cycles for a car is quite high, every time you press the brake then accelerate, yes?


a partial charge/discharge is not the same as a full cycle.

constantly doing small charges/discharges based on regenerative braking will indeed reduce the life of the battery substantially, however, the huge number of cycles that this battery should be capable of, combined with mitigating measures such as capacitors and heterogeneous cell loading would essentially nullify this concern.

More news stories

'Exotic' material is like a switch when super thin

(Phys.org) —Ever-shrinking electronic devices could get down to atomic dimensions with the help of transition metal oxides, a class of materials that seems to have it all: superconductivity, magnetoresistance ...

Innovative strategy to facilitate organ repair

A significant breakthrough could revolutionize surgical practice and regenerative medicine. A team led by Ludwik Leibler from the Laboratoire Matière Molle et Chimie (CNRS/ESPCI Paris Tech) and Didier Letourneur ...

Researchers successfully clone adult human stem cells

(Phys.org) —An international team of researchers, led by Robert Lanza, of Advanced Cell Technology, has announced that they have performed the first successful cloning of adult human skin cells into stem ...