New technology improves both energy capacity and charge rate in rechargeable batteries

Nov 14, 2011

Imagine a cellphone battery that stayed charged for more than a week and recharged in just 15 minutes. That dream battery could be closer to reality thanks to Northwestern University research.

A team of engineers has created an electrode for batteries -- such as those found in cellphones and iPods -- that allows the batteries to hold a charge up to 10 times greater than current technology. Batteries with the new electrode also can charge 10 times faster than current batteries.

The researchers combined two chemical engineering approaches to address two major battery limitations -- and charge rate -- in one fell swoop. In addition to better batteries for cellphones and iPods, the technology could pave the way for more efficient, smaller batteries for .

The technology could be seen in the marketplace in the next three to five years, the researchers said.

A paper describing the research is published by the journal Advanced .

"We have found a way to extend a new lithium-ion battery's charge life by 10 times," said Harold H. Kung, lead author of the paper. "Even after 150 charges, which would be one year or more of operation, the battery is still five times more effective than lithium-ion batteries on the market today."

Kung is professor of chemical and in the McCormick School of Engineering and Applied Science. He also is a Dorothy Ann and Clarence L. Ver Steeg Distinguished Research Fellow.

Lithium-ion batteries charge through a chemical reaction in which lithium ions are sent between two ends of the battery, the and the cathode. As energy in the battery is used, the lithium ions travel from the anode, through the electrolyte, and to the cathode; as the battery is recharged, they travel in the reverse direction.

With current technology, the performance of a lithium-ion battery is limited in two ways. Its energy capacity -- how long a battery can maintain its charge -- is limited by the charge density, or how many lithium ions can be packed into the anode or cathode. Meanwhile, a battery's charge rate -- the speed at which it recharges -- is limited by another factor: the speed at which the lithium ions can make their way from the electrolyte into the anode.

In current rechargeable batteries, the anode -- made of layer upon layer of carbon-based graphene sheets -- can only accommodate one lithium atom for every six carbon atoms. To increase energy capacity, scientists have previously experimented with replacing the carbon with silicon, as silicon can accommodate much more lithium: four lithium atoms for every silicon atom. However, silicon expands and contracts dramatically in the charging process, causing fragmentation and losing its charge capacity rapidly.

Currently, the speed of a battery's charge rate is hindered by the shape of the graphene sheets: they are extremely thin -- just one carbon atom thick -- but by comparison, very long. During the charging process, a lithium ion must travel all the way to the outer edges of the graphene sheet before entering and coming to rest between the sheets. And because it takes so long for lithium to travel to the middle of the graphene sheet, a sort of ionic traffic jam occurs around the edges of the material.

Now, Kung's research team has combined two techniques to combat both these problems. First, to stabilize the silicon in order to maintain maximum charge capacity, they sandwiched clusters of silicon between the graphene sheets. This allowed for a greater number of lithium atoms in the while utilizing the flexibility of graphene sheets to accommodate the volume changes of silicon during use.

"Now we almost have the best of both worlds," Kung said. "We have much higher energy density because of the silicon, and the sandwiching reduces the capacity loss caused by the silicon expanding and contracting. Even if the silicon clusters break up, the silicon won't be lost."

Kung's team also used a chemical oxidation process to create miniscule holes (10 to 20 nanometers) in the graphene sheets -- termed "in-plane defects" -- so the lithium ions would have a "shortcut" into the anode and be stored there by reaction with . This reduced the time it takes the battery to recharge by up to 10 times.

This research was all focused on the anode; next, the researchers will begin studying changes in the that could further increase effectiveness of the batteries. They also will look into developing an electrolyte system that will allow the to automatically and reversibly shut off at high temperatures -- a safety mechanism that could prove vital in electric car applications.

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More information: The paper is titled "In-Plane Vacancy-Enabled High-Power Si-Graphene Composite Electrode for Lithium-Ion Batteries."

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User comments : 17

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Eikka
1.4 / 5 (11) Nov 14, 2011
Wow - 50% reduction in capacity in one year? How are you going to make an electric car out of that? You'd swap out batteries more often than you change the oil in a regular car - and an oil change doesn't cost you thousands of dollars.

My cellphone goes for two weeks on a two-hour charge, and lasts for 4-5 years without significant loss in capacity. I think that would be acceptable for a car as well.
Yevgen
5 / 5 (1) Nov 14, 2011
One problem with composites of such kind is low energy density by volume, because they are "fluffy". Energy by volume is more critical then energy by weight for most portable applications.
Of cause, pure cycleability is a common problem for all new
developments, but in this particular case high surface caused by fluffy composites is likely causing high self discharge
rate and accumulation of decomposition products that shorted
the life of the battery.

Regards,
Yevgen
ashraf fazili
not rated yet Nov 14, 2011
Batteries to last for a longer periods are here.
ekim
not rated yet Nov 14, 2011
Wow - 50% reduction in capacity in one year?

Where did you get that number?
Besides, car batteries can be recycled. No need to pay for new materials, the only cost is refurbishing.
Ethelred
4.1 / 5 (11) Nov 14, 2011
It follows quite clearly from this:
"Even after 150 charges, which would be one year or more of operation, the battery is still five times more effective than lithium-ion batteries on the market today."
Odd though how Eikka emphasized the decrease and ignored it still being 5 times better than present batteries.

I am beginning to wonder about what kind of agenda he has.

My problem with this is the one he usually harps on. It's still lithium and it gets the higher capacity by using more of it. There simply isn't enough lithium to replace petroleum in transportation.

IF the bloody tech actually gets used for once, these articles are endemic here, it would allow for more powerful tablet pcs running longer or lighter. Of course if the charge decrease continues at the same rate of 50% a year its just a waste of lithium.

Eikka
lasts for 4-5 years
You must be the only person on Earth with a 5 year old cellphone.

Ethelred
Jeddy_Mctedder
1 / 5 (4) Nov 14, 2011
i smell bullshit on this article.
rastafari-luc
5 / 5 (1) Nov 15, 2011
battery lasting 2 weeks on a 2 hour charge, dam my GS2 is lucky to go half a day on a 3 hour charge. i love the phone but no matter how they try to spin it, batteries these days just cant keep up with the use people want out of their devices
Ricochet
not rated yet Nov 15, 2011
Eikka

lasts for 4-5 years

You must be the only person on Earth with a 5 year old cellphone.

The other person is my mother-in-law, whose in her 50s and has vision problems. She's also a bit technophobic, even though she used to be a programmer.
Ricochet
not rated yet Nov 15, 2011
battery lasting 2 weeks on a 2 hour charge, dam my GS2 is lucky to go half a day on a 3 hour charge. i love the phone but no matter how they try to spin it, batteries these days just cant keep up with the use people want out of their devices

And now the Tegra3 processor is out with its 5 cores. I'm anxious to play the new games that will come out for 5 minutes between charges.
joefarah
1 / 5 (3) Nov 15, 2011
OK... there are several technologies that have existed for some time with this capability (fast charge). Altairnano, for example, has been selling its batteries for years. They'll recycle for 15 years or more with little drop in capacity. They can be charged in minutes. They're also safe (won't catch fire, explode when pierced, etc.).

But they are not 10x capacity (less than 2x capacity of existing). However, I've read several other posts here in the last couple of years that are. Let's get some of these other batteries commercialized quickly, or perhaps work with ALtair to extend their battery lifetimes.
ugosugo
not rated yet Nov 15, 2011
Great! All you have to do is going to the nearest shop and buy a pack of graphene sheets for a few million bucks!
CHollman82
1 / 5 (10) Nov 16, 2011
Wow - 50% reduction in capacity in one year? How are you going to make an electric car out of that? You'd swap out batteries more often than you change the oil in a regular car.


Umm... do you own a car? How often do you change your oil? Even with full synthetic I change mine every 6,000 miles which turns out to be about 3 times a year.

My cellphone goes for two weeks on a two-hour charge


No it doesn't, or you have a shitty outdated phone. My Evo 4G with an extended battery will last about 16 hours on an overnight charge.

and lasts for 4-5 years without significant loss in capacity. I think that would be acceptable for a car as well.


This is wrong also, assuming your phone was made in the last decade...
Eikka
1.3 / 5 (3) Nov 17, 2011
Odd though how Eikka emphasized the decrease and ignored it still being 5 times better than present batteries.


Here's the rub: you want your car to drive for 40 miles at minimum. The batteries we have now allow you to do that for 5-7 years before they're too worn out.

If you lose 50% of the capacity every year, and you want your battery to last you 5 years, you need to start with a battery that has an initial capacity of 1280 miles.

The battery being 10 times better at start would equal in weight a battery that has 128 miles, whereas current electric cars have batteries that hold 70-100 miles per charge, which means that to get the same performance out of the "superior" battery, you'd still need more of it.

No it doesn't, or you have a shitty outdated phone. My Evo 4G with an extended battery will last about 16 hours on an overnight charge.


It sounds like you have the shitty phone. Is it worth that so you can play Angry Birds?
Eikka
1 / 5 (3) Nov 17, 2011

lasts for 4-5 years
You must be the only person on Earth with a 5 year old cellphone.

Ethelred


I have a couple that are even older than that, and still work although the batteries have gone down. My current model is made in 2008 and uses the same type of battery as the one I bought in 2003. Both got 400-450 hours of standby when new, which is roughly 16-18 days.

I'm also one of the few people who still have the same SIM card they bought in the 90's, and it still works. I don't see the point of buying a $600 phone when its battery won't get you through the whole day.

It's a telephone for crying out loud. That's the purpose of it, and getting a 16 hour battery life is like going back to 1982 in terms of how useful the phone actually is.

"911 how may I help you? - There's a ro.... beep beep beep..."
Eikka
1 / 5 (3) Nov 17, 2011
Of course if the charge decrease continues at the same rate of 50% a year its just a waste of lithium.

Ethelred


Actually, the rate that a litium battery ages depends on the watt-hours put through versus the capacity of the battery. Assuming that you drive a steady n-miles per day, by the time you've gone down to 50% capacity you're recharging the battery twice as often, which means that the next halving in capacity will happen half as soon.

So in one year it goes from 100 -> 50%
In the next 6 months it goes from 50 -> 25%
In the next 3 months it goes from 25% -> 12.5%
In the next 1.5 months it goes from 12.5 -> 6.25%

So by the year 3 you won't have a battery any longer.

This is the reason why lithium batteries are generally considered "dead" when they reach down to 2/3 capacity remaining. After that point, the breakdown accelerates under the same constant load.
rsklyar
1 / 5 (5) Nov 21, 2011
Another prominent result of plagiaristic cooperation between Northwestern University with the Italian Institute of Technology (IIT) and Universities of Ferrara and Genova at http://issuu.com/...saivaldi
CHollman82
1 / 5 (4) Nov 29, 2011

lasts for 4-5 years
You must be the only person on Earth with a 5 year old cellphone.

Ethelred


I have a couple that are even older than that, and still work although the batteries have gone down. My current model is made in 2008 and uses the same type of battery as the one I bought in 2003. Both got 400-450 hours of standby when new, which is roughly 16-18 days.

I'm also one of the few people who still have the same SIM card they bought in the 90's, and it still works. I don't see the point of buying a $600 phone when its battery won't get you through the whole day.

It's a telephone for crying out loud. That's the purpose of it, and getting a 16 hour battery life is like going back to 1982 in terms of how useful the phone actually is.

"911 how may I help you? - There's a ro.... beep beep beep..."


congratulations on being poor