Self-charging battery both generates and stores energy

Aug 17, 2012 by Lisa Zyga feature
(a) In the self-charging power cell, the piezoelectric material PVDF replaces the conventional separator material and acts as a nanogenerator inside a Li-ion battery. (b) On the bottom of a shoe, the power cell converts the compressive energy generated by walking into chemical energy and stores it without converting it to electricity. Image credit: Xue, et al. ©2012 American Chemical Society

(Phys.org) -- Renewable energy technologies generally consist of two distinct processes: energy generation (using sources such as coal, solar, wind, etc.) and energy storage (such as batteries). These two processes are always accomplished through two separate units, with the first process converting the original form of energy to electricity, and the second process converting electricity to chemical energy. Now for the first time, engineers have demonstrated that energy can be generated and stored in a single device that converts mechanical energy directly to chemical energy, bypassing the intermediate step of electricity generation. The device basically acts as a hybrid generator-battery unit, or in other words, a self-charging power cell.

The researchers, Xinyu Xue, Sihong Wang, Wenxi Guo, Yan Zhang, and Zhong Lin Wang, from the Georgia Institute of Technology in Atlanta, Georgia, have published their study on combining and storage in a single unit in a recent issue of .

“This is a project that introduces a new approach in battery technology that is fundamentally new in science,” Zhong Lin Wang told Phys.org. “This has a general and broad application because it is a unit that not only harvests but also stores it. It does not need a constant wall jet DC source to charge the battery. It is mostly to be used for driving small, portable electronics.”

To fabricate the self-charging power cell, the researchers started with a coin-type Li-ion battery and replaced the polyethylene separator that normally separates the two electrodes with PVDF film. As a piezoelectric material, PVDF film generates a charge when under an applied stress. Because of its position between the battery electrodes, the PVDF film causes positive Li ions to migrate from the cathode to the anode in order to maintain a charge equilibrium across the battery. This ion migration process charges the battery without the need for any external voltage source; since the PVDF separator provides the voltage, or potential difference between electrodes, the battery is essentially self-charging.

A cross-sectional scanning electron microscope image of the self-charging power cell (left), and the enlarged TiO2 nanotube anode (right). Image credit: Xue, et al. ©2012 American Chemical Society

In order to apply a stress to the separator, the researchers attached the coin-sized battery to the bottom of a shoe, and found that walking could generate enough compressive energy to charge the battery. A compressive force with a frequency of 2.3 Hz could increase the voltage of the device from 327 to 395 mV in 4 minutes. This 65 mV increase is significantly higher than the 10 mV increase it took when the power cell was separated into a PVDF piezoelectric generator and Li-ion battery with the conventional polyethylene separator. The improvement shows that achieving a mechanical-to- conversion in one step is much more efficient than the mechanical-to-electric and electric-to-chemical two-step process used for charging a traditional battery.

Once the new equilibrium between electrodes is reached, the self-charging process ceases. The cell can begin supplying power after the applied stress is released, since the piezoelectric field disappears and the Li ions can diffuse back from the anode to the cathode to reach a new equilibrium. As in a conventional Li-ion battery, ion diffusion involves electrochemical reduction-oxidation reactions, which here generate a current of about 1 μA that can be used to power a small electronic device.

“The Li ions will not flow back immediately after the applied stress is removed because it forms a new compound with the anode material (LiTiO),” Zhong Lin Wang said. “The charges are preserved as in a conventional . They are released at a later time when power is required.”

Although these voltages and currents are low, the researchers showed that the power cell can also self-charge with higher voltages of around 1.5 V, which could make it useful for a broader range of applications. The researchers predict they can further improve the power cell’s performance by making several modifications, such as by using flexible casing to allow for greater deformation of the piezoelectric material.

Explore further: Scientists craft atomically seamless, thinnest-possible semiconductor junctions

More information: Xinyu Xue, et al. “Hybridizing Energy Conversion and Storage in a Mechanical-to-Electrochemical Process for Self-Charging Power Cell.” Nano Letters. DOI: 10.1021/nl302879t

Journal reference: Nano Letters search and more info website

4.7 /5 (26 votes)

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User comments : 25

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88HUX88
4.6 / 5 (10) Aug 17, 2012
the first step in this technology
Shakescene21
5 / 5 (3) Aug 17, 2012
the first step in this technology


Pun intended? I hope there will be further steps along this technological path. I can see some problems with this technology, but some important applications as well.
El_Nose
3.9 / 5 (7) Aug 17, 2012
a step in the right direction
SatanLover
2.3 / 5 (12) Aug 17, 2012
The first step into zero point modules.
Deathclock
3 / 5 (12) Aug 17, 2012
That's one small step for man...
dschlink
1 / 5 (2) Aug 17, 2012
Add it to your iTrash and every time you sit on it, it dials someone and charges itself.
antialias_physorg
3.7 / 5 (6) Aug 17, 2012
Hey, at least it will be an excuse for people to go to the gym ("gotta go hit the treadmill, my multi-hyper-smart-phone ran out of juice again")

On second thought: Do fat people generate more juice with these? In that case going to the gym might be counterproductive in the long run. Better go get another ten happy-meals (and strap that generator to your a** ).
Deathclock
1.7 / 5 (6) Aug 17, 2012
someone doesn't like puns...
foolspoo
1 / 5 (2) Aug 17, 2012
keep downsizing cellphone batteries. integrate this into an insole cushion. woo! never plug in again (potentially)
wiyosaya
3.7 / 5 (3) Aug 17, 2012
The first step into zero point modules.

Not quite. This is not even a perpetual motion machine. It will run out of charge unless it is kept charged by mechanical motions.

It will be interesting to see if this is ever commercialized.
Tangent2
1 / 5 (2) Aug 17, 2012
I guess it is a step in the right direction if they use it for the right purposes. I hope I don't start seeing cell phones coming out that has a little pump/crank on the back of it that you can use to charge up the device again.. much like the crank start on the first few generations of cars.
Neurons_At_Work
not rated yet Aug 17, 2012
I guess it is a step in the right direction if they use it for the right purposes. I hope I don't start seeing cell phones coming out that has a little pump/crank on the back of it that you can use to charge up the device again.. much like the crank start on the first few generations of cars.


http://www.amazon...d_pt_0_0

These have been around for quite a while, though they are external to the phone, and take substantial time to do the job. Still, pretty neat idea...
packrat
1 / 5 (2) Aug 18, 2012
If the entire battery can be made flexible and have it charge by flexing there are many things this would work well for besides charging personal toys. Vibration powered machinery sensor systems is one spot. Fire, temp and humidity sensors in forests are another. Put them on small branches and the wind would keep them charged maybe.
DGBEACH
2 / 5 (4) Aug 18, 2012
Perhaps they could be embedded into car tires, and used to power the electric hub-motors attached to them :)
86daily
1 / 5 (6) Aug 18, 2012
Say why don't they tell us about what the KesheFoundation.com is inventing? Eternal batteries that never needs recharging. Check out the site and learn, and learn, and learn. There's 6000 CIA Patents that are kept secret on US books. These people had to patent them in Europe to bring these new technology to the world. Good Luck and God Bless.
tej1
3 / 5 (2) Aug 18, 2012
every step worth 0.65 mV . Every step counts.
Feldagast
1 / 5 (3) Aug 19, 2012
I thought of this exact thing 20 years ago, but in Army boots for powering night vision goggles.
Deathclock
2.6 / 5 (5) Aug 20, 2012
I thought of this exact thing 20 years ago, but in Army boots for powering night vision goggles.


People have been thinking of this for a century or more... thinking about it and figuring out how to do it are two completely different things.
matsci
3 / 5 (2) Aug 20, 2012
"Now for the first time, engineers have demonstrated that energy can be generated and stored in a single device that converts mechanical energy directly to chemical energy, bypassing the intermediate step of electricity generation."

This is not the first example of mechanical energy converted directly into chemical energy... Xudong Wang's group at UW-madison has already published a paper on that concept with experiments.

paper was titled : "Piezopotential-Driven Redox Reactions at the Surface of Piezoelectric Materials" Give credit where it is due please.
SatanLover
1 / 5 (2) Aug 25, 2012
The first step into zero point modules.

Not quite. This is not even a perpetual motion machine. It will run out of charge unless it is kept charged by mechanical motions.

It will be interesting to see if this is ever commercialized.

Have you even watched stargate? ZPMs are not perpetual motion machines but batteries that hold very large charge and very efficient recycling energy. in stargate universe they use a spaceship , fly it into the surface of a star to recharge it.
antialias_physorg
1 / 5 (2) Aug 25, 2012
I hate to tell you this...but this is real life: not the movies.
SatanLover
1 / 5 (1) Aug 25, 2012
I hate to tell you this...but this is real life: not the movies.


Same for star trek, yet it has inspired many great minds to realize it in real life.
get a grip dude, its not like i was serious.
antialias_physorg
1 / 5 (1) Aug 26, 2012
You were offended enough to downvote...so yeah: That means you were serious.

And just because personal communicators from star trek have come into being doesn't mean personal teleporters will.

It's a show. It uses pseudo-technical mumbo jumbo. Not every bit of such mumbo jumbo is meaningful enough to make it into real life products.
SatanLover
1 / 5 (2) Aug 26, 2012
You were offended enough to downvote...so yeah: That means you were serious.

And just because personal communicators from star trek have come into being doesn't mean personal teleporters will.

It's a show. It uses pseudo-technical mumbo jumbo. Not every bit of such mumbo jumbo is meaningful enough to make it into real life products.

I ma down-voting because you are making deal about nothing just as the other guy was without even knowing the concept of ZPMs.

It might be "psuedo-technical" mumbo jumbo but like i said it has shaped our world more than you think and it is still to date used for many inspirations.

And that is not just a "communicator".
antialias_physorg
1 / 5 (1) Aug 27, 2012
I ma down-voting because you are making deal about nothing just as the other guy was without even knowing the concept of ZPMs.

Believe it or not: I, too, have watched Stargate (probably most episodes, anyway). And there are no 'details' in there - just Star Trek mumbo-jumbo (which I do enjoy...it's one of the reasons why I watch shows like that. But that doesn't change the fact that it's mumbo-jumbo).