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New microbatteries combine the advantages of lithium-ion batteries and supercapacitors

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May 8, 2013

Artist's conception of the interlocking 3D battery electrodes exchanging ions (Image: Univ...

Artist's conception of the interlocking 3D battery electrodes exchanging ions (Image: University of Illinois)

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There can be little doubt that people love their mobile devices. But, by leaving them high and dry at the most inconvenient of times, this love generally doesn't extend to the batteries that power said devices. New microbatteries developed by researchers at the University of Illinois at Urbana-Champaign (UIUC) that measure just a few millimeters in size, yet are powerful enough to power a mobile phone may be more likely to inspire a little love.

A battery's ability to store and provide energy faces the fundamental limitation that its energy source is chemical in nature. Conventional battery designs are essentially a pair of plates made of different metals separated by an electrolyte that allows movement of electrons and ions between them.

This construction leads to three significant limitations that affect most batteries:
  • Energy capacity is related to the physical size of the battery and the energy of the chemical reactions powering it.
  • Power capacity is roughly determined by the internal resistance of the battery, so plates with larger surface area can deliver more power.
  • Given a multi-layer battery in some form of packaging, it is at times difficult for the heat generated by the inner cells to escape.

These factors place remarkably tight limits on the performance of practical batteries for mobile devices.

This graph compares the power density and energy density of various types of batteries - t...

At present, the common rechargeable battery which supplies the most energy is the lithium-ion battery, with an energy density of about 300 mWh/cc (milliwatt-hours per cubic centimeter). For comparison, burning one cubic centimeter of gasoline produces 9700 mWh/cc. The power density of such a battery, meaning the rate at which the energy can be delivered, is about 100 mW/cc.

At times, more power is more important than more energy storage. For example, powering a 100-kW electric car with conventional lithium-ion batteries would require a cubic meter of batteries weighing roughly 2.5 metric tonnes (2.75 tons). This is why so much engineering effort is going into the design of lithium-ion battery packs for electric vehicles.

When the need for power is paramount, engineers often turn to supercapacitors. These electric double-layer capacitors offer enormously fast delivery of energy (up to about 40 W/cc – hundreds of times faster than conventional lithium-ion batteries), but suffer from a rather small energy capacity (only a few mW-hr/cc).

Microstructure of the Illinois interdigitated 3D battery (Image: UIUC)

William King's team at the University of Illinois at Urbana-Champaign sought to achieve a more favorable balance between energy and power density. To provide good energy density they used a lithium-ion chemistry for their batteries, and to obtain large power density they maximized surface area by using electrodes with a highly porous 3D structure arranged in the form of interlocking strips with a separation of about a millimeter.

Microscopic views of the nanostructure and microstructure of the Illinois interdigitated 3...

With this structure, the Illinois 3D microbatteries provide more power density (up to about 100 W/cc) than even the best supercapacitors and nearly as much energy density (up to 15 mW-hr/cc) as conventional lithium-ion batteries: factors that could drive new small-scale battery applications in radio communications, medical devices, computer hardware, and compact electronics.

The team's 3D microbattery design is particularly suited to physically small circuits, for example an implanted heart pacemaker and defibrillator, where a comparatively large battery must currently be used to supply large spikes of current when needed. Such spikes could easily be delivered by a tiny 3D microbattery. In addition, the new batteries can be charged as fast as they discharge, meaning recharge times of under a minute are possible, a quality that largely offsets the limited energy storage offered by any tiny battery.

"Now we can think outside of the box," says James Pikul, lead author of the associated paper, published in Nature. "It's a new enabling technology. It's not a progressive improvement over previous technologies; it breaks the normal paradigms of energy sources. It's allowing us to do different, new things."

Source: University of Illinois

About the Author
Brian Dodson From an early age Brian wanted to become a scientist. He did, earning a Ph.D. in physics and embarking on an R&D career which has recently broken the 40th anniversary. What he didn't expect was that along the way he would become a patent agent, a rocket scientist, a gourmet cook, a biotech entrepreneur, an opera tenor and a science writer.   All articles by Brian Dodson
9 Comments

Great news. This is sure to make quite a revolution in design of technology. What isn't clear from the article is weather these micro-cells can actually power a mobile for longer than current avg smartphone batteries ie 2 days at max. Or does it mean that these micro-cells will require more frequent and short re-charges?

Aurovrata
9th May, 2013 @ 02:56 am PDT

Another thing to know would be how much would it cost to produce? Would it be easy to manufacture which would mean a low cost? IMO; I think this is really good news for those with portable electronics. Perhaps it could be upscaled so one can smaller batteries for electric vehicles? Inquiring minds want to know. I think it has a lot of potential.

BigWarpGuy
9th May, 2013 @ 05:42 am PDT

This is old news. This was reported early April. Several commenters notes errors in the reported densities by comparison. The energy density numbers are mediocre at best. So while using this as a cell phone battery would allow you to charge it in minute or so it would only power the device for 8% as long. Meaning your all day battery would become a 2hour battery at best. There are ultra capacitors that are fairly cheap that could provide similar performance.

As far as energy densities the statement of “15mWh/cc” is not much assuming my math is correct. I saw this math done on another blog but can not access it at the moment and I apologize for not being able to quote the source post.

Lithium batteries are quoted around 4.32MJ/L with rechargeableLiIon around 2.63MJ/L.

If:

1L=1000CC

1KWh=3.6MJ; 1Wh=3.6KJ; 1mWh=3.6J

Lithium Batteries have an energy density of 4.32KJ/cc or 1200mWh/cc; using the lower end rechargeable Li-Ion battery number of 2.63MJ/L that still works out to 730mWh/cc. This micro-battery has an energy density of 15mWh/cc or 3.6J*15mWh=54J/cc.

So to recap 15mWh/cc isn't really very much energy density and makes the statement about comparable density laughable. These are scientists, at least theoretically, so they should know these conversions. Now there is a great deal of confusion between energy density versus power density. This device has a high power density but a low energy density. So would compare better to a capacitor than to a battery.

VirtualGathis
9th May, 2013 @ 07:30 am PDT

I like it and wonder if the power density could be brought up by incorporating the battery/capacitor design into the body , interior and chassis of automobiles, much like a honeycomb core?

Mirmillion
9th May, 2013 @ 07:34 am PDT

i would add a coolant system to the battery itself.

Hahn Jackson
9th May, 2013 @ 09:44 am PDT

What's the difference between this and a Batcap -

http://www.batcap.net/

streetdrivenquad
9th May, 2013 @ 11:47 am PDT

I do not understand why there is no discussion of scaling this up to a size that could be used in electric cars. It seems to me that this would be a more pressing need than microcircuits.

David Charles Leithauser
9th May, 2013 @ 03:07 pm PDT

@streetdrivenquad: That website looks like a scammer site. At the very least they have extremely vague details about their products and the person who built the site has a very poor understanding of how their product works. They talk about the weight and amperage, but never the amp hours or joules stored. I'd put money on these only supplying the "9600 amps" for a minute or so which would put them below lead acid for energy density. That is just a wild guess since they never provide a useful datasheet. Before I bought those things I'd make them provide the joules per liter and life cycle count. If it has a very low joules per liter compare them to a good ultra capacitor like these: http://www.maxwell.com/ultracapacitors/

VirtualGathis
9th May, 2013 @ 05:42 pm PDT

can this work in cars, trucks, planes??

Stephen N Russell
9th May, 2013 @ 06:02 pm PDT
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