Liquid Battery Offers Promising Solar Energy Storage Technique

Mar 06, 2009 by Lisa Zyga weblog
The all-liquid battery: discharged (left), charging (middle), and charged (right). Molten magnesium (blue) is the top electrode, in the middle is the electrolyte (green), and molten antimony (yellow) is the bottom electrode. Image credit: Arthur Mount.

(PhysOrg.com) -- One of the biggest challenges currently facing large-scale solar energy technology is finding an effective way to store the energy, which is essential for using the electricity at night or on cloudy days.

Recently, researchers from MIT have designed a new kind of battery that, unlike conventional batteries, is made of all-liquid active materials. Donald Sadoway, a materials chemistry professor at MIT, and his team have fabricated prototypes of the liquid battery, and have demonstrated that the materials can quickly absorb large amounts of electricity, as required for solar energy storage.

"No one had been able to get their arms around the problem of energy storage on a massive scale for the power grid," says Sadoway. "We're literally looking at a battery capable of storing the grid."

The battery consists of three layers of liquids: two electrode liquids on the top and bottom (electrodes are usually solid in conventional batteries), and an electrolyte liquid in the middle. In the researchers' first prototype, the electrodes were molten metals - magnesium on the top and antimony on the bottom - while the electrolyte was a molten salt such as sodium sulfide. In later prototypes, the researchers investigated using other materials for improved performance.

Since each liquid has a different density, the liquids automatically form the three distinct layers. When charging, the solid container holding the liquids collects electrons from exterior solar panels or another power supply, and later, for discharging, the container carries the electrons away to the electrical grid to be used as electricity.

As electrons flow into the battery cell, magnesium ions in the electrolyte gain electrons and form magnesium metal, rising to form the upper molten magnesium electrode. At the same time, antimony ions in the electrolyte lose electrons, and sink to form the lower molten antimony electrode. At this point, the battery is fully charged, since the battery has thick electrode layers and a small layer of electrolyte. To discharge the electrical current, the process is reversed, and the metal atoms become ions again.

As Sadoway explained in a recent article in MIT's Technology Review, the liquid battery is a promising candidate for solar energy storage for several reasons. For one thing, it costs less than a third of the cost of today's batteries, since the materials are inexpensive and the design allows for simple manufacturing. Further, the liquid battery has a longer lifetime than conventional batteries, since there are no solid active materials to degrade. The liquid battery is also useful in a wide range of locations compared with other proposed solar storage methods, such as pumping water. Most importantly, the liquid battery's electrodes can operate at electrical currents tens of times higher than any previous battery, making it capable of quickly absorbing large amounts of electricity.

The researchers hope to commercialize the liquid battery in the next five years. As Sadoway explained, connecting the batteries into a giant battery pack to supply electricity for New York City would require nearly 60,000 square meters of land. Such a battery pack could store energy from enormous solar farms, which would replace today's power plants and transmission lines as they become old.

via: Technology Review

© 2009 PhysOrg.com

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User comments : 13

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david_42
5 / 5 (2) Mar 06, 2009
Liquid sodium-sulfur (NaS) batteries have been in production since 2002. American Electric Power (AEP), has been using a 1.2 megawatt NaS battery in Charleston, W.Va for the last three years. What advantages does the new chemistry hold over NaS?
vivcollins
4 / 5 (2) Mar 06, 2009
A fire could be an interesting experience but the idea certainly seems worth developing
sterlingda
3 / 5 (2) Mar 06, 2009
My associate from the New Energy Congress, Robert Pritchett, wrote:

Antimony is toxic and "rare" - http://en.wikiped...Antimony

Have you ever seen a magnesium motor block catch fire? It is highly flammable in liquid form.
http://en.wikiped...agnesium

These guys have obviously not considered the safety issues regarding these metals and a magnesium battery around sparks.
ryuuguu
not rated yet Mar 06, 2009
In the original MIT article at the end it mentions that the metals and elctrolyte used have been changed, but they are not publishng the new components yet as they looking at going comercial. So some of the above concerns may or may not be valid.

I am not sure but an advtage of this battery type over NaS or VRB (Redox flow (Vanadium type)) maybe simplicty of deisgn/manufaturing and maintence. I think they are hoping for lower cost in large instalation.

As is normal fro press releases there is something potential usefull here but it is over stated by the inventors.
E_L_Earnhardt
1 / 5 (2) Mar 06, 2009
It is a good idea and I hope it is further developed! Each atom of a liquid can store many electrons. Yes it's been done before but the "devil is in the discharge!" Sloshing around in a vehicle may require new dialectic materials. though
glaubel
4 / 5 (1) Mar 07, 2009
Well more power to their arm, but solar thermal as produced on industrial scale by ausra.com appears to be coming to grips with by-passing chemical storage.
Icester
not rated yet Mar 07, 2009
60,000 sq meters is only 803ft x 803ft. That's pretty small for a city - especially the size of New York. This is an interesting idea for a stationary battery. Storage has always been the crippling factor to alternative energy.
docatomic
not rated yet Mar 08, 2009
It is a good idea and I hope it is further developed! Each atom of a liquid can store many electrons. Yes it's been done before but the "devil is in the discharge!" Sloshing around in a vehicle may require new dialectic materials. though


Agree. It/s all nice and horribly toxic and everything, and although I don't know what the cell operating temprange would be it does sound as though the fire potential could be enormous, and the whole deal is sufficiently simple for any old backyard 'inventor'-type kook to both understand and attempt to implement, so yeah - I can see it. As you've implied, it's not really suited for vehicular storage, unfortunately - but that won't prevent some goof from trying it at home anyway. Magnesium rod is readily available, and antimony may be gleaned from dead car batteries... ooh! So slow and chemically poisonous and everything! Mmmmm.... shall we scrounge some carbon rods from more dead batteries for electrodes, or should we just buy some from the local welding supply?

Thanks!
etabeta
5 / 5 (1) Mar 08, 2009
I wouldn't want to be anywhere near a facility using these batteries. Molten magnesium will spontaneously catch fire when exposed to air, and antimony is extremely toxic. If for any reason a battery's container should break and let air in, the resulting fire would be very difficult to extinguish. Magnesium will even burn in pure nitrogen and carbon dioxide!
Plus I want to add another point; how much energy would be needed to keep a battery at operating temperature? Magnesium melts at 650 C and antimony at 630 C, so the whole battery must be kept at least at a slightly higher temperature. What materials would be used to electrically and thermally insulate this?
deatopmg
1 / 5 (1) Mar 08, 2009
This is a great idea. Energy density is high and the temperature issue is not insurmountable. NASA developed a liquid energy storage system in the 80's using solutions of Fe(II)/Fe(III) and Cr(III)/Cr(II). It never went anywhere because of potential release of Cr(II) or (III) that might be oxidized to highly toxic Cr(VI) in the environment and for other reasons. Hopefully, this liquid battery will be developed further possibly using lower melting eutectics.

The environmental and temperature issues here have relatively simple engineering solutions. The fire issue with magnesium (like gasoline, NOT spontaneously combustible in air, N2, or CO2 when molten)(or another metal) has simple engineering solutions. Remember, people drive around every day risking an accident and fire with the gasoline in a plastic tank their cars. This is proposed as a stationary system. Massive gasoline and natural gas storage tanks can be found in every metropolitan area. How often do they leak and catch fire?
TJ_alberta
1 / 5 (1) Mar 09, 2009
"Magnesium will even burn in pure nitrogen and carbon dioxide!"
Etabeta: You just wrote this to see if someone would go up in flames.
AtlasGemini
not rated yet Mar 26, 2009
So what would happen if you were to shake a fully charged battery? That might discharge the battery "all at the same time." Kaboom! Interesting idea though.
zilqarneyn
not rated yet Sep 06, 2009
People know how to have risk-reduction. For example, for forests not to all burn together, they have gaps. Likewise, the battery would be in zillions of battery-compartments, presumably. Likely to fill and discharge cell-by-cell, individually.

Furthermore, with that modularity, the cells of all NYC need not be together -- unless they would think that to cut out of the fixed costs of the containing facility (concrete/etc walls to contain the worst-case).




BTW, I'm not chemistry expert, but reductions to contain the faults within cells, is a well-known strategy, in computer science, too. That is, as opposed to macros which are not well-isolated ( http://mid80.net/...kruh.htm ). If reductions in formal-nets would interest you,
http://mid80.net/...duce.htm

I had thought that for safety (guarding), too. For example, think a mediator as a valve, in
http://zilqarneyn...ator.htm

I had thought reductions as good for not only explosives-containment, but for containing environmental side-effects, too. That is, if your neighbor experiments with new biotech (or, how @docatomic is reflecting, weekend chemists might hack batteries), you would not like the mess to visit you, too. Reduction, is a safety wall, that is worth thinking, when possible to block some chemicals.