Magnetically controlled battery could store energy for power grids

October 19, 2015 by Lisa Zyga feature
Images of the magnetic fluid containing superparamagnetic nanoparticles that move with an applied magnetic field. (e) shows the color difference between a pure polysulfide solution without magnetic nanoparticles (left) and a biphasic magnetic polysulfide solution (right) with a high and low concentration of polysulfide. Credit: Li, et al. ©2015 American Chemical Society

(Phys.org)—Scientists have built a battery containing a magnetic fluid that can be moved in any direction by applying a magnetic field. The magnetically controlled battery concept could be especially useful for flow batteries, where it could eliminate the need for the pumps that are typically required for moving the electrolyte from an external storage tank to the inside of a power stack to provide electricity. Flow batteries are being actively researched as large-scale energy storage devices for power grids, where they could store energy captured by intermittent alternative energy sources such as wind and solar.

The researchers, led by Yi Cui, Professor at Stanford University, have published a paper on the new magnetically controlled battery in a recent issue of Nano Letters.

"The greatest significance of our work lies in the innovative idea of using a magnetic field to control and enhance the mass and electron transport in a battery system," lead author Weiyang Li, previously at Stanford University and now at Dartmouth College, told Phys.org.

The key to the new battery design is the composition of the catholyte (the part of the electrolyte near the cathode), which contains lithium polysulfide mixed with magnetic . By applying a magnetic field, the researchers could pull the nanoparticle colloids in a desired direction, and due to strong binding between the iron oxide nanoparticles and the lithium polysulfide, the lithium polysulfide could be pulled along with the magnetic particles. This creates a biphasic magnetic solution, with a high concentration of polysulfide on one side of the container and a low concentration on the other.

Magnetically moving the electrochemically active materials in the electrolyte in this way would be very useful for flow batteries because the goal in these batteries is to move the active molecules so that they are in close contact with a current collector. This allows a greater number of the active materials to be used, resulting in a higher energy density for the battery.

Tests showed that the new magnetic fluid containing the nanoparticles leads to improvements in several areas compared to an electrolyte without the nanoparticles, including a higher capacity (350 mAh/g vs. 126 mAh/g), which corresponds to a high volumetric energy density of 66 Wh/L, as well as better capacity retention and efficiency. The researchers attribute these improvements to the magnetic field's ability to transport more polysulfide molecules and to minimize the undesirable "shuttle effect"—which occurs when the polysulfide molecules shuttle to the anode—because the magnetic nanoparticles can anchor the polysulfide molecules at the cathode.

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The researchers demonstrate that the magnetic fluid forms a concentrated polysulfide phase that moves in the direction of a magnet. Credit: Li, et al. ©2015 American Chemical Society

In the future, if the -control concept could replace the need for pumps in flow batteries, it would eliminate parasitic pumping losses, which in turn could significantly increase the efficiency and lower the cost of these .

"Our idea can be potentially applied to a wide range of flow battery systems, not only confined to the lithium polysulfide in our paper," Cui said. "We are planning to extend our idea to other systems for electric grids, portable electronics, and transportation, as well."

Explore further: New lithium ion battery strategy offers more energy, longer life cycle

More information: Weiyang Li, et al. "Magnetic Field-Controlled Lithium Polysulfide Semiliquid Battery with Ferrofluidic Properties." Nano Letters. DOI: 10.1021/acs.nanolett.5b02818

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6 comments

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gkam
1 / 5 (4) Oct 19, 2015
Good-bye coal and nukes. In ten years, our electrical systems will be much different,with more diversification and distribution of sources.

The biggest problem is control of it all, with the required security. People cannot just add stuff to the grid, it has to be programmed and allowed as needed. If the corporations and government cannot keep anything secure now, how can we do this?
ProcrastinationAccountNumber3659
1 / 5 (2) Oct 19, 2015
In the future, if the magnetic-field-control concept could replace the need for pumps in flow batteries, it would eliminate parasitic pumping losses, which in turn could significantly increase the efficiency and lower the cost of these energy storage systems.


Magnetic fields are usually generated with electromagnets which requires a fair amount of current. I have a hard time seeing this reducing pumping losses much if at all. They need one that is controlled with an electric field.

@gkam Security is an issue in a whole slew of industries already. We need a larger push by governments to beef up security to the level that only large countries could be able to compromise it.

gkam
2.3 / 5 (6) Oct 19, 2015
PAN3659, I do not have much hope in the near term, given this:

http://www.cnn.co...dex.html

And magnetic fields are used to drive the motors for pumps, too, but add the mechanical losses not encountered in the magnetic flow units. It will be interesting to see how it develops.
ProcrastinationAccountNumber3659
1 / 5 (2) Oct 19, 2015
@gkam: That is extremely poor judgement he exercised and could have been easily avoided. I guess we need a push on both increased security and training people on common sense methods to keep information secure.

You do make a point that there should still be less loss than the mechanical approach.
gkam
1.8 / 5 (5) Oct 19, 2015
"You do make a point that there should still be less loss than the mechanical approach."

It's a guess.
antialias_physorg
not rated yet Oct 20, 2015
Magnetic fields are usually generated with electromagnets which requires a fair amount of current. I have a hard time seeing this reducing pumping losses much if at all.

Well, it requires no moving parts - which is always a big plus given the large-ish installations we're talking about when considering nation-size backup power capability.
(There's also an undeniable sort of elegance to doing stuff in a "look, ma - no hands" kinda way)

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