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Liquid-like solid could boost battery life

Liquid-like solid could boost battery life

The copper-selenium compound analysed by the team acts as both a liquid and a solid, making it an incredibly efficient material for thermoelectric systems.

Researchers from the Chinese Academy of Science's Shanghai Institute of Ceramics, Brookhaven National Laboratory, the University of Michigan and the California Institute of Technology (Caltech) have released details of a liquid-like compound they claim could lead to more efficient thermoelectric devices.

Thermoelectric materials turn heat into electricity, and are seeing increasing use in waste energy reclamation projects. Using a thermoelectric material, it's possible to turn wasted heat from industrial facilities or vehicle engines into useful electricity.

The technology works by exploiting the temperature differential between its two ends. Electrons in the hot end diffuse to the cold end, producing a small but useful electric current. While current thermoelectric systems are typically bulky, the technology shows real promise for extending battery life in laptops and even smartphones by harnessing wasted heat - or even the heat of the user's hand - to generate a top-up current for the battery.

A key milestone in achieving this is increasing the efficiency of the thermoelectric material, which will result in the creation of smaller thermoelectric devices. It's this goal that the team at Caltech had in mind while experimenting with new compounds - including their most promising candidate yet, a mixture of copper and selenium which exhibits liquid-like behaviours despite being a solid.

'It's like a wet sponge,' explained Jeff Snyder, a faculty associate in applied physics and materials science at Caltech and a research team member, at the announcement. 'If you have a sponge with very fine pores in it, it looks and acts like a solid. But inside, the water molecules are diffusing just as fast as they would if they were a regular liquid. That's how I imagine this material works. It has a solid framework of selenium atoms, but the copper atoms are diffusing around as fast as they would in a liquid.'

The new compound features a mixture of crystalline and amorphous properties, allowing electrons to flow easily while inhibiting the transmission of the vibrations which carry heat. Using the crystal structure of selenium with free-flowing copper atoms which act like a liquid, the team created a compound with a thermoelectric figure of merit of 1.5 at 1000 degrees Kelvin - one of the highest values of any mass-producible material, the team claims.

A compound of copper and selenium isn't new: back in 1970 NASA was using a similar material in the construction of spacecraft power systems. Its liquid-like nature, however, was poorly understood and made it difficult to work with. The team's new research sheds light on the reasons for its high figure of merit, while paving the way for exploitation of other liquid-like thermoelectric materials in the future.

The team's research has been published in the Nature Materials journal.

13 Comments

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west 27th March 2012, 13:04 Quote
"Electrons in the hot end diffuse to the cold end, producing a small but useful electric current."
"allowing electrons to flow easily while inhibiting..."

You mean the copper atoms are diffusing. Electrons don't defuse according to temperature, they "defuse" according to electric potential.
Jack_Pepsi 27th March 2012, 13:11 Quote
Quote:
Liquid-like solid could boost battery life

What, custard?

o.O
Gareth Halfacree 27th March 2012, 13:25 Quote
Quote:
Originally Posted by west
"Electrons in the hot end diffuse to the cold end, producing a small but useful electric current."
"allowing electrons to flow easily while inhibiting..."

You mean the copper atoms are diffusing. Electrons don't defuse according to temperature, they "defuse" according to electric potential.
Don't look at me - I'm quoting Caltech directly there. Also: diffuse != defuse.
fallenphoenix 27th March 2012, 14:26 Quote
Quote:
Originally Posted by Jack_Pepsi
Quote:
Liquid-like solid could boost battery life

What, custard?

o.O

Too much custard makes me sluggish and slow to respond; hopefully the same won't be true if they apply this tech to processors.
dunx 27th March 2012, 16:55 Quote
No such thing as too much custard... IMHO

But I would avoid OD-ing on selenium myself...

dunx
Fused 27th March 2012, 23:11 Quote
Quote:
Originally Posted by west
"Electrons in the hot end diffuse to the cold end, producing a small but useful electric current."
"allowing electrons to flow easily while inhibiting..."

You mean the copper atoms are diffusing. Electrons don't defuse according to temperature, they "defuse" according to electric potential.

I believe if I have understood this correctly the electrons are diffusing or moving from the hot to cold end and this creates an electric potential hence how it generates electricity.

I doubt the 'liquid' copper atoms actually move very much. I believe what they are refering to is that they are not rigid which reduces the amount of energy lost to vibrations normallytravelling through a solid which.

I am sure the answer is in there somewhere. At the end of the day I am a chemist, hunt down a physicist for a long and complicated answer
west 27th March 2012, 23:50 Quote
@Fused
"I believe if I have understood this correctly the electrons are diffusing or moving from the hot to cold end and this creates an electric potential hence how it generates electricity."

Electrons don't diffuse according to temperature. Heat one side of a wire up and see if the electrons move to one end (spoiler: they don't).
One of the researchers explicitly said "...the copper atoms are diffusing..."

When one side of this material is heated the copper atoms (at least some of which will be charged) are free to diffuse to the cold end of the material. The electrons (presumably any free electrons) themselves don't care about the temperature.

Copper atoms diffuse through the material because they are getting knocked around more at one and than the other (thermal diffusion). Electrons don't knock each other around and therefore cannot diffuse (in a thermal manner that is, they will diffuse by repelling each other according to the electrical potential of whatever material they are in).

The movement of these charged copper atoms from one end to the other creates the overall charge.
west 28th March 2012, 04:15 Quote
to elaborate further:

the charged copper ions move within the selenium crystal lattice (so it is theorized) which creates a voltage difference, i.e. not an even distribution of charged particles (copper ions in this case).

The trick to Thermoelectric materials is that they conduct electricity, don't conduct heat well, and have some ability to get charged particles to move around within them.

When you apply a current to a thermoelectric material the charged particles within the material feel the force of the magnetic field (created by the current going through the material) and are pushed along the field lines (until they hit the edge of the material). Since these charge carriers (the copper ions) now find themselves crowded in one end of the material they end up bouncing around off each other more and more (this is heat).

When you remove the current the magnetic field dissipates and the charge carriers (copper ions) bounce off of each other into less populated regions of the material until they are (mostly) evenly spread out (the material comes to a stable temperature - aka diffusion).

If, for whatever reason this material became warmer on one side that another the copper ions in the warm side will start colliding with other copper ions harder than the copper at the cold end of the material (they are warmer and have more energy). This results in a general crowding of copper ions at the cold end of the material, at least until all of the ions reach the same temperature, at which time they will spread out to an even distribution again. The act of these charge particles moving to and crowding one end of the material creates a voltage difference for the overall material (which can be exploited and used to power things).

Since they only will crowd together in the cold end of the material you will only get power out of the device when one end is hotter than the other, so when you slap it on your laptop it will only produce energy while it heats up, when its hot it will stop producing energy.

So by these actions the material is able to produce a temperature gradient when current is applied and conversely is able to produce current when a temperature gradient exists.

This tech is nothing new, its just that the material this article is talking about has a very good ability to allow charge carriers to travel within it, while inhibiting thermal conductivity (because the longer the temperature gradient lasts the longer the material will produce a voltage difference).

I guess this post is just to clarify that electrons are not involved in any direct way here, as suggested above.
Blarte 28th March 2012, 09:01 Quote
Personally I find this type of technology fascinating
The potential for ever lasting energy from one initial source is getting ever closer
Converting and harnessing and then reusing the types of energy given off as a waste product off one source to fuel another. Sublime
Omnituens 28th March 2012, 18:53 Quote
Quote:
Originally Posted by Blarte
The potential for ever lasting energy from one initial source is getting ever closer
http://www.youtube.com/watch?v=Xy0UBpagsu8&t=0m16s
west 28th March 2012, 19:05 Quote
@ Omnituens

ha
technogiant 28th March 2012, 19:35 Quote
Or conversely to the copper ions migrating it could be that at the hot end more electrons become "free" from the copper atoms due the the heat energy, the mutual repulsion between the electrons causes them to migrate toward the colder end and so set up an electo potential between the hot and cold ends, the cold end becoming negative, the copper ions remain fixed in place in the selenium lattice.
jon 29th March 2012, 05:03 Quote
Quote:
Originally Posted by fallenphoenix
Quote:
Originally Posted by Jack_Pepsi
Quote:
Liquid-like solid could boost battery life

What, custard?

o.O

Too much custard makes me sluggish and slow to respond; hopefully the same won't be true if they apply this tech to processors.

AMD should name their next chip "Custard" ... ;)
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