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It may not be the first material that springs to mind when thinking about batteries, but experts have created a highly-conductive film using clay. 

Called 'conductive MXene clay', the scientists found that not only does it have the same conductivity as many metals, it can also be easily moulded into a variety of shapes and sizes.

This makes it ideal for being fitted inside curved smartwatches, tiny sensors and other unusually-shaped devices.

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Called 'conductive MXene clay', the scientists found that not only does it have the same conductivity as many metals, it can also be easily moulded. This makes it ideal for being fitted inside curved smartwatches, tiny sensors and other unusually-shaped devices. The material is pictured completing a circuit to power a fan

Experts from Drexel University's College of Engineering, who designed the clay, said the breakthrough represents a turn away from the complicated and expensive processing of current lithium-ion batteries and supercapacitors.  

'Both the physical properties of the clay, as well as its performance, seem to make it an exceptionally viable candidate for use in energy storage devices,' said lead researcher Professor Yury Gogotsi.

'The procedure to make the clay also uses much safer, readily available ingredients than the ones we used to produce MXene electrodes in the past.'

The discovery was made when Michael Ghidiu, a doctoral student in the Department of Materials Science Engineering at Drexel, was testing a new method for making MXenes.

MXenes are two-dimensional materials, invented at Drexel, designed to be used in next-generation batteries and supercapacitors.

Phones of the future could be powered by PLAY-DOH

MXenes are two-dimensional materials designed to be used in next-generation batteries. The original process uses toxic hydrofluoric acid, but the chemists instead used a fluoride salt and hydrochloric acid to take aluminum out of a titanium-based, layered ceramic material called a MAX phase (process pictured)

The original process uses toxic hydrofluoric acid, but Mr Ghidiu instead used a fluoride salt and hydrochloric acid to take aluminum out of a titanium-based, layered ceramic material called a MAX phase.

These two ingredients are much safer to handle than hydrofluoric acid, and turned the MAX phase to a pile of black particles.

To stop the reaction and remove any residual chemicals, Mr Ghidiu washed the material in water.

But, rather than finding the layered MXene particles, he discovered that the sediment absorbed the water to form a clay-like material.

HOW SIGNIFICANT IS CONDUCTIVE CLAY?

An electron microscopic study of the clay particles in water revealed it is made up of single layers of MXene about a nanometre - just a few atoms - thick. This thin structure indicates that researchers are likely to find the clay has many electronic and optical properties as they continue to learn more about it

An electron microscopic study of the clay particles in water revealed that the clay is made up of single layers of MXene about one nanometre - just a few atoms - thick.

This atomically thin structure indicates that researchers are likely to find the clay has many electronic and optical properties as they continue to learn more about it.

Investigations of the clay's performance found the clay's ability to store an electrical charge is three times that reported for MXenes produced by hydrofluoric acid.

This means it could find uses in the batteries that power phones and start cars, or even in a supercapacitor that could one day help renewable energy sources fit into a regional power grid.

Despite it being a 'very first generation' material, the experts said the clay is already showing a higher charge storage, per unit of volume, than most other materials.

It also doesn't lose any of this so-called capacitance even after more than 10,000 charge and discharge cycles.

Elsewhere, the clay could also be watered down into a conductive paint that hardens within a few minutes, while still retaining its conductive properties.

'As anybody who has played with mud can attest, clay is water-loving,' fellow author Professor Michel Barsoum said.

'Clay is also layered, and when hydrated, the water molecules slide between the layers and render it plastic that in turn can be readily shaped into complex shapes.

'The same happens here; when we add water to MXene, water penetrates between the layers and endows the resulting material with plasticity and moldability.' 

The salt and acid are much safer to handle than toxic chemicals used previously, and created a pile of black particles. To stop the reaction and remove any residual chemicals, the researchers washed the material in water. The sediment absorbed the water to form a clay-like material that could be rolled (illustrated)

One of the first tests the team performed on the clay was to see if it could be pressed into a thin layer (pictured) while retaining its conductive properties. The clay was found to store an electrical charge three times that reported for other MXenes and didn't lose this ability even after 10,000 charge and discharge cycles

'What we discovered is a conductive two-dimensional layered material that also loves water.

'The fact that we can now roll our electrodes rapidly and efficiently, and not have to use binders and conductive additives renders this material quite attractive from a mass production point of view.' 

Mr Ghidu admitted he was just hoping for a safer, less expensive way to make MXenes, and didn't expect anything like this.

The clay has been compared to Play-doh (pictured) as well as chocolate chip cookie dough

Now the researchers can simply wash the resulting material and roll the resultant clay into films of various thicknesses.

One of the first tests the team performed on the clay was to see if it could be pressed into a thin layer while retaining its conductive properties.

The clay was found to store an electrical charge three times that reported for other MXenes and didn't lose this ability even after 10,000 charge and discharge cycles. 

'Being able to roll clay into a film is quite a contrast in production time, safety and cost when compared to the two most common practices for making electrode materials,' Mr Ghidiu continued.

'I would say the most important benefit to the new method - besides its increased capacitance - is that we can now make an electrode ready-to-go in about 15 minutes, whereas the total process before from the same starting point would be on the order of a day.'

Plus, being able to make conductive clay using common chemistry class items is the 'materials equivalent of making a chocolate chip cookie - everybody has these ingredients in the pantry', explained Professor Barsoum.

This work was supported by the Ceramics Program of the National Science Foundation and by the U.S. Department of Energy's FIRST Energy Frontier Research Centre.

The findings are published in the journal Nature.