Salt can make energy storage devices better: study

Common table salt may prove to be a key ingredient in making better materials for energy
storage devices, according to new research.

Using salt crystals as a template to grow thin sheets of conductive metal oxides make the materials turn out larger and more chemically pure - which makes them better suited for gathering ions and storing energy, researchers said.

"The challenge of producing a metal oxide that reaches theoretical performance values is that the methods for making it inherently limit its size and often foul its chemical purity, which makes it fall short of predicted energy storage performance," said Jun Zhou from Huazhong University of Science and Technology (HUST) in China.

"Our research reveals a way to grow stable oxide sheets with less fouling that are on the order of several hundreds of times larger than the ones that are currently being fabricated," said Zhou.

In an energy storage device - a battery or a capacitor, for example - energy is contained in the chemical transfer of ions from an electrolyte solution to thin layers of conductive materials, they said.

As these devices evolve, they are becoming smaller and capable of holding an electric charge for longer periods of time without needing a recharge.

The reason for their improvement is that researchers are fabricating materials that are better equipped, structurally and chemically, for collecting and disbursing ions. Using salt crystals as a substrate for growing the crystals lets them spread out and form a larger sheet of oxide material, researchers said.

"This method of synthesis, called 'templating' - where we use a sacrificial material as a substrate for growing a crystal - is used to create a certain shape or structure," said Yury Gogotsi from Drexel University in the US.

"The trick in this work is that the crystal structure of salt must match the crystal structure of the oxide, otherwise it will form an amorphous film of oxide rather than a thing, strong and stable nanocrystal," said Drexel.

"This is the key finding of our research - it means that different salts must be used to produce different oxides," he added.

Researchers have used a variety of chemicals, compounds, polymers and objects as growth templates for nanomaterials.  But this discovery shows the importance of matching a template to the structure of the material being grown.

Salt crystals turn out to be the perfect substrate for growing oxide sheets of magnesium, molybdenum and tungsten, researchers said.

The precursor solution coats the sides of the salt crystals as the oxides begin to form, they said.

The findings were published in the journal Nature Communications.
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