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Transparent battery powers the way
to translucent devices
Researchers fabricate electrodes that are too small to see.
Flexible, transparent lithium-ion batteries have been made by a team of
researchers at Stanford University in California, a technological leap that
could spawn see-through electronic gadgets such as translucent iPads.
Many electronic components can be fabricated to be transparent, but so
far this hasn't been possible for the power supply, says materials scientist
Yi Cui, who led the work, which is published today in Proceedings of the
National Academy of Sciences.
A transparent, flexible battery could help
reduce the size of electronic gadgets.
Batteries are normally made up of a pair of electrodes separated by an
electrolytic solution, with something to conduct the current to an external
circuit, and packaging to hold it all together. But only the electrolyte is
naturally transparent, says Cui. And to make matters worse, he says,
these components need to be piled on top of each other, which means all
of them must be clear for the device to be transparent.
Nothing to see here
While transparent materials can easily be found for the casing and
conductors, the electrodes tend to be naturally opaque. Cui's solution was
to make the components so small that they are beyond the resolution of
human eyes. This is done by creating each electrode out of a very fine
mesh, instead of a solid sheet or rod of the material. Because no individual
strand within the mesh is wider than 35 micrometres, they are too small for
the eye to detect and so when stacked they appear transparent, much like
looking through two very fine sieves.
Creating such tiny features out of active electrode materials is tricky, says
Cui. Lithographic fabrication techniques are capable of creating structures
at this scale but these processes involve using solvents that would be
harmful to the electrodes.
So Cui's group used microfabrication techniques to first create a grid
pattern mould out of silicon. Then a 100-micrometre-thick layer of
polydimethylsiloxane (PDMS), a flexible, transparent polymer, was applied
using a technique called electro-spinning. When the PDMS was removed
from the silicon an aqueous slurry solution containing the active electrode
material was applied to it, which filled the grid-like trenches to form a
mesh, says Cui.
Cui and his colleagues show that they can create lithium-ion batteries that
let 60% of the light that hit them pass right through, and an energy
density of 10 watt-hours per litre. "That's very transparent," says Cui. Not
as good as glass, but clear enough to read text through.
Low density
But 10 watt-hours per litre is a low energy density. The energy densities of
conventional Lithium-ion batteries are typically an order of magnitude
greater than this, says Hiroyuki Nishide, a chemist at Waseda University in
Tokyo, whose own group is working on a type of transparent battery that
uses nitroxide radicals as charge carriers.
Cui agrees, but says it should be relatively easy to push the energy
density to roughly half that of conventional batteries. Making the electrode
meshes deeper will increase the volume of the active material and the
amount of stored energy without making the battery any more visible, he
says.
Besides the aesthetic appeal of creating transparent gadgets, this sort of
battery could also help reduce the size of portable devices, says Nishide.
For example integrating the power supplies of smart phones within their
displays should make them more compact. But the main innovation here
seems to be the fabrication technique, which may not be limited to just
lithium-ion batteries. This strategy seems pretty versatile and may be
applicable to a range of different battery types, says Nishide.
So, it seems we may be one step closer to this:
to translucent devices
Researchers fabricate electrodes that are too small to see.
Flexible, transparent lithium-ion batteries have been made by a team of
researchers at Stanford University in California, a technological leap that
could spawn see-through electronic gadgets such as translucent iPads.
Many electronic components can be fabricated to be transparent, but so
far this hasn't been possible for the power supply, says materials scientist
Yi Cui, who led the work, which is published today in Proceedings of the
National Academy of Sciences.
A transparent, flexible battery could help
reduce the size of electronic gadgets.
Batteries are normally made up of a pair of electrodes separated by an
electrolytic solution, with something to conduct the current to an external
circuit, and packaging to hold it all together. But only the electrolyte is
naturally transparent, says Cui. And to make matters worse, he says,
these components need to be piled on top of each other, which means all
of them must be clear for the device to be transparent.
Nothing to see here
While transparent materials can easily be found for the casing and
conductors, the electrodes tend to be naturally opaque. Cui's solution was
to make the components so small that they are beyond the resolution of
human eyes. This is done by creating each electrode out of a very fine
mesh, instead of a solid sheet or rod of the material. Because no individual
strand within the mesh is wider than 35 micrometres, they are too small for
the eye to detect and so when stacked they appear transparent, much like
looking through two very fine sieves.
Creating such tiny features out of active electrode materials is tricky, says
Cui. Lithographic fabrication techniques are capable of creating structures
at this scale but these processes involve using solvents that would be
harmful to the electrodes.
So Cui's group used microfabrication techniques to first create a grid
pattern mould out of silicon. Then a 100-micrometre-thick layer of
polydimethylsiloxane (PDMS), a flexible, transparent polymer, was applied
using a technique called electro-spinning. When the PDMS was removed
from the silicon an aqueous slurry solution containing the active electrode
material was applied to it, which filled the grid-like trenches to form a
mesh, says Cui.
Cui and his colleagues show that they can create lithium-ion batteries that
let 60% of the light that hit them pass right through, and an energy
density of 10 watt-hours per litre. "That's very transparent," says Cui. Not
as good as glass, but clear enough to read text through.
Low density
But 10 watt-hours per litre is a low energy density. The energy densities of
conventional Lithium-ion batteries are typically an order of magnitude
greater than this, says Hiroyuki Nishide, a chemist at Waseda University in
Tokyo, whose own group is working on a type of transparent battery that
uses nitroxide radicals as charge carriers.
Cui agrees, but says it should be relatively easy to push the energy
density to roughly half that of conventional batteries. Making the electrode
meshes deeper will increase the volume of the active material and the
amount of stored energy without making the battery any more visible, he
says.
Besides the aesthetic appeal of creating transparent gadgets, this sort of
battery could also help reduce the size of portable devices, says Nishide.
For example integrating the power supplies of smart phones within their
displays should make them more compact. But the main innovation here
seems to be the fabrication technique, which may not be limited to just
lithium-ion batteries. This strategy seems pretty versatile and may be
applicable to a range of different battery types, says Nishide.
So, it seems we may be one step closer to this:
Originally posted by -Gulalai
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