A see-through smartphone you can roll up and stick in your pocket – how about that for a must-have product? It's now one step closer to reality, thanks to the development of a transparent battery.
Transparent screens, circuitry and keyboards have already been developed in an effort to produce see-through devices, but the bulk of any phone is its stubbornly opaque battery. Now, Yi Cui, who led the research at Stanford University, California, says his new battery is the last piece needed to make transparent gadgets.
Other transparent components are essentially just ultra-thin versions of their opaque counterparts, but an equivalently slimmed-down battery wouldn't store much energy. Instead, Cui and colleagues created a grid of electrodes, embedded it in a transparent electrolyte gel and sealed it in plastic. The grid lines are smaller than the resolution of the human eye, rendering the entire thing transparent, while the gel allows the battery to be flexible.
"The transparency is tuneable, so it could be as transparent as glass, in principle," explains Cui. "However, there is a trade-off between transparency and energy density. A reasonable transparency is 50 to 80 per cent." Such batteries store between a third and a half of the energy of an ordinary battery of the same size, but Cui says increasing the thickness would allow them to provide comparable levels.
Cui believes we could see transparent batteries in consumer devices in the next two to four years, depending on how easy it is to scale up the manufacturing process. The see-through components also have a scientific application, however: researchers can use optical detecting tools to study a battery's chemical reactions as they happen, which previously was impossible.
Andrew Flewitt, who researches plastic electronics at the University of Cambridge, says the battery will be key in producing transparent devices. "It's a really important step along that road. I've not seen anyone even attempt to put that piece of the jigsaw in yet," he says, though he adds that integrating the battery into a fully flexible device is likely to be an extra challenge.
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