A transparent battery could replace glass in windows. The battery still has a low output, but could eventually add extra energy storage to smart glasses or cars.
Most battery research focuses on increasing power output or energy density, a measure of how much energy can be stored in a certain volume. But Hironobu Minowa and his colleagues at Japanese communications giant NTT decided instead to focus on making a battery that is as inconspicuous as possible.
The team had to create new versions of battery components to reduce overall light absorption and reflection. The result is a battery the size of an A4 or a US letter sheet of paper that is as see-through as window glass.
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The battery lacks the capacity of a conventional one: it holds only 1 milliamp hour (mAh) compared with more than 1000 in an AA battery. But it lets 69 per cent of light pass through it, which is at the lower end of what window glass achieves.
This is enough, however, to power an LED or a digital clock, says Minowa, who demonstrated the battery at NTT鈥檚 R&D Forum in Tokyo this week.
As homes fill up with sensors and small smart devices, used for everything from monitoring temperature to optimising lighting, transparent batteries like this could help clear up the associated mess of wires and battery packs.
Since building the prototype battery last year, the team has already doubled its output and tripled its transparency, says Minowa.
Although the team can鈥檛 yet make batteries any larger than an A4 sheet, it is possible to link multiple panes together to boost capacity.
The ability to turn a window into a battery could be revolutionary, says Kevin Curran at Ulster University, UK. Transparent batteries could also have applications in smart glasses, cars and even sensor-packed contact lenses, he says.
