There's one big obstacle holding back flexible electronics and conformable wearables, and that's stiff and bulky li-ion batteries. Now, a team of scientists has developed a stretchable mesh of power cells that sticks to surfaces like a plaster to skin — and it can even charge itself. The device has been built by a team of international scientists led by John Rogers from University of Illinois at Urbana-Champaign. It uses a series of very thin tiles of lithium-ion battery, bonded together with a soft, rubbery material. Their interconnecting wires are excessively long, which allows the whole thing to stretch in all directions.
The researchers also added extra hardware to the stretchable panel: Tiny solar panels on top of the battery cells, and several sensors across the surface of the rubbery sheet. The result is a medical sensing device that the team claims "will provide a never-ending stream of bio-sensor data". In tests published in PNAS, the team showed that the device could be stretched by 30 per cent of its original length while still working perfectly.
The advance overcomes part of the difficulty with flexible power sources. In the past, Rogers has told me that "you can make most components small enough in lateral dimensions that you can engineer the soft mechanics you ultimately want", but that's simply not the case with batteries. Instead, their capacity is dictated by volume: Make one thin enough to be flexible, and it barely holds any charge. That's of little use, especially given the rate at which most devices now chew through charge.
Adding solar cells means that the cells are constantly topped up — though the flexible device will only be useful for devices that require modest amounts of power.