Transparent iPhone? Researchers may have answer

It is said to be comparable in cost to regular batteries, with the potential to be used in a range of applications in consumer electronics. Partially transparent gadgets have already been created but to achieve complete transparency has not been possible due to the inclusion of the battery. Since key active materials in batteries cannot yet be made transparent, or replaced with transparent alternatives, the team set out to construct a battery such that its nontransparent components were too small to be seen by the naked eye. The maximum resolving power of the human eye is somewhere between 50 to 100µ, so the team set about constructing something smaller than 50µ. A mesh like framework for the battery electrodes was devised, with each 'line' in the grid being approximately 35µ wide. Light could pass through the transparent gaps between the gridlines and because the individual lines are so thin, the entire meshwork appeared transparent. A transparent, slightly rubbery compound known as polydimethylsiloxane (PDMS) was used. Although it is cheap, it is not conductive, so metals had to be deposited onto it. To do so, PDMS was poured into silicon moulds to create grid patterned trenches and a metal film was evaporated over the trenches, creating a conductive layer. The researchers then dropped a liquid slurry solution containing minuscule, nanosized active electrode materials into the trenches. A special transparent substance was then developed to be sandwiched between electrodes. This was achieved by modifying an existing gel electrolyte to make it serve as both an electrolyte and a separator. All of the materials used to make separators in regular batteries are nontransparent, so this was a vital step. By precisely placing an electrolyte layer between two electrodes, one functional battery was created. According to the team, multiple layers can be added in order to create a larger and more powerful battery. As long as the gridlines are matched accurately, transparency is maintained; light transmittance tests showed a 62% transparency in visible light and approximately 60% transparency even with three full cells stacked on top of each other. The entire battery is also highly flexible and costs similar to regular batteries. Although the transparent battery is only about half as powerful as comparably sized lithium-ion counterparts, the energy density is comparable with nickel cadmium batteries. Professor Yi Cui, associate professor of materials science and engineering and of photon science at SLAC National Accelerator Laboratory, believes advancements in materials science will enable the improvement of the energy density of the transparent battery and that the manufacturing process is definitely scalable. "It's very exciting for doing fundamental scientific research," he said. "You can study what is happening inside batteries since they are transparent now. I want to talk to Steve Jobs about this. I want a transparent iPhone!"