Transparent lithium-ion batteriesPNAS ∣ August 9, 2011 ∣ vol. 108 ∣ no. 32 ∣ 13013–13018Transparent devices have recently attracted substantial attention.Various applications have been demonstrated, including displays,touch screens, and solar cells; however, transparent batteries, akey component in fully integrated transparent devices, have notyet been reported. As battery electrode materials are not transparentand have to be thick enough to store energy, the traditionalapproach of using thin films for transparent devices is not suitable.Here we demonstrate a grid-structured electrode to solve thisdilemma, which is fabricated by a microfluidics-assisted method.The feature dimension in the electrode is below the resolution limitof human eyes, and, thus, the electrode appears transparent. Moreover,by aligning multiple electrodes together, the amount of energystored increases readily without sacrificing the transparency.This results in a battery with energy density of 10 Wh∕L at a transparencyof 60%. The device is also flexible, further broadeningtheir potential applications. The transparent device configurationalso allows in situ Raman study of fundamental electrochemicalreactions in batteries
