Researchers at Rensselaer Polytechnic Institute have developed a new energy storage device that they claim could easily be mistaken for a simple sheet of black paper. The nanoengineered battery is lightweight, ultra thin, completely flexible, and geared toward meeting the trickiest design and energy requirements of tomorrow’s gadgets, implantable medical equipment, and transportation vehicles.
Along with its ability to function in temperatures up to 300°F and down to 100 below zero, the device is completely integrated and can be printed like paper. The device is also unique in that it can function as both a high-energy battery and a high-power supercapacitor, which are generally separate components in most electrical systems. Another key feature is the capability to use human blood or sweat to help power the battery.
Details of the project are outlined in the paper "Flexible Energy Storage Devices Based on Nanocomposite Paper" published Aug. 13 in the Proceedings of the National Academy of Sciences.
The semblance to paper is no accident: more than 90% of the device is made up of cellulose. Rensselaer researchers infused this paper with aligned carbon nanotubes, which give the device its black color. The nanotubes act as electrodes and allow the storage devices to conduct electricity. The device, engineered to function as both a lithium-ion battery and a supercapacitor, can provide the long, steady power output comparable to a conventional battery, as well as a supercapacitor’s quick burst of high energy.
The device can be rolled, twisted, folded, or cut into any number of shapes with no loss of mechanical integrity or efficiency. The paper batteries can also be stacked, like a ream of printer paper, to boost the total power output. The researchers used ionic liquid, essentially a liquid salt, as the battery’s electrolyte. It’s important to note that ionic liquid contains no water, which means there’s nothing in the batteries to freeze or evaporate. Along with use in small handheld electronics, the paper batteries’ light weight could make them ideal for use in automobiles, aircraft, and even boats. The paper also could be molded into different shapes, such as a car door, which would enable important new engineering innovations.
Paper is also extremely biocompatible and these new hybrid battery/supercapcitors have potential as power supplies for devices implanted in the body. The team printed paper batteries without adding any electrolytes, and demonstrated that naturally occurring electrolytes in human sweat, blood, and urine can be used to activate the battery device.
The materials required to create the paper batteries are inexpensive, but the team has not yet developed a way to inexpensively mass produce the devices. The end goal is to print the paper using a roll-to-roll system similar to how newspapers are printed. The team of researchers has already filed a patent protecting the invention. They are now working on ways to boost the efficiency of the batteries and supercapacitors, and investigating different manufacturing techniques.