A paper battery is a thin, flexible energy production and storage device that is formed by combining carbon nanotubes with a conventional sheet of cellulose-based paper. In addition to being disposable, paper batteries may be folded, cut or otherwise shaped for different applications without any loss of integrity or efficiency.
As sensors are increasingly being embedded in everyday objects, there has been a corresponding need for alternative power sources in the Internet of Things (IoT). The high cellulose content and lack of toxic chemicals in paper batteries make them both biocompatible and environmentally friendly, especially when compared to the lithium ion batteries used in many present-day electronic devices.
Specialized paper batteries are expected to act as power sources for any number of devices implanted in humans and animals, including RFID tags, drug-delivery systems and pacemakers. In theory, a capacitor introduced into an organism could be implanted fully dry and then be gradually exposed to bodily fluids over time to generate voltage.
Ten years ago, scientists at Rensselaer Polytechnic Institute and MIT grew nanotubes on a silicon substrate and then impregnated gaps in the matrix with cellulose. When two sheets were combined with the cellulose sides facing inwards, a supercapacitor could be activated with ionic liquid forms, including salt-laden solutions like human saliva, blood, sweat or urine.
Recently, researchers at the State University of New York printed thin layers of metals and polymers onto a paper surface that contains freeze-dried exoelectrogens, a type of bacteria that can transfer electrons outside the bacteria's cellular walls. Any type of bio-liquid can be used to revive the exoelectrogens and activate the paper battery by allowing bacteria to pass through cell membranes and make contact with external electrodes.