Lee, a battery chemist at the Ulsan National Institute of Science and Technology (UNIST) in South Korea, empties the ink cartridges and refills them with specially formulated battery materials and conductive inks. When loaded with treated paper, his hacked printers make flexible, durable supercapacitors and simple circuit components in the form of a high-resolution map of the Republic of Korea, a flower, a logo, or any other desired design.
He had to tailor all the materials in the recipe. If the inks smear or run in the paper, the supercapacitor won’t work. So the first layer to be printed is a cellulose primer that absorbs inks and won’t run. That’s followed by carbon nanotubes, which replace the foil current collector in a battery, and silver nanowire electrodes, followed by an electrolyte ink. Each ink had to be formulated so that it would flow through the print head and not clump up while sitting in the cartridge.
The key to Lee’s system was developing an electrolyte compatible with ink-jet printing. The electrolyte, the medium that conducts ions and electrons, is typically a liquid. Lee is the first to make a fully ink-jet-compatible set of materials that includes the electrolyte. Other research projects, he says, require a liquid electrolyte to be added after the other parts are printed. The need to hold in that liquid constrains the design of the printed battery. There are solid-state electrolyte materials, but they’re not compatible with ink-jet printing and may not be flexible.
Energy and Environmental Science - All-inkjet-printed, solid-state flexible supercapacitors on paper
The next step is to continue to improve the total energy storage of the printed devices, he says, and try printing on different materials besides paper.
The forthcoming ubiquitous innovations driven by flexible/wearable electronics and Internet of Things (IoT) have inspired the relentless pursuit of advanced power sources with versatile aesthetics. Here, we demonstrate a new class of solid-state flexible power sources that are fabricated directly on conventional A4 paper using a commercial desktop inkjet printer. A salient feature of the inkjet-printed power sources is their monolithic integration with paper, i.e., they look like inkjet-printed letters or figures that are commonly found in office documents. A supercapacitor (SC), which is composed of activated carbon/carbon nanotubes (CNTs) and an ionic liquid/ultraviolet-cured triacrylate polymer-based solid-state electrolyte, is chosen as a model power source to explore the feasibility of the proposed concept. Cellulose nanofibril-mediated nanoporous mats are inkjet-printed on top of paper as a primer layer to enable high-resolution images. In addition, CNT-assisted photonic interwelded Ag nanowires are introduced onto the electrodes to further improve the electrical conductivity of the electrodes. The inkjet-printed SCs can be easily connected in series or parallel, leading to user-customized control of cell voltage and capacitance. Notably, a variety of all-inkjet-printed SCs featuring computer-designed artistic patterns/letters are aesthetically unitized with other inkjet-printed images and smart glass cups, underscoring their potential applicability as unprecedented object-tailored power sources.
SOURCES- Technology Review, Energy and Environmental Science