Manufacturing energy-storage devices such as batteries and supercapacitors have never been an eco-friendly business. But researchers are trying to change that with the use of new materials that can be sustainably sourced and don’t use toxic chemicals.
To that end, a group of researchers at Graz University of Technology has developed a new hybrid supercapacitor system based on very simple and natural ingredients—carbon and aqueous sodium iodide (NaI) electrolyte, which is basically saltwater.
“This makes this system particularly environmentally friendly, cost-effective, incombustible and easy to recycle," Christian Prehal, a researcher who worked on the project at the Institute of Chemistry and Technology of Materials at TU Graz, said in a press statement. Prehal has since moved on to join scientists at ETH Zurich.
The device is deemed a “hybrid” in that it can be charged and discharged quickly—which is a benefit of supercaps—but also can store almost as much energy as conventional batteries.
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It also can be charged and discharged much faster and much more frequently than batteries, managing around 1 million charging cycles versus a typical lithium-ion battery’s few thousand cycles.
Previous research by the team—which also included Qamar Abbas of the Institute of Chemistry and Technology of Materials—already had success in using carbon and an aqueous sodium iodide electrolyte to create a hybrid supercap with a positive battery electrode and a negative supercap electrode.
However, the current study explored in depth how the electrochemical energy storage in this type of works, paving the way for further optimization and viability for a variety of more sustainable energy-storage needs.
Specifically, researchers used a combination of small-angle X-ray scattering and Raman spectroscopy to peer into the nanometer-sized pores of the carbon electrode, where they observed and demonstrated for the first time that solid iodine nanoparticles form there during charging, and then dissolve during discharge.
Their discovery sets the record straight on what was previously believed to be the reaction mechanism of this type of hybrid supercapacitor. This, in turn, will affect future designs of the device and could inform other research in this area, Prehal said.
"The degree of filling of the nanopores with solid iodine determines how much energy can be stored in the electrode,” he said in a press statement. “This enables the energy storage capacity of the iodine carbon electrodes to reach unexpectedly high values by storing all chemical energy in the solid iodine particles."
Knowing this, scientists now can develop hybrid supercapacitors or battery electrodes with higher energy density and extremely fast charging and discharging processes.
Researchers published a paper on their work in the journal Nature Communications.
The team plans to continue to develop hybrid supercapacitors as a more sustainable, eco-friendly, and non-flammable alternative to current energy-storage devices. In particular, researchers are eyeing their use as storage for solar energy in residential deployments.