Korea University Develops Binder-Free Textile Supercapacitor Electrode Using Carbon Nano-Oligomer Interfacial Bonding
Professor Cho Jin-han’s group from the Department of Chemical and Biological Engineering and KU-KIST Graduate School of Converging Science and Technology and Dr. Ko Yong-min’s group from Daegu Gyeongbuk Institute of Science and Technology developed a nanoparticle-based binder-free textile type supercapacitor electrode using a carbon nano-oligomer, surfaced-modified with a hydrophilic functional group.
Their results were published online in Energy Storage Materials (IF = 20.4), a renowned international journal in materials science and nanotechnology, on April 12.
Supercapacitors store electric charges based on reactions that rapidly occur on the surface of an electrode. Therefore, when an electrode material is produced in the form of nanoparticles with a high specific surface area, the active area can be increased, thereby improving the charge transfer efficiency. In order to effectively utilize the advantages of these nanoparticles, it is important that they are uniformly distributed within an electrode through stable combination with other supporting components such as the conductive fillers or binders required for manufacturing an electrode.
However, the slurry coating method, a common method of manufacturing electrodes, has limitations when applied to nanoparticle-based electrodes. First, in order to realize high energy density, the ratio of the supporting components to active materials needs be minimized. However, since nanoparticles have a high specific surface area, the ratio of the supporting components required for slurry production must be increased. In addition, the ligand present on the surface of the nanoparticles is an insulating organic material that acts as resistance within an electrode. Furthermore, slurries based on physical mixing are prepared without considering the bond between nanoparticles and conductive additives, so it is difficult to induce uniform distribution within an electrode.
In charge transfer, the wettability between an electrode and an electrolyte is also a factor to be considered. In most supercapacitors that use an aqueous electrolyte solution, conductive additives (carbon nanotubes, carbon black) or binders (poly(vinylidene fluoride)), which are non-polar materials, form a thick diffusion layer on the interface between an electrode and an electrolyte, thereby hindering charge transfer. In particular, carbon nanotubes or carbon black have poor dispersibility and are prone to agglomeration, which can induce uneven charge distribution within the electrode.
Accordingly, the research team prepared carbon nano-oligomers in functional groups through chemical treatment of carbon black, a conductive additive, and manufactured an electrode that ensures an established uniform charge transfer path even without a binder, through an assembly technology based on interfacial bonding with active material nanoparticles.
The carbon nano oligomers have functional groups that can directly and strongly bind to the surface of active material nanoparticles without the assistance of a binder, so they were able to serve as both a conductive additive and a binder within the electrode. In particular, it was possible to completely remove insulating organic substances in the electrode through an assembly based on a ligand substitution reaction in which the ligand on the surface of the nanoparticles is detached and a carbon nano oligomer is combined with the nanoparticles at that site.
The researchers applied the nanoparticles to a 3D textile type conductor to drastically increase the loading amounts of an active material compared to a flat plate, and to maintain smooth charge transfer even at high loading amounts. The electrode provided an excellent and stable areal capacitance of 1,725 mFcm-2.
The study was supported by the National Research Foundation of Korea, funded by the Ministry of Science and ICT, and the KU-KIST Graduate School of Converging Science and Technology Program.