Development of ink formulation for the inkjet printing of flexible supercapacitor electrodes and interconnects
Lead Research Organisation:
Loughborough University
Department Name: School of Science
Abstract
The project aims to produce a flexible supercapacitor, using inkjet printed electrodes that can easily be integrated with fabric for powering wearable electronic devices. The student will utilize BET particle size analysis, viscosity measurements, SEM of powders and films, AC impedance, cycle voltammetry and charge-discharge cycling techniques to characterise the inks and electrodes produced within the project. Once produced, the supercapacitors will be tested for flexibility and durability in a range of scenarios (for example being able to be put in a washing machine). The shelf life of the inks and electrodes after printing will be investigated. Once a supercapacitor of a desired specification is produced, a demonstrator unit will be developed in which the supercapacitor will power a wearable electronic device.
The project is highly multi-disciplinary, involving nanoparticle synthesis, ink formulation, material science and electrochemistry.
The project is highly multi-disciplinary, involving nanoparticle synthesis, ink formulation, material science and electrochemistry.
Organisations
Studentship Projects
| Project Reference | Relationship | Related To | Start | End | Student Name |
|---|---|---|---|---|---|
| EP/N509516/1 | 30/09/2016 | 29/09/2021 | |||
| 2066342 | Studentship | EP/N509516/1 | 01/01/2018 | 29/06/2021 | Paulo Filipe Serobaba Soares Luis |
| Description | Although inkjet printing was the original technique of the project, it had to be changed to a different printing technique, due to the high cost of the equipment. Currently screen-printing is being used through-out all the project. Different printing technologies require different ink compositions; viscosity-wise, inkjet printing requires an ink that resembles water, and screen printing inks that resemble. i.e. honey, toothpaste or yogurt. When it comes to flexible printed electronic components, one expects to maximize the amount of solid load in the ink, to ensure close functionalities to it's solid-state counterpart, while maintaining a good adhesion and flexibility. Inkjet inks demonstrate low solid load uptakes compared to screen printing inks. When it comes to carbon supercapacitors, the storing process is electrostatic (contrary to batteries, where a reduction-oxidation takes place, and phase changes occur) and it relies in materials with high surface area. Typically, supercapacitor electrodes are made of activated carbon, obtained from the calcination of organic matter. To make the storing process more efficient, the electrodes should demonstrate high electrical conductivities, and therefore carbon blacks, nanometre-sized conductive spherical particles, are added in small quantities. Moreover, to maintain a certain structural stability after manufactured, polymers are added. Conventional supercapacitor formulations are not suitable for flexible substrates, therefore ink formulation is required. Inks were formulated and their properties studied. The studies are separated in 2 stages, wet stage and dry stage. At the wet stage, the formulated ink is rheologically analysed to understand the stability and viscosity changes upon a range of shear rates. At the dry stage, after the electrode is printed, its adhesion is rated and the electrochemical performance assessed. Studies have been performed to inks with different grades of carbon blacks, to understand the effect each employ in the storing of energy. It was found that carbon blacks with higher surface area allow 1) increase of activated carbon uptake, which resulted in the increase of energy storage, and 2) similar electrical properties at low amounts, which is comparable to printed electrodes with other carbon blacks with lower surface area. These results demonstrated quite useful since high power outputs and high energy storing could be achieved through the integration of high surface carbon blacks, a side-product of petroleum refining. Moreover, activated carbons can be obtained through the combustion of organic matter, therefore of easy sourcing. After optimizing the ink's formulation to achieve high power and high energy, textile energy storing devices were manufactured. Conventionally, flexible energy storage devices, i.e. flexible batteries, integrate a printed current collector, a layer of highly conductive material, typically silver, and the active layer, which comprises the energy storing materials. Another component in an energy storage is the electrolyte, a source of ionic species required to complete the electrochemical cell. These can be aqueous (water and a salt), organic (carbonates) and ionic liquids. The stability of the electrochemical cell strongly depends in the chemical compatibility of all the components. Silver can be used as a current collector material if a non-aqueous electrolyte is employed, however, to maintain an environmental friendly status to the electrochemical device, aqueous electrolytes are desired. Given the conventional architecture of a flexible device, and the need to use aqueous electrolytes, it was necessary to find a solution to incorporate both silver and aqueous electrolytes, or else imminent degradation of silver would occur. To solve this problem, a printed layer of conductive carbon ink was added between the active layer and the current collector. It was found that no degradation occured, concluding that this method clearly mitigates the aforementioned issues. The device manufactured demonstrated high power capabilities, however a low energy density. This could be due to the fact of the nature of the electrolyte, which in this case is in a gel state to cease any leakage. Moreover, the device was sliced to half of its original size, and still fully worked. |
| Exploitation Route | Ink formulation is, according to several sources, a "dark magic", meaning that the performance of the printed element can be improved. Although a in-depth study is being performed towards the manufacture of printed supercapacitors, which is currently a niche in both academic and industrial levels, this might be further improved. Therefore, I welcome other groups and industrial partners to continue my current work towards a low-cost, high performance, all-carbon printed and flexible supercapacitor. |
| Sectors | Aerospace Defence and Marine Digital/Communication/Information Technologies (including Software) Electronics Energy Environment Healthcare Security and Diplomacy |
| URL | https://www.mdpi.com/2504-3900/32/1/10 |