Optimizing the Approaches to Printed Electronics for Energy Storage

Conductive inks continue to become more relevant in the electronics industry as they prove their value in solar applications[1], sensors[2], supercapacitor electrodes[3], fuel cell electrodes[4], and many other applications including circuit components. IDTechEx predicted the conducting inks market to be greater than 1900 tonnes in 2017[5] while "Markets and Markets" have forecast the conducting inks market to be worth $3.91bn by 2021[6]. The majority of the market value of conductive inks is attributed to silver flake inks. These are used extensively in solar applications due to their great conductivity performance. The other major inks include carbon, graphene, silver powder and copper flake. Conductive inks are increasingly finding relevance in industry which in turn is spurring research into the nature of the inks and how to achieve the best conductivities. The combination of these two is what is driving the rapid growth of the market. Printed electronics also offer an interesting opportunity to the fast-developing "Internet of Things". This is a concept that devices and everyday objects will become smarter, more informative, and more powerful through constant sensing, learning and connection to the rest of the world.

The aim of this research project is to look at printed energy storage as a system and identify areas that could be optimized. While much research is aimed directly at the electrodes of batteries or supercapacitors, this study will look at the circuit and components around it that allow it work, and look for optimisations or ways to print previously unseen printed electronic components. To highlight this concept is Figure 1 shows a simple circuit with a current source charging a supercapacitor and an unknown load in parallel. Between the current source and the supercapacitor is a diode which would prevent the backflow of current from the supercapacitor to the current source. Visualising printed energy storage as a circuit rather than a component allows one to see the bigger picture and what is necessary for it to become a valuable technology. The areas of study that need further study highlighted by this circuit are printable diodes; effective, potentially printable electrolytes; effective heatsinking; and reduction of unnecessary bulk from non-essential components of the printing process.

To achieve the aims outlined a series of objectives were established:

1) Identify components and aspects for optimisation
In reference to the model energy storage circuit shown in section 1.2, identify aspects of existing components, or currently unavailable components that with optimisation or introduction to printed electronics would improve the system as a whole. Further, a printing method must be identified.

2) Develop an experimental process from raw materials to ink formulation
Depending on the components identified in objective 1 and raw materials associated with them, an experimental method is needed to take those materials and make them suitable for development of inks.

3) Establish methods to construct and test components
The parameters by which a component is tested must be identified as well as the means to construct said component in a printing setup. This will lead to a standard construction, and a standard testing method.

4) Produce demonstration components in a relevant circuit
Working optimised components, or newly introduced components must be able to work in a circuit such as that shown in Figure 1 and prove some form of benefit to the system compared to the previous standard for printed electronics.