Manufacturers of portable consumer electronics like cell phones and PDAs are constantly under pressure to augment the number of features in their products while meeting the highly demanding energy and size requirements. So far as the electrical energy required for the functioning of such compact gadgets is concerned, two devices that fit the bill are batteries and capacitors. Though both are energy storage devices, batteries are known to store more volume of electrical energy in them; however, the rate of power discharge is a shortfall. On the contrary, capacitors are known for their ability to quickly discharge higher bursts of electrical power but have lesser storage capability compared to batteries. Owing to this, a combination of capacitors and batteries is used to power portable electronic devices where both the qualities (higher volume of electrical power and rapid discharge of energy) are required at different times.
University of California, Los Angeles (UCLA) and Stanford University researchers have developed a cost effective and economical method for manufacturing supercapacitors which are flexible yet boasts of power density and energy density higher than the commercially available devices. The team devised a method of spray printing single walled carbon nanotubes (SWCNTs) on two flexible plastic films and sandwiching a gel electrolyte between them. CNT networks exhibit low resistances while having high surface areas. As a result, these carbon nanotube networks can behave not only as electrode materials but also charge collector, streamlining the architecture. The two plastic films on which CNTs are printed play a dual role of charge storage elements as well as electrodes. The gel electrolyte is prepared by mixing powdered polyvinyl alcohol (PVOH) with phosphoric acid and water. After a voltage is applied to the sandwiched polymer electrolyte gel, the surface of the SWCNTs on plastic films collects the charges thereby leading to energy storage. This novel thin film supercapacitor exhibits a power density of 70 kilowatts/kg which is extensively superior to the currently available commercial capacitors. Even though the high power density, economic printing methods and flexibility may prompt its use in compact digital devices, the supercapacitor shows scope for improving its energy density (volume of electrical energy that can be stored). Once this feat is achieved, the day is not far when these supercapacitors will replace batteries in such tiny portable devices.
However, the flexible nature and lightweight of these supercapacitors serves the purpose for flexible electronics like foldable displays, e-readers and the like, though in combination with batteries. Part of the reason for this is that the new tests show charge storage device generates high internal resistance thereby causing a drop in energy stored. The simplification of structural design and easy-to-implement inkjet printing techniques is set to give rise to a new breed of flexible printable charge-storage devices for plastic electronics. Printed electronics has faced a two-pronged uphill task of raising the features while managing the energy efficiency in a highly compressed space. The new manufacturing method for thin film supercapacitor is a giant lead ahead to integrate power and energy storage devices into manufacturing process by printing all of it at one go. Previously, devices employing carbon nanotubes were developed using costly methods which didn’t allow large scale commercial fabrication. These cumbersome methods included allowing the vertically aligned growth of CNTs on metallic substrates which involved high costs and low flexibility in development. The novel method is a step change in manufacturing thin film carbon nanotube capacitors by roll-to-roll mass manufacturing techniques unlike its preceding counterparts. The field of printed electronics is a sure benefactor of the technology though there still remains a huge scope for scientists to boost the energy density to match the range provided by batteries.
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