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Printed Electronics World
Posted on March 25, 2011 by  & 

Supercapacitors for pulse applications more affordable

Cellergy develops and manufactures Electrochemical Double Layer Capacitors (EDLC) also called supercapacitors for use in battery-operated devices as well as battery-less devices (for energy harvesting systems).
On demand from some applications, electronic circuits need high current pulses to operate efficiently. As in the case of battery-operated devices, which use primary batteries, driving high currents is next to impossible. An example of this would be an active radio frequency identification (RFID) or an automatic meter reading (AMR) - these are usually operated with a primary lithium battery that is programmed to transmit data for a few milliseconds, but need currents in the range of 10's to 100's milli-Amps. Batteries have high energy and are capable of operating for more than 10 years, but are, however, limited by low currents and fail at high current pulses. When the temperature is low, the problem is increased further while trying to drive high current using such a battery thereby damaging the system. As a response to this, coupling of supercapacitors in parallel to the battery is seen as a viable solution. It has been noticed that supercapacitors can be charged during standby times between the pulses and still be able to drive the high current pulses instead of the battery. In addition, supercapacitors can be used in energy harvesting systems for energy storage and pulse delivery in low power battery-free devices, such as wireless sensor networks (WSN); thus achieving extended life span and eliminating the need for battery replacement or recharging.
Following this trend of finding newer supercapacitor technologies, a considerable number of improvements have been made in materials, design and production processes of pulse supercapacitors. These improvements have been directed in the development of low-profile prismatic devices that can supply high peak currents up to 2-3A, thereby programmed to address the peak power demands of many battery-powered electronics, consumer, and industrial devices that suffer from limited energy sources. In response to this, Israel-based Cellergy has patented a screen printing technology based on conventional printing techniques that enable the automatic construction of supercapacitors.
The core aspect of this technology is a printable aqueous electrode paste made of high surface area activated carbon material, which is printed as an electrode matrix structure on an electronically conductive film (the current collector). Following this, the electrodes are encapsulated with a porous ionic superconducting separator and another electrode matrix is printed on second current collector, thus creating a unit capacitor. Repeating this process of printing and assembly creates a multi-layered capacitor (known as a bipolar capacitor), consisting of stacked unit capacitors connected in series.
The operating voltage of the supercapacitor may be increased by repeating this printing process many times. Cellergy's printing technology ensures the production of capacitors in different voltages, dimensions and shapes making the product customizable as per the requirement. Notably, this technique has enabled the production of the smallest footprint pulse supercapacitor of 12 mm × 12.5 mm size, which is clearly a suitable option for space-limited applications.
The use of aqueous electrolyte in the manufacture of pulse supercapacitors is advantageous because the product is more ecofriendly, as against organic electrolyte products. In addition, since the screen printing technique enables automation; it results in the reduction of labor costs and improved uniformity. The flexibility, shape and size of the products are also notable benefits.
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