The “Super” Energy Storage Devices

“The Super Supercapacitor” by Brian Golden Davis charts the story of a scientist who sets out to find a new method to make graphene, and ends up treading a path that helps him power the world in a unique manner. With this movie entering the GE FOCUS FORWARD $200,000 Filmmaker Competition as a finalist, it sure does throw light on the growing importance of supercapacitors in this new world.

So here is supercapacitors-101…

Renewable energy is the fastest growing energy source for electricity generation. Renewable resource-enabled electricity generation in The United States is estimated to increase by 3.1% annually and the renewable share of world electricity generation will grow from 19% in 2008 to 23 percent in 2035. A vast majority (82%) is from hydroelectric and wind power. Solar power is currently a “niche” source of renewable energy that requires optimization in both technology and cost. Since sun does
not shine all the time, and wind does not blow whenever required, we need energy storage devices such as batteries and supercapacitors.

Supercapacitors (also known as ultracapacitors or electrical double layer capacitors) are energy storage devices where the electrical energy is stored at the interface between an electrode and electrolyte. They are high-power devices that can be fully charged/discharged in seconds.  Due to their extremely high power uptake and delivery (> 10kW/kg), supercaps are considered to be devices between batteries and conventional capacitors. Their role is important in complementing or replacing batteries in applications involving uninterruptible power supplies. Their attractive features include long cycle life (>100 000 cycles), simple principle, and high shelf life. So, if batteries are marathon runners in terms of energy, supercaps are sprinters in terms of power.

As in batteries, supercapacitors consist of three important components – electrodes, electrolyte
and separators. Various types of carbon have been explored as candidates for electrode materials, including activated and carbon-derived carbons, carbon aerogels, nanotubes, carbon fabrics, carbon onions, and more recently, reduced graphene oxide. Another class of supercapacitors based on pseudocapacitance employs metallic oxides as electrodes. Electrolytes can be aqueous, organic or ionic liquids. Separators are porous membranes permeable to ionic current that flows between the electrodes, but are electronic insulators.

Some of the important players in supercapacitor manufacturing include Maxwell Technologies, Cap-XX, Advanced Capacitor Technologies, IOXUS, Nesscap, and ADA Technologies Inc. Research groups in Drexel University, University of Texas, UC Davis (USA), Institute of Metal Research (Chinese Academy of Sciences), Université Paul Sabatier (France), Jawaharlal Nehru Centre for Advanced Scientific Research (India), National Institute of Advanced Industrial Science and Technology (Japan) have
contributed significantly towards achieving improved devices in terms of cost and performance.

Vastly accelerated adoption of electrochemical capacitor technology, now mainly based on porous carbons, is currently hindered by its low energy storage density (5 Wh/kg) and relatively high effective series resistance. Achieving a high energy density while keeping other parameters such as power still high, electrochemical capacitor technology faces challenges in terms of innovation of new electrode materials and suitable electrolytes. Both industry and academic research labs are actively working towards addressing these problems, improving their efficiency for consumer electronics and automotive industry. We will soon be seeing emerging innovations that push these “super” performing clean-technology devices to new heights.

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Dr. Shanthi Murali
Dr. Shanthi Murali

When she isn’t getting the chip off the block, Shanthi enjoys sharing her knowledge on the semiconductor industry through her blogs.

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