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Are Ultracapacity Polymeric Supercapacitors viable alternatives to Batteries?
Posted on June 19th, 2017 by Dr. Sina Ebnesajjad in New Materials & Applications
Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)
The answer depends on whether the recent advances in supercapacitor development help overcome the disadvantages of the capacitance technology, i.e. small amounts of energy storage. According to Dr. Brendan Howlin, at the University of Surrey Department of Chemistry, the ultracapacity supercapacitors have the potential to “open the door to unimaginably exciting developments”. There are good reasons why supercapacitors are being pursued as alternatives to battery power. In addition to electric vehicles a number of industries would benefit from ultracapacity supercapacitors: transport, aerospace, energy generation, mobile phones, flat screen electronic devices, and biosensors.
In spite of all its advantages electricity has the drawback of being difficult to store. Batteries and supercapacitors are two means of storing electrochemical energy though with significant differences between them. Batteries can hold large amounts of energy but they take a long time to charge. Just think of charging your smart phone – it is definitely not fast. On the other hand capacitors of any kind charge almost instantaneously but because of low energy density they only store small amounts of energy.
Supercapacitors, an alternative power storage device to batteries, store energy using electrodes and electrolytes and both charge and deliver energy quickly. Unlike conventional batteries, which do so in a much slower, more sustained way. Supercapacitors have the ability to charge and discharge rapidly over very large numbers of cycles. However, because of their poor energy density they have, until now, been unable to compete with conventional battery energy storage in many applications. Lithium ion batteries store 20 times more energy than today’s supercapacitors. Recent supercapacitor material developments to increase the energy density levels, by orders of magnitude, appear promising.
Basic Technology of Supercapacitors
The basic technology was adapted from the principles used by Dr. Donald Highgate to make soft contact lenses in the 1970’s. Researchers from Augmented Optics Ltd. and the University of Surrey, in collaboration with the University of Bristol, have developed new, cross-linked gel-matrix polymer electrolytes. The materials are based on large organic molecules composed of many repeated sub-units and bonded together to form a 3-dimensional network. They exhibit measured capacitance values more than 100 times those of conventional electrolytes. The new gel electrolytes are compatible with all normal commercial electrodes.
The proprietary materials developed in this project are electrically active hydrophilic polymers. Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is a polymer mixture of two ionomers. One component in this mixture is made up of sodium polystyrene sulfonate, which is sulfonated polystyrene. Part of the sulfonyl groups are deprotonated and carry a negative charge. The other component PEDOT is a conjugated polymer and carries positive charges and is based on polythiophene. Together the charged macromolecules form a macromolecular salt.
One electrolyte candidate material is an industrial grade version based on a hydrophilic structure amalgamated with a transparent conducting polymer called PEDOT:PSS. The second candidate is a higher performance polymer where Imidazole is used instead of the PEDOT:PSS. Imidazole is an organic compound with the formula C3N2H4.
Teams at the University of Surrey’s Department of Chemistry, where Dr. Donald Highgate of Augmented Optics initiated the project, conducted the development program. The research team was co-led by the Principal Investigators Dr Ian Hamerton and Dr Brendan Howlin at the University of Bristol who said: “While this research has potentially opened the route to very high density supercapacitors, these polymers have many other possible uses in which tough, flexible conducting materials are desirable, including bioelectronics, sensors, wearable electronics, and advanced optics.”
Augmented Optics has formed a subsidiary, SuperCapacitor Materials (www.Supercapacitormaterials.com), to commercialize the new polymers. The company believes the combination of existing electrodes and the new electrolytes have the potential to create supercapacitors with energy storage capacities approaching or even exceeding the existing battery systems (Figure 1). Test results from the new polymers suggest extremely high energy density supercapacitors could be constructed in the near future. SuperCapacitor Materials is now actively searching for commercial partners in order to build the ultra high energy density storage devices.
Figure 1 Supercapacitor Market Shares in 2014 and 2020 by Application (Source: www.idtechex.com)
All opinions shared in this post are the author’s own.
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Dr. Sina Ebnesajjad
President at FluoroConsultants Group, LLC