supercapacitor technology
alternative to lithium ion battery

The Universities of Bristol and Surrey have made progress on the development of polymer materials that could signal a future alternative to lithium-ion batteries.

A year ago, the two universities announced development of novel polymer materials that have dielectric properties 1,000 to 10,000 times greater than existing electrolytes. They are now ready to demonstrate their results.

These findings have now been converted into ‘device scale’ technical demonstrators in which the researchers have achieved practical capacitance values of up to 4F/cm2 on smooth low-cost metal foil electrodes. Existing supercapacitors on the market typically reach 0.3F/cm2 depending upon complex extended surface electrodes.

The researchers also managed to achieve results of 11-20F/cm2 when the polymers were used with specially treated stainless-steel electrodes. If these values can be achieved in production, it could potentially mean supercapacitors achieving energy densities of up to 180whr/kg – greater than those of current lithium ion batteries.

Supercapacitors store energy using electrodes and electrolytes and both charge and deliver energy quickly. Conventional batteries perform the same task but in a much slower and more sustained way.

Supercapacitors have the ability to charge and discharge rapidly over very large numbers of cycles. However, because existing supercapacitors have poor energy density per kilogramme (currently around one twentieth of existing battery technology), they have been unable to compete with conventional battery energy storage.

Even with this restriction, supercapacitor buses are already being used in China, but the current technology means that they need to stop to be recharged frequently, usually at almost every bus stop.

The scientists have tested the materials in two ways. They have used small single layer cells charged to 1.5 volts for two to five minutes and then run demonstration devices, including a small fan. They have also used a three-cell series stack that is able to be rapidly charged to five volts and operate an LED.

Additionally, the University of Bristol is going much further by producing a complex series-parallel cell structure in which both the total capacitance and operating voltage can be separately controlled.

“Following the unveiling of the preliminary results at the first press conference just 14 months ago, the team has worked hard to increase the storage capability of these innovative materials still further” said Dr Ian Hamerton, Reader in Polymers and Composite Materials from the Department of Aerospace Engineering at the University of Bristol.

“Our foremost challenge is now to translate these scientific findings into robust engineered devices and unlock their revolutionary potential.”

Dr Brendan Howlin, Senior Lecturer in Computational Chemistry at the University of Surrey, added that this could be the start of a new chapter in the technology of low-cost electrical energy storage that could shape the future of industry and society for many years to come.

According to Dr Donald Highgate, Director of Research for Superdielectrics Ltd, the present work promises to make rapid charging possible for electric vehicles, as well as offering a much-needed low-cost method of storing the transient output from renewable energy systems, particularly wind, wave and solar.

 

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