Supercapacitors

Australia has become a world leader in supercapacitor technology through a CSIRO initiated research program that began in early 1992. The program was led by Tony Vassallo and Calum Drummond and involved 34 researchers from seven CSIRO Divisions. Over a decade of leading-edge research and development resulted in a product with a clear competitive advantage through the tailored use of nano-structured materials and nano-scale processes.

In this project CSIRO worked closely with Plessey Ducon Pty Ltd, and later the start-up company CAP-XX Pty Ltd, to first develop and then commercialise the world’s most advanced high power small form factor supercapacitors. Conventional capacitors have very high power, but very low energy while batteries have very high energy, but low power.

Supercapacitors are energy storage devices with both high power and high energy. The unique combination of power and energy in the CSIRO co-developed supercapacitors fills a gap in energy storage systems for miniaturised wireless communication applications where supercapacitors can extend battery life and device useability over a wide range of operating conditions, and enable some new functions.

These supercapacitors are used globally to improve the performance of GPRS mobile stations and have given CAP-XX a competitive edge in the global marketplace. The total available market for high power small form factor supercapacitors is expected to be greater than US$1 billion by 2010.

The problem

As the information revolution unfolds, consumers want a better mobile experience. They want devices that are smaller, more portable and more highly functional. Anyone who has had their Digital Still Camera, notebook, PDA or cell phone die while attempting to complete an important task, wants longer run times and rapid recharge. Manufacturers are therefore seeking lower power consumption components and operational algorithms that are now leading to increased peak power/average power ratios. As manufacturers strive to meet these demands, they are coming up against the limits of the performance capabilities of batteries, fuel cells and capacitors.

Inefficient battery, fuel cell and capacitor solutions

Both batteries and fuel cells have very limited power capabilities, which means they cannot provide the high power required for higher functionality, nor provide the burst (or pulse) power that is required for wireless communication, nor be recharged quickly, without significantly increasing the power solution’s size and weight. They also cannot work effectively below 0 ºC.

Capacitors have very limited energy storage capacity, so they cannot power high functionality without significantly increasing the power solution’s size and weight.

These limits were already causing problems in advanced applications, forcing some manufacturers to adopt costly, inefficient solutions to meet their products’ power needs. Moreover, these limits meant that current battery and capacitor power solutions will not be able to meet the higher power needs of next-generation products without compromising the products’ size and portability.

Both battery and capacitor technologies are mature, so further research is unlikely to yield dramatic improvements in their capabilities. Fuel cell technologies are not mature but are focused on large-scale power delivery, while small-scale portable fuel cells under development are unable to provide pulsed power. This means manufacturers must find an alternative power solution.

Supercapacitors provide that alternative

These revolutionary devices have a unique ability to store large amounts of energy, release this energy in fast bursts (or pulses) if required, recharge rapidly, and operate at temperatures down to -40 ºC. In the relevant markets they deliver as much power as needed for as long as is needed from a much smaller size than batteries and capacitors.

These performance characteristics mean that supercapacitors enable the development of new power solutions that can meet the high power demands of tomorrow’s applications such as:

• mobile products that incorporate several functions (e.g. PDA, voice transmission, internet access, camera, scanner and MP3 player)
• more sophisticated digital still cameras or toys
• more versatile medical devices, without compromising their portability or reliability.

Technical Comparison of Energy Storage Technologies

Batteries, fuel cells, capacitors and supercapacitors are all energy storage devices. Batteries and micro-fuel cells rely on the conversion of chemical energy into electrical energy. In contrast, capacitors rely on the physical separation of electrical charge across a dielectric medium such as a polymer film or an oxide layer, while supercapacitors rely on the separation of chemically charged species at an electrified interface between a solid electrode and an electrolyte.

As the following graph illustrates, each type of device provides a different combination of power density and energy density. Only supercapacitors can provide a combination of high power density and relatively high energy density in this space.

What is a supercapacitor?

A supercapacitor stores energy electrostatically by polarising an electrolyte solution. A supercapacitor can be viewed as two non-reactive porous plates suspended within an electrolyte, with a voltage applied across the plates. The applied potential on the positive electrode plate attracts the negative ions in the electrolyte, while the potential on the negative plate attracts the positive ions.

This effectively creates two layers of capacitive storage, one where the charges are separated at the positive plate, and another at the negative plate. The two oppositely charged electrode plates are attached to current collectors and are kept apart, prevented from causing a short-circuit, by an ionically conductive but electronically insulating separator material.

What CSIRO did

Australia has become a world leader in supercapacitor technology as a result of a CSIRO research program that began in early 1992. CSIRO initially worked closely with Plessey Ducon Pty Ltd and later with the start-up company CAP-XX Pty Ltd to first develop and then commercialise the world’s most advanced high power small form factor supercapacitors. The ultra-high performance of the CAP-XX supercapacitors has been enabled through the tailored use of nano-structured materials and nano-scale processes developed by CSIRO over a decade.

The supercapacitor project team comprised 34 researchers from seven CSIRO Divisions. The major developments were as follows.

The development of large capacitance (= High Energy) electrode plates resulted from the:

• identification of low resistivity high surface area nano-porous activated carbon and formulation of electrode by Tony Pandolfo, Tony Vassello and Claude Sachetta (all from the Division of Energy Technology)
• discovery, identification and formulation of organic electrolytes with good electrochemical and thermal stability, conductivity and charged ion sizes (standard and high temperature CAP-XX products by Tony Vassello, Tony Pandolfo, Claude Sachetta and Calum Drummond (Division of Molecular Science).

The development of the Ultra-low ESR (= High Power) components resulted from the:

• identification and formulation of very low resistivity carbon electrode bed by incorporating nano-particulate graphitic carbon in addition to activated carbon by Tony Pandolfo, Tony Vassello and Claude Sachetta
• identification and formulation of binder that provides stable coating dispersions, provides excellent current collector-electrode bed adhesion and electrode inter-particle cohesion, and minimises contact resistances by Tony Vassello and Tony Pandolfo
• discovery of surface modification for aluminium current collector that increases power delivery by 50% and increases lifetime of the device four-fold by Claude Sachetta and Calum Drummond
• identification of thin, strong, very low resistivity separator by Tony Vassello and Calum Drummond.

Other CSIRO contributions to CAP-XX’s Development

• Wireless communication application development by Trevor Smith ex the Division of Telecommunications & Industrial Physics
• Teaching and performing factorial design of experiments by Richard Jarrett and Doug Shaw, both from CSIRO Mathematical & Information Systems
• Teaching problem solving methods and facilitating problem solving activities by Doug Shaw
• Modeling of supercapacitor aging by Richard Jarrett
• Failure Modes Effect Analysis (FMEA) of entire manufacturing process by Calum Drummond
• Company R&D management (Calum Drummond 2001-2004)
• IP portfolio management and strategy development (Calum Drummond 2001-2004)

CAP-XX milestones

Key dates in the history of CAP-XX are:

Comparison with Competitors

As shown in the competitive analysis graph (provided below) CAP-XX supercapacitors were significantly better than all other supercapacitors in the marketplace in the 2000s. Note that in the graph the scale in the both axes are logarithmic.

In general, a product to the right and/or above another on this chart delivers superior performance. CAP-XX products being the closest to the top right are the most favourably placed.

Significance and recognition

In the 2000s the CAP-XX supercapacitors were significantly better than all other supercapacitors in the marketplace. The unique combination of power and energy in the CSIRO co-developed supercapacitors filled a gap in energy storage systems for miniaturised wireless communication applications where supercapacitors can extend battery life and device useability over a wide range of operating conditions, and enable some new functions.

In its Press Release of the 29 November 2004 the World Economic Forum in Geneva selected CAP-XX as one of the 29 companies it assigned the status of 2005 Technology Pioneers. To be selected as a Technology Pioneer: a company must be truly innovative; must have potential long-term impact on business and society; is expected to show signs of a long-term market leader; its technology must be proven; and it must have visionary leadership.

The total available market for high power small form factor supercapacitors has been estimated to be greater than US$1 billion by 2010.

For this development the researchers were awarded a CSIRO Medal for Research Achievement in 2004.

Source

• Drummond CJ, 2009, Personal communication.