A new type of air-fuelled battery could give up to ten times the energy storage of designs currently available.
This step-change in capacity could pave the way for a new generation of electric cars, mobile phones and laptops.
The research work, funded by the Engineering and Physical Sciences Research Council (EPSRC), is being led by researchers at the University of St Andrews with partners at Strathclyde and Newcastle.
The new design has the potential to improve the performance of portable electronic products and give a major boost to the renewable energy industry. The batteries will enable a constant electrical output from sources such as wind or solar, which stop generating when the weather changes or night falls.
Improved capacity is thanks to the addition of a component that uses oxygen drawn from the air during discharge, replacing one chemical constituent used in rechargeable batteries today. Not having to carry the chemicals around in the battery offers more energy for the same size battery. Reducing the size and weight of batteries with the necessary charge capacity has been a long-running battle for developers of electric cars.
An early demonstration model of the STAIR (St Andrews air) cell.
The STAIR (St Andrews Air) cell should be cheaper than today’s rechargeables too. The new component is made of porous carbon, which is far less expensive than the lithium cobalt oxide it replaces.
This four-year research project, which reaches its halfway mark in July, builds on the discovery at the university that the carbon component’s interaction with air can be repeated, creating a cycle of charge and discharge. Subsequent work has more than tripled the capacity to store charge in the STAIR cell.
Principal investigator on the project, Professor Peter Bruce of the Chemistry Department at the University of St Andrews, says: “Our target is to get a five to ten fold increase in storage capacity, which is beyond the horizon of current lithium batteries. Our results so far are very encouraging and have far exceeded our expectations.”
“The key is to use oxygen in the air as a re-agent, rather than carry the necessary chemicals around inside the battery,” says Bruce.
Cells used in the laboratory to investigate the lithium-air cell.
The oxygen, which will be drawn in through a surface of the battery exposed to air, reacts within the pores of the carbon to discharge the battery. “Not only is this part of the process free, the carbon component is much cheaper than current technology,” says Bruce. He estimates that it will be at least five years before the STAIR cell is commercially available.
The project is focused on understanding more about how the chemical reaction of the battery works and investigating how to improve it. The research team is also working towards making a STAIR cell prototype suited, in the first instance, for small applications, such as mobile phones or MP3 players.
Notes for Editors
The four-year research project “An O2 Electrode for a Rechargeable Lithium Battery” began on 1 July 2007 and is scheduled to end on 30 June 2011. It has received EPSRC funding of £1,579,137.
Rechargeable lithium batteries are currently comprised of a graphite negative electrode, an organic electrolyte and lithium cobalt oxide as the positive electrode. Lithium is removed from the layered intercalation compound (lithium cobalt oxide) on charging and re-inserted on discharge.
Energy storage is limited by the lithium cobalt oxide electrode (0.5 Li/Co, 130 mAhg-1). The University of St Andrews design replaces the lithium cobalt oxide electrode with a porous carbon electrode and allows Li+ and e- in the cell to react with oxygen from the air.
Initial results from the project found a capacity to weight ratio of 1,000 milli-amp / hours per gram of carbon (mA/hours/g), while recent work has obtained results of up to 4,000 mA/hours/g. Although the two designs work very differently, this equates to an eight-fold increase compared to a standard cobalt oxide battery found in a mobile phone.
The application to renewable energy could help get round the problems of intermittent supply. By discharging batteries to provide electricity and recharging them when the wind blows or sun shines, renewables become a much more viable option.
The Engineering and Physical Sciences Research Council (EPSRC) is the UK’s main agency for funding research in engineering and the physical sciences. The EPSRC invests around £740 million a year in research and postgraduate training, to help the nation handle the next generation of technological change. The areas covered range from information technology to structural engineering, and mathematics to materials science. This research forms the basis for future economic development in the UK and improvements for everyone’s health, lifestyle and culture. EPSRC also actively promotes public awareness of science and engineering. EPSRC works alongside other Research Councils with responsibility for other areas of research. The Research Councils work collectively on issues of common concern via Research Councils UK.