A charge time and capacity record for organic and non–toxic batteries has been set by using algae, claim researchers from Uppsala University, Sweden.

Batteries based on this material can be charged with currents as high as 600 mA cm_2 with only six per cent loss in capacity over 100 subsequent charge and discharge cycles. Charge capacities range between 25–33mAh g_1 or 38_50 mAh g_1 per weight of the active material.

The team at Uppsala argue that, up until now, no–one has been able to make an organic-based battery perform comparably to lithium-ion batteries.

This research opens up possibilities for producing environmentally friendly, cost efficient, up-scalable and lightweight energy storage systems.

The researchers have coated cellulose from Cladophora algae with a 50nm layer of prolypyrrole (PPy) (a conductive polymer) to make flexible, thin and durable batteries. After optimisation, they are expected to be integrated in applications where Li–Ion batteries cannot be used, such as in clothing and books.

Two cellulose electrodes are separated with filter paper soaked in salt water. One of the electrodes is coated with a thin layer of oxidised PPy while the other is coated with reduced PPy. The potential difference between the two layers provides the voltage of the battery, as during charging and discharging.

The enhanced performance is due to the thin PPy layer and the cellulose’s large surface area of 80m2/g. The thin layer enables fast charging and discharging while the surface area provides the battery’s relatively high capacity. Previous conducting polymers had been too thick to act as batteries in sufficient capacities. The algae–based device can be charged within 11s and is also more stable.

It is hoped that the batteries will be easily manufactured without advanced equipment so that they can be built on site in developing countries. So far only a proof of principle device has been created and the researchers are investigating this further. Unwanted discharging must also be prevented.

Maria Strømme, Professor of Nanotechnology and Head of the Nanotechnology and Functional Materials Division at the Ångström Laboratory, Uppsala University, says, ‘Our battery gives a lower voltage than a Li battery but it can be charged much faster. These algae grow worldwide and in large abundance in Asia. Hopefully they will have a large impact on the marketplace.

‘We envision that it will open up new opportunities for battery driven devices that do not exist today.’

Professor Mike Petty from the School of Engineering and Computer Science at Durham University, UK, says ‘The report looks very interesting – and certainly plausible. There is a real need to produce rechargeable lightweight batteries that can be used in portable applications. The key, as with a lot of the new organic electronics products (displays, transistors, photovoltaics, etc), will be to produce the devices with long lifetimes.’ Author : Rachel ConnollyMaterials World Magazine, 01 Nov 2009