There is an increasing drive to make a completely wireless world. However, while battery technology has come a long way, it has not come far enough. Sustainable operation of battery-powered wireless embedded systems remains a key challenge. There are numerous alternative technologies being explored including thin-film and printed batteries, energy harvesting and new strategies for recharging conventional lithium-ion batteries, among others. One of the alternatives that has recently made headlines-several times-is biomaterial-based batteries.

Sony has just announced the development of a bio battery that generates electricity from carbohydrates using enzymes as its catalyst, through the applications of power generation principles found in living organisms. According to the company, test cells of the battery have achieved power output of 50 mW, which it claims is the highest level for passive-type bio batteries. Such output is sufficient to power music playback on a memory-type Walkman.

In order to realize the high power output, Sony has developed a system of breaking down sugar to generate electricity that involves efficiently immobilizing enzymes and the mediator (electronic conduction materials) while retaining the activity of the enzymes at the anode. The company also developed a new cathode structure which efficiently supplies oxygen to the electrode while ensuring that the appropriate water content is maintained. Optimizing the electrolyte for these two technologies has enabled these power output levels to be reached.

It is a passive-type battery, simply supplying sugar solution into the battery unit. The cubic (39 mm along each edge) cell produces 50 mW. By connecting four cubic cells, it is possible to power a memory-type Walkman (NW-E407) together with a pair of passive-type speakers (no external power source). The bio battery casing is made of vegetable-based plastic (polylactate), and designed in the image of a biological cell.

Moving towards commercialization, Sony is working on better methods to immobilize the enzyme and improve battery performance and durability. Matsushita Electric Industry Co. is also developing a sugar battery.

Since sugar is a naturally occurring energy source produced by plants through photosynthesis, it is regenerative. Thus, as a future energy source, sugar-based batteries would be environmentally friendlyeliminating the battery disposal issue of today's batteries.

In another announcement two weeks ago, researchers at Rensselaer Polytechnic Institute discussed a paper-sized device that functions as a high-energy battery and a super capacitor that can use human blood and sweat to recharge. The lightweight, ultra thin and flexible battery is targeted towards areas such as implantable medical equipment.

An Ionic liquid-a liquid salt that does not contain water-serves as the battery's electrolyte and allows it to withstand extreme temperatures. In addition, researchers have demonstrated that the printed batteries could be printed without electrolytes so that naturally occurring electrolytes in human body fluids could activate it. Researchers said it doesn't contain toxic chemicals and is environmentally safe.

The device has been engineered to function both as a battery and a super capacitor. In addition, since it is more than 90 percent cellulose, it is biocompatible and could be used in the human body. Currently, the device is created with inexpensive materials, but the researchers are looking into options for inexpensive mass production. The goal would be to print the paper using a roll-to-roll system similar to newspaper printing. Having applied for a patent, the researchers are looking to improve the device in such areas as power output.

Each piece is a step; together they represent a giant step in the field. However, there is still a long way to go though toward the ultimate goal of making such bio batteries three to ten times the energy of lithium ion batteries. Moreover, prototypes do not always translate well into commercial products.

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NanoMarkets will be releasing a new report in October titled, Thin-Film and Printed Batteries Markets: 2007-2014. Follow the report title for details.