March 22, 2007 All is no longer as it seems – the clear flexible plastic in the image is a battery – it is a polymer based rechargeable battery made by Japanese scientists. Drs Hiroyuki Nishide, Hiroaki Konishi and Takeo Suga at Waseda University have designed the battery – which consists of a redox-active organic polymer film around 200 nanometres thick. Nitroxide radical groups are attached, which act as charge carriers. Because of its high radical density, the battery has a high charge/discharge capacity. This is just one of many advantages the ‘organic radical’ battery has over other organic based materials according to the researchers. The power rate performance is strikingly high – it only takes one minute to fully charge the battery and it has a long cycle life, often exceeding 1,000 cycles.
The team made the thin polymer film by a solution-processable method – a soluble polymer with the radical groups attached is “spin-coated” onto a surface. After UV irradiation, the polymer then becomes crosslinked with the help of a bisazide crosslinking agent.
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A drawback of some organic radical polymers is the fact they are soluble in the electrolyte solution which results in self-discharging of the battery – but the polymer must be soluble so it can be spin-coated.
However, the photocrosslinking method used by the Japanese team overcomes the problem and makes the polymer mechanically tough.
Dr Nishide said: “This has been a challenging step, since most crosslinking reactions are sensitive to the nitroxide radical.”
Professor Peter Skabara, an expert in electroactive materials at the University of Strathclyde , praised the high stability and fabrication strategy of the polymer-based battery. “The plastic battery plays a part in ensuring that organic device technologies can function in thin film and flexible form as a complete package.” The news is reported in the latest edition of The Royal Society of Chemistry journal Chemical Communications.