Prototype of an ultrathin and extremely flexible film battery. Focus on polymer-based energy storage at the international conference “Polymers and Energy” at Jena University. Photo: Jan-Peter Kasper/ FSU
At first glance, it looks like a perfectly normal sheet of stickers that you buy at a stationery store, apart from the fact that it is not quite as colourful. The little rectangular objects that can be pressed out of the sheet with one of your fingers are prototypes of film batteries, however, printed on a screen printer, ultrathin and extremely flexible. They still contain metal, but they are to be made entirely from innovative plastics in future.
“Batteries based on polymers, that are known as organic radical batteries, are low-risk and sustainable, because they do not contain any environmentally harmful or rare metals and metallic compounds in the electrodes, like lithium or cobalt”, says Dr Martin Hager from the Centre for Energy and Environmental Chemistry at Jena University. The chemist, who heads the research group “New polymer materials for efficient energy storage”, stresses that they close a major gap in the context of a completely renewable energy supply system. Although there have been “green” technologies for energy generation in the past, there have not been any “green” energy storage facilities.
Martin Hager presented the concept of printable film batteries made from organic raw materials last month at the international conference “Polymers and Energy”, an event held at Friedrich Schiller University by the macromolecular chemistry group of the Association of German Chemists (GDCh).
Stable radicals – which are molecules that contain at least one unpaired electron – are one of the options chosen to store electrical energy in the plastic batteries. The polymers act as a kind of spine, to which the radicals are attached as active units, like a string of pearls. Further components are conductive additives, such as graphite or nanofibres, as well as a bonding agent. “The active units are crucial, because their structure determines the electric voltage”, says Hager. Both the electrodes – i.e. the anode and the cathode – have to be co-ordinated too. ”There already are numerous well-known cathode materials, which explains why we are now doing research primarily into polymers for the anode”, the chemist explains. The scientists from Jena are opting in this context for concepts that are suitable for industrial production: “To us, one of the preconditions for an optimum electrode blend is that synthesis of it is as simple and inexpensive as possible”, Hager emphasises.
The manufacturing operations for the organic radical batteries are suitable for mass industrial production too: because the conductive polymers can be printed out simply within a few minutes as paste or liquid “ink” via screen or inkjet printing. “With inkjet printing, we can customise the shape of the battery to meet the needs of the application for it, while thicker and thus more powerful batteries can be produced with the help of screen printing”, explains Hager.
Although the capacity of the ultrathin plastic batteries is said to be smaller than that of a conventional battery containing metal, the capacity of the polymer batteries is sufficient for many applications, e.g. for light-emitting diodes or smart packaging that indicates whether the use-by date has been exceeded or the cold chain has been interrupted. The batteries can apparently be recharged within a few minutes too – up to 1,000 times. GD