Since the end of February 2013, the team from the Japanese Kogakuin University – six men, led by Professor Sato, have been engaged in the development and implementation of innovative idea – almost transparent lithium-ion battery.
Finally, after two and a half years, namely 27 August 2015, on held in Tokyo exhibition «Innovation Japan 2015», researchers presented to the public a working prototype, translucent battery that can be charging by the light of different wavelengths, from red to near ultraviolet.
Thin films of electrodes of anode and cathode, the thickness of 90 and 80 nanometers respectively, have turned out almost transparent. The larger the charging light wavelength, the more transparent electrodes-films after charging. Thus, under the effect of green light, whose wavelength is 550 nanometers, general transparency is 60%, and under the action of sunlight, the density of the electrodes of lithium is significantly increased, and the transparency is decreased to 30%.
The basis of electrolyte for the positive electrode, it has been decided to use Li3Fe2 (PO4) 3 (LFP), and for negative – Li4Ti5O12 (LTO) and LiPF6 (hexafluorophosphate of lithium). In the production of conventional, non-transparent lithium-ion batteries also are widely used these materials.
In 2013, the researchers chose their as the most suitable for this goal. The films of anode and cathode were applied on glass substrates at an air temperature of 550 degrees for 30 and 10 minutes, respectively.
These batteries can be charged both by sunlight, replacing the solar panels, and by other light sources of appropriate brightness. The demonstration at the exhibition showed how the new battery five times was charged and discharged from the ultraviolet with the energy density of 10 mW / cm², which is about 10% of normal sunlight. The output voltage was 3.6 volts, as in conventional lithium batteries.
Tests in the laboratory prior to exhibition showed that 20 cycles of charge-discharge, a new type of battery can withstand without loss in the characteristics.
Inventors believe that their transparent batteries will be fully perspective solution to cover the windows of buildings, car glasses and other transparent surfaces as a light toning, capable of producing an electric current.
This is exactly that will allow to unite renewable energy sources, methods of accumulation and storage of this energy, with the latest systems of so-called “smart buildings”, the windows of which will collect and store solar energy.