A Japanese research team from the Kogakuin University in Tokyo (Shinjuku) unveiled a translucent lithium-ion battery-solar panel at the Innovation Japan 2015, a trade fair end of August 2015 in Tokyo. The special feature is the fact that it recharges itself by using sunlight. No additional equipment is needed, such as photovoltaic generators or wind power plants. The research team is led by the professor at the Department of Applied Physics an president of Kogakuin University, Mitsunoba Sato. Already 2013, the group announced the rechargeable battery in a thesis.
The translucent feature of the solar battery opens interesting fields of application. Windows or whole glass facades could power offices or apartments with emission-free energy. Another possible application might be the use in cars or smartphones.
The presented prototype has an output voltage of about 3.6V with a specific power output of 10mW/cm2, which is about 1/10 that of sunlight. It can be charged and discharged 20 times. The thickness of 80 to 90 nanometers is the reason for the light transmission of the battery. Whilst the negative electrode is made of lithium titanate (Li4Ti5O12) and lithium hexafluorophosphate (LiPF6) the positive electrode of the battery is lithium iron phosphate (Li3Fe2(PO4)3). The light transmittance of the battery lowers for a wavelength of about 550nm to about 30% after charging.