The Furukawa Battery Co Ltd developed a magnesium (Mg)-air fuel cell for emergency use.
When water is poured into the cell, it begins generating power. It can generate electricity for up to five days. The cell has a capacity of 300Wh and can charge a smartphone up to 30 times, the company said. It was unveiled at the 5th Int'l Rechargeable Battery Expo, which runs from Feb 26 to 28, 2014, in Tokyo.
Though the exhibited cell was a prototype, Furukawa Battery named it "Mg Box" and designed a package for it. The cell measures 233 x 226 x 226mm and weighs about 1.6kg before water is added. It can be stored for 10 years. The cell is equipped with two USB output ports and has an output voltage of DC5.0V and maximum current of 1.2A.
A Mg-air fuel cell is a kind of metal-air battery and a primary cell that uses Mg for the negative electrode and ambient air as an active material for the positive electrode. It utilizes a phenomenon in which Mg is bound to hydroxide ions and emits electrons. So, after the use of the cell, Mg at the negative electrode becomes magnesium hydroxide.
The prototype contains four battery cells and starts power generation when 500mL of water is poured into each of the cells (a total of 2L). In general, a Mg-air fuel cell uses salt solution as an electrolyte. On the other hand, the prototype can use not only seawater but also fresh water because it contains an electrolyte. Therefore, it can be easily used in a time of emergency.
"It can generate power even with unclean river water or urine," Furukawa Battery said.
Mg-air fuel cells have problems related to their safety and long-term use because Mg is inflammable and melted by salt solution (electrolyte). To address those issues, Furukawa Battery employed a flame-retardant Mg alloy for the negative electrode. The package is made of cardboard so that it becomes easy to discard or recycle the cell. Moreover, there are vent holes on the sides of the package to intake enough oxygen.