A team of Empa researchers has developed a disposable paper battery that can be activated by water. This can be used to power a wide range of small disposable electronic devices with low power consumption, such as intelligent labels for tracking objects, environmental sensors or medical diagnostic devices. The environmental impact is minimal.
The battery developed by Empa researcher Gustav Nyström and his team consists of at least one electrochemical cell measuring around one square centimeter. Three different inks are printed on a rectangular strip of paper. Salt, in this case simply sodium chloride or common salt, is distributed throughout the paper strip, and one of the two shorter ends of the strip has been dipped in wax. An ink containing graphite flakes is printed on one side of the paper and acts as the positive pole of the battery - the cathode; a second ink containing zinc powder is printed on the reverse side and acts as the negative pole of the battery - the anode. A third ink, containing graphite flakes and carbon black, is printed on both sides of the paper over the other two inks. This forms the current collectors that connect the two poles of the battery to two wires located at the end of the paper strip dipped in wax. If a small amount of water is added, the salt contained in the paper dissolves, charged ions are released and the electrolyte becomes ionically conductive. This step activates the battery.
