Surface modification of nickel battery electrodes by cobalt plasma immersion ion implantation and deposition

Nickel hydroxide is the electrochemically active material in the positive electrode of several important rechargeable alkaline-electrolyte batteries. It is believed that the Ni2+ in nickel hydroxide is converted to Ni3+ in nickel oxy-hydroxide as the electrode is electrochemically oxidized during the battery charging process, and the reverse reaction (electrochemical reduction) occurs during the battery discharge. However, the details of this process are not completely understood. Because these electrochemical reactions involve surface charge-transfer processes, it is anticipated that the modification of the electrode surface may result in an improved battery performance. We used broad-beam metal ion implantation and the new technique of metal plasma immersion ion implantation and deposition (MePIIID) to add cobalt and other species to the nickel electrode surface. The principle of the latter technique is explained in detail. It has been demonstrated that implanted and deposited cobalt ions (acting as electronic dopants) balance the huge difference in the conductivities of nickel hydroxide and nickel oxy-hydroxide. This beneficial effect promotes a more complete interconversion between the nickel hydroxide and the nickel oxy-hydroxide and leads to a higher capacity and efficiency of the nickel hydroxide electrode in the batteries applications.