(722e) Influence of Electrolyte Composition and Positive Electrode Materials on the Mg-Containing Type Nimh Batteries

Nickelemetal hydride (NiMH) batteries have been widely used in today’s power tools and portable applications due to their advantages such as flexible design, excellent power, long cycle life etc.  Traditionally, KOH solutions with high concentration are widely used as electrolyte in NiMH batteries.  However, KOH solution is highly corrosive and not environmental friendly, especially for some active materials that contained in metal hydride electrode, such as Mg, Al metals.  KOH solutions with high concentration can easily react with Mg, Al, and greatly decrease the electrochemical performance of cathode electrode. Some MgNi2, Mg2Ni base alloys have been reported having high discharge capacity and high energy density. However, because KOH reacts with Mg in alloy and changed the surface structure of anode electrode material, NiMgH cells show a very short cyclic life and commercialization becomes impossible.  In this research some additives are used to minimize the negative effect of KOH electrolyte in NiMgH.  A series of Cl^- and F^- containing salts are proved to efficiently decrease the corrosion of KOH solutions and promote the electrochemical performance of electrolytes, such as LiCl and KF.  New electrolytes are prepared and characterized in NiMgH system.  In this study, a series of modified Ni(OH)2 are prepared and used as positive electrode materials.  The effects of new electrolytes on these modified Ni(OH)2 are investigated. It shows that α-Ni(OH)2 phase in the positive electrode materials is stabilized in new electrolytes, which greatly prolong the cyclic life of NiMgH cells.