Studies on the improvement in performance of nickel-metal hydride battery

为了提高镍氢电池负极的性能，研究了化学镀、电镀、含还原剂的碱性溶液处理和金属氧化物的混合处理对合金的表面改性，用异质金属部分替代组成金属控制合金的整体成分，以及合金成分偏离AB_2和AB_5等化学计量比对储氢合金电化学性能的影响。从这项工作中获得的信息可概括如下1.通过用杂质金属替代部分组成金属，使合金成分偏离化学计量比，如AB5和AB2.2，改善了储氢合金的电化学性能。通过在稀土储氢合金表面修饰各种金属和金属氧化物，提高了对氢电极反应的催化活性和高倍率充电性。采用还原剂对Laves相储氢合金进行表面改性，有利于合金的初始活化，提高合金的高倍率放电性能。通过用原子半径较小的异种金属代替组成金属，提高了用电势阶梯法计算的氢在储氢合金中的扩散系数。由于合金成分偏离化学计量比，导致氢在储氢合金中扩散的活化能降低，放电效率提高，从而为高性能二次电池负极材料的设计和开发提供了依据。

For the purpose of improving the performance of negative electrode in a nickel-metal hydride battery, the effects of surface modification of alloys by electroless plating, electroplating, treatment with an alkaline solution containing a reducing agent and mixing of metal oxides and bulk-composition control of alloys by the partial substitution of foreign metals for constituent metals and the deviation of alloy composition from stoichiometric ratio such as AB_2 and AB_5 on the electrochemical characteristics of hydrogen storage alloys were investigated. The information obtained from this work can be summarized as follows.1. Electrochemical characteristics of the hydrogen storage alloys was improved by substituting foreign metals for a part of constituent metals and deviating alloy composition from stoichiometric ratio such as AB_5 and AB_2.2. Catalytic activity for hydrogen electrode reaction and high-rate chargeability increased by modifying various metals and metal oxides on the surface of the rare earth hydrogen storage alloys.3. Surface modification of the Laves-phase hydrogen storage alloys by a reducing agent resulted in easier initial activation and the increase in the high-rate dischargeability.4. Diffusion coefficient of hydrogen in the hydrogen storage alloys evaluated from the potential step method increased by substituting foreign metals having smaller atomic radius for constituent metals.5. Additional deviations of the alloy composition from the stoichiometric ratio lead to the decrease in activation energy for the hydrogen diffusion in the hydrogen storage alloys and the increase in discharge efficiency.Thus, several guidelines of designing the hydrogen storage alloys and developing the negative electrodes for high performance secondary batteries could be proposed.