Influence of surface pretreatment and charge–discharge mode on cycle performance of metal hydride electrodes

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Abstract

The influence of surface pretreatment and charge–discharge mode on the cycle performance of metal hydride (MH) electrodes is studied by using stable, AB5-type, hydrogen-storage, alloy particles. The initial electrochemical performance of MH electrodes, which use copper-coated and electroless nickel-plated hydrogen-storage alloy particles, respectively, is improved, but the cycle lives are the same as that of a bare MH electrode. It is considered that the cycle lives of MH electrodes depend primarily on the bulk properties of hydrogen-storage alloy particles. The pulverization of these particles is the main cause of the degradation in electrode life. In addition, it is found that overcharging accelerates the decline in the capacity of the MH electrode. The decreasing charge efficiency of the MH electrode during the course of charge–discharge cycling is due partly to the declining charge–discharge coulombic efficiency of the MH electrode, and its accumulated effect is an important cause of performance degradation of sealed MH/Ni batteries.

Introduction

The nickel/metal hydride (Ni/MH) battery which uses an AB5-type metal hydride (MH) electrode has attracted much interest because of its higher electrochemical performance than the nickel/cadmium battery 1, 2. The MH electrode plays an important role in the Ni/MH battery, and its performance is affected by many factors such as the bulk and surface properties of hydrogen-storage alloy particles, the preparation method and the charge–discharge mode of electrode, etc. [3]. To date, copper-coating, electroless nickel-plating and other surface pretreatment methods have been investigated extensively and even some of these methods have been applied to the production of Ni/MH batteries 4, 5, 6, 7, 8, 9, 10, 11, 12, 13. Nevertheless, the effects of different pretreatment method on the cycle life and other performances characteristics of the electrode are usually ignored. Moreover, it is necessary to investigate the change in the characteristics of the MH electrode under different working conditions, particular the charge–discharge mode of the MH electrode, in order to increase the performance of the MH/Ni battery.

In this paper, the cycle life of MH electrodes is examined for different surface pretreatment set the hydrogen-storage alloy particles and by changing the charge capacity of MH electrode.

Section snippets

Experimental

A hydrogen-storage alloy (La0.54Ce0.32Pr0.03Nd0.11Ni3.5Co0.8Mn0.4Al0.3) ingot, which was supplied by Beijing General Research Institute for Non-Ferrous Metals, was crushed mechanically to produce a powder of less than 200 mesh. Two kinds of hydrogen-storage alloy particles, which were pretreated either by a copper-coating method [8]or by a electroless nickel-plating method [14], were prepared. The electrodes were constructed by the following procedure. After mixing 75 wt.% alloy particles with

Cycle performance of MH electrodes subjected to different surface pretreatment

Copper-coated and electroless nickel-plated hydrogen storage alloy particles were used to investigate the effects of different surface pretreatment methods on the cycle performance of the MH electrode. The discharge capacity of a bare MH electrode and two copper-coated MH electrodes as a function of cycle number are shown in Fig. 1. Compared with the bare MH electrode, the initial discharge capacity of both copper-coated MH electrodes increases faster with cycling. The 5 wt.% copper-coated and

Conclusions

For AB5-type, hydrogen-storage alloy particles with stable properties, it is demonstrated that proper surface pretreatment of the alloy particles will improve the initial electrochemical performance of the MH electrode. By contrast, the effect of surface pretreatment on cycle life is insignificant. The similarity in the pulverization of the hydrogen-storage alloy pretreated by different methods produces similar changes in the characteristics during long-term cycling. In addition, it is shown

Acknowledgements

The authors are grateful for the financial support of the National Science Foundation and New Material Division, National High-Technology Research and Development Committee.

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