| The application of popularly used Ni/MH battery has been restricted in military devices and gelid areas for its poor discharge performances at low-temperature, especially at -40 ℃ or even blow. Hydrogen storage electrode alloys play a key role in discharge processing of Ni/MH battery at low-temperature. In this dissertation, the present development of low-temperature performances of hydrogen storage alloy was reviewed and some unsovled problems were presented. The effects of compositions and stoichiometry of Nd-free AB5 type hydrogen storage alloy on the low-temperature performances were studied and discussed, and the following important results were obtained.1. The effects of A-side elements, B-side elements and non-stoichiometry on the low-temperature and room temperature performances of the hydrogen storage alloys were investigated systematically.1) Effects of A-side elements: (1) For single rare earth element hydrogen storage alloys, CeB5 has the far better low-temperature performances than LaB5 and PrB5, and the low-temperature discharge capacity of LaB5 is a little bit higher than that of PrB5.(2) For binary rare earth elements hydrogen storage alloys, the increaseof Ce content in the alloys is beneficial to improve the low-temperature discharge capacity, but the increase of La and Pr content in the alloys decrease the low-temperature discharge capacity. However, when the La and Ce contents in the alloys set among20%~40%, the low-temperature discharge capacity of the alloys remains the same, and the La-containing alloy has higher discharge capacity than the Pr-containing alloy. (3) For ternary rare earth elements hydrogen storage alloys tested with a uniform design method, the aggregation analysis shows that the low-temperature discharge capacity correlates well with the square of the Ce content in the alloy. (4) On the basis of the alloy optimized with the uniform design, the Ce content in the alloy was adjusted, and it shows that the increase of Ce content tends to decrease the low-temperature discharge capacity of the alloy. Then the Pr content was changed, and it shows that a certain amount of Pr does good to the low-temperature discharge capacity of the alloy.2) Effects of B-side elements: (1) The optimized results of B-side elements with the uniform design shows that the low-temperature discharge capacity of the alloy correlates negatively with the Co content in the alloy. (2) Based on the above B-side optimized results, Co content was adjusted, and it shows that with the increase of Co content the low-temperature discharge capacity first decreases and then increases.(3) Based on (2), the Al content was varied, and it shows that there is a increase tendency of low-temperature discharge capacity with the increase of Al content. (4) Based on (3), the Mn content was further adjusted, and it shows that Mn tends to improve low-temperature discharge capacity .3) Non-stoichiometry does harm to the low-temperature discharge capacity.4) The compositions have a little effect on the specific area and the cycle life of the alloy at the room temperature.2. Hydrogen diffusion coefficient and kinetics parameters, including exchange current density and symmetry factor of the electrode discharging process , were determined at -40℃, and the factors that evidently influence the low-temperature performances of the alloys were analyzed.l)Effects of A-side elements: (1) For single rare earth element hydrogenstorage alloy, the low-temperature discharge capacity mainly depends on the hydrogen diffusion coefficient, and the exchange current density also influences the low-temperature discharge capacity to a certain extent. (2) For binary rare earth elements hydrogen storage alloy, 0.2C low-temperature discharge capacity of La1-xCexB5 is determined by the hydrogen diffusion coefficient, but 0.4C discharge capacity is independent of the hydrogen diffusion and the exchange current density; the low-temperature discharge capacity of La1-xPrxB5 is mainly determined by the hydrogen diffusion coefficient, and the exchange current density affects the capacity to some extent; 0.4C discharge capacity of Ce1-x PrxB5 is determined by the hydrogen diffusion coefficient, but 0.2C discharge capacity is determined by the hydrogen diffusion and the exchange current density. (3) For ternary rare earth elements hydrogen storage alloy tested with the uniform design method, the low-temperature discharge capacity is controlled by the hydrogen diffusion coefficient and the exchange current density. (4)For the above optimized ternary rare earth elements hydrogen storage alloy which was adjusted again with different Ce contents, 0.4C discharge capacity is mainly affected by the exchange current density, but 0.2C capacity is influenced by the hydrogen diffusion coefficient to a great extent. (5) For the above optimized ternary rare earth elements hydrogen storage alloy which was adjusted again with different Pr contents, 0.4C discharge capacity is mainly affected by the exchange current density, but 0.2C capacity is influenced by the hydrogen diffusion coefficient greatly.2) Effects of B-side elements: (1) For the uniform designed alloys with different contents of B-side elements, the low-temperature discharge capacity is determined by the hydrogen diffusion coefficient and the exchange current density. (2) Based on (1), Co content was adjusted, and the low-temperature discharge capacity of the alloys with different Co content is mainly controlled by the exchange current density. (3) Based on (2), Al content was adjusted, and the low-temperature discharge capacity of the alloys with different Al content is not related with the hydrogen diffusion coefficient and the exchange current density. (4) Based on (3), Mn content was also adjusted, and the low-temperature discharge capacity of thealloy with different Mn content is mainly determined by the exchange current density.3) For the non-stiochiometric alloy, the discharge capacity is mainly determined by the exchange current density, and the hydrogen diffusion coefficient affects the capacity to a certain degree.3. Pressure-Composition-Temperature (PCT) curves of the alloys were determined at -40 ℃, and the thermodynamics parameters including the change of enthalpy, entropy and change of free energyi were calculated. The relationship between change of free energy and hydrogen diffusion coefficient was analyzed. It was found that for the single rare earth element alloy, binary rare earth elements alloy and the ternary rare earth elements alloy designed by uniform method, the hydrogen diffusion coefficient correlates well with the change of free energy, which indicates that the hydrogen diffusion coefficient is mainly determined by the stability of the hydride. But for the other alloys, the hydrogen diffusion coefficient is not related to the stability of the alloys.4. Phase structure and lattice parameters of the alloys were examined, and effect of lattice parameters of the alloys on the low-temperature discharge performances was analyzed. It was found that all alloys except AB5-x alloys are CaCu5 single phase. It was found that the alloys with large c axis have higher low-temperature discharge capacity. The reason for this is that the alloys with large c axis will cause less crystal lattice distortion energy when hydrogen atoms diffuse in the alloy. Crystal cell volume is mainly determined by a axis, and the larger the a axis, the higher the discharge capacity at room temperature. In AB5-x alloys, when the stoichiometry decreases from 5 to less than 5, some second phases emerge in the alloys, LaNiSb, LaNiSb+La2Ni3Sb4 and LaNiSb+La2Ni3Sb4+La2Ni7. The second phase has bad effect on the low-temperature discharge capacity.5. The affecting mechanism between compositions and low-temperature discharge capacity was analyzed. The role of A-side elements is to adjust the interaction between hydrogen and B-side atoms . The interaction between hydrogen and B-side atoms is stronger than that between hydrogen and A-side atoms, and thestability of the hydride is mainly determined by A-side elements. B-side elements themselves have little effect on the interaction between hydrogen and B-side atoms. The main role of B-side elements is to change the state of electrode surface and therefore the exchange current density.6. A wide range temperature D-type Ni/MH battery was made with the low-temperature hydrogen storage alloy, and the battery shows excellent performances. At room temperature, the battery can deliver 9.2 and 9.0 Ah at 0.2C and 1C respectively. The battery has a self discharge rate of 20% after 28 days at room temperature. The cycle life of the battery is over 300. the battery can release 70% of its maximal capacity at -40℃/0.2C, 78% of its maximal capacity at -40℃ /0.4C, and 59% of its maximal capacity at -45℃/0.2C when terminal voltage reaches 1.0V, 0.9V and 1.0V respectively. But the battery delivers only a small fraction of the real capacity at -40℃/1C. The charge efficiency of the battery is about 70% at +55 ℃. The battery can discharge 91% of its maximal capacity at +55 ℃, and it remains the same capacity after stored at +50℃ for 28 days. The performances of the wide temperature range Ni/MH battery exceed apparently the Chinese standard of military Ni/MH battery.
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