Non-stoichiometric hydrogen storage alloy Ml (Ni 0.71 Co 0.15 Al )

Non-stoichiometric hydrogen storage alloy Li Quanan Sang Ge 2, Li Jianwen 2, Chen Yungui 2, Tu Mingyan 2 (1. Department of Materials Engineering, Luoyang Institute of Technology, Luoyang 471039; 2. Department of Metal Materials, Sichuan University, Chengdu 610065) Match X to hydrogen storage alloy (0.700.10.06.08). (4.11 (5.2) The structure 'organization' electrochemical performance and; rcT characteristics of the impact. The results show that as x increases non-stoichiometric alloy lattice constant a value decreases, c value increases, unit cell The volume decreases, c/a reaches its maximum value when x = 5.2, x = 5.0 stoichiometric alloy has the smallest lattice constant and unit cell volume, discharge capacity, charge and discharge cycle stability, and / cT curve plateau pressure Both increase with increasing x, reaching maximum discharge capacity and optimum cycle stability when x=5.2.

Hydrogen storage alloys; Metal hydride electrodes; Rare earth alloys; Electrochemical properties Buschow et al.1 found that the stoichiometric ratio has a great influence on the hydrogen absorption and desorption properties of hydrogen storage alloys, and Tadokoro et al.2 further studied the stoichiometry of Mm(NiCoAlMn)x ( 4.5 1. The newly-developed patented composition of Fuying Misch Ml was used to melt the alloy in a vacuum induction furnace and cast it into a copper mold. After the alloy ingot was broken up, it was milled using a ball milling machine and sieved. The charge and discharge current was 0.2C and 0.4C. And 1C, the discharge cut-off voltage is 0. Table 1 alloy lattice parameters scanning electron microscopy and EDAX9100 spectrometer on the alloy phase structure analysis in Japan on the D / max-rAX-ray diffraction machine, using CuKa radiation.

The curve was measured by electrochemical method, the test temperature was C, and the hydrogen absorption of the alloy was calculated using its plateau pressure. 1 Funding of Sichuan Key Scientific Research Achievements and Transformation Projects (Chuanji 1997-1191) 1999- 11-15; 2000-0 Bu 25 7 for the test brief introduction Li Quanan tcahe male ic Associate Professor Dr. Research (research students should be entropy and ç„“. Segregation in the phase, which is still related to the substitution of the B side of the excess after the element.

2 is the relationship between the discharge capacity and the number of charge and discharge cycles when the alloy is charged and discharged at 0.4C. It can be seen that as the chemical ratio x increases, the discharge capacity increases, the electrochemical cycle stability increases, and the initial discharge capacity increases when the chemical composition x deviates from the range of 0.2. When x=5.2, the maximum discharge capacity reaches 329.9 mAh/g, the discharge capacity still has 190 mAh/g at 427 cycles, and its good electrochemical cycling stability is attributed to the non-stoichiometric alloy having the largest c /a value. It can also be seen that the alloy with x = 5.0 also has good electrochemical cycling stability, because this alloy has better tissue homogeneity.

2.3.2 High-rate discharge performance The discharge capacity of the alloy under different charge/discharge conditions at 20C is shown in Table 3, and the ratio of the discharge capacity to the 20C0.2C discharge capacity at various times of charge/discharge conditions is shown.

It can be seen from Table 3 that the discharge capacity of the 20C elbow decreases to varying degrees with the increase of the discharge rate, but the ratio of the discharge capacity of the alloy to the Table 3 under the different charge and discharge conditions is basically the same. More than 93%. At 1C discharge, the discharge performance slightly increases with increasing x, then decreases slightly when x>5.0; the discharge performance at 1C is best when x=5.0, slightly better than the discharge performance of non-stoichiometric alloy 1C .

2.3.3 Discharge Capacity at Different Temperatures The discharge capacity at 0C for C temperature is also listed in Table 3. From Table 3, it can be seen that compared with 20C, the discharge capacity of all alloys at 40C almost did not decrease, and the ratio was above 98%. Among them, the non-stoichiometric alloys are kept above 99%. This shows that all alloy discharge capacities are insensitive to temperature in the range of 20-40C, especially for nonstoichiometric alloys.

The effect of temperature change on the discharge capacity is twofold. Increasing the temperature generally increases the discharge capacity, but if the temperature is too high, the discharge capacity decreases. This is because, on the one hand, the charge-discharge process is actually an alloy hydrogen absorption and desorption process, the hydrogen release reaction is an endothermic reaction, and the temperature increase is conducive to the endothermic reaction, so a higher temperature is favorable for discharge (dehydration) The reaction proceeds; on the other hand, the equilibrium hydrogen pressure increases as the temperature increases, and the hydrogen inside the hydride is more easily desorbed and oxidized into water, which is favorable for the discharge; however, when the temperature is too high, hydrogen diffuses inside the alloy. Rapidly increased, due to the limitations of the surface catalysis and reaction speed of the alloy, hydrogen atoms diffused from the interior of the alloy to the surface will be desorbed into H2 due to partial oxidation, resulting in a decrease in the discharge capacity of the alloy at higher temperatures. According to the results of this study, non-stoichiometric alloys at 40C have almost no drop in discharge capacity stoichiometric alloys with higher tables! The role of cathodic activation is related to the presence of a small amount of secondary phase in the alloy.

The pc-T curves for the alloys are shown in Table 4 and their midpoint pressures are shown in Table 4. From Table 4 and Table 4, it can be seen that as the stoichiometry x increases, the alloy plateau pressure increases, and LaNix (4. 5.4) and Mn (B5) x (0.88 using 20C and 40C plateau pressures can be used to calculate the hydriding heat of the alloy.ç„“ah and entropy change As, and the results are also listed in Table 4. It can be seen from Table 4 that as the chemical ratio x increases, an ah and an as decrease, because a side is a strong hydride element, forming hydrogenation The ah of the material is large, and the b side decreases by one AH of the hydrogenation reaction of the alloy with the relative content (X) of the side B. This shows that the hydride stability of the poor Ml alloy is low, and the hydrogen atom has a weak effect on the metal atom. It facilitates the discharge reaction.

Metal Materials and Engineering). 1997, 26(3) (editor Peng Chaoqun)