CN1173055C - New Rare Earth Hydrogen Storage Electrode Alloys for Nickel-Metal Hydride Secondary Batteries - Google Patents

Abstract

The invention discloses a novel rare earth hydrogen storage electrode alloy for a nickel-metal hydride (Ni-MH) secondary battery. Its composition is: AB _x , where A=La _1-y M _y , B=(NiCoN), 0.01≤y≤0.8; 2.0≤x≤4.0; M=one or two of Mg and Ca, N=one or two or more of Mn, Fe, Mo, Co, Al, Si, Ga, S, Ti, V, Cr, Cu, Zn, Zr, B, Sn. By changing the stoichiometric ratio of the B-side components of the alloy, the material makes the alloy have a chemical composition such as AB _x (2.0≤X≤4.0), that is, a new type of rare earth stoichiometric alloy is formed, and the electrochemical capacity is high. A new type of rare earth hydrogen storage electrode alloy for nickel-metal hydride secondary batteries with long cycle life and good high rate characteristics.

Description

New Rare Earth Hydrogen Storage Electrode Alloys for Nickel-Metal Hydride Secondary Batteries

Technical field

The invention relates to a metal hydride secondary battery, in particular to a novel rare earth hydrogen storage electrode alloy for a nickel-metal hydride secondary battery.

Background technique

In recent years, compared with Ni-Cd secondary batteries, nickel-metal hydride (Ni-MH) secondary batteries have high capacity, long cycle life, no memory effect, strong resistance to overcharge and overdischarge, and No environmental pollution and other advantages have become the focus of many scholars at home and abroad.

At present, the more researched hydrogen storage electrode alloys include rare earth-based AB ₅ -type alloys, AB ₂ -type alloys, magnesium-based alloys and vanadium-based solid solution alloys. Among them, the research on the rare earth-based AB ₅ type alloy is the most mature, and has achieved industrialization. However, due to the low capacity of rare earth-based AB ₅ alloys, this has prompted people to research and develop hydrogen storage electrode alloys with higher capacities.

The AB ₂ type Laves phase alloy once attracted people's attention. It has high electrochemical discharge capacity and long cycle life, but its high current discharge capacity and initial activation performance are relatively poor, and its cost is high, so it is difficult to Practical. Magnesium-based alloys use relatively cheap elements such as magnesium and nickel as raw materials, so the cost is quite low, and magnesium-based alloys have high initial electrochemical discharge capacity and excellent activation performance, but the alloy in alkaline electrolyte Corrosion is quite serious, leading to a sharp decline in capacity, and it cannot be practical in the short term. Vanadium-based solid solution alloys, like magnesium-based alloys, also have high initial electrochemical discharge capacity, but due to the serious desolvation of vanadium in alkaline electrolyte, it will also lead to a sharp decline in capacity, and because vanadium is relatively expensive rather than practical value.

Contents of invention

The object of the present invention is to provide a novel rare earth hydrogen storage electrode alloy for nickel-metal hydride secondary batteries.

Its composition is: AB _x , where A=La _1-y M _y , B=(NiCoN), 0.01≤y≤0.8; 2.0≤x≤4.0; M=one or two of Mg, Ca, , N=one or two or more of Mn, Fe, Mo, Co, Al, Si, Ga, S, Ti, V, Cr, Cu, Zn, Zr, B, Sn.

The comprehensive electrochemical performance of the novel rare earth hydrogen storage alloy electrode for nickel-metal hydride (Ni-MH) secondary battery negative electrode proposed by the present invention, including discharge capacity, cycle stability and high rate characteristics, has been significantly improved . Under low current charging and discharging conditions, its performance has surpassed that of the commercialized traditional AB ₅ hydrogen storage electrode alloy. In addition, its cost is relatively low, so in the near future, it will replace the existing traditional AB ₅ hydrogen storage electrode alloy and become a new generation of nickel-metal hydride (Ni-MH) hydrogen storage electrode alloy for the negative electrode of secondary batteries , and its cost performance will greatly exceed that of lithium-ion secondary batteries, thereby greatly improving the market competitiveness of nickel-metal hydride (Ni-MH) secondary batteries.

Description of drawings

Fig. 1 is according to the relationship curve between the discharge capacity of the electrode and the number of cycles of the novel rare earth system hydrogen storage electrode alloy La _0.7 Mg _0.3 (NiCoAl) _x (x=2,3,3.5,4) described in Example 1;

Fig. 2 is according to the high rate discharge characteristic curve of the rare earth hydrogen storage electrode alloy La _0.7 Mg _0.3 (NiCoAl) _x (x=2,3,3.5,4) electrode described in embodiment 2;

Fig. 3 is the discharge capacity and number of cycles of the new rare earth hydrogen storage electrode alloy La _0.7 Mg _0.3 (NiCoAl) _3.5 electrode obtained according to the commercialized traditional AB ₅ hydrogen storage alloy electrode described in the comparative example and the method described in Example 1 relationship curve between them.

Detailed ways

The B-side stoichiometric ratio x of the novel rare earth hydrogen storage electrode alloy for nickel-metal hydride (Ni-MH) secondary battery negative electrode is 2, 3, 3.5, 4. The smelting of the new rare earth hydrogen storage electrode alloy is prepared by vacuum magnetic levitation furnace or electric arc furnace.

Example 1

According to the design composition of the new rare earth hydrogen storage electrode alloy AB _x (x = 2, 2.5, 3, 3.5), it is prepared by melting in a vacuum magnetic levitation furnace. The melted alloys include: La _0.7 Mg _0.3 (NiCo) _x , La _0.7 Mg _0.3 (NiCoMn) _x , La _0.7 Mg _0.3 (NiCoAl) _x , La _0.7 Mg _0.3 (NiCoFe) _x , La _0.7 Mg _0.3 (NiCoMnAl) _x , La _0.7 Mg _0.3 (NiCoMo) _x , La _0.7 Mg _0.3 (NiCoS) _x , La _0.7 Mg _0.3 (NiCoSi) _x , La _0.7 Mg _0.3 (NiCoGa) _x . Wherein, x=2, 2.5, 3, 3.5, and the purity of the alloy components La, Mg, Mn, Ni, Fe, Mo, Co, Al, Si, Ga, S is all above 90%. Then each part of the alloy was taken for electrochemical cycle life test. The test is carried out in an open three-electrode system, which includes a working electrode (ie hydrogen storage alloy electrode), a sintered Ni(OH) ₂ /NiOOH auxiliary electrode and a Hg/HgO reference electrode. The electrolyte is 6N KOH aqueous solution, and the test temperature is kept at 303K. All test electrodes are made by uniformly mixing 100mg hydrogen storage electrode alloy powder (300 mesh) and 400mg carbonyl nickel powder and pressing them into electrode sheets with a diameter of 10mm and a thickness of 1mm under a pressure of 20Mpa. The electrode is charged with a current of 100mA/g and discharged with a current of 60mA/g, wherein the charging time is 5 hours, and the discharge cut-off potential is -0.6V (relative to the Hg/HgO reference electrode).

Example 2

The new rare earth hydrogen storage electrode alloy AB _x (x=2, 3, 3.5, 4, 5) smelted in Example 1 was still selected as the alloy, and part of the alloy was selected for high rate performance test. The manufacturing method of the test system and the electrode sheet is the same as that of Example 1. The test temperature was maintained at 303K. The electrode is charged with a current of 100mA/g, discharged with a current of 60mA/g, charged for 5 hours, and then discharged at different discharge current densities (I _d =60mA/g, 250mA/g, 500mA/g, 750mA/g, 1000mA/g, 1250mA/g, 1500mA/g), the discharge cut-off potential is -0.6V (relative to Hg/HgO reference electrode).

Comparative example

Some commercial rare earth-based AB ₅ hydrogen storage electrode alloys produced by Sanpu were selected for electrochemical cycle life testing. The system and conditions of the test are the same as in Example 1.

It can be seen from Figure 1 that with the increase of the stoichiometric ratio x of the B-side components of the new rare earth hydrogen storage electrode alloy AB _x , the discharge capacity and cycle stability of the alloy electrode have been significantly improved, especially the chemical The highest discharge capacity of metered alloy AB _3.5 reaches 396mAh/g, and the capacity retention rate still reaches 77.5% after 250 cycles.

It can be seen from Figure 2 that with the change of the stoichiometric ratio x of the B-side components of the new rare earth hydrogen storage electrode alloy AB _x , the high-rate discharge performance of the alloy electrode has also been significantly improved. For stoichiometric alloy AB _3.5 , when the discharge current density is 250mA/g, its HRD value is as high as 96.91%, and when the discharge current density is 1500mA/g, its HRD value can still reach 75.61%.

It can be seen from Figure 3 that under the condition of 60mA/g current charge and discharge, the comprehensive electrochemical performance of the new rare earth stoichiometric alloy AB _3.5 is significantly better than that of the commercialized rare earth based AB ₅ hydrogen storage electrode alloy, and its highest capacity ratio The highest capacity of the commercial rare earth-based AB ₅ hydrogen storage electrode alloy is nearly 80mAh/g higher, and the cycle stability is no less than that of the commercial rare earth-based AB ₅ hydrogen storage electrode alloy.

Claims (1)

1. a new rare-earth based hydrogen storage electrode alloy used for Nickel-Metal Hydride rechargeable batteries is characterized in that, its composition is: AB _x, A=La wherein _1-yM _y, B=(NiCoN), 0.01≤y≤0.8; 2.0≤x≤4.0; One or both compositions among M=Mg, the Ca, one or both among N=Mn, Fe, Mo, Co, Al, Si, Ga, S, Ti, V, Cr, Cu, Zn, Zr, B, the Sn or two or more composition.

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