CN1182609C - Preparation method of nickel-metal hydride battery negative electrode alloy material - Google Patents

Abstract

The invention belongs to a preparation method of a high-power negative electrode alloy material for a nickel-metal hydride battery. Using commercially available 99.9% (mass) La or La-rich mixed rare earth metals, vacuum smelting to remove interstitial impurities, and commercially available Mg, Ni, Al, Zn, Co and Mo as raw materials, Mg is made of 30% Mg by mass The form of Mg-La master alloy is added according to La _1-k Mg _k Ni _3-xyzj Al _x Mn _y Zn _z Co _j Mo (300-1000ppm) chemical formula ratio metal, prepared into AB3 type non-stoichiometric ratio rare earth alloy, wherein , x=0.1-0.3, y=0.1-0.15, z=0.05-0.08, j=0.1-0.2. After smelting, cooling and crushing, it is ground into alloy powder with a mesh size of less than 250, which is used as the negative electrode active material of the nickel-hydrogen battery. The alloy has a current discharge of 60mA/g at room temperature and an electrochemical capacity of 300mAh/g; when it is discharged at a current above 3,000mA/g, it has the characteristics of high capacity, even at a high current of 4,200mA/g. The electrochemical capacity still reaches 161mAh/g.

Description

Preparation method of nickel-metal hydride battery negative electrode alloy material

technical field

The invention belongs to a preparation method of a nickel-metal hydride battery negative electrode alloy material.

Background technique

Nickel-metal hydride batteries are recognized as green batteries with high specific energy and high specific power. Nickel-hydrogen batteries using AB ₅ -type rare earth alloys as negative electrode materials have been widely used in power supplies for mobile phones, laptop computers, photography, etc., and have also been tested as power supplies for hybrid electric vehicles and electric vehicles. In the future, the main direction of nickel-metal hydride battery development is power batteries, and the main application areas are as power sources for vehicles such as hybrid electric vehicles, electric vehicles, mopeds and electric tools; in some fields such as aviation, communications and Backup power, partial replacement of nickel-cadmium batteries is also an important application aspect. This requires nickel-metal hydride batteries to have a large capacity such as 30-100Ah and high power, which can be discharged at a current above 15-20C. At present, the nickel-metal hydride battery with AB ₅ rare earth alloy as the negative electrode material has a discharge current in the range of 5-10C, which cannot meet the requirements of high-power use.

CN1,285,621A reported that the addition of boron can improve the high-current discharge performance of the AB ₅ type rare earth hydrogen storage alloy. When the current discharge is 3000mA/g, the discharge cut-off voltage is 0.3V relative to the Hg/HgO reference electrode, and the maximum discharge capacity is 196mAh/g. US Patent No. 5,851,698 reports a nickel-metal hydride battery in which Ti-V-Zr-Ni alloy is used as the negative electrode to connect the high-power electrode and the low-resistance electrode. The key technology of high-power nickel-metal hydride batteries is the negative electrode material. Of course, a high-capacity positive electrode, a thin diaphragm with a strong ability to retain the electrolyte solution, and a small internal resistance of the battery are all necessary. During the charging/discharging process, the kinetic performance of the electrochemical reaction at the interface between the negative electrode material and the electrolyte is better, the reaction speed is fast, and the activation overpotential is low, which are the basic requirements for high-power negative electrode materials for nickel-metal hydride batteries.

Contents of the invention

The object of the invention is to provide a method for preparing a nickel-metal hydride battery negative electrode alloy material. The method uses La or La-rich mixed rare earth M with a mass purity of 99.9%, vacuum smelting to remove interstitial impurities, and commercially available Mg, Ni, Al, Zn, Co, Mn and Mo as raw materials in a vacuum electric arc furnace. After entering the dehydrated argon, carry out high-temperature melting.

The present invention is based on the following three principles in terms of alloy material component design:

(1) The electron transfer of hydrogen is the controlling step of its oxidation reaction;

(2) Hydrogen exists between the crystal planes, and the hydrogen diffusion channel should be smooth;

(3) The second phase present in the alloy acts as an electrochemical catalyst.

In the design of the negative electrode alloy material composition described in this application, La, or rich La mixed rare earth M and Mg are selected as elements that can form stable hydrides with hydrogen; Ni, Al, Zn, Co, Mn and Mo are selected as Elements that cannot generate stable hydrides, but Ni can catalyze the oxidation-reduction reaction of hydrogen; Co can improve the cycle life of alloy materials; Al, Zn oxides have anti-corrosion effects on the alloy surface; Mn is conducive to improving the electrical properties of the alloy. Chemical capacity, Mo is beneficial to increase the exchange current density and form the second phase, which plays an electrochemical catalytic role; the addition of Mg can also improve the electrochemical capacity of the alloy. The negative electrode alloy material prepared by this method has a current discharge of 60mA/g at room temperature and an electrochemical capacity of 300mAh/g; when the current discharge is above 3000mA/g, it has the characteristics of a very high electrochemical capacity, even at 4200mA/g When discharged at a high current, the electrochemical capacity still reaches 161.6mAh/g, while the capacity of the commercial AB ₅ type rare earth alloy as a comparison is only 53.4mAh/g, see Table 1 for details.

The invention uses commercially available La or La-rich mixed rare earths M, Mg, Ni, Al, Zn, Co, Mn and Mo with a purity of 99.9% as raw materials. Mg is added in the form of Mg-La master alloy containing 30% Mg, or Mg-La-rich mixed rare earth master alloy. The composition of the rare earth elements in the La-rich mixed rare earth M is: La=75-77%, Ce=5-6%, Pr=15-16%, and the purity of the rare earth is greater than 99%. According to the following chemical formula: M _1-k Mg _k Ni _3-xyzj Al _x Mn _y Zn _z Co _j and containing Mo300-1000ppm ratio metals, AB ₃ type non-stoichiometric ratio rare earth alloy is prepared. Where k=0.05-0.3, x=0.1-0.3, y=0.1-0.15, z=0.05-0.08, j=0.1-0.2. When the vacuum degree in the vacuum electric arc furnace reaches (3～0.5)×10 ^-3 Pa, fill it with dehydrated argon gas to (0.03～1) MPa, melt with electric arc and turn over several times to ensure the uniformity of alloy composition . The alloy is cooled, crushed and ground to make alloy powder, or the alloy is heat-treated at 550°C to 800°C under an argon atmosphere for 5 to 10 hours, the alloy is cooled, crushed, and ground to make alloy powder, and the alloy powder below 250 mesh is taken as the negative electrode active substance. After mixing with Ni powder at a mass ratio of 1:5, keep it under 10Mpa pressure for 2 minutes, and cold press it into a thin disc with a diameter of 10mm as the negative electrode. Sintered NiOOH/Ni(OH) ₂ is used as positive electrode, polymer non-woven fabric is used as diaphragm, and a simulated battery is formed in 6M KOH solution. The discharge capacity of the alloy material is measured at room temperature using a computer-controlled DC-5 charge/discharge instrument. Determination.

The present invention provides embodiment as follows:

Example 1:

In the La _1-k Mg _k Ni _3-xyzj Al _x Mn _y Zn _z Co _j Mo system, k=0.05, x=0.1, y=0.05, z=0.05, j=0.1, Mo=300ppm. After the vacuum degree in the vacuum electric arc furnace reaches 3×10 ^-3 Pa, it is filled with dehydrated argon gas to 0.03 MPa, melted by electric arc and turned over several times to ensure the uniformity of alloy composition. The alloy was heat-treated at 550°C for 5 hours under an argon atmosphere. After the alloy is cooled, it is crushed and ground into alloy powder, and the alloy powder below 250 mesh is taken as the negative electrode active material, and its electrochemical capacity is measured. At room temperature, charge at 60mA/g for 5 hours, then discharge at 1,500mA/g after a 2-minute pause, and the discharge cut-off voltage is 0.9V. The electrochemical capacity is 208.1mAh/g.

Example 2:

All the other are with embodiment 1. Take k=0.1, x=0.3, y=0.1, z=0.08, j=0.15, Mo=1,000ppm. After the vacuum degree in the vacuum electric arc furnace reaches 0.5×10 ^-3 Pa, it is filled with dehydrated argon gas to 1 MPa, melted by electric arc and turned over several times to ensure the uniformity of alloy composition. The alloy was heat-treated at 800°C for 10 hours under an argon atmosphere. Discharged at a current of 2,100mA/g, the discharge cut-off voltage was 0.9V, and the electrochemical capacity was 187.3mAh/g.

Example 3:

The rest are the same as in Example 1, with La-rich mixed rare earth instead of La; k=0.2, x=0.2, y=0.15, z=0.08, j=0.15, Mo=500ppm. After the vacuum degree in the vacuum electric arc furnace reaches 1.5×10 ^-3 Pa, it is filled with dehydrated argon gas to 0.05MPa, melted by electric arc and turned over several times to ensure the uniformity of alloy composition. The alloy was heat-treated at 600°C for 7 hours under an argon atmosphere. Discharge with a current of 3,000mA/g, and the discharge cut-off voltage is 0.9V. The electrochemical capacity is 153.7mAh/g.

Example 4:

The rest are the same as in Example 1, with La-rich mixed rare earths instead of La; k=0.3, x=0.25, y=0.1, z=0.06, j=0.15, Mo=500ppm; the alloy is heat-treated at 650°C for 6 hours under an argon atmosphere Cool, crush and grind to make alloy powder, and take the alloy powder below 250 mesh as the negative electrode active material. Discharged at a current of 3,300mA/g, the discharge cut-off voltage was 0.9V, and the electrochemical capacity was 163.6mAh/g.

Example 5:

All the other are the same as Example 1, replace La with rich La mixed rare earth; Get k=0.3, x=0.25, y=0.1, z=0.06, j=0.15; With 4,200mA/g current discharge, discharge cut-off voltage 0.9V, electric The chemical capacity is 161.6mAh/g.

Table 1 The discharge capacity of the embodiment and the commercial AB ₅ type rare earth alloy under different discharge current conditions, mAh/g Discharge current/mA/g Example 1 Example 2 Example 3 Example 4 Example 5 Commercial AB Type ₅ Alloy 1500 208.1 203.8 191.3 219.7 251 235.6 1700 201 197.6 185 210.3 242.5 207.8 2100 189.6 187.3 175.3 196.2 225 176.7 2500 178.6 176 165.3 182.9 211.4 140.2 3000 166.1 163.2 153.7 169.3 193.6 104.4

3300 159.9 159.5 149.1 163.6 186.1 101.2 4200 139.5 139.2 125.3 141.5 161.6 53.4

Claims (2)

1. a kind of preparation method of nickel-metal hydride battery negative electrode alloy material is characterized in that with M, Mg, Ni, Al, Zn, Co, Mn and Mo as raw material, by following chemical formula: M _1-k Mg _k Ni _3-xyzj Al _x Mn _y Zn _z Co _j and containing Mo300-1000ppm ratio metal, wherein M is La with a purity of 99.9% or a La-rich mixed rare earth with a purity greater than 99%, prepared into an AB ₃ type non-stoichiometric rare earth alloy ; where k=0.05~0.3, x=0.1~0.3, y=0.1~0.15, z=0.05~0.08, j=0.1~0.2; when the vacuum degree in the vacuum electric arc furnace reaches 3~0.5×10 ^-3 Pa, Fill it with dehydrated argon gas to 0.03-1MPa, smelt it with an electric arc and turn it over. After the alloy is heat-treated at 550°C-800°C in an argon atmosphere for 5-10 hours, the alloy is cooled, crushed, and ground to make alloy powder. Take 250 The alloy powder below the mesh is the negative electrode active material. 2. the preparation method of nickel-metal hydride battery negative electrode alloy material as claimed in claim 1 is characterized in that Mg is the Mg-La master alloy containing 30% Mg, or the form of Mg-rich La mixed rare earth master alloy join in.