AB5-BASED HYDROGEN STORAGE ALLOY, ELECTRODE FOR Ni-MH BATTERY, SECONDARY BATTERY, AND PREPARATION METHOD OF HYDROGEN STORAGE ALLOY

Abstract

The present invention relates to a hydrogen storage alloy, an electrode for a Ni-MH battery, a secondary battery, and a method for preparing the hydrogen storage alloy. The chemical composition of the hydrogen storage alloy is expressed by the general formula La.sub.(3.0˜3.2)xCe.sub.xZr.sub.ySm.sub.(1−(4.11˜4.2)x−y)Ni.sub.zCo.sub.uMn.sub.vAl.sub.w, where x, y, z, u, v, w are molar ratios, and 0.14≤x≤0.17, 0.02≤y≤0.03, 4.60≤z+u+v+w≤5.33, 0.10≤u≤0.20, 0.25≤v≤0.30, and 0.30≤w≤0.40. The atomic ratio of the metal lanthanum (La) to the metal cerium (Ce) is fixed at 3.0 to 3.2, which satisfies the requirements of the overcharge performance of the electrode material. A side elements are largely substituted by samarium (Sin) element, that is, the atomic ratio of Sin on the A side is 25.6% to 42%, so as to solve the problem of shortened cycle life caused by the small amount of cobalt (Co) atoms. The equilibrium pressure is adjusted by the change in the ratio of Sin to La and Ce to satisfy the requirements of the charge and discharge dynamic performance of the electrode material. The nucleation rate of the solidification process is improved by the addition of zirconium (Zr) to the A side at an atomic ratio of 2% to 3%. The Ni-MH battery negative-electrode material obtained from the hydrogen storage alloy has high overcharge resistance, and good high-rate discharge performance and cycle stability.

Claims

1. An AB.sub.5-based hydrogen storage alloy, characterized in that: its chemical composition is represented by the following general formula:
La.sub.(3.0˜3.2)xCe.sub.xZr.sub.ySm.sub.(1−(4.0˜4.2)x−y)Ni.sub.zCo.sub.uMn.sub.vAl.sub.w, where x, y, z, u, v, w are molar ratios, and 0.14≤x≤0.17, 0.02≤y≤0.03, 4.60≤z+u+v+w≤5.33, 0.10≤u≤0.20, 0.25≤v≤0.30, and 0.30≤w≤0.40.

2. The hydrogen storage alloy according to claim 1, characterized in that: 0.10≤u≤0.20, 5.03≤z+u+v+w5.33, and the hydrogen storage alloy is an AB.sub.5 alloy, where A represents lanthanum, cerium, samarium and zirconium, B represents nickel, cobalt, manganese and aluminum, and the atomic ratio of Sin on the A side is 25.6% to 42%.

3. The hydrogen storage alloy according to claim 1, characterized in that: 0.10≤u≤0.20, 4.60≤z+u+v+w≤4.90, and the hydrogen storage alloy comprises an A.sub.2B.sub.7 phase and an AB.sub.5 phase, where A represents lanthanum, cerium, samarium and zirconium, and B represents nickel, cobalt, manganese and aluminum.

4. The hydrogen storage alloy according to claim 1 or 3, characterized in that: the hydrogen storage alloy is an AB.sub.5 alloy catalyzed by A.sub.2B.sub.7, and the atomic ratio of Sin on the A side is 25.6% to 42%.

5. A method for preparing the AB.sub.5-based hydrogen storage alloy, characterized in that: the method comprises the following steps: the metals lanthanum, cerium, samarium, zirconium, nickel, cobalt, manganese and aluminum are subjected to low-vacuum induction melting at 1400° C. to 1600° C. for 0.5 to 3 h respectively at a molar ratio of 0.42 to 0.544, 0.14 to 0.17, 0.256 to 0.42, 0.02 to 0.03, 3.7 to 4.68, 0.10 to 0.20, 0.25 to 0.30, and 0.30 to 0.40, and then cooled to produce an alloy ingot; and the alloy ingot is annealed in a protective-atmosphere furnace.

6. The preparation method according to claim 5, characterized in that: the molar ratios of the metals lanthanum, cerium, samarium, zirconium, nickel, cobalt, manganese and aluminum are 0.42 to 0.544, 0.14 to 0.17, 0.256 to 0.42, 0.02 to 0.03, 4.25 to 4.68, 0.10 to 0.20, 0.25 to 0.30, and 0.30 to 0.40, respectively.

7. The preparation method according to claim 5, characterized in that: the molar ratios of the metals lanthanum, cerium, samarium, zirconium, nickel, cobalt, manganese and aluminum are 0.420 to 0.544, 0.140 to 0.170, 0.256 to 0.420, 0.020 to 0.030, 3.700 to 4.200, 0.100 to 0.200, 0.250 to 0.300, and 0.300 to 0.400, respectively.

8. The preparation method according to any one of claims 5 to 7, characterized in that: the conditions of the low-vacuum induction melting include evacuating to 10.sup.−1 to 10.sup.−2 Pa, and then filling with argon to 0.01-0.07 MPa; the conditions of the annealing7 treatment include placing the alloy ingot in the protective-atmosphere furnace, evacuating to 10.sup.−1 to 10.sup.−2 Pa, then filling with argon to 0.05-0.08 MPa, and annealing at 1020° C. to 1100° C. for 1 to 10 h.

9. An electrode for a Ni-MH battery, characterized in that: the electrode uses the hydrogen storage alloy according to any one of claims 1 to 4 as a hydrogen storage medium.

10. A secondary battery, characterized in that: this battery uses the electrode for a Ni-MH battery according to claim 9 as a negative electrode.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] FIG. 1 shows a charge-discharge cycle life curve of the Ni-MH battery negative-electrode material in Example 1 of the present invention.

[0025] FIG. 2 shows an XRD test chart of the Ni-MH battery negative-electrode material in Example 20 of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The present invention will be described in further detail below with reference to examples and drawings, but the embodiments of the present invention are not limited thereto.

[0027] The present invention uses metals lanthanum (La), cerium (Ce), zirconium (Zr), samarium (Sin), nickel (Ni), cobalt (Co), manganese (Mn) and aluminum (Al) to form an AB.sub.5 hydrogen storage alloy, and fixes the ratio of lanthanum (La) to cerium (Ce) at 3.0-3.2 to satisfy the requirements of the overcharge performance of the electrode material; A side elements are largely substituted by samarium (Sin) element, that is, the atomic ratio of Sin on the A side is 25.6% to 42.0%, so as to solve the problem of shortened cycle life caused by the small amount of cobalt (Co) atoms; the nucleation rate of the solidification process is improved by the addition of zirconium (Zr) to the A side at an atomic ratio of 2% to 3%; the B-side elements include nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al), and the atomic ratio of nickel (Ni):cobalt (Co):manganese (Mn):aluminum (Al) is (3.70 to 4.68):(0.10 to 0.20):(0.25 to 0.30):(0.30 to 0.40), so as to perform multi-component alloying to improve corrosion resistance and economy.

EXAMPLE 1

[0028] A hydrogen storage alloy La.sub.(3.0˜3.2)xCe.sub.xZr.sub.ySm.sub.(1−(4.0˜4.2)x−y)Ni.sub.zCo.sub.uMn.sub.vAl.sub.w was set to contain La 7.79 at %, Ce 2.49 at %, Zr 0.46 at %, Sin 5.39 at %, Ni 71.60 at %, Co 2.63 at %, Mn 4.08 at %, and Al 5.64 at %, wherein the elements La, Ce, Zr and Sin were A-side elements, and the elements Ni, Co, Mn and Al were B-side elements, thereby forming an AB.sub.5 hydrogen storage alloy La.sub.0.50Ce.sub.0.16Sm.sub.0.34Zr.sub.0.03Ni.sub.4.57Co.sub.0.17Mn.sub.0.26Al.sub.0.36. The atomic ratio of La to Ce was fixed at about 3.1 to satisfy the requirements of the overcharge performance of the electrode material; A side elements are largely substituted by samarium (Sin) element, that is, the atomic ratio of Sin on the A side was about 33%, so as to solve the problem of shortened cycle life caused by the small amount of cobalt (Co) atoms. The equilibrium pressure was adjusted by the change in the ratio of Sin to La and Ce to satisfy the requirements of the charge and discharge dynamic performance of the electrode material. The nucleation rate of the solidification process was improved by the addition of zirconium (Zr) to the A side at an atomic ratio of 2.9%. The B-side elements included nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al), and the atomic ratio of nickel (Ni):cobalt (Co):manganese (Mn):aluminum (Al) was 4.57:0.17:0.26:0.36, so as to perform multi-component alloying to improve corrosion resistance and economy. The ratio of the A-side elements to the B-side elements was adjusted to B/A>5.03, so as to adjust the phase structure, and avoid the formation of the AB.sub.3 phase and A.sub.2B.sub.7 phase with a small excessive amount of the B-side elements.

[0029] Preparation of hydrogen storage alloy La.sub.0.50Ce.sub.0.16Sm.sub.0.34Zr.sub.0.03Ni.sub.4.57Co.sub.0.17Mn.sub.0.26Al.sub.0.36

[0030] Step (1): placing respectively 350.7 g of La, 113.0 g of Ce, 262.7 g of Sin, 11.6 g of Zr, 1362.5 g of Ni, 50.2 g of Co, 72.7 g of Mn, and 49.3 g of Al with purity higher than 99.5% in a crucible of a ZG vacuum induction melting furnace, covering with a furnace lid, then evacuating to a vacuum degree of 10.sup.−1 Pa, filling with argon to a pressure of 0.07 MPa, and melting at 1550° C. for 2 h to obtain a molten metal liquid; pouring the molten metal liquid into a water-cooled ingot mold and cooling, and then discharging to obtain an alloy ingot.

[0031] Step (2): placing the alloy ingot obtained in the previous step in a protective-atmosphere furnace, evacuating to a vacuum degree of 10.sup.−1 Pa, filling with argon to a pressure of 0.08 MPa, and annealing at 1095° C. for 4 h, so as to ensure the homogeneity of the composition of the ABs alloy with high Sin substitution, avoid the formation of the AB.sub.3 phase and A.sub.2B.sub.7 phase with a small excessive amount of the B-side elements, improve the corrosion resistance and cycle life, and finally obtain the hydrogen storage alloy La.sub.0.50Ce.sub.0.16Sm.sub.0.34Zr.sub.0.03Ni.sub.4.57Co.sub.0.17Mn.sub.0.26Al.sub.0.36.

[0032] Removing the oxide layer from the hydrogen storage alloy La.sub.0.50Ce.sub.0.16Sm.sub.0.34Zr.sub.0.03Ni.sub.4.57Co.sub.0.17Mn.sub.0.26Al.sub.0.36, then successively pulverizing, grinding and sieving, and selecting alloy powder with a particle size less than 200 meshes; accurately weighing 0.1 g of the alloy powder and 0.2 g of hydroxy nickel powder, mixing them evenly, then holding them at 15 MPa for 1 min by a powder tablet press to cold press them into an electrode pad with a diameter of Φ=10 mm, and then removing the floats with burrs removed and surface uncompressed; before the test, fixing the alloy electrode pad between two pieces of foamed nickel current collector, leading a nickel wire out, and making the foamed nickel in full contact with the alloy powder; then carrying out the performance test.

[0033] The test results showed that when 120 mA/g was used for the discharge test, the capacity was 302.4 mA.h/g, the capacity retention rate after 242 cycles was 91.14%, 1C discharge capacity reached 96.7% of the maximum capacity, 3C discharge capacity reached 85.7% of the maximum capacity, and 5C discharge capacity reached 72.9% of the maximum capacity.

EXAMPLES 2-18

[0034] A low-vacuum induction melting method, a cooling method, and an annealing treatment were adopted to obtain a hydrogen storage alloy.

[0035] Each element was weighed according to the composition shown in Table 1 below, and the alloy ingot thereof was heat-treated by a ZG vacuum induction melting furnace in an argon atmosphere and then cooled, with the specific steps of the heat treatment and cooling being the same as those in step (1) of Example 1. Then the annealing treatment was carried out; in the specific process of the annealing treatment, except for the heat treatment temperature, the other process conditions were the same as those in step (2) of Example 1; the heat treatment temperature, time, 120 mA/g discharge capacity and 5C discharge capacity percentage were shown in Table 1.

TABLE-US-00001 TABLE 1 Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- ple 2 ple 3 ple 4 ple 5 ple 6 ple 7 ple 8 ple 9 ple 10 ple 11 La (g) 340.3 363.0 351.7 427.0 414.9 427.0 340.3 363.0 351.7 364.6 Ce (g) 114.4 114.4 114.4 114.4 114.4 114.4 114.4 114.4 114.4 114.4 Sm (g) 386.0 361.5 373.7 292.2 305.3 292.2 386.0 361.5 373.7 359.7 Zr (g) 11.6 10.6 12.6 10.6 10.6 10.6 14.6 11.8 10.6 15.6 Ni (g) 1489.3 1489.3 1489.3 1472.1 1489.3 1489.3 1472.1 1472.1 1455.0 1472.1 Co (g) 51.6 51.6 51.6 68.8 51.6 51.6 68.8 51.6 51.6 51.6 Mn (g) 80.1 80.1 80.1 80.1 80.1 80.1 80.1 80.1 80.1 80.1 Al (g) 47.2 47.2 47.2 47.2 47.2 47.2 47.2 47.2 47.2 47.2 Heat treatment 1050 1090 1085 1095 1100 1080 1090 1050 1095 1100 temperature (° C.) 120 mA/g 309.2 301.3 304.6 306.2 302.4 306.1 309.2 303.6 306.8 307.7 discharge capacity 5 C discharge capacity 73.0 74.0 73.6 73.5 73.8 73.1 73.0 74.0 73.4 73.1 percentage Exam- Exam- Exam- Exam- Exam- Exam- Exam- ple 12 ple 13 ple 14 ple 15 ple 16 ple 17 ple 18 La (g) 414.9 427.0 340.3 363.0 351.7 364.6 351.7 Ce (g) 114.4 114.4 114.4 114.4 114.4 114.4 114.4 Sm (g) 305.3 292.2 386.0 361.5 373.7 359.7 373.7 Zr (g) 10.9 13.6 15.6 10.6 13.6 10.6 10.6 Ni (g) 1420.8 1437.9 1585.1 1557.7 1523.5 1482.4 1448.2 Co (g) 68.8 68.8 51.6 51.6 51.6 51.6 51.6 Mn (g) 80.1 80.1 80.1 80.1 80.1 80.1 80.1 Al (g) 47.2 47.2 47.2 47.2 47.2 47.2 47.2 Heat treatment 1050 1090 1085 1060 1090 1095 1100 temperature (° C.) 120 mA/g 301.5 306.3 308.4 301.7 305.9 307.6 306.5 discharge capacity 5 C discharge capacity 73.9 73.4 73.0 74.0 73.6 73.6 73.5 percentage

[0036] Charge-discharge test was performed on the Ni-MH battery negative-electrode material La.sub.0.50Ce.sub.0.16Sm.sub.0.34Zr.sub.0.03Ni.sub.4.57Co.sub.0.17Mn.sub.0.26Al.sub.0.36 prepared in Example 1. With 120 mA/g used for the discharge test, the discharge capacity was 302.4 mA.h/g, the capacity retention rate after 242 cycles was 91.14%, 1C discharge capacity reached 96.7% of the maximum capacity, 3C discharge capacity reached 85.7% of the maximum capacity, and 5C discharge capacity reached 72.9% of the maximum capacity, and the overcharge resistance was high. The charge-discharge cycle life curve was shown in FIG. 1. It could be seen from FIG. 1 that the alloy could still maintain more than 90% of the capacity after 250 cycles, and had excellent cycle performance.

[0037] In the hydrogen storage alloy in the above example, the ratio of lanthanum to cerium was fixed at 3.0 to 3.2, thus satisfying the requirements of the overcharge performance of the electrode material; A side elements are largely substituted by samarium (Sin) element, i.e., the atomic ratio of Sin on the A side was 25.6% to 42%, which could solve the problem of shortened cycle life caused by the small number of cobalt (Co) atoms; the equilibrium pressure was adjusted by the change in the ratio of Sm to La and Ce to satisfy the requirements of the charge and discharge dynamic performance of the electrode material; the nucleation rate of the solidification process was improved by the addition of zirconium (Zr) to the A side at an atomic ratio of 2% to 3%; the ratio of the A-side elements to the B-side elements in the above alloy was adjusted to 5.03≤B/A≤5.33, thereby adjusting the phase structure, and avoiding the formation of the AB.sub.3 phase and A.sub.2B.sub.7 phase with a small excessive amount of the B-side elements.

[0038] In the following examples, based on the above-mentioned metal element ratio setting, the present invention also fixed the ratio of lanthanum to cerium to 3.0-3.2 to satisfy the requirements of the overcharge performance of the electrode material, A side elements are largely substituted by samarium (Sin) element, i.e., making the atomic ratio of Sin on the A side at 25.6% to 42.0%, so as to solve the problem of shortened cycle life caused by the small number of cobalt (Co) atoms, and fine adjusted the ratio of the A-side elements to the B-side elements to 4.60≤B/A≤4.90, thereby obtaining a magnesium-free A.sub.2B.sub.7 catalytic phase and adjusting the phase structure.

EXAMPLE 19

[0039] Step (1): placing pure metals, 362.0 g of La, 120.0 g of Ce, 395.0 g of Sm, 11.4 g of Zr, 1429.0 g of Ni, 50.0 g of Co, 82.8 g of Mn, and 50.0 g of Al, in a crucible of a induction melting furnace (a ZG vacuum induction melting furnace, the same below), covering with a furnace lid, then evacuating to a vacuum degree of 10.sup.−1 Pa, filling with argon to 0.07 MPa, and melting at 1550° C. for 2 h to obtain a molten metal liquid; pouring the molten metal liquid into a water-cooled ingot mold and cooling, and then discharging to obtain an alloy ingot.

[0040] Step (2): placing the alloy ingot obtained in step (1) in a protective-atmosphere furnace, evacuating to a vacuum degree of 10.sup.−1 Pa, filling with argon to a pressure of 0.08 MPa, and annealing at 1020° C. for 10 h to obtain a AB.sub.s Ni-MH battery negative-electrode material based on the magnesium-free A.sub.2B.sub.7 catalysis, La.sub.0.42Ce.sub.0.14Sm.sub.0.42Zr.sub.0.02Ni.sub.3.92Co.sub.0.14Mn.sub.0.24Al.sub.0.30.

[0041] Removing the oxide layer from the above alloy block La.sub.0.42Ce.sub.0.14Sm.sub.0.42Zr.sub.0.02Ni.sub.3.92Co.sub.0.14Mn.sub.0.24Al.sub.0.30, then successively pulverizing, grinding and sieving, and selecting alloy powder with a particle size less than 200 meshes; weighing 0.1 g of the alloy powder and 0.2 g of hydroxy nickel powder, mixing them evenly, then holding them at 15 MPa for 1 min by a powder tablet press to cold press them into electrode pads with a diameter of Φ=10 mm, and then removing the floats with burrs removed and surface uncompressed; before the test, fixing the alloy electrode pad between two pieces of foamed nickel current collector, leading a nickel wire out, and making the foamed nickel in full contact with the alloy powder; then carrying out the performance test. With 0.4C used for the discharge test, the discharge capacity was 325.7 mA.Math.h/g, the capacity retention rate after 118 cycles was 97.2%, 1C discharge capacity reached 98.0% of the maximum capacity, 3C discharge capacity reached 95.6% of the maximum capacity, and 5C discharge capacity reached 72.9% of the maximum capacity.

EXAMPLES 20-26

[0042] A low-vacuum induction melting method, a cooling method, and an annealing treatment were adopted to obtain a hydrogen storage alloy.

[0043] Each element was weighed according to the composition shown in Table 2 below (the percentages in Table 2 were weight percentages), and the alloy ingot thereof was heat-treated by a ZG vacuum induction melting furnace in an argon atmosphere and then cooled, with the specific steps of the heat treatment and cooling being the same as those in step (1) of Example 19. Then the annealing treatment was carried out; in the specific process of the annealing treatment, except for the heat treatment temperature, the other process conditions were the same as those in step (2) of Example 19. The heat treatment temperature, time, rate discharge ratio and capacity were shown in Table 2 below.

TABLE-US-00002 TABLE 2 Annealing process constant Rate discharge ratio (%) Ni Co Mn Al La Ce Zr Sm temperature/time/strong and capacity (mAh/g) % % % % % % % % B/A cooling 0.4 C 1 C 3 CC 5 C 10 C Example 19 57.14 2.00 3.31 2.00 14.46 4.78 0.46 15.80 4.60 1020/10/1020 100 98 95.6 94.2 87.8 325.7 319.1 311.4 306.8 286.1 Example 20 57.14 2.00 3.31 2.00 14.46 4.78 0.46 15.80 4.60 1085/10/500 100 97.3 91.6 89 83.4 311 302.6 285 276.8 259.3 Example 21 57.46 2.09 3.38 1.96 14.32 4.73 0.47 15.47 4.70 1020/10/1020 100 97.5 91.3 88.4 81 311.3 303.5 284.3 275.1 252.3 Example 22 57.46 2.09 3.38 1.96 14.32 4.73 0.47 15.47 4.70 1085/10/500 100 97.2 90.9 88.2 81.2 305 296.6 277.2 269.2 247.8 Example 23 58.53 2.08 3.23 1.94 16.56 4.65 0.44 12.52 4.84 1020/10/1020 100 96.7 92.6 90.1 81.4 315.1 304.8 291.7 284 256.5 Example 24 5853 2.08 3.23 1.94 16.56 4.65 0.44 12.52 4.84 1085/10/500 100 96.3 91.3 88.5 78.4 317.4 305.6 289.8 280.8 248.8 Example 25 58.53 2.08 3.23 1.94 16.56 4.65 0.44 12.52 4.84 1085/1/500 100 95.3 90.1 86.5 76.4 311.4 296.8 280.6 269.4 237.9 Example 26 57.46 2.09 3.38 1.96 14.32 4.73 0.47 15.47 4.70 1085/5/500 100 96.1 90.1 86.2 77.2 301.2 289.5 271.4 259.6 232.5

[0044] The XRD pattern and fitting curve test were performed on the Ni-MH battery negative-electrode material La.sub.0.42Ce.sub.0.14SM.sub.0.42Zr.sub.0.02Ni.sub.3.92Co.sub.0.14Mn.sub.0.24Al.sub.0.30 obtained in Example 19, and the results were shown in FIG. 2, with the weight percentage of the LaNi.sub.5 phase and the La.sub.2Ni.sub.7 phase being 90.3% and 9.7%, respectively.

[0045] It can be seen from Examples 19-26 that the atomic ratio of the metal lanthanum (La) to the metal cerium (Ce) was fixed at 3.0 to 3.2, which satisfied the requirements of the overcharge performance of the electrode materials; A side elements are largely substituted by samarium (Sm) element, i.e., making the atomic ratio of Sin on the A side at 25.6% to 42.0%, which solved the problem of shortened cycle life caused by the small number of cobalt (Co) atoms; zirconium (Zr) was added to the A-side at an atomic ratio of 2% to 3% (the A-side elements included lanthanum (La), cerium (Ce), samarium (Sin) and zirconium (Zr)), and the B-side elements included nickel (Ni), cobalt (Co), manganese (Mn) and aluminum (Al), with the atomic ratio of nickel (Ni):cobalt (Co):manganese (Mn): aluminum (Al) at (3.70-4.20):(0.10-0.20):(0.25-0.30):(0.30-0.40), thereby improving the corrosion resistance and economy by multi-component alloying; the ratio of the A-side elements to the B-side elements was adjusted to 4.60≤B/A≤4.90, thereby adjusting the phase structure and obtaining a magnesium-free A.sub.2B.sub.7 catalytic phase, with the magnesium-free A.sub.2B.sub.7 catalytic phase having good cycle performance, achieving good dynamic properties while fully maintaining the main AB.sub.5 phase, and improving the overcharge resistance, high-rate discharge performance and cycle performance of the alloy; the obtained AB.sub.5 Ni-MH battery negative-electrode material had high overcharge resistance, and good high-rate discharge performance and cycle stability.

[0046] The above examples are preferred embodiments of the present invention, but the embodiments of the present invention are not limited thereto, and any other alterations, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention should all be equivalent replacements and included in the scope of protection of the present invention.