High-capacity and long-life negative electrode hydrogen storage material of La—Mg—Ni type for secondary rechargeable nickel-metal hydride battery and method for preparing the same

Abstract

A high-capacity and long-life negative electrode hydrogen storage material of La—Mg—Ni type for secondary rechargeable nickel-metal hydride battery and a method for preparing the same are provided in the present invention. A chemical formula of the negative electrode hydrogen storage material of La—Mg—Ni type is La.sub.1-x-yRe.sub.xMg.sub.y(Ni.sub.1-a-bAl.sub.aM.sub.b).sub.z, wherein Re is at least one of Ce, Pr, Nd, Sm, Y, and M is at least one of Ti, Cr, Mo, Nb, Ga, V, Si, Zn, Sn; 0≤x≤0.10, 0.3≤y≤0.5, 0<a≤0.05, 0≤b≤0.02, 2.3≤z<3.0. The negative electrode hydrogen storage material of La—Mg—Ni type in the present invention has excellent charge-discharge capacity and cycle life. The negative electrode hydrogen storage material of La—Mg—Ni type can be applied in both common secondary rechargeable nickel-metal hydride battery and secondary rechargeable nickel-metal hydride battery with ultra-low self-discharge and long-term storage performance.

Claims

1. A high-capacity and long-life negative electrode hydrogen storage material of La—Mg—Ni type for secondary rechargeable nickel-metal hydride battery, wherein: the chemical formula of the negative electrode hydrogen storage material of La—Mg—Ni type is
La.sub.0.66Mg.sub.0.34(Ni.sub.0.96Al.sub.0.04).sub.2.99;
La.sub.0.65Ce.sub.0.02Mg.sub.0.33(Ni.sub.0.96Al.sub.0.04).sub.2.99;
La.sub.0.57Ce.sub.0.04Mg.sub.0.39(Ni.sub.0.95Al.sub.0.04Si.sub.0.01).sub.2.83;
La.sub.0.53Nd.sub.0.08Mg.sub.0.39(Ni.sub.0.95Al.sub.0.04Si.sub.0.01).sub.2.83;
La.sub.0.57Ce.sub.0.02Sm.sub.0.03Mg.sub.0.38(Ni.sub.0.95Al.sub.0.04Si.sub.0.01).sub.2.83;
La.sub.0.60Ce.sub.0.02Mg.sub.0.38(Ni.sub.0.96Al.sub.0.04).sub.2.80;
La.sub.0.53Pr.sub.0.03Nd.sub.0.06Mg.sub.0.38(Ni.sub.0.96Al.sub.0.04).sub.2.80;
La.sub.0.58Ce.sub.0.02Nd.sub.0.02Mg.sub.0.38(Ni.sub.0.96Al.sub.0.04).sub.2.75;
La.sub.0.54Ce.sub.0.02Mg.sub.0.44(Ni.sub.0.96Al.sub.0.04).sub.2.57; or
La.sub.0.49Ce.sub.0.01Mg.sub.0.50(Ni.sub.0.96Al.sub.0.04).sub.2.37.

2. The negative electrode hydrogen storage material of La—Mg—Ni type according to claim 1, wherein: the negative electrode hydrogen storage material of La—Mg—Ni type includes LaMgNi.sub.4 phase, LaMg.sub.12 phase, Ce.sub.2Ni.sub.7-type La.sub.2Ni.sub.7 phase and LaNi.sub.5 phase.

3. A secondary rechargeable nickel-metal hydride battery which comprises the high-capacity and long-life negative electrode hydrogen storage material comprising the La—Mg—Ni type material cited in claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is an X-ray diffraction pattern of the samples of La.sub.0.65Ce.sub.0.02Mg.sub.0.33(Ni.sub.0.96Al.sub.0.04).sub.2.99 in example 2, La.sub.0.60Ce.sub.0.02Mg.sub.0.38(Ni.sub.0.96Al.sub.0.04).sub.2.80 in example 6, La.sub.0.54Ce.sub.0.02Mg.sub.0.44(Ni.sub.0.96Al.sub.0.04).sub.2.57 in example 9 and La.sub.0.49Ce.sub.0.01Mg.sub.0.50(Ni.sub.0.96Al.sub.0.04).sub.2.37 in example 10 in the present invention.

(2) FIG. 2a is a graph of capacity change over time at 60° C. for batteries which are made of the hydrogen storage alloy of La—Mg—Ni type La.sub.0.53Pr.sub.0.03Nd.sub.0.06Mg.sub.0.38(Ni.sub.0.96Al.sub.0.04).sub.2.80 in example 7 and AB.sub.5 type MmNi.sub.3.55Co.sub.0.75Mn.sub.0.4Al.sub.0.3 in comparative example in the present invention.

(3) FIG. 2b is an capacity recovery characteristic diagram at 60° C. for batteries which are made of the hydrogen storage alloy of La—Mg—Ni type La.sub.0.53Pr.sub.0.03Nd.sub.0.06Mg.sub.0.38(Ni.sub.0.96Al.sub.0.04).sub.2.80 in example 7 and AB.sub.5 type MmNi.sub.3.55Co.sub.0.75Mn.sub.0.4Al.sub.0.3 in comparative example in the present invention.

(4) FIG. 2c is a graph of discharge voltage change over time at 60° C. for batteries which are made of the hydrogen storage alloy of La—Mg—Ni type La.sub.0.53Pr.sub.0.03Nd.sub.0.06Mg.sub.0.38(Ni.sub.0.96Al.sub.0.04).sub.2.80 in example 7 and AB.sub.5 type MmNi.sub.3.55Co.sub.0.75Mn.sub.0.4Al.sub.0.3 in comparative example in the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(5) The present invention is described in detail below by examples in combination with the drawings.

EXAMPLE

(6) Raw materials are proportioned according to the weight percentage of each element of alloy in table 3, and the proportioned raw materials of alloy are smelt in the intermediate frequency induction melting furnace into which an argon gas, a helium gas, or a mixture gas composed of the argon gas and the helium gas(they can be mixed in any proportion) have been introduced after the intermediate frequency induction melting furnace had been vacuumized. During the smelting, the maximum temperature of molten steel is controlled at 1400±20° C. Then the molten steel is cast into a water-cooled ingot mould to form an ingot casting with the thickness no larger than 35 mm. The ingot casting is taken out from the melting furnace after cooling and is transferred into vacuum heat treatment furnace to perform homogenization treatment. Before performing homogenization treatment, the argon gas, the helium gas, or the mixture of the argon gas and the helium gas (they can be mixed in any proportion) are introduced into the vacuum heat treatment furnace which has been vacuumized. A temperature of the homogenization treatment is 850˜1000° C. and a holding time is 1˜30 h. After the holding time ends, the cool argon gas, the cool helium gas, or the cool mixture gas of the argon gas and the helium gas (they can be mixed in any proportion) are introduced into vacuum heat treatment furnace for cooling. The ingot casting is taken out after it is cooled to the room temperature. The temperature and time of the homogenization treatment of the ingot casting in each example in Table 3 are determined according to the composition for synthesis and the thickness of the ingot casting.

(7) TABLE-US-00003 TABLE 3 composition comparison of examples 1-10 in the present invention and comparative example (wt %) Weight percentage(wt %) No. Composition La Ce Pr Nd Sm Mg Ni Al Si The Example 1 La.sub.0.66Mg.sub.0.34(Ni.sub.0.96Al.sub.0.04).sub.2.99 33.97 — — — — 2.99 61.89 1.14 — present Example 2 La.sub.0.65Ce.sub.0.02Mg.sub.0.33(Ni.sub.0.96Al.sub.0.04).sub.2.99 33.06 0.91 — — — 2.99 61.89 1.14 — invention Example 3 La.sub.0.57Ce.sub.0.04Mg.sub.0.39(Ni.sub.0.95Al.sub.0.04Si.sub.0.01).sub.2.83 31.10 2.24 — — — 3.67 61.60 1.12 0.27 Example 4 La.sub.0.53Nd.sub.0.08Mg.sub.0.39(Ni.sub.0.95Al.sub.0.04Si.sub.0.01).sub.2.83 28.84 — — 4.61 — 3.67 61.50 1.12 0.27 Example 5 La.sub.0.57Ce.sub.0.02Sm.sub.0.03Mg.sub.0.38(Ni.sub.0.95Al.sub.0.04Si.sub.0.01).sub.2.83 31.10 0.90 — — 1.35 3.67 61.60 1.12 0.27 Example 6 La.sub.0.60Ce.sub.0.02Mg.sub.0.38(Ni.sub.0.96Al.sub.0.04).sub.2.80 32.53 0.90 — — — 3.68 61.77 1.13 — Example 7 La.sub.0.53Pr.sub.0.03Nd.sub.0.06Mg.sub.0.38(Ni.sub.0.96Al.sub.0.04).sub.280 28.93 — 1.35 3.24 — 3.68 61.69 1.12 — Example 8 La.sub.0.58Ce.sub.0.02Nd.sub.0.02Mg.sub.0.38(Ni.sub.0.96Al.sub.0.04).sub.2.75 31.81 1.36 — 0.93 — 3.62 61.16 1.13 — Example 9 La.sub.0.54Ce.sub.0.02Mg.sub.0.44(Ni.sub.0.96Al.sub.0.04).sub.2.57 31.81 0.88 — — — 4.60 61.61 1.10 — Example 10 La.sub.0.49Ce.sub.0.01Mg.sub.0.50(Ni.sub.0.96Al.sub.0.04).sub.2.37 31.04 0.86 — — — 5.58 61.45 1.07 — NO. Composition La Ce Pr Nd Mg Ni Co Mn Al Comparative Comparative MmNi.sub.3.55Co.sub.0.75Mn.sub.0.4Al.sub.0.3 21.83 7.61 0.99 2.65 — 49.34 10.47 5.20 1.92 example example 1

Test Example

(8) 1) The X-ray diffraction tests are made on the samples of La.sub.0.65Ce.sub.0.02Mg.sub.0.33(Ni.sub.0.96Al.sub.0.04).sub.2.99 in example 2, La.sub.0.60Ce.sub.0.02Mg.sub.0.38(Ni.sub.0.96Al.sub.0.04).sub.2.80 in example 6, La.sub.0.54Ce.sub.0.02Mg.sub.0.44(Ni.sub.0.96Al.sub.0.04).sub.2.57 in example 9 and La.sub.0.49Ce.sub.0.01Mg.sub.0.50(Ni.sub.0.96Al.sub.0.04).sub.2.37 in example 10. The results are shown in FIG. 1. The results of the X-ray diffraction in FIG. 1 demonstate that the compounds shown in example 2, 6, 9, 10 are mainly collectively composed of LaMgNi.sub.4 phase, LaMg.sub.12 phase, La.sub.2Ni.sub.7 phase of Ce.sub.2Ni.sub.7 type and LaNi.sub.5 phase, wherein the contents of LaMgNi.sub.4 phase and LaMg.sub.12 phase increase as the z-value decreases.

(9) 2) The test of maximum electrochemical capacity and activation number:

(10) Firstly, the hydrogen storage alloy ingot casting obtained in the above-mentioned example are ground into an alloy powder of less than 200 mesh at room temperature. Then 0.25 g alloy powder of less than 200 mesh and a nickel powder are mixed in a ratio of 1:4, and are cold-pressed into a round cake (shape) with diameter (d) being 15 mm. Then the round cake is wrapped totally using a nickel foam on which nickel strap is weld and the openings of the nickel foam are sealed by a spot-welder, and it is used as the negative electrode. The positive electrode used is the same [Ni(OH).sub.2—NiOOH] electrode as nickel-metal hydride battery. The capacity of the positive electrode is designed to be much higher than that of the negative electrode so that the negative electrode material can reach full saturation during charging. [Hg/HgO/6M KOH] is the reference electrode. In the process of the electrode performance test, firstly the hydrogen storage negative electrode material is fully activated at the current density of 60 mA/g at 30° C., wherein the system of activation is as follows: charging 450 min with the current density of 60 mA/g, pausing for 15 minutes, and then discharging at a current density of 60 mA/g until the electrode potential of the negative electrode hydrogen storage alloy powder is −0.5V relative to the electrode potential of the reference electrode, then the next charge-discharge cycle is performed. As the activation number increases, the electrochemical discharge capacity of the negative electrode hydrogen storage alloy powder will gradually increase and become relatively stable after reaching a maximum value. At this time, the activation ends. The maximum value is defined as the electrochemical hydrogen absorption and desorption capacity of the material at 30° C., and the number of charge-discharge cycles required to obtain this maximum is called the activation number. Table 4 shows the results of the maximum electrochemical capacity and activation number of the hydrogen storage material in examples 1-10 and comparative example 1 at 30° C. and the charge-discharge current density of 60 mA/g according to the above-mentioned method.

(11) Cycle life test: firstly, the test samples are activated with a current density of 60 mA/g at 30° C. according to the above-mentioned method for testing the capacity and activation number. After the activation, the hydrogen storage negative electrode material is charged for 85 min with the current density of 60 mA/g at 30° C. After charging, there is a pause of 15 minutes. Then the hydrogen storage negative electrode material is discharged until the electrode potential of the hydrogen storage negative electrode materials is −0.5V relative to the electrode potential of the reference electrode. Then the next charge-discharge cycle is performed. For comparison conveniently, the cycle life of the samples is defined as the number of cycles when its capacity drops to 60% of the maximum capacity in the case of being discharged at the current density of 300 mA/g. Table 4 shows the results of the cycle life of hydrogen storage material in examples 1-10 and comparative example 1 according to the above-mentioned method.

(12) TABLE-US-00004 TABLE 4 Maximum Activation capacity Cycle No. Composition number (mAh/g) life The present Example 1 La.sub.0.66Mg.sub.0.34(Ni.sub.0.96Al.sub.0.04).sub.2.99 3 381 435 invention Example 2 La.sub.0.65Ce.sub.0.02Mg.sub.0.33(Ni.sub.0.96Al.sub.0.04).sub.2.99 3 373 452 Example 3 La.sub.0.57Ce.sub.0.04Mg.sub.0.39(Ni.sub.0.95Al.sub.0.04Si.sub.0.01).sub.2.83 3 362 430 Example 4 La.sub.0.53Nd.sub.0.08Mg.sub.0.39(Ni.sub.0.95Al.sub.0.04Si.sub.0.01).sub.2.83 3 361 510 Example 5 La.sub.0.57Ce.sub.0.02Sm.sub.0.03Mg.sub.0.38(Ni.sub.0.95Al.sub.0.04Si.sub.0.01).sub.2.83 3 356 443 Example 6 La.sub.0.60Ce.sub.0.02Mg.sub.0.38(Ni.sub.0.96Al.sub.0.04).sub.2.80 3 372 451 Example 7 La.sub.0.53Pr.sub.0.03Nd.sub.0.06Mg.sub.0.38(Ni.sub.0.96Al.sub.0.04).sub.2.80 3 376 462 Example 8 La.sub.0.58Ce.sub.0.02Nd.sub.0.02Mg.sub.0.38(Ni.sub.0.96Al.sub.0.04).sub.2.75 3 378 449 Example 9 La.sub.0.54Ce.sub.0.02Mg.sub.0.44(Ni.sub.0.96Al.sub.0.04).sub.2.57 3 356 133 Example 10 La.sub.0.49Ce.sub.0.01Mg.sub.0.50(Ni.sub.0.96Al.sub.0.04).sub.2.37 3 349 93 Comparative Comparative MmNi.sub.3.55Co.sub.0.75Mn.sub.0.4Al.sub.0.3 3 328 565 example Example 1

(13) It can be known from the data in Table 4 that the hydrogen storage material obtained in the present invention have a higher capacity, and especially when the content of z on the B side is 2.75≤z<3.0, both the capacity and the cycle life of the multiphase hydrogen storage material are good. A small amount of Ce, Pr, Nd instead of La can improve the capacity and the cycle life of the materials, especially Pr and Nd are more beneficial to the improvement of the capacity and the cycle life. Compared with the conventional alloy of AB.sub.5 type, although the life is slightly worse, yet the capacity has greatly increased. The maximum electrochemical capacity thereof exceed 370 mAh/g, which is much higher than the electrochemical capacity value of hydrogen storage material of AB.sub.5 type currently sold on the market.

(14) 3) An AAA800 battery is made of the sample of La.sub.0.53Pr.sub.0.03Nd.sub.0.06Mg.sub.0.38(Ni.sub.0.96Al.sub.0.04).sub.2.80 (Example 7) and MmNi.sub.3.55Co.sub.0.75Mn.sub.0.4Al.sub.0.3 hydrogen storage alloy of AB.sub.5 type(Comparative example 1), and a self-discharge performance thereof are studied.

(15) The method for manufacturing the batteries is specifically:

(16) (a) Negative electrode:

(17) Continuous gum dipping, drying and roll pressing are performed to obtain the electrode plate. The total mass of electrode plate is 4.40˜4.45 g, the net amount of powder is 3.68˜3.73 g;

(18) Size: 68±0.5 (mm)×38±0.1 (mm)×(0.25˜0.28) (mm);

(19) Copper mesh: 37.6 (mm)×0.25 (mm); surface density of copper mesh is 260±20 (g/m.sup.2), and 260 (g/m.sup.2) is taken to be used in calculation.

(20) The mass of substrate: m=0.068×(0.038+0.005)×260/1.05=0.72 (g);

(21) (b) Positive electrode:

(22) The mass of electrode plate (tail serging) is 3.82˜3.87 g;

(23) Mass ratio in formula: spherical nickel hydroxide Ni (OH).sub.251%;

(24) Cobalt-coated spherical nickel hydroxide Ni (OH).sub.2 45%;

(25) Cobalt Monoxide: 3%;

(26) Yttrium oxide: 1%.

(27) Size: 43.5±0.3×38±0.2×0.72˜0.75 (mm); the surface density of nickel foam: 280 g/m.sup.2;

(28) Substrate: m=0.0435×0.038×280/1.05+0.10=0.54 (g);

(29) The net mass of powder: 3.28˜3.33 g.

(30) (c) Electrolyte:

(31) TABLE-US-00005 Formula of theelectrolyte Specific Concentration of proportion (wt) gravity OH.sup.− No. LiOH•H.sub.2O NaOH KOH H.sub.2O Ba(OH).sub.2•8H.sub.2O g/cm.sup.3 mol/L 1 90 780 220 2370 2.37 1.287 ± 0.002 8.4~8.6

(32) The amount of electrolyte injected: m=1.15-1.17 g/each battery.

(33) (d) Separator: FV4384; 116×41×0.12 (mm);

(34) (e) The pressure of cap: 2.6˜2.8 MPa;

(35) (f) Steel can (shell): h43.6 (mm)×Ø10.10 (mm)×t0.15 (mm);

(36) (g) The activation of battery:

(37) The battery is placed for 48˜60 hours in an environment of 25˜30° C., and then the charge-discharge activation is performed for two times.

(38) The first charge-discharge activation: charging for 3 h at 0.05 C, then charging for 4 h at 0.2 C, then charging for 5 h at 0.1 C, discharging to 1V at 1 C and then discharging to 1V at 0.2 C.

(39) The second charge-discharge activation: charging for 2 h at 0.5 C, then charging for 2 h at 0.2 C, discharging to 1V at 1 C and then discharging to 1V at 0.2 C.

(40) (h) Test of a capacity retention rate and a capacity recovery rate

(41) The twenty-five batteries made of hydrogen storage material La.sub.0.53Pr.sub.0.03Nd.sub.0.06Mg.sub.0.38(Ni.sub.0.96Al.sub.0.04).sub.2.80 of La—Mg—Ni type and hydrogen storage alloy MmNi.sub.3.55Co.sub.0.75Mn.sub.0.4Al.sub.0.3 of AB.sub.5 type are taken and marked. Then these batteries are charged for 2 h at 0.5 C, and then charged for 2 h at 0.2 C and are discharged to 1V at 0.2 C at room temperature. Such cycle is performed for 3 times. The capacities of each battery are recorded, and the discharge capacity of the last time shall prevail. The batteries after being recorded are charged for 2 h at 0.5 C at room temperature, and then charged for 2 h at 0.2 C, and then stored in a thermo tank with the temperature of 60° C. Five batteries are respectively taken out on day 7, day 14, day 24, day 31 and day 60 after being stored, and are discharged to 1V with (at) 0.2 C at room temperature. Their capacities are recorded, and are divided by the discharge capacity of the last time recorded before storage to obtain the value that is capacity retention rate of the battery during the storage periods. The maximum and minimum are removed from the results of five batteries, and the results of the remaining three batteries are calculated to obtain the average value as the capacity retention rate of this battery. The results of the capacity retention rate are shown in FIG. 2a.

(42) Then these batteries are charged for 2 h at 0.5 C, charged for 2 h at 0.2 C and are discharged to 1V at 0.2 C at room temperature. Such cycle is done for 2 times. The results of capacity obtained in the second cycle are divided by the discharge capacity of the last time recorded before storage to obtain the value that is capacity recovery rate of the battery during the storage periods. The results of the capacity recovery rate are shown in FIG. 2b.

(43) (i) Test of a discharge state voltage storage characteristics:

(44) The forty-five batteries made of hydrogen storage material La0.53Pr0.03Nd0.06Mg0.38(Ni0.96Al0.04).sub.2.80 of La—Mg—Ni type and hydrogen storage alloy MmNi3.55Co0.75Mn0.4A10.3 of AB5 type are taken and marked. Then these batteries are charged for 2 h at 0.5 C, then charged for 2 h at 0.2 C, are discharged to 1V at 0.2 C and are placed for 20 min at room temperature. Such cycle is performed for 3 times. The voltage is recorded after each battery is discharged and placed for 20 min in each cycle, and the voltage of the last time shall prevail. The batteries after being recorded are stored in a thermo tank with the temperature of 60° C. Five batteries are respectively taken out on day 7, day 12, day 17, day 27, day 34, day 40, day 45, day 54, day 62 after being stored, and are placed for 1 h at room temperature. Then the voltage of each battery is measured, and that is the discharge state voltage storage characteristics of the battery during the storage period. The maximum and minimum are removed from the results of five batteries, and the results of the remaining three batteries are calculated to obtain the average value as the discharge voltage storage characteristics of this battery. The results are shown in FIG. 2c.

(45) It can be seen from the figure that compared with the battery made of hydrogen storage alloy MmNi.sub.3.55Co.sub.0.75Mn.sub.0.4Al.sub.0.3 of AB.sub.5 type, the battery made of alloy La.sub.0.53Pr.sub.0.03Nd.sub.0.06Mg.sub.0.38(Ni.sub.0.96Al.sub.0.04).sub.2.80 of La—Mg—Ni type in the present invention maintains a higher level in the capacity retention rate and capacity recovery rate as well as discharge state voltage storage characteristics. Especially there are significant advantages in the capacity retention rate and discharge state voltage storage characteristics. So this alloy in the present invention is also suitable for making nickel-metal hydride batteries with ultra-low self-discharge and long-term storage performance.