CN1268779C - Method for preparing nano rare earth hydrogen storage alloy and equipment - Google Patents

Abstract

The present invention relates to a method and a device thereof for preparing nanometer crystal rare-earth hydrogen storage alloy, which is characterized in that an included angle between an overflow outlet of a tundish and the horizontal diameter of the cross section of a cooling roller is from 90 to 180 degrees, and the surface linear speed of the cooling roller is from 1 to 6 m/s. One side of the tundish facing the cooling roller is provided with an overflow outlet for alloy liquid, and the lower edge of the overflow outlet is higher than the inner bottom surface of the tundish. The grain size of a prepared hydrogen storage alloy sheet is from 1 to 1000 nm. Compared with the traditional process, the present invention has the advantages that the steps of roughly and moderately breaking alloy, thermally processing alloy, etc. are reduced, the process flow is shortened, and the production cost is reduced. The nanometer crystal structure prepared by the method and the device provides abundant diffusion channels for hydrogen atoms, reduces the microcrack and the pulverization of alloy in the course of sucking and releasing hydrogen, improves the dynamic performance of sucking and releasing hydrogen of the alloy, and increases electrochemical performance, particularly the stability of charge and discharge cycles and the charge and discharge performance of high current.

Description

Preparation method and device of a nanocrystalline rare earth hydrogen storage alloy

technical field

The present invention relates to a method and device for preparing a hydrogen storage alloy, in particular to an AB _{5 ±x} alloy (wherein A is one or more rare earth elements, including lanthanides and yttrium; B=Ni, Co, Mn, One or more of Ti, Al, Zn, Cu, Sn, W, Mo, Fe, Zr, Cr and non-metallic elements Si, B, C, N, 0≤x≤0.75) nanocrystalline rare earth hydrogen storage Alloy preparation method and device.

Background technique

The traditional process of preparing rare earth hydrogen storage alloys is to melt in an ordinary medium-frequency induction furnace to make alloy ingots. The alloy ingots are heat-treated at high temperature, and then coarsely crushed, medium crushed, and finally ball milled or jet milled to make powder. Due to poor cooling effect and serious component segregation of the alloy ingot in this method, the charge-discharge cycle stability of the alloy is very poor. In order to improve the cycle life of the alloy, Japanese Patent Laid-Open Specification No. 89066/1985 proposes heat treatment of the alloy. Although the cycle life of the heat-treated alloy is longer than that of the unheated alloy due to its low composition segregation ratio, the electrochemical performance of the alloy is poor due to the large grain size (greater than 20 μm).

Chinese patent publication numbers 1134046, 1190677 and European patent EP0588310A2 all provide a preparation method, that is, first melt the master alloy ingot, then remelt the master alloy and use the nozzle at the bottom of the tundish or the bottom of the crucible to spray the alloy liquid to the roller by gravity Rapid solidification made of hydrogen storage alloy flakes. In Chinese Patent Publication No. 1134046 and European Patent EP0588310A2, the minimum grain size of the alloy prepared therein is more than 2 μm, which is unfavorable to the high-current charge-discharge stability of the alloy. Publication No. 1190677 patent, although the alloy with grain size below 2 μm can be obtained, most of them are amorphous, and the obtained alloy is a mixture of amorphous, nanocrystalline and microcrystalline. The thickness of the sheet prepared by the above patents mainly depends on the rotating speed of the roller, the gap from the nozzle to the rotating roller and the aperture size of the nozzle. Because the alloy liquid is affected by gravity differently, during the preparation process, the flow of the alloy liquid is unstable, and the contact mode with the roll is unstable, so that the thickness uniformity of the prepared alloy sheet is poor, the grain size is uneven, and the components in the alloy are segregated and circulated. Poor stability, high production cost, etc., so that the overall performance of the material cannot be significantly improved.

Contents of the invention

The purpose of the present invention is to propose a method for preparing a nanocrystalline hydrogen storage alloy with good thickness consistency and single grain size.

Another object of the invention is to propose a device that ensures the implementation of the above-mentioned method.

The purpose of the present invention can be realized by the following measures: the raw material by AB _{5 ± x} composition ratio is placed in the smelting crucible 1 of the quick-setting furnace, the working frequency of the furnace is 800～2000Hz, and the power is 100～400Kw, Melting in an inert gas or vacuum environment, directly refining for 5-40 minutes after melting, and then pouring the alloy liquid into the preheated tundish 2, the preheating temperature of the tundish 2 is 800-1300°C. The tundish 2 is provided with an overflow port 3 for the alloy liquid on the side facing the roller 5, the lower edge 4 of the overflow port is higher than the inner bottom surface of the tundish 2, and the width of the overflow port is 5-400mm. The tundish can be a whole or a combination of several materials. The included angle θ between the overflow port 3 of the tundish and the horizontal diameter of the section of the cooling roller 5 is 90°-180°, and the surface linear velocity of the cooling roller 5 is 1-6 m/s. When the alloy liquid overflows the overflow port 3, due to the inherent tension effect of the alloy liquid, when it wants to flow out but does not flow out, the alloy liquid is scraped on by the rotating cooling roller 5, so that the alloy liquid is cooled on the cooling roller 5 to form into a hydrogen storage alloy sheet. By controlling the temperature of the tundish 2, the temperature of the alloy liquid is kept stable, so as to ensure that the tension formed by the alloy liquid in contact with the cooling roller 5 remains consistent, so that under the action of the tension, the alloy liquid is continuously, uniformly, and free from the influence of gravity The ground flows from the side to the cooling roller 5, and through the rotation of the cooling roller 5, a nanocrystalline hydrogen storage alloy sheet with good thickness consistency and single grain size is produced, and the material performance is obviously improved. The grain size of the hydrogen storage alloy sheet prepared by the method is 1-1000 nm, and the thickness is 0.02-1 mm.

Figure 1 is a schematic diagram of a hydrogen storage alloy sheet preparation device.

Figure 2 is a schematic diagram of a tundish.

Fig. 3 is an A-A sectional view of the tundish.

1. The melting crucible of the quick-setting furnace; 2. The tundish; 3. The overflow port; 4. The lower edge of the overflow port; 5. The cooling roller.

The method and device of the invention obtain a single nanocrystalline alloy with uniform grain size, a typical CaCu ₅ -type hexagonal structure, and no impurity phase (including amorphous phase), so the capacity and high-current discharge capacity of the alloy are improved. At the same time, because the nanocrystals provide abundant hydrogen atom diffusion channels, the internal stress generated by the alloy during the charging and discharging process is reduced, the pulverization rate of the alloy sheet is effectively controlled during the charging and discharging process, and the stability of the charging and discharging cycle of the alloy is improved. , and improve the service life of the alloy. Moreover, because the composition of the alloy sheet prepared by this rapid condensation method is uniform, the alloy has good discharge voltage platform characteristics. In addition, the structure of the alloy sheet is a single nano-crystal or micro-crystal, without heat treatment, which maintains the advantages of good activation performance of the cast alloy (only need to activate 3 times, the capacity can reach more than 340mAh/g), and the process is simple and the product is consistent Good sex.

The method and tundish structure adopted by the invention reduce the steps of coarse and medium crushing and heat treatment of the alloy compared with the traditional technology, shorten the production process and reduce the production cost of the alloy. On the other hand, the alloy prepared by this method is nanocrystalline, and the nanocrystalline structure provides rich diffusion channels for hydrogen atoms, which reduces the microcracking and pulverization of the alloy during the hydrogen absorption and desorption process, and improves the hydrogen absorption and desorption of the alloy. Kinetic performance, thereby greatly improving the electrochemical performance of the alloy, especially the stability of the alloy's charge-discharge cycle and high-current charge-discharge performance.

Detailed ways

The present invention is described in further detail below in conjunction with embodiment.

Example

The selected composition is AB _5±x alloy (where A is one or several rare earth elements, including lanthanides and yttrium; B=Ni, Co, Mn, Ti, Al, Zn, Cu, Sn, W, Mo, Fe , Zr, Cr and one or more of the non-metallic elements Si, B, C, N, 0≤x≤0.75) the raw materials are placed in the vacuum quick-setting furnace, the working frequency of the furnace is 800-2000Hz, the power 100-400Kw, melting in an inert gas or vacuum environment, directly refining for 5-40 minutes after melting, and then pouring the alloy into the preheated tundish 2, the preheating temperature of the tundish is 800-1300°C, cooling roll The linear speed of 5 is in the range of 1-6m/s, the angle θ between the overflow port 3 of the tundish and the horizontal diameter of the section of the cooling roller 5 is in the range of 90°-180°, the width of the overflow port 3 of the tundish is 250mm, and the Alloy flakes were made into powder and assembled into a simulated battery to test its performance. The results are shown in the table below. sample Linear speed(m/s) θ(°) 60mA/g discharge specific capacity 3000mA/g discharge specific capacity Thickness Grain C _{60, Max} (mAh/g) S _60,500 (%) C _{3000, Max} (mAh/g) S _{3000, 500} (%) mm nm 1 1 90 315 28.9 178 36.0 ~0.8 400 2 2 150 318 20.1 205 25.5 ~0.2 100 3 3 100 332 19.4 231 20.2 ~0.4 40 4 3 120 340 17.7 241 20.5 ~0.3 40 5 3 150 338 16.3 236 18.0 ~0.2 40 6 4 120 335 13.2 235 17.5 ~0.3 35 7 6 120 319 11.1 231 16.4 ~0.3 15 8 6 150 315 10.8 228 14.2 ~0.2 15 9 6 180 301 10.1 215 13.9 ~0.1 10 10 Comparative example (1) 320 31.8 142 100 ^* Ingot ＞1μm 11 Comparative example (2) 300 15.4 170 100 ^# <0.1 mixed crystal

Note: The symbols used in this table are explained as follows:

^* : In the case of 3000mA/g discharge, the capacity decay rate reaches 100% at the 68th discharge.

#: In the case of 3000mA/g discharge, the capacity decay rate reaches 100% at the 180th discharge.

C _{60, Max} : the maximum discharge specific capacity with a discharge current of 60mA/g;

S _60,500 : the capacity decay rate when the discharge current is 60mA/g at the 500th cycle;

C _{3000, Max} : the maximum discharge specific capacity with a discharge current of 3000mA/g;

S _{3000, 500} : the capacity decay rate when the discharge current is 3000mA/g at the 500th cycle;

Claims (4)

1. A preparation method for a nanocrystalline rare earth hydrogen storage alloy, comprising induction melting, pouring, and rapid condensation, characterized in that the composition is AB _5±x , wherein A is one or more rare earth elements, including lanthanides and Yttrium; B is one or more of Ni, Co, Mn, Ti, Al, Zn, Cu, Sn, W, Mo, Fe, Zr, Cr and non-metallic elements Si, B, C, N; 0≤ The alloy liquid with x≤0.75 is poured into the tundish (2) with a preheating temperature of 800-1300°C, and the overflow port (3) and the cooling roll (5) for the alloy liquid are provided on the side facing the cooling roll (5) The angle θ between the horizontal diameters of the sections is 90°-180°, the lower edge (4) of the overflow outlet is higher than the inner bottom surface of the tundish (2), and the surface linear velocity of the cooling roller (5) is 1-6m/s, The alloy liquid flows to the cooling roller (5) from the side, and is cooled to make a hydrogen storage alloy sheet. 2. A device for implementing the method for preparing nanocrystalline rare earth hydrogen storage alloys as claimed in claim 1, comprising a smelting crucible for a quick-setting furnace, a tundish, and a cooling roll, wherein the tundish (2) is cooled in the face One side of the roller (5) is provided with an overflow port (3) for the alloy liquid, the lower edge (4) of the overflow port is higher than the inner bottom surface of the tundish (2), and the cross section of the tundish overflow port (3) and the cooling roller (5) The angle θ between the horizontal diameters is 90°-180°. 3. The device according to claim 2, characterized in that the overflow opening (3) has a width of 5-400 mm. 4. The device according to claim 2, characterized in that the tundish (2) is a whole, or is composed of several pieces of material.

Images