A double-layer carbon-coated hydrogen storage alloy and a preparation method and application thereof

Abstract

The application discloses a double-layer carbon-coated hydrogen storage alloy as well as a preparation method and application thereof, and belongs to the technical field of hydrogen storage alloy negative electrodes for nickel-hydrogen batteries. The application solves the problem of poor cycle stability of the existing A2B7 type La-Y-Ni-based alloy when used as a negative electrode. The application first uniformly coats a polydopamine carbon layer on the surface of the hydrogen storage alloy, and then utilizes the catalytic effect of the rare earth hydrogen storage alloy to catalyze acetylene into carbon nanotubes at high temperature, which are attached to the surface of the rare earth hydrogen storage alloy without the polydopamine and the surface of the polydopamine carbon layer, so as to obtain a hydrogen storage alloy negative electrode coated by a double-layer carbon of polydopamine pyrolytic carbon and carbon nanotubes. The modification method provided by the application can improve the oxidation resistance of the alloy surface, effectively alleviate material pulverization, and prolong the service life of the alloy. Meanwhile, the double carbon layer has the advantages of a large specific surface area and adjustable pore size, so that the electrochemical performance is optimized, and the cycle stability is improved.

Description

Technical Field

[0001] This invention relates to a double-layer carbon-coated hydrogen storage alloy, its preparation method and application, belonging to the technical field of hydrogen storage alloy anode for nickel-metal hydride batteries and its preparation. Background Technology

[0002] Hydrogen storage alloys are widely used in nickel-metal hydride (NiMH) battery anode materials, hydrogen compression, solid-state hydrogen storage, and thermal storage due to their high safety and good reversibility of hydrogen absorption and desorption. They are important functional materials in the development and application of hydrogen energy. As anode materials for NiMH batteries, they have advantages such as excellent wide-temperature performance, good kinetic performance, environmental friendliness, and high safety, and are widely used in electric vehicles, large-scale energy storage, coal mine lighting, and the ice and snow industry.

[0003] Hydrogen storage alloys suitable for use as anodes in nickel-metal hydride (NiMH) batteries mainly include AB5, A2B, AB2, A2B7, and vanadium-based solid solutions. However, A2B, AB2, and vanadium-based solid solutions have difficulty absorbing and desorbing hydrogen at room temperature, limiting their application in the battery field. LaNi5 hydrogen storage alloys, on the other hand, are the primary anode material for NiMH batteries due to their long cycle life, mature technology, and environmental friendliness. However, the maximum discharge capacity of commercially available LaNi5 hydrogen storage alloys is only 350 mAh / g, which is close to the theoretical value (372 mAh / g). -1 However, it also suffers from problems such as poor high-rate discharge performance and high cost. Therefore, developing new hydrogen storage alloys is crucial for the development of high-energy-density nickel-metal hydride batteries.

[0004] In recent years, high-capacity A2B7-type La-Y-Ni based rare-earth hydrogen storage alloys have attracted widespread attention from researchers. However, their poor oxidation resistance leads to poor cycle performance and rate capability, severely limiting their practical applications. Studies have shown that the surface composition, microstructure, and electrocatalytic activity of the alloy have a significant impact on the performance of nickel-metal hydride batteries. Therefore, existing technologies often employ surface coating modification to alter the surface properties of the alloy, improve its electrode performance, and accelerate its widespread application.

[0005] Existing research indicates that surface modification of hydrogen storage alloy electrode materials is an effective solution to improve the performance of nickel-metal hydride (NiMH) battery anodes. This approach effectively alters the surface state of the hydrogen storage alloy while maintaining its overall properties, thereby improving its electrochemical and kinetic performance. Common alloy surface modification methods include surface metal coating, alkaline and acidic solution treatments, and surface polymer modification. However, surface metal coating is prone to detachment and failure due to the lack of a symbiotic phase between the coating layer and the alloy. Alkaline and acidic solution treatments often cause excessive corrosion of the alloy, resulting in loss of effective capacity and reduced cycle stability. Another method, surface polymer modification, creates microspaces on the surface. By selecting different surface groups, H2 diffusion can be controlled, preventing material detachment, improving utilization, and enhancing the cycle stability of NiMH battery anode materials, thus achieving the goal of commercial application. Current patents primarily focus on optimizing alloy material composition, with only limited research addressing alloy surface coating. For example, patent CN110835091A employs methods such as reflux, calcination, and ball milling to load Zr-based MOFs onto the surface of PAN-based porous carbon-magnesium alloy materials. Therefore, developing new surface coating modification methods without altering the existing production processes and equipment for A2B7-type La-Y-Ni-based rare earth hydrogen storage alloy materials is of significant practical importance. This approach facilitates large-scale production and greatly improves the electrochemical performance of A2B7-type La-Y-Ni-based rare earth hydrogen storage alloy materials, effectively meeting the needs of current societal development. Summary of the Invention

[0006] In order to solve the above-mentioned problems existing in the use of existing A2B7 type La-Y-Ni based rare earth hydrogen storage alloy materials as hydrogen storage alloy anodes for nickel-metal hydride batteries, this invention provides a double-layer carbon-coated hydrogen storage alloy, its preparation method and application.

[0007] The technical solution of the present invention:

[0008] One objective of this invention is to provide a method for preparing a double-layer carbon-coated hydrogen storage alloy, the method comprising the following steps:

[0009] (1) Disperse the hydrogen storage alloy in an aqueous solution of tris(hydroxymethyl)aminomethane and stir until homogeneous to obtain a mixture;

[0010] (2) Add dopamine hydrochloride to the mixture, stir and let stand to obtain a mixed turbid liquid;

[0011] (3) The mixed turbid liquid was centrifuged, washed and vacuum dried in sequence to obtain a hydrogen storage alloy coated with polydopamine;

[0012] (4) The hydrogen storage alloy coated with polydopamine was heat-treated in an argon / acetylene mixed atmosphere to obtain a double-layer carbon-coated hydrogen storage alloy.

[0013] Further specifying, (1) the hydrogen storage alloy is an A2B7 type La-Y-Ni based rare earth hydrogen storage alloy with a particle size of 200-400 mesh.

[0014] To further specify, the hydrogen storage alloy is LaY2Ni. 9.5 Mn 0.5 Al 0.5 .

[0015] Further specified, (1) the mass-to-volume ratio of hydrogen storage alloy and tris(hydroxymethyl)aminomethane aqueous solution is 0.5-3g:100mL, the mass concentration of tris(hydroxymethyl)aminomethane aqueous solution is 0.01-1mol / L, and the pH value is 8.0-10.5.

[0016] Further specified, the mass ratio of dopamine hydrochloride and hydrogen storage alloy in the mixed turbid liquid of (2) is 0.1-0.6:1-3.

[0017] Further, in (2), the stirring time is 6 to 48 hours and the standing time is 5 to 10 minutes.

[0018] Further specified, (3) uses deionized water and anhydrous ethanol as detergents.

[0019] Further specified, (3) the vacuum drying temperature is 40-60℃ and the time is 5-15h.

[0020] Further specifying, in (4) the volume ratio of argon to acetylene in the argon / acetylene mixture is 85-95:5-15.

[0021] Further specified, (4) the heat treatment temperature is 450-500℃, the time is 30-60 min, and the heating rate is 2-5℃ / min. -1 .

[0022] The second objective of this invention is to provide a double-layer carbon-coated hydrogen storage alloy prepared by the above method.

[0023] The third objective of this invention is to provide an application of the above-mentioned double-layer carbon-coated hydrogen storage alloy, specifically as a hydrogen storage alloy negative electrode for nickel-metal hydride batteries.

[0024] Beneficial effects of this invention:

[0025] This invention first uniformly coats a polydopamine carbon layer onto the surface of a rare-earth hydrogen storage alloy. Then, utilizing the catalytic effect of the rare-earth hydrogen storage alloy, acetylene is catalyzed at high temperature to form carbon nanotubes, which adhere to the surface of both the uncoated rare-earth hydrogen storage alloy and the polydopamine carbon layer. This results in a rare-earth hydrogen storage alloy anode for nickel-metal hydride batteries coated with a double layer of carbon consisting of pyrolytic polydopamine carbon and carbon nanotubes. The modification method for rare-earth hydrogen storage alloys provided by this invention can improve the oxidation resistance of the alloy surface, effectively alleviate material pulverization, and extend the alloy's service life. Simultaneously, leveraging the advantages of the large specific surface area and adjustable pore size of the polydopamine pyrolytic carbon and carbon nanotube double carbon layer, the performance of the rare-earth hydrogen storage alloy can be optimized, improving cycle stability. Furthermore, the modification method for rare-earth hydrogen storage alloys provided by this invention is simple and easy to implement, facilitating widespread application. Attached Figure Description

[0026] Figure 1 LaY2Ni 9.5 Mn 0.5 Al 0.5 SEM images of rare earth hydrogen storage alloys;

[0027] Figure 2 LaY2Ni prepared for Comparative Example 1 9.5 Mn 0.5 Al 0.5 SEM image of a PDA rare earth hydrogen storage alloy;

[0028] Figure 3 LaY2Ni prepared in Example 1 9.5 Mn 0.5 Al 0.5 SEM image of @PDA@CNT rare earth hydrogen storage alloy;

[0029] Figure 4 A comparison graph showing the electrochemical performance of the negative electrodes prepared in Comparative Example 1 and Example 1. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0031] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0032] Comparative Example 1

[0033] (1) LaY2Ni 9.5 Mn0.5 Al 0.5 Rare earth hydrogen storage alloy materials are thoroughly ground and sieved in a mortar, and alloy powder with a particle size of 200-400 mesh is selected.

[0034] (2) Weigh 2g of LaY2Ni 9.5 Mn 0.5 Al 0.5 Rare earth hydrogen storage alloy material and 0.5 g of dopamine hydrochloride were dissolved in 100 mL of 0.1 mol / L tris(hydroxymethyl)aminomethane aqueous solution. The mixture was stirred for 24 h to obtain a mixed solution. After standing for 5 min, the solution was centrifuged, washed three times each with deionized water and anhydrous ethanol, and then vacuum dried in a 60 °C vacuum drying oven for 12 h to obtain LaY2Ni coated with polydopamine. 9.5 Mn 0.5 Al 0.5 Rare earth hydrogen storage alloy materials.

[0035] (3) The obtained LaY2Ni coated with polydopamine 9.5 Mn 0.5 Al 0.5 Rare-earth hydrogen storage alloy material was heat-treated in a tube furnace filled with argon atmosphere. The heating rate was 3℃ / min, the heating temperature was 500℃, and the holding time was 60min. The final product was a rare-earth hydrogen storage alloy anode material for nickel-metal hydride batteries coated with polydopamine pyrolysis carbon, named LaY2Ni. 9.5 Mn 0.5 Al 0.5 @PDA.

[0036] (4) LaY2Ni 9.5 Mn 0.5 Al 0.5 @PDA and carbonyl nickel powder are mixed at a mass ratio of 1:4 and pressed into tablets at 15 MPa. After being wrapped with nickel foam, tabs are welded to obtain a negative electrode with an active material loading of about 100 mg.

[0037] Example 1

[0038] (1) LaY2Ni 9.5 Mn 0.5 Al 0.5 Rare earth hydrogen storage alloy materials are thoroughly ground and sieved in a mortar, and alloy powder with a particle size of 200-400 mesh is selected.

[0039] (2) Weigh 2g of LaY2Ni 9.5 Mn 0.5 Al 0.5Rare earth hydrogen storage alloy material and 0.5 g of dopamine hydrochloride were dissolved in 100 mL of 0.1 mol / L tris(hydroxymethyl)aminomethane aqueous solution. The mixture was stirred for 24 h to obtain a mixed solution. After standing for 5 min, the solution was centrifuged, washed three times each with deionized water and anhydrous ethanol, and then vacuum dried in a 60 °C vacuum drying oven for 12 h to obtain LaY2Ni coated with polydopamine. 9.5 Mn 0.5 Al 0.5 Rare earth hydrogen storage alloy materials.

[0040] (3) Coating LaY2Ni with polydopamine 9.5 Mn 0.5 Al 0.5 Rare-earth hydrogen storage alloy material was heat-treated in a tube furnace filled with an argon / acetylene (95% Ar / 5% C2H2) mixed atmosphere. The heating rate was 3℃ / min, the heating temperature was 500℃, and the holding time was 60min. The final product was a rare-earth hydrogen storage alloy anode material for nickel-metal hydride batteries, named LaY2Ni, which is a bilayer carbon coating of polydopamine pyrolytic carbon and carbon nanotubes. 9.5 Mn 0.5 Al 0.5 @PDA@CNT.

[0041] (4) LaY2Ni 9.5 Mn 0.5 Al 0.5 @PDA@CNT and carbonyl nickel powder were mixed at a mass ratio of 1:4 and pressed into tablets at 15 MPa. After being wrapped with nickel foam, tabs were welded to obtain a negative electrode with an active material loading of about 100 mg.

[0042] Example of effect

[0043] (1) For LaY2Ni 9.5 Mn 0.5 Al 0.5 Rare earth hydrogen storage alloys and LaY2Ni prepared in Comparative Example 1 and Example 1 9.5 Mn 0.5 Al 0.5 @PDA and LaY2Ni 9.5 Mn 0.5 Al 0.5 The surface microstructure of @PDA@CNT was characterized, and the results are as follows: Figures 1-3 As shown in the figure. From the figure, it can be seen that LaY2Ni 9.5 Mn 0.5 Al 0.5 Rare earth hydrogen storage alloys have relatively smooth and flat surfaces. LaY2Ni... 9.5 Mn 0.5 Al 0.5The uniform wrinkled structure on the surface of the @PDA indicates that it is uniformly coated with polydopamine pyrolytic carbon. LaY2Ni 9.5 Mn 0.5 Al 0.5 In addition to a uniform wrinkled structure, the surface of @PDA@CNT also has a carbon nanotube structure, namely, in LaY2Ni 9.5 Mn 0.5 Al 0.5 The surface of the rare earth hydrogen storage alloy is uniformly coated with a bilayer carbon structure consisting of polydopamine pyrolytic carbon and carbon nanotubes.

[0044] (2) LaY2Ni 9.5 Mn 0.5 Al 0.5 The anode was mixed with nickel carbonyl powder at a mass ratio of 1:4 and pressed into a sheet at 15 MPa. After being coated with nickel foam, tabs were welded to obtain a negative electrode with an active material loading of approximately 100 mg. This negative electrode, along with those prepared in Comparative Example 1 and Example 1, were used to prepare batteries. The positive electrode was sintered α-nickel hydroxide, and a sulfonated polypropylene grafted membrane was used as the separator. A 6M KOH solution was used as the electrolyte, and electrochemical performance was tested in the voltage range of 0.8–1.6 V. The activation performance at 0.2C and the discharge cycle performance at 1C are as follows: Figure 4 As shown in the figure. From the figure, it can be seen that LaY2Ni 9.5 Mn 0.5 Al 0.5 、LaY2Ni 9.5 Mn 0.5 Al 0.5 @PDA、LaY2Ni 9.5 Mn 0.5 Al 0.5 The @PDA@CNT rare earth hydrogen storage alloy material has a maximum discharge capacity of 381 mAh·g at a 0.2C rate. -1 362mAh·g -1 and 348mAh·g -1 After 100 cycles, LaY2Ni 9.5 Mn 0.5 Al 0.5 、LaY2Ni 9.5 Mn 0.5 Al 0.5 @PDA and LaY2Ni 9.5 Mn 0.5 Al 0.5 The @PDA@CNT rare earth hydrogen storage alloy material has a maximum discharge capacity of 198 mAh·g at a 0.5C rate. -1 254mAh·g -1 and 280.5mAh g -1 .

[0045] In summary, carbon-coated LaY2Ni 9.5 Mn 0.5 Al 0.5 The cycle stability of rare earth hydrogen storage alloy materials is significantly better than that of uncoated LaY2Ni. 9.5 Mn 0.5 Al 0.5 Rare earth hydrogen storage alloy materials, this fully demonstrates that carbon coating plays a very good role in stabilizing LaY2Ni. 9.5 Mn 0.5 Al 0.5 The surface structure of rare-earth hydrogen storage alloys effectively prevents material pulverization and electrolyte corrosion, thereby significantly improving cycle performance under high current density and making them more commercially viable. Furthermore, LaY2Ni alloys with double-layer carbon coating... 9.5 Mn 0.5 Al 0.5 The discharge capacity of @PDA@CNT is significantly better than that of single-layer carbon-coated LaY2Ni. 9.5 Mn 0.5 Al 0.5 @PDA.

[0046] The above description is only a preferred embodiment of the present invention. Given that those skilled in the art can make appropriate changes and modifications to the above embodiments, the present invention is not limited to the specific embodiments described above, and some modifications and changes to the present invention should also fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a double-layer carbon-coated hydrogen storage alloy, characterized in that, include: (1) Disperse the hydrogen storage alloy in an aqueous solution of tris(hydroxymethyl)aminomethane and stir until homogeneous to obtain a mixture; (2) Add dopamine hydrochloride to the mixture, stir and let stand to obtain a mixed turbid liquid; (3) The mixed turbid liquid was centrifuged, washed and vacuum dried in sequence to obtain a hydrogen storage alloy coated with polydopamine; (4) The hydrogen storage alloy coated with polydopamine was heat-treated in an argon / acetylene mixed atmosphere to obtain a double-layer carbon-coated hydrogen storage alloy.

2. The preparation method according to claim 1, characterized in that, (1) The hydrogen storage alloy is an A2B7 type La-Y-Ni based rare earth hydrogen storage alloy with a particle size of 200-400 mesh.

3. The preparation method according to claim 1, characterized in that, (1) The mass-to-volume ratio of the hydrogen storage alloy and the aqueous solution of tris(hydroxymethyl)aminomethane is 0.5–3 g: 100 mL, the mass concentration of the aqueous solution of tris(hydroxymethyl)aminomethane is 0.01–1 mol / L, and the pH value is 8.0–10.

5.

4. The preparation method according to claim 1, characterized in that, (2) The mass ratio of dopamine hydrochloride and hydrogen storage alloy in the mixed turbid liquid is 0.1-0.6:1-3.

5. The preparation method according to claim 1, characterized in that, (2) The stirring time is 6 to 48 hours and the standing time is 5 to 10 minutes.

6. The preparation method according to claim 1, characterized in that, (3) Deionized water and anhydrous ethanol are used as detergents; the vacuum drying temperature is 40-60℃ and the time is 5-15h.

7. The preparation method according to claim 1, characterized in that, (4) The volume ratio of argon to acetylene in the argon / acetylene mixture is 85-95:5-15.

8. The preparation method according to claim 1, characterized in that, (4) The intermediate heat treatment temperature is 450-500℃, the time is 30-60 min, and the heating rate is 2-5℃ / min. -1 .

9. A double-layer carbon-coated hydrogen storage alloy prepared by the method according to any one of claims 1 to 8.

10. An application of the double-layer carbon-coated hydrogen storage alloy according to claim 9, characterized in that, It is used as a hydrogen storage alloy negative electrode for nickel-metal hydride batteries.

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