Modified la-mg-ni system a2b7 type hydrogen storage alloy powder, and preparation method and application thereof

Abstract

The application provides a modified La-Mg-Ni type A2B7 hydrogen storage alloy powder and a preparation method and application thereof, and relates to the technical field of nickel-hydrogen battery negative electrode materials. The modified La-Mg-Ni type A2B7 hydrogen storage alloy powder provided by the application comprises a La-Mg-Ni type A2B7 hydrogen storage alloy powder and a nitrogen-doped amorphous graphite-like carbon layer coated on the surface of the hydrogen storage alloy powder. The amorphous graphite-like carbon layer is coated on the surface of the La-Mg-Ni type A2B7 hydrogen storage alloy powder, which can effectively inhibit the dissolution of the hydrogen storage alloy in an alkaline electrolyte solution and reduce unnecessary side reactions. The nitrogen doping can effectively improve the active sites and the electrical conductivity of the alloy and improve the rate performance of the alloy. When the modified La-Mg-Ni type A2B7 hydrogen storage alloy powder is used as a nickel-hydrogen battery negative electrode material, the rate performance, capacity performance and cycle stability are all obviously improved.

Description

Technical Field

[0001] This invention relates to the field of nickel-metal hydride battery anode material technology, and in particular to a modified La-Mg-Ni A2B7 type hydrogen storage alloy, its preparation method and application. Background Technology

[0002] Superlattice La-Mg-Ni A2B7 alloys possess excellent hydrogen storage performance, exhibiting extremely high hydrogen storage capacity during charge-discharge processes when applied as anode materials in nickel-metal hydride batteries. However, the high reactivity and susceptibility to oxidation and corrosion of the alloy components (La, Mg) lead to reduced battery capacity, poor cycle life, and room for improvement in electrochemical stability over long cycles.

[0003] Thin film treatment of alloy powder surfaces is an economical and feasible method to improve battery performance. By altering the surface chemical properties of the alloy powder or providing a protective layer, direct contact between the active material and the electrolyte (alkaline electrolyte in nickel-metal hydride batteries) is reduced, effectively inhibiting corrosion and improving electrochemical stability. For example, Chinese patent CN109396420A discloses a NAFION-coated La-Mg-Ni A2B7 hydrogen storage alloy. NAFION coating effectively improves the thermal and chemical stability of the La-Mg-Ni A2B7 hydrogen storage alloy and enhances its corrosion resistance; however, the coated alloy exhibits poor electrical conductivity. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a modified La-Mg-Ni A2B7 type hydrogen storage alloy powder, its preparation method, and its applications. The modified La-Mg-Ni A2B7 type hydrogen storage alloy powder provided by this invention, as a negative electrode material for nickel-metal hydride batteries, not only exhibits good corrosion resistance in alkaline electrolyte solutions but also possesses excellent electrochemical performance.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] The present invention provides a modified La-Mg-Ni A2B7 type hydrogen storage alloy powder, comprising La-Mg-Ni A2B7 type hydrogen storage alloy powder and a nitrogen-doped amorphous graphite-like carbon layer coated on the surface of the La-Mg-Ni A2B7 type hydrogen storage alloy powder.

[0007] Preferably, the thickness of the nitrogen-doped amorphous graphitic carbon layer is 1–100 nm.

[0008] Preferably, the nitrogen doping amount in the nitrogen-doped amorphous graphitic carbon layer is 5-8 wt%.

[0009] This invention provides a method for preparing the modified La-Mg-Ni A2B7 type hydrogen storage alloy described above, comprising the following steps:

[0010] Using a graphite target as the sputtering target, La-Mg-Ni A2B7 hydrogen storage alloy powder was sputtered at medium frequency to obtain La-Mg-Ni A2B7 hydrogen storage alloy powder coated with an amorphous graphite-like carbon layer.

[0011] The surface of the La-Mg-Ni A2B7 hydrogen storage alloy powder coated with an amorphous graphitic carbon layer was subjected to nitrogen plasma treatment to obtain the modified La-Mg-Ni A2B7 hydrogen storage alloy powder.

[0012] Preferably, during the intermediate frequency magnetron sputtering process, the magnetic core of the graphite target is always fixed downward, the target-substrate distance is maintained at 110 mm, and the target surface of the graphite target and the tool holder carrying the La-Mg-Ni A2B7 type hydrogen storage alloy powder rotate in opposite directions at a constant speed of 10 rpm.

[0013] Preferably, the duty cycle of the power supply for the medium-frequency magnetron sputtering is 0.1 to 0.6, the current is 4 to 10 A, and the frequency is 20 to 200 kHz; the working pressure during the medium-frequency magnetron sputtering process is 1 to 3 Pa; and the duration of the medium-frequency magnetron sputtering is 10 to 60 min.

[0014] Preferably, in the nitrogen plasma treatment, the nitrogen plasma is generated by nitrogen gas under a high bias voltage, wherein the voltage of the high bias voltage is -(800~2000)V.

[0015] Preferably, the working pressure during nitrogen plasma treatment is 30-40 Pa, and the treatment time is 10-20 min.

[0016] Preferably, before performing the intermediate frequency magnetron sputtering, the La-Mg-Ni A2B7 type hydrogen storage alloy powder is further subjected to glow discharge cleaning under argon gas conditions. The working pressure of the glow discharge cleaning is 1-30 Pa, the bias voltage is -(800-1000) V, and the glow discharge cleaning time is 3-5 min.

[0017] This invention provides the application of the modified La-Mg-Ni A2B7 hydrogen storage alloy powder described in the above technical solutions or the modified La-Mg-Ni A2B7 hydrogen storage alloy powder prepared by the preparation method described in the above technical solutions as a negative electrode material for nickel-metal hydride batteries.

[0018] The modified La-Mg-Ni A2B7 hydrogen storage alloy powder provided by this invention comprises La-Mg-Ni A2B7 hydrogen storage alloy powder and a nitrogen-doped amorphous graphite-like carbon layer coated on the surface of the La-Mg-Ni A2B7 hydrogen storage alloy powder. By coating the surface of the La-Mg-Ni A2B7 hydrogen storage alloy powder with an amorphous graphite-like carbon layer, this invention effectively inhibits the dissolution of the hydrogen storage alloy in alkaline electrolyte solutions and reduces unnecessary side reactions. Nitrogen doping effectively improves the active sites and conductivity of the alloy, thereby enhancing its rate performance as an electrode material. Using the modified La-Mg-Ni A2B7 hydrogen storage alloy powder provided by this invention as a negative electrode material for nickel-metal hydride batteries not only exhibits good corrosion resistance in alkaline electrolyte solutions but also demonstrates excellent electrochemical performance, with significantly improved rate performance, capacity performance, and cycle stability, showing broad market application prospects. The results of the examples show that, in a 6 mol / L KOH electrolyte and at a current density of 0.6 A / g, the specific capacity of the modified La-Mg-Ni A2B7 type hydrogen storage alloy powder provided by this invention is as high as 335 mA·hg. -1 After 100 cycles, there is still 300 mA·hg -1 Capacity reservation.

[0019] This invention provides a method for preparing the modified La-Mg-Ni A2B7 hydrogen storage alloy powder described in the above technical solution. Using a graphite target as the carbon source, this invention employs mid-frequency magnetron sputtering to deposit an amorphous graphitic carbon layer on the surface of the La-Mg-Ni A2B7 hydrogen storage alloy powder. To further improve the conductivity of the thin film and obtain better rate performance, the film surface is treated with nitrogen plasma to obtain a nitrogen-doped amorphous graphitic carbon layer-coated La-Mg-Ni A2B7 hydrogen storage alloy powder. This invention utilizes mid-frequency magnetron sputtering, resulting in fast film deposition, uniform film formation, and controllable thickness. Furthermore, the low chamber temperature of mid-frequency magnetron sputtering effectively avoids capacity decay and safety issues caused by grain growth in the hydrogen storage alloy due to temperature increases. In addition, mid-frequency magnetron sputtering has a short processing time, low energy consumption, and high efficiency, reducing production costs. The preparation method provided by this invention can process up to 2 kg of La-Mg-Ni A2B7 hydrogen storage alloy powder in a single batch, demonstrating broad market application prospects. Attached Figure Description

[0020] Figure 1 This is a transmission electron microscope (TEM) image of the hydrogen storage alloy powder coated with a nitrogen-doped carbon thin film layer prepared in Example 1.

[0021] Figure 2 The graph shows the electrochemical specific capacity versus cycle number at a current density of 0.6 A / g when the hydrogen storage alloy powders of Examples 1-3 and the comparative examples are used as the negative electrode of nickel-metal hydride batteries. Detailed Implementation

[0022] The present invention provides a modified La-Mg-Ni A2B7 type hydrogen storage alloy powder, comprising La-Mg-Ni A2B7 type hydrogen storage alloy powder and a nitrogen-doped amorphous graphite-like carbon layer coated on the surface of the La-Mg-Ni A2B7 type hydrogen storage alloy powder.

[0023] The present invention does not have any special requirements on the source of the La-Mg-Ni A2B7 type hydrogen storage alloy powder. La-Mg-Ni A2B7 type hydrogen storage alloy powder well known to those skilled in the art can be used, and there are no special requirements on its preparation process and elemental composition.

[0024] In this invention, the thickness of the nitrogen-doped amorphous graphitic carbon layer is preferably 1-100 nm, more preferably 5-30 nm; the nitrogen doping amount in the nitrogen-doped amorphous graphitic carbon layer is preferably 5-8 wt%.

[0025] This invention effectively inhibits the dissolution of the hydrogen storage alloy in alkaline electrolyte solutions and reduces unnecessary side reactions by coating the surface of La-Mg-Ni A2B7 type hydrogen storage alloy powder with an amorphous graphite-like carbon layer. Furthermore, nitrogen doping effectively increases the active sites (making the amorphous graphite-like carbon layer have more electrochemical active sites) and conductivity of the alloy, thereby improving the rate performance of the alloy as an electrode material.

[0026] This invention provides a method for preparing the modified La-Mg-Ni A2B7 type hydrogen storage alloy described above, comprising the following steps:

[0027] Using a graphite target as the sputtering target, La-Mg-Ni A2B7 hydrogen storage alloy powder was sputtered at medium frequency to obtain La-Mg-Ni A2B7 hydrogen storage alloy powder coated with an amorphous graphite-like carbon layer.

[0028] The surface of the La-Mg-Ni A2B7 hydrogen storage alloy powder coated with an amorphous graphitic carbon layer was subjected to nitrogen plasma treatment to obtain the modified La-Mg-Ni A2B7 hydrogen storage alloy powder.

[0029] This invention uses a graphite target as the sputtering target material to perform mid-frequency magnetron sputtering on La-Mg-Ni A2B7 hydrogen storage alloy powder, obtaining La-Mg-Ni A2B7 hydrogen storage alloy powder coated with an amorphous graphitic carbon layer. Before the mid-frequency magnetron sputtering, this invention preferably dries the La-Mg-Ni A2B7 hydrogen storage alloy powder and then performs glow discharge cleaning under argon gas conditions. In this invention, the drying is preferably vacuum drying, with a preferred temperature of 110°C and a preferred time of 120 min. In this invention, the working pressure during glow discharge cleaning is preferably 1–30 Pa, more preferably 1 Pa; the bias voltage is preferably -(800–1000) V, and the glow discharge cleaning time is preferably 3–5 min. In this invention, the specific operation of glow discharge cleaning is preferably as follows: the dried La-Mg-Ni A2B7 hydrogen storage alloy powder is placed on a support frame in a vacuum coating chamber, the target-substrate distance is adjusted to 110 mm, and a vacuum is drawn to 10 °C. -4 Pa; then argon gas is introduced to maintain the working pressure in the chamber at 1-30 Pa and the bias voltage at -(800-1000) V, and glow discharge cleaning is performed on the surface of the alloy powder. This glow discharge cleaning removes impurities adsorbed on the surface of the La-Mg-Ni A2B7 type hydrogen storage alloy powder and prevents target poisoning.

[0030] In this invention, during the intermediate-frequency magnetron sputtering process, the magnetic core of the graphite target is preferably always fixed downwards, the target-substrate distance is preferably maintained at 110 mm, and the target surface of the graphite target and the fixture carrying the La-Mg-Ni A2B7 hydrogen storage alloy powder are preferably rotating in opposite directions at a uniform speed, preferably 10 rpm. In this invention, the duty cycle of the power supply for the intermediate-frequency magnetron sputtering is preferably 0.1–0.6, more preferably 0.6; the current is preferably 4–10 A, more preferably 4–7 A; the frequency is preferably 20–200 kHz, more preferably 80–200 kHz; the working pressure during the intermediate-frequency magnetron sputtering process is preferably 1–3 Pa, more preferably 1 Pa; and the time (i.e., deposition time) of the intermediate-frequency magnetron sputtering is preferably 10–60 min, more preferably 20–50 min.

[0031] In this invention, the preferred specific operation of the medium-frequency magnetron sputtering is as follows: the rotating device in the vacuum coating chamber is turned on, so that the graphite target and the stand carrying the La-Mg-Ni A2B7 hydrogen storage alloy powder rotate at a constant speed, and a carbon layer is deposited on the surface of the La-Mg-Ni A2B7 hydrogen storage alloy by medium-frequency magnetron sputtering. By controlling the sputtering current, a La-Mg-Ni A2B7 hydrogen storage alloy powder with an amorphous graphite-like carbon layer uniformly coated on the surface is obtained.

[0032] After obtaining La-Mg-Ni A2B7 hydrogen storage alloy powder coated with an amorphous graphitic carbon layer, the present invention applies nitrogen plasma treatment to the surface of the La-Mg-Ni A2B7 hydrogen storage alloy powder coated with the amorphous graphitic carbon layer to obtain the modified La-Mg-Ni A2B7 hydrogen storage alloy powder. In the present invention, the nitrogen plasma treatment preferably uses nitrogen gas generated under a high bias voltage, wherein the high bias voltage is preferably -(800~2000)V, more preferably -(1200~1500)V; the working pressure during the nitrogen plasma treatment is preferably 30~40Pa, more preferably 30Pa; and the treatment time is preferably 10~20min, more preferably 15~20min.

[0033] In this invention, the preferred specific operation of the nitrogen plasma treatment is as follows: nitrogen gas is introduced into the vacuum coating chamber, and the working pressure and bias voltage in the chamber are maintained within the specified range. Under high bias voltage conditions, nitrogen plasma is generated and induced to effectively bombard or etch the surface of the La-Mg-Ni A2B7 hydrogen storage alloy powder coated with an amorphous graphitic carbon layer, thereby obtaining a nitrogen-doped amorphous graphitic carbon layer coated with a La-Mg-Ni A2B7 hydrogen storage alloy powder.

[0034] The preparation method provided by this invention is simple, easy to operate, and low in cost, which is conducive to industrial application.

[0035] This invention provides the application of modified La-Mg-Ni A2B7 hydrogen storage alloy powder, as described in the above technical solutions, or modified La-Mg-Ni A2B7 hydrogen storage alloy powder prepared by the above preparation methods, as a negative electrode material for nickel-metal hydride batteries. This invention does not impose any particular requirements on the specific methods of application; any application methods well-known to those skilled in the art can be used. Using the modified La-Mg-Ni A2B7 hydrogen storage alloy powder provided by this invention as a negative electrode material for nickel-metal hydride batteries not only exhibits good corrosion resistance in alkaline electrolyte solutions but also demonstrates excellent electrochemical performance, with significantly improved rate performance, capacity performance, and cycle stability, showing broad market application prospects.

[0036] The modified La-Mg-Ni A2B7 hydrogen storage alloy powder, its preparation method, and its application provided by the present invention are described in detail below with reference to the embodiments. However, these should not be construed as limiting the scope of protection of the present invention.

[0037] Example 1

[0038] A nitrogen-doped amorphous graphitic carbon thin film was prepared on the surface of a La-Mg-Ni type A2B7 hydrogen storage alloy powder as the substrate. The process is as follows:

[0039] (1) Surface cleaning of hydrogen storage alloy: After drying the hydrogen storage alloy powder, place it into the tooling in the vacuum chamber and evacuate to 10. -4 Pa, turn on the rotating device to make the graphite target and the tooling rotate in opposite directions at a uniform speed of 10 revolutions per minute; introduce argon gas to maintain the working pressure of the chamber at 1 Pa, the bias voltage at -800V, and the processing time at 3 min to remove impurities adsorbed on the alloy surface and prevent target poisoning.

[0040] (2) Preparation of carbon thin film: The working pressure of the chamber is kept at 1 Pa. The graphite target is energized by a medium frequency magnetron sputtering power supply with a duty cycle of 0.6, a current of 7 A, a frequency of 80 kHz, and a deposition time of 30 min to obtain hydrogen storage alloy powder with uniform surface amorphous graphite carbon coating.

[0041] (3) Introduction of nitrogen doping atoms: Nitrogen gas is introduced to keep the working pressure of the chamber at 30 Pa, the bias voltage at -1300 V, and the processing time at 15 min, to obtain hydrogen storage alloy powder coated with nitrogen doped amorphous graphite carbon thin film layer.

[0042] Figure 1 This is a transmission electron microscope (TEM) image of the hydrogen storage alloy powder coated with a nitrogen-doped carbon thin film layer prepared in Example 1. Figure 1 It can be seen that the powder surface is coated with a uniform carbon film with a thickness of about 10 nm.

[0043] The nitrogen-doped carbon thin film-coated hydrogen storage alloy powder was subjected to XPS testing, and its nitrogen content was 5 wt%.

[0044] The nitrogen-doped carbon thin film-coated hydrogen storage alloy powder was used as the negative electrode material for a nickel-metal hydride battery (the positive electrode for the nickel-metal hydride battery is nickel hydroxide). Its electrochemical performance was tested, and the results showed that in an electrolyte of 6 mol / L KOH, at a current density of 0.6 A / g, the specific capacity was 335 mA·hg. -1 After 100 cycles, there is still 300 mA·hg -1 Capacity reservation.

[0045] Example 2

[0046] (1) Cleaning of hydrogen storage alloy surface: After drying the hydrogen storage alloy powder, place it in a vacuum chamber and evacuate to 10. -4 Pa, turn on the rotating device to make the graphite target and the tooling rotate in opposite directions at a uniform speed of 10 revolutions per minute; introduce argon gas to maintain the working pressure of the chamber at 1 Pa, the bias voltage at -1000V, and the processing time at 5 min to remove impurities adsorbed on the alloy surface and prevent target poisoning.

[0047] (2) Preparation of carbon thin film: The working pressure of the chamber is kept at 3 Pa. The graphite target is energized by a medium frequency magnetron sputtering power supply with a duty cycle of 0.6, a current of 4 A, a frequency of 20 kHz, and a deposition time of 50 min to obtain hydrogen storage alloy powder with uniform amorphous graphite coating on the surface.

[0048] (3) Introduction of nitrogen doping atoms: Nitrogen gas is introduced to keep the working pressure of the chamber at 40 Pa, the bias voltage at -1500 V, and the processing time at 20 min, to obtain hydrogen storage alloy powder coated with nitrogen doped amorphous graphite carbon thin film layer.

[0049] The nitrogen-doped carbon thin film-coated hydrogen storage alloy powder was used as the negative electrode material for a nickel-metal hydride battery (the positive electrode for the nickel-metal hydride battery is nickel hydroxide). XPS analysis showed that its nitrogen content was 8 wt%. Electrochemical performance testing revealed that in a 6 mol / L KOH electrolyte, at a current density of 0.6 A / g, the specific capacity reached 325 mA·hg. -1 After 100 cycles, there is still 295 mA·hg -1 Capacity reservation.

[0050] Example 3

[0051] (1) Cleaning of hydrogen storage alloy surface: After drying the hydrogen storage alloy powder, place it in a vacuum chamber and evacuate to 10. -4 Pa, turn on the rotating device to make the graphite target and tooling rotate in opposite directions at a uniform speed of 10 revolutions per minute; introduce argon gas, maintain the working pressure of the chamber at 1 Pa, bias voltage -900V, and the processing time at 4 min to remove impurities adsorbed on the surface.

[0052] (2) Preparation of carbon thin film: The working pressure of the chamber is kept at 1 Pa. The graphite target is energized by a medium frequency magnetron sputtering power supply with a duty cycle of 0.6, a current of 10 A, a frequency of 200 kHz, and a deposition time of 20 min to obtain hydrogen storage alloy powder with uniform amorphous graphite carbon coating.

[0053] (3) Introduction of nitrogen doping atoms: Nitrogen gas is introduced to keep the working pressure of the chamber at 30 Pa, the bias voltage at -1200 V, and the processing time at 10 min, to obtain hydrogen storage alloy powder coated with nitrogen doped amorphous graphite carbon thin film layer.

[0054] The nitrogen-doped carbon thin film-coated hydrogen storage alloy powder was used as the negative electrode material for a nickel-metal hydride battery (the positive electrode for the nickel-metal hydride battery is nickel hydroxide). XPS analysis showed that its nitrogen content was 5 wt%. Electrochemical performance testing revealed that in a 6 mol / L KOH electrolyte, at a current density of 0.6 A / g, the specific capacity was 310 mA·hg. -1 After 100 cycles, there is still 285 mA·hg-1 Capacity reservation.

[0055] Comparative Example

[0056] Uncoated La-Mg-Ni A2B7 hydrogen storage alloy powder was used as the negative electrode material for nickel-metal hydride batteries (the positive electrode for nickel-metal hydride batteries is nickel hydroxide). Electrochemical performance tests were conducted, and the results showed that in a 6 mol / L KOH electrolyte, at a current density of 0.6 A / g, the specific capacity was 300 mA·hg. -1 After 100 cycles, the result is 275 mA·hg. -1 Capacity reservation.

[0057] Figure 2 The graph shows the electrochemical specific capacity versus cycle number at a current density of 0.6 A / g when the hydrogen storage alloy powders of Examples 1-3 and the comparative examples are used as negative electrodes in nickel-metal hydride batteries. Figure 2 It can be seen that the nitrogen-doped carbon thin film coated hydrogen storage alloy powder prepared in Examples 1-3 can effectively improve the specific capacitance and cycle stability of the hydrogen storage alloy of nickel-metal hydride battery anode.

[0058] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A modified La-Mg-Ni A2B7 type hydrogen storage alloy powder, characterized in that, It includes La-Mg-Ni type A2B7 hydrogen storage alloy powder and a nitrogen-doped amorphous graphite-like carbon layer coated on the surface of the La-Mg-Ni type A2B7 hydrogen storage alloy powder; The preparation method of the modified La-Mg-Ni A2B7 type hydrogen storage alloy includes the following steps: Using a graphite target as the sputtering target, La-Mg-Ni A2B7 hydrogen storage alloy powder was sputtered at medium frequency to obtain La-Mg-Ni A2B7 hydrogen storage alloy powder coated with an amorphous graphite-like carbon layer. The surface of the La-Mg-Ni A2B7 hydrogen storage alloy powder coated with an amorphous graphitic carbon layer was subjected to nitrogen plasma treatment to obtain the modified La-Mg-Ni A2B7 hydrogen storage alloy powder.

2. The modified La-Mg-Ni A2B7 type hydrogen storage alloy powder according to claim 1, characterized in that, The thickness of the nitrogen-doped amorphous graphitic carbon layer is 1~100 nm.

3. The modified La-Mg-Ni A2B7 type hydrogen storage alloy powder according to claim 1 or 2, characterized in that, The nitrogen doping amount in the nitrogen-doped amorphous graphitic carbon layer is 5~8wt%.

4. The method for preparing the modified La-Mg-Ni A2B7 type hydrogen storage alloy according to any one of claims 1 to 3, characterized in that, Includes the following steps: Using a graphite target as the sputtering target, La-Mg-Ni A2B7 hydrogen storage alloy powder was sputtered at medium frequency to obtain La-Mg-Ni A2B7 hydrogen storage alloy powder coated with an amorphous graphite-like carbon layer. The surface of the La-Mg-Ni A2B7 hydrogen storage alloy powder coated with an amorphous graphitic carbon layer was subjected to nitrogen plasma treatment to obtain the modified La-Mg-Ni A2B7 hydrogen storage alloy powder.

5. The preparation method according to claim 4, characterized in that, During the mid-frequency magnetron sputtering process, the magnetic core of the graphite target is always fixed downward, and the target-substrate distance is maintained at 110 mm; the target surface of the graphite target and the fixture carrying the La-Mg-Ni A2B7 hydrogen storage alloy powder rotate in opposite directions at a constant speed of 10 rpm.

6. The preparation method according to claim 4, characterized in that, The duty cycle of the power supply for the medium-frequency magnetron sputtering is 0.1~0.6, the current is 4~10A, and the frequency is 20~200kHz; the working pressure during the medium-frequency magnetron sputtering process is 1~3Pa; and the duration of the medium-frequency magnetron sputtering is 10~60min.

7. The preparation method according to claim 4, characterized in that, In the nitrogen plasma treatment, the nitrogen plasma is generated by nitrogen gas under a high bias voltage, wherein the high bias voltage is -(800~2000)V.

8. The preparation method according to claim 4 or 7, characterized in that, The working pressure during nitrogen plasma treatment is 30~40Pa; the treatment time is 10~20min.

9. The preparation method according to any one of claims 4 to 6, characterized in that, Before performing the intermediate frequency magnetron sputtering, the La-Mg-Ni A2B7 type hydrogen storage alloy powder is subjected to glow discharge cleaning under argon gas conditions. The working pressure of the glow discharge cleaning is 1~30 Pa, the bias voltage is -(800~1000) V, and the glow discharge cleaning time is 3~5 min.

10. The application of the modified La-Mg-Ni A2B7 hydrogen storage alloy powder according to any one of claims 1 to 3 or the modified La-Mg-Ni A2B7 hydrogen storage alloy powder prepared by the preparation method according to any one of claims 4 to 9 as a negative electrode material for nickel-metal hydride batteries.

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