Y-Mg-Ni-Ti-Cu-Sn hydrogen storage alloy composite electrode material and preparation method thereof

Abstract

This invention relates to a Y-Mg-Ni-Ti-Cu-Sn based hydrogen storage alloy composite electrode material and its preparation method, belonging to the field of hydrogen storage alloy materials. It solves the problems of low room temperature discharge capacity and poor electrochemical cycle stability of existing magnesium-based hydrogen storage electrode materials. The composite electrode material of this invention includes an alloy core and nano-Ni powder coated on at least a portion of the surface of the alloy core. The alloy core has the chemical formula Mg... 25‑x Y x Ni 20‑y‑z‑m Ti y Cu z Sn m The composition is represented by x, y, z, and m, where x, y, z, and m satisfy 0 < x ≤ 2, 0 < y ≤ 1.5, 0 < z ≤ 1.5, and 0 < m ≤ 1; the mass of the nano-Ni powder accounts for 40% to 60% of the total mass of the composite electrode material. The composite electrode material of this invention possesses both high discharge capacity and excellent cycle stability. After 200 cycles at a charge-discharge current density of 300 mA / g, the capacity retention rate can reach over 60%, meeting the application requirements of Ni-MH secondary batteries for high-capacity and long-life negative electrode materials.

Description

Technical Field

[0001] This invention relates to the field of hydrogen storage alloy materials technology, and in particular to an AB-type Y-Mg-Ni-Ti-Cu-Sn system hydrogen storage alloy composite electrode material and its preparation method. Background Technology

[0002] Nickel-metal hydride (Ni-MH) secondary batteries are widely used in hybrid vehicles and other fields due to their safety and environmental advantages. Currently, commercially available AB5 rare-earth hydrogen storage alloys are approaching their theoretical capacity (approximately 330 mAh / g), leaving limited room for improvement.

[0003] Magnesium-based hydrogen storage alloys have become a research hotspot for next-generation Ni-MH battery anode materials due to their high theoretical capacity (e.g., Mg2Ni can reach 999 mAh / g) and abundant resources. However, magnesium-based alloys are prone to oxidation and corrosion in alkaline electrolytes, forming a dense Mg(OH)2 layer on the surface, which hinders charge transfer and hydrogen diffusion. At the same time, repeated hydrogen absorption and desorption lead to alloy pulverization, and newly exposed surfaces corrode more rapidly. After 20 cycles, the capacity decay rate is as high as 70% or more, which seriously restricts its commercial application.

[0004] To improve the performance of magnesium-based alloys, researchers have conducted extensive work: firstly, by adding Al, Mn, rare earth elements (La, Ce, Y, etc.) and transition metals (Ti, Zr, Sn) for alloying modification to improve the alloy's corrosion resistance and anti-pulverization ability; secondly, by using surface modification methods such as mechanical coating with nano-Ni powder to improve initial discharge capacity. However, alloying modification often comes at the cost of capacity, and conventional surface coatings are prone to detachment and failure during long cycles, making it difficult to achieve both high capacity and long lifespan. Some studies have attempted to add precious metals such as Pd, but the cost is too high, lacking commercial competitiveness. Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide a Y-Mg-Ni-Ti-Cu-Sn hydrogen storage alloy composite electrode material and its preparation method, in order to solve the technical problem that existing magnesium-based electrode materials are difficult to simultaneously achieve high discharge capacity and long cycle life.

[0006] On one hand, embodiments of the present invention provide a Y-Mg-Ni-Ti-Cu-Sn system hydrogen storage alloy composite electrode material, the composite electrode material comprising: an alloy core and nano-Ni powder coated on at least a portion of the surface of the alloy core; The alloy core has the chemical formula Mg 25-x Y x Ni 20-y-z-m Ti y Cu z Sn mThe composition of the expression is such that x, y, z, and m satisfy: 0 < x ≤ 2, 0 < y ≤ 1.5, 0 < z ≤ 1.5, and 0 < m ≤ 1. The mass of the nano-Ni powder accounts for 40% to 60% of the total mass of the composite electrode material.

[0007] Furthermore, in the alloy core, x:y:z:m = 1:1:1:0.5.

[0008] Furthermore, the alloy core has a nanocrystalline structure with an average grain size of 20 nm to 100 nm.

[0009] Furthermore, at a charge / discharge current density of 300 mA / g, the capacity retention S of the composite electrode material after 200 charge / discharge cycles is... 200 ≥60%.

[0010] On the other hand, embodiments of the present invention provide a method for preparing the above-described composite electrode material, comprising the following steps: S1: According to the chemical formula Mg 25-x Y x Ni 20-y-z-m Ti y Cu z Sn m Weigh the raw metal, smelt and cast it to obtain the master alloy ingot; S2: Remelt the master alloy ingot obtained in step S1, spray it onto a rotating cooling roller through a rapid quenching process, and obtain a rapid quenching alloy strip after cooling. S3: The rapidly quenched alloy strip obtained in step S2 is crushed and sieved to obtain alloy powder; the alloy powder is mixed with nano Ni powder and mechanically ball-milled to obtain the composite electrode material; In step S3, the amount of nano-Ni powder added accounts for 40% to 60% of the total mass of the final composite electrode material.

[0011] Furthermore, in step S1, the order in which the raw material metals are placed is as follows: rare earth Y is placed at the bottom of the crucible, Ni and Cu are placed above rare earth Y, Ti is placed above Ni and Cu, and Mg and Sn are placed at the very top.

[0012] Furthermore, in step S2, the parameters of the rapid quenching process include: the surface linear velocity of the cooling roller is 5m / s to 30m / s; and the thickness of the resulting rapid quenching alloy strip is 50μm to 300μm.

[0013] Furthermore, in step S3, the process parameters for the mechanical ball milling include: a ball-to-material ratio of 15~25:1, a rotation speed of 250~450 rpm, and a ball milling time of 5~20 hours.

[0014] Furthermore, the ball milling time is 10 hours.

[0015] Furthermore, in step S3, the mechanical ball milling is carried out under a protective atmosphere, and the ball milling process is carried out intermittently, with a shutdown period of 0.25 to 0.75 hours after each 0.5 to 1.5 hours of operation.

[0016] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: 1) This invention, through the synergistic combination of a Y-Mg-Ni-Ti-Cu-Sn multi-element alloy core and 40%~60% nano-Ni powder coated on its surface, exhibits good comprehensive performance in terms of both discharge capacity and cycle stability. According to the test results of the examples and comparative examples, the discharge capacity of the alloy core without nano-Ni coating is 208.9 mAh / g; while the composite electrode material of the embodiments of this invention has a maximum discharge capacity of 510~601 mAh / g at a current density of 300 mA / g, a capacity retention rate of 60%~74% after 200 cycles, and a cycle life of 202~302 cycles.

[0017] 2) This invention, through the synergistic alloying of Y, Ti, Cu, and Sn elements, helps to improve the structural stability and electrochemical performance of the alloy core. Specifically, Y helps improve the material's resistance to pulverization; the introduction of Ti, Cu, and Sn helps to regulate the phase composition, surface stability, and structural changes during hydrogen absorption and desorption, thereby improving the material's cycle stability and kinetic performance.

[0018] 3) The preparation method of this invention yields a composite electrode material possessing both a nanocrystalline structure and uniform nano-Ni powder coating. Vacuum rapid quenching produces nanocrystalline alloy ribbons with an average grain size of 20–100 nm, where high-density grain boundaries provide rapid channels for hydrogen atom diffusion. High-energy ball milling achieves uniform coating of nano-Ni powder (40%–60%), preserving the stability of the rapidly quenched nanocrystalline structure while fully utilizing the catalytic and protective effects of the coated nano-Ni powder. The resulting composite electrode material exhibits a high-rate discharge performance (HRD) of 88%–96% at a current density of 300 mA / g, demonstrating excellent kinetic performance.

[0019] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0020] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0021] Figure 1 These are scanning electron microscope (SEM) images of the microstructure of the cast alloys prepared in Examples 1-6 of this invention.

[0022] Figure 2 The phase diagrams are for four different binary alloy systems: (a) Mg-Ni binary phase diagram, (b) Y-Ni binary phase diagram, (c) Ti-Ni binary phase diagram, and (d) Ti-Sn binary phase diagram. Figure 3 The following are test results of the rapidly quenched alloy prepared in Example 1 of the present invention: (a) is a photograph of the rapidly quenched alloy strip; (b) is a high-resolution transmission electron microscope (HRTEM) microstructure of the rapidly quenched alloy.

[0023] Figure 4 These are scanning electron microscope (SEM) images of the ball-milled composite materials prepared in Examples 1-6 of this invention.

[0024] Figure 5 The X-ray diffraction (XRD) spectra of the ball-milled composite materials prepared in Examples 1-6 of this invention are shown.

[0025] Figure 6 These are high-resolution transmission electron microscopy (HRTEM) images of the ball-milled composite materials prepared in Examples 1-6 of this invention. Detailed Implementation

[0026] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0027] To address the technical challenge of rapid capacity decay and difficulty in balancing high capacity and long lifespan in Ni-MH battery applications using magnesium-based alloys, this invention provides a Y-Mg-Ni-Ti-Cu-Sn hydrogen storage alloy composite electrode material and its preparation method through the synergistic combination of alloying modification and surface coating.

[0028] A specific embodiment of the present invention discloses a Y-Mg-Ni-Ti-Cu-Sn hydrogen storage alloy composite electrode material, the composite electrode material comprising: an alloy core and nano-Ni powder coated on at least a portion of the surface of the alloy core; The alloy core has the chemical formula Mg 25-x Y x Ni 20-y-z-m Tiy Cu z Sn m The composition is represented by x, y, z, and m, where x, y, z, and m satisfy the following conditions: 0 < x ≤ 2 (e.g., x is 0.5, 1.0, 1.2, 1.5, 1.8, 2.0), 0 < y ≤ 1.5 (e.g., y is 0.3, 0.5, 0.8, 1.0, 1.2, 1.5), 0 < z ≤ 1.5 (e.g., z is 0.3, 0.5, 0.8, 1.0, 1.2, 1.5), and 0 < m ≤ 1 (e.g., m is 0.2, 0.4, 0.5, 0.7, 0.9, 1.0). The mass of the nano-Ni powder accounts for 40% to 60% of the total mass of the composite electrode material, for example, 40%, 45%, 50%, 55%, 58%, or 60%.

[0029] It should be noted that the "alloy core" refers to the core component mainly composed of the specific multi-element alloy and undertaking the reversible hydrogen storage function. The nano-Ni powder is coated on at least a portion of the surface of the alloy core by means such as mechanical ball milling.

[0030] The composite electrode material of this invention is used as the negative electrode active material in Ni-MH secondary batteries. During charging and discharging, the alloy core undertakes the absorption, storage, and release of hydrogen. The Y-Mg-Ni-Ti-Cu-Sn multi-element alloy composition, through the synergistic effect of multiple elements, helps to improve the alloy's resistance to pulverization and corrosion. The nano-Ni powder coated on at least part of the surface of the alloy core can play an electrocatalytic, conductive, and surface protective role, thereby promoting charge transfer and hydrogen adsorption / desorption reactions, and slowing down the corrosion of the alloy core by the electrolyte.

[0031] Compared with the prior art, this embodiment combines the intrinsic hydrogen storage capacity of the alloy core with the catalytic and protective functions of the nano-Ni powder, which accounts for 40% to 60% of the total mass of the composite electrode material, through the synergistic cooperation of the Y-Mg-Ni-Ti-Cu-Sn multi-element alloy core. This helps to balance high discharge capacity and good cycle life.

[0032] The amounts of each component added in this invention and their specific mechanisms of action are as follows: Ni: Ni exhibits optimal electrocatalytic activity. Without Ni in the magnesium-based electrode alloy, room-temperature electrochemical hydrogen storage is difficult to achieve. Figure 2 As shown in (a), Ni mainly exists in the alloy as the Mg2Ni phase, with some MgNi2 phase as well. However, Ni itself is not a hydrogen-absorbing element, and the theoretical electrochemical hydrogen storage capacity of the alloy decreases with increasing Ni content. In addition, Ni is expensive, and excessive use will significantly increase the raw material cost of the alloy.

[0033] Y: Rare earth element Y is a hydrogen-absorbing element. Theoretically, the addition of rare earth elements will increase the electrochemical hydrogen storage capacity of the alloy. Y can significantly improve the fracture toughness of the alloy, increase its resistance to pulverization, and thus improve its electrochemical cycling stability. Y can form various phases such as YNi3 and YNi5 in the alloy (see...). Figure 2 In (b), these phases can all electrochemically store hydrogen and have a certain catalytic effect on the electrochemical hydrogen storage of Mg-based alloys. However, excessive use of Y will consume Ni in the alloy, causing the main phase to transform into YNi5, which has a low electrochemical hydrogen storage capacity. In addition, Y is a rare element and has a high price; excessive use will significantly increase the raw material cost of the alloy.

[0034] Ti: Ti exhibits high reactivity and possesses a certain catalytic effect on the electrochemical hydrogen storage of magnesium-based alloys. Due to the immiscibility of Ti and Mg, Ti primarily forms Ni3Ti in the alloy (see...). Figure 2 (c) and Sn5Ti6 (see Figure 2 In (d), the formation of these phases can significantly increase the phase interface of the alloy and improve the electrochemical hydrogen storage kinetics. Ti has good corrosion resistance in alkaline electrolytes, which is beneficial to improving the electrochemical cycle stability of the alloy.

[0035] Sn: Adding trace amounts of Sn can improve the corrosion resistance of the alloy in KOH electrolyte and enhance its electrochemical cycling stability. However, the amount of Sn added should be strictly controlled, as excessive use of Sn will significantly reduce the alloy's electrochemical hydrogen storage capacity.

[0036] Cu: Cu and Ni are infinitely miscible, and Cu is completely dissolved in the Mg₂Ni main phase in the alloy. The addition of Cu increases the lattice constant of the alloy, reduces the cell volume expansion during hydrogen absorption, and thus improves the cycle stability of the alloy. In addition, the addition of Cu can improve the corrosion resistance of the alloy in the electrolyte, further enhancing the electrochemical cycle stability of the alloy. It should be noted that the electrocatalytic activity of Cu is significantly lower than that of Ni, therefore the amount of Cu substitution should be appropriately controlled.

[0037] Furthermore, in the alloy core, x:y:z:m = 1:1:1:0.5. This ratio is beneficial for obtaining a more suitable phase composition and microstructure, thereby improving the overall electrochemical performance of the composite electrode material.

[0038] Furthermore, the alloy core has a nanocrystalline structure with an average grain size of 20 nm to 100 nm, for example, 20 nm, 30 nm, 45 nm, 60 nm, 80 nm, or 100 nm. Nanocrystals of this size provide a high density of grain boundaries, which is beneficial for the diffusion of hydrogen atoms, thereby improving the kinetic properties of the alloy.

[0039] Furthermore, the nano-Ni powder is a nano-sized particle with a high specific surface area and excellent electrocatalytic activity, and can be uniformly adhered to the surface of the alloy core during ball milling.

[0040] Furthermore, at a charge / discharge current density of 300 mA / g, the capacity retention S of the composite electrode material after 200 charge / discharge cycles is... 200 ≥60%, for example, S 200 The percentages are 60%, 62%, 65%, 68%, 70%, 71%, 72%, 73%, and 74%.

[0041] On the other hand, a specific embodiment of the present invention discloses a method for preparing the composite electrode material as described above, comprising the following steps: S1: According to the chemical formula Mg 25-x Y x Ni 20-y-z-m Ti y Cu z Sn m Weigh the raw metal, smelt and cast it to obtain the master alloy ingot; S2: Remelt the master alloy ingot obtained in step S1, spray it onto a rotating cooling roller through a rapid quenching process, and obtain a rapid quenching alloy strip after cooling. S3: The rapidly quenched alloy strip obtained in step S2 is crushed and sieved to obtain alloy powder; the alloy powder is mixed with nano Ni powder and mechanically ball-milled to obtain the composite electrode material.

[0042] In step S3, the amount of nano-Ni powder added accounts for 40% to 60% of the total mass of the final composite electrode material, for example, 40%, 45%, 50%, 55%, 58%, 60%.

[0043] In practice, the method of the present invention can adopt the above preferred step sequence: first, a master alloy ingot with uniform composition is obtained by conventional melting (S1), which ensures the accuracy of the basic composition of the alloy core; then, the master alloy is remelted and rapidly solidified by a rapid quenching process (S2), and sprayed onto a rotating water-cooled copper roller to obtain an alloy strip with a nanocrystalline structure; finally, the rapidly quenched strip is crushed into powder by mechanical ball milling (S3), and the uniform coating of nano-Ni powder on the surface of the alloy particles is achieved simultaneously.

[0044] The preparation method provided in this embodiment integrates three technical means—alloying modification, structural control, and surface modification—into the same process flow, achieving synergistic control of the material from composition to structure to surface. Moreover, the process is simple, highly controllable, and suitable for large-scale production.

[0045] Furthermore, in step S1, the raw material metals are placed in the following order: rare earth Y is placed at the bottom of the crucible, Ni and Cu are placed above rare earth Y, Ti is placed above Ni and Cu, and Mg and Sn are placed on top. This placement order facilitates the gradual melting and mixing of each component during the smelting process, thereby improving the uniformity of the alloy composition.

[0046] It should be noted that, because metallic Mg, rare earth Y, and Sn are easily lost through volatilization during high-temperature smelting, additional loss allowances need to be added when preparing the Mg, Y, and Sn ingredients in step S1. By mass, the loss allowance for Mg and Sn is approximately 8%, and for rare earth Y, it is approximately 5%.

[0047] As an optional implementation, the smelting and casting process in step S1 can be carried out according to the following process parameters: the raw material metal weighed according to the stoichiometric ratio is placed in a crucible (e.g., a magnesium oxide crucible for a medium-frequency induction furnace) in the order described above; after the furnace lid is closed, a vacuum is drawn to a vacuum degree of 5×10⁻⁶. -2 The pressure is increased to 0.01-0.1 MPa (e.g., 0.04 MPa) by evacuating for more than 30 minutes (preferably). Then, a protective gas (e.g., high-purity helium, or a 1:1 volume ratio of helium and argon) is introduced until the pressure reaches 0.01-0.1 MPa. The mixture is then heated to a lower temperature (e.g., 650°C) at a lower power (e.g., 5 kW) to melt the Mg metal. The power is then increased to a higher power (e.g., 30 kW) and heated to the melting temperature (e.g., 1500-1600°C) to completely melt the remaining metal. Finally, the molten alloy is poured into a mold (e.g., a copper mold) and cooled to obtain a master alloy ingot.

[0048] Further, in step S2, the parameters of the rapid quenching process include: the surface linear velocity of the cooling roller is 5 m / s to 30 m / s, for example, 5 m / s, 10 m / s, 15 m / s, 20 m / s, 25 m / s, or 30 m / s; and the thickness of the resulting rapid quenched alloy strip is 50 μm to 300 μm, for example, 50 μm, 100 μm, 150 μm, 200 μm, 250 μm, or 300 μm. Preferably, when the linear velocity of the cooling roller is 8 m / s, a rapid quenched strip with an average thickness of approximately 191 μm and an average grain size of approximately 54 nm can be obtained.

[0049] Regarding the detailed optimization of the rapid quenching process, in specific implementation, the slit width at the bottom of the quartz tube is preferably 0.3 mm. This width was optimized and determined as follows: if it is too wide (>0.5 mm), the liquid alloy will flow out due to its own weight when there is no gas pressure, making it impossible to accurately control the injection timing; if it is too narrow (<0.2 mm), it is prone to clogging and requires higher gas pressure to eject, increasing the risk of the quartz tube bursting. 0.3 mm achieves the best balance between maintaining atmospheric pressure and injection pressure, ensuring that the liquid alloy can be smoothly ejected under the action of protective gas pressure (e.g., about 1.05 atm), while also remaining inside the tube due to surface tension when no pressure is applied, thereby achieving precise control of the rapid quenching process.

[0050] Further, in step S3, the process parameters for the mechanical ball milling include: a ball-to-material ratio of 15~25:1, for example, 15:1, 18:1, 20:1, 22:1, 24:1, 25:1; a rotational speed of 250~450 rpm, for example, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 420 rpm, 450 rpm; and a milling time of 5~20 hours, for example, 5h, 8h, 10h, 12h, 16h, 20h. Too short a milling time may result in insufficient coating of nano-Ni powder, while too long a milling time may cause excessive refinement of the alloy particles. Preferably, the milling time is 10 hours.

[0051] Furthermore, in step S3, the mechanical ball milling is carried out under a protective atmosphere, and the ball milling process is carried out intermittently, with each operation lasting 0.5 to 1.5 hours, for example, 0.5h, 0.8h, 1.0h, 1.2h, 1.4h, or 1.5h; and each shutdown lasting 0.25 to 0.75 hours, for example, 0.25h, 0.4h, 0.5h, 0.6h, 0.7h, or 0.75h.

[0052] It should be noted that the nanocrystals prepared by the rapid quenching process in this invention are fundamentally different from those obtained by mechanical ball milling: ball-milled nanocrystals are refined by strong plastic deformation, and the grain boundaries are in a high-energy non-equilibrium state, resulting in poor thermodynamic stability and easy grain growth during subsequent cycles or heat treatment; while rapid quenching nanocrystals are formed by direct solidification of the liquid phase at extremely high cooling rates, and the grain boundaries are in a lower energy state, resulting in higher thermodynamic stability. The grains are not easy to grow during long-term cycling, which is beneficial to maintaining stable electrochemical performance.

[0053] In addition, nano-Ni powder plays an important process aid role in mechanical ball milling: its low hardness and good ductility can be used as a lubricant to effectively prevent alloy powder from cold welding and agglomeration during ball milling, avoid material adhesion to the ball mill jar wall, thereby improving ball milling efficiency and ensuring the uniformity of the coating layer.

[0054] The present invention will be described in more detail below through specific embodiments. These embodiments are merely descriptions of the best implementation of the invention and do not limit the scope of the invention in any way.

[0055] Examples 1-10 below all use the following method to prepare Y-Mg-Ni-Ti-Cu-Sn hydrogen storage alloy composite electrode materials. The specific differences in parameters between each example are shown in Table 1.

[0056] S1: Select bulk metal Mg, bulk rare earth Y, electrolytic Ni and Cu, sponge Ti and metal Sn according to the chemical formula composition of each embodiment. The metal purity is required to be ≥99.5%. After grinding the selected bulk metal to remove the surface oxide layer, weigh it according to the chemical dosage ratio. Among them, the proportion of metal Mg and Sn is increased by 8%, and the proportion of rare earth Y is increased by 5% to compensate for the burn-off during smelting. The prepared raw materials are placed sequentially into a magnesium oxide crucible, evacuated, filled with a protective gas, and induction heated to obtain a molten liquid alloy. The molten alloy is then poured into a copper mold to obtain a master alloy ingot. Heating process parameters: Vacuum is drawn to 5×10 during induction heating. -2 The gas is filled with high-purity helium or a mixture of helium and argon with a volume ratio of 1:1 at a pressure of 0.01~0.1MPa; the melting temperature is 1500~1600 ℃. S2: Place the ingot prepared in step S1 into a quartz tube with a slit at the bottom, and heat it by induction until the ingot is completely melted. Under the pressure of protective gas, the liquid alloy is sprayed from the slit at the bottom of the quartz tube onto the surface of a rotating water-cooled copper roller to obtain a fast-quenched alloy strip with a thickness between 50 and 300 μm. S3: After mechanically crushing the rapid quenching sheet and passing it through a 200-mesh sieve, mix it with nano Ni powder and stainless steel grinding balls and load it into a stainless steel ball mill jar. Use an all-around planetary ball mill to ball mill for 5 to 20 hours. Stop the ball mill for 0.5 hours every 1 hour of continuous operation to obtain ball-milled powder, which is the composite electrode material. In step S3, the amount of nano-Ni powder added accounts for 40% to 60% of the total mass of the final composite electrode material.

[0057] S4: The structure of the ball-milled powder was tested using XRD. See the XRD pattern of the ball-milled composite material. Figure 5 The morphology and microstructure of the composite material before and after ball milling were observed using high-resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM). The HRTEM microstructure of the ball-milled composite material is shown in [reference needed]. Figure 6 SEM morphology (see [reference]) Figure 4The crystal state of the alloy was determined using selected area electron diffraction (SAED). The electrochemical discharge capacity, cycle stability, and high-rate discharge performance of the composite material were tested using a simulated battery tester.

[0058] Example 1 This embodiment provides a Y-Mg-Ni-Ti-Cu-Sn system hydrogen storage alloy composite electrode material, comprising: The alloy core has a chemical composition of Mg. 24 Y1Ni 17.5 Ti1Cu1Sn 0.5 ; A coating layer is applied to the surface of the alloy core. The coating layer contains nano-Ni powder, and the mass of the nano-Ni powder accounts for 50% of the total mass of the composite electrode material.

[0059] The specific preparation parameters for this embodiment are as follows: S1: According to the chemical formula Mg 24 Y1Ni 17.5 Ti1Cu1Sn 0.5 The raw materials selected are bulk Mg and rare earth Y, electrolytic Ni and Cu, sponge Ti and metallic Sn. The metal purity is 99.5%, and the raw materials are weighed according to the chemical dosage ratio, with 5 kg of raw materials per furnace.

[0060] The weighed bulk metal was placed in the magnesium oxide crucible of the medium-frequency induction furnace according to the designed process. Bulk rare earth Y was placed at the bottom of the crucible, followed by electrolytic Ni and Cu on top of the rare earth Y, then sponge Ti on top of the electrolytic Ni and Cu, and finally bulk Mg and Sn on top. The furnace lid was then closed, and a vacuum was evacuated for 30 minutes until the vacuum level reached 5 × 10⁻⁶. -2 Above a pressure of 0.04 MPa, high-purity helium protective gas is introduced until the pressure reaches 0.04 MPa. The power is adjusted to 5 kW, and the temperature is controlled at 650℃ to melt the Mg metal. Then, the power is adjusted to 30 kW, and the temperature is controlled at approximately 1600℃ to melt the remaining metals. The molten alloy is poured into a copper mold to obtain a master alloy ingot.

[0061] S2: The ingot prepared in step S1 is placed inside a quartz tube with a slit at the bottom. Induction heating is used to completely melt the ingot. Under the pressure of a protective gas, the liquid alloy is sprayed from the slit at the bottom of the quartz tube onto the surface of a rotating water-cooled copper roller (quenching rate 8 m / s), resulting in a fast-quenched alloy ribbon with an average thickness of approximately 191 μm and an average grain size of approximately 54 nm. For its macroscopic morphology and microstructure, see [link to relevant documentation]. Figure 4 .

[0062] S3: Mechanically crush and pass the rapidly quenched Mg24Y1Ni17.5Ti1Cu1Sn0.5 alloy flakes through a 200-mesh sieve. Weigh 20 grams of the sieved alloy powder, 20 grams of nano-Ni powder, and 400 grams of stainless steel grinding balls. Mix them together and place them in a 250 ml stainless steel ball mill jar. Vacuum the jar, fill it with high-purity argon, and then seal it. Grind the jar in an all-around planetary high-energy ball mill for 10 hours, stopping the mill for 0.5 hours after every hour of continuous operation.

[0063] Examples 2-10 The raw materials for Examples 2-6 were weighed according to their chemical formulas, and other preparation process parameters were the same as in Example 1; the microstructure morphology of the cast alloys prepared in Examples 1-6 is described in [reference needed]. Figure 1 The as-cast alloy has a multiphase structure, including the Mg2Ni main phase, MgNi2 phase, Y2Ni7 phase, Sn5Ti6 phase and Ni3Ti phase.

[0064] The preparation processes of Examples 7 and 8 are the same as those of Example 1, except that different amounts of nano-Ni powder are added; The ingredients for Examples 9 and 10 are exactly the same as those for Example 1, the difference being the use of different ball milling times.

[0065] Table 1. Formulations and process parameters for Examples 1-10

[0066] Comparative Example 1 The raw materials for this comparative example were weighed according to their chemical formulas. Other preparation process parameters were the same as in Example 1, except that nano-Ni powder was not added during ball milling in Comparative Example 1.

[0067] Comparative Example 2 This comparative example uses the method disclosed in CN102368546A to prepare a Mg2NiH4+2Ni (molar ratio 1:2) composite electrode material as a comparison. Example 1 of that patent describes a Mg2NiH4+2Ni (molar ratio) material prepared by a combination of hydrogenation combustion synthesis and mechanical ball milling, which achieved an initial discharge capacity of 946 mAh / g, but after 8 cycles, the capacity decreased to 359 mAh / g, with a capacity retention of approximately 38%.

[0068] For ease of comparison, the formulations and process parameters of Comparative Examples 1 and 2 are summarized in Table 2.

[0069] Table 2 Formulations and process parameters for Comparative Examples 1-2

[0070] The composite material powders prepared in the above embodiments and comparative examples were mixed with nickel carbonyl powder at a mass ratio of 1:4, and then cold-pressed into cylindrical electrode sheets with a diameter of 15 mm under a pressure of 35 MPa. Electrochemical performance was tested using a standard three-electrode testing system.

[0071] The discharge regime used to test the activation performance and maximum discharge capacity of the alloy was: a charge / discharge current density of 100 mA / g, a charging time of 480 minutes, and a discharge cutoff voltage of -0.6 V. The discharge regime used to test the electrochemical cycle stability of the alloy was: a charge / discharge current density of 300 mA / g, a charging time of 180 minutes, and a discharge cutoff voltage of -0.6 V. The cycle life of the alloy is defined as the number of cycles corresponding to a decrease in discharge capacity to 60% of the maximum discharge capacity at a charge / discharge current density of 300 mA / g. (The last sentence appears to be incomplete and possibly refers to a different topic.) 200 This represents the retention rate of the alloy capacity after 200 cycles, i.e., S. 200 =C 200,300 / C max,300 ×100%. C max,300 : Maximum discharge capacity at a charge / discharge current density of 300 mA / g; C 200,300 The discharge capacity after 200 charge-discharge cycles at a charge-discharge current density of 300 mA / g. The high-rate discharge performance of the composite material is denoted by HRD, where HRD = C. 300 / C 100 ×100%. C 300 Discharge capacity at a charge / discharge current density of 300 mA / g, C 100 : Discharge capacity at a charge / discharge current density of 100 mA / g.

[0072] The test results of the composite electrode materials prepared in the above embodiments and comparative examples are listed in Table 3.

[0073] Table 3 Electrochemical properties of alloys from the examples and comparative examples

[0074] Note 1: Comparative Example 2 has an extremely short cycle life. After 8 cycles, its capacity has decayed to 359 mAh / g, and its cycle life cannot be calculated according to the definition of "capacity reduced to 60%" in this invention.

[0075] Note²: The original text of Comparative Example 2 did not disclose HRD data.

[0076] Test results show that the composite electrode materials of Examples 1-10 of this invention have a maximum discharge capacity of 510-600 mAh / g, a capacity retention rate of 60%-74% after 200 cycles, a cycle life of 200-302 cycles, and a high-rate discharge performance of 88%-95%. In contrast, the maximum discharge capacity of Comparative Example 1 is only 208.9 mAh / g, far lower than that of the other examples; although Comparative Example 2 has a higher initial discharge capacity, its cycle stability is significantly worse than that of this invention. These results demonstrate that this invention successfully achieves a balance between high capacity and long cycle life through the synergistic effect of pentagonal alloying and nano-Ni coating.

[0077] In summary, this invention combines Y-Mg-Ni-Ti-Cu-Sn pentagonal alloying with vacuum rapid quenching technology to obtain an alloy core with a stable nanocrystalline structure. Then, it is coated with high-content nano-Ni powder by mechanical ball milling, successfully preparing a composite electrode material with both high discharge capacity and long cycle life. The preparation process is simple and controllable, and suitable for large-scale production.

[0078] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A Y-Mg-Ni-Ti-Cu-Sn based hydrogen storage alloy composite electrode material, characterized in that, The composite electrode material includes: an alloy core and nano-Ni powder coated on at least a portion of the surface of the alloy core; The alloy core has the chemical formula Mg 25-x Y x Ni 20-y-z-m Ti y Cu z Sn m The composition of the expression is such that x, y, z, and m satisfy: 0 < x ≤ 2, 0 < y ≤ 1.5, 0 < z ≤ 1.5, and 0 < m ≤ 1. The mass of the nano-Ni powder accounts for 40% to 60% of the total mass of the composite electrode material.

2. The composite electrode material according to claim 1, characterized in that, In the alloy core, x:y:z:m = 1:1:1:0.

5.

3. The composite electrode material according to claim 1 or 2, characterized in that, The alloy core has a nanocrystalline structure with an average grain size of 20 nm to 100 nm.

4. The composite electrode material according to claim 1 or 2, characterized in that, At a charge / discharge current density of 300 mA / g, the capacity retention S of the composite electrode material after 200 charge / discharge cycles is... 200 ≥60%.

5. A method for preparing the composite electrode material according to any one of claims 1 to 4, characterized in that, Includes the following steps: S1: According to the chemical formula Mg 25-x Y x Ni 20-y-z-m Ti y Cu z Sn m Weigh the raw metal, smelt and cast it to obtain the master alloy ingot; S2: Remelt the master alloy ingot obtained in step S1, spray it onto a rotating cooling roller through a rapid quenching process, and obtain a rapid quenching alloy strip after cooling. S3: The rapidly quenched alloy strip obtained in step S2 is crushed and sieved to obtain alloy powder; the alloy powder is mixed with nano Ni powder and mechanically ball-milled to obtain the composite electrode material; In step S3, the amount of nano-Ni powder added accounts for 40% to 60% of the total mass of the final composite electrode material.

6. The preparation method according to claim 5, characterized in that, In step S1, the order in which the raw material metals are placed is as follows: rare earth Y is placed at the bottom of the crucible, Ni and Cu are placed above rare earth Y, Ti is placed above Ni and Cu, and Mg and Sn are placed at the very top.

7. The preparation method according to claim 5, characterized in that, In step S2, the parameters of the rapid quenching process include: the surface linear velocity of the cooling roller is 5m / s to 30m / s; and the thickness of the resulting rapid quenching alloy strip is 50μm to 300μm.

8. The preparation method according to claim 5, characterized in that, In step S3, the process parameters of the mechanical ball mill include: a ball-to-material ratio of 15~25:1, a rotation speed of 250~450 rpm, and a ball milling time of 5~20 hours.

9. The preparation method according to claim 8, characterized in that, The ball milling time is 10 hours.

10. The preparation method according to claim 5, characterized in that, In step S3, the mechanical ball milling is carried out under a protective atmosphere, and the ball milling process is carried out intermittently, with a shutdown period of 0.25 to 0.75 hours after each 0.5 to 1.5 hours of operation.

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