A magnesium-ion battery anode material Mg-Sm alloy, its preparation method and application

Abstract

This invention provides a Mg-Sm alloy anode material for magnesium-ion batteries, its preparation method, and its applications, relating to the technical field of magnesium-ion battery anode materials. The Mg-Sm alloy anode material of this invention is obtained by melting, solution treatment, and extrusion deformation of magnesium blocks and a magnesium-samarium alloy. The alloy, by mass percentage, comprises: Sm 3wt%, with the balance being Mg. The Mg-Sm alloy has a uniform micron-scale equiaxed grain structure, containing only an α-Mg single phase and no precipitated phases. Through composition design and process optimization, this invention significantly improves the electrochemical performance and cycle stability of the magnesium-ion battery anode. The successful preparation of a high-performance Mg-Sm alloy anode material has promising application prospects.

Description

Technical Field

[0001] This invention relates to the field of magnesium-ion battery anode material technology, and in particular to a magnesium-ion battery anode material Mg-Sm alloy, its preparation method and application. Background Technology

[0002] With the rapid development of the electric vehicle industry, magnesium-ion batteries (MIBs) have become one of the important technologies in the "post-lithium battery era," demonstrating enormous application potential.

[0003] Magnesium is the eighth most abundant element in the Earth's crust (approximately 2.1%), with abundant reserves and wide distribution. Its price is only one-fifth to one-tenth that of lithium, resulting in a more stable supply chain and a more balanced geographical distribution, which helps reduce battery manufacturing costs. Furthermore, magnesium metal anodes have a high mAh / cm³ capacity. 3 The theoretical volumetric specific capacity is that of lithium metal (2062 mAh / cm³). 3 Magnesium has a capacitance approximately 1.8 times higher than that of lithium, which facilitates smaller, higher-capacity battery designs. Furthermore, magnesium's standard electrode potential is -2.37 V, close to that of lithium (-3.04 V), providing a higher operating voltage. More importantly, magnesium is less prone to dendrite formation during deposition, thus reducing the risk of short circuits and thermal runaway, significantly improving battery safety.

[0004] However, pure magnesium metal faces many challenges in practical applications as a negative electrode material. Specifically, pure magnesium metal easily forms an ion-insulating passivation layer (mainly composed of MgO, Mg(OH)2, etc.) with conventional electrolytes. This passivation layer severely hinders the absorption of Mg. 2+ The reversible deposition / dissolution of magnesium leads to high polarization, low coulombic efficiency, and significant voltage hysteresis, resulting in severe energy loss during battery charging and discharging. During charging and discharging, the dissolution-deposition process of magnesium in the anode is typically uneven, easily forming porous structures, hemispherical deposits, or exhibiting abnormal peeling behavior on the electrode surface. This leads to electrode pulverization, decreased mechanical strength, and loss of active material, subsequently causing short circuits or rapid capacity decay. Due to the combined effects of the aforementioned passivation layer and uneven deposition problems, the cycle life of pure magnesium anodes often fails to meet practical application requirements, and the overpotential continuously increases with the number of cycles, resulting in rapid battery performance degradation. Furthermore, pure magnesium has stringent requirements for the electrolyte system and poor compatibility with most conventional electrolytes, limiting the design flexibility and material selection range of the battery system.

[0005] In existing technologies, researchers have attempted to improve the performance of pure magnesium anodes through methods such as artificial interface construction, electrolyte optimization, and the addition of alloying elements. Among these, magnesium alloying is considered an effective strategy, as the crystal structure, surface properties, and electrochemical behavior of magnesium can be controlled by introducing alloying elements. However, existing magnesium alloy anode materials still have the following shortcomings: one is the intrinsic kinetic barrier, Mg... 2+ The high charge density of Mg makes its migration in the solid phase difficult, and Mg 2+ It binds strongly to the electrolyte solvent (such as ethers), and the energy barrier for detachment from the solvent sheath is very high, especially at low temperatures; secondly, there is interfacial passivation, Mg 2+ It readily reacts with electrolytes and impurities (such as water and oxygen) to form non-ion-conducting insulating layers such as MgO, MgCO3, and MgF2 on the surface of the negative electrode. Thirdly, uneven deposition, Mg 2+ Uneven distribution on the negative electrode surface leads to local electric field distortion. Although pure magnesium is theoretically dendrite-free, hard magnesium dendrites can still grow under extreme conditions such as high areal capacity or high current density; fourth, irreversible side reactions continuously consume active magnesium and electrolyte, generating "dead magnesium".

[0006] Therefore, developing magnesium alloy anode materials with low overpotential, excellent reaction kinetics, low dendrite growth, and compatibility with various electrolytes is an effective solution to synergistically improve the cycle life, safety, and energy density of magnesium-ion battery anodes, and is of great significance for promoting the application of magnesium-ion batteries. Summary of the Invention

[0007] In view of this, the present invention provides a Mg-Sm alloy anode material for magnesium-ion batteries, its preparation method, and its applications. By precisely controlling the Sm element content (3wt%) and employing a melting-two-stage solution-extrusion process, the present invention prepares a Mg-Sm alloy anode material with a uniform micron-scale equiaxed grain structure, containing only α-Mg single phase and no precipitated phases. This material effectively inhibits the formation of the passivation layer, promotes the uniform deposition / dissolution of magnesium, significantly reduces overpotential, greatly extends cycle life, and achieves stable coulombic efficiency. It solves the problems faced by pure magnesium anodes in magnesium-ion battery applications, providing a novel anode material for the development of high-performance magnesium-ion batteries and showing promising application prospects.

[0008] The first aspect of this invention is to provide a magnesium-ion battery negative electrode material Mg-Sm alloy, which is obtained by melting magnesium blocks and magnesium-smium alloy, solution treatment, and extrusion deformation treatment; The alloy comprises, by mass percentage: 3 wt% Sm, with the balance being Mg; The Mg-Sm alloy has a uniform micron-scale equiaxed grain structure, contains only α-Mg single phase, and has no precipitated phase.

[0009] Preferably, the average grain size of the Mg-Sm alloy is 4.7 μm.

[0010] A second aspect of the present invention is to provide a method for preparing the above-mentioned magnesium-ion battery anode material Mg-Sm alloy, comprising the following steps: S1. Melting: Under a protective atmosphere of mixed CO2 and SF6, magnesium blocks and magnesium-samarium master alloys are melted sequentially to obtain an alloy liquid. After removing the oxide film on the surface of the melt, a refining agent is added to the alloy liquid for refining treatment. The billet is cast and then solidified in air to obtain an ingot. S2. Solution treatment: The ingot is subjected to a two-stage solution treatment under a pure argon protective atmosphere. S3. Extrusion Deformation Treatment: The ingot after the two-stage solution treatment is subjected to hot extrusion treatment to obtain the Mg-Sm alloy, a magnesium-ion battery anode material.

[0011] Preferably, in step S1, the volume ratio of CO2 to SF6 in the CO2 and SF6 mixed protective gas is 40:1; the purity of the magnesium block is greater than 99.9%; the magnesium-smarium master alloy is a Mg-30.0wt%Sm master alloy; and the amount of magnesium-smarium master alloy added is calculated based on the Sm content in the Mg-Sm alloy being 3wt%; the melting temperature is 750℃, and the holding time is 20-40 min; the refining agent is a mixture of MgCl2, KCl, BaCl2, CaF2, and CaCl2, with a mass ratio of 46:40:8:5:25.

[0012] Preferably, in step S2, the two-stage solution treatment includes: solution treatment at 320°C for 1-2 hours, then solution treatment at 500°C for 5-8 hours, followed by water quenching.

[0013] Preferably, in step S3, the temperature of the hot extrusion is 300-350°C and the extrusion ratio is 25:1.

[0014] A third aspect of this invention is to provide the application of the above-mentioned magnesium-ion battery anode material Mg-Sm alloy in the preparation of magnesium-ion battery anodes.

[0015] Preferably, the magnesium-ion battery uses a chlorine-containing electrolyte.

[0016] Compared with the prior art, the beneficial technical effects of the present invention are as follows: The overpotential of the Mg-3Sm alloy anode material prepared by this invention is significantly lower than that of the pure magnesium anode. The addition of Sm element effectively regulates the surface electrochemical behavior of magnesium, inhibits the formation of the ion-insulating passivation layer, and reduces the magnesium ion transport resistance, thereby significantly reducing electrode polarization and improving energy conversion efficiency.

[0017] The Mg-3Sm alloy anode of the present invention operates at a current density of 1 mA·cm⁻¹. -2 Capacity 1 mAh·cm -2 The cycle time under these conditions exceeds 1800 hours, which is more than 4.5 times that of a pure magnesium anode (approximately 400 hours). The uniform micron-scale equiaxed grain structure and single-phase α-Mg microstructure eliminate localized corrosion and stress concentration caused by grain boundary precipitates, ensuring uniform magnesium deposition / dissolution, effectively suppressing electrode pulverization and capacity decay, and significantly extending battery life.

[0018] The Mg-3Sm / / Cu half-cell of the present invention operates at a current density of 1.0 mA·cm⁻¹. -2 Capacity 1.0 mAh·cm -2 After 350 cycles under the given conditions, the average coulombic efficiency remained above 98%, indicating that the magnesium deposition / dissolution process is reversible, with few side reactions and high utilization of active materials, which is beneficial to improving the energy density and cycle life of the battery.

[0019] This invention employs a two-stage solution treatment combined with hot extrusion to achieve complete solution and uniform distribution of Sm elements in an α-Mg matrix, resulting in a uniform micron-scale equiaxed grain structure containing only the α-Mg single phase and free of precipitated phases. This microstructure avoids the electrochemical performance inhomogeneity caused by second-phase precipitation, ensuring the stability and consistency of material properties.

[0020] The preparation process of this invention includes three main steps: melting, two-stage solution treatment, and extrusion deformation. The process parameters are well-defined and highly controllable, making it easy to scale up for industrial production. Compared to complex surface modification or nanostructure preparation processes, the method of this invention is more practical and economical.

[0021] The Mg-3Sm alloy anode of this invention is highly compatible with chlorine-containing electrolytes (such as APC electrolytes), and exhibits excellent electrochemical performance in both symmetrical cell and half-cell tests, providing greater flexibility in the selection of electrolyte systems for magnesium-ion batteries. Attached Figure Description

[0022] The present invention will be further described below with reference to the accompanying drawings.

[0023] Figure 1 This is a SEM microstructure image of the alloy prepared in Example 1 of the present invention; Figure 2 The XRD pattern of the alloy prepared in Example 1 of this invention; Figure 3 This is a diagram showing the average grain size distribution of the alloy prepared in Example 1 of the present invention; Figure 4The symmetrical battery composed of the alloy prepared in Example 1 of this invention (electrolyte is APC solution) at a current density of 1 mA·cm -2 1 mAh cm -2 Deposition and dissolution curves of magnesium; Figure 5 The CV curve of the Mg-3Sm / / Cu half-cell composed of the alloy prepared in Example 1 of this invention in APC electrolyte; Figure 6 The coulombic efficiency diagram (current density 1 mA·cm⁻¹) of the Mg-3Sm / / Cu half-cell composed of the alloy prepared in Example 1 of this invention in APC electrolyte. -2 1 mAh cm -2 ). Detailed Implementation

[0024] This invention provides a magnesium-ion battery anode material Mg-Sm alloy, which is obtained by melting magnesium blocks and magnesium-sammonia alloy, solution treatment, and extrusion deformation treatment; The alloy comprises, by mass percentage: 3 wt% Sm, with the balance being Mg; The Mg-Sm alloy has a uniform micron-scale equiaxed grain structure, contains only α-Mg single phase, and has no precipitated phase.

[0025] In some specific embodiments, the average grain size of the Mg-Sm alloy is 4.7 μm.

[0026] This invention also provides a method for preparing the above-mentioned magnesium-ion battery anode material Mg-Sm alloy, comprising the following steps: S1, Alloy Smelting: (1) Weigh the raw materials according to the formula, and place the pure magnesium block with a purity greater than 99.9%, Mg-30.0wt.%Sm master alloy, refining agent and casting mold in a drying oven at 200℃ for 30 min; (2) The surfaces of the crucible, stirring rod and slag scraper are evenly brushed with a coating made of talc powder. The crucible is placed in a resistance furnace at about 300°C and kept warm for 20 minutes. After taking it out, the coating is evenly applied to the inner surface of the crucible. The above steps are repeated 3 times to ensure that the inner surface of the crucible is completely covered by the coating and the inner surface is smooth. The coating is a mixture of zinc oxide, water and water glass. (3) When the temperature of the resistance furnace reaches 700℃, put in a large piece of dried pure magnesium, close the furnace lid, and then introduce CO2+SF6 protective gas to isolate the air. (4) Adjust the temperature of the resistance furnace to 710℃. After the furnace temperature rises to the preset temperature, keep it at the temperature for 25 minutes. At this time, the pure magnesium block will be completely melted. Next, use a slag scraper to remove the oxide film on the surface of the magnesium alloy liquid. Then, quickly add the small piece of magnesium samarium alloy into the alloy liquid, and then put in a small piece of pure magnesium. The purpose is to press the alloy block under the surface of the molten magnesium alloy liquid, which is conducive to full dissolution and to prevent burn-out. (5) Adjust the resistance furnace temperature to 750℃ again. After the furnace temperature rises to the preset temperature again, keep it at the temperature for 20 minutes so that the added Sm alloying elements have enough time to fully diffuse in the molten magnesium alloy liquid after melting, so that the alloy composition is homogenized. (6) After the heat preservation is completed, adjust the furnace temperature to 740℃ and prepare to refine the molten metal. Slowly add the refining agent taken from the oven and stir vigorously. Maintain the process for 1-2 minutes until the surface of the alloy liquid is mirror-like. After the refining is completed, raise the furnace temperature back to 740℃ and keep it warm for 20 minutes. The refining agent is a mixture of MgCl2, KCl, BaCl2, CaF2 and CaCl2 in a mass ratio of 46:40:8:5:25. (7) After the heat preservation is completed, the furnace temperature is reduced to 710°C, the oxide film on the surface of the melt is removed, and then the alloy melt is poured into a copper mold preheated to 200°C under CO2+SF6 atmosphere protection to obtain a plate-shaped sample billet; after the ingot is air-cooled and solidified, the ingot is taken out; theoretically, there is no limitation on the casting mold, but the copper mold is selected in this embodiment of the invention. S2, Solution treatment: The ingots were homogenized in an OTF-1200X heat treatment furnace under a pure argon protective atmosphere. To ensure that the added alloying elements were fully dissolved into the matrix and to homogenize the alloy structure, a two-stage solution treatment was adopted with the following parameters: 320℃×1 h + 500℃×6 h, followed by water quenching. S3. Extrusion deformation treatment: The solution-treated ingot is machined to produce an extrusion billet with a diameter of 58 mm and a height of 60 mm. Then, it is hot-extruded at 300°C with an extrusion ratio of 25:1 to obtain the extruded sheet, which is the Mg-Sm alloy, a magnesium-ion battery anode material.

[0027] In some specific embodiments, step S3 is followed by electrode sheet preparation, which is carried out as follows: the extruded plate is cut to prepare a square sheet with a length of 15 mm and a thickness of 600 μm; then the square sheet is ground to a thickness of 300 μm using mechanical grinding; then the square sheet is processed into a circular electrode sheet with a diameter of 12 mm and a thickness of 300 μm using a slicing machine; finally, the oxide layer on the surface of the alloy electrode sheet is removed using 2000-grit sandpaper.

[0028] This invention also provides the application of the above-mentioned magnesium-ion battery anode material Mg-Sm alloy in the preparation of magnesium-ion battery anodes.

[0029] In some specific embodiments, the symmetrical battery composed of the Mg-Sm alloy as the negative electrode material operates at a current density of 1 mA·cm⁻¹. -2 1mAh·cm -2 Under these conditions, the overpotential is 0.05-0.15 V and the cycle time is greater than 1800 h.

[0030] In some specific embodiments, the Mg-Sm alloy used as the negative electrode material in the Mg-Sm / / Cu half-cell operates at a current density of 1.0 mA·cm⁻¹. -2 Capacity 1.0 mAh·cm -2 Under these conditions, the average coulombic efficiency remained above 98% after 350 cycles.

[0031] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0032] Unless otherwise specified, all experiments were repeated three times. Results are expressed as mean ± standard deviation, and P < 0.05 indicates a significant difference.

[0033] Example 1: A method for preparing a Mg-Sm alloy anode material for magnesium-ion batteries, comprising the following steps: S1. Raw material preparation: Weigh 540 g of pure magnesium blocks with a purity of 99.99% and 60 g of Mg-30.0wt%Sm master alloy (to make the Sm content in the Mg-Sm alloy 3wt%) according to the formula. Dry the magnesium blocks and magnesium-sammarium alloy in an oven at 200℃ for 30 min. Prepare 8 g of refining agent, which is a mixture of MgCl2, KCl, BaCl2, CaF2 and CaCl2 in a mass ratio of 46:40:8:5:25. S2. Melting: Preheat the crucible at 300℃ for 20 min. Evenly brush the surfaces of the crucible, stirring rod, and slag scraper with a talc-based coating (coating formula: 22.5 g zinc oxide, 120 mL water, 22.5 g water glass). Place the crucible in a 300℃ resistance furnace and hold for 20 min. After removing it, evenly coat the inner surface of the crucible with the coating. Repeat the above steps three times to ensure the inner surface of the crucible is completely covered with the coating and smooth. Place 320 g of dried magnesium blocks into the crucible and introduce a CO2 + SF6 protective gas (CO2 to SF6 volume ratio 40:1). Heat to 710℃ and hold for 25 min. Remove the oxide film from the surface of the magnesium alloy liquid. Add a magnesium-samarium alloy block and 205.6 g of magnesium blocks. Heat to 750℃ and hold for 20 min to allow the alloying elements to diffuse fully. Cool to 740℃, add 8 g of refining agent, and stir vigorously for 1 min. Hold for 20 minutes. After min, the temperature is lowered to 710℃, and the alloy melt is poured into a copper mold preheated to 200℃ under CO2+SF6 atmosphere protection, and then air-cooled and solidified to obtain an ingot. S3. Solution treatment: The ingot is subjected to a two-stage solution treatment under a pure argon protective atmosphere: 320℃×1 h+500℃×6 h, followed by water quenching (25℃, 1 min). S4. Extrusion Deformation Treatment: The ingot after solution treatment is polished with 2000# sandpaper to make its surface bright, and then machined to make an extrusion billet with a diameter of 58 mm and a height of 60 mm. It is then hot extruded at 300℃ with an extrusion ratio of 25:1 to obtain the extruded sheet, namely the magnesium-ion battery negative electrode material Mg-Sm alloy. S5. Electrode sheet preparation: The extruded plate is cut into square thin sheets of 15 mm × 15 mm × 600 μm, mechanically ground to 300 μm, and then processed into circular electrode sheets with a diameter of 12 mm and a thickness of 300 μm. The surface is polished with 2000 grit sandpaper.

[0034] Depend on Figure 1-4 As can be seen, the Mg-Sm alloy prepared in this embodiment has a uniform micron-sized equiaxed grain structure without precipitates, with an average grain size (AGS) of 4.7 μm, and only the α-Mg single phase can be observed. The overpotential of the Mg-Sm alloy anode is much lower than that of the pure Mg anode, indicating that the Sm element can effectively reduce the overpotential of Mg as an anode, thus giving it better cycle stability.

[0035] Test Example 1 The performance of the electrode sheet obtained in Example 1 was tested, and the results are shown in Table 1.

[0036] Table 1

[0037] As shown in Table 1, the Mg-Sm alloy anode material maintains good cycling stability under low current conditions in terms of overpotential and cycle time. With increasing current density, the overpotential increases, while the cycle time decreases.

[0038] Comparative Example 1 The difference from Example 1 is that the negative electrode is replaced with pure magnesium.

[0039] Comparative Example 2 The difference from Example 1 is that the mass percentage of Sm in the Mg-Sm alloy is 1 wt%, with the balance being Mg, and other conditions are the same.

[0040] Comparative Example 3 The difference from Example 1 is that the two-stage solution treatment parameters are 320℃×2 h+500℃×5 h, and other conditions are the same.

[0041] Comparative Example 4 The difference from Example 1 is that the extrusion temperature is changed to 350°C, the extrusion ratio is 25:1, and other conditions are the same.

[0042] Comparative Example 5 The difference from Example 1 is that the refining agent used is commercially available RJ-6 magnesium alloy refining agent, and the refining agent of the present invention is not used, while other conditions are the same.

[0043] Comparative Example 6 The difference from Example 1 is that a Mg-3wt%Sm alloy is used, but the smelting protective atmosphere is pure Ar gas, and a CO2+SF6 mixture is not used, while other conditions are the same.

[0044] Test Example 2 The performance of the electrode sheets obtained in Example 1 and Comparative Example 1 was tested, and the results are shown in Table 2.

[0045] Table 2

[0046] As can be seen from Table 2, at a current density of 1 mA·cm -2 Capacity 1 mAh·cm -2 In the following example, the Mg-Sm alloy anode material prepared in Example 1, especially as a magnesium-ion battery anode material, exhibited a smaller overpotential and better cycle stability than pure magnesium.

[0047] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A Mg-Sm alloy as a negative electrode material for magnesium-ion batteries, characterized in that, It is obtained by melting, solution treatment and extrusion deformation of magnesium blocks and magnesium-samarium alloy; The alloy comprises, by mass percentage: 3 wt% Sm, with the balance being Mg; The Mg-Sm alloy has a uniform micron-scale equiaxed grain structure, contains only α-Mg single phase, and has no precipitated phase.

2. The Mg-Sm alloy as a magnesium-ion battery anode material according to claim 1, characterized in that, The average grain size of the Mg-Sm alloy is 4.7 μm.

3. The method for preparing the Mg-Sm alloy anode material for magnesium-ion batteries according to claim 1 or 2, characterized in that, Includes the following steps: S1. Melting: Under a protective atmosphere of mixed CO2 and SF6, magnesium blocks and magnesium-samarium master alloys are melted sequentially to obtain an alloy liquid. After removing the oxide film on the surface of the melt, a refining agent is added to the alloy liquid for refining treatment. The billet is cast and then solidified in air to obtain an ingot. S2. Solution treatment: The ingot is subjected to a two-stage solution treatment under a pure argon protective atmosphere. S3. Extrusion Deformation Treatment: The ingot after the two-stage solution treatment is subjected to hot extrusion treatment to obtain the Mg-Sm alloy, a magnesium-ion battery anode material.

4. The preparation method according to claim 3, characterized in that, In step S1, the volume ratio of CO2 to SF6 in the CO2 and SF6 mixed protective gas is 40:

1.

5. The preparation method according to claim 3, characterized in that, In step S1, the purity of the magnesium block is greater than 99.9%, the magnesium-samarium master alloy is Mg-30.0wt%Sm master alloy, and the amount of magnesium-samarium master alloy added is calculated based on the Sm content in the Mg-Sm alloy being 3wt%.

6. The preparation method according to claim 3, characterized in that, In step S1, the melting temperature is 750℃ and the holding time is 20-40 min.

7. The preparation method according to claim 3, characterized in that, In step S1, the refining agent is a mixture of MgCl2, KCl, BaCl2, CaF2 and CaCl2, with a mass ratio of 46:40:8:5:

25.

8. The preparation method according to claim 3, characterized in that, In step S2, the two-stage solution treatment includes: solution treatment at 320°C for 1-2 hours, followed by solution treatment at 500°C for 5-8 hours, and then water quenching.

9. The preparation method according to claim 3, characterized in that, In step S3, the temperature of the hot extrusion is 300°C and the extrusion ratio is 25:

1.

10. The application of a Mg-Sm alloy, a magnesium-ion battery anode material, in the preparation of magnesium-ion battery anodes, characterized in that... The Mg-Sm alloy is the Mg-Sm alloy according to claim 1 or 2, or the Mg-Sm alloy prepared by the method according to any one of claims 4-9.

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