High-performance Mo6S8 material as well as preparation method and application thereof

Abstract

The invention relates to the field of battery materials, in particular to a high-performance Mo6S8 material as well as a preparation method and application thereof, and the high-performance Mo6S8 material comprises the following components in parts by mass: 3-5 parts of molybdenum disulfide, 2-4 parts of molybdenum powder, 1-3 parts of copper sulfide and 30-50 parts of potassium chloride. The preparation method comprises the following steps: ball milling: uniformly grinding raw materials in a ball mill; sintering: sintering the uniformly ground raw materials in an inert gas atmosphere, firstly heating to 300 DEG C and preserving heat, then heating to 900-1100 DEG C and preserving heat, and then naturally cooling to room temperature to obtain a mixture of Cu1Mo6S8 and KCl; cleaning: putting the mixture in ionized water, cleaning by using an ultrasonic cleaning instrument and a magnetic stirrer in sequence, centrifugally washing, and drying to obtain Cu1Mo6S8; and acid pickling is conducted, specifically, the dried Cu1Mo6S8 is placed in a hydrochloric acid solution, continuous stirring is conducted at the room temperature, centrifugal washing is conducted, and pure-phase Mo6S8 is obtained after drying. By implementing the scheme, the pure phase of Mo6S8 is high, and the cycle performance and the rate capability of the magnesium ion battery are remarkably improved by using the material as the positive electrode of the magnesium ion battery.

Description

Technical Field

[0001] The present invention relates to the field of magnesium ion battery materials, and particularly to a high-performance Mo6S8 material, a preparation method thereof, and an application thereof. Background Art

[0002] Magnesium ion batteries have shown greater application potential compared to other lithium ion battery technologies due to the good air stability of metallic magnesium, a smaller ionic radius (0.072 nm), and a higher volumetric specific capacity (3833 mAh / cm3). In addition, the reserves of magnesium in the earth's crust (2.3%) are 1045 times that of lithium reserves (0.0022%), and the abundant magnesium resources make magnesium ion batteries have lower production costs. Currently, due to the small magnesium ion radius and high charge density, there is a strong Coulomb interaction with electrode materials, showing a sluggish kinetic characteristic during the process of insertion / extraction and diffusion into the host material.

[0003] Chalcogenide phase compounds have a rich variety of materials, a stable crystal structure, good electrolyte compatibility, and allow reversible deintercalation / insertion of magnesium ions, and are the most studied cathode materials in magnesium ion batteries. The general structural formula of chalcogenide phase compounds is Mo6T8 (T = S, Se, and Te). Inside each Mo6T8 unit, Mo atoms are distributed on the six faces of a cube to form an octahedron, and T anions occupy eight vertices. Each Mo6T8 unit can accommodate up to two magnesium ions. Taking the chalcogenide phase compound Mo6S8 as an example, during the battery cycling process, the material undergoes two consecutive magnesium storage reactions:

[0004] Stage 1: Mg2+ + 2e- + Mo6S8 → MgMo6S8,

[0005] Stage 2: Mg2+ + 2e- + MgMo6S8 → Mg2Mo6S8.

[0006] Currently, the main synthesis methods of Mo6S8 are: solid-phase method, self-propagating high-temperature synthesis method, high-energy ball milling method, and molten salt method. In the solid-phase method, a molybdenum source and a sulfur source are mixed in a certain proportion, and then sintered to obtain an intermediate phase, which is pickled to obtain Mo6S8. However, the disadvantages of this method are a long preparation period and easy agglomeration of the product Mo6S8; the synthesis rate of the self-propagating high-temperature synthesis method is short, but the synthesis temperature is usually as high as 4000 K, with high energy consumption; the high-energy ball milling method also has a short preparation period, but has high requirements for the ball milling equipment (above 8000 rpm), and the final product is impure; the preparation method of the molten salt method is to grind a molybdenum source, a sulfur source, and a salt (usually NaCl or KCl) in a certain proportion and then sinter. During the sintering process, the salt melts to assist in generating an intermediate phase, and then pickling is performed to obtain the final product Mo6S8.

[0007] It is not difficult to see that the molten salt method combines many advantages of the above synthesis methods, with a relatively short synthesis time, a relatively low reaction temperature, the reaction products are not prone to agglomeration, low requirements for equipment, and is suitable for large-scale preparation. However, no matter which of the above methods, the intermediate phase generated during the synthesis process is mostly Cu2Mo6S8, such as the preparation method of cubic-like Mo6S8 as a high-performance magnesium ion battery cathode material in Patent Publication No. CN111977692A. Not only in the subsequent pickling process, to completely remove the Cu element in the intermediate phase, a large amount of hydrochloric acid needs to be used for pickling multiple times or for a long time or at high temperature or oxygen is introduced during the pickling process to promote the reaction, and finally Mo6S8 is obtained. In addition, the cycle performance is limited when used as a magnesium battery cathode material.

[0008] Therefore, in view of the above problems, it is necessary to develop a Mo6S8 material with a simple process and pure phase, and excellent cycle performance at the same time. Summary of the Invention

[0009] The first object of the present invention is to provide a high-performance Mo6S8 material to obtain a low-cost and pure-phase magnesium ion battery cathode material.

[0010] To achieve the above object, the present invention adopts the following technical solution: A high-performance Mo6S8 material, comprising 3-5 parts of molybdenum disulfide, 2-4 parts of molybdenum powder, 1-3 parts of copper sulfide, and 30-50 parts of potassium chloride.

[0011] Preferably, as an improvement, 4 parts of molybdenum disulfide, 3 parts of molybdenum powder, 2 parts of copper sulfide, and 40 parts of potassium chloride.

[0012] The second object of the present invention also provides a preparation method of the high-performance Mo6S8 material to simplify the preparation process and improve the purity of Mo6S8 at the same time.

[0013] Specifically, it includes the following steps:

[0014] S1. Raw material preparation: Weigh 3-5 parts of molybdenum disulfide, 2-4 parts of molybdenum powder, 1-3 parts of copper sulfide, and 30-50 parts of potassium chloride for standby;

[0015] S2. Ball milling: Place the raw materials in a ball mill and grind them evenly;

[0016] S3. Sintering: Sinter the evenly ground raw materials in an inert gas atmosphere. First, heat them at a heating rate of 5-10 °C / min to 300 °C and keep them warm, then heat them at a heating rate of 3-6 °C / min to 900-1100 °C and keep them warm, and then let them cool naturally to room temperature to obtain a mixture of Cu1Mo6S8 and KCl;

[0017] S4. Cleaning: Place the mixture in deionized water, and clean it thoroughly using an ultrasonic cleaner and a magnetic stirrer in sequence. Then, perform centrifugal washing, and after drying, Cu1Mo6S8 is obtained.

[0018] S5. Pickling: Place the dried Cu1Mo6S8 in a hydrochloric acid solution, continuously stir at room temperature for 12 - 72 h, perform centrifugal washing, and after drying, pure-phase Mo6S8 is obtained.

[0019] Preferably, as an improvement, in step S2, the raw materials are ball-milled in a ball mill at a speed of 200 - 600 rpm for 3 h.

[0020] Preferably, as an improvement, in step S4, clean in the ultrasonic cleaner for 2 h, and then clean in the magnetic stirrer for 6 h.

[0021] Preferably, as an improvement, in step S3, first heat up to 300 °C at a heating rate of 10 °C / min and hold for 1 h, then heat up to 1000 °C at a heating rate of 5 °C / min and hold for 24 h.

[0022] Preferably, as an improvement, in step S1, when ball-milling, add ball stones with a mass 5 times that of the total mass of the raw materials to the ball mill as the grinding medium.

[0023] The third object of the present invention also provides the application of the high-performance Mo6S8 material in the field of magnesium-ion batteries, enabling the magnesium-ion battery to have excellent cycling performance and rate performance.

[0024] The principle and advantages of this solution are as follows:

[0025] 1. High purity of Mo6S8 material: Through the reasonable configuration of the raw materials of the precursor and the precise control of its ratio, the purity of Mo6S8 obtained after cleaning and pickling is extremely high, and no precursor remains doped in the product. Therefore, by using this Mo6S8 as the cathode material of the magnesium-ion battery, the battery performance will be greatly improved.

[0026] 2. The battery has excellent cycling performance: Using the Mo6S8 material obtained by this solution as the cathode material of the magnesium-ion battery, it has excellent cycling stability at a relatively high current density, and the capacity retention rate is relatively high after multiple cycles. As Figure 7 、 Figure 8 shown, after the magnesium-ion battery is cycled 350 times at a rate of 0.5C, the discharge specific capacity still exceeds 80 mAh / g, and the Coulomb efficiency is close to 100%. Compared with the traditional magnesium-ion battery, after 100 cycles, the battery capacity is only about 60 mAh / g. The cycling performance of this solution has been significantly improved.

[0027] 3. It has excellent rate performance: As Figure 11, at the rates of 0.2C, 0.5C, 1C, and 2C, its discharge capacities are 85.9 mAh / g, 78.23 mAh / g, 73.24 mAh / g, and 67.15 mAh / g respectively. When returning to the 0.2C rate again, its capacity exceeds 90 mAh / g (a 4.7% increase compared to the initial value), demonstrating excellent rate performance and dynamic optimization ability.

[0028] 4. Low production cost: In this solution, the raw materials of the precursor, MoS2, Mo, and CuS, are all common industrial raw materials, with low cost and easy availability. In contrast, ammonium tetrathiomolybdate is expensive, about 100 times more expensive than molybdenum disulfide; sulfur powder is an explosive-precursor drug and belongs to controlled drugs, which greatly limits its application. Therefore, this solution has the advantages of large-scale production and good market promotion prospects.

[0029] 5. Simple preparation process: In this solution, by reasonably configuring the ratio of the precursor and coordinating the corresponding preparation method of the precursor, a pure-phase Cu1Mo6S8 can be generated as an intermediate phase after sintering, and then a pure-phase Mo6S8 can be obtained after simple pickling. Compared with the common Cu2Mo6S8 intermediate phase, Cu1Mo6S8 is easier to completely remove the Cu element during pickling, not only making the operation process simpler and more convenient, but also making Mo6S8 purer.

[0030] 6. Controllable reaction path: MoS2 and Mo directly provide the Mo source, and CuS serves as the S source and Cu source. At high temperatures, the intermediate phase Cu x Mo6S8 is formed, avoiding the volatilization loss of sulfur elements at high temperatures; if sulfur powder or organic sulfur sources (such as thiourea) are used, the sulfur partial pressure needs to be precisely controlled, and the process difficulty is extremely high. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is the XRD pattern of Cu1Mo6S8.

[0032] Figure 2 It is the XRD pattern of Mo6S8 in the present invention.

[0033] Figure 3 It is the structural schematic diagram of the embodiment of the present invention.

[0034] Figure 4 It is the XRD pattern of Mo6S8 of Comparative Example 1.

[0035] Figure 5 It is the XRD pattern of Mo6S8 of Comparative Example 2.

[0036] Figure 6 It is the XRD pattern of Mo6S8 of Comparative Example 3.

[0037] Figure 7Cycling performance graph of a magnesium-ion battery at a charge-discharge rate of 0.5C.

[0038] Figure 8 Discharge capacity and Coulombic efficiency graph of a magnesium-ion battery at a charge-discharge rate of 0.5C under different numbers of cycles.

[0039] Figure 9 Cycling performance graph of a magnesium-ion battery at a charge-discharge rate of 1C.

[0040] Figure 10 Discharge capacity and Coulombic efficiency graph of a magnesium-ion battery at a charge-discharge rate of 1C under different numbers of cycles.

[0041] Figure 11 Rate performance graph of a magnesium-ion battery at charge-discharge rates of 0.2C, 0.5C, 1C, and 2C. Detailed implementation mode

[0042] The following is a further detailed description through specific implementation modes:

[0043] A high-performance Mo6S8 material, the components of which by mass fraction include: 3 - 5 parts of molybdenum disulfide, 2 - 4 parts of molybdenum powder, 1 - 3 parts of copper sulfide, and 30 - 50 parts of potassium chloride.

[0044] A preparation method of a high-performance Mo6S8 material, comprising the following steps:

[0045] S1. Raw material preparation: Weigh 3.2 g of molybdenum disulfide, 2.4 g of molybdenum powder, 1.6 g of copper sulfide, and 32 g of potassium chloride respectively for standby;

[0046] S2. Ball milling: Place the above raw materials in a 500 mL polytetrafluoroethylene ball milling tank, and at the same time add agate ball stones 5 times the total mass of the raw materials to the ball milling tank as the grinding medium, and ball mill at a speed of 450 rpm for 3 h to make the precursor and salt mix evenly.

[0047] S3. Sintering: Place the evenly ground raw materials in a clean alumina porcelain boat with a lid, and sinter in an argon atmosphere. First, heat at a heating rate of 10 °C / min to 300 °C and hold for 1 h, then heat at a heating rate of 5 °C / min to 1000 °C and hold for 24 h, and then let it cool naturally to room temperature to obtain a mixture of Cu1Mo6S8 and KCl.

[0048] In this solution, the sintering stage is divided into two stages for the following purposes: enabling the preliminary solid-phase reaction of the mixture MoS2, Mo powder, CuS, and KCl after ball milling, such as the decomposition of CuS and the adjustment of the oxidation state of Mo, to form intermediate compounds, which is conducive to providing a more uniform reaction substrate for the high-temperature reaction in the latter stage. The more uniform the reaction substrate, the higher the purity of the obtained Mo6S8.

[0049] Meanwhile, in the first stage, it is heated to 300 °C at a rate of 10 °C / min and held isothermally, which can alleviate the thermal expansion difference of the ball-milled powder caused by rapid heating, reduce the microcracks or grain boundary stress inside the material, and improve the crystallization integrity of the final product. For KCl, this stage can promote the initial interfacial wetting between KCl and the raw materials, laying the foundation for the molten salt-assisted ion diffusion (accelerating the migration of Mo / Cu / S atoms) at high temperatures subsequently.

[0050] In addition, the termination temperature of the first stage in this solution is designed to be 300 °C, and the purpose is as follows: CuS begins to decompose at 300 °C, and holding at this temperature can slowly release sulfur vapor and react with Mo powder / MoS2, reducing the excessive volatilization of sulfur caused by direct high temperature and ensuring the sulfur stoichiometric accuracy of Mo6S8.

[0051] S4. Cleaning: The mixture is placed in deionized water, and is successively cleaned with an ultrasonic cleaner for 2 h, then cleaned with a magnetic stirrer for 6 h, centrifuged and washed, and Cu1Mo6S8 is obtained after drying.

[0052] S5. Pickling: The dried Cu1Mo6S8 is placed in an 8M hydrochloric acid solution and continuously stirred at room temperature for 48 h, centrifuged and washed, and pure-phase Mo6S8 is obtained after drying.

[0053] I. Phase characteristic test of Mo6S8

[0054] The following is to conduct phase characteristic test on Mo6S8 prepared with the same preparation method and raw materials in different ratios, respectively forming Examples 1 - 3 (the ratio range is within the range specified in this solution), and Comparative Examples 1 - 3 (the ratio range is outside the range specified in this solution), as shown in Table 1 specifically.

[0055] Table 1 Comparison of raw material ratios

[0056]

[0057] The XRD patterns of the intermediate phase Cu1Mo6S8 and the obtained final product Mo6S8 produced according to this solution are as Figure 1 、 Figure 2 shown. According to the XRD results, it can be known that the intermediate phase prepared according to this invention is pure-phase Cu1Mo6S8, and the final product is pure-phase Mo6S8, without any impurities generated.

[0058] Figure 3It is the SEM image of Mo6S8 material. As can be seen from the figure, the Mo6S8 of the present invention presents a uniform nano-morphology, and the grain size is in the range of 200 - 500 nm. The smaller grains can shorten the diffusion path of magnesium ions, accelerate the insertion and extraction speed, and improve the charge-discharge performance and rate performance. At the same time, the high specific surface area can increase the active sites, improve the charge-discharge efficiency and specific capacity, and enhance the energy density. In addition, the small grains can better adapt to the volume change and extend the battery cycle life.

[0059] In Comparative Example 1, the content of the molten salt was changed, reducing the reaction medium for the chemical reaction, resulting in a large number of side reactions occurring in the precursor and a large amount of by-products being generated, such as Figure 4 shown.

[0060] In Comparative Example 2 and Comparative Example 3, the addition amount of the precursor was changed. It can be seen that the main phase of the product is still Mo6S8, but there are still a small amount of impurity phases generated, as shown in Figure 5 and Figure 6 shown respectively.

[0061] II. Battery performance test:

[0062] The Mo6S8 cathode material prepared by this solution was assembled into a magnesium-ion battery, and the assembly method is as follows:

[0063] S1. Electrode sheet preparation: The active substance Mo6S8, conductive agent Super P, and binder PVDF prepared by this solution were uniformly mixed according to a mass ratio of 7:2:1, and an appropriate amount of N-methylpyrrolidone (NMP) was added. It was uniformly coated on the current collector and dried, and then cut into a circular sheet with a diameter of 12 mm as the positive electrode sheet.

[0064] S2. Anode preparation: Magnesium metal was used as the anode of the magnesium-ion battery. A 0.1 mm magnesium foil was polished with 1000-mesh sandpaper to remove the surface oxide film, and then cut into a circular sheet with a diameter of 14 mm and immediately sent into the glove box.

[0065] S3. Battery assembly: A CR2032-sized button battery was used for assembly and testing. The negative electrode shell, spring piece, gasket, magnesium sheet, electrolyte (50 μL), glass fiber separator (diameter 17 mm), electrolyte (50 μL), positive electrode sheet, and positive electrode shell were assembled in sequence and compacted. Finally, a magnesium-ion battery with Mo6S8 as the active substance was obtained. Among them, the electrolyte was 0.3 M Mg[B(hfip)4]2 / DME.

[0066] The assembled battery was subjected to electrochemical performance testing, and the battery was left to rest for 12 hours before testing. The battery testing method included cycle performance testing and rate performance testing, with a discharge cut-off voltage of 0.1V, a charge cut-off voltage of 2.0V, and charge and discharge currents of 0.2C, 0.5C, 1C, and 2C (1C = 120mA / g).

[0067] Summary of magnesium battery performance:

[0068] Figure 7 、 Figure 8 The cycling performance of the magnesium-ion battery using Mo6S8 as the positive electrode at a rate of 0.5C shows that after 350 cycles, its discharge specific capacity is still over 80mAh / g and its coulombic efficiency is close to 100%, showing its excellent cycling performance.

[0069] Figure 9 、 Figure 10 The magnesium ion battery using Mo6S8 as the positive electrode has excellent cycle performance at a rate of 1C. Even at a higher rate, the battery can still cycle stably for more than 500 cycles. After 500 cycles, the discharge capacity exceeds 60mAh / g, and the coulombic efficiency is close to 100%, showing excellent cycle performance.

[0070] Figure 11 The rate performance of the magnesium ion battery using Mo6S8 as the positive electrode is that at the rates of 0.2C, 0.5C, 1C, and 2C, its discharge capacity is 85.9mAh / g, 78.23mAh / g, 73.24mAh / g, and 67.15mAh / g, respectively. When the rate returns to 0.2C, its capacity exceeds 90mAh / g.

[0071] In summary, using this Mo6S8 as the positive electrode of magnesium-ion batteries exhibits excellent cycling performance at various rates, significantly extending the battery's service life. The material also exhibits excellent rate performance and structural flexibility: during the 0.2C to 2C discharge process, the capacity retention rate reaches 78.1%, demonstrating high rate tolerance. In particular, after undergoing a 2C high-voltage cycle, the capacity rebounds to 90 mAh / g (a 4.7% increase from the initial value) when returning to 0.2C, demonstrating significant dynamic optimization capabilities.

[0072] Therefore, this material has both high rate tolerance and capacity recovery capability while having excellent cycle performance, which makes it have great application potential in magnesium-based energy storage systems.

[0073] The above are only embodiments of the present invention, and common general technical solutions and / or characteristics in the solution are not described in detail herein. It should be noted that for those skilled in the art, without departing from the technical solution of the present invention, several modifications and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the implementation effect of the present invention and the practicability of the patent. The protection scope claimed in this application shall be subject to the content of its claims, and the specific implementation manners and the like recorded in the specification can be used to interpret the content of the claims.

Claims

1. A high-performance Mo6S8 material, characterized in that: The components thereof include, by mass, 3-5 parts of molybdenum disulfide, 2-4 parts of molybdenum powder, 1-3 parts of copper sulfide and 30-50 parts of potassium chloride.

2. A high-performance Mo6S8 material according to claim 1, characterized in that: 4 parts of molybdenum disulfide, 3 parts of molybdenum powder, 2 parts of copper sulfide and 40 parts of potassium chloride.

3. A method for preparing a high-performance Mo6S8 material, characterized in that: The following steps are involved: S1. Raw material preparation: Weigh 3-5 parts of molybdenum disulfide, 2-4 parts of molybdenum powder, 1-3 parts of copper sulfide, 30-50 parts of potassium chloride for standby; S2. Ball milling: Grind the raw materials evenly in a ball mill; S3. Sintering: The uniformly ground raw material was sintered in an inert gas atmosphere, first at a heating rate of 5-10 ° C / min to 300 ° C and kept warm, then at a heating rate of 3-6 ° C / min to 900-1100 ° C and kept warm, and then naturally cooled to room temperature to obtain a mixture of Cu1Mo6S8 and KCl; S4. Cleaning: The mixture was placed in deionized water, cleaned using an ultrasonic cleaner and a magnetic stirrer, centrifuged, washed, and dried to obtain Cu1Mo6S8; S5. Acid washing: Place the dried Cu1Mo6S8 in a hydrochloric acid solution, stir continuously at room temperature for 12-72 hours, centrifuge and wash, and dry to obtain pure Mo6S8.

4. The preparation method of a high-performance Mo6S8 material according to claim 3, characterized in that: In step S2, the raw materials were ball milled in a ball mill at a speed of 200-600 rpm for 3 h.

5. The preparation method of a high-performance Mo6S8 material according to claim 4, characterized in that: In step S4, the sample was cleaned in an ultrasonic cleaner for 2 h and then in a magnetic stirrer for 6 h.

6. The method for preparing a high-performance Mo6S8 material according to claim 5, characterized in that: In step S3, the temperature was first increased to 300°C at a heating rate of 10°C / min and kept at that temperature for 1 hour, and then increased to 1000°C at a heating rate of 5°C / min and kept at that temperature for 24 hours.

7. The method for preparing a high-performance Mo6S8 material according to claim 6, characterized in that: In step S1, during ball milling, 5 times the amount of raw materials is added to the ball mill as grinding media.

8. Application of the high-performance Mo6S8 material according to claims 1-2 in the field of magnesium ion batteries.

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