Preparation method and application of Cu micro-doped CoSe2 positive electrode material of magnesium ion battery

Abstract

The invention discloses a preparation method of a Cu micro-doped CoSe2 positive electrode material of a magnesium ion battery. The method comprises the following steps: 1, mixing a cobalt source and a copper source, and adding the mixture into methanol to obtain a liquid 1; 2, preparing a methanol solution of dimethylimidazole and recording the methanol solution as liquid 2; 3, mixing the liquid 1 and the liquid 2 under stirring, continuously stirring, and standing after the stirring is completed; 4, collecting a precipitate in the mixed solution after standing, centrifugally washing, and drying to obtain a precursor of the positive electrode material; 5, mixing the precursor of the positive electrode material with selenium powder, sintering, cooling, taking out and grinding; the invention also discloses application of the positive electrode material in a magnesium ion battery. According to the invention, Cu is slightly doped into the CoSe2 positive electrode material, so that the CoSe2 capacity is improved, and meanwhile, the CoSe2 positive electrode material has a relatively good capacity retention ratio, so that the electrochemical performance of the CoSe2 positive electrode material is improved, the charge-discharge efficiency and the cycling stability of the magnesium ion battery are further improved, and the method is simple, low in cost and suitable for the field of magnesium ion batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of cathode materials for batteries, and particularly relates to a preparation method and application of a Cu micro-doped CoSe2 cathode material for a magnesium ion battery. Background Art

[0002] With the increasing global energy demand and the increasingly serious environmental problems, it has become particularly important to develop new and efficient energy storage systems. Among many battery technologies, magnesium ion batteries have attracted much attention due to their unique advantages. Magnesium ion batteries have characteristics such as high theoretical volumetric energy density, low cost, not easily generating dendrites, and abundant magnesium resources, and are potential candidate technologies for the next-generation energy storage system.

[0003] However, the development of magnesium ion batteries still faces some key challenges, especially in the selection and optimization of cathode materials. An ideal cathode material for a magnesium ion battery should have high specific capacity, good cycle stability, and fast ion diffusion ability. CoSe2 is a conversion-type cathode material with a relatively high theoretical capacity. However, pure CoSe2 materials have problems such as harsh synthesis conditions, low yield, low conductivity, and poor cycle performance in practical applications, which limit their performance in magnesium ion batteries.

[0004] To solve these problems, researchers have tried various methods to improve the performance of CoSe2. Xu et al. (Nanoscale, 2019, 11, 23173-23181) prepared CoSe2 cathode materials with different morphological structures by a hydrothermal method, but the preparation process was very complex, the reaction time was long, and the yield was extremely low. In addition, the nanomaterials obtained by the reported method were particularly prone to aggregation, which limited their application in industrial production. They also reported the research results of Ni-doped CoSe2 (ACS Sustainable Chem. Eng. 2020, 8, 2964-297), but it also had the disadvantages of complex synthesis process, extremely low yield, and low material capacity, and could not be applied on a large scale. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a preparation method of a Cu micro-doped CoSe2 cathode material for a magnesium ion battery in view of the above-mentioned deficiencies of the prior art. By micro-doping Cu into the CoSe2 cathode material, combining the control of the doping ratio of Cu and optimizing the process, the CoSe2 cathode material is rapidly activated by the micro-doping of Cu, and while greatly improving the capacity of CoSe2, it has a good capacity retention rate, thereby improving the electrochemical performance of the CoSe2 cathode material and solving the problem of poor cycle performance of the conversion-type cathode material.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is as follows: A preparation method of a Cu micro-doped CoSe2 cathode material for a magnesium ion battery, characterized in that the chemical formula of the cathode material is Co 1-x Cu x Se2, where the value range of x is 0.01 to 0.05, and the preparation method of the cathode material includes the following steps:

[0007] Step 1: Mix a cobalt source and a copper source and add them to methanol for dissolution to obtain a solution denoted as liquid 1; the total concentration of cobalt ions and copper ions in the liquid 1 is 0.01 mol / L to 0.2 mol / L;

[0008] Step 2: Prepare a methanol solution of 2-methylimidazole, denoted as liquid 2; the concentration of the liquid 2 is 0.04 mol / L to 3.2 mol / L;

[0009] Step 3: Under a stirring state, drop the liquid 1 in Step 1 into the liquid 2 in Step 2, or drop the liquid 2 in Step 2 into the liquid 1 in Step 1 to form a mixed solution, and continue to maintain stirring for 0.1 h to 2 h, then stop stirring and let it stand for 2 h to 24 h;

[0010] Step 4: Collect the precipitate in the mixed solution after standing in Step 3, and centrifuge and wash it 3 times, and dry it to obtain the precursor of the cathode material;

[0011] Step 5: Mix the precursor of the cathode material obtained in Step 4 with selenium powder, then put it into an atmosphere furnace for sintering, cool it with the furnace, take it out after the temperature drops to room temperature, and grind it evenly to obtain the Cu micro-doped CoSe2 cathode material for a magnesium ion battery.

[0012] In the above preparation method of a Cu micro-doped CoSe2 cathode material for a magnesium ion battery, it is characterized in that the cobalt source in Step 1 is cobalt nitrate, cobalt acetate, cobalt sulfate or cobalt chloride, the copper source is copper nitrate, copper acetate, copper sulfate or copper chloride, and the concentration ratio of cobalt ions and copper ions in the liquid 1 is 0.01 to 0.6.

[0013] In the above preparation method and application of a Cu micro-doped CoSe2 cathode material for a magnesium ion battery, it is characterized in that the stirring state and the stirring rate for continuously maintaining stirring in Step 3 are 300 rpm to 1000 rpm, and the dropping rate is 10 mL / min to 100 mL / min. By controlling the stirring rate, splashing of the solution caused by too fast rotation speed or uneven stirring caused by too slow rotation speed can be avoided, and by controlling the dropping rate, low efficiency caused by too slow dropping or too fast nucleation affecting the performance of the cathode material caused by too fast dropping can be avoided.

[0014] The preparation method and application of the above-mentioned Cu micro-doped CoSe2 cathode material for magnesium ion batteries are characterized in that the drying process in step four is as follows: drying at 50°C to 100°C for 2h to 10h. By controlling the drying temperature, it is avoided that the temperature is too low and the drying time is too long, or the temperature is too high resulting in material decomposition.

[0015] The preparation method and application of the above-mentioned Cu micro-doped CoSe2 cathode material for magnesium ion batteries are characterized in that the mass ratio of the precursor of the cathode material to selenium powder in step five is 0.5 to 2, and the sintering process is as follows: the heating rate is 1°C / min to 5°C / min, heating to 300°C to 700°C and sintering for 1h to 5h.

[0016] Meanwhile, the present invention also discloses an application of the Cu micro-doped CoSe2 cathode material for magnesium ion batteries prepared by the above-mentioned method, which is characterized in that the cathode electrode sheet is prepared by using this cathode material and applied to magnesium ion batteries.

[0017] The present invention has the following advantages compared with the prior art:

[0018] 1. In the present invention, the cobalt source and copper source are mixed and dissolved in methanol, then mixed and stirred with the methanol solution of dimethylimidazole and left to stand. After washing, centrifuging, and drying, they are mixed and sintered with the selenium source, and then the Cu micro-doped CoSe2 cathode material can be obtained. By the micro-doping of Cu, the CoSe2 cathode material is rapidly activated, while greatly improving the capacity of CoSe2, having a good capacity retention rate, improving the diffusion kinetics of magnesium ions in the cathode material, and solving the problem of poor cycle performance of the conversion-type cathode material.

[0019] 2. In the present invention, the electronic structure of CoSe2 is adjusted by the micro-doping of Cu, increasing the conductivity of CoSe2. At the same time, the Cu ions doped into the lattice enhance the structural stability of CoSe2, optimizing the interfacial charge transfer characteristics of CoSe2, thereby reducing the structural change of the electrode material during charge and discharge, and improving the charge and discharge efficiency and cycle stability of the battery.

[0020] 3. In the present invention, Cu is micro-doped into the CoSe2 cathode material by a solution mixing method, ensuring the uniform doping of Cu and not generating other impurity phases, and thus ensuring the performance of the Cu micro-doped CoSe2 cathode material.

[0021] 4. The preparation process of the present invention is simple, has low requirements for equipment, low cost, the prepared magnesium ion battery cathode material has excellent electrochemical performance, has the prospect of large-scale application, and provides new possibilities for the development of magnesium ion batteries.

[0022] The technical solution of the present invention will be further described in detail below through the drawings and embodiments. Description of the Drawings

[0023] Figure 1 XRD patterns of the cathode materials prepared in Example 1, Example 2 and Comparative Example 1 of the present invention.

[0024] Figure 2 Scanning electron microscope images of the cathode materials prepared in Example 1, Example 2 and Comparative Example 1 of the present invention at different rates.

[0025] Figure 3 Transmission electron microscope images of the cathode materials prepared in Example 1 and Comparative Example 1 of the present invention at different rates.

[0026] Figure 4 Element distribution map of the cathode material prepared in Example 1 of the present invention.

[0027] Figure 5 Cycling performance graphs of the cathode materials prepared in Example 1 and Comparative Example 1 of the present invention at a current density of 50 mA·g -1 -1.

[0028] Figure 6 Cycling performance graphs of the cathode materials prepared in Example 1 and Comparative Example 1 of the present invention at a current density of 200 mA·g -1 -1. Detailed implementation manners

[0029] Example 1

[0030] The chemical formula of the Cu micro-doped CoSe2 cathode material for the magnesium ion battery in this example is Co 0.98 Cu 0.02 Se2. The preparation method of the cathode material includes the following steps:

[0031] Step 1: Weigh 2.024 g of cobalt nitrate hexahydrate and 0.16 g of copper acetate monohydrate, mix and add them to 80 mL of methanol for dissolution. The obtained solution is denoted as liquid 1; the total concentration of cobalt ions and copper ions in liquid 1 is 0.1 mol / L;

[0032] Step 2: Weigh 2.627 g of dimethylimidazole and add it to 80 mL of methanol for dissolution, denoted as liquid 2; the concentration of liquid 2 is 0.4 mol / L;

[0033] Step 3: Under the stirring state with a stirring rate of 500 rpm, add liquid 2 in step 2 dropwise to liquid 1 in step 1 at a dropping rate of 50 mL / min to form a mixed solution, and continue to maintain the stirring rate at 500 rpm and stir for 1 h, then stop stirring and let it stand for 24 h;

[0034] Step 4: Collect the precipitate in the mixed solution after standing in Step 3, wash the precipitate by centrifugation with methanol three times, and dry it at 80 °C for 10 h to obtain the precursor of the cathode material;

[0035] Step 5: Mix the precursor of the cathode material obtained in Step 4 with selenium powder in a mass ratio of 1:1, then put it into an atmosphere furnace, heat it to 500 °C at a heating rate of 2 °C / min under an argon atmosphere and sinter for 1 h, cool it with the furnace, take it out after the temperature drops to room temperature, and grind it evenly to obtain the Cu micro-doped CoSe2 cathode material for magnesium ion batteries, namely Co 0.98 Cu 0.02 Se2.

[0036] The cobalt source in this example can also be replaced with cobalt acetate, cobalt sulfate or cobalt chloride, and the copper source can also be replaced with copper nitrate, copper sulfate or copper chloride.

[0037] Example 2

[0038] The chemical formula of the Cu micro-doped CoSe2 cathode material for magnesium ion batteries in this example is Co 0.96 Cu 0.04 Se2, and the preparation method of this cathode material includes the following steps:

[0039] Step 1: Weigh 1.8 g of cobalt nitrate hexahydrate and 0.319 g of copper acetate monohydrate, mix and add them to 80 mL of methanol for dissolution, and record the obtained solution as liquid 1; the total concentration of cobalt ions and copper ions in the liquid 1 is 0.1 mol / L;

[0040] Step 2: Weigh 2.627 g of dimethylimidazole and add it to 80 mL of methanol for dissolution, and record it as liquid 2; the concentration of the liquid 2 is 0.4 mol / L;

[0041] Step 3: Under the stirring state with a stirring rate of 500 rpm, drop the liquid 2 in Step 2 into the liquid 1 in Step 1 at a dropping rate of 50 mL / min to form a mixed solution, and continue to maintain the stirring rate of 500 rpm and stir for 1 h, then stop stirring and stand for 24 h;

[0042] Step 4: Collect the precipitate in the mixed solution after standing in Step 3, wash the precipitate by centrifugation with methanol three times, and dry it at 80 °C for 10 h to obtain the precursor of the cathode material;

[0043] Step 5: Mix the precursor of the cathode material obtained in Step 4 with selenium powder in a mass ratio of 1:1, then put it into an atmosphere furnace, heat it to 500 °C at a heating rate of 2 °C / min under an argon atmosphere and sinter for 1 h, cool it with the furnace, take it out after the temperature drops to room temperature, and grind it evenly to obtain the Cu micro-doped CoSe2 cathode material for magnesium ion batteries, namely Co 0.96Cu 0.04 Se2。

[0044] In this embodiment, the cobalt source can also be replaced with cobalt acetate, cobalt sulfate or cobalt chloride, and the copper source can also be replaced with copper nitrate, copper sulfate or copper chloride.

[0045] Comparative Example 1

[0046] The chemical formula of the CoSe2 cathode material for the magnesium ion battery in this comparative example is CoSe2, and the preparation method of the cathode material includes the following steps:

[0047] Step 1: Weigh 2.328 g of cobalt nitrate hexahydrate and add it to 80 mL of methanol for dissolution. The resulting solution is denoted as Liquid 1; the concentration of cobalt ions in Liquid 1 is 0.1 mol / L;

[0048] Step 2: Weigh 2.627 g of dimethylimidazole and add it to 80 mL of methanol for dissolution, denoted as Liquid 2; the concentration of Liquid 2 is 0.4 mol / L;

[0049] Step 3: Under the stirring state with a stirring rate of 500 rpm, add Liquid 2 in Step 2 to Liquid 1 in Step 1 at a dropping rate of 50 mL / min to form a mixed solution, and continue to maintain the stirring rate of 500 rpm and stir for 1 h, then stop stirring and let it stand for 24 h;

[0050] Step 4: Collect the precipitate in the mixed solution after standing in Step 3, and centrifuge and wash the precipitate with methanol 3 times, and dry it at 80 °C for 10 h to obtain the precursor of the cathode material;

[0051] Step 5: Mix the precursor of the cathode material obtained in Step 4 with selenium powder according to a mass ratio of 1:1, then put it into an atmosphere furnace, heat it to 500 °C at a heating rate of 2 °C / min under an argon atmosphere and sinter for 1 h, cool it with the furnace, take it out after the temperature drops to room temperature, and grind it evenly to obtain the CoSe2 cathode material for the magnesium ion battery, that is, CoSe2.

[0052] Example 3

[0053] The chemical formula of the Cu micro-doped CoSe2 cathode material for the magnesium ion battery in this embodiment is Co 0.95 Cu 0.05 Se2, and the preparation method of the cathode material includes the following steps:

[0054] Step 1: Weigh 1.781 g of cobalt nitrate hexahydrate and 0.399 g of copper acetate monohydrate and mix them and add them to 40 mL of methanol for dissolution. The resulting solution is denoted as Liquid 1; the total concentration of cobalt ions and copper ions in Liquid 1 is 0.2 mol / L;

[0055] Step 2: Weigh 2.627 g of dimethylimidazole and dissolve it in 10 mL of methanol, denoted as Liquid 2; the concentration of Liquid 2 is 3.2 mol / L;

[0056] Step 3: Under the stirring state with a stirring rate of 1000 rpm, drop Liquid 2 in Step 2 into Liquid 1 in Step 1 at a dropping rate of 100 mL / min to form a mixed solution, and continue to maintain the stirring rate of 1000 rpm and stir for 2 h, then stop stirring and let it stand for 24 h;

[0057] Step 4: Collect the precipitate in the mixed solution after standing in Step 3, wash the precipitate with methanol by centrifugation 3 times, and dry it at 100 °C for 2 h to obtain the precursor of the positive electrode material;

[0058] Step 5: Mix the precursor of the positive electrode material obtained in Step 4 with selenium powder according to a mass ratio of 2:1, then put it into an atmosphere furnace, heat it to 700 °C at a heating rate of 5 °C / min under an argon atmosphere and sinter for 1 h, cool it with the furnace, take it out after the temperature drops to room temperature, and grind it evenly to obtain the Cu micro-doped CoSe2 positive electrode material for magnesium ion batteries, namely Co 0.95 Cu 0.05 Se2.

[0059] The cobalt source in this example can also be replaced with cobalt acetate, cobalt sulfate or cobalt chloride, and the copper source can also be replaced with copper nitrate, copper sulfate or copper chloride.

[0060] Example 4

[0061] The chemical formula of the Cu micro-doped CoSe2 positive electrode material for magnesium ion batteries in this example is Co 0.96 Cu 0.04 Se2, and the preparation method of this positive electrode material includes the following steps:

[0062] Step 1: Weigh 1.8 g of cobalt nitrate hexahydrate and 0.319 g of copper acetate monohydrate, mix and dissolve them in 800 mL of methanol, and the obtained solution is denoted as Liquid 1; the total concentration of cobalt ions and copper ions in Liquid 1 is 0.01 mol / L;

[0063] Step 2: Weigh 2.627 g of dimethylimidazole and dissolve it in 800 mL of methanol, denoted as Liquid 2; the concentration of Liquid 2 is 0.04 mol / L;

[0064] Step 3: Under the stirring state with a stirring rate of 300 rpm, drop Liquid 2 in Step 2 into Liquid 1 in Step 1 at a dropping rate of 10 mL / min to form a mixed solution, and continue to maintain the stirring rate of 300 rpm and stir for 0.1 h, then stop stirring and let it stand for 2 h;

[0065] Step 4: Collect the precipitate in the mixed solution after standing in Step 3, centrifuge and wash the precipitate with methanol three times, and dry it at 50 °C for 10 h to obtain the precursor of the cathode material;

[0066] Step 5: Mix the precursor of the cathode material obtained in Step 4 with selenium powder according to a mass ratio of 1:2, then put it into an atmosphere furnace, heat it to 300 °C at a heating rate of 1 °C / min under an argon atmosphere and sinter for 5 h, cool it with the furnace, take it out after the temperature drops to room temperature, and grind it evenly to obtain the Cu micro-doped CoSe2 cathode material for magnesium ion batteries, namely Co 0.96 Cu 0.04 Se2.

[0067] The cobalt source in this embodiment can also be replaced with cobalt acetate, cobalt sulfate or cobalt chloride, and the copper source can also be replaced with copper nitrate, copper sulfate or copper chloride.

[0068] 1. Characterize the structure and morphology of the cathode materials prepared in Examples 1-4 and Comparative Example 1 of the present invention.

[0069] (1) XRD characterization

[0070] Figure 1 are the XRD patterns of the cathode materials prepared in Example 1, Example 2 and Comparative Example 1 of the present invention. It can be seen from Figure 1 that compared with Comparative Example 1, no impurity phase is generated in the cathode materials of Example 1 and Example 2 after Cu doping, and the XRD patterns of each cathode material can perfectly match the standard diffraction card PDF#53-0449 of CoSe2. Among them, the doping of Cu will cause the angle of the (200) peak to become larger. According to the Bragg equation, it is speculated that the interplanar spacing of the cathode materials in Example 1 and Example 2 becomes smaller, and the radius of Cu 2+ is smaller than that of Co 2+ , so Cu is indeed doped into the CoSe2 lattice. The lattice constants of the three cathode materials are obtained by full-spectrum fitting and refinement of the XRD patterns, as shown in Table 1 below.

[0071] Table 1

[0072]

[0073]

[0074] As can be seen from Table 1, with the increase of the Cu doping amount, the unit cell parameters of the cathode material gradually become smaller, indicating that the Cu element is indeed doped into the CoSe2 lattice, which is beneficial to improving the electrochemical performance of the cathode material.

[0075] (2) SEM and TEM characterization

[0076] Figure 2SEM images of the cathode materials prepared in Example 1, Example 2 and Comparative Example 1 of the present invention at different rates. Among them, Figure a represents Comparative Example 1, Figure b represents Example 1, and Figure c represents Example 2. From Figure 2 It can be seen that the particle size of the Cu-doped cathode materials prepared in Example 1 and Example 2 is about 3 μm, maintaining the rhombic dodecahedron structure of the cathode material precursor, and there is almost no obvious damage on the surface; while the particle size of the CoSe2 prepared in Comparative Example 1 is smaller, about 1 μm, and there are certain damages on the particle surface.

[0077] Figure 3 TEM images of the cathode materials prepared in Example 1 and Comparative Example 1 of the present invention at different rates. Among them, Figures a-c represent Example 1, and Figures d-f represent Comparative Example 1. From Figures a-c, it can be seen that the Co 0.98 Cu 0.02 Se2 of Example 1 has polycrystalline diffraction rings, indicating its polycrystalline structure. Further, it can be seen from the high-resolution transmission electron microscope that the interplanar spacing is 0.256 nm, corresponding to the (111) crystal plane; from Figures d-f, it can be seen that the CoSe2 of Comparative Example 1 also has polycrystalline diffraction rings and is semi-hollow, with an interplanar spacing of 0.258 nm, corresponding to the (111) crystal plane. Since the copper ion radius is relatively small, its doping into the CoSe2 lattice will cause a decrease in the interplanar spacing, further proving that Cu is indeed doped into CoSe2 in Example 1.

[0078] Figure 4 Element distribution maps of the cathode material prepared in Example 1 of the present invention. From Figure 4 It can be seen that the distributions of the three elements Co, Cu, and Se in the Co 0.98 Cu 0.02 Se2 cathode material of Example 1 are very uniform, and there are no obvious impurity phases.

[0079] II. Electrochemical performance test of the cathode material

[0080] The cathode materials prepared in Example 1 and Comparative Example 1 of the present invention were mixed with conductive carbon black and polyvinylidene fluoride in a mass ratio of 8:1:1. After adding N-methylpyrrolidone to adjust the viscosity, it was evenly coated on a copper foil and dried in a vacuum drying oven at 120 °C for 12 h, and then cut into small round pieces with a diameter of 12 mm as the positive electrode sheets, and the loading amount of the active material was 0.8 mg / cm 2 ~1.5 mg / cm 2 .

[0081] The electrochemical performance test of the present invention adopted a traditional two-electrode system of a button cell, using AZ31 magnesium alloy as the negative electrode, glass fiber as the separator, and 0.4 M phenylmagnesium chloride-aluminum chloride-tetrahydrofuran solution as the electrolyte to assemble a magnesium-ion battery.

[0082] Figure 5 The cyclic performance graphs of the positive electrode materials prepared in Example 1 and Comparative Example 1 of the present invention during charge and discharge tests at a current density of 50 mA·g -1 can be seen from Figure 5 It can be seen that for the undoped CoSe2 positive electrode material in Comparative Example 1, the capacity slowly increases with the increase of the number of cycles, and the capacity increases to 63.5 mAh / g after 60 cycles. After doping 2% of Cu into CoSe2 in Example 1, the CoSe2 positive electrode is rapidly activated, the capacity increases rapidly, and the maximum capacity has reached 141.1 mAh / g.

[0083] Figure 6 The cyclic performance graphs of the positive electrode materials prepared in Example 1 and Comparative Example 1 of the present invention during charge and discharge tests at a current density of 200 mA·g -1 can be seen from Figure 6 It can be seen that at high current, due to the poor conductivity of the undoped CoSe2 positive electrode material in Comparative Example 1, the polarization is very large, and the specific capacity after 210 cycles is only 26.9 mAh / g. After 210 cycles of the Co 0.98 Cu 0.02 Se2 positive electrode material in Example 1, the specific capacity reaches 133.8 mAh / g, indicating that the energy band structure of Cu-doped CoSe2 has changed, significantly increasing the conductivity of the material. During the test, CoSe2 is rapidly activated, thus releasing a large amount of capacity.

[0084] As mentioned above, it is only a preferred embodiment of the present invention and does not impose any limitation on the present invention. Any simple modification, change and equivalent change made to the above embodiments according to the technical essence of the invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing a Cu slightly doped CoSe2 positive electrode material for a magnesium ion battery, characterized in that: The chemical formula of the positive electrode material is Co 1-x Cu x Se2, x ranges from 0.01 to 0.05, and the preparation method of the positive electrode material comprises the following steps: Step 1: Mix a cobalt source and a copper source and add them into methanol to dissolve. The obtained solution is recorded as liquid 1; the total concentration of cobalt ions and copper ions in the liquid 1 is 0.01 mol / L to 0.2 mol / L; Step 2: prepare a methanol solution of dimethylimidazole, referred to as liquid 2; the concentration of the liquid 2 is 0.04 mol / L to 3.2 mol / L; Step 3: under stirring, add the liquid 1 in step 1 dropwise to the liquid 2 in step 2, or add the liquid 2 in step 2 dropwise to the liquid 1 in step 1 to form a mixed solution, and continue to stir for 0.1h to 2h, then stop stirring and let stand for 2h to 24h; Step 4: collecting the precipitate in the mixed solution after standing in step 3, washing it by centrifugation for 3 times, and obtaining a precursor of the positive electrode material after drying; Step 5: Mix the precursor of the positive electrode material obtained in step 4 with selenium powder, then put it into an atmosphere furnace for sintering, cool it with the furnace, take it out after the temperature drops to room temperature, and grind it evenly to obtain the Cu slightly doped CoSe2 positive electrode material for magnesium ion battery.

2. The method for preparing a Cu slightly doped CoSe2 positive electrode material for a magnesium ion battery according to claim 1, characterized in that: In step 1, the cobalt source is cobalt nitrate, cobalt acetate, cobalt sulfate or cobalt chloride, the copper source is copper nitrate, copper acetate, copper sulfate or copper chloride, and the concentration ratio of cobalt ions to copper ions in the liquid 1 is 0.01 to 0.

6.

3. The preparation method and application of a Cu slightly doped CoSe2 positive electrode material for a magnesium ion battery according to claim 1, characterized in that: The stirring state and the stirring rate for continuing to maintain stirring in step 3 are 300 rpm to 1000 rpm, and the dropping rate is 10 mL / min to 100 mL / min.

4. The preparation method and application of a Cu slightly doped CoSe2 positive electrode material for a magnesium ion battery according to claim 1, characterized in that: The drying process in step 4 is: drying at 50°C to 100°C for 2h to 10h.

5. The preparation method and application of a Cu slightly doped CoSe2 positive electrode material for a magnesium ion battery according to claim 1, characterized in that: In step 5, the mass ratio of the precursor of the positive electrode material to the selenium powder is 0.5-2, and the sintering process is: the heating rate is 1°C / min-5°C / min, the temperature is raised to 300°C-700°C and sintered for 1h-5h.

6. An application of Cu slightly doped CoSe2 positive electrode material for magnesium ion battery prepared by the method according to any one of claims 1 to 5, characterized in that: The positive electrode material is used to prepare a positive electrode plate for use in magnesium ion batteries.

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