Carbon-coated manganese-cobalt-carbon composite material and application thereof in aqueous zinc ion battery

Abstract

The invention belongs to the field of water-based zinc ion battery electrode materials based on carbides, and discloses a carbon-coated manganese-cobalt-carbon composite material and application thereof in a water-based zinc ion battery, and a preparation method of the composite material comprises the following steps: carrying out double decomposition reaction on manganese salt and cobalt potassium cyanide to generate a cobalt manganese cyanide Mn3 [Co (CN) 6] 2 precursor; and calcining and carbonizing the precursor to obtain the carbon-coated manganese-cobalt-carbon composite material which is formed by coating a carbon layer on the surface of a compound of Mn2Co2C and Mn5C2. The preparation method is simple, and the obtained composite material not only can stabilize the structure of a manganese-based electrode material and inhibit manganese dissolution, but also can improve the conductivity of the material, thereby improving the rate capability and cycle stability of the aqueous zinc ion battery.

Description

Technical Field

[0001] The present invention relates to the field of electrode materials for aqueous zinc-ion batteries based on carbides, and particularly relates to a carbon-coated manganese-cobalt-carbon composite material and its application in aqueous zinc-ion batteries. Background Art

[0002] Among various energy storage devices, secondary batteries have received extensive attention because of their relatively simple system and relatively high energy storage efficiency. Compared with lithium-ion batteries based on organic electrolytes, aqueous metal-ion secondary batteries, especially aqueous zinc-ion batteries using aqueous electrolytes, have the advantages of high safety, low cost, easy assembly, etc., and have many advantages in many battery systems. Among them, manganese-based oxides are considered to be one of the most promising cathode materials for aqueous zinc-ion batteries because of their high capacity and high energy density, and their unique self-advantages such as low cost, rich reserves, environmental friendliness, and diverse valence states and crystal structures.

[0003] However, manganese-based oxides are prone to dissolve in the electrolyte during the cycling process, resulting in the loss of active substances, and then leading to a decrease in the cycling capacity and reducing the service life of the battery. Moreover, at present, the cathode of aqueous zinc-ion batteries uses a single manganese-based material. Due to the Jahn-Teller effect, the cycling stability will be affected. Coating modification and doping on the material surface are common methods to solve the cycling stability problem of manganese-based electrode materials, but they can only inhibit the Jahn-Teller effect to a certain extent and cannot completely eliminate it. And the processes of coating and doping are relatively complex, which limits their further development. Therefore, it is of great significance to develop and design a new manganese-based cathode material for aqueous zinc-ion batteries. Summary of the Invention

[0004] Based on the above deficiencies of the prior art, the present invention proposes a carbon-coated manganese-cobalt-carbon composite material and its application in aqueous zinc-ion batteries, aiming to inhibit the dissolution problem of manganese-based materials during the charge and discharge process of the battery, eliminate the Jahn-Teller effect existing in single manganese-based materials, and improve the electronic conductivity of the electrode material, thereby effectively improving the rate performance and cycling stability of aqueous zinc-ion batteries.

[0005] To achieve the purpose, the present invention adopts the following technical solutions: The present invention first discloses a preparation method of a carbon-coated manganese cobalt carbon composite material, which is as follows: Manganese salt and potassium cobalt cyanide are respectively dissolved and then mixed according to a molar ratio of 3:2. The obtained mixed solution undergoes a double decomposition reaction at room temperature to generate a precipitate. The precipitate is centrifuged, washed, and dried to obtain a manganese cobalt cyanide Mn3[Co(CN)6]2 precursor; the precursor is calcined and carbonized to obtain a carbon-coated manganese cobalt carbon composite material, denoted as Mn2Co2C@Mn5C2@C; the carbon-coated manganese cobalt carbon composite material is coated with a layer of carbon on the surface of the manganese cobalt carbon composite material, and the manganese cobalt carbon composite material is a composite of Mn2Co2C and Mn5C2. Specifically, it includes the following steps: Step 1: Add potassium cobalt cyanide to deionized water and stir until it is fully dissolved to obtain a potassium cobalt cyanide solution; add manganese salt to a mixed solvent of ethanol and deionized water, and add an active agent polyvinylpyrrolidone, and stir until it is fully dissolved to obtain a manganese salt solution; Step 2: While magnetically stirring at room temperature, slowly drop the potassium cobalt cyanide solution into the manganese salt solution for a double decomposition reaction. After the dropping is completed, continue magnetic stirring until the reaction is complete, and let it stand to obtain a white precipitate; Step 3: Centrifuge and wash the obtained white precipitate with ethanol, and then dry it to obtain a manganese cobalt cyanide Mn3[Co(CN)6]2 precursor powder; Step 4: Place the precursor powder in an inert atmosphere for calcination and carbonization to obtain a carbon-coated manganese cobalt carbon composite material.

[0006] Further, the manganese salt is any one of manganese chloride, manganese acetate, manganese nitrate, and manganese sulfate. Taking manganese acetate as an example, the following chemical reactions are included in the double decomposition and carbonization reaction processes:

[0007]

[0008] A white precipitate is generated through the double decomposition chemical reaction shown in formula (1). After the precipitate is centrifuged, washed, and dried, the precursor Mn3[Co(CN)6]2 is obtained. Finally, through high-temperature calcination, the precursor undergoes a carbonization reaction shown in formula (2) to obtain a manganese cobalt carbon composite material Mn2Co2C@Mn5C2, and at the same time, a carbon coating layer is formed on the surface of the manganese cobalt carbon composite material.

[0009] Further, in step 1, the addition amount of the active agent polyvinylpyrrolidone is 2-3 times the mass of the manganese salt. Adding polyvinylpyrrolidone can accelerate the dissolution of the manganese salt, so that a precursor with more uniform dispersion and more regular particle morphology can be formed during the double decomposition chemical reaction process.

[0010] Further, in step 2, the rotation speed of the magnetic stirring is 1000 - 1500 rpm, the continuous stirring time after the dropping is completed is 10 - 30 minutes, and the standing time is 12 - 24 hours.

[0011] Further, in step 3, the drying conditions are drying in an oven at 100 - 120 °C for 6 - 12 hours.

[0012] Further, in step 4, the conditions for calcination and carbonization are: heating from room temperature to 700 - 900 °C at a heating rate of 3 - 5 °C per minute, holding for calcination for 3 - 6 hours, and then naturally cooling to room temperature.

[0013] The carbon - coated manganese - cobalt - carbon composite material prepared by the present invention exhibits excellent rate performance and cycle stability in aqueous zinc - ion batteries.

[0014] Compared with the existing preparation methods, the beneficial effects of the present invention are as follows: The present invention first forms a manganese cobalt cyanide precursor through a metathesis reaction, and then calcines the precursor to carbonize the cyanide radicals therein, obtaining a composite of Mn2Co2C and Mn5C2, while forming a carbon layer and attaching it to the surface of the material. The heterostructure composed of Mn2Co2C and Mn5C2 eliminates the Jahn - Teller effect existing in single manganese - based materials, and the introduction of cobalt ions broadens the inherent voltage window of traditional manganese - based materials, improves the conductivity of the materials, and reduces the diffusion barrier of Zn 2+ inside the material, promoting the insertion and extraction of Zn 2+ inside the material. The carbon - coated layer can inhibit the dissolution of manganese during the repeated charge and discharge of the battery. At the same time, different from traditional manganese - based materials, the synthesized carbon - coated manganese - cobalt - carbon composite material of the present invention has a nanoscale cubic particle morphology, with a smaller particle size and a regular morphology structure, which is beneficial to reducing the stress of the material during the charge and discharge of the battery. Under the synergistic effect of the above - mentioned conditions, the composite material of the present invention can significantly improve the cycle stability of the electrode material and the rate performance of the battery, and is a very promising positive electrode material for aqueous zinc - ion batteries.

[0015] The synthesis method of the present invention is simple, the process is easy to implement, does not require harsh conditions such as high pressure, and is easy to be popularized and applied on a large scale. Description of the Drawings

[0016] Figure 1 SEM image of the manganese cobalt cyanide Mn3[Co(CN)6]2 precursor obtained in Example 1.

[0017] Figure 2 SEM image of Mn2Co2C@Mn5C2@C obtained in Example 1.

[0018] Figure 3HRTEM images of Mn2Co2C@Mn5C2@C obtained in Example 1, where: (a) is the image of the composite coating layer; (b) is the enlarged lattice fringe image of the carbon layer; (c) is the lattice spacing of the carbon layer.

[0019] Figure 4 XRD pattern of the manganese cobalt cyanide Mn3[Co(CN)6]2 precursor obtained in Example 1.

[0020] Figure 5 XRD patterns of Mn2Co2C@Mn5C2 and Mn2Co2C@C obtained in Example 1.

[0021] Figure 6 XPS spectra of Mn3[Co(CN)6]2, Mn2Co2C@Mn5C2@C, and Mn2Co2C@C, where: (a) are the 2p 3 / 2 and 2p 1 / 2 spin-split orbitals of Mn; (b) is the 3s spin-split orbital of Mn; (c) are the 2p 3 / 2 and 2p 1 / 2 spin-split orbitals of Co.

[0022] Figure 7 Comparison chart of the rate performance of CR2032 coin cells assembled with Mn3[Co(CN)6]2, Mn2Co2C@Mn5C2@C, and Mn2Co2C@C.

[0023] Figure 8 Comparison chart of the charge-discharge curves of CR2032 coin cells assembled with Mn3[Co(CN)6]2, Mn2Co2C@Mn5C2@C, and Mn2Co2C@C at a current density of 0.1 A g -1 -1.

[0024] Figure 9 Comparison chart of the cycling capacities of CR2032 coin cells assembled with Mn3[Co(CN)6]2, Mn2Co2C@Mn5C2@C, and Mn2Co2C@C at a current density of 0.5 A g -1 -1.

[0025] Figure 10 XRD patterns of the composite materials obtained at calcination temperatures of 500 °C, 600 °C, and 700 °C in Example 2.

[0026] Figure 11 Comparison chart of the rate performance of CR2032 coin cells assembled with the composite materials obtained at calcination temperatures of 500 °C, 600 °C, and 700 °C in Example 2.

[0027] Figure 12XRD patterns of the composite materials obtained at the heat preservation times of 3 h and 4 h in Example 3; Figure 13 Comparison diagram of the rate performance of the CR2032 button batteries assembled with the composite materials obtained at the heat preservation times of 3 h and 4 h in Example 3.

[0028] Figure 14 Comparison diagram of the rate performance of the CR2032 button batteries assembled with the composite materials obtained by using manganese chloride, manganese nitrate and manganese sulfate as raw materials in Example 4. Detailed implementation mode

[0029] The embodiments of the present invention will be described in detail below. These embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operation processes are given. However, the protection scope of the present invention is not limited to the following embodiments.

[0030] The test method for the electrochemical performance of the composite materials obtained in the following embodiments used as the positive electrode material for aqueous zinc ion batteries is as follows: Mix the obtained active material, acetylene black, and PVDF in a mass ratio of 7:2:1, grind them, add an appropriate amount of NMP solvent, and stir for 10 hours to make a positive electrode slurry. Then, uniformly coat it on a carbon paper current collector with a thickness of 75 μm, dry it, and cut out a positive electrode disc with a diameter of 12 mm using a slicing machine; Use a metal zinc foil disc with a diameter of 16 mm as the negative electrode, WHATMAN G / D glass fiber as the separator, and an aqueous solution of 2M ZnSO4 + 0.2M MnSO4 as the electrolyte. Assemble and press them into a CR2032 button battery in the order of negative electrode shell - zinc foil - separator - electrolyte - positive electrode sheet - steel sheet - elastic sheet - positive electrode shell in the atmospheric environment.

[0031] Example 1 The carbon-coated manganese cobalt carbon composite material is prepared according to the following steps in this example: 1. Weigh 2 mmol of potassium hexacyanoferrate in a beaker, add 60 mL of deionized water, and stir magnetically until it is fully dissolved to obtain a potassium hexacyanoferrate solution. Weigh 3 mmol of manganese acetate, add it to a mixed solvent of 80 mL of ethanol and 20 mL of deionized water, and add 1.5 g of polyvinylpyrrolidone. Stir magnetically until it is fully dissolved to obtain a manganese acetate solution.

[0032] 2. While stirring magnetically at room temperature (rotation speed 1200 rpm), slowly drip the potassium hexacyanoferrate solution into the manganese acetate solution using a peristaltic pump (peristaltic pump rotation speed is 4 rpm) for a double decomposition reaction. After the dripping is completed, continue to stir magnetically for 10 minutes, and let it stand for 12 hours to obtain a white precipitate.

[0033] 3. After washing the obtained white precipitate by centrifugation with ethanol multiple times, dry it in an oven at 110 °C for 10 hours to obtain a manganese hexacyanocobaltate Mn3[Co(CN)6]2 precursor powder.

[0034] 4. The precursor powder is placed in argon for calcination carbonization to obtain a carbon-coated manganese cobalt carbon composite material (Mn2Co2C@Mn5C2@C). The conditions for calcination carbonization are as follows: heating from room temperature to 900 °C at a heating rate of 4 °C per minute, holding for calcination for 5 hours, and then naturally cooling to room temperature.

[0035] For comparison, in this example, a carbon-coated pure Mn2Co2C material (denoted as Mn2Co2C@C) was prepared. Its preparation method is the same as that of Mn2Co2C@Mn5C2@C, except that the amount of manganese acetate in step 1 was adjusted to 2 mmol.

[0036] Figure 1 Figure 9 is the SEM image of the manganese cobalt cyanide Mn3[Co(CN)6]2 precursor, showing that the material presents a nano-cubic morphology with a particle size of 50 - 200 nm. Figure 2 Figure 11 is the SEM image of Mn2Co2C@Mn5C2@C. It can be seen that the material still presents a nano-cubic morphology.

[0037] Figure 3 Figure 15 is the HRTEM image of Mn2Co2C@Mn5C2@C. Among them: (a) is the image of the composite coating layer, and it can be seen that there is a carbon coating layer on the surface of the material; (b) is the enlarged lattice fringe image of the carbon layer, and it can be clearly seen that the carbon layer has obvious lattice fringes; (c) is the lattice spacing of the carbon layer. By measurement and comparison, it is found that the lattice fringe spacing can correspond to graphitized carbon.

[0038] Figure 4 Figure 19 is the XRD pattern of the manganese cobalt cyanide Mn3[Co(CN)6]2 precursor. It can be seen that the precursor powder can be indexed to manganese cobalt cyanide Mn3[Co(CN)6]2 (PDF#01 - 073 - 6627), and there are no obvious other impurity phases, indicating that the synthesized precursor is a pure phase.

[0039] Figure 5 Figure 23 is the XRD patterns of Mn2Co2C@Mn5C2@C and Mn2Co2C@C. It can be seen that the Mn2Co2C@Mn5C2@C powder can be indexed to Mn2Co2C (PDF# 01 - 0773 - 6627) and Mn5C2 (04 - 007 - 1125) and contains graphitized carbon, and the spectrum shows that each crystal plane is aligned with the standard card, indicating that the calcination obtained a carbon-coated Mn2Co2C@Mn5C2 composite. No diffraction peak of Mn5C2 was found in Mn2Co2C@C, indicating that adjusting the raw material ratio can control the product composition.

[0040] Figure 6XPS spectra of Mn3[Co(CN)6]2, Mn2Co2C@Mn5C2@C, and Mn2Co2C@C, where: (a) are the 2p 3 / 2 and 2p 1 / 2 spin-split orbitals of Mn. It is observed that the precursor is dominated by Mn 2+ while Mn2Co2C@C is dominated by Mn 0 in a certain valence state, and Mn2Co2C@Mn5C2@C is dominated by a mixed valence state of Mn 2+ / 3+ , indicating that the composite material has a high mixed valence state; (b) are the 3s spin-split orbitals of Mn. It is observed that Mn2Co2C@Mn5C2@C has a larger difference between the 3s peaks, further indicating that it has a high-valence Mn electronic structure, leading to a stronger electron correlation effect; (c) are the 2p 3 / 2 and 2p 1 / 2 spin-split orbitals of Co. It is observed that the precursor is dominated by Co 3+ / 2+ , while Mn2Co2C@Mn5C2@C and Mn2Co2C@C are dominated by Co 0 in a certain valence state, indicating that the composite material has metallic properties.

[0041] The ICP atomic ratios of manganese and cobalt in each sample are shown in Table 1. The data in the table show that the manganese and cobalt in Mn3[Co(CN)6]2, Mn2Co2C@Mn5C2@C, and Mn2Co2C@C satisfy the atomic ratio of the product.

[0042] Table 1

[0043] Figure 7 Comparison chart of the rate performance of CR2032 coin cells assembled with Mn3[Co(CN)6]2, Mn2Co2C@Mn5C2@C, and Mn2Co2C@C. It can be seen that the rate performance of Mn2Co2C@Mn5C2@C is significantly better than that of the Mn3[Co(CN)6]2 precursor and the single Mn2Co2C@C material.

[0044] Figure 8 Comparison chart of the charge-discharge curves of CR2032 coin cells assembled with Mn3[Co(CN)6]2, Mn2Co2C@Mn5C2@C, and Mn2Co2C@C at a current density of 0.1 A g -1 . It can be seen that the voltage platforms of the charge-discharge curves of each sample are basically the same, and the discharge specific capacity of the Mn2Co2C@Mn5C2@C sample is higher.

[0045] Figure 9The CR2032 button batteries assembled with Mn3[Co(CN)6]2, Mn2Co2C@Mn5C2@C and Mn2Co2C@C at 0.5 A g -1 The cyclic capacity comparison diagram at a current density shows that: The discharge specific capacity of Mn2Co2C@Mn5C2@C can reach 409.26 mAh g -1 after 45 cycles at a current density of 0.5 A g -1 and does not decline. The discharge specific capacity of Mn2Co2C@C is only 343.7 mAh g -1 and can only maintain 35 cycles, while the discharge specific capacity of the Mn3[Co(CN)6]2 precursor rapidly decays to 38.6 mAh g -1 after activation, indicating that the Mn2Co2C@Mn5C2@C composite material has higher stability.

[0046] Example 2 The carbon-coated manganese cobalt carbon composite material was prepared by the same method as in Example 1 in this example. The only difference is that the calcination temperature in step 4 was adjusted to 500 °C, 600 °C, and 700 °C. The XRD patterns of the obtained composite materials are as Figure 10 shown. It can be seen that the composite material Mn2Co2C@Mn5C2@C obtained at 700 °C has no obvious other impurity phases, indicating that the product composition can be regulated by controlling the calcination temperature.

[0047] Using the obtained composite material as the active material to assemble a CR2032 button battery, the rate performance comparison diagram is as Figure 11 shown. It can be seen that the rate performance of the products synthesized at 700 °C - 900 °C is more excellent.

[0048] Example 3 The carbon-coated manganese cobalt carbon composite material was prepared by the same method as in Example 1 in this example. The only difference is that the calcination time in step 4 was adjusted to 2 h, 3 h, and 4 h. The XRD patterns of the obtained composite materials are as Figure 12 shown. It can be seen that the product obtained by holding for 2 h contains more impurity phases, and the product phases obtained at 3 h and 4 h are basically the same, indicating that the product can be obtained by holding for 3 h.

[0049] Using the obtained composite material as the active material to assemble a CR2032 button battery, the rate performance comparison diagram is as Figure 13 shown. It can be seen that the rate performance of the products has little difference, indicating that this synthesis method can flexibly adjust the calcination duration without affecting the battery rate performance.

[0050] Example 4 The carbon-coated manganese cobalt carbon composite material was prepared in the same manner as in Example 1, except that the manganese salt in Step 1 was adjusted to manganese chloride, manganese nitrate, and manganese sulfate.

[0051] The obtained composite material was used as the active material to assemble a CR2032 type button battery. The comparison chart of its rate performance is as Figure 14 shown. It can be seen that the rate performance of the products has little difference, indicating that this synthesis method can flexibly adjust the manganese salt raw materials without affecting the rate performance of the battery.

[0052] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. Preparation method of carbon-coated manganese cobalt carbon composite material, characterized in that: The manganese salt and potassium cobalt cyanide are separately dissolved according to a molar ratio of 3:2 and then mixed. The resulting mixed solution undergoes a double decomposition reaction at room temperature to form a precipitate. The precipitate is centrifuged, washed, and dried to obtain a manganese cobalt cyanide Mn3[Co(CN)6]2 precursor; the precursor is calcined and carbonized to obtain a carbon-coated manganese cobalt carbon composite material, denoted as Mn2Co2C@Mn5C2@C; the carbon-coated manganese cobalt carbon composite material has a carbon layer coated on the surface of the manganese cobalt carbon composite material, and the manganese cobalt carbon composite material is a composite of Mn2Co2C and Mn5C2.

2. The preparation method of the carbon-coated manganese cobalt carbon composite material according to claim 1, characterized in that, The specific steps are as follows: Step 1: Potassium cobalt cyanide is added to deionized water and stirred until completely dissolved to obtain a potassium cobalt cyanide solution; the manganese salt is added to a mixed solvent of ethanol and deionized water, and the surfactant polyvinylpyrrolidone is added, and stirred until completely dissolved to obtain a manganese salt solution; Step 2: While magnetically stirring at room temperature, the potassium cobalt cyanide solution is slowly added dropwise to the manganese salt solution for a double decomposition reaction. After the addition is completed, magnetic stirring is continued until the reaction is complete, and then left standing to obtain a white precipitate; Step 3: The obtained white precipitate is centrifuged and washed with ethanol and then dried to obtain a manganese cobalt cyanide Mn3[Co(CN)6]2 precursor powder; Step 4: The precursor powder is placed in an inert atmosphere for calcination and carbonization to obtain a carbon-coated manganese cobalt carbon composite material.

3. The preparation method of the carbon-coated manganese cobalt carbon composite material according to claim 1 or 2, characterized in that: The manganese salt is any one of manganese chloride, manganese acetate, manganese nitrate, and manganese sulfate.

4. The preparation method of the carbon-coated manganese cobalt carbon composite material according to claim 2, characterized in that: In Step 1, the addition amount of the surfactant polyvinylpyrrolidone is 2-3 times the mass of the manganese salt.

5. The preparation method of the carbon-coated manganese cobalt carbon composite material according to claim 2, characterized in that: In Step 2, the rotation speed of the magnetic stirring is 1000-1500 rpm, the continuous stirring time after the addition is completed is 10-30 minutes, and the standing time is 12-24 hours.

6. The preparation method of the carbon-coated manganese cobalt carbon composite material according to claim 2, characterized in that: In Step 3, the drying conditions are drying in an oven at 100-120 °C for 6-12 hours.

7. The preparation method of the carbon-coated manganese cobalt carbon composite material according to claim 2, characterized in that, In Step 4, the calcination and carbonization conditions are: heating from room temperature to 700-900 °C at a heating rate of 3-5 °C / minute, holding for calcination for 3-6 hours, and then naturally cooling to room temperature.

8. A carbon-coated manganese cobalt carbon composite material prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the carbon-coated manganese cobalt carbon composite material according to claim 8, characterized in that: It is used as a positive electrode active material for an aqueous zinc ion battery.

10. Aqueous zinc-ion battery, characterized in that: The carbon-coated manganese cobalt carbon composite material according to claim 8 is used as the positive electrode active material.

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