Carbon-coated manganese-cobalt-carbon composites and their applications in aqueous zinc-ion batteries

Abstract

The present invention belongs to the field of carbide-based aqueous zinc-ion battery electrode materials and discloses a carbon-coated manganese-cobalt-carbon composite material and its application in aqueous zinc-ion batteries. The composite material is prepared by: generating a manganese cobalt cyanide precursor, Mn3[Co(CN)6]2, through a double decomposition reaction between a manganese salt and potassium cobalt cyanide; and calcining and carbonizing the precursor to obtain a carbon-coated manganese-cobalt-carbon composite material. The material comprises a carbon layer coated on the surface of a composite of Mn2Co2C and Mn5C2. The preparation method of the present invention is simple, and the resulting composite material not only stabilizes the structure of the manganese-based electrode material and inhibits manganese dissolution, but also improves the material's electrical conductivity, thereby enhancing the rate capability and cycle stability of aqueous zinc-ion batteries.

Description

Technical Field

[0001] The present invention relates to the field of carbide-based aqueous zinc ion battery electrode materials, and in particular 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 garnered widespread attention due to their relatively simple systems and high energy storage efficiency. Compared to lithium-ion batteries based on organic electrolytes, aqueous metal-ion secondary batteries, particularly aqueous zinc-ion batteries, utilize aqueous electrolytes and offer advantages such as high safety, low cost, and ease of assembly, offering numerous advantages over other battery systems. Manganese-based oxides, among others, are considered one of the most promising cathode materials for aqueous zinc-ion batteries due to their high capacity and energy density, combined with unique advantages such as low cost, abundant reserves, environmental friendliness, and diverse valence states and crystal structures.

[0003] However, manganese-based oxides are easily dissolved in the electrolyte during the cycle, resulting in loss of active materials, which in turn leads to a decrease in cycle capacity and shortened battery life. Moreover, the positive electrode of the current aqueous zinc-ion battery uses a single manganese-based material, which affects the cycle stability due to the Jahn-Teller effect. Coating and doping the surface of the material are common methods to solve the problem of cycle stability of manganese-based electrode materials, but they can only suppress the Jahn-Teller effect to a certain extent and cannot completely eliminate it. In addition, the coating and doping processes are relatively complex, which limits its further development. Therefore, it is of great significance to develop and design a new manganese-based positive electrode material for aqueous zinc-ion batteries. Summary of the Invention

[0004] Based on the shortcomings of the above-mentioned 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 charging and discharging 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 cycle stability of the aqueous zinc-ion battery.

[0005] To achieve the purpose, the present invention adopts the following technical solutions:

[0006] The present invention first discloses a method for preparing a carbon-coated manganese-cobalt-carbon composite material, which comprises: dissolving a manganese salt and potassium cobalt cyanide in a molar ratio of 3:2 and then mixing them; the resulting 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 precursor, Mn3[Co(CN)6]2; 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 its surface, and the manganese-cobalt-carbon composite material is a composite of Mn2Co2C and Mn5C2. Specifically, the method comprises the following steps:

[0007] Step 1: adding potassium cobalt cyanide to deionized water and stirring until fully dissolved to obtain a potassium cobalt cyanide solution; adding manganese salt to a mixed solvent of ethanol and deionized water, and adding an active agent polyvinyl pyrrolidone, stirring until fully dissolved to obtain a manganese salt solution;

[0008] Step 2: While magnetically stirring at room temperature, slowly dropwise add the potassium cobalt cyanide solution to the manganese salt solution to carry out a double decomposition reaction; after the dropwise addition is completed, continue magnetic stirring until the reaction is sufficient, and let stand to obtain a white precipitate;

[0009] Step 3: washing the obtained white precipitate with ethanol by centrifugation, and then drying to obtain cobalt cyanide manganese Mn3[Co(CN)6]2 precursor powder;

[0010] Step 4: placing the precursor powder in an inert atmosphere for calcination and carbonization to obtain a carbon-coated manganese-cobalt-carbon composite material.

[0011] Furthermore, the manganese salt is any one of manganese chloride, manganese acetate, manganese nitrate and manganese sulfate. Taking manganese acetate as an example, the double decomposition and carbonization reaction process includes the following chemical reactions:

[0012]

[0013]

[0014] A white precipitate is produced by a double decomposition chemical reaction as shown in formula (1). The precipitate is centrifuged, washed, and dried to obtain a precursor Mn3[Co(CN)6]2. Finally, the precursor is subjected to a carbonization reaction as shown in formula (2) by high-temperature calcination to obtain a manganese-cobalt-carbon composite material Mn2Co2C@Mn5C2, and a carbon coating layer is formed on the surface of the manganese-cobalt-carbon composite material.

[0015] Furthermore, in step 1, the amount of polyvinyl pyrrolidone added as the active agent is 2-3 times the mass of the manganese salt. Adding polyvinyl pyrrolidone 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 metathesis chemical reaction.

[0016] Furthermore, in step 2, the rotation speed of the magnetic stirring is 1000-1500 rpm, the stirring time after the dropwise addition is continued for 10-30 minutes, and the standing time is 12-24 hours.

[0017] Furthermore, in step 3, the drying condition is oven drying at 100-120° C. for 6-12 hours.

[0018] Furthermore, 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. / min, calcining at this temperature for 3-6 hours, and then naturally cooling to room temperature.

[0019] 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.

[0020] Compared with the existing preparation method, the beneficial effects of the present invention are embodied in:

[0021] The present invention first forms a cobalt cyanide precursor through a double decomposition reaction, and then carbonizes the cyanide in the precursor through calcination to obtain a complex of Mn2Co2C and Mn5C2, while forming a carbon layer and adhering to the surface of the material. The heterogeneous structure 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 material, and reduces the Zn 2+ The diffusion barrier inside the material promotes the Zn 2+ Embedding and removal inside the material. The carbon coating layer can inhibit the dissolution of manganese during repeated charging and discharging of the battery. At the same time, unlike traditional manganese-based materials, the carbon-coated manganese-cobalt-carbon composite material synthesized by the present invention has a nano-scale cubic particle morphology, a small particle size and a regular morphological structure, which is beneficial to reducing the stress of the material during the charging and discharging process of the battery. Under the synergistic effect of the above 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 highly promising aqueous zinc-ion battery positive electrode material.

[0022] The synthesis method of the invention is simple, easy to process, does not require harsh conditions such as high pressure, and is easy to promote and apply on a large scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the SEM image of the cobalt cyanide manganese Mn3[Co(CN)6]2 precursor obtained in Example 1.

[0024] Figure 2 This is the SEM image of Mn2Co2C@Mn5C2@C obtained in Example 1.

[0025] Figure 3 HRTEM images of Mn2Co2C@Mn5C2@C obtained in Example 1, where: (a) is the composite material coating layer image; (b) is the enlarged lattice fringe image of the carbon layer; and (c) is the lattice spacing of the carbon layer.

[0026] Figure 4 This is the XRD pattern of the cobalt cyanide manganese Mn3[Co(CN)6]2 precursor obtained in Example 1.

[0027] Figure 5 XRD patterns of Mn2Co2C@Mn5C2 and Mn2Co2C@C obtained in Example 1.

[0028] Figure 6 XPS graphs of Mn3[Co(CN)6]2, Mn2Co2C@Mn5C2@C and Mn2Co2C@C, where: (a) is the 2p 3 / 2 and 2p 1 / 2 Spin split orbitals; (b) is the 3s spin split orbital of Mn; (c) is the 2p spin split orbital of Co 3 / 2 and 2p 1 / 2 Spin-split orbitals.

[0029] Figure 7 A comparison of the rate performance of CR2032 button batteries assembled with Mn3[Co(CN)6]2, Mn2Co2C@Mn5C2@C and Mn2Co2C@C.

[0030] Figure 8 The CR2032 button cell assembled with Mn3[Co(CN)6]2, Mn2Co2C@Mn5C2@C and Mn2Co2C@C was tested at 0.1A g -1 Comparison of charge and discharge curves under different current densities.

[0031] Figure 9 The CR2032 button cell assembled with Mn3[Co(CN)6]2, Mn2Co2C@Mn5C2@C and Mn2Co2C@C was tested at 0.5A g -1 Comparison of cycling capacity under different current densities.

[0032] Figure 10 1 is the XRD pattern of the composite material obtained at calcination temperatures of 500°C, 600°C and 700°C in Example 2.

[0033] Figure 11 This is a comparison chart of the rate performance of CR2032 button batteries assembled with the composite materials obtained at calcination temperatures of 500°C, 600°C and 700°C in Example 2.

[0034] Figure 12The XRD patterns of the composite materials obtained at holding times of 3 h and 4 h in Example 3 are shown;

[0035] Figure 13 This is a comparison chart of the rate performance of CR2032 button batteries assembled with the composite materials obtained at 3h and 4h holding times in Example 3.

[0036] Figure 14 This is a comparison chart of the rate performance of CR2032 button batteries assembled with the composite materials obtained using manganese chloride, manganese nitrate and manganese sulfate as raw materials in Example 4. DETAILED DESCRIPTION

[0037] The following is a detailed description of an embodiment of the present invention. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process. However, the protection scope of the present invention is not limited to the following embodiment.

[0038] The electrochemical performance of the composite material obtained in the following example for the positive electrode material of an aqueous zinc ion battery is tested as follows: the obtained active material is mixed with acetylene black and PVDF in a mass ratio of 7:2:1 and ground, an appropriate amount of NMP solvent is added and stirred for 10 hours to prepare a positive electrode slurry, which is then evenly coated on a carbon paper current collector with a thickness of 75 μm. After drying, a positive electrode disc with a diameter of 12 mm is cut using a slicer; a metal zinc foil disc with a diameter of 16 mm is used as the negative electrode, a WHATMAN G / D glass fiber is used as the separator, and a 2M ZnSO4+0.2M MnSO4 aqueous solution is used as the electrolyte. The cells are assembled and pressed into a CR2032 button cell in an atmospheric environment in the order of negative electrode shell-zinc foil-diaphragm-electrolyte-positive electrode sheet-steel sheet-shrapnel-positive electrode shell.

[0039] Example 1

[0040] In this embodiment, the carbon-coated manganese-cobalt-carbon composite material is prepared according to the following steps:

[0041] 1. Weigh 2 mmol of potassium cobalt cyanide into a beaker, add it to 60 mL of deionized water, and stir magnetically until fully dissolved to obtain a potassium cobalt cyanide solution. Weigh 3 mmol of manganese acetate into a mixed solvent of 80 mL of ethanol and 20 mL of deionized water, and add 1.5 g of polyvinyl pyrrolidone. Stir magnetically until fully dissolved to obtain a manganese acetate solution.

[0042] 2. While magnetically stirring at room temperature (speed 1200 rpm), the potassium cobalt cyanide solution was slowly added dropwise to the manganese acetate solution using a peristaltic pump (peristaltic pump speed 4 rpm) to carry out a double decomposition reaction. After the addition was completed, magnetic stirring was continued for 10 minutes and the solution was allowed to stand for 12 hours to obtain a white precipitate.

[0043] 3. The obtained white precipitate was washed by centrifugation with ethanol several times and then dried in an oven at 110°C for 10 hours to obtain cobalt cyanide manganese Mn3[Co(CN)6]2 precursor powder.

[0044] 4. The precursor powder was calcined and carbonized in an argon atmosphere to obtain a carbon-coated manganese-cobalt-carbon composite material (Mn2Co2C@Mn5C2@C). The calcination and carbonization conditions were as follows: heating from room temperature to 900°C at a rate of 4°C / min, calcining for 5 hours, and then naturally cooling to room temperature.

[0045] For comparison, in this example, a carbon-coated pure Mn2Co2C material (denoted as Mn2Co2C@C) was prepared. The preparation method was the same as that of Mn2Co2C@Mn5C2@C, except that the amount of manganese acetate in step 1 was adjusted to 2 mmol.

[0046] Figure 1 This is the SEM image of the cobalt cyanide manganese Mn3[Co(CN)6]2 precursor, showing that the material has a nanocubic morphology with a particle size of 50-200nm. Figure 2 This is the SEM image of Mn2Co2C@Mn5C2@C. It can be seen that the material still presents a nanocubic morphology.

[0047] Figure 3 These are HRTEM images of Mn2Co2C@Mn5C2@C, where: (a) is the composite material coating layer image, from which 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, from which it can be clearly seen that the carbon layer has obvious lattice fringes; (c) is the lattice spacing of the carbon layer. Through measurement and comparison, it is found that the lattice fringe spacing can correspond to graphitized carbon.

[0048] Figure 4 This is the XRD pattern of the Mn3[Co(CN)6]2 precursor. It can be seen that the precursor powder can be indexed as manganese cobalt cyanide Mn3[Co(CN)6]2 (PDF#01-073-6627), with no obvious other impurity phases, indicating that the synthesized precursor is a pure phase.

[0049] Figure 5 The XRD patterns of Mn2Co2C@Mn5C2@C and Mn2Co2C@C are shown. The Mn2Co2C@Mn5C2@C powder can be identified as Mn2Co2C (PDF# 01-0773-6627) and Mn5C2 (04-007-1125), containing graphitized carbon. The pattern also shows that all crystal planes align with the standard card, indicating that the carbon-coated Mn2Co2C@Mn5C2 composite was obtained after calcination. However, no diffraction peaks for Mn5C2 were observed in Mn2Co2C@C, indicating that the product composition can be controlled by adjusting the raw material ratio.

[0050] Figure 6 XPS graphs of Mn3[Co(CN)6]2, Mn2Co2C@Mn5C2@C and Mn2Co2C@C, where: (a) is the 2p 3 / 2 and 2p 1 / 2 Spin-splitting orbitals, it was observed that the precursor is composed of Mn 2+ Dominant, Mn2Co2C@C is composed of Mn 0 Valence state dominates, Mn2Co2C@Mn5C2@C is composed of Mn 2+ / 3+ The mixed valence state dominates, indicating that the composite material has a high mixed valence state; (b) is the 3s spin split orbital of Mn. It is observed that Mn2Co2C@Mn5C2@C has a higher 3s peak difference, which further indicates that it has a high-valence Mn electronic structure, resulting in a stronger electron correlation effect; (c) is the 2p 3 / 2 and 2p 1 / 2 Spin-splitting orbitals, it was observed that the precursor was composed of Co 3+ / 2+ Dominant, Mn2Co2C@Mn5C2@C and Mn2Co2C@C are composed of Co 0 The valence state is dominant, indicating that the composite material has metallic properties.

[0051] The ICP atomic ratios of manganese and cobalt elements in each sample are shown in Table 1. The data in the table show that the atomic ratios of manganese and cobalt in Mn3[Co(CN)6]2, Mn2Co2C@Mn5C2@C and Mn2Co2C@C meet the product requirements.

[0052] Table 1

[0053]

[0054] Figure 7 The rate performance comparison chart of CR2032 button batteries assembled with Mn3[Co(CN)6]2, Mn2Co2C@Mn5C2@C and Mn2Co2C@C shows that the rate performance of Mn2Co2C@Mn5C2@C is significantly better than that of Mn3[Co(CN)6]2 precursor and single Mn2Co2C@C material.

[0055] Figure 8 The CR2032 button cell assembled with Mn3[Co(CN)6]2, Mn2Co2C@Mn5C2@C and Mn2Co2C@C was tested at 0.1A g -1 From the comparison of the charge and discharge curves under different current densities, it can be seen that the voltage platforms of the charge and discharge curves of each sample are basically the same, and the discharge specific capacity of the Mn2Co2C@Mn5C2@C sample is higher.

[0056] Figure 9The CR2032 button cell assembled with Mn3[Co(CN)6]2, Mn2Co2C@Mn5C2@C and Mn2Co2C@C was tested at 0.5A g -1 The comparison of the cycle capacity under current density shows that: Mn2Co2C@Mn5C2@C at 0.5A g -1 The discharge capacity can reach 409.26 mAh g after 45 cycles at a current density of -1 The discharge capacity of Mn2Co2C@C is only 343.7 mAh g -1 The discharge capacity of the Mn3[Co(CN)6]2 precursor rapidly decayed to 38.6 mAh g after activation. -1 , indicating that the Mn2Co2C@Mn5C2@C composite material has higher stability.

[0057] Example 2

[0058] In this example, a carbon-coated manganese-cobalt-carbon composite material was prepared by the same method as in Example 1, except 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 shown in FIG. Figure 10 As shown, it can be seen that the composite material Mn2Co2C@Mn5C2@C obtained at 700℃ has no obvious other impurity phases, indicating that the composition of the product can be controlled by regulating the calcination temperature.

[0059] The obtained composite material was used as the active material to assemble CR2032 button battery. The rate performance comparison is shown in the figure below. Figure 11 As shown, it can be seen that the product synthesized at 700℃-900℃ has better rate performance.

[0060] Example 3

[0061] In this example, a carbon-coated manganese-cobalt-carbon composite material was prepared by the same method as in Example 1, except 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 shown in FIG. Figure 12 As shown, it can be seen that the product obtained after 2 hours of heat preservation contains more impurities, and the product phases obtained after 3 hours and 4 hours are basically the same, indicating that the product can be obtained after 3 hours of heat preservation.

[0062] The obtained composite material was used as the active material to assemble CR2032 button battery. The rate performance comparison is shown in the figure below. Figure 13 As shown, it can be seen that the rate performance of the products is not much different, indicating that the synthesis method can flexibly adjust the calcination time without affecting the battery rate performance.

[0063] Example 4

[0064] In this embodiment, a carbon-coated manganese-cobalt-carbon composite material was prepared by the same method as in Example 1, except that the manganese salt in step 1 was adjusted to manganese chloride, manganese nitrate, and manganese sulfate.

[0065] The obtained composite material was used as the active material to assemble CR2032 button battery. The rate performance comparison is shown in the figure below. Figure 14 As shown, it can be seen that the rate performance of the products is not much different, indicating that the synthesis method can flexibly adjust the manganese salt raw materials without affecting the battery rate performance.

[0066] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a carbon-coated manganese-cobalt-carbon composite material, characterized in that: The specific steps are as follows: Step 1: adding potassium cobalt cyanide to deionized water and stirring until fully dissolved to obtain a potassium cobalt cyanide solution; adding manganese salt to a mixed solvent of ethanol and deionized water, and adding an active agent polyvinyl pyrrolidone, stirring until fully dissolved to obtain a manganese salt solution; Step 2: While magnetically stirring at room temperature, slowly dropwise add the potassium cobalt cyanide solution to the manganese salt solution in a molar ratio of manganese salt to potassium cobalt cyanide of 3:2 to carry out a double decomposition reaction; after the dropwise addition is completed, continue magnetic stirring until the reaction is fully reacted, and let stand to obtain a white precipitate; Step 3: After washing the obtained white precipitate with ethanol by centrifugation, drying it in an oven at 100-120° C. for 6-12 hours to obtain a cobalt cyanide manganese 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, recorded as Mn2Co2C@Mn5C2@C; the carbon-coated manganese-cobalt-carbon composite material is a manganese-cobalt-carbon composite material with a carbon layer coated on the surface, and the manganese-cobalt-carbon composite material is a composite of Mn2Co2C and Mn5C2; the calcination and carbonization conditions are: heating from room temperature to 700-900°C at a heating rate of 3-5°C / min, keeping warm and calcining for 3-6 hours, and then naturally cooling to room temperature.

2. The method for preparing the carbon-coated manganese-cobalt-carbon composite material according to claim 1, wherein: The manganese salt is any one of manganese chloride, manganese acetate, manganese nitrate and manganese sulfate.

3. The method for preparing the carbon-coated manganese-cobalt-carbon composite material according to claim 1, wherein: In step 1, the amount of polyvinyl pyrrolidone added as the active agent is 2-3 times the mass of the manganese salt.

4. The method for preparing the carbon-coated manganese-cobalt-carbon composite material according to claim 1, wherein: In step 2, the rotation speed of the magnetic stirring is 1000-1500 rpm, the stirring time after the dropwise addition is continued for 10-30 minutes, and the standing time is 12-24 hours.

5. A carbon-coated manganese-cobalt-carbon composite material prepared by the preparation method according to any one of claims 1 to 4.

6. An application of the carbon-coated manganese-cobalt-carbon composite material according to claim 5, characterized in that: Used as positive electrode active material for aqueous zinc ion batteries.

7. An aqueous zinc ion battery, characterized in that: The carbon-coated manganese-cobalt-carbon composite material according to claim 5 is used as the positive electrode active material.

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