Conductive metal compound coated hard carbon and preparation method and application thereof

Abstract

The invention relates to conductive metal compound coated hard carbon as well as a preparation method and application thereof, and belongs to the technical field of new materials. Aiming at the technical problems of low initial coulombic efficiency (80-85%) and obvious capacity attenuation of the existing hard carbon material, and too high cost caused by complex traditional surface modification process, the invention provides a technical scheme for constructing a conductive metal compound coating layer on the hard carbon surface. The core-shell composite structure material with a hard carbon core / metal oxide shell is prepared by dispersing metal salts such as nickel salt and iron salt with hard carbon through a solvent and combining a chemical reaction with a calcining process. The technology realizes triple beneficial effects that (1) the first effect is obviously improved to 90-93%, (2) the 1000-time circulation capacity retention rate under 300mA / g reaches 92-94%, and (3) through reaction reagent system innovation and two-step process optimization, the advantage of low cost of raw materials is maintained, and meanwhile, the composite coating process flow is obviously shortened. The material can be widely applied to the field of manufacturing of high-performance ion battery negative electrodes, and has remarkable industrial popularization and application values.

Description

Technical Field

[0001] The present invention belongs to the technical field of new materials, and relates to hard carbon coated with a conductive metal compound, and a preparation method and application thereof. Background Art

[0002] As a green and environmentally friendly energy storage device, lithium-ion batteries have been widely used in energy storage fields such as the electronics market and new energy vehicles due to their outstanding advantages such as high energy density, long cycle life, safety and no pollution, greatly improving the production and living standards of mankind. However, due to the scarcity of lithium resources, their high cost and extremely uneven distribution have greatly restricted the further application of lithium-ion batteries in large-scale energy storage systems. Sodium-ion batteries have attracted wide attention due to the abundance, low price and wide distribution of sodium resources, and are expected to become substitutes for lithium-ion batteries.

[0003] Although sodium-ion batteries have significant advantages, the development of their negative electrode materials still faces problems such as poor kinetic performance, significant volume expansion, insufficient capacity and initial efficiency, and unstable interfaces. As one of the negative electrode materials for sodium-ion batteries, hard carbon has become a research hotspot for negative electrode materials for sodium-ion batteries due to its high capacity, structural stability and low cost. However, due to the consumption of irreversible sodium ions and the formation of solid electrolyte interfaces during the cycling process, the loss of active sodium ions leads to a low initial efficiency. Although the hard carbon structure is relatively stable, under high-rate or long-cycle conditions, certain volume expansion may still occur, resulting in poor cycling performance. In addition, due to the continuous formation and decomposition of the solid electrolyte interface, the cycling stability is further deteriorated.

[0004] To solve the problems of low initial efficiency and poor cycling stability, a large amount of work has been carried out and effective results have been achieved. Among them, surface engineering is favored because it can directly improve the physical and chemical properties of the material surface by modifying the original surface or constructing a new interface. By surface engineering modification of hard carbon materials, the active sites on their surfaces can be reduced, the occurrence of unknown side reactions and the decomposition of electrolytes can be inhibited, the consumption of irreversible sodium can be reduced, and a thinner and more stable solid electrolyte interface can be formed, effectively improving the initial efficiency and cycling stability. Although general surface engineering greatly improves the initial efficiency, it also leads to a significant reduction in capacity.

[0005] Balancing the first-cycle efficiency and sodium storage performance is very challenging in the surface engineering of hard carbon. Chinese invention patent CN118495505A discloses a preparation method of a coated hard carbon material and a negative electrode of a sodium-ion battery. This technical solution obtains a hard carbon material with an alumina coating layer, but alumina is an insulating metal compound. Chinese invention patent CN 114420938A discloses a metal oxide amorphous carbon-coated hard carbon composite material, its preparation method, application and process. In this technical solution, an amorphous carbon material doped with a metal is coated on the surface of a hard carbon material doped with phosphorus, but its outer layer is not entirely a metal oxide. Chinese invention patent CN113889625B discloses a modified hard carbon composite material, its preparation method and application. This technical solution coats titanium carbide and amorphous carbon on the surface of hard carbon, but part of the rare earth element cerium is doped in the outer layer titanium carbide, resulting in an increase in material cost and defects, and an increase in the consumption of irreversible ions.

[0006] Therefore, a metal oxide or other conductive metal compound with high conductivity and low cost is coated on the surface of the hard carbon negative electrode to improve the conductivity of the carbon material and enhance the sodium ion storage kinetics, and at the same time reduce the surface defects of the hard carbon material through it, thereby improving the first-cycle efficiency and cycle stability of the material. Summary of the Invention

[0007] In view of this, one of the purposes of the present invention is to provide a hard carbon coated with a conductive metal compound, the second purpose is to provide a preparation method of a hard carbon coated with a conductive metal compound, and the third purpose is the application of a hard carbon coated with a conductive metal compound in the preparation of a battery negative electrode sheet.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] The present invention provides a hard carbon coated with a conductive metal compound. One or several of a metal oxide, metal carbide, metal sulfide, and metal nitride with good conductivity are coated on the outer surface of the hard carbon. The metal is one or several of nickel, iron, manganese, cobalt, and zinc. The hard carbon is one or several of biomass hard carbon, pitch-based hard carbon, and polymer-based hard carbon;

[0010] Furthermore, for the preparation method of a hard carbon coated with a conductive metal compound, the preparation steps are as follows:

[0011] S1. Add a conductive metal compound and hard carbon to a solvent, and add a reaction reagent and stir at room temperature for 30-50 minutes to obtain a suspension precursor. React the suspension precursor fully to obtain a suspension of the reaction product;

[0012] S2. Dry or filter and dry the suspension to obtain a powder;

[0013] S3. Calcinate the powder. The content of the conductive metal compound in the powder is 1-5 wt%, and cool to obtain the hard carbon coated with the conductive metal compound.

[0014] Preferably, the mass ratio of the hard carbon, conductive metal compound, and reaction reagent in step S1 is 100:(4-10):(10-40).

[0015] Preferably, the hard carbon in step S1 is one or more of biomass hard carbon, pitch-based hard carbon, and polymer-based hard carbon.

[0016] Preferably, the conductive metal compound in step S1 is one or more of oxides, nitrides, sulfides, and carbides of nickel, iron, manganese, cobalt, and zinc.

[0017] Preferably, the solvent in step S1 is one or more of secondary water, methanol, acetone, ethanol, and isopropanol, and the volume of the solvent is 100 ml.

[0018] Preferably, the reaction reagent in step S1 is one or more of a precipitating agent, a binder, and a ligand reagent.

[0019] Preferably, the precipitating agent is one or more of urea, ammonium chloride, and ammonia water; the binder is one or more of polyacrylic acid and polyvinyl alcohol; the ligand reagent is one or more of 2-methylimidazole, 2-aminoimidazole, and 2-carboxyimidazole.

[0020] Preferably, the reaction in step S1 is one or more of a hydrothermal reaction, a thermal evaporation reaction, a precipitation reaction, and a coordination self-assembly reaction; the reaction product is one or more of a hydrothermal product, a thermal evaporation product, a precipitation product, and a ligand self-assembly product.

[0021] Preferably, the temperature of the hydrothermal reaction in the reaction in step S1 is 120-180 °C, the heating rate is 1-10 °C per minute, keep the temperature for 4-6 hours, and cool to room temperature; the temperature of the thermal evaporation reaction in the reaction is 80-100 °C, the stirring rate is 500-600 r / min until the solvent is evaporated to dryness.

[0022] Preferably, the temperature of the precipitation reaction in the reaction in step S1 is 40-80 °C, the stirring rate is 300-400 r / min, and the stirring time is 1-2 hours; the temperature of the ligand self-assembly reaction in the reaction is room temperature, the stirring rate is 200-300 r / min, and the stirring time is 3-4 hours.

[0023] Preferably, the drying condition in step S2 is 60-100 °C, and the heat preservation time is 8-12 hours; the powder needs to be ground sufficiently in an agate mortar and transferred to a porcelain boat.

[0024] Preferably, the ambient atmosphere for the calcination treatment in step S3 is one or more of argon, nitrogen, and air, the reaction temperature is 400 - 800 °C, the heating rate is 5 - 10 °C per minute, and the holding time is 3 - 5 hours. When the conductive metal compound is a metal nitride, one or more of urea, melamine, and ammonium chloride are added during calcination; when the conductive metal compound is a metal sulfide, one or more of sulfur powder and thiourea are added during calcination; when the conductive metal compound is a metal carbide, the temperature is controlled at 900 - 1500 °C during calcination; cooling to room temperature gives hard carbon coated with a conductive metal compound, where the hard carbon is in the inner layer and the conductive metal compound is in the outer layer;

[0025] Furthermore, the application of the hard carbon coated with a conductive metal compound in the preparation of a battery negative electrode sheet;

[0026] Preferably, the application of the hard carbon coated with a conductive metal compound in the preparation of negative electrode sheets for sodium and lithium-ion batteries.

[0027] The beneficial effects of the present invention are as follows:

[0028] The hard carbon coated with a conductive metal compound prepared by the present invention obtains a negative electrode material with hard carbon in the inner layer and a conductive metal compound in the outer layer. Compared with the original hard carbon, the electrochemical performance of the hard carbon coated with a conductive metal compound is significantly improved, specifically manifested in the initial efficiency and cycle stability. Since the conductive metal compound is coated on the surface of the hard carbon, the surface active sites are reduced, and the formed solid electrolyte interface is thinner, stronger, and more stable, with both high ionic conductivity and interface compatibility with the hard carbon.

[0029] Synergistic performance improvement: It promotes the initial efficiency to increase from the original 80 - 85% to 90 - 93%, and at the same time, the capacity retention rate after cycling 1000 times at a current density of 300 mA / g increases from the original 85 - 88% to 92 - 94%, without sacrificing the high rate performance of the hard carbon.

[0030] Interface optimization: By reducing the surface active sites and forming a thinner and more stable SEI layer, irreversible sodium consumption and side reactions are inhibited, while capacity loss is avoided.

[0031] Process simplification: The present invention prepares a negative electrode material for a sodium-ion battery with a higher initial efficiency and better cycle stability through two simple steps, only requiring two reactions of hydrothermal + calcination. The raw materials required are abundant and the cost is low, suitable for large-scale production. The raw material cost is low (such as using easily available chemicals such as nickel nitrate and urea), suitable for industrial production, and is more feasible compared to complex composite coating processes (such as doping + coating).

[0032] Other advantages, objects, and features of the present invention will be set forth in part in the following description, and in part will be obvious to those skilled in the art upon examination of the following, or may be learned from the practice of the present invention. The objects and other advantages of the present invention may be realized and obtained by the following description. Brief Description of the Drawings

[0033] In order to make the objects, technical solutions, and advantages of the present invention clearer, the present invention will be described in detail preferably with reference to the accompanying drawings, where:

[0034] Figure 1 is the XRD pattern of the materials shown in Comparative Example 1 and Example 1;

[0035] Figure 2 is the comparison chart of the first charge-discharge curves of the materials shown in Comparative Example 1 and Example 1 (current density 30 mA / g);

[0036] Figure 3 is the comparison chart of the capacity cycles of the materials shown in Comparative Example 1 and Example 1 (current density 300 mA / g);

[0037] Figure 4 is the scanning electron microscope image of the material shown in Example 1 after 1 cycle;

[0038] Figure 5 is the scanning electron microscope image of the material shown in Comparative Example 1 after 1 cycle;

[0039] Figure 6 is a schematic diagram of nickel oxide coated on the surface of hard carbon and forming a thinner and more stable solid electrolyte interface and a thicker electrolyte interface formed by untreated hard carbon. Detailed Description of the Embodiments

[0040] The following specific examples illustrate the embodiments of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. The details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the drawings provided in the following examples only illustrate the basic concept of the present invention schematically. Without conflict, the following examples and the features in the examples can be combined with each other.

[0041] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0042] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0043] The purity of nickel nitrate hexahydrate, hard carbon, urea and ammonium chloride used in the following examples and comparative examples is not less than 97%.

[0044] Example 1

[0045] This embodiment discloses a method for preparing nickel oxide-coated hard carbon, and the specific steps are as follows:

[0046] S1. Mix hard carbon, nickel nitrate hexahydrate, urea and ammonium chloride in a mass ratio of 100:7:15:15, add 100 ml of secondary water, stir at room temperature for 30 minutes to obtain a suspension precursor of the reaction product; put the suspension precursor of the reaction product into the inner elixir of a reactor with a volume of 100 ml, put the inner elixir into the reactor, tighten it and transfer it to an oven for hydrothermal reaction, the reaction temperature is 120°C, the heating rate is 1-10°C per minute, keep warm for 4 hours, and cool to room temperature to obtain a suspension of the hydrothermal product;

[0047] S2. After filtering the suspension of the hydrothermal product, the hydrothermal product was obtained, and placed in an oven at 60° C. and dried for 12 hours to obtain a dry powder.

[0048] S3. Grind the powder in an agate mortar thoroughly, transfer it to a porcelain boat, and calcine it in an argon atmosphere at a reaction temperature of 600°C and a heating rate of 5°C per minute. Keep the temperature for 3 hours and cool it to room temperature to obtain metal oxide-coated hard carbon.

[0049] Example:

[0050]

[0051]

[0052]

[0053] Comparative Example 1

[0054] Source of ordinary activated hard carbon: Kureha hard carbon type1 purchased from Taobao.

[0055] The materials of Example 1 and Comparative Example 1 were respectively subjected to X-ray diffraction analysis, and the results are as Figure 1 shown.

[0056] Preparation of the negative electrode sheet of the battery in Example 9

[0057] Preparation of the negative electrode sheet of the lithium-ion battery. The specific method is as follows:

[0058] The hard carbon material coated with nickel oxide prepared in Example 1 and the activated hard carbon described in Comparative Example 1 were respectively mixed with sodium alginate as a binder at a mass ratio of 9:1, an appropriate amount of secondary water was added, and the mixture was homogenized in a homogenizer. Then, the slurry was uniformly coated on the current collector copper foil and dried in a vacuum oven at 100 °C for 12 hours, and then transferred to a glove box for standby. The battery was assembled in a glove box under an argon atmosphere. A sodium metal sheet was used as the counter electrode, a 1M NaPF6 / DME (dimethyl glycol ether) solution was used as the electrolyte, and PP (polypropylene) was used as the separator to assemble a button battery.

[0059] Performance test of Example 10

[0060] The button batteries with the materials of Example 1 and Comparative Example 1 as the negative electrode sheets were respectively cycled 1 time at a current density of 30 mA / g, and the charge-discharge curve results are as Figure 2 shown: It can be seen from Figure 2 that the initial Coulomb efficiency of Example 1 was improved from 83.54% to 92.05% compared with that of the comparative example.

[0061] The button batteries with the materials of Example 1 and Comparative Example 1 as the negative electrode sheets were respectively cycled 1000 times at a current density of 300 mA / g, and the cyclic performance test results are as Figure 3 shown: It can be seen from Figure 3 that the capacity retention rate of Example 1 was improved from 87.24% to 92.75% compared with that of Comparative Example 1.

[0062] After the button batteries with the materials of Example 1 and Comparative Example 1 as the negative electrode sheets were cycled 1 time at a current density of 30 mA / g, the batteries were disassembled in a glove box under an argon atmosphere, the active material on the current collector was scraped off, and the obtained materials were subjected to scanning electron microscope imaging detection, and the detection images of Figure 4 and Figure 5 were respectively obtained.Figure 4 The image processed in Example 1 Figure 5 The image processed in Comparative Example 1 Figure 4 and Figure 5 It can be seen from the comparison that the solid electrolyte in Example 1 is thinner and has better strength than that in Comparative Example 1

[0063] It can be seen from the comparison of the above data that the hard carbon coated with nickel oxide has better electrochemical performance than the untreated hard carbon, especially in terms of better initial efficiency and cycle stability, and the formed solid electrolyte interface is thinner and has better strength Figure 6 It is a schematic diagram of nickel oxide coated on the surface of hard carbon to form a thinner and more stable solid electrolyte interface and the thicker electrolyte interface formed by the untreated hard carbon

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the present technical solution, and they should all be covered within the scope of the claims of the present invention

Claims

1. Hard carbon coated with a conductive metal compound, characterized in that: The outer surface of the hard carbon is coated with one or more of metal oxides, metal carbides, metal sulfides, and metal nitrides. The metal is one or more of nickel, iron, manganese, cobalt, and zinc. The hard carbon is one or more of biomass hard carbon, pitch-based hard carbon, and polymer-based hard carbon.

2. The preparation method of the hard carbon coated with the conductive metal compound according to claim 1, characterized in that, The preparation steps are as follows: S1. Add a conductive metal compound precursor and hard carbon into a solvent, and add a reaction reagent, then stir at room temperature for 30 - 50 minutes to obtain a suspension precursor. React the suspension precursor sufficiently to obtain a suspension of reaction products. S2. Dry or filter and dry the suspension to obtain a powder. S3. Calcinate the powder. The content of the conductive metal compound in the powder is 1 - 5 wt%, and cool to obtain the hard carbon coated with the conductive metal compound.

3. The preparation method of the hard carbon coated with the conductive metal compound according to claim 2, wherein: In step S1, the mass ratio of the hard carbon, conductive metal compound precursor, and reaction reagent is 100:(4 - 10):(10 - 40).

4. The preparation method of the hard carbon coated with the conductive metal compound according to claim 2, wherein: The solvent in step S1 is one or more of secondary water, methanol, acetone, ethanol, and isopropanol, and the volume of the solvent is 100 mL. The reaction reagent in step S1 is one or more of a precipitating agent, a binder, and a ligand reagent. The precipitating agent is one or more of urea, ammonium chloride, and ammonia water. The binder is one or more of polyacrylic acid and polyvinyl alcohol. The ligand reagent is one or more of 2-methylimidazole, 2-aminoimidazole, and 2-carboxyimidazole.

5. The preparation method of the hard carbon coated with the conductive metal compound according to claim 2, wherein: The reaction in step S1 is one or more of a hydrothermal reaction, a thermal evaporation reaction, a precipitation reaction, and a coordination self-assembly reaction. The reaction product is one or more of a hydrothermal product, a thermal evaporation product, a precipitation product, and a ligand self-assembly product.

6. The preparation method of the hard carbon coated with the conductive metal compound according to claim 2, characterized in that: In the hydrothermal reaction in step S1, the temperature is 120 - 180 °C, the heating rate is 1 - 10 °C per minute, keep the temperature for 4 - 6 hours, and cool to room temperature. In the thermal evaporation reaction in step S1, the temperature is 80 - 100 °C, the stirring rate is 500 - 600 r / min until the solvent is evaporated to dryness. In the precipitation reaction in step S1, the temperature is 40 - 80 °C, the stirring rate is 300 - 400 r / min, and the stirring time is 1 - 2 hours. In the ligand self-assembly reaction in step S1, the temperature is room temperature, the stirring rate is 200 - 300 r / min, and the stirring time is 3 - 4 hours.

7. The preparation method of the hard carbon coated with the conductive metal compound according to claim 2, wherein: The drying conditions in step S2 are 60 - 100 °C, and the holding time is 8 - 12 hours. The powder needs to be ground sufficiently in an agate mortar and transferred to a porcelain boat.

8. The preparation method of the hard carbon coated with the conductive metal compound according to claim 2, wherein: The ambient atmosphere for the calcination treatment of the powder described in step S3 is one or more of argon, nitrogen, and air, the reaction temperature is 400 - 800 °C, the heating rate is 5 - 10 °C per minute, and the heat preservation is 3 - 5 hours; when the conductive metal compound is a metal nitride, one or more of urea, melamine, and ammonium chloride are also added during calcination; when the conductive metal compound is a metal sulfide, one or more of sulfur powder and thiourea are also added during calcination; when the conductive metal compound is a metal carbide, the temperature is controlled at 900 - 1500 °C during calcination; after cooling to room temperature, hard carbon coated with a conductive metal compound is obtained, where the hard carbon is in the inner layer and the conductive metal compound is in the outer layer.

9. Application of the hard carbon coated with the conductive metal compound according to claim 1 in the preparation of a battery negative electrode sheet.

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