A hard carbon composite material, a preparation method thereof, an electrode sheet, a battery, and an electric device

Abstract

The application provides a hard carbon composite material and a preparation method, an electrode sheet, a battery and an electric device, and the hard carbon composite material comprises: a hard carbon inner core, a first coating layer arranged on at least part of the surface of the hard carbon inner core, and a second coating layer arranged on at least part of the surface of the first coating layer; the first coating layer comprises soft carbon, and the second coating layer comprises a nitrogen-containing conductive polymer. The hard carbon composite material is designed in a three-layer structure: the inner core hard carbon, the first coating layer and the second coating layer, so that the capacity, the initial efficiency and the rate performance of the sodium ion battery negative electrode material are synergistically optimized.

Description

Technical Field

[0001] This invention relates to the field of battery materials, and more particularly to a hard carbon composite material and its preparation method, electrode sheet, battery, and electrical equipment. Background Technology

[0002] With the advancement of global energy structure transformation goals, large-scale electrochemical energy storage systems have become a core technology supporting the consumption of renewable energy (such as photovoltaic and wind power) and the construction of smart grids. Sodium-ion batteries, due to their abundant sodium resources, low cost, and environmental friendliness, are widely used in energy storage power stations, low-speed electric vehicles, and power tools. Among them, hard carbon composite materials, with their unique disordered layered structure and abundant nanopores, can provide high sodium storage capacity and excellent rate performance, making them the most commercially promising anode material for sodium-ion batteries.

[0003] However, the hard carbon composite materials used in commercially available sodium-ion batteries currently have defects such as low specific capacity, low initial efficiency, and poor electronic conductivity. Summary of the Invention

[0004] This invention provides a hard carbon composite material, which achieves synergistic optimization of capacity, initial efficiency, and rate performance of sodium-ion battery anode materials through a three-layer structure design: a hard carbon core, a first coating layer, and a second coating layer.

[0005] The present invention also provides a method for preparing the above-mentioned hard carbon composite material, which can prepare the above-mentioned hard carbon composite material and the process is simple.

[0006] The present invention also provides an electrode sheet, which, because it comprises the aforementioned hard carbon composite material, helps to improve the capacity, first-efficiency and rate performance of sodium-ion batteries.

[0007] The present invention also provides a battery that, because it includes the above-mentioned electrode plates, has the characteristics of high capacity, high initial efficiency and high rate performance.

[0008] The present invention also provides an electrical device that, since it includes the aforementioned battery, has high energy output and long service life.

[0009] In a first aspect, the present invention provides a hard carbon composite material comprising: a hard carbon core, a first coating layer disposed on at least a portion of the surface of the hard carbon core, and a second coating layer disposed on at least a portion of the surface of the first coating layer; the first coating layer comprises soft carbon, and the second coating layer comprises a nitrogen-containing conductive polymer.

[0010] Optionally, the nitrogen content of the nitrogen-containing conductive polymer is greater than or equal to 15% by weight.

[0011] Optionally, the nitrogen content of the nitrogen-containing conductive polymer is greater than or equal to 60%;

[0012] And / or, by mass, the carbon content of the hard carbon core is greater than or equal to 95%;

[0013] And / or, by mass, the carbon content of the first coating layer is greater than or equal to 95%.

[0014] Optionally, the hard carbon composite material includes a closed-cell structure with a pore volume of 0.02 cm³. 3 / g-0.1 cm 3 / g.

[0015] Optionally, the average size of the hard carbon core is 2μm-20μm;

[0016] And / or, the average thickness of the first coating layer is 10nm-40nm;

[0017] And / or, the average thickness of the second coating layer is 5nm-40nm.

[0018] Optionally, the specific surface area of ​​the hard carbon composite material is 0.8 m² / g-25 m² / g;

[0019] Preferably, the nitrogen-containing conductive polymer comprises polymelamine and / or polypyrrole;

[0020] Preferably, the nitrogen content in the hard carbon composite material is 3%-7% by weight.

[0021] Secondly, the present invention provides a method for preparing hard carbon composite materials, comprising the following steps:

[0022] Provides a hard carbon core;

[0023] The hard carbon core and the soft carbon precursor are mixed and sintered to obtain a hard carbon core with a first coating layer.

[0024] A mixture comprising a hard carbon core with a first coating layer, a nitrogen-containing conductive polymer monomer, and a solvent is subjected to a polymerization reaction to form a second coating layer on one side of the first coating layer, thereby obtaining the hard carbon composite material.

[0025] Optionally, the hard carbon core is prepared by the following process:

[0026] The hard carbon precursor is activated, pore-forming, and subjected to a first calcination treatment to obtain the hard carbon core.

[0027] Optionally, the hard carbon precursor includes at least one of bamboo, coconut shell, wood chips, and straw;

[0028] Preferably, the activation treatment is performed at a temperature of 400℃-600℃ for 4-6 hours.

[0029] Preferably, the pore-forming treatment includes: introducing steam for a second calcination treatment, the second calcination temperature being 650℃-1250℃; and the time being 4h-8h; preferably, the steam flow rate is 4 mL / min / g. 硬碳前驱体 -15 mL / min / g 硬碳前驱体 ;

[0030] Preferably, the temperature of the first calcination treatment is 1000℃-1500℃, and the time is 0.5h-7h;

[0031] Preferably, the first calcination treatment is followed by an acid washing treatment.

[0032] Optionally, the sintering treatment is performed at a temperature of 1000℃-1500℃ for 1 hour to 7 hours.

[0033] And / or, the polymerization reaction is carried out at a constant potential voltage, preferably 4V-12V.

[0034] Optionally, the mixture further includes an acid solution and a metal salt; preferably, the metal salt includes potassium chloride.

[0035] Optionally, the mass concentration ratio of the melamine monomer, acid solution, and metal salt is 0.5-1:0.05-0.06:0.1-0.2;

[0036] And / or, the soft carbon precursor includes at least one of pitch, petroleum coke, and coal tar;

[0037] And / or, the nitrogen-containing conductive polymer monomer includes melamine monomer and / or pyrrole monomer;

[0038] And / or, the soft carbon precursor is 5%-15% of the mass of the hard carbon core.

[0039] Thirdly, the present invention provides an electrode sheet comprising a current collector and an active material layer coated on at least one side of the current collector, wherein the active material layer comprises a hard carbon composite material of the first aspect or a hard carbon composite material prepared by the preparation method of the second aspect.

[0040] Fourthly, the present invention provides a battery comprising the electrode sheet described in the third aspect.

[0041] In one possible implementation, the battery is a sodium-ion battery, and the electrode sheet is a negative electrode sheet.

[0042] Fifthly, the present invention provides an electrical device comprising a hard carbon composite material of the first aspect, a hard carbon composite material prepared by the preparation method of the second aspect, an electrode sheet as described in the third aspect, or a battery as described in the fourth aspect.

[0043] The hard carbon composite material provided by this invention has a three-layer structure design: the hard carbon core provides sodium storage sites, the first coating layer modifies defects, and the second coating layer improves conductivity and nitrogen doping, so as to realize the synergistic effect of each layer structure and provide a solution for sodium-ion battery anode materials with high capacity, high initial efficiency and high rate performance. Attached Figure Description

[0044] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0045] Figure 1 The charge / discharge capacity curves of the battery prepared from the hard carbon composite material of Example 1.

[0046] Figure 2 This is a SEM image of the hard carbon composite material from Example 1.

[0047] Figure 3 This is a TEM image of the hard carbon composite material from Example 1. Detailed Implementation

[0048] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0049] In this application, the terms "first" and "second" are used for descriptive purposes only, to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. For example, without departing from the scope of the embodiments of this application, "first XX" may also be referred to as "second XX," and similarly, "second XX" may also be referred to as "first XX." Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of that feature.

[0050] In this application, references to "an embodiment," "an example," or "an example" mean that a specific feature, structure, or characteristic described in connection with that embodiment, example, or example is included in at least one embodiment of the invention. Therefore, the phrases "an embodiment," "an example," "an example," "an example," or "an example" appearing in various places throughout the specification do not necessarily refer to the same embodiment or example. Furthermore, specific features, structures, or characteristics can be combined in one or more embodiments or examples in any suitable combination and / or sub-combination.

[0051] The high capacity of sodium-ion battery hard carbon anode materials requires a large number of closed micropores. Therefore, the hard carbon precursor needs to undergo pore-forming pretreatment. Pore-forming pretreatment will result in a large specific surface area and high surface defects in the product. Excessive surface defects will result in a low first efficiency of the product. High rate capability requires the hard carbon product to have high ramp capacity and good conductivity. Currently used coatings such as asphalt and acetylene cannot effectively improve the conductivity of the product, resulting in poor rate performance of hard carbon anode materials.

[0052] To develop a hard carbon composite material that combines high capacity, high initial efficiency, and high rate capability, the present invention adopts the following technical solution:

[0053] In a first aspect, the present invention provides a hard carbon composite material, comprising: a hard carbon core, a first coating layer disposed on at least a portion of the surface of the hard carbon core, and a second coating layer disposed on at least a portion of the surface of the first coating layer; the first coating layer comprises soft carbon, and the second coating layer comprises a nitrogen-containing conductive polymer.

[0054] This invention provides a solution for sodium-ion battery anode materials that combines high capacity, high initial efficiency, and high rate performance through a three-layer structure design consisting of a hard carbon core, a first coating layer, and a second coating layer. The main reasons are: the hard carbon core, with its abundant closed-pore structure, provides sodium storage sites, thereby enhancing the high capacity performance of the hard carbon composite material; the first coating layer, comprising soft carbon, modifies the pore-forming defects of the hard carbon core, thus improving the initial efficiency performance of the hard carbon composite material; and the second coating layer, comprising a nitrogen-containing conductive polymer, allows the lone pair electrons of nitrogen atoms to alter the electron cloud density of surrounding carbon atoms, making them more conducive to binding with sodium ions, thereby enhancing the insertion / extraction reaction and improving the material's conductivity and nitrogen doping level, thus improving the high rate performance of the hard carbon composite material.

[0055] In summary, the hard carbon composite material of the present invention combines high capacity, high initial efficiency, and high rate capability, and can be used to develop high-performance fast-charging and fast-discharging cell systems based on sodium-ion batteries.

[0056] In some embodiments, the structure of the hard carbon composite material can be characterized by the following methods:

[0057] 1) First, use XPS to detect nitrogen on the outer surface and analyze its chemical state to confirm the existence of the second coating layer;

[0058] 2) Focused ion beam (FIB) was used to acquire cross-sectional samples of hard carbon composite materials. Starting from the second outermost coating layer, the laser spot of the Raman spectrometer was moved from the outside to the inside, traversing the second coating layer, the first coating layer, and finally to the hard carbon core. The intensity ratio (Ig) of the D peak to the G peak was used to determine the cross-sectional area. d / I g Analysis, I d / I g A thickness of 1.4 or less constitutes the first coating layer, while a thickness greater than 1.4 constitutes the hard carbon core.

[0059] Among them, the above Id / I g I in d The D band (approximately 1350 cm) represents the hard carbon composite material in Raman testing. -1 The peak intensity of I g The G-band (approximately 1580 cm) representing hard carbon composites in Raman testing -1 The ratio of the peak intensities of the two peaks is I. d / I g .

[0060] Using a nitrogen-containing conductive polymer as a second coating layer can improve the electrical conductivity and nitrogen doping of hard carbon composite materials, enabling the material to exhibit high rate performance. In some alternative embodiments, the nitrogen content of the nitrogen-containing conductive polymer is greater than or equal to 15% by mass.

[0061] To further improve the electrical conductivity and nitrogen doping of hard carbon composite materials, in some optional embodiments, the nitrogen content of the nitrogen-containing conductive polymer is greater than or equal to 60% by mass.

[0062] The nitrogen content of the nitrogen-containing conductive polymer can be obtained by detecting it using a CHNOS elemental analyzer.

[0063] For example, the nitrogen content of the nitrogen-containing conductive polymer is any value or a range of any two of the following: 15%, 17%, 19%, 60%, 62%, 65%, 67%, 70%, 72%, 75%, 77%, 80%, 82%, 85%, 87%, 90%.

[0064] In some alternative embodiments, the carbon content of the hard carbon core is greater than or equal to 95% by weight. Among them, the core with a carbon content of ≥95% has high hardness and mechanical strength due to its short-range ordered graphitized microcrystalline structure, which can extend the cycle life of the battery in battery anode applications.

[0065] For example, the carbon content of the hard carbon core is any value or a range of any two of the following: 95%, 96%, 97%, 98%, 99%, 100%.

[0066] In some alternative embodiments, the carbon content of the first coating layer is greater than or equal to 95% by weight. A first coating layer with a carbon content of ≥95% has lower resistivity, which is beneficial for the rapid insertion / extraction of sodium ions, thereby further ensuring the rate performance of the battery.

[0067] For example, the carbon content of the first coating layer is any value or a range of any two of 95%, 96%, 97%, 98%, 99%, 100%.

[0068] In some alternative embodiments, the hard carbon composite material includes a closed-cell structure with a pore volume of 0.02 cm³. 3 / g-0.1 cm 3 / g.

[0069] This pore volume ensures that the core has a rich closed-pore structure, thereby further enhancing the high-capacity performance of hard carbon composites.

[0070] The pore volume of a closed cell can be calculated from its true density, using the following formula:

[0071] .

[0072] The true density value was determined using a quantum helium true density tester according to the specifications in GB / T 24203-2024.

[0073] In some alternative embodiments, the nitrogen-containing polymer includes polymelamine and / or polypyrrole.

[0074] The high nitrogen content and lone pair electron structure of polymelamine can further promote the rapid adsorption and insertion of sodium ions, significantly enhancing the rate performance of the battery. Simultaneously, the conductivity of polymelamine further reduces interfacial impedance, further improving electrochemical stability.

[0075] The structure of polymelamine is shown in Formula 1:

[0076] Formula 1,

[0077] Where n > 300.

[0078] In some alternative implementations, the average size of the hard carbon core is 2 μm-20 μm.

[0079] Among them, the average size of the hard carbon core is within the above range, which makes the hard carbon composite material have a more complete bulk structure, making it less prone to agglomeration during cycling and exhibiting excellent overall structural stability.

[0080] For example, the average size of the hard carbon core is any value or a range of any two of the following: 2μm, 4μm, 6μm, 8μm, 10μm, 12μm, 14μm, 16μm, 18μm, 20μm.

[0081] The morphology of hard carbon cores includes, but is not limited to, spheres, irregular particles, cubic particles, etc. The average size refers to the average of the maximum sizes of multiple hard carbon cores. For example, the testing method includes: randomly selecting at least 50 hard carbon composite materials in the TEM image of hard carbon composite materials, measuring and recording the maximum size of the hard carbon core of each hard carbon composite material particle, and summing and averaging the values ​​to obtain the average size of the hard carbon core.

[0082] In some alternative embodiments, the average thickness of the first coating layer is 10 nm to 40 nm.

[0083] The thickness of the first coating layer within the above range can form a three-dimensional conductive network on the core surface, further improving the transport efficiency of electrons from the insulating / semiconductor hard carbon core to the second coating layer. In addition, the soft carbon first coating layer usually has a certain degree of toughness and plasticity, which can serve as a stress buffer layer. During charging and discharging, the core will expand / contract in volume. The first coating layer can effectively absorb and disperse stress, preventing the second coating layer from brittlely cracking, thereby further ensuring the improved cycle stability of the battery.

[0084] For example, the average thickness of the first coating layer is any value or a range of any two of the following: 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, etc.

[0085] In some alternative implementations, the average thickness of the second coating layer is 5 nm to 50 nm.

[0086] The above embodiments control the average thickness of the second coating layer to 1nm-50nm, achieving a balance between protecting the first coating layer and further promoting the rapid adsorption and insertion of sodium ions, thereby enabling the battery to balance rate performance and electrochemical stability.

[0087] For example, the average thickness of the second coating layer is any value or a range of any two of the following: 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm.

[0088] In some implementations, the size of the hard carbon core, the average thickness of the first coating layer, and the average thickness of the second coating layer can be measured by TEM analysis.

[0089] A larger specific surface area of ​​the hard carbon composite material provides more reaction sites and a larger contact area with the electrolyte, leading to more side reactions, the formation of a thicker SEI film, and thus the consumption of more active sodium. This results in a sharp drop in the first-cycle coulombic efficiency. In some optional embodiments, the specific surface area of ​​the hard carbon composite material is 0.8 m² / g-25 m² / g. Controlling the specific surface area within 0.8 m² / g-25 m² / g reduces the active sites available for side reactions, limiting the amount of SEI film formation at its source. This allows for more reversible insertion and extraction of sodium ions, thereby improving the first-cycle efficiency.

[0090] For example, the specific surface area of ​​the hard carbon composite material is any value or a range of any two of the following: 25 m² / g, 20 m² / g, 15 m² / g, 10 m² / g, 5 m² / g, 2.5 m² / g, 2 m² / g, 1.5 m² / g, 1 m² / g, 0.8 m² / g.

[0091] In some alternative embodiments, the nitrogen content in the hard carbon composite material is 3%-7% by weight.

[0092] Within the aforementioned range, the total nitrogen content can introduce a sufficient number of active sites to improve capacity and conductivity while ensuring the relative stability of the carbon framework structure is avoided. This balances the conductivity and stability of hard carbon composite materials.

[0093] Secondly, the present invention provides a method for preparing hard carbon composite materials, comprising the following steps:

[0094] Provides a hard carbon core;

[0095] Hard carbon core and soft carbon precursor are mixed and sintered to obtain hard carbon core with a first coating layer.

[0096] A mixture comprising a hard carbon core with a first coating layer, a nitrogen-containing conductive polymer monomer, and a solvent is subjected to a polymerization reaction to form a second coating layer on one side of the first coating layer, thereby obtaining a hard carbon composite material.

[0097] The above preparation method involves mixing a hard carbon core and a soft carbon precursor, followed by sintering to ensure the pores of the hard carbon core are sealed and the structure is stabilized, thus ensuring the high capacity characteristics of the core. Sintering can also modify surface defects of the hard carbon, reduce the specific surface area, and improve the first efficiency. It also ensures that the first coating layer is uniform and dense. Finally, a second coating layer is formed through in-situ polymerization, which further reduces the specific surface area of ​​the hard carbon composite material. At the same time, the high nitrogen content and conductivity of the second coating layer can further enhance the electrical conductivity of the hard carbon composite material, and the lone pair electron structure of nitrogen can promote the rapid adsorption and insertion of sodium ions, thereby achieving high rate performance of the hard carbon composite material.

[0098] In some alternative embodiments, the hard carbon core is prepared by the following process:

[0099] The hard carbon precursor is activated, pore-forming, and subjected to a first calcination treatment to obtain a hard carbon core.

[0100] Hard carbon precursors undergo activation and pore-forming treatments to create a porous structure, providing sites for sodium storage.

[0101] To further ensure the stability, low specific surface area, and low cost of hard carbon composite materials, hard carbon precursors include at least one of bamboo, coconut shell, wood chips, and straw.

[0102] To further ensure the conductivity, stability, and low specific surface area of ​​the hard carbon composite material, in some alternative embodiments, the soft carbon precursor includes at least one of pitch, petroleum coke, and coal tar.

[0103] In some alternative embodiments, the activation treatment is carried out at a temperature of 400°C-600°C for a time of 4-6 hours.

[0104] The above embodiments, by limiting the temperature and time of the activation treatment, can remove impurities in the hard carbon precursor, ensure the stability of the core and sodium storage sites, and further regulate the capacity parameters of the hard carbon composite material. For example, the activation treatment temperature is any value or a range of any combination of 400°C, 450°C, 500°C, 550°C, 600°C, etc.; the time is any value or a range of any combination of 4.0 h, 4.5 h, 5.0 h, 5.5 h, 6.0 h, etc.

[0105] In some alternative embodiments, when the hard carbon precursor is bamboo, the activation treatment further includes: crushing the bamboo into 3cm-5cm long pieces using a crusher.

[0106] In some optional embodiments, the temperature of the first calcination treatment is 1000℃-1500℃, and the time is 0.5h-7h. By limiting the temperature and time of the first calcination treatment, the above embodiments can enable the core to form a richer closed-pore structure, ensuring the stability and high-capacity characteristics of the core, and further controlling the core diameter. For example, the temperature of the first calcination treatment is any value or a range of any combination of 1000℃, 1200℃, 1300℃, 1400℃, 1500℃, etc.; the time is any value or a range of any combination of 0.5h, 1h, 2h, 3h, 4h, 4.5h, 5h, 5.5h, 6h, 7h, etc.

[0107] In some alternative embodiments, the pore-forming process includes: introducing steam for a second calcination treatment, wherein the temperature of the second calcination treatment is 650°C-1250°C and the time is 4h-8h.

[0108] It is understandable that the pore-forming process is carried out in a protective atmosphere, which can be any inert atmosphere such as nitrogen or argon.

[0109] The above-described embodiments can ensure the formation of more 1-3 nm pores in the hard carbon precursor, providing conditions for subsequent sintering and pore closing. Exemplarily, the second calcination treatment is performed at any value or combination of any two of the following: 650°C, 700°C, 800°C, 900°C, 1000°C, 1200°C, 1250°C, etc., for 4 h, 4.5 h, 5 h, 5.5 h, 6 h, 8 h, etc.

[0110] In some alternative embodiments, the water vapor flow rate is 4 mL / min. 硬碳前驱体 -15 mL / min 硬碳前驱体 For example, the flow rate of water vapor is 4 mL / min. 硬碳前驱体 7 mL / min 硬碳前驱体 10 mL / min 硬碳前驱体 12 mL / min 硬碳前驱体 15 mL / min 硬碳前驱体 A range consisting of any value in the range, or any combination of both.

[0111] In some optional embodiments, when the hard carbon precursor is bamboo, the process after pore-forming further includes: air crushing, followed by grading and screening to obtain bamboo powder with a D50 of 1μm-10μm.

[0112] In some optional embodiments, the sintering temperature is 1000℃-1500℃, and the time is 1h-7h. This sintering treatment can further modify surface defects in hard carbon, reduce the specific surface area of ​​the hard carbon composite material, and improve its initial efficiency. Exemplarily, the sintering temperature is any value or a range of any combination of 1000℃, 1200℃, 1300℃, 1400℃, 1500℃, etc.; and the time is any value or a range of any combination of 1h, 2h, 3h, 4h, 4.5h, 5h, 5.5h, 6h, 7h, etc.

[0113] The sintering process is carried out in a protective atmosphere, which can be any inert atmosphere such as nitrogen or argon.

[0114] In some alternative embodiments, the first calcination treatment is followed by an acid washing treatment.

[0115] Pickling can remove non-carbon impurities generated during the first calcination process, such as metallic impurities, uncarbonized residues, and sulfur. In some alternative embodiments, pickling includes: stirring in a 1-5 mol / L acid solution for 6-12 hours, washing the pickled bamboo powder with deionized water by filtration or centrifugation until neutral.

[0116] For example, the acid solution may be a single or combined use of sulfuric acid, hydrochloric acid, hydrofluoric acid, etc.

[0117] In some alternative embodiments, the polymerization reaction is an electropolymerization reaction, for example, carried out at a constant potential voltage, preferably 4V-12V.

[0118] When the polymerization reaction is an electropolymerization reaction, in some optional embodiments, the mixture may also include an acid solution and a metal salt.

[0119] In some alternative embodiments, the metal salt includes potassium chloride, sodium chloride, etc.; the acid solution is sulfuric acid, hydrochloric acid, etc.

[0120] To further adjust the thickness of the outer shell, in some optional embodiments, the mass concentration ratio of melamine monomer, acid solution, and metal salt is 0.5-1:0.05-0.06:0.1-0.2.

[0121] To further ensure the conductivity, rate capability, and low cost of hard carbon composites, in some alternative embodiments, the nitrogen-containing conductive polymer monomers include melamine monomers and / or pyrrole monomers.

[0122] In some alternative embodiments, the structure of the melamine monomer is shown in Formula 2:

[0123] Formula 2.

[0124] To further adjust the thickness of the first coating layer, in some alternative embodiments, the soft carbon precursor is 5%-15% of the mass of the hard carbon core.

[0125] For example, the soft carbon precursor is any value or a range of any two of the following: 5%, 6%, 7%, 58%, 9%, 1%, 11%, 12%, 13%, 14%, 15% of the mass of the hard carbon core.

[0126] In some alternative embodiments, the specific surface area of ​​the product obtained after activating and pore-forming the hard carbon precursor is 800 m². 2 / g-1500m 2 / g. The specific surface area of ​​this product ensures that there are enough sodium storage sites in the core, thereby guaranteeing the battery capacity.

[0127] For example, the specific surface area of ​​the above product is 800 m². 2 / g, 1000 m 2 / g、1100 m 2 / g、1200 m 2 / g、1300 m 2 / g, 1400 m 2 / g, 1500 m 2 Any value in / g, or a range consisting of any two of them.

[0128] In some alternative embodiments, the specific surface area of ​​the hard carbon core is 50 m². 2 / g-500m 2 / g. The specific surface area of ​​this product can further ensure that there are enough sodium storage sites in the core, thereby guaranteeing the battery capacity.

[0129] For example, the specific surface area of ​​the hard carbon core is 50 m². 2 / g, 100 m 2 / g, 150 m 2 / g、200 m 2 / g、300 m 2 / g、400 m 2 / g、500 m 2 Any value in / g, or a range consisting of any two of them.

[0130] In some alternative embodiments, the specific surface area of ​​the hard carbon core, at least partially covered by the first coating layer, is ≤100 m². 2 / g. The specific surface area of ​​this product ensures the uniformity and thickness of the first coating layer, thereby guaranteeing the battery's initial efficiency.

[0131] For example, the specific surface area of ​​the hard carbon core with at least a portion of its surface having a first coating layer is 20 m². 2 / g, 50m 2 / g、70 m 2 / g、90 m 2 / g, 100 m 2 Any value in / g, or a range consisting of any two of them.

[0132] In some embodiments, the drying process is vacuum freeze drying.

[0133] Thirdly, the present invention provides an electrode sheet comprising a hard carbon composite material of the first aspect or a hard carbon composite material prepared by the preparation method of the second aspect.

[0134] It is understood that the electrode sheet of the present invention can be either a positive electrode sheet or a negative electrode sheet. The present invention does not specifically limit the composition and material of the positive and negative electrode sheets of the battery. Exemplarily, the aforementioned negative electrode sheet includes a current collector and a negative electrode active material layer located on at least one side of the current collector. The negative electrode active material layer includes a hard carbon composite material, a conductive agent, a binder, and a dispersant. The conductive agent can be selected from at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotubes, metal powder, and graphene. The binder can be selected from at least one of carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate. The dispersant can be at least one of sodium carboxymethyl cellulose, triethylhexyl phosphate, and sodium dodecyl sulfate. The negative electrode current collector can be a conventional negative electrode current collector in the art, such as copper foil. In some embodiments, the negative electrode active material layer comprises: a hard carbon composite material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and carbon black in a mass ratio of 100:1.5:3:1.5.

[0135] The aforementioned positive electrode sheet includes a current collector and a positive electrode active material layer located on at least one side of the current collector. The positive electrode active material layer includes a positive electrode active material, a conductive agent, and a binder. The positive electrode active material includes at least one of sodium cobaltate, sodium nickel manganese cobaltate, sodium iron manganeseate, sodium vanadium phosphate, sodium iron sulfate, sodium iron phosphate, and sodium vanadium fluorophosphate. The conductive agent includes the aforementioned hard carbon composite material, and optionally includes at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotubes, metal powder, and graphene. The binder may be selected from at least one of carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate. The material of the positive electrode current collector may be selected from any one or more of copper foil, titanium foil, tin foil, chromium foil, and composite foils of the above metals.

[0136] Fourthly, the present invention provides a battery comprising a hard carbon composite material of the first aspect, a hard carbon composite material prepared by the preparation method of the second aspect, or an electrode sheet of the third aspect; the battery comprises any one of a single cell, a battery module, or a battery pack.

[0137] In some specific implementations, the battery is a sodium-ion battery, and the electrode sheet is a negative electrode sheet.

[0138] Exemplarily, the battery further includes a separator; the present invention does not impose any particular limitation on the separator, and any known porous structure separator with electrochemical and chemical stability can be selected, such as at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, or polyvinylidene fluoride. The separator can be single-layer or multi-layer.

[0139] Exemplarily, the battery further includes an electrolyte comprising an organic solvent and an electrolyte salt. The organic solvent serves as a medium for ion transport in the electrochemical reaction and can be any organic solvent known in the art for use in battery electrolytes. Exemplarily, the organic solvent can be at least one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butenyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0140] For example, the battery of the present invention can be manufactured according to conventional methods in the art. For instance, the positive electrode, separator and negative electrode can be stacked in sequence, and then assembled into a cell by a winding process or a stacking process. After packaging and baking, electrolyte is injected, and then the battery is manufactured by hot pressing and other processes.

[0141] Fifthly, the present invention provides an electrical device comprising a hard carbon composite material of the first aspect, a hard carbon composite material prepared by the preparation method of the second aspect, an electrode sheet of the third aspect, or a battery of the fourth aspect.

[0142] It should be noted that the above-mentioned electrical equipment can be any equipment that conventionally requires electricity, such as, but not limited to, computers, electric vehicles, air conditioners, refrigerators, washing machines, microwave ovens, printers, fax machines, etc.

[0143] To further understand the present invention, the technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0144] Unless otherwise specified, all reagents involved in the embodiments of this invention are commercially available products and can be purchased through commercial channels.

[0145] Example 1

[0146] This example provides a hard carbon composite material, comprising: a hard carbon core, a first coating layer disposed on at least a portion of the surface of the hard carbon core, and a second coating layer disposed on at least a portion of the surface of the first coating layer; the first coating layer is soft carbon, and the second coating layer is a nitrogen-containing conductive polymer, wherein the hard carbon and the composite material include a closed-cell structure. Specific parameters are shown in Table 1.

[0147] Its preparation method includes the following steps:

[0148] S1. Activation treatment: Fresh bamboo is crushed into bamboo chips and then calcined in a box furnace at 500℃ for 5 hours. The calcined bamboo chips are then crushed into bamboo blocks with a length of 3-5 cm using a crusher.

[0149] S2. Hole Formation Process: The bamboo blocks from step S1 are placed in a rotary kiln and steam is introduced to form holes. The parameters of the rotary kiln are: steam flow rate: 8 mL / min per gram of bamboo block; temperature: 950℃; holding time: 8 hours; protective gas: nitrogen. A specific surface area of ​​1430 m² is obtained. 2 / g of pore-forming precursor sample.

[0150] S3. Air-crushing treatment: The pore-forming precursor sample obtained in S2 is air-crushed, and after grading and screening, bamboo powder with D50=4-6 μm is obtained.

[0151] S4. Acid washing treatment: Stir the bamboo powder in a mixture of 1 mol / L sulfuric acid and 0.5 mol / L hydrofluoric acid for 10 h. Wash the acid-washed bamboo powder with deionized water by vacuum filtration or centrifugation until neutral.

[0152] S5. Calcination Treatment: The bamboo powder from step S4 is placed in a pusher kiln and calcined at high temperature (1500℃) with nitrogen as a protective gas for 5 hours to obtain a specific surface area of ​​250 m². 2 / g hard carbon core.

[0153] S6. Sintering Treatment: After the hard carbon core is sieved through a 200-mesh sieve, it is mixed with asphalt in a mechanical blending machine in a solid-solid manner. The blend is then placed in a pusher kiln for sintering. The asphalt content is 10% of the core mass. The sintering temperature of the pusher kiln is 1300℃, the sintering time is 5 hours, the protective gas is nitrogen, and the specific surface area is 20 m². 2 / g of sintered product.

[0154] S7. Polymerization Reaction: The sintered product is added to a sulfuric acid solution containing melamine monomer and potassium chloride and electrolyzed at a constant potential (constant potential voltage = 8 V). Under electrochemical oxidation conditions, the melamine monomer undergoes a polymerization reaction and then settles in the solution. The in-situ generated polymelamine polymer is uniformly attached to the surface of the hard carbon. After the reaction is complete, the mixture is filtered and dried, and then dried in an oven at 100℃ for 25 hours to obtain the final hard carbon composite material. The specific surface area of ​​the obtained product is 1.52 m². 2 / g. The composition of the melamine monomer polymerization solution is: 0.75 M melamine monomer, 0.05 M sulfuric acid, and 0.1 M potassium chloride.

[0155] Figure 2 This is a SEM image of the hard carbon composite material from Example 1. Figure 3 The image shown is a TEM image of the hard carbon composite material from Example 1. Figure 3 It can be seen that the first coating layer and the second coating layer are sequentially coated on the surface of the hard carbon core.

[0156] Example 2

[0157] The preparation method of the hard carbon composite material in this embodiment is basically the same as that in Example 1, except that the constant potential voltage in S7 is 4 V.

[0158] Example 3

[0159] The preparation method of the hard carbon composite material in this embodiment is basically the same as that in Example 1, except that the constant potential voltage in S7 is 12 V.

[0160] Example 4

[0161] The preparation method of the hard carbon composite material in this embodiment is basically the same as that in Example 1, except that in S6, the mass content of asphalt is 5% of the hard carbon core.

[0162] Example 5

[0163] The preparation method of the hard carbon composite material in this embodiment is basically the same as that in Example 1, except that in S6, the mass content of asphalt is 15% of the hard carbon core.

[0164] Example 6

[0165] The preparation method of the hard carbon composite material in this embodiment is basically the same as that in Example 1, except that: S2, pore-forming treatment: the bamboo block from step S1 is placed in a rotary kiln and steam is introduced to form pores. The parameters of the rotary kiln are: steam flow rate: 8 mL / min per gram of bamboo block; temperature: 650℃; holding time: 8 hours; the protective gas is nitrogen, and a specific surface area of ​​876 m² is obtained. 2 / g of pore-forming precursor sample.

[0166] Example 7

[0167] The preparation method of the hard carbon composite material in this embodiment is basically the same as that in Example 1, except that: S2, pore-forming treatment: the bamboo block from step S1 is placed in a rotary kiln and steam is introduced to form pores. The parameters of the rotary kiln are: steam flow rate: 8 mL / min per gram of bamboo block; temperature: 1000℃; holding time: 8 hours; the protective gas is nitrogen, and a specific surface area of ​​1500 m² is obtained. 2 / g of pore-forming precursor sample.

[0168] Example 8

[0169] The preparation method of the hard carbon composite material in this embodiment is basically the same as that in Example 1, except that: S7, polymerization reaction: the melamine monomer is replaced with pyrrole monomer.

[0170] Comparative Example 1

[0171] This example provides a hard carbon composite material, comprising: a hard carbon core, and a first coating layer disposed on at least a portion of the surface of the core; the first coating layer comprises soft carbon. Specific parameters are shown in Table 1.

[0172] The preparation method of the hard carbon composite material in this comparative example is basically the same as that in Example 6, except that:

[0173] After S6 is completed, hard carbon composite material is obtained directly.

[0174] Comparative Example 2

[0175] This example provides a hard carbon composite material, comprising: a hard carbon core, and a second coating layer disposed on at least a portion of the surface of the hard carbon core; the second coating layer comprises a nitrogen-containing conductive polymer. Specific parameters are shown in Table 1.

[0176] The preparation method of the hard carbon composite material in this comparative example is basically the same as that in Example 1, except that:

[0177] S6 is skipped; the product obtained from S5 is directly processed into S7.

[0178] Application examples

[0179] The hard carbon composite materials obtained in the implementation and comparative examples were used as negative electrode active materials. After being slurried according to the mass ratio of hard carbon composite material: carboxymethyl cellulose: styrene-butadiene rubber latex: conductive carbon black = 100:2:3.5:3, the slurry was coated on copper foil. The prepared hard carbon composite material electrode sheet was used as the negative electrode of the coin cell, the sodium metal sheet was used as the positive electrode, and the commercial electrolyte LB68 was used as the electrolyte to assemble the coin cell.

[0180] Test case

[0181] 1. Specific surface area (BET) test

[0182] According to the provisions of GB / T 19587, the specific surface area of ​​the sample to be tested shall be determined using a Bessler specific surface area analyzer under N2 atmosphere.

[0183] The specific test results for hard carbon composite materials are summarized in Table 1.

[0184] 2. Closed-cell volume test

[0185] According to the provisions of GB / T 24203-2024, the true density of hard carbon composite materials is determined by using the Quantum helium true density tester, and the closed-cell volume is calculated based on the true density.

[0186] The specific test results are summarized in Table 1.

[0187] 3. Element content test

[0188] The overall elemental content of the material was tested using a CHONS elemental analyzer. The testing steps were as follows: 1) Sample pretreatment: drying, grinding, and weighing; 2) Instrument calibration: calibrating the carbon, hydrogen, nitrogen, and sulfur detectors using standard substances; 3) Sample detection: after high-temperature combustion, CO2, H2O, N2, and SO2 were simultaneously detected by infrared absorption, thermal conductivity detection, and chemiluminescence methods; 4) Data processing: the elemental content was calculated based on the gas mass and verified by the oxygen content difference subtraction method.

[0189] The presence of the second coating layer was confirmed by detecting nitrogen on the outer surface and analyzing its chemical state using XPS, and the elemental content of the coating layer was also determined.

[0190] 4. Thickness test

[0191] Microscopic images of hard carbon composite materials were obtained using TEM. Fifty hard carbon composite materials were randomly selected, and 20 test points were randomly selected for each particle. The dimensions of the core, first coating layer, and second coating layer of each hard carbon composite particle were measured, and the values ​​were summed and averaged.

[0192] 5. First-time efficiency and charge / discharge specific capacity

[0193] Electrochemical performance was tested using a Wuhan Landian CT2001A battery tester. The charge / discharge voltage range was controlled between 0-2V, and the charge / discharge rate was 0.1A / g. The initial sodium insertion and extraction capacities were recorded, and the initial coulombic efficiency was calculated, i.e., initial efficiency (reversible capacity) = initial sodium extraction capacity / initial sodium insertion capacity; where, Figure 1 The charge / discharge capacity curves of the battery prepared from the hard carbon composite material of Example 1.

[0194] 6. 10C Capacity Retention Rate: Under an environment of (25±2)℃, the battery was discharged at a standard 1C constant current until the discharge termination voltage of 2.7V, and then rested for 30 minutes; then charged at a standard 1C constant current and constant voltage until the charging limit voltage of 4.2V, with a cutoff current of 0.05C, and rested for 30 minutes; then discharged at a standard 1C constant current until the discharge termination voltage of 2.7V to obtain the actual cell capacity C0, and rested for 30 minutes; charge and discharge cycles were performed at a 10C rate within the charge and discharge cutoff voltage range. The discharge capacity of the first cycle was measured as x1mAh, and the discharge capacity of the 50th cycle was measured as y1mAh; the capacity of the 50th cycle was divided by the capacity of the first cycle to obtain the cycle capacity retention rate R1 = y1 / x1 × 100%. The above test results are summarized in Table 1-2.

[0195] Table 1:

[0196]

[0197] Table 2:

[0198]

[0199] As can be seen from Tables 1-2, compared with the comparative example, the hard carbon composite material of the embodiment has a three-layer structure design: the core provides sodium storage sites, the first coating layer modifies defects, and the second coating layer improves conductivity and nitrogen doping, so as to achieve the synergistic effect of each layer structure, enabling the sodium-ion battery to have higher capacity, first efficiency and rate performance.

[0200] 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 foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A hard carbon composite material, characterized in that, The hard carbon composite material includes: a hard carbon core, a first coating layer disposed on at least a portion of the surface of the hard carbon core, and a second coating layer disposed on at least a portion of the surface of the first coating layer; the first coating layer includes soft carbon, and the second coating layer includes a nitrogen-containing conductive polymer.

2. The hard carbon composite material according to claim 1, characterized in that, The nitrogen content of the nitrogen-containing conductive polymer is greater than or equal to 15% by weight; preferably, the nitrogen content of the nitrogen-containing conductive polymer is greater than or equal to 60%. And / or, by mass, the carbon content of the hard carbon core is greater than or equal to 95%; And / or, by mass, the carbon content of the first coating layer is greater than or equal to 95%.

3. The hard carbon composite material according to claim 1 or 2, characterized in that, The hard carbon composite material includes a closed-cell structure with a pore volume of 0.02 cm³. 3 / g-0.1 cm 3 / g.

4. The hard carbon composite material according to any one of claims 1-3, characterized in that, The average size of the hard carbon core is 2μm-20μm; And / or, the average thickness of the first coating layer is 10nm-40nm; And / or, the average thickness of the second coating layer is 5nm-40nm.

5. The hard carbon composite material according to claims 1-4, characterized in that, The specific surface area of ​​the hard carbon composite material is 0.8 m² / g-25 m² / g; Preferably, the nitrogen-containing conductive polymer comprises polymelamine and / or polypyrrole; Preferably, the nitrogen content in the hard carbon composite material is 3%-7% by weight.

6. A method for preparing a hard carbon composite material as described in any one of claims 1-5, characterized in that, Includes the following steps: Provides a hard carbon core; The hard carbon core and the soft carbon precursor are mixed and sintered to obtain a hard carbon core with a first coating layer. A mixture comprising a hard carbon core with a first coating layer, a nitrogen-containing conductive polymer monomer, and a solvent is subjected to a polymerization reaction to form a second coating layer on one side of the first coating layer, thereby obtaining the hard carbon composite material.

7. The preparation method according to claim 6, characterized in that, The hard carbon core is prepared through the following process: The hard carbon precursor is activated, pore-forming, and subjected to a first calcination treatment to obtain the hard carbon core.

8. The preparation method according to claim 7, characterized in that, The hard carbon precursor includes at least one of bamboo, coconut shell, wood chips, and straw; Preferably, the activation treatment is performed at a temperature of 400℃-600℃ for 4-6 hours. Preferably, the pore-forming process includes: introducing steam for a second calcination treatment, the temperature of which is 650℃-1250℃ and the time is 4h-8h; preferably, the steam flow rate is 4 mL / min / g. 硬碳前驱体 -15 mL / min / g 硬碳前驱体 ; Preferably, the temperature of the first calcination treatment is 1000℃-1500℃, and the time is 0.5h-7h; Preferably, the first calcination treatment is followed by an acid washing treatment.

9. The preparation method according to any one of claims 6-8, characterized in that, The sintering process is carried out at a temperature of 1000℃-1500℃ for 1h-7h. And / or, the polymerization reaction is carried out at a constant potential voltage, preferably 4V-12V.

10. The preparation method according to any one of claims 6-9, characterized in that, The mixture also includes an acid solution and a metal salt; preferably, the metal salt includes potassium chloride. Preferably, the mass concentration ratio of the melamine monomer, acid solution, and metal salt is 0.5-1:0.05-0.06:0.1-0.2; And / or, the soft carbon precursor includes at least one of pitch, petroleum coke, and coal tar; And / or, the nitrogen-containing conductive polymer monomer includes melamine monomer and / or pyrrole monomer; And / or, the soft carbon precursor is 5%-15% of the mass of the hard carbon core.

11. An electrode sheet, the electrode sheet comprising a current collector and an active material layer coated on at least one side of the current collector, characterized in that, The active material layer comprises the hard carbon composite material according to any one of claims 1-5 or the hard carbon composite material prepared by any one of the preparation methods according to claims 6-10.

12. A battery, characterized in that, Includes the electrode sheet as described in claim 11.

13. The battery according to claim 12, characterized in that, The battery is a sodium-ion battery, and the electrode sheet is a negative electrode sheet.

14. An electrical appliance, characterized in that, This includes the hard carbon composite material according to any one of claims 1-5, the hard carbon composite material prepared by any one of the preparation methods according to claims 6-10, the electrode sheet according to claim 11, or the battery according to claim 12 or 13.

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