Anode materials and their preparation methods, anode sheets and batteries

Abstract

This application relates to an anode material and its preparation method, an anode sheet, and a battery. The preparation method of the anode material includes the following steps: S1: Mixing a monolayer MXene suspension and a resin prepolymer dispersion evenly, adding perylene-2,5,8,11-tetracarboxylic acid, and stirring evenly to obtain a precursor solution; S2: Performing a hydrothermal reaction on the precursor solution to obtain a carbon precursor; S3: Carbonizing the carbon precursor under a protective gas atmosphere to obtain the anode material. This effectively improves the initial efficiency, capacity performance, and cycle performance of the anode material.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a negative electrode material and its preparation method, a negative electrode sheet, and a battery. Background Technology

[0002] Currently, sodium-ion batteries mainly use hard carbon as the anode material. However, hard carbon anode materials have low sodium storage capacity and low initial coulombic efficiency (first efficiency). Therefore, developing novel anode materials with high initial efficiency and long lifespan has high research and application value.

[0003] The molecular structure of resin-based precursors is relatively simple and controllable, and the relevant molecular structure can be designed as needed to precisely construct adjustable pore structures and active sites at the molecular level. This gives hard carbon materials prepared using resin-based precursors advantages such as high specific capacity, good electrochemical performance, and good consistency. Therefore, resin-based hard carbon materials have received extensive research and attention.

[0004] With the increasing demands for battery performance, how to further improve the performance of hard carbon anode materials in order to enhance the battery's initial efficiency, capacity performance, and cycle performance has always been a problem that the industry has been committed to solving. Summary of the Invention

[0005] In view of this, the present application provides a negative electrode material, a method for preparing the same, a negative electrode sheet, and a battery to solve at least one problem existing in the prior art.

[0006] In a first aspect, embodiments of this application provide a method for preparing a negative electrode material, comprising the following steps:

[0007] S1: Mix the monolayer MXene suspension and the resin prepolymer dispersion evenly, add perylene-2,5,8,11-tetracarboxylic acid, and stir evenly to obtain the precursor solution;

[0008] S2: Perform a hydrothermal reaction on the precursor solution to obtain a carbon precursor;

[0009] S3: The carbon precursor is carbonized under a protective gas atmosphere to obtain the negative electrode material.

[0010] In conjunction with the first aspect of this application, in an optional embodiment, the preparation of the monolayer MXene suspension in step S1 includes the following steps:

[0011] Monolayer MXene powder was added to deionized water and dispersed evenly to obtain the monolayer MXene suspension.

[0012] In conjunction with the first aspect of this application, in an optional embodiment, the preparation of the resin prepolymer dispersion in step S1 includes the following steps:

[0013] The resin prepolymer is added to a solvent and dispersed evenly to obtain the resin prepolymer dispersion; optionally, the solvent includes an alcohol solvent and deionized water, and the volume ratio of the alcohol solvent to the deionized water is 1:(1~10).

[0014] In conjunction with the first aspect of this application, in an alternative embodiment, step S1 satisfies at least one of the following features:

[0015] (1) The MXene includes at least one of Ti3C2, Ti2C, Ti3CN, V4C3, V2C, Nb2C, and Nb4C3;

[0016] (2) The mass concentration of the monolayer MXene suspension is 0.01 g / ml to 0.05 g / ml;

[0017] (3) The resin prepolymer includes at least one of phenolic resin prepolymer, epoxy resin prepolymer, urea-formaldehyde resin prepolymer, melamine-formaldehyde resin prepolymer, lignin phenolic resin prepolymer, and cellulose phenolic resin prepolymer;

[0018] (4) The mass concentration of the resin prepolymer dispersion is 0.05 g / ml to 0.5 g / ml.

[0019] In conjunction with the first aspect of this application, in an optional embodiment, in step S1, the mass of MXene in the monolayer MXene suspension is 10% to 50% of the mass of the resin prepolymer in the resin prepolymer dispersion; and / or, the mass of perylene-2,5,8,11-tetracarboxylic acid is 1% to 10% of the mass of the resin prepolymer in the resin prepolymer dispersion.

[0020] In conjunction with the first aspect of this application, in an optional embodiment, in step S2, the temperature of the hydrothermal reaction is 100°C to 150°C; and / or, the time of the hydrothermal reaction is 5h to 10h.

[0021] In conjunction with the first aspect of this application, in an alternative embodiment, step S3 satisfies at least one of the following features:

[0022] (1) The carbonization temperature is 1000℃~1500℃;

[0023] (2) The heat preservation time for the carbonization treatment is 2h to 5h;

[0024] (3) The heating rate of the carbonization treatment is 0.5℃ / min to 5℃ / min;

[0025] (4) The protective gas includes at least one of nitrogen, argon, and helium;

[0026] (5) The flow rate of the protective gas is 40 ml / min to 80 ml / min.

[0027] Secondly, embodiments of this application provide a negative electrode material, which is prepared by the method for preparing a negative electrode material as described in any one of the first aspects.

[0028] Thirdly, embodiments of this application provide a negative electrode sheet, the negative electrode sheet comprising the negative electrode material described in the second aspect.

[0029] Fourthly, embodiments of this application provide a battery including the negative electrode sheet as described in the third aspect.

[0030] Compared with the prior art, the embodiments of this application have the following beneficial effects:

[0031] The negative electrode material, its preparation method, negative electrode sheet, and battery provided in this application embodiment are described below. The negative electrode material preparation method utilizes the condensation reaction between monolayer MXene nanosheets in a monolayer MXene suspension and resin prepolymer in a resin prepolymer dispersion with perylene-2,5,8,11-tetracarboxylic acid (PTCA). This allows for one-step chemical connection between MXene and the resin prepolymer via PTCA, resulting in a simple, low-cost, and highly controllable process. PTCA not only connects MXene and the resin prepolymer but also acts as an intercalating molecule to expand the interlayer spacing and enhance structural stability. This effectively improves the self-stacking of MXene sheets, prevents aggregation, and provides more sodium storage sites. In the negative electrode material obtained by carbonizing the carbon precursor, the hard carbon attached to the MXene surface forms a physical barrier and confinement effect, effectively inhibiting MXene oxidation and improving its structural stability. MXene improves the overall electronic conductivity of the resin-based hard carbon material and shortens the sodium ion diffusion path, thereby effectively enhancing the first-cycle efficiency, capacity performance, and cycle performance of the negative electrode material.

[0032] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0033] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments of this application and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0034] Figure 1 A schematic flowchart illustrating a method for preparing a negative electrode material according to an embodiment of this application;

[0035] Figure 2This is a scanning electron microscope image of the negative electrode material prepared in Example 1;

[0036] Figure 3 This is a transmission electron microscope (TEM) image of the negative electrode material prepared in Example 1;

[0037] Figure 4 The images show the XRD patterns of the negative electrode materials prepared in Example 1 and Comparative Example 1. Detailed Implementation

[0038] To make the technical solution and beneficial effects of the present invention more apparent and understandable, a detailed description is provided below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed under conventional experimental conditions. Unless otherwise specified, all reagents and raw materials used in this invention are commercially available.

[0039] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of this application. However, it will be apparent to those skilled in the art that this application can be practiced without one or more of these details. In other instances, to avoid confusion with this application, some technical features well-known in the art have not been described; that is, not all features of actual embodiments are described herein, nor are well-known functions and steps described in detail.

[0040] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. When used herein, the singular forms “a,” “an,” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising” and / or “including,” when used in this specification, identify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups. When used herein, the term “and / or” includes any and all combinations of the associated listed items.

[0041] To fully understand this application, detailed steps and structures will be presented in the following description to illustrate the technical solution of this application. Preferred embodiments of this application are described in detail below; however, in addition to these detailed descriptions, this application may have other implementation methods.

[0042] Unless otherwise defined, the technical and scientific terms used in this application have the same meanings as those in the technical and scientific field to which this application pertains.

[0043] Unless otherwise specified, the techniques or conditions described in the following embodiments are generally performed in accordance with conventional techniques or conditions described in the literature in this field, or in accordance with the product manual and the manufacturer's recommendations. All numerical ranges in the following embodiments include endpoint values.

[0044] MXene is a novel two-dimensional transition metal carbide / nitride with a graphene-like structure, and its chemical formula is M. n+1 X n In this model, M represents an early transition metal, X represents C and / or N, and n (1, 2, or 3) indicates the number of X atoms. MXene possesses a unique layered structure and a transition metal carbide / nitride chemical composition, giving it a large specific surface area, good electrical conductivity, excellent mechanical properties, and photothermal properties. To broaden the applications of MXene, it is often composited with carbon-based materials. In recent years, the applications of MXene and MXene / carbon composites in energy storage, biosensors, and biomedicine have been extensively studied. Research on anode materials has found that MXene, due to its high specific surface area, excellent electronic conductivity and hydrophilicity, and tunable surface structure, is well-suited for use as a substrate in carbon composite materials.

[0045] Currently, MXene can be composited with carbon-based materials through coating methods, such as coating MXene onto the surface of carbon-based materials through electrostatic assembly. However, coating methods usually have problems such as complex operation, high environmental pollution, and high energy consumption. Moreover, the current coating process cannot achieve precise control.

[0046] Based on this, this application provides a method for preparing a negative electrode material. Please refer to... Figure 1 The method for preparing the negative electrode material provided in this application includes the following steps:

[0047] S1: Mix the monolayer MXene suspension and the resin prepolymer dispersion evenly, add perylene-2,5,8,11-tetracarboxylic acid, and stir evenly to obtain the precursor solution;

[0048] S2: Hydrothermal reaction of the precursor solution yields a carbon precursor;

[0049] S3: Carbonization of the carbon precursor is carried out under a protective gas atmosphere to obtain the anode material.

[0050] PTCA contains four carboxyl groups. These carboxyl groups can undergo dehydration condensation reactions with the hydroxyl groups in MXene and resin prepolymers to form CO bonds, achieving molecular-level connections (also known as molecular welding). Furthermore, PTCA possesses a rigid structure similar to a benzene ring, allowing it to act as a bridge connecting MXene and resin prepolymers while also supporting structural stability. In this application, the condensation reaction between monolayer MXene nanosheets in a monolayer MXene suspension and resin prepolymer in a resin prepolymer dispersion with perylene-2,5,8,11-tetracarboxylic acid (PTCA) is utilized to achieve a one-step chemical connection (also known as chemical welding) between MXene and resin prepolymer via PTCA. This method is simple, low-cost, and highly controllable. PTCA not only connects MXene and resin prepolymers but also acts as an intercalating molecule to expand interlayer spacing and enhance structural stability. It effectively improves the self-stabilization of MXene sheets, prevents aggregation, and provides more sodium storage sites. The rigid benzene ring structure of PTCA is also advantageous. To improve structural stability, after carbonizing the carbon precursor, PTCA is also carbonized, which helps to increase the carbon content of the obtained anode material and expand the interlayer spacing of the hard carbon material. In the final anode material, the resin-based hard carbon attached to the surface of MXene can form a physical barrier and confinement effect, thereby effectively inhibiting the oxidation of MXene and improving the structural stability of MXene. MXene can improve the overall electronic conductivity of the resin-based hard carbon material, protect the surface of the resin-based hard carbon material, shorten the sodium ion diffusion path, and improve the electrolyte mobility, thereby effectively improving the first-efficiency, capacity performance and cycle performance of the anode material.

[0051] The preparation of the monolayer MXene suspension in step S1 may include the following steps: adding monolayer MXene powder to deionized water and dispersing it evenly to obtain a monolayer MXene suspension.

[0052] In actual preparation processes, ultrasonic treatment can be used, for example, to uniformly disperse the monolayer MXene powder in deionized water. Exemplarily, MXene may include at least one of Ti3C2, Ti2C, Ti3CN, V4C3, V2C, Nb2C, and Nb4C3. Specifically, MXene may be, for example, a layered nano-MXene material.

[0053] In some embodiments, the mass concentration of the monolayer MXene suspension can be from 0.01 g / ml to 0.05 g / ml, for example, 0.01 g / ml, 0.02 g / ml, 0.03 g / ml, 0.04 g / ml, 0.05 g / ml, or any value between any two of the above ranges. This ensures that the monolayer MXene powder is more uniformly dispersed in deionized water, avoids the aggregation of MXene sheets, forms a higher quality monolayer MXene suspension, and thus helps to improve the quality of the obtained carbon precursor.

[0054] The preparation of the resin prepolymer dispersion in step S1 may include the following steps: adding the resin prepolymer to a solvent and dispersing it evenly to obtain the resin prepolymer dispersion.

[0055] In actual preparation processes, ultrasonic treatment can be used, for example, to uniformly disperse the resin prepolymer in the solvent. Exemplarily, the resin prepolymer may include at least one of phenolic resin prepolymer, epoxy resin prepolymer, urea-formaldehyde resin prepolymer, melamine-formaldehyde resin prepolymer, lignin-phenolic resin prepolymer, and cellulose-phenolic resin prepolymer. The solvent may include, for example, an alcohol solvent and deionized water; the alcohol solvent may include, for example, at least one of ethanol, methanol, and propanol; further, the volume ratio of the alcohol solvent to deionized water may be 1:(1-10). This is more conducive to the dispersion of the resin prepolymer in the solvent, resulting in a higher quality resin prepolymer dispersion. In a specific embodiment, the solvent includes ethanol and deionized water.

[0056] In some embodiments, the mass concentration of the resin prepolymer dispersion can be from 0.05 g / ml to 0.5 g / ml, for example, 0.05 g / ml, 0.1 g / ml, 0.15 g / ml, 0.2 g / ml, 0.25 g / ml, 0.3 g / ml, 0.35 g / ml, 0.4 g / ml, 0.45 g / ml, 0.5 g / ml, or any value between any two of the above ranges. This ensures that the resin prepolymer is more uniformly dispersed in the solvent, forming a higher quality resin prepolymer dispersion, which in turn helps to improve the quality of the obtained carbon precursor.

[0057] In some embodiments, in step S1, the mass of MXene in the monolayer MXene suspension can be 10% to 50% of the mass of the resin prepolymer in the resin prepolymer dispersion, for example, it can be 10%, 20%, 30%, 40%, 50% or any value between any two of the above ranges.

[0058] Controlling the mass of MXene in the monolayer MXene suspension and the resin prepolymer in the resin prepolymer dispersion to meet the above range is beneficial for connecting MXene and resin prepolymer through PTCA to form a carbon precursor with appropriate interlayer spacing and more stable structure. This allows for the full utilization of the advantages of both materials, enhances their synergistic effect, and further improves the first-efficiency, capacity performance, and cycle performance of the final anode material.

[0059] In some embodiments, the mass of perylene-2,5,8,11-tetracarboxylic acid can be 1% to 10% of the mass of the resin prepolymer in the resin prepolymer dispersion, for example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or any value between any two of the above ranges.

[0060] Controlling the mass of perylene-2,5,8,11-tetracarboxylic acid and resin prepolymer in the dispersion to meet the above range is beneficial for sufficient condensation reaction between perylene-2,5,8,11-tetracarboxylic acid and resin prepolymer, thereby improving the quality of the obtained carbon precursor.

[0061] Furthermore, by controlling the mass of MXene in the monolayer MXene suspension to 10%–50% of the mass of the resin prepolymer in the resin prepolymer dispersion, and by controlling the mass of perylene-2,5,8,11-tetracarboxylic acid to 1%–10% of the mass of the resin prepolymer in the resin prepolymer dispersion, it is more conducive to the full condensation reaction between perylene-2,5,8,11-tetracarboxylic acid, the resin prepolymer, and MXene, achieving a more stable connection between the resin prepolymer and MXene, thereby further improving the quality of the obtained carbon precursor.

[0062] In step S2, the precursor solution can be placed in a hydrothermal reactor for a hydrothermal reaction to obtain the carbon precursor. Specifically, the hydrothermal reaction temperature can be between 100℃ and 150℃, for example, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, or any value between any two of the above ranges. This ensures sufficient condensation reaction between PTCA, the resin prepolymer, and MXene, while avoiding damage to the structure of the reactants and products due to excessively high temperatures.

[0063] In the embodiments of this application, the carbon precursor formed by the condensation reaction of PTCA with resin prepolymer and MXene has a multilayer structure and can be called a carbon precursor with an oatmeal structure.

[0064] Furthermore, the hydrothermal reaction time can be 5h to 10h, for example, 5h, 6h, 7h, 8h, 9h, 10h, or any value within any two of the above ranges. This can further ensure that the condensation reaction between PTCA, the resin prepolymer, and MXene is sufficient, thereby further improving the quality of the obtained carbon precursor.

[0065] In step S3, the carbon precursor is carbonized under a protective gas atmosphere to obtain the anode material. Exemplarily, the carbonization process can be carried out in a tube furnace. Specifically, the carbonization temperature can be between 1000°C and 1500°C, for example, 1000°C, 1100°C, 1200°C, 1300°C, 1400°C, 1500°C, or any value between any two of the above ranges. This ensures sufficient carbonization of the carbon precursor, resulting in a high-quality anode material.

[0066] Furthermore, the holding time for carbonization can be 2h to 5h, for example, 2h, 3h, 4h, 5h, or any value between any two of the above ranges. Even further, the heating rate for carbonization can be 0.5℃ / min to 5℃ / min, for example, 0.5℃ / min, 1℃ / min, 1.5℃ / min, 2℃ / min, 2.5℃ / min, 3℃ / min, 3.5℃ / min, 4℃ / min, 4.5℃ / min, 5℃ / min, or any value between any two of the above ranges.

[0067] By controlling the holding time and heating rate of the carbonization process within the above range, the carbonization effect can be improved, thereby further enhancing the quality of the obtained anode material.

[0068] For example, the protective gas may include at least one of nitrogen, argon, and helium. Further, the flow rate of the protective gas may be 40 ml / min to 80 ml / min, for example, 40 ml / min, 50 ml / min, 60 ml / min, 70 ml / min, 80 ml / min, or any value between any two of the above ranges. This can further improve the effect of the carbonization process.

[0069] It should be noted that PTCA is also carbonized after the carbonization process. This means that in the final anode material, PTCA exists as carbon between the resin-based hard carbon material and the MXene material. This is beneficial for increasing the carbon content and widening the interlayer spacing of the anode material. The anode material prepared in this embodiment can also be called an MXene heterojunction composite hard carbon material.

[0070] In this embodiment, the negative electrode material is obtained by carbonizing the carbon precursor. Since PTCA in the carbon precursor connects MXene and resin prepolymer and acts as an intercalating molecule to expand the interlayer spacing and enhance structural stability, it can effectively improve the self-stacking of MXene sheets, prevent aggregation, and thus provide more sodium storage sites. Furthermore, PTCA has a rigid structure similar to a benzene ring, which is beneficial for improving structural stability. Therefore, the final negative electrode material has a large carbon interlayer spacing and a stable structure, providing more sodium storage sites. In addition, the resin-based hard carbon attached to the MXene surface can form a physical barrier and confinement effect, effectively inhibiting MXene oxidation and improving MXene structural stability. The MXene in the negative electrode material can improve the overall electronic conductivity of the resin-based hard carbon material, protect the surface of the resin-based hard carbon material, shorten the sodium ion diffusion path, and improve the electrolyte mobility, thereby effectively improving the first-efficiency, capacity performance, and cycle performance of the negative electrode material.

[0071] Based on this, this application also provides a negative electrode material, which is prepared by the negative electrode material preparation method described in any of the above embodiments.

[0072] It should be understood that all the features and advantages of the negative electrode materials prepared by the methods described in the above embodiments are also applicable to the negative electrode materials in the embodiments of this application, and will not be repeated here.

[0073] Based on this, this application also provides a negative electrode sheet, including the negative electrode material described in the above embodiments.

[0074] It should be understood that since the negative electrode sheet in the embodiments of this application includes the negative electrode material described in the above embodiments, the beneficial effects of the negative electrode material described in the above embodiments apply to the negative electrode sheet.

[0075] In some embodiments, the negative electrode sheet may include a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer may include the negative electrode material described in the above embodiments.

[0076] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0077] This application does not impose any particular restrictions on the preparation method of the negative electrode sheet. Any preparation method known in the art can be used, as long as it can achieve the purpose of this application.

[0078] Based on this, this application also provides a battery, including the negative electrode sheet described in the above embodiments.

[0079] It should be understood that, since the battery in this application embodiment includes the negative electrode sheet described in the above embodiments, that is, the negative electrode material prepared by the preparation method of the negative electrode material described in any of the above embodiments, the battery has good electrochemical performance and can exhibit high initial charge-discharge capacity, excellent initial coulombic efficiency and good cycle stability.

[0080] In some embodiments, the battery can be a secondary battery, specifically a sodium-ion secondary battery. Typically, a secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, sodium ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor for sodium ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between the electrodes while allowing sodium ions to pass through.

[0081] The technical solution of this application will be further described below with reference to several embodiments and comparative examples.

[0082] Example 1

[0083] The preparation of the negative electrode material in this embodiment includes the following steps:

[0084] Step S101: Disperse 2g of monolayer MXene powder in 100ml of deionized water, ultrasonically disperse for 10min, and after uniform dispersion, obtain a monolayer MXene suspension with a mass concentration of 0.02g / ml.

[0085] Step S102: Disperse 10g of resin prepolymer in 80ml of deionized water and 20ml of ethanol solution (solvent), and ultrasonically disperse for 30min. After uniform dispersion, a resin prepolymer dispersion with a mass concentration of 0.1g / ml is obtained.

[0086] Step S103: Add the monolayer MXene suspension obtained in step S101 to the resin prepolymer dispersion obtained in step S102, stir evenly, then add 0.5g of perylene-2,5,8,11-tetracarboxylic acid (PTCA), and continue stirring until evenly mixed to obtain the precursor solution.

[0087] Step S104: Transfer the precursor solution obtained in step S103 to a hydrothermal reactor and keep it at 120°C for 8 hours to obtain a carbon precursor with an oatmeal structure.

[0088] Step S105: The carbon precursor obtained in step S104 is subjected to high-temperature carbonization (carbonization treatment). The specific conditions are: in a nitrogen environment, it is kept at 1200℃ for 2 hours to obtain MXene heterojunction composite hard carbon material (MXene / PTCA / HC), which is also the anode material.

[0089] Example 2

[0090] The preparation of the negative electrode material in this embodiment is basically the same as in Example 1, except that:

[0091] In step S101, the amount of monolayer MXene powder added is 10g, and the mass concentration of the obtained monolayer MXene suspension is 0.02g / ml.

[0092] Example 3

[0093] The preparation of the negative electrode material in this embodiment is basically the same as in Example 1, except that:

[0094] The solvent in step S102 is 90 ml of deionized water and 10 ml of ethanol solution.

[0095] Example 4

[0096] The preparation of the negative electrode material in this embodiment is basically the same as in Example 1, except that:

[0097] In step S103, the amount of perylene-2,5,8,11-tetracarboxylic acid added is 0.01 g.

[0098] Comparative Example 1

[0099] The preparation of the negative electrode material in this comparative example includes the following steps:

[0100] Step S201: Disperse 10g of resin prepolymer in 80ml of deionized water and 20ml of ethanol solution, ultrasonically disperse for 30min, and after uniform dispersion, obtain a resin prepolymer dispersion with a mass concentration of 0.1g / ml.

[0101] Step S202: Transfer the resin prepolymer dispersion obtained in step S201 to a hydrothermal reactor and keep it at 120°C for 8 hours to obtain a carbon precursor.

[0102] Step S203: The carbon precursor obtained in step S202 is subjected to high-temperature carbonization. The specific conditions are: in a nitrogen atmosphere, it is kept at 1200℃ for 2 hours to obtain hard carbon material (HC), which is also the anode material.

[0103] The main difference between Comparative Example 1 and Example 1 is that it does not include the steps of preparing the monolayer MXene suspension in step S101 of Example 1 and adding the monolayer MXene suspension to the resin prepolymer dispersion in step S103.

[0104] Comparative Example 2

[0105] The preparation of the negative electrode material in this comparative example includes the following steps:

[0106] Step S301: Disperse 2g of monolayer MXene powder in 100ml of deionized water, ultrasonically disperse for 10min, and after uniform dispersion, obtain a monolayer MXene suspension with a mass concentration of 0.02g / ml.

[0107] Step S302: Disperse 10g of resin prepolymer in 80ml of deionized water and 20ml of ethanol solution, and ultrasonically disperse for 30min. After uniform dispersion, a resin prepolymer dispersion with a mass concentration of 0.1g / ml is obtained.

[0108] Step S303: Add the monolayer MXene suspension obtained in step S301 to the resin prepolymer dispersion obtained in step S302, stir evenly, and obtain the precursor solution.

[0109] Step S304: Transfer the precursor solution obtained in step S303 to a hydrothermal reactor and keep it at 120°C for 8 hours to obtain a carbon precursor.

[0110] Step S305: The carbon precursor obtained in step S304 is subjected to high-temperature carbonization. The specific conditions are: in a nitrogen atmosphere, it is kept at 1200℃ for 2 hours to obtain MXene composite hard carbon material (MXene@HC), which is also the anode material.

[0111] The main difference between Comparative Example 2 and Example 1 is that perylene-2,5,8,11-tetracarboxylic acid is not added in step S303.

[0112] Comparative Example 3

[0113] The preparation of the negative electrode material in this comparative example includes the following steps:

[0114] Step S401: Disperse 10g of resin prepolymer in 80ml of deionized water and 20ml of ethanol solution, ultrasonically disperse for 30min, and after uniform dispersion, obtain a resin prepolymer dispersion with a mass concentration of 0.1g / ml.

[0115] Step S402: Add 0.05 g of perylene-2,5,8,11-tetracarboxylic acid to the resin prepolymer dispersion obtained in step S401, and stir until the mixture is homogeneous to obtain the precursor solution.

[0116] Step S403: Transfer the precursor solution obtained in step S402 to a hydrothermal reactor and keep it at 120°C for 8 hours to obtain a carbon precursor.

[0117] Step S404: The carbon precursor obtained in step S403 is subjected to high-temperature carbonization. The specific conditions are: in a nitrogen environment, it is kept at 1200℃ for 2 hours to obtain PTCA modified hard carbon composite material (PTCA-HC), which is also the negative electrode material.

[0118] The main difference between Comparative Example 3 and Example 1 is that no monolayer MXene suspension was added in step S402.

[0119] The negative electrode materials obtained in the above embodiments and comparative examples were used to prepare batteries for testing the electrochemical performance of the batteries.

[0120] The battery preparation steps are as follows: the negative electrode material, binder and conductive agent are mixed in a mass ratio of 8:1:1, deionized water is added and stirred evenly to obtain a negative electrode slurry. The negative electrode slurry is evenly coated on the negative electrode current collector aluminum foil using a coater. After drying, rolling and cutting, a disc negative electrode sheet is obtained. A sodium metal sheet is used as the positive electrode, and a 1.0 mol / L LiPF6 solution is used as the electrolyte. The solvent of the electrolyte is a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC) and fluoroethylene carbonate (FEC), wherein the volume ratio of EC, DMC and FEC is 4.5:4.5:1. The battery is assembled into a button cell in an argon glove box.

[0121] The battery performance was tested in the battery testing system, and the specific tests are as follows:

[0122] (1) Initial discharge capacity, initial charge capacity and initial coulombic efficiency test: Using a battery testing system, under the condition of 25℃, first discharge at a constant current rate of 0.1C to 0V, let stand for 5 minutes, then discharge at a rate of 0.05C to 0V to obtain the initial discharge capacity C1; then let stand for 5 minutes, and charge at a constant current rate of 0.1C to 2.0V to obtain the initial charge capacity C2; initial coulombic efficiency = (C2 / C1)*100%.

[0123] (2) Capacity retention rate test after 200 cycles: Under the condition of 25℃, first discharge to 0V at a constant current rate of 0.2C, let stand for 5 minutes, and then charge to 2.0V at a constant current rate of 0.2C. Perform cycle test according to this process, record the charging capacity at the 1st and 200th cycles, and obtain the capacity retention rate after 200 cycles by dividing the charging capacity at the 200th cycle by the charging capacity at the 1st cycle.

[0124] The test results are shown in Table 1.

[0125] As can be seen from the data in Table 1, the initial discharge capacity and initial charge capacity of the batteries in Examples 1 to 4 are all higher than those of the batteries in Comparative Examples 1 to 3. Furthermore, the initial discharge capacity of the batteries in these examples is generally above 450 mAh / g, which is relatively high. This indicates that the capacity performance of the batteries in these examples has been significantly improved. The initial coulombic efficiency of the batteries in Examples 1 to 4 is higher than that of Comparative Examples 1 and 2. In addition, the capacity retention rate of the batteries in Examples 1 to 4 after 200 cycles is greater than 80%, significantly higher than that of the batteries in Comparative Examples 1 to 3 after 200 cycles, indicating that the batteries in these examples have superior cycle stability. As the above analysis shows, this application utilizes the condensation reaction between monolayer MXene nanosheets and resin prepolymer with perylene-2,5,8,11-tetracarboxylic acid (PTCA) to achieve one-step chemical bonding of MXene and resin prepolymer via PTCA. This method is not only simple, low-cost, and highly controllable, but also allows PTCA to both bond MXene and resin prepolymer and act as an intercalating molecule to expand interlayer spacing and enhance structural stability. This effectively improves the self-stacking of MXene sheets, prevents aggregation, and thus provides more sodium storage sites. After carbonization of the carbon precursor, PTCA… The carbonization process also helps to increase the carbon content of the resulting anode material and expand the interlayer spacing of the hard carbon material. In the final anode material, the resin-based hard carbon attached to the surface of MXene can form a physical barrier and confinement effect, thereby effectively inhibiting the oxidation of MXene and improving the structural stability of MXene. Meanwhile, MXene can improve the overall electronic conductivity of the resin-based hard carbon material, protect the surface of the resin-based hard carbon material, shorten the sodium ion diffusion path, and improve the electrolyte mobility. Therefore, the final anode material has high initial coulombic efficiency, high capacity performance, and high cycle performance.

[0126] Table 1

[0127]

[0128] The negative electrode material prepared in Comparative Example 1 is a resin-based hard carbon material. A comparison of the data from Example 1 and Comparative Example 1 in Table 1 shows that, compared to Comparative Example 1, the battery in Example 1 exhibits significantly improved initial discharge capacity, initial charge capacity, initial coulombic efficiency, and capacity retention after 200 cycles. This further demonstrates that, in this application, by connecting MXene and the resin prepolymer via PTCA, PTCA, acting as a connection point (also known as a welding point), not only connects MXene and the resin prepolymer but also serves as an intercalation molecule to expand the interlayer spacing and support structural stability. This effectively improves the self-stabilization of MXene sheets, preventing agglomeration and thus providing more sodium storage sites. Furthermore, MXene improves the overall electronic conductivity of the resin-based carbon material and shortens the sodium ion diffusion path, resulting in the prepared MXene heterojunction composite hard carbon material exhibiting excellent capacity performance and cycle stability.

[0129] Compared to Example 1, Comparative Example 2 only added MXene material and did not add PTCA in the preparation of the negative electrode material, thus obtaining MXene composite hard carbon material. As can be seen from the comparison of data between Example 1 and Comparative Example 2 in Table 1, compared with Example 1, the battery in Comparative Example 2 has poorer first discharge capacity, first charge capacity, first coulombic efficiency, and capacity retention rate after 200 cycles. This indicates that connecting MXene and resin prepolymer with PTCA in this application is a key technical means to improve the performance of the prepared negative electrode material. Otherwise, it is difficult to effectively improve the capacity performance, first coulombic efficiency, and cycle performance of the negative electrode material.

[0130] Compared to Example 1, Comparative Example 3 only added PTCA to the preparation of the negative electrode material, without adding MXene, thus obtaining a PTCA-modified hard carbon composite material. As can be seen from the comparison of the data of Example 1 and Comparative Example 3 in Table 1, compared with Example 1, the battery in Comparative Example 3 has poorer initial discharge capacity, initial charge capacity, initial coulombic efficiency, and capacity retention rate after 200 cycles. This further indicates that the connection of MXene and resin prepolymer by PTCA in this application is a key technical means to improve the performance of the prepared negative electrode material. Otherwise, it is difficult to effectively improve the capacity performance, initial coulombic efficiency, and cycle performance of the negative electrode material.

[0131] Figure 2 and Figure 3 The images shown are scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the negative electrode material prepared in Example 1. Figure 2 It can be seen that the negative electrode material prepared in this application has a multilayer structure. Figure 3It can be seen that the negative electrode material contains a graphite-like microcrystalline structure with short-range order and long-range disorder, and there are also closed pores formed by the stacking of short-range disordered structures. This structure can provide a large amount of storage space for sodium ions, thereby improving the battery capacity, which is consistent with the above electrochemical performance test results.

[0132] Figure 4 The images show the XRD patterns of the negative electrode materials prepared in Example 1 and Comparative Example 1. Calculations from the XRD results show that the graphite interlayer spacing in the negative electrode material prepared in Comparative Example 1 is 0.365 nm, while the graphite interlayer spacing in the negative electrode material prepared in Example 1 is 0.389 nm. This indicates that in this application, perylene-2,5,8,11-tetracarboxylic acid is used as a bridge to chemically weld MXene and the resin prepolymer. Perylene-2,5,8,11-tetracarboxylic acid, acting as a welding point, not only connects MXene and the resin but also serves as an intercalation molecule to expand the interlayer spacing and enhance structural stability. This effectively improves the self-stacking of MXene sheets, avoids agglomeration, and provides more sodium storage sites. Therefore, the graphite interlayer spacing in the negative electrode material of this application is relatively large, which can effectively improve the sodium ion diffusion rate and the ability to intercalate sodium ions in the intercalation, thereby improving the capacity performance of the negative electrode material. This is consistent with the above electrochemical performance test results.

[0133] It should be noted that the negative electrode material embodiments, negative electrode material preparation method embodiments, negative electrode sheet embodiments, and battery embodiments provided in this application belong to the same concept; the technical features in the technical solutions described in each embodiment can be arbitrarily combined without conflict.

[0134] It should be understood that the above embodiments are exemplary and are not intended to encompass all possible implementations included in the claims. Various modifications and changes can be made to the above embodiments without departing from the scope of this disclosure. Similarly, the various technical features of the above embodiments can be arbitrarily combined to form other embodiments of the present invention that may not be explicitly described. Therefore, the above embodiments only illustrate several implementations of the present invention and do not limit the scope of protection of this patent.

Claims

1. A method for preparing a negative electrode material, characterized in that, Includes the following steps: S1: Mix the monolayer MXene suspension and the resin prepolymer dispersion evenly, add perylene-2,5,8,11-tetracarboxylic acid, and stir evenly to obtain the precursor solution; S2: The precursor solution is subjected to a hydrothermal reaction, and the monolayer MXene in the monolayer MXene suspension and the resin prepolymer in the resin prepolymer dispersion undergo a dehydration condensation reaction with the perylene-2,5,8,11-tetracarboxylic acid to chemically link MXene and resin prepolymer through the perylene-2,5,8,11-tetracarboxylic acid to obtain a carbon precursor; S3: The carbon precursor is carbonized under a protective gas atmosphere to obtain MXene heterojunction composite hard carbon material; the carbonization temperature is 1000℃~1500℃.

2. The method for preparing the negative electrode material according to claim 1, characterized in that, The preparation of the monolayer MXene suspension in step S1 includes the following steps: Monolayer MXene powder was added to deionized water and dispersed evenly to obtain the monolayer MXene suspension.

3. The method for preparing the negative electrode material according to claim 1, characterized in that, The preparation of the resin prepolymer dispersion in step S1 includes the following steps: The resin prepolymer is added to a solvent and dispersed evenly to obtain the resin prepolymer dispersion; optionally, the solvent includes an alcohol solvent and deionized water, and the volume ratio of the alcohol solvent to the deionized water is 1:(1~10).

4. The method for preparing the negative electrode material according to any one of claims 1 to 3, characterized in that, Step S1 satisfies at least one of the following characteristics: (1) The MXene includes at least one of Ti3C2, Ti2C, Ti3CN, V4C3, V2C, Nb2C, and Nb4C3; (2) The mass concentration of the monolayer MXene suspension is 0.01 g / ml to 0.05 g / ml; (3) The resin prepolymer includes at least one of phenolic resin prepolymer, epoxy resin prepolymer, urea-formaldehyde resin prepolymer, melamine-formaldehyde resin prepolymer, lignin phenolic resin prepolymer, and cellulose phenolic resin prepolymer; (4) The mass concentration of the resin prepolymer dispersion is 0.05 g / ml to 0.5 g / ml.

5. The method for preparing the negative electrode material according to any one of claims 1 to 3, characterized in that, In step S1, the mass of MXene in the monolayer MXene suspension is 10% to 50% of the mass of the resin prepolymer in the resin prepolymer dispersion; and / or, the mass of perylene-2,5,8,11-tetracarboxylic acid is 1% to 10% of the mass of the resin prepolymer in the resin prepolymer dispersion.

6. The method for preparing the negative electrode material according to any one of claims 1 to 3, characterized in that, In step S2, the temperature of the hydrothermal reaction is 100℃~150℃; and / or, the time of the hydrothermal reaction is 5h~10h.

7. The method for preparing the negative electrode material according to any one of claims 1 to 3, characterized in that, Step S3 satisfies at least one of the following characteristics: (1) The heat preservation time for the carbonization treatment is 2h~5h; (2) The heating rate of the carbonization treatment is 0.5℃ / min to 5℃ / min; (3) The protective gas includes at least one of nitrogen, argon, and helium; (4) The flow rate of the protective gas is 40 ml / min to 80 ml / min.

8. A negative electrode material, characterized in that, The negative electrode material is prepared by any one of claims 1 to 7.

9. A negative electrode sheet, characterized in that, The negative electrode sheet comprises the negative electrode material as described in claim 8.

10. A battery, characterized in that, Includes the negative electrode sheet as described in claim 9.

Images