Resin-based hard carbon microspheres, and preparation method and application thereof

Abstract

The application relates to the technical field of sodium ion negative electrode material preparation, and particularly discloses resin-based hard carbon microspheres, a preparation method and application thereof. The resin-based hard carbon microspheres are prepared from PMMA and cyano-modified phenolic resin through mixing, solidification and carbonization treatment, have the advantages of high first-week coulomb efficiency and high rate performance and the like, and have excellent sodium storage performance. The preparation method is simple and efficient, the production process is mature, the batch product is stable, the carbonization residual carbon rate is high, and the quality and purity of the carbonization product are improved. The resin-based hard carbon microspheres can be used for preparing high-performance battery negative electrode sheets, and meet the demand of different fields for high-performance negative electrode materials.

Description

Technical Field

[0001] This invention belongs to the field of sodium ion anode material preparation technology, specifically relating to resin-based hard carbon microspheres, their preparation methods, and applications. Background Technology

[0002] Sodium-ion batteries are considered a key candidate for future large-scale energy storage systems due to the abundance, wide distribution, and low cost of sodium resources. With the increasing demand for renewable energy and energy storage, developing high-performance sodium-ion battery anode materials has become a crucial research issue. Because of the large radius of sodium ions, traditional lithium-ion battery anode materials cannot adequately accommodate sodium ion intercalation behavior, leading researchers to explore various materials as anodes for sodium-ion batteries. Hard carbon materials have emerged as one of the most promising anode materials. The microstructure of hard carbon materials, composed of amorphous carbon and microcrystalline graphite, provides more sodium storage sites and pore space, effectively mitigating the volume change problem during sodium ion intercalation. Simultaneously, hard carbon materials have a large interlayer spacing, which facilitates sodium ion diffusion, thus exhibiting good electrochemical performance. Hard carbon exhibits a low sodium intercalation potential (typically 0.1-0.2V vs. Na / Na). + It can provide higher energy density, making it a significant potential application in sodium-ion batteries. These characteristics make it a popular choice for the anode of sodium-ion batteries.

[0003] Patent CN 115535998 A prepares phenolic resin microspheres by adding phenolic resin prepolymer and catalyst to a specific solvent for gelation. However, the solid content of the phenolic resin microspheres prepared by this method is only about 5%-10%, resulting in extremely low efficiency and high cost, thus lacking commercial application prospects. Patent CN109742383B prepares phenolic resin hard carbon materials by hydrothermal curing, mechanical pulverization, and high-temperature sintering of phenolic resin. The hard carbon materials prepared by this method have irregular shapes, requiring a relatively complex pulverization process, leading to high energy consumption and low material bulk density, resulting in low coulombic efficiency and low volumetric capacity. In the prior art, the initial coulombic efficiency (ICE) of hard carbon anode materials is low, usually because some sodium ions are irreversibly embedded into the pores or defects of the material during the first charging process, leading to capacity loss. Therefore, how to improve the initial efficiency and capacity of hard carbon materials remains a key research focus in this field.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] This invention provides a resin-based hard carbon microsphere prepared from PMMA (polymethyl methacrylate) and cyano-modified phenolic resin, and its preparation method. The preparation process is simple and low-cost. At the same time, it provides a battery anode sheet prepared using the microspheres, which aims to solve the problems of low initial coulombic efficiency and capacity loss of hard carbon anode materials in the prior art, and meet the demand of sodium-ion batteries for high-performance anode materials.

[0006] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0007] The primary objective of this invention is to provide a resin-based hard carbon microsphere, which is prepared by mixing, curing, and carbonizing PMMA and cyano-modified phenolic resin. The resin-based hard carbon microsphere has a particle size of 1-5.0 μm and a specific surface area of ​​3-21 m². 2 / g.

[0008] This invention utilizes cyano-modified phenolic resin to prepare resin-based hard carbon microspheres. The interaction between the cyano group and the phenolic resin matrix promotes a more uniform carbon layer arrangement and a more efficient charge transport path. The introduction of cyano groups enhances the thermal stability and chemical inertness of the material, enabling the hard carbon microspheres to maintain structural stability and resist degradation even under high temperatures and complex chemical environments. During carbonization, they exhibit higher thermal stability and pyrolysis char yield, resulting in stable products and a high residual carbon rate after carbonization, thereby improving the quality and purity of the carbonization products. Simultaneously, the introduction of cyano groups optimizes the microstructure of the material, increasing porosity and sodium storage sites, thereby enhancing electrochemical activity, including higher initial coulombic efficiency and capacity, as well as superior cycling performance.

[0009] The particle size of the resin-based hard carbon microspheres is controlled at 1-5.0 μm, and the specific surface area is 3-21 m². 2 / g, such a microstructure provides more sodium storage sites and pore space, effectively alleviating the volume change problem during sodium ion insertion.

[0010] In the above technical solution, the phenolic hydroxyl groups in the cyano-modified phenolic resin are replaced by phthalonitrile groups, and the structure of the cyano-modified phenolic resin is shown in Formula I:

[0011]

[0012] in,

[0013] n is any integer between 1 and 8;

[0014] Optionally, the grafting rate of phthalonitrile groups is 30-75%.

[0015] Optionally, the grafting rate of phthalonitrile groups is 50-75%.

[0016] In this invention, the grafting rate of phthalonitrile groups refers to the molar percentage of phenolic hydroxyl groups replaced by phthalonitrile groups in the phenolic resin. That is, a higher grafting rate of phthalonitrile groups means a larger proportion of cyano groups introduced into the phenolic resin. Within a certain range, a larger proportion of cyano groups results in a lower specific surface area and correspondingly better electrochemical performance.

[0017] This invention can utilize phenolic resins modified with phthalonitrile, cyanate esters, cyanosilanes, cyanoacrylates, etc. However, phthalonitrile groups are preferred for modification. Firstly, because phthalonitrile groups contain two active cyano groups, they can react with various groups to form a highly cross-linked three-dimensional network. This structure significantly improves the mechanical strength of the phenolic resin, giving it superior physical and chemical properties. Secondly, during resin processing, the reaction of phthalonitrile groups does not produce small-molecule byproducts. This characteristic avoids the adverse effects of small-molecule byproducts on resin performance and also helps maintain the purity and stability of the resin. Therefore, cyano-modified phenolic resin obtained by phthalonitrile modification is a more reasonable choice for improving the performance of carbon materials and achieving a higher cross-linking density. It not only meets our high requirements for resin performance but also maintains the purity and stability of the resin during processing.

[0018] In the above technical solution, the mass ratio of PMMA and cyano-modified phenolic resin is 1:(2-3).

[0019] Optionally, the PMMA has an apparent viscosity with an average molecular weight range of 70,000-100,000.

[0020] Optional, PMMA has an apparent viscosity with an average molecular weight range of 80,000-99,400.

[0021] In this invention, for the sake of simplicity, "PMMA apparent viscosity average molecular weight" is simply referred to as "PMMA molecular weight".

[0022] The molecular weight of PMMA is in the range of 70,000-100,000. The larger the molecular weight of PMMA, the more beneficial it is to the phase separation of resin spheres during the curing process. The smaller the specific surface area of ​​hard carbon microspheres, the better the electrochemical performance. However, if the molecular weight of PMMA is too large, it may lead to an increase in the viscosity of the resin solution, making processing difficult, limiting the contact between the electrolyte and the active material, and affecting the charge and discharge efficiency and capacity of the battery. On the other hand, if the molecular weight is too low, the dispersibility of the resin spheres may be poor before curing, reducing the uniformity and stability of the product, which in turn affects the charge and discharge efficiency and capacity of the battery. At the same time, the mechanical strength may also be insufficient.

[0023] A second objective of this invention is to provide a method for preparing the above-mentioned resin-based hard carbon microspheres, comprising the following steps:

[0024] (1) PMMA and cyano-modified phenolic resin were added to a solvent and mixed evenly, and then the solvent was removed to obtain a blend.

[0025] (2) The blend was subjected to a step-curing process to obtain cured resin microspheres;

[0026] (3) The cured resin microspheres are broken up and carbonized by two-step heat treatment under an inert atmosphere to obtain resin-based hard carbon microspheres.

[0027] In the above technical solution, in step (1), PMMA and cyano-modified phenolic resin are added to the solvent under heating conditions and mixed evenly by continuous stirring.

[0028] In step (1), heating can be achieved through a water bath or an oil bath.

[0029] The heating temperature is optional, ranging from 70 to 85℃.

[0030] The stirring time is optional, ranging from 1 to 2 hours.

[0031] Optionally, the solvent may be selected from one or more of acetone, dimethylformamide, dimethyl sulfoxide, methyl ethyl ketone, and N-methylpyrrolidone.

[0032] Acetone is an optional solvent. Considering factors such as cost, boiling point, and toxicity, acetone is the optimal solvent. Both PMMA and cyano-modified phenolic resin are soluble in acetone. Acetone can dissolve PMMA and simultaneously allow for better and more uniform mixing of PMMA and cyano-modified phenolic resin.

[0033] In step (1), after PMMA and cyano-modified phenolic resin are mixed evenly in a solvent, the solvent can be removed by methods such as evaporation, evaporation, or vacuum distillation.

[0034] In the above technical solution, the conditions for the stepped curing in step (2) include:

[0035] First, heat the temperature to 150-190℃ and cure for 1-2 hours;

[0036] Continue heating to 200-240℃ and cure for 1-2 hours;

[0037] Continue heating to 250-280℃ and cure for 4-6 hours to obtain cured resin microspheres.

[0038] Alternatively, heat to 160-180℃ and cure for 1 hour;

[0039] Continue heating to 200-220℃ and cure for 1 hour;

[0040] Continue heating to 270-280℃ and cure for 4 hours to obtain cured resin microspheres.

[0041] This invention utilizes a stepped curing process to control the reaction rate of the blend, reduce side reactions, lower internal stress, prevent cracking, and improve the material's thermal stability and mechanical properties. During curing, appropriate curing temperature and time promote full cross-linking of the resin, forming a stable three-dimensional network structure. Insufficient curing temperature or time may lead to incomplete curing, affecting the product's stability and performance.

[0042] In the above technical solution, in step (3), when performing two-step heat treatment carbonization, the first heat treatment is to raise the temperature from room temperature to 500-800℃ at a rate of 5-10℃ / min and hold for 2-4 hours; the second heat treatment continues to raise the temperature to 1000℃-1800℃ at a rate of 5-10℃ / min and hold for 1-3 hours.

[0043] In the above technical solution, during carbonization in step (3), the inert atmosphere is nitrogen or argon.

[0044] The core objective of step (3) in the two-step heat treatment carbonization process is to optimize the carbonization reaction, balance the structural formation and performance requirements of the carbon material, reduce internal stress, avoid material defects, and control the release of volatile gases to prevent structural damage. Appropriate carbonization temperature and time can promote the enrichment of carbon elements in the resin and increase the degree of graphitization, thereby enhancing the conductivity and sodium storage capacity of the hard carbon microspheres; however, excessively high carbonization temperature or excessively long time may lead to the destruction of the hard carbon microsphere structure and a decrease in electrochemical performance.

[0045] A third objective of this invention is to provide a battery negative electrode sheet prepared using the above-mentioned resin-based hard carbon microspheres.

[0046] Alternatively, the above-mentioned battery negative electrode preparation process involves mixing resin-based hard carbon microspheres, conductive agent, binder, and solvent, coating them onto a metal substrate, and then vacuum drying to obtain the battery negative electrode.

[0047] Optionally, the conductive agent is a Super P conductive agent. Alternatively, conductive carbon black agents such as Ketjen Black, as well as single-walled or multi-walled carbon nanotube conductive agents, can be used. These conductive agents can enhance the conductivity of the negative electrode.

[0048] Optionally, the adhesive is polyvinylidene fluoride (PVDF). Other water-based adhesives (such as sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyacrylic acid), organic solvent-based adhesives (such as polytetrafluoroethylene), and other novel adhesives may also be selected. The adhesive is used to fix active materials, conductive agents, etc., onto a metal substrate.

[0049] Optionally, the solvent is N-methylpyrrolidone. The solvent should be selected as an aqueous or organic solvent system compatible with the process. For example, when polyvinylidene fluoride is used as the binder, N-methylpyrrolidone is a suitable solvent selection.

[0050] In the preparation of battery negative electrode sheets, the selection of conductive agents, binders, and solvents should be matched according to specific process and performance requirements to ensure the conductivity, mechanical strength, and stability of the negative electrode sheet. The coating process should be uniform and smooth to avoid uneven coating thickness or defects. The vacuum drying process should strictly control temperature and time to avoid damage to the negative electrode sheet or affecting its performance.

[0051] The fourth objective of this invention is to provide an application of resin-based hard carbon microspheres or battery negative electrode sheets in the preparation of sodium-ion batteries.

[0052] By adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art.

[0053] This invention combines PMMA (polymethyl methacrylate) and cyano-modified phenolic resin to prepare resin-based hard carbon microspheres with more sodium storage sites and pore space, effectively alleviating the volume change problem during sodium ion insertion, improving the structural stability and electrochemical activity of hard carbon materials, thereby improving the initial coulombic efficiency and capacity. As a result, the resin-based hard carbon microspheres have the advantages of high first-cycle coulombic efficiency and high rate performance, resulting in excellent sodium storage performance.

[0054] This invention provides a simpler and more efficient method for preparing resin-based hard carbon microspheres through polymer phase separation during curing and a two-step high-temperature calcination process. Furthermore, the method uses cyano-modified phenolic resin and PMMA as raw materials to prepare resin-based hard carbon microspheres. This process is mature, the batch products are stable, and the residual carbon rate after carbonization is high, thereby improving the quality and purity of the carbonized products.

[0055] The resin-based hard carbon microspheres prepared by this invention can be used to prepare high-performance battery anode sheets, meeting the needs of different fields for high-performance anode materials.

[0056] The specific embodiments of the present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0057] The accompanying drawings, as part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention, but do not constitute an undue limitation of the invention. Obviously, the drawings described below are merely some embodiments, and those skilled in the art can obtain other drawings based on these drawings without creative effort. In the drawings:

[0058] Figure 1The first-week charge-discharge curve of the resin-based hard carbon microspheres prepared in Example 3;

[0059] Figure 2 These are morphology and size distribution diagrams of the resin-based hard carbon microspheres prepared in Example 5;

[0060] Figure 3 The nitrogen adsorption-desorption curves of the resin-based hard carbon microspheres prepared in Example 5 are shown.

[0061] Figure 4 The first-week charge-discharge curve of the resin-based hard carbon microspheres prepared in Example 5 is shown.

[0062] It should be noted that these accompanying drawings and textual descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art by referring to specific embodiments. Detailed Implementation

[0063] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0064] In this invention, the term "PNx" is used to refer to a cyano-modified phenolic resin having a specific grafting rate of phthalonitrile groups, where "x" represents a specific numerical value of the grafting rate in percentage form. For example:

[0065] PN20: Indicates a cyano-modified phenolic resin with a grafting rate of 20% of phthalonitrile groups in the modified phenolic resin.

[0066] PN30: Indicates a cyano-modified phenolic resin in which the grafting rate of phthalonitrile groups in the modified phenolic resin is 30%.

[0067] Similarly, other cyano-modified phenolic resins with different grafting rates can be named and represented using the form "PNx".

[0068] Detection methods

[0069] 1. The specific surface area of ​​carbon materials was determined using the nitrogen adsorption BET method according to the national standard GB / T 19587-2017 "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method". The test steps are as follows:

[0070] (1) Sample preparation

[0071] ① Sample pretreatment: The sample is degassed to remove physically adsorbed substances (such as water or gas) from its surface. The sample is then heated in a vacuum or inert gas environment (the heating temperature is usually between 90-300℃, depending on the properties of the sample). In this embodiment of the invention, the heating temperature is 105℃, and the time is 2-12 hours.

[0072] ② Sample mass determination: Accurately weigh the degassed sample.

[0073] (2) Adsorption test

[0074] ① Selection of adsorption gas: High-purity nitrogen (≥99.99%) was used as the adsorption gas. Liquid nitrogen was used for cooling to maintain the sample adsorption environment at 77.3K.

[0075] ②Isotherm determination: The amount of gas adsorbed is measured by controlling the relative pressure of the adsorbed gas. Adsorption and desorption data are recorded using an automatic gas adsorption analyzer.

[0076] (3) Data processing:

[0077] ① Plotting adsorption isotherms: Plot nitrogen adsorption isotherms based on adsorption data.

[0078] ②Based on the BET specific surface area, the monolayer adsorption amount is determined by linear fitting, and the specific surface area is calculated.

[0079] 2. Electrochemical performance testing (first week of charge / discharge) of button batteries was conducted using a Newway battery tester:

[0080] Test method: Let stand for 12 hours, discharge to 0V at 0.1C, discharge to 0V at 0.05C, discharge to 0V at 0.02C, discharge to 0V at 0.01C, let stand for 10 minutes, and charge to 2.5V at 0.1C.

[0081] Example 1

[0082] Preparation of a resin-based hard carbon microsphere:

[0083] (1) Under the condition of water bath heating temperature of 85℃, PMMA with a molecular weight of 84155 and cyano-modified phenolic resin PN30 with a grafting rate of 30% of phthalonitrile groups are stirred evenly in acetone solvent at a mass ratio of 1:3. After the two are evenly mixed, the solvent is evaporated under water bath heating to obtain the blend.

[0084] (2) The blend was transferred to an oven for step curing. First, the temperature was raised to 170°C and cured for 1 hour; then the temperature was raised to 200°C and cured for 1 hour; then the temperature was raised to 280°C and cured for 4 hours. After curing, the cured resin microspheres were obtained.

[0085] (3) The solidified resin microspheres were broken into smaller pieces using a crusher and placed in a crucible. The crucible was then placed in a tube furnace under an inert atmosphere and carbonized through a two-step heat treatment. The first heat treatment involved raising the temperature from room temperature to 800℃ at a rate of 5℃ / min and holding it at that temperature for 2 hours to obtain pre-carbonized resin. The second heat treatment involved further heating to 1400℃ at a rate of 5℃ / min and holding it at that temperature for 2 hours to obtain resin-based hard carbon microspheres. The particle size of the hard carbon microspheres was approximately 4 μm, and their specific surface area was measured to be 8.02 m². 2 / g.

[0086] Preparation of a button cell battery:

[0087] The resin-based hard carbon microspheres, Super P conductive agent, and polyvinylidene fluoride (PVDF) binder prepared above were added to N-methylpyrrolidone (NMP) at a mass ratio of 8.9:0.5:0.6 to form a uniform slurry. This slurry was then uniformly coated onto copper foil using a coating method. After drying, the slurry was punched into a circular negative electrode sheet and vacuum-dried at 120°C for 12 hours. Using the prepared negative electrode sheet as the positive electrode and a sodium metal sheet as the negative electrode, a 1M sodium hexafluorophosphate electrolyte in EC:DMC = 1:1 vol%, and a glass fiber separator, button batteries were assembled in a glove box. The electrochemical performance of the button batteries was tested using a Newway battery tester (test conditions: room temperature, voltage range 0.001-2.5V vs. Na / Na). + The test results show that hard carbon materials can withstand current densities of 30 mA·g. -1 At that time, the initial specific capacity was 393.23 mA·g. -1 The initial Coulomb efficiency was 76.09%.

[0088] Example 2

[0089] Preparation of a resin-based hard carbon microsphere:

[0090] (1) Under the condition of water bath heating temperature of 85℃, PMMA with a molecular weight of 84155 and cyano-modified phenolic resin PN50 with a grafting rate of 50% of phthalonitrile groups are stirred evenly in acetone solvent at a mass ratio of 1:3. After the two are evenly mixed, the solvent is evaporated under water bath heating to obtain the blend.

[0091] (2) The blend was transferred to an oven for step curing. First, the temperature was raised to 170℃ and cured for 1 hour; then the temperature was raised to 200℃ and cured for 1 hour; then the temperature was raised to 280℃ and cured for 4 hours. After curing, the cured resin microspheres were obtained.

[0092] (3) The solidified resin microspheres were broken into smaller pieces using a crusher and placed in a crucible. The crucible was then placed in a tube furnace under an inert atmosphere and carbonized through a two-step heat treatment. The first heat treatment involved raising the temperature from room temperature to 800℃ at a rate of 5℃ / min and holding it at that temperature for 2 hours to obtain pre-carbonized resin. The second heat treatment involved further raising the temperature to 1400℃ at a rate of 5℃ / min and holding it at that temperature for 2 hours to obtain resin-based hard carbon microspheres. The particle size of the hard carbon microspheres was approximately 3 μm, and their specific surface area was measured to be 8.11 m². 2 / g.

[0093] Preparation of a button cell battery:

[0094] The resin-based hard carbon microspheres, Super P conductive agent, and polyvinylidene fluoride (PVDF) binder prepared above were added to N-methylpyrrolidone (NMP) at a mass ratio of 8.9:0.5:0.6 to form a uniform slurry. This slurry was then uniformly coated onto copper foil using a coating method. After drying, the slurry was punched into a circular negative electrode sheet and vacuum-dried at 120°C for 12 hours. Using the prepared negative electrode sheet as the positive electrode and a sodium metal sheet as the negative electrode, a 1M sodium hexafluorophosphate electrolyte in EC:DMC = 1:1 vol%, and a glass fiber separator, button batteries were assembled in a glove box. The electrochemical performance of the button batteries was tested using a Newway battery tester (test conditions: room temperature, voltage range 0.001-2.5V vs. Na / Na). + The test results show that hard carbon materials can withstand current densities of 30 mA·g. -1 At that time, the initial specific capacity was 356.63 mA·g. -1 The initial Coulomb efficiency was 81.62%.

[0095] Example 3

[0096] Preparation of a resin-based hard carbon microsphere:

[0097] (1) Under the condition of water bath heating temperature of 85℃, PMMA with a molecular weight of 84155 and cyano-modified phenolic resin PN75 with a grafting rate of 75% of phthalonitrile groups are stirred evenly in acetone solvent at a mass ratio of 1:3. After the two are evenly mixed, the solvent is evaporated under water bath heating to obtain the blend.

[0098] (2) The blend was transferred to an oven for step curing. First, the temperature was raised to 170°C and cured for 1 hour; then the temperature was raised to 200°C and cured for 1 hour; then the temperature was raised to 280°C and cured for 4 hours. After curing, the cured resin microspheres were obtained.

[0099] (3) The solidified resin microspheres were broken into smaller pieces using a crusher and placed in a crucible. The crucible was then placed in a tube furnace under an inert atmosphere and carbonized through a two-step heat treatment. The first heat treatment involved raising the temperature from room temperature to 800℃ at a rate of 5℃ / min and holding it at that temperature for 2 hours to obtain pre-carbonized resin. The second heat treatment involved further raising the temperature to 1400℃ at a rate of 5℃ / min and holding it at that temperature for 2 hours to obtain resin-based hard carbon microspheres. The particle size of the hard carbon microspheres was approximately 2 μm, and their specific surface area was measured to be 7.08 m². 2 / g.

[0100] Preparation of a button cell battery:

[0101] The resin-based hard carbon microspheres, Super P conductive agent, and polyvinylidene fluoride (PVDF) binder prepared above were added to N-methylpyrrolidone (NMP) at a mass ratio of 8.9:0.5:0.6 to form a uniform slurry. This slurry was then uniformly coated onto copper foil using a coating method. After drying, the slurry was punched into a circular negative electrode sheet and vacuum-dried at 120°C for 12 hours. Using the prepared negative electrode sheet as the positive electrode and a sodium metal sheet as the negative electrode, a 1M sodium hexafluorophosphate electrolyte in EC:DMC = 1:1 vol%, and a glass fiber separator, button batteries were assembled in a glove box. The electrochemical performance of the button batteries was tested using a Newway battery tester (test conditions: room temperature, voltage range 0.001-2.5V vs. Na / Na). + The test results are shown below. Figure 1 The test results show that hard carbon materials can withstand current densities of 30 mA·g -1 At that time, the initial specific capacity was 370.62 mA·g. -1 The initial Coulomb efficiency was 85.13%.

[0102] Example 4

[0103] Preparation of a resin-based hard carbon microsphere:

[0104] Resin-based hard carbon microspheres were prepared using PMMA with a molecular weight of 74983. Other raw materials and the preparation process were exactly the same as in Example 3. The resulting resin-based hard carbon microspheres had a particle size of approximately 2 μm and a measured specific surface area of ​​20.55 m². 2 / g.

[0105] Preparation of a button cell battery:

[0106] The resin-based hard carbon microspheres, Super P conductive agent, and polyvinylidene fluoride (PVDF) binder prepared above were added to N-methylpyrrolidone (NMP) at a mass ratio of 8.9:0.5:0.6 to form a uniform slurry. This slurry was then uniformly coated onto copper foil using a coating method. After drying, the slurry was punched into a circular negative electrode sheet and vacuum-dried at 120°C for 12 hours. Using the prepared negative electrode sheet as the positive electrode and a sodium metal sheet as the negative electrode, a 1M sodium hexafluorophosphate electrolyte in EC:DMC = 1:1 vol%, and a glass fiber separator, button batteries were assembled in a glove box. The electrochemical performance of the button batteries was tested using a Newway battery tester (test conditions: room temperature, voltage range 0.001-2.5V vs. Na / Na). + The test results show that hard carbon materials can withstand current densities of 30 mA·g. -1 At that time, the initial specific capacity was 370.95 mA·g. -1 The initial Coulomb efficiency was 84.43%.

[0107] Example 5

[0108] Preparation of a resin-based hard carbon microsphere:

[0109] Resin-based hard carbon microspheres were prepared using PMMA with a molecular weight of 99326. Other raw materials and the preparation process were exactly the same as in Example 3. The resulting resin-based hard carbon microspheres had a particle size of approximately 2 μm, and their morphology and particle size distribution are as follows. Figure 2 The tested specific surface area was 4.95 m². 2 / g.

[0110] Preparation of a button cell battery:

[0111] The resin-based hard carbon microspheres, Super P conductive agent, and polyvinylidene fluoride (PVDF) binder prepared above were added to N-methylpyrrolidone (NMP) at a mass ratio of 8.9:0.5:0.6 to form a uniform slurry. This slurry was then uniformly coated onto copper foil using a coating method. After drying, the slurry was punched into a circular negative electrode sheet and vacuum-dried at 120°C for 12 hours. Using the prepared negative electrode sheet as the positive electrode and a sodium metal sheet as the negative electrode, a 1M sodium hexafluorophosphate electrolyte in EC:DMC = 1:1 vol%, and a glass fiber separator, button batteries were assembled in a glove box. The electrochemical performance of the button batteries was tested using a Newway battery tester (test conditions: room temperature, voltage range 0.001-2.5V vs. Na / Na). + The test results are shown below. Figure 3 and Figure 4 The test results show that hard carbon materials can withstand current densities of 30 mA·g -1 At that time, the initial specific capacity was 371.48 mA·g. -1 The initial Coulomb efficiency was 88.18%.

[0112] Example 6

[0113] Preparation of a resin-based hard carbon microsphere:

[0114] (1) Under the condition of water bath heating temperature of 85℃, PMMA with a molecular weight of 99326 and cyano-modified phenolic resin PN75 with a grafting rate of 75% of phthalonitrile groups are stirred evenly in acetone solvent at a mass ratio of 1:2. After the two are evenly mixed, the solvent is evaporated under water bath heating to obtain the blend.

[0115] (2) The blend was transferred to an oven for step curing. First, the temperature was raised to 170℃ and cured for 1 hour; then the temperature was raised to 200℃ and cured for 1 hour; then the temperature was raised to 280℃ and cured for 4 hours. After curing, the cured resin microspheres were obtained.

[0116] (3) The solidified resin microspheres were broken into smaller pieces using a crusher and placed in a crucible. The crucible was then placed in a tube furnace under an inert atmosphere and carbonized through a two-step heat treatment. The first heat treatment involved raising the temperature from room temperature to 800℃ at a rate of 5℃ / min and holding it at that temperature for 2 hours to obtain pre-carbonized resin. The second heat treatment involved further raising the temperature to 1400℃ at a rate of 5℃ / min and holding it at that temperature for 2 hours to obtain resin-based hard carbon microspheres. The particle size of the hard carbon microspheres was approximately 1 μm, and their specific surface area was measured to be 5.02 m². 2 / g.

[0117] Preparation of a button cell battery:

[0118] The resin-based hard carbon microspheres, Super P conductive agent, and polyvinylidene fluoride (PVDF) binder prepared above were added to N-methylpyrrolidone (NMP) at a mass ratio of 8.9:0.5:0.6 to form a uniform slurry. This slurry was then uniformly coated onto copper foil using a coating method. After drying, the slurry was punched into a circular negative electrode sheet and vacuum-dried at 120°C for 12 hours. Using the prepared negative electrode sheet as the positive electrode and a sodium metal sheet as the negative electrode, a 1M sodium hexafluorophosphate electrolyte in EC:DMC = 1:1 vol%, and a glass fiber separator, button batteries were assembled in a glove box. The electrochemical performance of the button batteries was tested using a Newway battery tester (test conditions: room temperature, voltage range 0.001-2.5V vs. Na / Na). + The test results show that hard carbon materials can withstand current densities of 30 mA·g. -1 At that time, the initial specific capacity was 366.87 mA·g. -1 The initial Coulomb efficiency was 83.26%.

[0119] Example 7

[0120] Preparation of a resin-based hard carbon microsphere:

[0121] (1) Under the condition of water bath heating temperature of 85℃, PMMA with a molecular weight of 99326 and cyano-modified phenolic resin PN75 with a grafting rate of 75% of phthalonitrile groups are stirred evenly in acetone solvent at a mass ratio of 1:3. After the two are evenly mixed, the solvent is evaporated under water bath heating to obtain the blend.

[0122] (2) The blend was transferred to an oven for step curing. First, the temperature was raised to 170°C and cured for 1 hour; then the temperature was raised to 200°C and cured for 1 hour; then the temperature was raised to 280°C and cured for 4 hours. After curing, the cured resin microspheres were obtained.

[0123] (3) The solidified resin microspheres were broken into smaller pieces using a crusher and placed in a crucible. The crucible was then placed in a tube furnace under an inert atmosphere and carbonized through a two-step heat treatment. The first heat treatment involved raising the temperature from room temperature to 800°C at a rate of 5°C / min and holding it at that temperature for 2 hours to obtain pre-carbonized resin. The second heat treatment involved further heating to 1200°C at a rate of 5°C / min and holding it at that temperature for 2 hours to obtain resin-based hard carbon microspheres. The particle size of the hard carbon microspheres was approximately 2 μm, and their specific surface area was measured to be 4.24 m². 2 / g.

[0124] Preparation of a button cell battery:

[0125] The resin-based hard carbon microspheres, Super P conductive agent, and polyvinylidene fluoride (PVDF) binder prepared above were added to N-methylpyrrolidone (NMP) at a mass ratio of 8.9:0.5:0.6 to form a uniform slurry. This slurry was then uniformly coated onto copper foil using a coating method. After drying, the slurry was punched into a circular negative electrode sheet and vacuum-dried at 120°C for 12 hours. Using the prepared negative electrode sheet as the positive electrode and a sodium metal sheet as the negative electrode, a 1M sodium hexafluorophosphate electrolyte in EC:DMC = 1:1 vol%, and a glass fiber separator, button batteries were assembled in a glove box. The electrochemical performance of the button batteries was tested using a Newway battery tester (test conditions: room temperature, voltage range 0.001-2.5V vs. Na / Na). + The test results show that hard carbon materials can withstand current densities of 30 mA·g. -1 At that time, the initial specific capacity was 371.35 mA·g. -1 The initial Coulomb efficiency was 83.77%.

[0126] Example 8

[0127] Preparation of a resin-based hard carbon microsphere:

[0128] (1) Under the condition of water bath heating temperature of 85℃, PMMA with a molecular weight of 99326 and cyano-modified phenolic resin PN75 with a grafting rate of 75% of phthalonitrile groups are stirred evenly in acetone solvent at a mass ratio of 1:3. After the two are evenly mixed, the solvent is evaporated under water bath heating to obtain the blend.

[0129] (2) The blend was transferred to an oven for step curing. First, the temperature was raised to 170°C and cured for 1 hour; then the temperature was raised to 200°C and cured for 1 hour; then the temperature was raised to 280°C and cured for 4 hours. After curing, the cured resin microspheres were obtained.

[0130] (3) The solidified resin microspheres were broken into smaller pieces using a crusher and placed in a crucible. The crucible was then placed in a tube furnace under an inert atmosphere and carbonized through a two-step heat treatment. The first heat treatment involved raising the temperature from room temperature to 800℃ at a rate of 5℃ / min and holding it at that temperature for 2 hours to obtain pre-carbonized resin. The second heat treatment involved further heating to 1600℃ at a rate of 5℃ / min and holding it at that temperature for 2 hours to obtain resin-based hard carbon microspheres. The particle size of the hard carbon microspheres was approximately 2 μm, and their specific surface area was measured to be 8.38 m². 2 / g.

[0131] Preparation of a button cell battery:

[0132] The resin-based hard carbon microspheres, Super P conductive agent, and polyvinylidene fluoride (PVDF) binder prepared above were added to N-methylpyrrolidone (NMP) at a mass ratio of 8.9:0.5:0.6 to form a uniform slurry. This slurry was then uniformly coated onto copper foil using a coating method. After drying, the slurry was punched into a circular negative electrode sheet and vacuum-dried at 120°C for 12 hours. Using the prepared negative electrode sheet as the positive electrode and a sodium metal sheet as the negative electrode, a 1M sodium hexafluorophosphate electrolyte in EC:DMC = 1:1 vol%, and a glass fiber separator, button batteries were assembled in a glove box. The electrochemical performance of the button batteries was tested using a Newway battery tester (test conditions: room temperature, voltage range 0.001-2.5V vs. Na / Na). + The test results show that hard carbon materials can withstand current densities of 30 mA·g. -1 At that time, the initial specific capacity was 301.53 mA·g. -1 The initial Coulomb efficiency was 80.15%.

[0133] Comparative Example 1

[0134] Preparation of a resin-based hard carbon microsphere:

[0135] (1) Under the condition of water bath heating temperature of 85℃, PMMA with a molecular weight of 84155 and cyano-modified phenolic resin PN20 with a grafting rate of 20% of phthalonitrile groups are stirred evenly in acetone solvent at a mass ratio of 1:3. After the two are evenly mixed, the solvent is evaporated under water bath heating to obtain the blend.

[0136] (2) The blend was transferred to an oven for step curing. First, the temperature was raised to 170°C and cured for 1 hour; then the temperature was raised to 200°C and cured for 1 hour; then the temperature was raised to 280°C and cured for 4 hours. After curing, the cured resin microspheres were obtained.

[0137] (3) The solidified resin microspheres were broken into smaller pieces using a crusher and placed in a crucible. The crucible was then placed in a tube furnace under an inert atmosphere and carbonized through a two-step heat treatment. The first heat treatment involved raising the temperature from room temperature to 800℃ at a rate of 5℃ / min and holding it at that temperature for 2 hours to obtain pre-carbonized resin. The second heat treatment involved further heating to 1400℃ at a rate of 5℃ / min and holding it at that temperature for 2 hours to obtain resin-based hard carbon microspheres. The particle size of the hard carbon microspheres was approximately 4 μm, and their specific surface area was measured to be 20.55 m². 2 / g.

[0138] Preparation of a button cell battery:

[0139] The resin-based hard carbon microspheres, Super P conductive agent, and polyvinylidene fluoride (PVDF) binder prepared above were added to N-methylpyrrolidone (NMP) at a mass ratio of 8.9:0.5:0.6 to form a uniform slurry. This slurry was then uniformly coated onto copper foil using a coating method. After drying, the slurry was punched into a circular negative electrode sheet and vacuum-dried at 120°C for 12 hours. Using the prepared negative electrode sheet as the positive electrode and a sodium metal sheet as the negative electrode, a 1M sodium hexafluorophosphate electrolyte in EC:DMC = 1:1 vol%, and a glass fiber separator, button batteries were assembled in a glove box. The electrochemical performance of the button batteries was tested using a Newway battery tester (test conditions: room temperature, voltage range 0.001-2.5V vs. Na / Na). + The test results show that hard carbon materials can withstand current densities of 30 mA·g. -1 At that time, the initial specific capacity was 210.69 mA·g. -1 The initial Coulomb efficiency was 60.27%.

[0140] Comparative Example 2

[0141] Preparation of a resin-based hard carbon microsphere:

[0142] (1) Under the condition of water bath heating temperature of 85℃, PMMA with a molecular weight of 84155 and cyano-modified phenolic resin PN80 with a grafting rate of 80% of phthalonitrile groups are stirred evenly in acetone solvent at a mass ratio of 1:3. After the two are evenly mixed, the solvent is evaporated under water bath heating to obtain the blend.

[0143] (2) The blend was transferred to an oven for step curing. First, the temperature was raised to 170°C and cured for 1 hour; then the temperature was raised to 200°C and cured for 1 hour; then the temperature was raised to 280°C and cured for 4 hours. After curing, the cured resin microspheres were obtained.

[0144] (3) The solidified resin microspheres were broken into smaller pieces using a crusher and placed in a crucible. The crucible was then placed in a tube furnace under an inert atmosphere and carbonized through a two-step heat treatment. The first heat treatment involved raising the temperature from room temperature to 800℃ at a rate of 5℃ / min and holding it at that temperature for 2 hours to obtain pre-carbonized resin. The second heat treatment involved further heating to 1400℃ at a rate of 5℃ / min and holding it at that temperature for 2 hours to obtain resin-based hard carbon microspheres. The particle size of the hard carbon microspheres was approximately 2 μm, and their specific surface area was measured to be 4.05 m². 2 / g.

[0145] Preparation of a button cell battery:

[0146] The resin-based hard carbon microspheres, Super P conductive agent, and polyvinylidene fluoride (PVDF) binder prepared above were added to N-methylpyrrolidone (NMP) at a mass ratio of 8.9:0.5:0.6 to form a uniform slurry. This slurry was then uniformly coated onto copper foil using a coating method. After drying, the slurry was punched into a circular negative electrode sheet and vacuum-dried at 120°C for 12 hours. Using the prepared negative electrode sheet as the positive electrode and a sodium metal sheet as the negative electrode, a 1M sodium hexafluorophosphate electrolyte in EC:DMC = 1:1 vol%, and a glass fiber separator, button batteries were assembled in a glove box. The electrochemical performance of the button batteries was tested using a Newway battery tester (test conditions: room temperature, voltage range 0.001-2.5V vs. Na / Na). + The test results show that hard carbon materials can withstand current densities of 30 mA·g. -1 At that time, the initial specific capacity was 296.57 mA·g. -1 The initial Coulomb efficiency was 69.54%.

[0147] Comparative Example 3

[0148] PMMA with a molecular weight of 60,000 was used, and other raw material conditions and preparation processes were the same as in Example 1. The specific steps are as follows:

[0149] Preparation of a resin-based hard carbon microsphere:

[0150] (1) Under the condition of water bath heating temperature of 85℃, PMMA with a molecular weight of 60000 and cyano-modified phenolic resin PN30 with a grafting rate of 30% of phthalonitrile groups are stirred evenly in acetone solvent at a mass ratio of 1:3. After the two are evenly mixed, the solvent is evaporated under water bath heating to obtain the blend.

[0151] (2) The blend was transferred to an oven for step curing. First, the temperature was raised to 170°C and cured for 1 hour; then the temperature was raised to 200°C and cured for 1 hour; then the temperature was raised to 280°C and cured for 4 hours. After curing, the cured resin microspheres were obtained.

[0152] (3) The solidified resin microspheres were broken into smaller pieces using a crusher and placed in a crucible. The crucible was then placed in a tube furnace under an inert atmosphere and carbonized through a two-step heat treatment. The first heat treatment involved raising the temperature from room temperature to 800℃ at a rate of 5℃ / min and holding it at that temperature for 2 hours to obtain pre-carbonized resin. The second heat treatment involved further heating to 1400℃ at a rate of 5℃ / min and holding it at that temperature for 2 hours to obtain resin-based hard carbon microspheres. The hard carbon microspheres had a particle size of approximately 4 μm and a specific surface area of ​​17.87 m². 2 / g.

[0153] Preparation of a button cell battery:

[0154] The resin-based hard carbon microspheres, Super P conductive agent, and polyvinylidene fluoride (PVDF) binder prepared above were added to N-methylpyrrolidone (NMP) at a mass ratio of 8.9:0.5:0.6 to form a uniform slurry. This slurry was then uniformly coated onto copper foil using a coating method. After drying, the slurry was punched into a circular negative electrode sheet and vacuum-dried at 120°C for 12 hours. Using the prepared negative electrode sheet as the positive electrode and a sodium metal sheet as the negative electrode, a 1M sodium hexafluorophosphate electrolyte in EC:DMC = 1:1 vol%, and a glass fiber separator, button batteries were assembled in a glove box. The electrochemical performance of the button batteries was tested using a Newway battery tester (test conditions: room temperature, voltage range 0.001-2.5V vs. Na / Na). + The test results show that hard carbon materials can withstand current densities of 30 mA·g. -1 At that time, the initial specific capacity was 274.32 mA·g. -1 The initial Coulomb efficiency was 50.29%.

[0155] Comparative Example 4

[0156] PMMA with a molecular weight of 110,000 was used, and other raw material conditions and preparation processes were the same as in Example 1. The specific steps are as follows:

[0157] Preparation of a resin-based hard carbon microsphere:

[0158] (1) Under the condition of water bath heating temperature of 85℃, PMMA with a molecular weight of 110000 and cyano-modified phenolic resin PN30 with a grafting rate of 30% of phthalonitrile groups are stirred evenly in acetone solvent at a mass ratio of 1:3. After the two are evenly mixed, the solvent is evaporated under water bath heating to obtain the blend.

[0159] (2) The blend was transferred to an oven for step curing. First, the temperature was raised to 170°C and cured for 1 hour; then the temperature was raised to 200°C and cured for 1 hour; then the temperature was raised to 280°C and cured for 4 hours. After curing, the cured resin microspheres were obtained.

[0160] (3) The solidified resin microspheres were broken into smaller pieces using a crusher and placed in a crucible. The crucible was then placed in a tube furnace under an inert atmosphere and carbonized through a two-step heat treatment. The first heat treatment involved raising the temperature from room temperature to 800℃ at a rate of 5℃ / min and holding it at that temperature for 2 hours to obtain pre-carbonized resin. The second heat treatment involved further heating to 1400℃ at a rate of 5℃ / min and holding it at that temperature for 2 hours to obtain resin-based hard carbon microspheres. The particle size of the hard carbon microspheres was approximately 4 μm, and their specific surface area was measured to be 3.54 m². 2 / g.

[0161] Preparation of a button cell battery:

[0162] The resin-based hard carbon microspheres, Super P conductive agent, and polyvinylidene fluoride (PVDF) binder prepared above were added to N-methylpyrrolidone (NMP) at a mass ratio of 8.9:0.5:0.6 to form a uniform slurry. This slurry was then uniformly coated onto copper foil using a coating method. After drying, the slurry was punched into a circular negative electrode sheet and vacuum-dried at 120°C for 12 hours. Using the prepared negative electrode sheet as the positive electrode and a sodium metal sheet as the negative electrode, a 1M sodium hexafluorophosphate electrolyte in EC:DMC = 1:1 vol%, and a glass fiber separator, button batteries were assembled in a glove box. The electrochemical performance of the button batteries was tested using a Newway battery tester (test conditions: room temperature, voltage range 0.001-2.5V vs. Na / Na). + The test results show that hard carbon materials can withstand current densities of 30 mA·g. -1 At that time, the initial specific capacity was 272.19 mA·g. -1 The initial Coulomb efficiency was 52.31%.

[0163] Comparative Example 5

[0164] Preparation of a resin-based hard carbon microsphere:

[0165] (1) Under the condition of water bath heating temperature of 85℃, PMMA with a molecular weight of 99326 and cyano-modified phenolic resin PN75 with a grafting rate of 75% of phthalonitrile groups are stirred evenly in acetone solvent at a mass ratio of 1:3. After the two are evenly mixed, the solvent is evaporated under water bath heating to obtain the blend.

[0166] (2) The blend was transferred to an oven for curing. The curing conditions were 150℃ for 4 hours. After curing, the cured resin microspheres were obtained.

[0167] (3) The solidified resin microspheres were broken into smaller pieces using a crusher and placed in a crucible. The crucible was then placed in a tube furnace under an inert atmosphere and carbonized through a two-step heat treatment. The first heat treatment involved raising the temperature from room temperature to 800℃ at a rate of 5℃ / min and holding it at that temperature for 2 hours to obtain pre-carbonized resin. The second heat treatment involved further raising the temperature to 1400℃ at a rate of 5℃ / min and holding it at that temperature for 2 hours to obtain resin-based hard carbon microspheres. The particle size of the hard carbon microspheres was approximately 2 μm, and their specific surface area was measured to be 9.44 m². 2 / g.

[0168] Preparation of a button cell battery:

[0169] The resin-based hard carbon microspheres, Super P conductive agent, and polyvinylidene fluoride (PVDF) binder prepared above were added to N-methylpyrrolidone (NMP) at a mass ratio of 8.9:0.5:0.6 to form a uniform slurry. This slurry was then uniformly coated onto copper foil using a coating method. After drying, the slurry was punched into a circular negative electrode sheet and vacuum-dried at 120°C for 12 hours. Using the prepared negative electrode sheet as the positive electrode and a sodium metal sheet as the negative electrode, a 1M sodium hexafluorophosphate electrolyte in EC:DMC = 1:1 vol%, and a glass fiber separator, button batteries were assembled in a glove box. The electrochemical performance of the button batteries was tested using a Newway battery tester (test conditions: room temperature, voltage range 0.001-2.5V vs. Na / Na). + The test results show that hard carbon materials can withstand current densities of 30 mA·g. -1 At that time, the initial specific capacity was 203.23 mA·g. -1 The initial Coulomb efficiency was 44.09%.

[0170] Comparative Example 6

[0171] Preparation of a resin-based hard carbon microsphere:

[0172] (1) Under the condition of water bath heating temperature of 85℃, PMMA with a molecular weight of 99326 and cyano-modified phenolic resin PN75 with a grafting rate of 75% of phthalonitrile groups are stirred evenly in acetone solvent at a mass ratio of 1:3. After the two are evenly mixed, the solvent is evaporated under water bath heating to obtain the blend.

[0173] (2) The blend was transferred to an oven for step curing. First, the temperature was raised to 170℃ and cured for 1 hour; then the temperature was raised to 280℃ and cured for 4 hours. After curing, the cured resin microspheres were obtained.

[0174] (3) The solidified resin microspheres were broken into smaller pieces using a crusher and placed in a crucible. The crucible was then placed in a tube furnace under an inert atmosphere and carbonized through a two-step heat treatment. The first heat treatment involved raising the temperature from room temperature to 800℃ at a rate of 5℃ / min and holding it at that temperature for 2 hours to obtain pre-carbonized resin. The second heat treatment involved further heating to 1400℃ at a rate of 5℃ / min and holding it at that temperature for 2 hours to obtain resin-based hard carbon microspheres. The particle size of the hard carbon microspheres was approximately 2 μm, and their specific surface area was measured to be 8.77 m². 2 / g.

[0175] Preparation of a button cell battery:

[0176] The resin-based hard carbon microspheres, Super P conductive agent, and polyvinylidene fluoride (PVDF) binder prepared above were added to N-methylpyrrolidone (NMP) at a mass ratio of 8.9:0.5:0.6 to form a uniform slurry. This slurry was then uniformly coated onto copper foil using a coating method. After drying, the slurry was punched into a circular negative electrode sheet and vacuum-dried at 120°C for 12 hours. Using the prepared negative electrode sheet as the positive electrode and a sodium metal sheet as the negative electrode, a 1M sodium hexafluorophosphate electrolyte in EC:DMC = 1:1 vol%, and a glass fiber separator, button batteries were assembled in a glove box. The electrochemical performance of the button batteries was tested using a Newway battery tester (test conditions: room temperature, voltage range 0.001-2.5V vs. Na / Na). + The test results show that hard carbon materials can withstand current densities of 30 mA·g. -1 At that time, the initial specific capacity was 293.55 mA·g. -1 The initial Coulomb efficiency was 59.09%.

[0177] The test results of Examples 1-8 and Comparative Examples 1-6 are summarized in Table 1.

[0178] Table 1

[0179]

[0180] Summary: Table 1 shows that Examples 1-3 only changed the cyano content in the modified phenolic resin, while the other preparation steps were exactly the same. This indicates that within a certain range, the higher the proportion of cyano groups in the cyano-modified phenolic resin, the lower the specific surface area, and the better the corresponding electrochemical performance. Examples 3-5 show that within a certain range, a larger molecular weight of PMMA is more conducive to phase separation of the resin spheres during curing, and a smaller specific surface area of ​​the carbon spheres results in better electrochemical performance. Compared with Example 7, Example 5 differs only in the carbonization temperature; within a certain range, a higher carbonization temperature results in better electrochemical performance. Comparing Comparative Examples 1 and 2 with Example 1, it can be seen that if the proportion of cyano groups in the cyano-modified phenolic resin is too high or too low, the specific surface area of ​​the hard carbon microspheres will increase, significantly reducing their electrochemical performance. Comparing Comparative Examples 3 and 4 with Example 5, both excessively small and excessively large molecular weights of PMMA will affect the charge / discharge efficiency and capacity of the battery, reducing its electrochemical performance. The curing processes in Comparative Examples 5 and 6 differed from those in Example 5, resulting in a significant reduction in the electrochemical performance of the products obtained.

[0181] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A resin-based hard carbon microsphere, characterized in that, The resin-based hard carbon microspheres are prepared by mixing, curing, and carbonizing PMMA and cyano-modified phenolic resin. The particle size of the resin-based hard carbon microspheres is 1-5.0 μm, and the specific surface area is 3-21 m². 2 / g.

2. The resin-based hard carbon microspheres according to claim 1, characterized in that, The phenolic hydroxyl groups in the cyano-modified phenolic resin are replaced by phthalonitrile groups, and the structure of the cyano-modified phenolic resin is shown in Formula I: Where n is selected from any integer between 1 and 8; Preferably, the grafting rate of the phthalonitrile group is 30-75%; Preferably, the grafting rate of the phthalonitrile group is 50-75%.

3. The resin-based hard carbon microsphere according to claim 1 or 2, characterized in that, The mass ratio of PMMA to cyano-modified phenolic resin is 1:(2-3); The PMMA has an apparent viscosity with an average molecular weight range of 70,000-100,000. Preferably, the apparent viscosity of PMMA has an average molecular weight range of 80,000-99,400.

4. A method for preparing resin-based hard carbon microspheres as described in any one of claims 1-3, comprising the following steps: (1) PMMA and cyano-modified phenolic resin were added to a solvent and mixed evenly, and then the solvent was removed to obtain a blend. (2) The blend was subjected to a step-curing process to obtain cured resin microspheres; (3) The cured resin microspheres are broken up and carbonized by two-step heat treatment under an inert atmosphere to obtain resin-based hard carbon microspheres.

5. The preparation method according to claim 4, characterized in that, In step (1), PMMA and cyano-modified phenolic resin are added to the solvent under heating conditions and mixed evenly by continuous stirring. Preferably, the water bath heating temperature is 70-85℃; Preferably, the stirring time is 1-2 hours; Preferably, the solvent is selected from one or more of acetone, dimethylformamide, dimethyl sulfoxide, methyl ethyl ketone, and N-methylpyrrolidone; Preferably, the solvent is acetone.

6. The method for preparing resin-based hard carbon microspheres according to claim 4, characterized in that, In step (2), the conditions for the stepped curing include: First, heat the temperature to 150-190℃ and cure for 1-2 hours; Continue heating to 200-240℃ and cure for 1-2 hours; Continue heating to 250-280℃ and cure for 4-6 hours to obtain cured resin microspheres; Preferably, the temperature is first raised to 160-180℃ and cured for 1 hour; Continue heating to 200-220℃ and cure for 1 hour; Continue heating to 270-280℃ and cure for 4 hours to obtain cured resin microspheres.

7. The method for preparing resin-based hard carbon microspheres according to claim 4, characterized in that, In step (3), when performing two-step heat treatment carbonization, the first heat treatment is to raise the temperature from room temperature to 500-800℃ at a rate of 5-10℃ / min and hold for 2-4 hours; the second heat treatment continues to raise the temperature to 1000-1800℃ at a rate of 5-10℃ / min and hold for 1-3 hours.

8. The method for preparing resin-based hard carbon microspheres according to claim 6, characterized in that, During carbonization in step (3), the inert atmosphere is nitrogen or argon.

9. A battery negative electrode sheet, characterized in that, It was prepared using the resin-based hard carbon microspheres as described in any one of claims 1-3; Preferably, the preparation process includes: mixing resin-based hard carbon microspheres, conductive agent, binder and solvent, coating them on a metal substrate, and then vacuum drying to obtain the battery negative electrode sheet; Preferably, the conductive agent is a Super P conductive agent; Preferably, the adhesive is polyvinylidene fluoride; Preferably, the solvent is N-methylpyrrolidone.

10. The application of the resin-based hard carbon microspheres according to any one of claims 1-3 or the battery negative electrode sheet according to claim 9 in the preparation of sodium-ion batteries.

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