Asphalt soft carbon coated phenolic resin-based hard carbon composite material as well as preparation method and application thereof

Abstract

The invention provides an asphalt soft carbon coated phenolic resin-based hard carbon composite material as well as a preparation method and application thereof. The asphalt soft carbon coated phenolic resin-based hard carbon composite material comprises an internal phenolic resin-based hard carbon material and an external asphalt soft carbon layer. The preparation method of the asphalt soft carbon coated phenolic resin-based hard carbon composite material comprises the step of pre-oxidizing a mixed precursor of asphalt and phenolic resin, and the step can effectively improve the first-circle coulombic efficiency of the material, reduce irreversible consumption of Na ions and enhance the electrochemical performance of the material.

Description

Technical Field

[0001] This invention belongs to the field of electrode material preparation technology, specifically relating to a pitch-coated soft carbon phenolic resin-based hard carbon composite material, its preparation method, and its application. Background Technology

[0002] In recent years, research on sodium-ion batteries has been increasingly popular. However, compared to lithium-ion batteries, sodium-ion batteries mainly suffer from poor sodium storage performance due to the difficulty in intercalation and deintercalation caused by the larger radius of sodium ions. The key to improving this problem lies in the electrode materials.

[0003] Currently, hard carbon materials are the most widely used anode materials for sodium-ion batteries. Industrially, hard carbon materials are mainly prepared from raw materials such as biomass, synthetic resins, coal, and asphalt. Among these, biomass or artificial synthetic resins are the best precursors for hard carbon materials, as they can produce highly disordered hard carbon structures without modification or treatment. However, commercially available phenolic resin-based hard carbon materials currently face problems such as high cost, low capacity, poor stability and rate performance, and low initial coulombic efficiency. Asphalt, as a byproduct of the petroleum industry, is readily available and inexpensive. However, due to the strong π-π interactions between aromatic molecules at high temperatures, it forms a planar orientation structure, which makes it prone to graphitization under high-temperature carbonization. This easily forms highly graphitized soft carbon with small interlayer spacing. Although it has good conductivity, this highly long-range ordered structure is not conducive to the insertion and extraction of sodium ions.

[0004] Soft carbon-coated hard carbon composites are functional materials formed by coating highly graphitized soft carbon onto the surface of hard carbon derived from phenolic resins, etc. The soft carbon layer provides high conductivity and structural flexibility, improves electron transport, and alleviates volumetric strain during charge and discharge, while the porous structure of the hard carbon core endows the material with high specific capacity and excellent ion diffusion capabilities. This composite material not only effectively suppresses side reactions of the electrolyte on the hard carbon surface and improves interfacial stability, but also synergistically enhances the material's rate performance and cycle life, making it exhibit significant advantages in energy storage fields such as lithium / sodium-ion battery anodes.

[0005] CN117334900A discloses a method for preparing a composite hard carbon anode material. The method uses a biomass structure containing phenolic resin as a hard carbon precursor. The biomass is selected from coconut shells, peanut shells, walnut shells, etc. The hard carbon precursor is mixed with softened and pulverized small-particle-size asphalt powder and then heated and carbonized to prepare a composite hard carbon anode material with a soft carbon coating. This method improves the rate charge / discharge performance and coulombic efficiency of the anode material at low temperatures.

[0006] CN102082272A discloses a lithium-ion battery anode material with hard carbon coating. The graphite surface coating material is composed of a heteroatom modifier, a hard carbon precursor material, and a soft carbon precursor material. The heteroatom modifier is a boron-containing modifier. The hard carbon precursor is selected from phenolic resin, furfural resin, epoxy resin, furan resin, polyvinyl alcohol, or polyacrylonitrile. The soft carbon precursor is pitch. When this material is used as a lithium-ion battery anode, the lithium battery exhibits high capacity and excellent fast-charging performance.

[0007] It is evident that existing technologies for soft carbon-coated hard carbon composites mainly focus on improvements in material selection and additives, and further improvements in material performance are still necessary. Summary of the Invention

[0008] This invention addresses the problems of high cost, low capacity, poor stability and rate performance, and low initial coulombic efficiency of currently available commercial phenolic resin-based hard carbon materials. It proposes a pitch-coated phenolic resin-based hard carbon composite material. By using inexpensive pitch-coated soft carbon to coat the surface of phenolic resin-based hard carbon, the material's economic efficiency is improved. Furthermore, the open pores on the hard carbon surface, encapsulated by the pitch-coated soft carbon, transform into closed-pore structures during high-temperature carbonization and rearrangement. Aromatic molecules from the pitch also fill or penetrate into the interior of the hard carbon, further altering its pore structure. Simultaneously, the cross-linking between the pitch and the phenolic resin hard carbon inhibits further carbon layer rearrangement, forming numerous short-range ordered graphite-like microcrystals on the hard carbon surface, providing Na... + The embedding provides a large number of active sites, effectively improving the first-cycle coulombic efficiency of the material and reducing Na+. + The irreversible consumption enhances the electrochemical performance of the material.

[0009] Specifically, one aspect of the present invention provides a phenolic resin-based hard carbon composite material coated with asphalt soft carbon, the composite material comprising an inner phenolic resin-based hard carbon material and an outer asphalt soft carbon layer;

[0010] The carbon interlayer spacing of the phenolic resin-based hard carbon material is 0.35-0.42 nm;

[0011] The carbon layer spacing of the asphalt soft carbon layer is 0.345-0.36 nm, and the thickness is 10-50 nm;

[0012] The composite material has micropores with a pore size of 1-5 nm and a specific surface area of ​​0.35-144.84 m². 2 / g, the pore volume of the micropores is 0.0002-0.06cm³. 3 / g;

[0013] The specific surface area of ​​the composite material is 0.40-151.52 m². 2 / g, total pore volume is 0.0027-0.069cm³ 3 / g.

[0014] Another aspect of the present invention provides a method for preparing a pitch-coated soft carbon phenolic resin-based hard carbon composite material, comprising the following steps:

[0015] S1: After crushing the asphalt, mix it with phenolic resin in a ratio of 1:9-9:1 and grind it to obtain a mixed precursor;

[0016] S2: The mixed precursor is pre-oxidized in an oxygen-containing atmosphere at 200-300°C for 1-5 hours to obtain a pre-oxidized precursor;

[0017] S3: After crushing the pre-oxidized precursor, sinter it at 1100-1500℃ for 2-5 hours in an inert atmosphere to obtain a pitch soft carbon coated phenolic resin-based hard carbon composite material.

[0018] In one or more embodiments, in S1, the asphalt is petroleum asphalt.

[0019] In one or more embodiments, in S1, the asphalt is crushed and then passed through a 300-mesh sieve.

[0020] In one or more embodiments, in S1, the grinding is manual grinding or ball milling.

[0021] In one or more embodiments, in S2, the oxygen-containing atmosphere is air.

[0022] In one or more embodiments, in S2, the heating rate of the pre-oxidation is 1-10 °C / min.

[0023] In one or more embodiments, in S3, the pre-oxidized precursor is crushed and then passed through a 300-mesh sieve.

[0024] In one or more embodiments, in step S3, the inert atmosphere is selected from nitrogen and argon.

[0025] In one or more embodiments, in S3, the heating rate of the sintering is 1-10 °C / min.

[0026] The present invention also provides a negative electrode sheet containing the pitch soft carbon coated phenolic resin-based hard carbon composite material described herein, or the pitch soft carbon coated phenolic resin-based hard carbon composite material obtained by the preparation method described herein.

[0027] The present invention also provides a sodium-ion battery, wherein the sodium-ion battery includes the negative electrode sheet described herein. Attached Figure Description

[0028] Figure 1 SEM image of the asphalt soft carbon coated phenolic resin-based hard carbon composite material of Example 1;

[0029] Figure 2 TEM image of the asphalt soft carbon coated phenolic resin-based hard carbon composite material of Example 1;

[0030] Figure 3 : Overall SEM image of the phenolic resin hard carbon material of Comparative Example 1;

[0031] Figure 4 : Overall SEM image of the asphalt soft carbon coated phenolic resin-based hard carbon composite material without oxidation treatment in Comparative Example 2;

[0032] Figure 5 XRD patterns of Example 1 and Comparative Example 2;

[0033] Figure 6 Raman spectra of Example 1 and Comparative Example 2;

[0034] Figure 7 Results of rate performance tests for Example 1 and Comparative Example 2;

[0035] Figure 8 Charge-discharge curves of Example 1 and Comparative Example 1 during the first week;

[0036] Figure 9 Charge-discharge curves of Example 1 and Comparative Example 2 during the first week. Detailed Implementation

[0037] To enable those skilled in the art to understand the features and effects of this invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the conventional meaning understood by those skilled in the art regarding this invention, and in case of conflict, the definitions in this specification shall prevail.

[0038] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0039] In this document, the terms “contains,” “includes,” “containing,” and similar terms encompass the meanings of “basically composed of” and “composed of.” For example, when this document discloses “A contains B and C,” “A is basically composed of B and C” and “A is composed of B and C” should be considered as having been disclosed in this document.

[0040] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0041] Unless otherwise specified, percentages refer to mass percentages and proportions refer to mass ratios in this article.

[0042] In this document, when describing embodiments or examples, it should be understood that it is not intended to limit the invention to those embodiments or examples. Rather, all alternatives, modifications, and equivalents of the methods and materials described herein are covered within the scope defined by the claims.

[0043] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0044] The following provides a detailed description of this application.

[0045] Asphalt soft carbon coated phenolic resin-based hard carbon composite material

[0046] The pitch-coated phenolic resin-based hard carbon composite material of the present invention comprises an inner phenolic resin-based hard carbon material and an outer pitch-coated soft carbon layer. The composite material has micropores with a specific surface area of ​​0.35-144.84 m². 2 / g, the pore volume of the micropores is 0.0002-0.06cm³. 3 / g; the specific surface area of ​​the composite material is 0.40-151.52m². 2 / g, total pore volume is 0.0027-0.069cm³ 3 / g.

[0047] The carbon interlayer spacing of the phenolic resin-based hard carbon composite material is 0.35-0.42 nm. The disordered carbon layers and micropores within the hard carbon material provide abundant sodium ion adsorption sites, with its sodium storage mechanism primarily based on insertion-filling: sodium ions embed into the carbon layers in the ramp region and fill the closed-pore structure in the plateau region. The rigid cross-linked network, such as the COC bonds of the phenolic resin, can withstand volume changes during charging and discharging, preventing material collapse. Oxygen-containing functional groups on the hard carbon surface, such as hydroxyl and carbonyl groups, form chemical anchors with the pitch soft carbon, such as COC bonds or π-π interactions, enhancing interlayer bonding.

[0048] The carbon interlayer spacing of the soft carbon layer in the composite material is 0.345-0.36 nm, and the thickness is 10-50 nm. The soft carbon exhibits graphite-like microstructures and high sp2 content. 2 The high carbon content results in an intensity ratio (ID / IG) of less than 1 for the D peak to the G peak in the Raman spectrum, forming a continuous electron transport channel that rapidly extracts electrons from the hard carbon interior, reducing interfacial impedance. The layered structure and surface micropores of the soft carbon serve as fast channels for sodium ions, improving rate performance. The continuous soft carbon layer isolates the electrolyte from direct contact with the hard carbon, reducing side reactions and capacity decay. The soft carbon layer inhibits dendrite growth, enhancing thermal stability.

[0049] The asphalt soft carbon coated phenolic resin-based hard carbon composite material of the present invention has a parallel carbon layer arrangement structure of soft carbon or micrographite, which improves the conductivity of the material, reduces internal resistance, and improves the rate performance of the material.

[0050] Preparation of Phenolic Resin-Based Hard Carbon Composite Materials Coated with Pitch Soft Carbon

[0051] The preparation method of the asphalt soft carbon coated phenolic resin-based hard carbon composite material of the present invention includes the following steps:

[0052] S1: After crushing the asphalt, mix it with phenolic resin in a ratio of 1:9-9:1 and grind it to obtain a mixed precursor;

[0053] S2: Pre-oxidize the mixed precursor in an oxygen-containing atmosphere at 200-300℃ for 1-5 hours to obtain the pre-oxidized precursor;

[0054] S3: After crushing the pre-oxidized precursor, sinter it at 1100-1500℃ for 2-5 hours in an inert atmosphere to obtain a pitch soft carbon coated phenolic resin-based hard carbon composite material.

[0055] The pre-oxidation treatment of this invention enhances the crosslinking of aromatic segments in soft and hard carbon, increases the oxygen content of the material, and increases Na+. + The embedded active sites enhance the material's sodium storage capacity; on the other hand, the pre-oxidation treatment reacts away the organic reactants between the soft and hard carbon layers, effectively expanding the interlayer spacing of the carbon layers, which is beneficial for Na... + Intercalation embedding.

[0056] The high-temperature sintering process of this invention causes the disordered carbon layers of phenolic resin to shrink, forming a disordered hard carbon material containing closed pores. The high-temperature sintering temperature is 1100-1500℃. This invention uniformly coats the surface of hard carbon with soft carbon material, improving the surface morphology of the material and blocking the macropores and open pores on the surface of hard carbon. During the high-temperature carbonization process, the carbon layers rearrange to form a large number of closed-pore structures, improving the sodium storage capacity of the material. Graphitization of soft carbon usually occurs significantly above 1700℃, while hard carbon requires higher temperatures or specific treatments to form a disordered structure. The sintering temperature required for hard carbon has not reached the critical value (e.g., below 2000℃). Although the polycyclic aromatic hydrocarbons in asphalt cannot be completely graphitized, they can still form graphite-like microcrystals through dehydrogenation condensation. In an inert atmosphere, high-temperature sintering may promote the ordered arrangement of carbon atoms, failing to further destroy the partially cross-linked structure formed by pre-oxidation, leading to a dominant graphitization trend. The oxygen bridges formed by single pre-oxidation are easily broken at high temperatures, so synergistic cross-linking methods (such as the addition of phenolic resin) need to be introduced to form a double cross-linking network with the original COC bonds.

[0057] Negative electrode and sodium-ion battery

[0058] The present invention also provides a negative electrode sheet comprising a pitch soft carbon coated phenolic resin-based hard carbon composite material containing any embodiment herein, and a sodium-ion battery containing the negative electrode sheet.

[0059] The negative electrode sheet includes a negative electrode current collector and a negative electrode material layer formed on the surface of the negative electrode current collector. The negative electrode material layer is composed of a negative electrode active material (hard carbon), a conductive agent (such as superconducting carbon black, carbon nanotubes or graphene) and a binder (such as polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose, styrene-butadiene rubber or polyacrylic acid). The slurry is prepared by mixing the components in a certain proportion (e.g., 80-95% negative electrode active material, 2-10% conductive agent, 3-10% binder) and adding a solvent. The slurry is then coated onto the negative electrode current collector (such as copper foil or stainless steel foil), dried, rolled and cut.

[0060] Sodium-ion batteries consist of a positive electrode, a negative electrode, a separator, and an electrolyte (containing sodium salt and organic solvent). The assembly process includes steps such as electrode preparation, stacking or winding, packaging, electrolyte injection, and formation. Ultimately, they can be made into cylindrical, pouch, square aluminum-cased, or button cell forms.

[0061] The present invention has the following beneficial effects:

[0062] (1) This invention utilizes asphalt soft carbon to coat the surface of phenolic resin-based hard carbon. On the one hand, this improves the economic efficiency of the material; on the other hand, the asphalt soft carbon coats the open pores on the surface of the hard carbon, which, during high-temperature carbonization and rearrangement, form a closed-pore structure. Some aromatic molecules in the asphalt also fill or penetrate into the interior of the hard carbon, further altering its pore structure. Simultaneously, the cross-linking effect between the asphalt and the phenolic resin hard carbon inhibits further rearrangement of the carbon layer, forming a large number of short-range ordered graphite-like microcrystals on the surface of the hard carbon, providing Na... + The embedding provides a large number of active sites, effectively improving the first-cycle coulombic efficiency of the material and reducing Na+. + The irreversible consumption enhances the electrochemical performance of the material.

[0063] (2) The asphalt raw materials of the present invention are widely available and inexpensive, which effectively improves economic benefits.

[0064] (3) The preparation process of this invention is simple, has no by-products, and is easy to mass-produce.

[0065] The present invention will be described below by way of specific embodiments. It should be understood that these embodiments are merely illustrative and are not intended to limit the scope of the invention. The methods, reagents, and materials used in the embodiments are conventional methods, reagents, and materials in the art, unless otherwise stated. The raw material compounds in the embodiments are all commercially available.

[0066] In the following examples and comparative examples, the relevant parameters were obtained through the following test methods:

[0067] (1) XRD: The sample was characterized using an X-ray diffractometer (Rigaku Smart Lab SE) with Cu-Kα radiation. XRD data were collected to identify the crystal structure and phase composition. The XRD data were collected within an angular range of 10–90° at a scan rate of 5° / min.

[0068] (2) SEM morphology test: obtained by scanning electron microscope of JSM7401.

[0069] (3) Specific surface area test: obtained by Bessler instrument.

[0070] (4) Pore volume test: obtained by Bessler instrument.

[0071] (5) Raman spectroscopy test: obtained by testing with a Bessler instrument.

[0072] (6) First week charge and discharge performance test: At room temperature, charge and discharge performance test was performed on the LAND-CT2001A test system at a rate of 0.1C. The system was left to stand for 5-10 minutes between charge and discharge to ensure voltage stability and reduce the influence of concentration polarization.

[0073] (7) Rate Performance Test: The assembled lithium-ion coin cells were left to stand in a constant temperature environment (25±2℃) for 12-24 hours. The rate performance was tested using the LAND-CT2001A testing system at the following rates: 0.1C→0.2C→0.3C→0.5C→1C→0.1C (1C=300mAh·g). -1 Electrochemical tests were performed sequentially at each rate, with five cycles at each rate. The last stable data was taken to avoid the accumulation of battery polarization affecting high-rate data.

[0074] In the following examples and comparative examples, the method for preparing the negative electrode is as follows:

[0075] The composite material was mixed with conductive carbon black (SP) and polyvinylidene fluoride (PVDF) at a mass ratio of 8:1:1 and stirred for 12 hours to obtain a mixed slurry. The mixed slurry was coated on aluminum foil to obtain a coating thickness of 50 μm and then vacuum dried at 100 °C for 6 hours to obtain a negative electrode sheet.

[0076] In the following examples and comparative examples, the sodium-ion batteries were prepared as follows:

[0077] Using a sodium sheet as the counter electrode, and NaPF6 in DME at a concentration of 1 mol / L = 100 vol% as the electrolyte additive, with glass fiber (GF / A) as the separator, the battery was assembled in an argon-filled glove box, left to age for 24 hours, and then subjected to charge-discharge tests.

[0078] In the following examples and comparative examples, the phenolic resin and asphalt were purchased from Krohde.

[0079] Example 1

[0080] This embodiment provides a method for preparing a pitch-coated soft carbon phenolic resin-based hard carbon composite material, including:

[0081] Step 1: Weigh 3g of industrial asphalt, ball mill and crush it through a 300-mesh sieve, then mix and grind the crushed asphalt with 7g of phenolic resin until uniform.

[0082] Step 2: Place the uniformly ground mixture in a muffle furnace, and pre-oxidize it at 250°C for 2 hours under an air atmosphere at a heating rate of 5°C / min. Then allow it to cool naturally to obtain the pre-oxidized precursor.

[0083] Step 3: The pre-oxidized precursor is ball-milled and crushed, and then sieved through a 300-mesh sieve to control the particle size between 6-8 μm. Under a nitrogen atmosphere, the temperature is raised at a rate of 5℃ / min and sintered at 1200℃ for 2 hours. After natural cooling, the asphalt soft carbon coated phenolic resin-based hard carbon composite material is obtained.

[0084] The properties of the asphalt soft carbon coated phenolic resin-based hard carbon composite material obtained in this embodiment are as follows:

[0085] Specific surface area is 1.1480 m² 2 / g, total pore volume is 0.004cm³ 3 / g, with a microporous specific surface area of ​​0.4591m². 2 / g, micropore volume is 0.0005cm³ 3 / g,

[0086] The carbon interlayer spacing of hard carbon materials is 0.38-0.4 nm; the carbon interlayer spacing of soft carbon layers is 0.345-0.36 nm, and the thickness is 10-20 nm.

[0087] Example 2

[0088] This embodiment provides a method for preparing a pitch-coated soft carbon phenolic resin-based hard carbon composite material, including:

[0089] Step 1: Weigh 7g of industrial asphalt, ball mill and crush it through a 300-mesh sieve, then mix and grind the crushed asphalt with 3g of phenolic resin until uniform.

[0090] Step 2: Place the uniformly ground mixture in a muffle furnace, and pre-oxidize it at 250°C for 2 hours under an air atmosphere at a heating rate of 5°C / min. Then allow it to cool naturally to obtain the pre-oxidized precursor.

[0091] Step 3: The pre-oxidized precursor is ball-milled and crushed, and then sieved through a 300-mesh sieve to control the particle size between 6-8 μm. Under a nitrogen atmosphere, the temperature is raised at a rate of 5℃ / min and sintered at 1200℃ for 2 hours. After natural cooling, the asphalt soft carbon coated phenolic resin-based hard carbon composite material is obtained.

[0092] Example 3

[0093] This embodiment provides a method for preparing a pitch-coated soft carbon phenolic resin-based hard carbon composite material, including:

[0094] Step 1: Weigh 3g of industrial asphalt, ball mill and crush it through a 300-mesh sieve, then mix and grind the crushed asphalt with 7g of phenolic resin until uniform.

[0095] Step 2: Place the uniformly ground mixture in a muffle furnace, and pre-oxidize it at 300℃ for 2 hours under an air atmosphere at a heating rate of 5℃ / min. Then, allow it to cool naturally to obtain the pre-oxidized precursor.

[0096] Step 3: The pre-oxidized precursor is ball-milled and crushed, and then sieved through a 300-mesh sieve to control the particle size between 6-8 μm. Under a nitrogen atmosphere, the temperature is raised at a rate of 5℃ / min and sintered at 1200℃ for 2 hours. After natural cooling, the asphalt soft carbon coated phenolic resin-based hard carbon composite material is obtained.

[0097] Example 4

[0098] This embodiment provides a method for preparing a pitch-coated soft carbon phenolic resin-based hard carbon composite material, including:

[0099] Step 1: Weigh 3g of industrial asphalt, ball mill and crush it through a 300-mesh sieve, then mix and grind the crushed asphalt with 7g of phenolic resin until uniform.

[0100] Step 2: Place the uniformly ground mixture in a muffle furnace, heat it at a rate of 5℃ / min in air atmosphere, pre-oxidize it at 200℃ for 2 hours, and then allow it to cool naturally to obtain the pre-oxidized precursor.

[0101] Step 3: The pre-oxidized precursor is ball-milled and crushed, and then sieved through a 300-mesh sieve to control the particle size between 6-8 μm. Under a nitrogen atmosphere, the temperature is raised at a rate of 5℃ / min and sintered at 1200℃ for 2 hours. After natural cooling, the asphalt soft carbon coated phenolic resin-based hard carbon composite material is obtained.

[0102] Comparative Example 1

[0103] This comparative example provides a method for preparing a phenolic resin hard carbon material without asphalt soft carbon coating, including:

[0104] Phenolic resin was placed in a muffle furnace and pre-oxidized in air at 250°C for 2 hours. It was then crushed and sieved to obtain a uniformly sized hard carbon precursor. Subsequently, it was placed in a tube furnace and annealed at 1200°C for 2 hours in a nitrogen atmosphere to prepare hard carbon material.

[0105] Comparative Example 2

[0106] This comparative example provides a method for preparing a phenolic resin hard carbon material coated with asphalt soft carbon, which does not include an oxidation treatment step. Specifically, it includes: grinding phenolic resin and asphalt evenly, wherein the ratio of asphalt to phenolic resin is 3:7, and reacting at 1200°C for 2 hours under a N2 atmosphere to obtain the phenolic resin hard carbon material coated with asphalt soft carbon.

[0107] Figure 1 The image shows the overall SEM image of the asphalt soft carbon coated phenolic resin-based hard carbon composite material of Example 1. It can be seen that the surface of the phenolic resin-based hard carbon is uniformly coated with asphalt soft carbon and the surface is rough. Figure 2 The image shown is a TEM image of the asphalt soft carbon coated phenolic resin-based hard carbon composite material of Example 1. It can be seen that the asphalt soft carbon coated phenolic resin-based hard carbon composite material includes internal phenolic resin-based hard carbon (HC) and external asphalt soft carbon (SC). Figure 3 The image shows the overall SEM image of the phenolic resin hard carbon material in Comparative Example 1. Comparative Example 1 shows that the surface of the phenolic resin-based hard carbon is not coated with pitch soft carbon. Figure 4The image shows the overall SEM image of the asphalt soft carbon coated phenolic resin-based hard carbon composite material of Comparative Example 2. Since there is no oxidation step, there is basically no reaction between the asphalt and the phenolic resin, and the surface is relatively smooth overall.

[0108] Figure 5 The XRD patterns are for Example 1 and Comparative Example 2. The asphalt-coated phenolic resin hard carbon composites of Example 1 and Comparative Example 2 both exhibit characteristic broad peaks at 23° and 44°, which can be attributed to the 002 and 100 diffraction peaks of amorphous carbon. After the addition of asphalt, the (002) diffraction peak narrowed, while the (100) diffraction peak slightly increased, demonstrating that the pre-oxidation step of the present invention improves the orderliness of both the interlayer stacking (002 direction) and in-plane arrangement (100 direction) of the carbon phase by influencing the interaction between the asphalt and the original amorphous carbon (promoting structural fusion).

[0109] Figure 6 The images show the Raman spectra of Example 1 and Comparative Example 2. The phenolic resin hard carbon composite materials coated with pitch soft carbon in Example 1 and Comparative Example 2 both showed a Raman spectrum at 1345 cm⁻¹. -1 and 1600cm -1 Characteristic broad D and G peaks were observed, corresponding to graphite and amorphous carbon structures, respectively. The degree of disorder was assessed by calculating the ID / IG ratio. The ID / IG ratio of Example 1 (1.10) was lower than that of Comparative Example 2 (1.22), demonstrating that in the pitch-coated phenolic resin hard carbon composite material of the present invention, the pitch implants a long-range ordered structure on the surface of the phenolic resin-based hard carbon, increasing the degree of order in the material and improving graphitization and conductivity. This is beneficial for Na… + The insertion and extraction processes improve the electrochemical properties of the material.

[0110] Figure 7 The results show the rate performance test results for Example 1 and Comparative Example 2. Example 1 demonstrates outstanding rate performance, providing 346.7 mAh g⁻¹ at 0.1C, 0.2C, 0.3C, 0.5C, 1C, and 0.1C. -1 309.5mAhg -1 292.6mAhg -1 269.5mAhg -1 223.1 mAhg -1 and 316.2mAhg -1 The rate of increase. Specifically, when the test rate is 0.1C, Example 1 is able to provide 346.7 mAh g. -1 The high specific capacity demonstrates the ability to fully utilize electrochemical performance at low rates; even in a high-rate test at 1C, Example 1 still outputs 223.1 mAh g. -1The specific capacity demonstrates its strong adaptability under high-current charge and discharge scenarios; when the rate drops back to 0.1C, its specific capacity can quickly recover to 316.2 mAh g. -1 This indicates that the internal structure of the composite material was not severely damaged after undergoing high-rate cycling, and it exhibits excellent reversibility and structural stability. Compared with Example 1, the rate performance of Comparative Example 2 is significantly worse.

[0111] Figure 8 and Figure 9 The first-week charge-discharge curves for Example 1 and Comparative Examples 1 and 2 are shown. Compared to Comparative Example 1 (222.8 mAh g / g),... -1 ) and Comparative Example 2 (305.2 mAh g) -1 Compared to Example 1, Example 1 has a higher reversibility capacity (346.7 mAh g). -1 Comparative Example 1, which did not use pitch-coated soft carbon to coat phenolic resin hard carbon, had an initial coulombic efficiency of only 65.21%. Comparative Example 2, which used pitch-coated soft carbon to coat phenolic resin hard carbon and did not include a pre-oxidation step in the preparation process, had an initial coulombic efficiency of 61.46%. Example 1, which used pitch-coated soft carbon to coat phenolic resin hard carbon and included a pre-oxidation step in the preparation process, achieved an initial coulombic efficiency of 75.18%, indicating that pre-oxidation treatment can effectively improve the charge utilization efficiency of the material during the first charge and discharge process.

[0112] Although the preferred embodiments of the present invention have been disclosed above, they are not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, 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 content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

Claims

1. A pitch-coated soft carbon phenolic resin-based hard carbon composite material, characterized in that, The composite material comprises an inner phenolic resin-based hard carbon material and an outer asphalt soft carbon layer. The carbon interlayer spacing of the phenolic resin-based hard carbon material is 0.35-0.42 nm; The carbon layer spacing of the asphalt soft carbon layer is 0.345-0.36 nm, and the thickness is 10-50 nm; The composite material has micropores with a pore size of 1-5 nm and a specific surface area of ​​0.35-144.84 m². 2 / g, the pore volume of the micropores is 0.0002-0.06cm³. 3 / g; The specific surface area of ​​the composite material is 0.40-151.52 m². 2 / g, total pore volume is 0.0027-0.069cm³ 3 / g.

2. A method for preparing the asphalt soft carbon coated phenolic resin-based hard carbon composite material according to claim 1, characterized in that, Includes the following steps: S1: After crushing the asphalt, mix it with phenolic resin in a ratio of 1:9-9:1 and grind it to obtain a mixed precursor; S2: The mixed precursor is pre-oxidized in an oxygen-containing atmosphere at 200-300°C for 1-5 hours to obtain a pre-oxidized precursor; S3: After crushing the pre-oxidized precursor, sinter it at 1100-1500℃ for 2-5 hours in an inert atmosphere to obtain a pitch soft carbon coated phenolic resin-based hard carbon composite material.

3. The method for preparing the asphalt soft carbon coated phenolic resin-based hard carbon composite material according to claim 2, characterized in that, In S1, The asphalt is petroleum asphalt; And / or, the asphalt is crushed and then passed through a 300-mesh sieve; And / or, the grinding is manual grinding or ball milling.

4. The method for preparing the asphalt soft carbon coated phenolic resin-based hard carbon composite material according to claim 2, characterized in that, In S2, The oxygen-containing atmosphere is air; And / or, the heating rate of the pre-oxidation is 1-10 °C / min.

5. The method for preparing the asphalt soft carbon coated phenolic resin-based hard carbon composite material according to claim 2, characterized in that, In S3, The pre-oxidized precursor is crushed and then passed through a 300-mesh sieve; And / or, the inert atmosphere is selected from nitrogen and argon; And / or, the sintering heating rate is 1-10℃ / min.

6. A negative electrode sheet comprising the pitch soft carbon coated phenolic resin-based hard carbon composite material of claim 1, or comprising the pitch soft carbon coated phenolic resin-based hard carbon composite material obtained by any of the preparation methods of claims 2-5.

7. A sodium-ion battery, characterized in that, The sodium-ion battery includes the negative electrode sheet as described in claim 6.

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