Composite carbon material, and preparation method therefor and use thereof

Abstract

A composite carbon material, and a preparation method therefor and a use thereof. The composite carbon material comprises activated carbon and a soft carbon layer covering the surface of the activated carbon; the activated carbon is selected from at least one of coal-based activated carbon, coconut shell activated carbon, and bamboo charcoal activated carbon; the soft carbon layer comprises sodium storage active pores, and the soft carbon layer is prepared by melting a soft carbon precursor, and then coating the surface of activated carbon with the soft carbon precursor and carrying out primary calcination. The material is easy to prepare and environmentally friendly, has low raw material costs, a small specific surface area, abundant sodium storage active pores and a stable structure, and can fully exert the matrix and mass transfer effects of activated carbon; because of the fluidity of the soft carbon precursor and the activity of soft carbon, pores in the surface of activated carbon are effectively converted into the sodium storage active pores; and a sodium-ion battery prepared by using the composite carbon material as a negative electrode active material can have the advantages of high specific capacity, high initial coulombic efficiency, good cycle reversibility, good long-cycle stability, good rate performance, etc.

Description

A composite carbon material and its preparation method and application Technical Field

[0001] The present invention belongs to the technical field of electrode materials and batteries, and particularly relates to a composite carbon material and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries are widely used in a variety of electronic products, including electric vehicles, computers, and mobile phones, and the demand for lithium continues to rise annually. However, global lithium reserves are extremely limited, and lithium is expensive, costly, and difficult to recycle. These factors hinder the development of low-cost, large-scale energy storage devices. Sodium, with its outermost electron structure similar to lithium, possesses similar electrochemical properties. It is also abundant and inexpensive, making it the next generation of commercially viable secondary batteries after lithium-ion batteries. Currently, sodium-ion batteries have energy densities approaching those of lithium-ion batteries, but at significantly lower costs. Common anode materials for sodium-ion batteries include carbon-based, titanium-based, organic, and alloy-based anodes. Titanium-based oxides, metal oxides, sulfides, and phosphides offer excellent cycling performance but low specific capacity. Organic composites offer reversible capacities that meet application requirements, but suffer from low conductivity and initial coulombic efficiency. Carbon-based anode materials, by contrast, hold the greatest commercial potential.

[0003] Among carbon-based negative electrode materials, hard carbon is considered to be the most widely studied type of negative electrode material for sodium ion batteries, as its specific capacity can generally reach 300 mAh / g. CN 108682815 A typically prepares hard carbon by carbonizing biomass such as dandelion, sycamore, foxtail grass, rabbit tail grass, and Penicillium; CN 109742383 A prepares hard carbon using chemical product polymers such as phenol-phenolic resin, m-diphenol-formaldehyde resin, p-diphenol-formaldehyde resin, and phenol-furfural resin as raw materials; CN 115566145 A proposes a method for preparing a negative electrode material for a sodium ion battery and a sodium ion battery, by combining cobalt tetroxide with carbon nanotubes. The cobalt tetroxide-filled carbon nanotube composite material has obvious structural advantages. The tubular structure not only provides active sites for the storage of sodium ions and ensures the uniform distribution of cobalt tetroxide, but also leaves a large buffer space for the volume expansion of cobalt tetroxide, dispersing the stress of its volume change, and improving its battery cycle performance, etc. However, existing carbon-based anode materials for sodium-ion batteries include hard carbon, soft carbon, graphene, carbon nanotubes, and their composites. However, due to the high cost and low sodium storage capacity of carbon materials such as carbon nanotubes and graphene, they are difficult to implement on a large scale. Moreover, although hard carbon utilizes a chaotic carbon layer structure and defective active sites to store sodium, its initial efficiency is low and it cannot simultaneously achieve high rate and high capacity. Technical issues

[0004] Therefore, existing carbon-based anodes still have drawbacks and problems, such as the need for impurities and transition metals, high preparation costs, complex processes, low initial coulombic efficiency, poor structural stability and long-term electrochemical cycle stability, and the inability to simultaneously achieve high capacity and high rate performance. Therefore, there is an urgent need to develop a composite carbon material that is simple to prepare, low in cost, environmentally friendly, simple in composition, structurally stable, and has stable electrochemical performance. Technical Solutions

[0005] In order to overcome the problems of the prior art such as low specific capacity of carbon-based negative electrodes and the first coulombic efficiency of sodium-ion batteries, poor cycle stability and rate performance of sodium-ion batteries, and high cost, one of the purposes of the present invention is to provide a composite carbon material.

[0006] In order to solve the problems existing in the prior art such as complex preparation process, expensive raw materials, multiple components, high pollution and toxicity, the second purpose of the present invention is to provide a method for preparing a composite carbon material.

[0007] A third object of the present invention is to provide applications of the above-mentioned composite carbon material.

[0008] The inventive concept of the present invention: The present invention provides a composite carbon material including activated carbon with a rich pore structure on the surface and a soft carbon coating layer loaded on the surface of the activated carbon, thereby utilizing the respective advantages of the activated carbon and the soft carbon to work together to obtain a negative electrode active material with a stable structure and a rich sodium storage active pore structure on the surface.

[0009] At the same time, activated carbon is a typical amorphous carbon, whose carbon layer is long-range disordered and has a rich pore structure on the surface. Soft carbon can be transformed into a graphite structure at high temperature. The present invention provides a method for preparing a composite carbon material that can be used for the negative electrode of a sodium ion battery by coating activated carbon with soft carbon. At the calcination temperature in the embodiment of the present invention, the carbon layer of the soft carbon is short-range ordered, and after covering the surface of the activated carbon, the invalid pores can be converted into sodium storage active pores. After the solvated sodium ions migrate to the interface of the sodium storage active pores of the composite carbon material, a desolvation reaction occurs, and the solvent molecules in the electrolyte are blocked outside the pores and continue to transport the next batch of sodium ions. The sodium ions that enter the pores gain electrons during the electrochemical reaction and are stored in the pores in the form of sodium clusters. Therefore, the assembled sodium ion battery also has high initial coulombic efficiency and cycle stability.

[0010] In order to achieve the above object, the technical solution adopted by the present invention is:

[0011] In a first aspect, the present invention provides a composite carbon material comprising activated carbon and a soft carbon layer coated on the surface of the activated carbon;

[0012] The activated carbon is selected from at least one of coal-based activated carbon, coconut shell activated carbon, and activated carbon with bamboo as the carbon source (bamboo charcoal activated carbon);

[0013] The soft carbon layer includes sodium storage active pores, and the soft carbon layer is prepared by coating a soft carbon precursor on the surface of activated carbon after melting and calcining once.

[0014] In some embodiments, the composite carbon material consists of activated carbon and a soft carbon layer coated on the surface of the activated carbon.

[0015] In some embodiments, the activated carbon is selected from at least one of coal-based activated carbon and coconut shell activated carbon.

[0016] In some embodiments, the soft carbon precursor is selected from at least one of mesophase pitch, medium-temperature pitch, low-temperature pitch, high-temperature pitch, coal tar pitch, aromatic coal pitch, ethylene tar pitch, coal tar, petroleum coke, needle coke, coke, anthracite, mesophase carbon microbeads, and medium-temperature coal tar.

[0017] In some preferred embodiments, the soft carbon precursor is selected from at least one of mesophase pitch, medium-temperature pitch, aromatic coal pitch, ethylene tar pitch, petroleum coke, needle coke, coke, anthracite, mesophase carbon microbeads, and medium-temperature coal tar.

[0018] In some embodiments, the sodium storage active pore is a semi-closed pore, and the pore diameter of the sodium storage active pore is 0.1-30 nm.

[0019] Specifically, sodium storage active pores with a pore size of 0.1~30nm are conducive to the transportation and storage of sodium.

[0020] In some preferred embodiments, the sodium storage active pores have a pore diameter of about 1 nm.

[0021] Specifically, the composite carbon material prepared by the present invention has abundant sodium storage active pores (reflected in: long platform capacity in BET test and charge-discharge curve), can store sodium ions with high capacity and high rate, and greatly improves the problem of electrolyte decomposition.

[0022] In some embodiments, the mass ratio of the soft carbon precursor to the activated carbon is 1:3 to 3:1.

[0023] In some preferred embodiments, the mass ratio of the soft carbon precursor to the activated carbon is 1:1 to 2:1.

[0024] In some embodiments, the specific surface area of ​​the composite carbon material is ≤20 m 2 / g.

[0025] In some preferred embodiments, the specific surface area of ​​the composite carbon material is 1 to 10 m 2 / g.

[0026] In some preferred embodiments, the specific surface area of ​​the composite carbon material is 2 to 6 m 2 / g.

[0027] In some embodiments, the specific surface area of ​​the activated carbon is 500 m 2 / g ~3200m 2 / g.

[0028] In some preferred embodiments, the specific surface area of ​​the activated carbon is 800 m 2 / g ~2500m 2 / g.

[0029] In some more preferred embodiments, the specific surface area of ​​the activated carbon is 1200 m 2 / g ~1800m 2 / g.

[0030] In some embodiments, the activated carbon has a porous structure, and the pore size of the porous structure is 0.1 nm to 5 μm.

[0031] In a second aspect, the present invention provides a method for preparing the composite carbon material according to the first aspect, comprising the following steps:

[0032] S1: After mixing the activated carbon and the dispersant, the soft carbon precursor is added and mixed, and heated until the soft carbon precursor is melted to obtain an intermediate;

[0033] S2: placing the intermediate in an inert atmosphere for calcination to obtain a composite carbon material.

[0034] In some embodiments, in step S1, the activated carbon is selected from at least one of coal-based activated carbon, coconut shell activated carbon, and activated carbon with bamboo as the carbon source.

[0035] In some embodiments, in step S1, the dispersant is selected from at least one of ethanol, deionized water, methanol, ethylene glycol, glycerol, acetone, benzene, toluene, diethyl ether, and tetrahydrofuran.

[0036] In some preferred embodiments, in step S1, the dispersant is selected from at least one of ethanol, deionized water, methanol, ethylene glycol, and glycerol.

[0037] In some embodiments, in step S1, the soft carbon precursor is selected from at least one of mesophase pitch, medium-temperature pitch, low-temperature pitch, high-temperature pitch, coal tar pitch, aromatic coal pitch, ethylene tar pitch, coal tar, petroleum coke, needle coke, coke, anthracite, mesophase carbon microbeads, and medium-temperature coal tar.

[0038] In some preferred embodiments, in step S1, the soft carbon precursor is selected from at least one of mesophase pitch, medium-temperature pitch, aromatic coal pitch, ethylene tar pitch, petroleum coke, needle coke, coke, anthracite, mesophase carbon microbeads, and medium-temperature coal tar.

[0039] In some embodiments, in step S1, the mass ratio of the soft carbon precursor to the activated carbon is 1:3 to 3:1.

[0040] In some preferred embodiments, in step S1, the mass ratio of the soft carbon precursor to the activated carbon is 1:1 to 2:1.

[0041] In some embodiments, in step S1, the volume ratio of the activated carbon mass to the dispersant is 0.01-0.5 g / mL.

[0042] In some embodiments, in step S1, the heating process further includes a stirring step.

[0043] In some embodiments, in step S1, the heating temperature is 30-80°C.

[0044] In some embodiments, in step S1, the heating time is 1 to 20 hours. Preferably, the heating time is 5 to 15 hours.

[0045] In some embodiments, in step S2, a drying step is further provided before calcination.

[0046] In some embodiments, in step S2, the inert atmosphere is selected from at least one of nitrogen, argon, and neon.

[0047] In some embodiments, in step S2, the heating rate of the calcination is 2°C / min to 10°C / min.

[0048] In some preferred embodiments, the heating rate of the calcination is 5°C / min.

[0049] In some embodiments, in step S2, the calcination temperature is 500°C to 1900°C.

[0050] In some preferred embodiments, in step S2, the calcination temperature is 700°C to 1600°C. Specifically, the calcination temperature can be 700°C to 1000°C, or 1300°C to 1500°C.

[0051] In some more preferred embodiments, in step S2, the calcination temperature is 1000°C to 1400°C.

[0052] In some embodiments, in step S2, the calcination time is 0.5 h to 10 h.

[0053] In some preferred embodiments, in step S2, the calcination time is 1 to 10 hours, specifically 1 hour, 3 hours, 5 hours, 7 hours, or 10 hours.

[0054] Specifically, the present invention selects activated carbon with suitable specific surface area and pore size distribution, a soft carbon precursor with high fluidity and coating effect, and controls the mass ratio of the soft carbon precursor to the activated carbon. A simple process is used to achieve the composite and uniform mixing of the activated carbon and the soft carbon precursor, and a medium-high temperature calcination (one-time calcination) is used to achieve a composite structure of soft carbon-coated activated carbon, thereby converting the inactive pores exposed on the surface into high-capacity and highly reversible sodium storage active pores. At the same time, the preparation process of the present invention is not only simple, pollution-free, and low-cost, suitable for large-scale production, but also the assembled sodium-ion battery has the advantages of high energy density, high first coulombic efficiency, and good cycle stability.

[0055] In a third aspect, the present invention provides a negative electrode slurry comprising the composite carbon material described in the first aspect.

[0056] In some embodiments, the negative electrode slurry further includes a binder and carbon black, and the mass ratio of the composite carbon material, the binder and the carbon black is (5-10):1:1.

[0057] In some embodiments, the binder is selected from at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polymethyl methacrylate, polyacrylonitrile, polyimide, polyvinyl pyrrolidone, polyethylene oxide, polyvinyl alcohol, sodium carboxymethyl cellulose, styrene-butadiene rubber, and gelatin.

[0058] In some embodiments, the negative electrode slurry further includes a solvent for the binder.

[0059] In some embodiments, the solvent of the binder is selected from at least one of methanol, ethanol, propanol, glycerol, N-methylpyrrolidone, dimethyl sulfoxide, tetrahydrofuran, and N,N-dimethylformamide.

[0060] In a fourth aspect, the present invention provides a composite carbon material for a negative electrode as described in the first aspect.

[0061] In some embodiments, the negative electrode further comprises a current collector. Preferably, the current collector is one or more of aluminum and copper.

[0062] In some embodiments, the effective loading of the negative electrode is 1 to 5 mg / cm 2 .

[0063] In some preferred embodiments, the effective loading of the negative electrode is about 2 mg / cm 2 .

[0064] Specifically, the effective loading amount is the effective loading amount of the negative electrode active material.

[0065] In a fifth aspect, the present invention provides a sodium ion battery comprising the negative electrode described in the fourth aspect.

[0066] In some embodiments, the sodium ion battery further comprises: metallic sodium as the negative electrode, and carbonate-sodium salt or ether-sodium salt as the electrolyte.

[0067] In some preferred embodiments, the electrolyte in the electrolyte is at least one of NaPF6 and NaClO4.

[0068] In some preferred embodiments, the solvent in the electrolyte is at least one of ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethylene glycol dimethyl ether (DEGDME), diethyl carbonate (DEC), and fluoroethylene carbonate (FEC).

[0069] In some preferred embodiments, the electrolyte comprises: 0.5-4 mol / L carbonate-sodium salt or ether-sodium salt electrolyte. Beneficial effects

[0070] The composite carbon material of the present invention not only has a simple composition and low raw material cost, but also possesses abundant sodium-storage active pores, a small specific surface area, and a stable structure. Furthermore, it fully utilizes the matrix and mass transfer functions of the activated carbon, the fluidity of the soft carbon precursor, and the inherent advantages of the soft carbon, making it particularly suitable for use as a negative electrode active material. The large specific surface area of ​​the activated carbon and the enhanced fluidity of the soft carbon precursor during heating create conditions for effective coating of the activated carbon surface and the production of abundant sodium-storage active pores.

[0071] The preparation method of the composite carbon material of the present invention only relies on heating, melting, mixing and one medium-high temperature calcination to evenly cover the soft carbon on the porous surface of the activated carbon, thereby achieving the coating of the activated carbon and converting the ineffective pores on the surface of the activated carbon into sodium storage active pores, thereby obtaining a composite carbon material with abundant sodium storage active pores. Therefore, this method has the characteristics of simple process, environmental protection and low cost, and is suitable for large-scale production and practical application.

[0072] Due to the good coating effect of the composite carbon material, rich sodium storage active pores, small specific surface area, and stable structure, the sodium ion battery prepared with the composite carbon material of the present invention as the negative electrode active material has the advantages of large specific capacity, high initial coulombic efficiency, good cycle reversibility, good long-term cycle stability, and excellent rate performance. Specifically:

[0073] (1) The present invention can solve the problems of low negative electrode capacity of existing sodium ion batteries (most of the current commercial hard carbon specific capacity is less than 350 mAh / g), low first coulombic efficiency (hard carbon itself has a relatively rich pore structure, and the electrolyte is easily decomposed on the surface to produce side reactions during the first charge and discharge process, and some intercalation and pore-filling capacity cannot be reversibly released, resulting in low first coulombic efficiency), poor rate performance (the kinetic performance of the capacity in the platform area of ​​conventional hard carbon negative electrodes is poor, and the degree of irreversibility is large under high current, so the capacity decays seriously at high rates), and poor cycle stability (the intercalation, pore-filling and adsorption capacity of hard carbon are somewhat irreversible, especially at high current, the capacity decays rapidly, and the cycle stability needs to be improved).

[0074] (2) The innovation of the present invention lies in the use of inexpensive activated carbon as raw material and the soft carbon coating of the porous surface of the activated carbon. Based on the derived sodium storage active pores, the platform capacity of the carbon negative electrode of the sodium ion battery is greatly improved. Since the pore size range of the activated carbon surface is large and densely distributed, high-speed sodium exchange can be achieved between the derived sodium storage active pores, thereby improving the sodium ion transfer kinetics and thus improving the rate performance of the sodium ion battery. After the soft carbon coating, the solvated ion groups are desolvated on the surface of the active pores (i.e., the sodium storage active pores), which greatly reduces the decomposition of the electrolyte solvent molecules and the occurrence of side reactions, thereby improving the first coulombic efficiency and cycle stability of the sodium ion battery.

[0075] The sodium-ion half-cell assembled in this invention achieved an initial coulombic efficiency of 90.5%, and the composite carbon prepared using the preferred method achieved a specific capacity of 419 mAh / g. When the charge / discharge rate was increased from 0.1C to 5C, the capacity retention rate reached 75%, and when the charge / discharge rate was reduced to 0.1C, the capacity recovered to 400 mAh / g, demonstrating excellent rate performance.

[0076] (3) The composite carbon material of the present invention has a simple preparation process, abundant and inexpensive raw materials, is environmentally friendly, suitable for large-scale production, complies with the sustainable development strategy and green economic principles, and can be widely used in the field of energy storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0077] FIG1 is a schematic structural diagram of the composite carbon material of the present invention;

[0078] FIG2 is an SEM image of the coal-based activated carbon and the composite carbon material in Example 1;

[0079] FIG3 is a nitrogen adsorption / desorption curve and pore size distribution diagram of the coal-based activated carbon in Comparative Example 1;

[0080] FIG4 is a nitrogen adsorption / desorption curve diagram and pore size distribution diagram of the composite carbon material in Example 1;

[0081] FIG5 is a small-angle X-ray diffraction graph of the composite carbon materials in Example 1, Example 108, and Example 127;

[0082] FIG6 is an XRD spectrum of the composite carbon material, activated carbon and soft carbon in Example 1;

[0083] FIG7 is a constant current charge and discharge curve of a sodium ion battery made of the composite carbon material in Example 1 at 0.1C;

[0084] FIG8 is a long cycle curve of a sodium ion battery made of the composite carbon material as the negative electrode material in Example 1 at 0.1C;

[0085] FIG9 is a rate performance test curve of a sodium ion battery made of the composite carbon material as the negative electrode material in Example 1. Best Mode for Carrying Out the Invention

[0086] The present invention is further described in detail below through specific examples.

[0087] The composite carbon material prepared by the present invention utilizes coal-based activated carbon and biomass-based activated carbon with different specific surface areas as the matrix; petrochemical and coal chemical by-products such as asphalt and anthracite are used as soft carbon precursors, and a composite structure of soft carbon-coated activated carbon is achieved through medium and high temperature "one-step" calcination. The raw material cost is low and pollution-free. The prepared composite carbon negative electrode material has improved specific capacity, cycle performance and first coulombic efficiency, and is particularly suitable for use in high-performance sodium ion battery negative electrodes.

[0088] Furthermore, the preparation process of the present invention is simple, the equipment cost is low, and it is suitable for large-scale production. The emergence of sodium-ion batteries not only alleviates the problem of limited lithium-ion resources and high costs, but also has simple, inexpensive, readily available, environmentally friendly, and safe positive and negative electrode materials, and a simple and low-cost production process. This is a sodium-ion battery with high specific capacity, high cycle performance, and high safety.

[0089] A schematic diagram of the structure of the composite carbon material in the present invention is shown in FIG1 .

[0090] As shown in Figure 1, the composite carbon material provided by the present invention is composed of activated carbon particles and a soft carbon layer uniformly coated on the surface of the activated carbon particles. This effectively modifies the inactive pores exposed on the surface of the activated carbon, converting them into high-capacity and highly reversible sodium-storage active pores (semi-enclosed pores with a pore diameter of approximately 0.1 to 30 nm), thereby synergistically leveraging the pore structure of the activated carbon particles as a matrix and the inherent advantages of the soft carbon. Furthermore, the present invention can produce a low-cost composite carbon material with a simple composition, stable structure, and excellent electrochemical performance through a simple preparation process and without the need for additional metal and heteroatom doping. This material is particularly suitable for use as a negative electrode active material in sodium-ion batteries.

[0091] Example 1

[0092] This embodiment provides a method for preparing a composite carbon material, comprising the following steps:

[0093] S1: Disperse 1g of activated carbon particles in a dispersant, gradually add 1g of soft carbon precursor, continue heating to 70℃ and stirring for 10 hours to obtain an intermediate;

[0094] S2: The intermediate was dried at 65°C to constant weight, and then placed in a tube furnace and calcined at 1300°C for 5 h (heating rate: 5°C / min) under argon atmosphere to obtain a composite carbon material;

[0095] In step S1, the activated carbon particles are coal-based activated carbon, specifically coal-based-1600, whose Langmuir specific surface area is 1600±50 m 2 / g; the dispersant is ethanol, and the amount of the dispersant is 20mL; the soft carbon precursor is mesophase pitch.

[0096] This embodiment provides a method for preparing a negative electrode slurry and a sodium ion battery half-cell, comprising the following steps:

[0097] 1) The composite carbon material of this embodiment was mixed with polyvinylidene fluoride (PVDF binder, solid) and conductive carbon black (SP conductive agent) in a mass ratio of 8:1:1. After grinding for 30 minutes, N-methylpyrrolidone (NMP) was added and stirred until a paste formed to obtain a negative electrode slurry;

[0098] 2) The negative electrode slurry was coated on a carbon-coated aluminum foil with a size of 15 cm × 25 cm to prepare an electrode with an effective loading of about 2 mg / cm 2 A sodium ion battery half-cell was assembled using a sodium sheet as the counter electrode and a NaPF4 carbonate electrolyte.

[0099] Among them, the NaPF4 carbonate electrolyte is composed of an electrolyte and a solvent; the concentration of the electrolyte NaPF4 is 1 mol / L; the solvent is ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) mixed in a volume ratio of 1:1:1.

[0100] Among them, in the negative electrode slurry, the added amount of N-methylpyrrolidone NMP is 3 mL (N-methylpyrrolidone) / g.

[0101] Characterization and performance testing:

[0102] 1. A scanning electron microscope (SEM) image of the coal-based activated carbon in Example 1, measured at a magnification of 3700, is shown in Figure 2 (a). SEM images of the composite carbon material in Example 1, measured at different magnifications, are shown in Figures 2 (b) and (c), respectively.

[0103] As shown in Figure 2 (a), coal-based activated carbon has a distinct macroporous structure (pore size > 50 nm, primarily micron-sized pores, particularly those with a pore size of 1-5 μm). While these macropores can improve kinetics and facilitate material transport, they are ineffective sodium storage pores and can easily lead to electrolyte decomposition.

[0104] It should be noted that sodium-storage active pores are pores with a pore diameter of approximately 0.1 to 30 nm (preferably pores with a pore diameter of 1 nm). Due to the small size of the active pores, they cannot be accurately characterized by SEM and BET tests. However, combined with the electrochemical performance, it can be shown that the composite carbon material of Example 1 has abundant sodium-storage active pores. After carbonization, the mesophase pitch, which serves as a soft carbon precursor, can be deposited and coated on the surface of the activated carbon pores (pore diameter 0.1 nm to 5 μm), converting the micropores in the activated carbon into sodium-storage pores and inhibiting the decomposition of the electrolyte on the surface of the activated carbon mesopores and macropores.

[0105] (b) and (c) in Figure 2 show that the number of macropores on the surface of the composite carbon material provided in Example 1 is significantly reduced, and a layer of soft carbon material is covered on the surface of the macropores, thereby effectively modifying the surface structure of the activated carbon and converting ineffective pores into pores that can achieve sodium storage, and can also reduce the decomposition of the electrolyte.

[0106] 2. The nitrogen adsorption / desorption curve and pore size distribution of the coal-based activated carbon in Comparative Example 1 are shown in Figures 3(a) and (b), respectively. The nitrogen adsorption / desorption curve and pore size distribution of the composite carbon material in Example 1 are shown in Figures 4(a) and (b), respectively.

[0107] From Figures 3 and 4, we can see that Figure 3 (a) shows that: by different analysis methods, the coal-based activated carbon (coal-based-1600 activated carbon) was analyzed. By single-point BET specific surface area analysis, the specific surface area of ​​the coal-based activated carbon (coal-based-1600 activated carbon) was 1402.55 m 2 / g; the specific surface area measured by multi-point BET specific surface area method is 1435.21 m 2 / g; Langmuir specific surface area (i.e. Langmuir surface area) is 1671.32 m 2 / g; t-plot micropore specific surface area is 1198.65m2 / g. Based on the nitrogen desorption curve, the pore size distribution diagram (Figure 3(b)) was derived using the Harkins & Jura method. Figure 3(b) shows that the pore size of coal-based-1600 activated carbon is primarily distributed between 1 and 50 nm, indicating that its pores are primarily microporous and mesoporous.

[0108] Figure 4 (a) shows that the composite carbon material of Example 1 was analyzed by different analysis methods. The specific surface area of ​​the composite carbon material of Example 1 was 3.76 m by single-point BET specific surface area analysis. 2 / g; the specific surface area measured by multi-point BET specific surface area method is 3.80 m 2 / g; Langmuir specific surface area (i.e. Langmuir surface area) is 2.78 m 2 / g; t-plot micropore specific surface area is 5.78 m 2 / g. Based on the nitrogen desorption curve, the Harkins & Jura method was used to generate a pore size distribution (Figure 4(b)). Figure 4(b) shows that after high-temperature soft carbon coating, the original micropores of the activated carbon become active sodium storage pores. Because the soft carbon covers the pore surfaces, they cannot be identified in the BET test, and the electrolyte does not decompose on these sodium storage pores to form an SEI film. However, due to the inherent pore structure of the carbon material, Figure 4(b) consistently shows a consistent pore structure distribution.

[0109] Figure 5 shows that the small-angle X-ray diffraction curves of the composite carbon materials prepared in Example 1, Example 108, and Example 127 all have obvious peaks, corresponding to the scattering intensity Q in the range of 0.5 to 2 nm. -1 The range of the nanopore size distribution of the three composite carbons is shown in Figure 1, indicating that these pores are not detected by BET. Examples 1, 127, and 108 are all preferred examples, and all have nanoscale active storage pores (pore diameter: 0.1-30 nm). Furthermore, it is clear that the small-angle X-ray diffraction peaks of the composite carbons prepared in Examples 1, 127, and 108 gradually increase, indicating that their nanoscale active storage pores gradually decrease, and therefore their sodium storage capacity also decreases accordingly.

[0110] 3. X-ray diffraction (XRD) spectra of the soft carbon prepared by calcining the soft carbon precursor mesophase pitch raw material in Example 1 at 1300°C for 5 hours under an argon atmosphere, the composite carbon material in Example 1, and the coal-based activated carbon are shown in Figure 6.

[0111] Figure 6 shows that compared to composite carbon and soft carbon, the activated carbon has a flatter (002) peak near 24°, indicating a high degree of disorder in its carbon layer along the c-axis. After soft carbon coating and high-temperature calcination, the (002) peak becomes sharper, indicating an increase in the order of the composite carbon's carbon layer structure. It should be noted that while both soft carbon and activated carbon are amorphous carbon, they differ in their carbon layer order and surface morphology, and thus in their roles in sodium ion storage and transport.

[0112] 4. Electrochemical performance test:

[0113] The sodium half-cell provided in Example 1 was subjected to charge-discharge tests at various rates, and a long-cycle test was performed at 0.1C. The number of cycles at which the capacity dropped to 80% during the long-cycle test was recorded. Simultaneously, the remaining Examples 2-141, Comparative Example 1, and Comparative Examples 3-9 were subjected to charge-discharge tests at various rates using the same testing methods and conditions, and a long-cycle test was performed at 0.1C. The number of cycles at which the capacity dropped to 80% during the long-cycle test was recorded.

[0114] Unless otherwise specified, the first coulombic efficiency of the examples and comparative examples in the present invention was measured at a rate of 0.1 C and a charge-discharge condition of 0.001-2 V. The specific electrochemical properties measured are shown in Tables 1 to 9 and Figures 7 to 9.

[0115] The rate performance test curve of the sodium ion battery made of the composite carbon material in Example 1 as the negative electrode material is shown in Figure 9; the constant current charge and discharge curve of the sodium ion battery made of the composite carbon material in Example 1 under 0.1C conditions is shown in Figure 7; the long cycle curve of the sodium ion battery made of the composite carbon material in Example 1 as the negative electrode material at 0.1C is shown in Figure 8.

[0116] As shown in Figures 7, 8, 9, and Table 9, the sodium-ion battery of Example 1 has a specific capacity of 419 mAh / g at 0.1C constant current charge and discharge, and a specific capacity of 388 mAh / g at 0.5C constant current charge and discharge. The initial coulombic efficiency measured at 0.1C is 90.5%.

[0117] At the same time, when conducting a long cycle test at 0.1C, the number of cycles for the capacity to decay to 80% was measured to be 2109 cycles.

[0118] Further analysis shows that in the sodium ion half-cell made from the composite carbon material of Example 1, the platform area below 0.1V belongs to the pore sodium storage capacity. Sodium is stored in the form of sodium clusters in the nanopores, and the capacity is provided by the sodium storage active pores of the composite carbon. Therefore, the platform capacity in the constant current charge and discharge curve of Example 1 of the present invention reaches more than 300mAh / g.

[0119] The BET test and the long platform capacity test results of the charge-discharge curve ( FIG. 4 and FIG. 7 ) can show that the composite carbon material prepared in the present invention has abundant sodium storage active pores.

[0120] In addition, FIG9 shows that the composite carbon material of Example 1 has excellent rate performance and good electrochemical stability. Modes for Carrying Out the Invention

[0121] Example 2 to Example 21

[0122] The preparation methods of the composite carbon materials, negative electrode slurries, and sodium ion battery half-cells of Examples 2 to 21 differ from those of Example 1 only in the type of activated carbon used. For the rest, refer to Example 1.

[0123] Test conditions and methods for electrochemical performance of negative electrode:

[0124] The composite carbon materials were assembled into sodium ion battery half cells according to the method of Example 1. Specifically:

[0125] (1) Test conditions for rate performance: Cross-current charge and discharge for 10 cycles at current densities of 0.1C, 0.5C, 1C, 2C, and 5C, then return to 0.1C for long cycling, and record the specific capacity at 0.1C and 0.5C conditions.

[0126] (2) Test conditions for the first coulombic efficiency: The coulombic efficiency is measured during the first cycle of charge and discharge at 0.1C.

[0127] (3) Long cycle test conditions: The number of cycles required for the capacity to decay to 80% is measured under a constant current of 0.1C.

[0128] The types of activated carbon used in Examples 1 to 21 and the electrochemical properties of the negative electrodes after being assembled into sodium ion batteries are specifically shown in Table 1.

[0129] Table 1 Parameters of activated carbon and performance of sodium ion batteries in Examples 1 to 21

[0130]

[0131] Note: The composite carbon materials for the negative electrode in Table 1 all use mesophase pitch as the soft carbon precursor, and the mass ratio of activated carbon to soft carbon precursor is 1:1 during the preparation process;

[0132] The specific surface area in Table 1 is the reference value of the specific surface area given by the purchased activated carbon. Due to the differences in the accuracy of the specific surface area testing instruments, the differences in the testing environment, and the theoretical differences in the specific surface area obtained based on nitrogen adsorption and desorption, there will be certain differences between the specific surface area measured in the scheme of the present invention and the reference value given by the product. However, the values ​​are at the same level and are within the normal range.

[0133] As can be seen in Table 1, different types of activated carbon have a significant impact on the performance of the composite carbon anode, primarily due to differences in their specific surface area and micromorphology. The micromorphology of activated carbon prepared from different activated carbon precursors varies significantly. The specific surface area and pore size distribution of activated carbon can be controlled by varying the pore-forming process and parameters. However, as an anode material, a higher specific surface area is not necessarily better; material stability also needs to be considered.

[0134] In contrast, the specific surface area of ​​the coconut shell prepared in Example 5 was 1500 ± 50 m 2 / activated carbon (coconut shell-1500), and the specific surface area of ​​1600±50 m prepared by coal in Example 1 2 Composite carbon materials made from activated carbon (coal-based-1600) with a concentration of 100 μg / g are preferred as negative electrode materials. They not only exhibit good electrochemical performance in sodium-ion batteries, but also have excellent electrochemical stability.

[0135] In summary, one of the key points of the present invention is: the type of activated carbon. Examples 1 to 21 show that the specific surface area of ​​activated carbon is 1200 to 1800 m 2 / g of coal-based activated carbon as the raw material to obtain a composite carbon material with good electrochemical properties and stability (including structural stability and electrochemical stability), and coconut shell-1500 and coal-based-1600 activated carbon are more preferred activated carbon raw materials.

[0136] The purpose of the present invention is to use soft carbon to coat activated carbon, so that the ineffective pores exposed on the surface are converted into high-capacity, highly reversible sodium storage active pores; therefore, another key to the present invention is to use soft carbon to coat activated carbon, and the key to this step is to control the process parameters such as the type of soft carbon precursor, the ratio of activated carbon and soft carbon precursor, and temperature, so as to realize and achieve the purpose of converting the ineffective pores exposed on the surface of activated carbon into high-capacity, highly reversible sodium storage active pores.

[0137] Example 22 to Example 27

[0138] The preparation methods of the composite carbon materials, negative electrode slurries, and sodium ion battery half-cells of Examples 22, 24, and 26 differ from those of Example 1 only in the different mass ratios of the soft carbon precursor and activated carbon used. For other details, refer to Example 1.

[0139] The preparation methods of the composite carbon materials, negative electrode slurries, and sodium ion battery half-cells of Examples 23, 25, and 27 differ from those of Example 5 only in the different mass ratios of the soft carbon precursor and activated carbon used. For other details, refer to Example 5.

[0140] The electrochemical performance test conditions of Examples 22 to 27 are the same as those of Example 1;

[0141] The mass ratios of the soft carbon precursor and activated carbon used in Examples 22 to 27, and the electrochemical properties of the sodium ion battery half-cells or negative electrodes are specifically shown in Table 2.

[0142] Table 2 Performance of the sodium ion batteries of Example 1, Example 5, and Examples 22 to 27

[0143]

[0144] Note: The examples in Table 2 all use mesophase pitch as the soft carbon precursor.

[0145] As can be seen from Table 2, the composite carbon materials prepared using different mass ratios of mesophase pitch to activated carbon affect the effect of soft carbon coating activated carbon and the transformation of the activated carbon surface structure into sodium storage pores, thereby affecting the specific capacity, first coulombic efficiency, rate performance and long-cycle stability of the composite carbon material as a negative electrode in sodium ion batteries.

[0146] When the mass ratio of the soft carbon precursor to the activated carbon is 1:2~1:3, the first coulombic efficiency in Examples 22~25 is low and the capacity is low. This is mainly because the content of soft carbon is too low to completely cover the pores on the surface of the activated carbon. The mass ratio of the soft carbon precursor needs to be further increased.

[0147] As the proportion of the soft carbon precursor increases, the specific capacity, first coulombic efficiency, and the number of cycles required for the capacity to decay to 80% at different current densities initially increase and then rapidly decrease. This indicates that within a certain ratio range (soft carbon precursor to activated carbon mass ratio of 1:3 to 1:1), increasing the mass ratio of the soft carbon precursor can improve the coating effect on the activated carbon. Furthermore, based on the comprehensive electrochemical performance, the optimal mass ratio of the mesophase pitch to activated carbon is 2:1 to 1:1.

[0148] However, when the mass ratio of soft carbon precursor to activated carbon was 2:1, the electrochemical performance of Examples 26-27 decreased. This is because the excessive amount of soft carbon coating precursor would reduce the active mass ratio of the composite carbon material, which in turn would lead to a decrease in sodium storage capacity. Therefore, the optimal mass ratio of soft carbon precursor to activated carbon is 1:1.

[0149] Example 28 to Example 54

[0150] The preparation methods of the composite carbon materials, negative electrode slurries, and sodium ion battery half-cells of Examples 28 to 54 differ from those of Example 1 or Example 5 only in the type of soft carbon precursor used. For the rest of the content, refer to Example 1 or Example 5.

[0151] The electrochemical performance test conditions of Examples 28 to 54 were the same as those of Example 1;

[0152] The types of soft carbon precursors used in Examples 28 to 54, as well as the electrochemical performance of the assembled sodium ion batteries, are specifically shown in Table 3.

[0153] Table 3 Performance of the sodium ion batteries of Example 1, Example 5, and Examples 28 to 54

[0154]

[0155] Note: The mass ratio of the soft carbon precursor to the activated carbon in the examples in Table 3 is 1:1.

[0156] Example 55 to Example 79

[0157] The preparation methods of the composite carbon materials, negative electrode slurries, and sodium ion battery half-cells of Examples 55 to 79 differ from those of Example 1 or Example 5 only in that the types of soft carbon precursors used and the mass ratios of the soft carbon precursors and activated carbon are different. For the rest of the description, refer to Example 1 or Example 5.

[0158] The electrochemical performance test conditions of Examples 55 to 79 were the same as those of Example 1;

[0159] The types of soft carbon precursors used in Examples 55 to 79, the mass ratio of the soft carbon precursor to the activated carbon, and the electrochemical properties of the assembled sodium ion batteries are specifically shown in Table 4.

[0160] Table 4 Performance of the sodium ion batteries of Example 26, Example 27, and Examples 55 to 79

[0161]

[0162] Note: The mass ratio of the soft carbon precursor to the activated carbon in the examples in Table 4 is 2:1.

[0163] Example 80 to Example 105

[0164] The preparation methods of the composite carbon materials, negative electrode slurries, and sodium ion battery half-cells of Examples 80 to 105 differ from those of Example 1 or Example 5 only in that the types of soft carbon precursors used and the mass ratios of the soft carbon precursors and activated carbon are different. For the rest of the description, refer to Example 1 or Example 5.

[0165] The electrochemical performance test conditions of Examples 80 to 105 were the same as those of Example 1;

[0166] The types of soft carbon precursors used in Examples 80 to 105, the mass ratio of the soft carbon precursor to the activated carbon, and the electrochemical properties of the assembled sodium ion batteries are specifically shown in Table 5.

[0167] Table 5 Performance of the sodium ion batteries of Examples 24, 25, 80 to 105

[0168]

[0169] Note: The mass ratio of the soft carbon precursor to the activated carbon in the examples in Table 5 is 1:2.

[0170] It can be seen from Tables 3, 4 and 5 that when coconut shell-1500 or coal-1600 activated carbon is selected, the composite carbon materials of Examples 1, 5 and 22 to 105 of the present invention have a specific capacity of 324 to 419 mAh / g at 0.1C; a specific capacity of 301 to 388 mAh / g at 0.5C; a first coulombic efficiency of 80.6% to 90.5%; and a cycle number for the capacity to decay to 80% of 953 to 2109.

[0171] In contrast, when the mass ratio of soft carbon precursor to activated carbon was 1:1, 2:1, and 1:2, the composite carbon materials prepared when using mesophase pitch, aromatic coal pitch, and needle coke as soft carbon precursors showed relatively excellent electrochemical performance as the negative electrode of sodium ion batteries. At the same time, for different types of soft carbon precursors, a mass ratio of soft carbon precursor to activated carbon of 1:1 is generally the most preferred ratio, and the composite carbon materials obtained have relatively excellent electrochemical performance and structural stability.

[0172] Based on this, the examples in Table 3 use the preferred coconut shell-1500 and coal-1600 as activated carbon, and control the ratio of soft carbon precursor to activated carbon to be 1:1, so that the prepared composite carbon material can have a better coating effect, more effective sodium storage pores and good electrochemical properties.

[0173] Example 106 to Example 134

[0174] The preparation methods of the composite carbon materials, negative electrode slurries, and sodium ion battery half-cells of Examples 106 to 134 differ from those of Example 1 only in that the calcination process parameters, specifically the calcination temperature and calcination time, are different. For the rest, refer to Example 1.

[0175] The electrochemical performance test conditions of Examples 106 to 134 were the same as those of Example 1;

[0176] The calcination process parameters used in Examples 106 to 134, the mass ratio of the soft carbon precursor to the activated carbon, and the electrochemical performance of the assembled sodium ion batteries are specifically shown in Table 6.

[0177] Table 6 Performance of the sodium ion batteries of Example 1 and Examples 106 to 134

[0178]

[0179] Note: The soft carbon precursors of the examples in Table 6 are all mesophase pitch, the activated carbons are all coal-based-1600 activated carbon, and the mass ratio of the soft carbon precursor to the activated carbon is 1:1.

[0180] As can be seen from Table 6, the calcination temperature and time parameters have a significant impact on the performance of the prepared composite carbon negative electrode. The main reason is that under a suitable calcination process, the structure, defects, and some pore structures of the soft carbon coating layer will be continuously optimized, thereby achieving a better coating effect, and then obtaining high-capacity, highly reversible sodium storage active pores on the activated carbon surface, resulting in a low-cost, structurally stable, and electrochemically excellent composite carbon material suitable for use as a negative electrode in sodium ion batteries. In comparison, the preferred calcination process parameters of the present invention are: in an argon atmosphere, the calcination temperature is set to 700-1900°C and the calcination time is 1-10 hours; the optimal calcination process parameters of the present invention are: in an argon atmosphere, the calcination temperature is set to about 1300°C and the calcination time is 3-7 hours.

[0181] Example 135 to Example 141

[0182] The preparation methods of the composite carbon materials, negative electrode slurries, and sodium ion battery half-cells of Examples 135 to 141 differ from those of Example 1 only in that the dispersants are different. For the rest, refer to Example 1.

[0183] The electrochemical performance test conditions of Examples 135 to 141 were the same as those of Example 1;

[0184] The dispersant types of Examples 135 to 141, as well as the electrochemical performance of the assembled sodium ion batteries, are specifically shown in Table 7.

[0185] Table 7 Performance of the sodium ion batteries of Example 1 and Example 135 to Example 141

[0186]

[0187] Note: The soft carbon precursors of the examples in Table 7 are all mesophase pitch, the activated carbons are all coal-based-1600 activated carbon, the mass ratio of the soft carbon precursor to the activated carbon is 1:1, and the calcination process parameters are: argon atmosphere, calcination temperature of 1300°C, and calcination time of 5 hours.

[0188] The soft carbon precursor and activated carbon need to be evenly dispersed in a system to achieve uniform coating of the activated carbon by the soft carbon. It is necessary to select a water-soluble or fat-soluble soft carbon precursor, or to mix the two by stirring and evaporating them. Therefore, a suitable dispersant is required to evenly disperse the activated carbon and soft carbon precursor.

[0189] As can be seen from Table 7, the performance of the composite carbon negative electrode prepared with ethanol, acetone, ether and tetrahydrofuran as active solvents is not much different, but benzene, toluene, ether and tetrahydrofuran are highly toxic and expensive. In order to achieve a green, environmentally friendly and low-cost preparation process, ethanol can be selected as the preferred dispersant. Industrial Applicability

[0190] Comparative Example 1

[0191] This comparative example provides an activated carbon, which is the coal-based activated carbon (coal-based-1600) of Example 1.

[0192] This comparative example provides a method for preparing a negative electrode slurry and a sodium ion battery half-cell. The only difference between the comparative example and Example 1 is that the composite carbon material is replaced with coal-based activated carbon (coal-1600). The performance test methods are the same as those in Example 1, and the measured performance is shown in Table 8.

[0193] Comparative Example 2

[0194] This comparative example provides a method for preparing a hard carbon negative electrode material, which can be specifically referred to Example 2 of Application No. 201811631507.1, Publication No. CN109742383A, and entitled “Hard Carbon Negative Electrode Material for Sodium Ion Batteries Based on Phenolic Resin, Preparation Method, and Application thereof”; specifically, the method comprises the following steps:

[0195] Liquid phenolic resin and ethanol were mixed in a volume ratio of 2:1 and stirred evenly; the mixture of phenolic resin and ethanol was transferred to a reactor and hydrothermally treated at 180°C for 4 hours to solidify the phenolic resin; the solidified phenolic resin was taken out and mechanically ground into particles; the particles were then placed in a tubular furnace and heated to 1550°C at a heating rate of 3°C / min. The raw material was subjected to high-temperature treatment for 2 hours under argon protection to crack and carbonize it; finally, it was cooled to room temperature, the material was taken out, and a hard carbon negative electrode material was obtained; and the performance of the sodium ion battery of Example 2 was shown in Table 8.

[0196] Comparative Example 3

[0197] This comparative example provides a method for preparing a composite carbon material, which differs from Example 1 of the present invention only in that the coal-based activated carbon is replaced by the chitosan of Example 4 of CN115911320A. The rest of the preparation process and its parameters, the preparation of the sodium ion half-cell, and the electrochemical performance testing method are consistent with Example 1 of the present invention. The measured performance is shown in Table 9.

[0198] Comparative Example 4

[0199] This comparative example provides a method for preparing a composite hard carbon material, which differs from Example 4 of CN115911320A only in that chitosan is replaced by coal-based activated carbon (coal-1600). The rest of the preparation process and process parameters are the same as Example 4 of CN115911320A.

[0200] The composite hard carbon material prepared in this comparative example was used as the negative electrode active material, and the sodium ion battery preparation method, electrochemical performance testing method and conditions of Example 1 of the present invention were used. The measured performance is shown in Table 9.

[0201] Comparative Example 5

[0202] This comparative example provides a method for preparing a composite carbon material, which differs from Example 1 of the present invention only in that the coal-based activated carbon is replaced with charcoal activated carbon (i.e., wood-based activated carbon with a specific surface area of ​​1100 ± 100 m 2 / g), the rest of the preparation process and its parameters, the preparation of the sodium ion half-cell and the electrochemical performance testing method were consistent with those in Example 1 of the present invention, and the measured performance is shown in Table 9.

[0203] Comparative Example 6

[0204] This comparative example provides a method for preparing a composite carbon material, which differs from Example 3 of CN109148838A only in that the ironwood charcoal is replaced by the coal-based activated carbon (coal-based-1600) in Example 1 of the present invention. The rest of the preparation process and process parameters are the same as Example 3 of CN109148838A.

[0205] The composite carbon material prepared in this comparative example was used as the negative electrode active material, and the sodium ion battery preparation method, electrochemical performance test method and conditions of Example 1 of the present invention were used. The measured performance is shown in Table 9.

[0206] Comparative Example 7

[0207] This comparative example provides a method for preparing a composite carbon material, which differs from Example 4 of CN115911320A only in that chitosan is replaced by charcoal activated carbon, and the rest of the preparation process and process parameters are the same as Example 4 of CN115911320A.

[0208] The composite hard carbon material prepared in this comparative example was used as the negative electrode active material, and the sodium ion battery preparation method, electrochemical performance testing method and conditions of Example 1 of the present invention were used. The measured performance is shown in Table 9.

[0209] Comparative Example 8

[0210] This comparative example provides a method for preparing a composite carbon material, which differs from Example 3 of CN109148838A only in that the ironwood charcoal is replaced by chitosan, and the rest of the preparation process and process parameters are the same as Example 3 of CN109148838A.

[0211] The composite carbon material prepared in this comparative example was used as the negative electrode active material, and the sodium ion battery preparation method, electrochemical performance test method and conditions of Example 1 of the present invention were used. The measured performance is shown in Table 9.

[0212] Table 8 Comparison of electrochemical performance of sodium ion batteries in Example 1, Comparative Example 1 and Comparative Example 2

[0213]

[0214] Note: For the test conditions of the electrochemical performance of the sodium ion battery and negative electrode of Comparative Example 2, please refer to Example 2 of Publication No. CN109742383A.

[0215] As can be seen from Table 8, in comparison, the negative electrode directly prepared from activated carbon and the hard carbon negative electrode material prepared in Example 2 of CN109742383A are used as negative electrode active materials for sodium ion batteries. The specific capacity, first coulombic efficiency and cycle performance of the composite carbon negative electrode material of the present invention are better.

[0216] Table 9 Comparison of electrochemical performance of sodium ion batteries in Example 1 and Comparative Examples 3 to 9

[0217]

[0218] Note: The sodium ion batteries or negative electrodes in Table 9 were all tested for electrochemical performance using the same electrochemical test method and conditions.

[0219] As shown in Table 9, compared with Example 1, Comparative Example 3 uses chitosan as the main material, and the composite material obtained based on the preparation parameters of Example 1 of the present invention has very poor performance in sodium ion batteries. The difference from CN115911320A is that the innovation of the present invention is to use activated carbon with rich pore structure and large specific surface area as the matrix material, and through a suitable soft carbon precursor, raw material dosage and a single calcination process, the ineffective pores on its surface are converted into efficient sodium storage active pores. Moreover, the preparation process of the present invention does not require tedious steps such as doping, and good rate performance can be obtained by utilizing the electrochemical coupling between active pores.

[0220] Compared to Example 1, Comparative Example 4, using the preferred coal-based activated carbon (i.e., Coal-1600 activated carbon) from Example 1 as the primary material and prepared using the parameters described in CN115911320A, yielded a composite material with significantly poor performance in sodium-ion batteries. This is due to significant differences between the hard carbon obtained by carbonizing chitosan and the activated carbon in terms of surface structure, carbon layer order, and internal pores. The two experimental schemes employed different types of materials.

[0221] It can be seen that the present invention is different from CN115911320A in terms of the inventive concept, raw materials used, performance improvement mechanism and process steps.

[0222] Compared with Example 1, Comparative Example 5, which uses charcoal activated carbon as the main material and uses the same preparation parameters as Example 1, exhibits very poor performance in a sodium-ion battery. This is because charcoal activated carbon and coal-based activated carbon belong to different categories of carbon materials, and the pore structure on the surface of charcoal activated carbon is uncontrollable, making it ineffective in converting into active pores for sodium storage.

[0223] Compared to Example 1, Comparative Example 6, which uses the coal-based activated carbon (coal-1600) from Example 1 as the primary material and is prepared using the parameters described in CN109148838A, exhibits significantly poor performance in sodium-ion batteries. This is because the CN109148838A preparation method fails to convert inactive pores on the surface of the coal-based activated carbon into active pores for sodium storage.

[0224] Compared to Example 1, Comparative Example 7, which uses the charcoal activated carbon in CN109148838A as the main material and the preparation parameters of CN115911320A to obtain a composite material for sodium-ion batteries, has very poor performance; the composite material using the chitosan in CN115911320A as the main material and the preparation parameters of CN109148838A also has poor performance for sodium-ion batteries. The reason is that the charcoal activated carbon in CN109148838A cannot be converted into a carbon material with high sodium storage efficiency using the preparation method of CN115911320A. Similarly, the chitosan in CN115911320A cannot be converted into a carbon material with high sodium storage efficiency using the preparation method of CN109148838A.

[0225] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and should be included in the scope of protection of the present invention.

Claims

1. A composite carbon material, characterized in that: It comprises activated carbon and a soft carbon layer coated on the surface of the activated carbon; The activated carbon is selected from at least one of coal-based activated carbon, coconut shell activated carbon, and bamboo charcoal activated carbon; The soft carbon layer comprises sodium storage active pores, and the soft carbon layer is prepared by coating a soft carbon precursor on the surface of activated carbon after melting and calcining once.

2. The composite carbon material according to claim 1, characterized in that The composite carbon material consists of activated carbon and a soft carbon layer coated on the surface of the activated carbon.

3. The composite carbon material according to claim 1 or 2, characterized in that: The sodium storage active pores are semi-closed pores, and the pore diameter of the sodium storage active pores is 0.1-30 nm.

4. The composite carbon material according to claim 3, characterized in that: The specific surface area of ​​the composite carbon material is ≤20 m 2 / g.

5. The composite carbon material according to claim 3, characterized in that: The activated carbon is selected from at least one of coal-based activated carbon and coconut shell activated carbon; and / or, The specific surface area of ​​the activated carbon is 500 m 2 / g ~3200m 2 / g.

6. The composite carbon material according to claim 5, characterized in that: The activated carbon has a porous structure, and the pore size of the porous structure is 0.1nm~5μm.

7. The composite carbon material according to claim 4, characterized in that: The soft carbon precursor is selected from at least one of mesophase pitch, medium-temperature pitch, low-temperature pitch, high-temperature pitch, coal tar pitch, aromatic coal pitch, ethylene tar pitch, coal tar, petroleum coke, needle coke, coke, anthracite, mesophase carbon microbeads, and medium-temperature coal tar.

8. The method for preparing a composite carbon material according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1: After mixing the activated carbon and the dispersant, adding the soft carbon precursor and mixing, and heating until the soft carbon precursor is melted to obtain an intermediate; S2: placing the intermediate in an inert atmosphere for calcining to obtain the composite carbon material.

9. The method for preparing a composite carbon material according to claim 8, characterized in that: In step S1, the mass ratio of the soft carbon precursor to the activated carbon is (1:3) to (3:1).

10. The method for preparing a composite carbon material according to claim 9, characterized in that: In step S1, the mass ratio of the soft carbon precursor to the activated carbon is (1~2):

1.

11. The method for preparing a composite carbon material according to claim 8, characterized in that: In step S2, the calcination temperature is 500°C to 1900°C; and / or the calcination time is 0.5h to 10h.

12. The method for preparing a composite carbon material according to any one of claims 8 to 11, characterized in that: In step S1, the heating process further includes a stirring step; and / or the heating time is 1 to 20 hours.

13. The method for preparing a composite carbon material according to any one of claims 8 to 11, characterized in that: In step S1, the dispersant is selected from at least one of ethanol, deionized water, methanol, ethylene glycol, and glycerol.

14. A negative electrode slurry, characterized in that: A composite carbon material comprising any one of claims 1 to 7; The negative electrode slurry also includes a binder and carbon black; And / or, the mass ratio of the composite carbon material, the binder and the carbon black is (5-10):1:

1.

15. A negative electrode, characterized in that: The composite carbon material comprises the composite carbon material according to any one of claims 1 to 7.

16. A sodium ion battery, characterized in that: Comprising the negative electrode as claimed in claim 15.

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