Carbon material, preparation method and application thereof

Abstract

The invention discloses a carbon material, a preparation method and application thereof, and belongs to the field of carbon materials. The carbon material is hard carbon, and the carbon vacancy of the carbon material is 0.11-0.58; the relational expression of the carbon vacancy tau is defined as # imgabs0 #, and IGC is the density of carbon atoms existing in the highly oriented pyrolytic graphite in the form of SP2 hybrid carbon atom pairs; iHC is the density of carbon atoms present as SP2 hybrid carbon atom pairs in the hard carbon material. The carbon material is obtained through the steps of high-temperature hot isostatic pressing sintering, oxygen plasma etching ball milling, sintering carbonization in a kiln and the like. The carbon material with a specific carbon vacancy ratio is defined, the carbon material has excellent sodium storage performance, and a new negative electrode material selection and a technical breakthrough point are provided for sodium ion battery industrialization.

Description

Technical Field

[0001] The present invention relates to the field of carbon materials, and more specifically to a carbon material, a preparation method thereof, and an application thereof. Background Art

[0002] The structure and working principle of sodium-ion batteries are basically the same as those of lithium-ion batteries, both belonging to the "rocking chair battery". Since 2020, due to the increasingly prominent scarcity of lithium resource supply, sodium-ion batteries have received extensive attention from academia and industry at home and abroad, and their related industrialization research has witnessed an explosive growth. At present, sodium-ion batteries have gradually entered the stage of moving from the laboratory to practical applications. Similar to lithium-ion batteries, according to the manufacturing process, sodium-ion batteries are mainly divided into several categories such as cylindrical, soft-pack, square, and blade-shaped batteries. According to the technical characteristics of sodium-ion batteries, sodium-ion batteries will first enter the market from applications in various low-speed electric vehicles and gradually penetrate into various energy storage application scenarios, such as the storage of renewable energy, data centers, 5G communication base stations, home and grid-scale energy storage, and other fields.

[0003] At the present stage, the industrialization of sodium-ion batteries is mainly restricted by the negative electrode. Due to thermodynamic reasons, it is difficult for sodium ions to be embedded in the graphite interstices and it is not easy to form a stable intercalation compound with carbon. Therefore, graphite negative electrodes hardly have the ability to store sodium in carbonate electrolytes, and thus only amorphous carbon can be used as the negative electrode. The sodium storage performance of amorphous carbon has become the key to the industrialization of sodium-ion batteries.

[0004] Amorphous carbon is non-crystalline and includes two materials, hard carbon and soft carbon. At present, the following problems still need to be solved urgently for the industrialization of hard carbon materials for sodium-ion batteries:

[0005] 1. The sodium storage capacity is relatively low. The sodium storage capacity of currently commercially available hard carbon is 250-300 mAh / g, which is lower than the capacity of commercial lithium-ion battery negative electrodes of 350-370 mAh / g, resulting in the mass energy density of sodium-ion batteries being much lower than that of lithium-ion batteries and making it difficult to meet market demands.

[0006] 2. The true density is relatively low. The micropores formed by turbostratic graphene are the main sodium storage sites of hard carbon. However, current preparation methods will increase ineffective closed pores while forming turbostratic graphene micropores, resulting in too low true density of hard carbon materials, and correspondingly lower tapped density and compression density, leading to the volume energy density of sodium-ion batteries being much lower than that of lithium-ion batteries and making it difficult to meet market demands.

[0007] 3. Lack of analytical methods for micro-nano structures. Hard carbon belongs to amorphous carbon, and traditional characterization methods are difficult to accurately analyze its micro-nano structure and cannot effectively guide the research and development of high-performance hard carbon. Summary of the Invention

[0008] Based on the above technical problems, the present invention proposes a carbon material, which is a carbon material with a defined carbon vacancy ratio; the present invention also provides a preparation method and application of the above carbon material.

[0009] The technical solution adopted by the present invention is as follows:

[0010] A carbon material, which is hard carbon, and the carbon vacancy degree of the carbon material is 0.21 - 0.58;

[0011] The relational expression for defining the carbon vacancy degree τ is:

[0012] In the formula, I GC is the density of carbon atoms existing as pairs of SP2 hybridized carbon atoms in highly oriented pyrolytic graphite;

[0013] I HC is the density of carbon atoms existing as pairs of SP2 hybridized carbon atoms in the hard carbon material.

[0014] The biggest feature of the carbon material provided by the present invention is that it is a carbon material with a defined carbon vacancy ratio, that is, carbon vacancy degree. Carbon vacancy is the position left by the absence of carbon atoms in the carbon lattice structure, and the carbon vacancy density of the carbon material is the ratio of the number of carbon atoms missing in the carbon material lattice structure to the total number of carbon atoms in the perfect carbon lattice structure. Based on the graphite lattice structure, all carbon atoms in the perfect graphite crystal exist in the form of SP2 hybridization, and the distance between adjacent two SP2 hybridized carbon atoms is 1.42 angstroms. In order to obtain the carbon vacancy ratio in the carbon material, the inventor introduces pairs of SP2 hybridized carbon atoms as density probes, and accurately detects the density (I HC ) of pairs of SP2 hybridized carbon atoms existing in different carbon materials through the pair distribution function analysis method, and then inversely deduces the density of carbon vacancies in the carbon material (calculated based on the density I GC of pairs of SP2 hybridized carbon atoms in highly oriented pyrolytic graphite closest to the single crystal graphite structure), and the proportion τ of carbon vacancies is

[0015] The sodium storage capacity of the carbon material provided by the present invention is 290 - 500 mAh / g, which improves the energy density of sodium ion batteries and promotes the industrialization process of sodium ion batteries.

[0016] In the carbon vacancy degree relational expression, I GC is the density of carbon atoms existing as pairs of SP2 hybridized carbon atoms in highly oriented pyrolytic graphite, and its value is the peak area of the pair distribution function spectrum of highly oriented pyrolytic graphite at ; I HC is the density of carbon atoms existing as pairs of SP2 hybridized carbon atoms in the amorphous carbon material (i.e., the carbon material of the present invention), and its value is the pair distribution function spectrum of the amorphous carbon material at The peak area at

[0017] The above atomic pair distribution function spectrum is obtained by Fourier transform of the total scattering experimental data measured by a Malvern Panalytical Ag target X-ray source total scattering experimental device.

[0018] Preferably, the carbon vacancy degree or the proportion of carbon vacancies in the carbon material is 0.25 - 0.54, and more preferably 0.35 - 0.50.

[0019] The above carbon material is hard carbon particles, and the average particle size of the hard carbon particles is 3 - 19 μm, preferably 3.1 - 15 μm, and more preferably 4.0 - 14.5 μm; the tapped density is 0.69 - 0.91 g / cm 3 , preferably 0.7 - 0.85 g / cm 3 ; the compression density is 0.92 - 1.32 g / cm 3 , preferably 0.95 - 1.25 g / cm 3 ; the true density is 1.65 - 2.15 g / cm 3 , preferably 1.65 - 2.00 g / cm 3 , and more preferably 1.70 - 1.90 g / cm 3 .

[0020] And / or, the specific surface area of the carbon material measured by the BET method is 0.45 - 24.55 m 2 / g, preferably 0.5 - 9.8 m 2 / g; the average pore diameter is 2.5 - 14.5 nm, preferably 3.5 - 10.5 nm.

[0021] And / or, the carbon material satisfies the following conditions:

[0022] And Q1 ≥ 200;

[0023] Where Q1 mAh / g represents the reversible sodium storage capacity of the carbon material (carbon negative electrode material) between 0 V (vs Na + / Na) and 0.2 V (vs Na + / Na) with a metal sodium counter electrode and the carbon material as the negative electrode; Q2 mAh / g represents the reversible sodium storage capacity of the carbon material between 0 V (vs Na + / Na) and 2.5 V (vs Na + / Na) with a metal sodium counter electrode and the carbon material as the negative electrode.

[0024] The d002 value of the carbon layer spacing of the above carbon material is 0.35 - 0.45 nm; the carbon layer spacing is calculated based on Bragg's equation by X-ray diffraction using Cu target Kα rays as the radiation source. The mass ratio of heteroatoms to carbon atoms in the carbon material is less than 0.09.

[0025] The present invention also provides a preparation method of a carbon material, which is used to prepare the amorphous carbon material as described above, and includes the following steps:

[0026] (1) Put the carbon source material into a mold, and obtain a first carbonized product through high-temperature hot isostatic pressing sintering in an inert atmosphere.

[0027] (2) Put the first carbonized product into an oxygen plasma ball mill, and obtain a second carbonized product through oxygen plasma etching and ball milling.

[0028] (3) Disperse the second carbonized product into an organic liquid, atomize it into suspension droplets under the protection of an inert gas, and sinter and carbonize it in a kiln to obtain the carbon material.

[0029] Preferably, in step (1):

[0030] The carbon source material is selected from one or more of natural biomass, plant extracts, resin or polymer carbon sources, mineral carbon materials, and derivatives modified by physical and chemical methods.

[0031] The above natural biomass includes at least one of coconut shell, walnut shell, pistachio, peanut shell, walnut shell, peach pit shell, cotton, wood chips, bamboo, straw, and lignin. The above plant extracts include at least one of starch, glucose, sucrose, cellulose, and natural rubber. The above resin or polymer carbon sources include at least one of phenolic resin, epoxy resin, melamine resin, polyfurfuryl alcohol, polyaniline, furfural resin, polyethylene glycol, polyethylene oxide, polyvinylidene fluoride, acrylic resin, and polyacrylonitrile. The mineral carbon materials include at least one of lignite, bituminous coal, anthracite, coking coal, petroleum, asphalt, petroleum coke, oxidized asphalt, and calcined coke.

[0032] The gas used for the inert atmosphere is one or more of argon, hydrogen, nitrogen, helium, neon, krypton, and xenon.

[0033] Control the temperature of the high-temperature hot isostatic pressing sintering to be 900 - 1600 °C, preferably 1100 - 1500 °C; the heating rate is 5 - 50 °C / min, preferably 10 - 20 °C / min; the pressure of the high-temperature hot isostatic pressing sintering is 20 - 160 MPa, preferably 50 - 120 MPa; the time of the high-temperature hot isostatic pressing sintering is 1 - 10 h.

[0034] The carbon vacancy degree τ of the obtained first carbonized product is 0.1 to 0.2, and the true density is 1.85 to 2.15 g / cm 3 .

[0035] Preferably, in step (2):

[0036] The ball-to-material ratio of the oxygen plasma ball mill is 5 to 60:1, and the rotation speed is 300 to 2000 revolutions per minute. The applied voltage of the oxygen plasma ball mill is 5 to 50 kV, the current is 0.5 to 5 A, and the frequency is 10 to 100 kHz. The amount of oxygen charged into the oxygen plasma ball mill is 0.01 to 2 MPa. The ball milling time of the oxygen plasma ball mill is 20 to 200 minutes.

[0037] The carbon vacancy degree τ of the obtained second carbonized product is 0.25 to 0.65, and the true density is 1.35 to 1.85 g / cm 3 , and the average particle size is 0.2 to 15.5 μm.

[0038] Preferably, in step (3):

[0039] The organic liquid is selected from one or more of ethanol, methanol, acetone, cyclohexane, glycerol, ethylene glycol, and sucrose; the mass ratio of the organic liquid to the second carbonized product is 0.5 to 4:1.

[0040] The inert gas is one or more of argon, hydrogen, nitrogen, helium, krypton, and xenon.

[0041] Control the temperature of sintering carbonization to 600 to 1100 °C, and the time to 2 to 3 h.

[0042] The present invention also provides a negative electrode plate, which includes a negative electrode current collector and a negative electrode active material layer located on at least one surface of the negative electrode current collector, and the negative electrode active material layer uses the carbon material as described above.

[0043] Furthermore, an electrochemical device is provided, which includes the negative electrode plate as described above.

[0044] Even further, an electrical device is provided, which includes the electrochemical device as described above.

[0045] The beneficial technical effects of the present invention are as follows:

[0046] The present invention defines a carbon material with a specific carbon vacancy ratio, and this carbon material has excellent sodium storage performance, providing a new negative electrode material selection and a technological breakthrough point for the industrialization of sodium ion batteries.

[0047] The present invention also specifically defines the particle size and tap density of the carbon material, etc., further improving the sodium storage performance of the carbon material.

[0048] The present invention involves the synergistic participation of various elements such as reasonable raw material screening, advanced preparation processes, and innovative structural analysis methods to obtain the carbon material with the above-specified carbon vacancy ratio. In the preparation process, hot isostatic pressing sintering is a process that subjects the material to balanced pressure in all directions during heating and promotes material densification through the combined action of high temperature and high pressure. It can produce materials with uniform microstructures, finer grains, and complete densification at the same sintering temperature. By preparing amorphous carbon through hot isostatic pressing sintering, the true density of the carbon material can be effectively increased. For the high-true-density carbon material, oxygen plasma ball milling is used to crush and etch the carbon material. Since the electron temperature of the plasma is extremely high, it can instantaneously heat the micro-regions of the carbon material in the plasma ball mill locally. When the carbon material leaves the plasma, its temperature drops sharply, inducing a huge thermal effect, forming a "thermal explosion - quenching" powder treatment. In addition, the oxygen plasma will bombard the carbon material during ball milling, causing the carbon-carbon bonds in the carbon material to break. The carbon atoms combine with oxygen atoms to generate carbon monoxide and carbon dioxide gases, realizing the etching of the carbon material and introducing a large number of carbon vacancies into the carbon material. The present invention also precisely monitors the carbon vacancy density of the carbon material through the atom pair analysis method, prepares the carbon material with a limited carbon vacancy ratio, regulates the reversible sodium storage capacity in the low voltage range (0 - 0.2V), and effectively designs and regulates the micro-nano structure of the carbon material to improve the sodium storage capacity. The atomized "carbon fine powder - organic liquid" suspension is subjected to in-situ carbonization coating granulation in a high-temperature furnace under a protective atmosphere, which not only reduces the specific surface area of the carbon material and increases the initial Coulomb efficiency of the amorphous carbon material but also realizes the spheroidization granulation of the carbon material particles, improving the tap density and compaction density of the carbon material.

[0049] The present invention aims to improve the sodium storage capacity and energy density of sodium-ion batteries by limiting the carbon vacancy ratio of the carbon material, which is of great significance for the large-scale industrial development of sodium-ion batteries.

[0050] The preparation method of the carbon material of the present invention also has the advantages of simple process, green and environmentally friendly raw materials used, being suitable for batch production. The prepared carbon material with a limited carbon vacancy ratio can be used as the negative electrode material of sodium-ion batteries, having the advantages of high capacity, high compaction density, low specific surface area, high cycle stability, excellent safety, etc., and can effectively improve the mass energy density and volume energy density of sodium-ion batteries. Brief Description of the Drawings

[0051] Figure 1 It is the atom pair distribution function diagram of the carbon materials obtained in Examples 1 - 5 and Comparative Examples 1 - 3 of the present application and highly oriented pyrolytic graphite; among them, (a) is the full spectrum; (b) is the characteristic peak diagram of SP2 hybridized carbon atom pairs;

[0052] Figure 2 It is the first charge-discharge diagram of the carbon materials obtained in Examples 1 - 5 and Comparative Examples 1 - 3 of the present application;

[0053] Figure 3 It is the SEM image of the carbon material obtained in Example 1 of the present application; among them, (a) is the SEM image of the first carbonization product; (b) is the SEM image of the second carbonization product; (c) is the SEM image of the second carbonization product dispersed in an organic liquid and atomized to form particles; (d) is the SEM image of the carbon material product;

[0054] Figure 4 It is the SEM image of the carbon material obtained in Example 4 of the present application;

[0055] Figure 5 It is the SEM image of the carbon material obtained in Example 5 of the present application;

[0056] Figure 6 It is the SEM image of the carbon material obtained in Comparative Example 1 of the present application;

[0057] Figure 7 It is the SEM image of the carbon material obtained in Comparative Example 2 of the present application;

[0058] Figure 8 It is the SEM image of the carbon material obtained in Comparative Example 3 of the present application. Detailed implementation manners

[0059] Hereinafter, with appropriate reference to the drawings, the implementation manners of the carbon material, the negative electrode sheet containing the same, the electrochemical device, and the electrical device of the present application will be specifically described. However, there may be cases where unnecessary detailed descriptions are omitted. For example, detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to avoid making the following descriptions unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the scope defined in the claims.

[0060] Hard carbon is currently one of the few carbon materials with high sodium storage capacity. The sodium storage performance of hard carbon mainly comes from its highly distorted micro-nano structure formed by the stacking of incompletely developed bent turbostratic short graphene sheets (also called pseudo-graphite domains). The sub-nanometer pores formed by the bent turbostratic graphene short films and the carbon vacancies on the incompletely developed graphene sheets are the main sodium storage sites of hard carbon. During the sodium storage process, these closed pores only provide the function of sodium ion transmission. The main sodium storage sites are the C-Na insertion / extraction sites formed by carbon vacancies and sodium ions. During the entire sodium storage process, these closed pore structures will not be filled with sodium ions, which causes serious waste of the internal space of the carbon material, making the true density and tap density of the hard carbon material much lower than that of graphite, seriously restricting the design of the mass energy density and volume energy density of the sodium ion battery cell, and severely limiting the prospect of the industrial application of sodium ion batteries.

[0061] The present invention provides a novel sodium-storing carbon material. By regulating the proportion of carbon vacancies in the structure of the carbon material, more thermodynamically stable C-Na insertion / extraction sites are imparted to the carbon material, along with better sodium ion diffusion kinetics and structural stability during the cycling process.

[0062] A carbon vacancy refers to the vacancy left by the absence of a carbon atom at a lattice node in a carbon crystal. Using the atomic pair distribution function analysis technique, by comparing with the atomic pair distribution function spectrum of a standard carbon crystal, the carbon vacancies in the carbon material can be accurately calculated.

[0063] With the birth of modern physics, especially quantum mechanics, people's understanding of matter has entered the atomic-level electron scale. Researchers have also found that a large number of microscopic disordered structures (vacancies, impurity atoms, clusters, dislocations, etc.) existing in the material growth and manufacturing process have a significant impact on the properties of the material. By designing the microscopic disordered structures, the performance of the material can be controllably changed. With the progress of science and technology, especially the development of the atomic pair distribution function analysis technique, the characterization of the micro-nano structure of materials can be accurate to the angstrom level, and the microscopic disordered structures in the materials can be more accurately characterized and analyzed.

[0064] Researchers call the technique of simultaneously processing the Bragg scattering signal and the diffuse scattering signal of matter the total scattering technique. It is a method that uses the correspondence between the real space and the reciprocal space to obtain information in the real space after processing a series of data in a certain Q value range. By performing a Fourier transform on the total scattering signal of matter, the function related to the atomic pair distribution in the matter, that is, the atomic pair distribution function (atomic pair distribution function analysis), can be obtained. Its standard expression is:

[0065]

[0066] Among them, the structure function S(Q) is a directly measurable quantity, ρ0 represents the microscopic atomic pair density, and g(r) is a physical quantity that can directly obtain the relative positions of atoms in the matter. It is like a map of the distances between the internal atoms of the measured matter, and with it, two atoms with a distance of r can be found.

[0067] Since the carbon atoms in the standard graphite crystal structure exist in the form of SP2 hybridization, the distance between atoms is Therefore, in the atomic pair distribution function diagram of standard graphite the peak area I at GCrepresents the density of carbon atoms in the form of sp2 hybridization in a standard graphite crystal. Since it is almost impossible to obtain a standard graphite single crystal, highly oriented pyrolytic graphite is generally used instead of the graphite single crystal. Similarly, for other carbon materials, through the analysis of the pair distribution function, the peak area I at HC represents the density of carbon atoms in the form of sp2 hybridization in this carbon material. Therefore, I GC -I HC is the density of carbon atoms missing at the sp2 hybridization sites in this carbon material, that is, the density of carbon vacancies. Through the synergistic action of various factors such as reasonable raw material screening, advanced preparation processes, and innovative structure analysis methods, the inventor has defined a carbon material with a specific carbon vacancy ratio. The optimal range of the carbon vacancy τ of the carbon material is 0.11-0.58. When the τ of the carbon material is greater than 0.58, it indicates that the lattice structure of the carbon material is severely damaged. Although it has a high sodium storage capacity, the structural stability of the hard carbon micro-nano structure decreases during the charge and discharge process, and it is extremely easy to collapse, resulting in a poor retention rate of the sodium storage capacity of the carbon material. When the carbon vacancy τ of the hard carbon material is less than 0.1, the lattice structure of the carbon material is too complete, the sodium storage sites are few, and the sodium storage capacity of the carbon material is low, without practical application prospects.

[0068] Hot isostatic pressing sintering is a process that enables materials (powders, green compacts or sintered bodies) to withstand isotropic pressure during heating, and promotes the densification of materials through the combined action of high temperature and high pressure. Characteristics of the hot isostatic pressing sintering technology: Materials with uniform microstructure, finer grains and complete densification can be prepared at a relatively low sintering temperature. In theory, by preparing hard carbon through hot isostatic pressing sintering, the generation of closed pores during the carbonization process of the carbon material can be effectively reduced, and the true density of the carbon material can be increased.

[0069] Oxygen plasma etching is an effective method for creating defects in carbon materials and controllably increasing the disordered domains of carbon materials. Its principle is to bombard the carbon materials with oxygen plasma, which will not only cause the breakage of carbon-carbon bonds in the carbon materials, but also promote the combination of carbon atoms and oxygen atoms to generate carbon monoxide and carbon dioxide gases, realizing the etching of hard carbon materials and preparing carbon materials with a high carbon vacancy concentration.

[0070] Therefore, through the combination of hot isostatic pressing sintering and oxygen plasma etching technology, the present invention has developed a carbon material with controllable defect degree to improve the thermodynamic and kinetic properties of sodium / lithium ion storage in the carbon material, achieving the purpose of increasing the capacity of the carbon negative electrode material and the energy density of the secondary battery, which is of great significance to the development of secondary batteries.

[0071] The test methods involved in the present invention are as follows:

[0072] 1. Carbon vacancy test

[0073] The total scattering experiment was carried out on a PANalytical Empyrean diffractometer. In 2015, Malvern Panalytical released the unique GaliPIX3D heavy element semiconductor matrix detector, and constructed a high-energy hard X-ray transmission optical path based on silver target radiation on the Empyrean X-ray diffraction platform for PDF analysis. Since then, high-quality PDF data can be obtained on the laboratory platform.

[0074] This configuration uses: a silver target X-ray tube, an incident beam focusing mirror or slit collimation system, a capillary spin sample stage, a hybrid pixel detector (GaliPIX3D), a linear detector (X'Celerator), and an anti-scattering kit for background suppression, and can obtain a clean and featureless background, which is crucial for obtaining meaningful results on highly disordered or completely amorphous materials. The experimental data obtained through the Malvern Panalytical system is corrected by Fourier transform and fitted with the PDFgui software, and the accuracy of the experimental data can be compared with the synchrotron results. GC For the peak area of the pair distribution function map of highly oriented pyrolytic graphite at I HC For the peak area of the pair distribution function map of the carbon material at The carbon vacancy value is calculated therefrom

[0075]

[0076] 2. Particle size measurement

[0077] Refer to GB / T 19077-2016 Laser diffraction method for particle size distribution, and use a Malvern Mastersizer 3000 laser particle size analyzer from the UK for measurement.

[0078] 3. Specific surface area and pore size measurement

[0079] After drying and degassing pretreatment of the carbon material powder, use an ASAP2020 physical adsorption analyzer for testing. The test atmosphere is nitrogen, draw the adsorption and desorption isotherms, and obtain the specific surface area. Determine the pore shape according to the shape of the hysteresis loop, and use the DFT model to fit the pore structure and pore size distribution curve.

[0080] 4. True density measurement

[0081] Carry out the true density measurement according to the national standard GB / T24586-2009.

[0082] 5. Compacted density measurement

[0083] Carry out the compacted density measurement according to the requirements in the national standard GB / T 24533-2019 "Graphite Anode Materials for Lithium-Ion Batteries".

[0084] 6. Tap density test

[0085] The tap density test is carried out according to the requirements in the national standard GB / T 21354-2008 "General Method Standard for Determination of Tap Density of Powder Products".

[0086] The present invention will be further described below in conjunction with specific embodiments.

[0087] Embodiment 1

[0088] (1) Put the citrate ester modified starch into a mold and sinter it by high-temperature hot isostatic pressing in an Ar atmosphere to obtain the first carbonized product.

[0089] Specifically, maintain a pressure of 70 MPa, increase the temperature at a rate of 10 °C / min to 1300 °C, hold the pressure and keep the temperature for 2 h, then release the pressure and cool down to obtain the first carbonized product with τ = 0.12 and a true density of 2.09 g / cm 3 .

[0090] (2) Put the first carbonized product into an oxygen plasma ball mill and carry out oxygen plasma etching and ball milling to obtain the second carbonized product.

[0091] Specifically, put the grinding balls according to the ball-to-material ratio = 10:1, control the applied voltage of the oxygen plasma ball mill to be 25 kV, the current to be 3 A, the frequency to be 50 kHz, the oxygen amount of the oxygen plasma ball mill to be 0.1 MPa, the rotation speed to be 1000 revolutions / min, and the ball milling time to be 30 min to obtain the second carbonized product with τ = 0.45, a true density of 1.85 g / cm 3 and an average particle size of 3.5 μm.

[0092] (3) Mix the second carbonized product, ethylene glycol, and sucrose into a uniform suspension according to the mass ratio of 1:1.5:0.05, atomize it into suspension droplets under Ar protection, and introduce it into a rotary tube furnace preheated to 1000 °C under the drive of Ar, and heat for 2 h to obtain the carbon material.

[0093] The powder particle morphology of the carbon material prepared by the above method is as Figure 3 shown. Among them, Figure 3 (a) is the SEM image of the first carbonized product; Figure 3 (b) is the SEM image of the second carbonized product; Figure 3 (c) is the SEM image of the second carbonized product dispersed in an organic liquid and atomized to form particles; Figure 3 (d) is the SEM image of the carbon material product.

[0094] Take a small amount of the carbon material prepared above and measure the carbon vacancy degree τ, true density, BET, and particle size. The measured carbon material vacancy degree τ = 0.42, and the true density is 1.89 g·cm -3 , and the tap density is 1.15 g·cm -3 , the specific surface area is 2.5 m 2 ·g -1 , and the average particle size is about 5.5 μm.

[0095] Use the carbon material prepared above as the active material of the battery anode material for the preparation of sodium-ion batteries.

[0096] The results of the electrochemical test are shown in Table 1 below and Figure 2 , from Figure 2 the first charge-discharge curve, it can be seen that for the half-cell with 1.0 mol / L NaPF6 in EC / DEC (1:1) (V:V) as the electrolyte, the reversible charge-discharge specific capacity (Q2) is 506 mAh·g at a current density of 10 mA·g -1 , and the plateau capacity (Q1) is 398 mAh·g -1 . -1 .

[0097] Example 2

[0098] (1) Put the citric acid ester-modified starch into a mold and sinter it by high-temperature hot isostatic pressing with Ar gas to obtain the first carbonized product.

[0099] Specifically, maintain a pressure of 70 MPa, increase the temperature at a rate of 10 °C / min to 1300 °C, keep the pressure and temperature for 2 h, and then keep the pressure and cool down to obtain the first carbonized product with τ of 0.12 and a true density of 2.09 g / cm 3 .

[0100] (2) Put the first carbonized product into an oxygen plasma ball mill and perform oxygen plasma etching ball milling to obtain the second carbonized product.

[0101] Specifically, put the grinding balls according to the ball-to-material ratio = 5:1. The applied voltage of the oxygen plasma ball mill is 5 kV, the current is 0.5 A, the frequency is 50 kHz, the oxygen amount of the oxygen plasma ball mill is 0.01 MPa, the rotation speed is 300 r / min, and ball milling is carried out for 20 min to obtain the second carbonized product with τ = 0.35, a true density of 1.92 g / cm 3 , and an average particle size of 15.5 μm.

[0102] (3) The second carbonized product, ethylene glycol, and sucrose are formulated into a uniform suspension according to a mass ratio of 1:1.5:0.05, atomized into suspension droplets under Ar protection, and introduced into a rotary tube furnace preheated to 1000 °C under the drive of Ar gas, and heated for 2 h to obtain the carbon material.

[0103] Take a small amount of the carbon material prepared above for τ, true density, BET, and particle size measurement. It is measured that the carbon material has τ = 0.36 and a true density of 1.95 g·cm -3 , and a specific surface area of 1.8 m 2 ·g -1 , and the average particle size is about 18 μm.

[0104] The carbon material prepared above is used as the active material of the battery negative electrode material for the preparation of sodium ion batteries.

[0105] The results of the electrochemical test are shown in Table 1 and Figure 2 as shown. From Figure 2 the first charge-discharge curve, it can be seen that for a half-cell with 1.0 mol / L NaPF6 in EC / DEC (1:1) (V:V) as the electrolyte, the reversible charge-discharge specific capacity (Q2) is 353 mAh·g -1 at a current density of 10 mA·g -1 , and the plateau capacity (Q1) is 273 mAh·g -1 .

[0106] Example 3

[0107] (1) Put the citric acid ester modified starch into a mold and sinter it by high temperature hot isostatic pressing in an Ar atmosphere to obtain the first carbonized product.

[0108] Specifically, maintain a pressure of 70 MPa, increase the temperature at a rate of 10 °C / min to 1300 °C, keep the pressure and temperature for 2 h, and then reduce the pressure to obtain the first carbonized product with τ = 0.12 and a true density of 2.09 g / cm 3 .

[0109] (2) Put the first carbonized product into an oxygen plasma ball mill and perform oxygen plasma etching ball milling to obtain the second carbonized product.

[0110] Specifically, put the grinding balls according to a ball-to-material ratio of 10:1, control the applied voltage of the oxygen plasma ball mill to be 50 kV, the current to be 5 A, the frequency to be 100 kHz, the oxygen amount of the oxygen plasma ball mill to be 2 MPa, the rotation speed to be 2000 r / min, and the ball milling time to be 30 min to obtain the second carbonized product with τ = 0.65, a true density of 1.75 g / cm 3 , and an average particle size of 0.5 μm.

[0111] (3) The second carbonized product, ethylene glycol, and sucrose are formulated into a uniform suspension according to a mass ratio of 1:1.5:0.05, atomized into suspension droplets under Ar protection, and introduced into a preheated rotary tube furnace at 1000 °C under the drive of Ar gas, and heated for 2 h to obtain the carbon material.

[0112] Take a small amount of the carbon material prepared above for τ, true density, BET, and particle size measurement. The measured τ of the carbon material is 0.58, and the true density is 1.78 g·cm -3 , and the specific surface area is 12.8 m 2 ·g -1 , and the average particle size is 3.2 μm.

[0113] The carbon material prepared above is used as the active material of the battery negative electrode material for the preparation of a sodium ion battery.

[0114] The results of the electrochemical test are shown in Table 1 and Figure 2 as shown. From Figure 2 the first charge-discharge curve, it can be seen that for a half-cell with 1.0 mol / L NaPF6 in EC / DEC (1:1) (V:V) as the electrolyte, the reversible charge-discharge specific capacity (Q2) is 481 mAh·g -1 at a current density of 10 mA·g -1 , and the plateau capacity (Q1) is 360 mAh·g -1 .

[0115] Example 4

[0116] (1) Put coconut shell powder into a mold and sinter it by high-temperature hot isostatic pressing in an Ar atmosphere to obtain a first carbonized product.

[0117] Specifically, maintain a pressure of 70 MPa, increase the temperature at a rate of 10 °C / min to 1100 °C, hold the pressure and temperature for 2 h, and then reduce the pressure to obtain a first carbonized product with τ of 0.15 and a true density of 2.01 g / cm 3 .

[0118] (2) Put the first carbonized product into an oxygen plasma ball mill and perform oxygen plasma etching and ball milling to obtain a second carbonized product.

[0119] Specifically, put grinding balls according to a ball-to-material ratio of 10:1, control the applied voltage of the oxygen plasma ball mill to be 25 kV, the current to be 3 A, the frequency to be 50 kHz, the oxygen amount of the oxygen plasma ball mill to be 0.1 MPa, the rotation speed to be 1000 revolutions / min, and the ball milling time to be 30 min to obtain a second carbonized product with τ = 0.42, a true density of 1.78 g / cm 3 , and an average particle size of 4.5 μm.

[0120] (3) The second carbonized product, ethylene glycol, and sucrose are prepared into a uniform suspension according to a mass ratio of 1:1.5:0.05, atomized into suspension droplets under Ar protection, and introduced into a preheated rotary tube furnace at 1000 °C under the drive of Ar gas, and heated for 2 h to obtain the carbon material.

[0121] The particle morphology of the prepared carbon material powder is as Figure 4 shown.

[0122] Take a small amount of the above-prepared carbon material for τ, true density, BET, and particle size measurement. The measured carbon material has τ = 0.48, a true density of 1.82 g·cm -3 , a specific surface area of 24.5 m 2 ·g -1 , and an average particle size of about 5.5 um.

[0123] The above-prepared carbon material is used as the active material of the battery negative electrode material for the preparation of a sodium ion battery.

[0124] The results of the electrochemical test are shown in Table 1 and Figure 2 shown. From Figure 2 the first charge-discharge curve, it can be seen that for a half-cell with 1.0 mol / L NaPF6 in EC / DEC (1:1) (V:V) as the electrolyte, the reversible charge-discharge specific capacity (Q2) is 455 mAh·g -1 at a current density of 10 mA·g -1 , and the plateau capacity (Q1) is 350 mAh·g -1 .

[0125] Example 5

[0126] (1) Put the oxidized asphalt powder into a mold and sinter it by high-temperature hot isostatic pressing in an Ar atmosphere to obtain the first carbonized product.

[0127] Specifically, maintain a pressure of 70 MPa, increase the temperature at a rate of 10 °C / min to 1100 °C, hold the pressure and keep the temperature for 2 h, and then release the pressure and cool down to obtain the first carbonized product with τ = 0.10 and a true density of 2.15 g / cm 3 .

[0128] (2) Put the first carbonized product into an oxygen plasma ball mill and perform oxygen plasma etching and ball milling to obtain the second carbonized product.

[0129] Specifically, put the grinding balls according to a ball-to-material ratio of 10:1, control the applied voltage of the oxygen plasma ball mill to be 25 kV, the current to be 3 A, the frequency to be 50 kHz, the oxygen amount of the oxygen plasma ball mill to be 0.1 MPa, the rotation speed to be 1000 rpm, and the ball milling time to be 30 min to obtain τ = 0.28 and a true density of 1.92 g / cm3 The second carbonized product with an average particle size of 3.6 μm.

[0130] (3) The second carbonized product, ethylene glycol, and sucrose are formulated into a uniform suspension according to a mass ratio of 1:1.5:0.05, atomized into suspension droplets under Ar protection, and introduced into a rotary tube furnace preheated to 1000 °C under the drive of Ar gas, and heated for 2 h to obtain the carbon material.

[0131] The morphology of the prepared carbon material powder particles is as Figure 5 shown.

[0132] Take a small amount of the above-prepared carbon material for τ, true density, BET, and particle size measurement. It is measured that the carbon material τ = 0.31, and the true density is 2.02 g·cm -3 , the specific surface area is 0.8 m 2 ·g -1 , and the average particle size is about 5.5 μm.

[0133] The above-prepared carbon material is used as the active material of the battery negative electrode material for the preparation of a sodium ion battery.

[0134] The results of the electrochemical test are shown in Table 1 and Figure 2 shown. From Figure 2 the first charge-discharge curve, it can be seen that for a half-cell with 1.0 mol / L NaPF6 in EC / DEC (1:1) (V:V) as the electrolyte, the reversible charge-discharge specific capacity (Q2) is 311 mAh·g -1 at a current density of 10 mA·g -1 , and the plateau capacity (Q1) is 232 mAh·g -1 .

[0135] Example 6

[0136] (1) Put the natural rubber powder into a mold and sinter it by high-temperature hot isostatic pressing in an Ar atmosphere to obtain the first carbonized product.

[0137] Specifically, maintain a pressure of 150 MPa, increase the temperature at a rate of 30 °C / min to 1500 °C, keep the pressure and temperature for 2 h, keep the pressure and cool down to obtain the first carbonized product with τ of 0.11 and a true density of 2.08 g / cm 3 .

[0138] (2) Put the first carbonized product into an oxygen plasma ball mill and perform oxygen plasma etching and ball milling to obtain the second carbonized product.

[0139] Specifically, grinding balls are put in at a ball-to-material ratio of 20:1, and the applied voltage of the oxygen plasma ball mill is controlled at 30 kV, the current is 1 A, the frequency is 70 kHz, the oxygen amount of the oxygen plasma ball mill is 1 MPa, the rotation speed is 1500 revolutions per minute, and the ball milling time is 100 min, obtaining a second carbonized product with τ = 0.58 and a true density of 1.74 g / cm 3 , and an average particle size of 0.15 μm.

[0140] (3) The second carbonized product, cyclohexane, and sucrose are formulated into a uniform suspension according to a mass ratio of 1:1.5:0.05, atomized into suspension droplets under Ar protection, and introduced into a rotary tube furnace preheated to 1100 °C under the drive of Ar, and heated for 3 h to obtain the carbon material.

[0141] A small amount of the carbon material prepared above is taken for the measurement of τ, true density, BET, and particle size. It is measured that the carbon material has τ = 0.54, a true density of 1.82 g·cm -3 , a specific surface area of 8.8 m 2 ·g -1 , and an average particle size of 2.2 μm.

[0142] The carbon material prepared above is used as the active substance of the battery anode material for the preparation of a sodium ion battery.

[0143] The results of the electrochemical test are shown in Table 1. The half-cell with 1.0 mol / L NaPF6 in EC / DEC (1:1) (V:V) as the electrolyte has a reversible charge-discharge specific capacity (Q2) of 453 mAh·g -1 at a current density of 10 mA·g -1 , and a plateau capacity (Q1) of 269 mAh·g -1 .

[0144] Example 7

[0145] (1) Epoxy resin is put into a mold and sintered by high-temperature hot isostatic pressing in an Ar atmosphere to obtain a first carbonized product.

[0146] Specifically, maintaining a pressure of 30 MPa, with a heating rate of 20 °C / min, heating to 900 °C, holding the pressure and temperature for 2 h, and then releasing the pressure and cooling to obtain a first carbonized product with τ of 0.19 and a true density of 1.98 g / cm 3 .

[0147] (2) The first carbonized product is put into an oxygen plasma ball mill and etched and ball milled by oxygen plasma to obtain a second carbonized product.

[0148] Specifically, grinding balls were put in at a ball-to-material ratio of 30:1, the applied voltage of the oxygen plasma ball mill was controlled at 50 kV, the current was 3 A, the frequency was 30 kHz, the oxygen amount of the oxygen plasma ball mill was 0.05 MPa, the rotation speed was 2,000 revolutions per minute, and the ball milling time was 150 min, obtaining a second carbonized product with τ = 0.62 and a true density of 1.74 g / cm 3 , and an average particle size of 0.1 μm.

[0149] (4) The second carbonized product and ethylene glycol were prepared into a uniform suspension at a mass ratio of 1:1, atomized into suspension droplets under Ar protection, and introduced into a pre-heated rotary tube furnace at 800 °C under the drive of Ar, and heated for 3 h to obtain the carbon material.

[0150] A small amount of the carbon material prepared above was taken for the determination of τ, true density, BET and particle size. It was measured that the carbon material had τ = 0.58, a true density of 1.79 g·cm -3 , a specific surface area of 6.8 m 2 ·g -1 , and an average particle size of 3.2 μm.

[0151] The carbon material prepared above was used as the active material of the battery negative electrode material for the preparation of a sodium ion battery.

[0152] (5) The results of the electrochemical test are shown in Table 1. The half-cell with 1.0 mol / L NaPF6 in EC / DEC (1:1) (V:V) as the electrolyte had a reversible charge-discharge specific capacity (Q2) of 388 mAh·g -1 at a current density of 10 mA·g -1 , and a plateau capacity (Q1) of 329 mAh·g -1 .

[0153] Comparative Example 1

[0154] A preparation method of a carbon material, the steps of which include:

[0155] Put the citrate ester modified starch into a porcelain boat, put it into a tube furnace, and carry out high-temperature carbonization under Ar protection to obtain a carbonized product.

[0156] Specifically, at a heating rate of 5 °C / min, it was heated to 1,300 °C, pressure was maintained and heat was kept for 2 h, and then it was cooled naturally to obtain a carbonized product, that is, a carbon material.

[0157] The powder particle morphology of the prepared carbon material is as Figure 6 shown.

[0158] A small amount of the carbon material prepared above was taken for the determination of τ, true density, BET and particle size. It was measured that the carbon material had τ = 0.48 and a true density of 1.45 g·cm-3 , with a specific surface area of 7.3 m 2 ·g -1 , an average pore diameter of 8.4 nm, and an average particle size of about 28.5 μm.

[0159] The carbon material prepared above is used as the active material of the battery negative electrode material for the preparation of a sodium ion battery.

[0160] The results of the electrochemical test are shown in Table 1 and Figure 2 as shown. From Figure 2 the first charge-discharge curve, it can be seen that for a half-cell with 1.0 mol / L NaPF6 in EC / DEC (1:1) (V:V) as the electrolyte, the reversible charge-discharge specific capacity (Q2) is 292 mAh·g -1 at a current density of 10 mA·g -1 , and the plateau capacity (Q1) is 197 mAh·g -1 .

[0161] Comparative Example 2

[0162] A preparation method of a carbon material, the steps of which include:

[0163] (1) Put the citrate-modified starch into a mold, and sinter it by high-temperature hot isostatic pressing in an Ar atmosphere to obtain a first carbonized product.

[0164] Specifically, maintain a pressure of 70 MPa, heat at a heating rate of 10 °C / min to 1300 °C, keep the pressure and temperature for 2 h, and then release the pressure and cool down to obtain a first carbonized product with τ = 0.12 and a true density of 2.09 g / cm 3 .

[0165] (2) Put the first carbonized product into a ball mill and ball mill it to obtain a second carbonized product.

[0166] Specifically, put grinding balls according to a ball-to-material ratio of 10:1, with a rotation speed of 300 revolutions / min, and ball mill for 30 min to obtain a second carbonized product with τ = 0.16, a true density of 2.05 g / cm 3 , and an average particle size of 2.8 μm.

[0167] (3) Mix the second carbonized product, ethylene glycol, and sucrose according to a mass ratio of 1:1.5:0.05 to form a uniform suspension, atomize it into suspension droplets under Ar protection, and introduce it into a rotary tube furnace preheated to 1000 °C under the drive of Ar gas, and heat for 2 h to obtain the carbon material.

[0168] The particle morphology of the prepared carbon material powder is as Figure 7 shown.

[0169] Take a small amount of the carbon material prepared above for the measurement of τ, true density, BET and particle size. The measured τ of the carbon material is 0.14, and the true density is 1.95 g·cm -3 , the specific surface area is 0.5 m 2 ·g -1 , and the average particle size is about 5.5 μm.

[0170] Use the carbon material prepared above as the active material of the battery negative electrode material for the preparation of sodium ion batteries.

[0171] The results of electrochemical tests are shown in Table 1 and Figure 2 as shown. It can be seen from Figure 2 the first charge-discharge curve that the reversible charge-discharge specific capacity (Q2) of the half-cell with 1.0 mol / L NaPF6 in EC / DEC (1:1) (V:V) as the electrolyte is 252 mAh·g -1 at a current density of 10 mA·g -1 , and the plateau capacity (Q1) is 162 mAh·g -1 .

[0172] It can be found from this comparative example that the sodium storage performance has a strong correlation with the τ value of the carbon material. A small τ value indicates that there are fewer sodium storage sites in the carbon material, and the sodium storage capacity decreases significantly.

[0173] Comparative Example 3

[0174] A preparation method of a carbon material, the steps of which include:

[0175] (1) Put the citric acid ester modified starch into a porcelain boat, put it into a tube furnace, and carry out high-temperature carbonization under Ar protection to obtain a first carbonized product.

[0176] Specifically, at a heating rate of 5 °C / min, heat up to 1300 °C, keep the pressure and temperature for 2 h, and cool naturally to obtain a first carbonized product with τ of 0.48 and a true density of 1.45 g / cm 3 .

[0177] (2) Put the first carbonized product into an oxygen plasma ball mill, and carry out oxygen plasma etching and ball milling to obtain a second carbonized product.

[0178] Specifically, put the grinding balls according to the ball-to-material ratio = 10:1. The applied voltage of the oxygen plasma ball mill is 25 kV, the current is 3 A, the frequency is 50 kHz, and the oxygen amount of the oxygen plasma ball mill is 0.1 MPa to obtain a second carbonized product with τ = 0.55, a true density of 1.52 g / cm 3 , and an average particle size of 1 μm.

[0179] (3) Prepare a uniform suspension by mixing the second carbonization product, ethylene glycol, and sucrose in a mass ratio of 1:1.5:0.05. Atomize the suspension into droplets under Ar protection and introduce them into a preheated rotary tube furnace at 1000 °C under the drive of Ar gas. Heat for 2 h to obtain the carbon material.

[0180] The morphology of the prepared carbon material powder particles is as Figure 8 shown.

[0181] Take a small amount of the above-prepared carbon material for τ, true density, BET, and particle size measurements. The measured τ of the carbon material is 0.53, the true density is 1.75 g·cm -3 , the specific surface area is 86.2 m 2 ·g -1 , the average pore diameter is 1.8 nm, and the average particle size is about 8.5 μm.

[0182] Use the above-prepared carbon material as the active material of the battery negative electrode material for the preparation of sodium-ion batteries.

[0183] The results of the electrochemical test are shown in Table 1 and Figure 2 as shown. From Figure 2 the first charge-discharge curve, it can be seen that for a half-cell with 1.0 mol / L NaPF6 in EC / DEC (1:1) (V:V) as the electrolyte, the reversible charge-discharge specific capacity (Q2) is 295 mAh·g -1 at a current density of 10 mA·g -1 , and the plateau capacity (Q1) is 12 mAh·g -1 .

[0184] It can be found from this comparative example that the sodium storage performance has a strong correlation with the τ value of the carbon material. If the τ value is too large, the carbon skeleton is severely damaged, and the sodium storage mechanism between sodium ions and the carbon material becomes adsorption sodium storage. The plateau capacity decreases sharply, and the median sodium storage voltage increases, which is not suitable as the negative electrode material of a full cell.

[0185] The steps for using the carbon materials obtained in the above Examples 1-7 and Comparative Examples 1-3 to prepare sodium-ion batteries are as follows:

[0186] Weigh 160 mg of the prepared carbon material powder, 20 mg of conductive carbon black, and 20 mg of PVDF according to a mass ratio of 8:1:1 into an agate mortar and stir evenly. Drop in an appropriate amount of N-methylpyrrolidone (NMP) and stir for 8 h until it becomes a uniform paste. Use a 100 μm scraper to evenly coat it on the surface of a copper (Cu) foil. Dry it at 80 °C for 12 hours under vacuum conditions. Cut the Cu foil with the active material into round negative electrode plates and immediately transfer them to the glove box for standby.

[0187] The assembly of the simulated battery was carried out in a MIKROUNA glove box filled with Ar atmosphere. The prepared carbon material electrode was used as the negative electrode, commercial electrolyte 1.0 mol / L NaPF6 in EC / DEC (1:1) (V:V) was used as the electrolyte, and Na metal sheet was used as the counter electrode to assemble a 2016 coin cell.

[0188] After the assembled coin cell was left standing for 6 h, it was placed in a constant temperature test system at 30 °C. In the voltage range of 0.01 - 2.0 V (vs. Na + / Na, the same below), charge-discharge tests were carried out on it. The results of the electrochemical tests are shown in Table 1 and Figure 2 as shown. From Figure 2 the first charge-discharge curve, it can be seen that for the half-cell with 1.0 mol / L NaPF6 in EC / DEC (1:1) (V:V) as the electrolyte, the reversible charge-discharge specific capacity is 292 mAh·g -1 at a current density of 10 mA·g -1 , and the plateau capacity is 192 mAh·g -1 .

[0189] Table 1

[0190]

[0191] The capacity of hard carbon is closely related to the value of the structural carbon vacancy degree τ of it. When τ < 0.21, there are fewer sites in the hard carbon structure that can provide the insertion and extraction of sodium ions, and the sodium storage capacity of hard carbon is too low; when τ > 0.58, the proportion of the ordered carbon structure in the hard carbon structure is too small, and the sodium storage mechanism of hard carbon becomes mainly adsorption, the proportion of the plateau capacity (sodium storage capacity < 0.2 V) decreases, and the median voltage of sodium storage in hard carbon increases. When applied to a full cell, it is detrimental to the energy density of the battery and is not suitable for commercial applications. Through a large number of experiments and studies by the inventors, it is found that only when the τ value of hard carbon is controlled between 0.25 and 0.58, the hard carbon material can not only exhibit excellent reversible sodium storage capacity, but also the proportion of the plateau capacity meets the range required by commercial products of 0.57 - 0.85.

[0192] According to Figure 2Calculate the τ value. Hard carbon materials with different τ values exhibit different sodium storage properties, and conform to the τ value rule in Table 1: when the τ value < 0.21, there are fewer sites in the hard carbon structure that can provide sodium ion insertion and extraction, and the sodium storage capacity of the hard carbon is too low; when the τ value > 0.58, the proportion of the ordered carbon structure in the hard carbon structure is too small, and the sodium storage mechanism of the hard carbon becomes mainly adsorption, the proportion of the plateau capacity (sodium storage capacity < 0.2V) decreases, and the median voltage of sodium storage in the hard carbon increases. When applied to a full cell, it is detrimental to the energy density of the battery and is not suitable for commercial applications. Through a large number of experiments and studies by the inventors, it is found that only when the τ value of the hard carbon is controlled between 0.25 and 0.58, the hard carbon material can not only exhibit excellent reversible sodium storage capacity, but also the proportion of the plateau capacity meets the range required for commercial products of 0.57 - 0.85.

[0193] Through Figures 3 - 8 the SEM images of

[0194] Based on the above embodiments, the present invention can further provide a negative electrode plate, which includes a negative electrode current collector and a negative electrode active material layer located on at least one surface of the negative electrode current collector, and the negative electrode active material layer uses the carbon material prepared as in Embodiments 1 - 5.

[0195] Furthermore, the present invention provides an electrochemical device, which includes the negative electrode plate as described above.

[0196] Even further, the present invention also provides an electrical device, which includes the electrochemical device as described above.

[0197] For the parts not described in the above manner, the existing technology can be adopted or borrowed to achieve.

[0198] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A carbon material, characterized in that: The carbon material is hard carbon, and the carbon vacancy degree of the carbon material is 0.21 to 0.58; The relational expression for defining the carbon vacancy degree τ is as follows: Where, I GC is the density of carbon atoms existing as pairs of SP2 hybridized carbon atoms in highly oriented pyrolytic graphite; I HC is the density of carbon atoms existing as pairs of SP2 hybridized carbon atoms in the hard carbon material.

2. The carbon material according to claim 1, wherein: The carbon material is hard carbon particles, and the average particle size of the hard carbon particles is 3 to 19 μm, and the tapped density is 0.69 to 0.91 g / cm 3 , and the compression density is 0.92 to 1.32 g / cm 3 , and the true density is 1.65 to 2.15 g / cm 3 ; And / or, the specific surface area of the carbon material measured by the BET method is 0.45 to 24.55 m 2 / g, and the average pore diameter is 2.5 to 14.5 nm; and / or, the carbon material satisfies the following conditions: and Q1 ≥ 200; where Q1 mAh / g represents the reversible sodium storage capacity of the carbon material between 0 V and 0.2 V with metallic sodium as the counter electrode and the carbon material as the negative electrode; Q2 mAh / g represents the reversible sodium storage capacity of the carbon material between 0 V and 2.5 V with metallic sodium as the counter electrode and the carbon material as the negative electrode.

3. A carbon material according to claim 1, characterized in that: The carbon layer spacing of the carbon material is 0.35 to 0.45 nm; the mass ratio of heteroatoms to carbon atoms in the carbon material is less than 0.

09.

4. The preparation method of the carbon material according to any one of claims 1 to 3, characterized in that It includes the following steps: (1) Put the carbon source material into a mold and sinter it by high-temperature hot isostatic pressing in an inert atmosphere to obtain a first carbonized product; (2) Put the first carbonized product into an oxygen plasma ball mill and etch and mill it through oxygen plasma to obtain a second carbonized product; (3) Disperse the second carbonized product into an organic liquid, atomize it into suspension droplets under the protection of an inert gas, and sinter and carbonize it in a kiln to obtain the carbon material.

5. The preparation method of the carbon material according to claim 4, characterized in that, In step (1): The carbon source material is selected from one or more of natural biomass, plant extracts, resin or polymer carbon sources, mineral carbon materials and modified derivatives; The gas used for the inert atmosphere is one or more of argon, hydrogen, nitrogen, neon, krypton, and xenon; Control the temperature of the high-temperature hot isostatic pressing sintering to be 900 to 1600 °C, and the heating rate to be 5 to 50 °C / min; the pressure of the high-temperature hot isostatic pressing sintering is 20 to 160 MPa, and the time of the high-temperature hot isostatic pressing sintering is 1 to 10 h; The carbon vacancy degree τ of the first carbonized product is 0.1 to 0.2, and the true density is 1.85 to 2.15 g / cm 3 .

6. The preparation method of the carbon material according to claim 4, wherein, In step (2): The ball-to-material ratio of the oxygen plasma ball mill is 5 to 60:1, and the rotation speed is 300 to 2000 revolutions / min; the applied voltage of the oxygen plasma ball mill is 5 to 50 kV, the current is 0.5 to 5 A, and the frequency is 10 to 100 kHz; the oxygen amount of the oxygen plasma ball mill is 0.01 to 2 MPa; the ball milling time of the oxygen plasma ball mill is 20 to 200 min; The carbon vacancy degree τ of the second carbonization product is 0.25 to 0.65, and the true density is 1.35 to 1.85 g / cm 3 , and the average particle size is 0.2 to 15.5 μm.

7. The preparation method of the carbon material according to claim 4, characterized in that, In step (3): The organic liquid is selected from one or more of ethanol, methanol, acetone, cyclohexane, glycerol, ethylene glycol, and sucrose; the mass ratio of the organic liquid to the second carbonized product is 0.5 to 4:1; The inert gas is one or more of argon, hydrogen, nitrogen, helium, neon, krypton, and xenon; Control the temperature of the sintering and carbonization to be 600 to 1100 °C, and the time to be 2 to 3 h.

8. A negative electrode sheet, characterized in that: It includes a negative electrode current collector and a negative electrode active material layer located on at least one surface of the negative electrode current collector, and the negative electrode active material layer uses the carbon material according to any one of claims 1 to 3.

9. An electrochemical device, characterized in that: It includes the negative electrode plate according to claim 8.

10. An electrical device, characterized in that: It includes the electrochemical device according to claim 9.

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