Carbon-carbon composite material and preparation method thereof, negative pole piece and sodium ion battery

Abstract

The invention relates to the technical field of sodium ion batteries, in particular to a carbon-carbon composite material and a preparation method thereof, a negative electrode plate and a sodium ion battery. The carbon-carbon composite material comprises a composite matrix and a soft carbon coating layer coating the composite matrix, and the composite matrix comprises graphite and hard carbon; the compaction density rho pc of the carbon-carbon composite material satisfies 1.00 g / cm < 3 > < = rho pclt; 1.10 g / cm < 3 >; the volume resistivity rho of the carbon-carbon composite material is 2.20 omega.mlt; rho < lt >; and 3.20 omega.m. By doping the graphite and coating the soft carbon, the electronic conductivity of the carbon-carbon composite material can be effectively improved, and the inherent high compaction characteristic of the graphite and the soft carbon is beneficial to the improvement of the compaction density of the carbon-carbon composite material.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a carbon-carbon composite material and a preparation method thereof, a negative electrode sheet and a sodium ion battery. Background Art

[0002] Sodium-ion batteries have become one of the most popular new secondary batteries due to their many advantages, including abundant raw material reserves, cost advantages, green and environmentally friendly characteristics, excellent rate performance and good adaptability to high and low temperatures. They have huge application potential in the field of large-scale energy storage.

[0003] In the construction of sodium-ion batteries, negative electrode materials play an extremely critical role, and carbon-based negative electrode materials have emerged among many materials with their many advantages, providing strong support for the commercialization and widespread application of sodium-ion batteries. In terms of the degree of graphitization, carbon-based negative electrode materials are mainly divided into two categories: graphitic carbon and amorphous carbon. Amorphous carbon has the best overall performance among many negative electrode materials. It has a low sodium storage potential, a moderate sodium storage capacity, a small volume deformation after sodium insertion, and good cycle performance. At the same time, the precursor sources of amorphous carbon are very wide, and the preparation process is relatively simple. Therefore, it has been the first to achieve industrial application in the field of sodium-ion battery negative electrode materials.

[0004] Coal-based amorphous carbon materials, due to their abundant resources, can effectively reduce raw material costs when used as carbon-based anode materials for sodium-ion batteries, which is of great significance for promoting the commercialization of sodium-ion battery technology. However, compared with the graphite anode commonly used in lithium-ion batteries, hard carbon materials have certain shortcomings in electronic conductivity and compaction density, which to some extent limit the full performance of sodium-ion batteries.

[0005] Therefore, it is of great significance to solve the problems of poor electronic conductivity and low compaction density of existing hard carbon materials in the negative electrode of sodium ion batteries.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] The first objective of the present invention is to provide a carbon-carbon composite material that, by doping with graphite and coating it with soft carbon, effectively improves the electronic conductivity of the carbon-carbon composite material. The inherent high compaction properties of graphite and soft carbon contribute to an increased compaction density of the carbon-carbon composite material. This addresses the issues of poor electronic conductivity and low compaction density of existing hard carbon materials used in sodium ion battery anodes.

[0008] The second object of the present invention is to provide a method for preparing a carbon-carbon composite material, wherein the raw materials used in the method are abundant in source and low in cost; and the production process is simple and easy to achieve large-scale production.

[0009] The third object of the present invention is to provide a negative electrode sheet. The sodium-ion battery prepared by using this negative electrode sheet has advantages such as high charge-discharge capacity, high initial Coulomb efficiency, and high rate performance.

[0010] The fourth object of the present invention is to provide a sodium-ion battery, which has high charge-discharge capacity, high initial Coulomb efficiency, and high rate performance.

[0011] In order to achieve the above objects of the present invention, the following technical solutions are specifically adopted:

[0012] The present invention first provides a carbon-carbon composite material, which includes a composite matrix and a soft carbon coating layer covering the composite matrix. The composite matrix includes graphite and hard carbon; the tap density ρ of the carbon-carbon composite material pc satisfies 1.00 g / cm 3 ≤ρ pc <1.10 g / cm 3 ; the volume resistivity ρ of the carbon-carbon composite material satisfies 2.20 Ω·m < ρ < 3.20 Ω·m.

[0013] Furthermore, the tapped density ρ of the carbon-carbon composite material bt satisfies 0.700 g / cm 3 <ρ bt <0.850 g / cm 3 .

[0014] Furthermore, the tapped density ρ of the carbon-carbon composite material bt satisfies 0.780 g / cm 3 <ρ bt <0.850 g / cm 3 .

[0015] Furthermore, the graphite abundance R of the carbon-carbon composite material satisfies 0.5% < R < 12%; wherein, the graphite abundance R is the area ratio of the amorphous carbon 00₂ peak to the graphite 00₂ peak in the XRD pattern of the carbon-carbon composite material.

[0016] Furthermore, the graphite abundance R of the carbon-carbon composite material satisfies 3% < R < 7%.

[0017] Furthermore, in the XRD pattern of the carbon-carbon composite material, the position 2θ of the amorphous carbon 00₂ peak is 23.0° - 25.0°, and the position 2θ of the graphite 00₂ peak is 26.3° - 26.8°.

[0018] Furthermore, the specific surface area S of the carbon-carbon composite material satisfies 3.0 m 2 / g < S ≤ 6.0 m 2 / g.

[0019] The present invention further provides a method for preparing the above-mentioned carbon-carbon composite material, comprising the following steps: mixing a hard carbon source with graphite and then pickling to obtain a de-impurity-removed material; pre-carbonizing the de-impurity-removed material to obtain a pre-carbonized material; and mixing the pre-carbonized material with a soft carbon source and then carbonizing to obtain the carbon-carbon composite material.

[0020] Furthermore, the hard carbon source includes at least one of anthracite, bituminous coal and lignite.

[0021] Furthermore, the graphite includes natural graphite and / or artificial graphite.

[0022] Furthermore, the mass ratio of the hard carbon source to the graphite is 100:1-10.

[0023] Furthermore, the acid solution used for pickling includes at least one of a hydrochloric acid solution, a nitric acid solution and a hydrofluoric acid solution.

[0024] Furthermore, the pre-carbonization temperature is 600-900° C., and the holding time is 2-5 hours.

[0025] Furthermore, the soft carbon source includes petroleum asphalt and / or coal asphalt.

[0026] Furthermore, the mass ratio of the pre-carbonized material to the soft carbon source is 100:2-8.

[0027] Furthermore, the carbonization temperature is 1200-1400° C., and the holding time is 2-5 hours.

[0028] The present invention further provides a negative electrode plate, comprising the above-mentioned carbon-carbon composite material.

[0029] Furthermore, the compaction density of the negative electrode sheet is cd Satisfying 0.95<ρ cd <1.05g / cm 3 .

[0030] The present invention also provides a sodium ion battery comprising the above-mentioned negative electrode plate.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] (1) The carbon-carbon composite material provided by the present invention, wherein the soft carbon coating layer and the graphite doping therein can effectively improve the electronic conductivity of the carbon-carbon composite material, and the inherent high compaction properties of graphite and soft carbon contribute to the improvement of the compaction density of the carbon-carbon composite material. Therefore, the battery made using this carbon-carbon composite material has high charge and discharge capacity, high initial coulombic efficiency, and high rate performance.

[0033] (2) The carbon-carbon composite material provided by the present invention has a high tap density, and it is easier to achieve a high electrode compaction density under the same compaction pressure. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0035] Figure 1 This is an SEM image of the carbon-carbon composite material prepared in Example 5;

[0036] Figure 2 is the XRD pattern of the carbon-carbon composite material prepared in Example 5;

[0037] Figure 3 is an SEM image of the carbon-carbon composite material prepared in Comparative Example 1;

[0038] Figure 4 is the XRD pattern of the carbon-carbon composite material prepared in Comparative Example 1;

[0039] Figure 5 This is a test diagram of the compacted density of the carbon-carbon composite material prepared in Example 5;

[0040] Figure 6 This is a volume resistivity test graph of the carbon-carbon composite material prepared in Example 5;

[0041] Figure 7 This is a charge and discharge curve of a battery made from the carbon-carbon composite material of Example 5. DETAILED DESCRIPTION

[0042] The technical scheme of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. Those who do not specify specific conditions in the embodiments are carried out according to normal conditions or the conditions recommended by the manufacturer. Those whose reagents or instruments are not specified by the manufacturer are conventional products that can be purchased commercially.

[0043] Unless otherwise specified, in the present invention, terms such as "first aspect," "second aspect," "third aspect," and "fourth aspect" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor as implicitly indicating the importance or quantity of the technical features indicated. Furthermore, terms such as "first," "second," "third," and "fourth" serve only as non-exhaustive enumeration and description, and should not constitute closed-ended limitations on quantity.

[0044] Unless otherwise specified, the terms "include" and "comprising" used in the present invention may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0045] Unless otherwise specified, in the present invention, "one or more" or "at least one" refers to any one, any two, or any two or more of the listed items. Among them, "several" refers to any two or any two or more.

[0046] In a first aspect, the present invention provides a carbon-carbon composite material comprising a composite matrix and a soft carbon coating layer coated on the surface of the composite matrix, wherein the composite matrix comprises graphite and hard carbon.

[0047] It can be understood that the material of the soft carbon coating layer is soft carbon.

[0048] The compacted density of the carbon-carbon composite material is pc (Compacted density at the pressure relief stage under 60MPa pressure) meets 1.00g / cm 3 ≤ρ pc <1.10g / cm 3 , including but not limited to 1.00 g / cm 3 , 1.01g / cm 3 , 1.02g / cm 3 , 1.03g / cm 3 , 1.04g / cm 3 , 1.05g / cm 3 , 1.06g / cm 3 , 1.07g / cm 3 、1.08g / cm 3 、1.09g / cm 3 The compaction density of the carbon-carbon composite material is a key factor affecting the density and porosity of the negative electrode sheet made therefrom. A high compaction density can enable the electrode to achieve a higher density and lower porosity under the same pressure.

[0049] The volume resistivity ρ of the carbon-carbon composite material (under a pressure of 60 MPa) satisfies 2.20Ω·m<ρ<3.20Ω·m, including but not limited to 2.21Ω·m, 2.30Ω·m, 2.40Ω·m, 2.50Ω·m, 2.60Ω·m, 2.70Ω·m, 2.80Ω·m, 2.90Ω·m, 3.00Ω·m, 3.10Ω·m, 3.15Ω·m, and 3.19Ω·m, or any range between two thereof. Low volume resistivity supports faster electron conduction, which helps improve the rate performance of the battery.

[0050] The carbon-carbon composite material provided by the present invention, wherein the soft carbon coating layer and the doping of graphite can effectively improve the electronic conductivity of the carbon-carbon composite material, and the inherent high compaction properties of graphite and soft carbon help to improve the compaction density of the carbon-carbon composite material.

[0051] Specifically, due to the doping of graphite, the compacted density and tap density of the carbon-carbon composite material are improved, which helps to make the contact between the material particles closer, reduces the contact resistance between the particles, and is beneficial to the transmission and transfer of electrons during the use of the battery, thereby reducing the charge transfer resistance and improving the battery's rate performance. At the same time, due to the doping of graphite with good conductivity, the volume resistivity of the carbon-carbon composite material is greatly reduced (the volume resistivity of the hard carbon materials currently sold on the market is generally above 2.8Ω·m), which helps to reduce the internal resistance of the battery, improve the material's rate performance, and reduce the heat generated during the battery's charge and discharge process.

[0052] After being coated with the soft carbon coating, the carbon-carbon composite material has fewer surface defects and oxygen-containing functional groups, which inhibits the side reaction between the hard carbon and the electrolyte, reduces irreversible capacity loss, and improves the material's first efficiency (first coulombic efficiency). At the same time, the soft carbon coating and graphite play a wrapping role, which can improve the repeated dissolution of the SEI film caused by the catalytic effect of hard carbon surface defects and unsaturated carbon atoms, thereby improving the gas production problem of sodium-ion batteries.

[0053] Therefore, the carbon-carbon composite material has high charge and discharge capacity, high first coulombic efficiency, and high rate performance.

[0054] In some specific embodiments, the tap density of the carbon-carbon composite material is bt Meet 0.700g / cm 3 <ρ bt <0.850g / cm 3 , including but not limited to 0.701 g / cm 3 , 0.720g / cm 3 、0.750g / cm 3 、0.780g / cm 3, 0.800 g / cm 3 , 0.820 g / cm 3 , 0.830 g / cm 3 , 0.840 g / cm 3 The point value of any one of them or the range value between any two of them. The high tapped density of the carbon-carbon composite material indicates that the powder particles are easy to be closely packed, and it is easier to achieve a high tap density of the electrode sheet under the same compaction pressure.

[0055] It can be understood that since the true density of graphite is higher than that of hard carbon, with the increase of the graphite content, the tapped density of the carbon-carbon composite material and the tapped density of the negative electrode sheet will increase.

[0056] In some specific embodiments, the tapped density ρ of the carbon-carbon composite material bt satisfies 0.780 g / cm 3 <ρ bt <0.850 g / cm 3 . This is beneficial to further improve the compaction density of the negative electrode sheet made of the carbon-carbon composite material.

[0057] In some specific embodiments, the graphite abundance R of the carbon-carbon composite material satisfies 0.5% < R < 12%, including but not limited to the point value of any one of 0.6%, 0.8%, 1.0%, 1.5%, 2.0%, 2.5%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%,​​​​​​​​Among them, the graphite abundance R is related to the amount of graphite added during the synthesis of the carbon-carbon composite material. However, during the material preparation process (such as purification and mixing), the graphite structure may be damaged, resulting in the inability to achieve a one-to-one correspondence between the graphite abundance and the amount of graphite added. According to the experimental data, for carbon-carbon composite materials with the same process parameters, the applicant found that the graphite abundance R and the amount of graphite added X satisfy the following formula 1: R = 0.661×X^1.254 ± 0.1. Here, X refers to the mass ratio of graphite to the mass of the hard carbon source.

[0061] In the present invention, the carbonization temperature used is not sufficient to cause the graphitization transformation of the hard carbon, and the formation of a small amount of graphite microcrystals in the hard carbon structure during the carbonization process is not sufficient to affect the area of the graphite 002 peak. At the same time, the soft carbon material formed after the high-temperature carbonization of the soft carbon source has a limited impact on the graphite 002 peak. Therefore, reasonably setting the graphite abundance R is only related to the amount of graphite added X, and then the above empirical formula is summarized. This formula 1 establishes a direct connection between R and X, which helps to reasonably set the amount of graphite added during production according to the target R value.

[0062] Since the volume resistivity of graphite is much lower than that of hard carbon, as the graphite content increases, the resistivity of the carbon-carbon composite material will decrease. The following formula 2 can be established between the graphite abundance R and the volume resistivity ρ value: ρ = -0.099×R + 0.0042×R^2 + 2.85. Under the condition that the preparation process parameters remain unchanged, the doping of graphite with good conductivity can introduce a highly conductive "skeleton" into the hard carbon matrix, making the electron transport in the hard carbon material smoother, thereby reducing the overall resistance. As the graphite abundance increases, the proportion of the skeleton volume increases, and the volume resistivity gradually decreases. The empirical formulas 1 and 2 can be used to reasonably design the amount of graphite added to control the volume resistivity of the carbon-carbon composite material.

[0063] In some specific embodiments, the graphite abundance R of the carbon-carbon composite material satisfies 3% < R < 7%, and more preferably 5%.

[0064] In some specific embodiments, in the XRD pattern of the carbon-carbon composite material, the position 2θ of the amorphous carbon 002 peak is 23.0° to 25. °, such as 23.0°, 23.2°, 23.5°, 23.7°, 24.0°, 24.2°, 24.5°, 24.7° or 25.0°; the position 2θ of the graphite 002 peak is 26.3° to 26.8°, such as 26.3°, 26.4°, 26.5°, 26.6°, 26.7° or 26.8°. Among them, the XRD test results can be used to confirm the coexistence state of hard carbon and graphite in the carbon-carbon composite material.

[0065] In some specific embodiments, the specific surface area S of the carbon-carbon composite material satisfies 3.0m 2 / g <S≤6.0m 2 / g, including but not limited to 3.1m 2 / g, 3.5m 2 / g, 4.0m 2 / g, 4.5m 2 / g, 5.0m 2 / g, 5.5m 2 / g, 6.0m 2 / g, or any range between them. Due to the coating effect of the soft carbon, some pores are no longer exposed; at the same time, the specific surface area of ​​the graphite is smaller, which makes the specific surface area of ​​the carbon-carbon composite material lower than that before coating.

[0066] In a second aspect, the present invention provides a method for preparing the above-mentioned carbon-carbon composite material, comprising the following steps:

[0067] The hard carbon source and graphite are uniformly mixed and then acid-washed to obtain a decontaminated material. Mixing methods include mechanical mixing, such as dry grinding, wet grinding, and ball milling. Acid washing can remove impurities in the hard carbon source and graphite that may adversely affect the hard carbon material.

[0068] In some specific embodiments, the step of mixing the hard carbon source with graphite specifically includes: uniformly mixing the hard carbon source, graphite and water, and then performing solid-liquid separation and drying.

[0069] Then, the impurity-removed material is pre-carbonized to obtain a pre-carbonized material.

[0070] The pre-carbonized material is then mixed evenly with a soft carbon source and carbonized to obtain the carbon-carbon composite material. The mixing method includes mechanical mixing, such as ball milling.

[0071] The carbon-carbon composite material prepared by the method has high electronic conductivity and high compaction density.

[0072] Moreover, the raw materials used in this method are abundant in source and the overall cost is controllable; at the same time, the production process is simple, which is conducive to the promotion of materials for large-scale mass production.

[0073] In some specific embodiments, the hard carbon source includes at least one of anthracite, bituminous coal, and lignite.

[0074] In some specific embodiments, the graphite includes natural graphite and / or artificial graphite.

[0075] In some specific embodiments, the median particle size of the hard carbon source is 1 to 10 μm, preferably 3 to 7 μm.

[0076] In some specific embodiments, the median particle size of the graphite is 1 to 10 μm, preferably 3 to 7 μm.

[0077] In some specific embodiments, the mass ratio of the hard carbon source to the graphite is 100:1 to 10, including but not limited to any one of 100:1, 100:2, 100:3, 100:4, 100:5, 100:6, 100:7, 100:8, 100:9, and 100:10, or a range between any two of the values.

[0078] In some specific embodiments, the acid solution used for pickling includes at least one of a hydrochloric acid solution, a nitric acid solution, and a hydrofluoric acid solution.

[0079] In some specific embodiments, the molar concentration of the hydrochloric acid solution is 1 to 5 mol / L.

[0080] In some specific embodiments, the molar concentration of the nitric acid solution is 1 to 5 mol / L.

[0081] In some specific embodiments, the mass fraction of the hydrofluoric acid solution is 5% to 15%.

[0082] In some specific embodiments, the ratio of the mass of the acid solution to the sum of the mass of the hard carbon source and the graphite is 3 to 5:1.

[0083] In some specific embodiments, the pre-carbonization temperature is 600-900°C, including but not limited to any one of 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, and 900°C, or a range between any two of them; the pre-carbonization holding time is 2-5h, including but not limited to any one of 2h, 3h, 4h, and 5h, or a range between any two of them.

[0084] In some specific embodiments, the pre-carbonization is performed under the protection of an inert gas, such as a nitrogen atmosphere or an argon atmosphere.

[0085] In some specific embodiments, the soft carbon source includes petroleum pitch and / or coal pitch.

[0086] In some specific embodiments, the mass ratio of the pre-carbonized material to the soft carbon source is 100:2-8, including but not limited to any one of 100:2, 100:3, 100:4, 100:5, 100:6, 100:7, 100:8 or a range between any two of them.

[0087] By rationally adjusting the soft carbon coating amount and graphite doping amount, carbon-carbon composite materials can achieve both high capacity and first efficiency.

[0088] In some specific embodiments, the carbonization temperature is 1200-1400°C, including but not limited to any one of 1200°C, 1250°C, 1300°C, 1350°C, and 1400°C, or a range between any two of them; the carbonization holding time is 2-5h, including but not limited to any one of 2h, 3h, 4h, and 5h, or a range between any two of them.

[0089] In some specific embodiments, the carbonization is performed under the protection of an inert gas, such as a nitrogen atmosphere or an argon atmosphere.

[0090] In a third aspect, the present invention provides a negative electrode plate comprising the above-mentioned carbon-carbon composite material.

[0091] Among them, carbon-carbon composite materials are used as negative electrode active materials for negative electrode sheets of sodium ion batteries.

[0092] The sodium ion battery made with the negative electrode sheet has the advantages of high charge and discharge capacity, high first coulombic efficiency, and high rate performance.

[0093] In some specific embodiments, the compaction density of the negative electrode sheet is cd Satisfying 0.95<ρ cd <1.05g / cm 3 Properly increasing the compaction density of the negative electrode sheet can accommodate more active materials in a limited space, allowing the battery to store more energy per unit mass or volume, thereby effectively improving the energy density of the sodium ion battery cell. However, excessive compaction of the electrode sheet may lead to poor battery rate performance and cycle performance. Therefore, this application controls the compaction density of the negative electrode sheet ρ cd Satisfying 0.95<ρ cd <1.05g / cm 3 .

[0094] In a fourth aspect, the present invention provides a sodium ion battery comprising the above-mentioned negative electrode plate.

[0095] This sodium ion battery has high charge and discharge capacity, high first coulombic efficiency and high rate performance.

[0096] In some specific embodiments, the sodium ion battery further includes a positive electrode sheet, a separator and an electrolyte, which is not limited in the present invention.

[0097] The embodiments of the present invention will be described in detail below with reference to the examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present invention and should not be construed as limiting the scope of the invention. Where specific conditions are not specified in the examples, the methods were performed according to conventional conditions or the conditions recommended by the manufacturer. Where the manufacturers of the reagents or instruments are not specified, they are all commercially available conventional products.

[0098] Example 1

[0099] The method for preparing the carbon-carbon composite material provided in this embodiment comprises the following steps:

[0100] (1) The hard carbon source bituminous coal is crushed to Dv50 = 5 μm, and the natural graphite is crushed to Dv50 = 5 μm; then 100 g of the crushed bituminous coal and 1 g of the crushed natural graphite (i.e., the mass ratio of the hard carbon source to the graphite is 100:1) are added into pure water and stirred for 4 h. The mixed material is separated into solid and liquid by suction filtration, and then placed in a blast oven at 80°C for 12 h to obtain a mixed material.

[0101] (2) The mixed material is acid-washed and purified with a 4 mol / L hydrochloric acid solution to remove impurities, wherein the mass ratio of the hydrochloric acid solution to the mixed material is 4:1, and then the acid-washed material is washed with water and filtered until the filtrate satisfies the pH>6, and the washed material is dried to obtain the impurity-removed material.

[0102] (3) The impurity-removed material was pre-carbonized at 700°C under nitrogen atmosphere protection, with a heating rate of 3°C / min and a holding time of 3h to obtain the pre-carbonized material.

[0103] (4) The pre-carbonized material and the soft carbon source petroleum asphalt with a mass ratio of 100:5 were ball-milled and mixed, and then the ball-milled mixed material was carbonized at 1300 °C under nitrogen atmosphere protection, with a heating rate of 3 °C / min, and kept warm for 3 hours. The discharge temperature was 50 °C to obtain a carbon-carbon composite material.

[0104] The carbon-carbon composite material comprises a composite matrix and a soft carbon coating layer coated on the surface of the composite matrix, and the composite matrix consists of graphite and hard carbon.

[0105] Example 2

[0106] The preparation method of the carbon-carbon composite material provided in this embodiment is basically the same as that in Example 1, except that in step (1), the mass of natural graphite is replaced with 2 g.

[0107] Example 3

[0108] The preparation method of the carbon-carbon composite material provided in this embodiment is basically the same as that in Example 1, except that in step (1), the mass of natural graphite is replaced with 3 g.

[0109] Example 4

[0110] The preparation method of the carbon-carbon composite material provided in this embodiment is basically the same as that in Example 1, except that in step (1), the mass of natural graphite is replaced with 4 g.

[0111] Example 5

[0112] The preparation method of the carbon-carbon composite material provided in this embodiment is basically the same as that in Example 1, except that in step (1), the mass of natural graphite is replaced with 5 g.

[0113] The SEM morphology of the carbon-carbon composite material prepared in this example is shown in Figure 1 shown.

[0114] The X-ray diffraction pattern of the carbon-carbon composite material prepared in this example is shown in Figure 2 shown.

[0115] pass Figure 2 It can be seen that in the XRD test results of the carbon-carbon composite material, the 2θ position of the amorphous carbon 002 peak is 23.0°~25.0°, and the 2θ position of the graphite 002 peak is 26.3°~26.8°.

[0116] Example 6

[0117] The preparation method of the carbon-carbon composite material provided in this embodiment is basically the same as that in Example 1, except that in step (1), the mass of natural graphite is replaced by 6 g.

[0118] Example 7

[0119] The preparation method of the carbon-carbon composite material provided in this embodiment is basically the same as that in Example 1, except that in step (1), the mass of natural graphite is replaced with 7 g.

[0120] Example 8

[0121] The preparation method of the carbon-carbon composite material provided in this embodiment is basically the same as that in Example 1, except that in step (1), the mass of natural graphite is replaced with 8 g.

[0122] Example 9

[0123] The preparation method of the carbon-carbon composite material provided in this embodiment is basically the same as that in Example 1, except that in step (1), the mass of natural graphite is replaced with 9 g.

[0124] Example 10

[0125] The preparation method of the carbon-carbon composite material provided in this embodiment is basically the same as that in Example 1, except that in step (1), the mass of natural graphite is replaced with 10 g.

[0126] Example 11

[0127] The preparation method of the carbon-carbon composite material provided in this embodiment is basically the same as that in Example 1, except that the mass of natural graphite in step (1) is replaced by 5 g, and the mass ratio of the pre-carbonized material to petroleum asphalt in step (4) is replaced by 100:2.

[0128] Example 12

[0129] The preparation method of the carbon-carbon composite material provided in this embodiment is basically the same as that in Example 1, except that the mass of natural graphite in step (1) is replaced by 5 g, and the mass ratio of the pre-carbonized material to petroleum asphalt in step (4) is replaced by 100:8.

[0130] Example 13

[0131] The method for preparing the carbon-carbon composite material provided in this embodiment comprises the following steps:

[0132] (1) The hard carbon source anthracite is crushed to Dv50 = 5 μm, and the natural graphite is crushed to Dv50 = 5 μm; then 100 g of the crushed anthracite and 1 g of the crushed natural graphite (i.e., the mass ratio of the hard carbon source to the graphite is 100:1) are added into pure water and stirred for 4 h. The mixed material is separated into solid and liquid by suction filtration, and then placed in a blast oven at 80°C for 12 h to obtain a mixed material.

[0133] (2) The mixed material is acid-washed and purified with a 4 mol / L nitric acid solution to remove impurities, wherein the mass ratio of the nitric acid solution to the mixed material is 4:1, and then the acid-washed material is washed with water and filtered until the filtrate satisfies the pH>6, and the washed material is dried to obtain the impurity-removed material.

[0134] (3) The impurity-removed material was pre-carbonized at 600°C under nitrogen atmosphere protection, with a heating rate of 3°C / min and a holding time of 5h to obtain the pre-carbonized material.

[0135] (4) The pre-carbonized material and the soft carbon source coal tar were ball-milled in a mass ratio of 100:5, and then the ball-milled mixed material was carbonized at 1200 °C under nitrogen atmosphere protection, with a heating rate of 3 °C / min, and kept warm for 4 hours. The discharge temperature was 50 °C to obtain a carbon-carbon composite material.

[0136] The carbon-carbon composite material comprises a composite matrix and a soft carbon coating layer coated on the surface of the composite matrix, and the composite matrix consists of graphite and hard carbon.

[0137] Example 14

[0138] The method for preparing the carbon-carbon composite material provided in this embodiment comprises the following steps:

[0139] (1) The hard carbon source lignite was crushed to Dv50 = 5 μm, and the artificial graphite was crushed to Dv50 = 5 μm; then 100 g of the crushed lignite and 1 g of the crushed artificial graphite (i.e., the mass ratio of the hard carbon source to the graphite was 100:1) were added into pure water and stirred for 4 h. The mixed material was separated into solid and liquid by suction filtration, and then placed in a blast oven at 80°C for 12 h to obtain a mixed material.

[0140] (2) The mixed material is pickled and purified with a hydrofluoric acid solution having a mass fraction of 10% to remove impurities, wherein the mass ratio of the hydrofluoric acid solution to the mixed material is 4:1, and then the pickled material is washed with water and filtered until the filtrate satisfies the pH>6, and the washed material is dried to obtain the impurity-removed material.

[0141] (3) The impurity-removed material was pre-carbonized at 900°C under nitrogen atmosphere protection, with a heating rate of 3°C / min and a holding time of 2h to obtain the pre-carbonized material.

[0142] (4) The pre-carbonized material and the soft carbon source petroleum asphalt with a mass ratio of 100:5 were ball-milled and mixed, and then the ball-milled mixed material was carbonized at 1400 °C under nitrogen atmosphere protection, with a heating rate of 3 °C / min, and kept warm for 2 h. The discharge temperature was 50 °C to obtain a carbon-carbon composite material.

[0143] The carbon-carbon composite material comprises a composite matrix and a soft carbon coating layer coated on the surface of the composite matrix, and the composite matrix consists of graphite and hard carbon.

[0144] Comparative Example 1

[0145] The preparation method of the carbon-carbon composite material provided in this comparative example is basically the same as that of Example 5, except that: natural graphite is not added in step (1), and petroleum asphalt as a soft carbon source is not added in step (4).

[0146] The SEM morphology of the carbon-carbon composite material prepared in this comparative example is shown in Figure 3 shown.

[0147] The X-ray diffraction pattern of the carbon-carbon composite material prepared in this comparative example is shown in FIG. Figure 4 shown.

[0148] Comparative Example 2

[0149] The preparation method of the carbon-carbon composite material provided in this comparative example is basically the same as that of Example 5, except that no natural graphite is added in step (1).

[0150] Comparative Example 3

[0151] The preparation method of the carbon-carbon composite material provided in this comparative example is basically the same as that of Example 5, except that petroleum asphalt as a soft carbon source is not added in step (4).

[0152] Comparative Example 4

[0153] The preparation method of the carbon-carbon composite material provided in this comparative example is basically the same as that of Example 5, except that in step (1), the mass of natural graphite is replaced with 20 g.

[0154] Comparative Example 5

[0155] The preparation method of the carbon-carbon composite material provided in this comparative example is basically the same as that of Example 5, except that in step (4), the mass ratio of the pre-carbonized material to the petroleum asphalt is replaced with 100:20.

[0156] The compacted density ρ of the carbon-carbon composite materials prepared in each embodiment and each comparative example was tested respectively. pc , volume resistivity ρ of carbon-carbon composites, tap density ρ of carbon-carbon composites bt , graphite abundance R of carbon-carbon composite material, specific surface area S of carbon-carbon composite material, the results are shown in Table 1. The test results of compacted density of carbon-carbon composite material prepared in Example 5 are shown in Table 1. Figure 5 The volume resistivity test results of the carbon-carbon composite material prepared in Example 5 are shown in FIG. Figure 6 shown.

[0157] The carbon-carbon composite materials prepared in each embodiment and each comparative example were respectively used as negative electrode active materials, and negative electrode sheets were prepared according to a mass ratio of negative electrode active material: CMC: SP = 90:5:5. The compaction density of each negative electrode sheet was then tested, and the results are shown in Table 1.

[0158] Among them, the tests of compaction density and tap density of carbon-carbon composite materials refer to GB / T24533-2019 "Graphite Anode Materials for Lithium-ion Batteries".

[0159] The volume resistivity test of carbon-carbon composite materials refers to GB / T 31838.2-2019 "Dielectric and resistive properties of solid insulating materials - Part 2: Resistance characteristics (DC method) Volume resistance and volume resistivity".

[0160] The graphite abundance R value of the carbon-carbon composite material was obtained by fitting and analyzing the XRD results of the sample using Jade software, and the areas of the 002 crystal plane graphite peak and the amorphous peak were calculated respectively. The R value can be obtained by dividing the graphite peak area by the total area of ​​the graphite peak and the amorphous peak.

[0161] Test conditions for specific surface area of ​​carbon-carbon composite materials: The specific surface area of ​​hard carbon materials was tested using a JW-DX dynamic adsorption specific surface analyzer from Jingwei Gaobo using a dynamic multi-point BET method. Nitrogen was selected as the adsorbent, argon was the carrier gas, and the sample tube was placed in liquid nitrogen to maintain a low-temperature test environment.

[0162] The compaction density of the negative electrode is measured using a thickness gauge. The thickness and mass of the negative electrode are simultaneously measured. The compaction density is calculated using the formula ρ = m / [(h - h0) × A], where m is the mass of the electrode, h is the thickness of the electrode after compaction, h0 is the thickness of the copper foil current collector, and A is the area of ​​the electrode.

[0163] Table 1 Parameters of carbon-carbon composite materials and compaction density of negative electrode sheets

[0164]

[0165]

[0166] It can be seen from Table 1 that the carbon-carbon composite materials prepared in each embodiment have high compaction density, high tap density, low volume resistivity, and high electronic conductivity, and the negative electrode sheets prepared from the carbon-carbon composite materials in each embodiment have high compaction density.

[0167] In Comparative Example 1, since neither natural graphite nor soft carbon source petroleum asphalt is added, the volume resistivity of the material is high, the compaction density of the material is lower than that of Example 5, and the specific surface area is relatively high.

[0168] Since no graphite is added in Comparative Example 2, the volume resistivity of the material is high. Although the compaction density has the gain of soft carbon, it is still lower than that of Example 5.

[0169] In Comparative Example 3, since no soft carbon source is added for coating, the specific surface area of ​​the material is relatively high, which affects the initial effect.

[0170] In Comparative Example 4, due to the excessive addition of graphite, the material compaction density is relatively high and the volume resistivity is relatively low, which seriously affects the material capacity and its usability.

[0171] In Comparative Example 5, since the addition amount of soft carbon carbon source is too high, the sodium storage performance of soft carbon is worse than that of hard carbon, resulting in a high compaction density and low volume resistivity of the material, which in turn leads to a significant reduction in the capacity of the material.

[0172] Experimental example

[0173] The carbon-carbon composite materials obtained in each embodiment and each comparative example were respectively used as the negative electrode material powder of button batteries, and the negative electrode sheets were prepared according to the mass ratio of negative electrode material powder: CMC: SP = 90:5:5. The metal sodium sheet was used as the positive electrode, and 1mol / LNaPF6 / EC+DEC (1:1) was used as the electrolyte. The CR2032 button batteries were assembled in a glove box, and the contents of H2O and O2 in the glove box were guaranteed to be <0.1ppm throughout the process. Subsequently, the blue battery test system was used to test each CR2032 button battery. The charge and discharge test was carried out at a current density of 0.1C, with a discharge cut-off voltage of 0V and a charge cut-off voltage of 2.0V. The first-week reversible capacity and the first-week coulomb efficiency of the material were obtained (first-week coulomb efficiency = (the amount of electricity released during the first discharge / the amount of electricity stored during the first charge) × 100%). The results are shown in Table 2. The charge and discharge curves of the battery made of the carbon-carbon composite material of Example 5 are shown in Table 2. Figure 7 shown.

[0174] Table 2 Electrochemical performance test results of each battery

[0175]

[0176]

[0177] It can be seen from Table 1 that the capacity and initial efficiency of the batteries made from the carbon-carbon composite materials in each embodiment are relatively high.

[0178] In summary, the carbon-carbon composite material provided by the present invention, along with the soft carbon coating and graphite doping, effectively improves the electronic conductivity of the carbon-carbon composite material. Furthermore, the inherent high compaction properties of graphite and soft carbon contribute to an increase in the compaction density of the carbon-carbon composite material. This carbon-carbon composite material exhibits high charge-discharge capacity, high initial coulombic efficiency, and high rate capability.

[0179] Although the present invention has been illustrated and described using specific embodiments, it should be appreciated that the above embodiments are merely intended to illustrate the technical solutions of the present invention rather than to limit them. Those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents, without departing from the spirit and scope of the present invention. However, these modifications or replacements do not deviate from the essence of the corresponding technical solutions within the scope of the technical solutions of the embodiments of the present invention. Therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A carbon-carbon composite material, characterized in that: It includes a composite matrix and a soft carbon coating layer covering the composite matrix, and the composite matrix includes graphite and hard carbon; The compacted density of the carbon-carbon composite material is pc Meet 1.00g / cm 3 ≤ρ pc <1.10g / cm 3 ; The volume resistivity ρ of the carbon-carbon composite material satisfies 2.20 Ω·m < ρ < 3.20 Ω·m.

2. The carbon-carbon composite material according to claim 1, characterized in that: The tap density ρ of the carbon-carbon composite material bt Meet 0.700g / cm 3 <ρ bt <0.850g / cm 3 .

3. The carbon-carbon composite material according to claim 1, characterized in that: The tap density ρ of the carbon-carbon composite material bt Meet 0.780g / cm 3 <ρ bt <0.850g / cm 3 .

4. The carbon-carbon composite material according to claim 1, characterized in that: The graphite abundance R of the carbon-carbon composite material satisfies 0.5% < R < 12%; wherein, the graphite abundance R is the area ratio of the amorphous carbon 002 peak to the graphite 002 peak in the XRD pattern of the carbon-carbon composite material; Preferably, the graphite abundance R of the carbon-carbon composite material satisfies 3% < R < 7%.

5. The carbon-carbon composite material according to claim 1, characterized in that: In the XRD pattern of the carbon-carbon composite material, the position 2θ of the amorphous carbon 002 peak is 23.0° - 25.0°, and the position 2θ of the graphite 002 peak is 26.3° - 26.8°.

6. The carbon-carbon composite material according to claim 1, characterized in that: The specific surface area S of the carbon-carbon composite material satisfies 3.0 m 2 / g <S≤6.0m 2 / g.

7. The method for preparing a carbon-carbon composite material according to any one of claims 1 to 6, wherein: It includes the following steps: Mix the hard carbon source and graphite and then pickling to obtain the impurity-removed material; subject the impurity-removed material to pre-carbonization to obtain the pre-carbonized material; Mix the pre-carbonized material and the soft carbon source and then carbonize to obtain the carbon-carbon composite material.

8. The method for preparing the carbon-carbon composite material according to claim 7, characterized in that: Meet at least one of the following conditions: (1) The hard carbon source includes at least one of anthracite, bituminous coal and lignite; (2) The graphite includes natural graphite and / or artificial graphite; (3) The mass ratio of the hard carbon source to the graphite is 100:1 - 10; (4) The acid solution used for pickling includes at least one of hydrochloric acid solution, nitric acid solution and hydrofluoric acid solution; (5) The temperature of the pre-carbonization is 600 - 900 °C, and the heat preservation time is 2 - 5 h; (6) The soft carbon source includes petroleum pitch and / or coal pitch; ​ ​ 9. A negative electrode plate, characterized in that: ​ Preferably, the compaction density of the negative electrode sheet is cd Satisfying 0.95<ρ cd <1.05g / cm 3 .

10. A sodium ion battery, characterized in that: ​

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