Composite carbon material, method for preparing the same, negative electrode sheet, and secondary battery

Abstract

The application relates to a composite carbon material and a preparation method thereof, a negative plate and a secondary battery. The composite carbon material has a core-shell structure, and from the core layer outward, comprises mesocarbon microbeads, a self-assembled monolayer and a conductive layer. The self-assembled monolayer contains mercaptan or organosilane. By arranging the self-assembled monolayer containing mercaptan or organosilane between the mesocarbon microbeads and the conductive layer, the self-assembled monolayer can improve the bonding force between the self-assembled monolayer and the conductive layer, thereby improving the structural stability and uniformity of the composite carbon material, and arranging the conductive layer can improve the electron conduction performance of the composite carbon material. The composite carbon material has good rate performance and high-low temperature performance as a negative material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, in particular to a composite carbon material, a preparation method thereof, a negative electrode sheet and a secondary battery. BACKGROUND

[0002] A lithium ion battery is a kind of secondary battery which can be charged, and it mainly relies on the movement of lithium ions between the positive electrode and the negative electrode to work. During the charging and discharging process, Li + embeds and de-embeds between two electrodes: when charging, Li + de-embeds from the positive electrode, embeds in the negative electrode through the electrolyte, and the negative electrode is in a lithium-rich state; when discharging, it is the opposite. The lithium ion battery has the characteristics of high voltage, large specific energy, long cycle life, small self-discharge, etc., and is widely used in consumer electronics, new energy vehicles, energy storage equipment and other fields.

[0003] Among them, the selection of the negative electrode material of the lithium ion battery directly affects the performance and cost of the lithium ion battery. Mesocarbon microbeads (MCMB) are a new type of carbon material with a relatively complete spherical structure, which can be used to prepare various carbon materials with high density, high strength and high thermal conductivity, and are also a common battery negative electrode material. Compared with natural graphite and artificial graphite, mesocarbon microbeads have the characteristics of perfect structure, superior lithium embedding performance, high specific capacity and long cycle life. However, the working temperature of the traditional mesocarbon microbead negative electrode material is 0-45℃, and the electrochemical performance deteriorates obviously beyond this temperature range, which is difficult to meet the use requirements of the battery in harsh temperature environment. SUMMARY

[0004] Based on this, the present application provides a composite carbon material and a preparation method thereof, which can improve the rate performance of the secondary battery and have high capacity and cycle stability at high and low temperatures.

[0005] In addition, a negative electrode sheet and a secondary battery containing the above-mentioned composite carbon material are also provided.

[0006] In one aspect of the present application, a composite carbon material is provided, which has a core-shell structure, and the core-shell structure comprises, from the core layer outwardly:

[0007] Mesocarbon microbeads, the mesocarbon microbeads being the core layer of the composite carbon material;

[0008] A self-assembled monolayer, the self-assembled monolayer being arranged on the surface of the mesocarbon microbeads, and the self-assembled monolayer containing mercaptan or organosilane; and

[0009] A conductive layer, the conductive layer being arranged on the surface of the self-assembled monolayer.

[0010] In some embodiments, the mesocarbon microbeads have an average particle size D50 of 8-12 μm.

[0011] In some embodiments, the self-assembled monolayer has a thickness of 10-100 nm.

[0012] In some embodiments, the conductive layer has a thickness of 0.1-1 μm.

[0013] In some embodiments, the conductive layer comprises one or more of a conductive polymer and metal nanoparticles.

[0014] In some embodiments, the conductive polymer comprises one or more of polypyrrole and polyaniline.

[0015] In some embodiments, the metal nanoparticles comprise one or more of gold nanoparticles and silver nanoparticles.

[0016] In some embodiments, the metal nanoparticles have a particle size of 1-100 nm.

[0017] In a second aspect, the present application also provides a method for preparing the composite carbon material described above, comprising the following steps:

[0018] pyrolyzing the carbon source at 600-1000°C to prepare mesocarbon microbeads;

[0019] immersing the mesocarbon microbeads in a solution comprising a mercaptan or organosilane to prepare a self-assembled monolayer on the surface of the mesocarbon microbeads;

[0020] preparing a conductive layer on the surface of the self-assembled monolayer.

[0021] In some embodiments, the carbon source comprises one or more of petroleum coke and coal tar.

[0022] In some embodiments, the pyrolyzing is performed for 1-5 hours.

[0023] In some embodiments, the pyrolyzing is performed under a protective atmosphere.

[0024] In some embodiments, the step of preparing mesocarbon microbeads comprises:

[0025] mixing the carbon source and an additive to prepare a mixture; wherein the additive comprises one or more of diatomite, activated carbon and carbonate;

[0026] under a protective atmosphere, heating the mixture to 600-1000°C at a rate of 2-4°C / min;

[0027] The mixture is kept at 600-1000℃ for 1-5 hours under a protective atmosphere;

[0028] After the keeping, the mixture is cooled at a rate of 2-4℃ / min to obtain the mesocarbon microbeads.

[0029] In some embodiments, the step of preparing the conductive layer comprises:

[0030] The mesocarbon microbeads with self-assembled monolayers on the surface are immersed in a slurry containing conductive polymers and / or metal nanoparticles to form a wet film on the surface of the self-assembled monolayers;

[0031] The mesocarbon microbeads are dried to remove the solvent of the wet film and form the conductive layer.

[0032] In a third aspect, the application further provides a negative electrode sheet comprising the composite carbon material described above or prepared by the method described above.

[0033] In a fourth aspect, the application further provides a secondary battery comprising the negative electrode sheet described above.

[0034] The composite carbon material provided by the embodiments of the application comprises, from the core layer outward, mesocarbon microbeads, self-assembled monolayers and a conductive layer. The self-assembled monolayers containing mercaptan or organosilane are arranged between the mesocarbon microbeads and the conductive layer. The self-assembled monolayers can improve the bonding force between the mesocarbon microbeads and the conductive layer, thereby improving the structural stability and uniformity of the composite carbon material. The conductive layer can improve the electron conduction performance of the composite carbon material. The composite carbon material described above has good rate performance and high-temperature performance as a negative electrode material. DETAILED DESCRIPTION

[0035] In order to facilitate the understanding of the present application, the present application will be described more fully below. The present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0036] In the present application, the selection range involving "and / or", "or / and", "and / or" includes any one of two or more related listed items, and also includes any and all combinations of related listed items, which includes any two related listed items, any more related listed items, or all related listed items. It should be noted that when at least two conjunctions selected from "and / or", "or / and", "and / or" are combined to connect at least three items, it should be understood that the technical solution undoubtedly includes the technical solution connected by "logical and", and also undoubtedly includes the technical solution connected by "logical or". For example, "A and / or B" includes three parallel schemes of A, B and A+B. For another example, the technical solution of "A, and / or, B, and / or, C, and / or, D" includes any one of A, B, C and D (i.e. the technical solution connected by "logical or"), and also includes any and all combinations of A, B, C and D, i.e. includes the combination of any two or any three of A, B, C and D, and also includes the four-item combination of A, B, C and D (i.e. the technical solution connected by "logical and").

[0037] In the present application, "multiple", "multiple", "multiple", "multiple" and the like are used without special limitation, which means more than two or equal to two in quantity. For example, "one or more" means one or more than two.

[0038] In the present application, "combination thereof", "any combination thereof", "any combination thereof" and the like include all suitable combinations of any two or more listed items.

[0039] In the present application, "suitable combination", "suitable manner", "any suitable manner" and the like are described as "suitable" to implement the technical solutions of the present application, solve the technical problems of the present application, and achieve the expected technical effects of the present application.

[0040] In the present application, "preferably", "better", "better", "preferably" are only used to describe the better implementation or embodiment, and it should be understood that it does not constitute a limitation on the protection scope of the present application.

[0041] In the present application, "further", "further", "particularly" and the like are used for description purposes, indicating differences in content, but should not be understood as a limitation on the protection scope of the present application.

[0042] In the present application, "optionally", "optional", "optional" means optional, i.e. selected from two parallel schemes of "yes" or "no". If there are multiple "optional" in a technical solution, and there is no special description, and no contradictory relationship or mutual restriction.

[0043] In the present application, the terms "first", "second", "third", "fourth" and the like in the description and in the claims - are used for descriptive purposes only and not to be construed as indicating or implying relative importance or a quantity of the indicated technical features. Furthermore, the terms "first", "second", "third", "fourth" and the like are used only to describe the different embodiments and do not imply that two or more claimed embodiments are mutually exclusive.

[0044] In the present application, the technical features described in an open way include both the closed technical solution consisting of the listed features and the open technical solution comprising the listed features.

[0045] In the present application, in relation to a numerical interval (i.e. a numerical range), if not otherwise specified, the optional numerical distribution within the numerical interval is considered to be continuous and includes both numerical end points (i.e. the minimum and maximum values) of the numerical range and every numerical value between the two numerical end points. If not otherwise specified, when a numerical interval refers only to integers within the numerical interval, including both end point integers of the numerical range and every integer between the two end point integers, in the present text, it is equivalent to directly listing every integer, for example, t is an integer selected from 1 to 10, which means that t is any one integer selected from the group consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10. In addition, when multiple ranges are provided to describe a feature or a characteristic, these ranges can be combined. In other words, unless otherwise specified, the ranges disclosed in the present text should be understood to include any and all sub-ranges incorporated therein.

[0046] In the present application, the temperature parameters, if not otherwise specified, allow both constant temperature treatment and variation within a certain temperature interval. It should be understood that the constant temperature treatment allows the temperature to fluctuate within the accuracy range controlled by the instrument. It is allowed to fluctuate within the range of, for example, ±5°C, ±4°C, ±3°C, ±2°C, ±1°C.

[0047] In the present application, in relation to percentage content, if not otherwise specified, it refers to mass percentage for solid-liquid mixing and solid-solid mixing, and to volume percentage for liquid-liquid mixing.

[0048] In the present application, in relation to percentage concentration, if not otherwise specified, it refers to final concentration. The final concentration refers to the proportion of the added ingredient in the system after the ingredient is added.

[0049] In the present application, % (w / w) and wt% both represent weight percentage, % (v / v) refers to volume percentage, and % (w / v) refers to mass volume percentage. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0050] In one aspect of the present application, a composite carbon material is provided, which has a core-shell structure including, from the core layer outward, mesocarbon microbeads, a self-assembled monolayer, and a conductive layer.

[0051] The mesocarbon microbeads are the core layer of the composite carbon material. Compared with natural graphite, the mesocarbon microbeads have a larger specific surface area and better lithium storage performance.

[0052] The self-assembled monolayer is a molecular assembly spontaneously formed by adsorption on a surface and has good uniformity. In the embodiments of the present application, the self-assembled monolayer contains mercaptan or organosilane. By providing the self-assembled monolayer containing mercaptan or organosilane, the self-assembled monolayer can improve the bonding force with the conductive layer.

[0053] The conductive layer is provided on the surface of the self-assembled monolayer. The conductive layer can improve the electronic conductivity of the material.

[0054] The composite carbon material described above improves the structural stability and uniformity of the composite carbon material by providing the self-assembled monolayer containing mercaptan or organosilane between the mesocarbon microbeads and the conductive layer, which can improve the bonding force with the conductive layer, and improves the electronic conductivity of the composite carbon material by providing the conductive layer. The composite carbon material described above has good rate performance and high-temperature performance as a negative electrode material.

[0055] In some embodiments, the mesocarbon microbeads have an average particle size D50 of 8 μm to 12 μm. Controlling the D50 of the mesocarbon microbeads within the above range can provide the composite carbon material with a suitable tap density and specific surface area. Alternatively, the mesocarbon microbeads have an average particle size D50 of 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, or any range defined by any two of the above values.

[0056] In some embodiments, the self-assembled monolayer has a thickness of 10 nm to 100 nm. Alternatively, the self-assembled monolayer has a thickness of 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, or any range defined by any two of the above values.

[0057] In some embodiments, the conductive layer has a thickness of 0.1-1 μm. Optionally, the conductive layer has a thickness of 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, or any range formed by any of these values.

[0058] In some embodiments, the conductive layer comprises one or more of a conductive polymer and metal nanoparticles. Specifically, the conductive polymer comprises one or more of polypyrrole and polyaniline. The metal nanoparticles comprise one or more of gold nanoparticles and silver nanoparticles. The conductive polymer and metal nanoparticles have good conductivity, which can improve the electron conductivity of the composite carbon material.

[0059] In some embodiments, the metal nanoparticles have a particle size of 1-100 nm. Optionally, the metal nanoparticles have a particle size of 1 nm, 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, or any range formed by any of these values. Controlling the particle size of the metal nanoparticles within the above range can make the structure of the conductive layer denser and improve the conductivity of the conductive layer.

[0060] In some embodiments, the self-assembled monolayer contains mercaptan and the conductive layer contains gold nanoparticles. The mercaptan in the self-assembled monolayer has good bonding ability with the gold nanoparticles, which can further enhance the bonding force between the self-assembled monolayer and the conductive layer.

[0061] In some embodiments, the composite carbon material has a particle size D10 of 2-5 μm, a particle size D50 of 8-12 μm, and a particle size D90 of 15-25 μm.

[0062] In some embodiments, the composite carbon material has a tap density of ≥1.15 g / cm 3 .

[0063] In some embodiments, the composite carbon material has a specific surface area of ≤2.0 m 2 / g.

[0064] Another embodiment of the present application also provides a preparation method of the composite carbon material, comprising the following steps S100, S200, and S300.

[0065] Step S100: pyrolyzing a carbon source at 600-1000 °C to prepare mesocarbon microbeads. Specifically, the pyrolysis temperature is 600 °C, 700 °C, 800 °C, 900 °C, 1000 °C, or any range formed by any of these values.

[0066] In some embodiments, the carbon source includes one or more of petroleum coke, coal tar.

[0067] In some embodiments, the pyrolysis process is performed for 1 hour to 5 hours. Alternatively, the pyrolysis process is performed for 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, or any range derivable therein.

[0068] In some embodiments, the pyrolysis process is performed under a protective atmosphere. Performing the pyrolysis process under a protective atmosphere prevents the material from oxidizing at high temperature. Exemplarily, the protective atmosphere includes one or more of nitrogen, argon.

[0069] In some embodiments, the step S100 includes S110-S140.

[0070] Step S110: mixing the carbon source and the additive to prepare a mixture. The additive includes one or more of diatomite, activated carbon, carbonate. By mixing the carbon source and the additive, it is helpful to form the mesocarbon microbead with a porous structure.

[0071] Step S120: under a protective atmosphere, the mixture is heated to 600-1000°C at a rate of 2-4°C / min. Alternatively, the heating rate is 2°C / min, 3°C / min, 4°C / min, or any range derivable therein.

[0072] Step S130: under a protective atmosphere, the mixture is kept at 600-1000°C for 1-5 hours.

[0073] Step S140: after the keeping, the mixture is cooled at a rate of 2-4°C / min to obtain the mesocarbon microbead. Alternatively, the cooling rate is 2°C / min, 3°C / min, 4°C / min, or any range derivable therein.

[0074] In one embodiment, the step S100 is specifically: mixing the carbon source and the additive to prepare a mixture. Under a protective atmosphere, the mixture is heated from room temperature to 200°C at a rate of 2°C / min to remove water and low-molecular-weight volatile substances. Then heated from 200°C to 800°C at a rate of 4°C / min to make the carbon source start forming mesophase structure. Kept at 800°C for 1 hour to make the carbon source pyrolyze completely to form stable mesocarbon microbead structure. Then cooled to room temperature at a rate of 4°C / min.

[0075] Step S200: immersing the mesocarbon microbead in a solution containing mercaptan or organosilane to prepare a self-assembled monolayer on the surface of the mesocarbon microbead.

[0076] In some embodiments, before step S200, there is further included a step of cleaning the surface of the mesocarbon microbeads. Specifically, the cleaning solvent is one or more of acetone, ethanol. By cleaning the surface of the mesocarbon microbeads, the adhesion of the SAM molecules can be improved.

[0077] In some embodiments, the mercaptan includes one or more of methyl mercaptan, ethyl mercaptan, propyl mercaptan, butyl mercaptan, pentyl mercaptan, hexyl mercaptan, heptyl mercaptan, octyl mercaptan, nonyl mercaptan, decyl mercaptan, undecyl mercaptan, dodecyl mercaptan, tridecyl mercaptan, tetradecyl mercaptan, pentadecyl mercaptan, hexadecyl mercaptan, heptadecyl mercaptan, octadecyl mercaptan, nonadecyl mercaptan.

[0078] In some embodiments, the concentration of the mercaptan in the solution containing mercaptan is 10mmol·L -1 ~30mmol·L -1 .

[0079] In some embodiments, the organosilane includes one or more of silane amine, chlorosilane, oxysilane.

[0080] In some embodiments, in step S200, the soaking time is 2 hours to 24 hours. Alternatively, the soaking time is 2 hours, 4 hours, 8 hours, 12 hours, 16 hours, 20 hours, 24 hours or any range formed by any of the above values.

[0081] In some embodiments, after step S200, there is further included a step of washing and drying the mesocarbon microbeads. After the soaking, the SAM molecules that are not fixed on the surface can be removed by washing.

[0082] Step S300: preparing a conductive layer on the surface of the self-assembled monolayer.

[0083] In some embodiments, step S300 includes S310 and S320.

[0084] Step S310: soaking the mesocarbon microbeads with the self-assembled monolayer on the surface in a slurry containing conductive polymers and / or metal nanoparticles to form a wet film on the surface of the self-assembled monolayer.

[0085] Step S320: drying the mesocarbon microbeads to remove the solvent of the wet film to form the conductive layer.

[0086] The above method for preparing the composite carbon material has a simple processing technology, and the prepared composite carbon material has good rate performance and high and low temperature performance.

[0087] Another embodiment of the present application also provides a negative electrode sheet comprising the composite carbon material described above or prepared by the method described above. The negative electrode sheet comprising the composite carbon material has good rate performance and high-low temperature performance.

[0088] Another embodiment of the present application also provides a secondary battery comprising the negative electrode sheet described above. The secondary battery has good high-low temperature performance and rate performance, and is suitable for special batteries used in unmanned aerial vehicles, model aircrafts, electronic cigarettes and other special fields.

[0089] In order to make the purpose, technical solutions and advantages of the present application more concise and clear, the present application is described by the following specific examples, but the present application is not limited to these examples. The examples described below are only good examples of the present application, which can be used to describe the present application, and should not be understood as limiting the scope of the present application. It should be noted that any modification, equivalent replacement and improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.

[0090] Example 1

[0091] This embodiment provides a composite carbon material as a negative electrode material, which is prepared according to the following steps:

[0092] (1) Petroleum coke and carbonate additives are mixed, and the mixture is heated from room temperature to 200℃ at a rate of 2℃ / min under a nitrogen atmosphere to remove moisture and low molecular weight volatile substances. Then, the temperature is increased from 200℃ to 800℃ at a rate of 4℃ / min to make the carbon source begin to form mesophase structure. The temperature is kept at 800℃ for 1 hour to make the carbon source pyrolyze completely and form stable mesophase carbon microsphere structure. Then, the temperature is decreased to room temperature at a rate of 4℃ / min to prepare mesophase carbon microspheres.

[0093] (2) The mesophase carbon microspheres prepared in step (1) are soaked in a 15mmol·L -1 of dodecanethiol solution for 12 hours, then the soaked mesophase carbon microspheres are washed with ethanol and dried in an oven to obtain mesophase carbon microspheres with a SAM layer on the surface.

[0094] (3) The mesophase carbon microspheres obtained in step (2) are soaked in a 1mg / mL gold nanoparticle dispersion to form a wet film on the surface of the mesophase carbon microspheres, and then dried to form a conductive layer.

[0095] The composite carbon material prepared in this embodiment comprises, from the inside out, mesophase carbon microspheres, a SAM layer and a conductive layer. By scanning electron microscopy, the average particle size of the mesophase carbon microspheres of the composite carbon material is 8μm-12μm, the thickness of the SAM layer is 10nm-100nm, and the thickness of the conductive layer is 0.1μm-1μm.

[0096] Comparative Example 1

[0097] In this comparative example, commercially available natural graphite was used as the negative electrode material.

[0098] Comparative Example 2

[0099] In this comparative example, the mesocarbon microbeads prepared in step (1) of Example 1 were used as the negative electrode material.

[0100] Preparation of negative electrode sheet: the negative electrode material, the conductive agent Super P and the binder PVDF of the above examples or comparative examples were mixed in a mass ratio of 92:3:5 to prepare a slurry. Then the slurry was coated on a copper foil to prepare a negative electrode sheet.

[0101] Preparation of battery: the positive electrode sheet, the separator and the negative electrode sheet were assembled into a battery cell, and then the electrolyte was injected into the battery cell to obtain a test battery after a formation process.

[0102] The battery prepared above was subjected to electrochemical tests, and the test method was as follows. The test results are shown in Tables 1 and 2.

[0103] First charge capacity and first discharge capacity test: the battery was charged to a specified upper limit voltage at a rate of C / 10, and the charge capacity was recorded, which was the first charge capacity. Then the battery was discharged to a specified lower limit voltage at a rate of C / 10. The discharge capacity was recorded, which was the first discharge capacity.

[0104] Discharge capacity test: the battery was charged to a specified upper limit voltage, and then discharged to a specified lower limit voltage at different rates (0.1C, 0.5C, 1C, 2C, 5C, 10C). The discharge capacity was recorded, which was the discharge capacity at different rates.

[0105] Cycle capacity retention rate test: the battery was subjected to N cycles of charge and discharge, and the discharge capacity after the Nth cycle was compared with the first discharge capacity. The capacity retention rate = (discharge capacity after the Nth cycle / first discharge capacity) * 100%.

[0106] Internal resistance test: the battery internal resistance tester was used for the test.

[0107] Table 1 Discharge capacity and cycle capacity retention rate of Example 1 and Comparative Examples 1-2

[0108] Test item Example 1 Comparative Example 1 Comparative Example 2 Initial charge capacity (mAh / g) 360 310 355 Initial discharge capacity (mAh / g) 350 300 345 0.1C discharge capacity (mAh / g) 350 300 345 0.5C discharge capacity (mAh / g) 340 280 330 1C discharge capacity (mAh / g) 330 260 320 2C discharge capacity (mAh / g) 310 240 290 5C discharge capacity (mAh / g) 300 230 260 10C discharge capacity (mAh / g) 280 200 220 20℃, capacity retention rate after 500 cycles (%) 95 85 89

[0109] From the data in Table 1, it can be seen that, compared with Comparative Examples 1-2, the battery prepared by using the composite carbon material of the present application in Example 1 has higher discharge capacity at different rates and higher cycle capacity retention rate. It can be seen that the composite carbon material provided by the present application has better rate performance and cycle stability when used for preparing a battery.

[0110] Table 2 Electrochemical performance of the battery of Example 1 at different temperatures

[0111] Test item -20℃ 0℃ 25℃ 60℃ 0.1C discharge capacity (mAh / g) 250 300 350 330 Internal resistance (mΩ) 120 80 50 70 Capacity retention rate after 200 cycles (%) 90 93 95 92

[0112] As can be seen from the data in Table 2, the discharge capacity of the battery of Example 1 is ≥ 250 mAh / g, the internal resistance is ≤ 120 mΩ, and the capacity retention rate after 200 cycles is ≥ 90% in the temperature range of -20°C to 60°C. It can be seen that the composite carbon material of Example 1 has good electrochemical performance in the temperature range of -20°C to 60°C when used in a secondary battery.

[0113] The technical features of the above-described embodiments can be combined in any manner. In order to make the description simple, all possible combinations of the technical features in the above-described embodiments are not described, however, as long as the combinations of the technical features do not contradict each other, they should be considered as falling within the scope of the present disclosure.

[0114] The above-described embodiments only express several implementation manners of the present application, facilitate understanding of the technical solutions of the present application in detail, but should not be understood as a limitation on the scope of patent protection. It should be pointed out that, for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which all fall within the scope of protection of the present application. It should be understood that, on the basis of the technical solutions provided by the present application, the technical solutions obtained by logical analysis, reasoning or limited experiments by those skilled in the art all fall within the scope of protection of the appended claims. Therefore, the scope of protection of the patent of the present application should be subject to the contents of the appended claims, and the description can be used to explain the contents of the claims.

Claims

1. A composite carbon material, characterized by, The composite carbon material has a core-shell structure, which comprises, from the core layer outwardly: mesocarbon microbeads, which are the core layer of the composite carbon material; a self-assembled monolayer, which is arranged on the surface of the mesocarbon microbeads, and contains mercaptan or organosilane; and a conductive layer, which is arranged on the surface of the self-assembled monolayer.

2. The composite carbon material of claim 1, wherein The mesocarbon microbeads have an average particle size D50 of 8 μm to 12 μm; and / or, the self-assembled monolayer has a thickness of 10 nm to 100 nm; and / or, the conductive layer has a thickness of 0.1 μm to 1 μm.

3. The composite carbon material according to claim 1 or 2, wherein The conductive layer comprises one or more of a conductive polymer and metal nanoparticles.

4. The composite carbon material of claim 3, wherein, The conductive polymer comprises one or more of polypyrrole and polyaniline; and / or, the metal nanoparticles comprise one or more of gold nanoparticles and silver nanoparticles; and / or, the metal nanoparticles have a particle size of 1 nm to 100 nm.

5. The method for producing a composite carbon material according to any one of claims 1 to 4, wherein The method comprises the following steps: pyrolyzing a carbon source at 600°C to 1000°C to prepare mesocarbon microbeads; immersing the mesocarbon microbeads in a solution containing mercaptan or organosilane to prepare a self-assembled monolayer on the surface of the mesocarbon microbeads; and preparing a conductive layer on the surface of the self-assembled monolayer.

6. The method for producing a composite carbon material according to claim 5, wherein The carbon source comprises one or more of petroleum coke and coal tar; and / or, the pyrolyzing is performed for 1 hour to 5 hours; and / or, the pyrolyzing is performed under a protective atmosphere.

7. The method for producing a composite carbon material according to claim 5, wherein The step of preparing mesocarbon microbeads comprises: mixing the carbon source and an additive to prepare a mixture; wherein the additive comprises one or more of diatomite, activated carbon and carbonate; under a protective atmosphere, warming the mixture to 600°C to 1000°C at a rate of 2°C / min to 4°C / min; under a protective atmosphere, the mixture is kept at 600°C to 1000°C for 1 hour to 5 hours; after the keeping, the mixture is cooled at a rate of 2°C / min to 4°C / min to obtain the mesocarbon microbeads.

8. The method for producing a composite carbon material according to any one of claims 5 to 7, wherein The step of preparing a conductive layer comprises: immersing the mesocarbon microbeads having the self-assembled monolayer on the surface in a slurry containing a conductive polymer and / or metal nanoparticles to form a wet film on the surface of the self-assembled monolayer; drying the mesocarbon microbeads to remove the solvent of the wet film and form the conductive layer.

9. A negative electrode sheet characterized by comprising: The composite carbon material comprises the composite carbon material as claimed in any one of claims 1 to 4 or the composite carbon material prepared by the method as claimed in any one of claims 5 to 8.

10. A secondary battery characterized by comprising: The negative electrode sheet comprises the negative electrode as claimed in claim 9.