Mesocarbon microbead negative electrode material and preparation method thereof, negative electrode sheet, and secondary battery

Abstract

The application relates to a mesocarbon microbead negative material, a preparation method thereof, a negative plate and a secondary battery. The preparation method comprises the following steps: heating a carbon source to 400-600 DEG C at a rate of 5-20 DEG C / min to perform first heat treatment to prepare a first intermediate; performing second heat treatment on the first intermediate at 1000-1500 DEG C to prepare a second intermediate; preparing a modified layer on the surface of the second intermediate to prepare a third intermediate; wherein the modified layer comprises a silane coupling agent; and doping nitrogen atoms or boron atoms on the surface of the third intermediate to prepare the mesocarbon microbead negative material. The mesocarbon microbead negative material prepared by the preparation method has high capacity under high rate, low temperature and high temperature, and is beneficial to improving the rate performance and high and low temperature performance of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium negative electrode materials, and particularly relates to a mesocarbon microbead negative electrode material, a preparation method thereof, a negative electrode sheet and a secondary battery. BACKGROUND

[0002] Lithium ion batteries are widely used in the fields of consumer electronics, new energy vehicles, energy storage devices and the like due to their high energy density, long service life, high rated voltage and low self-discharge rate. The negative electrode materials actually used in lithium ion batteries are basically carbon materials, such as artificial graphite, natural graphite, mesocarbon microbeads, soft carbon and hard carbon. Among them, mesocarbon microbeads (MCMB) are spherical carbon materials composed of high molecular weight condensed aromatic hydrocarbons, which are beneficial to the embedding and de-embedding of lithium ions in different directions. However, compared with artificial graphite and natural graphite, the capacity of mesocarbon microbeads is relatively low, and the mesocarbon microbeads prepared by traditional processes have high surface density and high graphitization degree under high-temperature heat treatment, which is not conducive to the rapid embedding and de-embedding of lithium and affects the rate performance and high-low temperature performance of the negative electrode material. SUMMARY

[0003] Based on this, the present application provides a mesocarbon microbead negative electrode material and a preparation method thereof, which can improve the rate performance and high-low temperature performance of the mesocarbon microbead negative electrode material.

[0004] In addition, a negative electrode sheet and a secondary battery comprising the above mesocarbon microbead negative electrode material are also provided.

[0005] In one aspect of the present application, a preparation method of a mesocarbon microbead negative electrode material is provided, which comprises the following steps:

[0006] The carbon source is heated to 400-600 DEG C at a rate of 5-20 DEG C / min to perform first heat treatment, to prepare a first intermediate;

[0007] The first intermediate is subjected to second heat treatment at 1000-1500 DEG C to prepare a second intermediate;

[0008] A modified layer is prepared on the surface of the second intermediate to prepare a third intermediate; wherein the modified layer comprises a silane coupling agent; and

[0009] The surface of the third intermediate is doped with nitrogen atoms or boron atoms to prepare the mesocarbon microbead negative electrode material.

[0010] In some embodiments, the heating rate in the step of preparing the first intermediate is 5-10 DEG C / min.

[0011] In some embodiments, the first heat treatment is performed for 2-6 hours, optionally 3-4 hours.

[0012] In some embodiments, the first heat treatment is performed in a low-oxygen environment, wherein the volume content of oxygen in the low-oxygen environment is less than or equal to 0.5%.

[0013] In some embodiments, the step of preparing the second intermediate comprises:

[0014] The first intermediate is heated to 1000-1500℃ at a rate of 5-10℃ / min;

[0015] The first intermediate is kept at 1000-1500℃ for 1-2 hours for the second heat treatment;

[0016] The product after the second heat treatment is cooled to room temperature at a rate of 10-20℃ / min to obtain the second intermediate;

[0017] In some embodiments, the step of preparing the second intermediate is performed in a low-oxygen environment, wherein the volume content of oxygen in the low-oxygen environment is less than or equal to 0.5%.

[0018] In some embodiments, the thickness of the modified layer is 5-10 nm.

[0019] In some embodiments, the step of doping nitrogen atoms on the surface of the third intermediate comprises:

[0020] The third intermediate and ammonia are mixed at a mass ratio of 1:5, heated to 80℃ under inert atmosphere, and kept for 2-3 hours for reaction; then the mixed system is heated to 180℃ and kept for 1 hour;

[0021] The mixed system is cooled to room temperature, and the obtained solid product is washed with deionized water and ethanol, dried, to obtain the mesocarbon microbead negative electrode material.

[0022] Alternatively, the step of doping boron atoms on the surface of the third intermediate comprises:

[0023] The third intermediate and ethyl borate solution are mixed at a mass ratio of 1:2, reacted at room temperature under inert atmosphere for 6-8 hours; then the mixed system is heated to 60℃ and kept for 2 hours;

[0024] The mixed system is cooled to room temperature, and the obtained solid product is washed with deionized water, dried, to obtain the mesocarbon microbead negative electrode material.

[0025] In a second aspect, the application further provides a mesocarbon microbead negative material prepared according to the preparation method of the mesocarbon microbead negative material described above.

[0026] Optionally, the mesocarbon microbead negative material has a particle size D10 of 5 μm to 8 μm, a particle size D50 of 10 μm to 14 μm, and a particle size D90 of 16 μm to 25 μm.

[0027] In a third aspect, the application further provides a negative sheet comprising the mesocarbon microbead negative material described above.

[0028] In a fourth aspect, the application further provides a secondary battery comprising the negative sheet described above.

[0029] The preparation method of the mesocarbon microbead negative material according to the embodiments of the application comprises the following steps: preparing a second intermediate by sequentially subjecting a carbon source to heat treatment at 400 ℃ to 600 ℃ and 1000 ℃ to 1500 ℃, preparing a modified layer containing a silane coupling agent on the surface of the second intermediate, and doping nitrogen atoms or boron atoms on the surface of the second intermediate. The mesocarbon microbead negative material prepared by the method has a high capacity at high rate, low temperature and high temperature, and is beneficial to improving the rate performance and high and low temperature performance of the battery. DETAILED DESCRIPTION

[0030] In order to facilitate the understanding of the application, the application will be described more fully below. The 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 application more thorough and comprehensive.

[0031] 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").

[0032] 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.

[0033] 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.

[0034] In the present application, "suitable combination", "suitable manner", "any suitable manner" and the like are described as "suitable" which can 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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 a range such as ±5°C, ±4°C, ±3°C, ±2°C, ±1°C.

[0042] 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.

[0043] 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.

[0044] 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 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.

[0045] An embodiment of the present application provides a preparation method of mesocarbon microbead negative electrode material, comprising the following steps S100-S400.

[0046] Step S100: heating the carbon source to 400-600°C at a rate of 5-20°C / min, performing first heat treatment, and preparing a first intermediate.

[0047] In some embodiments, the carbon source comprises one or more of coal tar and pitch. Through the treatment of step S100, the carbon source undergoes thermal polymerization and pyrolysis to obtain the first intermediate with a spherical structure.

[0048] The first heat treatment of the carbon source at 400-600°C can cause pyrolysis of the carbon source. Alternatively, the temperature of the first heat treatment is 400°C, 450°C, 500°C, 550°C, 600°C, or any range formed by any of the above values.

[0049] By controlling the heating rate to be 5-20°C / min, uniform pyrolysis of the carbon source can be ensured, avoiding local overheating or incomplete pyrolysis. Alternatively, the heating rate is 5°C / min, 6°C / min, 8°C / min, 10°C / min, 12°C / min, 14°C / min, 15°C / min, 16°C / min, 18°C / min, 20°C / min, or any range formed by any of the above values. Further, the heating rate is 5-10°C / min. Through thermogravimetric analysis (TGA) of the weight loss during the first heat treatment, it is found that when the heating rate is kept at 5-10°C / min, the pyrolysis process is relatively mild, and the pyrolysis time is moderate.

[0050] In some embodiments, the first heat treatment is performed for 2-6 hours. Alternatively, the first heat treatment is performed for 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, or any range formed by any of the above values. Further, the first heat treatment is performed for 3-4 hours.

[0051] In some embodiments, step S100 comprises:

[0052] Step S110: heating the carbon source to 400-600°C at a rate of 5-20°C / min.

[0053] Step S120: keeping the carbon source at 400-600°C for a period of time to make the pyrolysis of the carbon source sufficient, and to prepare a first intermediate. Specifically, the time for keeping is 1-4 hours, and further 1-2 hours.

[0054] Step S130: cooling to room temperature, and collecting the first intermediate.

[0055] In some embodiments, step S100 is performed in a low-oxygen environment. The volume content of oxygen in the low-oxygen environment is less than or equal to 0.5%. Specifically, step S100 can be performed in an argon environment or an environment with an oxygen volume content of ≤0.5%. By controlling the oxygen content of step S100, the degree of oxidation and structure of the microspheres can be controlled.

[0056] Step S200: performing a second heat treatment on the first intermediate at 1000-1500°C to prepare a second intermediate. By heat treatment at 1000-1500°C, the crystallinity and electrical conductivity of the material can be improved, and the electrochemical performance of the material can be improved. Optionally, the temperature of the second heat treatment is 1000°C, 1100°C, 1200°C, 1300°C, 1400°C, 1500°C, or any range consisting of any of the above values.

[0057] In some embodiments, step S200 includes:

[0058] Step S210: heating the first intermediate to 1000-1500°C at a rate of 5-10°C / min. Optionally, the heating rate is 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, or any range consisting of any of the above values. By controlling the heating rate within the above range, the internal thermal stress of the material can be ensured to be uniform, and deformation or rupture of the microsphere structure can be avoided.

[0059] Step S220: keeping the first intermediate at 1000-1500°C for 1-2 hours to perform the second heat treatment.

[0060] Step S230: cooling the product after the second heat treatment to room temperature at a rate of 10°C / min to 20°C / min to obtain a second intermediate. Optionally, the rate of cooling is 10°C / min, 11°C / min, 12°C / min, 13°C / min, 14°C / min, 15°C / min, 16°C / min, 17°C / min, 18°C / min, 19°C / min, 20°C / min, or any range derived from any of these values. By controlling the rate of cooling within the above range, the uniformity of thermal stress within the material can be ensured, and deformation or rupture of the microsphere structure caused by temperature changes can be avoided.

[0061] In some embodiments, step S200 is performed in a low-oxygen environment. The volume content of oxygen in the low-oxygen environment is less than or equal to 0.5%. Specifically, step S200 can be performed in an argon environment or an environment with an oxygen volume content of ≤0.5%. By controlling the oxygen content of step S200, the degree of oxidation and structure of the microsphere result can be controlled.

[0062] Step S300: preparing a modified layer on the surface of the second intermediate to obtain a third intermediate. The modified layer includes a silane coupling agent. By preparing a modified layer containing a silane coupling agent on the surface of the second intermediate, the ion diffusion capacity of the material can be enhanced.

[0063] In some embodiments, the modified layer can be prepared by immersing the second intermediate in a silane coupling agent solution and then drying.

[0064] In some embodiments, the thickness of the modified layer is 5 nm to 10 nm. Optionally, the thickness of the modified layer is 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, or any range derived from any of these values.

[0065] Step S400: doping nitrogen atoms or boron atoms on the surface of the third intermediate to obtain a mesocarbon microbead negative electrode material. By doping nitrogen atoms or boron atoms on the surface of the third intermediate, the electrochemical performance of the material can be further improved, and the rate performance and high-low temperature performance of the material can be improved.

[0066] In some embodiments, the step of doping nitrogen atoms on the surface of the third intermediate includes:

[0067] Step S412: mixing the third intermediate and ammonia water at a mass ratio of 1:5, heating to 80°C under an inert atmosphere, and maintaining the reaction for 2 hours to 3 hours; then heating the mixed system to 180°C and maintaining for 1 hour.

[0068] Step S414: cooling the mixed system to room temperature, washing the obtained solid product with deionized water and ethanol, and drying to obtain a mesocarbon microbead negative electrode material.

[0069] In some embodiments, the step of doping the surface of the third intermediate with boron atoms comprises:

[0070] Step S422: The third intermediate and ethyl borate solution are mixed at a mass ratio of 1:2, and the mixture is reacted at room temperature for 6-8 hours under an inert atmosphere; then the mixture is heated to 60°C and kept at this temperature for 2 hours.

[0071] Step S424: The mixture is cooled to room temperature, and the obtained solid product is washed with deionized water and dried to obtain the mesocarbon microbead negative electrode material.

[0072] In a second aspect, the present application also provides a mesocarbon microbead negative electrode material, which is prepared according to the above-mentioned method for preparing a mesocarbon microbead negative electrode material. The mesocarbon microbead negative electrode material prepared by the above-mentioned preparation method has high capacity under different rates, high temperature or low temperature conditions, and has good rate performance and high and low temperature performance.

[0073] In some embodiments, the mesocarbon microbead negative electrode material has a particle size D10 of 5-8 μm; the mesocarbon microbead negative electrode material has a particle size D50 of 10-14 μm; and the mesocarbon microbead negative electrode material has a particle size D90 of 16-25 μm.

[0074] In a third aspect, the present application also provides a negative electrode sheet comprising the above-mentioned mesocarbon microbead negative electrode material.

[0075] In a fourth aspect, the present application also provides a secondary battery comprising the above-mentioned negative electrode sheet.

[0076] In some embodiments, the secondary battery comprises a lithium ion battery, a lithium metal battery, a sodium ion battery, etc.

[0077] In order to make the purpose, technical scheme and advantages of the present application more concise and clear, the present application is described by the following specific embodiments, but the present application is not limited to these embodiments. The embodiments described below are only preferred embodiments of the present application, which can be used to describe the present application, and cannot 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 principles of the present application should be included in the protection scope of the present application.

[0078] Example 1

[0079] (1) First heat treatment: The pitch is heated to 420°C at a heating rate of 10°C / min under an argon atmosphere, then kept at this temperature for 2 hours, and then naturally cooled to room temperature to collect the first intermediate.

[0080] (2) Second heat treatment: the first intermediate was heated to 1500℃ at a heating rate of 5℃ / min under argon atmosphere, then kept for 2 hours, and then cooled to room temperature at a rate of 10℃ / min to obtain a second intermediate.

[0081] (3) Modification layer preparation: the second intermediate was immersed in a silane coupling agent solution for 30 min, then taken out and dried to obtain a third intermediate with a modification layer on the surface.

[0082] (4) Doping nitrogen atoms: the third intermediate and ammonia water were mixed according to a mass ratio of 1:5, heated to 80℃ under inert atmosphere, and kept for 2 hours of reaction, then the mixed system was heated to 180℃ and kept for 1 hour. Then the mixed system was cooled to room temperature, and the obtained solid product was washed with deionized water and ethanol, dried to obtain the mesocarbon microbead negative electrode material.

[0083] Example 2

[0084] The preparation method of the mesocarbon microbead negative electrode material of this example was basically the same as that of Example 1, except that step (4) was doping boron atoms: the third intermediate and ethyl borate solution were mixed according to a mass ratio of 1:2, reacted at room temperature for 6 hours under inert atmosphere; then the mixed system was heated to 60℃ and kept for 2 hours. Then the mixed system was cooled to room temperature, and the obtained solid product was washed with deionized water and dried to obtain the mesocarbon microbead negative electrode material.

[0085] Comparative Example 1

[0086] The negative electrode material of this comparative example was the second intermediate prepared in step (2) of Example 1.

[0087] Negative electrode sheet preparation: the negative electrode material, conductive agent Super P and binder PVDF of the above examples or comparative examples were prepared into a slurry according to a mass ratio of 92:3:5. Then the slurry was coated on a copper foil to prepare a negative electrode sheet.

[0088] Battery preparation: the positive electrode sheet, separator and negative electrode sheet were assembled into a battery cell, then electrolyte was injected, and a test battery was obtained after formation process.

[0089] The above prepared battery was subjected to electrochemical test, and the test method was as follows. The test results are recorded in Table 1.

[0090] Discharge capacity test at different rates: at 25℃, the battery was charged to a specified upper limit voltage, then discharged to a specified lower limit voltage at different rates (0.1C, 0.5C, 1C, 2C, 3C). The discharge capacity was recorded, i.e. the discharge capacity at different rates. Discharge gram capacity = discharge capacity / mass of negative electrode material.

[0091] Discharge capacity test at different temperatures: in different temperature (-20℃, 0℃, 25℃, 60℃) constant temperature box, the battery is charged to the specified upper limit voltage, and then discharged to the specified lower limit voltage at 0.1C rate. Record the discharge capacity, that is, the discharge capacity at different temperatures. Discharge gram capacity = discharge capacity / mass of negative material.

[0092] 100 cycle capacity retention test: the battery is subjected to 100 charge-discharge cycles at 25℃, and the discharge capacity after the 100th cycle is compared with the initial discharge capacity. Capacity retention = (discharge capacity after the 100th cycle / initial discharge capacity) * 100%.

[0093] Table 1

[0094]

[0095] From the data in Table 1, it can be seen that the negative electrode material prepared in Examples 1-2 is used to prepare a secondary battery, and after 100 charge-discharge cycles, the capacity retention is above 93%; at 0.1C-3C rate, or at -20℃-60℃, the discharge gram capacity of Examples 1-2 is higher than that of Comparative Example 1. It can be seen that the negative electrode material prepared by the preparation method of the present application has better rate performance and high-low temperature performance, and better cycle stability.

[0096] Each technical feature of the above-described embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described, however, as long as the combinations of the technical features do not contradict, they should be considered as within the scope of the present disclosure.

[0097] The above-described embodiments only express several embodiments of the present application, facilitate specific and detailed understanding of the technical solutions of the present application, but should not be construed as limiting the scope of patent protection. It should be noted 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 are within the scope of the present application. It should be understood that the technical solutions obtained by those skilled in the art through logical analysis, reasoning or limited experiments on the basis of the technical solutions provided by the present application are within the scope of the appended claims. Therefore, the scope of protection of the present patent should be based on the contents of the appended claims, and the description can be used to explain the contents of the claims.

Claims

1. A method for preparing mesocarbon microbead negative electrode material, characterized by, The method comprises the following steps: a first intermediate is prepared by heating the carbon source to 400-600℃ at a rate of 5-20℃ / min and performing a first heat treatment; a second intermediate is prepared by performing a second heat treatment on the first intermediate at 1000-1500℃; a modified layer is prepared on the surface of the second intermediate to obtain a third intermediate, wherein the modified layer comprises a silane coupling agent and is prepared by immersing the second intermediate in a silane coupling agent solution and then drying; the surface of the third intermediate is doped with nitrogen atoms or boron atoms to obtain the mesocarbon microbead negative electrode material; the step of doping the surface of the third intermediate with nitrogen atoms comprises: the third intermediate and ammonia are mixed in a mass ratio of 1:5, heated to 80℃ in an inert atmosphere, and kept at the temperature for 2-3 hours; then the mixed system is heated to 180℃ and kept at the temperature for 1 hour; the mixed system is cooled to room temperature, the obtained solid product is washed with deionized water and ethanol, and dried to obtain the mesocarbon microbead negative electrode material; or, the step of doping the surface of the third intermediate with boron atoms comprises: the third intermediate and an ethyl borate solution are mixed in a mass ratio of 1:2, reacted at room temperature in an inert atmosphere for 6-8 hours, and then the mixed system is heated to 60℃ and kept at the temperature for 2 hours; the mixed system is cooled to room temperature, the obtained solid product is washed with deionized water, and dried to obtain the mesocarbon microbead negative electrode material.

2. The method for producing mesocarbon microbead negative electrode material according to claim 1, characterized by, In the step of preparing the first intermediate, the heating rate is 5-10℃ / min.

3. The method of producing mesocarbon microbead negative electrode material according to claim 1, characterized by, The first heat treatment is performed for 2-6 hours.

4. The method of producing mesocarbon microbead negative electrode material according to claim 1, characterized by, The first heat treatment is performed in a low-oxygen environment, wherein the volume content of oxygen in the low-oxygen environment is less than or equal to 0.5%.

5. The method of producing mesocarbon microbead negative electrode material according to claim 1, characterized by, The step of preparing the second intermediate comprises: the first intermediate is heated to 1000-1500℃ at a rate of 5-10℃ / min; the first intermediate is kept at 1000-1500℃ for 1-2 hours to perform the second heat treatment; the product after the second heat treatment is cooled to room temperature at a rate of 10-20℃ / min to obtain the second intermediate; The step of preparing the second intermediate is performed in a low-oxygen environment, wherein the volume content of oxygen in the low-oxygen environment is less than or equal to 0.5%.

6. The method of producing mesocarbon microbead negative electrode material according to claim 1, characterized by, The thickness of the modified layer is 5-10 nm.

7. An intermediate phase carbon microbead negative electrode material, characterized by, The mesocarbon microbead negative electrode material is prepared according to the method of any one of claims 1-6; The particle size D10 of the mesocarbon microbead negative electrode material is 5-8 μm, the particle size D50 is 10-14 μm, and the particle size D90 is 16-25 μm.

8. A negative electrode sheet characterized by comprising: The mesocarbon microbead negative electrode material of claim 7 is included.

9. A secondary battery characterized by comprising: The negative electrode sheet of claim 8 is included.

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