Negative electrode composite, method for manufacturing the same, negative electrode sheet, and secondary battery

Abstract

The application relates to a negative electrode composite material and a preparation method thereof, a negative electrode sheet and a secondary battery. The preparation method comprises the following steps: preparing a coating layer on the surface of coke; once granulating the coke with the coating layer on the surface to prepare primary particles; twice granulating the primary particles to prepare secondary particles; once heat treating the secondary particles at 800 DEG C-1200 DEG C to prepare an intermediate; twice heat treating the intermediate at 2000 DEG C-3000 DEG C to prepare the negative electrode composite material; wherein, from the surface of the coke to the outside, the coating layer comprises a first sublayer, a second sublayer and a third sublayer in sequence; the first sublayer comprises at least one of graphene and porous carbon material; the second sublayer comprises at least one of carbon nanotubes and carbon nanofibers; and the third sublayer comprises at least one of carbon black and graphite. The negative electrode composite material prepared by the preparation method has high specific capacity and conductivity.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a negative electrode composite 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 mainly relies on the movement of lithium ions between the positive electrode and the negative electrode to work. The positive electrode material of the lithium ion battery usually includes metal oxides, etc., and the negative electrode material is usually graphite or non-graphite material. The lithium ion battery has the following characteristics: ① high energy density: the energy density of the lithium ion battery is higher than that of the traditional lead-acid battery, nickel-cadmium battery, etc., which can provide longer endurance time. ② High voltage: the voltage of the lithium ion battery is usually higher than that of the traditional battery, so it has better application effect in some devices that require high voltage. ③ No memory effect: the lithium ion battery has no memory effect and can be charged at any time without affecting the performance of the battery. ④ Long life: the lithium ion battery has a relatively long life and can be used for multiple cycles, which is suitable for devices that need to be used for a long time. ⑤ Environmentally friendly: the lithium ion battery does not contain harmful substances such as mercury and lead, and is friendly to the environment. Due to the above characteristics, the lithium ion battery is widely used in consumer electronics, power battery, energy storage, etc.

[0003] Artificial graphite is a commonly used negative electrode material for lithium ion batteries, which has controllable structural characteristics. However, the traditional artificial graphite has low conductivity and specific capacity, which limits the improvement of the rate performance and energy density of the lithium ion battery when used as a negative electrode material for lithium ion batteries. SUMMARY

[0004] Therefore, it is necessary to provide a negative electrode composite material with high energy density and rate performance, and a preparation method thereof.

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

[0006] In one aspect of the present application, a preparation method of a negative electrode composite material is provided, which comprises the following steps:

[0007] Preparation of a coating layer on the surface of the coke;

[0008] Primary granulation treatment of the coke with the coating layer on the surface to prepare primary particles;

[0009] Secondary granulation treatment of the primary particles to prepare secondary particles;

[0010] Primary heat treatment of the secondary particles at 800-1200°C to prepare an intermediate;

[0011] Secondary heat treatment of the intermediate at 2000-3000°C to prepare the negative electrode composite material;

[0012] The coating layer comprises, from the surface of the coke outward, a first sub-layer, a second sub-layer and a third sub-layer in sequence.

[0013] The first sub-layer comprises at least one of graphene and porous carbon material.

[0014] The second sub-layer comprises at least one of carbon nanotube and carbon nanofiber.

[0015] The third sub-layer comprises at least one of carbon black and graphite.

[0016] In one embodiment, the first sub-layer comprises graphene, the second sub-layer comprises carbon nanotube, and the third sub-layer comprises carbon black.

[0017] The first sub-layer and the second sub-layer are respectively prepared by a chemical vapor deposition process, and the third sub-layer is prepared by physical mixing.

[0018] In one embodiment, the first sub-layer comprises porous carbon material, the second sub-layer comprises carbon nanofiber, and the third sub-layer comprises graphite.

[0019] The first sub-layer is prepared by a solvothermal method, the second sub-layer is respectively prepared by an electrospinning process, and the third sub-layer is prepared by a chemical vapor deposition process.

[0020] In one embodiment, the secondary granulation process comprises:

[0021] The primary particles are heat treated at 500-1000°C.

[0022] The heat-treated primary particles and the binder are mixed and compacted to prepare the secondary particles.

[0023] In one embodiment, the primary granulation process is performed by a dry granulator.

[0024] The average particle size of the primary particles is 10-30 μm.

[0025] In one embodiment, the primary heat treatment comprises:

[0026] The secondary particles are heated from room temperature to 800-1200°C at a rate of 50-200°C / h, and held for 1-10 hours.

[0027] In a second aspect, the application further provides a negative electrode composite material prepared according to the above method.

[0028] In one embodiment, the particle size D10 of the negative electrode composite material is 6-10 μm; the particle size D50 of the negative electrode composite material is 11-14 μm; and the particle size D90 of the negative electrode composite material is 17-26 μm.

[0029] In a third aspect, the application further provides a negative electrode sheet comprising the negative electrode composite material.

[0030] In a fourth aspect, the application further provides a secondary battery comprising the negative electrode sheet.

[0031] The preparation method of the negative electrode composite material provided in the embodiments of the application comprises the following steps: preparing a multilayer coating structure on the surface of the coke, then performing twice granulation treatment to obtain secondary particles with controllable particle size and compact structure, and then performing twice heat treatment to improve the crystallinity and order degree of the crystal structure of the material. The prepared negative electrode composite material has high specific capacity and good conductivity.

[0032] In addition, the negative electrode composite material prepared by the preparation method can also improve the cycle life of the secondary battery. DETAILED DESCRIPTION

[0033] 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.

[0034] In this document, the technical features described in an open form include both the closed technical solution consisting of the listed features and the open technical solution containing the listed features.

[0035] In this document, when referring to a numerical interval, the numerical interval is considered to be continuous and includes the minimum value and the maximum value of the range and each value between the minimum value and the maximum value, unless otherwise specified. Further, when the range refers to an integer, each integer between the minimum value and the maximum value of the range is included. In addition, when multiple ranges are provided to describe a feature or a characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges falling within the range.

[0036] In this document, when referring to a data range, if only the unit is indicated after the right endpoint, it means that the units of the left endpoint and the right endpoint are the same. For example, 800-850 nm means that the units of the left endpoint "800" and the right endpoint "850" are both nm (nanometer).

[0037] Only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with any other lower limit to form a range not explicitly recited, as can any upper limit with any other upper limit to form a range not explicitly recited. Further, each individual disclosed point or singular number can be combined with any other point or singular number as a lower limit or upper limit to form a range not explicitly recited.

[0038] The temperature parameters herein, if not specifically defined, allow both constant temperature treatment and treatment within a certain temperature range. The constant temperature treatment allows fluctuations within the accuracy of the instrument control.

[0039] In the present disclosure, the terms "first", "second", etc. are used only for the purpose of description, and should not be understood as indicating or implying relative importance or implying the number of the technical features indicated. Therefore, the features defined with "first", "second", etc. can explicitly or implicitly include at least one of the features. In the description of the application, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise specifically defined. In the description of the present application, the meaning of "several" is at least one, such as one, two, etc., unless otherwise specifically defined.

[0040] If not specifically stated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0041] If not specifically stated, all steps of the present application can be performed in sequence or randomly, preferably in sequence. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method also comprises step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0042] 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.

[0043] In an embodiment of the present application, a preparation method of a negative electrode composite material is provided, comprising the following steps:

[0044] Step S100: preparing a coating layer on the surface of the coke. The coating layer comprises, from the surface of the coke outward, a first sub-layer, a second sub-layer and a third sub-layer in sequence. The first sub-layer comprises at least one of graphene and porous carbon material. The second sub-layer comprises at least one of carbon nanotube and carbon nanofiber. The third sub-layer comprises at least one of carbon black and graphite.

[0045] The first sub-layer is in contact with the surface of the coke, has good bonding strength and electrochemical stability; the second sub-layer comprises carbon nanotube and carbon nanofiber, has good electrical conductivity; and the third sub-layer comprises carbon black and graphite, has good mechanical properties and chemical stability, so as to protect the internal structure from being eroded by electrolyte. Compared with the traditional single-layer coating, the coating layer structure can improve the electrochemical stability, electrical conductivity and structural uniformity.

[0046] In one embodiment, the first sub-layer comprises graphene, the second sub-layer comprises carbon nanotube, and the third sub-layer comprises carbon black. The first sub-layer and the second sub-layer are prepared by a chemical vapor deposition process, and the third sub-layer is prepared by physical mixing. Specifically, the step of preparing the coating layer comprises: growing a uniform and continuous graphene layer on the surface of the coke as the first sub-layer by using a chemical vapor deposition technology; then growing carbon nanotube on the surface of the graphene layer as the second sub-layer by using the chemical vapor deposition technology; and mixing the coke with the first sub-layer and the second sub-layer with carbon black, so that the carbon black is uniformly distributed on the surface of the second sub-layer to form the third sub-layer.

[0047] In one embodiment, the first sub-layer comprises porous carbon material, the second sub-layer comprises carbon nanofiber, and the third sub-layer comprises graphite. The first sub-layer is prepared by a solvothermal method, the second sub-layer is prepared by an electrospinning process, and the third sub-layer is prepared by a chemical vapor deposition process. Specifically, the step of preparing the coating layer comprises: depositing a porous carbon structure on the surface of the coke by using a solvothermal method to form the first sub-layer; then growing carbon nanofiber on the surface of the porous carbon layer by using an electrospinning technology to form the second sub-layer; and depositing a graphite layer on the surface of the second sub-layer by using a chemical vapor deposition technology.

[0048] Step S200: once granulating the coke with the coating layer on the surface to prepare primary particles.

[0049] In one embodiment, the once granulating is performed by using a dry granulator. The coke with the coating layer can be compressed and granulated by the dry granulator to form the primary particles, and the preparation process is simple and has low energy consumption. It can be understood that the particle size of the primary particles can be controlled by adjusting the parameters such as the rotation speed and pressure of the drum of the dry granulator, which will not be described herein.

[0050] In some embodiments, the average particle size of the primary particles is 10-30 μm. Controlling the average particle size of the primary particles within the above range, the primary particles have a suitable particle size and specific surface area, which facilitates the subsequent preparation process. Alternatively, the average particle size of the primary particles is 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, or any range defined by any two of the above values.

[0051] Step S300: The primary particles are subjected to secondary granulation to prepare secondary particles.

[0052] In one embodiment, step S300 comprises step S310 and step S320.

[0053] Step S310: The primary particles are heat treated at 500-1000 °C. By heat treating the primary particles within the above temperature range, recrystallization of the primary particles and bonding between the particles are promoted. Alternatively, the heat treatment temperature is 500 °C, 550 °C, 600 °C, 650 °C, 700 °C, 750 °C, 800 °C, 850 °C, 900 °C, 950 °C, 1000 °C, or any range defined by any two of the above values.

[0054] Step S320: The heat treated primary particles and a binder are mixed and compacted to prepare secondary particles. By mixing and compacting the primary particles and the binder, the bonding force between the primary particles and the structural stability are increased, thereby forming secondary particles with a compact and stable structure.

[0055] Step S400: The secondary particles are subjected to a first heat treatment at 800-1200 °C to prepare an intermediate. By subjecting the secondary particles to a first heat treatment within the above temperature range, impurities on the surface of the secondary particles are removed, and the purity and stability of the material are improved. Alternatively, the first heat treatment temperature is 800 °C, 900 °C, 1000 °C, 1100 °C, 1200 °C, or any range defined by any two of the above values.

[0056] In one embodiment, step S400 comprises: heating the secondary particles from room temperature to 800-1200 °C at a rate of 50-200 °C / h, and holding for 1-10 hours. Alternatively, the heating rate is 50 °C / h, 60 °C / h, 80 °C / h, 100 °C / h, 120 °C / h, 140 °C / h, 150 °C / h, 160 °C / h, 180 °C / h, 200 °C / h, or any range defined by any two of the above values. The holding time is 1 hour, 2 hours, 4 hours, 5 hours, 6 hours, 8 hours, 10 hours, or any range defined by any two of the above values.

[0057] In some embodiments, the first heat treatment is performed in an inert gas or reducing gas atmosphere. Specifically, the inert gas includes nitrogen or argon. The reducing gas includes hydrogen.

[0058] Step S500: the intermediate is subjected to a second heat treatment at 2000-3000°C to prepare the negative electrode composite material. By performing the second heat treatment at the above temperature, the crystallinity of the material can be further improved, and the material is endowed with better conductivity and electrochemical performance. Alternatively, the temperature of the second heat treatment is 2000°C, 2200°C, 2400°C, 2600°C, 2800°C, 3000°C or any range consisting of any of the above values.

[0059] In some embodiments, the second heat treatment is performed for 4-36 hours. Alternatively, the second heat treatment is performed for 4 hours, 8 hours, 12 hours, 18 hours, 24 hours, 30 hours, 36 hours or any range consisting of any of the above values.

[0060] In some embodiments, the second heat treatment is performed in an inert gas or reducing gas atmosphere. Specifically, the inert gas includes nitrogen or argon. The reducing gas includes hydrogen.

[0061] In some embodiments, the preparation method further comprises step S600.

[0062] Step S600: a conductive coating is prepared on the surface of the negative electrode composite material prepared in step S500. The material of the conductive coating includes a conductive polymer, a metal oxide and a conductive carbon material.

[0063] Specifically, step S600 comprises:

[0064] Step S610: the material of the conductive coating is dispersed in a solvent to prepare a coating slurry.

[0065] Step S620: the coating slurry is used to prepare the conductive coating on the surface of the negative electrode composite material by a dipping method or a spraying method.

[0066] The above preparation method prepares a multi-layer coating structure on the surface of the coke, and then prepares a secondary particle with controllable particle size and dense structure through two granulation processes, and further improves the crystallinity and order degree of the crystal structure of the material through two heat treatments. The prepared negative electrode composite material has high specific capacity and good conductivity.

[0067] In addition, the negative electrode composite material prepared by the above preparation method can also improve the cycle life when used in a secondary battery.

[0068] In a second aspect, the present application provides a negative electrode composite material, which is prepared according to the above-mentioned method for preparing a negative electrode composite material. The negative electrode composite material has a high specific capacity, good electrical conductivity and good cycle stability.

[0069] In one embodiment, the particle size D10 of the negative electrode composite material is 6 μm to 10 μm; the particle size D50 of the negative electrode composite material is 11 μm to 14 μm; and the particle size D90 of the negative electrode composite material is 17 μm to 26 μm.

[0070] In some embodiments, the tap density of the negative electrode composite material is ≥ 1.0 g / cm 3 .

[0071] In some embodiments, the specific surface area of the negative electrode composite material is ≤ 2.5 m 2 / g.

[0072] In a third aspect, the present application provides a negative electrode sheet comprising the above-mentioned negative electrode composite material. The negative electrode sheet comprising the above-mentioned negative electrode composite material has the beneficial effects of the above-mentioned negative electrode composite material, and has good electrical conductivity, good cycle stability and a high specific capacity.

[0073] In a fourth aspect, the present application provides a secondary battery comprising the above-mentioned negative electrode sheet. The secondary battery comprising the above-mentioned negative electrode sheet has a high energy density, good rate performance and a long cycle life.

[0074] 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 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 principle of the present application should be included in the protection scope of the present application.

[0075] Embodiment 1

[0076] The method for preparing the negative electrode composite material of the present embodiment comprises the following steps:

[0077] (1) Preparation of the coating layer: a uniform and continuous graphene layer is grown on the surface of the coke as a first sublayer by using chemical vapor deposition technology; then carbon nanotubes are grown on the surface of the graphene layer as a second sublayer by using chemical vapor deposition technology; and then the coke with the first sublayer and the second sublayer is mixed with carbon black, so that the carbon black is uniformly distributed on the surface of the second sublayer to form a third sublayer, thereby obtaining the coating layer modified coke.

[0078] (2) Primary granulation: the coke obtained in step (1) is subjected to primary granulation treatment by using a dry granulator to obtain primary particles with an average particle size of 15 μm.

[0079] (3) Secondary granulation: the primary particles obtained in step (2) are heat treated at 750°C for 2 hours and then cooled to room temperature. The heat treated primary particles are mixed with a binder at a mass ratio of 100:1, mechanically compacted to obtain secondary particles.

[0080] (4) Primary heat treatment: the secondary particles of step (3) are heated from room temperature to 1000°C at a rate of 100°C / h under a nitrogen atmosphere, and kept for 5 hours. After the heat treatment, the product is cooled to room temperature.

[0081] (5) Secondary heat treatment: the product of step (4) is heat treated at 2500°C for 10 hours under a nitrogen atmosphere. After the heat treatment, the product is cooled to room temperature to obtain the negative electrode composite material of the present example.

[0082] Example 2

[0083] The preparation method of the negative electrode composite material of the present example is basically the same as that of Example 1, except that:

[0084] In step (1), the preparation of the coating layer is as follows: a porous carbon structure is deposited on the surface of the coke by using a solvothermal method to form a first sub-layer; then carbon nanofibers are grown on the surface of the porous carbon layer by using an electrospinning technique to form a second sub-layer; and then a layer of graphite is deposited on the surface of the second sub-layer by using a chemical vapor deposition technique to obtain the coke modified by the coating layer.

[0085] Comparative Example 1

[0086] In the present comparative example, commercially available artificial graphite is used as the negative electrode material.

[0087] Comparative Example 2

[0088] The preparation method of the negative electrode composite material of the present comparative example is basically the same as that of Example 1, except that:

[0089] In step (1), the preparation of the coating layer is as follows: a uniform and continuous graphene layer is grown on the surface of the coke by using a chemical vapor deposition technique as the coating layer.

[0090] Preparation of working electrode: the negative electrode material, the conductive agent Super P and the binder PVDF of the above examples or comparative examples are prepared into a slurry at a mass ratio of 92:3:5. Then the slurry is coated on a copper foil to prepare a working electrode.

[0091] Battery preparation: lithium foil as the counter electrode; electrolyte containing 1M LiPF6, its solvent is a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), methyl ethyl carbonate (EMC) in a volume ratio of 1:1:1, and the electrolyte also contains 1wt% of additive vinylene carbonate (VC). The working electrode, the separator and the counter electrode are laminated to prepare the battery cell, and then the electrolyte is injected to prepare the battery to be tested.

[0092] The battery to be tested prepared above is subjected to electrochemical test, and the test method is as follows. The test results are recorded in Table 1.

[0093] Specific capacity test: charge the battery to the cut-off voltage at room temperature by constant current and constant voltage mode, and record the charge capacity at this time. Then discharge the battery to the cut-off voltage at room temperature by constant current mode, and record the discharge capacity at this time. Specific capacity = discharge capacity / mass of negative electrode material.

[0094] 300 cycle capacity retention rate test: the battery is subjected to 300 charge and discharge cycles, and the discharge capacity after the 300th cycle is compared with the initial discharge capacity. Capacity retention rate = (discharge capacity after the 300th cycle / initial discharge capacity) * 100%.

[0095] 1C discharge capacity test: charge and discharge the battery to be tested at 1C discharge rate, and record the discharge capacity of the battery to be tested.

[0096] First charge and discharge efficiency test: charge the test battery to the full state of charge, and record the charge capacity; then discharge for the first time, and record the discharge capacity. First charge and discharge efficiency = (first discharge capacity / first charge capacity) * 100%.

[0097] Table 1

[0098]

[0099]

[0100] As can be seen from the data in Table 1, the negative electrode composite prepared in Examples 1-2 has high specific capacity, first charge and discharge efficiency, cycle capacity retention rate and rate performance. It can be seen that the above preparation method, by reasonably designing the structure of the coating layer and adjusting the granulation treatment and heat treatment process, the negative electrode composite prepared has high energy density, good rate performance and long cycle life.

[0101] The technical features of the above-described embodiments can be combined in any manner. In order to make the description concise, all possible combinations of the technical features in the above-described embodiments are not described, but as long as the combinations of the technical features do not exist, they should be considered as the scope of the description.

[0102] The above-described embodiments only express several implementation manners of the present application, facilitate specific and detailed understanding of the technical solutions of the present application, but cannot be understood as a limitation on the patent protection scope of the present application. It should be noted that, for ordinary skilled persons in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope 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 the skilled person in the art all belong to the protection scope of the appended claims of the present application. Therefore, the patent protection scope of the present application should be subject to the content of the appended claims, and the description can be used to explain the content of the claims.

Claims

1. A method for producing a negative electrode composite material, characterized by, The method comprises the following steps: preparing a coating layer on the surface of the coke; primary granulating the coke with the coating layer on the surface to prepare primary particles; secondary granulating the primary particles to prepare secondary particles; primary heat-treating the secondary particles at 800-1200°C to prepare an intermediate; secondary heat-treating the intermediate at 2000-3000°C to prepare the negative electrode composite material; wherein, from the surface of the coke outward, the coating layer comprises a first sub-layer, a second sub-layer and a third sub-layer in sequence; the first sub-layer comprises at least one of graphene and porous carbon material; the second sub-layer comprises at least one of carbon nanotube and carbon nanofiber; the third sub-layer comprises at least one of carbon black and graphite; the secondary granulating process comprises: heat-treating the primary particles at 500-1000°C; mixing the heat-treated primary particles and a binder, and compacting to prepare the secondary particles.

2. The method of claim 1, wherein the negative electrode composite is prepared by mixing the active material, the binder, and the conductive agent. the first sub-layer comprises graphene, the second sub-layer comprises carbon nanotube, and the third sub-layer comprises carbon black; wherein, the first sub-layer and the second sub-layer are prepared by a chemical vapor deposition process, and the third sub-layer is prepared by physical mixing.

3. The method of claim 1, wherein the negative electrode composite is prepared by mixing the carbon material, the binder, and the lithium metal oxide. the first sub-layer comprises porous carbon material, the second sub-layer comprises carbon nanofiber, and the third sub-layer comprises graphite; wherein, the first sub-layer is prepared by a solvothermal method, the second sub-layer is prepared by an electrospinning process, and the third sub-layer is prepared by a chemical vapor deposition process.

4. The method of producing a negative electrode composite according to any one of claims 1 to 3, characterized by, the primary granulating process is performed by a dry granulator; and / or, the average particle size of the primary particles is 10-30 μm.

5. The method of producing a negative electrode composite according to any one of claims 1 to 3, characterized by, the primary heat-treating process comprises: ramping the secondary particles from room temperature to 800-1200°C at a rate of 50-200°C / h, and holding for 1-10 hours.

6. A negative electrode composite, characterized by comprising: prepared according to the method of any one of claims 1-5.

7. The negative electrode composite of claim 6, wherein the particle size D10 of the negative electrode composite material is 6-10 μm, the particle size D50 of the negative electrode composite material is 11-14 μm, and the particle size D90 of the negative electrode composite material is 17-26 μm.

8. A negative electrode sheet characterized by comprising: comprising the negative electrode composite material of claim 6 or 7.

9. A secondary battery characterized by comprising: comprising the negative electrode sheet of claim 8.

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