Composite graphite materials and their preparation methods, negative electrode sheets, secondary batteries

Abstract

This application discloses a composite graphite material and its preparation method, a negative electrode sheet, and a secondary battery. The composite graphite material includes bulk particles and a coating layer located on at least a portion of the surface of the bulk particles. The bulk particles are secondary particles formed by the aggregation of two or more primary particles, and the bulk particles include artificial graphite. The coating layer includes amorphous carbon. The air oxidation temperature T0 of the composite graphite material is 630℃~730℃. The composite graphite material of this application enables the secondary battery to have high energy density while also exhibiting significantly improved fast charging performance and low-temperature power performance.

Description

[0001] This application is a divisional application of patent application 202111079771.0, filed on September 15, 2021, entitled "Composite Graphite Material and Preparation Method Thereof, Negative Electrode Sheet, and Secondary Battery". TECHNICAL FIELD

[0002] The present application belongs to the technical field of batteries, and in particular relates to a composite graphite material and a preparation method thereof, a negative electrode sheet, and a secondary battery. BACKGROUND

[0003] Secondary batteries rely on the reciprocating intercalation and deintercalation of active ions between the positive electrode and the negative electrode to charge and discharge, and have the outstanding characteristics of high energy density, long cycle life, and no pollution, no memory effect. Therefore, as a clean energy, secondary batteries have gradually penetrated from electronic products to large-scale device fields such as electric vehicles to adapt to the sustainable development strategy of the environment and energy. However, compared with the quick and timely refueling of traditional fuel vehicles, electric vehicles are generally charged at a small rate, which often requires a long charging time, causing consumers to be anxious about the range, and limiting the rapid popularization of electric vehicles. SUMMARY

[0004] The purpose of the present application is to provide a composite graphite material and a preparation method thereof, a negative electrode sheet, and a secondary battery, aiming to make the secondary battery have high energy density, and also have greatly improved rapid charging performance and low-temperature power performance.

[0005] The first aspect of the present application provides a composite graphite material, which comprises body particles and a coating layer on at least a part of the surface of the body particles, the body particles are secondary particles formed by the aggregation of two or more primary particles, the body particles comprise artificial graphite, the coating layer comprises amorphous carbon, and the air oxidation temperature T0 of the composite graphite material is 630-730℃. The air oxidation temperature T0 is the temperature corresponding to the intersection point of two tangent lines at two points on the thermogravimetric curve of the composite graphite material corresponding to 500℃ and T1 temperature, the T1 temperature is the peak top temperature of the maximum area peak in the differential thermogravimetric curve of the composite graphite material, and the thermogravimetric curve and the differential thermogravimetric curve can be obtained by thermogravimetric analysis under the following conditions: sample mass 10±0.05mg, purging gas is air and airflow rate is 60mL / min, temperature rising rate is 5℃ / min, and test temperature range is 35-950℃.

[0006] The air oxidation temperature T0 of the composite graphite material can accurately represent the temperature at which the composite graphite material starts to lose weight during air oxidation, and can accurately reflect the number of end faces and defects of the composite graphite material. When the air oxidation temperature T0 of the composite graphite material is 630-730°C, the number of end faces and defects contained in the composite graphite material is moderate, the composite graphite material has good active ion and electron transport performance, the active ion and electron have a fast surface charge exchange speed on the surface of the composite graphite material, and the active ion has a high solid-phase transport capacity in the composite graphite material. Therefore, the secondary battery can have greatly improved rapid charging performance and low-temperature power performance while maintaining high energy density.

[0007] In any embodiment of the present application, the air oxidation temperature T0 of the composite graphite material is 660-710°C. The air oxidation temperature T0 of the composite graphite material in the appropriate range can make the composite graphite material have a more appropriate number of end faces and defects, further improve the active ion and electron transport performance, and improve the rapid charging performance and low-temperature power performance of the secondary battery.

[0008] In any embodiment of the present application, the composite graphite material further comprises a kinetic carbon material.

[0009] In any embodiment of the present application, the kinetic carbon material is located at at least part of the interfaces between primary particles in the bulk particles.

[0010] In any embodiment of the present application, the kinetic carbon material is located in the coating layer.

[0011] In any embodiment of the present application, the kinetic carbon material is simultaneously located at at least part of the interfaces between primary particles in the bulk particles and in the coating layer.

[0012] In any embodiment of the present application, the kinetic carbon material raw material is selected from one or more of hard carbon, micro-expanding graphite, expanding graphite, and graphene, and the interlayer spacing d 002 of the (002) crystal plane of the kinetic carbon material raw material is ≥0.3358 nm.

[0013] Alternatively, the interlayer spacing d 002 of the (002) crystal plane of the kinetic carbon material raw material is 0.3359-0.3366 nm.

[0014] When the kinetic carbon material obtained from the above kinetic carbon material raw material is uniformly distributed in the bulk particles and / or the coating layer of the composite graphite material, it is beneficial to the rapid embedding and extraction of active ions, thereby improving the transport performance of active ions and electrons, and further improving the rapid charging performance and low-temperature power performance of the secondary battery without loss of energy density of the secondary battery.

[0015] In any embodiment of the present application, the kinetic carbon material has a mass percentage of 1% to 30% based on the total mass of the composite graphite material. Alternatively, the kinetic carbon material has a mass percentage of 8% to 15%. The mass percentage of the kinetic carbon material in the above range can make the composite graphite material have a high capacity and a high active ion solid-phase transmission capacity and a high active ion and electron charge exchange speed.

[0016] In any embodiment of the present application, the composite graphite material has a layer spacing d 002 of (002) crystal face of 0.3355 nm to 0.3364 nm. Alternatively, the composite graphite material has a layer spacing d 002 of (002) crystal face of 0.3356 nm to 0.3361 nm. The composite graphite material has a higher layer spacing d 002 , which can improve the solid-phase transmission capacity of the active ion, the rapid charging performance and the low-temperature power performance of the secondary battery.

[0017] In any embodiment of the present application, the composite graphite material has a volume average particle size Dv50 of 8.5 μm to 14.5 μm. Alternatively, the composite graphite material has a volume average particle size Dv50 of 10 μm to 12 μm. The composite graphite material has a volume average particle size Dv50 in the above range, which can make the composite graphite material have better active ion and electron transmission performance and rapid charging performance, and the composite graphite material also has a higher powder compaction density.

[0018] In any embodiment of the present application, the bulk particles have a volume average particle size Dv50 of 7.5 μm to 13.5 μm. Alternatively, the bulk particles have a volume average particle size Dv50 of 9.0 μm to 11.5 μm. The bulk particles of the composite graphite material have a volume average particle size Dv50 in the above range, which can make the composite graphite material have a better active ion and electron transmission performance and a higher capacity.

[0019] In any embodiment of the present application, the ratio of the volume average particle size Dv50 of the primary particles to the volume average particle size Dv50 of the secondary particles composed of the primary particles is 0.45 to 0.75. Alternatively, the ratio of the volume average particle size Dv50 of the primary particles to the volume average particle size Dv50 of the secondary particles composed of the primary particles is 0.55 to 0.65. The above ratio in the above range can make the bulk particles of the composite graphite material have a better secondary particle degree, which is beneficial to improving the active ion and electron transmission performance of the composite graphite material and making the composite graphite material have a higher structural stability.

[0020] In any embodiment of the present application, the mass percentage of amorphous carbon in the coating layer is 1% to 8% based on the total mass of the composite graphite material. Alternatively, the mass percentage of amorphous carbon in the coating layer is 2% to 5%. The content of amorphous carbon in the appropriate range can make the composite graphite material have high capacity while also having high active ion solid-phase transmission capacity.

[0021] In any embodiment of the present application, the powder compaction density of the composite graphite material under a force of 20,000 N is 1.45 g / cm 3 to 1.75 g / cm 3 . Alternatively, the powder compaction density of the composite graphite material under a force of 20,000 N is 1.55 g / cm 3 to 1.65 g / cm 3 . The powder compaction density of the composite graphite material in the appropriate range can make the negative electrode film layer have high compaction density, and thus the secondary battery has high energy density; in addition, the composite graphite material has strong ability to maintain the pore structure of the negative electrode film layer during the cycle process, and the electrolyte wettability of the negative electrode sheet is better, thus also being beneficial to improving the cycle performance of the secondary battery.

[0022] The second aspect of the present application provides a method for preparing a composite graphite material, comprising the steps of: S10, providing coke powder or coke powder added with kinetic carbon material raw material powder, and performing graphitization treatment on the coke powder or the coke powder added with kinetic carbon material raw material powder to obtain bulk particles, the bulk particles being secondary particles formed by aggregation of two or more primary particles, and the bulk particles comprising artificial graphite; S20, mixing the bulk particles with an organic carbon source, or mixing the bulk particles with an organic carbon source and the kinetic carbon material raw material powder, and forming a coating layer comprising amorphous carbon on at least part of the surface of the bulk particles after carbonization treatment to obtain the composite graphite material. In at least one of steps S10 and S20, the kinetic carbon material raw material powder is added, and the kinetic carbon material raw material is selected from one or more of hard carbon, micro-expanding graphite, expanding graphite, and graphene, and the interlayer spacing d 002 of the (002) crystal plane of the kinetic carbon material raw material is ≥0.3358 nm.

[0023] The air oxidation temperature T0 of the obtained composite graphite material is 630-730°C, the air oxidation temperature T0 is the temperature corresponding to the intersection of two lines corresponding to two points on the thermogravimetric curve of the composite graphite material, respectively 500°C and T1 temperature, the T1 temperature is the peak top temperature of the maximum area peak in the differential thermogravimetric curve of the composite graphite material, the thermogravimetric curve and the differential thermogravimetric curve can be obtained by thermogravimetric analysis under the following conditions: sample mass 10±0.05mg, purge gas is air and the gas flow rate is 60mL / min, the temperature rising rate is 5°C / min, the test temperature range is 35-950°C.

[0024] The preparation method of the composite graphite material of the present application is simple in operation and controllable in cost, and can be mass-produced in industry. The method of the present application can obtain a composite graphite material with moderate end face and defect content, and then the secondary battery has greatly improved rapid charging performance and low temperature power performance on the premise of high energy density.

[0025] In any embodiment of the present application, the interlayer spacing d of the (002) crystal plane of the kinetic carbon material raw material is 0.3359-0.3366nm. 002 In any embodiment of the present application, the interlayer spacing d of the (002) crystal plane of the kinetic carbon material raw material is 0.3359-0.3366nm.

[0026] In any embodiment of the present application, the total mass percentage of the kinetic carbon material raw material powder added in steps S10 and S20 is 1-30% based on the total mass of the obtained composite graphite material. Alternatively, the total mass percentage of the kinetic carbon material raw material powder added in steps S10 and S20 is 8-15%.

[0027] In any embodiment of the present application, the volume average particle size Dv50 of the coke powder is 6-12μm. Alternatively, the volume average particle size Dv50 of the coke powder is 8-10μm.

[0028] In any embodiment of the present application, the volume average particle size Dv50 of the kinetic carbon material raw material powder is 3-12μm. Alternatively, the volume average particle size Dv50 of the kinetic carbon material raw material powder is 4-9μm.

[0029] In any embodiment of the present application, the ratio of the volume average particle size Dv50 of the coke powder to the volume average particle size Dv50 of the kinetic carbon material raw material powder is 1.05-1.75. Alternatively, the ratio of the volume average particle size Dv50 of the coke powder to the volume average particle size Dv50 of the kinetic carbon material raw material powder is 1.2-1.5. The ratio of the volume average particle size Dv50 of the coke powder to the volume average particle size Dv50 of the kinetic carbon material raw material powder in a suitable range can make the bulk particles of the composite graphite material have better secondary particle degree.

[0030] In any of the embodiments of the present application, the method further comprises the step of adding a binder in S10, mixing the binder with the coke powder, and then granulating and graphitizing to obtain the bulk particles. Alternatively, the method further comprises the step of adding a binder in S10, mixing the binder with the coke powder to which the kinetic carbon material raw material powder is added, and then granulating and graphitizing to obtain the bulk particles. The addition of the binder can make the bulk particles of the composite graphite material have a better secondary particle degree, which is conducive to improving the active ion and electron transport performance of the composite graphite material while making it have higher structural stability.

[0031] In any of the embodiments of the present application, the mass percentage content of the binder is 3% to 12% based on the total mass of the obtained composite graphite material. Alternatively, the mass percentage content of the binder is 5% to 8%. The content of the binder in a suitable range can avoid excessive agglomeration of the particles, so that the bulk particles of the composite graphite material have a better secondary particle degree.

[0032] In any of the embodiments of the present application, the binder is selected from pitch.

[0033] In any of the embodiments of the present application, the volume average particle size Dv50 of the particles obtained after granulation is 8 μm to 14 μm. Alternatively, the volume average particle size Dv50 of the particles obtained after granulation is 9.5 μm to 12 μm.

[0034] In any of the embodiments of the present application, in S20, the organic carbon source is selected from one or more of coal pitch, petroleum pitch, phenolic resin, and coconut shell. Alternatively, the organic carbon source is selected from petroleum pitch.

[0035] In any of the embodiments of the present application, the amount of the organic carbon source added is such that the mass percentage content of the amorphous carbon obtained after carbonization of the organic carbon source is 1% to 8% based on the total mass of the obtained composite graphite material. Alternatively, the amount of the organic carbon source added is such that the mass percentage content of the amorphous carbon obtained after carbonization of the organic carbon source is 2% to 5%. The amount of the organic carbon source added in a suitable range can make the composite graphite material have high gravimetric capacity while also having high active ion solid-phase transport capacity.

[0036] The third aspect of the present application provides a negative electrode tab, which comprises a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, and the negative electrode film layer comprises the composite graphite material according to the first aspect of the present application or prepared by the method according to the second aspect of the present application.

[0037] In any of the embodiments of the present application, the negative electrode film layer further comprises an additive selected from one or more of hard carbon, micro-expanding graphite, expanding graphite, and graphene, and the additive has a layer spacing d of (002) crystal face of 0.34 nm to 0.36 nm.002 ≥0.3358nm. These additives have good active ion and electron transport performance, and can make the secondary battery have greatly improved rapid charging performance and low-temperature power performance on the premise of having high energy density.

[0038] In any embodiment of the present application, the interlayer spacing d of the crystal face of the additive (002) is 0.3359nm-0.3366nm. 002 is 0.3359nm-0.3366nm.

[0039] In any embodiment of the present application, the mass percentage content of the additive is 1%-20% based on the total mass of the negative electrode film layer. Alternatively, the mass percentage content of the additive is 3%-8%. The mass percentage content of the additive in the appropriate range can make the secondary battery have greatly improved rapid charging performance and low-temperature power performance on the premise of having high energy density. At the same time, the mass percentage content of the additive in the appropriate range is better in maintaining the pore structure of the negative electrode film layer during the cycle process, the electrolyte wettability of the negative electrode plate is better, and the secondary battery can also have good cycle performance.

[0040] The fourth aspect of the present application provides a secondary battery comprising the negative electrode plate of the third aspect of the present application.

[0041] The fifth aspect of the present application provides a battery module comprising the secondary battery of the fourth aspect of the present application.

[0042] The sixth aspect of the present application provides a battery pack comprising one of the secondary battery of the fourth aspect of the present application and the battery module of the fifth aspect of the present application.

[0043] The seventh aspect of the present application provides a power utilization device comprising at least one of the secondary battery of the fourth aspect of the present application, the battery module of the fifth aspect of the present application, and the battery pack of the sixth aspect of the present application.

[0044] The secondary battery of the present application can have greatly improved rapid charging performance and low-temperature power performance on the premise of having high energy density. The battery module, the battery pack and the power utilization device of the present application comprise the secondary battery provided by the present application, and thus at least have the same advantages as the secondary battery. BRIEF DESCRIPTION OF DRAWINGS

[0045] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiments of the present application will be briefly introduced as follows. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of the drawings.

[0046] FIG. 1is a schematic view of another embodiment of the composite graphite material of the present application.

[0047] FIG. 2 is a schematic view of another embodiment of the composite graphite material of the present application.

[0048] FIG. 3 is a schematic view of another embodiment of the composite graphite material of the present application.

[0049] FIG. 4 is a schematic view of an embodiment of the secondary battery of the present application.

[0050] FIG. 5 is a schematic view of an embodiment of the secondary battery of the present application.

[0051] FIG. 6 is a schematic view of an embodiment of the battery module of the present application.

[0052] FIG. 7 is a schematic view of an embodiment of the battery pack of the present application.

[0053] FIG. 8 is a schematic view of an embodiment of the battery pack of the present application. FIG. 4

[0054] FIG. 9 is a schematic view of an embodiment of the power consuming device using the secondary battery of the present application as a power source.

[0055] FIG. 10 is a graph of the thermogravimetric curve and the differential thermogravimetric curve of the composite graphite material of Example 3 and Comparative Example 2. DETAILED DESCRIPTION

[0056] Hereinafter, embodiments of the composite graphite material of the present application, a method for producing the same, a negative electrode sheet, and a secondary battery will be specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there will be cases where unnecessary detailed description is omitted. For example, there will be cases where detailed description of matters that are already well known, and repeated description of practically identical structures, are omitted. This is to avoid the following description becoming unnecessarily lengthy, and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided so that those skilled in the art can fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0057] ​The ranges disclosed herein are intended to be "open" ranges, i.e., the upper and lower limits of the range are not included. The ranges are also intended to include any and all sub-ranges of the range, i.e., all combinations of any two of the range limits, unless otherwise indicated. For example, a range of "1 to 10" is intended to include any number from 1 to 10, including the integers 1 and 10. Unless otherwise indicated, the use of "or" in the disclosed aspects herein is the inclusive, and not the exclusive use. Only the context, and not the number of times an item is used, can determine that it is the exclusive use. For example, the phrase "A uses B or C" means that A can use B, or A can use C, or A can use both B and C. Also, the use of the term "one" or "a" or "the" is intended to be singular as well as plural, unless only the singular form is used. For example, the phrase "one or more of A, B, and C" means that A, B, or C can be present, and that one of A, B, and C can be present, and that two of A, B, and C can be present, and that all of A, B, and C can be present.

[0058] All embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, unless otherwise specified.

[0059] All technical features and optional technical features of the present application can be combined with each other to form new technical solutions, unless otherwise specified.

[0060] All steps of the present application can be performed in sequence or randomly, preferably in sequence, unless otherwise specified. 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 can further comprise 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.

[0061] Unless otherwise specified, "including" and "comprising" mentioned in the present application are open-ended, and can also be closed. For example, "including" and "comprising" can mean that other components not listed can also be included or contained, or only the listed components can be included or contained.

[0062] If not specifically stated, the term "or" in this application is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following satisfy the condition "A or B": A is true (or present) and B is false (or not present); A is false (or not present) and B is true (or present); or both A and B are true (or present).

[0063] In this application, "micro-expansion graphite" refers to graphite with a bulk volume change (i.e. expansion ratio) of 80-200 before and after expansion; "expanded graphite" refers to graphite with a bulk volume change (i.e. expansion ratio) of >200 before and after expansion.

[0064] In this application, "coke raw material" refers to a component that can be processed to obtain "coke", i.e. a raw material for preparing coke; "coke" refers to a product obtained by coking treatment of coke raw material, "coke powder" is completely consistent in composition with "coke", and "coke powder" refers to "coke" in the form of a powder with a certain particle size, which is obtained by crushing and other treatments of "coke".

[0065] In this application, "kinetic carbon material raw material" and "kinetic carbon material raw material powder" are completely consistent in composition, wherein "kinetic carbon material raw material powder" refers to "kinetic carbon material raw material" in the form of a powder with a certain particle size. "Kinetic carbon material" refers to a product obtained by graphitization treatment and / or carbonization treatment of "kinetic carbon material raw material" or "kinetic carbon material raw material powder".

[0066] In this application, "amorphous carbon" refers to a transition state carbon material with very low graphitization crystallization degree, which is in a quasi-amorphous state (or structure with no fixed shape and periodicity). In this application, "amorphous carbon" refers to a product obtained by carbonization treatment of an organic carbon source.

[0067] The key to improving the rapid charging performance of a secondary battery lies in improving the performance of the negative electrode sheet and the negative electrode active material. In order to improve the rapid charging performance of a secondary battery, the prior art usually selects hard carbon as the negative electrode active material, but the specific capacity and the compaction density of hard carbon are low, and it is difficult for a secondary battery to have high energy density, and the cruising range of an electric vehicle is greatly reduced. Using graphite as the negative electrode active material, a secondary battery can have high energy density, but the rapid charging performance and low-temperature power performance of the secondary battery are poor.

[0068] The inventors have proposed a new type of composite graphite material through a large amount of research, which can greatly improve the rapid charging performance and low-temperature power performance of a secondary battery on the premise of high energy density.

[0069] Composite graphite material

[0070] A first aspect of this application provides a composite graphite material comprising bulk particles and a coating layer located on at least a portion of the surface of the bulk particles. The bulk particles are secondary particles formed by the aggregation of two or more primary particles, and the bulk particles comprise artificial graphite. The coating layer comprises amorphous carbon. The air oxidation temperature T0 of the composite graphite material is 630℃~730℃. The air oxidation temperature T0 is the temperature corresponding to the intersection of two tangents at two points corresponding to 500℃ and T1 on the thermogravimetric curve of the composite graphite material. The T1 temperature is the peak temperature of the largest area peak in the differential thermogravimetric curve of the composite graphite material. The thermogravimetric curve and the differential thermogravimetric curve can be obtained by thermogravimetric analysis under the following conditions: sample mass 10±0.05mg, purge gas is air with a flow rate of 60mL / min, heating rate is 5℃ / min, and test temperature range is 35℃~950℃.

[0071] The air oxidation temperature T0 can be determined by thermogravimetric analysis including the following steps: The composite graphite material is subjected to thermogravimetric analysis under the following conditions: a weight of 10±0.05mg, purge gas is air with a flow rate of 60mL / min, heating rate is 5℃ / min, and test temperature range is 35℃~950℃. The thermogravimetric curve (also known as the TG curve) and the differential thermogravimetric curve (also known as the DTG curve) are obtained. The peak temperature T1 of the maximum area peak is read from the differential thermogravimetric curve. The intersection of the two tangents at two points corresponding to the temperatures of 500℃ and T1 is determined on the thermogravimetric curve. The temperature corresponding to the intersection point on the thermogravimetric curve is the air oxidation temperature T0 of the composite graphite material.

[0072] The more end faces and defects graphite has, the more sites within it are available for the insertion and extraction of active ions, resulting in better fast-charging and low-temperature power performance of the secondary battery. The inventors unexpectedly discovered a close correlation between the number of end faces and defects in graphite and the temperature at which weight loss begins during air oxidation. The lower the temperature at which weight loss begins during air oxidation, the more end faces and defects graphite has, and consequently, the better the fast-charging and low-temperature power performance of the secondary battery.

[0073] The inventors unexpectedly discovered that the temperature corresponding to the intersection of the two tangents on the thermogravimetric curve at two points—500℃ and the peak temperature T1 of the maximum area peak, respectively—is the air oxidation temperature T0 of graphite. This temperature accurately represents the temperature at which graphite begins to lose weight during air oxidation, and thus accurately reflects the number of end faces and defects in the graphite. The air oxidation temperature T0 of the composite graphite material in the first aspect of this application is 630℃ to 730℃. At this temperature, the composite graphite material contains a moderate number of end faces and defects, exhibiting good active ion and electron transport properties. The charge exchange rate between active ions and electrons on the surface of the composite graphite material is relatively fast, and the solid-phase transport capacity of active ions within the composite graphite material is high. Therefore, the secondary battery can achieve significantly improved fast charging performance and low-temperature power performance while maintaining high energy density. The inventors also found that existing graphite has a small interlayer spacing and a relatively small number of end faces and defects, resulting in a high air oxidation temperature T0, making it difficult to achieve better fast charging performance and low-temperature power performance in secondary batteries.

[0074] In some embodiments, the air oxidation temperature T0 of the composite graphite material is 630℃~730℃, 640℃~730℃, 650℃~730℃, 660℃~730℃, 670℃~730℃, 680℃~730℃, 690℃~730℃, 700℃~730℃, 710℃~730℃, 720℃~730℃, 630℃~720℃, 640℃~720℃, 650℃~720℃, 660℃~720℃, 670℃~720℃, 680℃~720℃, 690℃~720℃, 700℃~720℃, 710℃~720℃, 630℃~710℃, 640℃~710℃, 650℃~72 ...40℃~710℃, 650℃~720℃, 650℃~720℃, 640℃~710℃, 650℃~720℃, 650℃~720℃, 640℃~710℃, 650℃~720℃ ℃~710℃, 660℃~710℃, 670℃~710℃, 680℃~710℃, 690℃~710℃, 700℃~710℃, 630℃~700℃, 640℃~700℃, 650℃~700℃, 660℃~700℃, 670℃~700℃, 680℃~700℃, 690℃~700℃, 630℃~690℃, 640℃~690℃, 650℃~690℃, 660℃~690℃, 670℃~690℃, 680℃~690℃, 630℃~680℃, 640℃~680℃, 650℃~680℃, 660℃~680℃, or 670℃~680℃.

[0075] When the air oxidation temperature T0 of composite graphite materials is within a suitable range, the composite graphite materials can have more suitable end faces and defect numbers, further improving the active ion and electron transport performance, and enhancing the fast charging performance and low-temperature power efficiency of secondary batteries.

[0076] In some embodiments, the composite graphite material further includes kinetic carbon material. In some embodiments, the kinetic carbon material is located at at least a portion of the interface between primary particles in the bulk particles. In this case, the bulk particles of the negative electrode active material include artificial graphite primary particles and kinetic carbon material located between the primary particles.

[0077] In some embodiments, kinetic carbon material is located within the coating layer. In this case, the coating layer comprises both amorphous carbon and kinetic carbon material.

[0078] In some embodiments, the kinetic carbon material is located simultaneously at at least a portion of the interface between primary particles in the bulk particles and in the coating layer.

[0079] FIG. 1 to FIG. 3 These are schematic diagrams illustrating different embodiments of the composite graphite material of this application. (Refer to...) FIG. 1 to FIG. 3 The composite graphite material includes bulk particles and a coating layer 102 located on at least a portion of the surface of the bulk particles. The bulk particles are secondary particles formed by the aggregation of two or more primary particles 101. (Reference) FIG. 1 The kinetic carbon material 103 may be located at at least a portion of the interface between primary particles 101 in the bulk particles; Reference FIG. 2 The kinetic carbon material 102 may also be located in the coating layer 102; Reference FIG. 3 The kinetic carbon material 103 may also be located at at least part of the interface between primary particles 101 in the bulk particles and in the coating layer 102.

[0080] In some embodiments, the mass percentage of kinetic carbon material is 1% to 30% based on the total mass of the composite graphite material. For example, the mass percentage of kinetic carbon material is 3% to 30%, 3% to 25%, 3% to 20%, 3% to 15%, 5% to 30%, 5% to 25%, 5% to 20%, 5% to 15%, 8% to 30%, 8% to 25%, 8% to 20%, 8% to 15%, or 8% to 12%. The mass percentage of kinetic carbon material is the sum of the mass percentage of kinetic carbon material located at at least a portion of the interface between primary particles in the bulk particles and the mass percentage of kinetic carbon material located in the coating layer.

[0081] When the mass percentage of kinetic carbon material is within a suitable range, composite graphite materials can achieve high specific capacity while also possessing high active ion solid-phase transport capability and high active ion and electron charge exchange rate. Consequently, the secondary battery not only achieves high energy density but also exhibits significantly improved fast charging performance and low-temperature power performance. Furthermore, within a suitable mass percentage range, the kinetic carbon material better maintains the pore structure of the negative electrode film during cycling, resulting in better electrolyte wettability of the negative electrode sheet and allowing the secondary battery to also possess excellent cycle performance.

[0082] In some embodiments, the kinetic carbon material raw material is selected from one or more of hard carbon, micro-expanded graphite, expanded graphite, and graphene.

[0083] Optionally, the hard carbon powder has a specific capacity of ≥320mAh / g below 1V, and a powder compaction density of ≥1.05g / cm³ under a force of 20000N. 3 .

[0084] Optionally, the raw material for the kinetic carbon material is selected from one or more of micro-expanded graphite and expanded graphite. In particular, the raw material for the kinetic carbon material is selected from expanded graphite.

[0085] In some embodiments, the interlayer spacing d of the kinetic carbon material raw material (002) crystal plane is... 002 ≥0.3358nm. Optionally, the interlayer spacing d of the (002) crystal plane of the kinetic carbon material raw material. 002 The wavelength ranges from 0.3359 nm to 0.3366 nm.

[0086] The interlayer spacing d of the above-mentioned kinetic carbon material raw materials 002 Both are larger than conventional graphite. When the kinetic carbon material obtained from it is uniformly distributed in the bulk particles and / or coating layer of the composite graphite material, it is conducive to the rapid insertion and extraction of active ions, thereby improving the transport performance of active ions and electrons, and thus improving the fast charging performance and low-temperature power performance of the secondary battery, without causing a loss of energy density of the secondary battery.

[0087] The aforementioned kinetic carbon material raw materials also have high compressive strength, strong ability to maintain the pore structure of the negative electrode film during cycling, and better electrolyte wettability of the negative electrode sheet, thus also helping to improve the cycle performance of secondary batteries.

[0088] In some embodiments, the interlayer spacing d of the composite graphite material (002) crystal planes 002 The wavelength range is 0.3355 nm to 0.3364 nm. Optionally, the interlayer spacing d of the (002) crystal plane of the composite graphite material is... 002 The wavelength ranges from 0.3356 nm to 0.3361 nm.

[0089] Composite graphite materials have a high interlayer spacing d 002 It can enhance the solid-phase transport capability of active ions, thereby improving the fast charging performance and low-temperature power performance of secondary batteries.

[0090] In some embodiments, the volume average particle size Dv50 of the composite graphite material is 8.5 μm to 14.5 μm. Optionally, the volume average particle size Dv50 of the composite graphite material is 10 μm to 12 μm.

[0091] When the volume average particle size Dv50 of the composite graphite material is within a suitable range, the composite graphite material can have better active ion and electron transport performance as well as fast charging performance. At the same time, the composite graphite material also has a high powder compaction density.

[0092] In some embodiments, the volume average particle size Dv50 of the bulk particles is 7.5 μm to 13.5 μm. Optionally, the volume average particle size Dv50 of the bulk particles is 9.0 μm to 11.5 μm.

[0093] When the volume average particle size Dv50 of the bulk graphite material is within a suitable range, the composite graphite material can have a higher specific capacity while having better active ion and electron transport performance.

[0094] In some embodiments, the ratio of the volume average particle size Dv50 of the primary particles to the volume average particle size Dv50 of the secondary particles (i.e., the bulk particles) they comprise is 0.45 to 0.75. Optionally, the ratio of the volume average particle size Dv50 of the primary particles to the volume average particle size Dv50 of the secondary particles they comprise is 0.55 to 0.65.

[0095] When the ratio of the volume average particle size (Dv50) of the primary particles to the volume average particle size (Dv50) of the secondary particles they comprise is within a suitable range, the bulk particles of the composite graphite material exhibit a good degree of secondary particle size distribution. This is beneficial for improving the active ion and electron transport performance of the composite graphite material while simultaneously enhancing its structural stability. Furthermore, the bulk particles demonstrate a strong ability to maintain the pore structure of the negative electrode film during cycling, resulting in better electrolyte wettability of the negative electrode sheet. Therefore, this also contributes to improving the cycle performance of the secondary battery.

[0096] In some embodiments, the mass percentage of amorphous carbon in the coating layer is 1% to 8% based on the total mass of the composite graphite material. Optionally, the mass percentage of amorphous carbon in the coating layer is 2% to 5%.

[0097] When the content of amorphous carbon is within a suitable range, composite graphite materials can have both high specific capacity and high active ion solid-phase transport capability.

[0098] In some embodiments, at least a portion of the surface of the bulk particles is coated with a coating layer. Optionally, the composite graphite material includes bulk particles and a coating layer covering at least 80% of the surface of the bulk particles. In particular, the composite graphite material includes bulk particles and a coating layer covering at least 90% of the surface of the bulk particles.

[0099] In some embodiments, the compacted density of the composite graphite material powder under a force of 20,000 N is 1.45 g / cm³. 3 ~1.75g / cm 3 Optionally, the compacted density of the composite graphite material under a force of 20000N is 1.55 g / cm³. 3 ~1.65g / cm 3 .

[0100] When the powder compaction density of composite graphite materials is within a suitable range, the negative electrode film can have a high compaction density, thereby resulting in a high energy density for the secondary battery. Furthermore, when the powder compaction density of composite graphite materials is within a suitable range, the ability to maintain the pore structure of the negative electrode film is stronger during cycling, and the electrolyte wettability of the negative electrode sheet is better, thus also contributing to improved cycle performance of the secondary battery.

[0101] In this application, the volume average particle size Dv50 of the material has a well-known meaning in the art, representing the particle size corresponding to a cumulative volume distribution percentage of 50%, which can be determined using instruments and methods known in the art. For example, it can be conveniently determined using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK, in accordance with GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0102] In this application, the interlayer spacing d of the material 002 As is well known in the art, d can be determined using instruments and methods well known in the art. For example, JIS K 0131-1996 and JB / T 4220-2011 can be consulted, and an X-ray powder diffractometer (e.g., PANalytical X'pert PRO) can be used to determine d. 002 .

[0103] In this application, the powder compaction density of the material has a meaning known in the art and can be determined using instruments and methods known in the art. For example, it can be determined using an electronic pressure testing machine (e.g., UTM7305 type) according to standard GB / T24533-2009. An exemplary test method is as follows: Weigh 1g of material and add it to a container with a bottom area of ​​1.327cm². 2In the mold, the pressure is increased to 2000 kg (equivalent to 20000 N), held for 30 s, then depressurized and held for 10 s. The compaction density of the powder under a force of 20000 N is then recorded and calculated.

[0104] In this application, the specific capacity of the material has a meaning known in the art and can be tested using methods known in the art. An exemplary test method is as follows: The material to be tested, conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) are mixed uniformly with solvent N-methylpyrrolidone (NMP) at a mass ratio of 91.6:1.8:6.6 to prepare a slurry; the prepared slurry is coated onto a copper foil current collector and dried in an oven for later use. A lithium metal sheet is used as the counter electrode, and a polyethylene (PE) film is used as the separator. Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed at a volume ratio of 1:1:1, and then LiPF6 is uniformly dissolved in the above solution to obtain an electrolyte, wherein the concentration of LiPF6 is 1 mol / L. A CR2430 coin cell is assembled in an argon-protected glove box. After the obtained button cells were left to stand for 12 hours, they were discharged at 25°C with a constant current of 0.05C to 0.005V. After standing for 10 minutes, they were discharged again with a constant current of 50μA to 0.005V. After standing for 10 minutes, they were discharged again with a constant current of 10μA to 0.005V. Then, they were charged at a constant current of 0.1C to 2V, and the charging capacity was recorded. The ratio of the charging capacity to the mass of the material is the specific capacity of the material.

[0105] Method for producing composite graphite material

[0106] A second aspect of this application provides a method for preparing a composite graphite material. The method includes the steps of: S10, providing coke powder or coke powder containing kinetic carbon material raw material powder, and performing graphitization treatment on the coke powder or the coke powder containing kinetic carbon material raw material powder to obtain bulk particles, wherein the bulk particles are secondary particles formed by the aggregation of two or more primary particles, and the bulk particles include artificial graphite; S20, mixing the bulk particles with an organic carbon source, or mixing the bulk particles with an organic carbon source and the kinetic carbon material raw material powder, and after carbonization treatment, forming a coating layer including amorphous carbon on at least a portion of the surface of the bulk particles to obtain the composite graphite material.

[0107] In at least one of steps S10 and S20, the kinetic carbon material raw material powder is added. The kinetic carbon material raw material is selected from one or more of hard carbon, micro-expanded graphite, expanded graphite, and graphene. The interlayer spacing d of the (002) crystal plane of the kinetic carbon material raw material is... 002 ≥0.3358nm.

[0108] The air oxidation temperature T0 of the obtained composite graphite material is 630℃~730℃. The air oxidation temperature T0 is the temperature corresponding to the intersection of the two tangents at two points corresponding to 500℃ and T1 on the thermogravimetric curve of the composite graphite material. The T1 temperature is the peak temperature of the largest area peak in the differential thermogravimetric curve of the composite graphite material. The thermogravimetric curve and the differential thermogravimetric curve can be obtained by thermogravimetric analysis under the following conditions: sample mass 10±0.05mg, purge gas is air with a flow rate of 60mL / min, heating rate is 5℃ / min, and test temperature range is 35℃~950℃.

[0109] Specifically, the air oxidation temperature T0 can be determined by thermogravimetric analysis including the following steps: The composite graphite material is subjected to thermogravimetric analysis under the following conditions: a weight of 10±0.05mg, air as the purging gas with a flow rate of 60mL / min, a heating rate of 5℃ / min, and a test temperature range of 35℃~950℃. The thermogravimetric curve and the differential thermogravimetric curve are obtained. The peak temperature T1 of the maximum area peak is read from the differential thermogravimetric curve. The intersection of the two tangents at two points corresponding to the temperatures of 500℃ and T1 is determined on the thermogravimetric curve. The temperature corresponding to the intersection point on the thermogravimetric curve is the air oxidation temperature T0 of the composite graphite material.

[0110] The method for preparing the composite graphite material of this application is simple to operate, cost-controllable, and can be used for large-scale industrial production.

[0111] The method of this application can obtain composite graphite materials with appropriate end face and defect content, thereby enabling secondary batteries to have high energy density while also having significantly improved fast charging performance and low-temperature power performance.

[0112] In some embodiments, the specific capacity of hard carbon below 1V is ≥320mAh / g, and the compacted density of hard carbon powder under a force of 20000N is ≥1.05g / cm³. 3 .

[0113] In some embodiments, the kinetic carbon material raw material is selected from one or more of micro-expanded graphite and expanded graphite. Optionally, the kinetic carbon material raw material is selected from expanded graphite.

[0114] In some embodiments, the interlayer spacing d of the kinetic carbon material raw material (002) crystal plane is... 002 The wavelength ranges from 0.3359 nm to 0.3366 nm.

[0115] In some embodiments, the method of providing coke powder includes the steps of: coking coke raw material to obtain coke, and crushing, shaping and classifying the obtained coke to obtain coke powder.

[0116] In some implementations, the coke can be obtained commercially.

[0117] Optionally, the coke feedstock may be selected from one or more of petroleum-based and coal-based feedstocks. For example, petroleum-based feedstocks may be selected from one or more of heavy oil, residual oil, and vacuum residue, while coal-based feedstocks may primarily be selected from coal tar pitch. Heavy oil, residual oil, and vacuum residue are typically produced in petroleum refining processes, while coal tar pitch is typically produced in coal dry distillation processes.

[0118] In some embodiments, the coke includes one or more of petroleum-based non-needle coke, petroleum-based needle coke, coal-based non-needle coke, and coal-based needle coke. Optionally, the coke includes one or more of petroleum-based non-needle coke (e.g., petroleum calcined coke, petroleum-based green coke) and petroleum-based needle coke. In particular, the coke includes petroleum-based green coke. Using a suitable coke can enable the prepared composite graphite material to have a suitable number of end faces and defects, thereby exhibiting better active ion and electron transport properties and higher structural stability, thus improving the fast charging performance, low-temperature power performance, and cycle performance of secondary batteries.

[0119] Optionally, the coking of the coking feedstock is carried out in a delayed coking unit. The delayed coking unit includes a heating furnace and a coking tower. The delayed coking process refers to the process of rapidly heating the coking feedstock to the required coking temperature in the heating furnace, and then feeding it into the coking tower, where it undergoes preheating, cooling, and other processes to produce coke.

[0120] The coke can be crushed using equipment and methods known in the art, such as air jet mills, mechanical mills, roller mills or other crushing equipment.

[0121] The morphology of the coke powder obtained after crushing can include one or more of the following: blocky, spherical, and near-spherical. After crushing, the coke powder is then shaped to smooth out its sharp edges. The greater the degree of shaping, the closer the powder particles are to spherical shapes, which increases the number of active ion insertion / extraction sites on the surface of the composite graphite material. Shaping also benefits the subsequent granulation process, giving the secondary particles in the resulting composite graphite material higher structural stability.

[0122] Coke powder can be shaped using equipment and methods known in the art, such as shaping machines or other shaping equipment.

[0123] Crushing and shaping processes often produce a large number of excessively small particles, and sometimes excessively large particles as well. Therefore, grading can be performed as needed to remove these excessively small and large particles from the powder. Grading results in coke powder with a better particle size distribution, which facilitates subsequent granulation and coating processes. Grading can be carried out using equipment and methods known in the art, such as grading sieves, gravity classifiers, and centrifugal classifiers.

[0124] In some embodiments, the volume average particle size Dv50 of the coke powder is 6 μm to 12 μm. Optionally, the volume average particle size Dv50 of the coke powder is 8 μm to 10 μm.

[0125] In some embodiments, the method for providing kinetic carbon material raw material powder includes the steps of: pulverizing, shaping, and classifying the kinetic carbon material raw material to obtain kinetic carbon material raw material powder. The pulverizing, shaping, and classifying methods are the same as those used for pulverizing, shaping, and classifying coke as described above.

[0126] In some embodiments, the volume average particle size Dv50 of the kinetic carbon material raw material powder is 3 μm to 12 μm. Optionally, the volume average particle size Dv50 of the kinetic carbon material raw material powder is 4 μm to 9 μm.

[0127] In some embodiments, the ratio of the volume average particle size Dv50 of the coke powder to the volume average particle size Dv50 of the kinetic carbon material raw material powder is 1.05 to 1.75. Optionally, the ratio is 1.2 to 1.5. When the ratio of the volume average particle size Dv50 of the coke powder to the volume average particle size Dv50 of the kinetic carbon material raw material powder is within a suitable range, the bulk particles of the composite graphite material can have a better secondary particle size distribution.

[0128] In some embodiments, the mass ratio of coke powder to kinetic carbon material raw material powder in the coke powder is 1–20:99–80. Optionally, the mass ratio is 3–12:97–88. Maintaining a suitable mass ratio of coke powder to kinetic carbon material raw material powder is beneficial for obtaining composite graphite materials with moderate end-face and defect contents. Consequently, the secondary battery can achieve high energy density while also exhibiting significantly improved fast-charging performance and low-temperature power performance.

[0129] In some embodiments, based on the total mass of the obtained composite graphite material, the total mass percentage of the kinetic carbon material raw material powder added in steps S10 and S20 is 1% to 30%. For example, 3% to 30%, 3% to 25%, 3% to 20%, 3% to 15%, 5% to 30%, 5% to 25%, 5% to 20%, 5% to 15%, 8% to 30%, 8% to 25%, 8% to 20%, 8% to 15%, or 8% to 12%.

[0130] In some embodiments, the method further includes the step of adding a binder in S10. The binder is mixed with coke powder and then granulated, followed by graphitization to obtain bulk particles; or the binder is mixed with coke powder containing kinetic carbon material raw material powder and then granulated, followed by graphitization to obtain bulk particles.

[0131] Adding a binder can give the bulk particles of the composite graphite material a better degree of secondary particle size, which is beneficial to improving the active ion and electron transport performance of the composite graphite material while giving it higher structural stability.

[0132] Optionally, based on the total mass of the obtained composite graphite material, the mass percentage of the binder is 3% to 12%. More preferably, the mass percentage of the binder is 5% to 8%. A binder content within a suitable range can prevent excessive particle agglomeration, resulting in better secondary particle size distribution in the bulk particles of the composite graphite material.

[0133] Optionally, the binder is selected from asphalt. Optionally, the asphalt has a softening point of 200°C or higher.

[0134] Optionally, the asphalt is selected from one or more of coal tar pitch and petroleum asphalt.

[0135] Optionally, the volume average particle size Dv50 of the particles obtained after granulation is 8 μm to 14 μm. In particular, the volume average particle size Dv50 of the particles obtained after granulation is 9.5 μm to 12 μm.

[0136] Granulation can be performed using equipment and methods known in the art, such as granulators. Granulators typically include a stirred reactor and a module for temperature control of the reactor. By adjusting the stirring speed, heating rate, granulation temperature, and cooling rate during the granulation process, the degree of granulation and the structural strength of the particles can be controlled, ensuring that the volume average particle size Dv50 of the bulk particles of the final composite graphite material is within the desired range.

[0137] In some embodiments, the graphitization temperature in S10 can be 2800°C to 3200°C. Optionally, the graphitization temperature can be 2900°C to 3100°C. Graphitization treatment can give the bulk particles a suitable degree of graphitization, thereby giving the composite graphite material a high specific capacity. Graphitization treatment also reduces the lattice expansion of the bulk particles during the insertion / extraction of active ions. Furthermore, graphitization treatment can effectively eliminate bulk structural defects in the bulk particles, improving the cycle performance of the secondary battery.

[0138] In some implementations, the graphitization process in S10 takes 10 to 15 days.

[0139] Graphitization can be performed using equipment and methods known in the art, such as graphitization furnaces, particularly the Atchison graphitization furnace. After graphitization, a small number of excessively large particles formed during the graphitization process can be removed by sieving. This prevents excessively large particles from affecting the processing performance of the composite graphite material, such as the stability of the negative electrode slurry and the coating performance.

[0140] In some embodiments, in S10, the volume average particle size Dv50 of the obtained bulk particles is 7.5 μm to 13.5 μm. Optionally, the volume average particle size Dv50 of the obtained bulk particles is 9.0 μm to 11.5 μm.

[0141] In some embodiments, in step S20, the organic carbon source is selected from one or more of coal tar pitch, petroleum asphalt, phenolic resin, and coconut shell. Optionally, the organic carbon source is selected from petroleum asphalt. Optionally, the softening point of the coal tar pitch or petroleum asphalt is below 250°C.

[0142] In some embodiments, based on the total mass of the obtained composite graphite material, the amount of organic carbon source added is such that the mass percentage of amorphous carbon obtained after carbonization of the organic carbon source is 1% to 8%. Optionally, the amount of organic carbon source added is such that the mass percentage of amorphous carbon obtained after carbonization of the organic carbon source is 2% to 5%. When the amount of organic carbon source added is within a suitable range, the composite graphite material can have both high specific capacity and high active ion solid-phase transport capability.

[0143] In some embodiments, the carbonization temperature in S20 is 700°C to 1800°C. Optionally, the carbonization temperature is 1000°C to 1300°C. Within a suitable range, the carbonization temperature allows the organic carbon source (and optionally, a kinetic carbon material raw material) to carbonize and form a coating layer containing amorphous carbon on at least a portion of the surface of the artificial graphite.

[0144] In some embodiments, the carbonization treatment time in S20 is 1h to 6h.

[0145] In some embodiments, the preparation method of the composite graphite material includes the following steps: S10, providing coke powder and kinetic carbon material raw material powder, mixing the binder with the coke powder and kinetic carbon material raw material powder, granulating the mixture, and then graphitizing it to obtain bulk particles, wherein the bulk particles are secondary particles formed by the aggregation of two or more primary particles, and the bulk particles include artificial graphite; S20, mixing the bulk particles with an organic carbon source, and after carbonization, forming a coating layer including amorphous carbon on at least a portion of the surface of the bulk particles to obtain the composite graphite material.

[0146] In some embodiments, the preparation method of the composite graphite material includes the following steps: S10, providing coke powder, mixing a binder with the coke powder and then granulating it, followed by graphitization treatment to obtain bulk particles, wherein the bulk particles are secondary particles formed by the aggregation of two or more primary particles, and the bulk particles include artificial graphite; S20, mixing the bulk particles with an organic carbon source and a kinetic carbon material raw material powder, and after carbonization treatment, forming a coating layer including amorphous carbon on at least a portion of the surface of the bulk particles to obtain the composite graphite material.

[0147] In some embodiments, the preparation method of the composite graphite material includes the following steps: S10, providing coke powder and kinetic carbon material raw material powder, mixing the binder with the coke powder and kinetic carbon material raw material powder, granulating the mixture, and then graphitizing it to obtain bulk particles, wherein the bulk particles are secondary particles formed by the aggregation of two or more primary particles, and the bulk particles include artificial graphite; S20, mixing the bulk particles with an organic carbon source and kinetic carbon material raw material powder, and after carbonization treatment, forming a coating layer including amorphous carbon on at least a portion of the surface of the bulk particles to obtain the composite graphite material.

[0148] In the preparation method of this application, coke powder or coke powder containing kinetic carbon material raw material is graphitized to obtain bulk particles, and the bulk particles are secondary particles formed by the aggregation of two or more primary particles. Specifically, the coke powder obtained after crushing, shaping, and other treatments is mainly composed of single particles; morphologically, the coke powder is a primary particle (or primary particle). The bulk particles obtained after granulation and graphitization of coke powder or coke powder containing kinetic carbon material raw material are aggregates of multiple of the aforementioned primary particles; therefore, morphologically, the bulk particles are secondary particles.

[0149] In the preparation method of this application, composite graphite materials with different air oxidation temperatures T0 can be obtained by adjusting the volume average particle size Dv50 of coke powder and its addition amount, the volume average particle size Dv50 of kinetic carbon material raw material powder and its addition amount, the amount of binder added, and the amount of organic carbon source added.

[0150] Secondary battery

[0151] Secondary batteries, also known as rechargeable batteries or storage batteries, are batteries that can be recharged after being discharged to activate the active materials and continue to be used.

[0152] Typically, a secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing active ions to pass through. The electrolyte, located between the positive and negative electrodes, conducts the active ions.

[0153] [Negative electrode plate]

[0154] In the secondary battery of this application, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector. For example, the negative current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0155] The negative electrode current collector can be a metal foil or a composite current collector. As an example of a metal foil, copper foil can be used. The composite current collector may include a polymer material substrate and a metal material layer formed on at least one surface of the polymer material substrate. As an example, the metal material may be selected from one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer material substrate may be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0156] The negative electrode film typically comprises a negative electrode active material, optional binder, optional conductive agent, and other optional additives. The negative electrode film is usually formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry coating is typically formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0157] In some embodiments, the negative electrode active material may include one of the composite graphite material of the first aspect of the present application and the composite graphite material prepared by the method of the second aspect of the present application.

[0158] In some embodiments, the negative electrode active material may also include other negative electrode active materials known in the art for use in secondary batteries. As examples, other negative electrode active materials may include one or more of natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials may include one or more of elemental silicon, silicon oxide, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxide, and tin alloys. This application is not limited to these materials, and other conventionally known materials that can be used as negative electrode active materials for secondary batteries may also be used. These other negative electrode active materials may be used alone or in combination of two or more.

[0159] In some embodiments, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the binder may include one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, other optional additives may include thickeners (e.g., sodium carboxymethyl cellulose CMC-Na), PTC thermistor materials, etc.

[0160] In some embodiments, the negative electrode film layer may further include additives. In this case, the additives, composite graphite material, optional conductive agent, optional binder, and other optional auxiliaries can be dispersed in a solvent and stirred evenly to form a negative electrode slurry. The negative electrode slurry is then coated onto a negative electrode current collector, dried, and cold-pressed to form the negative electrode film layer. The additives are selected from one or more of hard carbon, micro-expanded graphite, expanded graphite, and graphene. The interlayer spacing d of the (002) crystal plane of the additives... 002 ≥0.3358nm. These additives have good active ion and electron transport properties, which can enable secondary batteries to have high energy density while also having significantly improved fast charging performance and low-temperature power performance.

[0161] Optionally, the hard carbon powder has a specific capacity of ≥320mAh / g below 1V, and a powder compaction density of ≥1.05g / cm³ under a force of 20000N. 3 .

[0162] Optionally, the additive is selected from one or more of micro-expanded graphite and expanded graphite. In particular, the additive is selected from expanded graphite.

[0163] Optionally, the interlayer spacing d of the additive (002) crystal plane 002The wavelength ranges from 0.3359 nm to 0.3366 nm.

[0164] Optionally, the mass percentage of the additive is 1% to 20% based on the total mass of the negative electrode film. For example, the mass percentage of the additive can be 1% to 20%, 1% to 18%, 1% to 15%, 1% to 12%, 1% to 10%, 1% to 8%, 1% to 5%, 2% to 20%, 2% to 18%, 2% to 15%, 2% to 12%, 2% to 10%, 2% to 8%, 2% to 5%, 3% to 20%, 3% to 18%, 3% to 15%, 3% to 12%, 3% to 10%, 3% to 8%, or 3% to 5%. Within a suitable range, the mass percentage of the additive can enable the secondary battery to achieve high energy density while also significantly improving fast-charging performance and low-temperature power performance. Simultaneously, within a suitable range, the additive's ability to maintain the pore structure of the negative electrode film during cycling is better, the electrolyte wettability of the negative electrode sheet is better, and the secondary battery can also exhibit good cycle performance.

[0165] In some embodiments, the areal density of the negative electrode film is 0.035 kg / m³. 2 ~0.125kg / m 2 Optionally, the areal density of the negative electrode film is 0.078 kg / m³. 2 ~0.107kg / m 2 .

[0166] When the areal density of the negative electrode film is within the above range, the negative electrode sheet can have a high reversible capacity while also having a low impedance for transporting active ions and electrons, thereby further improving the energy density, fast charging performance, low-temperature power performance and cycle performance of the secondary battery.

[0167] In this application, the areal density of the negative electrode film has a meaning known in the art and can be tested using methods known in the art. For example, take a negative electrode sheet that has been coated on one side and cold-pressed (if it is a negative electrode sheet coated on both sides, the negative electrode film on one side can be wiped off first), cut it into a small circular piece with an area of ​​S1, weigh it, and record its weight as M1. Then wipe off the negative electrode film of the weighed negative electrode sheet, weigh the negative current collector, and record it as M0. The areal density of the negative electrode film = (M1-M0) / S1.

[0168] In some embodiments, the compaction density of the negative electrode film is 1.2 g / cm³. 3 ~1.75g / cm 3 Optionally, the compaction density of the negative electrode film is 1.4 g / cm³. 3 ~1.6g / cm 3 .

[0169] When the compaction density of the negative electrode film is within the above range, the negative electrode sheet can have high reversible capacity, as well as low cycle expansion and good kinetic performance, thereby further improving the energy density, fast charging performance, low temperature power performance and cycle performance of the secondary battery.

[0170] In this application, the compaction density of the negative electrode film has a meaning known in the art and can be tested using methods known in the art. The compaction density of the negative electrode film = areal density of the negative electrode film / thickness of the negative electrode film. In this application, the thickness of the negative electrode film has a meaning known in the art and can be tested using methods known in the art. For example, a 4-digit precision micrometer can be used.

[0171] In some embodiments, the porosity of the negative electrode film is 25% to 45%. Optionally, the porosity of the negative electrode film is 28% to 35%.

[0172] When the porosity of the negative electrode film is within the aforementioned range, the negative electrode sheet possesses suitable electrolyte wettability and a good reaction interface, improving the charge-discharge performance of the negative electrode at high rates, thereby enhancing the fast-charging performance of the secondary battery. Simultaneously, the negative electrode film also maintains a suitable electrolyte retention level, resulting in a lower mass of the secondary battery, which is beneficial for achieving a higher gravimetric energy density.

[0173] In this application, the porosity of the negative electrode film has a meaning known in the art and can be determined using methods known in the art. For example, GB / T24586-2009 can be referenced, and the gas displacement method can be used for measurement. The test method is as follows: Take a negative electrode sheet that has been coated on one side and cold-pressed (if it is a negative electrode sheet coated on both sides, the negative electrode film layer on one side can be wiped off first), and cut it into small circular samples with a diameter of 14 mm; test the thickness of the negative electrode film layer (thickness of the negative electrode sheet - thickness of the negative electrode current collector); calculate the apparent volume V1 of the negative electrode film layer according to the formula for calculating the volume of a cylinder; use an inert gas such as helium or nitrogen as a medium, and use the gas displacement method to measure the true volume of the negative electrode sheet using a true density meter (such as Micromeritics AccuPyc II 1340), and the test can be referenced in GB / T 24586-2009; subtract the volume of the negative electrode current collector from the true volume of the negative electrode sheet to obtain the true volume V2 of the negative electrode film layer. The porosity of the negative electrode film is calculated as (V1-V2) / V1×100%. Multiple negative electrode samples (e.g., 30 sheets) can be tested, and the average value of the results can be taken, thereby improving the accuracy of the test results.

[0174] In some embodiments, the adhesion force between the negative electrode film layer and the negative electrode current collector is 4.5 N / m to 15 N / m. Optionally, the adhesion force between the negative electrode film layer and the negative electrode current collector is 8 N / m to 12 N / m.

[0175] Within the aforementioned range, the adhesion strength between the negative electrode film and the negative electrode current collector can improve the fast-charging performance and cycle performance of the secondary battery. A higher adhesion strength between the negative electrode film and the negative electrode current collector results in good electron conductivity of the negative electrode sheet, which is beneficial for increasing the insertion rate of active ions. Furthermore, the adhesion strength between the negative electrode film and the negative electrode current collector also reflects the ability of the negative electrode sheet to maintain adhesive reliability during cycling, which is beneficial for maintaining good electron conductivity throughout the entire life cycle of the secondary battery, thereby further improving the cycle performance of the secondary battery.

[0176] In this application, the adhesive force between the negative electrode film layer and the negative electrode current collector is a term known in the art and can be measured using methods known in the art. An exemplary test method is as follows: Cut the negative electrode sheet into a test sample 100 mm long and 10 mm wide; take a 25 mm wide stainless steel plate, apply double-sided tape (11 mm wide), and attach the test sample to the double-sided tape on the stainless steel plate; roll the surface back and forth three times (300 mm / min) with a 2000g roller; bend the test sample 180 degrees, manually peel the negative electrode film layer from the negative electrode current collector by 25 mm, fix the test sample on a testing machine (e.g., INSTRON 336), ensuring the peeling surface is aligned with the machine's force line, and continuously peel at 30 mm / min. The average value of the obtained peel force curve at a stable point is taken as the peel force F0. The adhesive force between the negative electrode film layer and the current collector = F0 / width of the test sample.

[0177] In this application, the relevant parameters of the negative electrode film layer all refer to the parameters of a single-sided negative electrode film layer. That is, when the negative electrode film layer is disposed on both surfaces of the negative electrode current collector, if the parameters of the negative electrode film layer on either surface meet the parameter range of this application, it is considered to fall within the protection scope of this application.

[0178] In the secondary battery of this application, the negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of this application further includes a conductive undercoat layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode sheet of this application further includes a protective layer covering the surface of the negative electrode film layer.

[0179] [Positive electrode plate]

[0180] In the secondary battery of this application, the positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector and comprising a positive electrode active material. For example, the positive current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0181] In the secondary battery of this application, the positive electrode active material may be any positive electrode active material known in the art for use in secondary batteries. For example, the positive electrode active material may include one or more of lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and their respective modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxides, lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, and their respective modified compounds. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their respective modified compounds. This application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for secondary batteries may also be used.

[0182] In some embodiments, to further improve the energy density of the secondary battery, the positive electrode active material may include one or more of the lithium transition metal oxides and their modified compounds as shown in Formula 1.

[0183] Li a Ni b Co c M d O e A f Formula 1,

[0184] In Formula 1, 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M is selected from one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A is selected from one or more of N, F, S and Cl.

[0185] In this application, the modified compounds of the above-mentioned materials can be used to dope or surface-coat the positive electrode active material.

[0186] In the secondary battery of this application, the positive electrode film layer typically comprises a positive electrode active material, an optional binder, and an optional conductive agent. The positive electrode film layer is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring until homogeneous. The solvent may be N-methylpyrrolidone (NMP), but is not limited to it. As an example, the binder used for the positive electrode film layer may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0187] In the secondary battery of this application, the positive electrode current collector can be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil can be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material can be selected from one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer material base layer can be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0188] [Electrolytes]

[0189] The secondary battery of this application does not have specific restrictions on the type of electrolyte, and can be selected according to needs. For example, the electrolyte can be selected from at least one of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions).

[0190] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0191] This application does not impose specific limitations on the type of electrolyte salt, which can be selected according to requirements. In some embodiments, as examples, the electrolyte salt may be selected from one or more of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiAsF6 (lithium hexafluoroarsenate), LiFSI (lithium bis(fluorosulfonyl)imide), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalate borate), LiBOB (lithium dioxalate borate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluorodioxalate phosphate), and LiTFOP (lithium tetrafluorooxalate phosphate).

[0192] This application does not impose specific limitations on the type of solvent, which can be selected according to requirements. In some embodiments, as an example, the solvent may be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0193] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature power performance.

[0194] [Isolation membrane]

[0195] Secondary batteries using electrolytes, and some secondary batteries using solid electrolytes, also include a separator. The separator is positioned between the positive and negative electrodes, serving a separating function. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected. In some embodiments, the separator material can be selected from one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0196] In some implementations, the positive electrode, separator, and negative electrode can be fabricated into an electrode assembly using a winding or stacking process.

[0197] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the aforementioned electrode assembly and electrolyte.

[0198] In some implementations, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0199] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. FIG. 4 This is an example of a square-structured secondary battery 5.

[0200] In some implementations, refer to FIG. 5 The outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity. Positive electrode sheets, negative electrode sheets, and a separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be adjusted according to requirements.

[0201] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be multiple, the specific number of which can be adjusted according to the application and capacity of the battery module.

[0202] FIG. 6 This is battery module 4, used as an example. (See reference...) FIG. 6 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0203] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0204] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0205] FIG. 7 and FIG. 8 This is battery pack 1 as an example. (See reference...) FIG. 7 and FIG. 8 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3. The upper body 2 covers the lower body 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0206] The method for preparing the secondary battery described in this application is well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a secondary battery. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding or stacking process. The electrode assembly is then placed in an outer package, dried, and injected with an electrolyte. After vacuum sealing, settling, formation, and shaping processes, a secondary battery is obtained.

[0207] Electric device

[0208] This application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack described in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device can be, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0209] The electrical device can be equipped with a secondary battery, battery module, or battery pack according to its usage requirements.

[0210] FIG. 9 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0211] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use rechargeable batteries as their power source.

[0212] Example

[0213] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0214] Example 1

[0215] Production of composite graphite material

[0216] Petroleum residue oil was subjected to delayed coking at 490℃~510℃ to obtain petroleum non-needle coke raw coke; the raw coke was crushed, shaped and graded to obtain coke powder with a volume average particle size Dv50 of 9.5μm, which was used as the main raw material for composite graphite materials.

[0217] For the interlayer spacing d 002 Micro-expanded graphite with a particle size of 0.3363 nm (expansion ratio of 180) was pulverized, shaped and classified to obtain micro-expanded graphite powder with a volume average particle size Dv50 of 7.5 μm.

[0218] Coke powder and micro-expanded graphite powder were mixed, then mixed with coal tar pitch as a binder, and granulated. The resulting particles had a volume average particle size (Dv50) of approximately 13 μm. The granulated product was placed in a graphite crucible, which was then placed in an Atchison graphitization furnace. Resistance material was filled around the graphite crucible, and an electric current was passed through the resistance material to generate heat. Graphitization was then performed at approximately 3000°C to obtain bulk particles.

[0219] The obtained bulk particles are mixed with organic carbon source petroleum asphalt and then carbonized in a track kiln at a maximum temperature of about 1150°C for about 4 hours to form a coating layer on at least a portion of the surface of the bulk particles, thus obtaining a composite graphite material.

[0220] Among them, based on the total mass of the obtained composite graphite material, the mass percentage of the added micro-expanded graphite powder is 1%, the mass percentage of the added binder is 6%, and the mass percentage of the added organic carbon source is 3% such that the amorphous carbon obtained after carbonization of the organic carbon source is 3%.

[0221] Production of negative electrode sheet

[0222] The composite graphite material prepared above was used as the negative electrode active material and mixed with styrene-butadiene rubber (SBR) as a binder, sodium carboxymethyl cellulose (CMC-Na) as a thickener, and carbon black (Super P) as a conductive agent in a weight ratio of 96.2:1.8:1.2:0.8 in an appropriate amount of deionized water to form a uniform negative electrode slurry. The negative electrode slurry was uniformly coated onto the surface of a copper foil negative electrode current collector, and after drying and cold pressing, a negative electrode sheet was obtained. The areal density of the negative electrode film layer was 0.097 kg / m³. 2 The compacted density is 1.64 g / cm³. 3 .

[0223] Production of positive electrode sheet

[0224] LiNi, the positive electrode active material 0.5 Co 0.2 Mn0.3 O2 (NCM523), conductive carbon nanotubes (CNTs), conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) were thoroughly mixed in an appropriate amount of NMP solvent at a weight ratio of 97.5:0.5:0.9:1.1 to form a uniform positive electrode slurry. The positive electrode slurry was then uniformly coated onto the surface of a positive electrode current collector aluminum foil. After drying and cold pressing, the positive electrode sheet was obtained. The areal density of the positive electrode film was 0.178 kg / m³. 2 The compacted density is 3.4 g / cm³. 3 .

[0225] Separator

[0226] Porous polyethylene (PE) membrane is used as the separator.

[0227] Production of electrolyte

[0228] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent; LiPF6 was uniformly dissolved in the above organic solvent to obtain an electrolyte, wherein the concentration of LiPF6 was 1 mol / L.

[0229] Production of secondary battery

[0230] The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain an electrode assembly. The electrode assembly is placed in an outer packaging, the electrolyte is added, and after processes such as encapsulation, standing, formation, and aging, a secondary battery is obtained.

[0231] Example 2

[0232] The preparation method of the secondary battery is similar to that of Example 1, except that the mass percentage of the added micro-expanded graphite powder is 3% based on the total mass of the obtained composite graphite material, the mass percentage of the added binder is 6%, and the mass of the added organic carbon source is such that the mass percentage of the amorphous carbon obtained after carbonization of the organic carbon source is 3%.

[0233] Example 3

[0234] The preparation method of the secondary battery is similar to that of Example 1, except that the mass percentage of the added micro-expanded graphite powder is 8%, the mass percentage of the added binder is 6%, and the mass percentage of the added organic carbon source is 3% so that the amorphous carbon obtained after carbonization of the organic carbon source is 3%.

[0235] Example 4

[0236] The preparation method of the secondary battery is similar to that of Example 1, except that the mass percentage of the added micro-expanded graphite powder is 12% based on the total mass of the obtained composite graphite material, the mass percentage of the added binder is 6%, and the mass percentage of the added organic carbon source is 3% to obtain amorphous carbon after carbonization of the organic carbon source.

[0237] Example 5

[0238] The preparation method of the secondary battery is similar to that of Example 1, except that the mass percentage of the added micro-expanded graphite powder is 20%, the mass percentage of the added binder is 6%, and the mass percentage of the added organic carbon source is 3% so that the amorphous carbon obtained after carbonization of the organic carbon source is 3%.

[0239] Example 6

[0240] The preparation method of the secondary battery is similar to that of Example 1, except that the mass percentage of the added micro-expanded graphite powder is 30%, the mass percentage of the added binder is 6%, and the mass percentage of the added organic carbon source is 3% so that the amorphous carbon obtained after carbonization of the organic carbon source is obtained.

[0241] Example 7

[0242] The preparation method of the secondary battery is similar to that in Example 3, except that the interlayer spacing d is used. 002 Hard carbon powder with a particle size of 0.33615 nm and a volume average particle size Dv50 of 5.3 μm was used to replace micro-expanded graphite powder.

[0243] Example 8

[0244] The preparation method of the secondary battery is similar to that in Example 3, except that the interlayer spacing d is used. 002 Expanded graphite powder with a particle size of 0.33638 nm and a volume average particle size Dv50 of 7.2 μm (expansion ratio of 300) was used to replace micro-expanded graphite powder.

[0245] Example 9

[0246] The preparation method of the secondary battery is similar to that in Example 3, except that the interlayer spacing d is used. 002 Graphene powder with a diameter of 0.33620 nm and a volume average particle size Dv50 of 8.0 μm was used to replace micro-expanded graphite powder.

[0247] Example 10

[0248] The preparation method of the secondary battery is similar to that in Example 1, except that the composite graphite material is prepared according to the following method.

[0249] Petroleum residue oil was subjected to delayed coking at 490℃~510℃ to obtain petroleum non-needle coke raw coke; the raw coke was crushed, shaped and graded to obtain coke powder with a volume average particle size Dv50 of 9.5μm, which was used as the main raw material for composite graphite materials.

[0250] For the interlayer spacing d 002 Micro-expanded graphite with a particle size of 0.3363 nm (expansion ratio of 180) was pulverized, shaped and classified to obtain micro-expanded graphite powder with a volume average particle size Dv50 of 7.5 μm.

[0251] Coke powder was mixed with coal tar pitch as a binder, and then granulated. The resulting granules had a volume average particle size (Dv50) of approximately 13 μm. The granulated product was placed in a graphite crucible, which was then placed in an Atchison graphitization furnace. Resistance material was filled around the graphite crucible, and an electric current was passed through the resistance material to generate heat. Graphitization was then performed at approximately 3000°C to obtain bulk particles.

[0252] The obtained bulk particles are mixed with micro-expanded graphite powder and organic carbon source petroleum asphalt, and then carbonized in a track kiln at a maximum temperature of about 1150°C for about 4 hours to form a coating layer on at least a portion of the surface of the bulk particles, thus obtaining a composite graphite material.

[0253] Among them, based on the total mass of the obtained composite graphite material, the mass percentage of the added micro-expanded graphite powder is 8%, the mass percentage of the added binder is 6%, and the mass percentage of the added organic carbon source is 3% so that the amorphous carbon obtained after carbonization of the organic carbon source is 3%.

[0254] Example 11

[0255] The preparation method of the secondary battery is similar to that in Example 1, except that the composite graphite material is prepared according to the following method.

[0256] Petroleum residue oil was subjected to delayed coking at 490℃~510℃ to obtain petroleum non-needle coke raw coke; the raw coke was crushed, shaped and graded to obtain coke powder with a volume average particle size Dv50 of 9.5μm, which was used as the main raw material for composite graphite materials.

[0257] For the interlayer spacing d 002 Micro-expanded graphite with a particle size of 0.3363 nm (expansion ratio of 180) was pulverized, shaped and classified to obtain micro-expanded graphite powder with a volume average particle size Dv50 of 7.5 μm.

[0258] Coke powder and micro-expanded graphite powder were mixed, then mixed with coal tar pitch as a binder, and granulated. The resulting particles had a volume average particle size (Dv50) of approximately 13 μm. The granulated product was placed in a graphite crucible, which was then placed in an Atchison graphitization furnace. Resistance material was filled around the graphite crucible, and an electric current was passed through the resistance material to generate heat. Graphitization was then performed at approximately 3000°C to obtain bulk particles.

[0259] The obtained bulk particles are mixed with micro-expanded graphite powder and organic carbon source petroleum asphalt, and then carbonized in a track kiln at a maximum temperature of about 1150°C for about 4 hours to form a coating layer on at least a portion of the surface of the bulk particles, thus obtaining a composite graphite material.

[0260] Among them, based on the total mass of the obtained composite graphite material, the total mass percentage of the micro-expanded graphite powder added twice is 10%, the mass percentage of the added binder is 6%, and the mass of the added organic carbon source is such that the mass percentage of the amorphous carbon obtained after the organic carbon source is carbonized is 3%.

[0261] Example 12

[0262] The preparation method of the secondary battery is similar to that in Example 3, except that the negative electrode sheet is prepared according to the following method.

[0263] The composite graphite material prepared above was used as the negative electrode active material and mixed with styrene-butadiene rubber (SBR) binder, sodium carboxymethyl cellulose (CMC-Na) thickener and carbon black (Super P) conductive agent in a weight ratio of 96.2:1.8:1.2:0.8. Then, it was mixed with the micro-expanded graphite powder in a mass ratio of 96:4. An appropriate amount of deionized water solvent was added and the mixture was stirred thoroughly to form a uniform negative electrode slurry. The negative electrode slurry was uniformly coated on the surface of the negative electrode current collector copper foil. After drying and cold pressing, the negative electrode sheet was obtained.

[0264] Example 13

[0265] The preparation method of the secondary battery is similar to that of Example 10, except that the negative electrode sheet is prepared according to the following method.

[0266] The composite graphite material prepared above was used as the negative electrode active material and mixed with styrene-butadiene rubber (SBR) binder, sodium carboxymethyl cellulose (CMC-Na) thickener and carbon black (Super P) conductive agent in a weight ratio of 96.2:1.8:1.2:0.8. Then, it was mixed with the micro-expanded graphite powder in a mass ratio of 96:4. An appropriate amount of deionized water solvent was added and the mixture was stirred thoroughly to form a uniform negative electrode slurry. The negative electrode slurry was uniformly coated on the surface of the negative electrode current collector copper foil. After drying and cold pressing, the negative electrode sheet was obtained.

[0267] Example 14

[0268] The preparation method of the secondary battery is similar to that of Example 11, except that the negative electrode sheet is prepared according to the following method.

[0269] The composite graphite material prepared above was used as the negative electrode active material and mixed with styrene-butadiene rubber (SBR) binder, sodium carboxymethyl cellulose (CMC-Na) thickener and carbon black (Super P) conductive agent in a weight ratio of 96.2:1.8:1.2:0.8. Then, it was mixed with the micro-expanded graphite powder in a mass ratio of 96:4. An appropriate amount of deionized water solvent was added and the mixture was stirred thoroughly to form a uniform negative electrode slurry. The negative electrode slurry was uniformly coated on the surface of the negative electrode current collector copper foil. After drying and cold pressing, the negative electrode sheet was obtained.

[0270] Example 15

[0271] The preparation method of the secondary battery is similar to that in Example 1, except that the composite graphite material is prepared according to the following method.

[0272] Petroleum residue oil was subjected to delayed coking at 490℃~510℃ to obtain petroleum non-needle coke raw coke; the raw coke was crushed, shaped and graded to obtain coke powder with a volume average particle size Dv50 of 7.0μm, which was used as the main raw material for composite graphite materials.

[0273] For the interlayer spacing d 002 Micro-expanded graphite with a particle size of 0.3363 nm (expansion ratio of 180) was pulverized, shaped and classified to obtain micro-expanded graphite powder with a volume average particle size Dv50 of 6.5 μm.

[0274] Coke powder and micro-expanded graphite powder were mixed, then mixed with coal tar pitch as a binder, and granulated. The resulting granules had a volume average particle size (Dv50) of approximately 9 μm. The granulated product was placed in a graphite crucible, which was then placed in an Atchison graphitization furnace. Resistance material was filled around the graphite crucible, and an electric current was passed through the resistance material to generate heat. Graphitization was then performed at approximately 3000°C to obtain bulk particles.

[0275] The obtained bulk particles are mixed with organic carbon source petroleum asphalt and then carbonized in a track kiln at a maximum temperature of about 1150°C for about 4 hours to form a coating layer on at least a portion of the surface of the bulk particles, thus obtaining a composite graphite material.

[0276] Among them, based on the total mass of the obtained composite graphite material, the mass percentage of the added micro-expanded graphite powder is 20%, the mass percentage of the added binder is 6%, and the mass percentage of the added organic carbon source is 3% such that the mass percentage of the amorphous carbon obtained after the organic carbon source is carbonized is 3%.

[0277] Example 16

[0278] The preparation method of the secondary battery is similar to that in Example 1, except that the composite graphite material is prepared according to the following method.

[0279] Petroleum residue oil was subjected to delayed coking at 490℃~510℃ to obtain petroleum non-needle coke raw coke; the raw coke was crushed, shaped and graded to obtain coke powder with a volume average particle size Dv50 of 11.5μm, which was used as the main raw material for composite graphite materials.

[0280] For the interlayer spacing d 002 Micro-expanded graphite with a particle size of 0.3363 nm (expansion ratio of 180) was pulverized, shaped and classified to obtain micro-expanded graphite powder with a volume average particle size Dv50 of 7.5 μm.

[0281] Coke powder and micro-expanded graphite powder were mixed, then mixed with coal tar pitch as a binder, and granulated. The resulting granules had a volume average particle size (Dv50) of approximately 14.5 μm. The granulated product was placed in a graphite crucible, which was then placed in an Atchison graphitization furnace. Resistance material was filled around the graphite crucible, and an electric current was passed through the resistance material to generate heat. Graphitization was then performed at approximately 3000°C to obtain bulk particles.

[0282] The obtained bulk particles are mixed with organic carbon source petroleum asphalt and then carbonized in a track kiln at a maximum temperature of about 1150°C for about 4 hours to form a coating layer on at least a portion of the surface of the bulk particles, thus obtaining a composite graphite material.

[0283] Among them, based on the total mass of the obtained composite graphite material, the mass percentage of the added micro-expanded graphite powder is 1%, the mass percentage of the added binder is 6%, and the mass percentage of the added organic carbon source is 3% such that the amorphous carbon obtained after carbonization of the organic carbon source is 3%.

[0284] Comparative Example 1

[0285] The preparation method of the secondary battery is similar to that of Example 1, except that conventional uncoated artificial graphite is used as the negative electrode active material. The artificial graphite is prepared according to the following method.

[0286] Petroleum residue oil was subjected to delayed coking at 490℃~510℃ to obtain petroleum non-needle coke raw coke; the raw coke was then crushed, shaped and graded to obtain coke powder with a volume average particle size Dv50 of 9.5μm.

[0287] Coke powder was mixed with coal tar pitch as a binder, and then granulated. The resulting particles had a volume average particle size (Dv50) of approximately 13 μm. The granulated product was placed in a graphite crucible, which was then placed in an Atchison graphitization furnace. Resistance material was filled around the crucible, and an electric current was applied to generate heat. Graphitization was then performed at approximately 3000°C to obtain artificial graphite. The binder content was 6% by mass, based on the total mass of the obtained artificial graphite.

[0288] Comparative Example 2

[0289] The preparation method of the secondary battery is similar to that in Example 1, except that the composite graphite material is prepared according to the following method.

[0290] Petroleum residue oil was subjected to delayed coking at 490℃~510℃ to obtain petroleum non-needle coke raw coke; the raw coke was crushed, shaped and graded to obtain coke powder with a volume average particle size Dv50 of 9.5μm, which was used as the main raw material for composite graphite materials.

[0291] Coke powder was mixed with coal tar pitch as a binder, and then granulated. The resulting granules had a volume average particle size (Dv50) of approximately 13 μm. The granulated product was placed in a graphite crucible, which was then placed in an Atchison graphitization furnace. Resistance material was filled around the graphite crucible, and an electric current was passed through the resistance material to generate heat. Graphitization was then performed at approximately 3000°C to obtain bulk particles.

[0292] The obtained bulk particles are mixed with organic carbon source petroleum asphalt and then carbonized in a track kiln at a maximum temperature of about 1150°C for about 4 hours to form a coating layer on at least a portion of the surface of the bulk particles, thus obtaining a composite graphite material.

[0293] Among them, based on the total mass of the obtained composite graphite material, the mass percentage of the added binder is 6%, and the mass percentage of the added organic carbon source is 3% such that the amorphous carbon obtained after carbonization of the organic carbon source is 3%.

[0294] Test section

[0295] The Dv50 of the negative electrode active material and the compaction density of the powder, as well as the compaction density of the negative electrode film, were tested according to the methods described in the instruction manual.

[0296] (1) Test of air oxidation temperature T0 of composite graphite materials

[0297] The tests were conducted using a Netzsch STA 449F3 simultaneous thermal analyzer (Germany). First, 10 ± 0.05 mg of the composite graphite material sample was weighed into a flat-bottomed Al₂O₃ crucible, without a lid. The instrument parameters were set as follows: purge gas was air with a flow rate of 60 mL / min; protective gas was nitrogen with a flow rate of 20 mL / min; the heating rate was set to 5 °C / min; and the test temperature range was 35 °C to 950 °C. Below 500 °C, since there are no characteristic peaks in this stage, rapid heating can be performed, for example, with a heating rate set to 10 °C / min.

[0298] After the thermogravimetric test, the thermogravimetric curve (TG) and differential thermogravimetric curve (DTG) of the composite graphite material are obtained. The peak temperature T1 of the maximum area peak is read from the differential thermogravimetric curve. The intersection of the two tangents at two points corresponding to the temperatures of 500℃ and T1 is determined on the thermogravimetric curve. The temperature corresponding to the intersection on the thermogravimetric curve is the air oxidation temperature T0 of the composite graphite material.

[0299] (2) Specific capacity testing of composite graphite materials

[0300] Composite graphite material, conductive carbon black (SuperP), and binder polyvinylidene fluoride (PVDF) were mixed uniformly with solvent N-methylpyrrolidone (NMP) at a mass ratio of 91.6:1.8:6.6 to prepare a slurry. The prepared slurry was coated onto a copper foil current collector and dried in an oven for later use. A lithium metal sheet was used as the counter electrode, and a polyethylene (PE) film was used as the separator. Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed at a volume ratio of 1:1:1, and LiPF6 was uniformly dissolved in the above solution to obtain the electrolyte, wherein the concentration of LiPF6 was 1 mol / L. A CR2430 coin cell was assembled in an argon-protected glove box. After the obtained coin cells were left to stand for 12 hours, they were discharged at 25°C with a constant current of 0.05C to 0.005V. After standing for 10 minutes, they were discharged again with a constant current of 50μA to 0.005V. After standing for 10 minutes, they were discharged again with a constant current of 10μA to 0.005V. Then, they were charged at a constant current of 0.1C to 2V, and the charging capacity was recorded. The ratio of the charging capacity to the mass of the composite graphite material is the specific capacity of the prepared composite graphite material.

[0301] (3) Secondary battery fast charging performance test

[0302] At 25℃, the secondary battery was charged at a constant current of 0.33C to the charging cutoff voltage of 4.4V, then charged at a constant voltage to a current of 0.05C, left to stand for 5 minutes, and then discharged at a constant current of 0.33C to the discharge cutoff voltage of 2.8V. Its actual capacity was recorded as C0.

[0303] Then, the secondary battery was sequentially charged at a constant current of 0.5C0, 1C0, 1.5C0, 2C0, 2.5C0, 3C0, 3.5C0, 4C0, and 4.5C0 until the full battery charging cutoff voltage of 4.4V or the negative terminal cutoff potential of 0V (whichever comes first). After each charging, it was discharged at 1C0 until the full battery discharge cutoff voltage of 2.8V. The state of charge (SOC) was recorded at different charging rates until 10%, 20%, 30%...80%. By plotting the negative electrode potential corresponding to the state of charge (SOC), rate-negative electrode potential curves are generated for different SOC states. Linear fitting yields the charging rate corresponding to a negative electrode potential of 0V for each SOC state. This charging rate is the charging window for that SOC state, denoted as C10%SOC, C20%SOC, C30%SOC, C40%SOC, C50%SOC, C60%SOC, C70%SOC, and C80%SOC. The charging time T (min) from 10% SOC to 80% SOC is calculated using the formula (60 / C20%SOC + 60 / C30%SOC + 60 / C40%SOC + 60 / C50%SOC + 60 / C60%SOC + 60 / C70%SOC + 60 / C80%SOC) × 10%. A shorter time indicates better fast-charging performance of the secondary battery.

[0304] (4) Secondary battery cycle life test

[0305] At 25℃, the secondary battery was charged at a constant current of 0.33C to the charging cutoff voltage of 4.4V, then charged at a constant voltage to a current of 0.05C, allowed to stand for 5 minutes, and then discharged at a constant current of 0.33C to the discharge cutoff voltage of 2.8V. Its initial capacity was recorded as C0. Then, the charging and discharging were performed according to the strategy described in Table 1, recording the discharge capacity Cn for each cycle until the cycle capacity retention (i.e., Cn / C0 × 100%) reached 80%, at which point the number of cycles was recorded. A higher number of cycles indicates a longer cycle life for the secondary battery.

[0306] Table 1

[0307] State of charge SOC of secondary battery Charge rate (C) 0～10％ 0.33 10％～20％ 5.2 20％～30％ 4.5 30％～40％ 4.2 40％～50％ 3.3 50％～60％ 2.6 60％～70％ 2 70％～80％ 1.5 80％～100％ 0.33

[0308] (5) Low-temperature power performance test of secondary batteries

[0309] At 25℃, the secondary battery was charged at a constant current of 0.33C to the charging cutoff voltage of 4.4V, then charged at a constant voltage to a current of 0.05C, allowed to stand for 5 minutes, and then discharged at a constant current of 0.33C to the discharge cutoff voltage of 2.8V. The initial energy was recorded as P0. The same secondary battery was then charged at a constant current of 0.33C to the charging cutoff voltage of 4.4V, then charged at a constant voltage to a current of 0.05C, allowed to stand for 5 minutes, and then the temperature of the constant temperature chamber was adjusted to -30℃ and allowed to stand for 3 hours. Finally, the battery was discharged at a constant current of 0.33C to the discharge cutoff voltage of 2.5V, and the energy at this point was recorded as P1. P1 / P0 is the discharge energy retention rate of the secondary battery.

[0310] Table 2 shows the preparation parameters of the composite graphite materials in Examples 1-16 and Comparative Examples 1-2.

[0311] Table 3 shows the test results of Examples 1-16 and Comparative Examples 1-2.

[0312] Table 2

[0313]

[0314] Table 3

[0315]

[0316] As can be seen from the test results in Table 3, when the air oxidation temperature T0 of the composite graphite material is between 630℃ and 730℃, the secondary battery can achieve not only high energy density but also significantly improved fast charging performance and low-temperature power performance. Furthermore, the high-rate cycle performance of the secondary battery is also markedly improved.

[0317] FIG. 10 These are the thermogravimetric curves and differential thermogravimetric curves of the composite graphite materials prepared in Example 3 and Comparative Example 2. From... FIG. 10 It can be seen that the composite graphite material of Example 3 has a low air oxidation temperature T0, and the composite graphite material contains a moderate number of end faces and defects, which can enable the secondary battery to have significantly improved fast charging performance and low-temperature power performance while maintaining high energy density.

[0318] The composite graphite materials of Comparative Example 1 and Comparative Example 2 both have high air oxidation temperature T0. The composite graphite materials contain fewer end faces and defects, have poor kinetic performance, and are difficult to use in secondary batteries under high-rate charge and discharge conditions. In addition, the low-temperature power performance of the secondary batteries is also poor.

[0319] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A composite graphite material comprising bulk particles and a coating layer on at least a part of the surface of the bulk particles, the bulk particles being secondary particles in which two or more primary particles are aggregated, the bulk particles comprising artificial graphite, and the coating layer comprising amorphous carbon, characterized in that, The interlayer spacing d of the (002) crystal plane of the composite graphite material is 0.3355 nm to 0.3364 nm. 002 0.3355 nm to 0.3364 nm. The air oxidation temperature T0 of the composite graphite material is 630-710℃; The air oxidation temperature T0 is the temperature corresponding to the intersection of two tangent lines at two points on the thermogravimetric curve of the composite graphite material, the two points corresponding to temperatures of 500℃ and T1, respectively, wherein the T1 is the peak temperature of the maximum area peak in the differential thermogravimetric curve of the composite graphite material, and the thermogravimetric curve and the differential thermogravimetric curve can be obtained by thermogravimetric analysis under the following conditions: sample mass 10±0.05 mg, purge gas air and airflow rate 60 mL / min, temperature rising rate 5℃ / min, and test temperature range 35-950℃; The composite graphite material further comprises a kinetic carbon material, and the raw material of the kinetic carbon material is selected from one or more of hard carbon, micro-expanding graphite, expanded graphite, and graphene.

2. The composite graphite material of claim 1, wherein, The interlayer spacing d of the (002) crystal plane of the composite graphite material is 0.3356 nm to 0.3361 nm. 002 The interlayer spacing d of the (002) crystal plane of the composite graphite material is 0.3356 nm to 0.3361 nm.

3. The composite graphite material of claim 1, wherein, The kinetic carbon material is located at least part of the interface between primary particles in the bulk particles and / or in the coating layer.

4. The composite graphite material of claim 1, wherein, The mass percentage of the kinetic carbon material is 1-30% based on the total mass of the composite graphite material.

5. The composite graphite material of claim 4, wherein, The mass percentage of the kinetic carbon material is 3-30% based on the total mass of the composite graphite material.

6. The composite graphite material of claim 5, wherein, The mass percentage of the kinetic carbon material is 3-20% based on the total mass of the composite graphite material.

7. The composite graphite material of claim 6, wherein, The mass percentage of the kinetic carbon material is 8-15% based on the total mass of the composite graphite material.

8. The composite graphite material according to any one of claims 3-7, wherein, The interlayer spacing d of the (002) crystal plane of the kinetic carbon material feedstock 002 ≥ 0.3358 nm.

9. The composite graphite material of claim 8, wherein, The interlayer spacing d of the (002) crystal plane of the kinetic carbon material raw material is 0.3359 nm to 0.3366 nm. 002 is 0.3359 nm to 0.3366 nm.

10. The composite graphite material of claim 1, wherein, The hard carbon has a specific capacity ≥ 320 mAh / g at 1 V, and / or; the hard carbon has a powder compaction density ≥ 1.05 g / cm3 under a 20000 N acting force 3 .

11. The composite graphite material according to claim 1, wherein, The volume average particle size Dv50 of the composite graphite material is 8.5-14.5μm; and / or, The volume average particle size Dv50 of the bulk particles is 7.5-13.5μm; and / or, The powder compaction density of the composite graphite material under 20000N force is 1.45g / cm 3 1.75g / cm 3 .

12. The composite graphite material according to claim 11, wherein, The volume average particle size Dv50 of the composite graphite material is 10-12μm; and / or, The volume average particle size Dv50 of the bulk particles is 9.0-11.5μm; and / or, The powder compaction density of the composite graphite material under 20000N force is 1.55g / cm 3 1.65g / cm 3 .

13. The composite graphite material of claim 1, wherein, The ratio of the volume average particle size Dv50 of the primary particles to the volume average particle size Dv50 of the secondary particles composed of the primary particles is 0.45-0.

75.

14. The composite graphite material of claim 13, wherein, The ratio of the volume average particle size Dv50 of the primary particles to the volume average particle size Dv50 of the secondary particles composed of the primary particles is 0.55-0.

65.

15. The composite graphite material of claim 1, wherein, The mass percentage of the amorphous carbon in the coating layer is 1-8% based on the total mass of the composite graphite material.

16. The composite graphite material of claim 15, wherein, The mass percentage of the amorphous carbon in the coating layer is 2-5% based on the total mass of the composite graphite material.

17. The composite graphite material of claim 1, wherein, The composite graphite material comprises bulk particles and a coating layer covering at least 80% of the surface of the bulk particles.

18. The composite graphite material of claim 17, wherein, The composite graphite material comprises bulk particles and a coating layer covering at least 90% of the surface of the bulk particles.

19. A method for preparing a composite graphite material, characterized by, The method comprises the steps of: S10, providing a coke powder or a coke powder added with a kinetic carbon material raw material powder, and graphitizing the coke powder or the coke powder added with the kinetic carbon material raw material powder to obtain bulk particles, the bulk particles being secondary particles formed by aggregation of two or more primary particles, the bulk particles comprising artificial graphite; S20, mixing the bulk particles with an organic carbon source, or mixing the bulk particles with the organic carbon source and the kinetic carbon material raw material powder, and forming a coating layer comprising amorphous carbon on at least a part of surfaces of the bulk particles after carbonization treatment to obtain the composite graphite material; the amount of the organic carbon source added based on the total mass of the obtained composite graphite material is such that the mass percentage of amorphous carbon obtained after carbonization of the organic carbon source is 1% to 8%; wherein the kinetic carbon material raw material powder is added in at least one of steps S10 and S20, the kinetic carbon material raw material being selected from one or several of hard carbon, micro-expanding graphite, expanding graphite, graphene, the kinetic carbon material raw material having an interlayer distance d 002 ≥ 0.3358 nm; The air oxidation temperature T0 of the obtained composite graphite material is 630°C to 710°C, the air oxidation temperature T0 being a temperature corresponding to an intersection point of two lines of tangents at two points on a thermogravimetric curve of the composite graphite material, the two points respectively corresponding to 500°C and a T1 temperature, the T1 temperature being a peak top temperature of a maximum area peak in a differential thermogravimetric curve of the composite graphite material, the thermogravimetric curve and the differential thermogravimetric curve being obtained by thermogravimetric analysis performed under the following conditions: sample mass 10±0.05 mg, purging gas being air and gas flow rate being 60 mL / min, temperature rising rate being 5°C / min, and test temperature range being 35°C to 950°C.

20. The method of claim 19, wherein, The interlayer spacing d of the (002) crystal plane of the kinetic carbon material raw material is 0.3359 nm to 0.3366 nm. 002 0.3359 nm to 0.3366 nm.

21. The method of claim 19 or 20, wherein, The total mass percentage of the kinetic carbon material raw material powder added in steps S10 and S20 based on the total mass of the obtained composite graphite material is 1% to 30%.

22. The method of claim 21, wherein, The total mass percentage of the kinetic carbon material raw material powder added in steps S10 and S20 based on the total mass of the obtained composite graphite material is 8% to 15%.

23. The method according to claim 19, wherein the volume average particle size Dv50 of the coke powder is 6 μm to 12 μm; and / or the volume average particle size Dv50 of the kinetic carbon material raw material powder is 3 μm to 12 μm; the ratio of the volume average particle size Dv50 of the coke powder to the volume average particle size Dv50 of the kinetic carbon material raw material powder is 1.05 to 1.

75.

24. The method according to claim 23, wherein the volume average particle size Dv50 of the coke powder is 8 μm to 10 μm; and / or the volume average particle size Dv50 of the kinetic carbon material raw material powder is 4 μm to 9 μm; the ratio of the volume average particle size Dv50 of the coke powder to the volume average particle size Dv50 of the kinetic carbon material raw material powder is 1.2 to 1.

5.

25. The method of claim 19, wherein, The method for providing the coke powder comprises the steps of: graphitizing a coke raw material to obtain coke, and crushing, shaping and classifying the obtained coke to obtain the coke powder; The coke raw material is selected from one or more of a petroleum-based raw material and a coal-based raw material.

26. The method of claim 25, wherein, The coke raw material comprises one or more of a petroleum-based non-needle coke, a petroleum-based needle coke, a coal-based non-needle coke and a coal-based needle coke.

27. The method of claim 19, wherein, In the coke powder added with the kinetic carbon material raw powder, the mass ratio of the coke powder to the kinetic carbon material raw powder is 1-20:99-80.

28. The method of claim 27, wherein, In the coke powder added with the kinetic carbon material raw powder, the mass ratio of the coke powder to the kinetic carbon material raw powder is 3-12:97-88.

29. The method of claim 19, wherein, Further comprising the step of adding a binder in S10, mixing the binder with the coke powder, and then granulating to obtain the bulk granules, or mixing the binder with the coke powder added with the kinetic carbon material raw powder, and then granulating to obtain the bulk granules.

30. The method of claim 29, wherein, The mass percentage of the binder is 3%-12% based on the total mass of the obtained composite graphite material.

31. The method of claim 30, wherein, The mass percentage of the binder is 5%-8% based on the total mass of the obtained composite graphite material.

32. The method of claim 29, wherein, The binder is selected from pitch.

33. The method of claim 29, wherein, The volume average particle size Dv50 of the obtained particles after granulation is 8 μm-14 μm.

34. The method of claim 33, wherein, The volume average particle size Dv50 of the obtained particles after granulation is 9.5 μm-12 μm.

35. The method of claim 19, wherein in S10, the graphitization treatment temperature can be 2800°C-3200°C; and / or; The graphitization treatment time is 10 days-15 days.

36. The method of claim 35, wherein in S10, the graphitization treatment temperature can be 2900°C-3100°C.

37. The method of claim 27, wherein, In S20, the organic carbon source is selected from one or more of coal pitch, petroleum pitch, phenolic resin, and coconut shell.

38. The method of claim 37, wherein, In S20, the organic carbon source is petroleum pitch.

39. The method of claim 19, wherein, The amount of the organic carbon source added is such that the mass percentage of the amorphous carbon obtained after carbonization of the organic carbon source is 2%-5% based on the total mass of the obtained composite graphite material.

40. The method of claim 19, wherein, In S20, the carbonization treatment temperature is 700°C-1800°C; and / or; The carbonization treatment time is 1 h-6 h.

41. The method of claim 40, wherein, In S20, the carbonization treatment temperature is 1000°C-1300°C.

42. A negative electrode sheet comprising a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, characterized by, The negative electrode film layer comprises the composite graphite material according to any one of claims 1-18, or the composite graphite material prepared according to the method of any one of claims 19-41.

43. The method of claim 42, wherein, The negative electrode film layer further comprises an additive selected from one or several of hard carbon, micro-expanded graphite, expanded graphite, graphene, the interlayer spacing d 002 ≥ 0.3358 nm.

44. The method of claim 43, wherein, The interlayer distance d of the additive (002) crystal plane is 0.3359 nm to 0.3366 nm. 002 is 0.3359 nm to 0.3366 nm.

45. The method of claim 42, wherein, The mass percentage of the additive is 1%-20% based on the total mass of the negative electrode film layer.

46. The method of claim 45, wherein, The mass percentage of the additive is 3%-8% based on the total mass of the negative electrode film layer.

47. The negative electrode sheet according to claim 42, wherein The face density of the negative electrode film layer is 0.035 kg / m 2 0.125 kg / m 2 ; and / or; The compaction density of the negative electrode film layer is 1.2 g / cm 3 1.75 g / cm 3 ; and / or; The porosity of the negative electrode film layer is 25%-45%; and / or; The adhesion between the negative electrode film layer and the negative electrode current collector is 4.5 N / m-15 N / m.

48. The negative electrode sheet according to claim 47, wherein The face density of the negative electrode film layer is 0.078 kg / m 2 0.107 kg / m 2 ; and / or; The compaction density of the negative electrode film layer is 1.4 g / cm 3 1.6 g / cm 3 ; and / or; The porosity of the negative electrode film layer is 28%-35%; and / or; The adhesion between the negative electrode film layer and the negative electrode current collector is 8 N / m-12 N / m.

49. A secondary battery comprising the negative electrode sheet according to any one of claims 42-48.

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