Modified graphite and preparation method thereof, battery and electric device

Abstract

The invention provides modified graphite and a preparation method thereof, a battery and an electric device, and belongs to the technical field of batteries. The battery comprises a negative pole piece, the negative pole piece comprises a negative pole film layer, the negative pole film layer comprises modified graphite, and the modified graphite comprises a graphite core, a carbonized asphalt layer coating at least part of the surface of the graphite core and a graphene layer coating at least part of the surface of the carbonized asphalt layer. The high-strength graphene layer is used as the outer layer of the modified graphite, so that the volume expansion of graphite particles in a graphite core when lithium ions are embedded can be limited, and the crushing and cracking of the graphite particles are reduced, thereby reducing the structural change and stress accumulation of the pole piece in the circulation process, further reducing the fracture and reconstruction of an SEI film, and improving the performance of the lithium ion battery. And the cycle stability and the service life of the battery can be improved. Therefore, the cycle performance of the battery can be improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a modified graphite and its preparation method, a battery, and an electrical device. Background Technology

[0002] Graphite, as one of the commonly used negative electrode materials in lithium-ion batteries, has good conductivity, and its layered structure is suitable for lithium insertion and extraction. However, graphite undergoes volume expansion during lithium-ion insertion and volume contraction during extraction. This repeated volume change can lead to the destruction of the graphite interlayer structure, and even cause cracks and breakage of graphite particles. It can also cause the SEI film to rupture and rebuild, increasing the battery's internal resistance and thus reducing the battery's cycle performance. Summary of the Invention

[0003] In view of the above problems, this application provides a modified graphite and its preparation method, a battery and an electrical device, which aim to improve the cycle performance of the battery.

[0004] In a first aspect, this application provides a battery including a negative electrode sheet, the negative electrode sheet including a negative electrode film layer, the negative electrode film layer including modified graphite, the modified graphite including a graphite core, a carbonized pitch layer covering at least a portion of the surface of the graphite core, and a graphene layer covering at least a portion of the surface of the carbonized pitch layer.

[0005] In the technical solution of this application embodiment, the outer layer of the modified graphite is a graphene layer. The high-strength graphene layer acts as a mechanical barrier, which can limit the volume expansion of graphite particles in the graphite core during lithium-ion insertion, reduce the breakage and cracking of graphite particles, thereby reducing structural changes and stress accumulation of the electrode during cycling, and further reducing the rupture and reconstruction of the SEI film, which helps to improve the cycle stability and life of the battery. Therefore, this application can improve the cycle performance of the battery.

[0006] In some embodiments, the carbonized bitumen layer covers the entire surface of the graphite core; and / or, the graphene layer covers the entire surface of the carbonized bitumen layer.

[0007] In the technical solution of this application embodiment, the carbonized asphalt layer and the graphene layer are fully encapsulated, which can further improve the inhibition of graphite particle expansion.

[0008] In some embodiments, the total thickness of the carbonized bitumen layer and the graphene layer is 150 nm to 400 nm.

[0009] In the technical solution of this application embodiment, when the average total thickness of the carbonized asphalt layer and the graphene layer is between 150nm and 400nm, it can effectively suppress the expansion of graphite particles and reduce the resistance of lithium ions during the insertion and extraction process, thereby reducing the impact on the charging and discharging rate of the battery.

[0010] In some embodiments, the mass of the graphene layer is less than the mass of the carbonized asphalt layer; and / or, the thickness of the graphene layer is less than the thickness of the carbonized asphalt layer.

[0011] In the technical solution of this application embodiment, the graphene layer has a small mass. On the one hand, it is not easy to agglomerate during coating, which would affect the dispersion and stability. On the other hand, the small mass of the graphene layer helps to form a thinner graphene layer. When used as a negative electrode material, it can reduce the obstruction to the lithium ion diffusion and deintercalation process, thereby helping to improve the lithium ion migration rate and thus help to improve the rate performance of the battery.

[0012] In some embodiments, the mass ratio of the carbonized bitumen layer to the graphite core is (5-15):100; and / or, the mass ratio of the graphene layer to the graphite core is (0.35-4):100.

[0013] In the technical solution of this application embodiment, when the mass of the carbonized asphalt layer is within this ratio range, it can not only enhance conductivity but also effectively enhance the overall mechanical strength of the modified graphite. When the mass of the graphene layer is within this ratio range, it helps to form a thinner graphene layer, which can not only effectively suppress the expansion of graphite but also does not significantly increase the volume and weight of the battery. Furthermore, the space reserved for expansion in the battery design can be reduced, which is beneficial to improving the energy density of the battery.

[0014] In some embodiments, the particle size D of the graphite core V50 The particle size D of the modified graphite is 10 μm-20 μm; and / or, the particle size D of the modified graphite is... V50 It ranges from 12μm to 23μm.

[0015] In the technical solution of this application embodiment, the particle size D of the modified graphite is... V50 When the graphite core particle size is between 12μm and 23μm, it can reduce the stress generated during lithium-ion intercalation and also reduce the formation of a SEI film on the surface by more lithium ions, thus reducing the initial coulombic efficiency of the battery. The graphite core particle size D... V50 When the particle size is between 10 μm and 20 μm, it is conducive to the formation of particle size D. V50 Modified graphite between 12μm and 23μm.

[0016] In some embodiments, the modified graphite satisfies at least one of the following conditions: the degree of carbonization of the modified graphite is 96.0%-98.8%; the specific surface area of ​​the modified graphite is 1.0 m². 2 / g-2.5m 2 / g; the modified graphite has a powder compaction density of 1.8g / cc-2.1g / cc at 50000N; the modified graphite has a specific capacity of 360mAh / g-370mAh / g.

[0017] In the technical solution of this application embodiment, highly carbonized modified graphite has superior electrical conductivity, chemical stability, and mechanical strength; the specific surface area of ​​the modified graphite is 1.0 m². 2 / g-2.5m 2 When the specific capacity of graphite is between 1.8 g / cc and 2.1 g / cc, it can provide a suitable electrode / electrolyte interface, which is beneficial for ion transport and storage, thereby helping to improve the cycle stability of the battery. When the specific capacity of modified graphite is between 1.8 g / cc and 2.1 g / cc at 50000 N, it can not only enhance the conductivity, but also improve the volumetric energy density of the battery, which helps to improve the battery's range. When the specific capacity of graphite is between 360 mAh / g and 370 mAh / g, it helps to improve the energy density of the battery.

[0018] In some embodiments, the modified graphite accounts for 85%-98% of the mass of the negative electrode film layer.

[0019] In the technical solution of this application embodiment, when the amount of modified graphite added is between 85% and 98%, it can improve both the structural stability of the negative electrode sheet and the capacity of the battery.

[0020] Secondly, this application provides a method for preparing modified graphite, comprising: providing a core material; coating the core material with pitch, carbonizing the pitch-coated product, and coating the carbonized product with graphene to obtain modified graphite; or, coating the core material with pitch, coating the pitch-coated product with graphene, and carbonizing the graphene-coated product to obtain modified graphite.

[0021] In the technical solutions of this application, carbonizing the asphalt-coated product, or carbonizing the asphalt-coated product after graphene coating, can carbonize the asphalt, increasing the overall carbonization degree of the modified graphite, thereby helping to enhance the conductivity and hardness of the modified graphite. Compared to carbonizing the graphene-coated product directly, carbonizing the asphalt-coated product before graphene coating can reduce the damage to the graphene structure caused by the high temperature during the carbonization process. Furthermore, the method of coating graphene first and then carbonizing is easier to control and helps to achieve uniform coating.

[0022] In some embodiments, the mass ratio of the bitumen to the nuclear material is (5-15):100.

[0023] In the technical solution of this application embodiment, when the mass ratio of asphalt to nuclear material is within this range, not only can the conductivity be enhanced, but the overall mechanical strength of modified graphite can also be effectively enhanced.

[0024] In some embodiments, the mass ratio of graphene to carbonized product is (0.3-2.5):100; and / or, the mass ratio of graphene to asphalt coating product is (0.3-2.5):100.

[0025] In the technical solution of this application embodiment, when the amount of graphene added is within this mass ratio range, it can reduce the agglomeration of graphene, which affects its dispersibility and stability, and form a graphene layer with high strength, thereby reducing the shedding of the graphene layer due to mechanical stress during charging and discharging, and thus improving the suppression of graphite particle expansion.

[0026] In some embodiments, the "coating of the core material with asphalt" includes: mixing the core material and asphalt evenly at room temperature.

[0027] In the technical solution of this application embodiment, stirring and mixing at room temperature is beneficial to maintaining the stability of the material during the asphalt coating process, and stirring and mixing at room temperature helps to control the coating process.

[0028] In some embodiments, the "carbonization treatment of the asphalt-coated product" includes: heating the asphalt-coated product to 800℃-1500℃ under an inert atmosphere and holding it at that temperature for 1h-6h; and / or, the "carbonization treatment of the graphene-coated product" includes: heating the graphene-coated product to 800℃-1500℃ under an inert atmosphere and holding it at that temperature for 1h-6h.

[0029] In the technical solution of this application embodiment, the above-mentioned temperature and time help the asphalt to be completely carbonized, and can reduce the impact on graphene.

[0030] In some embodiments, the "graphene coating of carbonized products" includes: mixing the carbonized products and graphene uniformly in a solvent to obtain a mixture, and spray-drying the mixture; and / or, the "graphene coating of asphalt coating products" includes: mixing the asphalt coating products and graphene uniformly in a solvent to obtain a mixture, and spray-drying the mixture.

[0031] In the technical solution of this application embodiment, spray drying can transform a mixture containing carbonized products / asphalt-coated products and graphene into tiny droplets. These droplets are rapidly dried in a hot air stream, allowing graphene to be uniformly distributed on the surface of the carbonized products / asphalt-coated products particles, which helps to form a uniformly coated graphene layer. Furthermore, the spray drying method allows for precise control of the thickness and quality of the graphene layer.

[0032] In some embodiments, "providing the core material" includes: selecting natural graphite ore, coarsely crushing and flotation to obtain the raw material; and crushing, classifying, spheroidizing and purifying the flotation raw material to obtain the core material.

[0033] In the technical solution of this application embodiment, natural graphite has a high specific capacity and compaction density. Using natural graphite as the core material helps to improve the energy density of the battery.

[0034] In the technical solution of this application embodiment, the above-mentioned temperature and time can effectively carbonize asphalt, thereby improving the stability of the asphalt layer during carbonization treatment.

[0035] Thirdly, this application provides a modified graphite, the modified graphite comprising a graphite core, a carbonized pitch layer covering at least a portion of the surface of the graphite core, and a graphene layer covering at least a portion of the surface of the carbonized pitch layer.

[0036] In the technical solution of this application embodiment, the outer layer of modified graphite is a graphene layer. The high-strength graphene layer acts as a mechanical barrier to limit the volume expansion of graphite particles in the graphite core during lithium ion insertion, reduce the breakage and cracking of graphite particles, thereby reducing the structural changes and stress accumulation of the electrode during cycling, and further reducing the rupture and reconstruction of the SEI film, which helps to improve the cycle stability and life of the battery.

[0037] In some embodiments, the carbonized bitumen layer covers the entire surface of the graphite core; and / or, the graphene layer covers the entire surface of the carbonized bitumen layer.

[0038] In the technical solution of this application embodiment, the carbonized asphalt layer and the graphene layer are fully encapsulated, which can further improve the inhibition of graphite particle expansion.

[0039] In some embodiments, the total thickness of the carbonized bitumen layer and the graphene layer is 150 nm to 400 nm.

[0040] In the technical solution of this application embodiment, when the average total thickness of the carbonized asphalt layer and the graphene layer is between 150nm and 400nm, it can effectively suppress the expansion of graphite particles and reduce the resistance of lithium ions during the insertion and extraction process, thereby reducing the impact on the charging and discharging rate of the battery.

[0041] In some embodiments, the mass of the graphene layer is less than the mass of the carbonized asphalt layer; and / or, the thickness of the graphene layer is less than the thickness of the carbonized asphalt layer.

[0042] In the technical solution of this application embodiment, the graphene layer has a small mass. On the one hand, it is not easy to agglomerate during coating, which would affect the dispersion and stability. On the other hand, the small mass of the graphene layer helps to form a thinner graphene layer. When used as a negative electrode material, it can reduce the obstruction to the lithium ion diffusion and deintercalation process, thereby helping to improve the lithium ion migration rate and thus help to improve the rate performance of the battery.

[0043] In some embodiments, the mass ratio of the carbonized bitumen layer to the graphite core is (5-15):100; and / or, the mass ratio of the graphene layer to the graphite core is (0.35-4):100.

[0044] In the technical solution of this application embodiment, when the mass of the carbonized asphalt layer is within this ratio range, it can not only enhance conductivity but also effectively enhance the overall mechanical strength of the modified graphite. When the mass of the graphene layer is within this ratio range, it helps to form a thinner graphene layer, which can not only effectively suppress the expansion of graphite but also does not significantly increase the volume and weight of the battery. Furthermore, the space reserved for expansion in the battery design can be reduced, which is beneficial to improving the energy density of the battery.

[0045] In some embodiments, the particle size D of the graphite core V50 The particle size D of the modified graphite is 10 μm-20 μm; and / or, the particle size D of the modified graphite is... V50 It ranges from 12μm to 23μm.

[0046] In the technical solution of this application embodiment, the particle size D of the modified graphite is... V50 When the graphite core particle size is between 12μm and 23μm, it can reduce the stress generated during lithium-ion intercalation and also reduce the formation of a SEI film on the surface by more lithium ions, thus reducing the initial coulombic efficiency of the battery. The graphite core particle size D... V50 When the particle size is between 10 μm and 20 μm, it is conducive to the formation of particle size D. V50 Modified graphite between 12μm and 23μm.

[0047] In some embodiments, the modified graphite satisfies at least one of the following conditions: the degree of carbonization of the modified graphite is 96.0%-98.8%; the specific surface area of ​​the modified graphite is 1.0 m². 2 / g-2.5m 2 / g; the modified graphite has a powder compaction density of 1.8g / cc-2.1g / cc at 50000N; the modified graphite has a specific capacity of 360mAh / g-370mAh / g.

[0048] In the technical solution of this application embodiment, highly carbonized modified graphite has superior electrical conductivity, chemical stability, and mechanical strength; the specific surface area of ​​the modified graphite is 1.0 m². 2 / g-2.5m 2 When the specific capacity of graphite is between 1.8 g / cc and 2.1 g / cc, it can provide a suitable electrode / electrolyte interface, which is beneficial for ion transport and storage, thereby helping to improve the cycle stability of the battery. When the specific capacity of modified graphite is between 1.8 g / cc and 2.1 g / cc at 50000 N, it can not only enhance the conductivity, but also improve the volumetric energy density of the battery, which helps to improve the battery's range. When the specific capacity of graphite is between 360 mAh / g and 370 mAh / g, it helps to improve the energy density of the battery.

[0049] Fourthly, this application provides an electrical device including any of the batteries described above.

[0050] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0051] Figure 1 This is a schematic diagram of the vehicle structure in some embodiments of this application;

[0052] Figure 2 This is a schematic diagram showing the exploded structure of the battery in some embodiments of this application;

[0053] Figure 3 This is a schematic diagram showing the exploded structure of a single battery cell in some embodiments of this application.

[0054] Marker explanation:

[0055] 1000 vehicles;

[0056] Battery 100, controller 200, motor 300;

[0057] Box 10, Part 11, Part 2 12;

[0058] Battery cell 20, end cap 21, housing 22, electrode assembly 23. Detailed Implementation

[0059] The following embodiments are only used to illustrate the technical solutions of this application more clearly, and are therefore only examples and should not be used to limit the scope of protection of this application.

[0060] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0061] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0062] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0063] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0064] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces). The term "at least one" refers to one or more.

[0065] Graphite expands in volume when lithium ions are inserted and contracts in volume when they are extracted. This repeated volume change can damage the interlayer structure of graphite, and even cause cracks and breakage of graphite particles. It can also cause the SEI film to rupture and rebuild, increasing the internal resistance of the battery and thus reducing the battery's cycle performance.

[0066] In some embodiments, graphite is made into smaller particles to reduce stress during lithium-ion intercalation, thereby reducing expansion. However, the increased specific surface area of ​​smaller graphite particles may lead to more lithium ions forming an SEI film on the surface, resulting in a decrease in the battery's initial coulombic efficiency. Other embodiments reduce electrode compaction density to provide more space to buffer volume changes during lithium-ion intercalation; however, reducing electrode compaction density significantly reduces the battery's volumetric energy density, contradicting the development trend of high energy density in lithium batteries. Modification of the material itself can be used to reduce its volume change.

[0067] Based on the above considerations, a battery is designed and disclosed, wherein the negative electrode film layer of the negative electrode sheet includes modified graphite, the modified graphite including a graphite core, a carbonized pitch layer covering at least a portion of the surface of the graphite core, and a graphene layer covering at least a portion of the surface of the carbonized pitch layer.

[0068] In such batteries, the high-strength graphene layer acts as a mechanical barrier, limiting the volume expansion of graphite particles during lithium-ion insertion, reducing graphite particle breakage and cracking, thereby reducing structural changes and stress accumulation in the electrode during cycling, and further reducing the rupture and rebuilding of the SEI film, which helps improve the cycle stability and lifespan of the battery.

[0069] The batteries disclosed in this application can be used, but are not limited to, in electrical devices such as vehicles, ships, or aircraft. The power system of such electrical devices can also be composed of batteries disclosed in this application.

[0070] This application provides an electrical device that uses a battery as a power source. The electrical device can be, but is not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0071] For ease of explanation, the following embodiments will be described using a vehicle 1000 as an example of an electrical device according to an embodiment of this application.

[0072] Reference Figure 1As shown, vehicle 1000 can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. A battery 100 is installed inside vehicle 1000, and the battery 100 can be located at the bottom, front, or rear of vehicle 1000. The battery 100 can be used to power vehicle 1000; for example, the battery 100 can serve as the operating power source for vehicle 1000. Vehicle 1000 may also include a controller 200 and a motor 300. The controller 200 is used to control the battery 100 to supply power to the motor 300, for example, to meet the power needs of vehicle 1000 during starting, navigation, and driving.

[0073] In some embodiments of this application, the battery 100 can not only serve as the operating power source for the vehicle 1000, but also as the driving power source for the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0074] In some embodiments of this application, the battery 100 may be a single battery cell, a battery module, or a battery pack, see reference. Figure 2 As shown, taking battery 100 as an example of a battery module, battery 100 may include a housing 10 and a battery cell 20, with the battery cell 20 housed within the housing 10. The housing 10 provides a space for the battery cell 20 and can have various structures. In some embodiments, the housing 10 may include a first portion 11 and a second portion 12, which overlap each other, jointly defining a space for accommodating the battery cell 20. The second portion 12 may be a hollow structure with one open end, and the first portion 11 may be a plate-like structure, covering the open side of the second portion 12 so that the first portion 11 and the second portion 12 jointly define the space. Alternatively, both the first portion 11 and the second portion 12 may be hollow structures with one open side, with the open side of the first portion 11 covering the open side of the second portion 12. Of course, the housing 10 formed by the first portion 11 and the second portion 12 can have various shapes, such as a cylinder, a cuboid, etc.

[0075] In battery 100, there can be multiple battery cells 20, which can be connected in series, parallel, or in a mixed manner. A mixed connection means that multiple battery cells 20 are connected in both series and parallel configurations. Multiple battery cells 20 can be directly connected in series, parallel, or in a mixed manner, and then the entire assembly of the multiple battery cells 20 is housed within the housing 10. Alternatively, battery 100 can also be composed of multiple battery cells 20 first connected in series, parallel, or in a mixed manner to form a battery module, and then multiple battery modules are connected in series, parallel, or in a mixed manner to form a whole, which is also housed within the housing 10. Battery 100 may also include other structures; for example, it may include a busbar component for electrical connection between the multiple battery cells 20.

[0076] Each battery cell 20 can be a secondary battery or a primary battery; the battery cell 20 can be cylindrical, flat, cuboid or other shapes.

[0077] refer to Figure 3 As shown, the battery cell 20 refers to the smallest unit that makes up the battery. The battery cell 20 includes an end cap 21, a housing 22, an electrode assembly 23, and other functional components.

[0078] End cap 21 refers to a component that covers the opening of housing 22 to isolate the internal environment of battery cell 20 from the external environment. The shape of end cap 21 can be adapted to the shape of housing 22 to fit it. Optionally, end cap 21 can be made of a material with certain hardness and strength (such as aluminum alloy), so that end cap 21 is not easily deformed under pressure or impact, allowing battery cell 20 to have higher structural strength. Functional components such as electrode terminals can be provided on end cap 21. Electrode terminals can be used for electrical connection with electrode assembly 23 for outputting or inputting electrical energy into battery cell 20. In some embodiments, end cap 21 can also be provided with a pressure relief mechanism for releasing internal pressure when the internal pressure or temperature of battery cell 20 reaches a threshold. The material of end cap 21 can also be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and this application embodiment does not impose any special limitations on this. In some embodiments, an insulating element may be provided on the inner side of the end cap 21. The insulating element can be used to isolate the electrical connecting pieces inside the housing 22 from the end cap 21 to reduce the risk of short circuit. For example, the insulating element may be made of plastic, rubber, etc.

[0079] The housing 22 is a component used to cooperate with the end cap 21 to form the internal environment of the battery cell 20. This internal environment can accommodate the electrode assembly 23, electrolyte, and other components. The housing 22 and the end cap 21 can be independent components. An opening can be provided on the housing 22, and the end cap 21 can be used to close the opening to form the internal environment of the battery cell 20. Alternatively, the end cap 21 and the housing 22 can be integrated. Specifically, the end cap 21 and the housing 22 can form a common connecting surface before other components are inserted into the housing. When it is necessary to encapsulate the interior of the housing 22, the end cap 21 closes the housing 22. The housing 22 can be of various shapes and sizes, such as cuboid, cylindrical, hexagonal prism, etc. Specifically, the shape of the housing 22 can be determined according to the specific shape and size of the electrode assembly 23. The material of the housing 22 can be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc. This application embodiment does not impose any special limitations on this.

[0080] Electrode assembly 23 is the component in the battery cell 20 where electrochemical reactions occur. The casing 22 may contain one or more electrode assemblies 23. The electrode assembly 23 is mainly formed by winding or stacking positive and negative electrode sheets, and typically a separator is provided between the positive and negative electrode sheets. The portions of the positive and negative electrode sheets containing active material constitute the main body of the electrode assembly, while the portions without active material each constitute a tab. The positive and negative tabs may be located together at one end of the main body or separately at both ends. During the charging and discharging process of the battery, the positive and negative active materials react with the electrolyte, and the tabs connect to the electrode terminals to form a current loop.

[0081] Of course, in some other embodiments, the battery 100 may also be integrated with the chassis / body.

[0082] According to some embodiments of this application, this application provides a battery including a negative electrode sheet, the negative electrode sheet including a negative electrode film layer, the negative electrode film layer including modified graphite, the modified graphite including a graphite core, a carbonized asphalt layer covering at least a portion of the surface of the graphite core, and a graphene layer covering at least a portion of the surface of the carbonized asphalt layer.

[0083] Graphite core refers to graphite core material, which can be natural graphite or artificial graphite. This application does not impose any specific restrictions.

[0084] Carbonized asphalt layer refers to the coating layer formed after asphalt has undergone carbonization treatment. Carbonized asphalt layer can improve the overall carbonization degree of modified graphite, which helps to improve the electrical conductivity, chemical stability and mechanical properties of modified graphite.

[0085] The graphene layer refers to a coating layer formed using graphene, which possesses extremely high mechanical strength, excellent electrical conductivity, and chemical stability. Graphene's high mechanical strength and elastic modulus effectively suppress the volume expansion of graphite during lithium-ion intercalation and deintercalation, reducing graphite particle breakage and cracking, and minimizing SEI film rupture and rebuilding, thereby improving battery cycle stability and lifespan. Graphene's excellent electronic conductivity enhances its electron transport efficiency, accelerating lithium-ion transport and allowing for more uniform lithium-ion distribution throughout the graphite anode structure, reducing localized stress concentration and mitigating graphite expansion. Graphene's chemical stability effectively protects the graphite anode from electrolyte corrosion, reduces SEI film formation, lowers anodic expansion, and reduces battery internal resistance, further improving battery cycle stability and safety. Therefore, this application can improve battery cycle performance.

[0086] According to some embodiments of this application, a carbonized bitumen layer covers the entire surface of a graphite core; and / or, a graphene layer covers the entire surface of the carbonized bitumen layer.

[0087] The carbonized bitumen layer covering the entire surface of the graphite core means that the carbonized bitumen completely encapsulates the graphite core, and the graphene layer covering the entire surface of the carbonized bitumen layer means that the graphene completely encapsulates the carbonized bitumen layer. This complete encapsulation by both the carbonized bitumen layer and the graphene layer can further enhance the inhibition of graphite particle expansion.

[0088] According to some embodiments of this application, the total thickness of the carbonized bitumen layer and the graphene layer is 150nm-400nm.

[0089] For example, the total thickness of the carbonized asphalt layer and the graphene layer can be 150nm, 180nm, 200nm, 220nm, 250nm, 270nm, 300nm, 330nm, 350nm, 380nm, or 400nm. It should be noted that, due to uneven coating of the carbonized asphalt layer and the graphene layer, the coating thickness of the carbonized asphalt layer and the graphene layer may differ in different locations, resulting in an inconsistency in the total thickness of the carbonized asphalt layer and the graphene layer. In this case, the total thickness of the carbonized asphalt layer and the graphene layer can be the average of the total thickness at multiple points.

[0090] When the average total thickness of the carbonized asphalt layer and the graphene layer is between 150nm and 400nm, it can effectively suppress the expansion of graphite particles and reduce the resistance of lithium ions during insertion and extraction, thereby reducing the impact on the charge and discharge rate of the battery.

[0091] According to some embodiments of this application, the mass of the graphene layer is less than the mass of the carbonized asphalt layer, and / or the thickness of the graphene layer is less than the thickness of the carbonized asphalt layer.

[0092] The small mass of graphene layers makes them less prone to aggregation during coating, which affects dispersion and stability. Furthermore, the small mass of graphene layers helps to form thinner graphene layers, which can reduce the obstruction to lithium-ion diffusion and deintercalation processes when used as a negative electrode material. This helps to improve the migration rate of lithium ions and thus improve the rate performance of the battery.

[0093] According to some embodiments of this application, the mass ratio of the carbonized bitumen layer to the graphite core is (5-15):100; and / or, the mass ratio of the graphene layer to the graphite core is (0.35-4):100.

[0094] For example, the mass ratio of the carbonized bitumen layer to the graphite core can be 5:100, 8:100, 10:100, 12:100 or 15:100. When the mass of the carbonized bitumen layer is within this range, it can not only enhance the conductivity, but also effectively enhance the overall mechanical strength of the modified graphite.

[0095] The mass ratio of graphene layers to graphite cores can be 0.35:100, 0.4:100, 0.5:100, 0.8:100, 1:100, 1.5:100, 2:100, 2.5:100, 3:100, 3.5:100, or 4:100. When the mass ratio of graphene layers is within this range, it helps to form thinner graphene layers, which can not only effectively suppress the expansion of graphite, but also does not significantly increase the volume and weight of the battery. Furthermore, the space reserved for expansion during battery design can be reduced, which is beneficial to improving the energy density of the battery.

[0096] According to some embodiments of this application, the particle size D of the graphite core is... V50 The particle size of the modified graphite is 10 μm-20 μm; and / or, the particle size D of the modified graphite is... V50 It ranges from 12μm to 23μm.

[0097] Particle size D V50 It also refers to the median particle size, which is the particle size that corresponds to the cumulative percentage of particle size distribution in a particle size distribution. In other words, in a particle group, particles smaller than this particle size and particles larger than this particle size each account for 50%.

[0098] For example, the particle size D of the graphite core V50 The particle size D of the modified graphite can be 10μm, 12μm, 15μm, 17μm, 19μm, or 20μm. V50 The corresponding sizes can be 12μm, 13μm, 16μm, 18μm, 20μm, or 23μm. The particle size D of the modified graphite... V50When the graphite core particle size is between 12μm and 23μm, it can reduce the stress generated during lithium-ion intercalation and also reduce the formation of a SEI film on the surface by more lithium ions, thus reducing the initial coulombic efficiency of the battery. The graphite core particle size D... V50 When the particle size is between 10 μm and 20 μm, it is conducive to the formation of particle size D. V50 Modified graphite between 12μm and 23μm.

[0099] According to some embodiments of this application, the modified graphite satisfies at least one of the following conditions: the degree of carbonization of the modified graphite is 96.0%-98.8%; the specific surface area of ​​the modified graphite is 1.0 m². 2 / g-2.5m 2 / g; the compaction density of modified graphite powder at 50000N is 1.8g / cc-2.1g / cc; the specific capacity of modified graphite is 360mAh / g-370mAh / g.

[0100] The degree of carbonization refers to the ratio of the mass (or number of atoms, etc.) of the carbonaceous structure after carbonization treatment to the mass (or number of atoms) of the carbonizable components in the original material. The degree of carbonization of modified graphite can be measured by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), or Raman spectroscopy.

[0101] When the degree of carbonization of modified graphite is between 96.0% and 98.8%, its carbon atoms form a regular layered arrangement. The increased overlap of electron clouds between layers facilitates electron movement, resulting in superior electrical conductivity. Furthermore, its regular layered structure gives modified graphite a degree of chemical inertness and low surface energy, thus exhibiting high chemical stability. Secondly, the more compact crystal structure of highly carbonized modified graphite enhances its mechanical strength.

[0102] The specific surface area of ​​modified graphite refers to the surface area per unit mass of modified graphite, and can be measured using either gas adsorption or microscopy. Gas adsorption utilizes the adsorption of gases on a solid surface to measure the specific surface area. Commonly used adsorbed gases include nitrogen and argon. By measuring the amount of gas adsorbed under different pressures, the specific surface area is calculated based on an adsorption theory model. Microscopy involves observing the surface morphology of modified graphite using an electron microscope or atomic force microscope, measuring its particle size and shape, and then calculating the specific surface area based on a geometric model.

[0103] The specific surface area of ​​modified graphite is 1.0 m². 2 / g-2.5m 2 When the ratio is between / g, a suitable electrode / electrolyte interface can be provided, which is beneficial for ion transport and storage, thereby helping to improve the cycle stability of the battery.

[0104] The compacted density of modified graphite powder at 50,000 N refers to the mass per cubic centimeter of modified graphite powder after being compacted under a pressure of 50,000 Newtons. The compacted density of modified graphite can be tested using an electronic pressure testing machine.

[0105] When modified graphite powder has a compaction density between 1.8 g / cc and 2.1 g / cc at 50,000 N, the particles are more tightly packed, which facilitates electron transport and enhances conductivity. Furthermore, higher compaction density means more active material can be accommodated in the same volume, thus increasing the battery's volumetric energy density and contributing to improved battery life.

[0106] The specific capacity of modified graphite refers to the amount of charge that a unit mass of graphite can store or release under specific conditions. The specific capacity of modified graphite can be determined through constant current charge-discharge testing or electrochemical impedance spectroscopy analysis. A specific capacity of modified graphite between 360 mAh / g and 370 mAh / g helps to improve the energy density of batteries.

[0107] According to some embodiments of this application, the modified graphite accounts for 85%-98% of the mass of the negative electrode film layer.

[0108] For example, the mass percentage of modified graphite in the negative electrode film can be 85%, 88%, 90%, 92%, 94%, 96%, or 95%. When the amount of modified graphite added is between 85% and 98%, it can improve both the structural stability of the negative electrode sheet and the capacity of the battery.

[0109] In some embodiments, the negative electrode film layer may optionally include a binder. Exemplarily, the binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS). The negative electrode film layer may also optionally include a conductive agent. Exemplarily, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0110] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0111] According to some embodiments of this application, this application also provides a method for preparing modified graphite, comprising: providing a core material; coating the core material with pitch, carbonizing the pitch-coated product, and coating the carbonized product with graphene to obtain modified graphite; or, coating the core material with pitch, coating the pitch-coated product with graphene, and carbonizing the graphene-coated product to obtain modified graphite.

[0112] The material can be natural graphite ore, natural graphite, or artificial graphite; this application does not impose any specific restrictions.

[0113] Asphalt can be either coal tar pitch, a byproduct of coal tar processing, or petroleum pitch. Coal tar pitch has a high carbon content and rich aromatic structures. It has a high viscosity and, after softening upon heating, flows well and coats the surface of the material. Asphalt can also be petroleum pitch, a byproduct of petroleum refining. Petroleum pitch is mainly composed of hydrocarbons and has a wider softening point and viscosity range. Compared to coal tar pitch, petroleum pitch has a relatively lower impurity content.

[0114] Coating the core material with bitumen can be done by mixing bitumen and the core material solids, or by dissolving bitumen to form a bitumen solution and then adding the core material to the bitumen solution for coating. Bitumen itself has a certain degree of conductivity, and after being coated on the surface of the core material, it can form a conductive network, which helps to improve the conductivity of modified graphite; in addition, bitumen coating of the core material can increase its mechanical strength.

[0115] Graphene can be single-layer graphene, a two-dimensional material composed of only one layer of carbon atoms, which has extremely high electrical conductivity and mechanical strength. Graphene can also be few-layer graphene, which refers to graphene materials composed of 2-10 layers of carbon atoms. Furthermore, graphene can be multilayer graphene, which refers to graphene materials composed of more than 10 layers of carbon atoms.

[0116] Graphene coating of carbonized products can be achieved by directly mixing the carbonized products with graphene powder using a mechanical stirrer or ball mill, or by adding the carbonized products to a graphene-containing solution and stirring or ultrasonically treating them to ensure sufficient contact between the carbonized products and graphene. The same principle applies to graphene coating of asphalt-coated products.

[0117] Carbonizing asphalt-coated products, or carbonizing asphalt-coated products after graphene coating, can carbonize the asphalt and increase the overall carbonization degree of modified graphite, thereby helping to enhance the conductivity and hardness of modified graphite.

[0118] Compared to carbonizing graphene-coated products, carbonizing asphalt-coated products before graphene coating can reduce the damage to the graphene structure caused by high temperatures during the carbonization process. Furthermore, the method of coating graphene first and then carbonizing is easier to control and helps to achieve uniform coating.

[0119] According to some embodiments of this application, the mass ratio of bitumen to core material is (5-15):100. When the mass ratio of bitumen to core material is within this range, not only can the conductivity be enhanced, but the overall mechanical strength of the modified graphite can also be effectively enhanced.

[0120] According to some embodiments of this application, the mass ratio of graphene to carbonized product is (0.3-2.5):100; and / or, the mass ratio of graphene to pitch-coated product is (0.3-2.5):100. When the mass of the graphene layer is within this ratio range, it helps to form a thinner graphene layer, which not only effectively suppresses graphite expansion but also does not significantly increase the volume and weight of the battery. Furthermore, the space reserved for expansion during battery design can be reduced, which is beneficial for improving the energy density of the battery.

[0121] According to some embodiments of this application, "coating the nuclear material with asphalt" includes: mixing the nuclear material and asphalt evenly at room temperature.

[0122] The mixing of nuclear materials and asphalt can be carried out in a reaction vessel, which can be a mixer, a vertical vessel, a horizontal vessel, or other similar equipment. There is no specific limitation on the stirring speed during the mixing of nuclear materials and asphalt; in some embodiments, the stirring speed can be 200 r / min-500 r / min, and the stirring time can be 30 min-60 min.

[0123] Nuclear materials do not readily undergo chemical reactions at room temperature, and asphalt also retains its original physical and chemical properties at room temperature. Therefore, mixing at room temperature is beneficial for maintaining the stability of the material during the asphalt coating process. Furthermore, mixing at room temperature allows for easy control of parameters such as mixing speed and time, thus aiding in the control of the coating process.

[0124] According to some embodiments of this application, "carbonizing the asphalt-coated product" includes: heating the asphalt-coated product to 800℃-1500℃ under an inert atmosphere and holding it at that temperature for 1h-6h; and / or, "carbonizing the graphene-coated product" includes: heating the graphene-coated product to 800℃-1500℃ under an inert atmosphere and holding it at that temperature for 1h-6h.

[0125] An inert atmosphere can be an inert gas such as nitrogen, argon, or helium, which can prevent the asphalt coating from oxidizing at high temperatures.

[0126] For example, the carbonization temperature can be 800°C, 1000°C, 1300°C or 1500°C, and the holding time can be 1h, 3h, 4h or 6h. The above temperatures and times help the asphalt to be completely carbonized, while reducing the impact of high temperature on the graphene structure.

[0127] This application does not impose specific limitations on the heating rate. In some embodiments, the heating rate can be set to 5℃ / min-20℃ / min.

[0128] According to some embodiments of this application, "coating carbonized products with graphene" includes: mixing carbonized products and graphene uniformly in a solvent to obtain a mixture, and spray-drying the mixture; and / or, "coating asphalt coating products with graphene" includes: mixing asphalt coating products and graphene uniformly in a solvent to obtain a mixture, and spray-drying the mixture.

[0129] The solvent can be water, ethanol, N-methylpyrrolidone, or dimethylformamide. Water has a certain dispersibility for graphene and is environmentally friendly and cost-effective, making it suitable for large-scale production. Ethanol has a good dispersibility for graphene and can evaporate rapidly during spray drying. Both N-methylpyrrolidone and dimethylformamide have good dispersibility for graphene and can form stable suspensions.

[0130] Spray drying transforms a mixture containing carbonized products / asphalt-coated products and graphene into tiny droplets. These droplets are rapidly dried in a hot air stream, allowing graphene to be uniformly distributed on the surface of the carbonized / asphalt-coated product particles, thus facilitating the formation of a uniformly coated graphene layer. Furthermore, spray drying allows for precise control over the thickness and quality of the graphene layer.

[0131] In some embodiments, a demagnetization step may be included after spray drying. Demagnetization can remove some magnetic impurities, improve the purity of the modified graphite, and give it better conductivity.

[0132] According to some embodiments of this application, "providing the core material" includes: selecting natural graphite ore, obtaining raw material through coarse crushing and flotation; and crushing, classifying, spheroidizing, and purifying the flotation raw material to obtain the core material.

[0133] Natural graphite ore can be ore with a carbon content of ≥94%. High carbon content ore helps to improve the electrical conductivity and mechanical strength of modified graphite. In addition, natural graphite has a high specific capacity and compaction density. Using natural graphite as a core material helps to improve the energy density of batteries.

[0134] Coarse crushing can be carried out using jaw crushers and other coarse crushing equipment to crush the raw ore to a particle size between 10mm and 10cm. The purpose of coarse crushing is to reduce the particle size of the raw ore for subsequent processing.

[0135] Flotation is the process of adding reagents to a slurry to obtain graphite concentrate. Reagents are typically added during or after grinding. Grinding involves feeding the coarsely crushed ore into a ball mill or similar equipment to further refine the ore, ensuring complete liberation of graphite minerals from gangue minerals. The resulting particle size is between 90μm and 500μm. The slurry with added flotation reagents is then fed into a flotation machine for flotation. The flotation machine generates a large number of bubbles through agitation and aeration. Hydrophobic graphite minerals adhere to these bubbles and float to the surface, forming a froth layer, while gangue minerals remain in the slurry. The graphite minerals in the froth layer are scraped off, yielding the graphite concentrate.

[0136] Crushing can be done using impact crushers or ball mills. Classification refers to sorting graphite concentrate according to particle size and / or density to obtain particles within the desired size range; classification can be done using vibrating screens or hydrocyclones. Spheroidization is the process of turning particles into spherical shapes through continuous collision and friction; spheroidization can be done using spheroidizing machines or air jet mills. Purification is the process of removing impurities from the ore, which can be done using chemical purification or high-temperature purification. Chemical purification involves mixing the spheroidized material with chemical reagents such as hydrochloric acid or hydrofluoric acid, reacting it under specific temperature and pressure to remove impurities. High-temperature purification involves placing the spheroidized material in a high-temperature furnace and treating it at high temperatures under an inert atmosphere to remove impurities.

[0137] According to some embodiments of this application, this application provides a modified graphite, including a graphite core, a carbonized pitch layer covering at least a portion of the surface of the graphite core, and a graphene layer covering at least a portion of the surface of the carbonized pitch layer.

[0138] According to some embodiments of this application, a carbonized bitumen layer covers the entire surface of a graphite core; and / or, a graphene layer covers the entire surface of the carbonized bitumen layer.

[0139] According to some embodiments of this application, the total thickness of the carbonized bitumen layer and the graphene layer is 150nm-400nm.

[0140] According to some embodiments of this application, the mass of the graphene layer is less than the mass of the carbonized asphalt layer, and / or the thickness of the graphene layer is less than the thickness of the carbonized asphalt layer.

[0141] According to some embodiments of this application, the particle size D of the graphite core is... V50 The particle size of the modified graphite is 10 μm-20 μm; and / or, the particle size D of the modified graphite is... V50 It ranges from 12μm to 23μm.

[0142] According to some embodiments of this application, the modified graphite satisfies at least one of the following conditions: the degree of carbonization of the modified graphite is 96.0%-98.8%; the specific surface area of ​​the modified graphite is 1.0 m². 2 / g-2.5m 2 / g; the compaction density of modified graphite powder at 50000N is 1.8g / cc-2.1g / cc; the specific capacity of modified graphite is 360mAh / g-370mAh / g.

[0143] According to some embodiments of this application, this application also provides an electrical device including any of the batteries described above.

[0144] Example

[0145] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0146] Example 1

[0147] [Preparation of Modified Graphite]

[0148] (1) Select natural graphite ore, and obtain raw materials after coarse crushing and flotation; crush, classify, spheroidize and purify the raw materials after flotation to obtain core materials;

[0149] (2) The core material is coated with asphalt, and the mass ratio of asphalt to core material is 9:100;

[0150] (3) Heat the asphalt-coated product to 1000℃ and keep it at that temperature for 3 hours for carbonation treatment;

[0151] (4) The monolayer graphene and the carbonization product are mixed evenly in deionized water to obtain a mixed solution. The mass ratio of graphene to carbonization product is 1:100. The mixed solution is spray-dried and then demagnetized and sieved to obtain modified graphite.

[0152] [Positive electrode plate]

[0153] The positive electrode sheet includes a positive current collector and a positive electrode film. The positive current collector is aluminum foil, and the positive electrode film includes lithium iron sulfate, conductive carbon black and polyvinylidene fluoride. The mass ratio of lithium iron sulfate, conductive carbon black and polyvinylidene fluoride is 96:2:2.

[0154] Lithium iron phosphate, carbon black, and polyvinylidene fluoride were mixed thoroughly in an appropriate amount of N-methylpyrrolidone solvent at a mass ratio of 96:2:2 to obtain a positive electrode slurry with a solid content of 67%. The positive electrode slurry was uniformly coated onto both surfaces of an aluminum foil using a coating machine. After being air-dried at room temperature, the foil was dried in an oven at 80°C for 12 hours and then cold-pressed to obtain a positive electrode sheet.

[0155] [Negative electrode plate]

[0156] The negative electrode sheet includes a negative current collector and a negative electrode film. The negative current collector is copper foil, and the negative electrode film includes modified graphite, conductive carbon black, thickener sodium carboxymethyl cellulose and binder styrene-butadiene rubber. The mass ratio of modified graphite, conductive carbon black, sodium carboxymethyl cellulose and styrene-butadiene rubber is 96.4:1:1.2:1.4.

[0157] Modified graphite, conductive carbon black, sodium carboxymethyl cellulose, and styrene-butadiene rubber were mixed thoroughly in an appropriate amount of deionized water at a mass ratio of 96.4:1:1.2:1.4 to obtain a negative electrode slurry with a solid content of 53%. The negative electrode slurry was uniformly coated onto both surfaces of a copper foil using a coating machine. After being air-dried at room temperature, it was dried in an oven at 80°C for 12 hours and then cold-pressed to obtain the negative electrode sheet.

[0158] [Isolation membrane]

[0159] The separator is made of 12μm polyethylene film.

[0160] Electrolyte

[0161] 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 then dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0162] [Assembly of button cells]

[0163] The above negative electrode slurry was coated on both surfaces of a copper foil and dried in a vacuum drying oven for later use. A lithium metal sheet was used as the counter electrode and a 12μm polyethylene film was used as the separator. The CR2430 coin cell was assembled with the above electrolyte in an argon-protected glove box.

[0164] [Assembly of a secondary full-cell battery]

[0165] The positive electrode, separator, and negative electrode are stacked in sequence and then wound to obtain an electrode assembly. The electrode assembly is placed in an outer packaging, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a secondary battery is obtained.

[0166] Example 2

[0167] Unlike Example 1, the mass ratio of graphene to carbonized product in this example is 2:100, while the rest is the same as in Example 1.

[0168] Example 3

[0169] Unlike Example 1, the mass ratio of graphene to carbonization product in this example is 2.5:100, while the rest is the same as in Example 1.

[0170] Example 4

[0171] Unlike Example 1, the mass ratio of graphene to carbonization product in this example is 0.3:100, while the rest is the same as in Example 1.

[0172] Example 5

[0173] Unlike Example 1, the mass ratio of asphalt to nuclear material in this example is 11:100, while the rest is the same as in Example 1.

[0174] Example 6

[0175] Unlike Example 1, the mass ratio of asphalt to nuclear material in this example is 7:100, while the rest is the same as in Example 1.

[0176] Example 7

[0177] Unlike Example 1, this example first coats the asphalt coating product with graphene, and then performs carbonization treatment. That is, the preparation method of modified graphite in this example includes:

[0178] (1) Select natural graphite ore, and obtain raw materials after coarse crushing and flotation; crush, classify, spheroidize and purify the raw materials after flotation to obtain core materials;

[0179] (2) The core material is coated with asphalt, and the mass ratio of asphalt to core material is 9:100;

[0180] (3) The monolayer graphene and the asphalt coating product are mixed evenly in deionized water to obtain a mixture. The mass ratio of graphene to carbonized product is 1:100. The mixture is spray-dried to obtain the graphene coating product.

[0181] (4) The graphene-coated product was heated to 1000℃ and kept at that temperature for 3 hours for carbonization treatment.

[0182] (5) Demagnetize and sieve to obtain modified graphite.

[0183] Comparative Example 1

[0184] Unlike Example 1, the graphite in this comparative example is not coated with graphene, and its preparation method includes:

[0185] (1) Select natural graphite ore with a carbon content of ≥94%, and obtain raw materials after coarse crushing and flotation. Then, crush, classify, spheroidize and purify the raw materials after flotation to obtain the core material.

[0186] (2) The core material is coated with asphalt, and the mass ratio of asphalt to core material is 9:100;

[0187] (3) The asphalt-coated product is heated to 1000℃ and kept at that temperature for 3 hours to obtain graphite.

[0188] Comparative Example 2

[0189] Unlike Example 1, the modified graphite in this comparative example comprises a graphite core, a graphene layer, and a carbonized pitch layer arranged sequentially from the inside out. The preparation method of the modified graphite in this comparative example includes:

[0190] (1) Select natural graphite ore with a carbon content of ≥94%, and obtain raw materials after coarse crushing and flotation. Then, crush, classify, spheroidize and purify the raw materials after flotation to obtain the core material.

[0191] (2) The monolayer graphene and the core material are mixed evenly in deionized water to obtain a mixture with a mass ratio of graphene to core material of 1:100. The mixture is then spray-dried.

[0192] (3) The spray-dried product is coated with asphalt, and the mass ratio of asphalt to spray-dried product is 9:100.

[0193] (4) The asphalt-coated product is heated to 1000℃ and kept at that temperature for 3 hours for carbonization treatment. Then it is demagnetized and sieved to obtain modified graphite.

[0194] Performance testing

[0195] Particle size D V50 Particle size distribution was determined by laser diffraction method according to GB / T 19077-2016. The test instrument was a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0196] Specific surface area test: The nitrogen adsorption specific surface area analysis method was adopted according to GB / T 19587-2017, and the result was calculated by the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis was performed using a Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, USA.

[0197] Powder compaction density test at 50000N: The test was conducted according to GB / T 24533-2009 using an electronic pressure testing machine (UTM7305 type). An exemplary test method is as follows: Weigh 1g of modified graphite powder and add it to a container with a bottom area of ​​1.327cm². 2 In the mold, the pressure is increased to 5000 kg (equivalent to 50000 N), held for 30 seconds, then depressurized and held for 10 seconds. The compaction density of the carbon material powder under 50000 N pressure is then recorded and calculated.

[0198] Specific capacity test: At 25℃, the prepared coin cell was first discharged to 0.005V with a constant current of 0.15mA, allowed to stand for 5 minutes, and then discharged to 0.005V with a constant current of 10μA. The first discharge capacity of the coin cell was recorded. After that, it was charged to 2.0V with a constant current of 0.3mA, and the first charge capacity of the coin cell was recorded. The ratio of the charge capacity to the sample mass is the specific capacity of the material.

[0199] Cyclic performance: At 25℃, the secondary battery was charged to 3.65V at a constant current of 0.33C, and then charged to 0.05C at a constant voltage. After standing for 5 minutes, the secondary battery was discharged to 2.5V at a constant current of 0.33C. The discharge capacity at this time was recorded as the initial discharge capacity C0.

[0200] After standing at 45℃ for 1 hour, the secondary battery is charged to 3.65V at a constant current of 1C0, then charged at a constant voltage to a current of 0.05C0. After standing for 5 minutes, the secondary battery is discharged to 2.5V at a constant current of 1C0. After standing for 5 minutes, the above steps are repeated 300 times. The capacity retention rate (%) of the secondary battery after 300 cycles at 45℃ is calculated as: (Discharge capacity of the first cycle / Discharge capacity of the 300th cycle) × 100%.

[0201] Full-charge expansion rate test of fresh electrode sheet of secondary battery: The thickness of negative electrode sheet after cold pressing was measured with a micrometer; at 25°C, the secondary battery that has not been cycled was charged to 3.65V at a constant current of 0.33C, and then charged to 0.05C at a constant voltage.

[0202] Disassemble the above secondary batteries to obtain fully charged electrode sheets, and use a micrometer to test the electrode sheet thickness; Full charge expansion rate (%) of fresh electrode sheets of secondary batteries = (Fully charged disassembled electrode sheet thickness - Cold-pressed electrode sheet thickness) / Cold-pressed electrode sheet thickness × 100%.

[0203] Secondary battery fully charged electrode expansion rate test after 300 cycles at 45℃: The thickness of the negative electrode sheet was obtained after cold pressing using a micrometer; at 25℃, the secondary battery after 300 cycles at 45℃ was charged to 3.65V with a constant current of 0.33C, and then charged to 0.05C with a constant voltage.

[0204] Disassemble the above batteries to obtain fully charged electrode sheets, and use a micrometer to test the electrode sheet thickness; after the secondary battery is cycled at 45℃ for 300 cycles, the fully charged electrode sheet expansion rate (%) = (fully charged disassembled electrode sheet thickness - cold-pressed electrode sheet thickness) / cold-pressed electrode sheet thickness × 100%.

[0205] Test Results

[0206] The test results of Examples 1-7 and Comparative Examples 1-2 are shown in Table 1.

[0207] Table 1 shows the test results of Examples 1-7 and Comparative Examples 1-2.

[0208]

[0209] As shown in Table 1, in the embodiments of this application, the full-charge expansion rate of the fresh negative electrode sheet is at least 24.2% and at most 26.41%, while the full-charge expansion rate of the fresh negative electrode sheet in Comparative Example 1 is 29.1%, which is significantly higher than that of the embodiments of this application. This indicates that the graphene coating in this application can effectively suppress the expansion rate of the electrode sheet. In the embodiments of this application, the full-charge expansion rate of the electrode sheet after 300 cycles at 45°C is at least 29.9% and at most 35.1%, while the full-charge expansion rate of the electrode sheet after 300 cycles at 45°C in Comparative Example 1 is 37.0%. This indicates that the graphene coating layer in this application can effectively suppress the electrode sheet expansion caused by lithium ion insertion / extraction during battery cycling, thereby helping to improve the cycle performance of the battery.

[0210] Furthermore, the full-charge expansion rate of the fresh negative electrode sheet and the full-charge expansion rate of the electrode sheet after 300 cycles at 45°C in the embodiments of this application are both lower than those of Comparative Example 2, indicating that the carbonized asphalt layer first formed on the surface of the graphite core and then the graphene coating can further suppress the expansion of the electrode sheet.

[0211] Comparing Examples 1 and 7, it can be seen that, compared with first coating the graphene and then carbonizing the graphene-coated product, the modified graphite prepared by first carbonizing the pitch-coated product and then coating it with graphene has lower expansion performance, which can further reduce the expansion rate of the negative electrode sheet.

[0212] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A battery comprising a negative electrode sheet, said negative electrode sheet comprising a negative electrode film layer, characterized in that, The negative electrode film layer includes modified graphite, which includes a graphite core, a carbonized pitch layer covering at least a portion of the surface of the graphite core, and a graphene layer covering at least a portion of the surface of the carbonized pitch layer.

2. The battery as described in claim 1, characterized in that, The carbonized bitumen layer covers the entire surface of the graphite core; and / or, the graphene layer covers the entire surface of the carbonized bitumen layer.

3. The battery as described in claim 1 or 2, characterized in that, The total thickness of the carbonized asphalt layer and the graphene layer is 150nm-400nm.

4. The battery as described in claim 3, characterized in that, The mass of the graphene layer is less than the mass of the carbonized asphalt layer; and / or, the thickness of the graphene layer is less than the thickness of the carbonized asphalt layer.

5. The battery as described in claim 4, characterized in that, The mass ratio of the carbonized bitumen layer to the graphite core is (5-15):100; and / or, The mass ratio of the graphene layer to the graphite core is (0.35-4):

100.

6. The battery as described in claim 1 or 2, characterized in that, The particle size D of the graphite core V50 10μm-20μm; and / or, The particle size D of the modified graphite V50 It ranges from 12μm to 23μm.

7. The battery according to any one of claims 1 to 6, characterized in that, The modified graphite satisfies at least one of the following conditions: The degree of carbonization of the modified graphite is 96.0%-98.8%; The modified graphite has a specific surface area of ​​1.0 m². 2 / g-2.5m 2 / g; The modified graphite powder has a compaction density of 1.8 g / cc to 2.1 g / cc at 50,000 N. The specific capacity of the modified graphite is 360mAh / g-370mAh / g.

8. The battery according to any one of claims 1 to 7, characterized in that, The modified graphite accounts for 85%-98% of the mass of the negative electrode film.

9. A method for preparing modified graphite, characterized in that, include: Provide nuclear materials; Modified graphite can be obtained by coating the core material with asphalt, carbonizing the asphalt-coated product, and then coating the carbonized product with graphene. or, Modified graphite is obtained by coating the nuclear material with asphalt, coating the asphalt-coated product with graphene, and then carbonizing the graphene-coated product.

10. The method for preparing modified graphite as described in claim 9, characterized in that, The mass ratio of the asphalt to the nuclear material is (5-15):

100.

11. The method for preparing modified graphite as described in claim 9, characterized in that, The mass ratio of graphene to carbonized product is (0.3-2.5):100; and / or, The mass ratio of graphene to asphalt coating product is (0.3-2.5):

100.

12. The method for preparing modified graphite according to any one of claims 9 to 11, characterized in that, The phrase "coating the nuclear material with asphalt" includes: At room temperature, the core material and asphalt are stirred and mixed evenly.

13. The method for preparing modified graphite according to any one of claims 9 to 11, characterized in that, The "carbonization treatment of asphalt-coated products" includes: Under an inert atmosphere, the asphalt-coated product is heated to 800℃-1500℃ and held at that temperature for 1-6 hours; and / or, The "carbonization treatment of the graphene-coated product" includes: The graphene-coated product was heated to 800℃-1500℃ under an inert atmosphere and held at that temperature for 1h-6h.

14. The method for preparing modified graphite according to any one of claims 9 to 11, characterized in that, The "graphene coating of carbonized products" includes: The carbonized product is mixed uniformly with graphene in a solvent to obtain a mixture, and the mixture is then spray-dried; and / or, The "graphene coating of asphalt coating products" includes: The asphalt coating product and graphene are mixed evenly in a solvent to obtain a mixture, and the mixture is spray-dried.

15. The method for preparing modified graphite according to any one of claims 9 to 11, characterized in that, The "providing of nuclear materials" includes: Natural graphite ore is selected, and the raw material is obtained through coarse crushing and flotation. The raw material after flotation is then crushed, classified, spheroidized, and purified to obtain the core material.

16. A modified graphite, characterized in that, The modified graphite includes a graphite core, a carbonized pitch layer covering at least a portion of the surface of the graphite core, and a graphene layer covering at least a portion of the surface of the carbonized pitch layer.

17. The modified graphite as described in claim 16, characterized in that, The carbonized bitumen layer covers the entire surface of the graphite core; and / or, the graphene layer covers the entire surface of the carbonized bitumen layer.

18. The modified graphite as described in claim 16 or 17, characterized in that, The total thickness of the carbonized asphalt layer and the graphene layer is 150nm-400nm.

19. The modified graphite as described in claim 18, characterized in that, The mass of the graphene layer is less than the mass of the carbonized asphalt layer; and / or, the thickness of the graphene layer is less than the thickness of the carbonized asphalt layer.

20. The modified graphite as described in claim 19, characterized in that, The mass ratio of the carbonized bitumen layer to the graphite core is (5-15):100; and / or, The mass ratio of the graphene layer to the graphite core is (0.35-4):

100.

21. The modified graphite as described in claim 16 or 17, characterized in that, The particle size D of the graphite core V50 10μm-20μm; and / or, The particle size D of the modified graphite V50 It ranges from 12μm to 23μm.

22. The modified graphite according to any one of claims 16 to 21, characterized in that, The modified graphite satisfies at least one of the following conditions: The degree of carbonization of the modified graphite is 96.0%-98.8%; The modified graphite has a specific surface area of ​​1.0 m². 2 / g-2.5m 2 / g; The modified graphite powder has a compaction density of 1.8 g / cc to 2.1 g / cc at 50,000 N. The specific capacity of the modified graphite is 360mAh / g-370mAh / g.

23. An electrical appliance, characterized in that, Includes the battery as described in any one of claims 1 to 8.

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