Secondary battery and power consumption device

Abstract

The present application provides a secondary battery and a power consumption device. The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer. The negative electrode film layer has a first surface away from the negative electrode current collector and a second surface provided opposite to the first surface. Let the thickness of the negative electrode film layer be H. The region within the thickness range from 0.3H from the second surface of the negative electrode film layer is defined as the first region of the negative electrode film layer, and the region within the thickness range from 0.3H from the first surface of the negative electrode film layer is defined as the second region of the negative electrode film layer. The first region contains a first active material, the first active material contains a first carbon-based material, the first carbon-based material has a pore structure, the second region contains a second active material, the second active material contains a second carbon-based material, and at least a part of the surface of the second carbon-based material has a carbon coating layer. On the premise that the secondary battery has a high energy density, the present application can achieve both good kinetic performance and storage performance.

Description

Technical Field

[0001] This application belongs to the technical field of batteries, and specifically relates to secondary batteries and power consumption devices.

Background Art

[0002] In recent years, secondary batteries have been widely used in many fields such as energy storage power systems of hydroelectric, thermal, wind, and solar power plants, power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. As the application range of secondary batteries becomes increasingly wide, serious challenges are required for the performance of secondary batteries. For example, secondary batteries need to balance various performances such as energy density, kinetic performance, and service life. However, the problem faced in the prior art is that when improving the kinetic performance of secondary batteries, it is often difficult to balance the energy density of secondary batteries, and when improving the energy density of secondary batteries, it often affects the kinetic performance and service life of secondary batteries.

Summary of the Invention

[0003] This application is made in view of such problems, and its purpose is to provide a secondary battery and a power consumption device that can balance good kinetic performance and storage performance while the secondary battery has a high energy density.

[0004] A first aspect of the present application is a secondary battery including a negative electrode sheet, the negative electrode sheet including a negative electrode current collector and a negative electrode film layer formed on at least one surface of the negative electrode current collector, the negative electrode film layer having a first surface away from the negative electrode current collector and a second surface provided opposite to the first surface, with the thickness of the negative electrode film layer being H, a region within a thickness range from the second surface of the negative electrode film layer to 0.3H being defined as the first region of the negative electrode film layer, a region within a thickness range from the first surface of the negative electrode film layer to 0.3H being defined as the second region of the negative electrode film layer, the first region including a first active material, the first active material including a first carbon-based material having a pore structure, the second region including a second active material, the second active material including a second carbon-based material, and at least a part of the surface of the second carbon-based material having a carbon coating layer.

[0005] Through intensive research, the inventors have found that by including a second carbon-based material having a carbon coating layer on at least a part of its surface in the second region of the negative electrode film layer and including a first carbon-based material having a pore structure in the first region of the negative electrode film layer, the synergistic effect between the first carbon-based material and the second carbon-based material can be fully exerted. As a result, the negative electrode sheet provided by the present application has a good pore channel structure, high compression density, low volume change, and high active ion transport rate, and on the premise that the secondary battery has a high energy density, it can achieve both good kinetic performance and storage performance.

[0006] In any embodiment of the present application, the second carbon-based material includes secondary particles. Optionally, the quantitative ratio of the secondary particles in the second carbon-based material is 50% or more, and optionally 60% - 80%. When the second carbon-based material contains an appropriate proportion of secondary particles, the active ion channels in the negative electrode film layer can be increased, and the insertion path of active ions can be shortened. As a result, the kinetic performance of the secondary battery can be further improved, the battery polarization can be reduced, and the occurrence of side reactions can also be reduced, thereby enabling the secondary battery to achieve good storage performance.

[0007] In any embodiment of the present application, the graphitization degree of the second carbon-based material is smaller than that of the first carbon-based material. By adjusting the graphitization degree of the second carbon-based material to be smaller than that of the first carbon-based material, it is advantageous for the secondary battery to achieve both high energy density and good kinetic performance.

[0008] In any embodiment of the present application, the gram capacity (capacity per gram) of the second carbon-based material is smaller than that of the first carbon-based material. By combining and using a first carbon-based material having a high capacity and a second carbon-based material having a carbon coating layer, it is advantageous for the secondary battery to achieve both high energy density and good kinetic performance.

[0009] In any embodiment of the present application, the second carbon-based material includes at least one of artificial graphite and natural graphite. Optionally, the second carbon-based material includes artificial graphite.

[0010] In any embodiment of the present application, the graphitization degree of the second carbon-based material is 90.0% - 95.5%, and optionally 90.5% - 95.5%. When the graphitization degree of the second carbon-based material is within the above range, it is advantageous for improving the active ion transport performance of the negative electrode film layer, and thereby the secondary battery can achieve both high energy density and good kinetic performance.

[0011] In any embodiment of the present application, the powder OI value of the second carbon-based material is 2.0 - 6.5, and optionally 2.0 - 6.0. Since the powder OI value of the second carbon-based material is small and each direction of the particles has an active ion insertion port, active ions from the positive electrode can be quickly received, thereby further improving the kinetic performance of the secondary battery.

[0012] In any embodiment of the present application, the volume distribution particle size Dv50 of the second carbon-based material is 10.0 μm - 22.0 μm, and optionally 11.5 μm - 20.0 μm. When the volume distribution particle size Dv50 of the second carbon-based material is within the above range, it is advantageous for improving the transport performance of active ions and electrons, thereby further improving the kinetic performance of the secondary battery. In addition, the specific surface area of the second carbon-based material can be reduced, the occurrence of side reactions can be reduced, and the storage performance of the secondary battery can be improved.

[0013] In any embodiment of the present application, the particle size distribution (Dv90 - Dv10) / Dv50 of the second carbon-based material is ≦1.65, and optionally 0.90 - 1.65. When the particle size distribution (Dv90 - Dv10) / Dv50 of the second carbon-based material is within the above range, its particle deposition performance is good, which is advantageous for improving the compression density of the negative electrode film layer. Thereby, the energy density of the secondary battery can be further improved. In addition, it is advantageous for the negative electrode film layer to have an appropriate void distribution, thereby improving the kinetic performance of the secondary battery.

[0014] In any embodiment of the present application, the tap density of the second carbon-based material is 0.85 g / cm 3 - 1.25 g / cm 3 and optionally 0.90 g / cm 3 - 1.25 g / cm 3 When the tap density of the second carbon-based material is within the above range, the compression density of the negative electrode film layer can be improved, and the energy density of the secondary battery can be improved. In addition, the negative electrode film layer has an appropriate void distribution, which is advantageous for improving the transport performance of active ions and electrons, improving the wetting characteristics of the negative electrode film layer with respect to the electrolyte, and improving the kinetic performance and / or cycle performance of the secondary battery.

[0015] In any embodiment of the present application, the gram capacity of the second carbon-based material is 340 mAh / g - 360 mAh / g, and optionally 345 mAh / g - 360 mAh / g. When the gram capacity of the second carbon-based material is within the above range, while the energy density of the secondary battery can be improved, the second carbon-based material can also have good active ion transport performance, which is also beneficial to the improvement of the kinetic performance of the secondary battery.

[0016] In any embodiment of the present application, the specific surface area of the second carbon-based material is ≤ 2.5 m 2 / g, and optionally 0.95 m 2 / g - 2.5 m 2 / g. When the specific surface area of the second carbon-based material is within the above range, it is advantageous to reduce the occurrence of side reactions and reduce the consumption of active ions due to the formation of the SEI film. Thereby, the secondary battery can achieve both high initial Coulomb efficiency and good cycle performance and storage performance.

[0017] In any embodiment of the present application, the second carbon-based material satisfies I D / I G ≥ 0.280, and optionally, 0.280 ≤ I D / I G ≤ 0.500, where I D represents the D peak intensity at 1350 ± 50 cm -1 in the Raman spectrum, and I G represents the G peak intensity at 1580 ± 50 cm -1 in the Raman spectrum. When the I D / I G of the second carbon-based material is within the above range, the active ion transport performance of the second carbon-based material becomes better, which is thereby advantageous to the improvement of the kinetic performance of the secondary battery.

[0018] In any embodiment of the present application, the first carbon-based material has a carbon coating layer on at least a part of its surface.

[0019] In any embodiment of the present application, the first carbon-based material is 0.15 μm 2including one or more pore structures having the above pore area, and optionally, 0.15 μm 2 -2.0 μm 2 including one or more pore structures having a pore area. When the first carbon-based material includes a pore structure having the above pore area, the pore structure can secure an expansion space necessary for the volume change of its particles, thereby further reducing the risk of generating a new interface due to particle crushing, reducing the occurrence of side reactions, and improving the storage performance of the secondary battery.

[0020] In any embodiment of the present application, the first carbon-based material includes an external region and an internal region located inside the external region. The external region refers to a region formed by extending 0.25L from the surface of the particles of the first carbon-based material to the inside of the particles, where L refers to the minor axis length of the particles of the first carbon-based material. Let the total pore area of the external region be S1 and the total pore area of the internal region be S2, and S2 > S1. When the first carbon-based material further satisfies S2 > S1, the initial Coulomb efficiency of the secondary battery can be further improved, and the storage performance of the secondary battery can be further improved.

[0021] In any embodiment of the present application, 1.5 ≤ S2 / S1 ≤ 500, and optionally, 2 ≤ S2 / S1 ≤ 450. When the S2 / S1 of the first carbon-based material further satisfies being within the above range, the secondary battery can better balance high energy density and good storage performance.

[0022] In any embodiment of the present application, the area of the pore structure in the external region of the first carbon-based material is 0.15 μm 2 or less, and optionally 0.10 μm 2 or less. By controlling the area of the pore structure in the external region of the first carbon-based material within the above range, the external region of the first carbon-based material can have a dense structure, thereby effectively improving the structural stability of the first carbon-based material, avoiding as much as possible the penetration of the electrolyte into the pore structure inside the first carbon-based material particles, reducing the occurrence of side reactions, and effectively improving the storage performance of the secondary battery.

[0023] In any embodiment of the present application, the internal region of the first carbon-based material has one or more pore structures with an area of 0.15 μm 2 or more, and optionally, one or more pore structures with an area of 0.15 μm 2 -2.0 μm 2 . By including pore structures of the above size in the internal region of the first carbon-based material, the pressing force of the roll pressing of the negative electrode sheet can be effectively reduced, particle damage can be effectively reduced, a sufficient and stable expansion space can be ensured for the volume change of the first carbon-based material particles, the risk of crushing of the first carbon-based material particles can be reduced, while the compression density of the negative electrode film layer can be improved, and the energy density of the secondary battery can be improved.

[0024] In any embodiment of the present application, the first carbon-based material includes primary particles. Optionally, the quantitative ratio of the primary particles in the first carbon-based material is 50% or more. When the first carbon-based material includes an appropriate ratio of primary particles, it can have high structural stability, and the occurrence of side reactions can also be reduced. Thereby, the storage performance of the secondary battery can be improved, and the compression density of the negative electrode film layer can also be improved, thereby improving the energy density of the secondary battery.

[0025] In any embodiment of the present application, the first carbon-based material satisfies 0.152 ≦ I D / I G ≦ 0.280, and optionally, 0.155 ≦ I D / I G ≦ 0.220, where I D represents the D peak intensity at 1350 ± 50 cm -1 in the Raman spectrum, and I G represents the G peak intensity at 1580 ± 50 cm -1 in the Raman spectrum. When the I D / I G of the first carbon-based material is within the above range, the first carbon-based material has less irregular carbon and can have a high gram capacity and high chemical stability. Thereby, the occurrence of side reactions can be reduced, and the energy density and storage performance of the secondary battery can be improved.

[0026] In any embodiment of the present application, the X-ray diffraction pattern of the first carbon-based material has a diffraction peak of the 3R-phase 101 crystal plane. Thereby, many active sites can exist on the surface of the first carbon-based material, which is advantageous for the rapid insertion and desorption of active ions.

[0027] In any embodiment of the present application, the X-ray diffraction pattern of the first carbon-based material does not have a diffraction peak of the 3R-phase 012 crystal plane. Thereby, the first carbon-based material particles have few internal defects, which can further reduce the occurrence of side reactions, reduce the irreversible consumption of active ions, and improve the initial Coulomb efficiency and storage performance of the secondary battery.

[0028] In any embodiment of the present application, the specific surface area of the first carbon-based material is 1.0 m 2 / g - 2.1 m 2 / g, and optionally 1.1 m 2 / g - 2.0 m 2 / g. The first carbon-based material has a low specific surface area, which can reduce the consumption of active ions due to the formation of the SEI film and improve the initial Coulomb efficiency and storage performance of the secondary battery.

[0029] In any embodiment of the present application, the volume distribution particle size Dv50 of the first carbon-based material is 8.0 μm - 25.0 μm, and optionally 8.0 μm - 22.0 μm.

[0030] In any embodiment of the present application, the volume distribution particle size Dv90 of the first carbon-based material is 16.0 μm - 45.0 μm, and optionally 16.5 μm - 42.0 μm.

[0031] When the volume distribution particle size Dv50 and / or Dv90 of the first carbon-based material is within the above range, it is advantageous for improving the transport performance of active ions and electrons, which can further improve the kinetic performance of the secondary battery. Also, it can reduce the specific surface area of the first carbon-based material, reduce the occurrence of side reactions, and improve the storage performance of the secondary battery.

[0032] In any embodiment of the present application, the particle size distribution (Dv90 - Dv10) / Dv50 of the first carbon-based material is ≦1.55, and optionally 0.90 - 1.50. When the particle size distribution (Dv90 - Dv10) / Dv50 of the first carbon-based material is within the above range, its particle deposition performance is good, which is beneficial to improving the compression density of the negative electrode film layer. Thereby, the energy density of the secondary battery can be further improved, and it is also beneficial to adjusting the void distribution of the negative electrode film layer, improving the kinetic performance of the secondary battery.

[0033] In any embodiment of the present application, the powder compression density of the first carbon-based material under a pressing force of 20000N is 1.65 g / cm 3 - 2.0 g / cm 3 and optionally 1.68 g / cm 3 - 1.98 g / cm 3 When the powder compression density of the first carbon-based material is within the above range, the compression density of the negative electrode film layer can be improved, and the energy density of the secondary battery can be improved. Also, a reasonable pore structure can be formed between the particles of the negative electrode film layer, improving the transport performance of active ions and electrons, and further being beneficial to improving the kinetic performance of the secondary battery.

[0034] In any embodiment of the present application, the tap density of the first carbon-based material is 0.85 g / cm 3 - 1.30 g / cm 3 and optionally 0.90 g / cm 3 - 1.25 g / cm 3 When the tap density of the first carbon-based material is within the above range, the compression density of the negative electrode film layer can be improved, and the energy density of the secondary battery can be improved. Also, a reasonable pore structure can be formed between the particles of the negative electrode film layer, improving the transport performance of active ions and electrons, and further being beneficial to improving the kinetic performance of the secondary battery.

[0035] In any embodiment of the present application, the gram capacity of the first carbon-based material is ≧ 355 mAh / g, and optionally 355 mAh / g - 370 mAh / g. This is advantageous for improving the energy density of the secondary battery.

[0036] In any embodiment of the present application, the graphitization degree of the first carbon-based material is ≧ 95.5%, and optionally 95.5% - 98.0%. This is advantageous for improving the energy density of the secondary battery.

[0037] In any embodiment of the present application, in the thermogravimetric analysis test of the first carbon-based material under an air atmosphere, the weight loss rate of the first carbon-based material between 35°C and 790°C is ≦ 52%, and optionally 8% - 48%. In this case, the first carbon-based material can have fewer surface defects and / or bulk phase defects, can reduce the consumption of active ions during the storage process of the secondary battery, and is advantageous for improving the storage performance of the secondary battery.

[0038] In any embodiment of the present application, in the thermogravimetric analysis test of the first carbon-based material under an air atmosphere, the maximum weight loss rate of the first carbon-based material is ≦ 5.0% / min, and optionally ≦ 4.8% / min. In this case, the first carbon-based material can have fewer surface defects and / or bulk phase defects, can reduce the consumption of active ions during the storage process of the secondary battery, and is advantageous for improving the storage performance of the secondary battery.

[0039] In any embodiment of the present application, the first active material further includes a third carbon-based material, and the third carbon-based material includes artificial graphite in the form of primary particles. Using the first carbon-based material and the third carbon-based material in combination is advantageous for the negative electrode film layer to have an appropriate pore structure and is also advantageous for improving the active ion transport performance of the negative electrode film layer.

[0040] In any embodiment of the present application, the artificial graphite in the form of primary particles does not have a carbon coating layer on its surface. The artificial graphite in the form of primary particles has a relatively stable surface. When it does not have a carbon coating layer on its surface, it is advantageous for maintaining its relatively low side reaction activity, reducing the occurrence of side reactions, and thereby further improving the cycle performance and storage performance of the secondary battery.

[0041] In any embodiment of the present application, the mass ratio of the third carbon-based material in the first active material is 70 wt% or less, and optionally 15 wt% - 60 wt%.

[0042] In any embodiment of the present application, the graphitization degree of the third carbon-based material is 92.5% - 95.5%, and optionally 92.7% - 95.5%. When the graphitization degree of the third carbon-based material is within the above range, it is advantageous for improving the active ion transport performance of the negative electrode film layer, particularly in the first region, and thereby for enabling the secondary battery to achieve both high energy density and good kinetic performance.

[0043] In any embodiment of the present application, the powder OI value of the third carbon-based material is 4.5 - 11.5, and optionally 4.5 - 11.0. Since the powder OI value of the third carbon-based material is small and it has active ion insertion ports in all directions of the particles, it is advantageous for quickly receiving active ions from the positive electrode, and thereby for further improving the kinetic performance of the secondary battery.

[0044] In any embodiment of the present application, the particle size distribution (Dv90 - Dv10) / Dv50 of the third carbon-based material is ≤ 1.65, and optionally 0.90 - 1.65. When the particle size distribution (Dv90 - Dv10) / Dv50 of the third carbon-based material is within the above range, its particle deposition performance is good, which is advantageous for improving the compression density of the negative electrode film layer, thereby further improving the energy density of the secondary battery, and also advantageous for adjusting the void distribution of the negative electrode film layer and improving the kinetic performance of the secondary battery.

[0045] In any embodiment of the present application, the volume distribution particle size Dv50 of the third carbon-based material is 12.0 μm - 22.0 μm, and optionally 13.5 μm - 20.0 μm. When the volume distribution particle size Dv50 of the third carbon-based material is within the above range, it is beneficial to improve the transport performance of active ions and electrons, thereby further improving the kinetic performance of the secondary battery. In addition, the specific surface area of the third carbon-based material can be reduced, the occurrence of side reactions can be reduced, and the storage performance of the secondary battery can be improved.

[0046] In any embodiment of the present application, the specific surface area of the third carbon-based material is 1.0 m 2 / g - 2.0 m 2 / g, and optionally 1.05 m 2 / g - 1.95 m 2 / g. The third carbon-based material has a low specific surface area, thereby reducing the consumption of active ions due to the formation of the SEI film, reducing the occurrence of side reactions, and improving the initial Coulomb efficiency and storage performance of the secondary battery.

[0047] In any embodiment of the present application, the tap density of the third carbon-based material is 0.95 g / cm 3 -1.25 g / cm 3 and optionally 1.00 g / cm 3 -1.25 g / cm 3 . When the tap density of the third carbon-based material is within the above range, the compression density of the negative electrode film layer can be improved, the energy density of the secondary battery can be improved, and a reasonable pore structure can be formed between the particles of the negative electrode film layer to improve the transport performance of active ions and electrons, which is also beneficial to further improve the kinetic performance of the secondary battery.

[0048] In any embodiment of the present application, the gram capacity of the third carbon-based material is 350 mAh / g - 363 mAh / g, and optionally 352 mAh / g - 362 mAh / g. When the gram capacity of the third carbon-based material is within the above range, the energy density of the secondary battery can be improved, while the transport performance of active ions in the negative electrode film layer can be improved, which is also beneficial to the improvement of the kinetic performance of the secondary battery.

[0049] In any embodiment of the present application, the first region and / or the second region further includes a silicon-based material. The silicon-based material plays a role in improving the pore structure in the negative electrode film layer, facilitating the infiltration and liquid storage of the electrolyte, improving the kinetic performance of the secondary battery, and improving the negative electrode capacity, thereby further improving the energy density of the secondary battery.

[0050] In any embodiment of the present application, both the first region and the second region include a silicon-based material, and the mass ratio of the silicon-based material in the first region is less than or equal to the mass ratio of the silicon-based material in the second region. This is advantageous for improving the infiltration characteristics of the negative electrode film layer with respect to the electrolyte, improving the transport performance of active ions, and improving the cycle performance and / or kinetic performance of the secondary battery.

[0051] In any embodiment of the present application, the intermediate region located between the first region and the second region includes the first active material and / or the second active material.

[0052] In any embodiment of the present application, the porosity of the negative electrode film layer is 18.0% - 36.7%, and optionally 19.0% - 34.0%. This is advantageous for enabling the negative electrode film layer to have both a high capacity and an appropriate pore structure, and further for enabling the secondary battery to have both a high energy density and good storage performance and kinetic performance.

[0053] In any embodiment of the present application, the compression density of the negative electrode film layer is 1.45 g / cm 3 -1.90 g / cm 3 and optionally 1.50 g / cm 3 -1.85 g / cm 3 This is advantageous for enabling the negative electrode film layer to have both a high capacity and good transport performance of active ions and electrons, and further for enabling the secondary battery to have both a high energy density and good storage performance and kinetic performance.

[0054] In any embodiment of the present application, the areal density of the negative electrode film layer is 5.0 mg / cm 2 -25.0 mg / cm 2 and optionally 5.5 mg / cm 2 -22.5 mg / cm 2 . Thereby, it is advantageous for the negative electrode film layer to achieve both high capacity and good transport performance of active ions and electrons, and further advantageous for the secondary battery to achieve both high energy density and good storage performance and kinetic performance.

[0055] In any embodiment of the present application, the OI value of the negative electrode film layer is 35.0 or less, and optionally 8.0 - 35.0. Thereby, it is advantageous for improving the active ion insertion performance of the negative electrode film layer, the negative electrode film layer can also have a low thickness repulsion rate, and further advantageous for the secondary battery to achieve both good storage performance and kinetic performance.

[0056] In any embodiment of the present application, the thickness of the negative electrode film layer is 70 μm - 250 μm, and optionally 90 μm - 220 μm.

[0057] The second aspect of the present application provides a power consumption device including the secondary battery of the first aspect of the present application.

[0058] Since the power consumption device of the present application includes the secondary battery of the present application, it has at least the same advantages as the secondary battery.

Brief Description of Drawings

[0059] To more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that need to be used in the embodiments of the present application are briefly described below. Obviously, the drawings described below are only some embodiments of the present application, and those skilled in the art can also obtain other drawings based on these drawings without creative efforts.

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Description of Reference Numerals

[0060] In the drawings, they are not necessarily drawn to actual scale. The descriptions of the drawing symbols are as follows. 1 Battery pack 2 Upper housing 3 Lower housing 4 Battery module 5 Secondary battery 51 Case 52 Electrode assembly 53 Cover plate 10 Negative electrode sheet 101 Negative electrode current collector 102 Negative electrode film layer 102a First surface 102b Second surface 1021 First region 1022 Second region 1023 Intermediate region 200 First carbon-based material 201 External region 202 Internal region

Embodiments for Carrying Out the Invention

[0061] Hereinafter, embodiments specifically disclosing the secondary battery and the power consumption device of the present application will be described in detail with reference to the drawings as appropriate. However, there may be cases where more detailed explanations than necessary are omitted. For example, detailed explanations of well-known matters or duplicate explanations of actually the same structure may be omitted. This is to avoid the following explanations from becoming unnecessarily redundant and to facilitate the understanding of those skilled in the art. Furthermore, the drawings and the following explanations are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0062] The "range" disclosed in the present application is limited in the form of a lower limit and an upper limit, and a predetermined range is limited by selecting the lower limit and the upper limit that define the boundary of the specific range. The range defined in this way may or may not include the end values, and any combination is possible, that is, it is possible to form one range by combining any lower limit value and any upper limit value. For example, when ranges of 60 - 120 and 80 - 110 are given for a specific parameter, it can be understood that ranges of 60 - 110 and 80 - 120 are also expected. Also, when the minimum range values are 1 and 2, and the maximum range values are 3, 4, and 5, ranges of 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5 are all expected. In the present application, unless otherwise specified, the range of "a - b" represents a shortened expression of any combination of real numbers between a and b. Here, both a and b are real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" are included in this specification, and "0 - 5" is a shortening of the combination of these numerical values. Also, when a certain parameter is described as an integer of 2 or more, it corresponds to the disclosure that the parameter is an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0063] Unless otherwise specified, all embodiments and selectable embodiments of the present application can be combined with each other to form a new technical solution, and such a technical solution should be regarded as being included in the disclosure content of the present application.

[0064] Unless otherwise specified, all technical features of this application and selectable technical features can be combined with each other to form a new technical solution, and such a technical solution should be regarded as being included in the disclosure content of this application.

[0065] Unless otherwise specified, all steps of this application may be performed sequentially, randomly, or preferably sequentially. For example, if the method includes steps (a) and (b), it indicates that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, when it is mentioned that the method may further include step (c), it indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), steps (a), (c), and (b), or steps (c), (a), and (b).

[0066] Unless otherwise specified, the terms "include", "have", and "comprise" described in this application are open-ended and may also be closed-ended. For example, the above "include", "have", and "comprise" can represent further "including", "having", and "comprising" other components not listed, or only "including", "having", and "comprising" the listed components.

[0067] Unless otherwise specified, the term "or" in this application is inclusive. For example, the phrase "A or B" represents "A, B, or both A and B". More specifically, any of the following conditions is satisfied. A is true (or exists) and B is false (or does not exist). A is false (or does not exist) and B is true (or exists). Or both A and B are true (or exist).

[0068] Unless otherwise specified, the terms used in this application have the meanings known to those skilled in the art.

[0069] Unless otherwise specified, the numerical values of the various parameters mentioned in this application can be measured by various test methods commonly used in this field. For example, they can be measured according to the test methods provided in this application.

[0070] Unless otherwise specified, in this application, the term "active ion" refers to an ion that can be inserted and desorbed reciprocally between the positive electrode and the negative electrode of a secondary battery, including but not limited to lithium ions.

[0071] In this application, the terms "a plurality" and "a plurality of types" refer to two or more.

[0072] The inventors have found that in order to improve the kinetic performance of a secondary battery, especially the rapid charging performance, it is important to improve the kinetic performance of the negative electrode. Currently, the kinetic performance of the negative electrode is often improved by reducing the areal density of the negative electrode film layer or reducing the compression density of the negative electrode film layer. However, as proven by many studies, the above methods for improving the negative electrode kinetics only improve the kinetic performance to a certain extent at the initial stage of battery charging, and have no significant effect on improving the kinetic performance at the end stage of battery charging. The kinetic performance of the secondary battery cannot be effectively improved, and thus the secondary battery cannot actually be charged at a high rate. In addition, the energy density of the secondary battery also decreases significantly.

[0073] For example, when improving the energy density of a secondary battery by increasing the compression density of the negative electrode film layer, it often leads to deterioration of the kinetic performance of the secondary battery. In addition, the electrolyte infiltration characteristics of the negative electrode film layer at a high compression density deteriorate, and the risk of crushing of the negative active material particles increases, resulting in an increase in side reactions inside the battery and further affecting the storage performance of the secondary battery.

[0074] Therefore, it is difficult for current secondary batteries to achieve both high energy density and good kinetic performance and storage performance.

[0075] The inventors of the present invention have conducted further research and ingeniously improved the structure of the negative electrode film layer, thereby solving the above problems.

[0076] Specifically, a first aspect of the embodiment of the present application provides a secondary battery.

[0077] In the present application, the type of the secondary battery is not particularly limited. For example, the secondary battery may be a lithium-ion battery or the like. Generally, the secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and the like. In the charge and discharge process of the secondary battery, active ions reciprocate between the positive electrode sheet and the negative electrode sheet for insertion and desorption, and the electrolyte plays a role of conducting active ions between the positive electrode sheet and the negative electrode sheet. The present application does not particularly limit the type of the electrolyte, and it can be selected according to actual needs. For example, the electrolyte may be at least one selected from a solid electrolyte and a liquid electrolyte (i.e., an electrolytic solution). The secondary battery using an electrolytic solution and the secondary battery using a solid electrolyte may further include a separator provided between the positive electrode sheet and the negative electrode sheet to play a role of isolation. [Negative electrode sheet]

[0078] FIGS. 1-3 are schematic diagrams of an embodiment of the negative electrode sheet of the present application. As shown in FIGS. 1-3, the negative electrode sheet 10 includes a negative electrode current collector 101 and a negative electrode film layer 102 formed on at least one surface of the negative electrode current collector 101. The negative electrode film layer 102 has a first surface 102a away from the negative electrode current collector 101 and a second surface 102b provided opposite to the first surface 102a. Let the thickness of the negative electrode film layer be H, and the region within the thickness range from 0.3H from the second surface 102b of the negative electrode film layer be the first region 1021 of the negative electrode film layer, and the region within the thickness range from 0.3H from the first surface 102a of the negative electrode film layer be the second region 1022 of the negative electrode film layer. The first region 1021 includes a first active material including a first carbon-based material, and the first carbon-based material has a pore structure. The second region 1022 includes a second active material including a second carbon-based material, and at least a part of the surface of the second carbon-based material has a carbon coating layer. The thickness H of the negative electrode film layer is the thickness of the negative electrode film layer located on one side of the negative electrode current collector.

[0079] In the present application, "the first carbon-based material has a pore structure" means that the first carbon-based material has a pore structure that can be directly observed from a cross-sectional image (for example, a scanning electron microscope image at a magnification of 1000 times), that is, the pore structure in the main body structure of the raw material for manufacturing the first carbon-based material is not completely filled.

[0080] The inventors have found through research that the first region of the negative electrode film layer contains a first carbon-based material, the second region contains a second carbon-based material, the first carbon-based material has a pore structure, and at least a part of the surface of the second carbon-based material has a carbon coating layer, so that good kinetic performance and storage performance can be achieved simultaneously on the premise that the secondary battery has a high energy density.

[0081] By having a carbon coating layer on at least a part of the surface of the second carbon-based material, its kinetic performance is good, the speed at which active ions are inserted into the negative electrode film layer is improved, the active ion transport performance of the negative electrode film layer is improved, which is advantageous for improving the kinetic performance of the secondary battery. At the same time, the second carbon-based material is located in the second region of the negative electrode film layer, which is advantageous for fully exerting the advantage of its excellent kinetic performance, and is also advantageous for improving the infiltration and retention characteristics of the negative electrode film layer with respect to the electrolyte.

[0082] The first carbon-based material has a pore structure, its compression density is large, the compression density of the negative electrode film layer can be improved, and the energy density of the secondary battery can be improved. Also, it is easy to deform during cold pressing. Thus, when it is located in the first region of the negative electrode film layer, the pressing force of the roll pressing of the negative electrode sheet can be effectively reduced, the particle damage can be effectively reduced, and the occurrence of side reactions can be reduced. The first carbon-based material has a pore structure, and the pore structure can also ensure the expansion space required for the volume change of the particles, reduce the risk of generating new interfaces due to particle crushing, and further reduce the occurrence of side reactions. Also, when the first carbon-based material is located in the first region of the negative electrode film layer, the advantages of its high capacity and high compression density can be fully exerted, and the energy density of the secondary battery can be improved.

[0083] Through intensive research, the inventors of the present invention have found that by including a second carbon-based material having a carbon coating layer on at least a part of the surface in the second region of the negative electrode film layer and including a first carbon-based material having a pore structure in the first region of the negative electrode film layer, the synergistic effect between the first carbon-based material and the second carbon-based material can be further fully exerted. As a result, the negative electrode sheet provided by the present application has a good pore structure, high compression density, low volume change and high active ion transmission rate, and can achieve good kinetic performance and storage performance while the secondary battery has a high energy density.

[0084] In some embodiments, the second carbon-based material includes secondary particles. Optionally, the quantitative ratio of the secondary particles in the second carbon-based material is 50% or more, optionally 55%-95%, 55%-90%, 55%-85%, 55%-80%, 60%-95%, 60%-90%, 60%-85%, 60%-80%. When the second carbon-based material contains an appropriate proportion of secondary particles, the active ion channels in the negative electrode film layer can be increased, and the active ion insertion path can be shortened. As a result, the kinetic performance of the secondary battery can be further improved, the battery polarization can be reduced, and the occurrence of side reactions can be reduced, thereby enabling the secondary battery to have good storage performance.

[0085] In the present application, the quantitative ratio of the secondary particles in the second carbon-based material means that any one test sample is selected in the negative electrode film layer, any plurality of test regions are selected in the test sample, images of the plurality of test regions are obtained using a scanning electron microscope, and the ratio of the number of the second carbon-based material in the secondary particle form to the total number of the second carbon-based material particles is statistically calculated for each image, and the average value of the plurality of statistical results is the quantitative ratio of the secondary particles in the second carbon-based material.

[0086] In some embodiments, the second carbon-based material includes at least one of artificial graphite and natural graphite. Optionally, the second carbon-based material includes artificial graphite.

[0087] In some embodiments, the second carbon-based material includes artificial graphite having a carbon coating layer on at least a part of its surface. Optionally, the quantitative ratio of the artificial graphite in the form of secondary particles in the second carbon-based material is 50% or more, and optionally, it is 55%-95%, 55%-90%, 55%-85%, 55%-80%, 60%-95%, 60%-90%, 60%-85%, 60%-80%.

[0088] In the present application, the quantitative ratio of the artificial graphite in the form of secondary particles in the second carbon-based material means that any one test sample is selected in the negative electrode film layer, any plurality of test regions are selected in the test sample, images of the plurality of test regions are obtained using a scanning electron microscope, and the ratio of the quantity of the artificial graphite in the form of secondary particles to the total number of the second carbon-based material particles in the second region of the negative electrode film layer in each image is statistically analyzed. The average value of the plurality of statistical results is the quantitative ratio of the artificial graphite in the form of secondary particles in the second carbon-based material.

[0089] In some embodiments, 80% or more of the surface of the second carbon-based material is coated with a carbon coating layer, and optionally, 90%-100% of the surface of the second carbon-based material is coated with a carbon coating layer.

[0090] In some embodiments, the carbon in the coating layer on the surface of the second carbon-based material includes amorphous carbon, which is advantageous for improving the kinetic performance of the secondary battery. The carbon may be obtained by carbonizing an organic carbon source. As the organic carbon source, a carbon-containing material suitable for coating known in the art can be employed. For example, it can include one or more of coal pitch, petroleum pitch, phenolic resin, coconut shell, etc.

[0091] In some embodiments, the graphitization degree of the second carbon-based material is smaller than that of the first carbon-based material. Since the second carbon-based material has a small graphitization degree, it has a large interlayer distance, which is advantageous for the rapid insertion and desorption of active ions. The first carbon-based material has a high graphitization degree and a high gram capacity. Therefore, adjusting the graphitization degree of the second carbon-based material to be smaller than that of the first carbon-based material is advantageous for achieving both high energy density and good kinetic performance of the secondary battery.

[0092] In some embodiments, the gram capacity of the second carbon-based material is smaller than that of the first carbon-based material. By combining and using a first carbon-based material having a high capacity and a second carbon-based material having a carbon coating layer, it is advantageous for the secondary battery to achieve both high energy density and good kinetic performance.

[0093] Through further research, the inventors have found that when the second carbon-based material further satisfies one or more of the following conditions while meeting the above design, the performance of the secondary battery can be further improved. For example, at least one of the energy density, storage performance, kinetic performance, and cycle performance of the secondary battery can be improved.

[0094] In some embodiments, the graphitization degree of the second carbon-based material is 90.0% - 95.5%, and optionally 90.5% - 95.5%. When the graphitization degree of the second carbon-based material is within the above range, it is advantageous for improving the active ion transport performance of the negative electrode film layer, and thereby the secondary battery can achieve both high energy density and good kinetic performance.

[0095] In some embodiments, the powder OI value of the second carbon-based material is 2.0 - 6.5, and optionally 2.0 - 6.0. Since the powder OI value of the second carbon-based material is small and it has active ion insertion ports in all directions of the particles, it can rapidly receive active ions from the positive electrode, thereby further improving the kinetic performance of the secondary battery.

[0096] In some embodiments, the volume distribution particle size Dv50 of the second carbon-based material is 10.0 μm - 22.0 μm, and optionally 11.5 μm - 20.0 μm. When the volume distribution particle size Dv50 of the second carbon-based material is within the above range, it is beneficial to improve the transport performance of active ions and electrons, thereby further improving the kinetic performance of the secondary battery. In addition, the specific surface area of the second carbon-based material can be reduced, the occurrence of side reactions can be reduced, and the storage performance of the secondary battery can be improved.

[0097] In some embodiments, the particle size distribution (Dv90 - Dv10) / Dv50 of the second carbon-based material is ≦1.65, and optionally 0.90 - 1.65. When the particle size distribution (Dv90 - Dv10) / Dv50 of the second carbon-based material is within the above range, its particle deposition performance is good, which is beneficial to improving the compression density of the negative electrode film layer, and the energy density of the secondary battery can be further improved. In addition, it is beneficial for the negative electrode film layer to have an appropriate void distribution, improving the kinetic performance of the secondary battery.

[0098] In some embodiments, the tap density of the second carbon-based material is 0.85 g / cm 3 - 1.25 g / cm 3 and optionally 0.90 g / cm 3 - 1.25 g / cm 3 When the tap density of the second carbon-based material is within the above range, the compression density of the negative electrode film layer can be improved, and the energy density of the secondary battery can be improved. In addition, the negative electrode film layer has an appropriate void distribution, improving the transport performance of active ions and electrons, improving the infiltration characteristics of the negative electrode film layer with respect to the electrolyte, and further being beneficial to improving the kinetic performance and / or cycle performance of the secondary battery.

[0099] In some embodiments, the gram capacity of the second carbon-based material is 340 mAh / g - 360 mAh / g, and optionally 345 mAh / g - 360 mAh / g. When the gram capacity of the second carbon-based material is within the above range, while the energy density of the secondary battery can be improved, the second carbon-based material can also have good active ion transport performance, which is also beneficial to the improvement of the kinetic performance of the secondary battery.

[0100] In some embodiments, the specific surface area of the second carbon-based material is ≤ 2.5 m 2 / g, and optionally 0.95 m 2 / g - 2.5 m 2 / g, 0.95 m 2 / g - 2.45 m 2 / g. When the specific surface area of the second carbon-based material is within the above range, it is beneficial to reduce the occurrence of side reactions and reduce the consumption of active ions due to the formation of the SEI film. Thereby, high initial Coulomb efficiency, good cycle performance, and good storage performance can be achieved simultaneously in the secondary battery.

[0101] In some embodiments, the second carbon-based material satisfies I D / I G ≥ 0.280, and optionally, 0.280 ≤ I D / I G ≤ 0.500, where I D represents the intensity of the D peak at 1350 ± 50 cm -1 in the Raman spectrum, and I G represents the intensity of the G peak at 1580 ± 50 cm -1 in the Raman spectrum. When the I D / I G of the second carbon-based material is within the above range, the active ion transport performance of the second carbon-based material becomes better, which is beneficial to the improvement of the kinetic performance of the secondary battery.

[0102] In some embodiments, at least a part of the surface of the first carbon-based material has a carbon coating layer. Optionally, 80% or more of the surface of the first carbon-based material is coated with the carbon coating layer, and further, 90%-100% of the surface of the first carbon-based material is coated with the carbon coating layer.

[0103] In some embodiments, the carbon coating layer includes amorphous carbon and / or crystalline carbon with a graphitization degree of 65%-89%. Thereby, the kinetic performance of the secondary battery can be improved.

[0104] Of course, in some embodiments, the first carbon-based material may not have a carbon coating layer. The first carbon-based material of the present application has a more stable surface. When it does not have a carbon coating layer on its surface, it maintains its low side reaction activity, which is advantageous for reducing the occurrence of side reactions, thereby further improving the cycle performance and / or storage performance of the secondary battery.

[0105] In some embodiments, the first carbon-based material includes one or more pore structures having a pore area of 0.15 μm 2 or more, and optionally, includes one or more pore structures having a pore area of 0.15 μm 2 -2.0 μm 2 When the first carbon-based material includes a pore structure having the above pore area, the pore structure can ensure the expansion space required for the volume change of its particles. Thereby, it is possible to further reduce the risk of generating a new interface due to particle crushing, reduce the occurrence of side reactions, and improve the storage performance of the secondary battery.

[0106] In some embodiments, the first carbon-based material includes an external region and an internal region located inside the external region. The external region is a region formed by extending 0.25L from the particle surface of the first carbon-based material into the particle interior, where L is the short axis length of the first carbon-based material particle. Let the total pore area of the external region be S1 and the total pore area of the internal region be S2, and S2 > S1.

[0107] When the first carbon-based material further satisfies S2 > S1, the first carbon-based material further has the characteristics that the number of pores in the internal region is large and / or the pore size is large, but the number of pores in the external region is small and / or the pore size is small. The pore structure in the internal region of the first carbon-based material can effectively reduce the pressing force of the roll of the negative electrode sheet, effectively reduce the damage of the particles, and further ensure the expansion space required for the volume change of the particles. Thereby, the risk of generating a new interface due to particle crushing can be reduced, and the occurrence of side reactions can be effectively reduced. Since the number of pores in the external region of the first carbon-based material is small and / or the pore size is small, the first carbon-based material particles have a stable structure, and the electrolyte can be avoided from entering the pore structure inside the first carbon-based material particles as much as possible. Thereby, the occurrence of side reactions can be further reduced, and the consumption of active ions due to the formation of the SEI film inside the particles can be reduced. Therefore, when the first carbon-based material further satisfies S2 > S1, the initial Coulomb efficiency of the secondary battery can be further improved, and the storage performance of the secondary battery can be further improved.

[0108] In some embodiments, 1.5 ≤ S2 / S1 ≤ 500, 2 ≤ S2 / S1 ≤ 450, 2.2 ≤ S2 / S1 ≤ 400, 2.4 ≤ S2 / S1 ≤ 300, 2.5 ≤ S2 / S1 ≤ 250, 2.6 ≤ S2 / S1 ≤ 200, 2.8 ≤ S2 / S1 ≤ 150, 3.0 ≤ S2 / S1 ≤ 100. The inventors have further found through research that when the S2 / S1 of the first carbon-based material further satisfies being within the above range, the secondary battery can better balance high energy density and good storage performance.

[0109] In this application, the total pore area S1 of the external region and the total pore area S2 of the internal region of the first carbon-based material can be obtained by testing according to the cross-sectional image of the first carbon-based material.

[0110] In this application, the cross-sectional image of the first carbon-based material includes the cross-sectional image passing through the center of the particles of the first carbon-based material. The "particle center" refers to the range within a radius of 0.1 μm from the geometric center of the particle towards the particle surface.

[0111] In the present application, the minor axis length of a particle refers to the minimum value when the connecting line of two points on the surface of the particle passes through the geometric center of the particle.

[0112] FIG. 4 is a schematic diagram of a cross-sectional image of the particles of the first carbon-based material 200 of the present disclosure, and the cross-sectional image passes through the center of the particles of the first carbon-based material 200. As shown in FIG. 4, L represents the minor axis length of the particles of the first carbon-based material 200, and the region formed by extending a distance of 0.25L from the surface of the particles of the first carbon-based material 200 into the particles is the outer region 201, and the region inside the outer region 201 is the inner region 202.

[0113] The cross-section of the first carbon-based material can be manufactured by using a cross-section polisher (for example, IB-09010 CP type argon ion cross-section polisher of JEOL Ltd., Japan). Then, referring to JY / T010-1996, the cross-section of the first carbon-based material is scanned by using a scanning electron microscope (for example, Sigma300 type scanning electron microscope of ZEISS, Germany), and finally, by using image processing software (for example, AVIZO), the total pore area S1 of the outer region and the total pore area S2 of the inner region of the first carbon-based material are calculated.

[0114] In some embodiments, the minor axis length L of the particles of the first carbon-based material satisfies L≧6 μm, and optionally, 6 μm≦L≦25 μm, 6 μm≦L≦20 μm, 7 μm≦L≦20 μm, 8 μm≦L≦20 μm, 8 μm≦L≦18 μm, 8 μm≦L≦16 μm.

[0115] In some embodiments, the area of the pore structure in the outer region of the first carbon-based material is 0.15 μm 2 is as follows, and optionally 0.10 μm 2The following is the case. Through further research, the inventors of the present invention can control the area of the pore structure in the outer region of the first carbon-based material within the above range, so that the outer region of the first carbon-based material can have a dense structure. Thereby, the structural stability of the first carbon-based material can be effectively improved, the penetration of the electrolyte into the pore structure inside the first carbon-based material particles can be avoided as much as possible, the occurrence of side reactions can be reduced, and the storage performance of the secondary battery can be effectively improved. Of course, this application does not limit that the area of all pore structures in the outer region of the first carbon-based material is all 0.15 μm 2 or less. For example, the area of 95% or more, optionally 99% or more of the pore structures is 0.15 μm 2 or less, optionally 0.10 μm 2 or less can be controlled.

[0116] In some embodiments, the inner region of the first carbon-based material includes one or more pore structures having an area of 0.15 μm 2 or more, and optionally includes one or more pore structures having an area of 0.15 μm 2 -2.0 μm 2 Through further research, the inventors of the present invention can effectively reduce the pressing force of the roll pressing of the negative electrode sheet and effectively reduce particle damage by including pore structures of the above size in the inner region of the first carbon-based material, ensure a sufficient and stable expansion space for the volume change of the first carbon-based material particles, reduce the risk of crushing of the first carbon-based material particles, while improving the compression density of the negative electrode film layer and improving the energy density of the secondary battery.

[0117] In some embodiments, the first carbon-based material includes primary particles. Optionally, the quantitative ratio of the primary particles in the first carbon-based material is 50% or more, for example, 50%-100%, 55%-95%, 60%-100%, 65%-90%, 65%-80%, 70%-100%, 75%-90%, 80%-100%, 90%-100%, or 95%-100%. The first carbon-based material contains an appropriate proportion of primary particles, can have high structural stability, can also reduce the occurrence of side reactions, thereby improving the storage performance of the secondary battery. In addition, the compression density of the negative electrode film layer can also be improved, thereby improving the energy density of the secondary battery.

[0118] In the present application, the quantitative ratio of the primary particles in the first carbon-based material means that in the negative electrode film layer, one test sample is arbitrarily selected, a plurality of test regions are arbitrarily selected in the test sample, images of the plurality of test regions are obtained using a scanning electron microscope, and the ratio of the number of the first carbon-based material in the primary particle form to the total number of the first carbon-based material particles in each image is statistically calculated, and the average value of the plurality of statistical results is the quantitative ratio of the primary particles in the first carbon-based material.

[0119] In some embodiments, all of the first carbon-based materials may be primary particles, that is, the quantitative ratio of the primary particles in the first carbon-based material is 100%.

[0120] In some embodiments, the first carbon-based material satisfies 0.152 ≦ I D / I G ≦ 0.280, and optionally, 0.152 ≦ I D / I G ≦ 0.260, 0.153 ≦ I D / I G ≦ 0.240, 0.155 ≦ I D / I G ≦ 0.220, 0.155 ≦ I D / I G ≦ 0.200, 0.155 ≦ I D / I G ≦ 0.180, and I D is the Raman spectrum at 1350 ± 50 cm-1 represents the D peak intensity in G and I is the G peak intensity in the Raman spectrum at 1580 ± 50 cm -1 of the first carbon-based material. When the I D / I G of the first carbon-based material is within the above range, the first carbon-based material can have less irregular carbon, high gravimetric capacity, and high chemical stability, thereby reducing the occurrence of side reactions and improving the energy density and storage performance of the secondary battery.

[0121] In some embodiments, the X-ray diffraction pattern of the first carbon-based material has a diffraction peak of the 3R phase 101 crystal plane.

[0122] In some embodiments, the X-ray diffraction pattern of the first carbon-based material does not have a diffraction peak of the 3R phase 012 crystal plane.

[0123] The 3R (Rhombohedral) phase is a rhombohedral crystalline carbon having an ABCABC… stacking structure, and the corresponding 2θ in the X-ray diffraction pattern of the diffraction peak of the 3R phase 101 crystal plane is within the range of 43° - 44°, and the corresponding 2θ in the X-ray diffraction pattern of the diffraction peak of the 3R phase 012 crystal plane is within the range of 46° - 47°.

[0124] When the first carbon-based material has a diffraction peak of the 3R phase 101 crystal plane, many active sites can exist on the surface of the first carbon-based material, which is advantageous for the rapid insertion and desorption of active ions.

[0125] Since the first carbon-based material does not have a diffraction peak of the 3R phase 012 crystal plane, the first carbon-based material particles have few internal defects, thereby further reducing the occurrence of side reactions, reducing the irreversible consumption of active ions, and improving the initial Coulomb efficiency and storage performance of the secondary battery.

[0126] As a result of further research, the inventors of the present invention have found that when the first carbon-based material further satisfies one or more of the following conditions while satisfying the above design, the performance of the secondary battery can be further improved. For example, at least one of the energy density, storage performance, kinetic performance, and cycle performance of the secondary battery can be further improved.

[0127] In some embodiments, the specific surface area of the first carbon-based material is 1.0 m 2 / g - 2.1 m 2 / g, and optionally 1.1 m 2 / g - 2.0 m 2 / g, 1.15 m 2 / g - 1.8 m 2 / g. Since the first carbon-based material has a low specific surface area, it can reduce the consumption of active ions due to the formation of the SEI film, and improve the initial Coulomb efficiency and storage performance of the secondary battery.

[0128] In some embodiments, the volume distribution particle size Dv50 of the first carbon-based material is 8.0 μm - 25.0 μm, and optionally 8.0 μm - 22.0 μm.

[0129] In some embodiments, the volume distribution particle size Dv90 of the first carbon-based material is 16.0 μm - 45.0 μm, and optionally 16.5 μm - 42.0 μm.

[0130] When the volume distribution particle size Dv50 and / or Dv90 of the first carbon-based material is within the above range, it is advantageous for improving the transport performance of active ions and electrons, thereby further improving the kinetic performance of the secondary battery. In addition, the specific surface area of the first carbon-based material can be reduced, the occurrence of side reactions can be reduced, and the storage performance of the secondary battery can be improved.

[0131] In some embodiments, the particle size distribution (Dv90 - Dv10) / Dv50 of the first carbon-based material is ≦1.55, and optionally 0.90 - 1.50. When the particle size distribution (Dv90 - Dv10) / Dv50 of the first carbon-based material is within the above range, its particle deposition performance is good, which is beneficial to improving the compression density of the negative electrode film layer. Thereby, the energy density of the secondary battery can be further improved, and it is also beneficial to adjust the void distribution of the negative electrode film layer, improving the kinetic performance of the secondary battery.

[0132] In some embodiments, the powder compression density of the first carbon-based material under a pressing force of 20000N is 1.65 g / cm 3 - 2.0 g / cm 3 and optionally 1.68 g / cm 3 - 1.98 g / cm 3 When the powder compression density of the first carbon-based material is within the above range, the compression density of the negative electrode film layer can be improved, and the energy density of the secondary battery can be improved. Also, a reasonable pore structure can be formed between the particles of the negative electrode film layer, improving the transport performance of active ions and electrons, which is further beneficial to improving the kinetic performance of the secondary battery.

[0133] In some embodiments, the tap density of the first carbon-based material is 0.85 g / cm 3 - 1.30 g / cm 3 and optionally 0.90 g / cm 3 - 1.25 g / cm 3 When the tap density of the first carbon-based material is within the above range, the compression density of the negative electrode film layer can be improved, and the energy density of the secondary battery can be improved. Also, a reasonable pore structure can be formed between the particles of the negative electrode film layer, improving the transport performance of active ions and electrons, which is further beneficial to improving the kinetic performance of the secondary battery.

[0134] In some embodiments, the gram capacity of the first carbon-based material is ≧355 mAh / g, and optionally 355 mAh / g - 370 mAh / g. When the gram capacity of the first carbon-based material is within the above range, it is beneficial to improve the energy density of the secondary battery.

[0135] In some embodiments, the graphitization degree of the first carbon-based material is ≧95.5%, and optionally 95.5%-98.0%. When the graphitization degree of the first carbon-based material is within the above range, it is beneficial to improve the energy density of the secondary battery.

[0136] In some embodiments, in the thermogravimetric analysis test of the first carbon-based material under an air atmosphere, the weight loss rate of the first carbon-based material between 35°C and 790°C is ≦52%, and optionally 8%-48%, 8%-45%, 10%-42%. In this case, the first carbon-based material can have fewer surface defects and / or bulk phase defects, can reduce the consumption of active ions during the storage process of the secondary battery, and is beneficial to improving the storage performance of the secondary battery.

[0137] In some embodiments, in the thermogravimetric analysis test of the first carbon-based material under an air atmosphere, the maximum weight loss rate of the first carbon-based material is ≦5.0% / min, and optionally ≦4.8% / min, ≦4.5% / min. In this case, the first carbon-based material can have fewer surface defects and / or bulk phase defects, can reduce the consumption of active ions during the storage process of the secondary battery, and is beneficial to improving the storage performance of the secondary battery.

[0138] The thermogravimetric analysis test of the first carbon-based material can be carried out with reference to JY / T 014-1996. This application can be carried out under the conditions that the weighed mass of the sample is 10±0.05 mg, air is used as the purge gas, the gas flow rate is 60 mL / min, the heating rate is 5°C / min, and the test temperature range is 35°C-950°C. The test equipment may be a NETZSCH STA 449F3 type simultaneous thermal analyzer of NETZSCH Company in Germany.

[0139] In some embodiments, the first active material further includes a third carbon-based material, and the third carbon-based material includes artificial graphite in the form of primary particles. Using the first carbon-based material and the third carbon-based material in combination is advantageous for the negative electrode film layer to have an appropriate pore structure and is also advantageous for improving the active ion transport performance of the negative electrode film layer.

[0140] In some embodiments, the surface of the artificial graphite in the form of primary particles does not have a carbon coating layer. The artificial graphite in the form of primary particles has a relatively stable surface. When it does not have a carbon coating layer on its surface, it is advantageous for maintaining its relatively low side reaction activity and reducing the occurrence of side reactions, thereby further improving the cycle performance and storage performance of the secondary battery.

[0141] In some embodiments, the mass ratio of the third carbon-based material in the first active material is 70 wt% or less, and optionally 15 wt% - 70 wt%, 25 wt% - 70 wt%, 35 wt% - 70 wt%, 40 wt% - 70 wt%, 15 wt% - 60 wt%, 20 wt% - 60 wt%, 30 wt% - 60 wt%, 40 wt% - 60 wt%.

[0142] The inventors further found through further research that when the third carbon-based material further satisfies one or more of the following conditions while meeting the above design, the performance of the secondary battery can be further improved. For example, it was found that at least one of the energy density, storage performance, kinetic performance, and cycle performance of the secondary battery can be improved.

[0143] In some embodiments, the graphitization degree of the third carbon-based material is 92.5% - 95.5%, and optionally 92.7% - 95.5%. When the graphitization degree of the third carbon-based material is within the above range, it is advantageous for improving the active ion transport performance of the negative electrode film layer, especially in the first region. Thereby, it is advantageous for the secondary battery to achieve both high energy density and good kinetic performance.

[0144] In some embodiments, the OI value of the powder of the third carbon-based material is 4.5 - 11.5, and optionally 4.5 - 11.0. Since the OI value of the powder of the third carbon-based material is small and each direction of the particles has active ion insertion ports, it is advantageous for quickly receiving active ions from the positive electrode, thereby further improving the kinetic performance of the secondary battery. Also, in this case, the anisotropy of the third carbon-based material particles is high, which is advantageous for the dispersion of the expansion rate during active ion insertion. By reducing the thickness expansion rate of the negative electrode film layer, the cycle performance and storage performance of the secondary battery can be further improved.

[0145] In some embodiments, the particle size distribution (Dv90 - Dv10) / Dv50 of the third carbon-based material is ≤ 1.65, and optionally 0.90 - 1.65. When the particle size distribution (Dv90 - Dv10) / Dv50 of the third carbon-based material is within the above range, its particle deposition performance is good, which is advantageous for improving the compression density of the negative electrode film layer. Thereby, the energy density of the secondary battery can be further improved, and it is also advantageous for adjusting the void distribution of the negative electrode film layer, improving the kinetic performance of the secondary battery.

[0146] In some embodiments, the volume distribution particle size Dv50 of the third carbon-based material is 12.0 μm - 22.0 μm, and optionally 13.5 μm - 20.0 μm. When the volume distribution particle size Dv50 of the third carbon-based material is within the above range, it is advantageous for improving the transport performance of active ions and electrons, thereby further improving the kinetic performance of the secondary battery. Also, it can reduce the specific surface area of the third carbon-based material, reduce the occurrence of side reactions, and improve the storage performance of the secondary battery.

[0147] In some embodiments, the specific surface area of the third carbon-based material is 1.0 m 2 / g - 2.0 m 2 / g, and optionally 1.05 m 2 / g - 1.95 m 2It is / g. Due to the low specific surface area of the third carbon-based material, the consumption of active ions due to the formation of the SEI film can be reduced, the occurrence of side reactions can be reduced, and the initial Coulomb efficiency and storage performance of the secondary battery can be improved.

[0148] In some embodiments, the tap density of the third carbon-based material is 0.95 g / cm 3 -1.25 g / cm 3 and optionally 1.00 g / cm 3 -1.25 g / cm 3 When the tap density of the third carbon-based material is within the above range, the compression density of the negative electrode film layer can be improved, the energy density of the secondary battery can be improved, and a reasonable pore structure can be formed between the particles of the negative electrode film layer, improving the active ion and electron transport performance, and further being advantageous for improving the kinetic performance of the secondary battery.

[0149] In some embodiments, the gram capacity of the third carbon-based material is 350 mAh / g - 363 mAh / g, and optionally 352 mAh / g - 362 mAh / g. When the gram capacity of the third carbon-based material is within the above range, the energy density of the secondary battery can be improved, while the active ion transport performance of the negative electrode film layer can be improved, which is also advantageous for improving the kinetic performance of the secondary battery.

[0150] As shown in FIGS. 1 - 3, the negative electrode film layer 102 further includes an intermediate region 1023 located between the first region 1021 of the negative electrode film layer and the second region 1022 of the negative electrode film layer, and having a thickness of 0.4H (H represents the thickness of the negative electrode film layer 102).

[0151] In some embodiments, the intermediate region contains the first active material and / or the second active material. For example, as shown in FIG. 2, the composition of the intermediate region 1023 may be the same as that of the first region 1021. Thus, the distribution region of the first active material in the thickness direction of the negative electrode film layer 102 is within the thickness range from the second surface 102b of the negative electrode film layer to 0.7H. Alternatively, as shown in FIG. 3, the composition of the intermediate region 1023 may be the same as that of the second region 1022. Thus, the distribution region of the second active material in the thickness direction of the negative electrode film layer 102 is within the thickness range from the first surface 102a of the negative electrode film layer to 0.7H. Alternatively, as shown in FIG. 1, the intermediate region 1023 contains both the first active material and the second active material. In this case, the intermediate region 1023 simultaneously includes a layer structure having the first active material and a layer structure having the second active material, and the two-layer structure may further have a layer interface.

[0152] In some embodiments, the first region of the negative electrode film layer may further contain other negative electrode active materials known in the art other than the first carbon-based material and the third carbon-based material. For example, it may further contain a silicon-based material. The silicon-based material plays a role in improving the pore structure in the negative electrode film layer, facilitating the infiltration and liquid storage of the electrolyte, improving the kinetic performance of the secondary battery, and improving the negative electrode capacity, thereby further improving the energy density of the secondary battery. Optionally, the silicon-based material may include one or more of silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy material.

[0153] In some embodiments, when the first region of the negative electrode film layer further contains a silicon-based material, the mass ratio of the silicon-based material in the first region of the negative electrode film layer may be ≤ 10%, for example, 1-8%, 2-6%, or 3-7%. Thereby, while improving the kinetic performance and energy density of the secondary battery, the secondary battery can achieve good cycle performance and storage performance at the same time.

[0154] In some embodiments, the second region of the negative electrode film layer may further include other negative electrode active materials known in the art other than the above-mentioned second carbon-based material. For example, it may further include a silicon-based material. The silicon-based material plays a role in improving the pore structure in the negative electrode film layer, facilitating the infiltration and liquid storage of the electrolyte, improving the kinetic performance of the secondary battery, and increasing the negative electrode capacity. Thereby, the energy density of the secondary battery can be further improved. Optionally, the silicon-based material may include one or more of silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy material.

[0155] In some embodiments, when the second region of the negative electrode film layer further includes a silicon-based material, the mass ratio of the silicon-based material in the second region of the negative electrode film layer may be ≤10%, for example, it may be 1-8%, 2-6%, or 3-7%. Thereby, while improving the kinetic performance and energy density of the secondary battery, the secondary battery can achieve both good cycle performance and storage performance.

[0156] In some embodiments, both the first region and the second region include a silicon-based material, and the mass ratio of the silicon-based material in the first region is less than or equal to the mass ratio of the silicon-based material in the second region. During the charge and discharge process of the secondary battery, since the volume expansion of the silicon-based material is larger than that of the carbon-based material, it is advantageous for the second region of the negative electrode film layer to have a high porosity. Thereby, it is advantageous to improve the infiltration characteristics of the negative electrode film layer with respect to the electrolyte, improve the transport performance of active ions, and improve the cycle performance and / or kinetic performance of the secondary battery. Also, due to the high porosity of the second region of the negative electrode film layer, the transport performance of active ions in the first region of the negative electrode film layer can also be improved.

[0157] In some embodiments, the intermediate region of the negative electrode film layer further includes a silicon-based material.

[0158] In some embodiments, the first region, the second region, and the intermediate region of the negative electrode film layer may contain a negative electrode conductive agent and / or a negative electrode binder.

[0159] In the present application, the type of the negative electrode conductive agent is not particularly limited. By way of example, the negative electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0160] In the present application, the type of the negative electrode binder is not particularly limited. By way of example, the negative electrode binder may include one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, aqueous acrylic resin (for example, polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0161] In some embodiments, the first region, the second region, and the intermediate region of the negative electrode film layer may contain other auxiliary agents. By way of example, the other auxiliary agents may include a thickener, for example, sodium carboxymethyl cellulose (CMC), PTC thermistor materials, and the like.

[0162] In some embodiments, the porosity of the negative electrode film layer is 18.0% - 36.7%, and optionally 19.0% - 34.0%. This is advantageous for the negative electrode film layer to achieve both high capacity and an appropriate pore structure, and further advantageous for the secondary battery to achieve both high energy density and good storage performance and kinetic performance.

[0163] In some embodiments, the compression density of the negative electrode film layer is 1.45 g / cm 3 - 1.90 g / cm 3 and optionally 1.50 g / cm 3 - 1.85 g / cm 3This is advantageous for enabling the negative electrode film layer to achieve both high capacity and good active ion and electron transport performance, and further advantageous for enabling the secondary battery to achieve both high energy density and good storage performance and kinetic performance.

[0164] In some embodiments, the areal density of the negative electrode film layer is 5.0 mg / cm 2 -25.0 mg / cm 2 and optionally 5.5 mg / cm 2 -22.5 mg / cm 2 This is advantageous for enabling the negative electrode film layer to achieve both high capacity and good active ion and electron transport performance, and further advantageous for enabling the secondary battery to achieve both high energy density and good storage performance and kinetic performance.

[0165] In some embodiments, the OI value of the negative electrode film layer is 35.0 or less, and optionally 8.0 - 35.0. This is advantageous for improving the active ion insertion performance of the negative electrode film layer, and the negative electrode film layer can also have a low thickness repulsion rate, and further advantageous for enabling the secondary battery to achieve both good storage performance and kinetic performance.

[0166] In some embodiments, the thickness of the negative electrode film layer is 70 μm - 250 μm, and optionally 90 μm - 220 μm.

[0167] In some embodiments, the negative electrode current collector can use a metal foil or a composite current collector. As an example of the metal foil, a copper foil can be used. The composite current collector can 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 may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0168] The negative electrode sheet does not exclude other additional functional layers other than the negative electrode film layer. For example, in some embodiments, the negative electrode sheet according to the present application further includes a conductive undercoat layer (for example, composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode film layer and provided on the surface of the negative electrode current collector. In some embodiments, the negative electrode sheet according to the present application further includes a protective layer covering the surface of the negative electrode film layer.

[0169] The negative electrode current collector has two surfaces facing each other in the thickness direction, and the negative electrode film layer is provided on one or both of the two opposing surfaces of the negative electrode current collector. It should be noted that each negative electrode film layer parameter (for example, compression density, areal density, porosity, OI value, etc.) provided in the present application refers to the parameter of the negative electrode film layer on one side of the negative electrode current collector. When the negative electrode film layer is provided on both sides of the negative electrode current collector, if the negative electrode film layer parameter on one side satisfies the present application, it is considered to be within the protection scope of the present application.

[0170] In the present application, whether a carbon coating layer exists on the surface of a material (for example, the first carbon-based material, the second carbon-based material, the third carbon-based material, etc.) can be determined by a transmission electron microscope.

[0171] In the present application, the specific surface area of a material (for example, the first carbon-based material, the second carbon-based material, the third carbon-based material, etc.) has the meaning known in the art and can be measured by equipment and methods known in the art. For example, referring to GB / T 19587-2017, it can be measured by the nitrogen gas adsorption specific surface area analysis test method and calculated by the BET (Brunauer Emmett Teller) method. The measuring equipment may be a Tri-Star 3020 type specific surface area pore size analysis measuring instrument manufactured by Micromeritics, USA.

[0172] In this application, the graphitization degree of a material (e.g., the first carbon-based material, the second carbon-based material, the third carbon-based material, etc.) has the meaning known in the art and can be measured by equipment and methods known in the art. For example, it can be measured using an X-ray diffractometer (e.g., Bruker D8 Discover). The measurement is carried out with reference to JIS K 0131-1996 and JB / T 4220-2011 to obtain the average interlayer distance d of the C(002) crystal plane in the crystal structure of the material. 002 After obtaining 002 , the graphitization degree can be calculated based on the formula g = (0.344 - d 002 ) / (0.344 - 0.3354) × 100%. In the above formula, d 002 is the average interlayer distance of the C(002) crystal plane in the crystal structure of the material, expressed in nanometers (nm).

[0173] In this application, the volume distribution particle sizes Dv10, Dv50, and Dv90 of a material (e.g., the first carbon-based material, the second carbon-based material, the third carbon-based material, etc.) have the meaning known in the art, and respectively indicate the particle sizes corresponding when the cumulative volume distribution percentage of the material reaches 10%, 50%, and 90%, and can be measured by equipment and methods known in the art. For example, with reference to GB / T 19077-2016, it can be measured using a laser particle size analyzer. The test equipment may be a Mastersizer 3000 type laser particle size analyzer from Malvern Instruments, UK.

[0174] In this application, the powder compression density of a material (e.g., the first carbon-based material, the second carbon-based material, the third carbon-based material, etc.) has the meaning known in the art and can be measured by equipment and methods known in the art. For example, with reference to GB / T 24533-2009, it can be measured using an electronic pressure tester (e.g., UTM7305 type electronic pressure tester). As an exemplary measurement method, 1 g of sample powder is weighed, placed in a mold with a bottom area of 1.327 cm 2 , pressurized to 2000 kg, held under pressure for 30 s, then the pressure is released and held for 10 s, and then the powder compression density of the material under a press force of 20000 N is recorded and calculated.

[0175] In the present application, the tap density of a material (e.g., the first carbon-based material, the second carbon-based material, the third carbon-based material, etc.) has the meaning known in the art and can be measured by equipment and methods known in the art. For example, referring to GB / T 5162-2006, it can be measured using a powder tap density meter. The test equipment can adopt Dandong Bait BT-301, and the test parameters are a vibration frequency of 250 ± 15 times / minute, an amplitude of 3 ± 0.2 mm, a vibration number of 5000 times, and a graduated cylinder of 25 mL.

[0176] In the present application, the I of the first carbon-based material D / I G can be measured using a Raman spectrometer, and I D represents the D peak intensity at 1350 ± 50 cm -1 in the Raman spectrum of the material, and I G represents the G peak intensity at 1580 ± 50 cm -1 in the Raman spectrum of the material. The test conditions are that the excitation wavelength is 532 nm, the diffraction grating is 600 lines, the objective lens is 50 times, the integration time is 10 s, the accumulation number is 3 times, and the surface is scanned to obtain the D peak and G peak intensities of 100 points. The I of 100 points D / I G is calculated, and the maximum and minimum 30 I D / I G are removed, and the average value of the remaining 40 points is the I of the material D / I G . As the measuring instrument, a Horiba LabRAM HR800 Raman spectrometer can be used.

[0177] In the present application, the powder OI value of a material (e.g., the second carbon-based material, the third carbon-based material, etc.) has the meaning known in the art and can be measured by equipment and methods known in the art. For example, it can be measured using an X-ray diffractometer (e.g., Bruker D8 Discover). The measurement refers to JIS K 0131-1996 and JB / T 4220-2011 to obtain the X-ray diffraction pattern of the powder sample, and OI value = I 004 / I 110Based on this, the powder OI value of the sample can be calculated. I 004 is the integrated area of the diffraction peak of the 004 crystal plane of crystalline carbon in the powder sample, and I 110 is the integrated area of the diffraction peak of the 110 crystal plane of crystalline carbon in the powder sample. In the X-ray diffraction analysis test of the present application, a copper target is used as the anode target, CuKα rays are used as the radiation source, the wavelength λ = 1.5418 Å, the scanning 2θ angle range is 20° - 80°, and the scanning speed is 4° / min.

[0178] In the present application, both the primary particles and the secondary particles have the meanings known in the art. The primary particles refer to non-aggregated particles. The secondary particles refer to aggregated particles in which two or more primary particles are aggregated. The primary particles and the secondary particles can be distinguished using a scanning electron microscope (SEM) image.

[0179] In the present application, the gram capacity of a material (e.g., the first carbon-based material, the second carbon-based material, the third carbon-based material, etc.) has the meaning known in the art and can be measured by methods known in the art. An exemplary test method is as follows: Sample powder, carbon black (Super P) as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder are uniformly mixed with N-methylpyrrolidone (NMP) as a solvent at a mass ratio of 91.6:1.8:6.6 to produce a slurry. The produced slurry is applied to the surface of a copper foil which is a negative electrode current collector and dried in an oven to be prepared. Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed at a volume ratio of 1:1:1 to obtain an organic solvent. Then, LiPF6 is dissolved in the above organic solvent to produce an electrolyte solution with a concentration of 1 mol / L. Thereafter, a CR2430 coin cell is assembled in a glove box protected by the above electrolyte solution and argon gas, with a metallic lithium sheet as a counter electrode and a polyethylene (PE) thin film as a separator. After the obtained coin cell is allowed to stand for 12 h, at 25°C, it is discharged at a constant current of 0.05C to 0.005V, allowed to stand for 10 minutes, discharged at a constant current of 50 μA to 0.005V, allowed to stand for 10 minutes, and discharged at a constant current of 10 μA to 0.005V. Then, it is charged at a constant current of 0.1C to 2V, and the charging capacity is recorded. The ratio of the charging capacity to the mass of the sample is the gram capacity of the corresponding material (e.g., the first carbon-based material, the second carbon-based material, the third carbon-based material, etc.).

[0180] In the present application, the areal density of the negative electrode film layer has the meaning known in the art and can be measured by methods known in the art. For example, take a negative electrode sheet 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), punch it into a small disc with an area of S1, and record its weight as M1. Then, wipe off the negative electrode film layer of the weighed negative electrode sheet, weigh the weight of the negative electrode current collector, and record it as M0. The areal density of the negative electrode sheet = (M1 - M0) / S1.

[0181] In the present application, the compression density of the negative electrode film layer has the meaning known in the art and can be measured by methods known in the art. Compression density of the negative electrode film layer = areal density of the negative electrode film layer / thickness of the negative electrode film layer. The thickness of the negative electrode film layer has the meaning known in the art and can be measured using methods known in the art. For example, a micrometer (e.g., Mitutoyo 293-100 type, accuracy 0.1 μm) can be used.

[0182] In the present application, the porosity of the negative electrode film layer has the meaning known in the art and can be measured by methods known in the art. As an exemplary measurement method, a negative electrode sheet coated on one side and cold-pressed (if it is a negative electrode sheet coated on both sides, first wipe off the negative electrode film layer on one side) is taken, punched into small disc samples of a certain area, and the apparent volume V1 of the negative electrode sheet is calculated. Referring to GB / T 24586-2009, using an inert gas (e.g., helium gas or nitrogen gas) as the medium, adopting the gas displacement method, and using a true density measuring instrument to measure the true volume V2 of the negative electrode sheet. Porosity of the negative electrode film layer = (V1 - V2) / V1 × 100%. By measuring samples of multiple (e.g., 30) negative electrode sheets with good appearance and no powder falling off at the edges and adopting the average value of the results, the accuracy of the measurement results can be improved. As the measuring instrument, a Micromeritics AccuPyc II 1340 type true density measuring instrument can be used.

[0183] In the present application, the OI value of the negative electrode film layer has the meaning known in the art and can be measured by instruments and methods known in the art. For example, it can be measured using an X-ray diffractometer (e.g., Bruker D8 Discover). The measurement refers to JIS K 0131-1996 and JB / T 4220-2011 to obtain the X-ray diffraction pattern of the negative electrode sheet, and the OI value = I 004 / I 110 Based on this, the OI value of the negative electrode film layer can be calculated. I 004 is the integrated area of the diffraction peak of the 004 crystal plane of crystalline carbon in the negative electrode film layer, and I 110It is the integrated area of the diffraction peak of the crystal carbon 110 crystal plane in the negative electrode film layer. In the X-ray diffraction analysis test of this application, a copper target is used as the anode target, CuKα rays are used as the radiation source, the wavelength λ = 1.5418 Å, the scanning 2θ angle range is 20° - 80°, and the scanning speed is 4° / min.

[0184] In addition, the measurement of various parameters for the above-mentioned first active material, second active material, or negative electrode film layer can be sampled and measured from a secondary battery manufactured according to the following steps.

[0185] The secondary battery is discharged (for safety, generally the secondary battery is brought to a fully discharged state), after removing the secondary battery, the negative electrode sheet is taken out, and the negative electrode sheet is immersed in dimethyl carbonate for a certain period of time (for example, 2h - 10h), then the negative electrode sheet is taken out and dried at a certain temperature and time (for example, 60°C, 4h or more), and the negative electrode sheet is taken out after drying. In this case, in the negative electrode sheet after drying, various parameters related to the above-mentioned negative electrode film layer, such as the areal density, compression density, porosity, OI value, etc. of the negative electrode film layer can be sampled and measured.

[0186] The above-mentioned negative electrode sheet after drying is fired at a certain temperature and time (for example, 400°C, 2h or more), any one region in the negative electrode sheet after firing is selected, first the second active material is sampled (it may be sampled by scraping the powder with a blade), the sampling position is the second region of the negative electrode film layer, then the first active material is sampled in the same manner, the sampling position is the first region of the negative electrode film layer, the collected first active material and second active material are each sieved (for example, passed through a 200-mesh sieve), and finally samples of the first active material and second active material for measuring the above-mentioned various material parameters of this application are obtained. [Manufacturing method of negative electrode sheet]

[0187] The present application further provides a method for manufacturing the negative electrode sheet of the present application. The method includes the steps of providing a first slurry containing a first active material and a second slurry containing a second active material, applying the first slurry to a negative electrode current collector, applying the second slurry to the first slurry, drying, cold pressing, and then obtaining a negative electrode sheet.

[0188] In some embodiments, the first slurry can be formed by dispersing the first active material and optional conductive agent, optional binder, and optional other auxiliaries in a solvent (such as deionized water).

[0189] In some embodiments, the second slurry can be formed by dispersing the second active material and optional conductive agent, optional binder, and optional other auxiliaries in a solvent (such as deionized water).

[0190] In some embodiments, the first active material includes a first carbon-based material or a mixture of a first carbon-based material and a third carbon-based material.

[0191] In some embodiments, the second active material includes a second carbon-based material.

[0192] In some embodiments, the first slurry and / or the second slurry further includes a silicon-based material.

[0193] The first slurry and the second slurry may be applied simultaneously in one time or applied in two times. In some embodiments, the first slurry and the second slurry are applied simultaneously in one time. By applying in one time, the resistance of the negative electrode film layer can be reduced, and the mechanical performance and cycle performance of the secondary battery can be further improved.

[0194] The coating weights of the first slurry and the second slurry can be adjusted according to the actual situation.

[0195] In the present application, the above-mentioned first active material, second active material, etc. can be commercially available products or can be manufactured by the following methods of the present application.

[0196] In some embodiments, the method for manufacturing the first carbon-based material includes: Step 1 of providing a raw material having a plurality of pore structures; Step 2 of uniformly mixing the raw material and a filler at a predetermined ratio, then holding at a first temperature T1 for a first time t1, and after completion, cooling to room temperature to obtain an intermediate; and Step 3 of holding the obtained intermediate at a second temperature T2 for a second time t2, and after completion, obtaining the first carbon-based material.

[0197] In some embodiments, in Step 1, the raw material for manufacturing the first carbon-based material includes natural graphite. Optionally, the natural graphite includes one or more of flaky graphite, natural spherical graphite, and microcrystalline graphite, and more preferably includes natural spherical graphite.

[0198] "Natural spherical graphite" means natural graphite having a spherical or quasi-spherical shape, and does not control all natural graphite particles into ideal spheres. In some embodiments, by performing pretreatment on flaky graphite, natural spherical graphite with a desired particle size and morphology can be obtained. Optionally, the pretreatment includes processes such as crushing, classification, spheroidization, and purification.

[0199] In some embodiments, in Step 1, when the graphitization degree of the raw material is ≧94.5%, it is advantageous for adjusting the graphitization degree of the first carbon-based material.

[0200] In some embodiments, in Step 1, the volume distribution particle size Dv50 of the raw material may be 7.5 μm - 25.0 μm, and optionally 8.0 μm - 24.5 μm, which is advantageous for manufacturing the first carbon-based material with a desired volume distribution particle size.

[0201] In some embodiments, in Step 1, the specific surface area of the raw material may be ≧2.5 m 2 / g, and optionally 2.5 m 2 / g - 10.0 m 2 It is / g. When the specific surface area of the raw material is within the above range, it is advantageous for subsequent filling treatment to obtain the first carbon-based material with the desired specific surface area, and it is also advantageous for the first carbon-based material to have a high capacity and a high initial Coulomb efficiency, and it is also advantageous for the first carbon-based material to have better kinetic performance.

[0202] In some embodiments, in step 2, the softening point temperature of the filler is 92°C - 160°C, and optionally, the softening point temperature of the filler is 100°C - 155°C, 100°C - 150°C, 100°C - 140°C, 105°C - 155°C, 105°C - 150°C, 105°C - 140°C, 115°C - 150°C, or 115°C - 140°C.

[0203] In some embodiments, in step 2, the coke value of the filler is 15% - 45%, and optionally 20% - 34%. In the present application, the coking value of the filler has the meaning known in this field and can be measured by the equipment and methods known in this field. For example, it can be measured with reference to GB / T 8727 - 2008.

[0204] In some embodiments, in step 2, the volume distribution particle size Dv50 of the filler is 6 μm or less, and optionally 1 μm - 6 μm, 1 μm - 5 μm, 2 μm - 5 μm, 3 μm - 5 μm. Thereby, it is advantageous for the filler to be filled into the pore structure of the raw material after melting by heat, and it is also advantageous to improve the dispersion uniformity between the filler and the raw material.

[0205] In some embodiments, in step 2, the filler includes one or more of coal pitch, petroleum pitch, polymer compounds, and resins, and optionally includes one or more of coal pitch and petroleum pitch.

[0206] In some embodiments, in step 2, the mass ratio of the filler to the raw material is (10 - 40):100, and optionally, (10 - 30):100, (10 - 25):100, (10 - 20):100, (12 - 30):100, (12 - 20):100, (14 - 28):100, (15 - 25):100.

[0207] In step 2, by adjusting one or more parameters such as the type, softening point, coke value, addition amount, etc. of the filler within the above range, it is advantageous to adjust the number and / or size of pores in the external region and the internal region of the first carbon-based material within an appropriate range, and it is also advantageous to adjust S2 / S1 of the first carbon-based material within an appropriate range.

[0208] By adjusting the parameters such as the type, softening point, coke value, addition amount, etc. of the filler within the above range, after the filler is melted by heat, its viscosity is not high, it maintains good fluidity, the raw material particles are not easily adhered, and the aggregation of raw material particles in the subsequent manufacturing process can be reduced. Thereby, since it is necessary to increase the depolymerization process, problems such as an increase in surface defects of the first carbon-based material particles and an increase in interfacial active sites can also be reduced.

[0209] In some embodiments, in step 2, after uniformly mixing the raw material and the filler at a predetermined ratio, the temperature-rising process of rising to the first temperature T1 is a stepwise temperature-rising process.

[0210] In some embodiments, the stepwise temperature-rising process includes a first temperature-rising process, a second temperature-rising process, and a third temperature-rising process.

[0211] In some embodiments, the first temperature-rising process rises to 200°C - 250°C and holds the temperature at this temperature for 0.5 h - 3 h.

[0212] In some embodiments, in the second heating process, the temperature is raised to 450°C - 550°C and held at this temperature for 0 h - 2 h. When the holding time is 0 h, it means that no holding treatment is performed when the temperature is raised within the range of 450°C - 550°C, and the temperature continues to be raised to the first temperature T1.

[0213] In some embodiments, in the third heating process, the temperature is raised to the first temperature T1 and held at this temperature for the first time t1.

[0214] In the stepwise heating process, first, the temperature is raised to 200°C - 250°C. Since the heating temperature is higher than the softening point temperature of the filler, at this time, the filler is melted and softened by heat, and can be held for 0.5 h - 3 h to be fluidly filled into the pore structure of the raw material. Then, the temperature is raised to 450°C - 550°C. At this time, the melted and softened filler undergoes a carbonization reaction and gradually becomes in a semi-coke state, becoming a viscous liquid or solid. This avoids the filler entering all the pore structures of the raw material. Finally, the temperature is raised to the first temperature. At this time, the filler undergoes a carbonization reaction, whereby the pore structure occupied by the filler can be effectively filled.

[0215] In some embodiments, in step 2, the temperature is raised to the first temperature T1 at a rate of 1°C / min - 10°C / min. For example, the heating rate may be in the range consisting of 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min or any value above. Optionally, the heating rate is 1.5°C / min - 8°C / min, 1.5°C / min - 6°C / min, 2°C / min - 6°C / min, 2°C / min - 5°C / min.

[0216] In some embodiments, the heating rate of the first heating process may be 1°C / min - 10°C / min, and optionally 1.5°C / min - 8°C / min, 1.5°C / min - 6°C / min, 2°C / min - 6°C / min, 2°C / min - 5°C / min.

[0217] In some embodiments, the heating rate of the second heating process may be 1°C / min - 10°C / min, and optionally 2°C / min - 8°C / min.

[0218] In some embodiments, the heating rate of the third heating process may be 1°C / min - 10°C / min, and optionally 2°C / min - 8°C / min.

[0219] In some embodiments, in step 2, the first temperature T1 is 700°C - 1200°C. For example, the first temperature T1 may be in the range consisting of 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, 1000°C, 1050°C, 1100°C, 1200°C or any numerical value thereabove. Optionally, the first temperature T1 is 750°C - 1100°C, 800°C - 1100°C, 850°C - 1000°C.

[0220] In some embodiments, in step 2, the first time t1 is 1h - 5h. For example, the first time t1 may be in the range consisting of 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h or any numerical value thereabove. Optionally, the first time t1 is 2h - 4h.

[0221] In some embodiments, in step 2, the heat treatment can be carried out by equipment capable of performing programmed heating, such as an intermediate frequency furnace, a roller hearth kiln, a rotary kiln, a pusher hearth kiln, a vertical granulation kettle, a horizontal granulation kettle, a vertical reaction kettle, a horizontal reaction kettle or a drum furnace.

[0222] In some embodiments, in step 2, the heat treatment atmosphere may be a protective gas atmosphere. The protective gas may include one or more of nitrogen gas, argon gas, and helium gas.

[0223] In step 2, by adjusting one or more of the heating rate, the first temperature, the first time, the heating process, etc. within the above ranges, it is advantageous to adjust the number and / or size of pores in the external and internal regions of the first carbon-based material within an appropriate range, and it is advantageous to adjust S2 / S1 of the first carbon-based material within an appropriate range.

[0224] In some embodiments, in step 3, the second temperature T2 is 1900°C - 2650°C. Optionally, the second temperature T2 is 1960°C - 2550°C, 1960°C - 2500°C, 1960°C - 2450°C, 1960°C - 2400°C, 1960°C - 2350°C, 2000°C - 2550°C, 2000°C - 2500°C, 2000°C - 2450°C, 2000°C - 2400°C, 2000°C - 2350°C, 2080°C - 2550°C, 2080°C - 2500°C, 2080°C - 2450°C, 2080°C - 2400°C, 2080°C - 2350°C.

[0225] In some embodiments, in step 3, the second time t2 is 1.5 h - 6 h. For example, the second time t2 may be in the range consisting of 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h or any numerical value above. Optionally, the second time t2 is 2 h - 5 h.

[0226] In some embodiments, in step 3, the heat treatment can be carried out in an intermediate frequency furnace, a box-type graphitization furnace, an Acheson-type graphitization furnace, a continuous graphitization furnace or an internal series graphitization furnace.

[0227] In some embodiments, in step 3, the atmosphere of the intermediate frequency furnace or the continuous graphitization heat treatment may be a protective gas atmosphere. The protective gas may include one or more of nitrogen gas, argon gas, and helium gas.

[0228] In step 3, by adjusting one or more of the second temperature and the second time within the above range, it is advantageous to adjust the content of irregular carbon in the first carbon-based material to an appropriate range, and the first carbon-based material has an appropriate I D / I G and / or an appropriate graphitization degree, etc., which is advantageous.

[0229] In the method for producing the first carbon-based material, by adjusting one or more of the parameters of natural graphite, the parameters of the filler, the heating rate, the first temperature, the first time, the heating process, the second temperature, the second time, etc. within the above range, the S2 / S1 of the first carbon-based material, I D / I G , parameters such as graphitization degree, gram capacity, specific surface area, particle size, powder compression density, tap density, and weight loss rate can be adjusted advantageously.

[0230] In some embodiments, the method for producing the second carbon-based material includes step 11 of providing a raw material, step 12 of performing a crushing treatment and a shaping treatment on the raw material to obtain a first intermediate, step 13 of performing a graphitization treatment on the first intermediate to obtain a second intermediate after completion, step 14 of performing a carbonization treatment after mixing the second intermediate and an organic carbon source, and finally performing sieving to obtain the second carbon-based material.

[0231] In some embodiments, in step 11, the raw material may include one or more of petroleum coke, needle coke, pitch coke, and metallurgical coke.

[0232] In some embodiments, in step 12, the raw material can be crushed using mechanical milling or roll milling.

[0233] In some embodiments, in step 12, the shaping treatment may be performed using a shaper.

[0234] In some embodiments, in step 13, the graphitization temperature is 2,800°C - 3,200°C.

[0235] By adjusting the graphitization temperature and / or the graphitization time, it is advantageous for the second carbon-based material to have an appropriate degree of graphitization and / or I D / I G to have.

[0236] In some embodiments, in step 14, the organic carbon source can employ a carbon-containing material suitable for coatings known in the art. For example, it can include one or more of coal pitch, petroleum pitch, phenolic resin, coconut shell, etc. By adjusting the addition amount of the organic carbon source, it is advantageous to adjust parameters such as the specific surface area, degree of graphitization, gram capacity, I D / I G of the second carbon-based material.

[0237] In some embodiments, in step 14, the carbonization temperature is 900°C - 1,300°C.

[0238] In step 14, by adjusting the carbonization temperature and / or the carbonization heat preservation time, it is advantageous to adjust parameters such as the specific surface area, degree of graphitization, gram capacity, I D / I G of the second carbon-based material.

[0239] In some embodiments, a granulation step may be further included between step 12 and step 13, whereby the quantity ratio of secondary particles can be adjusted. For example, the first intermediate and the binder can be mixed and granulated. Optionally, the binder includes asphalt.

[0240] In the method for producing the second carbon-based material, by adjusting one or more parameters among the parameters of each device (for example, mechanical milling or roll milling, shaping machine, granulator, etc.), the parameters of the raw materials, the addition amount of the organic carbon source, the addition amount of the binder, the graphitization temperature, the graphitization time, the carbonization temperature, the carbonization time, etc., it is advantageous to adjust the parameters such as I D / I G , graphitization degree, gram capacity, powder OI value, particle size, specific surface area, tap density, etc. [Positive electrode sheet]

[0241] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector. For example, the positive electrode current collector has two surfaces facing each other in its own thickness direction, and the positive electrode film layer is provided on one or both of the two opposing surfaces of the positive electrode current collector.

[0242] The positive electrode current collector can use a metal foil or a composite current collector. As an example of the metal foil, an aluminum foil can be used. The composite current collector can 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 may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0243] The positive electrode film layer usually includes a positive electrode active material, an optional binder, and an optional conductive agent. The positive electrode film layer is usually formed by applying a positive electrode slurry to the positive electrode current collector, drying, and cold pressing. The positive electrode slurry is usually formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder, and an optional other component in a solvent and stirring uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP). As an example, the binder used in the positive electrode film layer may include, for example, any one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin. As an example, the conductive agent used in the positive electrode film layer includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0244] The positive electrode active material can adopt a positive electrode active material for secondary batteries known in the art.

[0245] When the secondary battery of the present application is a lithium ion battery, the positive electrode active material may include, but is not limited to, one or more of lithium-containing transition metal oxides, lithium-containing phosphates, and their modified compounds. Examples of the lithium transition metal oxide include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. Examples of the lithium-containing phosphate include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite material of lithium manganese iron phosphate and carbon, and their modified compounds.

[0246] In some embodiments, in order to further improve the energy density of the secondary battery, the positive electrode active material used in the lithium ion battery may include one or more of lithium transition metal oxides and their modified compounds having the general formula Li a Ni b Co c M d O e A f where 0.8 ≦ a ≦ 1.2, 0.5 ≦ b < 1, 0 < c < 1, 0 < d < 1, 1 ≦ e ≦ 2, 0 ≦ f ≦ 1, M is one or more selected from Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and A is one or more selected from N, F, S, and Cl.

[0247] In some embodiments, as an example, the positive electrode active material for the lithium ion battery is LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM333), LiNi 0.5 Co0.2 Mn 0.3 O2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), LiNi 0.80 Co 0.15 Al 0.05 It may contain one or more of O2, LiFePO4, and LiMnPO4.

[0248] In the present application, the modified compound of each of the above cathode active materials is obtained by performing doping modification and / or surface coating modification on the cathode active material. [Electrolyte]

[0249] In some embodiments, the electrolyte uses an electrolytic solution containing an electrolyte salt and a solvent.

[0250] The type of the electrolyte salt is not specifically limited and can be selected according to actual needs.

[0251] When the secondary battery of the present application is a lithium-ion battery, for example, the electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium bis(oxalate) borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalate) phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0252] The type of the solvent is not particularly limited and can be selected according to actual demands. In some embodiments, by way of example, the organic solvent may include 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), butylene 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).

[0253] In some embodiments, the electrolyte may optionally contain an additive. For example, the additive may include a negative electrode film-forming additive, a positive electrode film-forming additive, and an additive that can improve certain performance of the secondary battery, such as an additive that improves the overcharge performance of the secondary battery, an additive that improves the high-temperature performance of the secondary battery, an additive that improves the low-temperature output performance of the secondary battery, and the like. [Separator]

[0254] In the present application, the type of the separator is not particularly limited, and any known porous structure separator having good chemical stability and mechanical stability can be selected.

[0255] In some embodiments, the material of the separator may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may 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.

[0256] In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet can be used to manufacture an electrode assembly by a winding process or a lamination process.

[0257] In some embodiments, the secondary battery may include an exterior. The exterior is used for sealing the above-described electrode assembly and electrolyte.

[0258] In some embodiments, the exterior may be a hard case such as a hard plastic case, an aluminum case, or a steel case. The exterior may also be a soft bag, for example, a soft bag. The material of the soft package may be one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0259] The shape of the secondary battery of the present application is not particularly limited, and it may be cylindrical, rectangular, or any other shape. FIG. 5 shows a rectangular-structured secondary battery 5 as an example.

[0260] In some embodiments, as shown in FIG. 6, the exterior may include a case 51 and a cover plate 53. The case 51 includes a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates surround to form a housing chamber. The case 51 has an opening communicating with the housing chamber, and the cover plate 53 closes the opening so as to close the housing chamber. The positive electrode sheet, the negative electrode sheet, and the separator can form an electrode assembly 52 by a winding process or a lamination process. The electrode assembly 52 is packaged in the housing chamber. The electrolyte infiltrates the electrode assembly 52. The number of electrode assemblies 52 included in the secondary battery 5 may be one or more, and may be adjusted according to demand.

[0261] The manufacturing method of the secondary battery of the present application is known. In some embodiments, a secondary battery can be formed by assembling a positive electrode sheet, a separator, a negative electrode sheet, and an electrolytic solution. As an example, a positive electrode sheet, a separator, and a negative electrode sheet are formed into an electrode assembly by a winding process or a lamination process. The electrode assembly is placed in an exterior package, dried, and then the electrolytic solution is injected. After passing through processes such as vacuum encapsulation, standing, formation, and shaping, a secondary battery can be obtained.

[0262] In some embodiments of the present application, the secondary battery of the present application may be assembled into a battery module. The number of secondary batteries included in the battery module may be plural, and the specific number may be adjusted according to the application and capacity of the battery module.

[0263] FIG. 7 is a schematic diagram of a battery module 4 as an example. As shown in FIG. 7, in the battery module 4, a plurality of secondary batteries 5 may be provided side by side in order along the longitudinal direction of the battery module 4. Of course, they may be arranged in any other manner. Further, the plurality of secondary batteries 5 may be fixed by a fixture.

[0264] Optionally, the battery module 4 further includes an external case having an accommodation space, and the plurality of secondary batteries 5 are accommodated in the accommodation space.

[0265] In some embodiments, the above battery module may be assembled as a battery pack, and the number of battery modules included in the battery pack may be adjusted according to the use and capacity of the battery pack.

[0266] FIGS. 8 and 9 are schematic diagrams of a battery pack 1 as an example. As shown in FIGS. 8 and 9, the battery pack 1 may include a battery case and a plurality of battery modules 4 provided in the battery case. The battery case includes an upper case 2 and a lower case 3, and the upper case 2 covers the lower case 3 to form a sealed space for accommodating the battery module 4. The plurality of battery modules 4 may be arranged in the battery case in any manner.

[0267] Embodiments of the present application provide a power consumption device including at least one of a secondary battery, a battery module, or a battery pack of the present application. The secondary battery, battery module, or battery pack may be used as a power source of the power consumption device or as an energy storage means of the power consumption device. The power consumption device may be a mobile device (e.g., a mobile phone, a notebook computer, etc.), an electric vehicle (e.g., a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), a train, a ship, a satellite, an energy storage system, etc., but is not limited thereto.

[0268] The power consumption device can select a secondary battery, a battery module, or a battery pack according to demand.

[0269] FIG. 10 is a schematic diagram of a power consumption device as an example. This power consumption device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc. In order to meet the requirements of high output and high energy density of this power consumption device, a battery pack or a battery module can be adopted.

[0270] Another example of the power consumption device may be a mobile phone, a tablet computer, a notebook computer, etc. This power consumption device is generally required to be thin, and a secondary battery can be adopted as a power source.

Example

[0271] The following examples illustrate the content of the present application in more detail. However, these examples are merely illustrative explanations, and it is obvious to those skilled in the art that various modifications and changes can be made within the scope of the disclosure of the present application. Unless otherwise specified, all parts, percentages, and ratio values described in the following examples are all based on mass standards. Also, all reagents used in the examples may be commercially available or synthesized according to conventional methods, and can be used as they are without further treatment. Additionally, all devices used in the examples are commercially available.

[0272] In the following examples and comparative examples, the first carbon-based material employed can be manufactured by the following method of the present application. (1) Manufacture of the first carbon-based material

[0273] The flaky graphite was mechanically pulverized, classified, spheroidized, and purified to obtain natural spherical graphite. After mixing the obtained natural spherical graphite and petroleum pitch, the mixed material was placed in a device capable of programmed temperature increase, and stepwise temperature increase heat treatment was performed. After completion, it was cooled to room temperature to obtain an intermediate. The obtained intermediate was placed in a graphitization furnace and heat treated. After completion, it was demagnetized and sieved to obtain the first carbon-based material. In the above process, S2 / S1, graphitization degree, I D / I G can be controlled according to the manufacturing process of the first carbon-based material of the present application so as to be within the range shown in Table 1.

[0274] S2 / S1 of the first carbon-based material is measured by the following method.

[0275] After uniformly mixing the binder for sample production with the first carbon-based material powder, it was applied to a copper foil and dried at 60°C for 30 min to prepare a sample. The sample was cut into a size of 6 mm × 6 mm and attached to the sample stage of a CP-type argon ion cross-section polisher. The sample was cut using a plasma beam to obtain a cross-section of the first carbon-based material, and the cross-section of the first carbon-based material passes through the center of the first carbon-based material particles. As the test apparatus, an IB-09010 CP-type argon ion cross-section polisher manufactured by JEOL, Japan can be used. The cross-section of the first carbon-based material was scanned using a scanning electron microscope. The test can refer to JY / T010-1996. The test equipment may be a Sigma 300-type scanning electron microscope manufactured by ZEISS, Germany. A region formed by extending a distance of 0.25L from the particle surface to the particle interior of the first carbon-based material is defined as the external region, and the region inside the external region is defined as the internal region, where L represents the minor axis length of the particles of the first carbon-based material. Using image processing software, the total pore area S1 of the outer region of the first carbon-based material and the total pore area S2 of the inner region of the first carbon-based material were calculated. The image processing software may be AVIZO.

[0276] In each of the following examples and comparative examples, the second carbon-based material employed can be manufactured by the following method of the present application. Also, when manufacturing the second carbon-based material of Comparative Example 3, the coating carbonization treatment was not performed. (2) Manufacture of the second carbon-based material

[0277] Using petroleum coke, it was pulverized to obtain a petroleum coke raw material. The raw material of petroleum coke was shaped and classified to obtain a precursor. The precursor was granulated using pitch as a binder. Then, the granulated product was graphitized at 2800°C - 3200°C to obtain artificial graphite. After further coating the artificial graphite with pitch, carbonization treatment and sieving were performed to obtain the second carbon-based material.

[0278] In the above process, the specific surface area, graphitization degree, quantity ratio of secondary particles, and I D / I G can be controlled according to the manufacturing process of the second carbon-based material described in the present application so that they are within the ranges shown in Table 1.

[0279] In each of the following Examples and Comparative Examples, the third carbon-based material is commercially available. The secondary batteries of Examples 1-32 and Comparative Examples 1-3 were all manufactured by the following method.

[0280] The first carbon-based material (see Table 1 for details), carbon black (Super P) as a conductive agent, sodium carboxymethyl cellulose as a thickener, and styrene-butadiene rubber as a binder were sufficiently stirred and mixed in an appropriate amount of deionized water as a solvent at a weight ratio of 96.4:1:1.2:1.4 to form a first slurry. The second carbon-based material (see Table 1 for details), carbon black (Super P) as a conductive agent, sodium carboxymethyl cellulose as a thickener, and styrene-butadiene rubber as a binder were sufficiently stirred and mixed in an appropriate amount of deionized water as a solvent at a weight ratio of 96.4:1:1.2:1.4 to form a second slurry. The first slurry and the second slurry were simultaneously extruded by a double-cavity coating die. The first slurry was applied to the copper foil of the negative electrode current collector, the second slurry was applied to the first slurry, and after drying and cold pressing, a negative electrode sheet was obtained. The coating weights of the first slurry and the second slurry are the same.

[0281] LiNi 0.5 Co 0.2 Mn 0.3 LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), carbon black (Super P) as a conductive agent, and polyvinylidene fluoride as a binder were mixed at a weight ratio of 96:2:2, an appropriate amount of NMP as a solvent was added, and the mixture was uniformly stirred to obtain a positive electrode slurry. The positive electrode slurry was applied to two surfaces of an aluminum foil as a positive electrode current collector, and after drying and cold pressing, a positive electrode sheet was obtained.

[0282] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed at a volume ratio of 1:1:1 to obtain an organic solvent, and then LiPF6 was dissolved in the above organic solvent to produce an electrolytic solution with a concentration of 1 mol / L.

[0283] Using a polyethylene film as a separator, the positive electrode sheet and the negative electrode sheet manufactured above are arranged in order, and the separator is positioned between the positive electrode sheet and the negative electrode sheet to perform an isolation function. Then, it is wound to obtain an electrode assembly. The electrode assembly is placed in an outer package, and after drying, an electrolyte is injected. Through processes such as vacuum sealing, standing, forming, and shaping, a secondary battery is obtained. Example 33

[0284] The secondary battery of Example 33 was manufactured by a method similar to that of Example 1. The difference is the manufacture of the first slurry. The first carbon-based material and the third carbon-based material (specifically, in Table 2, the mass ratio is 50:50), carbon black (Super P) as a conductive agent, sodium carboxymethyl cellulose as a thickening agent, and styrene-butadiene rubber as an adhesive were sufficiently stirred and mixed in an appropriate amount of solvent deionized water at a weight ratio of 96.4:1:1.2:1.4 to form the first slurry. Performance test (1) Test on the rapid charging performance of the secondary battery

[0285] At 25°C, after the secondary battery was charged at a constant current of 0.33C to 4.3V, it was charged at a constant voltage until the current reached 0.05C. After standing for 5 minutes, the secondary battery was discharged at a constant current of 0.33C to 2.8V, and its actual capacity was designated as C0.

[0286] After that, the secondary battery was sequentially charged at 1.0C0, 1.3C0, 1.5C0, 1.8C0, 2.0C0, 2.3C0, 2.5C0, and 3.0C0 to a negative electrode cut-off potential of 4.3V or 0V (based on the one reached first) at a constant current, and after each charging was completed, it was discharged at 1C0 to 2.8V. The negative electrode potential corresponding to when charging was performed to 10%, 20%, 30%, …, 80% SOC (State of Charge) at different charging rates was recorded, the charge rate - negative electrode potential curve at different SOC states was drawn, and after linear fitting, the charging rate corresponding to when the negative electrode potential was 0V at different SOC states was obtained. This charging rate is the charging window at that SOC state, denoted as C10%SOC, C20%SOC, C30%SOC, C40%SOC, C50%SOC, C60%SOC, C70%SOC, and C80%SOC respectively. Based on the formula (60 / C20%SOC + 60 / C30%SOC + 60 / C40%SOC + 60 / C50%SOC + 60 / C60%SOC + 60 / C70%SOC + 60 / C80%SOC) × 10% with the unit being min, the charging time T of the secondary battery from 10% SOC to 80% SOC (on the premise that lithium does not precipitate in the secondary battery) was calculated. The shorter the charging time, the better the kinetic performance of the secondary battery. (2) Test on the storage performance of the secondary battery

[0287] At 25°C, the secondary battery manufactured above was charged at a constant current of 1C to 4.3V, and then charged at a constant voltage until the current reached 0.05C. After standing for 5 minutes, the secondary battery was discharged at a constant current of 1C to 2.8V, and the discharge capacity at this time was recorded, which is the discharge capacity before storage.

[0288] At 25°C, the secondary battery manufactured above was charged at a constant current of 1C to 4.3V and then charged at a constant voltage until the current reached 0.05C. Then, the secondary battery was placed in a constant temperature bath at 60°C and stored for 200 days. The capacity retention rate (%) of the secondary battery stored at 60°C for 200 days = discharge capacity after storage / discharge capacity before storage × 100%.

[0289]

Table 1

[0290] [Table 2]

[0291] As can be seen from the results in Tables 1 and 2, the first region of the negative electrode film layer contains a first carbon-based material, the second region contains a second carbon-based material, and the first carbon-based material has a porous structure and at least a portion of the surface of the second carbon-based material has a carbon coating layer, so that the battery has high energy density and can achieve both good kinetic performance and storage performance.

[0292] The second carbon-based material used in Comparative Example 3 had no carbon coating layer on its surface, and the battery had poor fast charging ability, poor dynamic performance, and poor storage performance.

[0293] Taking the results of Example 1, Comparative Example 1 and Comparative Example 2 together, it can be seen that by the first region of the negative electrode film layer comprising a first carbon-based material having a pore structure and the second region of the negative electrode film layer comprising a second carbon-based material having a carbon coating layer on at least a portion of its surface, the advantages of the synergistic effect between the first carbon-based material and the second carbon-based material can be fully exerted, and the battery has a longer storage life.

[0294] The present application is not limited to the above-mentioned embodiment. The above-mentioned embodiment is an example, and any configuration that has substantially the same technical idea as the technical scope of the present application and exhibits similar effects is included in the technical scope of the present application. In addition, various modifications to the embodiment that a person skilled in the art can conceive, and other forms constructed by combining some of the components in the embodiment, are also included in the scope of the present application, within the scope of the present application.

Claims

1. A secondary battery including a negative electrode sheet, The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer formed on at least one surface of the negative electrode current collector, The negative electrode film layer has a first surface away from the negative electrode current collector and a second surface provided opposite to the first surface, Let the thickness of the negative electrode film layer be H, the region within the thickness range from 0.3H from the second surface of the negative electrode film layer be the first region of the negative electrode film layer, and the region within the thickness range from 0.3H from the first surface of the negative electrode film layer be the second region of the negative electrode film layer, The first region contains a first active material, the first active material contains a first carbon-based material, and the first carbon-based material has a pore structure, The second region contains a second active material, the second active material contains a second carbon-based material, and at least a part of the surface of the second carbon-based material has a carbon coating layer. Secondary battery.

2. The second carbon-based material includes secondary particles. Optionally, the quantitative ratio of the secondary particles in the second carbon-based material is 50% or more, and optionally 60-80%. The secondary battery according to claim 1.

3. The graphitization degree of the second carbon-based material is smaller than the graphitization degree of the first carbon-based material. The secondary battery according to claim 1 or 2.

4. The gram capacity of the second carbon-based material is smaller than the gram capacity of the first carbon-based material. The secondary battery according to any one of claims 1-3.

5. The second carbon-based material includes at least one of artificial graphite and natural graphite. Optionally, the second carbon-based material includes artificial graphite. The secondary battery according to any one of claims 1-4.

6. The second carbon-based material satisfies at least one of the following (1)-(8). The secondary battery according to any one of claims 1-5. (1) The graphitization degree of the second carbon-based material is 90.0% - 95.5%, optionally 90.5% - 95.5%, (2) The powder OI value of the second carbon-based material is 2.0 - 6.5, optionally 2.0 - 6.0, (3) The volume distribution particle size Dv50 of the second carbon-based material is 10.0 μm - 22.0 μm, optionally 11.5 μm - 20.0 μm, (4) The particle size distribution (Dv90 - Dv10) / Dv50 of the second carbon-based material is 1.65 or less, optionally 0.90 - 1.65, (5) The tap density of the second carbon-based material is 0.85 g / cm ３ - 1.25 g / cm ３ and optionally 0.90 g / cm ３ - 1.25 g / cm ３ and (6) The gram capacity of the second carbon-based material is 340 mAh / g - 360 mAh / g, optionally 345 mAh / g - 360 mAh / g, (7) The specific surface area of the second carbon-based material is 2.5 m ２ / g or less, optionally 0.95 m ２ / g - 2.5 m ２ / g, (8) The second carbon-based material satisfies I Ｄ / I Ｇ ≧ 0.280, and optionally 0.280 ≦ I Ｄ / I Ｇ ≦ 0.500, where I Ｄ represents the D peak intensity at 1350 ± 50 cm －１ in the Raman spectrum, and I Ｇ represents the G peak intensity at 1580 ± 50 cm －１ in the Raman spectrum.

7. The first carbon-based material has a carbon coating layer on at least a part of its surface, and the secondary battery according to any one of claims 1 - 6.

8. The first carbon-based material is 0.15 μm ２including one or more pore structures having the above pore area, optionally, 0.15 μm ２ -2.0 μm ２ The secondary battery according to any one of claims 1-7, including one or more pore structures having a pore area of.

9. The first carbon-based material includes an external region and an internal region located inside the external region. The external region is a region formed by extending a distance of 0.25L from the particle surface to the particle interior of the first carbon-based material, where L is the minor axis length of the first carbon-based material particles. Let the total pore area of the external region be S １ and the total pore area of the internal region be S ２ and S ２ > S １ Optionally, 1.5 ≤ S ２ / S １ ≤ 500, 2 ≤ S ２ / S １ ≤ 450. The secondary battery according to any one of claims 1-8.

10. The area of the pore structure in the external region of the first carbon-based material is 0.15 μm ２ or less, optionally 0.10 μm ２ or less, and / or The internal region of the first carbon-based material includes one or more pore structures having an area of 0.15 μm ２ or more, optionally including one or more pore structures having an area of 0.15 μm ２ -2.0 μm ２ The secondary battery according to claim 9.

11. The first carbon-based material includes primary particles. Optionally, the quantity ratio of the primary particles in the first carbon-based material is 50% or more. The secondary battery according to any one of claims 1-10.

12. The first carbon-based material satisfies 0.152 ≤ I Ｄ / I Ｇ ≤ 0.280, optionally 0.155 ≤ I Ｄ / I Ｇ ≤ 0.220, where I Ｄrepresents the D-peak intensity at 1350 ± 50 cm of the Raman spectrum, and I －１ represents the G-peak intensity at 1580 ± 50 cm of the Raman spectrum. The secondary battery according to any one of claims 1 - 11. Ｇ －１ －１ －１ **Claim 13** The X-ray diffraction pattern of the first carbon-based material has a diffraction peak of the 3R-phase 101 crystal plane. The secondary battery according to any one of claims 1 - 12. **Claim 14** The X-ray diffraction pattern of the first carbon-based material does not have a diffraction peak of the 3R-phase 012 crystal plane. The secondary battery according to any one of claims 1 - 13. **Claim 15** The first carbon-based material satisfies at least one of the following (1) - (10). The secondary battery according to any one of claims 1 - 14. (1) The specific surface area of the first carbon-based material is 1.0 m ２ / g - 2.1 m ２ / g, and optionally 1.1 m ２ / g - 2.0 m ２ / g, (2) The volume distribution particle size Dv50 of the first carbon-based material is 8.0 μm - 25.0 μm, and optionally 8.0 μm - 22.0 μm, (3) The volume distribution particle size Dv90 of the first carbon-based material is 16.0 μm - 45.0 μm, and optionally 16.5 μm - 42.0 μm, (4) The particle size distribution (Dv90 - Dv10) / Dv50 of the first carbon-based material is 1.55 or less, and optionally 0.90 - 1.50, (5) The powder compression density of the first carbon-based material under a pressing force of 20000 N is 1.65 g / cm ３ -2.0 g / cm ３ and optionally 1.68 g / cm ３ -1.98 g / cm ３ and, (6) The tap density of the first carbon-based material is 0.85 g / cm ３ -1.30 g / cm ３and is optionally 0.90 g / cm ３ -1.25 g / cm ３ and (7) The gram capacity of the first carbon-based material is 355 mAh / g or more, and is optionally 355 mAh / g - 370 mAh / g, (8) The graphitization degree of the first carbon-based material is 95.5% or more, and is optionally 95.5% - 98.0%, (9) In the thermogravimetric analysis test of the first carbon-based material in an air atmosphere, the weight loss rate of the first carbon-based material between 35°C and 790°C is 52% or less, and is optionally 8% - 48%, (10) In the thermogravimetric analysis test of the first carbon-based material in an air atmosphere, the maximum weight loss rate of the first carbon-based material is 5.0% / min or less, and is optionally 4.8% / min or less.

16. The secondary battery according to any one of claims 1 - 15, wherein the first active material further includes a third carbon-based material containing artificial graphite in the form of primary particles.

17. The secondary battery according to claim 16, wherein the artificial graphite in the form of primary particles has no carbon coating layer on its surface.

18. The mass ratio of the third carbon-based material in the first active material is 70% by weight or less, and is optionally 15% by weight - 60% by weight, for the secondary battery according to claim 16 or 17.

19. The secondary battery according to any one of claims 16 - 18, wherein the third carbon-based material satisfies at least one of the following (1) - (7). (1) The graphitization degree of the third carbon-based material is 92.5% - 95.5%, and is optionally 92.7% - 95.5%, (2) The powder OI value of the third carbon-based material is 4.5 - 11.5, and is optionally 4.5 - 11.0, (3) The particle size distribution (Dv90 - Dv10) / Dv50 of the third carbon-based material is 1.65 or less, and is optionally 0.90 - 1.65, (4) The volume distribution particle size Dv50 of the third carbon-based material is 12.0 μm - 22.0 μm, and optionally 13.5 μm - 20.0 μm, (5) The specific surface area of the third carbon-based material is 1.0 m ２ / g - 2.0 m ２ / g, and optionally 1.05 m ２ / g - 1.95 m ２ / g, (6) The tap density of the third carbon-based material is 0.95 g / cm ３ - 1.25 g / cm ３ and optionally 1.00 g / cm ３ - 1.25 g / cm ３ and (7) The gram capacity of the third carbon-based material is 350 mAh / g - 363 mAh / g, and optionally 352 mAh / g - 362 mAh / g.

20. The first region and / or the second region further comprises a silicon-based material. Optionally, both the first region and the second region comprise a silicon-based material, and the mass ratio of the silicon-based material in the first region is less than or equal to the mass ratio of the silicon-based material in the second region. The secondary battery according to any one of claims 1 - 19.

21. The intermediate region located between the first region and the second region comprises the first active material and / or the second active material. The secondary battery according to any one of claims 1 - 20.

22. The negative electrode film layer satisfies at least one of the following (1) - (5). The secondary battery according to any one of claims 1 - 21. (1) The porosity of the negative electrode film layer is 18.0% - 36.7%, and optionally 19.0% - 34.0%, (2) The compression density of the negative electrode film layer is 1.45 g / cm ３ - 1.90 g / cm ３ and optionally 1.50 g / cm ３ - 1.85 g / cm ３ and (3) The areal density of the negative electrode film layer is 5.0 mg / cm ２ -25.0 mg / cm ２ and optionally 5.5 mg / cm ２ -22.5 mg / cm ２ and (4) The OI value of the negative electrode film layer is 35.0 or less, and optionally 8.0 - 35.0, (5) The thickness of the negative electrode film layer is 70 μm - 250 μm, and optionally 90 μm - 220 μm.

23. A power consumption device comprising the secondary battery according to any one of Claims 1 - 22.

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