Secondary battery and electric device

Abstract

A secondary battery and an electric device. The secondary battery comprises a negative electrode sheet; the negative electrode sheet comprises 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 comprises a lower region and an upper region; the lower region contains a first negative electrode active material; the upper region contains a second negative electrode active material; the median of the Raman value ID / IG of the first negative electrode active material is denoted as R150; the median of the Raman value ID / IG of the second negative electrode active material is denoted as R250; R150 is less than R250; and the graphitization degree of the first negative electrode active material is greater than that of the second negative electrode active material. The design is beneficial to improving the fast charging performance and energy density of the secondary battery.

Description

Secondary batteries and electrical devices

[0001] Cross-references

[0002] This application claims priority to the Chinese invention patent application with application number 202410046330.8 filed on January 12, 2024, and with the invention name “Secondary battery, electrical device”, the contents of which are incorporated herein by reference. Technical Field

[0003] The present application relates to a secondary battery and an electrical device. Background Art

[0004] In recent years, with the development of lithium-ion secondary battery technology, lithium-ion secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. As lithium-ion secondary batteries have achieved great development, higher requirements have been placed on their energy density and fast charging performance.

[0005] Summary of the Invention

[0006] The purpose of this application is to provide a secondary battery and an electrical device.

[0007] The embodiment of the present application is implemented as follows:

[0008] In a first aspect, an embodiment of the present application provides a secondary battery, comprising a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode film formed on at least one surface of the negative electrode current collector; the negative electrode film comprises a lower region and an upper region, the lower region comprises a first negative electrode active material, and the upper region comprises a second negative electrode active material; the median of the Raman value ID / IG of the first negative electrode active material is recorded as R1 50 The median of the Raman value ID / IG of the second negative electrode active material is recorded as R2 50 ; said R1 50 Less than the R2 50 ; The degree of graphitization of the first negative electrode active material is greater than the degree of graphitization of the second negative electrode active material.

[0009] The above technical solution controls the median Raman value ID / IG of the first negative electrode active material in the negative electrode film layer close to the negative electrode current collector (i.e., the lower region) to be lower, and the median Raman value ID / IG of the second negative electrode active material in the negative electrode film layer far from the negative electrode current collector (i.e., the upper region) to be higher; and the degree of graphitization of the first negative electrode active material is greater than the degree of graphitization of the second negative electrode active material, thereby achieving the improvement of the fast charging performance of the lithium-ion battery while taking into account the improvement of the energy density of the lithium-ion battery.

[0010] In some alternative embodiments, R1 50 is 0.05 to 0.15; optionally, R1 50 0.05 to 0.1; and / or,

[0011] R2 50 is 0.20 to 0.40; optionally, R2 50 It is 0.25~0.35.

[0012] The above technical solution, by controlling the median Raman value ID / IG of the first negative electrode active material of the negative electrode film layer close to the negative electrode current collector to be lower, and the median Raman value ID / IG of the second negative electrode active material of the negative electrode film layer far from the negative electrode current collector to be higher, can work together to achieve the improvement of the fast charging performance of the lithium-ion battery while taking into account the improvement of the energy density of the lithium-ion battery.

[0013] In some optional embodiments, the graphitization degree of the first negative electrode active material is ≥92%, optionally 93%-95%; and / or,

[0014] The graphitization degree of the second negative electrode active material is ≥91%, and can be optionally 92%-94%.

[0015] In the above technical solution, the graphitization degree of the first negative electrode active material is greater than that of the second negative electrode active material, or is within the above range, which is beneficial to improving the energy density of the lithium-ion battery and at the same time is beneficial to improving the fast charging performance of the lithium-ion battery.

[0016] In some optional embodiments, the powder compaction density of the first negative electrode active material is greater than the powder compaction density of the second negative electrode active material.

[0017] In some optional embodiments, the powder compaction density of the first negative electrode active material tested under a pressure of 49000N is ≥1.95g / cm 3 , optional 1.96g / cm 3 ~1.99g / cm 3 and / or,

[0018] The powder compaction density of the second negative electrode active material tested under a pressure of 49000N is 1.81g / cm 3 ~1.87g / cm 3 , optional 1.82

[0019] g / cm 3 ~1.86g / cm 3 .

[0020] The above technical solution sets the powder compaction density of the first negative electrode active material to be greater than the powder compaction density of the second negative electrode active material, or within the above range, which can improve the fast charging performance of the lithium-ion battery while also improving the energy density of the lithium-ion battery.

[0021] In some optional embodiments, the powder OI of the first negative electrode active material is greater than the powder OI of the second negative electrode active material.

[0022] In some optional embodiments, the powder OI of the first negative electrode active material is 2.0-10.0, optionally 4.0-8.0; and / or,

[0023] The powder OI of the second negative electrode active material is 1.0-8.0, and can be optionally 2.5-5.5.

[0024] In the above technical solution, the OI of the powder of the first negative electrode active material is greater than the OI of the powder of the second negative electrode active material, or is within the above range, which is beneficial to improving the energy density of the lithium-ion battery and at the same time is beneficial to improving the fast charging performance of the lithium-ion battery.

[0025] In some optional embodiments, the tap density of the first negative electrode active material is less than the tap density of the second negative electrode active material.

[0026] In some optional embodiments, the tap density of the first negative electrode active material is ≥0.8 g / cm 3 , optional 0.9g / cm 3 -1.1g / cm 3 and / or,

[0027] The tap density of the second negative electrode active material is 3.0 m 2 / g~4.3m 2 / g, optional 3.2m 2 / g~4.0m 2 / g.

[0028] In the above technical solution, the tap density of the first negative electrode active material is less than the tap density of the second negative electrode active material, or is within the above range, which can further effectively improve the energy density of the lithium-ion battery and is conducive to improving the fast charging performance of the lithium-ion battery.

[0029] In some optional embodiments, the volume distribution particle size Dv1 of the first negative electrode active material is smaller than the volume distribution particle size Dv1 of the second negative electrode active material.

[0030] In some optional embodiments, the volume distribution particle size Dv1 of the first negative electrode active material is 1.0 μm to 8.0 μm, and can be 3.0 μm.

[0031] ~5.0μm; and / or,

[0032] The volume distribution particle size Dv1 of the second negative electrode active material is 3.5 μm to 10.0 μm, and can be optionally 5.5 μm to 8.0 μm.

[0033] In some optional embodiments, the volume distribution particle size Dv50 of the first negative electrode active material is greater than the volume distribution particle size Dv50 of the second negative electrode active material.

[0034] In some optional embodiments, the volume distribution particle size Dv50 of the first negative electrode active material is 10 μm to 20 μm, and can be 15 μm.

[0035] ~16.5μm;

[0036] The volume distribution particle size Dv50 of the second negative electrode active material is 10 μm to 20 μm, and can be optionally 13 μm to 14.5 μm.

[0037] In some optional embodiments, the particle size distribution (D V 90-D V 10) / D V 50 is greater than the particle size distribution of the second negative electrode active material (D V 90-D V 10) / D V 50.

[0038] In some optional embodiments, the particle size distribution (D V 90-D V 10) / D V 50 is ≤2.0, and can be selected as 1.2-1.8;

[0039] The particle size distribution of the second negative electrode active material (D V 90-D V 10) / D V 50 is ≤1.8, and can be selected as 1.0-1.6.

[0040] The above technical solution sets the particle size distribution (D V 90-D V 10) / D V 50 is greater than the particle size distribution of the second negative electrode active material (D V 90-D V 10) / D V 50, which can form a better normal distribution of particle size, which is beneficial to improving the energy density of lithium-ion batteries and at the same time is beneficial to improving the fast charging performance of lithium-ion batteries.

[0041] In some optional embodiments, the specific surface area of ​​the first negative electrode active material is smaller than the specific surface area of ​​the second negative electrode active material.

[0042] In some optional embodiments, the specific surface area of ​​the first negative electrode active material is 0.5 m 2 / g~3.0m 2 / g, optional 1.0m 2 / g~2.5m 2 / g; and / or,

[0043] The specific surface area of ​​the second negative electrode active material is 2.5 m 2 / g~4.4m 2 / g, optional 3.0m 2 / g~4.0m 2 / g.

[0044] In some optional embodiments, the first negative electrode active material satisfies at least one of the following characteristics;

[0045] (1) D of the first negative electrode active material V 10 is 5μm~9μm, optional is 5.8μm~7.8μm;

[0046] (2) D of the first negative electrode active material V 90≤30μm, optional 20μm~30μm;

[0047] (3) D of the first negative electrode active material V 99≤40μm, optional 30μm~40μm;

[0048] (4) The gram capacity of the first negative electrode active material is 355 mAh / g to 365 mAh / g, and can be optionally 357 mAh / g to 363 mAh / g.

[0049] In some optional embodiments, the second negative electrode active material satisfies at least one of the following characteristics;

[0050] (1) D of the second negative electrode active material V 10 is 6μm~10.0μm, optional is 7.5μm~9.0μm;

[0051] (2) D of the second negative electrode active material V 90≤30μm, optional 20μm~30μm;

[0052] (3) D of the second negative electrode active material V 99≤40μm, optional 30μm~40μm;

[0053] (4) The gram capacity of the second negative electrode active material is 352 mAh / g to 362 mAh / g, and can be optionally 354 mAh / g to 360 mAh / g;

[0054] (5) At least a portion of the surface of the second negative electrode active material has a carbon coating layer.

[0055] In some optional embodiments, the first negative electrode active material and / or the second negative electrode active material are both artificial graphite.

[0056] In some optional embodiments, the compaction density of the negative electrode film layer is greater than or equal to 1.25 g / cm 3 , optional 1.28g / cm 3 -1.65g / cm 3 and / or,

[0057] The coating weight per unit area of ​​the negative electrode film is greater than or equal to 0.075 mg / mm 2 , optional 0.08mg / mm 2 -0.11mg / mm 2 .

[0058] In a second aspect, an embodiment of the present application provides an electrical device, which includes the secondary battery provided in the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0060] FIG1 is a schematic diagram of an embodiment of a negative electrode sheet of the present application.

[0061] FIG2 is a schematic diagram of another embodiment of the negative electrode sheet of the present application.

[0062] FIG3 is a schematic diagram of another embodiment of the negative electrode sheet of the present application.

[0063] FIG4 is a schematic diagram of a battery cell according to an embodiment of the present application.

[0064] FIG. 5 is an exploded view of the battery cell shown in FIG. 4 according to an embodiment of the present application.

[0065] FIG6 is a schematic diagram of a battery module according to an embodiment of the present application.

[0066] FIG7 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0067] FIG8 is an exploded view of the battery pack shown in FIG7 according to an embodiment of the present application.

[0068] FIG. 9 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0069] Description of reference numerals:

[0070] 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 battery cell; 51 shell; 52 electrode assembly; 53 top cover assembly; 10 negative electrode plate; 101 negative electrode current collector; 102 negative electrode film layer; 102a second surface; 102b first surface; 1021 lower area; 1022 upper area; 1023 middle area; 200 first carbon-based material; 201 external area; 202 internal area. DETAILED DESCRIPTION

[0071] Below, the embodiments of the secondary battery and electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description 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.

[0072] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0073] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0074] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0075] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0076] The negative electrode has a certain impact on the energy density and fast charging capability of the battery; it is surprising to find that by regulating the negative electrode in the present application, a secondary battery with both high energy density and fast charging characteristics can be obtained.

[0077] Based on this, the first aspect of the present application provides a secondary battery that can improve the fast charging performance of the battery while also improving the energy density of the battery.

[0078] The term "secondary battery" referred to herein refers to a battery cell, a battery module, or a battery pack.

[0079] Typically, a secondary battery cell consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0080] [Negative electrode]

[0081] The secondary battery includes a negative electrode plate, which includes a negative electrode current collector and a negative electrode film layer formed on at least one surface of the negative electrode current collector.

[0082] The negative electrode film layer has a first surface close to the negative electrode current collector and a second surface arranged opposite to the first surface; the area of ​​the negative electrode film layer from the first surface to a certain thickness in the thickness direction constitutes a lower area; the area of ​​the negative electrode film layer from the second surface to a certain thickness in the thickness direction constitutes an upper area.

[0083] The thickness of the negative electrode film layer is denoted as H, and the thickness of the lower region can be any value in the range of 0.1H-0.9H; for example, the thickness of the lower region can be 0.1H, 0.2H, 0.3H, 0.4H, 0.5H, 0.6H, 0.7H, 0.8H, or 0.9H.

[0084] The thickness of the upper region can also be any value within the range of 0.1H-0.9H; for example, the thickness of the upper region can be 0.1H, 0.2H, 0.3H, 0.4H, 0.5H, 0.6H, 0.7H, 0.8H, or 0.9H.

[0085] Optionally, the negative electrode film layer further includes a middle region.

[0086] Referring to Figures 1 to 3 , schematic diagrams illustrating several different specific embodiments of the negative electrode sheet of the present application are shown. As shown in Figures 1 to 3 , the negative electrode sheet 10 includes a negative electrode current collector 101 and a negative electrode film 102 formed on at least one surface of the negative electrode current collector 101. The negative electrode film 102 has a first surface 102b adjacent to the negative electrode current collector 101 and a second surface 102a disposed opposite the first surface 102b. The thickness of the negative electrode film 102 is denoted as H. The thickness H of the negative electrode film refers to the thickness of the negative electrode film located on a single side of the negative electrode current collector. The region from the second surface 102a of the negative electrode film to a certain thickness range (e.g., 0.3H) is denoted as the upper region 1022 of the negative electrode film. The region from the first surface 102b of the negative electrode film to a certain thickness range (e.g., 0.3H) is denoted as the lower region 1021 of the negative electrode film. The lower region 1021 includes the first negative electrode active material, and the upper region 1022 includes the second negative electrode active material. The region between the upper region 1022 and the lower region 1021, which occupies a thickness range of 0.4H, is denoted as the middle region 1023. It is easy to understand, according to Figures 1 to 3, that the middle region 1023 may contain only the first negative electrode active material, only the second negative electrode active material, or both the first and second negative electrode active materials.

[0087] It should be understood that in the embodiments shown in Figures 1 to 3, the first surface 102b is in contact with the upper surface of the negative electrode current collector 101, but the structure of the negative electrode plate of the present application is not limited thereto. For example, there may be an additional layer between the negative electrode film layer 102 and the negative electrode current collector 101. In this case, the first surface 102b does not directly contact the negative electrode current collector 101.

[0088] Specifically, Figures 1 to 3 illustrate that the first negative electrode active material and the second negative electrode active material are sequentially coated on the negative electrode current collector 101. Figure 1 shows that the thickness of the lower region and the upper region each account for approximately half of the thickness of the negative electrode film layer 102. Figure 2 shows that the thickness of the upper region accounts for approximately 30% of the thickness of the negative electrode film layer 102, while the thickness of the lower region accounts for approximately 70% of the thickness of the negative electrode film layer 102. Figure 3 shows a configuration opposite to Figure 2, namely, the thickness of the lower region accounts for approximately 30% of the thickness of the negative electrode film layer 102, while the thickness of the upper region accounts for approximately 70% of the thickness of the negative electrode film layer 102.

[0089] It should be understood that Figures 1 to 3 illustrate idealized schematic diagrams. The present application does not particularly limit the thickness ratio of the lower region to the upper region; for example, the ratio can be any ratio within the range of 1:9 to 9:1. For example, the ratio of the thickness of the lower region to the upper region can be 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2, 9:1, or any ratio between these two ratios.

[0090] It should also be understood that although FIG1 to FIG3 show clear boundaries between the regions, such clear interfaces may not exist in the product.

[0091] In this application, the median of the Raman value ID / IG of the first negative electrode active material is recorded as R1 50 The median of the Raman value ID / IG of the second negative electrode active material is recorded as R2 50 ; R1 50 Less than R2 50 In the above technical solution, the median Raman value ID / IG represents the overall disorder of the material surface. The smaller the median Raman value ID / IG, the lower the overall disorder of the material surface; the smaller the median Raman value ID / IG of the material, the more favorable it is for energy density.

[0092] In some embodiments of the present application, the first negative electrode active material can be selected from a highly anisotropic raw material, or a highly graphitized material prepared by a high-temperature graphitization process; for example, such as a needle coke graphite matrix, a petroleum coke graphite matrix, etc.

[0093] In some embodiments of the present application, the second negative electrode active material can be a highly disordered graphite material, thereby obtaining a second negative electrode active material having a large median Raman value ID / IG. Furthermore, the second negative electrode active material can be prepared by coating graphite with a highly disordered coating, for example, by coating graphite with a hard carbon coating.

[0094] Furthermore, in the above technical solution, the median of the Raman value ID / IG of the first negative electrode active material in the lower region is relatively low, which is beneficial to the energy density of the battery.

[0095] Furthermore, a larger median of the Raman value ID / IG indicates a greater overall disorder on the material surface. A greater degree of disorder is more conducive to charge exchange between ions on the surface of the negative electrode active material.

[0096] In the above technical solution, the median of the Raman value ID / IG of the second negative electrode active material in the upper region is relatively high, which is beneficial to the charge exchange on the surface of the negative electrode active material, thereby improving the kinetic performance.

[0097] Furthermore, in some embodiments of the present application, the median of the Raman value ID / IG of the second negative electrode active material is not only larger but also evenly distributed, thereby being more conducive to lithium ion transfer and kinetic performance.

[0098] Furthermore, in some embodiments of the present application, the graphitization degree of the first negative electrode active material is greater than the graphitization degree of the second negative electrode active material.

[0099] In the present application, by controlling the median Raman value ID / IG of the first negative electrode active material in the lower region to be lower, the median Raman value ID / IG of the second negative electrode active material in the upper region to be higher, and the degree of graphitization of the first negative electrode active material being greater than the degree of graphitization of the second negative electrode active material; it is possible to achieve an improvement in the fast charging performance of the lithium-ion battery while also taking into account an improvement in the energy density of the lithium-ion battery.

[0100] Furthermore, in some embodiments of the present application, the above-mentioned R1 50 It is 0.05~0.15.

[0101] Further optionally, illustratively, in some embodiments of the present application, the above R1 50 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15 or the range between any two of the foregoing values.

[0102] In the above technical solution, by setting R1 50 is 0.05 to 0.15, which can be compared with the aforementioned R2 50 Matching can improve the fast charging performance of lithium-ion batteries while also improving the energy density of lithium-ion batteries.

[0103] Further optionally, in some embodiments of the present application, the above R1 50 It is 0.05~0.10.

[0104] For example, in some embodiments of the present application, the above R1 50 It is 0.05, 0.06, 0.07, 0.08, 0.09 or 0.10.

[0105] In the above technical solution, R1 is further 50 Limiting it to the range of 0.05 to 0.10 is more conducive to improving the fast charging performance of lithium-ion batteries while taking into account improving the energy density of lithium-ion batteries.

[0106] Further, in some embodiments of the present application, R2 50 It is 0.20~0.40.

[0107] For example, in some embodiments of the present application, the above R2 50 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.28, 0.30, 0.35, 0.35, 0.38, 0.39, 0.40 or a range between any two of the foregoing values.

[0108] In the above technical solution, by setting R2 50 0.20~0.40, can be combined with R1 50 Matching can improve the fast charging performance of lithium-ion batteries while also improving the energy density of lithium-ion batteries.

[0109] Further optionally, in some embodiments of the present application, R2 50 It is 0.25~0.35.

[0110] For example, R2 50 It is 0.25, 0.26, 0.28, 0.31, 0.32 or 0.35.

[0111] In the above technical solution, R2 50 Limiting it to the range of 0.25 to 0.35 is more conducive to improving the fast charging performance of lithium-ion batteries while taking into account improving the energy density of lithium-ion batteries.

[0112] Furthermore, in some embodiments of the present application, the graphitization degree of the first negative electrode active material is ≥92%; optionally 93-95%.

[0113] The above technical solution, by setting the graphitization degree of the first negative electrode active material to ≥94%, can further effectively improve the energy density of the lithium-ion battery, and is also beneficial to improving the fast charging performance of the lithium-ion battery.

[0114] Further optionally, in some optional embodiments of the present application, the degree of graphitization of the first negative electrode active material is 92%, 93%, 94%, 95% or a range between any two of the foregoing values.

[0115] Furthermore, in some embodiments of the present application, the graphitization degree of the second negative electrode active material is ≥91%, and may be 92-94%.

[0116] The above technical solution, by setting the graphitization degree of the second negative electrode active material to ≥91%, can further effectively improve the energy density of the lithium-ion battery, and is also beneficial to improving the fast charging performance of the lithium-ion battery.

[0117] Further optionally, in some optional embodiments of the present application, the degree of graphitization of the second negative electrode active material is 91%, 92%, 93%, 94% or a range between any two of the foregoing values.

[0118] Furthermore, in some embodiments of the present application, the powder compaction density of the first negative electrode active material is greater than the powder compaction density of the second negative electrode active material.

[0119] The powder compaction density of the first negative electrode active material is greater than the powder compaction density of the second negative electrode active material; this indicates that the compaction density of the lower area of ​​the negative electrode film layer is higher, and the compaction density of the upper area of ​​the negative electrode film layer is lower. Therefore, the particles are densely stacked in the lower area of ​​the negative electrode film layer, which can give full play to the characteristics of high pressure, density and high capacity of the active material, and ensure the energy density of the film layer; in the upper area of ​​the negative electrode film layer, due to its low compaction density and rich pores, it provides sufficient paths for the transfer of lithium ions inside the electrode sheet, thereby ensuring the fast charging capability of the film layer.

[0120] In the above technical solution, the powder compaction density of the first negative electrode active material is set to be greater than the powder compaction density of the second negative electrode active material; this can improve the fast charging performance of the lithium-ion battery while also improving the energy density of the lithium-ion battery.

[0121] Furthermore, in some embodiments of the present application, the powder compaction density of the first negative electrode active material tested under a pressure of 49000N is

[0122] ≥1.95g / cm 3 , optional 1.96g / cm 3 ~1.99g / cm 3 .

[0123] For example, in some embodiments of the present application, the powder compaction density of the first negative electrode active material tested under a pressure of 49000N is 1.96g / cm 3 , 1.97g / cm 3, 1.98g / cm 3 , 1.99g / cm 3 .

[0124] Furthermore, in some embodiments of the present application, the powder compaction density of the second negative electrode active material tested under a pressure of 49000N is 1.81g / cm 3 ~1.87g / cm 3 , optional 1.82g / cm 3 ~1.86g / cm 3 .

[0125] For example, in some embodiments of the present application, the powder compaction density of the second negative electrode active material tested under a pressure of 49000N is 1.81g / cm 3 , 1.82g / cm 3 , 1.83g / cm 3 , 1.84g / cm 3 , 1.85g / cm 3 or 1.86 g / cm 3 .

[0126] Furthermore, in some embodiments of the present application, the OI of the powder of the first negative electrode active material is greater than the OI of the powder of the second negative electrode active material.

[0127] Furthermore, in some embodiments of the present application, the OI of the first negative electrode active material is 4.0-8.0.

[0128] In some embodiments of the present application, the powder OI of the second negative electrode active material is 1.0-8.0.

[0129] The OI in the above technical solution refers to the voltage of the first or second negative electrode active material during discharge. The OI value of the first or second negative electrode active material directly affects the energy density of the lithium-ion battery.

[0130] In the above technical solution, by setting the OI of the first negative electrode active material to 4.0-8.0 and the OI of the powder of the second negative electrode active material to 1.0-8.0, it is beneficial to improve the energy density of the lithium-ion battery and at the same time it is beneficial to improve the fast charging performance of the lithium-ion battery.

[0131] Illustratively, in some embodiments of the present application, the OI of the first negative electrode active material is 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, or a range between any two of the foregoing values.

[0132] Illustratively, in some embodiments of the present application, the OI of the second negative electrode active material is 1.0, 2.0, 3.0, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, or a range between any two of the foregoing values.

[0133] Furthermore, in some embodiments of the present application, the tap density of the first negative electrode active material is less than the tap density of the second negative electrode active material.

[0134] Furthermore, in some embodiments of the present application, the tap density of the first negative electrode active material is ≥0.8 g / cm 3 , optional 0.9g / cm 3 -1.1g / cm 3 .

[0135] Furthermore, in some embodiments of the present application, the tap density of the second negative electrode active material is 3.0 m 2 / g~4.3m 2 / g, optional 3.2m 2 / g~4.0m 2 / g.

[0136] Furthermore, in the above technical solution, the tap density of the first or second negative electrode active material is within the above range, which can effectively improve the energy density of the lithium-ion battery and is conducive to improving the fast charging performance of the lithium-ion battery.

[0137] For example, in some embodiments of the present application, the tap density of the first negative electrode active material is 0.9 g / cm 3 , 1g / cm 3 or 1.1 g / cm 3 The tap density of the second negative electrode active material is 3.0m 2 / g, 3.2m 2 / g, 3.5m 2 / g, 3.8m 2 / g or 4.0g / cm 3 .

[0138] Furthermore, in some embodiments of the present application, the volume distribution particle size Dv1 of the first negative electrode active material is smaller than the volume distribution particle size Dv1 of the second negative electrode active material.

[0139] Furthermore, in some embodiments of the present application, the volume distribution particle size Dv1 of the first negative electrode active material is 1.0 μm to 8.0 μm, and can be optionally 3.0 μm to 5.0 μm.

[0140] Furthermore, in some embodiments of the present application, the volume distribution particle size Dv1 of the second negative electrode active material is 3.5 μm to 10.0 μm, and can be optionally 5.5 μm to 8.0 μm.

[0141] For example, in some embodiments of the present application, the volume distribution particle size Dv1 of the first negative electrode active material is 1.0 μm, 2.0 μm,

[0142] 3.0μm, 4.0μm, 5.0μm or 8.0μm; the volume distribution particle size Dv1 of the second negative electrode active material is 3.5μm, 3.8μm, 4μm, 4.5μm,

[0143] 6μm, 8μm or 10.0μm.

[0144] Furthermore, in some embodiments of the present application, the volume distribution particle size Dv50 of the first negative electrode active material is greater than the volume distribution particle size Dv50 of the second negative electrode active material.

[0145] Furthermore, in some embodiments of the present application, the volume distribution particle size Dv50 of the first negative electrode active material is 10 μm to 20 μm, and can be optionally 15 μm to 16.5 μm.

[0146] Furthermore, in some embodiments of the present application, the volume distribution particle size Dv50 of the second negative electrode active material is 10 μm to 20 μm, and can be optionally 13 μm to 14.5 μm.

[0147] Further, for example, in some embodiments of the present application, the D of the first negative electrode active material is V 50 is 13.0 μm, 13.5 μm, 14.0 μm, 14.5 μm, 15.0 μm, 15.5 μm, 16.0 μm, 16.5 μm, 17.0 μm or a range between any two of the foregoing values.

[0148] Further, for example, in some embodiments of the present application, the D of the second negative electrode active material is V 50 is 13.0 μm, 13.2 μm, 13.4 μm, 13.5 μm, 14.0 μm, 14.5 μm or a range between any two of the foregoing values.

[0149] Furthermore, in some embodiments of the present application, the particle size distribution (D V 90-D V 10) / D V 50 is greater than the particle size distribution of the second negative electrode active material (D V 90-D V 10) / D V 50.

[0150] Furthermore, in some embodiments of the present application, the particle size distribution (D V 90-D V 10) / D V 50 is ≤2.0, and can be selected as 1.2-1.8.

[0151] Furthermore, in some embodiments of the present application, the particle size distribution (D V 90-D V 10) / D V 50 is ≤1.8, and can be selected as 1.0-1.6.

[0152] In the above technical solution, by setting the first and second negative electrode active materials (D V 90-D V 10) / D V 50 Within the above range, a better normal distribution of particle size can be formed, which is beneficial to improving the energy density of lithium-ion batteries and at the same time is beneficial to improving the fast charging performance of lithium-ion batteries.

[0153] For example, in some embodiments of the present application, the first negative electrode active material (D V 90-D V 10) / D V 50 is 1.2, 1.3, 1.4, 1.5, 1.6, 1.7 or 1.8.

[0154] The second negative electrode active material (D V 90-D V 10) / D V 50 is 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6 or a range between any two of the foregoing values.

[0155] Furthermore, in some embodiments of the present application, the specific surface area of ​​the first negative electrode active material is smaller than the specific surface area of ​​the second negative electrode active material.

[0156] Furthermore, in some embodiments of the present application, the specific surface area of ​​the first negative electrode active material is 0.5 m 2 / g~3.0m 2 / g, optional 1.0m 2 / g~2.5m 2 / g.

[0157] Furthermore, in some embodiments of the present application, the specific surface area of ​​the second negative electrode active material is 2.5 m 2 / g~4.4m 2 / g, optional 3.0m 2 / g~4.0m 2 / g.

[0158] For example, in some embodiments of the present application, the specific surface area of ​​the first negative electrode active material is 0.5 m 2 / g、1m 2 / g, 1.5m 2 / g, 2m 2 / g, 2.5m 2 / g or 3.0m 2 / g. The specific surface area of ​​the second negative electrode active material is 2.5m 2 / g, 2.8m 2 / g、3m 2 / g, 3.5m 2 / g、4m 2 / g or 4.4m 2 / g.

[0159] Furthermore, in the above technical solution, the specific surface area of ​​the first or second negative electrode active material is the specific surface area of ​​the material measured when CO2 is used as the carrier gas. Since CO2 molecules are relatively small and can enter the microporous structure of the material, the CO2 adsorption specific surface area can reflect information such as the proportion of the number of micropores in the material. When the CO2 adsorption specific surface area of ​​the specific surface area of ​​the first negative electrode active material is within the above range, it can effectively improve the energy density of the lithium-ion battery and is also beneficial to improving the fast charging performance of the lithium-ion battery.

[0160] Furthermore, in some embodiments of the present application, the first negative electrode active material satisfies at least one of the following characteristics:

[0161] (1) D of the first negative electrode active material V 10 is 5μm~9μm, optional is 5.8μm~7.8μm;

[0162] (2) D of the first negative electrode active material V 90≤30μm, optional 20μm~30μm;

[0163] (3) D of the first negative electrode active material V 99≤40μm, optional 30μm~40μm;

[0164] (4) The gram capacity of the first negative electrode active material is 355 mAh / g to 365 mAh / g, and can be optionally 357 mAh / g to 363 mAh / g.

[0165] Furthermore, in some embodiments of the present application, the second negative electrode active material satisfies at least one of the following characteristics:

[0166] (1) D of the second negative electrode active materialV 10 is 6μm~10.0μm, optional is 7.5μm~9.0μm;

[0167] (2) D of the second negative electrode active material V 90≤30μm, optional 20μm~30μm;

[0168] (3) D of the second negative electrode active material V 99≤40μm, optional 30μm~40μm;

[0169] (4) The gram capacity of the second negative electrode active material is 352 mAh / g to 362 mAh / g, and can be optionally 354 mAh / g to 360 mAh / g;

[0170] (5) At least a portion of the surface of the second negative electrode active material has a carbon coating layer.

[0171] Furthermore, in the above technical solution, the gram capacity of the first or second negative electrode active material is within the above range, which can enable the battery to effectively achieve both higher energy density and better fast charging performance.

[0172] Furthermore, in the above technical solution, the first coulombic efficiency of the first or second negative electrode active material is within the above range, which can effectively improve the energy density of the lithium-ion battery and is conducive to improving the fast charging performance of the lithium-ion battery.

[0173] In the above technical solution, D of the first or second negative electrode active material v 10. D V 50. D V 90.D v 99.D v 1 is set within the above range, which is beneficial to improving the energy density of lithium-ion batteries and at the same time is beneficial to improving the fast charging performance of lithium-ion batteries.

[0174] Furthermore, in some embodiments of the present application, the first negative electrode active material and / or the second negative electrode active material are both artificial graphite.

[0175] Furthermore, in some embodiments of the present application, the compaction density of the negative electrode film layer is greater than or equal to 1.25 g / cm 3 , optional 1.28g / cm 3 -1.65g / cm 3 .

[0176] For example, in some embodiments of the present application, the compaction density of the negative electrode film layer is 1.28 g / cm 3 , 1.3g / cm 3 , 1.35g / cm 3 , 1.4g / cm3 , 1.45g / cm 3 , 1.5g / cm 3 , 1.55g / cm 3 , 1.6g / cm 3 or 1.65g / cm 3 .

[0177] Furthermore, in some embodiments of the present application, the coating weight per unit area of ​​the negative electrode film layer is greater than or equal to 0.075 mg / mm 2 , optional 0.08mg / mm 2 -0.11mg / mm 2 .

[0178] For example, in some embodiments of the present application, the coating weight per unit area of ​​the negative electrode film layer is 0.08 mg / mm 2 , 0.09mg / mm 2 , 0.1mg / mm 2 or 0.11 mg / mm 2 .

[0179] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0180] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0181] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0182] The above-mentioned conductive agent, binder and other additives, if any, are not particularly limited in the present application to their types and amounts, and those skilled in the art can select and determine them according to actual needs.

[0183] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0184] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0185] The negative electrode current collector has two surfaces that face each other in the thickness direction, and the negative electrode film is disposed on either or both of these opposing surfaces. It should be noted that the negative electrode film parameters given in this application refer to the parameters of the negative electrode film on a single side of the negative electrode current collector. When the negative electrode film is disposed on both sides of the negative electrode current collector, the parameters of the negative electrode film on either side satisfy the requirements of this application and are considered to fall within the scope of protection of this application.

[0186] In the present application, the negative electrode plate does not exclude the possibility of including other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode plate further includes a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector; in some embodiments, the negative electrode plate further includes a protective layer covering the surface of the negative electrode film layer.

[0187] In this application, the I of a material (eg, a first negative electrode active material, a second negative electrode active material, etc.) D / I G The value can be tested using Raman spectrometer, I D The Raman spectrum of the material is 1350±50cm -1 The D peak intensity at I G The Raman spectrum of the material is 1580±50cm -1 The test conditions can be: excitation wavelength 532nm, grating 600 lines, objective lens 50 times, integration time 10s, accumulation times 3 times, surface scanning, obtain 100 points of D peak and G peak intensity, calculate the I of 100 points D / I G, remove the largest and smallest 25 I D / I G The average value of the remaining 50 points is the I D / I G The testing instrument may be a Horiba LabRAM HR800 Raman spectrometer.

[0188] In this application, the compacted density of the powder of the negative electrode active material has a meaning well known in the art and can be measured using methods known in the art. For example, referring to GB / T 24533-2009, an electronic pressure testing machine (such as UTM7305) can be used for testing: a certain amount M of the powder sample to be tested is placed on a special compaction mold (bottom area S), different pressures are set (49000N can be used in this application), the pressure is maintained for 30 seconds, the pressure is released, and the device is left for 10 seconds. The thickness H of the powder after compaction under the pressure is read on the device, and the compacted density under the pressure can be calculated. The compacted density of the negative electrode active material under the pressure = M / (H * S).

[0189] In this application, the degree of graphitization of a material (e.g., the first negative electrode active material and the second negative electrode active material) is known in the art and can be tested using instruments and methods known in the art. For example, an X-ray diffractometer (e.g., a Bruker D8 Discover) can be used for testing. The test can refer to JIS K 0131-1996 and JB / T 4220-2011 to obtain the average interlayer spacing d002 of the C(002) plane in the material's crystal structure. The degree of graphitization is then calculated using the formula g = (0.344-d002) / (0.344-0.3354) × 100%. In the above formula, d002 is the average interlayer spacing of the C(002) plane in the material's crystal structure expressed in nanometers (nm).

[0190] In this application, the OI of a material (e.g., the first negative electrode active material and the second negative electrode active material) has a well-known meaning in the art and can be measured using instruments and methods known in the art. According to the general principles of X-ray diffraction analysis and the method for determining the lattice parameters of graphite (JIS K 0131-1996 and JB / T 4220-2011), an X-ray diffraction spectrum is obtained using an X'pert PRO diffractometer. The orientation index of the negative electrode material can be calculated according to OI = C004 / C110, where C004 is the peak area of ​​the 004 characteristic diffraction peak and C110 is the peak area of ​​the 110 characteristic diffraction peak.

[0191] In this application, the tap density of a material (e.g., the first negative electrode active material and the second negative electrode active material) has a meaning well known in the art and can be measured using instruments and methods known in the art. For example, it can be measured using a powder tap density tester in accordance with GB / T 5162-2006. The test instrument can be a Dandong Better BT-301, with the following test parameters: vibration frequency 250±15 times / minute, amplitude 3±0.2mm, vibration number 5000 times, and a 25mL graduated cylinder.

[0192] In this application, the volume distribution particle sizes Dv1, Dv10, Dv50, and Dv90 of materials (e.g., the first negative electrode active material, the second negative electrode active material, etc.) are well known in the art and represent the particle sizes corresponding to the cumulative volume distribution percentages of the materials reaching 1%, 10%, 50%, and 90%, respectively. They can be measured using instruments and methods known in the art. For example, a laser particle size analyzer can be used for measurement with reference to GB / T 19077-2016. The test instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0193] In this application, the specific surface area of ​​a material (e.g., the first negative electrode active material and the second negative electrode active material) is well known in the art and can be measured using instruments and methods known in the art. For example, it can be measured using the nitrogen adsorption specific surface area analysis test method in accordance with GB / T 19587-2017 and calculated using the BET (Brunauer Emmett Teller) method. The testing instrument can be a Tri-Star 3020 specific surface area pore size analyzer from Micromeritics, Inc., USA.

[0194] In the present application, whether there is a coating layer on the surface of a material (eg, the first negative electrode active material, the second negative electrode active material, etc.) can be determined by transmission electron microscopy.

[0195] In this application, the gram capacity of materials (such as the first negative electrode active material and the second negative electrode active material) has a meaning well known in the art and can be tested using methods known in the art. The exemplary test method is as follows: the sample powder is mixed evenly with the conductive agent carbon black (Super P), the binder polyvinylidene fluoride (PVDF) and the solvent N-methylpyrrolidone (NMP) in a mass ratio of 91.6:1.8:6.6 to prepare a slurry; the prepared slurry is applied on the surface of the negative electrode current collector copper foil, dried in an oven and set aside; ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and then LiPF6 is dissolved in the above organic solvent to prepare a concentrated The electrolyte solution was prepared with a concentration of 1 mol / L. A lithium metal sheet was then used as the counter electrode, and a polyethylene (PE) film was used as the separator. These electrolytes were then used to assemble a CR2430 button cell in an argon-protected glove box. The resulting button cell was left to rest for 12 hours and then discharged at 0.05C to 0.005V at 25°C. The cell was then left to rest for 10 minutes, and then discharged again at 50μA to 0.005V. The cell was left to rest for 10 minutes, and then discharged again at 10μA to 0.005V. The discharge capacity was then recorded. The ratio of discharge capacity to sample mass is the gram capacity of the corresponding material (e.g., the first negative electrode active material, the second negative electrode active material, etc.).

[0196] The thickness of the negative electrode film layer is well known in the art and can be measured using methods known in the art, such as using a micrometer (e.g., Mitutoyo 293-100, with an accuracy of 0.1 μm). The thickness ranges given in this application are for the thickness of the negative electrode film layer on one side of the negative electrode current collector. If the thickness of the negative electrode film layer on either side of the negative electrode current collector falls within the ranges given in this application, the negative electrode film layer meets the requirements of this application.

[0197] It should be noted that the various parameter tests on the negative electrode active material or the negative electrode film layer can be performed by sampling and testing the prepared secondary battery according to the following steps.

[0198] Discharge the secondary battery (for safety reasons, the secondary battery is generally fully discharged). Disassemble the secondary battery, remove the negative electrode, and soak the negative electrode in dimethyl carbonate for a certain period of time (e.g., 2-10 hours). Then remove the negative electrode and dry it at a certain temperature and time (e.g., 60°C for more than 4 hours). After drying, remove the negative electrode. Samples can now be taken from the dried negative electrode to test the aforementioned parameters related to the negative electrode film, such as the compaction density, OI value, and thickness of the negative electrode film.

[0199] The dried negative electrode sheet is baked at a certain temperature and time (for example, 400°C for more than 2 hours), and a sample of the negative electrode active material is taken from any area of ​​the baked negative electrode sheet (a blade can be used for scraping powder sampling); the collected negative electrode active material is sieved (for example, sieved with a 200-mesh sieve) to finally obtain a sample that can be used to test the parameters of the above-mentioned negative electrode active materials.

[0200] In the present application, the first negative electrode active material and the second negative electrode active material mentioned above can be obtained commercially, or can also be prepared by the following method of the present application.

[0201] In some embodiments, the first negative electrode active material may be prepared as follows:

[0202] 1) Use petroleum-based needle coke as raw material and carry out crushing, shaping and grading treatment;

[0203] 2) Heat treatment: The process material after step 1) is mixed with the adhesive in a ratio of (8-12):1 and granulated. The granulation temperature is raised to 600-700°C for 8-12 hours, and then cooled for 5-10 hours to obtain intermediate product 1;

[0204] 3) Graphitization: The intermediate product 1 in 2) is graphitized at a graphitization temperature of 2800 to 3200°C.

[0205] The granulation treatment in step 2) is heated and maintained at 600°C, 610°C, 620°C, 630°C, 640°C, 650°C, 660°C, 670°C, 680°C, 690°C, or 700°C, or a range between any two of the foregoing values. The mass ratio in step 2) is selected to be 8:1, 9:1, 10:1, 11:1, or 12:1, or a range between any two of the foregoing values.

[0206] The graphitization temperature in the above step 3) is 2800° C., 2900° C., 3000° C., 3100° C., 3200° C. or a range between any two of the above values.

[0207] In some embodiments, the second negative electrode active material can be prepared according to the following method:

[0208] 1) Use petroleum-based needle coke as raw material and carry out crushing, shaping and grading treatment;

[0209] 2) Heat treatment: The process material after step 1) is mixed with the adhesive in a mass ratio of (5-10):1 and granulated. The granulation temperature is raised to 600-700°C for 8-12 hours, and then cooled for 5-10 hours to obtain the intermediate product 1;

[0210] 3) Graphitization: The intermediate product 1 in 2) is graphitized at a graphitization temperature of 3000-3400° C. to obtain an intermediate product 2.

[0211] 4) Fusion Coating and Carbonization: The intermediate product 2 from step 3) is coated using a coating agent such as an organic carbon source for solid-liquid fusion. The coating agent is added in an amount of 1-10% of the total mass of the intermediate product 2. Carbonization is then performed at a temperature of 1000-1200°C. The granulation temperature in step 2) is raised and maintained at 600°C, 610°C, 620°C, 630°C, 640°C, 650°C, 660°C, 670°C, 680°C, 690°C, or 700°C, or a range between any two of the aforementioned values. The mass ratio in step 2) is selected from 5:1, 6:1, 7:1, 8:1, 9:1, or 10:1, or a range between any two of the aforementioned values.

[0212] The graphitization temperature in the above step 3) is 3000° C., 3100° C., 3200° C., 3300° C., 3400° C. or a range between any two of the above values.

[0213] The organic carbon source in step 4) can include one or more of coal tar, petroleum asphalt, phenolic resin, coconut shell, etc. The amount of the coating agent added in step 4) is 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% of the total mass of the intermediate product 2, or a range between any two of the aforementioned values. The carbonization temperature in step 4) can be selected from 1000°C, 1010°C, 1050°C, 1100°C, 1150°C, 1180°C, 1200°C, or a range between any two of the aforementioned values.

[0214] [Positive electrode]

[0215] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes the positive electrode active material of the first aspect of the present application.

[0216] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0217] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0218] In some embodiments, when the battery cell is a lithium-ion battery, the positive electrode active material may adopt the positive electrode active material for lithium-ion batteries known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0219] In some embodiments, when the battery cell is a sodium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for sodium-ion batteries. For example, the positive electrode active material may include at least one of the following materials: a sodium transition metal oxide, a polyanionic compound, or a Prussian blue-based compound.

[0220] The battery's charge and discharge processes involve the intercalation and deintercalation of lithium, leading to different molar Li contents at different discharge states. The molar Li contents listed in this application for cathode materials refer to the initial state of the material, i.e., the state before addition of the materials. When the cathode material is used in a battery system, the molar Li content will change after charge and discharge cycles.

[0221] In the list of positive electrode materials in this application, the molar content of O is only a theoretical value. Lattice oxygen release will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0222] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0223] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0224] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0225] [Electrolytes]

[0226] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0227] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0228] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0229] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0230] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0231] [Isolation film]

[0232] In some embodiments, the battery cell further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0233] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0234] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0235] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0236] In some embodiments, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the battery cell may be a soft shell, such as a pouch-type soft shell. The soft shell may be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0237] The present application has no particular limitation on the shape of the battery cell, which can be cylindrical, square, or any other shape. For example, FIG4 shows a battery cell 5 with a square structure as an example.

[0238] In some embodiments, referring to Figure 5, the outer packaging may include a shell 51 and a top cover assembly 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the top cover assembly 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0239] In some embodiments, battery cells may be assembled into a battery module. The battery module may contain one or more battery cells. The specific number may be selected by those skilled in the art based on the application and capacity of the battery module.

[0240] Figure 6 shows an example battery module 4. Referring to Figure 6 , within the battery module 4, multiple battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the multiple battery cells 5 may be secured together using fasteners.

[0241] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0242] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0243] Figures 7 and 8 illustrate an example battery pack 1. Referring to Figures 7 and 8 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be positioned over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0244] In addition, the second aspect of the present application further provides an electrical device, the electrical device comprising the secondary battery provided in the present application. The secondary battery can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0245] As the electrical device, a battery cell, a battery module or a battery pack can be selected according to its usage requirements.

[0246] Figure 9 shows an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0247] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be lightweight and thin, and may use a battery cell as a power source.

[0248]

[0249] Example

[0250] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0251] The materials used in the examples and comparative examples of the present application can be obtained commercially or prepared by the following process.

[0252] Preparation of Materials 1-1 (First Negative Electrode Active Material):

[0253] 1) Use petroleum-based needle coke as raw material and carry out crushing, shaping and grading treatment;

[0254] 2) Heat treatment: The process material after step 1) is mixed with the adhesive in a mass ratio of 10:1 and granulated. The granulation temperature is raised to 650°C for 10 hours, and then cooled for 8 hours to obtain intermediate product 1;

[0255] 3) Graphitization: The intermediate product 1 in 2) is graphitized at a graphitization temperature of 3000°C.

[0256] Among them, the negative electrode active material 1-1 meets the following requirements: Raman value ID / IG median R1 50 The compacted density of the powder at 49000N is 1.95g / cm 3 , graphitization degree is 94.5%, powder OI is 4.8, volume distribution particle size D V 50 is 15 μm, volume distribution particle size D V 1 is 3.1 μm, and the specific surface area is 2.0 m 2 / g.

[0257]

Materials 1-2, 1-3 preparation

[0258] The difference from the preparation method of material 1-1 is: graphitization temperature, see Table 1 for details.

[0259] Table 1

[0260] Preparation of Materials 2-1 (Second Negative Electrode Active Material):

[0261] 1) Use petroleum-based needle coke as raw material and carry out crushing, shaping and grading treatment;

[0262] 2) Heat treatment: The process material after step 1) is mixed with the adhesive in a mass ratio of 8:1 and granulated. The granulation temperature is raised to 650°C for 10 hours, and then cooled for 8 hours to obtain intermediate product 1;

[0263] 3) Graphitization: The intermediate product 1 in 2) was graphitized at a graphitization temperature of 3200° C. to obtain an intermediate product 2.

[0264] 4) Fusion coating and carbonization: The intermediate product 2 in 3) is coated with a liquid phenolic resin coating agent for solid-liquid fusion. The amount of coating agent added is 5% of the total mass of the intermediate product 2. Then, carbonization treatment is performed at a carbonization temperature of 1150°C to obtain the negative electrode active material 1-1.

[0265] Among them, the negative electrode active material 1-1 satisfies: Raman value ID / IG median R1 50 The compacted density of the powder at 49000N is 1.81g / cm 3 , graphitization degree is 93.5%, powder OI is 3.3, volume distribution particle size D V 50 is 14.5μm, volume distribution particle size D V 1 is 6.8 μm and the specific surface area is 3.4 m 2 / g.

[0266] [Preparation of Materials 2-2, 2-3, and 2-4]:

[0267] The preparation method is similar to that of material 2-1, except that the amount of coating agent added or the carbonization temperature is different, see Table 2 for details.

[0268] Table 2

[0269] Example 1

[0270] Preparation of secondary batteries:

[0271] 1. Preparation of negative electrode sheet

[0272] The first negative electrode active material (material 1-1) was thoroughly stirred and mixed with a conductive agent, carbon black (Super P), a thickener, sodium carboxymethyl cellulose, and a binder, styrene-butadiene rubber, 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 negative electrode slurry.

[0273] The second negative electrode active material (material 2-1) was thoroughly stirred and mixed with a conductive agent, carbon black (Super P), a thickener, sodium carboxymethyl cellulose, and a binder, styrene-butadiene rubber, 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 negative electrode slurry.

[0274] The first negative electrode slurry is coated on the surface of the negative electrode current collector copper foil to form the lower area of ​​the negative electrode film layer, and the second negative electrode slurry is coated on the first negative electrode film layer to form the upper area of ​​the negative electrode film layer. After drying and cold pressing, the negative electrode sheet is obtained. The mass ratio of the first negative electrode slurry to the second negative electrode slurry is 6:4, and the compacted density of the negative electrode film layer is 1.6g / cm 3 The single-sided coating weight of the negative electrode film is 8.6 mg / cm 2 .

[0275] 2. Preparation of positive electrode sheet

[0276] The positive electrode active material NCM622 (LiNi 0.6 Co 0.2 Mn 0.2 O2), conductive agent (Super P), binder polyvinylidene fluoride (PVDF), etc. are mixed in a mass ratio of 96:2:2, solvent N-methylpyrrolidone (NMP) is added and fully stirred to obtain a positive electrode slurry; the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil to form a positive electrode film layer; after drying, cold pressing and other processes, the positive electrode sheet is obtained.

[0277] 3. Preparation of electrolyte

[0278] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1, and then fully dried lithium salt LiPF6 is dissolved in a mixed organic solvent at a ratio of 1 mol / L to prepare an electrolyte. Then, fluoroethylene carbonate (FEC) is added, and the content of FEC is 1 wt% of the total mass of the electrolyte.

[0279] 4. Isolation film

[0280] Use polypropylene film.

[0281] 5. Secondary battery preparation

[0282] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrode sheets to serve as an isolation, and then wound to obtain an electrode assembly; the electrode assembly is placed in an outer package, and the prepared electrolyte is injected into the dried electrode assembly. After vacuum packaging, standing, formation, shaping and other processes, a secondary battery is obtained.

[0283] Examples 2-3

[0284] The battery preparation methods of Examples 2 to 3 are similar to those of Example 1, except that different materials 1-2 and 1-3 are selected as the first negative electrode active material. See Table 3 for details.

[0285] Examples 4 to 6

[0286] The battery preparation methods of Examples 4 to 6 are similar to those of Example 1, except that different materials 2-2, 2-3, and 2-4 are selected as the second negative electrode active materials. See Table 3 for details.

[0287] Comparative Example 1

[0288] A secondary battery was assembled similarly to the preparation method of Example 1, except that: the first negative electrode active material was material 2-1; the second negative electrode active material was material 1-1. See Table 3 for details.

[0289] Comparative Example 2

[0290] The negative electrode active material (material 1-1 and material 2-1 were mixed in a mass ratio of 6:4), the conductive agent carbon black (Super P), the thickener sodium carboxymethyl cellulose and the binder styrene-butadiene rubber in a weight ratio of 96.4:1:1.2:1.4 in an appropriate amount of solvent deionized water to form a negative electrode slurry;

[0291] The negative electrode slurry is coated on the surface of the negative electrode current collector copper foil to form a negative electrode film layer, which is then dried, cold pressed, and other processes to obtain a negative electrode sheet. The compacted density of the negative electrode film layer is 1.6 g / cm 3The single-sided coating weight of the negative electrode film is 8.6 mg / cm 2 .

[0292] Comparative Example 3

[0293] A secondary battery was assembled similarly to the preparation method of Comparative Example 2, except that the negative electrode active material only included Material 1-1.

[0294] Comparative Example 4

[0295] A secondary battery was assembled similarly to the preparation method of Comparative Example 2, except that the negative electrode active material only included Material 2-1.

[0296]

Performance test method

[0297] All performance parameters involved in the examples and comparative examples were measured according to the following methods:

[0298] (1) Raman median number R of negative electrode active material in negative electrode film layer 50 .

[0299] The Raman spectrum of each carbon material can be obtained by a laser microscope confocal Raman spectrometer, and the laser wavelength can be 532nm. During the test, an appropriate amount of sample can be taken to perform a full-surface scan of its surface. The scanning area is 100μm×100μm, the step length is 2μm, and the total number of scanning points is 2500. Raman maps at different positions are obtained, and the corresponding Raman values ​​ID / IG are obtained. The testing instrument can be a high-precision Renishaw laser microscope confocal Raman spectrometer. The Raman values ​​ID / IG obtained from the 2500 scanned points are arranged in order from small to large, and are marked as 1#, 2#, 3#, ..., 2500# respectively. When the number of scanning points is ranked 50% (corresponding to 1250#), the corresponding Raman value ID / IG is defined as R50, also known as the median of the Raman value ID / IG. In this application, the median of the Raman value ID / IG of the first negative electrode active material is recorded as R1 50 , the median of the Raman value ID / IG of the second negative electrode active material is recorded as R2 50 (2) Gram capacity of the material.

[0300] The negative electrode active material, conductive agent Super P, binder (PVDF) were mixed uniformly with solvent NMP (N-methylpyrrolidone) in a mass ratio of 91.6:1.8:6.6 to prepare a slurry. The prepared slurry was coated on a copper foil current collector to prepare a negative electrode film layer. After drying in an oven, it was cold pressed for use. The compaction density of the negative electrode film layer was 1.3 g / cm 3A lithium metal sheet was used as the counter electrode; a polyethylene (PE) film was used as the separator; ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1, and LiPF6 was uniformly dissolved in the above solution to obtain an electrolyte, wherein the concentration of LiPF6 was 1 mol / L; and the above components were assembled into a CR2430 button cell in an argon-protected glove box. The resulting button cell was allowed to stand for 12 hours, then discharged at a constant current of 0.05C to 0.005V, allowed to stand for 10 minutes, and then discharged at a constant current of 50μA to 0.005V. The battery was allowed to stand for 10 minutes, and then discharged at a constant current of 10μA to 0.005V. The total of the three discharge capacities was the gram capacity of the material.

[0301] (3) Powder compaction density test

[0302] The compacted density of the powder of the negative electrode active material is well known in the art and can be measured using methods known in the art. For example, referring to GB / T 24533-2009, an electronic pressure testing machine (such as UTM7305) can be used for testing: a certain amount M of the powder sample to be tested is placed on a special compaction mold (bottom area S), and different pressures are set (49000N can be used in this application). The pressure is maintained for 30 seconds, the pressure is released, and the device is left for 10 seconds. The thickness H of the powder after compaction under the pressure is read on the device, and the compacted density under the pressure can be calculated. The compacted density of the negative electrode active material under the pressure = M / (H * S).

[0303] (4) Thickness H of the single-sided negative electrode film layer. The thickness H of the single-sided negative electrode film layer can be measured using a micrometer. The thickness of the negative electrode film layer described in this application refers to the thickness of the negative electrode film layer after cold pressing and used for battery assembly.

[0304] (5) Orientation degree OI of negative electrode active material.

[0305] According to the general rules of X-ray diffraction analysis and the method for determining the lattice parameters of graphite JIS K 0131-1996 and JB / T4220-2011, the X-ray diffraction spectrum is obtained using an X'pert PRO. The orientation index of the negative electrode material can be calculated according to OI=C004 / C110, where C004 is the peak area of ​​the 004 characteristic diffraction peak and C110 is the peak area of ​​the 110 characteristic diffraction peak.

[0306] (6) Battery mass energy density

[0307] At 25°C, the battery cell was charged at a constant current of 0.33C to 4.4V, and then charged at a constant voltage to a current of 0.05C. After standing for 5 minutes, the battery cell was discharged at a constant current of 0.33C to 2.8V, and the discharge capacity D0 was obtained.

[0308] Mass energy density = D0 / mass of secondary battery; (mass energy density unit: Wh / kg)

[0309] Where D0 is the measured discharge capacity of the battery cell

[0310] (7) Battery rate performance test.

[0311] At 25°C, the secondary battery was charged to 4.4V at a constant current of 0.33C, then charged to a current of 0.05C at a constant voltage. After standing for 5 minutes, the secondary battery was discharged to 2.8V at a constant current of 0.33C, and its actual capacity was recorded as C0.

[0312] Then the secondary battery is charged with a constant current of 0.5C0, 1.3C0, 2.0C0, 2.8C0, 3.5C0, 4.5C0, and 6.0C0 in sequence to a negative electrode cutoff potential of 4.4V or 0V (whichever is reached first). After each charge, it is discharged to 2.8V with a constant current of 1C0. The SOC (State of Charge) of the battery is recorded at different charge rates. The charge rate-negative electrode potential curve under different SOC states was drawn, and the charge rate corresponding to the negative electrode potential of 0 V under different SOC states was obtained after linear fitting. The charge rate is the charging window under the SOC state, which is recorded as C10% SOC, C20% SOC, C30% SOC, C40% SOC, C50% SOC, C60% SOC, C70% SOC, and C80% SOC, respectively. The charging time T of the secondary battery from 10% SOC to 80% SOC (assuming that the secondary battery does not undergo lithium deposition) is calculated according to the formula (60 / C20% SOC + 60 / C30% SOC + 60 / C40% SOC + 60 / C50% SOC + 60 / C60% SOC + 60 / C70% SOC + 60 / C80% SOC) × 10%, and the unit is min. The shorter the charging time, the better the fast charging performance of the secondary battery.

[0313] The performance parameters of each embodiment and comparative example are shown in Table 3.

[0314] Table 3

[0315] From the above table data we can see that:

[0316] Examples 1-6 meet the design of this application, and the battery can simultaneously achieve good fast charging performance and high energy density.

[0317] According to Comparative Example 1, its R1 50 Greater than R2 50, which is not within the scope of this application and the fast charging performance is affected.

[0318] According to Comparative Example 2, its negative electrode active material is a physical mixture of material 1-1 and material 2-1, and the Raman median values ​​of the negative electrode active materials in the lower region and the upper region tend to be consistent, which does not conform to the design of this application and the fast charging performance is also affected.

[0319] According to Comparative Examples 3 and 4, when the negative electrode active material only includes Material 1-1 or Material 2-1, the battery cannot achieve both good fast charging performance and high energy density.

[0320] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

Claims

1. A secondary battery, characterized in that, It includes a negative electrode plate, and the negative electrode plate 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 includes a lower region and an upper region, the lower region includes a first negative electrode active material, and the upper region includes a second negative electrode active material; the median value of the Raman value ID / IG of the first negative electrode active material is denoted as R1 50 , and the median value of the Raman value ID / IG of the second negative electrode active material is denoted as R2 50 ; the R1 50 is less than the R2 50 ; the graphitization degree of the first negative electrode active material is greater than that of the second negative electrode active material.

2. The secondary battery according to claim 1, wherein The R1 50 is 0.05 to 0.15; and / or, The R2 50 is 0.20 to 0.

40.

3. The secondary battery according to claim 1 or 2, wherein The R1 50 is 0.05 to 0.1; and / or, The said R2 50 is 0.25 to 0.

35.

4. The secondary battery according to any one of claims 1-3, wherein the graphitization degree of the first negative electrode active material is ≥92%, and / or the graphitization degree of the second negative electrode active material is ≥91%.

5. The secondary battery according to any one of claims 1-4, wherein the graphitization degree of the first negative electrode active material is 93%-95%; and / or the graphitization degree of the second negative electrode active material is 92%-94%.

6. The secondary battery according to any one of claims 1-5, wherein the powder compaction density of the first negative electrode active material is greater than that of the second negative electrode active material.

7. The secondary battery according to any one of claims 1-6, wherein The powder tap density of the first negative electrode active material tested under a pressure of 49000 N is ≥ 1.95 g / cm 3 ; and / or, The powder compaction density of the second negative electrode active material tested under a pressure of 49000 N is 1.81 g / cm 3 ~1.87 g / cm 3 .

8. The secondary battery according to any one of claims 1-7, wherein The powder tap density of the first negative electrode active material tested under a pressure of 49,000 N is 1.96 g / cm 3 ~1.99 g / cm 3 ; and / or, The powder tap density of the second negative electrode active material tested under a pressure of 49000 N is 1.82 g / cm 3 ~1.86 g / cm 3 .

9. The secondary battery according to any one of claims 1-8, wherein the OI of the powder of the first negative electrode active material is greater than the OI of the powder of the second negative electrode active material.

10. The secondary battery according to any one of claims 1-9, wherein the OI of the powder of the first negative electrode active material is 2.0-10.0; and / or the OI of the powder of the second negative electrode active material is 1.0-8.

0.

11. The secondary battery according to any one of claims 1-10, wherein the OI of the powder of the first negative electrode active material is 4.0-8.0; and / or the OI of the powder of the second negative electrode active material is 2.5-5.

5.

12. The secondary battery according to any one of claims 1-11, wherein the tapped density of the first negative electrode active material is less than that of the second negative electrode active material.

13. The secondary battery according to any one of claims 1-12, wherein The tap density of the first negative electrode active material ≥ 0.8 g / cm 3 ; and / or, The specific surface area of the second negative electrode active material is 3.0 m 2 / g to 4.3 m 2 / g.

14. The secondary battery according to any one of claims 1-13, wherein The tap density of the first negative electrode active material is 0.85 g / cm 3 - 1.15 g / cm 3 ; and / or, The specific surface area of the second negative electrode active material is 3.2 m 2 / g to 4.1 m 2 / g.

15. The secondary battery according to any one of claims 1-14, wherein the volume distribution particle size Dv1 of the first negative electrode active material is less than the volume distribution particle size Dv1 of the second negative electrode active material.

16. The secondary battery according to any one of claims 1-15, wherein the volume distribution particle size Dv1 of the first negative electrode active material is 1.0 μm to 8.0 μm; and / or the volume distribution particle size Dv1 of the second negative electrode active material is 3.5 μm to 10.0 μm.

17. The secondary battery according to any one of claims 1-16, wherein the volume distribution particle size Dv1 of the first negative electrode active material is 3.0 μm to 5.0 μm; and / or the volume distribution particle size Dv1 of the second negative electrode active material is 5.5 μm to 8.0 μm.

18. The secondary battery according to any one of claims 1-17, wherein The volume-based median particle size Dv50 of the first negative electrode active material is greater than the volume-based median particle size Dv50 of the second negative electrode active material.

19. The secondary battery according to any one of claims 1-18, characterized in that the volume-based median particle size Dv50 of the first negative electrode active material is 10 μm to 20 μm, and / or the volume-based median particle size Dv50 of the second negative electrode active material is 10 μm to 20 μm.

20. The secondary battery according to any one of claims 1-19, characterized in that the volume-based median particle size Dv50 of the first negative electrode active material is 14 μm to 16.5 μm; and / or the volume-based median particle size Dv50 of the second negative electrode active material is 13 μm to 15.5 μm.

21. The secondary battery according to any one of claims 1-20, characterized in that The particle size distribution (D V 90 - D V 10) / D V 50 of the first negative electrode active material is greater than the particle size distribution (D V 90 - D V 10) / D V 50.

22. The secondary battery according to any one of claims 1-21, characterized in that The particle size distribution (D V 90 - D V 10) / D V 50 is ≤ 2.0; and / or, The particle size distribution (D V 90 - D V 10) / D V 50 is ≤ 1.

8.

23. The secondary battery according to any one of claims 1-22, characterized in that The particle size distribution (D V 90 - D V 10) / D V 50 is 1.2 - 1.8; and / or, The particle size distribution (D V 90 - D V 10) / D V 50 is 1.0 - 1.

6.

24. The secondary battery according to any one of claims 1-23, characterized in that the specific surface area of the first negative electrode active material is smaller than the specific surface area of the second negative electrode active material.

25. The secondary battery according to any one of claims 1-24, characterized in that The specific surface area of the first negative electrode active material is 0.5 m 2 / g to 3.0 m 2 / g; and / or, The specific surface area of the second negative electrode active material is 2.5 m 2 / g to 4.4 m 2 / g.

26. The secondary battery according to any one of claims 1-25, characterized in that The specific surface area of the first negative electrode active material is 1.0 m 2 / g to 2.5 m 2 / g; and / or, The specific surface area of the second negative electrode active material is 3.0 m 2 / g to 4.0 m 2 / g.

27. The secondary battery according to any one of claims 1-26, characterized in that the first negative electrode active material satisfies at least one of the following characteristics; (1) The D of the first negative electrode active material V 10 is 5 μm to 9 μm; (2) The D of the first negative electrode active material V 90 ≤ 30 μm; (3) The D of the first negative electrode active material V 99 ≤ 40 μm; (4) The specific capacity of the first negative electrode active material is 355 mAh / g to 365 mAh / g.

28. The secondary battery according to any one of claims 1-27, characterized in that the first negative electrode active material satisfies at least one of the following characteristics; (1) The D of the first negative electrode active material V 10 is 5.8 μm to 7.8 μm; (2) The D of the first negative electrode active material V 90 is 20 μm to 30 μm; (3) The D of the first negative electrode active material V 99 is 30 μm to 40 μm; (4) The specific capacity of the first negative electrode active material is 357 mAh / g to 363 mAh / g.

29. The secondary battery according to any one of claims 1-28, characterized in that the second negative electrode active material satisfies at least one of the following characteristics; (1) The D of the second negative electrode active material V is 6 μm to 10.0 μm; (2) The D of the second negative electrode active material V 90 ≤ 30 μm; (3) The D of the second negative electrode active material V 99 ≤ 40 μm; (4) The specific capacity of the second negative electrode active material is 352 mAh / g to 362 mAh / g; (5) At least a part of the surface of the second negative electrode active material has a carbon coating layer.

30. The secondary battery according to any one of claims 1-29, characterized in that the second negative electrode active material satisfies at least one of the following characteristics; (1) The D of the second negative electrode active material V 10 is 7.5 μm to 9.0 μm; (2) The D of the second negative electrode active material V 90 is 20 μm to 30 μm; (3) The D of the second negative electrode active material V 99 is 30 μm to 40 μm; (4) The specific capacity of the second negative electrode active material is 354 mAh / g to 360 mAh / g; (5) At least a part of the surface of the second negative electrode active material has a carbon coating layer.

31. The secondary battery according to any one of claims 1 to 30, characterized in that, The first negative electrode active material and / or the second negative electrode active material are both artificial graphite.

32. The secondary battery according to any one of claims 1 to 31, characterized in that, The compaction density of the negative electrode film layer is greater than or equal to 1.25 g / cm 3 ; and / or, The coating weight per unit area of the negative electrode film layer is greater than or equal to 0.075 mg / mm 2 .

33. The secondary battery according to any one of claims 1 to 32, characterized in that, The compaction density of the negative electrode film layer is 1.28 g / cm 3 -1.65 g / cm 3 ; and / or, The coating weight per unit area of the negative electrode film layer is 0.08 mg / mm 2 - 0.11 mg / mm 2 .

34. An electrical device, characterized in that, The electrical device includes the secondary battery according to any one of claims 1-33.

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