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 located on at least one surface of the negative electrode current collector, wherein the negative electrode film layer has a first surface away from the negative electrode current collector and a second surface arranged opposite the first surface; the thickness of the negative electrode film layer is denoted as H; a region within a thickness range from the first surface of the negative electrode film layer to 0.3H is denoted as a first region, which comprises a first negative electrode active material; the first negative electrode active material comprises a first carbon-based material; and the first carbon-based material satisfies the condition that the total pore area S1 of an external region is less than the total pore area S2 of an internal region. The secondary battery has improved dynamic performance, and the volume distribution particle size Dv50 of the first carbon-based material is less than or equal to 15 μm.

Description

Secondary battery and power-consuming device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This disclosure is based on the Chinese patent application with application number 202311643955.4, application date November 30, 2023, and invention name “A secondary battery and electrical device”, and claims the priority of the Chinese patent application. The entire content of the Chinese patent application is hereby introduced into the present disclosure as a reference. Technical Field

[0003] The present disclosure relates to the field of battery technology, and in particular to a secondary battery and an electrical device. Background Art

[0004] In recent years, secondary batteries have been widely used in energy storage systems such as hydropower, thermal, wind, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, and aerospace applications. With this increasing range of applications, the performance of these batteries is facing significant challenges. For example, in electric devices, the rapid charge and discharge performance of secondary batteries is becoming increasingly important. Therefore, secondary batteries are required to exhibit superior dynamic performance.

[0005] Summary of the Invention

[0006] The present disclosure is made in view of the above-mentioned problems, and its purpose is to provide a secondary battery and an electric device, wherein the secondary battery has improved dynamic performance.

[0007] To achieve the above objectives, the first aspect of the present disclosure provides a secondary battery. The secondary battery includes a negative electrode plate, the negative electrode plate including a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector, the negative electrode film layer having a first surface remote from the negative electrode current collector and a second surface opposite to the first surface, the thickness of the negative electrode film layer being denoted as H;

[0008] Among them, the area within the thickness range from the first surface of the negative electrode film layer to 0.3H is recorded as the first area of ​​the negative electrode film layer, the first area includes a first negative electrode active material, the first negative electrode active material includes a first carbon-based material, the volume distribution particle size Dv50 of the first carbon-based material is recorded as D, the first carbon-based material includes an external area and an internal area located inside the external area, the external area refers to the area extending from the particle surface of the first carbon-based material to the interior of the particle by a distance of 0.25D, in the cross-sectional view of the first carbon-based material, the total pore area of ​​the external area is recorded as S1, and the total pore area of ​​the internal area is recorded as S2, then the first carbon-based material satisfies S2>S1, and the volume distribution particle size Dv50 of the first carbon-based material is less than or equal to 15μm.

[0009] In the present disclosure, when the first carbon-based material defined above is arranged at least on the side of the negative electrode film layer of the negative electrode sheet away from the negative electrode current collector, the kinetic characteristics of the first carbon-based material can be exerted, thereby improving the kinetic performance of the secondary battery.

[0010] According to some embodiments, the volume distribution particle size Dv50 of the first carbon-based material is 7 μm-13 μm. When the volume distribution particle size Dv50 of the first carbon-based material is within the above range, it is further beneficial to improve the dynamic performance of the secondary battery.

[0011] According to some embodiments, the first carbon-based material satisfies 1.5≤S2 / S1≤500, optionally, 2.5≤S2 / S1≤450.

[0012] According to some embodiments, the area of ​​the pore structure in the outer region of the first carbon-based material is less than or equal to 0.15 μm 2 , can be selected to be less than or equal to 0.13μm 2 ; and / or, the internal region of the first carbon-based material includes one or more pores with an area greater than or equal to 0.15 μm 2 The pore structure may include one or more pores with an area of ​​0.15-2.00 μm 2 The pore structure of the outer region of the particles of the first carbon-based material having the above structure is denser than that of the inner region. In this way, on the one hand, the compaction density of the negative electrode film layer can be improved, thereby improving the energy density of the secondary battery; on the other hand, sufficient and stable expansion space can be reserved for the volume change of the first carbon-based material particles, reducing the risk of breakage of the first carbon-based material particles, reducing the entry of electrolyte into the particles, thereby reducing the occurrence of side reactions and the consumption of active ions, thereby further improving the storage performance of the secondary battery, and on the other hand, it can also improve the compaction density of the negative electrode film layer.

[0013] According to some embodiments, at least a portion of the surface of the first carbon-based material has a carbon coating. When at least a portion of the surface of the first carbon-based material has a carbon coating, the dynamic performance of the secondary battery can be effectively improved. According to some embodiments, the entire surface of the first carbon-based material has a carbon coating.

[0014] According to some embodiments, the first carbon-based material includes primary particles. Optionally, the primary particles account for ≥80% of the first carbon-based material. When the first carbon-based material is primarily in the form of primary particles, it is beneficial to the dynamic performance of the secondary battery.

[0015] According to some embodiments, the area from the second surface of the negative electrode film layer to a thickness of 0.3H is recorded as the second area of ​​the negative electrode film layer, the second area is arranged between the negative electrode current collector and the first area, the second area includes a second negative electrode active material, and the second negative electrode active material includes a second carbon-based material. In the embodiment, the second area of ​​the negative electrode film layer is close to the negative electrode current collector. The arrangement of a second carbon-based material different from the first carbon-based material in this area will not significantly affect the dynamic performance of the secondary battery, and can also improve other secondary performance, such as energy density, by leveraging the characteristics of the second carbon-based material.

[0016] Optionally, the second carbon-based material includes artificial graphite. When artificial graphite is arranged in at least the second region, it does not significantly affect the dynamic performance of the secondary battery. At the same time, due to its good powder compaction density, artificial graphite can improve the capacity density of the secondary battery. Furthermore, due to the cold-pressed deformation of artificial graphite, when arranged in the lower layer of the negative electrode film layer, it can effectively reduce the rolling pressure of the electrode sheet and reduce damage to the carbon-based material, thereby improving the cycle life of the secondary battery.

[0017] According to some embodiments, the volume distribution particle size Dv50 of the first carbon-based material is smaller than the volume distribution particle size Dv50 of the second carbon-based material. Optionally, the volume distribution particle size Dv50 of the second carbon-based material is 13 μm-19 μm, and further optionally 14 μm-18 μm. When the second carbon-based material has a larger particle size than the first carbon-based material, it can increase the powder compaction density, thereby increasing the compaction density difference between the upper and lower layers of the negative electrode membrane, and improving the dynamic performance of the secondary battery.

[0018] According to some embodiments, the second carbon-based material has a powder compaction density of 1.80 g / cm3 under a pressure of 50,000 N. 3 -2.05g / cm 3 , optional 1.85g / cm 3 -2.03g / cm 3The powder compaction density of the second carbon-based material is within the above range, which is beneficial to improving the energy density of the secondary battery.

[0019] According to some embodiments, the surface of the second carbon-based material does not have a coating layer. The second carbon-based material is disposed in the second region of the negative electrode film layer near the negative electrode current collector. If a coating layer is disposed on the surface of the second carbon-based material, the powder compaction density will be affected. Therefore, not having the coating layer is more beneficial to the energy density of the secondary battery.

[0020] According to some embodiments, the second carbon-based material includes artificial graphite in the form of secondary particles. Optionally, the amount of artificial graphite in the second carbon-based material is greater than or equal to 80%. When the second carbon-based material includes secondary particles, compared to using it only in the form of primary particles, it can improve the isotropy of the negative electrode sheet, thereby further benefiting the dynamic performance of the secondary battery. In particular, when the second carbon-based material is mainly in the form of secondary particles, it can improve the dynamic performance of the secondary battery.

[0021] According to some embodiments, the particle size distribution of the second carbon-based material satisfies (Dv90-Dv10) / Dv50≤1.25, which can be 0.90-1.25. When the particle size distribution of the second carbon-based material is narrow, it is beneficial to improve the energy density of the secondary battery while taking into account the dynamic performance.

[0022] According to some embodiments, the gram capacity of the first carbon-based material is greater than the gram capacity of the second carbon-based material. Optionally, the gram capacity of the first carbon-based material is ≥355mAh / g, optionally 355mAh / g-368mAh / g. Optionally, the gram capacity of the second carbon-based material is 350mAh / g-365mAh / g, optionally 352mAh / g-362mAh / g. The higher gram capacity of the first carbon-based material and the second carbon-based material can jointly improve the energy density of the secondary battery.

[0023] According to some embodiments, the first carbon-based material has a degree of graphitization of ≥95.0%, optionally ranging from 95.5% to 98.0%; and / or the second carbon-based material has a degree of graphitization of 90.0% to 95.5%, optionally ranging from 92.0% to 95.5%. The higher degree of graphitization of both materials is beneficial for improving the energy density of the secondary battery.

[0024] According to some embodiments, the specific surface area of ​​the first carbon-based material is 1.0 m 2 / g-2.8m 2 / g, optional 1.3m 2 / g-2.1m 2 / g; and / or, the specific surface area of ​​the second carbon-based material is 0.8m 2 / g-2.0m2 / g, optional 1.1m 2 / g-1.7m 2 A specific surface area within a suitable range is beneficial to the kinetic performance of the secondary battery.

[0025] According to some embodiments, the first carbon-based material satisfies at least one of the following:

[0026] (1) The first carbon-based material satisfies the following conditions: (Dv90-Dv10) / Dv50≤1.40, which may be 0.90-1.40;

[0027] (2) The powder compaction density of the first carbon-based material under a pressure of 50,000 N is 1.75 g / cm 3 -2.00g / cm 3 , optional 1.80g / cm 3 -1.98g / cm 3 ;

[0028] (3) The tap density of the first carbon-based material is 0.90-1.30 g / cm 3 , optionally 0.95-1.25 g / cm 3 ;

[0029] (4) The volume distribution particle size Dv90 of the first carbon-based material is 13 μm-30 μm, optionally 16 μm-23 μm.

[0030] According to some embodiments, the second carbon-based material satisfies at least one of the following:

[0031] (1) The tap density of the second carbon-based material is 0.85-1.25 g / cm 3 , optional 0.90-1.15g / cm 3 ;

[0032] (2) The second carbon-based material satisfies 0.050≤I D / I G ≤0.300, optionally, 0.070≤I D / I G ≤0.200, I D Indicates that the Raman spectrum is at 1350±50cm -1 The D peak intensity at I G Indicates that the Raman spectrum is at 1580±50cm -1 The G peak intensity at .

[0033] According to some embodiments, the first negative electrode active material and / or the second negative electrode active material further include a silicon-based material; optionally, the mass proportion of the first negative electrode active material is less than or equal to 10%, optionally 5%-10%, and / or the mass proportion of the second negative electrode active material is less than or equal to 10%, optionally 5%-10%.

[0034] According to some embodiments, the negative electrode film layer satisfies at least one of the following:

[0035] (1) The compaction density of the negative electrode film layer is ≤1.85g / cm 3 , optionally 1.45-1.75 g / cm 3 ;

[0036] (2) The porosity of the negative electrode film layer is 18.0%-38.0%, optionally 19.0%-34.0%;

[0037] (3) The OI value of the negative electrode film layer is ≤30.0, optionally 8.0-23.0;

[0038] (4) The thickness of the negative electrode film layer is ≥40 μm, and can be optionally 40 μm-140 μm.

[0039] A second aspect of the present disclosure provides an electrical device. The electrical device includes any one of the secondary batteries described in the above embodiments. When the electrical device includes the secondary battery with improved dynamic performance, it can be charged at a faster speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] FIG1 is a schematic diagram of an embodiment of a negative electrode sheet of the present disclosure.

[0041] FIG2 is a schematic diagram of a cross-sectional image of a particle of the first carbon-based material of the present disclosure.

[0042] FIG3 is an ion polished cross-sectional (CP) view of one embodiment of the first carbon-based material disclosed herein.

[0043] FIG4 is a schematic diagram of an embodiment of a negative electrode plate of the present disclosure.

[0044] FIG5 is a schematic diagram of another embodiment of the negative electrode sheet disclosed herein.

[0045] FIG6 is a schematic diagram of another embodiment of the negative electrode sheet disclosed herein.

[0046] FIG. 7 is a schematic diagram of a battery cell according to an embodiment of the present disclosure.

[0047] FIG. 8 is an exploded view of the battery cell according to the embodiment of the present disclosure shown in FIG. 7 .

[0048] FIG. 9 is a schematic diagram of a battery module according to an embodiment of the present disclosure.

[0049] FIG. 10 is a schematic diagram of a battery pack according to an embodiment of the present disclosure.

[0050] FIG. 11 is an exploded view of the battery pack shown in FIG. 10 according to one embodiment of the present disclosure.

[0051] FIG. 12 is a schematic diagram of an electric device using a secondary battery according to an embodiment of the present disclosure as a power source.

[0052] Explanation of the accompanying drawings: 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 first surface; 102b second surface; 1021 first region; 1022 second region; 1023 middle region; 200 first carbon-based material; 201 external region; 202 internal region. DETAILED DESCRIPTION

[0053] Below, the embodiments of the secondary battery and the electrical device disclosed in the present invention 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 may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures 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 disclosure and are not intended to limit the subject matter described in the claims.

[0054] " scope " disclosed in the present disclosure 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 selected lower limit and upper limit define the boundary of special scope.The scope that this mode limits can be to include end value or not include end value, and can be combined arbitrarily, and promptly any lower limit can form a scope with any upper limit combination.For example, if the scope of 60-120 and 80-110 is listed for specific parameter, 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 listed, and if the maximum range value 3,4 and 5 listed, then the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5.In the present disclosure, unless otherwise specified, numerical range " ab " represents the abbreviation of any real number combination between a and b, and 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.

[0055] Unless otherwise specified, all embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions.

[0056] Unless otherwise specified, all technical features and optional technical features disclosed herein can be combined with each other to form a new technical solution.

[0057] Unless otherwise specified, all steps of the present disclosure 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.

[0058] Unless otherwise specified, the terms used in the present disclosure have the common meanings that are generally understood by those skilled in the art.

[0059] Unless otherwise specified, the numerical values ​​of the parameters mentioned in the present disclosure can be measured using various test methods commonly used in the art, for example, they can be measured according to the test methods given in the present disclosure.

[0060] Unless otherwise specified, in the present disclosure, the term "active ions" refers to ions that can be intercalated and extracted back and forth between the positive electrode and the negative electrode of a secondary battery, including but not limited to lithium ions.

[0061] In the embodiments of the present disclosure, the battery may be a battery cell (sometimes also referred to as a battery cell), or a battery module or battery pack comprising a plurality of battery cells. A battery cell refers to a basic unit that can realize the mutual conversion of chemical energy and electrical energy, and can be used to make a battery module or battery pack, thereby being used to supply power to electrical devices. A battery cell may be a secondary battery, which refers to a battery cell that can be activated by charging the active material after the battery cell is discharged and can continue to be used. The battery cell may be a lithium-ion battery, a sodium-ion battery, a sodium-lithium-ion battery, a lithium metal battery, a sodium metal battery, a lithium-sulfur battery, a magnesium-ion battery, a nickel-hydrogen battery, a nickel-cadmium battery, a lead-acid battery, etc., and the embodiments of the present disclosure are not limited thereto.

[0062] With the widespread use of secondary batteries, higher requirements have been placed on their charging speed, or kinetic performance. However, the key to improving the kinetic performance of secondary batteries, especially their fast charging performance, lies in improving the kinetic performance of the negative electrode by reducing the surface density or compaction density of the negative electrode film. However, numerous studies have shown that these methods of improving the kinetics of the negative electrode only improve the battery's kinetic performance to a certain extent, while significantly reducing the energy density of the secondary battery.

[0063] Therefore, it is currently difficult for secondary batteries to achieve both high energy density and improved kinetic performance.

[0064] In view of this, a first aspect of the embodiments of the present disclosure provides a secondary battery. This secondary battery improves the dynamic performance of the secondary battery through the design of the negative electrode plate. According to further embodiments, the secondary battery also has a good energy density.

[0065] The term "secondary battery" mentioned herein refers to a battery cell, a battery module, or a battery pack.

[0066] 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.

[0067] [Negative electrode]

[0068] The secondary battery disclosed herein includes a negative electrode plate, the negative electrode plate including a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector, the negative electrode film layer having a first surface away from the negative electrode current collector and a second surface opposite to the first surface, the thickness of the negative electrode film layer being denoted as H; wherein, the region within a thickness range of 0.3H from the first surface of the negative electrode film layer is denoted as the first region of the negative electrode film layer, the first region including a first negative electrode active material, the first negative electrode active material including a first carbon-based material, the volume distribution particle size Dv50 of the first carbon-based material being denoted as D, the first carbon-based material including an outer region and an inner region located inside the outer region, the outer region being a region extending a distance of 0.25D from the particle surface of the first carbon-based material to the interior of the particle, in a cross-sectional view of the first carbon-based material, the total pore area of ​​the outer region being denoted as S1, and the total pore area of ​​the inner region being denoted as S2, the first carbon-based material satisfies S2>S1, and the volume distribution particle size Dv50 of the first carbon-based material is less than or equal to 15 μm.

[0069] Refer to Figure 1, which shows a schematic diagram of an embodiment of the negative electrode plate of the present disclosure. As shown in Figure 1, in the embodiment, the negative electrode plate 10 includes a negative electrode current collector 101 and a negative electrode film layer 102 formed on at least one surface of the negative electrode current collector 101. The negative electrode film layer 102 has a first surface 102a away from the negative electrode current collector 101 and a second surface 102b arranged opposite to the first surface 102a. The thickness of the negative electrode film layer 102 is recorded as H. The area within the thickness range from the second surface 102b of the negative electrode film layer to 0.3H is recorded as the first area 1021 of the negative electrode film layer. The area of ​​the negative electrode film layer within the thickness range of 0.7H outside the first area 1021 is recorded as the remaining area 1020. The thickness H of the negative electrode film layer refers to the thickness of the negative electrode film layer located on a single side of the negative electrode current collector.

[0070] It should be understood that in the embodiment shown in the figure, the second 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 disclosure is not limited to this. 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 second surface 102b does not directly contact the negative electrode current collector 101.

[0071] In the embodiment, the first carbon-based material is disposed in the first region 1021 of the negative electrode film layer. According to some embodiments, at least one negative electrode active material different from the first carbon-based material is disposed in at least a portion of the remaining region 1020. Exemplarily, an additional negative electrode active material (e.g., an additional carbon-based material) is disposed in at least a portion of the remaining region 1020. Exemplarily, the first carbon-based material is also present in at least a portion of the remaining region 1020 adjacent to the first region 1021, for example, the first carbon-based material is present in the region adjacent to the first region 1021.

[0072] In the present disclosure, the total pore area S1 of the outer region of the first carbon-based material is smaller than the total pore area S2 of the inner region. This means that the structure of the outer region of the first carbon-based material is denser than that of the inner region. In addition, the first carbon-based material in the present disclosure satisfies "S2>S1", which means that the first carbon-based material has a pore structure that can be directly observed from a cross-sectional image (e.g., a scanning electron microscope image with a magnification of 1000 times). That is, the outer region has a smaller pore area in the main structure of the first carbon-based material.

[0073] Referring to Figure 2 , a schematic diagram of a cross-sectional image of a particle of the first carbon-based material 200 of the present disclosure is shown, and the cross-sectional image passes through the center of the particle of the first carbon-based material 200. As shown in Figure 2 , D represents the volume distribution particle size Dv50 of the particle of the first carbon-based material 200, and the region extending from the particle surface of the first carbon-based material 200 to the interior of the particle by a distance of 0.25D is denoted as the outer region 201, and the region inside the outer region 201 is denoted as the inner region 202.

[0074] The pore structure in the first carbon-based material can be observed by a cross-sectional polisher, for example, by performing an ion polishing cross-sectional morphology (CP) test on the negative electrode sheet. Specifically, the negative electrode sheet is cut into a sample to be tested of a certain size (e.g., 2 cm×2 cm), and the negative electrode sheet is fixed on a sample stage using paraffin wax; the sample stage is placed in a sample holder and locked and fixed, the argon ion cross-sectional polisher (e.g., IB-09010CP argon ion cross-sectional polisher from JEOL, Japan) is powered on and vacuumed (e.g., 10-4 Pa), the argon flow rate (e.g., 0.15 MPa) and voltage (e.g., 8 KV) and polishing time (e.g., 2 h) are set, and the sample stage is adjusted to a rocking mode to start polishing; a certain area in the first area 1021 is randomly selected from the sample to be tested for scanning testing (e.g., referring to JY / T010-1996, scanning is performed using a scanning electron microscope), and an ion polishing cross-sectional morphology (CP) image of the negative electrode sheet is obtained at a certain magnification (e.g., 1000 times). This method can also be used to observe the internal structure of other negative electrode active materials (e.g., additional carbon-based materials) in other regions 1020, thereby distinguishing the first carbon-based material from the other negative electrode active materials. Figure 3 is an ion polishing cross-sectional (CP) image of one embodiment of the first carbon-based material disclosed herein. As can be seen from the image, the outer region of the second carbon-based material particles is denser than the inner region, satisfying S2>S1.

[0075] The pole piece design disclosed in the present invention adopts a first carbon material with a specific structure in the upper layer. The carbon material particles have a pore structure, and the pore area of ​​the inner region is larger than the pore area of ​​the outer region, so it has better storage performance; the smaller pore area of ​​the outer region reflects from the side that the density near the surface of the material is higher, which effectively reduces the side reactions on the surface of the particles. At the same time, the pore structure with a larger area inside reserves a certain space, which can effectively alleviate the stress caused by the expansion of the material during the battery cycle, thereby making the battery have better cycle performance. In addition, when the material has a smaller particle size and is arranged in the first region of the negative electrode film layer, the dynamic performance of the battery can be improved. Therefore, the secondary battery provided by the present invention has further improved dynamic performance on the premise of having better storage performance and cycle performance.

[0076] According to some embodiments, the volume distribution particle size Dv50 of the first carbon-based material is 7 μm-13 μm. Exemplarily, the volume distribution particle size Dv50 of the first carbon-based material is 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, etc. When the volume distribution particle size Dv50 of the first carbon-based material is within the above range, it is further beneficial to improve the dynamic performance of the secondary battery.

[0077] According to some embodiments, the first carbon-based material satisfies 1.5≤S2 / S1≤500, optionally, 2.5≤S2 / S1≤450. Exemplarily, the first carbon-based material satisfies 2.2≤S2 / S1≤400, 2.5≤S2 / S1≤300, 2.5≤S2 / S1≤250, 2.6≤S2 / S1≤200, 2.8≤S2 / S1≤150, or 3.0≤S2 / S1≤100. When S2 / S1 is within the above range, the storage performance and cycle performance of the battery can be further improved.

[0078] According to some embodiments, the area of ​​the pore structure in the outer region of the first carbon-based material is less than or equal to 0.15 μm 2 , can be selected to be less than or equal to 0.13μm 2 ; and / or, the internal region of the first carbon-based material includes one or more pores with an area greater than or equal to 0.15 μm 2 The pore structure may include one or more pores with an area of ​​0.15-2.0 μm 2 pore structure. The outer region of the first carbon-based material includes a pore structure of the above size, which reflects that the outer region of the particles of the material is relatively dense and the pores of the pore structure are small. The electrolyte of the first carbon-based material with this structure is not easy to enter the interior of the particles, thereby reducing side reactions with the electrolyte. In addition, when the first carbon-based material has a pore structure with a specific pore area, on the one hand, sufficient and stable expansion space can be reserved for the volume change of the first carbon-based material particles, and on the other hand, the compaction density of the negative electrode film layer can be improved, thereby improving the storage performance, cycle performance and energy density of the secondary battery.

[0079] According to some embodiments, at least a portion of the surface of the first carbon-based material has a carbon coating. When at least a portion of the surface of the first carbon-based material has a carbon coating, it is conducive to the rapid migration of active ions, thereby further improving the kinetic performance of the secondary battery. Typically, the carbon coating can be an amorphous carbon coating. According to a specific embodiment, the entire surface of the first carbon-based material has a carbon coating.

[0080] The terms "coating layer" or "carbon coating layer" as used herein have the same meaning as those in the art. They generally refer to a carbon coating formed by coating a negative electrode active material, such as natural graphite particles, with a carbon source material (e.g., asphalt), which is then heat-treated. The present disclosure does not specify the thickness of the carbon coating layer; conventional coating thicknesses may be used in the embodiments described.

[0081] According to some embodiments, the first carbon-based material includes primary particles. When the first carbon-based material exists mainly in the form of primary particles, it is conducive to the transmission of active ions, thereby improving the kinetic performance of the secondary battery. In some embodiments, the number of primary particles in the first carbon-based material accounts for ≥80%, optionally ≥85%, and further optionally ≥90%. In some specific embodiments, the first carbon-based material is entirely primary particles.

[0082] In some embodiments, the gram capacity of the first carbon-based material is ≥355 mAh / g, and can be optionally 355 mAh / g-368 mAh / g. Exemplarily, the gram capacity of the first carbon-based material is 355 mAh / g, 360 mAh / g, 363 mAh / g, 365 mAh / g, 367 mAh / g, or the like, or a value between any two values. A higher gram capacity is beneficial to the capacity density of the secondary battery.

[0083] In some embodiments, the degree of graphitization of the first carbon-based material is ≥95.0%, optionally ranging from 95.5% to 98.0%. Exemplarily, the degree of graphitization of the first carbon-based material is 95.0%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, or any value between two values. A higher degree of graphitization is beneficial to the compaction of the powder, thereby benefiting the energy density of the secondary battery.

[0084] In some embodiments, the specific surface area of ​​the first carbon-based material is 1.0 m 2 / g-2.8m 2 / g, optional 1.3m 2 / g-2.1m 2 / g. Exemplarily, the specific surface area of ​​the first carbon-based material is 1.1m 2 / g, 1.3m 2 / g, 1.5m 2 / g, 1.7m 2 / g, 1.9m 2 / g, 2.1m 2 / g, 2.4m 2 / g, etc., or a value between any two values. A larger specific surface area is further beneficial to improving the kinetic performance of the secondary battery.

[0085] According to some embodiments, when the first carbon-based material satisfies at least one of the following items, it is beneficial to at least one of the kinetic performance, energy density, and cycle performance of the secondary battery.

[0086] (1) The first carbon-based material satisfies: (Dv90-Dv10) / Dv50≤1.40, which can be selected as 0.90-1.40.

[0087] (2) The powder compaction density of the first carbon-based material under a pressure of 50,000 N is 1.75 g / cm 3 -2.0g / cm 3 , optional 1.82g / cm 3 -1.98g / cm 3 .

[0088] (3) The tap density of the first carbon-based material is 0.90-1.30 g / cm 3 , optionally 0.95-1.25 g / cm 3 .

[0089] (4) The volume distribution particle size Dv90 of the first carbon-based material is 13.0 μm-30.0 μm, optionally 16.0 μm-23.0 μm.

[0090] According to some embodiments, the area within the thickness range from the second surface of the negative electrode film layer to 0.3H is recorded as the second region of the negative electrode film layer, and the second region is arranged between the negative electrode collector and the first region. The second region includes a second negative electrode active material, and the second negative electrode active material includes a second carbon-based material.

[0091] In the embodiment, the second region of the negative electrode film layer is adjacent to the negative electrode current collector (also referred to as the lower layer of the negative electrode film layer when the negative electrode current collector serves as the base layer). Arranging a second carbon-based material different from the first carbon-based material in this region does not significantly affect the kinetic performance of the secondary battery, and can also improve other secondary battery properties, such as energy density, by leveraging the characteristics of the second carbon-based material.

[0092] In some specific embodiments, the second carbon-based material includes artificial graphite. Artificial graphite has inferior kinetic performance compared to other carbon-based materials, such as soft carbon, hard carbon, and natural graphite. When artificial graphite is placed in the second region, it does not significantly affect the kinetic performance of the secondary battery. At the same time, due to its good powder compaction density, artificial graphite can improve the energy density of the secondary battery.

[0093] In the embodiment, the aforementioned first carbon-based material is mainly arranged in the first area of ​​the negative electrode film layer, and the second carbon-based material including artificial graphite is mainly arranged in the second area of ​​the negative electrode film layer. The combination of the two can enable the secondary battery to improve the dynamic performance while taking into account the energy density and cycle performance.

[0094] More specifically, the first carbon-based material in the first region has good kinetic properties, which can improve the charging speed, especially the speed in the early stage of charging (such as the first 50% of the capacity after starting charging) can be significantly improved. In addition, because the two different carbon-based materials have different densities after cold pressing under the same pressure, different densities are formed in the upper and lower layers of the negative electrode film layer. The density of the upper layer, which is mainly the first carbon-based material, is smaller than the density of the lower layer, which is mainly artificial graphite. It can provide more migration channels for active ions, which is beneficial for the active ions to migrate to the lower layer of the negative electrode film layer and further contact with the second carbon-based material, thereby also helping to improve the speed in the later stage of charging (such as the last 50% of the capacity after starting charging).

[0095] Compared with the method of reducing the compaction density of the negative electrode film layer to improve the kinetic performance of the negative electrode, or increasing the compaction density of the negative electrode film layer to improve the energy density, the embodiment can improve the kinetic performance of the secondary battery while also taking into account the energy density.

[0096] In addition, the stable structure of artificial graphite is beneficial to the cycle life of secondary batteries.

[0097] Further referring to Figures 4 to 6 , schematic diagrams illustrating three different embodiments of a negative electrode sheet having a first region and a second region with different negative electrode active materials in these regions are shown. As shown in Figures 4 to 6 , similar to Figure 1 , 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 102a distal from the negative electrode current collector 101 and a second surface 102b opposite the first surface 102a. The thickness of the negative electrode film 102 is H. On the side distal from the negative electrode current collector 101, the region from the second surface 102b of the negative electrode film to a thickness of 0.3H is referred to as the first region 1021 of the negative electrode film. On the side proximal to the negative electrode current collector 101, the region from the first surface 102a of the negative electrode film to a thickness of 0.3H is referred to as the second region 1022 of the negative electrode film. The first region 1021 includes a first negative electrode active material, which includes the aforementioned first carbon-based material. The second region 1022 includes a second negative electrode active material, which includes a second carbon-based material different from the aforementioned first carbon-based material. The region between the first region 1021 and the second region 1022, occupying a thickness range of 0.4H, is denoted as the intermediate region 1023. It is easy to understand, according to Figures 4 to 7, that the intermediate region 1023 includes at least one of the first carbon-based material and the second carbon-based material.

[0098] Specifically, the figure shows that the second carbon-based material and the first carbon-based material are sequentially coated on the negative electrode current collector 101. Figure 4 shows that the thickness of the two materials each accounts for approximately half of the thickness of the negative electrode film layer 102. Figure 5 shows that the thickness of the second carbon-based material accounts for approximately 70% of the thickness of the negative electrode film layer 102, while the thickness of the first carbon-based material accounts for approximately 30% of the thickness of the negative electrode film layer 102. Figure 6 shows a configuration opposite to Figure 5, that is, the thickness of the first carbon-based material accounts for approximately 70% of the thickness of the negative electrode film layer 102, while the thickness of the second carbon-based material accounts for approximately 30% of the thickness of the negative electrode film layer 102.

[0099] It should be understood that the diagrams shown in Figures 4 to 6 are schematic diagrams of ideal situations. The present disclosure does not particularly limit the thickness ratio of the first carbon-based material to the second carbon-based material. For example, the thickness ratio of the first carbon-based material to the second carbon-based material can be in the range of 3:7-7:3. Exemplarily, the thickness ratio of the first carbon-based material to the second carbon-based material is 4:6, 5:5, 6:4, etc., or any ratio between the two ratios.

[0100] It should also be understood that while the middle region 1023 in Figures 4 to 6 shows a clear boundary between the other two regions, in reality, no such clear interface exists. As previously mentioned, the first carbon-based material and the second carbon-based material may coexist within the middle region 1023. Similarly, no clear interface exists between the coating layer containing the first carbon-based material and the coating layer containing the second carbon-based material.

[0101] According to some embodiments, the volume distribution particle size Dv50 of the first carbon-based material is smaller than the volume distribution particle size Dv50 of the second carbon-based material. Specifically, the volume distribution particle size Dv50 of the second carbon-based material is 13μm-19μm, and can be further optionally 14μm-18μm. The volume distribution particle size Dv50 of the second carbon-based material is 14μm, 15μm, 16μm, 17μm, 18μm, etc., or a value between any two values. When the second carbon-based material has a larger particle size than the first carbon-based material, its adverse effect on the kinetic performance of the secondary battery can be minimized.

[0102] According to some embodiments, the second carbon-based material, especially the artificial graphite, has a powder compaction density of 1.80 g / cm3 under a pressure of 50,000 N. 3 -2.05g / cm 3 , optional 1.85g / cm 3 -2.03g / cm 3 For example, the powder compaction density of the second carbon-based material under a pressure of 50,000 N is 1.80 g / cm 3 , 1.85g / cm 3 、1.90g / cm 3, 1.95g / cm 3 , 2.00g / cm 3 , 2.05g / cm 3 , or a value between any two values ​​of the composition range. The second carbon-based material with high powder compression density is beneficial to improving the energy density of the secondary battery when arranged in the lower layer of the negative electrode film layer.

[0103] According to some embodiments, the second carbon-based material includes artificial graphite in the form of secondary particles. Optionally, the amount of artificial graphite in the form of secondary particles in the second carbon-based material accounts for greater than or equal to 80%. When the second carbon-based material includes artificial graphite in the form of secondary particles, during cold pressing, the individual primary particles in the secondary particles are not easily changed in crystal orientation due to pressure. Therefore, compared to using it only in the form of primary particles, the use of secondary particles can effectively reduce the situation where the crystal orientation of artificial graphite in cold pressing tends to be parallel to the negative electrode current collector, thereby facilitating shortening the embedding and extraction of active particles, thereby further facilitating the kinetic performance of the secondary battery, in particular improving the charging speed in the latter stage of charging. In some specific embodiments, when the second carbon-based material is mainly in the form of secondary particles, or all in the form of secondary particles, the kinetic performance of the secondary battery can be improved.

[0104] According to some embodiments, the particle size distribution of the second carbon-based material satisfies (Dv90-Dv10) / Dv50≤1.25, which can be optionally 0.90-1.25. Exemplarily, the particle size distribution of the second carbon-based material satisfies (Dv90-Dv10) / Dv50, which is 0.9, 1, 1.1, 1.2, etc., or a value between the ranges consisting of any two values. When the particle size distribution of the second carbon-based material is narrower, the number of particles with larger particle size is reduced, which is more conducive to contact with active ions, thereby improving the energy density of the secondary battery while better taking into account the kinetic performance.

[0105] According to some embodiments, the gram capacity of the first carbon-based material is greater than the gram capacity of the second carbon-based material. In some embodiments, the gram capacity of the second carbon-based material is 350mAh / g-365mAh / g, optionally 352mAh / g-362mAh / g. Exemplarily, the gram capacity of the second carbon-based material is 352mAh / g, 355mAh / g, 358mAh / g, 360mAh / g, 362mAh / g, etc., or a value between the ranges consisting of any two numerical values. The higher gram capacity of the first carbon-based material and the second carbon-based material can jointly improve the energy density of the secondary battery.

[0106] According to some embodiments, the degree of graphitization of the first carbon-based material is greater than the degree of graphitization of the second carbon-based material. In some embodiments, the degree of graphitization of the second carbon-based material is 90.0%-95.5%, optionally 92%-95.5%. Exemplarily, the degree of graphitization of the second carbon-based material is 92%, 92.5%, 93%, 93.5%, 94%, 94.5%, 95%, 95.5%, etc., or a value between the ranges consisting of any two values. A higher degree of graphitization is beneficial to powder compaction, which is beneficial to the energy density of the secondary battery.

[0107] According to some embodiments, the specific surface area of ​​the first carbon-based material is greater than the specific surface area of ​​the second carbon-based material. In some embodiments, the specific surface area of ​​the second carbon-based material is 0.8 m 2 / g-2m 2 / g, optional 1.1m 2 / g-1.7m 2 / g. Exemplarily, the specific surface area of ​​the second carbon-based material is 1.0m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 / g, 1.6m 2 / g, 1.7m 2 Controlling the second carbon-based material to have a smaller specific surface area is beneficial to reducing side reactions and further improving the cycle performance of the secondary battery.

[0108] According to some embodiments, the second carbon-based material can further contribute to the energy density of the secondary battery when satisfying at least one of the following items.

[0109] (1) The tap density of the second carbon-based material is 0.85-1.25 g / cm 3 , optional 0.90-1.15g / cm 3 ;

[0110] (2) The second carbon-based material satisfies 0.050≤I D / I G ≤0.300, optionally, 0.070≤I D / I G ≤0.200, I D Indicates that the Raman spectrum is at 1350±50cm -1 The D peak intensity at I G Indicates that the Raman spectrum is at 1580±50cm -1The G peak intensity at .

[0111] According to some embodiments, the negative electrode film layer also includes a silicon-based material. Optionally, the mass proportion of the silicon-based material in the negative electrode film layer is less than or equal to 10%, and can be optionally 5%-10%. Silicon-based materials have higher lithium insertion potentials, which are beneficial to improving the kinetic performance of secondary batteries. At the same time, silicon-based materials have high gram capacity, which is beneficial to improving the energy density of secondary batteries. However, the lithium insertion expansion of silicon-based materials is large and the stability is low, which is not conducive to cycle performance, so the amount added cannot be too much. Exemplarily, the mass proportion of the silicon-based material in the negative electrode film layer is 3%, 5%, 6%, 8%, etc., or a value between any two values. The silicon-based material can be mixed with the first carbon-based material as the first negative electrode active material, and / or the silicon-based material can be mixed with the second carbon-based material as the second negative electrode active material.

[0112] The present disclosure does not particularly limit the silicon-based material, and silicon-based materials conventionally used as negative electrode active materials in the art can be used. Exemplarily, the silicon-based material can be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys.

[0113] 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.).

[0114] In some embodiments, the negative electrode active material may further employ negative electrode active materials for batteries known in the art. For example, the negative electrode active material may further include at least one of the following materials: natural graphite, soft carbon, hard carbon, tin-based materials, and lithium titanate. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present disclosure is not limited to these materials; other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used singly or in combination.

[0115] 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).

[0116] 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.

[0117] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0118] The present disclosure does not particularly limit the content of the binder and / or other auxiliary agents, if any, in the negative electrode film layer. A person skilled in the art can determine the appropriate content of the binder and / or other auxiliary agents through routine experiments in the relevant field.

[0119] According to some embodiments, the negative electrode film layer satisfies at least one of the following items, which is beneficial to at least one of the kinetic performance, energy density, and cycle performance of the secondary battery.

[0120] (1) The compaction density of the negative electrode film layer is ≤1.85g / cm 3 , optionally 1.7-1.85 g / cm 3 The compaction density within this range is beneficial to the energy density of the secondary battery. For example, the compaction density of the negative electrode film layer is 1.7 g / cm 3 , 1.75g / cm 3 , 1.8g / cm 3 , 1.85g / cm 3 etc., or any value between any two values.

[0121] (2) The porosity of the negative electrode film layer is 18.0% to 38.0%, and optionally 19.0% to 34.0%. Examples of the porosity of the negative electrode film layer include 19%, 21%, 23%, 25%, 27%, 29%, 31%, 33%, and the like, or values ​​between any two values. Porosity within this range facilitates the migration of active ions, thereby improving the kinetic performance of the secondary battery.

[0122] (3) The OI value of the negative electrode film layer is ≤30.0, and can optionally be 8.0-23.0. For example, the OI value of the negative electrode film layer is 8, 10, 12, 14, 16, 18, 20, 22, or any value between two values. An OI value within this range reflects that the crystal plane orientation of the carbon-based material in the negative electrode film layer is not completely parallel to the negative electrode current collector, thereby shortening the migration path of active ions and improving the kinetic performance of the secondary battery.

[0123] (4) The thickness of the negative electrode film layer is greater than or equal to 40 μm, and optionally is 40-140 μm. For example, the thickness of the negative electrode film layer is 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, or the like, or a value between any two values, but is not limited thereto.

[0124] The above embodiments are described only by taking the composition of the negative electrode film layer on the surface of one side of the negative electrode current collector as an example. It should be understood that the negative electrode film layer described in the above embodiments can be provided on any one or both of the two surfaces of the negative electrode current collector that are opposite to each other in the thickness direction of the negative electrode current collector. It should be noted that the various negative electrode film layer parameters (such as compaction density, surface density, porosity, thickness, etc.) given in the present disclosure refer to the parameters of the negative electrode film layer on a single side of the negative electrode current collector. When the negative electrode film layer is provided on both sides of the negative electrode current collector, the parameters of the negative electrode film layer on either side meet the requirements of the present disclosure and are considered to fall within the scope of protection of the present disclosure.

[0125] In the present disclosure, the negative electrode sheet may include other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode sheet 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 sheet further includes a protective layer covering the surface of the negative electrode film layer.

[0126] In the present disclosure, the pore area, S1, and S2 values ​​of the first carbon-based material can be obtained by using a cross-section polisher (such as the IB-09010CP argon ion cross-section polisher from JEOL of Japan) to obtain the cross-section of the first carbon-based material; then, referring to JY / T010-1996, a scanning electron microscope (such as the Sigma 300 scanning electron microscope from ZEISS of Germany) is used to scan the cross-section of the first carbon-based material; finally, the pore area of ​​any one hole in the first carbon-based material is obtained respectively through image processing software (such as AVIZO); and the total pore area S1 of the external region and the total pore area S2 of the internal region, and thereby the value of S2 / S1 is obtained. For example, samples can be obtained from different areas of the negative electrode sheet in the secondary battery, and at least 5 positions (such as 5, 10, 15 or even more) are randomly selected from the sample to obtain cross sections using a cross-section polisher, and at least 10 particles (such as 10, 20, 50 or even more particles) are randomly selected from the scanning electron microscope images of each cross section. The total pore area S2' and the total pore area S1' of the inner region of each particle cross section are obtained using image processing software according to the above definition, and the S2' / S1' value of each particle cross section is obtained. The arithmetic average of the S2' / S1' of all the measured particle cross sections is calculated as the S2 / S1 value of the first carbon-based material.

[0127] In the X-ray diffraction (XRD) analysis test disclosed herein, a copper target can be used as an anode target, and CuKα rays can be used as a radiation source with a wavelength of The scanning 2θ angle range was 20°-80°, and the scanning rate was 4° / min.

[0128] In the present disclosure, the volume distribution particle size Dv10, Dv50, and Dv90 of the material (e.g., the first carbon-based material, the second carbon-based material, etc.) are well-known in the art, and respectively represent the particle size corresponding to when the cumulative volume distribution percentage of the material reaches 10%, 50%, and 90%, and can be measured using instruments and methods known in the art. For example, it can be measured using a laser particle size analyzer with reference to GB / T 19077-2016. The test instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0129] In the present disclosure, whether there is a coating layer on the surface of a material (eg, the first carbon-based material, the second carbon-based material, etc.) can be determined by transmission electron microscopy.

[0130] In the present disclosure, the specific surface area BET of a material (e.g., a first carbon-based material, a second carbon-based material, etc.) is a well-known meaning 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 according to GB / T 19587-2017 and calculated using the BET (Brunauer Emmett Teller) method. The test instrument can be a Tri-Star 3020 specific surface area pore size analysis tester from Micromeritics, USA.

[0131] In the present disclosure, the degree of graphitization of a material (e.g., the first carbon-based material, the second carbon-based material) has a well-known meaning in the art and can be tested using instruments and methods known in the art. For example, an X-ray diffractometer (e.g., 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 d of the C(002) plane in the crystal structure of the material. 002 Then according to the formula g=(0.344-d 002 ) / (0.344-0.3354)×100% to calculate the degree of graphitization. In the above formula, d 002 It is the average interlayer spacing of the C(002) planes in the material's crystal structure expressed in nanometers (nm).

[0132] In the present disclosure, the gram capacity of a material (such as a first carbon-based material, a second carbon-based material, etc.) has a meaning well known in the art and can be tested using methods known in the art. An 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) in a mass ratio of 91.6:1.8:6.6 and the solvent N-methylpyrrolidone (NMP) to form a slurry; the prepared slurry is applied to 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 a concentration of 1 mol / L The electrolyte was then added. A lithium metal sheet was used as the counter electrode, and a polyethylene (PE) film was used as the separator. The cells were assembled into CR2430 button cells in an argon-protected glove box with the electrolyte. After standing for 12 hours, the cells were discharged at 0.05C to 0.005V at 25°C. The cells were then allowed to stand for 10 minutes, and then discharged again at 50μA to 0.005V. The cells were allowed to stand for 10 minutes, and then discharged again at 10μA to 0.005V. The cells were then charged at 0.1C to 2V, and the charge capacity was recorded. The ratio of the charge capacity to the sample mass is the gram capacity of the corresponding material (e.g., the first carbon-based material, the second carbon-based material, etc.).

[0133] In the present disclosure, the powder compaction density of a material (e.g., a first carbon-based material, a second carbon-based material, etc.) is a well-known meaning in the art and can be measured using instruments and methods known in the art. For example, it can be measured using an electronic pressure testing machine (e.g., a UTM7305 electronic pressure testing machine) with reference to GB / T 24533-2009. An exemplary test method is as follows: 1 g of sample powder is weighed and added to a container with a bottom area of ​​1.327 cm 2 In the mold, pressurize to 50000N, hold the pressure for 30s, then release the pressure, hold for 10s, and then record and calculate the powder compaction density of the material under 50000N pressure.

[0134] In the present disclosure, the tap density of a material (such as a first carbon-based material, a second carbon-based material, etc.) is a meaning well known in the art and can be measured using instruments and methods known in the art. For example, GB / T 5162-2006 can be referred to and a powder tap density tester can be used for measurement. The test instrument can be Dandong Baxter BT-301, and the test parameters are as follows: vibration frequency 250 ± 15 times / minute, amplitude 3 ± 0.2 mm, vibration number 5000 times, and graduated cylinder 25 mL.

[0135] In this disclosure, primary particles and secondary particles have meanings well known in the art. Primary particles refer to non-agglomerated particles. Secondary particles refer to agglomerated particles formed by aggregation of primary particles. Primary particles and secondary particles can be distinguished using scanning electron microscopy (SEM) images.

[0136] In the present disclosure, the ratio of the number of primary particles in the first carbon-based material and / or the second carbon-based material refers to: for example, randomly selecting a test sample in the negative electrode film layer, randomly selecting multiple test areas in the test sample, using a scanning electron microscope to obtain images of the multiple test areas, and counting the ratio of the number of first carbon-based materials with primary particle morphology in each image to the total number of first carbon-based material particles. The average value of multiple statistical results is the ratio of the number of primary particles in the first carbon-based material.

[0137] In the present disclosure, the number ratio of secondary particles in the first carbon-based material and / or the second carbon-based material refers to: for example, randomly taking a test sample in the negative electrode film layer, randomly taking multiple test areas in the test sample, using a scanning electron microscope to obtain images of the multiple test areas, and counting the number of second carbon-based materials with secondary particle morphology in each image as a ratio of the total number of second carbon-based material particles, and the average value of multiple statistical results is the number ratio of secondary particles in the second carbon-based material.

[0138] In the present disclosure, the surface density of the negative electrode film layer has a meaning well known in the art and can be tested using methods known in the art. For example, a negative electrode sheet coated on one side and cold pressed can be taken (if it is a double-sided coated negative electrode sheet, the negative electrode film layer on one side can be wiped off first), punched into small discs with an area of ​​S', weighed, and recorded as M1. Then wipe off the negative electrode film layer of the weighed negative electrode sheet, weigh the weight of the negative electrode current collector, and record it as M0. Surface density of negative electrode sheet = (M1-M0) / S'.

[0139] In the present disclosure, the compacted density of the negative electrode film layer is a well-known term in the art and can be measured using methods known in the art. [Compacted density of the negative electrode film layer = area density of the negative electrode film layer / thickness of the negative electrode film layer].

[0140] In the present disclosure, the porosity of the negative electrode film layer has a well-known meaning in the art and can be measured using methods known in the art. An exemplary test method is as follows: take a negative electrode sheet that has been coated on one side and cold-pressed (if it is a negative electrode sheet coated on both sides, the negative electrode film layer on one side can be wiped off first), punch it into small disc samples of a certain area, and calculate the apparent volume V1 of the negative electrode sheet; refer to GB / T24586-2009, use an inert gas (such as helium or nitrogen) as a medium, adopt a gas replacement method, and use a true density tester to measure the true volume V2 of the negative electrode sheet. The porosity of the negative electrode film layer = (V1-V2) / V1×100%. Multiple negative electrode sheet samples with good appearance and no powder falling off on the edges (such as 30 pieces) can be taken for testing, and the results are averaged, thereby improving the accuracy of the test results. The testing instrument can be a Micromeritics AccuPyc II 1340 true density tester.

[0141] In the present disclosure, the OI value of the negative electrode film layer has a well-known meaning in the art and can be tested using instruments and methods known in the art. For example, an X-ray diffractometer (such as Bruker D8 Discover) can be used for testing. The test can refer to JIS K 0131-1996 and JB / T4220-2011 to obtain an X-ray diffraction pattern of the negative electrode sheet. According to the OI value = I 004 / I 110 The OI value of the negative electrode film layer is calculated. 004 is the integrated area of ​​the diffraction peak of the 004 crystal plane of crystalline carbon in the negative electrode film layer, I 110 The integrated area of ​​the diffraction peak of the 110 crystal plane of the crystalline carbon in the negative electrode film layer. In the X-ray diffraction analysis test disclosed in the present invention, a copper target can be used as the anode target, and CuKα rays can be used as the radiation source. The ray wavelength is The scanning 2θ angle range was 20°-80°, and the scanning rate was 4° / min.

[0142] 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 provided in this disclosure 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 provided in this disclosure, the present disclosure is satisfied.

[0143] 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.

[0144] 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 surface density, compacted density, porosity, and thickness of the negative electrode film.

[0145] 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.

[0146] In the present disclosure, the first carbon-based material can be prepared by the following method of the present disclosure; the second carbon-based material can be commercially available, or can also be prepared by the following method of the present disclosure.

[0147] In some embodiments, the preparation method of the first carbon-based material includes: step 1, providing a raw material having a plurality of pore structures; step 2, mixing the above raw material and the filling material uniformly in a predetermined proportion, then keeping it warm at a first temperature T1 for a first time t1, and cooling it to room temperature to obtain an intermediate; step 3, keeping the obtained intermediate warm at a second temperature T2 for a second time t2, and obtaining the first carbon-based material after the end.

[0148] In some embodiments, in step 1, the raw material for preparing the first carbon-based material includes natural graphite. Optionally, the natural graphite includes one or more of flake graphite, natural spherical graphite, and microcrystalline graphite, especially natural spherical graphite.

[0149] "Natural spherical graphite" refers to natural graphite with a spherical or quasi-spherical shape, and not all natural graphite particles are controlled to be ideal spheres. In some embodiments, natural spherical graphite with a desired particle size and morphology can be obtained by pre-treating flake graphite. Optionally, the pre-treatment includes crushing, classification, spheroidization, purification, and other processes.

[0150] In some embodiments, in step 1, the volume distribution particle size Dv50 of the raw material may be 6 μm to 13 μm.

[0151] In some embodiments, in step 1, the specific surface area of ​​the raw material may be ≥2.5m 2 / g, optional 2.5m 2 / g~10.0m 2 When the specific surface area of ​​the raw material is within the above range, it is beneficial to carry out subsequent filling processing and obtain the first carbon-based material with the required specific surface area. It is also beneficial for the first carbon-based material to have both high capacity and high first coulombic efficiency. In addition, it is also beneficial for the first carbon-based material to have better kinetic properties.

[0152] In some embodiments, in step 2, the softening point temperature of the filling material is 90° C. to 150° C. Optionally, the softening point temperature of the filling material is 94° C. to 146° C., 94° C. to 142° C., 94° C. to 138° C., 94° C. to 134° C., 94° C. to 130° C., 104° C. to 146° C., 104° C. to 142° C., 104° C. to 138° C., 104° C. to 134° C., 104° C. to 130° C.

[0153] In some embodiments, in step 2, the volume distribution particle size Dv50 of the filler material is less than or equal to 6 μm, and can be selected from 1 μm to 6 μm, 1 μm to 5 μm, 2 μm to 5 μm, and 3 μm to 5 μm. This facilitates the filler material to melt under heat and fill into the pore structure of the raw material, and also helps to improve the uniformity of the dispersion of the filler material and the raw material.

[0154] In some embodiments, in step 2, the coking value of the filler material is 15% to 40%, and optionally 18% to 34%. In this disclosure, the coking value of the filler 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 in accordance with GB / T 8727-2008.

[0155] In some embodiments, in step 2, the filling material includes one or more of coal tar, petroleum asphalt, polymer compounds and resins, and may optionally include one or more of coal tar and petroleum asphalt.

[0156] In some embodiments, in step 2, the mass ratio of the above-mentioned filling material to the above-mentioned raw material is (10-40):100, and can be optionally (10-30):100, (10-25):100, (10-20):100, (12-30):100, (14-28):100, (15-25):100.

[0157] In step 2, by adjusting one or more parameters such as the type, softening point, coking value, and addition amount of the filling material within the above-mentioned range, it is beneficial to adjust the number of pores and / or pore size in the outer and inner areas of the first carbon-based material within a suitable range, which is beneficial to adjust the S2 / S1 of the first carbon-based material within a suitable range.

[0158] By adjusting the type, softening point, coking value, addition amount and other parameters of the filling material within the above range, the viscosity of the filling material is not high after being heated and melted, and it maintains good fluidity. At the same time, it is not easy to adhere to the raw material particles, which can reduce the agglomeration of the raw material particles in the subsequent preparation process. This can also reduce the problems of increased surface defects of the first carbon-based material particles and increased surface active sites due to the need to add a depolymerization process.

[0159] In some embodiments, in step 2, the heating process of uniformly mixing the raw material and the filling material in a predetermined ratio and then heating the mixture to the first temperature T1 may be a staged heating process.

[0160] In some embodiments, the staged temperature increasing process includes a first temperature increasing process, a second temperature increasing process, and a third temperature increasing process.

[0161] In some embodiments, the first temperature rising process is to raise the temperature to 200° C. to 250° C. and keep the temperature at this temperature for 0.5 h to 3 h.

[0162] In some embodiments, the second temperature increase process is to increase the temperature to 450°C to 550°C and maintain the temperature at this temperature for 0 to 2 hours. When the temperature is maintained for 0 hours, it means that when the temperature is increased to the range of 450°C to 550°C, no temperature maintenance treatment is performed, and the temperature is continued to be increased to the first temperature T1.

[0163] In some embodiments, the third temperature increasing process is to increase the temperature to the first temperature T1 and keep the temperature at the first time t1.

[0164] In the staged heating process, the temperature is first raised to 200℃~250℃. Since the heating temperature is higher than the softening point of the filling material, the filling material is melted and softened by the heat. It can be kept warm for 0.5h~3h to allow it to flow and fill into the pore structure of the raw material; then the temperature is raised to 450℃~550℃, at which time the melted and softened filling material undergoes a carbonization reaction, gradually forming a semi-coke state and turning into a viscous liquid or solid, thereby preventing the filling material from entering the entire pore structure of the raw material; finally, the temperature is raised to the first temperature, at which time the filling material undergoes a carbonization reaction, thereby enabling the pore structure occupied by the filling material to be effectively filled.

[0165] In some embodiments, in step 2, the temperature is raised to the first temperature T1 at a rate of 1°C / min to 10°C / min. For example, the heating rate can be 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, or any range thereof. Alternatively, the heating rate is 1.5°C / min to 8°C / min, 1.5°C / min to 6°C / min, 2°C / min to 6°C / min, or 2°C / min to 5°C / min.

[0166] In some embodiments, the heating rate of the first heating process may be 1°C / min to 10°C / min, optionally 1.5°C / min to 8°C / min, 1.5°C / min to 6°C / min, 2°C / min to 6°C / min, or 2°C / min to 5°C / min. In some embodiments, the heating rate of the second heating process may be 1°C / min to 10°C / min, optionally 2°C / min to 8°C / min. In some embodiments, the heating rate of the third heating process may be 1°C / min to 10°C / min, optionally 2°C / min to 8°C / min.

[0167] In some embodiments, in step 2, the first temperature T1 is 800° C. to 1200° C. For example, the first temperature T1 can be 800° C., 850° C., 900° C., 950° C., 1000° C., 1050° C., 1100° C., 1200° C., or any range thereof. Alternatively, the first temperature T1 is 800° C. to 1100° C., 850° C. to 1100° C., 900° C. to 1100° C., or 850° C. to 1000° C.

[0168] In some embodiments, in step 2, the first time t1 is 1 hour to 5 hours. For example, the first time t1 can be 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, or any range thereof. Optionally, the first time t1 is 2 hours to 4 hours.

[0169] In some embodiments, in step 2, the heat treatment can be carried out in a device capable of programmed temperature increase, such as a medium frequency furnace, a roller kiln, a rotary kiln, a push plate kiln, a vertical granulation kettle, a horizontal granulation kettle, a vertical reactor, a horizontal reactor or a drum furnace.

[0170] In some embodiments, in step 2, the heat treatment atmosphere may be a protective gas atmosphere, which may include one or more of nitrogen, argon, and helium.

[0171] In step 2, by adjusting one or more of the heating rate, the first temperature, the first time, the heating process, etc. within the above-mentioned range, it is beneficial to adjust the number of pores and / or the pore size in the outer area and the inner area of ​​the first carbon-based material within a suitable range, and thus it is beneficial to adjust the S2 / S1 of the first carbon-based material within a suitable range.

[0172] In some embodiments, in step 3, the first temperature T2 is 1600° C. to 2800° C. Optionally, the second temperature T2 is 1600° C. to 2700° C., 1600° C. to 2600° C., 1600° C. to 2500° C., 1600° C. to 2400° C., 1800° C. to 2600° C., 1800° C. to 2500° C., 1800° C. to 2400° C., 2000° C. to 2500° C., or 2000° C. to 2400° C.

[0173] In some embodiments, in step 3, the second time t2 is 1.5 hours to 6 hours. For example, the second time t1 can be 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, or any range thereof. Optionally, the second time t2 is 2 hours to 5 hours.

[0174] In some embodiments, in step 3, the heat treatment may be performed in a medium frequency furnace, a box-type graphitization furnace, an Acheson graphitization furnace, a continuous graphitization furnace, or an internal string graphitization furnace.

[0175] In some embodiments, in step 3, the medium frequency furnace and the continuous graphitization heat treatment atmosphere may be a protective gas atmosphere. The protective gas may include one or more of nitrogen, argon, and helium.

[0176] In step 3, by adjusting one or more of the second temperature and the second time within the above range, it is beneficial to adjust the content of disordered carbon in the first carbon-based material to be within a suitable range, which is beneficial for the first carbon-based material to have a suitable graphitization degree, interlayer spacing and I D / I G wait.

[0177] In the preparation method of the above-mentioned first carbon-based material, by adjusting one or more of the parameters of natural graphite, the parameters of the filling material, the heating rate, the first temperature, the first time, the heating process, the second temperature, the second time, etc. within the above-mentioned range, it is beneficial to adjust the S2 / S1, graphitization degree, gram capacity, specific surface area, particle size, powder compaction density, tap density and other parameters of the second carbon-based material.

[0178] According to some embodiments, the first carbon-based material may have a coating layer. The preparation method further includes step 4: mixing the first carbon-based material prepared above with an organic carbon source and carbonizing it at a third temperature T3. The organic carbon source may be a carbon-containing material suitable for coating known in the art, for example, it may include one or more of coal tar, petroleum asphalt, phenolic resin, coconut shell, etc. In some embodiments, the first carbon-based material mixed with the organic carbon source is kept at a third temperature T3 of 1150 to 1500°C for 1-3 hours for carbonization, thereby obtaining a first carbon-based material having a carbon coating layer on at least part of its surface.

[0179] In some embodiments, artificial graphite as the second carbon-based material can be prepared according to methods in the prior art. For example, the following method can be used.

[0180] Providing raw materials; crushing and shaping the raw materials to obtain a first intermediate; graphitizing the first intermediate to obtain a second intermediate; mixing the second intermediate with an organic carbon source and then carbonizing the mixed product; and finally screening the mixed product to obtain a second carbon-based material.

[0181] The raw materials can be one or more of petroleum coke, needle coke, pitch coke and metallurgical coke. The raw materials can be crushed using a mechanical mill or a roller mill and shaped using a shaping machine.

[0182] In some embodiments, the graphitization temperature is 2800° C.-3200° C. By adjusting the graphitization temperature and / or the graphitization time, the second carbon-based material can be helped to have a suitable graphitization degree.

[0183] In some embodiments, the organic carbon source may be a carbon-containing material suitable for coating known in the art, for example, it may include one or more of coal tar, petroleum asphalt, phenolic resin, coconut shell, etc. By adjusting the amount of the organic carbon source added, it is beneficial to adjust the specific surface area, graphitization degree, gram capacity and other parameters of the second carbon-based material. The carbonization temperature may be 900°C-1300°C. By adjusting the carbonization temperature and / or the carbonization holding time, it is beneficial to adjust the specific surface area, graphitization degree, gram capacity and other parameters of the second carbon-based material.

[0184] During the preparation process, by adjusting one or more parameters of the equipment (such as mechanical mill or roller mill, shaper, granulator, etc.), raw material parameters, organic carbon source addition amount, binder addition amount, graphitization temperature, graphitization time, etc., it is beneficial to adjust the graphitization degree, powder compaction density, gram capacity, particle size, specific surface area and other parameters of the second carbon-based material.

[0185] In order to obtain artificial graphite of secondary particles, the precursor can be granulated with a binder asphalt before graphitization, and then the granulated product is graphitized at 2800°C-3200°C to obtain artificial graphite of secondary particles.

[0186] The present disclosure also provides a method for preparing a negative electrode sheet of the present disclosure. The method comprises the following steps: providing a first negative electrode slurry comprising the first negative electrode active material of each of the above embodiments and a second negative electrode slurry comprising the second negative electrode active material of each of the above embodiments; coating the second negative electrode slurry on a negative electrode current collector, coating the first negative electrode slurry on the second negative electrode slurry, and drying and cold pressing to obtain a negative electrode sheet.

[0187] In some embodiments, the first negative electrode slurry and the second negative electrode slurry may further optionally include the aforementioned conductive agent, binder, other optional auxiliary agents, and solvent (eg, deionized water).

[0188] The first slurry and the second slurry can be applied simultaneously at one time or in two separate applications. In some embodiments, the first slurry and the second slurry are applied simultaneously at one time. Applying them simultaneously at one time can reduce the negative electrode film resistance, thereby further improving the kinetic performance and cycle performance of the secondary battery.

[0189] The coating weight of the first slurry and the second slurry can be adjusted according to actual conditions.

[0190] [Positive electrode]

[0191] The secondary battery of the present disclosure further includes a positive electrode sheet. The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material. The present disclosure does not particularly limit the positive electrode sheet.

[0192] 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.

[0193] 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.).

[0194] 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 disclosure 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.

[0195] During the charge and discharge process of a battery, active ions, such as Li, are intercalated and deintercalated, and consumed. The molar content of active ions, such as Li, varies when the battery is discharged to different states. The molar content of Li in the positive electrode materials listed in this disclosure refers to the material's initial state, i.e., before addition of the materials. When the positive electrode material is used in a battery system, the molar content of Li will change after charge and discharge cycles.

[0196] In the list of positive electrode materials in this disclosure, 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.

[0197] 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.

[0198] 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.

[0199] 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.

[0200] [Electrolytes]

[0201] The electrolyte conducts ions between the positive and negative electrodes. This disclosure does not specifically limit the type of electrolyte, and the electrolyte can be selected based on needs. For example, the electrolyte can be liquid, gel, or solid.

[0202] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0203] 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.

[0204] 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.

[0205] 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.

[0206] [Isolation film]

[0207] In some embodiments, the battery cell further includes a separator. The present disclosure has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0208] 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.

[0209] 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.

[0210] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0211] 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.

[0212] The present disclosure has no particular limitation on the shape of the battery cell, which may be cylindrical, square, or any other shape. For example, FIG7 shows a battery cell 5 with a square structure as an example.

[0213] In some embodiments, referring to Figure 8, 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.

[0214] 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.

[0215] Figure 9 shows an example battery module 4. Referring to Figure 9 , 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.

[0216] 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.

[0217] 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.

[0218] Figures 10 and 11 illustrate an exemplary 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 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.

[0219] In addition, the second aspect of the present disclosure further provides an electric device, which includes the secondary battery of each of the above embodiments. The secondary battery can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device can 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.

[0220] As the electrical device, a battery cell, a battery module or a battery pack can be selected according to its usage requirements.

[0221] Figure 12 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.

[0222] 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.

[0223] Example

[0224] The following examples are provided. The examples described below are illustrative and are intended only to explain the present disclosure and are not to be construed as limiting the present disclosure. Where specific techniques or conditions are not specified in the examples, the methods were performed according to those described in the literature in the art or according to the product specifications. Reagents or instruments used without manufacturer's indication are all commercially available conventional products.

[0225] The materials used in the embodiments of the present disclosure are prepared by the following process.

[0226] Preparation of material 1-1:

[0227] The flake graphite is mechanically crushed, and the volume distribution particle size Dv50 after spheroidization is 12μm, and then purified to obtain natural spherical graphite. The obtained natural spherical graphite is mixed with filler petroleum asphalt (the softening point of petroleum asphalt is 110℃) in a ratio of 100:22, and then the mixed material is placed in a device that can perform programmed temperature increase, heated to 200℃ and kept warm for 1h, and then continuously heated to 700℃ and kept warm for 1h, and then cooled to room temperature to obtain an intermediate. The obtained intermediate is placed in a graphitization furnace and graphitized at 2510℃ for heat treatment. After the end, it is demagnetized and sieved. The obtained material and asphalt are mixed in a ratio of 100:15 and heat-treated at 1100℃ to obtain material 1-1 with a coating layer. Material 1-1 meets: S2 / S1=15, volume distribution particle size Dv50=12.0μm, specific surface area BET=2.0m 2 / g and degree of graphitization = 96.8%.

[0228] Preparation of materials 1-2 to 1-6:

[0229] The preparation methods of materials 1-2 to 1-6 are similar to those of material 1-1, except that the volume distribution particle size Dv50 of the natural spherical graphite is adjusted to obtain materials 1-2 to 1-6. The details are as follows:

[0230] Table 1.

[0231] Preparation of Material 2-1:

[0232] Needle coke was used as the raw material, crushed by a roller mill, and shaped by a sizing machine. The shaped raw material was granulated using petroleum pitch as a binder. The granulated material was then graphitized at 3000°C to produce artificial graphite material 2-1, which is a secondary particle of the second carbon-based material. The volume distribution particle size (Dv50) of material 2-1 (secondary particles) was 14.5, and the degree of graphitization was 94.3%.

[0233] Preparation of materials 2-2 to 2-6:

[0234] The preparation method of materials 2-2 to 2-6 is similar to that of material 2-1, except that the granulation time is adjusted to obtain materials 2-2 to 2-6.

[0235] The details are as follows:

[0236] Table 2.

[0237] Example 1

[0238] Preparation of secondary batteries:

[0239] 1. Negative electrode sheet: The first negative electrode active material (Material 1-1, serving as the first carbon-based material) and the second negative electrode active material (Material 2-1, serving as the second carbon-based material) were respectively 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 and a second negative electrode slurry. The second negative electrode slurry and the first negative electrode slurry were sequentially coated on both surfaces of the negative electrode current collector copper foil in equal weight ratios. After drying and cold pressing, a negative electrode sheet was obtained.

[0240] 2. Positive electrode: LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523) is mixed with carbon black (Super P), a conductive agent, and polyvinylidene fluoride (PVDF) as a binder in a weight ratio of 96:2:2. An appropriate amount of N-methylpyrrolidone (NMP) is added as a solvent and stirred evenly to obtain a positive electrode slurry. The positive electrode slurry is then coated on both surfaces of the positive electrode current collector aluminum foil. After drying and cold pressing, a positive electrode sheet is obtained.

[0241] 3. Electrolyte: 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 an electrolyte with a concentration of 1 mol / L.

[0242] 4. Isolation film: polypropylene film.

[0243] 5. Preparation of secondary batteries: Place the positive and negative electrodes prepared above in order, with the separator between the positive and negative electrodes to act as an isolation film, and then wind them to obtain an electrode assembly; place the electrode assembly in an outer package, dry it, and inject the electrolyte. After vacuum packaging, standing, forming, shaping, and other processes, a secondary battery is obtained.

[0244] Examples 2 to 6

[0245] A secondary battery was prepared in a similar manner to Example 1, except that the volume distribution particle size Dv50 of the first carbon-based material was different.

[0246] Comparative Example 1

[0247] A battery was prepared in a similar manner to Example 1, except that the volume distribution particle size Dv50 of the first carbon-based material was greater than 15 μm.

[0248] Performance Testing

[0249] 1. Material testing

[0250] The S2 / S1 of the first carbon-based material is obtained by testing using the following method.

[0251] A sample preparation binder and the first carbon-based material powder are mixed evenly and then applied to a copper foil. The mixture is then dried at 60°C for 30 minutes before use. Five samples to be tested are cut into 6 mm x 6 mm pieces at five different locations and attached to the sample stage of a CP-type argon ion cross-section polisher. The samples are then cut using a plasma beam to obtain cross-sections of each sample. The testing instrument can be the IB-09010CP-type argon ion cross-section polisher from Japan's JEOL.

[0252] Each sample cross section of the first carbon-based material was scanned using a scanning electron microscope, and a scanned image was obtained from an arbitrarily selected region within each sample cross section. The test may refer to JY / T010-1996. The testing instrument may be a Sigma 300 scanning electron microscope from ZEISS, Germany.

[0253] Randomly select cross sections of 20 particles of the first carbon-based material from the scanned image. The area formed by extending 0.25 μm from the particle surface of the first carbon-based material to the interior of the particle is recorded as the external area, and the area inside the external area is recorded as the internal area. Use image processing software to obtain the total pore area S1' of the external area of ​​each particle cross section and the pore area S2' of the internal area of ​​the first carbon-based material, and calculate the value of S2' / S1'; and calculate the arithmetic average of S2' / S1' of all 20 particles as the value of S2 / S1 of the first carbon-based material. The image processing software can be AVIZO.

[0254] 2. Battery performance test

[0255] (1) Cycle performance test of secondary batteries

[0256] At 45°C, the prepared secondary battery was charged at a constant current of 1C to the upper cutoff voltage (corresponding to 100% SOC), then charged at a constant voltage to a current of 0.05C. After standing for 5 minutes, the secondary battery was discharged at a constant current of 1C to the lower cutoff voltage (corresponding to 0% SOC). The discharge capacity at this point was recorded as the discharge capacity of the first cycle. The secondary battery was subjected to cyclic charge and discharge tests according to the above method, and the discharge capacity after each cycle was recorded.

[0257] Capacity retention rate (%) of the secondary battery after 1000 cycles at 45° C. = discharge capacity after 1000 cycles / discharge capacity at the first cycle×100%.

[0258] (2) Storage performance test of secondary batteries

[0259] At 25°C, the prepared secondary battery was charged at a constant current of 1C to 4.3V, then charged at a constant voltage to a current of 0.05C. After standing for 5 minutes, the secondary battery was discharged at a constant current of 1C to 2.8V. The discharge capacity at this time was recorded, which was the discharge capacity before storage.

[0260] At 25°C, the prepared secondary battery was charged at a constant current of 1C to 4.3V, and then charged at a constant voltage to a current of 0.05C. The secondary battery was then stored in a thermostat at 60°C for 180 days. Capacity retention (%) of the secondary battery after 180 days of storage at 60°C = discharge capacity after storage / discharge capacity before storage × 100%.

[0261] (3) Dynamic testing of secondary batteries

[0262] At 25°C, the secondary battery was charged to 4.3V 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.

[0263] Then the secondary battery is charged with constant current in sequence at 1.0C0, 1.3C0, 1.5C0, 1.8C0, 2.0C0, 2.3C0, 2.5C0, 3.0C0 to 4.3V or 0V negative electrode cut-off potential (whichever is reached first). After each charge, it is discharged to 2.8V at 1C0. Record the charge rate at different charge rates to 10%, 20%, 30%, etc. until 80% SOC (State of 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 dynamic performance of the secondary battery.

[0264] (4) Energy density test of secondary batteries

[0265] At 25°C, charge the secondary battery at a constant current of 1 / 3C to 4.3V. Then, charge it at a constant voltage at 4.3V to a current of 0.05C. Let it rest for 5 minutes, and then discharge it at a constant current of 1 / 3C to 2.8V. Record the battery discharge energy at this time. The battery discharge energy divided by the battery volume is the battery volume energy density, measured in Wh / L.

[0266] The batteries prepared in Examples 1 to 6 and Comparative Example 1 were tested according to the above test methods (1) to (3). The negative electrode active materials used and the test results are shown in Table 4.

[0267] Table 3.

[0268] From Table 3 above, it can be seen that as the particle size of the first carbon-based material decreases, the charging time gradually shortens, indicating that the kinetic performance gradually improves, while the cycle performance and storage performance slightly decrease. In Comparative Example 1, the particle size of the first carbon-based material is larger, and the cycle performance and storage performance are both good, while the kinetic performance decreases significantly.

[0269] Examples 7 to 11

[0270] Secondary batteries were prepared using a method similar to that of Example 1. The difference was that the volume distribution particle size Dv50 of the second carbon-based material was different. The batteries prepared in Example 1 and Examples 7-11 were tested using the above test methods (3)-(4). The negative electrode active materials used and the test results are shown in Table 4.

[0271] Table 4.

[0272] It can be seen from Table 3 above that as the particle size of the second carbon-based material decreases, the charging time gradually shortens, indicating that the kinetic performance gradually improves while the energy density decreases.

[0273] It should be noted that the present disclosure is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present disclosure, embodiments having substantially the same structure as the technical concept and exerting the same effects are all included in the technical scope of the present disclosure. In addition, within the scope of the present disclosure, various modifications that can be imagined by those skilled in the art to the embodiments, and other methods constructed by combining some of the constituent elements of the embodiments are also included in the scope of the present disclosure.

Claims

1. A secondary battery, comprising a negative electrode plate, wherein the negative electrode plate comprises a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector, The negative electrode film layer has a first surface away from the negative electrode current collector and a second surface arranged opposite to the first surface, and the thickness of the negative electrode film layer is recorded as H; in, The area within the thickness range from the first surface of the negative electrode film layer to 0.3H is recorded as the first area of ​​the negative electrode film layer, the first area includes a first negative electrode active material, the first negative electrode active material includes a first carbon-based material, in the cross-sectional view of the first carbon-based material, the volume distribution particle size Dv50 of the first carbon-based material is recorded as D, the first carbon-based material includes an external area and an internal area located inside the external area, the external area refers to the area extending from the particle surface of the first carbon-based material to the inside of the particle by a distance of 0.25D, the total pore area of ​​the external area is recorded as S1, and the total pore area of ​​the internal area is recorded as S2, then the first carbon-based material satisfies S2>S1, and the volume distribution particle size Dv50 of the first carbon-based material is less than or equal to 15μm.

2. The secondary battery according to claim 1, wherein The volume distribution particle size Dv50 of the first carbon-based material is 7 μm-13 μm.

3. The secondary battery according to claim 1 or 2, wherein: 1.5≤S2 / S1≤500, optionally, 2.5≤S2 / S1≤450.

4. The secondary battery according to any one of claims 1 to 3, wherein: The area of ​​the pore structure in the outer region of the first carbon-based material is less than or equal to 0.15 μm 2 , can be selected to be less than or equal to 0.13μm 2 and / or, The inner region of the first carbon-based material includes at least one area greater than or equal to 0.15 μm 2 The pore structure may include one or more pores with an area of ​​0.15 μm 2 -2.0μm 2 The pore structure.

5. The secondary battery according to any one of claims 1 to 4, wherein: At least a portion of the surface of the first carbon-based material has a carbon coating layer.

6. The secondary battery according to any one of claims 1 to 5, wherein: The first carbon-based material includes primary particles; optionally, the primary particles account for ≥80% of the first carbon-based material.

7. The secondary battery according to any one of claims 1 to 6, wherein: The area within the thickness range from the second surface of the negative electrode film layer to 0.3H is recorded as the second area of ​​the negative electrode film layer, the second area is arranged between the negative electrode collector and the first area, the second area includes a second negative electrode active material, and the second negative electrode active material includes a second carbon-based material; optionally, the second carbon-based material includes artificial graphite.

8. The secondary battery according to any one of claims 7, wherein The volume distribution particle size Dv50 of the first carbon-based material is smaller than the volume distribution particle size Dv50 of the second carbon-based material; Optionally, the volume distribution particle size Dv50 of the second carbon-based material is 13 μm-19 μm, and more optionally 14 μm-18 μm.

9. The secondary battery according to claim 7 or 8, wherein: The powder compaction density of the second carbon-based material under a pressure of 50000N is 1.80g / cm 3 -2.05g / cm 3 , optional 1.85g / cm 3 -2.03g / cm 3 .

10. The secondary battery according to any one of claims 7 to 9, wherein: The surface of the second carbon-based material has no coating layer.

11. The secondary battery according to any one of claims 7 to 10, wherein: The second carbon-based material includes secondary particles of artificial graphite; optionally, the secondary particles of artificial graphite account for greater than or equal to 80% of the second carbon-based material.

12. The secondary battery according to any one of claims 7 to 11, wherein: The particle size distribution of the second carbon-based material satisfies (Dv90-Dv10) / Dv50≤1.25, which can be selected as 0.90-1.

25.

13. The secondary battery according to any one of claims 7 to 12, wherein: The gram capacity of the first carbon-based material is greater than the gram capacity of the second carbon-based material; Optionally, the gram capacity of the first carbon-based material is ≥355 mAh / g, and can further be 355 mAh / g-368 mAh / g; Optionally, the gram capacity of the second carbon-based material is 350 mAh / g-365 mAh / g, and further optionally 352 mAh / g-362 mAh / g.

14. The secondary battery according to any one of claims 7 to 13, wherein: The graphitization degree of the first carbon-based material is 95.0%, optionally 95.5%-98.0%; and / or, The graphitization degree of the second carbon-based material is 90.0%-95.5%, and can be optionally 92.0%-95.5%.

15. The secondary battery according to any one of claims 7 to 14, wherein: The specific surface area of ​​the first carbon-based material is 1.0 m 2 / g-2.8m 2 / g, optional 1.3m 2 / g-2.1m 2 / g; and / or, The specific surface area of ​​the second carbon-based material is 0.8 m 2 / g-2.0m 2 / g, optional 1.1m 2 / g-1.7m 2 / g.

16. The secondary battery according to any one of claims 1 to 15, wherein: The first carbon-based material satisfies at least one of the following: (1) The first carbon-based material satisfies: (Dv90-Dv10) / Dv50≤1.40, which can be 0.90-1.40; (2) The powder compaction density of the first carbon-based material under a pressure of 50,000 N is 1.75 g / cm 3 -2.0g / cm 3 , optional 1.80g / cm 3 -1.98g / cm 3 ; (3) The tap density of the first carbon-based material is 0.90-1.30 g / cm 3 , optionally 0.95-1.25g / cm 3 ; (4) The volume distribution particle size Dv90 of the first carbon-based material is 13 μm-30 μm, optionally 16 μm-23 μm.

17. The secondary battery according to any one of claims 7 to 16, wherein: The second carbon-based material satisfies at least one of the following: (1) The tap density of the second carbon-based material is 0.85-1.25 g / cm 3 , optional: 0.90-1.15g / cm 3 ; (2) The second carbon-based material satisfies 0.050≤I D / I G ≤0.300, optionally, 0.070≤I D / I G ≤0.200, I D Indicates that the Raman spectrum is at 1350±50cm -1 The D peak intensity at I G Indicates that the Raman spectrum is at 1580±50cm -1 The G peak intensity at .

18. The secondary battery according to any one of claims 7 to 17, wherein: The first negative electrode active material and / or the second negative electrode active material also include a silicon-based material; optionally, the mass proportion of the silicon-based material in the first negative electrode active material is less than or equal to 10%, optionally 5%-10%, and / or the mass proportion of the silicon-based material in the second negative electrode active material is less than or equal to 10%, optionally 5%-10%.

19. The secondary battery according to any one of claims 1 to 18, wherein: The negative electrode film layer satisfies at least one of the following: (1) The compaction density of the negative electrode film layer is ≤1.85 g / cm 3 , optionally 1.45-1.75 g / cm 3 ; (2) The porosity of the negative electrode film layer is 18.0%-38.0%, optionally 19.0%-34.0%; (3) The OI value of the negative electrode film layer is ≤30.0, and can be optionally 8.0-23.0; (4) The thickness of the negative electrode film layer is greater than or equal to 40 μm, and can be optionally 40 μm-140 μm.

20. An electrical device comprising the secondary battery according to any one of claims 1 to 19.

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