Secondary battery and power-consuming device

Abstract

This application provides a secondary battery and an electrical device. The secondary battery includes a negative electrode sheet, which includes a negative current collector and a negative electrode film layer located on at least one surface of the negative current collector. The negative electrode film layer has a first surface away from the negative current collector and a second surface disposed opposite to the first surface. The thickness of the negative electrode film layer is denoted as H. A region extending from the first surface of the negative electrode film layer to a thickness of 0.3H is denoted as a first region, which includes a first negative electrode active material. The first negative electrode active material includes a first carbon-based material, and the first carbon-based material satisfies the condition that the total pore area S1 of the outer region is less than the total pore area S2 of the inner region. The secondary battery has improved kinetic performance, and the volumetric particle size Dv50 of the first carbon-based material is less than or equal to 15 μm.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more particularly to a secondary battery and an electrical device. Background Technology

[0002] In recent years, rechargeable batteries have been widely used in energy storage systems for hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. With the increasingly widespread application of rechargeable batteries, significant challenges have been placed on their performance. For example, in electric devices, the rapid charge and discharge performance of rechargeable batteries is becoming increasingly important. Therefore, better kinetic performance is required for rechargeable batteries. Summary of the Invention

[0003] This application is made in view of the above-mentioned problems, and its object is to provide a secondary battery and an electrical device. The secondary battery described herein has improved kinetic performance.

[0004] To achieve the above objectives, a first aspect of this application provides a secondary battery. The secondary battery includes a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative electrode film layer located on at least one surface of the negative current collector, the negative electrode film layer having a first surface away from the negative current collector and a second surface disposed opposite to the first surface, the thickness of the negative electrode film layer being denoted as H;

[0005] The region extending from the first surface of the negative electrode film to a thickness of 0.3H is denoted as the first region of the negative electrode film. The first region includes a first negative electrode active material, which includes a first carbon-based material. The volume distribution particle size Dv50 of the first carbon-based material is denoted as D. The first carbon-based material includes an outer region and an inner region located inside the outer region. The outer region refers to the region formed by extending 0.25D from the particle surface of the first carbon-based material into the particle interior. In the cross-sectional view of the first carbon-based material, the total pore area of ​​the outer region is denoted as S1, and the total pore area of ​​the inner region is 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 15μm.

[0006] In this application, when the first carbon-based material as defined above is arranged at least on the side of the negative electrode film layer away from the negative electrode current collector of the negative electrode sheet, the kinetic characteristics of the first carbon-based material can be utilized, thereby improving the kinetic performance of the secondary battery.

[0007] According to some embodiments, the volumetric particle size Dv50 of the first carbon-based material is 7 μm-13 μm. When the volumetric particle size Dv50 of the first carbon-based material is within the above range, it is further beneficial to improve the kinetic performance of the secondary battery.

[0008] According to some embodiments, the first carbon-based material satisfies 1.5≤S2 / S1≤500, and optionally, 2.5≤S2 / S1≤450.

[0009] 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 The option is 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 optionally includes one or more pores with an area of ​​0.15-2.00 μm. 2 The porous structure of the first carbon-based material particles is such that the outer region of the particles is denser than the inner region. This has several advantages: firstly, it increases the compaction density of the negative electrode film, thereby improving the energy density of the secondary battery; secondly, it allows for sufficient and stable expansion space for volume changes in the first carbon-based material particles, reducing the risk of particle breakage, minimizing electrolyte ingress into the particles, thus reducing side reactions and the consumption of active ions, further enhancing the storage performance of the secondary battery. Additionally, it increases the compaction density of the negative electrode film.

[0010] According to some embodiments, at least a portion of the surface of the first carbon-based material has a carbon coating layer. When at least a portion of the surface of the first carbon-based material has a carbon coating layer, the kinetic 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 layer.

[0011] According to some embodiments, the first carbon-based material comprises primary particles. Optionally, the primary particles account for ≥80% of the first carbon-based material. When the first carbon-based material exists primarily in the form of primary particles, it is beneficial to the kinetic performance of the secondary battery.

[0012] According to some embodiments, a region extending from the second surface of the negative electrode film to a thickness of 0.3H is designated as the second region of the negative electrode film. This second region is disposed between the negative electrode current collector and the first region. The second region includes a second negative electrode active material, which comprises a second carbon-based material. In these embodiments, the second region of the negative electrode film is located close to the negative electrode current collector. 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. Furthermore, the properties of the second carbon-based material can be used to improve other secondary battery performance aspects, such as energy density.

[0013] Optionally, the second carbon-based material includes artificial graphite. Arranging artificial graphite at least in the second region does not significantly affect the kinetic performance of the secondary battery, while simultaneously improving the energy density of the secondary battery due to the good powder compaction density of artificial graphite. Furthermore, due to the easily deformable nature of artificial graphite under cold pressing, when arranged in the lower layer of the negative electrode film, it can effectively reduce the rolling pressure on the electrode sheet, minimizing damage to the carbon-based material, thereby benefiting the cycle life of the secondary battery.

[0014] According to some embodiments, the volumetric particle size Dv50 of the first carbon-based material is smaller than that of the second carbon-based material. Optionally, the volumetric particle size Dv50 of the second carbon-based material is 13 μm-19 μm, and more preferably 14 μm-18 μm. When the second carbon-based material has a larger particle size than the first carbon-based material, the powder compaction density can be increased, thereby increasing the compaction density difference between the upper and lower layers of the negative electrode film and improving the kinetic performance of the secondary battery.

[0015] According to some embodiments, the compacted density of the second carbon-based material powder under a pressure of 50,000 N is 1.80 g / cm³. 3 -2.05g / cm 3 The option is 1.85g / cm³. 3 -2.03g / cm 3 The compacted density of the second carbon-based material powder is within the above range, which is beneficial to improving the energy density of the secondary battery.

[0016] 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 provided on the surface of the second carbon-based material, it will affect the powder compaction density. Therefore, not having a coating layer is more advantageous for the energy density of the secondary battery.

[0017] According to some embodiments, the second carbon-based material includes artificial graphite in the form of secondary particles. Optionally, the proportion of the artificial graphite in the secondary particles 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, the isotropy of the negative electrode sheet can be improved, thereby further benefiting the kinetic performance of the secondary battery. In particular, when the second carbon-based material is mainly in the form of secondary particles, the kinetic performance of the secondary battery can be improved.

[0018] According to some embodiments, the particle size distribution of the second carbon-based material satisfies (Dv90-Dv10) / Dv50≤1.25, and can be selected as 0.90-1.25. When the particle size distribution of the second carbon-based material is narrower, it is beneficial to improve the energy density of the secondary battery while taking into account the kinetic performance.

[0019] According to some embodiments, the specific capacity of the first carbon-based material is greater than that of the second carbon-based material. Optionally, the specific capacity of the first carbon-based material is ≥355 mAh / g, and can be selected as 355 mAh / g-368 mAh / g. Optionally, the specific capacity of the second carbon-based material is 350 mAh / g-365 mAh / g, and can be selected as 352 mAh / g-362 mAh / g. The high specific capacity of the first and second carbon-based materials can jointly improve the energy density of the secondary battery.

[0020] According to some embodiments, 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%, optionally 92.0%-95.5%. Higher graphitization degrees in both materials are beneficial for improving the energy density of the secondary battery.

[0021] According to some embodiments, the specific surface area of ​​the first carbon-based material is 1.0 m². 2 / g-2.8m 2 / g, can be selected as 1.3m 2 / g-2.1m 2 / g; and / or, the specific surface area of ​​the second carbon-based material is 0.8m². 2 / g-2.0m 2 / g, can be selected as 1.1m 2 / g-1.7m 2 / g. A suitable specific surface area is beneficial to the kinetic performance of secondary batteries.

[0022] According to some embodiments, the first carbon-based material satisfies at least one of the following:

[0023] (1) The first carbon-based material satisfies: (Dv90-Dv10) / Dv50≤1.40, which can be selected as 0.90-1.40;

[0024] (2) The compacted density of the first carbon-based material under a pressure of 50,000 N is 1.75 g / cm³. 3 -2.00g / cm 3 1.80g / cm³ is an optional value. 3 -1.98g / cm 3 ;

[0025] (3) The tap density of the first carbon-based material is 0.90-1.30 g / cm³. 3 The optional concentration is 0.95-1.25 g / cm³. 3 ;

[0026] (4) The volume distribution particle size Dv90 of the first carbon-based material is 13μm-30μm, and optionally 16μm-23μm.

[0027] According to some embodiments, the second carbon-based material satisfies at least one of the following:

[0028] (1) The tap density of the second carbon-based material is 0.85-1.25 g / cm³. 3 The selectable value is 0.90-1.15 g / cm³. 3 ;

[0029] (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 This indicates that the Raman spectrum is at 1350±50 cm⁻¹ -1 The intensity of peak D at I G This indicates that the Raman spectrum is at 1580±50 cm⁻¹. -1 The intensity of the G peak at that location.

[0030] According to some embodiments, the first negative electrode active material and / or the second negative electrode active material further include silicon-based materials; optionally, the mass percentage of the first negative electrode active material is less than or equal to 10%, which can be 5%-10%, and / or the mass percentage of the second negative electrode active material is less than or equal to 10%, which can be 5%-10%.

[0031] According to some embodiments, the negative electrode film layer satisfies at least one of the following:

[0032] (1) The compaction density of the negative electrode film is ≤1.85 g / cm³.3 The optional value is 1.45-1.75 g / cm³. 3 ;

[0033] (2) The porosity of the negative electrode film is 18.0%-38.0%, optionally 19.0%-34.0%;

[0034] (3) The OI value of the negative electrode film is ≤30.0, and optionally 8.0-23.0;

[0035] (4) The thickness of the negative electrode film is ≥40μm, and optionally 40μm-140μm.

[0036] A second aspect of this application provides an electrical device. The electrical device includes any 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 rate. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of one embodiment of the negative electrode sheet of this application.

[0038] Figure 2 This is a schematic diagram of a cross-sectional image of the particles of the first carbon-based material of this application.

[0039] Figure 3 This is an ion-polished cross-section (CP) diagram of one embodiment of the first carbon-based material of this application.

[0040] Figure 4 A schematic diagram of one embodiment of the negative electrode sheet of this application.

[0041] Figure 5 This is a schematic diagram of another embodiment of the negative electrode sheet of this application.

[0042] Figure 6 This is a schematic diagram of another embodiment of the negative electrode sheet of this application.

[0043] Figure 7 This is a schematic diagram of a battery cell according to one embodiment of this application.

[0044] Figure 8 yes Figure 7 An exploded view of a battery cell according to one embodiment of this application is shown.

[0045] Figure 9 This is a schematic diagram of a battery module according to one embodiment of this application.

[0046] Figure 10 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0047] Figure 11 yes Figure 10 An exploded view of a battery pack according to one embodiment of this application is shown.

[0048] Figure 12 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0049] Explanation of reference numerals in the attached figures:

[0050] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly; 10 Negative electrode sheet; 101 Negative current collector; 102 Negative electrode film; 102a First surface; 102b Second surface; 1021 First region; 1022 Second region; 1023 Intermediate region; 200 First carbon-based material; 201 External region; 202 Internal region. Detailed Implementation

[0051] The embodiments of the secondary battery and power-consuming device of this application are hereby disclosed in detail with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0052] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0053] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0054] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0055] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0056] Unless otherwise specified, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0057] Unless otherwise specified, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, such as the testing methods provided in this application.

[0058] Unless otherwise specified, in this application, the term "active ion" refers to ions that can be inserted and extracted back and forth between the positive and negative electrodes of a secondary battery, including but not limited to lithium ions.

[0059] With the widespread application of rechargeable batteries, higher demands are being placed on their charging speed, i.e., their kinetic performance. However, the key to improving the kinetic performance of rechargeable batteries, especially their fast-charging performance, lies in enhancing the kinetic performance of the negative electrode by reducing the areal density or compaction density of the negative electrode film. However, numerous studies have shown that these methods only improve the battery's kinetic performance to a certain extent, while significantly reducing the energy density of the rechargeable battery.

[0060] Therefore, it is currently difficult for secondary batteries to achieve both improved kinetic performance and high energy density.

[0061] In view of this, a first aspect of the present application provides a secondary battery. This secondary battery improves its kinetic performance through the design of the negative electrode. According to a further embodiment, the secondary battery also achieves good energy density.

[0062] The term "secondary battery" as used in this article refers to a single battery cell, battery module, or battery pack.

[0063] Typically, a single secondary battery cell includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0064] [Negative electrode plate]

[0065] The secondary battery of this application includes a negative electrode sheet, which includes a negative current collector and a negative electrode film layer located on at least one surface of the negative current collector. The negative electrode film layer has a first surface away from the negative current collector and a second surface disposed opposite to the first surface. The thickness of the negative electrode film layer is denoted as H. The region from the first surface of the negative electrode film layer to a thickness of 0.3H is denoted as the first region of the negative electrode film layer. The first region includes a first negative electrode active material, which includes a first carbon-based material. The volume distribution particle size Dv50 of the first carbon-based material is denoted as D. The first carbon-based material includes an outer region and an inner region located inside the outer region. The outer region refers to the region formed by extending a distance of 0.25D from the particle surface of the first carbon-based material into the particle interior. In the cross-sectional view of the first carbon-based material, the total pore area of ​​the outer region is denoted as S1, and the total pore area of ​​the inner region is denoted 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.

[0066] See Figure 1 The diagram illustrates one embodiment of the negative electrode sheet of this application. Figure 1 As shown, in this embodiment, the negative electrode 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 disposed opposite to the first surface 102a. The thickness of the negative electrode film layer 102 is denoted as H. The region from the second surface 102b of the negative electrode film layer to a thickness range of 0.3H is denoted as the first region 1021 of the negative electrode film layer. The negative electrode film layer region outside the first region 1021 with a thickness range of 0.7H is denoted as the remaining region 1020. The thickness H of the negative electrode film layer refers to the thickness of the negative electrode film layer located on one side of the negative electrode current collector.

[0067] 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 sheet of this application 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 is not in direct contact with the negative electrode current collector 101.

[0068] In the described embodiment, a first carbon-based material is disposed in a 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 regions 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 regions 1020 adjacent to the first region 1021. Exemplarily, the first carbon-based material is also present in at least a portion of the remaining regions 1020 adjacent to the first region 1021, for example, the first carbon-based material is present in the region of the remaining regions 1020 adjacent to the first region 1021.

[0069] In this application, 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. Furthermore, the first carbon-based material in this application satisfies "S2>S1", meaning 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 at 1000x magnification). That is, the outer region of the main structure of the first carbon-based material has a smaller pore area.

[0070] refer to Figure 2 The diagram shows a schematic cross-sectional image of particles of the first carbon-based material 200 of this application, with the cross-sectional image passing through the center of the particles of the first carbon-based material 200. Figure 2 As shown, D represents the volume distribution particle size Dv50 of the first carbon-based material 200 particles. The region formed by extending 0.25D from the surface of the first carbon-based material 200 particles into the particle interior is denoted as the outer region 201, and the region inside the outer region 201 is denoted as the inner region 202.

[0071] The pore structure within the first carbon-based material can be observed using a cross-section polishing instrument, for example, by testing the ion-polished cross-sectional morphology (CP) of the negative electrode sheet. Specifically, the negative electrode sheet is cut into a sample of a certain size (e.g., 2cm × 2cm), and fixed on the sample stage using paraffin wax; the sample stage is installed and locked in place on the sample holder, the power of the argon ion cross-section polishing instrument (e.g., the IB-09010 CP type argon ion cross-section polishing instrument from JEOL Corporation of Japan) is turned on and a vacuum is drawn (e.g., 10⁻⁴ Pa), the argon flow rate (e.g., 0.15MPa), voltage (e.g., 8KV), and polishing time (e.g., 2h) are set, and the sample stage is adjusted to swing mode to begin polishing; a region in the first region 1021 of the sample is randomly selected for scanning testing (e.g., referring to JY / T010-1996, scanning is performed using a scanning electron microscope), and the ion-polished cross-sectional morphology (CP) image of the negative electrode sheet is obtained at a certain magnification (e.g., 1000x). 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 other negative electrode active materials. Figure 3 This is an ion-polished cross-section (CP) diagram of an embodiment of the first carbon-based material of this application. As can be seen from the diagram, the outer region of the second carbon-based material particles is denser than the inner region, satisfying S2>S1.

[0072] The electrode design of this application employs a first carbon material with a specific structure in the upper layer. This carbon material particles have a porous structure, with the pore area in the internal region being larger than that in the external region, thus exhibiting better storage performance. The smaller pore area in the external region indicates a higher density near the material surface, effectively reducing side reactions on the particle surface. Simultaneously, the larger pore area in the internal region provides sufficient space to effectively alleviate stress caused by material expansion during battery cycling, thereby enhancing the battery's cycle performance. Furthermore, when this material has a smaller particle size and is arranged in the first region of the negative electrode film layer, it can improve the battery's kinetic performance. Therefore, the secondary battery provided by this application, while possessing good storage and cycle performance, further improves kinetic performance.

[0073] According to some embodiments, the volumetric particle size distribution Dv50 of the first carbon-based material is 7 μm-13 μm. For example, the volumetric particle size distribution 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 volumetric particle size distribution Dv50 of the first carbon-based material is within the above range, it further facilitates the improvement of the kinetic performance of the secondary battery.

[0074] According to some embodiments, the first carbon-based material satisfies 1.5 ≤ S2 / S1 ≤ 500, and optionally, 2.5 ≤ S2 / S1 ≤ 450. For example, 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 ranges, the storage performance and cycle performance of the battery can be further improved.

[0075] 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 The option is 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 optionally includes one or more pores with an area of ​​0.15-2.0 μm. 2 The pore structure of the first carbon-based material, with its external region exhibiting the aforementioned pore size, reflects the relatively dense external region of the material particles and the small porosity of the pore structure. This structure makes it difficult for electrolyte to penetrate the particles, thus reducing side reactions between the first carbon-based material and the electrolyte. Furthermore, a pore structure with a specific pore area in the first carbon-based material can, on the one hand, provide sufficient and stable expansion space for volume changes in the first carbon-based material particles, and on the other hand, increase the compaction density of the negative electrode film, thereby improving the storage performance, cycle performance, and energy density of the secondary battery.

[0076] According to some embodiments, at least a portion of the surface of the first carbon-based material has a carbon coating layer. When at least a portion of the surface of the first carbon-based material has a carbon coating layer, it facilitates the rapid migration of active ions, thereby further improving the kinetic performance of the secondary battery. Typically, the carbon coating layer can be an amorphous carbon coating layer. According to a specific embodiment, the entire surface of the first carbon-based material has a carbon coating layer.

[0077] The terms "coating" or "carbon coating" used herein have the same meaning as those used in the art. They generally refer to coating a negative electrode active material, such as natural graphite particles, with a layer of carbon source material (e.g., pitch), followed by heat treatment to form a carbon coating layer. This application does not impose any particular limitation on the thickness of the carbon coating layer; conventional coating thicknesses can be used in the described embodiments.

[0078] According to some embodiments, the first carbon-based material comprises primary particles. When the first carbon-based material exists primarily in the form of primary particles, it facilitates the transport of active ions, thereby improving the kinetic performance of the secondary battery. In some embodiments, the primary particles account for ≥80% of the first carbon-based material, optionally ≥85%, and further optionally ≥90%. In some specific embodiments, the first carbon-based material is entirely composed of primary particles.

[0079] In some embodiments, the specific capacity of the first carbon-based material is ≥355 mAh / g, optionally between 355 mAh / g and 368 mAh / g. For example, the specific capacity of the first carbon-based material is 355 mAh / g, 360 mAh / g, 363 mAh / g, 365 mAh / g, 367 mAh / g, etc., or any value between two of these. A higher specific capacity is beneficial to the capacity density of the secondary battery.

[0080] In some embodiments, the graphitization degree of the first carbon-based material is ≥95.0%, optionally 95.5%-98.0%. For example, the graphitization degree of the first carbon-based material is 95.0%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, etc., or any value between two such values. A higher graphitization degree is beneficial for powder compaction, thereby improving the energy density of the secondary battery.

[0081] In some embodiments, the specific surface area of ​​the first carbon-based material is 1.0 m². 2 / g-2.8m 2 / g, can be selected as 1.3m 2 / g-2.1m 2 / g. For example, the specific surface area of ​​the first carbon-based material is 1.1 m². 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, or any value between two values. A larger specific surface area further contributes to improving the kinetic performance of the secondary battery.

[0082] According to some embodiments, when the first carbon-based material satisfies at least one of the following, it is beneficial to at least one of the following properties of the secondary battery: kinetic performance, energy density, and cycle performance.

[0083] (1) The first carbon-based material satisfies: (Dv90-Dv10) / Dv50≤1.40, which can be selected as 0.90-1.40.

[0084] (2) The compacted density of the first carbon-based material under a pressure of 50,000 N is 1.75 g / cm³. 3 -2.0g / cm 3 The option is 1.82g / cm³. 3 -1.98g / cm 3 .

[0085] (3) The tap density of the first carbon-based material is 0.90-1.30 g / cm³. 3 The optional concentration is 0.95-1.25 g / cm³. 3 .

[0086] (4) The volume distribution particle size Dv90 of the first carbon-based material is 13.0μm-30.0μm, and optionally 16.0μm-23.0μm.

[0087] According to some embodiments, a region extending from the second surface of the negative electrode film to a thickness of 0.3H is referred to as the second region of the negative electrode film. The second region is disposed between the negative electrode current collector and the first region. The second region includes a second negative electrode active material, which includes a second carbon-based material.

[0088] In the described embodiment, the second region of the negative electrode film is located close to the negative electrode current collector (when the negative electrode current collector is used as the base layer, it is also called the lower layer of the negative electrode film). Arranging a second carbon-based material different from the first carbon-based material in this region will not significantly affect the kinetic performance of the secondary battery, and at the same time, the characteristics of the second carbon-based material can be used to improve other performance aspects of the secondary battery, such as energy density.

[0089] In some specific embodiments, the second carbon-based material includes artificial graphite. Compared to other carbon-based materials, such as soft carbon, hard carbon, and natural graphite, artificial graphite has insufficient kinetic properties. Arranging artificial graphite in the second region 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.

[0090] In the aforementioned embodiment, the first carbon-based material is mainly arranged in the first region of the negative electrode film layer, and the second carbon-based material, including artificial graphite, is mainly arranged in the second region of the negative electrode film layer. The combination of the two enables the secondary battery to improve its dynamic performance while taking into account its energy density and cycle performance.

[0091] More specifically, the first carbon-based material in the first region exhibits excellent kinetic properties, which can significantly improve the charging speed, especially in the early stages of charging (such as the first 50% of the capacity after charging begins). Furthermore, 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. The upper layer, mainly composed of the first carbon-based material, has a lower density than the lower layer, which is mainly composed of artificial graphite. This provides more migration channels for active ions, facilitating their migration to the lower layer of the negative electrode film and further contact with the second carbon-based material. This also helps to improve the charging speed in the later stages of charging (such as the last 50% of the capacity after charging begins).

[0092] Compared to reducing the compaction density of the negative electrode film to improve the kinetic performance of the negative electrode, or increasing the compaction density of the negative electrode film to improve the energy density, the above-described embodiment can improve the kinetic performance of the secondary battery while also taking into account the energy density.

[0093] Furthermore, the stable structure of artificial graphite contributes to the cycle life of secondary batteries.

[0094] See further Figures 4 to 6 The diagram illustrates three different embodiments of a negative electrode sheet having a first region and a second region, with different negative electrode active materials present in these two regions. Figures 4 to 6 As shown, with Figure 1 Similarly, the negative electrode 10 includes a negative current collector 101 and a negative electrode film 102 formed on at least one surface of the negative current collector 101. The negative electrode film 102 has a first surface 102a away from the negative current collector 101 and a second surface 102b disposed opposite to the first surface 102a. The thickness of the negative electrode film 102 is H. On the side away from the negative current collector 101, the region from the second surface 102b of the negative electrode film to a thickness of 0.3H is designated as the first region 1021 of the negative electrode film. On the side close to the negative current collector 101, the region from the first surface 102a of the negative electrode film to a thickness of 0.3H is designated 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 occupying a thickness range of 0.4H between the first region 1021 and the second region 1022 is designated as the intermediate region 1023. It is easy to understand that, according to... Figures 4 to 7 The intermediate region 1023 contains at least one of a first carbon-based material and a second carbon-based material.

[0095] 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 The diagram shows that the thickness of each of the two layers accounts for approximately half the thickness of the negative electrode film layer 102. Figure 5 The diagram shows that the thickness of the second carbon-based material accounts for approximately 70% of the thickness of the negative electrode film 102, while the thickness of the first carbon-based material accounts for approximately 30% of the thickness of the negative electrode film 102. Figure 6 It shows the relationship with Figure 5 In the opposite configuration, the thickness of the first carbon-based material accounts for approximately 70% of the thickness of the negative electrode film 102, while the thickness of the second carbon-based material accounts for approximately 30% of the thickness of the negative electrode film 102.

[0096] It should be understood that, Figures 4 to 6 The diagram shown is a schematic representation of an ideal scenario. This application does not impose any particular limitation on the thickness ratio of the first carbon-based material and the second carbon-based material; for example, they can be in the range of 3:7 to 7:3. Exemplary examples include thickness ratios of 4:6, 5:5, 6:4, etc., or any ratio between two such ratios.

[0097] It should also be understood that, Figures 4 to 6 The intermediate region 1023 appears to have a clear boundary with the other two regions, but in reality, no such clear interface exists. As mentioned earlier, both the first carbon-based material and the second carbon-based material may coexist within the intermediate region 1023. Similarly, there is no clear interface between the coating containing the first carbon-based material and the coating containing the second carbon-based material.

[0098] According to some embodiments, the volumetric particle size Dv50 of the first carbon-based material is smaller than that of the second carbon-based material. Specifically, the volumetric particle size Dv50 of the second carbon-based material is 13 μm-19 μm, and more preferably 14 μm-18 μm. The volumetric particle size Dv50 of the second carbon-based material is 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, etc., or any value between two of these values. When the second carbon-based material has a larger particle size than the first carbon-based material, its adverse effects on the kinetic performance of the secondary battery can be minimized.

[0099] According to some embodiments, the second carbon-based material, particularly 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 The option is 1.85g / cm³. 3 -2.03g / cm 3 For example, the compacted density of the second carbon-based material powder under a pressure of 50,000 N is 1.80 g / cm³.3 1.85g / cm 3 1.90g / cm 3 1.95g / cm 3 2.00g / cm 3 2.05g / cm 3 The value is either a value within the range of any two values ​​described. A second carbon-based material with high powder compressibility, arranged in the lower layer of the negative electrode film, is beneficial for improving the energy density of the secondary battery.

[0100] According to some embodiments, the second carbon-based material includes artificial graphite with secondary particles. Optionally, the proportion of artificial graphite with secondary particles in the second carbon-based material is greater than or equal to 80%. When the second carbon-based material includes artificial graphite with secondary particles, during cold pressing, the individual primary particles in the secondary particles are less likely to change their crystal orientation due to pressure. Therefore, compared to using only primary particles, using secondary particles can effectively reduce the tendency of the crystal orientation of artificial graphite to be parallel to the negative electrode current collector during cold pressing, thereby shortening the insertion and extraction of active particles, which further benefits the kinetic performance of the secondary battery, especially improving the charging speed in the later stages of charging. In some specific embodiments, when the second carbon-based material is mainly in the form of secondary particles, or is entirely in the form of secondary particles, the kinetic performance of the secondary battery can be improved.

[0101] According to some embodiments, the particle size distribution of the second carbon-based material satisfies (Dv90-Dv10) / Dv50 ≤ 1.25, and can be optionally 0.90-1.25. For example, the particle size distribution of the second carbon-based material satisfies (Dv90-Dv10) / Dv50 as 0.9, 1, 1.1, 1.2, etc., or any value within a range of two such values. When the particle size distribution of the second carbon-based material is narrower, the number of larger particles decreases, which is more conducive to contact with active ions, thereby improving the energy density of the secondary battery while better considering kinetic performance.

[0102] According to some embodiments, the specific capacity of the first carbon-based material is greater than that of the second carbon-based material. In some embodiments, the specific capacity of the second carbon-based material is 350 mAh / g-365 mAh / g, optionally 352 mAh / g-362 mAh / g. For example, the specific capacity of the second carbon-based material is 352 mAh / g, 355 mAh / g, 358 mAh / g, 360 mAh / g, 362 mAh / g, etc., or a value within a range of any two values. The higher specific capacity of the first and second carbon-based materials can jointly improve the energy density of the secondary battery.

[0103] According to some embodiments, the graphitization degree of the first carbon-based material is greater than that of the second carbon-based material. In some embodiments, the graphitization degree of the second carbon-based material is 90.0%-95.5%, optionally 92%-95.5%. Exemplarily, the graphitization degree of the second carbon-based material is 92%, 92.5%, 93%, 93.5%, 94%, 94.5%, 95%, 95.5%, etc., or a value within a range of any two values. A higher graphitization degree is beneficial for powder compaction, thereby improving the energy density of the secondary battery.

[0104] According to some embodiments, the specific surface area of ​​the first carbon-based material is greater than that of the second carbon-based material. In some embodiments, the specific surface area (BET) of the second carbon-based material is 0.8 m². 2 / g-2m 2 / g, can be selected as 1.1m 2 / g-1.7m 2 / g. For example, the specific surface area (BET) of the second carbon-based material is 1.0 m². 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 / g, or any value within a range of two values. Controlling the specific surface area of ​​the second carbon-based material to be small is beneficial for reducing side reactions and further improving the cycle performance of the secondary battery.

[0105] According to some embodiments, the second carbon-based material can further improve the energy density of the secondary battery when it satisfies at least one of the following conditions.

[0106] (1) The tap density of the second carbon-based material is 0.85-1.25 g / cm³. 3 The selectable value is 0.90-1.15 g / cm³. 3 ;

[0107] (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 This indicates that the Raman spectrum is at 1350±50 cm⁻¹ -1 The intensity of peak D at I G This indicates that the Raman spectrum is at 1580±50 cm⁻¹. -1The intensity of the G peak at that location.

[0108] According to some embodiments, the negative electrode film layer further includes a silicon-based material. Optionally, the mass percentage of the silicon-based material in the negative electrode film layer is less than or equal to 10%, and can be selected as 5%-10%. Silicon-based materials have a higher lithium intercalation potential, which is beneficial for improving the kinetic performance of the secondary battery. Simultaneously, silicon-based materials have a high specific capacity, which is beneficial for improving the energy density of the secondary battery. However, silicon-based materials exhibit significant lithium intercalation expansion and low stability, which is detrimental to cycle performance; therefore, the amount added cannot be excessive. For example, the mass percentage of the silicon-based material in the negative electrode film layer is 3%, 5%, 6%, 8%, etc., or any value between two of these. The silicon-based material can be mixed with a first carbon-based material to serve as a first negative electrode active material, and / or the silicon-based material can be mixed with a second carbon-based material to serve as a second negative electrode active material.

[0109] This application does not impose any particular limitation on silicon-based materials; any silicon-based materials conventionally used as negative electrode active materials in the art may be used. For example, the silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys.

[0110] 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 substrate and a metal layer formed on at least one surface of the polymer substrate. 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 substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0111] In some embodiments, the negative electrode active material may further employ negative electrode active materials known in the art for use in batteries. As an example, the negative electrode active material may also include at least one of the following materials: natural graphite, soft carbon, hard carbon, tin-based materials, and lithium titanate, etc. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, this application is not limited to these materials, and 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 alone or in combination of two or more.

[0112] In some embodiments, the negative electrode film layer may optionally 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).

[0113] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0114] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0115] This application does not impose any particular limitation on the content of binders and / or other additives, if present, in the negative electrode film layer. Those skilled in the art can determine the appropriate content of binders and / or other additives through conventional testing in the relevant field.

[0116] According to some implementations, the negative electrode film layer satisfies at least one of the following conditions, which is beneficial to at least one of the kinetic performance, energy density, and cycle performance of the secondary battery.

[0117] (1) The compaction density of the negative electrode film is ≤1.85 g / cm³. 3 The optional value is 1.7-1.85 g / cm³. 3 This compaction density range is beneficial to the energy density of secondary batteries. For example, the compaction density of the negative electrode film is 1.7 g / cm³. 3 1.75g / cm 3 1.8g / cm 3 1.85g / cm 3 etc., or the value between any two numbers.

[0118] (2) The porosity of the negative electrode film is 18.0%-38.0%, optionally 19.0%-34.0%. Examples of porosity for the negative electrode film include 19%, 21%, 23%, 25%, 27%, 29%, 31%, 33%, etc., or any value between two of these ranges. Porosity within this range is beneficial for the migration of active ions, thereby improving the kinetic performance of the secondary battery.

[0119] (3) The OI value of the negative electrode film is ≤30.0, optionally 8.0-23.0. Examples of OI values ​​for the negative electrode film include 8, 10, 12, 14, 16, 18, 20, 22, etc., or any value between two of these. An OI value within this range reflects that the crystal orientation of the carbon-based material in the negative electrode film is not completely parallel to the negative electrode current collector, which helps to shorten the migration path of active ions and improves the kinetic performance of the secondary battery.

[0120] (4) The thickness of the negative electrode film is greater than or equal to 40 μm, and optionally 40-140 μm. Examples of the thickness of the negative electrode film include 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, etc., or any value between two such values, but not limited thereto.

[0121] The above embodiments are described using the composition of the negative electrode film layer on one surface of the negative electrode current collector as an example only. It should be understood that the negative electrode film layer described in the above embodiments can be disposed on either or both of the two surfaces of the negative electrode current collector that are opposite each other in its thickness direction. It should be noted that the negative electrode film layer parameters (e.g., compacted density, areal density, porosity, thickness, etc.) given in this application refer to the parameters of the negative electrode film layer on one side of the negative electrode current collector. When the negative electrode film layer is disposed on both sides of the negative electrode current collector, if the parameters of the negative electrode film layer on either side satisfy those of this application, it is considered to fall within the protection scope of this application.

[0122] In this application, the negative electrode sheet may include other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet may also include a conductive undercoat layer (e.g., composed of a conductive agent and an adhesive) sandwiched between the negative current collector and the negative electrode film layer and disposed on the surface of the negative current collector; in some embodiments, the negative electrode sheet may also include a protective layer covering the surface of the negative electrode film layer.

[0123] In this application, the pore area, S1, and S2 values ​​of the first carbon-based material can be obtained by using a cross-section polisher (e.g., the IB-09010 CP argon ion cross-section polisher from JEOL Corporation, Japan) to obtain the cross-section of the first carbon-based material; then, referring to JY / T010-1996, the cross-section of the first carbon-based material is scanned using a scanning electron microscope (e.g., the Sigma300 scanning electron microscope from ZEISS Corporation, Germany); finally, the pore area of ​​any pore in the first carbon-based material is obtained by image processing software (e.g., AVIZO); as well as the total pore area S1 of the outer region and the total pore area S2 of the inner region, and the value of S2 / S1 is obtained from this. For example, samples can be obtained from different regions of the negative electrode in a secondary battery. At least five locations (e.g., 5, 10, 15, or more) are randomly selected from the samples, and cross-sections are obtained using a cross-section polishing instrument. From the scanning electron microscope images of each cross-section, at least ten particles (e.g., 10, 20, 50, or more particles) are randomly selected for their cross-sections. Using image processing software as defined above, the total pore area S2' of the internal region and the total pore area S1' of the external region of each particle's cross-section are obtained, thus yielding the S2' / S1' value for each particle's cross-section. The arithmetic mean of S2' / S1' for all tested particle cross-sections is calculated as the S2 / S1 value of the first carbon-based material.

[0124] In the X-ray diffraction (XRD) analysis and testing of this application, a copper target can be used as the anode target, and CuKα rays can be used as the radiation source, with a wavelength of... The scanning 2θ angle range is 20°-80°, and the scanning rate is 4° / min.

[0125] In this application, the volumetric particle sizes Dv10, Dv50, and Dv90 of the materials (e.g., the first carbon-based material, the second carbon-based material, etc.) have meanings known in the art, representing the particle sizes corresponding to a cumulative volumetric distribution percentage of 10%, 50%, and 90%, respectively, and can be determined using instruments and methods known in the art. For example, they can be determined using a laser particle size analyzer, referring to GB / T19077-2016. The testing instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0126] In this application, the presence of a coating layer on the surface of a material (e.g., a first carbon-based material, a second carbon-based material, etc.) can be determined by transmission electron microscopy.

[0127] In this application, the specific surface area (BET) of a material (e.g., a first carbon-based material, a second carbon-based material, etc.) has a meaning known in the art and can be determined using instruments and methods known in the art. For example, it can be tested using the nitrogen adsorption specific surface area analysis method according to GB / T 19587-2017, and calculated using the BET (Brunauer Emmett Teller) method. The testing instrument can be the Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, USA.

[0128] In this application, the degree of graphitization of the materials (e.g., the first carbon-based material, the second carbon-based material) has a meaning known in the art and can be tested using instruments and methods known in the art. For example, it can be tested using an X-ray diffractometer (such as a Bruker D8 Discover), and the testing can be performed with reference to JIS K 0131-1996 and JB / T 4220-2011 to obtain the average interlayer spacing d of the C(002) crystal plane in the material's crystal structure. 002 Then, according to the formula g = (0.344 - d) 002 The degree of graphitization is calculated as d / (0.344-0.3354)×100%. In the above formula, d... 002 It is the average interlayer spacing of the C(002) crystal plane in the material crystal structure, expressed in nanometers (nm).

[0129] In this application, the specific capacity of materials (e.g., first carbon-based material, second carbon-based material, etc.) has a meaning known in the art and can be tested using methods known in the art. An exemplary testing method is as follows: Sample powder is mixed uniformly with conductive agent carbon black (Super P), binder polyvinylidene fluoride (PVDF) at a mass ratio of 91.6:1.8:6.6 and solvent N-methylpyrrolidone (NMP) to prepare a slurry; the prepared slurry is coated onto the surface of the negative electrode current collector copper foil and dried in an oven for later use; ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed at a volume ratio of 1:1:1 to obtain an organic solvent, and then LiPF6 is dissolved in the above organic solvent to prepare a solution with a concentration of 1 mol / L. The electrolyte was prepared; then, using a lithium metal sheet as the counter electrode and a polyethylene (PE) film as the separator, the CR2430 coin cell was assembled with the electrolyte in an argon-protected glove box. After the coin cell was left to stand for 12 hours, it was discharged at 25°C with a constant current of 0.05C to 0.005V, left to stand for 10 minutes, and then discharged again with a constant current of 50μA to 0.005V. After standing for 10 minutes, it was discharged again with a constant current of 10μA to 0.005V. Then, it was charged at a constant current of 0.1C to 2V, and the charging capacity was recorded. The ratio of the charging capacity to the sample mass is the specific capacity of the corresponding material (e.g., the first carbon-based material, the second carbon-based material, etc.).

[0130] In this application, the powder compaction density of materials (e.g., first carbon-based material, second carbon-based material, etc.) has a meaning known in the art and can be determined using instruments and methods known in the art. For example, it can be determined by referring to GB / T 24533-2009 using an electronic pressure testing machine (e.g., a UTM7305 type electronic pressure testing machine). An exemplary test method is as follows: Weigh 1g of sample powder and add it to a container with a bottom area of ​​1.327cm². 2 In the mold, the pressure is increased to 50,000 N, held for 30 seconds, then the pressure is released and held for 10 seconds. The compaction density of the powder under 50,000 N pressure is then recorded and calculated.

[0131] In this application, the tap density of materials (e.g., first carbon-based material, second carbon-based material, etc.) has a meaning known in the art and can be determined using instruments and methods known in the art. For example, it can be determined using a powder tap density tester according to GB / T 5162-2006. The testing instrument can be Dandong Baite BT-301, with the following testing parameters: vibration frequency 250±15 times / minute, amplitude 3±0.2mm, number of vibrations 5000 times, and a measuring cylinder of 25mL.

[0132] In this application, primary particles and secondary particles have meanings known in the art. Primary particles refer to non-agglomerated particles. Secondary particles refer to aggregated particles formed by the aggregation of primary particles. Primary particles and secondary particles can be distinguished using scanning electron microscopy (SEM) images.

[0133] In this application, the proportion of primary particles in the first carbon-based material and / or the second carbon-based material refers to: for example, taking a test sample randomly in the negative electrode film layer, taking multiple test areas randomly in the test sample, acquiring images of multiple test areas using a scanning electron microscope, and statistically analyzing the proportion of the number of primary particles in the first carbon-based material in each image to the total number of primary particles in the first carbon-based material. The average of the multiple statistical results is the proportion of primary particles in the first carbon-based material.

[0134] In this application, the percentage of secondary particles in the first carbon-based material and / or the second carbon-based material refers to: for example, taking a test sample randomly in the negative electrode film layer, taking multiple test areas randomly in the test sample, acquiring images of multiple test areas using a scanning electron microscope, and statistically analyzing the percentage of the number of secondary particles in the second carbon-based material in each image relative to the total number of particles in the second carbon-based material. The average of the multiple statistical results is the percentage of secondary particles in the second carbon-based material.

[0135] In this application, the areal density of the negative electrode film has a meaning known in the art and can be tested using methods known in the art. For example, a negative electrode sheet coated on one side and cold-pressed (if it is a double-sided coated negative electrode sheet, the negative electrode film layer on one side can be wiped off first) can be cut into small circular pieces with an area of ​​S', weighed, and recorded as M1. Then, the negative electrode film layer of the weighed negative electrode sheet is wiped off, and the weight of the negative electrode current collector is weighed and recorded as M0. The areal density of the negative electrode sheet = (M1-M0) / S'.

[0136] In this application, the compaction density of the negative electrode film has a meaning known in the art and can be tested using methods known in the art. [Compaction density of the negative electrode film = areal density of the negative electrode film / thickness of the negative electrode film].

[0137] In this application, the porosity of the negative electrode film layer has a meaning known in the art and can be determined using methods known in the art. An exemplary test method is as follows: Take a negative electrode sheet coated on one side and cold-pressed (if it is a double-sided coated negative electrode sheet, the negative electrode film layer on one side can be wiped off first), cut it into small circular samples of a certain area, and calculate the apparent volume V1 of the negative electrode sheet; referring to GB / T24586-2009, using an inert gas (such as helium or nitrogen) as the medium, employ the gas displacement method and use a true density meter 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 (e.g., 30 sheets) with good appearance and no powder shedding at the edges can be tested, and the average value of the results is taken, thereby improving the accuracy of the test results. The testing instrument can be a Micromeritics AccuPyc II 1340 true density meter.

[0138] In this application, the OI value of the negative electrode film has a meaning known in the art and can be tested using instruments and methods known in the art. For example, an X-ray diffractometer (such as a Bruker D8 Discover) can be used for testing, and the testing can be performed with reference to JIS K 0131-1996 and JB / T 4220-2011 to obtain the X-ray diffraction pattern of the negative electrode sheet. Based on the formula OI value = I... 004 / I 110 The OI value of the negative electrode film was calculated. 004 I is the integrated area of ​​the diffraction peaks of the crystalline carbon 004 crystal plane in the negative electrode film. 110 This represents the integrated area of ​​the diffraction peak on the 110 crystal plane of crystalline carbon in the negative electrode film. In the X-ray diffraction analysis of this application, a copper target can be used as the anode target, with CuKα rays as the radiation source, and the ray wavelength... The scanning 2θ angle range is 20°-80°, and the scanning rate is 4° / min.

[0139] The thickness of the negative electrode film layer is a term known in the art and can be measured using methods known in the art, such as a micrometer (e.g., a Mitutoyo 293-100 with an accuracy of 0.1 μm). The thickness range given in this application refers to the thickness range 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 is within the range given in this application, it satisfies the requirements of this application.

[0140] It should be noted that the above-mentioned tests on various parameters of the negative electrode active material or negative electrode film can be performed by sampling and testing from the prepared secondary battery according to the following steps.

[0141] The secondary battery is discharged (for safety, it is generally left fully discharged); after disassembling the secondary battery, the negative electrode is removed and soaked in dimethyl carbonate for a certain period of time (e.g., 2-10 hours); then the negative electrode is removed and dried at a certain temperature and time (e.g., 60°C for more than 4 hours), and then the negative electrode is removed. At this point, samples can be taken from the dried negative electrode to test the parameters related to the negative electrode film, such as the areal density, compaction density, porosity, and thickness of the negative electrode film.

[0142] The dried negative electrode sheet is baked at a certain temperature and time (e.g., 400℃ for more than 2 hours). A sample of the negative electrode active material is taken from a random area of ​​the baked negative electrode sheet (a blade can be used to scrape the powder for sampling). The collected negative electrode active material is sieved (e.g., sieved through 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.

[0143] In this application, the first carbon-based material can be prepared by the method described in this application; the second carbon-based material mentioned above can be obtained commercially, or can also be prepared by the method described in this application.

[0144] 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 a filler material uniformly according to a predetermined ratio, then holding it at a first temperature T1 for a first time t1, and then cooling it to room temperature to obtain an intermediate; step 3, holding the obtained intermediate at a second temperature T2 for a second time t2, and then obtaining the first carbon-based material.

[0145] In some embodiments, in step 1, the raw material used to prepare the first carbon-based material includes natural graphite. Optionally, natural graphite includes one or more of flake graphite, natural spherical graphite, and microcrystalline graphite, particularly natural spherical graphite.

[0146] "Natural spherical graphite" refers to natural graphite with a spherical or near-spherical shape, but not all natural graphite particles are controlled to be ideally spherical. In some embodiments, natural spherical graphite with the desired particle size and morphology can be obtained by pre-treating flake graphite. Optionally, the pre-treatment includes processes such as crushing, grading, spheroidizing, and purification.

[0147] In some embodiments, in step 1, the volume distribution particle size Dv50 of the above-mentioned raw material can be 6μm to 13μm.

[0148] In some embodiments, in step 1, the specific surface area of ​​the raw material may be ≥2.5m². 2 / g, optional 2.5m 2 / g~10.0m 2 / g. When the specific surface area of ​​the raw material is within the above range, it is beneficial for subsequent filling processing and obtaining 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 initial coulombic efficiency. In addition, it is beneficial for the first carbon-based material to have better kinetic performance.

[0149] In some embodiments, in step 2, the softening point temperature of the filler material is 90°C to 150°C. Optionally, the softening point temperature of the filler 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, or 104°C to 130°C.

[0150] 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 as 1 μm to 6 μm, 1 μm to 5 μm, 2 μm to 5 μm, or 3 μm to 5 μm. This is beneficial for the filler material to fill into the pore structure of the raw material after being heated and melted, and also helps to improve the dispersion uniformity of the filler material and the raw material.

[0151] In some embodiments, in step 2, the coking value of the filler material is 15% to 40%, optionally 18% to 34%. In this application, the coking value of the filler material has a meaning known in the art and can be measured using instruments and methods known in the art. For example, it can be measured with reference to GB / T 8727-2008.

[0152] In some embodiments, in step 2, the filler material includes one or more of coal tar pitch, petroleum pitch, polymer compounds and resins, and may optionally include one or more of coal tar pitch and petroleum pitch.

[0153] In some embodiments, in step 2, the mass ratio of the filler material to the raw material is (10-40):100, which can be (10-30):100, (10-25):100, (10-20):100, (12-30):100, (14-28):100, or (15-25):100.

[0154] In step 2, by adjusting one or more parameters such as the type of filler material, softening point, coking value, and amount added to be within the above range, it is beneficial to adjust the number and / or size of pores in the outer and inner regions of the first carbon-based material to be within a suitable range, and to adjust the S2 / S1 ratio of the first carbon-based material to be within a suitable range.

[0155] By adjusting parameters such as the type of filler material, softening point, coking value, and amount added to be within the above range, the filler material has low viscosity after being heated and melted, maintaining good fluidity. At the same time, it is not easy to stick to the raw material particles, which can reduce the agglomeration of raw material particles in subsequent preparation processes. This can also reduce problems such as increased surface defects and increased surface active sites of the first carbon-based material particles due to the need to add a deagglomeration process.

[0156] In some embodiments, the heating process in step 2, which involves uniformly mixing the raw materials and the filler materials in a predetermined ratio and then heating them to a first temperature T1, can be a staged heating process.

[0157] In some embodiments, the above-mentioned staged heating process includes a first heating process, a second heating process, and a third heating process.

[0158] In some embodiments, the first heating process described above involves heating to 200°C to 250°C and holding at that temperature for 0.5 h to 3 h.

[0159] In some embodiments, the second heating process described above involves heating to 450°C to 550°C and holding at that temperature for 0 to 2 hours. When the holding time is 0 hours, it indicates that when the temperature reaches the range of 450°C to 550°C, no holding process is performed, but the temperature continues to rise to the first temperature T1.

[0160] In some embodiments, the third heating process described above involves heating to the first temperature T1 and holding at that temperature for a first time t1.

[0161] 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 filler material, the filler material melts and softens upon heating. Holding at this temperature for 0.5h~3h allows it to flow and fill the pore structure of the raw material. Then, the temperature is raised to 450℃~550℃. At this point, the molten and softened filler material undergoes a carbonization reaction, gradually forming a semi-coke state, becoming a viscous liquid or solid, thereby preventing the filler material from entering all the pore structures of the raw material. Finally, the temperature is raised to the first temperature. At this point, the filler material undergoes a carbonization reaction, which allows the pore structure occupied by the filler material to be effectively filled.

[0162] In some embodiments, in step 2, the temperature is increased 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 of the above values. Optionally, the heating rate can be 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.

[0163] In some embodiments, the heating rate of the first heating process can be 1℃ / min to 10℃ / min, and can be selected as 1.5℃ / min to 8℃ / min, 1.5℃ / min to 6℃ / min, 2℃ / min to 6℃ / min, or 2℃ / min to 5℃ / min. In some embodiments, the heating rate of the second heating process can be 1℃ / min to 10℃ / min, and can be selected as 2℃ / min to 8℃ / min. In some embodiments, the heating rate of the third heating process can be 1℃ / min to 10℃ / min, and can be selected as 2℃ / min to 8℃ / min.

[0164] In some embodiments, in step 2, the first temperature T1 is 800℃ to 1200℃. For example, the first temperature T1 can be a range of 800℃, 850℃, 900℃, 950℃, 1000℃, 1050℃, 1100℃, 1200℃, or any of the above values. Optionally, the first temperature T1 is 800℃ to 1100℃, 850℃ to 1100℃, 900℃ to 1100℃, or 850℃ to 1000℃.

[0165] In some embodiments, in step 2, the first time t1 is 1h to 5h. For example, the first time t1 can be a range of 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, or any of the above values. Optionally, the first time t1 is 2h to 4h.

[0166] In some embodiments, in step 2, the heat treatment can be carried out in equipment capable of programmed temperature rise, such as an induction furnace, roller kiln, rotary kiln, pusher kiln, vertical granulation kettle, horizontal granulation kettle, vertical reactor, horizontal reactor, or drum furnace.

[0167] In some embodiments, in step 2, the heat treatment atmosphere may be a protective gas atmosphere. The protective gas may include one or more of nitrogen, argon, and helium.

[0168] In step 2, by adjusting one or more of the heating rate, first temperature, first time, heating process, etc., within the above range, it is beneficial to adjust the number and / or size of pores in the outer and inner regions of the first carbon-based material within a suitable range, thereby facilitating the adjustment of S2 / S1 of the first carbon-based material within a suitable range.

[0169] In some embodiments, in step 3, the first temperature T2 is 1600℃~2800℃. Optionally, the second temperature T2 is 1600℃~2700℃, 1600℃~2600℃, 1600℃~2500℃, 1600℃~2400℃, 1800℃~2600℃, 1800℃~2500℃, 1800℃~2400℃, 2000℃~2500℃, or 2000℃~2400℃.

[0170] In some embodiments, in step 3, the second time t2 is 1.5h to 6h. For example, the second time t1 can be a range of 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, or any of the above values. Optionally, the second time t2 is 2h to 5h.

[0171] In some embodiments, in step 3, the heat treatment described above can be carried out in an intermediate frequency furnace, a box-type graphitization furnace, an Atchison graphitization furnace, a continuous graphitization furnace, or an internal series graphitization furnace.

[0172] 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.

[0173] In step 3, by adjusting one or more of the second temperature and the second time within the aforementioned range, it is beneficial to adjust the content of disordered carbon in the first carbon-based material within a suitable range, and to ensure that the first carbon-based material has a suitable degree of graphitization, interlayer spacing, and Ig. D / I G wait.

[0174] In the above-mentioned method for preparing the first carbon-based material, by adjusting one or more of the parameters of natural graphite, the parameters of the filler material, the heating rate, the first temperature, the first time, the heating process, the second temperature, and the second time within the above-mentioned range, it is beneficial to adjust the parameters of the second carbon-based material such as S2 / S1, degree of graphitization, specific capacity, specific surface area, particle size, powder compaction density, and tap density.

[0175] 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 known in the art suitable for coating, for example, it may include one or more of coal tar pitch, petroleum asphalt, phenolic resin, coconut shell, etc. In some embodiments, the first carbon-based material mixed with the organic carbon source is carbonized at a third temperature T3 of 1150–1500°C for 1–3 hours to obtain a first carbon-based material with at least a partial carbon coating layer on its surface.

[0176] In some embodiments, the artificial graphite, as the second carbon-based material, can be prepared according to methods in the prior art. For example, it can be prepared using the following method.

[0177] The process involves 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 mixture, and finally sieving it to obtain a second carbon-based material.

[0178] 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 roller mill, and shaped using a shaping machine.

[0179] In some embodiments, the graphitization temperature is 2800℃-3200℃. By adjusting the graphitization temperature and / or graphitization time, it is beneficial for the second carbon-based material to have a suitable degree of graphitization.

[0180] In some embodiments, the organic carbon source may be a carbon-containing material known in the art suitable for coating, such as one or more of coal tar pitch, petroleum asphalt, phenolic resin, and coconut shell. Adjusting the amount of organic carbon source added facilitates the adjustment of parameters such as the specific surface area, degree of graphitization, and specific capacity of the second carbon-based material. The carbonization temperature can be 900℃-1300℃. Adjusting the carbonization temperature and / or the carbonization holding time facilitates the adjustment of parameters such as the specific surface area, degree of graphitization, and specific capacity of the second carbon-based material.

[0181] During the preparation process, adjusting one or more parameters of various equipment (such as mechanical mills or roller mills, shaping machines, granulators, etc.), raw material parameters, amount of organic carbon source added, amount of binder added, graphitization temperature, graphitization time, etc., can help regulate the graphitization degree, powder compaction density, specific capacity, particle size, specific surface area, and other parameters of the second carbon-based material.

[0182] To obtain artificial graphite with secondary particles, the precursor can be granulated using a binder asphalt before graphitization. The granulated product is then graphitized at 2800℃-3200℃ to obtain artificial graphite with secondary particles.

[0183] This application also provides a method for preparing the negative electrode sheet of this application. The method includes the following steps: providing a first negative electrode slurry containing the first negative electrode active material in the above embodiments and a second negative electrode slurry containing the second negative electrode active material in the above embodiments; coating the second negative electrode slurry onto a negative electrode current collector, coating the first negative electrode slurry onto the second negative electrode slurry, and obtaining the negative electrode sheet after drying and cold pressing.

[0184] In some embodiments, the first negative electrode slurry and the second negative electrode slurry may optionally include the conductive agent, binder, other optional additives and solvent (e.g., deionized water) described above.

[0185] The first and second slurries can be coated simultaneously in one step or in two separate steps. In some embodiments, the first and second slurries are coated simultaneously in one step. Simultaneous coating in one step can reduce the negative electrode film resistance, thereby further improving the kinetic and cycle performance of the secondary battery.

[0186] The coating weights of the first and second slurries can be adjusted according to actual conditions.

[0187] [Positive electrode plate]

[0188] The secondary battery in this application also includes a positive electrode sheet. The positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material. This application does not impose any particular limitation on the positive electrode sheet.

[0189] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0190] In some embodiments, the positive 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 substrate and a metal layer formed on at least one surface of the polymer substrate. 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 substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0191] In some embodiments, when the battery cell is a lithium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials 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 include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0192] During the charging and discharging process of a battery, active ions, such as Li, undergo insertion / extraction and consumption. The molar content of active ions, such as Li, varies depending on the battery's discharge state. In the examples of cathode materials in this application, the molar content of Li refers to the initial state of the material, i.e., the state before feeding. When the cathode material is applied to the battery system, the molar content of Li changes after charge-discharge cycles.

[0193] In the examples of cathode materials in this application, the molar content of O is only a theoretical value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of O will fluctuate.

[0194] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0195] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0196] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0197] [Electrolytes]

[0198] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0199] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0200] 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 difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0201] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0202] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0203] [Isolation membrane]

[0204] In some embodiments, the battery cell also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0205] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven 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.

[0206] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0207] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0208] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0209] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 7 The example shown is a square-structured battery cell 5.

[0210] In some implementations, refer to Figure 8 The outer packaging may include a housing 51 and a top cover assembly 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can cover the opening to close the receiving cavity. A positive electrode sheet, a negative electrode sheet, and a separator can be formed into an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in a single battery cell 5 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0211] In some implementations, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0212] Figure 9 This is battery module 4, used as an example. (See reference...) Figure 9 In battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0213] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0214] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0215] Figure 10 and Figure 11 This is battery pack 1 as an example. (See reference...) Figure 7 and Figure 8 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0216] Furthermore, a second aspect of this application provides an electrical device comprising the secondary battery described in the above embodiments. The secondary battery can be used as a power source for the electrical device or as an energy storage unit. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks), electric trains, ships and satellites, energy storage systems, etc.

[0217] As the electrical device, a single battery cell, a battery module, or a battery pack can be selected according to its usage requirements.

[0218] Figure 12 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0219] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0220] Example

[0221] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0222] The materials used in the embodiments of this application are prepared by the following process.

[0223] Preparation of Material 1-1:

[0224] Flake graphite was mechanically pulverized and spheroidized to obtain a volume distribution particle size (Dv50) of 12 μm. After purification, natural spherical graphite was obtained. The obtained natural spherical graphite was mixed with petroleum asphalt (softening point of petroleum asphalt is 110℃) at a ratio of 100:22. The mixture was then placed in a programmable temperature-controlled environment, heated to 200℃ and held for 1 hour, then further heated to 700℃ and held for 1 hour. After cooling to room temperature, an intermediate was obtained. The intermediate was placed in a graphitization furnace and subjected to graphitization heat treatment at 2510℃. After treatment, it was demagnetized and sieved. The resulting material was mixed with asphalt at a ratio of 100:15 and heat-treated at 1100℃ to obtain material 1-1 with a coating layer. Material 1-1 satisfies the following conditions: S2 / S1 = 15, volume distribution particle size (Dv50) = 12.0 μm, and specific surface area (BET) = 2.0 m². 2 / g and graphitization degree = 96.8%.

[0225] Preparation of materials 1-2 to 1-6:

[0226] The preparation methods for materials 1-2 to 1-6 are similar to those for material 1-1, except that the volume distribution particle size Dv50 of the aforementioned natural spherical graphite is adjusted to obtain materials 1-2 to 1-6. Details are as follows:

[0227] Table 1.

[0228]

[0229] Preparation of Material 2-1:

[0230] Needle coke was used as raw material, crushed by a roller mill, and shaped by a shaping machine. Petroleum asphalt was used as a binder to granulate the shaped raw material. Then, graphitization was performed at 3000℃ to obtain artificial graphite material 2-1, which consists of secondary particles as a second carbon-based material. The volume distribution of material 2-1 (secondary particles) has a particle size Dv50 of 14.5 mm and a degree of graphitization of 94.3%.

[0231] Preparation of materials 2-2 to 2-6:

[0232] The preparation methods of materials 2-2 to 2-6 are similar to those of material 2-1, except that the granulation time is adjusted to obtain materials 2-2 to 2-6.

[0233] Specifically as follows:

[0234] Table 2.

[0235]

[0236] Example 1

[0237] Preparation of secondary batteries:

[0238] 1. Negative Electrode Sheet: The first negative electrode active material (material 1-1, as the first carbon-based material) and the second negative electrode active material (material 2-1, as the second carbon-based material) are respectively mixed with conductive agent carbon black (Super P), thickener sodium carboxymethyl cellulose, and binder styrene-butadiene rubber in a weight ratio of 96.4:1:1.2:1.4 in an appropriate amount of deionized water to form the first negative electrode slurry and the second negative electrode slurry. The second negative electrode slurry and the first negative electrode slurry are coated sequentially on the two surfaces of the negative electrode current collector copper foil in an equal mass ratio. After drying and cold pressing, the negative electrode sheet is obtained.

[0239] 2. Positive electrode: LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523) is mixed with conductive agent carbon black (Super P) and binder polyvinylidene fluoride in a weight ratio of 96:2:2. An appropriate amount of solvent N-methylpyrrolidone (NMP) is added and stirred until homogeneous to obtain a positive electrode slurry. The positive electrode slurry is coated on both surfaces of the positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet is obtained.

[0240] 3. Electrolyte: Ethyl 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. LiPF6 is then dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0241] 4. Separation membrane: Polypropylene membrane is used.

[0242] 5. Preparation of secondary battery: The positive and negative electrode sheets prepared above are placed in sequence, with the separator in the middle of the positive and negative electrode sheets to provide isolation. Then, the electrode assembly is wound up to obtain the electrode assembly. The electrode assembly is placed in the outer packaging, dried, and then injected with electrolyte. After vacuum sealing, standing, formation, and shaping, the secondary battery is obtained.

[0243] Examples 2-6

[0244] The secondary battery was prepared using a method similar to that in Example 1. The difference lies in the selection of a different volume distribution particle size Dv50 for the first carbon-based material.

[0245] Comparative Example 1

[0246] The battery was prepared using a method similar to that in Example 1. The difference was that the volume distribution particle size Dv50 of the first carbon-based material was greater than 15 μm.

[0247] Performance testing

[0248] 1. Materials Testing

[0249] The S2 / S1 ratio of the first carbon-based material was obtained by testing using the following method.

[0250] The sample preparation adhesive was mixed evenly with the first carbon-based material powder and then coated onto copper foil. The mixture was dried at 60°C for 30 minutes. Five samples, each 6mm x 6mm in size, were cut at five different locations and attached to the sample stage of a CP-type argon ion cross-section polisher. The samples were then cut using a plasma beam to obtain the cross-section of each sample. The testing instrument can be a JEOL IB-09010 CP-type argon ion cross-section polisher.

[0251] The cross-sections of each sample of the first carbon-based material were scanned using a scanning electron microscope (SEM). Scanned images were obtained by arbitrarily selecting a region within each sample cross-section. The testing procedure is based on JY / T010-1996. The testing instrument can be a ZEISS Sigma 300 scanning electron microscope (Germany).

[0252] Cross-sections of 20 particles of the first carbon-based material were randomly selected from the scanned image. The region extending 0.25 μm from the particle surface into the particle's interior was designated as the outer region, and the region inside the outer region was designated as the inner region. Image processing software was used to obtain the total pore area S1' of the outer region of each particle cross-section and the pore area S2' of the inner region of the first carbon-based material. The value of S2' / S1' was calculated. The arithmetic mean of S2' / S1' for all 20 particles was then calculated as the S2 / S1 value of the first carbon-based material. AVIZO could be used as the image processing software.

[0253] 2. Battery performance test

[0254] (1) Cyclic performance test of secondary batteries

[0255] 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 resting for 5 minutes, the secondary battery was discharged at a constant current of 1C to the lower cutoff voltage (corresponding to 0% SOC), and the discharge capacity at this point was recorded, which is the discharge capacity of the first cycle. The secondary battery was subjected to cyclic charge-discharge tests according to the above method, and the discharge capacity after each cycle was recorded.

[0256] The capacity retention rate (%) of a secondary battery after 1000 cycles at 45℃ = discharge capacity after 1000 cycles / discharge capacity of the first cycle × 100%.

[0257] (2) Storage performance test of secondary batteries

[0258] At 25°C, the prepared secondary battery was charged to 4.3V with a constant current of 1C, and then charged to 0.05C with a constant voltage. After standing for 5 minutes, the secondary battery was discharged to 2.8V with a constant current of 1C. The discharge capacity at this time was recorded, which is the discharge capacity before storage.

[0259] The prepared secondary battery was charged at a constant current of 1C to 4.3V at 25℃, and then charged at a constant voltage to a current of 0.05C. The secondary battery was then stored in a 60℃ constant temperature chamber for 180 days. The capacity retention rate (%) of the secondary battery after 180 days of storage at 60℃ = (discharge capacity after storage / discharge capacity before storage) × 100%.

[0260] (3) Kinetic testing of secondary batteries

[0261] At 25°C, the secondary battery was charged to 4.3V at a constant current of 0.33C, then charged to 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.

[0262] Then, the secondary battery is sequentially charged at constant current rates of 1.0C0, 1.3C0, 1.5C0, 1.8C0, 2.0C0, 2.3C0, 2.5C0, and 3.0C0 until it reaches 4.3V or 0V negative terminal cutoff potential (whichever comes first). After each charge, it must be discharged to 2.8V at 1C0. The charging rate is recorded at different rates until it reaches 10%, 20%, 30%, etc., up to 80% SOC (State of Charge). By plotting the negative electrode potential corresponding to the state of charge (SOC), the charging rate-negative electrode potential curves under different SOC states are obtained. After linear fitting, the charging rate corresponding to the negative electrode potential of 0V under different SOC states is obtained. This charging rate is the charging window under that SOC state, denoted as C10%SOC, C20%SOC, C30%SOC, C40%SOC, C50%SOC, C60%SOC, C70%SOC, and C80%SOC, respectively. The charging time T (assuming no lithium plating in the secondary battery) from 10%SOC to 80%SOC 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%, in minutes. The shorter the charging time, the better the kinetic performance of the secondary battery.

[0263] (4) Energy density test of secondary batteries

[0264] At 25℃, the secondary battery was charged at a constant current of 1 / 3C to 4.3V, then charged at a constant voltage of 4.3V to a current of 0.05C. After resting for 5 minutes, it was discharged at a constant current of 1 / 3C to 2.8V. The battery discharge energy was recorded. The battery discharge energy divided by the battery volume is the battery's volumetric energy density, expressed in Wh / L.

[0265] 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.

[0266] Table 3.

[0267]

[0268] As shown in Table 3 above, the charging time gradually shortens with decreasing particle size of the first carbon-based material, indicating a gradual improvement in kinetic performance. Meanwhile, the cycle performance and storage performance decrease slightly. In Comparative Example 1, the first carbon-based material has a larger particle size, resulting in better cycle and storage performance, but a significant decrease in kinetic performance.

[0269] Examples 7-11

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

[0271] Table 4.

[0272]

[0273] As can be seen from Table 3 above, 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.

[0274] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A secondary battery, comprising a negative electrode, characterized in that, The negative electrode sheet includes 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 disposed opposite to the first surface, and the thickness of the negative electrode film layer is denoted as H; The region extending from the first surface of the negative electrode film to a thickness of 0.3H is denoted as the first region of the negative electrode film. The first region includes a first negative electrode active material, which 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 denoted as D. The first carbon-based material includes an outer region and an inner region located inside the outer region. The outer region refers to the region formed by extending 0.25D from the particle surface of the first carbon-based material into the particle interior. The total pore area of ​​the outer region is denoted as S1, and the total pore area of ​​the inner region is 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 15μm.

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

3. The secondary battery according to claim 1, wherein, 1.5≤S2 / S1≤500.

4. The secondary battery according to claim 1, wherein, 2.5≤S2 / S1≤450.

5. The secondary battery according to claim 1, 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 ; and / or, The internal region of the first carbon-based material includes one or more particles with an area greater than or equal to 0.15 μm. 2 The porous structure.

6. The secondary battery according to claim 5, wherein, The area of ​​the pore structure in the outer region of the first carbon-based material is less than or equal to 0.13 μm. 2 ; and / or, The internal region of the first carbon-based material includes one or more particles with an area of ​​0.15 μm. 2 -2.0μm 2 The porous structure.

7. The secondary battery according to any one of claims 1-6, wherein, The first carbon-based material has at least a portion of its surface covered with a carbon coating.

8. The secondary battery according to any one of claims 1-6, wherein, The first carbon-based material comprises primary particles.

9. The secondary battery according to claim 8, wherein, The primary particles account for ≥80% of the total amount in the first carbon-based material.

10. The secondary battery according to claim 1, wherein, The region extending from the second surface of the negative electrode film to a thickness of 0.3H is referred to as the second region of the negative electrode film. The second region is disposed between the negative electrode current collector and the first region. The second region includes a second negative electrode active material, which includes a second carbon-based material.

11. The secondary battery according to claim 10, wherein, The second carbon-based material includes artificial graphite.

12. The secondary battery according to claim 10, wherein, The volume distribution particle size Dv50 of the first carbon-based material is smaller than that of the second carbon-based material.

13. The secondary battery according to claim 12, wherein, The volumetric particle size Dv50 of the second carbon-based material is 13μm-19μm.

14. The secondary battery according to claim 13, wherein, The volumetric particle size Dv50 of the second carbon-based material is 14μm-18μm.

15. The secondary battery according to claim 10, wherein, 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.

16. The secondary battery according to claim 15, wherein, The second carbon-based material has a powder compaction density of 1.85 g / cm³ under a pressure of 50,000 N. 3 -2.03g / cm 3 .

17. The secondary battery according to any one of claims 10-16, wherein, The surface of the second carbon-based material does not have a coating layer.

18. The secondary battery according to any one of claims 10-16, wherein, The second carbon-based material includes artificial graphite with secondary particles.

19. The secondary battery according to claim 18, wherein, The proportion of artificial graphite in the secondary particles is greater than or equal to 80% in the second carbon-based material.

20. The secondary battery according to any one of claims 10-16, wherein, The particle size distribution of the second carbon-based material satisfies (Dv90-Dv10) / Dv50≤1.

25.

21. The secondary battery according to claim 20, wherein, The particle size distribution of the second carbon-based material satisfies (Dv90-Dv10) / Dv50 as 0.90-1.

25.

22. The secondary battery according to any one of claims 10-16, wherein, The specific capacity of the first carbon-based material is greater than that of the second carbon-based material.

23. The secondary battery according to claim 22, wherein, The specific capacity of the first carbon-based material is ≥355mAh / g.

24. The secondary battery according to claim 23, wherein, The specific capacity of the first carbon-based material is 355mAh / g-368mAh / g.

25. The secondary battery according to claim 22, wherein, The specific capacity of the second carbon-based material is 350mAh / g-365mAh / g.

26. The secondary battery according to claim 25, wherein, The specific capacity of the second carbon-based material is 352 mAh / g-362 mAh / g.

27. The secondary battery according to any one of claims 10-16, wherein, The graphitization degree of the first carbon-based material is ≥95.0%; and / or, The graphitization degree of the second carbon-based material is 90.0%-95.5%.

28. The secondary battery according to claim 27, wherein, The graphitization degree of the first carbon-based material is 95.5%-98.0%; and / or, The degree of graphitization of the second carbon-based material is 92.0%-95.5%.

29. The secondary battery according to any one of claims 10-16, wherein, The specific surface area of ​​the first carbon-based material is 1.0 m². 2 / g-2.8m 2 / g; and / or, The specific surface area of ​​the second carbon-based material is 0.8 m². 2 / g-2.0m 2 / g.

30. The secondary battery according to claim 29, wherein, The specific surface area of ​​the first carbon-based material is 1.3 m². 2 / g-2.1m 2 / g; and / or, The specific surface area of ​​the second carbon-based material is 1.1 m². 2 / g-1.7m 2 / g.

31. The secondary battery according to any one of claims 1-6, wherein, The first carbon-based material satisfies at least one of the following conditions: (1) The first carbon-based material satisfies: (Dv90-Dv10) / Dv50≤1.40; (2) The compacted density of the first carbon-based material under a pressure of 50,000 N is 1.75 g / cm³. 3 -2.0g / cm 3 ; (3) The tap density of the first carbon-based material is 0.90-1.30 g / cm³. 3 ; (4) The volume distribution particle size Dv90 of the first carbon-based material is 13μm-30μm.

32. The secondary battery according to any one of claims 1-6, wherein, The first carbon-based material satisfies at least one of the following conditions: (1) The first carbon-based material satisfies: (Dv90-Dv10) / Dv50 is 0.90-1.40; (2) The compacted density of the first carbon-based material under a pressure of 50,000 N is 1.80 g / cm³. 3 -1.98g / cm 3 ; (3) The tap density of the first carbon-based material is 0.95-1.25 g / cm³. 3 ; (4) The volume distribution particle size Dv90 of the first carbon-based material is 16μm-23μm.

33. The secondary battery according to any one of claims 10-16, wherein, The second carbon-based material satisfies at least one of the following conditions: (1) The tap density of the second carbon-based material is 0.85-1.25 g / cm³. 3 ; (2) The second carbon-based material satisfies 0.050≤I D / I G ≤0.300, I D This indicates that the Raman spectrum is at 1350±50 cm⁻¹ -1 The intensity of peak D at I G This indicates that the Raman spectrum is at 1580±50 cm⁻¹. -1 The intensity of the G peak at that location.

34. The secondary battery according to any one of claims 10-16, wherein, The second carbon-based material satisfies at least one of the following conditions: (1) The tap density of the second carbon-based material is 0.90-1.15 g / cm³. 3 ; (2) The second carbon-based material satisfies 0.070≤I D / I G ≤0.200, I D This indicates that the Raman spectrum is at 1350±50 cm⁻¹ -1 The intensity of peak D at I G This indicates that the Raman spectrum is at 1580±50 cm⁻¹. -1 The intensity of the G peak at that location.

35. The secondary battery according to any one of claims 10-16, wherein, The first negative electrode active material and / or the second negative electrode active material further include silicon-based materials.

36. The secondary battery according to claim 35, wherein, The silicon-based material accounts for less than or equal to 10% of the mass of the first negative electrode active material; and / or, the second negative electrode active material accounts for less than or equal to 10% of the mass.

37. The secondary battery according to claim 36, wherein, The silicon-based material accounts for 5%-10% of the mass of the first negative electrode active material; and / or, the silicon-based material accounts for 5%-10% of the mass of the second negative electrode active material.

38. The secondary battery according to any one of claims 1-6, wherein, The negative electrode film layer satisfies at least one of the following conditions: (1) The compaction density of the negative electrode film is ≤1.85 g / cm³. 3 ; (2) The porosity of the negative electrode film is 18.0%-38.0%; (3) The OI value of the negative electrode film is ≤30.0; (4) The thickness of the negative electrode film is greater than or equal to 40 μm.

39. The secondary battery according to any one of claims 1-6, wherein, The negative electrode film layer satisfies at least one of the following conditions: (1) The compaction density of the negative electrode film is 1.45-1.75 g / cm³. 3 ; (2) The porosity of the negative electrode film is 19.0%-34.0%; (3) The OI value of the negative electrode film is 8.0-23.0; (4) The thickness of the negative electrode film is 40μm-140μm.

40. An electrical device, characterized in that, The secondary battery includes any one of claims 1-39.

Images