Secondary battery and electric device

Abstract

A secondary battery and an electric device. The secondary battery comprises a negative electrode sheet. The negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector, wherein the negative electrode film layer comprises a negative electrode active material; the negative electrode active material comprises a first carbon-based material and a second carbon-based material, both of which have a pore structure; and ID / IG of the first carbon-based material is less than or equal to 0.27, and ID / IG of the second carbon-based material is greater than or equal to 0.38, ID representing the D-peak intensity of a Raman spectrum at 1350±50 cm-1, and IG representing the G-peak intensity of the Raman spectrum at 1580±50 cm-1.

Description

Secondary battery and power-consuming device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This disclosure is based on the Chinese patent application with application number 202311643139.3, application date November 30, 2023, and invention name “A secondary battery and electrical device”, and claims the priority of the Chinese patent application. The entire content of the Chinese patent application is hereby introduced into the present disclosure as a reference. Technical Field

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

[0004] In recent years, secondary batteries have been widely used in energy storage systems such as hydropower, thermal, wind, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. As the scope of secondary battery applications expands, so too does the demand for their performance. For example, they are required to have both excellent dynamic performance and a long shelf life, particularly the ability to operate over a wide range of ambient temperatures.

[0005] Summary of the Invention

[0006] The present disclosure is made in view of the above-mentioned problems, and its object is to provide a secondary battery and an electric device, wherein the secondary battery has improved low-temperature kinetic performance and high-temperature storage life.

[0007] The first aspect of the present disclosure provides a secondary battery. The secondary battery includes a negative electrode plate, the negative electrode plate 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 includes a negative electrode active material, and the negative electrode active material includes a first carbon-based material and a second carbon-based material, wherein the first carbon-based material and the second carbon-based material both have a pore structure, and the I of the first carbon-based material is 1. D / I G ≤0.27, I of the second carbon-based material D / I G ≥0.38, where I D Indicates that the Raman spectrum is at 1350±50cm -1 The D peak intensity at I G Indicates that the Raman spectrum is at 1580±50cm -1 The G peak intensity at .

[0008] Thus, the present disclosure is provided by combining the two components having the same pore structure but with different I D / IG The first carbon-based material and the second carbon-based material are combined to obtain a mixed negative electrode active material. The first carbon-based material and the second carbon-based material both have a pore structure, which can provide a transmission channel for active ions, accelerate the reaction of active ions with the negative electrode active material, and thus improve the kinetic performance of the secondary battery. On this basis, the first carbon-based material I D / I G ≤0.27, reflecting that the carbon surface of the material has a high degree of order and fewer defects, thus having fewer side reactions with the electrolyte, which is beneficial to the high temperature storage performance of the secondary battery. D / I G The characteristics of ≥0.38 and high reaction activity further provide good low-temperature kinetic performance. The combined use of the two as negative electrode active materials can give full play to the advantages of both, making the secondary battery have both good low-temperature kinetic performance and high-temperature storage performance.

[0009] In some embodiments, the first carbon-based material D / I G is 0.13-0.25; and / or, I of the second carbon-based material D / I G The first carbon-based material has an I of 0.40-0.60. D / I G When the carbon content in the material is within the above range, the amorphous degree of the carbon in the material is low, the material has fewer side reactions at high temperatures, and is beneficial to the high temperature storage performance of the secondary battery. D / I G When the content is within the above range, the reaction activity is suitable, thereby improving the low-temperature kinetics performance of the secondary battery.

[0010] In some embodiments, the XRD diffraction pattern of the first carbon-based material is 3R(101) / I 2H(004) The XRD diffraction pattern of the second carbon group is smaller than I 3R(101) / I 2H(004) Optionally, the XRD diffraction pattern of the first carbon-based material is 3R(101) / I 2H(004) Less than or equal to 0.06, further optionally 0-0.06. Optionally, the I of the second carbon-based material 3R / I 2H ≥0.2, further optionally 0.22-0.4. 3R(101 ) is the diffraction peak intensity of the 101 crystal plane of graphite 3R phase corresponding to 43°-44° in the XRD diffraction pattern, I 2H(004) is the diffraction peak intensity of the 004 crystal plane of graphite 2H phase corresponding to 53°-55° in the XRD diffraction pattern.

[0011] In some embodiments, the volume distribution particle size Dv50 of the first carbon-based material is greater than the volume distribution particle size Dv50 of the second carbon-based material. Adjusting the volume distribution particle sizes of the first carbon-based material and the second carbon-based material, especially when the second carbon-based material has a relatively smaller volume distribution particle size, is beneficial to increasing the specific surface area of ​​the material, thereby further improving the kinetic performance of the secondary battery.

[0012] In some embodiments, the volume distribution particle size Dv50 of the first carbon-based material is ≥15 μm, optionally 16 μm ≤ Dv50 ≤ 20 μm; and / or the Dv50 of the second carbon-based material is ≤13 μm, optionally 7 μm ≤ Dv50 ≤ 12 μm. When the volume distribution particle size Dv50 of the first carbon-based material is within the above range, the consumption of active ions can be reduced and the high-temperature storage performance of the secondary battery can be improved. When the volume distribution particle size Dv50 of the second carbon-based material is smaller and within the above range, it helps to improve the contact between materials, reduce the transmission distance of active ions, and further improve the kinetic performance of the secondary battery at low temperatures.

[0013] In some embodiments, the BET specific surface area of ​​the first carbon-based material is smaller than the BET specific surface area of ​​the second carbon-based material. By adjusting the specific surface area of ​​the materials, the first carbon-based material has a smaller specific surface area, which reduces side reactions with the electrolyte and helps improve the high-temperature storage performance of the secondary battery. At the same time, the second carbon-based material has a larger specific surface area, which provides a larger reaction surface, facilitates the reaction of active ions, and improves the kinetic performance of the secondary battery.

[0014] In some embodiments, the specific surface area of ​​the first carbon-based material is less than or equal to 2.1 m 2 / g, optional 1.3m 2 / g-1.9m 2 / g; and / or, the BET of the second carbon-based material is ≤3.6m 2 / g, optionally 1.8m 2 / g-3.4m 2 When the specific surface area of ​​the first carbon-based material is within the above range, it is beneficial to the high-temperature storage performance and cycle performance of the secondary battery. When the specific surface area of ​​the second carbon-based material is within the above range, it can provide better low-temperature kinetic performance.

[0015] In some embodiments, the first carbon-based material has a greater degree of graphitization than the second carbon-based material.

[0016] In some embodiments, the graphitization degree of the first carbon-based material is ≥95%, and may be 96.0%-98.5%; the graphitization degree of the second carbon-based material is ≥95%, and may be 95.0%-97.5%.

[0017] The high degree of graphitization of both the first and second carbon-based materials increases the specific capacity of the negative electrode active material and improves the electron transport performance of the negative electrode film layer, thereby enabling the secondary battery to achieve both high energy density and good kinetic performance. Furthermore, the high degree of graphitization of the material surface is beneficial to the high-temperature storage performance of the secondary battery.

[0018] In some embodiments, the first carbon-based material includes an external region and an internal region located inside the external region, wherein the external region refers to a region extending 2.5 μm inward from the particle surface of the first carbon-based material. In a cross-sectional view of the first carbon-based material, the total pore area of ​​the external region of the first carbon-based material is denoted as S1, and the total pore area of ​​the internal region is denoted as S2, then the first carbon-based material satisfies S2>S1.

[0019] When 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, the structure of the outer region of the carbon material is denser than that of the inner region. This structure is more conducive to material stability, reducing expansion during charge and discharge cycles, thereby improving the cycle life of the secondary battery. In addition, the smaller pore area of ​​the outer region helps reduce side reactions and the consumption of active ions, which is beneficial for improving the high-temperature storage performance of the secondary battery.

[0020] Optionally, the first carbon-based material satisfies 2.5≤S2 / S1≤460. The outer region of the first carbon-based material has a relatively small porous structure, which helps reduce side reactions between the first carbon-based material and the electrolyte, reduces active ion consumption, and thus improves the storage performance of the secondary battery. In addition, it can also inhibit the expansion of the first carbon-based material during charge and discharge cycles, thereby improving the cycle life of the secondary battery.

[0021] In some embodiments, the area of ​​a single pore structure in the outer region of the first carbon-based material is less than or equal to 0.15 μm 2 , can be selected to be less than or equal to 0.13μm 2 ; and / or, the internal region of the first carbon-based material includes one or more pores with an area greater than or equal to 0.15 μm 2 The pore structure may include one or more pores with an area of ​​0.15 μm 2 -2.0μm 2The outer region of the particles of the first carbon-based material having the above structure is relatively dense, while the inner region has a certain pore structure. In this way, on the one hand, sufficient and stable expansion space can be reserved for the volume change of the first carbon-based material particles, reducing the risk of first carbon-based material particles breaking, reducing the entry of electrolyte into the particles to reduce the occurrence of side reactions, and reducing the consumption of active ions, thereby further improving the storage performance of the secondary battery. On the other hand, it can also improve the compaction density of the negative electrode film layer.

[0022] In some embodiments, at least a portion of the surface of the second carbon-based material has a carbon coating layer. Further coating at least a portion of the surface of the second carbon-based material with a carbon coating layer can further enhance active ion transport under low temperature conditions, thereby improving the low-temperature kinetic performance of the secondary battery.

[0023] In some embodiments, the first carbon-based material satisfies at least one of the following.

[0024] (1) The powder compaction density of the first carbon-based material under 50,000 N is ≤ 2.10 g / cm 3 , optionally 1.85 g / cm 3 -2.00g / cm 3 When the powder compaction density of the first carbon-based material is within the above range, the compaction density of the negative electrode film layer can be increased, thereby increasing the energy density of the secondary battery. This is also conducive to forming a reasonable pore structure between the particles of the negative electrode film layer, thereby improving the active ion and electron transport performance, and thus improving the kinetic performance of the secondary battery.

[0025] (2) The volume distribution particle size Dv90 of the first carbon-based material is less than or equal to 40 μm, and optionally is 30 μm to 38 μm. When the volume distribution particle size Dv90 of the particles of the first carbon-based material is within the above range, it is beneficial to reduce the specific surface area of ​​the first carbon-based material, reduce the occurrence of side reactions, and improve the storage performance of the secondary battery.

[0026] (3) The particle size distribution of the first carbon-based material is [(Dv90)-(Dv10)] / (Dv50)] ≤ 1.55, optionally 0.90-1.50. When the particle size distribution of the first carbon-based material is within the above range, its particle packing performance is good, which is beneficial to improving the compaction density of the negative electrode film layer and the energy density of the secondary battery. In addition, it is beneficial to form a reasonable pore structure between the particles of the negative electrode film layer, improve the active ion and electron transport performance, and improve the kinetic performance of the secondary battery.

[0027] (4) The gram capacity of the first carbon-based material is ≥362 mAh / g, optionally 365 mAh / g-372 mAh / g. When the gram capacity of the first carbon-based material is within the above range, the secondary battery can have a higher energy density.

[0028] (5) The first carbon-based material includes primary particles. Optionally, the primary particles account for greater than or equal to 80% of the first carbon-based material.

[0029] When the first carbon-based material satisfies any of the above items, it can further improve one or more of the low-temperature kinetics, high-temperature storage performance, energy density and other properties of the secondary battery.

[0030] In some embodiments, the second carbon-based material satisfies at least one of the following.

[0031] (1) The gram capacity of the second carbon-based material is ≥358 mAh / g, and can be optionally 360 mAh / g-367 mAh / g. When the gram capacity of the second carbon-based material is within the above range, the secondary battery can have a higher energy density.

[0032] (2) The compaction density of the second carbon-based material under 50,000 N is ≤ 1.95 g / cm 3 , optionally 1.75 g / cm 3 -1.90g / cm 3 When the powder compaction density of the second carbon-based material is within the above range, it is beneficial to form a reasonable pore structure between the particles of the negative electrode film layer, improve the active ion and electron transport performance, and thus improve the kinetic performance of the secondary battery.

[0033] (3) The second carbon-based material includes primary particles. Optionally, the primary particles account for greater than or equal to 80% of the second carbon-based material.

[0034] (4) The second carbon-based material is natural graphite.

[0035] When the second carbon-based material satisfies any of the above items, the low-temperature kinetics, energy density and other properties of the secondary battery can be further improved.

[0036] In some embodiments, the mass proportion of the first carbon-based material in the negative electrode active material is greater than the mass proportion of the second carbon-based material in the negative electrode active material. Optionally, the mass proportion of the first carbon-based material in the negative electrode active material is ≥55wt%, optionally 60wt%-80wt%. When the mass proportion of the first carbon-based material in the negative electrode active material is within the above range, it can work together with the second carbon-based material to achieve improved high-temperature storage performance and low-temperature kinetic performance.

[0037] In some embodiments, the negative electrode active material satisfies at least one of the following.

[0038] (1) The volume distribution particle size Dv50 of the negative electrode active material is ≤17.0 μm, and can be optionally 12 μm-16.5 μm.

[0039] (2) The volume distribution particle size Dv90 of the negative electrode active material is ≤35 μm, and can be selected from 25 μm to 33 μm.

[0040] (3) The volume particle size distribution of the negative electrode active material satisfies: (Dv90-Dv10) / Dv50≤1.50, which can be 1.0-1.45.

[0041] (4) The specific surface area of ​​the negative electrode active material is ≤3.0m 2 / g, optional 1.5m 2 / g-2.8m 2 / g.

[0042] In some embodiments, the negative electrode film layer satisfies at least one of the following conditions.

[0043] (1) The compaction density of the negative electrode film is ≥1.55 g / cm 3 , optionally 1.6 g / cm 3 -1.7g / cm 3 .

[0044] (2) The surface density of the negative electrode film layer is ≥10.0 mg / cm 2 , optionally 11.0 mg / cm 2 -15.5mg / cm 2 .

[0045] (3) The porosity of the negative electrode film layer is 16%-30%, and optionally 19%-27%. This helps the negative electrode film layer achieve both high capacity and a suitable pore structure, and further helps the secondary battery achieve both high energy density and good storage performance and dynamic performance.

[0046] (4) The thickness of the negative electrode film layer is ≥70 μm, optionally 90-130 μm.

[0047] The negative electrode film layer has at least one of the above characteristics, which is beneficial to at least one of the high-temperature storage performance, low-temperature dynamic performance, energy density and other properties of the secondary battery.

[0048] A second aspect of the present disclosure further provides an electrical device comprising the secondary battery according to the first aspect of the present disclosure.

[0049] The electric device of the present disclosure includes the secondary battery provided by the present disclosure, and thus has at least the same advantages as the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] FIG1 is a scanning electron microscope photograph of a longitudinal section of a negative electrode sheet prepared according to Example 1.

[0051] FIG2 is a schematic diagram of a cross-sectional image of particles of the first carbon-based material of the present disclosure.

[0052] FIG. 3 is a schematic diagram of a battery cell according to an embodiment of the present disclosure.

[0053] FIG. 4 is an exploded view of the battery cell shown in FIG. 3 according to an embodiment of the present disclosure.

[0054] FIG5 is a schematic diagram of a battery module according to an embodiment of the present disclosure.

[0055] FIG6 is a schematic diagram of a battery pack according to an embodiment of the present disclosure.

[0056] FIG. 7 is an exploded view of the battery pack shown in FIG. 6 according to an embodiment of the present disclosure.

[0057] FIG8 is a schematic diagram of an electric device using a secondary battery according to an embodiment of the present disclosure as a power source.

[0058] Explanation of reference numerals: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 battery cell; 51 housing; 52 electrode assembly; 53 top cover assembly DETAILED DESCRIPTION

[0059] Below, the embodiments of the secondary battery and the electrical device disclosed in the present invention are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present disclosure and are not intended to limit the subject matter described in the claims.

[0060] The "range" disclosed in this disclosure is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The range defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. For example, if a range of 60-120 and 80-110 is listed for a particular parameter, it is understood that a range of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4, and 5 are listed, then the following ranges can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this disclosure, unless otherwise specified, the numerical range "ab" represents an abbreviation of any real number combination between a and b, wherein a and b are both real numbers. For example, the numerical range "-5" represents that all real numbers between "-5" have been listed herein, and "0-5" is just an abbreviation of these numerical value combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0061] Unless otherwise specified, all embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions.

[0062] Unless otherwise specified, all technical features and optional technical features disclosed herein can be combined with each other to form a new technical solution.

[0063] Unless otherwise specified, all steps of the present disclosure may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0064] Unless otherwise specified, the terms used in the present disclosure have the common meanings that are generally understood by those skilled in the art.

[0065] Unless otherwise specified, the numerical values ​​of the parameters mentioned in the present disclosure can be measured using various test methods commonly used in the art, for example, they can be measured according to the test methods given in the present disclosure.

[0066] Unless otherwise specified, in the present disclosure, the term "active ions" refers to ions that can be intercalated and extracted back and forth between the positive electrode and the negative electrode of a secondary battery, including but not limited to lithium ions.

[0067] With the widespread use of secondary batteries, higher requirements are being placed on their performance under different operating environments, such as high and low temperatures. The kinetic performance of secondary batteries at low temperatures and their storage performance at high temperatures still need to be improved. Kinetic performance, especially at low temperatures, often requires higher reactivity of the negative electrode active material and shorter active ion transport pathways. However, this can lead to side reactions between the negative electrode active material and the electrolyte, reducing its storage performance. Storage performance at high temperatures is particularly adversely affected.

[0068] Therefore, it is often difficult for current secondary batteries to balance high-temperature storage performance and low-temperature kinetic performance.

[0069] In view of this, a first aspect of an embodiment of the present disclosure provides a secondary battery.

[0070] The term "secondary battery" referred to herein refers to a battery cell, a battery module, or a battery pack.

[0071] Typically, a secondary battery cell consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0072] [Negative electrode]

[0073] The secondary battery of the present disclosure includes a negative electrode plate, the negative electrode plate 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 includes a negative electrode active material. The negative electrode active material includes a first carbon-based material and a second carbon-based material. The first carbon-based material and the second carbon-based material both have a pore structure, and the I of the first carbon-based material D / I G ≤0.27, I of the second carbon-based material D / I G ≥0.38, where I D Indicates that the Raman spectrum is at 1350±50cm -1 The D peak intensity at I G Indicates that the Raman spectrum is at 1580±50cm -1 The G peak intensity at .

[0074] First carbon-based material I D / IG ≤≤0.27, reflecting that the carbon in the surface area of ​​the material has a high degree of order and few defects, thus having few side reactions with the electrolyte, which can improve the high-temperature storage performance of the secondary battery. The second carbon-based material has a porous structure and I D / I G ≥0.38, reflecting the low degree of order of carbon in the material's surface region, which results in high reactivity and facilitates rapid reaction and transport of active ions, resulting in excellent low-temperature kinetics for the secondary battery. The combination of a first carbon-based material and a second carbon-based material with these properties as the negative electrode active material leverages the strengths of both, resulting in a secondary battery with both excellent low-temperature kinetics and high-temperature storage performance.

[0075] In some embodiments, the first carbon-based material D / I G is 0.13-0.25. D / I G It can be 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25 or a value between any two values. According to some embodiments, the I of the first carbon-based material D / I G The I of the first carbon-based material may be in the range of 0.13-0.20, 0.20-0.25, 0.18-0.25, etc. D / I G When the value is within the above range, it reflects that the amorphous degree of carbon in the material, especially on the surface of the material, is low, so the first carbon-based material has fewer side reactions at high temperatures, which is beneficial to the high-temperature storage performance of the secondary battery.

[0076] In some embodiments, the second carbon-based material D / I G is 0.40-0.60. Exemplarily, the I of the second carbon-based material D / I G It can be 0.40, 0.42, 0.44, 0.46, 0.48, 0.50, 0.60, or any value between two values. According to some embodiments, the I of the second carbon-based material D / I G The carbon content of the second carbon-based material may be in the range of 0.40-0.47, 0.40-0.45, 0.41-0.50, 0.42-0.47, 0.46-0.60, 0.48-0.60, 0.50-0.60, etc. D / I GWhen the carbon content is within the above range, the disorder degree of carbon on the surface of the material is relatively high, thereby providing suitable reaction activity and improving the low-temperature kinetic performance of the secondary battery.

[0077] When the first carbon-based material and the second carbon-based material, respectively having the above ranges, are combined and used together as negative electrode active materials, their respective advantageous properties can be brought into play to provide improved high-temperature storage performance and low-temperature kinetic performance for the secondary battery.

[0078] In some embodiments, the XRD diffraction pattern of the first carbon-based material is 3R(101) / I 2H(004) The XRD diffraction pattern of the second carbon group is smaller than I 3R(101) / I 2H(004) In a more specific embodiment, the XRD diffraction pattern of the first carbon-based material is 3R(101) / I 2H(004) Less than or equal to 0.06, optionally 0-0.06. In a more specific embodiment, the I of the second carbon-based material 3R(101) / I 2H(004) ≥0.2, optionally 0.22-0.4. 3R(001) is the diffraction peak intensity of the 101 crystal plane of the carbon-based material 3R phase corresponding to 43°-44° in the XRD diffraction pattern, I 2H(004) is the diffraction peak intensity of the 004 crystal plane of the carbon-based material 2H phase corresponding to 53°-55° in the XRD diffraction pattern. 3R / I 2H It can be 0, 0.01, 0.02, 0.03, 0.04, 0.06, etc. For example, in the XRD diffraction pattern of the second carbon-based material, I 3R / I 2H It can be 0.20, 0.23, 0.25, 0.27, 0.30, 0.33, 0.35, 0.38, 0.4, etc.

[0079] In the XRD diffraction pattern, the obvious diffraction peak of the 3R phase relative to the diffraction peak of the 2H phase usually reflects that the material being tested is natural graphite.

[0080] According to a specific embodiment, the second carbon-based material is natural graphite. Natural graphite has more pores and can provide a larger reaction surface, which is conducive to the transportation of active particles and accelerates the reaction, and thus has excellent low-temperature kinetics. Therefore, the surface properties of the first carbon-based material are stable, with few side reactions, and can improve the high-temperature storage performance of the secondary battery. Therefore, combining the first carbon-based material and the second carbon-based material as negative electrode active materials can enable the secondary battery to take into account both low-temperature kinetics and high-temperature storage performance. In some embodiments, the volume distribution particle size Dv50 of the first carbon-based material is greater than the volume distribution particle size Dv50 of the second carbon-based material. The first carbon-based material mainly improves the high-temperature storage performance of the battery. When its particle size is relatively large, it helps to further reduce the side reactions between the material surface and the electrolyte, thereby further improving the high-temperature storage performance of the secondary battery; in addition, the particle size of the second carbon-based material is relatively small, so that the pores between the particles in the first carbon material and the second carbon material can be reasonably distributed, thereby further improving the low-temperature kinetics.

[0081] In some specific embodiments, the volume distribution particle size Dv50 of the first carbon-based material is ≥15 μm, optionally 16 μm ≤ Dv50 ≤ 20 μm. For example, the volume distribution particle size Dv50 of the first carbon-based material can be 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, etc., or a value between any two values. When the volume distribution particle size Dv50 of the particles of the first carbon-based material is within the above range, it is beneficial to reduce the specific surface area of ​​the first carbon-based material, reduce the occurrence of side reactions, and improve the storage performance of the secondary battery without causing excessive loss of kinetic performance, thereby maintaining a balance between the low-temperature kinetics and high-temperature storage performance of the secondary battery.

[0082] In some specific embodiments, the volume distribution particle size Dv50 of the second carbon-based material is ≤13μm, optionally 7μm≤Dv50≤12μm. According to the specific embodiment, the volume distribution particle size Dv50 of the second carbon-based material may range from 9μm-12μm, 10μm-12μm. Exemplarily, the volume distribution particle size Dv50 of the second carbon-based material may be 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, etc., or a value between any two values. The small volume distribution particle size of the second carbon-based material helps to improve the contact between carbon-based materials and reduce the transmission distance of active ions, thereby further improving the kinetic performance of the secondary battery at low temperatures.

[0083] In some embodiments, the first carbon-based material has a smaller BET surface area than the second carbon-based material. The first carbon-based material has a relatively small surface area and exhibits fewer side reactions with the electrolyte, further improving the high-temperature storage performance of the secondary battery.

[0084] In some embodiments, the specific surface area of ​​the first carbon-based material is BET ≤ 2.1 m 2 / g, optionally 1.3m 2 / g-1.9m 2 / g. For example, the specific surface area of ​​the first carbon-based material is 1.3 m 2 / g, 1.4m 2 / g, 1.5m 2 / g, 1.6m 2 / g, 1.7m 2 / g, 1.8m 2 / g, 1.9m 2 When the specific surface area of ​​the first carbon-based material is within the above range, a smaller specific surface area is beneficial to the storage performance of the secondary battery.

[0085] In some embodiments, the specific surface area of ​​the second carbon-based material is BET ≤ 3.6 m 2 / g, optionally 1.8-3.4m 2 / g. Exemplarily, the specific surface area of ​​the second carbon-based material can be 1.8m 2 / g, 1.9m 2 / g, 2.0m 2 / g, 2.1m 2 / g, 2.2m 2 / g, 2.3m 2 / g, 2.4m 2 / g, 2.5m 2 / g, 2.6m 2 / g, 2.7m 2 / g, 2.8m 2 / g, 2.9m 2 / g, 3.0m 2 / g, 3.1m 2 / g, 3.2m 2 / g, 3.3m 2 / g, 3.4m 2 When the specific surface area of ​​the second carbon-based material is within the above range, it can provide better low-temperature kinetic properties.

[0086] In some embodiments, the first carbon-based material has a greater degree of graphitization than the second carbon-based material.

[0087] In some specific embodiments, the degree of graphitization of the first carbon-based material is ≥95%, and can be 96.0%-98.5%. For example, the degree of graphitization of the first carbon-based material can be 95%-98%, 96-98%, etc. The degree of graphitization of the second carbon-based material is ≥95%, and can be 95.0%-97.5%. For example, the degree of graphitization of the second carbon-based material is 95%-97.3%, 96%-97.3%, etc. Both carbon-based materials have a high degree of graphitization, which can further improve the energy density of the battery.

[0088] In some embodiments, the first carbon-based material includes an external region and an internal region located inside the external region, wherein the external region refers to a region extending 2.5 μm inward from the particle surface of the first carbon-based material. In a cross-sectional view of the first carbon-based material, the total pore area of ​​the external region of the first carbon-based material is denoted as S1, and the total pore area of ​​the internal region is denoted as S2, then the first carbon-based material satisfies S2>S1.

[0089] In the present disclosure, the first carbon-based material 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 a magnification of 1000x). In other words, the first carbon-based material has a relatively small amount of pore structure in the outer region of the main structure.

[0090] In contrast, as described above, the second carbon-based material "has a pore structure" means that the second carbon-based material also has a pore structure that can be directly observed from a cross-sectional image (for example, a scanning electron microscope image with a magnification of 1000 times), and there is no obvious difference in the distribution of these pore structures in different areas of the cross-sectional image.

[0091] The first carbon-based material and the second carbon-based material can be distinguished by a cross-section polisher. For example, the first carbon-based material and the second carbon-based material can be distinguished by performing an ion polishing cross-section morphology (CP) test on the negative electrode. Specifically, the negative electrode can be cut into a sample of a certain size (e.g., 2cm×2cm) and fixed on a sample stage; the sample stage is placed in a sample holder and locked, and the power of an argon ion cross-section polisher (e.g., IB-09010CP argon ion cross-section polisher from JEOL, Japan) is turned on and vacuumed (e.g., 10 -7Pa), set the argon flow rate (e.g., 0.12 MPa) and the polishing time (e.g., 90 min), adjust the sample stage to the rocking mode and start polishing; randomly select an area in the sample to be tested for scanning testing (e.g., refer to JY / T010-1996, use a scanning electron microscope for scanning), and obtain an ion polishing cross-sectional morphology (CP) image of the negative electrode sheet at a certain magnification (e.g., 1000 times). From the image, the first carbon-based material and the second carbon-based material can be distinguished by the pore structure of the carbon-based material particle cross-sectional view.

[0092] For example, see Figure 1, which is a scanning electron microscope (SEM) photograph of a longitudinal section of a negative electrode sheet according to Example 1 of the present disclosure. As can be seen from the figure, the number of pore structures in the outer region of some particles (first carbon-based material particles) is significantly lower than that in the inner region, while the distribution of pore structures in various regions of the cross-section of some particles (second carbon-based material particles) is generally consistent.

[0093] Further referring to FIG2 , there is shown a schematic diagram of a cross-sectional image of a particle of the first carbon-based material 100 of the present disclosure, and the cross-sectional image passes through the center of the particle of the first carbon-based material 100. As shown in FIG2 , the region extending 2.5 μm from the particle surface of the first carbon-based material 100 toward the interior of the particle is the outer region 101, and the region inside the outer region 101 is the inner region 102.

[0094] According to the above definition, when the first carbon-based material satisfies S2 greater than S1, the structure of the outer region of the material is denser than that of the inner region. This structure is beneficial for material stability, reducing expansion during charge and discharge cycles, thereby improving the cycle life of the secondary battery. In addition, the reduced porosity in the outer region helps reduce side reactions and the consumption of active ions, which is beneficial for improving the high-temperature storage performance of the secondary battery.

[0095] Furthermore, the first carbon-based material satisfies 2.5≤52 / S1≤460. Exemplarily, the first carbon-based material satisfies 2.5≤52 / S1≤400, 2.8≤52 / S1≤300, 2.5≤52 / S1≤200, 3.0≤52 / S1≤300, 5.0≤52 / S1≤200, 5.0≤52 / S1≤150, 5.0≤52 / S1≤100, etc. When the value of S2 / S1 is larger, it means that a larger pore area exists in the internal region, that is, the pore area in the external region is smaller, or the pore structure is less. The pore structure of the first carbon-based material that meets the above conditions is mainly located in the internal region of the particle, reserving the required expansion space for the volume change of the particle, reducing the risk of the first carbon-based material particle breaking and producing a new interface. At the same time, the smaller pore area in the external region, or the fewer pore structures, can reduce the side reactions between the material surface and the electrolyte, and reduce the consumption of active ions. Furthermore, the reduced pore structure in the outer region prevents the electrolyte from penetrating the pore structure within the material, and also reduces side reactions between the internal pore surfaces and the electrolyte. Therefore, the first carbon-based material enables the secondary battery to have good storage performance under high temperature conditions while also ensuring a good cycle life.

[0096] In some embodiments, the area of ​​a single pore structure in the outer region of the first carbon-based material is less than or equal to 0.15 μm 2 , can be selected to be less than or equal to 0.13μm 2 ; and / or, the internal region of the first carbon-based material includes one or more pores with an area greater than or equal to 0.15 μm 2 The pore structure may include one or more pores with an area of ​​0.15 μm 2 -2.0μm 2 pore structure. The fact that the outer region of the first carbon-based material includes a pore structure of the above-mentioned size reflects that the outer region of the particles of the material is relatively dense, and the pores of the pore structure are small. The electrolyte of the first carbon-based material with this structure is not easy to enter the interior of the particles, thereby reducing side reactions with the electrolyte. In addition, by making the inner region of the first carbon-based material include a pore structure of the above-mentioned size, on the one hand, sufficient and stable expansion space can be reserved for the volume change of the first carbon-based material particles, and on the other hand, the compaction density of the negative electrode film layer can also be improved. The first carbon-based material with this structural characteristic can improve the high-temperature storage performance and energy density of the secondary battery, while taking into account the cycle performance.

[0097] When the first carbon-based material further satisfies one or more of the following properties on the basis of meeting the above design, the performance of the secondary battery can be further improved, for example, at least one of the energy density, high-temperature storage performance, and low-temperature kinetic performance of the secondary battery can be further enhanced.

[0098] The first carbon-based material disclosed herein is natural graphite. Natural graphite particles typically have a relatively large porous structure throughout their entire area. For example, if the natural graphite particles are divided into an inner region and an outer region (the outer region is defined as the region extending 2.5 μm from the surface of the natural graphite particles to the interior of the particles), both the inner and outer regions of the natural graphite have relatively large porous structures.

[0099] In some embodiments, the powder compaction density of the first carbon-based material at 50,000 N is ≤ 2.10 g / cm 3 , optionally 1.85 g / cm 3 -2.00g / cm 3 For example, the powder compaction density of the first carbon-based material under 50000N is 1.85g / cm 3 、1.90g / cm 3 , 1.95g / cm 3 , 2.00g / cm 3 , 2.05g / cm 3 When the powder compaction density of the first carbon-based material is within the above range, it can increase the compaction density of the negative electrode film layer and improve the energy density of the secondary battery. It is also conducive to the formation of a reasonable pore structure between the particles of the negative electrode film layer, improving the active ion and electron transport performance, and thus improving the kinetic performance of the secondary battery.

[0100] In some embodiments, the volume distribution particle size Dv90 of the first carbon-based material is ≤40 μm, optionally 30 μm-38 μm. For example, the volume distribution particle size Dv90 of the first carbon-based material is 30 μm, 33 μm, 35 μm, 37 μm, 38 μm, etc., or a value between any two values. When the volume distribution particle size Dv90 of the particles of the first carbon-based material is within the above range, it is beneficial to reduce the specific surface area of ​​the first carbon-based material, reduce the occurrence of side reactions, and improve the storage performance of the secondary battery.

[0101] In some embodiments, the particle size distribution of the first carbon-based material [(Dv90)-(Dvl0)] / (Dv50)] ≤ 1.55, optionally 0.90-1.50. For example, the particle size distribution of the first carbon-based material [(Dv90)-(Dv10)] / (Dv50)] is 0.90, 1.00, 1.10, 1.20, 1.30, 1.40, 1.50, etc., or a value between any two values. When the particle size distribution of the first carbon-based material is within the above range, its particle stacking performance is good, which is beneficial to improve the compaction density of the negative electrode film layer and improve the energy density of the secondary battery; in addition, it is also beneficial to form a reasonable pore structure between the particles of the negative electrode film layer, improve the active ion and electron transport performance, and improve the kinetic performance of the secondary battery.

[0102] In some embodiments, the gram capacity of the first carbon-based material is ≥362 mAh / g, optionally 365 mAh / g-372 mAh / g. Exemplarily, the gram capacity of the first carbon-based material is 363 mAh / g, 365 mAh / g, 368 mAh / g, 370 mAh / g, or 372 mAh / g. When the gram capacity of the first carbon-based material is within the above range, the secondary battery can have a higher energy density.

[0103] In some embodiments, the first carbon-based material includes primary particles. Optionally, the primary particles comprise 80% or more of the first carbon-based material. According to some embodiments, the primary particles comprise 85%, 90%, 95%, or even all of the first carbon-based material. The primary particles in the first carbon-based material are beneficial to the low-temperature kinetic performance of the secondary battery.

[0104] According to some embodiments, the surface of the first carbon-based material has no coating layer.

[0105] According to other embodiments, at least part of the surface of the first carbon-based material, optionally the entire surface, may also have a coating, in particular a carbon coating (e.g., an amorphous carbon coating). Typically, a coating material such as asphalt is mixed with a raw material (e.g., a first carbon-based material having a predetermined particle size), and then heat-treated at a certain temperature to form a carbon coating on the surface of the material. The present disclosure does not particularly limit the thickness of the coating of the first carbon-based material and its preparation method. A person of ordinary skill in the art can obtain a first carbon-based material having a coating on the surface by any known method according to actual needs.

[0106] According to some embodiments, at least part of the surface of the second carbon-based material, optionally the entire surface, has a coating layer, in particular a carbon coating layer (e.g., an amorphous carbon coating layer), which can further promote active ion transport, thereby further improving the low-temperature kinetics of the secondary battery.

[0107] Typically, a coating material such as asphalt is mixed with a raw material (e.g., natural graphite having a predetermined particle size) and then heat-treated at a certain temperature to form a carbon coating layer on the surface of the material. The present disclosure does not particularly limit the thickness of the coating layer of the second carbon-based material and its preparation method. A person skilled in the art can use any known method to obtain the second carbon-based material having a surface coating layer according to actual needs.

[0108] When the second carbon-based material further meets one or more of the following properties on the basis of meeting the above design, it can further improve the performance of the secondary battery, for example, further enhance at least one of the high-temperature storage performance, low-temperature dynamic performance, etc. of the secondary battery.

[0109] In some embodiments, the gram capacity of the second carbon-based material is ≥358 mAh / g, and optionally 360 mAh / g-367 mAh / g. Exemplarily, the gram capacity of the second carbon-based material is 360 mAh / g, 362 mAh / g, 364 mAh / g, or 366 mAh / g. When the gram capacity of the second carbon-based material is within the above range, the secondary battery can have a higher energy density.

[0110] In some embodiments, the compaction density of the second carbon-based material at 50,000 N is ≤ 1.95 g / cm 3 , optionally 1.75 g / cm 3 -1.90g / cm 3 For example, the powder compaction density of the second carbon-based material under 50000N is 1.75g / cm 3 , 1.80g / cm 3 , 1.85g / cm 3 、1.90g / cm 3 When the powder compaction density of the second carbon-based material is within the above range, it is beneficial to form a reasonable pore structure between the particles of the negative electrode film layer, improve the active ion and electron transport performance, and thus improve the kinetic performance of the secondary battery.

[0111] In some embodiments, the second carbon-based material includes primary particles. Optionally, the primary particles account for greater than or equal to 80% of the second carbon-based material. According to other embodiments, the primary particles in the second carbon-based material account for greater than or equal to 85%, 90%, 95%, or even all of the primary particles. The inclusion of primary particles in the second carbon-based material is beneficial to the low-temperature kinetic performance of the secondary battery.

[0112] In a specific embodiment, the second carbon-based material comprises or is natural graphite. Advantageously, the second carbon-based material comprises or is natural graphite with a coating layer.

[0113] In some embodiments, in the negative electrode active material, the mass proportion of the first carbon-based material is greater than the mass proportion of the second carbon-based material in the negative electrode active material. D / I G It is relatively large and has many surface defects. If used in excessive amounts, it will further affect the high-temperature storage performance of the battery. Therefore, a suitable mixing ratio of the two can enable the battery to have both better high-temperature storage performance and low-temperature dynamic performance.

[0114] According to a specific embodiment, the mass proportion of the first carbon-based material is ≥55wt%, optionally 60wt%-80wt%, further optionally 65wt%-80wt%, or even 70wt%-80wt%. Exemplarily, in the negative electrode active material, the mass proportion of the first carbon-based material is 60wt%, 65wt%, 70wt%, 75wt%, or 80wt%. When the mass proportion of the first carbon-based material in the negative electrode active material is within the above range, it can work together with the second carbon-based material to exert their respective advantages to obtain improved storage performance while having good cycle performance and energy density.

[0115] In some embodiments, the mass proportion of the second carbon-based material in the negative electrode active material is ≤45wt%, optionally 20wt%-40wt%, further optionally 20wt%-35wt%, or even 20wt%-30wt%. Exemplarily, in the negative electrode active material, the mass proportion of the second carbon-based material is 20wt%, 25wt%, 30wt%, 35wt%, or 40wt%.

[0116] In some embodiments, the negative electrode active material is composed of the first carbon-based material and the second carbon-based material.

[0117] In other embodiments, the negative electrode active material may also include other negative electrode active materials known in the art, such as silicon-based materials. Silicon-based materials can improve the pore structure in the negative electrode film, facilitating electrolyte infiltration and retention, thereby enhancing the dynamic performance of the secondary battery. They can also increase the negative electrode capacity, thereby further improving the energy density of the secondary battery.

[0118] The present disclosure does not particularly limit the silicon-based material, and silicon-based materials conventionally used as negative electrode active materials in the art can be used. Exemplarily, the silicon-based material can be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys.

[0119] In some embodiments, the mass proportion of the silicon-based material in the negative electrode active material is ≤15wt%, optionally 3wt%-10wt%. This can improve the kinetic performance and energy density of the secondary battery while ensuring good cycle performance and storage performance.

[0120] The negative electrode active material in each of the above embodiments advantageously further satisfies at least one of the following items.

[0121] (1) The volume distribution particle size Dv50 of the negative electrode active material is ≤17.0 μm, and can be optionally 12 μm-16.5 μm.

[0122] (2) The volume distribution particle size Dv90 of the negative electrode active material is ≤35 μm, and can be selected from 25 μm to 33 μm.

[0123] (3) The volume particle size distribution of the negative electrode active material satisfies: (Dv90-Dv10) / Dv50≤1.50, which can be 1.0-1.45.

[0124] (4) The specific surface area of ​​the negative electrode active material is ≤3.0m 2 / g, optional 1.5m 2 / g-2.8m 2 / g.

[0125] In some embodiments, the negative electrode film layer may further 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. The present disclosure does not particularly limit the content of the conductive agent, if any, in the negative electrode film layer. A person skilled in the art can determine the appropriate content of the conductive agent through routine testing in the art.

[0126] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0127] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0128] The present disclosure does not particularly limit the content of the binder and / or other auxiliary agents, if any, in the negative electrode film layer. A person skilled in the art can determine the appropriate content of the binder and / or other auxiliary agents through routine experiments in the relevant field.

[0129] The negative electrode film layer satisfies at least one of the following items and can improve at least one of the high-temperature storage performance, low-temperature dynamic performance, energy density and other properties of the secondary battery.

[0130] In some embodiments, the compaction density of the negative electrode film layer is ≥1.5 g / cm 3 , optionally 1.6 g / cm 3 -1.7g / cm 3 For example, the compaction density of the negative electrode film is 1.6 g / cm 3 , 1.65g / cm 3 , 1.70g / cm 3etc., or any value between any two values.

[0131] In some embodiments, the surface density of the negative electrode film layer is ≥10 mg / cm 2 , optionally 11.0-15.5 mg / cm 2 For example, the compaction density of the negative electrode film is 10 mg / cm 2 、11mg / cm 2 , 12mg / cm 2 、13mg / cm 2 , 14mg / cm 2 、15mg / cm 2 、15.5mg / cm 2 etc., or any value between any two values, but not limited thereto.

[0132] In some embodiments, the porosity of the negative electrode film layer is 16%-30%, optionally 19%-27%. Examples include 17%, 19%, 21%, 23%, 25%, 27%, and the like, or any value between these two values. This facilitates the negative electrode film layer to achieve both high capacity and a suitable pore structure, thereby facilitating a secondary battery with both high energy density and good storage and kinetic performance.

[0133] In some embodiments, the thickness of the negative electrode film layer is ≥70 μm, optionally 90-130 μm. For example, the thickness of the negative electrode film layer is 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, etc., or a value between any two values, but not limited thereto.

[0134] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0135] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0136] The above embodiments are described only by taking the composition of the negative electrode film layer on the surface of one side of the negative electrode current collector as an example. It should be understood that the negative electrode current collector has two surfaces opposite to each other in the direction of its thickness, and the negative electrode film layer described in the above embodiments is arranged on any one or both of the two opposite surfaces of the negative electrode current collector. It should be noted that the various negative electrode film layer parameters (such as compaction density, surface density, porosity, thickness, etc.) given in the present disclosure refer to the parameters of the negative electrode film layer on a single side of the negative electrode current collector. When the negative electrode film layer is arranged on both sides of the negative electrode current collector, the parameters of the negative electrode film layer on either side meet the requirements of the present disclosure and are considered to fall within the scope of protection of the present disclosure.

[0137] In the present disclosure, the negative electrode sheet may include other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode sheet further includes a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector; in some embodiments, the negative electrode sheet further includes a protective layer covering the surface of the negative electrode film layer.

[0138] In the present disclosure, the I of a material (eg, a first carbon-based material, a second carbon-based material, etc.) D / I G The value can be tested using Raman spectrometer, I D The Raman spectrum of the material is 1350±50cm -1 The D peak intensity at I G The Raman spectrum of the material is 1580±50cm -1 The test conditions can be: excitation wavelength 532nm, grating 600 lines, objective lens 50 times, integration time 10s, accumulation times 3 times, surface scanning, obtain 100 points of D peak and G peak intensity, calculate the I of 100 points D / I G , remove the largest and smallest 25 I D / I G The average value of the remaining 50 points is the I D / I G The testing instrument may be a Hofiba LabRAM HR800 Raman spectrometer.

[0139] In the present disclosure, the XRD diffraction pattern of the material (eg, the first carbon-based material, the second carbon-based material, etc.) is 3R(101) / I 2H(004)The values ​​can be tested using an X-ray diffractometer in accordance with JIS K 0131-1996 to obtain an X-ray diffraction pattern of the carbon material. The test conditions can be: the carbon material is prepared using a flat sample preparation method, CuKα rays are used as the radiation source, a copper target is used as the anode target, a voltage of 40 kV, a current of 40 mA, an anti-scatter slit of 1 mm, a scanning 2θ angle range of 20°-80°, a step size of 0.01671°, a step length of 0.24 s per step, and a scanning rate of 4° / min. The test instrument can be a Bruker D8 Discover X-ray diffractometer. The 2θ of the diffraction peak of the 3R phase 101 crystal plane is in the range of 43°-44°, the 2θ of the diffraction peak of the 2H phase 004 crystal plane is in the range of 53°-55°, and the 2θ of the diffraction peak of the 3R phase 012 crystal plane is in the range of 46°-47°. The peak intensity of the diffraction peak of the 3R phase 101 crystal plane and the peak intensity of the diffraction peak of the 2H phase 004 crystal plane are expressed as the integrated areas of the corresponding diffraction peaks.

[0140] In the present disclosure, the volume distribution particle size Dv10, Dv50, and Dv90 of the material (e.g., the first carbon-based material, the second carbon-based material, etc.) are well-known in the art, and respectively represent the particle size corresponding to when the cumulative volume distribution percentage of the material reaches 10%, 50%, and 90%, and can be measured using instruments and methods known in the art. For example, it can be measured using a laser particle size analyzer with reference to GB / T 19077-2016. The test instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0141] In the present disclosure, the specific surface area BET of a material (e.g., a first carbon-based material, a second carbon-based material, etc.) is a well-known meaning in the art and can be measured using instruments and methods known in the art. For example, it can be measured using the nitrogen adsorption specific surface area analysis test method according to GB / T 19587-2017 and calculated using the BET (Brunauer Emmett Teller) method. The test instrument can be a Tri-Star 3020 specific surface area pore size analysis tester from Micromeritics, USA.

[0142] In the present disclosure, the degree of graphitization of a material (e.g., the first carbon-based material, the second carbon-based material) has a well-known meaning in the art and can be tested using instruments and methods known in the art. For example, an X-ray diffractometer (e.g., Bruker D8 Discover) can be used for testing. The test can refer to JIS K 0131-1996 and JB / T 4220-2011 to obtain the average interlayer spacing d of the C(002) plane in the crystal structure of the material. 002 Then according to the formula g=(0.344-d 002) / (0.344-0.3354)×100% to calculate the degree of graphitization. In the above formula, d 002 It is the average interlayer spacing of the C(002) planes in the material's crystal structure expressed in nanometers (nm).

[0143] In the present disclosure, the pore area, S1, and S2 values ​​of the first carbon-based material can be obtained by using a cross-section polisher (such as the IB-09010CP argon ion cross-section polisher from JEOL of Japan) to obtain the cross-section of the first carbon-based material; then, referring to JY / T010-1996, a scanning electron microscope (such as the Sigma 300 scanning electron microscope from ZEISS of Germany) is used to scan the cross-section of the first carbon-based material; finally, the pore area of ​​any one hole in the first carbon-based material is obtained respectively through image processing software (such as AVIZO); and the total pore area S2 of the internal area and the total pore area S1 of the external area, and thereby the value of S2 / S1 is obtained. For example, samples can be obtained from different areas of the negative electrode sheet in the secondary battery, and at least 5 positions (such as 5, 10, 15 or even more) are randomly selected from the sample to obtain cross sections using a cross-section polisher, and at least 10 particles (such as 10, 20, 50 or even more particles) are randomly selected from the scanning electron microscope images of each cross section. The total pore area S2' and the total pore area S1' of the inner region of each particle cross section are obtained using image processing software according to the above definition, and the S2' / S1' value of each particle cross section is obtained. The arithmetic average of the S2' / S1' of all the measured particle cross sections is calculated as the S2 / S1 value of the first carbon-based material.

[0144] In the present disclosure, the gram capacity of a material (such as a first carbon-based material, a second carbon-based material, etc.) has a meaning well known in the art and can be tested using methods known in the art. An exemplary test method is as follows: the sample powder is mixed evenly with the conductive agent carbon black (SuperP), the binder polyvinylidene fluoride (PVDF) in a mass ratio of 91.6:1.8:6.6 and the solvent N-methylpyrrolidone (NMP) to form a slurry; the prepared slurry is applied on the surface of the negative electrode current collector copper foil, dried in an oven and then used; ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and then LiPF6 is dissolved in the above organic solvent. An electrolyte solution with a concentration of 1 mol / L was prepared. A lithium metal sheet was then used as the counter electrode, and a polypropylene (PP) film was used as the separator. The electrolyte and the above-mentioned electrolyte were then assembled into a CR2430 button cell in an argon-protected glove box. The resulting button cell was left to stand for 12 hours and then discharged at a constant current of 0.05C to 0.005V at 25°C. The cell was left to stand for 10 minutes, and then discharged at a constant current of 50μA to 0.005V. The cell was left to stand for 10 minutes, and then discharged at a constant current of 10μA to 0.005V. The cell was then charged at a constant current of 0.1C to 2V, and the charge capacity was recorded. The ratio of the charge capacity to the sample mass is the gram capacity of the corresponding material (e.g., the first carbon-based material, the second carbon-based material, etc.).

[0145] In the present disclosure, whether there is a coating layer on the surface of a material (eg, the first carbon-based material, the second carbon-based material, etc.) can be determined by transmission electron microscopy.

[0146] In the present disclosure, the powder compaction density of a material (e.g., a first carbon-based material, a second carbon-based material, etc.) is a well-known meaning in the art and can be measured using instruments and methods known in the art. For example, it can be measured using an electronic pressure testing machine (e.g., a UTM7305 electronic pressure testing machine) with reference to GB / T 24533-2009. An exemplary test method is as follows: 1 g of sample powder is weighed and added to a container with a bottom area of ​​1.327 cm 2 In the mold, pressurize to 50000N, hold the pressure for 30s, then release the pressure, hold for 10s, and then record and calculate the powder compaction density of the material under 50000N pressure.

[0147] In the present disclosure, the proportion of primary particles in the first carbon-based material and / or the second carbon-based material refers to: randomly selecting a test sample in the negative electrode film layer, randomly selecting multiple test areas in the test sample, using a scanning electron microscope to obtain images of the multiple test areas, and counting the proportion of the number of first carbon-based materials with primary particle morphology in each image to the total number of first carbon-based material particles. The average value of multiple statistical results is the proportion of primary particles in the first carbon-based material.

[0148] In the present disclosure, the surface density of the negative electrode film layer has a meaning well known in the art and can be tested using methods known in the art. For example, a negative electrode sheet coated on one side and cold pressed can be taken (if it is a double-sided coated negative electrode sheet, the negative electrode film layer on one side can be wiped off first), punched into small discs with an area of ​​S', weighed, and recorded as M1. Then wipe off the negative electrode film layer of the weighed negative electrode sheet, weigh the weight of the negative electrode current collector, and record it as M0. Surface density of negative electrode sheet = (M1-M0) / S'.

[0149] In the present disclosure, the compacted density of the negative electrode film layer is a well-known term in the art and can be measured using methods known in the art. [Compacted density of the negative electrode film layer = area density of the negative electrode film layer / thickness of the negative electrode film layer].

[0150] The thickness of the negative electrode film layer is well known in the art and can be measured using methods known in the art, such as using a micrometer (e.g., Mitutoyo 293-100, with an accuracy of 0.1 μm). It should be noted that the thickness range given in this disclosure is 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 disclosure, it meets the requirements of this disclosure.

[0151] In the X-ray diffraction (XRD) analysis test disclosed herein, a copper target can be used as an anode target, and CuKα rays can be used as a radiation source. The scanning 2θ angle range was 20°-80°, and the scanning rate was 4° / min.

[0152] It should be noted that the above-mentioned various parameter tests on the negative electrode active material or the negative electrode film layer can be conducted by sampling and testing the prepared secondary battery according to the following steps.

[0153] Discharge the secondary battery (for safety reasons, the secondary battery is generally fully discharged). Disassemble the secondary battery, remove the negative electrode, and soak the negative electrode in dimethyl carbonate for a certain period of time (e.g., 2-10 hours). Then remove the negative electrode and dry it at a certain temperature and time (e.g., 60°C for more than 4 hours). After drying, remove the negative electrode. Samples can now be taken from the dried negative electrode to test the aforementioned parameters related to the negative electrode film, such as the surface density, compacted density, porosity, and thickness of the negative electrode film.

[0154] The dried negative electrode sheet is baked at a certain temperature and time (for example, 400°C for more than 2 hours), and a sample of the negative electrode active material is taken from any area of ​​the baked negative electrode sheet (a blade can be used to scrape the powder for sampling); the collected negative electrode active material is sieved (for example, with a 200-mesh sieve) to finally obtain a sample that can be used to test the parameters of the above-mentioned negative electrode active materials.

[0155] In the present disclosure, the first carbon-based material mentioned above can be prepared by the following method of the present disclosure; the second carbon-based material mentioned above can be obtained commercially, or can also be prepared by the following method of the present disclosure.

[0156] 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 raw material and the filler material in a predetermined ratio, then keeping the mixture at a first temperature T1 for a first time t1, and cooling the mixture to room temperature to obtain an intermediate; step 3, keeping the obtained intermediate at a second temperature T2 for a second time t2, and obtaining the first carbon-based material having a pore structure and satisfying I D / I G ≤0.27, where I D Indicates that the Raman spectrum is at 1350±50cm -1 The D peak intensity at I G Indicates that the Raman spectrum is at 1580±50cm -1 The G peak intensity at .

[0157] In some embodiments, in step 1, the raw material for preparing the first carbon-based material includes natural graphite. Natural graphite generally refers to graphite naturally formed in nature, which does not require graphitization, and the interior of natural graphite particles generally has a relatively large number of closed-pore structures. Optionally, the natural graphite includes one or more of flake graphite, natural spherical graphite, and microcrystalline graphite, and particularly includes natural spherical graphite.

[0158] "Natural spherical graphite" refers to natural graphite with a spherical or quasi-spherical shape, and not all natural graphite particles are controlled to be ideal spheres. In some embodiments, natural spherical graphite with a desired particle size and morphology can be obtained by pre-treating flake graphite. Optionally, the pre-treatment includes crushing, classification, spheroidization, purification, and other processes.

[0159] In some embodiments, in step 1, the volume distribution particle size Dv50 of the raw material may be 15 μm-20 μm.

[0160] In some embodiments, in step 1, the specific surface area of ​​the raw material may be ≥ 2.5 m 2 / g, optional 2.5m 2 / g-10.0m 2 When the specific surface area of ​​the raw material is within the above range, it is beneficial to perform subsequent filling treatment and obtain the first carbon-based material with a desired specific surface area.

[0161] In some embodiments, in step 2, the softening point temperature of the filling material is 90° C.-150° C. Alternatively, the softening point temperature of the filling material is 94° C.-146° C., 94° C.-142° C., 94° C.-138° C., 94° C.-134° C., 94° C.-130° C., 104° C.-146° C., 104° C.-142° C., 104° C.-138° C., 104° C.-134° C., 104° C.-130° C.

[0162] In some embodiments, in step 2, the volume distribution particle size Dv50 of the filler material is less than or equal to 6 μm, and can be selected from 1 μm-6 μm, 1 μm-5 μm, 2 μm-5 μm, and 3 μm-5 μm. This facilitates the filler material to be melted by heat and filled into the pore structure of the raw material, and also helps to improve the uniformity of the dispersion of the filler material and the raw material.

[0163] In some embodiments, in step 2, the coking value of the filler material is 15%-40%, and optionally 18%-34%. In this disclosure, the coking value of the filler material is well known in the art and can be measured using instruments and methods known in the art. For example, it can be measured in accordance with GB / T 8727-2008.

[0164] In some embodiments, in step 2, the filling material includes one or more of coal tar, petroleum asphalt, polymer compounds and resins, and may optionally include one or more of coal tar and petroleum asphalt.

[0165] In some embodiments, in step 2, the mass ratio of the filling material to the raw material is (10-40):100, and can be optionally (10-30):100, (10-25):100, (10-20):100, (12-30):100, (14-28):100, or (15-25):100.

[0166] In step 2, by adjusting one or more parameters such as the type, softening point, coking value, and addition amount of the filler material within the above-mentioned range, it is beneficial to adjust the number and / or pore size of the pores in the outer region and the inner region of the first carbon-based material within a suitable range, which is beneficial to adjust the S2 / S1 of the first carbon-based material within a suitable range. For example, this can be achieved by adjusting the temperature, coating amount, softening point, etc. For example, increasing the filling amount will reduce S2 / S1, while increasing the softening point of the filler material will increase S2 / S1, thereby obtaining the desired S2 / S1.

[0167] In addition, the I of the first carbon-based material can be adjusted to a certain extent by adjusting the type and softening point of the filler material. D / I G Generally speaking, the higher the softening point of the filling material, the D / I G The smaller the value.

[0168] By adjusting the type, softening point, coking value, addition amount and other parameters of the filling material within the above range, the viscosity of the filling material is not high after being heated and melted, and it maintains good fluidity. At the same time, it is not easy to adhere to the raw material particles, which can reduce the agglomeration of the raw material particles in the subsequent preparation process. This can also reduce the problems of increased surface defects of the first carbon-based material particles and increased surface active sites due to the need to add a depolymerization process.

[0169] In some embodiments, in step 2, the heating process of uniformly mixing the raw material and the filling material in a predetermined ratio and then heating the mixture to the first temperature T1 may be a staged heating process.

[0170] In some embodiments, the staged temperature increasing process includes a first temperature increasing process, a second temperature increasing process, and a third temperature increasing process.

[0171] In some embodiments, the first temperature raising process is to raise the temperature to 200° C.-250° C. and keep the temperature at this temperature for 0.5 h-3 h.

[0172] In some embodiments, the second heating process is to heat the material to 450°C-550°C and hold the temperature for 0-2 hours. When the holding time is 0 hours, it means that when the temperature is within the range of 450°C-550°C, no holding treatment is performed, but the temperature is continued to the first temperature T1.

[0173] In some embodiments, the third temperature increasing process is to increase the temperature to the first temperature T1 and keep the temperature at the first time t1.

[0174] In the staged heating process, the temperature is first raised to 200℃-250℃. Since the heating temperature is higher than the softening point of the filling material, the filling material is melted and softened by the heat. Keeping it warm for 0.5h-3h allows it to flow and fill into the pore structure of the raw material; then the temperature is raised to 450℃-550℃. At this time, the melted and softened filling material undergoes a carbonization reaction, gradually forming a semi-coke state and turning into a viscous liquid or solid, thereby preventing the filling material from entering the entire pore structure of the raw material; finally, the temperature is raised to the first temperature. At this time, the filling material undergoes a carbonization reaction, thereby enabling the pore structure occupied by the filling material to be effectively filled.

[0175] In some embodiments, in step 2, the temperature is raised to the first temperature T1 at a rate of 1°C / min-10°C / min. For example, the heating rate can be 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, or any range thereof.

[0176] In some embodiments, the heating rate of the first heating process may be 1°C / min-10°C / min, optionally 1.5°C / min-8°C / min, 1.5°C / min-6°C / min, 2°C / min-6°C / min, or 2°C / min-5°C / min. In some embodiments, the heating rate of the second heating process may be 1°C / min-10°C / min, optionally 2°C / min-8°C / min. In some embodiments, the heating rate of the third heating process may be 1°C / min-10°C / min, optionally 2°C / min-8°C / min.

[0177] In some embodiments, in step 2, the first temperature T1 is 700° C.-1200° C. For example, the first temperature T1 can be 700° C., 750° C., 800° C., 850° C., 900° C., 950° C., 1000° C., 1050° C., 1100° C., 1200° C., or any range thereof. Alternatively, the first temperature T1 is 750° C.-1100° C., 800° C.-1100° C., 850° C.-1100° C., 900° C.-1100° C., or 850° C.-1000° C.

[0178] In some embodiments, in step 2, the first time t1 is 1 hour to 5 hours. For example, the first time t1 can be 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, or any range thereof. Alternatively, the first time t1 is 2 hours to 4 hours.

[0179] When the first temperature and the first time are within the above ranges, it is beneficial to adjust the number of pores and / or the size of pores in the outer region and the inner region of the carbon material to be within an appropriate range.

[0180] In some embodiments, in step 2, the heat treatment can be carried out in a device capable of programmed temperature increase, such as a medium frequency furnace, a roller kiln, a rotary kiln, a pusher kiln, a vertical granulation kettle, a horizontal granulation kettle, a vertical reactor, a horizontal reactor or a drum furnace.

[0181] In some embodiments, in step 2, the heat treatment atmosphere may be a protective gas atmosphere, which may include one or more of nitrogen, argon, and helium.

[0182] In step 2, by adjusting one or more of the heating rate, the first temperature, the first time, the heating process, etc. within the above range, it is beneficial to adjust the number and / or pore size of the pores in the outer region and the inner region of the first carbon-based material within a suitable range, thereby facilitating the adjustment of the S1 / S of the first carbon-based material within a suitable range. For example, by adjusting the heating rate of each stage within the range of ≤3°C / min, S1 / S can be made ≥60%, and by adjusting the heating rate of each stage to 8-10°C / min, S1 / S can be made ≤85%.

[0183] In some embodiments, in step 3, the second temperature T2 is 2070° C.-2700° C. Optionally, the second temperature T2 is 2070° C.-2570° C., 2070° C.-2510° C., 2070° C.-2450° C., 2070° C.-2360° C., 2140° C.-2570° C., 2140° C.-2510° C., 2140° C.-2450° C., or 2140° C.-2360° C.

[0184] In some embodiments, in step 3, the second time t2 is 1.5 hours to 6 hours. For example, the second time t1 can be 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, or any range thereof. Alternatively, the second time t2 is 2 hours to 5 hours.

[0185] When the second temperature T2 and the second time t2 are within the above range, it is beneficial to adjust the I D / I G , which is also beneficial for the first carbon-based material to have a stable structure. Generally, the higher the second temperature and / or the longer the second time, the greater the stability of the first carbon-based material. D / I G The smaller.

[0186] In some embodiments, in step 3, the heat treatment may be performed in a medium frequency furnace, a box-type graphitization furnace, an Acheson graphitization furnace, a continuous graphitization furnace, or an inner-string graphitization furnace.

[0187] 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.

[0188] In step 3, by adjusting one or more of the second temperature and the second time within the above range, it is beneficial to adjust the content of disordered carbon in the first carbon-based material to be within a suitable range, which is beneficial for the first carbon-based material to have a suitable graphitization degree, interlayer spacing and I D / I G wait.

[0189] In the preparation method of the first carbon-based material, by adjusting one or more of the parameters of natural graphite, the parameters of the filling material, the heating rate, the first temperature, the first time, the heating process, the second temperature, the second time, etc. within the above range, it is beneficial to adjust the S1 / S, I D / IG, degree of graphitization, gram capacity, specific surface area, particle size, powder compaction density and other parameters.

[0190] In some embodiments, the second carbon-based material is natural graphite. Alternatively, the second carbon-based material is natural spherical graphite. Natural graphite having the above-mentioned properties can be directly provided as the second carbon-based material.

[0191] In some embodiments, the second carbon-based material has a carbon coating layer on at least a portion of its surface. A method for preparing the second carbon-based material having a carbon coating layer includes: providing natural graphite as a raw material; mixing the natural graphite and a coating agent in a certain proportion; and performing a heat treatment.

[0192] In some embodiments, the natural graphite is natural spherical graphite. The particle size of the natural graphite used as the raw material is ≤15 μm, optionally 6 μm-13 μm, such as 7 μm-12 μm.

[0193] In some embodiments, the coating agent is selected from one or more of coal tar, petroleum tar, phenolic resin, coconut shell, etc.

[0194] In some embodiments, the heat treatment temperature is 900°C-1200°C. In some embodiments, the heat treatment time is 1-5 hours. By adjusting the heat treatment temperature, different I D / I G The second most valuable carbon-based material.

[0195] The coating agent is carbonized by the heat treatment, so that at least a portion of the surface of the second carbon-based material has a carbon coating layer. In some embodiments, the carbon coating layer is an amorphous carbon coating layer.

[0196] [Positive electrode]

[0197] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes the positive electrode active material according to the first aspect of the present disclosure.

[0198] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0199] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0200] In some embodiments, when the battery cell is a lithium-ion battery, the positive electrode active material may adopt the positive electrode active material for lithium-ion batteries known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present disclosure is not limited to these materials, and other traditional materials that can be used as 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 may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi1 / 3Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 C o0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 C o0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 C o0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 C o0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 C o0.15 Al 0.05O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0201] The battery's charge and discharge processes involve the intercalation and deintercalation of lithium, leading to different molar Li contents at different discharge states. The molar Li contents listed in this disclosure for positive electrode active materials refer to the material's initial state, i.e., before addition. When a positive electrode active material is used in a battery system, its molar Li content will change over the course of charge and discharge cycles.

[0202] The molar oxygen content in the positive electrode active materials listed in this disclosure is only a theoretical value. Lattice oxygen release can cause the molar oxygen content to change, and the actual molar oxygen content will fluctuate. The molar content of other elements may also change after battery manufacturing and during use. Therefore, the molar ratios of the elements in the molecular formulas of the positive electrode active materials above are the molar ratios at the time of preparation.

[0203] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0204] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0205] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0206] [Electrolytes]

[0207] The electrolyte conducts ions between the positive and negative electrodes. This disclosure does not specifically limit the type of electrolyte, and the electrolyte can be selected based on needs. For example, the electrolyte can be liquid, gel, or solid.

[0208] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0209] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0210] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0211] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0212] [Isolation film]

[0213] In some embodiments, the battery cell further includes a separator. The present disclosure has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0214] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0215] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0216] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0217] In some embodiments, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the battery cell may be a soft shell, such as a pouch-type soft shell. The soft shell may be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0218] The present disclosure has no particular limitation on the shape of the battery cell, which may be cylindrical, square, or any other shape. For example, FIG3 shows a battery cell 5 having a square structure as an example.

[0219] In some embodiments, referring to Figure 4, the outer packaging may include a shell 51 and a top cover assembly 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the top cover assembly 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0220] In some embodiments, battery cells may be assembled into a battery module. The battery module may contain one or more battery cells. The specific number may be selected by those skilled in the art based on the application and capacity of the battery module.

[0221] FIG5 shows an example battery module 4. Referring to FIG5 , in the battery module 4, multiple battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the multiple battery cells 5 may be secured together using fasteners.

[0222] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0223] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0224] Figures 6 and 7 illustrate an example battery pack 1. Referring to Figures 6 and 7 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be positioned over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0225] In addition, the second aspect of the present disclosure provides an electric device, which includes the secondary battery provided by each of the above embodiments. The secondary battery can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0226] As the electrical device, a battery cell, a battery module or a battery pack can be selected according to its usage requirements.

[0227] Figure 8 shows an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0228] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be lightweight and thin, and may use a battery cell as a power source.

[0229] Example

[0230] The following examples are provided. The examples described below are illustrative and are intended only to explain the present disclosure and are not to be construed as limiting the present disclosure. Where specific techniques or conditions are not specified in the examples, the methods were performed according to those described in the literature in the art or according to the product specifications. Reagents or instruments used without manufacturer's indication are all commercially available conventional products.

[0231] The materials used in the examples and comparative examples of the present disclosure can be obtained commercially or prepared by the following process.

[0232] Preparation of material 1-1:

[0233] The flake graphite is mechanically crushed, classified, spheroidized and purified to obtain natural spherical graphite, wherein the volume distribution particle size of the natural spherical graphite is Dv50=16.3μm. The obtained natural spherical graphite is mixed with the filler petroleum asphalt in a mass ratio of 100:25, and the softening point of the petroleum asphalt is 115°C. The mixed material is then placed in a programmable temperature raising device, heated to 200°C and kept warm for 1 hour, and then continuously heated to 650°C (first treatment temperature), kept warm for 2 hours, and then cooled to room temperature to obtain an intermediate. The obtained intermediate is placed in a graphitization furnace and heat treated at 2490°C (second treatment temperature). After the end, it is demagnetized and sieved to obtain material 1-1. Material 1-1 meets: I D / I G =0.18, S2 / S1=16.1, volume distribution particle size Dv50=17.5 μm.

[0234] Preparation of materials 1-2 to 1-4:

[0235] The preparation methods of materials 1-2 to 1-4 are similar to those of material 1-1, except that the ratio of natural spherical graphite to filler is adjusted, and the second treatment temperature is adjusted within the range of 2000°C to 2600°C, so that the I D / I G In the range of 0.13-0.33. The details are as follows:

[0236] Table 1.

[0237] Preparation of materials 1-5 to 1-7:

[0238] The preparation methods of materials 1-5 to 1-7 are similar to those of material 1-1, except that the volume distribution particle size Dv50 of the natural spherical graphite is adjusted to be within the range of 15 μm-21 μm, so that the volume distribution particle size Dv50 of materials 1-5 to 1-7 is within the range of 16 μm-22 μm. The details are as follows:

[0239] Table 2.

[0240] Preparation of Material 2-1:

[0241] Provide natural spherical graphite, mix the natural spherical graphite and petroleum asphalt in a mass ratio of 100:10, the softening point of the petroleum asphalt is 250°C, and perform low-temperature heat treatment at 1130°C for 2 hours to obtain natural graphite with a carbon coating layer, namely material 2-1. Wherein, material 2-1 meets the following requirements: D / I G =0.42, volume distribution particle size Dv50=11.2μm, and degree of graphitization is 96.5%.

[0242] Preparation of materials 2-2 to 2-4:

[0243] The preparation methods of materials 2-2 to 2-4 are similar to those of material 2-1, except that the ratio of natural spherical graphite to petroleum asphalt is adjusted within the range of 100:8 to 100:12, and the low-temperature heat treatment is adjusted within the range of 900°C to 1200°C, so that the I D / I G The range is 0.38~0.60. The details are as follows: Table 3.

[0244] Table 3.

[0245] Preparation of materials 2-5 to 2-7:

[0246] The preparation methods of materials 2-5 to 2-7 are similar to those of material 2-1, except that the volume distribution particle size Dv50 of the natural spherical graphite is adjusted to be within the range of 7.0 μm-16 μm, and the volume distribution particle size Dv50 of materials 1-5 to 1-7 is within the range of 7.8 μm-17 μm. The details are as follows:

[0247] Table 4.

[0248] Example 1

[0249] Preparation of secondary batteries:

[0250] 1. Negative Electrode: Mix the negative electrode active material (Material 1-1 (as the first carbon-based material) and Material 2-1 (as the second carbon-based material) in a weight ratio of 70:30), conductive 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 as solvent, and stir thoroughly to form a negative electrode slurry. Apply the negative electrode slurry to both surfaces of the negative electrode current collector copper foil. After drying and cold pressing, the negative electrode sheet is obtained.

[0251] 2. Positive electrode: LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523) is mixed with conductive 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 evenly to obtain a positive electrode slurry. The positive electrode slurry is then coated on both surfaces of the positive electrode current collector aluminum foil. After drying and cold pressing, a positive electrode sheet is obtained.

[0252] 3. Electrolyte: Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and then LiPF6 is dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0253] 4. Isolation film: polypropylene film.

[0254] 5. Preparation of secondary batteries: Place the positive electrode and negative electrode sheets prepared above in order, with the separator placed between the positive and negative electrode sheets to act as an isolate, and then wind them to obtain an electrode assembly; place the electrode assembly in an outer package, inject the electrolyte after drying, and obtain a secondary battery through vacuum packaging, standing, formation, shaping and other processes.

[0255] Examples 2 to 7

[0256] The battery preparation methods of Examples 2-7 are similar to those of Example 1, except that different materials are selected for the first carbon-based material or the second carbon-based material. See Table 5 for details.

[0257] Comparative Example 1

[0258] A secondary battery was assembled similarly to the preparation method of Example 1, except that the negative electrode active material only contained the first carbon-based material used in Example 1 (the material 1-1 prepared above).

[0259] Comparative Example 2

[0260] A secondary battery was assembled similarly to the preparation method of Example 1, except that the negative electrode active material only contained the second carbon-based material used in Example 1 (the material 2-1 prepared above).

[0261] Performance Testing

[0262] 1. Material testing

[0263] The S2 / S1 of the first carbon-based material is obtained by testing using the following method.

[0264] A sample preparation binder and the first carbon-based material powder are mixed evenly and then applied to a copper foil. The mixture is then dried at 60°C for 30 minutes before use. Five samples to be tested are cut into 6 mm x 6 mm pieces at five different locations and attached to the sample stage of a CP-type argon ion cross-section polisher. The samples are then cut using a plasma beam to obtain cross-sections of each sample. The testing instrument can be the IB-09010 CP-type argon ion cross-section polisher from JEOL, Japan.

[0265] Each sample cross section of the first carbon-based material was scanned using a scanning electron microscope, and a scanned image was obtained from an arbitrarily selected region within each sample cross section. The test may refer to JY / T010-1996. The testing instrument may be a Sigma 300 scanning electron microscope from ZEISS, Germany.

[0266] Randomly select cross sections of 20 particles of the first carbon-based material from the scanned image. The area formed by extending 0.25 μm from the particle surface of the first carbon-based material to the interior of the particle is recorded as the external area, and the area inside the external area is recorded as the internal area. Use image processing software to obtain the total pore area S1' of the external area of ​​each particle cross section and the pore area S2' of the internal area of ​​the first carbon-based material, and calculate the value of S2' / S1'; and calculate the arithmetic average of S2' / S1' of all 20 particles as the value of S2 / S1 of the first carbon-based material. The image processing software can be AVIZO.

[0267] 2. Pole piece test

[0268] The negative electrode sheet was cut into 2 cm × 2 cm samples to be tested, and the samples to be tested were fixed on the sample stage with paraffin wax; the sample stage was placed in the sample holder and locked, and the argon ion cross-section polisher (IB-09010CP argon ion cross-section polisher from JEOL, Japan) was turned on and vacuumed to 10 -4 Pa, set the argon flow rate to 0.15 MPa, the voltage to 8 KV, and the polishing time to 2 h, adjust the sample stage to the swing mode and start polishing; randomly select areas in the sample to be tested for scanning testing (refer to JY / T010-1996, scanning electron microscope (Sigma 300 of ZEISS), and obtain the ion polishing cross-sectional morphology (CP) image of the negative electrode sheet at 500 times magnification, as shown in Figure 1. From the arrows in Figure 1, it can be seen that the pore structure distribution of the first carbon-based material and the second carbon-based material is significantly different. Among them, the first carbon-based material has a certain number of pores near the center of the particle, while almost no pores can be seen in the area close to the surface of the particle. On the contrary, significantly larger and more pores can be seen in each area of ​​the second carbon-based material. Mixing the two is conducive to giving full play to the advantages brought by their respective structures.

[0269] 3. Battery performance test

[0270] (1) Low-temperature fast charging performance test of secondary batteries

[0271] At 0°C, the secondary battery was charged to 4.3V at a constant current of 0.33C, then charged to a current of 0.05C at a constant voltage. After standing for 5 minutes, the secondary battery was discharged to 2.8V at a constant current of 0.33C, and its actual capacity was recorded as C0.

[0272] Then the secondary battery is charged with a constant current of 1.0C0, 1.3C0, 1.5C0, 1.8C0, 2.0C0, 2.3C0, 2.5C0, 3.0C0 in sequence to a negative electrode cutoff potential of 4.3V or 0V (whichever is reached first). After each charging is completed, it is necessary to discharge it to 2.8V at 1C0. The negative electrode potential corresponding to charging to 10%, 20%, 30%, etc. until 80% SOC (State of Charge) at different charging rates is recorded, and the charging rate-negative electrode potential curve under different SOC states is drawn. After linear fitting, the charging rate corresponding to the negative electrode potential of 0V under different SOC states is obtained. The charging rate is the charging window under the SOC state, which is recorded as C10% SOC, C20% SOC, C30% SOC, C40% SOC, For C50% SOC, C60% SOC, C70% SOC, and C80% SOC, the charging time T (in minutes) for charging the secondary battery from 10% SOC to 80% SOC (assuming lithium deposition does not occur in the secondary battery) is calculated using the formula (60 / C20% SOC + 60 / C30% SOC + 60 / C40% SOC + 60 / C50% SOC + 60 / C60% SOC + 60 / C70% SOC + 60 / C80% SOC) × 10%. The shorter the charging time, the better the secondary battery's kinetic performance.

[0273] (2) 60℃ storage performance test of secondary batteries

[0274] At 25°C, the prepared secondary battery was charged at a constant current of 1C to 4.3V, then charged at a constant voltage to a current of 0.05C. After standing for 5 minutes, the secondary battery was discharged at a constant current of 1C to 2.8V. The discharge capacity at this time was recorded, which was the discharge capacity before storage.

[0275] At 25°C, the prepared secondary battery was charged at a constant current of 1C to 4.3V, and then charged at a constant voltage to a current of 0.05C. The secondary battery was then stored in a thermostat at 60°C for 150 days. Capacity retention (%) of the secondary battery after 150 days of storage at 60°C = discharge capacity after storage / discharge capacity before storage × 100%.

[0276] The test results of the secondary batteries prepared in Examples 1 to 7 and Comparative Examples 1 to 2 are shown in Table 5 below.

[0277] Table 5.

[0278] Table 5 shows that in Comparative Example 1, the negative electrode active material is entirely the first carbon-based material used in Example 1. Although good high-temperature storage performance is achieved, the low-temperature charging time is too long. In contrast, in Comparative Example 2, the negative electrode active material is entirely the second carbon-based material used in Example 1. Although a shorter low-temperature charging time is achieved, the high-temperature storage performance is poor. In contrast, in Example 1, the use of a mixture of the first and second carbon-based materials allows the battery to achieve both good low-temperature kinetics and high-temperature storage performance.

[0279] Further, the I of the first carbon-based material is adjusted D / I G value, along with the I D / I G It is worth increasing gradually, and the low temperature charging time is gradually reduced, but it will affect the high temperature storage performance, mainly because when I D / I G When it increases, the defects on the material surface increase, the side reactions increase, and the lithium consumption increases, so the high-temperature storage performance is affected to a certain extent.

[0280] Similarly, the second carbonyl I D / I G The change of will also cause the corresponding change of charging capacity and high temperature storage performance. D / I G The increase of the value shortens the low temperature charging time. However, when the value is too high, as shown in Example 7, I D / I G When the value is 0.60, the high temperature storage performance decreases slightly.

[0281] Description Select the appropriate I D / I G The two material values ​​are beneficial for obtaining a balance of simultaneously improved low temperature kinetic properties and high temperature storage properties.

[0282] Examples 8 to 10

[0283] The second carbon-based material used in Example 1 is used, except that the first carbon-based material has different particle sizes, and is assembled into a secondary battery.

[0284] Examples 11 to 13

[0285] The first carbon-based material used in Example 1 is used, except that the second carbon-based material has different particle sizes, and is assembled into a secondary battery.

[0286] The parameters and test results of the secondary batteries prepared in Example 1 and Examples 8 to 13 are shown in Table 6 below.

[0287] Table 6.

[0288] It can be seen from Example 1 and Examples 8 to 10 in the above table that when the volume distribution particle size Dv50 of the first carbon-based material gradually decreases, the low-temperature charging time is shortened, which is beneficial to the low-temperature kinetic performance, but the high-temperature capacity retention rate is also slightly reduced. According to Example 1 combined with Examples 11 to 13, it can be seen that when the volume distribution particle size Dv50 of the second carbon-based material gradually decreases, the low-temperature kinetics is significantly improved, but the high-temperature storage performance is reduced. In addition, in Example 13, when the Dv50 of the first carbon-based material is similar to or even larger than the Dv50 of the second carbon-based material, the high-temperature storage performance is good, while the low-temperature kinetic performance is significantly reduced.

[0289] Examples 14-15

[0290] The first carbon-based material and the second carbon-based material used in Example 1 were used and assembled into a secondary battery. The only difference was the mass ratio of the first carbon-based material and the second carbon-based material. See Table 7 for details.

[0291] The test results of the secondary batteries prepared in Example 1 and Examples 14-15 are shown in Table 7 below.

[0292] Table 7.

[0293] It can be seen from Table 7 above that when the mass proportion of the first carbon-based material is more than 50%, especially 70%, and the mass proportion of the second carbon-based material is less than 50%, especially 30%, the low-temperature kinetic performance and 60°C / 180-day capacity retention rate of the secondary battery can achieve a better balance.

[0294] It should be noted that the present disclosure is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present disclosure, embodiments having substantially the same structure as the technical concept and exerting the same effects are all included in the technical scope of the present disclosure. In addition, within the scope of the present disclosure, various modifications that can be imagined by those skilled in the art to the embodiments, and other methods constructed by combining some of the constituent elements of the embodiments are also included in the scope of the present disclosure. Industrial Applicability

[0295] The present disclosure provides a secondary battery and an electric device. The secondary battery includes a negative electrode plate, the negative electrode plate 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 includes a negative electrode active material, and the negative electrode active material includes a first carbon-based material and a second carbon-based material, wherein the first carbon-based material and the second carbon-based material both have a pore structure, and the I of the first carbon-based material is 1.D / I G is ≤0.27, the I of the second carbon-based material D / I G ≥0.38, where I D Indicates that the Raman spectrum is at 1350±50cm -1 The D peak intensity at I G Indicates that the Raman spectrum is at 1580±50cm -1 The secondary battery has improved low-temperature kinetics and high-temperature storage performance.

Claims

1. A secondary battery, comprising a negative electrode plate, the negative electrode plate comprising 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 comprising a negative electrode active material, the negative electrode active material comprising a first carbon-based material and a second carbon-based material, the first carbon-based material and the second carbon-based material both having a pore structure, and the first carbon-based material having a pore structure. D / I G ≤0.27, I of the second carbon-based material D / I G ≥0.38, where I D Indicates that the Raman spectrum is at 1350±50cm -1 The D peak intensity at I G Indicates that the Raman spectrum is at 1580±50cm -1 The G peak intensity at .

2. The secondary battery according to claim 1, wherein The first carbon-based material D / I G is 0.13-0.25; and / or, The second carbon-based material I D / I G It is 0.40-0.

60.

3. The secondary battery according to claim 1 or 2, wherein: The XRD diffraction pattern of the first carbon-based material 3R(101) / I 2H(004) The XRD diffraction pattern of the second carbon group is smaller than 3R(101) / I 2H(004) ; Optionally, the XRD diffraction pattern of the first carbon-based material is 3R(101) / I 2H(004) Less than or equal to 0.06, preferably 0-0.06; Optionally, the second carbon-based material I 3R(101) / I 2H(004) ≥0.2, preferably 0.22-0.4; Among them I 3R is the diffraction peak intensity of the 101 crystal plane of the carbon-based material 3R phase corresponding to 43°-44° in the XRD diffraction spectrum, I 2H It is the diffraction peak intensity of 004 ​​crystal plane of 2H phase of carbon-based material corresponding to 53°-55° in the XRD diffraction pattern.

4. The secondary battery according to any one of claims 1 to 3, wherein: The volume distribution particle size Dv50 of the first carbon-based material is greater than the volume distribution particle size Dv50 of the second carbon-based material.

5. The secondary battery according to any one of claims 1 to 4, wherein: The volume distribution particle size of the first carbon-based material is Dv50 ≥ 15 μm, optionally 16 μm ≤ Dv50 ≤ 20 μm; and / or The volume distribution particle size of the second carbon-based material is Dv50≤13 μm, optionally 7 μm≤Dv50≤12 μm.

6. The secondary battery according to any one of claims 1 to 5, wherein: The BET specific surface area of ​​the first carbon-based material is smaller than the BET specific surface area of ​​the second carbon-based material.

7. The secondary battery according to claim 6, wherein The specific surface area of ​​the first carbon-based material is less than or equal to 2.1 m 2 / g, optional 1.3m 2 / g-1.9m 2 / g; and / or The specific surface area of ​​the second carbon-based material is less than or equal to 3.6 m 2 / g, optional 1.8m 2 / g-3.4m 2 / g.

8. The secondary battery according to any one of claims 1 to 7, wherein: The graphitization degree of the first carbon-based material is greater than the graphitization degree of the second carbon-based material.

9. The secondary battery according to any one of claims 1 to 8, wherein: The graphitization degree of the first carbon-based material is ≥ 95%, and can be 96.0%-98.5%; and / or The graphitization degree of the second carbon-based material is ≥95%, and can be optionally 95.0%-97.5%.

10. The secondary battery according to any one of claims 1 to 9, wherein: The first carbon-based material includes an external region and an internal region located inside the external region, wherein the external region refers to a region extending 2.5 μm inwardly from the particle surface of the first carbon-based material. In the cross-sectional view of the first carbon-based material, the total pore area of ​​the external region of the first carbon-based material is denoted as S1, and the total pore area of ​​the internal region is denoted as S2. The first carbon-based material satisfies S2>S1; optionally, 2.5≤S2 / S1≤460.

11. The secondary battery according to any one of claims 1 to 10, wherein: The area of ​​a single pore structure in the outer region of the first carbon-based material is less than or equal to 0.15 μm 2 , can be selected to be less than or equal to 0.13μm 2 and / or, The inner region of the first carbon-based material includes at least one area greater than or equal to 0.15 μm 2 The pore structure may include one or more pores with an area of ​​0.15 μm 2 -2.0urn 2 The pore structure.

12. The secondary battery according to any one of claims 1 to 11, wherein: At least part of the surface of the second carbon-based material has a coating layer; optionally, the coating layer is a carbon coating layer.

13. The secondary battery according to any one of claims 1 to 12, wherein: The first carbon-based material satisfies at least one of the following: (1) The compaction density of the first carbon-based material under 50000N is ≤ 2.10 g / cm 3 , optionally 1.85 g / cm 3 -2.00g / cm 3 ; (2) The volume distribution particle size Dv90 of the first carbon-based material is less than or equal to 40 μm, and optionally 30 μm-38 μm; (3) the particle size distribution of the first carbon-based material [(Dv90)-(Dv10)] / (Dv50)]≤1.55, optionally 0.90-1.50; (4) The gram capacity of the first carbon-based material is ≥362 mAh / g, optionally 365 mAh / g-372 mAh / g; (5) The first carbon-based material includes primary particles. Optionally, the primary particles account for more than or equal to 80% of the first carbon-based material.

14. The secondary battery according to any one of claims 1 to 13, wherein: The second carbon-based material satisfies at least one of the following: (1) The gram capacity of the second carbon-based material is ≥358 mAh / g, optionally 360 mAh / g-367 mAh / g; (2) The compaction density of the second carbon-based material under 50000N is ≤1.95g / cm 3 , optionally 1.75 g / cm 3 -1.90g / cm 3 ; (3) The second carbon-based material includes primary particles. Optionally, the primary particles account for a large proportion of the second carbon-based material. is equal to 80%; (4) The second carbon-based material is natural graphite.

15. The secondary battery according to any one of claims 1 to 14, wherein: The mass proportion of the first carbon-based material in the negative electrode active material is greater than the mass proportion of the second carbon-based material in the negative electrode active material; Optionally, the mass proportion of the first carbon-based material in the negative electrode active material is ≥55wt%, optionally 60wt%-80wt%.

16. The secondary battery according to any one of claims 1 to 15, wherein: The negative electrode active material satisfies at least one of the following: (1) The volume distribution particle size Dv50 of the negative electrode active material is ≤17.0 μm, which can be 12 μm-16.5 μm; (2) The volume distribution particle size Dv90 of the negative electrode active material is ≤35 μm, which can be 25 μm-33 μm; (3) The volume particle size distribution of the negative electrode active material satisfies: (Dv90-Dv10) / Dv50≤1.50, which can be 1.0-1.45; (4) The specific surface area of ​​the negative electrode active material is ≤3.0 m 2 / g, optional 1.5m 2 / g-2.8m 2 / g.

17. The secondary battery according to any one of claims 1 to 16, wherein: The negative electrode film layer satisfies at least one of the following: (1) The compaction density of the negative electrode film layer is ≥1.5 g / cm 3 , optionally 1.6 g / cm 3 -1.7g / cm 3 ; (2) The surface density of the negative electrode film layer is ≥10 mg / cm 2 , optionally 11.0 mg / cm 2 -15.0mg / cm 2 ; (3) The porosity of the negative electrode film layer is 16%-30%, optionally 19.0%-27%; (4) The thickness of the negative electrode film layer is ≥70 μm, and can be optionally 90 μm-130 μm.

18. An electrical device comprising the secondary battery according to any one of claims 1 to 17.

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