Secondary battery and electric device

Abstract

The invention provides a secondary battery and an electric device. The secondary battery comprises a negative electrode piece, the negative electrode piece comprises a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector, the negative electrode film layer comprises a negative electrode active material, the negative electrode active material comprises a first carbon-based material and a second carbon-based material, the first carbon-based material and the second carbon-based material both have pore structures, the ID / IG of the first carbon-based material is less than or equal to 0.27, the ID / IG of the second carbon-based material is greater than or equal to 0.38, ID represents the D peak intensity of a Raman spectrum at 1350 + / -50 cm <-1 >, and IG represents the G peak intensity of the Raman spectrum at 1580 + / -50 cm <-1 >. The secondary battery has improved low temperature dynamic performance and high temperature storage performance.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and particularly to a secondary battery and an electrical device. Background Art

[0002] In recent years, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power stations, as well as in multiple fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. With the increasingly wide application range of secondary batteries, severe challenges have been posed to the performance of secondary batteries. For example, it is required that the secondary battery has good kinetic performance while also having good storage life, especially being able to be used in a wide range of ambient temperatures. Summary of the Invention

[0003] The present application is made in view of the above problems, and its purpose is to provide a secondary battery and an electrical device, wherein the secondary battery simultaneously has improved low-temperature kinetic performance and high-temperature storage life.

[0004] The first aspect of the present application 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, the negative electrode active material includes a first carbon-based material and a second carbon-based material, wherein both the first carbon-based material and the second carbon-based material have a pore structure, and the I D / I G ≤0.27 for the first carbon-based material, and the I D / I G ≥0.38 for the second carbon-based material, where I D represents the intensity of the D peak of the Raman spectrum at 1350 ± 50 cm -1 , and I G represents the intensity of the G peak of the Raman spectrum at 1580 ± 50 cm -1 .

[0005] Thus, in the present application, by combining a first carbon-based material and a second carbon-based material that both have a pore structure but have different I D / I G values, a mixed negative electrode active material is obtained. Among them, both the first carbon-based material and the second carbon-based material have a pore structure, which can provide a transmission channel for active ions, accelerate the reaction between the active ions and the negative electrode active material, and thus improve the kinetic performance of the secondary battery. On this basis, the I D / I G≤0.27, reflecting a relatively high degree of surface carbon order and fewer defects in the material, thus resulting in fewer side reactions with the electrolyte and being beneficial to the high-temperature storage performance of the secondary battery. The second carbon-based material has the characteristic of I D / I G ≥0.38, with relatively high reactivity, thereby further providing good low-temperature kinetic performance. Using both of them as the negative electrode active material can give full play to the advantages of both, enabling the secondary battery to have both good low-temperature kinetic

[0006] performance and high-temperature storage performance.

[0007] In some embodiments, the I D / I G of the first carbon-based material is 0.13 - 0.25; and / or, the I D / I G of the second carbon-based material is within 0.40 - 0.60. When the I D / I G of the first carbon-based material is within the above range, the degree of amorphousness of carbon in the material is relatively low, and there are fewer side reactions at high temperatures, which is beneficial to the high-temperature storage performance of the secondary battery. When the I D / I G of the second carbon-based material is within the above range, it has appropriate reactivity, thereby improving the low-temperature kinetic performance of the secondary battery.

[0008] In some embodiments, the I 3R(101) / I 2H(004) in the XRD diffraction pattern of the first carbon-based material is less than the I 3R(101) / I 2H(004) in the XRD diffraction pattern of the second carbon-based material. Optionally, the I 3R(101) / I 2H(004) in the XRD diffraction pattern of the first carbon-based material is less than or equal to 0.06, and further optionally is 0 - 0.06. Optionally, the I 3R / I 2H of the second carbon-based material is ≥0.2, and further optionally is 0.22 - 0.4. Wherein I 3R(101) is the diffraction peak intensity of the 101 crystal plane of the graphite 3R phase corresponding to 43° - 44° in the XRD diffraction pattern, and I 2H(004) is the diffraction peak intensity of the 004 crystal plane of the graphite 2H phase corresponding to 53° - 55° in the XRD diffraction pattern.

[0009] In some embodiments, the volume-based particle size Dv50 of the first carbon-based material is greater than the volume-based particle size Dv50 of the second carbon-based material. Adjusting the volume-based particle sizes of the first and second carbon-based materials, especially when the second carbon-based material has a relatively small volume-based particle size, is beneficial to increasing the specific surface area of the material, thereby further improving the kinetic performance of the secondary battery.

[0010] In some embodiments, the volume-based 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-based 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-based particle size Dv50 of the second carbon-based material is small and within the above range, it helps to enhance the contact between materials, reduce the transport distance of active ions, and further improve the kinetic performance of the secondary battery at low temperatures.

[0011] In some embodiments, the BET specific surface area of the first carbon-based material is less than the BET specific surface area of the second carbon-based material. By adjusting the specific surface area of the materials, making the specific surface area of the first carbon-based material smaller results in fewer side reactions with the electrolyte, which is beneficial to improving the high-temperature storage performance of the secondary battery; at the same time, making the specific surface area of the second carbon-based material larger can provide a larger reaction surface, which is beneficial to the reaction of active ions and improves the kinetic performance of the secondary battery.

[0012] In some embodiments, the specific surface area of the first carbon-based material is less than or equal to 2.1 m 2 / g, optionally 1.3 m 2 / g - 1.9 m 2 / g; and / or, the BET of the second carbon-based material is ≤ 3.6 m 2 / g, optionally 1.8 m 2 / g - 3.4 m 2 / g. 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 cycling performance of the secondary battery. When the specific surface area of the second carbon-based material is within the above range, it can provide good low-temperature kinetic performance.

[0013] In some embodiments, the graphitization degree of the first carbon-based material is greater than the graphitization degree of the second carbon-based material.

[0014] In some embodiments, the graphitization degree of the first carbon-based material is ≥ 95%, optionally 96.0% - 98.5%; the graphitization degree of the second carbon-based material is ≥ 95%, optionally 95.0% - 97.5%.

[0015] The graphitization degrees of the first and second carbon-based materials are both relatively high, which improves the specific capacity of the negative electrode active material and is beneficial to enhancing the electron transport performance of the negative electrode film layer, so that the secondary battery can have both high energy density and good kinetic performance. In addition, the high graphitization degree on the material surface is beneficial to the high-temperature storage performance of the secondary battery.

[0016] In some embodiments, the first carbon-based material includes an outer region and an inner region located inside the outer region, where the outer region refers to the region formed by extending 2.5 μm inward 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 outer region of the first carbon-based material is denoted as S1, and the total pore area of the inner region is denoted as S2, then the first carbon-based material satisfies S2 > S1.

[0017] 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, it indicates that the structure of the outer region of the carbon material is denser than that of the inner region. Such a structure is more conducive to the stability of the material, reduces the swelling during charge and discharge cycles, and thus improves the cycle life of the secondary battery. In addition, the smaller pore area of the outer region is also beneficial to reducing side reactions and the consumption of active ions, and is beneficial to improving the high-temperature storage performance of the secondary battery.

[0018] Optionally, the first carbon-based material satisfies 2.5 ≤ S2 / S1 ≤ 460. The outer region of the first carbon-based material has fewer pore structures, which helps to reduce the side reactions between the first carbon-based material and the electrolyte, reduce the consumption of active ions, thereby improving the storage performance of the secondary battery. In addition, it can also inhibit the swelling of the first carbon-based material during charge and discharge cycles and improve the cycle life of the secondary battery.

[0019] 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 , and can be optionally less than or equal to 0.13 μm 2 ; and / or, the inner region of the first carbon-based material includes one or more pore structures with a pore area greater than or equal to 0.15 μm 2 , and optionally includes one or more pore structures with a pore area of 0.15 μm 2 -2.0 μm 2 . The outer region of the particles of the first carbon-based material with the above structure is relatively dense, while the inner region has certain pore structures. In this way, on the one hand, it can reserve sufficient and stable expansion space for the volume change of the first carbon-based material particles, reduce the risk of particle breakage of the first carbon-based material, reduce the entry of the electrolyte into the particle interior, thereby reducing the occurrence of side reactions and the consumption of active ions, and 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.

[0020] In some embodiments, at least a part of the surface of the second carbon-based material has a carbon coating layer. Further coating a carbon coating layer on at least a part of the surface of the second carbon-based material can further enhance the active ion transport under low-temperature conditions, which is beneficial to improving the low-temperature kinetic performance of the secondary battery.

[0021] In some embodiments, the first carbon-based material satisfies at least one of the following items.

[0022] (1) The powder compaction density of the first carbon-based material at 50000 N is ≤ 2.10 g / cm 3 , optionally 1.85 g / cm 3 - 2.00 g / 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 improved, and the energy density of the secondary battery can be increased; 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 thus improve the kinetic performance of the secondary battery.

[0023] (2) The volume distribution particle size Dv90 of the first carbon-based material is less than or equal to 40 μm, optionally 30 μm - 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.

[0024] (3) The particle size distribution [(Dv90)-(Dv10)] / (Dv50)] of the first carbon-based material is ≤ 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 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.

[0025] (4) The specific capacity of the first carbon-based material is ≥ 362 mAh / g, optionally 365 mAh / g - 372 mAh / g. When the specific capacity of the first carbon-based material is within the above range, the secondary battery can have a relatively high energy density.

[0026] (5) The first carbon-based material includes primary particles. Optionally, the proportion of the number of the primary particles in the first carbon-based material is greater than or equal to 80%.

[0027] When the first carbon-based material satisfies any one of the above items, it can further improve one or more of the low-temperature kinetic performance, high-temperature storage performance, energy density and other performances of the secondary battery.

[0028] In some embodiments, the second carbon-based material satisfies at least one of the following items.

[0029] (1) The specific capacity of the second carbon-based material ≥ 358 mAh / g, optionally 360 mAh / g - 367 mAh / g. When the specific capacity of the second carbon-based material is within the above range, the secondary battery can have a higher energy density.

[0030] (2) The tap density of the second carbon-based material under 50000 N ≤ 1.95 g / cm 3 , optionally 1.75 g / cm 3 -1.90 g / cm 3 . When the powder tap 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.

[0031] (3) The second carbon-based material includes primary particles. Optionally, the proportion of the number of the primary particles in the second carbon-based material is greater than or equal to 80%.

[0032] (4) The second carbon-based material is natural graphite.

[0033] When the second carbon-based material satisfies any one of the above items, it can further improve the low-temperature kinetic performance, energy density and other performances of the secondary battery.

[0034] 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 ≥ 55 wt%, optionally 60 wt% - 80 wt%. When the mass proportion of the first carbon-based material in the negative electrode active material is within the above range, it can play their respective advantages together with the second carbon-based material to obtain improved high-temperature storage performance and low-temperature kinetic performance.

[0035] In some embodiments, the negative electrode active material satisfies at least one of the following items.

[0036] (1) The volume distribution particle size Dv50 of the negative electrode active material ≤ 17.0 μm, optionally 12 μm - 16.5 μm.

[0037] (2) The volume-based particle size Dv90 of the negative electrode active material is ≤ 35 μm, and can be optionally 25 μm - 33 μm.

[0038] (3) The volume-based particle size distribution of the negative electrode active material satisfies: (Dv90 - Dv10) / Dv50 ≤ 1.50, and can be optionally 1.0 - 1.45.

[0039] (4) The specific surface area of the negative electrode active material is ≤ 3.0 m 2 / g, and can be optionally 1.5 m 2 / g - 2.8 m 2 / g.

[0040] In some embodiments, the negative electrode film layer satisfies at least one of the following items.

[0041] (1) The tap density of the negative electrode film layer is ≥ 1.55 g / cm 3 , and can be optionally 1.6 g / cm 3 - 1.7 g / cm 3 .

[0042] (2) The areal density of the negative electrode film layer is ≥ 10.0 mg / cm 2 , and can be optionally 11.0 mg / cm 2 - 15.5 mg / cm 2 .

[0043] (3) The porosity of the negative electrode film layer is 16% - 30%, and can be optionally 19% - 27%. This is beneficial for the negative electrode film layer to balance high capacity and a suitable pore structure, and further beneficial for the secondary battery to balance high energy density and good storage performance and kinetic performance.

[0044] (4) The thickness of the negative electrode film layer is ≥ 70 μm, and can be optionally 90 - 130 μm.

[0045] The negative electrode film layer having at least one of the above characteristics is beneficial for at least one of the performance of the secondary battery such as high-temperature storage performance, low-temperature kinetic performance, and energy density.

[0046] The second aspect of the present application further provides an electrical device including the secondary battery of the first aspect of the present application.

[0047] The electrical device of the present application includes the secondary battery provided by the present application, and thus has at least the same advantages as the secondary battery. Description of the Drawings

[0048] Figure 1 It is a scanning electron microscope photograph of the longitudinal section of the negative electrode plate prepared according to Example 1.

[0049] Figure 2 It is a schematic diagram of the cross-sectional image of the particles of the first carbon-based material of this application.

[0050] Figure 3 It is a schematic diagram of a battery cell of an embodiment of this application.

[0051] Figure 4 It is Figure 3 An exploded view of the battery cell of an embodiment of this application shown.

[0052] Figure 5 It is a schematic diagram of a battery module of an embodiment of this application.

[0053] Figure 6 It is a schematic diagram of a battery pack of an embodiment of this application.

[0054] Figure 7 It is Figure 6 An exploded view of the battery pack of an embodiment of this application shown.

[0055] Figure 8 It is a schematic diagram of an electrical device using a secondary battery of an embodiment of this application as a power source.

[0056] Explanation of reference numerals:

[0057] 1 Battery pack; 2 Upper box body; 3 Lower box body; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly Detailed implementation manners

[0058] Hereinafter, embodiments of the secondary battery and the electrical device of this application specifically disclosed will be described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to avoid the following description becoming unnecessarily long and to facilitate the understanding of those skilled in the art. In addition, the accompanying drawings and the following description are provided for those skilled in the art to fully understand this application and are not intended to limit the subject matter recited in the claims.

[0059] The "ranges" disclosed in this application are 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 ranges defined in this way can include the end values or not include the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are listed for a specific parameter, ranges of 60 - 110 and 80 - 120 are also contemplated. 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 are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In this application, unless otherwise specified, the numerical range "a - b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" are fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0060] If there is no special instruction, all embodiments and optional embodiments of this application can be combined with each other to form new technical solutions.

[0061] If there is no special instruction, all technical features and optional technical features of this application can be combined with each other to form new technical solutions.

[0062] If there is no special instruction, all steps of this application can be carried out sequentially or randomly, and preferably sequentially. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out sequentially, or can also include steps (b) and (a) carried out sequentially. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0063] If there is no special instruction, the terms used in this application have the well-known meanings commonly understood by those skilled in the art.

[0064] If there is no special instruction, the numerical values of the various parameters mentioned in this application can be measured by various common testing methods in the art. For example, they can be measured according to the testing methods given in this application.

[0065] Unless otherwise specified, in this application, the term "active ion" refers to an ion that can intercalate and deintercalate between the positive electrode and the negative electrode of a secondary battery, including but not limited to lithium ions.

[0066] With the wide application of secondary batteries, higher requirements are put forward for the performance of secondary batteries under different usage environments, such as high temperature, low temperature and other conditions. The kinetic performance of secondary batteries at low temperature and the storage performance at high temperature still need to be improved. For the kinetic performance, especially the kinetic performance at low temperature, it is often desired that the negative electrode active material has higher reaction activity and shorter active ion transport paths. However, this will lead to side reactions between the negative electrode active material and the electrolyte, thus reducing its storage performance, especially the storage performance at high temperature is often adversely affected.

[0067] Therefore, it is often difficult for current secondary batteries to balance the high-temperature storage performance and low-temperature kinetic performance.

[0068] In view of this, the first aspect of the embodiments of this application provides a secondary battery.

[0069] The term "secondary battery" mentioned in this article refers to a battery cell, a battery module or a battery pack.

[0070] Generally, a secondary battery cell includes a positive electrode plate, a negative electrode plate, an electrolyte and a separator. During the charge and discharge process of the battery, active ions intercalate and deintercalate between the positive electrode plate and the negative electrode plate. The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. The separator is arranged between the positive electrode plate and the negative electrode plate, mainly playing a role in preventing short circuit between the positive and negative electrodes, and at the same time allowing ions to pass through.

[0071] [Negative electrode plate]

[0072] The secondary battery of this application 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, and 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. Both the first carbon-based material and the second carbon-based material have a pore structure, and I D / I G ≤0.27 for the first carbon-based material, and I D / I G ≥0.38 for the second carbon-based material, where I D represents the intensity of the D peak of the Raman spectrum at 1350±50 cm -1 , and I G represents the intensity of the G peak of the Raman spectrum at 1580±50 cm -1 .

[0073] The I D / IG ≤ 0.27, reflecting a relatively high degree of carbon order and fewer defects in the surface region of the material, thus resulting in fewer side reactions with the electrolyte and enabling an improvement in the high-temperature storage performance of the secondary battery. The second carbon-based material has a pore structure and I D / I G ≥ 0.38, reflecting a relatively low degree of carbon order and a high reactivity in the surface region of the material, which is beneficial for the rapid reaction and transport of active ions, thereby endowing the secondary battery with good low-temperature kinetic performance. The first carbon-based material and the second carbon-based material with the above-mentioned properties are used in combination as the negative electrode active material, leveraging the advantages of both and enabling the secondary battery to possess both good low-temperature kinetic performance and high-temperature storage performance.

[0074] In some embodiments, the I D / I G of the first carbon-based material is 0.13 - 0.25. Exemplarily, the I D / I G of the first carbon-based material 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 of these numerical values. According to some embodiments, the I D / I G of the first carbon-based material can be within ranges such as 0.13 - 0.20, 0.20 - 0.25, 0.18 - 0.25, etc. When the I D / I G of the first carbon-based material is within the above ranges, it reflects that the degree of carbon amorphization in the material, especially on the surface of the material, is relatively low. Thus, the first carbon-based material has fewer side reactions at high temperatures, which is beneficial for the high-temperature storage performance of the secondary battery.

[0075] In some embodiments, the I D / I G of the second carbon-based material is 0.40 - 0.60. Exemplarily, the I D / I G of the second carbon-based material can be 0.40, 0.42, 0.44, 0.46, 0.48, 0.50, 0.60, or a value between any two of these numerical values. According to some embodiments, the I D / I G of the second carbon-based material can be within ranges such as 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. When the I D / I GWhen within the above range, the degree of disorder of carbon on the material surface is relatively high, thus being able to provide appropriate reactivity and improve the low-temperature kinetic performance of the secondary battery.

[0076] When the first carbon-based material and the second carbon-based material, each having the above range, are combined and used together as the negative electrode active material, their respective excellent properties can be exerted to provide the secondary battery with improved high-temperature storage performance and low-temperature kinetic performance.

[0077] In some embodiments, I 3R(101) / I 2H(004) in the XRD diffraction pattern of the first carbon-based material is less than I 3R(101) / I 2H(004) in the XRD diffraction pattern of the second carbon-based material. In more specific embodiments, I 3R(101) / I 2H(004) in the XRD diffraction pattern of the first carbon-based material is less than or equal to 0.06, optionally 0 - 0.06. In more specific embodiments, I 3R(101) / I 2H(004) of the second carbon-based material is ≥ 0.2, optionally 0.22 - 0.4. Wherein I 3R(001) is the diffraction peak intensity of the 101 plane of the 3R phase of the carbon-based material corresponding to 43° - 44° in the XRD diffraction pattern, and I 2H(004) is the diffraction peak intensity of the 004 plane of the 2H phase of the carbon-based material corresponding to 53° - 55° in the XRD diffraction pattern. Exemplarily, in the XRD diffraction pattern of the first carbon-based material, I 3R / I 2H can be 0, 0.01, 0.02, 0.03, 0.04, 0.06, etc. Exemplarily, in the XRD diffraction pattern of the second carbon-based material, I 3R / I 2H can be 0.20, 0.23, 0.25, 0.27, 0.30, 0.33, 0.35, 0.38, 0.4, etc.

[0078] In the XRD diffraction pattern, relative to the diffraction peak of the 2H phase, an obvious diffraction peak of the 3R phase generally indicates that the measured material is natural graphite.

[0079] According to the specific embodiments, the second carbon-based material is natural graphite. Natural graphite has more pores, which can provide a larger reaction surface, facilitate the transport of active particles and accelerate the reaction, and thus has excellent low-temperature kinetic performance. Therefore, the surface properties of the first carbon-based material are stable and there are few side reactions, which can improve the high-temperature storage performance of the secondary battery. Thus, combining the first carbon-based material and the second carbon-based material as the negative electrode active material can enable the secondary battery to balance the low-temperature kinetic performance and the 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 reaction between the material surface and the electrolyte, thereby further improving the high-temperature storage performance of the secondary battery; in addition, when the particle size of the second carbon-based material is relatively small, the pores between the particles in the first carbon material and the second carbon material can be reasonably distributed, thereby further enhancing the low-temperature kinetic performance.

[0080] In some specific embodiments, the volume distribution particle size Dv50 of the first carbon-based material is Dv50≥15 μm, and optionally 16 μm≤Dv50≤20 μm. It can be exemplified that 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 values 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, improve the storage performance of the secondary battery, and at the same time will not cause excessive loss of kinetic performance, maintaining the balance of the low-temperature kinetics and high-temperature storage performance of the secondary battery.

[0081] In some specific embodiments, the volume distribution particle size Dv50 of the second carbon-based material is Dv50≤13 μm, and optionally 7 μm≤Dv50≤12 μm. According to the specific embodiments, the range of the volume distribution particle size Dv50 of the second carbon-based material can be 9 μm - 12 μm, 10 μm - 12 μm. Exemplarily, the volume distribution particle size Dv50 of the second carbon-based material can be 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, etc., or values between any two values. The small volume distribution particle size of the second carbon-based material helps to enhance the contact between the carbon-based materials and reduce the transport distance of active ions, thereby further enhancing the kinetic performance of the secondary battery at low temperatures.

[0082] In some embodiments, the BET specific surface area of the first carbon-based material is less than the BET specific surface area of the second carbon-based material. The first carbon-based material has a relatively small specific surface area and fewer side reactions with the electrolyte, which is further beneficial to improving the high-temperature storage performance of the secondary battery.

[0083] In some specific embodiments, the specific surface area BET of the first carbon-based material is ≤ 2.1 m 2 / g, optionally 1.3 m 2 / g - 1.9 m 2 / g. Exemplarily, the specific surface area BET of the first carbon-based material is 1.3 m 2 / g, 1.4 m 2 / g, 1.5 m 2 / g, 1.6 m 2 / g, 1.7 m 2 / g, 1.8 m 2 / g, 1.9 m 2 / g, etc., or values between any two numerical values. When the specific surface area of the first carbon-based material is within the above range, the smaller specific surface area is beneficial to the storage performance of the secondary battery.

[0084] In some specific embodiments, the specific surface area BET of the second carbon-based material is ≤ 3.6 m 2 / g, optionally 1.8 - 3.4 m 2 / g. Exemplarily, the specific surface area of the second carbon-based material can be 1.8 m 2 / g, 1.9 m 2 / g, 2.0 m 2 / g, 2.1 m 2 / g, 2.2 m 2 / g, 2.3 m 2 / g, 2.4 m 2 / g, 2.5 m 2 / g, 2.6 m 2 / g, 2.7 m 2 / g, 2.8 m 2 / g, 2.9 m 2 / g, 3.0 m 2 / g, 3.1 m 2 / g, 3.2 m 2 / g, 3.3 m 2 / g, 3.4 m 2 / g, etc., or values between any two numerical values. When the specific surface area of the second carbon-based material is within the above range, it can provide better low-temperature kinetic performance.

[0085] In some embodiments, the graphitization degree of the first carbon-based material is greater than the graphitization degree of the second carbon-based material.

[0086] In some specific embodiments, the graphitization degree of the first carbon-based material is ≥95%, and can be optionally 96.0%-98.5%. Exemplarily, the graphitization degree of the first carbon-based material can be 95%-98%, 96%-98%, etc. The graphitization degree of the second carbon-based material is ≥95%, and can be optionally 95.0%-97.5%. Exemplarily, the graphitization degree of the second carbon-based material is 95%-97.3%, 96%-97.3%, etc. The high graphitization degrees of the two carbon-based materials can further improve the energy density of the battery.

[0087] In some embodiments, the first carbon-based material includes an outer region and an inner region located inside the outer region, where the outer region refers to the region formed by extending 2.5 μm inward 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 outer region of the first carbon-based material is denoted as S1, and the total pore area of the inner region is denoted as S2, then the first carbon-based material satisfies S2 > S1.

[0088] The first carbon-based material in this application satisfying "S2 > S1" means that the first carbon-based material has a pore structure that can be directly observed from a cross-sectional image (such as a scanning electron microscope image with a magnification of 1000 times). That is, there are fewer pore structures in the outer region of the main structure of the first carbon-based material.

[0089] In contrast, as described above, the second carbon-based material "having 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 (such as a scanning electron microscope image with a magnification of 1000 times), and the distribution of these pore structures in different regions of the cross-sectional image has no obvious difference.

[0090] The first carbon-based material and the second carbon-based material can be distinguished by a cross-section polisher. For example, the types of the first carbon-based material and the second carbon-based material can be distinguished by testing the cross-sectional polishing surface morphology (CP) of the negative electrode sheet. Specifically, the negative electrode sheet can be cut into a test sample of a certain size (such as 2 cm × 2 cm), and the negative electrode sheet can be fixed on the sample stage; the sample stage can be loaded into the sample holder and locked and fixed, and the power supply of the argon ion cross-section polisher (such as the IB-09010CP type argon ion cross-section polisher of JEOL Company, Japan) can be turned on and vacuumized (such as 10 -7Pa), set the argon gas 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 areas in the sample to be measured for scanning tests (e.g., refer to JY / T 010-1996 and use a scanning electron microscope for scanning), and obtain the ion-polished cross-sectional morphology (CP) picture of the negative electrode plate at a certain magnification (e.g., 1000 times). The first carbon-based material and the second carbon-based material can be distinguished from the picture through the pore structure of the carbon-based material particle profile diagram.

[0091] Exemplarily, refer to Figure 1 , Figure 1 is a scanning electron microscope (SEM) photograph of the longitudinal section of the negative electrode plate according to Embodiment 1 of the present application. As can be seen from the figure, the number of pore structures in the outer region of some particles (the first carbon-based material particles) is significantly lower than that in the inner region, while the distribution of pore structures in each region of the cross-section of some particles (the second carbon-based material particles) is generally consistent.

[0092] Further refer to Figure 2 , which shows a schematic diagram of a cross-sectional image of a particle of the first carbon-based material 100 of the present application, and the cross-sectional image passes through the center of the particle of the first carbon-based material 100. As Figure 2 shown, the region formed by the distance of 2.5 μm extending from the surface of the particle of the first carbon-based material 100 into the particle is the outer region 101, and the region inside the outer region 101 is the inner region 102.

[0093] According to the above definition, when the first carbon-based material satisfies that S2 is greater than S1, it indicates that the structure of the outer region of the material is denser than that of the inner region. Such a structure is beneficial to the stability of the material, reduces the expansion during charge and discharge cycles, and thus improves the cycle life of the secondary battery. In addition, fewer pores in the outer region are also beneficial to reducing side reactions and the consumption of active ions, and are beneficial to improving the high-temperature storage performance of the secondary battery.

[0094] Further, the first carbon-based material satisfies 2.5 ≤ S2 / S1 ≤ 460. Exemplarily, the first carbon-based material satisfies 2.5 ≤ S2 / S1 ≤ 400, 2.8 ≤ S2 / S1 ≤ 300, 2.5 ≤ S2 / S1 ≤ 200, 3.0 ≤ S2 / S1 ≤ 300, 5.0 ≤ S2 / S1 ≤ 200, 5.0 ≤ S2 / S1 ≤ 150, 5.0 ≤ S2 / S1 ≤ 100, etc. When the value of S2 / S1 is larger, it indicates that a larger pore area exists in the internal region, that is, the pore area in the external region is smaller, or in other words, the pore structure is less. The pore structure of the first carbon-based material satisfying the above conditions is mainly located in the internal region of the particles, reserving the required expansion space for the volume change of the particles, and reducing the risk of new interfaces generated by the fragmentation of the first carbon-based material particles. At the same time, the smaller pore area in the external region, or in other words, the fewer pore structures, can reduce the side reactions between the material surface and the electrolyte and reduce the consumption of active ions. In addition, the fewer pore structures in the external region can prevent the electrolyte from infiltrating into the pore structures inside the material and also reduce the side reactions between the internal pore surface and the electrolyte. Therefore, the first carbon-based material enables the secondary battery to have good storage performance under high-temperature conditions and can also take into account the cycle life.

[0095] In some embodiments, the area of a single pore structure in the external region of the first carbon-based material is less than or equal to 0.15 μm 2 , and can be optionally less than or equal to 0.13 μm 2 ; and / or, the internal region of the first carbon-based material includes more than one pore structure with a pore area greater than or equal to 0.15 μm 2 , and optionally includes more than one pore structure with a pore area of 0.15 μm 2 - 2.0 μm 2 . The external region of the first carbon-based material including pore structures of the above sizes reflects that the external region of the particles of this material is relatively dense and the pores of the pore structure are small. For the first carbon-based material with this structure, the electrolyte is not easily introduced into the particles, thus reducing the side reactions with the electrolyte. In addition, by making the internal region of the first carbon-based material include pore structures of the above sizes, on the one hand, sufficient and stable expansion space can be reserved for the volume change of the first carbon-based material particles, and on the other hand, the compaction density of the negative electrode film layer can be improved. The first carbon-based material with this structural feature can improve the high-temperature storage performance and energy density of the secondary battery and also take into account the cycle performance.

[0096] When the first carbon-based material further satisfies one or more of the following performances on the basis of meeting the above design, it can further improve the performance of the secondary battery, such as further improving at least one of the energy density, high-temperature storage performance, and low-temperature kinetic performance of the secondary battery.

[0097] The first carbon-based material of this application is natural graphite. Generally, natural graphite particles have numerous pore structures throughout the region. For example, if the natural graphite particles are also divided into an internal region and an external region (the region formed by extending 2.5 μm from the surface of the natural graphite particle into the particle is the external region), then both the internal region and the external region of the natural graphite have numerous pore structures.

[0098] In some embodiments, the powder compaction density of the first carbon-based material under 50000 N is ≤ 2.10 g / cm 3 , optionally 1.85 g / cm 3 - 2.00 g / cm 3 . Exemplarily, the powder compaction density of the first carbon-based material under 50000 N is 1.85 g / cm 3 , 1.90 g / cm 3 , 1.95 g / cm 3 , 2.00 g / cm 3 , 2.05 g / 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 improved, and the energy density of the secondary battery can be enhanced. 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 further improve the kinetic performance of the secondary battery.

[0099] In some embodiments, the volume distribution particle size Dv90 of the first carbon-based material is ≤ 40 μm, optionally 30 μm - 38 μm. It can be listed that 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 values between any two of these 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.

[0100] In some embodiments, the particle size distribution [(Dv90)-(Dv10)] / (Dv50)] of the first carbon-based material is ≤ 1.55, optionally 0.90 - 1.50. It can be listed that the particle size distribution [(Dv90)-(Dv10)] / (Dv50)] of the first carbon-based material is 0.90, 1.00, 1.10, 1.20, 1.30, 1.40, 1.50, etc., or values between any two of these values. 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 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.

[0101] In some embodiments, the specific capacity of the first carbon-based material is ≥362 mAh / g, optionally 365 mAh / g - 372 mAh / g. Exemplarily, the specific capacity of the first carbon-based material is 363 mAh / g, 365 mAh / g, 368 mAh / g, 370 mAh / g, 372 mAh / g. When the specific capacity of the first carbon-based material is within the above range, the secondary battery can have a relatively high energy density.

[0102] In some embodiments, the first carbon-based material includes primary particles. Optionally, the proportion of the number of the primary particles in the first carbon-based material is greater than or equal to 80%. According to some embodiments, the proportion of the number of the primary particles in the first carbon-based material is greater than or equal to 85%, 90%, 95%, or even all are primary particles. The first carbon-based material being primary particles is beneficial to the low-temperature kinetic performance of the secondary battery.

[0103] According to some embodiments, the surface of the first carbon-based material has no coating layer.

[0104] 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 layer, especially a carbon coating layer (for example, an amorphous carbon coating layer). Generally, by mixing a coating material such as pitch with a raw material (such as the first carbon-based material with a predetermined particle size), and then performing heat treatment at a certain temperature, a carbon coating layer is formed on the surface of the material. In the present application, there is no particular limitation on the thickness of the coating layer of the first carbon-based material and its preparation method. Those of ordinary skill in the art can obtain the first carbon-based material with a coating layer on the surface by using any known method according to actual needs.

[0105] According to some embodiments, at least part of the surface of the second carbon-based material, optionally the entire surface, has a coating layer, especially a carbon coating layer (for example, an amorphous carbon coating layer), which can further promote the transport of active ions, thereby further improving the low-temperature kinetic performance of the secondary battery.

[0106] Generally, by mixing a coating material such as pitch with a raw material (such as natural graphite with a predetermined particle size), and then performing heat treatment at a certain temperature, a carbon coating layer is formed on the surface of the material. In the present application, there is no particular limitation on the thickness of the coating layer of the second carbon-based material and its preparation method. Those of ordinary skill in the art can obtain the second carbon-based material with a coating layer on the surface by using any known method according to actual needs.

[0107] When the second carbon-based material further satisfies one or more of the following performances on the basis of meeting the above design, the performance of the secondary battery can be further improved, such as further improving at least one of the high-temperature storage performance and low-temperature kinetic performance of the secondary battery.

[0108] In some embodiments, the specific capacity of the second carbon-based material is ≥ 358 mAh / g, optionally 360 mAh / g - 367 mAh / g. Exemplarily, the specific capacity of the second carbon-based material is 360 mAh / g, 362 mAh / g, 364 mAh / g, 366 mAh / g. When the specific capacity of the second carbon-based material is within the above range, the secondary battery can have a relatively high energy density.

[0109] In some embodiments, the tap density of the second carbon-based material under 50000 N is ≤ 1.95 g / cm 3 , optionally 1.75 g / cm 3 -1.90 g / cm 3 . Exemplarily, the tap density of the second carbon-based material under 50000 N is 1.75 g / cm 3 , 1.80 g / cm 3 , 1.85 g / cm 3 , 1.90 g / cm 3 . When the tap 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 transport performance of active ions and electrons, and thus improve the kinetic performance of the secondary battery.

[0110] In some embodiments, the second carbon-based material includes primary particles. Optionally, the proportion of the number of primary particles in the second carbon-based material is greater than or equal to 80%. According to some other embodiments, the proportion of the number of primary particles in the second carbon-based material is greater than or equal to 85%, 90%, 95%, or even all are primary particles. The second carbon-based material being primary particles is beneficial to the low-temperature kinetic performance of the secondary battery.

[0111] 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.

[0112] 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. Since the I D / I G of the second carbon-based material is relatively large and there are many surface defects, if the dosage is too much, 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 take into account better high-temperature storage performance and low-temperature kinetic performance at the same time.

[0113] According to a specific embodiment, the mass ratio of the first carbon-based material is ≥55 wt%, optionally 60 wt% - 80 wt%, further optionally 65 wt% - 80 wt%, and even 70 wt% - 80 wt%. Exemplarily, in the negative electrode active material, the mass ratio of the first carbon-based material is 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%. When the mass ratio of the first carbon-based material in the negative electrode active material is within the above range, it can cooperate with the second carbon-based material to give full play to their respective advantages, obtain improved storage performance, and at the same time have good cycle performance and energy density.

[0114] In some embodiments, in the negative electrode active material, the mass ratio of the second carbon-based material is ≤45 wt%, optionally 20 wt% - 40 wt%, further optionally 20 wt% - 35 wt%, and even 20 wt% - 30 wt%. Exemplarily, in the negative electrode active material, the mass ratio of the second carbon-based material is 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%.

[0115] In some embodiments, the negative electrode active material is composed of the above-mentioned first carbon-based material and second carbon-based material.

[0116] In other embodiments, the negative electrode active material further includes other negative electrode active materials known in the art, such as silicon-based materials. The silicon-based material can play a role in improving the pore structure in the negative electrode film layer, facilitating the infiltration and liquid retention of the electrolyte, and improving the kinetic performance of the secondary battery; at the same time, it can also increase the negative electrode capacity, thereby further improving the energy density of the secondary battery.

[0117] The present application has no particular limitation on 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 oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys.

[0118] In some embodiments, the mass ratio of the silicon-based material in the negative electrode active material is ≤15 wt%, optionally 3 wt% - 10 wt%. Thereby, while improving the kinetic performance and energy density of the secondary battery, the secondary battery can also have good cycle performance and storage performance.

[0119] The negative electrode active materials in the above embodiments advantageously further satisfy at least one of the following items.

[0120] (1) The volume distribution particle size Dv50 of the negative electrode active material is ≤17.0 μm, optionally 12 μm - 16.5 μm.

[0121] (2) The volume-based particle size distribution Dv90 of the negative electrode active material is ≤ 35 μm, and can be optionally 25 μm - 33 μm.

[0122] (3) The volume particle size distribution of the negative electrode active material satisfies: (Dv90 - Dv10) / Dv50 ≤ 1.50, and can be optionally 1.0 - 1.45.

[0123] (4) The specific surface area of the negative electrode active material is ≤ 3.0 m 2 / g, and can be optionally 1.5 m 2 / g - 2.8 m 2 / g.

[0124] In some embodiments, the negative electrode film layer may further optionally include a conductive agent. The conductive agent can 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 application has no particular limitation on the content of the conductive agent, if any, in the negative electrode film layer. Those skilled in the art can determine the appropriate content of the conductive agent through conventional tests in the art.

[0125] In some embodiments, the negative electrode film layer may further optionally include a binder. The binder can 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).

[0126] In some embodiments, the negative electrode film layer may further optionally include other additives, such as thickeners (such as sodium carboxymethyl cellulose (CMC-Na)), etc.

[0127] The present application has no particular limitation on the content of the binder and / or other additives, if any, in the negative electrode film layer. Those skilled in the art can determine the appropriate content of the binder and / or other additives through conventional tests in the art.

[0128] The negative electrode film layer satisfying at least one of the following can improve at least one of the performance of the secondary battery, such as high-temperature storage performance, low-temperature kinetic performance, energy density, etc.

[0129] In some embodiments, the tap density of the negative electrode film layer is ≥ 1.5 g / cm 3 , and can be optionally 1.6 g / cm 3 - 1.7 g / cm 3 . For example, the tap density of the negative electrode film layer can be 1.6 g / cm 3 , 1.65 g / cm 3 , 1.70 g / cm 3etc., or values between any two numerical values.

[0130] In some embodiments, the areal density of the negative electrode film layer ≥ 10 mg / cm 2 , optionally 11.0 - 15.5 mg / cm 2 . Exemplarily, the tap density of the negative electrode film layer is 10 mg / cm 2 , 11 mg / cm 2 , 12 mg / cm 2 , 13 mg / cm 2 , 14 mg / cm 2 , 15 mg / cm 2 , 15.5 mg / cm 2 etc., or values between any two numerical values, but not limited thereto.

[0131] In some embodiments, the porosity of the negative electrode film layer is 16% - 30%, optionally 19% - 27%. Exemplarily, the porosity of the negative electrode film layer is 17%, 19%, 21%, 23%, 25%, 27%, etc., or values between any two numerical values. This is beneficial for the negative electrode film layer to balance high capacity and a suitable pore structure, and further beneficial for the secondary battery to balance high energy density and good storage performance and kinetic performance.

[0132] In some embodiments, the thickness of the negative electrode film layer is ≥ 70 μm, optionally 90 - 130 μm. Exemplarily, the thickness of the negative electrode film layer is 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, etc., or values between any two numerical values, but not limited thereto.

[0133] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as substrates of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0134] In some embodiments, the negative electrode plate can be prepared by the following method: dispersing the above components for preparing the negative electrode plate, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent (such as deionized water) to form a negative electrode slurry; coating the negative electrode slurry on the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode plate can be obtained.

[0135] The above embodiments are only described by taking the composition of the negative electrode film layer on one surface of the negative electrode current collector as an example. It should be understood that the negative electrode current collector has two opposite surfaces in its own thickness direction, and the negative electrode film layer described in the above embodiments is provided on any one or both of the two opposite surfaces of the negative electrode current collector. It should be noted that the parameters of each negative electrode film layer given in the present application (such as compaction density, areal density, porosity, thickness, etc.) refer to the parameters of the negative electrode film layer on one side of the negative electrode current collector. When the negative electrode film layer is provided on both sides of the negative electrode current collector, the parameters of the negative electrode film layer on any one side meet the present application, that is, it is considered to fall within the protection scope of the present application.

[0136] In the present application, it is not excluded that the above negative electrode tab may further include other additional functional layers in addition to the above negative electrode film layer. For example, in some embodiments, the negative electrode tab further includes a conductive bottom coating (such as composed of a conductive agent and a binder) provided on the surface of the negative electrode current collector and sandwiched between the negative electrode current collector and the negative electrode film layer; in some embodiments, the negative electrode tab further includes a protective layer covering the surface of the negative electrode film layer.

[0137] In the present application, the I D / I G value of a material (such as the first carbon-based material, the second carbon-based material, etc.) can be tested using a Raman spectrometer. I D represents the intensity of the D peak of the Raman spectrum of the material at 1350 ± 50 cm -1 , and I G represents the intensity of the G peak of the Raman spectrum of the material at 1580 ± 50 cm -1 . The test conditions can be: the excitation wavelength is 532 nm, the grating is 600 lines, the objective lens is 50 times, the integration time is 10 s, the accumulation times is 3 times, and the surface scan is performed to obtain the D peak and G peak intensities of 100 points, and calculate the I D / I G of 100 points. Remove the largest and smallest 25 I D / I G , and the average value of the remaining 50 points is the I D / I G of the material. The test instrument can use a Horiba LabRAM HR800 Raman spectrometer.

[0138] In the present application, in the XRD diffraction pattern of a material (such as the first carbon-based material, the second carbon-based material, etc.), I 3R(101) / I 2H(004)The value can be tested by using an X-ray diffractometer with reference to JIS K 0131-1996 to obtain the X-ray diffraction pattern of the carbon material. The test conditions can be as follows: The carbon material is prepared by the flat sample preparation method, using CuKα ray as the radiation source, a copper target as the anode target, with a voltage of 40 KV, a current of 40 mA, a scattering prevention slit of 1 mm, scanning the 2θ angle range from 20° to 80°, a step size of 0.01671°, a time of 0.24 s for each 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 101 crystal plane of the 3R phase is in the range of 43° - 44°, the 2θ of the diffraction peak of the 004 crystal plane of the 2H phase is in the range of 53° - 55°, and the 2θ of the diffraction peak of the 012 crystal plane of the 3R phase is in the range of 46° - 47°. The peak intensity of the diffraction peak of the 101 crystal plane of the 3R phase and the peak intensity of the diffraction peak of the 004 crystal plane of the 2H phase are represented by the integral area of the corresponding diffraction peaks.

[0139] In this application, the volume distribution particle sizes Dv10, Dv50, and Dv90 of the material (such as the first carbon-based material, the second carbon-based material, etc.) have the well-known meanings in the art, which respectively represent the particle sizes corresponding to when the cumulative volume distribution percentage of the material reaches 10%, 50%, and 90%, and can be measured by the instruments and methods known in the art. For example, it can be measured with reference to GB / T19077-2016 by using a laser particle size analyzer. The test instrument can be a Mastersizer 3000 type laser particle size analyzer of Malvern Instruments Limited in the UK.

[0140] In this application, the BET specific surface area of the material (such as the first carbon-based material, the second carbon-based material, etc.) has the well-known meaning in the art and can be measured by the instruments and methods known in the art. For example, it can be tested with reference to GB / T 19587-2017 by using the nitrogen adsorption specific surface area analysis test method and calculated by the BET (Brunauer Emmett Teller) method. The test instrument can be a Tri-Star 3020 type specific surface area and pore size analyzer of Micromeritics in the United States.

[0141] In this application, the graphitization degree of the material (such as the first carbon-based material, the second carbon-based material) has the well-known meaning in the art and can be tested by the instruments and methods known in the art. For example, it can be tested by using an X-ray diffractometer (such as Bruker D8 Discover), and the test can refer to JIS K 0131-1996 and JB / T 4220-2011 to obtain the average layer spacing d of the C(002) crystal plane in the crystal structure of the material 002 and then according to the formula g=(0.344 - d 002) / (0.344 - 0.3354)×100% is used to calculate the graphitization degree. In the above formula, d 002 is the average interlayer spacing of the C(002) crystal plane in the crystal structure of the material, expressed in nanometers (nm).

[0142] In this application, for the pore area, S1, and S2 values of the first carbon-based material, a cross-section of the first carbon-based material can be obtained using a cross-section polisher (such as the IB-09010CP type argon ion cross-section polisher from JEOL, Japan); then, referring to JY / T 010-1996, the cross-section of the first carbon-based material is scanned using a scanning electron microscope (such as the Sigma300 type scanning electron microscope from ZEISS, Germany); finally, the pore area of any one pore in the first carbon-based material, the total pore area S2 of the internal region, and the total pore area S1 of the external region are obtained respectively through image processing software (such as AVIZO), and the value of S2 / S1 is thus obtained. Exemplarily, samples can be obtained from different regions of the negative electrode sheet in a secondary battery, and at least 5 positions (such as 5, 10, 15, or even more) are randomly selected from the samples 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. According to the above definition, the total pore area S2' of the internal region and the total pore area S1' of the external region of each particle cross-section are obtained using image processing software, and the value of S2' / S1' of each particle cross-section is thus obtained. The arithmetic mean of S2' / S1' of all measured particle cross-sections is calculated as the S2 / S1 value of the first carbon-based material.

[0143] In this application, the specific capacity of the material (such as the first carbon-based material, the second carbon-based material, etc.) has a well-known meaning 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 conductive agent carbon black (Super P), binder polyvinylidene fluoride (PVDF) in a mass ratio of 91.6:1.8:6.6 with solvent N-methylpyrrolidone (NMP) to form a slurry; the prepared slurry is coated on the surface of the negative electrode current collector copper foil and dried in an oven for later use; ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and then LiPF 6Dissolve it in the above-mentioned organic solvent to prepare an electrolyte with a concentration of 1 mol / L; then use a lithium metal sheet as the counter electrode and a polypropylene (PP) film as the separator, and assemble it with the above-mentioned electrolyte into a CR2430 coin cell in a glove box under argon protection; after standing the obtained coin cell for 12 h, at 25 °C, perform a constant current discharge at 0.05 C to 0.005 V, stand for 10 minutes, then perform a constant current discharge at a current of 50 μA to 0.005 V, stand for 10 minutes, and then perform a constant current discharge at 10 μA to 0.005 V; then perform a constant current charge at 0.1 C to 2 V and record the charge capacity. The ratio of the charge capacity to the sample mass is the specific capacity of the corresponding material (such as the first carbon-based material, the second carbon-based material, etc.).

[0144] In the present application, whether there is a coating layer on the surface of the material (such as the first carbon-based material, the second carbon-based material, etc.) can be judged by a transmission electron microscope.

[0145] In the present application, the bulk density of the powder of the material (such as the first carbon-based material, the second carbon-based material, etc.) has the meaning well-known in the art and can be measured by the instruments and methods known in the art. For example, it can be measured with reference to GB / T 24533-2009 by an electronic pressure testing machine (such as a UTM7305 type electronic pressure testing machine). The exemplary test method is as follows: Weigh 1 g of the sample powder, add it to a mold with a bottom area of 1.327 cm 2 and apply a pressure of 50000 N, hold the pressure for 30 s, then release the pressure and keep it for 10 s, and then record and calculate the bulk density of the material under a pressure of 50000 N.

[0146] In the present application, the proportion of the number of primary particles in the first carbon-based material and / or the second carbon-based material means: randomly select a test sample in the negative electrode film layer, randomly select multiple test areas in the test sample, obtain images of the multiple test areas by a scanning electron microscope, and count the proportion of the number of the first carbon-based materials with the morphology of primary particles in each image in the total number of the first carbon-based material particles. The average value of the multiple statistical results is the proportion of the number of primary particles in the first carbon-based material.

[0147] In the present application, the areal density of the negative electrode film layer has the meaning well-known in the art and can be tested by the methods known in the art. For example, a single-sided coated and cold-pressed negative electrode plate can be taken (if it is a double-sided coated negative electrode plate, the negative electrode film layer on one side can be wiped off first), punched into small round pieces with an area of S', weighed, and recorded as M1. Then wipe off the negative electrode film layer of the above-mentioned weighed negative electrode plate and weigh the weight of the negative electrode current collector, recorded as M0. The areal density of the negative electrode plate = (M1 - M0) / S'.

[0148] In the present application, the tap density of the negative electrode film layer has the meaning well-known in the art and can be tested by methods known in the art. [The tap density of the negative electrode film layer = the areal density of the negative electrode film layer / the thickness of the negative electrode film layer].

[0149] The thickness of the negative electrode film layer has the meaning well-known in the art and can be tested by methods known in the art, such as using a micrometer (e.g., Mitutoyo 293-100 type, with an accuracy of 0.1 μm). It should be noted that the thickness range given in the present application is the thickness range of the negative electrode film layer on one side of the negative electrode current collector. As long as the thickness of the negative electrode film layer on either side of the negative electrode current collector is within the range given in the present application, the requirements of the present application are met.

[0150] In the X-ray diffraction (XRD) analysis test of the present application, a copper target can be used as the anode target, with CuKα rays as the radiation source, and the ray wavelength The scanning range of the 2θ angle is 20° - 80°, and the scanning rate is 4° / min.

[0151] It should be noted that the various parameter tests for the negative electrode active material or the negative electrode film layer can be sampled and tested from the prepared secondary battery according to the following steps.

[0152] Discharge the secondary battery (for safety reasons, generally make the secondary battery in a fully discharged state); disassemble the secondary battery and take out the negative electrode plate, soak the negative electrode plate in dimethyl carbonate for a certain period of time (e.g., 2 h - 10 h); then take out the negative electrode plate and dry it at a certain temperature and for a certain time (e.g., 60 °C, for 4 h or more), and take out the negative electrode plate after drying. At this time, samples can be taken from the dried negative electrode plate to test the above-mentioned parameters related to the negative electrode film layer, such as the areal density, tap density, porosity, thickness, etc. of the negative electrode film layer.

[0153] Bake the above-mentioned dried negative electrode plate at a certain temperature and for a certain time (e.g., 400 °C, for 2 h or more), select an area from the baked negative electrode plate, and sample the negative electrode active material (blade scraping for powder sampling can be used); sieve the collected negative electrode active material (e.g., sieve it with a 200-mesh sieve), and finally obtain a sample that can be used to test the above-mentioned parameters of the negative electrode active material.

[0154] In the present application, the above-mentioned first carbon-based material can be prepared by the following method of the present application; the above-mentioned second carbon-based material can be obtained by commercial purchase, or can also be prepared by the following method of the present application.

[0155] In some embodiments, the preparation method of the first carbon-based material includes: Step 1, providing a raw material with a plurality of pore structures; Step 2, uniformly mixing the above raw material with a filling material in a predetermined ratio, and then at a first temperature T1 The first heat preservation time t of the lower heat preservation 1 , and after the end, it is cooled to room temperature to obtain an intermediate; Step 3, the obtained intermediate is kept warm at the second temperature T 2 for the second time t 2 , and after the end, a first carbon-based material is obtained, which has a pore structure and satisfies I D / I G ≤0.27, where I D represents the intensity of the D peak of the Raman spectrum at 1350±50 cm -1 , and I G represents the intensity of the G peak of the Raman spectrum at 1580±50 cm -1 .

[0156] In some embodiments, in Step 1, the raw materials for preparing the first carbon-based material include natural graphite. Natural graphite generally refers to graphite naturally formed in nature, without the need for graphitization, and there are usually many closed pore structures inside natural graphite particles. Optionally, natural graphite includes one or more of flake graphite, natural spherical graphite, and microcrystalline graphite, especially including natural spherical graphite.

[0157] "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 the required particle size and morphology can be obtained by pretreating flake graphite. Optionally, the above pretreatment includes processes such as crushing, classification, spheroidization, and purification.

[0158] In some embodiments, in Step 1, the volume distribution particle size Dv50 of the above raw materials can be 15μm - 20μm.

[0159] In some embodiments, in Step 1, the specific surface area of the above raw materials can be ≥2.5 m 2 / g, and can be optionally 2.5 m 2 / g - 10.0 m 2 / g. When the specific surface area of the raw materials is within the above range, it is beneficial for subsequent filling treatment and obtaining the first carbon-based material with the required specific surface area.

[0160] In some embodiments, in Step 2, the softening point temperature of the above filling material is 90°C - 150°C. Optionally, the softening point temperature of the above 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.

[0161] In some embodiments, in step 2, the volume distribution particle size Dv50 of the above-mentioned filling material is less than or equal to 6 μm, and may be optionally 1 μm - 6 μm, 1 μm - 5 μm, 2 μm - 5 μm, 3 μm - 5 μm. This is beneficial for the filling material to be filled into the pore structure of the raw material after being heated and melted, and is also beneficial for improving the dispersion uniformity of the filling material and the raw material.

[0162] In some embodiments, in step 2, the coking value of the above-mentioned filling material is 15% - 40%, and may be optionally 18% - 34%. In the present application, the coking value of the filling material has the meaning well-known in the art and can be measured by instruments and methods known in the art. For example, it can be measured with reference to GB / T 8727 - 2008.

[0163] In some embodiments, in step 2, the above-mentioned filling material includes one or more of coal tar pitch, petroleum pitch, high molecular compounds, and resins, and may be optionally one or more of coal tar pitch and petroleum pitch.

[0164] In some embodiments, in step 2, the mass ratio of the above-mentioned filling material to the above-mentioned raw material is (10 - 40):100, and may be optionally (10 - 30):100, (10 - 25):100, (10 - 20):100, (12 - 30):100,

[0165] (14 - 28):100, (15 - 25):100.

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

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

[0168] By adjusting parameters such as the type, softening point, coking value, and addition amount of the filler material within the above ranges, after the filler material is heated and melted, its viscosity is not high, maintaining good fluidity. At the same time, it is not easy to adhere to the raw material particles, which can reduce the agglomeration of raw material particles during subsequent preparation processes. Therefore, it can also reduce problems such as an increase in surface defects and an increase in surface active sites on the surface of the first carbon-based material particles due to the need to add a depolymerization process.

[0169] In some embodiments, in step 2, the above raw materials and the above filler material are mixed evenly in a predetermined ratio and then heated to the first temperature T 1 The heating process to can be a staged heating process.

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

[0171] In some embodiments, the above first heating process is to heat to 200°C - 250°C and hold at this temperature for 0.5 h - 3 h.

[0172] In some embodiments, the above second heating process is to heat to 450°C - 550°C and hold at this temperature for 0 h - 2 h. When the holding time is 0 h, it means that when heating to the range of 450°C - 550°C, no heat preservation treatment is carried out, but continue to heat to the first temperature T 1 。

[0173] In some embodiments, the above third heating process is to heat to the above first temperature T 1 and hold at this temperature for the first time t 1 。

[0174] During the staged heating process, first heat to 200°C - 250°C. Since the heating temperature is higher than the softening point temperature of the filler material, at this time, the filler material is heated and melted and softened. Holding for 0.5 h - 3 h can make it flow and fill into the pore structure of the raw material; then heat to 450°C - 550°C. At this time, the melted and softened filler material undergoes a carbonization reaction and gradually forms a semi-coke state, becoming a viscous liquid or solid, thereby preventing the filler material from entering all the pore structures of the raw material; finally heat to the first temperature. At this time, the filler material undergoes a carbonization reaction, which can effectively fill the pore structures occupied by the filler material.

[0175] In some embodiments, in step 2, heat to the above first temperature T at a rate of 1°C / min - 10°C / min 1For 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 composed of values above.

[0176] In some embodiments, for the above-mentioned first heating process, the heating rate can 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, 2 °C / min - 5 °C / min. In some embodiments, for the above-mentioned second heating process, the heating rate can be 1 °C / min - 10 °C / min, optionally 2 °C / min - 8 °C / min. In some embodiments, for the above-mentioned third heating process, the heating rate can be 1 °C / min - 10 °C / min, optionally 2 °C / min - 8 °C / min.

[0177] In some embodiments, in step 2, the above-mentioned first temperature T 1 is 700 °C - 1200 °C. For example, the first temperature T 1 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 composed of values above. Optionally, the above-mentioned first temperature T 1 is 750 °C - 1100 °C, 800 °C - 1100 °C, 850 °C - 1100 °C, 900 °C - 1100 °C, 850 °C - 1000 °C.

[0178] In some embodiments, in step 2, the above-mentioned first time t 1 is 1 h - 5 h. For example, the first time t 1 can be 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h or any range composed of values above. Optionally, the above-mentioned first time t 1 is 2 h - 4 h.

[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 pore size in the external and internal regions of the carbon material within a suitable range.

[0180] In some embodiments, in step 2, the heat treatment can be carried out in equipment capable of programmed heating such as intermediate frequency furnaces, roller kilns, rotary kilns, pusher kilns, vertical granulation kettles, horizontal granulation kettles, vertical reaction kettles, horizontal reaction kettles or drum furnaces.

[0181] In some embodiments, in step 2, the heat treatment atmosphere may be a protective gas atmosphere. The above-mentioned protective gas 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 pores in the outer region and the inner region of the first carbon-based material within a suitable range, and further beneficial to adjust S1 / S of the first carbon-based material within a suitable range. For example, by adjusting the heating rate in each stage to be ≤3 °C / min, S1 / S≥60%, and by adjusting the heating rate in each stage to be 8 - 10 °C / min, S1 / S≤85%.

[0183] In some embodiments, in step 3, the second temperature T 2 is 2070 °C - 2700 °C. Optionally, the second temperature T 2 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, 2140 °C - 2360 °C.

[0184] In some embodiments, in step 3, the second time t 2 is 1.5 h - 6 h. For example, the second time t 1 can be 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h or any range composed of the above values. Optionally, the second time t 2 is 2 h - 5 h.

[0185] When the second temperature T 2 and the second time t 2 are within the above range, it is beneficial to adjust I D / I G , and it 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 smaller I D / I G of the first carbon-based material.

[0186] In some embodiments, in step 3, the above heat treatment may be carried out in an intermediate frequency furnace, a box-type graphitization furnace, an Acheson graphitization furnace, a continuous graphitization furnace or an internal series graphitization furnace.

[0187] In some embodiments, in step 3, the heat treatment atmosphere of the intermediate frequency furnace and the continuous graphitization may be a protective gas atmosphere. The above-mentioned 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 ranges, it is beneficial to adjust the content of disordered carbon in the first carbon-based material 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 etc.

[0189] In the above 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 ranges, it is beneficial to adjust the S1 / S, I D / I G , graphitization degree, specific capacity, specific surface area, particle size, powder compact density and other parameters of the first carbon-based material.

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

[0191] In some embodiments, at least part of the surface of the second carbon-based material has a carbon coating layer. The preparation method of the second carbon-based material with a carbon coating layer includes: providing natural graphite as a raw material; mixing the natural graphite and the coating agent evenly in proportion; and performing heat treatment.

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

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

[0194] In some embodiments, the heat treatment temperature is 900°C - 1200°C. In some examples, the heat treatment time is 1 - 5 hours. By adjusting the heat treatment temperature, a second carbon-based material with different I D / I G values can be obtained.

[0195] Through the above heat treatment, the coating agent is carbonized, so that at least part 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 plate]

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

[0198] As an example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is provided on any one 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, as the metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material (such as 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 be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO 2 ), lithium nickel oxide (such as LiNiO 2 ), lithium manganese oxide (such as LiMnO 2 , LiMn 2 O 4 ), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (which can also be abbreviated as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (which can also be abbreviated as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O 2 (which can also be abbreviated as NCM211 )), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (which can also be abbreviated as NCM 622 ))), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (which can also be abbreviated as NCM 811 ))), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O 2 )) and at least one of its modified compounds, etc. Examples of olivine-structured lithium-containing phosphates may include but are not limited to lithium iron phosphate (such as LiFePO 4 (which can also be abbreviated as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO 4 ))), a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and at least one of a composite material of lithium manganese iron phosphate and carbon.

[0201] During the charge and discharge process of the battery, the deintercalation and consumption of Li will occur, and the molar content of Li is different when the battery is discharged to different states. In the listing of the positive electrode active material in this application, the molar content of Li is the initial state of the material, that is, the state before feeding. When the positive electrode active material is applied to the battery system, after charge and discharge cycles, the molar content of Li will change.

[0202] In the listing of the positive electrode active material in this application, the molar content of oxygen is only the theoretical state value. The release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual molar content of oxygen will fluctuate. The molar content of other elements also changes after battery manufacturing and during use. Therefore, the molar ratio of each element in the molecular formula of the above positive electrode active material is the molar ratio during preparation.

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

[0204] In some embodiments, the positive electrode film layer may also optionally include a conductive agent. As an 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 in the following manner: the above-mentioned 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 processes such as drying and cold pressing, the positive electrode sheet can be obtained.

[0206] [Electrolyte]

[0207] The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. There is no specific limitation on the type of electrolyte in this application, and it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or all-solid-state.

[0208] In some embodiments, the electrolyte uses an electrolytic solution. The electrolytic solution includes an electrolyte salt and a solvent.

[0209] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(oxalato)borate, lithium difluoro bis(oxalato)phosphate, and lithium tetrafluorooxalate phosphate.

[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, methyl propyl carbonate, ethyl propyl 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, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0211] In some embodiments, the electrolytic solution may also optionally include additives. For example, the additives can include negative electrode film-forming additives, positive electrode film-forming additives, and can also include additives that can improve certain battery performances, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature or low-temperature performance of the battery, etc.

[0212] [Separator]

[0213] In some embodiments, the battery cell further includes a separator. There is no particular limitation on the type of separator in this application, and any well-known porous structure separator with good chemical stability and mechanical stability can be selected.

[0214] In some embodiments, the material of the separator membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator membrane 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 plate, the negative electrode plate, and the separator membrane can be made into an electrode assembly through a winding process or a stacking process.

[0216] In some embodiments, the battery cell can include an outer package. The outer package can be used to encapsulate the above-mentioned electrode assembly and electrolyte.

[0217] In some embodiments, the outer package of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the battery cell can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic. As plastics, polypropylene, polybutylene terephthalate, and polybutylene succinate can be listed, etc.

[0218] This application does not have particular limitations on the shape of the battery cell, and it can be cylindrical, square, or any other arbitrary shape. For example, Figure 3 is a battery cell 5 with a square structure as an example.

[0219] In some embodiments, referring to Figure 4 , the outer package can include a housing 51 and a top cover assembly 53. Among them, the housing 51 can include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can be covered on the opening to close the receiving cavity. The positive electrode plate, the negative electrode plate, and the separator membrane can form an electrode assembly 52 through a winding process or a stacking 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 included 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, the battery cells can be assembled into a battery module. The number of battery cells included in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0221] Figure 5 is a battery module 4 as an example. Referring to Figure 5 , in the battery module 4, a plurality of battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other arbitrary manner. Further, the plurality of battery cells 5 can be fixed by fasteners.

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

[0223] In some embodiments, the above battery modules may also be assembled into a battery pack. The number of battery modules included in the battery pack may be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery pack.

[0224] Figure 6 and Figure 7 is a battery pack 1 as an example. Refer to Figure 6 and Figure 7 , in the battery pack 1, a battery box and a plurality of battery modules 4 provided in the battery box may be included. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0225] In addition, a second aspect of the present application provides an electrical device, and the electrical device includes the secondary battery provided in each of the above embodiments. The secondary battery can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include mobile devices (such as mobile phones, laptop computers, 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, satellites, energy storage systems, etc., but is not limited thereto.

[0226] As the electrical device, battery cells, battery modules or battery packs can be selected according to its usage requirements.

[0227] Figure 8 is an electrical device as an example. The electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the electrical device for the secondary battery, a battery pack or a battery module can be used.

[0228] Another example of the device may be a mobile phone, a tablet computer, a laptop computer, etc. This device usually requires thin and light, and battery cells can be used as the power source.

[0229] Embodiment

[0230] Hereinafter, embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application and should not be construed as a limitation to the present application. For those not specified in the embodiments regarding specific techniques or conditions, the techniques or conditions described in the literature in the art or according to the product specification are followed. Those reagents or instruments not specified as to the manufacturer can be conventional products obtained through commercial purchase.

[0231] In the embodiments and comparative examples of the present application, all materials can be obtained commercially or can be prepared by the following processes.

[0232] Preparation of Material 1-1

[0233] The flake graphite is mechanically crushed, classified, spheroidized, and purified to obtain natural spherical graphite. Among them, the volume distribution particle size Dv50 of the natural spherical graphite is 16.3 μm. The obtained natural spherical graphite is mixed with the filler petroleum pitch at a mass ratio of 100:25. The softening point of the petroleum pitch is 115 °C. Then, the mixed material is placed in a device with programmable temperature rise, heated to 200 °C and held for 1 h, then continuously heated to 650 °C (the first treatment temperature) and held for 2 h. After that, it is cooled to room temperature to obtain an intermediate. The obtained intermediate is placed in a graphitization furnace and heat-treated at 2490 °C (the second treatment temperature). After that, it is demagnetized and screened to obtain Material 1-1. Material 1-1 satisfies: I D / I G = 0.18, S2 / S1 = 16.1, and the 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 that of Material 1-1. The differences are as follows: Adjust the ratio of natural spherical graphite to the filler, and adjust the second treatment temperature in the range of 2000 °C to 2600 °C, so that the I D / I G is in the range of 0.13 - 0.33. Specifically as follows:

[0236] Table 1.

[0237]

[0238] Preparation of Materials 1-5 to 1-7

[0239] The preparation methods of Materials 1-5 to 1-7 are similar to that of Material 1-1. The differences are as follows: Adjust the volume distribution particle size Dv50 of the above natural spherical graphite so that it is in the range of 15 μm - 21 μm, and make the volume distribution particle size Dv50 of Materials 1-5 to 1-7 in the range of 16 μm - 22 μm. Specifically as follows:

[0240] Table 2.

[0241]

[0242] Preparation of Material 2-1

[0243] Provide natural spherical graphite, mix the natural spherical graphite and petroleum pitch evenly at a mass ratio of 100:10. The softening point of the petroleum pitch is 250 °C, and perform low-temperature heat treatment at 1130 °C for 2 hours to obtain natural graphite with a carbon coating layer, that is, Material 2-1. Among them, Material 2-1 satisfies: I D / I G = 0.42, the volume distribution particle size Dv50 = 11.2 μm, and the graphitization degree is 96.5%.

[0244] Preparation of Materials 2-2 to 2-4

[0245] The preparation methods of Materials 2-2 to 2-4 are similar to that of Material 2-1. The difference is: adjust the ratio of natural spherical graphite to petroleum pitch within the range of 100:8 to 100:12, and adjust the low-temperature heat treatment

[0246] treatment within the range of 900 °C to 1200 °C, so that the I D / I G of Materials 2-1 to 2-4 is within the range of 0.38 to 0.60. Specifically as follows: Table 3.

[0247] Table 3.

[0248]

[0249] Preparation of Materials 2-5 to 2-7

[0250] The preparation methods of Materials 2-5 to 2-7 are similar to that of Material 2-1. The difference is: adjust the volume distribution particle size Dv50 of the above natural spherical graphite so that it is within the range of 7.0 μm - 16 μm, and make the volume distribution particle size Dv50 of Materials 1-5 to 1-7 within the range of 7.8 μm - 17 μm. Specifically as follows:

[0251] Table 4.

[0252]

[0253] Example 1

[0254] Preparation of the secondary battery

[0255] 1. Negative electrode plate: Mix the negative electrode active materials (Material 1-1 (as the first carbon-based material) and Material 2-1 (as the second carbon-based material) at a mass ratio of 70:30), conductive agent carbon black (Super P), thickening agent sodium carboxymethyl cellulose, and binder styrene-butadiene rubber in an appropriate amount of solvent deionized water and stir well to form a negative electrode slurry. Coat the negative electrode slurry on both surfaces of the negative electrode current collector copper foil, and after drying and cold pressing, obtain the negative electrode plate.

[0256] 2. Positive electrode sheet: LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523) is mixed with conductive agent carbon black (Super P) and binder polyvinylidene fluoride in a weight ratio of 96:2:2, and an appropriate amount of solvent N-methylpyrrolidone NMP is added and stirred evenly to obtain the positive electrode slurry. The positive electrode slurry is coated on both surfaces of the positive electrode current collector aluminum foil, and after drying and cold pressing, the positive electrode sheet is obtained.

[0257] 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 LiPF 6 is dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0258] 4. Separator: A polypropylene film is used.

[0259] 5. Preparation of secondary battery: The positive electrode sheet and the negative electrode sheet prepared above are placed in order, and the separator is placed in the middle of the positive electrode sheet and the negative electrode sheet to play a separating role, and then wound to obtain an electrode assembly; the electrode assembly is placed in an outer package, dried and then injected with electrolyte, and after vacuum packaging, standing, forming, shaping and other processes, the secondary battery is obtained.

[0260] Examples 2 to 7

[0261] The battery preparation methods of Examples 2 - 7 are similar to those of Example 1, and the differences are that different materials are selected for the first carbon-based material or the second carbon-based material. For details, see Table 5.

[0262] Comparative Example 1

[0263] A secondary battery is assembled in a similar manner to the preparation method of Example 1, and the difference is that the negative electrode active material only contains the first carbon-based material (Material 1-1 prepared above) used in Example 1.

[0264] Comparative Example 2

[0265] A secondary battery is assembled in a similar manner to the preparation method of Example 1, and the difference is that the negative electrode active material only contains the second carbon-based material (Material 2-1 prepared above) used in Example 1.

[0266] Performance test

[0267] 1. Material testing

[0268] The S2 / S1 of the first carbon-based material is obtained by the following method for testing.

[0269] Mix the binder for sample preparation with the first carbon-based material powder evenly and coat it on the copper foil. Dry it at 60 °C for 30 min for standby. Cut it into 5 test samples of 6 mm × 6 mm in size at 5 different positions and paste them on the sample stage of the CP type argon ion cross-section polishing instrument respectively. Use the plasma beam to cut the samples to obtain the cross-sections of each sample. The testing instrument can be the IB-09010CP type argon ion cross-section polishing instrument of JEOL Company, Japan.

[0270] Use a scanning electron microscope to scan the cross-sections of each sample of the first carbon-based material, and obtain scanning images by randomly selecting areas in each sample cross-section. The test can refer to JY / T010-1996. The testing instrument can be the Sigma 300 type scanning electron microscope of ZEISS Company, Germany.

[0271] Randomly select the cross-sections of 20 particles of the first carbon-based material from the scanning images. The area formed by extending 0.25 μm from the surface of the particles of the first carbon-based material towards the inside of the particles is denoted as the external area, and the area inside the external area is denoted 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 mean 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.

[0272] 2. Electrode testing

[0273] Cut the negative electrode into test samples of 2 cm × 2 cm, and fix the test samples on the sample stage with paraffin; put the sample stage into the sample holder, lock it and fix it, turn on the power of the argon ion cross-section polishing instrument (IB-09010CP type argon ion cross-section polishing instrument of JEOL Company, Japan) and evacuate to 10 -4 Pa, set the argon gas 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 test samples for scanning test (refer to JY / T010-1996, scanning electron microscope (Sigma 300 of ZEISS Company)), and obtain the ion polishing cross-section morphology (CP) picture of the negative electrode at a magnification of 500 times, as Figure 1 shown. As can be seen from the Figure 1 arrow, there are obvious different pore structure distributions of the first carbon-based material and the second carbon-based material. Among them, the first carbon-based material has a certain number of pores at the position near the center of the particles, while almost no pores can be seen in the area near the surface of the particles. On the contrary, obvious 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.

[0274] 3. Battery Performance Test

[0275] (1) Low-temperature Fast Charging Performance Test of Secondary Battery

[0276] At 0°C, the secondary battery is charged at a constant current of 0.33C to 4.3V, then charged at a constant voltage until the current is 0.05C. After standing for 5 minutes, the secondary battery is discharged at a constant current of 0.33C to 2.8V, and its actual capacity is recorded as C0.

[0277] Then the secondary battery is successively charged at a constant current of 1.0C0, 1.3C0, 1.5C0, 1.8C0, 2.0C0, 2.3C0, 2.5C0, 3.0C0 to 4.3V or the 0V negative electrode cut-off potential (whichever reaches first). After each charging is completed, it needs to be discharged to 2.8V at 1C0. Record the negative electrode potential corresponding to 10%, 20%, 30%, etc. until 80% SOC (State of Charge) under different charging rates, and plot the charging rate-negative electrode potential curve under different SOC states. After linear fitting, obtain the charging rate corresponding to the negative electrode potential of 0V under different SOC states. This charging rate is the charging window under this SOC state, denoted as C10%SOC, C20%SOC, C30%SOC, C40%SOC, C50%SOC, C60%SOC, C70%SOC, C80%SOC respectively. According to the formula (60 / C20%SOC + 60 / C30%SOC + 60 / C40%SOC + 60 / C50%SOC + 60 / C60%SOC + 60 / C70%SOC + 60 / C80%SOC) × 10%, calculate the charging time T of the secondary battery from 10% SOC to 80% SOC (on the premise that the secondary battery does not lithium plate out), with the unit of min. The shorter this charging time, the better the kinetic performance of the secondary battery.

[0278] (2) 60°C Storage Performance Test of Secondary Battery

[0279] At 25°C, the above-prepared secondary battery is charged at a constant current of 1C to 4.3V, then charged at a constant voltage until the current is 0.05C. After standing for 5 minutes, the secondary battery is discharged at a constant current of 1C to 2.8V, and the discharge capacity at this time is recorded as the discharge capacity before storage.

[0280] At 25°C, the above-prepared secondary battery is charged at a constant current of 1C to 4.3V, then charged at a constant voltage until the current is 0.05C. Then the secondary battery is placed in a 60°C constant temperature oven for 150 days. The capacity retention rate (%) of the secondary battery after 60°C storage for 150 days = discharge capacity after storage / discharge capacity before storage × 100%.

[0281] 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.

[0282] Table 5.

[0283]

[0284] As can be seen from Table 5 above, in Comparative Example 1, all of the negative electrode active material is the first carbon-based material used in Example 1. Although good high-temperature storage performance can be obtained, the low-temperature charging time is too long. In Comparative Example 2, all of the negative electrode active material is the second carbon-based material used in Example 1. Although a shorter low-temperature charging time can be obtained, the high-temperature storage performance is poor. In contrast, when the first carbon-based material and the second carbon-based material are used in combination in Example 1, the battery can achieve both good low-temperature kinetic performance and high-temperature storage performance.

[0285] Further, adjust the I D / I G value of the first carbon-based material. As the I D / I G value of the first carbon-based material gradually increases, the low-temperature charging time gradually decreases, but the high-temperature storage performance will be affected. This is mainly because when the I D / I G increases, the defects on the material surface increase, the side reactions increase, and the lithium consumption increases. Therefore, the high-temperature storage performance is

[0286] affected to a certain extent.

[0287] Similarly, the change of the I D / I G of the second carbon-based material will also cause corresponding changes in the charging ability and high-temperature storage performance. As the I D / I G value of the second carbon-based material increases, the low-temperature charging time shortens. However, when this value is too high, as shown in Example 7, when the I D / I G value is 0.60, the high-temperature storage performance decreases slightly.

[0288] It shows that selecting two materials with appropriate I D / I G values is beneficial to obtaining a balance of simultaneously improved low-temperature kinetic performance and high-temperature storage performance.

[0289] Examples 8 to 10

[0290] The second carbon-based material used in Example 1 is adopted, except that the first carbon-based material selected has different particle sizes of the first carbon-based material, and a secondary battery is assembled.

[0291] Examples 11 to 13

[0292] The first carbon-based material used in Example 1 is adopted, with the difference that the second carbon-based material selected is a second carbon-based material with different particle sizes, and they are assembled into a secondary battery.

[0293] The parameters and test results of the secondary batteries prepared in Example 1 and Examples 8 to 13 are shown in Table 6 below.

[0294] Table 6.

[0295]

[0296] 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 also decreases slightly. According to Example 1 in combination 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 decreases. In addition, in Example 13, when the Dv50 of the first carbon-based material is close to or even larger than the Dv50 of the second carbon-based material, the high-temperature storage performance is better, while the low-temperature kinetic performance is significantly reduced.

[0297] Examples 14 to 15

[0298] The first carbon-based material and the second carbon-based material used in Example 1 are adopted and assembled into a secondary battery, with the difference only in the mass ratio of the first carbon-based material and the second carbon-based material. See Table 7 for details.

[0299] The test results of the secondary batteries prepared in Example 1 and Examples 14 to 15 are shown in Table 7 below.

[0300] Table 7.

[0301]

[0302] It can be seen from Table 7 above that when the mass ratio of the first carbon-based material is more than 50%, especially 70%, and at the same time the mass ratio of the second carbon-based material is less than 50%, especially 30%, the low-temperature kinetic performance and the capacity retention rate at 60 °C / 180 days of the secondary battery can achieve a better balance.

[0303] It should be noted that this application is not limited to the above embodiments. The above embodiments are only examples, and embodiments with the same composition and the same function and effect as the technical idea within the scope of the technical solution of this application are all included in the technical scope of this application. In addition, within the scope of not departing from the gist of this application, various modifications that those skilled in the art can think of and other ways constructed by combining some constituent elements in the embodiments are also included in the scope of this application.

Claims

1. A secondary battery, comprising a negative electrode plate, the negative electrode plate including a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector, the negative electrode film layer including a negative electrode active material, the negative electrode active material including a first carbon-based material and a second carbon-based material, Characterized in that, Both the first carbon-based material and the second carbon-based material have a pore structure, and the I of the first carbon-based material D / I G ≤ 0.27, and the I of the second carbon-based material D / I G ≥ 0.38, where I D represents the intensity of the D peak of the Raman spectrum at 1350 ± 50 cm -1 and I G represents the intensity of the G peak of the Raman spectrum at 1580 ± 50 cm -1 .

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

60.

3. The secondary battery according to claim 1 or 2, wherein, The I 3R(101) / I 2H(004) in the XRD diffraction pattern of the first carbon-based material is less than the I 3R(101) / I 2H(004) in the XRD diffraction pattern of the second carbon-based material; Optionally, in the XRD diffraction pattern of the first carbon-based material, I 3R(101) / I 2H(004) is less than or equal to 0.06, and more optionally is 0 - 0.06; Optionally, the I of the second carbon-based material 3R(101) / I 2H(004) ≥ 0.2, more optionally 0.22 - 0.4; Where I 3R is the diffraction peak intensity of the 101 crystal plane of the 3R phase of the carbon-based material corresponding to 43° - 44° in the XRD diffraction pattern, and I 2H is the diffraction peak intensity of the 004 crystal plane of the 2H phase of the carbon-based material corresponding to 53° - 55° in the XRD diffraction pattern.

4. The secondary battery according to any one of claims 1-3, 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 1-4, wherein, the volume distribution particle size Dv50 of the first carbon-based material is ≥ 15 μm, optionally 16 μm ≤ Dv50 ≤ 20 μm; and / or the volume distribution particle size Dv50 of the second carbon-based material is ≤ 13 μm, optionally 7 μm ≤ Dv50 ≤ 12 μm.

6. The secondary battery according to any one of claims 1-5, wherein, the specific surface area BET of the first carbon-based material is less than the specific surface area BET 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, and can be optionally 1.3 m 2 / g - 1.9 m 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, and can be optionally 1.8 m 2 / g - 3.4 m 2 / g.

8. The secondary battery according to any one of claims 1-7, 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 1-8, wherein, the graphitization degree of the first carbon-based material is ≥ 95%, optionally 96.0% - 98.5%; and / or the graphitization degree of the second carbon-based material is ≥ 95%, optionally 95.0% - 97.5%.

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

11. The secondary battery according to any one of claims 1-10, 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 , optionally less than or equal to 0.13 μm 2 ; and / or The internal region of the first carbon-based material includes more than one pore structure with an area greater than or equal to 0.15 μm 2 Optionally, it includes more than one pore structure with an area of 0.15 μm 2 -2.0 μm 2 ​ 12. The secondary battery according to any one of claims 1-11, wherein, at least a 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 1-12, wherein, the first carbon-based material satisfies at least one of the following items: (1) The compacted density of the first carbon-based material under 50,000 N ≤ 2.10 g / cm 3 , optionally 1.85 g / cm 3 - 2.00 g / cm 3 ; (2) The volume distribution particle size Dv90 of the first carbon-based material is less than or equal to 40 μm, optionally 30 μm - 38 μm; (3) The particle size distribution [(Dv90)-(Dv10)] / (Dv50)] of the first carbon-based material is ≤ 1.55, optionally 0.90 - 1.50; (4) The specific 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 proportion of the number of the primary particles in the first carbon-based material is greater than or equal to 80%.

14. The secondary battery according to any one of claims 1 - 13, wherein, the second carbon-based material satisfies at least one of the following items: (1) The specific 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 50,000 N ≤ 1.95 g / cm 3 , optionally 1.75 g / cm 3 - 1.90 g / cm 3 ; (3) The second carbon-based material includes primary particles. Optionally, the proportion of the number of the primary particles in the second carbon-based material is greater than or equal to 80%; (4) The second carbon-based material is natural graphite.

15. The secondary battery according to any one of claims 1 - 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 ≥ 55 wt%, optionally 60 wt% - 80 wt%.

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

17. The secondary battery according to any one of claims 1 - 16, wherein, the negative electrode film layer satisfies at least one of the following items: (1) The compaction density of the negative electrode film layer is ≥ 1.5 g / cm 3 , optionally 1.6 g / cm 3 -1.7 g / cm 3 ; (2) The areal density of the negative electrode film layer ≥ 10 mg / cm 2 , optionally 11.0 mg / cm 2 -15.0 mg / 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, optionally 90 μm - 130 μm.

18. An electrical device, characterized in that, it includes the secondary battery according to any one of claims 1 - 17.

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