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 has a pore structure, and the second carbon-based material has a pore structure. The total pore area S2 of the internal area is larger than the total pore area S1 of the external area; the second carbon-based material satisfies ID / IG < = 0.140. The secondary battery has good storage performance and energy density, and also has good cycle life.

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 hydro, thermal, wind, and solar power stations, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. With the increasingly wide application range of secondary batteries, people have posed severe challenges to the performance of secondary batteries. For example, in the face of the development of various green energy sources, it is required that secondary batteries have higher storage performance and energy density. 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 has improved storage performance and energy density.

[0004] A 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, wherein the negative electrode active material includes a first carbon-based material and a second carbon-based material, the first carbon-based material includes an outer region and an inner region located inside the outer region, wherein the outer region refers to a region formed by extending 2.5 μm from the surface of the first carbon-based material towards the inside. In the cross-sectional view of the first carbon-based material, the first carbon-based material has a pore structure. 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 of the first carbon-based material is denoted as S2. Then the first carbon-based material satisfies: S2 > S1; the second carbon-based material satisfies I D / I G ≤ 0.140, wherein, I D represents the intensity of the D peak in the Raman spectrum of the second carbon-based material at 1350 ± 50 cm -1 , and I G represents the intensity of the G peak in the Raman spectrum of the second carbon-based material at 1580 ± 50 cm -1 .

[0005] The total pore area S1 of the outer region of the first carbon-based material is smaller than the total pore area S2 of the inner region. This means that the structure of the outer region of the first carbon-based material is denser than that of the inner region. Compared with traditional natural graphite materials, the stability of the material is improved and the specific capacity is increased, but its storage performance is still not ideal. The second carbon-based material satisfies I D / I G≤0.140, reflecting that there are few surface defects in the material, the side reactions are reduced, and the consumption of active lithium is less. Therefore, the initial Coulombic efficiency is good, which can improve the storage performance of the battery. Thus, the negative electrode active material obtained by combining the first carbon-based material and the second carbon-based material in this application can give full play to the advantages of both to improve the storage performance and energy density of the secondary battery.

[0006] In some embodiments, the second carbon-based material satisfies 0.10 ≤ I D / I G ≤0.14, optionally, 0.11 ≤ I D / I G ≤0.13. When the second carbon-based material satisfies the above I D / I G range, it is beneficial to improve the initial Coulombic efficiency and storage performance of the secondary battery.

[0007] In some embodiments, the I D / I G of the first carbon-based material is greater than the I D / I G .

[0008] In some embodiments, the first carbon-based material satisfies I D / I G ≤0.30, optionally, 0.15 ≤ I D / I G ≤0.28.

[0009] By adjusting the I D / I G value of the first and second carbon-based materials, the reaction activity of the negative electrode active material can be reduced, and the side reactions between the negative electrode active material and the electrolyte are less, which is beneficial to improving the storage performance of the secondary battery.

[0010] In some embodiments, the second carbon-based material is artificial graphite. Artificial graphite has a relatively dense structure and basically no pores in the particles, so there are few side reactions and it has good storage performance and cycling performance.

[0011] In some embodiments, the interlayer spacing of the 002 crystal plane of the first carbon-based material is smaller than that of the 002 crystal plane of the second carbon-based material. Optionally, the interlayer spacing of the 002 crystal plane of the first carbon-based material ≤ 0.33569 nm, and optionally is 0.33557 - 0.33569 nm. Optionally, the interlayer spacing of the 002 crystal plane of the second carbon-based material ≤ 0.336088 nm, and optionally is 0.335744 - 0.336088 nm. When the interlayer spacing of the 002 crystal plane of the first carbon-based material is within the above range, it reflects a relatively high degree of graphitization and a relatively high specific capacity, thus effectively improving the energy density of the battery. For the second carbon-based material, the smaller interlayer spacing of the 002 crystal plane reflects a high degree of graphitization of the second carbon-based material. The higher degree of graphitization enables the second carbon-based material to have a high specific capacity and powder compaction density, which is beneficial to improving the energy density of the secondary battery.

[0012] In any embodiment, the first carbon-based material includes one or more pore structures with a pore area of ≥ 0.15 μm 2 ², and optionally includes one or more pore structures with a pore area of 0.15 - 2.0 μm 2 ². By making the internal region of the first carbon-based material include pore structures of the above sizes, on the one hand, it can reserve sufficient and stable expansion space for the volume change of the first carbon-based material particles, and on the other hand, it can also improve the compaction density of the negative electrode film layer, thereby increasing the energy density of the secondary battery.

[0013] In some embodiments, the first carbon-based material satisfies: 1.5 ≤ S2 / S1 ≤ 450, and optionally, 2 ≤ S2 / S1 ≤ 400. When S2 / S1 of the first carbon-based material is within the above range, it has balanced specific capacity and stability, and can improve its storage performance, enabling the secondary battery to have better energy density and cycle performance.

[0014] 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 ≥ 80%. The first carbon-based material is mainly in the form of primary particles, which is beneficial to maintaining its relatively low side reaction activity and reducing the occurrence of side reactions, thereby further improving the storage performance of the secondary battery. Optionally, the surface of the first carbon-based material does not have a coating layer. The absence of a carbon coating layer on the surface of the first carbon-based material can reduce the surface reaction activity, which is beneficial to the storage performance of the secondary battery.

[0015] In some embodiments, 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 ≥80%. Optionally, the surface of the second carbon-based material does not have a coating layer. Similarly, the second carbon-based material is mainly in the form of primary particles, and further its surface does not have a carbon coating layer, which is beneficial to maintaining a relatively low side reaction activity on the particle surface, reducing the occurrence of side reactions, thereby being able to further improve the storage performance of the secondary battery and reducing the impact on the energy density.

[0016] In some embodiments, the graphitization degree of the first carbon-based material is greater than that of the second carbon-based material. When the two are combined, the relatively high graphitization degree of the first carbon-based material can increase the specific capacity per gram of the negative electrode active material, which is beneficial to improving the energy density of the secondary battery.

[0017] In some embodiments, the graphitization degree of the first carbon-based material is ≥96%, optionally 96.5%-98.5%; and / or, the graphitization degree of the second carbon-based material is 91%-96.5%, optionally 92%-96%. The graphitization degrees of the first carbon-based material and the second carbon-based material within the above ranges enable the secondary battery to have a relatively high energy density.

[0018] In some embodiments, the specific surface area of the first carbon-based material is greater than that of the second carbon-based material. By adjusting the specific surface areas of the first and second carbon-based materials, the occurrence of side reactions can be reduced, and the consumption of active ions during the formation of the SEI film can be reduced, thereby being beneficial to the cycling performance and storage performance and being able to take into account a relatively high initial Coulomb efficiency.

[0019] 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 - 2.1 m 2 / g; the specific surface area of the second carbon-based material is less than or equal to 1.3 m 2 / g, optionally 0.8 m 2 / g - 1.2 m 2 / g. When the specific surface areas of the first carbon-based material and the second carbon-based material are respectively within the above ranges, the secondary battery has improved storage performance while taking into account the cycling performance.

[0020] In any embodiment, 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.

[0021] In some embodiments, the negative electrode active material satisfies at least one of the following items:

[0022] (1) The volume distribution particle size Dv50 of the negative electrode active material is ≥10 μm, and can be selected to be 10 μm-23 μm.

[0023] (2) The volume distribution particle size Dv90 of the negative electrode active material is ≤40 μm, and can be selected to be 23 μm-40 μm.

[0024] (3) The particle size distribution of the negative electrode active material [(Dv90)-(Dv10)] / (Dv50)] is ≤1.20, and can be optionally 0.9-1.20.

[0025] (4) The gram capacity of the negative electrode active material is ≥358 mAh / g, and can be selected from 358 mAh / g to 370 mAh / g.

[0026] (5) The negative electrode active material satisfies I D / I G ≤0.2, optionally 0.13-0.20, I D Indicates that the Raman spectrum is at 1350±50cm -1 The D peak intensity at I G Indicates that the Raman spectrum is at 1580±50cm -1 The G peak intensity at .

[0027] By combining the first carbon-based material and the second carbon-based material having the above-mentioned properties, a negative electrode active material having any one of the properties (1)-(5) above can be obtained, thereby improving the overall storage performance and gram capacity of the negative electrode active material, thereby making the secondary battery have improved storage performance and energy density, while taking into account the cycle performance.

[0028] In some embodiments, the first carbon-based material satisfies at least one of the following:

[0029] (1) The volume distribution particle size Dv50 of the first carbon-based material is ≥13 μm, and can be optionally 15 μm-25 μm.

[0030] (2) The volume distribution particle size Dv90 of the first carbon-based material is ≤40 μm, and can be optionally 28 μm-40 μm.

[0031] The particles of the first carbon-based material have a relatively large particle size. When the volume distribution particle size Dv50 and / or Dv90 thereof 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.

[0032] (3) The particle size distribution of the first carbon-based material, [(Dv90)-(Dv10)] / (Dv50), 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 enhancing the energy density of the secondary battery.

[0033] (4) The specific capacity of the first carbon-based material is ≥ 360 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 higher energy density.

[0034] When the first carbon-based material further has any one of the above (1)-(5) properties, it is beneficial to at least one of the storage performance and energy density cycling performance of the secondary battery.

[0035] In some embodiments, the second carbon-based material satisfies at least one of the following:

[0036] (1) The volume distribution particle size Dv50 of the second carbon-based material is ≤ 18 μm, optionally 13 μm - 18 μm. When the volume distribution particle size Dv50 of the second carbon-based material is within the above range, it can reduce the specific surface area of the second carbon-based material, reduce the occurrence of side reactions, and improve the storage performance of the secondary battery.

[0037] (2) The particle size distribution of the second carbon-based material, [(Dv90)-(Dv10)] / (Dv50), is ≤ 1.35, optionally 1.0 - 1.30. When the particle size distribution of the second 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, thereby further enhancing the energy density of the secondary battery.

[0038] (3) The specific capacity of the second carbon-based material is ≥ 357 mAh / g, optionally 357 mAh / g - 363 mAh / g. When the specific capacity of the second carbon-based material is within the above range, it can enhance the energy density of the secondary battery.

[0039] When the second carbon-based material further has any one of the above (1)-(3) properties, it can improve at least one of the storage performance, energy density, and cycling performance of the secondary battery.

[0040] In some embodiments, the mass percentage of the first carbon-based material in the negative electrode active material is ≥ 30 wt%, optionally 50 wt% - 80 wt%. When the mass percentage of the first carbon-based material in the negative electrode active material is within the above range, it can jointly play the respective advantages with the second carbon-based material to obtain improved storage performance and good energy density at the same time.

[0041] In some embodiments, the negative electrode active material further includes a silicon-based material. The silicon-based material can play a role in improving the pore structure in the negative electrode film layer, facilitating the infiltration and retention of the electrolyte, and enhancing the kinetic performance of the secondary battery; at the same time, it can also increase the negative electrode capacity, thereby further increasing the energy density of the secondary battery.

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

[0043] (1) The compaction density of the negative electrode film layer is ≥ 1.40 g / cm 3 , optionally 1.45 g / cm 3 -1.90 g / cm 3 .

[0044] (2) The areal density of the negative electrode film layer is ≥ 6.0 g / cm 2 , optionally 7.0 g / cm 2 -15 g / cm 2 .

[0045] (3) The porosity of the negative electrode film layer is 18.0% - 36.7%, optionally 19.0% - 34.0%.

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

[0047] When the negative electrode film layer has any one of the above (1) - (4) properties, it is beneficial to at least one of the storage performance and energy density of the secondary battery.

[0048] The second aspect of the present application further provides an electrical device including the secondary battery of each embodiment of the first aspect of the present application.

[0049] The electrical device of the present application includes any one of the secondary batteries of each embodiment of the above first aspect, and thus has at least the same advantages as the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 is a schematic diagram of a cross-sectional image of the particles of the first carbon-based material of the present application.

[0051] Figure 2 is an ion-polished cross-section (CP) diagram of an embodiment of the first carbon-based material of the present application.

[0052] Figure 3 is a schematic diagram of a battery cell of an embodiment of the present application.

[0053] Figure 4 is Figure 3Exploded view of a battery cell according to an embodiment of the present application as shown.

[0054] Figure 5 Schematic diagram of a battery module according to an embodiment of the present application.

[0055] Figure 6 Schematic diagram of a battery pack according to an embodiment of the present application.

[0056] Figure 7 is Figure 6 Exploded view of the battery pack according to an embodiment of the present application as shown.

[0057] Figure 8 Schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of the present application.

[0058] Description of reference numerals:

[0059] 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

[0060] Hereinafter, embodiments of the secondary battery and the electrical device of the present application specifically disclosed will be described in detail with appropriate reference to the 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 making the following description unnecessarily long and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0061] 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 or exclude 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 understood to be contemplated as well. Additionally, 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 stated, the numerical range "a - b" represents an abbreviated representation of any combination of real numbers between a and b, where both a and b are 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 just 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.

[0062] Unless otherwise specified, all embodiments and alternative embodiments of this application can be combined with each other to form new technical solutions.

[0063] Unless otherwise specified, all technical features and alternative technical features of this application can be combined with each other to form new technical solutions.

[0064] Unless otherwise specified, all steps of this application can be carried out in sequence or randomly, preferably in sequence. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out in sequence, or can also include steps (b) and (a) carried out in sequence. 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.

[0065] Unless otherwise specified, the terms used in this application have the well-known meanings commonly understood by those skilled in the art.

[0066] Unless otherwise specified, the numerical values of the various parameters mentioned in this application can be measured using various commonly used testing methods in the art. For example, they can be measured according to the testing methods given in this application.

[0067] Unless otherwise specified, in this application, the term "active ion" refers to an ion that can intercalate and deintercalate between the positive and negative electrodes of a secondary battery, including but not limited to lithium ions.

[0068] When improving the storage performance of a secondary battery, it is desirable to use a carbon material with a stable surface and few internal defects, such as artificial graphite. However, such materials often have an unsatisfactory specific capacity, resulting in a low energy density of the secondary battery. Natural graphite has a high degree of graphitization and a relatively high specific capacity, and there are many pores inside natural graphite, which is easy to obtain a high tap density and improve the capacity density of the secondary battery. However, natural graphite has many surface defects, and the porous structure leads to more side reactions and a low initial Coulomb efficiency, which reduces the storage performance of the secondary battery. Moreover, during the charge and discharge process, the material is prone to swelling, resulting in an unsatisfactory cycle life of the secondary battery. Coating the natural graphite particles with carbon can, to a certain extent, inhibit its swelling. However, the carbon coating layer often forms amorphous carbon with relatively high reaction activity, which is not conducive to the storage performance of the secondary battery. In addition, when improving the energy density of the secondary battery by, for example, increasing the tap density of the negative electrode film layer, the electrolyte infiltration characteristics of the negative electrode film layer deteriorate under a high tap density, and the risk of fragmentation of the negative active material particles increases, resulting in an increase in side reactions inside the battery, which further affects the storage performance of the secondary battery.

[0069] Therefore, currently, it is often difficult for secondary batteries to achieve both a high energy density, good storage performance, and a long cycle life.

[0070] In view of this, a first aspect of the embodiments of this application provides a secondary battery.

[0071] The term "secondary battery" mentioned herein refers to a battery cell, a battery module, or a battery pack.

[0072] 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 disposed between the positive electrode plate and the negative electrode plate, mainly to prevent short circuit between the positive and negative electrodes, and at the same time allows ions to pass through.

[0073] [Negative electrode plate]

[0074] The secondary battery of the present application includes a negative electrode plate, and 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 including a negative electrode active material. The negative electrode active material includes a first carbon-based material and a second carbon-based material. The first carbon-based material includes an outer region and an inner region located inside the outer region, where the outer region refers to the region formed by extending a distance of 2.5 μm from the surface of the first carbon-based material toward the inside. In the cross-sectional view of the first carbon-based material, the first carbon-based material has a pore structure. 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 of the first carbon-based material is denoted as S2. Then, the first carbon-based material satisfies: S2 > S1; the second carbon-based material satisfies I D / I G ≤ 0.140, where I D represents the intensity of the D peak at 1350 ± 50 cm -1 in the Raman spectrum of the second carbon-based material, and I G represents the intensity of the G peak at 1580 ± 50 cm -1 in the Raman spectrum of the second carbon-based material.

[0075] In the present application, the total pore area S1 of the outer region of the first carbon-based material is smaller than the total pore area S2 of the inner region. This means that the structure of the outer region of the first carbon-based material is denser than that of the inner region. In addition, the first carbon-based material in the present application satisfying "S1 > S2" 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, part of the pore structure in the main structure of the first carbon-based material, especially the pores in the outer region, is significantly smaller in area than the pores in the inner region.

[0076] Reference Figure 1 , which shows a schematic diagram of a cross-sectional image of the particles of the first carbon-based material 100 of the present application, and this cross-sectional image passes through the center of the particles of the first carbon-based material 100. As Figure 1 shown, the region formed by extending a distance of 2.5 μm from the surface of the particles of the first carbon-based material 100 toward the particle interior is denoted as the outer region 101, and the region inside the outer region 101 is denoted as the inner region 102.

[0077] The pore structure within the first carbon-based material can be observed using a cross-section polishing instrument. For example, the cross-sectional morphology (CP) of the negative electrode sheet can be tested by ion polishing. Specifically, the negative electrode sheet is cut into a test sample of a certain size (e.g., 2 cm × 2 cm), and the negative electrode sheet is fixed on the sample stage using paraffin; the sample stage is loaded into the sample holder and locked in place, the power of the argon ion cross-section polishing instrument (e.g., the IB-09010 CP type argon ion cross-section polishing instrument from JEOL Ltd. of Japan) is turned on and vacuum pumping is performed (e.g., 10-4 Pa), the argon gas flow rate (e.g., 0.15 MPa), voltage (e.g., 8 KV), and polishing time (e.g., 2 h) are set, the sample stage is adjusted to the rocking mode and polishing begins; a certain area within the first region 1021 is randomly selected in the test sample for scanning and testing (e.g., referring to JY / T 010-1996 and using a scanning electron microscope for scanning), and an image of the ion-polished cross-sectional morphology (CP) of the negative electrode sheet is obtained at a certain magnification (e.g., 1000 times). As Figure 2 shown, it can be seen that the first carbon-based material has a certain number of pores in the inner region near the center of the particles, while the outer region near the surface of the particles has a denser structure.

[0078] The second carbon-based material of the present application satisfies I D / I G ≤ 0.140. The I D / I G value reflects the degree of carbon disorder on the surface of the material to a certain extent. The lower this value, the fewer surface defects the material has, the lower the degree of carbon disorder, the lower the reaction activity, the fewer side reactions with the electrolyte, the less consumption of active ions, the higher the initial Coulombic efficiency, and it is beneficial to improving the storage performance of the secondary battery.

[0079] According to the above definition, when the particles of the first carbon-based material satisfy S2 > S1, it is beneficial to the stability of the material, reduces swelling during charge-discharge cycles, and has an increased specific capacity, thus being beneficial to improving the energy density of the secondary battery and having improved cycle performance. However, the storage performance of the first carbon-based material is still insufficient. By mixing with the second carbon-based material that satisfies I D / I G ≤ 0.140, the deficiency in the storage performance of the first carbon-based material can be compensated. Thus, a secondary battery with improved energy density and storage performance can be obtained.

[0080] In some embodiments, the second carbon-based material satisfies 0.10 ≤ I D / I G ≤ 0.14, optionally, 0.11 ≤ I D / I G ≤ 0.13. When the second carbon-based material satisfies the above I D / I GWhen in the range, the surface stability is high, the side reactions with the electrolyte are few, the consumption of active ions is small, the first Coulombic efficiency of the negative electrode can be improved, which is beneficial to the storage performance of the secondary battery, including the improvement of the high-temperature storage performance.

[0081] In some embodiments, the I of the first carbon-based material D / I G is greater than the I of the second carbon-based material D / I G .

[0082] In some embodiments, the first carbon-based material satisfies I D / I G ≤0.30. Optionally, 0.15 ≤ I D / I G ≤0.28.

[0083] When the I of the first carbon-based material D / I G is within the above range, the surface properties of the material are relatively stable, which can reduce the overall reactivity of the negative electrode active material, resulting in fewer side reactions between the negative electrode active material and the electrolyte, and is beneficial to the secondary battery having further improved storage performance.

[0084] In some embodiments, the second carbon-based material is artificial graphite. Artificial graphite has a relatively dense structure and basically no pores in the particles, so there are few side reactions and it has good storage performance.

[0085] In the present application, artificial graphite generally refers to crystalline carbon obtained by high-temperature graphitization treatment. There are usually no pore structures in the particles, or no pore structures that can be directly observed from the cross-sectional image (such as a scanning electron microscope image with a magnification of 1000 times). Thus, according to the above method of obtaining the cross-section of the negative electrode plate with a cross-section polisher and observing through a microscope, it can be distinguished from the first carbon-based material.

[0086] Mixing the second carbon material of artificial graphite with excellent storage performance and cycle performance with the first carbon material with high specific capacity and improved cycle performance can enable the secondary battery to have a high energy density and storage performance, and also take into account good cycle performance.

[0087] In some embodiments, the layer spacing of the 002 crystal plane of the first carbon-based material is smaller than the layer spacing of the 002 crystal plane of the second carbon-based material. In the present application, by adjusting the layer spacing of the 002 crystal plane of the two carbon-based materials, the first and second carbon-based materials with good storage performance and specific capacity are combined to obtain the negative electrode active material. Among them, the smaller layer spacing of the 002 crystal plane of the first carbon-based material contributes more specific capacity.

[0088] According to some embodiments, the interlayer spacing of the 002 crystal plane of the first carbon-based material is ≤ 0.33569 nm, optionally 0.33557 - 0.33569 nm. According to some embodiments, the interlayer spacing of the 002 crystal plane of the second carbon-based material is ≤ 0.336088 nm, optionally 0.335744 - 0.336088 nm. The smaller interlayer spacing of the 002 crystal plane of the first carbon-based material reflects that the material has a higher degree of graphitization, thus having a higher specific capacity, and therefore can effectively improve the energy density of the secondary battery. For the second carbon-based material, the smaller interlayer spacing of the 002 crystal plane reflects that the second carbon-based material also has a high degree of graphitization. The higher degree of graphitization enables the second carbon-based material to have a high specific capacity and powder compaction, which is beneficial to improving the energy density of the battery cell.

[0089] In some embodiments, the first carbon-based material includes one or more pore structures with a pore area of ≥ 0.15 μm 2 ², optionally including one or more pore structures with a pore area of 0.15 - 2.0 μm 2 ².

[0090] The material in this application (such as the first carbon-based material) having "pore structures in the internal region" means that the material has pore structures 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, the main structure of the first carbon-based material has pore structures. More specifically, at least the interior of the main structure has pore structures.

[0091] By making the internal region of the first carbon-based material include pore structures of the above sizes, sufficient and stable expansion space can be reserved for the volume change of the first carbon-based material particles, which is beneficial to the cycle life of the secondary battery.

[0092] In some embodiments, the first carbon-based material satisfies: 1.5 ≤ S2 / S1 ≤ 450, optionally, 2 ≤ S2 / S1 ≤ 400. Exemplarily, the first carbon-based material satisfies: 2.0 ≤ S 2 / S 1 ≤ 400, 2.4 ≤ S 2 / S 1 ≤ 300, 2.5 ≤ S 2 / S 1 ≤ 250, 2.6 ≤ S 2 / S 1 ≤ 200, 2.8 ≤ S 2 / S 1 ≤ 150, or 3.0 ≤ S 2 / S 1≤100. When S2 / S1 of the first carbon-based material is within the above range, it reflects that the pore structure in the outer region of the particles is relatively small and has a relatively dense structure. Thus, while improving the material stability, it helps to reduce the side reactions between the first carbon-based material and the electrolyte and reduces the formation of the SEI film inside the particles, reducing the loss of active substances. Therefore, the first carbon-based material has balanced specific capacity and stability and can improve its storage performance, enabling the secondary battery to have better energy density and cycling performance.

[0093] In some embodiments, the first carbon-based material includes primary particles. Optionally, the proportion of the number of primary particles in the first carbon-based material is greater than or equal to 80%. It can be exemplified that the proportion of the number of primary particles in the first carbon-based material is greater than or equal to 80%, 85%, 90%, 95%, or even all are primary particles. Advantageously, the first carbon-based material is mainly primary particles. Primary particles are beneficial for maintaining the stability of their surface, thereby reducing side reactions and being beneficial for the storage performance and high energy density of the secondary battery.

[0094] In some embodiments, the surface of the primary particles of the first carbon-based material does not have a coating layer. Conventionally, the carbon coating layer on the surface of the carbon-based material is soft carbon, with low specific capacity and high consumption of active ions, resulting in poor storage performance. Therefore, when the first carbon-based material does not have a coating layer, it is beneficial for maintaining its low side reaction activity, reducing the occurrence of side reactions, and thus being able to maintain the storage performance of the secondary battery; in addition, it will not have an adverse effect on the energy density of the secondary battery.

[0095] 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%. It can be exemplified that the proportion of the number of primary particles in the second carbon-based material is greater than or equal to 80%, 85%, 90%, 95%, or even all are primary particles. Similarly, the second carbon-based material is advantageously mainly primary particles. Primary particles are beneficial for maintaining the stability of their surface, thereby reducing side reactions and being beneficial for the storage performance of the secondary battery.

[0096] In some embodiments, the surface of the primary particles of the second carbon-based material does not have a coating layer. Similarly, the primary particles of the second carbon-based material without a coating layer are beneficial for maintaining their low side reaction activity, reducing the occurrence of side reactions, and thus being able to further improve the storage performance of the secondary battery; and it will not have an adverse effect on the energy density of the secondary battery.

[0097] In some embodiments, the graphitization degree of the first carbon-based material is greater than that of the second carbon-based material. Adjusting the graphitization degrees of the first carbon-based material and the second carbon-based material can enable the negative electrode active material to have a higher specific capacity, thereby being beneficial for improving the energy density of the secondary battery.

[0098] In some embodiments, the graphitization degree of the first carbon-based material is greater than or equal to 96.0%, optionally 96.5%-98.5%. Exemplarily, the graphitization degree of the first carbon-based material can be 96.0%, 96.5%, 97.0%, 97.5%, 98.0%, 98.5%, or a value between any two of these values. By adjusting the graphitization degree of the first carbon-based material within the above range, it is beneficial for the negative electrode active material to have a high specific capacity, thereby enabling the secondary battery to have an improved energy density.

[0099] In some embodiments, the graphitization degree of the second carbon-based material is 91%-96.5%, optionally 92%-96%. Exemplarily, the graphitization degree of the first carbon-based material can be 91.5%, 92%, 92.5%, 93%, 93.5%, 94%, 94.5%, 95%, 95.5%, 96%, or a value between any two of these values. Selecting a relatively high graphitization degree for the second carbon-based material is beneficial for the energy density of the secondary battery while providing good storage performance.

[0100] In some embodiments, the BET specific surface area of the first carbon-based material is greater than the BET specific surface area of the second carbon-based material.

[0101] In some specific embodiments, the BET specific surface area of the first carbon-based material is ≤ 2.1 m 2 / g, optionally 1.3 m 2 / g - 2.1 m 2 / g. Exemplarily, the surface area of the first carbon-based material can be 1.3 m 2 / g, 1.5 m 2 / g, 1.7 m 2 / g, 1.9 m 2 / g, 2.1 m 2 / g, or a value between any two of these values. Since the internal region of the first carbon-based material has a pore structure, its specific surface area is relatively large compared to the second carbon material including artificial graphite with a dense overall structure. Controlling the specific surface area of the first carbon-based material to be less than or equal to 2.1 m 2 / g can reduce the reactivity of the first carbon-based material and is beneficial for the storage performance of the secondary battery.

[0102] In some specific embodiments, the specific surface area of the second carbon-based material is less than or equal to 1.3 m 2 / g, optionally 0.8 m 2 / g - 1.2 m 2 / g. Exemplarily, the surface area of the second carbon-based material can be 0.8 m 2 / g, 0.9 m 2 / g, 1.0 m 2 / g, 1.1 m 2 / g, 1.2 m 2 / g, 1.3 m 2 / g, or a value between any two numerical values.

[0103] By adjusting so that both the first and second carbon-based materials have a relatively small specific surface area, the reactivity of the materials can be reduced, the occurrence of side reactions can be decreased, and the consumption of active ions during the formation of the SEI film can be reduced. As a result, a higher initial Coulombic efficiency can be achieved, which is beneficial to the cycling performance and storage performance.

[0104] 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.

[0105] In some embodiments, the tap density of the first carbon-based material is greater than the tap density of the second carbon-based material.

[0106] When the first and second carbon-based materials that meet the above design are combined as the negative electrode active material, the negative electrode active material satisfies one or more of the following characteristics, thereby enabling the secondary battery to have good energy density and storage performance and taking into account the cycle life.

[0107] The volume distribution particle size Dv50 of the negative electrode active material is ≥ 10 μm, and can be optionally 10 μm - 23 μm.

[0108] The volume distribution particle size Dv90 of the negative electrode active material is ≤ 40 μm, and can be optionally 23 μm - 40 μm.

[0109] The particle size distribution of the negative electrode active material [(Dv90) - (Dv10)] / (Dv50)] ≤ 1.20, and can be optionally 0.9 - 1.20.

[0110] The specific capacity of the negative electrode active material is ≥ 358 mAh / g, and can be optionally 358 mAh / g - 370 mAh / g.

[0111] The negative electrode active material satisfies I D / I G ≤ 0.2, and can optionally be 0.13 - 0.2. I D represents the intensity of the D peak in the Raman spectrum at 1350 ± 50 cm -1 , and I G represents the intensity of the G peak in the Raman spectrum at 1580 ± 50 cm -1 .

[0112] By combining the first carbon-based material and the second carbon-based material with the above-mentioned properties, a negative electrode active material with any one of the above-mentioned properties can be obtained, improving the overall storage performance and capacity of the negative electrode active material, so that the secondary battery has improved storage performance and energy density, and also taking into account the cycle performance.

[0113] In some embodiments, when the first carbon-based material further satisfies one or more of the following conditions on the basis of meeting the above design, the adverse effect on the reaction performance of the material surface can be further reduced, the specific capacity can be increased, and further, the performance of the secondary battery can be further improved, for example, at least one of the energy density, storage performance, cycle performance, etc. of the secondary battery can be further improved.

[0114] In some embodiments, the volume distribution particle size Dv50 of the first carbon-based material is ≥ 13 μm, optionally 15 μm - 25 μm. Exemplarily, the volume distribution particle size Dv50 of the first carbon-based material is 15 μm, 17 μm, 20 μm, 23 μm, 25 μm, etc., or a value within the range composed of any two numerical values, but not limited thereto.

[0115] In some embodiments, the volume distribution particle size Dv90 of the first carbon-based material is ≤ 40 μm, optionally 28 μm - 40 μm. Exemplarily, the volume distribution particle size Dv90 of the first carbon-based material is 28 μm, 30 μm, 33 μm, 35 μm, 37 μm, 40 μm, etc., or a value within the range composed of any two numerical values, but not limited thereto.

[0116] The particles of the first carbon-based material have a relatively large particle size. When its volume distribution particle size Dv50 and / or Dv90 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.

[0117] In some embodiments, the particle size distribution [(Dv90) - (Dv10)] / (Dv50) of the first carbon-based material is ≤ 1.55, optionally 0.90 - 1.50. Exemplarily, 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, 1.55, etc., or a value within the range composed of any two numerical values, but not limited thereto. 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.

[0118] In some embodiments, the specific capacity of the first carbon-based material is ≥ 360 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.

[0119] In some embodiments, when the second carbon-based material further satisfies one or more of the following conditions on the basis of meeting the above design, while having good cycling performance, it can further reduce the reactivity of the negative electrode active material, increase the specific capacity of the negative electrode active material, and increase the compaction density of the negative electrode film layer, etc., in at least one aspect, thereby further improving the performance of the secondary battery, such as further enhancing at least one of the energy density, storage performance, cycling performance, etc. of the secondary battery.

[0120] In some embodiments, the volume distribution particle size Dv50 of the second carbon-based material is ≤ 18 μm, optionally 13 μm - 18 μm. Exemplarily, the volume distribution particle size Dv50 of the second carbon-based material is 13 μm, 14 μm, 15 μm, 15.5 μm, 16 μm, 17 μm, 18 μm, etc., or a value between any two of these values. When the volume distribution particle size Dv50 of the second carbon-based material is within the above range, it can reduce the specific surface area of the second carbon-based material, reduce the occurrence of side reactions, and improve the storage performance of the secondary battery.

[0121] In some embodiments, the particle size distribution [(Dv90) - (Dv10)] / (Dv50) of the second carbon-based material is ≤ 1.35, optionally 1.0 - 1.35. Exemplarily, the particle size distribution [(Dv90) - (Dv10)] / (Dv50) of the second carbon-based material is 1.0, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, etc., or a value between any two of these values. When the particle size distribution of the second carbon-based material is within the above range, its particle packing performance is good, which is beneficial to increasing the compaction density of the negative electrode film layer, thereby further enhancing the energy density of the secondary battery.

[0122] In some embodiments, the specific capacity of the second carbon-based material is greater than or equal to 357 mAh / g, optionally 357 mAh / g - 363 mAh / g. Exemplarily, the specific capacity of the second carbon-based material is 357 mAh / g, 359 mAh / g, 360 mAh / g, 361 mAh / g, 362 mAh / g, 363 mAh / g, etc., or a value between any two of these values. When the specific capacity of the second carbon-based material is within the above range, on the one hand, it can enhance the energy density of the secondary battery.

[0123] In some embodiments, in the negative electrode active material, the mass percentage of the first carbon-based material is ≥30 wt%, optionally 50 wt%-80 wt%. Exemplarily, in the negative electrode active material, the mass percentage of the first carbon-based material is 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%, or a value or a range formed by any two values therebetween.

[0124] When the mass percentage of the first carbon-based material in the negative electrode active material is within the above range, the respective advantages of the first and second carbon-based materials can be jointly exerted to obtain improved storage performance, while also having good cycle performance and energy density.

[0125] In some embodiments, in the negative electrode active material, the mass percentage of the second carbon-based material is ≤70 wt%, optionally 20-50 wt%. Exemplarily, in the negative electrode active material, the mass percentage of the second carbon-based material is 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, etc., or a value or a range formed by any two values therebetween.

[0126] In some embodiments, the negative electrode active material is composed of the above-mentioned first carbon-based material and second carbon-based material.

[0127] 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 retention of the electrolyte, and enhancing the kinetic performance of the secondary battery; at the same time, it can also increase the negative electrode capacity, thereby further enhancing the energy density of the secondary battery.

[0128] The silicon-based material can be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys.

[0129] In some embodiments, the mass percentage of the silicon-based material in the negative electrode active material is less than or equal to 10%, optionally 3%-10%. Thereby, while enhancing the energy density of the secondary battery, the secondary battery can also have good cycle performance and storage performance.

[0130] 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.

[0131] In some embodiments, the negative electrode film layer may further optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0132] In some embodiments, the negative electrode film layer may further optionally include other additives, such as a thickener (e.g., sodium carboxymethyl cellulose (CMC-Na)), etc.

[0133] Further research has found that when the negative electrode film layer satisfies one or more of the following conditions, the performance of the secondary battery can be further improved, such as further enhancing at least one of the energy density, storage performance, cycling performance, etc. of the secondary battery.

[0134] In some embodiments, the compaction density of the negative electrode film layer is ≤ 1.40 g / cm 3 , optionally 1.45 g / cm 3 - 1.90 g / cm 3 . Exemplarily, the compaction density of the negative electrode film layer is 1.40, 1.50, 1.60, 1.70, 1.80, 1.90, etc., or a value between any two numerical values, but not limited thereto. When the compaction density of the negative electrode film layer is within the above range, it is beneficial for the negative electrode film layer to have both high capacity, and thus beneficial for the secondary battery to have both high storage performance and high energy density.

[0135] In some embodiments, the areal density of the negative electrode film layer ≥ 6.0 g / cm 2 , optionally 7.0 g / cm 2 - 15 g / cm 2 . Exemplarily, the compaction density of the negative electrode film layer is 6.0 g / cm 2 , 7.0 g / cm 2 , 8.0 g / cm 2 , 9.0 g / cm 2 , 10.0 g / cm 2 , 11.0 g / cm 2 , 12.0 g / cm 2 , 13.0 g / cm 2 , 14.0 g / cm 2 , 15.0 g / cm 2 etc., or a value between any two numerical values.

[0136] When the areal density of the negative electrode film layer is within the above range, it is beneficial for the negative electrode film layer to have both high capacity, and thus beneficial for the secondary battery to have both high energy density and good storage performance.

[0137] In some embodiments, the porosity of the negative electrode film layer is 18.0% - 36.7%, optionally 19.0% - 34.0%. For example, the compaction density of the negative electrode film layer can be 18.0%, 20.0%, 22.0%, 24.0%, 26.0%, 28.0%, 30.0%, 32.0%, 34.0%, etc., or any value within the range formed by any two of these values. This is beneficial for the negative electrode film layer to have both high capacity, and further beneficial for the secondary battery to have both high energy density and good storage performance.

[0138] In any embodiment, the thickness of the negative electrode film layer ≥ 70, optionally 90μm - 130μm. For example, the thickness of the negative electrode film layer can be 70μm, 80μm, 90μm, 100μm, 110μm, 120μm, 130μm, etc., or any value within the range formed by any two of these values.

[0139] 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 a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0140] In some embodiments, the negative electrode plate can be prepared in the following way: dispersing the components for preparing the negative electrode plate described above, such as the negative electrode active material including the first carbon-based material and the second carbon-based material, the conductive agent, the 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.

[0141] 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 either 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 this application (such as compaction density, surface 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, as long as the parameters of the negative electrode film layer on any one side meet the requirements of this application, it is considered to fall within the protection scope of this application.

[0142] In the present application, it is not excluded that in addition to the above-mentioned negative electrode film layer, the negative electrode sheet may further include other additional functional layers. For example, in some embodiments, the negative electrode sheet further includes a conductive bottom coating (for example, composed of a conductive agent and a binder) disposed 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 sheet further includes a protective layer covering the surface of the negative electrode film layer.

[0143] In the present application, the total pore area S1 of the external region and the total pore area S2 of the internal region of the material (such as the first carbon-based material) can be obtained by using a cross-section polishing instrument (such as the IB-09010 CP type argon ion cross-section polishing instrument of JEOL, Japan) to obtain the cross-section of the carbon material; then referring to JY / T010-1996, using a scanning electron microscope (such as the Sigma300 type scanning electron microscope of ZEISS, Germany) to scan the cross-section of the carbon material; finally, using an image processing software (such as AVIZO) to respectively obtain the total pore area S1 of the external region and the total pore area S2 of the internal region in the carbon material, and the value of S2 / S1 can be obtained therefrom. Exemplarily, samples can be obtained from different regions of the negative electrode sheet in the secondary battery, and at least 5 positions (such as 5, 10, 15 or even more) are randomly selected from the samples to obtain cross-sections by using a cross-section polishing instrument, and at least 10 particles (such as 10, 20, 50 or even more particles) of cross-sections are randomly selected from the images of the scanning electron microscope 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 by using an image processing software, and the value of S2' / S1' of each particle cross-section is obtained therefrom. Calculate the arithmetic mean of S2' / S1' of all measured particle cross-sections as the S2 / S1 value of the first carbon-based material.

[0144] In the present application, the I D / I G value of the 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 are as follows: 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 intensities of the D peak and the G peak at 100 points. Calculate the I D / I G , remove the largest and smallest 25 I D / I G , and the average value of the remaining 50 points is the I of the materialD / I G The testing instrument can adopt Horiba LabRAM HR800 Raman spectrometer.

[0145] In this application, the interlayer spacing of the 002 crystal plane of the material (such as the first carbon-based material, the second carbon-based material) has the meaning well known in the art and can be tested by the instruments and methods known in the art. For example, it can be tested using an X-ray diffractometer (such as Bruker D8 Discover), and the testing can refer to JIS K0131-1996 and JB / T 4220-2011 to obtain the interlayer spacing of the C(002) crystal plane in the crystal structure of the material.

[0146] In this application, the graphitization degree of the material (such as the first carbon-based material, the second carbon-based material) has the meaning well known in the art and can be tested by the instruments and methods known in the art. For example, it can be tested using an X-ray diffractometer (such as Bruker D8 Discover), and the testing can refer to JIS K 0131-1996 and JB / T 4220-2011 to obtain the average interlayer spacing d of the C(002) crystal plane in the crystal structure of the material. 002 , and then the graphitization degree is calculated according to the formula g = (0.344 - d 002 ) / (0.344 - 0.3354) × 100%. 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).

[0147] In this application, both the primary particles and the secondary particles have the meaning well known in the art. The primary particles refer to non-agglomerated particles. The secondary particles refer to agglomerated particles formed by the aggregation of two or more primary particles. The primary particles and the secondary particles can be distinguished by using a scanning electron microscope (SEM) image.

[0148] In this application, taking the first carbon-based material as an example, the proportion of the number of primary particles in the first carbon-based material and / or the second carbon-based material refers to: taking a test sample randomly in the negative electrode film layer, taking multiple test regions randomly in the test sample, obtaining images of multiple test regions by using a scanning electron microscope, and counting the proportion of the number of primary carbon-based materials with the morphology of primary particles in each image to the total number of carbon-based material particles. The average value of multiple statistical results is the proportion of the number of primary particles in the first carbon-based material.

[0149] In this 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 using a transmission electron microscope.

[0150] In this application, the specific surface area 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 by referring to GB / T 19587-2017 using the nitrogen adsorption specific surface area analysis test method and calculated by the BET (Brunauer Emmett Teller) method. The test instrument can be the Tri-Star 3020 specific surface area and pore size analyzer of Micromeritics, USA.

[0151] 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 meaning well-known 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 by referring to GB / T19077-2016 using a laser particle size analyzer. The test instrument can be the Mastersizer 3000 laser particle size analyzer of Malvern Instruments Ltd., UK.

[0152] In this application, the specific capacity 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 tested by the methods known in the art. An exemplary test method is as follows: Mix the sample powder with conductive agent carbon black (Super P) and binder polyvinylidene fluoride (PVDF) in a mass ratio of 91.6:1.8:6.6 with solvent N-methylpyrrolidone (NMP) to make a slurry; coat the prepared slurry on the surface of the negative current collector copper foil, dry it in an oven and set aside; Mix ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 1:1:1 to obtain an organic solvent, and then dissolve LiPF 6 in the above organic solvent to prepare an electrolyte with a concentration of 1 mol / L; then use a lithium metal sheet as the counter electrode, a polyethylene (PE) film as the separator, and assemble it with the above electrolyte into a CR2430 type button cell in a glove box under argon protection; After the obtained button cell is left standing for 12 h, at 25 °C, it is discharged at a constant current of 0.05C to 0.005V, left standing for 10 minutes, then discharged at a constant current of 50 μA to 0.005V, left standing for 10 minutes, and then discharged at a constant current of 10 μA to 0.005V; Then it is charged at a constant current of 0.1C to 2V, and the charging capacity is recorded. The ratio of the charging 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.).

[0153] In this application, the tap density of the material (such as the first carbon-based material, the second carbon-based material, etc.) has a 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 24533-2009 using an electronic pressure testing machine (such as a UTM7305 type electronic pressure testing machine). An exemplary testing method is as follows: Weigh 1 g of the sample powder and add it to a mold with a bottom area of 1.327 cm 2 and apply pressure up to 50000 N, hold the pressure for 30 s, then release the pressure, keep it for 10 s, and then record and calculate the tap density of the material under a pressure of 50000 N.

[0154] In this application, the areal density of the negative electrode film layer has a meaning well-known in the art and can be tested by 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 1 , weigh it, and record it as M 1 . 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, and record it as M 0 . The areal density of the negative electrode plate = (M 1 - M 0 ) / S 1 .

[0155] In this application, the tap density of the negative electrode film layer has a 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. The thickness of the negative electrode film layer has a meaning well-known in the art and can be tested by methods known in the art, such as using a micrometer (such as Mitutoyo293-100 type with an accuracy of 0.1 μm).

[0156] In this application, the thickness of the negative electrode film layer has a meaning well-known in the art and can be tested by methods known in the art, such as using a micrometer (such as Mitutoyo293-100 type with an accuracy of 0.1 μm).

[0157] In the X-ray diffraction analysis test of this application, a copper target can be used as the anode target, with CuKα rays as the radiation source, and the ray wavelength The scanning 2θ angle range is 20° - 80°, and the scanning rate is 4° / min.

[0158] 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.

[0159] Discharge the secondary battery (for safety reasons, the secondary battery is generally fully discharged); disassemble the secondary battery and take out the negative electrode sheet, and soak the negative electrode sheet in dimethyl carbonate for a certain period of time (e.g., 2h-10h); then take out the negative electrode sheet and dry it at a certain temperature and time (e.g., 60°C, more than 4h), and take out the negative electrode sheet after drying. At this time, you can take samples from the dried negative electrode sheet to test the above-mentioned parameters related to the negative electrode film, such as the surface density, compaction density, porosity, OI value, thickness, etc. of the negative electrode film.

[0160] The dried negative electrode sheet is baked at a certain temperature and time (for example, 400°C for more than 2h), and a region of the baked negative electrode sheet is selected to sample the negative electrode active material (a blade can be used to scrape the powder for sampling); the collected negative electrode active material is sieved (for example, sieved with a 200-mesh sieve), and finally a sample that can be used to test the parameters of the above-mentioned negative electrode active materials is obtained.

[0161] In the present application, the first carbon-based material and the second carbon-based material mentioned above can be obtained through commercial purchase, or can also be prepared by the following method of the present application.

[0162] In some embodiments, the preparation method of the first carbon-based material comprises: step 1, providing a raw material having a plurality of pore structures; step 2, mixing the raw material and the filler material in a predetermined ratio, and then heating the raw material at a first temperature T 1 The first time of heat preservation 1 After the reaction is completed, the intermediate is cooled to room temperature to obtain an intermediate; Step 3, the intermediate is heated at a second temperature T 2 Second insulation time t 2 After the process is completed, a first carbon-based material is obtained. The first carbon-based material has a pore structure. The total pore area of ​​the outer region of the first carbon-based material is recorded as S1, and the total pore area of ​​the inner region of the first carbon-based material is recorded as S2. Then the first carbon-based material satisfies: S2>S1.

[0163] In some embodiments, in step 1, the raw material for preparing the first carbon-based material includes natural graphite. Natural graphite generally refers to graphite formed naturally in nature, which does not need to be graphitized, and there are usually more closed-pore structures inside the natural graphite particles. Optionally, the natural graphite includes one or more of flake graphite, natural spherical graphite and microcrystalline graphite, especially natural spherical graphite.

[0164] "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 desired particle size and morphology can be obtained by pretreating flake graphite. Optionally, the above pretreatment includes processes such as crushing, classification, spheroidization, and purification.

[0165] In some embodiments, in step 1, the volume distribution particle size Dv50 of the above raw material can be 6.0 μm - 25.0 μm.

[0166] In some embodiments, in step 1, the specific surface area of the above raw material can be ≥ 2.5 m 2 / g, optionally 2.5 m 2 / g - 10.0 m 2 / g. When the specific surface area of the raw material is within the above range, it is beneficial for subsequent filling treatment and obtaining the first carbon-based material with the desired specific surface area.

[0167] 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.

[0168] In some embodiments, in step 2, the volume distribution particle size Dv50 of the above filling material is less than or equal to 6 μm, 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 melt and fill into the pore structure of the raw material after heating, and is also beneficial for improving the dispersion uniformity of the filling material and the raw material.

[0169] In some embodiments, in step 2, the coking value of the above filling material is 15% - 40%, optionally 18% - 34%. In this 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.

[0170] In some embodiments, in step 2, the above filling material includes one or more of coal tar pitch, petroleum pitch, high molecular compounds, and resins, optionally including one or more of coal tar pitch and petroleum pitch.

[0171] In some embodiments, in step 2, the mass ratio of the above-mentioned filling material to the above-mentioned raw material is (10 - 40):100, and can be optionally (10 - 30):100, (10 - 25):100, (10 - 20):100, (12 - 30):100, (14 - 28):100, (15 - 25):100.

[0172] 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, the number and / or size of pores in the outer region and the inner region of the first carbon-based material can be adjusted within a suitable range, so that the S of the first carbon-based material 2 / S 1 is within a suitable range.

[0173] By adjusting parameters such as the type, softening point, coking value, addition amount, etc. of the filling material within the above range, after the filling material is heated and melted, its viscosity is not high, it maintains good fluidity, and at the same time it is not easy to adhere to the raw material particles, which can reduce the agglomeration of raw material particles in the subsequent preparation process. Therefore, it can also reduce problems such as an increase in surface defects and an increase in surface active sites of the first carbon-based material particles due to the need to increase the depolymerization process.

[0174] In some embodiments, in step 2, after mixing the above-mentioned raw material and the above-mentioned filling material evenly according to a predetermined ratio, the temperature is raised to the first temperature T 1 The heating process can be a staged heating process.

[0175] In some embodiments, the above-mentioned staged heating process includes a first heating process, a second heating process, and a third heating process.

[0176] In some embodiments, the above-mentioned first heating process is to raise the temperature to 200°C - 250°C and keep it at this temperature for 0.5 h - 3 h.

[0177] In some embodiments, the above-mentioned second heating process is to raise the temperature to 450°C - 550°C and keep it at this temperature for 0 h - 2 h. When the holding time is 0 h, it means that when the temperature is raised to the range of 450°C - 550°C, no heat preservation treatment is carried out, but the temperature is continuously raised to the first temperature T 1 。

[0178] In some embodiments, the above-mentioned third heating process is to raise the temperature to the above-mentioned first temperature T 1 and keep it at this temperature for the first time t 1 。

[0179] During the staged heating process, first heat up to 200°C - 250°C. Since the heating temperature is higher than the softening point temperature of the filling material, at this time, the filling material is heated and melted and softened. Insulating for 0.5h - 3h can make it flow and fill into the pore structure of the raw material; then heat up to 450°C - 550°C. At this time, the melted and softened filling material undergoes a carbonization reaction and gradually forms a semi-coke state, turning into a viscous liquid or solid, thereby preventing the filling material from entering all the pore structures of the raw material; finally heat up to the first temperature. At this time, the filling material undergoes a carbonization reaction, whereby the pore structure occupied by the filling material can be effectively filled.

[0180] In some embodiments, in step 2, heat up to the above-mentioned first temperature T at a rate of 1°C / min - 10°C / min 1 . For example, the heating rate can be 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min or any range composed of the above values. Optionally, the heating rate is 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.

[0181] In some embodiments, the heating rate of the above-mentioned first heating process 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, the heating rate of the above-mentioned second heating process can be 1°C / min - 10°C / min, optionally 2°C / min - 8°C / min. In some embodiments, the heating rate of the above-mentioned third heating process can be 1°C / min - 10°C / min, optionally 2°C / min - 8°C / min.

[0182] 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 the above values. 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.

[0183] In some embodiments, in step 2, the above-mentioned first time t 1 is 1h - 5h. For example, the first time t1 It may be a range composed of any value of 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h or above. Optionally, the above-mentioned first time t 1 is 2 h - 4 h.

[0184] 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.

[0185] In some embodiments, in step 2, the heat treatment atmosphere can be a protective gas atmosphere. The above-mentioned protective gas may include one or more of nitrogen, argon, and helium.

[0186] 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 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 the S of the first carbon-based material 2 / S 1 within a suitable range.

[0187] In some embodiments, in step 3, the above-mentioned second temperature T 2 is 2070 °C - 2700 °C. Optionally, the above-mentioned 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.

[0188] In some embodiments, in step 3, the above-mentioned second time t 2 is 1.5 h - 6 h. For example, the second time t 1 may be a range composed of any value of 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h or above. Optionally, the above-mentioned second time t 2 is 2 h - 5 h.

[0189] In some embodiments, in step 3, the above-mentioned heat treatment can 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.

[0190] The second temperature T 2 and the second time t 2 within the above range are beneficial to adjust the I of the first carbon-based material D / I G, which also helps 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 the I of the first carbon-based material. D / I G The smaller.

[0191] In some embodiments, in step 3, the medium-frequency furnace and the continuous graphitization heat treatment atmosphere can be a protective gas atmosphere. The above-mentioned protective gas can include one or more of nitrogen, argon, and helium.

[0192] In step 3, by adjusting one or more of the second temperature and the second time within the above range, it is beneficial to adjust the content of disordered carbon in the first carbon-based material 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.

[0193] In the above method for preparing the first carbon-based material, by adjusting one or more of the parameters of natural graphite, the parameters of the filling material, the heating rate, the first temperature, the first time, the heating process, the second temperature, the second time, etc. within the above range, it is beneficial to adjust the S of the first carbon-based material 2 / S 1 、I D / I G 、graphitization degree, specific capacity, specific surface area, particle size, interlayer spacing of the 002 crystal plane, powder compacted density, tapped density and other parameters.

[0194] In some embodiments, the method for preparing artificial graphite in the second carbon-based material includes: step 11, providing raw materials; step 12, performing crushing treatment and shaping treatment on the raw materials to obtain a first intermediate; step 13, performing graphitization treatment on the first intermediate, and after completion, obtaining a second carbon-based material, and the second carbon-based material satisfies I D / I G ≤0.140.

[0195] In some embodiments, in step 11, the raw materials may include one or more of petroleum coke, needle coke, pitch coke, and metallurgical coke.

[0196] In some embodiments, in step 12, a mechanical mill or a roller press mill can be used to perform crushing treatment on the raw materials. Additionally, a shaping machine can be used for shaping treatment.

[0197] In some embodiments, in step 13, the graphitization temperature is 2800°C - 3200°C.

[0198] By adjusting the graphitization temperature and / or the graphitization time, the second carbon-based material can have a suitable I D / I GValue and graphitization degree.

[0199] In the above preparation method of the second carbon-based material, by adjusting one or more parameters among the parameters of each device (such as mechanical mill or roller press mill, shaper, granulator, etc.), the parameters of raw materials, the addition amount of organic carbon source, the addition amount of binder, graphitization temperature, graphitization time, carbonization temperature, carbonization time, etc., it is beneficial to adjust the 002 crystal plane layer spacing, I D / I G 、graphitization degree, specific capacity, volume distribution particle size, specific surface area, powder compacted density, tapped density and other parameters.

[0200] [Positive electrode sheet]

[0201] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, and the positive electrode film layer includes the positive electrode active material of the first aspect of the present application.

[0202] 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.

[0203] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, aluminum 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 base layer. The composite current collector can 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.).

[0204] In some embodiments, when the battery cell is a lithium-ion battery, the positive electrode active material can be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material can include at least one of the following materials: lithium-containing phosphate with olivine structure, lithium transition metal oxide 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 can also be used. These positive electrode active materials can be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides can 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 NCM 211 ), 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 the lithium-containing phosphate with olivine structure may include but are not limited to lithium iron phosphate (such as LiFePO 4 (which can also be abbreviated as LFP)), composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO 4 ), composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and at least one of the composite material of lithium manganese iron phosphate and carbon.

[0205] For other active ion batteries, such as sodium ion batteries, the positive electrode active material may include the conventionally known positive electrode active materials for sodium ion batteries. For example, the positive electrode active material includes at least one of sodium transition metal oxides, polyanion-type compounds, and Prussian blue compounds.

[0206] 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 enumeration 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, the molar content of Li will change after charge and discharge cycles.

[0207] In the enumeration of the positive electrode active material in this application, the molar content of oxygen is only the theoretical value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of oxygen will fluctuate. The molar content of other elements also changes during battery manufacturing and 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.

[0208] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0209] In some embodiments, the positive electrode film layer may further 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.

[0210] In some embodiments, the positive electrode plate can be prepared in the following manner: Disperse the components for preparing the positive electrode plate, such as the positive electrode active material, conductive agent, binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coat the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode plate can be obtained.

[0211] [Electrolyte]

[0212] The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. This application does not specifically limit the type of electrolyte, and it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or all-solid-state.

[0213] In some embodiments, the electrolyte uses an electrolytic solution. The electrolytic solution includes an electrolyte salt and a solvent.

[0214] 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(oxalate) borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0215] In some embodiments, the solvent may 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.

[0216] In some embodiments, the electrolyte may also optionally include additives. For example, the additives may include anode film-forming additives, cathode film-forming additives, and may 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, and the like.

[0217] [Separator membrane]

[0218] In some embodiments, the battery cell further includes a separator membrane. The present application does not particularly limit the type of the separator membrane, and any well-known porous structure separator membrane with good chemical stability and mechanical stability can be selected.

[0219] In some embodiments, the material of the separator membrane may be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The separator membrane may 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 may be the same or different, without particular limitation.

[0220] In some embodiments, the positive electrode plate, the negative electrode plate and the separator membrane can be made into an electrode assembly by a winding process or a stacking process.

[0221] In some embodiments, the battery cell may include an outer package. The outer package can be used to encapsulate the above-mentioned electrode assembly and electrolyte.

[0222] 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 soft package. The material of the soft package can be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate and polybutylene succinate.

[0223] The present application does not particularly limit 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.

[0224] In some embodiments, with reference to Figure 4, the outer packaging may include a housing 51 and a top cover assembly 53. Among them, the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose to form 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 can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. The number of electrode assemblies 52 included in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual requirements.

[0225] In some embodiments, the battery cells can be assembled into a battery module, and the number of battery cells included in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0226] Figure 5 is a battery module 4 as an example. Refer 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 way. Further, the plurality of battery cells 5 can be fixed by fasteners.

[0227] Optionally, the battery module 4 may further include a housing having a receiving space, and a plurality of battery cells 5 are received in the receiving space.

[0228] In some embodiments, the above battery module can be further assembled into a battery pack, and the number of battery modules included in the battery pack can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0229] Figure 6 and Figure 7 is a battery pack 1 as an example. Refer to Figure 6 and Figure 7 , the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can be covered on the lower box body 3 and form a closed space for receiving the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any way.

[0230] In addition, a second aspect of the present application further provides an electrical device, which 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, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc., but is not limited thereto.

[0231] As the electrical device, battery cells, battery modules or battery packs can be selected according to its usage requirements.

[0232] Figure 8 The electrical device shown as an example is a pure electric vehicle, a hybrid electric vehicle, 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 adopted.

[0233] Another example of the device can be a mobile phone, a tablet computer, a laptop, etc. This device usually requires being thin and light, and battery cells can be adopted as the power source.

[0234] Embodiment

[0235] 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 technologies or conditions, the technologies or conditions described in the literature in the art or according to the product specifications shall be followed. Those reagents or instruments not specified by the manufacturer can be obtained as conventional products through commercial purchase.

[0236] In the following embodiments and comparative examples, the first carbon-based material used can be prepared by the method of the present application as follows.

[0237] Preparation of Material 1-1

[0238] 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 16.7 μm. The obtained natural spherical graphite is mixed with the filler petroleum pitch at a mass ratio of 100:20. The softening point of the petroleum pitch is 135 °C. Then, the mixed material is placed in an equipment with programmable temperature rise, heated to 680 °C (the first treatment temperature), kept warm for 2.5 h, and after cooling to room temperature, an intermediate is obtained. The obtained intermediate is placed in a graphitization furnace and heat-treated at 2450 °C (the second treatment temperature). After demagnetization and screening, material 1-1 is obtained. Material 1-1 satisfies: S2 / S1 = 7.9, I D / I G = 0.17, the volume distribution particle size Dv50 = 17.0 μm, and the graphitization degree is 97%.

[0239] Preparation of Materials 1-2 to 1-3

[0240] The preparation methods of materials 1-2 to 1-3 are similar to that of material 1, the differences are: adjusting the ratio of natural spherical graphite to the filler and the first treatment temperature to obtain materials 1-2 to 1-3. Specifically as follows:

[0241] Table 1

[0242]

[0243] Preparation of Material 1-4

[0244] Providing natural spherical graphite, mixing the natural spherical graphite and petroleum pitch evenly at a mass ratio of 100:6. The softening point of the petroleum pitch is 250 °C, and low-temperature heat treatment is carried out at 1100 °C for 2 hours to obtain natural graphite with a carbon coating layer, that is, material 1-4. Among them, material 1-4 satisfies: S2 / S1 = 0.8, I D / I G = 0.36, the volume distribution particle size Dv50 = 17.8 μm, and the graphitization degree is 97%.

[0245] Preparation of Material 2-1

[0246] Providing needle coke raw materials, crushing them through a roller press mill, and shaping them with a shaper to obtain a first intermediate. The first intermediate is graphitized at a temperature of 3050 °C in a graphitization furnace for 6 h. Thus, material 2-1 is obtained. Among them, material 2-1 satisfies: I D / I G = 0.12, the volume distribution particle size Dv50 = 16.0 μm, the specific surface area BET = 1.05 m 2 / g, and the graphitization degree is 95.0%.

[0247] Preparation of Materials 2-2 to 2-4

[0248] The preparation methods of Materials 2-2 to 2-4 are similar to that of Material 1, except that: the graphitization temperature is adjusted to adjust I of Materials 2-2 to 2-4 D / I G . Specifically as follows:

[0249] Table 2

[0250] Material Number Heat Treatment Temperature (°C) <![CDATA[I D / I G > 2-1 3000 0.12 2-2 3230 0.10 2-3 2850 0.14 2-4 2580 0.17

[0251] Example 1

[0252] Preparation of Secondary Battery

[0253] 1. Negative electrode sheet: The negative electrode active materials (70 wt% of Material 1-1 and 30 wt% of Material 2-1), conductive agent carbon black (Super P), thickening agent sodium carboxymethyl cellulose, and binder styrene-butadiene rubber are fully stirred and mixed in an appropriate amount of solvent deionized water according to a weight ratio of 96.4:1:1.2:1.4 to form a negative electrode slurry. The negative electrode slurry is coated on both surfaces of the negative electrode current collector copper foil, and after drying and cold pressing, a negative electrode sheet is obtained.

[0254] 2. Positive electrode sheet: LiFePO 4 is mixed with conductive agent carbon black (Super P) and binder polyvinylidene fluoride according to a weight ratio of 96:2:2, and an appropriate amount of solvent NMP is added and stirred evenly to obtain a positive electrode slurry. The positive electrode slurry is coated on both surfaces of the positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet is obtained.

[0255] 3. Electrolyte: Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed according to 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. Then vinylene carbonate (VC) is added, and the content of VC is 1% of the total mass of the electrolyte.

[0256] 4. Separator: A polypropylene membrane is used.

[0257] 5. Preparation of secondary battery: The prepared positive electrode sheet and negative electrode sheet 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, a secondary battery is obtained.

[0258] Examples 2 to 3

[0259] The battery preparation methods of Examples 2 to 3 are similar to that of Example 1, except that: the first carbon-based materials are respectively selected as Materials 1-2 to 1-3, for details, see Table 1.

[0260] Comparative Example 1

[0261] It is similar to the preparation method of Example 1, except that: the first carbon-based material is selected as Material 1-4, for details, see Table 1.

[0262] Comparative Example 2

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

[0264] Comparative Example 3

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

[0266] Performance Test

[0267] 1. Material Testing

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

[0269] Mix the binder for sample preparation with the first carbon-based material powder evenly and coat it on the copper foil, then dry it at 60 °C for 30 min for standby; cut it into 5 test samples of 6 mm × 6 mm at 5 different positions and paste them on the sample stage of the CP type argon ion cross-section polishing instrument; use the plasma beam to cut the samples to obtain the cross-sections of each sample. The test instrument can be the IB-09010 CP 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 a scanning image by arbitrarily selecting an area in each sample cross-section. The test can refer to JY / T010-1996. The test 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 scanned image. The region formed by extending a distance of 0.25 μm from the surface of the particles of the first carbon-based material towards the interior of the particles is denoted as the outer region, and the region inside the outer region is denoted as the inner region. Use image processing software to obtain the total pore area S1' of the outer region of each particle cross-section, and the pore area S2' of the inner region of the first carbon-based material, 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. Battery performance test

[0273] (1) Storage performance test of secondary battery

[0274] At 25 °C, charge the above-prepared secondary battery at a constant current of 1C to 3.65V, then charge at a constant voltage until the current is 0.05C. After standing for 5 minutes, discharge the secondary battery at a constant current of 1C to 2.5V, and record the discharge capacity at this time, which is the discharge capacity before storage.

[0275] At 25 °C, charge the above-prepared secondary battery at a constant current of 1C to 3.65V, then charge at a constant voltage until the current is 0.05C. Then place the secondary battery in a constant temperature oven at 60 °C for 240 days. The capacity retention rate (%) of the secondary battery stored at 60 °C for 240 days = discharge capacity after storage / discharge capacity before storage × 100%.

[0276] (3) Energy density of secondary battery

[0277] At 25 °C, charge the secondary battery at a constant current of 1 / 3C to 3.65V, then charge at a constant voltage of 3.65V until the current is 0.05C. After standing for 5 minutes, discharge at a constant current of 1 / 3C to 2.5V, and record the battery discharge energy at this time. The battery discharge energy divided by the volume of the battery is the volume energy density of the battery, with the unit of Wh / L. The measurement data are shown in Table 1.

[0278] (3) Initial Coulomb efficiency of the negative electrode

[0279] At 45 °C, initially charge the above-prepared secondary battery at a constant current of 0.02C to 20% SOC, and record the charge capacity as C0; lower the temperature to 25 °C, stand for 30 minutes, then discharge at a constant current of 0.2C to 2.5V, and record the discharge capacity as D0. After standing for 5 minutes, charge at a constant current of 1 / 3C to 3.65V and then charge at a constant voltage to 0.05C, and record the charge capacity as C1. After standing for 5 minutes, discharge at a constant current of 1 / 3C to 2.5V, and record the discharge capacity as D1.

[0280] First Coulombic efficiency (%) of the secondary battery = D1 / (C0 + C1 - D1) × 100%

[0281] The batteries prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were tested according to the above test methods (1) to (3). The negative electrode active materials used and the test results are shown in Table 3 below.

[0282] Table 3

[0283]

[0284] As can be seen from Table 1 above, according to Comparative Example 2 and Comparative Example 3 which respectively use only the first carbon-based material and the second carbon-based material, it can be known that the first carbon-based material can bring good energy density to the secondary battery, but the high-temperature storage performance is relatively low; the second carbon-based material has good first Coulombic efficiency and brings relatively high high-temperature storage performance to the secondary battery, but the energy density is relatively low. By mixing the first carbon-based material and the second carbon-based material as the negative electrode active material in the present invention, the secondary battery has both good energy density and high-temperature storage performance at the same time.

[0285] From Examples 1 to 3 and Comparative Example 1, it can be seen that changing the value of S2 / S1 of the first carbon-based material mainly affects the first Coulombic efficiency of the negative electrode and the storage performance of the secondary battery. The larger the value of S2 / S1, the better the high-temperature storage performance. On the contrary, when S2 is less than S1 (that is, the pore area in the inner region of the particle is relatively low, while the pore area in the outer region of the particle is relatively high), it will lead to a decrease in the first Coulombic efficiency of the storage performance.

[0286] Examples 4 to 5

[0287] The battery preparation methods of Examples 4 to 5 are similar to those of Example 1. Among them, the first carbon-based material is all Material 1-1, and the second carbon-based materials are respectively selected from Materials 2-2 to 2-3.

[0288] Comparative Example 4

[0289] The battery preparation method of Comparative Example 4 is similar to that of Example 1, except that: the second carbon-based material is selected as Material 2-4.

[0290] The batteries prepared in Examples 4 to 5 and Comparative Example 4 were tested according to the above test methods (1) to (3). The negative electrode active materials used and the test results are shown in Table 4 below.

[0291] Table 4

[0292]

[0293] As can be seen from Table 4 above, changing the I D / I G value of the second carbon-based material can affect its surface activity, ID / I G The larger the value, the higher the surface activity, which leads to a decrease in the first coulombic efficiency of the negative electrode and affects the high-temperature storage performance of the secondary battery, but has little effect on the energy density.

[0294] Examples 6 and 7

[0295] The battery preparation methods of Examples 6 and 7 are similar to those of Example 1, except that the amounts of the first carbon-based material and the second carbon-based material are changed. See Table 5 for details.

[0296] The batteries prepared in Examples 6 and 7 were tested according to the above test methods (1) to (3). The negative electrode active materials used and the test results are shown in Table 5.

[0297] Table 5

[0298]

[0299] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present 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, Characterized in that, The negative electrode active material includes a first carbon-based material and a second carbon-based material, 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 a distance of 2.5 μm from the surface of the first carbon-based material inward. In the cross-sectional view of the first carbon-based material, the first carbon-based material has a pore structure. 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 of the first carbon-based material is denoted as S2. Then the first carbon-based material satisfies: S2 > S1; The second carbon-based material satisfies I D / I G ≤0.14, where I D represents the intensity of the D peak at 1350 ± 50 cm -1 in the Raman spectrum of the second carbon-based material, and I G represents the intensity of the G peak at 1580 ± 50 cm -1 in the Raman spectrum of the second carbon-based material.

2. The secondary battery according to claim 1, Wherein, The second carbon-based material satisfies 0.10 ≤ I D / I G ≤ 0.14, optionally, 0.11 ≤ I D / I G ≤ 0.

13.

3. The secondary battery according to claim 1 or 2, Wherein, The I of the first carbon-based material D / I G is greater than the I of the second carbon-based material D / I G .

4. The secondary battery according to any one of claims 1-3, Wherein, The first carbon-based material satisfies I D / I G ≤0.30, optionally, 0.15 ≤ I D / I G ≤0.28; wherein, I D represents the intensity of the D peak of the Raman spectrum of the first carbon-based material at 1350 ± 50 cm -1 and I G represents the intensity of the G peak of the Raman spectrum of the first carbon-based material at 1580 ± 50 cm -1 .

5. The secondary battery according to any one of claims 1-4, Wherein, The second carbon-based material is artificial graphite.

6. The secondary battery according to any one of claims 1-5, Wherein, The layer spacing of the 002 crystal plane of the first carbon-based material is smaller than the layer spacing of the 002 crystal plane of the second carbon-based material; Optionally, the layer spacing of the 002 crystal plane of the first carbon-based material ≤ 0.33569 nm, and can be optionally 0.33557 - 0.33569 nm; Optionally, the layer spacing of the 002 crystal plane of the second carbon-based material ≤ 0.336088 nm, and can be optionally 0.335744 - 0.336088 nm.

7. The secondary battery according to any one of claims 1-6, Wherein, The first carbon-based material includes one or more pore structures with a pore area of greater than or equal to 0.15 μm 2 and optionally includes one or more pore structures with a pore area of 0.15 - 2.0 μm 2 .

8. The secondary battery according to any one of claims 1-7, Wherein, The first carbon-based material satisfies: 1.5 ≤ S2 / S1 ≤ 450; optionally, 2 ≤ S2 / S1 ≤ 400.

9. The secondary battery according to any one of claims 1-8, Wherein, The first carbon-based material includes primary particles; Optionally, the proportion of the number of primary particles in the first carbon-based material ≥ 80%; Optionally, the surface of the first carbon-based material does not have a coating layer.

10. The secondary battery according to any one of claims 1-9, Wherein, The second carbon-based material includes primary particles; Optionally, the proportion of the number of primary particles in the second carbon-based material ≥ 80%; Optionally, the surface of the second carbon-based material does not have a coating layer.

11. The secondary battery according to any one of claims 1-10, Wherein, The graphitization degree of the first carbon-based material is greater than the graphitization degree of the second carbon-based material.

12. The secondary battery according to any one of claims 1-11, Wherein, The graphitization degree of the first carbon-based material ≥ 96%, and can be optionally 96.5% - 98.5%; The graphitization degree of the second carbon-based material is 91% - 96.5%, and can be optionally 92% - 96%.

13. The secondary battery according to any one of claims 1-12, Wherein, The specific surface area of the first carbon-based material is larger than that of the second carbon-based material.

14. The secondary battery according to any one of claims 1-13, wherein, The specific surface area of the first carbon-based material is less than or equal to 2.1 m 2 / g, optionally 1.3 - 2.0 m 2 / g; The specific surface area of the second carbon-based material is less than or equal to 1.3 m 2 / g, and may be optionally 0.8 - 1.2 m 2 / g.

15. The secondary battery according to any one of claims 1-14, wherein, The volume distribution particle size Dv50 of the first carbon-based material is larger than the volume distribution particle size Dv50 of the second carbon-based material.

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 ≥ 10 μm, and can be optionally 10 μm - 23 μm; (2) The volume distribution particle size Dv90 of the negative electrode active material is ≤ 40 μm, and can be optionally 23 μm - 40 μm; (3) The particle size distribution [(Dv90) - (Dv10)] / (Dv50) of the negative electrode active material is ≤ 1.20, and can be optionally 0.9 - 1.20; (4) The gram capacity of the negative electrode active material is ≥ 358 mAh / g, and can be optionally 358 mAh / g - 370 mAh / g; (5) The negative electrode active material satisfies I D / I G is ≤ 0.2, optionally 0.13 - 0.20, where I D represents the intensity of the D peak of the Raman spectrum at 1350 ± 50 cm -1 −1, and I G represents the intensity of the G peak of the Raman spectrum at 1580 ± 50 cm -1 −1.

17. The secondary battery according to any one of claims 1-16, wherein, The first carbon-based material satisfies at least one of the following items: (1) The volume distribution particle size Dv50 of the first carbon-based material is ≥ 13 μm, and can be optionally 15 μm - 20 μm; (2) The volume distribution particle size Dv90 of the first carbon-based material is ≤ 40 μm, and can be optionally 28 μm - 40 μm; (3) The particle size distribution [(Dv90) - (Dv10)] / (Dv50) of the first carbon-based material is ≤ 1.55, and can be optionally 0.90 - 1.50; (4) The gram capacity of the first carbon-based material is ≥ 360 mAh / g, and can be optionally 365 mAh / g - 372 mAh / g.

18. The secondary battery according to any one of claims 1-17, wherein, The second carbon-based material satisfies at least one of the following items: (1) The volume distribution particle size Dv50 of the second carbon-based material is ≤ 18 μm, and can be optionally 13 μm - 18 μm; (2) The particle size distribution [(Dv90) - (Dv10)] / (Dv50) of the second carbon-based material is ≤ 1.35, and can be optionally 1.0 - 1.30; (3) The gram capacity of the second carbon-based material is ≥ 357 mAh / g, and can be optionally 357 mAh / g - 363 mAh / g.

19. The secondary battery according to any one of claims 1-18, wherein, The mass proportion of the first carbon-based material in the negative electrode active material is ≥ 30 wt%, and can be optionally 50 wt% - 80 wt%.

20. The secondary battery according to any one of claims 1-19, wherein, The negative electrode active material further includes a silicon-based material.

21. The secondary battery according to any one of claims 1-20, 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 ≥ 1.40 g / cm 3 , optionally 1.45 g / cm 3 -1.90 g / cm 3 ; (2) The areal density of the negative electrode film layer ≥ 6.0 mg / cm 2 , optionally 7.0 mg / cm 2 - 15.0 mg / cm 2 ; (3) The porosity of the negative electrode film layer is 18.0% - 36.7%, and can be optionally 19.0% - 34.0%; (4) The thickness of the negative electrode film layer is ≥ 70 μm, and optionally is 90 μm - 130 μm.

22. An electrical device, characterized in that, it includes the secondary battery according to any one of claims 1 - 21.

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