Lithium secondary battery, negative pole piece for lithium secondary battery and electric device

Abstract

The invention belongs to the field of batteries, and relates to a lithium secondary battery, a negative pole piece for the lithium secondary battery and an electric device. The lithium secondary battery comprises a negative electrode plate, wherein the negative electrode plate comprises a negative electrode current collector, a first negative electrode active layer positioned on at least one side of the negative electrode current collector and a second negative electrode active layer positioned on one side, far away from the negative electrode current collector, of the first negative electrode active layer; the first negative active layer and the second negative active layer respectively comprise a first negative material and a second negative material, and the first negative material and the second negative material respectively comprise a first graphite material and a second graphite material; the OI value of the second graphite material powder is 1-10; the gram volume of the first negative electrode material is greater than that of the second negative electrode material, and the powder compaction density under 150MPa is greater than that of the second negative electrode material; the gram capacity of the second negative electrode material is 345-365 mAh / g; and the powder compaction density of the first negative electrode material under 150MPa is 1.70-2.10 g / cm < 3 >. According to the lithium secondary battery, the energy density of the secondary battery is improved while the high dynamic performance of the lithium secondary battery is guaranteed.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a lithium secondary battery, a negative electrode sheet for a lithium secondary battery, and an electrical device. Background Art

[0002] In recent years, as the application scope of batteries has become more and more extensive, batteries are widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields. As batteries have made great progress, higher requirements have been put forward for their fast charging performance and energy density. Summary of the invention

[0003] The present application provides a lithium secondary battery, a negative electrode plate for the lithium secondary battery, and an electric device. The present application improves the energy density of the secondary battery while ensuring the high dynamic performance of the lithium secondary battery.

[0004] In a first aspect, the present application provides a lithium secondary battery, comprising a negative electrode plate, wherein the negative electrode plate comprises a negative electrode current collector, a first negative electrode active layer located on at least one side of the negative electrode current collector, and a second negative electrode active layer located on a side of the first negative electrode active layer away from the negative electrode current collector; the first negative electrode active layer comprises a first negative electrode material, the second negative electrode active layer comprises a second negative electrode material, the first negative electrode material comprises a first graphite material, and the second negative electrode material comprises a second graphite material; The powder OI value of the second graphite material is 1-10, and the powder OI value of the second graphite material is the peak area ratio of the characteristic diffraction peak of the 004 crystal plane to the characteristic diffraction peak of the 110 crystal plane in the XRD spectrum of the second graphite material; the second graphite material includes secondary particles; The gram capacity of the first negative electrode material is greater than the gram capacity of the second negative electrode material; the gram capacity of the second negative electrode material is 345-365 mAh / g; wherein the gram capacity of the first negative electrode material or the gram capacity of the second negative electrode material is the ratio of the discharge capacity of the lithium secondary battery to the mass of the first negative electrode material or the second negative electrode material, and the discharge capacity of the lithium secondary battery is the discharge capacity obtained by the lithium secondary battery being discharged from 2.0V to 5mV at a constant current of 0.05C at room temperature; The powder compaction density of the first negative electrode material at 150 MPa is greater than the powder compaction density of the second negative electrode material at 150 MPa; the powder compaction density of the first negative electrode material at 150 MPa is 1.70 - 2.10 g / cm 3 .

[0005] Therefore, the present application reduces the OI value of the second graphite material to 1-10 by granulating into secondary particles based on an anisotropic graphite material with high gram capacity and large OI value (greater than 10 and less than or equal to 25), while maintaining a high gram capacity of 345-365 mAh / g. Compared with the isotropic graphite material, the material gram capacity is higher; while the second negative electrode material adopts the high gram capacity second graphite material, the gram capacity and powder compaction density of the first negative electrode material are higher than those of the second negative electrode material, and the powder compaction density of the first negative electrode material is 1.70-2.10 g / cm 3 , which is conducive to matching and balancing the contributions of the first negative electrode material and the second negative electrode material to the overall energy density of the secondary battery; and, the secondary particles of the second graphite material used in the second negative electrode material provide more channels for lithium ion transmission; thereby helping to improve the energy density of the secondary battery while ensuring the high dynamic performance of the secondary battery.

[0006] In any embodiment, the powder OI value of the second graphite material is greater than 1.1 and less than or equal to 10; and / or, The gram capacity of the second negative electrode material is 350-365 mAh / g.

[0007] Therefore, based on the anisotropic graphite material with high gram capacity and large OI value, the present application reduces the OI value of the second graphite material by granulating it into secondary particles, while maintaining the high gram capacity of the second negative electrode material, which is beneficial to improving the overall energy density while ensuring the kinetic performance of the secondary battery.

[0008] In any embodiment, the difference in powder compaction density between the first negative electrode material and the second negative electrode material at 150 MPa is 0.05-0.60 g / cm 3 and / or, The difference in gram capacity between the first negative electrode material and the second negative electrode material is 5-36.3 mAh / g or 5-25 mAh / g.

[0009] Since the gram capacity and powder compaction density of the material are related to the energy density of the secondary battery, the above-mentioned powder compaction density difference and / or the above-mentioned gram capacity difference between the first negative electrode material and the second negative electrode material is beneficial to improving the mutual matching degree between the first negative electrode material and the second negative electrode material, so as to better balance the contribution of the first negative electrode material and the second negative electrode material to the energy density of the secondary battery, thereby further improving the overall energy density of the secondary battery.

[0010] In any embodiment, the secondary particles in the second graphite material account for 35% to 90% or 58% to 89% of the total number of particles in the second graphite material. This provides more transmission channels for lithium ions, ensures the dynamic performance of the secondary battery, and improves the energy density of the secondary battery; on the other hand, it reduces the adverse effects of the increase in the proportion of secondary particles, such as easy agglomeration of particles and difficulty in processing.

[0011] In any embodiment, the second graphite material further includes primary particles, and the ratio of the average particle size of the secondary particles in the second graphite material to the average particle size of the primary particles is 1.1-3.4. Thus, it is beneficial for the secondary particles to be composed of more primary particles, providing more channels for lithium ion transmission and ensuring the dynamic performance of the secondary battery; in addition, the increase in the average particle size of the secondary particles may lead to a decrease in the contact area with the electrolyte and reduce the interface reaction rate. The above ratio range reduces the adverse effect of the increase in the average particle size of the secondary particles on the dynamic performance of the secondary battery.

[0012] In any embodiment, the average particle size of the secondary particles in the second graphite material is 8 μm-25.3 μm or 8 μm-16 μm. This is beneficial to provide more channels for lithium ion transmission to improve the kinetic performance of the secondary battery, and is beneficial to reduce the impact of the increase in the average particle size of the secondary particles, which leads to a decrease in the contact area with the electrolyte and the impact on the interface reaction rate, which is beneficial to improve the kinetic performance of the secondary battery.

[0013] In any embodiment, the surface of the second graphite material has a coating layer, and the coating layer includes carbon elements; and / or, The thickness of the coating layer is greater than 0 nm and ≤ 500 nm.

[0014] Therefore, the coating layer on the surface of the second graphite material is conducive to the rapid conduction of lithium ions into the lattice of the second graphite material for embedding, thereby improving the kinetic performance of the secondary battery. In addition, it reduces the impact of increased coating layer thickness on the high-temperature storage capacity of the secondary battery.

[0015] In any embodiment, the R value of the second negative electrode material is 0.13 - 0.25; and / or, The R50 value of the second negative electrode material is 1.0 - 1.4; The R value of the second negative electrode material is the ratio of the difference between the R90 value of the second negative electrode material and the R10 value of the second negative electrode material to the R50 value of the second negative electrode material; The plurality of particles of the second negative electrode material are D / I G Accumulate from small to large, when ID / I G The cumulative value reaches I D / I G I corresponding to 10% of the total value D / I G is R10 of the second negative electrode material, when I D / I G The cumulative value reaches I D / I G I corresponding to 50% of the total value D / I G is R50 of the second negative electrode material, when I D / I G The cumulative value reaches I D / I G I corresponding to 90% of the total value D / I G R90 of the second negative electrode material; In the Raman spectrum of a single particle of the second negative electrode material, the Raman shift is 1300 cm -1 ~ 1380cm -1 The intensity of the peak within the range is I D , Raman shift is 1520cm -1 ~ 1590cm -1 The intensity of the peak within the range is I G .

[0016] Therefore, the above R value range of the second negative electrode material can improve the uniformity of the surface coating layer of the second graphite material, which is beneficial to improve the more uniform conduction of lithium ions into the second graphite material lattice and embedding, thereby improving the kinetic performance of the secondary battery.

[0017] The above R50 value range of the second negative electrode material, on the one hand, is conducive to improving the disorder degree of the surface of the second negative electrode material, providing more channels or spaces for lithium ion conduction, and improving the fast charging performance of the secondary battery. On the other hand, it reduces the impact of the increased disorder degree of the surface of the second negative electrode material on the high-temperature storage capacity of the secondary battery.

[0018] In any embodiment, the powder OI value of the first graphite material is greater than 6 and less than or equal to 25 or greater than 10 and less than or equal to 25, and the powder OI value of the first graphite material is the peak area ratio of the characteristic diffraction peak of the 004 crystal plane to the characteristic diffraction peak of the 110 crystal plane in the XRD spectrum of the first graphite material.

[0019] Therefore, the first graphite material in the first negative electrode material adopts an anisotropic graphite material with high capacity and OI value greater than 10 and less than or equal to 25, so as to match and balance with the second negative electrode material to improve the overall energy density of the secondary battery.

[0020] In any embodiment, the first graphite material includes primary particles. Thus, the first graphite material in the first negative electrode material includes primary particles, which is beneficial for matching and balancing with the second negative electrode material to improve the energy density of the secondary battery.

[0021] In any embodiment, the average particle size of the primary particles in the first graphite material is 8-19 μm. Thus, the first graphite material in the first negative electrode material includes primary particles with large particle sizes, which is conducive to matching with the second negative electrode material to improve the energy density of the secondary battery.

[0022] In any embodiment, the first graphite material further includes secondary particles, and the proportion of the secondary particles in the first graphite material to the total number of the first graphite material particles is 35% - 90% or 50% - 80%. Therefore, adding secondary particles to the first graphite material in the first negative electrode material can, on the one hand, provide more channels for lithium ion transmission to improve the kinetic performance of the secondary battery, and on the other hand, reduce the impact of the increase in the proportion of secondary particles on the battery energy density.

[0023] In some embodiments, the first negative electrode active layer further comprises natural graphite material. Thus, the first negative electrode material uses natural graphite material, and there are many pores inside the structure of the natural graphite material, so that the natural material has good contact with the electrolyte, which is beneficial to improving the dynamic performance of the secondary battery.

[0024] In a second aspect, the present application provides a negative electrode sheet for a lithium secondary battery, comprising a negative electrode current collector, a first negative electrode active layer located on at least one side of the negative electrode current collector, and a second negative electrode active layer located on a side of the first negative electrode active layer away from the negative electrode current collector; the first negative electrode active layer comprises a first negative electrode material, the second negative electrode active layer comprises a second negative electrode material, the first negative electrode material comprises a first graphite material, and the second negative electrode material comprises a second graphite material; The powder OI value of the second graphite material is 1-10, and the powder OI value of the second graphite material is the peak area ratio of the characteristic diffraction peak of the 004 crystal plane to the characteristic diffraction peak of the 110 crystal plane in the XRD spectrum of the second graphite material; the second graphite material includes secondary particles; The gram capacity of the first negative electrode material is greater than the gram capacity of the second negative electrode material; the gram capacity of the second negative electrode material is 345-365 mAh / g; wherein the gram capacity of the first negative electrode material or the gram capacity of the second negative electrode material is the ratio of the discharge capacity of the lithium secondary battery to the mass of the first negative electrode material or the second negative electrode material, and the discharge capacity of the lithium secondary battery is the discharge capacity obtained by the lithium secondary battery being discharged from 2.0V to 5mV at a constant current of 0.05C at room temperature; The powder compaction density of the first negative electrode material at 150 MPa is greater than the powder compaction density of the second negative electrode material at 150 MPa; the powder compaction density of the first negative electrode material at 150 MPa is 1.70 - 2.10 g / cm 3 .

[0025] Therefore, the present application reduces the OI value of the second graphite material to 1-10 by granulating into secondary particles based on an anisotropic graphite material with high gram capacity and large OI value (greater than 10 and less than or equal to 25), while maintaining a high gram capacity of 345-365 mAh / g. Compared with the isotropic graphite material, the material gram capacity is higher; while the second negative electrode material adopts the high gram capacity second graphite material, the gram capacity and powder compaction density of the first negative electrode material are higher than those of the second negative electrode material, and the powder compaction density of the first negative electrode material is 1.70-2.10 g / cm 3 , which is conducive to matching and balancing the contributions of the first negative electrode material and the second negative electrode material to the overall energy density of the secondary battery; and, the secondary particles of the second graphite material used in the second negative electrode material provide more channels for lithium ion transmission; thereby helping to improve the energy density of the secondary battery while ensuring the high dynamic performance of the secondary battery.

[0026] In any embodiment, the powder OI value of the second graphite material is greater than 1.1 and less than or equal to 10; and / or, The gram capacity of the second negative electrode material is 350-365 mAh / g.

[0027] In any embodiment, the difference in powder compaction density between the first negative electrode material and the second negative electrode material at 150 MPa is 0.05-0.60 g / cm 3 and / or, The difference in gram capacity between the first negative electrode material and the second negative electrode material is 5-36.3 mAh / g or 5-25 mAh / g.

[0028] In any embodiment, the secondary particles in the second graphite material account for 35% - 90% or 58% - 89% of the total number of particles in the second graphite material; and / or, The second graphite material further includes primary particles, and the ratio of the average particle size of the secondary particles in the second graphite material to the average particle size of the primary particles is 1.1-3.4; and / or, The average particle size of the secondary particles in the second graphite material is 8 μm - 25.3 μm or 8 μm - 16 μm.

[0029] In any embodiment, the surface of the second graphite material has a coating layer, and the coating layer includes carbon elements; and / or, The thickness of the coating layer is greater than 0 nm and ≤ 500 nm.

[0030] In any embodiment, the R value of the second negative electrode material is 0.13 - 0.25; and / or, The R50 value of the second negative electrode material is 1.0 - 1.4; The R value of the second negative electrode material is the ratio of the difference between the R90 value of the second negative electrode material and the R10 value of the second negative electrode material to the R50 value of the second negative electrode material; The plurality of particles of the second negative electrode material are D / I G Accumulate from small to large, when I D / I G The cumulative value reaches I D / I G I corresponding to 10% of the total value D / I G is R10 of the second negative electrode material, when I D / I G The cumulative value reaches I D / I G I corresponding to 50% of the total value D / I G is R50 of the second negative electrode material, when I D / I G The cumulative value reaches I D / I G I corresponding to 90% of the total value D / I G R90 of the second negative electrode material; In the Raman spectrum of a single particle of the second negative electrode material, the Raman shift is 1300 cm -1 ~ 1380cm -1 The intensity of the peak within the range is I D , Raman shift is 1520cm -1 ~ 1590cm -1 The intensity of the peak within the range is I G .

[0031] In any embodiment, the powder OI value of the first graphite material is greater than 6 and less than or equal to 25 or greater than 10 and less than or equal to 25, and the powder OI value of the first graphite material is the peak area ratio of the characteristic diffraction peak of the 004 crystal plane to the characteristic diffraction peak of the 110 crystal plane in the XRD spectrum of the first graphite material.

[0032] In any embodiment, the first graphite material comprises primary particles; and / or, The average particle size of the primary particles in the first graphite material is 8-19 μm; and / or, The first graphite material also includes secondary particles, and the secondary particles in the first graphite material account for 35%-90% or 50%-80% of the total number of particles of the first graphite material.

[0033] In any embodiment, the first negative electrode active layer further comprises natural graphite material.

[0034] A third aspect of the present application provides an electrical device, comprising the lithium secondary battery of the first aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without paying creative work.

[0036] Figure 1 is a schematic diagram of a secondary battery according to one embodiment of the present application.

[0037] Figure 2 yes Figure 1 An exploded view of a secondary battery according to an embodiment of the present application is shown.

[0038] Figure 3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0039] Figure 4 It is a schematic diagram of a battery pack according to one embodiment of the present application.

[0040] Figure 5 yes Figure 4 An exploded view of a battery pack according to an embodiment of the present application is shown.

[0041] Figure 6 FIG. 1 is a schematic diagram of an electric device using a secondary battery according to an embodiment of the present application as a power source.

[0042] Figure 7 This is a SEM photo of the second graphite material in Example 1 of the present application; Figure 8 This is a magnified SEM photograph of secondary particles in the second graphite material in Example 1 of the present application.

[0043] In the drawings, the drawings are not drawn to scale.

[0044] Description of reference numerals: 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery cell; 51 shell; 52 electrode assembly; 53 top cover assembly. DETAILED DESCRIPTION

[0045] The following detailed description and drawings of the embodiments of the present application are used to illustrate the principles of the present application, but cannot be used to limit the scope of the present application, that is, the present application is not limited to the described embodiments.

[0046] Below, the embodiments of the secondary battery, battery module, battery pack and power device of the present application are specifically disclosed with appropriate reference to the detailed description of the drawings. However, there are cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0047] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0048] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0049] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0050] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0051] If there is no special explanation, the "include" and "comprising" mentioned in this application represent open-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or comprised.

[0052] If not specifically stated, in this application, the term "or" is inclusive. For example, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0053] [Secondary battery] Secondary batteries, also known as rechargeable batteries or storage batteries, refer to batteries that can continue to be used by recharging to activate the active materials after the battery is discharged.

[0054] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte. During the battery charging and discharging process, active ions (such as lithium ions) are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, and at the same time allow active ions to pass through. The electrolyte is between the positive electrode sheet and the negative electrode sheet, mainly to conduct active ions.

[0055] One embodiment of the present application provides a lithium secondary battery, including a negative electrode plate, the negative electrode plate including a negative electrode current collector, a first negative electrode active layer located on at least one side of the negative electrode current collector, and a second negative electrode active layer located on a side of the first negative electrode active layer away from the negative electrode current collector; the first negative electrode active layer includes a first negative electrode material, the second negative electrode active layer includes a second negative electrode material, the first negative electrode material includes a first graphite material, and the second negative electrode material includes a second graphite material; The powder OI value of the second graphite material is 1-10 (e.g., 1, 1.2, 1.3, 1.9, 2, 2.5, 3, 4, 5, 6, 7, 8, 8.7, 8.9, 9, 9.8, 10 or a range consisting of any of the above values), and the powder OI value of the second graphite material is the peak area ratio of the characteristic diffraction peak of the 004 crystal plane to the characteristic diffraction peak of the 110 crystal plane in the XRD spectrum of the second graphite material; the second graphite material includes secondary particles; The gram capacity of the first negative electrode material is greater than the gram capacity of the second negative electrode material; the gram capacity of the second negative electrode material is 345-365 mAh / g (for example, 345.3 mAh / g, 346.9 mAh / g, 347.7 mAh / g, 350.4 mAh / g, 355 mAh / g, 357.6 mAh / g, 358.1 mAh / g, 359 mAh / g, 360 mAh / g, 365 mAh / g or a range consisting of any of the above values); wherein the gram capacity of the first negative electrode material or the gram capacity of the second negative electrode material is the ratio of the discharge capacity of the lithium secondary battery to the mass of the first negative electrode material or the second negative electrode material, and the discharge capacity of the lithium secondary battery is the discharge capacity obtained by the lithium secondary battery being discharged from 2.0V to 5mV at a constant current of 0.05C at room temperature; The powder compaction density of the first negative electrode material at 150 MPa is greater than the powder compaction density of the second negative electrode material at 150 MPa; the powder compaction density of the first negative electrode material at 150 MPa is 1.70 - 2.10 g / cm 3 (e.g. 1.7 g / cm 3 , 1.79 g / cm 3 , 1.8 g / cm 3 , 1.9 g / cm 3 , 2.0 g / cm 3 , 2.1 g / cm 3 or any range consisting of the above values).

[0056] In the existing negative electrode sheet including a double-layer negative electrode active layer, the upper negative electrode active layer away from the negative electrode current collector usually uses secondary particles of isotropic graphite materials with a smaller OI value as the negative electrode material to improve the fast charging performance of the secondary battery. At the same time, the lower negative electrode active layer close to the negative electrode current collector usually uses single particles of graphite materials with a higher gram capacity as the negative electrode material. However, due to the high degree of structural disorder of the isotropic graphite material used in the upper negative electrode active layer and the presence of a large number of unrepaired interfaces, lithium ion insertion / extraction is difficult, and the material gram capacity is low. Generally, the gram capacity of isotropic graphite materials with a smaller OI value is less than 340 mAh / g, which leads to a decrease in the energy density of the secondary battery monomer.

[0057] In order to solve the aforementioned technical problems, the present application is based on an anisotropic graphite material with high gram capacity and large OI value (greater than 10 and less than or equal to 25), and the OI value of the second graphite material is reduced to 1-10 by granulating into secondary particles, while maintaining a high gram capacity of 345-365 mAh / g. Compared with the isotropic graphite material, the crystal order is higher, the insertion / extraction of lithium ions is easier, and the material gram capacity is higher; while the second negative electrode material adopts the high gram capacity second graphite material, the gram capacity and powder compaction density of the first negative electrode material are higher than those of the second negative electrode material, and the powder compaction density of the first negative electrode material is 1.70-2.10 g / cm 3 , which is conducive to matching and balancing the contributions of the first negative electrode material and the second negative electrode material to the overall energy density of the secondary battery; and, the secondary particles of the second graphite material used in the second negative electrode material enrich the number of channels for lithium ions to be embedded and de-embedded in the material lattice, providing more channels for lithium ion transmission and ensuring the kinetic performance of the secondary battery; thereby, it is conducive to improving the energy density of the secondary battery while ensuring the high kinetic performance of the secondary battery.

[0058] In some embodiments, the powder OI value of the second graphite material is greater than 1.1 and less than or equal to 10; and / or, The gram capacity of the second negative electrode material is 350-365 mAh / g.

[0059] Therefore, based on the anisotropic graphite material with high gram capacity and large OI value, the present application reduces the OI value of the second graphite material by granulating it into secondary particles, while maintaining the high gram capacity of the second negative electrode material, which is beneficial to improving the overall energy density while ensuring the kinetic performance of the secondary battery.

[0060] In some embodiments, the difference in powder compaction density between the first negative electrode material and the second negative electrode material at 150 MPa is 0.05-0.60 g / cm 3 , for example 0.05 g / cm 3 , 0.1 g / cm 3 , 0.12 g / cm 3 , 0.13 g / cm 3 , 0.14 g / cm 3 , 0.15 g / cm 3 , 0.17 g / cm 3 , 0.18 g / cm 3 , 0.2 g / cm 3 , 0.29 g / cm 3 , 0.3 g / cm 3, 0.34g / cm 3 , 0.4 g / cm 3 , 0.5 g / cm 3 , 0.6 g / cm 3 or a range consisting of any of the above values; and / or, The difference between the gram capacity of the first negative electrode material and the second negative electrode material is 5-36.3 mAh / g or 5-25 mAh / g, for example, 5 mAh / g, 5.9 mAh / g, 6.4 mAh / g, 7 mAh / g, 7.4 mAh / g, 8 mAh / g, 9 mAh / g, 10 mAh / g, 11 mAh / g, 12 mAh / g, 13 mAh / g, 13.6 mAh / g, 14 mAh / g, 15 mAh / g, 16 mAh / g, 16.3 mAh / g, 17 mAh / g, 18 mAh / g, 19 mAh / g, 20 mAh / g, 21 mAh / g, 22 mAh / g, 23 mAh / g, 24 mAh / g, 25 mAh / g, 30 mAh / g, 36.3 mAh / g or a range consisting of any of the above values.

[0061] Since the gram capacity and powder compaction density of the material are related to the energy density of the secondary battery, the above-mentioned powder compaction density difference and / or the above-mentioned gram capacity difference between the first negative electrode material and the second negative electrode material is beneficial to improving the mutual matching degree between the first negative electrode material and the second negative electrode material, so as to better balance the contribution of the first negative electrode material and the second negative electrode material to the energy density of the secondary battery, thereby further improving the overall energy density of the secondary battery.

[0062] In some embodiments, the second negative electrode material has a powder compaction density of 1.45-1.85 g / cm at 150 MPa. 3 , for example 1.45 g / cm 3 , 1.5 g / cm 3 , 1.61 g / cm 3 , 1.62 g / cm 3 , 1.65 g / cm 3 , 1.66 g / cm 3 , 1.7 g / cm 3 , 1.74 g / cm 3 , 1.76 g / cm 3 , 1.8 g / cm 3 , 1.85 g / cm 3 Or any range consisting of the above values.

[0063] In some embodiments, the gram capacity of the first negative electrode material is 355 - 381.3 mAh / g, for example, 360 mAh / g, 362.6 mAh / g, 364 mAh / g, 365 mAh / g, 368 mAh / g, 370 mAh / g, 375 mAh / g, 380 mAh / g, 381.3 mAh / g or a range consisting of any of the above values.

[0064] In the present application, the test method of the OI value of the graphite material powder is well known in the art. As an example, the secondary battery is disassembled, the negative electrode plate is taken out, cleaned and dried, the negative electrode material on the negative electrode active layer is scraped, and the graphite material is observed by scanning electron microscopy. Since the particle morphology of the graphite material is different from the morphology of the auxiliary agent (binder, conductive agent, etc.), the graphite material powder OI value test can be performed based on the national standard GB / T 24533-2019 to obtain an X-ray diffraction spectrum; the OI value of the graphite material powder is calculated according to the formula OI=C004 / C110, wherein C004 is the peak area of ​​the 004 characteristic diffraction peak in the X-ray diffraction spectrum, and C110 is the peak area of ​​the 110 characteristic diffraction peak in the X-ray diffraction spectrum.

[0065] In the present application, "normal temperature" has the common definition in the art; for example, it may be generally between about 15°C and 30°C.

[0066] In the present application, the powder compaction density of the first negative electrode material or the second negative electrode material at 150 MPa is tested by conventional methods in the art. As an example, the test method may be: disassemble the secondary battery, take out the negative electrode plate, clean and dry it, scrape the negative electrode material of the first negative electrode active layer or the second negative electrode active layer, take a certain mass of powder sample (e.g., 50-100 g) and put it into a special compaction density mold, then put the special compaction density mold on the compaction density instrument, apply a constant pressure of 150 MPa for a certain time (e.g., 1-5 minutes) to briquette the powder, use a vernier caliper or a laser rangefinder to measure and calculate the volume of the briquette, and calculate the powder compaction density of the first negative electrode material or the second negative electrode material at 150 MPa based on the mass of the powder and the volume of the briquette.

[0067] In the present application, the test method of the gram capacity of the first negative electrode material or the second negative electrode material is well known in the art. As an example test method, it can be: disassemble the secondary battery, take out the negative electrode plate, wash and dry, scrape the negative electrode material of the first negative electrode active layer or the second negative electrode active layer, take a certain mass of negative electrode material to make a positive electrode slurry, coat it on the positive electrode current collector aluminum foil and dry it to obtain a positive electrode plate, use metal lithium as the negative electrode plate, and use a conventional isolation film (such as a polyethylene film) and an electrolyte (such as ethylene carbonate / ethyl methyl carbonate / diethyl carbonate solution containing 1 mol / L lithium hexafluorophosphate, volume ratio 1:1:1) to assemble into a secondary battery. At room temperature, after the secondary battery is charged to 2.0V, it is discharged from 2.0V to 5mV at a constant current of 0.05C to obtain the discharge capacity, and the ratio of the discharge capacity to the mass of the negative electrode material is calculated to obtain the gram capacity of the first negative electrode material or the second negative electrode material.

[0068] In some embodiments, the secondary particles in the second graphite material account for 35% - 90% or 58% - 89% of the total number of particles in the second graphite material, such as 35%, 40%, 45%, 50%, 58%, 60%, 70%, 75%, 82%, 83%, 84%, 85%, 87%, 89%, 90% or any range of the above values. This provides more transmission channels for lithium ions, ensures the dynamic performance of the secondary battery, and improves the energy density of the secondary battery; on the other hand, it reduces the adverse effects of the increase in the proportion of secondary particles, such as easy agglomeration and difficulty in processing.

[0069] In the present application, the total number of graphite material particles is the sum of the number of primary graphite material particles and the number of secondary graphite material particles.

[0070] In some embodiments, the second graphite material further includes primary particles, and the ratio of the average particle size of the secondary particles in the second graphite material to the average particle size of the primary particles is 1.1-3.4, such as 1.1, 1.2, 1.4, 1.5, 1.6, 1.8, 1.9, 2, 2.1, 2.2, 2.4, 2.6, 2.8, 3, 3.1, 3.3, 3.4 or a range consisting of any of the above values. Thus, it is beneficial for the secondary particles to be composed of more primary particles, providing more channels for lithium ion transmission and ensuring the kinetic performance of the secondary battery; in addition, the increase in the average particle size of the secondary particles may lead to a decrease in the contact area with the electrolyte and reduce the interface reaction rate. The above ratio range reduces the adverse effect of the increase in the average particle size of the secondary particles on the kinetic performance of the secondary battery.

[0071] In some embodiments, the average particle size of the secondary particles in the second graphite material is 8 μm-25.3 μm or 8 μm-16 μm, such as 8 μm, 9 μm, 9.9 μm, 10.7 μm, 11 μm, 12 μm, 13 μm, 13.79 μm, 14 μm, 14.2 μm, 14.6 μm, 15 μm, 15.1 μm, 15.2 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 23 μm, 24 μm, 25.3 μm or any range of the above values. Thus, it is beneficial to provide more channels for lithium ion transmission to improve the kinetic performance of the secondary battery, and it is beneficial to reduce the influence of the increase in the average particle size of the secondary particles on the interface reaction rate due to the reduction in the contact area with the electrolyte, which is beneficial to improve the kinetic performance of the secondary battery.

[0072] In this application, the proportion of secondary particles of graphite material in the total number of graphite material particles is tested by conventional methods in the field; as an example, the test method can be: disassemble the secondary battery, take out the negative electrode plate, clean and dry it, scrape the negative electrode material, and disperse the negative electrode material using vacuum negative pressure airflow dispersion technology. Use a scanning electron microscope (such as ZEISS Sigma 300) to obtain a scanning electron microscope (SEM) image of the dispersed negative electrode material. The graphite material particles are different from the morphology of the additives (binders, conductive agents, etc.) and can be distinguished. As an example, the test can be carried out in the following way: randomly select multiple test areas (for example, 5), and at a certain magnification (for example, 1000 times), count the number of secondary particles of graphite material in each test area (primary particles and secondary particles can be distinguished according to the degree of concave and convexity of the particle surface) and the total number of graphite material particles (including primary particles and secondary particles), add the number of secondary particles of graphite material in each test area and the total number of graphite material particles, and then calculate the proportion of secondary particles of graphite material in the total number of graphite material particles. In order to ensure the accuracy of the test results, the above test can be repeated by sampling multiple times and the average value is taken as the final test result.

[0073] In the present application, the average primary particle size and the average secondary particle size of the graphite material can be tested using equipment and methods known in the art. As an example, the test method can be: disassemble the secondary battery, take out the negative electrode plate, clean and dry it, scrape the negative electrode material, use vacuum negative pressure airflow dispersion technology to disperse the negative electrode material, and use a scanning electron microscope (such as ZEISS Sigma 300) to obtain a scanning electron microscope (SEM) image of the dispersed negative electrode material. Since the graphite material particles are different from the morphology of the additives (binders, conductive agents, etc.), they can be distinguished. As an example, the test can be conducted in the following manner: randomly select multiple test areas (e.g., 5), and at a certain magnification (e.g., 1000 times), primary particles and secondary particles can be distinguished according to the degree of concavity and convexity of the particle surface, and the particle size of the primary particles and secondary particles of the graphite material in each test area is measured (i.e., the distance between the two farthest points on the primary particle or secondary particle is taken as the particle size), and the number and particle size value of the primary particles and secondary particles of the graphite material in each test area are counted, and the arithmetic mean of the particle size of the primary particles of the graphite material and the arithmetic mean of the particle size of the secondary particles of the graphite material in each test area are taken, which is the average particle size of the primary particles and the average particle size of the secondary particles of the graphite material in the test sample. In order to ensure the accuracy of the test results, the above test can be repeated for multiple times, and the average value is taken as the final test result.

[0074] In some embodiments, the surface of the second graphite material has a coating layer, and the coating layer includes carbon elements; and / or, The thickness of the coating layer is greater than 0 nm and ≤ 500 nm, for example, 50 nm, 100 nm, 150 nm, 200 nm, 245 nm, 264 nm, 266 nm, 271 nm, 274 nm, 280 nm, 287 nm, 290 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm or a range consisting of any of the above values.

[0075] Therefore, the coating layer on the surface of the second graphite material is conducive to the rapid conduction of lithium ions into the lattice of the second graphite material for embedding, thereby improving the kinetic performance of the secondary battery. In addition, it reduces the impact of increased coating layer thickness on the high-temperature storage capacity of the secondary battery.

[0076] In the present application, the thickness of the surface coating layer of the second graphite material can be tested by conventional methods in the art; as an example, the testing method can be: disassembling the secondary battery, taking out the negative electrode plate, cleaning and drying it, observing it through a scanning electron microscope, and the graphite material particles are different from the morphology of the additives (binders, conductive agents, etc.), and can be distinguished, using an ion beam to cut the graphite particles, and observing the cross-section of the graphite particles through a scanning electron microscope to test the thickness of its coating layer.

[0077] In some embodiments, the R value of the second negative electrode material is 0.13-0.25, for example, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2, 0.21, 0.22, 0.23, 0.24, 0.25 or any range thereof; and / or, The R50 value of the second negative electrode material is 1.0-1.4, for example, 1.0, 1.1, 1.2, 1.29, 1.3, 1.31, 1.32, 1.33, 1.34, 1.35, 1.4 or a range consisting of any of the above values; The R value of the second negative electrode material is the ratio of the difference between the R90 value of the second negative electrode material and the R10 value of the second negative electrode material to the R50 value of the second negative electrode material; The plurality of particles of the second negative electrode material are D / I G Accumulate from small to large, when I D / I G The cumulative value reaches I D / I G I corresponding to 10% of the total value D / I G is R10 of the second negative electrode material, when I D / I G The cumulative value reaches I D / I G I corresponding to 50% of the total value D / I G is R50 of the second negative electrode material, when I D / I G The cumulative value reaches I D / I G I corresponding to 90% of the total value D / I G R90 of the second negative electrode material; In the Raman spectrum of a single particle of the second negative electrode material, the Raman shift is 1300 cm -1 ~ 1380cm -1 The intensity of the peak within the range is I D , Raman shift is 1520cm -1 ~ 1590cm -1 The intensity of the peak within the range is I G .

[0078] Therefore, the above R value range of the second negative electrode material can improve the uniformity of the surface coating layer of the second graphite material, which is beneficial to improve the more uniform conduction of lithium ions into the second graphite material lattice and embedding, thereby improving the kinetic performance of the secondary battery.

[0079] The above R50 value range of the second negative electrode material, on the one hand, is conducive to improving the disorder degree of the surface of the second negative electrode material, providing more channels or spaces for lithium ion conduction, and improving the fast charging performance of the secondary battery. On the other hand, it reduces the impact of the increased disorder degree of the surface of the second negative electrode material on the high-temperature storage capacity of the secondary battery.

[0080] In the present application, the intensity of a peak within a certain Raman shift range refers to the maximum value of the intensity value within the Raman shift range in the Raman spectrum.

[0081] In the present application, the Raman spectrum of a single particle of the second negative electrode material is tested using conventional methods in the field; for example, a Renishaw confocal micro-Raman spectrometer is used to perform surface point-by-point scanning on a single particle of the second negative electrode material; wherein the surface point-by-point scanning area is 100μm×100μm, the scanning step length is 2μm, the single point scanning time is 0.7s, and a total of 2500 points are recorded; a solid-state laser with a wavelength of 532nm is used as the light source, and the laser intensity is 10%.

[0082] In some embodiments, the powder OI value of the first graphite material is greater than 6 and less than or equal to 25 or greater than 10 and less than or equal to 25 (for example, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25 or a range consisting of any of the above values), and the powder OI value of the first graphite material is the peak area ratio of the characteristic diffraction peak of the 004 crystal plane to the characteristic diffraction peak of the 110 crystal plane in the XRD spectrum of the first graphite material.

[0083] Therefore, the first graphite material in the first negative electrode material adopts an anisotropic graphite material with high capacity and OI value greater than 10 and less than or equal to 25, so as to match and balance with the second negative electrode material to improve the overall energy density of the secondary battery.

[0084] In some embodiments, the first graphite material includes primary particles. Thus, the first graphite material in the first negative electrode material includes primary particles, which is beneficial for matching and balancing with the second negative electrode material to improve the energy density of the secondary battery.

[0085] In some embodiments, the average particle size of the primary particles in the first graphite material is 8-19 μm, such as 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 16.2 μm, 16.4 μm, 17 μm, 18 μm, 18.9 μm, 19 μm or any range thereof. Thus, the first graphite material in the first negative electrode material includes primary particles with large particle size, which is conducive to matching with the second negative electrode material to improve the energy density of the secondary battery.

[0086] In the present application, the average particle size of the primary particles in the first graphite material is tested with reference to the method described above.

[0087] In some embodiments, the first graphite material further includes secondary particles, and the proportion of the secondary particles in the first graphite material to the total number of the first graphite material particles is 35% - 90% or 50% - 80%, such as 35%, 40%, 50%, 60%, 70%, 80%, 84%, 90% or a range consisting of any of the above values. Thus, adding secondary particles to the first graphite material in the first negative electrode material can, on the one hand, provide more channels for lithium ion transmission to improve the kinetic performance of the secondary battery, and on the other hand, can reduce the impact of the increase in the proportion of secondary particles on the energy density of the secondary battery.

[0088] In the present application, the proportion of the secondary particles in the first graphite material in the total number of the first graphite material particles is tested with reference to the method described above.

[0089] In some embodiments, the first graphite material includes secondary particles, and the average particle size of the secondary particles in the first graphite material is 12-22 μm. This can provide more channels for lithium ion transmission to improve the dynamic performance of the secondary battery, and can also help reduce the impact on the dynamic performance of the secondary battery caused by the increase in the average particle size of the secondary particles, which leads to a reduction in the contact area with the electrolyte.

[0090] In the present application, the average particle size of the secondary particles in the first graphite material is tested with reference to the method described above.

[0091] In some embodiments, the first negative electrode active layer further comprises natural graphite material. Thus, the first negative electrode material uses natural graphite material, and there are many pores inside the structure of the natural graphite material, so that the natural material has good contact with the electrolyte, which is beneficial to improving the dynamic performance of the secondary battery.

[0092] [Negative electrode] An embodiment of the present application provides a method for preparing a graphite material, comprising the following steps: The anisotropic raw coke particles are mixed with a binder and subjected to a first heating treatment to obtain an intermediate material; The intermediate material is graphitized, and the graphitized product obtained is the graphite material.

[0093] In some embodiments, the method further comprises: mixing the graphitized product with a carbon source, and subjecting the mixture to a second heating treatment to obtain a graphite material having a carbon-containing coating layer on the surface.

[0094] In some embodiments, the streamline structure in the polarized photograph of the anisotropic raw coke particles accounts for 7%-99%, for example, 7%, 10%, 13%, 20%, 30%, 40%, 50%, 60%, 63%, 70%, 80%, 83%, 90%, 97%, 99% or a range consisting of any of the above values.

[0095] In some embodiments, the average particle size of the raw coke particles is 6 μm-15 μm, for example 6 μm, 6.3 μm, 7.3 μm, 7.4 μm, 7.5 μm, 7.6 μm, 8 μm, 9 μm, 10 μm, 12 μm, 14 μm, 15 μm or a range consisting of any of the above values.

[0096] In some embodiments, the graphite material includes secondary particles, wherein the ratio of the average particle size of the secondary particles of the graphite material to the average particle size of the raw coke particles is 1-4, such as 1.2, 1.5, 1.9, 2, 3, 3.4, 4 or a range consisting of any of the above values.

[0097] Therefore, the above-mentioned range of the ratio of the average particle size of the secondary particles of the graphite material to the average particle size of the raw coke particles is beneficial to improving the fast charging performance of the battery cell, and reducing the impact of the increase in the secondary particles of the graphite material resulting in a decrease in the contact area with the electrolyte and thus on the lithium ion transmission rate.

[0098] In some embodiments, the mass ratio of the binder to the raw coke particles is 2.3% to 20%, such as 2.3%, 4%, 10%, or 20%.

[0099] In some embodiments, the mass ratio of the carbon source to the graphitized product is 2%-20%, for example, 2%, 5%, 5.8%, 7%, 8%, 10%, 13%, 15%, 17%, 20% or a range consisting of any of the above values.

[0100] In some embodiments, the temperature of the first heat treatment is 300-700°C (e.g., 300°C, 400°C, 445°C, 500°C, 600°C, 700°C, or a range consisting of any of the above values) and the time is 3-9h (e.g., 3h, 3.6h, 4h, 6h, 9h, or a range consisting of any of the above values).

[0101] In some embodiments, the second heat treatment is performed at a temperature of 700-1300°C (e.g., 700°C, 800°C, 900°C, 1000°C, 1150°C, 1200°C, 1300°C, or any range consisting of the above values) and for a time of 4-20 h (e.g., 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, or any range consisting of the above values).

[0102] In some embodiments, the temperature of the graphitization treatment is 2800°C - 3800°C (e.g., 2900°C, 3000°C, 3100°C, 3300°C, 3500°C, 3600°C, 3800°C, or a range consisting of any of the above values), and the time of the graphitization treatment is 20 days - 40 days (e.g., 20 days, 25 days, 30 days, 33 days, 35 days, 38 days, 40 days, or a range consisting of any of the above values).

[0103] In some embodiments, the raw coke particles are obtained by crushing and shaping raw coke.

[0104] In some embodiments, the method further comprises: screening and demagnetizing the product.

[0105] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0106] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0107] In some embodiments, the negative electrode material may also use other negative electrode active materials for batteries that are well known in the art. As an example, the negative electrode material may include at least one of the following materials: soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0108] In some embodiments, the negative electrode active layer may further include a binder. As an example, 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).

[0109] In some embodiments, the negative electrode active layer may further include a conductive agent. As an example, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0110] In some embodiments, the negative electrode active layer may further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0111] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0112] [Positive electrode] In some embodiments, the positive electrode may be a positive electrode sheet, and the positive electrode sheet may include a positive electrode current collector and a positive electrode active material disposed on at least one surface of the positive electrode current collector.

[0113] As an example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material is disposed on either or both of the two facing surfaces of the positive electrode current collector.

[0114] As an example, the positive electrode current collector may be a metal foil, a conductive polymer material, a carbon material or a composite current collector. For example, as the metal foil, a pure metal, an alloy, a surface-treated metal, including but not limited to stainless steel, copper, aluminum, nickel, nickel, titanium or silver, etc. may be used. The composite current collector may include a polymer material base layer and a metal layer. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0115] In some embodiments, the battery cell is a lithium-ion battery, and the positive electrode active material may adopt the positive electrode active material for lithium-ion batteries known in the art. The positive electrode active material may include at least one of the following materials: lithium-containing phosphates, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4, also referred to as LFP), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3Mn 1 / 3 O2, also known as NCM 333 、LiNi 0.5 Co 0.2 Mn 0.3 O2, also known as NCM 523 、LiNi 0.5 Co 0.25 Mn 0.25 O2, also known as NCM 211 、LiNi 0.6 Co 0.2 Mn 0.2 O2, also known as NCM 622 、LiNi 0.8 Co 0.1 Mn 0.1 O2, also known as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co0.05 Al 0.05 O2) and at least one of its modified compounds. The modified compound refers to a substance obtained by modifying the above substances by means of doping or coating.

[0116] During the charging and discharging process of the battery, active ions (Li + ) is inserted and consumed, and the molar content of Li is different when the battery is discharged to different states. In the list of positive electrode active materials in this application, the molar content of Li is the initial state of the material, that is, the state before feeding. The positive electrode active material is used in the battery system, and the molar content of Li will change after charge and discharge cycles.

[0117] In the list of positive electrode active materials in this application, the molar content of oxygen is only a theoretical value. The release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual molar content of oxygen will fluctuate.

[0118] 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 fluorine-containing acrylate resin.

[0119] In some embodiments, the positive electrode film layer may further include a conductive agent, for example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0120] In some embodiments, the positive electrode may be a foamed metal. The foamed metal may be a foamed nickel, a foamed copper, a foamed aluminum, a foamed alloy, or a foamed carbon. When the foamed metal is used as the positive electrode, the positive electrode active material may not be disposed on the surface of the foamed metal, but of course, the positive electrode active material may also be disposed. As an example, the positive electrode active material is filled or / and deposited in the foamed metal.

[0121] In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0122] [Electrolytes] In some embodiments, the battery cell further includes an electrolyte, which acts as a conductor of ions between the positive and negative electrodes. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. The electrolyte can be liquid, gel or solid.

[0123] The liquid electrolyte includes an electrolyte salt and a solvent.

[0124] 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 difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0125] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone. The solvent can also be selected from ether solvents. Ether solvents can include one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyltetrahydrofuran, diphenyl ether and crown ether.

[0126] In some embodiments, the electrolyte may further include additives, for example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain properties of battery cells, such as additives that improve overcharge / fast charge performance of battery cells, additives that improve high temperature performance of battery cells, additives that improve low temperature performance of battery cells, etc.

[0127] Among them, the gel electrolyte includes a polymer as a skeleton network and can be used in combination with an ionic liquid-lithium salt.

[0128] Among them, solid electrolytes include polymer solid electrolytes, inorganic solid electrolytes, and composite solid electrolytes.

[0129] As examples, the polymer of the polymer solid electrolyte may include polyether (polyethylene oxide), polysiloxane, polycarbonate, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, a single ion polymer, a polyionic liquid, cellulose, and the like.

[0130] As an example, the inorganic solid electrolyte can be an oxide solid electrolyte (crystalline perovskite, sodium superconducting ion conductor, garnet, amorphous LiPON film), a sulfide solid electrolyte (crystalline lithium superion conductor (lithium germanium phosphosulfide, silver germanium sulfide), amorphous sulfide) and one or more of a halide solid electrolyte, a nitride solid electrolyte and a hydride solid electrolyte.

[0131] As an example, the composite solid electrolyte is formed by adding an inorganic solid electrolyte filler to a polymer solid electrolyte.

[0132] [Isolator] In some embodiments, the electrode assembly further includes a separator disposed between the positive electrode and the negative electrode.

[0133] In some embodiments, the separator is a separator. The present application has no particular limitation on the type of separator, and any known separator with a porous structure having good chemical stability and mechanical stability can be selected.

[0134] As an example, the main material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, polyimide porous membrane, polyvinylidene fluoride, and ceramic. The separator can be a single-layer film or a multi-layer composite film, without special restrictions. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without special restrictions. The separator can be a separate component located between the positive and negative electrodes, or it can be attached to the surface of the positive and negative electrodes. An inorganic particle coating, an organic particle coating, or an organic / inorganic composite coating can also be coated on the surface of the separator.

[0135] In some embodiments, the separator is a solid electrolyte, which is disposed between the positive electrode and the negative electrode and serves to transmit ions and isolate the positive and negative electrodes.

[0136] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0137] [Structure of electrode assembly] The electrode assembly may be a wound structure, a laminated structure, or a mixed structure of a wound structure and a laminated structure.

[0138] In some embodiments, the electrode assembly is a wound structure, wherein the positive electrode sheet and the negative electrode sheet are wound into the wound structure.

[0139] In some embodiments, the electrode assembly is a laminate structure.

[0140] As an example, a plurality of positive electrode sheets and a plurality of negative electrode sheets may be provided respectively, and the plurality of positive electrode sheets and the plurality of negative electrode sheets may be alternately stacked.

[0141] As an example, a plurality of positive electrode sheets may be provided, and the negative electrode sheet may be folded to form a plurality of stacked folded segments, with a positive electrode sheet being sandwiched between adjacent folded segments.

[0142] As an example, both the positive electrode sheet and the negative electrode sheet are folded to form a plurality of folded sections that are stacked.

[0143] As an example, a plurality of separators may be provided, each of which is provided between any adjacent positive electrode sheets or negative electrode sheets.

[0144] As an example, the separator may be disposed continuously, and may be disposed between any adjacent positive electrode sheets or negative electrode sheets by folding or winding.

[0145] In some embodiments, the shape of the electrode assembly can be cylindrical, flat, or polygonal.

[0146] In some embodiments, the electrode assembly is provided with tabs, which can lead current out of the electrode assembly. The tabs include a positive tab and a negative tab.

[0147] [shell] In some embodiments, the battery cell may include a shell. The shell may be a steel shell, an aluminum shell, a plastic shell (such as polypropylene), a composite metal shell (such as a copper-aluminum composite shell) or an aluminum-plastic film. In some embodiments, the shell may be a sealed structure or a non-sealed structure. As an example, when the shell is a non-sealed structure, the shell plays a role in protecting the electrode assembly, and a sealed bag is also included between the shell and the electrode assembly, and the sealed bag is used to encapsulate the electrode assembly and the electrolyte. Specifically, the sealed bag may be a bag-shaped insulating member or an aluminum-plastic film. When the shell is a sealed structure, it is used to encapsulate components such as the electrode assembly and the electrolyte.

[0148] As an example, the battery cell can be a cylindrical battery cell, a prismatic battery cell, a soft-pack battery cell or a battery cell of other shapes. The prismatic battery cell includes a square shell battery cell, a blade-shaped battery cell, a polygonal battery, such as a hexagonal battery, etc. There is no special limitation in this application.

[0149] In some embodiments, the housing includes an end cap and a shell, the shell is provided with an opening, and the end cap is provided to cover the opening. The shell may be provided with one or more openings. One or more end caps may also be provided.

[0150] [Electrode terminal] In some embodiments, at least one electrode terminal is disposed on the housing, and the electrode terminal is electrically connected to the electrode tab. The electrode terminal may be directly connected to the electrode tab, or may be indirectly connected to the electrode tab through a current collecting member. The electrode terminal may be disposed on an end cap, or may be disposed on the housing.

[0151] [Pressure relief mechanism] In some embodiments, a pressure relief mechanism is provided on the housing, and the pressure relief mechanism is used to discharge the internal gas of the battery cell.

[0152] As an example, when the internal pressure or temperature of the battery cell reaches a predetermined threshold, it is actuated to release the internal pressure or temperature. When the internal pressure or temperature of the battery cell reaches a predetermined threshold, the pressure relief mechanism performs an action or a weak structure provided in the pressure relief mechanism is destroyed, thereby forming an opening or channel for the internal pressure or temperature to be released. The threshold design varies according to different design requirements. The threshold may depend on one or more materials of the positive electrode sheet, negative electrode sheet, electrolyte and separator in the battery cell.

[0153] As an example, the pressure relief mechanism may be integrally formed with the housing.

[0154] As an example, the pressure relief mechanism may also be separately provided and connected to the housing.

[0155] The "actuation" mentioned in this application means that the pressure relief mechanism is in action or activated to a certain state, so that the internal pressure and temperature of the battery cell can be released. The action produced by the pressure relief mechanism may include but is not limited to: the components in the pressure relief mechanism move to form an exhaust channel, at least a part of the pressure relief mechanism ruptures, breaks, is torn or opened, etc. When the pressure relief mechanism is actuated, the high-temperature and high-pressure substances inside the battery cell will be discharged from the actuated part as emissions. In this way, the battery cell can be depressurized and cooled under controllable pressure or temperature, thereby avoiding potential more serious accidents.

[0156] In some embodiments, when the outer shell is a non-sealed structure, the pressure relief mechanism can be set as a through hole to discharge the gas inside the battery cell.

[0157] The emissions from the battery cells mentioned in this application include, but are not limited to: electrolyte, dissolved or split positive and negative electrode sheets, fragments of separators, high-temperature and high-pressure gases produced by the reaction, flames, and the like.

[0158] [Battery device] The battery apparatus mentioned in the embodiments of the present application may include one or more battery cell assemblies for providing voltage and capacity. The battery cell assembly may include multiple battery cells, which are connected in series, in parallel or in mixed connection through a busbar component.

[0159] In some embodiments, a battery cell assembly is generally formed by arranging a plurality of battery cells.

[0160] As an example, the battery cell assembly may be a battery module, which is formed by arranging and fixing a plurality of battery cells to form an independent module. As an example, the battery module may be formed by bundling a plurality of battery cells by a cable tie.

[0161] In some embodiments, the battery device may be a battery pack, which includes a box and one or more battery cell assemblies, wherein the battery cell assemblies are accommodated in the box.

[0162] As an example, the battery cell assembly may be a battery module, and the battery cell assembly may be accommodated in the box by fixing the battery module in the box.

[0163] As an example, the battery cell assembly may also be housed in the case by directly fixing a plurality of battery cells to the case.

[0164] As an example, the box may include a first box and a second box. The first box and the second box are buckled together to form a closed space inside the box to accommodate the battery cell assembly. The closed here means covered or closed, which can be sealed or unsealed. The first box can be a top cover or a bottom plate.

[0165] As an example, the box body may include a top cover, a frame and a bottom plate. The top cover and the bottom plate are respectively connected to the frame, so that a closed space is formed inside the box body to accommodate the battery cell assembly.

[0166] In some embodiments, the box body can be used as a part of the chassis structure of the vehicle. For example, part of the box body can become at least a part of the floor of the vehicle, or part of the box body can become at least a part of the cross beam and longitudinal beam of the vehicle.

[0167] The technical solutions described in the embodiments of the present application are applicable to various electrical devices that use battery cells, such as mobile phones, portable devices, laptop computers, electric vehicles, electric toys, electric tools, vehicles, ships and spacecraft, for example, spacecraft include airplanes, rockets, space shuttles and spacecraft, etc.

[0168] For example, Figure 1 The battery cell 5 is a square structure as an example.

[0169] In some embodiments, reference Figure 2, the outer packaging may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0170] In some embodiments, battery cells may be assembled into a battery module. The number of battery cells contained in the battery module may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.

[0171] Figure 3 4 is an example of a battery module. Figure 3 In the battery module 4, the plurality of battery cells 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells 5 may be fixed by fasteners.

[0172] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0173] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery pack.

[0174] Figure 4 and Figure 5 1 is a battery pack 1 as an example. Figure 4 and Figure 5 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 cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0175] In addition, the present application also provides an electrical device, which includes at least one of the battery cells, battery modules, or battery packs provided in the present application. The battery cells, battery modules, or battery packs can be used as power sources for the electrical device, or as energy storage units for 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 and satellites, energy storage systems, etc., but are not limited thereto.

[0176] As an electrical device, a battery cell, a battery module or a battery pack can be selected according to its usage requirements.

[0177] Figure 6 The power consumption device is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the power consumption device's requirements for high power and high energy density of battery cells, a battery pack or a battery module can be used.

[0178] [Example] Hereinafter, the 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 limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially. Example 1

[0179] (1) Preparation of the second graphite material: The streamline structure accounts for 83% in the polarized photo of anisotropic petroleum coke. The anisotropic petroleum coke is ground and shaped to obtain aggregate with an average particle size of 7.4μm. The aggregate and binder asphalt are mixed in a mass ratio of 10:1, placed in a horizontal reactor and heated to 445℃ for 3.6 hours, cooled to ≤50℃ for discharge, and controlled to a suitable particle size by depolymerization to obtain an intermediate material with a granulation degree (average particle size of the intermediate material divided by the average particle size of the aggregate) of 1.9. The intermediate material is graphitized at 3000℃ in an Acheson furnace for 33 days to obtain a graphitized product. The graphitized product is mixed with the coating agent asphalt in a mass ratio of 100:5.8, placed in a horizontal reactor and heated to 1150℃ for 12 hours, and the second graphite material is obtained after screening and demagnetization. The finished particle size is 13.7μm, and the thickness of the carbon coating layer on the surface of the second graphite material is 274nm.

[0180] The SEM photo of the second graphite material and the enlarged SEM photo of the secondary particles are shown in Figure 7-8 As shown, it can be seen that the second graphite material includes a certain number of secondary particles.

[0181] The parameters of the second graphite material are shown in Table 1.

[0182] (2) Preparation of negative electrode sheet: The first graphite material with an OI value of 11 and an average primary particle size of 16.4 μm, dispersant sodium carboxymethyl cellulose, binder styrene-butadiene rubber (SBR), and conductive agent carbon black were mixed in a mass ratio of 96.4:1.1:2.0:0.4, and prepared into a negative electrode slurry with deionized water under the action of a vacuum mixer. The slurry was evenly coated on the negative electrode current collector copper foil, dried at room temperature, and then transferred to an oven for drying to form a first negative electrode active layer on one side of the negative electrode current collector. The first negative electrode material had a powder compaction density of 1.79 g / cm at 150 MPa. 3 .

[0183] The second graphite material, dispersant sodium carboxymethyl cellulose, binder styrene-butadiene rubber (SBR), and conductive agent carbon black are mixed in a mass ratio of 97.2:1.1:0.8:0.7, and prepared into a negative electrode slurry with deionized water under the action of a vacuum mixer. The slurry is evenly coated on the side of the first negative electrode active layer away from the negative electrode current collector, and after drying at room temperature, it is transferred to an oven for drying, and cold pressed and cut to obtain a negative electrode sheet. The negative electrode sheet includes a negative electrode current collector, a first negative electrode active layer located on one side of the negative electrode current collector, and a second negative electrode active layer located on the side of the first negative electrode active layer away from the negative electrode current collector. The R value of the second negative electrode material is 0.17, and the R50 value is 1.34.

[0184] (3) Preparation of positive electrode sheet: The positive electrode active material LiFePO4, the conductive agent Super P, and the binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 96:2:2, and the solvent N-methylpyrrolidone (NMP) is added, and stirred evenly under the action of a vacuum mixer to obtain a positive electrode slurry; the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil, dried at room temperature, transferred to an oven for drying, and then cold pressed and cut to obtain a positive electrode sheet.

[0185] (4) Isolation film: polyethylene film with a thickness of 12 μm.

[0186] (5) Preparation of electrolyte: Ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1, and fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent to prepare an electrolyte. The molar concentration of LiPF6 in the electrolyte is 1 mol / L.

[0187] (6) Assembly of battery cells: The positive electrode sheet, the isolation film, and the negative electrode sheet are stacked in order, so that the isolation film is between the positive and negative electrode sheets to play an isolating role, and then a bare battery cell is obtained; the bare battery cell is placed in an outer packaging shell, and the prepared electrolyte is injected into the dried bare battery cell. After vacuum packaging, standing, forming, shaping and other processes, a lithium-ion battery cell is obtained.

[0188] Battery Test Methods (1) Battery cell charging time test method: At 25°C, the battery cell was charged at a constant current of 1C to 4.4V, then charged at a constant voltage to a current ≤0.05C, left to stand for 5 minutes, and then discharged at a constant current of 0.33C to 2.8V. The discharge capacity was recorded as C0.

[0189] At 25°C, the battery cells were charged at a constant current of 1.0C0, 1.3C0, 1.5C0, 1.8C0, 2.0C0, 2.3C0, 2.5C0, 3.0C0, 3.5C0, 4C0, 4.5C0, and 5C0 to a charge cut-off voltage of 4.4V or a negative electrode cut-off potential of 0V (whichever is reached first). After each charge, the battery cells were discharged at 1C0 to a discharge cut-off voltage of 2.8V. The battery cells were charged at different charge rates to 10% SOC, 20% SOC, 30% SOC, 40% SOC, 50% SOC, 60% SOC, 70% SOC, and 80% SOC (State ofCharge, state of charge, when "SOC=0" means the battery is fully discharged, when "SOC=100%" means the battery is fully charged) the corresponding negative electrode potential, draw the charging rate-negative electrode potential curve under different SOC states, and obtain the charging rate corresponding to the negative electrode potential of 0V under different SOC states after linear fitting. The charging rate is the charging window under the SOC state, which is recorded as C10%SOC, C20%SOC, C30%SOC, C40% SOC, C50% SOC, C60% SOC, C70% SOC, C80% SOC, the charging time T of the battery cell from 10% SOC to 80% SOC is calculated according to the formula (60 / C20% SOC + 60 / C30% SOC + 60 / C40% SOC + 60 / C50% SOC + 60 / C60% SOC + 60 / C70% SOC + 60 / C80% SOC) × 10%, in min.

[0190] (2) Volume energy density test method of battery cells: Place the battery cell at 25°C, charge it at a constant current of 1C to 4.4V, then charge it at a constant voltage to a current ≤0.05C, let it stand for 5 minutes, and then discharge it at a constant current of 0.33C to 2.8V, and record the discharge capacity A0 and discharge platform voltage V at this time; use a caliper to measure the length, thickness, and height of the battery cell (generally calculated based on the outer shell size of the battery cell, excluding the height of the electrode terminals and the insulating film outside the outer shell), and calculate the volume of the battery cell V0; the volume energy density of the battery cell VED=(A0×V) / V0, unit Wh / L.

[0191] Example 2 In the preparation steps of the second graphite material, the streamline structure in the polarized photograph of the anisotropic petroleum coke accounted for 64%, the average aggregate particle size was 7.3 μm, the finished particle size of the second graphite material was 13.6 μm, and the thickness of the carbon coating layer on the surface of the second graphite material was 266 nm.

[0192] In the step of preparing the negative electrode sheet, the R value of the second negative electrode material is 0.15 and the R50 value is 1.31.

[0193] The remaining operations are the same as those in Example 1.

[0194] Example 3 In the preparation steps of the second graphite material, the streamline structure in the polarized photograph of the anisotropic petroleum coke accounts for 13%, the average aggregate particle size is 7.6 μm, the finished particle size of the second graphite material is 13.4 μm, and the thickness of the carbon coating layer on the surface of the second graphite material is 271 nm.

[0195] In the step of preparing the negative electrode sheet, the R value of the second negative electrode material is 0.16 and the R50 value is 1.31.

[0196] The remaining operations are the same as those in Example 1.

[0197] Example 4 In the preparation steps of the second graphite material, the streamline structure in the polarized photograph of the anisotropic petroleum coke accounts for 97%, the average aggregate particle size is 7.4 μm, the finished particle size of the second graphite material is 13.6 μm, and the thickness of the carbon coating layer on the surface of the second graphite material is 280 nm.

[0198] In the step of preparing the negative electrode sheet, the R value of the second negative electrode material is 0.17 and the R50 value is 1.32.

[0199] The remaining operations are the same as those in Example 1.

[0200] Example 5 In the preparation step of the second graphite material, the streamline structure in the polarized photograph of the anisotropic petroleum coke accounted for 99%, the average aggregate particle size was 7.5 μm, the finished particle size of the second graphite material was 13.8 μm, and the thickness of the carbon coating layer on the surface of the second graphite material was 264 nm.

[0201] In the preparation step of the negative electrode sheet, a first graphite material with an OI value of 15.2 and an average primary particle size of 18.9 μm is used; the R value of the second negative electrode material is 0.16 and the R50 value is 1.35.

[0202] The remaining operations are the same as those in Example 1.

[0203] Comparative Example 1 In the preparation step of the second graphite material, isotropic petroleum coke is used, the average aggregate particle size is 7.4 μm, the finished particle size of the second graphite material is 13.4 μm, and the thickness of the carbon coating layer on the surface of the second graphite material is 271 nm.

[0204] In the step of preparing the negative electrode sheet, the R value of the second negative electrode material is 0.18 and the R50 value is 1.31.

[0205] The remaining operations are the same as those in Example 1.

[0206] The parameters in the table below include: Graphite 1 is a first graphite material; Graphite 2 is a second graphite material; The gram capacity difference is the difference between the gram capacity of the first negative electrode material and the gram capacity of the second negative electrode material; The 150 MPa powder compaction difference is the difference between the compaction density of the first negative electrode material powder and the compaction density of the second negative electrode material powder at 150 MPa; P is the proportion of secondary particles in the second graphite material to the total number of particles; A is the ratio of the average particle size of the secondary particles to the average particle size of the primary particles of the second graphite material.

[0207] Table 1 Partial parameters and test results of Examples 1-5 and Comparative Example 1 serial number Graphite 2 powder OI value Second negative electrode material gram capacity (mAh / g) <![CDATA[The powder compaction of the first negative electrode material at 150 MPa (g / cm 3 ).]]> Gram capacity difference (mAh / g) <![CDATA[Powder compaction difference at 150 MPa (g / cm 3 )]]> P A Average particle size of graphite 2 secondary particles (μm) 25℃ Charging time (min) Volumetric energy density (wh / L) Example 1 2.5 357.6 1.79 6.4 0.14 87% 1.9 14.6 11.7 422.31 Example 2 1.3 350.4 Same as Example 1 13.6 0.17 82% 2.4 15.2 11.4 417.79 Example 3 1.2 345.3 Same as Example 1 19 0.29 85% 1.6 14.2 10.7 413.78 Example 4 9.8 359 Same as Example 1 5 0.05 83% 2.4 15.1 12.7 423.96 Example 5 10 365 2.1 5 0.34 84% 2.4 15.2 15.9 434.56 Comparative Example 1 0.7 333.7 Same as Example 1 30.3 0.34 85% 1.6 14.2 12.3 412.11 It can be seen from the above table that compared with the isotropic graphite material of the second graphite material in Comparative Example 1, the second graphite material in Examples 1-5 of the present application adopts anisotropic graphite, and the OI value of the second graphite material is reduced by granulating into secondary particles, thereby significantly improving the energy density of the secondary battery while ensuring the kinetic performance of the secondary battery.

[0208] Example 6 In the preparation step of the negative electrode sheet, a first graphite material with an OI value of 10.3 and an average primary particle size of 16.2 μm is used. The remaining operations are the same as those in Example 1.

[0209] Example 7 In the preparation steps of the second graphite material, the streamline structure in the polarized photograph of the anisotropic petroleum coke accounted for 7%, the average aggregate particle size was 6.3 μm, the finished particle size of the second graphite material was 11.9 μm, and the thickness of the surface coating layer of the second graphite material was 290 nm.

[0210] In the preparation step of the negative electrode sheet, a first graphite material with an OI value of 15.2 and an average primary particle size of 18.9 μm is used, and a second negative electrode material with an R value of 0.19 and an R50 value of 1.31 is used.

[0211] The remaining operations are the same as those in Example 1.

[0212] Example 8 In the preparation steps of the second graphite material, the streamline structure in the polarized photograph of the anisotropic petroleum coke accounted for 7%, the average aggregate particle size was 6.3 μm, the finished particle size of the second graphite material was 11.9 μm, and the thickness of the surface coating layer of the second graphite material was 290 nm.

[0213] In the preparation step of the negative electrode sheet, a first graphite material with an OI value of 17 and an average primary particle size of 19 μm is used, and a second negative electrode material with an R value of 0.19 and an R50 value of 1.31 is used.

[0214] The remaining operations are the same as those in Example 1.

[0215] Comparative Example 2 In the preparation step of the negative electrode sheet, a first graphite material with an OI value of 7.1 and an average primary particle size of 13.7 μm is used. The remaining operations are the same as those in Example 1.

[0216] Comparative Example 3 In the preparation step of the negative electrode sheet, a first graphite material with an OI value of 19 and an average primary particle size of 17.4 μm is used. The remaining operations are the same as those in Example 1.

[0217] Table 2 Partial parameters and test results of Examples 1, 6-8 and Comparative Examples 2-3 serial number Graphite 2 powder OI value Second negative electrode material gram capacity (mAh / g) First negative electrode material 150MPa powder compaction (g / cm3) Gram capacity difference (mAh / g) 150MPa powder compaction difference (g / cm3) P A Average particle size of graphite 2 secondary particles (μm) 25℃ Charging time (min) Volumetric energy density (wh / L) Example 1 2.5 357.6 1.79 6.4 0.14 87% 1.9 14.6 11.7 422.31 Example 6 Same as Example 1 Same as Example 1 1.7 5 0.05 Same as Example 1 Same as Example 1 Same as Example 1 12.3 416.23 Example 7 1.0 345 2.1 25 0.6 70% 2.6 14.6 13.1 426.12 Example 8 1 345 2.1 36.3 0.6 70% 2.6 14.6 13.9 428.1 Comparative Example 2 Same as Example 1 Same as Example 1 1.67 0.4 0.02 Same as Example 1 Same as Example 1 Same as Example 1 11.3 410.45 Comparative Example 3 Same as Example 1 Same as Example 1 2.26 13.4 0.61 Same as Example 1 Same as Example 1 Same as Example 1 17 428.44 It can be seen from the above table: Compared with comparative example 2 in which the first negative electrode material powder is too under-compacted, the energy density of the secondary batteries in examples 1 and 6 of the present application is significantly improved.

[0218] Compared with comparative example 3 in which the first negative electrode material powder is too densely compacted, the fast charging performance of the secondary batteries in examples 1 and 6 of the present application is significantly improved.

[0219] Compared with the larger difference in gram capacity between the first negative electrode material and the second negative electrode material in Example 8, the kinetic performance of the secondary batteries in Examples 1, 6-7 of the present application is significantly higher.

[0220] Example 9 In the preparation step of the second graphite material, the mass ratio of the binder to the aggregate is 4%, the granulation degree is 1.5, the finished particle size of the second graphite material is 9.3 μm, and the thickness of the surface coating layer of the second graphite material is 264 nm.

[0221] In the step of preparing the negative electrode sheet, the R value of the second negative electrode material is 0.15 and the R50 value is 1.29.

[0222] The remaining operations are the same as those in Example 1.

[0223] Example 10 In the preparation step of the second graphite material, the mass ratio of the binder to the aggregate is 20%, the granulation degree is 3.4, the finished particle size of the second graphite material is 23.3 μm, and the thickness of the surface coating layer of the second graphite material is 287 nm.

[0224] In the step of preparing the negative electrode sheet, the R value of the second negative electrode material is 0.14 and the R50 value is 1.30.

[0225] The remaining operations are the same as those in Example 1.

[0226] Embodiment 11 In the preparation step of the second graphite material, the mass ratio of the binder to the aggregate is 2.3%, the granulation degree is 1.2, the finished particle size of the second graphite material is 8.7 μm, and the thickness of the surface coating layer of the second graphite material is 245 nm.

[0227] In the step of preparing the negative electrode sheet, the R value of the second negative electrode material is 0.13 and the R50 value is 1.30.

[0228] The remaining operations are the same as those in Example 1.

[0229] Comparative Example 4 No binder is added in the preparation step of the second graphite material, the granulation degree is 0, the finished particle size of the second graphite material is 7.8 μm, and the thickness of the surface coating layer of the second graphite material is 220 nm.

[0230] In the step of preparing the negative electrode sheet, the R value of the second negative electrode material is 0.17 and the R50 value is 1.33.

[0231] The remaining operations are the same as those in Example 1.

[0232] Table 3 Partial parameters and test results of Examples 1, 9-11 and Comparative Example 4 serial number Graphite 2 powder OI value Second negative electrode material gram capacity (mAh / g) Gram capacity difference (mAh / g) <![CDATA[150 MPa powder compaction difference (g / cm 3 )]]> P A Average particle size of graphite 2 secondary particles (μm) 25℃ Charging time (min) Volumetric energy density (wh / L) Example 1 2.5 357.6 6.4 0.14 87% 1.9 14.6 11.7 422.31 Example 9 8.7 347.7 16.3 0.18 58% 1.5 10.7 12.7 414.22 Example 10 1.9 359 5 0.15 89% 3.4 25.3 15.6 423.11 Embodiment 11 8.9 346.9 13.6 0.18 35% 1.2 9.9 14.5 413.13 Comparative Example 4 14.1 345.1 18.9 0.29 0% / / 16.8 412.3 It can be seen from the above table: Compared with the comparative example 4 in which the secondary particles in the second graphite material account for 0 in the total number of particles, the second graphite materials in Examples 1, 9-11 of the present application include secondary particles, and the kinetic performance of the secondary battery thereof is significantly improved and the energy density is higher.

[0233] Compared with Example 11, in which the secondary particles account for 35% of the total number of particles in the second graphite material, the secondary particles in the second graphite material of Examples 1, 9-10 of the present application have a higher proportion, and the energy density of their secondary batteries is higher, among which the secondary batteries in Examples 1 and 9 of the present application have higher kinetic performance.

[0234] Example 12 In the preparation step of the second graphite material, the operation of mixing and reacting the graphitized product and the coating agent is omitted, and the particle size of the obtained second graphite material product is 13 μm.

[0235] The R value and R50 value of the second negative electrode material were not measured. The remaining operations were the same as those in Example 1.

[0236] Table 4 Partial parameters and test results of Examples 1 and 12 serial number Graphite 2 powder OI value Second negative electrode material gram capacity (mAh / g) Gram capacity difference (mAh / g) <![CDATA[150 MPa powder compaction difference (g / cm 3 )]]> P A Average particle size of graphite 2 secondary particles (μm) Average particle size of graphite 2 primary particles (μm) Thickness of the second graphite carbon coating layer (nm) 25℃ Charging time (min) Volumetric energy density (wh / L) Example 1 2.5 357.6 6.4 0.14 87% 1.9 14.6 7.7 274 11.7 422.31 Example 12 2.5 358.1 5.9 0.13 87% 1.8 13.79 7.7 / 19.1 423.31 It can be seen from the above table that compared with Example 12 in which the surface of the second graphite material does not have a coating layer, the dynamic performance of the secondary battery in Example 1 of the present application is significantly higher.

[0237] Example 13 In the preparation step of the negative electrode sheet, the first graphite material used includes secondary particles, and the average particle size of the secondary particles is 20 μm. The remaining operations are the same as those in Example 1.

[0238] Embodiment 14 In the step of preparing the negative electrode sheet, when preparing the first negative electrode active layer, natural graphite, the first graphite material, the dispersant sodium carboxymethyl cellulose, the binder styrene butadiene rubber (SBR), and the conductive agent carbon black are mixed in a mass ratio of 57.8:96.4:1.1:2.0:0.4. Table 5 Partial parameters and test results of Examples 1, 13-14 serial number <![CDATA[150 MPa powder compaction of the first negative electrode material (g / cm 3 )]]> Gram capacity difference (mAh / g) 150MPa powder compaction difference (g / cm3) Graphite 1 powder OI value Average primary particle size of graphite 1 (μm) The proportion of graphite 1 secondary particles in the total number of particles Whether the first negative electrode active layer includes natural graphite 25℃ Charging time (min) Volumetric energy density (wh / L) Example 1 1.79 6.4 0.14 11 16.4 0 no 11.7 422.31 Embodiment 13 1.8 7.4 0.15 6.2 16.4 84% no 11.2 425.33 Embodiment 14 1.8 7.4 0.15 6.2 16.4 84% yes 10.7 425.8 It can be seen from the above table: Based on Example 1, the first graphite material of Example 13 of the present application includes secondary particles, and the fast charging performance and energy density of the secondary battery are improved.

[0239] Based on Example 13, the first negative electrode material of Example 14 of the present application further includes natural graphite, and the fast charging performance and energy density of the secondary battery are further improved.

[0240] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and parts thereof may be replaced with equivalents without departing from the scope of the present application. In particular, the various technical features mentioned in the various embodiments may be combined in any manner as long as there are no structural conflicts. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A lithium secondary battery, characterized in that: The lithium secondary battery comprises a negative electrode plate, the negative electrode plate comprises a negative electrode current collector, a first negative electrode active layer located on at least one side of the negative electrode current collector, and a second negative electrode active layer located on a side of the first negative electrode active layer away from the negative electrode current collector; the first negative electrode active layer comprises a first negative electrode material, the second negative electrode active layer comprises a second negative electrode material, the first negative electrode material comprises a first graphite material, and the second negative electrode material comprises a second graphite material; The powder OI value of the second graphite material is 1-10, and the powder OI value of the second graphite material is the peak area ratio of the characteristic diffraction peak of the 004 crystal plane to the characteristic diffraction peak of the 110 crystal plane in the XRD spectrum of the second graphite material; the second graphite material includes secondary particles; The gram capacity of the first negative electrode material is greater than the gram capacity of the second negative electrode material; the gram capacity of the second negative electrode material is 345-365 mAh / g; wherein the gram capacity of the first negative electrode material or the gram capacity of the second negative electrode material is the ratio of the discharge capacity of the lithium secondary battery to the mass of the first negative electrode material or the second negative electrode material, and the discharge capacity of the lithium secondary battery is the discharge capacity obtained by the lithium secondary battery being discharged from 2.0V to 5mV at a constant current of 0.05C at room temperature; The powder compaction density of the first negative electrode material at 150 MPa is greater than the powder compaction density of the second negative electrode material at 150 MPa; the powder compaction density of the first negative electrode material at 150 MPa is 1.70 - 2.10 g / cm 3 .

2. The lithium secondary battery according to claim 1, characterized in that: The powder OI value of the second graphite material is greater than 1.1 and less than or equal to 10; and / or, The gram capacity of the second negative electrode material is 350-365 mAh / g.

3. The lithium secondary battery according to claim 1, characterized in that The difference between the powder compaction density of the first negative electrode material and the second negative electrode material at 150 MPa is 0.05-0.60 g / cm 3 and / or, The difference in gram capacity between the first negative electrode material and the second negative electrode material is 5-36.3 mAh / g.

4. The lithium secondary battery according to claim 1, characterized in that The difference in gram capacity between the first negative electrode material and the second negative electrode material is 5-25 mAh / g.

5. The lithium secondary battery according to claim 1, characterized in that The secondary particles in the second graphite material account for 35% to 90% of the total number of particles in the second graphite material; and / or, The second graphite material further includes primary particles, and the ratio of the average particle size of the secondary particles in the second graphite material to the average particle size of the primary particles is 1.1-3.4; and / or, The average particle size of the secondary particles in the second graphite material is 8 μm to 25.3 μm.

6. The lithium secondary battery according to claim 1, characterized in that The secondary particles in the second graphite material account for 58% to 89% of the total number of particles in the second graphite material; and / or, The average particle size of the secondary particles in the second graphite material is 8 μm to 16 μm.

7. The lithium secondary battery according to claim 1, characterized in that: The surface of the second graphite material has a coating layer, and the coating layer includes carbon elements; and / or, The thickness of the coating layer is greater than 0 nm and less than or equal to 500 nm.

8. The lithium secondary battery according to claim 1, characterized in that The R value of the second negative electrode material is 0.13-0.25; and / or, The R50 value of the second negative electrode material is 1.0 - 1.4; The R value of the second negative electrode material is the ratio of the difference between the R90 value of the second negative electrode material and the R10 value of the second negative electrode material to the R50 value of the second negative electrode material; The plurality of particles of the second negative electrode material are D / I G Accumulate from small to large, when I D / I G The cumulative value reaches I D / I G I corresponding to 10% of the total value D / I G is R10 of the second negative electrode material, when I D / I G The cumulative value reaches I D / I G I corresponding to 50% of the total value D / I G is R50 of the second negative electrode material, when I D / I G The cumulative value reaches I D / I G I corresponding to 90% of the total value D / I G R90 of the second negative electrode material; In the Raman spectrum of a single particle of the second negative electrode material, the Raman shift is 1300 cm -1 ~ 1380cm -1 The intensity of the peak within the range is I D , Raman shift is 1520cm -1 ~ 1590cm -1 The intensity of the peak within the range is I G .

9. The lithium secondary battery according to claim 1, characterized in that: The powder OI value of the first graphite material is greater than 6 and less than or equal to 25, and the powder OI value of the first graphite material is the peak area ratio of the characteristic diffraction peak of the 004 crystal plane to the characteristic diffraction peak of the 110 crystal plane in the XRD spectrum of the first graphite material.

10. The lithium secondary battery according to claim 1, characterized in that: The first graphite material comprises primary particles; and / or, The average particle size of the primary particles in the first graphite material is 8-19 μm; and / or, The first graphite material also includes secondary particles, and the secondary particles in the first graphite material account for 35% to 90% of the total number of particles in the first graphite material.

11. The lithium secondary battery according to any one of claims 1 to 10, characterized in that: The first negative electrode active layer also includes natural graphite material.

12. A negative electrode plate for a lithium secondary battery, characterized in that: The negative electrode sheet comprises a negative electrode current collector, a first negative electrode active layer located on at least one side of the negative electrode current collector, and a second negative electrode active layer located on a side of the first negative electrode active layer away from the negative electrode current collector; the first negative electrode active layer comprises a first negative electrode material, the second negative electrode active layer comprises a second negative electrode material, the first negative electrode material comprises a first graphite material, and the second negative electrode material comprises a second graphite material; The powder OI value of the second graphite material is 1-10, and the powder OI value of the second graphite material is the peak area ratio of the characteristic diffraction peak of the 004 crystal plane to the characteristic diffraction peak of the 110 crystal plane in the XRD spectrum of the second graphite material; the second graphite material includes secondary particles; The gram capacity of the first negative electrode material is greater than the gram capacity of the second negative electrode material; the gram capacity of the second negative electrode material is 345-365 mAh / g; wherein the gram capacity of the first negative electrode material or the gram capacity of the second negative electrode material is the ratio of the discharge capacity of the lithium secondary battery to the mass of the first negative electrode material or the second negative electrode material, and the discharge capacity of the lithium secondary battery is the discharge capacity obtained by the lithium secondary battery being discharged from 2.0V to 5mV at a constant current of 0.05C at room temperature; The powder compaction density of the first negative electrode material at 150 MPa is greater than the powder compaction density of the second negative electrode material at 150 MPa; the powder compaction density of the first negative electrode material at 150 MPa is 1.70 - 2.10 g / cm 3 .

13. The negative electrode sheet according to claim 12, characterized in that: The powder OI value of the second graphite material is greater than 1.1 and less than or equal to 10; and / or, The gram capacity of the second negative electrode material is 350-365 mAh / g.

14. The negative electrode plate according to claim 12, characterized in that: The difference between the powder compaction density of the first negative electrode material and the second negative electrode material at 150 MPa is 0.05-0.60 g / cm 3 and / or, The difference in gram capacity between the first negative electrode material and the second negative electrode material is 5-36.3 mAh / g.

15. The negative electrode plate according to claim 12, characterized in that: The difference in gram capacity between the first negative electrode material and the second negative electrode material is 5-25 mAh / g.

16. The negative electrode plate according to claim 12, characterized in that: The secondary particles in the second graphite material account for 35% to 90% of the total number of particles in the second graphite material; and / or, The second graphite material further includes primary particles, and the ratio of the average particle size of the secondary particles in the second graphite material to the average particle size of the primary particles is 1.1-3.4; and / or, The average particle size of the secondary particles in the second graphite material is 8 μm to 25.3 μm.

17. The negative electrode plate according to claim 12, characterized in that: The secondary particles in the second graphite material account for 58% to 89% of the total number of particles in the second graphite material; and / or, The average particle size of the secondary particles in the second graphite material is 8 μm to 16 μm.

18. The negative electrode sheet according to claim 12, characterized in that: The surface of the second graphite material has a coating layer, and the coating layer includes carbon elements; and / or, The thickness of the coating layer is greater than 0 nm and less than or equal to 500 nm.

19. The negative electrode plate according to claim 12, characterized in that: The R value of the second negative electrode material is 0.13-0.25; and / or, The R50 value of the second negative electrode material is 1.0 - 1.4; The R value of the second negative electrode material is the ratio of the difference between the R90 value of the second negative electrode material and the R10 value of the second negative electrode material to the R50 value of the second negative electrode material; The plurality of particles of the second negative electrode material are D / I G Accumulate from small to large, when I D / I G The cumulative value reaches I D / I G I corresponding to 10% of the total value D / I G is R10 of the second negative electrode material, when I D / I G The cumulative value reaches I D / I G I corresponding to 50% of the total value D / I G is R50 of the second negative electrode material, when I D / I G The cumulative value reaches I D / I G I corresponding to 90% of the total value D / I G R90 of the second negative electrode material; In the Raman spectrum of a single particle of the second negative electrode material, the Raman shift is 1300 cm -1 ~ 1380cm -1 The intensity of the peak within the range is I D , Raman shift is 1520cm -1 ~ 1590cm -1 The intensity of the peak within the range is I G .

20. The negative electrode sheet according to claim 12, characterized in that: The powder OI value of the first graphite material is greater than 6 and less than or equal to 25, and the powder OI value of the first graphite material is the peak area ratio of the characteristic diffraction peak of the 004 crystal plane to the characteristic diffraction peak of the 110 crystal plane in the XRD spectrum of the first graphite material.

21. The negative electrode plate according to claim 12, characterized in that: The first graphite material comprises primary particles; and / or, The average particle size of the primary particles in the first graphite material is 8-19 μm; and / or, The first graphite material also includes secondary particles, and the secondary particles in the first graphite material account for 35% to 90% of the total number of particles in the first graphite material.

22. The negative electrode sheet according to any one of claims 12 to 21, characterized in that: The first negative electrode active layer also includes natural graphite material.

23. An electrical device, characterized in that: The electrical device comprises the lithium secondary battery according to any one of claims 1 to 11.

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