A lithium secondary battery, a negative electrode sheet for a lithium secondary battery, and an electric device

Abstract

The application belongs to the field of batteries, and relates to a lithium secondary battery, a negative electrode sheet for the lithium secondary battery, and an electric device. The lithium secondary battery comprises a negative electrode sheet, 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 and second negative electrode active layers respectively comprise first and second negative electrode materials, and the first and second negative electrode materials respectively comprise first and second graphite materials; the second graphite material powder has an OI value of 1 to 10; the first negative electrode material has a mass capacity greater than that of the second negative electrode material and a powder compaction density under a pressure of 150 MPa; the mass capacity of the second negative electrode material is 345-365 mAh / g; and the powder compaction density of the first negative electrode material under a pressure of 150 MPa is 1.70-2.10 g / cm 3 The application improves the energy density of the secondary battery while guaranteeing the high kinetic performance of the lithium secondary battery.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to lithium secondary batteries, negative electrode sheets for lithium secondary batteries, and electrical devices. Background Technology

[0002] In recent years, with the increasingly wide range of applications, batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. Due to the significant advancements in battery technology, higher demands have been placed on their fast-charging performance and energy density. Summary of the Invention

[0003] This application provides a lithium secondary battery, a negative electrode sheet for the lithium secondary battery, and an electrical device. This application improves the energy density of the secondary battery while ensuring high kinetic performance.

[0004] This application provides a lithium secondary battery, including a negative electrode sheet, the negative electrode sheet 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 the 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.

[0005] The powder OI value of the second graphite material is 1-10, and the powder OI value of the second graphite material is the ratio of the peak area 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;

[0006] The specific capacity of the first negative electrode material is greater than that of the second negative electrode material; the specific capacity of the second negative electrode material is 345-365 mAh / g; wherein, the specific capacity of the first negative electrode material or the specific 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 discharging the lithium secondary battery from 2.0V to 5mV at a constant current of 0.05C at room temperature;

[0007] The compacted powder density of the first negative electrode material at 150 MPa is greater than that of the second negative electrode material at 150 MPa; the compacted powder density of the first negative electrode material at 150 MPa is 1.70 - 2.10 g / cm³. 3 .

[0008] Therefore, based on anisotropic graphite materials with high specific capacity and a relatively large OI value (greater than 10 and less than or equal to 25), this application reduces the OI value of the second graphite material to 1-10 by granulation into secondary particles, while maintaining a high specific capacity of 345-365 mAh / g. Compared with isotropic graphite materials, this material has a higher specific capacity. While using a high-specific-capacity second graphite material for the second anode material, the specific capacity and powder compaction density of the first anode material are made higher than those of the second anode material, and the powder compaction density of the first anode material is 1.70-2.10 g / cm³. 3 This is beneficial for matching and balancing the contributions of the first and second anode materials to the overall energy density of the secondary battery; furthermore, the use of secondary graphite particles in the second anode material provides more channels for lithium-ion transport; thus, it is beneficial for improving the energy density of the secondary battery while ensuring its high dynamic performance.

[0009] In any embodiment, the OI value of the second graphite material powder is greater than 1.1 and less than or equal to 10; and / or,

[0010] The specific capacity of the second negative electrode material is 350-365 mAh / g.

[0011] Therefore, based on anisotropic graphite materials with high specific capacity and large OI value, this application reduces the OI value of the second graphite material by granulation into secondary particles, while maintaining the high specific capacity of the second anode material, which is beneficial to improve the overall energy density while ensuring the dynamic performance of the secondary battery.

[0012] 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 / cm³. 3 ; and / or,

[0013] The difference in specific capacity between the first negative electrode material and the second negative electrode material is 5 - 36.3 mAh / g or 5 - 25 mAh / g.

[0014] Since the specific capacity and powder compaction density of a material are related to the energy density of a secondary battery, the difference in powder compaction density and / or specific capacity between the first and second negative electrode materials can help improve the matching degree between the first and second negative electrode materials, so as to better balance the contribution of the first and second negative electrode materials to the energy density of the secondary battery, thereby further improving the overall energy density of the secondary battery.

[0015] 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. This provides more transport channels for lithium ions, ensuring the kinetic performance of the secondary battery and improving its energy density. On the other hand, it reduces the adverse effects of increased secondary particle proportion, such as particle agglomeration and difficulty in processing.

[0016] In any embodiment, the second graphite material further includes primary particles, and the ratio of the average particle size of the secondary particles to the average particle size of the primary particles in the second graphite material is 1.1–3.4. This facilitates the secondary particles being composed of more primary particles, providing more channels for lithium-ion transport and ensuring the kinetic performance of the secondary battery. Furthermore, an increase in the average particle size of the secondary particles may lead to a reduction in their contact area with the electrolyte, decreasing the interfacial reaction rate. The aforementioned ratio range mitigates the adverse effects of an increase in the average particle size of the secondary particles on the kinetic performance of the secondary battery.

[0017] 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 facilitates providing more channels for lithium-ion transport, thereby improving the kinetic performance of the secondary battery. Furthermore, it helps to reduce the impact on the interfacial reaction rate caused by the increased average particle size of the secondary particles leading to a reduced contact area with the electrolyte, thus further enhancing the kinetic performance of the secondary battery.

[0018] In any embodiment, the surface of the second graphite material has a coating layer comprising carbon elements; and / or,

[0019] The thickness of the coating layer is greater than 0 nm and ≤ 500 nm.

[0020] Therefore, the coating layer on the surface of the second graphite material facilitates the rapid conduction of lithium ions into the lattice of the second graphite material for embedding, thereby improving the dynamic 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.

[0021] In any embodiment, the R value of the second negative electrode material is 0.13 - 0.25; and / or,

[0022] The R50 value of the second negative electrode material is 1.0 - 1.4;

[0023] Wherein, the R value of the second negative electrode material is the ratio of the difference between the R90 value and the R10 value of the second negative electrode material to the R50 value of the second negative electrode material;

[0024] I of multiple particles of the second negative electrode material D / I G Accumulate from smallest to largest, when I D / I G The cumulative value reaches I D / I G I corresponding to 10% of the total value D / I G R10 is 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 R50 is 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 is the second negative electrode material;

[0025] The Raman shift of a single particle of the second negative electrode material is 1300 cm⁻¹. -1 ~ 1380cm -1 The intensity of the peak within the range is I D The Raman displacement is 1520 cm. -1 ~ 1590cm -1 The intensity of the peak within the range is I G .

[0026] Therefore, the above-mentioned R value range of the second negative electrode material can improve the uniformity of the coating layer on the surface of the second graphite material, which is beneficial to improve the more uniform conduction of lithium ions into the lattice of the second graphite material, thereby improving the dynamic performance of the secondary battery.

[0027] The aforementioned R50 value range of the second anode material is beneficial in two ways: firstly, it helps to increase the disorder on the surface of the second anode material, providing more channels or space for lithium-ion conduction and improving the fast-charging performance of the secondary battery; secondly, it reduces the impact of increased disorder on the surface of the second anode material on the high-temperature storage capacity of the secondary battery.

[0028] 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 ratio of the peak area 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.

[0029] Therefore, the first graphite material in the first negative electrode material is an anisotropic graphite material with high capacity and an 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.

[0030] In any embodiment, the first graphite material comprises primary particles. Therefore, the inclusion of primary particles in the first graphite material in the first negative electrode material facilitates matching and balancing with the second negative electrode material to improve the energy density of the secondary battery.

[0031] In any embodiment, the average particle size of the primary particles in the first graphite material is 8-19 μm. Therefore, the first graphite material in the first anode material includes large-diameter primary particles, which is beneficial for matching with the second anode material to improve the energy density of the secondary battery.

[0032] In any embodiment, the first graphite material further includes secondary particles, wherein the proportion of secondary particles in the total number of particles in the first graphite material 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 transport to improve the kinetic performance of the secondary battery, and on the other hand, reduce the impact of increasing the proportion of secondary particles on the battery energy density.

[0033] In some embodiments, the first negative electrode active layer further includes natural graphite material. Therefore, the use of natural graphite material in the first negative electrode material, with its porous structure, allows for good contact between the natural material and the electrolyte, which is beneficial for improving the kinetic performance of the secondary battery.

[0034] A second aspect of this 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 the 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.

[0035] The powder OI value of the second graphite material is 1-10, and the powder OI value of the second graphite material is the ratio of the peak area 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;

[0036] The specific capacity of the first negative electrode material is greater than that of the second negative electrode material; the specific capacity of the second negative electrode material is 345-365 mAh / g; wherein, the specific capacity of the first negative electrode material or the specific 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 discharging the lithium secondary battery from 2.0V to 5mV at a constant current of 0.05C at room temperature;

[0037] The compacted powder density of the first negative electrode material at 150 MPa is greater than that of the second negative electrode material at 150 MPa; the compacted powder density of the first negative electrode material at 150 MPa is 1.70 - 2.10 g / cm³. 3 .

[0038] Therefore, based on anisotropic graphite materials with high specific capacity and a relatively large OI value (greater than 10 and less than or equal to 25), this application reduces the OI value of the second graphite material to 1-10 by granulation into secondary particles, while maintaining a high specific capacity of 345-365 mAh / g. Compared with isotropic graphite materials, this material has a higher specific capacity. While using a high-specific-capacity second graphite material for the second anode material, the specific capacity and powder compaction density of the first anode material are made higher than those of the second anode material, and the powder compaction density of the first anode material is 1.70-2.10 g / cm³. 3 This is beneficial for matching and balancing the contributions of the first and second anode materials to the overall energy density of the secondary battery; furthermore, the use of secondary graphite particles in the second anode material provides more channels for lithium-ion transport; thus, it is beneficial for improving the energy density of the secondary battery while ensuring its high dynamic performance.

[0039] In any embodiment, the OI value of the second graphite material powder is greater than 1.1 and less than or equal to 10; and / or,

[0040] The specific capacity of the second negative electrode material is 350-365 mAh / g.

[0041] 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 / cm³. 3 ; and / or,

[0042] The difference in specific capacity between the first negative electrode material and the second negative electrode material is 5 - 36.3 mAh / g or 5 - 25 mAh / g.

[0043] 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,

[0044] The second graphite material further includes primary particles, and the ratio of the average particle size of the secondary particles to the average particle size of the primary particles in the second graphite material is 1.1 – 3.4; and / or,

[0045] The average particle size of the secondary particles in the second graphite material is 8 μm – 25.3 μm or 8 μm – 16 μm.

[0046] In any embodiment, the surface of the second graphite material has a coating layer comprising carbon elements; and / or,

[0047] The thickness of the coating layer is greater than 0 nm and ≤ 500 nm.

[0048] In any embodiment, the R value of the second negative electrode material is 0.13 - 0.25; and / or,

[0049] The R50 value of the second negative electrode material is 1.0 - 1.4;

[0050] Wherein, the R value of the second negative electrode material is the ratio of the difference between the R90 value and the R10 value of the second negative electrode material to the R50 value of the second negative electrode material;

[0051] I of multiple particles of the second negative electrode material D / I G Accumulate from smallest to largest, when I D / I G The cumulative value reaches I D / I G I corresponding to 10% of the total value D / I G R10 is 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 R50 is 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 is the second negative electrode material;

[0052] The Raman shift of a single particle of the second negative electrode material is 1300 cm⁻¹. -1 ~ 1380cm -1 The intensity of the peak within the range is I D The Raman displacement is 1520 cm. -1 ~ 1590cm -1 The intensity of the peak within the range is I G .

[0053] 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 ratio of the peak area 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.

[0054] In any embodiment, the first graphite material comprises primary particles; and / or,

[0055] The average particle size of the primary particles in the first graphite material is 8-19 μm; and / or,

[0056] The first graphite material also includes secondary particles, and the proportion of secondary particles in the total number of particles in the first graphite material is 35% - 90% or 50% - 80%.

[0057] In any embodiment, the first negative electrode active layer further includes natural graphite material.

[0058] A third aspect of this application provides an electrical device, including the lithium secondary battery of the first aspect of this application. Attached Figure Description

[0059] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0060] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0061] Figure 2 yes Figure 1 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0062] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0063] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0064] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0065] Figure 6 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0066] Figure 7 This is a SEM image of the second graphite material in Embodiment 1 of this application;

[0067] Figure 8 This is a magnified SEM image of the secondary particles in the second graphite material of Embodiment 1 of this application.

[0068] The accompanying drawings are not drawn to scale.

[0069] Explanation of reference numerals in the attached figures:

[0070] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0071] The embodiments of this application will be described in further detail below with reference to the accompanying drawings and examples. The detailed description of the following embodiments and the accompanying drawings are used to illustrate the principles of this application by way of example, but should not be used to limit the scope of this application, that is, this application is not limited to the described embodiments.

[0072] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the secondary battery, battery module, battery pack, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0073] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0074] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0075] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0076] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0077] Unless otherwise specified, the terms "comprising" and "including" as used in this application are open-ended. For example, "comprising" and "including" may mean that other components not listed may also be included or contained.

[0078] Unless otherwise specified, the term "or" is inclusive in this application. 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).

[0079] [Rechargeable Battery]

[0080] Secondary batteries, also known as rechargeable batteries or storage batteries, are batteries that can be recharged after being discharged to activate the active materials and continue to be used.

[0081] Typically, a secondary battery consists of a positive electrode, a negative electrode, a separator, and an electrolyte. During charging and discharging, active ions (such as lithium ions) repeatedly insert and extract between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing active ions to pass through. The electrolyte, also positioned between the positive and negative electrodes, mainly serves to conduct active ions.

[0082] One embodiment of this application provides a lithium secondary battery, including a negative electrode sheet, the negative electrode sheet including a negative current collector, a first negative active layer located on at least one side of the negative current collector, and a second negative active layer located on the side of the first negative active layer away from the negative current collector; the first negative active layer includes a first negative electrode material, the second negative 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.

[0083] 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 any range of the above values). The powder OI value of the second graphite material is the ratio of the peak area of ​​the characteristic diffraction peak of the 004 crystal plane to the characteristic diffraction peak of the 110 crystal plane in the XRD pattern of the second graphite material. The second graphite material includes secondary particles.

[0084] The specific capacity of the first negative electrode material is greater than that of the second negative electrode material; the specific capacity of the second negative electrode material is 345-365 mAh / g (e.g., 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 any range of the above values); wherein, the specific capacity of the first negative electrode material or the specific 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 discharging the lithium secondary battery from 2.0V at a constant current of 0.05C to 5mV at room temperature;

[0085] The compacted powder density of the first negative electrode material at 150 MPa is greater than that of the second negative electrode material at 150 MPa; the compacted powder density of the first negative electrode material at 150 MPa is 1.70 - 2.10 g / cm³. 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 a range consisting of any of the above values).

[0086] In existing negative electrode sheets that include a double-layer negative electrode active layer, the upper negative electrode active layer, farther from the negative electrode current collector, typically uses secondary particles of isotropic graphite material with a low OI value as the negative electrode material to improve the fast-charging performance of the secondary battery. Meanwhile, the lower negative electrode active layer, closer to the negative electrode current collector, typically uses single particles of graphite material with a higher specific 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, there are many unrepaired interfaces, making lithium-ion insertion / extraction difficult and resulting in low specific capacity. Typically, the specific capacity of isotropic graphite materials with low OI values ​​is below 340 mAh / g, thus leading to a decrease in the energy density of the secondary battery cell.

[0087] To address the aforementioned technical issues, this application, based on anisotropic graphite materials with high specific capacity and a relatively large OI value (greater than 10 and less than or equal to 25), reduces the OI value of the second graphite material to 1-10 by granulation into secondary particles, while maintaining a high specific capacity of 345-365 mAh / g. Compared to isotropic graphite materials, this second graphite material exhibits higher crystal order, facilitates lithium-ion insertion / extraction, and results in a higher specific capacity. Furthermore, while employing a high-specific-capacity second graphite material for the second anode material, the specific capacity and powder compaction density of the first anode material are made higher than those of the second anode material, with the powder compaction density of the first anode material being 1.70-2.10 g / cm³. 3 This is beneficial for matching and balancing the contributions of the first and second anode materials to the overall energy density of the secondary battery. Furthermore, the use of secondary graphite particles in the second anode material enriches the number of channels for lithium ions to be inserted and extracted within the material lattice, providing more channels for lithium ion transport and ensuring the kinetic performance of the secondary battery. Thus, it is beneficial to improve the energy density of the secondary battery while ensuring its high kinetic performance.

[0088] In some embodiments, the OI value of the second graphite material powder is greater than 1.1 and less than or equal to 10; and / or,

[0089] The specific capacity of the second negative electrode material is 350-365 mAh / g.

[0090] Therefore, based on anisotropic graphite materials with high specific capacity and large OI value, this application reduces the OI value of the second graphite material by granulation into secondary particles, while maintaining the high specific capacity of the second anode material, which is beneficial to improve the overall energy density while ensuring the dynamic performance of the secondary battery.

[0091] 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 / cm³. 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 / cm3 0.4 g / cm 3 0.5 g / cm 3 0.6 g / cm 3 Or a range of any of the above values; and / or,

[0092] The difference in specific capacity between 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 any range of the above values.

[0093] Since the specific capacity and powder compaction density of a material are related to the energy density of a secondary battery, the difference in powder compaction density and / or specific capacity between the first and second negative electrode materials can help improve the matching degree between the first and second negative electrode materials, so as to better balance the contribution of the first and second negative electrode materials to the energy density of the secondary battery, thereby further improving the overall energy density of the secondary battery.

[0094] In some embodiments, the powder compaction density of the second negative electrode material at 150 MPa is 1.45-1.85 g / cm³. 3 For example, 1.45 g / cm³ 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 a range consisting of any of the above values.

[0095] In some embodiments, the specific 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 any range of the above values.

[0096] In this application, the method for testing the OI value of graphite powder is well known in the art. As an example, the secondary battery is disassembled, the negative electrode sheet is removed, cleaned and dried, and the negative electrode material on the active layer of the negative electrode is scraped off. Observation is performed using a scanning electron microscope. Since the particle morphology of graphite material is different from that of additives (binders, conductive agents, etc.), the OI value of graphite powder can be tested based on the national standard GB / T 24533-2019 to obtain an X-ray diffraction pattern. The OI value of the graphite powder is calculated according to the formula OI=C004 / C110, where C004 is the peak area of ​​the 004 characteristic diffraction peak in the X-ray diffraction pattern, and C110 is the peak area of ​​the 110 characteristic diffraction peak in the X-ray diffraction pattern.

[0097] In this application, "room temperature" has the common definition in the art; for example, it can generally be between approximately 15°C and 30°C.

[0098] In this application, the powder compaction density of the first or second negative electrode material at 150 MPa is tested using conventional methods in the art. An example test method may be as follows: disassemble the secondary battery, remove the negative electrode sheet, clean and dry it, scrape off the negative electrode material of the first or second negative electrode active layer, take a certain mass of powder sample (e.g., 50-100 g) and place it in a compaction density mold, then place the compaction density mold on a compaction density instrument, apply a constant pressure of 150 MPa and maintain it for a certain time (e.g., 1-5 minutes) to compact the powder, measure and calculate the volume of the compacted block using a vernier caliper or laser rangefinder, and calculate the powder compaction density of the first or second negative electrode material at 150 MPa based on the mass of the powder and the volume of the compacted block.

[0099] In this application, the method for testing the specific capacity of the first or second negative electrode material is well known in the art. An example testing method may be as follows: Disassemble the secondary battery, remove the negative electrode sheet, clean and dry it, scrape off the negative electrode material from the first or second negative electrode active layer, take a certain mass of the negative electrode material to make a positive electrode slurry, coat it onto the positive electrode current collector aluminum foil, and dry it to obtain a positive electrode sheet. Use lithium metal as the negative electrode sheet, and assemble the secondary battery using a conventional separator (e.g., polyethylene film) and electrolyte (e.g., a solution containing 1 mol / L lithium hexafluorophosphate in a ethylene carbonate / methyl ethyl carbonate / diethyl carbonate solution, volume ratio 1:1:1). At room temperature, charge the secondary battery to 2.0V, then discharge it at a constant current of 0.05C from 2.0V to 5mV to obtain the discharge capacity. Calculate the ratio of the discharge capacity to the mass of the negative electrode material to obtain the specific capacity of the first or second negative electrode material.

[0100] 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, for example, 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 transport channels for lithium ions, ensuring the kinetic performance of the secondary battery and improving its energy density; on the other hand, it reduces the adverse effects of increased secondary particle proportion, such as particle agglomeration and difficulty in processing.

[0101] In this 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.

[0102] In some embodiments, the second graphite material further includes primary particles, and the ratio of the average particle size of the secondary particles to the average particle size of the primary particles in the second graphite material is 1.1–3.4, for example, 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 any range of the above values. This is beneficial because the secondary particles consist of more primary particles, providing more channels for lithium-ion transport and ensuring the kinetic performance of the secondary battery. Furthermore, an increase in the average particle size of the secondary particles may lead to a reduction in their contact area with the electrolyte, decreasing the interfacial reaction rate; the aforementioned ratio range reduces the adverse effects of an increase in the average particle size of the secondary particles on the kinetic performance of the secondary battery.

[0103] 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, for example, 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 combination of the above values. This is beneficial for providing more channels for lithium-ion transport, thereby improving the kinetic performance of the secondary battery. Furthermore, it helps to reduce the impact on the interfacial reaction rate caused by the increased average particle size of the secondary particles leading to a reduced contact area with the electrolyte, thus further enhancing the kinetic performance of the secondary battery.

[0104] In this application, the proportion of secondary graphite particles in the total number of graphite particles is tested using conventional methods in the art. An example testing method could be: disassembling the secondary battery, removing the negative electrode sheet, cleaning and drying it, scraping off the negative electrode material, dispersing the negative electrode material using vacuum negative pressure airflow dispersion technology, and obtaining a scanning electron microscope (SEM) image of the dispersed negative electrode material using a scanning electron microscope (e.g., ZEISS Sigma 300). The morphology of the graphite particles differs from that of additives (binders, conductive agents, etc.), making them distinguishable. As an example, the test could be conducted as follows: randomly selecting multiple test areas (e.g., 5), and at a certain magnification (e.g., 1000x), counting the number of secondary graphite particles (which can be distinguished from primary particles based on the surface roughness) and the total number of graphite particles (including primary and secondary particles) in each test area. The number of secondary graphite particles and the total number of graphite particles in each test area are then summed, and the proportion of secondary graphite particles in the total number of graphite particles is calculated. To ensure the accuracy of the test results, the above test can be repeated multiple times, and the average value can be taken as the final test result.

[0105] In this application, the average particle size of the primary and secondary particles of the graphite material can be tested using equipment and methods known in the art. An example testing method could be: disassembling the secondary battery, removing the negative electrode sheet, cleaning and drying it, scraping off the negative electrode material, dispersing the negative electrode material using a vacuum negative pressure airflow dispersion technique, and obtaining a scanning electron microscope (SEM) image of the dispersed negative electrode material using a scanning electron microscope (e.g., ZEISS Sigma 300). Since the graphite material particles differ in morphology from those of additives (binders, conductive agents, etc.), they can be distinguished. As an example, the test can be conducted as follows: Randomly select multiple test areas (e.g., 5), and at a certain magnification (e.g., 1000x), primary and secondary particles can be distinguished based on the surface roughness of the particles. Measure the particle size of the primary and secondary graphite particles in each test area (i.e., take the distance between the two furthest points on either a primary or secondary particle as the particle size). Count the particle size and number of secondary graphite particles in each test area, and take the arithmetic mean of the primary and secondary particle sizes in each test area. This arithmetic mean is the average particle size of the primary and secondary graphite particles in the test sample. To ensure the accuracy of the test results, the above test can be repeated multiple times, and the average value can be taken as the final test result.

[0106] In some embodiments, the surface of the second graphite material has a coating layer comprising carbon elements; and / or,

[0107] 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 any range of the above values.

[0108] Therefore, the coating layer on the surface of the second graphite material facilitates the rapid conduction of lithium ions into the lattice of the second graphite material for embedding, thereby improving the dynamic 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.

[0109] In this application, the thickness of the coating layer on the surface of the second graphite material can be tested using conventional methods in the art. As an example, the test method can be: disassemble the secondary battery, remove the negative electrode sheet, clean and dry it, observe it with a scanning electron microscope, and distinguish the graphite material particles from the morphology of the additives (binders, conductive agents, etc.). Then, cut the graphite particles with an ion beam and observe the cross-section of the graphite particles with a scanning electron microscope to test the thickness of its coating layer.

[0110] 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 of the above values; and / or,

[0111] 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 any range of the above values;

[0112] Wherein, the R value of the second negative electrode material is the ratio of the difference between the R90 value and the R10 value of the second negative electrode material to the R50 value of the second negative electrode material;

[0113] I of multiple particles of the second negative electrode material D / I G Accumulate from smallest to largest, when I D / I G The cumulative value reaches I D / I G I corresponding to 10% of the total value D / I G R10 is 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 R50 is 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 is the second negative electrode material;

[0114] The Raman shift of a single particle of the second negative electrode material is 1300 cm⁻¹. -1 ~ 1380cm-1 The intensity of the peak within the range is I D The Raman displacement is 1520 cm. -1 ~ 1590cm -1 The intensity of the peak within the range is I G .

[0115] Therefore, the above-mentioned R value range of the second negative electrode material can improve the uniformity of the coating layer on the surface of the second graphite material, which is beneficial to improve the more uniform conduction of lithium ions into the lattice of the second graphite material, thereby improving the dynamic performance of the secondary battery.

[0116] The aforementioned R50 value range of the second anode material is beneficial in two ways: firstly, it helps to increase the disorder on the surface of the second anode material, providing more channels or space for lithium-ion conduction and improving the fast-charging performance of the secondary battery; secondly, it reduces the impact of increased disorder on the surface of the second anode material on the high-temperature storage capacity of the secondary battery.

[0117] In this application, the intensity of a peak within a certain Raman displacement range refers to the maximum intensity value within that Raman displacement range in the Raman spectrum.

[0118] In this application, the Raman spectra of individual particles of the second anode material are tested using conventional methods in the art; for example, a Renishaw confocal micro Raman spectrometer is used to perform surface-by-point scanning of individual particles of the second anode material; wherein the area of ​​surface-by-point scanning is 100μm×100μm, the scanning step size 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%.

[0119] 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 (e.g., 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25 or any range of the above values), and the powder OI value of the first graphite material is the ratio of the peak area 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.

[0120] Therefore, the first graphite material in the first negative electrode material is an anisotropic graphite material with high capacity and an 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.

[0121] In some embodiments, the first graphite material comprises primary particles. Therefore, the inclusion of primary particles in the first graphite material in the first negative electrode material facilitates matching and balancing with the second negative electrode material to improve the energy density of the secondary battery.

[0122] In some embodiments, the average particle size of the primary particles in the first graphite material is 8-19 μm, for example, 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 of the above values. Therefore, the first graphite material in the first negative electrode material includes large-diameter primary particles, which is beneficial for matching with the second negative electrode material to improve the energy density of the secondary battery.

[0123] In this application, the average particle size of the primary particles in the first graphite material is tested in accordance with the method described above.

[0124] In some embodiments, the first graphite material further includes secondary particles, wherein the proportion of secondary particles in the total number of particles in the first graphite material is 35%-90% or 50%-80%, for example, 35%, 40%, 50%, 60%, 70%, 80%, 84%, 90%, or any range of the above values. Therefore, adding secondary particles to the first graphite material in the first anode material can, on the one hand, provide more channels for lithium-ion transport to improve the kinetic performance of the secondary battery, and on the other hand, reduce the impact of increasing the proportion of secondary particles on the energy density of the secondary battery.

[0125] In this application, the proportion of secondary particles in the total number of particles in the first graphite material is tested in accordance with the method described above.

[0126] In some embodiments, the first graphite material includes secondary particles with an average particle size of 12-22 μm. This provides more channels for lithium-ion transport, thus improving the kinetic performance of the secondary battery, and also helps to reduce the impact on the kinetic performance of the secondary battery caused by the increased average particle size of the secondary particles leading to a reduced contact area with the electrolyte.

[0127] In this application, the average particle size of the secondary particles in the first graphite material is tested in accordance with the method described above.

[0128] In some embodiments, the first negative electrode active layer further includes natural graphite material. Therefore, the use of natural graphite material in the first negative electrode material, with its porous structure, allows for good contact between the natural material and the electrolyte, which is beneficial for improving the kinetic performance of the secondary battery.

[0129] [Negative electrode plate]

[0130] One embodiment of this application provides a method for preparing graphite materials, comprising the following steps:

[0131] Anisotropic raw coke particles are mixed with a binder and subjected to a first heat treatment to obtain an intermediate material;

[0132] The graphitized product obtained by graphitizing the intermediate material is the graphite material.

[0133] In some embodiments, the method further includes: mixing the graphitized product with a carbon source and subjecting it to a second heat treatment to obtain a graphite material with a carbon-containing coating on its surface.

[0134] In some embodiments, the proportion of streamline structure in the polarized photographs of anisotropic coke particles is 7%-99%, for example, 7%, 10%, 13%, 20%, 30%, 40%, 50%, 60%, 63%, 70%, 80%, 83%, 90%, 97%, 99%, or any range of the above values.

[0135] In some embodiments, the average particle size of the raw coke particles is 6μm-15μm, for example 6μm, 6.3μm, 7.3μm, 7.4μm, 7.5μm, 7.6μm, 8μm, 9μm, 10μm, 12μm, 14μm, 15μm or any range of the above values.

[0136] 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, for example, 1.2, 1.5, 1.9, 2, 3, 3.4, 4 or any range of the above values.

[0137] Therefore, the above-mentioned ratio range of the average particle size of secondary graphite particles to the average particle size of raw coke particles is beneficial to improving the fast charging performance of battery cells and reducing the impact on lithium-ion transport rate caused by the decrease in the contact area between the secondary graphite particles and the electrolyte due to the increase in the size of the secondary graphite particles.

[0138] In some embodiments, the mass ratio of binder to raw coke particles is 2.3% – 20%, for example 2.3%, 4%, 10%, 20%.

[0139] In some embodiments, the mass ratio of carbon source to graphitized product is 2% to 20%, for example, 2%, 5%, 5.8%, 7%, 8%, 10%, 13%, 15%, 17%, 20%, or any combination of the above values.

[0140] 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 any range of the above values) and the time is 3-9h (e.g., 3h, 3.6h, 4h, 6h, 9h or any range of the above values).

[0141] In some embodiments, the temperature of the second heat treatment is 700-1300°C (e.g., 700°C, 800°C, 900°C, 1000°C, 1150°C, 1200°C, 1300°C or any range of the above values) and the time is 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 of the above values).

[0142] In some embodiments, the graphitization treatment temperature is 2800℃ - 3800℃ (e.g., 2900℃, 3000℃, 3100℃, 3300℃, 3500℃, 3600℃, 3800℃ or any range of the above values), and the graphitization treatment time is 20 days - 40 days (e.g., 20 days, 25 days, 30 days, 33 days, 35 days, 38 days, 40 days or any range of the above values).

[0143] In some embodiments, the raw coke particles are obtained by crushing and shaping the raw coke.

[0144] In some embodiments, the method further includes: sieving and demagnetizing the product.

[0145] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0146] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate 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.).

[0147] In some embodiments, the negative electrode material may also employ other negative electrode active materials known in the art for use in batteries. As examples, the negative electrode material may include at least one of the following: soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0148] In some embodiments, the negative electrode active layer may optionally 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).

[0149] In some embodiments, the negative electrode active layer may optionally 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.

[0150] In some embodiments, the negative electrode active layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0151] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0152] [Positive electrode plate]

[0153] In some embodiments, the positive electrode can be a positive electrode sheet, which may include a positive current collector and a positive active material disposed on at least one surface of the positive current collector.

[0154] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material is disposed on either or both of the two opposite surfaces of the positive current collector.

[0155] As an example, the positive current collector can be a metal foil, a conductive polymer material, a carbon material, or a composite current collector. For example, as a metal foil, pure metals, alloys, or surface-treated metals can be used, including but not limited to stainless steel, copper, aluminum, nickel, titanium, or silver. The composite current collector may include a polymer material base layer and a metal layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0156] In some embodiments, the battery cell is a lithium-ion battery, and the positive electrode active material can be a positive electrode active material known in the art for lithium-ion batteries. The positive electrode active material may include at least one of the following materials: lithium phosphate, lithium transition metal oxide, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium phosphate include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4, also referred to as LFP), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium iron manganese phosphate and carbon composites. Examples of lithium transition metal oxides 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, and 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 At least one of O2 and its modified compounds. Modified compounds refer to substances obtained by modification methods such as doping or coating based on the above-mentioned substances.

[0157] During the charging and discharging process, the battery produces active ions (Li). + Due to the intercalation and deintercalation of Li, the molar content of Li varies when the battery is discharged to different states. In the examples of positive electrode active materials in this application, the molar content of Li refers to the initial state of the material, i.e., the state before feeding. When the positive electrode active material is applied to the battery system, the molar content of Li will change after charge-discharge cycles.

[0158] In the examples of positive electrode active materials in this application, the molar content of oxygen is only a theoretical value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of oxygen will fluctuate.

[0159] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0160] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0161] In some embodiments, the positive electrode can be a foamed metal. The foamed metal can be foamed nickel, foamed copper, foamed aluminum, foamed alloy, or foamed carbon, etc. When foamed metal is used as the positive electrode, the surface of the foamed metal may or may not contain a positive electrode active material. As an example, a positive electrode active material is filled and / or deposited within the foamed metal.

[0162] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0163] [Electrolytes]

[0164] In some embodiments, the battery cell also includes an electrolyte, which acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. The electrolyte can be liquid, gel, or solid.

[0165] Liquid electrolytes include electrolyte salts and solvents.

[0166] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0167] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone. The solvent may also be an ether solvent. Ether solvents may 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, methyl tetrahydrofuran, diphenyl ether, and crown ethers.

[0168] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain properties of the battery cell, such as additives that improve the overcharge / fast charge performance of the battery cell, additives that improve the high-temperature performance of the battery cell, and additives that improve the low-temperature performance of the battery cell.

[0169] The gel electrolyte includes a polymer as a backbone network and can be used in conjunction with an ionic liquid-lithium salt.

[0170] Solid electrolytes include polymer solid electrolytes, inorganic solid electrolytes, and composite solid electrolytes.

[0171] As an example, the polymers of polymeric solid electrolytes may include polyethers (polyoxyethylene), polysiloxanes, polycarbonates, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, monoionic polymers, polyionic liquids, cellulose, etc.

[0172] As an example, inorganic solid electrolytes can be one or more of the following: oxide solid electrolytes (crystalline perovskite, sodium superconducting ion conductor, garnet, amorphous LiPON thin film), sulfide solid electrolytes (crystalline lithium superconducting ion conductor (lithium germanium phosphorus sulfide, silver sulfide germanium ore), amorphous sulfides), halide solid electrolytes, nitride solid electrolytes, and hydride solid electrolytes.

[0173] As an example, composite solid electrolytes are formed by adding inorganic solid electrolyte fillers to polymer solid electrolytes.

[0174] [Isolation Component]

[0175] In some embodiments, the electrode assembly further includes an isolator disposed between the positive and negative electrodes.

[0176] In some embodiments, the separator is a separator membrane. This application does not impose any particular limitation on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0177] 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 particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation. The separator can be a single component located between the positive and negative electrodes, or it can be attached to the surfaces of the positive and negative electrodes. An inorganic particle coating, an organic particle coating, or an organic / inorganic composite coating can also be applied to the surface of the separator.

[0178] In some embodiments, the separator is a solid electrolyte. The solid electrolyte is disposed between the positive and negative electrodes, serving both to transport ions and to isolate the positive and negative electrodes.

[0179] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0180] [Structure of the electrode assembly]

[0181] The electrode assembly can be a wound structure, a stacked structure, or a hybrid structure of wound and stacked.

[0182] In some implementations, the electrode assembly is a wound structure. The positive and negative electrode sheets are wound into a wound structure.

[0183] In some implementations, the electrode assembly is a stacked structure.

[0184] As an example, multiple positive and negative electrodes can be set, and multiple positive and multiple negative electrodes can be stacked alternately.

[0185] As an example, multiple positive electrode plates can be provided, and negative electrode plates can be folded to form multiple stacked folded segments, with a positive electrode plate sandwiched between adjacent folded segments.

[0186] As an example, both the positive and negative electrode plates are folded to form multiple stacked folded segments.

[0187] As an example, multiple separators can be provided, each positioned between any adjacent positive or negative electrode plates.

[0188] As an example, the separators can be continuously arranged, either by folding or rolling between any adjacent positive or negative electrode plates.

[0189] In some embodiments, the electrode assembly can be cylindrical, flat, or polygonal, etc.

[0190] In some embodiments, the electrode assembly is provided with tabs that allow current to be drawn from the electrode assembly. The tabs include a positive tab and a negative tab.

[0191] [shell]

[0192] In some embodiments, the battery cell may include a casing. The casing may be a steel casing, an aluminum casing, a plastic casing (such as a polypropylene casing), a composite metal casing (such as a copper-aluminum composite casing), or an aluminum-plastic film, etc. In some embodiments, the casing may be a sealed structure or a non-sealed structure. As an example, when the casing is a non-sealed structure, the casing serves to protect the electrode assembly, and a sealing bag is included between the casing and the electrode assembly to encapsulate the electrode assembly and electrolyte. Specifically, the sealing bag may be a bag-shaped insulating component or an aluminum-plastic film. When the casing is a sealed structure, it is used to encapsulate components such as the electrode assembly and electrolyte.

[0193] As an example, the battery cell can be a cylindrical battery cell, a prismatic battery cell, a pouch battery cell, or a battery cell of other shapes. Prismatic battery cells include prismatic battery cells, blade-shaped battery cells, and multi-prismatic batteries, such as hexagonal prismatic batteries. This application does not have any particular limitations.

[0194] In some embodiments, the housing includes an end cap and a housing, the housing having an opening, and the end cap covering the opening. The housing may have one or more openings. The end cap may also have one or more.

[0195] [Electrode terminals]

[0196] In some embodiments, at least one electrode terminal is provided on the housing, and the electrode terminal is electrically connected to the tab. The electrode terminal can be directly connected to the tab, or it can be indirectly connected to the tab through a current collector. The electrode terminal can be provided on the end cap or on the housing.

[0197] [Pressure relief mechanism]

[0198] In some embodiments, a pressure relief mechanism is provided on the casing. The pressure relief mechanism is used to release the internal gas of the battery cell.

[0199] As an example, the internal pressure or temperature of a battery cell is actuated to release the internal pressure or temperature when it reaches a predetermined threshold. When the internal pressure or temperature of the battery cell reaches the predetermined threshold, the pressure relief mechanism is activated or a weak structure in the pressure relief mechanism is broken, thereby creating an opening or channel for the internal pressure or temperature to be released. The threshold design varies depending on the design requirements. The threshold may depend on the materials of one or more of the positive electrode, negative electrode, electrolyte, and separator in the battery cell.

[0200] As an example, the pressure relief mechanism can be integrally molded with the housing.

[0201] As an example, the pressure relief mechanism can also be separately installed and connected to the housing.

[0202] The term "actuation" as used in this application refers to the activation or actuation of the pressure relief mechanism to a certain state, thereby releasing the internal pressure and temperature of the battery cell. The actions of the pressure relief mechanism may include, but are not limited to: movement of components within the mechanism to form an exhaust channel, rupture, breakage, tearing, or opening of at least a portion of the mechanism, etc. When the pressure relief mechanism is activated, the high-temperature, high-pressure substances inside the battery cell are discharged as waste from the activated portion. This method allows for pressure and temperature relief of the battery cell under controllable pressure or temperature, thereby preventing potentially more serious accidents.

[0203] In some embodiments, when the housing is a non-sealed structure, the pressure relief mechanism can be configured as a through hole for venting gas inside the battery cell.

[0204] The emissions from battery cells mentioned in this application include, but are not limited to: electrolyte, dissolved or split positive and negative electrode plates, fragments of separators, high-temperature and high-pressure gases generated by the reaction, flames, etc.

[0205] [Battery Device]

[0206] The battery apparatus mentioned in the embodiments of this application may include one or more battery cell assemblies for providing voltage and capacity. A battery cell assembly may include multiple battery cells connected in series, parallel, or mixed connections via a busbar.

[0207] In some embodiments, a battery cell assembly is typically formed by arranging multiple battery cells.

[0208] As an example, a battery cell assembly can be a battery module, which is formed by arranging and fixing multiple battery cells together to form an independent module. As another example, a battery module can be formed by bundling multiple battery cells together with cable ties.

[0209] In some embodiments, the battery device may be a battery pack, which includes a housing and one or more individual battery cells housed within the housing.

[0210] As an example, the battery cell assembly can be a battery module, which can be housed in a housing by fixing the battery module in the housing.

[0211] As an example, battery cell assemblies can also be housed in a housing by directly fixing multiple battery cells to the housing.

[0212] As an example, the enclosure may include a first enclosure and a second enclosure. The first enclosure and the second enclosure are fastened together to form a closed space inside the enclosure to house the individual battery cells. Here, "closed" refers to covering or closing, and can be either sealed or unsealed. The first enclosure may be a top cover or a bottom plate.

[0213] As an example, the enclosure may include a top cover, a frame, and a bottom plate. The top cover and bottom plate are connected to the frame, creating an enclosed space inside the enclosure to house the individual battery cells.

[0214] In some embodiments, the housing may be part of the vehicle's chassis structure. For example, a portion of the housing may be at least a part of the vehicle's floor, or a portion of the housing may be at least a part of the vehicle's crossbeams and longitudinal beams.

[0215] The technical solutions described in the embodiments of this application are applicable to various electrical devices that use individual battery cells, such as mobile phones, portable devices, laptops, electric vehicles, electric toys, power tools, vehicles, ships, and spacecraft. For example, spacecraft include airplanes, rockets, space shuttles, and spacecraft.

[0216] For example, Figure 1 The example shown is a square-structured battery cell 5.

[0217] In some implementations, refer to Figure 2 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in a single battery cell 5 may be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0218] In some implementations, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0219] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0220] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0221] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0222] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0223] In addition, this application also provides an electrical device, which includes at least one of the battery cell, battery module, or battery pack provided in this application. The battery cell, battery module, or battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, 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.

[0224] As an electrical device, you can choose individual battery cells, battery modules, or battery packs according to your usage requirements.

[0225] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of individual battery cells, a battery pack or battery module can be used.

[0226] [Example]

[0227] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially. Example 1

[0228] (1) Preparation of the second graphite material:

[0229] In the polarized light image of anisotropic petroleum coke, the streamline structure accounts for 83%. The anisotropic petroleum coke was ground and shaped to obtain aggregate with an average particle size of 7.4 μm. The aggregate and binder pitch were mixed at a mass ratio of 10:1 and placed in a horizontal reactor. The mixture was heated to 445℃ and held for 3.6 hours, then cooled to ≤50℃ and discharged. The particle size was controlled to a suitable level through deagglomeration to obtain intermediate material. The granulation degree (average particle size of intermediate material divided by average particle size of aggregate) was 1.9. The intermediate material was graphitized in an Atchison furnace at 3000℃ for 33 days to obtain graphitized product. The graphitized product and coating pitch were mixed at a mass ratio of 100:5.8 and placed in a horizontal reactor. The mixture was heated to 1150℃ and held for 12 hours. After sieving and demagnetization, a second graphite material was obtained with a finished particle size of 13.7 μm and a carbon coating layer thickness of 274 nm.

[0230] SEM images of the second graphite material and magnified SEM images of the secondary particles are shown below. Figure 7-8As shown, the second graphite material contains a certain number of secondary particles.

[0231] The parameters of the second graphite material are shown in Table 1.

[0232] (2) Preparation of negative electrode sheet:

[0233] A first graphite material with an OI value of 11 and an average primary particle size of 16.4 μm, sodium carboxymethyl cellulose as a dispersant, styrene-butadiene rubber (SBR) as a binder, and carbon black as a conductive agent were mixed at a mass ratio of 96.4:1.1:2.0:0.4. This mixture was then combined with deionized water under vacuum stirring to prepare a negative electrode slurry. This slurry was uniformly coated onto the copper foil of the negative electrode current collector. After air-drying at room temperature, it was transferred to an oven for further drying, forming the first negative electrode active layer on one side of the current collector. The compacted density of the first negative electrode material at 150 MPa was 1.79 g / cm³. 3 .

[0234] The second graphite material, dispersant sodium carboxymethyl cellulose, binder styrene-butadiene rubber (SBR), and conductive agent carbon black were mixed in a mass ratio of 97.2:1.1:0.8:0.7 and then mixed with deionized water in a vacuum mixer to prepare a negative electrode slurry. This slurry was uniformly coated onto the side of the first negative electrode active layer away from the negative electrode current collector. After being air-dried at room temperature, the slurry was transferred to an oven for drying. After cold pressing and slitting, a negative electrode sheet was obtained. The negative electrode sheet includes a negative electrode current collector, a first negative electrode active layer located on the 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.

[0235] (3) Preparation of the positive electrode sheet:

[0236] The positive electrode active material LiFePO4, conductive agent Super P, and binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 96:2:2. The solvent N-methylpyrrolidone (NMP) was added, and the mixture was stirred evenly under vacuum to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated onto the positive electrode current collector aluminum foil, dried at room temperature, and then transferred to an oven for drying. After cold pressing and slitting, the positive electrode sheet was obtained.

[0237] (4) Separation film: a polyethylene film with a thickness of 12μm.

[0238] (5) Preparation of electrolyte:

[0239] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1. The thoroughly dried lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a LiPF6 molar concentration of 1 mol / L.

[0240] (6) Assembly of individual battery cells:

[0241] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes, thus obtaining a bare cell. The bare cell is placed in an outer packaging shell, and the prepared electrolyte is injected into the dried bare cell. After vacuum sealing, settling, formation, and shaping, a lithium-ion battery cell is obtained.

[0242] Battery testing methods

[0243] (1) Battery cell charging time test method:

[0244] At 25℃, the battery cell was charged at a constant current rate of 1C to 4.4V, then charged at a constant voltage rate until the current was ≤0.05C, left to stand for 5 minutes, and then discharged at a constant current rate of 0.33C to 2.8V. Its discharge capacity was recorded as C0.

[0245] At 25℃, the battery cells were sequentially charged at constant current rates of 1.0C0, 1.3C0, 1.5C0, 1.8C0, 2.0C0, 2.3C0, 2.5C0, 3.0C0, 3.5C0, 4C0, 4.5C0, and 5C0 until the charging cutoff voltage of 4.4V or the negative terminal cutoff potential of 0V (whichever comes first). After each charging, the cells were discharged at 1C0 until the discharge cutoff voltage of 2.8V. The charging rates were recorded at 10%, 20%, 30%, 40%, 50%, 60%, 70%, and 80% SOC (State of Charge). State of Charge (SOC) refers to the negative electrode potential at which the battery is fully discharged (SOC=0) and fully charged (SOC=100%). Charging rate-negative electrode potential curves are plotted for different SOC states. Linear fitting yields the charging rate corresponding to a negative electrode potential of 0V at each SOC state. This charging rate is the charging window for that SOC state, denoted as C10%SOC, C20%SOC, C30%SOC, etc. The charging time T for a single battery cell from 10% SOC to 80% SOC is calculated using the formula (60 / C20% SOC + 60 / C30% SOC + 60 / C40% SOC + 60 / C50% SOC + 60 / C60% SOC + 60 / C70% SOC + 60 / C80% SOC) × 10%, with the unit being minutes.

[0246] (2) Method for testing the volumetric energy density of a single battery cell:

[0247] Place the battery cell at 25℃ and charge it at a constant current rate of 1C to 4.4V. Then charge it at a constant voltage rate until the current is ≤0.05C. Let it stand for 5 minutes, and then discharge it at a constant current rate of 0.33C to 2.8V. Record the discharge capacity A0 and the discharge plateau voltage V at this time. Use calipers 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 shell), and calculate the volume of the battery cell V0. The volumetric energy density of the battery cell VED=(A0×V) / V0, in Wh / L.

[0248] Example 2

[0249] In the preparation steps of the second graphite material, the proportion of streamline structure in the polarized light photograph of anisotropic petroleum coke is 64%, the average particle size of the aggregate is 7.3 μm, the particle size of the finished second graphite material is 13.6 μm, and the thickness of the carbon coating layer on the surface of the second graphite material is 266 nm.

[0250] In the preparation steps of the negative electrode sheet, the R value of the second negative electrode material is 0.15 and the R50 value is 1.31.

[0251] The remaining operations are the same as in Example 1.

[0252] Example 3

[0253] In the preparation steps of the second graphite material, the proportion of streamline structure in the polarized light photograph of anisotropic petroleum coke is 13%, the average particle size of the aggregate is 7.6 μm, the particle size of the finished 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.

[0254] In the preparation steps of the negative electrode sheet, the R value of the second negative electrode material is 0.16 and the R50 value is 1.31.

[0255] The remaining operations are the same as in Example 1.

[0256] Example 4

[0257] In the preparation steps of the second graphite material, the proportion of streamline structure in the polarized light photograph of anisotropic petroleum coke is 97%, the average particle size of the aggregate is 7.4 μm, the particle size of the finished 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.

[0258] In the preparation steps of the negative electrode sheet, the R value of the second negative electrode material is 0.17 and the R50 value is 1.32.

[0259] The remaining operations are the same as in Example 1.

[0260] Example 5

[0261] In the preparation steps of the second graphite material, the proportion of streamline structure in the polarized light photograph of anisotropic petroleum coke is 99%, the average particle size of the aggregate is 7.5 μm, the particle size of the finished second graphite material is 13.8 μm, and the thickness of the carbon coating layer on the surface of the second graphite material is 264 nm.

[0262] In the preparation steps of the negative electrode sheet, the first graphite material with an OI value of 15.2 and an average primary particle size of 18.9 μm is used; the second negative electrode material has an R value of 0.16 and an R50 value of 1.35.

[0263] The remaining operations are the same as in Example 1.

[0264] Comparative Example 1

[0265] In the preparation step of the second graphite material, isotropic petroleum coke is used, the average particle size of the aggregate is 7.4 μm, the particle size of the finished 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.

[0266] In the preparation steps of the negative electrode sheet, the R value of the second negative electrode material is 0.18 and the R50 value is 1.31.

[0267] The remaining operations are the same as in Example 1.

[0268] The parameters in the table below include:

[0269] Graphite 1 is the first graphite material;

[0270] Graphite 2 is a second graphite material;

[0271] The specific capacity difference is the difference between the specific capacity of the first negative electrode material and the specific capacity of the second negative electrode material.

[0272] The 150MPa powder compaction difference is the difference between the compacted density of the first negative electrode material powder and the compacted density of the second negative electrode material powder at 150MPa.

[0273] P is the proportion of secondary particles in the total number of particles in the second graphite material;

[0274] A is the ratio of the average secondary particle size to the average primary particle size of the second graphite material.

[0275] Table 1. Parameters and test results of Examples 1-5 and Comparative Example 1

[0276] serial number OI value of graphite powder The specific capacity (mAh / g) of the second anode material <![CDATA[150 MPa powder compaction of the first negative electrode material (g / cm 3 )]]> Difference in gram capacity (mAh / g) <![CDATA[Powder compaction difference at 150 MPa (g / cm 3 )]]> P A Average particle size (μm) of secondary graphite particles Charging time (min) at 25℃ 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

[0277] As can be seen from the table above, compared with the isotropic graphite material of Comparative Example 1, the second graphite material of Examples 1-5 of this application adopts anisotropic graphite, and the OI value of the second graphite material is reduced by granulation into secondary particles, which significantly improves the energy density of the secondary battery while ensuring the dynamic performance of the secondary battery.

[0278] Example 6

[0279] In the preparation steps 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 was used. The remaining operations were the same as in Example 1.

[0280] Example 7

[0281] In the preparation steps of the second graphite material, the proportion of streamline structure in the polarized light photograph of anisotropic petroleum coke is 7%, the average particle size of the aggregate is 6.3 μm, the particle size of the finished second graphite material is 11.9 μm, and the thickness of the coating layer on the surface of the second graphite material is 290 nm.

[0282] In the preparation steps of the negative electrode sheet, the first graphite material with an OI value of 15.2 and an average primary particle size of 18.9 μm is used, and the second negative electrode material has an R value of 0.19 and an R50 value of 1.31.

[0283] The remaining operations are the same as in Example 1.

[0284] Example 8

[0285] In the preparation steps of the second graphite material, the proportion of streamline structure in the polarized light photograph of anisotropic petroleum coke is 7%, the average particle size of the aggregate is 6.3 μm, the particle size of the finished second graphite material is 11.9 μm, and the thickness of the coating layer on the surface of the second graphite material is 290 nm.

[0286] In the preparation steps of the negative electrode sheet, the first graphite material with an OI value of 17 and an average primary particle size of 19 μm is used, and the second negative electrode material has an R value of 0.19 and an R50 value of 1.31.

[0287] The remaining operations are the same as in Example 1.

[0288] Comparative Example 2

[0289] In the preparation steps 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 was used. The remaining operations were the same as in Example 1.

[0290] Comparative Example 3

[0291] In the preparation steps 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 was used. The remaining operations were the same as in Example 1.

[0292] Table 2. Some parameters and test results of Examples 1, 6-8 and Comparative Examples 2-3

[0293] serial number OI value of graphite powder The specific capacity (mAh / g) of the second anode material First negative electrode material 150MPa powder compaction (g / cm3) Difference in gram capacity (mAh / g) Powder compaction difference at 150 MPa (g / cm3) P A Average particle size (μm) of secondary graphite particles Charging time (min) at 25℃ 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

[0294] It can be seen from the above table:

[0295] Compared with the low compaction of the first negative electrode material powder in Comparative Example 2, the energy density of the secondary batteries in Examples 1 and 6 of this application is significantly improved.

[0296] Compared with the excessively high compaction of the first negative electrode material powder in Comparative Example 3, the fast charging performance of the secondary batteries in Examples 1 and 6 of this application is significantly improved.

[0297] Compared to Example 8, where the difference in specific capacity between the first and second negative electrode materials is greater, the secondary batteries of Examples 1 and 6-7 of this application exhibit significantly higher kinetic performance.

[0298] Example 9

[0299] In the preparation steps of the second graphite material, the mass ratio of binder to 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.

[0300] In the preparation steps of the negative electrode sheet, the R value of the second negative electrode material is 0.15 and the R50 value is 1.29.

[0301] The remaining operations are the same as in Example 1.

[0302] Example 10

[0303] In the preparation steps of the second graphite material, the mass ratio of binder to 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.

[0304] In the preparation steps of the negative electrode sheet, the R value of the second negative electrode material is 0.14 and the R50 value is 1.30.

[0305] The remaining operations are the same as in Example 1.

[0306] Example 11

[0307] In the preparation steps of the second graphite material, the mass ratio of binder to 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 coating layer on the surface of the second graphite material is 245 nm.

[0308] In the preparation steps of the negative electrode sheet, the R value of the second negative electrode material is 0.13 and the R50 value is 1.30.

[0309] The remaining operations are the same as in Example 1.

[0310] Comparative Example 4

[0311] No binder is added in the preparation steps 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.

[0312] In the preparation steps of the negative electrode sheet, the R value of the second negative electrode material is 0.17 and the R50 value is 1.33.

[0313] The remaining operations are the same as in Example 1.

[0314] Table 3. Some parameters and test results of Examples 1, 9-11 and Comparative Example 4

[0315] serial number OI value of graphite powder The specific capacity (mAh / g) of the second anode material Difference in gram capacity (mAh / g) <![CDATA[150 MPa powder compaction difference (g / cm 3 )]]> P A Average particle size (μm) of secondary graphite particles Charging time (min) at 25℃ 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 Example 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

[0316] It can be seen from the above table:

[0317] Compared to Comparative Example 4, where the proportion of secondary particles in the second graphite material is 0, the second graphite materials in Examples 1 and 9-11 of this application include secondary particles, resulting in significantly improved kinetic performance and higher energy density in their secondary batteries.

[0318] Compared with Example 11, where secondary particles account for 35% of the total number of particles in the second graphite material, the proportion of secondary particles in the second graphite materials of Examples 1 and 9-10 of this application is higher, resulting in higher energy density of the secondary batteries. Among them, the secondary batteries of Examples 1 and 9 of this application have higher kinetic performance.

[0319] Example 12

[0320] In the preparation steps of the second graphite material, the operation of mixing and reacting graphitization products with coating agents is omitted, and the resulting second graphite material has a particle size of 13 μm.

[0321] The R value and R50 value of the second negative electrode material were not measured. The remaining operations were the same as in Example 1.

[0322] Table 4. Some parameters and test results of Examples 1 and 12

[0323] serial number OI value of graphite powder The specific capacity (mAh / g) of the second anode material Difference in gram capacity (mAh / g) <![CDATA[150 MPa powder compaction difference (g / cm 3 )]]> P A Average particle size (μm) of secondary graphite particles Average particle size (μm) of primary graphite particles Second graphite carbon coating thickness (nm) Charging time (min) at 25℃ 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 As can be seen from the table above, compared with the second graphite material in Example 12 which does not have a coating layer on its surface, the secondary battery in Example 1 of this application has significantly higher kinetic performance.

[0324] Example 13

[0325] In the preparation steps of the negative electrode sheet, the first graphite material used includes secondary particles with an average particle size of 20 μm. The remaining operations are the same as in Example 1.

[0326] Example 14

[0327] In the preparation steps of the negative electrode sheet, when preparing the first negative electrode active layer, natural graphite, first graphite material, dispersant sodium carboxymethyl cellulose, binder styrene-butadiene rubber (SBR), and conductive agent carbon black are mixed in a mass ratio of 57.8:96.4:1.1:2.0:0.4.

[0328] Table 5. Parameters and test results of Examples 1 and 13-14

[0329] serial number <![CDATA[First negative electrode material, powder compaction at 150 MPa (g / cm 3 )]]> Difference in gram capacity (mAh / g) Powder compaction difference at 150 MPa (g / cm3) OI value of graphite powder Average particle size (μm) of primary graphite particles 1 The proportion of secondary graphite particles in the total number of particles Does the first negative electrode active layer include natural graphite? Charging time (min) at 25℃ Volumetric energy density (Wh / L) Example 1 1.79 6.4 0.14 11 16.4 0 no 11.7 422.31 Example 13 1.8 7.4 0.15 6.2 16.4 84% no 11.2 425.33 Example 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:

[0330] Based on Example 1, the first graphite material in Example 13 of this application includes secondary particles, which improves the fast charging performance and energy density of the secondary battery.

[0331] Based on Example 13, the first negative electrode material of Example 14 of this application further includes natural graphite, which further improves the fast charging performance and energy density of the secondary battery.

[0332] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This 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 includes a negative electrode sheet, which includes 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 the 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, and 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 surface of the second graphite material has a coating layer, which includes carbon elements. The powder OI value of the second graphite material is 1-10, and the powder OI value of the second graphite material is the ratio of the peak area 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 specific capacity of the first negative electrode material is greater than that of the second negative electrode material; the specific capacity of the second negative electrode material is 345-365 mAh / g; wherein, the specific capacity of the first negative electrode material or the specific 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 discharging the lithium secondary battery from 2.0V to 5mV at a constant current of 0.05C at room temperature; The compacted powder density of the first negative electrode material at 150 MPa is greater than that of the second negative electrode material at 150 MPa; the compacted powder density of the first negative electrode material at 150 MPa is 1.70 - 2.10 g / cm³. 3 ; The R value of the second negative electrode material is 0.13 - 0.25; the R value of the second negative electrode material is the ratio of the difference between the R90 value and the R10 value of the second negative electrode material to the R50 value of the second negative electrode material; the I of multiple particles of the second negative electrode material... D / I G Accumulate from smallest to largest, when I D / I G The cumulative value reaches I D / I G I corresponding to 10% of the total value D / I G R10 is 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 R50 is 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 The second negative electrode material has an R90 value; the Raman shift of a single particle of the second negative electrode material is 1300 cm⁻¹. -1 ~ 1380cm -1 The intensity of the peak within the range is I D The Raman displacement is 1520 cm. -1 ~ 1590cm -1 The intensity of the peak within the range is I G .

2. The lithium secondary battery according to claim 1, characterized in that, The OI value of the second graphite material powder is greater than 1.1 and less than or equal to 10; and / or, The specific 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 in powder compaction density between the first and second negative electrode materials at 150 MPa is 0.05 - 0.60 g / cm³. 3 ; and / or, The difference in specific 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 specific 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% - 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 to the average particle size of the primary particles in the second graphite material 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.

6. The lithium secondary battery according to claim 1, characterized in that, The secondary particles in the second graphite material account for 58% - 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 - 16 μm.

7. The lithium secondary battery according to claim 1, characterized in that, 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 R50 value of the second negative electrode material is 1.0 - 1.

4.

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. The powder OI value of the first graphite material is the ratio of the peak area 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.

11. The lithium secondary battery according to claim 10, characterized in that, The average particle size of the primary particles in the first graphite material is 8-19 μm.

12. The lithium secondary battery according to claim 10, characterized in that, The first graphite material also includes secondary particles, and the proportion of secondary particles in the total number of particles in the first graphite material is 35%-90%.

13. The lithium secondary battery according to any one of claims 1 to 12, characterized in that, The first negative electrode active layer also includes natural graphite material.

14. A negative electrode sheet for a lithium secondary battery, characterized in that, The negative electrode sheet includes a negative current collector, a first negative active layer located on at least one side of the negative current collector, and a second negative active layer located on the side of the first negative active layer away from the negative current collector; the first negative active layer includes a first negative electrode material, the second negative 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 surface of the second graphite material has a coating layer, the coating layer including carbon elements. The powder OI value of the second graphite material is 1-10, and the powder OI value of the second graphite material is the ratio of the peak area 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 specific capacity of the first negative electrode material is greater than that of the second negative electrode material; the specific capacity of the second negative electrode material is 345-365 mAh / g; wherein, the specific capacity of the first negative electrode material or the specific 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 discharging the lithium secondary battery from 2.0V to 5mV at a constant current of 0.05C at room temperature; The compacted powder density of the first negative electrode material at 150 MPa is greater than that of the second negative electrode material at 150 MPa; the compacted powder density of the first negative electrode material at 150 MPa is 1.70 - 2.10 g / cm³. 3 ; The R value of the second negative electrode material is 0.13 - 0.25; the R value of the second negative electrode material is the ratio of the difference between the R90 value and the R10 value of the second negative electrode material to the R50 value of the second negative electrode material; the I of multiple particles of the second negative electrode material... D / I G Accumulate from smallest to largest, when I D / I G The cumulative value reaches I D / I G I corresponding to 10% of the total value D / I G R10 is 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 R50 is 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 The second negative electrode material has an R90 value; the Raman shift of a single particle of the second negative electrode material is 1300 cm⁻¹. -1 ~ 1380cm -1 The intensity of the peak within the range is I D The Raman displacement is 1520 cm. -1 ~ 1590cm -1 The intensity of the peak within the range is I G .

15. The negative electrode sheet according to claim 14, characterized in that, The OI value of the second graphite material powder is greater than 1.1 and less than or equal to 10; and / or, The specific capacity of the second negative electrode material is 350-365 mAh / g.

16. The negative electrode sheet according to claim 14, characterized in that, The difference in powder compaction density between the first and second negative electrode materials at 150 MPa is 0.05 - 0.60 g / cm³. 3 ; and / or, The difference in specific capacity between the first negative electrode material and the second negative electrode material is 5 - 36.3 mAh / g.

17. The negative electrode sheet according to claim 14, characterized in that, The difference in specific capacity between the first negative electrode material and the second negative electrode material is 5-25 mAh / g.

18. The negative electrode sheet according to claim 14, characterized in that, The secondary particles in the second graphite material account for 35% - 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 to the average particle size of the primary particles in the second graphite material 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.

19. The negative electrode sheet according to claim 14, characterized in that, The secondary particles in the second graphite material account for 58% - 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 - 16 μm.

20. The negative electrode sheet according to claim 14, characterized in that, The thickness of the coating layer is greater than 0 nm and less than or equal to 500 nm.

21. The negative electrode sheet according to claim 14, characterized in that, The R50 value of the second negative electrode material is 1.0 - 1.

4.

22. The negative electrode sheet according to claim 14, characterized in that, The powder OI value of the first graphite material is greater than 6 and less than or equal to 25. The powder OI value of the first graphite material is the ratio of the peak area 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.

23. The negative electrode sheet according to claim 14, characterized in that, The first graphite material comprises primary particles.

24. The negative electrode sheet according to claim 23, characterized in that, The average particle size of the primary particles in the first graphite material is 8-19 μm.

25. The negative electrode sheet according to claim 23, characterized in that, The first graphite material also includes secondary particles, and the proportion of secondary particles in the total number of particles in the first graphite material is 35%-90%.

26. The negative electrode sheet according to any one of claims 14 to 25, characterized in that, The first negative electrode active layer also includes natural graphite material.

27. An electrical appliance, characterized in that, The electrical device includes a lithium secondary battery as described in any one of claims 1 to 13.

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