Negative active material, method of manufacturing, secondary battery, and electric device

Abstract

The present application relates to a negative active material comprising graphite particles having internal pores and a lithium salt coating layer coated on the internal pores of the graphite particles and the external surface of the particles, wherein the weight ratio of lithium elements in the internal pores of the graphite particles to lithium elements on the external surface of the graphite particles is 1-10:1, and a preparation method thereof, a corresponding secondary battery and an electric device. The internal pores and the surface of the particles of the negative active material are both coated with a lithium salt, so that the negative active material has higher structural stability, thereby effectively improving the initial coulombic efficiency and cycle stability of the corresponding battery.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, and in particular to a negative electrode active material, a manufacturing method, a secondary battery, and an electrical device. Background Technology

[0002] In recent years, with the increasingly widespread application of lithium-ion batteries, they have been widely used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. Due to the significant development of lithium-ion batteries, higher requirements have been placed on their energy density, cycle performance, and safety performance. After assembly, a solid electrolyte interphase (SEI) film forms on the surface of the negative electrode during the first charge of a lithium-ion battery. This process continues until the SEI film completely covers the negative electrode surface and the reaction stops; this is the formation process of a lithium-ion battery. The SEI film consists of an inner layer of inorganic lithium salts, including Li₂CO₃, Li₂O, and LiF, and an outer layer of organic lithium salts, including alkyl lithium esters.

[0003] The formation of the SEI film has a crucial impact on the performance of electrode materials. On the one hand, the formation of the SEI film consumes some active lithium, increasing the irreversible capacity during the initial charge-discharge cycle and reducing the charge-discharge efficiency of the electrode material. On the other hand, the SEI film is insoluble in organic solvents and can exist stably in organic electrolyte solutions. Solvent molecules cannot pass through this passivation film, effectively preventing the co-intercalation of solvent molecules and avoiding damage to the electrode material caused by solvent molecule co-intercalation. Therefore, it greatly improves the cycle performance and lifespan of the electrode. Thus, finding effective ways to improve the performance of the SEI film has always been a hot research topic in the global electrochemical community. Summary of the Invention

[0004] This application is made in view of the above-mentioned problems, and its purpose is to provide a negative electrode active material in which the internal pores and particle surfaces are coated with lithium salt, so that the negative electrode active material has higher structural stability, thereby effectively improving the first coulombic efficiency and cycle stability of the corresponding battery.

[0005] To achieve the above objectives, a first aspect of this application provides a negative electrode active material comprising graphite particles with internal pores and a lithium salt coating layer covering the internal pores and the outer surface of the graphite particles, wherein the weight ratio of lithium elements in the internal pores of the graphite particles to lithium elements on the outer surface of the graphite particles is 1 to 10:1.

[0006] Therefore, the negative electrode active material of this application is coated with lithium salt in both its internal pores and particle surface, achieving a specific weight ratio of lithium in the internal pores to lithium on the outer surface of the graphite particles. The lithium salt component of the coating layer is part of the spontaneously formed SEI film component in the lithium-ion electrochemical system, and the coating layer can suppress active sites, thereby reducing the consumption of active lithium during the initial formation of the SEI film in the corresponding battery. Since the internal pores of the negative electrode active material are also coated with lithium salt, it protects the graphite surface and further reduces lithium salt consumption after the internal pores of the graphite are exposed due to the expansion and contraction of the cycling volume. Therefore, when used as the negative electrode of a lithium-ion battery, this negative electrode active material can effectively improve the initial coulombic efficiency and cycle stability of the lithium-ion battery.

[0007] In any embodiment, the lithium salt coating layer satisfies at least one of the following characteristics:

[0008] (1) The content of the lithium salt coating layer is 0.01%-6%, based on the total weight of the negative electrode active material;

[0009] (2) The thickness of the lithium salt coating layer in the internal pores of the graphite particles is 1-20 nm, and the thickness of the lithium salt coating layer on the outer surface of the graphite particles is 1-30 nm. Thus, by limiting the above parameters of the lithium salt coating, the structural stability of the negative electrode active material is further improved, thereby effectively improving the initial coulombic efficiency and cycle stability of the corresponding battery.

[0010] In any embodiment, the negative electrode active material satisfies at least one of the following characteristics:

[0011] (1) The graphite mentioned is natural graphite;

[0012] (2) The lithium salt is an inorganic lithium salt, which may be selected from one or more of carbonates, lithium oxides, lithium phosphates and lithium fluorides.

[0013] Therefore, by further limiting the types of graphite and lithium salt, the structural stability of the negative electrode active material is further improved, thereby effectively improving the initial coulombic efficiency and cycle stability of the corresponding battery.

[0014] In any embodiment, the average volume particle size D of the negative electrode active material v50 It is 10-30μm.

[0015] Therefore, by further improving the average volume particle size of the negative electrode active material, the structural stability of the negative electrode active material is further improved, thereby effectively improving the initial coulombic efficiency and cycle stability of the corresponding battery.

[0016] In any embodiment, a carbon coating layer is also present between the graphite and the lithium salt coating layer; optionally, the coating amount of the carbon coating layer is 0.2-10% based on the total weight of the negative electrode active material. Thus, by adding a carbon coating layer between the graphite and the lithium salt coating layer, the surface instability after the internal pores of the particles are exposed is further suppressed, improving the structural stability of the negative electrode active material, thereby effectively improving the initial coulombic efficiency and cycle stability of the corresponding battery.

[0017] A second aspect of this application provides a method for preparing a negative electrode active material, comprising:

[0018] (1) Provide flake graphite;

[0019] (2) Using lithium-containing raw materials to coat flake graphite, so that a lithium salt coating layer is formed on the surface of flake graphite;

[0020] (3) Shape the flake graphite obtained in step (2) to obtain spherical graphite;

[0021] (4) The spherical graphite is coated with lithium-containing raw materials to form a lithium salt coating layer on the surface of the spherical graphite, thereby obtaining the negative electrode active material;

[0022] The negative electrode active material comprises graphite with internal pores and a lithium salt coating layer covering the internal pores and the outer surface of the graphite, wherein the weight ratio of lithium element in the internal pores of the graphite to lithium element on the outer surface of the graphite is 1 to 10:1.

[0023] Therefore, the method of this application, by sequentially coating flake graphite and shaped spherical graphite, obtains a negative electrode active material in which both the internal pores and outer surface of the graphite are coated with lithium salt, wherein the surface of the coated flake graphite forms the internal pore surface of the spherical graphite after shaping. The resulting negative electrode active material has higher surface stability, thereby effectively improving the initial coulombic efficiency and cycle stability of the corresponding battery.

[0024] In any embodiment, carbon coating or surface treatment is performed between steps (1) and (2) or between steps (3) and (4). This further suppresses graphite surface defects and the activity of active sites, improves the surface stability of the negative electrode active material, and thus effectively improves the initial coulombic efficiency and cycle stability of the corresponding battery.

[0025] In any embodiment, carbon coating or surface treatment is performed between steps (3) and (4). This further suppresses graphite surface defects and the activity of active sites, improves the surface stability of the negative electrode active material, and thus effectively improves the initial coulombic efficiency and cycle stability of the corresponding battery.

[0026] In any embodiment, in step (2), the lithium-containing raw material comprises at least one of lithium carbonate, lithium hydroxide, lithium carboxylates, lithium sulfate, lithium fluoride, and lithium phosphate, and optionally at least one of lithium carbonate, lithium acetate, lithium citrate, lithium oxalate, lithium sulfate, lithium fluoride, and lithium phosphate. Therefore, the type of lithium salt in the coating layer is further preferred, resulting in higher surface stability of the negative electrode active material, thereby effectively improving the initial coulombic efficiency and cycle stability of the corresponding battery.

[0027] In any embodiment, step (2) includes: preparing a lithium-containing raw material into a corresponding solution; dispersing the flake graphite in the solution to obtain a mixture; filtering, drying, and dispersing the mixture to obtain a solid powder; and sintering the solid powder at 300-900°C for 0.5-8 hours under a protective atmosphere or vacuum to form a lithium salt coating layer on the surface of the flake graphite. This further optimizes the quality of the flake graphite surface coating layer, improves the surface stability of the negative electrode active material, and effectively enhances the initial coulombic efficiency and cycle stability of the corresponding battery.

[0028] A third aspect of this application also provides a secondary battery, characterized in that,

[0029] This includes the negative electrode active material described in the first aspect of this application or the negative electrode active material prepared according to the method described in the second aspect of this application. The resulting secondary battery has improved initial coulombic efficiency and cycle stability.

[0030] A fourth aspect of this application provides an electrical device comprising a secondary battery selected from the second aspect of this application.

[0031] The negative electrode active material of this application has its internal pores and particle surface coated with lithium salt, which makes the negative electrode active material have higher structural stability, thereby effectively improving the first coulombic efficiency and cycle stability of the corresponding battery. Attached Figure Description

[0032] Figure 1 SEM image of a cross section of natural graphite coated with the negative electrode active material of Example 1 of this application;

[0033] Figure 2 SEM images of cross sections of existing artificial graphite

[0034] Figure 3 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0035] Figure 4 yes Figure 1 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0036] Figure 5This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0037] Explanation of reference numerals in the attached figures:

[0038] 5. Secondary battery; 51. Housing; 52. Electrode assembly; 53. Cover plate; 6. Electrical device. Detailed Implementation

[0039] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the negative electrode active material, its preparation method, secondary battery, and power application 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.

[0040] 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.

[0041] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0042] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0043] 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.

[0044] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0045] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: 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).

[0046] After assembly, a solid electrolyte interphase (SEI) film forms on the surface of the negative electrode during the first charge of a lithium-ion battery. This process continues until the SEI film completely covers the negative electrode surface and the reaction ceases; this is the formation process of a lithium-ion battery. The SEI film consists of an inner layer of inorganic lithium salts, including Li₂CO₃, Li₂O, and LiF, and an outer layer of organic lithium salts, including alkyl lithium esters. The formation of the SEI film has a crucial impact on the performance of the electrode materials. On the one hand, the formation of the SEI film consumes some active lithium, increasing the irreversible capacity during the first charge-discharge cycle and reducing the charge-discharge efficiency of the electrode materials. On the other hand, the SEI film is insoluble in organic solvents and can exist stably in organic electrolyte solutions. Solvent molecules cannot pass through this passivation film, effectively preventing the co-intercalation of solvent molecules and avoiding damage to the electrode materials caused by solvent molecule co-intercalation. This significantly improves the cycle performance and lifespan of the electrode. Therefore, finding effective ways to improve the performance of the SEI film has always been a hot topic in the global electrochemical community. The inventors discovered that the negative electrode active material of the first aspect of the present invention, by pre-coating its internal pores and particle surface with lithium salt, which constitutes part of the SEI film, and achieving a specific weight ratio of lithium element in the internal pores to lithium element on the outer surface of the graphite particles, reduces the consumption of active lithium during the initial formation of the SEI film in the corresponding battery. Since the internal pores of the negative electrode active material are also coated with lithium salt, the graphite surface is protected and lithium salt consumption is further reduced after the internal pores of the graphite are subsequently exposed due to the expansion and contraction of the cycling volume. Therefore, when the negative electrode active material is used as the negative electrode of a lithium-ion battery, it can effectively improve the initial coulombic efficiency and cycle stability of the lithium-ion battery.

[0047] Negative electrode active materials

[0048] In some embodiments, the first aspect of this application provides a negative electrode active material comprising graphite particles having internal pores and a lithium salt coating layer covering the internal pores and the outer surface of the graphite particles, wherein the weight ratio of lithium element in the internal pores of the graphite particles to lithium element on the outer surface of the graphite particles is 1 to 10:1, preferably 1 to 5:1, and more preferably 2 to 3:1.

[0049] Therefore, the negative electrode active material of this application is coated with lithium salt in both its internal pores and particle surface, achieving a specific weight ratio of lithium in the internal pores to lithium on the outer surface of the graphite particles. The lithium salt component of the coating layer is part of the spontaneously formed SEI film component in the lithium-ion electrochemical system, and the coating layer can suppress active sites, thereby reducing the consumption of active lithium during the initial formation of the SEI film in the corresponding battery. Since the internal pores of the negative electrode active material are also coated with lithium salt, it protects the graphite surface and further reduces lithium salt consumption after the internal pores of the graphite are exposed due to the expansion and contraction of the cycling volume. Therefore, when used as the negative electrode of a lithium-ion battery, this negative electrode active material can effectively improve the initial coulombic efficiency and cycle stability of the lithium-ion battery.

[0050] The term "internal porosity" refers to pores or gaps within graphite particles that may or may not be connected to the outside air. See also: Figure 1 The lithium salt coating layer of the internal pores is obtained by first coating the surface of flake graphite with lithium salt, and then shaping it so that the lithium salt coating layer on the surface of the flake graphite forms the lithium salt coating layer on the surface of the internal pores of spherical graphite.

[0051] In some embodiments, the lithium salt coating content is 0.01%-6%, preferably 1%-5.2%, more preferably 2.7-5.15%, based on the total weight of the negative electrode active material.

[0052] In some embodiments, the thickness of the lithium salt coating layer within the pores of the graphite particles is 1-20 nm, preferably 2-25 nm, and more preferably 5-12 nm; the thickness of the lithium salt coating layer on the outer surface of the graphite particles is 1-30 nm, preferably 2-25 nm, and more preferably 5-12 nm. Thus, by limiting the above parameters of the lithium salt coating, the structural stability of the negative electrode active material is further improved, thereby effectively improving the initial coulombic efficiency and cycle stability of the corresponding battery.

[0053] In some embodiments, at least 70%, preferably 90%, more preferably 95%, even more preferably 98%, and most preferably 100% of the surface area of ​​the internal pores of the graphite particles are covered by a lithium salt coating layer, based on the surface area of ​​all the internal pores of the graphite particles.

[0054] In some embodiments, the graphite is natural graphite with a specific surface area of ​​2–15 m². 2 / g. The lithium salt is an inorganic lithium salt, optionally selected from one or more of carbonates, lithium oxide, lithium phosphate, and lithium fluoride, and more preferably selected from one or more of lithium carbonate, lithium oxide, and lithium fluoride. The inorganic lithium salt is generally preferred to be a component in the spontaneously formed SEI film of the lithium battery or a component that plays the same role as the spontaneously formed SEI film, that is, it can conduct lithium ions but not electrons. The natural graphite has a large specific surface area and many surface active sites, which will consume more active lithium during the initial formation of the SEI film. The negative electrode active material of this application, which has lithium salt coatings on both the internal pores and the external surface of natural graphite, can reduce the consumption of active lithium during the initial formation process when applied to lithium-ion batteries. It can also protect the surface of natural graphite and further reduce lithium salt consumption after the internal pores of natural graphite are exposed due to the expansion and contraction of the cycle volume. Thus, the structural stability of the negative electrode active material is further improved, thereby effectively improving the initial coulombic efficiency and cycle stability of the corresponding battery.

[0055] In some embodiments, the average volumetric particle size D of the negative electrode active material v50 The particle size is 10-30 μm, preferably 14-18 μm. The average volumetric particle size Dv50 is the particle size corresponding to a cumulative volume distribution percentage of 50% in the sample; it is determined using a laser particle size analyzer, such as the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0056] Therefore, by further improving the average volume particle size of the negative electrode active material, the structural stability of the negative electrode active material is further improved, thereby effectively improving the initial coulombic efficiency and cycle stability of the corresponding battery.

[0057] In some embodiments, a carbon coating layer is also present between the graphite and the lithium salt coating layer; optionally, the coating amount of the carbon coating layer is 0.2-10%, preferably 0.5-3%, more preferably 1.5-2.5%, and more preferably 1.78-2.08%, based on the total weight of the negative electrode active material. Thus, by adding a carbon coating layer between the graphite and the lithium salt coating layer, the surface instability after the internal pores of the particles are exposed is further suppressed, improving the structural stability of the negative electrode active material, thereby effectively improving the initial coulombic efficiency and cycle stability of the corresponding battery.

[0058] In some preferred embodiments, the coating layer on the outer surface of the graphite particles, such as a lithium salt coating layer or a carbon coating layer, is uniformly or patchily coated on the outer surface of the graphite particles. When the coating layer is patchily coated on the outer surface of the graphite particles, the area of ​​the coating layer accounts for more than 80% of the particle surface area, preferably more than 90%, and more than 97%.

[0059] In some preferred embodiments, the coating layer for the internal pores of graphite particles may fill the pores or only cover the surface of the pores.

[0060] A second aspect of this application provides a method for preparing a negative electrode active material, comprising:

[0061] (1) Provide flake graphite;

[0062] (2) Using lithium-containing raw materials to coat flake graphite, so that a lithium salt coating layer is formed on the surface of flake graphite;

[0063] (3) Shape the flake graphite obtained in step (2) to obtain spherical graphite;

[0064] (4) The spherical graphite is coated with lithium-containing raw materials to form a lithium salt coating layer on the surface of the spherical graphite, thereby obtaining the negative electrode active material;

[0065] The negative electrode active material comprises graphite with internal pores and a lithium salt coating layer covering the internal pores and the outer surface of the graphite, wherein the weight ratio of lithium element in the internal pores of the graphite to lithium element on the outer surface of the graphite is 1 to 10:1.

[0066] Therefore, the method of this application, by sequentially coating flake graphite and shaped spherical graphite, obtains a negative electrode active material in which both the internal pores and outer surface of the graphite are coated with lithium salt, wherein the surface of the coated flake graphite forms the internal pore surface of the spherical graphite after shaping. The resulting negative electrode active material has higher surface stability, thereby effectively improving the initial coulombic efficiency and cycle stability of the corresponding battery.

[0067] In some preferred embodiments, the flake graphite is natural flake graphite with a planar size of approximately 50-200 μm, as measured by scanning electron microscopy; its fixed carbon content is 99.5%, as determined by a high-frequency infrared carbon-sulfur analyzer.

[0068] The negative electrode active material includes all the technical features described in the first aspect of the present invention.

[0069] In some embodiments, carbon coating or surface treatment is performed between steps (1) and (2) or between steps (3) and (4). This further suppresses graphite surface defects and the activity of active sites, improves the surface stability of the negative electrode active material, and thus effectively improves the initial coulombic efficiency and cycle stability of the corresponding battery.

[0070] In some embodiments, carbon coating or surface treatment is performed between steps (3) and (4). This further suppresses graphite surface defects and the activity of active sites, improves the surface stability of the negative electrode active material, and thus effectively improves the initial coulombic efficiency and cycle stability of the corresponding battery.

[0071] In some embodiments, the carbon coating step includes mixing (e.g., stirring) the material to be coated with a carbon-containing material in a heating device, such as a furnace, at a temperature of 150-300°C for 10-60 minutes, and then placing the resulting mixture in a sintering device at a temperature of 900-1500°C under an inert gas atmosphere of 0.05-0.2 MPa, optionally atmospheric pressure, such as 0.1 MPa, for 1-10 hours, preferably 4-6 hours, to obtain the carbon-coated material. The carbon-containing material includes one or more of asphalt, phenolic resin, epoxy resin, sucrose, and glucose, preferably asphalt or phenolic resin. The inert gas includes one or more of nitrogen, argon, helium, etc., preferably nitrogen.

[0072] In some embodiments, the surface treatment includes surface oxidation, wherein surface oxidation includes immersing the powder in a solution of strong oxidizing agents such as nitric acid or hydrogen peroxide for oxidation and high-temperature heat treatment in air or oxygen.

[0073] In some embodiments, in step (2), the lithium-containing raw material comprises at least one of lithium carbonate, lithium hydroxide, lithium carboxylates, lithium sulfate, lithium fluoride, and lithium phosphate, and optionally at least one of lithium carbonate, lithium acetate, lithium citrate, lithium oxalate, lithium sulfate, lithium fluoride, and lithium phosphate. More preferably, it comprises at least one of lithium carbonate, lithium acetate, lithium citrate, and lithium fluoride. Therefore, the type of lithium salt in the coating layer is further preferred, resulting in higher surface stability of the negative electrode active material, thereby effectively improving the initial coulombic efficiency and cycle stability of the corresponding battery.

[0074] In some embodiments, step (2) includes: preparing a lithium-containing raw material into a corresponding solution; dispersing the flake graphite in the solution to obtain a mixture; filtering, drying, and dispersing the mixture to obtain a solid powder; and sintering the solid powder at 300-900°C for 0.5-8 hours under a protective atmosphere or vacuum to form a lithium salt coating layer on the surface of the flake graphite. This further optimizes the quality of the flake graphite surface coating layer, improves the surface stability of the negative electrode active material, and thus effectively improves the initial coulombic efficiency and cycle stability of the corresponding battery.

[0075] In some preferred embodiments, in step (2), the solvent used in the lithium-containing raw material solution is water or ethanol; the concentration of the lithium-containing raw material is 10-50% by weight, based on the total weight of the solution. The flake graphite is dispersed in the solution by stirring at 500-1200 rpm, preferably 600-1000 rpm, using a stirring and mixing device to obtain a mixture; wherein the weight ratio of flake graphite to lithium-containing raw material is 1:0.01-0.5, preferably 1:0.05-0.2. The mixture is filtered using a vacuum filter at room temperature and a pressure of 0.002-0.05 MPa, preferably 0.008-0.012 mPa. It is then dried in a drying oven at 50-150°C, preferably 80-100°C, for 3-12 hours or 4-8 hours, and dispersed using an air-jet disperser for 0.5-5 hours, preferably 1-3 hours, to obtain a solid powder. The solid powder is then sintered at 300-900°C, preferably 400-900°C, for 0.5-8 hours, preferably 0.5-5 hours, under a protective atmosphere or vacuum to form a lithium salt coating layer on the surface of the flake graphite, and then naturally cooled to room temperature.

[0076] In some preferred embodiments, in step (2), when lithium carbonate and lithium carboxylates are used as lithium-containing raw materials, the lithium salt coating layer is typically composed of lithium carbonate when the solid powder is sintered at 300-750°C for 3-8 hours; when the solid powder is sintered at 750-900°C for 0.5-3 hours, the lithium salt coating layer is typically composed of lithium carbonate and lithium oxide. When the sintering temperature is sufficiently high or long, the lithium salt coating layer may eventually consist only of lithium oxide.

[0077] In some embodiments, in step (3), the flake graphite obtained in step (2) is shaped to obtain spherical graphite with an average volumetric particle size Dv50 of 5-40 μm, wherein the average volumetric particle size Dv50 is measured as described above. Specifically, step (3) includes pulverizing and shaping the flake graphite obtained in step (2) in an air-jet mill, dispersing it in an air-jet disperser for 0.5-5 hours, preferably 1-3 hours, and sieving it in a vibrating screen to obtain spherical graphite particles with an average volumetric particle size Dv50 of 5-40 μm. In this step, the surface of the coated flake graphite forms the surface of the internal pores of the spherical particles, and the surface lithium salt coating layer of the flake graphite also forms the surface coating layer of the internal pores of the spherical particles. It should be noted that it is not excluded that the surface lithium salt coating layer of the flake graphite may also form a coating layer on a portion of the outer surface of the spherical particles, and the proportion of this portion of the outer surface area of ​​the spherical particles does not exceed 40% of the particle surface area.

[0078] In some embodiments, in step (4), the spherical graphite is coated with a lithium-containing raw material to form a lithium salt coating layer on the surface of the spherical graphite, thereby obtaining the negative electrode active material. Specifically, the lithium-containing raw material is prepared into a corresponding solution; the spherical graphite is dispersed in the solution to obtain a mixture; the mixture is filtered, dried, and dispersed to obtain a solid powder; the solid powder is sintered at 300-900°C for 0.5-8 hours under a protective atmosphere or vacuum to form a lithium salt coating layer on the surface of the spherical graphite. The lithium-containing raw material in step (4) is as described in step (2), and may be the same as or different from that described in step (4). Other required technical features of step (4) are as described in step (2).

[0079] A third aspect of this application also provides a secondary battery, characterized in that,

[0080] This includes the negative electrode active material described in the first aspect of this application or the negative electrode active material prepared according to the method described in the second aspect of this application. The resulting secondary battery has improved initial coulombic efficiency and cycle stability.

[0081] A fourth aspect of this application provides an electrical device comprising a secondary battery selected from the second aspect of this application.

[0082] The secondary battery and power-consuming device of this application will be described below with appropriate reference to the accompanying drawings.

[0083] In one embodiment of this application, a secondary battery is provided.

[0084] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0085] Positive electrode sheet

[0086] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including the positive electrode active material of the first aspect of this application.

[0087] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0088] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material 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 on the polymer material substrate. The metal material includes, but is not limited to, aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The polymer material substrate may be (e.g., polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0089] In some embodiments, the positive electrode active material may comprise positive electrode active materials known in the art for use in batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 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 Co 0.15 Al 0.05At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, 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 manganese iron phosphate, and lithium manganese iron phosphate and carbon composites. The positive electrode active material accounts for 80-100% by weight in the positive electrode film, based on the total weight of the positive electrode film.

[0090] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a terpolymer of PVDF-tetrafluoroethylene-propylene, a terpolymer of PVDF-hexafluoropropylene-tetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorinated acrylate resin. The binder constitutes 0-20% by weight of the positive electrode film layer, based on the total weight of the positive electrode film layer.

[0091] 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. The conductive agent accounts for 0-20% by weight of the positive electrode film, based on the total weight of the positive electrode film.

[0092] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive electrode active material, conductive agent, binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry, wherein the solid content of the positive electrode slurry is 40-80 wt%, and the viscosity at room temperature is adjusted to 5000-25000 mPa·s. The positive electrode slurry is coated on the surface of the positive electrode current collector, dried, and then cold-pressed using a cold rolling mill to form the positive electrode sheet; the areal density of the positive electrode powder coating is 150-350 mg / m³. 2 The compaction density of the positive electrode sheet is 3.0-3.6 g / cm³. 3 The concentration can be selected as 3.3-3.5 g / cm³. 3 The formula for calculating the compaction density is as follows:

[0093] Compacted density = Coated surface density / (Extreme electrode thickness after extrusion - Current collector thickness).

[0094] Negative electrode sheet

[0095] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer comprising a negative electrode active material prepared according to the first aspect of the present invention or according to the second aspect of the present invention.

[0096] 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.

[0097] 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 on the polymer material substrate. The metal material includes, but is not limited to, copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc., and the polymer material substrate includes, but is not limited to, polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0098] In some embodiments, the negative electrode active material accounts for 70-100% by weight in the negative electrode film, based on the total weight of the negative electrode film.

[0099] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS). The binder accounts for 0-30% by weight of the negative electrode film layer, based on the total weight of the negative electrode film layer.

[0100] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The conductive agent accounts for 0-20% by weight of the negative electrode film, based on the total weight of the negative electrode film.

[0101] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)). The other additives constitute 0-15% by weight of the negative electrode film, based on the total weight of the negative electrode film.

[0102] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry, wherein the solid content of the negative electrode slurry is 30-70 wt%, and the viscosity at room temperature is adjusted to 2000-10000 mPa·s; the obtained negative electrode slurry is coated onto a negative electrode current collector, and after a drying process, it is cold-pressed, for example, by rollers, to obtain the negative electrode sheet. The areal density of the negative electrode powder coating is 75-220 mg / m³. 2 The compacted density of the negative electrode sheet is 1.2-2.0 g / m³. 3 .

[0103] electrolytes

[0104] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0105] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0106] In some embodiments, the electrolyte salt may be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP). The concentration of the electrolyte salt is typically 0.5-5 mol / L.

[0107] In some embodiments, the solvent may be selected from one or more of fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0108] 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 may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0109] Separating membrane

[0110] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0111] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0112] In some embodiments, the thickness of the isolation membrane is 6-40 μm, optionally 12-20 μm; the porosity is 30-60%, and the pore size is 100 nm-1.0 μm.

[0113] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0114] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0115] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0116] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 3 This is an example of a square-structured secondary battery 5.

[0117] In some implementations, refer to Figure 4The 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. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0118] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module 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 module.

[0119] 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.

[0120] A fourth aspect of this application provides an electrical device comprising a secondary battery, battery module, or battery pack selected from the second aspect of this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., 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.

[0121] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0122] Figure 5 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 the secondary battery for this device, a battery pack or battery module can be used.

[0123] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0124] Example

[0125] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the application will be further described in detail below with reference to embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0126] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0127] I. Preparation Examples

[0128] Preparation of negative electrode active materials

[0129] Preparation Example 1

[0130] (1) Add 10 kg of flake natural graphite with a planar size of 100 μm to a mixer equipped with a stirring device.

[0131] (2) Add 10 kg of 3 wt% lithium acetate aqueous solution to the equipment in step (1) and stir at 1200 rpm for 5 hours to completely disperse the flake natural graphite. Then filter using a vacuum filter at 0.01 MPa pressure, dry the filtrate in a drying oven at 90°C for 6 hours, and then disperse the resulting solid using an air-jet disperser for 2 hours. Finally, place the solid in a tube furnace and sinter at 450°C under nitrogen atmosphere and normal pressure for 5 hours, and allow it to cool naturally to room temperature to obtain Li2CO3-coated flake natural graphite.

[0132] (3) The Li2CO3-coated flake natural graphite obtained in step (2) is crushed and shaped in an air-flow pulverizer and then dispersed in an air-flow disperser for 2 hours and sieved in a vibrating screen to obtain spherical graphite particles with a Dv50 of 20μm.

[0133] (3i) The spherical particles and asphalt were stirred and mixed in a heating machine at 200°C and 600 rpm for 30 min under normal pressure. The resulting mixture was then placed in a sintering furnace and carbonized at 1200°C under N2 atmosphere for 5 hours to obtain carbon-coated spherical particles.

[0134] (4) In a mixer equipped with a stirring device, 10 kg of the carbon-coated spherical particles were added to 10 kg of a 3 wt% lithium acetate aqueous solution and stirred at 1200 rpm for 5 hours. Then, the mixture was filtered using a vacuum filter at a pressure of 0.01 MPa. The filtrate was dried in a drying oven at 90°C for 6 hours. The resulting solid was then dispersed using an air-jet disperser for 2 hours. Finally, the solid was placed in a tube furnace and sintered at 450°C under nitrogen atmosphere and atmospheric pressure for 5 hours to obtain the negative electrode active material, which is spherical natural graphite with Li2CO3 coating on the outer surface and internal pores.

[0135] The average volumetric particle size Dv50 of the negative electrode active material is 17 μm; its SEM image is shown below. Figure 1 Other relevant product parameters are summarized in Table 1.

[0136] Preparation Example 2

[0137] The steps of Example 1 were repeated, except that the sintering temperature in steps (2) and (4) was increased to 750°C and sintered for 1 hour. At this temperature, Li2CO3 began to decompose into Li2O and CO2, thus adjusting the composition of the artificial SEI film to a state where Li2CO3 and Li2O coexist.

[0138] Preparation Example 3

[0139] The steps of Example 1 were repeated, except that the sintering temperature in steps (2) and (4) was increased to 850°C and sintered for 1 hour.

[0140] Preparation Example 4

[0141] The steps of Preparation Example 1 were repeated, except that step (3i) was not included.

[0142] Preparation Example 5

[0143] The steps of Example 1 were repeated, except that lithium acetate in steps (2) and (4) was replaced with lithium citrate.

[0144] Preparation Example 6

[0145] The steps of Example 1 were repeated, except that in steps (2) and (4), lithium acetate was replaced with lithium carbonate, and no sintering step was performed after dispersing. Because lithium carbonate has very low solubility in water, 10 kg of saturated lithium carbonate aqueous solution was added instead, and step (2) was repeated twice.

[0146] Preparation Example 7

[0147] The steps of Example 1 were repeated, except that in step (2), the amount of lithium acetate solution used was 10 kg of 8 wt% lithium acetate aqueous solution, and in step (4), the amount of lithium acetate solution used was 10 kg of 1 wt% lithium acetate aqueous solution.

[0148] Preparation Example 8

[0149] The steps of Example 1 were repeated, except that in step (2), the amount of lithium acetate solution used was 10 kg of 1 wt% lithium acetate aqueous solution, and in step (4), the amount of lithium acetate solution used was 10 kg of 8 wt% lithium acetate aqueous solution.

[0150] Preparation Example 9

[0151] The steps of Example 1 were repeated, except that the concentration of lithium acetate was set to 1 wt% in steps (2) and (4).

[0152] Preparation Example 10

[0153] The steps of Example 1 were repeated, except that the concentration of lithium acetate was set to 5 wt% in steps (2) and (4).

[0154] Example 11

[0155] The steps of Example 1 were repeated, except that before step (3i), a surface treatment was performed: the spherical graphite particles were soaked in an 80% hydrogen peroxide aqueous solution for 3 hours, then filtered, and then placed in a sintering furnace and kept at 400°C for 1 hour in an oxygen atmosphere, and then cooled naturally.

[0156] Comparative Example 1

[0157] The steps of preparation Example 1 were repeated, except that step (2) was not performed.

[0158] The relevant parameters of the above embodiments and comparative examples are summarized in Table 1.

[0159] Test methods

[0160] Method for testing lithium element in coating layer of anode active material

[0161] The lithium content in the negative electrode active material particles can be measured using inductively coupled plasma atomic emission spectrometry (ICP). When the negative electrode active material is added to a hydrochloric acid solution, the hydrochloric acid acts as a digestion reagent, dissolving only the outer lithium salt layer and failing to dissolve the internal lithium salt coating and graphene. In this case, the lithium content measured by ICP is the outer surface lithium content (Li). 外The negative electrode active material, after dissolving the external lithium salt, is added to concentrated nitric acid, which serves as the digestion reagent. Microwave digestion completely dissolves the graphene and the internal lithium salt. The lithium content obtained by ICP testing at this point represents the lithium elemental content (Li) within the internal pores. 内 The total carbon content was also obtained; therefore, the weight ratio of lithium in the pores inside the graphite particles to lithium on the outer surface of the graphite particles (Li) was calculated. 内 Li 外 ).

[0162] Table 1. Relevant parameters of preparation methods and products for each embodiment and comparative example.

[0163]

[0164] II. Application Examples

[0165] Example 1

[0166] 1) Preparation of positive electrode sheet

[0167] Lithium iron phosphate (LiFePO4), conductive carbon black (SP), and PVDF binder were dispersed in NMP solvent at a weight ratio of 98:1:1 and mixed evenly to obtain a positive electrode slurry. The positive electrode slurry was then uniformly coated onto an aluminum foil current collector. After drying and cold pressing, a positive electrode sheet was obtained, with a coating weight of 0.27 g / 1540.25 mm². 2 .

[0168] 2) Preparation of negative electrode sheet

[0169] The negative electrode active material prepared in Example 1, the thickener sodium carboxymethyl cellulose, the binder styrene-butadiene rubber, and the conductive agent carbon black were mixed in a mass ratio of 96:1:1:2. Deionized water was added, and the mixture was stirred under vacuum to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated onto copper foil. After the copper foil was dried at room temperature, it was transferred to a 120°C oven to dry for 1 hour. Then, it was cold-pressed and slit to obtain a negative electrode sheet with a coating weight of 0.17 g / 1540.25 mm². 2 .

[0170] 3) Separating membrane

[0171] A 12μm thick polypropylene separator with a porosity of 50% was selected.

[0172] 4) Preparation of electrolyte

[0173] The organic solvent was a mixture containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), with a volume ratio of EC:20:20:60. Thoroughly dried lithium salt LiPF6 was dissolved in the organic solvent and mixed thoroughly in an argon-atmosphere glove box with a water content of <10 ppm to obtain the electrolyte. The concentration of the lithium salt was 1 mol / L.

[0174] 5) Battery manufacturing

[0175] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. After being wound into a square bare cell, it is placed in an aluminum-plastic film, baked at 80°C to remove water, and then 10g of the corresponding non-aqueous electrolyte is injected and sealed. After processes such as standing, hot and cold pressing, formation, clamping, and capacity testing, a finished battery with a capacity of 4000mAh is obtained.

[0176] The secondary batteries in Examples 2-11 and Comparative Example 1 are prepared using methods similar to those in Example 1, but the corresponding negative electrode active materials from the preparation examples are used.

[0177] III. Battery Performance Testing

[0178] Cyclic performance test

[0179] Place the battery in a 60℃ oven and let it stand for 2 hours. Once the battery temperature is maintained at 60℃, perform a charge-discharge test. Charge the battery with a 1 / 3C constant current to 3.65V, then continue charging with a constant voltage until the charging current is less than 0.05C. Record the charging capacity C01. Pause for 5 minutes. Discharge the battery with a 1 / 3C constant current to 2.0V and record the discharge capacity C02.

[0180] Charge the battery with a constant current of 1C to 3.65V, then continue charging with a constant voltage until the charging current is less than 0.05C, at which point the charging capacity is recorded as C11. Pause for 5 minutes. Then discharge the battery with a constant current of 1C to 2.5V, recording the discharge capacity as C12. Pause for 5 minutes. This completes the first charge-discharge cycle of the battery. Repeat this process until the battery has completed 300 cycles, recording the discharge capacity as C3002.

[0181] Initial Coulomb efficiency = CO2 / C01;

[0182] 300-cycle capacity retention rate = C3002 / C12

[0183] III. Test Results of Each Embodiment and Comparative Example

[0184] Batteries for each embodiment and comparative example were prepared according to the above method, and various performance parameters were measured. The results are shown in Table 2 below.

[0185] Table 2 Performance tests of each embodiment and comparative example

[0186]

[0187] As can be seen from the above embodiments and comparative examples, the negative electrode active material of this application effectively improves the initial coulombic efficiency and cycle stability of the corresponding battery; for example, the initial coulombic efficiency of the corresponding secondary battery can reach more than 89%, and the capacity retention rate after 300 cycles can reach more than 95%.

[0188] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A negative electrode active material comprising graphite particles with internal pores and a lithium salt coating layer covering the internal pores and the outer surface of the graphite particles, wherein the weight ratio of lithium element in the internal pores of the graphite particles to lithium element on the outer surface of the graphite particles is 1~10:1; the lithium salt is an inorganic lithium salt.

2. The negative electrode active material according to claim 1, characterized in that, The lithium salt coating layer satisfies at least one of the following characteristics: (1) The content of the lithium salt coating layer is 0.01%-6%, based on the total weight of the negative electrode active material; (2) The thickness of the lithium salt coating layer in the internal pores of the graphite particles is 1-20 nm, and the thickness of the lithium salt coating layer on the outer surface of the graphite particles is 1-30 nm.

3. The negative electrode active material according to claim 1 or 2, characterized in that, It satisfies at least one of the following characteristics: (1) The graphite is natural graphite; (2) The lithium salt is selected from one or more of carbonates, lithium oxide, lithium phosphate and lithium fluoride.

4. The negative electrode active material according to claim 1 or 2, characterized in that, The average volume particle size D of the negative electrode active material v50 It is 10-30µm.

5. The negative electrode active material according to claim 3, characterized in that, The average volume particle size D of the negative electrode active material v50 It is 10-30µm.

6. The negative electrode active material according to claim 1, 2, or 5, characterized in that, Between the graphite and lithium salt coating, there is also a carbon coating layer.

7. The negative electrode active material according to claim 3, characterized in that, Between the graphite and lithium salt coating, there is also a carbon coating layer.

8. The negative electrode active material according to claim 4, characterized in that, Between the graphite and lithium salt coating, there is also a carbon coating layer.

9. The negative electrode active material according to claim 6, characterized in that, The carbon coating layer has a coating amount of 0.2-10%, based on the total weight of the negative electrode active material.

10. The negative electrode active material according to claim 7, characterized in that, The carbon coating layer has a coating amount of 0.2-10%, based on the total weight of the negative electrode active material.

11. The negative electrode active material according to claim 8, characterized in that, The carbon coating layer has a coating amount of 0.2-10%, based on the total weight of the negative electrode active material.

12. A method for preparing a negative electrode active material, comprising: (1) Provide flake graphite; (2) Using lithium-containing raw materials to coat flake graphite, so that a lithium salt coating layer is formed on the surface of flake graphite; (3) Shape the flake graphite obtained in step (2) to obtain spherical graphite; (4) The spherical graphite is coated with lithium-containing raw materials to form a lithium salt coating layer on the surface of the spherical graphite, thereby obtaining the negative electrode active material; The negative electrode active material comprises graphite with internal pores and a lithium salt coating layer covering the internal pores and the outer surface of the graphite, wherein the weight ratio of lithium element in the internal pores of the graphite to lithium element on the outer surface of the graphite is 1~10:

1.

13. The method according to claim 12, characterized in that, Carbon coating or surface treatment is performed between steps (1) and (2) or between steps (3) and (4).

14. The method according to claim 12 or 13, characterized in that, Between steps (3) and (4), carbon coating or surface treatment is performed.

15. The method according to claim 12 or 13, characterized in that, In step (2), the lithium-containing raw material includes at least one of lithium carbonate, lithium hydroxide, lithium carboxylates, lithium sulfate, lithium fluoride and lithium phosphate.

16. The method according to claim 14, characterized in that, In step (2), the lithium-containing raw material includes at least one of lithium carbonate, lithium hydroxide, lithium carboxylates, lithium sulfate, lithium fluoride and lithium phosphate.

17. The method according to claim 15, characterized in that, In step (2), the lithium-containing raw material includes at least one of lithium carbonate, lithium acetate, lithium citrate, lithium oxalate, lithium sulfate, lithium fluoride and lithium phosphate.

18. The method according to claim 16, characterized in that, In step (2), the lithium-containing raw material includes at least one of lithium carbonate, lithium acetate, lithium citrate, lithium oxalate, lithium sulfate, lithium fluoride and lithium phosphate.

19. The method according to claim 12 or 13, characterized in that, Step (2) includes: preparing a lithium-containing raw material into a corresponding solution; dispersing the flake graphite in the solution to obtain a mixture; filtering, drying and dispersing the mixture to obtain a solid powder; sintering the solid powder at 300-900℃ for 0.5-8h under a protective atmosphere or vacuum to form a lithium salt coating layer on the surface of the flake graphite.

20. The method according to claim 14, characterized in that, Step (2) includes: preparing a lithium-containing raw material into a corresponding solution; dispersing the flake graphite in the solution to obtain a mixture; filtering, drying and dispersing the mixture to obtain a solid powder; sintering the solid powder at 300-900℃ for 0.5-8h under a protective atmosphere or vacuum to form a lithium salt coating layer on the surface of the flake graphite.

21. The method according to claim 15, characterized in that, Step (2) includes: preparing a lithium-containing raw material into a corresponding solution; dispersing the flake graphite in the solution to obtain a mixture; filtering, drying and dispersing the mixture to obtain a solid powder; sintering the solid powder at 300-900℃ for 0.5-8h under a protective atmosphere or vacuum to form a lithium salt coating layer on the surface of the flake graphite.

22. The method according to claim 16, characterized in that, Step (2) includes: preparing a lithium-containing raw material into a corresponding solution; dispersing the flake graphite in the solution to obtain a mixture; filtering, drying and dispersing the mixture to obtain a solid powder; sintering the solid powder at 300-900℃ for 0.5-8h under a protective atmosphere or vacuum to form a lithium salt coating layer on the surface of the flake graphite.

23. The method according to claim 17, characterized in that, Step (2) includes: preparing a lithium-containing raw material into a corresponding solution; dispersing the flake graphite in the solution to obtain a mixture; filtering, drying and dispersing the mixture to obtain a solid powder; sintering the solid powder at 300-900℃ for 0.5-8h under a protective atmosphere or vacuum to form a lithium salt coating layer on the surface of the flake graphite.

24. The method according to claim 18, characterized in that, Step (2) includes: preparing a lithium-containing raw material into a corresponding solution; dispersing the flake graphite in the solution to obtain a mixture; filtering, drying and dispersing the mixture to obtain a solid powder; sintering the solid powder at 300-900℃ for 0.5-8h under a protective atmosphere or vacuum to form a lithium salt coating layer on the surface of the flake graphite.

25. A secondary battery, characterized in that, Includes the negative electrode active material according to any one of claims 1-11 or the negative electrode active material prepared by the method according to any one of claims 12-24.

26. An electrical appliance, characterized in that, Includes the secondary battery selected from that described in claim 25.

Images