Negative electrode material, method for preparing the same, and secondary battery

Abstract

This invention provides a negative electrode material, its preparation method, and a secondary battery. The negative electrode material provided in this application comprises multiple spherical graphite composite particles. The average porosity of the cross-section of the spherical graphite composite particles is [value missing], the average porosity of the inner layer region a is [value missing], the average porosity of the outer layer region b is [value missing], and its compaction orientation OI value y, upper limit OI value y1, lower limit OI value y2, and compaction density x satisfying y1=6.89x-6.04, y2=8.9x-7.76, y1≤y≤y2, 4.3≤y≤10, and 1.5g / cm³. 3 ≤x≤2.0g / cm 3 The negative electrode material provided in this application has reduced internal porosity, reduced specific surface area, increased powder compaction density, and reduced orientation, thereby reducing the impact of SEI film formation on Li during the first charge-discharge process. + Consumption increases the efficiency of the first coulomb run.

Description

Technical Field

[0001] This invention relates to the field of battery materials, and more specifically, to a negative electrode material, its preparation method, and a secondary battery. Background Technology

[0002] As an important energy storage device, the performance of the positive and negative electrode materials of a secondary battery determines its capacity and lifespan. With the widespread use of digital consumer electronics such as mobile phones, computers, and digital cameras in our daily lives, the requirements for secondary batteries are constantly increasing. Natural graphite anode materials have advantages such as high charge / discharge capacity, low charge / discharge platform, and low cost, and are widely used in secondary batteries. However, natural graphite has high anisotropy and surface defects, which pose challenges in lithium-ion (Li-ion) batteries. + Solvent co-intercalation is prone to occur during the intercalation process, making it difficult to form a dense SEI film during the first charge and discharge process. Graphite sheet shedding is also likely to occur, resulting in problems such as short cycle life and high expansion rate.

[0003] To improve the electrochemical performance of natural graphite, researchers have employed various methods to physicochemically modify and surface-modify it. Some researchers purified flake graphite at high temperatures under nitrogen protection, then pulverized, spheroidized, and soaked in a mixed solution of ethylenediamine and ammonia. After drying, it was coated with pitch and carbonized under an inert gas atmosphere. This process improved charge-discharge and cycle performance by creating pores and introducing functional groups. Other researchers mixed spherical graphite with coal tar pitch and, by setting different carbonization temperature curves, obtained a graphite anode material with high rate performance. All of these techniques improve interfacial stability and enhance electrochemical performance by coating the surface with amorphous carbon. However, natural graphite has a high porosity; during charge-discharge, the electrolyte gradually penetrates into the graphite's internal pores, leading to an increase in electrode volume and a decrease in capacity stability and cycle performance.

[0004] Some researchers have also developed a processing method for high-cycle natural graphite anode materials. The method includes: ① uniformly mixing natural graphite and a modifier at a ratio of 100:0-30; ② isostatically pressing the mixture at 50-300 MPa; ③ pulverizing the mixture and mixing it with the modifier, followed by high-temperature carbonization; ④ cooling and grading to obtain the natural graphite anode material. However, this material has a low powder compaction density, only 1.5-1.6 g / cm³. 3 Specific surface area 4.5-5.5m² 2 / g, initial coulombic efficiency is low, only 90%-91%.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The main objective of this invention is to provide a negative electrode material, its preparation method, and a secondary battery, in order to solve the problems of capacity stability and cycle performance degradation in the prior art of coating amorphous carbon with natural graphite, and the problems of limited filling effect, low material powder compaction density, and low initial coulombic efficiency when using natural graphite and modifiers for molding.

[0007] To achieve the above objectives, according to one aspect of the present invention, a negative electrode material is provided, comprising a plurality of spherical graphite composite particles, wherein the pores inside the spherical graphite composite particles are filled with amorphous carbon, and the cross-section of the spherical graphite composite particles is divided into an inner layer region a and an outer layer region b, wherein the outer layer region b surrounds the periphery of the inner layer region a; the average porosity of the cross-section of the spherical graphite composite particles is [missing information]. The average porosity of inner region a is The average porosity of the outer region b is and

[0008]

[0009] The OI value of the negative electrode material under different compaction densities is y, with the upper limit OI being y1 and y2 respectively. The compaction density of the negative electrode material under different pressures is x, where y1 = 6.89x - 6.04, y2 = 8.9x - 7.76, and y1 ≤ y ≤ y2, 1.5 g / cm³. 3 ≤x≤2.0g / cm 3 .

[0010] Furthermore, the average particle size D50 of the spherical graphite composite particles is 5-20 μm, the particle size symmetry Φ is 1.45-1.70, and Φ=(D90-D50) / (D50-D10).

[0011] Furthermore, the specific surface area (SSA) of the spherical graphite composite particles is 2 m². 2 / g-5m 2 / g.

[0012] Furthermore, the shape of the spherical graphite composite particles includes at least one of spherical and near-spherical shapes.

[0013] Furthermore, the compaction density of the anode material under 2T pressure is 1.7 g / cm³. 3 -2.0g / cm 3 .

[0014] Furthermore, the tap density of the negative electrode material is 0.9-1.5 g / cm³. 3 .

[0015] To achieve the above objectives, according to another aspect of the present invention, a method for preparing the above-mentioned negative electrode material is provided, the method comprising: step S1, mixing natural flake graphite particles with a modifier and performing coating and shaping treatments to obtain a spherical graphite modified composite; step S2, subjecting the spherical graphite modified composite to low-temperature heat treatment to soften the modifier and obtain a spherical graphite modified heat-treated material; step S3, subjecting the spherical graphite modified heat-treated material to molding and pulverizing treatments to obtain a spherical graphite composite precursor; and step S4, subjecting the spherical graphite composite precursor to calcination treatment to obtain the negative electrode material.

[0016] Further, step S1 includes: mixing natural flake graphite particles with a first modifier for preliminary coating treatment, followed by pulverization and shaping treatment to obtain a spherical graphite preliminary coating; mixing the spherical graphite preliminary coating with a second modifier for further coating treatment to obtain a spherical graphite modified composite; wherein the modifier includes a first modifier and a second modifier.

[0017] Furthermore, the average particle size D50 of the preliminary spherical graphite coating is 1-20 μm.

[0018] Furthermore, the D50 of natural flake graphite particles is 60-110 μm, and the fixed carbon content is ≥99%.

[0019] Furthermore, the modifier includes asphalt, which is selected from at least one of petroleum asphalt, coal tar pitch, and mesophase asphalt.

[0020] Furthermore, the mass ratio of natural flake graphite particles to the first modifier is 100:(0-2.5).

[0021] Furthermore, the mass ratio of the initial spherical graphite coating to the second modifier is 100:(5-12).

[0022] Further, in step S2, the temperature of the low-temperature heat treatment is 100-200℃ higher than the softening point of the modifier.

[0023] Furthermore, the low-temperature heat treatment time is 3-4 hours.

[0024] Furthermore, the low-temperature heat treatment is carried out under the protection of an inert gas, which includes at least one of nitrogen, argon, or helium.

[0025] Further, in step S3, the pressure of the molding process is 10-60 MPa, and the molding process includes at least two of the following: hydraulic, mechanical, rotary, cold isostatic, warm isostatic, or hot isostatic.

[0026] Further, in step S4, the calcination temperature is 1000-1500℃, and the calcination time is 8-15h.

[0027] According to another aspect of the present invention, a secondary battery is provided, the secondary battery comprising the negative electrode material provided in the first aspect above or the negative electrode material obtained by the preparation method provided in the second aspect above.

[0028] The negative electrode material provided in this application has an amorphous carbon coating layer on the spherical graphite composite particles, which can improve interfacial stability, prevent solvent co-intercalation, and improve the initial coulombic efficiency. Simultaneously, the internal pores of the spherical graphite composite particles are filled with amorphous carbon, and the average porosity of the inner layer region a is... The average porosity of the outer region b is satisfy Furthermore, the orientation OI value y, upper limit OI value y1, lower limit OI value y2, and compaction density x of the graphite anode material satisfy y1=6.89x-6.04, y2=8.9x-7.76, and y1≤y≤y2, 4.3≤y≤10, 1.5g / cm³ 3 ≤x≤2.0g / cm 3 The reduced internal porosity, decreased specific surface area, and increased powder compaction density reduce the impact of SEI film formation on Li during the initial charge-discharge process. + Consumption increases initial coulomb efficiency. Additionally, Li... + During the insertion and extraction process, volume expansion occurs. The disorder of amorphous carbon inside and outside the spherical graphite composite particles reduces the orientation of the material during pressing and increases its isotropy, which further improves the structural stability, alleviates volume expansion, and thus effectively improves the electrical performance of the negative electrode material. Attached Figure Description

[0029] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0030] Figure 1 This is a schematic diagram of the structure of a secondary battery during charging, provided in some embodiments of this application;

[0031] Figure 2 This is a schematic diagram of the structure of a secondary battery during discharge, provided in some embodiments of this application;

[0032] Figure 3 A cross-sectional view of a single spherical graphite composite particle in the graphite anode material provided in Embodiment 1 of this application is shown;

[0033] Figure 4 The graphs showing the relationship between the average compaction density and the average orientation OI value of the negative electrode materials provided in Examples 1-6 and Comparative Examples 1-4 of this application under different pressures are illustrated.

[0034] The above figures include the following reference numerals:

[0035] 100. Electrode assembly; 101. Positive electrode; 102. Negative electrode; 103. Separator. Detailed Implementation

[0036] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0037] As described in the background section of this application, physicochemical modification and surface alteration of natural graphite are used to improve interfacial stability by coating the surface of natural graphite with amorphous carbon. However, due to the high porosity of natural graphite, the electrolyte gradually penetrates into the pores during charge and discharge, leading to decreased capacity stability and cycle performance. Furthermore, using natural graphite and a modifier for molding to fill the internal pores results in low powder compaction density and low initial charge efficiency. To address these issues, this application provides a negative electrode material, its preparation method, and a secondary battery.

[0038] In one typical embodiment of this application, a negative electrode material is provided, comprising a plurality of spherical graphite composite particles. Each spherical graphite composite particle has an amorphous carbon coating layer, and the pores of the spherical graphite composite particles are filled with amorphous carbon. The cross-section of each spherical graphite composite particle is divided into an inner layer region a and an outer layer region b, with the outer layer region b surrounding the inner layer region a. The average porosity of the cross-section of the spherical graphite composite particle is [missing information - likely a percentage]. The average porosity of inner region a is The average porosity of the outer layer region b is and The OI value of the negative electrode material under different compaction densities is y, and the upper and lower limits of the OI value are y1 and y2, respectively. The compaction density of the negative electrode material under different pressures is x, where y1 = 6.89x - 6.04, y2 = 8.9x - 7.76, and y1 ≤ y ≤ y2, 4.3 ≤ y ≤ 10, and 1.5 g / cm³. 3 ≤x≤2.0g / cm 3 It should be noted that in this application, the inner layer region a is elliptical, and the center of the ellipse is the intersection of the transverse median line L1 and the longitudinal median line L2 of the cross-section of the spherical graphite composite particle, where L1 > L2, and the major axis L of the inner layer region a is... a =1 / 2L1, minor axis L b =1 / 2L2.

[0039] In this application, n≥20; Where {i|1≤i≤n,n≥20}.

[0040] The negative electrode material provided in this application has an amorphous carbon coating layer on the spherical graphite composite particles, which improves interfacial stability, prevents solvent co-intercalation, and increases the initial coulombic efficiency. Simultaneously, the internal pores of the spherical graphite composite particles are filled with amorphous carbon, and the average porosity of the inner layer region a is... The average porosity of the outer region b is satisfy The reduced internal porosity, decreased specific surface area, and increased powder compaction density reduce the impact of SEI film formation on Li during the initial charge-discharge process. + Consumption increases initial coulomb efficiency. Additionally, Li... + During the insertion and extraction process, volume expansion occurs. The disorder of amorphous carbon inside and outside the spherical graphite composite particles reduces the orientation of the material during pressing and increases its isotropy, which further improves the structural stability, alleviates volume expansion, and thus effectively improves the electrical performance of the negative electrode material.

[0041] The OI value is an important parameter describing the degree of order in the arrangement of graphite sheets in graphite materials. A lower OI value indicates increased isotropy and better material dynamics; however, an excessively low OI value can lead to Li... + Shortened diffusion paths limit battery capacity and affect SEI film stability, thus impacting initial coulombic efficiency. The anode material provided in this application features spherical graphite composite particles with an amorphous carbon coating layer. The internal pores are filled with amorphous carbon. The disorder of the amorphous carbon reduces the 004 / 110 orientation of the anode material, increases isotropy, further improves its structural stability, alleviates volume expansion, and enhances electrochemical performance.

[0042] In this application, the average porosity of the cross-section of the spherical graphite composite particles is... It can be a range of values, such as 1.9%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any two values. The value can be a range of 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, or any two values. The compaction density x of the negative electrode material under different pressures can be 1.5 g / cm³. 3 1.6g / cm 3 1.7g / cm 3 1.8g / cm 3 1.9g / cm 3 2.0g / cm 3Or a range of values ​​consisting of any two values. The OI value y of the negative electrode material under different compaction densities is such as 4, 5, 6, 8, 10, 11 or a range of values ​​consisting of any two values.

[0043] To further improve the cycle stability of the anode material, in some embodiments, the average particle size D50 of the spherical graphite composite particles is 5-20 μm, and the particle size symmetry Φ is 1.45-1.70, where Φ = (D90-D50) / (D50-D10). Specifically, the average particle size D50 of the spherical graphite composite particles can be 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, or any two of these values, and the particle size symmetry Φ can be 1.45, 1.50, 1.55, 1.60, 1.65, 1.70, or any two of these values.

[0044] In some embodiments, the specific surface area (SSA) of the spherical graphite composite particles is 2-5 m². 2 / g, to further increase the compaction density of the negative electrode material and further improve its electrical performance. Specifically, the specific surface area (SSA) of the spherical graphite composite particles can be 2m². 2 / g, 2.5m 2 / g、3m 2 / g, 3.5m 2 / g、4m 2 / g, 4.5m 2 / g、5m 2 / g or a range of values ​​consisting of any two numbers.

[0045] To further improve the compaction density and cycle stability of the anode material, in some embodiments, the spherical graphite composite particles have a shape including at least one of spherical and near-spherical shapes, thereby exhibiting excellent regularity. In some embodiments, the sphericity Sh (50%) of the spherical graphite composite particles is 0.83-0.86, and the Sh (90%) is 0.89-0.95. Specifically, the sphericity Sh (50%) of the spherical graphite composite particles can be 0.83, 0.84, 0.85, 0.86, or any range of two values; the Sh (%) can be 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, or any range of two values.

[0046] To further improve the electrical performance of the negative electrode material, in some embodiments, the compaction density of the negative electrode material under 2T pressure is 1.7-2.0 g / cm³. 3 Specifically, the compaction density of the negative electrode material under 2T pressure can be 1.7 g / cm³. 3 1.75g / cm 3 1.8g / cm3 1.85g / cm 3 1.9g / cm 3 1.95g / cm 3 2.0g / cm 3 Or a range of values ​​consisting of any two numerical values.

[0047] In a second typical embodiment of this application, a method for preparing a negative electrode material is provided. The method includes: step S1, mixing natural flake graphite particles with a modifier and performing coating and shaping treatments, so that the modifier is coated on the surface of the natural flake graphite particles to obtain a spherical graphite modified composite; step S2, subjecting the spherical graphite modified composite to low-temperature heat treatment, so that the modifier is softened, and the heat-treated spherical graphite modified material is subjected to molding and pulverizing treatments to obtain a spherical graphite composite precursor; step S4, subjecting the spherical graphite composite precursor to calcination treatment to obtain the negative electrode material.

[0048] The method for preparing the negative electrode material provided in this application first involves coating and shaping the material with a modifier to obtain a spherical graphite modified composite. Then, the spherical graphite modified composite is subjected to low-temperature heat treatment to soften the modifier and initially fill the internal pores. Next, a molding process is performed to press the modifier into the interior and fill the internal pores again, thereby increasing the compaction density. After pulverization, the material is calcined to obtain multiple spherical graphite composite particles with an amorphous carbon coating layer and internal pores filled with amorphous carbon, thus obtaining the negative electrode material.

[0049] The method for preparing the negative electrode material provided in this application is simple, easy to operate, and can further reduce costs.

[0050] To further improve the electrical performance of the negative electrode material, in some embodiments, in step S1, the D50 of the natural flake graphite particles is 60-110 μm, and the carbon content is fixed at ≥99%. Specifically, the D50 of the natural flake graphite particles can be 60 μm, 65 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, or any range of two values.

[0051] In some specific embodiments, step S1 includes: mixing natural flake graphite particles with a first modifier for preliminary coating treatment, followed by pulverization and shaping treatment to obtain a spherical graphite preliminary coating with a spherical structure and a surface coated with a modifier; mixing the spherical graphite preliminary coating with a second modifier for a second coating treatment to obtain a spherical graphite composite, thereby further improving the preparation efficiency of the spherical graphite composite and further improving the uniformity of the modifier coating layer, thereby further improving the structural stability of the prepared negative electrode material.

[0052] In some embodiments, the D50 of the spherical graphite pre-coating is 1-20 μm to further improve the filling rate of amorphous carbon. Specifically, the D50 of the spherical graphite pre-coating is a range of 1 μm, 2 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, or any combination of two such values.

[0053] The modifiers mentioned above can be any substances that can generate amorphous carbon after carbonization, and there are no restrictions on this. In order to facilitate filling the voids inside the graphite, the modifiers preferably include bitumen, which includes, but is not limited to, any one or a mixture of at least two of petroleum bitumen, coal bitumen, and mesophase bitumen.

[0054] To balance capacity and cycling stability, in some embodiments, the mass ratio of natural flake particles to the first modifier is 100:(0-2.5). Specifically, the mass ratio of natural flake particles to the modifier is, for example, 100:0.01, 100:0.1, 100:0.2, 100:0.5, 100:1, 100:2, 100:3, 100:4, 100:5, 100:6, 100:7, 100:8, 100:9, 100:10, or any range of two such values.

[0055] To balance capacity and cycling stability, in some embodiments, the mass ratio of the initial spherical graphite coating to the second modifier is 100:(5-12). Specifically, the mass ratio of the initial spherical graphite coating to the second modifier is, for example, 100:5, 100:6, 100:7, 100:8, 100:9, 100:10, 100:11, 100:12, or any range of two such values.

[0056] In step S2 above, the modifier is softened by low-temperature heat treatment and initially filled into the pores inside the graphite. The temperature of the low-temperature heat treatment is higher than the softening point of the modifier but lower than the carbonization point of the modifier. Preferably, the low-temperature heat treatment temperature is 100-200°C higher than the softening point of the modifier to further reduce energy consumption.

[0057] In some embodiments, the low-temperature heat treatment time is 3-4 hours to allow the modifier to soften more fully, making it easier to press into the internal pores of the graphite during subsequent molding. Specifically, the low-temperature heat treatment time can be 3 hours, 3.2 hours, 3.5 hours, 3.8 hours, 4.0 hours, or any range of two values.

[0058] To further reduce the impact of impurities on the electrochemical performance of graphite composites, in some embodiments, low-temperature heat treatment is carried out under inert gas protection, which includes, but is not limited to, nitrogen, argon, or any one or a mixture of at least two of argon.

[0059] In step S3 above, the pressing method is not limited, and any method that can press the modifier into the pores inside the graphite is acceptable, including but not limited to hydraulic pressing, mechanical pressing, rotary pressing, cold isostatic pressing, warm isostatic pressing, or hot isostatic pressing, or a combination of at least two of these methods. Specifically, to further promote the pressing of more modifier into the pores inside the graphite and improve the density of the graphite, it is preferable to press for 3-4 hours, and to perform pulverization after pressing to facilitate the preparation of anode materials with appropriate particle size.

[0060] To further improve the efficiency of the molding process and promote the infiltration of more modifier into the pores inside the graphite, in some embodiments, the molding pressure is 10-60 MPa. Specifically, the molding pressure is a range of 10 MPa, 15 MPa, 20 MPa, 25 MPa, 30 MPa, 40 MPa, 50 MPa, 60 MPa, or any combination of two values.

[0061] To further improve the carbonization efficiency of the modifier and the generation efficiency of amorphous carbon, in some embodiments, the calcination temperature in step S4 is 1000-1500℃, and the calcination time is 8-15h. Specifically, the calcination temperature is such as 1000℃, 1100℃, 1200℃, 1300℃, 1400℃, 1500℃, or any range of two values; the calcination time is such as 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, or any range of two values.

[0062] In a third typical embodiment of this application, a secondary battery is provided, which includes the negative electrode material provided in the first typical embodiment or the negative electrode material obtained according to the preparation method provided in the second typical embodiment.

[0063] The secondary battery provided in this application uses a negative electrode material, which comprises multiple spherical graphite composite particles. These spherical graphite composite particles have an amorphous carbon coating layer, improving interfacial stability, preventing solvent co-intercalation, and increasing the initial coulombic efficiency. Simultaneously, the internal pores of the spherical graphite composite particles are filled with amorphous carbon, and the average porosity of the inner layer region a is... The average porosity of the outer region b is satisfy The reduced internal porosity, decreased specific surface area, and increased powder compaction density reduce the impact of SEI film formation on Li during the initial charge-discharge process. +It can reduce energy consumption and improve the initial coulombic efficiency. At the same time, it can also utilize the disorder of the amorphous carbon filling inside the spherical graphite composite particles and the amorphous carbon coating layer on the outside to further improve structural stability, alleviate volume expansion, and further improve the electrical performance of the secondary battery.

[0064] In some embodiments, the secondary battery includes a casing, an electrode assembly, and an electrolyte. Both the electrode assembly and the electrolyte are located within the casing.

[0065] The outer casing can be a packaging bag encapsulated with a film (such as aluminum-plastic film), for example, a pouch battery. In other embodiments, it can also be a steel-cased battery, an aluminum-cased battery, etc.

[0066] Please see Figure 1 and Figure 2 The electrode assembly 100 includes a positive electrode 101, a negative electrode 102, and a separator 103, with the separator 103 disposed between the positive electrode 101 and the negative electrode 102. When an electrolyte (not shown) is present, please refer to [reference needed] for charging. Figure 1 Active ions (such as lithium ions) are extracted from the lattice of the positive electrode material (such as a lithium-ion intercalation compound) in the positive electrode 101, pass through the electrolyte and the separator 103, reach the negative electrode 102, and insert into the lattice of the negative electrode material. For discharge procedures, please refer to [link to relevant documentation]. Figure 2 Active ions (such as lithium ions) are deintercalated from the lattice of the negative electrode material of the negative electrode 102, pass through the electrolyte through the separator 103, reach the positive electrode 101 and are embedded in the lattice of the positive electrode material (such as lithium intercalation compound), generating electrons that travel from the negative electrode 102 to the positive electrode 101 through the external circuit. The reverse movement of electrons forms an electric current, which can be used by electrical appliances.

[0067] In some embodiments, the electrode assembly 100 may be a stacked structure, which is formed by alternatingly stacking a positive electrode 101, a separator 103, and a negative electrode 102. In other embodiments, the electrode assembly 100 may also be a wound structure, which is formed by sequentially stacking and then winding the positive electrode 101, the separator 103, and the negative electrode 102.

[0068] Positive electrode film

[0069] The positive electrode 101 includes a positive current collector and a positive electrode material active layer disposed on at least one surface of the positive current collector. The positive current collector can be aluminum foil or nickel foil, or any composite current collector disclosed in the prior art, such as, but not limited to, current collectors formed by combining the aforementioned conductive foil and polymer substrate. The positive electrode material active layer includes a positive electrode active material, which includes a compound that reversibly inserts and extracts lithium ions (i.e., a lithiation intercalation compound). In some embodiments, the positive electrode active material may include a lithium transition metal composite oxide. This lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel. In some embodiments, the positive electrode active material may include, but is not limited to, lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt ternary materials (NCM), lithium manganese oxide (LiMn2O4), and lithium nickel manganese oxide (LiNi). 0.5 Mn 1.5 At least one of lithium iron phosphate (LiFePO4) or lithium iron phosphate (LiFePO4).

[0070] The positive electrode material active layer also includes an adhesive for bonding the positive electrode active material particles to facilitate the formation of the film layer, and also to improve the bonding force between the positive electrode material active layer and the positive electrode current collector. In some embodiments, the adhesive may include, but is not limited to, at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0071] The positive electrode material active layer may further include a conductive material, which includes, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, or any combination thereof. In some embodiments, carbon-based materials may include, but are not limited to, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, metal-based materials may include, but are not limited to, metal powders or metal fibers, such as copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer may be a polyphenylene derivative.

[0072] negative electrode sheet

[0073] The negative electrode 102 includes a negative electrode current collector and an active layer of negative electrode material disposed on at least one surface of the negative electrode current collector. The negative electrode current collector can be at least one of copper foil, nickel foil, stainless steel foil, titanium foil or carbon-based current collector, or any composite current collector disclosed in the prior art, such as, but not limited to, a current collector formed by combining the aforementioned conductive foil and polymer substrate.

[0074] The active layer of the negative electrode material includes the negative electrode material, which includes graphite, silicon, etc.

[0075] The active layer of the negative electrode material also includes a binder to bond the negative electrode active material particles, thereby facilitating the formation of the film layer and improving the bonding force between the active layer of the negative electrode material and the negative electrode current collector. In some embodiments, the binder may include, but is not limited to, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon, etc.

[0076] The active layer of the negative electrode material may further include a conductive material, which includes, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, or any combination thereof. In some embodiments, carbon-based materials may include, but are not limited to, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, metal-based materials may include, but are not limited to, metal powders or metal fibers, such as copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer may be a polyphenylene derivative.

[0077] Separating membrane

[0078] The separator 103 includes a membrane layer with a porous structure, and its material includes, but is not limited to, at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, the separator 103 may be a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane, etc.

[0079] electrolytes

[0080] The electrolyte serves to conduct ions between the positive electrode 101 and the negative electrode 102. The electrolyte can be in one or more of the following states: gel, solid, and liquid. In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution conducts active ions between the positive electrode 101 and the negative electrode 102. In some embodiments, the electrolyte solution includes a lithium salt and an organic solvent. The lithium salt may be selected from, but is not limited to, lithium hexafluorophosphate (LiPF6). 6)One or more of the following lithium salts are used: lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), lithium tetraphenylborate (LiB(C6H5)4), lithium methanesulfonate (LiCH3SO3), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethanesulfonyl)imide (LiN(SO2CF3)2), lithium tris(trifluoromethanesulfonyl)methyl lithium (LiC(SO2CF3)3), lithium dioxarate borate (LiBOB), and lithium difluorophosphate (LiPO2F2). For example, LiPF6 is chosen as the lithium salt because it provides high ionic conductivity and improves cycling characteristics. The organic solvent can be a carbonate compound, a carboxylic acid ester compound, an ether compound, a nitrile compound, or others. Organic solvents or combinations thereof. Examples of carbonate compounds include, but are not limited to, diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, or combinations thereof.

[0081] The beneficial effects of this application will be further illustrated below with reference to embodiments and comparative examples.

[0082] Example 1

[0083] This embodiment provides a negative electrode material comprising multiple spherical graphite composite particles. Each spherical graphite composite particle has an amorphous carbon coating layer, and the pores within the spherical graphite composite particles are filled with amorphous carbon. The material is prepared according to the following steps:

[0084] (1) Take 40 kg of natural flake graphite particles (D50 = 100.5 μm) and mix them with 1.0 kg of petroleum asphalt (softening point 250℃) for preliminary coating treatment. After multiple crushing and shaping treatments, 20 kg of spherical graphite preliminary coating material (D50 = 16 μm) is obtained.

[0085] (2) Add 20 kg of spherical graphite pre-coated material and 1.7 kg of petroleum asphalt (softening point 250℃) to a VC mixer and mix for 25 min. After mixing evenly, heat treat at 400℃ for 4 h under nitrogen protection and cool to room temperature to obtain spherical graphite modified heat-treated material.

[0086] (3) The spherical graphite modified heat-treated material was placed in a hydraulic press for reciprocating molding. The hydraulic press pressure was 30 MPa, the time was 1 min, and the reciprocating process was repeated 3 times. Then, isostatic pressing was performed. The isostatic pressing pressure was 60 MPa, the holding time was 3 min, and after the isostatic pressing was completed, it was crushed to obtain the spherical graphite composite precursor.

[0087] (4) The spherical graphite composite precursor was carbonized at 1250℃ for 8 hours under nitrogen protection. After carbonization, it was dispersed, demagnetized and sieved to obtain a negative electrode material containing multiple spherical graphite composite particles.

[0088] Example 2

[0089] This embodiment provides a negative electrode material, which is prepared according to the following steps:

[0090] (1) Take 40 kg of natural flake graphite particles (D50 = 100.5 μm) and mix them with 1.0 kg of petroleum asphalt (softening point 180℃) for preliminary coating treatment. After multiple crushing and shaping treatments, 20 kg of spherical graphite preliminary coating material (D50 = 16 μm) is obtained.

[0091] (2) Add 20 kg of spherical graphite pre-coated material and 2 kg of petroleum asphalt (softening point 180℃) to a VC mixer and mix for 25 min. After mixing evenly, heat treat at 350℃ for 4 h under nitrogen protection and cool to room temperature to obtain spherical graphite modified heat-treated material.

[0092] (3) The spherical graphite modified heat-treated material was placed in a mechanical press for preliminary molding treatment. The pressure of the mechanical press was 20 MPa, the time was 1 min, and the process was repeated 3 times. Then, isostatic pressing was performed. The isostatic pressing pressure was 60 MPa, the holding time was 4 min, and after the isostatic pressing was completed, the spherical graphite composite precursor was obtained by crushing.

[0093] (4) The spherical graphite composite precursor was carbonized at 1250℃ for 10h under nitrogen protection. After carbonization, it was dispersed, demagnetized and sieved to obtain a negative electrode material containing multiple spherical graphite composite particles.

[0094] Example 3

[0095] This embodiment provides a negative electrode material, which is prepared according to the following steps:

[0096] (1) Take 40 kg of natural flake graphite particles (D50 = 96.8 μm) and mix them with 0.8 kg of petroleum asphalt (softening point 180℃) for preliminary coating treatment. After multiple crushing and shaping treatments, 20 kg of spherical graphite preliminary coating material (D50 = 16 μm) is obtained.

[0097] (2) Add 20 kg of spherical graphite pre-coated material and 1.0 kg of petroleum asphalt (softening point 180℃) to a VC mixer and mix for 25 min. After mixing evenly, heat treat at 350℃ for 4 h under nitrogen protection and cool to room temperature to obtain spherical graphite modified heat-treated material.

[0098] (3) The spherical graphite modified heat-treated material was placed in a mechanical press for preliminary molding. The pressure of the mechanical press was 10 MPa and the time was 1 min, repeated twice. Then, it was molded again under a hydraulic press, molded twice, and the pressure of the hydraulic press was 40 MPa. After the molding was completed, it was crushed to obtain the spherical graphite composite precursor.

[0099] (4) The spherical graphite composite precursor was carbonized at 1150℃ for 8 hours under nitrogen protection. After carbonization, it was dispersed, demagnetized and sieved to obtain a negative electrode material containing multiple spherical graphite composite particles.

[0100] Example 4

[0101] This embodiment provides a negative electrode material, which is prepared according to the following steps:

[0102] (1) Take 40 kg of natural flake graphite particles (D50 = 82.4 μm) and mix them with 1.0 kg of petroleum asphalt (softening point 250℃) for preliminary coating treatment. After multiple crushing and shaping treatments, 20 kg of spherical graphite preliminary coating material (D50 = 14.5 μm) is obtained.

[0103] (2) Add 20 kg of spherical graphite pre-coated material and 1.7 kg of petroleum asphalt (softening point 250℃) to a VC mixer and mix for 25 min. After mixing evenly, heat treat at 400℃ for 4 h under nitrogen protection and cool to room temperature to obtain spherical graphite modified heat-treated material.

[0104] (3) The spherical graphite modified heat-treated material was placed in a hydraulic press for reciprocating molding. The pressure of the hydraulic press was 30 MPa, and the reciprocating process was repeated 3 times. Then, isostatic pressing was performed. The isostatic pressing pressure was 60 MPa, and the holding time was 3 min. After the isostatic pressing was completed, the material was crushed to obtain the spherical graphite composite precursor.

[0105] (4) The spherical graphite composite precursor was carbonized at 1250℃ for 12h under nitrogen protection. After carbonization, it was dispersed, demagnetized and sieved to obtain a negative electrode material containing multiple spherical graphite composite particles.

[0106] Example 5

[0107] This embodiment provides a negative electrode material, which is prepared according to the following steps:

[0108] (1) Take 40 kg of natural flake graphite particles (D50 = 76.8 μm) and mix them with 1.0 kg of coal tar pitch (softening point 250℃) for preliminary coating treatment. After multiple crushing and shaping treatments, 20 kg of spherical graphite preliminary coating material (D50 = 14 μm) is obtained.

[0109] (2) Add 20 kg of spherical graphite pre-coated material and 1.7 kg of coal tar pitch (softening point 250℃) to a VC mixer and mix for 25 min. After mixing evenly, heat treat at 400℃ for 4 h under nitrogen protection and cool to room temperature to obtain spherical graphite modified heat-treated material.

[0110] (3) The spherical graphite modified heat-treated material was placed in a hydraulic press for reciprocating molding. The pressure of the hydraulic press was 30 MPa, the time was 1 min, and the reciprocating process was repeated 3 times. Then, isostatic pressing was performed. The isostatic pressing pressure was 60 MPa, the holding time was 3 min, and after the isostatic pressing was completed, it was crushed to obtain the spherical graphite composite precursor.

[0111] (4) The spherical graphite composite precursor was carbonized at 1250℃ for 8 hours under nitrogen protection. After carbonization, it was dispersed, demagnetized and sieved to obtain a negative electrode material containing multiple spherical graphite composite particles.

[0112] Example 6

[0113] This embodiment provides a negative electrode material, which is prepared according to the following steps:

[0114] (1) Take 40 kg of natural flake graphite particles (D50 = 62.4 μm) and mix them with 1.0 kg of petroleum asphalt (softening point 250℃) for preliminary coating treatment. After multiple crushing and shaping treatments, 20 kg of spherical graphite preliminary coating material (D50 = 10 μm) is obtained.

[0115] (2) Add 20 kg of spherical graphite pre-coated material and 1.7 kg of petroleum asphalt (softening point 250℃) to a VC mixer and mix for 25 min. After mixing evenly, heat treat at 400℃ for 4 h under nitrogen protection and cool to room temperature to obtain spherical graphite modified heat-treated material.

[0116] (3) The spherical graphite modified heat-treated material was placed in a hydraulic press for reciprocating molding. The pressure of the hydraulic press was 30 MPa and the time was 1 min for 3 reciprocating cycles. Then, isostatic pressing was performed. The isostatic pressing pressure was 60 MPa and the holding time was 3 min. After the isostatic pressing was completed, the spherical graphite composite precursor was obtained by crushing.

[0117] (4) The spherical graphite composite precursor was carbonized at 1250℃ for 14h under nitrogen protection. After carbonization, it was dispersed, demagnetized and sieved to obtain a negative electrode material containing multiple spherical graphite composite particles.

[0118] Example 7

[0119] A negative electrode material is provided, which is prepared according to the following steps:

[0120] (1) Take 40 kg of natural flake graphite particles (D50 = 100.5 μm) and pulverize and shape them multiple times to obtain 20 kg of spherical graphite composite particles (D50 = 16 μm);

[0121] (2) Add 20 kg of spherical graphite composite particles and 2.2 kg of petroleum asphalt (softening point 250℃) to a VC mixer and mix for 25 min to obtain spherical graphite modified composite.

[0122] (3) The spherical graphite modified heat-treated material was placed in a hydraulic press for reciprocating molding. The hydraulic press pressure was 30 MPa and the time was 1 min for 3 reciprocating cycles. Then, isostatic pressing was performed. The isostatic pressing pressure was 60 MPa and the holding time was 3 min. After the isostatic pressing was completed, the material was crushed to obtain the spherical graphite composite precursor.

[0123] (4) The spherical graphite composite precursor was carbonized at 1250℃ for 8 hours under nitrogen protection. After carbonization, it was dispersed, demagnetized and sieved to obtain a negative electrode material containing multiple spherical graphite composite particles.

[0124] Comparative Example 1

[0125] This comparative example provides a negative electrode material, which is prepared according to the following steps:

[0126] (1) Take 40 kg of natural flake graphite particles (D50 = 100.5 μm) and pulverize and shape them multiple times to obtain 20 kg of spherical graphite composite particles (D50 = 16 μm);

[0127] (2) Add 20 kg of spherical graphite composite particles and 2.2 kg of petroleum asphalt (softening point 250℃) to a VC mixer and mix for 25 min to obtain spherical graphite modified composite.

[0128] (3) The spherical graphite modified composite was carbonized at 1250℃ for 8 hours under a nitrogen protective atmosphere. After carbonization, the negative electrode material was obtained by breaking it up, sieving and demagnetizing it.

[0129] Comparative Example 2

[0130] This comparative example provides a negative electrode material, which is prepared according to the following steps:

[0131] (1) Take 40 kg of natural flake graphite particles (D50 = 64.2 μm) and mix with 1.0 kg of petroleum asphalt (softening point 250℃). After multiple crushing and shaping, 20 kg of spherical graphite preliminary coating material (D50 = 10 μm) is obtained.

[0132] (2) Add 20 kg of spherical graphite pre-coated material and 2.2 kg of petroleum asphalt (softening point 180℃) to a VC mixer and mix for 25 min to obtain spherical graphite modified composite material;

[0133] (3) The spherical graphite modified composite was carbonized at 1250℃ for 8 hours under a nitrogen protective atmosphere. After carbonization, the negative electrode material was obtained by breaking it up, sieving and demagnetizing it.

[0134] Comparative Example 3

[0135] This comparative example provides a negative electrode material, which is prepared according to the following steps:

[0136] (1) Take 40 kg of natural flake graphite particles (D50 = 100.5 μm) and mix with 1.0 kg of petroleum asphalt (softening point 250℃). After multiple crushing and shaping, 20 kg of spherical graphite preliminary coating material (D50 = 16 μm) is obtained.

[0137] (2) Add 20 kg of spherical graphite pre-coated material and 1.7 kg of petroleum asphalt (softening point 250℃) to a VC mixer and mix for 25 min to obtain spherical graphite modified composite.

[0138] (3) The spherical graphite modified composite was subjected to isostatic pressing densification treatment with an isostatic pressing pressure of 60 MPa and a holding time of 3 min. After crushing, the spherical graphite composite precursor was obtained.

[0139] (4) The spherical graphite composite precursor was carbonized at 1250℃ for 8 hours under a nitrogen protective atmosphere. After carbonization, the negative electrode material was obtained by breaking it up, demagnetizing it and sieving it.

[0140] Comparative Example 4

[0141] This comparative example provides a negative electrode material, which is prepared according to the following steps:

[0142] (1) 40 kg of natural flake graphite particles (D50 = 100.5 μm) were crushed and shaped multiple times to obtain 20 kg of spherical graphite composite particles (D50 = 16 μm);

[0143] (2) 20 kg of spherical graphite composite particles were placed in a hydraulic press for reciprocating molding. The pressure of the hydraulic press was 30 MPa, the time was 1 min, and the reciprocating process was repeated 3 times. Then, isostatic pressing was performed. The isostatic pressing pressure was 60 MPa, the holding time was 3 min, and after the isostatic pressing was completed, the particles were crushed to obtain 20 kg of spherical graphite molded particles (D50 = 16 μm).

[0144] (3) Add 20 kg of spherical graphite granules and 2.2 kg of petroleum asphalt (softening point 250℃) to a VC mixer and mix for 25 min to obtain a spherical graphite composite precursor;

[0145] (4) The spherical graphite composite precursor was carbonized at 1250℃ for 8 hours under a nitrogen protective atmosphere. After carbonization, the negative electrode material was obtained by breaking it up, demagnetizing it and sieving it.

[0146] Comparative Example 5

[0147] The difference between this comparative example and Example 1 is that in step (2), the amount of petroleum asphalt is adjusted so that the mass ratio of natural flake graphite particles to petroleum asphalt is 100:2.

[0148] Comparative Example 6

[0149] The difference between this comparative example and Example 1 is that in step (2), the amount of petroleum asphalt is adjusted so that the mass ratio of natural flake graphite particles to petroleum asphalt is 100:20.

[0150] Performance testing

[0151] The negative electrode materials provided in the above embodiments and comparative examples were subjected to performance tests, and the results are shown in Tables 1 and 2. The specific test items and test methods are as follows.

[0152] (1) Anode material cross-sectional morphology test: The material particles were milled using an ion milling machine (HITACHI E3500) to allow observation of the particle cross-section. The samples were then placed under a high-magnification electron microscope (HITACHI S4800) to observe the particle cross-section. The magnification of a single particle was in the range of 2.5kX-9.0kX to ensure that the cross-sectional image showed a complete single particle. The area of ​​a single spherical graphite composite particle, the area of ​​regions a and b, and the pore cross-sectional area were statistically calculated using the Aztec Feature software of 0XFORD Instruments. The statistical results were used to calculate the area of ​​each spherical graphite composite particle. The value is thus obtained for the entire negative electrode material. value.

[0153] (2) Specific surface area test: The specific surface area of ​​the negative electrode material was tested using a Micron DX400 instrument. Under constant temperature and low temperature, the amount of gas adsorbed on the solid surface at different relative pressures was measured. Based on the Brown-Nauer-Etter-Taylor adsorption theory and its formula (BET formula), the amount of monolayer adsorption of the sample was obtained, thereby calculating the specific surface area and pore size distribution data of the material.

[0154] (3) Particle size test: D50 is the volume average particle size corresponding to 50% of the cumulative bulk density. The average particle size D50 of the negative electrode material was tested using a Malvern 3000 laser particle size analyzer. The sample to be tested and a small amount of dispersant (ethanol, pure water, and low-foaming surfactant) were added to a 50 mL beaker, followed by 40-45 mL of pure water. The mixture was stirred thoroughly with a glass rod to ensure uniform dispersion. The pump speed was set to 2400-2500 r / min, and the frequency was 19.5 Hz for particle size testing.

[0155] (4) Tap density test: The tap density of the negative electrode material was tested using a Canta Dual Autotap instrument. A 100 mL sample of negative electrode material was placed in a graduated cylinder and mechanically vibrated 1000 times. The tap density of the negative electrode material was calculated based on the sample mass and the volume after tapping.

[0156] (5) Orientation test of the tablet: The negative electrode material, carboxymethyl cellulose and styrene-butadiene rubber were mixed in a mass ratio of 19.3:25:0.8 and dispersed evenly by a high-speed disperser. The mixed slurry was spread evenly on the surface of aluminum foil and then placed in a constant temperature drying oven at 80-95℃ for more than 6 hours until the slurry was completely dry. The dried slurry was ground through a 200-mesh sieve and then pressed into tablets by a tablet press at pressures of 0.5T, 1T and 2T respectively. The tablets were then placed under a Mitutoyo Corp thickness gauge and the initial thickness of the tablets was recorded after 10 seconds. The pressed tablets were placed in a constant temperature environment (25±3℃) and left to stand for 16 hours. The thickness of the tablets after rebound was measured with a micrometer and the compaction density was calculated. The prepared tablets were then tested for orientation using an X-ray diffractometer X′pert PRO. The orientation OI value of the tablets = I004 / I110 was the ratio of the peak areas of (004) and (110).

[0157] (6) Powder compaction density test: Take 1.0±0.05g of negative electrode material and put it into the metal sleeve. Place the sleeve in the center of the compaction density tester CARVER 4350.22, slowly apply pressure to 2T, stop applying pressure, start the second hand, maintain the pressure for 30s and then quickly remove the pressure. Take the sample out of the metal mold cavity and place it on the horizontal worktable of the thickness gauge. Use the thickness gauge to measure the height after compaction and calculate the powder compaction density.

[0158] (7) Specific Surface Area (SSA) Test: The specific surface area of ​​the negative electrode material was tested using a JW-DX dynamic specific surface area analyzer. Based on the relevant theories of physical adsorption, the continuous flow method proposed by Nelsen and Eggertsen was used to determine the specific surface area of ​​the solid. A mixed gas with hydrogen as the carrier and nitrogen as the adsorbent gas was introduced into the sample tube. When the sample tube was immersed in liquid nitrogen to reach a low temperature environment, the nitrogen in the mixed gas was physically adsorbed by the sample until adsorption saturation. At this time, the proportion of nitrogen in the mixed gas will change. During the adsorption process, a high-precision thermal conductivity detector will complete the detection and calculation work.

[0159] (8) Electrochemical performance testing:

[0160] The negative electrode materials prepared in the examples and comparative examples, carboxymethyl cellulose and styrene-butadiene rubber were dissolved in pure water at a mass ratio of 96.5:1.5:2, respectively, with the solid content controlled at 50%. These materials were coated onto a copper foil current collector, and after vacuum drying at 95°C, rolling, and pressurization, a negative electrode sheet was obtained. A lithium metal sheet was used as the counter electrode, and the cells were assembled into coin cells in an argon-filled glove box. Charge-discharge tests were conducted at a current density of 0.1C, within a charge-discharge range of 0.01-1.5V, to obtain the initial reversible specific capacity, the first charge capacity, and the first discharge capacity. The initial coulombic efficiency was calculated as: first discharge capacity / first charge capacity.

[0161] (9) The electrode expansion rate was tested using the battery electrode thickness change measuring device and system disclosed in patent document CN209991940U. The negative electrode material, CMC (carboxymethyl cellulose), and SBR (styrene-butadiene rubber) obtained in the examples or comparative examples were uniformly mixed at a mass percentage of 96.5:1.5:2, with the solid content controlled at 50%, to obtain the negative electrode slurry. The negative electrode slurry was coated onto a copper foil current collector, and after vacuum drying and rolling, a compacted density of 1.60 g / cm³ was obtained. 3 The initial thickness d1 of the negative electrode 102 was tested. The positive electrode active material, lithium cobalt oxide, conductive carbon black, and PVDF were mixed uniformly at a mass ratio of 96.5:2:1.5 and coated onto aluminum foil (single-sided) to obtain the positive electrode. The prepared positive and negative electrode sheets were then placed into a self-made three-electrode testing device for testing. This device can record the electrode thickness changes in situ, and the electrode expansion rate can be calculated.

[0162] The compaction density and pellet orientation (I004 / I110) of the negative electrode materials prepared in each embodiment and comparative example under different pressures are shown in Table 1 and... Figure 2 The performance characterization results of each embodiment and comparative example are shown in Table 2.

[0163] Table 1. Results of negative electrode material sheeting orientation and powder compaction density prepared in each embodiment and comparative example.

[0164]

[0165] Note: x represents the compaction density of the negative electrode material under different pressures; y represents the OI value of the negative electrode material under different compaction densities.

[0166] Table 2. Performance characterization results of the anode materials prepared in each embodiment and comparative example.

[0167]

[0168] Figure 3 This diagram shows a cross-sectional view of a single spherical graphite composite particle in the graphite anode material provided in Embodiment 1 of this application; where a1 is the inner layer region and b1 is the outer layer region. Figure 3 As can be seen in the image, the particle... Porosity statistics were performed on 20 particles.

[0169] Figure 4 The graphs showing the relationship between the compaction density and orientation OI value of the negative electrode materials in Examples 1-6 of this application under different pressures are illustrated; from Figure 4 It can be seen that the OI values ​​of each embodiment are all within the range of y1 and y2 under different compaction densities.

[0170] Examples 1 to 6 all involved initial coating of natural flake graphite particles with asphalt, followed by crushing and shaping. Initial compaction was achieved through re-coating and low-temperature heat treatment. Subsequently, a combination of two molding methods was used for multi-step compaction, improving defects in both the inner and outer layers of the particles. The differences lay in the use of natural graphite raw materials, asphalt type, asphalt dosage, and molding methods. Compared to Comparative Examples 1-6, under different compaction densities of 1.5 ≤ x ≤ 2.0, the OI values ​​of the pressed sheet orientation all satisfied y1 ≤ y ≤ y2 and 4.3 ≤ y ≤ 10, while the pore size also met the requirements. The material exhibits reduced porosity, decreased OI value, and increased isotropy, which improves the structural stability of the anode material, alleviates its volume expansion, and enhances its initial coulombic efficiency and expansion performance.

[0171] Compared to Example 6, Example 7 involves pulverizing natural flake graphite particles and then mixing them with petroleum asphalt for coating. The coating uniformity in Example 7 is slightly worse than in Example 6, resulting in a lower average porosity. The electrode expansion rate was slightly higher than that of Example 6. Preliminary coating, crushing, and shaping of natural flake graphite particles with a portion of asphalt, followed by further coating with the remaining asphalt, improves the uniformity of the asphalt coating and the structural stability of the prepared negative electrode material.

[0172] Compared with Comparative Example 1, the graphite anode material provided in Comparative Example 1 does not satisfy the condition y1≤y≤y2 in the compaction orientation OI value under different compaction densities, and... This is not within the scope of the technical solution of this application. The average OI value of Example 1 at 2T pressure (8.25) is approximately half that of Comparative Example 1 at 2T pressure (15.26), indicating an increase in the density of the negative electrode material and improved pore filling rates in both the inner layer (a) and outer layer (b). Increase, the porosity inside the particles The efficiency was reduced to 1.95%, resulting in a first-ever increase in the coulombic efficiency of the anode material to 94.92%, improved expansion performance, and a 20-week electrode expansion rate of 23.1%.

[0173] Compared with Comparative Example 3, Example 1 used the same raw materials and asphalt types and amounts. The difference was that Comparative Example 3 only underwent one step of isostatic compaction, resulting in limited filling effect and its OI value did not satisfy y1≤y≤y2. Therefore, the initial coulombic efficiency and expansion performance are poor. Compared with Comparative Example 3, Example 1 has a higher content of amorphous carbon, increased disorder, and a lower OI value for the material under different compaction densities; the density of the inner layer region a is improved. Increased to 1.27, internal porosity of particles The efficiency was reduced to 1.95%, resulting in a first-ever increase in the coulombic efficiency of the anode material to 94.92%. Expansion performance was also improved, with the 20-week electrode expansion rate decreasing from 26.4% to 23.1%.

[0174] Compared with Comparative Example 4, Example 1 used the same raw materials and asphalt types and amounts. The difference was that in Comparative Example 4, after the flake graphite was crushed and shaped, it was initially compacted using a hydraulic press, and then compacted by isostatic pressing to reduce the internal porosity of the graphite, thus improving its internal porosity. Its characteristics meet the porosity characteristics described in this application, but the OI value of the material under different compaction densities does not satisfy y1≤y≤y2. Therefore, compared with Example 1, Comparative Example 4 mainly reduces its internal pores by applying pressure to change the graphite structure. Its OI value is low under different compaction densities, especially under 2.0T pressure, the OI value of Comparative Example 4 is only 6.23. It mainly provides reserved space for particle volume change through the internal pores of the particles. In contrast, Example 1 has an OI value of 8.25, a high amorphous carbon filling rate, which improves the structural stability of the material, alleviates the volume expansion of the material, and has better expansion performance.

[0175] Compared to Example 1, Comparative Example 5 has a lower asphalt coating amount, resulting in less surface asphalt coating and a greater likelihood of solvent co-intercalation, which exacerbates material volume expansion. Furthermore, it does not satisfy the condition y1≤y≤y2 for the compaction orientation OI values ​​under different compaction densities. This is not within the scope of the technical solution of this application. Therefore, compared with the electrode expansion rate of 23.1% in Example 1, the expansion performance of Comparative Example 5 is poor, with an electrode expansion rate of 28.4%.

[0176] Comparative Example 6 showed an increased asphalt coating amount compared to Example 1, but did not meet the requirements. This is not within the scope of the technical solution of this application. Excessive asphalt coating will cause the material structure to become loose, forming more pores or cracks during carbonization, accelerating volume expansion during cycling. Therefore, Comparative Example 6 has low initial capacity efficiency and poor expansion performance, with an electrode expansion rate of 27.5%.

[0177] In summary, the anode material provided in this application has an amorphous carbon coating layer on the spherical graphite composite particles, which improves interfacial stability, prevents solvent co-intercalation, and increases the initial coulombic efficiency. Simultaneously, the internal pores of the spherical graphite composite particles are filled with amorphous carbon, and the average porosity of the inner layer region a is [missing information]. The average porosity of the outer region b is satisfy Under different compaction densities, the OI value of the material does not satisfy y1≤y≤y2, the internal porosity decreases, the specific surface area of ​​the material decreases, the powder compaction density increases, and thus reduces the impact of SEI film formation on Li during the first charge and discharge process. + Consumption increases initial coulomb efficiency. Additionally, Li... + During the insertion and extraction process, volume expansion occurs. The disorder of amorphous carbon inside and outside the spherical graphite composite particles reduces the orientation of the material during pressing and increases its isotropy, which further improves the structural stability, alleviates volume expansion, and thus effectively improves the electrical performance of the negative electrode material.

[0178] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A negative electrode material, characterized in that, The negative electrode material comprises multiple spherical graphite composite particles, the pores inside of which are filled with amorphous carbon. The cross-section of each spherical graphite composite particle is divided into an inner layer region a and an outer layer region b, with the outer layer region b surrounding the inner layer region a. The average porosity of the cross-section of the spherical graphite composite particle is [missing information - likely a percentage]. The average porosity of the inner layer region a is The average porosity of the outer layer region b is and The negative electrode material has a compaction orientation OI value of y at different compaction densities, with upper and lower limits of y1 and y2, respectively. The compaction density of the negative electrode material under different pressures is x, where y1 = 6.89x - 6.04, y2 = 8.9x - 7.76, and y1 ≤ y ≤ y2, 4.3 ≤ y ≤ 10, and 1.5 g / cm³. 3 ≤x≤2.0g / cm 3 .

2. The negative electrode material according to claim 1, characterized in that, The average particle size D50 of the spherical graphite composite particles is 5μm-20μm, the particle size symmetry Φ is 1.45-1.70, and Φ=(D90-D50) / (D50-D10).

3. The negative electrode material according to claim 1, characterized in that, The specific surface area (SSA) of the spherical graphite composite particles is 2 m². 2 / g-5m 2 / g.

4. The negative electrode material according to claim 1, characterized in that, The shape of the spherical graphite composite particles includes at least one of spherical and near-spherical shapes.

5. The negative electrode material according to claim 1, characterized in that, The compaction density of the negative electrode material under 2T pressure is 1.7 g / cm³. 3 -2.0g / cm 3 ; And / or, the tap density of the negative electrode material is 0.9 g / cm³. 3 -1.5g / cm 3 .

6. A method for preparing a negative electrode material, characterized in that, The preparation method includes: Step S1: Natural flake graphite particles are mixed with a modifier and then coated and shaped to obtain a spherical graphite modified composite. Step S2: The spherical graphite modified composite is subjected to low-temperature heat treatment to soften the modifier and obtain the spherical graphite modified heat-treated product. Step S3: The spherical graphite modified heat-treated material is subjected to molding and crushing treatment to obtain the spherical graphite composite precursor; Step S4: The spherical graphite composite precursor is calcined to obtain the negative electrode material.

7. The method for preparing the negative electrode material according to claim 6, characterized in that, The modifier includes the first modifier and the second modifier, and step S1 includes: Natural flake graphite particles are mixed with a first modifier for preliminary coating treatment, followed by crushing and shaping treatment to obtain a spherical graphite preliminary coating. The spherical graphite preliminary coating is then mixed with a second modifier for a second coating treatment to obtain the spherical graphite modified composite.

8. The method for preparing graphite composite material according to claim 7, characterized in that, The preparation method satisfies at least one of the following characteristics: (1) The average particle size D50 of the spherical graphite pre-coated material is 1μm-20μm; (2) The D50 of the natural flake graphite particles is 60μm-110μm, and the fixed carbon content is ≥99%; (3) The modifier includes asphalt, wherein the asphalt is selected from at least one of petroleum asphalt, coal tar pitch, and mesophase asphalt; (4) The mass ratio of the natural flake graphite particles to the first modifier is 100:(0-2.5); (5) The mass ratio of the spherical graphite pre-coated material to the second modifier is 100:(5-12).

9. The method for preparing the negative electrode material according to claim 6, characterized in that, The preparation method satisfies at least one of the following characteristics: (1) In step S2, the temperature of the low-temperature heat treatment is 100℃-200℃ higher than the softening point of the modifier; (2) In step S2, the low-temperature heat treatment time is 3h-4h; (3) In step S2, the low-temperature heat treatment is carried out under the protection of an inert gas, wherein the inert gas includes at least one of nitrogen, argon or helium; (4) In step S3, the pressure of the molding process is 10MPa-60MPa, and the molding process includes at least two of the following: hydraulic pressure, mechanical pressure, rotary pressure, cold isostatic pressing, warm isostatic pressing or hot isostatic pressing. (5) In step S4, the calcination temperature is 1000℃-1500℃ and the calcination time is 8-15h.

10. A secondary battery, characterized in that, The secondary battery comprises the negative electrode material according to any one of claims 1 to 5 or the negative electrode material obtained by the preparation method according to any one of claims 6 to 9.

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