Negative electrode material and secondary battery

Abstract

Provided in the present application are a negative electrode material and a secondary battery. The negative electrode material has a particle hardness HIT of 0.28 GPa to 0.40 GPa and an elastic modulus EIT of 7.0 GPa to 8.0 GPa. The negative electrode material provided in the present application reflects the internal pore distribution of the negative electrode material and the densification degree of pore filling by means of the particle hardness and the elastic modulus. For a negative electrode substrate material made of the same material, the particle hardness HIT and the elastic modulus EIT are both changed after the pores are filled. The larger the particle hardness HIT, the lower the elastic modulus EIT, which indicates that the fewer internal pores of the negative electrode material there are, the higher the densification degree is, and the improvement of the densification degree can prevent an electrolyte from being immersed in the negative electrode material, thereby improving the interface transfer dynamic performance and improving the initial coulomb efficiency and cycling performance of the material.

Description

Anode materials and secondary batteries

[0001] Cross-references to related applications

[0002] This application claims priority to Chinese Patent Application No. 202411817738.7, filed on December 10, 2024, entitled “Anode Material and Preparation Method Thereof and Secondary Battery”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of battery materials technology, and more specifically, to a negative electrode material and a secondary battery. Background Technology

[0004] Secondary batteries are widely used in 3C products, power devices, and energy storage equipment due to their advantages such as portability, high energy density, good safety performance, and no memory effect. Natural graphite anode materials are widely used in secondary batteries due to their high charge / discharge capacity, low charge / discharge plateau, and low cost. 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 sheets are also prone to detachment, resulting in problems such as short cycle life and high expansion rate.

[0005] To improve the electrochemical performance of natural graphite, published patents have documented various methods for physicochemical modification and surface alteration of natural graphite. Some researchers coat a natural spherical graphite matrix with a layer of amorphous carbon material, approximately 0.5 μm-1.5 μm thick. The resulting natural graphite anode material is suitable for use in propylene carbonate (PC) electrolyte systems, and the resulting secondary batteries exhibit high capacity and efficiency. Other researchers use shaping techniques to spherize flake graphite, then coat the surface of the spherical graphite with a layer of amorphous carbon to prevent electrolyte ingress. All these techniques improve interfacial stability and cycle performance by coating the surface with amorphous carbon. However, natural graphite has a high porosity; during charge and 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.

[0006] In view of the above, this application is hereby submitted. Summary of the Invention

[0007] The main objective of this application is to provide a negative electrode material and a secondary battery to solve the problem in the prior art that improves interface stability by coating amorphous carbon on the surface of natural spherical graphite. However, due to the high internal porosity of natural graphite, the electrolyte gradually penetrates into the internal pores of the graphite during charging and discharging, resulting in an increase in electrode volume and a decrease in capacity stability and cycle performance.

[0008] To achieve the above objectives, according to a first aspect of this application, a negative electrode material is provided, wherein the particle hardness (HIT) of the negative electrode material is 0.28 GPa-0.40 GPa and the elastic modulus (EIT) is 7.0 GPa-8.0 GPa.

[0009] According to a second aspect of this application, a secondary battery is also provided, which includes the negative electrode material provided in the first aspect.

[0010] Applying the technical solution of this application, the negative electrode material provided by this application reflects the internal pore distribution and the degree of pore filling density through particle hardness and elastic modulus. For negative electrode matrix materials of the same material, both particle hardness (HIT) and elastic modulus (EIT) will change after filling the pores. The larger the particle hardness (HIT) and the lower the elastic modulus (EIT), the fewer the pores inside the negative electrode material and the higher the degree of compaction. The increased degree of compaction can prevent electrolyte from embedding into the interior of the negative electrode material. The particle hardness (HIT) of the negative electrode material provided by this application is 0.28 GPa-0.40 GPa, and the elastic modulus (EIT) is 7.0 GPa-8.0 GPa, which can not only improve the interfacial transport kinetics performance, but also improve the material's initial coulombic efficiency and cycle performance. Attached Figure Description

[0011] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0012] Figure 1 is a schematic diagram of the structure of a secondary battery during charging according to some embodiments of this application;

[0013] Figure 2 is a schematic diagram of the structure of a secondary battery during discharge according to some embodiments of this application;

[0014] Figure 3 shows a SEM image of the negative electrode material provided according to Embodiment 1 of this application. Detailed Implementation

[0015] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present application will now be described in detail with reference to the embodiments.

[0016] As analyzed in the background section of this application, current research generally improves interfacial stability and enhances cycle performance by coating amorphous carbon onto the surface of natural spherical graphite. However, due to the high porosity of natural graphite, the electrolyte gradually penetrates into the pores during charge and discharge, leading to an increase in electrode volume and a decrease in capacity stability and cycle performance. To address this issue, this application provides a negative electrode material, its preparation method, and a secondary battery.

[0017] In a first typical embodiment of this application, a negative electrode material is provided, having a particle hardness (HIT) of 0.28 GPa-0.40 GPa and an elastic modulus (EIT) of 7.0 GPa-8.0 GPa.

[0018] The negative electrode material provided in this application reflects the internal pore distribution and the degree of pore compaction through particle hardness and elastic modulus. For negative electrode matrix materials of the same material, both particle hardness (HIT) and elastic modulus (EIT) change after pore filling. A higher particle hardness (HIT) and a lower elastic modulus (EIT) indicate fewer pores and a higher degree of compaction within the negative electrode material. Increased compaction prevents electrolyte from embedding into the negative electrode material. The negative electrode material provided in this application has a particle hardness (HIT) of 0.28 GPa-0.40 GPa and an elastic modulus (EIT) of 7.0 GPa-8.0 GPa, which not only improves interfacial transport kinetics but also enhances the material's initial coulombic efficiency and cycle performance.

[0019] In some embodiments, the negative electrode material particles comprise natural spherical graphite, the interior of which is filled with amorphous carbon. Natural graphite is inherently soft; when filled with amorphous carbon, the particle hardness increases. A higher hardness (HIT) and lower elastic modulus (EIT) of the negative electrode material particles indicate that the more amorphous carbon is filled within the natural spherical graphite, the higher the density of the negative electrode material particles. The disordered nature of the amorphous carbon filling the natural spherical graphite prevents electrolyte penetration into the internal pores, thereby improving interfacial transport kinetics and enhancing initial coulombic efficiency and cycle performance.

[0020] Specifically, the particle hardness HIT of the negative electrode material provided in this application can be any value within the range of 0.28 GPa, 0.30 GPa, 0.32 GPa, 0.35 GPa, 0.38 GPa, 0.40 GPa, or any combination of two values. It can be any value between 0.28 GPa and 0.32 GPa, between 0.32 GPa and 0.35 GPa, or between 0.35 GPa and 0.40 GPa, without any special limitation. The elastic modulus EIT can be any value within the range of 7.0 GPa, 7.2 GPa, 7.5 GPa, 7.8 GPa, 8.0 GPa, or any combination of two values. It can be any value between 7.0 GPa and 7.2 GPa, between 7.2 GPa and 7.5 GPa, or between 7.5 GPa and 8.0 GPa, without any special limitation.

[0021] To further improve the interfacial transport dynamics performance of the anode material, in some embodiments, the anode material includes multiple graphite composite particles. The cross-section of the graphite composite particles is divided into an inner layer region a and an outer layer region b. The outer layer region b surrounds the periphery of the inner layer region a. The average porosity of the cross-section of the graphite composite particles is [missing information]. The average pore filling rate of inner region a is The average pore filling rate of the outer region b is and n≥20.

[0022] In this application, the graphite composite particles include a graphite core and an amorphous carbon coating layer located on at least a portion of the surface of the graphite core. The pores of the graphite core are filled with amorphous carbon. The amorphous carbon can be distinguished by TEM observation.

[0023] 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 graphite composite particles. The major axis L of the inner layer region a is... a =1 / 2L1, minor axis L b =1 / 2L2; n≥20; = Inner layer pore area of ​​the cross section of the i-th spherical graphite / Inner layer area * 100% = (Outer layer pore area of ​​the cross-section of the i-th spherical graphite sheet / Outer layer area * 100%) = (Pore area of ​​spherical graphite cut surface in the i-th slice / slice area) * 100%, where {i|1≤i≤n,n≥20}. (The above...) This not only indicates that the average porosity inside the graphite composite particles is ≤5%, but also that the porosity of the outer layer region b is significantly lower than that of the inner layer region a, thus better inhibiting the electrolyte from entering the pores inside the graphite composite particles, thereby further improving the interfacial transport dynamics performance of the negative electrode material.

[0024] Specifically, It can be a range of values, including 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, or any two values. It can be a range of values, such as 1.8%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any two values.

[0025] To further improve the capacity stability and cycle stability of the secondary battery prepared from the negative electrode material, in some embodiments, the negative electrode material satisfies Δ=│shape factor φ-sphericity Sh(90%)│, and Δ≤0.08, where the shape factor φ=D50 / D(4,3), D50 is 5μm-20μm, D50 is the particle size corresponding to the cumulative volume distribution percentage reaching 50%, D(4,3) is the average particle size of equal volume, which is the average particle size of spheres with the same average particle volume; Sh(90%) is determined by a dynamic particle pattern analyzer.

[0026] The above-mentioned negative electrode material satisfies Δ=│shape factor φ-sphericity Sh(90%)│, Δ≤0.08, and D50 is 5μm-20μm; in addition to helping to further improve the first coulombic efficiency and cycle stability of the battery, it can also make the diffusion path of lithium ions shorter, which can reduce the transport resistance of lithium ions during insertion and extraction, thereby improving the charge and discharge efficiency.

[0027] Specifically, the D50 of the negative electrode material can be 5μm, 8μm, 10μm, 12μm, 15μm, 18μm, 20μm or any range of two values.

[0028] In some embodiments, D(4,3) is 10 μm-20 μm. Specifically, but not limitingly, D(4,3) can be 11.2 μm-17.9 μm, or any value within the range of 11.2 μm, 15.2 μm, 17.3 μm, 17.5 μm, 17.7 μm, 17.9 μm, or any combination of two of the above values. Controlling D(4,3) of the negative electrode material within the above range helps to regulate the shape factor φ of the negative electrode material, thereby helping to improve the cycle stability of the negative electrode material.

[0029] In some embodiments, the sphericity Sh (90%) is 0.89-0.95. Specifically, but not limitingly, the sphericity Sh (90%) can be 0.89-0.93, or any value within the range of 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, or any combination of two of the above values. Controlling the sphericity of the anode material within the above range helps improve its processing performance and compaction density, thereby contributing to improved energy density of the anode material.

[0030] In some embodiments, the specific surface area SSA of the negative electrode material particles is 2m². 2 / g-5m 2 / g, to further increase the compaction density of the anode material and further improve its electrical performance. Specifically, the specific surface area (SSA) of the anode material 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.

[0031] To further improve the electrical performance of the negative electrode material, in some embodiments, the tap density (Tap) of the negative electrode material is 0.9 g / cm³. 3 -1.5g / cm 3 Specifically, the compaction density of the negative electrode material can be 0.9 g / cm³. 3 1.0g / cm 3 1.1g / cm 3 1.2g / cm 3 1.3g / cm 3 1.4g / cm 3 1.5g / cm 3 Or a range of values ​​consisting of any two numerical values.

[0032] To further improve the electrical performance of the negative electrode material, in some embodiments, the I of the negative electrode material... D / I G It is 0.9-1.3; where I D I represents the area of ​​peak D in the Raman scattering spectrum of the negative electrode material. G I represents the area of ​​the G peak in the Raman scattering spectrum of the negative electrode material. Specifically, I D / I G It can be a range of values, including 0.9, 1.0, 1.1, 1.2, 1.3, or any two values. It reflects the orderliness of the internal structure of the negative electrode material particles and the variations in its surface properties. D / I G A higher value indicates that there is more amorphous carbon or defect structure in the material, while a lower value indicates that the material is more graphitized and has a more ordered structure.

[0033] In a second typical embodiment of this application, a method for preparing the above-mentioned negative electrode material is also provided. The method includes: step S1, providing natural spherical graphite and performing a pressing process on the natural spherical graphite to obtain pressed graphite particles; step S2, mixing the pressed graphite particles with a modifier and performing a coating process to obtain coated pressed graphite particles; step S3, performing a low-temperature heat treatment on the coated pressed graphite particles to soften the modifier and obtain a graphite-coated heat-treated material; step S4, performing isostatic pressing and compaction on the graphite-coated heat-treated material and pulverizing it to obtain a negative electrode material precursor; and step S5, performing a calcination process on the negative electrode material precursor to obtain the negative electrode material.

[0034] The method for preparing the negative electrode material provided in this application involves first pressing natural spherical graphite to reduce the pore volume inside the particles, then coating the pressed graphite particles with a modifier, followed by low-temperature heat treatment to allow the modifier to initially fill the pores inside the graphite particles, then using isostatic pressing to compact the modifier into the pores inside the graphite particles, and finally calcining to carbonize the modifier into amorphous carbon, which fills the interior of the graphite particles, thus obtaining the negative electrode material.

[0035] Furthermore, the anode material preparation method provided in this application significantly reduces the internal porosity and increases the compactness of the anode material, which can effectively suppress the electrolyte from embedding into the interior of the anode material, thereby improving the interfacial transport dynamics of the anode material and enhancing the material's first coulombic efficiency and cycle performance.

[0036] In step S1 above, the specific particle size of the natural spherical graphite is not limited, and commercially available natural spherical graphite can be used. In some embodiments, the particle size D50 of the natural spherical graphite is 5μm-20μm. Specifically, the D50 of the natural spherical graphite can be 5μm, 8μm, 10μm, 12μm, 15μm, 18μm, 20μm, or any range of two values.

[0037] To further improve the efficiency of the molding process, the preferred molding pressure is 10MPa-30MPa, and the holding time is 0.5min-2min. Specifically, the molding pressure can be 10MPa, 15MPa, 20MPa, 30MPa, or any range of two values; the holding time can be 0.5min, 1.0min, 1.5min, 2.0min, or any range of two values.

[0038] In some specific embodiments, a hydraulic press is used for the molding process, with the hydraulic press pressure set to 0-30MPa, the pressure holding time to 0.5min-2min, and the process repeated twice.

[0039] To further improve the filling rate of amorphous carbon inside the negative electrode material particles, it is preferable to control the D50 of the pressed graphite particles within the range of 5μm-20μm by crushing. Specifically, the D50 of the pressed graphite particles can be 5μm, 8μm, 10μm, 12μm, 15μm, 18μm, 20μm, or any combination of two values.

[0040] In step S2 above, the modifier is a carbonaceous substance capable of carbonization to generate amorphous carbon. In some embodiments, the modifier includes asphalt, the softening point of which is 100℃-300℃. The specific type of asphalt is not limited, including but not limited to any one or more mixtures of petroleum asphalt, coal tar pitch, and mesophase asphalt.

[0041] To further improve the cycle stability of the negative electrode material, the preferred mass ratio of modifier to pressed graphite particles is (7-15):100. Specifically, the mass ratio of modifier to pressed graphite particles can be, for example, 7:100, 8:100, 10:100, 12:100, 15:100, or any range of two values.

[0042] The specific time for the above coating treatment is not limited. However, to further promote the uniform coating of the modifier on the surface of the pressed graphite particles, the preferred coating treatment time is 25-30 minutes. Specifically, the coating treatment time can be 25 minutes, 28 minutes, 30 minutes, or any range of two values.

[0043] In step S3 above, the low-temperature heat treatment softens the modifier, facilitating subsequent isostatic pressing compaction to allow the softener to fill the pores within the pressed graphite particles. To further improve the efficiency of the low-temperature heat treatment, in some embodiments, the temperature of the low-temperature heat treatment is 100℃-200℃ higher than the softening point of the modifier, thereby improving the softening efficiency of the modifier while further reducing energy consumption.

[0044] In step S3 above, to avoid introducing impurity elements during the low-temperature heat treatment, it is preferable to carry out the low-temperature heat treatment under a protective atmosphere. The protective atmosphere gas includes, but is not limited to, any one or more of nitrogen, argon, and helium.

[0045] In step S4 above, to further improve the efficiency of isostatic pressing densification, it is preferable to perform the isostatic pressing densification under vacuum conditions to facilitate the compaction and filling of the pressed graphite particles. In some embodiments, the graphite-coated heat-treated material is subjected to vacuum treatment for 30 minutes, followed by isostatic pressing densification.

[0046] To further improve the porosity of amorphous carbon within the pressed graphite particles, the preferred isostatic pressing (OSP) pressure is 50-70 MPa, and the holding time is 2-5 min. The efficiency of the modifier within the pressed graphite particles is controlled by adjusting the pressure and holding time. Specifically, the OSP pressure can be 50 MPa, 55 MPa, 60 MPa, 65 MPa, 70 MPa, or any combination of two values; the holding time can be 2 min, 3 min, 4 min, 5 min, or any combination of two values.

[0047] The above-mentioned isostatic pressing densification treatment method is not specifically limited and can be any one or a combination of cold isostatic pressing or warm isostatic pressing.

[0048] In some embodiments, step S4 above further includes a pulverization process following isostatic pressing to prepare a negative electrode material precursor with a suitable particle size.

[0049] In step S5 above, to avoid introducing impurity elements during calcination, it is preferable to carry out the calcination treatment under a protective atmosphere. The protective atmosphere includes, but is not limited to, a mixture of one or more gases selected from nitrogen, argon, and helium.

[0050] To further improve the efficiency of calcination, the preferred calcination temperature is 900℃-1500℃ and the calcination time is 10h-24h, which helps to reduce energy consumption while improving the efficiency of calcination.

[0051] In this application, calcination treatment causes the modifier pressed into the molded graphite particles to generate amorphous carbon, which fills the pores inside the graphite. Specifically, the calcination temperature can be 900℃, 1000℃, 1100℃, 1200℃, 1300℃, 1400℃, 1500℃ or any combination of two values, and the calcination time can be 10h, 12h, 15h, 18h, 20h, 24h or any combination of two values.

[0052] In order to obtain a negative electrode material with a suitable particle size, it is preferable that step S5 above includes the steps of dispersing, demagnetizing and sieving after calcination.

[0053] In a third typical embodiment of this application, a secondary battery is also 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.

[0054] The secondary battery provided in this application has a negative electrode material with a particle hardness (HIT) of 0.28 GPa-0.40 GPa and an elastic modulus (EIT) of 7.0 GPa-8.0 GPa. This material can effectively suppress the intercalation of electrolyte into the interior of the negative electrode material, thereby improving the interfacial transport dynamics and enhancing the material's initial coulombic efficiency and cycle performance.

[0055] 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.

[0056] The outer casing can be a packaging bag encapsulated with a sealing 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.

[0057] Referring to Figures 1 and 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, during charging (referring to Figure 1), active ions (such as lithium ions) are extracted from the lattice of the positive electrode material (such as a lithium-ion intercalated compound) of the positive electrode 101, pass through the separator 103 via the electrolyte, reach the negative electrode 102, and are inserted into the lattice of the negative electrode material. During discharging (referring to Figure 2), active ions (such as lithium ions) are extracted from the lattice of the negative electrode material of the negative electrode 102, pass through the separator 103 via the electrolyte, reach the positive electrode 101, and are inserted into the lattice of the positive electrode material (such as a lithium-ion intercalated compound). Electrons are generated and travel from the negative electrode 102 to the positive electrode 101 via an external circuit. The reverse movement of these electrons forms an electric current, which can be used by electrical appliances.

[0058] 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.

[0059] Positive electrode film

[0060] 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).

[0061] 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.

[0062] 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.

[0063] negative electrode sheet

[0064] 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.

[0065] The active layer of the negative electrode material includes the negative electrode material, which includes graphite, silicon, etc.

[0066] 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.

[0067] 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.

[0068] Separating membrane

[0069] 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.

[0070] electrolytes

[0071] 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.

[0072] The beneficial effects of this application will be further illustrated below with reference to embodiments and comparative examples.

[0073] Example 1

[0074] This embodiment provides a negative electrode material, which is prepared according to the following steps:

[0075] (1) Take 20 kg of natural spherical graphite (D50 = 16 μm) and press it in a hydraulic press. The pressure of the hydraulic press is 20 MPa and the holding time is 1 min. Repeat the process twice. After pressing, crush the graphite to obtain pressed graphite particles with an average particle size of D50 = 16.6 μm.

[0076] (2) Take 2.2 kg of asphalt (softening point 250℃) and 20 kg of pressed graphite particles and add them to the VC mixer and mix for 30 min to obtain coated pressed graphite particles.

[0077] (3) The coated and pressed graphite particles were heat-treated at 400°C for 4 hours under a nitrogen protective atmosphere and then cooled to room temperature to obtain the graphite-coated product.

[0078] (4) The graphite-coated material was subjected to isostatic pressing to densify it. The pressure of the isostatic pressing was 70 MPa and the holding time was 2 min. After crushing, a graphite anode precursor with a particle size D50 of 16.7 μm was obtained.

[0079] (5) The graphite anode precursor was calcined at 1250℃ for 16h under nitrogen protection. After carbonization, it was dispersed, demagnetized and sieved to obtain the anode material.

[0080] Example 2

[0081] This embodiment provides a negative electrode material, which is prepared according to the following steps:

[0082] (1) Take 20 kg of natural spherical graphite (D50 = 16 μm) and press it in a hydraulic press. The pressure of the hydraulic press is 30 MPa and the holding time is 0.5 min. Repeat the process twice. After pressing, crush the graphite to obtain pressed graphite particles with an average particle size of D50 = 16.6 μm.

[0083] (2) Take 3.0 kg of asphalt (softening point 120℃) and 20 kg of pressed graphite particles and add them to the VC mixer and mix for 25 min to obtain coated pressed graphite particles.

[0084] (3) The coated and pressed graphite particles were heat-treated at 350°C for 4 hours under a nitrogen protective atmosphere and then cooled to room temperature to obtain the graphite-coated product.

[0085] (4) The graphite-coated material was subjected to isostatic pressing to densify it. The pressure of the isostatic pressing was 60 MPa, and the holding time was 3 min. After crushing, a graphite anode precursor with a particle size D50 of 16.9 μm was obtained.

[0086] (5) The graphite anode precursor was calcined at 1250℃ for 14h under nitrogen protection. After carbonization, it was broken up, demagnetized and sieved to obtain the anode material.

[0087] Example 3

[0088] This embodiment provides a negative electrode material, which is prepared according to the following steps:

[0089] (1) Take 20 kg of natural spherical graphite (D50 = 16 μm) and press it in a hydraulic press. The pressure of the hydraulic press is 10 MPa and the holding time is 2 min. Repeat the process twice. After pressing, crush the graphite to obtain pressed graphite particles with an average particle size of D50 = 16.4 μm.

[0090] (2) Take 1.4 kg of asphalt (softening point 180℃) and 20 kg of pressed graphite particles and add them to the VC mixer and mix for 25 min to obtain coated pressed graphite particles.

[0091] (3) The coated and pressed graphite particles were heat-treated at 400°C for 4 hours under a nitrogen protective atmosphere and then cooled to room temperature to obtain the graphite-coated product.

[0092] (4) The graphite-coated material was subjected to isostatic pressing to densify it. The pressure of the isostatic pressing was 50 MPa, and the holding time was 5 min. After crushing, a graphite anode precursor with a particle size D50 of 16.5 μm was obtained.

[0093] (5) The graphite anode precursor was calcined at 1250℃ for 10h under nitrogen protection. After carbonization, it was broken up, demagnetized and sieved to obtain the anode material.

[0094] Example 4

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

[0096] (1) Take 20 kg of natural spherical graphite (D50 = 14 μm) and press it in a hydraulic press. The pressure of the hydraulic press is 20 MPa, the holding time is 1 min, and the process is repeated twice. After pressing, the graphite is crushed to obtain pressed graphite particles with an average particle size of D50 = 14.1 μm.

[0097] (2) Take 2.2 kg of asphalt (softening point 250℃) and 20 kg of pressed graphite particles and add them to the VC mixer and mix for 25 min to obtain coated pressed graphite particles.

[0098] (3) The coated and pressed graphite particles were heat-treated at 400°C for 4 hours under a nitrogen protective atmosphere and then cooled to room temperature to obtain the graphite-coated product.

[0099] (4) The graphite-coated material was subjected to isostatic pressing to densify it. The pressure of the isostatic pressing was 70 MPa, and the holding time was 3 min. After crushing, a graphite anode precursor with a particle size D50 of 14.3 μm was obtained.

[0100] (5) The graphite anode precursor was calcined at 1250℃ for 14h under nitrogen protection. After carbonization, it was broken up, demagnetized and sieved to obtain the anode material.

[0101] Example 5

[0102] This embodiment provides a negative electrode material, which is prepared according to the following steps:

[0103] (1) Take 20 kg of natural spherical graphite (D50 = 10 μm) and press it in a hydraulic press. The pressure of the hydraulic press is 20 MPa and the holding time is 1 min. Repeat the process twice. After pressing, crush the graphite to obtain pressed graphite particles with an average particle size of D50 = 10.2 μm.

[0104] (2) Take 2.2 kg of asphalt (softening point 250℃) and 20 kg of pressed graphite particles and add them to the VC mixer and mix for 25 min to obtain coated pressed graphite particles.

[0105] (3) The coated and pressed graphite particles were heat-treated at 400°C for 4 hours under a nitrogen protective atmosphere and then cooled to room temperature to obtain the graphite-coated product.

[0106] (4) The graphite-coated material was subjected to isostatic pressing to densify it. The pressure of the isostatic pressing was 70 MPa, and the holding time was 3 min. After crushing, a graphite anode precursor with a particle size D50 of 10.4 μm was obtained.

[0107] (5) The graphite anode precursor was calcined at 1250℃ for 12h under nitrogen protection. After carbonization, it was broken up, demagnetized and sieved to obtain the anode material.

[0108] Example 6

[0109] The difference between this embodiment and embodiment 1 is that in step (1), the pressure of the hydraulic press is adjusted to 5MPa.

[0110] Example 7

[0111] The difference between this embodiment and embodiment 1 is that the pressure of the isostatic pressing process in step (4) is adjusted to 100 MPa.

[0112] Comparative Example 1

[0113] This comparative example provides a negative electrode material, the preparation method of which includes:

[0114] (1) Add 20 kg of natural spherical graphite (D50 = 16 μm) and 2.2 kg of asphalt (softening point 250℃) to a VC mixer and mix for 25 min to obtain coated graphite particles;

[0115] (2) The coated graphite particles were calcined at 1250°C for 16 hours under a nitrogen protective atmosphere, and then the negative electrode material was obtained by dispersing, demagnetizing and sieving.

[0116] Comparative Example 2

[0117] This comparative example provides a negative electrode material, the preparation method of which includes:

[0118] (1) Add 20 kg of natural spherical graphite (D50 = 10 μm) and 2.2 kg of asphalt (softening point 250℃) to a VC mixer and mix for 25 min to obtain coated graphite particles;

[0119] (2) The coated graphite particles were calcined at 1250°C for 16 hours under a nitrogen protective atmosphere, and then the negative electrode material was obtained by dispersing, demagnetizing and sieving.

[0120] Comparative Example 3

[0121] This comparative example provides a negative electrode material, the preparation method of which includes:

[0122] (1) Take 20 kg of natural spherical graphite (D50 = 16 μm) and press it in a hydraulic press. The pressure of the hydraulic press is 20 MPa, the holding time is 0.5 min, and after depressurization for 0.5 min, repeat 3 times. After pressing, crush it to obtain pressed graphite particles with an average particle size of D50 = 16.4 μm.

[0123] (2) The pressed graphite particles were subjected to isostatic pressing to densify them. The pressure of the isostatic pressing was 60 MPa, the holding time was 2 min, and then they were crushed to obtain dense graphite particles with a particle size D50 of 16.6 μm.

[0124] (3) Take 2.2 kg of asphalt (softening point 250℃) and 20 kg of dense graphite particles and add them to the VC mixer and mix for 25 min to obtain coated dense graphite particles.

[0125] (4) The densely coated graphite particles were calcined at 1250°C for 16 hours under a nitrogen protective atmosphere. After carbonization, the particles were dispersed, demagnetized, and sieved to obtain the negative electrode material.

[0126] Comparative Example 4

[0127] The difference between this comparative example and Example 1 is that in step (1), the pressure of the hydraulic press is adjusted to 40 MPa.

[0128] Comparative Example 5

[0129] The difference between this comparative example and Example 1 is that the pressure of the isostatic pressing process in step (4) is adjusted to 30 MPa.

[0130] Comparative Example 6

[0131] The difference between this embodiment and embodiment 1 is that in step (2), the amount of asphalt used is 1.0 kg, so that the mass ratio of asphalt to pressed graphite particles is 5:100.

[0132] Comparative Example 7

[0133] The difference between this embodiment and embodiment 1 is that in step (2), the amount of asphalt used is 4.0 kg, so that the mass ratio of asphalt to pressed graphite particles is 20:100.

[0134] Performance testing

[0135] The negative electrode materials provided in the above embodiments and comparative examples were analyzed for cross-sectional morphology, particle hardness (HIT), elastic modulus (EIT), specific surface area, particle size, sphericity Sh (90%), tap density, and I. D / I G The electrochemical performance was also tested, and the results are shown in Tables 1 and 2.

[0136] The specific methods for various performance tests are as follows:

[0137] (1) Morphology test of the cross-section of the negative electrode material: The negative electrode material was ionized into argon ions (Ar) under high vacuum using an ion mill (HITACHI E3500) through an ion source. + Argon ions are then accelerated by a high-voltage electric field to bombard the sample surface with high energy, thereby removing the surface material and achieving the effects of grinding and polishing. The cross-section of the particles is observed under a high-magnification electron microscope (HITACHI S4800), with a magnification of 2.5kX to 9.0kX for each particle to ensure the cross-section shows a complete single particle.

[0138] Select at least 20 particle cross-sections; take the intersection of the transverse median and the longitudinal median of the cross-section of a single particle's kernel as the center of an ellipse, with the major axis of the ellipse being 1 / 2 the length of the transverse median and the minor axis being 1 / 2 the length of the longitudinal median. Divide the kernel cross-section into an inner region (a1) and an outer region (b1) using the outline of the ellipse as the boundary, as shown in Figure 3. The inner region (a1) is inside the outline of the ellipse, and the outer region (b1) is outside the outline of the ellipse.

[0139] The aforementioned transverse median line is the longest horizontal diameter of the cut surface. The longitudinal median line is perpendicular to the transverse median line and passes through the midpoint of the transverse median line, intersecting with the edge of the material cut surface.

[0140] Software such as Image Pro Plus, Image J, and Aztec Feature were used to statistically analyze and calculate the pore area ratio of the core section, the inner layer region, the outer layer region, and the ratio of the pore area ratios of the inner and outer layers of a single particle. in, = Pore area of ​​the inner layer region of the i-th particle cross-section / Area of ​​the inner layer region * 100% = Pore area of ​​the outer layer of the i-th particle cross-section / Area of ​​the outer layer * 100%;

[0141] Taking Image Pro Plus as an example, the statistical process is illustrated as follows: 1) After opening Image Pro Plus software, open the electron microscope cross-sectional morphology image of a single particle by pressing File (F), Open (O), or Ctrl+O; 2) Perform scale calibration in Measure (M), Calibration (C), and Spatial Calibration Wizard; 3) Click Irregular AOI and draw the outline of a single particle in Trace mode; 4) Click Measure (M) and Count / Size and select Colors..., click Histogram Based, select the range of 0-255, click Count to fill the selected area, and click View and Statistics to record the area of ​​a single particle at Sum; 5) In RGB mode, use the extractor to extract the RGB values ​​of the pores, and then click Count to identify them; then click Draw / Merge Objects in Edit to select the unfilled pores, click OK after selection, and click View and Statistics to record the area value at Sum, which is the pore area of ​​a single particle; 6) Click Measure (M), Measure... Draw a line parallel to the ruler using the distance tool, and move this line segment to the selected area of ​​the AOI to obtain the horizontal median line (the maximum value of the line segment). Click Measure distance to draw a line segment with a length of 1 / 2 the horizontal median line starting from the endpoint. At the midpoint of the horizontal median line, draw a vertical median line perpendicular to the horizontal median line and intersecting the particle outline. 7) Using the center of the horizontal median line as the center of an ellipse, with the major axis of the ellipse being 1 / 2 the length of the horizontal median line and the minor axis being 1 / 2 the length of the short side of the vertical median line, first use Measure distance to mark the length range, and then use Elliptical AOI to draw an ellipse at the marked location as the inner layer region. 8) Repeat steps 4) and 5) to calculate the area and pore area of ​​the inner layer region. 9) Calculate the area and pore area of ​​the outer layer region using the particle area, particle pore area, and the area and pore area of ​​the inner layer region, and calculate the proportion of pore area in the core section of a single particle. Value, pore area ratio of the inner layer region Pore ​​area ratio of the outer layer and the ratio of the pore area of ​​the inner and outer layers ( (Value); 10) Perform steps 1)-9) above on 20 particles and calculate the negative electrode material. and The values ​​and average values ​​are used to obtain the entire negative electrode material. value.

[0142] (2) Hardness (HIT) and Elastic Modulus (EIT) Testing of Anode Materials: The hardness (HIT) and elastic modulus (EIT) of the anode materials were tested using an Anton Paar NHT2 nanoindenter. The anode materials were embedded in epoxy resin, cured, and then ground and polished. The resulting sample containing the anode material was placed on the indenter stage. A static displacement mode was used, with a glass triangular pyramid indenter positioned close to the center of the anode material particles; the indentation should not approach the particle edges. The indentation depth was set to 1200 nm, the loading and unloading rate to 5 mN / min, the holding time to 15 s, and the Poisson's ratio to 0.3. Hardness was calculated based on the indentation depth and load magnitude, while the elastic modulus was calculated based on the slope of the fitted line from 40% to 98% of the unloading curve. Ten particles were tested for each sample, and the average value was taken. Outlier handling method for test data: Box plot analysis was performed on the tested data, and outliers (values ​​exceeding Q1-1.5IQR (interquartile range) or Q3+1.5IQR) were removed. The hardness (HIT) and elastic modulus (EIT) of the negative electrode material in this application are average values.

[0143] (3) Specific surface area test: The specific surface area of ​​the negative electrode material was tested using a Microt TriStar3030 instrument. At a liquid nitrogen temperature of -196℃, the amount of nitrogen gas adsorbed on the solid surface was measured at a relative pressure of 0.05-0.3. Based on the Brown-Nauer-Etter-Taylor adsorption theory and its formula (BET formula), the amount of monolayer adsorption of the sample was calculated, thereby calculating the specific surface area and pore size distribution data of the negative electrode material.

[0144] (4) Particle size test: D50 is the particle size corresponding to a cumulative volume distribution percentage of 50%. D(4,3) is the average particle size at equal volumes, which is the average particle size of spheres with the same average particle volume. The average particle sizes D50 and D(4,3) of the negative electrode material were 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 a certain amount of pure water. The mixture was stirred thoroughly with a glass rod to ensure uniform dispersion. The pump speed was set to 2400 r / min-2500 r / min, and the frequency was 19.5 Hz for particle size testing.

[0145] (5) Sphericity Sh (90%) test: The sphericity Sh (90%) of the negative electrode material was tested using SYMPATEC's QICPIC dynamic particle image analyzer.

[0146] (6) Tap density test: The tap density of the negative electrode material was tested using a Quanta 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.

[0147] (7)I D / I G Testing: The Raman scattering spectrum of the negative electrode material was measured using a HORIBA-XPLORA laser confocal Raman spectrometer with a laser wavelength of 532 nm. Data was collected from 30 points on each sample surface, and the scattering spectrum obtained from each point was then subjected to peak fitting. The material's D peak is located at 1350 cm⁻¹. -1 ±3cm -1 At this location, the G peak is at 1580cm. -1 ±3cm -1 After labeling peaks D and G, the area ratio of peak D to peak G is calculated as I. D / I G value.

[0148] (8) Electrochemical performance testing:

[0149] First reversible specific capacity and first coulombic efficiency tests: The negative electrode materials prepared in the examples and comparative examples, carboxymethyl cellulose and styrene-butadiene rubber were dissolved in N-methylpyrrolidone in a mass ratio of 96.5:1.5:2, with the solid content controlled at 50wt%. The solutions were coated onto copper foil current collectors, and after vacuum drying at 95℃, rolling, and pressurization, a negative electrode sheet was obtained. A lithium metal sheet was used as the counter electrode, and Guotai Huarong LB5315C was used as the electrolyte. A coin cell was assembled 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 first reversible specific capacity, first charge capacity, and first discharge capacity. The first coulombic efficiency was calculated as: first discharge capacity / first charge capacity.

[0150] 400-cycle capacity retention test: Large single-crystal lithium nickel cobalt manganese oxide (NCM523) was mixed with conductive carbon black and PVDF at a mass ratio of 94:3.0:3.0 and dissolved in N-methylpyrrolidone, with the solid content controlled at 50wt%, to obtain a positive electrode slurry; the positive electrode slurry was coated onto an aluminum foil current collector, and after vacuum drying at 95℃, rolling and pressing, a positive electrode sheet was obtained;

[0151] The negative electrode materials, carboxymethyl cellulose, styrene-butadiene rubber, and conductive carbon black of the examples and comparative examples were dissolved in N-methylpyrrolidone at a mass ratio of 95:1.5:2.1:1.2, respectively, and the solid content was controlled at 50 wt% to obtain a negative electrode slurry. The negative electrode slurry was coated on a copper foil current collector, and after vacuum drying at 95°C, rolling, and pressurizing, a negative electrode sheet was obtained.

[0152] The positive electrode, separator, and negative electrode are assembled into a secondary battery, and an electrolyte is injected to obtain a soft-pack battery with a capacity of about 40mAh. The electrolyte is 1mol / L LiPF6 / ethylene carbonate (EC) + propylene carbonate (PC) + diethyl carbonate (DEC) + EMC (volume ratio 1:0.3:1:1), and the separator is a PP / PE / PP three-layer composite separator.

[0153] The aforementioned pouch cell was used to test the cycle performance of the material. It was charged at a constant current rate of 1C to 4.20V, then charged at a constant voltage rate with the current gradually decreasing to 0.05C, and finally discharged at a discharge rate of 1C to 2.75V. This charge-discharge cycle was repeated 400 times. The discharge capacity Q1 at the first cycle and the discharge capacity Q400 at the 400th cycle were measured. The 400-cycle capacity retention rate was calculated as Q400 / Q1 × 100%.

[0154] Table 1 Test results of negative electrode material parameters

[0155] Table 2. Electrochemical performance test results of anode materials

[0156] Figure 3 is an SEM image of a single particle cross-section of the negative electrode material provided in Example 1, where a1 is the inner layer and b1 is the outer layer. As can be seen from Figure 3, a1 is elliptical, with its center at the intersection of the transverse and longitudinal median lines of the particle. Its major axis is half the length of the transverse median line, and its minor axis is the length of the longitudinal median line. b1 represents the area in the cross-section excluding a1. Within a magnification range of 2.5kX to 9.0kX, the single particle of the negative electrode material appears complete, and the particle… Meanwhile, the particle hardness (HIT) of the negative electrode material provided in Example 1 is 0.324 GPa, and the elastic modulus (EIT) is 7.34 GPa.

[0157] Compared to Examples 1-7, Comparative Examples 1-3 did not use dense packing technology and therefore did not meet the negative electrode material characteristics of HIT = 0.28 GPa-0.4 GPa and EIT = 7.0 GPa-8.0 GPa. Consequently, their initial coulombic efficiency and cycle performance were poor, with the 400-cycle capacity retention rate decreasing to 85.64%. Comparative Example 2 also did not use dense packing technology and did not meet the negative electrode material characteristics of EIT = 7.0 GPa-8.0 GPa. However, because its particle size was smaller than that of Comparative Example 1, its HIT met the negative electrode material characteristics of 0.28 GPa-0.4 GPa. Therefore, its cycle performance was better than that of Comparative Example 1, with a 400-cycle capacity retention rate of 87.56%. Comparative Example 3 adopted a densification treatment and then coated with amorphous carbon. Although the porosity of the material was improved, it did not meet the characteristics of the negative electrode material with HIT = 0.28 GPa-0.4 GPa and EIT = 7.0 GPa-8.0 GPa. The improvement in cycle performance was limited, and the capacity retention rate after 400 cycles was 90.05%.

[0158] Compared to Examples 1-7, Comparative Examples 4-7 show that the hydraulic press pressure in Comparative Example 4 was 40 MPa, which was too high, preventing the amorphous carbon from fully filling the particles. This did not meet the EIT (Energy Intake) requirement of 7.0 GPa-8.0 GPa for the anode material, resulting in poorer initial coulombic efficiency and cycle performance compared to Examples 1-7, with a capacity retention of only 90.34% after 400 cycles. In Comparative Example 5, the pressure applied during isostatic pressing for densification was too low, resulting in limited internal filling and high porosity. This also failed to meet the EIT (Energy Intake) requirement of 7.0 GPa-8.0 GPa for the anode material, leading to lower initial coulombic efficiency and cycle performance compared to Examples 1-7, with a capacity retention of only 89.67% after 400 cycles. In Comparative Example 6, the asphalt coating amount was too low, resulting in insufficient filling of amorphous carbon into the graphite interior and inadequate uniform coating on the graphite surface. The material did not meet the negative electrode material characteristics of HIT = 0.28 GPa-0.4 GPa and EIT = 7.0 GPa-8.0 GPa, and was prone to solvent co-intercalation during charge-discharge, leading to a decrease in cycle performance. In Comparative Example 7, the asphalt coating was excessive. Excessive asphalt during carbonization formed more pores and cracks, increasing porosity and reducing material structural stability. This also prevented the material from meeting the negative electrode material characteristics of HIT = 0.28 GPa-0.4 GPa and EIT = 7.0 GPa-8.0 GPa, exacerbating the decrease in capacity retention during charge-discharge, and resulting in worse material performance compared to Examples 1-7.

[0159] Furthermore, compared to Example 7, the anode materials provided in Examples 1-6, while satisfying HIT = 0.28 GPa-0.40 GPa and elastic modulus EIT = 7.0 GPa-8.0 GPa, have a higher average porosity of the graphite composite particle cross-section. Average pore filling rate of the inner region Average pore filling rate of the outer region Furthermore, it satisfies: It can improve the density of the anode material, reduce the porosity, and further improve the structural stability. At the same time, the high disorder of amorphous carbon improves the interfacial transport dynamics, further improving the first coulombic efficiency and cycle performance of the anode material, and making the capacity retention rate ≥92% after 400 cycles.

[0160] As can be seen from the above description, the embodiments of this application achieve the following technical effects: The negative electrode material provided by this application reflects the degree of compaction of the pores inside the negative electrode material through particle hardness and elastic modulus. Under the same particle size, the larger the particle hardness (HIT) and the lower the elastic modulus (EIT), the fewer the pores inside the negative electrode material and the higher the degree of compaction. This can better prevent the electrolyte from embedding into the interior of the negative electrode material, thereby improving the interfacial transport dynamics performance and enhancing the material's first coulombic efficiency and cycle performance.

[0161] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A negative electrode material, characterized by, The particle hardness (HIT) of the negative electrode material is 0.28 GPa-0.40 GPa, and the elastic modulus (EIT) is 7.0 GPa-8.0 GPa.

2. The negative electrode material according to claim 1, characterized in that, The particle hardness HIT of the negative electrode material is 0.28 GPa, 0.30 GPa, 0.32 GPa, 0.35 GPa, 0.38 GPa, 0.40 GPa, or any value within the range of any two of the above values. Alternatively, the particle hardness (HIT) of the negative electrode material may be any value between 0.28 GPa and 0.32 GPa; Alternatively, the particle hardness (HIT) of the negative electrode material may be any value between 0.32 GPa and 0.35 GPa; Alternatively, the particle hardness (HIT) of the negative electrode material may be any value between 0.35 GPa and 0.40 GPa.

3. The negative electrode material of claim 1, wherein, The elastic modulus EIT of the negative electrode material is 7.0 GPa, 7.2 GPa, 7.5 GPa, 7.8 GPa, 8.0 GPa, or any value within the range of any two of the above values. Alternatively, the elastic modulus EIT of the negative electrode material is any value between 7.0 GPa and 7.2 GPa; Alternatively, the elastic modulus EIT of the negative electrode material is any value between 7.2 GPa and 7.5 GPa; Alternatively, the elastic modulus EIT of the negative electrode material is any value between 7.5 GPa and 8.0 GPa.

4. The negative electrode material of claim 1, wherein, The negative electrode material includes natural spherical graphite and amorphous carbon filling the interior of the natural spherical graphite.

5. The negative electrode material of claim 1, wherein, The negative electrode material includes a plurality of graphite composite particles, a section of the graphite composite particles is divided into an inner layer region a and an outer layer region b, the outer layer region b is located at a peripheral side of the inner layer region a, an average porosity of the section of the graphite composite particles is An average porosity filling rate of the inner layer region a is An average porosity filling rate of the outer layer region b is 6. The negative electrode material of claim 1, wherein, The negative electrode material satisfies the following relationship: Δ=│shape factor φ-sphericity Sh(90%)│, and Δ≤0.08, where the shape factor φ=D50 / D(4,3), D50 is 5μm-20μm, D50 is the particle size corresponding to the cumulative volume distribution percentage reaching 50%, D(4,3) is the average particle size of equal volume, which is the average particle size of spheres with the same average particle volume, and the sphericity Sh(90%) is determined by a dynamic particle pattern analyzer.

7. The negative electrode material according to claim 6, characterized in that, The sphericity Sh (90%) is 0.89-0.

95.

8. The negative electrode material according to claim 7, characterized in that, At least one of the following conditions must be met: (1) The sphericity Sh (90%) is any value within the range of 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95 or any two of the above values; (2) The sphericity Sh (90%) is 0.89-0.

93.

9. The negative electrode material of claim 6, wherein, The D(4,3) is 10μm-20μm.

10. The negative electrode material according to claim 9, characterized in that, At least one of the following conditions must be met: (1) D(4,3) is any value within the range of 11.2μm, 15.2μm, 17.3μm, 17.5μm, 17.7μm, 17.9μm or any two of the above values; (2) The D(4,3) is 11.2μm-17.9μm.

11. The negative electrode material according to any one of claims 1 to 10, characterized in that, The specific surface area SSA of the negative electrode material is 2 m 2 / g-5 m 2 / g; and / or the tap density Tap of the negative electrode material is 0.9 g / cm 3 -1.5 g / cm 3 .

12. The negative electrode material according to any one of claims 1 to 10, characterized in that, I D / I G is 0.9-1.3; wherein, I D is an area of a D peak in a Raman scattering spectrum of the negative electrode material, I G is an area of a G peak in the Raman scattering spectrum of the negative electrode material.

13. A secondary battery characterized by comprising: The secondary battery comprises the negative electrode material according to any one of claims 1 to 12.

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