Negative electrode active material, negative electrode sheet, and lithium-ion battery

Abstract

A negative electrode active material, a negative electrode sheet, and a lithium-ion battery. The negative electrode active material comprises single particles and secondary particles, wherein the mass percentage t of the single particles does not exceed 30%, the particle size Dv90 of the single particles is 13 μm-20 μm, and the particle size Dv'90 of the secondary particles is 18 μm-26 μm and is greater than the particle size Dv90 of the single particles. The single particles exhibit high capacity and first-cycle efficiency but poor charging and expansion performance while the secondary particles exhibit the opposite properties. Thus, by blending the single particles and the secondary particles according to a specific ratio and relative particle sizes, a balance between charging performance and energy density can be achieved. Moreover, the surfaces of the single particles and the secondary particles are oxidized to remove low-crystallinity regions, thereby improving the overall capacity and compaction level.

Description

Negative electrode active materials, negative electrode sheets, and lithium-ion batteries Technical Field

[0001] This application belongs to the field of lithium-ion battery technology, and relates to negative electrode active materials, negative electrode sheets and lithium-ion batteries. Background Technology

[0002] With the scarcity of fossil fuel resources and increasingly serious environmental and ecological problems, people are beginning to pursue cleaner and more environmentally friendly energy sources. Lithium-ion batteries have received increasing attention due to their high energy density and high power density. Today, lithium-ion batteries are widely used in our daily lives, such as in portable electronic products like laptops and mobile phones, as well as electric vehicles. These products place increasingly higher demands on the energy density and high-temperature performance of lithium-ion batteries, while the energy density of lithium-ion batteries is greatly affected by the active materials used.

[0003] Furthermore, the capacity released by different active materials, especially graphite, varies significantly at different temperatures, directly affecting the usable capacity of the battery cell, i.e., its actual energy density. This difference in discharge capacity is often related to the activity of the lithium insertion / extraction reaction within the cell. However, this activity conflicts with high-temperature performance, as high internal reactivity leads to more vigorous reactions at high temperatures, causing side reactions such as the decomposition of the SEI film on the negative electrode surface, resulting in severe gas generation and ultimately failure. Therefore, it is necessary to improve the energy density of the negative electrode active material while ensuring high-temperature performance.

[0004] Summary of the Invention

[0005] This application aims to address at least one of the technical problems existing in the prior art. To this end, this application proposes a negative electrode active material, a negative electrode sheet, and a lithium-ion battery. The lithium-ion battery formed using this negative electrode active material has high energy density and high-temperature performance.

[0006] In a first aspect, this application provides a negative electrode active material, comprising single particles and secondary particles;

[0007] Among them, the mass percentage of a single particle in the total mass of single particles and secondary particles does not exceed 30%;

[0008] The particle size Dv90 of a single particle is 13 to 20 μm, and the particle size Dv′90 of a secondary particle is 18 to 26 μm, which is larger than the particle size Dv90 of a single particle.

[0009] The negative electrode active material according to the first aspect of this application has the following beneficial effects:

[0010] Single-particle batteries have high capacity and initial efficiency, but poor charging and expansion performance; conversely, secondary-particle batteries exhibit the opposite characteristics. Therefore, this design combines single-particle and secondary-particle batteries in a specific ratio and with appropriate relative particle sizes to balance charging performance and energy density. Specifically, the ratio and relative particle size of single-particle and secondary-particle batteries also affect their compatibility. These constraints further enhance lithium-ion insertion / extraction capabilities, reduce side reactions, and thus effectively increase the battery's energy density and improve its high-temperature performance.

[0011] In this context, "single particle" refers to a powder particle that can be separated and exist independently; it can be a single crystal or a polycrystalline particle. "Secondary particle" refers to a secondary particle formed by the aggregation of single particles in some way. For example, it can be formed from a single crystal or polycrystalline form of the corresponding compound through one or more physicochemical reactions such as decomposition, calcination, reduction, displacement, or combination, followed by phase transformation or crystal form change; or it can be formed from single particles through high-temperature treatment (such as calcination or annealing). These secondary particles are aggregates or agglomerates. Furthermore, secondary particles can also be formed by the aggregation of single particles through agglomeration or flocculent formation.

[0012] Particle size refers to the size of a particle expressed as its diameter. For spherical particles, the particle size refers to the diameter of the particle; for irregular particles, the particle size is usually the equivalent diameter, such as the volume equivalent diameter or the projected area diameter. D90, also known as coarse-end particle size, refers to the particle size corresponding to 90% of the cumulative particle size distribution in a sample. The cumulative particle size distribution refers to the percentage of particles smaller than a certain size among all particles (e.g., the percentage of particles by mass, volume, or number). Particle size can be measured by any of the following methods: sieving, microscopy, sedimentation, electronic sensor, laser, or acoustic spectroscopy. Typically, the particle size of negative electrode active materials can be measured using laser methods, such as laser particle size analyzers, to measure single and secondary particles. Depending on the type of particle size distribution measurement, it can be divided into intensity distribution Di90, volume distribution Dv90, and number distribution Dn90. The testing standard refers to "Particle Size Distribution—Laser Diffraction Method" (GB / T 19077-2016).

[0013] In some embodiments of this application, the OI value r of the negative electrode active material satisfies 6. <r<17。

[0014] The OI value represents the orientation degree of a negative electrode active material, especially graphite-based negative electrode active materials. Specifically, it refers to the ratio of the peak intensities of the (004) crystal plane to the (110) crystal plane. Since the (110) crystal plane is parallel to the Z-axis, while the (004) crystal plane is perpendicular to the Z-axis, the ratio of the peak intensities of these two crystal planes can be used to characterize the isotropy of the negative electrode active material. OI value = I(004) / I(110), where I represents the peak intensity of the crystal plane. The peak intensity can be obtained at least through XRD (X-ray Diffraction). The sample used for testing can be a negative electrode active material or a negative electrode sheet formed using that negative electrode active material.

[0015] A smaller OI value indicates better isotropy, with end faces in all directions increasing lithium-ion transport ports; a larger OI value indicates poorer isotropy, with obvious orientation of the negative electrode active material, limited port orientation, and reduced lithium-ion rapid insertion capability.

[0016] In some embodiments, the mass percentage H of the surface oxygen content of the negative electrode active material satisfies 200H / Dv90+10 / r<3.2, where Dv90 is a dimensionless value with units omitted in μm during calculation.

[0017] Surface oxygen content refers to the proportion of oxygen on the outer surface of a particle at the nanometer to micrometer scale, relative to the total amount of all elements, and is therefore usually expressed as a mass percentage. Surface oxygen content can be measured using methods such as EDX (Energy Dispersive X-ray Spectroscopy), AES (Auger Electron Spectroscopy), XPS (X-ray Photoelectron Spectroscopy), and TOF-SIMS (Time of Flight-Secondary Ion Mass Spectrometry). Different methods correspond to different surface detection depths. For example, TOF-SIMS can detect the oxygen content on a 1 nm particle surface, XPS can detect the oxygen content on a 3-10 nm particle surface, AES can detect the oxygen content on a 1-5 nm particle surface, and EDX can detect the oxygen content on a 10 nm-3 μm particle surface. In the embodiments of this application, XPS is generally used to detect the surface oxygen content of single and secondary particles.

[0018] Surface oxygen content indicates the degree of oxidation of the negative electrode active material. After single or secondary particles are oxidized, the low-crystallinity regions are etched away, resulting in an improvement in overall specific capacity and compaction level. In addition, oxidation etching creates certain pores, which provide more transport ports for lithium ions, improving kinetic performance and allowing more lithium ions to be inserted and extracted during charging and discharging.

[0019] In the embodiments of this application, the temperature coefficient is used to characterize the difference in discharge capacity of the negative electrode active material, that is, the ratio of the discharge capacity at room temperature to the discharge capacity at 45°C. The temperature coefficient is related to the lithium insertion / extraction reaction activity inside the cell; the greater the lithium insertion / extraction reaction activity, the higher the temperature coefficient.

[0020] Regarding the three characteristics mentioned in the above formula, the smaller the OI value, the better the isotropy, with end faces in all directions increasing lithium-ion transport ports; the larger the OI value, the worse the isotropy, the more pronounced the orientation of the negative electrode active material, the more limited the port orientation, and the reduced ability for rapid lithium-ion insertion. Smaller particle size results in a shorter lithium-ion diffusion path, which is more conducive to lithium-ion insertion, but excessively small particle size significantly increases the specific surface area, leading to increased side reactions. Oxidation etching increases the porosity of the particle surface. These pores can provide more transport ports for lithium ions, improving kinetic performance and allowing more lithium ions to be inserted and extracted during charging and discharging, thus enhancing the activity of lithium insertion / extraction reactions and effectively improving the temperature coefficient. However, etching increases the specific surface area, which, combined with the inherently high specific surface area of ​​small particle size, significantly increases side reactions and deteriorates high-temperature storage performance.

[0021] Therefore, when the particle size Dv90 and OI value of a single particle are combined to meet the above conditions, the problem of severe side reactions caused by using a small particle size single particle can be avoided under low OI and high oxidation etching conditions. The temperature coefficient is significantly improved, while ensuring that the high-temperature storage performance is not deteriorated.

[0022] In some embodiments of this application, the mass percentage H1 of the surface oxygen content of a single particle is 0 to 10%, for example, the mass percentage H1 of the surface oxygen content of a single particle is 0%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%.

[0023] In some embodiments of this application, the mass percentage H2 of the surface oxygen content of the secondary particles is 5% to 15%, for example, the mass percentage H2 of the surface oxygen content of the secondary particles is 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%.

[0024] In some embodiments of this application, the mass percentage H of the surface oxygen content of the negative electrode active material is 4% to 15%, for example, the mass percentage H of the surface oxygen content of the negative electrode active material is 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%.

[0025] Single-particle lithium ion insertion (LPI) particles are small and have a single lithium-ion insertion facet. Oxidation processes can increase the number of LPI transport ports, but excessive oxidation etching can increase the defect rate of small particles and exacerbate side reactions. Secondary particles themselves have multiple LPI ports and good charging capabilities, but their specific capacity is reduced due to the presence of binders. Therefore, increasing the degree of oxidation can significantly reduce the low crystallinity region, further improving the specific capacity of secondary particles and thus increasing the overall energy density of the negative electrode active material. However, excessive etching and oxidation can cause the port structure to collapse, hindering lithium-ion insertion and extraction and worsening the temperature coefficient.

[0026] In some embodiments of this application, the mass percentage t of a single particle is 30%, 29%, 28%, 27%, 26%, 25%, 24%, 23%, 22%, 21%, 20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, or 1%.

[0027] In some embodiments of this application, the particle size Dv90 of a single particle is 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, or 20μm.

[0028] In some embodiments of this application, the particle size Dv′90 of the secondary particles is 18μm, 19μm, 20μm, 21μm, 22μm, 23μm, 24μm, 25μm, or 26μm.

[0029] As the particle size of single and secondary particles increases, the specific surface area decreases, side reactions are reduced, and the high-temperature performance of lithium-ion batteries is better.

[0030] In some embodiments of this application, the ratio A of the particle size Dv′90 of the secondary particles to the particle size Dv90 of the single particles is 1.2 to 2.0, for example, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2.0.

[0031] In some embodiments of this application, both single particles and secondary particles are graphite materials.

[0032] In some embodiments of this application, graphite includes at least one of natural graphite and artificial graphite.

[0033] In some embodiments of this application, natural graphite includes natural flake graphite.

[0034] In some embodiments of this application, the raw materials for artificial graphite include at least one of petroleum-based needle coke, coal-based needle coke, and mesophase carbon microspheres.

[0035] In some embodiments of this application, the single particles are selected from any one of natural graphite and artificial graphite, and the secondary particles are selected from at least one of natural graphite and artificial graphite.

[0036] In some embodiments of this application, the secondary particles are secondary particles formed from the same type of single particles.

[0037] In some embodiments of this application, the shape of the single or secondary particles can be a regular shape (e.g., spherical, near-spherical, elliptical, needle-like, plate-like, fibrous, sheet-like, etc.) or an irregular shape.

[0038] It is understandable that the aforementioned single and secondary particles can be doped with oxygen on their surface by contacting air, thereby bringing about a certain surface oxygen content. For example, a certain surface oxygen content can be achieved by introducing a set amount of air or oxygen and then performing ball milling, sintering, or other methods.

[0039] A second aspect of this application provides a negative electrode sheet, which includes a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector, wherein the raw materials for preparing the negative electrode active material layer include the aforementioned negative electrode active material.

[0040] In some embodiments of this application, the raw materials for the negative electrode active material layer further include at least one of a conductive agent and a binder. The conductive agent includes, but is not limited to, conductive graphite (such as KS-6, KS-15, SFG-6, SFG-15, SO, etc.), conductive carbon black (such as Super P, Super S, 350G, acetylene black, Ketjen black, etc.), conductive carbon fiber (such as VGCF, CNT), and graphene. The binder includes, but is not limited to, at least one of polyvinylidene fluoride, polytetrafluoroethylene, carboxymethyl cellulose, styrene-butadiene rubber, polyurethane, polyvinyl alcohol, and polyvinyl butyral.

[0041] In some embodiments of this application, the negative electrode active material layer comprises 70 wt% to 99 wt% of negative electrode active material, 0.5 wt% to 6 wt% of conductive agent and 0.5 wt% to 20 wt% of binder.

[0042] A third aspect of this application provides a lithium-ion battery comprising the aforementioned negative electrode.

[0043] In some embodiments of this application, the lithium-ion battery includes a positive electrode, a negative electrode, an electrolyte, and a separator.

[0044] In some embodiments of this application, the positive electrode sheet includes a positive current collector and a positive active material layer located on the positive current collector. The positive active material layer includes a positive active material, such as at least one of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium nickel manganese aluminum oxide.

[0045] In some embodiments of this application, the positive electrode active material layer further includes at least one of a conductive agent and a binder. The conductive agent includes, but is not limited to, conductive graphite (such as KS-6, KS-15, SFG-6, SFG-15, SO, etc.), conductive carbon black (such as Super P, Super S, 350G, acetylene black, Ketjen black, etc.), conductive carbon fiber (such as VGCF, CNT), and graphene. The binder includes, but is not limited to, at least one of polyvinylidene fluoride, polytetrafluoroethylene, carboxymethyl cellulose, styrene-butadiene rubber, polyurethane, polyvinyl alcohol, and polyvinyl butyral.

[0046] In some embodiments of this application, the positive electrode active material layer comprises 70 wt% to 99 wt% of positive electrode active material, 0.5 wt% to 6 wt% of conductive agent, and 0.5 wt% to 20 wt% of binder.

[0047] In some embodiments of this application, when positive electrode active material / negative electrode active material, conductive agent and binder are used to form positive electrode active material layer / negative electrode active material layer, the process includes dispersing positive electrode active material / negative electrode active material, conductive agent and binder in solvent, coating the mixture on positive electrode current collector / negative electrode current collector, and drying to obtain positive electrode active material layer / negative electrode active material layer.

[0048] In some embodiments of this application, the positive electrode current collector / negative electrode current collector includes at least one of the following: metal foil (such as aluminum foil, silver foil, tin foil, iron foil, titanium foil, nickel foil, copper foil, or alloy foil of the above metals) and metal mesh (such as aluminum mesh, silver mesh, tin mesh, iron mesh, titanium mesh, nickel mesh, copper mesh, or alloy mesh of the above metals).

[0049] In some embodiments of this application, the positive electrode, negative electrode, and separator are obtained by at least one of winding, stacking, or other methods to form a cell and a lithium-ion battery.

[0050] In some embodiments of this application, the electrolyte may be at least one of a solid electrolyte or an electrolyte solution.

[0051] A fourth aspect of this application provides an electrical device comprising the aforementioned lithium-ion battery. The electrical device refers to any device capable of utilizing electrical energy and converting it into mechanical energy, thermal energy, light energy, or one or more other energy-generating devices, such as electric motors, electric heaters, and electric light sources. This includes mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc.; mobile devices can be mobile phones, laptops, drones, robotic vacuum cleaners, e-cigarettes, etc.; electric vehicles can be pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.

[0052] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Detailed Implementation

[0053] The following will clearly and completely describe the concept and technical effects of this application in conjunction with embodiments, so as to fully understand the purpose, features and effects of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are all within the scope of protection of this application.

[0054] The embodiments of this application are described in detail below. The described embodiments are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0055] In the description of this application, "several" means one or more, "multiple" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number, and "approximately" means within the range of ±20%, ±10%, ±8%, ±5%, ±4%, ±3%, ±2%, ±1%, ±0.5%, ±0.2%, ±0.1%, etc. of the specified number. If "first" or "second" is used, it is only for the purpose of distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0056] In the description of this application, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0057] The present application will be described below with reference to specific embodiments.

[0058] Example 1

[0059] This embodiment provides a negative electrode active material, which is composed of a mixture of single particles and secondary particles, both of which are artificial graphite particles.

[0060] Among them, the particle size Dv90 of a single particle is 13 μm, and the surface oxygen content H1 is 2%;

[0061] The secondary particles have a particle size Dv′90 of 18 μm and a surface oxygen content H2 of 5%.

[0062] The methods for adjusting the surface oxygen content of single and secondary particles are as follows:

[0063] Take 100g of single particles (or secondary particles) and put them into a reaction vessel. React them by passing air through them at 600℃. The single particles (or secondary particles) with specific surface oxygen content are then detected.

[0064] The mass percentage of a single particle to the total mass of both is 30%, and the ratio A of the particle size Dv′90 of the secondary particle to the particle size Dv90 of the single particle is 1.38.

[0065] The negative electrode active material has an OI value r of 16, a surface oxygen content H of 4%, and a 200H / Dv90+10 / r ratio of 1.24.

[0066] The particle size Dv90 of single and secondary particles was obtained by measuring the particle size distribution using a laser diffraction particle size distribution measuring instrument (Malvern Mastersizer 3000) according to the particle size distribution laser diffraction method GB / T19077-2016.

[0067] The OI value was measured by XRD. According to the international standard JJS K 0131-1996 "General Rules for X-ray Diffraction Analysis", an X-ray diffractometer (Bruker D8 ADVANCE) was used with CuKα radiation, voltage 40KV, current 40mA, test angle from 20° to 80°, and a step time of 0.3s. The powder of the negative electrode active material was scanned to obtain the XRD spectrum. The peak intensities I(004) of the (004) crystal plane diffraction peak C(004) and I(110) of the (110) crystal plane diffraction peak C(110) were analyzed. The OI value of the negative electrode active material was calculated according to OI = I(004) / I(110).

[0068] The surface oxygen content of the negative electrode active material, as well as single and secondary particles, was measured by XPS.

[0069] This embodiment also provides a lithium-ion battery, the preparation process of which is as follows:

[0070] (1) Preparation of negative electrode

[0071] The aforementioned negative electrode active material, binder styrene-butadiene rubber, and dispersant sodium carboxymethyl cellulose were dissolved in deionized water at a mass ratio of 98:1:1 and thoroughly mixed to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated onto a negative electrode current collector copper foil and vacuum baked at 80°C for 12 hours. Then, through steps such as cold pressing, edge trimming, cutting, and slitting, the negative electrode sheet for lithium-ion batteries was produced.

[0072] (2) Preparation of positive electrode

[0073] The positive electrode active material NCM523, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 97:2:1. N-methylpyrrolidone (NMP) solvent was added, and the mixture was stirred under vacuum until homogeneous to obtain the positive electrode slurry. The positive electrode slurry was uniformly coated onto the positive electrode current collector aluminum foil, air-dried at room temperature, and then transferred to an oven for further drying. Finally, the positive electrode sheet was obtained through cold pressing and slitting.

[0074] (3) Preparation of electrolyte

[0075] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0076] (4) Preparation of lithium-ion batteries

[0077] The positive electrode, polyethylene separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. Then, they are wound to obtain a bare cell. The bare cell is placed in an outer aluminum casing, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a lithium-ion battery is obtained.

[0078] Examples 2-13 and Comparative Examples 1-4

[0079] Based on Example 1, negative electrode active materials and lithium-ion batteries of Examples 2-13 and Comparative Examples 1-4, differing only in at least one of particle size, orientation degree, and surface oxygen content, are provided, as detailed in Table 1 below. Simultaneously, 100g of single or secondary particles were placed in a reaction vessel and reacted at 600°C with different gases introduced; specific parameter settings are shown in Table 2.

[0080] Table 1. Different parameters of single and secondary particles in the examples and comparative examples

[0081] Table 2. Control of surface oxygen content of particles

[0082] The performance of the negative electrode sheets and lithium-ion batteries of the examples and comparative examples was tested using the following methods:

[0083] (1) Energy density (Wh / kg) = initial discharge capacity (Wh) / lithium-ion battery mass (kg).

[0084] (2) Temperature coefficient test: At 25℃, the lithium-ion battery was discharged at 0.2C, fully charged at 0.5C, and then discharged at 0.2C to 3.0V. The discharge capacity was recorded as C1. The cell was then fully charged at 0.5C and the lithium-ion battery was moved to a 45℃ environment and discharged at 0.2C to 3.0V. The discharge capacity was recorded as C2. Temperature coefficient = C1 / C2×100%.

[0085] (3) High temperature storage performance test: At 25℃, the lithium-ion battery was fully charged at 5C and discharged at 1C once. Then, the lithium-ion battery was fully charged at 5C. The cell thickness was measured with a 500PPG battery thickness gauge as the initial thickness D1. The lithium-ion battery was placed in a 60℃ oven for 30 days. The cell thickness D2 was measured with a 500PPG battery thickness gauge. The thickness expansion rate (%) = (D2-D1) / D1×100%.

[0086] The results are shown in Table 3:

[0087] Table 3. Performance test results of the examples and comparative examples

[0088] Analysis of the above comparative examples and embodiments shows that, compared to Example 4, the particle size difference between single particles and secondary particles in Comparative Example 1 is smaller, resulting in poor matching between the two, reduced ED, larger single particles, and a longer lithium intercalation path, leading to a significant decrease in battery energy density, deterioration of kinetic performance, and a decrease in temperature coefficient, while improving high-temperature storage performance. Compared to Example 1, the OI value of the negative electrode active material in Comparative Example 2 is too high, and the orientation of the graphite particles is too obvious, resulting in fewer lithium intercalation faces and a decrease in the temperature coefficient of the lithium-ion battery. Compared to Example 13, all parameters in Comparative Example 3 are within the corresponding range, but do not meet the range requirements of the 200H / d+10 / r formula. The particle size is small, and the superposition of strong oxidation etching leads to severe side reactions during battery operation and serious deterioration of high-temperature storage. Compared to Example 1, the excessive etching of single particles and excessive oxidation etching of secondary particles in Comparative Example 4 result in excessively high oxygen content on the surface of the negative electrode active material, port collapse, deterioration of window charge and discharge capability, and excessive oxidation exacerbates side reactions, also leading to significant deterioration of high-temperature storage.

[0089] As can be seen from Comparative Examples 1-4, as the surface oxygen content of the negative electrode active material and single and secondary particles gradually increases, the degree of oxidation etching gradually deepens. During the oxidation etching process, the low crystallinity region is oxidized, which can improve the overall capacity compaction, increase the number of ports, and gradually increase the energy density and temperature coefficient of the battery. However, the high-temperature storage performance gradually decreases, and the thickness expansion rate becomes higher and higher.

[0090] Comparing Examples 1 and 5, it can be seen that as the particle size of the secondary particles increases, the demand for binder increases, leading to a decrease in capacity and energy density; however, the increased number of end faces improves kinetic performance and increases the temperature coefficient. Comparing Examples 5 and 6, the increased particle size of the individual particles leads to worse kinetic performance and a decrease in temperature coefficient; however, the increased capacity and energy density compensate for the changes in secondary particles.

[0091] Comparing Examples 1 and 8-10, it can be seen that as the OI value of the negative electrode active material gradually decreases, the energy density of the battery gradually decreases, the temperature coefficient gradually increases, but the high-temperature storage performance also gradually decreases, and the thickness expansion rate increases. This may be because granulation reduces the OI of the negative electrode active material, but the specific surface area increases accordingly, increasing the lithium intercalation facets and intensifying side reactions, thus weakening the high-temperature storage performance. Furthermore, the introduction of trace amounts of binder during granulation leads to a decrease in specific capacity, thereby reducing the energy density.

[0092] Comparing Examples 1 and 11-12, it is evident that the surface oxygen content of single and secondary particles changes, causing the overall surface oxygen content of the negative electrode active material to gradually increase. Within the limited range of 200H / Dv90+10 / r, oxidation etching reduces the low-crystallinity region of the negative electrode active material, thereby increasing the overall specific capacity and compaction density, compensating for the capacity reduction caused by granulation. Ultimately, the energy density and temperature coefficient increase, although the high-temperature storage performance decreases slightly but remains relatively good. In Example 13, both single and secondary particles are directly etched using oxygen, requiring a shorter etching time and resulting in a higher surface oxygen content. The increased oxidation degree, combined with medium-sized single and secondary particles, increases the temperature coefficient, while minimizing the deterioration of side reactions.

[0093] The present application has been described in detail above with reference to the embodiments. However, the present application is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present application. Furthermore, unless otherwise specified, the embodiments and features in the embodiments of the present application can be combined with each other.

Claims

1. A negative electrode active material, characterized in that, Including single-particle and secondary-particle types; Wherein, the mass percentage t of the single particle to the total mass of the single particle and the secondary particle does not exceed 30%; The particle size Dv90 of the single particle is 13 to 20 μm, and the particle size Dv′90 of the secondary particle is 18 to 26 μm and is larger than the particle size Dv90 of the single particle.

2. The negative electrode active material according to claim 1, characterized in that, The OI value r of the negative electrode active material satisfies 6. <r<17。 3. The negative electrode active material according to claim 2, characterized in that, The mass percentage H of the surface oxygen content of the negative electrode active material satisfies 200H / Dv90+10 / r<3.2, where Dv90 is a dimensionless value with units omitted in μm during calculation.

4. The negative electrode active material according to claim 3, characterized in that, The mass percentage H1 of the surface oxygen content of the single particle is 0 to 10%, and / or the mass percentage H2 of the surface oxygen content of the secondary particle is 5% to 15%.

5. The negative electrode active material according to claim 1 or 4, characterized in that, The surface oxygen content H of the negative electrode active material is 4% to 15% by mass.

6. The negative electrode active material according to claim 1, characterized in that, The ratio A of the particle size Dv′90 of the secondary particles to the particle size Dv90 of the single particles is 1.2 to 2.

0.

7. The negative electrode active material according to claim 1, characterized in that, The single particle is selected from any one of natural graphite and artificial graphite, and the secondary particle is selected from at least one of natural graphite and artificial graphite.

8. A negative electrode sheet, characterized in that, It includes a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector, wherein the raw materials for preparing the negative electrode active material layer include the negative electrode active material according to any one of claims 1 to 7.

9. A lithium-ion battery, characterized in that, Includes the negative electrode sheet as described in claim 8.

10. Electrical equipment, characterized in that, Including the lithium-ion battery as described in claim 9.

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