Lithium ion battery, positive electrode active material and preparation method therefor, and electric device

Abstract

The present application discloses a lithium ion battery, a positive electrode active material and a preparation method therefor, and an electric device. The lithium ion battery comprises a positive electrode sheet, the positive electrode sheet comprising: a positive electrode current collector, and a positive electrode active material layer, wherein the positive electrode active material layer is located on at least one side of the positive electrode current collector; the positive electrode active material layer comprises a positive electrode active material; the positive electrode active material comprises a core and a carbon coating layer, the carbon coating layer at least covering part of the surface of the core; the carbon coating layer comprises a boron element, and the thickness standard deviation of the carbon coating layer is 0-1.6 nm.

Description

Lithium-ion batteries, positive electrode active materials and their preparation methods, and electrical devices

[0001] Cross-reference of related applications

[0002] This application is based on and claims priority to Chinese Patent Application No. 202510220763.5, filed on February 26, 2025, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to the field of battery technology, and in particular to a lithium-ion battery, a positive electrode active material and its preparation method, and an electrical device. Background Technology

[0004] Lithium-ion batteries are widely used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. As the application range of batteries expands, the performance requirements for lithium-ion batteries are becoming increasingly stringent. Summary of the Invention

[0005] The present invention aims to at least partially solve one of the technical problems in the related art.

[0006] To achieve the above objectives, a first aspect of this application provides a lithium-ion battery, including a positive electrode sheet, the positive electrode sheet comprising: a positive current collector; a positive active material layer, the positive active material layer being located on at least one side of the positive current collector; the positive active material layer comprising a positive active material; the positive active material comprising a core and a carbon coating layer, the carbon coating layer at least covering a portion of the surface of the core; the carbon coating layer comprising boron, the carbon coating layer having a thickness standard deviation of 0-1.6 nm.

[0007] This application includes at least the following beneficial effects: Boron can stabilize the growth process of carbon atoms, reducing the possibility of abnormal growth phenomena such as agglomeration or migration of carbon atoms during growth, thereby facilitating the formation of a carbon coating layer with uniform thickness. In this application, the standard deviation of the carbon coating layer thickness is 0-1.6 nm, indicating good uniformity. A uniformly thick carbon coating layer can effectively reduce electron conduction obstruction caused by uneven thickness or the presence of insulating regions on the core surface, providing a more consistent conduction path for electrons, reducing scattering and obstruction during conduction, and making electron conduction smoother. This, in turn, helps improve the electronic conductivity of the positive electrode active material, further enhancing the fast-charging performance of the battery.

[0008] In some embodiments, the thickness of the carbon coating layer is 1 nm to 5 nm. Therefore, selecting a carbon coating layer of appropriate thickness aims to balance the battery's fast charging performance and specific capacity.

[0009] In some embodiments, the carbon coating layer comprises carbon elements, with the positive electrode active material containing 0.5 wt% to 5 wt% of the carbon elements based on the total mass of the positive electrode active material. Therefore, selecting an appropriate carbon element content aims to balance the battery's fast-charging performance and specific capacity.

[0010] In some embodiments, the positive electrode active material contains 0.1 wt% to 2 wt% of boron, based on the total mass of the positive electrode active material. Therefore, selecting an appropriate boron content aims to balance the battery's fast-charging performance and specific capacity.

[0011] In some embodiments, the core comprises a lithium-containing transition metal phosphate, the lithium-containing transition metal phosphate satisfying the chemical formula Li a Fe x Mn (1-x-y) M y P b O c In this model, element M includes one or more metallic elements from Groups IVB, VB, VIII, IIA, IIIA, IVA, and VA, where x ranges from 0 to 1, y from 0 to 0.1, a from 1 to 1.05, b from 0.9 to 1.01, and c from 3.9 to 4.01. Therefore, by selecting a suitable core material, the electrochemical performance of lithium-ion batteries can be optimized.

[0012] In some embodiments, the core includes one or more of lithium manganese iron phosphate, lithium iron phosphate, lithium iron manganese titanium phosphate, lithium iron manganese vanadium phosphate, lithium iron manganese chromium phosphate, lithium iron manganese magnesium phosphate, lithium iron manganese aluminum phosphate, lithium iron manganese phosphate, lithium iron manganese zirconium phosphate, lithium iron manganese niobium phosphate, lithium iron manganese calcium phosphate, lithium iron manganese gallium phosphate, and lithium iron manganese germanium phosphate. Therefore, by selecting core materials of different types, the battery performance requirements of different application scenarios can be met, improving the battery's applicability.

[0013] In some embodiments, the positive electrode active material satisfies at least one of the following conditions: the Dv50 particle size of the positive electrode active material is 200nm-500nm; the resistivity of the positive electrode active material is 5Ω·cm-200Ω·cm. Therefore, selecting a positive electrode active material with a suitable particle size helps to reduce polarization and maintain battery capacity during charging and discharging. The positive electrode active material of this application has good conductivity, thereby improving the fast-charging performance of the battery.

[0014] In a second aspect, this application provides an electrical device including the lithium-ion battery of the first aspect. Thus, the battery possesses all the features and advantages of the aforementioned lithium-ion battery, which will not be repeated here.

[0015] In a third aspect, this application provides a positive electrode active material comprising a core and a carbon coating layer, the carbon coating layer covering the surface of the core; the carbon coating layer comprises boron, and the standard deviation of the thickness of the carbon coating layer is 0-1.6 nm. Therefore, the conductivity of the positive electrode active material of this application is further improved.

[0016] In some embodiments, the thickness of the carbon coating layer is 1 nm to 5 nm. Therefore, selecting a carbon coating layer of appropriate thickness aims to balance the conductivity and specific capacity of the positive electrode active material.

[0017] In some embodiments, the carbon coating layer comprises carbon elements, with the positive electrode active material containing 0.5 wt% to 5 wt% of the carbon elements based on the total mass of the positive electrode active material. Therefore, selecting an appropriate carbon element content aims to balance the conductivity and specific capacity of the positive electrode active material.

[0018] In some embodiments, the positive electrode active material contains 0.1 wt% to 2 wt% of boron, based on the total mass of the positive electrode active material. Therefore, selecting an appropriate boron content aims to balance the conductivity and specific capacity of the positive electrode active material.

[0019] In some embodiments, the core satisfies the chemical formula LiFe (1-x) Mn x M y PO4, where element M includes one or more metallic elements from Groups IVB, VB, VIII, IIA, IIIA, IVA, and VA, and x is 0-1, y is 0-0.1. Therefore, by selecting a suitable core material, the specific capacity of the positive electrode active material can be optimized.

[0020] In some embodiments, the positive electrode active material satisfies at least one of the following conditions: the Dv50 particle size of the positive electrode active material is 200nm-500nm; the resistivity of the positive electrode active material is 5Ω·cm-200Ω·cm.

[0021] In a fourth aspect, this application provides a method for preparing a positive electrode active material, comprising: mixing boron oxide with a core to obtain a first mixture; performing a first sintering treatment on the first mixture to obtain a boron-coated core; mixing the boron-coated core with a carbon source to obtain a second mixture; performing a second sintering treatment on the second mixture to obtain the positive electrode active material; the positive electrode active material comprising a core and a carbon coating layer, the carbon coating layer at least covering a portion of the surface of the core; the carbon coating layer comprising boron, and the standard deviation of the thickness of the carbon coating layer being 0-1.6 nm.

[0022] When the carbon source undergoes pyrolysis, boron can stabilize the growth process of carbon atoms, reducing the possibility of abnormal growth phenomena such as agglomeration or migration, thus facilitating the formation of a uniformly thick carbon coating layer. The preparation method of this application can produce a carbon coating layer with a thickness standard deviation of 0-1.6 nm, indicating good uniformity. A uniformly thick carbon coating layer can effectively reduce electron conduction obstruction caused by uneven thickness or the presence of insulating regions on the core surface, providing a more consistent conduction path for electrons, reducing scattering and obstruction during conduction, and making electron conduction smoother, thereby contributing to improved electronic conductivity of the positive electrode active material.

[0023] In some embodiments, the boron oxide includes one or more of boron oxide, boric acid, and metaboric acid. Thus, these boron oxides, in addition to boron, include only one or two of oxygen and hydrogen elements, without introducing other impurity elements into the positive electrode active material.

[0024] In some embodiments, the step of mixing boron oxide with the core further includes: mixing the boron oxide with a solvent to obtain a boron oxide solution; and mixing the core with the boron oxide solution to obtain the first mixture. Thus, the boron oxide forms a boron oxide solution; subsequently, the core is dispersed in the boron oxide solution to ensure that the boron oxide is uniformly adsorbed on the core surface, thereby improving the uniform distribution of boron on the core surface.

[0025] In some embodiments, the solvent includes one or more of water, ethanol, ethylene glycol, glycerol, methanol, acetone, and tetrahydrofuran. Thus, by selecting a suitable solvent, boron oxide can be dissolved to form a solution.

[0026] In some embodiments, the mass ratio of the boron oxide to the core is (0.001-0.05):1. Therefore, by controlling the mass ratio of boron oxide to the core, the boron oxide can be uniformly adsorbed onto the core surface, thereby improving the uniform distribution of boron on the core surface.

[0027] In some embodiments, the carbon source includes one or more of starch, sucrose, glucose, citric acid, polyethylene glycol, polyvinyl alcohol, polyacrylonitrile, and urea.

[0028] In some embodiments, the mass ratio of the carbon source to the boron-coated core is (0.05-0.25):1. This optimizes the thickness and uniformity of the carbon coating, thereby improving the electronic conductivity of the positive electrode active material.

[0029] In some embodiments, the temperature of the first sintering treatment is 300℃-500℃, and the time of the first sintering treatment is 0.5h-4h. Thus, through the first sintering treatment, the boron oxide on the core surface is pyrolyzed into boron oxide, so that the boron oxide is uniformly and tightly coated on the core surface.

[0030] In some embodiments, the temperature of the first sintering treatment is 400℃-450℃, and the time of the first sintering treatment is 1h-2h. Thus, through the first sintering treatment, the boron oxide on the core surface can be further pyrolyzed into boron oxide, and the boron oxide can be uniformly and tightly coated on the core surface.

[0031] In some embodiments, the temperature of the second sintering treatment is 600℃-800℃, and the time of the second sintering treatment is 2h-18h. Thus, by controlling the temperature and time of the second sintering treatment, the carbon source undergoes a pyrolysis reaction at high temperature. Simultaneously, under the influence of boron, the boron element can stabilize the carbon atom growth process, reducing the possibility of abnormal growth phenomena such as agglomeration or migration of carbon atoms during growth, thereby facilitating the formation of a uniformly thick carbon coating layer; further improving the conductivity of the positive electrode active material.

[0032] In some embodiments, the temperature of the second sintering treatment is 700℃-750℃, and the time of the second sintering treatment is 4h-8h. This can further improve the conductivity of the positive electrode active material. Attached Figure Description

[0033] Figure 1 is an electron energy loss spectrum of positive electrode active material particles according to an embodiment of this application. In Figure 1a, the boron element distribution of one random particle of the positive electrode active material is shown; Figure 1b shows the boron element distribution of another random particle of the positive electrode active material.

[0034] Figure 2 is a transmission electron microscope (TEM) image of the positive electrode active material particles of Example 1. In Figure 2, image a is a TEM image of the positive electrode active material; image b is a magnified view of region A in image a of Figure 2.

[0035] Figure 3 is a transmission electron microscope (TEM) image of the positive electrode active material particles in Comparative Example 1. In Figure 3a, the TEM image of the positive electrode active material is shown; Figure 3b is a magnified view of region B in Figure 3a.

[0036] Figure 4 is a schematic diagram of a lithium-ion battery according to an embodiment of this application.

[0037] Figure 5 is an exploded view of a lithium-ion battery according to an embodiment of this application, as shown in Figure 4.

[0038] Figure 6 is a schematic diagram of a battery module according to one embodiment of this application.

[0039] Figure 7 is a schematic diagram of a battery pack according to one embodiment of this application.

[0040] Figure 8 is an exploded view of a battery pack according to an embodiment of this application, as shown in Figure 7.

[0041] Figure 9 is a schematic diagram of an electrical device using a lithium-ion battery as a power source according to an embodiment of this application.

[0042] Figure 10 is a transmission electron microscope (TEM) image of the positive electrode active material particles in Comparative Example 2. In Figure 10, image a is a TEM image of the positive electrode active material; image b is a magnified view of region C in image a.

[0043] Explanation of reference numerals in the attached diagram: 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Lithium-ion battery; 51 Casing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0044] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the lithium-ion battery, positive electrode active material, preparation method thereof, and electrical device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0045] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0046] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0047] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0048] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0049] Lithium iron phosphate (LiFePO4) is widely used as the positive electrode active material in lithium-ion batteries due to its advantages such as low cost, good cycle performance, wide availability of raw materials, and environmental friendliness. However, with the continuous improvement of the performance requirements of lithium-ion batteries, the energy density of lithium iron phosphate has approached its theoretical limit, making it difficult to meet the demand for higher energy densities. In addition, the relatively low operating voltage of lithium iron phosphate (approximately 3.4V) further limits the improvement of energy density.

[0050] Lithium manganese iron phosphate (LMP) partially replaces iron with manganese, achieving an operating voltage of approximately 4.1V and a theoretical energy density higher than lithium iron phosphate (LFP), thus compensating for LFP's lower energy density. However, LMP's electronic conductivity is lower than LFP, resulting in poorer kinetic performance and weaker high-rate charging capability. This inferior high-rate charging capability limits the application scenarios of LMP batteries, making it difficult to meet the fast-charging requirements of electric vehicles that need rapid recharging.

[0051] Currently, the main approach to improving the kinetic performance of lithium manganese iron phosphate (LFP) is to optimize its electronic conductivity. A common method is to apply a carbon coating layer to the surface of LFP. Specifically, this is usually achieved by solid-state mixing of a carbon source with LFP, or a mixture of a carbon source and LFP, followed by sintering. However, this solid-state coating method has significant drawbacks. During the coating process, the carbon layer tends to form dot-like or layered deposits on the LFP surface, limiting its effectiveness in improving the electronic conductivity of LFP. Furthermore, during battery charge-discharge cycles, these dot-like or layered carbon layers are prone to detachment, not only failing to effectively improve the electronic conductivity of LFP but also negatively impacting the overall battery performance.

[0052] Therefore, how to further improve the fast charging performance of lithium-ion batteries has become an urgent problem to be solved.

[0053] Based on this, the first aspect of this application provides a lithium-ion battery, including a positive electrode sheet, the positive electrode sheet including: a positive current collector; a positive active material layer, the positive active material layer being located on at least one side of the positive current collector; the positive active material layer including a positive active material; the positive active material including a core and a carbon coating layer, the carbon coating layer at least covering a portion of the surface of the core; the carbon coating layer including boron element, the standard deviation of the thickness of the carbon coating layer being 0-1.6 nm.

[0054] Boron can stabilize the growth process of carbon atoms, reducing the likelihood of abnormal growth phenomena such as aggregation or migration, thus promoting the formation of a uniformly thick carbon coating layer. The uniformity of the carbon coating layer thickness can be reflected by the standard deviation of the carbon coating layer thickness.

[0055] In this application, the test method for the standard deviation of the carbon coating thickness is as follows:

[0056] First, the average thickness of the carbon coating layer needs to be obtained. Specifically, m single particles of positive electrode active material are randomly selected, and n test sites are selected evenly distributed on the surface of each particle. The thickness d of the carbon coating layer at the i-th test site is recorded. i (i≤m×n), through the formula The average thickness of the carbon coating can be calculated. Here, m×n represents the total number of test sites, and the thickness of the carbon coating is the distance d between the outer surface of the positive electrode active material particle and the outer surface of the core along the diameter direction of the particle. i .

[0057] The standard deviation of the carbon coating thickness is further obtained by using the average thickness of the carbon coating, and then calculated using the formula. The standard deviation of the carbon coating thickness can be calculated. Here, m×n represents the total number of test sites. This represents the average thickness of m×n test sites.

[0058] In this application, the thickness of the carbon coating layer can be measured using a transmission electron microscope (TEM).

[0059] Transmission electron microscopy (TEM) utilizes a high-energy electron beam to penetrate an ultrathin sample. The beam is then focused and magnified by an electromagnetic lens system, ultimately forming a high-resolution microscopic image on a fluorescent screen or imaging device. The electron beam is generated and accelerated by an electron gun. After penetrating the sample, it interacts with atoms in the sample, leading to electron scattering and absorption. Unscattered electrons pass through the objective lens to form a magnified inverted real image, which is further magnified by intermediate and projection lenses to finally form a visible image.

[0060] The specific testing method is as follows: 1. Take the positive electrode active material and disperse the particles in a solvent (the solvent can be water) using an ultrasonic disperser. Then, dry the powder using a spray dryer. Next, place the powder in a vacuum drying oven to further remove the solvent from the particle surface. Finally, uniformly disperse the dried particles on a copper mesh or other support coated with a thin carbon film or silicon oxide film, and fix the sample support under vacuum conditions. 2. After the instrument preheats, adjust the focus and intensity of the electron beam to ensure it is stable and uniform. Insert the sample into the TEM sample chamber and position it in the path of the electron beam by moving and tilting the sample stage. Select bright-field or dark-field imaging mode and adjust the current of the objective lens, intermediate lens, and projector lens to optimize the imaging effect. Acquire images through a fluorescent screen or imaging device and record the imaging parameters and sample information. Finally, analyze the acquired images, extract useful information, and properly preserve the data and sample. Thus, the thickness of the coating layer can be measured using TEM images.

[0061] In this application, the standard deviation of the carbon coating thickness is 0-1.6 nm, indicating good uniformity of the carbon coating. A uniformly thick carbon coating can effectively reduce electron conduction obstruction caused by uneven thickness or the presence of insulating regions on the core surface, providing a more consistent conduction path for electrons. This reduces electron scattering and obstruction during conduction, making electron conduction smoother, which in turn helps improve the electronic conductivity of the positive electrode active material and further enhances the fast-charging performance of the battery.

[0062] As an example, the standard deviation of the carbon coating thickness can be 0, 0.1nm, 0.2nm, 0.3nm, 0.4nm, 0.5nm, 0.6nm, 0.7nm, 0.8nm, 0.9nm, 1.0nm, 1.1nm, 1.2nm, 1.3nm, 1.4nm, 1.5nm, 1.6nm, etc., or a range consisting of any two of the above values.

[0063] In some implementations, the thickness of the carbon coating layer is 1 nm to 5 nm. A carbon coating layer thickness less than 1 nm affects the electronic conductivity of the positive electrode active material, thus impacting the battery's fast-charging performance. Conversely, a carbon coating layer thickness greater than 5 nm lengthens the lithium-ion conduction path, affecting lithium-ion conductivity and the battery's specific capacity. Therefore, selecting a carbon coating layer of appropriate thickness aims to balance the battery's fast-charging performance and specific capacity.

[0064] As an example, the thickness of the carbon coating can be 1 nm, 1.2 nm, 1.4 nm, 1.6 nm, 1.8 nm, 2.0 nm, 2.2 nm, 2.4 nm, 2.6 nm, 2.8 nm, 3.0 nm, 3.2 nm, 3.4 nm, 3.6 nm, 3.8 nm, 4.0 nm, 4.2 nm, 4.4 nm, 4.6 nm, 4.8 nm, 5.0 nm, or a range of any two of the above values.

[0065] In some implementations, the carbon coating completely covers the surface of the core.

[0066] The degree of carbon coating can be reflected by the distribution of boron in the carbon coating.

[0067] In this application, the boron element in the carbon coating layer can be tested using electron energy loss spectroscopy (EELS).

[0068] EELS (Electron Electron Beam Lamination) is a technique that uses the interaction of a high-energy electron beam with a sample to obtain information about the sample's electronic structure by measuring the energy loss of scattered electrons. The specific principle is as follows: among inelastic scattered electrons, there exist Auger electrons with certain characteristic energies. The characteristic energy of Auger electrons depends only on the elements of the material. By detecting the number of these Auger electrons on the sample and analyzing their energy distribution, the elemental composition of the material can be determined. Since the characteristic energy of Auger electrons depends not only on the elements of the material but also on the energy of the incident electrons, they are called characteristic energy loss electrons.

[0069] The number of energy-loss electrons detected on a sample and their energy distribution yields a series of spectral peaks, known as the electron energy loss spectrum. Based on the magnitude of the scattering energy, the electron energy loss spectrum can typically be divided into three regions: the zero-loss region, the low-energy-loss region, and the high-energy-loss region. The absorption edge in the high-energy-loss region corresponds to the difference between the inner-shell electron energy and the Fermi energy, i.e., the energy required for the ionization of inner-shell electrons. Different elements require different energies for inner-shell electron ionization, so the absorption edge can be used to determine the element type. For example, the absorption edge of boron is approximately 187 eV.

[0070] The specific testing method is as follows: 1. Take the positive electrode active material and disperse the particles in a solvent (the solvent can be water) using an ultrasonic disperser. Then, dry the powder using a spray dryer. Next, place the powder in a vacuum drying oven for further drying to remove the solvent from the particle surface. Finally, uniformly disperse the dried particles on a copper or molybdenum grid coated with a thin carbon or silicon oxide film, and fix the sample on the grid under vacuum conditions. 2. Use a high-resolution transmission electron microscope (HR-TEM), such as the Titan Themis Z TEM model, with an accelerating voltage of 300kV, an energy resolution better than 0.5eV, and a probe size smaller than [missing information]. It is equipped with a high-sensitivity and high-dynamic-range EELS detector. 3. Insert the sample-laden grid into the HR-TEM sample chamber, adjust the electron beam focusing parameters, select a suitable scanning mode (spot scan or line scan), set the energy loss range to 0-1000 eV and a suitable acquisition time (1-10 seconds / spot) to acquire the energy loss spectrum. 4. After the test is completed, the acquired data is subjected to background subtraction, and the characteristic energy loss peak of boron is identified.

[0071] Figure 1 shows the boron distribution in the positive electrode active material particles according to one embodiment of this application. In Figure 1, the distribution of boron is represented by light gray, and the light gray area reflects the distribution of boron. Figures 1a and 1b are boron distribution diagrams of two randomly selected different positive electrode active material particles. As shown in Figures 1a and 1b, boron was detected on the surface of both random positive electrode active material particles, and the boron was distributed throughout the entire surface of the positive electrode active material particles. Since the distribution of these positive electrode active material particles is random, it can be reasonably inferred that the surface of the positive electrode active material contains boron, indicating that the carbon coating layer covers the core surface.

[0072] In some embodiments, the carbon coating layer includes carbon elements, with the positive electrode active material containing 0.5 wt% to 5 wt% carbon elements based on the total mass of the positive electrode active material. When the carbon element content is below 0.5 wt%, it affects the electronic conductivity of the positive electrode active material, thus impacting the battery's fast-charging performance; when the carbon element content is above 5 wt%, it affects the diffusion ability of lithium ions, thus affecting the battery's specific capacity. Therefore, selecting an appropriate carbon element content aims to balance the battery's fast-charging performance and specific capacity.

[0073] The mass fraction of carbon in the positive electrode active material can be tested using methods known in the art. For example, inductively coupled plasma optical emission spectrometry (ICP-OES) can be used. Specifically, the test conditions are: the sample must be a liquid; if the sample contains solid particles, it must be digested with acid or filtered to remove the solid particles. The range of the element to be measured must be within the standard curve range; if it exceeds the range, the sample must be diluted. The main operating procedures are: 1. Test the standard curve; 2. Dilute the sample; 3. Test the diluted sample; 4. Calculate and process the data to obtain the concentration of the element to be measured.

[0074] As an example, based on the total mass of the positive electrode active material, the positive electrode active material may contain 0.5wt%, 1.0wt%, 1.5wt%, 2.0wt%, 2.5wt%, 3.0wt%, 3.5wt%, 4.0wt%, 4.5wt%, 5.0wt%, or any range of two of the above values ​​of carbon element.

[0075] In some implementations, the positive electrode active material contains 0.1 wt% to 2 wt% boron, based on the total mass of the positive electrode active material. A boron content below 0.1 wt% affects the uniformity of the carbon coating thickness, thus impacting the electronic conductivity of the positive electrode active material and consequently affecting the battery's fast-charging performance. A boron content above 2 wt% affects the battery's specific capacity. Therefore, selecting an appropriate boron content aims to balance the battery's fast-charging performance and specific capacity.

[0076] The mass fraction of boron in the positive electrode active material can be tested using methods known in the art. For example, inductively coupled plasma optical emission spectrometry (ICP-OES) can be used.

[0077] As an example, based on the total mass of the positive electrode active material, the positive electrode active material may contain 0.1wt%, 0.3wt%, 0.5wt%, 0.7wt%, 0.9wt%, 1.1wt%, 1.3wt%, 1.5wt%, 1.7wt%, 1.9wt%, 2.0wt%, or any range of two of the above values ​​of boron.

[0078] In some embodiments, the core comprises a lithium-containing transition metal phosphate, which satisfies the chemical formula Li a Fe x Mn (1-x-y) M y P b O c In this model, element M includes one or more metallic elements from Groups IVB, VB, VIII, IIA, IIIA, IVA, and VA, where x ranges from 0 to 1, y from 0 to 0.1, a from 1 to 1.05, b from 0.9 to 1.01, and c from 3.9 to 4.01. Therefore, by selecting a suitable core material, the electrochemical performance of lithium-ion batteries can be optimized.

[0079] As an example, Group IVB metals can be titanium, zirconium, and hafnium.

[0080] As an example, the metal elements in Group VB can be vanadium, niobium, and tantalum.

[0081] As an example, Group VIII metals can be iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, and platinum.

[0082] As an example, the metal elements in Group IIA can be beryllium, magnesium, calcium, strontium, barium, and radium.

[0083] As an example, Group IIIA metals can be aluminum, gallium, indium, and thallium.

[0084] As an example, Group IVA metals can be germanium, tin, and lead.

[0085] As an example, Group VA metals can be antimony or bismuth.

[0086] As an example, x can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, etc., or a range of any two of the above values.

[0087] As an example, y can be 0, 0.001, 0.003, 0.005, 0.007, 0.008, 0.01, 0.012, 0.015, 0.02, 0.023, 0.025, 0.03, 0.035, 0.04, 0.045, 0.05, 0.056, 0.06, 0.065, 0.07, 0.075, 0.08, 0.085, 0.09, 0.095, 0.098, 0.1, or a range of any two of the above values.

[0088] As an example, 'a' can be 1, 1.01, 1.02, 1.03, 1.04, 1.05, etc., or a range consisting of any two of the above values.

[0089] As an example, b can be 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.00, 1.01, etc., or a range consisting of any two of the above values.

[0090] As an example, c can be 3.90, 3.91, 3.92, 3.93, 3.94, 3.95, 3.96, 3.97, 3.98, 3.99, 4.00, 4.01, etc., or a range consisting of any two of the above values.

[0091] As an example, the core material includes one or more of the following: lithium iron manganese phosphate, lithium iron phosphate, lithium iron manganese titanium phosphate, lithium iron manganese vanadium phosphate, lithium iron manganese chromium phosphate, lithium iron manganese magnesium phosphate, lithium iron manganese aluminum phosphate, lithium iron manganese phosphate, lithium iron manganese zirconium phosphate, lithium iron manganese niobium phosphate, lithium iron manganese calcium phosphate, lithium iron manganese gallium phosphate, and lithium iron manganese germanium phosphate. Therefore, by selecting core materials of different types, the battery performance requirements of different application scenarios can be met, improving the battery's applicability.

[0092] In some embodiments, the positive electrode active material satisfies at least one of the following conditions: the Dv50 particle size of the positive electrode active material is 200nm-500nm; the resistivity of the positive electrode active material is 5Ω·cm-200Ω·cm.

[0093] Selecting a suitable particle size for the positive electrode active material helps reduce polarization and maintain battery capacity during charge and discharge. For example, the Dv50 particle size of the positive electrode active material can be 200nm, 220nm, 240nm, 260nm, 280nm, 300nm, 320nm, 340nm, 360nm, 380nm, 400nm, 420nm, 440nm, 460nm, 480nm, 500nm, or a range of any two of these values.

[0094] The resistivity of the positive electrode active material is in the range of 5 Ω·cm to 200 Ω·cm, indicating that the positive electrode active material has good conductivity, thereby improving the fast charging performance of the battery. The resistivity of the positive electrode active material can be tested using methods known in the art. As an example, the resistivity of the positive electrode active material can be tested at 100 MPa using a powder resistivity tester (Yuaneng Technology Co., Ltd. PRCD1100 model). The reciprocal of the powder resistivity is the electronic conductivity of the positive electrode active material. As an example, the resistivity of the positive electrode active material can be 5 Ω·cm, 20 Ω·cm, 35 Ω·cm, 50 Ω·cm, 65 Ω·cm, 80 Ω·cm, 95 Ω·cm, 110 Ω·cm, 125 Ω·cm, 140 Ω·cm, 155 Ω·cm, 170 Ω·cm, 185 Ω·cm, 200 Ω·cm, etc., or any range of two of the above values.

[0095] In lithium-ion batteries, Li insertion / extraction and consumption occur during charging and discharging, resulting in different molar Li content at different discharge states. In the examples of positive electrode active materials in this application, the molar Li content refers to the initial state of the material, i.e., before feeding. After charge-discharge cycles, the molar Li content changes when the positive electrode active material is applied to the battery system.

[0096] In the examples of positive electrode active materials for lithium-ion batteries in this application, the molar content of O is only a theoretical state value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of O will fluctuate.

[0097] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0098] In some embodiments, the positive electrode active material layer may optionally include a binder. As an example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0099] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0100] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0101] [Negative electrode plate]

[0102] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, wherein the negative active material layer includes a negative active material.

[0103] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0104] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0105] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0106] In some embodiments, the negative electrode active material layer may optionally include a binder. The binder may include one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0107] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0108] In some embodiments, the negative electrode active material layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0109] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0110] [Electrolytes]

[0111] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0112] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0113] In some embodiments, the electrolyte salt may include one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0114] In some embodiments, the solvent may include one or more of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0115] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0116] [Isolation membrane]

[0117] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0118] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0119] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0120] [Lithium-ion battery]

[0121] In some embodiments, the lithium-ion battery may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0122] In some implementations, the outer packaging of a lithium-ion battery can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of a lithium-ion battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0123] This application does not impose any particular limitation on the shape of the lithium-ion battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 4 shows a square-structured lithium-ion battery 5 as an example.

[0124] In some embodiments, referring to FIG5, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. A positive electrode sheet, a negative electrode sheet, and a separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The lithium-ion battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0125] [Battery Module]

[0126] In some implementations, lithium-ion batteries can be assembled into battery modules, and the number of lithium-ion batteries contained in a battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0127] Figure 6 shows a battery module 4 as an example. Referring to Figure 6, in the battery module 4, multiple batteries 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other arbitrary way. Furthermore, the multiple batteries 5 can be fixed in place using fasteners.

[0128] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of batteries 5 are received.

[0129] [Battery Pack]

[0130] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0131] Figures 7 and 8 show a battery pack 1 as an example. Referring to Figures 7 and 8, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box 2 and a lower box 3, with the upper box 2 covering the lower box 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0132] In a second aspect, this application provides an electrical device, wherein the battery possesses all the features and advantages of the aforementioned positive electrode, which will not be repeated here. The electrical device includes one or more of the lithium-ion battery, battery module, or battery pack provided in this application. The lithium-ion battery, battery module, or battery pack can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0133] As an electrical device, batteries, battery modules, or battery packs can be selected according to their usage requirements.

[0134] Figure 9 shows an example of an electrical device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of this device, a battery pack or battery module can be used.

[0135] Another example device could be a mobile phone, tablet, laptop, etc. These devices typically require a slim and lightweight design and can use a battery as their power source.

[0136] In a third aspect, this application provides a positive electrode active material comprising a core and a carbon coating layer, wherein the carbon coating layer at least covers a portion of the surface of the core; the carbon coating layer comprises boron, and the standard deviation of the carbon coating layer thickness is 0-1.6 nm. Therefore, the conductivity of the positive electrode active material of this application is further improved.

[0137] As an example, the standard deviation of the carbon coating thickness can be 0, 0.1nm, 0.2nm, 0.3nm, 0.4nm, 0.5nm, 0.6nm, 0.7nm, 0.8nm, 0.9nm, 1.0nm, 1.1nm, 1.2nm, 1.3nm, 1.4nm, 1.5nm, 1.6nm, etc., or a range consisting of any two of the above values.

[0138] In some implementations, the thickness of the carbon coating layer is 1 nm to 5 nm. Therefore, selecting a suitable thickness of carbon coating layer aims to balance the conductivity and specific capacity of the positive electrode active material.

[0139] As an example, the thickness of the carbon coating can be 1 nm, 1.2 nm, 1.4 nm, 1.6 nm, 1.8 nm, 2.0 nm, 2.2 nm, 2.4 nm, 2.6 nm, 2.8 nm, 3.0 nm, 3.2 nm, 3.4 nm, 3.6 nm, 3.8 nm, 4.0 nm, 4.2 nm, 4.4 nm, 4.6 nm, 4.8 nm, 5.0 nm, or a range of any two of the above values.

[0140] In some embodiments, the carbon coating layer comprises carbon elements, with the positive electrode active material containing 0.5 wt% to 5 wt% carbon elements based on the total mass of the positive electrode active material. Therefore, selecting an appropriate carbon element content aims to balance the conductivity and specific capacity of the positive electrode active material.

[0141] As an example, based on the total mass of the positive electrode active material, the positive electrode active material may contain 0.5wt%, 1.0wt%, 1.5wt%, 2.0wt%, 2.5wt%, 3.0wt%, 3.5wt%, 4.0wt%, 4.5wt%, 5.0wt%, or any range of two of the above values ​​of carbon element.

[0142] In some embodiments, the positive electrode active material contains 0.1 wt% to 2 wt% boron, based on the total mass of the positive electrode active material. Therefore, selecting an appropriate boron content aims to balance the conductivity and specific capacity of the positive electrode active material.

[0143] As an example, based on the total mass of the positive electrode active material, the positive electrode active material may contain 0.1wt%, 0.3wt%, 0.5wt%, 0.7wt%, 0.9wt%, 1.1wt%, 1.3wt%, 1.5wt%, 1.7wt%, 1.9wt%, 2.0wt%, or any range of two of the above values ​​of boron.

[0144] In some embodiments, the core comprises a lithium-containing transition metal phosphate, which satisfies the chemical formula Li a Fe x Mn (1-x-y) M y P b O c In this model, element M includes one or more metallic elements from Groups IVB, VB, VIII, IIA, IIIA, IVA, and VA, where x is 0-1, y is 0-0.1, a is 1-1.05, b is 0.9-1.01, and c is 3.9-4.01. Therefore, by selecting a suitable core material, the specific capacity of the positive electrode active material can be optimized.

[0145] As an example, Group IVB metals can be titanium, zirconium, and hafnium.

[0146] As an example, the metal elements in Group VB can be vanadium, niobium, and tantalum.

[0147] As an example, Group VIII metals can be iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, and platinum.

[0148] As an example, the metal elements in Group IIA can be beryllium, magnesium, calcium, strontium, barium, and radium.

[0149] As an example, Group IIIA metals can be aluminum, gallium, indium, and thallium.

[0150] As an example, Group IVA metals can be germanium, tin, and lead.

[0151] As an example, Group VA metals can be antimony or bismuth.

[0152] As an example, x can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, etc., or a range of any two of the above values.

[0153] As an example, y can be 0, 0.001, 0.003, 0.005, 0.007, 0.008, 0.01, 0.012, 0.015, 0.02, 0.023, 0.025, 0.03, 0.035, 0.04, 0.045, 0.05, 0.056, 0.06, 0.065, 0.07, 0.075, 0.08, 0.085, 0.09, 0.095, 0.098, 0.1, or a range of any two of the above values.

[0154] As an example, 'a' can be 1, 1.01, 1.02, 1.03, 1.04, 1.05, etc., or a range consisting of any two of the above values.

[0155] As an example, b can be 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.00, 1.01, etc., or a range consisting of any two of the above values.

[0156] As an example, c can be 3.90, 3.91, 3.92, 3.93, 3.94, 3.95, 3.96, 3.97, 3.98, 3.99, 4.00, 4.01, etc., or a range consisting of any two of the above values.

[0157] In some embodiments, the positive electrode active material satisfies at least one of the following conditions: the Dv50 particle size of the positive electrode active material is 200nm-500nm; the resistivity of the positive electrode active material is 5Ω·cm-200Ω·cm.

[0158] As an example, the Dv50 particle size of the positive electrode active material can be 200nm, 220nm, 240nm, 260nm, 280nm, 300nm, 320nm, 340nm, 360nm, 380nm, 400nm, 420nm, 440nm, 460nm, 480nm, 500nm, etc., or a range consisting of any two of the above values.

[0159] As an example, the resistivity of the positive electrode active material can be 5 Ω·cm, 20 Ω·cm, 35 Ω·cm, 50 Ω·cm, 65 Ω·cm, 80 Ω·cm, 95 Ω·cm, 110 Ω·cm, 125 Ω·cm, 140 Ω·cm, 155 Ω·cm, 170 Ω·cm, 185 Ω·cm, 200 Ω·cm, etc., or a range of any two of the above values.

[0160] As an example, the positive electrode active material simultaneously meets the following conditions: the Dv50 particle size of the positive electrode active material is 200nm-500nm; the resistivity of the positive electrode active material is 5Ω·cm-200Ω·cm.

[0161] In a fourth aspect, this application provides a method for preparing a positive electrode active material, specifically including:

[0162] S100. Mix boron oxide with the core to obtain a first mixture.

[0163] In some embodiments, the step of mixing boron oxide with the core further includes: mixing the boron oxide with a solvent to obtain a boron oxide solution; and mixing the core with the boron oxide solution to obtain a first mixture.

[0164] First, boron oxides form a boron oxide solution; then the core is dispersed in the boron oxide solution so that the boron oxides are uniformly adsorbed on the core surface, thereby improving the uniformity of boron distribution on the core surface.

[0165] In some embodiments, the boron oxide includes one or more of boron oxide, boric acid, and metaboric acid. Thus, these boron oxides, in addition to boron, include only one or two of oxygen and hydrogen elements, without introducing other impurity elements into the positive electrode active material.

[0166] In some embodiments, the step of mixing the core with the boron oxide solution further includes one or more of the following: a first ball milling treatment, a sand milling treatment, and an ultrasonic dispersion treatment. As a result, the boron oxide is uniformly adhered to the surface of the core particles.

[0167] In some embodiments, the ball milling speed of the first ball milling process is 200 rpm to 600 rpm; the ball milling time of the first ball milling process is 6 h to 14 h. As an example, the ball milling speed of the first ball milling process can be 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, 550 rpm, 600 rpm, etc., or a range consisting of any two of the above values. The ball milling time of the first ball milling process can be 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, etc., or a range consisting of any two of the above values.

[0168] In some embodiments, the solvent includes one or more of water, ethanol, ethylene glycol, glycerol, methanol, acetone, and tetrahydrofuran. Thus, by selecting a suitable solvent, the boron oxide can be dissolved to form a solution.

[0169] In some embodiments, the mass ratio of boron oxide to the core is (0.001-0.05):1. Therefore, by controlling the mass ratio of boron oxide to the core, boron oxide can be uniformly adsorbed onto the core surface, thereby improving the uniform distribution of boron on the core surface. As examples, the mass ratio of boron oxide to the core can be 0.001:1, 0.002:1, 0.004:1, 0.006:1, 0.008:1, 0.01:1, 0.015:1, 0.02:1, 0.025:1, 0.03:1, 0.035:1, 0.04:1, 0.045:1, 0.05:1, etc., or a range consisting of any two of the above values.

[0170] In some embodiments, the first mixture is dried. This removes the solvent adhering to the surface of the first mixture. As an example, the drying process includes, but is not limited to, spray drying.

[0171] S200, The first mixture is subjected to a first sintering treatment to obtain a boron-coated core.

[0172] In some embodiments, the temperature of the first sintering treatment is 300℃-500℃, and the time of the first sintering treatment is 0.5h-4h. Thus, through the first sintering treatment, the boron oxide on the core surface is pyrolyzed into boron oxide, so that the boron oxide is uniformly and tightly coated on the core surface.

[0173] As an example, the temperature of the first sintering treatment can be 300℃, 320℃, 340℃, 360℃, 380℃, 400℃, 420℃, 440℃, 460℃, 480℃, 500℃, etc., or a range consisting of any two of the above values. The time of the first sintering treatment can be 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, etc., or a range consisting of any two of the above values. In other embodiments, the temperature of the first sintering treatment is 400℃-450℃, and the time of the first sintering treatment is 1h-2h.

[0174] In some embodiments, the first sintering process is carried out in an air atmosphere. This air oxidation treatment can improve the bonding strength between boron oxide and the core, thereby reducing the degree to which boron oxide detaches during ball milling.

[0175] S300: Mix the boron-coated core with a carbon source to obtain a second mixture.

[0176] In some embodiments, the carbon source includes one or more of starch, sucrose, glucose, citric acid, polyethylene glycol, polyvinyl alcohol, polyacrylonitrile, and urea.

[0177] In some embodiments, the mass ratio of carbon source to boron-coated core is (0.05-0.25):1. This optimizes the thickness and uniformity of the carbon coating layer, thereby improving the electronic conductivity of the cathode active material. As an example, the mass ratio of carbon source to boron-coated core can be 0.05:1, 0.1:1, 0.15:1, 0.2:1, 0.25:1, or a range of any two of these values.

[0178] In some embodiments, the second mixture undergoes a second ball milling process. This allows for thorough mixing of the boron-coated core with the carbon source, resulting in a uniform distribution of the carbon source on the core surface. This uniform distribution facilitates the formation of a uniform carbon coating layer during subsequent sintering, further enhancing the conductivity of the cathode active material.

[0179] In some embodiments, the second ball milling process satisfies at least one of the following conditions: the solvent for the second ball milling process includes at least one of ethanol, isopropanol, and water; the ball milling speed for the second ball milling process is 200 rpm to 600 rpm; and the ball milling time for the second ball milling process is 6 h to 14 h. Thus, selecting a suitable solvent helps reduce the frictional force between the core and carbon source particles, reducing agglomeration; selecting a suitable ball milling speed ensures appropriate impact and shear forces between the core and carbon source, which can both refine the second mixture and reduce excessive wear of the second mixture. Selecting a suitable ball milling time helps to fully mix and refine the core and carbon source, and can also reduce heat loss in the second mixture caused by prolonged ball milling. As an example, the ball milling speed for the second ball milling process can be 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, 550 rpm, 600 rpm, etc., or a range consisting of any two of the above values. The ball milling time for the second ball milling process can be 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, or a range consisting of any two of the above values.

[0180] S400, The second mixture is subjected to a second sintering treatment to obtain the positive electrode active material.

[0181] In some embodiments, the temperature of the second sintering treatment is 600℃-800℃, and the time of the second sintering treatment is 2h-18h. Thus, by controlling the temperature and time of the second sintering treatment, the carbon source undergoes a pyrolysis reaction at high temperature. At the same time, under the influence of boron, the boron element can stabilize the growth process of carbon atoms, reducing the possibility of abnormal growth phenomena such as agglomeration or migration of carbon atoms during the growth process, thereby facilitating the formation of a carbon coating layer of uniform thickness.

[0182] As an example, the temperature of the second sintering treatment can be 600℃, 620℃, 640℃, 660℃, 680℃, 700℃, 720℃, 740℃, 760℃, 780℃, 800℃, etc., or a range consisting of any two of the above values. The time of the second sintering treatment can be 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, etc., or a range consisting of any two of the above values. In some other embodiments, the temperature of the second sintering treatment is 700℃-750℃, and the time of the second sintering treatment is 4h-8h.

[0183] In some embodiments, the second sintering process is carried out in a protective atmosphere. This protective atmosphere prevents the carbon source from undergoing oxidation with oxygen in the air at high temperatures. As an example, the protective atmosphere includes one or both of nitrogen and argon.

[0184] In summary, during the pyrolysis reaction of the carbon source, boron can stabilize the growth process of carbon atoms, reducing the possibility of abnormal growth phenomena such as agglomeration or migration, thus facilitating the formation of a uniformly thick carbon coating layer. The preparation method of this application can prepare a carbon coating layer with a thickness standard deviation of 0-1.6 nm, indicating good uniformity. A uniformly thick carbon coating layer can effectively reduce the obstruction of electron conduction caused by uneven thickness or the presence of insulating regions on the core surface, providing a more consistent conduction path for electrons, reducing scattering and obstruction during conduction, and making electron conduction smoother, thereby helping to improve the electronic conductivity of the positive electrode active material.

[0185] Example

[0186] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0187] Example 1

[0188] (1) Preparation of positive electrode active material

[0189] S100, take boron oxide, dissolve it in water to form a boron oxide aqueous solution; then add lithium manganese iron phosphate (LiFe). 0.4 Mn 0.6Lithium manganese iron phosphate (PMP) was placed in an aqueous solution of boron oxide, and the solution was thoroughly mixed by a first ball milling process. Then, the water was removed by spray drying to obtain a first mixture. The mass ratio of boron oxide to lithium manganese iron phosphate was 0.01:1. The ball milling speed of the first ball milling process was 300 rpm. The ball milling time of the first ball milling process was 4 h.

[0190] S200. The first mixture is placed in a muffle furnace and sintered at 400°C for 1 hour in an air atmosphere to obtain boron-coated lithium manganese iron phosphate.

[0191] S300, Boron oxide-coated lithium manganese iron phosphate and carbon source are mixed at a mass ratio of 0.075:1, and subjected to a second ball milling treatment using ethanol as the grinding medium; after removing the ethanol at 80°C, a second mixture is obtained; wherein, the ball milling speed of the second ball milling treatment is 260 rpm; the ball milling time of the second ball milling treatment is 8 h;

[0192] S400. The second mixture is placed in a tube furnace and sintered at 725°C for 6 hours under an inert atmosphere to obtain the positive electrode active material.

[0193] (2) Preparation of positive electrode sheet

[0194] The above-mentioned positive electrode active material (the Dv50 particle size of the positive electrode active material is 300nm), the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black were dissolved in the solvent N-methylpyrrolidone (NMP) at a weight ratio of 92:5.5:2.5. After being thoroughly stirred and mixed evenly, a positive electrode slurry was prepared. The positive electrode slurry was uniformly coated on the positive electrode current collector aluminum foil, and then dried, cold-pressed, and slit to obtain the positive electrode sheet.

[0195] (3) Negative electrode plate

[0196] Lithium metal sheets were selected as the negative electrode.

[0197] (4) Separating membrane

[0198] Polypropylene film is selected as the separator, and one side of the polypropylene film is coated with an aluminum oxide coating.

[0199] (5) Preparation of electrolyte

[0200] Ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 1:1:1 to obtain a mixed solvent; then lithium hexafluorophosphate (LiPF6) was dissolved in the above mixed solvent to obtain an electrolyte. The concentration of LiPF6 in the electrolyte was 1 mol / L.

[0201] (6) Preparation of button cells

[0202] The positive electrode, separator, and negative electrode are assembled in a button cell and injected with electrolyte to obtain a button cell.

[0203] Comparative Example 1

[0204] The difference between Comparative Example 1 and Example 1 is that step S100 is not included in the preparation of the positive electrode active material. Specifically, lithium manganese iron phosphate and carbon source are mixed at a mass ratio of 0.075:1 and subjected to a second ball milling treatment using ethanol as the grinding medium. After removing the alcohol at 80°C, a second mixture is obtained. The ball milling speed of the second ball milling treatment is 260 rpm, and the ball milling time of the second ball milling treatment is 8 h. The second mixture is placed in a tube furnace and sintered at 725°C for 6 h under an inert atmosphere to obtain the positive electrode active material.

[0205] Comparative Example 2

[0206] The difference between Comparative Example 2 and Example 1 lies in the different step S100 in the preparation of the positive electrode active material. Specifically, boron oxide and lithium manganese iron phosphate are mixed, and the lithium manganese iron phosphate and boron oxide are fully mixed by a first ball milling process to obtain a first mixture; wherein, the mass ratio of boron oxide to lithium manganese iron phosphate is 0.01:1; the ball milling speed of the first ball milling process is 260 rpm; and the ball milling time of the first ball milling process is 8 h.

[0207] The battery preparation methods in Examples 2-15 are the same as in Example 1, and the specific parameters involved are detailed in Table 1.

[0208] Table 1

[0209] In Example 6, the chemical formula of lithium iron phosphate is LiFePO4, and in Example 7, the chemical formula of lithium iron manganese titanium phosphate is LiFe 0.35 Mn 0.55 Ti 0.1 PO4.

[0210] Material characterization and performance testing

[0211] 1. Average thickness of the carbon coating layer

[0212] The method for testing the average thickness of the carbon coating is as follows: randomly select m single particles of positive electrode active material, select n uniformly distributed test sites on the surface of each particle, and record the carbon coating thickness d at the i-th test site. i (i≤m×n), through the formula The average thickness of the carbon coating can be calculated. Here, m×n represents the total number of test sites, and the thickness of the carbon coating is the distance d between the outer surface of the positive electrode active material particle and the outer surface of the core along the diameter direction of the particle. i .

[0213] In this application, for the positive electrode active materials of the embodiments and comparative examples, 15 positive electrode active material particles were randomly selected, and 15 detection sites were selected evenly distributed on each particle for testing.

[0214] The thickness of the carbon coating can be measured using transmission electron microscopy (TEM). The specific testing method is as follows: 1. Take the positive electrode active material and disperse the particles in a solvent (water can be the solvent) using an ultrasonic disperser. Then, dry the dispersed particles in a spray dryer to form a powder. Next, place the powder in a vacuum drying oven to further remove the solvent from the particle surface. Finally, uniformly disperse the dried particles on a copper mesh or other support coated with a thin carbon or silicon oxide film, and fix the sample support under vacuum. 2. After the instrument has warmed up, adjust the focus and intensity of the electron beam to ensure it is stable and uniform. Insert the sample into the TEM sample chamber and position it within the electron beam path by moving and tilting the sample stage. Select bright-field or dark-field imaging mode and adjust the current of the objective lens, intermediate lens, and projector lens to optimize the imaging effect. Acquire images through a fluorescent screen or imaging device and record the imaging parameters and sample information. Finally, analyze the acquired images, extract useful information, and properly preserve the data and sample.

[0215] 2. Standard deviation of carbon coating thickness

[0216] The standard deviation of the carbon coating thickness can be obtained from the average thickness of the carbon coating. The standard deviation of the carbon coating thickness is calculated using the formula... The calculation yielded the result. Where m×n represents the total number of test sites. This represents the average thickness of m×n test sites.

[0217] In this application, for the positive electrode active materials of the embodiments and comparative examples, 15 positive electrode active material particles were randomly selected, and 15 detection sites were selected evenly distributed on each particle for testing.

[0218] 3. Degree of graphitization of the carbon coating layer

[0219] The degree of graphitization of the carbon coating layer can also be tested using transmission electron microscopy (TEM). Taking Example 1, Comparative Example 1, and Comparative Example 2 as examples, the TEM images of the positive electrode active material particles of Example 1, Comparative Example 1, and Comparative Example 2 are shown in Figure 2a, Figure 3a, and Figure 10a, respectively.

[0220] In Example 1, any region in Figure 2a was randomly selected, such as region A in Figure 2a. Figure 2b is an enlarged view of region A. As shown in Figure 2b, the carbon coating layer in region A (shown as a closed curve in Figure 2b) has a uniform thickness and exhibits a layered structure, indicating that the carbon coating layer in Example 1 has a high degree of graphitization.

[0221] In Comparative Example 1, any region in Figure 3a was randomly selected, such as region B in Figure 3a. Figure 3b is an enlarged view of region B. As shown in Figure 3b, the carbon coating layer in region B (shown as a closed curve in Figure 3b) has an uneven thickness and a disordered structure, indicating that the graphitization degree of the carbon coating layer in Comparative Example 1 is low.

[0222] In Comparative Example 2, any region in Figure 10a was randomly selected, such as region C in Figure 10a. Figure 10b is an enlarged view of region C. As shown in Figure 10b, the carbon coating layer in region C (shown as a closed curve in Figure 10b) still exhibits a disordered structure, indicating that the graphitization degree of the carbon coating layer in Comparative Example 2 is relatively low.

[0223] 4. Resistivity of the positive electrode active material

[0224] The resistivity of the positive electrode active material was tested at 100 MPa using a powder resistivity tester (PRCD1100 model from Yuaneng Technology Co., Ltd.). The lower the resistivity, the stronger the conductivity of the positive electrode active material.

[0225] 5. Detection of the composition of positive electrode active material

[0226] a. Mass fraction of carbon element

[0227] The method for determining the mass fraction of carbon is as follows: An appropriate amount of sample is weighed into a special crucible, and a suitable amount of flux is added and mixed thoroughly. The sample is then burned in oxygen to convert carbon into CO2. This CO2 enters the absorption cell and is converted into a corresponding signal by a detector. This signal is sampled by a computer, linearly corrected, and converted into a value proportional to the CO2 concentration. The values ​​from the entire analysis process are then accumulated. After the analysis, this accumulated value is divided by the weight value in the computer, multiplied by a correction factor, and the blank is subtracted to obtain the mass fraction of carbon in the sample.

[0228] b. Mass fraction of boron

[0229] The method for testing the mass fraction of boron is as follows: Take 5 mL of concentrated nitric acid to digest a sample of mass M to obtain a digestion solution. Dilute the digestion solution with deionized water 5 times, and then send the sample into an ICP instrument through a nebulizer to collect spectra and calculate the boron concentration C1. The mass fraction of boron is obtained by the formula (C1 / 5) / M.

[0230] 6. Battery specific capacity test

[0231] At 25℃, the battery is charged at a constant current of 0.1C to 4.3V, then charged at a constant voltage of 4.3V to a current of 0.01C. After resting for 5 minutes, it is discharged at 0.1C to 2.0V. The resulting discharge capacity is recorded as c1. The discharge capacity obtained after one cycle is recorded as c2. Three parallel samples are prepared. The average value of c2 of the three parallel samples is taken and divided by the weight of the positive electrode active material to obtain the specific capacity of the battery.

[0232] 7. Battery charge / discharge rate performance test

[0233] At 25℃, the coin cell battery was first charged at a constant current of 0.1C to 4.3V, then charged at a constant voltage of 4.3V to a current of 0.01C, rested for 5 minutes, and then discharged at 0.1C to 2.0V. This cycle was repeated 5 times. Subsequently, the charge / discharge rates were changed to 0.5C, 1C, 2C, and 3C, and the cycle was repeated 5 times. The fast-charging performance of the material was evaluated by the charging capacity at different rates. In particular, if the material can still maintain a high charging capacity at high charge / discharge rates, it indicates that its fast-charging performance is good.

[0234] The test results of the positive electrode active materials and batteries in Examples 1-15 and Comparative Examples 1-2 are shown in Tables 2 and 3, respectively.

[0235] Table 2 Test results of positive electrode active materials

[0236] Table 3 Battery Test Results

[0237] As shown in Table 2, the electronic conductivity of the positive electrode active material in Examples 1-15 was further improved; as shown in Table 3, the fast charging performance of the batteries in Examples 1-15 was further improved, especially at high rates, such as 3C, the batteries in Examples 1-15 could still maintain a high battery charging capacity.

[0238] In contrast, Comparative Example 1 did not use boron as a catalytic carbon source, and Comparative Example 2 used a solid-solid mixture of boron oxide and lithium manganese iron phosphate. The electronic conductivity of the resulting positive electrode active material was worse than that of Examples 1-15, and the fast charging performance of the battery was worse than that of Examples 1-15. Especially at high rates, such as 3C, the charging capacity of the batteries in Comparative Examples 1 and 2 decreased significantly.

[0239] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A lithium-ion battery, wherein, Includes a positive electrode plate, wherein the positive electrode plate comprises: Positive current collector; A positive electrode active material layer is located on at least one side of the positive electrode current collector; the positive electrode active material layer includes a positive electrode active material. The positive electrode active material includes a core and a carbon coating layer, wherein the carbon coating layer covers at least a portion of the surface of the core; the carbon coating layer includes boron, and the standard deviation of the thickness of the carbon coating layer is 0-1.6 nm.

2. The lithium-ion battery according to claim 1, wherein, The thickness of the carbon coating layer is 1nm-5nm.

3. The lithium-ion battery according to any one of claims 1-2, wherein, The carbon coating layer includes carbon elements, and based on the total mass of the positive electrode active material, the positive electrode active material contains 0.5wt%-5wt% of the carbon elements.

4. The lithium-ion battery according to any one of claims 1-3, wherein, Based on the total mass of the positive electrode active material, the positive electrode active material contains 0.1wt%-2wt% of the boron element.

5. The lithium-ion battery according to any one of claims 1-4, wherein, The core comprises a lithium-containing transition metal phosphate, which satisfies the chemical formula Li a Fe x Mn (1-x-y) M y P b O c The element M includes one or more metallic elements from Groups IVB, VB, VIII, IIA, IIIA, IVA, and VA, where x is 0-1, y is 0-0.1, a is 1-1.05, b is 0.9-1.01, and c is 3.9-4.

01.

6. The lithium-ion battery according to claim 5, wherein, The core includes one or more of the following: lithium manganese iron phosphate, lithium iron phosphate, lithium iron manganese titanium phosphate, lithium iron manganese vanadium phosphate, lithium iron manganese chromium phosphate, lithium iron manganese magnesium phosphate, lithium iron manganese aluminum phosphate, lithium iron manganese phosphorus phosphate, lithium iron manganese zirconium phosphate, lithium iron manganese niobium phosphate, lithium iron manganese calcium phosphate, lithium iron manganese gallium phosphate, and lithium iron manganese germanium phosphate.

7. The lithium-ion battery according to any one of claims 1-6, wherein, The positive electrode active material satisfies at least one of the following conditions: The Dv50 particle size of the positive electrode active material is 200nm-500nm; The resistivity of the positive electrode active material is 5Ω·cm-200Ω·cm.

8. An electrical appliance, wherein, Including the lithium-ion battery according to any one of claims 1-7.

9. A positive electrode active material, wherein, The positive electrode active material includes a core and a carbon coating layer, wherein the carbon coating layer covers the surface of the core; The carbon coating layer includes boron, and the standard deviation of the thickness of the carbon coating layer is 0-1.6 nm.

10. The positive electrode active material according to claim 9, wherein, One or more of the following conditions must be met: The thickness of the carbon coating layer is 1nm-5nm; The carbon coating layer includes carbon elements, and based on the total mass of the positive electrode active material, the positive electrode active material contains 0.5wt%-5wt% of the carbon elements; Based on the total mass of the positive electrode active material, the positive electrode active material contains 0.1wt%-2wt% of the boron element.

11. The positive electrode active material according to any one of claims 9-10, wherein, The core comprises a lithium-containing transition metal phosphate, which satisfies the chemical formula Li a Fe x Mn (1-x-y) M y P b O c The element M includes one or more metallic elements from Groups IVB, VB, VIII, IIA, IIIA, IVA, and VA, where x is 0-1, y is 0-0.1, a is 1-1.05, b is 0.9-1.01, and c is 3.9-4.

01.

12. The positive electrode active material according to any one of claims 9-11, wherein, The positive electrode active material satisfies at least one of the following conditions: The Dv50 particle size of the positive electrode active material is 200nm-500nm; The resistivity of the positive electrode active material is 5Ω·cm-200Ω·cm.

13. A method for preparing a positive electrode active material, wherein, include: Boron oxide is mixed with the core to obtain a first mixture; The first mixture is subjected to a first sintering treatment to obtain a boron-coated core; The boron-coated core is mixed with a carbon source to obtain a second mixture; The second mixture is subjected to a second sintering treatment to obtain the positive electrode active material; the positive electrode active material includes a core and a carbon coating layer, wherein the carbon coating layer at least covers a portion of the surface of the core; The carbon coating layer includes boron, and the standard deviation of the thickness of the carbon coating layer is 0-1.6 nm.

14. The method according to claim 13, wherein, The boron oxide includes one or more of boron oxide, boric acid, and metaboric acid.

15. The method according to claim 14, wherein, The step of mixing boron oxide with the core further includes: The boron oxide is mixed with a solvent to obtain a boron oxide solution; The core is mixed with the boron oxide solution to obtain the first mixture.

16. The method according to claim 15, wherein, The solvent includes one or more of water, ethanol, ethylene glycol, glycerol, methanol, acetone, and tetrahydrofuran.

17. The method according to any one of claims 13-16, wherein, The mass ratio of the boron oxide to the core is (0.001-0.05):

1.

18. The method according to any one of claims 13-17, wherein, The carbon source includes one or more of starch, sucrose, glucose, citric acid, polyethylene glycol, polyvinyl alcohol, polyacrylonitrile, and urea.

19. The method according to any one of claims 13-18, wherein, The mass ratio of the carbon source to the boron-coated core is (0.05-0.25):

1.

20. The method according to any one of claims 13-19, wherein, One or two of the following conditions must be met: The temperature of the first sintering treatment is 300℃-500℃, and the time of the first sintering treatment is 0.5h-4h; The temperature of the second sintering treatment is 600℃-800℃, and the time of the second sintering treatment is 2h-18h.

21. The method according to claim 20, wherein, One or two of the following conditions must be met: The temperature of the first sintering treatment is 400℃-450℃, and the time of the first sintering treatment is 1h-2h; The temperature of the second sintering treatment is 700℃-750℃, and the time of the second sintering treatment is 4h-8h.

Images