Positive electrode active material and preparation method thereof, positive electrode plate, battery and electric equipment

Abstract

The invention relates to a positive active material and a preparation method thereof, a positive pole piece, a battery and electric equipment. The positive electrode active material comprises a matrix positive electrode material and a phosphate film coated on the surface of the matrix positive electrode material; and the coverage integrity of the phosphate film on the surface of the matrix positive electrode material is greater than or equal to 95%. According to the technical scheme, the coverage integrity of the phosphate film on the surface of the matrix positive electrode material is greater than or equal to 95%. The positive electrode active material has extremely high coverage integrity, realizes uniform lithium removal at the surface interface under the working condition of high-voltage deep lithium removal, reduces material cracking caused by stress, and improves the cycle and high-temperature storage performance of the material, thereby being beneficial to improving the battery capacity retention rate.

Description

Technical Field

[0001] The present application relates to a positive electrode active material and a preparation method thereof, a positive electrode plate, a battery, and an electrical device. Background Art

[0002] In recent years, with the development of lithium-ion secondary battery technology, lithium-ion secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. As lithium-ion secondary batteries have achieved great development, their capacity has also been put forward higher requirements. Summary of the Invention

[0003] The purpose of this application is to provide a positive electrode active material and a preparation method thereof, a positive electrode sheet, a battery, and an electrical device.

[0004] The embodiment of the present application is implemented as follows:

[0005] In a first aspect, an embodiment of the present application provides a positive electrode active material, the positive electrode active material comprising a base positive electrode material and a phosphate film coated on the surface of the base positive electrode material;

[0006] The coverage of the phosphate film on the surface of the base cathode material is greater than or equal to 95%;

[0007] The test method for coverage integrity comprises: detecting the mass percentage of the total elements excluding lithium in at least a portion of the area less than or equal to 5 nm from the surface of the positive electrode active material by an Auger spectrometer, and determining the mass percentage of the base metal element in the base positive electrode material contained in the total elements;

[0008] The coverage completeness is the ratio of the difference between the mass percentage of the total elements and the mass percentage of the base metal elements to the mass percentage of the total elements.

[0009] In the above technical solution, the phosphate film achieves greater than 95% coverage on the surface of the substrate positive electrode material. This high coverage of the positive electrode active material enables uniform lithium removal at the surface interface under high-voltage deep lithium removal conditions, reducing stress-induced material cracking, improving the material's cycling and high-temperature storage performance, and ultimately increasing battery capacity retention.

[0010] In some optional embodiments, the coverage completeness of the phosphate film on the surface of the base positive electrode material is 99% to 100%.

[0011] In the above technical solution, the coverage completeness of the phosphate film on the surface of the base positive electrode material is 99% to 100%, which is beneficial to improving the circulation and high-temperature storage performance of the material and improving the battery capacity retention rate.

[0012] In some optional embodiments, the coating thickness of the phosphate film on the surface of the base positive electrode material is less than 8.1 nm.

[0013] In the above technical solution, by setting the coating thickness of the phosphate film on the surface of the substrate positive electrode active material to be less than 8.1 nm, it is beneficial to the kinetic performance of the positive electrode active material.

[0014] In some optional embodiments, the coating thickness of the phosphate film on the surface of the base positive electrode material is 0.1 nm to 5 nm.

[0015] In the above technical solution, by setting the coating thickness of the phosphate film on the surface of the base positive electrode material to 0.1 nm to 5 nm, it is further beneficial to the kinetic performance of the positive electrode active material.

[0016] In some optional embodiments, the chemical formula of the phosphate film includes M1 y1 PO4, wherein M1 includes any one or a combination of at least two of Li, Al, Ti, W, Zr, Nb, Ta, Mg, Ge, Ga or Si; 0.6≤y1≤3.

[0017] In the above technical solution, the chemical expression of the phosphate film satisfies the above general formula, the composition of the phosphate film is close to the ideal stoichiometric ratio, the coating component is purer, with fewer impurities, and the coating is more stable, which is beneficial to the battery's cycle and high-temperature storage performance.

[0018] In some optional embodiments, the matrix cathode material comprises: at least one of a layered oxide, a spinel-type material, and an olivine-type material; and / or,

[0019] The chemical formula of layered oxides includes Li a1 Ni x1 Co y2 M2 1-x1-y2 O 2+d1 ; wherein M2 includes at least one of Mn, Zr, Al, B, Ta, Mo, W, Nb, Sb, and La, 0≤x1≤1.0, 0≤y2<1, x1+y2≤1, 0.2≤a1<1.2, -0.02≤d1<0.02; and / or,

[0020] The chemical formula of spinel materials includes Li a2 Mn 2-x2 M3 x2 O 4-n2 , wherein 0.5≤a1<1.1, 0≤x2≤0.6, 0≤n2≤0.1; M3 includes: any one or a combination of at least two of Ni, Co, Mg, Ga, Al, Cu, Cr or Fe; and / or,

[0021] The chemical formula of olivine-type materials includes Li a3 Fe b M4 1-b P 1-d2 O 4-n2 , wherein 0<a3≤1.1, 0≤b≤1; M4 includes: any one of Ni, Co, Mg, Ga, Al, Cu or Cr, or a combination of at least two thereof.

[0022] In some alternative embodiments, the base cathode material comprises LiCoO2.

[0023] In some optional embodiments, the base cathode material satisfies at least one of the following characteristics:

[0024] (1) The average particle size of the matrix positive electrode material is 100nm to 50μm;

[0025] (2) The specific surface area of ​​the matrix positive electrode material is 0.01m 2 / g~10m 2 / g.

[0026] In a second aspect, the present invention provides a method for preparing a positive electrode active material, comprising:

[0027] Providing a matrix positive electrode material;

[0028] Oxidizing the inactive groups of the phosphorus source to obtain an activated phosphorus source;

[0029] Using activated phosphorus source and metal source to carry out atomic layer deposition on the base cathode material to obtain the cathode active material;

[0030] The positive electrode active material includes a base positive electrode material and a phosphate film coated on the surface of the base positive electrode material;

[0031] The coverage of the phosphate film on the surface of the base cathode material is greater than or equal to 95%;

[0032] The test method for coverage integrity includes: detecting the mass percentage of the total elements other than lithium in at least a portion of the area less than or equal to 5 nm from the surface of the positive electrode active material by an Auger spectrometer, and determining the mass percentage of the base metal element in the base positive electrode material contained in the total elements;

[0033] The coverage completeness is the ratio of the difference between the mass percentage of the total elements and the mass percentage of the base metal elements to the mass percentage of the total elements.

[0034] In the above technical solution, by oxidizing the inactive groups of the phosphorus source, more active sites that can undergo atomic layer deposition reactions, namely activated phosphorus sources, can be obtained; this activated phosphorus source and metal source are used to perform atomic layer deposition on the base positive electrode material; the deposited coating layer can be made almost defect-free, thereby obtaining a phosphate film coating layer with an ideal stoichiometric ratio. The surface conductivity distribution of this phosphate film coating layer is more uniform, which is more conducive to improving the battery's cycle performance and high-temperature storage performance.

[0035] In some alternative embodiments, the non-reactive groups of the phosphorus source are oxidized, comprising:

[0036] A strong oxidizing activator is used to oxidize the inactive groups of the phosphorus source.

[0037] In the above technical solution, a strong oxidizing activator is used to oxidize the inactive groups of the phosphorus source, which can effectively activate the inactive groups such as organic carbon functional groups on the surface of the phosphorus source, making them active sites where atomic layer deposition reactions can occur, thereby greatly reducing the defect formation of the coating layer, and then effectively improving the surface conductivity distribution of the coating layer to be more uniform, which is more conducive to improving the cycle performance and high-temperature storage performance of the battery.

[0038] In some alternative embodiments, the strong oxidizing activator comprises ozone.

[0039] In the above technical solution, ozone is used as a strong oxidizing activator. Ozone can activate organic carbon-hydrides in the phosphorus source into free radicals or hydroxyl groups. This facilitates the formation of a phosphate film coating with an ideal stoichiometric ratio during subsequent atomic deposition, significantly reducing the amount of unreacted organic carbon functional groups from the phosphorus source remaining in the coating, greatly reducing the formation of defects in the coating, and greatly improving the self-polymerization of the phosphorus source during the reaction. This effectively improves the surface conductivity distribution of the coating, thereby further improving the battery's cycling performance and high-temperature storage performance.

[0040] In some optional embodiments, atomic layer deposition is performed, including:

[0041] Heating the base cathode material to above 200°C;

[0042] Performing atomic layer deposition on the surface of a base cathode material using an activated phosphorus source to obtain a first intermediate material;

[0043] Atomic layer deposition is performed on the surface of the first intermediate material using a metal source.

[0044] In some optional embodiments, an activated phosphorus source is used to perform atomic layer deposition on the surface of a base cathode material to obtain a first intermediate material, comprising:

[0045] The phosphorus source is heated to 85-90° C. and atomically deposited on the surface of the matrix positive electrode material; then a strong oxidizing activator is used to oxidize the inactive groups of the phosphorus source to obtain a first intermediate material.

[0046] In some optional embodiments, the phosphorus source includes: any one or a combination of two or more of trimethyl phosphate, triethyl phosphate, tris(dimethylamino)phosphine or diethyl phosphate; and / or,

[0047] The metal source includes one or more oxides, hydroxides, and salts containing the M1 element; the M1 element includes any one or a combination of at least two of Li, Al, Ti, W, Zr, Nb, Ta, Mg, Ge, Ga, or Si.

[0048] In a third aspect, an embodiment of the present application provides a positive electrode plate, comprising the positive electrode active material provided in the first aspect; or the positive electrode plate comprises the positive electrode active material prepared by the preparation method of the positive electrode active material provided in the second aspect.

[0049] In the above technical solution, the electrode sheet can effectively improve the capacity retention rate of the lithium-ion battery by setting the positive electrode active material provided by the first aspect, or by setting the positive electrode active material prepared by the preparation method of the positive electrode active material provided by the second aspect.

[0050] In a fourth aspect, an embodiment of the present application provides a battery, which includes the positive electrode plate provided in the third aspect.

[0051] In the above technical solution, the battery is helpful in improving the capacity of the battery by providing the positive electrode plate provided by the third aspect.

[0052] In a fifth aspect, an embodiment of the present application provides an electrical device, which includes the battery provided in the fourth aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0054] Figure 1 A schematic structural diagram of a vehicle provided in some embodiments of the present application;

[0055] Figure 2 An exploded view of a battery provided in accordance with some embodiments of the present application;

[0056] Figure 3 for Figure 2An exploded view of a battery cell is shown;

[0057] Figure 4 A schematic diagram of a partial structure of an electrode assembly provided in some embodiments of the present application;

[0058] Figure 5 A schematic diagram of a partial structure of a positive electrode sheet provided in some embodiments of the present application;

[0059] Figure 6 TEM scans of the positive electrode active materials prepared in Example 1, Comparative Example 1, and Comparative Example 2 are shown; Figure 6 From left to right, they correspond to Example 1, Comparative Example 1, and Comparative Example 2;

[0060] Figure 7 Shows the XPS graphs of the positive electrode active materials prepared in Example 1, Comparative Example 1, and Comparative Example 2;

[0061] Figure 8 shows a TOF-SIMS image of the positive electrode active material prepared in Example 1;

[0062] Figure 9 shows a TOF-SIMS image of the positive electrode active material prepared in Comparative Example 1;

[0063] Figure 10 Shown is a TOF-SIMS image of the positive electrode active material prepared in Comparative Example 2;

[0064] Figure 11 An AES chart of the positive electrode active material prepared in Example 1 is shown.

[0065] icon:

[0066] Vehicles 1000;

[0067] Battery 100; Controller 200; Motor 300;

[0068] Box body 10; first part 11; second part 12; accommodating space 13;

[0069] Battery cell 20; housing 21; electrode assembly 22; electrode terminal 23; pressure relief structure 24;

[0070] Housing 211; cover 212; positive electrode sheet 221; negative electrode sheet 222; separator 223;

[0071] Positive electrode current collector 2211; positive electrode active material layer 2212;

[0072] Negative electrode current collector 2221 ; negative electrode active material layer 2222 . DETAILED DESCRIPTION

[0073] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0074] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0075] In the description of the embodiments of the present application, technical terms such as "first" and "second" are only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0076] In the description of the embodiments of the present application, the orientations or positional relationships indicated by technical terms such as "inside" and "outside" are based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on the embodiments of the present application.

[0077] In the description of the embodiments of this application, unless otherwise specified or limited, technical terms such as "installed," "connected," "connected," and "fixed" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integration; they can refer to direct connections or indirect connections through an intermediate medium. Those skilled in the art will understand the specific meanings of the above terms in the embodiments of this application based on specific circumstances.

[0078] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0079] In the embodiments of this application, the same reference numerals represent the same components, and for the sake of brevity, detailed descriptions of the same components in different embodiments are omitted. It should be understood that the heights, lengths, widths, and other dimensions of the various components in the embodiments of this application, as well as the overall heights, lengths, widths, and other dimensions of the integrated device shown in the drawings are merely illustrative and do not constitute any limitation on this application.

[0080] With the vigorous development of the new energy vehicle industry, the lithium-ion battery industry has also entered a stage of rapid development. The positive electrode material is an important component of lithium-ion batteries, accounting for nearly 40% of the cost of lithium-ion batteries. Therefore, the improvement of the performance of the positive electrode material is crucial to the improvement of the performance of lithium-ion batteries. In order to meet the growing market demand and performance indicators, the development of higher voltage positive electrode materials to provide more capacity is of great significance to improving the energy density of lithium-ion batteries. However, in the case of high-voltage deep delithiation, due to the difference in the conductivity of the positive electrode material, uneven delithiation will occur at the surface interface, and large stress will be generated in local areas, leading to material cracking. After long-term cyclic storage, this local cracking will gradually extend to the bulk phase, seriously affecting the kinetic properties of the material, further leading to material capacity decay and reduced cyclic storage life.

[0081] At present, people mainly use surface coating methods to modify materials. The coating layer should have the following characteristics: (1) The coating layer has good conductivity, which can allow rapid diffusion of lithium ions, so that the positive electrode material has good kinetic properties; (2) The coating layer has good stability at high voltage, that is, chemical stability in hydrofluoric acid, a byproduct of the electrolyte; (3) The coating layer is uniform and completely covers the surface of the substrate.

[0082] Coating layers come in various types, most of which are metal oxides. Metal oxides have poor electrical conductivity, and the rate performance of the coated material is often lower than before coating, which can lead to more severe material cracking. Furthermore, metal oxides are unable to withstand the attack of hydrofluoric acid, leading to material failure after long-term cycling and storage. Compared to metal oxides, phosphates are more suitable as materials for coating and modifying cathode substrates. Numerous studies have shown that phosphates have good lithium-ion conductivity and better chemical stability in hydrofluoric acid environments, making them ideal targets for coating and modifying cathode materials.

[0083] Traditional phosphate coating methods, mainly solid-phase or liquid-phase methods, suffer from uneven coating, forming island-like coatings on the substrate surface. Under high-voltage deep delithiation conditions, high stresses occur in the uncoated and coated areas, leading to cracks in the material.

[0084] The embodiment of the present application provides a positive electrode active material, the positive electrode active material comprising a base positive electrode material and a phosphate film coated on the surface of the base positive electrode material;

[0085] The coverage of the phosphate film on the surface of the base cathode material is greater than or equal to 95%;

[0086] The test method for coverage integrity comprises: detecting the mass percentage of the total elements excluding lithium in at least a portion of the area less than or equal to 5 nm from the surface of the positive electrode active material by an Auger spectrometer, and determining the mass percentage of the base metal element in the base positive electrode material contained in the total elements;

[0087] The coverage completeness is the ratio of the difference between the mass percentage of the total elements and the mass percentage of the base metal elements to the mass percentage of the total elements.

[0088] In the above technical solution, the phosphate film has a coverage completeness of greater than 95% on the surface of the base positive electrode material. This high coverage of the positive electrode active material enables uniform lithium removal at the surface interface under high-voltage deep lithium removal conditions, reducing stress-induced material cracking, improving the material's cycling and high-temperature storage performance, and contributing to improved battery capacity retention.

[0089] Furthermore, the surface coverage of the material mentioned above refers to the proportion of the particle surface area occupied by the coating layer. The coverage integrity is closely related to the performance of the positive electrode active material. First, high coverage integrity provides better physical isolation, preventing electrolyte erosion of the positive electrode active material surface. Second, high coverage integrity means a more uniform surface of the positive electrode active material, more evenly disentangling lithium ions during charge and discharge, and less internal stress in the particles, resulting in better long-term stability.

[0090] Further optionally, in some embodiments of the present application, the coverage integrity of the above-mentioned material surface can be tested using AES, illustratively, according to the following method:

[0091] The positive electrode active material is subjected to EDS element surface scanning by an Auger spectrometer (AES) to obtain an EDS distribution diagram of the active elements on the surface of the positive electrode active material. Since the test depth of AES is less than 5nm, it is close to the thickness of the coating layer. Therefore, the coverage completeness can be judged by whether the elements of the base positive electrode material are tested. If the elements detected do not contain the elements in the base positive electrode material, it means that complete coating has been achieved; if the elements detected contain the elements in the base positive electrode material, the elements in the base positive electrode material can be regarded as exposed outside the coating layer. Therefore, the coverage completeness can be determined based on the proportion of the base positive electrode material elements exposed outside the coating layer.

[0092] Illustratively, in some embodiments of the present application, the method for testing coverage integrity includes: detecting by an Auger spectrometer the mass percentage of total elements excluding lithium in at least a portion of an area less than or equal to 5 nm from the surface of the positive electrode active material, and determining the mass percentage of a base metal element in the base positive electrode material contained in the total elements;

[0093] The coverage completeness is the ratio of the difference between the mass percentage of the total elements and the mass percentage of the base metal elements to the mass percentage of the total elements.

[0094] It can be calculated according to the following formula:

[0095] Coverage completeness = (1-mass percentage of matrix metal element) × 100%.

[0096] Further, illustratively, in some embodiments of the present application, the coverage completeness of the above-mentioned phosphate film on the surface of the base positive electrode material is 95%, 96%, 97%, 98%, 99%, 100% or a range between any two of the foregoing values.

[0097] Further optionally, in some embodiments of the present application, the coverage completeness of the phosphate film on the surface of the base positive electrode material is 99% to 100%.

[0098] In the above technical solution, the coverage completeness of the phosphate film on the surface of the base positive electrode material is 99% to 100%, which greatly improves the circulation and storage performance of the material, thereby facilitating the improvement of the battery capacity.

[0099] Furthermore, in some embodiments of the present application, the coating thickness of the above-mentioned phosphate film on the surface of the base positive electrode material is less than 8.1 nm.

[0100] In the above technical solution, by setting the coating thickness of the phosphate film on the surface of the substrate positive electrode active material to be less than 8.1 nm, it is beneficial to the kinetic performance of the positive electrode active material and the long-term stability of the battery.

[0101] Further optionally, in some embodiments of the present application, the coating thickness of the above-mentioned phosphate film on the surface of the base positive electrode material is 8.1nm, 8nm, 7.8nm, 7.5nm, 7.3nm, 7.2nm, 7.0nm, 6.5nm, 6.0nm, 5.5nm, 5.0nm, 4.5nm, 4.0nm, 3.5nm, 3.0nm, 2.5nm, 2.0nm, 1.5nm, 1.0nm or a range between any two of the above-mentioned values.

[0102] Furthermore, in some embodiments of the present application, the coating thickness of the above-mentioned phosphate film on the surface of the substrate positive electrode material can be tested by the following method:

[0103] The cathode active material is scanned by EDS at its particle edges using a transmission electron microscope (TEM). The TEM scan clearly distinguishes the base cathode material from the phosphate film coating the base surface. By measuring the thickness of the coated phosphorus element enriched on the surface of the cathode active material, the thickness of the coated phosphate film can be determined.

[0104] Compared with the common island-shaped coating layer morphology, in the above technical solution, the phosphate film is evenly coated on the surface of the base positive electrode material.

[0105] Furthermore, the thickness of the phosphate film refers to the average thickness of the coating layer. The average thickness can be measured using the following method:

[0106] The coating thickness of the positive electrode active material was measured by EDS scanning of the particle edges using a transmission electron microscope. At least three different particles were selected from each batch of samples for testing, and the coating thickness was measured at at least five different locations on each particle. The average of all the measured results was taken as the average coating thickness.

[0107] Further optionally, in some embodiments of the present application, the coating thickness of the phosphate film on the surface of the base positive electrode material is 0.1 nm to 5 nm.

[0108] Illustratively, in some embodiments of the present application, the coating thickness of the above-mentioned phosphate film on the surface of the base positive electrode material is 0.1nm, 0.2nm, 0.5nm, 0.8nm, 0.9nm, 1nm, 1.5nm, 2nm, 2.5nm, 3nm, 3.5nm, 4nm, 4.5nm, 5nm or a range between any two of the above-mentioned values.

[0109] In the above technical solution, by further limiting the coating thickness of the phosphate film on the surface of the base positive electrode material to 0.1 nm to 5 nm, it is further beneficial to the kinetic performance of the positive electrode active material.

[0110] Further optionally, in some embodiments of the present application, the coating thickness of the above-mentioned phosphate film on the surface of the base positive electrode material is 0.5 nm to 4.5 nm.

[0111] Furthermore, in some embodiments of the present application, the thickness uniformity of the phosphate film on the surface of the base positive electrode material is less than 1 nm.

[0112] In the above technical solution, by setting the thickness uniformity of the phosphate film on the surface of the base positive electrode material to less than 1nm, the base surface can be evenly coated, which is not easy to produce stress cracking, which is beneficial to improving the capacity of the material, thereby improving the cycle and high-temperature storage performance of the battery.

[0113] Furthermore, in some embodiments of the present application, the chemical expression of the phosphate film is M1 y1 PO4, wherein M1 includes any one or a combination of at least two of Li, Al, Ti, W, Zr, Nb, Ta, Mg, Ge, Ga or Si; 0.6≤y1≤3.

[0114] In the above technical solution, the chemical expression of the phosphate film satisfies the above general formula, the composition of the phosphate film is close to the ideal stoichiometric ratio, the coating component is purer, with fewer impurities, and the coating is more stable, which is beneficial to the battery's cycle and storage performance.

[0115] Illustratively, in some embodiments of the present application, the chemical expression of the above-mentioned phosphate film is AlPO4, LiPO4, Ti PO4, W PO4, ZrPO4, Nb PO4, Ta PO4, Mg PO4, Ge PO4, GaPO4, SiPO4.

[0116] Further optionally, in some embodiments of the present application, the chemical formula of the phosphate film includes at least one of AlPO4, LiPO4, TiPO4, WPO4, ZrPO4, NbPO4, TaPO4, MgPO4, Ge PO4, GaPO4 or SiPO4; or in some embodiments of the present application, the chemical formula of the phosphate film includes at least two of AlPO4, LiPO4, TiPO4, WPO4, ZrPO4, NbPO4, TaPO4, MgPO4, GePO4, GaPO4 or SiPO4.

[0117] Furthermore, in some embodiments of the present application, the chemical expression of the phosphate film can be detected by XPS.

[0118] Furthermore, in some embodiments of the present application, the matrix positive electrode material includes at least one of a layered oxide, a spinel-type material, and an olivine-type material.

[0119] Furthermore, in some embodiments of the present application, the chemical formula of the layered oxide includes Li a1 Ni x1 Co y2 M2 1-x1-y2 O 2+d1 ; Wherein, M2 includes at least one of Mn, Zr, Al, B, Ta, Mo, W, Nb, Sb, and La, 0≤x1≤1.0, 0≤y2<1, x1+y2≤1, 0.2≤a1<1.2, -0.02≤d1<0.02.

[0120] For example, in some embodiments of the present application, the chemical formula of the layered oxide is LiNi 0.1 Co 0.5 Mn 0.4 O2、LiNi 0.5 Co 0.4 Mn 0.1 O2、LiNi 0.8 Co 0.1 Mn0.1 O2 or LiNi 0.4 Co 0.1 Mn 0.5 O2.

[0121] Furthermore, in some embodiments of the present application, the chemical formula of the spinel material includes Li a2 Mn 2- x2 M3 x2 O 4-n2 , where 0.5≤a1<1.1, 0≤x2≤0.6, 0≤n2≤0.1; M3 includes: any one of Ni, Co, Mg, Ga, Al, Cu, Cr or Fe, or a combination of at least two of them.

[0122] For example, in some embodiments of the present application, the chemical formula of the spinel material is LiMn 1.5 M 0.5 O4、LiMn 1.1 M 0.1 O4、LiMn 1.9 M 0.9 O4 or LiMn2O4.

[0123] Furthermore, in some embodiments of the present application, the chemical formula of the olivine-type material includes Li a3 Fe b M4 1- b P 1-d2 O 4-n2 , wherein 0<a3≤1.1, 0≤b≤1; M4 includes: any one of Ni, Co, Mg, Ga, Al, Cu or Cr, or a combination of at least two thereof.

[0124] For example, in some embodiments of the present application, the chemical formula of the above-mentioned olivine-type material is LiFePO4, LiMgPO4, LiFe 0.5 Ga 0.5 PO4、LiFe 0.9 Al 0.1 PO4 or LiFe 0.1 Cu 0.9 PO4.

[0125] Furthermore, in some embodiments of the present application, the base positive electrode material includes: a layered oxide.

[0126] In the above technical solution, the base positive electrode material is selected as a layered oxide, which can better cooperate with the phosphate film, further facilitating the acquisition of a coating layer with uniform coating and higher coating integrity, thereby further improving the battery's cycle performance and high-temperature storage performance.

[0127] Furthermore, in some embodiments of the present application, the base positive electrode material includes: LiCoO2.

[0128] In the above technical solution, the base positive electrode material is selected as LiCoO2, which can better cooperate with the phosphate film, further facilitating the acquisition of a coating layer with uniform coating and higher coating integrity, thereby further improving the battery's cycle performance and high-temperature storage performance.

[0129] Furthermore, in some embodiments of the present application, the base cathode material satisfies at least one of the following characteristics:

[0130] (1) The average particle size of the matrix positive electrode material is 100nm to 50μm;

[0131] (2) The specific surface area of ​​the matrix positive electrode material is 0.01m 2 / g~10m 2 / g.

[0132] In the above technical solution, the average particle size of the base positive electrode material is 100nm~50μm, which can better cooperate with the phosphate film, further facilitating the acquisition of a coating layer with uniform coating and higher coating integrity, thereby further improving the battery's cycle performance and high-temperature storage performance.

[0133] In the above technical solution, the specific surface area of ​​the matrix positive electrode material is 0.01m 2 / g~10m 2 / g, which can better cooperate with the phosphate film, further helping to obtain a coating layer with uniform coating and higher coating integrity, thereby further improving the battery's cycle performance and high-temperature storage performance.

[0134] Further optionally, in some embodiments of the present application, the average particle size of the above-mentioned base positive electrode material is 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, 200nm, 500nm, 800nm, 900nm, 1μm, 2μm, 5μm, 10μm, 20μm, 30μm, 40μm, 50μm or any range between the above two values.

[0135] Further, illustratively, in some embodiments of the present application, the specific surface area of ​​the matrix positive electrode material is 0.01m 2 / g, 0.02m 2 / g, 0.05m 2 / g, 0.08m 2 / g, 0.1m 2 / g、1m 2 / g, 1.5m 2 / g, 2m 2 / g、3m 2 / g、4m 2 / g、5m 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g、10m 2 / g or any range between the above two values.

[0136] Some embodiments of the present application provide a method for preparing a positive electrode active material, comprising:

[0137] Providing a matrix positive electrode material;

[0138] Oxidizing the inactive groups of the phosphorus source to obtain an activated phosphorus source;

[0139] Using activated phosphorus source and metal source to carry out atomic layer deposition on the base cathode material to obtain the cathode active material;

[0140] The positive electrode active material includes a base positive electrode material and a phosphate film coated on the surface of the base positive electrode material;

[0141] The coverage of the phosphate film on the surface of the base cathode material is greater than or equal to 95%;

[0142] The test method for coverage integrity includes: detecting the mass percentage of the total elements other than lithium in at least a portion of the area less than or equal to 5 nm from the surface of the positive electrode active material by an Auger spectrometer, and determining the mass percentage of the base metal element in the base positive electrode material contained in the total elements;

[0143] The coverage completeness is the ratio of the difference between the mass percentage of the total elements and the mass percentage of the base metal elements to the mass percentage of the total elements.

[0144] There are inactive groups such as organic carbon functional groups on the surface of the phosphorus source, which will form defects in the coating layer when atomic layer deposition is performed directly. In addition, the phosphorus source will also undergo self-polymerization during the reaction, causing the components of the coating layer to deviate from the ideal stoichiometric ratio, resulting in uneven distribution of conductivity on the surface of the coating layer, seriously affecting the cycle performance and high-temperature storage performance.

[0145] In the above technical solution, by oxidizing the inactive groups of the phosphorus source, more active sites that can undergo atomic layer deposition reactions, namely activated phosphorus sources, can be obtained; this activated phosphorus source and metal source are used to perform atomic layer deposition on the base positive electrode material; the deposited coating layer can be made almost defect-free, thereby obtaining a phosphate film coating layer with an ideal stoichiometric ratio. The surface conductivity distribution of this phosphate film coating layer is more uniform, which is more conducive to improving the battery's cycle performance and high-temperature storage performance.

[0146] Furthermore, in some embodiments of the present application, the above-mentioned "whether the inactive groups are activated" can be verified by the following method: when the components of the prepared coating layer meet the ideal stoichiometric ratio, it means that the inactive groups are completely oxidized.

[0147] Furthermore, in some embodiments of the present application, the above-mentioned "whether the inactive groups are activated" can be verified by the following method: during the preparation process, the thin film ALD growth process can be synchronously monitored by mass spectrometry RGA. During the ozone oxidation stage, the generated CO2 and H2O reach saturation, that is, complete oxidation.

[0148] Furthermore, in some embodiments of the present application, the inactive groups of the phosphorus source are oxidized, comprising:

[0149] A strong oxidizing activator is used to oxidize the inactive groups of the phosphorus source.

[0150] In the above technical solution, a strong oxidizing activator is used to oxidize the inactive groups of the phosphorus source, which can effectively activate the inactive groups such as organic carbon functional groups on the surface of the phosphorus source, making them active sites where atomic layer deposition reactions can occur, thereby greatly reducing the defect formation of the coating layer, and then effectively improving the surface conductivity distribution of the coating layer to be more uniform, which is more conducive to improving the cycle performance and high-temperature storage performance of the battery.

[0151] Furthermore, in some embodiments of the present application, the strong oxidizing activator includes ozone.

[0152] In the above technical solution, ozone is used as a strong oxidizing activator. Ozone can activate organic carbon-hydrides in the phosphorus source into free radicals or hydroxyl groups. This facilitates the formation of a phosphate film coating with an ideal stoichiometric ratio during subsequent atomic deposition, significantly reducing the amount of unreacted organic carbon functional groups from the phosphorus source remaining in the coating, greatly reducing the formation of defects in the coating, and greatly improving the self-polymerization of the phosphorus source during the reaction. This effectively improves the surface conductivity distribution of the coating, thereby further improving the battery's cycling performance and high-temperature storage performance.

[0153] Furthermore, in some embodiments of the present application, atomic layer deposition is performed, including:

[0154] Heating the base cathode material to above 200°C;

[0155] Performing atomic layer deposition on the surface of a base cathode material using an activated phosphorus source to obtain a first intermediate material;

[0156] Atomic layer deposition is performed on the surface of the first intermediate material using a metal source.

[0157] Further optionally, illustratively, in some embodiments of the present application, the base positive electrode material is heated to 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C or a range between any two of the foregoing values.

[0158] Furthermore, in some embodiments of the present application, an activated phosphorus source is used to perform atomic layer deposition on the surface of a base cathode material to obtain a first intermediate material, comprising:

[0159] The phosphorus source is heated to 85-90° C. and atomically deposited on the surface of the matrix positive electrode material; then a strong oxidizing activator is used to oxidize the inactive groups of the phosphorus source to obtain a first intermediate material.

[0160] Further optionally, illustratively, in some embodiments of the present application, the phosphorus source is heated to 85° C., 86° C., 87° C., 88° C., 89° C., 90° C. or a range between any two of the foregoing values ​​to perform a phosphorus pulse.

[0161] Furthermore, in some embodiments of the present application, the phosphorus source includes: any one or a combination of two or more of trimethyl phosphate, triethyl phosphate, tris(dimethylamino)phosphine or diethyl phosphate.

[0162] Furthermore, in some embodiments of the present application, the metal source includes: one or a combination of two or more of a lithium source, an aluminum source, a titanium source, a tungsten source, a zirconium source, a niobium source, a tantalum source, a magnesium source, a germanium source, and a gallium source.

[0163] Furthermore, in some embodiments of the present application, the lithium source includes: lithium salt, lithium hydroxide or lithium oxide.

[0164] Furthermore, in some embodiments of the present application, the aluminum source includes: aluminum salt.

[0165] Furthermore, in some embodiments of the present application, the titanium source includes: titanium salt.

[0166] Furthermore, in some embodiments of the present application, the tungsten source includes: tungsten salt.

[0167] Furthermore, in some embodiments of the present application, the zirconium source includes: zirconium salt.

[0168] Furthermore, in some embodiments of the present application, the niobium source includes: niobium salt.

[0169] Furthermore, in some embodiments of the present application, the tantalum source includes: tantalum salt.

[0170] Furthermore, in some embodiments of the present application, the magnesium source includes: magnesium salt.

[0171] Furthermore, in some embodiments of the present application, the germanium source includes: germanium salt.

[0172] Furthermore, in some embodiments of the present application, the gallium source includes: a gallium salt.

[0173] Furthermore, in some embodiments of the present application, the lithium source includes: lithium tert-butoxide, lithium carbonate, lithium hydroxide, lithium acetate, and lithium oxide.

[0174] Furthermore, in some embodiments of the present application, the aluminum source includes: trimethylaluminum and triethylaluminum.

[0175] Furthermore, in some embodiments of the present application, the titanium source includes: titanium tetrachloride, tetraisopropyl titanate, and tetrabutyl titanate.

[0176] Furthermore, in some embodiments of the present application, the tungsten source includes: tungsten hexafluoride, bis(tert-butylimino)bis(dimethylamino)tungsten, tungsten dichloride, and tungsten hexacarbonyl.

[0177] Furthermore, in some embodiments of the present application, the zirconium source includes: tetrakis(dimethylamino)zirconium, tetrakis(ethylmethylamino)zirconium, and tris(dimethylamino)cyclopentadienylzirconium.

[0178] Furthermore, in some embodiments of the present application, the niobium source includes: niobium ethoxide and tert-butyliminotris(diethylamino)niobium.

[0179] Furthermore, in some embodiments of the present application, the tantalum source includes: tantalum ethoxide, penta(dimethylamino)tantalum, t-butylimino(dimethylamino)tantalum, tris(diethylamino)t-butylamide tantalum, and tris(ethylformamido)(t-butylimide)tantalum.

[0180] Furthermore, in some embodiments of the present application, the tantalum source includes: bis(methylcyclopentadienyl)tantalum.

[0181] Furthermore, in some embodiments of the present application, the tantalum source includes: tetrakis(dimethylamino)tantalum.

[0182] Furthermore, in some embodiments of the present application, the gallium source includes: trimethylgallium and triethylgallium.

[0183] For example, in some embodiments of the present application, the phosphorus source is trimethyl phosphate, triethyl phosphate, tris(dimethylamino)phosphine or diethyl phosphate.

[0184] For example, in some embodiments of the present application, the phosphorus source includes two or more of trimethyl phosphate, triethyl phosphate, tris(dimethylamino)phosphine, or diethyl phosphate. For example, the phosphorus source is a mixture of trimethyl phosphate and triethyl phosphate, and the two can be mixed in any proportion.

[0185] Illustratively, in some embodiments of the present application, the metal source is: lithium tert-butoxide, lithium carbonate, lithium hydroxide, lithium acetate, lithium oxide, trimethylaluminum, triethylaluminum, titanium tetrachloride, tetraisopropyl titanate, tetrabutyl titanate, tungsten hexafluoride, bis(tert-butylimino)bis(dimethylamino)tungsten, dichlorodipentenoyl tungsten, hexacarbonyl tungsten, tetrakis(dimethylamino)zirconium, tetrakis(ethylmethylamino)zirconium, tris(dimethylamino)cyclopentadienyl zirconium, ethoxide niobium, tert-butyliminotris(diethylamino)niobium, ethoxide tantalum, penta(dimethylamino)tantalum, tert-butylimino(dimethylamino)tantalum, tris(diethylamino)tert-butylamide tantalum, tris(ethylformamido)(tert-butylimide)tantalum, bis(methylcyclopentadienyl)magnesium, tetrakis(dimethylamino)germanium, trimethylgallium or triethylgallium.

[0186] For example, in some embodiments of the present application, the metal source includes a mixture of lithium tert-butoxide, lithium carbonate, and lithium hydroxide, and the three can be mixed in any proportion.

[0187] Some embodiments of the present application provide a positive electrode plate, comprising the positive electrode active material provided by any of the aforementioned embodiments.

[0188] The electrode sheet can improve the capacity retention rate of the lithium-ion battery by disposing the positive electrode active material provided by the aforementioned embodiment.

[0189] Some embodiments of the present application provide a battery, comprising the positive electrode sheet provided by any of the aforementioned embodiments.

[0190] The battery is provided with the positive electrode plate provided in the aforementioned embodiment, which is beneficial to improving the battery capacity retention rate.

[0191] Some embodiments of the present application provide an electrical device, comprising the battery provided by any of the aforementioned embodiments.

[0192] The electrical equipment has improved comprehensive performance by being provided with the battery provided in the aforementioned embodiment.

[0193] See also Figure 1 , Figure 1A schematic structural diagram of a vehicle 1000 provided for some embodiments of the present application. The vehicle 1000 may be a fuel vehicle, a gas vehicle or a new energy vehicle. The new energy vehicle may be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc. A battery 100 is provided inside the vehicle 1000. The battery 100 may be provided at the bottom, head or tail of the vehicle 1000. The battery 100 may be used to power the vehicle 1000. For example, the battery 100 may serve as an operating power source for the vehicle 1000. The vehicle 1000 may further include a controller 200 and a motor 300. The controller 200 is used to control the battery 100 to power the motor 300, for example, to meet the power requirements for starting, navigating and driving the vehicle 1000.

[0194] In some embodiments of the present application, the battery 100 can not only serve as the operating power source of the vehicle 1000, but also serve as the driving power source of the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0195] In this application, battery 100 refers to a single physical module that includes one or more battery cells 20 to provide voltage and capacity. Battery 100 generally includes a housing 10 for enclosing one or more battery cells 20. Housing 10 prevents liquids or other foreign matter from affecting the charging or discharging of battery cells 20.

[0196] See also Figure 2 , Figure 2 This is an exploded view of a battery 100 provided in some embodiments of the present application. The battery 100 may include a housing 10 and a battery cell 20, with the battery cell 20 housed within the housing 10. The housing 10 is used to house the battery cell 20 and may have various structures. In some embodiments, the housing 10 may include a first portion 11 and a second portion 12, which overlap each other and together define a storage space 13 for accommodating the battery cell 20. The second portion 12 may be a hollow structure with one end open, and the first portion 11 may be a plate-like structure. The first portion 11 overlaps the open side of the second portion 12 to form the housing 10 with the storage space 13. The first portion 11 and the second portion 12 may also be hollow structures with one end open, with the open side of the first portion 11 overlapping the open side of the second portion 12 to form the housing 10 with the storage space 13. Of course, the first portion 11 and the second portion 12 may have various shapes, such as a cylinder, a rectangular parallelepiped, etc.

[0197] In the battery 100, there can be one or more battery cells 20. If there are multiple battery cells 20, the multiple battery cells 20 can be connected in series, in parallel, or in a mixed connection. Mixed connection means that the multiple battery cells 20 are connected in series and in parallel. The multiple battery cells 20 can be directly connected in series, in parallel, or in a mixed connection, and then the whole formed by the multiple battery cells 20 is accommodated in the case 10. Alternatively, multiple battery cells 20 can be first connected in series, in parallel, or in a mixed connection to form a module, and the multiple modules are then connected in series, in parallel, or in a mixed connection to form a whole, and accommodated in the case 10. The battery 100 can also include other structures. For example, the multiple battery cells 20 can be electrically connected through a busbar component to achieve parallel, series, or mixed connection of the multiple battery cells 20.

[0198] See also Figure 3 , Figure 3 for Figure 2 The exploded view of the battery cell 20 is shown. The battery cell 20 is the smallest unit constituting the battery 100. The battery cell 20 may include a housing 21, an electrode assembly 22, and an electrolyte, wherein the electrode assembly 22 and the electrolyte are both contained in the housing 21.

[0199] The outer shell 21 may include a shell 211 and a cover 212. The shell 211 is a component used to cooperate with the cover 212 to form an internal sealed space of the battery cell 20, wherein the formed sealed space can be used to accommodate the electrode assembly 22, electrolyte and other components. The cover 212 refers to a component that covers the opening of the shell 211 to isolate the internal environment of the battery cell 20 from the external environment. The shape of the cover 212 can be adapted to the shape of the shell 211 to cooperate with the shell 211. Functional components such as electrode terminals 23 and pressure relief structures 24 can also be provided on the cover 212. A sealing ring can be configured between the opening of the shell 211 and the cover 212 to achieve sealing between the shell 211 and the cover 212.

[0200] The shell 211 and the cover 212 can be of various shapes and sizes, such as a rectangular parallelepiped, a cylindrical shape, a hexagonal prism, etc. Specifically, the shapes of the shell 211 and the cover 212 can be determined according to the specific shape and size of the electrode assembly 22. The material of the shell 211 and the cover 212 can be various, such as but not limited to metals such as copper, iron, aluminum, stainless steel, and aluminum alloy. The material of the sealing ring can be various, such as but not limited to PP (polypropylene), PC (polycarbonate), PET (polyethylene terephthalate) and other materials that are resistant to electrolyte corrosion, high toughness and fatigue resistance. A coating can be formed on the outer surface of the shell 211, and the material of the coating can be various, such as but not limited to corrosion-resistant materials such as Ni and Cr.

[0201] See also Figure 4The electrode assembly 22 may be composed of a positive electrode sheet 221, a negative electrode sheet 222, and a separator 223. The separator 223 is located between the positive electrode sheet 221 and the negative electrode sheet 222 to provide isolation. The electrode assembly 22 may be a wound structure or a laminated structure, but the present invention is not limited thereto.

[0202] See also Figure 5 The negative electrode sheet 222 includes a negative electrode current collector 2221 and a negative electrode active material layer 2222. The negative electrode current collector 2221 may be made of copper, and the negative electrode active material layer 2222 includes a negative electrode active material. The negative electrode active material includes at least one of graphite, silicon, a silicon alloy, or a tin alloy.

[0203] Please continue to see Figure 5 The positive electrode sheet 221 includes a positive electrode current collector 2211 and a positive electrode active material layer 2212. Taking a lithium-ion battery cell as an example, the material of the positive electrode current collector 2211 can be aluminum. The positive electrode active material layer 2212 includes a positive electrode active material. The positive electrode active material can be any of the positive electrode active materials provided in the aforementioned embodiments.

[0204] Some specific embodiments are listed below to better illustrate the present application.

[0205] Example 1

[0206] A battery is provided, which is prepared according to the following steps:

[0207] 1. Preparation method of positive electrode active material

[0208] 1. Load the base cathode material, LiCoO2 (along with a co-plated silicon wafer) into the atomic layer deposition (ALD) chamber. Before starting ALD deposition, heat the chamber to 260°C and cycle through vacuum and nitrogen purges several times to remove impurities from the LiCoO2 surface. The ALD chamber is then evacuated to a base pressure of 0.5 Torr, and the ALD deposition cycle begins. Each deposition cycle consists of four consecutive steps separated by nitrogen purges.

[0209] The deposition process of AlPO4 film is as follows:

[0210] (1) Trimethyl phosphate (TMPO) is heated to 85-90°C to obtain sufficient partial pressure; then the phosphorus source trimethyl phosphate (TMPO) is introduced into the ALD reaction chamber multiple times in pulse mode; until the surface active groups of the matrix cathode material LiCoO2 completely react with the phosphorus source trimethyl phosphate (TMPO) (synchronously monitored by mass spectrometry RGA, the generated methane and CO2 reach saturation, that is, the reaction is complete), the introduction of the phosphorus source trimethyl phosphate (TMPO) is stopped; then the ALD system is activated to purge nitrogen until there is no residual TMPO in the reaction chamber.

[0211] (2) The TMPO obtained in step (1) is exposed to an ozone pulse to oxidize the metal organic functional groups of TMPO (synchronously monitored by mass spectrometry RGA, the generated CO2 and H2O reach saturation, i.e., complete oxidation), thereby activating the TMPO surface to obtain a first intermediate material. Subsequently, the ALD system is activated with nitrogen purge until there is no residual ozone in the reaction chamber.

[0212] (3) Trimethylaluminum (TMA) is heated to 25-40°C to obtain a sufficient partial pressure; then the metal source (trimethylaluminum) is introduced into the ALD chamber multiple times in a nitrogen carrier in a pulse mode; until the surface active groups of the first intermediate material obtained in step (2) completely react with the metal source (trimethylaluminum) (TMA) (synchronously monitored by mass spectrometry RGA, the generated methane and CO2 reach saturation, that is, the reaction is complete), the introduction of the metal source (trimethylaluminum) (TMA) is stopped; then the ALD system starts nitrogen purge until there is no residual TMA in the reaction chamber.

[0213] 2. During the step of exposing the LiCoO2 particles to TMPO and TMA (TMPO and TMA are prepared in a 1:1 molar ratio), the particles are agitated and moved relative to themselves by a nitrogen flow between each pulse of TMPO and TMA to ensure that the deposition of the metal or phosphate is substantially uniform over the entire surface of the LiCoO2 particles; the final deposited phosphate film is AlPO4. One deposition cycle of AlPO4 coating includes the above steps (1)-(3), which are repeated five times.

[0214] 2. Preparation of positive electrode sheet

[0215] The positive electrode active material prepared above is used to prepare a positive electrode sheet.

[0216] Mix the positive electrode active material, conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) in a weight ratio of 96:2.5:1.5. Add an appropriate amount of solvent, N-methylpyrrolidone (NMP), and stir evenly to obtain a positive electrode slurry. Apply the positive electrode slurry onto aluminum foil and dry it after coating to obtain a positive electrode sheet.

[0217] 3. Preparation of negative electrode sheet

[0218] Mix 96% graphite, 0.5% binder (styrene-butadiene rubber (SBR), 1.5% conductive carbon, and 2% thickener (sodium carboxymethyl cellulose (CMC-Na)) by weight. Add an appropriate amount of water and stir evenly to obtain a negative electrode slurry. Apply the negative electrode slurry onto copper foil and dry it after coating to obtain a negative electrode sheet.

[0219] 4. Preparation of electrolyte

[0220] The electrolytes were prepared according to the following method:

[0221] In an argon atmosphere glove box with a water content of <10 ppm, EC (ethylene carbonate), DMC (dimethyl carbonate), and DEC (diethyl carbonate) were mixed in a weight ratio of EC:DMC:DEC = 3:3:3 to obtain a mixed solvent, and then 1 mol / L LiPF6 was added and stirred evenly to obtain an electrolyte.

[0222] 5. Preparation of batteries

[0223] A polyethylene film with a thickness of 12 μm was used as an isolating membrane. The positive electrode sheet, isolating membrane, and negative electrode sheet prepared above were placed in order, with the isolating membrane placed between the positive and negative electrode sheets to play an isolating role. The cells were dried in an oven at 100°C for 12 hours and cooled to room temperature. The above-mentioned electrolyte was then injected, and after formation and aging, a single-layer laminated lithium-ion battery was obtained.

[0224] The preparation process parameters of Example 1 are detailed in Table 1.

[0225] Example 2

[0226] The difference from Example 1 is that the metal source is lithium tert-butoxide (LiOtBu), and the final deposited phosphate film is Li3PO4. See Table 1 for details.

[0227] Example 3

[0228] The rest is the same as in Example 1, except that in step 2, steps (1) to (3) are repeated once. See Table 1 for details.

[0229] Example 4

[0230] The rest is the same as in Example 1, except that in step 2, steps (1) to (3) are repeated 20 times. See Table 1 for details.

[0231] Example 5

[0232] The rest is the same as in Example 1, except that in step 1, the heating temperature of the reaction chamber is 200° C. See Table 1 for details.

[0233] Example 6

[0234] The rest is the same as in Example 2, except that in step 2, steps (1) to (3) are repeated once. See Table 1 for details.

[0235] Example 7

[0236] The rest is the same as in Example 2, except that in step 2, steps (1) to (3) are repeated 20 times. See Table 1 for details.

[0237] Example 8

[0238] The rest is the same as in Example 2, except that in step 1, the heating temperature of the reaction chamber is 200° C. See Table 1 for details.

[0239] Comparative Example 1

[0240] The difference from Example 1 is that after the TMPO pulse, O3 was not introduced to activate the TMPO surface, that is, step (2) was omitted. See Table 1 for details.

[0241] Comparative Example 2

[0242] The difference from Example 1 is that after the TMPO pulse, H2O is introduced to activate the TMPO surface, that is, O3 is replaced by H2O in step (2). See Table 1 for details.

[0243] Comparative Example 3

[0244] The other aspects are the same as in Example 1, except that the positive electrode active material is LiCoO 2。

[0245]

Performance test

[0246] 1. Performance test of positive electrode active materials.

[0247] The positive electrode active materials prepared in various examples or comparative examples were used as test objects.

[0248] 1. Coating Thickness Test: The surfaces of the positive electrode active materials prepared in each Example and Comparative Example were scanned using a transmission electron microscope (EDS). At least three different particles were selected from each batch of samples for testing, and the coating thickness of each particle was measured at at least five different locations. The average of all measured results was taken to determine the average coating thickness. Figure 6 TEM scans of the positive electrode active materials prepared in Example 1, Comparative Example 1, and Comparative Example 2 are shown. Figure 6 From left to right, they correspond to Example 1, Comparative Example 1, and Comparative Example 2.

[0249] from Figure 6 It can be seen that Example 1 has a clear AlPO4 coating layer with a thickness of 2nm and a relatively uniform coating layer. No obvious AlPO4 coating layer was observed in Comparative Example 1. The coating layer of Comparative Example 2 has an island-like coating morphology and is uneven.

[0250] The test results of other embodiments and comparative examples are shown in Table 2.

[0251] 2. Coating layer component testing: The positive electrode active materials prepared in each example and comparative example were tested for metal element (M) and P element components by XPS to obtain XPS graphs. The coating layer components were analyzed based on the XPS graphs.

[0252] Figure 7 The XPS graphs of the positive electrode active materials prepared in Example 1, Comparative Example 1 and Comparative Example 2 are shown.

[0253] from Figure 7 It can be seen that the Al-2p spectrum of Example 1 has a strong single peak at 74eV, which is the characteristic signal of the Al-O bond; the P-2p spectrum of Example 1 has a strong single peak at 134eV, which is the characteristic signal of phosphate; the two spectra together indicate that the coating material is AlPO4 and the coating layer components are relatively pure. No peaks were detected in the Al-2p and P-2p spectra of Comparative Example 1, indicating that AlPO4 was not coated. Only inconspicuous broad peaks were detected in the Al-2p and P-2p spectra of Comparative Example 2, and the signal-to-noise ratio was poor, indicating that only a small amount of AlPO4 was coated on the substrate.

[0254] ICP analysis of the Al and P elemental compositions of the cathode materials prepared in Example 1 and Comparative Examples 1 and 2 is shown in Table 2. As can be seen from Table 2, the Al:P ratio in Example 1 is 1.02, close to the ideal stoichiometric ratio. Neither Al nor P was detected in Comparative Example 1, and the Al:P ratio in Comparative Example 2 was 1.23, deviating from the ideal stoichiometric ratio.

[0255] The test results of other embodiments and comparative examples are shown in Table 2.

[0256] 3. Carbon residue test of coating layer:

[0257] Time-of-flight secondary ion mass spectrometry (TOF-SIMS) was performed on the accompanying silicon wafers used in the preparation of each embodiment and comparative example. The TOF-SIMS detection limit is at the ppm-ppb level, effectively detecting trace amounts of residual carbon in the coating layer. The TOF-SIMS detection mass range is mass = 0-200, which is greater than the molar mass of the precursor. Therefore, the presence of residual carbon in the coating layer can be determined by the mass of the detected peak. The test results are as follows:

[0258] Figure 8 shows a TOF-SIMS image of the positive electrode active material prepared in Example 1;

[0259] Figure 9 shows a TOF-SIMS image of the positive electrode active material prepared in Comparative Example 1;

[0260] Figure 10 The TOF-SIMS graph of the positive electrode active material prepared in Comparative Example 2 is shown.

[0261] from Figure 8It can be seen from the mass spectrum of Example 1 that there are peaks at mass = 16, 63, and 79, which are O / PO2 / PO3 respectively, and carbon peaks at mass = 24, 25, and 26, which are carbon adsorbed by air. There is no obvious organic carbon peak signal in other areas. Figure 9 It can be seen that comparative example 1 has carbon peaks only at mass = 24, 25, and 26, which are carbon adsorbed by air. Figure 10 It can be seen that Comparative Example 2 has a peak at mass = 49, which is C4H.

[0262] This shows that the coating layer in Example 1 does not contain residual organic carbon functional groups and the coating layer components are purer. However, in Comparative Example 1, the precursor was not activated, so no aluminum phosphate was coated, and only air-adsorbed carbon was tested.

[0263] The test results of other embodiments and comparative examples are shown in Table 2.

[0264] From the above physical property tests, it can be seen that the degree of activation of the phosphorus source by ozone is crucial for forming an ideal phosphate coating. For the phosphorus source TMPO, there are three ester groups in its structure that are difficult to oxidize. The ester groups are not ALD reaction active sites and cannot combine with the methyl groups of TMA to undergo ALD reaction. Therefore, no AlPO4 was coated in Comparative Example 1. H2O is a weak oxidant and can only oxidize part of the ester groups into hydroxyl groups, forming a small amount of ALD reaction active sites. Therefore, only a small amount of AlPO4 was coated in Comparative Example 2, and there were residual organic carbon functional groups in the coating, forming defects. Ozone, which has strong oxidizing properties, can completely oxidize the ester groups in TMPO into hydroxyl groups, so it can combine with the methyl groups of TMA to undergo ALD reaction. The small amount of H2O generated in the reaction process cannot be completely discharged in the reaction chamber, and can convert the methyl groups on TMA into hydroxyl groups, forming reaction sites for the next cycle. Therefore, an AlPO4 coating layer is formed in Example 1.

[0265] 4. Coating integrity

[0266] The positive electrode active materials prepared in each example and comparative example were scanned on their surfaces using Auger Spectroscopy (AES) to obtain EDS profiles of active elements on the surface of the positive electrode active materials. The AES test depth was less than 5 nm. The mass percentage of the total elements, excluding lithium, detected in at least a portion of the region less than or equal to 5 nm from the surface of the positive electrode active material was used to determine the mass percentage of the base metal element in the base positive electrode material. The coverage completeness was calculated as the ratio of the difference between the mass percentage of the total elements and the mass percentage of the base metal element to the mass percentage of the total elements.

[0267] Calculated using the following formula:

[0268] Coverage completeness = (1-mass percentage of matrix metal element) × 100%.

[0269] Figure 11 The AES graph of the cathode active material prepared in Example 1 is shown. The main elements on the surface of the sample in Example 1 are C, O, Al, and P, accounting for 10.65%, 54.87%, 18.09%, and 16.39%, respectively. No substrate metal elements were detected, indicating that the surface of the cathode material in Example 1 was completely covered by the ALD phosphate film, with a coverage completeness of 100%.

[0270] The performance parameters of the positive electrode active materials prepared in various examples and comparative examples are detailed in Table 2.

[0271] 2. Battery performance test

[0272] The batteries prepared in various examples or comparative examples were used as test objects.

[0273] 1. Capacity test

[0274] The battery cell was left standing at 25°C for 30 minutes, and then the battery was charged to 4.5V at a constant current of 0.33C, and the first charge capacity was recorded. After standing for 5 minutes, the battery was discharged to 2.5V at a constant current of 0.33C, and the first discharge capacity was recorded.

[0275] First coulombic efficiency (%) = first discharge capacity / first charge capacity × 100%.

[0276] 2. High temperature storage test

[0277] The battery cell was placed at 60°C for 30 minutes, charged to 4.5V at a constant current of 0.33C, and then charged to a cut-off current of 0.05C at a constant voltage of 4.5V; placed at 60°C for 5 minutes; then discharged to 2.5V at a constant current of 0.33C; and then placed at 60°C for 30 minutes; this is one cycle.

[0278] The above cycle was performed every 7 days before and during storage until the 28th day, and the cycle discharge capacity before storage (discharge capacity after the first cycle) and the cycle discharge capacity on the 28th day of storage were recorded.

[0279] 28-day capacity retention rate = (cycle discharge capacity on the 28th day of storage / cycle discharge capacity before storage)

[0280] 3. High temperature cycle impedance test

[0281] Impedance was measured before storage and after 28 days of storage. The method for 28 days of storage was the same as above.

[0282] The impedance test steps are as follows: let the battery cell stand at 25°C for 30 minutes, charge it to 4.5V at a constant current of 0.33C, and then charge it to a cutoff current of 0.05C at a constant voltage of 4.5V; let it stand at 25°C for 5 minutes; test the impedance in the frequency range of 200kHz-20mHz, with a disturbance voltage of 5mV.

[0283] Impedance growth rate (%) = (impedance on the 28th day of storage (Ω) - impedance on the 0th day of storage (Ω)) / impedance on the 0th day of storage (Ω) * 100%

[0284] The test results of the batteries prepared in various embodiments and comparative examples are shown in Table 3.

[0285] Table 1

[0286]

[0287]

[0288] Table 2

[0289]

[0290] Table 3

[0291]

[0292] From the above table data we can see that:

[0293] Comparing Example 1, Example 2, Comparative Example 1, Comparative Example 2, and Comparative Example 3, Examples 1 and 2 have higher discharge capacities (180 mAh / g and 182 mAh / g), only slightly lower than Comparative Example 3. Examples 1 and 2 exhibit excellent capacity retention when stored at high temperatures. After 28 days of storage at 60°C, the capacity retention rates of Examples 1 and 2 were 90% and 89%, respectively, while those of Comparative Examples 1, 2, and 3 were only 30%, 36%, and 28%, respectively. The same pattern of changes is also reflected in the impedance changes. The impedances of Examples 1 and 2 on day 0 (0.80Ω and 0.87Ω) were higher than those of Comparative Examples 1, 2, and 3 (0.69Ω, 0.66Ω, and 0.63Ω). However, the impedance growth rates of Examples 1 and 2 after 28 days of storage (120.0% and 110.3%) were significantly lower than those of Comparative Examples 1, 2, and 3 (497.1%, 653.0%, and 571.4%). From the above data, it can be seen that the ALD-coated phosphate film can significantly improve the high-temperature capacity retention rate of the positive electrode material.

[0294] Comparing samples with different coating film thicknesses and thickness uniformity, the following patterns are also observed. Comparing Examples 1 and 3, Example 3 has a coating layer thickness (0.4 nm) lower than Example 1 (2.0 nm), resulting in a higher discharge capacity (181 mAh / g). However, its high-temperature capacity retention rate is only 75%, and its impedance growth rate (230.4%) is also higher than that of Example 1. Comparing Examples 1 and 4, Example 4 has a coating layer thickness (8.1 nm) higher than that of Example 1, resulting in a lower discharge capacity (171 mAh / g). However, its capacity retention rate (93%) and impedance growth rate (66.3%) are both better than those of Example 1. Comparing Examples 1 and 5, Example 5 has a lower coverage completeness (95%) than Example 1 (99%), and its thickness uniformity (0.4 nm) is worse than that of Example 1 (0.2 nm). Therefore, its discharge capacity (179 mAh / g), capacity retention rate (89%), and impedance growth rate (131.7%) are all worse than those of Example 1.

[0295] Comparing the Examples and Comparative Examples shows that phosphate ALD films can effectively improve the high-temperature capacity retention of cathode materials. This is due to their excellent stability, as evidenced by a lower impedance growth rate after high-temperature storage. Furthermore, the physical properties of phosphate films, such as average thickness and thickness uniformity, also affect the performance of cathode materials. Too thin a film reduces capacity retention, while too thick a film reduces initial discharge capacity. Increased thickness uniformity reduces both discharge capacity and capacity retention.

[0296] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

Claims

1. A positive electrode active material, characterized in that The positive electrode active material includes a base positive electrode material and a phosphate film coated on the surface of the base positive electrode material; The coverage completeness of the phosphate film on the surface of the base positive electrode material is greater than or equal to 95%; The coverage integrity test method includes: detecting the mass percentage of the total elements excluding lithium in at least a portion of the area less than or equal to 5 nm from the surface of the positive electrode active material by an Auger spectrometer, and determining the mass percentage of the base metal element in the base positive electrode material contained in the total elements; The coverage completeness is the ratio of the difference between the mass percentage of the total elements and the mass percentage of the matrix metal elements to the mass percentage of the total elements.

2. The positive electrode active material according to claim 1, characterized in that The coverage completeness of the phosphate film on the surface of the matrix positive electrode material is 99% to 100%.

3. The positive electrode active material according to any one of claims 1 or 2, characterized in that The coating thickness of the phosphate film on the surface of the base positive electrode material is less than 8.1 nm.

4. The positive electrode active material according to any one of claims 1 to 3, characterized in that The coating thickness of the phosphate film on the surface of the base positive electrode material is 0.1nm to 5nm.

5. The positive electrode active material according to any one of claims 1 to 4, characterized in that The chemical formula of the phosphate film includes M1 y1 PO4, wherein M1 includes any one or a combination of at least two of Li, Al, Ti, W, Zr, Nb, Ta, Mg, Ge, Ga or Si; 0.6≤y1≤3.

6. The positive electrode active material according to any one of claims 1 to 5, characterized in that The matrix positive electrode material comprises: at least one of a layered oxide, a spinel material and an olivine material; and / or, The chemical formula of the layered oxide includes Li a1 Ni x1 Co y2 M2 1-x1-y2 O 2+d1 ; wherein M2 includes at least one of Mn, Zr, Al, B, Ta, Mo, W, Nb, Sb, and La, 0≤x1≤1.0, 0≤y2<1, x1+y2≤1, 0.2≤a1<1.2, -0.02≤d1<0.02; and / or, The chemical formula of the spinel material includes Li a2 Mn 2-x2 M3 x2 O4-n2, wherein 0.5≤a1<1.1, 0≤x2≤0.6, 0≤n2≤0.1; M3 includes: any one or a combination of at least two of Ni, Co, Mg, Ga, Al, Cu, Cr or Fe; and / or, The chemical formula of the olivine-type material includes Li a3 Fe b M4 1-b P 1-d2 O 4-n2 , wherein 0<a3≤1.1, 0≤b≤1; M4 includes: any one of Ni, Co, Mg, Ga, Al, Cu or Cr, or a combination of at least two thereof.

7. The positive electrode active material according to any one of claims 1 to 6, characterized in that The matrix positive electrode material includes LiCoO2.

8. The positive electrode active material according to any one of claims 1 to 7, characterized in that The base positive electrode material satisfies at least one of the following characteristics: (1) The average particle size of the matrix positive electrode material is 100 nm to 50 μm; (2) The specific surface area of ​​the matrix positive electrode material is 0.01m 2 / g~10m 2 / g.

9. A method for preparing a positive electrode active material, characterized in that: include: Providing a matrix positive electrode material; Oxidizing the inactive groups of the phosphorus source to obtain an activated phosphorus source; Performing atomic layer deposition on the base cathode material using the activated phosphorus source and metal source to obtain a cathode active material; Wherein, the positive electrode active material comprises a base positive electrode material and a phosphate film coated on the surface of the base positive electrode material; The coverage completeness of the phosphate film on the surface of the base positive electrode material is greater than or equal to 95%; The method for testing the coverage integrity comprises: detecting the mass percentage of the total elements other than lithium in at least a portion of the area less than or equal to 5 nm from the surface of the positive electrode active material by an Auger spectrometer, and determining the mass percentage of the base metal element in the base positive electrode material contained in the total elements; The coverage completeness is the ratio of the difference between the mass percentage of the total elements and the mass percentage of the matrix metal elements to the mass percentage of the total elements.

10. The method for preparing a positive electrode active material according to claim 9, characterized in that: The step of oxidizing the inactive groups of the phosphorus source comprises: A strong oxidizing activator is used to oxidize the inactive groups of the phosphorus source.

11. The method for preparing a positive electrode active material according to claim 10, characterized in that: include: The strong oxidizing activator includes ozone.

12. The method for preparing a positive electrode active material according to any one of claims 9 to 11, characterized in that: The atomic layer deposition comprises: Heating the base cathode material to above 200°C; Performing atomic layer deposition on the surface of the base cathode material using the activated phosphorus source to obtain a first intermediate material; Atomic layer deposition is performed on the surface of the first intermediate material using a metal source.

13. The method for preparing a positive electrode active material according to claim 12, wherein: The method of performing atomic layer deposition on the surface of the base positive electrode material using the activated phosphorus source to obtain a first intermediate material comprises: The phosphorus source is heated to 85-90° C. and atomically deposited on the surface of the matrix positive electrode material; then a strong oxidizing activator is used to oxidize the inactive groups of the phosphorus source to obtain the first intermediate material.

14. The method for preparing a positive electrode active material according to any one of claims 9 to 13, characterized in that: The phosphorus source includes: any one or a combination of two or more of trimethyl phosphate, triethyl phosphate, tris(dimethylamino)phosphine or diethyl phosphate; and / or, The metal source includes one or more oxides, hydroxides, and salts containing the M1 element; the M1 element includes any one or a combination of at least two of Li, Al, Ti, W, Zr, Nb, Ta, Mg, Ge, Ga, or Si.

15. A positive electrode plate, characterized in that: The positive electrode active material comprises the positive electrode active material according to any one of claims 1 to 8; or the positive electrode plate comprises the positive electrode active material prepared by the preparation method of the positive electrode active material according to any one of claims 9 to 14.

16. A battery, characterized in that: The battery comprises the positive electrode sheet according to claim 15 .

17. An electrical device, characterized in that: The electric device comprises the battery according to claim 16.

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