Positive electrode active materials and their preparation methods, positive electrode sheets, batteries and electrical devices

Abstract

A positive electrode active material and its preparation method, a positive electrode sheet, a battery, and an electrical device are disclosed. The positive electrode includes a lithium-rich manganese-based positive electrode material and a coating layer distributed on at least a portion of the surface of the lithium-rich manganese-based positive electrode material. The coating layer includes at least one of a metal oxide and a metal fluoride. The specific capacity of the positive electrode active material is ≥220 mAh / g. The positive electrode active material satisfies at least one of the following conditions: oxygen defect index ≥2.12; microstress of 0.1%–1.5%; M-O / Mn-O peak intensity ratio of 25–40 in the Fourier transform infrared spectrum; and specific surface area of ​​0.9 m². 2 / g~3.5m 2 / g. By specifically coating lithium-rich manganese-based cathode materials before and after acid washing, cathode active materials that meet specific microscopic index ranges can be obtained, resulting in cathode active materials with high specific capacity and good cycle stability.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more specifically, to a positive electrode active material and its preparation method, a positive electrode sheet, a battery, and an electrical device. Background Technology

[0002] Currently, to improve the specific capacity of lithium-rich manganese-based cathode materials, some methods involve washing the materials with acid. However, after washing, the cycle stability of the lithium-rich manganese-based cathode materials decreases. Summary of the Invention

[0003] In view of the above problems, this application provides a positive electrode active material and its preparation method, a positive electrode sheet, a battery and an electrical device. The lithium-rich manganese-based positive electrode material is specifically coated before and after acid washing, and the resulting positive electrode active material has a high specific capacity and good cycle stability.

[0004] The embodiments of this application are implemented as follows:

[0005] In a first aspect, embodiments of this application provide a positive electrode active material, comprising a lithium-rich manganese-based positive electrode material and a coating layer distributed on at least a portion of the surface of the lithium-rich manganese-based positive electrode material; the lithium-rich manganese-based positive electrode material comprises an element M, which includes one or more of Mg, Nb, Cr, Ce, Fe, Ta, B, Al, V, Ti, Zr, Sn, and Mo; the coating layer comprises at least one of metal oxides and metal fluorides; the specific capacity of the positive electrode active material is ≥220 mAh / g; wherein the positive electrode active material satisfies at least one of the following conditions (a1) to (d1): (a1) In the refined X-ray diffraction pattern of the positive electrode active material, the oxygen defect index is ≥2.12; (b1) The microstress of the positive electrode active material is 0.1% to 1.5%; (c1) In the Fourier transform infrared spectrum of the positive electrode active material, the MO / Mn-O peak intensity ratio is 25 to 40; (d1) The specific surface area of ​​the positive electrode active material is 0.9 m². 2 / g~3.5m 2 / g.

[0006] The positive electrode active material provided in this application embodiment has a high specific capacity; at the same time, at least one of the oxygen defect index, microstress, MO / Mn-O peak intensity ratio and specific surface area meets a specific range, which makes the positive electrode active material have good storage performance and cycle stability.

[0007] In some embodiments, the positive electrode active material satisfies at least one of the following conditions (a2) to (d2): (a2) In the refined X-ray diffraction pattern of the positive electrode active material, the oxygen defect index is ≥2.72; (b2) The microstress of the positive electrode active material is 0.1% to 0.8%; (c2) In the Fourier transform infrared spectrum of the positive electrode active material, the MO / Mn-O peak intensity ratio is 30 to 40; (d2) The specific surface area of ​​the positive electrode active material is 1.5 m². 2 / g~2.5m 2 / g. In these embodiments, at least one of the oxygen defect index, microstress, MO / Mn-O peak intensity ratio, and specific surface area of ​​the positive electrode active material meets a further range, which is beneficial for the positive electrode active material to have better storage performance and cycle stability.

[0008] In some embodiments, the coating layer comprises one or more of Al, Ce, and Co elements, and one or more of Zr, B, and Ti elements. In these embodiments, the coating materials corresponding to Al, Ce, and Co elements can effectively protect the lithium-rich manganese-based cathode material during acid washing, while the coating materials corresponding to Zr, B, and Ti elements can effectively modify the lithium-rich manganese-based cathode material after acid washing, thereby improving the cycle stability of the cathode active material. Simultaneously, B element can activate the lithium-containing rock salt phase on the material surface, which is beneficial for increasing the specific capacity.

[0009] In some embodiments, the ratio of the total mass of Al and Ce elements to the total mass of Zr and B elements in the coating layer is 1:(0.5-2). In these embodiments, the elements in the coating layer meet specific ratios, and the coating layer can better improve the cycle stability of the positive electrode active material.

[0010] In some embodiments, the total content of Al, Ce, Co, Zr, B, and Ti elements in the coating layer of the positive electrode active material is ≤5000ppm. In these embodiments, the elemental composition of the coating layer is below a certain range in the positive electrode active material, which effectively improves the cycle stability of the positive electrode active material through the coating layer, while also giving the positive electrode active material a better specific capacity and improving the first-stage efficiency of the battery.

[0011] In some embodiments, the coating layer includes one or more of aluminum fluoride, alumina, cerium fluoride, and cerium oxide, and one or more of zirconium oxide, zirconium fluoride, boric acid, and zirconium boride. In these embodiments, aluminum fluoride, alumina, cerium fluoride, and cerium oxide have high sintering temperatures, enabling them to coat the surface of the lithium-rich manganese-based cathode material in a dense coating form at higher sintering temperatures. This provides better protection for the lithium-rich manganese-based cathode material during acid pickling, thus improving cycle stability. Zirconia, zirconium fluoride, boric acid, and zirconium boride can effectively modify the surface of the lithium-rich manganese-based cathode material, improving cycle stability, and can coat the surface of the lithium-rich manganese-based cathode material at lower sintering temperatures, which is beneficial for improving the specific capacity of the cathode active material and the battery's initial efficiency.

[0012] In some embodiments, the ratio of the volume average particle size Dv50 of the lithium-rich manganese-based cathode material to the thickness of the coating layer is (5.5–6.5):(0.2–0.8). In these embodiments, the lithium-rich manganese-based cathode material and the coating layer satisfy a suitable size ratio, which effectively improves the cycle stability of the cathode active material through the coating layer, while also enabling the cathode active material to have a good specific capacity and improving the first-stage efficiency of the battery.

[0013] In some embodiments, the thickness of the coating layer is 0.2 μm to 0.8 μm. In these embodiments, the coating layer has a suitable thickness, which can better play a protective role and improve cycle stability. Compared with an excessively thick coating layer, it is also beneficial to improve the specific capacity of the positive electrode active material and the first-time efficiency of the battery.

[0014] In some embodiments, lithium-rich manganese-based cathode materials include Li[Li] x Ni a Co b Mn c M d ]O 2-e The equations are: x + a + b + c + d = 1, x > 0, a > 0, 0 < b < 0.1, c > 0, d ≥ 0, 0 ≤ e ≤ 0.2. In these embodiments, the lithium-rich manganese-based cathode material has a low cobalt content, which can reduce costs.

[0015] Secondly, embodiments of this application provide a method for preparing a positive electrode active material, comprising coating a lithium-rich manganese-based positive electrode material with a primary coating material and sintering it to obtain a primary coating material; washing the primary coating material with a solution containing acid and / or acid salts to obtain a primary coated acid-washed material; coating the primary coated acid-washed material with a secondary coating material and sintering it to obtain a positive electrode active material; wherein, the primary coating material includes one or more of metal oxides and metal fluorides; the secondary coating material includes one or more of metal oxides, metal fluorides, and borides.

[0016] The method for preparing the positive electrode active material provided in this application improves the specific capacity through acid washing. Before acid washing, a specific type of primary coating material is used for coating, which protects the lithium-rich manganese-based positive electrode material and improves gas production during the acid washing process. After acid washing, a specific type of secondary coating material is used for coating, which modifies the surface of the lithium-rich manganese-based positive electrode material after acid washing. In this preparation method, the lithium-rich manganese-based positive electrode material is specifically coated before and after acid washing to form a positive electrode active material that meets specific microscopic index ranges. These specific microscopic indexes include at least one of oxygen defect index, microstress, MO / Mn-O peak intensity ratio, and specific surface area. The M element is a selectable doping element for the lithium-rich manganese-based positive electrode material, resulting in a positive electrode active material with good storage performance and cycle stability.

[0017] In some embodiments, the lithium-rich manganese-based cathode material is coated with a primary coating material and sintered at a temperature of 500°C to 750°C; optionally, the sintering time is 6 hours to 12 hours. In these embodiments, selecting a relatively high specific sintering temperature after primary coating is beneficial for better melting of the primary coating material and for ensuring its stable coating on the surface of the lithium-rich manganese-based cathode material, which also helps to better protect the lithium-rich manganese-based cathode material during acid pickling. Optionally, selecting an appropriate sintering time helps to balance efficiency and sintering effect.

[0018] In some embodiments, the primary coating material includes one or more of Al, Ce, and Co elements; optionally, the primary coating material includes one or more of aluminum fluoride, aluminum oxide, cerium fluoride, and cerium oxide. In these embodiments, the primary coating material has a specific composition, which can form a dense coating on the surface of the lithium-rich manganese-based cathode material after sintering, effectively protecting the lithium-rich manganese-based cathode material and improving cycle stability.

[0019] In some embodiments, the primary coated pickled material is coated with a secondary coated material and sintered at a temperature of 350°C to 550°C; optionally, the sintering time is 6 hours to 12 hours. In these embodiments, after the secondary coated material is coated, a relatively low specific sintering temperature is selected, which can better melt the secondary coated material, thereby better modifying the surface of the lithium-rich manganese-based cathode material; compared with excessively high sintering temperatures, it can also improve the transformation of the surface defect spinel structure into the rock salt phase, which is beneficial to improving the specific capacity of the cathode active material and the first-time efficiency of the battery. Optionally, selecting an appropriate sintering time is beneficial to balancing efficiency and sintering effect.

[0020] In some embodiments, the secondary coating material includes one or more of Zr, B, and Ti; optionally, the secondary coating material includes one or more of zirconium oxide, zirconium fluoride, boric acid, and zirconium boride. In these embodiments, the secondary coating material has a specific composition, which can effectively modify the surface of the lithium-rich manganese-based cathode material, thus improving cycle stability; simultaneously, it can coat the surface of the lithium-rich manganese-based cathode material at a relatively low sintering temperature, which is beneficial for improving the specific capacity of the cathode active material and the battery's initial efficiency.

[0021] In some embodiments, the primary coating material includes one or more of aluminum fluoride, alumina, cerium fluoride, and cerium oxide, and the secondary coating material includes one or more of zirconium oxide, zirconium fluoride, boric acid, and zirconium boride. The ratio of the total mass of Al and Ce elements in the primary coating material to the total mass of Zr and B elements in the secondary coating material is 1:(0.5-2). In these embodiments, the composition of the primary and secondary coating materials meets a specific ratio, and the coating layer can better improve the cycle stability of the positive electrode active material.

[0022] In some embodiments, the primary coating material includes one or more of Al, Ce, and Co elements, and the secondary coating material includes one or more of Zr, B, and Ti elements. The primary and secondary coating materials form a coating layer distributed on at least a portion of the surface of the lithium-rich manganese-based cathode material. In the cathode active material, the total content of Al, Ce, Co, Zr, B, and Ti elements in the coating layer is ≤5000ppm. In these embodiments, the elemental composition of the coating layer is below a specific range in the cathode active material. While effectively improving the cycle stability of the cathode active material through the coating layer, it also enables the cathode active material to have a better specific capacity and is beneficial to improving the first-stage efficiency of the battery.

[0023] In some embodiments, primary coating materials and secondary coating materials form a coating layer distributed on at least a portion of the surface of the lithium-rich manganese-based cathode material, and the thickness of the coating layer is 0.2 μm to 0.8 μm. In these embodiments, the coating layer has a suitable thickness, which can better play a protective role and improve cycle stability. Compared with an excessively thick coating layer, it is also beneficial to improve the specific capacity of the cathode active material and the first-cycle efficiency of the battery.

[0024] In some embodiments, lithium-rich manganese-based cathode materials include Li[Li] x Ni a Co b Mn c M d ]O 2-eThe formula is: x + a + b + c + d = 1, x > 0, a > 0, 0 < b < 0.1, c > 0, d ≥ 0, 0 ≤ e ≤ 0.2. Element M includes one or more of Mg, Nb, Cr, Ce, Fe, Ta, B, Al, V, Ti, Zr, Sn, and Mo. In these embodiments, the lithium-rich manganese-based cathode material has a low cobalt content, which reduces cost; the presence of specific doping element M in the lithium-rich manganese-based cathode material is beneficial for improving the specific capacity of the cathode active material and the initial efficiency of the battery.

[0025] In some embodiments, the primary coating material is washed with an acidic and / or acidic salt solution, which includes organic acids and / or organic acid salts, has a pH of 2 to 8, and the washing time is 0.25 h to 4 h. Optionally, the acidic and / or acidic salt solution includes one or more of citric acid, ammonium citrate, and diammonium hydrogen citrate. In these embodiments, acid washing under specific pH and washing time conditions can better improve the specific capacity of the positive electrode active material and the initial efficiency of the battery.

[0026] Thirdly, embodiments of this application provide a positive electrode sheet, including the positive electrode active material as described in the above embodiments, or the positive electrode active material prepared by the preparation method of the positive electrode active material as described in the above embodiments.

[0027] Fourthly, embodiments of this application provide a battery including the positive electrode sheet of the above embodiments.

[0028] Fifthly, embodiments of this application provide an electrical device including the battery described in the above embodiments.

[0029] The above description is merely an overview of the technical solutions of the embodiments of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, specific embodiments of this application are described below. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This application provides structural schematic diagrams of vehicles for some embodiments;

[0032] Figure 2 Exploded views of batteries provided for some embodiments of this application;

[0033] Figure 3 Exploded views of a single battery cell provided in some embodiments of this application;

[0034] Figure 4 This is a schematic diagram of the structure of an electrode assembly provided in some embodiments of this application;

[0035] Figure 5 This is a process flow diagram of the preparation method of the positive electrode active material provided in some embodiments of this application.

[0036] icon:

[0037] 1000 - Vehicles;

[0038] 100 - Battery; 200 - Controller; 300 - Motor;

[0039] 10-Box body; 11-First part; 12-Second part; 13-Accommodation space;

[0040] 20-Battery cell; 21-Casing; 22-Electrode assembly; 23-Electrode terminal; 24-Pressure relief structure;

[0041] 211-Shell; 212-Cover; 213-Sealed space;

[0042] 221 - Positive electrode; 222 - Negative electrode; 223 - Separator membrane. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0044] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0045] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0046] In the description of the embodiments of this application, the technical terms "first", "second", etc. are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0047] In the description of the embodiments of this application, the technical terms "and / or", such as "feature 1 and / or feature 2", all refer to "feature 1" alone, "feature 2" alone, or "feature 1" plus "feature 2". In addition, the character " / " in this document generally indicates that the objects before and after it are in an "or" relationship.

[0048] In the description of the embodiments of this application, unless otherwise stated, "multiple" in "one or more" means two or more.

[0049] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0050] In the embodiments of this application, the same reference numerals denote the same components, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments. It should be understood that the height, length, width, and other dimensions of various components in the embodiments of this application shown in the accompanying drawings, as well as the overall height, length, width, and other dimensions of the integrated device, are merely illustrative and should not constitute any limitation on this application.

[0051] From a market perspective, the application of power batteries is becoming increasingly widespread. Power batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but also extensively in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. With the continuous expansion of the application areas of power batteries, the market demand is also constantly increasing.

[0052] With the continuous development of the new energy industry, the market has put forward more diversified demands for cathode active materials. Among them, lithium-rich manganese-based cathode active materials have attracted much attention due to their advantages such as high voltage, high specific capacity, good safety, abundant resources, and low pollution, and are considered to be a highly promising next-generation cathode active material.

[0053] Improving the specific capacity of cathode active materials and the initial efficiency of batteries is a current research direction. In particular, considering cost reduction, some studies have begun to use lithium-rich manganese-based cathode materials with low cobalt content. However, low cobalt content lithium-rich manganese-based cathode materials lead to a decrease in specific capacity. Therefore, effectively improving their specific capacity has become more important.

[0054] To improve the specific capacity and initial efficiency of lithium-rich manganese-based cathode materials, some solutions employ washing as a treatment method. Some technical solutions use alkaline washing, employing aluminate solutions or pyrophosphate solutions as treatment liquids; however, this alkaline washing method leads to an increase in the material's pH, excessive residual alkali, and the introduction of new impurity ions such as sodium, thus affecting the performance of the cathode active material. Due to the aforementioned problems with alkaline washing, some technical solutions employ acid washing, using solutions containing acids and / or acid salts as treatment liquids; however, this acid washing method easily damages the surface of the lithium-rich manganese-based cathode material, resulting in a decrease in its cycle stability.

[0055] Based on this, this application proposes a positive electrode active material and its preparation method. The lithium-rich manganese-based positive electrode material is washed with acid. Then, before and after acid washing, the lithium-rich manganese-based positive electrode material is specifically coated. The M element is a selectable doping element for the lithium-rich manganese-based positive electrode material, forming a positive electrode active material that meets specific microscopic index ranges. These specific microscopic indexes include at least one of oxygen defect index, microstress, MO / Mn-O peak intensity ratio, and specific surface area. A suitable oxygen defect index helps mitigate the aggravated oxygen release caused by oxygen defects. Suitable microstress can improve particle breakage caused by the generation and release of residual stress during cycling. A suitable MO / Mn-O peak intensity ratio indicates good coating protection and improves the long-term storage and cycling performance of the battery. A suitable specific surface area can simultaneously achieve good capacity utilization, good storage performance, and low gas generation performance in side reactions, resulting in a positive electrode active material with good storage performance and cycling stability. Therefore, in the technical solution provided in this application embodiment, the lithium-rich manganese-based cathode material is specifically coated before and after acid washing, and the resulting cathode active material has a high specific capacity and is conducive to improving the first efficiency of the battery, while also having good cycle stability.

[0056] The battery cell using the positive electrode disclosed in this application can be used, but is not limited to, in electrical devices such as vehicles, ships, or aircraft. This application provides an electrical device that uses a battery as a power source. This device can be, but is not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0057] For ease of explanation, the following embodiments use a vehicle as an example of an electrical device according to an embodiment of this application.

[0058] See Figure 1 , Figure 1 This is a schematic diagram of the structure of a vehicle 1000 provided in some embodiments of this application. The vehicle 1000 can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. A battery 100 is disposed inside the vehicle 1000, and the battery 100 can be located at the bottom, front, or rear of the vehicle 1000. The battery 100 can be used to power the vehicle 1000; for example, the battery 100 can serve as the operating power source for the vehicle 1000. The vehicle 1000 may also include a controller 200 and a motor 300. The controller 200 is used to control the battery 100 to supply power to the motor 300, for example, to meet the power needs of the vehicle 1000 during startup, navigation, and driving.

[0059] In some embodiments of this application, the battery 100 can not only serve as the operating power source for the vehicle 1000, but also as the driving power source for the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0060] In this application, battery 100 refers to a single physical module comprising one or more battery cells 20 to provide a certain voltage and capacity, which may be in the form of a battery pack, battery module, etc. Battery 100 may include a housing 10 for encapsulating one or more battery cells 20, the housing 10 preventing liquids or other foreign matter from affecting the charging or discharging of the battery cells 20.

[0061] See Figure 2 , Figure 2This is an exploded view of a battery 100 provided in some embodiments of this application. The battery 100 includes a housing 10 and a plurality of battery cells 20, which are housed within the housing 10. The housing 10 is used to house the battery cells 20 and can have various structures. In some embodiments, the housing 10 may include a first portion 11 and a second portion 12, which overlap each other, defining a receiving space 13 for accommodating the battery cells 20. The second portion 12 may be a hollow structure with one open end, and the first portion 11 may be a plate-like structure, overlapping the open side of the second portion 12 to form a housing 10 with the receiving space 13; alternatively, the first portion 11 and the second portion 12 may both be hollow structures with one open side, overlapping the open side of the second portion 12 to form a housing 10 with the receiving space 13. Of course, the first portion 11 and the second portion 12 can have various shapes, such as cylinders, cuboids, etc.

[0062] In battery 100, multiple battery cells 20 can be connected in series, parallel, or in a mixed configuration. A mixed configuration means that multiple battery cells 20 are connected in both series and parallel configurations. Multiple battery cells 20 can be directly connected in series, parallel, or in a mixed configuration, and then the entire assembly of the multiple battery cells 20 is housed within the housing 10. Alternatively, multiple battery cells 20 can first be connected in series, parallel, or in a mixed configuration to form modules, and then these modules can be connected in series, parallel, or in a mixed configuration to form a whole, which is also housed within the housing 10. Battery 100 may also include other structures; for example, multiple battery cells 20 can be electrically connected through a busbar component to achieve parallel, series, or mixed configurations of the multiple battery cells 20.

[0063] The battery cell 20 refers to the smallest unit that makes up the battery pack. The battery cell 20 can be a lithium-sulfur battery, a sodium-ion battery, or a magnesium-ion battery, but is not limited to these.

[0064] See Figure 3 The battery cell 20 may include a housing 21, an electrode assembly 22 and an electrolyte, with the electrode assembly 22 and the electrolyte both housed within the housing 21.

[0065] The outer casing 21 may include a housing 211 and a cover 212. The housing 211 is an assembly that fits with the cover 212 to form an internal sealed space 213 of the battery cell 20, wherein the formed sealed space 213 can be used to accommodate the electrode assembly 22, electrolyte, and other components. The cover 212 is a component that covers the opening of the housing 211 to isolate the internal environment of the battery cell 20 from the external environment. The shape of the cover 212 may be adapted to the shape of the housing 211 to fit the housing 211, and functional components such as electrode terminals 23 and pressure relief structures 24 may also be provided on the cover 212. A sealing ring may be provided between the opening of the housing 211 and the cover 212 to achieve a seal between the housing 211 and the cover 212.

[0066] The housing 211 and cover 212 can be of various shapes and sizes, such as cuboids, cylinders, and hexagonal prisms. Specifically, the shapes of the housing 211 and cover 212 can be determined according to the specific shape and size of the electrode assembly 22. The materials of the housing 211 and cover 212 can be various, such as, but not limited to, metals like copper, iron, aluminum, stainless steel, and aluminum alloys. The materials of the sealing ring can be various, such as, but not limited to, materials resistant to electrolyte corrosion, high toughness, and fatigue resistance, such as PP (polypropylene), PC (polycarbonate), and PET (polyethylene terephthalate). A plating layer can be formed on the outer surface of the housing 211, and the plating layer material can be various, such as, but not limited to, corrosion-resistant materials like Ni and Cr.

[0067] The battery cell 20 can also be in a pouch form, such as a bag-type pouch. The material of the pouch can be plastic, and examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0068] See Figure 4 The electrode assembly 22 includes a negative electrode 222, a separator 223, and a positive electrode 221. The battery cell 20 primarily functions by the movement of metal ions between the positive electrode 221 and the negative electrode 222. During charging and discharging, active ions repeatedly insert and extract between the positive and negative electrode 221 and the negative electrode 222. The separator 223, disposed between the positive and negative electrode 221 and the negative electrode 222, primarily serves to prevent short circuits between the positive and negative electrodes while allowing ions to pass through. The electrode assembly 22 can be a wound structure or a stacked structure; the embodiments of this application are not limited to either.

[0069] The negative electrode 222 includes a negative current collector and a negative active material layer. The negative active material layer is disposed on at least one side of the negative current collector. An undercoating layer may also be disposed between the negative current collector and the negative active material layer.

[0070] The negative electrode current collector can be a metal foil or a composite current collector. For example, the material of the negative electrode current collector can be copper. The composite current collector can include a polymer material substrate and a metal layer formed on at least one side of the polymer material substrate. The composite current collector can 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.).

[0071] The negative electrode active material in the negative electrode active material layer can be carbon, silicon, or other negative electrode active material materials. As an example, the negative electrode active material material may include at least one 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 be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one 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 material materials may also be used.

[0072] In some embodiments, the negative electrode active material layer may optionally include a binder. The binder may be selected from at least one 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).

[0073] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0074] 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)).

[0075] The separator 223 is located between the positive electrode 221 and the negative electrode 222, and plays a role in isolation. In this embodiment, there is no particular limitation on the type of separator 223, and any well-known porous structure separator 223 with good chemical and mechanical stability can be selected.

[0076] In some embodiments, the material of the separator 223 may be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator 223 may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator 223 is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0077] The positive electrode 221 includes a positive current collector and a positive active material layer. The positive active material layer is disposed on at least one side of the positive current collector. An undercoating layer may also be disposed between the positive active material layer and the positive current collector.

[0078] The positive electrode current collector can be a metal foil or a composite current collector; for example, the material of the positive electrode current collector can be aluminum. The composite current collector may include a polymer material base layer and a metal layer formed on at least one side of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum 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.).

[0079] The positive electrode active material layer includes the positive electrode active material provided in the embodiments of this application, or the positive electrode active material prepared by the method provided in the embodiments of this application; in addition, it may also include other types of active materials such as lithium cobalt oxide, lithium iron phosphate, ternary lithium, lithium manganese oxide, and lithium sulfur.

[0080] In some embodiments, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0081] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0082] The positive electrode active material and its preparation method proposed in the embodiments of this application will be described in detail below.

[0083] In a first aspect, embodiments of this application provide a positive electrode active material, comprising a lithium-rich manganese-based positive electrode material and a coating layer distributed on at least a portion of the surface of the lithium-rich manganese-based positive electrode material; the lithium-rich manganese-based positive electrode material comprises an element M, which includes one or more of Mg, Nb, Cr, Ce, Fe, Ta, B, Al, V, Ti, Zr, Sn, and Mo; the coating layer comprises at least one of metal oxides and metal fluorides; the specific capacity of the positive electrode active material is ≥220 mAh / g; wherein the positive electrode active material satisfies at least one of the following conditions (a1) to (d1): (a1) In the refined X-ray diffraction pattern of the positive electrode active material, the oxygen defect index is ≥2.12; (b1) The microstress of the positive electrode active material is 0.1% to 1.5%; (c1) In the Fourier transform infrared spectrum of the positive electrode active material, the MO / Mn-O peak intensity ratio is 25 to 40; (d1) The specific surface area of ​​the positive electrode active material is 0.9 m². 2 / g~3.5m 2 / g.

[0084] As an example, the battery 100, which includes this positive electrode active material, also meets the requirement of ≥84% initial efficiency.

[0085] Lithium-rich manganese-based cathode materials may include mixtures and / or solid solutions composed of Li₂MnO₃ phase and lithium nickel cobalt manganese oxide layered structures. The M element, for example, refers to a doping element in the lithium-rich manganese-based material.

[0086] The coating layer is distributed on at least a portion of the surface of the lithium-rich manganese-based cathode material. That is, the coating layer can partially or completely cover the surface of the lithium-rich manganese-based cathode material. As a structure covering at least a portion of the surface of the lithium-rich manganese-based cathode material, the coating material of the coating layer is, for example, mainly distributed in an island-like form on the surface of the lithium-rich manganese-based cathode material. Between the coating layer and the lithium-rich manganese-based cathode material, some of the coating material can be observed as small particles distributed dot-like on the surface of the host material. The interface between the two can be determined by conventional methods, such as direct observation of the material using an electron microscope, exemplarily using a transmission electron microscope.

[0087] Specific capacity and first-time efficiency can be obtained through conventional testing methods. For example, under a voltage range of 2.5V to 4.55V, charge at a rate of 0.1C to 4.55V, then charge at a constant voltage of 4.55V until the current is ≤0.05mA, and let it stand for 2 minutes. The charging capacity at this point is recorded as C0. Then discharge at a rate of 0.1C to 2.5V. The discharge capacity at this point is the specific capacity, recorded as D0. The first-time efficiency is D0 / C0*100%.

[0088] X-ray diffraction sepectrum, or XRD for short, can be obtained using an X-ray diffractometer and methods known in the art. For example, refer to the general rules for XRD testing, JIS K 0131-1996, which include the following requirements: (1) the sample must be dry; (2) the sample particle size must be <10 μm. If the sample is electrode powder or in block form, it must be ground through a 200-mesh sieve before delivery. The refined X-ray diffraction pattern is obtained using the Rietveld method. I101 and I102 represent the intensity values ​​of the (101) and (102) crystal plane diffraction peaks of the lithium-rich manganese-based cathode material in the X-ray diffraction pattern, respectively.

[0089] As examples, the above-mentioned oxygen deficiency indicators include, but are not limited to, ≥2.2, ≥2.3, ≥2.4, ≥2.5, ≥2.6, ≥2.7, ≥2.8, ≥2.9, ≥3.0, ≥3.1, etc.

[0090] The micro-stress of the positive electrode active material can be obtained through conventional testing methods. For example, the micro-stress of the positive electrode active material = (β...) hkl *cosθ hkl ) / (4sinθ hkl ), where θ hkl β represents the diffraction angle of the crystal plane diffraction peak of the lithium-rich manganese-based cathode material (hkl) in the XRD diffraction pattern. hkl The full width at half maximum (FWHM) of the diffraction peaks of the lithium-rich manganese-based cathode material (hkl) in the XRD diffraction pattern is shown.

[0091] As an example, the microstress of the positive electrode active material is, for example, but not limited to, any one of 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, and 1.5%, or a range between any two.

[0092] Fourier transform infrared spectroscopy, or FTIR for short, is obtained using a Fourier transform infrared spectrometer and methods known in the art. For example, refer to the national standard GB / T6040-2002. The MO / Mn-O peak intensity ratio refers to the ratio of the peak intensity of the absorption peak corresponding to MO to the peak intensity of the absorption peak corresponding to Mn-O. The peak intensity of the absorption peak corresponding to MO refers to the peak intensity of the absorption peak at the position corresponding to MO, and the peak intensity of the absorption peak corresponding to Mn-O refers to the peak intensity of the absorption peak at the position corresponding to Mn-O.

[0093] As an example, the above MO / Mn-O peak intensity ratio is, for example, but not limited to, any one of the points 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39 and 40 or a range between any two.

[0094] Specific surface area (BET) refers to the total surface area per unit mass of material. The specific surface area of ​​positive electrode active materials can be obtained through conventional methods. For example, refer to the national standard GB / T19587-2004.

[0095] As an example, the specific surface area of ​​the positive electrode active material is, for example, but not limited to, 0.9 m². 2 / g、1m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 / g, 1.6m 2 / g, 1.7m 2 / g, 1.8m 2 / g, 1.9m 2 / g、2m 2 / g、2.1m 2 / g, 2.2m 2 / g, 2.3m 2 / g, 2.4m 2 / g, 2.5m 2 / g, 2.6m 2 / g, 2.7m 2 / g, 2.8m 2 / g, 2.9m 2 / g、3m 2 / g, 3.1m 2 / g, 3.2m 2 / g, 3.3m 2 / g, 3.4m 2 / g and 3.5m 2 Any point value in / g or any range of values ​​between the two.

[0096] The positive electrode active material provided in this application embodiment has a high specific capacity; at the same time, at least one of the oxygen defect index, microstress, MO / Mn-O peak intensity ratio and specific surface area meets a specific range, which makes the positive electrode active material have good storage performance and cycle stability.

[0097] In some embodiments, the positive electrode active material satisfies at least one of the following conditions (a2) to (d2): (a2) In the refined X-ray diffraction pattern of the positive electrode active material, the oxygen defect index is ≥2.72; (b2) The microstress of the positive electrode active material is 0.1% to 0.8%; (c2) In the Fourier transform infrared spectrum of the positive electrode active material, the MO / Mn-O peak intensity ratio is 30 to 40; (d2) The specific surface area of ​​the positive electrode active material is 1.5 m². 2 / g~2.5m 2 / g.

[0098] In these embodiments, at least one of the oxygen defect index, microstress, MO / Mn-O peak intensity ratio, and specific surface area of ​​the positive electrode active material meets a further range, which is beneficial for the positive electrode active material to have better storage performance and cycle stability.

[0099] In some embodiments, the cladding layer comprises one or more of Al, Ce, and Co elements, and one or more of Zr, B, and Ti elements.

[0100] In the coating layer, metal oxides and metal fluorides refer to the compound composition therein, and elemental composition refers to the elemental composition of the compounds in the coating layer. For example, metal oxides and / or metal fluorides may include one or more of Al, Ce and Co elements.

[0101] In these embodiments, the coatings formed by the coating materials corresponding to Al, Ce and Co elements can effectively protect the lithium-rich manganese-based cathode material during the pickling process, while the coatings formed by the coating materials corresponding to Zr, B and Ti elements can effectively modify the lithium-rich manganese-based cathode material after pickling, so that the coating layer can effectively improve the cycle stability of the cathode active material; at the same time, B element can activate the lithium-containing rock salt phase on the surface of the material, which is beneficial to improving the specific capacity.

[0102] In some embodiments, the ratio of the total mass of Al and Ce elements to the total mass of Zr and B elements in the cladding layer is 1:(0.5 to 2).

[0103] The masses of Al, Ce, Zr, and B elements can be determined using conventional methods. For example, refer to EPA6010d-2014 Inductively Coupled Plasma Atomic Emission Spectrometry for testing.

[0104] As an example, the ratio of the total mass of Al and Ce elements to the total mass of Zr and B elements is, for example, but not limited to, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, etc.

[0105] In these embodiments, the elements in the coating layer meet specific ratios, and the coating layer can better improve the cycle stability of the positive electrode active material.

[0106] In some embodiments, the total content of Al, Ce, Co, Zr, B and Ti elements in the coating layer of the positive electrode active material is ≤5000ppm.

[0107] The total content of Al, Ce, Co, Zr, B and Ti elements in the coating layer can be determined using conventional methods. For example, the inductively coupled plasma atomic emission spectrometry method described in EPA6010d-2014 can be used for testing.

[0108] As an example, the total content of Al, Ce, Co, Zr, B and Ti elements in the coating layer is, for example, but not limited to, a point value of 1000 ppm, 2000 ppm, 3000 ppm, 4000 ppm and 5000 ppm or a range between any two.

[0109] In these embodiments, the composition of the coating layer elements is below a certain range in the content of the positive electrode active material. While effectively improving the cycle stability of the positive electrode active material through the coating layer, the positive electrode active material has a better specific capacity and is conducive to improving the first efficiency of the battery 100.

[0110] In some embodiments, the cladding layer includes one or more of aluminum fluoride, aluminum oxide, cerium fluoride and cerium oxide, and one or more of zirconium oxide, zirconium fluoride, boric acid and zirconium boride.

[0111] In these embodiments, aluminum fluoride, alumina, cerium fluoride, and cerium oxide have high sintering temperatures, enabling them to coat the surface of lithium-rich manganese-based cathode materials as dense coatings at higher sintering temperatures. This provides better protection for the lithium-rich manganese-based cathode materials during acid pickling, thus improving cycle stability. Zirconia, zirconium fluoride, boric acid, and zirconium boride can effectively modify the surface of lithium-rich manganese-based cathode materials, improving cycle stability. Furthermore, they can coat the surface of lithium-rich manganese-based cathode materials at lower sintering temperatures, which is beneficial for increasing the specific capacity of the cathode active material and the initial efficiency of battery 100.

[0112] In some embodiments, the ratio of the volume average particle size Dv50 of the lithium-rich manganese-based cathode material to the thickness of the coating layer is (5.5–6.5):(0.2–0.8).

[0113] The volume average particle size Dv50 refers to the particle size corresponding to 50% of the volume distribution. It can be obtained by conventional testing methods. As an example, referring to the national standard GB / T 19077-2016 / ISO13320:2009 Particle size distribution laser diffraction method, the measurement was performed using the Malvern 3000 equipment.

[0114] The thickness of the coating layer refers to the wall thickness from the inner surface to the outer surface of the coating layer. It can be obtained by taking the average value of the distance from the inner surface to the outer surface of the coating layer at multiple locations in the electron microscope image of the cross section of the positive electrode active material.

[0115] An exemplary method for testing the volume average particle size Dv50 of lithium-rich manganese-based cathode materials is as follows: the volume average particle size Dv50 of the cathode active material is measured by particle size distribution laser diffraction, and the volume average particle size Dv50 of the lithium-rich manganese-based cathode material is obtained by subtracting twice the thickness of the coating layer from the volume average particle size Dv50 of the cathode active material.

[0116] As an example, the ratio of the volume average particle size Dv50 of the lithium-rich manganese-based cathode material to the thickness of the coating layer is, for example, but not limited to, 5.5:(0.2 to 0.8), 6:(0.2 to 0.8), 6.5:(0.2 to 0.8), etc.

[0117] In these embodiments, the lithium-rich manganese-based cathode material and the coating layer satisfy a suitable size ratio. While effectively improving the cycle stability of the cathode active material through the coating layer, the cathode active material also has a good specific capacity and is conducive to improving the first efficiency of the battery 100.

[0118] In some embodiments, the thickness of the coating layer is 0.2 μm to 0.8 μm.

[0119] As an example, the thickness of the coating layer may be, for example, but not limited to, any one of 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm and 0.8 μm, or a range of any two.

[0120] In these embodiments, the coating layer has a suitable thickness, which can play a better protective role and improve cycle stability. Compared with an excessively thick coating layer, it is also beneficial to improve the specific capacity of the positive electrode active material and the first efficiency of the battery 100.

[0121] In some embodiments, lithium-rich manganese-based cathode materials include Li[Li] x Ni a Co b Mnc M d ]O 2-e , x+a+b+c+d=1, x>0, a>0, 0<b<0.1, c>0, d≥0, 0≤e≤0.2.

[0122] In lithium-rich manganese-based cathode materials, the chemical formula Li[Li] x Ni a Co b Mn c M d ]O 2-e It can be measured using conventional methods. For example, it can be measured using ICP emission spectroscopy (inductively coupled plasma atomic emission spectrometry).

[0123] It should be noted that in the positive electrode sheet 221, the battery cell 20, and the electrical equipment, due to the cycling process, oxygen elements in the positive electrode active material are lost, which may result in a decrease in the measured oxygen content in the positive electrode active material.

[0124] In these embodiments, the lithium-rich manganese-based cathode material has a lower cobalt content, which can reduce costs.

[0125] See Figure 5 Secondly, embodiments of this application provide a method for preparing a positive electrode active material, comprising coating a lithium-rich manganese-based positive electrode material with a primary coating material and sintering it to obtain a primary coating material; washing the primary coating material with a solution containing acid and / or acid salts to obtain a primary coated acid-washed material; coating the primary coated acid-washed material with a secondary coating material and sintering it to obtain a positive electrode active material; wherein, the primary coating material includes one or more of metal oxides and metal fluorides; the secondary coating material includes one or more of metal oxides, metal fluorides, and borides.

[0126] The method for preparing the positive electrode active material provided in this application embodiment is exemplarily used to prepare the positive electrode active material as provided in the first aspect embodiment.

[0127] In terms of raw material selection, the size, elemental composition, and dosage ratio of the lithium-rich manganese-based cathode material, the primary coating material, and the secondary coating material can all be selected with reference to the cathode active material provided in the first aspect embodiment. For example, the lithium-rich manganese-based cathode material includes element M, which includes one or more of Mg, Nb, Cr, Ce, Fe, Ta, B, Al, V, Ti, Zr, Sn, and Mo.

[0128] In terms of the performance of the prepared product, as an example, the specific capacity of the positive electrode active material is ≥220 mAh / g. Simultaneously, the positive electrode active material meets at least one of the following conditions (a1) to (d1): (a1) In the refined X-ray diffraction pattern of the positive electrode active material, the oxygen defect index is ≥2.12; (b1) The microstress of the positive electrode active material is 0.1% to 1.5%; (c1) In the Fourier transform infrared spectrum of the positive electrode active material, the MO / Mn-O peak intensity ratio is 25 to 40; (d1) The specific surface area of ​​the positive electrode active material is 0.9 m². 2 / g~3.5m 2 / g. Additionally, by way of example, the battery 100 including this positive electrode active material also meets the requirement of first-time efficiency ≥84%.

[0129] It should be noted that the descriptions of "first" and "second" in "first coating material" and "second coating material" do not refer to which pass the coating belongs to, nor to how many times the coating is repeated. They are only used to distinguish between different coating passes.

[0130] The method for preparing the positive electrode active material provided in this application improves the specific capacity through acid washing. Before acid washing, a specific type of primary coating material is used for coating, which protects the lithium-rich manganese-based positive electrode material and improves gas production during the acid washing process. After acid washing, a specific type of secondary coating material is used for coating, which modifies the surface of the lithium-rich manganese-based positive electrode material after acid washing. In this preparation method, the lithium-rich manganese-based positive electrode material is specifically coated before and after acid washing to form a positive electrode active material that meets specific microscopic index ranges. These specific microscopic indexes include at least one of oxygen defect index, microstress, MO / Mn-O peak intensity ratio, and specific surface area. The M element is a selectable doping element for the lithium-rich manganese-based positive electrode material, resulting in a positive electrode active material with good storage performance and cycle stability.

[0131] In some embodiments, the lithium-rich manganese-based cathode material is coated with a single coating material and sintered at a temperature of 500°C to 750°C; optionally, the sintering time is 6 hours to 12 hours.

[0132] As an example, the sintering temperature after coating with a single coating material is, for example, but not limited to, any one of 500°C, 550°C, 600°C, 650°C, 700°C, and 750°C, or a range between any two.

[0133] As an example, the sintering time after coating the raw material once is, for example, but not limited to, any one of 6h, 7h, 8h, 9h, 10h, 11h and 12h or any range between two.

[0134] In these embodiments, selecting a relatively high specific sintering temperature after the initial coating of the raw material is beneficial for better melting of the initial coating material and for ensuring its stable coating on the surface of the lithium-rich manganese-based cathode material. This also facilitates better protection of the lithium-rich manganese-based cathode material during the pickling process. Optionally, selecting an appropriate sintering time helps to balance efficiency and sintering effect.

[0135] In some embodiments, the primary coating material includes one or more of Al, Ce, and Co elements; optionally, the primary coating material includes one or more of aluminum fluoride, aluminum oxide, cerium fluoride, and cerium oxide.

[0136] In these embodiments, the primary coating material has a specific composition, which can form a dense coating on the surface of the lithium-rich manganese-based cathode material after sintering, thus effectively protecting the lithium-rich manganese-based cathode material and improving cycle stability.

[0137] In some embodiments, the primary coating pickling material is coated with a secondary coating material and sintered at a temperature of 350°C to 550°C; optionally, the sintering time is 6 hours to 12 hours.

[0138] As an example, the sintering temperature after coating with secondary coating material is, for example, but not limited to, any one of 350°C, 400°C, 450°C, 500°C and 550°C or a range between any two.

[0139] As an example, the sintering time after secondary coating of raw materials is, for example, but not limited to, any one of 6h, 7h, 8h, 9h, 10h, 11h and 12h or any range between two.

[0140] In these embodiments, after the secondary coating material is coated, a relatively low specific sintering temperature is selected, which can better melt the secondary coating material, thereby better modifying the surface of the lithium-rich manganese-based cathode material. Compared with excessively high sintering temperatures, it can also improve the transformation of surface defect spinel structures into rock salt phases, which is beneficial to improving the specific capacity of the cathode active material and the first-time efficiency of battery 100. Optionally, selecting an appropriate sintering time is beneficial to balancing efficiency and sintering effect.

[0141] In some embodiments, the secondary coating material includes one or more of Zr, B, and Ti; optionally, the secondary coating material includes one or more of zirconium oxide, zirconium fluoride, boric acid, and zirconium boride.

[0142] In these embodiments, the secondary coating material has a specific composition, which can effectively modify the surface of the lithium-rich manganese-based cathode material, thus improving cycle stability. At the same time, it can coat the surface of the lithium-rich manganese-based cathode material at a lower sintering temperature, which is beneficial to improving the specific capacity of the cathode active material and the first-time efficiency of the battery 100.

[0143] In some embodiments, the primary coating material includes one or more of aluminum fluoride, alumina, cerium fluoride, and cerium oxide, and the secondary coating material includes one or more of zirconium oxide, zirconium fluoride, boric acid, and zirconium boride. The ratio of the total mass of Al and Ce elements in the primary coating material to the total mass of Zr and B elements in the secondary coating material is 1:(0.5-2).

[0144] The exemplary selection of the ratio of the total mass of Al and Ce elements in the primary coating material to the total mass of Zr and B elements in the secondary coating material is given by reference to the relevant explanation of the first aspect embodiment.

[0145] In these embodiments, the composition of the primary coating material and the secondary coating material meets a specific ratio, and the coating layer can better improve the cycle stability of the positive electrode active material.

[0146] In some embodiments, the primary coating material includes one or more of Al, Ce, and Co elements, and the secondary coating material includes one or more of Zr, B, and Ti elements. The primary and secondary coating materials form a coating layer distributed on at least a portion of the surface of the lithium-rich manganese-based cathode material. In the cathode active material, the total content of Al, Ce, Co, Zr, B, and Ti elements in the coating layer is ≤5000ppm.

[0147] The exemplary selection of the total content of Al, Ce, Co, Zr, B and Ti elements in the coating layer is explained in the relevant description of the first aspect embodiment.

[0148] In these embodiments, the composition of the coating layer elements is below a certain range in the content of the positive electrode active material. While effectively improving the cycle stability of the positive electrode active material through the coating layer, the positive electrode active material has a better specific capacity and is conducive to improving the first efficiency of the battery 100.

[0149] In some embodiments, the primary coating material and the secondary coating material form a coating layer distributed on at least a portion of the surface of the lithium-rich manganese-based cathode material, and the thickness of the coating layer is 0.2 μm to 0.8 μm.

[0150] The exemplary selection of the thickness of the covering layer is explained in the relevant section of the first aspect embodiment.

[0151] In these embodiments, the coating layer has a suitable thickness, which can play a better protective role and improve cycle stability. Compared with an excessively thick coating layer, it is also beneficial to improve the specific capacity of the positive electrode active material and the first efficiency of the battery 100.

[0152] In some embodiments, lithium-rich manganese-based cathode materials include Li[Li] x Ni a Co b Mn c M d ]O 2-e x+a+b+c+d=1, x>0, a>0, 0<b<0.1, c>0, d≥0, 0≤e≤0.2, and the element M includes one or more of Mg, Nb, Cr, Ce, Fe, Ta, B, Al, V, Ti, Zr, Sn and Mo.

[0153] As an example, lithium-rich manganese-based cathode materials are prepared by the following method:

[0154] Low-cobalt hydroxide precursor, lithium salt, and milled zirconium beads were mixed in a drum ball mill mixer at a ball-to-material ratio of 25–80, with the Li / Me molar ratio controlled at 1.3–1.4. Me included nickel, cobalt, manganese, and the modifying element M. The mixture was then sintered in a muffle furnace at a temperature of 780–900℃, a heating rate of 2–5℃ / min, and a sintering time of 10–15 h in air atmosphere. This yielded a lithium-rich manganese-based cathode material intermediate product after a single sintering. The intermediate product was then mechanically ground and sieved to obtain the lithium-rich manganese-based cathode material.

[0155] Optionally, the lithium salt includes one or more of lithium hydroxide, lithium carbonate, lithium acetate, lithium nitrate, lithium oxalate, and lithium sulfate.

[0156] In these embodiments, the lithium-rich manganese-based cathode material has a low cobalt content, which can reduce costs; the lithium-rich manganese-based cathode material has a specific doping element M, which is beneficial to improving the specific capacity of the cathode active material and the first efficiency of the battery 100.

[0157] In some embodiments, the primary coating material is washed with a solution containing acid and / or acid salts, the solution containing acid and / or acid salts including organic acids and / or organic acid salts, the pH value of the solution containing acid and / or acid salts being 2 to 8, and the washing time being 0.25 h to 4 h; optionally, the solution containing acid and / or acid salts includes one or more of citric acid, ammonium citrate, and diammonium hydrogen citrate.

[0158] In the description of this application, pickling is a shorthand for the process of washing the primary coating material with a solution containing acid and / or acid salts. It should be noted that in the embodiments of this application, since the deionized water solvent commonly used for organic acid and / or its salt solutions is weakly alkaline, the initial pH value of the acid and / or acid salt solution may be greater than 7.

[0159] Salts are salts whose anion is an acid radical ion.

[0160] As an example, the pH value of a solution containing acid and / or acid salts may be, for example, but not limited to, a point value of any one of 2, 3, 4, 5, 6, 7, and 8, or a range of any two.

[0161] Optionally, the acid and / or acid salt includes one or more of citric acid, ammonium citrate, and diammonium hydrogen citrate.

[0162] As an example, the washing time value is, for example, but not limited to, any one of 0.25h, 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h and 4h, or a range of any two.

[0163] During the washing process, an agitation operation can be performed, with the agitation rate optionally ranging from 800 r / min to 1200 r / min, such as, but not limited to, 800 r / min, 900 r / min, 1000 r / min, 1100 r / min, 1200 r / min, etc.

[0164] In these embodiments, acid washing under specific pH and washing time conditions can better improve the specific capacity of the positive electrode active material and the first efficiency of the battery 100.

[0165] Thirdly, embodiments of this application provide a positive electrode sheet, including the positive electrode active material as described in the above embodiments, or the positive electrode active material prepared by the preparation method of the positive electrode active material as described in the above embodiments.

[0166] Fourthly, embodiments of this application provide a battery including the positive electrode sheet of the above embodiments.

[0167] Fifthly, embodiments of this application provide an electrical device including the battery described in the above embodiments.

[0168] The following specific embodiments are provided to better illustrate this application.

[0169] I. Preparation of battery cells

[0170] (1) Preparation of cathode materials

[0171] S1. Low-cobalt hydroxide precursor, lithium salt, and milled zirconium beads are mixed in a drum ball mill mixer at a ball-to-material ratio of 60. The Li / Me molar ratio is controlled at 1.35, and Me includes nickel, cobalt, manganese, and the modifying element M. The mixture is then sintered in a muffle furnace at 800℃, with a heating rate of 2℃ / min and a sintering time of 10h. The sintering atmosphere is air. This yields a lithium-rich manganese-based cathode material intermediate product after one sintering. The intermediate product is then mechanically ground and sieved to obtain the lithium-rich manganese-based cathode material.

[0172] The obtained lithium-rich manganese-based cathode material has the chemical formula Li 1.15 Ni 0.25 Co 0.05 Ti 0.02 Mn 0.53 O2, Dv50 is 6.5μm, SPAN = 1.15. Where SPAN represents the radial distance, SPAN = (Dv90 - Dv10) / Dv50.

[0173] S2. The lithium-rich manganese-based cathode material and a certain amount of primary coating raw material are placed in a drum ball mill mixer and mixed for 10 hours. Then, the mixture is placed in a muffle furnace for sintering. The heating rate is 2-5℃ / min. The sintering temperature and sintering time are shown in Table 1. The sintering atmosphere is air. After sintering, the material is mechanically ground and screened to obtain the primary coating material.

[0174] S3. Prepare a citric acid solution by dissolving citric acid in deionized water. The concentration of citric acid in the solution is 3 g / L, and the pH value of the solution is 2.57. Then, weigh the primary coating material from step S1 at a liquid-to-solid ratio of 25:1 and add it to the citric acid solution for washing. The treatment time is 0.5 h, and the stirring speed is 900 r / min. After washing, the material is filtered, rinsed with deionized water, filtered again, and then dried at 80℃ for 10 h. After mechanical grinding and sieving, the primary coated pickling material is obtained.

[0175] S4. The primary coated pickling material obtained in step S3 and a certain amount of secondary coated raw material are placed into a drum ball mill mixer and mixed for 10 hours. Then, the mixture is placed into a muffle furnace for sintering. The heating rate is 2℃ / min. The sintering temperature and sintering time are shown in Table 1. The sintering atmosphere is air. After sintering, the material is mechanically ground and sieved to obtain the positive electrode active material.

[0176] (2) Preparation of positive electrode sheet

[0177] The prepared positive electrode active material was premixed in a 5L mixing tank for 30 minutes. Then, acetylene black (SP) as a conductive agent and polyvinylidene fluoride (PVDF) as a binder were added for a second dry mixing process of 30 minutes. The mass ratio of the positive electrode active material, conductive agent, and binder was 96:2:2. N-methylpyrrolidone (NMP) as a solvent was added, and the mixture was rapidly stirred under vacuum to form a positive electrode slurry with a solid content of 70 wt%. The positive electrode slurry was uniformly coated onto both sides of a 12 μm thick aluminum foil. The coated electrode was dried in an oven at 100℃–130℃ for half an hour to obtain the positive electrode sheet. The positive electrode active material loading of the positive electrode sheet was 21.5 mg / cm³. 2 .

[0178] (3) Preparation of negative electrode sheet

[0179] Artificial graphite (anode active material), hard carbon, acetylene black (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC) (thickener) were prepared in a mass ratio of 90:5:2:2:1. The mixture was thoroughly stirred and mixed in a deionized water solvent system to obtain a cathode slurry. The cathode slurry was coated onto copper foil, dried, and cold-pressed to obtain the cathode sheet.

[0180] (4) Assemble the battery

[0181] Using a porous polyethylene polymer film as the separator, the positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a barrier between the positive and negative electrodes. After being wound up, the film is placed in an outer packaging and filled with a prepared basic electrolyte to obtain a battery cell. The basic electrolyte is a 1 mol / L LiPF6 / (EC+EMC+DMC) solution, with the volume ratio of EC, EMC, and DMC in the solvent being 1:1:1.

[0182] Those skilled in the art will understand that in the methods described above in the specific embodiments and comparative examples, the order in which the steps are written does not imply a strict execution order and does not constitute any limitation on the implementation process. The specific execution order of each step should be determined by its function and possible internal logic.

[0183] II. Testing Methods

[0184] (1) Quantity and first-efficiency test

[0185] Using a button cell as the test object, it is charged to 4.55V at a rate of 0.1C under a voltage range of 2.5V to 4.55V. Then, it is charged at a constant voltage at 4.55V until the current is ≤0.05mA. After resting for 2 minutes, the charging capacity at this time is recorded as C0. Then, it is discharged to 2.5V at a rate of 0.1C. The discharge capacity at this time is the specific capacity, recorded as D0. The first efficiency is D0 / C0*100%.

[0186] (2) Oxygen Defect Index Test

[0187] X-ray diffraction pattern testing conditions: Refer to the general rules for XRD testing JIS K 0131-1996, including the following requirements: (1) The sample must be dry; (2) The sample particle size must be <10μm. If it is an electrode scraping powder or a block sample, it must be ground through a 200-mesh sieve before being sent to the sample.

[0188] The refined X-ray diffraction pattern was obtained using the Rietveld method. I101 and I102 represent the intensity values ​​of the (101) and (102) crystal plane diffraction peaks of the lithium-rich manganese-based cathode material in the X-ray diffraction pattern, respectively.

[0189] (3) Micro-stress test

[0190] X-ray diffraction pattern testing shall be performed under the following conditions: refer to the general rules for XRD testing JIS K0131-1996, including the following requirements: (1) the sample is dry; (2) the sample particle size is <10μm. If it is an electrode scraping powder or a block sample, it must be ground through a 200-mesh sieve before being sent.

[0191] Microstress of positive electrode active material = (β) hkl *cosθ hkl ) / (4sinθ hkl ), where θ hkl β represents the diffraction angle of the crystal plane diffraction peak of the lithium-rich manganese-based cathode material (hkl) in the XRD diffraction pattern. hkl The full width at half maximum (FWHM) of the diffraction peaks of the lithium-rich manganese-based cathode material (hkl) in the XRD diffraction pattern is shown.

[0192] (4) MO / Mn-O peak intensity ratio test

[0193] For details, please refer to the national standard GB / T 6040-2002.

[0194] The method for confirming the MO peak intensity is as follows: M is Ti, and the peak intensity at 900 cm⁻¹ in the Fourier transform infrared spectrum is... -1 ~1000cm -1 The intensity of the diffraction peak.

[0195] The method for confirming the Mn-O peak intensity is as follows: The peak intensity at 600 cm⁻¹ in the Fourier transform infrared spectrum is... -1 ~620cm -1 The intensity of the diffraction peak.

[0196] (5) Specific surface area test

[0197] For details, please refer to the national standard GB / T 19587-2004.

[0198] 1) Pretreatment: Take an appropriate amount of sample in a special sample tube, heat and degas for 2 hours, and weigh the total weight after cooling to room temperature. Subtract the mass of the sample tube to obtain the sample mass.

[0199] 2) Testing: The sample tube is placed in the workstation and the amount of gas adsorbed on the solid surface under different adsorption pressures is measured at a constant low temperature. Based on the BET multilayer adsorption theory and its formula, the amount of monolayer adsorption of the sample is obtained, and the specific surface area of ​​the solid sample per unit mass is calculated.

[0200] 3) Adsorbed gas: nitrogen; Adsorption pressure points: 0.05, 0.10, 0.15, 0.20, 0.25, 0.30; Test atmosphere: high-purity liquid nitrogen atmosphere.

[0201] (6) Cyclic performance test

[0202] Using a full battery as the test object, under a constant temperature environment of 25℃, the battery was charged to 4.45V at a 1C rate at a voltage of 2.5V to 4.45V, and then charged at a constant voltage of 4.45V until the current was ≤0.05mA. After resting for 5 minutes, the battery was discharged to 2.5V at a 1C rate, and the discharge capacity was recorded. The previous process was repeated to obtain the capacity retention rate after a specified number of cycles. The capacity retention rate = discharge capacity in the first cycle / discharge capacity at the specified number of cycles × 100%.

[0203] III. Experimental Conditions and Test Results

[0204] The main experimental conditions for the preparation methods of each experimental group are shown in Table 1, the parameters of the prepared positive electrode active material are shown in Table 2, and the battery performance test results after the positive electrode active material is applied to the battery are shown in Table 3.

[0205] Table 1

[0206]

[0207]

[0208] In Table 1, Examples 31 and 32 indicate that no primary coating material was used for coating, Examples 33 and 34 indicate that no secondary coating material was used for coating, and Comparative Example 1 indicates that neither primary nor secondary coating material was used for coating.

[0209] Table 2

[0210]

[0211]

[0212] Table 3

[0213]

[0214]

[0215]

[0216] Based on Tables 1 to 3, a brief analysis is as follows:

[0217] In the embodiments, specific primary coating materials and secondary coating materials were used for coating and sintering before and after acid washing of the lithium-rich manganese-based cathode material; no coating was performed in Comparative Example 1. Compared with Comparative Example 1, the cathode active material prepared in the embodiments exhibits a higher cycle capacity retention rate when applied in batteries.

[0218] In Examples 1 to 5, the sintering temperatures after coating the raw materials were different. When the sintering temperature gradually increased in the range of 500℃ to 800℃, the cycle capacity first increased and then decreased. When the sintering temperature was between 500℃ and 750℃, the cycle capacity retention rate was relatively high.

[0219] In Examples 1 and 6 to 9, the sintering time after coating the raw material once is different. When the sintering time gradually increases in the range of 6h to 15h, the circulation capacity first increases and then decreases. When the sintering time is in the range of 6h to 12h, the circulation capacity retention rate is relatively high.

[0220] In Examples 1 and 10-13, the sintering temperatures after the secondary coating of the raw materials are different. When the sintering temperature gradually increases in the range of 350℃ to 600℃, the cycle capacity initially increases and then decreases. When the sintering temperature is between 350℃ and 550℃ (e.g., 350℃ to 450℃), it has a higher cycle capacity retention rate, as well as higher specific capacity and initial efficiency.

[0221] In Examples 1 and 14 to 17, the sintering time after the secondary coating of raw materials is different. When the sintering time gradually increases in the range of 6h to 15h, the circulation capacity first increases and then decreases. When the sintering time is 6h to 12h, the circulation capacity retention rate is relatively high.

[0222] In Examples 1 and 18-20, the types of raw materials coated in the first step are different, and the positive electrode active materials all have a high cycle capacity retention rate.

[0223] In Examples 1 and 21 to 23, the types of secondary coating raw materials are different, and the positive electrode active materials all have high cycle capacity retention rates.

[0224] In Examples 1 and 24-26, the total amount of Al, Ce, Zr, and B elements in the coating layer and the coating layer thickness differ. Increasing the coating layer thickness within a certain range is beneficial for improving cycle performance. Compared to excessive thickness, a suitable coating thickness is beneficial for uniform coating, reducing local transition metal dissolution, reducing capacity decay, and reducing polarization. Specifically, the total amount of the specified elements in the coating layer is 2000 ppm to 6000 ppm, and the coating layer thickness is 0.3 μm to 0.8 μm. The specific capacity, first-efficiency, and cycle capacity initially increase and then decrease. When the total amount of the specified elements in the coating layer is 2000 ppm to 5000 ppm, a higher retention rate of specific capacity, first-efficiency, and cycle capacity is observed.

[0225] In Examples 1 and 27-30, the ratio of the total mass of Al and Ce elements in the primary coating material to the total mass of Zr and B elements in the secondary coating material is slightly different. When the ratio is in the range of 1:(0.5-2), a higher cycle capacity retention rate is achieved.

[0226] In Examples 1 and Examples 31 to 34, Examples 31 and 32 indicate that no primary coating material was used for coating, and Examples 33 and 34 indicate that no secondary coating material was used for coating. Example 1 has a significantly higher cycle capacity retention rate.

[0227] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A positive electrode active material, characterized by, The positive electrode active material comprises a lithium-rich manganese-based positive electrode material and a coating layer distributed on at least part of the surface of the lithium-rich manganese-based positive electrode material; The lithium-rich manganese-based positive electrode material comprises M elements, and the M elements comprise one or more of Mg, Nb, Cr, Ce, Fe, Ta, B, Al, V, Ti, Zr, Sn and Mo; The coating layer comprises at least one of a metal oxide and a metal fluoride; and in the coating layer, the element composition comprises one or more of Al elements, Ce elements and Co elements, and one or more of Zr elements, B elements and Ti elements; The gram capacity of the positive electrode active material is ≥220 mAh / g; and the positive electrode active material satisfies at least one of conditions (a1) to (d1) below. (a1) In the X-ray diffraction spectrum refinement result of the positive electrode active material, the oxygen defect index is ≥2.12; (b1) The micro stress of the positive electrode active material is 0.1% to 1.5%; (c1) In the Fourier infrared spectrum of the positive electrode active material, the M-O / Mn-O peak intensity ratio is 25 to 40; (d1 ) the specific surface area of the positive electrode active material is 0.9 m2 / g to 3.5 m2 / g 2 (g) the specific surface area of the positive electrode active material is 0.9 m2 / g to 3.5 m2 / g 2 (g) the specific surface area of the positive electrode active material is 2. The positive electrode active material according to claim 1, characterized by The positive electrode active material satisfies at least one of conditions (a2) to (d2) below. (a2) In the X-ray diffraction spectrum refinement result of the positive electrode active material, the oxygen defect index is ≥2.72; (b2) The micro stress of the positive electrode active material is 0.1% to 0.8%; (c2) In the Fourier infrared spectrum of the positive electrode active material, the M-O / Mn-O peak intensity ratio is 30 to 40; (d2) the specific surface area of the positive electrode active material is 1.5 m2 / g to 2.5 m2 / g 2 / g~2.5m 2 / g.

3. The positive electrode active material according to claim 1, characterized by In the coating layer, the ratio of the total mass of the Al elements and the Ce elements to the total mass of the Zr elements and the B elements is 1:(0.5 to 2).

4. The positive electrode active material according to claim 1 or 3, characterized by In the positive electrode active material, the total content of the Al elements, the Ce elements, the Co elements, the Zr elements, the B elements and the Ti elements in the coating layer is ≤5000 ppm.

5. The positive electrode active material according to claim 1, characterized by The coating layer comprises one or more of aluminum fluoride, aluminum oxide, cerium fluoride and cerium oxide, and one or more of zirconium oxide, zirconium fluoride, boric acid and zirconium boride.

6. The positive electrode active material according to claim 1, characterized by The ratio of the volume average particle size Dv50 of the lithium-rich manganese-based positive electrode material to the thickness of the coating layer is (5.5 to 6.5):(0.2 to 0.8).

7. The positive electrode active material according to claim 1, characterized by The thickness of the coating layer is 0.2 μm to 0.8 μm.

8. The positive electrode active material according to claim 1, characterized by The lithium-rich manganese-based positive electrode material includes Li[Li x Ni a Co b Mn c M d ]O 2-e , x+a+b+c+d=1, x>0, a>0, 0 9. A method for producing a positive electrode active material, characterized by, Comprise: A lithium-rich manganese-based positive electrode material is coated with primary coating raw materials and sintered to obtain a primary coated material; the lithium-rich manganese-based positive electrode material comprises M elements, and the M elements comprise one or more of Mg, Nb, Cr, Ce, Fe, Ta, B, Al, V, Ti, Zr, Sn and Mo; A solution containing an acid and / or an acid salt is used to wash the primary coated material to obtain a primary coated acid washed material; The primary coated acid washed material is coated with secondary coating raw materials and sintered to obtain a positive electrode active material; The primary coating raw material includes one or more of metal oxide and metal fluoride, and the primary coating raw material includes one or more of Al element, Ce element and Co element; the secondary coating raw material includes one or more of metal oxide, metal fluoride and boride, and the secondary coating raw material includes one or more of Zr element, B element and Ti element.

10. The method of claim 9, wherein, In the coating and sintering of the lithium-rich manganese-based positive electrode material by using the primary coating raw material, the sintering temperature is 500-750 DEG C.

11. The preparation method according to claim 9, characterized in that, In the coating and sintering of the lithium-rich manganese-based positive electrode material by using the primary coating raw material, the sintering time is 6-12 h.

12. The method of claim 9, wherein, The primary coating raw material includes one or more of aluminum fluoride, aluminum oxide, cerium fluoride and cerium oxide.

13. The preparation method according to claim 9, characterized in that, In the coating and sintering of the primary coating pickling material by using the secondary coating raw material, the sintering temperature is 350-550 DEG C.

14. The method of claim 9, wherein, In the coating and sintering of the primary coating pickling material by using the secondary coating raw material, the sintering time is 6-12 h.

15. The preparation method according to claim 9, characterized in that, The secondary coating raw material includes one or more of zirconium oxide, zirconium fluoride, boric acid and zirconium boride.

16. The method of claim 9, wherein, The primary coating raw material includes one or more of aluminum fluoride, aluminum oxide, cerium fluoride and cerium oxide, and the secondary coating raw material includes one or more of zirconium oxide, zirconium fluoride, boric acid and zirconium boride, and the ratio of the total mass of Al element and Ce element in the primary coating raw material to the total mass of Zr element and B element in the secondary coating raw material is 1: (0.5-2).

17. The preparation method according to claim 9, characterized in that, The primary coating raw material and the secondary coating raw material form a coating layer distributed on at least part of the surface of the lithium-rich manganese-based positive electrode material; in the positive electrode active material, the total content of Al element, Ce element, Co element, Zr element, B element and Ti element in the coating layer is ≤5000 ppm.

18. The method of claim 9, wherein, The primary coating raw material and the secondary coating raw material form a coating layer distributed on at least part of the surface of the lithium-rich manganese-based positive electrode material, and the thickness of the coating layer is 0.2-0.8 μm.

19. The method of claim 9, wherein, The lithium-rich manganese-based positive electrode material includes Li[Li x Ni a Co b Mn c M d ]O 2-e , x+a+b+c+d=1, x>0, a>0, 0 20. The method of claim 9, wherein, In the pickling of the primary coating material by using the solution containing acid and / or acid salt, the solution containing acid and / or acid salt includes organic acid and / or organic acid salt, the pH value of the solution containing acid and / or acid salt is 2-8, and the pickling time is 0.25-4 h.

21. The method of claim 9, wherein, The solution containing acid and / or acid salt includes one or more of citric acid, ammonium citrate and diammonium hydrogen citrate.

22. A positive electrode sheet characterized by comprising: The positive electrode active material includes the positive electrode active material as claimed in any one of claims 1-8 or the positive electrode active material prepared by the preparation method of the positive electrode active material as claimed in any one of claims 9-21.

23. A battery, characterized by The positive electrode tab includes the positive electrode tab as claimed in claim 22.

24. An electrical device, comprising: The battery includes the battery as claimed in claim 23.

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