A positive electrode active material, a method for preparing the same, a positive electrode sheet, a secondary battery, and an electric device

Abstract

The present application provides a positive electrode active material, a method for preparing the same, a positive electrode sheet, a secondary battery, and an electric device. In particular, the present disclosure provides a positive electrode active material including a base body and a coating layer, the base body comprising a lithium-rich manganese-based material having a formula xLi2MnO3·(1-x)LiNi y Co z Mn a M 1‑y‑z‑a O2, wherein 0

Description

Technical Field

[0001] This application relates to the technical field of secondary batteries, and particularly to a positive electrode active material, a preparation method thereof, a positive electrode plate, a secondary battery, and an electrical device. Background Art

[0002] The lithium-rich manganese-based material has the advantages of high theoretical capacity, high voltage platform, low cost, no pollution, good safety, etc., and is considered to be the most promising next-generation positive electrode material for high-energy-density secondary batteries. However, when the lithium-rich manganese-based material is charged at a high voltage above 4.5V in the first cycle, a large amount of manganese ions will dissolve out, resulting in the instability of the structure of the positive electrode active material, and further causing the cycle performance and storage performance of the battery to deteriorate. Summary of the Invention

[0003] This application is made in view of the above problems, and its purpose is to provide a positive electrode active material, a preparation method thereof, a positive electrode plate, a secondary battery, and an electrical device, wherein the positive electrode active material has a low manganese dissolution amount, so that the secondary battery containing the positive electrode active material has good cycle performance and storage performance.

[0004] The inventors have found that by adopting the technical solution of the present invention, the above object can be achieved.

[0005] The first aspect of this application provides a positive electrode active material, which includes a matrix and a coating layer. The matrix contains a lithium-rich manganese-based material, and the lithium-rich manganese-based material has the formula xLi2MnO3·(1 - x)LiNi y Co z Mn a M 1-y-z-a O2, where 0 < x < 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, 0 ≤ a ≤ 1, 0 < y + z + a ≤ 1, M is one or more of Mg, B, Al, V, Ti, Zr, Sn, and Mo, the coating layer contains montmorillonite, the coating amount of the montmorillonite is 1000 - 5000 ppm, based on the weight of the lithium-rich manganese-based material, and the thickness of the coating layer is 0.05 - 1 μm.

[0006] The positive electrode active material of this application has a low manganese dissolution amount, and the secondary battery containing this positive electrode active material has good cycle performance and storage performance.

[0007] In any embodiment, the coating amount of the montmorillonite is 4000 - 5000 ppm, preferably 4500 - 5000 ppm, based on the weight of the lithium-rich manganese-based material.

[0008] When the montmorillonite coating content is 4000-5000 ppm, the positive electrode active material exhibits a lower manganese leaching rate, resulting in batteries containing this material with superior cycle and storage performance. When the montmorillonite coating content is 4500-5000 ppm, the positive electrode active material exhibits an even lower manganese leaching rate, leading to further superior cycle and storage performance in batteries containing this material.

[0009] In any embodiment, the thickness of the coating layer is 0.7-1 μm, preferably 0.95-1 μm.

[0010] When the coating thickness is 0.7-1 μm, the positive electrode active material exhibits a low manganese leaching amount, and the battery containing this positive electrode active material has better cycle performance and storage performance. When the coating thickness is 0.95-1 μm, the positive electrode active material exhibits an even lower manganese leaching amount, and the battery containing this positive electrode active material has even better cycle performance and storage performance.

[0011] In any embodiment, the cation exchange capacity of montmorillonite is 178-200 mmol / 100g.

[0012] In any embodiment, the specific surface area of ​​montmorillonite is 185-200 m². 2 / g.

[0013] In any embodiment, the specific surface area of ​​the positive electrode active material is 1.6-2 m². 2 / g, preferably 1.6-1.8m 2 / g.

[0014] When the specific surface area of ​​the positive electrode active material is 1.6-2m² 2 At a specific surface area of ​​1.6-1.8 m² / g, the positive electrode active material exhibits lower manganese leaching, resulting in batteries containing this material with superior cycle and storage performance. 2 At / g, the positive electrode active material has an even lower manganese leaching content, and the battery containing this positive electrode active material has even better cycle performance and storage performance.

[0015] In any embodiment, the median particle size Dv50 of the positive electrode active material is 15-20 μm.

[0016] When the median particle size Dv50 of the positive electrode active material is 15-20 μm, the positive electrode active material has a lower manganese leaching amount, and the battery containing this positive electrode active material has better cycle performance and storage performance.

[0017] A second aspect of this application also provides a method for preparing the positive electrode active material or the material of the first aspect of this application, the method comprising the following steps:

[0018] (1) Disperse the lithium-rich manganese-based material in a solvent;

[0019] (2) Mix the product from step (1) with montmorillonite and dry it;

[0020] (3) Sinter the product from step (2).

[0021] A third aspect of this application provides a positive electrode sheet comprising the positive electrode active material of the first aspect of this application or the positive electrode active material prepared according to the method of the second aspect of this application.

[0022] A fourth aspect of this application provides a secondary battery that includes the positive electrode sheet of the third aspect of this application.

[0023] The fifth aspect of this application provides an electrical device including the secondary battery of the fourth aspect of this application. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0025] Figure 2 yes Figure 1 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0026] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0027] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0028] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0029] Figure 6 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0030] Explanation of reference numerals in the attached figures:

[0031] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Casing; 52 Electrode assembly; 53 Top cover assembly Detailed Implementation

[0032] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the positive electrode active material, its manufacturing method, positive electrode sheet, secondary battery, and electrical device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0033] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0034] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0035] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0036] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0037] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0038] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0039] When lithium-rich manganese-based materials are charged at a high voltage of 4.5V or above during the first cycle, some lithium ions in the transition metal layer will be released together with oxygen to form Li2O. The formation of a large number of oxygen vacancies weakens the bond energy between the transition metal ions and oxygen, causing the transition metal ions (especially manganese) to migrate and dissolve, resulting in instability of the positive electrode active material structure, and consequently, a deterioration in the cycle performance and storage performance of the battery.

[0040] Based on this, this application proposes a technical solution to solve the above-mentioned technical problems.

[0041] [Positive electrode active material]

[0042] A first aspect of this application provides a positive electrode active material, the positive electrode active material comprising a matrix and a coating layer, the matrix comprising a lithium-rich manganese-based material having the formula xLi₂MnO₃·(1-x)LiNi y Co z Mn a M 1-y-z-aO2, where 0 < x < 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, 0 ≤ a ≤ 1, 0 < y + z + a ≤ 1, M is one or more of Mg, B, Al, V, Ti, Zr, Sn and Mo, the coating layer contains montmorillonite, the coating amount of the montmorillonite is 1000 - 5000 ppm, based on the weight of the lithium-rich manganese-based material, and the thickness of the coating layer is 0.05 - 1 μm.

[0043] In this article, the term "coating layer" refers to the part coated on the lithium-rich manganese-based material matrix, and this part may but does not necessarily completely coat the lithium-rich manganese-based material matrix. The use of the "coating layer" is only for convenience of description and is not intended to limit the present invention. Similarly, the term "thickness of the coating layer" refers to the thickness of the part coated on the lithium-rich manganese-based material matrix along the normal direction of the lithium-rich manganese-based material matrix.

[0044] By utilizing the good chemical stability of montmorillonite and the ability of montmorillonite to adsorb cations due to the negative charge generated by the replacement of hetero-valent ions, combined with its large specific surface area and pore volume, and the ability of its interlayer to adsorb cations, it has a significant effect on inhibiting the dissolution of manganese ions during the cycling or storage of lithium-rich manganese-based materials, effectively improving the structural stability of the materials, and protecting the materials from the erosion of hydrofluoric acid, a by-product of the electrolyte side reaction, so that the cathode active material of this application has a low manganese dissolution amount, and the secondary battery containing this cathode active material has higher 0.1C discharge capacity after charge cut-off, 0.33C discharge capacity after charge cut-off, initial efficiency and energy retention rate after 100 cycles at 25°C, thus having good cycling performance and storage performance.

[0045] In some embodiments, the coating amount of montmorillonite is 4000 - 5000 ppm, preferably 4500 - 5000 ppm, based on the weight of the lithium-rich manganese-based material.

[0046] When the coating amount of montmorillonite is 4000 - 5000 ppm, the cathode active material has a low manganese dissolution amount, and the battery containing this cathode active material has higher 0.1C discharge capacity after charge cut-off, 0.33C discharge capacity after charge cut-off, initial efficiency and energy retention rate after 100 cycles at 25°C, thus having better cycling performance and storage performance.

[0047] When the coating amount of montmorillonite is 4500 - 5000 ppm, the cathode active material has an even lower manganese dissolution amount, and the battery containing this cathode active material has an even higher 0.1C discharge capacity after charge cut-off, 0.33C discharge capacity after charge cut-off, initial efficiency and energy retention rate after 100 cycles at 25°C, thus having even better cycling performance and storage performance.

[0048] In some embodiments, the thickness of the coating layer is 0.7-1 μm, preferably 0.95-1 μm.

[0049] When the thickness of the coating layer is 0.7-1μm, the positive electrode active material has a lower manganese leaching amount. Batteries containing this positive electrode active material have higher 0.1C coin discharge capacity, 0.33C coin discharge capacity, first-efficiency and 100cls energy retention rate at 25°C, thus exhibiting better cycle performance and storage performance.

[0050] When the coating thickness is 0.95-1μm, the positive electrode active material has a further lower manganese leaching amount, and the battery containing the positive electrode active material has a further higher 0.1C coin discharge capacity, 0.33C coin discharge capacity, first efficiency and 100cls energy retention rate at 25°C, thus having further better cycle performance and storage performance.

[0051] In some embodiments, the cation exchange capacity of montmorillonite is 100-200 mmol / 100g. In some embodiments, the cation exchange capacity of montmorillonite is 178-200 mmol / 100g.

[0052] When the cation exchange capacity of montmorillonite is 178-200 mmol / 100g, the negative charge carried by montmorillonite is relatively large, and it has a strong cation adsorption capacity. It can effectively inhibit the dissolution of manganese in lithium-rich manganese-based materials during cycling or storage, thereby making the positive electrode active material have a low manganese dissolution. Batteries containing this positive electrode active material have good cycle performance and storage performance.

[0053] In some embodiments, the specific surface area of ​​montmorillonite is 100-200 m². 2 / g. In some embodiments, the specific surface area of ​​montmorillonite is 185-200 m² / g. 2 / g.

[0054] When the specific surface area of ​​montmorillonite is 185-200m² 2 At a concentration of / g, montmorillonite has a strong cation adsorption capacity, which can effectively inhibit the dissolution of manganese in lithium-rich manganese-based materials during cycling or storage, thereby resulting in a lower manganese dissolution of the positive electrode active material. Batteries containing this positive electrode active material have good cycle performance and storage performance.

[0055] In some implementations, the coating layer is substantially composed of montmorillonite.

[0056] In this document, the phrase "substantially composed of..." is intended to include any of the elements listed herein, but is limited to other components that do not interfere with or contribute to the effect of the listed elements. Therefore, in this application, "the coating layer is substantially composed of montmorillonite" covers situations where elements or substances in the lithium-rich manganese-based material, as well as other materials, liquids, etc., in contact with the coating layer dissolve or transfer into the coating layer; in such cases, it is still considered that "the coating layer is substantially composed of montmorillonite".

[0057] In some embodiments, the specific surface area of ​​the positive electrode active material is ≤2m². 2 / g. In some embodiments, the specific surface area of ​​the positive electrode active material is 1.6-2m². 2 / g, preferably 1.6-1.8m 2 / g.

[0058] When the specific surface area of ​​the positive electrode active material is 1.6-2m² 2 At / g, the positive electrode active material has a lower manganese leaching amount. Batteries containing this positive electrode active material have higher 0.1C coin discharge capacity, 0.33C coin discharge capacity, first efficiency and 100cls energy retention rate at 25°C, thus exhibiting better cycle performance and storage performance.

[0059] When the specific surface area of ​​the positive electrode active material is 1.6-1.8 m² 2 At / g, the positive electrode active material has a further lower manganese dissolution, and the battery containing this positive electrode active material has a further higher 0.1C coin discharge capacity, 0.33C coin discharge capacity, first efficiency and 100cls energy retention rate at 25°C, thus having further superior cycle performance and storage performance.

[0060] In some embodiments, the median particle size Dv50 of the positive electrode active material is 1-20 μm. In some embodiments, the median particle size Dv50 of the positive electrode active material is 8-20 μm or 8.6-20 μm. In some embodiments, the median particle size Dv50 of the positive electrode active material is 10-20 μm or 10.5-20 μm. In some embodiments, the median particle size Dv50 of the positive electrode active material is 13-20 μm or 13.2-20 μm. In some embodiments, the median particle size Dv50 of the positive electrode active material is 15-20 μm.

[0061] When the median particle size Dv50 of the positive electrode active material is 15-20 μm, the positive electrode active material has a lower manganese dissolution amount. Batteries containing this positive electrode active material have higher 0.1C coin discharge capacity, 0.33C coin discharge capacity, first efficiency and 100cls energy retention rate at 25℃, thus having better cycle performance and storage performance.

[0062] In some embodiments, the dislocation density of the positive electrode active material is ≤5*10 11 Preferably ≤4*10 11 Preferred size ≤2.5*10 11 In some embodiments, the dislocation density of the positive electrode active material is 2*102 11 Up to 5*10 11 In some embodiments, the dislocation density of the positive electrode active material is 2*102 11 Up to 4*10 11 .

[0063] The positive electrode active material has a low dislocation density, which can effectively reduce stacking faults and stress, improve voltage decay during cycling, and thus have better cycling performance and storage performance.

[0064] In some embodiments, the manganese leaching amount of the positive electrode active material is ≤50, preferably ≤40, preferably ≤30, preferably ≤25, and preferably ≤20.

[0065] A second aspect of this application also provides a method for preparing the positive electrode active material or the material of the first aspect of this application, the method comprising the following steps:

[0066] (1) Disperse the lithium-rich manganese-based material in a solvent;

[0067] (2) Mix the product from step (1) with montmorillonite and dry it;

[0068] (3) Sinter the product from step (2).

[0069] In some implementations, in step (1), the pH is adjusted to 2-5.

[0070] By dispersing lithium-rich manganese-based materials under acidic conditions, montmorillonite can be modified, resulting in a higher specific surface area and a more uniform pore size distribution. This improves the cation adsorption capacity of montmorillonite and allows a spinel layer to form on the surface of the lithium-rich manganese-based materials. Consequently, secondary batteries containing positive electrode active materials exhibit higher 0.1C coin discharge capacity, 0.33C coin discharge capacity, first-cycle efficiency, and energy retention rate after 100cls cycling at 25°C, thus demonstrating excellent cycle performance and storage performance.

[0071] In some embodiments, in step (1), the pH is adjusted by adding one or more of citric acid, ammonium sulfate, ammonium persulfate, or ammonium dihydrogen phosphate.

[0072] In some embodiments, in step (1), the solvent includes water and ethanol.

[0073] In some embodiments, the sintering is performed at 300-500°C in step (3).

[0074] Uniform coating can be achieved at a lower sintering temperature, reducing the amount of manganese leaching from the positive electrode active material. This results in secondary batteries containing this positive electrode active material having higher 0.1C coin discharge capacity, 0.33C coin discharge capacity, first-cycle efficiency, and 100cls energy retention rate at 25°C, thus exhibiting good cycle performance and storage performance.

[0075] In some implementations, the method includes the following steps:

[0076] (1) Disperse the lithium-rich manganese-based material in a solvent and adjust the pH of the solution to 2-5;

[0077] (2) Mix the product from step (1) with montmorillonite, stir at room temperature for 10-60 min, keep the stirring speed at 300-500 rpm, filter and dry after stirring for 5-30 min.

[0078] (3) Sinter the product from step (2) in an air atmosphere at 300-500℃ for 5-10 hours.

[0079] A third aspect of this application provides a positive electrode sheet comprising the positive electrode active material of the first aspect of this application or the positive electrode active material prepared according to the method of the second aspect of this application.

[0080] A fourth aspect of this application provides a secondary battery that includes the positive electrode sheet of the third aspect of this application.

[0081] The fifth aspect of this application provides an electrical device including the secondary battery of the fourth aspect of this application.

[0082] In addition, the secondary battery and power-consuming device of this application will be described below with appropriate reference to the accompanying drawings.

[0083] In one embodiment of this application, a secondary battery is provided.

[0084] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0085] [Positive electrode plate]

[0086] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including the positive electrode active material of the first aspect of this application.

[0087] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0088] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0089] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0090] In some embodiments, the positive electrode film 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.

[0091] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0092] [Negative electrode plate]

[0093] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0094] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0095] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0096] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include 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. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material 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 materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0097] In some embodiments, the negative electrode film 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).

[0098] In some embodiments, the negative electrode film 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.

[0099] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0100] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0101] [Electrolytes]

[0102] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0103] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0104] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0105] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0106] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0107] [Isolation membrane]

[0108] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0109] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0110] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0111] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0112] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0113] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured secondary battery 5.

[0114] In some implementations, refer to Figure 2 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0115] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0116] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0117] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0118] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0119] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0120] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0121] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0122] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0123] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0124] Example

[0125] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0126] Example 1

[0127] (1) The lithium-rich manganese-based material 0.35Li2MnO3·0.65LiNi 0.46 Co 0.09 Mn 0.45 O2 is uniformly dispersed in the aqueous solution, and citric acid is added to adjust the pH of the solution to 2;

[0128] (2) Add montmorillonite to the above solution, stir at room temperature for 10 min, keep the stirring speed at 300 rpm, stir for 5 min, filter and dry.

[0129] (3) The dried sample was sintered at 300°C in air atmosphere for 5 hours and then naturally cooled to room temperature to obtain lithium-rich manganese-based montmorillonite composite cathode material.

[0130] Example 2

[0131] (1) The lithium-rich manganese-based material 0.35Li2MnO3·0.65LiNi 0.46 Co 0.09 Mn 0.45 O2 is uniformly dispersed in the aqueous solution, and ammonium sulfate is added to adjust the pH of the solution to 3;

[0132] (2) Add montmorillonite to the above solution, stir at room temperature for 20 min, keep the stirring speed at 400 rpm, filter and dry after stirring for 20 min;

[0133] (3) The dried sample was sintered at 400℃ in air atmosphere for 8 hours, and then naturally cooled to room temperature to obtain lithium-rich manganese-based montmorillonite composite cathode material.

[0134] Example 3

[0135] (1) The lithium-rich manganese-based material 0.35Li2MnO3·0.65LiNi 0.46 Co 0.09 Mn 0.45 O2 is uniformly dispersed in the aqueous solution, and ammonium persulfate is added to adjust the pH of the solution to 5;

[0136] (2) Add montmorillonite to the above solution, stir at room temperature for 60 min, keep the stirring speed at 500 rpm, stir for 30 min, filter and dry.

[0137] (3) The dried sample was sintered at 500°C in air atmosphere for 10 hours and then naturally cooled to room temperature to obtain lithium-rich manganese-based montmorillonite composite cathode material.

[0138] Example 4

[0139] (1) The lithium-rich manganese-based material 0.35Li2MnO3·0.65LiNi 0.45 Co 0.09 Mn 0.45 Mg 0.01 O2 is uniformly dispersed in the solvent, and ammonium dihydrogen phosphate is added to adjust the pH of the solution to 2.5;

[0140] (2) Add montmorillonite to the above solution, stir at room temperature for 60 min, keep the stirring speed at 500 rpm, stir for 30 min, filter and dry.

[0141] (3) The dried sample was sintered at 350°C in air atmosphere for 10 hours and then naturally cooled to room temperature to obtain lithium-rich manganese-based montmorillonite composite cathode material.

[0142] Example 5

[0143] (1) The lithium-rich manganese-based material 0.35Li2MnO3·0.65LiNi 0.45 Co 0.09 Mn 0.45 Al 0.01 O2 was uniformly dispersed in ethanol, and citric acid was added to adjust the pH of the solution to 3.5;

[0144] (2) Add montmorillonite to the above solution, stir at room temperature for 60 min, keep the stirring speed at 500 rpm, stir for 30 min, filter and dry.

[0145] (3) The dried sample was sintered at 450°C in air atmosphere for 10 hours and then naturally cooled to room temperature to obtain lithium-rich manganese-based montmorillonite composite cathode material.

[0146] Example 6

[0147] (1) The lithium-rich manganese-based material 0.35Li2MnO3·0.65LiNi 0.46 Co 0.09 Mn 0.45 O2 is uniformly dispersed in the aqueous solution, and ammonium sulfate is added to adjust the pH of the solution to 4.5;

[0148] (2) Add montmorillonite to the above solution, stir at room temperature for 60 min, keep the stirring speed at 500 rpm, stir for 30 min, filter and dry.

[0149] (3) The dried sample was sintered at 360°C in air atmosphere for 10 hours and then naturally cooled to room temperature to obtain lithium-rich manganese-based montmorillonite composite cathode material.

[0150] Example 7

[0151] (1) The lithium-rich manganese-based material 0.35Li2MnO3·0.65LiNi 0.46 Co 0.09 Mn 0.45 O2 was uniformly dispersed in ethanol, and citric acid was added to adjust the pH of the solution to 4.3;

[0152] (2) Add montmorillonite to the above solution, stir at room temperature for 60 min, keep the stirring speed at 500 rpm, stir for 30 min, filter and dry.

[0153] (3) The dried sample was sintered at 420°C in air atmosphere for 10 hours and then naturally cooled to room temperature to obtain lithium-rich manganese-based montmorillonite composite cathode material.

[0154] Example 8

[0155] (1) The lithium-rich manganese-based material 0.35Li2MnO3·0.65LiNi 0.46 Co 0.09 Mn 0.45 O2 was uniformly dispersed in the solvent, and ammonium persulfate was added to adjust the pH of the solution to 2.3;

[0156] (2) Add montmorillonite to the above solution, stir at room temperature for 60 min, keep the stirring speed at 500 rpm, stir for 30 min, filter and dry.

[0157] (3) The dried sample was sintered at 500°C in air atmosphere for 10 hours and then naturally cooled to room temperature to obtain lithium-rich manganese-based montmorillonite composite cathode material.

[0158] Example 9

[0159] (1) The lithium-rich manganese-based material 0.35Li2MnO3·0.65LiNi 0.46 Co 0.09 Mn 0.45 O2 is uniformly dispersed in the aqueous solution, and ammonium sulfate is added to adjust the pH of the solution to 2.6;

[0160] (2) Add montmorillonite to the above solution, stir at room temperature for 60 min, keep the stirring speed at 500 rpm, stir for 30 min, filter and dry.

[0161] (3) The dried sample was sintered at 470°C in air atmosphere for 10 hours and then naturally cooled to room temperature to obtain lithium-rich manganese-based montmorillonite composite cathode material.

[0162] Example 10

[0163] (1) The lithium-rich manganese-based material 0.35Li2MnO3·0.65LiNi 0.46 Co 0.09 Mn 0.45 O2 is uniformly dispersed in the aqueous solution, and ammonium dihydrogen phosphate is added to adjust the pH of the solution to 3.2;

[0164] (2) Add montmorillonite to the above solution, stir at room temperature for 60 min, keep the stirring speed at 500 rpm, stir for 30 min, filter and dry.

[0165] (3) The dried sample was sintered at 350°C in air atmosphere for 10 hours and then naturally cooled to room temperature to obtain lithium-rich manganese-based montmorillonite composite cathode material.

[0166] Comparative Example 1

[0167] Same as Example 2, except that montmorillonite is not added, thus obtaining a lithium-rich manganese-based cathode material.

[0168] Comparative Example 2

[0169] Same as Example 9, except that the amount and thickness of montmorillonite coating are different, as shown in Table 1 below.

[0170] Comparative Example 3

[0171] Same as Example 9, except that the amount and thickness of montmorillonite coating are different, as shown in Table 1 below.

[0172] The relevant parameters of the cathode materials of Examples 1-10 and Comparative Examples 1-3 are shown in Table 1 below.

[0173] Table 1: Parameters of Examples 1-10 and Comparative Examples 1-3

[0174]

[0175] In addition, as described below, the positive electrode active materials obtained in Examples 1-10 and Comparative Examples 1-3 were respectively prepared into coin cells, and the performance of the positive electrode active materials and coin cells was tested. The test results are shown in Table 2 below.

[0176] (1) Coverage

[0177] The coating amount was measured using an inductively coupled plasma optical emission spectrometer (ICP-OES) and the following steps were followed: First, 1 g of the positive electrode material coated with montmorillonite was weighed into a beaker. 25 mL of 25% HNO3 solution was added to the material to dissolve it, and then it was diluted with 475 mL of deionized water. The diluted liquid was then placed in an inductively coupled plasma optical emission spectrometer (Thermo Fisher Scientific ICAP7400, USA) for target element analysis, and the coating amount of montmorillonite was calculated.

[0178] (2) Coating thickness

[0179] The electrode sheet before cold pressing was cut into 6cm*6cm samples with scissors, and then polished using an IB-19500CP ion section polisher to obtain polished samples with cut surfaces. The samples were then tested using a ZEISS sigma 300 instrument according to standard JY / T010-1996. Ten different locations were randomly selected from the test samples for testing, and the average value was used to obtain the coating thickness.

[0180] (3) Cation exchange capacity

[0181] The cation exchange capacity was determined according to the national standard JC / T593-1995. Montmorillonite samples were treated with an extractant containing the indicator cation NH4+ to displace all exchangeable cations in the sample into the extract, and the sample was saturated with adsorbed indicator cations converted to ammonium groups. The ammonium groups were then separated from the extract, and the potassium, sodium, calcium, and magnesium ions in the extract were measured to determine the corresponding exchangeable cation amounts.

[0182] (4) Specific surface area

[0183] The specific surface area was measured according to GB / T 19587-2017, using the nitrogen adsorption specific surface area analysis method, and calculated using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis was performed using a Tri-Star3020 specific surface area and pore size analyzer from Micromeritics, USA.

[0184] (5) Median particle size Dv50 of positive electrode active material

[0185] Equipment model: Malvern 3000 (MasterSizer 3000) laser particle size analyzer; reference standard procedure: GB / T19077-2016; specific test procedure: take an appropriate amount of the sample to be tested (the sample concentration should be 8-12% light-blocking degree), add 20ml of deionized water, and simultaneously incubate for 5 minutes (53KHz / 120W) to ensure that the sample is completely dispersed. Then, measure the sample according to the GB / T19077-2016 standard.

[0186] (6) Dislocation density

[0187] The XRD result based on X-ray diffraction is β = (1 / D). 2 ×10 16 Where D = Kλ / Bcosθ, K = 0.9, λ = 1.5406, B is the full width at half maximum (FWHM) of the lithium-rich manganese-based cathode material (hkl) in the XRD diffraction pattern, and θ is the diffraction angle.

[0188] (7) Manganese leaching

[0189] 1g of positive electrode active material was added to 200ml of 0.2wt% ascorbic acid solution. After stirring magnetically for 5min, the solution was allowed to stand for 24min, and then stirred magnetically for 1min. The solution was filtered through a glass funnel lined with filter paper. The filtrate was then diluted 100 times with 0.2wt% ascorbic acid solution. The manganese content in the filtrate was determined by inductively coupled plasma optical emission spectrometry (ICP-OES).

[0190] (8) Preparation of button cells

[0191] Carbon black (SP) was used as a conductive agent, polyvinylidene fluoride (PVDF) as a binder, and N-methylpyrrolidone (NMP) as a solvent. PVDF and NMP were mixed in a mass ratio of 2:8 to form a gel, and a positive electrode slurry was prepared according to a mass ratio of positive electrode active material, SP, and PVDF of 90:7:3. The positive electrode slurry was uniformly coated onto aluminum foil (13 μm thick) using a scraper and dried in a vacuum oven at 100°C for 12 hours. The aluminum foil was then stamped into a 12 mm diameter disc. A lithium metal sheet was used as the negative electrode, a Celgard 2325 separator was employed, and the electrolyte was a 1.0 mol / L LiPF6 EC / DMC solution (volume ratio 1:1), thus producing a CR2032 coin cell.

[0192] (9) Button battery test

[0193] The CR2032 coin cell half-cells prepared above were placed on a blue battery testing cabinet and activated by charge-discharge at rates of 0.1C, 0.33C, and 0.5C. Then, they were cycled at 1C for 100 cls at 25°C, with a charge-discharge voltage range of 2.5-4.6V. Initial efficiency (%) = (0.1C first-cycle discharge capacity / 0.1C first-cycle discharge capacity) × 100%. Battery capacity retention rate after 100 cls at 25°C (%) = (discharge capacity after 100 cycles / discharge capacity on the 4th cycle) × 100%.

[0194] Table 2: Performance test results of Examples 1-10 and Comparative Examples 1-3

[0195]

[0196] Based on the above results, the positive electrode active materials in Examples 1-10 all include a lithium-rich manganese-based material matrix and a montmorillonite coating layer. The montmorillonite coating amount is 1000-5000 ppm, and the coating layer thickness is 0.05-1 μm based on the weight of the lithium-rich manganese-based material. A comparison between Examples 1-10 and Comparative Examples 1-3 shows that this positive electrode active material has a lower manganese leaching amount. Batteries containing this positive electrode active material exhibit higher 0.1C coin discharge capacity, 0.33C coin discharge capacity, first-cycle efficiency, and energy retention rate after 100 cls cycling at 25°C, indicating superior cycle performance and storage performance.

[0197] As can be seen from the comparison between Example 9 and Comparative Examples 2-3, when the montmorillonite coating amount is 1000-5000 ppm (based on the weight of lithium-rich manganese-based material) and the coating thickness is 0.05-1 μm, the positive electrode active material has a lower manganese dissolution and dislocation density. The battery containing this positive electrode active material has a higher 0.1C coin discharge capacity, 0.33C coin discharge capacity, first-efficiency and 100cls energy retention rate at 25°C, thus indicating better cycle performance and storage performance.

[0198] As can be seen from the comparison of Examples 3, 6, 8 and Examples 1-2, 4-5, 7, 9-10, when the montmorillonite coating amount is 4000-5000 ppm (based on the weight of lithium-rich manganese-based material), the positive electrode active material has a lower manganese leaching amount. The battery containing this positive electrode active material has a higher 0.1C coin discharge capacity, 0.33C coin discharge capacity, first efficiency and 100cls energy retention rate at 25°C, thus indicating better cycle performance and storage performance.

[0199] As can be seen from the comparison of Examples 6 and 8 and Examples 1-3, 4-5, 7, 9-10, when the montmorillonite coating amount is 4500-5000 ppm (based on the weight of lithium-rich manganese-based material), the positive electrode active material has a lower manganese leaching amount. The battery containing this positive electrode active material has a higher 0.1C coin discharge capacity, 0.33C coin discharge capacity, first efficiency and 100cls energy retention rate at 25°C, thus indicating better cycle performance and storage performance.

[0200] As can be seen from the comparison of Examples 3, 6, 8 and Examples 1-2, 4-5, 7, 9-10, when the thickness of the coating layer is 0.7-1 μm, the positive electrode active material has a lower manganese leaching amount. The battery containing the positive electrode active material has a higher 0.1C coin discharge capacity, 0.33C coin discharge capacity, first efficiency and energy retention rate after 100cls cycling at 25°C, thus indicating better cycle performance and storage performance.

[0201] As can be seen from the comparison of Examples 6 and 8 and Examples 1-3, 4-5, 7, 9-10, when the thickness of the coating layer is 0.95-1 μm, the positive electrode active material has a lower manganese leaching amount. The battery containing the positive electrode active material has a higher 0.1C coin discharge capacity, 0.33C coin discharge capacity, first efficiency and energy retention rate after 100cls cycling at 25°C, thus indicating better cycle performance and storage performance.

[0202] As can be seen from the comparison of Examples 3, 6, 8 and Examples 1-2, 4-5, 7, 9-10, the specific surface area of ​​the positive electrode active material is 1.6-2 m². 2 At / g, the positive electrode active material has a lower manganese leaching amount, and the battery containing this positive electrode active material has a higher 0.1C coin discharge capacity, 0.33C coin discharge capacity, first efficiency and 100cls energy retention rate at 25°C, thus indicating better cycle performance and storage performance.

[0203] A comparison of Examples 6 and 8 with Examples 1-3, 4-5, 7, and 9-10 shows that the specific surface area of ​​the positive electrode active material is 1.6-1.8 m². 2 At / g, the positive electrode active material has a lower manganese leaching amount, and the battery containing this positive electrode active material has a higher 0.1C coin discharge capacity, 0.33C coin discharge capacity, first efficiency and 100cls energy retention rate at 25°C, thus indicating better cycle performance and storage performance.

[0204] As can be seen from the comparison of Examples 6 and 8 and Examples 1-3, 4-5, 7, 9-10, when the median particle size Dv50 of the positive electrode active material is 15-20 μm, the positive electrode active material has a lower manganese dissolution. The battery containing this positive electrode active material has a higher 0.1C coin discharge capacity, 0.33C coin discharge capacity, first efficiency and energy retention rate after 100cls cycling at 25°C, thus indicating better cycle performance and storage performance.

[0205] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A positive electrode active material, the positive electrode active material comprising a matrix and a coating layer, the matrix comprising a lithium-rich manganese-based material, the lithium-rich manganese-based material having the formula xLi2MnO3•(1 - x)LiNi y Co z Mn a M 1-y-z-a O2, where 0 < x < 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, 0 ≤ a ≤ 1, 0 < y + z + a ≤ 1, and M is one or more of Mg, B, Al, V, Ti, Zr, Sn, and Mo, The coating layer contains montmorillonite, the amount of montmorillonite is 1000-5000 ppm, and the thickness of the coating layer is 0.05-1 μm based on the weight of the lithium-rich manganese-based material.

2. The positive electrode active material according to claim 1, wherein the montmorillonite coating amount is 4000-5000 ppm, based on the weight of the lithium-rich manganese-based material.

3. The positive electrode active material according to claim 2, wherein the montmorillonite coating amount is 4500-5000 ppm, based on the weight of the lithium-rich manganese-based material.

4. The positive electrode active material according to any one of claims 1-3, wherein the thickness of the coating layer is 0.7-1 μm.

5. The positive electrode active material according to claim 4, wherein the thickness of the coating layer is 0.95-1 μm.

6. The positive electrode active material according to any one of claims 1-5, wherein the montmorillonite has a cation exchange capacity of 178-200 mmol / 100g.

7. The positive electrode active material according to any one of claims 1-6, wherein the specific surface area of ​​the montmorillonite is 185-200 m². 2 / g.

8. The positive electrode active material according to any one of claims 1-7, wherein the specific surface area of ​​the positive electrode active material is 1.6-2 m². 2 / g.

9. The positive electrode active material according to claim 8, wherein the specific surface area of ​​the positive electrode active material is 1.6-1.8 m². 2 / g.

10. The positive electrode active material according to any one of claims 1-9, wherein the median particle size Dv50 of the positive electrode active material is 15-20µm.

11. A method for preparing a positive electrode active material according to any one of claims 1-10, the method comprising the following steps: (1) Disperse the lithium-rich manganese-based material in a solvent; (2) Mix the product from step (1) with montmorillonite and dry it; (3) Sinter the product from step (2).

12. A positive electrode sheet, the positive electrode sheet comprising a positive electrode active material as described in any one of claims 1-10 or a positive electrode active material prepared by the method as described in claim 11.

13. A secondary battery comprising the positive electrode sheet as described in claim 12.

14. An electrical device comprising the secondary battery of claim 13.

Images