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

Abstract

The invention provides a positive active material, a preparation method thereof, a positive pole piece, a secondary battery and an electric device. In particular, the present disclosure provides a positive electrode active material comprising a substrate and a cladding layer, the substrate comprising a lithium-rich manganese-based material having the formula xLi2MnO3. (1-x) LiNiyCozMnaM1-y-z-aO2, where 0 lt; xlt; 0 < = y < = 1, 0 < = z < = 1, 0 < = a < = 1, 0 lt; the lithium-rich manganese-based material comprises a lithium-rich manganese-based material and a coating layer, y + z + a is less than or equal to 1, M is one or more of Mg, B, Al, V, Ti, Zr, Sn and Mo, the coating layer comprises montmorillonite, the coating amount of the montmorillonite is 1000-5000 ppm, and the thickness of the coating layer is 0.05-1 mu m based on the weight of the lithium-rich manganese-based material.

Description

Technical Field

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

[0002] The lithium-rich manganese-based material has advantages such as high theoretical capacity, high voltage platform, low cost, no pollution, and good safety, and is considered to be the most promising positive electrode material for the next generation of 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] The present 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 sheet, 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 the above object can be achieved by adopting the technical solution of the present invention.

[0005] The first aspect of the present 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 the present application has a low manganese dissolution amount, and the secondary battery containing the 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 coating amount of montmorillonite is 4000-5000ppm, the positive electrode active material has a lower manganese dissolution amount, and the battery containing the positive electrode active material has better cycle performance and storage performance. When the coating amount of montmorillonite is 4500-5000ppm, the positive electrode active material has a further lower manganese dissolution amount, and the battery containing the positive electrode active material has further better cycle performance and storage performance.

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

[0010] When the thickness of the coating layer is 0.7-1 μm, the positive electrode active material has a lower manganese dissolution amount, and the battery containing the positive electrode active material has better cycle performance and storage performance. When the thickness of the coating layer is 0.95-1 μm, the positive electrode active material has a further lower manganese dissolution amount, and the battery containing the positive electrode active material has further better cycle performance and storage performance.

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

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

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

[0014] When the specific surface area of ​​the positive electrode active material is 1.6-2m 2 / g, the positive electrode active material has a lower manganese dissolution amount, and the battery containing the positive electrode active material has better cycle performance and storage performance. When the specific surface area of ​​the positive electrode active material is 1.6-1.8m 2 / g, the positive electrode active material has a further lower manganese dissolution amount, and the battery containing the positive electrode active material has further 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 dissolution amount, and a battery containing the positive electrode active material has better cycle performance and storage performance.

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

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

[0019] (2) mixing the product of step (1) with montmorillonite and drying;

[0020] (3) Sintering the product of step (2).

[0021] The third aspect of the present application provides a positive electrode plate, which includes the positive electrode active material of the first aspect of the present application or the positive electrode active material prepared according to the method of the second aspect of the present application.

[0022] The fourth aspect of the present application provides a secondary battery, which includes the positive electrode plate of the third aspect of the present application.

[0023] A fifth aspect of the present application provides an electrical device, comprising the secondary battery of the fourth aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0026] Figure 3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0027] Figure 4 It is a schematic diagram of a battery pack according to one embodiment of the present application.

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

[0029] Figure 6 FIG. 1 is a schematic diagram of an electric device using a secondary battery according to an embodiment of the present application as a power source.

[0030] Description of reference numerals:

[0031] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 top cover assembly DETAILED DESCRIPTION

[0032] Below, the embodiments of the positive electrode active material and its manufacturing method, positive electrode sheet, secondary battery and electrical device of the present application are specifically disclosed with appropriate reference to the drawings. However, there are cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0033] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0034] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0035] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0036] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0037] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0038] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": 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 the lithium-rich manganese-based material is charged at a high voltage of more than 4.5V in the first cycle, some lithium ions in the transition metal layer will form Li2O together with oxygen and escape. The formation of a large number of oxygen vacancies causes the bond energy between the transition metal ions and oxygen to continue to weaken, causing the transition metal ions (especially manganese) to migrate and dissolve, resulting in the instability of the positive electrode active material structure, and further causing the battery's cycle performance and storage performance to deteriorate.

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

[0041] [Positive electrode active material]

[0042] The first aspect of the present application provides a positive electrode active material, the positive electrode active material comprising a substrate and a coating layer, the substrate comprising a lithium-rich manganese-based material, the lithium-rich manganese-based material having a formula of 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, and the coating amount of the montmorillonite is 1000 - 5000 ppm, based on the weight of the lithium-rich manganese-based material. 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 matrix of the lithium-rich manganese-based material. This part may or may not completely coat the matrix of the lithium-rich manganese-based material. 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 matrix of the lithium-rich manganese-based material along the normal direction of the matrix of the lithium-rich manganese-based material.

[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 the lithium-rich manganese-based material, effectively improving the structural stability of the material, and protecting the material from the erosion of the by-product hydrofluoric acid of the electrolyte, making the cathode active material of the present application have a low manganese dissolution amount. The secondary battery containing this cathode active material has a higher 0.1C discharge capacity, 0.33C discharge capacity, initial efficiency, and 25°C cycle 100cls energy retention rate, 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. The battery containing this cathode active material has a higher 0.1C discharge capacity, 0.33C discharge capacity, initial efficiency, and 25°C cycle 100cls energy retention rate, 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. The battery containing this cathode active material has an even higher 0.1C discharge capacity, 0.33C discharge capacity, initial efficiency, and 25°C cycle 100cls energy retention rate, thus having even better cycling performance and storage performance.

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

[0049] When the thickness of the coating layer is 0.7-1 μm, the positive electrode active material has a lower manganese dissolution amount, and the battery containing the positive electrode active material has higher 0.1C charge-discharge capacity, 0.33C charge-discharge capacity, first efficiency and 25°C cycle 100cls energy retention rate, thereby having better cycle performance and storage performance.

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

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

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

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

[0054] When the specific surface area of ​​montmorillonite is 185-200m 2 / g, montmorillonite has a strong cation adsorption capacity, which can effectively inhibit the manganese dissolution of lithium-rich manganese-based materials during circulation or storage, so that the positive electrode active material has a lower manganese dissolution amount, and the battery containing the positive electrode active material has good cycle performance and storage performance.

[0055] In some embodiments, the coating consists essentially of montmorillonite.

[0056] In this article, the expression "consisting essentially of..." is intended to include any of the elements listed therein, and is limited to other components that do not interfere with or contribute to the effects of the listed elements. Therefore, in this application, "the coating layer is substantially composed of montmorillonite" covers the situation where elements or substances in the lithium-rich manganese-based material and other materials, liquids, etc. in contact with the coating layer are dissolved or transferred into the coating layer, and in this case, 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 ≤ 2 m 2 In some embodiments, the specific surface area of ​​the positive electrode active material is 1.6-2 m 2 / g, preferably 1.6-1.8m 2 / g.

[0058] When the specific surface area of ​​the positive electrode active material is 1.6-2m 2 / g, the positive electrode active material has a lower manganese dissolution amount, and the battery containing the positive electrode active material has higher 0.1C charge-discharge capacity, 0.33C charge-discharge capacity, first efficiency and 25°C cycle 100cls energy retention rate, thereby having better cycle performance and storage performance.

[0059] When the specific surface area of ​​the positive electrode active material is 1.6-1.8m 2 / g, the positive electrode active material has a further lower manganese dissolution amount, and the battery containing the positive electrode active material has further higher 0.1C charge-discharge capacity, 0.33C charge-discharge capacity, first efficiency and 25°C cycle 100cls energy retention rate, thereby having further better 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 15-20μm, the positive electrode active material has a lower manganese dissolution amount, and the battery containing the positive electrode active material has higher 0.1C charge-discharge capacity, 0.33C charge-discharge capacity, first efficiency and 25℃ cycle 100cls energy retention rate, thereby 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 , preferably ≤2.5*10 11 In some embodiments, the dislocation density of the positive electrode active material is 2*10 11 Up to 5*10 11 In some embodiments, the dislocation density of the positive electrode active material is 2*10 11 Up to 4*10 11 .

[0063] The positive electrode active material has a lower dislocation density, which can effectively reduce stacking faults and stress and improve voltage decay during the cycle process, thereby having better cycle performance and storage performance.

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

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

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

[0067] (2) mixing the product of step (1) with montmorillonite and drying;

[0068] (3) Sintering the product of step (2).

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

[0070] By dispersing the lithium-rich manganese-based material under acidic conditions, montmorillonite can be modified so that the montmorillonite has a higher specific surface area and a more uniform pore size distribution, which is beneficial to improving the cation adsorption capacity of the montmorillonite. At the same time, a spinel layer can be formed on the surface of the lithium-rich manganese-based material, so that the secondary battery containing the positive electrode active material has a higher 0.1C charge-discharge capacity, 0.33C charge-discharge capacity, first efficiency and 25°C cycle 100cls energy retention rate, thereby having good 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, in step (3), the sintering is performed at 300-500°C.

[0074] Uniform coating can be achieved at a lower sintering temperature, reducing the manganese dissolution amount of the positive electrode active material, so that the secondary battery containing the positive electrode active material has higher 0.1C charge-discharge capacity, 0.33C charge-discharge capacity, first efficiency and 25°C cycle 100cls energy retention rate, thereby having good cycle performance and storage performance.

[0075] In some embodiments, the method comprises the following steps:

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

[0077] (2) mixing the product of step (1) with montmorillonite, stirring at room temperature for 10-60 min, maintaining the stirring speed at 300-500 rpm, stirring for 5-30 min, then filtering and drying;

[0078] (3) Sintering the product of step (2) at 300-500° C. in an air atmosphere for 5-10 hours.

[0079] The third aspect of the present application provides a positive electrode plate, which includes the positive electrode active material of the first aspect of the present application or the positive electrode active material prepared according to the method of the second aspect of the present application.

[0080] The fourth aspect of the present application provides a secondary battery, which includes the positive electrode plate of the third aspect of the present application.

[0081] A fifth aspect of the present application provides an electrical device, comprising the secondary battery of the fourth aspect of the present application.

[0082] In addition, the secondary battery and the electric device of the present application will be described below with reference to the drawings as appropriate.

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

[0084] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0085] [Positive electrode]

[0086] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes the positive electrode active material of the first aspect of the present application.

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

[0088] In some embodiments, the positive electrode 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 material base and a metal layer formed on at least one surface of the polymer material base. 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 material 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 further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0090] In some embodiments, the positive electrode film layer may further include a conductive agent, which may include, for example, at least one of 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 in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0092] [Negative electrode]

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

[0094] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one 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, as the metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0096] In some embodiments, the negative electrode active material may adopt the negative electrode active material for the battery known in the art. 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, 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, the present application is not limited to these materials, and other traditional 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 further 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 layer may further include a conductive agent, which 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 layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0100] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0101] [Electrolytes]

[0102] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

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

[0104] In some embodiments, the electrolyte salt can 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 difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

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

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

[0107] [Isolation film]

[0108] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.

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

[0110] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0111] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0112] In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0113] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. Figure 1 The secondary battery 5 is a square structure as an example.

[0114] In some embodiments, reference Figure 2 , the outer packaging may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

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

[0116] Figure 3 4 is an example of a battery module. Figure 3 In the battery module 4, the plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of secondary batteries 5 may be fixed by fasteners.

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

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

[0119] Figure 4 and Figure 5 1 is a battery pack 1 as an example. Figure 4 and Figure 5The battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0120] In addition, the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, and can also be used as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as 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., but are not limited thereto.

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

[0122] Figure 6 The power consumption device is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the high power and high energy density requirements of the power consumption device for the secondary battery, a battery pack or a battery module can be used.

[0123] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.

[0124] Example

[0125] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0126] Example 1

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

[0128] (2) adding montmorillonite to the above solution, stirring at room temperature for 10 min, maintaining the stirring speed at 300 rpm, stirring for 5 min, filtering and drying;

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

[0130] Example 2

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

[0132] (2) adding montmorillonite to the above solution, stirring at room temperature for 20 min, maintaining the stirring speed at 400 rpm, stirring for 20 min, filtering and drying;

[0133] (3) The obtained dried sample was sintered at 400° C. in an air atmosphere for 8 h, and then naturally cooled to room temperature to obtain a lithium-rich manganese-based-montmorillonite composite positive electrode material.

[0134] Example 3

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

[0136] (2) adding montmorillonite to the above solution, stirring at room temperature for 60 min, maintaining the stirring speed at 500 rpm, stirring for 30 min, filtering and drying;

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

[0138] Example 4

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

[0140] (2) adding montmorillonite to the above solution, stirring at room temperature for 60 min, maintaining the stirring speed at 500 rpm, stirring for 30 min, filtering and drying;

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

[0142] Example 5

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

[0144] (2) adding montmorillonite to the above solution, stirring at room temperature for 60 min, maintaining the stirring speed at 500 rpm, stirring for 30 min, filtering and drying;

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

[0146] Example 6

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

[0148] (2) adding montmorillonite to the above solution, stirring at room temperature for 60 min, maintaining the stirring speed at 500 rpm, stirring for 30 min, filtering and drying;

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

[0150] Example 7

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

[0152] (2) adding montmorillonite to the above solution, stirring at room temperature for 60 min, maintaining the stirring speed at 500 rpm, stirring for 30 min, filtering and drying;

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

[0154] Example 8

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

[0156] (2) adding montmorillonite to the above solution, stirring at room temperature for 60 min, maintaining the stirring speed at 500 rpm, stirring for 30 min, filtering and drying;

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

[0158] Example 9

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

[0160] (2) adding montmorillonite to the above solution, stirring at room temperature for 60 min, maintaining the stirring speed at 500 rpm, stirring for 30 min, filtering and drying;

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

[0162] Example 10

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

[0164] (2) adding montmorillonite to the above solution, stirring at room temperature for 60 min, maintaining the stirring speed at 500 rpm, stirring for 30 min, filtering and drying;

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

[0166] Comparative Example 1

[0167] The same as Example 2, the only difference is that no montmorillonite is added, thereby obtaining a lithium-rich manganese-based positive electrode material.

[0168] Comparative Example 2

[0169] The same as Example 9, the only difference is that the coating amount and coating thickness of montmorillonite are different, please see the following Table 1 for details.

[0170] Comparative Example 3

[0171] The same as Example 9, the only difference is that the coating amount and coating thickness of montmorillonite are different, please see the following Table 1 for details.

[0172] The relevant parameters of the positive electrode materials of the above-mentioned Examples 1-10 and Comparative Examples 1-3 are shown in the following Table 1.

[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 the above Examples 1-10 and Comparative Examples 1-3 were respectively prepared into button-type batteries, and the performance of the positive electrode active materials and button-type batteries was tested. The test results are shown in Table 2 below.

[0176] (1) Coating amount

[0177] The coating amount was measured by an ion emission spectrometer (ICP-OES) according to the following steps: first, 1 g of the positive electrode material coated with montmorillonite was weighed into a beaker, 25 mL of a 25% volume ratio HNO3 solution was added to the material to dissolve the material, and the material was diluted with 475 mL of deionized water. The diluted liquid was then placed in an ion emission spectrometer (ICAP7400, Thermo Fisher Scientific, USA) for target element analysis, and the coating amount of montmorillonite was obtained by calculation.

[0178] (2) Coating thickness

[0179] Use scissors to cut the electrode before cold pressing into samples of 6cm*6cm size, and then use IB-19500CP ion cross-section polisher for polishing to obtain polished samples with cut surfaces. Then, refer to the standard JY / T010-1996 and use ZEISSsigma 300 equipment to test the samples. Randomly select 10 different positions in the test sample for testing, and take the average value to obtain the thickness of the coating layer.

[0180] (3) Cation exchange capacity

[0181] The cation exchange capacity is determined using the national standard JC / T593-1995 method; the montmorillonite sample is treated with an extractant containing the indicator cation NH4+, all the exchangeable cations in the sample are replaced into the extract, and the sample is saturated with the indicator cations and converted into ammonium groups. The ammonium soil and the extract are separated, and the potassium, sodium, calcium and magnesium ions in the extract are determined, which are the corresponding exchangeable cation amounts;

[0182] (4) Specific surface area

[0183] The specific surface area is tested with reference to GB / T 19587-2017 using the nitrogen adsorption specific surface area analysis test method and calculated using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis test is performed using the Tri-Star 3020 specific surface area pore size analysis tester 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 process: GB / T19077-2016, specific test process: take an appropriate amount of the sample to be tested (the sample concentration is guaranteed to be 8-12% shading), add 20ml of deionized water, and simultaneously ultraviolet for 5min (53KHz / 120W) to ensure that the sample is completely dispersed, and then measure the sample according to GB / T19077-2016 standard.

[0186] (6) Dislocation density

[0187] XRD results based on X-ray diffractometer β=(1 / D) 2 ×10 16 , where D = Kλ / Bcosθ, K = 0.9, λ = 1.5406, B is the half-height width of the crystal plane of the lithium-rich manganese-based positive electrode material (hkl) in the XRD diffraction pattern, and θ is the diffraction angle.

[0188] (7) Manganese dissolution

[0189] 1 g of positive electrode active material was added to 200 ml of 0.2 wt% ascorbic acid solution, magnetically stirred for 5 min, allowed to stand for 24 min, and magnetically stirred for 1 min. The stirred solution was filtered through a glass funnel lined with filter paper, and the filtrate was diluted 100 times with 0.2 wt% 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] SP (carbon black) is used as a conductive agent, polyvinylidene fluoride (PVDF) is used as a binder, and N-methylpyrrolidone (NMP) is used as a solvent. PVDF and NMP are made into glue at a mass ratio of 2:8, and the positive electrode slurry is prepared according to the mass ratio of the positive electrode active material, SP and PVDF of 90:7:3. The above positive electrode slurry is evenly coated on an aluminum foil (thickness of 13μm) with a scraper and dried at 100°C in a vacuum oven for 12 hours. The aluminum foil is then punched into a disc with a diameter of 12mm, a metal lithium sheet is used as the negative electrode, a Celgard 2325 type diaphragm is used, and the electrolyte is an EC / DMC (volume ratio of 1:1) solution with a LiPF6 concentration of 1.0mol / L, thereby preparing a CR2032 button half-cell.

[0192] (9) Battery test

[0193] The CR2032 button half-cell prepared above was placed on a blue power test cabinet, and was first charged and discharged at rates of 0.1C, 0.33C and 0.5C for activation, and then charged and discharged at 25°C for 100cls at a rate of 1C, with a charge and discharge voltage range of 2.5-4.6V. First efficiency (%) = 0.1C first cycle discharge capacity / 0.1C first cycle discharge capacity × 100%. Battery 25°C cycle 100cls capacity retention rate (%) = discharge capacity after 100 cycles / 4th cycle discharge capacity × 100%.

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

[0195]

[0196] According to 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 coating amount of montmorillonite is 1000-5000ppm, and the thickness of the coating layer is 0.05-1μm based on the weight of the lithium-rich manganese-based material. From the comparison of Examples 1-10 and Comparative Examples 1-3, it can be seen that the positive electrode active material has a lower manganese dissolution amount, and the battery containing the positive electrode active material has a higher 0.1C charge discharge capacity, 0.33C charge discharge capacity, first efficiency and 25°C cycle 100cls energy retention rate, thereby indicating better cycle performance and storage performance.

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

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

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

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

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

[0202] From the comparison between Examples 3, 6, 8 and Examples 1-2, 4-5, 7, 9-10, it can be seen that the specific surface area of ​​the positive electrode active material is 1.6-2m 2 / g, the positive electrode active material has a lower manganese dissolution amount, and the battery containing the positive electrode active material has higher 0.1C charge-discharge capacity, 0.33C charge-discharge capacity, first efficiency and 25°C cycle 100cls energy retention rate, indicating better cycle performance and storage performance.

[0203] From the comparison between Examples 6 and 8 and Examples 1-3, 4-5, 7, 9-10, it can be seen that the specific surface area of ​​the positive electrode active material is 1.6-1.8 m 2 / g, the positive electrode active material has a lower manganese dissolution amount, and the battery containing the positive electrode active material has higher 0.1C charge-discharge capacity, 0.33C charge-discharge capacity, first efficiency and 25°C cycle 100cls energy retention rate, indicating better cycle performance and storage performance.

[0204] From the comparison between Examples 6 and 8 and Examples 1-3, 4-5, 7, and 9-10, it can be seen that 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, and the battery containing the positive electrode active material has higher 0.1C charge-discharge capacity, 0.33C charge-discharge capacity, first efficiency, and 25°C cycle 100cls energy retention rate, indicating better cycle performance and storage performance.

[0205] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present 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 comprises montmorillonite, the coating amount of the 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 coating amount of the montmorillonite is 4000-5000 ppm, preferably 4500-5000 ppm, based on the weight of the lithium-rich manganese-based material. 3 . The positive electrode active material according to claim 1 , wherein the coating layer has a thickness of 0.7-1 μm, preferably 0.95-1 μm. 4 . The positive electrode active material according to claim 1 , wherein the montmorillonite has a cation exchange capacity of 178-200 mmol / 100 g.

5. The positive electrode active material according to any one of the preceding claims, wherein the montmorillonite has a specific surface area of ​​185-200 m 2 / g.

6. The positive electrode active material according to any one of the preceding claims, wherein the specific surface area of ​​the positive electrode active material is 1.6-2 m 2 / g, preferably 1.6-1.8m 2 / g. 7 . The cathode active material according to claim 1 , wherein the cathode active material has a median particle size Dv50 of 15-20 μm.

8. A method for preparing a positive electrode active material according to any one of claims 1 to 7, the method comprising the following steps: (1) dispersing the lithium-rich manganese-based material in a solvent; (2) mixing the product of step (1) with montmorillonite and drying; (3) Sintering the product of step (2). 9 . A positive electrode sheet, comprising the positive electrode active material according to claim 1 or the positive electrode active material prepared by the method according to claim 8 . 10 . A secondary battery comprising the positive electrode sheet according to claim 9 .

11. An electric device comprising the secondary battery according to claim 10.

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