Positive electrode active material and preparation method therefor, secondary battery, and electric device

Abstract

Provided are a positive electrode active material and the preparation therefor, a secondary battery, and an electric device. The positive electrode active material comprises a lithium manganese iron phosphate substrate material and a carbon layer at least coated on the surface of the lithium manganese iron phosphate substrate material, wherein the powder compaction density of the positive electrode active material at 400 MPa is greater than or equal to 2.35 g / cm3. The positive electrode active material can improve the energy density of a battery.

Description

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

[0001] Cross-references

[0002] This application refers to Chinese Patent Application No. 202410397110X filed on April 2, 2024, entitled “Positive Electrode Active Material, Preparation Method Thereof, Secondary Battery and Electrical Device”, which is incorporated herein by reference in its entirety. Technical Field

[0003] The present application relates to the technical field of secondary batteries, and in particular to a positive electrode active material and a preparation method thereof, a secondary battery and an electrical device. Background Art

[0004] Secondary batteries have the advantages of high energy density, high operating voltage, low self-discharge rate, small size and light weight, and are widely used in the field of consumer electronics.

[0005] With the rapid development of electric vehicles and mobile electronic devices, people are increasingly demanding higher energy density in secondary batteries. Improving the energy density of batteries is a pressing scientific and technological issue in the field of secondary battery applications.

[0006] Summary of the Invention

[0007] The purpose of the present application is to provide a positive electrode active material and a preparation method thereof, a secondary battery and an electrical device, wherein the positive electrode active material can improve the energy density of the battery.

[0008] A first aspect of the present application provides a positive electrode active material, comprising a lithium iron manganese phosphate matrix material and a carbon layer at least coated on a surface of the lithium iron manganese phosphate matrix material.

[0009] The powder compaction density of the positive electrode active material at 400 MPa is greater than or equal to 2.35 g / cm 3 .

[0010] The positive electrode active material of the present application has a high powder compaction density, which is beneficial to improving the compaction density of the positive electrode film layer and improving the energy density of the battery.

[0011] In any embodiment, the powder compaction density of the positive electrode active material at 400 MPa is 2.35 g / cm 3 -2.50g / cm 3 .

[0012] The positive electrode active material has a high powder compaction density, which is conducive to high energy density secondary batteries.

[0013] In any embodiment, based on the total amount of the positive electrode active material, the positive electrode active material having a particle size of 4 μm to 6 μm accounts for 90% or more.

[0014] The percentage of the positive electrode active material with a particle size of 4μm-6μm is controlled to be greater than or equal to 90%, that is, the positive electrode active material has excellent particle size consistency, so that the discharge behavior of each particle tends to be consistent during the battery cycle, and the possibility of overcharging and over-discharging of each particle during the charging and discharging process is reduced, which is beneficial to ensuring the structural stability of the positive electrode active material. At the same time, the particle size of the particles accounting for greater than or equal to 90% is between 4μm and 6μm. The particle size of the material is relatively small, which is beneficial to improving the powder compaction density of the material. In addition, it can reduce the impact of large particles on the mechanical integrity of the positive electrode active material particles, and can also slow down the possibility of side reactions between small particles and the electrolyte, thereby comprehensively improving the low-temperature cycle performance of the battery and extending the service life of the battery.

[0015] In any embodiment, the tap density of the positive electrode active material is 1.0 g / cm 3 -1.3g / cm 3 .

[0016] The tap density of the positive electrode active material is within an appropriate range, which is conducive to obtaining a secondary battery with high energy density.

[0017] In any embodiment, the general formula of the lithium manganese iron phosphate matrix material is:

[0018] Li z Fe x Mn y M 1-x-y PO4

[0019] wherein z is 0.9 to 1.2, x is 0.001 to 0.999, y is 0.001 to 0.999, and 1-xy is 0 to 0.1; and M includes at least one of Al, Cu, Mg, Zn, Ni, Ti, V, Zr, Co, Ga, Sn, Sb, Nb, and Ge.

[0020] In any embodiment, based on the mass of the lithium iron manganese phosphate matrix material, the mass content of the carbon layer is 1.5%-2.5%.

[0021] The second aspect of the present application provides a method for preparing a positive electrode active material, comprising the following steps:

[0022] spray drying a mixed slurry comprising lithium manganese iron phosphate and a carbon source to obtain an intermediate product;

[0023] heat-treating the intermediate product to obtain a positive electrode active material;

[0024] Wherein, the heat source of the spray drying includes microwave,

[0025] The positive electrode active material includes a lithium iron manganese phosphate matrix material and a carbon layer at least coated on the surface of the lithium iron manganese phosphate matrix material.

[0026] The powder compaction density of the positive electrode active material at 400 MPa is greater than or equal to 2.35 g / cm 3 .

[0027] This application utilizes microwave spray drying to dry the slurry. Under the action of microwave energy, the slurry droplets rotate at high speed inside to produce a thermal effect, causing the material to instantly receive the heat source and lose moisture. The droplets are evenly heated from the inside out, and the particles first lose water and dry, and then the outside is coated with dried small spherical particles. This can obtain a lithium iron manganese phosphate intermediate product with a solid spherical structure, low hollow ratio, and high powder compaction density. At the same time, microwaves are used as a heat source to treat the slurry. The liquid drying time is short and uniform, which maximizes the uniformity of the particle growth rate and can obtain lithium iron manganese phosphate with a uniform particle size distribution. The lithium iron manganese phosphate intermediate product with a solid spherical structure, low hollow ratio, high powder compaction density, and uniform particle size distribution is heat-treated with carbon to obtain a carbon-coated lithium iron manganese phosphate with a solid spherical structure, low hollow ratio, high powder compaction density, and uniform particle size distribution, providing a material basis for the preparation of batteries with high energy density and long cycle life.

[0028] In any embodiment, the microwave frequency of the microwave is 50 GHz-100 GHz.

[0029] The microwave frequency of the microwave is within a suitable range, so that the outlet air temperature of the spray drying is within a suitable range, the slurry can be dried evenly and quickly, and carbon-coated lithium manganese iron phosphate with a solid spherical structure, low hollow rate, high powder compaction density and uniform particle size distribution can be obtained.

[0030] In any embodiment, the outlet air temperature of the spray drying is 100°C-120°C.

[0031] When the outlet air temperature of the spray drying is within an appropriate range, the slurry can be dried evenly and quickly, and carbon-coated lithium manganese iron phosphate with a solid spherical structure, low hollow rate, high powder compaction density and uniform particle size distribution can be obtained.

[0032] In any embodiment, it is characterized in that the solid content of the mixed slurry is 10%-30%.

[0033] The solid content of the mixed slurry is within an appropriate range, and the tighter the interior of the slurry droplets is, the more conducive it is to obtaining a lithium manganese iron phosphate intermediate product with a low hollow ratio and a high compaction density. At the same time, the solid content of the mixed slurry is within an appropriate range, and the viscosity of the mixed slurry is within an appropriate range, and the mixed slurry has good processing performance.

[0034] In any embodiment, the preparation method further comprises:

[0035] Stirring and ultrasonically dispersing an initial slurry containing lithium manganese iron phosphate to obtain a first slurry;

[0036] The first slurry is mixed with a carbon source to obtain the mixed slurry containing lithium manganese iron phosphate and the carbon source.

[0037] In any embodiment, the volume average particle size Dv50 of the lithium manganese iron phosphate in the first slurry is 100 nm to 300 nm.

[0038] The particle size of the lithium manganese iron phosphate in the first slurry is small, and the particle size of the lithium manganese iron phosphate raw material in the mixed slurry is small, which is conducive to obtaining a lithium manganese iron phosphate intermediate product with a small particle size and a positive electrode active material with a high compaction density. At the same time, it can also accelerate the drying speed of microwave spray drying and improve the preparation efficiency.

[0039] In any embodiment, the heat treatment specifically includes:

[0040] The intermediate product is heat-treated under an inert atmosphere to obtain a positive electrode active material.

[0041] Wherein, the treatment temperature of the heat treatment is 400° C.-800° C.; and / or the treatment time of the heat treatment is 4 h-10 h.

[0042] A third aspect of the present application provides a secondary battery, comprising a positive electrode plate, wherein the positive electrode plate comprises the positive electrode active material described in the first aspect or the positive electrode active material prepared by the preparation method described in the second aspect.

[0043] A fourth aspect of the present application provides an electrical device comprising the secondary battery described in the third aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] FIG1 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0045] FIG2 is an exploded view of the secondary battery according to one embodiment of the present application shown in FIG1 ;

[0046] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application;

[0047] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0048] FIG5 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG4 ;

[0049] FIG6 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0050] Reference numerals:

[0051] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 cover plate. DETAILED DESCRIPTION

[0052] Below, the embodiments of the positive electrode active material and its preparation method, secondary battery and electric device of the present application are described in detail with appropriate reference to the drawings. However, there may be 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 structures 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 description 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.

[0053] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and 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 special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this 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 all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this 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.

[0054] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0055] 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.

[0056] Unless otherwise specified, all steps of the present 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 may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating 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.

[0057] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0058] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: 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).

[0059] Lithium iron manganese phosphate (LiMnFePO4) cathode active materials have become one of the most popular cathode active materials due to their high capacity, excellent safety, and abundant raw material resources. However, the hollow structure of LiMnFePO4 particles currently results in a low compaction density of LiMnFePO4 powder, making it difficult to achieve high energy density batteries.

[0060] [Positive electrode active material]

[0061] The present application provides a positive electrode active material, which includes a lithium iron manganese phosphate matrix material and a carbon layer at least coated on the surface of the lithium iron manganese phosphate matrix material.

[0062] The powder compaction density of the positive electrode active material at 400 MPa is greater than or equal to 2.35 g / cm 3 .

[0063] In some embodiments, the powder compaction density of the positive electrode active material at 400 MPa can be greater than or equal to 2.35 g / cm 3 , greater than or equal to 2.40g / cm 3 , greater than or equal to 2.45g / cm 3 , greater than or equal to 2.50g / cm 3 Any one of .

[0064] The compacted density of the positive electrode active material powder at 400 MPa can be measured by methods and equipment known in the art. For example, referring to GB / T 24533-2009, 1 g of positive electrode active material powder is weighed and added to a container with a bottom area of ​​1.327 cm 2 The mold is pressurized to a specific pressure, for example, 400 MPa, maintained for 30 seconds, then released and maintained for 10 seconds, and the powder compaction density of the positive electrode active material under the selected pressure (or selected pressure) is measured by an electronic pressure testing machine (such as UTM7305 electronic pressure testing machine).

[0065] The positive electrode active material of the present application has a high powder compaction density, which is beneficial to improving the compaction density of the positive electrode film layer and improving the energy density of the battery.

[0066] In some embodiments, the powder compaction density of the positive electrode active material at 400 MPa is 2.35 g / cm 3 -2.50g / cm 3 In some embodiments, the powder compaction density of the positive electrode active material at 400 MPa may be 2.35 g / cm 3 , 2.37g / cm 3 , 2.39g / cm 3 , 2.40g / cm 3 , 2.42g / cm 3 , 2.44g / cm 3 , 2.46g / cm 3 , 2.48g / cm 3 , 2.50g / cm 3 or any range of values ​​between them.

[0067] The positive electrode active material has a high powder compaction density, which is conducive to high energy density secondary batteries.

[0068] In some embodiments, based on the total amount of the positive electrode active material, the positive electrode active material having a particle size of 4 μm to 6 μm accounts for 90% or more.

[0069] In some embodiments, based on the total amount of positive electrode active materials, the percentage of positive electrode active materials with a particle size of 4 μm-6 μm can be selected as any one of greater than or equal to 90%, greater than or equal to 92%, greater than or equal to 94%, greater than or equal to 96%, and greater than or equal to 98%.

[0070] In some embodiments, based on the total amount of the positive electrode active material, the percentage of the positive electrode active material with a particle size of 4 μm-6 μm can be selected as 90%, 92%, 94%, 96%, 98%, 99% or any numerical range therebetween.

[0071] The percentage content of the positive electrode active material with a particle size of 4μm-6μm can be measured by methods and equipment known in the art. For example, take an appropriate amount of positive electrode active material, add 20ml of deionized water (the sample concentration is guaranteed to be 8-12% shading), and ultrasonically disperse for 5min (53KHz / 120W) to ensure that the sample is completely dispersed. After that, the positive electrode active material sample is measured according to the GB / T 19077-2016 / ISO 13320:2009 standard, and the test equipment is Malvern 2000 (MasterSizer 2000) laser particle size analyzer. A particle size number distribution graph is drawn based on the test data. From the particle size volume distribution graph, it is obtained: based on the total number of positive electrode active materials, the percentage content of active materials with a particle size of 4μm-6μm.

[0072] The percentage of the positive electrode active material with a particle size of 4μm-6μm is controlled to be greater than or equal to 90%, that is, the positive electrode active material has excellent particle size consistency, so that the discharge behavior of each particle tends to be consistent during the battery cycle, and the possibility of overcharging and over-discharging of each particle during the charging and discharging process is reduced, which is beneficial to ensuring the structural stability of the positive electrode active material. At the same time, the particle size of the particles accounting for greater than or equal to 90% is between 4μm and 6μm. The particle size of the material is relatively small, which is beneficial to improving the powder compaction density of the material. In addition, it can reduce the impact of large particles on the mechanical integrity of the positive electrode active material particles, and can also slow down the possibility of side reactions between small particles and the electrolyte, thereby comprehensively improving the low-temperature cycle performance of the battery and extending the service life of the battery.

[0073] In some embodiments, the tap density of the positive electrode active material is 1.0 g / cm 3 -1.3g / cm 3 In some embodiments, the tap density of the positive electrode active material may be 1.0 g / cm 3 , 1.1g / cm 3 , 1.2g / cm 3 , 1.3g / cm 3 or any range of values ​​between them.

[0074] The tap density of the positive electrode active material can be measured using methods and equipment known in the art. For example, referring to GB / T 5162-2006, a powder tap density tester can be used. The tester can be a Dandong Better BT-301.

[0075] The tap density of the positive electrode active material is within an appropriate range, which can increase the compaction density of the positive electrode film layer, and is conducive to obtaining a secondary battery with high energy density.

[0076] In some embodiments, the general formula of the lithium manganese iron phosphate matrix material is:

[0077] Li z Fe x Mn y M 1-x-y PO4

[0078] wherein z is 0.9 to 1.2, x is 0.001 to 0.999, y is 0.001 to 0.999, and 1-xy is 0 to 0.1; and M includes at least one of Al, Cu, Mg, Zn, Ni, Ti, V, Zr, Co, Ga, Sn, Sb, Nb, and Ge.

[0079] In some embodiments, z can be selected as 0.9, 1.0, 1.1, 1.2, or any range of values ​​therebetween.

[0080] In some embodiments, x can be selected from 0.001, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.999, or any range therebetween.

[0081] In some embodiments, y can be selected from 0.001, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.999, or any range therebetween.

[0082] In some embodiments, 1-xy can be selected as 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or any range therebetween.

[0083] In some embodiments, based on the mass of the lithium iron manganese phosphate matrix material, the mass content of the carbon layer is 1.5%-2.5%.

[0084] In some embodiments, based on the mass of the lithium manganese iron phosphate matrix material, the mass content of the carbon layer may be 1.5%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.5% or any range therebetween.

[0085] The mass content of the carbon layer can be measured using methods and equipment known in the art. For example, it can be measured using infrared absorption, where the sample to be tested is burned in an oxygen stream to generate CO2. Because the energy absorbed by CO2 in infrared radiation under a certain pressure is proportional to its concentration, the mass content of the carbon layer can be calculated based on the energy change measured before and after the CO2 gas passes through the infrared absorber.

[0086] The mass content of the carbon layer is within an appropriate range, which can take into account the conductivity and gram capacity of the material, and comprehensively improve the rate performance and energy density of the battery.

[0087] A second aspect of the present application provides a method for preparing a positive electrode active material, comprising the following steps:

[0088] spray drying a mixed slurry comprising lithium manganese iron phosphate and a carbon source to obtain an intermediate product;

[0089] heat-treating the intermediate product to obtain a positive electrode active material;

[0090] Wherein, the heat source of the spray drying includes microwave,

[0091] The positive electrode active material includes a lithium iron manganese phosphate matrix material and a carbon layer at least coated on the surface of the lithium iron manganese phosphate matrix material.

[0092] The powder compaction density of the positive electrode active material at 400 MPa is greater than or equal to 2.35 g / cm 3 .

[0093] Lithium iron manganese phosphate (LiMnFePO4) is widely used in the field of secondary batteries due to its abundant raw materials, low cost, and high energy density. However, LiMnFePO4 suffers from low electrical conductivity. To improve the conductivity of LiMnFePO4, it is often coated with a carbon coating. Existing techniques often employ electric heating spray drying and high-temperature sintering for carbon coating. However, the carbon-coated LiMnFePO4 cathode active materials prepared in this manner have a high hollow ratio, resulting in a low powder compaction density, which affects their electrochemical performance.

[0094] During their research, the inventors of this application discovered that using microwaves as a heat source to spray-dry a slurry can produce carbon-coated lithium iron manganese phosphate with a low hollow ratio, high powder compaction density, and uniform particle size distribution. When spray-drying the slurry with microwaves, the high-speed rotation of the slurry droplets under the action of microwave energy produces a thermal effect, causing the material to instantly lose moisture due to the heat source. The droplets are evenly heated from the inside out, first drying the interior of the particles, and then coating the exterior with dried small spherical particles. This produces a lithium iron manganese phosphate intermediate product with a solid spherical structure, low hollow ratio, and high powder compaction density. Furthermore, using microwaves as a heat source to treat the slurry results in a short and uniform liquid drying time, maximizing the uniformity of particle growth rate and producing lithium iron manganese phosphate with a uniform particle size distribution. By heat-treating lithium manganese iron phosphate (LFP), which already possesses a solid spherical structure, low hollowness, high powder compaction density, and uniform particle size distribution, with carbon, a carbon-coated LFP with a solid spherical structure, low hollowness, high powder compaction density, and uniform particle size distribution can be obtained. This provides a material foundation for the preparation of batteries with high energy density and long cycle life. Furthermore, compared to traditional electric heating spray drying, this method offers faster drying speeds, lower energy consumption, and higher efficiency, making it more suitable for industrial production.

[0095] In some embodiments, the microwave frequency of the microwave is 50 GHz-100 GHz. In some embodiments, the microwave frequency of the microwave can be selected from 50 GHz, 60 GHz, 70 GHz, 80 GHz, 90 GHz, 100 GHz, or any range therebetween.

[0096] The microwave frequency of the microwave is within a suitable range, so that the outlet air temperature of the spray drying is within a suitable range, the slurry can be dried evenly and quickly, and carbon-coated lithium manganese iron phosphate with a solid spherical structure, low hollow rate, high powder compaction density and uniform particle size distribution can be obtained.

[0097] In some embodiments, the outlet air temperature of the spray drying is 100° C.-120° C. In some embodiments, the outlet air temperature of the spray drying can be selected from 100° C., 110° C., 120° C. or any range therebetween.

[0098] When the outlet air temperature of the spray drying is within an appropriate range, the slurry can be dried evenly and quickly, and carbon-coated lithium manganese iron phosphate with a solid spherical structure, low hollow rate, high powder compaction density and uniform particle size distribution can be obtained.

[0099] In some embodiments, the solid content of the mixed slurry is 10%-30%. In some embodiments, the solid content of the mixed slurry can be 10%, 15%, 20%, 25%, 30% or any range therebetween.

[0100] The solids content of the mixed slurry can be measured using methods and equipment known in the art. For example, aluminum foil is weighed in a weight loss meter (denoted as M0) and reset to zero. A small amount of the mixed slurry is applied to the foil and then placed in a moisture meter (denoted as M1). The meter is closed and drying begins. After drying, the weight is recorded as M2, and the solids content is calculated as (M2 - M0) / (M1 - M0).

[0101] The solid content of the mixed slurry is within an appropriate range, and the tighter the interior of the slurry droplets is, the more conducive it is to obtaining a lithium manganese iron phosphate intermediate product with a low hollow ratio and a high compaction density. At the same time, the solid content of the mixed slurry is within an appropriate range, and the viscosity of the mixed slurry is within an appropriate range, and the mixed slurry has good processing performance.

[0102] In some embodiments, the preparation method further comprises:

[0103] Stirring and ultrasonically dispersing an initial slurry containing lithium manganese iron phosphate to obtain a first slurry;

[0104] The first slurry is mixed with a carbon source to obtain the mixed slurry containing lithium manganese iron phosphate and the carbon source.

[0105] In some embodiments, the volume average particle size Dv50 of the lithium manganese iron phosphate in the first slurry is 100 nm to 300 nm. In some embodiments, the volume average particle size Dv50 of the lithium manganese iron phosphate in the first slurry can be 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, or any range therebetween.

[0106] The volume average particle size Dv50 of the lithium manganese iron phosphate in the first slurry can be measured by methods and equipment known in the art. For example, take an appropriate amount of the first slurry, add 10ml of deionized water (the sample concentration is guaranteed to be 8-12% shading), and ultrasonically disperse for 5min (53KHz / 120W) to ensure that the sample is completely dispersed. Then, the first slurry is measured in accordance with the GB / T 19077-2016 / ISO 13320:2009 standard, and the testing equipment is Malvern 2000 (MasterSizer 2000) laser particle size analyzer. A particle size volume distribution diagram is drawn based on the test data. From the particle size volume distribution diagram, the particle size Dv50 corresponding to the cumulative volume distribution percentage of the lithium manganese iron phosphate material in the first slurry reaches 50% is obtained, and the volume average particle size Dv50 of the lithium manganese iron phosphate in the first slurry can be obtained by calculation.

[0107] The particle size of the lithium manganese iron phosphate in the first slurry is small, and the particle size of the lithium manganese iron phosphate raw material in the mixed slurry is small, which is conducive to obtaining a lithium manganese iron phosphate intermediate product with a small particle size and a positive electrode active material with a high compaction density. At the same time, it can also accelerate the drying speed of microwave spray drying and improve the preparation efficiency.

[0108] In any embodiment, the heat treatment specifically includes:

[0109] The intermediate product is heat-treated under an inert atmosphere to obtain a positive electrode active material.

[0110] Wherein, the treatment temperature of the heat treatment is 400° C.-800° C.; and / or the treatment time of the heat treatment is 4 h-10 h.

[0111] In some embodiments, the heat treatment temperature may be 400° C., 500° C., 600° C., 800° C., or any range therebetween.

[0112] In some embodiments, the heat treatment time may be 4 h, 6 h, 8 h, 10 h, or any range therebetween.

[0113] Controlling the reaction time or reaction temperature of the heat treatment within a suitable range is conducive to forming a dense carbon coating layer on the surface of the lithium manganese iron phosphate intermediate product.

[0114] In some embodiments, the carbon source can be an organic carbon source or an inorganic carbon source.

[0115] In some embodiments, the carbon source comprises at least one of glucose, sucrose, fructose, polyethylene glycol, starch, polydopamine, polyvinylpyrrolidone, or tannic acid.

[0116] [Positive electrode]

[0117] The present application provides a positive electrode plate, comprising a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, the positive electrode film layer comprising a positive electrode active material, a binder and a conductive agent, the positive electrode active material being the positive electrode active material of an embodiment of the present application or the positive electrode active material prepared by the preparation method of an embodiment of the present application.

[0118] 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 either or both of the two opposite surfaces of the positive electrode current collector.

[0119] 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.).

[0120] 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), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0121] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0122] In some embodiments, the positive electrode sheet can be prepared by the following method: 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 current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0123] [Negative electrode]

[0124] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0125] 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 either or both of the two opposite surfaces of the negative electrode current collector.

[0126] 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 base layer and a metal layer formed on at least one surface of the polymer base material. 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 base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0127] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well 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 oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, 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.

[0128] 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).

[0129] 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.

[0130] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0131] In some embodiments, the negative electrode sheet can be prepared by the following method: 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 current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0132] [Electrolytes]

[0133] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0134] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0135] 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 difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0136] 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, methylpropyl carbonate, ethylpropyl 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, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0137] In some embodiments, the electrolyte may further include additives. For example, the additives may include 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, and additives that improve battery high or low temperature performance.

[0138] [Isolation film]

[0139] 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 and mechanical stability can be selected.

[0140] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven 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.

[0141] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0142] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0143] 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. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0144] [Secondary battery]

[0145] In one embodiment of the present application, a secondary battery is provided, comprising a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte, wherein the binder in the active material layer of the positive electrode sheet comprises the polymer of any embodiment of the present application.

[0146] In some embodiments, the secondary battery is a lithium-ion battery or a sodium-ion battery. During the battery's charge and discharge processes, active ions are intercalated and released between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. A separator is positioned between the positive and negative electrodes, primarily preventing short circuits between the positive and negative electrodes while allowing ions to pass through.

[0147] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0148] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0149] 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. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0150] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square, or any other shape. For example, FIG1 shows a secondary battery 5 with a square structure as an example.

[0151] In some embodiments, referring to FIG2 , the outer package may include a shell 51 and a cover plate 53. 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 be formed into 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.

[0152] In some embodiments, secondary batteries can be assembled into a battery module. The number of secondary batteries contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0153] Figure 3 shows an example battery module 4. Referring to Figure 3 , within the battery module 4, multiple secondary batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, any other arrangement is also possible. Furthermore, the multiple secondary batteries 5 may be secured together using fasteners.

[0154] 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.

[0155] 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 based on the application and capacity of the battery pack.

[0156] Figures 4 and 5 illustrate an example battery pack 1. Referring to Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0157] 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, or 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 is not limited thereto.

[0158] As an electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0159] Figure 6 shows an example of an electric device. This device is 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, a battery pack or battery module can be used.

[0160] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0161] Example

[0162] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0163] 1. Preparation method

[0164] Example 1

[0165] 1) Preparation of positive electrode active materials

[0166] 10 kg of lithium manganese iron phosphate (LiFe 0.3 Mn 0.6 Co 0.1 PO4) slurry (the solvent is deionized water) is poured into a homogenizer and fully stirred for 0.5 h by a high-speed dispersing disk. The stirring revolution speed is 2000 r / min and the rotation speed is 50 r / min. The stirred slurry is then transferred to an ultrasonic disperser, and the ultrasonic frequency (60 Hz) and the ultrasonic time are set to 0.5 h to obtain a first slurry. The volume average particle size Dv50 of the lithium manganese iron phosphate in the first slurry is 300 nm.

[0167] The first slurry was mixed with 0.2 kg of glucose to obtain a mixed slurry with a solid content of 20%. The mixed slurry was placed in a spray drying storage tank and stirred at a speed of 15 r / min. The "outlet air temperature-magnetron on" interlocking mode was selected. The microwave frequency was adjusted to 100 GHz by the magnetron to directly control the powder outlet air temperature to 120°C. The peristaltic pump was turned on, and the slurry in the storage tank quickly entered the drying main tower through the nozzle and dried for 28 minutes to obtain the intermediate.

[0168] The intermediate was calcined at a high temperature of 500° C. for 6 hours under nitrogen protection, and cooled to obtain a carbon-coated lithium manganese iron phosphate material, wherein the mass content of the carbon layer was 2% based on the lithium manganese iron phosphate material.

[0169] 2) Preparation of positive electrode sheet

[0170] The positive electrode active material, conductive carbon black, and binder polyvinylidene fluoride from each example or comparative example were dispersed in N-methylpyrrolidone at a weight ratio of 92%:2.5%:5.5%, and thoroughly stirred to obtain a positive electrode slurry. The positive electrode slurry was applied to both sides of a 12 μm thick aluminum foil using a scraper. After coating, the positive electrode sheets were dried, cold pressed, and slit.

[0171] 3) Negative electrode

[0172] The negative electrode material hard carbon, conductive agent acetylene black, binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose are dispersed in a deionized water solvent in a weight ratio of 95:2:2:1, and the mixture is fully stirred to obtain a negative electrode slurry with a solid content of 15%. The negative electrode slurry is applied on both sides of an aluminum foil with a thickness of 12 μm using a scraper. After coating, the negative electrode sheet is prepared by drying, cold pressing, and slitting.

[0173] 4) Electrolyte

[0174] In an argon atmosphere glove box (H2O < 0.1ppm, O2 < 0.1ppm), organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed uniformly in a volume ratio of 3:7, and LiPF6 lithium salt was dissolved in the organic solvent to prepare a solution with a weight content of 12.5% ​​to obtain an electrolyte.

[0175] 5) Diaphragm

[0176] Polypropylene film is used as the isolation film.

[0177] 6) Preparation of batteries

[0178] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the positive and negative electrodes to provide isolation. The cells are then wound to form a bare cell. The bare cell is then placed in an outer package and injected with the prepared electrolyte to form a cell. The cell undergoes packaging, electrolyte injection, formation, and venting to create a lithium-ion battery.

[0179] Examples 2-5

[0180] Compared with Example 1, Examples 2-5 adjusted the microwave frequency or the solid content of the mixed slurry. For specific parameters, see Table 1.

[0181] Comparative Example 1

[0182] Compared with Example 1, the preparation method of the positive electrode active material was adjusted as follows:

[0183] 10 kg of lithium manganese iron phosphate slurry with a solid content of 20% was poured into a homogenizer and fully stirred for 0.5 h using a high-speed dispersing disk. The stirring speed was 2000 r / min and the rotation speed was 50 r / min. The stirred slurry was then transferred to an ultrasonic disperser, and the ultrasonic frequency (60 Hz) and ultrasonic time were set to 0.5 h to obtain the first slurry.

[0184] The first slurry was mixed with 0.2 kg of glucose to obtain a mixed slurry. The volume average particle size (Dv50) of the lithium manganese iron phosphate in the mixed slurry was 300 nm. The mixed slurry was placed in a spray drying storage tank and stirred at a speed of 15 r / min. The "inlet air temperature-electric heating" interlocking mode was selected. The powder outlet air temperature was directly controlled to 120°C by adjusting the electric heating power. The peristaltic pump was turned on, and the slurry in the storage tank was quickly introduced into the main drying tower through the nozzle and dried for 105 minutes to obtain the intermediate.

[0185] The intermediate was calcined at a high temperature of 500° C. for 6 hours under nitrogen protection, and cooled to obtain a carbon-coated lithium manganese iron phosphate material, wherein the mass content of the carbon layer was 2% based on the lithium manganese iron phosphate material.

[0186] 2. Test Method

[0187] 1. Low temperature cycle performance of secondary batteries

[0188] At a temperature of 25°C, the battery was allowed to stand for 2 hours, and then charged to 4.3V at a constant current and constant voltage rate of 1C, and then allowed to stand at 4.3V for 2 hours, and then discharged to 2.0V at a constant current rate of 1C at a temperature of 25°C. This is a normal temperature charging and normal temperature discharge process. The discharge capacity at this time is the discharge capacity of the battery at 25°C, recorded as C1; after the battery was allowed to stand for 2 hours, it was charged to 4.3V at a constant current and constant voltage rate of 1C, and then allowed to stand at 4.3V for 2 hours, and then discharged to 2.0V at a constant current rate of 1C at a temperature of -20°C. This is a normal temperature charging and low temperature discharge process. The discharge capacity at this time is the discharge capacity of the battery at -20°C, recorded as C2; the battery low temperature capacity retention rate is calculated according to the following formula: Low temperature capacity retention rate (%) = (C2 / C1) × 100%.

[0189] 2. Energy density of secondary batteries

[0190] The battery cells of the embodiment and comparative example were left at 25°C for 2 hours to ensure that the temperature of the battery cells was 25°C. The battery cells were charged to 4.3V at 0.33C at 25°C, and constant voltage charging was continued at 4.3V until the current reached 0.05C, at which point charging was terminated (where C0 represents the rated capacity of the battery). After the battery cells were left at 25°C for 1 hour, they were discharged to 2.0V at 0.33C at 25°C, and the total discharge energy of the battery cells was recorded as E0.

[0191] The measured cell weight is M0;

[0192] Cell weight energy density = total discharge energy E0 of the cell / cell weight M0.

[0193] 3. Analysis of test results of various embodiments and comparative examples

[0194] The positive electrode active materials and secondary batteries of the embodiments and comparative examples were prepared according to the above methods, and various parameters were measured. The results are shown in the table below.

[0195] Table 1

[0196] The positive electrode active material in Examples 1-5 comprises a lithium manganese iron phosphate matrix material and a carbon layer at least coated on the surface of the lithium manganese iron phosphate matrix material, wherein the powder compaction density of the positive electrode active material at 400 MPa is greater than or equal to 2.35 g / cm 3 .

[0197] From the comparison of Examples 1-5 and Comparative Example 1, it can be seen that the use of the positive electrode active material of the present application can improve the energy density and low-temperature cycle performance of the battery.

[0198] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine 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, characterized in that The positive electrode active material includes a lithium iron manganese phosphate matrix material and a carbon layer at least coated on the surface of the lithium iron manganese phosphate matrix material. The powder compaction density of the positive electrode active material at 400 MPa is greater than or equal to 2.35 g / cm 3 .

2. The positive electrode active material according to claim 1, characterized in that The powder compaction density of the positive electrode active material at 400 MPa is 2.35 g / cm 3 -2.50g / cm 3 .

3. The positive electrode active material according to claim 1 or 2, characterized in that Based on the total amount of the positive electrode active material, the positive electrode active material having a particle size of 4 μm to 6 μm accounts for 90% or more.

4. The positive electrode active material according to any one of claims 1 to 3, characterized in that The tap density of the positive electrode active material is 1.0 g / cm 3 -1.3g / cm 3 .

5. The positive electrode active material according to any one of claims 1 to 4, characterized in that The general formula of the lithium manganese iron phosphate matrix material is: Li z Fe x Mn y M 1-x-y PO4 Wherein z is 0.9 to 1.2, x is 0.001 to 0.999, y is 0.001 to 0.999, and 1-xy is 0 to 0.1; M includes at least one of Al, Cu, Mg, Zn, Ni, Ti, V, Zr, Co, Ga, Sn, Sb, Nb, and Ge.

6. The positive electrode active material according to any one of claims 1 to 5, characterized in that Based on the mass of the lithium manganese iron phosphate matrix material, the mass content of the carbon layer is 1.5%-2.5%.

7. A method for preparing a positive electrode active material, characterized in that: The steps include: spray drying a mixed slurry comprising lithium manganese iron phosphate and a carbon source to obtain an intermediate product; heat-treating the intermediate product to obtain a positive electrode active material; Wherein, the heat source of the spray drying includes microwave, The positive electrode active material includes a lithium iron manganese phosphate matrix material and a carbon layer at least coated on the surface of the lithium iron manganese phosphate matrix material. The powder compaction density of the positive electrode active material at 400 MPa is greater than or equal to 2.35 g / cm 3 .

8. The preparation method according to claim 7, characterized in that The microwave frequency of the microwave is 50 GHz to 100 GHz.

9. The preparation method according to claim 7 or 8, characterized in that The outlet air temperature of the spray drying is 100°C-120°C.

10. The preparation method according to any one of claims 7 to 9, characterized in that The solid content of the mixed slurry is 10%-30%.

11. The preparation method according to any one of claims 7 to 10, characterized in that The preparation method further comprises: Stirring and ultrasonically dispersing an initial slurry containing lithium manganese iron phosphate to obtain a first slurry; The first slurry is mixed with a carbon source to obtain the mixed slurry containing lithium manganese iron phosphate and the carbon source.

12. The preparation method according to any one of claims 7 to 11, characterized in that The volume average particle size Dv50 of the lithium manganese iron phosphate in the first slurry is 100 nm to 300 nm.

13. The preparation method according to any one of claims 7 to 12, characterized in that The heat treatment specifically includes: The intermediate product is heat-treated under an inert atmosphere to obtain a positive electrode active material. Wherein, the treatment temperature of the heat treatment is 400° C.-800° C.; and / or the treatment time of the heat treatment is 4 h-10 h.

14. A secondary battery comprising a positive electrode plate, characterized in that: The positive electrode sheet includes the positive electrode active material according to any one of claims 1 to 6 or the positive electrode active material prepared by the preparation method according to any one of claims 7 to 13.

15. An electrical device, characterized in that: The secondary battery according to claim 14 is included.

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