Positive electrode active material and preparation method therefor, and positive electrode sheet, battery cell, battery, and electric device comprising same

Abstract

Disclosed in the present application are a positive electrode active material and a preparation method therefor, and a positive electrode sheet, a battery cell, a battery and an electric device comprising same. The preparation method for the positive electrode active material comprises the following steps: providing a lithium-containing phosphate active material or a precursor of a lithium-containing phosphate active material; providing an oxygen-free organic carbon source, wherein the oxygen-free organic carbon source comprises one or more of an oxygen-free polymer and an oxygen-free organic small molecule compound; and uniformly mixing the lithium-containing phosphate active material or the precursor of a lithium-containing phosphate active material with the oxygen-free organic carbon source to obtain a mixture, and then performing a sintering treatment in a protective gas atmosphere, so as to obtain a positive electrode active material. The present application makes the battery have good cycling performance and storage performance.

Description

Positive electrode active material and preparation method thereof, as well as positive electrode sheet, battery cell, battery and electric device containing the same

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202410002267.8 filed on January 2, 2024, entitled “Positive electrode active material, preparation method thereof, and positive electrode sheet, battery cell, battery and electrical device containing the same,” and the entire contents of that application are incorporated herein by reference. Technical Field

[0003] The present application relates to a positive electrode active material and a preparation method thereof, as well as a positive electrode sheet, a battery cell, a battery and an electrical device containing the same. Background Art

[0004] In recent years, batteries have been widely used in energy storage systems such as hydropower, thermal, wind, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. With the increasing application and promotion of batteries, their reliability has attracted increasing attention. Lithium-containing phosphate active materials, represented by lithium manganese iron phosphate, have become one of the most popular cathode active materials due to their advantages such as good reliability and abundant raw material resources. However, lithium-containing phosphate active materials suffer from serious drawbacks: low electronic conductivity and the easy dissolution of transition metal ions, especially manganese ions. To reduce the dissolution of transition metal ions and improve the electronic conductivity of lithium-containing phosphate active materials, they are typically coated with a carbon layer on their outermost layer. However, these carbon layers currently contain a high content of micropores and mesoporous structures and are prone to water absorption. This makes drying the cathode slurry difficult and results in high residual moisture content in the cathode electrode sheet. This high residual moisture content in the cathode electrode sheet can deteriorate the electrochemical performance of the battery.

[0005] Summary of the Invention

[0006] The present application provides a positive electrode active material and a preparation method thereof, as well as a positive electrode plate, a battery cell, a battery and an electrical device containing the same, which can enable the positive electrode active material to have higher surface density, less micropore and mesoporous structure content, lower water absorption rate and water absorption amount, enable the positive electrode plate to have lower residual moisture content, enable the positive electrode active material to have lower transition metal ion dissolution amount, and also enable the battery to have good cycle performance and storage performance.

[0007] In a first aspect, the present application provides a method for preparing a positive electrode active material, comprising the following steps: providing a lithium phosphate active material or a precursor of a lithium phosphate active material; providing an oxygen-free organic carbon source, wherein the oxygen-free organic carbon source includes one or more of an oxygen-free polymer and an oxygen-free organic small molecule compound; uniformly mixing the lithium phosphate active material or the precursor of the lithium phosphate active material with the oxygen-free organic carbon source to obtain a mixture, and then sintering the mixture under a protective gas atmosphere so that the oxygen-free organic carbon source is carbonized to form a carbon coating layer that coats at least a portion of the surface of the lithium phosphate active material to obtain a positive electrode active material.

[0008] The preparation method provided in the embodiment of the present application adopts an oxygen-free organic carbon source, which includes one or more oxygen-free polymers and oxygen-free organic small molecule compounds. The oxygen-free organic carbon source releases less gas during the pyrolysis process, and the carbon coating layer formed after carbonization has less micropores and mesoporous structures. The carbon coating layer has high density, thereby reducing the direct contact between the lithium phosphate active material and the electrolyte and reducing the side reactions at the positive electrode-electrolyte interface; at the same time, the dense carbon coating layer can also play a role in blocking the dissolution of transition metal ions.

[0009] The carbon coating layer formed after the carbonization of the oxygen-free organic carbon source has a small content of micropores and mesoporous structures, and the specific surface area of ​​the positive electrode active material is also low, so its water absorption rate and water absorption amount are low, and the positive electrode slurry is easier to dry, the residual moisture content of the positive electrode sheet is lower, and the amount of transition metal ions dissolved in the positive electrode active material is lower.

[0010] The carbon coating layer formed after the carbonization of the oxygen-free organic carbon source has fewer oxygen-containing functional groups and lower electrochemical activity, which can also reduce the catalytic decomposition of the electrolyte; at the same time, the carbon coating layer formed after the carbonization of the oxygen-free organic carbon source has fewer oxygen-containing functional groups, and the positive electrode active material has fewer water absorption sites, thereby reducing its water absorption rate and water absorption amount, and thus the positive electrode slurry is easier to dry, the residual moisture content of the positive electrode sheet is lower, and the amount of transition metal ions dissolved in the positive electrode active material is lower.

[0011] Therefore, the positive electrode active material obtained by the preparation method provided in the embodiment of the present application has a lower water absorption rate and water absorption amount, so that the positive electrode slurry is easier to dry, the residual moisture content of the positive electrode sheet is lower, and the transition metal ion dissolution amount of the positive electrode active material is lower; the positive electrode active material obtained by the preparation method provided in the embodiment of the present application has less micropore and mesoporous structure content, and higher surface density, thereby blocking the dissolution of transition metal ions and reducing the positive electrode-electrolyte interface side reactions, and thus the battery using the positive electrode active material prepared by the preparation method provided in the embodiment of the present application can have good cycle performance and storage performance.

[0012] In some embodiments, the oxygen-free organic carbon source comprises an oxygen-free polymer containing at least one of fluorine atoms, nitrogen atoms, and sulfur atoms.

[0013] Due to their longer molecular chains, oxygen-free polymers are more likely to form a carbon coating with a high degree of graphitization, low micropore and mesoporous content, and high density. The increased degree of graphitization in the carbon coating improves the electronic conductivity of the positive electrode active material, thereby facilitating the utilization of the specific capacity of the positive electrode active material. The carbon coating's low micropore and mesoporous content and high density can better isolate the lithium-phosphate active material from direct contact with the electrolyte, thereby further reducing side reactions at the positive electrode-electrolyte interface and further improving the battery's cycling and storage performance.

[0014] After pyrolysis, oxygen-free polymers containing at least one of fluorine, nitrogen, and sulfur atoms can leave a certain amount of fluorine, nitrogen, and sulfur atoms in the carbon coating layer, which can act as doping agents. The doping atoms can change the charge distribution around the carbon atoms, further improving the electronic conductivity of the carbon coating layer. The doping atoms can also form defect structures within the carbon coating layer, which facilitate the rapid migration of lithium ions, thereby improving the battery's cycling performance. Furthermore, the doping atoms can form functional groups containing doping atoms on the surface of the carbon coating layer. These functional groups can serve as new active sites, increasing the solvation and desolvation rates of lithium ions, thereby improving the battery's cycling performance.

[0015] In some embodiments, the oxygen-free polymer comprises one or more of polyolefin, fluoropolyolefin, polyalkyne, polyacrylonitrile, polypyrrole, polythiophene, polyaniline, and their respective derivatives. Alternatively, the oxygen-free polymer comprises one or more of fluoropolyolefin, polyacrylonitrile, polypyrrole, polythiophene, polyaniline, and their respective derivatives, and the fluoropolyolefin comprises one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl fluoride, perfluoroethylene-propylene copolymer, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, and tetrafluoroethylene-hexafluoropropylene copolymer.

[0016] In some embodiments, the oxygen-free organic small molecule compound includes one or more of phenothiazine compounds, aromatic hydrocarbon compounds, alkane compounds, olefin compounds, alkyne compounds, fluoroalkane compounds, fluoroolefin compounds, fluoroalkyne compounds, aniline compounds, and their respective derivatives.

[0017] In some embodiments, the number average molecular weight of the oxygen-free polymer is 1,000-5,000,000, optionally 50,000-1,000,000.

[0018] The number average molecular weight of the oxygen-free polymer is within the above range, which can form a carbon coating layer with a high degree of graphitization, a low content of micropores and mesoporous structures, and high density and uniformity. This can make the positive electrode active material have good electronic conductivity, effectively isolate the lithium phosphate active material from direct contact with the electrolyte, and better reduce the positive electrode-electrolyte interface side reactions, thereby better improving the cycle performance and storage performance of the battery.

[0019] In some embodiments, the oxygen-free polymer has a polydispersity index of 1-5, optionally 1-3.

[0020] When the polydispersity index of the oxygen-free polymer is within the above range, a carbon coating layer with a high degree of graphitization, a low content of micropores and mesoporous structures, and high density and uniformity can be formed, thereby enabling the positive electrode active material to have good electronic conductivity, effectively isolating the lithium phosphate active material from direct contact with the electrolyte, and better reducing the positive electrode-electrolyte interface side reactions, thereby better improving the cycle performance and storage performance of the battery.

[0021] In some embodiments, the thermal decomposition temperature of the oxygen-free polymer is 200°C-600°C, optionally 250°C-550°C.

[0022] The thermal decomposition temperature of the oxygen-free polymer is within the above range, so that it can be fully pyrolyzed during the sintering process, and the formed carbon coating layer can have a high degree of graphitization, so that the carbon coating layer has both good electronic conductivity and more lithium ion pathways, which is beneficial to improving the gram capacity and kinetic performance of the positive electrode active material; the formed carbon coating layer can also have a lower oxygen content, thereby reducing the water absorption rate and amount of the positive electrode active material, reducing the residual moisture content of the positive electrode sheet, and reducing battery side reactions, thereby making the battery have better cycle performance and storage performance.

[0023] In some embodiments, the mass ratio of the residual carbon mass of the oxygen-free organic carbon source after sintering under a protective gas atmosphere to the positive electrode active material is (0.01-6):100.

[0024] The mass ratio of the residual carbon mass of the oxygen-free organic carbon source after sintering in a protective gas atmosphere to the mass of the positive electrode active material is within the above range, which can not only form a complete coating on the lithium-phosphate active material, reduce the contact area between the lithium-phosphate active material and the electrolyte, reduce the side reaction at the positive electrode-electrolyte interface, and reduce the dissolution of transition metal ions; it can also effectively improve the electronic conductivity of the positive electrode active material and enable the positive electrode active material to have a higher gram capacity.

[0025] In some embodiments, the protective gas includes one or more of nitrogen, argon, and helium.

[0026] In some embodiments, the heating rate of the sintering process is less than or equal to 5° C. / min.

[0027] The heating rate of the sintering treatment is within the above range, which helps to form a carbon coating layer with low oxygen content, low micropore and mesoporous structure content, high density and uniformity, thereby reducing the water absorption rate and amount of the positive electrode active material, reducing the residual moisture content of the positive electrode plate, and reducing the direct contact between the lithium phosphate active material and the electrolyte, reducing the side reactions at the positive electrode-electrolyte interface, and thus making the battery have better cycle performance and storage performance.

[0028] In some embodiments, the sintering process is a step-by-step sintering process, which includes a first-stage sintering process and a second-stage sintering process. The difference between the insulation temperature of the first-stage sintering process and the thermal decomposition temperature of the oxygen-free organic carbon source is greater than or equal to -50°C, and the insulation temperature of the second-stage sintering process is 650°C-800°C.

[0029] The use of step-by-step sintering treatment helps to form a carbon coating layer with low oxygen content, low micropore and mesoporous structure content, high density and uniformity, thereby reducing the water absorption rate and amount of the positive electrode active material, reducing the residual moisture content of the positive electrode plate, reducing the direct contact between the lithium phosphate active material and the electrolyte, and reducing the side reactions at the positive electrode-electrolyte interface, thereby making the battery have better cycle performance and storage performance.

[0030] The difference between the holding temperature of the first-stage sintering treatment and the thermal decomposition temperature of the oxygen-free organic carbon source is greater than or equal to -50°C, which can enable the oxygen-free organic carbon source to be better decomposed and carbonized during the first-stage sintering treatment, thereby being beneficial to the rearrangement of carbon atoms in the subsequent second-stage sintering process, and being beneficial to the carbon coating layer having a higher degree of graphitization. It is also beneficial to reduce the micropore and mesoporous structure content of the carbon coating layer, improve the density and uniformity of the carbon coating layer, and improve the bonding strength between the carbon coating layer and the lithium phosphate active material, thereby helping to further improve the cycle performance and storage performance of the battery.

[0031] When the holding temperature of the second-stage sintering treatment is within the above-mentioned range, the lithium-phosphate active material can be made highly stable while the formed carbon coating layer has a high degree of graphitization, so that the carbon coating layer has both good electronic conductivity and more lithium ion pathways, thereby facilitating the improvement of the specific capacity and kinetic performance of the positive electrode active material. The formed carbon coating layer can also have a low oxygen content and a high density, thereby reducing the water absorption rate and amount of the positive electrode active material and the residual moisture content of the positive electrode sheet, thereby reducing battery side reactions and the amount of transition metal ions dissolved in the positive electrode active material. The positive electrode active material can also have a suitable particle size to avoid an increase in lithium ion diffusion paths due to an overly large particle size. Therefore, when the holding temperature of the second-stage sintering treatment is within the above-mentioned range, the battery can have better cycle performance and storage performance.

[0032] In some embodiments, the holding temperature of the first stage sintering treatment is greater than or equal to the thermal decomposition temperature of the oxygen-free organic carbon source.

[0033] This allows the oxygen-free organic carbon source to be fully decomposed and carbonized during the first sintering process, which is beneficial for the rearrangement of carbon atoms in the subsequent second sintering process, and is beneficial for the carbon coating layer to have a higher degree of graphitization. It is also beneficial to reduce the micropore and mesoporous structure content of the carbon coating layer, improve the density and uniformity of the carbon coating layer, and improve the bonding strength between the carbon coating layer and the lithium phosphate active material, which helps to further improve the cycle performance and storage performance of the battery.

[0034] In some embodiments, the holding time of the first sintering process is shorter than the holding time of the second sintering process.

[0035] In some embodiments, the holding time of the sintering treatment is 2 hours to 7 hours.

[0036] The holding time of a sintering treatment is within the above range, which is conducive to the carbon coating having a higher degree of graphitization, and is also conducive to reducing the micropore and mesoporous structure content of the carbon coating, improving the density and uniformity of the carbon coating, and improving the bonding strength between the carbon coating and the lithium phosphate active material, thereby helping to further improve the cycle performance and storage performance of the battery.

[0037] In some embodiments, the holding time of the second-stage sintering process is 8 hours to 20 hours.

[0038] The holding time of the second-stage sintering treatment within the above range can not only ensure high stability of the lithium-phosphate active material, but also ensure that the formed carbon coating has a high degree of graphitization, so that the carbon coating has both good electronic conductivity and a large number of lithium ion pathways, thereby facilitating improved specific capacity and kinetic performance of the positive electrode active material. The formed carbon coating can also have a low oxygen content, thereby reducing the water absorption rate and amount of the positive electrode active material and the residual moisture content of the positive electrode sheet, thereby reducing battery side reactions and reducing the amount of transition metal ion dissolution from the positive electrode active material. Therefore, the holding time of the second-stage sintering treatment within the above range can enable the battery to have better cycle performance and storage performance.

[0039] In some embodiments, the lithium phosphate active material includes one or more of lithium manganese iron phosphate, lithium iron phosphate, and their respective modified materials, and the modification methods include doping modification and / or surface coating modification, and the doping includes metal doping and / or non-metal doping.

[0040] In some embodiments, the precursor of the lithium phosphate active material includes one or more of ferromanganese phosphate, ferromanganese pyrophosphate, ammonium ferromanganese phosphate, ferromanganese oxalate, iron phosphate, doped ferromanganese phosphate, doped ferromanganese pyrophosphate, doped ammonium ferromanganese phosphate, doped ferromanganese oxalate, and doped iron phosphate, and the doping includes metal doping and / or non-metal doping.

[0041] In some embodiments, the preparation method of the lithium phosphate active material comprises any one of a solid phase synthesis method, a sol-gel method, a co-precipitation method, a hydrothermal method, or a solvothermal method.

[0042] In some embodiments, the preparation method of the precursor of the lithium phosphate active material includes any one of a solid phase synthesis method, a sol-gel method, a co-precipitation method, a hydrothermal method, or a solvothermal method.

[0043] In some embodiments, in the step of uniformly mixing the lithium phosphate active material or the precursor of the lithium phosphate active material with the oxygen-free organic carbon source, a dispersant is also added to the mixture, and the dispersant includes one or more of water, ethanol, acetone, toluene, and N-methylpyrrolidone.

[0044] In some embodiments, in the step of uniformly mixing the precursor of the lithium-phosphate active material and the oxygen-free organic carbon source, a lithium source is also added to the mixture, or a lithium source and a phosphorus source are added at the same time, so that the precursor of the lithium-phosphate active material forms a lithium-phosphate active material after sintering.

[0045] In some embodiments, the method further comprises drying the obtained mixture before sintering in a protective gas atmosphere.

[0046] In a second aspect, the present application provides a positive electrode active material prepared by the preparation method of the first aspect of the present application.

[0047] In a third aspect, the present application provides a positive electrode plate, comprising a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector, wherein the positive electrode film layer comprises a positive electrode active material prepared by the preparation method of the first aspect of the present application.

[0048] In a fourth aspect, the present application provides a battery cell comprising the positive electrode sheet according to the third aspect of the present application.

[0049] In a fifth aspect, the present application provides a battery comprising the battery cell according to the fourth aspect of the present application.

[0050] In a sixth aspect, the present application provides an electrical device comprising the battery according to the fifth aspect of the present application, wherein the battery is used to provide electrical energy.

[0051] The electric device of the present application includes the battery provided by the present application, and thus has at least the same advantages as the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] To more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on the drawings without inventive effort.

[0053] FIG1 is a schematic structural diagram of a vehicle provided in some embodiments of the present application.

[0054] FIG2 is a schematic diagram of an explosion of a battery provided in some embodiments of the present application.

[0055] FIG3 is a schematic structural diagram of a battery module provided in some embodiments of the present application.

[0056] FIG4 is a schematic structural diagram of a battery cell provided in some embodiments of the present application.

[0057] FIG5 is a schematic diagram of an explosion of a battery cell provided in some embodiments of the present application.

[0058] In the accompanying drawings, the drawings are not necessarily drawn to scale.

[0059] The figure numbers are explained as follows: 1. Vehicle; 2. Battery; 3. Controller; 4. Motor; 5. Box; 5a. First box part; 5b. Second box part; 5c. Accommodation space; 6. Battery module; 7. Battery cell; 71. Shell; 72. Electrode assembly; 73. Cover plate. DETAILED DESCRIPTION

[0060] Below, with appropriate reference to the accompanying drawings, the embodiments of the positive electrode active material and its preparation method, as well as the positive electrode sheet, battery cell, battery and electrical device containing the same are specifically disclosed. 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 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 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.

[0061] " 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.

[0062] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present application.

[0063] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of this application.

[0064] 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.

[0065] Unless otherwise specified, in this application, the terms "first", "second", etc. are used to distinguish different objects rather than to describe a specific order or a primary-secondary relationship.

[0066] In this application, the terms "plurality" and "multiple" refer to two or more.

[0067] In this application, the term "about" is used to describe and illustrate small variations, and when used in conjunction with a numerical value, the term may refer to a range of variation that is less than or equal to ±5% of the numerical value.

[0068] In the description of the embodiments of the present application, unless otherwise specified, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. Furthermore, a first feature being "above," "above," and "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is at a higher level than the second feature. A first feature being "below," "below," and "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0069] Unless otherwise specified, the terms used in this application have the common meanings that are commonly understood by those skilled in the art.

[0070] Unless otherwise stated, the numerical values ​​of the various parameters mentioned in this application can be measured using various test methods commonly used in the art, for example, they can be measured according to the test methods given in the examples of this application. Unless otherwise stated, the test temperature of each parameter is 25°C.

[0071] The battery mentioned in the embodiments of the present application may be a single physical module including one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in the present application may include a battery cell, a battery module or a battery pack, etc. A battery cell is the smallest unit that makes up a battery, which can independently realize the function of charging and discharging. When there are multiple battery cells, the multiple battery cells are connected in series, in parallel or in mixed connection through a busbar. In some embodiments, the battery may be a battery module; when there are multiple battery cells, the multiple battery cells are arranged and fixed to form a battery module. In some embodiments, the battery may be a battery pack, which includes a case and battery cells, and the battery cells or battery modules are housed in the case. In some embodiments, the case may serve as part of the chassis structure of the vehicle. For example, part of the case may become at least part of the floor of the vehicle, or part of the case may become at least part of the crossbeam and longitudinal beam of the vehicle.

[0072] In some embodiments, the battery may be an energy storage device, including an energy storage container, an energy storage cabinet, and the like.

[0073] The technical solutions described in the embodiments of the present application are applicable to batteries and electrical devices using batteries.

[0074] Batteries can be used as power sources or energy storage units for electrical devices. Electrical devices include, but are not limited to, mobile devices (e.g., mobile phones, tablets, laptops, etc.), vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, and energy storage systems.

[0075] The electrical device can select the type of battery according to its usage requirements, such as a battery cell, a battery module or a battery pack.

[0076] For the convenience of description, the following embodiments are described by taking a vehicle as an example of an electrical device.

[0077] FIG1 is a schematic structural diagram of a vehicle provided in some embodiments of the present application.

[0078] As shown in FIG1 , a battery 2 is provided inside the vehicle 1. The battery 2 may be provided at the bottom, head, or tail of the vehicle 1. The battery 2 may be used to power the vehicle 1. For example, the battery 2 may serve as an operating power source for the vehicle 1.

[0079] The vehicle 1 may further include a controller 3 and a motor 4 . The controller 3 is used to control the battery 2 to supply power to the motor 4 , for example, to meet the power requirements of the vehicle 1 during startup, navigation, and driving.

[0080] In some embodiments, the battery 2 can serve not only as an operating power source for the vehicle 1 , but also as a driving power source for the vehicle 1 , replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1 .

[0081] FIG2 is an exploded view of a battery according to some embodiments of the present application. As shown in FIG2 , the battery 2 includes a housing 5 and battery cells (not shown), which are housed in the housing 5 .

[0082] The housing 5 is used to house battery cells and can have various structures. In some embodiments, the housing 5 can include a first housing portion 5a and a second housing portion 5b. The first housing portion 5a and the second housing portion 5b overlap each other, and the first housing portion 5a and the second housing portion 5b together define a storage space 5c for accommodating the battery cells. The second housing portion 5b can be a hollow structure with one end open. The first housing portion 5a is a plate-like structure, and the first housing portion 5a overlaps the open side of the second housing portion 5b to form the housing 5 with the storage space 5c. The first housing portion 5a and the second housing portion 5b can also be hollow structures with one end open. The open side of the first housing portion 5a overlaps the open side of the second housing portion 5b to form the housing 5 with the storage space 5c. Of course, the first housing portion 5a and the second housing portion 5b can have various shapes, such as a cylinder, a rectangular parallelepiped, etc.

[0083] In order to improve the sealing performance after the first box body 5a and the second box body 5b are connected, a sealing member, such as a sealant, a sealing ring, etc., may also be provided between the first box body 5a and the second box body 5b.

[0084] Assuming that the first box body portion 5a covers the top of the second box body portion 5b, the first box body portion 5a can also be called an upper box cover, and the second box body portion 5b can also be called a lower box body.

[0085] In battery 2, there can be one or more battery cells. If there are multiple battery cells, they can be connected in series, in parallel, or in a hybrid configuration. A hybrid configuration refers to a combination of series and parallel connections. Multiple battery cells can be directly connected in series, in parallel, or in a hybrid configuration, and then the entire battery cell structure can be housed within housing 5. Alternatively, multiple battery cells can be first connected in series, in parallel, or in a hybrid configuration to form a battery module 6, and then multiple battery modules 6 can be connected in series, in parallel, or in a hybrid configuration to form a single unit and housed within housing 5.

[0086] FIG3 is a schematic structural diagram of a battery module provided in some embodiments of the present application.

[0087] As shown in FIG3 , in some embodiments, there are multiple battery cells 7, which are first connected in series, in parallel, or in hybrid to form a battery module 6. The multiple battery modules 6 are then connected in series, in parallel, or in hybrid to form a whole and housed in a box.

[0088] The multiple battery cells 7 in the battery module 6 can be electrically connected via a busbar component to achieve parallel connection, series connection, or mixed connection of the multiple battery cells 7 in the battery module 6 .

[0089] FIG4 is a schematic structural diagram of a battery cell provided in some embodiments of the present application.

[0090] The present application has no particular limitation on the shape of the battery cell, which can be cylindrical, square, or any other shape. FIG4 shows a square-shaped battery cell 7 as an example.

[0091] The battery cell 7 includes an electrode assembly and an outer packaging, which can be used to encapsulate the electrode assembly. The outer packaging can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging can also be a soft package, such as a bag-type soft package. The soft package can be made of plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0092] FIG5 is a schematic diagram of an explosion of a battery cell provided in some embodiments of the present application.

[0093] As shown in Figure 5, the outer packaging may include a housing 71 and a cover plate 73. The housing 71 may include a base plate and side plates connected to the base plate, which together form a receiving cavity. The housing 71 has an opening communicating with the receiving cavity, and the cover plate 73 is used to cover the opening, thereby sealing the receiving cavity. The electrode assembly 72 is enclosed in the receiving cavity. The number of electrode assemblies 72 contained in a battery cell 7 may be one or more, and can be adjusted according to needs.

[0094] The battery cells mentioned in the embodiments of the present application include lithium-ion primary battery cells, lithium-ion secondary battery cells, lithium metal battery cells, negative electrode-free lithium metal battery cells, etc., which are not limited in the embodiments of the present application.

[0095] The electrode assembly generally includes a positive electrode sheet and a negative electrode sheet. The electrode assembly may be a wound structure or a laminated structure, which is not limited in the embodiments of the present application.

[0096] As an important component of the positive electrode sheet, the performance of the positive electrode active material is crucial to the battery performance.

[0097] The serious defects of lithium-containing phosphate active materials represented by lithium manganese iron phosphate are: low electronic conductivity and easy dissolution of transition metal ions, especially manganese ions.

[0098] After the transition metal ions in the positive electrode active material dissolve and migrate to the negative electrode, they will be reduced to metal elements. These produced metal elements are equivalent to "catalysts" that can catalyze the decomposition of the SEI film (solid electrolyte interphase) on the surface of the negative electrode. Part of the byproducts produced are gases, which can easily cause the battery to swell, affecting the battery's reliability and storage performance. The other part is solid and will be deposited on the surface of the negative electrode, thereby blocking the passage of lithium ions in and out of the negative electrode, thereby increasing the impedance of the battery. In addition, in order to replenish the lost SEI film, the electrolyte and the active lithium ions inside the battery are also continuously consumed, which also has an irreversible effect on the battery's cycle capacity retention rate.

[0099] Residual moisture in the positive electrode can also affect battery performance. During the battery's charge and discharge process, residual moisture in the positive electrode dissolves into the electrolyte, causing the decomposition of the commonly used electrolyte salt LiPF6 in the electrolyte to produce HF. HF is an acidic substance that corrodes the positive electrode active material and exacerbates the dissolution of transition metal ions. The higher the residual moisture content in the positive electrode, the more severe the dissolution of transition metal ions in the positive electrode active material.

[0100] An embodiment of the present application provides a method for preparing a positive electrode active material, wherein the positive electrode active material prepared in this manner has a low water absorption rate and water absorption amount, thereby reducing the residual moisture content of the positive electrode plate and the amount of transition metal ions dissolved out of the positive electrode active material, and also enabling the battery using the same to have good cycle performance and storage performance.

[0101] The preparation method includes the following steps: providing a lithium-containing phosphate active material or a precursor of the lithium-containing phosphate active material; providing an oxygen-free organic carbon source, wherein the oxygen-free organic carbon source includes one or more of an oxygen-free polymer and an oxygen-free organic small molecule compound; uniformly mixing the lithium-containing phosphate active material or the precursor of the lithium-containing phosphate active material with the oxygen-free organic carbon source to obtain a mixture, and then sintering the mixture under a protective gas atmosphere to carbonize the oxygen-free organic carbon source to form a carbon coating layer that coats at least a portion of the surface of the lithium-containing phosphate active material, thereby obtaining a positive electrode active material.

[0102] At present, aerobic materials such as sucrose, glucose, starch, and polyethylene glycol are commonly used as carbon sources. The inventors have noticed that a large amount of carbon dioxide and carbon monoxide gas will be generated during the pyrolysis of aerobic materials. After the gas is released, the carbon coating layer will form a large number of micropores and mesoporous structures. On the one hand, the electrolyte can pass through the pore structure of the carbon coating layer and directly contact the lithium phosphate active material, thereby increasing the positive electrode-electrolyte interface side reactions and the irreversible consumption of active ions; on the other hand, the carbon coating layer formed after the carbonization of the aerobic material usually has a high specific surface area, which will also lead to an increase in the water absorption rate and water absorption of the positive electrode active material, an increase in the residual moisture content of the positive electrode sheet, and thus increase the side reactions of the battery and the amount of transition metal ions dissolved in the positive electrode active material.

[0103] During the pyrolysis of aerobic materials, oxygen cannot be completely removed, resulting in a high oxygen content in the carbon coating formed after carbonization. Oxygen usually exists in the form of oxygen-containing functional groups, such as hydroxyl and carboxyl groups. These oxygen-containing functional groups are highly electrochemically active and will catalyze the decomposition of the electrolyte during battery use, increasing the battery's volume expansion and affecting battery reliability. At the same time, the oxygen-containing functional groups in the carbon coating are also good water absorption sites, absorbing water vapor from the air. This will also increase the water absorption rate and amount of the positive electrode active material, increase the residual moisture content of the positive electrode sheet, and further increase the battery's side reactions and the amount of transition metal ions dissolved in the positive electrode active material.

[0104] The preparation method provided in the embodiment of the present application adopts an oxygen-free organic carbon source, which includes one or more oxygen-free polymers and oxygen-free organic small molecule compounds. The oxygen-free organic carbon source releases less gas during the pyrolysis process, and the carbon coating layer formed after carbonization has less micropores and mesoporous structures. The carbon coating layer has high density, thereby reducing the direct contact between the lithium phosphate active material and the electrolyte and reducing the side reactions at the positive electrode-electrolyte interface; at the same time, the dense carbon coating layer can also play a role in blocking the dissolution of transition metal ions.

[0105] The carbon coating layer formed after the carbonization of the oxygen-free organic carbon source has a small content of micropores and mesoporous structures, and the specific surface area of ​​the positive electrode active material is also low, so its water absorption rate and water absorption amount are low, and the positive electrode slurry is easier to dry, the residual moisture content of the positive electrode sheet is lower, and the amount of transition metal ions dissolved in the positive electrode active material is lower.

[0106] The carbon coating layer formed after the carbonization of the oxygen-free organic carbon source has fewer oxygen-containing functional groups and lower electrochemical activity, which can also reduce the catalytic decomposition of the electrolyte; at the same time, the carbon coating layer formed after the carbonization of the oxygen-free organic carbon source has fewer oxygen-containing functional groups, and the positive electrode active material has fewer water absorption sites, thereby reducing its water absorption rate and water absorption amount, and thus the positive electrode slurry is easier to dry, the residual moisture content of the positive electrode sheet is lower, and the amount of transition metal ions dissolved in the positive electrode active material is lower.

[0107] Therefore, the positive electrode active material obtained by the preparation method provided in the embodiment of the present application has a lower water absorption rate and water absorption amount, so that the positive electrode slurry is easier to dry, the residual moisture content of the positive electrode sheet is lower, and the transition metal ion dissolution amount of the positive electrode active material is lower; the positive electrode active material obtained by the preparation method provided in the embodiment of the present application has less micropore and mesoporous structure content, and higher surface density, thereby blocking the dissolution of transition metal ions and reducing the positive electrode-electrolyte interface side reactions, and thus the battery using the positive electrode active material prepared by the preparation method provided in the embodiment of the present application can have good cycle performance and storage performance.

[0108] In some embodiments, the oxygen-free organic small molecule compound may include one or more of phenothiazine compounds, aromatic hydrocarbon compounds, alkane compounds, olefin compounds, alkyne compounds, fluoroalkane compounds, fluoroolefin compounds, fluoroalkyne compounds, aniline compounds, and their respective derivatives. A derivative refers to a product derived from the replacement of a hydrogen atom or atomic group in a compound by another atom or atomic group. As an example, the oxygen-free organic small molecule compound may include one or more of ethylene, propylene, styrene, vinylidene fluoride, tetrafluoroethylene, and vinyl fluoride.

[0109] In some embodiments, the oxygen-free organic carbon source may include an oxygen-free polymer.

[0110] Alternatively, the oxygen-free organic carbon source may include an oxygen-free polymer containing at least one of a fluorine atom, a nitrogen atom, and a sulfur atom.

[0111] Due to their longer molecular chains, oxygen-free polymers are more likely to form a carbon coating with a high degree of graphitization, low micropore and mesoporous content, and high density. The increased degree of graphitization in the carbon coating improves the electronic conductivity of the positive electrode active material, thereby facilitating the utilization of the specific capacity of the positive electrode active material. The carbon coating's low micropore and mesoporous content and high density can better isolate the lithium-phosphate active material from direct contact with the electrolyte, thereby further reducing side reactions at the positive electrode-electrolyte interface and further improving the battery's cycling and storage performance.

[0112] After pyrolysis, oxygen-free polymers containing at least one of fluorine, nitrogen, and sulfur atoms can leave a certain amount of fluorine, nitrogen, and sulfur atoms in the carbon coating layer, which can act as doping agents. The doping atoms can change the charge distribution around the carbon atoms, further improving the electronic conductivity of the carbon coating layer. The doping atoms can also form defect structures within the carbon coating layer, which facilitate the rapid migration of lithium ions, thereby improving the battery's cycling performance. Furthermore, the doping atoms can form functional groups containing doping atoms on the surface of the carbon coating layer. These functional groups can serve as new active sites, increasing the solvation and desolvation rates of lithium ions, thereby improving the battery's cycling performance.

[0113] In some embodiments, the oxygen-free polymer may include one or more of polyolefins, fluoropolyolefins, polyalkynes, polyacrylonitrile, polypyrrole, polythiophene, polyaniline, and their respective derivatives. Derivatives refer to products derived from the substitution of hydrogen atoms or atomic groups in a polymer with other atoms or atomic groups.

[0114] Alternatively, the oxygen-free polymer may include one or more of fluorinated polyolefins, polyacrylonitrile, polypyrrole, polythiophene, polyaniline, and derivatives thereof.

[0115] Alternatively, the polyolefin may include one or more of polyethylene, polypropylene, and polystyrene.

[0116] Alternatively, the fluorinated polyolefin may include one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl fluoride, perfluoroethylene-propylene copolymer, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, and tetrafluoroethylene-hexafluoropropylene copolymer.

[0117] In some embodiments, the number average molecular weight of the oxygen-free polymer may be 1,000-5,000,000, optionally 50,000-1,000,000, 100,000-800,000, 200,000-600,000, or 300,000-500,000.

[0118] The number average molecular weight of the oxygen-free polymer decreases, its molecular chain becomes shorter, the degree of graphitization of the formed carbon coating decreases, the content of micropores and mesoporous structures increases, and the density decreases, which is not conducive to further improving the electronic conductivity of the positive electrode active material. At the same time, the effect of the carbon coating layer in isolating the lithium phosphate active material from direct contact with the electrolyte will also deteriorate, thereby further improving the battery cycle performance and / or storage performance.

[0119] As the number average molecular weight of the oxygen-free polymer increases, the difficulty of dispersing the slurry in the carbon coating process increases, which is not conducive to the formation of a uniform carbon coating layer. Therefore, the effect of the carbon coating layer in isolating the lithium phosphate active material from direct contact with the electrolyte will become worse, and the effect of reducing the side reactions at the positive electrode-electrolyte interface will also become worse, which will lead to a worse effect on further improving the battery cycle performance and / or storage performance.

[0120] The number average molecular weight of the oxygen-free polymer is within the above range, which can form a carbon coating layer with a high degree of graphitization, a low content of micropores and mesoporous structures, and high density and uniformity. This can make the positive electrode active material have good electronic conductivity, effectively isolate the lithium phosphate active material from direct contact with the electrolyte, and better reduce the positive electrode-electrolyte interface side reactions, thereby better improving the cycle performance and storage performance of the battery.

[0121] In some embodiments, the polydispersity index of the oxygen-free polymer may be 1-5, optionally 1-4, 1-3, or 1-2.

[0122] When the polydispersity index of the oxygen-free polymer is within the above range, a carbon coating layer with a high degree of graphitization, a low content of micropores and mesoporous structures, and high density and uniformity can be formed, thereby enabling the positive electrode active material to have good electronic conductivity, effectively isolating the lithium phosphate active material from direct contact with the electrolyte, and better reducing the positive electrode-electrolyte interface side reactions, thereby better improving the cycle performance and storage performance of the battery.

[0123] The polydispersity index of an oxygen-free polymer refers to the ratio of the weight average molecular weight to the number average molecular weight of the oxygen-free polymer. The number average molecular weight, weight average molecular weight, and polydispersity index of an oxygen-free polymer can be measured using gel permeation chromatography.

[0124] In some embodiments, the thermal decomposition temperature of the oxygen-free polymer may be 200°C-600°C, optionally 220°C-550°C, or 250°C-550°C.

[0125] The thermal decomposition temperature of the oxygen-free polymer is within the above range, so that it can be fully pyrolyzed during the sintering process, and the formed carbon coating layer can have a high degree of graphitization, so that the carbon coating layer has both good electronic conductivity and more lithium ion pathways, which is beneficial to improving the gram capacity and kinetic performance of the positive electrode active material; the formed carbon coating layer can also have a lower oxygen content, thereby reducing the water absorption rate and amount of the positive electrode active material, reducing the residual moisture content of the positive electrode sheet, and reducing battery side reactions, thereby making the battery have better cycle performance and storage performance.

[0126] The thermal decomposition temperature of the oxygen-free polymer has a well-known meaning generally understood by those skilled in the art, which refers to the temperature at which the mass of the oxygen-free polymer begins to remain stable during the thermal decomposition process, and can be obtained by thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) testing. The starting temperature of the test is 20°C-25°C, the heating rate is 10°C / min, and the atmosphere is nitrogen. An exemplary testing method is as follows: two parallel samples are taken and subjected to thermogravimetric analysis and differential scanning calorimetry analysis, respectively. Then, the temperature range at which the mass of the oxygen-free polymer begins to remain stable during the thermal decomposition process can be determined from the TG curve, and then the peak temperature in the corresponding temperature range is read from the DSC curve as the thermal decomposition temperature.

[0127] In some embodiments, the lithium-phosphate active material may include one or more of lithium manganese iron phosphate, lithium iron phosphate, and their respective modified materials. The modification methods include doping modification and / or surface coating modification, and the doping includes metal doping and / or non-metallic doping. When surface coating modification is adopted, the coating material may include a compound with ion conductivity and / or electron conductivity, for example, it may include one or more of polymers, oxides, fast ion conductors, phosphates, and pyrophosphates. The doping sites may be one or more of lithium sites, manganese sites, iron sites, phosphorus sites, and oxygen sites.

[0128] The lithium phosphate active material can be prepared using methods known in the art. In some embodiments, the preparation method of the lithium phosphate active material can include any one of solid phase synthesis, sol-gel method, coprecipitation method, hydrothermal method or solvothermal method.

[0129] In some embodiments, the precursor of the lithium phosphate-containing active material may include one or more of ferromanganese phosphate, ferromanganese pyrophosphate, ammonium ferromanganese phosphate, ferromanganese oxalate, iron phosphate, doped ferromanganese phosphate, doped ferromanganese pyrophosphate, doped ammonium ferromanganese phosphate, doped ferromanganese oxalate, and doped iron phosphate, wherein the doping may include metal doping and / or non-metal doping. The doping site may be one or more of manganese, iron, and phosphorus.

[0130] The precursor of the lithium phosphate active material can be prepared using methods known in the art. In some embodiments, the preparation method of the precursor of the lithium phosphate active material can include any one of solid phase synthesis, sol-gel method, coprecipitation method, hydrothermal method or solvothermal method.

[0131] In some embodiments, during the step of uniformly mixing the lithium phosphate-containing active material or the precursor of the lithium phosphate-containing active material with the oxygen-free organic carbon source, a dispersant is further added to the mixture. Optionally, the dispersant may include one or more of water, ethanol, acetone, toluene, and N-methylpyrrolidone (NMP).

[0132] In this way, the lithium phosphate active material or the precursor of the lithium phosphate active material can be fully and evenly mixed with the oxygen-free organic carbon source, which is conducive to forming a carbon coating layer with better quality in the subsequent sintering process.

[0133] The order of adding the lithium-containing phosphate active material or its precursor, the oxygen-free organic carbon source, and the dispersant is not particularly limited and can be adjusted according to actual conditions. For example, the oxygen-free organic carbon source and the dispersant can be first stirred evenly to obtain a coating solution, and then the lithium-containing phosphate active material or its precursor is added to the solution to obtain a mixture. Alternatively, the lithium-containing phosphate active material or its precursor, the oxygen-free organic carbon source, and the dispersant can be directly mixed to obtain a mixture.

[0134] In some embodiments, in the step of uniformly mixing the precursor of the lithium phosphate active material with the oxygen-free organic carbon source, a lithium source is also added to the mixture, or a lithium source and a phosphorus source are also added at the same time, so that the precursor of the lithium phosphate active material forms a lithium phosphate active material after sintering.

[0135] In some embodiments, the sintering process under a protective gas atmosphere further includes drying the resulting mixture. The drying process may be performed in a vacuum oven at a temperature of 150° C. to 200° C.

[0136] Optionally, the obtained mixture may be sand-milled before being dried.

[0137] In some embodiments, the mass ratio of the residual carbon mass after sintering the oxygen-free organic carbon source under a protective gas atmosphere to the positive electrode active material can be (0.01-6):100, optionally (0.5-4):100, (1-4):100.

[0138] The mass ratio of the residual carbon mass of the oxygen-free organic carbon source after sintering in a protective gas atmosphere to the mass of the positive electrode active material is within the above range, which can not only form a complete coating on the lithium-phosphate active material, reduce the contact area between the lithium-phosphate active material and the electrolyte, reduce the side reaction at the positive electrode-electrolyte interface, and reduce the dissolution of transition metal ions; it can also effectively improve the electronic conductivity of the positive electrode active material and enable the positive electrode active material to have a higher gram capacity.

[0139] In some embodiments, the shielding gas may include one or more of nitrogen, argon, and helium.

[0140] In some embodiments, the heating rate of the sintering process may be less than or equal to 5°C / min, and may be 0.5°C / min-3°C / min, 0.5°C / min-2°C / min, or 0.5°C / min-1°C / min.

[0141] The heating rate of the sintering treatment is within the above range, which helps to form a carbon coating layer with low oxygen content, low micropore and mesoporous structure content, high density and uniformity, thereby reducing the water absorption rate and amount of the positive electrode active material, reducing the residual moisture content of the positive electrode plate, and reducing the direct contact between the lithium phosphate active material and the electrolyte, reducing the side reactions at the positive electrode-electrolyte interface, and thus making the battery have better cycle performance and storage performance.

[0142] In some embodiments, the sintering process may be a step-by-step sintering process, which includes a first-stage sintering process and a second-stage sintering process.

[0143] The use of step-by-step sintering treatment helps to form a carbon coating layer with low oxygen content, low micropore and mesoporous structure content, high density and uniformity, thereby reducing the water absorption rate and amount of the positive electrode active material, reducing the residual moisture content of the positive electrode plate, reducing the direct contact between the lithium phosphate active material and the electrolyte, and reducing the side reactions at the positive electrode-electrolyte interface, thereby making the battery have better cycle performance and storage performance.

[0144] The difference between the holding temperature of the first stage sintering treatment and the thermal decomposition temperature of the oxygen-free organic carbon source may be greater than or equal to -50°C.

[0145] This allows the oxygen-free organic carbon source to be better decomposed and carbonized during the first-stage sintering process, which is beneficial for the rearrangement of carbon atoms in the subsequent second-stage sintering process, and is beneficial for the carbon coating layer to have a higher degree of graphitization. It is also beneficial to reduce the micropore and mesoporous structure content of the carbon coating layer, improve the density and uniformity of the carbon coating layer, and improve the bonding strength between the carbon coating layer and the lithium phosphate active material, which helps to further improve the cycle performance and storage performance of the battery.

[0146] Optionally, the holding temperature of the first stage sintering treatment may be greater than or equal to the thermal decomposition temperature of the oxygen-free organic carbon source.

[0147] This allows the oxygen-free organic carbon source to be fully decomposed and carbonized during the first sintering process, which is beneficial for the rearrangement of carbon atoms in the subsequent second sintering process, and is beneficial for the carbon coating layer to have a higher degree of graphitization. It is also beneficial to reduce the micropore and mesoporous structure content of the carbon coating layer, improve the density and uniformity of the carbon coating layer, and improve the bonding strength between the carbon coating layer and the lithium phosphate active material, which helps to further improve the cycle performance and storage performance of the battery.

[0148] Optionally, the holding temperature of the first stage sintering treatment may be 250°C-600°C, optionally 300°C-550°C.

[0149] The holding temperature of the second-stage sintering treatment can be 650°C-800°C, and can be optionally 680°C-750°C.

[0150] When the holding temperature of the second-stage sintering treatment is low, the graphitization degree of the carbon coating layer formed is low, and the improvement of the electronic conductivity of the carbon coating layer is not excellent enough, which is not conducive to improving the specific capacity and kinetic performance of the positive electrode active material; when the holding temperature of the second-stage sintering treatment is low, the oxygen content of the carbon coating layer formed is still high, which will cause the water absorption rate and water absorption amount of the positive electrode active material to be high, and the residual moisture content of the positive electrode plate to be high, which will lead to more battery side reactions and a high dissolution amount of transition metal ions of the positive electrode active material, and the effect of further improving the battery cycle performance and / or storage performance becomes poor.

[0151] When the holding temperature of the second-stage sintering treatment is high, the stability of the lithium phosphate active material decreases and impurities are easily generated, thereby reducing the specific capacity and stability of the positive electrode active material; when the holding temperature of the second-stage sintering treatment is high, the degree of graphitization of the carbon coating layer is high, but the lithium ion pathways are small and the lithium ion transfer kinetics are reduced, which will also lead to a further deterioration in the effect of improving the battery cycle performance and / or storage performance.

[0152] When the holding temperature of the second-stage sintering treatment is within the above-mentioned range, the lithium-phosphate active material can be made highly stable while the formed carbon coating layer has a high degree of graphitization, so that the carbon coating layer has both good electronic conductivity and more lithium ion pathways, thereby facilitating the improvement of the specific capacity and kinetic performance of the positive electrode active material. The formed carbon coating layer can also have a low oxygen content and a high density, thereby reducing the water absorption rate and amount of the positive electrode active material and the residual moisture content of the positive electrode sheet, thereby reducing battery side reactions and the amount of transition metal ions dissolved in the positive electrode active material. The positive electrode active material can also have a suitable particle size to avoid an increase in lithium ion diffusion paths due to an overly large particle size. Therefore, when the holding temperature of the second-stage sintering treatment is within the above-mentioned range, the battery can have better cycle performance and storage performance.

[0153] In some embodiments, the holding time of the first sintering process may be shorter than the holding time of the second sintering process.

[0154] Optionally, the holding time for one sintering treatment may be 2 hours to 7 hours.

[0155] The holding time of a sintering treatment is within the above range, which is conducive to the carbon coating having a higher degree of graphitization, and is also conducive to reducing the micropore and mesoporous structure content of the carbon coating, improving the density and uniformity of the carbon coating, and improving the bonding strength between the carbon coating and the lithium phosphate active material, thereby helping to further improve the cycle performance and storage performance of the battery.

[0156] Optionally, the holding time of the second-stage sintering treatment can be 8h-20h, optionally 8h-15h, or 8h-12h.

[0157] When the holding time of the second-stage sintering treatment is short, the graphitization degree of the carbon coating layer formed is low, and the improvement of the electronic conductivity of the carbon coating layer is not excellent enough, which is not conducive to improving the specific capacity and kinetic performance of the positive electrode active material; when the holding time of the second-stage sintering treatment is short, the oxygen content of the carbon coating layer formed is still high, which will cause the positive electrode active material to have a high water absorption rate and water absorption amount, and the positive electrode plate to have a high residual moisture content, which will lead to more battery side reactions and a high dissolution amount of transition metal ions of the positive electrode active material, and the effect of further improving the battery cycle performance and / or storage performance becomes worse.

[0158] When the holding time of the second-stage sintering treatment is long, the stability of the lithium phosphate active material decreases and impurities are easily generated, thereby reducing the specific capacity and stability of the positive electrode active material; when the holding time of the second-stage sintering treatment is long, the degree of graphitization of the carbon coating layer is high, but the lithium ion pathways are small and the lithium ion transfer kinetics are reduced, which will also lead to a further deterioration in the effect of improving the battery cycle performance and / or storage performance.

[0159] The holding time of the second-stage sintering treatment within the above range can not only ensure high stability of the lithium-phosphate active material, but also ensure that the formed carbon coating has a high degree of graphitization, so that the carbon coating has both good electronic conductivity and a large number of lithium ion pathways, thereby facilitating improved specific capacity and kinetic performance of the positive electrode active material. The formed carbon coating can also have a low oxygen content, thereby reducing the water absorption rate and amount of the positive electrode active material and the residual moisture content of the positive electrode sheet, thereby reducing battery side reactions and reducing the amount of transition metal ion dissolution from the positive electrode active material. Therefore, the holding time of the second-stage sintering treatment within the above range can enable the battery to have better cycle performance and storage performance.

[0160] [Positive electrode]

[0161] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material prepared by the preparation method provided in the embodiments of the present application.

[0162] In some embodiments, the weight content of the positive electrode active material prepared by the preparation method provided in the embodiments of the present application in the positive electrode film layer can be 50%-99.5%, optionally 90%-99.5%, 95%-99.5%, based on the total weight of the positive electrode film layer.

[0163] In some embodiments, the positive electrode film layer may further include other positive electrode active materials, for example, a lithium transition metal oxide. Examples of lithium transition metal oxides may include one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds. The modified compounds of the above-mentioned positive electrode active materials may be doping modification and / or surface coating modification of the positive electrode active materials.

[0164] In some embodiments, the positive electrode film layer may further include a positive electrode conductive agent. As an example, the positive electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0165] In some embodiments, the positive electrode film layer may further include a positive electrode binder. As an example, the positive electrode binder may include, but is not limited to, one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic resin.

[0166] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include, but is not limited to, one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include, but is not limited to, one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0167] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, drying it, and rolling it. The positive electrode slurry is typically formed by dispersing the positive electrode active material, positive electrode binder, and positive electrode conductive agent in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0168] [Negative electrode]

[0169] In some embodiments, 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. The negative electrode current collector has two opposing surfaces in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposing surfaces of the negative electrode current collector.

[0170] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As examples of metal foils, copper foil, copper alloy foil, aluminum foil, and aluminum alloy foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0171] The negative electrode active material may be a material known in the art. In some embodiments, as an example, the negative electrode active material may include, but is not limited to, one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials may include, but are not limited to, one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include, but are not limited to, one or more 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 may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0172] In some embodiments, the negative electrode film layer may further optionally include a negative electrode binder. As examples, the negative electrode binder may include, but is not limited to, one or more 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).

[0173] In some embodiments, the negative electrode film layer may further optionally include a negative electrode conductive agent. As an example, the negative electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0174] In some embodiments, the negative electrode film layer may further include other additives, such as thickeners, sodium carboxymethyl cellulose (CMC), PTC thermistor materials, and the like.

[0175] The negative electrode sheet can be prepared by dispersing the negative electrode active material, negative electrode binder, and negative electrode conductive agent in a solvent and stirring them uniformly to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying and cold pressing, the negative electrode sheet is formed. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited thereto.

[0176] In some embodiments, the negative electrode plate may not include a negative electrode active material capable of intercalating and deintercalating lithium ions. For example, the negative electrode plate may include a lithium plate or a lithium alloy plate; or, the negative electrode plate may include a three-dimensional skeleton layer in a network or foam form; or, the negative electrode plate may include a negative electrode current collector and a lithium-containing layer disposed on at least one surface of the negative electrode current collector.

[0177] [Electrolytes]

[0178] The battery cell includes an electrolyte. This application does not specifically limit the type of electrolyte, and the electrolyte can be selected according to needs. For example, the electrolyte can include one or more selected from solid electrolytes and liquid electrolytes (i.e., electrolytes).

[0179] In some embodiments, the electrolyte is an electrolyte solution including an electrolyte salt and a solvent.

[0180] In some embodiments, as examples, the electrolyte salt may include, but is not limited to, one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobisoxalatophosphate (LiDFOP), and lithium tetrafluorooxalatophosphate (LiTFOP).

[0181] In some embodiments, the solvent may include, but is not limited to, one or more of an ester solvent, a sulfone solvent, and an ether solvent. As an example, the solvent may include, but is not limited to, ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS), and one or more of diethyl sulfone (ESE).

[0182] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature power performance.

[0183] [Isolation film]

[0184] Battery cells using electrolytes, as well as some battery cells using solid electrolytes, also include a separator. The separator is placed between the positive and negative electrode sheets to prevent internal short circuits.

[0185] The present application has no particular limitation on the type of isolation membrane, and any known isolation membrane with a porous structure having good chemical stability and mechanical stability can be selected.

[0186] In some embodiments, the material of the isolation membrane may include, but is not limited to, one or more of fiberglass, non-woven fabric, polyethylene (PE), polypropylene (PP), and polyvinylidene fluoride. The isolation membrane may be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, the materials of each layer may be the same or different.

[0187] In some embodiments, the isolation film may further include a heat-resistant coating. Optionally, the heat-resistant coating may include one or more of inorganic heat-resistant particles and organic heat-resistant particles.

[0188] The preparation method of battery cells is well known. In some embodiments, the positive electrode sheet, separator, negative electrode sheet and electrolyte can be assembled to form a battery cell. As an example, the positive electrode sheet, separator, and negative electrode sheet can be formed into an electrode assembly through a winding process and / or a lamination process, and the electrode assembly is placed in an outer package, dried and injected with the above-mentioned electrolyte, and then subjected to packaging, standing, formation and other processes to obtain a battery cell. Multiple battery cells can also be further connected in series, in parallel or in a mixed connection to form a battery module. Multiple battery modules can also be connected in series, in parallel or in a mixed connection to form a battery pack. In some embodiments, multiple battery cells can also directly form a battery pack.

[0189] Example

[0190] The following examples describe the present disclosure in more detail. These examples are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing. The instruments used in the examples are commercially available.

[0191] Example 1-1

[0192] (1) Preparation of positive electrode active materials

[0193] Preparation of doped manganese oxalate

[0194] Thoroughly mix 1.3 mol of MnSO₄﹒H₂O and 0.7 mol of FeSO₄﹒H₂O in a mixer for approximately 6 hours. Transfer the mixture to a reactor, and add 10 L of deionized water and 2 mol of oxalic acid dihydrate (2 mol per oxalic acid mass). Heat the reactor to 80°C and stir at 600 rpm for approximately 6 hours until no bubbles form, yielding an Fe-doped manganese oxalate suspension. Filter the suspension, dry the resulting filter cake at 120°C, and grind it to produce Fe-doped manganese oxalate particles with a volume distribution particle size (Dv50) of approximately 100 nm.

[0195] Preparation of doped lithium manganese iron phosphate

[0196] Take 1 mol of the above-mentioned Fe-doped manganese oxalate particles, 0.497 mol of lithium carbonate, 0.001 mol of Mo(SO4)3, an 85% phosphoric acid aqueous solution containing 0.999 mol of phosphoric acid, 0.001 mol of H4SiO4, and 0.0005 mol of NH4HF2 and add them into 20L of deionized water. Transfer the mixture into a sand mill and grind and stir it thoroughly for about 10 hours to obtain a slurry. Transfer the obtained slurry to a spray drying equipment for spray drying and granulation, set the drying temperature to 250°C and the drying time to 4 hours to obtain powder particles. In a protective atmosphere of 90% by volume of nitrogen and 10% by volume of hydrogen, sinter the above-mentioned powder at 700°C for 10 hours to obtain doped lithium manganese iron phosphate, the elemental composition of which is Li 0.994 Mo 0.001 Mn 0.65 Fe 0.35 P 0.999 Si 0.001 O 3.999 F 0.001 The element content can be detected by inductively coupled plasma emission spectroscopy (ICP).

[0197] Carbon coating

[0198] 59.6g of polyvinylidene fluoride (PVDF) was dispersed in 500ml of deionized water, then stirred and thoroughly dispersed to obtain a coating solution. The doped lithium manganese iron phosphate was added to the coating solution and stirred for 6 hours. After uniform mixing, the solution was dried in a 150°C oven for 6 hours. The solution was then heated to 450°C and sintered at a rate of 1°C / min under a nitrogen atmosphere for 3 hours, followed by heating to 700°C and sintering at a rate of 1°C / min for 10 hours to obtain carbon-coated lithium manganese iron phosphate, the positive electrode active material. The mass of the carbon coating layer was 2% of the mass of the positive electrode active material. The number average molecular weight of the polyvinylidene fluoride (PVDF) measured by gel permeation chromatography was 400,000-410,000, and the polydispersity index was 1-5.

[0199] (2) Preparation of button batteries

[0200] The positive electrode active material, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) were added to N-methylpyrrolidone (NMP) at a weight ratio of 90:5:5 and stirred in a drying room to form a slurry. The slurry was coated on aluminum foil, dried, and cold pressed to form a positive electrode sheet. The coating amount was 0.015g / cm 2 , compacted density is 2.0g / cm 3 .

[0201] A lithium sheet was used as the counter electrode, a polyethylene (PE) porous film was used as the isolation membrane, and a solution of 1 mol / L LiPF6 in ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) in a volume ratio of 1:1:1 was used as the electrolyte. Together with the positive electrode sheet prepared above, they were assembled into a button battery in a button box.

[0202] (3) Preparation of full battery

[0203] The above-mentioned positive electrode active material, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) were mixed uniformly in N-methylpyrrolidone (NMP) at a weight ratio of 92:2.5:5.5 to prepare a positive electrode slurry. The positive electrode slurry was coated on aluminum foil and dried and cold pressed to obtain a positive electrode sheet. The coating amount was 0.018g / cm 2 , compacted density is 2.4g / cm 3 .

[0204] The negative electrode active material artificial graphite, hard carbon, conductive agent acetylene black, binder styrene butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) were mixed evenly in deionized water at a weight ratio of 90:5:2:2:1 to prepare a negative electrode slurry. The negative electrode slurry was coated on copper foil and dried and cold pressed to obtain a negative electrode sheet. The coating amount was 0.0075g / cm 2 , compacted density is 1.7g / cm3 .

[0205] Using a porous polyethylene (PE) film as a separator, 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 separation. The electrode assembly is then wound into a coil. The electrode assembly is placed in an outer packaging, and the same electrolyte used in preparing the button cell is injected and packaged to create a full battery.

[0206] Example 1-2

[0207] Except for the carbon coating process in the preparation process of the positive electrode active material, the preparation process of the positive electrode active material, the button cell, and the full cell is the same as that of Example 1-1.

[0208] Carbon coating

[0209] 82.7g of polytetrafluoroethylene was dispersed in 500ml of deionized water, then stirred and thoroughly dispersed to obtain a coating solution. The doped lithium manganese iron phosphate was added to the coating solution and stirred for 6 hours. After uniform mixing, the solution was dried in a 150°C oven for 6 hours. The solution was then heated to 550°C at a rate of 1°C / min and sintered under a nitrogen atmosphere for 3 hours, followed by heating to 700°C at a rate of 1°C / min and sintering for 10 hours to obtain carbon-coated lithium manganese iron phosphate, the positive electrode active material. The mass of the carbon coating layer was 2% of the mass of the positive electrode active material. The polytetrafluoroethylene had a number average molecular weight of 400,000-410,000 and a polydispersity index of 1-5 as determined by gel permeation chromatography.

[0210] Examples 1-3

[0211] Except for the carbon coating process in the preparation process of the positive electrode active material, the preparation process of the positive electrode active material, the button cell, and the full cell is the same as that of Example 1-1.

[0212] Carbon coating

[0213] 40.3 g of polypyrrole was dispersed in 500 ml of deionized water, then stirred and thoroughly dispersed to obtain a coating solution. The doped lithium manganese iron phosphate was added to the coating solution and stirred for 6 hours. After uniform mixing, the solution was dried in a 150°C oven for 6 hours. The solution was then heated to 400°C and sintered at a rate of 1°C / min under a nitrogen atmosphere for 3 hours, followed by a rate of 1°C / min to 700°C and sintered for 10 hours to obtain carbon-coated lithium manganese iron phosphate, the positive electrode active material. The mass of the carbon coating layer was 2% of the mass of the positive electrode active material. The polypyrrole had a number average molecular weight of 400,000-410,000 and a polydispersity index of 1-5 as determined by gel permeation chromatography.

[0214] Examples 1-4

[0215] Except for the carbon coating process in the preparation process of the positive electrode active material, the preparation process of the positive electrode active material, the button cell, and the full cell is the same as that of Example 1-1.

[0216] Carbon coating

[0217] 45.6g of polyacrylonitrile was dispersed in 500ml of deionized water, then stirred and thoroughly dispersed to obtain a coating solution. The doped lithium manganese iron phosphate was added to the coating solution and stirred for 6 hours. After uniform mixing, the solution was dried in a 150°C oven for 6 hours. The solution was then heated to 400°C and sintered at a rate of 1°C / min under a nitrogen atmosphere for 3 hours, followed by heating to 700°C and sintering at a rate of 1°C / min for 10 hours to obtain carbon-coated lithium manganese iron phosphate, the positive electrode active material. The mass of the carbon coating layer was 2% of the mass of the positive electrode active material. The polyacrylonitrile, as measured by gel permeation chromatography, had a number average molecular weight of 400,000-410,000 and a polydispersity index of 1-5.

[0218] Examples 1-5

[0219] Except for the carbon coating process in the preparation process of the positive electrode active material, the preparation process of the positive electrode active material, the button cell, and the full cell is the same as that of Example 1-1.

[0220] Carbon coating

[0221] 33.7g of polyethylene was dispersed in 500ml of deionized water, then stirred and thoroughly dispersed to obtain a coating solution. The doped lithium manganese iron phosphate was added to the coating solution and stirred for 6 hours. After uniform mixing, the solution was dried in a 150°C oven for 6 hours. The solution was then heated to 450°C and sintered under a nitrogen atmosphere at a rate of 1°C / min for 3 hours, followed by a rate of 1°C / min to 700°C and sintered for 10 hours to obtain carbon-coated lithium manganese iron phosphate, the positive electrode active material. The mass of the carbon coating layer was 2% of the mass of the positive electrode active material. The polyethylene had a number average molecular weight of 400,000-410,000 and a polydispersity index of 1-5 as determined by gel permeation chromatography.

[0222] Examples 1-6

[0223] Except for the carbon coating process in the preparation process of the positive electrode active material, the preparation process of the positive electrode active material, the button cell, and the full cell is the same as that of Example 1-1.

[0224] Carbon coating

[0225] 45.6g of acrylonitrile was dispersed in 500ml of deionized water, then stirred and thoroughly dispersed to obtain a coating solution. The doped lithium manganese iron phosphate was added to the coating solution and stirred for 6 hours. After uniform mixing, the solution was dried in a 150°C oven for 6 hours. The solution was then heated to 400°C and sintered at a rate of 1°C / min under a nitrogen atmosphere for 3 hours, followed by heating to 700°C and sintering at a rate of 1°C / min for 10 hours to obtain carbon-coated lithium manganese iron phosphate, the positive electrode active material. The mass of the carbon coating layer was 2% of the mass of the positive electrode active material.

[0226] Comparative Example 1-1

[0227] Except for the carbon coating process in the preparation process of the positive electrode active material, the preparation process of the positive electrode active material, the button cell, and the full cell is the same as that of Example 1-1.

[0228] Carbon coating

[0229] 74.2g of sucrose was dissolved in 500ml of deionized water, then stirred and fully dissolved to obtain a coating solution. The doped lithium manganese iron phosphate was added to the coating solution and stirred for 6 hours. After uniform mixing, the solution was dried in a 150°C oven for 6 hours. The solution was then heated to 450°C and sintered at a rate of 1°C / min under a nitrogen atmosphere for 3 hours, followed by heating to 700°C and sintering at a rate of 1°C / min for 10 hours to obtain carbon-coated lithium manganese iron phosphate, the positive electrode active material. The mass of the carbon coating layer was 2% of the mass of the positive electrode active material.

[0230] Positive electrode active materials, positive electrode sheets and battery performance test methods

[0231] 1. Measurement method of initial gram capacity of button cell batteries

[0232] Under a constant temperature environment of 25℃, charge the button battery to 4.3V at a rate of 0.1C, then charge at a constant voltage at 4.3V until the current is less than or equal to 0.05mA, let it stand for 5 minutes, and then discharge it to 2.0V at a rate of 0.1C. The discharge capacity at this time is the initial gram capacity.

[0233] 2. Button battery average discharge voltage (V) test:

[0234] Under a constant temperature environment of 25℃, let the button battery stand for 5 minutes, discharge it to 2.5V at a rate of 0.1C, let it stand for 5 minutes, charge it to 4.3V at a rate of 0.1C, then charge it at a constant voltage at 4.3V until the current is less than or equal to 0.05mA, let it stand for 5 minutes, and then discharge it to 2.5V at a rate of 0.1C. The discharge capacity at this time is the initial gram capacity, recorded as D0, the discharge energy is the initial energy, recorded as E0, and the average discharge voltage of the button battery is E0 / D0.

[0235] 3. Full battery 45℃ cycle performance test

[0236] At a constant temperature of 45°C, charge the full battery at a 1C rate to 4.3V. Then, charge it at a constant voltage at 4.3V until the current is less than or equal to 0.05mA. Let it rest for 5 minutes, then discharge it at a 1C rate to 2.5V. Record the discharge capacity at this point as E0. Repeat the charge and discharge cycle until the discharge capacity after the cycle drops to 80% of E0. Record the number of cycles the full battery has undergone at this point.

[0237] The discharge capacity after cycling at 45°C was reduced to 80% of E0. The full battery was discharged at a rate of 0.1C to a cut-off voltage of 2.0V. The full battery was then disassembled and the negative electrode sheet was removed. 30 unit areas were randomly selected on the negative electrode sheet, i.e., an area of ​​1540.25 mm 2 The wafers were analyzed by inductively coupled plasma emission spectroscopy (ICP) using an Agilent ICP-OES730. The amounts of Fe and Mn in the wafers were calculated based on the ICP results, and thus the amounts of Fe and Mn released after cycling were calculated. The testing standard was based on EPA-6010D-2014.

[0238] 4. Full battery 60℃ flatulence test

[0239] Store full batteries at 100% state of charge (SOC) in a constant temperature environment at 60°C. Measure the open circuit voltage (OCV) and AC internal resistance (IMP) of the full battery before, during, and after storage to monitor the SOC, and measure the volume of the full battery. Take out the full battery after every 48 hours of storage, test the open circuit voltage (OCV) and internal resistance (IMP) after standing for 1 hour, and measure the volume of the full battery using the water displacement method after cooling to 25°C. The water displacement method is to first use a balance that automatically converts units using dial data to measure the gravity F1 of the full battery alone, and then completely place the full battery in deionized water to measure the gravity F2 of the full battery at this time, and the buoyancy F of the full battery. 浮 That is F1-F2, and then according to Archimedes principle F 浮 =ρ×g×V 排 , the full battery volume V = (F1-F2) / (ρ×g). ρ is the density of water, 1g / cm 3 ; g is the acceleration due to gravity; V 排 is the volume of water displaced.

[0240] After 30 days of storage, the volume of the full battery was measured again, and the percentage increase in the volume of the full battery after storage relative to the volume of the full battery before storage was calculated. Percentage increase in the volume of the full battery after 30 days of storage = (volume of the full battery after 30 days of storage - volume of the full battery before storage) / volume of the full battery before storage.

[0241] 5. Saturated water absorption test of positive electrode active materials

[0242] The positive electrode active material powder was placed in a constant temperature and humidity chamber at 25°C and a relative humidity of 60%. After 2 hours, 1 g of the powder was taken out and placed in a vial and quickly sealed. The water content of the positive electrode active material powder was then determined using a Karl Fischer moisture meter and recorded as the saturated water absorption.

[0243] Table 1

[0244] The test results in Table 1 show that cathode active materials prepared using an oxygen-free organic carbon source exhibit lower saturated water absorption, a higher number of cycles corresponding to 80% capacity retention at 45°C, lower Fe and Mn dissolution after cycling, and less volume expansion after 30 days of storage at 60°C. This is due to the carbon coating formed by the oxygen-free organic carbon source, which has fewer micropores and mesoporous structures, higher density, and fewer oxygen-containing functional groups. This results in lower saturated water absorption for the cathode active material, making the cathode slurry easier to dry and lowering the residual moisture content in the cathode electrode sheet. Furthermore, the dense carbon coating further reduces direct contact between the lithium-phosphate active material and the electrolyte, further reducing side reactions at the cathode-electrolyte interface. Therefore, cathode active materials prepared using an oxygen-free organic carbon source can lead to better battery performance.

[0245] It can also be seen from the test results of Examples 1-4 and 1-6 that when the oxygen-free organic carbon source uses an oxygen-free polymer, the battery can have better performance, the number of cycles corresponding to 80% capacity retention at 45°C is higher, the amount of Fe and Mn dissolved after the battery cycle is less, and the volume expansion of the battery after storage at 60°C for 30 days is smaller. This is because the molecular chain of the oxygen-free polymer is longer, and it is easier to form a carbon coating layer with a high degree of graphitization, low content of micropores and mesoporous structures, and high density. The degree of graphitization of the carbon coating layer is improved, and the electronic conductivity of the positive electrode active material is improved, which is beneficial to the specific capacity of the positive electrode active material. The carbon coating layer has a low content of micropores and mesoporous structures and a high density, which can better isolate the lithium phosphate active material from direct contact with the electrolyte, thereby further reducing the side reactions at the positive electrode-electrolyte interface and further improving the cycle performance and storage performance of the battery.

[0246] The test results of Examples 1-1 to 1-5 also show that when the oxygen-free organic carbon source is an oxygen-free polymer containing at least one of fluorine atoms, nitrogen atoms, and sulfur atoms, the battery can have better performance, with a higher number of cycles corresponding to an 80% capacity retention rate at 45°C, less Fe and Mn dissolution after battery cycling, and less volume expansion after 30 days of storage at 60°C. This is because, after pyrolysis, the oxygen-free polymer containing at least one of fluorine atoms, nitrogen atoms, and sulfur atoms can leave a certain amount of fluorine atoms, nitrogen atoms, and sulfur atoms in the carbon coating layer, which can act as doping atoms. The doping atoms can change the charge distribution around the carbon atoms, further improving the electronic conductivity of the carbon coating layer. The doping atoms can also form some defect structures within the carbon coating layer. These defect structures are conducive to the rapid migration of lithium ions, thereby improving the battery's cycling performance. In addition, the doping atoms can also form some functional groups containing doping atoms on the surface of the carbon coating layer. These functional groups can serve as new active sites, increasing the solvation and desolvation rates of lithium ions, thereby improving the battery's cycling performance.

[0247] Example 2-1

[0248] Except for the carbon coating process in the preparation process of the positive electrode active material, the preparation process of the positive electrode active material, the button cell, and the full cell is the same as that of Example 1-1.

[0249] Carbon coating

[0250] 59.6g of polyvinylidene fluoride (PVDF) was dispersed in 500ml of deionized water, then stirred and thoroughly dispersed to obtain a coating solution. The doped lithium manganese iron phosphate was added to the coating solution and stirred for 6 hours. After uniform mixing, the solution was transferred to a 150°C oven and dried for 6 hours. The solution was then heated to 450°C and sintered at a rate of 1°C / min under a nitrogen atmosphere for 3 hours, followed by heating to 700°C and sintering at a rate of 1°C / min for 10 hours to obtain carbon-coated lithium manganese iron phosphate, the positive electrode active material. The mass of the carbon coating layer was 2% of the mass of the positive electrode active material. The polyvinylidene fluoride (PVDF) had a number average molecular weight of 1000-1100 and a polydispersity index of 1-5 as determined by gel permeation chromatography.

[0251] Example 2-2

[0252] Except for the carbon coating process in the preparation process of the positive electrode active material, the preparation process of the positive electrode active material, the button cell, and the full cell is the same as that of Example 1-1.

[0253] Carbon coating

[0254] 59.6g of polyvinylidene fluoride (PVDF) was dispersed in 500ml of deionized water, then stirred and thoroughly dispersed to obtain a coating solution. The doped lithium manganese iron phosphate was added to the coating solution and stirred for 6 hours. After uniform mixing, the solution was dried in a 150°C oven for 6 hours. The solution was then heated to 450°C and sintered under a nitrogen atmosphere at a rate of 1°C / min for 3 hours, followed by a rate of 1°C / min to 700°C and sintered for 10 hours to obtain carbon-coated lithium manganese iron phosphate, the positive electrode active material. The mass of the carbon coating layer was 2% of the mass of the positive electrode active material. The number average molecular weight of the polyvinylidene fluoride (PVDF) measured by gel permeation chromatography was 50,000-60,000, and the polydispersity index was 1-5.

[0255] Example 2-3

[0256] Except for the carbon coating process in the preparation process of the positive electrode active material, the preparation process of the positive electrode active material, the button cell, and the full cell is the same as that of Example 1-1.

[0257] Carbon coating

[0258] 59.6g of polyvinylidene fluoride (PVDF) was dispersed in 500ml of deionized water, then stirred and thoroughly dispersed to obtain a coating solution. The doped lithium manganese iron phosphate was added to the coating solution and stirred for 6 hours. After uniform mixing, the solution was transferred to a 150°C oven and dried for 6 hours. The solution was then heated to 450°C and sintered under a nitrogen atmosphere at a rate of 1°C / min for 3 hours, followed by a rate of 1°C / min to 700°C and sintered for 10 hours to obtain carbon-coated lithium manganese iron phosphate, the positive electrode active material. The mass of the carbon coating layer was 2% of the mass of the positive electrode active material. The number average molecular weight of the polyvinylidene fluoride (PVDF) measured by gel permeation chromatography was 990,000-1,000,000, and the polydispersity index was 1-5.

[0259] Examples 2-4

[0260] Except for the carbon coating process in the preparation process of the positive electrode active material, the preparation process of the positive electrode active material, the button cell, and the full cell is the same as that of Example 1-1.

[0261] Carbon coating

[0262] 59.6g of polyvinylidene fluoride (PVDF) was dispersed in 500ml of deionized water, then stirred and thoroughly dispersed to obtain a coating solution. The doped lithium manganese iron phosphate was added to the coating solution and stirred for 6 hours. After uniform mixing, the solution was dried in a 150°C oven for 6 hours. The solution was then heated to 450°C and sintered under a nitrogen atmosphere at a rate of 1°C / min for 3 hours, followed by a rate of 1°C / min to 700°C and sintered for 10 hours to obtain carbon-coated lithium manganese iron phosphate, the positive electrode active material. The mass of the carbon coating layer was 2% of the mass of the positive electrode active material. The number average molecular weight of the polyvinylidene fluoride (PVDF) measured by gel permeation chromatography was 4.99 million to 5 million, with a polydispersity index of 1 to 5.

[0263] Table 2

[0264] The test results in Table 2 show that further adjusting the number-average molecular weight of the oxygen-free polymer can lead to improved battery performance. This is because further adjusting the number-average molecular weight of the oxygen-free polymer can form a carbon coating with a high degree of graphitization, low micropore and mesoporous structure content, and high density and uniformity. This improves the positive electrode active material's electronic conductivity and specific capacity. It also effectively isolates the lithium-phosphate active material from direct contact with the electrolyte, thereby further reducing side reactions at the positive electrode-electrolyte interface and further improving the battery's cycling and storage performance.

[0265] Example 3-1

[0266] Except for the carbon coating process in the preparation process of the positive electrode active material, the preparation process of the positive electrode active material, the button cell, and the full cell is the same as that of Example 1-1.

[0267] Carbon coating

[0268] 59.6g of polyvinylidene fluoride (PVDF) was dispersed in 500ml of deionized water, then stirred and thoroughly dispersed to obtain a coating solution. The doped lithium manganese iron phosphate was added to the coating solution and stirred for 6 hours. After uniform mixing, the solution was dried in a 150°C oven for 6 hours. The solution was then heated to 450°C and sintered under a nitrogen atmosphere at a rate of 1°C / min for 3 hours, followed by a rate of 1°C / min to 600°C and sintered for 10 hours to obtain carbon-coated lithium manganese iron phosphate, the positive electrode active material. The mass of the carbon coating layer was 2% of the mass of the positive electrode active material. The number average molecular weight of the polyvinylidene fluoride (PVDF) measured by gel permeation chromatography was 400,000-410,000, and the polydispersity index was 1-5.

[0269] Example 3-2

[0270] Except for the carbon coating process in the preparation process of the positive electrode active material, the preparation process of the positive electrode active material, the button cell, and the full cell is the same as that of Example 1-1.

[0271] Carbon coating

[0272] 59.6g of polyvinylidene fluoride (PVDF) was dispersed in 500ml of deionized water, then stirred and thoroughly dispersed to obtain a coating solution. The doped lithium manganese iron phosphate was added to the coating solution and stirred for 6 hours. After uniform mixing, the solution was dried in a 150°C oven for 6 hours. The solution was then heated to 450°C and sintered under a nitrogen atmosphere at a rate of 1°C / min for 3 hours, followed by a rate of 1°C / min to 900°C and sintered for 10 hours to obtain carbon-coated lithium manganese iron phosphate, the positive electrode active material. The mass of the carbon coating layer was 2% of the mass of the positive electrode active material. The number average molecular weight of the polyvinylidene fluoride (PVDF) measured by gel permeation chromatography was 400,000-410,000, with a polydispersity index of 1-5.

[0273] Example 3-3

[0274] Except for the carbon coating process in the preparation process of the positive electrode active material, the preparation process of the positive electrode active material, the button cell, and the full cell is the same as that of Example 1-1.

[0275] Carbon coating

[0276] 59.6g of polyvinylidene fluoride (PVDF) was dispersed in 500ml of deionized water, then stirred and thoroughly dispersed to obtain a coating solution. The doped lithium manganese iron phosphate was added to the coating solution and stirred for 6 hours. After uniform mixing, the solution was dried in a 150°C oven for 6 hours. The solution was then heated to 450°C and sintered under a nitrogen atmosphere at a rate of 1°C / min for 3 hours, followed by a rate of 1°C / min to 700°C and sintered for 3 hours to obtain carbon-coated lithium manganese iron phosphate, the positive electrode active material. The mass of the carbon coating layer was 2% of the mass of the positive electrode active material. The number average molecular weight of the polyvinylidene fluoride (PVDF) measured by gel permeation chromatography was 400,000-410,000, and the polydispersity index was 1-5.

[0277] Examples 3-4

[0278] Except for the carbon coating process in the preparation process of the positive electrode active material, the preparation process of the positive electrode active material, the button cell, and the full cell is the same as that of Example 1-1.

[0279] Carbon coating

[0280] 59.6g of polyvinylidene fluoride (PVDF) was dispersed in 500ml of deionized water, then stirred and thoroughly dispersed to obtain a coating solution. The doped lithium manganese iron phosphate was added to the coating solution and stirred for 6 hours. After uniform mixing, the solution was dried in a 150°C oven for 6 hours. The solution was then heated to 450°C and sintered at a rate of 1°C / min under a nitrogen atmosphere for 3 hours, followed by heating to 700°C and sintering at a rate of 1°C / min for 22 hours to obtain carbon-coated lithium manganese iron phosphate, the positive electrode active material. The mass of the carbon coating layer was 2% of the mass of the positive electrode active material. The number average molecular weight of the polyvinylidene fluoride (PVDF) measured by gel permeation chromatography was 400,000-410,000, and the polydispersity index was 1-5.

[0281] Table 3

[0282] The test results in Table 3 show that further adjusting the holding temperature and / or holding time of the second-stage sintering process can improve battery performance. This is because further adjusting the holding temperature and / or holding time of the second-stage sintering process can simultaneously enhance the stability of the lithium-phosphate active material while also ensuring a high degree of graphitization in the formed carbon coating, resulting in both good electronic conductivity and a sufficient number of lithium ion pathways. Furthermore, the formed carbon coating can have a lower oxygen content, thereby reducing the water absorption rate and amount of the positive electrode active material and the residual moisture content of the positive electrode sheet.

[0283] 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 method for preparing a positive electrode active material, comprising the following steps: Providing a lithium-containing phosphate active material or a precursor of a lithium-containing phosphate active material; Providing an oxygen-free organic carbon source, which includes one or more of an oxygen-free polymer and an oxygen-free organic small molecule compound; Mixing the lithium-containing phosphate active material or the precursor of the lithium-containing phosphate active material with the oxygen-free organic carbon source evenly to obtain a mixture, and then performing a sintering treatment under a protective gas atmosphere so that the oxygen-free organic carbon source is carbonized to form a carbon coating layer covering at least a part of the surface of the lithium-containing phosphate active material, thereby obtaining the positive electrode active material.

2. The preparation method according to claim 1, wherein, The oxygen-free organic carbon source includes an oxygen-free polymer containing at least one of a fluorine atom, a nitrogen atom, and a sulfur atom.

3. The preparation method according to any one of claims 1-2, wherein The oxygen-free polymer includes one or more of polyolefins, fluorinated polyolefins, polyacetylenes, polyacrylonitrile, polypyrrole, polythiophene, polyaniline, and their respective derivatives; and / or, The oxygen-free organic small molecule compound includes one or more of phenothiazine compounds, aromatic hydrocarbon compounds, alkane compounds, alkene compounds, alkyne compounds, fluorinated alkane compounds, fluorinated alkene compounds, fluorinated alkyne compounds, aniline compounds, and their respective derivatives.

4. The preparation method according to claim 3, wherein The oxygen-free polymer includes one or more of fluorinated polyolefins, polyacrylonitrile, polypyrrole, polythiophene, polyaniline, and their respective derivatives, and the fluorinated polyolefin includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl fluoride, perfluoroethylene-propylene copolymer, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, and tetrafluoroethylene-hexafluoropropylene copolymer.

5. The preparation method according to any one of claims 1-4, wherein The number average molecular weight of the oxygen-free polymer is 1000-5000000; and / or, The polydispersity index of the oxygen-free polymer is 1-5; and / or, The thermal decomposition temperature of the oxygen-free polymer is 200°C-600°C.

6. The preparation method according to claim 5, wherein The number average molecular weight of the oxygen-free polymer is 50000-1000000; and / or, The polydispersity index of the oxygen-free polymer is 1-3; and / or, The thermal decomposition temperature of the oxygen-free polymer is 250°C-550°C.

7. The preparation method according to any one of claims 1-6, wherein, The mass ratio of the residual carbon after sintering treatment of the oxygen-free organic carbon source to the mass of the positive electrode active material is (0.01-6):

100.

8. The preparation method according to any one of claims 1-7, wherein The protective gas includes one or more of nitrogen, argon, and helium; and / or, The heating rate of the sintering treatment is less than or equal to 5°C / min.

9. The preparation method according to any one of claims 1-8, wherein The sintering treatment is a step-by-step sintering treatment, which includes a first-stage sintering treatment and a second-stage sintering treatment. The difference between the heat preservation temperature of the first-stage sintering treatment and the thermal decomposition temperature of the anaerobic organic carbon source is greater than or equal to -50°C, and the heat preservation temperature of the second-stage sintering treatment is 650°C - 800°C.

10. The preparation method according to claim 9, wherein, The heat preservation temperature of the first-stage sintering treatment is greater than or equal to the thermal decomposition temperature of the anaerobic organic carbon source.

11. According to the preparation method described in any one of claims 9-10, wherein, The heat preservation time of the first-stage sintering treatment is less than the heat preservation time of the second-stage sintering treatment.

12. The preparation method according to any one of claims 9-11, wherein, The heat preservation time of the first-stage sintering treatment is 2h - 7h; and / or, the heat preservation time of the second-stage sintering treatment is 8h - 20h.

13. The preparation method according to any one of claims 1-12, wherein The lithium-containing phosphate active material includes one or more of lithium iron manganese phosphate, lithium iron phosphate, and their respective modified materials. The modification methods include doping modification and / or surface coating modification. The doping includes metal doping and / or non-metal doping; and / or, The precursor of the lithium-containing phosphate active material includes one or more of manganese iron phosphate, manganese iron pyrophosphate, ammonium manganese iron phosphate, manganese iron oxalate, iron phosphate, doped manganese iron phosphate, doped manganese iron pyrophosphate, doped ammonium manganese iron phosphate, doped manganese iron oxalate, doped iron phosphate. The doping includes metal doping and / or non-metal doping; and / or, The preparation method of the lithium-containing phosphate active material includes any one of solid-phase synthesis method, sol-gel method, co-precipitation method, hydrothermal method, or solvothermal method; and / or, The preparation method of the precursor of the lithium-containing phosphate active material includes any one of solid-phase synthesis method, sol-gel method, co-precipitation method, hydrothermal method, or solvothermal method.

14. The preparation method according to any one of claims 1-13, wherein, In the step of uniformly mixing the lithium-containing phosphate active material or the precursor of the lithium-containing phosphate active material with the anaerobic organic carbon source, a dispersant is further added to the mixture. The dispersant includes one or more of water, ethanol, acetone, toluene, and N-methylpyrrolidone.

15. The preparation method according to any one of claims 1-14, wherein, In the step of uniformly mixing the precursor of the lithium-containing phosphate active material with the anaerobic organic carbon source, a lithium source is further added to the mixture, or a lithium source and a phosphorus source are added simultaneously, so that the precursor of the lithium-containing phosphate active material forms a lithium-containing phosphate active material after sintering treatment.

16. The preparation method according to any one of claims 14-15, wherein, Before the sintering treatment in a protective gas atmosphere, there is also a step of drying the obtained mixture.

17. A positive electrode active material is prepared by the preparation method according to any one of claims 1-16.

18. A positive electrode plate includes a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector, wherein, The positive electrode film layer includes a positive electrode active material prepared by the preparation method according to any one of claims 1-16.

19. A battery cell includes the positive electrode plate according to claim 18.

20. A battery includes the battery cell according to claim 19.

21. An electrical device includes the battery according to claim 20, and the battery is used to provide electrical energy.

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