Secondary battery, method for manufacturing the same, and electric device

Abstract

The application provides a secondary battery and a preparation method thereof and an electric device, and belongs to the technical field of batteries. The secondary battery comprises a positive electrode sheet, the positive electrode sheet comprises a positive electrode active material, the positive electrode active material comprises a core material and a polymer coating layer covering at least part of the surface of the core material, and the molecular chain of the polymer coating layer contains a chain segment: wherein R1 comprises at least one of hydrogen, an alkyl group, a phenyl group, a carboxyl group, an ester group, an amide group and a sulfonic acid group, R2 comprises at least one of an alkylene group, X comprises one of an ester group and an amide group, and M is a chain segment of a metal ion chelating agent; and the core material comprises one of a lithium-containing transition metal oxide and a lithium-containing transition metal phosphate. The application can reduce the dissolution of metal ions in the positive electrode active material, thereby helping to improve the cycle performance of the secondary battery.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a secondary battery, its preparation method, and an electrical device thereof. Background Technology

[0002] In secondary batteries, some positive electrode active materials suffer from the problem of transition metal ion dissolution. Taking high-nickel ternary positive electrode materials as an example, when their surface is in direct contact with the electrolyte, the corrosive effect of the electrolyte makes it easy for the originally tetravalent manganese ions in the crystal lattice to be reduced to divalent manganese ions that are soluble in the electrolyte. Divalent manganese ions not only damage the solid electrolyte interface (SEI) film of the negative electrode, but also lead to the deterioration of the stability and cycle performance of the secondary battery during charge and discharge. Summary of the Invention

[0003] In view of the above problems, this application provides a secondary battery and its preparation method and power device, aiming to improve the cycle performance of the secondary battery.

[0004] In a first aspect, this application provides a secondary battery, including a positive electrode sheet, the positive electrode sheet including a positive electrode active material, the positive electrode active material including a core material and a polymer coating layer covering at least a portion of the surface of the core material, the polymer coating layer containing segments of formula (I) in its molecular chain: Formula (I), Wherein, R1 includes at least one of hydrogen, alkane, phenyl, carboxyl, ester, amide, and sulfonic acid; R2 includes at least one of alkylene groups; X includes one of ester and amide groups; and M is a segment of a metal ion chelating agent. The core material includes one of lithium-containing transition metal oxides and lithium-containing transition metal phosphates.

[0005] In the technical solution of this application embodiment, lithium-containing transition metal oxides and lithium-containing transition metal phosphates suffer from metal ion dissolution. By applying a polymer coating layer to the surface of these materials, a physical barrier is formed, separating the electrolyte from the positive electrode active material. When metal ions dissolve from the interior of the positive electrode active material, they are trapped by the polymer network of the coating layer and cannot freely diffuse into the electrolyte, thereby reducing metal ion dissolution. Furthermore, the polymer coating layer contains metal ion chelating segments, which can anchor metal ions, further reducing the amount of metal ion dissolution. With reduced metal ion dissolution, the structural stability of the positive electrode active material is improved, making it less prone to structural damage during charge-discharge cycles, thus contributing to improved cycle performance of the secondary battery.

[0006] In some embodiments, R2 is an ester group, and the metal ion chelating agent contains a carboxyl group or a hydroxyl group.

[0007] In the technical solutions of this application embodiment, when the metal ion chelating agent contains carboxyl or hydroxyl groups, it can form ester groups through esterification reaction and attach them to the polymer chain.

[0008] In some embodiments, M includes at least one of ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, ethylene glycol bis(2-aminoethyl ether)tetraacetic acid, 8-hydroxyquinoline, and catechol.

[0009] In some embodiments, R2 is an amide group, and the metal ion chelating agent contains a carboxyl group or an amino group.

[0010] In the technical solutions of this application embodiment, when the metal ion chelating agent contains carboxyl or amino groups, it can form amide groups through an amidation reaction and attach them to the polymer chain.

[0011] In some embodiments, M includes at least one of ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, ethylene glycol bis(2-aminoethyl ether)tetraacetic acid, triethylenetetramine, and o-phenanthroline.

[0012] In some embodiments, the thickness of the polymer coating layer is 1 nm-5 nm.

[0013] In the technical solution of this application embodiment, when the thickness of the polymer coating layer is between 1nm and 5nm, it can introduce a sufficient number of groups to anchor metal ions while reducing the impact on ion conduction.

[0014] In some embodiments, the porosity of the positive electrode active material is 10%-20%.

[0015] In the technical solutions of this application, the porosity of lithium transition metal oxide and lithium transition metal phosphate core materials is generally between 20% and 40%, while the porosity of the positive electrode active material formed after coating with polymer is between 10% and 20%, which means that the polymer coating is relatively dense and can effectively block the electrolyte from contacting the positive electrode active material, thereby inhibiting the dissolution of metal ions.

[0016] In some embodiments, the particle size Dv50 of the positive electrode active material is 2μm-20μm.

[0017] In the technical solution of this application embodiment, when the particle size Dv50 of the positive electrode active material is between 2μm and 20μm, it is beneficial for lithium ion diffusion.

[0018] Secondly, this application provides a method for preparing a secondary battery, comprising: A positive electrode is provided, the positive electrode comprising a positive electrode active material, the positive electrode active material comprising a core material and a polymer coating layer covering at least a portion of the surface of the core material, the polymer coating layer containing segments of formula (I) in its molecular chain: Formula (I), Wherein, R1 includes at least one of hydrogen, alkane group, phenyl, carboxyl group, ester group, amide group, and sulfonic acid group; R2 includes at least one of alkylene group; X includes one of ester group and amide group; and M includes one of metal ion chelating agents. The core material includes one of lithium-containing transition metal oxide and lithium-containing transition metal phosphate. A negative electrode sheet, a separator, and an electrolyte are provided. The positive electrode sheet, separator, and negative electrode sheet are assembled into an electrode assembly, the electrode assembly is placed in an outer packaging for sealing, and the electrolyte is injected to obtain a secondary battery.

[0019] In some embodiments, the step of providing the positive electrode sheet includes: providing a polymer monomer, the polymer monomer including at least one of olefin monomers; providing a metal ion chelating agent modifier, the metal ion chelating agent modifier containing double bonds; mixing the core material, the polymer monomer, and the metal ion chelating agent modifier evenly, heating to 50℃-80℃, adding an initiator, and stirring the reaction for 4h-10h to obtain the positive electrode active material.

[0020] In the technical solution of this application embodiment, the polymer monomer and the metal ion chelating agent modifier crosslink under the action of the initiator, which can deposit on the surface of the core material to form a polymer coating layer. The formed polymer coating layer has a strong bonding force with the core material, and the in-situ deposition helps to form a uniform and dense coating layer, thereby improving the barrier effect of the coating layer.

[0021] In some embodiments, the step of providing the metal ion chelating agent modifier includes: providing a metal ion chelating agent containing one of carboxyl, hydroxyl, and amino groups; providing a chemical modifier containing a double bond, and further containing one of carboxyl and hydroxyl groups; and reacting the metal ion chelating agent with the chemical modifier to obtain a metal ion chelating agent modifier containing a double bond.

[0022] In the technical solution of this application embodiment, by chemically modifying the metal ion chelating agent, double bonds can be introduced, thereby achieving copolymerization with the polymer monomer, and the resulting copolymer can anchor metal ions more efficiently.

[0023] In some embodiments, the mass ratio of the core material to the polymer monomer is (85-98):(2-15); and / or, the mass ratio of the initiator to the polymer monomer is (0.1-0.3):100; and / or, the molar ratio of the metal ion chelating agent modifier to the second polymer monomer is 1:(8-12).

[0024] In the technical solutions of this application, when the mass ratio of core material to polymer monomer is (85-98):(2-15), it helps to form a coating layer with a thickness between 1nm and 5nm. When the mass ratio of initiator to polymer monomer is (0.1-0.3):100, it helps to form a polymer with a higher molecular weight, thereby helping to improve the density of the polymer coating layer. When the molar ratio of metal ion chelating agent modifier to polymer monomer is 1:(8-12), there is a relatively sufficient amount of metal ion chelating agent in the system, which can effectively chelate the target metal ions.

[0025] In some embodiments, the polymer monomer includes at least one of ethylene, propylene, 1-butene, styrene, acrylate, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, and dimethylaminoethyl acrylate; and / or, the metal ion chelating agent includes at least one of ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, ethylene glycol bis(2-aminoethyl ether)tetraacetic acid, 8-hydroxyquinoline, catechol, triethylenetetramine, and o-phenanthroline; and / or, the chemical modifier includes at least one of allyl alcohol, crotonol, geraniol, vinylphenol, acrylic acid, acryloyl chloride, caffeic acid, and ferulic acid.

[0026] In some embodiments, the step of uniformly mixing the core material and the polymer monomer and metal ion chelating agent modifier includes: adding the core material to a solvent and dispersing it to obtain a dispersion; adding the polymer monomer and metal ion chelating agent modifier to the dispersion and mixing them uniformly to remove oxygen.

[0027] In the technical solution of this application embodiment, the core material is first dispersed in a solvent and then polymer monomers and metal ion chelating agents are added for reaction, which can achieve uniform coating of the core material; after adding polymer monomers and metal ion chelating agents, deoxygenation can prevent the initiator from decomposing prematurely and can prevent the polymer monomers from oxidizing.

[0028] Thirdly, this application provides an electrical device, including any of the above-mentioned secondary batteries or secondary batteries prepared by any of the above-mentioned preparation methods.

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

[0030] Figure 1 This is a schematic diagram of the vehicle structure in some embodiments of this application; Figure 2 This is an exploded structural diagram of the secondary battery in some embodiments of this application; Figure 3 This is a schematic diagram showing the exploded structure of a single battery cell in some embodiments of this application; Figure 4 These are TEM images of the positive electrode active material in some embodiments of this application. Attached image description: 1000 vehicles; Secondary battery 100, controller 200, motor 300; Box 10, Part 11, Part 2 12; Battery cell 20, end cap 21, housing 22, electrode assembly 23. Detailed Implementation

[0032] The following embodiments are only used to illustrate the technical solutions of this application more clearly, and are therefore only examples and should not be used to limit the scope of protection of this application.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0034] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0035] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0036] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0037] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces). The term "at least one" refers to one or more.

[0038] During charge-discharge cycles, lithium salts in the electrolyte undergo hydrolysis under certain conditions, producing a small amount of hydrofluoric acid (HF). Manganese in the lithium transition metal oxide cathode material readily reacts with hydrofluoric acid to form manganese ion compounds soluble in the electrolyte, leading to manganese ion dissolution. As charge-discharge cycles continue, the number of active sites on the material surface increases, and the contact area with the electrolyte expands, accelerating acid corrosion and further promoting manganese ion dissolution.

[0039] To address the aforementioned issues, some embodiments involve coating the positive electrode active material with metal oxides, fluorides, etc., to form a physical barrier that isolates the electrolyte from the positive electrode active material, thereby suppressing the dissolution of metal ions. However, the coating layer is generally not completely dense, which means that in the complex electrochemical environment of the battery, tetravalent manganese ions may still be reduced to divalent manganese ions and released. In other words, conventional coating layers can only delay the dissolution of manganese ions, but cannot effectively solve the problem. Anchoring the dissolved manganese ions can be considered to prevent them from entering the electrolyte. This would reduce their redeposition at the negative electrode, thus reducing the damage to the SEI film growth. Anchoring the manganese ions can also stabilize the structure of the positive electrode active material.

[0040] Based on the above considerations, this application provides a secondary battery, wherein the positive electrode active material includes a core material and a polymer coating layer covering at least a portion of the surface of the core material, and the polymer coating layer contains the chain segments shown in formula (I): Formula (I), Wherein, R1 includes at least one of hydrogen, alkane group, phenyl, carboxyl group, ester group, amide group, and sulfonic acid group; R2 includes at least one of alkylene group; X includes one of ester group and amide group; and M is a segment of metal ion chelating agent.

[0041] In such a secondary battery, the polymer coating layer can form a physical barrier, separating the electrolyte from the positive electrode active material. When metal ions dissolve from the inside of the positive electrode active material, they are trapped by the polymer network of the polymer coating layer and cannot diffuse freely into the electrolyte, thereby reducing the dissolution of metal ions. In addition, the polymer coating layer contains metal ion chelating agent segments, which can anchor metal ions, thereby further reducing the amount of metal ions dissolved.

[0042] The secondary batteries disclosed in this application can be used, but are not limited to, in electrical devices such as vehicles, ships, or aircraft. A power system for such an electrical device can also be composed of the secondary batteries disclosed in this application.

[0043] This application provides an electrical device that uses a secondary battery as a power source. The secondary battery can be, but is not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0044] For ease of explanation, the following embodiments will be described using a vehicle 1000 as an example of an electrical device according to an embodiment of this application.

[0045] Reference Figure 1 As shown, vehicle 1000 can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. A secondary battery 100 is installed inside vehicle 1000, which can be located at the bottom, front, or rear of vehicle 1000. The secondary battery 100 can be used to power vehicle 1000; for example, it can serve as the operating power source for vehicle 1000. Vehicle 1000 may also include a controller 200 and a motor 300. The controller 200 controls the secondary battery 100 to supply power to the motor 300, for example, to meet the power needs of vehicle 1000 during starting, navigation, and driving.

[0046] In some embodiments of this application, the secondary battery 100 can not only serve as the operating power source for the vehicle 1000, but also as the driving power source for the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0047] In some embodiments of this application, the secondary battery 100 may be a single battery cell, a group of single battery cells, or a battery pack, see reference. Figure 2 As shown, taking a secondary battery 100 as an example, the secondary battery 100 may include a housing 10 and individual battery cells 20, with the individual battery cells 20 housed within the housing 10. The housing 10 provides a space for the individual battery cells 20 and can have various structures. In some embodiments, the housing 10 may include a first portion 11 and a second portion 12, which overlap each other, jointly defining a space for accommodating the individual battery cells 20. The second portion 12 may be a hollow structure with one open end, and the first portion 11 may be a plate-like structure, covering the open side of the second portion 12 so that the first portion 11 and the second portion 12 jointly define the space. Alternatively, both the first portion 11 and the second portion 12 may be hollow structures with one open side, with the open side of the first portion 11 covering the open side of the second portion 12. Of course, the housing 10 formed by the first portion 11 and the second portion 12 can have various shapes, such as a cylinder or a cuboid.

[0048] In the secondary battery 100, there can be multiple battery cells 20, which can be connected in series, parallel, or in a mixed manner. A mixed connection means that multiple battery cells 20 are connected in both series and parallel configurations. Multiple battery cells 20 can be directly connected in series, parallel, or in a mixed manner, and then the entire assembly of the multiple battery cells 20 is housed within the casing 10. Alternatively, the secondary battery 100 can also consist of multiple battery cells 20 first connected in series, parallel, or in a mixed manner to form a battery module, and then these battery modules are connected in series, parallel, or in a mixed manner to form a whole, which is also housed within the casing 10. The secondary battery 100 may also include other structures; for example, it may include a busbar component for electrical connection between the multiple battery cells 20.

[0049] Among them, the battery cell 20 can be in the form of a cylinder, a flat surface, a cuboid or other shapes.

[0050] refer to Figure 3 As shown, the battery cell 20 refers to the smallest unit that makes up the battery. The battery cell 20 includes an end cap 21, a housing 22, an electrode assembly 23, and other functional components.

[0051] End cap 21 refers to a component that covers the opening of housing 22 to isolate the internal environment of battery cell 20 from the external environment. The shape of end cap 21 can be adapted to the shape of housing 22 to fit it. Optionally, end cap 21 can be made of a material with certain hardness and strength (such as aluminum alloy), so that end cap 21 is not easily deformed under pressure or impact, allowing battery cell 20 to have higher structural strength. Functional components such as electrode terminals can be provided on end cap 21. Electrode terminals can be used for electrical connection with electrode assembly 23 for outputting or inputting electrical energy into battery cell 20. In some embodiments, end cap 21 can also be provided with a pressure relief mechanism for releasing internal pressure when the internal pressure or temperature of battery cell 20 reaches a threshold. The material of end cap 21 can also be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and this application embodiment does not impose any special limitations on this. In some embodiments, an insulating element may be provided on the inner side of the end cap 21. The insulating element can be used to isolate the electrical connecting pieces inside the housing 22 from the end cap 21 to reduce the risk of short circuit. For example, the insulating element may be made of plastic, rubber, etc.

[0052] The housing 22 is a component used to cooperate with the end cap 21 to form the internal environment of the battery cell 20. This internal environment can accommodate the electrode assembly 23, electrolyte, and other components. The housing 22 and the end cap 21 can be independent components. An opening can be provided on the housing 22, and the end cap 21 can be used to close the opening to form the internal environment of the battery cell 20. Alternatively, the end cap 21 and the housing 22 can be integrated. Specifically, the end cap 21 and the housing 22 can form a common connecting surface before other components are inserted into the housing. When it is necessary to encapsulate the interior of the housing 22, the end cap 21 closes the housing 22. The housing 22 can be of various shapes and sizes, such as cuboid, cylindrical, hexagonal prism, etc. Specifically, the shape of the housing 22 can be determined according to the specific shape and size of the electrode assembly 23. The material of the housing 22 can be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc. This application embodiment does not impose any special limitations on this.

[0053] Electrode assembly 23 is the component in the battery cell 20 where electrochemical reactions occur. The casing 22 may contain one or more electrode assemblies 23. The electrode assembly 23 is mainly formed by winding or stacking positive and negative electrode sheets, and typically a separator is provided between the positive and negative electrode sheets. The portions of the positive and negative electrode sheets containing active material constitute the main body of the electrode assembly, while the portions without active material each constitute a tab. The positive and negative tabs may be located together at one end of the main body or separately at both ends. During the charging and discharging process of the battery, the positive and negative active materials react with the electrolyte, and the tabs connect to the electrode terminals to form a current loop.

[0054] Of course, in some other embodiments, the secondary battery 100 may also be integrated with the chassis / body.

[0055] According to some embodiments of this application, this application provides a secondary battery, including a positive electrode sheet, the positive electrode sheet including a positive electrode active material, the positive electrode active material including a core material and a polymer coating layer covering at least a portion of the surface of the core material, the polymer coating layer containing segments of formula (I) in its molecular chain: Formula (I), Wherein, R1 includes at least one of hydrogen, alkane group, phenyl, carboxyl group, ester group, amide group, and sulfonic acid group; R2 includes at least one of alkylene group; X includes one of ester group and amide group; M is a segment of metal ion chelating agent; and the core material includes one of lithium-containing transition metal oxide and lithium-containing transition metal phosphate.

[0056] A polymer coating refers to a thin polymer layer covering at least a portion of the surface of a core material. When a polymer coating is applied to the core material surface, the polymer's macromolecular structure allows it to firmly bond with the core material surface through physical entanglement or chemical bonding, forming a stable coating that maintains its integrity over a long period. Furthermore, the polymer coating can isolate the electrolyte from the positive electrode active material. When metal ions dissolve from the interior of the positive electrode active material, they are trapped by the polymer network of the coating, preventing them from freely diffusing into the electrolyte, thus reducing the dissolution of metal ions.

[0057] The presence of segments of formula (I) in the molecular chain of the polymer coating layer can mean that the polymer coating layer is obtained by copolymerization of monomers of formulas (II) and (III). When the polymer obtained by copolymerization of monomers of formulas (II) and (III) is an alternating copolymer, the repeating unit of the molecular chain of the polymer coating layer is as shown in formula (I). When the polymer obtained by copolymerization of monomers of formulas (II) and (III) is a random alternating copolymer, the molecular chain of the polymer coating layer contains segments of formula (I).

[0058] Equation (II), Formula (III).

[0059] Metal ion chelating agents are a class of chemical substances that can bind to metal ions through multiple coordinating atoms to form stable cyclic complexes (chelates). Metal ion chelating agents encapsulate metal ions within their molecular structure through chelation, thereby reducing the dissolution of metal ions.

[0060] M represents the metal ion chelating agent segment, which refers to the metal ion chelating agent being introduced into the monomer shown in formula (III) through a reaction, thereby enabling copolymerization with formula (II) to obtain a polymer coating layer. The polymer coating layer formed through copolymerization allows the metal ion chelating agent segments to be uniformly distributed within the coating layer, thus improving the anchoring effect on metal ions and further reducing metal ion dissolution. With reduced metal ion dissolution, the structural stability of the positive electrode active material improves, and the structure is less prone to damage during charge-discharge cycles, thereby contributing to improved cycle performance of the secondary battery.

[0061] Lithium-containing transition metal oxides refer to composite materials composed of hydroxides or oxides of nickel (Ni), cobalt (Co), and manganese (Mn), typically exhibiting a layered crystal structure. In some embodiments, the molecular formula of the lithium-containing transition metal oxide is lithium nickel cobalt manganese oxide (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 At least one of the following: ) and its modified compounds.

[0062] Lithium-containing transition metal phosphates refer to cathode materials that use phosphate as their backbone while containing lithium ions and transition metal ions. In some embodiments, lithium-containing transition metal phosphates include lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), lithium cobalt phosphate (LiCoPO4), and lithium nickel phosphate (LiNiPO4).

[0063] Lithium-containing transition metal oxides and lithium-containing transition metal phosphates will leach out transition metal ions under the chemical corrosion of the electrolyte. The polymer coating layer mentioned above can effectively reduce the amount of metal ion leaching, thereby improving the cycle performance of the battery.

[0064] According to some embodiments of this application, X is an ester group, and the metal ion chelating agent contains a carboxyl group or a hydroxyl group.

[0065] When X is an ester group and the metal ion chelating agent contains a carboxyl group, the monomer shown in formula (III) can be obtained by esterification of the metal ion chelating agent containing a carboxyl group and the monomer shown in formula (IV): Formula (IV).

[0066] When X is an ester group and the metal ion chelating agent contains a hydroxyl group, the monomer shown in formula (III) can be obtained by esterification of the metal ion chelating agent containing a hydroxyl group and the monomer shown in formula (V): Formula (IV).

[0067] According to some embodiments of this application, the metal ion chelating agent includes at least one of ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, ethylene glycol bis(2-aminoethyl ether)tetraacetic acid, 8-hydroxyquinoline, and catechol.

[0068] Ethylenediaminetetraacetic acid (EDTA) has an ethylenediamine (H2N-CH2-CH2-NH2) backbone, with each of the two amino groups attached to two acetic acid groups (-CH2-COOH), forming a hexadectic ligand (two amino N groups and four carboxylic acid O groups). The structural formula of the chelate formed by EDTA and the metal ion M is shown in formula (I).

[0069] Formula (I).

[0070] Diethylenetriaminepentaacetic acid (DTPA) has a diethylenetriamine (H2N-CH2-CH2-NH-CH2-CH2-NH2) backbone, with three amino groups linked to five acetic acid groups, making it an octate ligand (3 amino N groups and 5 carboxylic acid O groups), which has a stronger chelating ability than ethylenediaminetetraacetic acid.

[0071] Ethylene glycol bis(2-aminoethyl ether)tetraacetic acid (EGTA) is a hexadecimal ligand (2 amino N and 4 carboxylic acid O) with ethylene glycol (HO-CH2-CH2-OH) as the center and two 2-aminoethyl groups (-O-CH2-CH2-NH2) at both ends connected by ether bonds.

[0072] 8-Hydroxyquinoline (8-HQ) has a hydroxyl group (-OH) at position 8 of its quinoline ring (benzopyridine), making it a bidentate ligand (N of the pyridine ring and O of the hydroxyl group). Catechol has two hydroxyl groups (-OH) at positions 1 and 2 of its benzene ring, making it a bidentate ligand (O of two hydroxyl groups).

[0073] According to some embodiments of this application, X is an amide group, and the metal ion chelating agent contains a carboxyl group or an amino group.

[0074] When X is an amide group and the metal ion chelating agent contains a carboxyl group, the monomer shown in formula (III) can be obtained by esterification of a metal ion chelating agent containing a carboxyl group and the monomer shown in formula (VI): Formula (VI).

[0075] When X is an amide group and the metal ion chelating agent contains an amino group, the monomer shown in formula (III) can be obtained by esterification of the metal ion chelating agent containing a carboxyl group and the monomer shown in formula (IV). According to some embodiments of this application, the metal ion chelating agent includes at least one of ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, ethylene glycol bis(2-aminoethyl ether)tetraacetic acid, triethylenetetramine, and o-phenanthroline.

[0076] The structural formula of triethylenetetramine is NH2-CH2-CH2-NH-CH2-CH2-NH-CH2-CH2-NH2, which is a tetradentate ligand (4 amino nitrogen atoms). o-Phenanthroline is formed by the fusion of two benzene rings and contains two pyridine nitrogen atoms (positions 1 and 10), making it a bidentate ligand (2 nitrogen atoms).

[0077] According to some embodiments of this application, the thickness of the polymer coating layer is 1nm-5nm.

[0078] In some embodiments, the thickness of the polymer coating can be measured using a high-resolution transmission electron microscope (TEM). For example, the thickness of the polymer coating can be 1 nm, 2 nm, 3 nm, 4 nm, or 5 nm. When the thickness of the polymer coating is between 1 nm and 5 nm, it is possible to introduce a sufficient number of functional groups to anchor metal ions while reducing the impact on ion conduction.

[0079] According to some embodiments of this application, the porosity of the positive electrode active material is 10%-20%.

[0080] The porosity of the positive electrode active material can be tested using the gas adsorption method: the sample is placed in a gas adsorption instrument, and nitrogen gas is adsorbed onto the sample surface under certain temperature and pressure conditions. By measuring the amount of nitrogen adsorbed at different pressures, adsorption isotherms are plotted. Finally, the porosity is calculated using the BET equation.

[0081] The porosity of the core material (the positive electrode active material before coating) is generally 20%-40%. When the porosity of the positive electrode active material formed after coating with a polymer coating layer is between 10%-20%, it means that the polymer coating layer is relatively dense and can effectively block the electrolyte from contacting the positive electrode active material, thereby inhibiting the dissolution of metal ions.

[0082] According to some embodiments of this application, the particle size Dv50 of the positive electrode active material is 2μm-20μm.

[0083] For example, the particle size Dv50 of the positive electrode active material can be 2 μm, 4 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, or 20 μm. When the particle size Dv50 of the positive electrode active material is between 2 μm and 20 μm, it is beneficial for lithium-ion diffusion.

[0084] According to some embodiments of this application, this application provides a method for preparing a secondary battery, comprising: providing a positive electrode sheet, the positive electrode sheet comprising a positive electrode active material, the positive electrode active material comprising a core material and a polymer coating layer covering at least a portion of the surface of the core material, wherein the molecular chain of the polymer coating layer contains a segment of formula (I): Formula (I), Wherein, R1 includes at least one of hydrogen, alkane group, phenyl, carboxyl group, ester group, amide group, and sulfonic acid group; R2 includes at least one of alkylene group; X includes one of ester group and amide group; M is a segment of metal ion chelating agent; the core material includes one of lithium-containing transition metal oxide and lithium-containing transition metal phosphate; a negative electrode sheet, a separator, and an electrolyte are provided; the positive electrode sheet, the separator, and the negative electrode sheet are assembled into an electrode assembly, the electrode assembly is placed in an outer packaging for sealing, and an electrolyte is injected to obtain a secondary battery.

[0085] The negative electrode sheet includes a negative electrode active material. When the secondary battery is a lithium-ion battery, the negative electrode active material can be a negative electrode active material known in the art for use in batteries. In some embodiments, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. In some embodiments, the negative electrode film layer may also optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS). In some embodiments, the negative electrode film layer may also optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the negative electrode film may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0086] The separator can be any known porous structure separator with good chemical and mechanical stability. In some embodiments, the separator material can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride.

[0087] The electrolyte comprises an electrolyte and a solvent. When the secondary battery is a lithium-ion battery, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate. The solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0088] The electrode assembly can be a stacked electrode assembly or a wound electrode assembly. The outer packaging can be a rigid shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging can also be a flexible package, such as a pouch. The material of the flexible package can be plastic, and examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0089] According to some embodiments of this application, the step of providing a positive electrode sheet includes: providing a polymer monomer, the polymer monomer including at least one of olefin monomers; providing a metal ion chelating agent modifier, the metal ion chelating agent modifier containing double bonds; mixing the core material, polymer monomer, and metal ion chelating agent modifier evenly, heating to 50℃-80℃, adding an initiator, and stirring the reaction for 4h-10h to obtain a positive electrode active material.

[0090] Olefin monomers are organic compounds containing carbon-carbon double bonds (C=C) that can form polymers through polymerization reactions (usually addition polymerization). Olefin monomer molecules contain one or more carbon-carbon double bonds, and the π bonds within these double bonds are easily broken, allowing monomers to link together through chain reactions to form long-chain polymers.

[0091] Metal ion chelating agent modifiers refer to products formed by introducing double bonds into metal ion chelating agents. The introduction of double bonds can lead to copolymerization reactions between the metal ion chelating agent modifier and olefin monomers, thereby allowing the metal ion chelating agent to enter the polymer coating layer.

[0092] Initiators are used to initiate copolymerization reactions between polymer monomers and metal ion chelating agents. Depending on the polymer monomer, the initiator can be at least one of the following: free radical polymerization initiator, coordination polymerization Zn initiator, metallocene initiator, or controlled-active free radical polymerization initiator. Free radical polymerization initiators generate free radicals through thermal, photochemical, or chemical decomposition, initiating monomer chain polymerization; these include at least one of benzoyl peroxide, persulfate, and azobisisobutyronitrile. Coordination polymerization Zn initiators are catalytic systems composed of transition metal halides and organometallic compounds, used for the directed polymerization of olefins, with TiCl4 and TiCl3 as cocatalysts and alkylaluminum as cocatalysts. Metallocene initiators are single-active-center transition metal complexes coordinated with cyclopentadienyl (Cp), with zirconium dichlorodichlorodicyclopentadiene as a cocatalyst and methylaluminoxane as a cocatalyst. Controllable living radical polymerization initiators achieve chain growth control through a reversible passivation mechanism, combining the universality of radical polymerization with the precision of living polymerization. These include atom transfer radical polymerization, reversible addition-fracture chain transfer, and nitroxide-stabilized radical polymerization. The initiator for atom transfer radical polymerization is a haloalkane, and the catalyst is CuBr / bipyridine ligand. The chain transfer agent for reversible addition-fracture chain transfer is a dithioester. The initiator for nitroxide-stabilized radical polymerization is TEMPO (2,2,6,6-tetramethylpiperidine-1-oxo radical).

[0093] This application copolymerizes polymer monomers with metal ion chelating agents under the action of an initiator, which can deposit a polymer coating layer on the surface of the core material. The formed polymer coating layer has a strong bonding force with the core material, and the in-situ deposition helps to form a uniform and dense coating layer, thereby improving the barrier effect of the coating layer.

[0094] According to some embodiments of this application, the step of providing a metal ion chelating agent modifier includes: providing a metal ion chelating agent containing one of carboxyl, hydroxyl, and amino groups; providing a chemical modifier including a double bond, and further including one of carboxyl and hydroxyl groups; and reacting the metal ion chelating agent with the chemical modifier to obtain a metal ion chelating agent modifier containing a double bond.

[0095] Since metal ion chelators need to chelate metal ions, when modifying them with chemical modifiers, the molar ratio of the functional groups of the metal ion chelator to the functional groups (non-double bonds) of the chemical modifier should be controlled at (2-4):1. This ensures that only a portion of the functional groups in the metal ion chelator undergo condensation, while the majority of the functional groups can be used to chelate metal ions. Furthermore, taking metal ion chelators containing carboxyl groups as an example, in addition to the carboxyl group, their nitrogen atoms contain lone pairs of electrons, which can also achieve chelation of metal ions.

[0096] This application introduces double bonds by chemically modifying the metal ion chelating agent, thereby achieving copolymerization with the second polymer monomer. The resulting copolymer can anchor metal ions more efficiently.

[0097] According to some embodiments of this application, the mass ratio of core material to polymer monomer is (85-98):(2-15); and / or, the mass ratio of initiator to polymer monomer is (0.1-0.3):100; and / or, the molar ratio of metal ion chelating agent modifier to polymer monomer is 1:(8-12).

[0098] For example, the mass ratio of the core material to the polymer monomer can be 85:15, 88:12, 90:10, 93:7, 95:5 or 98:2. When the mass ratio of the core material to the polymer monomer is (85-98):(2-15), it helps to form a coating layer with a thickness between 1nm and 5nm.

[0099] The mass ratio of initiator to polymer monomer can be 0.1:100, 0.15:100, 0.2:100, 0.25:100 or 0.3:100. When the mass ratio of initiator to polymer monomer is (0.1-0.3):100, it helps to form polymers with higher molecular weight, thereby helping to improve the compactness of the polymer coating layer.

[0100] The molar ratio of the metal ion chelating agent modifier to the polymer monomer can be 1:8, 1:9, 1:10, 1:11 or 1:12. When the molar ratio of the metal ion chelating agent modifier to the polymer monomer is between 1: (8-12), there is a relatively sufficient amount of metal ion chelating agent in the system, which can effectively chelate the target metal ion.

[0101] According to some embodiments of this application, the polymer monomer includes at least one of ethylene, propylene, 1-butene, styrene, acrylate, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, and dimethylaminoethyl acrylate; and / or, the metal ion chelating agent includes at least one of ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, ethylene glycol bis(2-aminoethyl ether)tetraacetic acid, 8-hydroxyquinoline, catechol, triethylenetetramine, and o-phenanthroline; and / or, the chemical modifier includes at least one of allyl alcohol, crotonol, geraniol, vinylphenol, acrylic acid, acryloyl chloride, caffeic acid, and ferulic acid.

[0102] When the metal ion chelating agent contains a carboxyl group, the chemical modifier includes one of allyl alcohol, crotonol, geraniol, and vinylphenol. When the metal ion chelating agent contains hydroxyl and amino groups, the chemical modifier includes one of acrylic acid, acryloyl chloride, caffeic acid, and ferulic acid.

[0103] According to some embodiments of this application, the step of uniformly mixing the core material, polymer monomer, and metal ion chelating agent includes: adding the core material to a solvent and dispersing it to obtain a dispersion; adding the polymer monomer and metal ion chelating agent to the dispersion and mixing them uniformly to remove oxygen.

[0104] When dispersing the core material in a solvent, ultrasonic dispersion or mechanical stirring can be used. Dispersing the core material in the solvent first, followed by adding polymer monomers and metal ion chelating agents for reaction, can achieve uniform coating of the core material.

[0105] Oxygen removal can be achieved by introducing inert gases such as nitrogen, helium, and argon into the system. Oxygen removal can prevent the initiator from decomposing prematurely and can also prevent the oxidation of polymer monomers.

[0106] According to some embodiments of this application, this application provides an electrical device including any of the aforementioned secondary batteries.

[0107] Example The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0108] Example 1 [EDTA Modification] 4 mol of EDTA, 1 mol of allyl alcohol, and 4 mol of catalyst 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDAC) were added to dichloromethane, stirred until dissolved, and reacted at 25 °C for 18 h to obtain the EDTA-modified compound. The molecular structure of the EDTA-modified compound is shown in Formula VII.

[0109] Equation VII.

[0110] [Positive electrode active material] LiNi containing lithium transition metal oxide 0.9 Co 0.05 Mn 0.05 O2 was dispersed in a round-bottom flask containing an equal mass of toluene, and ultrasonically dispersed for 10 min to allow LiNi to disperse. 0.9 Co 0.05 Mn 0.05 O2 is uniformly dispersed; EDTA modifier is added and dissolved with ethylene by stirring; LiNi 0.9 Co 0.05 Mn 0.05 The mass ratio of O2 to ethylene is 95:5, and the molar ratio of EDTA to ethylene is 1:10. Nitrogen gas is introduced for 15 minutes to remove oxygen from the system, and the temperature is raised to 60°C. After the system temperature stabilizes, azobisisobutyronitrile (AIBN) initiator, at a content of 0.2 wt% of the ethylene mass, is slowly added, and the reaction is continued with stirring for 6 hours. After the reaction is completed, the product is filtered, washed, and dried to obtain the ternary material, wherein the coating layer includes segments as shown in Formula VIII.

[0111] Formula VIII.

[0112] The prepared ternary material with the coating layer was tested by TEM, and the TEM image is shown below. Figure 4 As shown, the ternary material has a coating layer on its surface, and the coating layer is uniform and dense with a thickness of 2 nm.

[0113] [Positive electrode plate] The positive electrode active material prepared above was mixed with conductive carbon black (Super P) and binder polyvinylidene fluoride (PVDF) in an N-methylpyrrolidone (NMP) solvent at a mass ratio of 96:2.2:1.8 to form a positive electrode slurry. The positive electrode slurry was uniformly coated on both sides of an aluminum foil, and then dried, cold-pressed, and slit to obtain the positive electrode sheet.

[0114] [Negative electrode plate] Artificial graphite (anode active material), styrene-butadiene rubber (SBR) (binder), carbon black (Super P) (conductive agent), and sodium carboxymethyl cellulose (CMC-Na) (plasticizer) are dispersed in deionized water at a mass ratio of 95:3:1:1 and thoroughly stirred to obtain a cathode slurry. The slurry is then uniformly coated on both sides of a copper foil, and subsequently dried, cold-pressed, trimmed, cut, and slit to form a cathode sheet.

[0115] [Isolation membrane] Polypropylene film is used as the separating membrane.

[0116] Electrolyte In an argon-atmospheric glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 1:1:1. LiPF6 was then uniformly dissolved in the mixture to obtain the electrolyte. The concentration of LiPF6 in this electrolyte was 1 mol / L.

[0117] [Assembly] The positive electrode, separator, and negative electrode are stacked in sequence to form an electrode assembly. The electrode assembly is placed in a housing, injected with electrolyte, and then sealed. After formation and settling, a battery is obtained.

[0118] Example 2 Unlike Example 1, in this example, the molar ratio of EDTA to ethylene monomer is 1:12, and the thickness of the polymer coating layer is 4 nm.

[0119] Example 3 Unlike Example 1, in this example, the molar ratio of EDTA to ethylene monomer is 1:8, and the thickness of the resulting polymer coating layer is 1.5 nm.

[0120] Example 4 Unlike Example 1, the metal ion chelating agent in this example is catechol. The modification method of catechol includes: adding 2 mol of catechol, 1 mol of acrylic acid and 2 mol of the catalyst p-toluenesulfonic acid to dichloromethane, stirring to dissolve, and reacting at 80°C for 10 h to obtain the catechol modified product.

[0121] Example 5 Unlike Example 1, the metal ion chelating agent in this example is triethylenetetramine. The modification method of triethylenetetramine includes: dissolving 4 mol of triethylenetetramine in dichloromethane, slowly adding 1 mol of acryloyl chloride under ice bath cooling conditions, keeping the temperature below 5°C during the addition process, and obtaining the triethylenetetramine modified product after the reaction is completed.

[0122] Example 6 Unlike Example 1, the monomer used in this example is acrylic acid.

[0123] Example 7 Unlike Example 1, the core material in this example is lithium iron phosphate.

[0124] Comparative Example 1 Unlike Example 1, the lithium-containing transition metal oxide in this comparative example is not coated.

[0125] Comparative Example 2 Unlike Example 1, the preparation method of the positive electrode active material in this comparative example is as follows: Lithium-containing transition metal oxides were dispersed in a round-bottom flask containing an equal mass of toluene and ultrasonically dispersed for 10 min to ensure uniform dispersion. Ethylene was added and stirred to dissolve the oxides, with a mass ratio of lithium-containing transition metal oxides to ethylene of 95:5. Nitrogen gas was purged for 15 min to remove oxygen from the system, and the temperature was raised to 60°C. After the system temperature stabilized, an initiator at a content of 0.2 wt% of the ethylene mass was slowly added, and the reaction was continued with stirring for 6 h. After the reaction was complete, the product was filtered, washed, and dried to obtain the coated lithium-containing transition metal oxides. The coating thickness was 2 nm.

[0126] Comparative Example 3 Unlike Example 7, the lithium iron phosphate in this comparative example is not coated.

[0127] Performance testing Metal ion dissolution: The fully charged positive electrode sheet is cleaned and dried with dimethyl carbonate (DMC), then the electrode sheet is scraped to remove powder, and the powder is dissolved in concentrated hydrochloric acid to form a solution. The content of metal ions (manganese ions for lithium transition metal oxides and iron ions for lithium iron phosphate) in the solution is then accurately measured by inductively coupled plasma mass spectrometry (ICP-MS).

[0128] Electrochemical stability of the polymer coating material: A slurry was prepared by mixing the polymer coating material, binder polyvinylidene fluoride, conductive carbon black, and NMP in a ratio of 0.1:0.88:0.42:18.6 and coated onto aluminum foil as the positive electrode of a half-cell, with lithium as the negative electrode, and assembled into a coin cell. The CV curve of the coin cell was tested using an electrochemical workstation, with a voltage range of 2.5V-5.0V, a scan rate of 0.1mV / s, and 3 scan cycles, scanning from open circuit voltage to high voltage and then to low voltage.

[0129] Electrolyte leaching resistance of polymer coating material: Weigh approximately 1g of polymer coating material (A) and place it in a semi-permeable membrane (electrolyte permeable, sample powder impermeable) sample bag. Seal the bag and record the total weight B1. Then, immerse the sample bag in 10g of electrolyte (volume ratio EC:EMC=3:7) at 60℃ for 7 days. After immersion, remove the sample bag, drain, and dry at 120℃ for 12 hours. Weigh the sample bag again, B2. The formula for calculating the sample leaching rate R is as follows: R=(B1-B2) / A×100%.

[0130] Cycling performance: At 60°C, the secondary batteries in Examples 1-7 and Comparative Examples 1-2 were charged to 4.25V at a rate of 0.5C, and then discharged to 2.8V at a rate of 0.5C. The charge-discharge cycle was performed until the reversible capacity decay value of 90% SOH was reached, and the number of cycles at this point was recorded.

[0131] At 60°C, the secondary batteries in Example 7 and Comparative Example 3 were charged to 3.65V at a rate of 0.5C, and then discharged to 2.5V at a rate of 0.5C. The charge-discharge cycle was repeated until the reversible capacity decay value of 90% SOH was reached, and the number of cycles at this point was recorded.

[0132] Test Results The test results of Examples 1-7 and Comparative Examples 1-3 are shown in Table 1.

[0133] Table 1. Test results from Examples 1-7 and Comparative Examples 1-3

[0134] As can be seen from Table 1, the amount of manganese ions dissolved in the positive electrode sheets of Examples 1-6 of this application and the amount of iron ions dissolved in Example 7 are all less than those in the comparative example, indicating that the polymer coating layer of this application can significantly reduce the dissolution of metal ions, thereby helping to improve the cycle performance of the secondary battery.

[0135] Comparing Example 1 and Comparative Example 2, it can be seen that when the polymer coating layer is polyethylene, the amount of manganese ions leached is 7463 ppm, indicating that the present application can significantly reduce the amount of manganese ions leached by introducing EDTA segments into the polymer coating layer.

[0136] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A secondary battery, comprising a positive electrode sheet, said positive electrode sheet comprising a positive electrode active material, characterized in that, The positive electrode active material includes a core material and a polymer coating layer covering at least a portion of the surface of the core material, wherein the molecular chain of the polymer coating layer contains segments of formula (I): Equation (I), Wherein, R1 includes at least one of hydrogen, alkane, phenyl, carboxyl, ester, amide, and sulfonic acid; R2 includes at least one of alkylene groups; X includes one of ester and amide groups; and M is a segment of a metal ion chelating agent. The core material includes one of lithium-containing transition metal oxides and lithium-containing transition metal phosphates.

2. The secondary battery as described in claim 1, characterized in that, X is an ester group, and the metal ion chelating agent contains a carboxyl group or a hydroxyl group.

3. The secondary battery as described in claim 1 or 2, characterized in that, The metal ion chelating agent includes at least one of ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, ethylene glycol bis(2-aminoethyl ether)tetraacetic acid, 8-hydroxyquinoline, and catechol.

4. The secondary battery as described in claim 1, characterized in that, X is an amide group, and the metal ion chelating agent contains a carboxyl group or an amino group.

5. The secondary battery as described in claim 1 or 4, characterized in that, The metal ion chelating agent includes at least one of ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, ethylene glycol bis(2-aminoethyl ether)tetraacetic acid, triethylenetetramine, and o-phenanthroline.

6. The secondary battery according to any one of claims 1 to 5, characterized in that, The thickness of the polymer coating layer is 1nm-5nm.

7. The secondary battery according to any one of claims 1 to 6, characterized in that, The porosity of the positive electrode active material is 10%-20%.

8. The secondary battery according to any one of claims 1 to 7, characterized in that, The particle size Dv50 of the positive electrode active material is 2μm-20μm.

9. A method for preparing a secondary battery, characterized in that, include: A positive electrode is provided, the positive electrode comprising a positive electrode active material, the positive electrode active material comprising a core material and a polymer coating layer covering at least a portion of the surface of the core material, the polymer coating layer containing segments of formula (I) in its molecular chain: Equation (I), Wherein, R1 includes at least one of hydrogen, alkane group, phenyl, carboxyl group, ester group, amide group, and sulfonic acid group; R2 includes at least one of alkylene group; X includes one of ester group and amide group; M is a segment of metal ion chelating agent; and the core material includes one of lithium-containing transition metal oxide and lithium-containing transition metal phosphate. We provide negative electrode plates, separators, and electrolytes; The positive electrode, separator, and negative electrode are assembled into an electrode assembly, which is then placed in an outer packaging for sealing. After injecting the electrolyte, a secondary battery is obtained.

10. The method for preparing a secondary battery as described in claim 9, characterized in that, The step of providing the positive electrode sheet includes: A polymer monomer is provided, said polymer monomer comprising at least one of olefin monomers; A metal ion chelating agent modifier is provided, wherein the metal ion chelating agent modifier contains a double bond; The core material, polymer monomer, and metal ion chelating agent are mixed evenly, heated to 50℃-80℃, an initiator is added, and the mixture is stirred for 4-10 hours to obtain the positive electrode active material.

11. The method for preparing a secondary battery as described in claim 10, characterized in that, The step of providing the metal ion chelating agent modifier includes: A metal ion chelating agent is provided, wherein the metal ion chelating agent contains one of carboxyl, hydroxyl, and amino groups; A chemical modifier is provided, wherein the chemical modifier comprises a double bond, and further comprises one of a carboxyl group and a hydroxyl group; The metal ion chelating agent is reacted with the chemical modifier to obtain a metal ion chelating agent modified with double bonds.

12. The method for preparing a secondary battery as described in claim 10 or 11, characterized in that, The mass ratio of the core material to the polymer monomer is (85-98):(2-15); and / or, The mass ratio of the initiator to the polymer monomer is (0.1-0.3):100; and / or, The molar ratio of the metal ion chelating agent modifier to the polymer monomer is 1:(8-12).

13. The method for preparing a secondary battery as described in claim 11 or 12, characterized in that, The polymer monomer includes at least one selected from ethylene, propylene, 1-butene, styrene, acrylate, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, and dimethylaminoethyl acrylate; and / or, The metal ion chelating agent comprises at least one selected from ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, ethylene glycol bis(2-aminoethyl ether)tetraacetic acid, 8-hydroxyquinoline, catechol, triethylenetetramine, and o-phenanthroline; and / or, The chemical modifiers include at least one of allyl alcohol, crotonol, geraniol, vinylphenol, acrylic acid, acryloyl chloride, caffeic acid, and ferulic acid.

14. The method for preparing a secondary battery according to any one of claims 10 to 13, characterized in that, The step of uniformly mixing the core material, the polymer monomer, and the metal ion chelating agent modifier includes: The core material is added to a solvent and dispersed to obtain a dispersion. The polymer monomer and metal ion chelating agent modifier are added to the dispersion and mixed evenly to remove oxygen.

15. An electrical appliance, characterized in that, This includes the secondary battery as described in any one of claims 1 to 8 or the secondary battery prepared by any one of claims 9 to 14.

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