Positive electrode active material, positive electrode sheet, battery, and electric device

Abstract

This application provides a positive electrode active material, a positive electrode sheet, a battery, and an electrical device, relating to the field of batteries. The positive electrode active material includes a core, a first coating layer covering the core, and a second coating layer covering the first coating layer. The core includes a lithium transition metal oxide. The first coating layer includes a first polymer containing anionic groups, including at least one selected from cyano, halogen, phenyl, and ester groups. The second coating layer includes a second polymer containing hydrophilic groups, including at least one selected from amide, hydroxyl, and carboxyl groups. The positive electrode sheet includes a positive current collector and a positive electrode active material layer disposed on at least one surface of the positive current collector. The positive electrode active material layer contains the aforementioned positive electrode active material. The positive electrode active material, positive electrode sheet, battery, and electrical device of this application can improve the cycle life of the battery.

Description

Technical Field

[0001] This application relates to the field of batteries, specifically to a positive electrode active material, a positive electrode sheet, a battery, and an electrical device. Background Technology

[0002] With the continuous development and progress of society, the demand for energy consumption is rising, and the successful commercialization of lithium-ion batteries has greatly changed people's energy consumption patterns. However, with the increasing popularity of large-scale energy storage grids and electric vehicles, people have increasingly higher requirements for lithium-ion batteries.

[0003] As a crucial component of lithium-ion batteries, the positive electrode active material significantly influences their performance. To improve the stability of positive electrode active materials, modifications such as elemental doping and surface coating are commonly employed. Among these methods, polymer coating is a frequently used technique, but the cycle life of the resulting batteries still requires further improvement. Summary of the Invention

[0004] This application provides a positive electrode active material, a positive electrode sheet, a battery, and an electrical device, which can improve the cycle life of the battery.

[0005] In a first aspect, this application provides a positive electrode active material, comprising a core, a first coating layer covering the core, and a second coating layer covering the first coating layer, wherein the core comprises a lithium transition metal oxide, the first coating layer comprises a first polymer containing anionic groups, the anionic groups comprising at least one selected from cyano, halogen, phenyl, and ester groups; and the second coating layer comprises a second polymer containing hydrophilic groups, the hydrophilic groups comprising at least one selected from amide, hydroxyl, and carboxyl groups.

[0006] In the technical solution of this application embodiment, lithium transition metal oxide serves as the active part (core) of the positive electrode active material. Its surface is sequentially provided with a first coating layer and a second coating layer. The first coating layer located in the inner layer contains anionic groups, which can bond with the transition metal ions at the core interface (through chemical coordination chelation) to stabilize the active interface of the positive electrode active material, fix the transition metal ions on the core surface, and inhibit their dissolution and exudation, thereby improving the stability of the positive electrode active material. The second coating layer located in the outer layer contains hydrophilic groups, which can inhibit the dissolution of the inner first polymer after being immersed in the electrolyte, thereby effectively improving the stability of the coating layer at the interface of the positive electrode active material and improving the battery cycle life.

[0007] In some embodiments, the second polymer includes at least one selected from polyacrylamide, carboxymethyl cellulose, sodium alginate, and sodium polyacrylate. These second polymers protect the first coating layer and inhibit the dissolution of the first polymer in the electrolyte.

[0008] In some embodiments, the first polymer comprises the structural unit shown in Formula I.

[0009]

[0010] Wherein, R1, R2, R3, and R4 are each independently selected from H, substituted or unsubstituted C1-C10 alkyl, cyano, halogen, phenyl, and ester groups, and at least one of R1, R2, R3, and R4 is selected from cyano, halogen, phenyl, or ester groups.

[0011] The substituent groups in the substituted C1-C10 alkyl groups are independently selected from at least one of cyano, halogen, phenyl, and ester groups. The first polymer is compatible with the core of the positive electrode active material, providing oxidation resistance. These first polymers can coordinate with transition metal ions at the positive electrode interface, stabilizing the positive electrode interface.

[0012] In some embodiments, the first polymer includes at least one selected from polyacrylonitrile, polystyrene, polyvinyl chloride, and polymethyl methacrylate. These polymers have oxidation resistance and are capable of coordinating with transition metal ions.

[0013] In some embodiments, the molecular weight of the first polymer is 50,000 to 150,000. Polymers with this molecular weight can stabilize the active interface and are less likely to deteriorate the interfacial impedance. If the molecular weight of the polymer is too large, it is not resistant to swelling and dissolution and is prone to deteriorating the interfacial impedance of the core. If the molecular weight of the polymer is too small, its effect on stabilizing the active interface is poor.

[0014] In some embodiments, the thickness of the first coating layer is greater than the thickness of the second coating layer. The relatively large thickness of the first coating layer helps to stabilize the active interface, while the relatively small thickness of the second coating layer results in a lower overall impedance.

[0015] In some embodiments, the thickness of the first coating layer is 0.1 μm-2 μm, optionally 0.5 μm-1.5 μm. This thickness of the first coating layer can reduce the obstruction of electrolyte entering the interior.

[0016] In some embodiments, the thickness of the second coating layer is 0.1 μm-1.5 μm, optionally 0.2 μm-0.6 μm. This thickness of the second coating layer reduces the obstruction to electrolyte penetration.

[0017] In some embodiments, the lithium transition metal oxide has the chemical formula Li. a M b O c M includes at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, where 0 < a ≤ 1.2, 0 < b ≤ 2, and 2 ≤ c ≤ 4.

[0018] In some embodiments, the average particle size of the kernel is 1-20 μm, optionally 3-10 μm.

[0019] Secondly, this application provides a method for preparing a positive electrode active material, comprising:

[0020] A first polymer and a core are mixed, and the first polymer coats the core to obtain a material coated with a first coating layer; the material coated with the first coating layer is mixed with a second polymer, and the second polymer coats the first coating layer to obtain a positive electrode active material.

[0021] The positive electrode active material includes a core, a first coating layer covering the core, and a second coating layer covering the first coating layer. The core includes a lithium transition metal oxide. The first coating layer includes a first polymer containing anionic groups, wherein the anionic groups include at least one selected from cyano, halogen, phenyl, and ester groups. The second coating layer includes a second polymer containing hydrophilic groups, wherein the hydrophilic groups include at least one selected from amide, hydroxyl, and carboxyl groups.

[0022] In some embodiments, the mass ratio of the core to the first polymer is 90-99.9:0.1-10, and / or the mass ratio of the core to the second polymer is 90-99.9:0.1-10.

[0023] Thirdly, this application provides a positive electrode sheet, including a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, wherein the positive active material layer comprises the positive active material of the foregoing embodiments or the positive active material prepared by the preparation method of the foregoing embodiments.

[0024] Fourthly, this application provides a battery, including a cell composed of the positive electrode sheet of the aforementioned embodiments.

[0025] Fifthly, this application provides an electrical device including the battery of the aforementioned embodiments.

[0026] 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

[0027] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0028] Figure 1 This is a schematic diagram of the vehicle structure according to some embodiments of this application;

[0029] Figure 2 Exploded structural diagrams of batteries according to some embodiments of this application;

[0030] Figure 3 This is a schematic diagram of the structure of a battery cell provided in some embodiments of this application;

[0031] Figure 4 This is an exploded structural diagram of a battery cell according to some embodiments of this application.

[0032] Icons: 1000 - Vehicle; 100 - Battery; 10 - Housing; 11 - Storage space; 12 - First part; 13 - Second part; 20 - Battery cell; 21 - Housing; 211 - Opening; 22 - End cap assembly; 221 - End cap; 222 - Electrode terminal; 23 - Electrode assembly; 24 - Current collector; 25 - Insulation protection component; 200 - Controller; 300 - Motor. Detailed Implementation

[0033] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] In the description of the embodiments of this application, the technical terms "thickness", "upper", "lower", "front", "rear", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0039] In the description of the embodiments of this application, unless otherwise expressly specified and limited, the technical terms "connection" and "fixed" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0040] Currently, judging from market trends, the application of power batteries is becoming increasingly widespread. Power batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but also extensively used in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. With the continuous expansion of power battery applications, market demand is also constantly increasing.

[0041] Taking lithium-ion batteries as an example, during the charging process, lithium ions are released from the positive electrode active material, transported through the electrolyte, pass through the separator, and are embedded in the negative electrode active material. The positive electrode active material, as a crucial component of lithium-ion batteries, significantly influences their performance. To improve the stability of the positive electrode active material, modifications such as elemental doping and surface coating are commonly employed. One widely used method is to coat the positive electrode active material with polymers.

[0042] Traditional methods for polymer-coating cathode active materials inevitably involve the use of organic solvents. Typically, the polymer is dissolved in an organic solvent, the cathode active material is added, and after thorough mixing, the organic solvent is removed to obtain the polymer-coated cathode active material. Alternatively, polymer monomers dissolved in an organic solvent are added to the cathode active material to initiate polymerization, forming a coating structure, followed by solvent removal, also yielding polymer-coated cathode active materials. However, during the preparation of wet-process electrode sheets, the polymer in the coating layer may still dissolve in the organic solvent, leading to coating layer loss and poor stability modification of the cathode active material.

[0043] Moreover, during battery cycling, the polymer-coated positive electrode active material swells in the electrolyte, and the polymer gradually dissolves. The coating structure has a limited lifespan, and the stability of the positive electrode active material deteriorates, resulting in a poorer battery cycle life.

[0044] Based on the above considerations, in order to solve the problem of poor stability of the polymer-coated positive electrode active material, a positive electrode active material was designed. By coating the positive electrode active material with at least two layers, the stability of the positive electrode active material is improved and the cycle life of the battery is increased.

[0045] The batteries and battery cells disclosed in this application can be used, but are not limited to, in electrical devices such as vehicles, ships, or aircraft.

[0046] This application provides an electrical device that uses a battery as a power source. The electrical device 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.

[0047] 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.

[0048] Please refer to Figure 1 , Figure 1 This is a schematic diagram of the structure of a vehicle 1000 provided in some embodiments of this application. A battery 100 is disposed inside the vehicle 1000, and the battery 100 may be located at the bottom, front, or rear of the vehicle 1000. The battery 100 can be used to power the vehicle 1000; for example, the battery 100 can serve as the operating power source for the vehicle 1000.

[0049] The vehicle 1000 may also include a controller 200 and a motor 300. The controller 200 is used to control the battery 100 to supply power to the motor 300, for example, for the power needs of the vehicle 1000 during startup, navigation and driving.

[0050] In some embodiments of this application, the 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.

[0051] Figure 2 This is an exploded structural diagram of the battery 100 provided in some embodiments of this application. Please refer to... Figure 2 The battery 100 includes a housing 10 and a battery cell 20, with the battery cell 20 housed within the housing 10.

[0052] The housing 10 provides a receiving space 11 for the battery cell 20. In some embodiments, the housing 10 may include a first portion 12 and a second portion 13, which overlap each other to define the receiving space 11 for accommodating the battery cell 20. Of course, the connection between the first portion 12 and the second portion 13 may be sealed by a sealant (not shown), such as a sealing ring, sealant, etc.

[0053] The first part 12 and the second part 13 can be of various shapes, such as cuboids, cylinders, etc. The first part 12 can be a hollow structure with an opening on one side to form a cavity for accommodating the battery cell 20, and the second part 13 can also be a hollow structure with an opening on one side to form a cavity for accommodating the battery cell 20. When the opening side of the second part 13 covers the opening side of the first part 12, a housing 10 with an accommodating space 11 is formed. Of course, as... Figure 2 As shown, the first part 12 can also be a hollow structure with an opening on one side, and the second part 13 can be a plate-like structure. The second part 13 covers the opening side of the first part 12, thus forming a box 10 with a accommodating space 11.

[0054] In battery 100, there can be one or more battery cells 20. If there are multiple battery cells 20, they 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. Multiple battery cells 20 can be directly connected in series, parallel, or in a mixed manner, and then the whole assembly of multiple battery cells 20 is housed in the housing 10. Alternatively, multiple battery cells 20 can first be connected in series, parallel, or in a mixed manner to form a battery module, and then multiple battery modules can be connected in series, parallel, or in a mixed manner to form a whole, which is then housed in the housing 10. Battery cells 20 can be cylindrical, flat, cuboid, or other shapes. Figure 2 An example is shown where the battery cell 20 is square.

[0055] In some embodiments, the battery 100 may also include a busbar (not shown), through which multiple battery cells 20 can be electrically connected to each other to achieve series, parallel, or mixed connection of multiple battery cells 20.

[0056] Figure 3 This is a schematic diagram of the structure of a battery cell 20 provided in some embodiments of this application. Figure 4 Exploded views of a battery cell 20 provided for some embodiments of this application. Please refer to... Figure 3 and Figure 4 The battery cell 20 may include a housing 21, an end cap assembly 22, and an electrode assembly 23. The housing 21 has an opening 211, the electrode assembly 23 is housed within the housing 21, and the end cap assembly 22 is used to seal the opening 211.

[0057] The shape of the outer casing 21 can be determined according to the specific shape of the electrode assembly 23. For example, if the electrode assembly 23 is a cuboid structure, the outer casing 21 can be a cuboid structure. Figure 3 and Figure 4 An example is shown where the housing 21 and electrode assembly 23 are square.

[0058] The outer shell 21 can also be made of various materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, etc. This application embodiment does not impose any special restrictions on this.

[0059] The end cap assembly 22 includes an end cap 221 and electrode terminals 222. The end cap assembly 22 is used to seal the opening 211 of the housing 21 to form a sealed mounting space (not shown) for accommodating the electrode assembly 23. The mounting space also accommodates an electrolyte, such as an electrolyte solution. As a component that outputs electrical energy to the electrode assembly 23, the end cap assembly 22 has electrode terminals 222 for electrical connection to the electrode assembly 23, specifically, the electrode terminals 222 are electrically connected to the tabs of the electrode assembly 23. For example, the electrode terminals 222 and the tabs are connected via a current collector 24 to achieve the electrical connection between the electrode terminals 222 and the tabs.

[0060] It should be noted that the opening 211 of the outer casing 21 can be one or two. If the outer casing 21 has one opening 211, the end cap assembly 22 can also be one, and two electrode terminals 222 can be provided in the end cap assembly 22. The two electrode terminals 222 are used for electrical connection with the positive and negative electrode tabs of the electrode assembly 23, respectively. If the outer casing 21 has two openings 211, for example, the two openings 211 are located on opposite sides of the outer casing 21, the end cap assembly 22 can also be two, and the two end cap assemblies 22 respectively cover the two openings 211 of the outer casing 21. In this case, the electrode terminal 222 in one end cap assembly 22 can be a positive electrode terminal, used for electrical connection with the positive electrode tab of the electrode assembly 23; and the electrode terminal 222 in the other end cap assembly 22 can be a negative electrode terminal, used for electrical connection with the negative electrode plate of the electrode assembly 23.

[0061] In some embodiments, such as Figure 4 As shown, the battery cell 20 may further include an insulating protective member 25 fixed to the outer periphery of the electrode assembly 23. The insulating protective member 25 is used to insulate and isolate the electrode assembly 23 from the housing 21. Exemplarily, the insulating protective member 25 is adhesive tape bonded to the outer periphery of the electrode assembly 23. In some embodiments, there are multiple electrode assemblies 23, and the insulating protective member 25 surrounds the outer periphery of multiple electrode assemblies 23, forming a single integral structure to maintain the structural stability of the electrode assembly 23.

[0062] According to some embodiments of this application, this application provides a positive electrode active material, including a core, a first coating layer covering the core, and a second coating layer covering the first coating layer. The core includes a lithium transition metal oxide, the first coating layer includes a first polymer containing anionic groups, the anionic groups including at least one of cyano, halogen, phenyl, and ester groups; the second coating layer includes a second polymer containing hydrophilic groups, the hydrophilic groups including at least one of amide, hydroxyl, and carboxyl groups.

[0063] The aforementioned first polymer contains anionic groups, which can coordinate and chelate with transition metal ions in lithium transition metal oxides through chemical bonds to stabilize the interfacial structure and inhibit the dissolution of metal ions. These first polymers can be oxidation-resistant polymers, for example, with an oxidation potential of not less than 4.3V.

[0064] The second polymer contains hydrophilic groups and can be a non-oil-soluble polymer. It can swell during the wetting process of the organic electrolyte but does not dissolve in the organic electrolyte, thereby maintaining the stability of the coating structure of the first polymer.

[0065] This application forms a coating structure by coating the surface of the active part (core) of the positive electrode active material with at least two coating layers. The first coating layer contacts and coats the surface of the core, and can be a full coating or a partial coating. The second coating layer coats the outside of the first coating layer, and can be a full coating or a partial coating.

[0066] In some embodiments of this application, in addition to the first coating layer and the second coating layer, other coating layers may be provided between the first coating layer and the second coating layer and / or outside the second coating layer. The materials of all coating layers (including the first polymer and the second polymer) can swell in the electrolyte, thereby not affecting the normal transport of the electrolyte.

[0067] In the coating structure of this application, the first polymer in the first coating layer contains anionic groups, which can bond with the transition metal ions at the core interface, stabilize the positive electrode interface, and thus improve the stability of the active part; the second polymer in the second coating layer contains hydrophilic groups, which can inhibit the dissolution of the internal first polymer after being immersed in the electrolyte, thereby effectively improving the stability of the coating layer at the interface of the positive electrode active material, and thus improving the battery cycle life.

[0068] According to some embodiments of this application, the second polymer includes at least one of polyacrylamide (containing an amide group), carboxymethyl cellulose (containing a hydroxyl group), sodium alginate (containing a hydroxyl group), and sodium polyacrylate (containing a sodium carboxylate group).

[0069] According to some embodiments of this application, the first polymer includes the structural unit shown in Formula I.

[0070]

[0071] R1, R2, R3, and R4 are each independently selected from H, substituted or unsubstituted C1-C10 alkyl, cyano, halogen, phenyl, and ester groups, and at least one of R1, R2, R3, and R4 is selected from cyano, halogen, phenyl, or ester groups.

[0072] The substituent groups in the substituted C1-C10 alkyl groups are each independently selected from at least one of cyano, halogen, phenyl, and ester groups.

[0073] According to some embodiments of this application, the first polymer includes at least one selected from polyacrylonitrile (containing cyano groups), polystyrene (containing phenyl groups), polyvinyl chloride (containing halogens), and polymethyl methacrylate (containing ester groups).

[0074] According to some embodiments of this application, the molecular weight of the first polymer is 50,000 to 150,000. As an example, the molecular weight of the first polymer can be 50,000, 70,000, 100,000, 120,000 or 150,000, or any value within the above two numerical ranges.

[0075] According to some embodiments of this application, the thickness of the first covering layer is greater than the thickness of the second covering layer.

[0076] According to some embodiments of this application, the thickness of the first coating layer is 0.1 μm-2 μm, and can be selected as 0.5 μm-1.5 μm. As an example, the thickness of the first coating layer is 0.1 μm, 0.5 μm, 1 μm, 1.5 μm or 2 μm, or any value within the above two numerical ranges.

[0077] According to some embodiments of this application, the thickness of the second coating layer is 0.1 μm-1.5 μm, and can be selected as 0.2 μm-0.6 μm. As an example, the thickness of the second coating layer is 0.1 μm, 0.2 μm, 0.6 μm, 1 μm, 1.2 μm or 1.5 μm, or any value within the above two numerical ranges.

[0078] According to some embodiments of this application, the first polymer is polyacrylonitrile, and the second polymer is sodium alginate. In other embodiments, the first polymer includes polyacrylonitrile, and the second polymer includes polyacrylamide; or, the first polymer includes polystyrene, and the second polymer includes sodium polyacrylate; or, the first polymer includes polymethyl methacrylate, and the second polymer includes sodium alginate, or other combinations of materials.

[0079] According to some embodiments of this application, the chemical formula of the lithium transition metal oxide is Li. a M b O c M includes at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, where 0 < a ≤ 1.2, 0 < b ≤ 2, and 2 ≤ c ≤ 4. In some embodiments, the lithium transition metal oxide is a layered active material with the chemical formula Li. a MO2, in some embodiments, is a lithium transition metal oxide with a spinel structure and the chemical formula Li. a M2O4. Optionally, the lithium transition metal oxide includes 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 (e.g., lithium nickel cobalt manganese oxide NCM), lithium nickel cobalt aluminum oxide (e.g., lithium nickel cobalt aluminum oxide NCA), and modified compounds.

[0080] The core can be the particle size of conventional positive electrode active materials, with an average particle size of 1-20 μm, optionally 3-10 μm. For example, the core can be secondary particles with an average particle size of about 5 μm to 20 μm and / or single crystal particles with an average particle size of 1 μm to 5 μm.

[0081] According to some embodiments of this application, this application provides a method for preparing a positive electrode active material, including:

[0082] A first polymer and a core are mixed to coat the core with the first polymer, resulting in a material coated with a first coating layer. The material coated with the first coating layer is then mixed with a second polymer to coat the first coating layer, resulting in a positive electrode active material. The positive electrode active material includes a core, a first coating layer coating the core, and a second coating layer coating the first coating layer. The core comprises a lithium transition metal oxide. The first coating layer comprises a first polymer containing anionic groups, which include at least one of cyano, halogen, phenyl, and ester groups. The second coating layer comprises a second polymer containing hydrophilic groups, which include at least one of amide, hydroxyl, and carboxyl groups.

[0083] In some embodiments, the preparation method includes the following steps:

[0084] The first polymer and the core are mechanically mixed to obtain the material coated by the first coating layer;

[0085] Alternatively, the first polymer can be dissolved in an organic solvent, the core can be added and stirred to disperse it, and then the organic solvent can be removed to obtain the material coated by the first coating layer.

[0086] During the preparation of this positive electrode active material, the material of the first coating layer is used to coat the second polymer by a non-solvent method, which reduces the loss of the first polymer in the coating structure. Moreover, during the wet preparation of the electrode sheet, this positive electrode active material can also reduce the loss of the first polymer in the coating structure under the protection of the second coating layer.

[0087] According to some embodiments of this application, the mass ratio of the core to the first polymer is 90-99.9:0.1-10. As an example, the mass ratio of the core to the first polymer can be 90:10, 92:8, 94:6, 96:4, 98:2, 99.5:0.5, or 99.9:0.1, or any ratio within the above two ranges.

[0088] And / or, the mass ratio of the core and the second polymer is 90-99.9:0.1-10. As an example, the mass ratio of the core and the second polymer can be 90:10, 92:8, 94:6, 96:4, 98:2, 99.5:0.5, or 99.9:0.1, or any ratio within the above two ranges.

[0089] According to some embodiments of this application, this application provides a positive electrode sheet, including a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, the positive active material layer comprising the positive active material provided above.

[0090] According to some embodiments of this application, the thickness of the positive electrode active material layer is 25μm-60μm, and can be selected as 30μm-50μm.

[0091] In some implementations, other layers, such as an adhesive layer, may be provided between the positive current collector and the positive active material layer.

[0092] In some embodiments, positive electrode active material layers are respectively provided on both sides of the positive electrode current collector; optionally, the positive electrode active material layers on both sides of the positive electrode current collector are symmetrical about the positive electrode current collector, that is, they contain the same positive electrode active material provided above.

[0093] In some embodiments, the positive electrode active material layer further includes a conductive agent and a binder. The conductive agent is used to improve the conductivity of the positive electrode active material layer, and the binder is used to firmly bond the positive electrode active material and the binder to the positive electrode current collector. This application does not specifically limit the types of conductive agents and binders, and they can be selected according to actual needs. As an example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, Super P (SP), graphene, and carbon nanofibers. As an example, the binder may be one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0094] In some embodiments, the mass ratio of the positive electrode active material to the conductive agent and binder is (96-99):(0.5-2):(0.5-2). Therefore, by using the positive electrode active material, conductive agent, and binder formulated according to the present application to form the positive electrode slurry, it is beneficial to the conductivity of the positive electrode active material layer and the bonding strength with the positive electrode current collector.

[0095] To meet actual production needs, the coating area of ​​the single-layer positive electrode active material layer is 1540.25 mm². 2 The minimum coating weight is 50mg, and it is generally 50-200mg.

[0096] In some embodiments, the positive electrode current collector can be a conventional metal foil or a composite positive electrode current collector (a composite positive electrode current collector can be formed by depositing metal material on a polymer substrate). As an example, the metal foil may include one or more of aluminum foil, nickel foil, stainless steel foil, stainless steel mesh, and carbon-coated aluminum foil. The composite positive electrode current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate; the composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0097] In some embodiments, the method for preparing the positive electrode sheet may include forming a positive active material layer on at least one side of the positive current collector. As an example, the positive active material is mixed with a conductive agent, a binder and a solvent (e.g., N-methylpyrrolidone NMP) to form a positive electrode slurry, and then the positive electrode slurry is coated onto the positive current collector, followed by processes such as roller coating and drying to remove the solvent, to obtain the positive electrode sheet.

[0098] According to some embodiments of this application, this application also provides a battery, including a negative electrode, a separator, and a cell composed of the aforementioned positive electrode, as well as an electrolyte. The battery includes any one of the following forms: a single cell, a battery module, or a battery pack.

[0099] In some embodiments, the battery can be a lithium-ion battery or a lithium metal battery. That is, the positive electrode active material and positive electrode sheet of the embodiments of this application can be used in lithium-ion batteries or lithium metal batteries, and this application does not make any particular limitation. The following description uses a lithium-ion battery as an example to illustrate the battery structure. For lithium metal batteries, the battery structure can be adjusted accordingly.

[0100] [Negative electrode plate]

[0101] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, wherein the negative active material layer includes a negative active material.

[0102] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0103] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0104] In some embodiments, this application does not specifically limit the type of negative electrode active material, and it can be selected according to actual needs. As an example, the negative electrode active material may include one or more of the following materials: This application does not specifically limit the type of negative electrode material, and it can be selected according to actual needs. As an example, the negative electrode active material may be selected from one or more of graphite, lithium metal, a negative electrode-free current collector, silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials may be selected from one or more of elemental silicon, silicon oxide compounds, silicon-carbon composite materials, silicon-nitrogen composite materials, and silicon alloys. Tin-based materials may be selected from one or more of elemental tin, tin oxide compounds, and tin alloys.

[0105] In some embodiments, the negative electrode active material layer may optionally include a binder. The binder may be selected from 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).

[0106] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0107] In some embodiments, the negative electrode active material layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0108] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0109] [Isolation membrane]

[0110] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0111] In some embodiments, the material of the separator can be selected from one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0112] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0113] In some embodiments, the battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0114] In some implementations, the battery's outer packaging can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The battery's outer packaging can also be a soft pack, such as a pouch. The soft pack can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0115] [Electrolytes]

[0116] A single battery cell also includes an electrolyte, which acts as a conductor of ions between the positive and negative electrodes. The electrolyte can be liquid or gel-like.

[0117] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and an organic solvent.

[0118] In some embodiments, the electrolyte salt may be selected from one or more 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.

[0119] In some embodiments, the organic solvent may be selected from one or more 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.

[0120] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0121] According to some embodiments of this application, this application provides an electrical device including the battery provided above.

[0122] The following examples will describe one or more embodiments in more detail. Of course, these examples do not limit the scope of the one or more embodiments.

[0123] Example 1

[0124] (1) Preparation of positive electrode active material

[0125] The first polymer (polyacrylonitrile, molecular weight 100,000) was dissolved in an organic solvent (methylpyrrolidone NMP), and positive electrode active material particles (lithium nickel cobalt manganese oxide LiNi) were added as the core. 0.8 Mn 0.1 Co 0.1 O2 (NMC811, with an average particle size of approximately 10 μm) was stirred and dispersed. The mass ratio of the core to the first polymer was 97 wt%:3 wt%. After removing the organic solvent, the material coated with the first coating layer was obtained. The thickness of the first coating layer was measured using transmission electron microscopy, and it was approximately 0.7 μm. Subsequently, the material coated with the first coating layer and the second polymer (sodium alginate) were mixed and coated in a mechanical fusion machine to form the second coating layer. The core (lithium nickel cobalt manganese oxide LiNi) 0.8 Mn 0.1 Co 0.1 The mass ratio of O2 (NMC811) and the second polymer was 95wt%:5wt%. The thickness of the second coating layer was measured by transmission electron microscopy, and the thickness of the second coating layer was approximately 0.5μm, thus obtaining the positive electrode active material.

[0126] (2) Preparation of positive electrode sheet

[0127] The positive electrode active material, conductive agent Super P, and binder PVDF were mixed at a mass ratio of 97:2:1, and an organic solvent (NMP) was added to disperse and stir evenly to obtain a positive electrode slurry (solid content approximately 60%). The positive electrode slurry was coated on both sides of the positive electrode current collector (aluminum foil, 14 μm thick), and dried in a vacuum oven to remove the organic solvent, yielding a positive electrode sheet with an areal capacity of 3.5 mAh / cm². 2 .

[0128] (3) Preparation of electrolyte

[0129] Lithium bis(fluorosulfonyl)imide (LiFSI) was dissolved in an organic solvent (a mixture of ethylene glycol dimethyl ether (DME) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in a volume ratio of 50%:50%) and stirred until homogeneous to obtain an electrolyte with a concentration of 4 mol / L.

[0130] (4) Preparation of negative electrode sheet

[0131] A 50μm thick lithium foil is selected and rolled and composited with an 8μm thick copper foil to serve as a backup negative electrode. This negative electrode is used to form a lithium metal battery. The battery performance is evaluated using a lithium metal battery, which can reduce the influence of the negative electrode active material.

[0132] (5) Separating membrane

[0133] Polyethylene porous membrane was selected as the separator.

[0134] (6) Assembly of secondary batteries

[0135] The positive and negative electrode sheets are stacked together, separated by a separator, and wrapped in an aluminum-plastic film bag to form a lithium-ion stacked dry cell. The prepared electrolyte is injected, vacuum sealed, and left to stand at room temperature for 6 hours to obtain a secondary battery.

[0136] Examples 2-10

[0137] Except for a slight difference in the positive electrode active material formed in step (1), the rest is basically the same as in Example 1. See Table 1 for details.

[0138] Comparative Example 1

[0139] Except for step (1), in which the positive electrode active material particles were not coated, and NMC811 without any coating was used as the positive electrode active material, the rest is basically the same as in Example 1. See Table 1 for details.

[0140] Comparative Example 2

[0141] Except for step (1), in which only the positive electrode active material particles are coated with the first coating layer and not the second coating layer, and NMC811 coated with the first polymer is used as the positive electrode active material, the rest is basically the same as in Example 1. See Table 1 for details.

[0142] Comparative Example 3

[0143] Except for step (1), in which only the positive electrode active material particles are coated with the first coating layer and the coating material is sodium alginate, the rest is basically the same as in Example 1. See Table 1 for details.

[0144] Electrochemical Cyclic Performance Testing

[0145] The prepared secondary battery was subjected to electrochemical cycle performance testing at 25°C under constant current and constant voltage charging conditions of 0.2C and constant current discharging conditions of 1C. The charging cutoff voltage was set to 4.3V, and the discharging cutoff voltage was set to 2.8V. The constant current-constant voltage charging process involved charging at a constant current of 0.2C to the cutoff voltage of 4.3V, followed by charging at a constant voltage of 4.3V until the current decreased to 0.05C. The constant current discharging process involved discharging at a constant current of 1C to 2.8V. The discharge capacity at this point was recorded as C0. This charge-discharge cycle was repeated to reduce the impact of internal polarization on the charge-discharge capacity. The battery life was considered to have ended when the discharge capacity decay rate reached 80%.

[0146] The discharge capacity decay rate is calculated as follows: discharge capacity Cn of the nth cycle / discharge capacity C1 of the first cycle × 100%.

[0147] The battery performance obtained from the tests is shown in Table 1:

[0148] Table 1 Battery Performance

[0149]

[0150]

[0151] Example 11

[0152] Except for step (1), which uses spinel-structured LiMn2O4 material (average particle size of about 10 μm) as the core, the rest is basically the same as in Example 1. See Table 2 for details.

[0153] Comparative Example 4

[0154] Except for step (1), in which the positive electrode active material particles serving as the core are not coated, and LiMn2O4 without any coating is used as the positive electrode active material, the rest is basically the same as in Example 1. See Table 2 for details.

[0155] Electrochemical cycle performance was tested using the same method described above, and the battery performance results are shown in Table 2.

[0156] Table 2 Battery Performance

[0157]

[0158] Based on the results in Table 1, we can see that:

[0159] Compared with Comparative Examples 1 to 3, the positive electrode active material of the positive electrode sheet of Examples 1 to 10 is simultaneously coated with a first coating layer and a second coating layer. The inner first coating layer includes a first polymer containing anionic groups, and the outer second coating layer includes a second polymer containing hydrophilic groups, which can improve the cycle life of the battery.

[0160] Compared with the positive electrode active materials of Comparative Examples 2-3, which are only coated with the first polymer or the second polymer, the positive electrode active material of Example 1 is coated with the first polymer and the second polymer in sequence, which can improve the cycle life of the battery.

[0161] According to Examples 1 and 8-9, the molecular weight of the first polymer coated with the positive electrode active material is 50,000-150,000, which can improve the cycle life of the battery.

[0162] According to Examples 1 and 10, the thickness of the first coating layer of the positive electrode active material is greater than the thickness of the second coating layer, which can significantly improve the cycle life of the battery.

[0163] Based on the results in Table 2, we can see that:

[0164] Compared with Comparative Example 4, the positive electrode active material of Example 11 is simultaneously coated with a first coating layer and a second coating layer, which can improve the cycle life of the battery.

[0165] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. A positive electrode active material, characterized in that, The device includes a core, a first coating layer covering the core, and a second coating layer covering the first coating layer. The core comprises a lithium transition metal oxide. The first coating layer comprises a first polymer containing anionic groups, wherein the anionic groups include at least one selected from cyano, halogen, phenyl, and ester groups. The second coating layer comprises a second polymer containing hydrophilic groups, wherein the hydrophilic groups include at least one selected from amide, hydroxyl, and carboxyl groups. The thickness of the first coating layer is greater than the thickness of the second coating layer. The thickness of the first coating layer is 0.1μm-2μm, and the thickness of the second coating layer is 0.1μm-1.5μm.

2. The positive electrode active material according to claim 1, characterized in that, The second polymer includes at least one of polyacrylamide, carboxymethyl cellulose, sodium alginate, and sodium polyacrylate.

3. The positive electrode active material according to claim 1 or 2, characterized in that, The first polymer comprises the structural unit shown in Formula I. Equation 1; Wherein, R1, R2, R3, and R4 are each independently selected from H, substituted or unsubstituted C1-C10 alkyl, cyano, halogen, phenyl, and ester groups, and at least one of R1, R2, R3, and R4 is selected from cyano, halogen, phenyl, or ester groups. The substituent groups in the substituted C1-C10 alkyl groups are each independently selected from at least one of cyano, halogen, phenyl, and ester groups.

4. The positive electrode active material according to any one of claims 1-3, characterized in that, The first polymer includes at least one of polyacrylonitrile, polystyrene, polyvinyl chloride, and polymethyl methacrylate.

5. The positive electrode active material according to any one of claims 1-4, characterized in that, The molecular weight of the first polymer is 50,000 to 150,000.

6. The positive electrode active material according to any one of claims 1-5, characterized in that, The thickness of the first coating layer is 0.5μm-1.5μm.

7. The positive electrode active material according to any one of claims 1-6, characterized in that, The thickness of the second coating layer is 0.2μm-0.6μm.

8. The positive electrode active material according to any one of claims 1-7, characterized in that, The chemical formula of the lithium transition metal oxide is Li a M b O c M includes at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, where 0 < a ≤ 1.2, 0 < b ≤ 2, and 2 ≤ c ≤ 4.

9. The positive electrode active material according to any one of claims 1-8, characterized in that, The average particle size of the kernel is 1-20 μm.

10. The positive electrode active material according to any one of claims 1-9, characterized in that, The average particle size of the kernel is 3-10 μm.

11. A method for preparing a positive electrode active material, characterized in that, include: The first polymer and the core are mixed, and the first polymer is coated on the core to obtain a material coated with the first coating layer; The material coated by the first coating layer and the second polymer are mixed so that the second polymer coats the first coating layer to obtain a positive electrode active material; The positive electrode active material includes a core, a first coating layer covering the core, and a second coating layer covering the first coating layer. The core comprises a lithium transition metal oxide. The first coating layer comprises a first polymer containing anionic groups, wherein the anionic groups include at least one selected from cyano, halogen, phenyl, and ester groups. The second coating layer comprises a second polymer containing hydrophilic groups, wherein the hydrophilic groups include at least one selected from amide, hydroxyl, and carboxyl groups. The thickness of the first coating layer is greater than the thickness of the second coating layer, with the first coating layer having a thickness of 0.1 μm-2 μm and the second coating layer having a thickness of 0.1 μm-1.5 μm.

12. The method for preparing the positive electrode active material according to claim 11, characterized in that, The mass ratio of the core to the first polymer is 90-99.9:0.1-10, and / or the mass ratio of the core to the second polymer is 90-99.9:0.1-10.

13. A positive electrode plate, characterized in that, The device includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, wherein the positive active material layer comprises the positive active material as described in any one of claims 1-10 or the positive active material prepared by the preparation method as described in claim 11 or 12.

14. A battery, characterized in that, Includes the positive electrode sheet as described in claim 13.

15. An electrical appliance, characterized in that, Includes the battery as described in claim 14.

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