Positive active material, positive pole piece, battery and electric device

Abstract

The embodiment of the invention provides a positive active material, a positive pole piece, a battery and an electric device, and relates to the field of batteries. The positive electrode active material comprises an inner core, a first coating layer coating the inner core and a second coating layer coating the first coating layer, the inner core comprises a lithium transition metal oxide, the first coating layer comprises a first polymer containing an anionic group, and the anionic group comprises at least one of a cyano group, a halogen, a phenyl group and an ester group; the second coating layer comprises a second polymer containing a hydrophilic group, and the hydrophilic group comprises at least one of an amide group, a hydroxyl group and a carboxylate group. The positive pole piece comprises a positive current collector and a positive active material layer arranged on at least one surface of the positive current collector, and the positive active material layer comprises the positive active material. According to the positive electrode active material, the positive electrode plate, the battery and the electric device, the cycle life of the battery can be prolonged.

Description

Technical Field

[0001] The present application relates to the field of batteries, and in particular to a positive electrode active material, a positive electrode sheet, a battery and an electrical device. Background Art

[0002] With the continuous development and progress of society, the demand for energy consumption is increasing day by day. The successful commercialization of lithium-ion batteries has greatly changed the way people consume energy. However, with the increasing popularity of large-scale energy storage grids and electric vehicles, people's requirements for lithium-ion batteries are getting higher and higher.

[0003] As an important component of lithium-ion batteries, positive electrode active materials have a great impact on the performance of lithium-ion batteries. In order to improve the stability of positive electrode active materials, positive electrode active materials are usually modified by element doping, surface coating, etc. Among them, using polymers to coat positive electrode active materials is one of the common methods, but the cycle life of the resulting battery still needs to be improved. Summary of the invention

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

[0005] In a first aspect, the present application provides a positive electrode active material, comprising a core, a first coating layer coating the core, and a second coating layer coating the first coating layer, wherein the core comprises a lithium transition metal oxide, the first coating layer comprises a first polymer containing an anionic group, the anionic group comprises at least one of a cyano group, a halogen group, a phenyl group, and an ester group; the second coating layer comprises a second polymer containing a hydrophilic group, the hydrophilic group comprises at least one of an amide group, a hydroxyl group, and a carboxylate group.

[0006] In the technical solution of the embodiment of the present application, lithium transition metal oxide serves as the active part (core) of the positive electrode active material, and a first coating layer and a second coating layer are sequentially arranged on its surface. The first coating layer located in the inner layer contains anionic groups, which can bond with the transition metal ions at the interface of the core (can be coordinated and chelated by chemical bonds) to stabilize the active interface of the positive electrode active material, fix the transition metal ions on the surface of the core, and inhibit their dissolution and precipitation, 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 internal first polymer after infiltration of the electrolyte, thereby effectively improving the stability of the coating layer at the interface of the positive electrode active material to improve the battery cycle life.

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

[0008] In some embodiments, the first polymer comprises a structural unit of Formula I,

[0009]

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

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

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

[0013] In some embodiments, the molecular weight of the first polymer is 50,000-150,000. Polymers with such molecular weight can stabilize the active interface and are not likely to deteriorate the interface impedance; if the molecular weight of the polymer is too large, it is not resistant to swelling and dissolution, and is likely to deteriorate the interface impedance of the core; if the molecular weight of the polymer is too small, the effect of stabilizing the active interface is poor.

[0014] In some embodiments, the thickness of the first coating layer is greater than that of the second coating layer. The first coating layer is relatively thick and plays a role in stabilizing the active interface, while the second coating layer is relatively thin and has a relatively small overall impedance.

[0015] In some embodiments, the thickness of the first coating layer is 0.1 μm-2 μm, and can be 0.5 μm-1.5 μm. The first coating layer with such a thickness can reduce the obstacle of the electrolyte entering the interior.

[0016] In some embodiments, the thickness of the second coating layer is 0.1 μm-1.5 μm, and can be 0.2 μm-0.6 μm. The second coating layer with such a thickness reduces the obstacle of the electrolyte entering the interior.

[0017] In some embodiments, 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, 0<a≤1.2, 0<b≤2, 2≤c≤4.

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

[0019] In a second aspect, the present application provides a method for preparing a positive electrode active material, comprising:

[0020] Mixing a first polymer and a core, so that the first polymer is coated on the core, to obtain a material coated with a first coating layer; mixing the material coated with the first coating layer with a second polymer, so that the second polymer is coated on the first coating layer, to obtain a positive electrode active material;

[0021] 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, wherein the core includes a lithium transition metal oxide, the first coating layer includes a first polymer containing an anionic group, and the anionic group includes at least one of a cyano group, a halogen group, a phenyl group, and an ester group; the second coating layer includes a second polymer containing a hydrophilic group, and the hydrophilic group includes at least one of an amide group, a hydroxyl group, and a carboxylate group.

[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] In a third aspect, the present application provides a positive electrode plate, comprising a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer comprises the positive electrode active material of the aforementioned embodiment or the positive electrode active material prepared by the preparation method of the aforementioned embodiment.

[0024] In a fourth aspect, the present application provides a battery, comprising a battery cell composed of the positive electrode sheets of the aforementioned embodiments.

[0025] In a fifth aspect, the present application provides an electrical device comprising the battery of the aforementioned embodiment.

[0026] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present application. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0028] Figure 1 A schematic diagram of the structure of a vehicle according to some embodiments of the present application;

[0029] Figure 2 A schematic diagram of the exploded structure of a battery according to some embodiments of the present application;

[0030] Figure 3 A schematic diagram of the structure of a battery cell provided in some embodiments of the present application;

[0031] Figure 4 This is a schematic diagram of the exploded structure of a battery cell according to some embodiments of the present application.

[0032] Icons: 1000-vehicle; 100-battery; 10-casing; 11-accommodating space; 12-first part; 13-second part; 20-battery cell; 21-casing; 211-opening; 22-end cover assembly; 221-end cover; 222-electrode terminal; 23-electrode assembly; 24-current collecting member; 25-insulating protection member; 200-controller; 300-motor. DETAILED DESCRIPTION

[0033] The following embodiments of the technical solution of the present application are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0035] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0036] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0037] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0038] In the description of the embodiments of the present application, the orientations or positional relationships indicated by technical terms such as "thickness", "up", "down", "front", "back", "top", "bottom", "inside", and "outside" are based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on the embodiments of the present application.

[0039] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "connection" and "fixed" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0040] At present, from the perspective of market development, the application of power batteries is becoming more and more extensive. Power batteries are not only used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, but also widely used in electric vehicles such as electric bicycles, electric motorcycles, electric cars, as well as military equipment and aerospace and other fields. With the continuous expansion of the application field of power batteries, the market demand is also constantly expanding.

[0041] Taking lithium-ion batteries as an example, during the charging process of lithium-ion batteries, lithium ions are released from the positive electrode active material, transmitted through the electrolyte, passed through the isolation membrane, and embedded in the negative electrode active material. As an important component of lithium-ion batteries, positive electrode active materials have a great impact on the performance of lithium-ion batteries. In order to improve the stability of positive electrode active materials, element doping, surface coating and other methods are usually used to modify the positive electrode active materials. One of the most widely used methods is to coat the positive electrode active materials with polymers.

[0042] The traditional method of coating positive electrode active materials with polymers cannot avoid the use of organic solvents. Usually, the polymer is dissolved in an organic solvent, and then the positive electrode active material is added. After mixing evenly, the organic solvent is removed to obtain a polymer-coated positive electrode active material; or a polymer monomer dissolved in an organic solvent is added to the positive electrode active material to initiate polymerization to form a coating structure, and then the organic solvent is removed to obtain a polymer-coated positive electrode active material. However, in the process of preparing wet-process electrodes for such polymer-coated positive electrode active materials, the polymer in the coating layer may still dissolve in the organic solvent, resulting in loss of the coating layer and poor stability modification effect on the positive electrode active material.

[0043] Moreover, during the cycle of the battery, the polymer-coated positive electrode active material will be swollen by the electrolyte, and then the polymer will gradually dissolve. The duration of the coating structure is limited, and the stability of the positive electrode active material deteriorates, which is reflected in the poor cycle life of the battery.

[0044] Based on the above considerations, in order to solve the problem of poor stability of the above-mentioned polymer-coated positive electrode active material, a positive electrode active material is 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 the embodiments of the present application can be used in, but are not limited to, electrical devices such as vehicles, ships, or aircraft.

[0046] The embodiment of the present application provides an electric device using a battery as a power source, and the electric device may be, but is not limited to, a mobile phone, a tablet, a laptop, an electric toy, an electric tool, a battery car, an electric car, a ship, a spacecraft, etc. Among them, the electric toy may include a fixed or mobile electric toy, such as a game console, an electric car toy, an electric ship toy, and an electric airplane toy, etc., and the spacecraft may include an airplane, a rocket, a space shuttle, and a spacecraft, etc.

[0047] For the convenience of description, the following embodiments are described by taking a vehicle 1000 as an example of an electrical device according to an embodiment of the present application.

[0048] Please refer to Figure 1 , Figure 1 The schematic diagram of the structure of the vehicle 1000 provided in some embodiments of the present application. The vehicle 1000 is provided with a battery 100 inside, and the battery 100 can be provided at the bottom, head or tail of the vehicle 1000. The battery 100 can be used to power the vehicle 1000, for example, the battery 100 can be used as an operating power source of the vehicle 1000.

[0049] The vehicle 1000 may further include a controller 200 and a motor 300 , wherein the controller 200 is used to control the battery 100 to supply power to the motor 300 , for example, to meet the power requirements of starting, navigating, and driving the vehicle 1000 .

[0050] In some embodiments of the present application, the battery 100 can not only serve as an operating power source for the vehicle 1000, but also serve as a 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 a schematic diagram of the exploded structure of the battery 100 provided in some embodiments of the present application. Figure 2 The battery 100 includes a housing 10 and a battery cell 20 , and the battery cell 20 is accommodated in the housing 10 .

[0052] The box body 10 is used to provide a storage space 11 for the battery cell 20. In some embodiments, the box body 10 may include a first portion 12 and a second portion 13, and the first portion 12 and the second portion 13 cover each other to define the storage space 11 for accommodating the battery cell 20. Of course, the connection between the first portion 12 and the second portion 13 can be sealed by a sealing member (not shown in the figure), and the sealing member can be a sealing ring, a sealant, etc.

[0053] The first part 12 and the second part 13 can be in various shapes, such as a cuboid, a cylinder, etc. The first part 12 can be a hollow structure with one side open to form a receiving cavity for receiving the battery cell 20, and the second part 13 can also be a hollow structure with one side open to form a receiving cavity for receiving the battery cell 20. The opening side of the second part 13 covers the opening side of the first part 12, thereby forming a box body 10 with a receiving space 11. Of course, if Figure 2 As shown, the first part 12 may be a hollow structure with one side open, and the second part 13 may be a plate-like structure. The second part 13 covers the open side of the first part 12 to form a box body 10 with an accommodating space 11.

[0054] In the battery 100, there can be one or more battery cells 20. If there are more than one battery cell 20, the battery cells 20 can be connected in series, in parallel or in a mixed connection. A mixed connection means that the battery cells 20 are connected in series and in parallel. The battery cells 20 can be directly connected in series, in parallel or in a mixed connection, and then the whole formed by the battery cells 20 can be accommodated in the box 10; of course, the battery cells 20 can be connected in series, in parallel or in a mixed connection to form a battery module, and then the battery modules can be connected in series, in parallel or in a mixed connection to form a whole, and then accommodated in the box 10. The battery cell 20 can be cylindrical, flat, rectangular or in other shapes. Figure 2 The example shows that the battery cell 20 is in a square shape.

[0055] In some embodiments, the battery 100 may further include a busbar component (not shown), and the multiple battery cells 20 may be electrically connected via the busbar component to achieve series connection, parallel connection, or mixed connection of the 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 the present application. Figure 4 This is an exploded view of a battery cell 20 provided in some embodiments of the present application. 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 accommodated in the housing 21 , and the end cap assembly 22 is used to cover the opening 211 .

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

[0058] The shell 21 may be made of a variety of materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, etc., and the embodiment of the present application does not impose any special restrictions on this.

[0059] The end cap assembly 22 includes an end cap 221 and an electrode terminal 222. The end cap assembly 22 is used to seal the opening 211 of the housing 21 to form a closed installation space (not shown), and the installation space is used to accommodate the electrode assembly 23. The installation space is also used to accommodate an electrolyte, such as an electrolyte. The end cap assembly 22 is a component for outputting the electrical energy of the electrode assembly 23. The electrode terminal 222 in the end cap assembly 22 is used to be electrically connected to the electrode assembly 23, that is, the electrode terminal 222 is electrically connected to the tab of the electrode assembly 23. For example, the electrode terminal 222 is connected to the tab through the current collecting member 24 to achieve electrical connection between the electrode terminal 222 and the tab.

[0060] It should be noted that the opening 211 of the shell 21 can be one or two. If the opening 211 of the shell 21 is one, the end cap assembly 22 can also be one, and two electrode terminals 222 can be provided in the end cap assembly 22, and the two electrode terminals 222 are respectively used to electrically connect to the positive pole ear and the negative pole ear of the electrode assembly 23. If the opening 211 of the shell 21 is two, for example, the two openings 211 are provided on opposite sides of the shell 21, and the end cap assembly 22 can also be two, and the two end cap assemblies 22 are respectively covered at the two openings 211 of the shell 21. In this case, the electrode terminal 222 in one end cap assembly 22 can be a positive electrode terminal, which is used to electrically connect to the positive pole ear of the electrode assembly 23; the electrode terminal 222 in the other end cap assembly 22 can be a negative electrode terminal, which is used to electrically connect to the negative electrode sheet of the electrode assembly 23.

[0061] In some embodiments, Figure 4 As shown, the battery cell 20 may further include an insulating protective member 25 fixed to the periphery of the electrode assembly 23, and 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 a tape bonded to the periphery of the electrode assembly 23. In some embodiments, there are multiple electrode assemblies 23, and the insulating protective member 25 is arranged around the periphery of the multiple electrode assemblies 23, and the multiple electrode assemblies 23 are formed into an integral structure to keep the electrode assembly 23 structurally stable.

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

[0063] The 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 interface 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 a hydrophilic group and may be a non-oil-soluble polymer, which can swell during the infiltration process of the organic electrolyte but does not dissolve in the organic electrolyte, thereby playing a role in maintaining the stability of the first polymer coating structure.

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

[0066] In some embodiments of the present application, in addition to the first coating layer and the second coating layer, other coating layers may be arranged between the first coating layer and the second coating layer and / or outside the second coating layer, and the materials of all coating layers (including the first polymer and the second polymer) can swell in the electrolyte so as not to affect the normal transmission of the electrolyte.

[0067] In the coating structure of the present application, the first polymer in the first coating layer contains anionic groups, which can bond with the transition metal ions at the inner core interface to stabilize the positive electrode interface, thereby improving 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 infiltration of the electrolyte, thereby effectively improving the stability of the coating layer at the interface of the positive electrode active material, thereby improving the battery cycle life.

[0068] According to some embodiments of the present 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 the present application, the first polymer includes a structural unit shown in Formula I,

[0070]

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

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

[0073] According to some embodiments of the present application, the first polymer includes at least one of polyacrylonitrile (containing a cyano group), polystyrene (containing a phenyl group), polyvinyl chloride (containing a halogen), and polymethyl methacrylate (containing an ester group).

[0074] According to some embodiments of the present application, the molecular weight of the first polymer is 50,000-150,000. 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 the present application, the thickness of the first coating layer is greater than the thickness of the second coating layer.

[0076] According to some embodiments of the present application, the thickness of the first coating layer is 0.1 μm-2 μm, and can be 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 the present application, the thickness of the second coating layer is 0.1 μm-1.5 μm, and can be 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 the present 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 material combinations.

[0079] According to some embodiments of the present 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, 0<a≤1.2, 0<b≤2, 2≤c≤4, in some embodiments, the lithium transition metal oxide is a layered structure active material, and the chemical formula is Li a MO2, in some embodiments, the lithium transition metal oxide is a spinel structure active material with a chemical formula of 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 inner core can be the particle size of conventional positive electrode active materials, and the average particle size of the inner core is 1-20 μm, optionally 3-10 μm. Exemplarily, the inner core is 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 the present application, the present application provides a method for preparing a positive electrode active material, comprising:

[0082] The first polymer and the inner core are mixed so that the first polymer is coated on the inner 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 so that the second polymer is coated on the first coating layer to obtain a positive electrode active material; the positive electrode active material includes an inner core, a first coating layer coating the inner core and a second coating layer coating the first coating layer, wherein the inner core includes a lithium transition metal oxide, the first coating layer includes a first polymer containing an anionic group, and the anionic group includes at least one of a cyano group, a halogen group, a phenyl group and an ester group; the second coating layer includes a second polymer containing a hydrophilic group, and the hydrophilic group includes at least one of an amide group, a hydroxyl group and a carboxylate group.

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

[0084] Mechanically mixing the first polymer and the core to obtain a material coated with a first coating layer;

[0085] Alternatively, the first polymer is first dissolved in an organic solvent, added to the core and stirred and dispersed, and then the organic solvent is removed to obtain a material coated with the first coating layer.

[0086] During the preparation of the positive electrode active material, the material coated by the first coating layer is coated with the second polymer by a non-solvent method, thereby reducing the loss of the first polymer in the coating structure; and during the wet method of preparing the electrode sheet, the 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 the present 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 ratios.

[0088] And / or, the mass ratio of the core to the second polymer is 90-99.9:0.1-10. As an example, the mass ratio of the core to 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 ratios.

[0089] According to some embodiments of the present application, the present application provides a positive electrode plate, including a positive electrode collector and a positive electrode active material layer arranged on at least one surface of the positive electrode collector, and the positive electrode active material layer contains the positive electrode active material provided above.

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

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

[0092] In some embodiments, positive electrode active material layers are respectively disposed 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. The present application does not specifically limit the types of conductive agents and binders, and 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 fluorine-containing acrylate resin.

[0094] In some embodiments, the mass ratio of the positive electrode active material to the conductive agent and the binder is (96-99): (0.5-2): (0.5-2). Thus, by using the positive electrode active material, conductive agent and binder in the proportions of the present application to form a 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 single-layer positive electrode active material coating area is 1540.25mm 2 The minimum coating weight is 50 mg, generally 50-200 mg.

[0096] In some embodiments, the positive electrode current collector may be a conventional metal foil or a composite positive electrode current collector (a metal material may be disposed on a polymer substrate to form a composite positive electrode current collector). 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 material base layer and a metal layer formed on at least one surface of the polymer material base layer; the composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0097] In some embodiments, the method for preparing a positive electrode sheet may include: forming a positive electrode active material layer on at least one side of a positive electrode current collector. As an example, the positive electrode 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 on the positive electrode current collector, and then the solvent is removed by roller coating and drying to obtain a positive electrode sheet.

[0098] According to some embodiments of the present application, the present application further provides a battery, including a negative electrode sheet, a separator, a battery cell composed of the positive electrode sheet provided above, and an electrolyte. The battery includes any form of a single cell, a battery module, and 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 the positive electrode plate of the embodiments of the present application can be applied to lithium ion batteries or lithium metal batteries, and the present application does not specifically limit this. The battery structure is described below using a lithium ion battery as an example. For lithium metal batteries, the battery structure can be adjusted accordingly.

[0100] [Negative electrode]

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

[0102] As an example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode active material layer is disposed on any one or both of the two facing 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, as the metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0104] In some embodiments, the present 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: The present 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 can be selected from one or more of graphite, lithium metal, no negative electrode current collector, silicon-based material, tin-based material and lithium titanate. The silicon-based material can be selected from one or more of elemental silicon, silicon oxide compounds, silicon-carbon composite materials, silicon-nitrogen composite materials and silicon alloys. The tin-based material can 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 further 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 further include a conductive agent, which 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 further optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0108] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0109] [Isolation film]

[0110] The present application has no particular limitation on the type of isolation membrane, and any known porous isolation membrane with good chemical stability and mechanical stability can be selected.

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

[0112] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

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

[0114] In some embodiments, the outer packaging of the battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0115] [Electrolytes]

[0116] The battery cell also includes an electrolyte, which conducts ions between the positive electrode and the negative electrode. The electrolyte can be in liquid or gel form.

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

[0118] In some embodiments, the electrolyte salt can 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 difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate and lithium tetrafluorooxalatophosphate.

[0119] In some embodiments, the organic solvent can be selected from one or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

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

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

[0122] Next, one or more embodiments are described in more detail with reference to the following examples. Of course, these examples do not limit the scope of one or more embodiments.

[0123] Example 1

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

[0125] The first polymer (polyacrylonitrile, molecular weight 100,000) was dissolved in an organic solvent (methyl pyrrolidone NMP), and the positive electrode active material particles (lithium nickel cobalt manganese oxide LiNi) as the core were added. 0.8 Mn 0.1 Co 0.1 O2 (NMC811, average particle size of about 10 μm) was stirred and dispersed, the mass ratio of the core and the first polymer was 97wt%:3wt%, and after removing the organic solvent, the material coated with the first coating layer was obtained. The thickness of the first coating layer was tested by transmission electron microscopy, and the thickness of the first coating layer was about 0.7 μm; then, 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 a second coating layer, and the core (lithium nickel cobalt manganese oxide LiNi 0.8 Mn 0.1 Co 0.1 The feed mass ratio of O2(NMC811)) and the second polymer is 95wt%:5wt%, and the thickness of the second coating layer is tested by transmission electron microscopy. The thickness of the second coating layer is about 0.5μm, and finally the positive electrode active material is obtained.

[0126] (2) Preparation of positive electrode sheet

[0127] The positive electrode active material, conductive agent Super P, and binder PVDF were mixed in 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 of about 60%); the positive electrode slurry was coated on both sides of the positive electrode current collector (aluminum foil, thickness of 14 μm), and the organic solvent was removed by vacuum oven drying to obtain a positive electrode sheet with a surface capacity of 3.5 mAh / cm 2 .

[0128] (3) Preparation of electrolyte

[0129] The lithium salt lithium bis(fluorosulfonyl)imide (LiFSI) was dissolved in an organic solvent (a mixed solvent 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 evenly to obtain an electrolyte with a concentration of 4 mol / L.

[0130] (4) Preparation of negative electrode sheet

[0131] A 50 μm thick lithium foil is selected and rolled and compounded with an 8 μm thick copper foil as a spare negative electrode sheet. The negative electrode sheet is used to form a lithium metal battery. Using a lithium metal battery to evaluate battery performance can reduce the impact of negative electrode active materials.

[0132] (5) Isolation film

[0133] A polyethylene porous membrane was selected as the isolation membrane.

[0134] (6) Assembly of secondary batteries

[0135] The positive electrode sheet and the negative electrode sheet are stacked and combined, the positive and negative electrodes are separated by an isolation film, and wrapped with an aluminum-plastic film bag to form a lithium-ion stacked dry battery cell, injected with the prepared electrolyte, vacuum packaged, and left to stand at room temperature for 6 hours to obtain a secondary battery.

[0136] Embodiments 2 to 10

[0137] Except that the positive electrode active material formed in step (1) is slightly different, the rest is basically the same as Example 1, and the details are shown in Table 1.

[0138] Comparative Example 1

[0139] Except that the positive electrode active material particles are not coated in step (1), and NMC811 without any coating is used as the positive electrode active material, the rest is basically the same as Example 1. For details, see Table 1.

[0140] Comparative Example 2

[0141] Except that in step (1), only the first coating layer is coated on the positive electrode active material particles without 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 Example 1. For details, see Table 1.

[0142] Comparative Example 3

[0143] Except that in step (1), only the first coating layer is coated on the positive electrode active material particles, and the coating material is sodium alginate, the rest is basically the same as Example 1. For details, see Table 1.

[0144] Electrochemical cycle performance test

[0145] The electrochemical cycle performance test of the secondary battery prepared above was carried out at 25°C under the test conditions of 0.2C constant current and constant voltage charging and 1C constant current discharge. The cut-off voltage of charging was set to 4.3V, and the cut-off voltage of discharging was set to 2.8V. Constant current-constant voltage charging is specifically: charging at 0.2C constant current to a cut-off voltage of 4.3V, and continuing to charge at 4.3V constant voltage until the current drops to 0.05C. Constant current discharge is specifically: discharging at 1C constant current to 2.8V; recording the discharge capacity at this time as C0, repeating the above charge and discharge cycle, thereby reducing the influence of the internal polarization of the battery on the charge and discharge capacity. The battery life is considered to end when the discharge capacity decay rate reaches 80%.

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

[0147] The performance of the battery tested is shown in Table 1:

[0148] Table 1 Battery performance

[0149]

[0150]

[0151] Embodiment 11

[0152] Except that spinel-structured LiMn2O4 material (average particle size of about 10 μm) is used as the core in step (1), the rest is basically the same as Example 1. Details are shown in Table 2.

[0153] Comparative Example 4

[0154] Except that the positive electrode active material particles as the inner core are not coated in step (1), and uncoated LiMn2O4 is used as the positive electrode active material, the rest is basically the same as Example 1. For details, see Table 2.

[0155] The electrochemical cycle performance test was carried out in the same manner as above, and the performance of the battery obtained by the test is shown in Table 2:

[0156] Table 2 Battery performance

[0157]

[0158] Combining 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 sheets of Examples 1 to 10 is coated with a first coating layer and a second coating layer at the same time, 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 to 3, which are only coated with the first polymer or the second polymer, the positive electrode active material of Example 1 is sequentially coated with the first polymer and the second polymer, which can improve the cycle life of the battery.

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

[0162] According to Example 1 and Example 10, the thickness of the first coating layer coated with 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] Combining the results in Table 2, we can see that:

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

[0165] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents the selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present application.

Claims

1. A positive electrode active material, characterized in that: It includes an inner core, a first coating layer coating the inner core, and a second coating layer coating the first coating layer, wherein the inner core includes a lithium transition metal oxide, the first coating layer includes a first polymer containing an anionic group, and the anionic group includes at least one of a cyano group, a halogen group, a phenyl group, and an ester group; the second coating layer includes a second polymer containing a hydrophilic group, and the hydrophilic group includes at least one of an amide group, a hydroxyl group, and a carboxylate group.

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 a structural unit shown in formula I, wherein R1, R2, R3, and R4 are independently selected from H, substituted or unsubstituted C1-C10 alkyl, cyano, halogen, phenyl, and ester, and at least one of R1, R2, R3, and R4 is selected from cyano, halogen, phenyl, or ester; The substituent groups in the substituted C1-C10 alkyl group are 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 to 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 to 4, characterized in that The molecular weight of the first polymer is 50,000-150,000.

6. The positive electrode active material according to any one of claims 1 to 5, characterized in that: The thickness of the first cladding layer is greater than the thickness of the second cladding layer.

7. The positive electrode active material according to any one of claims 1 to 6, characterized in that: The thickness of the first coating layer is 0.1 μm-2 μm, and can be optionally 0.5 μm-1.5 μm.

8. The positive electrode active material according to any one of claims 1 to 7, characterized in that The thickness of the second coating layer is 0.1 μm-1.5 μm, and can be optionally 0.2 μm-0.6 μm.

9. The positive electrode active material according to any one of claims 1 to 8, 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, 0<a≤1.2, 0<b≤2, 2≤c≤4.

10. The positive electrode active material according to any one of claims 1 to 9, characterized in that The average particle size of the core is 1-20 μm, and can be 3-10 μm.

11. A method for preparing a positive electrode active material, characterized in that: include: Mixing a first polymer and a core, so that the first polymer is coated on the core, to obtain a material coated with a first coating layer; Mixing the material coated by the first coating layer with a second polymer so that the second polymer is coated on the first coating layer to obtain 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, wherein the core includes a lithium transition metal oxide, the first coating layer includes a first polymer containing an anionic group, and the anionic group includes at least one of a cyano group, a halogen group, a phenyl group, and an ester group; the second coating layer includes a second polymer containing a hydrophilic group, and the hydrophilic group includes at least one of an amide group, a hydroxyl group, and a carboxylate group.

12. The method for preparing a 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 sheet, characterized in that: The invention comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer comprises the positive electrode active material according to any one of claims 1 to 10 or the positive electrode active material prepared by the preparation method according to claim 11 or 12.

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

15. An electrical device, characterized in that: Comprising the battery of claim 14.

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