WO2024040471A1 - Positive electrode plate and preparation method therefor, secondary battery and electric device - Google Patents

Abstract

The present application provides a positive electrode plate and a preparation method therefor, a secondary battery and an electric device. The positive electrode plate comprises a positive current collector and a positive film layer, the positive current collector comprises a support layer and a conductive layer arranged on at least one surface of the support layer, the positive film layer is provided on a surface of the conductive layer away from the support layer, the positive film layer is formed by dry positive electrode powder including a positive electrode active material, and a protective layer is at least provided on a surface of the positive film layer away from the support layer. When the positive electrode plate is applied to a secondary battery, the cycling performance and storage performance of the secondary battery can be effectively improved.

Description

Positive electrode plate and preparation method thereof, secondary battery and electrical device Technical field

The present application relates to the field of batteries, specifically to a positive electrode plate and its preparation method, secondary batteries and electrical devices.

Background technique

Secondary batteries have the characteristics of high capacity and long life, so they are widely used in electronic equipment, such as mobile phones, laptop computers, battery cars, electric cars, electric airplanes, electric ships, electric toy cars, electric toy ships, electric toy airplanes and electric tools etc.

In the development of battery technology, the cycle performance and storage performance of secondary batteries are important indicators that determine the performance of secondary batteries. The cathode plate is an important part of the secondary battery, and its structural stability has an important impact on the cycle performance of the secondary battery. It has an important impact on performance and storage performance, so how to improve the structural stability of the cathode plate is an urgent technical problem that needs to be solved.

Contents of the invention

This application was made in view of the above-mentioned problems, and its purpose is to provide a positive electrode plate and its preparation method, a secondary battery and an electrical device.

A first aspect of the present application provides a positive electrode sheet for a secondary battery. The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer. The positive electrode current collector includes a support layer and is disposed on at least one surface of the support layer. The conductive layer; the positive electrode film layer is disposed on the surface of the conductive layer away from the support layer, the positive electrode film layer is formed by dry cathode powder containing the cathode active material; and the protective layer is at least disposed on the surface of the positive electrode film layer away from the support layer.

Therefore, the positive electrode sheet of the present application includes a positive electrode current collector, a positive electrode film layer and a protective layer. The conductive layer of the positive electrode current collector can play a role in drawing out current and provides a basis for the formation of the positive electrode film layer; the positive electrode film layer is made of dry Made of non-toxic positive electrode powder, the positive electrode film layer basically does not contain solvents, which can make the bonding force between the positive electrode film layer and the conductive layer more uniform, and can effectively reduce production costs; the protective layer is set on the positive electrode film layer away from the support layer On the surface, the positive electrode film layer is sandwiched between the protective layer and the conductive layer, which can protect the positive electrode film layer and reduce the risk of the positive electrode film layer falling off from the conductive layer, thereby improving the bonding force between the layers, thus ensuring Structural stability of the positive electrode plate. When the positive electrode sheet is applied to a secondary battery, the cycle performance and storage performance of the secondary battery can be effectively improved.

In some embodiments, the support layer includes one or more of an organic polymer layer and a metal layer; optionally, the organic polymer layer is made of polyethylene terephthalate (PET), polyvinyl chloride (PVC) , one or more of polyimide PI and polyacrylonitrile PAN; optionally, the material of the metal layer includes aluminum or aluminum alloy. The above-mentioned materials can provide good strength to the support layer, and are conducive to the composite of the support layer and the conductive layer, improving the connection strength between the support layer and the conductive layer.

In some embodiments, the conductive layer includes a first binder and a first conductive agent. The mass content of the first binder relative to the total mass of the conductive layer is A ₁ %; the first conductive agent has a mass content relative to the total mass of the conductive layer. The mass content of the mass is A ₂ %, and the conductive layer satisfies: 0.10 ≤ A ₁ /A ₂ ≤ 0.45.

Therefore, when the first binder and the first conductive agent of the conductive layer of the present application satisfy the above formula, the conductive layer can mainly play a conductive role, supplementary by playing a bonding performance, and conduct electrons in the positive electrode film layer On the basis of this, it can improve the conductivity of the positive electrode film layer and play a bonding role between the support layer and the positive electrode film layer, thus improving the overall structural stability of the positive electrode plate.

In some embodiments, 10≤A ₁ ≤30; and/or 70≤A ₂ ≤90. When the mass content of the first binder is within the above range, the bonding performance of the conductive layer can be fully guaranteed. When the mass content of the first conductive agent is within the above range, the conductive performance of the conductive layer can be fully guaranteed.

In some embodiments, the first binder includes an aqueous binder and/or an oily binder; optionally, the aqueous binder includes one of polyacrylic acid PAA, polyoxyethylene PEO, and a propanol-based compound. Or more; optionally, the oily binder includes polyvinylidene fluoride (PVDF) homopolymer or its copolymer. Both water-based binders and oil-based binders can play a good bonding role, and when the water-based binder is used, it is mainly located in the conductive layer, and less content penetrates into the positive electrode film layer. The water-based binder basically does not cause The metal ions of the positive electrode active material, such as lithium ions and/or manganese ions, are eluted, thereby ensuring the structural stability of the positive electrode film layer.

In some embodiments, the first conductive agent includes one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The above-mentioned conductive material has good conductivity and can provide good conductive properties for the conductive layer.

In some embodiments, the protective layer includes a second binder and a second conductive agent. The mass content of the second binder relative to the total mass of the protective layer is B ₁ %; the second conductive agent relative to the total mass of the protective layer The mass content of the mass is B ₂ %, and the protective layer satisfies: 30≤B ₁ /B ₂ ≤999.

Therefore, when the second binder and the second conductive agent of the protective layer of the present application satisfy the above formula, the protective layer can mainly play a bonding role to fully protect the positive electrode film layer; supplemented by a conductive role, it has Conducive to guiding the transmission of electrons.

In some embodiments, 97≤B ₁ ≤99.9; and/or 0.1 ≤ B ₂ ≤3. When the mass content of the second binder is within the above range, the bonding performance of the protective layer can be fully guaranteed. When the mass content of the second conductive agent is within the above range, the conductive performance of the protective layer can be fully guaranteed.

In some embodiments, the second binder includes an aqueous binder and/or an oily binder; optionally, the aqueous binder includes one of polyacrylic acid PAA, polyoxyethylene PEO, and a propanol-based compound. Or more; optionally, the oily binder includes polyvinylidene fluoride (PVDF) homopolymer or its copolymer. Both water-based binders and oil-based binders can play a good bonding role, and when the water-based binder is used, it is mainly located in the protective layer, and less content penetrates into the positive electrode film layer. The water-based binder basically does not cause The metal ions of the positive electrode active material, such as lithium ions and/or manganese ions, are eluted, thereby ensuring the structural stability of the positive electrode film layer.

In some embodiments, the second conductive agent includes one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The above-mentioned conductive materials have good conductivity and can provide good conductive properties for the protective layer.

In some embodiments, the positive electrode film layer includes a positive electrode active material and a third conductive agent. The mass content of the positive electrode active material relative to the cathode film layer is C ₁ %, and the mass content of the third conductive agent relative to the cathode film layer is C ₂ %, the positive electrode film layer satisfies: 15≤C ₁ /C ₂ ≤99; optionally, 95≤C ₁ ≤99; and/or 1≤C ₂ ≤5.

Therefore, in this application, when the positive active material and the third conductive agent satisfy the above formula, the proportion of the positive active material is high, which can increase the overall capacity of the positive electrode film layer, thereby increasing the energy density of the secondary battery; and the third conductive agent It can provide conductivity to the positive electrode film layer and assist the positive electrode film layer in transmitting electrons.

In some embodiments, part of the protective layer is embedded in the positive electrode film layer. This arrangement enables the protective layer embedded in the positive electrode film layer to provide adhesive force to the inside of the positive electrode film layer, further improving the connection strength between layers and reducing the risk of the positive electrode film layer falling off.

In some embodiments, the positive electrode plate also satisfies one or more of conditions (1) to (3): (1) The thickness of the support layer is L ₁ μm, and the thickness of the conductive layer is L ₂ μm, 0.5≤ L ₁ /L ₂ ≤1; (2) The thickness of the conductive layer is L ₂ μm, the thickness of the positive electrode film layer is L ₃ μm, 0.2≤L ₂ /L ₃ ≤1; (3) The thickness of the protective layer is L ₄ μm, the thickness of the positive electrode film layer is L ₃ μm, 0.01≤L ₄ /L ₃ ≤0.1.

Therefore, when this application satisfies the above formula, on the one hand, it can ensure the bonding strength between the layer structures of the positive electrode sheet and reduce the risk of interlayer detachment and peeling; on the other hand, it can improve the overall conductivity of the positive electrode sheet.

The second aspect of this application provides a method for preparing a positive electrode sheet, including:

S100, which provides a support layer;

S200, apply conductive slurry on at least one surface of the support layer;

S300, coat the dry cathode powder on the surface of the support layer coated with the conductive slurry to form a first composite;

S400, apply the protective slurry on the surface of the first composite body to form a positive electrode composite body,

S500, heat-treat the positive electrode composite to solidify the positive electrode composite to form a positive electrode piece, wherein,

The conductive slurry is cured to form a conductive layer, and the conductive layer is disposed on at least one surface of the support layer;

The dry cathode powder forms a cathode film layer, the cathode film layer is arranged on the surface of the conductive layer away from the support layer, and the cathode film layer includes cathode active material;

The protective slurry solidifies to form a protective layer, which is at least disposed on the surface of the positive electrode film layer away from the support layer.

Therefore, in this application, after the dry positive electrode powder is placed on the conductive slurry and the protective slurry is placed on the dry positive electrode powder, the positive electrode piece can be formed through one-time thermal compounding. The preparation method is simple, and the formed The positive electrode plate has high structural stability, and when applied to secondary batteries, it can significantly improve the cycle performance and storage performance of the secondary battery.

In some embodiments, the solid content of the conductive slurry is 10%-25%; and/or the solid content of the protective slurry is 4%-10%. When the solid content of the conductive slurry is within the above range, it is more conducive to spraying or brushing of the conductive slurry, and the thickness of the formed conductive slurry is uniform. When the solid content of the protective slurry is within the above range, it is more conducive to the spraying of the protective slurry, and the thickness of the formed protective slurry is uniform.

In some embodiments, in S200, a brushing or spraying process is used to apply the conductive slurry on at least one surface of the support layer; and/or in S400, a spraying process is used to apply the protective slurry to the first surface of the support layer. on the surface of the complex. The brushing or spraying process is faster to produce and can control the coating size accurately. The protective slurry is sprayed onto the positive electrode powder using a spraying process. The protective slurry can penetrate into the inside of the positive electrode film layer, thereby improving the adhesion within the positive electrode film layer and the adhesion between the positive electrode film layer and the protective layer. force.

In some embodiments, in S300, the dry cathode powder is charged or magnetized, and the charged or magnetized dry cathode powder is coated on the support layer coated with the conductive slurry. On the surface. After the dry cathode powder is charged or magnetized, the particles have the same charge or magnetic field, and the particles generate mutual repulsion, so that the dry cathode powder can be evenly distributed on the conductive slurry.

A third aspect of the present application also provides a secondary battery, including the positive electrode sheet obtained in any embodiment of the first aspect of the application or the positive electrode sheet obtained in any embodiment of the second aspect.

The fourth aspect of the present application also provides an electrical device, including a secondary battery as in any embodiment of the first aspect of the present application, a battery module as in the second embodiment of the present application, or a third embodiment of the present application. battery pack.

Description of drawings

In order to explain the technical solutions of the embodiments of the present application more clearly, the drawings required to be used in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. Those of ordinary skill in the art can also obtain other drawings based on the drawings without exerting creative efforts.

FIG. 1 is a schematic diagram of an embodiment of the positive electrode plate of the present application.

FIG. 2 is a cross-sectional view of the positive electrode plate shown in FIG. 1 taken along line A-A.

FIG. 3 is a schematic diagram of the electrode assembly of the secondary battery of the present application.

FIG. 4 is a schematic diagram of an embodiment of the secondary battery of the present application.

FIG. 5 is an exploded schematic view of the embodiment of the secondary battery of FIG. 4 .

FIG. 6 is a schematic diagram of an embodiment of the battery module of the present application.

FIG. 7 is a schematic diagram of an embodiment of the battery pack of the present application.

FIG. 8 is an exploded schematic view of the embodiment of the battery pack shown in FIG. 7 .

FIG. 9 is a schematic diagram of an embodiment of a power consumption device including the secondary battery of the present application as a power source.

The drawings are not necessarily drawn to actual scale.

The reference symbols are explained as follows:

1. Battery pack; 2. Upper box; 3. Lower box; 4. Battery module;

5. Secondary battery; 51. Case; 52. Electrode assembly; 521. Positive electrode plate; 5211. Support layer; 5212. Conductive layer; 5213. Positive electrode film layer; 5214. Protective layer;

522. Negative electrode piece; 523. Isolation film;

53. Cover plate;

6. Electrical devices.

Detailed ways

Hereinafter, the embodiments of the positive electrode sheet and its preparation method, secondary battery and electrical device of the present application will be described in detail. However, unnecessary detailed explanations may be omitted. For example, detailed descriptions of well-known matters may be omitted, or descriptions of substantially the same structure may be repeated. This is to prevent the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application, and are not intended to limit the subject matter described in the claims.

"Ranges" disclosed herein are defined in terms of lower and upper limits. A given range is defined by selecting a lower limit and an upper limit that define the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive of the endpoints, and may be arbitrarily combined, that is, any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, understand that ranges of 60-110 and 80-120 are also expected. Furthermore, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2- 3, 2-4 and 2-5. In this application, unless stated otherwise, the numerical range "a-b" represents an abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed in this article, and "0-5" is just an abbreviation of these numerical combinations. In addition, when stating that a certain parameter is an integer ≥ 2, it is equivalent to disclosing that the parameter is an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

If there is no special description, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions. If there is no special description, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

If there is no special instructions, all steps of the present application can be performed sequentially or randomly, and are preferably performed sequentially. For example, a method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, mentioning that the method may also include step (c) means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b) and (c), and may also include step (a). , (c) and (b), and may also include steps (c), (a) and (b), etc.

If there is no special explanation, the words "include" and "include" mentioned in this application represent open expressions, which may also be closed expressions. For example, "comprises" and "comprises" may mean that other components not listed may also be included or included, or that only the listed components may be included or included. The terms "first", "second", etc. in the description and claims of this application or the above-mentioned drawings are used to distinguish different objects, rather than to describe a specific order or priority relationship.

In this application, the term "or" is inclusive unless otherwise stated. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists) ; Or both A and B are true (or exist).

If there is no special explanation, in this application, the terms "installation", "connection", "connection" and "attachment" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection. Connection; it can be a direct connection, or an indirect connection through an intermediary, or an internal connection between two components. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

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

The secondary battery includes an electrode assembly, and the electrode assembly includes a positive electrode piece and a negative electrode piece. Metal ions such as lithium ions can migrate between the positive electrode piece and the negative electrode piece, thereby realizing charging and discharging of the secondary battery. The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on the positive electrode current collector. The positive electrode film layer is formed by curing the positive electrode slurry containing organic solvent, binder and positive electrode active material. During the solidification process of the positive electrode slurry, the organic solvent will evaporate, and the evaporated organic solvent will carry the binder towards the positive electrode film layer. Surface migration results in a higher distribution of the binder in the surface area of the cathode film layer away from the cathode current collector, and a lower distribution of the binder in the surface area of the cathode film layer close to the cathode current collector, which will result in the positive electrode film layer and The bonding force between the positive electrode current collectors is poor, and the positive electrode film layer may be peeled off from the positive electrode current collector or powder may fall off, resulting in poor structural stability of the positive electrode sheet, which is not conducive to the long-term recycling of secondary batteries. . And because the organic solvent is basically evaporated during the curing process, there is basically no residual organic solvent in the positive electrode film layer. The large use of organic solvents also significantly increases the process cost.

In view of this, the inventor has improved the preparation process of the positive electrode piece from the perspective of improving the structural stability of the positive electrode piece, thereby improving the structure of the positive electrode current collector and the positive electrode film layer, in order to achieve structural stability and lower cost. The positive electrode piece. Next, the specific structural form of the positive electrode plate will be described.

Positive electrode piece

In the first aspect, this application proposes a positive electrode plate.

As shown in Figures 1 and 2, the positive electrode sheet 521 includes a positive current collector, a positive electrode film layer 5213 and a protective layer 5214; the positive current collector includes a support layer 5211 and a conductive layer disposed on at least one surface of the support layer 5211 5212; The positive electrode film layer 5213 is provided on the surface of the conductive layer 5212 away from the support layer 5211. The positive electrode film layer 5213 is formed by dry positive electrode powder containing the positive electrode active material; and the protective layer 5214 is provided at least on the surface of the positive electrode film layer 5213. The surface of the support layer 5211.

The support layer 5211 serves as a fixed support, and can be made of conductive material, or of course can also be made of non-conductive material. The support layer 5211 has two surfaces facing each other along its own thickness direction, and the conductive layer 5212 can be disposed on any one of the two surfaces or on both surfaces. When the conductive layer 5212 is disposed on one surface, the positive electrode piece 521 includes a support layer 5211, a conductive layer 5212, a positive electrode film layer 5213 and a protective layer 5214 that are stacked in sequence; when the conductive layer 5212 is disposed on both surfaces of the support layer 5211, the positive electrode The pole piece 521 includes a protective layer 5214, a positive electrode film layer 5213, a conductive layer 5212, a support layer 5211, a conductive layer 5212, a positive electrode film layer 5213 and a protective layer 5214 that are stacked in sequence. FIG. 2 shows a schematic diagram of the conductive layer 5212 being disposed on both surfaces of the support layer 5211. In this application, the positive electrode current collector can protrude relative to the positive electrode film layer to facilitate welding of the positive electrode current collector and the tab.

When the support layer 5211 is made of non-conductive material, the conductive layer 5212 can drain electrons from the positive electrode film layer 5213 to ensure normal charging and discharging of the secondary battery. When the support layer 5211 is made of conductive material, the conductive layer 5212 can work with the support layer 5211 to drain the electrons in the positive electrode film layer 5213 to further ensure the normal charge and discharge of the secondary battery. In this case, the support layer 5211 and the conductive layer 5212 can be made of different materials, or of course it can be made of the same material; and when made of the same material, the same molding process can be used, or different molding processes can be used.

The positive electrode film layer 5213 is formed on the conductive layer 5212 from dry positive electrode powder. The dry positive electrode powder may not contain solvents such as organic solvents, thereby reducing process costs to a certain extent. The dry cathode powder is in solid granular form, which is formed on the conductive layer 5212 and is composited with the conductive layer 5212; and the conductive layer 5212 not only serves as a substrate for the cathode film layer 5213, but can also strengthen the solid granular form. The electrical conductivity and adhesion between substances improve the overall electrical conductivity of the positive electrode film layer 5213. The positive electrode film layer 5213 may only include the positive electrode active material, or may also include other additives such as conductive materials.

Since the positive electrode film layer 5213 is composed of solid granular substances, the granular substances may still have the risk of falling off from the conductive layer 5212. In this application, the protective layer 5214 is provided on the surface of the positive electrode film layer 5213, which can prevent the solid granular substances from falling off. The effect of the particle material makes the particulate matter sandwiched between the conductive layer 5212 and the protective layer 5214, thereby reducing the risk of the particulate matter falling off from the conductive layer 5212. Of course, in addition to being disposed on the surface of the positive electrode film layer 5213, the protective layer 5214 can also be disposed on the surface of the conductive layer 5212 that is not covered by the positive electrode film layer 5213, thereby protecting other surfaces of the positive electrode film layer 5213. , thereby providing a more comprehensive protective effect on the positive electrode film layer 5213 and further reducing the risk of solid particulate matter in the positive electrode film layer 5213 falling off. Moreover, the protective layer 5214 not only plays the role of protecting the positive electrode film layer 5213, but can also further strengthen the bonding performance between solid particulate matter, thereby playing a further protective role.

The positive electrode sheet 521 of the present application includes a positive electrode current collector, a positive electrode film layer 5213 and a protective layer 5214. The conductive layer 5212 of the positive electrode current collector can play a role in drawing out current and provides a molding basis for the positive electrode film layer 5213; the positive electrode film layer 5213 is made of dry positive electrode powder. The positive electrode film layer 5213 basically does not contain solvents, which can make the bonding force between the positive electrode film layer 5213 and the conductive layer 5212 more uniform, and can effectively reduce production costs; the protective layer 5214 is provided on the positive electrode On the surface of the film layer 5213 away from the support layer 5211, the positive electrode film layer 5213 is sandwiched between the protective layer 5214 and the conductive layer 5212, which can protect the positive electrode film layer 5213 and reduce the risk of the positive electrode film layer 5213 falling off from the conductive layer 5212. , thereby improving the bonding force between layers, thereby ensuring the structural stability of the positive electrode piece 521. When the positive electrode plate 521 is applied to a secondary battery, the cycle performance and storage performance of the secondary battery can be effectively improved.

In some embodiments, the support layer 5211 may include one or more of an organic polymer layer and a metal layer.

The support layer 5211 can be a single-layer structure or a multi-layer composite structure. The multi-layer composite structure can further improve the overall strength of the support layer 5211, thereby improving the overall strength of the positive electrode piece 521. When the support layer 5211 has a single-layer structure, the support layer 5211 may be an organic polymer layer or a metal layer. When the support layer 5211 is a multi-layer composite structure, the support layer 5211 may include an organic polymer layer and a metal layer. For example, the support layer 5211 may include a stacked organic polymer layer and a metal layer; or the support layer 5211 may include a stacked metal layer. layer, an organic polymer layer and a metal layer; or the support layer 5211 includes a stacked organic polymer layer, a metal layer, an organic polymer layer, etc.

Optionally, the material of the organic polymer layer includes one or more of polyethylene terephthalate PET, polyvinyl chloride PVC, polyimide PI and polyacrylonitrile PAN; optionally, metal The material of the layer includes aluminum or aluminum alloy. The above-mentioned materials can provide good strength for the support layer 5211, and are conducive to the composite of the support layer 5211 and the conductive layer 5212, improving the connection strength between the support layer 5211 and the conductive layer 5212.

In some embodiments, the conductive layer 5212 includes a first binder and a first conductive agent; the mass content of the first binder relative to the total mass of the conductive layer 5212 is A ₁ %, and the first conductive agent relative to the total mass of the conductive layer 5212 The mass content of the total mass of 5212 is A ₂ %, and the conductive layer 5212 satisfies: 0.10 ≤ A ₁ /A ₂ ≤ 0.45.

The first adhesive plays a bonding role, bonding the conductive layer 5212 itself and the support layer 5211 into one body; and when the positive electrode film layer 5213 is provided on the conductive layer 5212, in view of the fact that the positive electrode film layer 5213 is made of solid dry positive electrode powder The first binder can bind the dry positive electrode powder to the conductive layer 5212, and the first binder can penetrate into the positive electrode film layer 5213 and bind the adjacent solid particles in the positive electrode film layer 5213. The like substance is bonded to improve the bonding force between the positive electrode film layer 5213 and the conductive layer 5212.

As the name suggests, the first conductive agent has a conductive effect and provides conductive properties for the conductive layer 5212. The first conductive agent can also penetrate into the positive electrode film layer 5213 and electrically connect adjacent solid granular substances in the positive electrode film layer 5213, thereby Improve the conductivity of the positive electrode film layer 5213.

When the first binder and first conductive agent of the conductive layer 5212 of the present application satisfy the above formula, the conductive layer 5212 can mainly play a conductive role, supplemented by the adhesive performance, and conduct electrons in the positive electrode film layer 5213 On the basis of this, the conductivity of the positive electrode film layer 5213 can be improved, and the bonding effect between the support layer 5211 and the positive electrode film layer 5213 can be improved, thereby improving the overall structural stability of the positive electrode plate 521. For example, A ₁ /A ₂ can be 0.100, 0.110, 0.125, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40 or 0.45; or a range consisting of any two of the above values.

In some embodiments, the mass content of the first adhesive relative to the total mass of the conductive layer 5212 is A ₁ %, and 10 ≤ _{A 1} ≤ 30.

When the mass content of the first adhesive is within the above range, the bonding performance of the conductive layer 5212 can be fully guaranteed. For example, the mass content A ₁ % of the first binder may be 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28% or 30%; or any two of the above A range of values.

As an example of the first adhesive, the first adhesive may include a water-based adhesive and/or an oil-based adhesive. Both water-based binders and oil-based binders can play a good bonding role, and when the water-based binder is used, it is mainly located in the conductive layer 5212, and less content penetrates into the positive electrode film layer 5213, so the water-based binder is basically not used. This will cause the metal ions of the positive electrode active material, such as lithium ions and/or manganese ions, to be eluted, thereby ensuring the structural stability of the positive electrode film layer 5213.

In this application, the water-based binder can be considered to have higher solubility in water, and water can be used as the solvent. Oil-based binders can be considered to have low solubility or insolubility in water, but have greater solubility in some organic substances, and organic substances can be used as solvents.

Exemplarily, the water-based binder may include one or more of polyacrylic acid PAA, polyoxyethylene PEO, and propanol-based compounds. The propanol-based compound can be polypropyl alcohol, polypropylene glycol, etc.

Illustratively, the oily binder may include polyvinylidene fluoride (PVDF) homopolymer or copolymers thereof.

In some embodiments, the mass content of the first conductive agent relative to the total mass of the conductive layer 5212 is A ₂ %, and 70 ≤ _{A 2} ≤ 90.

When the mass content of the first conductive agent is within the above range, the conductive performance of the conductive layer 5212 can be fully guaranteed. For example, the mass content A ₂ % of the first conductive agent may be 70%, 72%, 75%, 78%, 80%, 82%, 85%, 88% or 90%; or any two of the above values. range of composition.

As an example of the first conductive agent, the first conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The above-mentioned conductive material has good conductivity and can provide good conductive performance for the conductive layer 5212.

In some embodiments, the protective layer 5214 may include a second adhesive and a second conductive agent; the mass content of the second adhesive relative to the total mass of the protective layer 5214 is B ₁ %; the second conductive agent relative to the total mass of the protective layer 5214 The mass content of the total mass of the protective layer 5214 is B ₂ %, and the protective layer 5214 satisfies: 30 ≤ B ₁ /B ₂ ≤ 999.

The second binder plays a bonding role, bonding the protective layer 5214 itself and the positive electrode film layer 5213 into one body, thus fully protecting the positive electrode film layer 5213, and the second binder can penetrate into the positive electrode film layer 5213, the adjacent solid granular substances in the positive electrode film layer 5213 are bonded to improve the bonding force between the positive electrode film layer 5213 and the protective layer 5214.

As the name implies, the second conductive agent has a conductive effect and provides conductive properties for the protective layer 5214. The second conductive agent can also penetrate into the positive electrode film layer 5213 and electrically connect adjacent solid granular substances in the positive electrode film layer 5213, thereby Improve the conductivity of the positive electrode film layer 5213.

When the second binder and the second conductive agent of the protective layer 5214 of the present application satisfy the above formula, the protective layer 5214 can mainly play a bonding role to fully protect the positive electrode film layer 5213; supplemented by a conductive role, there is Conducive to guiding the transmission of electrons. For example, B ₁ /B ₂ can be 30, 50, 100, 150, 180, 200, 300, 500, 600, 700, 800, 850, 900, 950, 980 or 999; or any two of the above values range of composition.

In some embodiments, the mass content of the second adhesive relative to the total mass of the protective layer 5214 is B ₁ %, and 97 ≤ B ₁ ≤ 99.9.

When the mass content of the second adhesive is within the above range, the bonding performance of the protective layer 5214 can be fully guaranteed. For example, the mass content B ₁ % of the second binder can be 97%, 97.5%, 98%, 98.5%, 99%, 99.5% or 99.9%; or it can be a range consisting of any two of the above values.

As examples of the second adhesive, the second adhesive may include a water-based adhesive and/or an oil-based adhesive. Both water-based binders and oil-based binders can play a good bonding role, and when the water-based binder is used, it is mainly located in the protective layer 5214, and less content penetrates into the positive electrode film layer 5213, so the water-based binder is basically not used. This will cause the metal ions of the positive electrode active material, such as lithium ions and/or manganese ions, to be eluted, thereby ensuring the structural stability of the positive electrode film layer 5213.

Exemplarily, the water-based binder may include one or more of polyacrylic acid PAA, polyoxyethylene PEO, and propanol-based compounds. The propanol-based compound can be polypropyl alcohol, polypropylene glycol, etc.

Illustratively, the oily binder may include polyvinylidene fluoride (PVDF) homopolymer or copolymers thereof.

In some embodiments, the mass content of the second conductive agent relative to the total mass of the protective layer 5214 is B ₂ %, and 0.1 ≤ B ₂ ≤ 3.

When the mass content of the second conductive agent is within the above range, the conductive performance of the protective layer 5214 can be fully guaranteed. For example, the mass content B ₂ % of the second conductive agent can be 0.1, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2.0, 2.5, 2.8 or 3; or it can be a range consisting of any two of the above values.

As an example of the second conductive agent, the second conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The above conductive material has good electrical conductivity and can provide good electrical conductivity for the protective layer 5214.

In some embodiments, part of the protective layer 5214 is embedded in the positive electrode film layer 5213; specifically, the protective layer 5214 includes a main body part and a protruding part, and the main body part is disposed on the surface of the positive electrode film layer 5213 away from the support layer 5211 , the protruding portion is connected to the main body portion and protrudes toward the direction of the support layer 5211 relative to the main body portion, and protrudes into the positive electrode film layer 5213. The protruding portion is equivalent to the portion where the protective layer 5214 is embedded in the positive electrode film layer 5213. This arrangement enables the protective layer 5214 embedded in the positive electrode film layer 5213 to provide adhesive force to the inside of the positive electrode film layer 5213, further improving the connection strength between layers and reducing the risk of the positive electrode film layer 5213 falling off.

In some embodiments, the cathode film layer 5213 may include a cathode active material and a third conductive agent. The mass content of the cathode active material relative to the cathode film layer 5213 is C ₁ %, and the third conductive agent relative to the cathode film layer 5213 The mass content is C ₂ %, and the positive electrode film layer 5213 satisfies: 15≤C ₁ /C ₂ ≤99.

In this application, when the positive active material and the third conductive agent satisfy the above formula, the proportion of the positive active material is relatively high, which can increase the overall capacity of the positive electrode film layer 5213, thereby increasing the energy density of the secondary battery; and the third conductive agent can be The positive electrode film layer 5213 provides conductivity and assists the positive electrode film layer 5213 in transmitting electrons.

In some embodiments, the cathode active material may be a cathode active material known in the art for secondary batteries. As an example, the positive active material may include at least one of the following materials: layered structure positive active material (such as ternary, lithium/sodium nickelate, lithium/sodium cobaltate, lithium/sodium manganate, rich lithium/sodium layer and rock salt phase layered materials), olivine-type phosphate active materials, spinel structure cathode active materials (such as spinel lithium manganate, spinel lithium nickel manganate, lithium-rich spinel manganese Lithium oxide and lithium nickel manganate, etc.). Illustratively, the general formula of the layered structure cathode active material is: Li _x A _y Ni _a Co _b Mn _c M _(1-abc) Y _z , where 0≤x≤2.1, 0≤y≤2.1, and 0.9 ≤x+y≤2.1; 0≤a≤1, 0≤b≤1, 0≤c≤1, and 0.1≤a+b+c≤1; 1.8≤z≤3.5; A is selected from Na, K, Mg One or more of them; M is selected from B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd , one or more of Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; Y is selected from one or more of O and F. Specifically, the layered structure cathode active material may include lithium cobalt oxide LCO, lithium nickel oxide LNO, lithium manganate LMO, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (NCM333), LiNi _0.8 Co _0.1 Mn _0.1 One or more of O ₂ (NCM811) and LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (NCM523). Exemplarily, the general formula of the olivine-type phosphate active material is: Li _x A _y Me _a M _b P _1-c X _c Y _z , where 0≤x≤1.3, 0≤y≤1.3, and 0.9≤ x+y≤1.3; 0.9≤a≤1.5, 0≤b≤0.5, and 0.9≤a+b≤1.5; 0≤c≤0.5; 3≤z≤5; A is selected from one of Na, K and Mg One or more; Me is selected from one or more of Mn, Fe, Co, and Ni; M is selected from B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, One or more of Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X is selected from S, Si, Cl, B, One or more of C and N; Y is selected from one or more of O and F. Specifically, the olivine-type phosphate active material includes one or more of LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , and LiCoPO ₄ . Illustratively, the general formula of the spinel structure cathode active material is: Li _x A _y Mn _a M _2-a Y _z , where 0≤x≤2, 0≤y≤1, and 0.9≤x+y ≤2; 0.5≤a≤2; 3≤z≤5; A is selected from one or more of Na, K, Mg; M is selected from Ni, Co, B, Mg, Al, Si, P, S, One of Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, Ce or Several; Y is selected from one or more of O and F. Specifically, the spinel structure cathode active materials include LiMn ₂ O ₄ , LiNi _0.5 Mn _1.5 O ₄ , LiCr _0.3 Mn _1.7 O ₄ , Li _1.1 Al _0.1 Mn _1.9 O ₄ , Li ₂ Mn ₂ O ₄ and Li _1.5 Mn One or more of ₂ O ₄ .

In some embodiments, the third conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some embodiments, the positive electrode film layer 5213 optionally further includes a binder. As examples, the binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene tripolymer. At least one of a meta-copolymer, a tetrafluoroethylene-hexafluoropropylene copolymer and a fluorine-containing acrylate resin.

In some embodiments, the positive electrode piece 521 also satisfies: one or more of conditions (1) to (3):

(1) The thickness of the support layer 5211 is L ₁ μm, the thickness of the conductive layer 5212 is L ₂ μm, 0.5≤L ₁ /L ₂ ≤1;

(2) The thickness of the conductive layer 5212 is L ₂ μm, the thickness of the positive electrode film layer 5213 is L ₃ μm, 0.2≤L ₂ /L ₃ ≤1;

(3) The thickness of the protective layer 5214 is L ₄ μm, the thickness of the positive electrode film layer 5213 is L ₃ μm, and 0.01≤L ₄ /L ₃ ≤0.1.

When this application satisfies the above formula, on the one hand, it can ensure the bonding strength between the layer structures of the positive electrode piece 521 and reduce the risk of detachment and peeling between layers; on the other hand, it can improve the overall conductivity of the positive electrode piece 521.

For example, L ₁ /L ₂ can be 0.5, 0.6, 0.7, 0.8, 0.9 or 1; or it can be a range consisting of any two of the above values.

For example, L ₂ /L ₃ can be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1; or a range consisting of any two of the above values.

For example, L ₄ /L ₃ can be 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08 or 0.1; or a range consisting of any two of the above values.

As an example, the thickness of the support layer 5211 is L ₁ μm, and 1≤L ₁ ≤10. When the thickness of the support layer 5211 is within the above range, the strength of the support layer 5211 can be ensured, thereby improving the overall structural strength of the positive electrode piece 521. Alternatively, 1≤L ₁ ≤9; for example, the thickness L ₁ μm of the support layer 5211 may be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm; or any two of the above A range of values.

As an example, the thickness of the conductive layer 5212 is L ₂ μm, 1≤L ₂ ≤20. When the thickness of the conductive layer 5212 is within the above range, on the one hand, it can improve the overall strength of the positive electrode current collector, and on the other hand, it can provide a sufficient bonding basis for the positive electrode film layer 5213. Alternatively, 1 ≤ L ₂ ≤ 11; for example, the thickness of the conductive layer 5212 is L ₂ μm, which may be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm or 20μm; or a range consisting of any two of the above values.

As an example, the thickness of the positive electrode film layer 5213 is L ₃ μm, and 1≤L ₃ ≤100. When the thickness of the positive electrode film layer 5213 is within the above range, it can provide a higher capacity for the secondary battery. For example, the thickness L ₃ μm of the positive electrode film layer 5213 may be 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm. , 90μm, 95μm or 100μm; or a range consisting of any two of the above values.

As an example, the thickness of the protective layer 5214 is L ₄ μm, and 0.1≤L ₄ ≤2. When the thickness of the protective layer 5214 is within the above range, it can sufficiently fix and protect the positive electrode film layer 5213 and reduce the risk of the positive electrode film layer 5213 falling off. Optionally, 0.1≤L ₄ ≤0.5. For example, the thickness L ₄ μm of the protective layer 5214 may be 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.2 μm, 1.5 μm, 1.8μm or 2μm; or a range consisting of any two of the above values.

Method for preparing positive electrode plate

In a second aspect, this application proposes a method for preparing a positive electrode sheet.

The methods include:

S100, which provides a support layer;

S200, apply conductive slurry on at least one surface of the support layer;

S300, apply dry cathode powder on the surface of the support layer coated with conductive slurry to form a first composite;

S400, apply the protective slurry on the surface of the first composite body to form a positive electrode composite body,

S500, heat-treat the positive electrode composite to solidify the positive electrode composite to form a positive electrode piece, wherein,

The conductive slurry is cured to form a conductive layer, and the conductive layer is disposed on at least one surface of the support layer;

The dry cathode powder forms a cathode film layer, the cathode film layer is arranged on the surface of the conductive layer away from the support layer, and the cathode film layer includes cathode active material;

The protective slurry solidifies to form a protective layer, which is at least disposed on the surface of the positive electrode film layer away from the support layer.

In this application, after the dry positive electrode powder is placed on the conductive slurry and the protective slurry is placed on the dry positive electrode powder, the positive electrode piece can be formed through one-time thermal compounding. The preparation method is simple, and the formed positive electrode piece It has high structural stability, and when applied to secondary batteries, it can significantly improve the cycle performance and storage performance of secondary batteries.

In some embodiments, in S200, a brushing or spraying process may be used to apply the conductive slurry on at least one surface of the support layer. The brushing or spraying process is faster to produce and can control the coating size accurately. Brushing can be done with a coating machine, and the coating width and coating weight can be set according to process requirements. Spraying can be done with a dry powder sprayer, and the amount of spray liquid can be set according to process requirements.

In some embodiments, in S400, a spraying process is used to coat the protective slurry on the surface of the first composite body. The protective slurry is sprayed onto the positive electrode powder using a spraying process. The protective slurry can penetrate into the inside of the positive electrode film layer, thereby improving the adhesion within the positive electrode film layer and the adhesion between the positive electrode film layer and the protective layer. force.

Spraying can be done with a dry powder sprayer, and the amount of spray liquid can be set according to process requirements.

In some embodiments, in S300, the dry cathode powder is charged or magnetized, and the charged or magnetized dry cathode powder is coated on the support layer coated with the conductive slurry. On the surface. After the dry cathode powder is charged or magnetized, the particles have the same charge or magnetic field, and the particles generate mutual repulsion, so that the dry cathode powder can be evenly distributed on the conductive slurry.

In some embodiments, the conductive paste has a solid content of 10%-25%. When the solid content of the conductive slurry is within the above range, it is more conducive to spraying or brushing of the conductive slurry, and the thickness of the formed conductive slurry is uniform. For example, the solid content of the conductive paste is 10%, 12%, 15%, 18%, 20%, 22% or 25%; or is a range consisting of any two of the above values.

In some embodiments. The solid content of the protective slurry is 4% to 10%. When the solid content of the protective slurry is within the above range, it is more conducive to the spraying of the protective slurry, and the thickness of the formed protective slurry is uniform. For example, the solid content of the protective slurry is 4%, 5%, 6%, 7%, 8%, 9% or 10%; or is a range consisting of any two of the above values.

secondary battery

In a third aspect, this application proposes a secondary battery.

As shown in FIGS. 3 and 4 , the secondary battery 5 includes a positive electrode plate 521 , a negative electrode plate 522 and an isolation film 523 . The isolation film 523 is disposed between the positive electrode plate 521 and the negative electrode plate 522 . The function of isolating the positive electrode piece 521 and the negative electrode piece 522. The positive electrode piece 521 can be the positive electrode piece 521 of any embodiment of the first aspect of the present application, thereby improving the conductivity, cycle performance and storage performance of the secondary battery 5 .

[Negative pole piece]

The negative electrode sheet 522 includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, where the negative electrode film layer includes a negative electrode active material.

As an example, the negative electrode current collector has two opposite surfaces in its own thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, copper foil can 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 base material. The composite current collector can be formed by forming metal materials (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyterephthalate It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, the negative active material may be a negative active material known in the art for batteries. As an example, the negative active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, and the like. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon carbon composites, silicon nitrogen composites and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as battery negative electrode active materials can also be used. Only one type of these negative electrode active materials may be used alone, or two or more types may be used in combination.

In some embodiments, the negative electrode film layer optionally further includes a binder. The binder can be selected from styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polysodium acrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), poly At least one of methacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

In some embodiments, the negative electrode film layer optionally further includes a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

In some embodiments, the negative electrode film layer optionally includes other auxiliaries, such as thickeners (such as sodium carboxymethylcellulose (CMC-Na)) and the like.

In some embodiments, the negative electrode sheet 522 may be prepared by dispersing the above-mentioned components used to prepare the negative electrode sheet 522 , such as negative active materials, conductive agents, binders, and any other components in a solvent (e.g., deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode piece 522 can be obtained.

[Isolation film]

In some embodiments, the secondary battery 5 further includes a separator 523. This application has no particular limitation on the type of isolation membrane 523, and any well-known porous structure isolation membrane 523 with good chemical stability and mechanical stability can be used.

In some embodiments, the material of the isolation membrane 523 can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation film 523 may be a single-layer film or a multi-layer composite film, and is not particularly limited. When the isolation film 523 is a multi-layer composite film, the materials of each layer may be the same or different, and are not particularly limited.

[Electrolyte]

In some embodiments, the secondary battery 5 further includes an electrolyte.

The electrolyte plays a role in conducting metal ions between the positive electrode plate 521 and the negative electrode plate 522. The electrolyte solution in this application can be an electrolyte solution known in the art and used for the secondary battery 5. The electrolyte includes lithium salt and organic solvent.

As an example, the lithium salt may include lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium perchlorate (LiClO ₄ ), lithium hexafluoroarsenate (LiAsF ₆ ), lithium bisfluorosulfonimide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluoromethanesulfonate borate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO ₂ F ₂ ), lithium difluorodioxalate phosphate (LiDFOP) and lithium tetrafluorooxalate phosphate (LiTFOP).

As an example, the organic solvent may include ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dimethyl carbonate, Propyl ester (DPC), methylpropyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), Propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4 - One or a combination of butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl sulfone (ESE).

The electrolyte solution of the present application can be prepared according to conventional methods in this field. For example, additives, solvents, electrolyte salts, etc. can be mixed uniformly to obtain an electrolyte solution. The order of adding each material is not particularly limited. For example, additives, electrolyte salts, etc. can be added to the non-aqueous solvent and mixed evenly to obtain a non-aqueous electrolyte.

In this application, each component and its content in the electrolyte can be determined according to methods known in the art. For example, it can be measured by gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), nuclear magnetic resonance spectroscopy (NMR), or the like.

It should be noted that when testing the electrolyte in this application, freshly prepared electrolyte can be directly obtained, or the electrolyte can be obtained from the secondary battery 5 . An exemplary method of obtaining electrolyte from the secondary battery 5 includes the following steps: discharging the secondary battery 5 to the discharge cutoff voltage (for safety reasons, the battery is generally in a fully discharged state), then centrifuging, and then centrifuging an appropriate amount. The liquid obtained by the treatment is the non-aqueous electrolyte. The non-aqueous electrolyte can also be obtained directly from the liquid filling port of the secondary battery 5 .

In some embodiments, the positive electrode piece 521 , the negative electrode piece 522 and the isolation film 523 can be formed into the electrode assembly 52 through a winding process or a lamination process.

In some embodiments, the secondary battery 5 may include an outer packaging. The outer packaging can be used to package the above-mentioned electrode assembly 52 and electrolyte.

In some embodiments, the outer packaging of the secondary battery 5 may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery 5 may also be a soft bag, such as a bag-type soft bag. The material of the soft bag may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, polybutylene succinate, and the like.

This application has no particular limitation on the shape of the secondary battery, which can be cylindrical, square or any other shape. FIG. 4 shows an example of a square-structured secondary battery 5 .

In some embodiments, as shown in FIGS. 4 and 5 , the outer package may include a housing 51 and a cover 53 . The housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The housing 51 has an opening communicating with the accommodation cavity, and the cover plate 53 is used to cover the opening to close the accommodation cavity. The positive electrode piece, the negative electrode piece and the isolation film can be formed into the electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is packaged in the containing cavity. The electrolyte soaks into the electrode assembly 52 . The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and can be adjusted according to needs.

The method for producing the secondary battery of the present application is well known. In some embodiments, the positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte may be assembled to form a secondary battery. As an example, the positive electrode sheet, isolation film, and negative electrode sheet can be formed into an electrode assembly through a winding process or a lamination process. The electrode assembly is placed in an outer package, dried, and then injected with electrolyte. After vacuum packaging, standing, and Through processes such as formation and shaping, secondary batteries are obtained.

In some embodiments of the present application, the secondary batteries according to the present application can be assembled into a battery module. The number of secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

FIG. 6 is a schematic diagram of the battery module 4 as an example. As shown in FIG. 6 , in the battery module 4 , a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4 . Of course, it can also be arranged in any other way. Furthermore, the plurality of secondary batteries 5 can be fixed by fasteners.

Optionally, the battery module 4 may further include a housing having a receiving space in which a plurality of secondary batteries 5 are received.

In some embodiments, the above-mentioned battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

7 and 8 are schematic diagrams of the battery pack 1 as an example. As shown in FIGS. 7 and 8 , the battery pack 1 may include a battery box and a plurality of battery modules 4 arranged in the battery box. The battery box includes an upper box 2 and a lower box 3 . The upper box 2 is used to cover the lower box 3 and form a closed space for accommodating the battery module 4 . Multiple battery modules 4 can be arranged in the battery box in any manner.

electrical device

In a fourth aspect, the present application provides an electrical device. The electrical device includes at least one of a secondary battery, a battery module and a battery pack of the present application. Secondary batteries, battery modules and battery packs can be used as power sources for power-consuming devices, and can also be used as energy storage units for power-consuming devices. Electric devices can be, but are not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, and electric golf balls). vehicles, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

The electrical device can select secondary batteries, battery modules or battery packs according to its usage requirements.

FIG. 9 is a schematic diagram of an electrical device as an example. The electric device 6 is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or the like. In order to meet the demand for high power and high energy density of the electrical device, a battery pack 1 or a battery module can be used.

As another example, the power-consuming device may be a mobile phone, a tablet computer, a laptop computer, etc. The electrical device is usually required to be light and thin, and secondary batteries can be used as power sources.

Example

The following examples more specifically describe the disclosure of the present application. These examples are for illustrative purposes only, since it will be apparent to those skilled in the art that various modifications and changes can be made within the scope of the disclosure of the present application. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods, and can be directly were used without further processing and the equipment used in the examples is commercially available.

1. Preparation of positive electrode pieces

A 5 μm PET base film is used as the supporting layer, and conductive slurry is sprayed on the PET base film. The conductive slurry includes the binder styrene-butadiene rubber (SBR) and the conductive agent carbon black (Super P).

Charge the dry powder of the positive active material NCM333 with a positive charge. Add a magnetic field between the spraying port of the active material NCM333 and the PET base film, so that when the dry powder is sprayed, electric field force and magnetic field force are formed, and the electric field force and magnetic field force are evenly hit on the surface of the conductive slurry and Inside; the mass ratio of active material NCM333 and conductive paste is 96:4.

Spray the protective slurry onto the outside of the dry powder. The protective slurry can penetrate between the dry powder particles and further fill the pores in the dry powder. The protective slurry includes the binder styrene-butadiene rubber (SBR) and the conductive agent carbon black (Super P).

The above structure is dried and rolled to obtain a positive electrode piece.

2. Preparation of negative electrode pieces

A copper foil with a thickness of 8 μm was used as the negative electrode current collector.

Thoroughly stir and mix the negative active material graphite, binder styrene-butadiene rubber (SBR), and conductive agent carbon black (Super P) in an appropriate amount of solvent deionized water at a weight ratio of 95:2:3 to form a uniform negative electrode slurry; The negative electrode slurry is evenly coated on the surface of the negative electrode current collector copper foil, and after drying and cold pressing, a negative electrode piece is obtained.

3. Isolation film

A porous polyethylene (PE) film is used as the isolation membrane.

4. Preparation of electrolyte

In an environment with a water content of less than 10 ppm, the non-aqueous organic solvents ethylene carbonate EC and diethyl carbonate DMC are mixed at a volume ratio of 1:1 to obtain an electrolyte solvent, and then the lithium salt and the mixed solvent are mixed to form The electrolyte with a lithium salt concentration of 1mol/L.

5. Preparation of secondary batteries

Stack the above-mentioned positive electrode piece, isolation film and negative electrode piece in order so that the isolation film is between the positive electrode piece and the negative electrode piece to play an isolation role, and then wind it to obtain the electrode assembly; place the electrode assembly in the outer packaging shell After drying, the electrolyte is injected, and through processes such as vacuum packaging, standing, formation, and shaping, a lithium-ion battery is obtained.

Example 2

Embodiment 2-1 and Embodiment 2-2 prepare secondary batteries according to a method similar to Embodiment 1. The difference from Embodiment 1 is that Embodiment 2-1 and Embodiment 2-2 adjust the first adhesiveness of the conductive layer. The mass content of the binder is A1.

Example 3

Examples 3-1 and 3-2 prepared secondary batteries in a similar manner to Example 1. The difference from Example 1 is that Examples 3-1 and 3-2 adjusted the second adhesion of the protective layer. The mass content of the binder is B1.

Example 4

Examples 4-1 to 4-5 prepare secondary batteries in a similar manner to Example 1. The difference from Example 1 is that in Examples 4-1 to 4-5, the conductive layer and the protective layer are adjusted at least The thickness of one can be adjusted specifically by adjusting the coating amount of conductive slurry and the spraying amount of protective slurry.

Comparative example 1

Comparative Example 1 A secondary battery was prepared in a similar manner to Example 1. The difference from Example 1 is that Comparative Example 1 adjusted the preparation method of the positive electrode sheet. The preparation method was as follows: an aluminum foil with a thickness of 12 μm was used as the positive electrode current collector. Mix the cathode active material NCM333, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) in an appropriate amount of solvent NMP in a weight ratio of 97.5:1.4:1.1 to form a uniform cathode slurry; It is evenly coated on the surface of the positive electrode current collector aluminum foil, and after drying and cold pressing, the positive electrode piece is obtained.

The parameters of Examples 1 to 4 and Comparative Examples are shown in Table 1.

Table 1

test part

1. Positive electrode piece resistance performance test

Take the positive electrode sheet of each example and comparative example and cut it into a test sample with an area of 4cm*25cm (longitudinal). After cleaning the probe, perform a pressure test. After calibrating the instrument, enter the parameters into the internal resistance meter, place the pole piece in the middle of the probe, and test 20 test points as a group.

2. Secondary battery cycle performance test

At 25°C, the secondary batteries prepared in each Example and Comparative Example were charged at a constant current rate of 1C to a charge cut-off voltage of 4.30V, then charged at a constant voltage to a current ≤ 0.05C, left to stand for 10 minutes, and then charged at a constant current rate of 1C. Discharge to the discharge cut-off voltage of 3.3V and let it sit for 10 minutes. This is a charge and discharge cycle. According to this method, the battery is tested for 1000 charge and discharge cycles, and the corresponding discharge capacity retention rate is recorded.

3. Secondary battery storage performance test

At 25°C, the secondary batteries prepared in each Example and Comparative Example were charged at a constant current rate of 1C to a charge cutoff voltage of 4.35V, and then charged at a constant voltage to a current of ≤0.05C, and then transferred to a 60°C environment. stored in. After 180 days of storage, place the secondary battery again at 25°C, charge at a constant current rate of 1C to a charge cut-off voltage of 4.35V, then charge at a constant voltage to a current ≤0.05C, and then discharge at a constant current rate of 1C to a discharge cut-off voltage of 2.8V. , record the discharge capacity retention rate of the secondary battery after 180 days of storage.

4. Test of shear strength of positive electrode pieces

The testing process is as follows:

Cut the double-sided tape about 60mm long and stick the tape along the MD direction of the pole piece. Use the blade to cut the pole piece along the edge of the double-sided tape. The double-sided tape is bonded to the steel plate. The distance between the bottom edge of the tape and the bottom edge of the steel plate is >1cm. Place the steel plate in an oven at 60-80°C for 5 minutes. Take out the steel plate and gently scrape off the release paper on the upper layer of the tape with a blade. Turn on the power of the tensile machine, the indicator light will be on, and adjust the limit block to the appropriate position. Clamp the pole piece to be tested in a suitable position and zero the instrument to start testing.

Test Results

The effect of this application on improving the performance of secondary batteries is shown in Table 2.

Table 2

Comparative Example 1 does not use a conductive layer, and the positive electrode film layer is directly compounded on the positive electrode current collector. There is a risk of separation between the two, resulting in deterioration of the cycle performance of the secondary battery.

In the embodiment of the present application, a conductive layer is provided, the dry powder is adhered to the conductive layer, and a protective layer is further provided outside the dry powder to cover the dry powder. The positive electrode piece thus formed has high stability and is not easy to separate from the layers. The shear strength of the positive electrode piece is increased, and can improve the cycle performance and storage performance of the secondary battery; and the surface resistance of the positive electrode piece with this structure is higher, which is conducive to further improving the electrochemical performance of the secondary battery.

While the present application has been described with reference to preferred embodiments, various modifications may be made and equivalents may be substituted for components thereof without departing from the scope of the application. In particular, as long as there is no structural conflict, the technical features mentioned in the various embodiments can be combined in any way. The application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims (19)

A positive electrode plate includes: A positive electrode current collector, which includes a support layer and a conductive layer disposed on at least one surface of the support layer; A positive electrode film layer, which is disposed on the surface of the conductive layer away from the support layer, the positive electrode film layer is formed by dry positive electrode powder containing a positive electrode active material; and A protective layer is provided at least on the surface of the positive electrode film layer away from the support layer. The positive electrode plate according to claim 1, wherein, The support layer includes one or more layers of an organic polymer layer and a metal layer; Optionally, the material of the organic polymer layer includes one or more of polyethylene terephthalate PET, polyvinyl chloride PVC, polyimide PI and polyacrylonitrile PAN; Optionally, the metal layer is made of aluminum or aluminum alloy. The positive electrode piece according to claim 1 or 2, wherein the conductive layer includes: The first binder has a mass content of A ₁ % relative to the total mass of the conductive layer; The first conductive agent has a mass content of A ₂ % relative to the total mass of the conductive layer, The conductive layer satisfies: 0.10≤A ₁ /A ₂ ≤0.45. The positive electrode plate according to claim 3, wherein 10≤A ₁ ≤30; and/or 70≤A ₂ ≤90. The positive electrode plate according to claim 3 or 4, wherein, The first adhesive includes a water-based adhesive and/or an oil-based adhesive; Optionally, the water-based binder includes one or more of polyacrylic acid PAA, polyoxyethylene PEO and propanol-based compounds; Optionally, the oily binder includes polyvinylidene fluoride (PVDF) homopolymer or copolymer thereof. The positive electrode plate according to any one of claims 3 to 5, wherein, The first conductive agent includes one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers. The positive electrode plate according to any one of claims 1 to 6, wherein the protective layer includes: The mass content of the second binder relative to the total mass of the protective layer is B ₁ %; The mass content of the second conductive agent relative to the total mass of the protective layer is B ₂ %, The protective layer satisfies: 30≤B ₁ /B ₂ ≤999. The positive electrode plate according to claim 7, wherein 97≤B ₁ ≤99.9; and/or 0.1≤B ₂ ≤3. The positive electrode plate according to claim 7 or 8, wherein, The second adhesive includes a water-based adhesive and/or an oil-based adhesive; Optionally, the water-based binder includes one or more of polyacrylic acid PAA, polyoxyethylene PEO and propanol-based compounds; Optionally, the oily binder includes polyvinylidene fluoride (PVDF) homopolymer or copolymer thereof. The positive electrode plate according to any one of claims 7 to 9, wherein, The second conductive agent includes one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers. The positive electrode sheet according to any one of claims 1 to 10, wherein the positive electrode film layer includes: The mass content of the cathode active material relative to the cathode film layer is C ₁ %, The third conductive agent has a mass content of C ₂ % relative to the positive electrode film layer, The positive electrode film layer satisfies: 15≤C ₁ /C ₂ ≤99; Optionally, 95≤C ₁ ≤99; and/or 1 ≤ C ₂ ≤5. The positive electrode sheet according to any one of claims 1 to 11, wherein part of the protective layer is embedded in the positive electrode film layer. The positive electrode piece according to any one of claims 1 to 12, wherein the positive electrode piece further satisfies one or more of conditions (1) to (3): (1) The thickness of the support layer is L ₁ μm, the thickness of the conductive layer is L ₂ μm, 0.5≤L ₁ /L ₂ ≤1; (2) The thickness of the conductive layer is L ₂ μm, the thickness of the positive electrode film layer is L ₃ μm, 0.2≤L ₂ /L ₃ ≤1; (3) The thickness of the protective layer is L ₄ μm, the thickness of the positive electrode film layer is L ₃ μm, and 0.01≤L ₄ /L ₃ ≤0.1. A method of preparing a positive electrode plate, including: S100, which provides a support layer; S200, apply conductive slurry on at least one surface of the support layer; S300, apply dry cathode powder on the surface of the support layer coated with the conductive slurry to form a first composite; S400, apply protective slurry on the surface of the first composite to form a positive electrode composite, S500, heat-treat the positive electrode composite to solidify the positive electrode composite to form a positive electrode piece, wherein, The conductive slurry is cured to form a conductive layer, and the conductive layer is disposed on at least one surface of the support layer; The dry cathode powder forms a cathode film layer, the cathode film layer is disposed on the surface of the conductive layer away from the support layer, and the cathode film layer includes a cathode active material; The protective slurry solidifies to form a protective layer, which is at least disposed on the surface of the positive electrode film layer away from the support layer. The positive electrode plate according to claim 14, wherein, The solid content of the conductive slurry is 10%-25%; and/or The solid content of the protective slurry is 4% to 10%. The positive electrode plate according to claim 14 or 15, wherein, In S200, apply the conductive slurry on at least one surface of the support layer using a brushing or spraying process; and/or In S400, a spraying process is used to apply protective slurry on the surface of the first composite body. The positive electrode plate according to any one of claims 14 to 16, wherein, In S300, the dry cathode powder is charged or magnetized, and the charged or magnetized dry cathode powder is coated on the support layer coated with the conductive slurry. On the surface. A secondary battery including the positive electrode piece according to any one of claims 1 to 13 or the positive electrode piece obtained by the method according to any one of claims 14 to 17. An electrical device including the secondary battery according to claim 18.

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