WO2024011465A1

WO2024011465A1 - Positive electrode sheet and preparation method therefor, battery cell, battery, and electric device

Info

Publication number: WO2024011465A1
Application number: PCT/CN2022/105564
Authority: WO
Inventors: 裴海乐; 程丛; 陈均桄; 杨丙梓; 张盛武; 王星会
Original assignee: 宁德时代新能源科技股份有限公司
Priority date: 2022-07-13
Filing date: 2022-07-13
Publication date: 2024-01-18
Also published as: CN117716540A

Abstract

A positive electrode sheet and a preparation method therefor, a battery cell, a battery, and an electric device, relating to the field of batteries. A positive electrode sheet (24) comprises a current collector (240), an aqueous conductive coating, and an electrode layer (243). The aqueous conductive coating comprises a first aqueous conductive coating (241) and a second aqueous conductive coating (242). The first aqueous conductive coating (241) is located on the side of the second aqueous conductive coating (242) facing the current collector (240). The peel force between the first aqueous conductive coating (241) and the current collector (240) is greater than or equal to 50 N/M. The second aqueous conductive coating (242) is soluble in water, and has a dissolution time greater than or equal to 200 s in ultrasonic cleaning. The peel force between the electrode layer (243) and the second aqueous conductive coating (242) is greater than or equal to 40 N/M. The positive electrode sheet (24) can mitigate the problem of poor cycling stability of existing batteries using aqueous positive electrodes.

Description

Positive electrode plate and preparation method thereof, battery cell, battery and electrical equipment

Technical field

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

Background technique

Existing lithium batteries are mostly using oil-based formulas. However, with the development of battery technology and the demand for green environmental protection, lithium battery cathodes are gradually turning to environmentally friendly and pollution-free water-based cathodes.

Aqueous positive electrodes include active materials and current collectors. However, insufficient wettability between the current collector interface and the active material results in a limited contact area between the active material particles and the aluminum foil, which will increase the interface resistance and cause an increase in the internal resistance of the battery, which has a negative impact on battery performance. Therefore, it is necessary to apply a layer of water-based conductive coating on the surface of the current collector to tightly bond the current collector and the active material to ensure adhesion and conductivity.

Existing aqueous cathode batteries have poor cycle stability.

Contents of the invention

This application provides a positive electrode plate and its preparation method, battery cells, batteries and electrical equipment, which can improve the problem of poor cycle stability of existing water-based positive electrode batteries.

In a first aspect, embodiments of the present application provide a positive electrode sheet, which includes a current collector, an aqueous conductive coating and an electrode layer. The aqueous conductive coating includes a first aqueous conductive coating and a second aqueous conductive coating. The first aqueous conductive coating The conductive coating is located on the side of the second aqueous conductive coating facing the current collector; the peeling force between the first aqueous conductive coating and the current collector is ≥50N/M; the second aqueous conductive coating is soluble in water and cleaned by ultrasonic waves. The dissolution time is ≥200s, and the peeling force between the electrode layer and the second aqueous conductive coating is ≥40N/M.

In the technical solution of the embodiment of the present application, the water-based conductive coating is arranged in layers, and the peeling force between the first water-based conductive coating and the current collector is ≥50N/M to ensure the adhesion between the water-based conductive coating and the current collector. Relay, since the second water-based conductive coating is located between the first conductive coating and the electrode layer, and during the actual production process, the drying time of the pole piece is about >3 minutes. If the drying speed is too fast, it is easy to cause extreme The film is cracked, so the second aqueous conductive coating is soluble in water and the dissolution time of ultrasonic cleaning is ≥ 200s, so that the second aqueous conductive coating has good water resistance, so that the aqueous conductive coating is used for water-based positive electrodes. During preparation, it can avoid the problem that the conductive coating is dissolved by the water in the cathode slurry forming the electrode layer during the preparation process, causing the resistance of the water-based cathode to increase and the coating to peel off, thereby effectively improving the tightness between the electrode layer and the current collector. It improves the compatibility and electrical connectivity of the battery, improving the cycle stability and capacity retention rate of the battery.

Optionally, the peeling force between the first aqueous conductive coating and the current collector is ≥54N/M.

In some embodiments, the cross-linking degree of the first aqueous conductive coating is 0, and the cross-linking degree of the second aqueous conductive coating is >0. Since the water-based conductive coating contains a water-based binder, using a cross-linking agent to cross-link the water-based binder will change the structure of the water-based binder, improve its solvent resistance and reduce the adhesive force. Therefore, the above method is used to use the second The cross-linking degree of a water-based conductive coating is 0, that is, the first water-based conductive coating is not cross-linked to provide better adhesion. The cross-linking degree of the second water-based conductive coating is >0, so that it has good adhesion. The water resistance can avoid the conductive coating being dissolved by the water in the cathode slurry forming the electrode layer during the preparation process, causing the water-based cathode resistance to increase and the coating to peel off, and improve the close contact between the electrode layer and the current collector. properties and electrical connectivity, improving the cycle stability and capacity retention rate of the battery.

In some embodiments, the cross-linking degree of the second aqueous conductive coating gradually decreases from a side close to the electrode layer to a side close to the first aqueous conductive coating. That is to say, the water resistance of the side of the second aqueous conductive coating close to the electrode layer is better than that of the side close to the first aqueous conductive coating, and the adhesiveness of the side of the second aqueous conductive coating close to the electrode layer is better. The bonding force is better than the side close to the first water-based conductive coating, thereby effectively enhancing the second water-based conductive coating and the first water-based conductive coating on the premise of achieving the water resistance of the second water-based conductive coating. the adhesive force between them.

In some embodiments, the method for determining the dissolution time of the second aqueous conductive coating during ultrasonic cleaning is as follows: place the positive electrode piece without an electrode layer in water, ultrasonic clean it under the conditions of a wave source distance of 50 mm to 55 mm and a wave source frequency of 25 KHZ. The moment when the positive electrode piece is observed to be exposed from the current collector is defined as the second aqueous conductive coating being dissolved, and the time from the start of ultrasonic cleaning to the dissolution of the second aqueous conductive coating is taken as the dissolution time of the ultrasonic cleaning of the second aqueous conductive coating. Since the first aqueous conductive coating is not water-resistant, the first conductive coating can be instantly dissolved in water during the ultrasonic cleaning process, without causing an error in the dissolution time of the second aqueous conductive coating.

In some embodiments, the thickness of the second aqueous conductive coating is less than the thickness of the first aqueous conductive coating, and the thickness of the second aqueous conductive coating is 0.3-0.7 μm. The above thickness ratio is reasonable, which can not only achieve the stability of the connection between the water-based conductive coating and the current collector, but also make the water-based conductive coating have good water resistance and meet actual needs. If the thickness of the second water-based conductive coating accounts for If the ratio is too large, the adhesion between the water-based conductive coating and the current collector will be small and it will be easily peeled off. If the thickness of the second water-based conductive coating is too small, the water-based conductive coating will not have enough water resistance. The conductive coating is dissolved by the water in the cathode slurry forming the electrode layer during the preparation process, causing the water-based cathode resistance to increase and the coating to peel off.

Optionally, the thickness of the aqueous conductive coating is 1-5 μm. The thickness of the water-based conductive coating is restricted. On the premise of ensuring that the conductive performance of the water-based conductive coating is fully utilized, the thickness of the water-based conductive coating is reduced. When the thickness of the positive electrode plate is constant, an additional current collector is installed. The thickness of the positive electrode layer on the positive electrode increases the energy density of the positive electrode piece.

In some embodiments, the resistance change rate is the result of dividing the resistance standard deviation by the resistance average value, and the resistance change rate of the aqueous conductive coating is ≤10%. That is to say, the resistance of the water-based conductive coating is basically evenly distributed, improving the performance consistency of the positive electrode piece.

In some embodiments, the thickness change rate is a result of dividing the thickness standard deviation by the thickness average, and the thickness change rate of the aqueous conductive coating is ≤10%. That is to say, the thickness of the water-based conductive coating is basically evenly distributed everywhere, improving the performance consistency of the positive electrode piece.

In a second aspect, this application provides a method for preparing the above-mentioned positive electrode sheet, which includes the following steps: forming an aqueous conductive coating on the surface of the current collector; coating the surface of the aqueous conductive coating with a positive electrode slurry, and drying to obtain Positive pole piece.

In the technical solution of the embodiment of the present application, the positive electrode sheet is obtained by first forming a water-based conductive coating, and then forming a positive electrode sheet on the surface of the water-based conductive coating. The preparation method is simple, and the obtained positive electrode sheet can effectively improve the electrode layer. The adhesion and electrical connectivity with the current collector improve the cycle stability and capacity retention rate of the battery.

In some embodiments, the step of forming an aqueous conductive coating on the surface of the current collector includes: coating an aqueous conductive slurry containing an aqueous binder on the surface of the current collector, and drying to form a pre-aqueous conductive coating; The surface of the coating is coated with a cross-linking agent aqueous solution and dried to form a water-based conductive coating. In the above steps, since the cross-linking agent aqueous solution is coated on the surface of the pre-water-based conductive coating and dried to form the water-based conductive coating, cross-linking of the conductive slurry after the cross-linking agent is added to the conductive slurry is effectively avoided. The reaction affects the stability of the conductive slurry, resulting in uneven thickness and resistance distribution of the formed water-based conductive coating, which cannot ensure the uniformity of the performance of the positive electrode piece.

In some embodiments, by mass percentage, the aqueous conductive slurry includes: conductive material 5%-15%, colloidal dispersant 0.1%-2%, aqueous binder 2%-10%, and water 80%-90% %. Within the above ratio range, the water-based conductive coating formed by the water-based conductive slurry has good electrical properties.

In some embodiments, the water-based binder is a water-soluble polymer with carboxyl groups. The binder is a water-soluble polymer with carboxyl groups. The cross-linking agent combines and cross-links with part of the carboxyl groups in the water-based binder, so that the molecular chain of the binder changes from linear to a stronger three-dimensional network structure. This improves the water resistance of the water-based conductive coating. At the same time, the carboxyl group serves as a hydrophilic group. When the water-based cathode slurry is subsequently coated on the conductive coating, it can better ensure the infiltration of the water-based cathode slurry on the water-based conductive coating. The spreading and bonding effects ensure the low resistance and high bonding force of the water-based conductive coating on the current collector.

In some embodiments, the water-based binder includes at least one of polyacrylic acid and its salts, water-soluble polyacrylate and salts, water-soluble ethylene vinyl acetate copolymer, and acrylonitrile multi-copolymer. The water-based conductive slurry containing the above-mentioned water-based binder not only has good wettability with the current collector and can be evenly coated on the current collector, but also has good wetting, spreading and bonding effects with the water-based cathode slurry subsequently, ensuring Low resistance and high adhesion of water-based conductive coating on current collector.

In some embodiments, the cross-linking agent in the cross-linking agent aqueous solution includes aziridine and its derivatives, polycarbodiimide and its salts, epoxy silane and its derivatives, and polymer grafted epoxy silane. One or more types of polyethylenimines. The above-mentioned cross-linking agent can combine and cross-link with part of the carboxyl groups in the water-based binder, so that the binder molecular chain changes from linear to a stronger three-dimensional network structure, thereby improving the water resistance of the conductive coating layer.

In some embodiments, the mass fraction of the cross-linking agent in the cross-linking agent aqueous solution is greater than 3% and not greater than 25%, optionally 10%-20%. Within the above range, the mass fraction of the cross-linking agent in the cross-linking agent aqueous solution is reasonable, so that the water-based conductive coating can meet the requirements for water resistance and adhesion.

In some embodiments, the conductive material includes at least one of carbon black, graphite, partially graphitized coke, carbon fiber, acetylene black, vapor grown carbon fiber, and fullerene nanotubes. The above-mentioned conductive materials are easy to obtain and have good conductive effects.

In some embodiments, the colloidal material is at least one of xanthan gum, locust bean gum, guar gum, arabic gum, gelatin, and carrageenan. The above-mentioned colloidal dispersant is easy to obtain, and has a good dispersion effect in uniformly dispersing the conductive material in the aqueous conductive slurry.

In some embodiments, the drying temperature to form the pre-aqueous conductive coating is 70°C-120°C, and the time is 10s-60s. Within the above temperature and time range, the pre-aqueous conductive coating can be effectively dried.

In some embodiments, the temperature for drying to form the aqueous conductive coating is 70°C-120°C, and the time is 10s-60s. Within the above temperature and time range, the cross-linking agent and the water-based binder can be effectively reacted and solidified to form a water-based conductive coating.

In a third aspect, the present application provides a battery cell, which includes the positive electrode plate in the above embodiment.

In a fourth aspect, the present application provides a battery, which includes the battery cell in the above embodiment.

In a fifth aspect, the present application provides an electrical device, which includes the battery in the above embodiment, and the battery is used to provide electrical energy.

The above description is only an overview of the technical solutions of the present application. In order to have a clearer understanding of the technical means of the present application, they can be implemented according to the content of the description, and in order to make the above and other purposes, features and advantages of the present application more obvious and understandable. , the specific implementation methods of the present application are specifically listed below.

Description of drawings

Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are for the purpose of illustrating preferred embodiments only and are not to be construed as limiting the application. Also, the same parts are represented by the same reference numerals throughout the drawings. In the attached picture:

Figure 1 is a schematic structural diagram of a vehicle according to some embodiments of the present application;

Figure 2 is a schematic diagram of the exploded structure of a battery according to some embodiments of the present application;

Figure 3 is a schematic diagram of the exploded structure of a battery cell according to some embodiments of the present application;

Figure 4 is a schematic structural diagram of a positive electrode plate according to some embodiments of the present application;

Figure 5 is a cross-sectional high-magnification SEM image of the water-based conductive coating in Example 1 of the present application;

Figure 6 is a low-magnification SEM image of the positive electrode plate provided in Example 1;

Figure 7 is a low-magnification SEM image of the cross-section of the positive electrode sheet of Comparative Example 1 of the present application (the positive electrode sheet includes aluminum foil-water-based conductive coating-positive electrode layer).

The reference numbers in the specific implementation are as follows:

1000-vehicle;

100-battery; 200-controller; 300-motor;

10-box; 11-first part; 12-second part;

20-battery cell; 21-end cover; 21a-electrode terminal; 22-casing; 23-electrode assembly; 23a-pole lug;

24-positive electrode plate; 240-current collector; 241-first aqueous conductive coating; 242-second aqueous conductive coating; 243-electrode layer.

Detailed ways

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

Unless otherwise defined, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the technical field belonging to this application; the terms used herein are for the purpose of describing specific embodiments only and are not intended to be used in Limitation of this application; the terms "including" and "having" and any variations thereof in the description and claims of this application and the above description of the drawings are intended to cover non-exclusive inclusion.

In the description of the embodiments of this application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying the relative importance or implicitly indicating the quantity or specificity of the indicated technical features. Sequence or priority relationship. In the description of the embodiments of this application, "plurality" means two or more, unless otherwise explicitly and specifically limited.

Reference herein to "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment can be included in at least one embodiment of the present application. The appearances of this phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Those skilled in the art understand, both explicitly and implicitly, that the embodiments described herein may be combined with other embodiments.

In the description of the embodiments of this application, the term "and/or" is only an association relationship describing associated objects, indicating that there can be three relationships, such as A and/or B, which can mean: A exists alone, and A exists simultaneously and B, there are three cases of B alone. In addition, the character "/" in this article generally indicates that the related objects are an "or" relationship.

In the description of the embodiments of this application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to two or more groups (including two groups), and "multiple pieces" refers to It is more than two pieces (including two pieces).

In the description of the embodiments of this application, the technical terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "back", "left", "right" and "vertical" The orientation or positional relationships indicated by "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. are based on those shown in the accompanying drawings. The orientation or positional relationship is only for the convenience of describing the embodiments of the present application and simplifying the description. It does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the implementation of the present application. Example limitations.

In the description of the embodiments of this application, unless otherwise clearly stated and limited, technical terms such as "installation", "connection", "connection" and "fixing" should be understood in a broad sense. For example, it can be a fixed connection or a removable connection. It can be disassembled and connected, or integrated; it can also be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be an internal connection between two elements or an interaction between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of this application can be understood according to specific circumstances.

The inventor noticed that during the preparation and use of the aqueous cathode system, the aqueous conductive coating will be dissolved by the water in the cathode slurry, causing the structure of the aqueous conductive coating to be destroyed, and the aqueous conductive coating to peel off from the current collector, thereby causing The water-based conductive coating loses conductivity and bonding, causing the battery resistance to increase or the positive electrode layer to peel off, affecting the performance and safety of the water-based positive electrode battery, and causing the water-based positive electrode battery to have poor cycle stability.

In order to alleviate the problem of poor cycle stability of water-based positive electrode batteries, the applicant found that the water-based conductive coating can be layered to meet the requirements of adhesion and water resistance, thereby solving the problem of poor cycle stability. Specifically, the adhesive force on the side of the conductive coating close to the current collector can be improved to improve the peeling force between the conductive coating and the current collector. In order to prevent the water-based conductive coating from being dissolved by the water in the cathode slurry, the conductivity can be improved. The water resistance of the side of the coating away from the current collector prevents the second aqueous conductive coating from being dissolved.

Based on the above considerations, in order to solve the problem of poor cycle stability of aqueous positive electrode batteries, the inventors conducted in-depth research and designed a positive electrode sheet, which includes a current collector, an aqueous conductive coating and an electrode layer. The aqueous conductive coating includes a first aqueous The conductive coating and the second aqueous conductive coating, the first aqueous conductive coating is located on the side of the second aqueous conductive coating facing the current collector; the peeling force between the first aqueous conductive coating and the current collector is ≥50N/M; The diaqueous conductive coating is soluble in water and the dissolution time of ultrasonic cleaning is ≥200s; the peeling force between the electrode layer and the second aqueous conductive coating is ≥40N/M.

In such a positive electrode piece, the water-based conductive coating is arranged in layers, and the peeling force between the first water-based conductive coating and the current collector is ≥50N/M to ensure the bonding between the water-based conductive coating and the current collector. Since the second aqueous conductive coating is located between the first conductive coating and the electrode layer, the diaqueous conductive coating is soluble in water and the dissolution time of ultrasonic cleaning is ≥ 200s, so that the second aqueous conductive coating has Good water resistance, so that when the water-based conductive coating is used in the preparation of aqueous positive electrodes, it can avoid the conductive coating being dissolved by the water in the positive electrode slurry forming the electrode layer during the preparation process, resulting in an increase in the resistance of the water-based positive electrode. The problem of layer peeling can be effectively improved, thereby effectively improving the adhesion and electrical connectivity between the electrode layer and the current collector, and improving the cycle stability and capacity retention rate of the battery.

The 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 aircrafts. The power supply system of the electrical device can be composed of battery cells, batteries, etc. disclosed in this application, which is beneficial to improving the cycle stability of the battery.

Embodiments of the present application provide an electrical device that uses a battery as a power source. The electrical 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 vehicle, a ship, a spacecraft, etc. Among them, electric toys can include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles, spaceships, etc.

For the convenience of explanation in the following embodiments, an electric device 1000 according to an embodiment of the present application is used as an example.

Please refer to FIG. 1 , which is a schematic structural diagram of a vehicle 1000 provided by some embodiments of the present application. The vehicle 1000 may be a fuel vehicle, a gas vehicle or a new energy vehicle, and the new energy vehicle may be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc. The vehicle 1000 is provided with a lithium ion battery 100 inside, and the lithium ion battery 100 may be provided at the bottom, head, or tail of the vehicle 1000 . The lithium ion battery 100 may be used to power the vehicle 1000 , for example, the lithium ion battery 100 may be used as an operating power source for the vehicle 1000 . The vehicle 1000 may also include a controller 200 and a motor 300. The controller 200 is used to control the lithium ion battery 100 to provide power to the motor 300, for example, for starting, navigation, and operating power requirements of the vehicle 1000 while driving.

In some embodiments of the present application, the lithium-ion battery 100 can not only be used as an operating power source of the vehicle 1000, but also can be used as a driving power source of the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

Please refer to FIG. 2 , which is an exploded view of the lithium-ion battery 100 provided by some embodiments of the present application. The lithium ion battery 100 includes a case 10 and battery cells 20 , and the battery cells 20 are accommodated in the case 10 . Among them, the box 10 is used to provide an accommodation space for the battery cells 20, and the box 10 can adopt a variety of structures. In some embodiments, the box 10 may include a first part 11 and a second part 12 , the first part 11 and the second part 12 cover each other, and the first part 11 and the second part 12 jointly define a space for accommodating the battery cells 20 of accommodation space. The second part 12 may be a hollow structure with one end open, and the first part 11 may be a plate-like structure. The first part 11 covers the open side of the second part 12 so that the first part 11 and the second part 12 jointly define a receiving space. ; The first part 11 and the second part 12 may also be hollow structures with one side open, and the open side of the first part 11 is covered with the open side of the second part 12. Of course, the box 10 formed by the first part 11 and the second part 12 can be in various shapes, such as cylinder, rectangular parallelepiped, etc.

In the lithium-ion battery 100, there may be multiple battery cells 20, and the multiple battery cells 20 may be connected in series, in parallel, or in mixed connection. Mixed connection means that the multiple battery cells 20 are connected in series and in parallel. Multiple battery cells 20 can be directly connected in series or in parallel or mixed together, and then the whole composed of multiple battery cells 20 can be accommodated in the box 10 ; of course, the lithium ion battery 100 can also be multiple battery cells. The body 20 is first connected in series, parallel, or mixed to form a battery module, and then multiple battery modules are connected in series, parallel, or mixed to form a whole, and are accommodated in the box 10 . The lithium ion battery 100 may also include other structures. For example, the lithium ion battery 100 may further include a bus component for realizing electrical connection between multiple battery cells 20 .

Each battery cell 20 may be a secondary battery or a primary battery; it may also be a lithium-sulfur battery, a sodium-ion battery or a magnesium-ion battery, but is not limited thereto. The battery cell 20 may be in the shape of a cylinder, a flat body, a rectangular parallelepiped or other shapes.

Please refer to FIG. 3 , which is an exploded structural diagram of a battery cell 20 provided in some embodiments of the present application. The battery cell 20 refers to the smallest unit that constitutes the battery. As shown in FIG. 3 , the battery cell 20 includes an end cover 21 , a case 22 , an electrode assembly 23 and other functional components.

The end cap 21 refers to a component that covers the opening of the case 22 to isolate the internal environment of the battery cell 20 from the external environment. Without limitation, the shape of the end cap 21 can be adapted to the shape of the housing 22 to fit the housing 22 . Optionally, the end cap 21 can be made of a material with a certain hardness and strength (such as aluminum alloy). In this way, the end cap 21 is less likely to deform when subjected to extrusion and collision, so that the battery cell 20 can have higher durability. Structural strength and safety performance can also be improved. The end cap 21 may be provided with functional components such as electrode terminals 21a. The electrode terminal 21a may be used to electrically connect with the electrode assembly 23 for outputting or inputting electrical energy of the battery cell 20 . In some embodiments, the end cap 21 may also be provided with a pressure relief mechanism for releasing the internal pressure when the internal pressure or temperature of the battery cell 20 reaches a threshold. The end cap 21 can also be made of various materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., which are not particularly limited in the embodiment of the present application. In some embodiments, an insulating member may also be provided inside the end cover 21 , and the insulating member may be used to isolate the electrical connection components in the housing 22 from the end cover 21 to reduce the risk of short circuit. For example, the insulating member may be plastic, rubber, etc.

The housing 22 is a component used to cooperate with the end cover 21 to form an internal environment of the battery cell 20 , wherein the formed internal environment can be used to accommodate the electrode assembly 23 , electrolyte, and other components. The housing 22 and the end cover 21 may be independent components, and an opening may be provided on the housing 22. The end cover 21 covers the opening at the opening to form the internal environment of the battery cell 20. Without limitation, the end cover 21 and the housing 22 can also be integrated. Specifically, the end cover 21 and the housing 22 can form a common connection surface before other components are put into the housing. When it is necessary to encapsulate the inside of the housing 22 At this time, the end cover 21 covers the housing 22 again. The housing 22 can be of various shapes and sizes, such as rectangular parallelepiped, cylinder, hexagonal prism, etc. Specifically, the shape of the housing 22 can be determined according to the specific shape and size of the electrode assembly 23 . The housing 22 may be made of a variety of materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., which are not particularly limited in the embodiments of the present application.

The electrode assembly 23 is a component in the battery cell 20 where electrochemical reactions occur. One or more electrode assemblies 23 may be contained within the housing 22 . The electrode assembly 23 is mainly formed by winding or stacking positive electrode sheets and negative electrode sheets, and a separator is usually provided between the positive electrode sheets and the negative electrode sheets. The portions of the positive electrode sheet and the negative electrode sheet that contain active material constitute the main body of the electrode assembly 23 , and the portions of the positive electrode sheet and the negative electrode sheet that do not contain active material constitute the tabs 23 a respectively. The positive electrode tab and the negative electrode tab can be located together at one end of the main body or respectively located at both ends of the main body. During the charging and discharging process of the battery, the positive active material and the negative active material react with the electrolyte, and the tab 23a is connected to the electrode terminal 21a to form a current loop.

Please refer to Figure 4. According to some embodiments of the present application, the positive electrode piece 24 includes a current collector 240, an aqueous conductive coating and an electrode layer 243. The aqueous conductive coating includes a first aqueous conductive coating 241 and a second aqueous conductive coating. 242, the first aqueous conductive coating 241 is located on the side of the second aqueous conductive coating 242 facing the current collector 240; the peeling force between the first aqueous conductive coating 241 and the current collector 240 is ≥50N/M; the second aqueous conductive coating 242 The coating 242 is soluble in water and the dissolution time of ultrasonic cleaning is ≥ 200 s; the peeling force between the electrode layer 243 and the second aqueous conductive coating 242 is ≥ 40 N/M.

The aqueous conductive coating means that the corresponding solvent of the slurry forming the aqueous conductive coating is water.

The dissolution time of the second aqueous conductive coating 242 during ultrasonic cleaning refers to: the second aqueous conductive coating 242 has a first side and a second side, and the first side is located on the side of the second side away from the first aqueous conductive coating 241, The total time required for the first surface to be exposed to water and then ultrasonic cleaned to dissolve the second aqueous conductive coating 242 from the first surface to the second surface and to dissolve the second surface.

In the technical solution of the embodiment of the present application, the water-based conductive coating is arranged in layers, and the peeling force between the first water-based conductive coating 241 and the current collector 240 is ≥50 N/M to ensure that the water-based conductive coating and the current collector 240 Since the second aqueous conductive coating 242 is located between the first conductive coating and the electrode layer 243, the second aqueous conductive coating 242 is soluble in water and the dissolution time of ultrasonic cleaning is ≥ 200 s. The second aqueous conductive coating 242 is made to have good water resistance, so that when the aqueous conductive coating is used in the preparation of an aqueous cathode, the conductive coating can be prevented from being formed in the cathode slurry of the electrode layer 243 during the preparation process. Water dissolution causes the water-based positive electrode resistance to increase and the coating to peel off, thereby effectively improving the adhesion and electrical connectivity between the electrode layer 243 and the current collector 240, and improving the cycle stability and capacity retention rate of the battery 100. The peeling force between the electrode layer and the second aqueous conductive coating is ≥40N/M, which can prevent the electrode layer and the second aqueous conductive coating from separating from each other and affecting the stability of the positive electrode piece.

Referring to Figure 4, according to some embodiments of the present application, optionally, the cross-linking degree of the first aqueous conductive coating 241 is 0, and the cross-linking degree of the second aqueous conductive coating 242 is >0.

Cross-linking refers to using a cross-linking agent to couple two or more molecules respectively so that these molecules are combined together.

The degree of cross-linking, also known as the cross-linking index, is usually expressed by the cross-linking density or the number average molecular weight between two adjacent cross-linking points or the number of moles per cubic centimeter of cross-linking points.

The cross-linking degree of the first aqueous conductive coating 241 is 0, that is, the first aqueous conductive coating 241 is not cross-linked, and the cross-linking degree of the second aqueous conductive coating 242 is >0, that is, the second aqueous conductive coating 242 is not cross-linked. Layer 242 has cross-links.

Since the water-based conductive coating contains a water-based binder, using a cross-linking agent to cross-link the water-based binder will change the structure of the water-based binder, improve its solvent resistance and reduce the adhesive force. Therefore, the above method is used to use the second The cross-linking degree of the first aqueous conductive coating 241 is 0, that is, the first aqueous conductive coating 241 is not cross-linked to provide better adhesion. The cross-linking degree of the second aqueous conductive coating 242 is >0, so that It has good water resistance, which can avoid the conductive coating being dissolved by the water in the cathode slurry forming the electrode layer 243 during the preparation process, causing the water-based cathode resistance to increase and the coating to peel off, and improve the connection between the electrode layer 243 and the current collector. The adhesion and electrical connectivity between 240 improve the cycle stability and capacity cycle retention rate of the battery 100 .

Referring to FIG. 4 , in some embodiments, the cross-linking degree of the second aqueous conductive coating 242 gradually decreases from the side close to the electrode layer 243 to the side close to the first aqueous conductive coating 241 .

That is to say, the water resistance of the side of the second aqueous conductive coating 242 close to the electrode layer 243 is better than that of the side close to the first aqueous conductive coating 241 , and the second aqueous conductive coating 242 is close to the electrode layer 243 The adhesion force on one side is better than that on the side close to the first aqueous conductive coating 241, thereby effectively enhancing the second aqueous conductive coating on the premise of achieving the water resistance of the second aqueous conductive coating 242. 242 and the first aqueous conductive coating 241.

According to some embodiments of the present application, optionally, the method for determining the dissolution time of the second aqueous conductive coating in ultrasonic cleaning is: placing the positive electrode piece without an electrode layer in water, at a wave source distance of 50 mm to 55 mm, and a wave source frequency of 25 KHZ Under ultrasonic cleaning conditions, the moment when the positive electrode piece is exposed to the current collector is defined as the second aqueous conductive coating being dissolved, and the time from starting ultrasonic cleaning to the time when the second aqueous conductive coating is dissolved is regarded as the second aqueous conductive coating. Dissolution time for ultrasonic cleaning.

Since the first aqueous conductive coating is not water-resistant, the first conductive coating can be instantly dissolved in water during the ultrasonic cleaning process, without causing an error in the dissolution time of the second aqueous conductive coating.

Referring to Figure 4, according to some embodiments of the present application, optionally, the thickness of the second aqueous conductive coating 242 is smaller than the thickness of the first aqueous cathode coating 241, and the thickness of the second aqueous conductive coating 242 is 0.3-0.7 μm.

The above thickness ratio is reasonable, which can not only achieve the stability of the connection between the water-based conductive coating and the current collector 240, but also make the water-based conductive coating have good water resistance and meet actual needs. If the second water-based conductive coating 242 If the thickness ratio is too large, the adhesive force between the water-based conductive coating and the current collector 240 will be small and it will be easily peeled off. If the thickness ratio of the second water-based conductive coating 242 is too small, the water-based conductive coating will be water-resistant. The conductive coating is dissolved by the water in the cathode slurry forming the electrode layer 243 during the preparation process, causing the water-based cathode resistance to increase and the coating to peel off.

Exemplarily, the thickness 242 of the second aqueous conductive coating is any one of 0.30 μm, 0.35 μm, 0.40 μm, 0.45 μm, 0.50 μm, 0.55 μm, 0.60 μm, 0.65 μm, 0.70 μm or between any two values. between values.

According to some embodiments of the present application, optionally, the thickness of the aqueous conductive coating is 1-5 μm.

The thickness of the water-based conductive coating is restricted, and on the premise of ensuring that the conductive performance of the water-based conductive coating is fully utilized, the thickness of the water-based conductive coating is reduced, so that when the thickness of the positive electrode piece 24 is constant, an additional The thickness of the positive electrode layer on the fluid 240 increases the energy density of the positive electrode piece 24 .

Exemplarily, the thickness of the aqueous conductive coating is any one of 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3.0, 3.5, 4.0 μm, 4.5 μm, 5.0 μm or between any two values.

According to some embodiments of the present application, optionally, the resistance change rate is the result of dividing the resistance standard deviation by the resistance average value, and the resistance change rate of the aqueous conductive coating is ≤10%.

That is to say, the resistance of the water-based conductive coating is basically evenly distributed, improving the performance consistency of the positive electrode piece 24 .

Optionally, the average resistance value is ≤1.5mΩ.

Referring to Figure 4, according to some embodiments of the present application, optionally, the thickness change rate is the result of dividing the thickness standard deviation by the thickness average, and the thickness change rate of the aqueous conductive coating is ≤10%.

That is to say, the thickness of the water-based conductive coating is basically uniformly distributed everywhere, improving the performance consistency of the positive electrode piece 24 .

According to some embodiments of the present application, the present application also provides a preparation method for preparing the above-mentioned positive electrode sheet, which includes the following steps: forming an aqueous conductive coating on the surface of the current collector; coating the positive electrode on the surface of the aqueous conductive coating The slurry is dried to obtain the positive electrode piece.

It should be noted that the step of forming the aqueous conductive coating on the surface of the current collector includes: first coating the first aqueous conductive slurry on the surface of the current collector, drying to form the first aqueous conductive coating; and then coating the first aqueous conductive coating on the surface of the current collector. The surface is coated with a second aqueous conductive slurry and dried to form a second conductive coating.

Wherein, the first aqueous conductive slurry is composed of conductive material, colloidal dispersant, aqueous binder and water, and the second aqueous conductive slurry is composed of conductive material, colloidal dispersant, aqueous binder, cross-linking agent and water.

The above preparation method is simple, but there is a reaction between the water-based binder and the cross-linking agent in the second water-based conductive slurry, which affects the thickness of the water-based conductive coating and the uniformity of resistance.

According to some embodiments of the present application, optionally, the step of forming an aqueous conductive coating on the surface of the current collector includes: coating an aqueous conductive slurry containing an aqueous binder on the surface of the current collector, and drying to form a pre-aqueous conductive coating. layer; apply a cross-linking agent aqueous solution on the surface of the pre-water-based conductive coating, and dry to form a water-based conductive coating.

In the above steps, since the cross-linking agent aqueous solution is coated on the surface of the pre-water-based conductive coating and dried to form the water-based conductive coating, the cross-linking effect on the conductive slurry caused by adding the cross-linking agent to the conductive slurry can be effectively avoided. The reaction affects the stability of the conductive slurry, resulting in uneven thickness and resistance distribution of the formed water-based conductive coating, which cannot guarantee the uniformity of the performance of the positive electrode piece.

According to some embodiments of the present application, optionally, in terms of mass percentage, the aqueous conductive slurry includes: 5%-15% of conductive material, 0.1%-2% of colloidal dispersant, 2%-10% of aqueous binder, and Water 80%-90%.

The conductive material acts as a conductor and can be dispersed in the water-based conductive slurry. The conductive agent can use various carbon material conductive agents commonly used in the prior art, but is not limited thereto.

Colloidal dispersants are used to coat and promote conductive materials to be evenly dispersed in aqueous conductive slurries to form a suspension system.

Water-based adhesives are adhesives that are soluble in water.

Within the above ratio range, the water-based conductive coating formed by the water-based conductive slurry has good electrical properties.

According to some embodiments of the present application, optionally, the water-based binder is a water-soluble polymer with carboxyl groups.

The binder is a water-soluble polymer with carboxyl groups. The cross-linking agent combines and cross-links with part of the carboxyl groups in the water-based binder, so that the molecular chain of the binder changes from linear to a stronger three-dimensional network structure. This improves the water resistance of the water-based conductive coating. At the same time, the carboxyl group serves as a hydrophilic group. When the water-based cathode slurry is subsequently coated on the conductive coating, it can better ensure the infiltration of the water-based cathode slurry on the water-based conductive coating. The spreading and bonding effects ensure the low resistance and high bonding force of the water-based conductive coating on the current collector.

According to some embodiments of the present application, optionally, the water-based binder includes at least one of polyacrylic acid and its salts, water-soluble polyacrylate and its salts, water-soluble ethylene vinyl acetate copolymer, and acrylonitrile multi-component copolymer.

The water-based conductive slurry containing the above-mentioned water-based binder not only has good wettability with the current collector and can be evenly coated on the current collector, but also has good wetting, spreading and bonding effects with the water-based cathode slurry subsequently, ensuring Low resistance and high adhesion of water-based conductive coating on current collector.

Polyacrylate includes but is not limited to polyacrylic acid sodium salt, and can also be polyacrylic acid potassium salt, etc. Those skilled in the art can select according to actual needs.

For example, the water-based binder is polyacrylic acid, or the water-based binder is sodium polyacrylate, or the water-based binder is a mixture of polyacrylate and water-soluble ethylene vinyl acetate copolymer, or the like.

According to some embodiments of the present application, optionally, the cross-linking agent in the cross-linking agent aqueous solution includes aziridine and its derivatives, polycarbodiimide and its salts, epoxy silane and its derivatives, graft One or more types of epoxy silane polymers and polyethylenimines.

The above-mentioned cross-linking agent can combine and cross-link with part of the carboxyl groups in the water-based binder, so that the binder molecular chain changes from linear to a stronger three-dimensional network structure, thereby improving the water resistance of the conductive coating layer.

According to some embodiments of the present application, optionally, the mass fraction of the cross-linking agent in the cross-linking agent aqueous solution is greater than 3% and not greater than 25%.

Within the above range, the mass fraction of the cross-linking agent in the cross-linking agent aqueous solution is reasonable, so that the water-based conductive coating can meet the requirements for water resistance and adhesion.

Exemplarily, the mass fraction of the cross-linking agent in the cross-linking agent aqueous solution is any value of 3.5%, 5.0%, 7.0%, 10.0%, 13.0%, 15.0%, 17.0%, 20.0%, 23.0%, 25.0% or Between any two values.

Optionally, the mass fraction of the cross-linking agent in the cross-linking agent aqueous solution is 10-20%.

According to some embodiments of the present application, optionally, the conductive material includes at least one of carbon black, graphite, partially graphitized coke, carbon fiber, acetylene black, vapor-grown carbon fiber, and fullerene nanotubes.

The above-mentioned conductive materials are easy to obtain and have good conductive effects.

According to some embodiments of the present application, optionally, the colloidal dispersant is a colloid, and optionally, the colloidal material is at least one of xanthan gum, locust bean gum, guar gum, arabic gum, gelatin, and carrageenan. kind.

The above-mentioned colloidal dispersant is easy to obtain, and has a good dispersion effect in uniformly dispersing the conductive material in the aqueous conductive slurry.

Exemplarily, the colloidal dispersant is xanthan gum, or the colloidal dispersant is a mixture of xanthan gum and gelatin.

According to some embodiments of the present application, optionally, the temperature for drying to form the pre-aqueous conductive coating is 70°C-120°C, and the time is 10s-60s.

Within the above temperature and time range, the pre-aqueous conductive coating can be effectively dried.

According to some embodiments of the present application, optionally, the temperature for drying to form the aqueous conductive coating is 70°C-120°C, and the time is 10s-60s.

Within the above temperature and time range, the cross-linking agent and the water-based binder can be effectively reacted and solidified to form a water-based conductive coating.

According to some embodiments of the present application, the present application also provides a battery cell, including the positive electrode plate of any of the above solutions.

According to some embodiments of the present application, the present application also provides a battery, including the battery cell of any of the above solutions.

According to some embodiments of the present application, the present application also provides an electrical device, including a battery according to any of the above solutions, and the battery is used to provide electrical energy to the electrical device.

The powered device can be any of the aforementioned devices or systems that use batteries.

Some specific examples are listed below to better illustrate this application.

Examples and Comparative Examples

[Preparation of water-based positive electrode pieces]

Current collector: aluminum foil.

Aqueous conductive slurries of Examples 1-6 and Comparative Examples 1-4 and 7-8: In terms of mass percentage, the conductive slurry includes: 10% conductive material, 0.2% colloidal dispersant, 7% binder, and Water 82.8%.

Aqueous conductive slurry of Example 7: In terms of mass percentage, the conductive slurry includes: 7% conductive material, 0.2% colloidal dispersant, 7% binder and 85.8% water.

Aqueous conductive slurry of Example 8: In terms of mass percentage, the conductive slurry includes: 12% conductive material, 0.2% colloidal dispersant, 7% binder and 80.8% water.

Water-based conductive slurry of Comparative Example 5: In terms of mass percentage, the conductive slurry includes: 16% conductive material, 0.2% colloidal dispersant, 1% binder and 82.8% water.

Water-based conductive slurry of Comparative Example 6: In terms of mass percentage, the conductive slurry includes: 3% conductive material, 0.2% colloidal dispersant, 15% binder and 82.8% water.

In the water-based conductive slurries of the above embodiments and comparative examples, conductive graphite (purchased from Shanghai Kaiyin Chemical Co., Ltd., brand name SP5000) is used as the conductive material; xanthan gum (molecular weight is about 1,000,000 g/mol, purchased from (from Shanghai Aladdin Biochemical Technology Co., Ltd.); the binder uses polyacrylic acid with an average molecular weight of 300,000-800,000.

Conductive slurry of Comparative Example 3: In terms of mass percentage, the conductive slurry includes: 10% conductive material, 0.2% colloidal dispersant, 7% binder and 82.8% water, in which the conductive material uses conductive graphite (purchased from Shanghai Kai Yin Chemical Co., Ltd., brand name is SP5000); the colloidal dispersant is xanthan gum (molecular weight is about 1,000,000g/mol, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.), and the adhesive is polyvinylidene fluoride.

Cross-linking agent aqueous solution: The cross-linking agent uses water-based polycarbodiimide with a molecular weight of 10,000 to 40,000.

Cathode slurry: Mix the lithium iron phosphate cathode active material lithium iron phosphate, the conductive agent conductive carbon black, the compound dispersion stabilizer, and the water-based binder in a weight ratio of 96:1:1.2:1.8, of which the compound dispersion stabilizer is A compound of xanthan gum (molecular weight approximately 1,000,000g/mol, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.) and polyethyleneimine (molecular weight approximately 1,200g/mol, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.) The mixture has a compound weight ratio of 1:1; the water-based binder is an acrylonitrile copolymer (codename LA133, purchased from Sichuan Indile Technology Co., Ltd.) and the remainder is stirred and mixed evenly with solvent deionized water to obtain a solid content of 50 % of the cathode slurry.

[Examples 1-8, Comparative Examples 3, 5-8] Preparation method of positive electrode plate:

The water-based conductive slurry is evenly coated on the surface of the current collector and dried to form a pre-water-based conductive coating.

The cross-linking agent aqueous solution is evenly coated on the surface of the pre-water-based conductive coating, and dried at 90°C to form a water-based conductive coating, in which the thickness of the water-based conductive coating is 1.5 μm.

The same positive electrode slurry is evenly coated on the surface of the water-based conductive coating, dried at 90°C to form an electrode layer of equal thickness, and then cold-pressed and cut to obtain positive electrode sheets.

[Comparative Example 1] The only difference between the preparation method of the positive electrode plate and Example 1 is:

The conductive slurry is evenly coated on the surface of the current collector and dried at 90°C to form a conductive coating (the same as the aqueous conductive slurry in Example 1), in which the thickness of the aqueous conductive coating is 1.5 μm.

[Comparative Example 2] The only difference between the preparation method of the positive electrode sheet and Example 1 is that it is directly carried out with a conductive slurry containing a cross-linking agent (the only difference from the aqueous conductive slurry in Example 1 is that it contains a cross-linking agent) Coating and drying at 90°C to form a water-based conductive coating, where the thickness of the water-based conductive coating is 1.5 μm.

[Comparative Example 4] The only difference between the preparation method of the positive electrode sheet and Example 1 is that the first aqueous conductive slurry that does not contain a cross-linking agent is evenly coated on the surface of the current collector (compared with the aqueous conductive slurry in Example 1 (the same material), and dried at 90°C to form the first aqueous conductive coating.

A second aqueous conductive slurry containing a cross-linking agent (which differs from the first aqueous conductive slurry only in that it contains a cross-linking agent) is evenly coated on the surface of the first aqueous conductive coating, and dried at 90°C to form a second aqueous conductive slurry. Coating, wherein the total thickness of the first aqueous conductive coating and the second aqueous conductive coating is 1.5 μm, and the thickness of the second aqueous conductive coating is 1 μm.

Some parameters of the above-mentioned embodiments and comparative examples are shown in Table 1.

[Preparation of negative electrode plates]

Dissolve the active material artificial graphite, conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethylcellulose (CMC) in the solvent deionized water in a weight ratio of 96.2:0.8:0.8:1.2 , mix evenly and prepare negative electrode slurry; the negative electrode slurry is evenly coated on the negative electrode current collector copper foil, and then dried, cold pressed, and cut to obtain negative electrode pieces.

[Preparation of electrolyte]

In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), mix the organic solvent ethylene carbonate (EC)/ethyl methyl carbonate (EMC) evenly according to the volume ratio of 3/7, and add the LiPF6 lithium salt Dissolve in an organic solvent and stir evenly to obtain an electrolyte. The mass percentage of LiPF6 in the electrolyte is 12.5%.

【Isolation film】

A PE porous film is coated with a ceramic coating with a thickness of 2 μm as an isolation membrane.

[Preparation of lithium-ion batteries]

Stack the positive electrode piece, isolation film, and negative electrode piece in order in Example 1 so that the isolation film plays an isolation role between the positive and negative electrode pieces, then wind it to obtain a bare battery core, and weld the tabs to the bare battery core. , put the bare battery core into an aluminum case, bake it at 80°C to remove water, then inject electrolyte and seal it to obtain an uncharged battery. The uncharged battery then goes through processes such as standing, hot and cold pressing, formation, shaping, and capacity testing to obtain lithium-ion battery products.

Performance test, the results are shown in Figure 5-7 and Table 1 and Table 2:

1. Water resistance test of the second water-based conductive coating:

Put the positive electrode piece that does not contain an electrode layer into the water and clean it ultrasonically under the conditions of a wave source distance of 50mm to 55mm and a wave source frequency of 25KHZ. The moment when the positive electrode piece is exposed to the current collector is defined as the second aqueous conductive coating being dissolved. The time from the start of ultrasonic cleaning to the time when the second aqueous conductive coating is dissolved is used as the dissolution time of the ultrasonic cleaning of the second aqueous conductive coating.

2. Peeling force test:

A tensile test machine will be used to measure the peeling force of the water-based conductive coating from the aluminum foil.

3. Thickness test:

Micrometer test: Take an area of 5cm*5cm of the aluminum foil and test 50 points randomly. Take the average thickness R1 of the aluminum foil and test 50 points randomly within the area of 5cm*5cm of the semi-finished product coated to form the pre-watery conductive coating. Take the average R2 of the total thickness of the aluminum foil + pre-water-based conductive coating, take the cross-linking agent aqueous solution, and dry the finished product to form the water-based conductive coating within an area of 5cm*5cm. Randomly test 50 points, take the aluminum foil + water-based conductive coating The average value of the total thickness of the layer is R3, the total thickness R4=R3-R1, and the thickness difference R5=R3-R2. The thickness of the second water-based conductive coating = [(R2-R1)*water-based glue mass fraction*0.40+curing agent mass fraction*R3*0.25]*thickness difference R5*1.15.

4. Resistance test:

Along the length of the positive electrode piece, test the resistance at 1cm intervals, and take a total of 100 electrical test data to obtain the average resistance value.

[Cathode coating system test]

1. Distinguish between water-based and oil-based positive electrode systems: use a gas chromatograph and refer to patent CN113804799A to test the NMP residue in the pole piece. The pole piece with a residual amount greater than 50PPM and a binder of polyvinylidene fluoride is an oil-based pole piece. On the contrary, it is the positive pole of the water system.

2. Water-based pole piece adhesion test

The positive electrode coating was tested using a tensile machine.

【Battery performance test】

1. Battery capacity retention test

The battery capacity retention rate test process is as follows: at 25°C, charge the battery to 3.65V at a constant current of 1/3C, then charge to a constant voltage of 3.65V until the current is 0.05C, leave it aside for 5 minutes, and then discharge it to 2.7 at a constant voltage of 1/3C. V, the obtained capacity is recorded as the initial capacity C0. Repeat the above steps for the same battery and record the discharge capacity Cn of the battery after the nth cycle. Then the battery capacity retention rate after each cycle Pn = Cn/C0*100%. During this test, the first cycle corresponds to n=1, the second cycle corresponds to n=2, and the 100th cycle corresponds to n=100. The battery capacity retention rate data corresponding to Example 1 in Table 1 is the data measured after 800 cycles under the above test conditions, that is, the value of P800.

Table 1 Examples and Comparative Examples Parameters and Partial Test Results

Table 2 Examples and Comparative Examples Test Results

In Table 2, the stability time of the conductive slurry is tested by the particle size change rate of the conductive slurry. According to industry experience, when the increase in particle size D50 exceeds 50%, it is considered that the particles in the slurry have been seriously agglomerated and should not be put into production again. According to According to actual production needs, the D50 of the slurry must achieve a change rate of less than 50% within 24 hours before the slurry can be judged to have qualified stability and the slurry can be put into production. The D50 here refers to the prepared conductive slurry. The particle size of the substance contained in the material when the particle size increase value is 50%.

According to Table 1 and Table 2, it can be seen that in the positive electrode sheet provided in each embodiment of the present application, the peeling force between the first aqueous conductive coating and the current collector is ≥50N/M; the second aqueous conductive coating is ultrasonically cleaned Dissolution time ≥200s.

According to Examples 1-3 and 6, it can be seen that different mass fractions of cross-linking agent aqueous solutions will affect the thickness of the second aqueous conductive coating, and the mass fraction of the cross-linking agent in the cross-linking agent aqueous solution is positively related to the thickness of the second aqueous conductive coating. . According to Example 6, although the positive electrode sheet of the present application can be prepared with a mass fraction of 25% cross-linking agent aqueous solution, compared with Examples 1-3, the thickness of the second aqueous conductive coating prepared is too large, which affects Battery capacity and pole piece size, so the mass fraction of cross-linking agent in the cross-linking agent aqueous solution is 10%-20%, which is better.

According to Examples 1, 4, and 5, it can be seen that the cross-linking agent can be selected from different components according to actual needs, and similar effects can be achieved to obtain a second water-based conductive coating with water resistance.

According to Examples 1, 7, and 8, it can be seen that the composition ratio of the aqueous conductive slurry is different. Even if the same cross-linking agent aqueous solution is used, even if the same preparation method is used, the electrochemical performance of the positive electrode sheet will eventually be affected.

Compared with Example 1, Comparative Example 1 does not contain a cross-linking agent, which means that the water-resistant second aqueous conductive coating is not formed. Although the peeling force between the first aqueous conductive coating and the aluminum foil is improved, the peeling force between the first aqueous conductive coating and the aluminum foil is 1.5 μm. The water resistance time of the conductive coating is only 12s, which not only fails to solve the technical problem of this application, but also significantly reduces the battery capacity retention rate.

Compared with Example 1, Comparative Example 2 directly adds the cross-linking agent to the conductive slurry, which results in the peeling force between the water-based conductive coating and the aluminum foil being too small, making it easy for the water-based conductive coating to detach from the aluminum foil and cannot be replaced. The two are stably connected together, and the above arrangement also causes the cross-linking agent and the adhesive to react before coating, resulting in uneven distribution of resistance and thickness of the final conductive coating.

The binder used in Comparative Example 3 is polyvinylidene fluoride (PVDF), which is insoluble in water, that is, the prepared positive electrode coating system is an oil-based positive electrode, and the first coating primer interface is hydrophobic. interface (hydrophobic effect similar to lotus leaves), so the water-based cathode slurry cannot be effectively coated on the primer interface.

The coating method of Comparative Example 4 is different from that of Example 1. Using the above method will reduce the uniformity of resistance and thickness distribution. The cross-linking agent in the second layer reacts with the water-based binder in the second layer to cross-link, which will cause abnormalities in the slurry system of the second layer, causing problems such as gelling, agglomeration, and delamination, which will cause problems when coating the second layer. , the thickness distribution and the particle size difference in the coating are too large, resulting in large differences in the overall thickness and resistance of the pole piece, affecting the use effect.

Compared with Example 1, Comparative Example 5 has too little mass percentage of aqueous binder in the conductive slurry, resulting in the inability of the aqueous binder to effectively cross-link, insufficient water resistance, and the adhesion of the aqueous conductive layer to the aluminum foil and electrode layer respectively. Insufficient relay makes the three easily separated from each other.

Comparative Example 6 Compared with Example 1, the mass percentage of the aqueous binder in the conductive slurry is too large and the conductive material is insufficient, which affects the dispersion of each component in the formed coating and the resistance of the coating, and reduces the battery cycle performance.

The difference between Comparative Example 7 and Example 1 lies in the selection of binder raw materials. Due to the presence of amide groups in polyacrylamide, it will gel in the aqueous solution, affecting the dispersion stability of the solution and thus affecting the formed conductive coating. The thickness of the layer and the uniformity of the resistance distribution, while the remaining amide groups in the final coating will react with the electrolyte to produce ammonia or other by-products, affecting battery performance.

Compared with Example 1, Comparative Example 8 has too little mass fraction of the cross-linking agent in the aqueous cross-linking agent solution, resulting in the thickness of the second aqueous conductive coating formed being too small and unable to meet the water resistance requirements.

Figure 5 is a cross-sectional high-magnification SEM image of the water-based conductive coating in Example 1 of the present application; it can be seen from Figure 5 that the water-based conductive coating includes a first water-based conductive coating formed on the aluminum foil, and a first water-based conductive coating formed on the aluminum foil. The second water-based conductive coating on the coating has agglomerates with larger particle sizes due to cross-linking reactions.

Figure 6 is a low-magnification SEM image of the positive electrode plate provided in Example 1. It can be seen that the water-based conductive coating and the aluminum foil are stably connected together.

Figure 7 is a low-magnification SEM image of the cross-section of the positive electrode sheet of Comparative Example 1 of the present application (the positive electrode sheet includes aluminum foil-water-based conductive coating-positive electrode layer). It can be seen that the water-based conductive coating is dissolved, causing the positive electrode layer to separate from the aluminum foil.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: The technical solutions described in the foregoing embodiments can still be modified, or some or all of the technical features can be equivalently replaced; and these modifications or substitutions do not deviate from the essence of the corresponding technical solutions from the technical solutions of the embodiments of the present application. The scope shall be covered by the claims and description of this 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

A positive electrode plate includes a current collector, an aqueous conductive coating and an electrode layer, wherein the aqueous conductive coating includes a first aqueous conductive coating and a second aqueous conductive coating, the first aqueous conductive coating is located The side of the second aqueous conductive coating facing the current collector;

The peeling force between the first aqueous conductive coating and the current collector is ≥50N/M;

The second aqueous conductive coating is soluble in water and the dissolution time of ultrasonic cleaning is ≥200s;

The peeling force between the electrode layer and the second aqueous conductive coating is ≥40N/M;

Optionally, the peeling force between the first aqueous conductive coating and the current collector is ≥54N/M.
The positive electrode piece according to claim 1, wherein the cross-linking degree of the first aqueous conductive coating is 0, and the cross-linking degree of the second aqueous conductive coating is >0.
The cathode plate according to claim 1 or 2, wherein the cross-linking degree of the second aqueous conductive coating is gradient from the side close to the electrode layer to the side close to the first aqueous conductive coating. Decreasingly.
The positive electrode plate according to any one of claims 1 to 3, wherein the method for determining the dissolution time of the second aqueous conductive coating in ultrasonic cleaning is:

The positive electrode piece that does not contain the electrode layer is placed in water and ultrasonically cleaned under the conditions of a wave source distance of 50 mm to 55 mm and a wave source frequency of 25 KHZ. The moment when the positive electrode piece is observed to be exposed to the current collector is defined as The second aqueous conductive coating is dissolved, and the time from the start of ultrasonic cleaning to the time when the second aqueous conductive coating is dissolved is used as the dissolution time of the ultrasonic cleaning of the second aqueous conductive coating.
The positive electrode plate according to any one of claims 1 to 4, wherein the thickness of the second aqueous conductive coating is less than the thickness of the first aqueous conductive coating, and the thickness of the second aqueous conductive coating is 0.3 -0.7μm;

Optionally, the thickness of the aqueous conductive coating is 1-5 μm.
The positive electrode plate according to any one of claims 1 to 5, wherein the resistance change rate is the result of dividing the resistance standard deviation by the resistance average value, and the resistance change rate of the aqueous conductive coating is ≤10% .
The positive electrode sheet according to any one of claims 1 to 6, wherein the thickness change rate is a result of dividing the thickness standard deviation by the thickness average, and the thickness change rate of the aqueous conductive coating is ≤ 10% .
A method for preparing the positive electrode sheet according to any one of claims 1-7, which includes the following steps:

Forming the aqueous conductive coating on the surface of the current collector;

The positive electrode slurry is coated on the surface of the aqueous conductive coating and dried to obtain the positive electrode sheet.
The preparation method according to claim 8, wherein the step of forming the aqueous conductive coating on the surface of the current collector includes:

Coat the surface of the current collector with an aqueous conductive slurry containing a water-based binder, and dry it to form a pre-aqueous conductive coating;

A cross-linking agent aqueous solution is coated on the surface of the pre-aqueous conductive coating, and dried to form the aqueous conductive coating.
The preparation method according to claim 9, wherein, in terms of mass percentage, the aqueous conductive slurry includes: 5%-15% conductive material, 0.1%-2% colloidal dispersant, 2%-10% aqueous binder %, and water 80%-90%.
The preparation method according to claim 10, wherein the aqueous binder is a water-soluble polymer with carboxyl groups.
The preparation method according to claim 10 or 11, wherein the water-based binder includes polyacrylic acid and its salts, water-soluble polyacrylate and salts, water-soluble ethylene vinyl acetate copolymers and acrylonitrile multi-component copolymers. At least one.
The preparation method according to any one of claims 9 to 12, wherein the cross-linking agent in the cross-linking agent aqueous solution includes aziridine and its derivatives, polycarbodiimide and its salts, epoxy One or more of silane and its derivatives, grafted epoxy silane polymer, and polyethyleneimine.
The preparation method according to any one of claims 9-12, wherein the mass fraction of the cross-linking agent in the cross-linking agent aqueous solution is greater than 3% and not greater than 25%, optionally 10%-20%.
The preparation method according to claim 10, wherein the conductive material includes at least one of carbon black, graphite, partially graphitized coke, carbon fiber, acetylene black, vapor-grown carbon fiber and fullerene nanotubes.
The preparation method according to claim 10, wherein the colloidal dispersant includes at least one of xanthan gum, locust bean gum, guar gum, acacia gum, gelatin, and carrageenan.
The preparation method according to any one of claims 9-16, wherein the temperature for drying to form the pre-aqueous conductive coating is 70°C-120°C and the time is 10s-60s.
The preparation method according to any one of claims 9-16, wherein the temperature for drying to form the aqueous conductive coating is 70°C-120°C and the time is 10s-60s.
A battery cell, which includes the positive electrode piece according to any one of claims 1-7.
A battery, comprising the battery cell according to claim 19.
An electrical device, comprising the battery according to claim 20.