CN117716540A

CN117716540A - Positive electrode plate, preparation method thereof, battery monomer, battery and electric equipment

Info

Publication number: CN117716540A
Application number: CN202280008847.7A
Authority: CN
Inventors: 裴海乐; 程丛; 陈均桄; 杨丙梓; 张盛武; 王星会
Original assignee: Contemporary Amperex Technology Co Ltd
Current assignee: Contemporary Amperex Technology Co Ltd
Priority date: 2022-07-13
Filing date: 2022-07-13
Publication date: 2024-03-15
Also published as: WO2024011465A1

Abstract

A positive pole piece, a preparation method thereof, a battery monomer, a battery and electric equipment relate to the field of batteries. The positive electrode plate (24) comprises a current collector (240), an aqueous conductive coating and an electrode layer (243), wherein the aqueous conductive coating comprises a first aqueous conductive coating (241) and a second aqueous conductive coating (242), and the first aqueous conductive coating (241) is positioned on one side of the second aqueous conductive coating (242) facing the current collector (240); the stripping force between the first aqueous conductive coating (241) and the current collector (240) is more than or equal to 50N/M; the second aqueous conductive coating (242) is soluble in water, the dissolution time of ultrasonic cleaning is more than or equal to 200s, and the stripping force between the electrode layer (243) and the second aqueous conductive coating (242) is more than or equal to 40N/M. The positive electrode plate (24) can solve the problem of poor cycling stability of the existing battery adopting the water-based positive electrode.

Description

Positive electrode plate, preparation method thereof, battery monomer, battery and electric equipment

Technical Field

The application relates to the field of batteries, in particular to a positive electrode plate, a preparation method thereof, a battery monomer, a battery and electric equipment.

Background

Most of the existing lithium battery anodes adopt oil-based formulas, but with the development of battery technology and the requirement of green environmental protection, the lithium battery anodes gradually turn to environment-friendly pollution-free water-based anodes.

The aqueous positive electrode includes an active material and a current collector. However, the insufficient wettability between the current collector interface and the active material leads to a limited contact area between the active material particles and the aluminum foil, which leads to an increase in interface resistance, causes an increase in internal resistance of the battery, and has a negative effect on the battery performance. Therefore, a layer of water-based conductive coating is required to be coated on the surface of the current collector to tightly bond the current collector and the active material, so that the bonding force and the conductivity are ensured.

The existing water-based positive electrode battery has the problem of poor cycling stability.

Disclosure of Invention

The application provides a positive pole piece, a preparation method thereof, a battery monomer, a battery and electric equipment, which can solve the problem that the existing water-based positive pole battery has poor circulation stability.

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, where the aqueous conductive coating includes a first aqueous conductive coating and a second aqueous conductive coating, and the first aqueous conductive coating is located on a side of the second aqueous conductive coating facing the current collector; the stripping force between the first aqueous conductive coating and the current collector is more than or equal to 50N/M; the second aqueous conductive coating is soluble in water, the dissolution time of ultrasonic cleaning is more than or equal to 200s, and the stripping force between the electrode layer and the second aqueous conductive coating is more than or equal to 40N/M.

According to the technical scheme, the water-based conductive coating is layered, the stripping force between the first water-based conductive coating and the current collector is more than or equal to 50N/M, so that the adhesion force between the water-based conductive coating and the current collector is guaranteed, the second water-based conductive coating is positioned between the first conductive coating and the electrode layer, the drying time of the pole piece is about more than 3min in the actual production process, the drying speed is too high, the pole piece is easy to crack, the second water-based conductive coating is soluble in water, the ultrasonic cleaning dissolution time is more than or equal to 200s, so that the second water-based conductive coating has good water resistance, the problem that the water-based positive electrode resistance is increased due to the fact that the conductive coating is dissolved by water in positive electrode slurry for forming the electrode layer in the preparation process is solved, the problem that the coating peels off is solved, the sealing property and the electrical connectivity between the electrode layer and the current collector are further effectively improved, and the circulation stability and capacity circulation retention rate of the battery are improved.

Optionally, the peel force between the first aqueous conductive coating and the current collector is greater than or equal to 54N/M.

In some embodiments, the first aqueous conductive coating has a degree of crosslinking of 0 and the second aqueous conductive coating has a degree of crosslinking of > 0. The aqueous conductive coating contains the aqueous binder, and the crosslinking agent is used for crosslinking the aqueous binder to change the structure of the aqueous binder, so that the solvent resistance of the aqueous binder is improved, and meanwhile, the adhesive force is reduced.

In some embodiments, the degree of crosslinking of the second aqueous conductive coating decreases in a gradient from a side proximate to the electrode layer to a side proximate to the first aqueous conductive coating. That is, the water resistance of the side of the second aqueous conductive coating layer near the electrode layer is better than that of the side of the second aqueous conductive coating layer near the first aqueous conductive coating layer, and the adhesive force of the side of the second aqueous conductive coating layer near the electrode layer is better than that of the side of the second aqueous conductive coating layer near the first aqueous conductive coating layer, so that the adhesive force between the second aqueous conductive coating layer and the first aqueous conductive coating layer is effectively enhanced on the premise of realizing the water resistance of the second aqueous conductive coating layer.

In some embodiments, the method of determining the dissolution time of the second aqueous conductive coating for ultrasonic cleaning is: the positive electrode sheet without the electrode layer is placed in water, ultrasonic cleaning is carried out under the conditions that the wave source distance is 50-55 mm and the wave source frequency is 25KHZ, the moment when the positive electrode sheet is observed to expose the current collector is defined as the time from the ultrasonic cleaning to the dissolution of the second aqueous conductive coating as the dissolution time of the ultrasonic cleaning of the second aqueous conductive coating. Because the first aqueous conductive coating is not waterproof, the first conductive coating can be instantly dissolved in water in the ultrasonic cleaning process, and the error of the dissolution time of the second aqueous conductive coating can not be caused.

In some embodiments, the second aqueous conductive coating thickness is less than the first aqueous conductive coating thickness, the second aqueous conductive coating thickness being from 0.3 to 0.7 μm. The thickness ratio is reasonable, the stability of connection between the water-based conductive coating and the current collector can be realized, the water-based conductive coating has good water resistance, actual requirements are met, if the thickness ratio of the second water-based conductive coating is too large, the adhesion between the water-based conductive coating and the current collector is small, the water-based conductive coating is easy to strip, and if the thickness ratio of the second water-based conductive coating is too small, the water resistance of the water-based conductive coating is insufficient, so that the water-based positive electrode resistance is increased due to the dissolution of the conductive coating in the positive electrode slurry for forming the electrode layer in the preparation process, and the coating is peeled off.

Alternatively, the aqueous conductive coating has a thickness of 1-5 μm. The thickness of the water-based conductive coating is restrained, the thickness of the water-based conductive coating is reduced on the premise that the conductivity of the water-based conductive coating is fully applied, the thickness of the positive electrode plate is enabled to be certain, the thickness of the positive electrode layer arranged on the current collector is increased, and the energy density of the positive electrode plate is improved.

In some embodiments, the resistivity of the aqueous conductive coating varies by 10% or less as a result of dividing the standard deviation of the resistance by the average value of the resistance. Namely, the resistance of the water-based conductive coating is basically and evenly distributed, and the performance consistency of the positive electrode plate is improved.

In some embodiments, the thickness variation rate of the aqueous conductive coating is less than or equal to 10% as the thickness standard deviation divided by the thickness average. That is, the thickness of the water-based conductive coating is basically and evenly distributed throughout, and the performance consistency of the positive electrode plate is improved.

In a second aspect, the present application provides a method for preparing the positive electrode sheet, which includes the following steps: forming an aqueous conductive coating on the surface of the current collector; coating positive electrode slurry on the surface of the water-based conductive coating, and drying to obtain a positive electrode plate.

In the technical scheme of the embodiment of the application, the positive electrode plate is obtained by forming the water-based conductive coating firstly and then forming the positive electrode plate on the surface of the water-based conductive coating, the preparation method is simple, the obtained positive electrode plate can effectively improve the adhesion and electrical connectivity between the electrode layer and the current collector, and the cycle stability and capacity cycle retention rate of the battery are improved.

In some embodiments, the step of forming an aqueous conductive coating on the surface of the current collector includes: coating aqueous conductive slurry containing an aqueous binder on the surface of a current collector, and drying to form a pre-aqueous conductive coating; and (3) coating an aqueous solution of a cross-linking agent on the surface of the pre-aqueous conductive coating, and drying to form the aqueous conductive coating. In the above steps, the aqueous conductive coating is formed by coating the surface of the pre-aqueous conductive coating with the aqueous cross-linking agent solution and drying, so that the problem that the uniformity of the performance of the positive electrode plate cannot be ensured due to uneven thickness and resistance distribution of the formed aqueous conductive coating caused by the influence of the cross-linking reaction generated on the conductive paste after the cross-linking agent is added into the conductive paste and the stability of the conductive paste is effectively avoided.

In some embodiments, the aqueous conductive paste comprises, in mass percent: 5% -15% of conductive material, 0.1% -2% of colloid dispersant, 2% -10% of water-based adhesive and 80% -90% of water. In the proportion range, the aqueous conductive coating formed by the aqueous conductive slurry has good electrical property.

In some embodiments, the aqueous binder is a water-soluble high molecular polymer with carboxyl groups. The binder is a water-soluble high polymer with carboxyl, and the crosslinking agent is combined with part of carboxyl in the aqueous binder to crosslink, so that the molecular chain of the binder is changed from linear to a firmer three-dimensional net structure, thereby improving the water resistance of the aqueous conductive coating, and simultaneously, the carboxyl is taken as a hydrophilic group, and when the aqueous positive electrode slurry is coated on the conductive coating, the wetting, spreading and bonding effects of the aqueous positive electrode slurry on the aqueous conductive coating can be better ensured, and the low resistance and high bonding force of the aqueous conductive coating on the current collector are ensured.

In some embodiments, the aqueous binder includes at least one of polyacrylic acid and salts thereof, water-soluble polyacrylates and salts, water-soluble ethylene vinyl acetate copolymers, and acrylonitrile copolymers. The aqueous conductive paste containing the aqueous binder has good wettability with a current collector, can be uniformly coated on the current collector, has good effects of infiltration, spreading and adhesion with the aqueous positive paste, and ensures low resistance and high adhesion of the aqueous conductive coating on the current collector.

In some embodiments, the crosslinking agent in the aqueous solution of the crosslinking agent includes one or more of aziridine and derivatives thereof, polycarbodiimide and salts thereof, epoxysilane and derivatives thereof, polymers of grafted epoxysilane, polyethylenimine. The cross-linking agent can be combined and cross-linked with part of carboxyl groups in the aqueous binder, so that the molecular chain of the binder is changed from linear to a firmer three-dimensional net structure, and the water resistance of the conductive coating is improved.

In some embodiments, the mass fraction of crosslinker in the aqueous crosslinker solution is greater than 3% and no greater than 25%, alternatively 10% -20%. In 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 meets the requirements of water resistance and adhesion.

In some embodiments, the conductive material comprises at least one of carbon black, graphite, partially graphitized coke, carbon fiber, acetylene black, vapor grown carbon fiber, and fullerene nanotubes. The conductive material is convenient to obtain and good in conductive effect.

In some embodiments, the colloidal material is at least one of xanthan gum, locust bean gum, guar gum, acacia, gelatin, carrageenan. The colloidal dispersing agent is convenient to obtain, and the dispersing effect of uniformly dispersing the conductive material in the aqueous conductive slurry is good.

In some embodiments, the pre-aqueous conductive coating is dried at a temperature of 70 ℃ to 120 ℃ for a time of 10s to 60s. The pre-aqueous conductive coating can be effectively dried at the above temperature and time ranges.

In some embodiments, the aqueous conductive coating is formed by drying at a temperature of 70 ℃ to 120 ℃ for a time of 10s to 60s. The crosslinking agent and the aqueous binder can be effectively reacted and cured to form the aqueous conductive coating within the above temperature and time range.

In a third aspect, the present application provides a battery cell including the positive electrode tab in the above embodiment.

In a fourth aspect, the present application provides a battery comprising the battery cell of the above embodiment.

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

The foregoing description is only an overview of the technical solutions of the present application, and may be implemented according to the content of the specification in order to make the technical means of the present application more clearly understood, and in order to make the above-mentioned and other objects, features and advantages of the present application more clearly understood, the following detailed description of the present application will be given.

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 only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the application. Also, like reference numerals are used to designate like parts throughout the accompanying drawings. In the drawings:

FIG. 1 is a schematic illustration of a vehicle according to some embodiments of the present application;

FIG. 2 is a schematic illustration of an exploded construction of a battery according to some embodiments of the present application;

fig. 3 is a schematic exploded view of a battery cell according to some embodiments of the present application;

fig. 4 is a schematic structural diagram of a positive electrode sheet according to some embodiments of the present application;

FIG. 5 is a cross-sectional high-magnification SEM image of an aqueous conductive coating of example 1 of the present application;

FIG. 6 is a SEM image of a low magnification of the positive electrode sheet provided in example 1;

fig. 7 is a low-magnification SEM image of the cross section of the positive electrode sheet of comparative example 1 of the present application (positive electrode sheet including aluminum foil-aqueous conductive coating-positive electrode layer).

Reference numerals in the specific embodiments are as follows:

1000-vehicle;

100-cell; 200-a controller; 300-motor;

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

20-battery cells; 21-end caps; 21 a-electrode terminals; 22-a housing; 23-an electrode assembly; 23 a-tab;

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

Detailed Description

Embodiments of the technical solutions of the present application will be described in detail below with reference to the accompanying drawings. The following examples are only for more clearly illustrating the technical solutions of the present application, and thus are only examples, and are not intended to limit the scope of protection of the present application.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application; the terms "comprising" and "having" and any variations thereof in the description and claims of the present application and in the description of the figures above are intended to cover non-exclusive inclusions.

In the description of the embodiments of the present application, the technical terms "first," "second," etc. are used merely to distinguish between different objects and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated, a particular order or a primary or secondary relationship. In the description of the embodiments of the present application, the meaning of "plurality" is two or more unless explicitly defined otherwise.

Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the present application. The appearances of such phrases 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 of skill in the art will explicitly and implicitly appreciate that the embodiments described herein may be combined with other embodiments.

In the description of the embodiments of the present application, the term "and/or" is merely an association relationship describing an association object, which means that three relationships may exist, for example, a and/or B may mean: a exists alone, A and B exist together, and B exists alone. In addition, the character "/" herein generally indicates that the front and rear associated objects are an "or" relationship.

In the description of the embodiments of the present application, the term "plurality" refers to two or more (including two), and similarly, "plural sets" refers to two or more (including two), and "plural sheets" refers to two or more (including two).

In the description of the embodiments of the present application, the orientation or positional relationship indicated by the technical terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. are based on the orientation or positional relationship shown in the drawings, and are merely for convenience of describing the embodiments of the present application and for simplifying the description, rather than indicating or implying that the apparatus or element referred to must have a specific orientation, be configured and operated in a specific orientation, and therefore should not be construed as limiting the embodiments of the present application.

In the description of the embodiments of the present application, unless explicitly specified and limited otherwise, the terms "mounted," "connected," "secured" and the like are to be construed broadly and may be, for example, fixedly connected, detachably connected, or integrally formed; or may be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communicated with the inside of two elements or the interaction relationship of the two elements. The specific meaning of the above terms in the embodiments of the present application will be understood by those of ordinary skill in the art according to the specific circumstances.

The inventor notices that when the aqueous positive electrode system is prepared and used, the aqueous conductive coating is dissolved by water in the positive electrode slurry, so that the structure of the aqueous conductive coating is damaged, the aqueous conductive coating is stripped from the current collector, the aqueous conductive coating loses conduction and bonding action, the resistance of the battery is increased, or the positive electrode layer is stripped, the performance and safety of the aqueous positive electrode battery are affected, and the circulation stability of the aqueous positive electrode battery is poor.

In order to alleviate the problem of poor cycling stability of the aqueous positive electrode battery, the applicant researches and discovers that the aqueous conductive coating can be arranged in a layered manner so as to meet the requirements of adhesion and water resistance, thereby solving the problem of poor cycling stability. Specifically, the adhesive force of one side of the conductive coating close to the current collector can be improved, so that the stripping force between the conductive coating and the current collector is improved, and in order to prevent the water-based conductive coating from being dissolved by water in the positive electrode slurry, the water resistance of one side of the conductive coating far away from the current collector can be improved, and the second water-based conductive coating is prevented from being dissolved.

Based on the above considerations, in order to solve the problem of poor cycling stability of the aqueous positive electrode battery, the inventors have conducted intensive studies to design a positive electrode sheet, which comprises a current collector, an aqueous conductive coating and an electrode layer, wherein the aqueous conductive coating comprises a first aqueous conductive coating and a second aqueous conductive coating, and the first aqueous conductive coating is positioned on one side of the second aqueous conductive coating facing the current collector; the stripping force between the first aqueous conductive coating and the current collector is more than or equal to 50N/M; the second aqueous conductive coating is soluble in water and the dissolution time of ultrasonic cleaning is more than or equal to 200s; the stripping force between the electrode layer and the second aqueous conductive coating is more than or equal to 40N/M.

In the positive electrode plate, the aqueous conductive coating is arranged in a layered manner, the stripping force between the first aqueous conductive coating and the current collector is more than or equal to 50N/M, so that the adhesion force between the aqueous conductive coating and the current collector is ensured, and as the second aqueous conductive coating is positioned between the first conductive coating and the electrode layer, the second aqueous conductive coating is soluble in water and the dissolution time of ultrasonic cleaning is more than or equal to 200s, so that the second aqueous conductive coating has good water resistance, and when the aqueous conductive coating is used in the preparation of an aqueous positive electrode, the problems that the resistance of the aqueous positive electrode is increased and the coating is stripped due to the dissolution of water in the positive electrode slurry for forming the electrode layer in the preparation process can be avoided, and the sealing property and the electrical connectivity between the electrode layer and the current collector are further effectively improved, and the cycle stability and the capacity cycle retention rate of the battery are improved.

The battery cell disclosed by the embodiment of the application can be used in electric devices such as vehicles, ships or aircrafts, but is not limited to the electric devices. The power supply system with the battery cells, the batteries and the like disclosed by the application can be used for forming the power utilization device, so that the circulation stability of the batteries is improved.

The embodiment of the application provides an electricity utilization device using a battery as a power supply, wherein the electricity utilization device can be, but is not limited to, a mobile phone, a tablet, a notebook computer, an electric toy, an electric tool, a battery car, an electric car, a ship, a spacecraft and the like. Among them, the electric toy may include fixed or mobile electric toys, such as game machines, electric car toys, electric ship toys, electric plane toys, and the like, and the spacecraft may include planes, rockets, space planes, and spacecraft, and the like.

For convenience of description, the following embodiment will take an electric device according to an embodiment of the present application as an example of the vehicle 1000.

Referring to fig. 1, fig. 1 is a schematic structural diagram of a vehicle 1000 according to some embodiments of the present application. The vehicle 1000 may be a fuel oil vehicle, a gas vehicle or a new energy vehicle, and the new energy vehicle may be a pure electric vehicle, a hybrid vehicle or a range-extended vehicle. The interior of the vehicle 1000 is provided with a lithium ion battery 100, and the lithium ion battery 100 may be provided at the bottom or at the head or at the tail of the vehicle 1000. The lithium ion battery 100 may be used for power supply of the vehicle 1000, for example, the lithium ion battery 100 may serve as an operating power source of the vehicle 1000. The vehicle 1000 may also include a controller 200 and a motor 300, the controller 200 being configured to control the lithium ion battery 100 to power the motor 300, for example, for operating power requirements during start-up, navigation, and travel of the vehicle 1000.

In some embodiments of the present application, lithium ion battery 100 may not only be used as an operating power source for vehicle 1000, but also as a driving power source for vehicle 1000, instead of or in part instead of fuel oil or natural gas, to provide driving power for vehicle 1000.

Referring to fig. 2, fig. 2 is an exploded view of a lithium ion battery 100 according to some embodiments of the present application. The lithium ion battery 100 includes a case 10 and a battery cell 20, and the battery cell 20 is accommodated in the case 10. The case 10 is used to provide an accommodating space for the battery cell 20, and the case 10 may have various structures. In some embodiments, the case 10 may include a first portion 11 and a second portion 12, the first portion 11 and the second portion 12 being overlapped with each other, the first portion 11 and the second portion 12 together defining an accommodating space for accommodating the battery cell 20. The second portion 12 may be a hollow structure with one end opened, the first portion 11 may be a plate-shaped structure, and the first portion 11 covers the opening side of the second portion 12, so that the first portion 11 and the second portion 12 together define a containing space; the first portion 11 and the second portion 12 may be hollow structures each having an opening at one side, and the opening side of the first portion 11 is engaged with the opening side of the second portion 12. Of course, the case 10 formed by the first portion 11 and the second portion 12 may be of various shapes, such as a cylinder, a rectangular parallelepiped, or the like.

In the lithium ion battery 100, the battery cells 20 may be plural, and the plural battery cells 20 may be connected in series or parallel or in series-parallel, and the series-parallel refers to that the plural battery cells 20 are connected in series or parallel. The plurality of battery cells 20 can be directly connected in series or in parallel or in series-parallel, and then the whole formed by the plurality of battery cells 20 is accommodated in the box 10; of course, the lithium ion battery 100 may also be a battery module formed by connecting a plurality of battery cells 20 in series or parallel or series-parallel connection, and then connecting a plurality of battery modules in series or parallel or series-parallel connection to form a whole and be accommodated in the case 10. The lithium ion battery 100 may further include other structures, for example, the lithium ion battery 100 may further include a bus member for making electrical connection between the plurality of battery cells 20.

Wherein each battery cell 20 may be a secondary battery or a primary battery; but not limited to, lithium sulfur batteries, sodium ion batteries, or magnesium ion batteries. The battery cell 20 may be in the shape of a cylinder, a flat body, a rectangular parallelepiped, or other shapes, etc.

Referring to fig. 3, fig. 3 is a schematic exploded view of a battery cell 20 according to some embodiments of the present disclosure. The battery cell 20 refers to the smallest unit constituting the battery. As shown in fig. 3, the battery cell 20 includes an end cap 21, a case 22, an electrode assembly 23, and other functional components.

The end cap 21 refers to a member that is covered at 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 may be adapted to the shape of the housing 22 to fit the housing 22. Optionally, the end cover 21 may be made of a material (such as an aluminum alloy) with a certain hardness and strength, so that the end cover 21 is not easy to deform when being extruded and collided, so that the battery cell 20 can have higher structural strength, and the safety performance can be improved. The end cap 21 may be provided with a functional member such as an electrode terminal 21 a. The electrode terminal 21a may be used to be electrically connected with the electrode assembly 23 for outputting or inputting electric power of the battery cell 20. In some embodiments, the end cap 21 may also be provided with a pressure relief mechanism for relieving the internal pressure when the internal pressure or temperature of the battery cell 20 reaches a threshold. The material of the end cap 21 may be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., which is not particularly limited in the embodiment of the present application. In some embodiments, insulation may also be provided on the inside of the end cap 21, which may be used to isolate electrical connection components within the housing 22 from the end cap 21 to reduce the risk of short circuits. By way of example, the insulation may be plastic, rubber, or the like.

The case 22 is an assembly for cooperating with the end cap 21 to form an internal environment of the battery cell 20, wherein the formed internal environment may be used to accommodate the electrode assembly 23, the electrolyte, and other components. The case 22 and the end cap 21 may be separate members, and an opening may be provided in the case 22, and the interior of the battery cell 20 may be formed by covering the opening with the end cap 21 at the opening. It is also possible to integrate the end cap 21 and the housing 22, but specifically, the end cap 21 and the housing 22 may form a common connection surface before other components are put into the housing, and when it is necessary to encapsulate the inside of the housing 22, the end cap 21 is then put into place with the housing 22. The housing 22 may be of various shapes and sizes, such as rectangular parallelepiped, cylindrical, hexagonal prism, etc. Specifically, the shape of the case 22 may be determined according to the specific shape and size of the electrode assembly 23. The material of the housing 22 may be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., which is not particularly limited in the embodiments of the present application.

The electrode assembly 23 is a component in which electrochemical reactions occur in the battery cell 20. One or more electrode assemblies 23 may be contained within the housing 22. The electrode assembly 23 is mainly formed by winding or stacking a positive electrode sheet and a negative electrode sheet, and a separator is generally provided between the positive electrode sheet and the negative electrode sheet. The portions of the positive and negative electrode sheets having active material constitute the main body portion of the electrode assembly 23, and the portions of the positive and negative electrode sheets having no active material constitute the tabs 23a, respectively. The positive electrode tab and the negative electrode tab may be located at one end of the main body portion together or located at two ends of the main body portion respectively. During charge and discharge of the battery, the positive electrode active material and the negative electrode active material react with the electrolyte, and the tab 23a is connected to the electrode terminal 21a to form a current loop.

Referring to fig. 4, according to some embodiments of the present application, positive electrode tab 24 includes a current collector 240, an aqueous conductive coating, and an electrode layer 243, the aqueous conductive coating including a first aqueous conductive coating 241 and a second aqueous conductive coating 242, the first aqueous conductive coating 241 being located on a side of the second aqueous conductive coating 242 facing the current collector 240; the stripping force between the first aqueous conductive coating 241 and the current collector 240 is more than or equal to 50N/M; the second aqueous conductive coating 242 is soluble in water and the dissolution time of ultrasonic cleaning is greater than or equal to 200 seconds; the stripping force between the electrode layer 243 and the second aqueous conductive coating 242 is more than or equal to 40N/M.

The aqueous conductive coating refers to the corresponding solvent of the slurry forming the aqueous conductive coating is water.

The dissolution time of the second aqueous conductive coating 242 for ultrasonic cleaning refers to: the second aqueous conductive coating 242 has a first side and a second side, the first side being located on a side of the second side facing away from the first aqueous conductive coating 241, and the first side is subjected to ultrasonic cleaning after being contacted with water, so that the second aqueous conductive coating 242 is dissolved from the first side to the second side and the total time required for dissolving the second side is required.

In the technical scheme of the embodiment of the application, the aqueous conductive coating is layered, the peeling force between the first aqueous conductive coating 241 and the current collector 240 is more than or equal to 50N/M, so that the adhesion force between the aqueous conductive coating and the current collector 240 is ensured, and as the second aqueous conductive coating 242 is positioned 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 more than or equal to 200s, so that the second aqueous conductive coating 242 has good water resistance, when the aqueous conductive coating is used in the preparation of an aqueous anode, the problems that the aqueous anode resistance is increased, and the coating peels off due to the dissolution of water in the anode slurry for forming the electrode layer 243 in the preparation process can be avoided, and the sealing property and the electrical connectivity between the electrode layer 243 and the current collector 240 are further effectively improved, and the cycle stability and the capacity cycle retention rate of the battery 100 are improved. The stripping force between the electrode layer and the second water-based conductive coating is more than or equal to 40N/M, so that the electrode layer and the second water-based conductive coating are prevented from being separated from each other, and the stability of the positive electrode plate is prevented from being influenced.

Referring to fig. 4, optionally, the first aqueous conductive coating 241 has a degree of crosslinking of 0 and the second aqueous conductive coating 242 has a degree of crosslinking > 0 according to some embodiments of the present application.

Crosslinking refers to coupling 2 or more molecules individually with a crosslinking agent to bind the molecules together.

The degree of crosslinking, also known as the crosslinking index, is generally expressed in terms of crosslink density or number average molecular weight between two adjacent crosslinks or moles per cubic centimeter of crosslinks.

The first aqueous conductive coating 241 has a degree of crosslinking of 0, i.e., the first aqueous conductive coating 241 is uncrosslinked, and the second aqueous conductive coating 242 has a degree of crosslinking of > 0, i.e., the second aqueous conductive coating 242 is crosslinked.

Since the aqueous conductive coating contains the aqueous binder, the crosslinking agent is used for crosslinking the aqueous binder to change the structure of the aqueous binder, so that the solvent resistance of the aqueous binder is improved, and meanwhile, the adhesive force is reduced, therefore, in the manner described above, the crosslinking degree of the first aqueous conductive coating 241 is 0, that is, the first aqueous conductive coating 241 is not crosslinked to provide a better adhesive force, and the crosslinking degree of the second aqueous conductive coating 242 is more than 0, so that the aqueous conductive coating has good water resistance, thereby avoiding the problems that the water resistance of the aqueous positive electrode is increased and the coating is peeled off due to the dissolution of water in the positive electrode slurry for forming the electrode layer 243 in the preparation process, improving the adhesion and electrical connectivity between the electrode layer 243 and the current collector 240, and improving the cycle stability and the capacity cycle retention rate of the battery 100.

Referring to fig. 4, in some embodiments, the degree of crosslinking of the second aqueous conductive coating 242 decreases gradually from the side near the electrode layer 243 to the side near the first aqueous conductive coating 241.

That is, the water resistance of the side of the second aqueous conductive coating 242 near the electrode layer 243 is better than that of the side thereof near the first aqueous conductive coating 241, and the adhesion of the side of the second aqueous conductive coating 242 near the electrode layer 243 is better than that of the side thereof near the first aqueous conductive coating 241, so that the adhesion between the second aqueous conductive coating 242 and the first aqueous conductive coating 241 is effectively enhanced on the premise of realizing the water resistance of the second aqueous conductive coating 242.

According to some embodiments of the present application, optionally, the method for determining the dissolution time of the ultrasonic cleaning of the second aqueous conductive coating is: the positive electrode sheet without the electrode layer is placed in water, ultrasonic cleaning is carried out under the conditions that the wave source distance is 50-55 mm and the wave source frequency is 25KHZ, the moment when the positive electrode sheet is observed to expose the current collector is defined as the time from when the second aqueous conductive coating is dissolved, and ultrasonic cleaning is started until the second aqueous conductive coating is dissolved, and the time from when the second aqueous conductive coating is dissolved is taken as the ultrasonic cleaning dissolving time of the second aqueous conductive coating.

Because the first aqueous conductive coating is not waterproof, the first conductive coating can be instantly dissolved in water in the ultrasonic cleaning process, and the error of the dissolution time of the second aqueous conductive coating can not be caused.

Referring to fig. 4, optionally, the second aqueous conductive coating 242 has a thickness less than the first aqueous positive electrode coating 241, and the second aqueous conductive coating 242 has a thickness of 0.3-0.7 μm, according to some embodiments of the present application.

The thickness ratio is reasonable, so that the stability of connection between the water-based conductive coating and the current collector 240 can be realized, the water-based conductive coating has good water resistance, actual requirements are met, if the thickness ratio of the second water-based conductive coating 242 is too large, the adhesion between the water-based conductive coating and the current collector 240 is small, the water-based conductive coating is easy to strip, and if the thickness ratio of the second water-based conductive coating 242 is too small, the water resistance of the water-based conductive coating is insufficient, so that the water in the positive electrode slurry of the electrode layer 243 is dissolved in the preparation process of the conductive coating, the water-based positive electrode resistance is increased, and the coating is stripped.

Illustratively, the second aqueous conductive coating thickness 242 is any one of, or between any two 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.

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

The thickness of the aqueous conductive coating is restrained, the thickness of the aqueous conductive coating is reduced on the premise that the conductivity of the aqueous conductive coating is fully applied, the thickness of the positive electrode plate 24 is made to be certain, the thickness of the positive electrode layer arranged on the current collector 240 is increased, and the energy density of the positive electrode plate 24 is improved.

Illustratively, the thickness of the aqueous conductive coating is any one of, or between any two 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.

According to some embodiments of the present application, the resistance change rate of the aqueous conductive coating is optionally less than or equal to 10% as the resistance standard deviation divided by the resistance average.

That is, the resistance of the aqueous conductive coating is substantially uniformly distributed, improving the uniformity of the performance of the positive electrode sheet 24.

Alternatively, the average resistance value is less than or equal to 1.5mΩ.

Referring to FIG. 4, according to some embodiments of the present application, the thickness variation rate of the aqueous conductive coating is optionally less than or equal to 10% as the thickness standard deviation divided by the thickness average.

That is, the thickness of the aqueous conductive coating is substantially uniformly distributed throughout, improving the uniformity of the performance of the positive electrode sheet 24.

According to some embodiments of the present application, the present application further provides a method for preparing the positive electrode sheet, which includes the following steps: forming an aqueous conductive coating on the surface of the current collector; coating positive electrode slurry on the surface of the water-based conductive coating, and drying to obtain a positive electrode plate.

The step of forming the aqueous conductive coating on the surface of the current collector includes: coating a first aqueous conductive paste on the surface of a current collector, and drying to form a first aqueous conductive coating; and then coating a second aqueous conductive slurry on the surface of the first conductive coating, and drying to form a second conductive coating.

The first aqueous conductive paste consists of a conductive material, a colloid dispersing agent, an aqueous binder and water, and the second aqueous conductive paste consists of a conductive material, a colloid dispersing agent, an aqueous binder, a crosslinking agent and water.

The preparation method is simple, but the aqueous binder in the second aqueous conductive slurry reacts with the crosslinking agent to influence the thickness and the resistance uniformity of the aqueous conductive coating.

According to some embodiments of the present application, optionally, the step of forming an aqueous conductive coating on the surface of the current collector comprises: coating aqueous conductive slurry containing an aqueous binder on the surface of a current collector, and drying to form a pre-aqueous conductive coating; and (3) coating an aqueous solution of a cross-linking agent on the surface of the pre-aqueous conductive coating, and drying to form the aqueous conductive coating.

In the above steps, the aqueous conductive coating is formed by coating the surface of the pre-aqueous conductive coating with the aqueous cross-linking agent solution and drying, so that the problem that the uniformity of the performance of the positive electrode plate cannot be ensured due to uneven thickness and resistance distribution of the formed aqueous conductive coating caused by the influence of the cross-linking reaction generated on the conductive paste after the cross-linking agent is added into the conductive paste and the stability of the conductive paste can be effectively avoided.

According to some embodiments of the present application, optionally, the aqueous conductive paste comprises, in mass percent: 5% -15% of conductive material, 0.1% -2% of colloid dispersant, 2% -10% of water-based adhesive and 80% -90% of water.

The conductive material functions as a conductor that can be dispersed in the aqueous conductive paste. The conductive agent may be any of various conductive agents for carbon materials commonly used in the art, but is not limited thereto.

The colloid dispersant is used for coating and promoting the conductive material to be uniformly dispersed in the aqueous conductive slurry to form a suspension system.

The aqueous adhesive is an adhesive that is soluble in water.

In the proportion range, the aqueous conductive coating formed by the aqueous conductive slurry has good electrical property.

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

The binder is a water-soluble high polymer with carboxyl, and the crosslinking agent is combined with part of carboxyl in the aqueous binder to crosslink, so that the molecular chain of the binder is changed from linear to a firmer three-dimensional net structure, thereby improving the water resistance of the aqueous conductive coating, and simultaneously, the carboxyl is taken as a hydrophilic group, and when the aqueous positive electrode slurry is coated on the conductive coating, the wetting, spreading and bonding effects of the aqueous positive electrode slurry on the aqueous conductive coating can be better ensured, and the low resistance and high bonding force of the aqueous conductive coating on the current collector are ensured.

According to some embodiments of the present application, the aqueous binder optionally includes at least one of polyacrylic acid and salts thereof, water-soluble polyacrylates and salts, water-soluble ethylene vinyl acetate copolymers, and acrylonitrile multipolymers.

The aqueous conductive paste containing the aqueous binder has good wettability with a current collector, can be uniformly coated on the current collector, has good effects of infiltration, spreading and adhesion with the aqueous positive paste, and ensures low resistance and high adhesion of the aqueous conductive coating on the current collector.

The polyacrylate includes, but is not limited to, sodium polyacrylate, potassium polyacrylate, etc., and can be selected by those skilled in the art according to practical requirements.

Illustratively, the aqueous binder is polyacrylic acid, or the aqueous binder is sodium polyacrylate, or the aqueous 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 crosslinker in the aqueous crosslinker solution comprises one or more of aziridine and derivatives thereof, polycarbodiimide and salts thereof, epoxysilane and derivatives thereof, polymers of grafted epoxysilane, polyethyleneimine.

The cross-linking agent can be combined and cross-linked with part of carboxyl groups in the aqueous binder, so that the molecular chain of the binder is changed from linear to a firmer three-dimensional net structure, and the water resistance of the conductive coating is improved.

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

In 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 meets the requirements of water resistance and adhesion.

Illustratively, the mass fraction of crosslinker in the aqueous crosslinker solution is any one of or between any two of 3.5%, 5.0%, 7.0%, 10.0%, 13.0%, 15.0%, 17.0%, 20.0%, 23.0%, 25.0%.

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

Optionally, in accordance with some embodiments of the present application, the conductive material comprises at least one of carbon black, graphite, partially graphitized coke, carbon fiber, acetylene black, vapor grown carbon fiber, and fullerene nanotubes.

The conductive material is convenient to obtain and good in conductive effect.

According to some embodiments of the present application, optionally, the colloidal dispersing agent is a colloid, optionally, the colloidal material is at least one of xanthan gum, locust bean gum, guar gum, acacia gum, gelatin, carrageenan.

The colloidal dispersing agent is convenient to obtain, and the dispersing effect of uniformly dispersing the conductive material in the aqueous conductive slurry is good.

Illustratively, 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, the pre-aqueous conductive coating is optionally dried at a temperature of 70 ℃ to 120 ℃ for a time of 10s to 60s.

The pre-aqueous conductive coating can be effectively dried at the above temperature and time ranges.

According to some embodiments of the present application, the aqueous conductive coating is optionally dried at a temperature of 70 ℃ to 120 ℃ for a time of 10s to 60s.

The crosslinking agent and the aqueous binder can be effectively reacted and cured to form the aqueous conductive coating within the above temperature and time range.

According to some embodiments of the present application, the present application further provides a battery cell, including the positive electrode tab of any one of the above schemes.

According to some embodiments of the present application, there is also provided a battery comprising the battery cell of any of the above aspects.

According to some embodiments of the present application, there is also provided an electrical device comprising a battery according to any of the above aspects, and the battery is used to provide electrical energy to the electrical device.

The powered device may be any of the aforementioned devices or systems employing batteries.

The following examples are set forth to better illustrate the present application.

Examples and comparative examples

[ preparation of Water-based Positive electrode sheet ]

Current collector: aluminum foil.

Aqueous electroconductive pastes of examples 1-6 and comparative examples 1-4 and comparative examples 7-8: the conductive paste comprises the following components in percentage by mass: 10% of conductive material, 0.2% of colloid dispersant, 7% of binder and 82.8% of water.

The aqueous electroconductive paste of example 7: the conductive paste comprises the following components in percentage by mass: 7% of conductive material, 0.2% of colloid dispersant, 7% of binder and 85.8% of water.

The aqueous electroconductive paste of example 8: the conductive paste comprises the following components in percentage by mass: 12% of conductive material, 0.2% of colloid dispersant, 7% of binder and 80.8% of water.

The aqueous electroconductive paste of comparative example 5: the conductive paste comprises the following components in percentage by mass: 16% of conductive material, 0.2% of colloid dispersant, 1% of binder and 82.8% of water.

The aqueous electroconductive paste of comparative example 6: the conductive paste comprises the following components in percentage by mass: 3% of conductive material, 0.2% of colloid dispersant, 15% of binder and 82.8% of water.

In the aqueous electroconductive pastes of the above examples and comparative examples, electroconductive graphite (trade name: SP5000, commercially available from kappat chemical engineering ltd. In Shanghai) was used as the electroconductive material; the colloidal dispersant used was xanthan gum (molecular weight about 1000000g/mol, available from Shanghai Ala Biochemical technologies Co., ltd.); the binder is polyacrylic acid with average molecular weight of 300000-800000.

Conductive paste of comparative example 3: the conductive paste comprises the following components in percentage by mass: 10% of conductive material, 0.2% of colloid dispersant, 7% of binder and 82.8% of water, wherein conductive graphite (purchased from Shanghai Kaijin chemical Co., ltd., brand name: SP 5000) is used as the conductive material; the colloidal dispersant was xanthan gum (molecular weight: about 1000000g/mol, available from Shanghai Ala Biochemical technologies Co., ltd.) and the binder was polyvinylidene fluoride.

Aqueous crosslinker solution: the cross-linking agent adopts water-based polycarbodiimide with molecular weight of 10000-40000.

Positive electrode slurry: lithium iron phosphate as an active material of the lithium iron phosphate, conductive carbon black as a conductive agent, a compound dispersion stabilizer and an aqueous binder according to the weight ratio of 96:1:1.2:1.8 mixing, wherein the compounded dispersion stabilizer adopts a compounded mixture of xanthan gum (with the molecular weight of about 1000000g/mol, purchased from Shanghai Ala Biotechnology Co., ltd.) and polyethylenimine (with the molecular weight of about 1200g/mol, purchased from Shanghai Ala Biotechnology Co., ltd.) and the weight ratio of the compounded mixture is 1:1; the water-based binder adopts acrylonitrile copolymer (code LA133, purchased from Sichuan Gele technology Co., ltd.) and the balance of deionized water as solvent, and the mixture is stirred and mixed uniformly to obtain the anode slurry with the solid content of 50%.

Examples 1 to 8 and comparative examples 3 and 5 to 8 are positive electrode sheet preparation methods:

and uniformly coating aqueous conductive slurry on the surface of the current collector, and drying to form the pre-aqueous conductive coating.

Uniformly coating the surface of the pre-aqueous conductive coating with a cross-linking agent aqueous solution, and drying at 90 ℃ to form the aqueous conductive coating, wherein the thickness of the aqueous conductive coating is 1.5 mu m.

Uniformly coating the same positive electrode slurry on the surface of the water-based conductive coating, drying at 90 ℃ to form an electrode layer with the same thickness, and then carrying out cold pressing and slitting to obtain the positive electrode plate.

Comparative example 1 the positive electrode sheet was prepared in a manner differing from example 1 only in that:

the surface of the current collector was uniformly coated with the conductive paste, and dried at 90 ℃ to form a conductive coating (the same as the aqueous conductive paste in example 1), wherein the thickness of the aqueous conductive coating was 1.5 μm.

The positive electrode sheet was prepared in a manner differing from that of example 1 only in: the aqueous conductive coating was directly coated with a conductive paste containing a crosslinking agent (differing from the aqueous conductive paste in example 1 only in that the crosslinking agent was contained), and dried at 90 ℃ to form an aqueous conductive coating, wherein the thickness of the aqueous conductive coating was 1.5 μm.

The positive electrode sheet was prepared in a manner differing from that of example 1 only in: the surface of the current collector was uniformly coated with a first aqueous electroconductive paste (same as the aqueous electroconductive paste in example 1) containing no crosslinking agent, and dried at 90 ℃ to form a first aqueous electroconductive coating.

The surface of the first aqueous conductive coating layer is uniformly coated with a second aqueous conductive paste containing a cross-linking agent (only the cross-linking agent is contained in the second aqueous conductive paste), and the second aqueous conductive coating layer is formed by drying at 90 ℃, wherein the total thickness of the first aqueous conductive coating layer and the second aqueous conductive coating layer is 1.5 mu m, and the thickness of the second aqueous conductive coating layer is 1 mu m.

The parameters of the examples and comparative examples are shown in Table 1.

[ preparation of negative electrode sheet ]

The active material artificial graphite, conductive agent carbon black, binder Styrene Butadiene Rubber (SBR) and thickener sodium hydroxymethyl cellulose (CMC) are mixed according to the weight ratio of 96.2:0.8:0.8:1.2, dissolving in deionized water serving as a solvent, and uniformly mixing to prepare negative electrode slurry; and uniformly coating the negative electrode slurry on a negative electrode current collector copper foil, and drying, cold pressing and cutting to obtain a negative electrode plate.

[ preparation of electrolyte ]

In an argon atmosphere glove box (H2O is less than 0.1ppm, O2 is less than 0.1 ppm), uniformly mixing organic solvent Ethylene Carbonate (EC)/ethylmethyl carbonate (EMC) according to a volume ratio of 3/7, dissolving the added LiPF6 lithium salt in the organic solvent, and uniformly stirring to obtain an electrolyte, wherein the mass percentage of the LiPF6 in the electrolyte is 12.5%.

[ isolation Membrane ]

The porous PE film was coated with a ceramic coating having a thickness of 2. Mu.m, and was used as a separator.

[ preparation of lithium ion Battery ]

The positive electrode plate, the isolating film and the negative electrode plate of the embodiment 1 are sequentially stacked, the isolating film is positioned between the positive electrode plate and the negative electrode plate to play a role of isolation, then the bare cell is obtained by winding, the tab is welded on the bare cell, the bare cell is arranged in an aluminum shell, baking and dewatering are carried out at 80 ℃, and then electrolyte is injected and sealed, so that the uncharged battery is obtained. And the uncharged battery is subjected to the procedures of standing, hot and cold pressing, formation, shaping, capacity testing and the like in sequence, so that a lithium ion battery product is obtained.

The performance test results are shown in fig. 5-7 and tables 1 and 2:

1. water resistance test of the second aqueous conductive coating:

the positive electrode sheet without the electrode layer is placed in water, ultrasonic cleaning is carried out under the conditions that the wave source distance is 50-55 mm and the wave source frequency is 25KHZ, the moment when the positive electrode sheet is observed to expose the current collector is defined as the time from when the second aqueous conductive coating is dissolved, and ultrasonic cleaning is started until the second aqueous conductive coating is dissolved, and the time from when the second aqueous conductive coating is dissolved is taken as the ultrasonic cleaning dissolving time of the second aqueous conductive coating.

2. Peel force test:

a tensile machine was used for testing, and the peel force of the aqueous conductive coating from the aluminum foil was measured.

3. Thickness test:

ten-thousandth test: taking an area of 5cm x 5cm of an aluminum foil, randomly testing 50 points, taking an average thickness R1 of the aluminum foil, randomly testing 50 points in an area of 5cm x 5cm of a semi-finished product coated to form a pre-aqueous conductive coating, taking an average thickness R2 of the aluminum foil and the pre-aqueous conductive coating, taking an aqueous solution of a coating cross-linking agent, drying to form an area of 5cm x 5cm of a finished product of the aqueous conductive coating, randomly testing 50 points, taking an average thickness R3 of the aluminum foil and the total thickness R3 of the aqueous conductive coating, wherein the total thickness R4=R3-R1 and the thickness difference R5=R3-R2. Second aqueous conductive coating thickness= [ R2-R1 ] aqueous gel mass fraction 0.40+ curing agent mass fraction R3 0.25 ] thickness difference r5.1.15.

4. Resistance test:

and taking points at intervals of 1cm along the length direction of the positive pole piece to test the resistance, and taking 100 pieces of electrical test data to obtain a resistance average value.

[ Positive electrode coating System test ]

1. Aqueous, oil positive electrode system distinction: the NMP residue in the pole piece was tested using a weather chromatograph, see patent CN113804799A, with a residue greater than 50PPM and the pole piece using polyvinylidene fluoride as the binder being the oil system, and vice versa being the water system positive electrode.

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 test procedure was as follows: the battery was charged to 3.65V at a constant current of 1/3C, then charged to 0.05C at a constant voltage of 3.65V, left for 5min, then discharged to 2.7V at 1/3C, and the resulting capacity was designated as initial capacity C0. Repeating the above steps for the same battery, and recording the discharge capacity Cn of the battery after the nth cycle, wherein the battery capacity retention rate pn=cn/c0 is 100% after each cycle. In this test procedure, the first cycle corresponds to n=1, the second cycle corresponds to n=2, and … … the 100 th cycle corresponds to n=100. The battery capacity retention rate data corresponding to example 1 in table 1 is data measured after cycling 800 times under the above test conditions, i.e., the value of P800.

Table 1 examples and comparative parameters and partial test results

Table 2 test results of examples and comparative examples

In table 2, the stability time of the conductive paste passes the particle size change rate test of the conductive paste, and industry experience shows that when the particle size D50 is increased by more than 50%, the particles in the paste are considered to be seriously agglomerated and are not suitable for being put into production, and according to the actual production requirement, the paste D50 needs to have the class change rate of less than 50% within 24 hours, so that the paste can be judged to have qualified stability, and the paste can be put into production, wherein D50 refers to the particle size of the substance contained in the prepared conductive paste when the particle size is increased by 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 not less than 50N/M; the dissolution time of ultrasonic cleaning of the second aqueous conductive coating is more than or equal to 200s.

From examples 1-3, 6, it is seen that different mass fractions of the aqueous crosslinker will affect the second aqueous conductive coating thickness, and that the mass fraction of crosslinker in the aqueous crosslinker solution is positively correlated with the second aqueous conductive coating thickness. As can be seen from example 6, although the positive electrode sheet of the present application can be prepared from the aqueous solution of the crosslinking agent with a mass fraction of 25%, the thickness of the prepared second aqueous conductive coating layer is too large compared with examples 1 to 3, which affects the battery capacity and the size of the electrode sheet, so that the effect of the crosslinking agent in the aqueous solution of the crosslinking agent with a mass fraction of 10% to 20% is better.

According to examples 1, 4 and 5, the cross-linking agent can be selected to select different components according to actual requirements, and similar effects can be achieved, so as to obtain the second water-based conductive coating with water resistance.

According to examples 1, 7 and 8, the composition ratio of the aqueous electroconductive pastes was different, and even if the same aqueous solution of the crosslinking agent was used, the electrochemical performance of the positive electrode sheet was affected even if the same preparation method was used.

Comparative example 1, which does not contain a crosslinking agent, corresponds to the second aqueous conductive coating layer having no water resistance formed, and the peeling force between the first aqueous conductive coating layer and the aluminum foil is improved, but the water resistance time of the conductive coating layer of 1.5 μm is only 12s, which cannot solve the technical problems of the present application, and the battery capacity retention rate is significantly reduced.

Comparative example 2 compared with example 1, since the crosslinking agent was directly added to the conductive paste, the peeling force between the aqueous conductive coating and the aluminum foil was too small, the aqueous conductive coating was easily detached from the aluminum foil, and the both could not be stably connected together, and the crosslinking agent and the adhesive were reacted before coating, resulting in uneven resistance and thickness distribution of the final conductive coating.

The binder used in comparative example 3 was polyvinylidene fluoride (pvdf), which was insoluble in water, i.e., the prepared positive electrode coating system was an oil-based positive electrode, and the first-coated primer interface was a hydrophobic interface (hydrophobic effect like lotus leaf), so that the aqueous positive electrode slurry could not be effectively coated on the primer interface in the following.

Comparative example 4 was different from the coating method of example 1 in that the uniformity of the resistance and thickness distribution was reduced. The crosslinking agent in the second layer reacts with the water-based binder in the second layer to crosslink, which can cause the abnormality of the second layer slurry system, the problems of gel, agglomeration, layering and the like, and when the second layer is coated, the thickness distribution and the particle size difference in the coating are overlarge, so that the overall thickness and resistance difference of the pole piece are large, and the using effect is influenced.

Comparative example 5 compared with example 1, the aqueous binder in the conductive paste was too small in mass percentage, resulting in the aqueous binder not being effectively crosslinked, insufficient in water resistance, and the aqueous conductive layer being insufficient in adhesion to the aluminum foil and the electrode layer, respectively, resulting in the three being easily peeled off from each other.

Comparative example 6 compared with example 1, the aqueous binder in the conductive paste was excessively large in mass percentage and the conductive material was insufficient, affecting the dispersion of each component in the formed coating layer and the resistance of the coating layer, and degrading the battery cycle performance.

Comparative example 7 differs from example 1 in that the binder raw material is selected differently, and polyacrylamide itself may gel in an aqueous solution due to the presence of an amide group, affecting solution dispersion stability, thereby affecting the thickness of a conductive coating formed and uniformity of distribution of resistance, and at the same time, remaining amide groups in the final coating may react with an electrolyte to generate ammonia gas or other byproducts, affecting battery performance.

Comparative example 8 the mass fraction of the crosslinking agent in the aqueous solution of the crosslinking agent was too small compared with example 1, resulting in the formation of a second aqueous conductive coating layer having too small a thickness to meet the water resistance requirement.

FIG. 5 is a cross-sectional high-magnification SEM image of an aqueous conductive coating of example 1 of the present application; as can be seen from fig. 5, the aqueous conductive coating layer includes a first aqueous conductive coating layer formed on the aluminum foil, and a second aqueous conductive coating layer formed on the first aqueous conductive coating layer, which has agglomerates having a larger particle size due to a crosslinking reaction.

Fig. 6 is a SEM image of the low magnification of the positive electrode sheet provided in example 1, and it can be seen that the aqueous conductive coating is stably connected with the aluminum foil.

Fig. 7 is a low-magnification SEM image of the cross-section of the positive electrode sheet of comparative example 1 of the present application (positive electrode sheet comprising aluminum foil-aqueous conductive coating-positive electrode layer), and it can be seen that the aqueous conductive coating is dissolved, resulting in separation of the positive electrode layer from the aluminum foil.

Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present application, and not for limiting the same; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the embodiments, and are intended to be included within the scope of the claims and description. In particular, the technical features mentioned in the respective embodiments may be combined in any manner as long as there is no structural conflict. The present application is not limited to the specific embodiments disclosed herein, but encompasses all technical solutions falling within the scope of the claims.

Claims

The positive electrode plate comprises a current collector, a water-based conductive coating and an electrode layer, wherein the water-based conductive coating comprises a first water-based conductive coating and a second water-based conductive coating, and the first water-based conductive coating is positioned on one side of the second water-based conductive coating facing the current collector;

the stripping force between the first aqueous conductive coating and the current collector is more than or equal to 50N/M;

the second aqueous conductive coating is soluble in water, and the dissolution time of ultrasonic cleaning is more than or equal to 200s;

the stripping force between the electrode layer and the second aqueous conductive coating is more than or equal to 40N/M;

optionally, the stripping force between the first aqueous conductive coating and the current collector is greater than or equal to 54N/M.
The positive electrode sheet of claim 1, wherein the first aqueous conductive coating has a degree of crosslinking of 0 and the second aqueous conductive coating has a degree of crosslinking of > 0.
The positive electrode sheet according to claim 1 or 2, wherein the degree of crosslinking of the second aqueous conductive coating layer decreases gradually from a side near the electrode layer to a side near the first aqueous conductive coating layer.
The positive electrode sheet according to any one of claims 1 to 3, wherein the determination method of the dissolution time of the second aqueous conductive coating by ultrasonic cleaning is:

And placing the positive electrode plate without the electrode layer into water, and ultrasonically cleaning under the conditions that the wave source distance is 50-55 mm and the wave source frequency is 25KHZ, wherein the moment at which the positive electrode plate is observed to expose the current collector is defined as the time from when the second aqueous conductive coating is dissolved to when the ultrasonic cleaning is started to when the second aqueous conductive coating is dissolved, as the ultrasonic cleaning dissolution time of the second aqueous conductive coating.
The positive electrode sheet of any one of claims 1-4, wherein the second aqueous conductive coating thickness is less than the first aqueous conductive coating thickness, the second aqueous conductive coating thickness being 0.3-0.7 μιη;

optionally, the aqueous conductive coating has a thickness of 1-5 μm.
The positive electrode sheet according to any one of claims 1 to 5, wherein a change in resistance is a change in resistance of 10% or less as a result of dividing a standard deviation of resistance by an average value of resistance.
The positive electrode sheet according to any one of claims 1 to 6, wherein the thickness variation rate of the aqueous conductive coating layer is 10% or less as a result of dividing a thickness standard deviation by a thickness average value.
A method for preparing the positive electrode sheet according to any one of claims 1 to 7, comprising the steps of:

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

and coating positive electrode slurry on the surface of the water-based conductive coating, and drying to obtain the positive electrode plate.
The method of preparing according to claim 8, wherein the step of forming the aqueous conductive coating on the surface of the current collector comprises:

coating aqueous conductive slurry containing an aqueous binder on the surface of the current collector, and drying to form a pre-aqueous conductive coating;

and coating a cross-linking agent aqueous solution on the surface of the pre-aqueous conductive coating, and drying to form the aqueous conductive coating.
The production method according to claim 9, wherein the aqueous electroconductive paste comprises, in mass percent: 5% -15% of conductive material, 0.1% -2% of colloid dispersant, 2% -10% of water-based adhesive and 80% -90% of water.
The method according to claim 10, wherein the aqueous binder is a water-soluble high molecular polymer having a carboxyl group.
The method of making according to claim 10 or 11, wherein the aqueous binder comprises at least one of polyacrylic acid and salts thereof, water-soluble polyacrylates and salts, water-soluble ethylene vinyl acetate copolymers, and acrylonitrile multipolymers.
The method of any of claims 9-12, wherein the cross-linking agent in the aqueous cross-linking agent solution comprises one or more of aziridine and derivatives thereof, polycarbodiimide and salts thereof, epoxysilane and derivatives thereof, a high polymer grafted epoxysilane, polyethylenimine.
The method of any one of claims 9-12, wherein the mass fraction of crosslinker in the aqueous crosslinker solution is greater than 3% and no greater than 25%, optionally between 10% and 20%.
The method of manufacturing of claim 10, wherein the conductive material comprises at least one of carbon black, graphite, partially graphitized coke, carbon fiber, acetylene black, vapor grown carbon fiber, and fullerene nanotubes.
The preparation method of claim 10, wherein the colloidal dispersant comprises at least one of xanthan gum, locust bean gum, guar gum, acacia, gelatin, and carrageenan.
The method of any one of claims 9-16, wherein the pre-aqueous conductive coating is formed by drying at a temperature of from 70 ℃ to 120 ℃ for a time of from 10s to 60s.
The production method according to any one of claims 9 to 16, wherein the aqueous conductive coating is formed by drying at a temperature of 70 ℃ to 120 ℃ for a time of 10s to 60s.
A battery cell comprising the positive electrode sheet according to any one of claims 1 to 7.
A battery comprising the battery cell of claim 19.
A powered device comprising the battery of claim 20.