WO2020134749A1

WO2020134749A1 - Electrode plate, electrochemical apparatus, battery module, battery and device

Info

Publication number: WO2020134749A1
Application number: PCT/CN2019/119967
Authority: WO
Inventors: 李伟; 薛庆瑞; 李静; 张子格; 杨献伟; 张扬
Original assignee: 宁德时代新能源科技股份有限公司
Priority date: 2018-12-29
Filing date: 2019-11-21
Publication date: 2020-07-02
Also published as: CN110660996A; CN110660996B

Abstract

The present application relates to an electrode plate, an electrochemical apparatus, a battery module, a battery and a device. The electrode plate comprises a current collector and an electrode active material layer disposed on at least one surface of the current collector. The current collector comprises a support layer and a conductive layer disposed on at least one surface of the support layer, and the thickness D2 of a single surface of the conductive layer satisfies: 30 nm≤D2≤3 μm. The electrode plate of the present application has good processability, and an electrochemical apparatus containing said electrode plate has high energy density and good electrical performance, as well as long term reliability.

Description

Electrode pole piece, electrochemical device, battery module, battery pack and equipment

Cross-reference of related applications

This application requires the priority of the Chinese patent application number 201811638368.5, entitled "An electrode pole piece and an electrochemical device", filed on December 29, 2018, the contents of which are incorporated into this application by reference.

Technical field

This application relates to the field of batteries, and in particular, to an electrode pole piece, an electrochemical device, a battery module, a battery pack, and equipment.

Background technique

Lithium ion batteries are widely used in electric vehicles and consumer electronic products due to their advantages such as high energy density, high output power, long cycle life, and low environmental pollution. With the continuous expansion of the application range of lithium-ion batteries, everyone's requirements for the weight energy density and volume energy density of lithium-ion batteries are becoming higher and higher.

In order to obtain a lithium ion battery with higher mass energy density and volume energy density, the lithium ion battery is usually improved as follows: 1) select a positive electrode material or a negative electrode material with a high specific discharge capacity; 2) optimize the mechanical design of the lithium ion battery, so that Minimize its volume; 3) Select positive pole pieces or negative pole pieces of high-pressure solid density; 4) Reduce the weight of each part of the lithium ion battery.

Among them, the improvement of the current collector is usually to select a lighter weight or a smaller thickness of the current collector, for example, a perforated current collector or a metal-plated plastic current collector can be used.

For pole pieces and batteries using a metal-plated plastic current collector, although the energy density is improved, there may be some performance degradation in processing performance, safety performance and electrical performance. To obtain pole pieces and current collectors with good electrochemical performance, many improvements are needed.

In order to overcome the shortcomings of the existing technology, this application is specifically filed.

Summary of the invention

Some embodiments of the present application provide an electrode pole piece, an electrochemical device, a battery module, a battery pack, and equipment.

In a first aspect, the present application provides an electrode pole piece including a current collector and an electrode active material layer disposed on at least one surface of the current collector. Wherein, the current collector includes a support layer and a conductive layer provided on at least one surface of the support layer, and the single-sided thickness D2 of the conductive layer satisfies: 30 nm≦D2≦3 μm. The electrode active material layer includes an electrode active material, a binder, and a conductive agent, and the conductive agent in the electrode active material layer has an uneven distribution in the thickness direction. Wherein based on the total weight of the electrode active material layer, the weight percentage of the conductive agent in the inner region of the electrode active material layer is higher than the weight percentage of the conductive agent in the outer region of the electrode active material layer, and The binder in the inner region of the electrode active material layer contains an acrylic-based/acrylate-based aqueous binder.

In a second aspect, the present application provides an electrochemical device, including a positive pole piece, a negative pole piece, a separator, and an electrolyte, wherein the positive pole piece and/or negative pole piece is the electrode described in the first aspect of the present application Pole piece.

In a third aspect, the present application also provides a battery module, including the electrochemical device according to the second aspect of the present invention.

According to a fourth aspect, the present application also provides a battery pack, including the battery module according to the third aspect of the present invention.

In a fifth aspect, the present application also provides an apparatus, including the electrochemical device described in the second aspect of the present application, the electrochemical device being used as a power source for the apparatus.

Compared with the prior art, the present application has at least the following advantages: 1) The electrode active material layer is divided into an inner region and an outer region in the thickness direction, the inner region has better conductivity than the outer region, and the outer region has an electrochemical capacity Higher than the inner area. 2) The inner area of the electrode active material layer can improve the interface of the composite current collector, improve the adhesion between the current collector and the electrode active material layer, and ensure that the electrode active material layer is more firmly placed on the surface of the composite current collector. 3) In addition, it can well overcome the disadvantages of poor conductivity of the composite current collector, and the conductive layer in the composite current collector is easily damaged. By effectively repairing and building a conductive network between the current collector and the active material in the electrode active material layer, Improve the electron transmission efficiency, reduce the resistance between the current collector and the electrode active material layer, which can effectively reduce the DC internal resistance of the battery, improve the power performance of the battery, and ensure that the battery is not prone to occur in the long-term cycle process. Phenomenon such as chemical decomposition and lithium precipitation effectively improve the long-term reliability of the battery cell.

Therefore, the electrode pole piece and the electrochemical device of the present application have good and balanced electrical performance, safety performance, and processing performance. The battery module, battery pack and equipment including the electrochemical device described in this application also have the same advantages as the electrochemical device.

BRIEF DESCRIPTION

The positive electrode sheet, electrochemical device, battery module, battery pack, and equipment of the present application will be described in detail below in conjunction with the drawings and specific embodiments.

FIG. 1 is a schematic structural diagram of a positive electrode current collector according to a specific embodiment of the present application.

2 is a schematic structural diagram of a positive electrode current collector according to another specific embodiment of the present application.

FIG. 3 is a schematic structural diagram of a positive electrode current collector according to yet another specific embodiment of the present application.

4 is a schematic structural diagram of a positive electrode current collector according to still another specific embodiment of the present application.

5 is a schematic structural diagram of a negative electrode current collector according to a specific embodiment of the present application.

6 is a schematic structural diagram of a negative electrode current collector according to another specific embodiment of the present application.

7 is a schematic structural diagram of a negative electrode current collector according to yet another specific embodiment of the present application.

8 is a schematic structural diagram of a negative electrode current collector according to still another specific embodiment of the present application.

9 is a schematic structural diagram of a positive pole piece of a specific embodiment of the present application.

FIG. 10 is a schematic structural diagram of a positive pole piece of another specific embodiment of the present application.

11 is a schematic structural diagram of a negative pole piece of a specific embodiment of the present application.

12 is a schematic structural diagram of a negative pole piece of another specific embodiment of the present application.

FIG. 13 is a surface microscopic observation diagram of a positive electrode current collector in a specific embodiment of the present application.

14 is a perspective view of an electrochemical device according to an embodiment of the present application as a lithium ion secondary battery.

15 is an exploded view of the lithium ion secondary battery shown in FIG. 14.

16 is a perspective view of a battery module according to an embodiment of the present application.

17 is a perspective view of a battery pack according to an embodiment of the application.

18 is an exploded view of the battery pack shown in FIG.

19 is a schematic diagram of an electrochemical device as a power supply device according to an embodiment of the present application.

Among them: the reference symbols are explained as follows:

10 positive collector

101 positive electrode support layer

102 positive electrode conductive layer

103 positive protective layer

11 Positive electrode active material layer

20 Negative current collector

201 negative electrode support layer

202 negative electrode conductive layer

203 Negative protective layer

21 Negative active material layer

1 Battery pack

2 Upper cabinet

3 Lower cabinet

4 Battery module

5 battery cells

51 Shell

52 electrode assembly

53 Top cover assembly

detailed description

The application is further elaborated below in conjunction with specific embodiments. It should be understood that these specific embodiments are only used to illustrate the present application and not to limit the scope of the present application.

The first aspect of the present application relates to an electrode pole piece (also called "pole piece", which can be used interchangeably), including a current collector and an electrode active material layer provided on at least one surface of the current collector. Wherein, the current collector includes a support layer and a conductive layer provided on at least one surface of the support layer, and the single-sided thickness D2 of the conductive layer satisfies: 30 nm≦D2≦3 μm. The electrode active material layer includes an electrode active material, a binder, and a conductive agent, and the conductive agent in the electrode active material layer has an uneven distribution in the thickness direction. Wherein based on the total weight of the electrode active material layer, the weight percentage of the conductive agent in the inner region of the electrode active material layer is higher than the weight percentage of the conductive agent in the outer region of the electrode active material layer, and The binder in the inner region of the electrode active material layer contains an acrylic-based/acrylate-based aqueous binder.

Obviously, the electrode pole piece may be a positive pole piece or a negative pole piece. When the electrode pole piece is a positive pole piece, correspondingly, the current collector and the electrode active material layer therein are the positive electrode current collector and the positive electrode active material layer, respectively. When the electrode pole piece is a negative pole piece, accordingly, the current collector and the electrode active material layer therein are the negative electrode current collector and the negative electrode active material layer, respectively.

The current collector used in the electrode pole piece of the first aspect of the present application is a composite current collector, which is composed of at least two materials. Structurally, the current collector includes a support layer and a conductive layer provided on at least one surface of the support layer, and the single-sided thickness D2 of the conductive layer satisfies: 30 nm≦D2≦3 μm. Therefore, the conductive layer in the current collector plays a conductive role. The thickness D2 of the conductive layer is much smaller than the thickness of metal current collectors commonly used in the prior art such as Al foil or Cu foil (the thickness of commonly used Al foil and Cu foil metal current collectors is usually 12 μm and 8 μm), so the use of this Mass energy density and volume energy density of the pole piece electrochemical device (such as a lithium battery). In addition, when the composite current collector is applied to a positive electrode current collector, it can greatly improve the safety performance of the positive electrode pole piece through nails.

However, because the conductive layer of this composite current collector is thin, compared to the traditional metal current collector (Al foil or Cu foil), the conductive ability of the composite current collector is poor, and the conductive layer is easy to process during the pole piece Breakage occurs, which in turn affects the electrical performance of the electrochemical device. In addition, the support layer (polymer material or polymer composite material) of the composite current collector rebounds more than the traditional metal current collector during the process of pole piece rolling, so the bonding force between the support layer and the conductive layer 3. The binding force between the composite current collector and the electrode active material layer preferably needs to be enhanced by improving the interface.

In the electrode pole piece according to the present application, the conductive agent has an uneven distribution in the thickness direction of the electrode active material layer provided on the current collector. Specifically, the electrode active material layer is divided into an inner region and an outer region in the thickness direction. The content of the conductive agent in the inner region of the electrode active material layer is higher than that of the conductive agent in the outer region of the electrode active material layer content. That is, the side of the electrode active material layer that is in contact with the current collector (that is, the inner region) is more conductive. Therefore, the shortcomings such as the poor conductivity of the composite current collector and the easy damage of the conductive layer in the composite current collector can be well overcome. The inner region of the electrode active material layer with stronger conductivity can effectively repair and build the conductive network between the current collector and the active material in the electrode active material layer to improve the electron transmission efficiency and reduce the resistance of the electrode sheet containing the composite current collector, which can effectively reduce The DC resistance of the battery (DCR) improves the power performance of the battery and ensures that the battery is not prone to large polarization and lithium precipitation during long-term cycling, which effectively improves the long-term reliability of the battery.

Electrode pole piece

The structure, materials and properties of the electrode pole piece (and current collector) described in the first aspect of the present application are described in detail below.

Current collector conductive layer

Compared with the conventional metal current collector, in the current collector of the embodiment of the present application, the conductive layer plays a role of electrical conduction and current collection, and is used to provide electrons for the electrode active material layer.

The material of the conductive layer is at least one selected from metal conductive materials and carbon-based conductive materials.

The metal conductive material is preferably at least one of aluminum, copper, nickel, titanium, silver, nickel-copper alloy, and aluminum-zirconium alloy.

The carbon-based conductive material is preferably at least one of graphite, acetylene black, graphene, and carbon nanotubes.

The material of the conductive layer is preferably a metal conductive material, that is, the conductive layer is preferably a metal conductive layer. Among them, when the current collector is a positive current collector, aluminum is usually used as the material of the conductive layer; when the current collector is a negative current collector, copper is usually used as the material of the conductive layer.

When the conductivity of the conductive layer is poor or the thickness is too small, it will cause a large internal resistance and large polarization of the battery. When the thickness of the conductive layer is too large, it is not enough to improve the weight energy density and volume energy density of the battery Effect.

The thickness of one side of the conductive layer is D2, and D2 preferably satisfies: 30 nm ≤ D2 ≤ 3 μm, more preferably 300 nm ≤ D2 ≤ 2 μm, most preferably 500 nm ≤ D2 ≤ 1.5 μm; in order to better ensure the lightweight performance of the current collector It also has good electrical conductivity.

In a preferred embodiment of the present application, the upper limit of the single-sided thickness D2 of the conductive layer may be 3 μm, 2.5 μm, 2 μm, 1.8 μm, 1.5 μm, 1.2 μm, 1 μm, 900 nm, and the lower limit of the single-sided thickness D2 of the conductive layer may be 800nm, 700nm, 600nm, 500nm, 450nm, 400nm, 350nm, 300nm, 100nm, 50nm, 30nm; the range of the single-sided thickness D2 of the conductive layer can be composed of any value of the upper limit or the lower limit. Preferably, 300 nm≦D2≦2 μm; more preferably 500 nm≦D2≦1.5 μm.

Due to the small thickness of the conductive layer of the present application, cracks and other damages are likely to occur in the process of making the pole piece. At this time, the conductive agent according to the present application is introduced into the electrode pole piece and the electrode active material has an uneven distribution in the thickness direction The layer can function as a buffer and protect the conductive layer, and a "repair layer" can be formed on the surface of the conductive layer to improve the bonding force and contact resistance between the current collector and the active material layer.

Generally, there are cracks in the conductive layer of the electrode pole piece described in this application. The cracks in the conductive layer usually exist irregularly in the conductive layer, which can be elongated cracks, cross cracks, divergent cracks, etc.; it can be a crack that penetrates the entire conductive layer, or it can be in the conductive layer Cracks formed in the surface layer. The cracks in the conductive layer are usually caused by the rolling during the pole piece processing, the amplitude of the welding lug is too large, and the winding tension of the substrate is too large.

The conductive layer can be formed on the support layer by at least one of mechanical rolling, bonding, vapor deposition, and electroless plating. The vapor deposition method is preferably a physical vapor deposition method (Physical Vapor Deposition, PVD) ); physical vapor deposition method is preferably at least one of evaporation method and sputtering method; evaporation method is preferably vacuum evaporation method (vacuum evaporation), thermal evaporation method (Thermal Evaporation Deposition), electron beam evaporation method (electron beam evaporation method), EBEM), the sputtering method is preferably a magnetron sputtering method.

At least one of vapor deposition method or electroless plating is preferable to make the bonding between the support layer and the conductive layer stronger.

Current collector support layer

In the current collector of the embodiment of the present application, the support layer plays a role of supporting and protecting the conductive layer. Since the support layer generally uses organic polymer materials, the density of the support layer is usually less than the density of the conductive layer, so that the weight energy density of the battery can be significantly improved compared to the traditional metal current collector.

Moreover, the metal layer adopts a metal layer with a small thickness, which can further increase the weight energy density of the battery. Moreover, since the supporting layer can play a good bearing and protection role on the conductive layer on the surface, it is not easy to produce the fracture phenomenon of the pole piece common in the traditional current collector.

The material of the support layer is selected from at least one of an insulating polymer material, an insulating polymer composite material, a conductive polymer material, and a conductive polymer composite material.

Insulating polymer material is selected from polyamide, polyterephthalate, polyimide, polyethylene, polypropylene, polystyrene, polyvinyl chloride, aramid, polybenzoyl diamine, acrylonitrile, for example -Butadiene-styrene copolymer, polybutylene terephthalate, polyparaphenylene terephthalamide, polypropylene, polyoxymethylene, epoxy resin, phenolic resin, polytetrafluoroethylene, poly Phenylene sulfide, polyvinylidene fluoride, silicone rubber, polycarbonate, cellulose and its derivatives, starch and its derivatives, protein and its derivatives, polyvinyl alcohol and its cross-linked products, polyethylene glycol and its At least one of the cross-linked.

The insulating polymer composite material is selected from, for example, a composite material formed of an insulating polymer material and an inorganic material, wherein the inorganic material is preferably at least one of ceramic materials, glass materials, and ceramic composite materials.

The conductive polymer material is, for example, at least one selected from polysulfide-based polymer materials or doped conjugated polymer materials, such as polypyrrole, polyacetylene, polyaniline, polythiophene, and the like.

The conductive polymer composite material is selected from, for example, a composite material formed of an insulating polymer material and a conductive material, wherein the conductive material is selected from at least one of a conductive carbon material, a metal material, and a composite conductive material, wherein the conductive carbon material is selected from carbon black, At least one of carbon nanotubes, graphite, acetylene black, graphene, the metal material is selected from at least one of nickel, iron, copper, aluminum, or alloys of the above metals, and the composite conductive material is selected from nickel-coated graphite powder At least one of carbon fibers coated with nickel.

According to factors such as the actual needs of the application environment and cost, those skilled in the art can reasonably select and determine the material of the support layer. The material of the support layer in the present application is preferably an insulating polymer material or an insulating polymer composite material, especially when the current collector is a positive electrode current collector.

When the current collector is a positive electrode current collector, by using a special current collector supported by an insulating layer and having a conductive layer of a specific thickness, the safety performance of the battery can be significantly improved. Since the insulating layer is not conductive, its resistance is large, which can increase the short-circuit resistance of the battery when a short circuit occurs under abnormal conditions, greatly reducing the short-circuit current, and thus can greatly reduce the short-circuit heat generation, thereby improving the safety performance of the battery. And the conductive layer is thin, so under abnormal conditions such as nail penetration, the local conductive network is cut off to prevent the internal short circuit of the electrochemical device over a large area or even the entire electrochemical device, which can cause The damage is limited to the puncture site and only forms a "point break" without affecting the normal operation of the electrochemical device within a certain period of time.

The thickness of the support layer is D1, and D1 preferably satisfies: 1 μm≦D1≦30 μm; more preferably 1 μm≦D1≦15 μm.

Since the content of the support layer is moderate, the mechanical strength of the support layer can be adapted to the pole piece processing technology, and the volumetric energy density of the current collector battery is improved.

The upper limit of the thickness D1 of the support layer may be 30 μm, 25 μm, 20 μm, 15 μm, 12 μm, 10 μm, 8 μm, and the lower limit may be 1 μm, 1.5 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm; the thickness of the support layer D1 The range can be composed of any value of the upper or lower limit. Preferably, 1 μm≦D1≦15 μm; more preferably 2 μm≦D1≦10 μm; most preferably 3 μm≦D1≦8 μm.

At the same time, the specific thickness of the present application can further ensure that the current collector has a greater resistance, significantly reduce the battery temperature rise when the battery is internally short-circuited, and when the conductive layer is aluminum, it can also significantly reduce or prevent the aluminum collector of the anode current collector Reaction to ensure that the battery has good safety performance.

In addition, when the conductive layer is a metal conductive layer, it is preferable that the normal temperature Young's modulus of the support layer satisfy: 20 GPa ≥ E ≥ 4 GPa.

The test method of the normal temperature Young's modulus of the support layer described in this application is as follows:

Take the support layer sample and cut it to 15mm×200mm, use a micrometer to measure the thickness h (μm) of the sample, use a high-speed rail tension machine to perform the tensile test at normal temperature and pressure, set the initial position, and make the sample between the fixtures 50mm long. Stretching is performed at a speed of 50 mm/min, and the load L(N) stretched to break and the displacement y(mm) of the equipment are recorded, then the stress ε=L/(15×h)×1000 and the strain η=y/50×100 , Draw a stress-strain curve, take the initial linear zone curve, the slope of the curve is the Young's modulus E.

Since the metal is relatively rigid relative to the polymer or polymer composite material, that is, the deformation is small during the rolling of the pole piece processing, etc., in order to ensure that the difference in deformation between the support layer and the conductive layer is not too large, so that To tear the conductive layer, the normal temperature Young's modulus of the support layer preferably satisfies: 20GPa≥E≥4Gpa, so that the support layer can have a certain rigidity, and the rigidity matching between the support layer and the conductive layer can be further improved In order to ensure that the deformation of the support layer and the conductive layer will not be too different during the processing of the current collector and electrode pole pieces.

Because the support layer has a certain rigidity (20GPa≥E≥4GPa), the current collector is not easy to deform or extend too much during the processing of the current collector and electrode pole pieces, so that the support layer and the conductive layer can be firmly bonded , It is not easy to detach, and can prevent the conductive layer from being "forced" to extend and cause damage to the conductive layer. And the current collector according to the present application has a certain toughness, so that the current collector and the electrode pole piece have a certain ability to withstand deformation, and it is not easy to break the band.

However, the Young's modulus of the support layer cannot be too large, otherwise the rigidity is too strong, which will cause difficulty in winding and winding, and the workability will be deteriorated. When 20GPa≥E, it can ensure that the support layer has a certain flexibility, and also makes the electrode pole piece have a certain ability to withstand deformation.

In addition, it is preferable that the heat shrinkage rate of the support layer at 90°C is not more than 1.5%. Therefore, during the processing of the pole piece, the thermal stability of the current collector can be better ensured.

Collector protective layer

In some preferred embodiments of the present application, the current collector is further provided with a protective layer, the protective layer is provided on one surface of the conductive layer of the current collector or on both surfaces of the conductive layer of the current collector On the surface, that is, the surface of the conductive layer away from the support layer and the surface facing the support layer.

The protective layer may be a metal protective layer or a metal oxide protective layer. The protective layer can prevent the conductive layer of the current collector from being damaged by chemical corrosion or mechanical damage, and can also enhance the mechanical strength of the current collector.

The protective layer is preferably provided on both surfaces of the conductive layer of the current collector. The lower protective layer of the conductive layer (that is, the protective layer provided on the surface of the conductive layer facing the support layer) can not only prevent the conductive layer from being damaged, enhance the mechanical strength of the current collector, but also enhance the strength between the support layer and the conductive layer The binding force prevents peeling (that is, the support layer is separated from the conductive layer).

The technical effect of the upper protective layer of the conductive layer (that is, the protective layer provided on the surface of the conductive layer away from the support layer) is mainly to prevent the conductive layer from being damaged and corroded during processing (such as electrolyte immersion, rolling, etc. The surface of the conductive layer affects). Since the electrode pole piece of the present application adopts the inner region of the electrode active material layer with stronger conductivity to repair the cracks that may be generated during the rolling and winding of the conductive layer, enhance the conductivity, and make up the composite current collector as a current collector Therefore, the upper protective layer of the conductive layer can cooperate with the inner region of the electrode active material layer to further provide protection for the conductive layer, thereby jointly improving the conductive effect of the composite current collector as a current collector.

Due to the good conductivity, the metal protective layer can not only further improve the mechanical strength and corrosion resistance of the conductive layer, but also reduce the polarization of the pole piece. The material of the metal protective layer is, for example, at least one selected from nickel, chromium, nickel-based alloys, and copper-based alloys, preferably nickel or nickel-based alloys.

Among them, the nickel-based alloy is an alloy composed of pure nickel as a matrix and adding one or several other elements. Preferably, it is a nickel-chromium alloy. The nickel-chromium alloy is an alloy formed of metallic nickel and metallic chromium. Optionally, the molar ratio of nickel element to chromium element is 1:99-99:1.

A copper-based alloy is an alloy composed of pure copper as a matrix with one or several other elements added. Preferably, it is a copper-nickel alloy. Optionally, in the copper-nickel alloy, the molar ratio of nickel to copper is 1:99 to 99:1.

When the metal oxide is used as the protective layer, due to the small ductility, large specific surface area and high hardness of the metal oxide, it can also form an effective support and protection for the conductive layer and improve the bonding force between the support layer and the conductive layer. Has a good technical effect. The material of the metal oxide protective layer is, for example, at least one selected from alumina, cobalt oxide, chromium oxide, and nickel oxide.

When used as a positive electrode current collector, the protective layer of the composite current collector according to the present application preferably uses metal oxides to further improve the safety performance of the positive electrode tab and battery while achieving good support and protection technical effects; When the negative electrode current collector is used, the protective layer of the composite current collector according to the present application is preferably made of metal, so as to achieve a good technical effect of support and protection, and further improve the conductivity of the pole piece and the dynamic performance of the battery to reduce The battery is polarized.

The thickness of the protective layer is D3, and D3 preferably satisfies: D3≤1/10D2 and 1nm≤D3≤200nm. If the protective layer is too thin, it is not enough to protect the conductive layer; if the protective layer is too thick, it will reduce the weight energy density and volume energy density of the battery. More preferably, 5nm≤D3≤500nm, further preferably 10nm≤D3≤200nm, most preferably 10nm≤D3≤50nm.

The materials of the protective layers on both surfaces of the conductive layer may be the same or different, and the thickness may be the same or different.

Preferably, the thickness of the lower protective layer is smaller than the thickness of the upper protective layer, to help improve the weight energy density of the battery.

Further optionally, the proportional relationship between the thickness D3" of the lower protective layer and the thickness D3' of the upper protective layer is: 1/2D3'≤D3"≤4/5D3'.

When the current collector is a positive electrode current collector, aluminum is generally used as the material of the conductive layer, and the lower protective layer is preferably a metal oxide material. Relative to the choice of metal for the lower protective layer, metal oxide materials have a greater resistance, so this type of lower protective layer can further increase the resistance of the positive electrode current collector to a certain extent, thereby further improving the battery under abnormal conditions The short-circuit resistance in the event of a short circuit improves the safety performance of the battery. In addition, because the specific surface area of the metal oxide is larger, the bonding force between the lower protective layer of the metal oxide material and the support layer is enhanced; at the same time, because the specific surface area of the metal oxide is larger, the lower protective layer can increase the support layer The roughness of the surface plays a role in enhancing the bonding force between the conductive layer and the supporting layer, thereby improving the overall strength of the current collector.

When the current collector is a negative electrode current collector, copper is generally used as the material of the conductive layer, and the protective layer is preferably a metal material. More preferably, on the basis of including at least one metal protective layer, at least one of the lower protective layer and the lower protective layer further includes a metal oxide protective layer, in order to simultaneously improve the conductivity and interface binding force of the negative electrode composite current collector.

Current collector

1 to 8 show schematic structural diagrams of current collectors used in electrode pole pieces according to some embodiments of the present application.

The schematic diagram of the positive electrode current collector is shown in FIGS. 1 to 4.

In FIG. 1, the positive electrode current collector 10 includes a positive electrode current collector support layer 101 and a positive electrode current collector conductive layer 102 provided on two surfaces opposite to the positive electrode current collector support layer 101, and further includes a positive electrode current collector conductive layer 102 provided on the positive electrode current collector support layer 101. The positive electrode current collector protective layer 103 on the lower surface (that is, the surface facing the positive electrode current collector supporting layer 101), that is, the lower protective layer.

In FIG. 2, the positive electrode current collector 10 includes a positive electrode current collector support layer 101 and a positive electrode current collector conductive layer 102 provided on two opposite surfaces of the positive electrode current collector support layer 101, and further includes a positive electrode current collector conductive layer 102 provided on the positive electrode current collector support layer 101. The positive electrode current collector protective layer 103 on the two opposite surfaces, that is, the lower protective layer and the upper protective layer.

In FIG. 3, the positive electrode current collector 10 includes a positive electrode current collector supporting layer 101 and a positive electrode current collector conductive layer 102 provided on one surface of the positive electrode current collector supporting layer 101, and further includes a positive electrode current collector facing layer provided on the positive electrode current collector conductive layer 102. The positive electrode current collector protective layer 103 on the surface of the fluid support layer 101, that is, the lower protective layer.

In FIG. 4, the positive electrode current collector current collector 10 includes a positive electrode current collector support layer 101 and a positive electrode current collector conductive layer 102 provided on one surface of the positive electrode current collector support layer 101, and further includes an opposite surface provided on the positive electrode current collector conductive layer 102. The positive electrode current collector protective layer 103 on both surfaces, namely the lower protective layer and the upper protective layer.

Similarly, schematic diagrams of the negative electrode current collector are shown in FIGS. 5 to 8.

In FIG. 5, the negative electrode current collector 20 includes a negative electrode current collector support layer 201 and a negative electrode current collector conductive layer 202 provided on opposite surfaces of the negative electrode current collector support layer 201, and further includes a negative electrode current collector conductive layer 202 provided on the negative electrode current collector support layer 201. The negative electrode current collector protective layer 203 on the surface facing the negative electrode current collector supporting layer 201, that is, the lower protective layer.

In FIG. 6, the negative electrode current collector 20 includes a negative electrode current collector support layer 201 and a negative electrode current collector conductive layer 202 provided on opposite surfaces of the negative electrode current collector support layer 201, and further includes a negative electrode current collector conductive layer 202 provided on the negative electrode current collector support layer 201. The negative electrode current collector protective layer 203 on the two opposite surfaces, that is, the lower protective layer and the upper protective layer.

In FIG. 7, the negative electrode current collector 20 includes a negative electrode current collector support layer 201 and a negative electrode current collector conductive layer 202 provided on one surface of the negative electrode current collector support layer 201, and further includes a negative electrode current collector conductive layer 202 provided on the negative electrode current collector conductive layer 202 The negative electrode current collector protective layer 203 in the direction of the fluid support layer 201, that is, the lower protective layer.

In FIG. 8, the negative electrode current collector 20 includes a negative electrode current collector supporting layer 201 and a negative electrode current collector conductive layer 202 provided on one surface of the negative electrode current collector supporting layer 201, and further includes two opposing two provided on the negative electrode current collector conductive layer 202. The negative electrode current collector protective layer 203 on the surface, that is, the lower protective layer and the upper protective layer.

The materials of the protective layers on two opposite surfaces of the conductive layer may be the same or different, and the thickness may be the same or different.

Wherein, as for the current collector used for the electrode pole piece according to the present application, as shown in FIGS. 1, 2, 5, and 6, a conductive layer may be provided on two opposite surfaces of the support layer, Alternatively, as shown in FIGS. 3, 4, 7, and 8, a conductive layer may be provided on only one side of the support layer.

In addition, although the composite current collector used in the electrode pole piece of the present application preferably includes a current collector protective layer as shown in FIGS. 1-8, it should be understood that the current collector protective layer is not a necessary structure of the current collector, in some embodiments The current collector used in may not contain a current collector protective layer.

Electrode active material layer

The electrode active material layer used for the electrode pole piece of the present application generally includes an electrode active material, a binder, and a conductive agent. The electrode active material layer may further include optional other additives or auxiliary agents as needed.

For the electrode pole piece of the present application, it is preferable that the average particle diameter D50 of the active material in the electrode active material layer is 5 to 15 μm. If D50 is too small, after compaction, the porosity of the pole piece is small, which is not conducive to the infiltration of the electrolyte, and its large specific surface area is likely to produce more side reactions with the electrolyte, reducing the reliability of the battery; if D50 If it is too large, it is easy to cause greater damage to the composite current collector during the compaction of the pole piece. D50 refers to the particle size corresponding to the cumulative volume percentage of the active material reaching 50%, that is, the median particle size of the volume distribution. D50 can be measured using a laser diffraction particle size distribution measuring instrument (eg, Malvern Mastersizer 3000).

For the positive pole piece, various electrode active materials commonly used in the art (ie, positive electrode active materials) can be selected. For example, for lithium batteries, the positive electrode active material may be selected from lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, transition Metal phosphates, lithium iron phosphate, etc., but the present application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for lithium ion batteries can also be used. Only one kind of these positive electrode active materials may be used alone, or two or more kinds may be used in combination. Preferably, the positive electrode active material may be selected from LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (NCM 333), LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (NCM 523), LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (NCM 622), LiNi _0.8 Co _0.1 Mn _0.1 O ₂ (NCM 811), LiNi _0.85 Co _0.15 Al _0.05 O ₂ , LiFePO ₄ , LiMnPO ₄ or Several.

For the negative pole piece, various electrode active materials commonly used in the art (ie, negative electrode active materials) can be selected. For example, for lithium batteries, the negative electrode active material may be selected from carbonaceous materials such as graphite (artificial graphite or natural graphite), conductive carbon black, carbon fiber, etc., such as Si, Sn, Ge, Bi, Sn, In, etc. Metal material or its alloy, lithium-containing nitride or lithium-containing oxide, lithium metal or lithium aluminum alloy, etc.

The conductive agent used in the electrode active material layer is preferably at least one of a conductive carbon material and a metal material.

For example, the conductive carbon material is selected from zero-dimensional conductive carbon (such as acetylene black, conductive carbon black), one-dimensional conductive carbon (such as carbon nanotubes), two-dimensional conductive carbon (such as conductive graphite, graphene), and three-dimensional conductive carbon (such as At least one of graphene oxide after reduction; the metal material is at least one selected from aluminum powder, iron powder, and silver powder.

An important feature of the electrode pole piece of the present application is that the conductive agent in the electrode active material layer has an uneven distribution in the thickness direction, that is, the weight percentage of the conductive agent in the electrode active material layer is uneven in the thickness direction , There are changes. More specifically, based on the total weight of the electrode active material layer, the weight percentage of the conductive agent in the inner region of the electrode active material layer (also called "lower electrode active material") is higher than that of the electrode active material layer The weight percentage of the conductive agent in the outer region of the (also called "upper electrode active material"). Preferably, the weight percent content of the electrochemically active material in the inner region is lower than the weight percent content of the electrochemically active material in the outer region.

In this application, when referring to the "inside" of the electrode active material, it refers to the side of the electrode active material layer close to the current collector in the thickness direction, and when referring to the "outside" of the electrode active material, refers to The electrode active material layer is away from the current collector in the thickness direction.

"The conductive agent has an uneven distribution in the thickness direction" and "the weight percentage of the conductive agent in the inner region of the electrode active material layer is higher than the weight percentage of the conductive agent in the outer region of the electrode active material layer There can be many different embodiments of the "content". For example, the weight percentage content of the conductive agent in the electrode active material layer may gradually decrease along the thickness direction from the inner region to the outer region; or the electrode active material layer may be divided into two or more in the thickness direction The area (that is, divided into two layers, three layers or more layers), and the weight percentage of the conductive agent in the area closest to the current collector is greater than the weight percentage of the conductive agent in each area away from the current collector. In a specific embodiment of the present application, the electrode active material layer is divided into two regions in the thickness direction (that is, divided into two layers of electrode active material layers), and the weight percentage of the conductive agent in the lower layer (inside) electrode active material The content is greater than the weight percentage of the conductive agent in the active material of the upper layer (outside) electrode.

In a preferred embodiment of the present application, the electrode active material layer is divided into two regions in the thickness direction, namely an inner region and an outer region. Based on the total weight of the inner region of the electrode active material layer, the conductive agent in the inner region The weight percentage content is 10% to 99%, preferably 20% to 80%, and more preferably 50% to 80%.

Preferably, the conductive agent in the inner region contains one-dimensional conductive carbon material and/or two-dimensional conductive carbon material. Because the addition of one-dimensional conductive carbon material helps to improve the conductivity of the conductive primer layer. After adding the two-dimensional conductive carbon material, the two-dimensional conductive carbon material in the inner area of the electrode active material layer can produce "horizontal sliding" during the compaction of the pole piece, thereby playing a buffering role and reducing the concentration during the compaction process. The destruction of the conductive layer of the fluid, thereby reducing cracks. The particle diameter D50 of the preferred two-dimensional conductive carbon material is 0.01 μm to 0.1 μm. Preferably, the one-dimensional conductive carbon material and/or the two-dimensional conductive carbon material in the inner region account for 1 wt% to 50 wt% of the conductive agent in the inner region, and the remaining conductive agents may be other types of conductive agents, preferably zero Victoria carbon material. The one-dimensional conductive carbon material and/or the two-dimensional conductive carbon material and the zero-dimensional carbon material can work together to better improve the conductivity of the entire active material layer, especially the inner region.

In a preferred embodiment, the conductive material is a combination of one-dimensional conductive carbon material and zero-dimensional conductive carbon material. One-dimensional carbon (such as carbon nanotubes) and zero-dimensional carbon (such as acetylene black carbon spheres) can be combined with dots and lines to form a uniform conductive network, which can effectively enhance the conductivity of the conductive primer layer; while a single acetylene black or carbon Nanotubes are not as good as the conductive carbon mixed with the two.

In another preferred embodiment, the conductive material is a combination of two-dimensional conductive carbon material and zero-dimensional conductive carbon material. Two-dimensional carbon (such as sheet-like conductive graphite or graphene) and zero-dimensional carbon (such as acetylene black carbon spheres) can be combined point by plane and mixed into a uniform conductive network, which can effectively enhance the conductivity of the conductive primer; and two-dimensional Carbon materials can play a "buffering role".

In yet another preferred embodiment, the conductive material is a combination of one-dimensional conductive carbon material, two-dimensional conductive carbon material and zero-dimensional conductive carbon material. One-dimensional carbon (such as carbon nanotubes), two-dimensional carbon (such as sheet-like conductive graphite or graphene) and zero-dimensional carbon (such as acetylene black carbon balls) can be combined point-line-surface, mixed into a uniform conductive network, which can be effectively enhanced The conductivity of the conductive primer layer; and the two-dimensional carbon material can play a "buffering role".

Preferably, based on the total weight of the conductive material, the conductive material includes at least one of 5wt%-50wt% of one-dimensional conductive material, two-dimensional conductive material, and 50wt%-95wt% of other conductive materials (such as zero-dimensional conductive carbon Or metal materials, preferably zero-dimensional conductive carbon).

Of course, in order to better play a buffering role and improve the conductive performance, the conductive agent in the outer region also preferably contains one-dimensional conductive carbon material and/or two-dimensional conductive carbon material.

Due to the uneven distribution of the conductive agent content, the content of the binder and the active material in the electrode active material may also vary along the thickness direction.

The binder used in the electrode active material layer can use various binders commonly used in the art, for example, it can be selected from styrene-butadiene rubber, oily polyvinylidene fluoride (PVDF), polyvinylidene fluoride copolymer (such as PVDF-HFP copolymer) Substances, PVDF-TFE copolymer), sodium carboxymethyl cellulose, polystyrene, polyacrylic acid, polytetrafluoroethylene, polyacrylonitrile, polyimide, water-based PVDF, polyurethane, polyvinyl alcohol, polyacrylate, At least one of polyacrylic acid-polyacrylonitrile copolymer and polyacrylate-polyacrylonitrile copolymer.

It has been found that the binder used in the inner region preferably contains an aqueous binder, that is, the binder used is an aqueous binder or a mixture of aqueous binder and oily binder, so that the DCR growth of the electrochemical device is small . Most preferably, the adhesive used in the inner region contains at least an acrylic-based/acrylate-based aqueous adhesive, because the acrylic-based/acrylate-based aqueous adhesive is beneficial to obtain a slurry with higher stability, which can improve the bottom The uniformity of the coating of the coating can further avoid phenomena such as lithium deposition due to coating or uneven concentration.

In this application, "aqueous" polymer material means that the polymer molecular chain is fully extended and dispersed in water, and "oily" polymer material means that the polymer molecular chain is fully extended and dispersed in the oily solvent. Those skilled in the art understand that the same type of polymer materials can be dispersed in water and oil by using suitable surfactants, that is, the same type of polymer materials can be made into high water Molecular materials and oily polymer materials. For example, those skilled in the art can modify PVDF to aqueous PVDF or oily PVDF as needed. When a mixture of an aqueous binder and an oily binder is used, it is preferred that the aqueous binder accounts for 30% to 100% of the total weight of the binder used. That is, in the inner region, the aqueous binder accounts for 30% to 100% of the total weight of the binder used in the inner region.

In the present application, the "acrylic group/acrylate group" binder refers to a homopolymer or copolymer containing an acryl group or an acrylic group that can be used as a binder. Those skilled in the art understand various acrylic-based/acrylate-based adhesives commonly used in the battery industry and can make appropriate selections according to actual needs. For example, the acrylic/acrylate-based binder may include, but is not limited to: polyacrylic acid, polymethacrylic acid, sodium polyacrylate, sodium polymethacrylate, lithium polyacrylate, lithium polymethacrylate, polyacrylic acid- Polyacrylonitrile copolymer, polyacrylate-polyacrylonitrile copolymer, polyacrylamide or polymethacrylamide and their various derivatives (such as poly N-hydroxymethyl acrylamide, poly N-hydroxyethyl acrylamide , Poly N-hydroxypropyl acrylamide, poly N-(2-hydroxypropyl) acrylamide ester, poly N-(2-dimethylaminoethyl) acrylamide, etc.), polyacrylate or polymethyl Acrylic esters (eg polymethyl acrylate, polymethyl methacrylate, polyethyl acrylate, polyethyl methacrylate, polyhydroxyethyl acrylate, polyhydroxyethyl methacrylate, polyhydroxypropyl acrylate, polymethacrylate Hydroxypropyl acrylate, polyhydroxybutyl acrylate, polyhydroxybutyl methacrylate, polydimethylaminoethyl methacrylate, polyethylaminoethyl methacrylate, 2-ethoxy polyacrylic acid Ethyl ester, poly-2-ethylcyanoacrylate, ethyl methacrylate, poly-n-butyl acrylate, polyisobutyl acrylate, poly-tert-butyl acrylate, polyisooctyl acrylate, poly-2-ethyl acrylate Hexyl ester, polylauryl acrylate, polylauryl methacrylate, etc.), polyglycidyl acrylate, polyglycidyl methacrylate, polyglycidyl acrylate, polyglycidyl methacrylate, with silicone Alkyl polyacrylate or polymethacrylate (such as poly γ-methacryloxypropyl trimethoxysilane, etc.). The acrylic/acrylate-based binder may also be a copolymer obtained by copolymerizing an acrylic group or an acrylic group monomer with other vinyl monomers, wherein the acrylic group or acrylic group monomer may be, for example, acrylic acid, Methacrylic acid, acrylate or methacrylate (methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, methylmethacrylate Hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, 2-ethoxyethyl acrylate, acrylic acid- 2-ethylcyanoethyl ester, ethyl methacrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, isooctyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, lauryl methacrylate Esters), glycidyl acrylate, glycidyl acrylate, glycidyl methacrylate, glycidyl methacrylate, acrylamide (eg acrylamide, N-methylolacrylamide, N-hydroxyethyl acrylamide , N-hydroxypropyl acrylamide, N-(2-hydroxypropyl) acrylamide ester, N-(2-dimethylaminoethyl) acrylamide, diacetone acrylamide, ethyl acetoacetate methacrylate, N-vinylacetamide, etc.), and the other vinyl monomers are, for example, ethylene, propylene, halogenated olefins, vinyl alcohol, vinyl acetate, vinyl siloxane, butadiene, isoprene, benzene Ethylene and so on. As described above, if necessary, those skilled in the art can appropriately modify the above acrylic-based/acrylate-based adhesive to obtain an acrylic-based/acrylate-based aqueous adhesive suitable for use in the present application.

For the inner region of the electrode active material layer of the present application, the most preferred acrylic-based/acrylate-based aqueous binders are polyacrylic acid, sodium polyacrylate, lithium polyacrylate, polyacrylate, polyacrylic acid-polyacrylonitrile copolymer , At least one of polyacrylate-polyacrylonitrile copolymer.

The adhesive in the inner region may be a mixture of an acrylic-based/acrylate-based aqueous adhesive and other adhesives, which may be selected from styrene-butadiene rubber, oil-based polyvinylidene fluoride (PVDF), Vinyl fluoride copolymer (such as PVDF-HFP copolymer, PVDF-TFE copolymer), sodium carboxymethyl cellulose, polystyrene, polyacrylic acid, polytetrafluoroethylene, polyacrylonitrile, polyimide, water-based PVDF, At least one of polyurethane, polyvinyl alcohol, and polyacrylate. The acrylic-based/acrylate-based aqueous binder accounts for 50% to 100% by weight of the total binder in the conductive primer layer. Most preferably, the adhesive in the inner region contains only acrylic-based/acrylate-based aqueous adhesives, and does not contain other types of adhesives, that is, all the adhesives in the inner region are acrylic-based/acrylate Based water-based binder.

In addition, for the electrode pole piece of the present application, when the content of the binder in the electrode active material layer is high, the binding force between the active material layer and the current collector is good, resulting in abnormalities such as nail penetration In this case, the active material layer can effectively wrap the metal burrs generated in the conductive layer to improve the safety performance of the battery through nails. However, if the binder content is too high, the active material content will be reduced, which is not conducive to ensuring that the battery has a higher electrochemical capacity. Therefore, in terms of further improving battery safety and ensuring a high capacity of the battery, it is preferable that the weight percentage of the binder in the inner region is higher than the weight percentage of the binder in the outer region.

In a preferred embodiment of the present application, the electrode active material layer is divided into two regions in the thickness direction, namely an inner region and an outer region, wherein the weight percentage of the binder in the inner region is higher than that in the outer region The weight percentage of the binder.

In a preferred embodiment of the present application, the electrode active material layer is divided into two regions in the thickness direction, namely an inner region and an outer region, wherein, based on the total weight of the electrode active material layer at the inner region, the inner region is bonded The weight percentage content of the agent is 1% to 90%, preferably 20% to 80%, and more preferably 20% to 50%.

In a preferred embodiment of the present application, the electrode active material layer is divided into two regions in the thickness direction, namely an inner region and an outer region, wherein, based on the total weight of the electrode active material layer at the inner region, the conductive agent in the inner region The percentage by weight of 10% to 99%, preferably 20% to 80%, more preferably 50% to 80%; the weight percentage of the binder in the inner region is 1% to 90%, preferably 20% to 80%, more preferably 20% to 50%; and the balance is the electrode active material. However, in this embodiment, the content of the electrode active material in the inner region may be 0%.

In another preferred embodiment of the present application, the pole piece is a positive pole piece, based on the total weight of the active material layer of the inner region electrode (positive electrode), the content of the conductive agent is preferably 10 wt% to 98 wt%, The content is preferably 1 wt% to 89 wt%, and the content of the electrode (positive electrode) active material is preferably 1 wt% to 89 wt%.

In order to further improve the safety of battery nail penetration, the content of the binder in the outer region of the electrode active material layer (relative to the total weight of the outer region of the electrode active material layer) is not less than 1 wt%, preferably not less than 1.5 wt%. When the binder content in the outer region is kept at a certain amount, the binding force between the entire active material layer (including the inner region and the outer region) and the composite current collector is good, so that under abnormal conditions such as nail penetration, the entire activity The material layer can effectively wrap the metal burrs generated in the conductive layer to improve the safety performance of the battery through the nail.

In a preferred embodiment of the present application, the electrode active material layer is divided into two regions in the thickness direction, that is, an inner region and an outer region, wherein the thickness of the inner region of the electrode active material layer (two-layer coating refers to one side Thickness) H is preferably 0.1-5 μm; preferably H/D2 is 0.5:1 to 5:1. If the ratio of H/D2 is too small, it can not effectively play the role of improving the crack of the conductive layer and the conductivity of the pole piece; if the ratio is too large, it will not only reduce the weight and energy density of the battery, but also increase the DCR of the battery, which is not conducive to the battery Improvement of kinetic performance.

It should be noted that in the embodiment where the electrode active material layer is divided into two regions of the inner region and the outer region in the thickness direction, the electrode active material, conductive agent and binder selected for the inner region and the outer region may be the same or different . The inner region preferably uses a conductive agent containing one-dimensional conductive carbon material and/or two-dimensional conductive carbon material and a binder containing an aqueous binder, and the outer region may use the same or different conductive agents and Binder. For the positive electrode tab, the positive electrode active material in the inner region may be the same as or different from the positive electrode active material in the outer region; the positive electrode active material in the inner region is preferably a material with high thermal stability, such as lithium iron phosphate and manganese phosphate At least one of lithium iron, lithium manganate, lithium manganese phosphate, NCM333, NCM523, etc.

The electrode active material layer with a non-uniform distribution of the conductive agent in the thickness direction can be prepared by a method known in the art, for example, a multi-layer coating method such as a double coating method, a triple coating method, etc. The application is not limited to this.

Positive electrode pole piece and negative electrode pole piece

9 to 12 show schematic structural diagrams of electrode pole pieces according to some embodiments of the present application.

Among them, schematic diagrams of the positive pole pieces are shown in FIGS. 9 to 10.

In FIG. 9, the positive electrode tab includes a positive electrode current collector 10 and a positive electrode active material layer 11 disposed on opposite surfaces of the positive electrode current collector 10, and the positive electrode current collector 10 includes a positive electrode current collector support layer 101 and a positive electrode current collector support layer 101 and a positive electrode current collector support layer 101 provided on the positive electrode current collector. The positive electrode current collector conductive layer 102 and the positive electrode protective layer 103 (not shown in the figure) provided on one or both sides of the positive electrode conductive layer 102 on opposite surfaces of the fluid support layer 101.

In FIG. 10, the positive electrode tab includes a positive electrode current collector 10 and a positive electrode active material layer 11 provided on one surface of the positive electrode current collector 10, and the positive electrode current collector 10 includes a positive electrode current collector support layer 101 and a positive electrode current collector support The positive electrode current collector conductive layer 102 on one surface of the layer 101 and the positive electrode protective layer 103 (not shown in the figure) provided on one side or both sides of the positive electrode conductive layer 102.

Among them, schematic diagrams of the negative pole pieces are shown in FIGS. 11 to 12.

In FIG. 11, the negative electrode tab includes a negative electrode current collector 20 and a negative electrode active material layer 21 provided on two opposite surfaces of the negative electrode current collector 20, and the negative electrode current collector 20 includes a negative electrode current collector support layer 201 and a negative electrode current collector support layer 201 and a negative electrode current collector support layer 201. The negative electrode current collector conductive layer 202 and the negative electrode protective layer 203 (not shown in the figure) provided on one or both sides of the negative electrode conductive layer 202 on opposite surfaces of the fluid support layer 201.

In FIG. 12, the negative electrode tab includes a negative electrode current collector 20 and a negative electrode active material layer 21 provided on one surface of the negative electrode current collector 20, and the negative electrode current collector 20 includes a negative electrode current collector support layer 201 and a negative electrode current collector support layer. The negative electrode current collector conductive layer 202 on one surface of the layer 201 and the negative electrode protective layer 203 (not shown) provided on one side or both sides of the negative electrode conductive layer 202.

As shown in FIGS. 9 to 12, the electrode active material layer may be provided on one surface of the current collector or on both surfaces of the current collector.

A person skilled in the art may understand that when a current collector provided with a double-sided conductive layer is used, the electrode pole piece may be coated on both sides (that is, the electrode active material layer is provided on both surfaces of the current collector), or may only be on one side Coating (that is, the electrode active material layer is only provided on one surface of the current collector); when a current collector provided with a single-sided conductive layer is used, the electrode pole piece can only be coated on one side, and the electrode active material layer It can only be coated on the side of the current collector where the conductive layer is provided.

Electrochemical device

A second aspect of the present application provides an electrochemical device, including a positive pole piece, a negative pole piece, a separator, and an electrolyte, wherein the positive pole piece and/or the negative pole piece are according to the first aspect of the present application Electrode pads.

The electrochemical device may be a capacitor, a primary battery, or a secondary battery. For example, it may be a lithium ion capacitor, a lithium ion primary battery, or a lithium ion secondary battery.

14 shows a perspective view of an electrochemical device according to an embodiment of the present invention as a lithium ion secondary battery, and FIG. 15 is an exploded view of the lithium ion secondary battery shown in FIG. 14. Referring to FIGS. 14 and 15, a lithium ion secondary battery 5 (hereinafter referred to as battery cell 5) according to the present application includes a case 51, an electrode assembly 52, a top cap assembly 53, a positive pole piece, a negative pole piece, a separator and Electrolyte (not shown). The electrode assembly 52 is accommodated in the housing 51, and the number of the electrode assembly 52 is not limited, and may be one or more.

It should be noted that the battery cell 5 shown in FIG. 14 is a can-type battery, but the application is not limited to this, the battery cell 5 may be a pouch-type battery, that is, the case 51 is replaced by a metal plastic film and the top cover is eliminated Component 53.

Except for the use of the positive pole pieces and/or negative pole pieces of the present application, the construction and preparation methods of these electrochemical devices are known per se. Due to the use of the electrode pole piece of the present application, the electrochemical device may have improved safety (such as nail safety) and electrical performance. Moreover, the electrode pole piece of the present application is easy to process, so the manufacturing cost of the electrochemical device using the electrode pole piece of the present application can be reduced.

In the electrochemical device of the present application, the specific types and compositions of the separator and the electrolyte are not specifically limited, and can be selected according to actual needs. Specifically, the separator may be selected from polyethylene films, polypropylene films, polyvinylidene fluoride films, and multilayer composite films thereof. When the battery is a lithium ion battery, a non-aqueous electrolyte is generally used as the electrolyte. As the non-aqueous electrolyte, a lithium salt solution dissolved in an organic solvent is usually used. Lithium salts are, for example, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ and other inorganic lithium salts, or LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , LiN(CF ₃ Organic lithium salts such as SO ₂ ) ₂ , LiC(CF ₃ SO ₂ ) ₃ , LiC _n F _2n+1 SO ₃ (n≥2). Organic solvents used in the non-aqueous electrolyte are, for example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, etc. Chain carbonates, chain esters such as methyl propionate, cyclic esters such as γ-butyrolactone, dimethoxyethane, diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, etc. Ethers, cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, nitriles such as acetonitrile and propionitrile, or a mixture of these solvents.

Battery module

Next, a battery module according to the third aspect of the present application will be briefly described.

FIG. 16 shows a perspective view of a battery module according to an embodiment of the application. Referring to FIG. 16, the battery module 4 according to the present application includes a plurality of battery cells 5 arranged in the longitudinal direction.

The battery module 4 can be used as a power source or an energy storage device. The number of battery cells 5 in the battery module 4 can be adjusted according to the application and capacity of the battery module 4.

Battery pack

Next, the battery pack according to the fourth aspect of the present application will be briefly described.

FIG. 17 shows a perspective view of a battery pack according to an embodiment of the present application, and FIG. 18 is an exploded view of the battery pack shown in FIG. 17. Referring to FIGS. 17 and 18, the battery pack 1 according to the present application includes an upper case 2, a lower case 3 and a battery module 4. Among them, the upper case 2 and the lower case 3 are assembled together to form a space for accommodating the battery module 4. The battery module 4 is placed in the space of the upper case 2 and the lower case 3 assembled together.

The output pole of the battery module 4 passes through one or both of the upper case 2 and the lower case 3 to supply power to or charge the outside.

It should be noted that the number and arrangement of battery modules 4 used in the battery pack 1 can be determined according to actual needs. The battery pack 1 can be used as a power source or an energy storage device.

equipment

Next, a device according to the fifth aspect of the present invention will be briefly described.

FIG. 19 shows a schematic diagram of an electrochemical device according to an embodiment of the present application as a power supply device. For example only, in FIG. 19, the device using the electrochemical device is an electric car. Of course, it is not limited to this. The equipment using the electrochemical device may be any electric vehicle other than electric vehicles (such as electric buses, electric trams, electric bicycles, electric motorcycles, electric scooters, electric golf carts, electric Trucks), electric ships, electric tools, electronic equipment and energy storage systems.

The electric vehicle may be an electric pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. Of course, according to the actual use form, the device provided in the fifth aspect of the present application may include the battery module described in the third aspect of the present invention. Of course, the device provided in the fifth aspect of the present application may also include the device described in the fourth aspect of the present invention. Battery pack.

Those skilled in the art may understand that the various limitations or preferred ranges for component selection, component content, and physical and chemical performance parameters of the electrochemically active materials in the different embodiments of the present application mentioned above can be arbitrarily combined, and combinations thereof The various embodiments obtained are still within the scope of this application, and are regarded as part of the disclosure of this specification.

Unless otherwise specified, the various parameters involved in this specification have a common meaning known in the art, and can be measured according to methods known in the art. For example, the test can be performed according to the method given in the embodiments of the present application. In addition, the preferred ranges and options of various parameters given in various preferred embodiments can be arbitrarily combined, and the resulting combinations are considered to be within the disclosure scope of the present application.

The advantages of the present application are further described below in conjunction with specific embodiments.

Examples

1. Preparation of current collector without protective layer

A support layer with a certain thickness is selected, and a conductive layer with a certain thickness is formed on the surface by vacuum evaporation, mechanical rolling or bonding.

Among them, the following process conditions were used for preparation.

(1) The formation conditions of the vacuum evaporation method are as follows: the support layer after surface cleaning treatment is placed in a vacuum plating chamber, and the high-purity metal wire in the metal evaporation chamber is melted and evaporated at a high temperature of 1600°C to 2000°C, and the evaporated metal After passing through the cooling system in the vacuum plating chamber, it is finally deposited on the surface of the support layer to form a conductive layer.

(2) The formation conditions of the mechanical rolling method are as follows: the foil of the conductive layer material is placed in the mechanical roller, and it is rolled to a predetermined thickness by applying a pressure of 20t to 40t, and then placed in a surface cleaning process The surface of the supporting layer is finally placed in a mechanical roller, and the two are closely combined by applying a pressure of 30t to 50t.

(3) The formation conditions of the bonding method are as follows: the foil of the conductive layer material is placed in a mechanical roller, and it is rolled to a predetermined thickness by applying a pressure of 20 t to 40 t; The surface is coated with a mixed solution of PVDF and NMP; finally, the above-mentioned conductive layer with a predetermined thickness is bonded to the surface of the support layer, and dried at 100°C.

2. Preparation of current collector with protective layer

There are several ways to prepare a current collector with a protective layer:

(1) First, a protective layer is provided on the surface of the support layer by vapor deposition or coating method, and then a conductive layer with a certain thickness is formed on the surface of the support layer with the protective layer by vacuum evaporation, mechanical rolling or bonding In order to prepare a current collector with a protective layer (the protective layer is located between the support layer and the conductive layer); in addition, on the basis of the above, and then on the surface of the conductive layer away from the direction of the support layer by vapor deposition method, in situ The forming method or the coating method forms another protective layer to prepare a current collector with a protective layer (the protective layer is located on two opposite surfaces of the conductive layer).

(2) First, a protective layer is formed on one surface of the conductive layer by vapor deposition method, in-situ formation method or coating method, and then the above conductive layer with protective layer is provided on the support by mechanical rolling or bonding The surface of the layer, and the protective layer is provided between the support layer and the conductive layer to prepare a current collector with a protective layer (the protective layer is located between the support layer and the conductive layer); In addition, on the basis of the above, the conductive layer Another protective layer is formed on the surface away from the direction of the support layer by vapor deposition, in-situ formation, or coating to prepare current collectors with protective layers (the protective layers are located on two opposite surfaces of the conductive layer).

(3) First, a protective layer is formed on one surface of the conductive layer by vapor deposition method, in-situ formation method or coating method, and then the above conductive layer with protective layer is provided on the support by mechanical rolling or bonding The surface of the layer, and the protective layer is disposed on the surface of the conductive layer away from the support layer to prepare a current collector with a protective layer (the protective layer is located on the surface of the conductive layer away from the support layer).

(4) First, a protective layer is formed on both surfaces of the conductive layer by vapor deposition, in-situ formation, or coating, and then the conductive layer with the protective layer is provided on the mechanical layer by rolling or bonding The surface of the support layer to prepare a current collector with a protective layer (the protective layer is located on two opposite surfaces of the conductive layer).

(5) Based on the above "Preparation of current collector without protective layer", another layer of protection is formed on the surface of the conductive layer away from the support layer by vapor deposition, in-situ formation or coating Layer to prepare a current collector with a protective layer (the protective layer is located on the surface of the conductive layer away from the support layer).

In the preparation example, the vapor deposition method uses a vacuum evaporation method, the in-situ formation method uses an in-situ passivation method, and the coating method uses a doctor blade coating method.

The formation conditions of the vacuum evaporation method are as follows: the surface-cleaned sample is placed in a vacuum plating chamber, and the protective layer material in the evaporation chamber is melted and evaporated at a high temperature of 1600°C to 2000°C, and the evaporated protective layer material passes through the vacuum plating chamber The cooling system is finally deposited on the surface of the sample to form a protective layer.

The formation conditions of the in-situ passivation method are as follows: the conductive layer is placed in a high-temperature oxidation environment, the temperature is controlled at 160 ℃ to 250 ℃, while maintaining the oxygen supply in the high-temperature environment, the treatment time is 30min, thereby forming a metal oxide type The protective layer.

The formation conditions of the gravure coating method are as follows: the protective layer material and NMP are stirred and mixed, and then the slurry of the above protective layer material (solid content is 20%-75%) is coated on the surface of the sample, followed by the gravure roll control coating The thickness is finally dried at 100℃-130℃.

3. Preparation of pole piece

1) The positive pole piece of the embodiment

A positive electrode sheet having a lower positive electrode active material layer (inner region) and an upper positive electrode active material layer (outer region) is coated by a double coating method.

A certain proportion of conductive agent (such as conductive carbon black), binder (such as PVDF or polyacrylic acid, etc.) and optional positive electrode active material are dissolved in a suitable solvent (such as NMP or water), and stirred evenly to form a bottom Tu slurry.

The primer coating slurry was evenly coated on both sides of the composite current collector prepared according to the above method at a coating speed of 20 m/min, and the primer coating was dried, the oven temperature was 70 to 100° C., and the drying time was 5 min.

After the primer layer is completely dried, mix 92wt% positive electrode active material, 5wt% conductive agent Super-P (abbreviated as "SP") and 3wt% PVDF with NMP as the solvent, mix evenly to form the upper layer slurry, and use extrusion Coating The upper layer slurry is coated on the surface of the dried primer layer; after drying at 85°C, a positive electrode active material layer is obtained.

Then, the current collector with each coating layer was cold-pressed, then cut, and then dried under a vacuum condition of 85° C. for 4 hours, and the tab was welded to obtain a positive pole piece.

2) Compare positive pole pieces

The preparation method is similar to the preparation method of the positive electrode sheet of the above embodiment, but in which the upper layer slurry is directly coated on the surface of the composite current collector without providing the lower positive electrode active material layer (undercoat layer).

3) Conventional positive pole piece

The current collector is an Al foil with a thickness of 12 μm. Similar to the preparation method of the above-mentioned positive electrode sheet, the upper layer slurry is directly coated on the surface of the Al foil current collector, and then the conventional positive electrode sheet is obtained by post-treatment.

4) The negative pole piece of the embodiment

A negative electrode sheet having a lower negative electrode active material layer (inner region) and an upper negative electrode active material layer (outer region) is coated by a double coating method.

A certain proportion of conductive agent (such as conductive carbon black), binder (such as PVDF or polyacrylic acid, etc.) and optional negative electrode active material are dissolved in a suitable solvent (such as NMP or water), and stirred evenly to form a bottom Tu slurry.

After the undercoat layer is completely dried, add the negative electrode active material artificial graphite, conductive agent Super-P, thickener CMC, and binder SBR according to the mass ratio of 96.5:1.0:1.0:1.5 to the solvent deionized water and mix uniformly. The upper layer slurry is formed; the upper layer slurry is coated on the surface of the undercoat layer by extrusion coating; the anode active material layer is obtained after drying at 85°C.

Then, the current collector with each coating layer was cold-pressed, then cut, and then dried under vacuum at 110°C for 4 hours, and the electrode lugs were welded to obtain a negative pole piece.

5) Compare negative pole pieces

The preparation method is similar to the preparation method of the negative electrode sheet of the above embodiment, but in which the upper layer slurry is directly coated on the surface of the composite current collector without providing a lower negative electrode active material layer (undercoat layer).

6) Conventional negative pole piece

The current collector is a Cu foil with a thickness of 8 μm. Similar to the preparation method of the negative electrode sheet in the above comparison, the upper layer slurry is directly coated on the surface of the Cu foil current collector, and then the conventional negative electrode sheet is obtained by post-treatment.

4. Preparation of the battery

Through the conventional battery manufacturing process, the positive pole piece (compacting density: 3.4g/cm ³ ), PP/PE/PP separator and negative pole piece (compacting density: 1.6g/cm ³ ) are wound together into a bare battery The core is then placed in the battery case, and the electrolyte is injected (EC:EMC volume ratio is 3:7, LiPF ₆ is 1mol/L), followed by sealing, chemical conversion and other processes, and finally a lithium ion secondary battery (following (Referred to as battery or lithium ion battery).

5. Test method

1) Lithium ion battery cycle life test method

Charge and discharge the lithium ion battery at 45°C, that is, first charge to 4.2V with a current of 1C, then discharge to 2.8V with a current of 1C, and record the discharge capacity of the first week; then make the battery perform 1C/1C The charge and discharge cycle was 1000 cycles, and the battery discharge capacity at the 1000th week was recorded, and the discharge capacity at the 1000th week was divided by the discharge capacity at the first week to obtain the capacity retention rate at the 1000th week.

2) Test method of DCR growth rate

At 25°C, the lithium ion battery was adjusted to 50% SOC with a current of 1C, and the voltage U1 was recorded. Then discharge at a current of 4C for 30 seconds, and record the voltage U2. DCR=(U1-U2)/4C. Then, the battery was subjected to a 1C/1C charge and discharge cycle for 500 weeks, and the DCR of the 500th week was recorded. The DCR of the 500th week was divided by the DCR of the first week and decreased by 1 to obtain the DCR growth rate of the 500th week.

3) Acupuncture test

Fully charge the lithium ion battery (10 samples) with a current of 1C to the charging cut-off voltage, and then charge it at a constant voltage until the current drops to 0.05C, and stop charging. use

The high temperature resistant steel needle penetrates at a speed of 25mm/s from the direction perpendicular to the battery plate. The penetration position should be close to the geometric center of the punctured surface. The steel needle stays in the battery and observes whether the battery is burning or exploding.

6. Test results and discussion

6.1 The role of composite current collectors in improving the weight and energy density of batteries

The specific parameters of the current collector and its pole pieces of each embodiment are shown in Table 1 (the current collectors of the embodiments listed in Table 1 are not provided with a protective layer). In Table 1, for the positive electrode current collector, the weight percentage of the current collector is the weight of the positive electrode current collector per unit area divided by the weight of the conventional positive electrode current collector per unit area. For the negative electrode current collector, the weight percentage of the current collector is the unit area The weight of the negative electrode current collector divided by the percentage of the weight of the conventional negative electrode current collector per unit area.

Table 1

According to Table 1, it can be seen that the weight of the positive electrode current collector and the negative electrode current collector of the present application are reduced to different degrees compared with the conventional current collector, so that the weight energy density of the battery can be improved. However, when the thickness of the conductive layer is greater than 1.5 μm, the degree of improvement in weight loss for the current collector becomes smaller, especially for the negative electrode current collector.

6.2 The role of the protective layer in improving the electrochemical performance of the composite current collector

Based on the current collectors of the embodiments listed in Table 1, a protective layer was further formed in order to study the role of the protective layer in improving the electrochemical performance of the composite current collector. The "positive electrode current collector 2-1" in Table 2 represents the current collector obtained by forming a protective layer on the basis of the "positive electrode current collector 2" in Table 1, and the numbers of other current collectors have similar meanings.

Table 2

Table 3 shows the cycle performance data measured after assembling the batteries listed in Table 2 into a battery.

table 3

As shown in Table 3, compared with the battery 1 using the conventional positive pole piece and the conventional negative pole piece, the battery using the current collector of the embodiment of the present application has a good cycle life, which is comparable to the cycle performance of the conventional battery. Especially for the battery made of the current collector containing the protective layer, the battery capacity retention rate can be further improved compared to the battery made of the current collector without the protective layer, indicating that the reliability of the battery is better.

6.3 The role of the undercoat layer (i.e. the inner area) in improving the electrochemical performance of the battery

In the embodiments, a double-layer coating method is used to form an electrode active material layer on a current collector to form a pole piece. Therefore, the electrode active material layer is divided into an inner region (which may be referred to as "lower electrode active material layer") and an outer region (which may be referred to as "upper electrode active material layer"). Since the content of the conductive agent in the lower active material layer is higher than the content of the conductive agent in the upper active material layer, the lower electrode active material layer may also be referred to as a conductive primer layer (or simply primer layer).

The following uses the positive pole piece as an example to illustrate the effect of the primer layer and the composition of the primer layer on improving the electrochemical performance of the battery. Table 4 shows the specific compositions and related parameters of the batteries of various examples and comparative examples, as well as the electrode pads and current collectors used therein. Table 5 shows the performance measurement results of each battery.

Table 4

table 5

It can be seen from the above test data:

1) When using a composite current collector with a thinner conductive layer (that is, a comparative positive electrode sheet 20 that is not coated with a double-layer coating method and does not contain a conductive primer layer), the composite current collector has a more conductive ability than a traditional metal current collector Poor, and the conductive layer in the composite current collector is easy to break, etc., the battery has a large DCR, and the cycle capacity retention rate is low. After the conductive undercoat layer is introduced by the double-layer coating method, the conductive undercoat layer effectively repairs and builds a conductive network between the current collector, the conductive base coat and the active material, improves the electron transmission efficiency, and reduces the current collector and the electrode The resistance between the active material layers can effectively reduce DCR.

2) As the content of the conductive agent in the conductive undercoat layer increases (positive pole pieces 21 to 26), the DCR of the battery can be improved to a greater extent.

3) Under the same composition, the introduction of the water-based binder can make the improvement of DCR more obvious (positive pole piece 24 vs positive pole piece 27 and positive pole piece 25 vs positive pole piece 28).

4) Because flake graphite can produce "horizontal sliding", which acts as a buffer and reduces the damage to the conductive layer of the current collector during compaction, thereby reducing cracks, the introduction of flake graphite can further reduce the battery DCR (positive electrode) Pole piece 24vs. Positive pole piece 29).

5) As the thickness of the conductive undercoat layer increases (positive pole piece 30 to positive pole piece 32), the DCR of the battery can also be more significantly improved. However, if the thickness of the conductive primer layer is too large, it is not conducive to the improvement of the energy density of the battery.

In addition, the influence of the relative proportion of the water-based binder and the oil-based binder in the binder of the conductive undercoat layer was also separately investigated. The specific pole piece composition and battery performance measurement results are shown in Table 4-1 and Table 5-1.

Table 4-1

Table 5-1

It can be seen from Table 4-1 and Table 5-1; with the increase of the proportion of the aqueous binder in the conductive primer coating binder (positive pole pieces 27, 27-B, 27-A, 24 medium-water adhesive The proportions of binders are 0%, 30%, 60%, and 100%, respectively. The growth of DCR shows a gradual decrease trend, which shows that it is more advantageous for the binder of the primer layer to contain the water-based binder. Specifically, it is particularly preferred that the aqueous binder accounts for 30% to 100% of the total weight of the binder used in the conductive undercoat layer.

6.4 Influence of electrode active materials in the undercoat

In the above embodiments, for the convenience of research, no electrode active material is added to all the undercoat layers. The following uses the positive pole piece as an example to test the influence on the battery performance after the positive electrode active material is introduced into the undercoat layer. See Table 6 and Table 7 for specific pole piece composition and battery composition.

Table 6

Table 7

It can be seen from the above test data: regardless of whether the undercoat layer contains electrode active materials, the introduction of the undercoat layer can effectively repair and build a conductive network between the current collector, the conductive undercoat layer and the active substance, improve the electron transmission efficiency, and reduce The resistance between the current collector and the electrode active material layer can effectively reduce DCR.

6.5 The role of the binder content in the electrode active material layer in improving the electrochemical performance of the battery

The binder content of the undercoat layer in the inner region is usually higher, so the bonding force between the undercoat layer and the current collector is stronger. However, the binding force between the upper electrode active material layer and the undercoat layer is affected by the binder content in the upper active material layer. In order to make the entire electrode active material layer effectively cover the metal burrs generated in the conductive layer under abnormal conditions such as nail penetration, in order to improve the safety of nail penetration of the battery, the binder content in the upper active material (ie the outer area) Preferably, it should be higher than a lower limit.

Taking the positive electrode tab as an example, the role of the content of the binder in the upper electrode active material layer to improve the electrochemical performance of the battery is described from the perspective of battery safety for nail penetration.

A positive pole piece was prepared according to the method described in the previous embodiment, but the composition of the upper layer slurry was adjusted to prepare multiple positive pole pieces with different binder contents in the upper positive electrode active material layer. The specific pole piece composition is shown in the table below.

Table 8

Table 9 shows the nail penetration test results when the above-mentioned different positive pole pieces are assembled into a battery. The results show that the higher the content of the binder in the upper positive electrode active material layer, the better the nail safety performance of the corresponding battery. Preferably, based on the total weight of the upper active material layer, the binder content in the upper positive electrode active material layer is not less than 1 wt%, more preferably not less than 1.5 wt%.

Table 9

6.6 Influence of the type of binder in the conductive primer on the process stability

It has been found that the binder in the conductive primer layer (ie the inner region) has a greater influence on the stability of the primer slurry. Table 10 shows the settling performance of conductive undercoat pastes with different compositions. The test method is as follows: 80ml of freshly mixed uniformly mixed slurry is placed in a 100ml beaker and allowed to stand for 48h. The upper and lower layers of slurry are taken to test the solid content. The greater the difference in solid content, the stronger the settling. The data in Table 10 shows that the slurry settling performance is poor when using aqueous PVDF, which is not conducive to the stability of the pole piece preparation process; when using aqueous polyacrylic acid or aqueous sodium polyacrylate, the slurry is very stable and should not be settled, which can improve the bottom The uniformity of the coating of the coating can further avoid phenomena such as lithium deposition due to coating or uneven concentration.

Table 10

浆料Slurry	浆料的沉降性能Settlement performance of slurry
导电炭黑20％，水性聚丙烯酸80％Conductive carbon black 20%, water-based polyacrylic acid 80%	上层固含量33.5％，下层固含量为35.2％The upper solid content is 33.5%, the lower solid content is 35.2%
导电炭黑20％，水性聚丙烯酸钠80％Conductive carbon black 20%, aqueous sodium polyacrylate 80%	上层固含量33.8％，下层固含量为34.9％The upper solid content is 33.8%, the lower solid content is 34.9%
导电炭黑20％，水性PVDF 80％Conductive carbon black 20%, water-based PVDF 80%	上层固含量20.8％，下层固含量为38.2％The upper solid content is 20.8%, the lower solid content is 38.2%

Therefore, in the conductive primer layer (the inner region of the active material layer), the use of an aqueous binder is more beneficial to improve the DCR of the battery than the oil-based binder. Among the water-based adhesives, acrylic-based/acrylate-based adhesives are preferred, such as polyacrylic acid, sodium polyacrylate, lithium polyacrylate, polyacrylate, polyacrylic acid-polyacrylonitrile copolymer, polyacrylate-polypropylene At least one of nitrile copolymers.

6.7 Surface morphology of composite current collector

During the preparation of the positive pole piece 24, take a small sample after cold pressing, wipe the surface of the positive pole piece 24 with DMC solvent with clean paper to expose the surface of the composite current collector, and observe the surface shape with a CCD microscope The appearance is shown in Figure 13. From Fig. 13, a clear crack can be seen. This kind of crack is unique to the surface of the conductive layer of the composite current collector, which is not observed on the surface of the traditional metal current collector. When the conductive layer of the composite current collector is relatively thin, cracks are likely to occur under pressure during the cold pressing process of the pole piece processing. At this time, if there is a conductive primer layer (that is, the inner region), the conductive network between the current collector and the active material can be effectively repaired and constructed to improve the electron transmission efficiency and reduce the resistance between the current collector and the electrode active material layer , Which can effectively reduce the DC resistance of the cell, improve the power performance of the cell, and ensure that the cell is not prone to large polarization and lithium precipitation during long-term cycling, that is, effectively improve the long-term reliability of the cell ; The specific performance is that DCR growth is significantly reduced, thereby improving battery performance. The above observations give a possible theoretical explanation for the mechanism of action of the conductive primer, but it should be understood that the present application is not limited to this specific theoretical explanation.

A person skilled in the art may understand that the above application example of the pole piece of the present application is only illustrated by a lithium battery, but the pole piece of the present application can also be applied to other types of batteries or electrochemical devices, and the application can still be obtained Good technical effect.

According to the disclosure and teaching of the above description, those skilled in the art to which this application belongs can also make appropriate changes and modifications to the above-mentioned embodiments. Therefore, this application is not limited to the specific embodiments disclosed and described above, and some modifications and changes to this application should also fall within the scope of protection of the claims of this application. In addition, although some specific terms are used in this specification, these terms are just for convenience of description, and do not constitute any limitation to this application.

Claims

An electrode pole piece, including:

Current collector, and

An electrode active material layer provided on at least one surface of the current collector;

Wherein, the current collector includes a supporting layer and a conductive layer disposed on at least one surface of the supporting layer,

The single-sided thickness D2 of the conductive layer satisfies: 30nm≤D2≤3μm,

The electrode active material layer includes an electrode active material, a binder, and a conductive agent, and the conductive agent in the electrode active material layer has an uneven distribution in the thickness direction;

Wherein based on the total weight of the electrode active material layer, the weight percent content of the conductive agent in the inner region of the electrode active material layer is higher than the weight percent of the conductive agent in the outer region of the electrode active material layer Content, and the binder in the inner region of the electrode active material layer contains an acrylic-based/acrylate-based aqueous binder.
The electrode pole piece according to claim 1, wherein the conductive layer is a metal conductive layer, and the material of the metal conductive layer is preferably at least one of aluminum, copper, nickel, titanium, silver, nickel-copper alloy, and aluminum-zirconium alloy ;and / or,

The material of the support layer is selected from at least one of an insulating polymer material, an insulating polymer composite material, a conductive polymer material, and a conductive polymer composite material, preferably an insulating polymer material or an insulating polymer composite material;

Preferably, the insulating polymer material is selected from polyamide, polyterephthalate, polyimide, polyethylene, polypropylene, polystyrene, polyvinyl chloride, aramid, polybenzoylbenzene Amine, acrylonitrile-butadiene-styrene copolymer, polybutylene terephthalate, polyparaphenylene terephthalamide, polypropylene, polyoxymethylene, epoxy resin, phenolic resin, polytetramethylene Vinyl fluoride, polyphenylene sulfide, polyvinylidene fluoride, silicone rubber, polycarbonate, cellulose and its derivatives, starch and its derivatives, protein and its derivatives, polyvinyl alcohol and its cross-linked products, polyethylene At least one of glycol and its cross-links;

Preferably, the insulating polymer composite material is selected from a composite material formed of an insulating polymer material and an inorganic material, wherein the inorganic material is preferably at least one of ceramic material, glass material, and ceramic composite material;

Preferably, the conductive polymer material is selected from polysulfide-based polymer materials or doped conjugated polymer materials, and more preferably, the conductive polymer material is selected from polypyrrole, polyacetylene, poly At least one of aniline, polythiophene, etc.;

Preferably, the conductive polymer composite material is selected from a composite material formed by an insulating polymer material and a conductive material, wherein the conductive material is selected from at least one of a conductive carbon material, a metal material, and a composite conductive material, wherein the The conductive carbon material is selected from at least one of carbon black, carbon nanotubes, graphite, acetylene black, and graphene. The metal material is selected from at least one of nickel, iron, copper, aluminum, or alloys of the above metals. The composite conductive material is selected from at least one of nickel-coated graphite powder and nickel-coated carbon fiber.
The electrode pole piece according to claim 1 or 2, wherein the thickness D1 of the support layer satisfies: 1 μm≦D1≦30 μm; preferably 1 μm≦D1≦15 μm; and/or

The normal temperature Young's modulus E of the support layer satisfies: 20GPa≥E≥4GPa; and/or

There is a crack in the conductive layer.
The electrode pole piece according to claim 1 or 2, wherein the single-sided thickness D2 of the conductive layer satisfies 300 nm ≤ D2 ≤ 2 μm, more preferably 500 nm ≤ D2 ≤ 1.5 μm.
The electrode pole piece according to any one of claims 1-4, a protective layer is further provided on the surface of the conductive layer, and the protective layer is only provided on one surface of the conductive layer of the current collector or on the surface On both surfaces of the conductive layer of the current collector;

The thickness D3 of the protective layer satisfies: D3≤1/10D2 and 1nm≤D3≤200nm, preferably 10nm≤D3≤50nm.
The electrode pole piece according to any one of claims 1 to 5, wherein:

The conductive agent is at least one of conductive carbon material and metal material;

Wherein, the conductive carbon material is selected from zero-dimensional conductive carbon, preferably acetylene black and/or conductive carbon black; one-dimensional conductive carbon, preferably carbon nanotube; two-dimensional conductive carbon, preferably conductive graphite and/or graphene ; Three-dimensional conductive carbon, preferably at least one of the reduced graphene oxide;

The metal material is selected from at least one of aluminum powder, iron powder and silver powder;

Preferably, the conductive agent in the inner region of the electrode active material layer contains the one-dimensional conductive carbon material and/or the two-dimensional conductive carbon material, preferably the one-dimensional conductive carbon material and/or the two The one-dimensional conductive carbon material accounts for 1% to 50% by weight of the conductive agent in the inner region of the electrode active material layer. More preferably, the conductive agent in the inner region of the electrode active material layer includes the one-dimensional conductive carbon material and The zero-dimensional conductive carbon material either contains the two-dimensional conductive carbon material and the zero-dimensional conductive carbon material or contains the one-dimensional conductive carbon material, the two-dimensional conductive carbon material and the zero-dimensional conductive carbon material;

And/or, the acrylic/acrylate-based aqueous binder is selected from polyacrylic acid, polyacrylate, sodium polyacrylate, lithium polyacrylate, polyacrylic acid-polyacrylonitrile copolymer, polyacrylate-polyacrylonitrile copolymerization At least one of them; preferably, the acrylic/acrylate-based aqueous binder accounts for 30% to 100% of the total weight of the binder in the inner region.
The electrode pole piece according to any one of claims 1 to 6, wherein the electrode active material layer is divided into two regions in the thickness direction, and based on the total weight of the electrode active material layer at the inner region, the conductive The weight percentage of the agent is 10% to 99%, preferably 20% to 80%, more preferably 50% to 80%; the weight percentage of the binder is 1% to 90%, preferably 20% to 80%, more preferably 20% to 50%;

Preferably, the weight percentage of the binder in the inner region is higher than the weight percentage of the binder in the outer region.
The electrode pole piece according to any one of claims 1-7, the thickness H of the inner region is 0.1-5 μm; preferably the ratio of H to D2 is 0.5:1 to 5:1.
The electrode pole piece according to any one of claims 1 to 8, wherein the average particle diameter D50 of the electrode active material is: 5 to 15 μm;

Preferably, based on the total weight of the electrode active material layer at the outer region, the weight percentage of the binder in the outer region is not less than 1 wt%.
An electrochemical device includes a positive pole piece, a negative pole piece, a separator and an electrolyte,

Wherein, the positive pole piece and/or the negative pole piece is the electrode pole piece according to any one of claims 1-9.
A battery module comprising the electrochemical device according to claim 10.
A battery pack comprising the battery module according to claim 11.
An apparatus comprising the electrochemical device according to claim 10, which serves as a power source for the device.
The apparatus according to claim 13, wherein the apparatus includes an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, an electric ship 3. Energy storage system.