WO2023240485A1

WO2023240485A1 - Positive electrode sheet and preparation method therefor, secondary battery, battery module, battery pack, and electric device

Info

Publication number: WO2023240485A1
Application number: PCT/CN2022/098892
Authority: WO
Inventors: 方小明; 吴燕英; 王星会
Original assignee: 宁德时代新能源科技股份有限公司
Priority date: 2022-06-15
Filing date: 2022-06-15
Publication date: 2023-12-21
Also published as: CN117597791A

Abstract

A positive electrode sheet, comprising a positive electrode current collector, an adhesive layer, and a positive electrode active material layer. The adhesive layer is provided on at least one surface of the positive electrode current collector, the adhesive layer comprises a polymer having a main chain containing an amide group, and the positive electrode active material layer is provided on the surface of the adhesive layer distant from the positive electrode current collector.

Description

Positive electrode plate and preparation method thereof, secondary battery, battery module, battery pack and electrical device

Technical field

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

Background technique

With the development of electric vehicles, energy storage systems and other fields, the market has put forward higher requirements for the energy density of secondary batteries such as lithium-ion batteries. Traditional processes usually increase the energy density of secondary batteries by increasing the compaction density of pole pieces or increasing the amount of active materials. However, this will also affect the cycle performance of secondary batteries.

Contents of the invention

Based on the above problems, this application provides a positive electrode plate with suitable electrode plate adhesion and a preparation method thereof, a secondary battery, a battery module, a battery pack and an electrical device, which can be used in secondary batteries to take into account higher Energy density and better cycle performance.

One aspect of this application provides a positive electrode sheet, including:

positive current collector;

An adhesive layer, the adhesive layer is disposed on at least one surface of the positive electrode current collector; the adhesive layer includes a polymer whose main chain contains an amide group; and

A positive electrode active material layer is provided on the surface of the adhesive layer away from the positive electrode current collector.

In some embodiments, the thickness of the adhesive layer is 0.03 μm to 2 μm;

Optionally, the thickness of the adhesive layer is 0.05 μm ~ 1 μm;

Optionally, the thickness of the adhesive layer is 0.1 μm ~ 0.8 μm.

In some embodiments, in the extension direction of the positive electrode current collector, the ratio of the total length of the adhesive layer to the length of the positive electrode current collector is a, and the positive electrode plate satisfies: 0.3≤a≤ 1;

Optionally, the positive electrode piece satisfies: 0.5≤a≤0.8.

In some embodiments, the adhesive layer is discontinuously distributed on the surface of the positive electrode current collector.

In some embodiments, the adhesive layer is distributed in a lattice, an island shape or a stripe distribution on the surface of the positive electrode current collector;

Optionally, the adhesive layer is distributed in a lattice on the surface of the positive electrode current collector.

In some embodiments, the weight average molecular weight of the polymer is 10,000 to 50,000;

Optionally, the weight average molecular weight of the polymer is 15,000 to 30,000.

In some embodiments, the polymer includes at least one of polyamide and polyamideimide.

In some embodiments, the polymer includes at least one of PA6, PA66, PA12, PA46, PA610, PA612, PA1010 and PAI.

In some embodiments, the viscosity of the polymer is 1000 mPa·s to 10000 mPa·s;

Optionally, the viscosity of the polymer is 1500 mPa·s～6000 mPa·s.

In some embodiments, the positive active material layer includes a positive active material, a binder and a conductive agent;

Optionally, in the positive active material layer, the mass percentage of the positive active material is 94% to 98%;

Optionally, in the positive active material layer, the mass percentage of the binder is 1% to 5%;

Optionally, in the cathode active material layer, the mass percentage of the conductive agent is 1% to 4%.

In some embodiments, the cathode active material layer further includes additives;

Optionally, in the positive active material layer, the mass percentage of the additive is 0.01% to 1%;

Optionally, in the positive active material layer, the mass percentage of the additive is 0.2% to 0.8%.

In some embodiments, the positive electrode current collector is aluminum foil.

In a second aspect, this application also provides a method for preparing a positive electrode sheet, including the following steps:

Coating a polymer containing an amide group in the main chain on at least one surface of the positive electrode current collector to prepare an adhesive layer;

The positive electrode slurry is coated on the surface of the adhesive layer away from the positive electrode current collector to prepare a positive electrode active material layer.

In a third aspect, the present application also provides a secondary battery, including the above-mentioned positive electrode sheet or the positive electrode sheet prepared according to the above-mentioned preparation method of the positive electrode sheet.

In a fourth aspect, the present application also provides a battery module, including the above-mentioned secondary battery.

In a fifth aspect, this application also provides a battery pack, including the above-mentioned battery module.

In a sixth aspect, the present application also provides an electrical device, including at least one selected from the above-mentioned secondary battery, the above-mentioned battery module, or the above-mentioned battery pack.

The positive electrode sheet of the present application is provided with an adhesive layer containing a polymer whose main chain contains an amide group. The adhesive force between the adhesive layer, the positive electrode current collector and the positive electrode active material layer is better, and the positive electrode sheet has suitable The pole piece has good adhesion and stability. Therefore, when the proportion of cathode active material in the cathode active material layer is high, both higher energy density and better cycle performance can be taken into consideration.

The details of one or more embodiments of the present application are set forth in the following drawings and description, and other features, objects, and advantages of the present application will be apparent from the description, drawings, and claims.

Description of the drawings

Figure 1 is a cross-sectional scanning electron microscope (SEM) photo of a positive electrode sheet according to an embodiment of the present application; a is the positive electrode current collector, b is the adhesive layer, and c is the positive electrode active material layer;

Figure 2 is a schematic diagram of a secondary battery according to an embodiment of the present application;

Figure 3 is an exploded view of the secondary battery according to an embodiment of the present application shown in Figure 2;

Figure 4 is a schematic diagram of a battery module according to an embodiment of the present application;

Figure 5 is a schematic diagram of a battery pack according to an embodiment of the present application;

Figure 6 is an exploded view of the battery pack according to an embodiment of the present application shown in Figure 5;

Figure 7 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of the present application;

Explanation of reference symbols:

1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 cover; 6 electrical device.

To better describe and illustrate embodiments and/or examples of those inventions disclosed herein, reference may be made to one or more of the accompanying drawings. The additional details or examples used to describe the drawings should not be construed as limiting the scope of any of the disclosed inventions, the embodiments and/or examples presently described, and the best modes currently understood of these inventions.

Detailed ways

In order to facilitate understanding of the present application, the present application will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present application are shown in the accompanying drawings. However, the present application may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that a thorough understanding of the disclosure of the present application will be provided.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this application belongs. The terminology used herein in the description of the application is for the purpose of describing specific embodiments only and is not intended to limit the application. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

Traditional processes usually increase the energy density of secondary batteries by increasing the compaction density of the pole pieces or increasing the amount of active materials. However, too high a compaction density will make it difficult to prepare the pole pieces and increase their brittleness; the content of the positive active material is too high , Correspondingly, the amount of auxiliary materials such as binders and conductive agents will be reduced, which will increase the internal resistance of the pole pieces. The pole pieces are easy to peel off and lose powder during the cycle, thus affecting the cycle performance of the secondary battery.

The present application provides an electrode pole piece, a secondary battery, a battery module, a battery pack and an electrical device using the electrode pole piece. This kind of secondary battery is suitable for various electrical devices that use batteries, such as mobile phones, portable devices, laptops, battery cars, electric toys, power tools, electric cars, ships and spacecraft. For example, spacecraft include aircraft, rockets , space shuttles and spacecrafts, etc.

One embodiment of the present application provides a positive electrode sheet, including: a positive electrode current collector, an adhesive layer and a positive electrode active material layer. The adhesive layer is disposed on at least one surface of the positive electrode current collector; and the adhesive layer includes a polymer whose main chain contains an amide group.

The cathode active material layer is disposed on the surface of the adhesive layer away from the cathode current collector. As an example, the positive electrode current collector has two surfaces opposite in its own thickness direction, and the adhesive layer is provided on any one or both of the two opposite surfaces of the positive electrode current collector.

The above-mentioned positive electrode sheet is provided with an adhesive layer containing a polymer whose main chain contains an amide group. Since the amide group in the polymer has a strong interaction with the positive electrode current collector, the adhesive layer and the positive electrode current collector and The bonding force between the positive electrode active material layers is good, and the positive electrode piece has appropriate bonding force and good stability. Therefore, when the proportion of positive active material in the positive active material layer is relatively high, both higher energy density and better cycle performance can be taken into consideration.

Specifically, regarding the polymer composition of the adhesive layer of the positive electrode piece, refer to the GB/T 17359-2012 "Quantitative Analysis of Microbeam Analysis Energy Spectrometry" standard and use a scanning electron microscope-energy spectrometer (SEM-EDS). Testing to determine the elemental composition of the adhesive layer polymer. At the same time, combined with infrared analysis testing, the molecular structure and functional groups of the adhesive layer polymer were determined.

In some embodiments, the thickness of the adhesive layer ranges from 0.03 μm to 2 μm. Controlling the thickness of the adhesive layer to 0.03 μm to 2 μm can ensure that the positive electrode piece has a more suitable adhesive force and the positive electrode piece has better mechanical properties. Optionally, the thickness of the adhesive layer is 0.03 μm, 0.05 μm, 0.1 μm, 0.2 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.8 μm or 2 μm. Further, the thickness of the adhesive layer is 0.05 μm to 1 μm or 0.1 μm to 0.8 μm.

In some embodiments, in the extension direction of the positive electrode current collector, the ratio of the total length of the adhesive layer to the length of the positive electrode current collector is a, and the positive electrode piece satisfies: 0.3≤a≤1. Specifically, the ratio a of the total length of the adhesive layer to the length of the positive electrode current collector can be calculated by analyzing a cross-sectional scanning electron microscope (SEM) photo of the positive electrode piece. In the cross-sectional SEM photo of the positive electrode sheet, it can be observed that the adhesive layer is continuously or discontinuously provided between the positive electrode active material layer and the positive electrode current collector. When the value a is less than 1, it means that the adhesive layer does not completely cover the surface of the positive electrode current collector. Further, the positive electrode piece satisfies: 0.5≤a≤0.8. The ratio of the total length of the adhesive layer to the length of the positive electrode current collector is a between 0.5 and 0.8. The positive electrode piece has relatively suitable electrode piece adhesion and conductive properties.

As an example, refer to FIG. 1 , which is a cross-sectional scanning electron microscope (SEM) photo of a positive electrode plate according to an embodiment of the present application. It can be seen from the figure that the adhesive layer b is discontinuously provided between the positive electrode current collector a and the positive electrode active material layer c.

In some embodiments, the adhesive layer is discontinuously distributed on the surface of the positive electrode current collector. Understandably, the adhesive layer does not completely cover the surface of the positive electrode current collector. Therefore, while ensuring appropriate adhesion of the electrode piece, it can ensure better conductive performance of the positive electrode piece and avoid a significant increase in the internal resistance of the positive electrode piece.

In some embodiments, the adhesive layer is distributed in a lattice, an island shape or a stripe distribution on the surface of the cathode current collector. Specifically, the lattice distribution may mean that the components of the adhesive layer are dispersed in dots on the surface of the cathode current collector; the island-like distribution may mean that the components of the adhesive layer are not completely covered on the surface of the cathode current collector. , distributed in an irregular shape; strip distribution means that the adhesive layer forms spaced strips on the surface of the positive electrode current collector. It can be understood that the width of these strips can be the same or different. Further, the adhesive layer is distributed in a lattice on the surface of the positive electrode current collector.

In some embodiments, the polymer has a weight average molecular weight of 10,000 to 50,000. The weight average molecular weight of the polymer is within the above range, the polymer has relatively suitable physical and chemical properties, and the positive electrode sheet has a relatively suitable adhesive force. Alternatively, the polymer has a weight average molecular weight of 10,000, 20,000, 30,000, 40,000 or 50,000. Further, the weight average molecular weight of the polymer is 15,000 to 30,000.

In some embodiments, the polymer includes at least one of polyamide and polyamideimide. The above-mentioned polymer has good adhesion and has good adhesion with the positive electrode current collector and the positive electrode active material layer.

In some embodiments, the viscosity of the polymer ranges from 1000 mPa·s to 10000 mPa·s. Controlling the viscosity of the polymer within the above range is beneficial to the preparation of the positive electrode sheet. Alternatively, the viscosity of the polymer is 1000 mPa·s, 2000 mPa·s, 4000 mPa·s, 5000 mPa·s, 6000 mPa·s, 8000 mPa·s or 10000 mPa·s. Further, the viscosity of the polymer is 1500mPa·s～6000mPa·s.

In some of these embodiments, the cathode active material layer includes a cathode active material. In some embodiments, the cathode active material may be a cathode active material known in the art for batteries. As an example, the cathode active material may include at least one of the following materials: an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials of batteries can also be used. Only one type of these positive electrode active materials may be used alone, or two or more types may be used in combination. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO ₂ ), lithium nickel oxides (such as LiNiO ₂ ), lithium manganese oxides (such as LiMnO ₂ , LiMn ₂ O ₄ ), lithium Nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (also referred to as NCM ₃₃₃ ), LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (can also be abbreviated to NCM ₅₂₃ ), LiNi _0.5 Co _0.25 Mn _0.25 O ₂ (can also be abbreviated to NCM ₂₁₁ ), LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (can also be abbreviated to NCM ₆₂₂ ), LiNi At least one of _0.8 Co _0.1 Mn _0.1 O ₂ (also referred to as NCM ₈₁₁ ), lithium nickel cobalt aluminum oxide (such as LiNi _0.85 Co _0.15 Al _0.05 O ₂ ) and its modified compounds. The olivine structure contains Examples of lithium phosphates may include, but are not limited to, lithium iron phosphate (such as LiFePO ₄ (also referred to as LFP)), composites of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO ₄ ), lithium manganese phosphate and carbon. At least one of composite materials, lithium iron manganese phosphate, and composite materials of lithium iron manganese phosphate and carbon.

In some embodiments, in the cathode active material layer, the mass percentage of the cathode active material is 94% to 98%. Due to the strong bonding force between the adhesive layer, the positive electrode current collector and the positive electrode active material layer, the mass percentage of the positive electrode active material in the positive electrode active material layer can reach 98%, thereby increasing the energy density of the secondary battery. Optionally, in the positive active material layer, the mass percentage of the positive active material is 94%, 95%, 96%, 97% or 98%.

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

In some embodiments, the mass percentage of the binder in the cathode active material layer is 1% to 5%. Optionally, in the positive active material layer, the mass percentage of the binder is 1%, 2%, 3%, 4% or 5%.

In some of these embodiments, the positive active material layer optionally further includes a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some embodiments, the mass percentage of the conductive agent in the cathode active material layer is 1% to 4%. Optionally, in the positive active material layer, the mass percentage of the conductive agent is 1%, 2%, 3% or 4%.

In some of these embodiments, the cathode active material layer further includes additives. In some embodiments, the mass percentage of the additive in the cathode active material layer is 0.01% to 1%. Optionally, in the positive active material layer, the mass percentage of the additive is 0.01%, 0.05%, 0.1%, 0.2%, 0.4%, 0.5%, 0.6%, 0.8% or 1%. Further, in the positive active material layer, the mass percentage of the additive is 0.2% to 0.8%.

In some of these embodiments, the additive may be a dispersant.

In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming metal materials (aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc.) on polymer material substrates (such as polypropylene (PP), polyterephthalate It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.). In some embodiments, the positive current collector is aluminum foil.

Another embodiment of the present application also provides a method for preparing a positive electrode sheet, including steps S110 and S120.

Step S110: Coat a polymer containing an amide group in the main chain on at least one surface of the positive electrode current collector to prepare an adhesive layer.

Step S120: Coat the positive electrode slurry on the surface of the adhesive layer away from the positive electrode current collector to prepare a positive electrode active material layer.

In some embodiments, after the positive electrode slurry is coated in step S120, cold pressing and drying steps are also included to obtain the positive electrode sheet.

In addition, the secondary battery, battery module, battery pack and electric device of the present application will be described below with appropriate reference to the drawings.

In one embodiment of the present application, a secondary battery is provided.

Typically, a secondary battery includes a positive electrode plate, a negative electrode plate, an electrolyte and a separator. During the charging and discharging process of the battery, active ions are inserted and detached back and forth between the positive and negative electrodes. The electrolyte plays a role in conducting ions between the positive and negative electrodes. The isolation film is placed between the positive electrode piece and the negative electrode piece. It mainly prevents the positive and negative electrodes from short-circuiting and allows ions to pass through.

Positive electrode piece

The positive electrode piece is the positive electrode piece provided in the first aspect of this application.

Negative pole piece

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

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

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

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

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

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

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

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

electrolyte

The electrolyte plays a role in conducting ions between the positive and negative electrodes. There is no specific restriction on the type of electrolyte in this application, and it can be selected according to needs. For example, the electrolyte can be liquid, gel, or completely solid.

In some embodiments, the electrolyte is an electrolyte solution. The electrolyte includes electrolyte salts and solvents.

In some embodiments, the electrolyte salt may be selected from the group consisting of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonimide, lithium bistrifluoromethanesulfonimide, lithium trifluoromethane At least one of lithium methanesulfonate, lithium difluorophosphate, lithium difluoroborate, lithium dioxaloborate, lithium difluorodioxalate phosphate and lithium tetrafluoroxalate phosphate.

In some embodiments, the solvent may be selected from the group consisting of ethylene carbonate, propylene carbonate, methylethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, and ethylpropyl carbonate. , butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, butyric acid At least one of ethyl ester, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

In some of these embodiments, the electrolyte optionally further includes additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain properties of the battery, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

Isolation film

In some embodiments, the secondary battery further includes a separator film. There is no particular restriction on the type of isolation membrane in this application. Any well-known porous structure isolation membrane with good chemical stability and mechanical stability can be used.

In some embodiments, the material of the isolation membrane can be selected from at least one selected from the group consisting of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation film can be a single-layer film or a multi-layer composite film, with no special restrictions. When the isolation film is a multi-layer composite film, the materials of each layer can be the same or different, and there is no particular limitation.

In some embodiments, the positive electrode piece, the negative electrode piece, and the separator film can be formed into an electrode assembly through a winding process or a lamination process.

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

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

This application has no particular limitation on the shape of the secondary battery, which can be cylindrical, square or any other shape. For example, FIG. 2 shows a square-structured secondary battery 5 as an example.

In some embodiments, referring to FIG. 3 , the outer package may include a housing 51 and a cover 53 . The housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The housing 51 has an opening communicating with the accommodation cavity, and the cover plate 53 can cover the opening to close the accommodation cavity. The positive electrode piece, the negative electrode piece and the isolation film can be formed into the electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is packaged in the containing cavity. The electrolyte soaks into the electrode assembly 52 . The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

In some embodiments, the secondary batteries can be assembled into battery modules, and the number of secondary batteries contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

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

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

In some embodiments, the above-mentioned battery modules can also be assembled into a battery pack. The number of battery modules contained in the battery pack can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

Figures 5 and 6 show the battery pack 1 as an example. Referring to FIGS. 5 and 6 , the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box 2 and a lower box 3 . The upper box 2 can be covered with the lower box 3 and form a closed space for accommodating the battery module 4 . Multiple battery modules 4 can be arranged in the battery box in any manner.

In addition, the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided by the present application. The secondary battery, battery module, or battery pack may be used as a power source for the power-consuming device, or may be used as an energy storage unit for the power-consuming device. Electrical devices may include mobile equipment, electric vehicles, electric trains, ships and satellites, energy storage systems, etc., but are not limited to these. Among them, mobile devices can be, for example, mobile phones, laptops, etc.; electric vehicles can be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc. , but not limited to this.

As a power-consuming device, secondary batteries, battery modules or battery packs can be selected according to its usage requirements.

FIG. 7 shows an electrical device 6 as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the secondary battery for the electrical device, a battery pack or battery module can be used.

As another example, the device may be a mobile phone, a tablet, a laptop, etc. The device is usually required to be thin and light, and a secondary battery can be used as a power source.

Example

Hereinafter, examples of the present application will be described. The embodiments described below are illustrative and are only used to explain the present application and are not to be construed as limitations of the present application. If specific techniques or conditions are not specified in the examples, the techniques or conditions described in literature in the field or product instructions will be followed. If the manufacturer of the reagents or instruments used is not indicated, they are all conventional products that can be purchased commercially.

Example 1:

Preparation of the positive electrode sheet: Coat the surface of the current collector aluminum foil with polymer PAI (weight average molecular weight 30000) to prepare an adhesive layer. The thickness of the coating is 0.5 μm. In the length direction of the current collector aluminum foil, the total length of the adhesive layer The ratio a to the length of the current collector aluminum foil is 0.6. The cathode active material NCM ₅₂₃ , binder PVDF, conductive agent SP and dispersant were mixed and dispersed in N-methylpyrrolidone (NMP) according to a mass ratio of 95.5:2:2:0.5 to obtain a cathode slurry. The positive electrode slurry is coated on the surface of the adhesive layer, dried, cold pressed, slit, and die-cut to obtain positive electrode sheets.

Preparation of negative electrode plate: artificial graphite, sodium carboxymethylcellulose (CMC-Na), styrene-butadiene emulsion (SBR) and conductive agent conductive carbon SP are mixed and dispersed in deionized water according to the mass ratio of 95.7:1:1.8:1.5. Negative electrode slurry was obtained. The negative electrode slurry is coated on both surfaces of the current collector copper foil, dried, cold pressed, slit, and die-cut to obtain negative electrode sheets.

Isolation film: PE porous polymer film is used as the isolation film.

Electrolyte: In an argon atmosphere glove box with a water content of <10 ppm, mix equal volumes of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) to obtain an organic solvent, and then uniformly dissolve 1 mol/L LiPF ₆ In the above organic solvent, an electrolyte solution is obtained.

Preparation of secondary battery: The positive electrode sheet, isolation film and negative electrode sheet are rolled into a bare battery core. After hot pressing, the bare battery core is assembled with the top cover and outer casing, and then the electrolyte is injected. After formation, exhaust, sealing, Test and other processes to obtain secondary batteries.

Examples 2 to 4:

The difference between Examples 2 to 4 and Example 1 is that the ratio a of the total length of the adhesive layer in the positive electrode sheet to the length of the current collector aluminum foil is different.

Embodiments 5 to 8:

The difference between Examples 5 to 8 and Example 1 is that the thickness of the adhesive layer is different.

Example 9:

The difference between Example 9 and Example 1 is that the mass ratio of the positive active material NCM ₅₂₃ , the binder and the conductive agent in the positive active material layer is 98:1:1.

Example 10:

The difference between Example 10 and Example 1 is that the polymer is PA6 (weight average molecular weight 28,000).

Examples 11 to 20:

The difference between Examples 11 to 20 and Examples 1 to 10 is that the positive active material is lithium iron phosphate (LFP).

Comparative example 1:

The difference between Comparative Example 1 and Example 1 is that no adhesive layer is provided on the surface of the current collector aluminum foil.

Comparative example 2:

The difference between Comparative Example 2 and Comparative Example 1 is that the mass ratio of the positive electrode active material NCM ₅₂₃ , binder, conductive agent and dispersant is 94.5:3:2:0.5.

Comparative example 3:

The difference between Comparative Example 3 and Example 1 is that the adhesive layer is made of PVDF.

Comparative example 4:

The difference between Comparative Example 4 and Example 9 is that no adhesive layer is provided on the surface of the current collector aluminum foil.

Comparative example 5:

The difference between Comparative Example 5 and Comparative Example 4 is that the mass ratio of the positive electrode active material LFP, binder, conductive agent and dispersant is 94.5:3:2:0.5.

Comparative example 6:

The difference between Comparative Example 6 and Example 9 is that the surface of the current collector aluminum foil is not provided with an adhesive layer, but is provided with a gravure-printed undercoat layer. The thickness of the undercoat layer is 2 μm. The composition of the undercoat layer includes 50wt% PVDF and 50wt% SP.

Comparative Example 7:

The difference between Comparative Example 7 and Comparative Example 6 is that the mass ratio of the positive electrode active material LFP, binder, conductive agent and dispersant is 94.5:3:2:0.5.

The structural compositions of the positive electrode plates of Examples 1 to 20 and Comparative Examples 1 to 7 are recorded in Table 1.

Table 1 Structural compositions of the positive electrode plates of Examples 1 to 20 and Comparative Examples 1 to 7.

Test part:

Pole piece adhesion test:

Cut out the pole piece sample to be tested that is 30mm wide and 160mm long. Paste the sample on a steel plate with double-sided tape with a width of 20mm and a length of 150mm. The test surface is facing down. Then, the width is the same as the pole piece, and the length is greater than the length of the sample. Insert the paper tape under the pole piece and fix it with wrinkle glue, then use the tensile machine to test. Stop when the test displacement reaches 50mm, and read the bonding force value.

Secondary battery capacity test:

The secondary battery is discharged to 2.8V at room temperature at 0.33C standard, left to stand for 10 minutes, charged to 4.2V at 0.33C, charged to 0.05C at 4.2V constant voltage, left to stand for 10 minutes, discharged to 2.8V at 0.33C, and recorded. discharge capacity.

Energy density test:

Charge to 4.2V at 0.33C standard at room temperature, charge to 0.05C at 4.2V constant voltage, let stand for 10 minutes, discharge to 2.8V at 0.33C, record the discharge capacity, and then calculate the energy density during discharge.

Energy density (Wh/kg) = discharge capacity (Wh)/secondary battery mass (kg).

Cycling stability test:

In an environment of 25°C, charge and discharge the lithium ion secondary battery for the first time, perform constant current charging at a charging current of 1C, then perform constant voltage charging until the voltage is 4.2V, and then continue charging at a discharging current of 1C Carry out constant current discharge until the final voltage is 2.8V, and record the discharge capacity of the first cycle. Then the charge and discharge cycle is repeated, and the discharge capacity of the 1000th cycle is recorded.

Discharge capacity retention rate = (discharge capacity at the 1000th cycle/discharge capacity at the first cycle) × 100%.

Table 2: Positive electrode sheet adhesion and electrochemical performance of secondary batteries in Examples 1 to 20 and Comparative Examples 1 to 7

It can be seen from the relevant data in Table 2 that by arranging an adhesive layer containing polyamide between the cathode current collector and the cathode active material layer, the adhesion force of the cathode plates of Examples 1 to 20 is between 13 N/m and Between 25N/m, it has high pole piece bonding force. In the positive electrode sheets of Examples 1 to 10, the positive active material is NCM, the capacity of the secondary battery is 4.9Ah to 5.5Ah, the energy density is 129Wh/kg to 137Wh/kg, and the discharge capacity retention rate after 1000 cycles of 1C/1C It is 83.3%~84.5%. In the positive electrode sheets of Examples 11 to 20, the positive active material is LFP, the capacity of the secondary battery is 3.6Ah~4.3Ah, the energy density is 104Wh/kg~115Wh/kg, and the discharge capacity retention rate after 1000 cycles of 1C/1C It is 87.4%~88.2%.

Compared with Examples 1 to 20, the positive electrode plates of Comparative Examples 1 to 7 have different structural designs, making it difficult to achieve both higher energy density and better cycle performance.

Compared with Example 1, the positive electrode plate of Comparative Example 1 is not provided with an adhesive layer, and the adhesive force of the electrode plate is only 9N/m. The capacity and energy density of the secondary battery are slightly higher than those of Example 1. However, 1C/1C The discharge capacity retention rate after 1000 cycles was 77.6%, and the cycle stability was poor. Similarly, the positive electrode plate of Comparative Example 4 has low electrode plate adhesion, and the capacity and energy density of the secondary battery are slightly higher than those of Example 10. However, the discharge capacity retention rate after 1000 cycles of 1C/1C is poor.

Comparative Example 2 is a cathode electrode sheet prepared by a traditional process, which does not have an adhesive layer. Compared with Example 1, the proportion of cathode active material in the cathode active material layer is also lower. The positive electrode plate of Comparative Example 2 has an adhesive force of 14 N/m, the capacity and energy density of the secondary battery are lower than those of Example 1, and the discharge capacity retention rate after 1,000 cycles of 1C/1C is equivalent to that of Example 1. Similarly, the positive electrode plate of Comparative Example 5 has a more suitable electrode plate bonding force, while the capacity and energy density of the secondary battery are slightly lower than those of Example 10. The discharge capacity retention rate after 1000 cycles of 1C/1C is the same as that of Example 10. quite.

In Comparative Example 3, the component of the adhesive layer is PVDF. Compared with Example 1, the adhesive force of the positive electrode sheet of Comparative Example 3 is not as good as that of Example 1, and the cycle performance of the secondary battery of Comparative Example 3 is also lower than that of Example 1. 1 secondary battery.

Comparative Examples 6 to 7 are positive electrode sheets of the LFP system prepared by traditional processes. A gravure printing primer with a thickness of 2 μm is set between the positive active material layer and the positive current collector. The setting of the primer is conducive to ensuring appropriate The adhesion of the electrode plate improves the cycle performance of the positive electrode plate. However, the thickness of the gravure printing undercoat layer is relatively large, which significantly reduces the capacity and energy density of the secondary battery; and the process of preparing the undercoat layer through gravure printing is more complicated and the preparation cost higher.

The technical features of the above-described embodiments can be combined in any way. To simplify the description, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, All should be considered to be within the scope of this manual.

The above-described embodiments only express several implementation modes of the present application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that, for those of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all fall within the protection scope of the present application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

A positive electrode plate includes:

positive current collector;

An adhesive layer, the adhesive layer is disposed on at least one surface of the positive electrode current collector; the adhesive layer includes a polymer whose main chain contains an amide group; and

A positive active material layer is provided on a surface of the adhesive layer away from the positive current collector.
The positive electrode plate according to claim 1, wherein the thickness of the adhesive layer is 0.03 μm to 2 μm;

Optionally, the thickness of the adhesive layer is 0.05 μm ~ 1 μm;

Optionally, the thickness of the adhesive layer is 0.1 μm ~ 0.8 μm.
The positive electrode sheet according to claim 1 or 2, characterized in that, in the extending direction of the positive electrode current collector, the ratio of the total length of the adhesive layer to the length of the positive electrode current collector is a, so The positive electrode piece satisfies: 0.3≤a≤1;

Optionally, the positive electrode piece satisfies: 0.5≤a≤0.8.
The positive electrode sheet according to any one of claims 1 to 3, wherein the adhesive layer is discontinuously distributed on the surface of the positive electrode current collector.
The positive electrode sheet according to any one of claims 1 to 4, characterized in that the adhesive layer is distributed in a lattice, an island shape or a strip on the surface of the positive electrode current collector;

Optionally, the adhesive layer is distributed in a lattice on the surface of the positive electrode current collector.
The positive electrode sheet according to any one of claims 1 to 5, wherein the weight average molecular weight of the polymer is 10,000 to 50,000;

Optionally, the weight average molecular weight of the polymer is 15,000 to 30,000.
The positive electrode sheet according to any one of claims 1 to 6, wherein the polymer includes at least one of polyamide and polyamide-imide.
The positive electrode sheet according to any one of claims 1 to 7, characterized in that the polymer includes at least one of PA6, PA66, PA12, PA46, PA610, PA612, PA1010 and PAI.
The positive electrode sheet according to any one of claims 1 to 8, wherein the viscosity of the polymer is 1000 mPa·s to 10000 mPa·s;

Optionally, the viscosity of the polymer is 1500 mPa·s～6000 mPa·s.
The positive electrode sheet according to any one of claims 1 to 9, wherein the positive active material layer includes a positive active material, a binder and a conductive agent;

Optionally, in the positive active material layer, the mass percentage of the positive active material is 94% to 98%;

Optionally, in the positive active material layer, the mass percentage of the binder is 1% to 5%;

Optionally, in the cathode active material layer, the mass percentage of the conductive agent is 1% to 4%.
The positive electrode sheet according to claim 10, wherein the positive active material layer further includes additives;

Optionally, in the positive active material layer, the mass percentage of the additive is 0.01% to 1%;

Optionally, in the positive active material layer, the mass percentage of the additive is 0.2% to 0.8%.
The positive electrode sheet according to any one of claims 1 to 11, wherein the positive electrode current collector is aluminum foil.
A method for preparing a positive electrode sheet, including the following steps:

Coating a polymer containing an amide group in the main chain on at least one surface of the positive electrode current collector to prepare an adhesive layer;

The positive electrode slurry is coated on the surface of the adhesive layer away from the positive electrode current collector to prepare a positive electrode active material layer.
A secondary battery including the positive electrode sheet according to any one of claims 1 to 12 or the positive electrode sheet prepared according to the method for preparing the positive electrode sheet according to claim 13.
A battery module including the secondary battery according to claim 14.
A battery pack including the battery module according to claim 15.
An electrical device including at least one selected from the group consisting of the secondary battery of claim 14, the battery module of claim 15, or the battery pack of claim 16.