CN111900356A - Negative plate and lithium ion battery comprising same - Google Patents

Negative plate and lithium ion battery comprising same Download PDF

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Publication number
CN111900356A
CN111900356A CN202010814453.3A CN202010814453A CN111900356A CN 111900356 A CN111900356 A CN 111900356A CN 202010814453 A CN202010814453 A CN 202010814453A CN 111900356 A CN111900356 A CN 111900356A
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negative electrode
active material
material layer
coating
gas
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欧长志
彭冲
李俊义
徐延铭
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Zhuhai Cosmx Battery Co Ltd
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Zhuhai Cosmx Battery Co Ltd
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Priority to CN202010814453.3A priority Critical patent/CN111900356A/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/04—Processes of manufacture in general
    • H01M4/0402—Methods of deposition of the material
    • H01M4/0404—Methods of deposition of the material by coating on electrode collectors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

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  • Chemical Kinetics & Catalysis (AREA)
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  • General Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
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  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Inorganic Chemistry (AREA)
  • Battery Electrode And Active Subsutance (AREA)

Abstract

The invention provides a negative plate and a lithium ion battery comprising the same. The negative plate is characterized in that a conductive coating is coated between a negative current collector and a first negative active material layer, so that the contact resistance between the first negative active material layer and the negative current collector can be reduced, the acting force between the first negative active material layer and the negative current collector is improved, the first negative active material layer is prevented from being peeled off, a buffer coating is coated between the first negative active material layer and a second negative active material layer, the contact resistance between the first negative active material layer and the second negative active material layer can be reduced, the acting force between the first negative active material layer and the second negative active material layer is improved, and the transmission rate of ions and electrons is improved; the surface of the second negative electrode active material layer is coated with a layer of safety coating, so that the volume expansion of the second negative electrode active material layer is further buffered, and meanwhile, the generation of lithium dendrites can be prevented from directly puncturing the diaphragm to cause internal short circuit, and the safety risk is reduced.

Description

Negative plate and lithium ion battery comprising same
Technical Field
The invention belongs to the technical field of lithium ion batteries, and particularly relates to a negative plate and a lithium ion battery comprising the same.
Background
In recent years, with the continuous expansion of lithium ion battery industrialization and the continuous development of technology, people have gradually increased the requirements for lithium ion batteries, and lithium ion batteries having high energy density, long cycle life and high safety have become the focus of research and development. At present, the main ways to improve the energy density of the battery are: 1. the compaction density of the anode and cathode materials is improved, but the high compaction can cause the porosity of the pole piece to be low, the liquid retention amount to be reduced, and the cycle life of the battery to be insufficient; 2. the gram capacity of the negative electrode material is improved, namely, the silicon-based negative electrode material is adopted to replace graphite, but the silicon-based material is pulverized due to great volume change in the charging and discharging processes, and is stripped from a current collector, so that the capacity is rapidly attenuated, and meanwhile, the safety problem is accompanied.
The existing solution, for example, includes that negative active materials with different compaction densities are adopted to improve the liquid retention of the pole piece and prolong the cycle life under the condition of ensuring high compaction density; or the method of coating different active material layers is adopted to realize the improvement of the whole capacity of the battery; however, these improvements have limited capability of improving battery performance, and there is an urgent need to develop a lithium ion battery having high energy density, long cycle life and high safety.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention aims to provide a negative plate and a lithium ion battery comprising the same. The negative plate comprises a negative current collector, and a conductive coating, a first negative active material layer, a buffer coating, a second negative active material layer and a safety coating which are sequentially coated on the surface of the negative current collector; the use of the negative plate can avoid the problems that the stripping between the negative active material layer and the negative current collector, the stripping between the two negative active material layers and the like easily occur in the two negative active material layers in the traditional double-layer coating mode, and fundamentally avoids the occurrence of the safety problem caused by the accelerated attenuation of the battery capacity. Meanwhile, the lithium ion battery comprising the negative plate can also realize high energy density, quick charge performance, safety performance and long cycle life.
The purpose of the invention is realized by the following technical scheme:
the utility model provides a negative pole piece, the negative pole piece includes the negative pole mass flow body and coats in proper order at the conductive coating, first negative pole active material layer, buffer coating, second negative pole active material layer and the safety coating of the first surface of the negative pole mass flow body.
According to the invention, the negative plate further comprises a conductive coating, a first negative electrode active material layer, a buffer coating, a second negative electrode active material layer and a safety coating which are sequentially coated on a second surface, opposite to the first surface, of the negative electrode current collector.
According to the invention, the negative current collector is a common copper foil (smooth foil, no other materials are coated on the surface).
According to the invention, the thickness of the negative electrode current collector is 6-12 μm.
According to the invention, the conductive coating comprises a first conductive agent and a first binder.
According to the invention, the conductive coating comprises the following components in percentage by mass:
90-99 wt% of first conductive agent, and 1-10 wt% of first binder.
Preferably, the conductive coating comprises the following components in percentage by mass:
93-99 wt% of first conductive agent, and 1-7 wt% of first binder.
Illustratively, the content of the first conductive agent is 90 wt%, 91 wt%, 92 wt%, 93 wt%, 94 wt%, 95 wt%, 96 wt%, 97 wt%, 98 wt%, 99 wt%.
Illustratively, the first binder is present in an amount of 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%.
According to the invention, the thickness of the conductive coating is 1-5 μm, for example 1 μm, 2 μm, 3 μm, 4 μm, 5 μm.
The conductive coating is arranged to increase the adhesion between the negative current collector and the first negative active material layer and reduce the contact resistance.
According to the present invention, the first anode active material layer includes a first anode active material, a second conductive agent, a first thickener, and a second binder.
According to the present invention, the first anode active material layer includes the following components in mass fraction:
90-98.5 wt% of first negative electrode active material, 0.5-4 wt% of second conductive agent, 0.5-3 wt% of first thickening agent and 0.5-3 wt% of second binder.
Preferably, the first anode active material layer includes the following components in mass fraction:
95-98 wt% of first negative electrode active material, 0.5-2 wt% of second conductive agent, 1-1.5 wt% of first thickening agent and 1-1.5 wt% of second binder.
Illustratively, the content of the first negative active material is 90 wt%, 91 wt%, 92 wt%, 93 wt%, 94 wt%, 95 wt%, 96 wt%, 97 wt%, 98 wt%, 98.5 wt%.
Illustratively, the second conductive agent is present in an amount of 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%.
Illustratively, the first thickener is present in an amount of 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%.
Illustratively, the second binder is present in an amount of 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%.
According to the present invention, the thickness of the first negative electrode active material layer is 20 to 150 μm, for example, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 150 μm.
According to the invention, D of the first negative electrode active material90≤50μm。
According to the present invention, the first negative electrode active material is selected from artificial graphite or natural graphite.
The first negative electrode active material layer is provided to function to increase the battery capacity.
According to the present invention, the buffer coating includes a third conductive agent and a third binder.
According to the invention, the buffer coating comprises the following components in percentage by mass:
90-99 wt% of third conductive agent and 1-10 wt% of third binder.
Preferably, the buffer coating comprises the following components in percentage by mass:
93-99 wt% of third conductive agent and 1-7 wt% of third binder.
Illustratively, the content of the third conductive agent is 90 wt%, 91 wt%, 92 wt%, 93 wt%, 94 wt%, 95 wt%, 96 wt%, 97 wt%, 98 wt%, 99 wt%.
Illustratively, the third binder is present in an amount of 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%.
According to the invention, the thickness of the buffer coating is 1-5 μm, for example 1 μm, 2 μm, 3 μm, 4 μm, 5 μm.
The buffer coat is provided for buffering volume expansion of the first anode active material layer and the second anode active material layer, increasing a force between the first anode active material layer and the second anode active material layer, reducing contact internal resistance, and preventing peeling between the first anode active material layer and the second anode active material layer.
According to the present invention, the second anode active material layer includes a second anode active material, a fourth conductive agent, a second thickener, and a fourth binder.
According to the present invention, the second anode active material layer includes the following components in mass fraction:
90-98.5 wt% of a second negative electrode active material, 0.5-4 wt% of a fourth conductive agent, 0.5-3 wt% of a second thickener, and 0.5-3 wt% of a fourth binder.
Preferably, the second anode active material layer includes the following components in mass fraction:
95-98 wt% of a second negative electrode active material, 0.5-2 wt% of a fourth conductive agent, 1-1.5 wt% of a second thickener, and 1-1.5 wt% of a fourth binder.
Illustratively, the content of the second negative active material is 90 wt%, 91 wt%, 92 wt%, 93 wt%, 94 wt%, 95 wt%, 96 wt%, 97 wt%, 98 wt%, 98.5 wt%.
Illustratively, the content of the fourth conductive agent is 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%.
Illustratively, the second thickener is present in an amount of 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%.
Illustratively, the content of the fourth binder is 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%.
According to the present invention, the thickness of the second anode active material layer is 10 to 100 μm, for example, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 80 μm, 90 μm, 100 μm.
According to the invention, D of the second negative electrode active material90≤50μm。
According to the invention, the second negative electrode active material is selected from silicon-carbon materials, and the content of silicon element in the proportion of the silicon-carbon materials accounts for 5-30 wt% of the total mass of the silicon-carbon materials.
The second negative electrode active material layer is provided to function to increase the battery capacity.
According to the invention, the security coating comprises ceramic particles and a fifth binder.
According to the invention, the safety coating comprises the following components in percentage by mass:
90-99 wt% of ceramic particles and 1-10 wt% of a fifth binder.
Preferably, the safety coating comprises the following components in percentage by mass:
93-99 wt% of ceramic particles and 1-7 wt% of a fifth binder.
Illustratively, the content of the ceramic particles is 90 wt%, 91 wt%, 92 wt%, 93 wt%, 94 wt%, 95 wt%, 96 wt%, 97 wt%, 98 wt%, 99 wt%.
Illustratively, the content of the fifth binder is 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%.
According to the invention, the thickness of the security coating is 1-5 μm, for example 1 μm, 2 μm, 3 μm, 4 μm, 5 μm.
The safety coating is arranged to prevent the surface of the second negative electrode active material layer from contacting with electrolyte for a long time to generate side reaction, avoid the lithium dendrite generated on the second negative electrode active material layer from directly puncturing the diaphragm, reduce safety risk, and buffer the volume expansion of the second negative electrode active material layer to a certain extent.
According to the invention, the ceramic particles are selected from one or a mixture of several of oxide ceramics, nitride ceramics and carbide ceramics.
According to the invention, D of said ceramic particles50Is 50nm-2 μm.
According to the invention, the first conductive agent, the second conductive agent, the third conductive agent, the fourth conductive agent and the fifth conductive agent are the same or different and are independently selected from one or a mixture of several of conductive carbon black, acetylene black, Ketjen black, Super P, graphene and CNT.
According to the invention, the first binder, the second binder, the third binder, the fourth binder and the fifth binder are the same or different and are independently selected from one or a mixture of styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), polyvinylidene fluoride (PVDF) and sodium polyacrylate (PAA-Na).
According to the invention, the first thickener and the second thickener are identical or different and are selected independently of one another from sodium carboxymethylcellulose (CMC) or polyether-modified silicone polymers or from mixtures of two thereof.
In the present invention, unless otherwise specified, the thickness of the coating layer refers to the thickness of the coating layer on one surface.
The invention also provides a preparation method of the negative plate, which comprises the following steps:
1) respectively preparing conductive slurry for forming a conductive coating, first negative electrode slurry for forming a first negative electrode active material layer, buffer slurry for forming a buffer coating, second negative electrode slurry for forming a second negative electrode active material layer and safety slurry for forming a safety coating;
2) and sequentially coating the conductive slurry for forming the conductive coating, the first negative electrode slurry for forming the first negative electrode active material layer, the buffer slurry for forming the buffer coating, the second negative electrode slurry for forming the second negative electrode active material layer and the safety slurry for forming the safety coating on the first surface of the negative electrode current collector by using a coating machine, and preparing the negative electrode sheet.
According to the present invention, in step 1), the solid contents of the conductive paste for forming the conductive coating, the first negative electrode paste for forming the first negative electrode active material layer, the buffer paste for forming the buffer coating, the second negative electrode paste for forming the second negative electrode active material layer, and the safety paste for forming the safety coating are all 40 wt% to 45 wt%.
According to the present invention, in step 2), on the first surface of the negative electrode current collector, the conductive paste forming the conductive coating is coated from one end of the negative electrode current collector and is coated to the other end to form the conductive coating, then the first negative electrode paste forming the first negative electrode active material layer is coated from one end of the negative electrode current collector and is coated to the other end to form the first negative electrode active material layer, then the buffer paste forming the buffer coating is coated from one end of the negative electrode current collector and is coated to the other end to form the buffer coating, then the second negative electrode paste forming the second negative electrode active material layer is coated from one end of the negative electrode current collector and is coated to the other end to form the second negative electrode active material layer, then the safety paste forming the safety coating is coated from one end of the negative electrode current collector and is coated to the other end to form the safety coating.
According to the invention, step 2) comprises in particular: and sequentially coating the conductive slurry for forming the conductive coating, the first negative electrode slurry for forming the first negative electrode active material layer, the buffer slurry for forming the buffer coating, the second negative electrode slurry for forming the second negative electrode active material layer and the safety slurry for forming the safety coating on the first surface and the second surface of the negative electrode current collector by using a coating machine, and preparing the negative electrode sheet.
According to the present invention, in step 2), on the first surface of the negative electrode current collector, the conductive slurry forming the conductive coating is coated from one end of the negative electrode current collector and is coated to the other end to form the conductive coating, then the first negative electrode slurry forming the first negative electrode active material layer is coated from one end of the negative electrode current collector and is coated to the other end to form the first negative electrode active material layer, then the buffer slurry forming the buffer coating is coated from one end of the negative electrode current collector and is coated to the other end to form the buffer coating, then the second negative electrode slurry forming the second negative electrode active material layer is coated from one end of the negative electrode current collector and is coated to the other end to form the second negative electrode active material layer, then the safety slurry forming the safety coating is coated from one end of the negative electrode current collector and is coated to the other end to form the safety coating;
on the second surface of the negative electrode current collector, coating conductive slurry for forming a conductive coating from one end of the negative electrode current collector and finishing the coating to the other end to form the conductive coating, then coating first negative electrode slurry for forming a first negative electrode active material layer from one end of the negative electrode current collector and finishing the coating to the other end to form a first negative electrode active material layer, then coating buffer slurry for forming a buffer coating from one end of the negative electrode current collector and finishing the coating to the other end to form the buffer coating, then coating second negative electrode slurry for forming a second negative electrode active material layer from one end of the negative electrode current collector and finishing the coating to the other end to form a second negative electrode active material layer coating, and then coating safety slurry for forming a safety coating from one end of the negative electrode current collector and finishing the coating to the other end to form the safety coating.
The invention also provides a lithium ion battery which comprises the negative plate.
According to the invention, the lithium ion battery further comprises a positive plate, a diaphragm and electrolyte.
The invention has the beneficial effects that:
the invention provides a negative plate and a lithium ion battery comprising the same.
The negative plate adopts a multilayer coating technology, and the conductive coating is coated between the negative current collector and the first negative active material layer, so that the contact resistance between the first negative active material layer and the negative current collector can be reduced, the acting force between the first negative active material layer and the negative current collector is improved, the first negative active material layer is prevented from being peeled off, and meanwhile, the conductive coating has strong conductivity and can improve the charging capacity of the negative electrode; the buffer coating is coated between the first negative electrode active material layer and the second negative electrode active material layer, so that the contact resistance between the first negative electrode active material layer and the second negative electrode active material layer can be reduced, the acting force between the first negative electrode active material layer and the second negative electrode active material layer is improved, the second negative electrode active material layer is prevented from being stripped from the first negative electrode active material layer, the transmission rate of ions and electrons is improved, and the volume expansion of the first negative electrode active material layer and the second negative electrode active material layer is buffered; the surface of the second negative electrode active material layer is coated with a layer of safety coating, so that the volume expansion of the second negative electrode active material layer is further buffered, and meanwhile, the generation of lithium dendrites can be prevented from directly puncturing the diaphragm to cause internal short circuit, and the safety risk is reduced.
The acting forces between the first negative electrode active material layer and the negative electrode current collector and between the first negative electrode active material layer and the second negative electrode active material layer in the negative electrode sheet are larger, so that sudden capacity drop caused by stripping of the negative electrode active material in the circulation process can be avoided. The negative plate can avoid the rapid attenuation of capacity under the rapid charging with larger multiplying power, avoids the formation of lithium dendrite and has better safety performance. The lithium ion battery has higher capacity performance and long cycle performance, and can meet the requirement of industrial application.
In summary, the present invention provides a negative electrode sheet with high energy density, fast charging performance, safety performance and long cycle life, and a lithium ion battery including the negative electrode sheet.
Drawings
Fig. 1 is a schematic structural view of a negative electrode sheet according to the present invention.
Reference numerals: 1: a negative current collector; 2: a conductive coating; 3: a first negative electrode active material layer; 4: a buffer coating; 5: a second negative electrode active material layer; 6: and (4) a safety coating.
FIG. 2 is a comparison of the cycle expansion of example 1 and comparative example 4 in accordance with the present invention.
FIG. 3 is a graph showing the comparison of cycle performance of example 1 with comparative examples 5, 6 and 7 according to the present invention.
Detailed Description
The present invention will be described in further detail with reference to specific examples. It is to be understood that the following examples are only illustrative and explanatory of the present invention and should not be construed as limiting the scope of the present invention. All the technologies realized based on the above-mentioned contents of the present invention are covered in the protection scope of the present invention.
The experimental methods used in the following examples are all conventional methods unless otherwise specified; reagents, materials and the like used in the following examples are commercially available unless otherwise specified.
In the description of the present invention, it should be noted that the terms "first", "second", "third", "fourth", "fifth", etc. are used for descriptive purposes only and are not intended to indicate or imply relative importance.
Example 1:
(1) preparing a positive plate:
LiCoO as positive electrode active material2PVDF as a binder and Super P as a conductive agent in a mass ratio of 97%: 1.5%: 1.5% inEvenly stirring in N-methyl pyrrolidone (NMP) to prepare slurry, evenly coating the slurry on the two side surfaces of an aluminum foil of a positive current collector, baking at the temperature of 100 ℃ and 150 ℃ for 4-8h, then cold pressing and cutting to prepare a positive plate of the lithium ion battery, wherein the compaction density is 4.1g/cm3The thickness of the one-side positive electrode active material layer was 62 μm.
(2) Preparing negative conductive slurry:
super P and PVDF were mixed and dissolved in NMP at a mass ratio of 97:3 to obtain a conductive coating slurry with a solid content of 45%.
(3) Preparing first cathode slurry of a cathode:
preparing artificial graphite, conductive agent SP, SBR and CMC into first negative electrode slurry according to the mass ratio of 97:0.5:1.5:1, wherein the particle size D of the graphite90Less than or equal to 25 mu m and solid content of 48 percent.
(4) Preparing cathode buffer slurry:
acetylene black and PVDF were mixed and dissolved in NMP in a mass ratio of 97:3 to obtain a buffer slurry with a solid content of 45%.
(5) Preparing a second cathode slurry of the cathode:
preparing a silicon-carbon material (silicon material accounts for 20 wt%), conductive carbon black, SBR and CMC into second negative electrode slurry according to a mass ratio of 97:0.5:1.5:1, wherein the particle size D of the silicon-carbon material is90Less than or equal to 15 mu m and solid content of 45 percent.
(6) Preparing cathode safety slurry:
mixing and dissolving alumina ceramic and PVDF in NMP according to a mass ratio of 97:3, wherein the particle size D of the alumina ceramic90Less than or equal to 2 mu m to obtain the safe slurry with the solid content of 40 percent.
(7) Preparing a negative plate:
uniformly coating conductive slurry and first negative electrode slurry on the first surface of a copper foil with the thickness of 6 microns in sequence, continuously coating buffer slurry and second negative electrode slurry after primary drying treatment and drying, continuously coating safe slurry after secondary drying treatment and drying, and performing third drying treatment, wherein the coating speed is 5m/min, and drying is performed by 5 sections of ovens, and the temperature of each section of oven is 60 ℃, 80 ℃, 110 ℃ and 100 ℃;
the thickness of the conductive coating is 3 micrometers, the thickness of the first negative electrode active material layer is 50 micrometers, the thickness of the buffer coating is 3 micrometers, the thickness of the second negative electrode active material layer is 30 micrometers, and the thickness of the safety coating is 3 micrometers; coating the second surface of the copper foil opposite to the first surface by repeating the coating, and performing pressurization treatment by using a roller press to obtain a compact density of 1.65g/cm3The negative electrode sheet of (1).
(8) Preparing a lithium ion battery:
selecting a base material, single-sided ceramic and double-sided glued composite diaphragm for the prepared positive plate and negative plate, and the diaphragm between the positive plate and the negative plate, then winding by using a winding machine to prepare a winding core of a winding structure with the positive plate wrapped externally, packaging by adopting an aluminum-plastic film, baking for 48 hours in a vacuum state to remove moisture, injecting electrolyte, and then carrying out conventional formation and sorting on the battery to obtain the square soft package lithium ion battery. The electrolyte is prepared by adopting a conventional electrolyte formula: LiPF6+ solvent (EC + FEC + DEC + DMC + PS).
Example 2:
this example differs from example 1 in that: replacement of Super P in conductive coating with carbon nanotubes, replacement of acetylene black in buffer coating with Ketjen black, and zirconium nitride ceramic (D)90Less than or equal to 2 mu m) to replace the alumina ceramic in the safety coating.
Example 3:
this example differs from example 1 in that: the thicknesses of the coating layers on the surface of the negative current collector are different, and are specifically shown in table 1; the compacted density of the negative plate is 1.55g/cm3(ii) a The thickness of the one-side positive electrode active material layer in the positive electrode sheet was adjusted to 22 μm due to the change in the negative electrode sheet press density.
Example 4:
this example differs from example 1 in that: the thicknesses of the coating layers on the surface of the negative current collector are different, and are specifically shown in table 1; the compacted density of the negative plate is 1.75g/cm3(ii) a The thickness of the one-side positive electrode active material layer in the positive electrode sheet was adjusted to 110 μm due to the change in the negative electrode sheet press density.
Example 5:
this example differs from example 1 in that: in the conductive coating slurry, the Super P and PVDF are mixed and dissolved in NMP at a mass ratio of 90:10 to obtain the conductive coating slurry with the solid content of 45%.
Example 6:
this example differs from example 1 in that: in the buffer coating slurry, the mass ratio of acetylene black to PVDF is 90:10, and the acetylene black and the PVDF are mixed and dissolved in NMP to obtain the buffer coating slurry with the solid content of 45%.
Example 7:
this example differs from example 1 in that: in the safe coating slurry, the mass ratio of the alumina ceramic to the PVDF is 90:10, and the alumina ceramic and the PVDF are mixed and dissolved in NMP to obtain the safe coating slurry with the solid content of 45%.
Example 8:
this example differs from example 1 in that: in the conductive coating slurry, the mass ratio of the Super P to the PVDF is 50:50, and the mixture is dissolved in NMP to obtain the conductive coating slurry with the solid content of 45%.
Example 9:
this example differs from example 1 in that: in the buffer coating slurry, the mass ratio of acetylene black to PVDF is 50:50, and the acetylene black and the PVDF are mixed and dissolved in NMP to obtain the buffer coating slurry with the solid content of 45%.
Example 10:
this example differs from example 1 in that: in the safe coating slurry, the mass ratio of the alumina ceramic to the PVDF is 50:50, and the alumina ceramic and the PVDF are mixed and dissolved in NMP to obtain the safe coating slurry with the solid content of 45%.
Comparative example 1:
this comparative example differs from example 1 in that: no security coating was applied.
Comparative example 2:
this comparative example differs from example 1 in that: no buffer coating was applied.
Comparative example 3:
this comparative example differs from example 1 in that: no conductive coating is applied.
Comparative example 4:
this comparative example differs from example 1 in that: the safety, buffer and conductive coatings were not applied.
Comparative example 5:
this comparative example differs from example 1 in that: only the conductive coating layer, the first anode active material layer, and the second anode active material layer are coated.
Comparative example 6:
this comparative example differs from example 1 in that: only the first anode active material layer, the buffer coat, and the second anode active material layer are coated.
Comparative example 7:
this comparative example differs from example 1 in that: only the first negative electrode active material layer, the second negative electrode active material layer, and the safety coat are coated.
Table 1 compositions of negative electrode sheets of examples and comparative examples
Figure BDA0002632186100000121
The following tests were carried out on the batteries of the above examples and comparative examples:
(1) peeling force test between the first negative electrode active material layer and the copper foil:
cutting the pole pieces prepared in the examples and the comparative examples into test samples with the size of 20 multiplied by 100mm for later use; bonding the pole piece to the surface to be tested by using a double-sided adhesive tape, and compacting by using a compression roller to ensure that the pole piece is completely attached to the pole piece; the other side of the double-sided adhesive tape of the sample is adhered to the surface of the stainless steel, and one end of the sample is reversely bent, wherein the bending angle is 180 degrees; the method comprises the steps of adopting a high-speed rail tensile machine for testing, fixing one end of stainless steel on a clamp below the tensile machine, fixing the bent tail end of a sample on an upper clamp, adjusting the angle of the sample to ensure that the upper end and the lower end are positioned at vertical positions, then stretching the sample at a speed of 50mm/min until the sample is completely stripped from a substrate, recording displacement and acting force in the process, and generally considering the force when the stress is balanced as the stripping force of a pole piece.
(2) Cycle life and battery cycle expansion rate testing:
the batteries of the examples and the comparative examples are subjected to constant current charging at a rate of 1.5C to 4.45V at a temperature of 25 ℃, then are subjected to constant voltage charging at a voltage of 4.45V, the cut-off current is 0.025C, and then are subjected to constant current discharging at a rate of 0.5C, the cut-off voltage is 3V, and the charging and discharging cycle process is repeated until the capacity retention rate of the battery is lower than 80% or the cycle number reaches 800 times; and simultaneously testing the battery cycle expansion rate of the battery at a specific cycle number, wherein the calculation method comprises the following steps: the full thickness of the cell was measured with a thickness tester before cycling as the initial thickness, the cell was tested for thickness and recorded at full power off after 100 cycles, and the cyclic expansion rate was 100% (cyclic full power off thickness/initial full power thickness).
(3) And (3) lithium separation:
the batteries of the examples and comparative examples were charged at 25 ℃ at a constant current of 1.5C rate to 4.45V, then charged at a constant voltage of 4.45V with a cutoff current of 0.025C, and then discharged at a constant current of 0.5C rate with a cutoff voltage of 3V, which is a charge-discharge cycle, and the charge-discharge cycle was repeated 10 times, after which the batteries were fully charged, the cells were disassembled in a dry room environment, and the lithium deposition on the surface of the negative electrode was observed. The degree of lithium separation is classified into no lithium separation, slight lithium separation and serious lithium separation. Slight lithium deposition means that the lithium deposition region on the surface of the negative electrode is 1/10 or less of the entire region, and severe lithium deposition means that the lithium deposition region on the surface of the negative electrode exceeds 1/3 of the entire region. The test results are shown in table 2.
Table 2 results of cell performance test of examples and comparative examples
Figure BDA0002632186100000141
From the above test results it can be seen that:
compared with the embodiment 1, the comparative examples 1 to 3 are respectively the schemes of not coating a safety coating, not coating a buffer coating and not coating a conductive coating, obviously, the situation that lithium precipitation on the surface of the negative plate is continuously accumulated and even aggregated in the circulation process due to the fact that the safety coating is not coated can cause serious lithium precipitation, and the potential safety hazard of puncturing a diaphragm exists; in the circulation process, the silicon substrate layer is easy to peel off the first negative electrode active material layer and the second negative electrode active material layer due to larger volume expansion in the absence of the buffer coating, and the contact resistance between the two negative electrode active material layers is large, so that the long circulation life is not facilitated; the contact resistance between the first negative electrode active material and the negative electrode current collector becomes large due to the fact that the conductive coating is not coated, peeling between the first negative electrode active material and the negative electrode current collector easily occurs in the circulation process, and long circulation life is not facilitated.
Comparative example 4 in comparison with example 1, in which the first negative electrode active material layer and the second negative electrode active material layer were coated only on the current collector, and the conductive coating, the buffer coating, and the safety coating were not coated, it is apparent that this would cause the contact resistance between the first negative electrode active material layer and the second negative electrode active material layer, and between the first negative electrode active material layer and the negative electrode current collector to become large, the applied force to become small, thereby causing the resistance of the entire negative electrode sheet to become large, and the peeling of the coating to easily occur during a long cycle; the existence of the non-safety coating can cause the lithium on the surface of the negative plate to be seriously precipitated and aggregated, and the capacity is sharply reduced. Fig. 2 is a comparison of the swelling of example 1 and comparative example 4 during cycling, and it is evident that without the introduction of a three-layer coating (comparative example 4), the initial swelling of the cell is greater and increases linearly during cycling until capacity fade fails, which is caused by excessive swelling of the negative electrode material; after the introduction of the three-layer coating (example 1), the initial swelling of the battery is obviously reduced, and the battery linearly increases with a small slope in the process of cycling, and the swelling rate is kept small after 800 cycles. Obviously, the three layers of coatings are introduced simultaneously, so that the buffering and protection of the negative active material are obviously enhanced, and the expansion of the negative material is reduced.
Comparative examples 5 to 7 in comparison with example 1, only the conductive coating layer, the buffer coating layer, and the safety coating layer were coated except for the first negative electrode active material layer and the second negative electrode active material layer, respectively. Similar to comparative examples 1 to 3, the application of only the conductive coating layer did not ensure the acting force and contact resistance between the first negative electrode active material layer and the second negative electrode active material layer, and lithium deposited on the surface of the negative electrode sheet was liable to aggregate; only the buffer coating is coated, so that the acting force and the contact resistance of the first negative electrode active material layer and the negative electrode current collector cannot be guaranteed, and lithium deposited on the surface of the negative electrode sheet is easy to gather; only coating the safety coating can not guarantee acting force and contact resistance between the first negative electrode active material layer and the second negative electrode active material layer and between the first negative electrode active material layer and the negative electrode current collector, and long cycle life is influenced. Fig. 3 is a comparison curve of the cycle performance of comparative examples 5 to 7 and example 1, and it is obvious that the introduction of three layers of coatings greatly improves the long cycle performance of the negative plate.
Examples 8-10 compared to example 1, the proportion of conductive agent in the conductive coating, the proportion of conductive agent in the buffer coating, and the proportion of ceramic particles in the security coating were reduced, respectively. By reducing the proportion of the conductive agent in the conductive coating, the acting force between the first negative electrode active material layer and the negative electrode current collector is strengthened, the coating is not easy to peel off, but the resistance between the first negative electrode active material layer and the negative electrode current collector is increased, lithium precipitation can be caused in the circulation process, and the long circulation life is shortened; similarly, by reducing the proportion of the conductive agent in the buffer coating, the acting force between the first negative electrode active material layer and the second negative electrode active material layer becomes strong and is not easy to be peeled off from each other, but the resistance between the first negative electrode active material layer and the second negative electrode active material layer is increased, which is not favorable for long cycle performance; by reducing the proportion of ceramic particles in the safety coating, the force between the safety coating and the second negative electrode active material layer is greater, but at the same time the lithium insertion resistance is improved, reducing the long cycle life.
In summary, on the basis of the negative electrode sheet of comparative example 4, which only includes the first negative electrode active material layer and the second negative electrode active material layer, when the conductive coating is singly introduced, a safety problem is easily caused when lithium deposition occurs on the surface of the negative electrode sheet; when the buffer coating is singly introduced, the contact resistance between the coating and the current collector is large (the problem of quick charge exists), and the safety problem exists when lithium precipitation occurs on the surface; when the safety coating is singly introduced, the acting force between the coating and the current collector and between the coating is insufficient, and the peeling of the coating is easy to occur to cause capacity attenuation (the problem of cycle life exists).
By simultaneously introducing three coatings, compared with a single coating, the thickness of the coating is slightly increased, and high volume energy density (existence of silicon-carbon materials) can be still maintained; the conductive coating and the buffer coating are introduced simultaneously, so that the contact resistance between the coatings and between the coating and a current collector can be greatly reduced (the stripping force is improved), the volume expansion of a negative active material layer is relieved, the quick charge performance is improved, and the cycle life is long; and the introduction of the safety coating avoids the penetration of the diaphragm by the lithium separated from the surface, thereby ensuring the safety performance.
The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiment. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. The negative plate comprises a negative current collector, and a conductive coating, a first negative active material layer, a buffer coating, a second negative active material layer and a safety coating which are sequentially coated on the first surface of the negative current collector.
2. The negative electrode sheet according to claim 1, wherein the negative electrode sheet further comprises a conductive coating, a first negative electrode active material layer, a buffer coating, a second negative electrode active material layer, and a safety coating, which are sequentially coated on a second surface of the negative electrode current collector opposite to the first surface.
3. The negative electrode sheet of claim 1 or 2, wherein the conductive coating comprises a first conductive agent and a first binder; and/or the presence of a gas in the gas,
the conductive coating comprises the following components in percentage by mass: 90-99 wt% of a first conductive agent, 1-10 wt% of a first binder; and/or the presence of a gas in the gas,
the thickness of the conductive coating is 1-5 μm.
4. The negative electrode sheet according to any one of claims 1 to 3, wherein the first negative electrode active material layer comprises a first negative electrode active material, a second conductive agent, a first thickener, and a second binder; and/or the presence of a gas in the gas,
the first negative electrode active material layer includes the following components in mass fraction:
90-98.5 wt% of a first negative electrode active material, 0.5-4 wt% of a second conductive agent, 0.5-3 wt% of a first thickener, and 0.5-3 wt% of a second binder; and/or the presence of a gas in the gas,
the thickness of the first negative electrode active material layer is 20 to 150 μm; and/or the presence of a gas in the gas,
d of the first negative electrode active material90Less than or equal to 50 mu m; and/or the presence of a gas in the gas,
the first negative electrode active material is selected from artificial graphite or natural graphite.
5. Negative electrode sheet according to any of claims 1 to 4, wherein the buffer coating comprises a third conductive agent and a third binder; and/or the presence of a gas in the gas,
the buffer coating comprises the following components in percentage by mass: 90-99 wt% of a third conductive agent, 1-10 wt% of a third binder; and/or the presence of a gas in the gas,
the thickness of the buffer coating is 1-5 μm.
6. The negative electrode sheet according to any one of claims 1 to 5, wherein the second negative electrode active material layer comprises a second negative electrode active material, a fourth conductive agent, a second thickener, and a fourth binder; and/or the presence of a gas in the gas,
the second negative electrode active material layer includes the following components in mass fraction:
90-98.5 wt% of a second negative electrode active material, 0.5-4 wt% of a fourth conductive agent, 0.5-3 wt% of a second thickener, and 0.5-3 wt% of a fourth binder.
7. The negative electrode sheet according to any one of claims 1 to 6, wherein the thickness of the second negative electrode active material layer is 10 to 100 μm; and/or the presence of a gas in the gas,
d of the second negative electrode active material90Less than or equal to 50 mu m; and/or the presence of a gas in the gas,
the second negative active material is selected from silicon-carbon materials, and the content of silicon element in the proportion of the silicon-carbon materials accounts for 5-30 wt% of the total mass of the silicon-carbon materials.
8. Negative electrode sheet according to any of claims 1 to 7, wherein the safety coating comprises ceramic particles and a fifth binder; and/or the presence of a gas in the gas,
the safety coating comprises the following components in percentage by mass: 90-99 wt% of ceramic particles and 1-10 wt% of a fifth binder.
9. Negative electrode sheet according to any one of claims 1 to 8, wherein the safety coating has a thickness of 1 to 5 μm; and/or the presence of a gas in the gas,
the ceramic particles are selected from one or a mixture of several of oxide ceramic, nitride ceramic and carbide ceramic; and/or the presence of a gas in the gas,
d of the ceramic particles50Is 50nm-2 μm.
10. A lithium ion battery comprising the negative electrode sheet of any one of claims 1 to 9.
CN202010814453.3A 2020-08-13 2020-08-13 Negative plate and lithium ion battery comprising same Pending CN111900356A (en)

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