WO2023093576A1

WO2023093576A1 - Pole piece and lithium ion battery

Info

Publication number: WO2023093576A1
Application number: PCT/CN2022/132059
Authority: WO
Inventors: 张健; 彭冲
Original assignee: 珠海冠宇电池股份有限公司
Priority date: 2021-11-29
Filing date: 2022-11-15
Publication date: 2023-06-01
Also published as: CN114156434A

Abstract

The present application provides a pole piece and a lithium ion battery. Firstly, the application provides a pole piece, comprising a substrate. The substrate comprises a current collector and a protective layer arranged on the surface of the current collector. An active substance layer is further arranged on the protective layer. The protective layer comprises, by mass percentage, 62%-96% of a non-active material, 0.1%-8% of a conductive agent, and 3%-30% of a binder. The thickness H1 of the protective layer and the D50 of the inactive material satisfy the relationship H1 ≥ 2*D50. The thickness H1 of the protective layer and the D90 of the inactive material satisfies the relationship H1 ≥ D90. The thickness H1 of the protective layer and the thickness H2 of the active substance layer satisfy the relationship H1/H2 ≤ 1/5. The pole piece provided in the present application can solve the problem that the safety and the electrical performance of a lithium ion battery cannot be both ensured.

Description

A kind of pole piece and lithium ion battery

This application claims the priority of the Chinese patent application with the application number 202111446122.X and the application title "A Pole Plate and Lithium-ion Battery" filed with the China Patent Office on November 29, 2021, the entire contents of which are hereby incorporated by reference In this application.

technical field

The application relates to a pole piece and a lithium ion battery, and relates to the technical field of electrochemistry.

Background technique

Lithium-ion batteries are widely used in smartphones, laptops, Bluetooth, wearable devices and other fields due to their advantages such as high platform voltage, high energy density, no memory effect, and long life. However, in some extreme cases, for example, when the lithium-ion battery is subjected to mechanical damage, such as acupuncture, heavy impact, etc., an internal short circuit will occur, and a large amount of heat will be released in a short period of time, causing the lithium-ion battery to catch fire and fail. big security risk.

Studies have found that when an internal short circuit occurs in a lithium-ion battery, there will be multiple short-circuit modes. At present, setting a protective layer on the surface of the current collector helps to improve the safety of the lithium-ion battery, but it will lead to a decline in the electrical performance of the lithium-ion battery. Therefore, how to balance the safety and electrical performance of lithium-ion batteries has received more and more attention.

Contents of the invention

The present application provides a pole piece, which is used to solve the problem that the safety and electrical performance of lithium-ion batteries cannot be balanced.

The application also provides a lithium ion battery, which has better safety and electrical performance.

The first aspect of the present application provides a pole piece, including a base, the base includes a current collector and a protective layer provided on the surface of the current collector, and an active material layer is also provided on the protective layer;

The protective layer includes 62%-96% of inactive materials, 0.1%-8% of conductive agent, and 3%-30% of binder according to mass percentage;

The thickness H1 of the protective layer and the D50 of the inactive material satisfy the relationship H1≥2*D50;

The thickness H1 of the protective layer and the D90 of the inactive material satisfy the relationship H1≥D90;

The thickness H1 of the protective layer and the thickness H2 of the active material layer satisfy the relationship H1/H2≦1/5.

According to one embodiment of the present application, the inactive material includes inorganic particles and/or organic particles, wherein:

The inorganic particles include one or more of oxides, carbides, nitrides, inorganic salts, and first carbon coating materials, and the first carbon coating materials include first matrix particles and coated on the A first carbon layer on at least part of the surface of the first base particle, wherein the first base particle is selected from one or more of oxides, carbides, nitrides, and inorganic salts;

The organic particles include one or more of polystyrene, polymethyl methacrylate, polytetrafluoroethylene, and a second carbon coating material, and the second carbon coating material includes a second matrix particle and a coating A second carbon layer covering at least part of the surface of the second base particle, wherein the second base particle is selected from one or more of polystyrene, polymethyl methacrylate, and polytetrafluoroethylene.

According to an embodiment of the present application, the oxide is selected from at least one of alumina, titanium oxide, magnesium oxide, zirconium oxide, stimbine, barium oxide, manganese oxide, silicon oxide, iron oxide, and ferroferric oxide. A kind; the carbide includes metal carbide and/or non-metal carbide, and the metal carbide includes at least one of titanium carbide, calcium carbide, chromium carbide, tantalum carbide, vanadium carbide, zirconium carbide, and tungsten carbide , the non-metallic carbides include boron carbide and/or silicon carbide; the nitrides include metal nitrides and/or non-metal nitrides, and the metal nitrides include lithium nitride, magnesium nitride, aluminum nitride, At least one of titanium nitride and tantalum nitride, the non-metallic nitride includes at least one of boron nitride, phosphorus pentanitride, and silicon nitride; the inorganic salt includes carbonate and / or sulfates.

According to an embodiment of the present application, the thickness H1 of the protective layer and the D10 of the inactive material satisfy a relationship H1≧8×D10.

According to an embodiment of the present application, D10≤0.5 μm, D50≤2 μm, and D90≤5 μm of the inactive material.

According to an embodiment of the present application, the D10 of the inactive material is 0.01-0.2 μm, the D50 is 0.05-0.5 μm, and the D90 is 1-3 μm.

According to an embodiment of the present application, the protective layer has a thickness of 0.1 μm-10 μm.

According to an embodiment of the present application, the pole piece is a positive pole piece.

According to an embodiment of the present application, at least one of the first end and the second end of the pole piece, the vertical distance from the protective layer to the outer edge of the current collector is smaller than the distance from the active material layer to the the vertical distance of the outer edge of the current collector, the first end and the second end are opposite; or,

At least one of the first end and the second end of the pole piece, there is an empty foil area between the protective layer and the outer edge of the current collector, the active material layer includes a first part, and the first part and the first part A connected second part, the first part is arranged on the surface of the protective layer, and the second part is arranged on the surface of the current collector in the empty foil area.

The second aspect of the present application provides a lithium-ion battery, including any one of the pole pieces described above.

The implementation of the present application has at least the following advantages:

1. The pole piece provided by the application includes a protective layer, and controls the mass fraction of each component in the protective layer, the relationship between the thickness of the protective layer and the particle size of the inactive material and the thickness of the active material layer, which not only effectively solves the problem of lithium-ion batteries Problems such as fire time limit caused by mechanical abuse, etc., while keeping the electrical performance of lithium-ion batteries basically unaffected, solve the problem that the safety and electrical performance of lithium-ion batteries cannot be balanced.

2. The lithium ion battery provided by this application has good safety and electrical performance.

Description of drawings

Fig. 1 is a schematic structural diagram of a pole piece provided by an embodiment of the present application;

Fig. 2 is a schematic structural diagram of a pole piece provided by another embodiment of the present application.

Explanation of reference signs:

100-collector;

200 - protective layer;

300 - active material layer.

Detailed ways

In order to make the purpose, technical solutions and advantages of the application clearer, the technical solutions in the embodiments of the application will be clearly and completely described below in conjunction with the embodiments of the application. Obviously, the described embodiments are part of the implementation of the application. example, not all examples. Based on the embodiments in this application, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the scope of protection of this application.

The first aspect of the present application provides a pole piece, including a base, the base includes a current collector and a protective layer arranged on the surface of the current collector, and an active material layer is also arranged on the protective layer;

The application provides a pole piece, including a base, the base includes a current collector and a protective layer arranged on the surface of the current collector, the protective layer is also provided with an active material layer, and the current collector is used in the pole piece to attach the protective layer material, active material The base metal of other materials, including two surfaces for attaching protective layer materials, active materials and other materials, the protective layer is set on the surface of the current collector, the current collector and the protective layer constitute the base of the pole piece, and the protective layer is also set There is an active material layer. In order to ensure that the electrical performance of the lithium-ion battery is not affected substantially, the application selects the inactive material as the main component of the protective layer. Relative function), in the charging and discharging process of lithium-ion batteries, it will not continue to deteriorate and affect the use of lithium-ion batteries, reduce the impact of the protective layer on the cycle stability of lithium-ion batteries, and take into account the electrical properties of lithium-ion batteries; inactive materials are used as protection The main component of the layer 200 mainly plays the role of supporting the protective layer. When the content of the inactive material is too low, the structural stability of the protective layer will be poor, and it will be destroyed by the action of the active material layer in the subsequent coating process of the active material layer. Or in the pole sheet rolling process, the protective layer is crushed under pressure, so the mass percentage of the inactive material should not be lower than 62%; it can be understood that the protective layer 200 also includes binder and Conductive agent, binder is used to bond inactive materials, conductive agents and other components together to form a coating, and to bond the protective layer with the current collector to improve the stability of the protective layer and the relationship between it and the current collector Adhesive force, thereby improving the stability and safety of the pole piece. When the content of the binder is too low, it cannot play a bonding role, which is not conducive to the good adhesion of the protective layer on the current collector. The binder Excessively high content will easily cause the pole piece to become brittle, reduce the compaction density, and affect the energy density of the lithium-ion battery; the conductive agent can build an electronic conductive network, especially when the protective layer is located between the current collector and the active material layer. The electronic pathway between the current collector and the active material layer is conducive to the function of the current collector and improves the performance of the electrode sheet. If the content is too low, the electrical conductivity of the protective layer will be insufficient, which will affect the electrical properties of the electrode sheet. If the mass content of the conductive agent is too large, it will also affect the protective function of the protective layer on the pole piece to a certain extent. When an internal short circuit occurs, the protective layer has high conductivity, and it contacts with the pole piece of the other polarity. It will cause severe heat generation at the short circuit point and cause thermal runaway. Therefore, in order to take into account the safety and electrical performance of the lithium-ion battery, the protective layer includes 62%-96% of inactive materials, 0.1%-8% of Conductive agent, 3%-30% binder, that is, the total mass of the protective layer is 100%, the mass of inactive materials is 62%-96% of the total mass of the protective layer, and the mass of the conductive agent is the total mass of the protective layer 0.1%-8% of the total mass of the adhesive, and the mass of the binder is 3%-30% of the total mass of the protective layer.

At the same time, the applicant found that the relationship between the thickness of the protective layer and the particle size of the inactive layer has an important impact on the protective effect of the protective layer. Specifically, the inactive material is a key factor for the protection support. When the inactive material in the protective layer At least two layers on the plane perpendicular to the current collector can have a good protective effect, so the thickness H1 of the protective layer and the average particle size D50 of the inactive material need to satisfy H1≥2×D50. Under this condition, it is beneficial to make the protective layer evenly distribute at least two inactive material particles in its thickness direction (direction perpendicular to the surface of the current collector), which is equivalent to forming at least two single-layer protective layers (each single-layer protective layer The average number of inactive material particles in the thickness direction of the layer is one), which is more conducive to the function of the protective layer and improves the safety of the pole piece; the thickness H1 of the protective layer and the D90 of the inactive material satisfy H1≥D90, thus ensuring protection The particle size of more than 90% of the particles in the layer is lower than the thickness of the protective layer, effectively avoiding the occurrence of coating scraping, avoiding the phenomenon of foil leakage, and improving the processing performance of the protective layer; D50 is in the volume-based particle size distribution, inactive The particle diameter at which the material reaches 50% of the volume accumulation from the small particle diameter side; D90 is the particle diameter at which the inactive material reaches 90% of the volume accumulation from the small particle diameter side in the volume-based particle size distribution.

Since the protective layer itself does not provide capacity, it will cause loss to the energy density of the lithium-ion battery. In order to further avoid the influence of the protective layer on the energy density of the lithium-ion battery, the thickness H1 of the protective layer is equal to the thickness H2 of the active material layer. The relationship satisfies H1/H2≤1/5.

The pole piece provided by the application includes a protective layer, and controls the mass fraction of each component in the protective layer, the relationship between the thickness of the protective layer and the particle size of the inactive material and the thickness of the active material layer, which can not only effectively improve the safety of lithium-ion batteries Especially in the event of mechanical abuse, reduce the probability of lithium-ion battery fire failure, improve the pass rate of lithium-ion battery nail penetration test, and keep the electrical performance of lithium-ion battery basically unaffected, solve the problem of lithium-ion battery safety and The problem that the electrical performance cannot be taken into account.

In a specific embodiment, the inactive material comprises inorganic particles and/or organic particles, wherein:

Further, the oxide is selected from at least one of aluminum oxide, titanium oxide, magnesium oxide, zirconium oxide, stibnite, barium oxide, manganese oxide, silicon oxide, iron oxide, and ferroferric oxide; Carbides include metal carbides and/or non-metal carbides, the metal carbides include at least one of titanium carbide, calcium carbide, chromium carbide, tantalum carbide, vanadium carbide, zirconium carbide, tungsten carbide, the non-metal Carbides include boron carbide and/or silicon carbide; the nitrides include metal nitrides and/or non-metal nitrides, and the metal nitrides include lithium nitride, magnesium nitride, aluminum nitride, titanium nitride, nitride At least one of tantalum nitride, the non-metallic nitride includes at least one of boron nitride, phosphorus pentanitride, and silicon nitride; the inorganic salt includes carbonate and/or sulfate. The carbon coating process is a conventional process in the art, and will not be repeated here.

The organic particle is a tiny particle composed of a polymer material, such as one or more of polystyrene, polymethyl methacrylate, polytetrafluoroethylene, and a second carbon coating material, and the second carbon The coating material includes a second matrix particle and a second carbon layer coated on at least part of the surface of the second matrix particle, and the second matrix particle is selected from polystyrene, polymethyl methacrylate, polytetrafluoroethylene one or more.

In order to further improve the protective effect of the protective layer, the thickness H1 of the protective layer and the D10 of the inactive material meet H1≥8×D10, and the selection of inactive materials in this particle size range helps to make the protective layer have enough small particles Material filling improves the compactness of the protective layer. D10 is the particle size of inactive materials starting from the small particle size side and reaching 10% of the volume accumulation in the volume-based particle size distribution.

Combined with the thickness range of the current lithium-ion battery active material layer, the thickness of the protective layer is 0.1 μm-10 μm, the D10 of the inactive material is ≤ 0.5 μm, the D50 is ≤ 2 μm, and the D90 is ≤ 5 μm. Further, the inactive material The D10 is 0.01-0.2μm, the D50 is 0.05-0.5μm, and the D90 is 1-3μm.

The binder and conductive agent in the protective layer can be conventional materials in the art, for example, the binder includes polyvinylidene fluoride (PVDF), carboxylic acid modified polyvinylidene fluoride (PVDF), polymethyl methacrylate ( PMMA), polyacrylonitrile (PAN), polyacrylic esters, polyimide (PI) in one or more, wherein, the PVDF of carboxylic acid modification comprises the PVDF of acrylic acid modification; Conductive agent comprises conductive carbon One or more of black, acetylene black, graphite, graphene, carbon nanotubes, carbon nanofibers, those skilled in the art can select appropriate materials and mix them with inactive materials to obtain a protective layer slurry, and coat On the surface of the current collector, a protective layer is obtained after drying.

The coating length of the protective layer and the active material layer on the surface of the current collector is not further limited in this application. The active material layer can be located entirely on the surface of the protective layer away from the current collector, or partially on the surface of the protective layer away from the current collector. Specifically, at least one of the first end and the second end of the pole piece, the vertical distance from the protective layer to the outer edge of the current collector is smaller than the vertical distance from the active material layer to the outer edge of the current collector distance, the first end and the second end are opposite; or,

For example, FIG. 1 is a schematic structural diagram of a pole piece provided by an embodiment of the present application. As shown in FIG. The active material layer 300, that is, the vertical distance from the protective layer 200 to the outer edge of the current collector 100 is smaller than the vertical distance from the active material layer 300 to the outer edge of the current collector 100; FIG. 2 is a schematic structural diagram of a pole piece provided by another embodiment of the present application , as shown in Figure 2, the pole piece includes a current collector 100, a protective layer 200 and an active material layer 300, the protective layer 200 is located on the upper surface of the current collector 100, the active material layer 300 includes two parts, the first part of the active material layer 300 is located in the protective The layer 200 is away from the upper surface of the current collector, and the second part of the active material layer 300 is located on the upper surface of the current collector without a protective layer. Figure 1-2 shows the arrangement of the protective layer and active material layer on the upper surface of the current collector. For The arrangement of the other surface of the current collector 100 may be the same as or different from the upper surface. For example, the lower surface of the current collector 100 may be provided with a protective layer 200 and an active material layer 300, or only the active material layer 300 may be provided, but the surface of the current collector 100 Among the two surfaces, at least one surface should be provided with a protective layer 200 , which can be provided by those skilled in the art according to actual needs, which is not further limited in this application.

In the present application, the above-mentioned pole piece can be a positive pole piece or a negative pole piece. When the pole piece is a positive pole piece, it includes a positive electrode current collector, a protective layer and a positive electrode active material layer. When the pole piece is a negative pole piece, it includes a negative electrode current collector, a protective layer layer and negative electrode active material layer, wherein the positive electrode current collector can be aluminum foil composed of aluminum as the main component, or a composite current collector formed by pressing aluminum foil and other materials (such as polymer materials, etc.), or a composite current collector comprising aluminum foil and a composite current collector of a conductive carbon layer coated on the surface of aluminum foil, etc., wherein the mass content of aluminum in the aluminum foil is generally not less than 95%; the negative current collector can be copper foil.

The active material layer includes an active material, a binder and a conductive agent. The active material is a material that participates in the electrochemical reaction during the charging and discharging process of the pole piece/electrochemical device. When the above-mentioned pole piece is a positive pole piece, the active material therein is a positive pole Active materials, such as positive electrode active materials that provide lithium ions, specifically include lithium positive electrode composite metal oxides (that is, lithium-containing inorganic materials), such as lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), manganic acid At least one of lithium (LiMn ₂ O ₄ ), lithium iron phosphate (LiFePO ₄ ), and a ternary material. The chemical formula of the ternary material may be _LiNix Co _y Mn _z O ₂ , where x+y+z=1. When the above-mentioned pole piece is a negative pole piece, the active material therein is a negative pole active material, and the negative pole active material can include artificial graphite, natural graphite, soft carbon, hard carbon, mesocarbon microspheres (MCMB), silicon, silicon-carbon composite At least one of silicon oxide, lithium titanate, and lithium metal.

The binder in the active material layer and the conductive agent have the same effect as the binder and the conductive agent in the protective layer. The selection of the binder and the conductive agent is as mentioned above. The conductive agent and the binder in the protective layer and the active material layer The binders can be the same or different.

In addition, when the pole piece is a negative pole piece, the negative electrode active material layer may further include a dispersant, and the dispersant includes sodium carboxymethylcellulose and the like.

Research has found that when an internal short circuit occurs in a lithium-ion battery, there will be multiple short-circuit modes, and the internal short-circuit caused by the contact between the positive electrode current collector and the negative electrode sheet is the most dangerous mode. The protective layer is provided on the surface of the positive electrode collector, while the negative electrode sheet is not provided with a protective layer.

The pole piece provided by the present application also includes a tab, and the position of the tab can be a conventional position in the field, for example, it can be set at the end or middle of the pole piece. When the pole piece is a positive pole piece, the positive pole tab can be aluminum foil; when the pole piece is a negative pole piece, the negative pole tab can be copper foil.

The pole piece provided by this application can be prepared by conventional methods in the field such as coating method. In practice, the raw materials of the protective layer can be dispersed in a solvent, stirred evenly to prepare a protective layer slurry, and then the protective layer slurry Coated on the surface of the current collector and dried to form a protective layer; disperse the raw materials of the active material layer in a solvent, stir evenly to prepare the active material layer slurry, and then apply the active material layer slurry on the protective layer away from the The surface of the current collector or the area where the protective layer is not provided on the surface of the current collector is dried and rolled to form an active material layer, and then the tab is placed on the surface of the current collector to obtain a pole piece.

In summary, the pole piece provided by this application includes a protective layer, and controls the mass fraction of each component in the protective layer, the relationship between the thickness of the protective layer and the particle size of the inactive material and the thickness of the active material layer, which not only effectively solves the problem of lithium-ion batteries. In the case of mechanical abuse and other problems such as fire aging, the electrical performance of the lithium-ion battery is basically not affected, and the problem that the safety and electrical performance of the lithium-ion battery cannot be balanced is solved.

The application provides a lithium-ion battery, including the pole piece provided in the first aspect of the application. When the pole piece is a positive pole piece, conventional technical means can be used to prepare a lithium-ion battery with a conventional negative pole piece, a separator, and an electrolyte, wherein, The diaphragm includes one or more of polyethylene (PE), polypropylene (PP), and polyimide, and the electrolyte includes carbonates, carboxylate solvents, lithium salts, and appropriate additives. During the preparation process, The above-mentioned positive electrode sheet, negative electrode sheet and separator are wound or stacked in order to form a battery cell, and then the battery cell is packaged with a packaging material such as aluminum-plastic film and injected with electrolyte, and the lithium-ion battery is prepared after charging and discharging. The lithium ion battery provided by the application has better safety and electrical properties.

The application is further elaborated below in conjunction with specific embodiments:

Example 1

The pole piece provided in this embodiment is a positive pole piece, including a current collector aluminum foil, a protective layer located on the surface of the current collector, and a positive electrode active material layer located on the protective layer away from the surface of the current collector, wherein:

The protective layer includes 62 parts by mass of aluminum oxide, 30 parts by mass of acrylic modified PVDF and 8 parts by mass of carbon black;

The thickness of the protective layer is 2 μm;

The D10 of alumina is 0.2 μm, the D50 is 0.5 μm, and the D90 is 2 μm;

The positive electrode active material layer includes 96 parts by mass of positive electrode active material LCO, 2 parts by mass of binder PVDF and 2 parts by mass of conductive agent carbon black;

The thickness of the positive electrode active material layer was 40 μm.

The preparation method of the pole piece provided in this embodiment includes: mixing alumina, acrylic acid-modified PVDF and carbon black according to the above mass fractions, dispersing in the solvent NMP and stirring uniformly to prepare a protective layer slurry, coating the protective layer slurry On the surface of the aluminum foil, dry to obtain a protective layer; mix LCO, PVDF and carbon black according to the above mass fractions, disperse them in the solvent NMP and stir evenly to prepare a positive electrode active material layer slurry, and coat the positive electrode active material layer slurry on the protective layer. The layer is far away from the surface of the current collector, and dried to obtain the positive electrode active material layer; the tab is welded on the surface of the current collector to obtain the positive electrode sheet;

Example 2

The pole piece provided in this example can refer to Example 1, the difference is that the protective layer includes 70 parts by mass of alumina, 25 parts by mass of acrylic-modified PVDF and 5 parts by mass of carbon black.

Example 3

For the pole piece provided in this example, refer to Example 1, except that the protective layer includes 80 parts by mass of alumina, 15 parts by mass of acrylic-modified PVDF, and 5 parts by mass of carbon black.

Example 4

For the pole piece provided in this example, refer to Example 1, except that the protective layer includes 90 parts by mass of alumina, 8 parts by mass of acrylic-modified PVDF, and 2 parts by mass of carbon black.

Example 5

The pole piece provided in this example can refer to Example 1, the difference is that the protective layer includes 96 parts by mass of alumina, 3.9 parts by mass of acrylic-modified PVDF and 0.1 part by mass of carbon black.

Example 6

The pole piece provided in this embodiment can refer to Embodiment 1, the difference is:

The D10 of alumina is 0.1 μm, the D50 is 0.5 μm, and the D90 is 2.3 μm;

The thickness of the protective layer was 4 μm.

Example 7

The pole piece provided in this embodiment can refer to Embodiment 6, the difference is:

The D10 of alumina is 0.2 μm, the D50 is 1 μm, and the D90 is 3 μm.

Example 8

The D10 of alumina is 0.5 μm, the D50 is 2 μm, and the D90 is 4 μm.

Example 9

The thickness of the protective layer is 4 μm.

Example 10

The thickness of the protective layer is 8 μm.

Comparative example 1

The pole piece provided in this comparative example can refer to Example 1, the difference is that the protective layer includes 50 parts by mass of alumina, 45 parts by mass of acrylic-modified PVDF and 5 parts by mass of carbon black.

Comparative example 2

The pole piece provided in this comparative example can refer to Example 1, the difference is that the protective layer includes 62 parts by mass of alumina, 20 parts by mass of acrylic-modified PVDF and 18 parts by mass of carbon black.

Comparative example 3

The pole piece provided in this comparative example can refer to Example 1, the difference is that the protective layer includes 92 parts by mass of alumina, 2 parts by mass of acrylic-modified PVDF and 6 parts by mass of carbon black.

Comparative example 4

The pole piece provided in this comparative example may refer to Example 1, except that the protective layer includes 92 parts by mass of aluminum oxide and 8 parts by mass of acrylic-modified PVDF.

Comparative example 5

The pole piece provided in this comparative example does not include a protective layer.

Comparative example 6

The pole piece that this comparative example provides can refer to embodiment 6, difference is:

The D10 of alumina is 0.8 μm, the D50 is 3 μm, and the D90 is 5 μm.

Comparative example 7

The D10 of alumina is 0.4 μm, the D50 is 2 μm, and the D90 is 6 μm.

Comparative example 8

The pole piece that this comparative example provides can refer to embodiment 1, difference is:

The thickness of the protective layer is 10 μm.

Comparative example 9

The D10 of alumina is 0.5 μm, the D50 is 2 μm, and the D90 is 7 μm.

The positive electrode sheet provided in Examples 1-10 and Comparative Example 1-9 is matched with the negative electrode sheet and the separator to prepare a bare battery cell, and the bare battery cell is packaged with an aluminum-plastic film, and a certain amount of electrolyte is injected and sealed, and the chemical synthesis is prepared. Lithium-ion battery, wherein, negative plate comprises the artificial graphite of 96 mass parts, the styrene-butadiene rubber of 1.5 mass parts, the carboxymethyl cellulose sodium of 1.5 mass parts and the carbon black of 1 mass part.

Subsequently, the safety and electrical properties of the lithium-ion batteries provided in Examples 1-10 and Comparative Examples 1-9 are tested, and the test results are shown in Table 1, and the test method is as follows:

(1) Nail penetration test

Get 10 lithium-ion batteries of each embodiment (comparative example), and place the fully charged battery on the nail penetration test device, start the device, and make the nail (diameter 3mm) penetrate perpendicular to the battery plane at a speed of 130mm/s At the center of the battery, stay for 10 minutes and then exit. If the battery does not catch fire, it will be considered as a pass, and the number of lithium-ion batteries that have passed will be counted.

(2) Magnification performance test

Discharge the battery at a rate of 0.5C to 3.0V. After standing for 5 minutes, charge the battery at a rate of 0.5C to the upper limit voltage, and then charge at a constant voltage with a cut-off current of 0.02C. After standing for 5 minutes, the battery is discharged to 3.0V at a rate of 0.2C, and the capacity is C0. After standing for 5 minutes, the battery is charged to the upper limit voltage at a rate of 0.5C, and then charged at a constant voltage with a cut-off current of 0.02C. After standing for 5 minutes, the battery is discharged to 3.0V at a rate of 0.5C, and the capacity is C1. C1/C0 is the discharge capacity ratio of 0.5C/0.2C, which is used to evaluate the rate discharge capability.

(3) Li-ion battery energy density test

Lithium-ion battery energy density ED=E/V, where E is the discharge energy of the battery. The test method is to fully charge the battery and then discharge it at 0.2C to 3.0V. The discharged energy is E. V is the system of the battery, which is obtained by measuring the length, width and height.

The energy density loss rate ΔED is the difference between the energy density ED5 of the lithium ion battery of Comparative Example ₅ and the energy density ED _n of the lithium ion battery of the corresponding embodiment (comparative example)/the energy density of the lithium ion battery of Comparative Example 5 ED ₅ , that is, ΔED=(ED ₅ −ED _n )/ED ₅ .

(4) Processing performance test of protective layer

After the coating of the protective layer is finished, observe whether there is a problem of foil leakage. If there is no abnormality, it means that the coating effect of the protective layer is good. Slight scraping and severe scraping refer to the problem of foil leakage, but the degree of foil leakage is different.

Compared with the data provided in Comparative Example 5, it can be seen that setting a protective layer helps to improve the safety of lithium-ion batteries (nail penetration test), but its energy density is loss in varying degrees; according to Examples 1-5 and Comparative Example 1 The data provided by -4 shows that the mass fraction of each component in the control protective layer is within the scope provided by the application, which helps to take into account the safety and electrical performance of lithium-ion batteries; according to embodiment 6-8 and comparative example 6- The data provided in 7 and 9 show that when D50 of the inactive material exceeds 1/2 of the thickness of the protective layer and D90 is greater than the thickness of the protective layer, the protective effect of the protective layer decreases, the safety performance of lithium-ion batteries deteriorates, and scratches are prone to occur. Material problems affect the processing performance of the protective layer; according to the data provided in Examples 9-10 and Comparative Example 8, when the thickness H1 of the protective layer and the thickness H2 of the active material layer satisfy H1/H2≤1/5, the lithium-ion battery The energy density loss can be controlled within 6%. When the H1/H2 exceeds 1/5, the energy density loss of the lithium-ion battery is relatively large, which affects the battery life.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, rather than limiting them; although the application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: It is still possible to modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions of the various embodiments of the present application. scope.

Claims

A pole piece, including a base, the base includes a current collector and a protective layer arranged on the surface of the current collector, and an active material layer is also arranged on the protective layer;

The protective layer includes 62%-96% of inactive materials, 0.1%-8% of conductive agent and 3%-30% of binder according to mass percentage;

The thickness H1 of the protective layer and the D50 of the inactive material satisfy the relationship H1≥2*D50;

The thickness H1 of the protective layer and the D90 of the inactive material satisfy the relationship H1≥D90;

The thickness H1 of the protective layer and the thickness H2 of the active material layer satisfy the relationship H1/H2≦1/5.
The pole piece according to claim 1, wherein the inactive material comprises inorganic particles and/or organic particles, wherein:

The inorganic particles include one or more of oxides, carbides, nitrides, inorganic salts, and first carbon coating materials, and the first carbon coating materials include first matrix particles and coated on the A first carbon layer on at least part of the surface of the first base particle, wherein the first base particle is selected from one or more of oxides, carbides, nitrides, and inorganic salts;

The organic particles include one or more of polystyrene, polymethyl methacrylate, polytetrafluoroethylene, and a second carbon coating material, and the second carbon coating material includes a second matrix particle and a coating A second carbon layer covering at least part of the surface of the second base particle, wherein the second base particle is selected from one or more of polystyrene, polymethyl methacrylate, and polytetrafluoroethylene.
The pole piece according to claim 2, wherein the oxide is selected from the group consisting of aluminum oxide, titanium oxide, magnesium oxide, zirconium oxide, antimonite, barium oxide, manganese oxide, silicon oxide, iron oxide, trioxide At least one of iron; the carbides include metal carbides and/or non-metallic carbides, and the metal carbides include titanium carbide, calcium carbide, chromium carbide, tantalum carbide, vanadium carbide, zirconium carbide, and tungsten carbide At least one of the non-metallic carbides includes boron carbide and/or silicon carbide; the nitrides include metal nitrides and/or non-metal nitrides, and the metal nitrides include lithium nitride, magnesium nitride, At least one of aluminum nitride, titanium nitride, and tantalum nitride, and the non-metallic nitride includes at least one of boron nitride, phosphorus pentanitride, and silicon nitride; the inorganic salt includes Carbonates and/or Sulfates.
The pole piece according to any one of claims 1-3, wherein the thickness H1 of the protective layer and the D10 of the inactive material satisfy a relationship H1≥8×D10.
The pole piece according to any one of claims 1-3, wherein D10≤0.5 μm, D50≤2 μm, and D90≤5 μm of the inactive material.
The pole piece according to claim 5, wherein D10 of the inactive material is 0.01-0.2 μm, D50 is 0.05-0.5 μm, and D90 is 1-3 μm.
The pole piece according to claim 1, wherein the protective layer has a thickness of 0.1 μm-10 μm.
The pole piece according to claim 1, wherein the pole piece is a positive pole piece.
The pole piece according to claim 1, wherein at least one of the first end and the second end of the pole piece, the vertical distance from the protective layer to the outer edge of the current collector is smaller than the active material layer to the outer edge of the current collector, the first end and the second end are opposite; or,

At least one of the first end and the second end of the pole piece, there is an empty foil area between the protective layer and the outer edge of the current collector, the active material layer includes a first part, and the first part and the first part A connected second part, the first part is arranged on the surface of the protective layer, and the second part is arranged on the surface of the current collector in the empty foil area.
A lithium ion battery, comprising the pole piece according to any one of claims 1-9.