CN113793930A - Positive plate and lithium ion battery - Google Patents

Abstract

The embodiment of the invention provides a positive plate and a lithium ion battery, wherein the positive plate comprises: a first active layer, a second active layer, and a current collector, the first active layer being disposed between the current collector and the second active layer, the first active layer including first lithium cobaltate particles and second lithium cobaltate particles, a particle diameter of the first lithium cobaltate particles being different from a particle diameter of the second lithium cobaltate particles; the second active layer includes third lithium cobaltate particles and fourth lithium cobaltate particles, and a particle diameter of the third lithium cobaltate particles is different from a particle diameter of the fourth lithium cobaltate particles. According to the positive plate provided by the embodiment of the invention, the energy density of the battery is improved by arranging the lithium cobaltate particles with different particle sizes in the first active layer and the second active layer, and the problem of non-uniform lithium removal of the positive plate in the prior art is solved.

Description

Positive plate and lithium ion battery

Technical Field

The invention relates to a lithium ion battery, in particular to a positive plate and a lithium ion battery.

Background

With the demand of energy density of lithium ion batteries, the trend of industry development is to match pole pieces with large surface density and large compaction. However, in the pole piece with large area density, due to the difference of the lithium removal potentials of the pole piece surface layer and the pole piece at the bottom layer, the situation that lithium removal is uneven exists on the pole piece surface layer and the pole piece at the bottom layer, so that the capacity retention rate of the battery is seriously deteriorated at the later cycle stage; and the pole piece has the condition of low wettability with the electrolyte under the condition of high compaction density, and electrolyte deficiency and water jump occur at the later stage of the battery circulation.

Disclosure of Invention

The positive plate and the lithium ion battery provided by the embodiment of the invention solve the problem of uneven lithium removal of the positive plate in the prior art.

In a first aspect, the present embodiment provides a positive electrode sheet, including: a first active layer, a second active layer, and a current collector, the first active layer being disposed between the current collector and the second active layer, the first active layer including first lithium cobaltate particles and second lithium cobaltate particles, a particle diameter of the first lithium cobaltate particles being different from a particle diameter of the second lithium cobaltate particles; the second active layer includes third lithium cobaltate particles and fourth lithium cobaltate particles, and a particle diameter of the third lithium cobaltate particles is different from a particle diameter of the fourth lithium cobaltate particles.

Optionally, the first active layer further comprises a conductive agent and a binder, the median particle diameter of the first lithium cobaltate particles is a1, the median particle diameter of the second lithium cobaltate particles is b1, and the compacted density of the first active layer is c1, then the relationship of a1, b1 and c1 is 14< b1/a1c 1< 26;

the second active layer further includes the conductive agent and the binder, the median particle diameter of the third lithium cobaltate particles is a2, the median particle diameter of the fourth lithium cobaltate particles is b2, and the compacted density of the second active layer is c2, the relationship of a2, b2, and c2 is 22<b2/a2*c2<28, the unit of the particle diameter is um, and the unit of the compacted density is g/cm³。

Optionally, the particle size of the first lithium cobaltate particles is smaller than the particle size of the second lithium cobaltate particles, the number of the first lithium cobaltate particles is larger than the number of the second lithium cobaltate particles, and the ratio of the number of the first lithium cobaltate particles to the number of the second lithium cobaltate particles is in the range of 1-5.

Optionally, the first lithium cobaltate particles have a particle size ranging from 4um to 5um, and the second lithium cobaltate particles have a particle size ranging from 20um to 28 um.

Optionally, the particle size of the third lithium cobaltate particles is smaller than the particle size of the fourth lithium cobaltate particles, the number of the third lithium cobaltate particles is smaller than the number of the fourth lithium cobaltate particles, and the ratio of the number of the third lithium cobaltate particles to the number of the fourth lithium cobaltate particles is in the range of 0.2-1.

Optionally, the third lithium cobaltate particle has a particle size ranging from 5um to 6um, and the fourth lithium cobaltate particle has a particle size ranging from 28um to 35 um.

Optionally, the compacted density of the second active layer is less than the compacted density of the first active layer.

Optionally, the thickness of the first active layer is greater than the thickness of the second active layer.

In a second aspect, an embodiment of the present invention further provides a lithium ion battery, including the positive electrode sheet according to the first aspect.

According to the positive plate provided by the embodiment of the invention, the energy density of the battery is improved and the wettability of the battery electrolyte is improved by arranging the lithium cobaltate particles with different particle sizes in the first active layer and the second active layer.

Drawings

Fig. 1 is a structural diagram of a positive electrode sheet according to an embodiment of the present invention.

Detailed Description

The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some, but not all, embodiments of the present application. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

Before discussing exemplary embodiments in more detail, it should be noted that some exemplary embodiments are described as processes or methods depicted as flowcharts. Although a flowchart may describe the steps as a sequential process, many of the steps can be performed in parallel, concurrently or simultaneously. In addition, the order of the steps may be rearranged. A process may be terminated when its operations are completed, but may have additional steps not included in the figure. A process may correspond to a method, a function, a procedure, a subroutine, a subprogram, etc.

Furthermore, the terms "first," "second," and the like may be used herein to describe various orientations, actions, steps, elements, or the like, but the orientations, actions, steps, or elements are not limited by these terms. These terms are only used to distinguish one direction, action, step or element from another direction, action, step or element. For example, the first speed difference may be referred to as a second speed difference, and similarly, the second speed difference may be referred to as a first speed difference, without departing from the scope of the present application. The first speed difference and the second speed difference are both speed differences, but they are not the same speed difference. The terms "first", "second", etc. are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.

Referring to fig. 1, fig. 1 is a structural diagram of a positive electrode sheet according to an embodiment of the present invention, specifically, the positive electrode sheet includes a firstactive layer 3, a secondactive layer 2, and acurrent collector 4, the firstactive layer 3 includes first lithium cobaltate particles and second lithium cobaltate particles, and a particle diameter of the first lithium cobaltate particles is different from a particle diameter of the second lithium cobaltate particles; the secondactive layer 2 includes third lithium cobaltate particles and fourth lithium cobaltate particles, and the particle diameter of the third lithium cobaltate particles is different from that of the fourth lithium cobaltate particles. In the present embodiment, the positive electrode sheet is disposed under theseparator 1, and specifically, the secondactive layer 2 is disposed between the firstactive layer 3 and theseparator 1.

In the present embodiment, it is preferred that,two kinds of active layers have been contained in the positive plate, wherein, firstactive layer 3 is close tomass flow body 4, and secondactive layer 2 is close todiaphragm 1, and in prior art, there is the potential difference in top layer and the bottom in the positive plate, and wherein positive pole top layer potential is higher, and the lithium volume is more taken off to top layer cathode material, and it is inhomogeneous to lead to the anodal material to take off lithium among the cycle process to the granule breakage is more serious, has worsened the cyclicity. Accordingly, in the present embodiment, a plurality of lithium cobaltate particles having different particle diameters, which is an inorganic compound having a chemical formula of LiCoO, are provided in the firstactive layer 3 and the secondactive layer 2₂Lithium cobaltate has the advantages of excellent electrochemical performance, excellent processing performance, large tap density (beneficial to improving the specific volume capacity of the battery), good stability and the like, and is generally used as a positive electrode material of a lithium ion battery. Specifically, the small-particle lithium cobalt oxide particles with a large proportion are arranged in the firstactive layer 3 through control, so that the uniformity of the lithium removal amount of the firstactive layer 3 in the positive plate is improved, meanwhile, the thickness of the secondactive layer 2 is controlled to be smaller than that of the firstactive layer 3, the quantity of the small-particle lithium cobalt oxide is more, the compaction density of the battery is improved, and the energy density of the battery is improved. Aiming at the problem that the porosity of the positive plate is low in the prior art, the size proportion of various lithium cobaltate particles is matched, specifically, large-particle lithium cobaltate particles are arranged in the secondactive layer 2 more, so that the positive plate is pressed down by a roller with the same pressure, the secondactive layer 2 has smaller compaction density, the porosity of the pole piece of the secondactive layer 2 is improved, and the wettability of the pole piece and electrolyte is improved.

Optionally, the firstactive layer 3 further includes a conductive agent and a binder, the median particle diameter of the first lithium cobaltate particles is a1, the median particle diameter of the second lithium cobaltate particles is b1, and the compacted density of the firstactive layer 3 is c1, then the relationship of a1, b1 and c1 is 14<b1/a1*c1<26; the secondactive layer 2 further includes the conductive agent and the binder, the median particle diameter of the third lithium cobaltate particles is a2, the median particle diameter of the fourth lithium cobaltate particles is b2, and the compacted density of the secondactive layer 2 is c2, the relationship of a2, b2, and c2 is 22<b2/a2*c2<28 units of the particle diameterIs um, the unit of the compacted density is g/cm³。

In the present example, each of the positive electrode pastes was composed of active materials, and specifically, the composition of the firstactive layer 3 included 97.8% of small-particle lithium cobaltate (composed of first lithium cobaltate particles and second lithium cobaltate particles), 1.1% of a conductive agent and 1.1% of a binder, wherein the conductive agent was a mixture composition of conductive carbon black and conductive carbon tubes at a mass ratio of 4:1, and the conductive carbon black was carbon black having low resistance or high resistance properties. Can impart conductive or antistatic action to the article. It features small grain size, large and coarse specific surface area, high structure and clean surface (less compound). The conductive carbon tube is a one-dimensional quantum material with a special structure (the radial dimension is nanometer magnitude, the axial dimension is micrometer magnitude, and two ends of the tube are basically sealed). Carbon nanotubes are coaxial circular tubes consisting of several to tens of layers of carbon atoms arranged in a hexagonal pattern. The layers are maintained at a fixed distance of about 0.34nm, with a diameter of typically 2-20 nm. And the carbon hexagons can be divided into three types, namely a zigzag type, an armchair type and a spiral type, according to different orientations of the carbon hexagons in the axial direction. The adhesive is polyvinylidene fluoride (PVDF), which mainly refers to vinylidene fluoride homopolymer or copolymer of vinylidene fluoride and other small amount of fluorine-containing vinyl monomers, has the characteristics of both fluororesin and general resin, and has special performances such as piezoelectric property, dielectric property, thermoelectric property and the like besides good chemical corrosion resistance, high temperature resistance, oxidation resistance, weather resistance and ray radiation resistance. The composition of the secondactive layer 2 includes 97.8% of small-particle lithium cobaltate (composed of third lithium cobaltate particles and fourth lithium cobaltate particles), 1.1% of a conductive agent and 1.1% of a binder, wherein the conductive agent is formed by mixing conductive carbon black and conductive carbon tubes according to a mass ratio of 4:1, and the binder is polyvinylidene fluoride.

Optionally, the particle size of the first lithium cobaltate particles is smaller than the particle size of the second lithium cobaltate particles, and the number of the first lithium cobaltate particles is greater than the number of the second lithium cobaltate particles.

In the present embodiment, the firstactive layer 3 close to thecurrent collector 4 contains two different types of lithium cobaltate particles, specifically, the first lithium cobaltate particle has aparticle diameter D-a 1, and the second lithium cobaltate particle has aparticle diameter D-b 1, wherein the ratio of the number of the first lithium cobaltate particles to the number of the second lithium cobaltate particles is between 1 and 5. Specifically, the lithium cobaltate in the firstactive layer 3 is small-particle lithium cobaltate, the particle size range of the first lithium cobaltate particles is 4um-5um, and the particle size range of the second lithium cobaltate particles is 20um-28 um. The particle size ranges of the first lithium cobaltate particle and the second lithium cobaltate particle given in this embodiment are preferred, and may be adaptively adjusted according to actual situations, and the alternatives in this embodiment are not limited.

Optionally, the particle size of the third lithium cobaltate particles is smaller than the particle size of the fourth lithium cobaltate particles, and the number of the third lithium cobaltate particles is smaller than the number of the fourth lithium cobaltate particles.

In the present embodiment, the secondactive layer 2 adjacent to theseparator 1 contains two different types of lithium cobaltate particles, specifically, a third lithium cobaltate particle having a particle diameter D of a2 and a fourth lithium cobaltate particle having a particle diameter D of b2, wherein the ratio of the number of the third lithium cobaltate particles to the number of the fourth lithium cobaltate particles is 0.2-1. Specifically, the lithium cobaltate in the secondactive layer 2 is large-particle lithium cobaltate, the particle size of the third lithium cobaltate particle is in the range of 5um to 6um, and the particle size of the fourth lithium cobaltate particle is in the range of 28um to 35 um. The particle size ranges of the third lithium cobaltate particle and the fourth lithium cobaltate particle given in this embodiment are preferred, and may be adaptively adjusted according to actual situations, and the alternatives in this embodiment are not limited.

Optionally, the compacted density of the secondactive layer 2 is greater than the compacted density of the firstactive layer 3.

In the present embodiment, the compacted density is the compacted density at half-life of the lithium battery, and generally, the compacted density of the firstactive layer 3 is 3.5 to 3.8g/cm³The second active layer has a compacted density of 3.7-4.1g/cm³The porosity of the pole piece is improved, and the wettability of the pole piece and electrolyte is improved.

Optionally, the thickness of the firstactive layer 3 is smaller than the thickness of the secondactive layer 2.

In this embodiment, for the purpose of ensuring the energy density of the battery, the thickness of the pole piece of the firstactive layer 3 is set to be smaller than the thickness of the pole piece of the secondactive layer 2, and the specific thickness is not specifically limited in this embodiment and can be adaptively adjusted according to the actual situation.

In the present embodiment, the negative electrode sheet generally adopts a conventional negative electrode formulation, and the slurry is composed of an active material, a conductive agent, a binder, and a dispersant. The negative active material is mainly graphite and at least one of soft carbon and hard carbon, and a silicon-based material. Wherein, the dispersant is a surfactant which has two opposite properties of lipophilicity and hydrophilcity in a molecule. The amphiphilic agent is capable of uniformly dispersing solid and liquid particles of inorganic and organic pigments which are difficult to dissolve in liquids, and also preventing settling and agglomeration of the particles to form stable suspensions.

Wherein, the dispersant is a dispersant containing lithium salt, and the content of lithium ions is between 2.0 and 3.5 percent. The conductive agent is used for ensuring that the electrode has good charge and discharge performance, a certain amount of conductive substances are usually added during the manufacture of the pole piece, and the function of collecting micro-current is achieved among the active substances and between the active substances and thecurrent collector 4, so that the movement rate of electrons accelerated by the contact resistance of the electrode is reduced, and meanwhile, the migration rate of lithium ions in the electrode material can be effectively improved, and the charge and discharge efficiency of the electrode is improved. The conductive agent material may be at least one of conductive carbon black, acetylene black, ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, metal powder, and carbon fiber. The binder is a guarantee of the bonding strength between the abrasive and the matrix. With the development of the chemical industry, various novel binders enter the field of coated abrasives, the performance of the coated abrasives is improved, and the development of the coated abrasive industry is promoted.

Besides the sizing material, the adhesive also comprises auxiliary components such as a solvent, a curing agent, a toughening agent, a preservative, a coloring agent, a defoaming agent and the like. Binders include synthetic resins, rubbers and paints in addition to the most commonly used animal glues. Specifically, the content of the active substance is 97.5%, the conductive agent is formed by mixing conductive carbon tubes and conductive carbon black according to the proportion of 0.25-0.5, the content of the conductive agent is 0.5%, the content of the binder is 1%, and the content of the dispersant is 1%.

In this embodiment, after the coating is completed, other processes are the same as those of the conventional lithium battery technology, and the soft-package polymer lithium ion battery is supported according to the normal processes of rolling, winding, packaging, injecting, forming, sorting and the like. Specifically, the coating method of the present invention can be prepared by extrusion coating or transfer coating, and for example, the extrusion coating process is a process in which one or more layers of coating liquid are extruded from a gap of an extrusion nozzle under pressure (optionally flowing through an inclined surface) to form a meniscus between a lip and a coated substrate, and then transferred to a running support to form a thin layer. After the coating of the positive electrode and the negative electrode of the lithium battery is finished by adopting the method, rolling is carried out according to the process design to determine that the compacted density of the positive electrode and the negative electrode meets the process requirements, then, sheet production (welding of a tab) and winding (positive electrode + diaphragm + negative electrode) are carried out, and the diaphragm adopts an Asahi 5+2+2 oil system diaphragm; and then packaging, injecting liquid, forming, performing secondary packaging, sorting, finishing the manufacture of the soft-package polymer lithium ion battery, and performing inspection and testing.

According to the positive plate provided by the embodiment of the invention, the energy density of the battery is improved by arranging the lithium cobaltate particles with different particle sizes in the first active layer and the second active layer, and the problems of non-uniform lithium removal of the positive plate and poor wettability of the battery electrolyte in the prior art are solved.

The results of preparing the positive electrode sheet in different ways are explained in detail below by specific examples and comparative examples.

In comparative example 1, the conventional positive and negative electrode sheets were prepared by the above-described method, in which the first active layer and the second active layer were coated with a slurry composed of a small-particle lithium cobaltate material (97.8% of small-particle lithium cobaltate, 1.1% of a conductive agent, 1.1% of a binder, a conductive agent in which conductive carbon black and a conductive carbon tube were mixed in a ratio of 4:1, and a binder in which PVDF was used), wherein the particle diameter D of the first lithium cobaltate was 4.5um, the particle diameter D of the second lithium cobaltate was 25um, and the compaction density was 3.9g/cm³。

In comparative example 2The conventional positive and negative electrode plates are prepared by the method, wherein the first active layer and the second active layer are coated by slurry consisting of large-particle lithium cobaltate materials (97.8% of large-particle lithium cobaltate, 1.1% of conductive agent and 1.1% of binder, the conductive agent is formed by mixing conductive carbon black and a conductive carbon tube according to a ratio of 4:1, and the binder is PVDF), wherein the particle diameter D of the first lithium cobaltate is 5.5um, the particle diameter D of the second lithium cobaltate is 29um, and the compaction density is 3.5g/cm³。

In example 1, a conventional negative electrode sheet was prepared by the above method, and the positive electrode slurry was prepared as described above to obtain a first active layer slurry (small-particle lithium cobaltate 97.8%, conductive agent 1.1%, binder 1.1%, conductive agent composed of conductive carbon black and conductive carbon tubes mixed at a ratio of 4:1, binder PVDF) and a second active layer slurry (large-particle lithium cobaltate 97.8%, conductive agent 1.1%, binder 1.1%, conductive agent composed of conductive carbon black and conductive carbon tubes mixed at a ratio of 4:1, binder PVDF). Sequentially coating the first active layer slurry and the second active layer slurry on a current collector, wherein the thickness of the first active layer and the second active layer is 6:4, the first lithium cobaltate D of the first active layer lithium cobaltate is 4.5um, the particle diameter D of the second lithium cobaltate is 25um, and the compaction density is 4.1g/cm³(ii) a In the second active layer, the particle diameter D of the third lithium cobaltate was 5.5um, the particle diameter D of the fourth lithium cobaltate was 29um, and the compacted density was 3.5g/cm³。

In example 2, the difference between this example and example 1 is that a first active layer slurry and a second active layer slurry are sequentially coated on a current collector, wherein the thickness of the first active layer and the second active layer is 7:3, the first lithium cobaltate D of the first active layer lithium cobaltate is 4.5um, the particle size of the second lithium cobaltate D is 25um, and the compaction density is 4.0g/cm³(ii) a In the second active layer, the particle diameter D of the third lithium cobaltate was 5.5um, the particle diameter D of the fourth lithium cobaltate was 29um, and the compacted density was 3.6g/cm³。

In example 3, the difference between this example and example 1 is that a first active layer slurry and a second active layer slurry are sequentially coated on a current collector, wherein the thickness of the first active layer and the second active layer is 8:2, and the first active layer is a first active layerThe first lithium cobaltate D is 4.5um, the second lithium cobaltate has a particle diameter D of 25um, and the compacted density is 3.9g/cm³(ii) a In the second active layer, the particle diameter D of the third lithium cobaltate was 5.5um, the particle diameter D of the fourth lithium cobaltate was 29um, and the compacted density was 3.7g/cm³。

As shown in table 1, in the above comparative examples and examples, by using the differential coating method between comparative example 1 and examples 1, 2 and 3, the uniformity of lithium intercalation and deintercalation of the battery can be improved, the liquid retention capacity of the battery can be improved, and the cycle performance of the battery can be improved. Through comparative example 2, all large-particle lithium cobaltate is selected, although the lithium cobaltate has excellent performance, the energy density is obviously lost, and the aim of balancing the energy density and the cycle performance can be fulfilled through the differential coating mode.

With respect to energy density, the lithium ion batteries of examples and comparative examples were measured at 25 ℃ using a charge-discharge regime of 0.2C charge, 0.5C discharge, 0.025C cut-off; the plateau voltage of the lithium ion battery is the plateau voltage under 0.2C-rate discharge. Energy Density (ED) the following formula was used to calculate ED ═ capacity × platform voltage/(cell length × cell width × cell thickness), cycle capacity retention rate at 45 ℃, and cycle expansion rate. The lithium ion batteries of the examples and comparative examples were cycled for 600T at 45 ℃ on a cycling regime of 1C charged, 0.5C discharged, 0.025C cut-off; capacity retention rate ═ discharge capacity (per revolution)/initial capacity; cyclic expansion ratio (thickness after cycle-initial thickness)/initial thickness.

TABLE 1

The embodiment of the invention also provides a lithium ion battery which comprises the positive plate in the embodiment. Since the technical solution of this embodiment includes all technical solutions of the above embodiments, at least all technical effects of the above embodiments can be achieved, and details are not repeated here.

The above description is only an embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of changes or substitutions within the technical scope of the present invention, and all such changes or substitutions are intended to be included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims (10)

1. A positive electrode sheet, comprising: a first active layer, a second active layer, and a current collector, the first active layer being disposed between the current collector and the second active layer, the first active layer including first lithium cobaltate particles and second lithium cobaltate particles, a particle diameter of the first lithium cobaltate particles being different from a particle diameter of the second lithium cobaltate particles; the second active layer includes third lithium cobaltate particles and fourth lithium cobaltate particles, and a particle diameter of the third lithium cobaltate particles is different from a particle diameter of the fourth lithium cobaltate particles.

2. The positive electrode sheet according to claim 1,

the first active layer further includes a conductive agent and a binder, the median particle diameter of the first lithium cobaltate particles is a1, the median particle diameter of the second lithium cobaltate particles is b1, and the compacted density of the first active layer is c1, the relationship of a1, b1 and c1 is 14< b1/a 1c 1< 26;

the second active layer further includes the conductive agent and the binder, the median particle diameter of the third lithium cobaltate particles is a2, the median particle diameter of the fourth lithium cobaltate particles is b2, and the compacted density of the second active layer is c2, the relationship of a2, b2, and c2 is 22<b2/a2*c2<28, the unit of the particle diameter is um, and the unit of the compacted density is g/cm³。

3. The positive electrode sheet according to claim 2, wherein the particle diameter of the first lithium cobaltate particles is smaller than the particle diameter of the second lithium cobaltate particles, the number of the first lithium cobaltate particles is larger than the number of the second lithium cobaltate particles, and the ratio of the number of the first lithium cobaltate particles to the number of the second lithium cobaltate particles is in the range of 1 to 5.

4. The positive electrode sheet according to claim 3, wherein the first lithium cobaltate particles have a particle size in a range of 4um to 5um, and the second lithium cobaltate particles have a particle size in a range of 20um to 28 um.

5. The positive electrode sheet according to claim 2, wherein the third lithium cobaltate particles have a particle diameter smaller than that of the fourth lithium cobaltate particles, the number of the third lithium cobaltate particles is smaller than that of the fourth lithium cobaltate particles, and the ratio of the number of the third lithium cobaltate particles to the number of the fourth lithium cobaltate particles is in the range of 0.2 to 1.

6. The positive electrode sheet according to claim 2, wherein the third lithium cobaltate particles have a particle size in a range of 5um to 6um, and the fourth lithium cobaltate particles have a particle size in a range of 28um to 35 um.

7. The positive electrode sheet according to claim 1, wherein the compacted density of the second active layer is less than the compacted density of the first active layer.

8. The positive electrode sheet according to claim 1, wherein the porosity of the second active layer is greater than the porosity of the first active layer.

9. The positive electrode sheet according to claim 1, wherein the thickness of the first active layer is smaller than the thickness of the second active layer.

10. A lithium ion battery comprising the positive electrode sheet according to any one of claims 1 to 9.

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