Electrode sheet and battery

Abstract

Provided are an electrode sheet and a battery. The electrode sheet comprises an electrode current collector (1) and an electrode coating (2) located on at least one side surface of the electrode current collector (1), wherein the electrode coating (2) comprises an electrode active material layer (22) and a priming coating (21) located between the electrode active material layer (22) and the electrode current collector (1). The priming coating (21) comprises a first conductive agent (20), and the included angle α between the length direction of the first conductive agent (20) and the surface of the electrode current collector (1) satisfies 60°≤α≤90°.

Description

Electrode sheet and battery

[0001] The present disclosure claims priority to the Chinese patent application No. 202410994800.3, filed on July 23, 2024, and entitled "Electrode sheet and battery", the entire content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present disclosure relates to the field of batteries, in particular to an electrode sheet and a battery. BACKGROUND

[0003] The electrode sheet is an important component of the battery. In the related art, due to the structure of the electrode sheet and other factors, the impedance of the electrode sheet is large, which makes the internal resistance of the battery large, affecting the electrochemical performance of the battery. Especially for thick electrodes, the thickness of the electrode sheet is large, the resistivity and the diffusion impedance of active ions (such as lithium ions in lithium ion batteries) in the electrode sheet are large, which further makes the battery have a larger internal resistance, affecting the electrochemical performance of the battery. SUMMARY

[0004] The present disclosure provides an electrode sheet and a battery, which can reduce the impedance of the electrode sheet, especially the impedance of thick electrodes, thereby reducing the internal resistance of the battery and effectively overcoming the defects existing in the prior art.

[0005] In an aspect of the present disclosure, an electrode sheet is provided, comprising an electrode current collector, and an electrode coating layer located on at least one side surface of the electrode current collector; the electrode coating layer comprises an electrode active material layer, and a primer layer located between the electrode active material layer and the electrode current collector; the primer layer comprises a first conductive agent, and an angle α between the length direction of the first conductive agent and the surface of the electrode current collector satisfies 60°≤α≤90°.

[0006] According to an embodiment of the present disclosure, 60°≤α≤88°.

[0007] According to an embodiment of the present disclosure, the first conductive agent comprises one or more of carbon black, carbon nanotubes, and graphene.

[0008] According to an embodiment of the present disclosure, the particle size D50 of the carbon black is 25-85 nm.

[0009] According to an embodiment of the present disclosure, the aspect ratio of the carbon nanotubes is 500-800.

[0010] According to an embodiment of the present disclosure, the average flake diameter of the graphene is 0.5-5 μm.

[0011] According to an embodiment of the present disclosure, the mass percentage content of the first conductive agent in the primer layer is 75%-98%.

[0012] According to an embodiment of the present disclosure, the undercoat layer further comprises a first binder.

[0013] According to an embodiment of the present disclosure, the undercoat layer further comprises an electrode active material.

[0014] According to an embodiment of the present disclosure, the undercoat layer has a thickness of 2-6 μm.

[0015] According to an embodiment of the present disclosure, the electrode active material layer has a thickness of 90-110 μm.

[0016] According to an embodiment of the present disclosure, the electrode sheet is a positive electrode sheet.

[0017] According to an embodiment of the present disclosure, the electrode active material layer comprises an electrode active material, which comprises one or more of lithium iron phosphate, lithium cobaltate, and a positive electrode ternary material.

[0018] According to an embodiment of the present disclosure, the electrode sheet is a negative electrode sheet.

[0019] According to another aspect of the present disclosure, a battery is provided, comprising the electrode sheet described above.

[0020] The present disclosure has at least the following beneficial effects: introducing an undercoat layer containing a first conductive agent between the electrode active material layer and the electrode current collector, and making the length direction of the first conductive agent in the undercoat layer and the angle a between the surface of the electrode current collector satisfy 60°≤a≤90°, so that the first conductive agent in the undercoat layer is vertically oriented as much as possible, which can reduce the contact impedance between the electrode active material layer and the electrode current collector, and the vertically oriented first conductive agent in the undercoat layer can also reduce the hindrance of active ion diffusion, and reduce the liquid phase diffusion impedance of the electrode sheet. Thus, the present disclosure can reduce the resistivity, liquid phase diffusion impedance and battery internal resistance of the electrode sheet, and improve the electrochemical performance of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0021] FIG. 1 is a structural schematic diagram of an electrode sheet according to an embodiment of the present disclosure;

[0022] FIG. 2 is a structural schematic diagram of a magnetic assembly in the preparation process of an electrode sheet according to an embodiment of the present disclosure;

[0023] FIG. 3 is a structural schematic diagram of the arrangement of N-pole magnetic blocks and S-pole magnetic blocks in a magnetic assembly according to an embodiment of the present disclosure.

[0024] Reference signs: 1: electrode current collector; 2: electrode coating; 20: first conductive agent; 21: undercoat layer; 22: electrode active material layer; 3: magnetic assembly; 31: S-pole magnetic block; 32: N-pole magnetic block; H 21: thickness of the undercoat layer; H 22 : thickness of the electrode active material layer; A: length direction of the first conductive agent; T: thickness direction of the electrode sheet; B: moving direction of the electrode current collector 1 coated with the undercoat slurry; C: first arrangement direction of the S-pole magnetic block and the N-pole magnetic block; D: magnetic field direction; E: thickness direction of the magnetic assembly; F: second arrangement direction of the S-pole magnetic block and the N-pole magnetic block; a: included angle between the length direction of the first conductive agent and the surface of the electrode current collector; b: included angle between the moving direction of the electrode current collector 1 coated with the undercoat slurry and the first arrangement direction of the S-pole magnetic block and the N-pole magnetic block. DETAILED DESCRIPTION

[0025] To make the skilled in the art better understand the scheme of the present disclosure, the present disclosure is further described in detail below. The following specific embodiments are only to describe the principles and characteristics of the present disclosure, and the examples are only used to explain the present disclosure, and do not limit the scope of the present disclosure. Based on the embodiments of the present disclosure, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present disclosure.

[0026] The embodiments of the present disclosure provide an electrode sheet, as shown in FIG. 1, which comprises an electrode current collector 1 and an electrode coating layer 2 located on at least one side surface of the electrode current collector 1; the electrode coating layer 2 comprises an electrode active material layer 22 and an undercoat layer 21 located between the electrode active material layer 22 and the electrode current collector 1; the undercoat layer 21 comprises a first conductive agent 20, and the included angle (perpendicularity of the first conductive agent) a between the length direction A of the first conductive agent 20 and the surface of the current collector satisfies 60°≤a≤90°.

[0027] According to the research of the applicant, the electrically conductive coating (or primer layer 21) is arranged between the electrode active material layer 22 and the electrode current collector 1 of the electrode sheet, and the angle a between the length direction A of the first electrically conductive agent 20 in the primer layer 21 and the surface of the electrode current collector 1 satisfies 60°≤a≤90°, so that the first electrically conductive agent 20 in the primer layer 21 has good verticality in the thickness direction of the primer layer 21 (i.e., the angle between the length direction A of the first electrically conductive agent 20 and the thickness direction T of the electrode coating 2 (also the thickness direction of the electrode sheet) is closer to 0°), the first electrically conductive agent 20 is basically vertically arranged in the primer layer 21, which is beneficial to connecting the electrode active material layer 22 and the electrode current collector 1 and providing a channel for the conduction of electricity, i.e., providing long-range electrical conductivity, reducing the contact resistance between the electrode active material layer 22 (or the coating layer) and the electrode current collector 1, and at the same time, the vertically oriented first electrically conductive agent 20 in the primer layer 21 is more consistent with the movement direction of active ions (such as lithium ions) in the battery charging and discharging process, which can reduce the hindrance to the transmission of active ions and reduce the ion diffusion resistance. Therefore, the electrode sheet of the embodiment of the present disclosure can reduce the resistivity, ion diffusion resistance (liquid phase diffusion resistance), and internal resistance of the battery, and improve the rate performance and other electrochemical properties of the electrode sheet and the battery.

[0028] Exemplarily, the angle a between the length direction A of the first electrically conductive agent 20 in the primer layer 21 and the surface of the electrode current collector 1 can be 60°, 63°, 65°, 68°, 70°, 73°, 75°, 78°, 80°, 83°, 85°, 88°, 90°, or a range formed by any two of them.

[0029] Generally, in the preparation process of the electrode sheet, the vertical orientation of the first electrically conductive agent 20 in the primer layer 21 can be induced by magnetic induction technology, so that the angle a between the length direction of the first electrically conductive agent 20 and the surface of the electrode current collector 1 satisfies 60°≤a≤90°. For example, the primer layer 21 is formed by a coating method. After the primer slurry for forming the primer layer 21 is coated on the electrode current collector 1, a magnetic field can be applied to induce the orientation of the first electrically conductive agent 20 in the primer layer 21, and then after subsequent treatments such as drying, the primer layer 21 is formed.

[0030] In some preferred embodiments, 60°≤a≤80°, so that the resistivity, liquid phase diffusion resistance, and internal resistance of the electrode sheet can be effectively reduced, and at the same time, the primer layer 21 can be formed by magnetic induction and other methods, and the manufacturing efficiency and yield of the electrode sheet can be improved.

[0031] In the above primer layer 21, the first electrically conductive agent 20 can include one or more of carbon black, carbon nanotubes (carbon tubes), and graphene, which is beneficial to reducing the resistivity, liquid phase diffusion resistance, and internal resistance of the electrode sheet.

[0032] In actual implementation, the primer slurry containing one or more of the carbon black, carbon nanotube (carbon tube), and graphene can be coated on the surface of the electrode current collector 1, and then a magnetic field is applied to induce the vertical orientation of the first conductive agent 20, so that good verticality is achieved and the impedance of the electrode sheet is reduced.

[0033] As shown in FIG. 1, the first conductive agent 20 exists in the primer layer 21 in the form of particles, which can be particles of the first conductive agent 20 (which can be spherical, quasi-spherical, long strip-shaped (such as carbon nanotube), or sheet-shaped (such as graphene), or agglomerates formed by agglomeration of the particles of the first conductive agent 20. The length direction A of the first conductive agent 20 can refer to the direction of the particles of the first conductive agent 20 or the length direction of the agglomerates formed by agglomeration of the particles of the first conductive agent 20.

[0034] Specifically, when the first conductive agent 20 includes carbon black, the carbon black mainly exists in the primer layer 21 in the form of aggregates (i.e., agglomerates or aggregates). That is, the carbon black particles in the primer layer 21 are agglomerated to form aggregate particles (carbon black agglomerates), which are distributed in the primer layer 21. The aggregate particles are generally in the form of a spindle structure with thin upper and lower ends and thick middle part, which are formed by mutual connection of the carbon black particles in the vertical direction (the thickness direction of the primer layer 21). The arrangement of the aggregate particles in the vertical direction can connect the electrode active material layer 22 and the electrode current collector 1, provide a smooth electron channel, reduce the contact impedance between the electrode active material layer 22 and the electrode current collector 1, and reduce the transmission resistance to active ions.

[0035] When the first conductive agent 20 is carbon black, the length direction A of the first conductive agent 20 refers to the length direction of the agglomerates formed by agglomeration of the carbon black (i.e., the length direction of the agglomerate particles formed by agglomeration of the carbon black particles). That is, the angle between the length direction of the agglomerates formed by agglomeration of the carbon black and the surface of the electrode current collector 1 is the above-mentioned angle a (60°≤a≤90°).

[0036] In addition, when the first conductive agent 20 is carbon nanotube, the length direction A of the first conductive agent 20 refers to the length direction of the carbon nanotube. The carbon nanotube has less agglomeration in the primer layer 21 and is in a vertical arrangement state (i.e., 60°≤a≤90°) as a whole in the primer layer 21. In actual implementation, the carbon nanotubes in the primer slurry can be uniformly dispersed by stirring or the like, which is conducive to further reducing the agglomeration of the carbon nanotubes. In the process of applying a magnetic field to the primer slurry, the carbon nanotubes are more effectively affected by the magnetic field, which is more conducive to the vertical arrangement of the carbon nanotubes as a whole and reduces the impedance of the electrode sheet.

[0037] In addition, when the first conductive agent 20 is graphene, the length direction A of the first conductive agent 20 refers to the length direction of graphene. Graphene has a sheet structure, and graphene sheets are arranged vertically in the undercoat layer 21, which is conducive to reducing the resistivity and ion diffusion impedance of the electrode sheet.

[0038] Specifically, the particle size D50 of the carbon black (i.e., the median particle size of the carbon black) can be 25-85 nm, such as 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, or a range formed by any two of them. Among them, the particle size D50 of the carbon black (25-85 nm) refers to the particle size before the carbon black is aggregated, that is, in the undercoat layer, the carbon black aggregate is formed by the aggregation of carbon black particles with a particle size D50 of 25-85 nm.

[0039] By controlling the particle size D50 of the carbon black within the above range (25-85 nm), it is conducive to reducing the resistivity, liquid phase diffusion impedance and battery internal resistance of the electrode sheet. The analysis reason is that when the particle size D50 of the carbon black is within the above range (25-85 nm), it is conducive to the carbon black having a more suitable aggregation degree under the induction of the magnetic field, improving the contact of the carbon black, and reducing the resistivity, liquid phase diffusion impedance and battery internal resistance of the electrode sheet.

[0040] Specifically, the aspect ratio of the carbon nanotube can be 500-800, such as 500, 550, 600, 650, 700, 750, 800, or a range formed by any two of them, which is conducive to reducing the resistivity, liquid phase diffusion impedance and battery internal resistance of the electrode sheet. The analysis reason is that by making the aspect ratio of the carbon nanotube within the above range (500-800), it is conducive to improving the contact between the carbon nanotubes, and at the same time, improving the dispersibility of the carbon nanotubes, inhibiting the mutual entanglement between the carbon nanotubes, making it easier to be separated during the magnetic field induction process, which is conducive to improving the perpendicularity α of the carbon nanotubes, thereby reducing the resistivity, liquid phase diffusion impedance and battery internal resistance of the electrode sheet.

[0041] Specifically, the average sheet size of the graphene can be 0.5-5 μm, such as 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, or a range formed by any two of them, which is conducive to reducing the resistivity, liquid phase diffusion impedance and battery internal resistance of the electrode sheet. The analysis reason is that by making the average sheet size of the graphene within the above range (0.5-5 μm), it is conducive to the graphene having a more suitable size, forming graphene particles with high perpendicularity α in the undercoat layer 21 after magnetic field induction, and at the same time, the graphene has a lower steric hindrance, which is conducive to the magnetic field acting on the graphene, that is, the graphene particles are induced by the magnetic field, improving the perpendicularity α of the graphene, thereby reducing the resistivity, liquid phase diffusion impedance and battery internal resistance of the electrode sheet.

[0042] In the embodiments of the present disclosure, the first conductive agent 20 in the undercoat layer 21 is vertically oriented, which is conducive to connecting the electrode active material layer 22 and the electrode current collector 1 and providing a channel for electron conduction, i.e., providing long-range electron conduction capability, by using less first conductive agent 20, thereby reducing the electrode sheet resistivity, liquid phase diffusion impedance and battery internal resistance while reducing the amount of first conductive agent 20.

[0043] In some embodiments, the mass percentage content of the first conductive agent 20 in the undercoat layer 21 (i.e., the ratio of the total mass of the first conductive agent 20 to the total mass of the undercoat layer 21) can be 75% to 98%, for example, 75%, 78%, 80%, 83%, 85%, 88%, 90%, 95%, 98% or a range consisting of any two of them, which is conducive to reducing the electrode sheet resistivity, liquid phase diffusion impedance and battery internal resistance. Among them, when the undercoat layer 21 contains multiple first conductive agents 20, the total mass of the first conductive agent 20 refers to the sum of the masses of these conductive agents.

[0044] In addition, the undercoat layer 21 can also include a first binder. By introducing the first binder, it is conducive to improving the adhesion between the electrode active material layer 22 and the undercoat layer 21, and the adhesion between the undercoat layer 21 and the electrode current collector 1 while reducing the impedance of the electrode sheet, thereby improving the structural stability of the electrode sheet.

[0045] Specifically, the first binder can be a conventional bonding material in the art, for example, the first binder includes polyvinylidene fluoride (PVDF).

[0046] Further considering factors such as the impedance and structural stability of the electrode sheet, in some embodiments, the mass percentage content of the first binder in the undercoat layer 21 can be 1.5% to 2.5%, for example, 1.5%, 1.8%, 2%, 2.3%, 2.5% or a range consisting of any two of them.

[0047] In addition, the undercoat layer 21 can or can not include an electrode active material, and the mass percentage content of the electrode active material in the undercoat layer 21 is 0 to 18%, for example, 0, 0.5%, 1%, 3%, 5%, 8%, 10%, 13%, 15%, 18% or a range consisting of any two of them.

[0048] Generally, the electrode active material layer 22 includes an electrode active material, and when the undercoat layer 21 contains an electrode active material, the electrode active material in the undercoat layer 21 can be the same as or different from the electrode active material in the electrode active material layer 22.

[0049] In addition, the thickness H of the undercoat layer 21 21The thickness can be 2 to 6 μm, for example, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm or any combination thereof. This allows the base coating 21 to provide more space for the vertical arrangement of the first conductive agent 20, improving the verticality α of the first conductive agent 20, while maintaining a relatively thin base coating 21 to improve the energy density and other properties of the electrode sheet.

[0050] In this embodiment, the base coating 21 can be provided on one side surface of the electrode current collector 1, or the base coating 21 can be provided on both opposite surfaces (i.e., the front and back surfaces of the electrode current collector 1) in the thickness direction. When the base coating 21 is provided on both the front and back surfaces of the electrode current collector 1, the thickness H of the base coating 21 is... 21 It refers to the thickness of the base coating 21 on one side of the electrode current collector 1, rather than the sum of the thicknesses of the base coating 21 on both sides.

[0051] Generally, for thick electrode sheets, the thickness of the electrode active material layer 22 is relatively large, which can maintain a high energy density of the electrode sheet and is beneficial for the battery's higher range requirements. However, the larger the thickness of the electrode active material layer 22, the relatively larger the impedance will also be. The embodiments of this disclosure can effectively reduce the impedance of thick electrodes, specifically by reducing the resistivity, ion diffusion impedance, and battery internal resistance of the thick electrode, thereby improving the battery's rate performance and other electrochemical performance.

[0052] In some embodiments, the thickness H of the electrode active material layer 22 in the electrode sheet described above is... 22 The thickness can be 90–110 μm, for example, 90 μm, 93 μm, 95 μm, 98 μm, 100 μm, 103 μm, 105 μm, 108 μm, 110 μm or any combination thereof. By introducing the aforementioned undercoating layer 21 between the electrode active material layer 22 and the electrode current collector 1, and controlling the angle α between the length direction A of the first conductive agent 20 in the undercoating layer 21 and the surface of the electrode current collector 1 to satisfy 60°≤α≤90°, the resistivity of the electrode sheet, the liquid phase diffusion impedance and the internal resistance of the battery can be effectively reduced, while maintaining the high energy density of the electrode sheet and other properties, thereby further improving the overall performance of the battery.

[0053] In this embodiment, an electrode active material layer 22 can be disposed on one side surface of the electrode current collector 1, or an electrode active material layer 22 can be disposed on both the front and back surfaces of the electrode current collector 1. When an electrode active material layer 22 is disposed on both the front and back surfaces of the electrode current collector 1, the thickness H of the electrode active material layer 22 is... 22 It refers to the thickness of the electrode active material layer 22 on one side surface of the electrode current collector 1, rather than the sum of the thicknesses of the electrode active material layers 22 on both sides.

[0054] In some embodiments, the electrode sheet described above is a positive electrode sheet, and correspondingly, the electrode current collector 1 described above is a positive electrode current collector, the electrode active material layer 22 is a positive electrode active material layer, and the electrode active material is a positive electrode active material, which can include one or more of lithium iron phosphate, lithium cobaltate, and a positive electrode ternary material, wherein the positive electrode ternary material includes, for example, a nickel-cobalt-manganese ternary material and / or a nickel-cobalt-aluminum ternary material.

[0055] The embodiments of the present disclosure can employ a conventional positive electrode current collector in the art, for example, the positive electrode current collector includes an aluminum foil.

[0056] In other embodiments, the electrode sheet described above can be a negative electrode sheet, and correspondingly, the electrode current collector 1 described above is a negative electrode current collector, the electrode active material layer 22 is a negative electrode active material layer, and the electrode active material described above is a negative electrode active material, which can include graphite.

[0057] The embodiments of the present disclosure can employ a conventional negative electrode current collector in the art, for example, the negative electrode current collector includes a copper foil.

[0058] Generally, the electrode active material layer 22 described above further includes a second binder and a second conductive agent and the like, and the mass fraction of the electrode active material (i.e., the ratio of the mass of the electrode active material to the total mass of the electrode active material layer 22) can be 70% to 99%, for example, 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99%, or a range consisting of any two of them, the mass fraction of the second conductive agent can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or a range consisting of any two of them, and the mass fraction of the second binder can be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15%, or a range consisting of any two of them, based on the total mass of the electrode active material layer 22.

[0059] In some embodiments, in the positive electrode active material layer, the ratio of the mass of the second conductive agent to the mass of the positive electrode active material can be 0.5% to 1.5%, and the ratio of the mass of the second binder to the mass of the positive electrode active material can be 1.5% to 2.5%.

[0060] In the embodiments of the present disclosure, the second conductive agent in the electrode active material layer 22 can be a conventional conductive material in the art, for example, the conductive agent includes one or more of conductive carbon black, carbon nanotubes (CNT), acetylene black, graphene, Ketjen black, and carbon fibers.

[0061] In the embodiments of the present disclosure, the second binder in the electrode active material layer 22 can be a conventional binder material in the art. For example, when the electrode sheet is a negative electrode sheet, the second binder can include one or more of styrene-butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, an oxirane-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate. When the electrode sheet is a positive electrode sheet, the second binder can include one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, an oxirane-containing polymer, polyvinylpyrrolidone, polyurethane, and the like.

[0062] In addition, when the electrode sheet is a negative electrode sheet, the electrode active material layer 22 (negative electrode active material layer) can further include a thickening agent. The thickening agent can include a carboxymethyl cellulose (CMC)-based thickening agent, and specifically can include a carboxymethyl cellulose salt, such as sodium carboxymethyl cellulose (CMC-Na).

[0063] In the embodiments of the present disclosure, the undercoat layer 21 and the electrode active material layer 22 can be formed by a coating method. In specific implementation, the undercoat slurry for forming the undercoat layer 21 can be coated on the surface of the electrode current collector 1, the electrode current collector 1 coated with the undercoat slurry can pass through a magnetic field region having a magnetic field, thereby magnetically inducing the second conductive agent in the undercoat slurry coated on the electrode current collector 1 to be vertically oriented and arranged. After the electrode current collector 1 coated with the undercoat slurry passes through the magnetic field region, drying is performed, and specifically, the electrode current collector 1 can be put into an oven to be dried, so that the undercoat slurry on the surface of the electrode current collector 1 is dried to form the undercoat layer 21. Then, the slurry for forming the electrode active material layer 22 is coated on the surface of the undercoat layer 21, and after drying, rolling, and other processes, the electrode active material layer 22 is formed on the surface of the undercoat layer 21, thereby obtaining the electrode sheet.

[0064] When the undercoat layer 21 is formed on both the front and back surfaces of the electrode current collector 1, the undercoat slurry can be first coated on one side surface of the electrode current collector 1, then the electrode current collector 1 passes through the magnetic field region, and the side of the electrode current collector 1 coated with the undercoat slurry faces away from the magnetic assembly 3 (i.e., the side of the electrode current collector 1 not coated with the undercoat slurry faces the magnetic assembly 3), so that after passing through the magnetic field region, drying is performed to form the undercoat layer 21 on one side surface of the electrode current collector 1. Then, the undercoat slurry is coated on the other side surface of the electrode current collector 1, and the electrode current collector 1 passes through the magnetic field region again, and the side of the electrode current collector 1 coated with the undercoat slurry faces away from the magnetic assembly 3 (i.e., the side of the electrode current collector 1 on which the undercoat layer 21 has been formed faces the magnetic assembly 3), so that after passing through the magnetic field region, drying is performed to form the undercoat layer 21 on the other side surface of the electrode current collector 1.

[0065] As shown in FIG. 2, the magnetic field of the magnetic field region is provided by the magnetic assembly 3, which includes N-pole magnetic blocks 32 and S-pole magnetic blocks 31 arranged alternately, wherein, as shown in FIGS. 2 and 3, the N-pole magnetic blocks 32 and the S-pole magnetic blocks 31 are arranged alternately in a first arrangement direction C and a second arrangement direction F, adjacent N-pole magnetic blocks 32 and S-pole magnetic blocks 31 can be in direct contact (close contact), the magnetic field direction D of the generated magnetic field is substantially perpendicular to the first arrangement direction C and the second arrangement direction F of the N-pole magnetic blocks 32 and the S-pole magnetic blocks 31, the length of the magnetic field region in the first arrangement direction C of the N-pole magnetic blocks 32 and the S-pole magnetic blocks 31 is substantially equal to the length of the magnetic assembly 3, and the width of the magnetic field region in the second arrangement direction F of the N-pole magnetic blocks 32 and the S-pole magnetic blocks 31 is substantially equal to the width of the magnetic assembly 3.

[0066] Wherein, the first arrangement direction C and the second arrangement direction F intersect, and specifically can be substantially perpendicular, specifically, as shown in FIGS. 2 and 3, the first arrangement direction C can be parallel to the length direction of the magnetic assembly 3, and the second arrangement direction F can be parallel to the width direction of the magnetic assembly 3.

[0067] Continuing to refer to FIGS. 2 and 3, the thickness direction E of the magnetic assembly 3 is substantially perpendicular to the first arrangement direction C and the second arrangement direction F of the N-pole magnetic blocks 32 and the S-pole magnetic blocks 31, during the process of the electrode current collector 1 coated with the primer slurry passing through the magnetic field region, the electrode current collector 1 coated with the primer slurry is located on one side of the thickness direction E of the magnetic assembly 3, and moves from one side of the magnetic assembly 3 in the first arrangement direction C to the other side of the magnetic assembly 3 in the first arrangement direction C, the width of the magnetic assembly 3 in the second arrangement direction F is greater than the width of the electrode current collector 1 coated with the primer slurry in the second arrangement direction F, so that the magnetic field can cover the electrode current collector 1 coated with the primer slurry.

[0068] Wherein, during the process of the electrode current collector 1 coated with the primer slurry passing through the magnetic field region, the moving direction B of the electrode current collector 1 coated with the primer slurry and the first arrangement direction C of the N-pole magnetic blocks 32 and the S-pole magnetic blocks 31 form an included angle β.

[0069] Specifically, the length of the magnetic field region, the moving speed (walking speed) of the electrode current collector 1 coated with the primer slurry when passing through the magnetic field region, the included angle (deflection angle) β formed by the moving direction B of the electrode current collector 1 coated with the primer slurry and the first arrangement direction C of the N-pole magnetic blocks 32 and the S-pole magnetic blocks 31, and the distance between the electrode current collector 1 coated with the primer slurry and the magnetic assembly 3 can be adjusted to adjust the magnetic field strength and other conditions, to induce the vertical arrangement of the first conductive agent 20 in the primer layer 21, and form the primer layer 21 that satisfies the preset α.

[0070] For example, the angle (the deflection angle of the electrode current collector 1 coated with the primer slurry) β formed by the moving direction B of the electrode current collector 1 coated with the primer slurry and the first arrangement direction C of the N-pole magnetic block 32 and the S-pole magnetic block 31 can satisfy 0°≤β≤10°; the length of the magnetic field region is, for example, 18-22 cm (e.g., 20 cm); the walking speed of the electrode current collector 1 coated with the primer slurry can be 1-5 m / min, for example, 1 m / min, 2 m / min, 3 m / min, 4 m / min, 5 m / min, or a range formed by any two of them; and the distance between the electrode current collector 1 coated with the primer slurry and the magnetic assembly 3 can be 1 mm-4 cm.

[0071] The distance between the electrode current collector 1 coated with the primer slurry and the magnetic assembly 3 refers to the vertical distance between the intermediate position of the magnetic assembly 3 in the first arrangement direction C of the N-pole magnetic block 32 and the S-pole magnetic block 31 and the electrode current collector 1 coated with the primer slurry.

[0072] In addition, the N-pole magnetic block 32 and the S-pole magnetic block 31 can have the same size, for example, each of the N-pole magnetic block 32 and the S-pole magnetic block 31 is a magnetic block with a length of 1 cm and a width of 1 cm (i.e., the size is 1 cm*1 cm), that is, the length of the cross section perpendicular to the thickness direction E of the magnetic assembly 3 of the N-pole magnetic block 32 is 1 cm and the width is 1 cm, and the length of the cross section perpendicular to the thickness direction E of the magnetic assembly 3 of the S-pole magnetic block 31 is 1 cm and the width is 1 cm, but is not limited thereto.

[0073] In the embodiments of the present disclosure, the primer slurry for forming the primer layer 21 and the electrode slurry for forming the electrode active material layer 22 can be prepared by conventional methods in the art, for example, the components for forming the primer layer 21 such as the first conductive agent 20 and the first binder are dispersed in a first solvent, for example, including N-methyl pyrrolidone (NMP) and / or water (in particular, deionized water), to prepare the primer slurry; the components for forming the electrode active material layer 22 such as the electrode active material, the second conductive agent, the second binder, etc. are dispersed in a second solvent, for example, including (NMP) and / or water (in particular, deionized water), to prepare the electrode slurry, and then the coating process is performed.

[0074] According to the research of the applicant, the steric hindrance between the second conductive agent and the main material (electrode active material) particles in the electrode active material layer 22 is large, and if a magnetic field is applied to the second conductive agent in the electrode active material layer 22 in order to induce vertical arrangement orientation, the requirement for the magnetic field strength and other conditions is harsh, and in the embodiment of the present disclosure, the bottom coating layer 21 containing the first conductive agent 20 is introduced between the electrode active material layer 22 and the electrode current collector 1, and a magnetic field is applied to the bottom coating layer 21 to induce the vertical arrangement orientation of the first conductive agent 20 therein. Since the particles of the first conductive agent 20 are small, they are significantly affected by the magnetic field, and the force between the particles of the first conductive agent 20 is small, and the steric hindrance between them is small, so a good magnetic field induction effect can be achieved, that is, the vertical arrangement state of the first conductive agent 20 in the bottom coating layer 21 is achieved, and it satisfies 60°≤α≤90°. Therefore, not only can the impedance of the electrode sheet be effectively reduced, but also the production of the electrode sheet is facilitated. Without changing the electrode sheet coating process, the demand for a super strong magnetic field is weakened, which has the advantages of simplicity, feasibility, etc., and is beneficial to practical industrial application.

[0075] The present disclosure also provides a battery comprising the above-mentioned electrode sheet, which has advantages corresponding to the above-mentioned electrode sheet, and will not be described again.

[0076] The battery of the embodiment of the present disclosure can be a lithium ion battery (such as a lithium ion power battery), a solar cell, or other new energy storage batteries.

[0077] Generally, a battery includes an electrolyte, a cell, and a packaging body for packaging the cell, the electrolyte is injected into the cell in the packaging body, and the cell includes a positive electrode sheet, a negative electrode sheet, and a separator between the positive electrode sheet and the negative electrode sheet. Among them, the cell can be a laminated cell, that is, the cell is formed by laminating the positive electrode sheet, the separator and the negative electrode sheet.

[0078] In the embodiment of the present disclosure, the positive electrode sheet can be an electrode sheet having the above-mentioned bottom coating layer 21, the negative electrode sheet can also be an electrode sheet having the above-mentioned bottom coating layer 21, or the positive electrode sheet and the negative electrode sheet can each be an electrode sheet having the above-mentioned bottom coating layer 21.

[0079] The electrolyte of the embodiment of the present disclosure can be a conventional electrolyte in the art, for example, the electrolyte is a non-aqueous electrolyte, which can specifically include an organic solvent and an electrolyte salt, the organic solvent includes one or more of ethylene carbonate (EC), methyl ethylene carbonate (EMC), dimethyl carbonate (DMC), and the like, and the lithium salt includes lithium hexafluorophosphate (LiPF6) and the like, but is not limited thereto.

[0080] In the embodiment of the present disclosure, the separator is used to separate the positive electrode sheet and the negative electrode sheet to avoid short circuit caused by contact between the positive electrode sheet and the negative electrode sheet. The separator of the present disclosure can adopt a conventional separator in the art, for example, the separator includes a polypropylene film, but is not limited thereto.

[0081] In the embodiments of the present disclosure, the battery cell can be packaged by using a conventional packaging body material in the art, and the battery can be of a conventional type and structure in the art. For example, the battery can be a soft-pack lithium ion battery, and the packaging body can include an aluminum-plastic film.

[0082] In the embodiments of the present disclosure, the battery can be assembled by using a conventional method in the art. For example, the positive electrode sheet, the separator and the negative electrode sheet can be stacked to obtain a laminated battery cell. Then, the battery cell is placed in a shell (outer package), and after processes such as liquid injection (i.e., injection of electrolyte) and packaging, the battery is obtained.

[0083] In the embodiments of the present disclosure, after obtaining the negative electrode sheet, the cross section of the electrode coating 2 (which is substantially parallel to the thickness direction of the electrode sheet) can be observed by a scanning electron microscope (SEM). According to the particle size and morphology of different regions, the film layers such as the undercoat layer 21 and the electrode active material layer 22 are determined, and the thickness H 21 of the undercoat layer 21, the thickness H 22 of the electrode active material layer 22, and the perpendicularity α of the first conductive agent are measured. When performing SEM analysis, the perpendicularity (i.e., the angle between the length direction of the first conductive agent and the surface of the electrode current collector) α of at least 20 particles of the first conductive agent 20 in the field of view is measured, and the average value is taken as the final test result.

[0084] In the embodiments of the present disclosure, after obtaining the electrode sheet, the undercoat layer 21 can be analyzed by SEM to measure the size and other characteristics of the first conductive agent 20. Specifically, when performing SEM analysis, the size of at least 20 particles of the first conductive agent 20 in the field of view is measured, and the average value is taken as the final test result. When the first conductive agent 20 is carbon black, the measured size of the first conductive agent 20 is the median particle size D50 of the carbon black. When the first conductive agent 20 is a carbon nanotube, the measured size of the first conductive agent 20 is the aspect ratio of the carbon nanotube. When the first conductive agent 20 is graphene, the measured size of the first conductive agent 20 is the average flake size of the graphene.

[0085] In specific implementations, the battery can be disassembled to obtain the electrode sheet, and the negative electrode sheet can be cleaned with an organic solvent (such as DMC) to wash away impurities such as electrolyte salts on the electrode sheet. After the electrode sheet is cleaned, the organic solvent is removed by drying, and then the above-mentioned SEM analysis and other processes are performed on the electrode sheet to measure the thickness H 21 of the undercoat layer 21, the thickness H 22 of the electrode active material layer 22, and the size of the first conductive agent 20 in the undercoat layer 21.

[0086] The present disclosure is further described below through specific embodiments.

[0087] 1. Preparation of positive electrode sheet

[0088] (1) Mix the first conductive agent and PVDF (the types and amounts of the first conductive agent are shown in Table 1), add NMP, stir evenly, and prepare a primer slurry;

[0089] (2) Apply a primer to one side of the aluminum foil. The aluminum foil coated with the primer enters the magnetic field region (20cm long) at a speed of 3m / min, with the side coated with the primer facing away from the magnetic component. This allows the first conductive agent in the primer to be vertically aligned within the magnetic field region. After passing through the magnetic field region, the foil is dried in an oven to form a primer coating on one side of the aluminum foil. The magnetic field in the magnetic field region is applied by the magnetic component shown in Figure 2, which consists of a 1cm*1cm N-pole magnetic block and a 1... The magnetic components are arranged in alternating patterns of 1 cm x 1 cm S-pole magnetic blocks, with adjacent N-pole and S-pole magnetic blocks in close contact. There are 10 N-pole and 10 S-pole magnetic blocks in total (the length of the magnetic component (also the length in the direction of the magnetic field) is 20 cm). The distance between the aluminum foil coated with the base coating and the magnetic component is about 1.5 mm. When the aluminum foil coated with the base coating passes through the magnetic field region, the moving direction B of the aluminum foil coated with the base coating and the first arrangement direction C of the N-pole and S-pole magnetic blocks form an angle (the deflection angle of the aluminum foil coated with the base coating) β (see Table 1).

[0090] (3) The base coating slurry of step (1) is continuously coated on the other side of the aluminum foil. Following the process of step (2) (when passing through the magnetic field area, the side of the aluminum foil coated with the base coating slurry is away from the magnetic component), a base coating is formed on the other side of the aluminum foil to obtain an electrode precursor with a base coating on both sides.

[0091] (4) Mix lithium iron phosphate, conductive carbon black and PVDF in a mass ratio of 100:0.8:2.5, add NMP, stir evenly, and prepare a positive electrode slurry;

[0092] (5) The positive electrode slurry is coated onto both the front and back surfaces of the electrode precursor using a continuous coating equipment, then dried in an oven, and finally rolled to form a positive electrode active material layer, thus obtaining the positive electrode sheet; wherein, the thickness H of the positive electrode active material layer is... 22 =96μm.

[0093] Examples 2 to 26 differ from Example 1 in that the angle α between the longitudinal direction A of the first conductive agent in the base coating and the surface of the electrode current collector (aluminum foil) (the perpendicularity of the first conductive agent), the type of the first conductive agent, the size of the first conductive agent (particle size D50 of carbon black, aspect ratio of carbon nanotubes, average sheet diameter of graphene), and the thickness H of the base coating are all different. 21Example 1: The conditions are different from those in Comparative Example 1 in the mass percentage content of the first conductive agent in the primer layer (the first conductive agent content in Table 1), the mass percentage content of the second conductive agent in the primer layer (the second conductive agent content in Table 1), the mass percentage content of the first conductive agent in the primer layer (the first conductive agent content in Table 1), and the running speed of the aluminum foil coated with the primer slurry (the aluminum foil running speed in Table 1) and the deflection angle β during the primer layer forming process, and the specific conditions are shown in Table 1. Except for the differences shown in Table 1, the other conditions are the same as those in Comparative Example 1.

[0094] Comparative Example 1: The difference from Example 1 is that no primer layer is provided, i.e., only the positive active material layer is provided on both surfaces of the aluminum foil, and the specific conditions are shown in Table 1. Except for the differences shown in Table 1, the other conditions are the same as those in Example 1.

[0095] Comparative Example 2: The difference from Example 1 is that no magnetic field induction is performed during the primer layer forming process, i.e., the aluminum foil coated with the primer slurry does not enter the magnetic field area. Except for the process and the differences shown in Table 1, the other conditions are the same as those in Example 1.

[0096] The positive electrode sheets of each example and comparative example are tested for performance by the following processes, and the results are shown in Table 2.

[0097] 3. 50% SOC direct current resistance test

[0098] (1) Preparation of negative electrode sheet

[0099] The graphite, conductive carbon black, SBR, and CMC-Na are mixed in a mass ratio of 100:1:2.7:1.2, and deionized water is added, stirred uniformly, and prepared into a negative electrode slurry.

[0100] The negative electrode slurry is coated on both surfaces of the copper foil, and after drying and rolling, the negative active material layer is formed on both surfaces of the copper foil to prepare the negative electrode sheet.

[0101] (2) Assembly of battery

[0102] The positive electrode sheet, the separator (a polypropylene film with a thickness of 14 μm), and the negative electrode sheet are alternately stacked to assemble a laminated core; the laminated core is placed in an aluminum plastic film, and after processes such as liquid injection and packaging, a soft-pack lithium ion battery is assembled; wherein the composition of the electrolyte used is as follows: the organic solvent is EC, EMC, and DMC, the mass ratio of EC, EMC, and DMC is 29:32:23, and the concentration of LiPF6 in the electrolyte is 1 mol / L.

[0103] (3) 50% SOC direct current resistance test: at room temperature (25±5°C), the soft-pack lithium ion battery is discharged at a rate of 1 / 3C to 2.0V, charged at a rate of 1 / 3C to 50% SOC, and left for 30 min; discharged at a rate of 1.5C for 30 s, and the 50% SOC direct current resistance is detected, and the results are shown in Table 2.

[0104] 4. Liquid phase diffusion impedance test

[0105] The liquid-phase diffusion impedance is measured by electrochemical impedance spectroscopy (EIS). A small-amplitude sinusoidal wave potential signal is applied to the electrode at a certain frequency on the basis of a reference potential, and the impedance of the electrode system is measured as a function of the frequency of the sinusoidal wave. The electrode process dynamics information and electrode interface structure are obtained by analyzing and fitting the spectrum, and the impedance value inside the battery is further characterized. The liquid-phase diffusion impedance test process is as follows:

[0106] The above two positive electrode sheets and the separator are sequentially assembled into an electrode core (the separator is spaced between the two positive electrode sheets); the electrode core is placed in an outer packaging shell (aluminum plastic film), and after baking, electrolyte is injected. After processes such as packaging and infiltration, a liquid-phase diffusion impedance battery is obtained; an electrochemical workstation (model Reference 3000) is used to test the liquid-phase diffusion impedance of the liquid-phase diffusion impedance battery in a frequency range of 300,000 Hz-0.05 Hz, and the liquid-phase diffusion impedance is measured. The results are shown in Table 2. The composition of the electrolyte used is as follows: the organic solvent is EC, EMC and DMC, the mass ratio of EC, EMC and DMC is 29:32:23, and the concentration of LiPF6 in the electrolyte is 1 mol / L.

[0107] 5. Positive electrode sheet resistivity test: The positive electrode sheet is placed in a positive electrode sheet resistivity tester (model BER2600) to test its resistivity at 25 MPa, and the pressure holding time is 25 s. The measured positive electrode sheet resistivity is shown in Table 2.

[0108] Table 1

[0109] Table 2

[0110] As can be seen from Table 2, compared with Comparative Examples 1-3, in the positive electrode sheets of Examples 1-26, the bottom coating layer is provided between the positive electrode active material layer and the positive electrode current collector (aluminum foil), and the verticality α of the first conductive agent in the bottom coating layer is controlled in the range of 60°≤α≤90°, which can reduce the positive electrode sheet resistivity, the liquid-phase diffusion impedance and the battery internal resistance, and improve the electrochemical performance of the battery.

[0111] In addition, compared with Example 5 (carbon black particle size <25 nm) and Example 9 (carbon black particle size >85 nm), the carbon black particle size in Examples 6-8 is in the range of 25-85 nm, which is beneficial to further reducing the positive electrode sheet resistivity, the liquid-phase diffusion impedance and the battery internal resistance.

[0112] In addition, compared with Example 13 (aspect ratio of carbon nanotubes < 500) and Example 17 (aspect ratio of carbon nanotubes > 800), the aspect ratio of carbon nanotubes in Examples 14-16 is in the range of 500-800, which is conducive to further reducing the positive plate resistivity, liquid phase diffusion impedance and battery internal resistance.

[0113] In addition, compared with Example 22 (average flake diameter of graphene < 0.5 μm) and Example 26 (average flake diameter of graphene > 5 μm), the average flake diameter of graphene in Examples 23-25 is in the range of 0.5-5 μm, which is conducive to further reducing the positive plate resistivity, liquid phase diffusion impedance and battery internal resistance.

[0114] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present disclosure, but not to limit it; although the present disclosure has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present disclosure.

Claims

1. An electrode sheet, characterized by, The electrode sheet comprises an electrode current collector (1) and an electrode coating (2) on at least one side surface of the electrode current collector (1); the electrode coating (2) comprises an electrode active material layer (22) and a primer coating (21) between the electrode active material layer (22) and the electrode current collector (1); the primer coating (21) comprises a first conductive agent (20), and an angle (a) between a length direction of the first conductive agent (20) and a surface of the electrode current collector (1) satisfies 60°≤a≤90°.

2. The electrode pad of claim 1, wherein 60°≤α≤88°。 3. The electrode sheet according to claim 1 or 2, characterized by The first conductive agent (20) comprises one or more of carbon black, carbon nanotubes and graphene.

4. The electrode pad of claim 3, wherein The carbon black has a particle size D50 of 25-85 nm.

5. The electrode pad of claim 3, wherein The carbon nanotubes have an aspect ratio of 500-800.

6. The electrode pad of claim 3, wherein The graphene has an average flake size of 0.5-5 µm.

7. The electrode sheet according to any one of claims 1 to 6, characterized by The first conductive agent (20) in the primer coating (21) has a mass percentage content of 75%-98%.

8. The electrode sheet according to any one of claims 1 to 7, characterized by The primer coating (21) further comprises a first binder.

9. The electrode sheet according to any one of claims 1 to 8, characterized by The primer coating (21) further comprises an electrode active material.

10. The electrode sheet according to any one of claims 1 to 9, characterized by The primer coating (21) has a thickness of 2-6 µm.

11. The electrode sheet according to any one of claims 1 to 10, characterized by The electrode active material layer (22) has a thickness of 90-110 µm.

12. The electrode sheet according to any one of claims 1 to 11, characterized by The electrode sheet is a positive electrode sheet.

13. The electrode pad of claim 12, wherein The electrode active material layer (22) comprises an electrode active material, and the electrode active material comprises one or more of lithium iron phosphate, lithium cobaltate and a positive electrode ternary material.

14. The electrode sheet according to any one of claims 1 to 10, characterized by The electrode sheet is a negative electrode sheet.

15. A battery, characterized by The electrode sheet comprises the electrode sheet according to any one of claims 1-14. The electrode sheet comprises the electrode sheet according to any one of claims 1-14.

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