Positive electrode sheet, preparation method therefor, battery, and electrical system

Abstract

The present application belongs to the technical field of batteries, and specifically discloses a positive electrode sheet, a preparation method therefor, a battery, and an electrical system. The positive electrode sheet comprises: a positive electrode current collector; and a positive electrode active material layer, the positive electrode active material layer being disposed on at least a portion of a surface of the positive electrode current collector, the positive electrode active material layer comprising a positive electrode conductive agent, and the positive electrode conductive agent comprising artificial graphite and conductive carbon black. The distance between two end points of the artificial graphite in the length direction is a, the actual length of the artificial graphite is b, K=a / b, and 0.6≤K<1 is satisfied.

Description

Positive electrode sheet, preparation method thereof, battery and power utilization system

[0001] Priority information

[0002] The present application claims priority to and the benefit of Chinese Patent Application No. 2024108736977, filed on July 1, 2024, entitled "Positive electrode sheet, preparation method thereof, battery and power utilization system", the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0003] The present application belongs to the technical field of batteries, and specifically relates to a positive electrode sheet, a preparation method thereof, a battery and a power utilization system. BACKGROUND

[0004] Lithium ion batteries, as a kind of green power, are widely used in energy storage base stations and the like due to their high energy density, long cycle life, low self-discharge rate, environmental friendliness and other advantages. A lithium ion battery mainly comprises a positive electrode sheet, a separator, a negative electrode sheet, an electrolyte and the like. The positive electrode sheet of the lithium ion battery is an important component of the lithium ion battery, and the preparation of the positive electrode slurry of the lithium ion battery directly affects the comprehensive performance of the lithium ion battery. The dispersion state and contact uniformity of the conductive additive and the positive electrode active material in the positive electrode sheet greatly affect the performance of the lithium ion battery, for example, affecting the rate performance and cycle performance of the battery. SUMMARY

[0005] The present application aims to at least partially solve one of the technical problems in the related art. To this end, the present application proposes a positive electrode sheet, a preparation method thereof, a battery and a power utilization system. By adding artificial graphite and conductive carbon black in the positive electrode sheet, the two have good complementary effects and can maximize the electron conduction between positive electrode active material particles. At the same time, the elongation of the positive electrode sheet is improved. In addition, the K value of the artificial graphite satisfies 0.6≤K<1, therefore, the artificial graphite has more positive electrode active material particles in contact within a unit length, and has more charge conduction sites, thereby effectively improving the electron conduction between active particles, significantly improving the conductive capacity, and significantly reducing the contact resistance of the positive electrode sheet.

[0006] In one aspect of the present application, the present application proposes a positive electrode sheet. According to the embodiments of the present application, the positive electrode sheet comprises:

[0007] a positive current collector;

[0008] a positive electrode active material layer, the positive electrode active material layer being disposed on at least part of the surface of the positive current collector, the positive electrode active material layer comprising a positive electrode conductive agent, the positive electrode conductive agent comprising artificial graphite and conductive carbon black;

[0009] The distance between the two end points of the artificial graphite along the length direction is a, the actual length of the artificial graphite is b, K = a / b, and 0.6≤K<1 is satisfied.

[0010] According to the positive electrode sheet of the embodiments of the present application, the artificial graphite and the conductive carbon black are uniformly distributed between the positive electrode active material particles, wherein the sheet-shaped artificial graphite forms point-surface contact with the positive electrode active material particles, which can realize long-range conduction on the electrode; the conductive carbon black is in a granular shape and adheres to the surface of the positive electrode active material particles, which can realize short-range conduction, and the two have good complementary effects, taking into account long-range conduction and short-range conduction, which can maximize the electron conduction between the positive electrode active material particles and ensure the rapid transmission of electrons. And improve the dispersibility between the active material and the conductive agent. At the same time, the elongation of the positive electrode sheet is improved. In addition, the K value of the artificial graphite satisfies 0.6≤K<1, so that the number of positive electrode active material particles contacted by the artificial graphite per unit length is relatively large, and the charge conduction site is relatively large, thereby effectively improving the electron conduction between the active particles, significantly improving the conductivity of the electrode, thereby significantly reducing the contact resistance of the positive electrode sheet, i.e. DCR is reduced, thereby reducing the polarization of the battery, so that the positive electrode sheet has excellent electrical performance.

[0011] In a second aspect of the present application, a method for preparing the positive electrode sheet described in the above embodiments is provided. According to the embodiments of the present application, the above method comprises:

[0012] (1) using a shearing stirring dispersion device to stir and disperse the artificial graphite, the conductive carbon black and the first solvent to obtain an initial slurry;

[0013] (2) adding the positive electrode active material, the positive electrode binder and the second solvent into the shearing stirring dispersion device, and stirring and dispersing to obtain a positive electrode slurry;

[0014] (3) coating the positive electrode slurry on at least part of the surface of the positive electrode current collector, and drying to obtain a positive electrode sheet.

[0015] According to the method for preparing the above cathode sheet according to the embodiments of the present application, the method can further reduce the bending and mixing degree of the artificial graphite in the slurry (i.e., further increase the K value of the artificial graphite) by providing shear forces in opposite directions, using surfactants, reducing the stirring speed and the dispersion speed, and pre-mixing the surfactants, artificial graphite, and conductive carbon black, and the like, which is further conducive to the reformation of a conductive network with a higher effective chain density by the conductive agent and the active material, so that the artificial graphite contacts a larger number of active material particles and has more charge conduction sites in a unit length, thereby effectively improving the electron conduction between the active particles, significantly improving the conductive capacity, improving the electrode electron conductivity, thereby significantly reducing the contact resistance (DCR) of the cathode sheet, thereby reducing the polarization of the battery, and making the cathode sheet have excellent electrical performance.

[0016] In a third aspect of the present application, a battery is provided. According to the embodiments of the present application, the battery has the cathode sheet of the above embodiments. Thus, the charge and discharge internal resistance of the battery can be effectively reduced, the battery efficiency can be improved, and the energy storage and release capacity of the battery can be enhanced.

[0017] In a fourth aspect of the present application, a power utilization system is provided. According to the embodiments of the present application, the power utilization system includes a power utilization device, and an energy storage device for supplying power to the power utilization device, and the energy storage device includes the battery of the above embodiments. Thus, the power utilization system has all the advantages of the battery, which will not be described herein again.

[0018] Additional aspects and advantages of the present application will be in part apparent and in part pointed out hereinafter. BRIEF DESCRIPTION OF DRAWINGS

[0019] The above and / or additional aspects and advantages of the present application will become apparent and be readily appreciated from the following description, including the appended drawings, wherein:

[0020] FIG. 1 is an SEM image of a cathode sheet according to Example 1 of the present application;

[0021] FIG. 2 is an SEM image of a cathode sheet according to Example 2 of the present application;

[0022] FIG. 3 is an SEM image of a cathode sheet according to Example 11 of the present application;

[0023] FIG. 4 is an SEM image of a cathode sheet according to Example 13 of the present application;

[0024] FIG. 5 is an SEM image of a cathode sheet according to Comparative Example 1 of the present application;

[0025] FIG. 6 is an SEM image of a cathode sheet according to Comparative Example 2 of the present application;

[0026] FIG. 7 is an SEM image of the positive electrode sheet of Comparative Example 3 of the present application. DETAILED DESCRIPTION

[0027] Embodiments of the present application are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by reference to the drawings are exemplary and are intended to explain the present application, and cannot be understood as limiting the present application.

[0028] In the related art, the positive electrode sheet uses conductive carbon black SP as a conductive additive. The conductive carbon black SP has good conductivity, and the conductive carbon black particles and the active material particles are in a point-to-point contact form. However, in the electrode sheet prepared by using the conductive carbon black as a conductive agent, the conductive carbon black has a large specific surface area, which leads to difficult dispersion, and there is a problem that the conductive agent and the active material are prone to agglomeration and cannot form a good conductive network, thereby limiting the conduction speed of electrons, resulting in a large contact resistance of the electrode sheet and an increase in DCR. During the rolling process of the positive electrode sheet, the active material particles slide under the action of pressure to achieve the purpose of close arrangement, but the sliding of the active material particles will cause the current collector (such as aluminum foil) to be significantly stretched, and the stretching of the current collector is not uniform in the entire electrode sheet range, which has a great influence on the performance of the electrode sheet. Therefore, reducing the stretching of the current collector caused by the sliding of the active material particles during the rolling process is of great significance to the subsequent processing performance and the final performance of the battery cell.

[0029] In view of this, in one aspect of the present application, the present application provides a positive electrode sheet. According to the embodiments of the present application, the positive electrode sheet comprises: a positive electrode current collector; a positive electrode active material layer, the positive electrode active material layer is arranged on at least part of the surface of the positive electrode current collector, the positive electrode active material layer comprises a positive electrode conductive agent, the positive electrode conductive agent comprises artificial graphite and conductive carbon black SP; the distance between the two end points of the artificial graphite along the length direction is a, the actual length of the artificial graphite is b, K = a / b, and 0.6≤K<1 is satisfied. Thus, the artificial graphite and the conductive carbon black SP are uniformly distributed between the positive electrode active material particles, wherein the artificial graphite with a sheet structure forms point-surface contact with the positive electrode active material particles, which can realize long-range conduction on the electrode; the conductive carbon black SP is in a granular form and adheres to the surface of the positive electrode active material particles, which can realize short-range conduction, and the two have good complementary effects, taking into account long-range conduction and short-range conduction, which can maximize the electron conduction between the positive electrode active material particles and ensure the rapid transmission of electrons. And the dispersibility between the active material and the conductive agent is improved. At the same time, the elongation of the positive electrode sheet is improved. In addition, the K value of the artificial graphite satisfies 0.6≤K<1, so that the number of positive electrode active material particles contacted by the artificial graphite per unit length is relatively large, and the charge conduction sites are relatively large, thereby effectively improving the electron conduction between the active particles, significantly improving the conductive capacity, improving the electron conductivity of the electrode, thereby significantly reducing the contact resistance of the positive electrode sheet, i.e. DCR is reduced, thereby reducing the polarization of the battery, so that the positive electrode sheet has excellent electrical performance.

[0030] The principle of the positive electrode sheet provided by the present application to achieve the above beneficial effects will be described in detail below:

[0031] In the present application, by adding artificial graphite and conductive carbon black SP in the positive electrode sheet, the artificial graphite and the conductive carbon black SP are uniformly distributed between the positive electrode active material particles, wherein the artificial graphite has a sheet structure, so it forms point-surface contact with the positive electrode active material particles instead of the conventional point-point contact form, thereby realizing long-range conduction on the electrode; the conductive carbon black SP is in a granular form and adheres to the surface of the positive electrode active material particles, which can realize short-range conduction, and the two have good complementary effects, taking into account long-range conduction and short-range conduction, which can maximize the electron conduction between the positive electrode active material particles and ensure the rapid transmission of electrons. And the dispersibility between the active material and the conductive agent is improved, forming a multi-dimensional conductive network in the positive electrode sheet.

[0032] At the same time, by selecting SP and artificial graphite (such as KS-6) with excellent slip performance as the conductive agent, the resistance of the active material particles when sliding on the surface of the current collector can be significantly reduced during the rolling of the electrode sheet, thereby fundamentally reducing the deformation of the current collector, thereby improving the elongation of the positive electrode sheet.

[0033] In addition, the K value of the artificial graphite satisfies 0.6≤K<1, and the K value is relatively large, that is, the bending and mixing degree of the artificial graphite is relatively small. Therefore, the number of the positive active material particles contacted by the artificial graphite in unit length is relatively large, and the charge conduction sites are relatively large, so that the electron conduction between the active particles is effectively improved, the conductive capacity is significantly improved, the electrode electron conductivity is improved, and the contact resistance of the positive plate is significantly reduced, that is, the DCR is reduced, so that the polarization of the battery is reduced, and the positive plate has excellent electrical performance. At the same time, the role of the conductive agent is maximized, and the amount of the conductive agent is reduced, so that the amount of the active material can be increased, and the capacity of the battery can be improved. It should be noted that the larger the K value of the artificial graphite is, the smaller the bending and mixing degree of the artificial graphite is, and the larger the number of the positive active material particles contacted by the artificial graphite in unit length is, and the larger the charge conduction sites are.

[0034] It should be noted that under a certain SEM magnification, the distance between the two end points of the artificial graphite along the length direction is a, as shown in FIGS. 1-4. The actual length of the artificial graphite is b, that is, the length when the bent artificial graphite is unfolded.

[0035] As some preferred embodiments, 0.7≤K≤0.98 is satisfied, so that the bending and mixing degree of the artificial graphite is further limited to be small, so that the number of the positive active material particles contacted by the artificial graphite in unit length is relatively large, and the charge conduction sites are relatively large, so that the electron conduction between the active particles is further effectively improved, the conductive capacity is significantly improved, and the electrode electron conductivity is improved, so that the contact resistance of the positive plate is further significantly reduced.

[0036] According to some specific embodiments of the present application, based on the total mass of the positive active material layer being 100%, the proportion of the sum of the mass of the artificial graphite and the conductive carbon black is 1.5% to 2.5%, for example, it can be 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, etc., so that by limiting the total content of the conductive agent within the above range, the electron conduction between the positive active material particles can be maximized to ensure the rapid transmission of electrons. Preferably, based on the total mass of the positive active material layer being 100%, the proportion of the sum of the mass of the artificial graphite and the conductive carbon black is 1.7% to 2.0%.

[0037] Further, the mass ratio of the artificial graphite and the conductive carbon black is (1 / 4-2):1, for example, can be 1 / 4:1, 1 / 2:1, 1:1, 2:1, etc. By limiting the mass ratio of the artificial graphite and the conductive carbon black in the above range, the synergistic complementary effect between the two can be further ensured, the long-range and short-range conductivities are taken into account, and thus the electron conduction between the positive active material particles can be maximized to ensure the rapid transmission of electrons. The inventors have found that if the content of the artificial graphite is too high, it will hinder the conduction of lithium ions, thereby causing the performance of the pole piece to deteriorate; if the content of the artificial graphite is too low, it will not form an effective conductive network, and the synergistic effect with the SP will deteriorate.

[0038] According to still some specific embodiments of the present application, the artificial graphite is in a sheet shape, the thickness of a single sheet of artificial graphite is 50-200 nm, for example, can be 50 nm, 70 nm, 100 nm, 120 nm, 150 nm, 170 nm, 200 nm, etc., and the length of a single sheet of artificial graphite is 1-60 μm, for example, can be 1 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, etc. By limiting the thickness and length of the artificial graphite in the above range, the contact between the artificial graphite and the active material particles can be further ensured to be point-surface contact, thereby ensuring that the artificial graphite has more contact sites with the active material particles, reducing the internal resistance of the battery, improving the electron conductivity of the electrode, and maximizing the role of the conductive agent. Further preferably, the length is 5-40 μm.

[0039] In the embodiments of the present application, the artificial graphite is in an equiaxed irregular sheet-spherical shape, which is different from different sheet-layer graphenes, has a high thickness and is easy to disperse and process, has high compressibility, can positively improve compaction, and has good lubricity and flexibility, which can alleviate the separation of the active material from the current collector and the conductive agent due to the large volume shrinkage and expansion of the active material, and form an inert single-particle "island".

[0040] According to still some specific embodiments of the present application, the average particle size of the conductive carbon black SP is 15-65 nm, for example, can be 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, etc. By limiting the average particle size of the conductive carbon black in the above range, the conductive carbon black SP can be further ensured to adhere to the surface of the positive active material particles to achieve short-range conductivity, and the synergistic complementary effect between the conductive carbon black SP and the artificial graphite is further ensured, the long-range and short-range conductivities are taken into account, and thus the electron conduction between the positive active material particles can be maximized to ensure the rapid transmission of electrons.

[0041] In the embodiments of the present application, the particle size of the conductive carbon black SP is small, and is distributed in the pores formed by the active particles to have stronger liquid absorption.

[0042] According to still some specific embodiments of the present application, in the CP cross-section view, the actual length of the artificial graphite and the number of the positive electrode active material particles directly contacting the artificial graphite satisfy: the ratio M of the number of the positive electrode active material particles directly contacting the artificial graphite to the actual length of the artificial graphite ranges from 4.5 to 7.5, the unit of the actual length of the artificial graphite is μm, and the number of the positive electrode active material particles is pieces. Thus, the number of the positive electrode active material particles contacting the artificial graphite in unit length is further ensured to be large, and the charge conduction sites are more, thereby effectively improving the electron conduction between the active particles, significantly improving the conductivity, and improving the electrode electron conductivity, thereby significantly reducing the contact resistance of the positive electrode sheet.

[0043] It can be understood that the CP cross-section view refers to the cross-section along the thickness direction of the positive electrode sheet, and the SEM view obtained by observing by SEM is the CP cross-section view.

[0044] According to still some specific embodiments of the present application, the positive electrode active material layer further comprises the positive electrode active material and the positive electrode binder; and the mass ratio of the positive electrode active material, the positive electrode binder and the positive electrode conductive agent is (95.64-97.12):(1.38-1.86):(1.5-2.5).

[0045] According to still some specific embodiments of the present application, the particle size Dv50 of the positive electrode active material is 0.8 μm-1.2 μm, thereby being beneficial to the electrolyte infiltration.

[0046] In some embodiments of the present application, the positive electrode current collector can comprise a metal foil or a composite positive electrode current collector. For example, the metal foil can be an aluminum foil. The composite positive electrode current collector can comprise a polymer material base layer and a metal layer formed on at least one side surface of the polymer material base layer, for example, the composite negative electrode current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, etc.) on a polymer material base material (such as a polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc. base material).

[0047] In some embodiments of the present application, the positive electrode binder can comprise at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylic ester resin.

[0048] In a second aspect of the present application, a method for preparing the positive electrode sheet of the above embodiments is provided. According to the embodiments of the present application, the above method comprises:

[0049] S100: stirring and dispersing artificial graphite, conductive carbon black and the first solvent

[0050] In this step, the artificial graphite, conductive carbon black and the first solvent are stirred and dispersed by a shearing stirring and dispersing device, which can revolve and rotate and provide shearing forces in opposite directions. Under the action of the opposite shearing forces, the artificial graphite in the slurry can effectively reduce the degree of bending and mixing (i.e., increase the K value of the artificial graphite), which is conducive to the subsequent step of re-forming a conductive network with a higher effective chain density with the active material, so that the artificial graphite contacts a larger number of positive active material particles and has more charge conduction sites in a unit length, thereby effectively improving the electron conduction between the active particles, significantly improving the conductive ability, improving the electrode electron conductivity, thereby significantly reducing the contact resistance (DCR) of the positive plate, thereby reducing the polarization of the battery, and making the positive plate have excellent electrical properties.

[0051] According to some specific embodiments of the present application, the surfactant, artificial graphite, conductive carbon black and the first solvent are stirred and dispersed by a shearing stirring and dispersing device to obtain an initial slurry. The surfactant can effectively prevent the aggregation of the components, so that the entire slurry system can build a good three-dimensional conductive network, and the surfactant molecules are adsorbed on the surface of the artificial graphite conductive agent to achieve dispersion by repulsive force and intermolecular forces, thereby further reducing the degree of bending and mixing of the artificial graphite (i.e., further increasing the K value of the artificial graphite), which is further conducive to the subsequent step of re-forming a conductive network with a higher effective chain density with the active material, so that the artificial graphite contacts a larger number of positive active material particles and has more charge conduction sites in a unit length, thereby effectively improving the electron conduction between the active particles, significantly improving the conductive ability, improving the electrode electron conductivity, thereby significantly reducing the contact resistance (DCR) of the positive plate, thereby reducing the polarization of the battery, and making the positive plate have excellent electrical properties.

[0052] As a specific example, the surfactant can be first dissolved in the first solvent by ultrasonic, and then the artificial graphite and conductive carbon black are pre-mixed.

[0053] The specific type of the surfactant is not particularly limited, and those skilled in the art can select according to the actual situation. As some preferred embodiments, the surfactant includes at least one of sodium dodecyl benzene sulfonate, sodium lignosulfonate and cetyltrimethylammonium bromide.

[0054] According to some specific embodiments of the present application, the surfactant has a mass of 0.5% to 4% of the initial slurry, for example, it can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, etc. By limiting the content of the surfactant within the above range, the agglomeration of the components can be further prevented, so that the entire slurry system can form a good three-dimensional conductive network, and the use of the surfactant can further reduce the degree of intercalated curling of the artificial graphite.

[0055] In the embodiments of the present application, by reducing the stirring speed and the dispersion speed of the shearing stirring dispersion device, the degree of bending intercalation of the artificial graphite can be further reduced (i.e., the K value of the artificial graphite is further increased), which is further beneficial to the subsequent step of re-forming an active material into a conductive network with a higher chain density, so that the artificial graphite has more positive active material particles in contact in a unit length and more charge conduction sites, thereby effectively improving the electron conduction between active particles.

[0056] According to still some specific embodiments of the present application, in step S100, the stirring speed is 20 r / min to 30 r / min (for example, it can be 20 r / min, 22 r / min, 24 r / min, 26 r / min, 28 r / min, 30 r / min, etc.), the dispersion speed is 100 r / min to 300 r / min (for example, it can be 100 r / min, 150 r / min, 200 r / min, 250 r / min, 300 r / min, etc.), and the stirring time is 5 min to 15 min (for example, it can be 5 min, 6 min, 8 min, 10 min, 12 min, 15 min, etc.). By limiting the stirring speed, the dispersion speed and the stirring time in step S100 within the above ranges, the effective dispersion of the artificial graphite and the conductive carbon black can be effectively ensured, and the degree of bending intercalation of the artificial graphite can be further reduced (i.e., the K value of the artificial graphite is further increased).

[0057] In the embodiments of the present application, the specific type of the first solvent is not particularly limited as long as it can achieve the dispersion between the components, for example, the first solvent can be NMP.

[0058] S200: adding the positive active material, the positive electrode binder and the second solvent into the shearing stirring dispersion device, and stirring and dispersing

[0059] In this step, the positive electrode active material, the positive electrode binder and the second solvent are added into a shearing stirring dispersion device, and are stirred and dispersed to obtain a positive electrode slurry. According to the present application, the surface active agent, the artificial graphite and the conductive carbon black are premixed first, and then the positive electrode active material and the positive electrode binder are added for mixing, which can further facilitate the dispersion of the artificial graphite and the conductive carbon black in the slurry, and can further reduce the bending and mixing degree of the artificial graphite (i.e., further increase the K value of the artificial graphite), and further facilitate the reformation of a conductive network with higher effective chain density from the conductive agent and the active material.

[0060] According to still some specific embodiments of the present application, in step S200, the stirring rotation speed is 20 r / min-30 r / min, the dispersion rotation speed is 200 r / min-1000 r / min, and the dispersion time is 2 h-4 h. By limiting the stirring rotation speed, the dispersion rotation speed and the stirring time in step S200 within the above ranges, the effective dispersion of the artificial graphite, the conductive carbon black, the positive electrode active material and the positive electrode binder in the slurry can be effectively ensured, and the bending and mixing degree of the artificial graphite can be further reduced (i.e., the K value of the artificial graphite is further increased).

[0061] S300: coating the positive electrode slurry on at least part of the surface of the positive electrode current collector, and drying

[0062] In this step, the positive electrode slurry is coated on at least part of the surface of the positive electrode current collector, and is dried to obtain a positive electrode sheet.

[0063] According to the method for preparing the above positive electrode sheet according to the embodiments of the present application, the artificial graphite and the conductive carbon black SP are added in the positive electrode slurry, the point-surface contact is constructed between the sheet structure artificial graphite and the positive electrode active material particles, the long-range conduction on the electrode can be realized, the conductive carbon black SP is in a particle form and is attached to the surface of the positive electrode active material particles, the short-range conduction can be realized, and the two have a good complementary effect in mutual cooperation, the long-range conduction and the short-range conduction are taken into account, the electron conduction between the positive electrode active material particles can be maximally improved, the fast transmission of the electrons is ensured, the dispersibility between the active material and the conductive agent is improved, the elongation of the positive electrode sheet is improved, in addition, the K value of the artificial graphite satisfies 0.6≤K<1, therefore, the number of the positive electrode active material particles contacted in unit length of the artificial graphite is relatively large, and the charge conduction sites are relatively large, so that the electron conduction between the active particles is effectively improved, the conductive ability is significantly improved, the electron conduction of the electrode is improved, and the contact resistance of the positive electrode sheet (i.e., DCR) is significantly reduced, so that the polarization of the battery is reduced, and the positive electrode sheet has excellent electrical performance.

[0064] Meanwhile, the method can further reduce the bending and mixing degree of artificial graphite in the slurry (i.e., further increase the K value of the artificial graphite) by providing shear force in the opposite direction, using surfactants, reducing the stirring speed and dispersion speed, and pre-mixing the surfactants, artificial graphite, and conductive carbon black, and the like, thereby further facilitating the reformation of a conductive network with a higher effective chain density from the artificial graphite conductive agent and the active material, so that the artificial graphite contacts a larger number of positive active material particles and has more charge conduction sites in a unit length, thereby effectively improving the electron conduction between active particles, significantly improving the conductivity, improving the electrode electron conductivity, thereby significantly reducing the contact resistance of the positive plate, i.e., the DCR, thereby reducing the polarization of the battery, and making the positive plate have excellent electrical performance.

[0065] In a third aspect of the present application, a battery is provided. According to embodiments of the present application, the battery has the positive plate of the above embodiments. Thus, the charge and discharge internal resistance of the battery can be effectively reduced, the battery efficiency can be improved, and the energy storage and release capacity of the battery can be enhanced.

[0066] In embodiments of the present application, the above battery can be either a lithium ion battery or a sodium ion battery. Hereinafter, a lithium ion battery is taken as an example for illustration.

[0067] Specifically, the lithium ion battery includes the positive plate, the negative plate, and the separator of the above embodiments, and the separator is arranged between the positive plate and the negative plate. During the charging and discharging process of the battery, the active ions lithium ions are embedded and extracted between the positive plate and the negative plate. The electrolyte plays a role in conducting ions between the positive plate and the negative plate. The separator is arranged between the positive plate and the negative plate, mainly to prevent short circuiting of the positive and negative electrodes, while allowing ions to pass through.

[0068] The specific material of the above separator is not particularly limited, and as some specific embodiments, the above separator includes at least one of a PP separator, a PE separator, a single-sided ceramic separator, a double-sided ceramic separator, a non-woven fabric separator, and a glass fiber separator.

[0069] The negative plate includes a negative current collector and a negative active material layer formed on the negative current collector, and the negative active material layer includes a negative active material (e.g., graphite), a negative dispersant, a conductive agent, and a negative adhesive.

[0070] The preparation method of the negative plate includes: uniformly mixing the negative active material, the negative dispersant, the conductive agent, and the negative adhesive in a predetermined ratio, adding a solvent to uniformly stir to form a negative slurry, then coating the negative slurry on the current collector, drying, and finally cutting the negative plate into a specific shape according to different battery housings for standby use.

[0071] The positive electrode sheet, the negative electrode sheet and the separator are wound, and then the positive and negative electrode tabs are welded. Then the bare battery cell is packaged in an aluminum plastic film. After packaging, the battery cell is vacuum baked for 10-20 hours. Then the battery cell is obtained by liquid injection, standing, high temperature and high pressure formation, degassing and packaging.

[0072] In a fourth aspect of the present application, a power utilization system is provided. According to embodiments of the present application, the power utilization system comprises: a power utilization device, and an energy storage device, which supplies power to the power utilization device, and the energy storage device comprises the battery described in the above embodiments. Thus, the power utilization system has all the advantages of the battery, which are not repeated here.

[0073] The above-mentioned energy storage device can be used as a power source of a power utilization device, or as an energy storage unit of a power utilization device. The above-mentioned power utilization device can include, but is not limited to, a mobile phone, a tablet computer, a notebook computer, a desktop computer, a smart bracelet, a smart watch, an e-book reader, a game console, and other portable electronic devices. It can also include, but is not limited to, a car, a truck, a sedan, a van, a bullet train, a high-speed rail, an electric automatic car, and other vehicles. In addition, it can also be various household appliances, such as refrigerators, electric lamps, air conditioners, and the like.

[0074] In addition, the energy storage device of the present application can include at least one of a power storage device for the power generation side of a power system, a power storage device (such as an electrochemical energy storage device) for the power distribution side of a power system, and a power storage device for the user side of a power system.

[0075] It should be noted that the features and advantages described above for the battery also apply to the power utilization device, which are not repeated here.

[0076] The embodiments of the present application are described in detail below. It should be noted that the embodiments described below are exemplary and are used to explain the present application, and cannot be understood as a limitation of the present application. In addition, if not specifically stated, all reagents used in the following examples are commercially available or can be synthesized according to the methods described herein or known methods, and the reaction conditions not listed are also readily available to those skilled in the art.

[0077] Example 1

[0078] The present embodiment provides a lithium ion battery, and a preparation method thereof comprises:

[0079] 1) First, the conductive agent (mass ratio of 1:1 artificial graphite KS-6 and SP) and NMP solvent are premixed using a high-speed shearing stirring dispersion device to obtain an initial slurry, stirring speed 25 r / min, dispersion speed 250 r / min, stirring for 10 min. Subsequently, the lithium iron phosphate powder and PVDF powder are added to the above high-speed shearing stirring dispersion device, dry mixed at 300 r / min, then kneaded with a certain proportion of NMP, and finally dispersed at 300 r / min for 3 h after adding the remaining NMP to obtain the positive electrode slurry. The solid content of the positive electrode slurry is about 62 wt%, and the mass ratio of lithium iron phosphate powder, PVDF powder and conductive agent is 96.62:1.48:1.90.

[0080] Then, the positive electrode slurry is coated on the positive electrode current collector aluminum foil, and the coating weight per unit area (1540.25 mm 2 ) of the positive electrode slurry is 250 mg. After drying, cold pressing, slitting and cutting, the positive electrode sheet is obtained.

[0081] 2) Preparation of negative electrode sheet

[0082] Preparation of negative electrode sheet: The negative electrode active material artificial graphite, conductive carbon SP, dispersant CMC and binder SBR are dispersed in deionized water according to a mass ratio of 96.5:0.5:1:2 to obtain a negative electrode slurry. The solid content of the negative electrode slurry is about 55%. The negative electrode slurry is coated on the negative electrode current collector copper foil, and the coating weight per unit area (1540.25 mm 2 ) of the negative electrode slurry is 122 mg. After drying, cold pressing, slitting and cutting, the negative electrode sheet is obtained.

[0083] 3) Preparation of electrolyte

[0084] In an argon atmosphere glove box with water content ≤1 ppm, ethylene carbonate (EC), methyl ethyl carbonate (EMC) and dimethyl carbonate (DMC) are mixed according to a mass ratio of 1:1:1. Then, the dry electrolyte lithium salt LiPF6 is dissolved in the solvent, and the mass ratio of LiPF6 in the electrolyte is 16%.

[0085] 4) Separator

[0086] A polyethylene film with a thickness of 16 microns is selected as the separator.

[0087] 5) Assembly of battery

[0088] The prepared positive plate, the separator, and the negative plate are stacked in sequence, so that the separator is in the middle of the positive and negative plates and separates the positive and negative plates, a bare cell is formed after winding, the bare cell is assembled into an outer package after welding the tabs, and the lithium ion battery is finally prepared after injecting the prepared electrolyte and performing packaging, standing, formation, shaping, capacity testing, and the like on the cell.

[0089] Example 2

[0090] The present embodiment provides a lithium ion battery, and the preparation method of the present embodiment is basically the same as that of example 1, and the only difference is that:

[0091] 1) First, the surfactant sodium dodecyl benzene sulfonate is ultrasonically dissolved in the NMP solvent to form a dispersant, and then the conductive agent (artificial graphite KS-6 and SP with a mass ratio of 1:1) and the dispersant are pre-mixed using a high-speed shearing stirring dispersion device to obtain an initial slurry. The mass of the surfactant sodium dodecyl benzene sulfonate is 1% of the initial slurry.

[0092] Example 3

[0093] The present embodiment provides a lithium ion battery, and the preparation method of the present embodiment is basically the same as that of example 2, and the only difference is that:

[0094] The stirring speed of the initial slurry is 20 r / min, the dispersion speed is 100 r / min, and the stirring time is 15 min.

[0095] Example 4

[0096] The present embodiment provides a lithium ion battery, and the preparation method of the present embodiment is basically the same as that of example 2, and the only difference is that:

[0097] The stirring speed of the initial slurry is 30 r / min, the dispersion speed is 300 r / min, and the stirring time is 5 min.

[0098] Example 5

[0099] The present embodiment provides a lithium ion battery, and the preparation method of the present embodiment is basically the same as that of example 2, and the only difference is that:

[0100] The speed of the high-speed shearing stirring dispersion device after adding the lithium iron phosphate powder and the PVDF powder is 500 r / min.

[0101] Example 6

[0102] The present embodiment provides a lithium ion battery, and the preparation method of the present embodiment is basically the same as that of example 2, and the only difference is that:

[0103] The speed of the high-speed shearing stirring dispersion device after adding the lithium iron phosphate powder and the PVDF powder is 800 r / min.

[0104] Example 7

[0105] This example provides a lithium ion battery, the preparation method of this example is basically the same as that of example 2, the only difference is that:

[0106] The mass ratio of KS-6 and SP is 1 / 4:1.

[0107] Example 8

[0108] This example provides a lithium ion battery, the preparation method of this example is basically the same as that of example 2, the only difference is that:

[0109] The mass ratio of KS-6 and SP is 1 / 2:1.

[0110] Example 9

[0111] This example provides a lithium ion battery, the preparation method of this example is basically the same as that of example 2, the only difference is that:

[0112] The mass ratio of KS-6 and SP is 2:1.

[0113] Example 10

[0114] This example provides a lithium ion battery, the preparation method of this example is basically the same as that of example 2, the only difference is that:

[0115] The mass ratio of KS-6 and SP is 4:1.

[0116] Example 11

[0117] This example provides a lithium ion battery, the preparation method of this example is basically the same as that of example 2, the only difference is that:

[0118] The mass of the surfactant sodium dodecyl benzene sulfonate is 2% of the initial slurry.

[0119] Example 12

[0120] This example provides a lithium ion battery, the preparation method of this example is basically the same as that of example 2, the only difference is that:

[0121] The mass of the surfactant sodium dodecyl benzene sulfonate is 4% of the initial slurry.

[0122] Example 13

[0123] This example provides a lithium ion battery, the preparation method of this example is basically the same as that of example 11, the only difference is that:

[0124] The surfactant is a mixture of sodium dodecyl benzene sulfonate and cetyl trimethyl ammonium bromide at a mass ratio of 1:1.

[0125] Comparative Example 1

[0126] This comparative example provides a lithium ion battery, and the preparation method of this example is basically the same as that of Example 1, and the only difference is that:

[0127] 1) Using a double planetary mixing device, lithium iron phosphate powder, PVDF powder, and a certain proportion of NMP are added to the stirring tank at a speed of 300 r / min for dry mixing, then kneaded with a certain proportion of NMP, and finally dispersed at a speed of 2000 r / min for 3h with the remaining NMP to form a positive electrode slurry.

[0128] Comparative Example 2

[0129] This comparative example provides a lithium ion battery, and the preparation method of this example is basically the same as that of Example 1, and the only difference is that:

[0130] 1) Using a double planetary mixing device, lithium iron phosphate powder, conductive agent SP powder, and PVDF powder are added to the stirring tank at a speed of 300 r / min for dry mixing, then kneaded with a certain proportion of NMP, and finally dispersed at a speed of 2000 r / min for 3h with the remaining NMP to form a positive electrode slurry.

[0131] Comparative Example 3

[0132] This comparative example provides a lithium ion battery, and the preparation method of this example is basically the same as that of Example 1, and the only difference is that:

[0133] 1) Using a high-speed shearing stirring dispersion device, the conductive agent (KS-6 and SP at a mass ratio of 1:1) and NMP solvent are premixed to obtain an initial slurry, the stirring speed is 100 r / min, the dispersion speed is 560 r / min, and the stirring time is 10 min. Subsequently, lithium iron phosphate powder and PVDF powder are added to the above high-speed shearing stirring dispersion device at a speed of 300 r / min for dry mixing, then kneaded with a certain proportion of NMP, and finally dispersed at a speed of 2000 r / min for 3h with the remaining NMP to obtain a positive electrode slurry.

[0134] The positive electrode sheets prepared in Examples 1, 2, 11 and 13 and Comparative Examples 1-3 are observed by SEM, and the results are shown in Figures 1-7.

[0135] The film sheet resistivity and the tab elongation of the positive electrode tab prepared from Examples 1-13 and Comparative Examples 1-3 were tested, and the results are shown in Table 1. The K value of the artificial graphite KS-6 in the positive electrode tab prepared from Examples 1-13 and Comparative Examples 1-3 was calculated, and the ratio M of the number of the positive electrode active material particles directly contacting the artificial graphite KS-6 to the actual length of the artificial graphite KS-6 was calculated, and the results are shown in Table 1.

[0136] The 50% SOC charge DCR and the 50% SOC discharge DCR of the lithium ion battery prepared from Examples 1-13 and Comparative Examples 1-3 were tested, and the results are shown in Table 1.

[0137] The test method of the film sheet resistivity of the positive electrode tab is as follows:

[0138] The electrode tab was taken, the controllable pressure four-wire double-probe resistance method was used, the voltage was controlled, the current was collected, the resistance of the film sheet (R = U / I) was obtained, and then the film sheet resistivity of the positive electrode tab was calculated.

[0139] The test method of the tab elongation of the positive electrode tab is as follows:

[0140] Before rolling, a piece of positive electrode tab with a length of about 1.5 meters was taken, laid flat on a marble table, and two straight lines with a distance of 1000±200 mm were marked with a fine ballpoint pen, the straight lines were perpendicular to the straight edge of the ceramic layer, and the measurement points on the straight lines and the middle region of the positive electrode tab were marked with a ballpoint pen. The distance D0 between the two straight line measurement points was measured with a flexible ruler, and the reading was estimated to 0.1 mm. After rolling the positive electrode tab, the positive electrode tab was laid flat on the marble table, and the two ends of the positive electrode tab were pressed with a press block to prevent the positive electrode tab from shrinking and arching. The distance D1 between the two straight line measurement points was measured with a flexible ruler, and the reading was estimated to 0.1 mm. The tab elongation of the positive electrode tab = (D1-D0) / D0.

[0141] The test and calculation of the K value of the artificial graphite KS-6 are as follows:

[0142] The CP cross-sectional diagram was processed by using SolidWorks software, and the distance between the two end points of KS-6 was taken as a; the actual length b of KS-6 was calculated by the KS-6 contour curve, i.e. a / b = K.

[0143] The calculation method of the ratio M of the number of the positive electrode active material particles directly contacting the artificial graphite KS-6 to the actual length of the artificial graphite KS-6 is as follows:

[0144] The CP diagram was processed by using SolidWorks software, and the actual length b of KS-6 was calculated by the KS-6 contour curve; the number of the positive electrode active material particles directly contacting the KS-6 was counted and recorded as c, i.e. c / b = M.

[0145] The test method of 50% SOC charge DCR of the lithium ion battery is as follows:

[0146] Firstly, the battery is charged from 0% SOC to 50% SOC by 0.5P constant power, then charged at 1C rate for 30S, rested for 40S, discharged for 30S, and rested for 40S; the voltage V1 at the beginning of the rate charge and the voltage V2 at the end of the charge rest are recorded, and the charge DCR is (V2-V1) / A, A is the current at 1C rate.

[0147] The test method of 50% SOC discharge DCR of the lithium ion battery is as follows:

[0148] Firstly, the battery is discharged from 100% SOC to 50% SOC by 0.5P constant power, then charged at 1C rate for 30S, rested for 40S, discharged for 30S, and rested for 40S; the voltage V3 at the beginning of the rate discharge and the voltage V4 at the end of the discharge rest are recorded, and the discharge DCR is (V4-V3) / A, A is the current at 1C rate.

[0149] Table 1

[0150] As can be seen from Table 1, compared with Comparative Examples 1 and 2, the sheet resistivity and the sheet ductility of the positive electrode sheet of Examples 1-13 are obviously reduced, and the 50% SOC charge DCR and the 50% SOC discharge DCR of the battery of Examples 1-13 are obviously reduced.

[0151] As can be seen from Table 1, compared with Comparative Example 3, the K value and the M value of the artificial graphite KS-6 in the positive electrode sheet of Examples 1-13 are obviously increased, the sheet resistivity and the sheet ductility of the positive electrode sheet of Examples 1-13 are obviously reduced, and the 50% SOC charge DCR and the 50% SOC discharge DCR of the battery of Examples 1-13 are obviously reduced. It can be seen that, in the formation process of the initial slurry and the positive electrode slurry, by reducing the stirring speed and the dispersion speed of the high-speed shearing and stirring dispersion equipment, the bending impurity degree of the artificial graphite KS-6 can be reduced (i.e., the K value and the M value of the artificial graphite KS-6 are increased), so that the sheet resistivity and the sheet ductility of the positive electrode sheet can be reduced, and the 50% SOC charge DCR and the 50% SOC discharge DCR of the battery can be reduced.

[0152] It can also be seen from Table 1 that, compared with Example 1, the K value and the M value of Example 2 are further increased, the membrane sheet resistivity and the tab ductility of the tab are further reduced, and the 50% SOC charge DCR and the 50% SOC discharge DCR are further reduced. It can be seen that, by adding the surfactant in the formation of the initial slurry and the positive electrode slurry, the bending and mixing degree of the artificial graphite KS-6 can be further reduced (i.e., the K value and the M value of the artificial graphite KS-6 are increased), so that the membrane sheet resistivity and the tab ductility of the positive electrode tab can be reduced, and the 50% SOC charge DCR and the 50% SOC discharge DCR of the battery can be reduced.

[0153] It can also be seen from Table 1 that, compared with Example 10, the charge and discharge DCRs of Examples 2, 7-9 are significantly reduced. Too much KS-6 content is not conducive to the conduction of lithium ions in the tab.

[0154] It can also be seen from Table 1 that, compared with Example 11, the K value and the M value of Example 13 are further increased, the membrane sheet resistivity and the tab ductility of the tab are further reduced, and the 50% SOC charge DCR and the 50% SOC discharge DCR are further reduced. It can be seen that, by adding two kinds of surfactants to mutually cooperate, the dispersion effect can be increased, so that the bending and mixing degree of the artificial graphite KS-6 can be further reduced (i.e., the K value and the M value of the artificial graphite KS-6 are increased), so that the membrane sheet resistivity and the tab ductility of the positive electrode tab can be reduced, and the 50% SOC charge DCR and the 50% SOC discharge DCR of the battery can be reduced.

[0155] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, different embodiments or examples described in the present specification and the features of different embodiments or examples can be combined and combined by those skilled in the art without contradiction.

[0156] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above embodiments within the scope of the present application.

Claims

1. A positive electrode sheet, wherein, Comprise: a positive electrode current collector; a positive electrode active material layer provided on at least part of the surface of the positive electrode current collector, the positive electrode active material layer comprising a positive electrode conductive agent, the positive electrode conductive agent comprising artificial graphite and conductive carbon black; the distance between the two end points of the artificial graphite along the length direction is a, the actual length of the artificial graphite is b, K = a / b, and 0.6 ≤ K < 1.

2. The positive electrode sheet according to claim 1, wherein 0.7 ≤ K ≤ 0.98 is satisfied.

3. The positive electrode sheet according to claim 1 or 2, wherein The total mass of the positive electrode active material layer is 100%, and the mass ratio of the artificial graphite and the conductive carbon black is 1.5% to 2.5%; The mass ratio of the artificial graphite and the conductive carbon black is (1 / 4-2):

1.

4. The positive electrode sheet according to any one of claims 1 to 3, wherein The artificial graphite is flaky, the thickness of a single piece of the artificial graphite is 50 nm to 200 nm, and the length of a single piece of the artificial graphite is 1 μm to 60 μm.

5. The positive electrode sheet according to any one of claims 1 to 4, wherein The average particle size of the conductive carbon black is 15 nm to 65 nm.

6. The positive electrode sheet according to any one of claims 1 to 5, wherein In the CP cross-sectional view, the actual length of the artificial graphite and the number of positive electrode active material particles directly contacting the artificial graphite satisfy: the ratio M of the number of positive electrode active material particles directly contacting the artificial graphite to the actual length of the artificial graphite is 4.5 to 7.5, the unit of the actual length of the artificial graphite is μm, and the number of positive electrode active material particles is the number.

7. The positive electrode sheet according to any one of claims 1 to 6, wherein The positive electrode active material layer further comprises a positive electrode active material and a positive electrode binder; the mass ratio of the positive electrode active material, the positive electrode binder and the positive electrode conductive agent is (95.64-97.12):(1.38-1.86):(1.5-2.5).

8. The positive electrode sheet according to claim 7, wherein The particle size Dv50 of the positive electrode active material is 0.8 μm to 1.2 μm.

9. A method of producing the positive electrode sheet according to any one of claims 1 to 8, wherein Comprise: (1) using a shearing stirring dispersion device to stir and disperse artificial graphite, conductive carbon black and a first solvent to obtain an initial slurry; (2) adding a positive electrode active material, a positive electrode binder and a second solvent into the shearing stirring dispersion device, stirring and dispersing to obtain a positive electrode slurry; (3) coating the positive electrode slurry on at least part of the surface of a positive electrode current collector and drying to obtain a positive electrode sheet.

10. The method of claim 9, wherein, In step (1), a shearing stirring dispersion device is used to stir and disperse a surfactant, artificial graphite, conductive carbon black and a first solvent to obtain an initial slurry.

11. The method of claim 10, wherein, The surfactant comprises at least one of sodium dodecyl benzene sulfonate, sodium lignosulfonate and cetyl trimethyl ammonium bromide; And / or, the mass of the surfactant is 0.5% to 4% of the initial slurry.

12. The method of claim 10 or 11, wherein, In step (1), the stirring speed is 20 r / min to 30 r / min, the dispersion speed is 100 r / min to 300 r / min, and the stirring time is 5 min to 15 min; And / or, in step (2), the stirring speed is 20 r / min to 30 r / min, the dispersion speed is 200 r / min to 1000 r / min, and the dispersion time is 2 h to 4 h.

13. A battery, wherein, The positive electrode sheet of any one of claims 1-8 or the positive electrode sheet prepared by the method of any one of claims 9-12.

14. An electric power utilization system wherein, Comprise: an electric device, and An energy storage device for powering the electrical device, the energy storage device comprising the battery of claim 13.

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