Positive electrode sheet, method for producing same, battery, and power supply system

Abstract

This application discloses a positive electrode sheet and its preparation method, a battery, and an electrical system. The positive electrode sheet includes: a positive electrode current collector; a positive electrode active material layer disposed on at least a portion of the surface of the positive electrode current collector, the positive electrode active material layer including a positive electrode conductive agent, the positive electrode conductive agent including artificial graphite and conductive carbon black; the distance between the two ends of the artificial graphite along its length direction is a, the actual length of the artificial graphite is b, K = a / b, satisfying 0.6 ≤ K < 1.

Description

Technical Field

[0001] This application belongs to the field of battery technology, specifically relating to a positive electrode sheet and its preparation method, a battery, and an electrical system. Background Technology

[0002] Lithium-ion batteries, as a green power source, are widely used in energy storage base stations and other applications due to their advantages such as high energy density, long cycle life, low self-discharge rate, and environmental friendliness. Lithium-ion batteries mainly consist of a positive electrode, separator, negative electrode, and electrolyte. The positive electrode is a crucial component of the lithium-ion battery, and the preparation of the positive electrode slurry directly affects the overall performance of the battery. Furthermore, the dispersion state and contact uniformity of the conductive additives and active materials in the positive electrode significantly influence the battery's performance, such as its rate capability and cycle performance. Summary of the Invention

[0003] This application aims to at least partially address one of the technical problems in related technologies. Therefore, the purpose of this application is to provide a positive electrode sheet and its preparation method, a battery, and an electrical system. This application adds artificial graphite and conductive carbon black to the positive electrode sheet. The two have a synergistic complementary effect, maximizing the electronic conduction between the positive electrode active material particles. Simultaneously, it improves the elongation of the positive electrode sheet. Furthermore, the K-value of artificial graphite satisfies 0.6 ≤ K < 1. Therefore, artificial graphite contacts a large number of positive electrode active material particles per unit length, resulting in more charge conduction sites, effectively improving the electronic conduction between active particles and significantly enhancing its conductivity, thereby significantly reducing the contact resistance of the positive electrode sheet.

[0004] In one aspect of this application, a positive electrode is provided. According to an embodiment of this application, the positive electrode comprises:

[0005] Positive current collector;

[0006] A positive electrode active material layer is disposed on at least a portion 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;

[0007] The distance between the two endpoints of the artificial graphite along its length is a, the actual length of the artificial graphite is b, K = a / b, and 0.6 ≤ K < 1.

[0008] According to the positive electrode sheet of this application embodiment, artificial graphite and conductive carbon black are uniformly distributed among the positive electrode active material particles. The sheet-like artificial graphite establishes point-to-surface contact with the positive electrode active material particles, enabling long-range conductivity on the electrode. The conductive carbon black, being granular, adheres to the surface of the positive electrode active material particles, enabling short-range conductivity. The two work synergistically, exhibiting a good complementary effect, balancing both long-range and short-range conductivity, maximizing electron conduction between the positive electrode active material particles, and ensuring rapid electron transport. This also improves the dispersibility between the active material and the conductive agent. Simultaneously, it improves the elongation of the positive electrode sheet. Furthermore, the K-value of artificial graphite satisfies 0.6 ≤ K < 1. Therefore, artificial graphite contacts a large number of positive electrode active material particles per unit length, resulting in more charge conduction sites, effectively improving electron conduction between active particles and significantly enhancing its conductivity. This improves the electrode's electronic conductivity, thereby significantly reducing the contact resistance (DCR) of the positive electrode sheet, thus reducing battery polarization and giving the positive electrode sheet superior electrical performance.

[0009] In addition, the positive electrode sheet according to the above embodiments of this application may also have the following additional technical features:

[0010] In some embodiments of this application, 0.7≤K≤0.98 is satisfied.

[0011] In some embodiments of this application, based on the total mass of the positive electrode active material layer being 100%, the combined mass of the artificial graphite and the conductive carbon black accounts for 1.5% to 2.5%; the mass ratio of the artificial graphite to the conductive carbon black is (1 / 4 to 2):1.

[0012] In some embodiments of this application, the artificial graphite is in sheet form, with a thickness of 50nm to 200nm and a length of 1μm to 60μm per sheet.

[0013] In some embodiments of this application, the average particle size of the conductive carbon black is 15 nm to 65 nm.

[0014] In some embodiments of this application, in the CP cross-sectional view, the actual length of the artificial graphite and the number of positive electrode active material particles in direct contact with it satisfy the following: the ratio M of the number of positive electrode active material particles in direct contact with the artificial graphite to the actual length of the artificial graphite is in the range of 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 of particles.

[0015] In some embodiments of this application, the positive electrode active material layer further includes 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).

[0016] In some embodiments of this application, the particle size Dv50 of the positive electrode active material is 0.8 μm to 1.2 μm.

[0017] In a second aspect, this application provides a method for preparing the positive electrode sheet described in the above embodiments. According to embodiments of this application, the method includes:

[0018] (1) Artificial graphite, conductive carbon black and the first solvent were stirred and dispersed using a shear stirring and dispersing device to obtain an initial slurry;

[0019] (2) Add the positive electrode active material, positive electrode binder and second solvent to the shearing and stirring dispersion device, stir and disperse to obtain positive electrode slurry;

[0020] (3) The positive electrode slurry is coated on at least a portion of the surface of the positive electrode current collector and dried to obtain a positive electrode sheet.

[0021] According to the method for preparing the above-mentioned positive electrode sheet according to the embodiments of this application, this method can further reduce the degree of bending and mixing of artificial graphite in the slurry (i.e., further increase the K value of artificial graphite) by providing shear force in opposite directions, using surfactants, reducing stirring speed and dispersion speed, and premixing surfactants, artificial graphite and conductive carbon black. This further facilitates the reformation of a conductive network with a higher effective chain density between the conductive agent and the active material, so that the artificial graphite contacts a larger number of positive electrode active material particles per unit length, and has more charge conduction sites. This effectively improves the electronic conduction between active particles, significantly enhances its conductivity, improves the electronic conductivity of the electrode, and thus significantly reduces the contact resistance of the positive electrode sheet, i.e., reduces the DCR, thereby reducing the polarization of the battery and giving the positive electrode sheet superior electrical performance.

[0022] In addition, the method according to the above embodiments of this application may also have the following additional technical features:

[0023] In some embodiments of this application, in step (1), a shearing and stirring dispersion device is used to stir and disperse the surfactant, artificial graphite, conductive carbon black and the first solvent to obtain an initial slurry.

[0024] In some embodiments of this application, the surfactant includes at least one of sodium dodecylbenzenesulfonate, sodium lignosulfonate, and hexadecyltrimethylammonium bromide; and / or, the surfactant is present in a mass of 0.5% to 4% of the initial slurry.

[0025] In some embodiments of this application, 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.

[0026] In a third aspect, this application proposes a battery. According to an embodiment of this application, the battery has the positive electrode sheet described in the above embodiments. This effectively reduces the battery's charging and discharging internal resistance, improves battery efficiency, and enhances the battery's energy storage and release capabilities.

[0027] A fourth aspect of this application proposes an electrical system. According to an embodiment of this application, the electrical system includes: an electrical device and an energy storage device that supplies power to the electrical device. The energy storage device includes the battery described in the above embodiments. Therefore, the electrical system possesses all the advantages of the battery, which will not be elaborated further here.

[0028] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0029] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0030] Figure 1 This is a SEM image of the positive electrode sheet of Embodiment 1 of this application;

[0031] Figure 2 This is a SEM image of the positive electrode sheet of Embodiment 2 of this application;

[0032] Figure 3 This is a SEM image of the positive electrode sheet of Embodiment 11 of this application;

[0033] Figure 4 This is a SEM image of the positive electrode sheet of Embodiment 13 of this application;

[0034] Figure 5 This is a SEM image of the positive electrode of Comparative Example 1 of this application;

[0035] Figure 6This is a SEM image of the positive electrode of Comparative Example 2 of this application;

[0036] Figure 7 This is a SEM image of the positive electrode of Comparative Example 3 of this application. Detailed Implementation

[0037] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0038] In related technologies, conductive carbon black (SP) is used as a conductive additive in the positive electrode. SP has good conductivity, and the conductive carbon black particles and active material particles have point-to-point contact. However, in electrodes prepared using conductive carbon black as a conductive agent, the large specific surface area of ​​the conductive carbon black makes dispersion difficult. This leads to the problem of easy agglomeration of the conductive agent and active material, preventing the formation of a good conductive network. This limits the electron conduction speed, resulting in high contact resistance and increased DCR (Displacement Resistance Rate). During the rolling process of the positive electrode, the active material particles slide under pressure to achieve a close arrangement. However, this sliding process causes significant stretching of the current collector (e.g., aluminum foil), and this stretching is not uniform across the entire electrode, significantly impacting the electrode's performance. Therefore, reducing the current collector stretching caused by active material particle slippage during the rolling process is crucial for subsequent processing performance and the final cell performance.

[0039] In view of this, in one aspect of this application, a positive electrode sheet is proposed. According to an embodiment of this application, the positive electrode sheet includes: a positive current collector; a positive active material layer disposed on at least a portion of the surface of the positive current collector, the positive active material layer including a positive conductive agent, the positive conductive agent including artificial graphite and conductive carbon black SP; the distance between the two ends of the artificial graphite along its length is a, the actual length of the artificial graphite is b, K = a / b, satisfying 0.6 ≤ K < 1. Thus, the artificial graphite and conductive carbon black SP are uniformly distributed between the positive active material particles, wherein the sheet-like artificial graphite establishes point-to-surface contact with the positive active material particles, enabling long-range conductivity on the electrode; the conductive carbon black SP is granular and adheres to the surface of the positive active material particles, enabling short-range conductivity. The two work together to have a good complementary effect, taking into account both long-range and short-range conductivity, maximizing the electron conduction between the positive active material particles, ensuring rapid electron transport, and improving the dispersibility between the active material and the conductive agent. Simultaneously, it improves the elongation of the positive electrode sheet. Furthermore, the K-value of artificial graphite satisfies 0.6 ≤ K < 1. Therefore, artificial graphite has a larger number of contacting positive electrode active material particles per unit length, resulting in more charge conduction sites. This effectively improves the electronic conduction between active particles, significantly enhancing its conductivity and improving electrode electronic conductivity. Consequently, it significantly reduces the contact resistance (DCR) of the positive electrode sheet, thereby reducing battery polarization and giving the positive electrode sheet superior electrical performance.

[0040] The principle by which the positive electrode proposed in this application achieves the above-mentioned beneficial effects will be explained in detail below:

[0041] In this application, artificial graphite and conductive carbon black SP are added to the positive electrode sheet. The artificial graphite and conductive carbon black SP are uniformly distributed among the positive electrode active material particles. The artificial graphite has a sheet-like structure, thus establishing point-to-surface contact with the positive electrode active material particles instead of the conventional point-to-point contact, thereby enabling long-range conductivity on the electrode. The conductive carbon black SP is granular and adheres to the surface of the positive electrode active material particles, enabling short-range conductivity. The two work synergistically, exhibiting a good complementary effect, balancing both long-range and short-range conductivity, maximizing electron conduction between the positive electrode active material particles, and ensuring rapid electron transport. This also improves the dispersion between the active material and the conductive agent, forming a multi-dimensional conductive network within the positive electrode sheet.

[0042] Meanwhile, by selecting SP and artificial graphite with excellent slip properties (such as KS-6) as conductive agents, the resistance of active material particles to slip on the surface of the current collector can be significantly reduced during electrode rolling, thereby fundamentally reducing the deformation of the current collector and improving the elongation of the positive electrode.

[0043] Furthermore, the K-value of artificial graphite satisfies 0.6 ≤ K < 1. A larger K-value indicates less bending and mixing in the artificial graphite. Therefore, artificial graphite contacts a greater number of positive electrode active material particles per unit length, resulting in more charge conduction sites. This effectively improves electron conduction between active particles, significantly enhancing its conductivity and reducing the contact resistance (DCR) of the positive electrode. Consequently, it reduces battery polarization and gives the positive electrode superior electrical performance. Simultaneously, it maximizes the role of the conductive agent, reducing its dosage and allowing for an increase in the amount of active material, thus improving battery capacity. It should be noted that a larger K-value in artificial graphite indicates less bending and mixing, meaning more positive electrode active material particles and more charge conduction sites per unit length.

[0044] It should be noted that, at a certain SEM magnification, the distance between the two endpoints of the artificial graphite along its length is denoted as 'a', as shown in the attached figure. Figure 1-4 As shown. The actual length of the artificial graphite is b, which is the length of the bent artificial graphite when unfolded.

[0045] In some preferred embodiments, the condition 0.7≤K≤0.98 is satisfied, which further limits the degree of bending and mixing of artificial graphite, thereby increasing the number of positive electrode active material particles in contact with the artificial graphite per unit length and increasing the number of charge conduction sites. This further effectively improves the electronic conduction between active particles, significantly enhances its conductivity, improves the electronic conductivity of the electrode, and thus significantly reduces the contact resistance of the positive electrode sheet.

[0046] According to some specific embodiments of this application, based on the total mass of the positive electrode active material layer being 100%, the combined mass percentage of artificial graphite and 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. Therefore, by limiting the total content of the conductive agent within the above range, the electron conduction between the positive electrode active material particles can be maximized, ensuring rapid electron transport. Preferably, based on the total mass of the positive electrode active material layer being 100%, the combined mass percentage of artificial graphite and conductive carbon black is 1.7% to 2.0%.

[0047] Furthermore, the mass ratio of artificial graphite to conductive carbon black is (1 / 4 to 2):1, for example, 1 / 4:1, 1 / 2:1, 1:1, 2:1, etc. By limiting the mass ratio of artificial graphite to conductive carbon black within the above range, the synergistic and complementary effect between the two can be further ensured, taking into account both long-range and short-range conductivity, thereby maximizing the electron conduction between the positive electrode active material particles and ensuring rapid electron transport. The inventors found that if the content of artificial graphite is too high, it will hinder the conduction of lithium ions, thus leading to a deterioration in electrode performance; if the content of artificial graphite is too low, it will result in the inability to form an effective conductive network, and the synergistic effect with SP will be poor.

[0048] According to further specific embodiments of this application, the artificial graphite is in sheet form, with a thickness of 50nm to 200nm for each sheet, such as 50nm, 70nm, 100nm, 120nm, 150nm, 170nm, 200nm, etc., and a length of 1μm to 60μm for each sheet, such as 1μm, 10μm, 20μm, 30μm, 40μm, 50μm, 60μm, etc. By limiting the thickness and length of the artificial graphite within the above ranges, it is possible to further ensure that the contact with the active material particles is a point-to-surface contact, thereby ensuring that the artificial graphite and the active material particles have more contact sites, reducing the internal resistance of the battery, improving the electronic conductivity of the electrode, and maximizing the role of the conductive agent. A further preferred thickness is 5μm to 40μm.

[0049] In the embodiments of this application, artificial graphite is an equiaxed irregular sheet-like sphere, which is different from different sheet graphene. It has a high thickness, is easy to disperse, and is easy to process. Artificial graphite has high compressibility, which can positively improve compaction. In addition, artificial graphite has good lubricity and flexibility, which can alleviate the situation where the active material separates from the current collector and conductive agent due to large volume shrinkage and expansion, forming inert single-particle "islands".

[0050] According to some specific embodiments of this application, the average particle size of conductive carbon black SP is 15nm to 65nm, for example, it can be 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, etc. By limiting the average particle size of conductive carbon black to the above range, it is possible to further ensure that conductive carbon black SP adheres to the surface of positive electrode active material particles, realize short-range conductivity, further ensure the synergistic complementary effect between conductive carbon black SP and artificial graphite, take into account both long-range conductivity and short-range conductivity, thereby maximizing the electron conduction between positive electrode active material particles and ensuring rapid electron transport.

[0051] In the embodiments of this application, the conductive carbon black SP has a small particle size and is distributed in the pores formed by the active particles, resulting in stronger liquid absorption and retention.

[0052] According to some specific embodiments of this application, in the CP cross-sectional view, the actual length of the artificial graphite and the number of positive electrode active material particles in direct contact satisfy the following: the ratio M of the number of positive electrode active material particles in direct contact with the artificial graphite to the actual length of the artificial graphite ranges from 4.5 to 7.5, where the unit of the actual length of the artificial graphite is μm, and the number of positive electrode active material particles is the count. This further ensures that the artificial graphite contacts a large number of positive electrode active material particles per unit length, resulting in more charge conduction sites. This effectively improves the electronic conduction between active particles, significantly enhancing its conductivity and improving the electrode's electronic conductivity, thereby significantly reducing the contact resistance of the positive electrode sheet.

[0053] It is understandable that the above CP cross-sectional image refers to a cross-section taken along the thickness direction of the positive electrode sheet, and then observed using SEM. The resulting SEM image is the CP cross-sectional image.

[0054] According to some specific embodiments of this application, the positive electrode active material layer further includes 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).

[0055] According to some specific embodiments of this application, the particle size Dv50 of the positive electrode active material is 0.8 μm to 1.2 μm, which is beneficial for electrolyte wetting.

[0056] In some embodiments of this application, the positive electrode current collector may include a metal foil or a composite positive electrode current collector. For example, the metal foil may be aluminum foil. The composite positive electrode current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. For example, the composite negative electrode current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0057] In some embodiments of this application, the positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0058] In a second aspect, this application provides a method for preparing the positive electrode sheet of the above embodiments. According to an embodiment of this application, the method includes:

[0059] S100: Stir and disperse artificial graphite, conductive carbon black, and the first solvent.

[0060] In this step, a shear-stirring dispersion device is used to stir and disperse artificial graphite, conductive carbon black, and the first solvent to obtain an initial slurry. The shear-stirring dispersion device can revolve and rotate, and can provide shear forces in opposite directions. Under the action of the opposite shear force, the artificial graphite in the slurry can effectively reduce the degree of bending and impurity of artificial graphite (i.e., increase the K value of artificial graphite), which is conducive to the subsequent steps to reform a conductive network with a higher effective chain density with the active material. This results in a larger number of positive electrode active material particles in contact with artificial graphite per unit length, and more charge conduction sites, thereby effectively improving the electronic conduction between active particles and significantly enhancing its conductivity. This improves the electrode's electronic conductivity, thereby significantly reducing the contact resistance of the positive electrode sheet, i.e., reducing the DCR, thus reducing the polarization of the battery and giving the positive electrode sheet superior electrical performance.

[0061] According to some specific embodiments of this application, a shear-stirring dispersion device is used to stir and disperse the surfactant, artificial graphite, conductive carbon black, and a first solvent to obtain an initial slurry. The surfactant effectively prevents the aggregation of the components, enabling the entire slurry system to construct a good three-dimensional conductive network. Furthermore, the surfactant molecules are adsorbed on the surface of the artificial graphite conductive agent, and dispersion is achieved through repulsion and intermolecular forces, thereby further reducing the degree of impurity and curling of the artificial graphite (i.e., further increasing the K value of the artificial graphite). This further facilitates the subsequent steps in reforming a conductive network with a higher effective chain density with the active material, resulting in a larger number of positive electrode active material particles in contact per unit length and more charge conduction sites. This effectively improves the electronic conduction between active particles, significantly enhancing its conductivity and improving the electrode's electronic conductivity. Consequently, the contact resistance (DCR) of the positive electrode sheet is significantly reduced, thereby reducing battery polarization and giving the positive electrode sheet superior electrical performance.

[0062] As a specific example, the surfactant can be ultrasonically dissolved in the first solvent first, and then artificial graphite and conductive carbon black can be added for premixing.

[0063] The specific types of surfactants mentioned above are not particularly limited, and those skilled in the art can select them according to the actual situation. As some preferred embodiments, the surfactants mentioned above include at least one of sodium dodecylbenzenesulfonate, sodium lignosulfonate, and hexadecyltrimethylammonium bromide.

[0064] According to some specific embodiments of this application, the mass of the surfactant is 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, it is possible to further ensure that the agglomeration of each component is effectively prevented, so that the entire slurry system can build a good three-dimensional conductive network, and the use of surfactant can further reduce the degree of impurity curling of artificial graphite.

[0065] In the embodiments of this application, by reducing the stirring speed and dispersion speed of the shear stirring dispersion device, the degree of bending and mixing of artificial graphite can be further reduced (i.e., the K value of artificial graphite is further increased), which is more conducive to the subsequent steps to reform a conductive network with a higher effective chain density with the active material. This allows the artificial graphite to contact a larger number of positive electrode active material particles and more charge conduction sites per unit length, thereby effectively improving the electronic conduction between active particles.

[0066] According to some specific embodiments of this application, in step S100, the stirring speed is 20 r / min to 30 r / min (e.g., 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 (e.g., 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 (e.g., 5 min, 6 min, 8 min, 10 min, 12 min, 15 min, etc.). By limiting the stirring speed, dispersion speed, and stirring time in step S100 to the above ranges, the effective dispersion of artificial graphite and conductive carbon black can be effectively ensured, and the degree of bending and impurity of artificial graphite can be further reduced (i.e., the K value of artificial graphite is further increased).

[0067] In the embodiments of this application, the specific type of the first solvent is not particularly limited, as long as it can achieve dispersion between the components. For example, the first solvent can be NMP.

[0068] S200: Add the positive electrode active material, positive electrode binder, and second solvent to the shearing and stirring dispersion device, and stir and disperse.

[0069] In this step, the positive electrode active material, positive electrode binder, and second solvent are added to a shear-stirring dispersion device and stirred and dispersed to obtain a positive electrode slurry. This application, by premixing the surfactant, artificial graphite, and conductive carbon black before adding the positive electrode active material and positive electrode binder, further facilitates the dispersion of artificial graphite and conductive carbon black in the slurry, further reduces the degree of bending and mixing of artificial graphite (i.e., further increases the K-value of artificial graphite), and further promotes the reformation of a conductive network with a higher effective chain density between the conductive agent and the active material.

[0070] According to some specific embodiments of this application, in step S200, 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. By limiting the stirring speed, dispersion speed, and stirring time in step S200 to the above range, it is possible to effectively ensure the effective dispersion of artificial graphite, conductive carbon black, positive electrode active material, and positive electrode binder in the slurry, and further reduce the degree of bending and mixing of artificial graphite (i.e., further increase the K value of artificial graphite).

[0071] S300: Coat the positive electrode slurry onto at least a portion of the surface of the positive electrode current collector and dry.

[0072] In this step, the positive electrode slurry is coated onto at least a portion of the surface of the positive electrode current collector and dried to obtain the positive electrode sheet.

[0073] The method for preparing the above-mentioned positive electrode sheet according to the embodiments of this application involves adding artificial graphite and conductive carbon black SP to the positive electrode slurry. The sheet-like artificial graphite establishes point-to-surface contact with the positive electrode active material particles, enabling long-range conductivity on the electrode. The conductive carbon black SP, being granular, adheres to the surface of the positive electrode active material particles, enabling short-range conductivity. The two complement each other effectively, balancing both long-range and short-range conductivity, maximizing electron conduction between the positive electrode active material particles, and ensuring rapid electron transport. This also improves the dispersibility between the active material and the conductive agent. Simultaneously, it improves the elongation of the positive electrode sheet. Furthermore, the K-value of artificial graphite satisfies 0.6 ≤ K < 1. Therefore, artificial graphite contacts a large number of positive electrode active material particles per unit length, resulting in more charge conduction sites, effectively improving electron conduction between active particles and significantly enhancing their conductivity. This improves the electrode's electronic conductivity, thereby significantly reducing the contact resistance (DCR) of the positive electrode sheet, thus reducing battery polarization and giving the positive electrode sheet superior electrical performance.

[0074] Meanwhile, this method, by providing shear forces in the opposite direction, using surfactants, reducing stirring and dispersion speeds, and premixing surfactants, artificial graphite, and conductive carbon black, can further reduce the degree of bending and mixing of artificial graphite in the slurry (i.e., further increase the K-value of artificial graphite). This further facilitates the reformation of a conductive network with a higher effective chain density between the artificial graphite conductive agent and the active material, resulting in a larger number of positive electrode active material particles in contact per unit length and more charge conduction sites. This effectively improves the electronic conduction between active particles, significantly enhancing their conductivity and improving the electrode's electronic conductivity. Consequently, it significantly reduces the contact resistance of the positive electrode, i.e., the DCR decreases, thereby reducing battery polarization and giving the positive electrode superior electrical performance.

[0075] In a third aspect, this application proposes a battery. According to an embodiment of this application, the battery has the positive electrode sheet described in the above embodiments. This effectively reduces the battery's charging and discharging internal resistance, improves battery efficiency, and enhances the battery's energy storage and release capabilities.

[0076] In the embodiments of this application, the battery described above can be either a lithium-ion battery or a sodium-ion battery. The following explanation uses a lithium-ion battery as an example.

[0077] Specifically, the lithium-ion battery includes a positive electrode, a negative electrode, and a separator as described in the above embodiments, with the separator disposed between the positive and negative electrode. During battery charging and discharging, active lithium ions repeatedly insert and extract between the positive and negative electrode. The electrolyte acts as a conductor of ions between the positive and negative electrode. The separator, disposed between the positive and negative electrode, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0078] The specific material of the diaphragm is not particularly limited. As some specific embodiments, the diaphragm includes at least one of PP diaphragm, PE diaphragm, single-sided ceramic diaphragm, double-sided ceramic diaphragm, non-woven fabric diaphragm, and glass fiber diaphragm.

[0079] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material (e.g., graphite), a negative electrode dispersant, a conductive agent, and a negative electrode binder.

[0080] The preparation method of the negative electrode sheet includes: mixing the negative electrode active material, negative electrode dispersant, conductive agent and negative electrode binder evenly according to the preset ratio, adding solvent and stirring evenly to form a negative electrode slurry, then coating it onto the current collector, drying it, and finally cutting it into a specific shape of negative electrode sheet for later use according to the different battery casings.

[0081] Cell preparation: The positive and negative electrode sheets are added to the separator and wound. After winding, the positive and negative electrode tabs are welded. Then, the bare cell is packaged in an aluminum-plastic film. After packaging, the cell is vacuum baked for 10-20 hours. Then, after liquid injection, standing, high temperature and high pressure formation, degassing and packaging, and capacity testing, a lithium-ion battery with a double-layer coated positive electrode is obtained.

[0082] A fourth aspect of this application proposes an electrical system. According to an embodiment of this application, the electrical system includes: an electrical device and an energy storage device that supplies power to the electrical device. The energy storage device includes the battery described in the above embodiments. Therefore, the electrical system possesses all the advantages of the battery, which will not be elaborated further here.

[0083] The aforementioned energy storage devices can be either the power source of the electrical equipment or the energy storage unit of the electrical equipment. These electrical equipment can include, but is not limited to, portable electronic devices such as mobile phones, tablets, laptops, desktop computers, smart bracelets, smartwatches, e-readers, and game consoles. They can also include, but are not limited to, vehicles such as cars, trucks, sedans, freight cars, bullet trains, high-speed trains, and electric vehicles. Furthermore, they can be used for various household appliances, such as, but not limited to, refrigerators, lights, and air conditioners.

[0084] In addition, the energy storage device of this application may include at least one of the following: a power energy storage device for the generation side of a power system, a power energy storage device (e.g., an electrochemical energy storage device) for the distribution side of a power system, and a power energy storage device for the user side of a power system.

[0085] It should be noted that the features and advantages described above for the battery also apply to this electrical device, and will not be repeated here.

[0086] The embodiments of this application are described in detail below. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. In addition, unless otherwise specified, all reagents used in the following embodiments are commercially available or can be synthesized according to the methods described herein or known methods. For reaction conditions not listed, they are also readily available to those skilled in the art.

[0087] Example 1

[0088] This embodiment provides a lithium-ion battery, the preparation method of which includes:

[0089] 1) First, the conductive agent (artificial graphite KS-6 and SP in a mass ratio of 1:1) and NMP solvent were premixed using a high-speed shear stirring and dispersing device to obtain an initial slurry. The stirring speed was 25 r / min, the dispersing speed was 250 r / min, and the stirring time was 10 min. Then, lithium iron phosphate powder and PVDF powder were added to the above high-speed shear stirring and dispersing device and dry-mixed at 300 r / min. After that, a certain proportion of NMP was added and kneaded. Finally, the remaining NMP was added and dispersed at 300 r / min for 3 h to obtain the positive electrode slurry. The solid content of the positive electrode slurry was about 62 wt%, and the mass ratio of lithium iron phosphate powder, PVDF powder and conductive agent was 96.62:1.48:1.90.

[0090] Then, the positive electrode slurry is coated onto the positive electrode current collector aluminum foil, with a unit area of ​​positive electrode slurry (1540.25 mm²). 2 The coating weight is 250mg. After drying, cold pressing, slitting, and cutting, the positive electrode sheet is obtained.

[0091] 2) Preparation of negative electrode sheet

[0092] Preparation of the negative electrode sheet: Artificial graphite (negative electrode active material), conductive carbon (SP), dispersant (CMC), and binder (SBR) were dispersed in deionized water at a mass ratio of 96.5:0.5:1:2 and mixed evenly to obtain a negative electrode slurry with a solid content of approximately 55%. The negative electrode slurry was then coated onto the copper foil of the negative electrode current collector. The unit area of ​​the negative electrode slurry was 1540.25 mm². 2 The coating weight is 122mg. After drying, cold pressing, slitting and cutting, the negative electrode sheet is obtained.

[0093] 3) Preparation of electrolyte

[0094] In an argon atmosphere glove box with a moisture content ≤1ppm, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a mass ratio of 1:1:1. Then, the dried electrolyte lithium salt LiPF6 was dissolved in the solvent, with LiPF6 accounting for 16% of the mass of the electrolyte.

[0095] 4) Separating membrane

[0096] A polyethylene film with a thickness of 16 micrometers was selected as the diaphragm.

[0097] 5) Battery assembly

[0098] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator in the middle of the positive and negative electrodes to separate them. After winding, a bare cell is formed. After welding the tabs, the bare cell is assembled into the outer packaging. After injecting the prepared electrolyte, the cell is packaged, left to stand, formed, shaped, and tested for capacity, and finally a lithium-ion battery is prepared.

[0099] Example 2

[0100] This embodiment provides a lithium-ion battery. The preparation method of this embodiment is basically the same as that of Embodiment 1, with the only difference being:

[0101] 1) First, the surfactant sodium dodecylbenzenesulfonate is ultrasonically dissolved in NMP solvent to form a dispersant. Then, the conductive agent (artificial graphite KS-6 and SP in a 1:1 mass ratio) and the dispersant are premixed using a high-speed shear stirring dispersion device to obtain the initial slurry. The mass of the surfactant sodium dodecylbenzenesulfonate is 1% of the initial slurry.

[0102] Example 3

[0103] This embodiment provides a lithium-ion battery. The preparation method of this embodiment is basically the same as that of Embodiment 2, except that:

[0104] The initial slurry was stirred at 20 r / min and dispersed at 100 r / min for 15 min.

[0105] Example 4

[0106] This embodiment provides a lithium-ion battery. The preparation method of this embodiment is basically the same as that of Embodiment 2, except that:

[0107] The initial slurry was stirred at 30 r / min and dispersed at 300 r / min for 5 min.

[0108] Example 5

[0109] This embodiment provides a lithium-ion battery. The preparation method of this embodiment is basically the same as that of Embodiment 2, except that:

[0110] The rotation speed of the lithium iron phosphate powder and PVDF powder after being added to the high-speed shear stirring and dispersing equipment is 500 r / min.

[0111] Example 6

[0112] This embodiment provides a lithium-ion battery. The preparation method of this embodiment is basically the same as that of Embodiment 2, except that:

[0113] The rotation speed of the lithium iron phosphate powder and PVDF powder after being added to the high-speed shear stirring and dispersing equipment is 800 r / min.

[0114] Example 7

[0115] This embodiment provides a lithium-ion battery. The preparation method of this embodiment is basically the same as that of Embodiment 2, except that:

[0116] The mass ratio of KS-6 to SP is 1 / 4:1.

[0117] Example 8

[0118] This embodiment provides a lithium-ion battery. The preparation method of this embodiment is basically the same as that of Embodiment 2, with the only difference being:

[0119] The mass ratio of KS-6 to SP is 1 / 2:1.

[0120] Example 9

[0121] This embodiment provides a lithium-ion battery. The preparation method of this embodiment is basically the same as that of Embodiment 2, except that:

[0122] The mass ratio of KS-6 to SP is 2:1.

[0123] Example 10

[0124] This embodiment provides a lithium-ion battery. The preparation method of this embodiment is basically the same as that of Embodiment 2, except that:

[0125] The mass ratio of KS-6 to SP is 4:1.

[0126] Example 11

[0127] This embodiment provides a lithium-ion battery. The preparation method of this embodiment is basically the same as that of Embodiment 2, except that:

[0128] The surfactant sodium dodecylbenzenesulfonate accounts for 2% of the initial slurry.

[0129] Example 12

[0130] This embodiment provides a lithium-ion battery. The preparation method of this embodiment is basically the same as that of Embodiment 2, except that:

[0131] The surfactant sodium dodecylbenzenesulfonate accounts for 4% of the initial slurry.

[0132] Example 13

[0133] This embodiment provides a lithium-ion battery. The preparation method of this embodiment is basically the same as that of Embodiment 11, except that:

[0134] The surfactant is a mixture of sodium dodecylbenzenesulfonate and hexadecyltrimethylammonium bromide in a mass ratio of 1:1.

[0135] Comparative Example 1

[0136] This comparative example provides a lithium-ion battery. The preparation method of this example is basically the same as that of Example 1, except that:

[0137] 1) Using a dual planetary mixing device, add lithium iron phosphate powder and PVDF powder together into a mixing tank and dry mix at 300 r / min. Then add a certain proportion of NMP for kneading, and finally add the remaining NMP for high-speed dispersion at 2000 r / min for 3 hours to form a positive electrode slurry.

[0138] Comparative Example 2

[0139] This comparative example provides a lithium-ion battery. The preparation method of this example is basically the same as that of Example 1, except that:

[0140] 1) Using a dual planetary mixing device, lithium iron phosphate powder, conductive agent SP powder, and PVDF powder are added to a mixing tank and dry-mixed at 300 r / min. Then, a certain proportion of NMP is added for kneading. Finally, the remaining NMP is added and dispersed at high speed of 2000 r / min for 3 hours to form a positive electrode slurry.

[0141] Comparative Example 3

[0142] This comparative example provides a lithium-ion battery. The preparation method of this example is basically the same as that of Example 1, except that:

[0143] 1) The conductive agent (KS-6 and SP in a mass ratio of 1:1) and NMP solvent were premixed using a high-speed shear stirring and dispersing device to obtain an initial slurry. The stirring speed was 100 r / min, the dispersing speed was 560 r / min, and the stirring time was 10 min. Subsequently, lithium iron phosphate powder and PVDF powder were added to the above high-speed shear stirring and dispersing device and dry-mixed at 300 r / min. Then, a certain proportion of NMP was added for kneading. Finally, the remaining NMP was added and dispersed at 2000 r / min for 3 h to obtain the positive electrode slurry.

[0144] SEM observations were performed on the positive electrode sheets prepared in Examples 1, 2, 11, and 13, as well as Comparative Examples 1-3. The results are as follows: Figure 1-7 As shown.

[0145] The film resistivity and electrode elongation of the positive electrode sheets prepared in Examples 1-13 and Comparative Examples 1-3 were tested respectively, and the results are shown in Table 1. The K value of artificial graphite KS-6 in the positive electrode sheets prepared in Examples 1-13 and Comparative Examples 1-3 was calculated, and the ratio M of the number of positive electrode active material particles in direct contact with artificial graphite KS-6 to the actual length of artificial graphite KS-6 was calculated, and the results are shown in Table 1.

[0146] The DCR of lithium-ion batteries prepared in Examples 1-13 and Comparative Examples 1-3 at 50% SOC charging and 50% SOC discharging were tested respectively, and the results are shown in Table 1.

[0147] The method for testing the film resistivity of the positive electrode is as follows:

[0148] Take the electrode sheet, use the controllable voltage four-wire dual-probe resistance method to control the voltage, collect the current, and obtain the resistance of the membrane (R=U / I). Then calculate the membrane resistivity of the positive electrode sheet.

[0149] The test method for the electrode elongation of the positive electrode is as follows:

[0150] Before rolling, take a positive electrode sheet approximately 1.5 meters long and lay it flat on a marble table. Use a fine ballpoint pen to draw two straight lines, 1000±200mm apart, perpendicular to the straight edge of the ceramic layer. Mark measurement points on the straight lines and in the middle area of ​​the electrode sheet with a ballpoint pen. Measure the distance D0 between the two straight line measurement points with a flexible measuring tape, estimating to 0.1mm. After rolling, lay the positive electrode sheet flat on the marble table, pressing down both ends with pressure blocks to prevent shrinkage and arching. Measure the distance D1 between the two straight line measurement points with a flexible measuring tape, estimating to 0.1mm. Then, the electrode elongation of the positive electrode sheet = (D1-D0) / D0.

[0151] The K-value of artificial graphite KS-6 was tested and calculated as follows:

[0152] The CP cross-sectional diagram was processed using SolidWorks software. The distance between the two ends of KS-6 was taken as a. The actual length b of KS-6 was calculated from the KS-6 profile curve, i.e., a / b = K.

[0153] The method for calculating the ratio M of the number of positive electrode active material particles in direct contact with artificial graphite KS-6 to the actual length of artificial graphite KS-6 is as follows:

[0154] The CP diagram was processed using SolidWorks software, and the actual length b of KS-6 was calculated from the KS-6 profile curve. The number of positive electrode active material particles that directly contacted the KS-6 point-to-surface was counted and denoted as c, i.e., c / b = M.

[0155] The test method for DCR of lithium-ion batteries at 50% SOC is as follows:

[0156] First, use 0.5P constant power charging to charge the battery from 0% SOC to 50% SOC. Then charge at 1C rate for 30 seconds, rest for 40 seconds, discharge for 30 seconds, and rest for 40 seconds. Record the starting voltage V1 of the rate charging and the ending voltage V2 of the charging rest. The charging DCR = (V2-V1) / A, where A is the current at 1C rate.

[0157] The test method for the discharge DCR of a lithium-ion battery at 50% SOC is as follows:

[0158] First, use 0.5P constant power discharge to discharge the battery from 100% SOC to 50% SOC. Then charge at 1C rate for 30 seconds, rest for 40 seconds, discharge for 30 seconds, and rest for 40 seconds. Record the discharge start voltage V3 and the discharge rest end voltage V4. Discharge DCR = (V4-V3) / A, where A is the current at 1C rate.

[0159] Table 1

[0160]

[0161]

[0162] As can be seen from Table 1, compared with Comparative Examples 1 and 2, the film resistivity and electrode elongation of the positive electrode sheets in Examples 1-13 are significantly reduced, and the DCR of the batteries at 50% SOC charging and 50% SOC discharging are significantly reduced.

[0163] As can be seen from Table 1, compared with Comparative Example 3, the K and M values ​​of artificial graphite KS-6 in the positive electrode sheets of Examples 1-13 are significantly increased, the film resistivity and electrode elongation of the positive electrode sheets of Examples 1-13 are significantly decreased, and the 50% SOC charging DCR and 50% SOC discharging DCR of the batteries of Examples 1-13 are significantly reduced. It is evident that during the formation of the initial slurry and the positive electrode slurry, reducing the stirring speed and dispersion speed of the high-speed shear stirring and dispersing equipment can reduce the degree of bending and mixing of artificial graphite KS-6 (i.e., increase the K and M values ​​of artificial graphite KS-6), thereby reducing the film resistivity and electrode elongation of the positive electrode sheet, and reducing the 50% SOC charging DCR and 50% SOC discharging DCR of the battery.

[0164] As can be seen from Table 1, compared with Example 1, the K and M values ​​of Example 2 are further increased, the resistivity of the electrode film and the elongation of the electrode are further decreased, and the DCR of 50% SOC charging and 50% SOC discharging are further decreased. It can be seen that by adding surfactants during the formation of the initial slurry and the positive electrode slurry, the degree of bending impurities of artificial graphite KS-6 can be further reduced (i.e., the K and M values ​​of artificial graphite KS-6 are increased), thereby reducing the resistivity of the positive electrode film and the elongation of the electrode, and reducing the DCR of 50% SOC charging and 50% SOC discharging of the battery.

[0165] As can also be seen from Table 1, compared with Example 10, the charge-discharge DCR of Examples 2 and 7-9 is significantly reduced, and excessive KS-6 content is not conducive to the conduction of lithium ions in the electrode.

[0166] As can be seen from Table 1, compared with Example 11, the K and M values ​​of Example 13 are further increased, the resistivity of the electrode film and the electrode elongation are further decreased, and the DCR of 50% SOC charging and 50% SOC discharging are further decreased. It can be seen that the addition of the two surfactants can enhance the dispersion effect, thereby further reducing the degree of bending impurities of artificial graphite KS-6 (i.e., increasing the K and M values ​​of artificial graphite KS-6), thereby reducing the resistivity of the positive electrode film and the electrode elongation, and reducing the DCR of 50% SOC charging and 50% SOC discharging of the battery.

[0167] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0168] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A positive electrode plate, characterized in that, include: Positive current collector; A positive electrode active material layer is disposed on at least a portion 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 endpoints of the artificial graphite along its length is a, the actual length of the artificial graphite is b, K=a / b, and 0.6≤K<1; The artificial graphite is in the form of flakes.

2. The positive electrode sheet according to claim 1, characterized in that, It satisfies 0.7≤K≤0.

98.

3. The positive electrode sheet according to claim 1, characterized in that, Based on the total mass of the positive electrode active material layer being 100%, the combined mass of the artificial graphite and the conductive carbon black accounts for 1.5% to 2.5% of the total mass. The mass ratio of the artificial graphite to the conductive carbon black is (1 / 4~2):

1.

4. The positive electrode sheet according to claim 1, characterized in that, The thickness of a single piece of artificial graphite is 50nm~200nm, and the length of a single piece of artificial graphite is 1µm~60µm.

5. The positive electrode sheet according to claim 1, characterized in that, The average particle size of the conductive carbon black is 15nm~65nm.

6. The positive electrode sheet according to claim 1, characterized in that, In the CP cross-sectional view, the actual length of the artificial graphite and the number of positive electrode active material particles in direct contact with it satisfy the following: the ratio M of the number of positive electrode active material particles in direct contact with the artificial graphite to the actual length of the artificial graphite is in the range of 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 of particles.

7. The positive electrode sheet according to any one of claims 1-6, characterized in that, The positive electrode active material layer further includes a positive electrode active material and a positive electrode binder; the mass 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, characterized in that, The particle size Dv50 of the positive electrode active material is 0.8 μm to 1.2 μm.

9. A method for preparing the positive electrode sheet according to any one of claims 1 to 8, characterized in that, include: (1) Artificial graphite, conductive carbon black and the first solvent were stirred and dispersed using a shear stirring and dispersing device to obtain an initial slurry; (2) Add the positive electrode active material, positive electrode binder and second solvent to the shearing and stirring dispersion device, stir and disperse to obtain positive electrode slurry; (3) The positive electrode slurry is coated on at least a portion of the surface of the positive electrode current collector and dried to obtain a positive electrode sheet.

10. The method according to claim 9, characterized in that, In step (1), a shear stirring and dispersing device is used to stir and disperse the surfactant, artificial graphite, conductive carbon black and the first solvent to obtain an initial slurry.

11. The method according to claim 10, characterized in that, The surfactant includes at least one of sodium dodecylbenzene sulfonate, sodium lignosulfonate, and hexadecyltrimethylammonium bromide. And / or, the mass of the surfactant is 0.5% to 4% of the initial slurry.

12. The method according to claim 10, characterized in that, 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, characterized in that, A positive electrode sheet having any one of claims 1 to 8 or a positive electrode sheet prepared by the method of any one of claims 9 to 12.

14. An electrical system, characterized in that, include: Electrical equipment, and An energy storage device that supplies power to the electrical equipment, the energy storage device comprising the battery of claim 13.

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