Negative electrode sheet, method for manufacturing the same, battery, and electric device

Abstract

The application belongs to the technical field of batteries, and specifically discloses a negative plate, a preparation method of the negative plate, a battery and a power utilization device. 3 ; Ra is an arithmetic average surface roughness of a surface of the negative material layer away from the current collector, in units of mu m; and ADW is a particle size distribution width of the negative active material, ADW = D 60 / D 30 . The negative plate has a structure of high porosity on the surface and high compaction in the interior, so that the lithium ion transmission path on the surface of the negative plate is smoother, the liquid phase and the solid phase kinetics of the negative plate are balanced, and the cycle life and the rate performance of the battery are considered.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to negative electrode sheets and their preparation methods, batteries, and electrical devices. Background Technology

[0002] Lithium-ion batteries have gradually become the mainstream power batteries due to their excellent energy density, high safety performance, low cost and long life. In recent years, people have been demanding higher and higher power density and energy density of lithium-ion batteries. However, power density and energy density are the competitive advantages of batteries. At present, balancing the rate performance and cycle life of batteries is one of the important challenges facing batteries. Summary of the Invention

[0003] This application aims to at least partially address one of the technical problems in the related art. Therefore, one objective of this application is to provide a negative electrode sheet and its preparation method, a battery, and an electrical device, wherein the negative electrode sheet enables the battery to simultaneously possess excellent rate performance and cycle life.

[0004] A first aspect of this application provides a negative electrode sheet, comprising: a current collector and a negative electrode material layer disposed on at least one side of the current collector, the negative electrode material layer comprising a negative electrode active material, the negative electrode sheet satisfying:

[0005] 0.5≤ρ×Ra / ADW≤2.7,

[0006] Where ρ is the compaction density of the negative electrode material layer, in g / cm³. 3 Ra is the arithmetic mean surface roughness of the surface of the negative electrode material layer away from the current collector, in μm; ADW is the particle size distribution width of the negative electrode active material, ADW=D 60 / D 30 D 60 The particle size value, in μm, corresponds to the cumulative distribution of the negative electrode active material reaching 60%. 30 The particle size, expressed in μm, corresponds to a cumulative distribution of 30% of the negative electrode active material. This negative electrode synergistically considers the electrode surface state, the compaction density of the electrode sheet, and the particle size distribution width of the active material, optimizing the structure of the negative electrode sheet to obtain an ideal electrode structure with high surface porosity and high internal compaction. This fully leverages the coupling effect among the three factors, effectively alleviating the problem of overpressure on the electrode surface, achieving efficient lithium ion transport on the electrode surface, and adapting to the ion conduction of the internal electrode structure. It balances the liquid and solid phase kinetics of the electrode sheet, taking into account both the rate performance and cycle life of the battery.

[0007] In addition, the negative electrode sheet according to the above embodiments of this application may also have the following additional technical features:

[0008] In some embodiments, 0.8 ≤ ρ × Ra / ADW ≤ 2.1. This helps to further improve the surface compaction and overall compaction distribution of the negative electrode, promotes lithium-ion transport on the surface, and thus further improves the rate performance and cycle life of the battery.

[0009] In some embodiments, the negative electrode meets at least one of the following conditions:

[0010] 5μm≤D 30 ≤12μm;

[0011] 10μm≤D 60 ≤18μm;

[0012] 1.05≤ADW≤2.8;

[0013] 0.5μm≤Ra≤2.4μm;

[0014] 1.32g / cm 3 ≤ρ≤1.8g / cm 3 .

[0015] This can improve the uniformity of the negative electrode active material, reducing the resistance to ion transport within a reasonable range, thus helping to obtain a negative electrode sheet with an ideal structure.

[0016] In some embodiments, the negative electrode meets at least one of the following conditions:

[0017] The negative electrode active material includes at least one of graphite, hard carbon, mesophase microspheres, silicon-carbon materials, silicon-oxygen materials, and elemental silicon.

[0018] The negative electrode material layer further includes a conductive agent, which includes at least one of SuperP, carbon black, graphene, and carbon nanotubes.

[0019] The negative electrode material layer further includes an adhesive, which includes at least one of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, and carboxymethyl chitosan.

[0020] The negative electrode material layer also includes a thickener, which includes sodium carboxymethyl cellulose.

[0021] This helps to improve the capacity and cycle performance of the negative electrode, further optimize the structure of the negative electrode, and thus significantly improve the rate performance and cycle stability of the battery.

[0022] A second aspect of this application discloses a method for preparing a negative electrode sheet, comprising: mixing a negative electrode material layer raw material and a solvent to obtain a negative electrode slurry; coating the negative electrode slurry onto at least one side of a current collector, and drying and rolling it to obtain a negative electrode sheet. Therefore, this preparation method is simple and easy to operate.

[0023] In some embodiments, the viscosity of the negative electrode slurry is 2000 mPa·s to 3000 mPa·s. This helps to ensure the uniformity of the slurry and the uniformity of the coating, resulting in a uniform and structurally stable negative electrode sheet.

[0024] In some embodiments, coating the negative electrode slurry onto at least one side of the current collector and then drying and rolling it includes: coating a portion of the negative electrode slurry onto at least one side of the current collector, and performing a first drying and a first rolling to form a first negative electrode material layer on the current collector; coating the remaining negative electrode slurry onto the side of the first negative electrode material layer away from the current collector, and performing a second drying and a second rolling to form a second negative electrode material layer, thereby obtaining the negative electrode sheet. This helps to prepare a negative electrode sheet with high surface porosity and high internal compaction.

[0025] In some embodiments, the above method satisfies at least one of the following conditions:

[0026] The ratio P of the areal density of the first negative electrode material layer to the areal density of the negative electrode material layer satisfies: 0 < P < 100%, specifically 20% ≤ P ≤ 100%;

[0027] The ratio Q of the compaction density of the first negative electrode material layer to the compaction density of the negative electrode material layer satisfies: 0.78 ≤ Q ≤ 1.17. This helps to obtain a structure with high surface porosity and high internal compaction, thereby making the lithium-ion transport pathway on the surface smoother and highly matched with the internal structure of the negative electrode material layer, thus improving the rate performance and cycle life of the battery.

[0028] A third aspect of this application provides a battery comprising the aforementioned negative electrode or a negative electrode prepared by the aforementioned method. Therefore, the battery exhibits excellent rate performance and cycle life.

[0029] A fourth aspect of this application provides an electrical device including the aforementioned battery. Therefore, this electrical device possesses excellent battery life and load capacity, as well as excellent fast charging capability and a long service life. Detailed Implementation

[0030] The embodiments of this application are described in detail below. The embodiments described below are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0031] This application is based on the inventor's following discoveries and understandings:

[0032] With the continuous improvement of fast charging performance in electric vehicles, range and fast charging capabilities have gradually become the focus of users, and are one of the key elements for electric vehicles to rival gasoline vehicles. To improve battery range, thick electrode designs are used in related technologies. However, the kinetic performance of thick electrodes mainly depends on their liquid phase transport capabilities, which are closely related to the electrode structure. Currently, power batteries are prone to lithium deposition on the electrode surface when charging at high rates, making it impossible to balance rate performance and cycle life, thus affecting the range and fast charging capabilities of electric vehicles. The inventors have found that current research focuses mainly on electrode compaction and particle arrangement, lacking research on electrode surface states and the interaction between electrode density and surface states at the interface.

[0033] Specifically, the inventors discovered through in-depth research that lithium deposition on the electrode surface during high-rate charging is due to the presence of an overpressure structure on the electrode surface. In other words, the dense closed-pore structure on the electrode surface hinders the liquid-phase transport of lithium ions, resulting in a large accumulation of lithium ions on the surface. The root cause is the mismatch between the pore pathways on the electrode surface and the pore structure inside the electrode.

[0034] Based on the above understanding, the inventors, taking into account the electrode surface condition, the compaction density of the electrode sheet, and the particle size distribution of the active material, optimized the structure of the electrode sheet, obtaining a more ideal electrode sheet structure with high surface porosity and high internal compaction. This fully leverages the coupling effect between the three, thereby alleviating the problem of overpressure on the electrode surface and achieving efficient lithium ion transport on the electrode surface. At the same time, it matches the internal structure and mass transfer force, resulting in good electrode uniformity. The performance of both the surface and internal structures can be fully utilized, balancing rate performance and cycle life.

[0035] A first aspect of this application provides a negative electrode sheet, comprising: a current collector and a negative electrode material layer disposed on at least one side of the current collector, the negative electrode material layer comprising a negative electrode active material, and the negative electrode sheet satisfying: 0.5 ≤ ρ × Ra / ADW ≤ 2.7. Wherein, ρ is the compaction density of the negative electrode material layer, in g / cm³. 3 Ra is the arithmetic mean surface roughness of the surface of the negative electrode material layer away from the current collector, in μm; ADW is the particle size distribution width of the negative electrode active material, ADW=D 60 / D 30 D 60 The particle size value, in μm, corresponds to the cumulative distribution of the negative electrode active material reaching 60%. 30 The particle size value is the value corresponding to the cumulative distribution of the negative electrode active material reaching 30%, in μm.

[0036] The inventors of this application comprehensively considered the interaction between various factors affecting battery performance and obtained an ideal negative electrode structure mainly through the synchronous optimization of the surface roughness of the negative electrode sheet, the particle size distribution of the negative electrode active material, and the negative electrode material layer.

[0037] Specifically, the arithmetic mean surface roughness Ra of the negative electrode material layer away from the current collector refers to the unevenness of the surface of the negative electrode material layer away from the current collector. It is related to the surface compaction of the negative electrode material layer and the uniformity of the particle size distribution of the negative electrode active material. In this paper, in order to make the surface roughness of the negative electrode material layer away from the current collector a parameter describing the overpressure state of the negative electrode sheet, the arithmetic mean roughness of the surface of the negative electrode material layer away from the current collector is normalized according to the particle size distribution width of the active material, i.e., Ra / ADW. The normalized Ra / ADW can reflect the surface compaction of the negative electrode material layer. If the value of Ra / ADW is too small, it means that the surface of the negative electrode material layer is too smooth, indicating that the surface particle compaction of the negative electrode material layer is too high, which will lead to surface overpressure and thus affect the entry of active ions into the interior of the negative electrode sheet. If the value of Ra / ADW is too large, it means that the surface roughness of the negative electrode material layer is too high, the surface particle compaction is low and the distribution uniformity is poor, which will affect the energy density of the battery.

[0038] Furthermore, to control the surface overpressure caused by an excessively small Ra / ADW value and the low energy density caused by an excessively large Ra / ADW value, it is necessary to regulate the compaction density ρ of the negative electrode material layer. The product of the compaction density ρ and Ra / ADW (i.e., ρ×Ra / ADW) should be controlled within a reasonable range to ensure a reasonable distribution of surface compaction and overall compaction of the negative electrode sheet, achieving an ideal state. That is, by controlling 0.5≤ρ×Ra / ADW≤2.7, the negative electrode sheet can have a more ideal structure of high porosity on the upper layer and high compaction on the lower layer, balancing the liquid and solid phase dynamics of the negative electrode sheet and taking into account both the rate performance and cycle life of the battery. If the value of ρ×Ra / ADW is too large, it indicates that the surface mass transfer resistance of the negative electrode is much lower than the overall mass transfer resistance. The waste of surface pores and excessive surface roughness will lead to uneven current density distribution, resulting in uneven electrochemical reaction and ultimately affecting the battery capacity and cycle performance. If the value of ρ×Ra / ADW is too small, it indicates that the surface of the negative electrode is too flat. Such a surface state often corresponds to a dense closed-pore stacking structure. The surface mass transfer resistance is much higher than the overall mass transfer resistance, i.e., a severe surface overpressure situation, which will degrade the liquid phase transport of active ions and ultimately lead to poor battery kinetic performance.

[0039] For example, the specific value of ρ×Ra / ADW can be 0.5, 0.8, 1, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6, 2.7, or any two of these ranges. Within the above range, the surface compaction and overall compaction of the negative electrode are reasonably distributed, giving the negative electrode a structure with high surface porosity and high internal compaction. This makes the lithium-ion transport pathways on the surface more unobstructed and adapts to the active ion conduction of the internal structure of the negative electrode. This helps to balance the liquid and solid phase kinetics of the negative electrode, resulting in batteries using this negative electrode exhibiting excellent rate performance and cycle life.

[0040] In this article, ρ represents the compaction density of the negative electrode material layer. Compaction density is a physical parameter that measures the mass of a unit volume of a loose solid material (negative electrode active material) after it has been compacted under external pressure. Essentially, it reflects the degree to which the voids between material particles are compressed. The average thickness of the negative electrode material layer can be measured and calculated using a micrometer. By calculating the ratio of surface density to thickness, the compaction density of the negative electrode material layer can be obtained.

[0041] In some embodiments, 1.32 g / cm 3 ≤ρ≤1.8g / cm 3 Specifically, it can be 1.32 g / cm³. 3 1.4g / cm 3 1.45g / cm 3 1.5g / cm 3 1.6g / cm 3 1.65g / cm 3 1.7g / cm 3 1.75g / cm 3 1.8g / cm 3 Or a range between or any two of these. A compaction density of the negative electrode material layer within the above range helps optimize the structure of the negative electrode sheet, promotes the transport of active ions, and improves the rate performance and cycle life of the battery.

[0042] In this paper, Ra represents the arithmetic mean surface roughness of the surface of the negative electrode material layer away from the current collector. The test can be performed as follows: Wipe the surface of the negative electrode material layer and the test platform of the precision roughness tester (model SPR1103G-sak) clean with a lint-free cloth. Place the negative electrode sheet stably on the test platform, ensuring there is no shaking or tilting in the contact area between the negative electrode sheet and the probe. Set the probe position to automatically adjust, allowing the probe to gently contact the surface of the negative electrode sheet. Set the measurement length of the negative electrode sheet surface to 6 mm, and directly measure Ra, which is the arithmetic mean surface roughness of the surface of the negative electrode material layer away from the current collector.

[0043] In some embodiments, 0.5 μm ≤ Ra ≤ 2.4 μm, specifically, it can be a range of 0.5 μm, 0.8 μm, 1.0 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm, 2.2 μm, 2.4 μm, or any two of these ranges. Ra being within the above range helps to keep the surface roughness of the negative electrode material layer away from the current collector within a reasonable range, thereby helping to promote reasonable surface compaction and overall compaction distribution of the negative electrode sheet, optimizing the structure of the negative electrode sheet, and improving the electrochemical performance of the battery.

[0044] In this paper, ADW represents the particle size distribution width of the negative electrode active material, which can be tested as follows: A flat cross-section is obtained by ion cutting the central region of the negative electrode material layer, and a SEM image of the cross-section is acquired. Further, the image is imported into ImageJ image recognition software: the pixel size is input, the main area image is cropped, threshold segmentation is performed for grayscale conversion, and obvious non-target feature noise is removed based on area and shape parameters, followed by particle size statistics. 30 D refers to the particle size corresponding to a cumulative volume of all particles in the sample reaching 30%. 60 This refers to the particle size corresponding to a cumulative volume of all particles in the sample reaching 60%. Then, it is calculated using ADW=D 60 / D 30 The particle size distribution width of the negative electrode active material was calculated. Specifically, ADW focuses on the uneven particle distribution in the middle section of the negative electrode active material, and is not sensitive to the maximum and minimum particle sizes, resulting in relatively more stable data.

[0045] In some embodiments, 1.05 ≤ ADW ≤ 2.8. Exemplarily, ADW can be a range of 1.05, 1.1, 1.3, 1.5, 1.7, 1.9, 2.1, 2.3, 2.5, 2.6, 2.8, or any two of these ranges. ADW within the above range helps to make the particle size distribution of the negative electrode active material more uniform, reduces the resistance to ion transport, and further promotes a uniform and efficient transport process of active ions, thereby improving the electrochemical performance of the battery.

[0046] In some embodiments, 5μm≤D 30 ≤12μm, specifically, D 30 It can be 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, or any range between two of them. D 30 Within the aforementioned range, it helps to control the particle size of the negative electrode active material within a suitable range, which can not only improve the uniformity of the particles of the negative electrode active material, but also control the ADW of the negative electrode active material within a reasonable range, thereby helping to obtain a negative electrode sheet with excellent performance.

[0047] In some embodiments, 10μm≤D60 ≤18μm, specifically, D 60 It can be 10μm, 11μm, 12μm, 3μm, 14μm, 15μm, 16μm, 17μm, 18μm, or any range between two of them. 60 Within the aforementioned range, it helps to control the particle size of the negative electrode active material within a suitable range, which can not only improve the uniformity of the particles of the negative electrode active material, but also control the ADW of the negative electrode active material within a reasonable range, thereby helping to obtain a negative electrode sheet with excellent performance.

[0048] In some embodiments, the value of ρ×Ra / ADW can be from 0.8 to 2.1. Exemplarily, it can be 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, or any combination thereof. A value of ρ×Ra / ADW within the above range helps to further improve the surface compaction and overall compaction distribution of the negative electrode, thereby further improving the energy density and power density of the battery.

[0049] In some embodiments, the negative electrode active material includes at least one selected from graphite, hard carbon, mesophase microspheres, silicon-carbon materials, silicon-oxygen materials, and elemental silicon. These negative electrode active materials exhibit high specific capacity and excellent cycle performance, which is beneficial for improving the rate performance and cycle stability of the battery.

[0050] In some embodiments, the negative electrode material layer further includes a conductive agent, which includes at least one selected from SuperP, carbon black, graphene, and carbon nanotubes. The aforementioned conductive agent can form dense conductive contact points between the negative electrode active material particles, helping to reduce the internal resistance of the negative electrode sheet, improve electron transport efficiency, and thus enhance the rate performance of the battery.

[0051] In some embodiments, the negative electrode material layer further includes an adhesive, said adhesive comprising at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS). This helps to improve the adhesion of the negative electrode material layer, enhance the structural stability of the negative electrode sheet, and prevent problems such as material shedding.

[0052] In some embodiments, the negative electrode material layer further includes a thickener, which includes sodium carboxymethyl cellulose (CMC). Using the aforementioned thickener helps improve the stability of the negative electrode material layer, thereby helping to optimize the electrode structure, making lithium-ion transport smoother, and improving the electrochemical performance of the battery.

[0053] A second aspect of this application discloses a method for preparing a negative electrode sheet, comprising:

[0054] S10: Mix the raw materials and solvent of the negative electrode material layer to obtain the negative electrode slurry.

[0055] In this step, there are no particular restrictions on the specific method of mixing the raw materials and solvent for the negative electrode material layer; it can be flexibly selected as needed. For example, the raw materials and solvent for the negative electrode material layer can be mixed and stirred, or mixed using a mixer to obtain the negative electrode slurry.

[0056] In some embodiments, the raw materials for the negative electrode material layer can be negative electrode active materials, conductive agents, thickeners, and binders, and the negative electrode active materials, conductive agents, thickeners, and binders can be consistent with those described above, and will not be repeated here.

[0057] In some embodiments, the solvents described above are not limited, and different solvents may be selected according to actual needs. As an example, the solvent may be water, N-methylpyrrolidone (NMP), etc.

[0058] In some embodiments, the mass ratio of the negative electrode active material, conductive agent, thickener, and binder can be 94~98:1~2:0.5~1.5:1.15~1.63. Maintaining the mass ratio of the negative electrode active material, conductive agent, thickener, and binder within the above range helps to obtain a negative electrode slurry with excellent conductivity, which in turn helps to obtain a negative electrode sheet with excellent structure through subsequent steps.

[0059] In some embodiments, the viscosity of the negative electrode slurry is 2000 mPa·s to 3000 mPa·s. Specifically, the viscosity of the negative electrode slurry can be 2000 mPa·s, 2100 mPa·s, 2200 mPa·s, 2300 mPa·s, 2400 mPa·s, 2500 mPa·s, 2600 mPa·s, 2700 mPa·s, 2800 mPa·s, 2900 mPa·s, 3000 mPa·s, or any range between two of these. The viscosity of the negative electrode slurry can be controlled by the amount of solvent used. Viscosity within the above range helps to ensure the uniformity of the slurry and the uniformity of the coating, which helps to obtain a uniform and structurally stable negative electrode sheet.

[0060] In this study, the viscosity of the negative electrode slurry was determined by quickly transferring the slurry sample from the mixing tank to the measuring container, taking care to avoid air bubbles. The sample was then allowed to stand at a constant temperature of 25℃±0.5℃ for 3 minutes to ensure temperature stability. The rotor was then immersed in the slurry up to the designated mark, and the viscometer was started. After the reading stabilized, the viscosity value was recorded, and the average value was taken from three measurements.

[0061] S20: The negative electrode slurry is coated on at least one side of the current collector, and then dried and rolled to obtain a negative electrode sheet.

[0062] In this step, the negative electrode slurry can be coated onto at least one side of the current collector in one go, or it can be coated onto at least one side of the current collector in several stages.

[0063] In some embodiments, the multi-coating process may include: coating a portion of the aforementioned prepared negative electrode slurry onto at least one side of the current collector, and performing a first drying and a first rolling process to form a first negative electrode material layer on the current collector; then coating the remaining negative electrode slurry onto the side of the first negative electrode material layer away from the current collector, and performing a second drying and a second rolling process to form a second negative electrode material layer, thereby obtaining a negative electrode sheet.

[0064] According to the embodiments of this application, there are no particular limitations on the specific operations of drying and rolling, and they can be flexibly adjusted and selected according to actual needs.

[0065] In some embodiments, the ratio P of the areal density of the first negative electrode material layer to the areal density of the negative electrode material layer satisfies: 0 < P < 100%, specifically 20% ≤ P ≤ 100%. For example, P can be 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, or any two of these ranges. P within the above range helps to obtain a structure with high surface porosity and high internal compaction, thereby making the lithium-ion transport pathways on the surface more unobstructed, and thus improving the energy density and power density of the battery.

[0066] In some embodiments, the ratio Q of the compaction density of the first negative electrode material layer to the compaction density of the negative electrode material layer satisfies: 0.78 ≤ Q ≤ 1.17, where Q can specifically be 0.78, 0.8, 0.85, 0.9, 0.95, 1.0, 1.05, 1.1, 1.15, 1.17, or any two of these ranges. Q within this range helps to obtain a structure with high surface porosity and high internal compaction, thereby making the lithium-ion transport pathways on the surface more unobstructed, and thus improving the energy density and power density of the battery.

[0067] It is understood that in the above preparation method, the negative electrode sheet can satisfy 0.5≤ρ×Ra / ADW≤2.7 by adjusting the type and particle size of the negative electrode active material, the steps in the preparation process, and specific parameters (including but not limited to coating method, coating parameters, rolling parameters, etc.).

[0068] In a third aspect, this application proposes a battery comprising the aforementioned negative electrode. This battery exhibits excellent energy density and power density.

[0069] According to the embodiments of this application, it can be understood that the specific type of battery is not particularly limited, and it can be a primary battery or a secondary battery; the shape of the battery can be a cylindrical battery, a square battery, or other batteries of any shape, and according to the outer packaging, the battery can be a hard-shell battery, a soft-pack battery, etc. In other embodiments, the battery can be a lithium-ion battery, a sodium-ion battery, etc.

[0070] Typically, a battery includes a positive electrode, a negative electrode (mentioned above), an electrolyte, and a separator. The positive electrode, negative electrode, and separator can be manufactured into a cell using winding or stacking processes. The cell and electrolyte can be housed in an outer package. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and extracting. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0071] The positive electrode in the battery may include a positive current collector and a positive active material layer, wherein the positive active material layer is disposed on at least one surface of the positive current collector.

[0072] In some embodiments, the positive current collector can be a metal current collector or a composite current collector. For example, metal current collectors include, but are not limited to, aluminum foil current collectors; composite current collectors may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. Composite current collectors can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0073] In some embodiments, the positive electrode active material layer may include positive electrode active material, binder and conductive agent, and may also include additives with specific functions and effects, such as thickeners, sodium supplements, film-forming additives, flame retardants, high temperature / low temperature stabilizers, etc., as needed.

[0074] As an example, positive electrode active materials may include lithium nickel cobalt manganese oxide (including but not limited to NCM811, NCM613, NCM523, etc.), lithium cobalt oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium manganese oxide, lithium nickel manganese oxide, lithium-rich manganese-based materials, or positive electrode active materials commonly used in the art.

[0075] As an example, the binder in the positive electrode active material layer 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.

[0076] As an example, the conductive agent in the positive electrode active material layer may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0077] According to embodiments of this application, the electrolyte may include lithium salt and solvent. Furthermore, additives with specific functions, such as film-forming additives, lithium replenishing agents, flame retardants, thermal stability additives, etc., may also be added to the electrolyte as needed. As an example, the electrolyte may include lithium salt, solvent, and additives.

[0078] According to embodiments of this application, lithium salts may include lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate, etc. Lithium salts can provide lithium ions to lithium-ion batteries, support electrolyte stability and electrochemical reactions, contribute to the formation of a protective SEI film, improve conductivity, and enhance the safety of lithium-ion batteries.

[0079] According to embodiments of this application, the solvent may include carbonates, fluorocarbonates, etc. This allows for the thorough dissolution of lithium salts, provides an ion transport medium, and also helps improve the electrochemical and safety performance of lithium-ion batteries.

[0080] According to the embodiments of this application, the battery can be a single cell, a battery module, or a battery pack. The specific structure of the battery module or battery pack is not particularly limited and can be carried out with reference to conventional techniques in the art.

[0081] A fourth aspect of this application provides an electrical device. According to an embodiment of this application, the electrical device includes the battery described above. This electrical device has excellent battery life, excellent fast charging capability, and a long service life.

[0082] According to embodiments of this application, the specific type of electrical device is not particularly limited and can be any device that uses a battery as a power source or energy storage unit. As examples, electrical devices include, but are not limited to, electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), mobile terminals (e.g., mobile phones, laptops, game consoles, wearable devices, etc.), drones, aerospace equipment, satellites, ships, energy storage systems, etc.

[0083] It is understood that, in addition to the battery mentioned above, the electrical device also includes other necessary structures and components, all of which can be made with reference to conventional technologies. For example, an electric vehicle may include a body, chassis, tires, navigation system, radar system, steering system, braking system, lubrication system, cooling system, driving system, etc., which will not be described in detail here.

[0084] The present application will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present application in any way. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in the art or in accordance with the product manual.

[0085] Example 1

[0086] Negative electrode slurry preparation: A slurry was prepared by mixing graphite (negative electrode active material), SuperP (conductive agent), CMC (thickener), and SBR (binder) in a mass ratio of 96:1.5:1:1.5. After thorough dispersion, water was added to adjust the slurry viscosity to 2500 mPa·s. The D content of the negative electrode active material... 30 9μm, D 60 The value is 12 μm, and the ADW is 1.33.

[0087] Negative electrode preparation: Using a 6μm thick copper foil as the current collector, a portion of the aforementioned negative electrode slurry (first slurry) is coated onto one surface of the copper foil to form a first slurry layer. The coating is then dried at 120°C and subjected to a first rolling process to form a first negative electrode material layer with an areal density of 110 mg / cm³. 2 The compacted density ρ1 is 1.6 g / cm³. 3 The remaining negative electrode slurry is then coated onto the surface of the first negative electrode material layer away from the copper foil to form a second slurry layer. This layer is then dried a second time at 120°C and subjected to a second rolling process to form a second negative electrode material layer with an areal density of 110 mg / cm³. 2 The compaction density ρ of the negative electrode material layer is 1.57 g / cm³. 3 This yields the negative electrode.

[0088] Preparation of electrolyte: Ethyl carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of EC:EMC:DEC=1:1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 was dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0089] Preparation of the positive electrode sheet: The positive electrode active material (LFP), conductive agent (carbon black), and binder (PVDF) were mixed in a mass ratio of 96.8:1.5:1.7. The mixture was first dry-mixed, then a suitable amount of solvent was added for wet mixing to obtain the positive electrode slurry. The solid content of the positive electrode slurry was controlled to be 65%. Further, the positive electrode slurry was coated onto a 14μm thick carbon-coated aluminum foil (where the aluminum foil thickness was 12 micrometers, and each side of the aluminum foil was coated with a 1-micrometer thick carbon layer), resulting in a double-sided areal density of 40 mg / cm³ for the positive electrode sheet. 2The positive electrode sheet is dried and rolled at 120℃ to achieve a compaction density of 2.30 g / cm³. 3 The prepared positive electrode sheet is die-cut according to the cell size and placed in a nitrogen oven at 100℃ for later use.

[0090] Battery fabrication: The above-mentioned negative electrode and positive electrode are stacked using a stacking process, in the order of PP separator, negative electrode, PP separator, positive electrode, PP separator, negative electrode. After vacuum baking at 105℃ for 12 hours, electrolyte is injected and the battery is encapsulated.

[0091] Examples 2-23

[0092] Similar to Example 1, the main differences are shown in Table 1. Specifically, Examples 11-16 employ a single coating process to form the negative electrode material layer, as follows: A negative electrode slurry is coated onto one surface of a copper foil to form a slurry layer, dried at 120°C, and then rolled to form the negative electrode material layer with an areal density of 220 mg / cm³. 2 A negative electrode sheet is obtained.

[0093] Comparative Examples 1-2

[0094] Same as Example 11, the main differences are shown in Table 1.

[0095] Comparative Examples 3-4

[0096] Same as Example 1, the main differences are shown in Table 1.

[0097] Detection methods

[0098] Room temperature cycling: Place the battery in an ambient temperature chamber (25℃) and let it rest for 4 hours before performing charge-discharge cycles. Discharge to 2.0V at 1 / 3C constant current and let it rest for 30 minutes; charge to 3.8V at 0.5C constant current and let it rest for 5 minutes; charge to 3.8V at 0.1C constant current and let it rest for 30 minutes; discharge to 2.0V at 0.5C constant current and let it rest for 30 minutes. Repeat the above steps until 1000 cycles are completed, and calculate the capacity retention rate.

[0099] Fast charging cycle: Capacity retention test of lithium-ion battery after 500 fast charging cycles: The prepared lithium-ion batteries were tested according to the following steps:

[0100] S1: Discharge to 2.0V at a constant current of 1 / 3C and let stand for 30 minutes;

[0101] S2: Charged at 4C constant current for 0.73 minutes, cutoff voltage 3.8V;

[0102] S3: Charged at a constant current of 3.5C for 1.18 minutes, cutoff voltage 3.8V;

[0103] S4: Charged at 3C constant current for 1.38 minutes, cutoff voltage 3.8V;

[0104] S5: Charged at a constant current of 2.5C for 1.66 minutes, cutoff voltage 3.8V;

[0105] S6: Charged at 2C constant current for 2.07 minutes, cutoff voltage 3.8V;

[0106] S7: Charged at 1.5C constant current for 2.76 minutes, cutoff voltage 3.8V;

[0107] S8: Charged at 1C constant current for 24.35 minutes, cutoff voltage 3.8V;

[0108] S9: Charge to 3.8V with a constant current of 1 / 3C, then let stand for 10 minutes;

[0109] S10: Discharge at a constant current of 1C to 2.0V and let stand for 10 minutes;

[0110] S11: Discharge at a constant current of 1 / 3C to 2.0V, let stand for 30 minutes, and record the discharge capacity of S10 as R10 and the discharge capacity of S11 as R11. The total discharge capacity is R1 = R10 + R11. Repeat the above steps 500 times, and record the discharge capacity of S10 as R20 and the discharge capacity of S11 as R21 after 500 cycles. The total discharge capacity is R2 = R20 + R21. The capacity retention rate of the lithium-ion battery after 500 fast charging cycles is R2 / R1 × 100%.

[0111] Liquid phase diffusion impedance test: The two negative electrode sheets and the separator were assembled sequentially into an electrode core; the electrode core was placed in the outer packaging shell, baked, and injected with the electrolyte. After encapsulation and wetting processes, a liquid phase diffusion impedance battery was obtained. Liquid phase diffusion impedance tests were performed using an electrochemical workstation (model: EC-LAB VMP-300) in the frequency range of 300000Hz-0.05Hz. The obtained curves were processed and calculated using Zview, and then linearly fitted based on the near-linear curves to obtain the slope and intercept. These were substituted into the formula Rion=3×(-intercept / slope-Rs), where Rs is the contact impedance obtained using Zview software, to calculate the negative electrode liquid phase diffusion impedance Rion.

[0112] Table 1

[0113]

[0114] The test results of the above embodiments and comparative examples are shown in Table 2.

[0115] Table 2

[0116]

[0117] As shown in Table 2 above, the negative electrode meets the condition 0.5≤ρ×Ra / ADW≤2.7, which indicates good liquid phase mass transfer capability, thus giving the battery good cycle stability and rate performance.

[0118] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is 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.

[0119] 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 negative electrode sheet, characterized in that, include: A current collector and a negative electrode material layer disposed on at least one side of the current collector, the negative electrode material layer comprising a negative electrode active material, the negative electrode sheet satisfying: 0.5≤ρ×Ra / ADW≤2.7, Where ρ is the compaction density of the negative electrode material layer, in g / cm³. 3 Ra is the arithmetic mean surface roughness of the surface of the negative electrode material layer away from the current collector, in μm; ADW is the particle size distribution width of the negative electrode active material, ADW=D 60 / D 30 D 60 The particle size value, in μm, corresponds to the cumulative distribution of the negative electrode active material reaching 60%. 30 The particle size value is the value corresponding to the cumulative distribution of the negative electrode active material reaching 30%, in μm. The negative electrode plate satisfies: 5μm≤D 30 ≤12μm; 10μm≤D 60 ≤18μm; 1.05≤ADW≤2.8; 0.5μm≤Ra≤2.4μm; 1.32g / cm 3 ≤ρ≤1.8g / cm 3 。 2. The negative electrode sheet according to claim 1, characterized in that, 0.8≤ρ×Ra / ADW≤2.

1.

3. The negative electrode sheet according to claim 1, characterized in that, At least one of the following conditions must be met: The negative electrode active material includes at least one of graphite, hard carbon, mesophase microspheres, silicon-carbon materials, silicon-oxygen materials, and elemental silicon. The negative electrode material layer further includes a conductive agent, which includes at least one of SuperP, carbon black, graphene, and carbon nanotubes. The negative electrode material layer further includes an adhesive, which includes at least one of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, and carboxymethyl chitosan. The negative electrode material layer also includes a thickener, which includes sodium carboxymethyl cellulose.

4. A method for preparing the negative electrode sheet according to any one of claims 1 to 3, characterized in that, include: The raw materials for the negative electrode material layer and the solvent are mixed to obtain the negative electrode slurry; The negative electrode slurry is coated on at least one side of the current collector, and then dried and rolled to obtain a negative electrode sheet.

5. The method according to claim 4, characterized in that, The viscosity of the negative electrode slurry is 2000 mPa·s to 3000 mPa·s.

6. The method according to claim 4 or 5, characterized in that, The negative electrode slurry is coated onto at least one side of the current collector, and then dried and rolled, comprising: A portion of the negative electrode slurry is coated onto at least one side of the current collector, and subjected to a first drying and a first rolling process to form a first negative electrode material layer on the current collector; The remaining negative electrode slurry is coated onto the side of the first negative electrode material layer away from the current collector, and then subjected to a second drying and a second rolling process to form a second negative electrode material layer, thereby obtaining the negative electrode sheet.

7. The method according to claim 6, characterized in that, At least one of the following conditions must be met: The ratio P of the areal density of the first negative electrode material layer to the areal density of the negative electrode material layer satisfies: 0 < P < 100%; The ratio Q of the compaction density of the first negative electrode material layer to the compaction density of the negative electrode material layer satisfies: 0.78≤Q≤1.

17.

8. The method according to claim 7, characterized in that, The ratio P of the areal density of the first negative electrode material layer to the areal density of the negative electrode material layer satisfies: 20% ≤ P ≤ 100%.

9. A battery, characterized in that, The negative electrode sheet includes any one of claims 1 to 3 or the negative electrode sheet prepared by any one of claims 4 to 8.

10. An electrical appliance, characterized in that, Includes the battery as described in claim 9.

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