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

Abstract

The present application relates to the technical field of lithium battery, and relates to a negative electrode sheet, a preparation method, a battery and an electric device. The negative electrode sheet comprises a negative electrode current collector and a negative electrode active coating arranged on at least one side surface of the negative electrode current collector. The negative electrode active coating comprises a negative electrode active material, the negative electrode active material comprises a carbon-based material, the OI value of the negative electrode active coating is 0.1-30, and the surface of the negative electrode active coating away from the negative electrode current collector is provided with a pore. The orientation degree OI value is the intensity ratio of the (004) diffraction peak to the (110) diffraction peak in the XRD diffraction spectrum of the negative electrode active coating. The negative electrode sheet increases the channel for lithium ions to be transmitted from the electrode surface to the bottom of the electrode sheet, shortens the path for lithium ions to be transmitted from the electrode surface to the bottom of the electrode, and significantly improves the fast-charging capacity of the battery.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and in particular to a negative electrode sheet and its preparation method, a battery, and an electrical device. Background Technology

[0002] Fast charging capability is a crucial performance indicator for lithium-ion batteries. During charging, lithium ions diffuse from the positive electrode and must spread from the surface of the negative electrode along the internal pores to intercalate into individual negative electrode particles. The electrode pore structure and the diffusion ability of lithium ions directly affect the battery's charging capability. Therefore, optimizing the negative electrode structure to reduce electrode tortuosity and shorten the lithium ion transport path is particularly important for improving fast charging capability. Currently, fast charging capability is mainly improved by reducing the amount of coating and compaction of the negative electrode sheet. However, this only increases the porosity of the electrode and reduces the thickness of the electrode sheet, without achieving optimized design of the electrode pore structure. Summary of the Invention

[0003] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, this invention provides a negative electrode sheet and its preparation method, a battery, and an electrical device. This negative electrode sheet increases the channels for lithium ions to transport from the electrode surface to the bottom of the electrode sheet, while also shortening the path of lithium ions from the electrode surface to the bottom of the electrode, significantly improving the charging capacity of the battery.

[0004] To this end, the first aspect of the present invention provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode active coating disposed on at least one side surface of the negative electrode current collector, the negative electrode active coating comprising a negative electrode active material, the negative electrode active material comprising a carbon-based material, the OI value of the negative electrode active coating being 0.1-30, and the surface of the negative electrode active coating away from the negative electrode current collector having channels.

[0005] The orientation degree OI value is the intensity ratio of the (004) diffraction peak to the (110) diffraction peak in the XRD diffraction pattern of the negative electrode active coating.

[0006] This invention discovers that when the OI value of the negative electrode active coating is between 0.1 and 30, the carbon-based material particles are arranged in an orientation perpendicular to or nearly perpendicular to the current collector. At this point, the tortuosity of the pore structure formed between the particles is reduced, shortening the path of lithium ions from the electrode surface to the bottom of the electrode, thus improving the lithium ion transport rate and charging capability. Simultaneously, setting openings on the surface of the negative electrode active coating away from the negative electrode current collector increases the number of channels for lithium ions to enter the electrode interior from the electrode surface, further enhancing the lithium ion diffusion capability and improving charging capability.

[0007] According to an embodiment of the present invention, the OI value of the negative electrode active coating is 0.1-10;

[0008] And / or, the angle between the carbon-based material and the negative electrode current collector is 45°-90°.

[0009] According to an embodiment of the present invention, the channel penetrates at least a portion of the negative electrode active coating in the thickness direction;

[0010] And / or, the depth of the pores is less than the thickness of the negative electrode active coating;

[0011] And / or, the ratio of the depth of the channel to the thickness of the negative electrode active coating is 0.1-0.8;

[0012] And / or, the depth of the channel is 10-50 μm;

[0013] And / or, the thickness of the negative electrode active coating is 62-95 μm.

[0014] According to an embodiment of the present invention, the total area of ​​the channels accounts for 0.20%-78% of the area of ​​the surface of the negative electrode active coating away from the negative electrode current collector.

[0015] According to an embodiment of the present invention, the aperture of the channel is 5-40 μm.

[0016] According to an embodiment of the present invention, the surface of the negative electrode active coating away from the negative electrode current collector has at least two channels, and the spacing between any two adjacent channels is 20-100 μm.

[0017] According to an embodiment of the present invention, the tortuosity of the negative electrode active coating is 2.2-3.5.

[0018] A second aspect of the present invention provides a method for preparing the negative electrode sheet described in the first aspect, the method comprising:

[0019] A negative electrode active slurry is prepared, the negative electrode active slurry comprising a carbon-based material, and the negative electrode active slurry is coated on at least one side surface of a negative electrode current collector;

[0020] The negative electrode active slurry coating process is processed by a magnetically induced orientation device, followed by drying and rolling to obtain the negative electrode active coating.

[0021] The surface of the negative electrode active coating away from the negative electrode current collector is subjected to an opening process to obtain the negative electrode sheet.

[0022] This yields a negative electrode sheet, in which carbon-based material particles are arranged in a certain orientation and the electrode surface has an open structure. Using this negative electrode sheet in a battery can improve the lithium-ion transport rate and enhance charging capability.

[0023] A third aspect of the present invention provides a battery comprising the negative electrode sheet described in the first aspect.

[0024] Therefore, this battery has good fast charging performance.

[0025] A fourth aspect of the present invention provides an electrical device comprising the battery described in the third aspect.

[0026] Therefore, this electrical device possesses all the advantages of the battery, which will not be elaborated upon here.

[0027] Additional aspects and advantages of the invention 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 the invention. Attached Figure Description

[0028] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0029] Figure 1 A structural diagram of the negative electrode sheet provided by the present invention is shown;

[0030] Figure 2 The diagram shows the structure of the negative electrode in the prior art. Detailed Implementation

[0031] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0032] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0033] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0034] To facilitate understanding of the invention, certain technical and scientific terms are specifically defined below. Unless otherwise expressly defined elsewhere in this document, all other technical and scientific terms used herein have the meanings commonly understood by one of ordinary skill in the art to which this invention pertains.

[0035] In this document, the terms “comprising” or “including” are open-ended expressions, meaning that they include the contents specified in this invention, but do not exclude other aspects.

[0036] In this document, the terms “optionally,” “optionally,” or “optionally” generally refer to an event or condition that may, but may not, occur, and the description includes both cases in which the event or condition occurs and cases in which the event or condition does not occur.

[0037] According to an embodiment of the present invention, the first aspect of the present invention provides a negative electrode sheet, see [link to previous document]. Figure 1 The present invention includes a negative electrode current collector and a negative electrode active coating disposed on at least one side surface of the negative electrode current collector. The negative electrode active coating includes a negative electrode active material, which includes a carbon-based material. The OI value of the negative electrode active coating is 0.1-30. The surface of the negative electrode active coating away from the negative electrode current collector is provided with channels.

[0038] The orientation degree OI value is the intensity ratio of the (004) diffraction peak to the (110) diffraction peak in the XRD diffraction pattern of the negative electrode active coating.

[0039] Currently, graphite is the most commonly used negative electrode active material in lithium-ion batteries. Graphite particles are generally lamellar or ellipsoidal in shape. After the prepared electrode sheet is rolled, the graphite particles tend to be arranged parallel to the direction of the current collector (see...). Figure 2 The inventors discovered that this arrangement and orientation leads to greater tortuosity in the pores formed between graphite particles, lengthening the path for lithium ions to travel from the electrode surface to the bottom, reducing lithium ion transport efficiency, and consequently generating greater diffusion resistance, thus affecting the battery's fast-charging performance. Furthermore, during the rolling process, the negative electrode surface directly contacts the rollers of the rolling mill, making it easier for a dense structure to form on the surface after rolling. This reduces the channels for lithium ions to enter the electrode from the surface, limiting lithium ion transport capacity and affecting the battery's fast-charging performance. To solve these problems, this invention modifies the arrangement and orientation of carbon-based materials in the electrode, altering the pore structure between electrode particles. This causes the carbon-based material particles to align more perpendicular to the current collector, reducing the tortuosity of the pore structure between particles and shortening the path for lithium ions to reach the bottom of the electrode, thereby improving the lithium ion transport rate and enhancing the battery's charging capacity. Simultaneously, the presence of channels on the electrode surface increases the number of channels for lithium ions to enter the electrode from the surface, further enhancing lithium ion diffusion capacity and improving the battery's charging capability.

[0040] Specifically, the orientation degree of carbon-based material particles in the electrode is related to the orientation degree (OI) value of the negative electrode active coating. "The orientation degree of carbon-based material particles in the electrode" refers to the state where the carbon-based material sheets in the electrode cross-section are perpendicular or nearly perpendicular to the current collector. This is quantified by the angle formed by the centerline of the carbon-based material sheets and the current collector. According to experimental verification results, when the angle between the carbon-based material sheets and the current collector is between 45° and 90°, it can be considered to have achieved an optimal orientation arrangement, corresponding to an orientation degree (OI) value of 10⁻⁰.⁻¹ for the carbon-based material in the electrode.

[0041] Specifically, the angle test between the carbon-based material sheet and the current collector can be performed as follows: the oriented electrode is ground and cut with an ion beam to expose a flat cross section, and the image is taken using a scanning electron microscope (SEM). The angle between the carbon-based material sheet and the current collector is then measured using image processing tools.

[0042] Specifically, the orientation degree OI value of the negative electrode active coating in the electrode sheet is the intensity ratio of the (004) diffraction peak to the (110) diffraction peak in the XRD diffraction pattern of the negative electrode active coating, which can be obtained by XRD measurement of the rolled electrode sheet.

[0043] Specifically, the type of carbon-based material is not particularly limited, and those skilled in the art can choose according to actual needs. As some specific examples, the carbon-based material can be graphite, soft carbon, hard carbon, etc.

[0044] Specifically, the number of pores on the surface of the negative electrode active coating away from the negative electrode current collector is not particularly limited. Those skilled in the art can choose according to actual needs. As some specific examples, one, two or more pores can be set.

[0045] According to a specific embodiment of the present invention, the channel penetrates at least a portion of the negative electrode active coating in the thickness direction, and may be a non-penetrating hole, that is, the depth of the channel is less than the thickness of the negative electrode active coating, and the ratio of the depth of the channel to the thickness of the negative electrode active coating is 0.1-0.8. As some specific examples, the ratio of the depth of the channel to the thickness of the negative electrode active coating is 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, etc., thereby providing an additional vertical transmission channel for lithium-ion transmission, shortening the lithium-ion transmission distance, reducing tortuosity, improving the lithium-ion transmission rate, reducing polarization during high-rate charging and discharging, and thus improving fast charging capability.

[0046] Specifically, the depth of the channel refers to the shortest vertical distance from the starting surface of the channel to the bottom of the channel, that is, the distance is perpendicular to the plane where the channel is located, i.e., the surface of the negative electrode active coating away from the negative electrode current collector, without considering the tilt or bending of the channel.

[0047] According to a specific embodiment of the present invention, the depth of the channel is 10-50 μm. Since the surface of the electrode is relatively dense and has fewer pores after roller pressing, mainly due to the tendency of surface particles to align in parallel under the roller pressure, the depth of the channel is limited to being greater than the thickness of a single graphite particle (the size of graphite particles is typically between ten and tens of micrometers). Specifically, the depth of the channel can be selected according to actual needs. As some specific examples, the opening depth can be selected as 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, etc., which can be measured by confocal microscopy. The thickness of the negative electrode active coating is 62-95 μm. As some specific examples, the thickness of the negative electrode active coating is 62 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, etc.

[0048] Specifically, the orientation of the channel can be parallel to the thickness direction of the current collector, i.e., the channel is a vertical channel. The shape of the channel in the top view perpendicular to the current collector direction is not particularly limited; those skilled in the art can choose according to actual needs. As some specific examples, a circle, square, or other regular geometric shape can be selected, with a circle being preferred. The cross-sectional view of the channel is also not particularly limited; those skilled in the art can choose according to actual needs. As some specific examples, a rectangle, triangle, trapezoid, or other geometric shape can be selected, with a triangle being preferred.

[0049] According to specific embodiments of the present invention, the total area of ​​the channels accounts for 0.20%-78% of the area of ​​the surface of the negative electrode active coating away from the negative electrode current collector. Those skilled in the art can select according to actual needs. As some specific examples, the total area of ​​the channels accounts for 0.20%, 1%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 78%, etc.

[0050] Specifically, the channel area refers to the area of ​​the channel outline projected onto the electrode surface, and the proportion of the channel area can be adjusted by adjusting the channel diameter and the channel spacing.

[0051] According to specific embodiments of the present invention, the aperture of the channel is 5-40 μm, and those skilled in the art can select according to actual needs. As some specific examples, the aperture of the channel can be 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, etc.

[0052] Specifically, the pore diameter represents its size on the surface of the negative electrode active coating, and this size is expressed differently for pores of different shapes. For example, when the pore's top view shape perpendicular to the current collector direction is circular, its pore diameter is its diameter; when the top view shape is square or rectangular, its pore diameter can be expressed by its side length (for squares) or its length and width (for rectangles); when the top view shape is elliptical, its pore diameter can be expressed by the lengths of its major and minor axes, and so on. The pore diameter can be specifically measured using a confocal microscope.

[0053] Specifically, the size of the pores should be close to the size of the gaps between the negative electrode active materials; excessively large pores will cause excessive loss of carbon-based materials.

[0054] According to a specific embodiment of the present invention, the surface of the negative electrode active coating away from the negative electrode current collector has at least two channels, and the distance between any two adjacent channels is 20-100 μm.

[0055] Specifically, the surface of the negative electrode active coating away from the negative electrode current collector may be provided with two or more channels, preferably in an array distribution. The spacing between any two adjacent channels is 20-100μm, which can be selected by those skilled in the art according to actual needs. As some specific examples, the spacing between any two adjacent channels can be selected as 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm, 100μm, etc.

[0056] Specifically, the spacing between the channels should be understood as the distance between the centers of the channels.

[0057] According to a specific embodiment of the present invention, the tortuosity of the negative electrode active coating is 2.2-3.5. This tortuosity is reduced compared to conventional electrodes (which have a tortuosity of 3.9), indicating a shortened path for lithium ions to travel from the electrode surface to the bottom of the electrode.

[0058] Among them, tortuosity refers to the fact that the transport of lithium ions in the electrolyte in the negative electrode active coating is not a straight line, but a tortuous movement. Tortuosity reflects the degree of this tortuosity. Tortuosity is equal to the ratio of the actual path length of lithium ions transport in the pores inside the negative electrode active coating to the apparent length (macroscopic distance, i.e. the thickness of the negative electrode active coating) of the negative electrode active material layer. In other words, it is the true length of the trajectory of lithium ions in the internal pores when traversing a unit distance through the negative electrode active coating.

[0059] The tortuosity of the negative electrode active coating can be measured using instruments and methods known in the art. For example, it can be obtained by the following method:

[0060] 1. Two identical electrodes and a separator are assembled to form a symmetrical cell;

[0061] 2. Immerse after injecting electrolyte;

[0062] 3. Perform electrochemical impedance spectroscopy and fit the electrode ion impedance Rion;

[0063] 4. The electrode has a thickness of L, a porosity of τ, and an area of ​​A; the electrolyte has a conductivity of σ.

[0064] The thickness L of the electrode sheet can be measured using a micrometer. Take 10 points in the horizontal and 10 points in the vertical direction of the electrode sheet, and take the average value as the electrode sheet thickness.

[0065] The porosity τ of the electrode can be determined using instruments and methods known in the art. For example, mercury intrusion porosimetry (MIP) can be used. The specific testing method is as follows: Place the dried sample in a suitable dilatometer, position the dilatometer in the low-pressure testing zone, evacuate the dilatometer, and then inject mercury. Test the mercury intrusion volume from 0 to 30 psi using nitrogen compression. After the test, place the dilatometer in the high-pressure testing zone and test the mercury intrusion volume from 30 to 33000 psi using hydraulic pressure. The porosity τ = V t / V0*100%, where Vt is the total volume of mercury injected and V0 is the sample volume.

[0066] The conductivity σ of the electrolyte can be measured using instruments and methods known in the art. For example, referring to the industry standard HG / T4067-2015 "Lithium Hexafluorophosphate Electrolyte", the density meter's measurement temperature is set to 20°C, the sample is injected into the instrument's measurement cell, the measurement is performed, and the data is read.

[0067] 5. The tortuosity is calculated using the formula: ε=(Rion×A×τ×σ) / L.

[0068] A second aspect of the present invention provides a method for preparing the negative electrode sheet described in the first aspect, comprising the following steps:

[0069] (1) Prepare a negative electrode active slurry, the negative electrode active slurry comprising a carbon-based material, and coat the negative electrode active slurry onto at least one side of the surface of the negative electrode current collector.

[0070] According to specific embodiments of the present invention, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0071] According to specific embodiments of the present invention, the raw material composition of the negative electrode active slurry is not particularly limited, and those skilled in the art can select it according to actual needs. As some specific examples, the negative electrode active slurry may include a negative electrode active material, which includes graphite, and may also include other commonly used negative electrode active materials, such as soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials may include at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include at least one of elemental tin, tin oxide compounds, and tin alloys.

[0072] Specifically, the negative electrode active slurry may optionally include a binder. The binder may include 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).

[0073] Specifically, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0074] Specifically, the negative electrode active material layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC)).

[0075] Specifically, the components used to prepare the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, are dispersed in a solvent (e.g., deionized water) to form a negative electrode slurry, and the negative electrode slurry is coated on the surface of the negative electrode current collector.

[0076] (2) The negative electrode active slurry is processed by a magnetic induction orientation device, and then dried and rolled to obtain a negative electrode active coating.

[0077] According to a specific embodiment of the present invention, a magnetically induced orientation device can achieve the orientation and alignment of carbon-based material particles in the negative electrode active slurry. The magnetically induced orientation device is not particularly limited; specifically, a magnetic block with a uniform magnetic field (magnetic field strength 0.5–2T) can be used, placed on the side of the current collector not coated with the negative electrode active slurry during the coating process. The orientation degree of the carbon-based material particles in the negative electrode active coating (i.e., the OI value of the electrode) can be controlled by adjusting the distance between the magnetic block and the copper foil (0–3 mm) and the time it takes for the current collector to pass through the magnetic block (5–60 s).

[0078] According to specific embodiments of the present invention, the drying and rolling methods in this step are not particularly limited, nor are the drying temperature and time particularly limited; those skilled in the art can select them according to actual needs.

[0079] (3) The surface of the negative electrode active coating away from the negative electrode current collector is subjected to pore treatment to obtain the negative electrode sheet.

[0080] According to specific embodiments of the present invention, the method of opening holes is not particularly limited, and those skilled in the art can choose according to actual needs. As some specific examples, laser etching, ion beam etching, mechanical hole making, and template hole making are preferred methods, such as laser etching and roller pressing hole making.

[0081] A third aspect of the present invention provides a battery comprising the negative electrode sheet described in the first aspect.

[0082] According to a specific embodiment of the present invention, the battery is a secondary battery. Typically, the battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator is disposed between the positive and negative electrodes to prevent short circuits while allowing ions to pass through.

[0083] According to a specific embodiment of the present invention, the battery is a lithium-ion battery.

[0084] According to a specific embodiment of the present invention, the positive electrode sheet includes a positive current collector and a positive active coating disposed on at least one side surface of the positive current collector, the positive active coating including a positive active material.

[0085] According to specific embodiments of the present invention, 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.).

[0086] According to specific embodiments of the present invention, the positive electrode active coating may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0087] According to specific embodiments of the present invention, the positive electrode active coating may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0088] According to a specific embodiment of the present invention, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive electrode active material, conductive agent, and binder, in a solvent (e.g., N-methylpyrrolidone, NMP) to form a positive electrode slurry; coating the positive electrode slurry onto a positive electrode current collector, and obtaining the positive electrode sheet after drying, cold pressing, and other processes.

[0089] According to a specific embodiment of the present invention, the composition and preparation of the negative electrode are as described above.

[0090] According to specific embodiments of the present invention, there are no particular limitations on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected. In some embodiments of the present invention, the material of the separator membrane may include at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, or polyvinylidene fluoride.

[0091] According to specific embodiments of the present invention, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly by a winding process or a stacking process.

[0092] According to a specific embodiment of the present invention, the battery may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and the electrolyte.

[0093] According to specific embodiments of the present invention, the outer packaging of the battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery can also be a soft pack, such as a pouch-type soft pack. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0094] A fourth aspect of the present invention provides an electrical device comprising the battery described in the third aspect.

[0095] According to a specific embodiment of the present invention, the battery can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The aforementioned electrical device can be, but is not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Among them, electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0096] The present invention will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0097] Example 1

[0098] (1) Preparation of electrolyte: Lithium salt (LiPF6), solvent (EC, EMC, DMC) and additive (VC) are mixed evenly in a mass ratio of 12.6:29.2:32.6:23.2:1.9 to fully dissolve the lithium salt.

[0099] (2) Preparation of the positive electrode sheet: The positive electrode material lithium iron phosphate (LiFePO4), binder PVDF, conductive agent (carbon black, carbon nanotubes) (mass ratio of 100:1.8:0.8:55) and solvent NMP are mixed evenly to form a slurry. After coating, baking and rolling, a surface density of 500 g / m³ is obtained. 2 Compacted to 2.65 g / cm³ 3 The positive electrode plate.

[0100] (3) Preparation of the negative electrode sheet: Graphite (negative electrode material), carbon black (conductive agent), CMC (thickener), SBR (binder), and water (solvent ratio 100:1:1.6:1.35:110) are mixed evenly to form a slurry. A uniformly thick layer of the slurry is coated onto the current collector. The slurry is then used to orient and align the graphite particles using a magnetic orientation device. During this process, the distance between the magnetic block and the copper foil, as well as the time it takes for the current collector to pass through the magnetic block, are adjusted to control the OI value of the electrode sheet. After baking and rolling, an area density of 230 g / m² is obtained. 2 Compacted to 1.6g / cm 3 The electrode sheet is then etched with a laser or pressed with a needle roller to create vertical channels with a diameter of 20 μm, a depth of 15 μm, and a spacing of 50 μm, arranged in an array.

[0101] (4) Separator: The selected diaphragm is a polypropylene (PP) diaphragm;

[0102] (5) Battery assembly: The positive electrode, separator and negative electrode are stacked in sequence so that the separator is between the positive electrode and the negative electrode to play a role in isolation. Then, they are wound into bare cells. After welding the tabs, the bare battery is placed in the outer packaging shell, dried and injected with the electrolyte. After vacuum sealing, standing, formation and shaping, a battery with a designed capacity of 900mAh is finally obtained.

[0103] Example 2

[0104] The only difference between Example 2 and Example 1 is that:

[0105] By altering the orientation of the graphite particles, the OI value of the electrode can be made close to 0.1.

[0106] Example 3

[0107] The only difference between Example 3 and Example 1 is that:

[0108] The orientation of the graphite particles is changed to make the OI value of the electrode close to 10.

[0109] Example 4

[0110] The only difference between Example 4 and Example 1 is that:

[0111] The orientation of the graphite particles was changed to make the OI value of the electrode close to 15.

[0112] Example 5

[0113] The only difference between Example 5 and Example 1 is that:

[0114] By altering the orientation of the graphite particles, the OI value of the electrode can be made close to 30.

[0115] Example 6

[0116] The only difference between Example 6 and Example 1 is that:

[0117] Vertical channels with a diameter of 5μm, a depth of 10μm, and a spacing of 20μm are created by laser etching or roller pressing on the surface of the electrode sheet. These channels are distributed in an array.

[0118] Example 7

[0119] The only difference between Example 7 and Example 1 is that:

[0120] Vertical channels with a diameter of 40μm, a depth of 50μm, and a spacing of 100μm are created by laser etching or roller pressing on the surface of the electrode sheet. These channels are distributed in an array.

[0121] Comparative Example 1

[0122] The only difference between Comparative Example 1 and Example 1 is that:

[0123] No vertical channels were constructed in an array on the electrode surface.

[0124] Comparative Example 2

[0125] The only difference between Comparative Example 2 and Example 1 is that:

[0126] No magnetic field was applied for orientation, and no array of vertical channels was constructed on the electrode surface.

[0127] Comparative Example 3

[0128] The only difference between Comparative Example 3 and Example 1 is that:

[0129] By altering the orientation of the graphite particles, the OI value of the electrode can be made close to 35.

[0130] Test case

[0131] (1) Testing of aperture, depth and spacing

[0132] The aperture, depth, and spacing of the array of openings on the surface of each electrode in the examples and comparative examples were measured using a confocal microscope.

[0133] (2) Angle test between graphite particles and current collector

[0134] The oriented electrode sheets were ground and cut with an ion beam to expose a flat cross section, which was then photographed under an electron microscope. The angle between the graphite sheet and the current collector was measured using image processing tools.

[0135] (3) Electrode OI value test

[0136] The negative electrode was placed on the sample stage of the XRD diffractometer for testing. The scanning range was 50-80°. The intensity of the (004) diffraction peak (54-55° position) and the intensity of the (110) diffraction peak (77-78° position) were obtained from the obtained XRD spectrum. The OI value of the electrode was calculated according to the formula OI=I(004) / I(110).

[0137] (4) Liquid phase diffusion impedance test

[0138] Two identical negative electrode sheets and a separator are assembled sequentially to form an electrode core. The electrode core is placed in an outer packaging shell, baked, and injected with electrolyte. After encapsulation and impregnation processes, a liquid-phase diffusion impedance battery is obtained. Liquid-phase diffusion impedance testing is performed using an electrochemical workstation within a frequency range of 100,000 Hz to 0.05 Hz. The obtained data are plotted on Z' (X-axis) and -Z" (Y-axis). The second derivative of all data in the curve is calculated, and the point where the absolute value of the second reciprocal between the 25th and 60th data points is found to be the inflection point. Linear fitting is performed on the data from the third to the thirteenth point after the inflection point to obtain the intercept a and slope b. The impedance data is fitted using Zview software to obtain Rs. The fitted equivalent circuit is as follows: The liquid phase diffusion impedance Rion is then calculated using the following formula:

[0139] (5) Torque test of negative electrode active coating

[0140] 1) Two identical electrodes and a separator are assembled into a symmetrical cell;

[0141] 2) Immerse after injecting electrolyte;

[0142] 3) Perform electrochemical impedance spectroscopy and fit the electrode ion impedance Rion;

[0143] 4) The electrode has a thickness of L, a porosity of τ, and an area of ​​A; the electrolyte has a conductivity of σ.

[0144] The thickness L of the electrode is measured using a micrometer. Ten points are taken in the horizontal and ten points in the vertical direction of the electrode, and the average value is taken as the electrode thickness.

[0145] The porosity τ of the electrode can be determined using instruments and methods known in the art. For example, mercury intrusion porosimetry (MIP) can be used. The specific testing method is as follows: Place the dried sample in a suitable dilatometer, position the dilatometer in the low-pressure testing zone, evacuate the dilatometer, and then inject mercury. Test the mercury intrusion volume from 0 to 30 psi using nitrogen compression. After the test, place the dilatometer in the high-pressure testing zone and test the mercury intrusion volume from 30 to 33000 psi using hydraulic pressure. The porosity τ = V t / V0*100%, where Vt is the total volume of mercury injected and V0 is the sample volume.

[0146] The conductivity σ of the electrolyte can be measured using instruments and methods known in the art. For example, referring to industry standard HG / T4067-2015 "Lithium Hexafluorophosphate Electrolyte", the density meter's measurement temperature is set to 20°C, the sample is injected into the instrument's measurement cell, the measurement is performed, and the data is read.

[0147] 5) The tortuosity is calculated using the formula: ε=(Rion×A×τ×σ) / L.

[0148] (6) Fast charging capability test

[0149] At room temperature, the batteries prepared in the examples and comparative examples were tested according to the following test steps:

[0150] 1) Discharge at a constant current of 0.2C to 2.0V, and let stand for 30 minutes;

[0151] 2) Charge at a constant current of 0.2C to 3.8V, then let stand for 30 minutes (#0.2C charging#);

[0152] 3) Discharge at a constant current of 0.2C to 2.0V, and let stand for 30 minutes;

[0153] 4) Charge at 3.0C constant current to 3.8V, then let stand for 30 minutes (#3C charging#);

[0154] The 3C / 0.2C charging ratio is obtained by dividing the capacity of 3C charging by the capacity of 0.2C charging.

[0155] The test results are shown in the table below.

[0156] Table 1

[0157]

[0158] In Table 1, " / " indicates that it does not exist.

[0159] The results show that, compared with the comparative example, the battery corresponding to the electrode with a certain orientation of graphite particles and a porous structure on the electrode surface has lower liquid phase diffusion resistance, smaller tortuosity, stronger lithium-ion diffusion ability, and better fast charging performance.

[0160] 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 the present invention. 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.

[0161] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A negative electrode sheet, characterized in that, The device includes a negative electrode current collector and a negative electrode active coating disposed on at least one side surface of the negative electrode current collector. The negative electrode active coating includes a negative electrode active material, which is a carbon-based material. The orientation degree OI value of the negative electrode active coating is 0.1-10. The surface of the negative electrode active coating away from the negative electrode current collector is provided with channels. Wherein, the orientation degree OI value is the intensity ratio of the (004) diffraction peak to the (110) diffraction peak in the XRD diffraction pattern of the negative electrode active coating; The channel penetrates at least a portion of the negative electrode active coating in the thickness direction. The ratio of the depth of the channel to the thickness of the negative electrode active coating is 0.1-0.

8. The total area of ​​the channels accounts for 0.20%-78% of the surface area of ​​the negative electrode active coating away from the negative electrode current collector. The surface of the negative electrode active coating away from the negative electrode current collector has at least two channels, and the distance between any two adjacent channels is 20-100 μm. The angle between the carbon-based material sheet and the negative electrode current collector is 45°-90°.

2. The negative electrode sheet according to claim 1, characterized in that, The depth of the channel is 10-50 μm; And / or, the thickness of the negative electrode active coating is 62-95 μm.

3. The negative electrode sheet according to claim 1, characterized in that, The diameter of the pores is 5-40 μm.

4. The negative electrode sheet according to claim 1, characterized in that, The tortuosity of the negative electrode active coating is 2.2-3.

5.

5. A method for preparing a negative electrode sheet according to any one of claims 1-4, characterized in that, include: A negative electrode active slurry is prepared, the negative electrode active slurry comprising a carbon-based material, and the negative electrode active slurry is coated on at least one side surface of a negative electrode current collector; The negative electrode active slurry coating process is processed by a magnetically induced orientation device, followed by drying and rolling to obtain the negative electrode active coating. The surface of the negative electrode active coating away from the negative electrode current collector is subjected to an opening process to obtain the negative electrode sheet.

6. A battery, characterized in that, Includes the negative electrode sheet as described in any one of claims 1-4.

7. An electrical appliance, characterized in that, Includes the battery as described in claim 6.

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