Negative plate and preparation method thereof, battery and electric equipment

Abstract

The invention relates to the technical field of lithium batteries, in particular to a negative plate, a preparation method, a battery and electric equipment. The negative electrode plate 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 substance, the negative electrode active substance comprises a carbon-based material, the OI value of the negative electrode active coating is 0.1-30, and the OI value of the negative electrode active coating is 0.1-30. Pore channels are formed in the surface, far away from the negative current collector, of the negative active coating; wherein the orientation degree OI value is an intensity ratio of a (004) diffraction peak to a (110) diffraction peak of the negative electrode active coating in an XRD diffraction pattern. According to the negative plate, a channel for transmitting lithium ions from the surface of the electrode to the bottom of the plate is added, a path for transmitting the lithium ions from the surface of the electrode to the bottom of the electrode is shortened, and the fast charging capacity of the battery is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a negative electrode sheet and a preparation method thereof, a battery, and an electrical device. Background Art

[0002] The fast-charging capability of lithium-ion batteries is a key performance indicator. When charging, lithium ions diffused from the positive electrode need to diffuse from the surface of the negative electrode along the pore channels within the negative electrode to embed into the individual negative electrode particles. The negative electrode pore structure and the diffusion capacity of lithium ions in the negative electrode directly affect the battery's charging capacity. Therefore, to improve fast-charging capability, it is particularly important to optimize the design of the negative electrode structure to reduce electrode tortuosity, shorten the lithium ion transmission path, and thus improve the lithium ion diffusion capacity. Currently, the main method to improve fast-charging capability is to reduce the amount of dressing and compaction of the negative electrode sheet, but this only increases the porosity of the electrode and reduces the thickness of the electrode sheet, without achieving the optimized design of the electrode pore structure. Summary of the Invention

[0003] The present invention aims to at least partially address one of the technical problems in the related art. To this end, the present invention provides a negative electrode sheet, a preparation method, a battery, and an electrical device. This negative electrode sheet increases the pathway for lithium ions to transfer from the electrode surface to the bottom of the electrode sheet, while also shortening the path for lithium ions to transfer from the electrode surface to the bottom, significantly improving the battery's charging capacity.

[0004] To this end, a 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 of the negative electrode current collector, wherein the negative electrode active coating comprises a negative electrode active material, wherein the negative electrode active material comprises a carbon-based material, and wherein the OI value of the negative electrode active coating is 0.1-30, and wherein the negative electrode active coating has pores on a surface away from the negative electrode current collector;

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

[0006] The present invention discovered that when the OI value of the negative electrode active coating is 0.1-30, the arrangement of the carbon-based material particles in the electrode is perpendicular or nearly perpendicular to the current collector. This reduces the curvature of the pore structure formed between the particles, shortening the path lithium ions travel from the electrode surface to the bottom, thereby increasing the lithium ion transmission rate and improving charging capacity. Furthermore, by providing openings on the surface of the negative electrode active coating away from the negative electrode current collector, the number of channels for lithium ions to enter the electrode from the surface increases, further enhancing the diffusion capacity of lithium ions and improving charging capacity.

[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 pores penetrate 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 pores to the thickness of the negative electrode active coating is 0.1-0.8;

[0012] and / or, the depth of the pores 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 pores accounts for 0.20% to 78% of the area of the surface of the negative electrode active coating layer away from the negative electrode current collector.

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

[0016] According to an embodiment of the present invention, the surface of the negative electrode active coating layer away from the negative electrode current collector has at least two pores, and the distance between any two adjacent pores 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 according to the first aspect, the method comprising:

[0019] Prepare a negative electrode active slurry, wherein the negative electrode active slurry includes a carbon-based material, and apply the negative electrode active slurry to at least one side of the negative electrode current collector;

[0020] The negative electrode active slurry coating process is processed by a magnetic induction orientation device, dried, and rolled to obtain a negative electrode active coating;

[0021] The surface of the negative electrode active coating layer away from the negative electrode current collector is subjected to a pore-forming treatment to obtain the negative electrode sheet.

[0022] Thus, a negative electrode sheet is obtained, in which the carbon-based material particles are arranged in a certain orientation and the surface of the electrode sheet has an open-pore structure. Using this negative electrode sheet in a battery can increase the transmission rate of lithium ions and improve the charging capacity.

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

[0024] Therefore, the battery has better fast charging performance.

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

[0026] Therefore, the electrical device has all the advantages of the battery, which will not be described in detail here.

[0027] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[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 with reference to the following drawings, in which:

[0029] Figure 1 Shows the structure of the negative electrode sheet provided by the present invention;

[0030] Figure 2 The diagram shows the structure of the negative electrode sheet in the prior art. DETAILED DESCRIPTION

[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 understood 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 understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, features defined as "first" or "second" may explicitly or implicitly include one or more of such features. Furthermore, in the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0033] The endpoints of the ranges and any values 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 endpoints of each range, the endpoints of each range and individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0034] In order to make the present invention more easily understood, certain technical and scientific terms are specifically defined below. Unless otherwise clearly defined elsewhere in this document, all other technical and scientific terms used herein have the meaning commonly understood by those skilled in the art to which the present invention belongs.

[0035] In this document, the terms “include” or “comprising” are open expressions, that is, including the contents specified in the present invention, but not excluding other contents.

[0036] As used herein, the terms "optionally," "optional," or "optionally" generally mean that the subsequently described event or circumstance may but need not occur, and that the description includes instances where the event or circumstance occurs and instances where it does not.

[0037] According to an embodiment of the present invention, a first aspect of the present invention provides a negative electrode sheet, see Figure 1 , comprising a negative electrode current collector and a negative electrode active coating provided on at least one side of the negative electrode current collector, wherein the negative electrode active coating comprises a negative electrode active material, wherein the negative electrode active material comprises a carbon-based material, wherein the OI value of the negative electrode active coating is 0.1-30, and wherein the surface of the negative electrode active coating away from the negative electrode current collector is provided with pores;

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

[0039] The negative electrode active material commonly used in lithium-ion batteries is graphite. The shape of graphite particles is generally lamellar and ellipsoidal. After the prepared electrode is rolled, the graphite particles tend to be arranged parallel to the direction of the current collector (see Figure 2 ). The inventors found that this arrangement orientation will cause the pores formed between the graphite particles to have a larger tortuosity, the path for lithium ions to reach the bottom of the electrode from the electrode surface becomes longer, the transmission efficiency of lithium ions becomes lower, and a larger diffusion impedance is generated, which affects the fast charging performance of the battery. In addition, during the rolling process, the surface of the negative electrode is in direct contact with the roller of the roller press. After rolling, the surface is more likely to form a dense structure, and the channels for lithium ions to enter the interior of the electrode from the electrode surface become fewer, which limits the transmission capacity of lithium ions and affects the fast charging performance of the battery. In order to solve the above problems, the present invention changes the pore structure between the electrode particles by regulating the arrangement orientation of the carbon-based material in the electrode, so that the carbon-based material particles tend to be arranged in the direction perpendicular to the current collector, the degree of curvature of the pore structure formed between the particles is reduced, and the path for lithium ions to be transmitted to the bottom of the electrode becomes shorter, thereby improving the transmission rate of lithium ions and improving the charging capacity of the battery. At the same time, pores are set on the electrode surface to increase the number of channels for lithium ions to enter the interior of the electrode from the electrode surface, further improving the diffusion capacity of lithium ions and improving the charging capacity of the battery.

[0040] Specifically, the degree of alignment and orientation of the carbon-based material particles in the electrode is correlated with the orientation index (OI) of the negative electrode active coating. "Orientation of the carbon-based material particles in the electrode" refers to the state in which the carbon-based material layer in the electrode cross-section is perpendicular or nearly perpendicular to the current collector. This is quantified here by the angle between the centerline of the carbon-based material layer and the current collector. Experimental verification results show that when the angle between the carbon-based material layer and the current collector is between 45° and 90°, the preferred orientation arrangement effect is achieved, corresponding to an OI value of 10-0.1 for the carbon-based material in the electrode.

[0041] Specifically, the angle test between the carbon-based material layer and the current collector can be specifically as follows: the oriented electrode is cut using ion beam milling to expose a flat cross-section, photographed using a scanning electron microscope (SEM), and the angle between the carbon-based material layer and the current collector is measured using image processing tools.

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

[0043] Specifically, the type of the carbon-based material is not particularly limited, and those skilled in the art can select it according to actual needs. As some specific examples, the carbon-based material can be selected from 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, and those skilled in the art may select it according to actual needs. As some specific examples, one, two or more pores may be provided.

[0045] According to a specific embodiment of the present invention, the pores penetrate at least a portion of the negative electrode active coating in the thickness direction and may be non-through holes, that is, the depth of the pores is less than the thickness of the negative electrode active coating, and the ratio of the depth of the pores 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 pores 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 thereby improving the fast charging capability.

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

[0047] According to a specific embodiment of the present invention, the depth of the pores is 10-50 μm. Since the surface of the pole piece is denser and has fewer pores after rolling, it is mainly because the surface particles tend to be arranged in parallel under the action of roller pressure. Therefore, the depth of the pores is limited here to be greater than the thickness of a single graphite particle (the size of graphite particles is usually between ten and tens of microns). Specifically, the depth of the pores can be selected according to actual needs. As some specific examples, the depth of the opening can be selected from 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 pores can be oriented parallel to the thickness direction of the current collector, i.e., the pores are vertical pores. The shape of the pores in a top view perpendicular to the current collector is not particularly limited and can be selected by those skilled in the art based on actual needs. As some specific examples, circular, square, or other regular geometric shapes can be selected, with circular shapes being preferred. The cross-sectional view of the pores is also not particularly limited and can be selected by those skilled in the art based on actual needs. As some specific examples, rectangular, triangular, trapezoidal, or other geometric shapes can be selected, with triangular shapes being preferred.

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

[0050] Specifically, the channel area refers to the channel contour area projected on the electrode surface, and the channel area ratio can be adjusted by adjusting the channel aperture and channel spacing.

[0051] According to a specific embodiment of the present invention, the pore diameter of the channel is 5-40 μm. Those skilled in the art can choose according to actual needs. As some specific examples, the pore diameter 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. This size is expressed differently for pores of different shapes. For example, when the pore shape is circular when viewed from above, perpendicular to the current collector, the pore diameter is the diameter; when the pore shape is square or rectangular when viewed from above, the pore diameter can be expressed as the side length (for a square) or the length and width (for a rectangle); when the pore shape is elliptical when viewed from above, the pore diameter can be expressed as the length of its major and minor axes, etc. The pore diameter can be 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. Excessive pore size 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 layer away from the negative electrode current collector has at least two pores, and the distance between any two adjacent pores is 20-100 μm.

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

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

[0057] According to a specific embodiment of the present invention, the tortuosity of the negative electrode active coating is 2.2-3.5, which is smaller than that of a conventional electrode (whose tortuosity is 3.9), indicating that the path for lithium ions to be transferred from the electrode surface to the bottom of the electrode is shortened.

[0058] Among them, tortuosity means that the transmission of lithium ions in the electrolyte in the negative electrode active coating is not in a straight line, but moves in a tortuous way. The tortuosity reflects the degree of this tortuosity. The tortuosity is equal to the ratio of the actual path length of lithium ions transmitted in the internal pores of the negative electrode active coating to the apparent length of the negative electrode active material layer (macroscopic distance, that is, the thickness of the negative electrode active coating), that is, the actual length of the movement trajectory of lithium ions in the internal pores when they pass through a unit distance of 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 pole pieces and diaphragms are assembled into a symmetrical battery;

[0061] 2. Inject electrolyte and then soak;

[0062] 3. Perform electrochemical impedance spectroscopy and obtain the electrode ion impedance Rion by fitting;

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

[0064] The thickness L of the pole piece can be measured using a micrometer. Use the micrometer to take 10 points in the horizontal and vertical directions of the pole piece, and take the average value as the pole piece thickness;

[0065] The electrode porosity τ can be measured using instruments and methods known in the art. For example, the mercury intrusion method uses the following test method: Place the dried sample in a suitable dilatometer, place the dilatometer in a low-pressure test area, evacuate the dilatometer, and then press mercury into it. Use nitrogen compression to test the mercury intrusion volume from 0 to 30 psi. After the test is completed, place the dilatometer in a high-pressure test area and use oil pressure to test the mercury intrusion volume from 30 to 33,000 psi. The porosity τ = V t / V0*100%, where Vt is the total volume of mercury intruded 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, the industry standard HG / T4067-2015, "Lithium Hexafluorophosphate Electrolyte," can be used. The density meter's measurement temperature can be set to 20°C, and the sample can be injected into the instrument's measuring cell to perform the measurement and read the data.

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

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

[0069] (1) preparing a negative electrode active slurry, wherein the negative electrode active slurry includes a carbon-based material, and coating the negative electrode active slurry on at least one side of a negative electrode current collector.

[0070] According to a specific embodiment 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 substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, etc.) on a polymer substrate (such as a substrate made 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 can be selected by those skilled in the art based on actual needs. As some specific examples, the negative electrode active slurry may include a negative electrode active material, wherein the negative electrode active material includes graphite. In addition, it 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. The silicon-based material may include at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may include at least one of elemental tin, tin oxide compounds, and tin alloys.

[0072] Specifically, the negative electrode active slurry may further 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 further optionally include a conductive agent, which 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 further include other auxiliary agents, such as a thickener (eg, sodium carboxymethyl cellulose (CMC)).

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

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

[0077] According to a specific embodiment of the present invention, a magnetic induction orientation device can orient the carbon-based material particles in the negative electrode active slurry. The magnetic induction orientation device is not particularly limited and can specifically use a magnetic block with a uniform magnetic field (magnetic field strength of 0.5 to 2T), which is placed on the side of the current collector that is not coated with the negative electrode active slurry during the coating process. By adjusting the distance between the magnetic block and the copper foil (0-3mm) and the time the current collector passes through the magnetic block (5-60s), the orientation degree of the carbon-based material particles in the negative electrode active coating (i.e., the OI value of the pole piece) can be controlled.

[0078] According to a specific embodiment of the present invention, the drying and rolling methods in this step are not particularly limited, and the drying temperature and time are not particularly limited. Those skilled in the art can select them according to actual needs.

[0079] (3) Performing a pore-forming treatment on the surface of the negative electrode active coating layer away from the negative electrode current collector to obtain the negative electrode sheet.

[0080] According to a specific embodiment of the present invention, the hole-making method is not particularly limited, and those skilled in the art can choose according to actual needs. As some specific examples, the hole-making method can be laser etching, ion beam etching, mechanical hole-making, and template-based hole-making methods, with laser etching and roller needle roller pressing being preferred.

[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 comprises a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are intercalated and released between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator is positioned 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 electrode current collector and a positive electrode active coating disposed on at least one side of the positive electrode current collector, and the positive electrode active coating includes a positive electrode active material.

[0085] According to a specific embodiment 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 base layer and a metal layer formed on at least one side of the polymer material base layer. 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 a specific embodiment of the present invention, the positive electrode active coating layer may further optionally include a conductive agent. As an example, 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.

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

[0088] According to a specific embodiment of the present invention, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, and the binder are dispersed in a solvent (such as N-methylpyrrolidone, NMP) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

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

[0090] According to specific embodiments of the present invention, there are no particular limitations on the type of separator. Any known porous separator with good chemical and mechanical stability may be used. In some embodiments of the present invention, the separator may be made of at least one of fiberglass, non-woven fabric, polyethylene, polypropylene, or polyvinylidene fluoride.

[0091] According to a specific embodiment of the present invention, the positive electrode sheet, the negative electrode sheet and the separator can be made into an electrode assembly through a winding process or a lamination process.

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

[0093] According to a specific embodiment 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 shell, such as a pouch-type soft shell. The material of the soft shell can be plastic, and examples of plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0094] A fourth aspect of the present invention provides an electrical device, which includes 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 electrical device may be, but is not limited to, a mobile phone, a tablet, a laptop computer, an electric toy, an electric tool, a battery-powered vehicle, an electric car, a ship, a spacecraft, and the like. The electric toy may include a fixed or mobile electric toy, such as a game console, an electric car toy, an electric ship toy, and an electric airplane toy, and the spacecraft may include an airplane, a rocket, a space shuttle, and a spacecraft, and the like.

[0096] Below, the scheme of the present invention will be explained in conjunction with embodiment.It will be understood by those skilled in the art that the following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention.In the embodiment, if specific technology or conditions are not indicated, the technology or conditions described in the literature in this area or the product instructions are used.The reagents or instruments used are not indicated by the manufacturer, and are all conventional products that can be obtained by commercial purchase.

[0097] Example 1

[0098] (1) Preparation of electrolyte: lithium salt (LiPF6), solvent (EC, EMC, DMC), and additive (VC) were 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 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 were mixed evenly to form a slurry. After coating, baking and rolling, a surface density of 500g / m 2 , compaction 2.65g / cm 3 The positive electrode.

[0100] (3) Preparation of negative electrode sheet: The negative electrode material graphite, conductive agent carbon black, thickener CMC, binder SBR and solvent water (mass ratio is 100:1:1.6:1.35:110) are mixed evenly to form a slurry, and a layer of slurry with uniform thickness is applied on the current collector. The slurry is oriented and arranged by a magnetic induction orientation device. In this process, the distance between the magnetic block and the copper foil and the time for the current collector to pass through the magnetic block are adjusted to achieve the control of the OI value of the electrode sheet. Subsequently, after baking and rolling, the surface density of 230g / m 2 , compaction 1.6g / cm 3 Then, laser etching or roller pressing is used to create vertical holes with a diameter of 20μm, a depth of 15μm, and a spacing of 50μm on the surface of the pole piece, which are distributed in an array.

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

[0102] (5) Battery assembly: stack the positive electrode sheet, separator, and negative electrode sheet in order, so that the separator is between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then wind them into a bare battery cell; after welding the tabs, place the bare battery cell in the outer packaging shell, dry it, and inject the above electrolyte, and finally obtain a battery with a designed capacity of 900mAh after vacuum packaging, standing, forming, shaping, etc.

[0103] Example 2

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

[0105] The orientation degree of graphite particles is changed so that the OI value of the electrode is close to 0.1.

[0106] Example 3

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

[0108] Changing the orientation of graphite particles makes the pole piece OI value close to 10.

[0109] Example 4

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

[0111] The orientation degree of graphite particles is changed to make the pole piece OI value close to 15.

[0112] Example 5

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

[0114] Change the orientation of graphite particles to make the pole piece OI value close to 30.

[0115] Example 6

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

[0117] Laser etching or roller needle rolling is used to produce vertical channels with a diameter of 5μm, a depth of 10μm, and a hole spacing of 20μm on the surface of the pole piece, which are distributed in an array.

[0118] Example 7

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

[0120] Laser etching or roller needle rolling is used to produce vertical channels with a diameter of 40μm, a depth of 50μm, and a hole spacing of 100μm on the surface of the pole piece, which are distributed in an array.

[0121] Comparative Example 1

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

[0123] No array of vertical channels is constructed on the electrode surface.

[0124] Comparative Example 2

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

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

[0127] Comparative Example 3

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

[0129] The orientation of graphite particles is changed to make the pole piece OI value close to 35.

[0130] Test Case

[0131] (1) Hole diameter, hole depth, and hole spacing test

[0132] The aperture, depth and spacing of the array openings on the surface of each pole piece in the embodiment and the comparative example were measured using a confocal microscope;

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

[0134] The oriented electrode is cut using ion beam milling to expose a flat cross section, photographed under an electron microscope, and the angle between the graphite sheet and the current collector is measured using image processing tools;

[0135] (3) Pole OI value test

[0136] The negative electrode was placed on the sample stage of the XRD diffractometer for testing, with a scanning range of 50-80°. The intensity of the (004) diffraction peak (54-55° position) and the (110) diffraction peak (77-78° position) were obtained from the obtained XRD spectrum, and 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 separators are assembled into a pole core in sequence; the pole core is placed in an outer packaging shell, baked and injected with electrolyte, and after packaging, infiltration and other processes, a liquid phase diffusion impedance battery is obtained. Liquid phase diffusion impedance testing is performed using an electrochemical workstation in the frequency range of 100,000 Hz-0.05 Hz. The Z' (X-axis) and -Z" (Y-axis) of the obtained data are plotted, and the quadratic derivative of all data in the curve is calculated. The point with the maximum absolute value of the quadratic reciprocal between the 25th and 60th data is found, which is the inflection point. A linear fit is performed on the data from the third point after the inflection point to the thirteenth point to obtain the fitted intercept a and slope b. The impedance data is fitted using Zview software to obtain Rs, and the fitted equivalent circuit is: The liquid phase diffusion impedance Rion is then calculated according to the following formula:

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

[0140] 1) Two identical pole pieces and diaphragms are assembled into a symmetrical battery;

[0141] 2) Inject electrolyte and then soak;

[0142] 3) Perform electrochemical impedance spectroscopy and obtain the electrode ionic impedance Rion by fitting;

[0143] 4) The thickness of the electrode is L, the porosity is τ, and the area is A; the conductivity of the electrolyte is σ;

[0144] The thickness L of the electrode is measured using a micrometer. 10 points are taken in the horizontal and vertical directions of the electrode, and the average value is taken as the electrode thickness.

[0145] The electrode porosity τ can be measured using instruments and methods known in the art. For example, the mercury intrusion method uses the following test method: Place the dried sample in a suitable dilatometer, place the dilatometer in a low-pressure test area, evacuate the dilatometer, and then press mercury into it. Use nitrogen compression to test the mercury intrusion volume from 0 to 30 psi. After the test is completed, place the dilatometer in a high-pressure test area and use oil pressure to test the mercury intrusion volume from 30 to 33,000 psi. The porosity τ = V t / V0*100%, where Vt is the total volume of mercury intruded 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, the industry standard HG / T4067-2015, "Lithium Hexafluorophosphate Electrolyte," can be used. The density meter's measurement temperature can be set to 20°C, and the sample can be injected into the instrument's measuring cell to perform the measurement and read the data.

[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) 0.2C constant current discharge to 2.0V, set aside for 30 minutes;

[0151] 2) Charge at 0.2C constant current to 3.8V and leave for 30 minutes (#0.2C charging#);

[0152] 3) 0.2C constant current discharge to 2.0V, leave for 30 minutes;

[0153] 4) Charge at 3.0C constant current to 3.8V and leave for 30 minutes (#3C charging#);

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

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

[0156] Table 1

[0157]

[0158] In Table 1, “ / ” indicates absence.

[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 pore structure on the electrode surface has lower liquid phase diffusion impedance, smaller tortuosity, stronger lithium ion diffusion capacity and better fast charging performance.

[0160] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0161] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A negative electrode sheet, characterized in that: The invention comprises a negative electrode current collector and a negative electrode active coating provided on at least one side of the negative electrode current collector, wherein the negative electrode active coating comprises a negative electrode active material, wherein the negative electrode active material comprises a carbon-based material, and wherein the orientation index (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 pores; The orientation degree OI value is the intensity ratio of the (004) diffraction peak to the (110) diffraction peak of the negative electrode active coating in the XRD diffraction pattern.

2. The negative electrode sheet according to claim 1, characterized in that: The orientation degree OI value of the negative electrode active coating is 0.1-10; And / or, the angle between the carbon-based material and the negative electrode current collector is 45°-90°.

3. The negative electrode sheet according to claim 1, characterized in that: The pores penetrate at least a portion of the negative electrode active coating in the thickness direction; And / or, the depth of the pores is less than the thickness of the negative electrode active coating; and / or, the ratio of the depth of the pores to the thickness of the negative electrode active coating is 0.1-0.8; and / or, the depth of the pores is 10-50 μm; And / or, the thickness of the negative electrode active coating is 62-95 μm.

4. The negative electrode sheet according to claim 1, characterized in that: The total area of the pores accounts for 0.20% to 78% of the area of the surface of the negative electrode active coating away from the negative electrode current collector.

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

6. The negative electrode sheet according to claim 1, characterized in that: The surface of the negative electrode active coating away from the negative electrode current collector has at least two pores, and the distance between any two adjacent pores is 20-100 μm.

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

5.

8. A method for preparing a negative electrode sheet according to any one of claims 1 to 7, characterized in that: include: Prepare a negative electrode active slurry, wherein the negative electrode active slurry includes a carbon-based material, and apply the negative electrode active slurry to at least one side of the negative electrode current collector; The negative electrode active slurry coating process is processed by a magnetic induction orientation device, dried, and rolled to obtain a negative electrode active coating; The surface of the negative electrode active coating layer away from the negative electrode current collector is subjected to a pore-forming treatment to obtain the negative electrode sheet.

9. A battery, characterized in that: The negative electrode sheet comprises the negative electrode sheet according to any one of claims 1 to 7.

10. An electrical device, characterized in that: A battery comprising the battery of claim 9.

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