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 plate comprises a negative current collector and a negative active material layer arranged on at least one side surface of the negative current collector; the negative electrode active material layer comprises a negative electrode active material, the negative electrode active material comprises a carbon-based material, and the OI value of the negative electrode active material layer meets 0 lt; oIt, OIt; 30); a groove is formed in the surface, far away from the negative electrode current collector, of the negative electrode active material layer; 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 material layer in an XRD diffraction pattern. Therefore, the negative plate has a higher charging rate and a longer fast charging cycle life at the same time.

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 rapid development and intensified competition in the new energy vehicle industry are placing higher demands on the performance of power batteries, requiring higher energy density and shorter charging times. To meet the performance requirements for high energy density, the current approach of increasing electrode surface density and compaction is currently widely adopted. As surface density and compaction increase, for the same capacity design, the number of electrode layers can be reduced, thereby reducing the proportion of inactive materials such as current collectors and separators, thereby achieving an increase in energy density. To meet the performance requirements for shorter charging times, the current density and compaction approach of reducing electrode surface density and compaction is generally adopted. As surface density and compaction decrease, the electrode thickness decreases, the porosity increases, and the lithium-ion transmission capacity is enhanced, thus achieving rapid charging. That is, increasing the electrode surface density and compaction can achieve the performance requirements of high energy density, and reducing the electrode surface density and compaction can achieve fast charging. However, these two methods are contradictory and cannot achieve high energy density and shorter charging time at the same time. This is because as the surface density and compaction increase, the thickness of the electrode increases, resulting in a longer lithium ion transmission path; the increased compaction causes the pores to become smaller, and under high compaction, the graphite particles of the negative electrode tend to be arranged parallel to the direction of the current collector. The tortuosity of the ion path formed by the pores between the electrode material particles from the electrode surface to the bottom of the electrode becomes larger, the lithium ion transmission path becomes longer, and the lithium ion transmission rate decreases, resulting in a larger polarization internal resistance during high current charging, resulting in poor fast charging performance. At the same time, high compaction will also make the electrode surface denser, and the electrolyte's ability to wet the electrode becomes worse, resulting in a shorter fast charging cycle life. Therefore, it is necessary to provide an electrode that can achieve high energy density and shorter charging time. 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 exhibits a faster charging rate and a longer fast-charge cycle life.

[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 material layer disposed on at least one side of the negative electrode current collector;

[0005] The negative electrode active material layer includes a negative electrode active material, the negative electrode active material includes a carbon-based material, and the OI value of the negative electrode active material layer satisfies: 0 <OI<30;

[0006] A groove is provided on the surface of the negative electrode active material layer away from the negative electrode current collector;

[0007] 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 material layer.

[0008] The present invention discovers that when the orientation degree OI value of the negative electrode active material layer satisfies 0 < OI < 30, the carbon-based material particles tend to be arranged perpendicular to the direction of the current collector in the electrode. At this time, the bending degree of the pore structure formed between the particles is reduced, greatly reducing the tortuosity of the ion path formed by the pores between the electrode material particles from the electrode surface to the electrode bottom, thereby shortening the transmission path of lithium ions, enhancing the diffusion ability of lithium ions, reducing the polarization internal resistance during high-current charging, and improving the fast charging performance. At the same time, the groove provided on the surface of the electrode can generate capillary action, which can greatly improve the wetting ability of the electrolyte to the electrode, and also has a certain liquid storage effect, avoiding the occurrence of lithium deposition due to low local electrolyte concentration or excessive consumption, resulting in cycle failure, and thus achieving a longer fast charging cycle life.

[0009] According to an embodiment of the present invention, the OI value of the negative electrode active material layer satisfies: 0.1 ≤ OI ≤ 5.

[0010] According to an embodiment of the present invention, the depth d of the groove, the compaction density V of the negative electrode sheet, and the orientation degree OI value of the carbon-based material satisfy:

[0011] According to an embodiment of the present invention, the depth of the groove is 10 μm - 70 μm;

[0012] And / or, the width of the groove is 20 μm - 150 μm.

[0013] According to an embodiment of the present invention, the compaction density of the negative electrode sheet is 1.2 g / cm 3 -1.9 g / cm 3 .

[0014] According to an embodiment of the present invention, the compaction density of the negative electrode sheet is 1.5 g / cm 3 -1.7 g / cm 3 .

[0015] According to an embodiment of the present invention, the groove includes a plurality of first grooves and a plurality of second grooves. The first grooves extend along the length direction of the negative electrode current collector, the second grooves extend along the width direction of the negative electrode current collector, and the first grooves intersect with the second grooves;

[0016] The distance between adjacent second grooves is g1, and the distance between adjacent first grooves is g2, and g1 and g2 satisfy: 0.1≤g1 / g2≤50.

[0017] According to an embodiment of the present invention, the g1 is 100 μm-5000 μm, and the g2 is 100 μm-1000 μm.

[0018] According to an embodiment of the present invention, the surface density of the negative electrode sheet is 150g / m 2 -500g / m 2 .

[0019] According to an embodiment of the present invention, the surface density of the negative electrode sheet is 200g / m 2 -300g / m 2 .

[0020] According to an embodiment of the present invention, the tortuosity of the negative electrode active material layer is 2.2-3.5.

[0021] A second aspect of the present invention provides a method for preparing the negative electrode sheet according to the first aspect, the method comprising:

[0022] 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;

[0023] The negative electrode active slurry is treated by a magnetic induction orientation device, dried, and rolled to obtain a negative electrode active material layer;

[0024] The surface of the negative electrode active material layer away from the negative electrode current collector is grooved to obtain the negative electrode sheet.

[0025] 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 grooves. Using this negative electrode sheet in a battery can increase the transmission rate of lithium ions, improve the electrolyte's ability to infiltrate the electrode, and thereby improve the fast charging capability and achieve a longer fast charging cycle life.

[0026] A third aspect of the present invention provides a battery, comprising the negative electrode sheet described in the first aspect.

[0027] Therefore, the battery has better fast charging performance.

[0028] A fourth aspect of the present invention provides an electrical device, which includes the battery described in the third aspect.

[0029] Therefore, the electrical device has all the advantages of the battery, which will not be described in detail here.

[0030] 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

[0031] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which:

[0032] Figure 1 Shows a schematic structural diagram of the negative electrode sheet provided by the present invention;

[0033] Figure 2 A schematic diagram showing the structure of the surface of the negative electrode sheet provided by the present invention is shown. DETAILED DESCRIPTION

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] According to an embodiment of the present invention, a first aspect of the present invention provides a negative electrode sheet, see Figure 1, including a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes a carbon-based material. The orientation degree OI value of the negative electrode active material layer satisfies: 0 < OI < 30; a groove is provided on the surface of the negative electrode active material layer away from the negative electrode current collector.

[0040] 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 material layer.

[0041] To solve the problem that high energy density and short charging time cannot be兼顾 simultaneously in the prior art, the present invention provides an electrode structure in which electrode material particles are oriented and arranged and the electrode surface has grooves. Specifically, in the prior art, after the prepared electrode sheet is roll-pressed, the electrode material particles tend to be arranged parallel to the direction of the current collector. This arrangement orientation will result in a large tortuosity of the pores formed between the electrode material particles, a longer path for lithium ions to reach the bottom of the electrode from the electrode surface, a lower transmission efficiency of lithium ions, and thus a large diffusion impedance, affecting the fast charging performance of the battery. The present invention adjusts the arrangement orientation of the carbon-based material in the electrode, making the carbon-based material particles of the negative electrode more inclined to be arranged perpendicular to the current collector, greatly reducing the tortuosity of the ion path formed by the pores between the electrode material particles from the electrode surface to the electrode bottom, thereby shortening the transmission path of lithium ions, enhancing the diffusion ability of lithium ions, reducing the polarization internal resistance during high-current charging, and improving the fast charging performance. At the same time, the grooves on the electrode surface have a capillary action, which can greatly improve the wetting ability of the electrolyte to the electrode, and also has a certain liquid storage effect, avoiding lithium deposition caused by too low local electrolyte concentration or too fast consumption, resulting in cycle failure, and thus achieving a longer fast charging cycle life.

[0042] Specifically, the orientation degree OI value of the negative electrode active material layer is related to the arrangement orientation degree of the carbon-based material particles in the electrode. The OI value of a conventionally prepared high surface density and high compaction negative electrode sheet is usually above 30. The OI value of the negative electrode active material layer in the negative electrode sheet provided by the present invention satisfies 0 < OI < 30. As some specific examples, the OI value of the negative electrode active material layer can be 0.1, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14, 14.5, 15, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 20.5, 21, 21.5, 22, 22.5, 23, 23.5, 24, 24.5, 25, 25.5, 26, 26.5, 27, 27.5, 28, 28.5, 29, 29.5, etc., preferably 0.1 ≤ OI ≤ 5, indicating that the carbon-based material particles in the negative electrode sheet tend to be arranged in a direction perpendicular to the current collector.

[0043] Specifically, the orientation degree OI value of the negative electrode active material layer can be obtained by measuring the electrode sheet with XRD. The scanning range is 50° - 80°. The intensities of the (004) diffraction peak (at the position of 54° - 55°) and the (110) diffraction peak (at the position of 77° - 78°) are obtained from the obtained XRD spectrum, and the OI value is calculated according to the formula OI = I(004) / I(110).

[0044] Specifically, the type of the carbon-based material is not particularly limited, and those skilled in the art can select according to actual needs. As some specific examples, the carbon-based material can be selected from graphite, soft carbon, hard carbon, etc.

[0045] Specifically, the shape of the groove on the surface of the negative electrode active material layer away from the negative electrode current collector is not particularly limited, and those skilled in the art can select according to actual needs. As some specific examples, the groove can be a strip groove. The cross-sectional shape of the groove is also not particularly limited, and those skilled in the art can select according to actual needs. As some specific examples, the cross-sectional shape can be rectangular, trapezoidal, triangular, and other geometric shapes, preferably triangular.

[0046] According to a specific embodiment of the present invention, the depth d (μm) of the groove, the compaction density V (g / cm 3 ) of the negative electrode sheet, and the orientation degree of the carbon-based material, that is, the OI value of the negative electrode active coating, satisfy: Each physical quantity in this formula is converted to dimensionless form by dividing by its respective unit. The groove depth d is affected by the compaction of the electrode and the arrangement orientation of the carbon-based material particles (i.e., the OI value of the negative electrode active material layer). For low-compacted electrodes, since the electrode itself has a relatively large porosity, the internal porosity is sufficient to meet the diffusion and infiltration of the electrolyte, and the area with low porosity on the surface of the electrode is relatively thin, the groove depth can be set shallower; high-compacted electrodes require deeper grooves, and the OI value has a similar influence.

[0047] According to a specific embodiment of the present invention, the depth of the groove refers to the vertical distance from the bottom of the groove to the edge of its opening, which can be measured using a confocal microscope. Specifically, the depth of the groove is 10μm-70μm. The depth of the groove can be selected according to actual needs. As some specific examples, the depth of the groove can be selected from 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, etc.

[0048] According to a specific embodiment of the present invention, the compaction density V of the negative electrode sheet refers to the mass per unit volume of the electrode sheet material after compaction during the battery manufacturing process. Specifically, the compaction density of the negative electrode sheet is 1.2g / cm 3 -1.9g / cm 3 , can be selected according to actual needs. As some specific examples, the compaction density of the negative electrode sheet can be selected as 1.2g / cm 3 , 1.3g / cm 3 , 1.4g / cm 3 , 1.5g / cm 3 , 1.6g / cm 3 , 1.7g / cm 3 , 1.8g / cm 3 , 1.9g / cm 3 etc., preferably the compacted density is 1.5 g / cm 3 -1.7g / cm 3 , thereby meeting the design requirements of battery energy density or power performance.

[0049] According to a specific embodiment of the present invention, the width of the groove refers to the width of the groove opening on the surface of the negative electrode active material layer. It can be measured using a confocal microscope. Specifically, the width of the groove is 20μm-150μm, which can be selected according to actual needs. As some specific examples, the width of the groove can be selected from 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm, 100μm, 105μm, 110μm, 115μm, 120μm, 125μm, 130μm, 135μm, 140μm, 145μm, 150μm, etc.

[0050] According to a specific embodiment of the present invention, the grooves include a plurality of first grooves and a plurality of second grooves, wherein the first grooves extend along the length of the negative electrode current collector, and the second grooves extend along the width of the negative electrode current collector, and the first grooves intersect with the second grooves. Specifically, the number of the first grooves and the plurality of second grooves is not particularly limited and can be selected by those skilled in the art based on actual needs.

[0051] According to a specific embodiment of the present invention, the distance between adjacent second grooves is g1, and the distance between adjacent first grooves is g2. Figure 2 , g1 and g2 satisfy: 0.1≤g1 / g2≤50. This ensures the electrolyte's wetting effect on the electrode. That is, when the groove spacing in two directions meets the above conditions, the electrolyte can be evenly diffused in all areas of the electrode, thereby improving the problem of uneven electrolyte concentration distribution in various areas of the electrode during the cycle, avoiding local low electrolyte concentration or excessive consumption, resulting in lithium plating and cycle failure, thereby improving the fast charge cycle life.

[0052] Specifically, the distance between adjacent grooves should be understood as the distance between the centers of two adjacent grooves.

[0053] Specifically, the value of g1 / g2 can be 0.1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, etc. The value of g1 is not particularly limited and can be selected by those skilled in the art according to actual needs. As some specific examples, g1 can be selected from 100 μm to 5000 μm, such as 100 μm, 500 μm, 1000 μm, 1500 μm, 2000 μm, 2500 μm, 3000 μm, 3500 μm, 4000 μm, 4500 μm, 5000 μm, etc. The value of g2 is not particularly limited and can be selected by those skilled in the art based on actual needs. As some specific examples, g2 can be selected from 100 μm to 1000 μm, such as 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, 900 μm, 1000 μm, etc. The distance between adjacent grooves can be measured using a confocal microscope.

[0054] According to a specific embodiment of the present invention, the surface density of the negative electrode sheet refers to the mass per unit area of the battery electrode sheet. Specifically, the surface density of the negative electrode sheet is 150g / m 2 -500g / m 2 , can be selected according to actual needs. As some specific examples, the surface density of the negative electrode sheet can be selected as 150g / m 2 , 200g / m 2 , 250g / m 2 , 300g / m 2 、350g / m 2 , 400g / m 2 , 450g / m 2 , 500g / m 2 etc., preferably with a surface density of 200 g / m 2 -300g / m 2 , thereby meeting the design requirements of battery energy density or power performance.

[0055] According to a specific embodiment of the present invention, the tortuosity of the negative electrode active material layer 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 electrode bottom is shortened.

[0056] Among them, tortuosity means that the transmission of lithium ions in the electrolyte in the negative electrode active material layer 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 (macroscopic distance, that is, the thickness of the negative electrode active coating) through the negative electrode active material layer, 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 material layer.

[0057] The tortuosity of the negative electrode active material layer can be measured using instruments and methods known in the art. For example, it can be obtained by the following method:

[0058] 1. Two identical pole pieces and diaphragms are assembled into a symmetrical battery;

[0059] 2. Inject electrolyte and then soak;

[0060] 3. Perform electrochemical impedance spectroscopy and obtain the electrode ion impedance Rion by fitting;

[0061] 4. The thickness of the electrode is L, the porosity is τ, and the area is A; the conductivity of the electrolyte is σ;

[0062] 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;

[0063] 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.

[0064] 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.

[0065] 5. The formula for calculating tortuosity is: ε = (Rion × A × τ × σ) / L.

[0066] 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:

[0067] (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.

[0068] 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.).

[0069] 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, which may include 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.

[0070] 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).

[0071] 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.

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

[0073] 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.

[0074] (2) The negative electrode active material slurry is treated by a magnetic induction orientation device, dried, and rolled to obtain a negative electrode active material layer.

[0075] 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 negative electrode active material layer) can be regulated.

[0076] 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.

[0077] (3) Grooving the surface of the negative electrode active material layer away from the negative electrode current collector to obtain the negative electrode sheet.

[0078] According to a specific embodiment of the present invention, the grooving method is not particularly limited, and those skilled in the art may select it according to actual needs. As some specific examples, it may be performed by laser etching, ion beam etching, mechanical indentation, etc., preferably laser etching.

[0079] A third aspect of the present invention provides a battery comprising the negative electrode sheet described in the first aspect.

[0080] 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.

[0081] According to a specific embodiment of the present invention, the battery is a lithium-ion battery.

[0082] 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.

[0083] 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.).

[0084] 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.

[0085] 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.

[0086] 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.

[0087] According to a specific embodiment of the present invention, the composition and preparation of the negative electrode sheet are as described above.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] A fourth aspect of the present invention provides an electrical device, which includes the battery described in the third aspect.

[0093] 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.

[0094] 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.

[0095] Example 1

[0096] (1) Preparation of electrolyte: lithium salt (LiPF6), solvent (EC, EMC, DMC), and additive (VC) were mixed uniformly in a mass ratio of 12.6:29.2:32.6:23.2:1.9 to fully dissolve the lithium salt;

[0097] (2) Preparation of positive electrode sheet: The positive electrode material lithium iron phosphate (LiFePO4), binder PVDF, conductive agent (carbon black, carbon nanotubes) and solvent NMP (mass ratio of 100:1.8:0.8:55) were mixed evenly to form a slurry. After coating, baking and rolling, a slurry with a surface density of 440g / m 2 , compaction 2.65g / cm 3 The positive electrode;

[0098] (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 front and back sides of the current collector. The slurry is oriented and arranged by a magnetic induction orientation device to orient the graphite particles. 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 make the pole piece OI value close to 0.1. Then, after baking and rolling, the surface density of 200g / m 2 , compacted density is 1.6g / cm 3 Then, laser etching is used to create square grooves with a width of 20 μm, a depth of 10 μm, and a horizontal and vertical spacing of 100 μm.

[0099] (4) Diaphragm: The selected diaphragm is polypropylene (PP) diaphragm;

[0100] (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.

[0101] Example 2

[0102] The difference between Example 2 and Example 1 is that:

[0103] A laser is used to etch the surface of the pole piece to produce square grooves with a width of 20 μm, a depth of 10 μm, a lateral spacing (g1) of 2500 μm, and a longitudinal spacing (g2) of 100 μm, arranged in a criss-cross pattern.

[0104] Example 3

[0105] The only difference between Example 3 and Example 1 is that:

[0106] The compaction density of the pole piece is 1.7g / cm 3 ;

[0107] A laser is used to etch the surface of the pole piece to produce grooves with a width of 20 μm, a depth of 10 μm, a lateral spacing (g1) of 2500 μm, and a longitudinal spacing (g2) of 550 μm, arranged in a criss-cross pattern. The minimum unit is a square groove.

[0108] Example 4

[0109] The only difference between Example 4 and Example 1 is that:

[0110] Change the orientation of graphite particles to make the pole piece OI value close to 2.5;

[0111] The surface density of the pole piece is 250g / m 2 , compacted density is 1.5g / cm 3 ;

[0112] A laser is used to etch the surface of the pole piece to produce square grooves with a width of 85 μm, a depth of 40 μm, a lateral spacing (g1) of 100 μm, and a longitudinal spacing (g2) of 1000 μm, arranged in a criss-cross pattern. The minimum unit is a square.

[0113] Example 5

[0114] The only difference between Example 5 and Example 1 is that:

[0115] Change the orientation of graphite particles to make the pole piece OI value close to 5;

[0116] The surface density of the pole piece is 300g / m 2 , compacted density is 1.5g / cm 3 ;

[0117] The laser etches on the surface of the pole piece to produce square grooves with a width of 150 μm, a depth of 70 μm, a lateral spacing (g1) of 5000 μm, and a longitudinal spacing (g2) of 100 μm, arranged in a criss-cross pattern. The minimum unit is a square.

[0118] Example 6

[0119] The only difference between Example 6 and Example 1 is that:

[0120] The compaction density of the pole piece is 1.2g / cm 3 .

[0121] Example 7

[0122] The only difference between Example 7 and Example 1 is that:

[0123] The compaction density of the pole piece is 1.9g / cm 3 .

[0124] Example 8

[0125] The only difference between Example 8 and Example 1 is that:

[0126] Changing the orientation of graphite particles makes the pole piece OI value close to 10.

[0127] Example 9

[0128] The only difference between Example 9 and Example 1 is that:

[0129] Changing the orientation of graphite particles makes the pole piece OI value close to 20.

[0130] Example 10

[0131] The only difference between Example 10 and Example 1 is that:

[0132] Changing the orientation of graphite particles makes the pole piece OI value close to 29.

[0133] Comparative Example 1

[0134] The difference between Comparative Example 1 and Example 1 is only that:

[0135] No grooves are constructed on the electrode surface.

[0136] Comparative Example 2

[0137] The difference between Comparative Example 2 and Example 1 is only that:

[0138] No magnetic field orientation was applied and no grooves were constructed on the electrode surface.

[0139] Comparative Example 3

[0140] The difference between Comparative Example 3 and Example 1 is only that:

[0141] No magnetic field orientation was applied.

[0142] Test Case

[0143] (1) Test of groove depth d, width w, distance g1 of the second groove, and distance g2 of the first groove

[0144] The depth d, width w, distance g1 of the second groove, and distance g2 of the first groove of each pole piece surface structure in the embodiment and the comparative example were measured using a confocal microscope;

[0145] (2) Test of compaction density V and surface density A of negative electrode

[0146] Take the negative electrode sheet and current collector copper foil after rolling and measure their thickness d with a micrometer N d Cu (Unit: μm), use a 15mm diameter circular cutter to cut 15mm negative electrode sheets and copper foil, and weigh them with an electronic balance to obtain m N 、m Cu (Unit: mg), then the compaction density of the negative electrode is V = 4×(m N -m Cu )÷(15×15×3.14×(d N -d Cu ))×1000, surface density A=4×(m N -m Cu)÷(15×15×3.14)×1000;

[0147] (3) Pole OI value test

[0148] 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);

[0149] (4) Liquid phase diffusion impedance test

[0150] 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:

[0151] (5) Tortuosity test of negative electrode active coating

[0152] 1) Two identical pole pieces and diaphragms are assembled into a symmetrical battery;

[0153] 2) Inject electrolyte and then soak;

[0154] 3) Perform electrochemical impedance spectroscopy and obtain the electrode ionic impedance Rion by fitting;

[0155] 4) The thickness of the electrode is L, the porosity is τ, and the area is A; the conductivity of the electrolyte is σ;

[0156] 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.

[0157] 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.

[0158] 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 can be set to a temperature of 20°C, the sample can be injected into the instrument's measuring cell, and the measurement can be performed and the data read.

[0159] 5) The tortuosity is calculated using the formula: ε = (Rion × A × τ × σ) / L.

[0160] (6) Energy density test

[0161] At room temperature, the weight W (kg) of the batteries prepared in the examples and comparative examples was measured using an electronic balance, and the batteries were then tested according to the following steps:

[0162] 1) 1 / 3C constant current discharge to 2.0V, leave for 30 minutes;

[0163] 2) 1 / 3C constant current and constant voltage charging to 3.8V, cut-off current 0.05C;

[0164] 3) 1 / 3C constant current discharge to 2.0V, leave for 30 minutes;

[0165] 4) Repeat steps 2)-3) three times and record the final discharge energy E (Wh);

[0166] Then the energy density ED = E / W.

[0167] (7) Fast charging capability test

[0168] At room temperature, the batteries prepared in the examples and comparative examples were tested according to the following steps:

[0169] 1) 0.2C constant current discharge to 2.0V, set aside for 30 minutes;

[0170] 2) Charge at 0.2C constant current to 3.8V and leave for 30 minutes (#0.2C charging#);

[0171] 3) 0.2C constant current discharge to 2.0V, leave for 30 minutes;

[0172] 4) Charge at 3.0C constant current to 3.8V and leave for 30 minutes (#3C charging#);

[0173] The 3C / 0.2C charging ratio is obtained by dividing the 3C charging capacity by the 0.2C charging capacity.

[0174] (8) Fast charge cycle test

[0175] At room temperature, the batteries prepared in the examples and comparative examples were tested according to the following steps:

[0176] 1) 1 / 3C constant current discharge to 2.0V, leave for 30 minutes;

[0177] 2) 4C constant current charging for 4.05 min, cut-off voltage 3.8 V;

[0178] 3) 3.5C constant current charging for 1.03 min, cut-off voltage 3.8V;

[0179] 4) 3C constant current charging for 2.2 minutes, cut-off voltage 3.8V;

[0180] 5) 2.5C constant current charging for 1.92 min, cut-off voltage 3.8V;

[0181] 6) 2C constant current charging for 2.1 min, cut-off voltage 3.8V;

[0182] 7) 1.5C constant current charging for 8.4 min, cut-off voltage 3.8V;

[0183] 8) Charge at 1 / 3C constant current to 3.8V and leave for 10 minutes;

[0184] 9) Discharge at 1C constant current to 2.0V, let it sit for 10 minutes, then discharge at 1 / 3C constant current to 2.0V, record the discharge capacity, and let it sit for 30 minutes;

[0185] 10) Follow steps 2) to 9) until the capacity decay reaches 80%, and record the corresponding number of cycles.

[0186] The test results are shown in the table below.

[0187] Table 1

[0188]

[0189]

[0190] Table 1

[0191] sample Energy density (Wh / kg) 3C / 0.2C charging ratio Fast charging cycles Example 1 131 0.96 1526 Example 2 131.1 0.93 1235 Example 3 130.5 0.9 1020 Example 4 134.6 0.92 1189 Example 5 136.7 0.9 1073 Example 6 130.8 0.89 977 Example 7 130.3 0.88 972 Example 8 131 0.89 989 Example 9 130.7 0.84 957 Example 10 130.5 0.84 950 Comparative Example 1 129.9 0.83 915 Comparative Example 2 129.8 0.79 762 Comparative Example 3 130 0.82 811

[0192] In Table 1, “ / ” indicates absence.

[0193] The results show that compared with the comparative example, the battery corresponding to the electrode with a certain orientation of graphite particles and a groove structure on the electrode surface has lower liquid phase diffusion impedance, smaller tortuosity, stronger lithium ion diffusion ability, better fast charging performance, and exhibits a longer fast charging cycle life.

[0194] 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.

[0195] 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: It includes a negative electrode current collector and a negative electrode active material layer provided on at least one side of the negative electrode current collector; The negative electrode active material layer includes a negative electrode active material, the negative electrode active material includes a carbon-based material, and the orientation degree OI value of the negative electrode active material layer satisfies: 0 <OI<30; A groove is provided on the surface of the negative electrode active material layer away from the negative electrode current collector; 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 material layer.

2. The negative electrode sheet according to claim 1, characterized in that: The OI value of the negative electrode active material layer satisfies: 0.1≤OI≤5.

3. The negative electrode sheet according to claim 1, characterized in that: The depth d of the groove, the compaction density V of the negative electrode sheet, and the orientation degree of the carbon-based material, that is, the OI value of the negative electrode active coating, satisfy the following conditions: 0.5V×OI≤d≤100√V×OI.

4. The negative electrode sheet according to claim 1, characterized in that: The depth of the groove is 10 μm-70 μm; And / or, the width of the groove is 20 μm-150 μm.

5. The negative electrode sheet according to claim 1, characterized in that: The compaction density of the negative electrode sheet is 1.2 g / cm 3 -1.9g / cm 3 .

6. The negative electrode sheet according to claim 1, characterized in that: The compaction density of the negative electrode sheet is 1.5 g / cm 3 -1.7g / cm 3 .

7. The negative electrode sheet according to claim 1, characterized in that: The grooves include a plurality of first grooves and a plurality of second grooves, wherein the first grooves extend along the length direction of the negative electrode current collector, the second grooves extend along the width direction of the negative electrode current collector, and the first grooves intersect with the second grooves; The distance between adjacent second grooves is g1, and the distance between adjacent first grooves is g2, and g1 and g2 satisfy: 0.1≤g1 / g2≤50.

8. The negative electrode sheet according to claim 7, characterized in that: The g1 is 100 μm-5000 μm, and the g2 is 100 μm-1000 μm.

9. The negative electrode sheet according to claim 1, characterized in that: The surface density of the negative electrode sheet is 150g / m 2 -500g / m 2 .

10. The negative electrode sheet according to claim 1, characterized in that: The surface density of the negative electrode sheet is 200g / m 2 -300g / m 2 .

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

5.

12. A method for preparing a negative electrode sheet according to any one of claims 1 to 11, 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 is treated by a magnetic induction orientation device, dried, and rolled to obtain a negative electrode active material layer; The surface of the negative electrode active material layer away from the negative electrode current collector is grooved to obtain the negative electrode sheet.

13. A battery, characterized in that: The negative electrode sheet comprises the negative electrode sheet according to any one of claims 1 to 11.

14. An electrical device, characterized in that: Including the battery according to claim 13.

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