Negative electrode sheet and its preparation method, battery, electrical equipment

Abstract

The present invention relates to the technical field of lithium batteries, and relates to a negative electrode sheet, a preparation method thereof, a battery, and an electrical equipment. The negative electrode sheet includes 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, 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; a groove is provided on the surface of the negative electrode active material layer away from the negative electrode current collector; wherein, the degree of orientation 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. Thus, the negative electrode sheet has a faster charging rate and also has a longer fast charging cycle life.

Description

Technical Field

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

[0002] With the rapid development and intensified competition in the new energy vehicle industry, higher demands are being placed on the performance of power batteries, namely, higher energy density and shorter charging times. For the high energy density requirement, the common approach is to increase electrode areal density and compaction. With increased areal density and compaction, 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, thus achieving increased energy density. Conversely, for the shorter charging time requirement, the common approach is to reduce electrode areal density and compaction. With reduced areal density and compaction, electrode thickness decreases, porosity increases, and lithium-ion transport capacity is enhanced, thus enabling fast charging. Increasing electrode areal density and compaction can achieve high energy density, while decreasing them enables fast charging. However, these two approaches are contradictory; both high energy density and shorter charging time cannot be achieved simultaneously. This is because increasing areal density and compaction increases electrode thickness, lengthening the lithium-ion transport path. Increased compaction reduces porosity, and under high compaction, graphite particles in the negative electrode tend to align parallel to the current collector. This increases the tortuosity of the ion pathway formed by the pores between electrode material particles from the electrode surface to the bottom, further lengthening the lithium-ion transport path and reducing the lithium-ion transport rate. This results in higher polarization resistance during high-current charging, leading to poor fast-charging performance. Simultaneously, high compaction also results in a denser electrode surface, reducing the electrolyte's wetting ability and shortening fast-charging cycle life. Therefore, an electrode that achieves both high energy density and shorter charging time is needed. Summary of the Invention

[0003] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, this invention provides a negative electrode sheet and its preparation method, a battery, and an electrical device. This negative electrode sheet has a faster charging rate and a longer fast-charging cycle life.

[0004] To this end, the first aspect of the present invention provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector;

[0005] The negative electrode active material layer includes a negative electrode active material, which is a carbon-based material. 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 finds 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 precipitation 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; <​​​​​​​​​​​​​​​​​​​​​Wherein, the distance between adjacent second grooves is g1, and the distance between adjacent first grooves is g2, wherein g1 and g2 satisfy: 0.1≤g1 / g2≤50.

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

[0018] According to an embodiment of the present invention, the areal density of the negative electrode sheet is 150 g / m². 2 -500g / m 2 .

[0019] According to an embodiment of the present invention, the areal density of the negative electrode sheet is 200 g / m². 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 described in the first aspect, the method comprising:

[0022] A negative electrode active slurry is prepared, the negative electrode active slurry comprising a carbon-based material, and the negative electrode active slurry is coated on at least one side surface of a negative electrode current collector;

[0023] The negative electrode active slurry is processed by a magnetically induced orientation device, and then 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] This yields a negative electrode sheet, in which carbon-based material particles are arranged in a certain orientation and the electrode surface has grooves. Using this negative electrode sheet in a battery can improve the lithium-ion transport rate, enhance the electrolyte's wetting ability on the electrode, thereby improving fast charging capability and achieving 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, this battery has good fast charging performance.

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

[0029] Therefore, this electrical device possesses all the advantages of the battery, which will not be elaborated upon here.

[0030] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

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

[0032] Figure 1 A schematic diagram of the negative electrode sheet provided by the present invention is shown;

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

[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 construed 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 construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0036] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0037] To facilitate understanding of the invention, certain technical and scientific terms are specifically defined below. Unless otherwise expressly defined elsewhere in this document, all other technical and scientific terms used herein have the meanings commonly understood by one of ordinary skill in the art to which this invention pertains.

[0038] In this document, the terms “comprising” or “including” are open-ended expressions, meaning that they include the contents specified in this invention, but do not exclude other aspects.

[0039] According to an embodiment of the present invention, the first aspect of the present invention provides a negative electrode sheet, see [link to previous document]. Figure 1, 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 lithium ion transport efficiency, 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 passage formed by the pores between the electrode material particles from the electrode surface to the electrode bottom, thereby shortening the lithium ion transport path, enhancing the lithium ion diffusion ability, 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 have a certain liquid storage effect, avoiding lithium deposition caused by low local electrolyte concentration or excessive consumption and 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 and 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 far 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: In this formula, each physical quantity is divided by its respective unit to convert it to a dimensionless form. The depth d of the groove is affected by the compaction degree of the electrode and the particle orientation of the carbon-based material (i.e., the OI value of the negative electrode active material layer). For electrodes with low compaction degree, since the porosity of the electrode itself is already relatively large, the internal porosity is sufficient to meet the diffusion and wetting of the electrolyte, and the area with low porosity on the surface of the electrode is also relatively thin, so the groove depth can be set shallower. Electrodes with high compaction degree require deeper grooves, and the OI value also has a similar effect.

[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 as 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 refers to the mass per unit volume of the electrode material after compaction during the battery manufacturing process. Specifically, the compaction density of the negative electrode is 1.2 g / cm³. 3 -1.9g / cm 3 The appropriate density can be selected based on actual needs. As a specific example, the compaction density of the negative electrode can be chosen as 1.2 g / cm³. 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 The preferred compaction density is 1.5 g / cm³. 3 -1.7g / cm 3 This allows the design requirements for battery energy density or power performance to be met.

[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, and can be selected according to actual needs. As some specific examples, the groove width 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 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, and the second grooves extend along the width direction of the negative electrode current collector. The first grooves and the second grooves intersect. Specifically, the number of the first grooves and the plurality of second grooves is not particularly limited, and those skilled in the art can select them according to 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. See [reference needed]. Figure 2 The values ​​of g1 and g2 satisfy: 0.1 ≤ g1 / g2 ≤ 50. This ensures the effective wetting of the electrode by the electrolyte. Specifically, when the spacing of the grooves meets the above conditions in both directions, the electrolyte can achieve uniform diffusion in all areas of the electrode, thereby improving the problem of uneven electrolyte concentration distribution in different areas of the electrode during cycling. This prevents localized low electrolyte concentrations or excessively rapid consumption leading to lithium plating and cycle failure, thus improving the fast-charging 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 selected from 0.1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, etc. The value of g1 is not particularly limited, and those skilled in the art can choose it according to actual needs. As some specific examples, g1 can be selected from 100μm to 5000μm, such as 100μm, 500μm, 1000μm, 1500μm, 2000μm, 2500μm, 3000μm, 3500μm, 4000μm, 4500μm, 5000μm, etc. The value of g2 is not particularly limited, and those skilled in the art can choose it according to actual needs. As some specific examples, g2 can be selected from 100μm to 1000μm, such as 100μm, 200μm, 300μm, 400μm, 500μm, 600μm, 700μm, 800μm, 900μm, 1000μm, etc. The distance between adjacent grooves can be measured by confocal microscopy.

[0054] According to a specific embodiment of the present invention, the areal density of the negative electrode refers to the mass per unit area of ​​the battery electrode. Specifically, the areal density of the negative electrode is 150 g / m². 2 -500g / m 2 The selection can be made according to actual needs. As some specific examples, the areal density of the negative electrode can be selected as 150 g / m². 2 200g / m 2 250g / m 2 300g / m 2 350g / m 2 400g / m 2 450g / m 2 500g / m 2 The preferred areal density is 200 g / m³. 2 -300g / m 2 This allows the design requirements for battery energy density or power performance to be met.

[0055] According to a specific embodiment of the present invention, the tortuosity of the negative electrode active material layer is 2.2-3.5. This tortuosity is reduced compared to conventional electrodes (which have a tortuosity of 3.9), indicating a shortened path for lithium ions to travel from the electrode surface to the bottom of the electrode.

[0056] Among them, tortuosity refers to the fact that the transport of lithium ions in the electrolyte in the negative electrode active material layer is not a straight line, but a tortuous movement. Tortuosity reflects the degree of this tortuosity. Tortuosity is equal to the ratio of the actual path length of lithium ions transported in the pores inside the negative electrode active coating to the apparent length (macroscopic distance, i.e. the thickness of the negative electrode active coating) through the negative electrode active material layer. In other words, it is the true length of the trajectory of lithium ions in the internal pores when traveling a unit distance through 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 electrodes and a separator are assembled to form a symmetrical cell;

[0059] 2. Immerse after injecting electrolyte;

[0060] 3. Perform electrochemical impedance spectroscopy and fit the electrode ion impedance Rion;

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

[0062] The thickness L of the electrode sheet can be measured using a micrometer. Take 10 points in the horizontal and 10 points in the vertical direction of the electrode sheet, and take the average value as the electrode sheet thickness.

[0063] The porosity τ of the electrode can be determined using instruments and methods known in the art. For example, mercury intrusion porosimetry (MIP) can be used. The specific testing method is as follows: Place the dried sample in a suitable dilatometer, position the dilatometer in the low-pressure testing zone, evacuate the dilatometer, and then inject mercury. Test the mercury intrusion volume from 0 to 30 psi using nitrogen compression. After the test, place the dilatometer in the high-pressure testing zone and test the mercury intrusion volume from 30 to 33000 psi using hydraulic pressure. The porosity τ = V t / V0*100%, where Vt is the total volume of mercury injected and V0 is the sample volume.

[0064] The conductivity σ of the electrolyte can be measured using instruments and methods known in the art. For example, referring to the industry standard HG / T4067-2015 "Lithium Hexafluorophosphate Electrolyte", the density meter's measurement temperature is set to 20°C, the sample is injected into the instrument's measurement cell, the measurement is performed, and the data is read.

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

[0066] A second aspect of the present invention provides a method for preparing the negative electrode sheet described in the first aspect, comprising the following steps:

[0067] (1) Prepare a negative electrode active slurry, the negative electrode active slurry comprising a carbon-based material, and coat the negative electrode active slurry onto at least one side of the surface of the negative electrode current collector.

[0068] According to specific embodiments of the present invention, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0069] According to specific embodiments of the present invention, the raw material composition of the negative electrode active slurry is not particularly limited, and those skilled in the art can select it according to actual needs. As some specific examples, the negative electrode active slurry may include a negative electrode active material, which may include graphite, and may also include other commonly used negative electrode active materials, such as soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials may include at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include at least one of elemental tin, tin oxide compounds, and tin alloys.

[0070] Specifically, the negative electrode active slurry may optionally include a binder. The binder may include at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0071] Specifically, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0072] Specifically, the negative electrode active material layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC)).

[0073] Specifically, the components used to prepare the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, are dispersed in a solvent (e.g., deionized water) to form a negative electrode slurry, and the negative electrode slurry is coated on the surface of the negative electrode current collector.

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

[0075] According to a specific embodiment of the present invention, a magnetically induced orientation device can achieve the orientation and alignment of carbon-based material particles in the negative electrode active slurry. The magnetically induced orientation device is not particularly limited; specifically, a magnetic block with a uniform magnetic field (magnetic field strength 0.5–2T) can be used, placed on the side of the current collector not coated with the negative electrode active slurry during the coating process. The degree of orientation 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 controlled by adjusting the distance between the magnetic block and the copper foil (0–3 mm) and the time it takes for the current collector to pass through the magnetic block (5–60 s).

[0076] According to specific embodiments of the present invention, the drying and rolling methods in this step are not particularly limited, nor are the drying temperature and time particularly limited; those skilled in the art can select them according to actual needs.

[0077] (3) Grooving is performed on 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 specific embodiments of the present invention, the grooving method is not particularly limited, and those skilled in the art can choose according to actual needs. As some specific examples, laser etching, ion beam etching, mechanical indentation and other methods can be used, with laser etching being preferred.

[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 includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator is disposed between the positive and negative electrodes to prevent short circuits while allowing ions to pass through.

[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 current collector and a positive active coating disposed on at least one side surface of the positive current collector, the positive active coating including a positive active material.

[0083] According to specific embodiments of the present invention, the positive electrode current collector may include a metal foil or a composite positive electrode current collector. For example, the metal foil may be aluminum foil. The composite positive electrode current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. For example, the composite negative electrode current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0084] According to specific embodiments of the present invention, the positive electrode active coating may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0085] According to specific embodiments of the present invention, the positive electrode active coating may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0086] According to a specific embodiment of the present invention, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive electrode active material, conductive agent, and binder, in a solvent (e.g., N-methylpyrrolidone, NMP) to form a positive electrode slurry; coating the positive electrode slurry onto a positive electrode current collector, and obtaining the positive electrode sheet after drying, cold pressing, and other processes.

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

[0088] According to specific embodiments of the present invention, there are no particular limitations on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected. In some embodiments of the present invention, the material of the separator membrane may include at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, or polyvinylidene fluoride.

[0089] According to specific embodiments of the present invention, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly by a winding process or a stacking process.

[0090] According to a specific embodiment of the present invention, the battery may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and the electrolyte.

[0091] According to specific embodiments of the present invention, the outer packaging of the battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery can also be a soft pack, such as a pouch-type soft pack. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0092] A fourth aspect of the present invention provides an electrical device comprising 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 aforementioned electrical device can be, but is not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Among them, electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0094] The present invention will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0095] Example 1

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

[0097] (2) Preparation of the 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) are mixed evenly to form a slurry. After coating, baking and rolling, a surface density of 440 g / m³ is obtained. 2 Compacted to 2.65 g / cm³ 3 The positive electrode plate;

[0098] (3) Preparation of negative electrode sheet: Graphite, carbon black (conductive agent), CMC (thickener), SBR (binder), and water (mass ratio 100:1:1.6:1.35:110) are mixed evenly to form a slurry. A layer of slurry of uniform thickness is coated on both sides of the current collector. The slurry is then used to orient the graphite particles through a magnetic orientation device. The distance between the magnetic block and the copper foil and the time it takes for the current collector to pass through the magnetic block are adjusted to make the OI value of the electrode sheet close to 0.1. After baking and rolling, an area density of 200 g / m³ is obtained. 2 The compacted density is 1.6 g / cm³. 3 The electrode is then etched with a laser to create a groove with a width of 20μm, a depth of 10μm, and a horizontal and vertical spacing of 100μm, the smallest unit of which is a square.

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

[0100] (5) Battery assembly: The positive electrode, separator and negative electrode are stacked in sequence so that the separator is between the positive electrode and the negative electrode to play a role in isolation. Then, they are wound into bare cells. After welding the tabs, the bare battery is placed in the outer packaging shell, dried and injected with the electrolyte. After vacuum sealing, standing, formation and shaping, a battery with a designed capacity of 900mAh is finally obtained.

[0101] Example 2

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

[0103] A laser is used to etch grooves on the surface of the electrode, 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. The smallest unit is a square groove.

[0104] Example 3

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

[0106] The compacted density of the electrode sheet is 1.7 g / cm³. 3 ;

[0107] A laser is used to etch grooves on the surface of the electrode, 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. The smallest unit is a square groove formed by the crisscrossing arrangement of the grooves.

[0108] Example 4

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

[0110] By altering the orientation of graphite particles, the OI value of the electrode can be made close to 2.5.

[0111] The areal density of the electrode is 250 g / m². 2 The compacted density is 1.5 g / cm³. 3 ;

[0112] A laser is used to etch grooves on the surface of the electrode, 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. The smallest unit is a square groove.

[0113] Example 5

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

[0115] By altering the orientation of graphite particles, the OI value of the electrode is made close to 5.

[0116] The areal density of the electrode is 300 g / m³. 2 The compacted density is 1.5 g / cm³. 3 ;

[0117] The laser etches grooves on the surface of the electrode, which are 150 μm wide, 70 μm deep, 5000 μm lateral spacing (g1) and 100 μm longitudinal spacing (g2) in an interlaced arrangement, with the smallest unit being a square groove.

[0118] Example 6

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

[0120] The compacted density of the electrode sheet is 1.2 g / cm³. 3 .

[0121] Example 7

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

[0123] The compacted density of the electrode is 1.9 g / cm³. 3 .

[0124] Example 8

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

[0126] The orientation of the graphite particles is changed to make the OI value of the electrode close to 10.

[0127] Example 9

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

[0129] By altering the orientation of the graphite particles, the OI value of the electrode can be made close to 20.

[0130] Example 10

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

[0132] By altering the orientation of the graphite particles, the OI value of the electrode can be made close to 29.

[0133] Comparative Example 1

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

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

[0136] Comparative Example 2

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

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

[0139] Comparative Example 3

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

[0141] Orientation without applying a magnetic field.

[0142] Test case

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

[0144] The depth d, width w, distance g1 of the second groove, and distance g2 of the first groove in the grooves constructed on the surface of each electrode in the examples and comparative examples were measured using a confocal microscope.

[0145] (2) Testing of compaction density V and areal density A of negative electrode sheet

[0146] Take the rolled negative electrode sheet and current collector copper foil, and measure their thickness d with a micrometer. N d Cu (Unit: μm) A 15mm diameter negative electrode sheet and copper foil were cut using a 15mm diameter circular cutter, and their weights were measured using an electronic balance to obtain the m. N m Cu (Unit: mg), then the compaction density of the negative electrode 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) Electrode OI value test

[0148] The negative electrode was placed on the sample stage of the XRD diffractometer for testing. The scanning range was 50°-80°. The intensity of the (004) diffraction peak (54°-55° position) and the intensity of the (110) diffraction peak (77°-78° position) were obtained from the obtained XRD spectrum. The OI value of the electrode was calculated according to the formula OI=I(004) / I(110).

[0149] (4) Liquid phase diffusion impedance test

[0150] Two identical negative electrode sheets and a separator are assembled sequentially to form an electrode core. The electrode core is placed in an outer packaging shell, baked, and injected with electrolyte. After encapsulation and impregnation processes, a liquid-phase diffusion impedance battery is obtained. Liquid-phase diffusion impedance testing is performed using an electrochemical workstation within a frequency range of 100,000 Hz to 0.05 Hz. The obtained data are plotted on Z' (X-axis) and -Z" (Y-axis). The second derivative of all data in the curve is calculated, and the point where the absolute value of the second reciprocal between the 25th and 60th data points is found to be the inflection point. Linear fitting is performed on the data from the third to the thirteenth point after the inflection point to obtain the intercept a and slope b. The impedance data is fitted using Zview software to obtain Rs. The fitted equivalent circuit is as follows: The liquid phase diffusion impedance Rion is then calculated using the following formula:

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

[0152] 1) Two identical electrodes and a separator are assembled into a symmetrical cell;

[0153] 2) Immerse after injecting electrolyte;

[0154] 3) Perform electrochemical impedance spectroscopy and fit the electrode ion impedance Rion;

[0155] 4) The electrode has a thickness of L, a porosity of τ, and an area of ​​A; the electrolyte has a conductivity of σ.

[0156] The thickness L of the electrode is measured using a micrometer. Ten points are taken in the horizontal and ten points in the vertical direction of the electrode, and the average value is taken as the electrode thickness.

[0157] The porosity τ of the electrode can be determined using instruments and methods known in the art. For example, mercury intrusion porosimetry (MIP) can be used. The specific testing method is as follows: Place the dried sample in a suitable dilatometer, position the dilatometer in the low-pressure testing zone, evacuate the dilatometer, and then inject mercury. Test the mercury intrusion volume from 0 to 30 psi using nitrogen compression. After the test, place the dilatometer in the high-pressure testing zone and test the mercury intrusion volume from 30 to 33000 psi using hydraulic pressure. The porosity τ = V t / V0*100%, where Vt is the total volume of mercury injected and V0 is the sample volume.

[0158] The conductivity σ of the electrolyte can be measured using instruments and methods known in the art. For example, referring to industry standard HG / T4067 2015 "Lithium Hexafluorophosphate Electrolyte", the density meter's measurement temperature is set to 20°C, the sample is injected into the instrument's measurement cell, and the measurement is performed and the data is 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 batteries prepared in the examples and comparative examples were weighed using an electronic balance, and then the batteries were tested according to the following steps:

[0162] 1) Discharge at a constant current of 1 / 3C to 2.0V, then let stand for 30 minutes;

[0163] 2) Charge to 3.8V using a 1 / 3C constant current and constant voltage method, with a cutoff current of 0.05C;

[0164] 3) Discharge at a constant current of 1 / 3C to 2.0V, then let stand for 30 minutes;

[0165] 4) Repeat steps 2)-3) three times, and record the energy E (Wh) of the last discharge.

[0166] Therefore, 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) Discharge at a constant current of 0.2C to 2.0V, and let stand for 30 minutes;

[0170] 2) Charge at a constant current of 0.2C to 3.8V, then let stand for 30 minutes (#0.2C charging#);

[0171] 3) Discharge at a constant current of 0.2C to 2.0V, and let stand for 30 minutes;

[0172] 4) Charge at 3.0C constant current to 3.8V, then let stand for 30 minutes (#3C charging#);

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

[0174] (8) Fast charging cycle test

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

[0176] 1) Discharge at a constant current of 1 / 3C to 2.0V, then let stand for 30 minutes;

[0177] 2) 4C constant current charging for 4.05 minutes, cutoff voltage 3.8V;

[0178] 3) 3.5C constant current charging for 1.03 minutes, cutoff voltage 3.8V;

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

[0180] 5) 2.5C constant current charging for 1.92 minutes, cutoff voltage 3.8V;

[0181] 6) 2C constant current charging for 2.1 minutes, cutoff voltage 3.8V;

[0182] 7) 1.5C constant current charging for 8.4 minutes, cutoff voltage 3.8V;

[0183] 8) Charge at 1 / 3C constant current to 3.8V, then let stand for 10 minutes;

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

[0185] 10) Repeat steps 2)-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] Continued from Table 1

[0191] sample Energy density (Wh / kg) 3C / 0.2C charging ratio Fast charging cycle count 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 that it does not exist.

[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 resistance, smaller tortuosity, stronger lithium-ion diffusion ability, better fast charging performance, and a longer fast charging cycle life.

[0194] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0195] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A negative electrode sheet, characterized in that, It includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector; The negative electrode active material layer includes a negative electrode active material, which is a carbon-based material, and the orientation degree (OI) value of the negative electrode active material layer satisfies:

0. <OI<30; The surface of the negative electrode active material layer away from the negative electrode current collector is provided with grooves; 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. The depth d of the groove, the compaction density V of the negative electrode sheet, and the OI value of the negative electrode active material layer satisfy the following condition: 0.5V×OI≤d≤100 Wherein, the depth d of the groove is in μm, and the compaction density V of the negative electrode sheet is in g / cm³. 3 .

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 of the groove is 10μm-70μm; And / or, the width of the groove is 20μm-150μm.

4. The negative electrode sheet according to claim 1, characterized in that, The compaction density of the negative electrode sheet is 1.2 g / cm³. 3 -1.9g / cm 3 .

5. The negative electrode sheet according to claim 1, characterized in that, The compaction density of the negative electrode sheet is 1.5 g / cm³. 3 -1.7g / cm 3 .

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

7. The negative electrode sheet according to claim 6, characterized in that, The g1 is 100μm-5000μm, and the g2 is 100μm-1000μm.

8. The negative electrode sheet according to claim 1, characterized in that, The areal density of the negative electrode is 150 g / m³. 2 -500g / m 2 .

9. The negative electrode sheet according to claim 1, characterized in that, The areal density of the negative electrode is 200 g / m³. 2 -300g / m 2 .

10. 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.

11. A method for preparing a negative electrode sheet according to any one of claims 1-10, characterized in that, include: A negative electrode active slurry is prepared, the negative electrode active slurry comprising a carbon-based material, and the negative electrode active slurry is coated on at least one side surface of a negative electrode current collector; The negative electrode active slurry is processed by a magnetically induced orientation device, and then 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.

12. A battery, characterized in that, Includes the negative electrode sheet as described in any one of claims 1-10.

13. An electrical appliance, characterized in that, Includes the battery as described in claim 12.

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