A negative electrode sheet, a method for manufacturing the same, and a battery

Abstract

The application provides a negative electrode sheet, a preparation method thereof and a battery, and the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer comprises a negative electrode active material, a conductive agent and a binder; the negative electrode sheet satisfies the following relationship: 0.1 V / S L ≤1.0, R / W0≤10%, 0.1%≤R≤0.5%, 1.0%≤W0≤5.0%; wherein, S L is the area of active particles corresponding to an angle θ<45° between the orientation of the negative electrode active material and the negative electrode current collector, S v is the area of active particles corresponding to an angle θ≥45°; R is the range of the mass percentage of the binder distribution; W0 is the total mass percentage of the binder; the application controls the range R of the binder distribution and the orientation S V / S L of the active particles through a novel manufacturing process, which can reduce the phenomenon of uneven distribution of the binder caused by the solvent volatilization process, and can also reduce the orientation degree of the active material particles on the electrode sheet in the rolling process, thereby reducing the battery impedance and improving the electrochemical performance of the battery.

Description

Technical Field

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

[0002] With the dramatic increase in global demand for sustainable energy, secondary batteries, as key components of energy storage solutions, have become a key focus of research and development, with performance optimization and cost control becoming key. Existing secondary battery slurry preparation typically utilizes a wet process, requiring large amounts of solvents, such as deionized water, for stirring and dispersion, followed by drying to remove the solvent. This process not only consumes significant energy but also volatilizes easily during drying, causing the binder to float upward, leading to uneven binder distribution within the electrode. Vertically perpendicular to the electrode, the binder is less at the bottom and more at the top. This uneven binder distribution can lead to several problems: 1. Reduced adhesion between the layer and the current collector; 2. Excessive binder in the upper layer increases electrode impedance, leading to degraded electrochemical performance; and 3. During the rolling process, the layer is prone to sticking to the rollers, making processing difficult. On the other hand, although the dry electrode process avoids the use of solvents, the only available binder in the solid phase batching process is PTFE. External high shear force needs to be applied to the dry mixture to fibrillate it and form a mesh-like bonded electrode powder, which has poor compatibility with existing processes and equipment. At the same time, there are problems such as uneven dry mixing and insufficient adhesive content, which causes film stretching and tearing. PTFE is unstable at low potentials and will undergo irreversible reactions with lithium. When used in the negative electrode, it will be lithiated and consume active lithium, reducing the bonding effect. In addition, the bonding strength between the membrane prepared by the dry electrode and the current collector is low, and it is usually necessary to set an additional bonding layer between the current collector and the membrane, which increases the complexity of the process and also increases the manufacturing cost. Therefore, how to overcome the above-mentioned technical problems and defects has become a key issue that needs to be solved. Summary of the Invention

[0003] In order to solve the problem of uneven distribution of binder in the preparation process of existing pole pieces, the present invention provides a negative pole piece, a preparation method thereof, and a battery.

[0004] The technical solutions adopted by the present invention to solve the above technical problems are as follows:

[0005] A first aspect of the present invention provides a negative electrode plate, 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, wherein the negative electrode active material layer comprises a negative electrode active material, a conductive agent, and a binder;

[0006] The negative electrode sheet satisfies the relationship: 0.1≤S V / S L ≤1.0, and R / W0≤10%, 0%≤R≤0.5%, 1.0%≤W0≤5.0%;

[0007] Wherein, SL is the angle between the orientation of the negative electrode active material and the negative electrode current collector θ < 45° corresponding to the area of ​​the active particles, the unit is m 2 ;

[0008] Sv is the angle θ between the orientation of the negative electrode active material and the negative electrode current collector ≥ 45°, corresponding to the area of ​​the active particles, in m 2 ;

[0009] R is the difference in mass percentage of the binder between the portion far from the current collector and the portion close to the current collector in the negative electrode active material layer, and is the range R of the binder distribution in the negative electrode active material layer, in units of %;

[0010] W0 is the mass content of the binder in the negative electrode active material layer, in %.

[0011] Optionally, the angle θ is the orientation of the negative electrode active material, and the line connecting the point closest to the negative electrode current collector in the outer contour of the negative electrode active material and the center of gravity of the negative electrode active material is the orientation of the negative electrode active material, and the angle formed by the orientation and the negative electrode current collector is θ.

[0012] Optionally, the method for testing the content of the binder in the negative electrode active material layer comprises the following steps:

[0013] 1) Peel off the negative electrode active material layer from the negative electrode current collector and record the initial weight of the negative electrode active material layer , dissolve the stripped negative electrode active material layer in the solvent, stir thoroughly, and centrifuge to separate the solid and liquid, and record the dry weight of the solid ;

[0014] 2) It is expressed as the total mass percentage W0 of the binder in the negative electrode active material layer.

[0015] Optionally, the test method for extremely poor binder distribution comprises the following steps:

[0016] 1) dividing the negative electrode active material layer into m negative electrode active material layers along a direction perpendicular to the plane of the negative electrode current collector, wherein the outermost negative electrode active material layer on the side away from the negative electrode current collector is the first layer, and the negative electrode active material layer closest to the negative electrode current collector is the mth layer;

[0017] 2) Peel off the first layer of negative electrode active material layer and record the initial weight of the first layer of negative electrode active material layer. , dissolve the stripped negative electrode active material layer in the solvent, stir thoroughly, and centrifuge to separate the solid and liquid, and record the dry weight of the solid ,Will The difference between W and W1 is recorded as the content of the binder in the first layer of the negative electrode active material layer.

[0018] 3) The second layer to the m-1 layer of the negative electrode active material sub-layer is peeled off layer by layer, and the content of the binder in the second layer is W2, …, the content of the binder in the m-1 layer is W m-1 ;

[0019] 4) The difference between W m and W1 is taken as the distribution range R of the binder in the negative electrode active material layer.

[0020] Optionally, in step 1), the thickness of the negative electrode active material sub-layer ranges from 10 um to 50 um.

[0021] In an embodiment, the ratio of the negative electrode active material, the conductive agent and the binder contained in the negative electrode active material layer is (92.0-98.5):(0.5-3.0):(1.0-5.0).

[0022] Optionally, the negative electrode active material includes one or more of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-carbon.

[0023] Optionally, the binder includes one or more of rubber, modified rubber, polyvinylidene fluoride, modified polyvinylidene fluoride, polyimide, modified polyimide, polyethylene, modified polyethylene, polypropylene, modified polypropylene, polyacrylic acid, modified polyacrylic acid, polytetrafluoroethylene and its modified polymer, polyacrylonitrile, modified polyacrylonitrile, polyvinyl alcohol, modified polyvinyl alcohol, polyvinyl butyral, modified polyvinyl butyral, polymethyl methacrylate and its modified polymer.

[0024] Optionally, the conductive agent includes one or more of carbon black, acetylene black, ketjen black, graphene microspheres, three-dimensional conductive metal organic framework, porous spherical carbon, conductive nanotube, nanofiber, graphene, graphite microsheet.

[0025] The second aspect of the present application provides a preparation method of a negative electrode sheet, comprising the following steps:

[0026] (1) Mixing the formula amount of negative electrode active material and conductive agent to obtain intermediate material;

[0027] (2) Adding the binder to the intermediate material and mixing uniformly to obtain a negative electrode mixture;

[0028] (3) Thinning the negative electrode mixture at least once to obtain a negative electrode active material layer, which can be screw extrusion thinning or roll thinning;

[0029] (4) The negative active material layer is compounded with the negative current collector, and is baked and rolled to obtain the negative electrode sheet.

[0030] Optionally, the step (2) further comprises adding a solvent to the negative electrode mixture.

[0031] Optionally, the solid content S of the negative electrode mixture in the step (2) satisfies 60%≤S≤100%.

[0032] The third aspect of the present application provides a battery comprising a positive electrode sheet, a separator and the negative electrode sheet as described above or the negative electrode sheet prepared by the preparation method of the negative electrode sheet as described above.

[0033] According to the negative electrode sheet, the preparation method thereof and the battery provided by the present application, the manufacturing process is improved, the distribution range R of the binder and the orientation S of the active particles are controlled V / S L The phenomenon of uneven distribution of the binder caused by the solvent volatilization process can be reduced, and the orientation degree of the active material particles on the electrode sheet in the rolling process can be reduced, so as to reduce the battery impedance and improve the electrochemical performance of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings used in the description of the embodiments of the present application will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0035] Figure 1 is a scanning electron microscope photograph of the cross section of the negative electrode sheet provided by an embodiment of the present application. DETAILED DESCRIPTION

[0036] In order to make the technical problems, technical solutions and beneficial effects of the present application more clearly understood, the following embodiments will be further described in detail. It should be understood that the specific embodiments described herein are only used to explain the present application and not to limit the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0037] The test methods used in the following examples are conventional methods unless otherwise specified; the materials, reagents and the like used are commercially available reagents and materials unless otherwise specified.

[0038] In an embodiment, the first aspect of the present application provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer arranged on at least one side of the negative electrode current collector, the negative electrode active material layer comprising a negative electrode active material, a conductive agent and a binder;

[0039] The negative electrode sheet satisfies the relationship: 0.1≤S V / S L ≤1.0, and R / W0≤10%, 0%≤R≤0.5%, 1.0%≤W0≤5.0%;

[0040] Wherein, S L is the area of the active particles corresponding to the angle θ between the orientation of the negative electrode active material and the negative electrode current collector, with a unit of m 2 ;

[0041] S V is the area of the active particles corresponding to the angle θ between the orientation of the negative electrode active material and the negative electrode current collector, with a unit of m 2 ;

[0042] R is the difference between the mass percentage of the binder at the position far from the current collector and the position close to the current collector in the negative electrode active material layer, which is the range R of the binder distribution in the negative electrode active material layer, with a unit of %;

[0043] W0 is the mass content of the binder in the negative electrode active material layer, with a unit of %.

[0044] Specifically, the value range of S V / S L is any one value or a range value composed of any two values in 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1.0. In a preferred embodiment, the value range of S V / S L is: 0.2≤S V / S L ≤1.0.

[0045] The active material in the negative electrode sheet containing a layered carbon layer structure active material will be oriented during the rolling process, i.e. the particles perpendicular to the current collector decrease and the particles parallel to the current collector increase. This orientation is not conducive to the embedding and de-embedding of lithium ions in the electrode sheet. The relationship serves to limit the number distribution of the particles perpendicular and parallel to the current collector, but this orientation cannot be completely removed at present.

[0046] The present application sets the orientation, when the S V and the S L satisfy the relationship: 0.1≤S V / SL When ≤1.0, the distribution number or proportion of active material particles perpendicular to the current collector in the negative electrode active layer can be increased to enhance the ability of lithium ion insertion and extraction, which is beneficial to improving the electrochemical performance.

[0047] When S V / S L When it is less than 0.1, the number of particles perpendicular to the current collector in the active material particles on the electrode will decrease, while the number of particles parallel to the current collector will increase. This orientation distribution is not conducive to the embedding and extraction of lithium ions in the electrode, and will affect the electrochemical performance of the battery, such as impedance and rate.

[0048] Specifically, the negative electrode active material layer is divided into m negative electrode active material sublayers along a direction perpendicular to the plane of the negative electrode current collector, wherein the outermost negative electrode active material sublayer away from the negative electrode current collector is the first layer, the negative electrode active material sublayer closest to the negative electrode current collector is the mth layer, the content of the binder in the first layer of the negative electrode active material sublayer is W1; the content of the binder in the mth layer is W m ;W m The difference from W1 indicates that the distribution of the binder in the negative electrode active material layer is extremely poor.

[0049] Specifically, the binder distribution range R in the negative electrode active material layer is any one of 0%, 0.1%, 0.2%, 0.3%, 0.4%, and 0.5%, or a range consisting of any two of these values. In a preferred embodiment, the binder distribution range R in the negative electrode active material layer is 0%-0.3%;

[0050] When the binder distribution range R in the negative electrode active material layer is 0%-0.5%, the difference in binder content between the active material layer in the electrode sheet, away from the current collector and close to the current collector in the direction perpendicular to the current collector plane is small, the binder distribution in the active material layer of the electrode sheet is more uniform, the active material layer and the current collector have a high bonding strength, and the impedance of the battery is also low, with better electrochemical performance; when the binder distribution range R in the negative electrode active material layer is greater than 0.5%, the binder content in the active material layer close to the current collector is low, and the binder content in the active material layer away from the current collector is high, resulting in poor electrochemical performance such as low bonding strength and high impedance between the active material layer and the current collector.

[0051] Specifically, the mass content W0 of the binder in the negative electrode active material layer is any one of 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, and 5.0%, or a range consisting of any two of these values. In a preferred embodiment, the mass content W0 of the binder in the negative electrode active material layer is 1.5%-4.0%.

[0052] When the mass content W0 of the binder in the negative electrode active material layer is 1.0%-5.0%, the negative electrode plate can be prepared by the scheme of the present invention under the condition of low binder addition amount and high solid content of the negative electrode mixture, and the active material layer and the current collector are bonded, and the plate has high electrochemical performance; when the mass content W0 of the binder in the negative electrode active material layer is less than 1.0%, the cohesion of the negative electrode mixture will be low, and a formed film cannot be obtained after thinning, and the bonding strength between the active material layer and the current collector is low, which affects the manufacturability and electrochemical performance of the plate; when the mass content W0 of the binder in the negative electrode active material layer is greater than 5.0%, the viscosity of the negative electrode mixture will be high, affecting the processing and manufacturing performance, and the binder content higher than 5% will significantly reduce the battery energy density while increasing the battery impedance and affecting the electrochemical performance.

[0053] Specifically, the value range of R / W0 is any value among 0%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, or a range consisting of any two values. In a preferred embodiment, 1%<R / W0<5%;

[0054] The present invention controls the distribution range R of the binder. When R and W0 satisfy the relationship: R / W0≤10%, the uneven distribution of the binder caused by the solvent volatilization process can be reduced with a small amount of binder added, thereby reducing the battery impedance and improving the battery electrochemical performance.

[0055] When R / W0>10%, the binder content in the active material layer close to the current collector will be low, while the binder content in the active material layer far from the current collector will be high, resulting in poor electrochemical performance such as low bonding strength between the active material layer and the current collector and high impedance.

[0056] In one embodiment, the angle θ is the orientation of the negative electrode active material. The line connecting the point closest to the negative electrode current collector in the outer contour of the negative electrode active material and the center of gravity of the negative electrode active material is the orientation of the negative electrode active material, and the angle formed by the orientation and the negative electrode current collector is θ.

[0057] Specifically, the value range of θ is 0-90°. In a preferred embodiment, the value range of θ is 45-90°, which can increase the distribution number or proportion of active material particles perpendicular to the current collector in the negative electrode active layer, thereby improving the ability of lithium ion insertion and extraction, which is beneficial to improving electrochemical performance.

[0058] In one embodiment, the method for testing the content of the binder in the negative electrode active material layer comprises the following steps:

[0059] 1) Peel off the negative electrode active material layer from the negative electrode current collector and record the initial weight of the negative electrode active material layer , dissolve the stripped negative electrode active material layer in the solvent, stir thoroughly, and centrifuge to separate the solid and liquid, and record the dry weight of the solid ;

[0060] 2) It is expressed as the total mass percentage W0 of the binder in the negative electrode active material layer.

[0061] Specifically, in step 1), the solvent includes one or more of deionized water, N-methylpyrrolidone, N,N-dimethylformamide, and dimethyl sulfoxide; the stripped negative electrode active material layer is dissolved in the solvent and stirred for 30-120 minutes, and then centrifuged and filtered to obtain a solid precipitate, which is placed in a drying oven and dried at 100-120°C for 6-24 hours to obtain a solid drying weight. .

[0062] The present invention obtains the content of the binder in the negative electrode active material layer through the above process, which facilitates further determination of the distribution state of the binder in the negative electrode active material layer.

[0063] In one embodiment, the method for testing poor adhesive distribution comprises the following steps:

[0064] 1) dividing the negative electrode active material layer into m negative electrode active material layers along a direction perpendicular to the plane of the negative electrode current collector, wherein the outermost negative electrode active material layer away from the negative electrode current collector is the first layer, and the negative electrode active material layer closest to the negative electrode current collector is the mth layer;

[0065] 2) Peel off the first layer of negative electrode active material layer and record the initial weight of the first layer of negative electrode active material layer. , dissolve the stripped negative electrode active material layer in the solvent, stir thoroughly, and centrifuge to separate the solid and liquid, and record the dry weight of the solid ,Will The difference is recorded as the binder content W1 in the first layer of the negative electrode active material layer;

[0066] 3) peeling off the negative electrode active material sublayers from the second layer to the m-1th layer layer by layer, all according to the operation of step 1), to obtain a binder content of W2 in the second layer, ..., a binder content of W in the m-1th layer, m-1 ;

[0067] 4) Set W1, W2, ..., W m The difference between the maximum and minimum values ​​in is taken as the distribution range R of the binder in the negative electrode active material layer.

[0068] When the binder distribution range R in the negative electrode active material layer is 0%-0.5%, the difference in binder content between the active material layer in the electrode sheet, away from the current collector and close to the current collector in the direction perpendicular to the current collector plane is small, the binder distribution in the active material layer of the electrode sheet is more uniform, the active material layer and the current collector have a high bonding strength, and the impedance of the battery is also low, with better electrochemical performance; when the binder distribution range R in the negative electrode active material layer is greater than 0.5%, the binder content in the active material layer close to the current collector is low, and the binder content in the active material layer away from the current collector is high, resulting in poor electrochemical performance such as low bonding strength and high impedance between the active material layer and the current collector.

[0069] In one embodiment, in step 1), the thickness of the negative electrode active material sub-layer is in the range of 10 um to 50 um.

[0070] Specifically, the thickness range of the negative electrode active material sublayer is any point value among 10um, 15um, 20um, 25um, 30um, 35um, 40um, 45um or 50um, or a range value composed of any two point values. In a preferred embodiment, the thickness range of the negative electrode active material sublayer is 20um-50um.

[0071] In one embodiment, the ratio of the negative electrode active material, the conductive agent, and the binder contained in the negative electrode active material layer is (92.0-98.5): (0.5-3.0): (1.0-5.0).

[0072] Specifically, the ratio of the conductive agent to the binder is any point value among 92.0:3.0:5.0, 93.3:2.5:4.2, 94.6:2:3.4, 95.9:1.5:2.6, 97.2:1:1.8 or 98.5:0.5:1.0, or a range value consisting of any two point values. In a preferred embodiment, the ratio of the conductive agent to the binder is (93.3~97.2):(1~2.5):(1.8~4.2).

[0073] When the ratio of the negative electrode active material, the conductive agent and the binder in the negative electrode active material layer is (92.0~98.5):(0.5~3.0):(1.0~5.0), a negative electrode sheet can be prepared by the scheme of the present invention with a low amount of binder added and a high solid content of the negative electrode mixture, and the active material layer can be bonded to the current collector, and the negative electrode sheet has high electrochemical performance.

[0074] In one embodiment, the negative electrode active material includes one or more of artificial graphite, natural graphite, soft carbon, hard carbon, and silicon carbon.

[0075] In one embodiment, the binder includes one or more of rubber, modified rubber, polyvinylidene fluoride, modified polyvinylidene fluoride, polyimide, modified polyimide, polyethylene, modified polyethylene, polypropylene, modified polypropylene, polyacrylic acid, modified polyacrylic acid, polytetrafluoroethylene and modified polymers thereof, polyacrylonitrile, modified polyacrylonitrile, polyvinyl alcohol, modified polyvinyl alcohol, polyvinyl butyral, modified polyvinyl butyral, polymethyl methacrylate and modified polymers thereof.

[0076] In one embodiment, the conductive agent includes one or more of carbon black, acetylene black, Ketjen black, graphene microspheres, three-dimensional conductive metal organic frameworks, porous spherical carbon, conductive nanotubes, nanofibers, graphene, and graphite microsheets.

[0077] In one embodiment, the second aspect of the present invention provides a method for preparing a negative electrode sheet, comprising the following steps:

[0078] 1) Mixing the negative electrode active material and the conductive agent in the formulated amount to obtain an intermediate material;

[0079] 2) Add a binder to the intermediate material and mix evenly to obtain a negative electrode mixture;

[0080] 3) thinning the negative electrode mixture at least once to obtain a negative electrode active material layer, which can be screw extrusion thinning or roller thinning;

[0081] 4) The negative electrode active material layer is compounded with the negative electrode current collector, and after baking and roller pressing, a negative electrode sheet is obtained.

[0082] The present invention adopts a semi-dry method to prepare the negative electrode sheet. The negative electrode mixture has a high solid content, which can reduce the use of solvents and reduce the energy loss in baking. In addition, through the technical route of thinning, compounding, and re-baking, the uneven distribution of the binder caused by the solvent volatilization process is reduced, the battery impedance is reduced, and the battery electrochemical performance is improved. At the same time, the distribution number or proportion of active material particles perpendicular to the current collector in the negative electrode active layer can be increased, which is beneficial to improving the electrochemical performance.

[0083] In one embodiment, step (2) further comprises adding a solvent to the negative electrode mixture.

[0084] Specifically, the solvent includes deionized water.

[0085] In one embodiment, the solid content S of the negative electrode mixture in step (2) is in the range of 60%≤S≤100%.

[0086] Specifically, when no solvent is added to the negative electrode mixture, the solid content S of the negative electrode mixture is 100%; when no solvent is added to the negative electrode mixture, the solid content S of the negative electrode mixture is 60%≤S<100%.

[0087] Specifically, the solid content of the negative electrode mixture is any point value of 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100%, or a range value consisting of any two point values; in a preferred embodiment, the solid content of the negative electrode mixture is 80%≤S≤100%.

[0088] When the solid content of the negative electrode mixture of the present invention is 60%-100%, the use of solvents can be reduced and the energy loss in baking can be reduced. When the value range of the solid content S is less than 60%, the thinned membrane will be difficult to form, which is no significantly different from the wet coating process commonly used in the current industry and cannot be effectively compounded with the negative electrode current collector. At the same time, low solid content will require an increase in the use of solvents and the energy consumption of baking the electrodes, increasing manufacturing costs, which has a huge impact on large-scale industrial manufacturing.

[0089] In one embodiment, the third aspect of the present invention provides a battery, comprising a positive electrode sheet, a separator, and the negative electrode sheet as described above or the negative electrode sheet prepared by the method for preparing the negative electrode sheet as described above.

[0090] In one embodiment, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer coated on one or both sides of the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material, a conductive agent, and a binder.

[0091] In some embodiments, the positive electrode active material includes one or more of layered sodium positive electrodes such as lithium iron phosphate, lithium manganese iron phosphate, lithium cobaltate, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium-rich manganese-based materials, sodium iron sulfate, sodium iron phosphate, sodium iron pyrophosphate, sodium iron pyrophosphate, sodium vanadium phosphate, sodium copper iron manganese oxide, sodium iron nickel manganese oxide, and Prussian blue positive electrodes.

[0092] In some embodiments, the positive electrode conductive agent includes one or more of carbon black, acetylene black, Ketjen black, graphene microspheres, three-dimensional conductive metal organic frameworks, porous spherical carbon, conductive nanotubes, nanofibers, graphene, graphite microsheets, etc.

[0093] In some embodiments, the cathode binder comprises one or more of rubber, modified rubber, polyvinylidene fluoride, modified polyvinylidene fluoride, polyimide, modified polyimide, polypropylene, modified polypropylene, polyacrylic acid, modified polyacrylic acid, polyvinyl alcohol, modified polyvinyl alcohol, polyvinyl butyral, modified polyvinyl butyral, and polyacrylonitrile and modified polyacrylonitrile, polytetrafluoroethylene and modified polymers thereof.

[0094] In some embodiments, the mass percentage of the cathode active material is 94.5% to 98.5%, the mass percentage of the conductive agent is 0.5% to 2.5%, and the mass percentage of the binder is 1.0% to 3.0%, based on 100% of the total mass of the cathode active material layer.

[0095] The cathode current collector is selected from metal materials that can conduct electrons, preferably, the cathode current collector comprises one or more of Al, Ni, tin, copper, and stainless steel, and in more preferred embodiments, the cathode current collector is selected from aluminum foil.

[0096] The cathode electrode sheet can be prepared according to conventional methods in the art. For example, the cathode active material layer is generally prepared by coating a cathode slurry comprising the cathode active material, the cathode conductive agent, the cathode binder, and any other components on a cathode current collector, and then drying and cold-pressing.

[0097] Specifically, the separator can be selected from one or more of polypropylene (PP), polyethylene (PE), PP / PE / PP composite film, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ceramic separator, ceramic polyamide (PI), aramid fiber (AF), and non-woven fabric.

[0098] In a preferred embodiment, the preparation of the battery comprises the following steps:

[0099] The cathode electrode sheet, the separator, and the cathode electrode sheet are stacked in order, with the separator in the middle of the cathode, serving as a separation function. The electrode sheet and the separator are placed in an aluminum plastic film bag in a laminated manner, the electrolyte is injected into the baked and dried battery cell, and the battery is obtained through vacuum packaging, standing, and formation processes.

[0100] The beneficial effects of the present application are further illustrated in the following examples.

[0101] In order to make the invention objectives, technical solutions and beneficial technical effects of the present invention clearer, the present invention is further described in detail below with reference to the examples. However, it should be understood that the examples of the present invention are only for the purpose of explaining the present invention and are not intended to limit the present invention, and the examples of the present invention are not limited to the examples given in the specification. In the examples, where no specific experimental conditions or operating conditions are specified, the products were prepared under conventional conditions or under the conditions recommended by the material supplier.

[0102] Furthermore, it should be understood that the one or more method steps mentioned in the present invention do not exclude the presence of other method steps before or after the combination step, or the insertion of other method steps between these explicitly mentioned steps, unless otherwise specified. It should also be understood that the combination connection relationship between one or more devices / apparatuses mentioned in the present invention does not exclude the presence of other devices / apparatuses before or after the combination device / apparatus, or the insertion of other devices / apparatuses between two explicitly mentioned devices / apparatuses, unless otherwise specified. Furthermore, unless otherwise specified, the numbering of each method step is merely a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or to define the scope of the present invention. Changes or adjustments to their relative relationships, without substantially changing the technical content, should also be considered within the scope of the present invention.

[0103] In the following examples, the reagents, materials and instruments used, unless otherwise specified, can be purchased commercially or obtained through synthetic methods known in the art.

[0104] Table 1 Design of negative electrode sheets of Examples 1-12 and Comparative Examples 1-6;

[0105]

[0106] This embodiment is used to illustrate the negative electrode sheet and battery disclosed in the present invention; it includes the following steps:

[0107] Production of negative electrode:

[0108] 1) artificial graphite, a negative electrode active material, and carbon black, a conductive agent, were mixed in a mass ratio of 95:2 to obtain intermediate material 1;

[0109] 2) Adding adhesive rubber to the intermediate material 1 and mixing uniformly to obtain the intermediate material 2; the mass percentage of rubber in the intermediate material 2 is 1%;

[0110] 3) adding deionized water as a solvent to the intermediate material 2 to obtain a negative electrode mixture having a solid content of 70%;

[0111] 4) thinning the negative electrode mixture at least once to obtain a self-supporting negative electrode active material layer;

[0112] 5) The negative electrode active material layer is compounded with the negative electrode current collector, and after baking and roll pressing, a negative electrode sheet is obtained.

[0113] Production of positive electrode:

[0114] The positive electrode active material, lithium iron phosphate, the conductive agent, carbon black, and the binder, polyvinylidene fluoride, were mixed in a solvent, NMP, at a mass ratio of 96.0:2.0:2.0 to form a uniform positive electrode slurry. This slurry was coated on the current collector and baked and roll-pressed to obtain the positive electrode sheet.

[0115] Diaphragm production:

[0116] PE porous polymer film is used as the separator substrate;

[0117] Battery production:

[0118] The positive electrode sheet, separator and positive electrode sheet are stacked in order, so that the separator is in the middle of the positive electrode to play an isolating role. The positive electrode sheet, separator and positive electrode sheet are repeatedly stacked to form a pole core, and then the stacked pole core is placed in an aluminum-plastic film bag formed by punching and forming the shell. The electrolyte prepared above is respectively injected into the baked and dried battery cells. After vacuum packaging, standing, formation and other processes, the battery is obtained.

[0119] Example 2-12

[0120] Examples 2-12 are used to illustrate the negative electrode sheet and battery disclosed in the present invention, and include most of the operating steps in Example 1, except that:

[0121] The various components, contents and solid contents of the mixture in the negative electrode sheet and battery shown in Table 1 were used.

[0122] Comparative Examples 1-6

[0123] Comparative Examples 1-6 are used to illustrate the negative electrode sheet and battery disclosed in the present invention, including most of the operating steps in Example 1, except that:

[0124] The various components, contents and solid contents of the mixture in the negative electrode sheet and battery shown in Table 1 were used.

[0125] Performance Testing

[0126] The batteries prepared in Examples 1-12 and Comparative Examples 1-6 were subjected to the following performance tests:

[0127] (1) Charging rate test:

[0128] Discharge: At 25±2℃, discharge the battery at a constant current of 0.5C to 2.5V;

[0129] Shelf: 25±2℃, shelf for 10min after discharge;

[0130] Constant current charging: 25±2℃, then charge at 2.0C constant current to 3.65V, record the charging capacity as C i ;

[0131] Constant voltage charging: 25±2℃, then charge at 3.65V constant voltage until the cut-off current is 0.05C, and record the charging capacity as C p ;

[0132] Charge rate: C i / (C i +C p )*100% is recorded as 2C constant current charging ratio.

[0133] (2) DC resistance test:

[0134] Adjust to 50% SOC: 25±2℃, charge the battery at a constant current rate of 0.5C to 3.65V, then switch to constant voltage charging. The cutoff condition is that the current is less than 0.05C. After charging, let it stand for 10 minutes, and then discharge it at a constant current of 0.5C to 50% SOC;

[0135] DC resistance test: Wait for 60 minutes, record the end voltage V1, then charge at 2C (2.4A) for 30 seconds, record the end voltage V2;

[0136] DC internal resistance: (V2-V1) / 2.4*1000 is recorded as the measured DC internal resistance value;

[0137] (3) Cyclic performance test:

[0138] Charging: At 45±2℃, charge the battery at a constant current rate of 1.C to 3.65V, then switch to constant voltage charging. The cutoff condition is that the current is less than 0.05C;

[0139] Shelf: 45±2℃, shelf for 10 minutes after charging;

[0140] Discharge: 45±2℃, then discharge at 1.0C constant current to 2.5V, record the discharge capacity as C1;

[0141] Shelf: 45±2℃, shelf for 10min after discharge;

[0142] Cycle: Repeat the above steps 1000 times and record the discharge capacity of the 1000th time as C 1000 ;

[0143] Capacity retention rate: C 1000 / C1*100% is recorded as the capacity retention rate corresponding to 1000 cycles.

[0144] The test results are shown in Table 2.

[0145] Table 2 Electrochemical performance of lithium batteries

[0146]

[0147] As can be seen from Table 2, compared with Comparative Example 1-2, when the mass content W0 of the binder in the negative electrode active material layer is 1.0%-5.0%, the negative electrode sheet can be prepared by the scheme of the present invention under the condition of low binder addition and high solid content of the negative electrode mixture, and the active material layer is bonded to the current collector, and has high electrochemical performance; when the mass content W0 of the binder in the negative electrode active material layer is less than 1.0%, the cohesion of the negative electrode mixture will be low, and a formed film cannot be obtained after thinning, and the bonding strength between the active material layer and the current collector is low, affecting the manufacturability and electrochemical performance of the electrode sheet; when the mass content W0 of the binder in the negative electrode active material layer is greater than 5.0%, the viscosity of the negative electrode mixture will be high, affecting the processing and manufacturing performance, and the binder content is higher than 5%, which will significantly reduce the battery energy density while increasing the battery impedance and affecting the electrochemical performance.

[0148] Compared with Comparative Example 3, when the binder distribution range R in the negative electrode active material layer is 0%-0.5%, the active material layer in the electrode has a smaller content of the binder away from the current collector and close to the current collector in the direction perpendicular to the current collector plane, and the binder in the active material layer of the electrode is more evenly distributed. The active material layer has a higher bonding strength with the current collector, and the impedance of the battery is also lower, with better electrochemical performance. When the binder distribution range R in the negative electrode active material layer is greater than 0.5%, the binder content in the active material layer close to the current collector is low, and the binder content in the active material layer away from the current collector is high, resulting in poor electrochemical performance such as low bonding strength between the active material layer and the current collector and high impedance.

[0149] Compared with Comparative Example 4, when R and W0 satisfy the relationship: R / W0≤10%, the uneven distribution of the binder caused by the solvent volatilization process can be reduced with a smaller amount of binder added, the battery impedance can be reduced, and the battery electrochemical performance can be improved.

[0150] When R / W0>10%, the binder content in the active material layer close to the current collector will be low, while the binder content in the active material layer far from the current collector will be high, resulting in poor electrochemical performance such as low bonding strength between the active material layer and the current collector and high impedance.

[0151] like Figure 1As shown, compared with Comparative Example 2 and Examples 8-9 and Comparative Example 5, when the S V and the S L When the relationship 0.1≤S V / S L ≤1.0 is met, the number or proportion of active material particles perpendicular to the current collector in the negative active layer can be increased, the ability of lithium ion intercalation and deintercalation is improved, and the electrochemical performance is improved; when S V / S L <0.1, the number of particles perpendicular to the current collector in the active material particles on the electrode sheet is reduced, and the number of particles parallel to the current collector is increased. This orientation distribution is not conducive to the intercalation and deintercalation of lithium ions in the electrode sheet, and affects the battery impedance and rate electrochemical performance.

[0152] Compared with Comparative Example 2 and Examples 10-12 and Comparative Example 6, when the solid content of the negative electrode mixture of the application is 60%-100%, the use of solvent can be reduced, and the energy loss in baking can be reduced. When the value range of the solid content S is less than 60%, the thinned film is difficult to form, and there is no significant difference from the current industry wet coating process, and the negative electrode current collector cannot be effectively compounded. At the same time, the low solid content requires an increase in the amount of solvent used and the energy consumption of the baked electrode sheet, increasing the manufacturing cost, which has a huge impact on large-scale industrial manufacturing.

[0153] The above only describes the preferred embodiments of the application and is not intended to limit the application. Any modification, equivalent replacement and improvement within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. A method for preparing a negative electrode sheet, characterized in that: The following steps are involved: 1) Mixing the negative electrode active material and the conductive agent in the formulated amount to obtain an intermediate material; 2) Add a binder to the intermediate material and mix evenly to obtain a negative electrode mixture; 3) thinning the negative electrode mixture at least once to obtain a self-supporting negative electrode active material layer, wherein the thinning is performed by screw extrusion thinning or roller thinning; 4) Compounding the negative electrode active material layer with the negative electrode current collector, baking, and rolling to obtain a negative electrode sheet; The solid content S of the negative electrode mixture in step (2) is in the range of 60% ≤ S ≤ 100%; The negative electrode sheet 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, wherein the negative electrode active material layer includes a negative electrode active material, a conductive agent and a binder; The negative electrode sheet satisfies the relationship: 0.1≤S V / S L ≤0.3, and R / W0≤10%, 0.125%≤R≤0.5%, 2.5%≤W0≤5.0%; Among them, S L The angle θ between the orientation of the negative electrode active material and the negative electrode current collector is less than 45°, and the area of ​​the active particles is expressed in m 2 ; S v The angle θ between the orientation of the negative electrode active material and the negative electrode current collector is ≥45°, corresponding to the area of ​​the active particles, in m 2 ; R is the difference in mass percentage of the binder between the portion far from the current collector and the portion close to the current collector in the negative electrode active material layer, and is the range R of the binder distribution in the negative electrode active material layer, in units of %; W0 is the mass content of the binder in the negative electrode active material layer, in units of %; The line connecting the point closest to the negative electrode current collector in the outer contour of the negative electrode active material and the center of gravity of the negative electrode active material is the orientation of the negative electrode active material, and the angle formed by the orientation and the negative electrode current collector is θ.

2. The method for preparing a negative electrode sheet according to claim 1, wherein: The method for testing the content of the binder in the negative electrode active material layer comprises the following steps: 1) Peel off the negative electrode active material layer from the negative electrode current collector and record the initial weight of the negative electrode active material layer , dissolve the stripped negative electrode active material layer in the solvent, stir thoroughly, and centrifuge to separate the solid and liquid, and record the dry weight of the solid ; 2) - ) / *100% represents the total mass percentage W0 of the binder in the negative electrode active material layer.

3. The method for preparing a negative electrode sheet according to claim 1, wherein: The test method for extremely poor binder distribution comprises the following steps: 1) dividing the negative electrode active material layer into m negative electrode active material sublayers along a direction perpendicular to the plane of the negative electrode current collector, wherein the outermost negative electrode active material sublayer on the side away from the negative electrode current collector is the first layer, and the negative electrode active material sublayer closest to the negative electrode current collector is the mth layer; 2) Peel off the negative electrode active material sublayer of the first layer and record the initial weight of the negative electrode active material sublayer of the first layer. , dissolve the stripped negative electrode active material sublayer in the solvent, stir thoroughly, and centrifuge to separate the solid and liquid, and record the dry weight of the solid ,Will( - ) / * 100% of the difference is recorded as the content of the binder in the first layer of the negative electrode active material sublayer W1; 3) Peel off the negative electrode active material sublayers from the second layer to the mth layer layer by layer, all according to the operation of step 2), and obtain a binder content of W2 in the second layer, ..., a binder content of W in the mth layer. m ; W m The difference from W1 is taken as the distribution range R of the binder in the negative electrode active material layer.

4. The method for preparing a negative electrode sheet according to claim 3, wherein: In step 1), the thickness of the negative electrode active material sublayer is in the range of 10 μm to 50 μm.

5. The method for preparing a negative electrode sheet according to claim 1, wherein: The ratio of the negative electrode active material, the conductive agent and the binder contained in the negative electrode active material layer is (92.0-98.5): (0.5-3.0): (1.0-5.0).

6. The method for preparing a negative electrode sheet according to claim 1, wherein: The negative electrode active material includes one or more of artificial graphite, natural graphite, soft carbon, hard carbon, and silicon carbon.

7. The method for preparing a negative electrode sheet according to claim 1, wherein: The binder includes one or more of rubber, modified rubber, polyvinylidene fluoride, modified polyvinylidene fluoride, polyimide, modified polyimide, polyethylene, modified polyethylene, polypropylene, modified polypropylene, polyacrylic acid, modified polyacrylic acid, polytetrafluoroethylene and modified polymers thereof, polyacrylonitrile, modified polyacrylonitrile, polyvinyl alcohol, modified polyvinyl alcohol, polyvinyl butyral, modified polyvinyl butyral, polymethyl methacrylate and modified polymers thereof.

8. The method for preparing a negative electrode sheet according to claim 1, wherein: The conductive agent includes one or more of carbon black, three-dimensional conductive metal organic framework, porous spherical carbon, conductive nanotubes, graphene, and graphite microsheets.

9. The method for preparing a negative electrode sheet according to claim 1, wherein: Step (2) also includes adding a solvent to the negative electrode mixture.

10. A battery, characterized in that: The invention comprises a positive electrode sheet, a separator and a negative electrode sheet prepared by the preparation method of the negative electrode sheet according to any one of claims 1 to 9.

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