Negative pole piece, preparation method thereof and battery

Abstract

The invention provides a negative pole piece, a preparation method thereof and a battery, the negative pole piece comprises a negative current collector and a negative active material layer, and the negative active material layer comprises a negative active material, a conductive agent and a binder; the negative pole piece meets the following relational expressions: 0.1 < = SV / SL < = 1.0, R / W < = 10%, 0.1% < = R < = 0.5%, 1.0% < = W < = 5.0%; wherein SL is the area of the active particles corresponding to the included angle theta between the orientation of the negative electrode active material and the negative electrode current collector being less than 45 degrees, and Sv is the area of the active particles corresponding to theta being greater than or equal to 45 degrees; r is the range of the distributed mass percentage content of the binder; w0 is the total mass percentage content of the binder; the distribution range R of the binder and the orientation SV / SL of the active particles are controlled through the novel manufacturing process, the phenomenon that the binder is not uniformly distributed in the solvent evaporation process can be reduced, the orientation degree of the active substance particles on the pole piece in the rolling process can be reduced, the battery impedance is reduced, and the battery performance is improved. The electrochemical performance of the battery is improved.

Description

Technical Field

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

[0002] With the rapid increase in global demand for sustainable energy, secondary batteries, as key components of energy storage solutions, have become the focus of research and development in terms of performance optimization and cost control. Existing secondary battery slurry preparation usually adopts a wet process, which requires a large amount of solvents such as deionized water for stirring and dispersion, and then needs to be dried to remove the solvent. This process not only consumes a lot of energy, but also causes the binder to float up during the drying process due to its easy volatilization, resulting in uneven distribution of binders in the pole piece. The longitudinal binder perpendicular to the pole piece is less at the bottom and more at the top. The uneven distribution of binders will lead to several problems: 1. The bonding force between the layer and the current collector is reduced; 2. The excess binder in the upper layer will cause the electrode impedance to increase, resulting in the degradation of electrochemical performance; 3. The layer is easily stuck to the roller during the rolling process, causing processing difficulties. 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. An external high shear force needs to be applied to the dry mixture to fibrillate it and then bond the electrode powder in a mesh-like manner. This has poor compatibility with existing processes and equipment. There are also problems such as uneven dry mixing and film stretching and tearing due to insufficient adhesive content. 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 diaphragm 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 diaphragm, 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 addressed. Summary of the invention

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

[0004] The technical solution adopted by the present invention to solve the above technical problems is as follows: A first aspect of the present invention provides a negative electrode plate, the 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, the negative electrode active material layer comprising a negative electrode active material, a conductive agent and a binder; 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%; 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, in units of m 2 ; Sv 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, in m 2 ; R is the difference in mass percentage of the binder in the negative electrode active material layer between the portion far from the current collector and the portion close to the current collector, which 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 %.

[0005] Optionally, the angle θ is the orientation of the negative electrode active material, and the line connecting a point in the outer contour of the negative electrode active material that is closest to the negative electrode current collector and the center of gravity of the negative electrode active material is the angle formed by the orientation and the negative electrode current collector is θ.

[0006] Optionally, 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 it thoroughly, and centrifuge it for solid-liquid separation, and record the dry weight of the solid ; 2) It is expressed as the total mass percentage content W0 of the binder in the negative electrode active material layer.

[0007] Optionally, the test method for extremely poor binder distribution comprises the following steps: 1) along the direction perpendicular to the plane of the negative electrode current collector, the negative electrode active material layer is divided into m layers of negative electrode active material layers, wherein the outermost layer of the 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; 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 it thoroughly, and centrifuge it for solid-liquid separation, and record the dry weight of the solid ,Will The difference is recorded as the content of the binder in the first layer of the negative electrode active material layer W1; 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 ; 4) W m The difference from W1 is taken as the distribution range R of the binder in the negative electrode active material layer.

[0008] Optionally, in step 1), the thickness of the negative electrode active material sublayer is in the range of 10 um to 50 um.

[0009] 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).

[0010] Optionally, the negative electrode active material includes one or more of artificial graphite, natural graphite, soft carbon, hard carbon, and silicon carbon.

[0011] 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 modified polymers thereof, polyacrylonitrile, modified polyacrylonitrile, polyvinyl alcohol, modified polyvinyl alcohol, polyvinyl butyral, modified polyvinyl butyral, polymethyl methacrylate and modified polymers thereof.

[0012] Optionally, 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.

[0013] A second aspect of the present invention provides a method for preparing a negative electrode sheet, comprising the following steps: (1) Mixing the negative electrode active material and the conductive agent in a prescribed amount to obtain an intermediate material; (2) Adding a binder to the intermediate material and mixing evenly to obtain a negative electrode mixture; (3) thinning the negative electrode mixture at least once to obtain a negative electrode active material layer, which may be screw extrusion thinning or roller thinning; (4) The negative electrode active material layer is compounded with the negative electrode current collector, and then baked and rolled to obtain a negative electrode sheet.

[0014] Optionally, step (2) further comprises adding a solvent to the negative electrode mixture.

[0015] Optionally, the solid content S of the negative electrode mixture in step (2) has a value range of S: 60%≤S≤100%.

[0016] A third aspect of the present invention provides a battery, comprising a positive electrode plate, a separator, and the negative electrode plate as described above or the negative electrode plate prepared by the method for preparing the negative electrode plate as described above.

[0017] According to the negative electrode sheet and its preparation method and battery provided by the present invention, the distribution range R of the binder and the orientation S of the active particles are improved by improving the manufacturing process. V / S L Controlling the process can not only reduce the uneven distribution of the binder caused by the solvent volatilization process, but also reduce the orientation degree of the active material particles on the electrode during the rolling process, thereby reducing the battery impedance and improving the electrochemical performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0019] Figure 1 This is a scanning electron microscope photograph of a cross section of a negative electrode plate provided in one embodiment of the present invention. DETAILED DESCRIPTION

[0020] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention clearer, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0021] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods; the materials and reagents used are reagents and materials that can be obtained from commercial channels unless otherwise specified.

[0022] In one embodiment, the first aspect of the present invention provides a negative electrode plate, the 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, the negative electrode active material layer comprising a negative electrode active material, a conductive agent and a binder; 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%; 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°, corresponding to the area of ​​the active particles, 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 in the negative electrode active material layer between the portion far from the current collector and the portion close to the current collector, which 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 %.

[0023] Specifically, S. V / S L The value range of is any point value among 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1.0 or a range of values ​​consisting of any two point values. In a preferred embodiment, S V / S L The value range: 0.2≤S V / S L ≤1.0; Usually, the active materials in the negative electrode sheets containing layered carbon layer structure active materials will be oriented during the rolling process, that is, the number of particles perpendicular to the current collector will decrease, and the number of particles parallel to the current collector will increase. This orientation is not conducive to the embedding and extraction of lithium ions in the electrode sheets. The role of this relationship is to limit the distribution of the number of particles perpendicular and parallel to the current collector, but this orientation cannot be completely removed at present.

[0024] The present invention is set by this orientation, when the S V and the S L Satisfy the relationship: 0.1≤S V / S L When ≤1.0, the distribution number or proportion of active material particles in the negative electrode active layer perpendicular to the current collector can be increased to enhance the ability of lithium ion embedding and extraction, which is beneficial to improving the electrochemical performance.

[0025] 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 properties such as battery impedance and rate.

[0026] Specifically, along a direction perpendicular to the plane where the negative electrode current collector is located, the negative electrode active material layer is divided into m layers of negative electrode active material sublayers, wherein the outermost layer of the negative electrode active material sublayer 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, and 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.

[0027] Specifically, the binder distribution range R in the negative electrode active material layer is any point value of 0%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, or a range value consisting of any two point values. In a preferred embodiment, the binder distribution range R in the negative electrode active material layer is 0%-0.3%; 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 in the direction perpendicular to the current collector plane, away from the current collector and close to the current collector 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%, it will result in a low binder content in the active material layer close to the current collector and a high binder content in the active material layer away from the current collector, resulting in poor electrochemical performance such as low bonding strength between the active material layer and the current collector and high impedance.

[0028] 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 the values. In a preferred embodiment, the mass content W0 of the binder in the negative electrode active material layer is 1.5%-4.0%; 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 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 is 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 is high, which affects 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.

[0029] Specifically, the value range of R / W0 is any point value of 0%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, or a range of values ​​consisting of any two point values. In a preferred embodiment, 1%<R / W0<5%; 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, the battery impedance can be reduced, and the battery electrochemical performance can be improved.

[0030] 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.

[0031] In one embodiment, 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 angle formed by the orientation and the negative electrode current collector is θ.

[0032] 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 in the negative electrode active layer that are perpendicular to the current collector, thereby improving the ability of lithium ion embedding and extraction, which is beneficial to improving the electrochemical performance.

[0033] In one embodiment, 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 it thoroughly, and centrifuge it for solid-liquid separation, and record the dry weight of the solid ; 2) It is expressed as the total mass percentage content W0 of the binder in the negative electrode active material layer.

[0034] 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, stirred for 30-120 minutes, and then centrifuged and filtered to obtain a solid precipitate, and the solid precipitate is placed in a drying oven and dried at 100-120° C. for 6-24 hours to obtain a solid drying weight of .

[0035] The present invention obtains the content of the binder in the negative electrode active material layer through the above process, which is convenient for further determining the distribution state of the binder in the negative electrode active material layer.

[0036] In one embodiment, the test method for extremely poor adhesive distribution comprises the following steps: 1) along a direction perpendicular to the plane of the negative electrode current collector, the negative electrode active material layer is divided into m layers of negative electrode active material layers, wherein the outermost layer of the negative electrode active material layer farthest 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; 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 it thoroughly, and centrifuge it for solid-liquid separation, and record the dry weight of the solid ,Will The difference is recorded as the content of the binder in the first layer of the negative electrode active material layer W1; 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 ; 4) Set W1, W2, ..., W m The difference between the maximum value and the minimum value in is taken as the distribution range R of the binder in the negative electrode active material layer.

[0037] 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 in the direction perpendicular to the current collector plane, away from the current collector and close to the current collector 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%, it will result in a low binder content in the active material layer close to the current collector and a high binder content in the active material layer away from the current collector, resulting in poor electrochemical performance such as low bonding strength between the active material layer and the current collector and high impedance.

[0038] In one embodiment, in step 1), the thickness of the negative electrode active material sublayer is in the range of 10 um to 50 um.

[0039] Specifically, the thickness of the negative electrode active material sublayer ranges from any point value of 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 of the negative electrode active material sublayer ranges from 20um to 50um.

[0040] 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).

[0041] 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).

[0042] 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 with high electrochemical performance.

[0043] In one embodiment, the negative electrode active material includes one or more of artificial graphite, natural graphite, soft carbon, hard carbon, and silicon carbon.

[0044] 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.

[0045] 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.

[0046] In one embodiment, the second aspect of the present invention provides a method for preparing a negative electrode sheet, comprising the following steps: 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 negative electrode active material layer, which can be screw extrusion thinning or roller thinning; 4) The negative electrode active material layer is compounded with the negative electrode current collector, and after baking and rolling, a negative electrode sheet is obtained.

[0047] The present invention adopts a semi-dry method to prepare the negative electrode plate, and the negative electrode mixture has a higher solid content, thereby reducing the use of solvents and reducing the energy loss in baking. In addition, through the technical route of thinning, compounding, and re-baking, the phenomenon of uneven binder distribution 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.

[0048] In one embodiment, step (2) further comprises adding a solvent to the negative electrode mixture.

[0049] Specifically, the solvent includes deionized water.

[0050] In one embodiment, the solid content S of the negative electrode mixture in step (2) is in the range of 60%≤S≤100%.

[0051] 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%.

[0052] Specifically, the solid content of the negative electrode mixture is any point value among 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%.

[0053] 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 not 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 electrode, increasing the manufacturing cost, which has a huge impact on large-scale industrial manufacturing.

[0054] In one embodiment, the third aspect of the present invention provides a battery, comprising a positive electrode plate, a separator, and the negative electrode plate as described above or the negative electrode plate prepared by the method for preparing the negative electrode plate as described above.

[0055] In one embodiment, the positive electrode plate includes a positive electrode current collector and a positive electrode active material layer coated on one side 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.

[0056] In some embodiments, the positive electrode active material includes one or more of layered sodium electric positive electrodes such as lithium iron phosphate, lithium manganese iron phosphate, lithium cobaltate, lithium manganate, lithium nickel cobalt manganate, 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 manganate, sodium iron nickel manganate, and Prussian blue positive electrodes.

[0057] 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.

[0058] In some embodiments, the positive electrode binder includes 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, polyacrylonitrile and modified polyacrylonitrile, polytetrafluoroethylene and modified polymers thereof.

[0059] In some embodiments, taking the total mass of the positive electrode active material layer as 100%, the mass percentage of the positive electrode active material is 94.5%~98.5%, the mass percentage of the conductive agent is 0.5%~2.5%, and the mass percentage of the binder is 1.0%~3.0%.

[0060] The positive electrode current collector is selected from a metal material that can conduct electrons. Preferably, the positive electrode current collector includes one or more of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the positive electrode current collector is selected from aluminum foil.

[0061] The positive electrode sheet can be prepared according to conventional methods in the art. For example, the positive electrode active material layer is usually prepared by coating a positive electrode slurry made of a positive electrode active material, a positive electrode conductive agent, a positive electrode binder and any other components on a positive electrode current collector, followed by drying and cold pressing.

[0062] Specifically, the diaphragm can be selected from one or more materials such as polypropylene (PP), polyethylene (PE), PP / PE / PP composite film, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ceramic diaphragm, ceramic polyamide (PI), aramid (AF), non-woven fabric, etc.

[0063] In a preferred embodiment, the production of the battery includes the following steps: The positive electrode sheet, the separator and the 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 electrode sheet and the separator are placed in an aluminum-plastic film bag formed by punching and shelling by stacking. The electrolyte is injected into the baked and dried battery cells respectively. After vacuum packaging, standing, formation and other processes, the battery is obtained.

[0064] The beneficial effects of the present invention are further illustrated below in conjunction with embodiments.

[0065] In order to make the invention purpose, technical scheme and beneficial technical effect of the present invention clearer, the present invention is further described in detail below in conjunction with examples. However, it should be understood that the examples of the present invention are only for explaining the present invention, not for limiting the present invention, and the examples of the present invention are not limited to the examples given in the specification. The specific experimental conditions or operating conditions not specified in the examples are made under conventional conditions, or are made under the conditions recommended by the material supplier.

[0066] In addition, it should be understood that one or more method steps mentioned in the present invention do not exclude the existence 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 existence of other devices / apparatuses before or after the combination device / apparatus or the insertion of other devices / apparatuses between these explicitly mentioned two devices / apparatuses, unless otherwise specified. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or the scope of the present invention. Changes or adjustments in their relative relationships should also be regarded as the scope of the present invention without substantially changing the technical content.

[0067] In the following examples, the reagents, materials and instruments used, unless otherwise specified, can be purchased commercially or obtained by synthetic methods known in the art.

[0068] Table 1 Design of negative electrode sheets of Examples 1-12 and Comparative Examples 1-6;

[0069] This embodiment is used to illustrate the negative electrode sheet and battery disclosed in the present invention; it includes the following operating steps: Negative electrode production: 1) Mixing artificial graphite as a negative electrode active material and carbon black as a conductive agent in a mass ratio of 95:2 to obtain an intermediate material 1; 2) Adding adhesive rubber to the intermediate material 1 and mixing evenly to obtain the intermediate material 2; the mass percentage of rubber in the intermediate material 2 is 1%; 3) adding deionized water as a solvent to the intermediate material 2 to obtain a negative electrode mixture, wherein the solid content of the negative electrode mixture is 70%; 4) thinning the negative electrode mixture at least once to obtain a self-supporting negative electrode active material layer; 5) The negative electrode active material layer is compounded with the negative electrode current collector, and after baking and rolling, a negative electrode sheet is obtained.

[0070] Production of positive electrode: The positive electrode active material lithium iron phosphate, the conductive agent carbon black, and the binder polyvinylidene fluoride are mixed in a solvent NMP at a mass ratio of 96.0:2.0:2.0 to form a uniform positive electrode slurry. The slurry is coated on the current collector, and the positive electrode sheet is obtained after baking and rolling.

[0071] Diaphragm production: PE porous polymer film is used as the diaphragm substrate; Battery production: The positive electrode sheet, the separator and the positive electrode sheet are stacked in order, and the separator is placed in the middle of the positive electrode to play an isolating role. The positive electrode sheet, the separator and the positive electrode sheet are repeatedly stacked to form a core. Then the stacked core is placed in an aluminum-plastic film bag formed by punching and forming. The electrolyte prepared above is respectively injected into the baked and dried battery cells. After vacuum packaging, standing, formation and other processes, a battery is obtained.

[0072] Example 2-12 Examples 2-12 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: The various components, contents and solid contents of the mixture in the negative electrode sheet and battery shown in Table 1 were used.

[0073] Comparative Examples 1-6 Comparative Examples 1-6 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: The various components, contents and solid contents of the mixture in the negative electrode sheet and battery shown in Table 1 were used.

[0074] Performance Testing The batteries prepared in the above Examples 1-12 and Comparative Examples 1-6 were subjected to the following performance tests: (1) Charging rate test: Discharge: 25±2℃, discharge the battery at a constant current of 0.5C to 2.5V; Shelf: 25±2℃, shelf for 10min after discharge; Constant current charging: 25±2℃, then charge at 2.0C constant current to 3.65V, record the charging capacity as C i ; 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 ; Charging rate: C i / (C i +C p )*100% is recorded as 2C constant current charging ratio.

[0075] (2) DC resistance test: 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, leave it for 10 minutes, and then discharge it at a constant current of 0.5C to 50% SOC; DC resistance test: leave it for 60 minutes, record the end voltage V1, then charge it at 2C (2.4A) for 30 seconds, record the end voltage V2; DC internal resistance: (V2-V1) / 2.4*1000 is recorded as the measured DC internal resistance value; (3) Cyclic performance test: Charging: 45±2℃, charge the battery at a constant current rate of 1.C to 3.65V, then switch to constant voltage charging, the cut-off condition is that the current is less than 0.05C; Shelf: 45±2℃, shelf for 10min after charging; Discharge: 45±2℃, then discharge at 1.0C constant current to 2.5V, record the discharge capacity as C1; Shelf: 45±2℃, shelf for 10min after discharge; Cycle: Repeat the above steps 1000 times and record the 1000th discharge capacity as C 1000 ; Capacity retention rate: C 1000 / C1*100% is recorded as the capacity retention rate corresponding to 1000 cycles.

[0076] The test results are shown in Table 2.

[0077] Table 2 Electrochemical performance of lithium batteries

[0078] As can be seen from Table 2, compared with Comparative Examples 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 is 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 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 is high, affecting the processing and manufacturing performance, and the binder content is higher than 5%, which significantly reduces the battery energy density while increasing the battery impedance and affecting the electrochemical performance.

[0079] 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 sheet in the direction perpendicular to the current collector plane, the difference in the binder content at the position far from the current collector and the position close to the current collector 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 far 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.

[0080] 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 small amount of binder added, the battery impedance can be reduced, and the battery electrochemical performance can be improved.

[0081] 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.

[0082] like Figure 1 As shown, compared with Comparative Example 5, when the S V and the S L Satisfy the relationship: 0.1≤S V / S L When S is ≤1.0, the number or proportion of active material particles in the negative electrode active layer perpendicular to the current collector can be increased to improve the ability of lithium ion insertion and extraction, which is beneficial to improving the electrochemical performance. 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 properties such as battery impedance and rate.

[0083] Compared with Example 2 and Examples 10-12 and Comparative Example 6, when the solid content of the negative electrode mixture of the present invention 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 will be difficult to form, which is no significantly different from the wet coating process commonly used in the industry and cannot be effectively compounded with the positive electrode current collector. At the same time, low solid content will require an increase in the use of solvent and the energy consumption of baking the electrode, which increases the manufacturing cost, which has a huge impact on large-scale industrial manufacturing.

[0084] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A negative electrode plate, characterized in that: The negative electrode sheet comprises 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; 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%; 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°, corresponding to the area of ​​the active particles, 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 in the negative electrode active material layer between the portion far from the current collector and the portion close to the current collector, which 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 %.

2. The negative electrode sheet according to claim 1, characterized in that: The angle θ is the orientation of the negative electrode active material, and the angle formed by the orientation and the negative electrode collector is θ.

3. The negative electrode sheet according to claim 1, characterized in that: 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 it thoroughly, and centrifuge it for solid-liquid separation, and record the dry weight of the solid ; 2) It is expressed as the total mass percentage content W0 of the binder in the negative electrode active material layer.

4. The negative electrode plate according to claim 1, characterized in that: The test method for extremely poor binder distribution comprises the following steps: The negative electrode active material layer is divided into m layers of negative electrode active material layers along a direction perpendicular to the plane of the negative electrode current collector, wherein the outermost layer of the 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; The first negative electrode active material layer is peeled off, and the initial weight of the first negative electrode active material layer is recorded. , dissolve the stripped negative electrode active material layer in the solvent, stir it thoroughly, and centrifuge it for solid-liquid separation, and record the dry weight of the solid ,Will The difference is recorded as the content of the binder in the first layer of the negative electrode active material layer W1; The negative electrode active material sublayers from the second layer to the m-1th layer are peeled off layer by layer according to the operation of step 1), and the content of the binder in the second layer is W2, ..., and the content of the binder in the mth layer is W. m ; 3) W m The difference from W1 is taken as the distribution range R of the binder in the negative electrode active material layer.

5. The negative electrode sheet according to claim 4, characterized in that: In step 1), the thickness of the negative electrode active material sublayer is in the range of 10 um to 50 um.

6. The negative electrode plate according to claim 1, characterized in that: 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).

7. The negative electrode sheet according to claim 1, characterized in that: The negative electrode active material includes one or more combinations of artificial graphite, natural graphite, soft carbon, hard carbon, and silicon carbon.

8. The negative electrode plate according to claim 1, characterized in that: 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.

9. The negative electrode plate according to claim 1, characterized in that: 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.

10. A method for preparing a negative electrode sheet according to any one of claims 1 to 9, characterized in that: The following steps are involved: Mixing the negative electrode active material and the conductive agent in a prescribed amount to obtain an intermediate material; Adding a binder to the intermediate material and mixing evenly to obtain a negative electrode mixture; Thinning the negative electrode mixture at least once to obtain a negative electrode active material layer, which may be screw extrusion thinning or roller thinning; The negative electrode active material layer is compounded with the negative electrode current collector, and then baked and rolled to obtain a negative electrode sheet.

11. The method for preparing a negative electrode sheet according to claim 10, characterized in that: Step (2) also includes adding a solvent to the negative electrode mixture.

12. The method for preparing a negative electrode sheet according to claim 11, characterized in that: The solid content S of the negative electrode mixture in step (2) has a value range of S: 60%≤S≤100%.

13. A battery, characterized in that: The invention comprises a positive electrode sheet, a separator and a negative electrode sheet according to any one of claims 1 to 9 or a negative electrode sheet prepared by the method for preparing a negative electrode sheet according to any one of claims 10 to 12.

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