Method for manufacturing pole piece, pole piece and lithium ion battery

Abstract

The application provides a preparation method of an electrode sheet, the electrode sheet and a lithium ion battery. The preparation method comprises the following steps: preparing a first slurry and a second slurry, the average particle size D50 of the active material in the first slurry is greater than the average particle size D50 of the active material in the second slurry; and / or, the mass percentage of the conductive agent in the first slurry is lower than the mass percentage of the conductive agent in the second slurry; and / or, the mass percentage of the binder in the first slurry is lower than the mass percentage of the binder in the second slurry; and / or, the second slurry further comprises an additive; the first slurry and the second slurry are co-extrusion coated on the middle area and the edge functional area in the width direction of the current collector; then, synchronous drying treatment is performed to form a first active material layer and a second active material layer, and the two layers are diffused and fused with each other at the joint to form a gradient transition layer. In the coating stage, the edge component is targeted and optimized, the process is simple, and the risk of powder falling off from the edge is eliminated.

Description

Technical Field

[0001] This application belongs to the field of battery manufacturing technology, and relates to a method for preparing an electrode, the electrode and a lithium-ion battery. Background Technology

[0002] After coating and drying, lithium-ion battery electrodes often experience problems such as powder shedding and cracking at the edges due to discontinuous conductive networks, insufficient adhesion, or stress concentration. In severe cases, this can lead to lithium plating, affecting battery safety and lifespan. Currently, "post-processing" of the coated electrodes is commonly used to improve edge performance. Key methods include applying a protective layer to the edges, edge thinning and embossing, multi-layer coating, and applying dispersant to the edges.

[0003] Existing technologies disclose a process where the active material of the entire electrode sheet is first coated and dried, followed by a secondary coating of insulating slurry on the edge area, and then dried again to form an edge protective layer. However, this approach is a "post-coating" process, where a clear physical interface exists between the active coating and the edge protective coating. During charging and discharging, the interface is prone to peeling due to volume expansion and contraction. Furthermore, the insulating coating does not contribute to capacity, reducing energy density, and the additional coating and drying steps increase manufacturing costs. Researchers have thinned the edges of the coated and dried electrode sheet and combined this with an embossing process to create specific textures in the edge functional areas. However, this alters the geometry (thickness, surface texture) of the electrode edge, rather than the material components themselves. The thinning process is difficult to control and can easily damage the edge coating, while embossing introduces additional mechanical stress, failing to address the intrinsic issues of edge conductivity and adhesion. Existing technologies disclose the sequential layering of slurry layers of different components along the thickness direction on the current collector, for example, using a high-adhesion slurry as the bottom layer and a high-conductivity slurry as the top layer, forming a multi-layer structure along the thickness direction. However, this method involves layering along the thickness direction, with each slurry layer covering the full width, which fails to address issues such as edge powder shedding and lithium plating. Currently, the edge-supplementary coating dispersion method involves coating and drying the middle region of the electrode, followed by applying a slurry containing a dispersant to the edge region. This is a step-by-step coating process; the slurry in the middle region has already dried before the edge slurry is applied. This creates a physical interface where a wet film covers a dry film, posing a risk of delamination over long-term cycling.

[0004] In summary, existing technologies do not solve the edge problem at the coating source. Instead, they involve physical processing after coating or secondary coating after coating, resulting in multiple manufacturing processes, high production costs, and the inability to eliminate the risk of peeling during long-term cycles. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this application aims to provide a method for preparing an electrode, an electrode, and a lithium-ion battery, which solves the problems of high risk of physical interface delamination, complex processes, and inability to achieve targeted optimization of edge components during the coating stage caused by post-processing for edge protection or step-by-step coating of existing electrodes.

[0006] To achieve this objective, the following technical solution is adopted in this application: In a first aspect, this application provides a method for preparing an electrode sheet, the method comprising: A first slurry and a second slurry are prepared, wherein the first slurry and the second slurry independently comprise an active material, a conductive agent, and a binder, respectively; The average particle size D50 of the active material in the first slurry is greater than the average particle size D50 of the active material in the second slurry; and / or, the mass percentage of the conductive agent in the first slurry is lower than the mass percentage of the conductive agent in the second slurry; and / or, the mass percentage of the binder in the first slurry is lower than the mass percentage of the binder in the second slurry; and / or, the second slurry also includes additives. A current collector is provided, and a first slurry and a second slurry are co-extruded and coated on different areas of the surface of the current collector to simultaneously form an intermediate area coated with the first slurry and an edge functional area coated with the second slurry, wherein the edge functional area is formed on at least one side of the intermediate area along the width direction of the current collector. Subsequently, a simultaneous drying process is performed, in which the first slurry and the second slurry respectively form a first active material layer and a second active material layer, and a portion of the first slurry and the second slurry diffuse and fuse with each other to form a gradient transition layer at the junction of the edge functional area and the middle area.

[0007] This application adopts a co-extrusion coating method for simultaneous coating, replacing the traditional single slurry full-width coating or multi-layer full-width stacking process. Starting from the coating source, the slurry components are distributed and differentiated along the width of the current collector to realize the construction of edge functional areas. After simultaneous drying, the first slurry and the second slurry diffuse and fuse with each other in a wet film state to form an integrated coating with continuous gradient transition of components and no physical layer interface.

[0008] As one embodiment of this application, when the second slurry further includes additives, the second slurry further includes additives, and the mass of the additives is 0.5% to 5% of the dry weight of the second slurry; the additives include any one or a combination of at least two of carbon nanotubes, graphene, nano-ceramic particles, flame retardants, and PTC materials.

[0009] This application allows for the selective improvement of the conductive network, flame retardant properties, and mechanical strength of the edge region by adding additional safety additives to the second slurry coated within the edge functional area.

[0010] As one embodiment of this application, the first slurry does not contain any additives, or the mass percentage of additives in the first slurry is lower than the mass percentage of additives in the second slurry.

[0011] As a preferred embodiment of this application, the average particle size D50 of the active material in the second slurry is 50% to 80% of the average particle size D50 of the active material in the first slurry.

[0012] In this application, when the average particle size D50 of the active material in the second slurry is greater than 80% of the D50 of the active material in the first slurry, the improvement in the compaction density of the edge region is limited, and the effect of improving edge stress concentration is not obvious. When the average particle size D50 of the active material in the second slurry is less than 50% of the D50 of the active material in the first slurry, it is easy to cause the specific surface area of ​​the edge region to be too large, the side reactions to increase, thereby reducing the initial coulombic efficiency, and the adhesion between small-diameter particles decreases, which in turn exacerbates the risk of powder shedding.

[0013] As one embodiment of this application, the mass percentage of the conductive agent in the second slurry is 2% to 10% higher than the mass percentage of the conductive agent in the first slurry.

[0014] This application reduces edge resistance by increasing the mass ratio of conductive agent in the second slurry coated in the edge functional area.

[0015] As one embodiment of this application, the mass percentage of the binder in the second slurry is 1% to 5% higher than the mass percentage of the binder in the first slurry.

[0016] This application enhances edge adhesion by increasing the mass ratio of binder in the second slurry coated in the edge functional area.

[0017] As a preferred technical solution of this application, the first slurry and the second slurry satisfy: η1 / η2=0.8~1.2, where η1 is the viscosity of the first slurry and η2 is the viscosity of the second slurry, both in mPa·s.

[0018] As one embodiment of this application, the solid content of the first slurry is greater than the solid content of the second slurry, and the difference is ≤5%.

[0019] As one embodiment of this application, the solvent system in the first slurry is the same as that in the second slurry.

[0020] In this application, the solvent systems of the two slurries are kept consistent to ensure good mutual solubility and diffusion in the wet film state.

[0021] As a preferred technical solution of this application, the relative deviation between the viscosity η1 of the first slurry and the viscosity η2 of the second slurry is 0%~20%.

[0022] As one embodiment of this application, the solid content of the first slurry is 50% to 70%, and the solid content of the second slurry is 45% to 65%.

[0023] This application can precisely control the viscosity and solid content of the first and second slurries, thereby regulating the mutual diffusion rate and diffusion depth of the two slurries in the wet film state, thus achieving precise control of the gradient transition layer width, while ensuring that the coating thickness is uniform in the middle and edge functional areas.

[0024] As a preferred technical solution of this application, the co-extrusion coating adopts a multi-channel slit extrusion coating die, the first slurry and the second slurry are extruded side by side along the width direction of the current collector at the die outlet, and the contact time between the first slurry and the second slurry at the die outlet is ≥0.1s.

[0025] As one embodiment of this application, the co-extrusion coating speed is 5m / min to 30m / min.

[0026] As one embodiment of this application, the lip gap of the multi-channel slit extrusion coating die is 100μm~300μm.

[0027] As one embodiment of this application, in the co-extrusion coating process, the first slurry and the second slurry satisfy: Q1 / Q2=5~100, where Q1 is the flow rate of the first slurry and Q2 is the flow rate of the second slurry, both in mL / min.

[0028] In the co-extrusion coating process, this application ensures that the coating amount per unit width of the two slurries is equal by independently controlling the flow rates of the first and second slurries, thereby achieving uniform thickness.

[0029] As a preferred technical solution of this application, the linear length of the gradient transition layer in the current collector width direction is 0.5mm~5mm.

[0030] This application can precisely control the linear length of the component gradient transition zone in the current collector width direction by adjusting the supply coating process conditions, such as the viscosity ratio, flow ratio and coating speed of the two slurries, thereby realizing the customized design of the performance transition zone at the edge of the electrode and meeting the requirements of different battery specifications for the edge gradient range.

[0031] As one embodiment of this application, in the direction of the current collector width, the mass percentage of the conductive agent in the gradient transition layer decreases from the edge functional area to the middle area.

[0032] As one embodiment of this application, in the direction of the current collector width, the mass ratio of the adhesive in the gradient transition layer decreases from the edge functional area to the middle area.

[0033] As one embodiment of this application, the mass percentage of the additive in the gradient transition layer decreases from the edge functional area to the middle area.

[0034] As one embodiment of this application, in the current collector width direction, the average particle size D50 of the active material in the gradient transition layer increases from the edge functional region to the middle region.

[0035] As one embodiment of this application, the EDS energy spectrum of the feature element in the gradient transition layer satisfies the following: the ratio of the full width at half maximum (FWHM) of the feature element to the linear length of the gradient transition layer in the current collector width direction is 0.8 to 1.2. The characteristic element includes at least one of carbon, metal, or additive characteristic elements.

[0036] In this application, the components in the gradient transition layer are distributed in a continuous gradient, achieving a smooth transition without step-like abrupt changes and eliminating interface delamination.

[0037] As one embodiment of this application, the temperature of the simultaneous drying process is 80℃~150℃.

[0038] As one embodiment of this application, the synchronous drying process takes 1 to 5 minutes.

[0039] As one embodiment of this application, the synchronous drying process adopts a multi-stage gradient heating and drying method.

[0040] In a second aspect, this application provides an electrode sheet, which is prepared by the preparation method described in the first aspect. The electrode sheet includes a current collector, which includes at least one intermediate region and at least one edge functional region disposed on at least one side of the intermediate region along the width direction of the current collector. A first active material layer is provided in the middle area, and a second active material layer is provided in the edge functional area. A gradient transition layer is provided at the junction of the first active material layer and the second active material layer. The first active material layer and the second active material layer each independently include an active material, a conductive agent, and a binder; the average particle size D50 of the active material in the first active material layer is greater than the average particle size D50 of the active material in the second active material layer, and / or, the mass percentage of the conductive agent in the first slurry is lower than the mass percentage of the conductive agent in the second slurry; and / or, the mass percentage of the binder in the first slurry is lower than the mass percentage of the binder in the second slurry; and / or, the second slurry also includes additives.

[0041] In this application, there is no physical layering interface between the middle area and the edge functional area of ​​the electrode, which realizes an integrated coating, avoids coating peeling, and is conducive to improving the long-term cycle performance of the battery.

[0042] As a preferred technical solution of this application, the linear length of the edge functional area in the direction of the current collector width is 2% to 15% of the current collector width.

[0043] In this application, when the width of the edge functional area is greater than 15% of the current collector width, the overall energy density of the electrode will be significantly reduced, and the amount of edge optimization slurry will increase, raising material costs. When the width of the edge functional area is less than 2% of the current collector width, the edge protection effect is insufficient, and it cannot effectively cover the edge stress concentration area, resulting in insignificant improvement in the risk of powder shedding and cracking. As one embodiment of this application, the number of intermediate areas is at least two. In the current collector width direction, the edge functional area is provided between two adjacent intermediate areas, and / or, the edge functional area is provided on the side of the two intermediate areas that are far apart from each other.

[0044] As one embodiment of this application, the linear length of the gradient transition layer in the width direction of the current collector is 0.5 mm to 5 mm.

[0045] As one embodiment of this application, the relative deviation of the thickness of the first active material layer and the second active material layer is ≤ ±3%.

[0046] Thirdly, this application provides a lithium-ion battery, including a positive electrode and a negative electrode, wherein the positive electrode and / or the negative electrode are the electrodes described in the second aspect.

[0047] Compared with the prior art, the beneficial effects of this application are as follows: (1) In this application, the wet film of two different slurries is fused to form a component gradient transition layer, which eliminates the physical interface between the intermediate layer and the edge functional layer and realizes structural integration. Compared with the traditional layered structure, the edge peeling force is increased from 15.2 N / m of conventional electrode to 28.5 N / m, an increase of about 87%. (2) This application effectively improves edge performance targeting by adjusting the average particle size D50 of active materials, the content of conductive agent, the content of binder, and adding safety additives in different slurries; (3) In this application, the edge functional area is integrated into the single co-extrusion coating process, which does not require additional post-processing, simplifies the manufacturing process, and improves production efficiency; (4) This application can precisely control the process conditions of co-extrusion coating, ensuring that the thickness of the edge functional area and the middle area are consistent, the overall thickness is uniform, and energy density loss is avoided. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of electrode fabrication provided in this application, wherein 1-current collector; 2-middle region; 3-edge functional region.

[0049] Figure 2 The schematic diagram of the electrode sheet provided in this application along the length of the current collector is shown, wherein 2-intermediate region; 3-edge functional region; 4-gradient transition layer; B-electrode sheet length direction.

[0050] Figure 3 The diagram shows the structure of the electrode in the width direction of the current collector provided in this application, where 1-current collector; 2-intermediate region; 3-edge functional region; 4-gradient transition layer; A-electrode width direction. Detailed Implementation

[0051] It should be understood that in the description of this application, the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0052] In this application, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0~5" means that all real numbers between 0 and 5 have been fully listed in this document, and "0~5" is only a shortened representation of this set of numerical combinations. When a parameter is expressed as an integer ≥2, it is equivalent to listing positive integers that meet the requirements, such as 2, 3, 4, 5, 6, 7, 8, 9, and 10. When a parameter is expressed as an integer selected from "2~10", it is equivalent to listing any one of the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10. The phrase "at least two combinations" in this application, unless otherwise specified, refers to a quantity greater than or equal to 2. For example, "any one or at least two combinations" means that any one of the listed items can be selected, or a combination formed by at least two of the listed items in a manner that does not conflict and enables the implementation of this application. In this application, unless otherwise specified, the features or solutions corresponding to "and / or" cover any one of two or more related listed items, as well as any and all combinations of the related listed items. The arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" represents a set consisting of A, B, and combinations of A and B. "Including A and / or B" can be understood, depending on the context of the statement, as including A, including B, or including both A and B.

[0053] The term "embodiment" as used in this application means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of this application. The appearance of this phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art can explicitly and implicitly understand that the embodiments described in this application can be combined with other embodiments that do not conflict with existing technologies. The ordinal numbers "first," "second," "third," and "fourth," etc., used in this application in the expressions "first aspect," "second aspect," "third aspect," and "fourth aspect," are for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly specifying the importance or quantity of the indicated technical features. They serve only as a non-exhaustive enumeration and do not constitute a closed limitation on quantity.

[0054] In this application, the order in which the steps are written in the methods described in the various embodiments does not imply a strict execution order. The actual execution order of each step should be determined according to its function and possible internal logic. Unless otherwise specified, all steps in this application can be executed in the order they are written, or in any order without technical conflict. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) executed sequentially, or it may include steps (b) and (a) executed sequentially. If the method also includes step (c), then step (c) can be added to the method in any order without conflict, including but not limited to the execution order of steps (a), (b), and (c), steps (a), (c), and (b), steps (c), (a), and (b), etc.

[0055] The technical solution of this application will be further described below with reference to the accompanying drawings and specific embodiments.

[0056] The coatings in different areas of the existing electrode have obvious physical delamination interfaces, which are prone to peeling during long-term cycling. In addition, the conventional post-coating or staged coating methods used in electrode preparation require post-processing, resulting in a complex process and low efficiency.

[0057] Therefore, in one specific embodiment, this application provides a method for preparing an electrode sheet, such as... Figure 1 As shown, the preparation method includes: Step (1) Prepare a first slurry and a second slurry, wherein the first slurry and the second slurry independently comprise an active material, a conductive agent, and a binder, wherein the average particle size D50 of the active material in the first slurry is greater than the average particle size D50 of the active material in the second slurry; and / or, the mass percentage of the conductive agent in the first slurry is lower than the mass percentage of the conductive agent in the second slurry; and / or, the mass percentage of the binder in the first slurry is lower than the mass percentage of the binder in the second slurry; and / or, the second slurry further comprises additives.

[0058] In this application, the types of active materials in the first slurry and the second slurry can be the same or different, and this application does not have any particular limitation in this regard. As an example, for the positive electrode sheet, the positive electrode active material may include lithium sheet or lithium-containing transition metal oxide. In some embodiments, the lithium-containing transition metal oxide includes lithium iron phosphate or nickel-cobalt-manganese ternary materials, and the nickel-cobalt-manganese ternary materials may include one or a combination of at least two of lithium nickel-cobalt-manganese oxide and its modified compounds. The modified compounds of lithium nickel-cobalt-manganese oxide may include materials known in the art, such as lithium nickel-cobalt-manganese oxide that has been doped or surface-modified; for the negative electrode sheet, the negative electrode active material may include, but is not limited to, at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials may include at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy materials. Tin-based materials may include at least one of elemental tin, tin oxide, and tin alloy materials. It should be noted that in this application, the average particle size D50 refers to the particle size value corresponding to the cumulative distribution reaching 50% in the sample particle size distribution curve.

[0059] In this application, the binder in the first slurry and the second slurry may be the same or different. This application does not impose any particular limitation on the type of conductive agent. As an example, for the positive electrode, the positive electrode conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers; for the negative electrode, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0060] Both the first slurry and the second slurry include a solvent system, and both are identical. This application does not impose any particular limitation on the type of binder. As an example, for the positive electrode sheet, the positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene-propylene terpolymer, ethylene-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins; for the negative electrode sheet, the negative electrode binder may include at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0061] Step (2) as follows Figure 1 , Figure 2 and Figure 3As shown, a current collector 1 is provided, and a first slurry and a second slurry are co-extruded and coated on different areas of the surface of the current collector 1 to achieve differentiated coating in the width direction, so as to simultaneously form an intermediate area 2 coated with the first slurry and an edge functional area 3 coated with the second slurry, and the edge functional area 3 is formed on at least one side of the intermediate area 2 along the width direction of the current collector 1.

[0062] This application does not specifically limit the type of current collector 1. As an example, the positive electrode current collector 1 may be a metal foil or a composite current collector 1. The metal foil may be aluminum foil. The composite current collector 1 may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. Exemplarily, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE). The negative electrode current collector 1 may be a metal foil or a composite current collector 1. The metal foil may be copper foil. The composite current collector 1 may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. Exemplarily, the metal material may include at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymeric material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0063] In this application, the slurry composition is different in different regions along the width direction A of the current collector 1 to improve the overall performance of the electrode edge region and reduce powder shedding and cracking in the electrode edge region. The intermediate region 2 and the edge functional region 3 are formed side by side along the width direction A of the current collector 1 and extend along the length direction B of the current collector 1.

[0064] In some embodiments, the average particle size D50 of the active material in the second slurry is 50% to 80% of the average particle size D50 of the active material in the first slurry, for example, it can be 50%, 55%, 60%, 65%, 70%, 75%, or 80%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. This application uses large-particle-size active material in the coating of the electrode edge region, which can improve edge compaction density. If the average particle size D50 of the active material in the second slurry is greater than 80% of the D50 of the active material in the first slurry, the improvement in edge region compaction density will be limited, and the effect of improving edge stress concentration will be insignificant. If the average particle size D50 of the active material in the second slurry is less than 50% of the D50 of the active material in the first slurry, the specific surface area of ​​the edge region will be too large, side reactions will increase, the initial coulombic efficiency will decrease, and the adhesion between small-particle-size particles will decrease, which will exacerbate the risk of powder shedding.

[0065] In some embodiments, the mass percentage of the conductive agent in the second slurry is 2% to 10% higher than that in the first slurry. For example, it can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 3% to 8%. This application increases the content of conductive agent in the coating in the electrode edge region, thereby reducing the edge resistance. If the difference in the mass percentage of the conductive agent between the first and second slurries is too large, exceeding 10%, it is easy to cause an excessive difference in conductivity between the middle region and the edge functional region, resulting in uneven current distribution and increased local polarization during charging and discharging, affecting the battery cycle life. If the difference in the mass percentage of the conductive agent between the first and second slurries is too small, below 2%, the improvement in conductivity in the edge region is insufficient, and the effect of reducing edge resistance is not significant.

[0066] In some embodiments, the mass percentage of binder in the second slurry is 1% to 5% higher than that in the first slurry. For example, it can be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 2% to 4%. This application increases the binder content in the coating in the electrode edge region, thereby enhancing edge adhesion. If the difference in the mass percentage of binder between the first and second slurries is too large, exceeding 5%, it is easy to cause excessively high binder content in the edge functional area, leading to increased ion conduction resistance in the edge region and an increase in battery internal resistance. If the difference in the mass percentage of binder between the first and second slurries is too small, less than 1%, the edge adhesion is not sufficiently improved, and the powder removal improvement effect is not significant.

[0067] In some embodiments, the second slurry further includes additives, the mass of which is 0.5% to 5% of the dry weight of the second slurry. For example, it can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. Meanwhile, the first slurry does not contain additives, or the mass percentage of additives in the first slurry is lower than the mass percentage of additives in the second slurry.

[0068] In one embodiment, the additive includes any one or a combination of at least two of carbon nanotubes, graphene, nano-ceramic particles, flame retardants, and PTC materials. In some embodiments, the nano-ceramic particles include, but are not limited to, any one or a combination of at least two of Al2O3, SiO2, and boehmite. The flame retardants include, but are not limited to, phosphorus-based and halogen-based flame retardants. The PTC materials include, but are not limited to, conductive polymers or ceramic composite materials known in the art.

[0069] In some embodiments, the combination of the first slurry and the second slurry simultaneously satisfies the following two conditions: the mass percentage of the conductive agent in the first slurry is lower than the mass percentage of the conductive agent in the second slurry, and the mass percentage of the binder in the first slurry is lower than the mass percentage of the binder in the second slurry.

[0070] In one embodiment, the mass percentage of the conductive agent in the second slurry is 2% to 10% higher than that of the conductive agent in the first slurry, and the mass percentage of the binder in the second slurry is 1% to 5% higher than that of the binder in the first slurry.

[0071] In some embodiments, the combination of the first slurry and the second slurry simultaneously satisfies the following two conditions: the mass percentage of conductive agent in the first slurry is lower than the mass percentage of conductive agent in the second slurry, and the second slurry also includes additives. Simultaneously, the first slurry does not contain additives, or the mass percentage of additives in the first slurry is lower than the mass percentage of additives in the second slurry.

[0072] In one embodiment, the mass percentage of the conductive agent in the second slurry is 2% to 10% higher than that in the first slurry, and the mass of the additive is 0.5% to 5% of the dry weight of the second slurry.

[0073] In some embodiments, the combination of the first slurry and the second slurry simultaneously satisfies the following two conditions: the mass percentage of binder in the first slurry is lower than the mass percentage of binder in the second slurry, and the second slurry also includes additives. Simultaneously, the first slurry does not contain additives, or the mass percentage of additives in the first slurry is lower than the mass percentage of additives in the second slurry.

[0074] In one embodiment, the mass percentage of the binder in the second slurry is 1% to 5% higher than that of the binder in the first slurry, and the mass of the additive is 0.5% to 5% of the dry weight of the second slurry.

[0075] In some embodiments, the combination of the first slurry and the second slurry simultaneously satisfies the following three conditions: the mass percentage of conductive agent in the first slurry is lower than the mass percentage of conductive agent in the second slurry; the mass percentage of binder in the first slurry is lower than the mass percentage of binder in the second slurry; and the second slurry also includes additives. Simultaneously, the first slurry does not contain additives, or the mass percentage of additives in the first slurry is lower than the mass percentage of additives in the second slurry.

[0076] In one embodiment, the mass percentage of the conductive agent in the second slurry is 2% to 10% higher than that of the conductive agent in the first slurry, and the mass percentage of the binder in the second slurry is 1% to 5% higher than that of the binder in the first slurry, and the mass of the additive is 0.5% to 5% of the dry weight of the second slurry.

[0077] In some embodiments, the first slurry and the second slurry satisfy the following ratio: η1 / η2 = 0.8~1.2, where η1 is the viscosity of the first slurry and η2 is the viscosity of the second slurry, both in mPa·s. In this application, η1 / η2 can be, for example, 0.8, 0.9, 1.0, 1.1, or 1.2, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, with 0.9~1.1 being preferred.

[0078] As one implementation, the relative deviation between the viscosity η1 of the first slurry and the viscosity η2 of the second slurry is 0% to 20%, for example, it can be 0%, 1%, 3%, 5%, 8%, 10%, 12%, 15%, 18% or 20%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable. If the difference in viscosity between the binder in the first slurry and the second slurry is too large, it is easy to cause a mismatch in the mutual diffusion rate of the two slurries in the wet film state, resulting in uncontrollable or uneven gradient transition layer width, or even local slurry cross-contamination, affecting the coating quality.

[0079] In some embodiments, the solid content of the first slurry is greater than the solid content of the second slurry, and the difference is ≤5%, for example, it can be 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5% or 5%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable, and the difference is preferably ≤3%.

[0080] In one embodiment, the solid content of the first slurry is 50% to 70%, for example, it can be 50%, 52%, 55%, 56%, 58%, 60%, 62%, 65%, 66%, 68%, or 70%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. The solid content of the second slurry is 45% to 65%, for example, it can be 45%, 46%, 48%, 50%, 52%, 65%, 68%, 60%, 63%, 64%, or 65%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0081] In some embodiments, the solvent system in the first slurry and the second slurry is the same, i.e., the same type of solvent is used, to ensure good miscibility and diffusion in the wet film state. The solvent system includes, but is not limited to, N-methylpyrrolidone and / or deionized water, to ensure mutual diffusion after the two slurries come into contact.

[0082] In some embodiments, the co-extrusion coating employs a multi-channel slit extrusion coating die, where the first slurry and the second slurry are extruded side-by-side along the width of the current collector 1 at the die outlet. The number of channels in the multi-channel slit extrusion coating die can be two, three, four, five, or six, etc. The first slurry is conveyed to the die outlet through the main channel to correspond to the position of the middle zone 2; the second slurry is conveyed to the die outlet through the side channel to correspond to the edge functional zone 3. The two slurries are in contact with each other in a wet film state and are extruded synchronously. The contact time between the first slurry and the second slurry at the die outlet is ≥0.1s, for example, it can be 0.1s, 0.2s, 0.3s, 0.4s, 0.5s, 0.6s, 0.8s, 1s, etc., but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0083] As an example, a dual-channel slit extrusion coating die is used, in which the first slurry is delivered from the main channel to the die outlet, and the second slurry is delivered from a side channel to the die outlet for coating, so that the first slurry and the second slurry are respectively coated in the middle area 2 and the edge functional area 3 arranged sequentially along the width direction on the surface of the current collector 1.

[0084] As an example, a three-channel slot extrusion coating die is used. The first slurry is delivered from the main channel in the middle to the die outlet, while the second slurry is delivered independently from the two side channels on both sides to the die outlet for coating. The second slurry, the first slurry, and the second slurry are respectively coated in the first edge functional area 3, the middle area 2, and the second edge functional area 3 arranged sequentially along the width direction on the surface of the current collector 1.

[0085] In some embodiments, during the co-extrusion coating process, the flow rates of the first and second slurries are controlled by independent metering pumps to ensure that the coating amount per unit width of the two slurries is equal, thereby achieving uniform thickness. The first and second slurries satisfy the condition: Q1 / Q2 = 5~100, where Q1 is the flow rate of the first slurry and Q2 is the flow rate of the second slurry, both in mL / min. In this application, Q1 / Q2 can be, for example, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, or 100, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 10~50.

[0086] In some embodiments, the lip gap of the multi-channel slit extrusion coating die is 100μm to 300μm, for example, it can be 100μm, 120μm, 150μm, 180μm, 200μm, 230μm, 250μm, 280μm or 300μm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable. It should be noted that "lip gap" refers to the precisely controllable vertical distance of the slit formed between the upper and lower lip of the coating die at the front end of the die exit, as is well known to those skilled in the art.

[0087] In some embodiments, the co-extrusion coating speed is 5 m / min to 30 m / min, for example, it can be 5 m / min, 6 m / min, 10 m / min, 15 m / min, 18 m / min, 20 m / min, 22 m / min, 25 m / min, 28 m / min or 30 m / min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0088] In some implementations, when the electrode sheet needs to be subsequently cut into multiple narrow electrode sheets, the number of parallel flow channels of the slit extrusion coating die can be adjusted, and the extrusion position of different slurries can be adjusted according to the actual cutting requirements.

[0089] As an example, a five-channel slot extrusion coating die is used, with a first side channel, a first main channel, a second side channel, a second main channel, and a third side channel arranged in parallel. The first main channel and the second main channel independently transport the first slurry to the die outlet, while the first side channel, the second side channel, and the third side channel independently transport the second slurry to the die outlet for coating. This allows the second slurry, the first slurry, the second slurry, the first slurry, and the second slurry to be coated in the first edge functional area 3, the first middle area 2, the second edge functional area 3, the second middle area 2, and the third edge functional area 3 arranged sequentially along the width direction on the surface of the current collector 1.

[0090] Step (3) is then synchronously dried, and the first slurry and the second slurry respectively form a first active material layer and a second active material layer, and part of the first slurry and the second slurry diffuse and fuse with each other to form a gradient transition layer 4 at the junction of the edge functional area 3 and the middle area 2.

[0091] In some embodiments, the temperature of the simultaneous drying process is 80°C to 150°C, for example, it can be 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C or 150°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0092] In some embodiments, the time for the simultaneous drying process is 1 min to 5 min, for example, it can be 1 min, 1.5 min, 2 min, 2.5 min, 3 min, 3.5 min, 4 min, 4.5 min or 5 min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0093] In some embodiments, the simultaneous drying process employs a multi-stage gradient temperature drying method.

[0094] In one implementation method, the simultaneous drying process employs a three-stage gradient heating drying method, comprising a single heating stage, a second heating stage, and a third heating stage. The temperature of the first heating stage is 80~100℃, the temperature of the second heating stage is 100~120℃, and the temperature of the third heating stage is 120~150℃. The time ratio of the first, second, and third heating stages is (2~4):(1~3):1.

[0095] The gradient transition layer 4 described in this application is formed by the first slurry and the second slurry being in contact in a wet film state and then fused together after being dried synchronously, thereby forming an integral coating structure on the surface of the current collector 1, so that there is no physical layering interface between the middle area 2 and the edge functional area 3.

[0096] In some embodiments, the linear length of the gradient transition layer 4 in the width direction of the current collector 1 is 0.5mm to 5mm, for example, it can be 0.5mm, 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm or 5mm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0097] The components in the gradient transition layer 4 described in this application, such as active materials, conductive agents, and binders, exhibit a continuous gradient change.

[0098] In some embodiments, the EDS energy spectrum of the characteristic element in the gradient transition layer 4 satisfies the following: the ratio of the full width at half maximum (FWHM) of the characteristic peak of the characteristic element to the linear length of the gradient transition layer 4 in the width direction A of the current collector 1 is 0.8 to 1.2, for example, it can be 0.8, 0.85, 0.9, 0.95, 1.05, 1.1, 1.15, or 1.2, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. The characteristic element includes at least one of carbon, metal, or additive characteristic elements. As an example, the carbon element is derived from conductive agents such as Super P, CNT, graphene, etc.; the metal element is derived from transition metals in active materials, such as Ni, Co, and Mn in NCM811; and the additive characteristic element is such as Al in Al2O3, Si in SiO2, P in phosphorus-based flame retardants, etc.

[0099] In some embodiments, in the current collector width direction, the mass percentage of conductive agent in the gradient transition layer decreases from the edge functional region to the middle region; and / or, the mass percentage of binder in the gradient transition layer decreases from the edge functional region to the middle region; and / or, when the second slurry contains additives, the mass percentage of additives in the gradient transition layer decreases from the edge functional region to the middle region; and / or, the average particle size D50 of the active material in the gradient transition layer increases from the edge functional region to the middle region.

[0100] In another specific embodiment, this application provides an electrode sheet prepared using the method described in a specific embodiment. The electrode sheet includes a current collector 1, which includes at least one intermediate region 2 and at least one edge functional region 3 disposed along the width direction of the current collector 1 on at least one side of the intermediate region 2. A first active material layer is disposed in the intermediate region 2, and a second active material layer is disposed in the edge functional region 3. A gradient transition layer 4 is disposed at the junction of the first active material layer and the second active material layer, so that there is no physical delamination interface between them, forming an integrated coating. The first active material layer and the second active material layer independently include an active material, a conductive agent, and a binder. The average particle size D50 of the active material in the first active material layer is greater than the average particle size D50 of the active material in the second active material layer.

[0101] In some embodiments, when there is one intermediate zone 2, an edge functional zone 3 is provided on either side of the intermediate zone 2 along the width direction of the current collector 1, or two edge functional zones 3 are provided on both sides of the intermediate zone 2 respectively.

[0102] In some embodiments, when the electrode sheet needs to be cut into multiple narrow electrode sheets and the number of intermediate regions 2 is at least two, an edge functional region 3 is provided between two adjacent intermediate regions 2 along the width direction of the current collector 1, and / or, the edge functional region 3 is provided on the side of the two intermediate regions 2 that are far apart from each other.

[0103] As an example, if the electrode needs to be cut into two narrow electrodes and there are two intermediate regions 2, referred to as the first intermediate region 2 and the second intermediate region 2, then an edge functional region 3 is provided between the first intermediate region 2 and the second intermediate region 2, and / or the first region is provided with an edge functional region 3 on the side away from the second region, and the second region is provided with an edge functional region 3 on the side away from the first region.

[0104] In some embodiments, the first active material layer and the second active material layer at least satisfy the following: The mass percentage of the conductive agent in the first active material layer is lower than that of the conductive agent in the second active material layer.

[0105] In some embodiments, the first active material layer and the second active material layer at least satisfy the following: The mass percentage of the binder in the first active material layer is lower than that of the binder in the second active material layer.

[0106] In some embodiments, the first active material layer and the second active material layer at least satisfy the following: The second active material layer also includes additives, the mass of which is 0.5% to 5% of the dry weight of the second active material layer. The first active material layer does not contain additives, or the mass percentage of additives in the first active material layer is lower than the mass percentage of additives in the second active material layer.

[0107] In some embodiments, the first active material layer and the second active material layer simultaneously satisfy at least two of the above conditions. As an example: The mass percentage of the conductive agent in the first active material layer is lower than that of the conductive agent in the second active material layer, and the mass percentage of the binder in the first active material layer is lower than that of the binder in the second active material layer. Alternatively, the mass percentage of the conductive agent in the first active material layer is lower than the mass percentage of the conductive agent in the second active material layer, and the second active material layer also includes additives, the mass of which is 0.5% to 5% of the dry weight of the second active material layer; the first active material layer does not contain additives, or the mass percentage of the additives in the first active material layer is lower than the mass percentage of the additives in the second active material layer. Alternatively, the mass percentage of the binder in the first active material layer is lower than the mass percentage of the binder in the second active material layer, and the mass percentage of the conductive agent in the first active material layer is lower than the mass percentage of the conductive agent in the second active material layer. The second active material layer also includes additives, the mass of which is 0.5% to 5% of the dry weight of the second active material layer. The first active material layer does not contain additives, or the mass percentage of the additives in the first active material layer is lower than the mass percentage of the additives in the second active material layer. Alternatively, the mass percentage of the conductive agent in the first active material layer is lower than the mass percentage of the conductive agent in the second active material layer, and the mass percentage of the binder in the first active material layer is lower than the mass percentage of the binder in the second active material layer. Furthermore, the second active material layer also includes additives, the mass of which is 0.5% to 5% of the dry weight of the second active material layer. The first active material layer does not contain any additives, or the mass percentage of the additives in the first active material layer is lower than the mass percentage of the additives in the second active material layer.

[0108] In some embodiments, the linear length of the edge functional area 3 in the width direction of the current collector 1 is 2% to 15% of the width of the current collector 1. For example, it can be 2%, 3%, 4%, 5%, 6%, 7%, 10%, 13%, or 15%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 3% to 10%.

[0109] In some embodiments, the linear length of the gradient transition layer 4 in the width direction of the current collector 1 is 0.5mm to 5mm, for example, it can be 0.5mm, 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm or 5mm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0110] In some embodiments, the relative deviation of the thickness of the first active material layer and the second active material layer is ≤ ±3%. It should be noted that the relative deviation of the thickness in this application is calculated using the formula: (thickness of the first active material layer - thickness of the second active material layer) / thickness of the first active material layer × 100%.

[0111] In another specific embodiment, this application provides a lithium-ion battery, including a positive electrode and a negative electrode, wherein the positive electrode and / or the negative electrode is the electrode described in another specific embodiment.

[0112] That is, this application provides the following three solutions: (1) the positive electrode adopts the electrode described in another specific embodiment, and the negative electrode adopts the conventional negative electrode known in the art; (2) the negative electrode adopts the electrode described in another specific embodiment, and the positive electrode adopts the conventional positive electrode known in the art; (3) the positive electrode and the negative electrode adopt the electrode described in another specific embodiment.

[0113] Example 1 This embodiment provides a highly conductive and highly adhesive positive electrode sheet and its preparation method, specifically including: (1) Slurry preparation; First slurry: Active material: NCM811, D50=10μm, content is 96wt% (dry weight ratio); Conductive agent: Super P / CNT mixture, content 2.5wt%; Adhesive: PVDF, content 1.5wt%; Solvent: NMP, the overall solid content of the first slurry is 60%, and the overall viscosity is 3500 mPa·s; Second slurry: Active material: NCM811, D50=10μm, content 92wt%; Conductive agent: Super P / CNT mixture, content of 5wt%, which is 2.5wt% higher than the conductive agent content in the first slurry; Adhesive: PVDF, content 3wt%; Solvent: NMP; the overall solid content of the second slurry is 58%, and the overall viscosity is 3400 mPa·s, with a viscosity ratio of approximately 0.97 to that of the first slurry. (2) Equipment and parameters for co-extrusion coating and simultaneous drying; Coating die head: Dual-channel slit extrusion die head, die head width 300mm, lip gap 200μm; Main lane width: 290mm; The width of the two flow channels on both sides is 5mm; Slurry supply: Two independent metering pumps, the flow ratio of the first slurry flow rate Q1 to the second slurry flow rate Q2 is 14.5; Coating speed: 15m / min; The first slurry and the second slurry are coated on the middle area 2 and the edge functional area 3 respectively using a dual-channel slit extrusion die to form a 200μm wet film. (3) Simultaneous drying conditions: The oven uses a three-stage gradient heating method: the first stage heats up to 80℃ for 2 minutes; the second stage heats up to 100℃ for 1.5 minutes; and the third stage heats up to 120℃ for 0.5 minutes. An aluminum foil with a thickness of 12μm and a width of 300mm is provided as the current collector 1. A first slurry forms a first active material layer in the middle region 2, and a second slurry forms an independent second active material layer in the two edge functional regions 3 on both sides. At the same time, the first slurry and the second slurry diffuse and fuse with each other after contacting the wet film, forming a gradient transition layer 4 at the junction of the middle region 2 and the edge functional regions 3.

[0114] In this embodiment, the electrode sheet has a linear length of 290 mm in the width direction of the current collector 1, and the width of the two edge functional areas 3 is 5 mm. A 1 mm gradient transition layer 4 is independently formed at the junction of the middle area 2 and the two edge functional areas 3. The total thickness of the coating is uniform in each area, about 100 μm, and the relative deviation of the thickness is ≤ ±1.5%, achieving a continuous transition. The entire coating is an integral structure without physical delamination interfaces.

[0115] EDS line scanning showed that the carbon element intensity in the gradient transition layer 4 of the electrode in this embodiment smoothly increases from the middle region 2 to the edge functional region 3, with a half-width at half-maximum of 0.9 mm and no abrupt steps.

[0116] Example 2 This embodiment provides a positive electrode sheet with optimized particle size, high conductivity, and high adhesion, and its preparation method. The difference between this embodiment and Embodiment 1 is that: First slurry: Active material: NCM811, D50=10μm, content is 96wt% (dry weight ratio); Conductive agent: Super P / CNT mixture, content 2.5wt%; Adhesive: PVDF, content 1.5wt%; Solvent: NMP, the overall solid content of the first slurry is 60%, and the overall viscosity is 3500 mPa·s; Second slurry: Active material: NCM811, D50=6μm, which accounts for 60% of the D50 of the active material in the first slurry, with a content of 92wt%; Conductive agent: Super P / CNT mixture, content of 5wt%, which is 2.5wt% higher than the conductive agent content in the first slurry; Binder: PVDF, content 3wt%, which is 1.5wt% higher than the binder content in the first slurry; Solvent: NMP; the overall solid content of the second slurry is 58%, and the overall viscosity is 3400 mPa·s, with a viscosity ratio of approximately 0.97 to that of the first slurry. The remaining materials, process equipment, operating parameters, etc. are the same as in Example 1.

[0117] Example 3 This embodiment provides a positive electrode sheet with optimized particle size and high conductivity, and its preparation method. The difference between this embodiment and Embodiment 1 is that: First slurry: Active material: NCM811, D50=10μm, content is 96wt% (dry weight ratio); Conductive agent: Super P / CNT mixture, content 2.5wt%; Adhesive: PVDF, content 1.5wt%; Solvent: NMP, the overall solid content of the first slurry is 60%, and the overall viscosity is 3500 mPa·s; Second slurry: Active material: NCM811, D50=6μm, which is 60% of the D50 of the active material in the first slurry, with a content of 93.5wt%; Conductive agent: Super P / CNT mixture, content of 5wt%, which is 2.5wt% higher than the conductive agent content in the first slurry; Adhesive: PVDF, content 1.5wt%; Solvent: NMP; the overall solid content of the second slurry is 58%, and the overall viscosity is 3400 mPa·s, with a viscosity ratio of approximately 0.97 to that of the first slurry. The remaining materials, process equipment, operating parameters, etc. are the same as in Example 1.

[0118] Example 4 This embodiment provides a particle size-optimized and highly bonded positive electrode sheet and its preparation method, which differs from Embodiment 1 in that: First slurry: Active material: NCM811, D50=10μm, content is 96wt% (dry weight ratio); Conductive agent: Super P / CNT mixture, content 2.5wt%; Adhesive: PVDF, content 1.5wt%; Solvent: NMP, solid content 60%, viscosity 3500 mPa·s; Second slurry: Active material: NCM811, D50=6μm, which is 60% of the D50 of the active material in the first slurry, with a content of 94.5wt%; Conductive agent: Super P / CNT mixture, content 2.5wt%; Binder: PVDF, content 3wt%, which is 1.5wt% higher than the binder content in the first slurry; Solvent: NMP; the overall solid content of the second slurry is 58%, and the overall viscosity is 3400 mPa·s, with a viscosity ratio of approximately 0.97 to that of the first slurry. The remaining materials, process equipment, operating parameters, etc. are the same as in Example 1.

[0119] Example 5 This embodiment provides a highly conductive, highly adhesive, and safety-enhanced positive electrode sheet and its preparation method. The difference between this embodiment and Embodiment 1 is that only 2% (by dry weight) of Al2O3 is added to the second slurry. The other materials, process equipment, operating parameters, etc. are the same as those in Embodiment 1.

[0120] Example 6 This embodiment provides a highly conductive, highly adhesive, and safety-enhanced positive electrode sheet and its preparation method. The difference between this embodiment and Embodiment 2 is that only 2% (by dry weight) of Al2O3 is added to the second slurry. The other materials, process equipment, operating parameters, etc. are the same as those in Embodiment 2.

[0121] Example 7 This embodiment provides a highly conductive positive electrode sheet and its preparation method, which differs from Embodiment 1 in that: First slurry: Active material: NCM811, D50=10μm, content is 96wt% (dry weight ratio); Conductive agent: Super P / CNT mixture, content 2.5wt%; Adhesive: PVDF, content 1.5wt%; Solvent: NMP, the overall solid content of the first slurry is 60%, and the overall viscosity is 3500 mPa·s; Second slurry: Active material: NCM811, D50=10μm, content 93.5wt%; Conductive agent: Super P / CNT mixture, content of 5wt%, which is 2.5wt% higher than the conductive agent content in the first slurry; Adhesive: PVDF, content 1.5wt%; Solvent: NMP; the overall solid content of the second slurry is 58%, and the overall viscosity is 3400 mPa·s, with a viscosity ratio of approximately 0.97 to that of the first slurry. The remaining materials, process equipment, operating parameters, etc. are the same as in Example 1.

[0122] Example 8 This embodiment provides a highly bonded positive electrode sheet and its preparation method, which differs from Embodiment 1 in that: First slurry: Active material: NCM811, D50=10μm, content is 96wt% (dry weight ratio); Conductive agent: Super P / CNT mixture, content 2.5wt%; Adhesive: PVDF, content 1.5wt%; Solvent: NMP, the overall solid content of the first slurry is 60%, and the overall viscosity is 3500 mPa·s; Second slurry: Active material: NCM811, D50=10μm, content 94.5wt%; Conductive agent: Super P / CNT mixture, content 2.5wt%; Binder: PVDF, content 3wt%, which is 1.5wt% higher than the binder content in the first slurry; Solvent: NMP; the overall solid content of the second slurry is 58%, and the overall viscosity is 3400 mPa·s, with a viscosity ratio of approximately 0.97 to that of the first slurry. The remaining materials, process equipment, operating parameters, etc. are the same as in Example 1.

[0123] Example 9 This embodiment provides a safety-enhanced positive electrode sheet and its preparation method, which differs from Embodiment 1 in that: First slurry: Active material: NCM811, D50=10μm, content is 96wt% (dry weight ratio); Conductive agent: Super P / CNT mixture, content 2.5wt%; Adhesive: PVDF, content 1.5wt%; Solvent: NMP, the overall solid content of the first slurry is 60%, and the overall viscosity is 3500 mPa·s; Second slurry: Active material: NCM811, D50=10μm, content 96wt%; Conductive agent: Super P / CNT mixture, content 2.5wt%; Adhesive: PVDF, content 1.5wt%; Additives: 2% (dry weight) of Al2O3 is added; Solvent: NMP; the overall solid content of the second slurry is 58%, and the overall viscosity is 3400 mPa·s, with a viscosity ratio of approximately 0.97 to that of the first slurry. The remaining materials, process equipment, operating parameters, etc. are the same as in Example 1.

[0124] Comparative Example 1 This comparative example provides a positive electrode sheet and its preparation method. The first slurry in Example 1 is used to coat the entire width of the current collector 1. The coating and drying process parameters are the same as in Example 1.

[0125] Comparative Example 2 This comparative example provides a positive electrode sheet and its preparation method. First, the first slurry in Example 1 is used to coat the entire width of the current collector 1. Then, a 5mm insulating ceramic slurry is coated on the edge area of ​​the electrode sheet. The coating of the two slurries is not completed simultaneously. The coating process parameters and drying process parameters are the same as those in Example 1.

[0126] The combination and content of each slurry in Examples 1-9 and Comparative Examples 1-2 of this application are shown in Table 1.

[0127] Table 1 Note: In Comparative Example 2 of Table 1, the edge is the post-coated insulating ceramic layer, not the co-extruded second slurry, so it is labeled as "post-coated insulating layer".

[0128] This application conducted performance tests on the electrodes of Examples 1-9 and Comparative Examples 1-2, and the results are shown in Table 2. The edge peel force was measured using the 180° peel test method (referring to GB / T 2792-2014, the electrode edge area was cut into 25mm wide strips, and 180° peeling was performed at a peeling speed of 100mm / min, and the average peel force was recorded); the edge resistance was measured using the four-probe method (the four probes were placed on the surface of the functional area of ​​the electrode edge, with a probe spacing of 1mm, and the sheet resistance of the edge area was measured); the edge powder loss area ratio after 1000 cycles was measured by microscopic image analysis (the edge area of ​​the cycled electrode was observed under a 200x optical microscope, and the proportion of powder loss area to the total edge area was calculated); the edge transition zone interface peel test was performed by immersing the electrode in electrolyte at 60℃ for 24 hours and then performing a 180° bending test to observe whether the gradient transition layer peeled off; the initial coulombic efficiency was measured using a coin cell half-cell (with a lithium sheet as the counter electrode, constant current charging and discharging at 0.1C, the ratio of the initial discharge capacity to the charging capacity was calculated).

[0129] Table 2 As can be seen from Table 2, Examples 1-9, through differentiated coating of slurry, can selectively improve the conductivity, adhesion and safety performance of the electrode edge, form an integrated coating, and effectively reduce powder shedding.

[0130] A comparison of Examples 1 and 8, and Examples 3 and 9, shows that increasing the conductive agent content in the second slurry coated on the edge functional area 3 effectively reduces the edge resistance of the electrode (Example 1 edge resistance 18.3 Ω·cm, while Example 8 edge resistance 38.6 Ω·cm; Example 3 edge resistance 18.0 Ω·cm, while Example 9 edge resistance 38.2 Ω·cm). A comparison of Examples 1 and 7, and Examples 4 and 3, shows that increasing the binder content in the second slurry coated on the edge functional area 3 increases the edge coating peel strength and reduces powder shedding (Example 1 peel strength 28.5 N / m, while Example 7 peel strength 20.8 N / m; Example 4 peel strength 31.5 N / m, while Example 3 peel strength 22.5 N / m). A comparison of Examples 5-6 with Examples 1-2 shows that adding Al2O3 to the second slurry improves edge safety performance while maintaining conductivity and adhesion. As can be seen from the comparison between Example 2 and Example 1, and between Example 6 and Example 5, reducing the particle size of the active material in the second slurry can further improve the edge compaction density, increase the peeling force and reduce the powder loss area ratio.

[0131] Compared to Comparative Examples 1 and 2, the electrode prepared in Example 1 showed an 87% increase in edge peeling force, a 57% decrease in edge resistance, and a reduction in the edge powder shedding area ratio from 5.8% to 0.3% after 1000 cycles, with no risk of interface peeling.

[0132] The applicant declares that the above description is only a specific implementation of this application, but the protection scope of this application is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application fall within the protection and disclosure scope of this application.

Claims

1. A method for preparing an electrode sheet, characterized in that, The preparation method includes: A first slurry and a second slurry are prepared, wherein the first slurry and the second slurry independently comprise an active material, a conductive agent, and a binder, respectively; The average particle size D50 of the active material in the first slurry is greater than the average particle size D50 of the active material in the second slurry; and / or, the mass percentage of the conductive agent in the first slurry is lower than the mass percentage of the conductive agent in the second slurry; and / or, the mass percentage of the binder in the first slurry is lower than the mass percentage of the binder in the second slurry; and / or, the second slurry also includes additives. A current collector is provided, and a first slurry and a second slurry are co-extruded and coated on different areas of the surface of the current collector to simultaneously form an intermediate area coated with the first slurry and an edge functional area coated with the second slurry, wherein the edge functional area is formed on at least one side of the intermediate area along the width direction of the current collector. Subsequently, a simultaneous drying process is performed, in which the first slurry and the second slurry respectively form a first active material layer and a second active material layer, and a portion of the first slurry and the second slurry diffuse and fuse with each other to form a gradient transition layer at the junction of the edge functional area and the middle area.

2. The preparation method according to claim 1, characterized in that, When the second slurry also includes additives, the mass of the additives is 0.5% to 5% of the dry weight of the second slurry; And / or, the additives include any one or a combination of at least two of the following: carbon nanotubes, graphene, nano-ceramic particles, flame retardants, and PTC materials.

3. The preparation method according to claim 1 or 2, characterized in that, The average particle size D50 of the active material in the second slurry is 50% to 80% of the average particle size D50 of the active material in the first slurry; And / or, the mass percentage of the conductive agent in the second slurry is 2% to 10% higher than the mass percentage of the conductive agent in the first slurry; And / or, the mass percentage of the binder in the second slurry is 1% to 5% higher than the mass percentage of the binder in the first slurry.

4. The preparation method according to any one of claims 1-3, characterized in that, The first slurry and the second slurry satisfy the following: η1 / η2 = 0.8~1.2, where η1 is the viscosity of the first slurry and η2 is the viscosity of the second slurry, both in mPa·s; And / or, the solid content of the first slurry is greater than the solid content of the second slurry, and the difference is ≤5%; And / or, the solvent system in the first slurry is the same as that in the second slurry.

5. The preparation method according to any one of claims 1-4, characterized in that, The relative deviation between the viscosity η1 of the first slurry and the viscosity η2 of the second slurry is 0%~20%; And / or, the solid content of the first slurry is 50% to 70%, and the solid content of the second slurry is 45% to 65%.

6. The preparation method according to any one of claims 1-5, characterized in that, The co-extrusion coating uses a multi-channel slit extrusion coating die. The first slurry and the second slurry are extruded side by side at the die outlet along the width direction of the collector, and the contact time between the first slurry and the second slurry at the die outlet is ≥0.1s. And / or, the co-extrusion coating speed is 5 m / min to 30 m / min; And / or, the lip gap of the multi-channel slit extrusion coating die is 100μm~300μm; And / or, during the co-extrusion coating process, the first slurry and the second slurry satisfy: Q1 / Q2=5~100, where Q1 is the flow rate of the first slurry and Q2 is the flow rate of the second slurry, both in mL / min.

7. The preparation method according to any one of claims 1-6, characterized in that, The linear length of the gradient transition layer in the width direction of the current collector is 0.5 mm to 5 mm; And / or, in the direction of the current collector width, the mass percentage of the conductive agent in the gradient transition layer decreases from the edge functional area to the middle area; And / or, in the direction of the current collector width, the mass percentage of the adhesive in the gradient transition layer decreases from the edge functional area to the middle area; And / or, when the second slurry includes additives, in the current collector width direction, the mass percentage of additives in the gradient transition layer decreases from the edge functional area to the middle area; And / or, in the width direction of the current collector, the average particle size D50 of the active material in the gradient transition layer increases from the edge functional region to the middle region; And / or, the EDS energy spectrum of the feature elements in the gradient transition layer satisfies the following: the ratio of the full width at half maximum (FWHM) of the feature elements to the linear length of the gradient transition layer in the current collector width direction is 0.8~1.2; The characteristic element includes at least one of carbon, metal, or additive characteristic elements; And / or, the temperature of the simultaneous drying process is 80℃~150℃; And / or, the duration of the simultaneous drying process is 1 min to 5 min; And / or, the synchronous drying process adopts a multi-stage gradient heating drying method.

8. An electrode sheet, characterized in that, The electrode is prepared by the preparation method according to any one of claims 1-7. The electrode includes a current collector, the current collector includes at least one intermediate region, and at least one edge functional region disposed on at least one side of the intermediate region along the width direction of the current collector. A first active material layer is provided in the middle area, and a second active material layer is provided in the edge functional area. A gradient transition layer is provided at the junction of the first active material layer and the second active material layer. The first active material layer and the second active material layer each independently include an active material, a conductive agent, and a binder; the average particle size D50 of the active material in the first active material layer is greater than the average particle size D50 of the active material in the second active material layer, and / or, the mass percentage of the conductive agent in the first slurry is lower than the mass percentage of the conductive agent in the second slurry; and / or, the mass percentage of the binder in the first slurry is lower than the mass percentage of the binder in the second slurry; and / or, the second slurry also includes additives.

9. The electrode sheet according to claim 8, characterized in that, The linear length of the edge functional area in the direction of the collector width is 2% to 15% of the collector width; And / or, the number of intermediate zones is at least two, and an edge functional zone is provided between two adjacent intermediate zones in the direction of the current collector width, and / or, the edge functional zones are respectively provided on the sides of the two intermediate zones that are far apart from each other; And / or, the linear length of the gradient transition layer in the width direction of the current collector is 0.5 mm to 5 mm; And / or, the relative deviation of the thickness of the first active material layer and the second active material layer is ≤ ±3%.

10. A lithium-ion battery, comprising a positive electrode and a negative electrode, characterized in that, The positive electrode and / or the negative electrode are the electrodes as described in claim 8 or 9.

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