Cathode plate, roll core and secondary battery

Abstract

The invention discloses a cathode piece, a roll core and a secondary battery, and belongs to the technical field of batteries, the cathode piece comprises a pole piece body and ceramic coatings, the pole piece body is provided with straight areas and corner areas which are alternately arranged in the length direction, and the ceramic coatings are located on at least one surface of the corner areas; the cathode sheet satisfies the following conditions: 0.22 < = V / rho < = 2.5 and 1.05 < = R1 / R2 < = 2.0; v mm < 3 > is the total volume of the ceramic coating; rho mg / mm < 3 > is the compaction density of the cathode plate; r1g / Ah is the liquid retention coefficient of the corner area; and R2g / Ah is the liquid retention coefficient of the straight area (111). The cathode plate disclosed by the invention can effectively improve interface lithium precipitation and effectively prolong the cycle life of the secondary battery.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a cathode sheet, a winding core, and a secondary battery. Background Art

[0002] Secondary batteries have outstanding advantages such as high energy density, long cycle life, low self-discharge, and no environmental pollution. They are widely used in consumer electronics, electric vehicles, energy storage and other fields.

[0003] Secondary batteries use a wound cell structure, which is a common structure. As the charging rate continues to increase, the interface problems of the wound cell (such as lithium plating), especially the interface problems at the corners, are more prominent, resulting in a decrease in the cycle life of the secondary battery.

[0004] In view of this, this application is filed.

[0005] Application Contents

[0006] The purpose of the present application is to overcome the shortcomings of the prior art and provide a cathode sheet, a winding core and a secondary battery. The cathode sheet can effectively improve the lithium deposition at the interface and effectively increase the cycle life of the secondary battery.

[0007] To achieve the above-mentioned object, a first aspect of the present application provides a cathode plate, comprising a plate body (11) and a ceramic coating (12), wherein the plate body (11) has a straight region (111) and a corner region (112) alternately arranged along a length direction, and the ceramic coating (12) is located on at least one surface of the corner region (112); the cathode plate satisfies the following conditions: 0.22≤V / ρ≤2.5 and 1.05≤R1 / R2≤2.0;

[0008] V mm 3 is the total volume of the ceramic coating (12);

[0009] ρmg / mm 3 is the compaction density of the cathode sheet;

[0010] R1 g / Ah is the liquid retention coefficient of the corner area (112);

[0011] R2 g / Ah is the liquid retention coefficient of the straight area (111).

[0012] As an embodiment of the present application, the cathode sheet satisfies: 0.81≤V / ρ≤0.61;

[0013] The cathode sheet satisfies: 1.32≤R1 / R2≤1.89.

[0014] As an embodiment of the present application, at least one of the following (I) to (IV) is satisfied:

[0015] (Ⅰ)1≤V≤10;

[0016] (II)4≤ρ≤4.5;

[0017] (III) 1.05≤R1≤2.45;

[0018] (Ⅳ)1.08≤R2≤1.18.

[0019] As an embodiment of the present application, the porosity of the ceramic coating (12) is Preferably,

[0020] As an embodiment of the present application, the thickness of the ceramic coating (12) is d, which satisfies: 1 μm≤d≤15 μm.

[0021] As an implementation scheme of the present application, the pole piece body (11) is provided with a plurality of coating areas (113) in the corner area (112), and each of the coating areas (113) is arranged at intervals along the length direction of the pole piece body (11), and each of the coating areas (113) is coated with the ceramic coating (12).

[0022] As an embodiment of the present application, the ceramic coating (12) includes an insulating material and a binder, the mass percentage of the binder in the ceramic coating (12) is δ, and the mass percentage of the insulating material in the ceramic coating (12) is β, satisfying: 0.01≤δ / β≤0.012.

[0023] As an embodiment of the present application, the following is satisfied: 1%≤δ≤10.5%.

[0024] As an embodiment of the present application, the pole piece body (11) includes a cathode current collector and a cathode active material layer located on at least one surface of the cathode current collector.

[0025] The second aspect of the present application provides a winding core, comprising a cathode sheet (1), an anode sheet (2) and a diaphragm (3), wherein the cathode sheet (1), the anode sheet (2) and the diaphragm (3) are wound, the diaphragm (3) is arranged between the cathode sheet (1) and the anode sheet (2), and the cathode sheet (1) comprises the cathode sheet (1) described in the above item.

[0026] A third aspect of the present application provides a secondary battery comprising the aforementioned winding core.

[0027] The beneficial effects of the present application are as follows: the cathode sheet of the present application is provided with a ceramic coating in the corner area, and the corner area of ​​the cathode sheet after winding corresponds to the corner interface of the battery cell, so that it occupies space in the corner area, increases the spacing between the cathode sheet and the diaphragm in the corner area, increases the storage space of the electrolyte in the corner area, and can also reserve the expansion space of the battery cell when the battery is heated, reducing the stress on the cathode sheet in the corner area. At the same time, the ceramic coating has a certain porosity, and the ceramic coating can absorb the electrolyte, thereby increasing the liquid retention capacity of the corner area and reducing the risk of lithium precipitation; controlling 0.22≤V / ρ≤2.5 and 1.05≤R1 / R2≤2.0 to avoid insufficient liquid retention capacity due to too small volume of the ceramic coating, and also to avoid insufficient contact between the cathode sheet and the anode sheet due to excessive ceramic coating, reducing the lithium ion conduction rate and causing worsening lithium precipitation, thereby effectively improving the cycle performance of the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of the structure of the cathode sheet of the present application after being coated with a ceramic coating on one side and wound into a core;

[0029] Figure 2 This is a schematic diagram of the structure of the cathode sheet of the present application after being coated with ceramic coating on both sides and wound into a core;

[0030] Figure 3 Schematic diagrams of different shapes of the ceramic coating of the cathode sheet of the present application;

[0031] Figure 4 This is a schematic diagram of the state when the ceramic coating of the cathode sheet of the present application is distributed in a circular shape;

[0032] Figure 5 This is a schematic diagram of the state when the ceramic coating of the cathode sheet of the present application is distributed in a rectangular shape;

[0033] Figure 6 This is a schematic diagram of the cathode sheet of the present application when the ceramic coating is uniformly distributed in a square shape;

[0034] Figure 7 This is a schematic diagram of the state when the ceramic coating of the cathode sheet of the present application is coated as a whole;

[0035] Figure 8 This is a schematic diagram of the state when the ceramic coating of the cathode plate of the present application is distributed in a directionally spaced manner.

[0036] In the figure, 1, cathode plate, 11, pole plate body, 111, straight area, 112, corner area, 113, coating area, 12, ceramic coating, 2, anode plate, 3, diaphragm. DETAILED DESCRIPTION

[0037] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of this application, not all of them. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0038] In this application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0039] In this application, when referring to numerical ranges, unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges subsumed therein.

[0040] Unless otherwise specified, the components, raw materials or instruments used in the examples and comparative examples of the present application are all commercially available raw materials or instruments, and the components and raw materials used in each parallel experiment are all of the same kind.

[0041] The inventors of this application have discovered that a wound cell is formed by a flat area and a corner area. The cathode sheet, anode sheet, and separator are wound together to form a core. The cathode sheet, separator, and anode sheet are tightly fitted together. The separator is located between the cathode sheet and the anode sheet, and the core is filled with electrolyte. After long-term circulation of lithium-ion batteries, on the one hand, the electrolyte will be gradually consumed. On the other hand, the electrode will expand during use, which will squeeze the electrolyte in the corner area, resulting in a decrease in the electrolyte in the corner area. Therefore, abnormal conditions such as lithium deposition at the corner interface of the battery cell in the late cycle often occur, affecting the life of the wound lithium-ion battery.

[0042] Therefore, based on the above questions, Figures 1 and 2As shown, an embodiment of the present application provides a cathode sheet 1, comprising a plate body 11 and a ceramic coating 12. The plate body 11 has straight regions 111 and corner regions 112 alternately arranged along the length direction, with multiple straight regions 111 and multiple corner regions 112. The length direction of the plate body 11 is consistent with the winding direction of the cathode sheet 1 when it is wound into a core. The cathode sheet 1 has multiple folds (i.e., the number of corner folds) when wound into a core, with each fold having two straight regions 111 and two corner regions 112. The ceramic coating 12 is located on at least one surface of the corner region 112. The cathode sheet 1 satisfies the following conditions: 0.22≤V / ρ≤2.5 and 1.05≤R1 / R2≤2.0.

[0043] V mm 3 is the total volume of the ceramic coating 12;

[0044] ρmg / mm 3 is the compaction density of the cathode sheet 1;

[0045] R1 g / Ah is the liquid retention coefficient of the corner area (112);

[0046] R2 g / Ah is the liquid retention coefficient of the straight area (111).

[0047] The inventors of this application have found that the ceramic coating 12 in the cathode sheet 1, the total volume of the ceramic coating 12, the compaction density of the cathode sheet 1, the liquid retention coefficient of the corner area 112, and the liquid retention coefficient of the straight area 111 can affect the performance of the cathode sheet 1.

[0048] The present application provides a ceramic coating 12 on at least one surface of the corner area 112 of the electrode body 11, thereby effectively improving the liquid retention capacity of the corner area 112. The ceramic coating 12 has a large porosity and can absorb and store part of the electrolyte to ensure ion transfer (the inability to transfer ions can easily lead to lithium deposition); in addition, after the ceramic coating 12 is coated on the corner area 112, the ceramic coating 12 can increase the gap between the cathode plate 1 and the diaphragm 3, increase the storage space of the electrolyte, and thus reduce the risk of lithium deposition due to insufficient electrolyte infiltration affecting ion transfer; and the space increased by the ceramic coating 12 can reserve the expansion space required for heat generation during use of the lithium-ion battery, reduce the stress on the cathode plate 1 in the corner area 112, and reduce the risk of lithium deposition.

[0049] The inventors of this application have found that when the compaction density of the cathode sheet 1 increases, lithium deposition in the corners is more likely to occur, and more ceramic coatings 12 are required to ensure the liquid retention capacity of the corner area. This application controls the total volume of the ceramic coating 12 and the compaction density of the cathode sheet 1 to meet the following conditions: 0.22≤V / ρ≤2.5, for example, it can be 0.22, 0.25, 0.5, 0.6, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.4, 2.5 or any two of them. The range of values ​​can effectively improve the liquid retention capacity of the corner area 112 and improve the lithium deposition phenomenon. When V / ρ≤0.22, the total volume of the ceramic coating 12 is too small, the liquid retention capacity provided is insufficient, and lithium deposition is more likely to occur; when 2.5≤V / ρ, the total volume of the ceramic coating 12 is too large, and it may even completely cover the corner area 112, resulting in the overall thickness of the wound core and the formed lithium-ion battery exceeding the specification, causing insufficient contact between the cathode and anode in the corner area 112, and worsening the lithium deposition phenomenon.

[0050] The present application controls the liquid retention coefficient of the corner area 112 and the liquid retention coefficient of the straight area 111 to meet the following conditions: 1.05≤R1 / R2≤2.0, for example, it can be 1.05, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.8, 1.9, 2 or a range consisting of any two values ​​therein, so as to adsorb a suitable electrolyte and improve the lithium ion conduction rate. If 2.0<R1 / R2, the liquid retention coefficient of the corner area 112 is too high, and the volume of the ceramic coating 12 is too large, which may cause the overall battery thickness and / or width to exceed the specification, resulting in the cathode sheet 1 and the secondary battery separator being unable to be in close contact over a large area, reducing the lithium ion conduction rate and causing lithium plating.

[0051] Therefore, the cathode sheet 1 of the present application is provided with a ceramic coating 12 on the surface of the corner area 112. After the cathode sheet 1 is wound, the corner area 112 corresponds to the corner interface of the battery cell, so that it occupies space in the corner area 112, increases the spacing between the cathode sheet 1 and the diaphragm 3 in the corner area 112, increases the storage space of the electrolyte in the corner area 112, and can also reserve the expansion space of the battery cell when the battery is heated, reducing the stress on the cathode sheet 1 in the corner area 112. At the same time, the porosity of the ceramic coating 12 is large, and the ceramic coating 12 can adsorb the electrolyte, thereby increasing the liquid retention capacity of the corner area 112 and reducing the risk of lithium precipitation; and controlling 0.22≤V / ρ≤2.5 can ensure that 1.05≤R1 / R2≤2.0, avoiding the ceramic coating 12 from being too small to cause insufficient liquid retention capacity, and also avoiding too much ceramic coating 12 to cause insufficient contact between the cathode sheet 1 and the anode sheet 2, and can avoid the lithium ion conduction rate from being reduced and causing deterioration of lithium precipitation, effectively improving the cycle performance of the secondary battery.

[0052] like Figures 1 and 2As shown, in the present application, the pole piece body 11 includes two opposite first and second surfaces in the thickness direction, and the ceramic coating 12 is provided on at least one surface of the pole piece body 11. It should be understood by those skilled in the art that the ceramic coating 12 can be provided on the first surface, or on the second surface, or on both the first and second surfaces. Those skilled in the art can make a choice based on actual needs. It should be noted that the above-mentioned "surface" can be the entire area of ​​the first surface and / or the second surface, or a partial area of ​​the first surface and / or the second surface. There is no special limitation in the present application, as long as the purpose of the present application can be achieved (i.e., the total volume of the ceramic coating 12 meets the requirements).

[0053] In some embodiments, the cathode sheet satisfies: 0.81≤V / ρ≤1.61. By controlling V / ρ within this range, the total volume of the ceramic coating 12 is appropriate. While increasing the liquid retention capacity of the corner area 112, it is also possible to avoid increasing the overall thickness of the corner area 112, thereby ensuring that the interface (cathode and cathode) at the corner area 112 is fully in contact.

[0054] In some embodiments, the cathode sheet satisfies: 1.32≤R1 / R2≤1.89.

[0055] In some embodiments, 1≤V≤10, for example, it can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or a range consisting of any two values ​​therein. By controlling the total volume of the ceramic coating 12 within this range, the liquid retention capacity of the ceramic coating 12 can be ensured, and the coverage area and thickness of the ceramic coating 12 can be avoided to be too large, resulting in the inability to effectively transfer ions between the cathode sheet 1 and the anode sheet 2 to cause lithium precipitation.

[0056] In some embodiments, 3.5≤V≤10.

[0057] The total volume V of the ceramic coating 12 is the sum of the volumes of the ceramic coating 12 on each fold of the cathode sheet 1, that is, V = ΣV n , n is the corresponding number of corner folds.

[0058] In some embodiments, 4≤ρ≤4.5, for example, it can be 4.1, 4.2, 4.3, 4.4, 4.5 or a range consisting of any two values ​​therein. The compaction density is the weight of the cathode sheet 1 per unit area. After the ceramic coating 12 is applied, the compaction density of the cathode sheet 1 increases. However, if the compaction density is too high, the distance between the cathode sheet 1 and the anode sheet 2 and the diaphragm 3 in the corner area 112 is too large, and the contact between the cathode sheet 1 and the anode sheet 2 is insufficient. If the compaction density is too low, the volume of the ceramic coating 12 is too small, and the liquid retention capacity of the corner area 112 is insufficient. By controlling the compaction density of the cathode sheet 1 to be in the range of 4.0 mg / mm 3≤ρ≤4.5mg / mm 3 , while increasing the liquid holding capacity, it can ensure that the anode and cathode plates 2 in the corner area 112 are in full contact.

[0059] In some embodiments, 4.3≤ρ≤4.35.

[0060] The compaction density of the cathode sheet 1 = the surface density of the cathode sheet 1 / (the thickness of the cathode sheet 1 - the thickness of the cathode current collector). The compaction density can be adjusted by adjusting the rolling parameters (such as the rolling pressure) during the electrode sheet process.

[0061] In some embodiments, 1.15≤R1≤2.45.

[0062] In some embodiments, 1.17≤R1≤2.15.

[0063] In some embodiments, 1.08≤R2≤1.18.

[0064] The liquid retention coefficient is the ratio of the mass of the electrolyte to the capacity of the battery cell, where the unit of the battery cell capacity is mAh. Therefore, the liquid retention coefficient of the corner area 112 refers to the ratio of the mass of the electrolyte in the corner area 112 to the capacity of the battery cell in the corner area 112, and the liquid retention coefficient of the straight area 111 refers to the ratio of the mass of the electrolyte in the straight area 111 to the capacity of the battery cell in the straight area 111.

[0065] In some embodiments, the porosity of the ceramic coating 12 is For example, it can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or a range consisting of any two of these values. By controlling the porosity of the ceramic coating 12 within this range, the liquid retention performance can be effectively improved, and sufficient space can be provided for the expansion of the battery core. The ceramic coating itself can absorb and store part of the electrolyte, and ion transfer can be guaranteed. If the porosity of the ceramic coating 12 is greater than 80%, the structural strength of the ceramic coating 12 will be too small. If the porosity of the ceramic coating 12 is less than 30%, it will cause pore blockage, and the coating will not serve the purpose of storing electrolyte.

[0066] In some embodiments,

[0067] In some embodiments, the thickness of the ceramic coating (12) is d, which satisfies the following conditions: 1 μm ≤ d ≤ 15 μm. For example, it can be 1 μm, 2 μm, 3 μm, 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 15 μm, or a range consisting of any two of these values. By controlling the thickness of the ceramic coating 12 within this range, while improving the liquid retention capacity, the thickness of the ceramic coating 12 in the corner area 112 can be avoided from exceeding the specification, thereby preventing the overall lithium-ion battery from exceeding the specification in thickness or width.

[0068] In some embodiments, the pole piece body 11 is provided with a plurality of coating areas 113 in the corner area 112, and each coating area 113 is arranged at intervals along the length direction of the pole piece body 11, and each coating area 113 is coated with a ceramic coating 12, and the ceramic coating 12 is in at least one of a circular, mesh, striped or square shape in the coating area 113, and the total volume of the ceramic coating 12 is the sum of the volumes of the ceramic coating 12 in each coating area 113.

[0069] like Figures 3 to 8 As shown, a plurality of coating areas 113 are provided in the corner area 112, and the ceramic coatings 12 are arranged in each coating area 113, with intervals between adjacent coating areas 113. Therefore, the ceramic coatings 12 are spaced apart along the winding direction of the corner area 112. After the cathode sheet 1 is wound into a core, the area between the ceramic coatings 12 can be used to store electrolyte, providing electrolyte storage space and improving the liquid retention capacity of the corner area 112.

[0070] like Figures 3 to 8 As shown, the shape of the ceramic coating 12 in the coating area 113 can be selected as needed. Circular, mesh, and striped shapes can all meet the requirements of adsorbing electrolyte and improving liquid retention capacity. The total volume of the ceramic coating 12 in each coating area 113 only needs to meet the specified volume. D in the figure is the width of the coating area 113 in the winding direction of the cathode sheet 1.

[0071] In some embodiments, the ceramic coating 12 includes an insulating material and a binder, the mass percentage of the binder in the ceramic coating 12 is δ, and the mass percentage of the insulating material in the ceramic coating 12 is β, satisfying: 0.01≤δ / β≤0.12, for example, it can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.12 or a range consisting of any two of these values. By controlling δ / β within this range, the liquid retention performance can be improved, the adsorption effect of the electrolyte can be improved, and the adhesion between the electrode body 11 can be improved.

[0072] In some embodiments, 0.03≤δ / β≤0.09 is satisfied.

[0073] In some embodiments, the insulating material includes at least one of alumina, boehmite, and polyimide (PI), and the binder includes at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polymethyl methacrylate (PMMA). After the insulating material is bonded and formed by the binder, pores exist between the insulating material, thereby having the effect of storing electrolyte.

[0074] In some embodiments, the following is satisfied: 1% ≤ δ ≤ 10.5%, for example, it can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a range consisting of any two values ​​therein. The component in the ceramic coating 12 that has the function of adsorbing the electrolyte is an insulating material. If the mass fraction δ of the binder is less than 1%, the bonding of the insulating material in the ceramic coating 12 will be poor. If the mass fraction δ of the binder is greater than 8%, the insulating material component will be too little, the porosity will be reduced, and the ability to adsorb the electrolyte will be poor.

[0075] In some embodiments, the following condition is satisfied: 3%≤δ≤8.4%.

[0076] In some embodiments, the electrode body 11 includes a cathode current collector and a cathode active material layer located on at least one surface of the cathode current collector.

[0077] The method for forming the ceramic coating (12) is as follows: mixing an insulating material with an adhesive, adding a dispersant and stirring evenly to obtain a ceramic slurry, applying the ceramic slurry to the surface of the corresponding position of the corner of the cathode active material layer, and drying to form the ceramic coating (12). Figures 3 to 8 As shown, the coating morphology includes but is not limited to points, lines, surfaces, staggered squares, etc.

[0078] In some embodiments, the dispersant includes at least one of polyvinylpyrrolidone (PVP), N-methylpyrrolidone (NMP), and hydrogenated nitrile rubber (HNBR).

[0079] In some embodiments, the type of the cathode current collector is not particularly limited, and the cathode current collector can be any material known to be suitable for use as a cathode current collector.

[0080] In some embodiments, the cathode current collector includes metal materials such as aluminum, stainless steel, nickel plating, titanium, tantalum, and carbon materials such as carbon cloth and carbon paper.

[0081] The form of the cathode current collector is not particularly limited. When the cathode current collector is a metal material, the cathode current collector may be in the form of metal foil, metal cylinder, metal strip, metal plate, metal foil, metal mesh, stamped metal, foamed metal, etc. When the cathode current collector is a carbon material, the cathode current collector may be in the form of, but not limited to, carbon plate, carbon film, carbon cylinder, etc.

[0082] In some embodiments, the cathode active material layer includes a cathode active material, and the cathode active material may include a lithium-containing phosphate, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials or substances, and other traditional materials or substances that can be used as secondary battery cathode active materials may also be used. These cathode active materials may be used alone or in combination of two or more. Among them, non-limiting examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds.

[0083] In some embodiments, the cathode active material layer further includes a cathode binder and a conductive agent.

[0084] One embodiment of the present application also provides a winding core, including a cathode sheet 1, an anode sheet 2 and a separator 3, wherein the cathode sheet 1, the anode sheet 2 and the separator 3 are wound and arranged, and the separator 3 is arranged between the cathode sheet 1 and the anode sheet 2, and the cathode sheet 1 includes the cathode sheet 1 described above.

[0085] In some embodiments, the anode sheet includes an anode current collector and an anode active material layer disposed on at least one surface of the anode current collector, wherein the anode active material layer includes an anode active material.

[0086] In the present application, there is no particular limitation on the anode current collector, as long as it can achieve the purpose of the present application. For example, it can be copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper or a composite current collector.

[0087] In some embodiments, the anode active material includes graphite, silicon-based materials, mesophase microcarbon beads (MCMB), hard carbon, soft carbon, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel structured lithium titanate Li4Ti5O 12 , at least one of Li-Al alloy and metallic lithium.

[0088] In some embodiments, the anode active material layer further includes a conductive agent and an anode binder.

[0089] In some embodiments, the type of the conductive agent mentioned in this application is not limited, and known conductive agents can be used.

[0090] In some embodiments, the conductive agent includes at least one of carbon materials such as acetylene black, needle coke, carbon nanotubes, and graphene.

[0091] In some embodiments, the cathode binder and the anode binder mentioned in the present application independently include at least one of cellulose, nitrocellulose, styrene-butadiene rubber, nitrile rubber, fluororubber, isoprene rubber, polybutadiene rubber, ethylene-propylene rubber, styrene-butadiene-styrene block copolymer or its hydride, ethylene-propylene-diene terpolymer, styrene-ethylene-butadiene-ethylene copolymer, styrene-isoprene-styrene block copolymer, syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymer.

[0092] In some embodiments, there is no particular limitation on the material and shape of the separator, as long as the effects of the present application are not significantly impaired.

[0093] In some embodiments, the separator comprises a porous sheet or non-woven fabric having excellent liquid retention. Materials for the resin or glass fiber separator include, but are not limited to, polyolefin, aromatic polyamide, polytetrafluoroethylene, polyethersulfone, and the like.

[0094] In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The materials of the above-mentioned diaphragm can be used alone or in any combination.

[0095] An embodiment of the present application further provides a secondary battery, comprising the winding core described above.

[0096] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the core.

[0097] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0098] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square, or any other shape.

[0099] The following examples are provided to facilitate understanding of the present application. These examples are not provided to limit the scope of the claims.

[0100] Example 1

[0101] A method for preparing a secondary battery comprises the following steps:

[0102] (1) Preparation of cathode sheet 1:

[0103] Lithium cobalt oxide, a conductive agent (conductive carbon black), and polyvinylidene fluoride (PVDF) are mixed uniformly in a mass ratio of 90:7:3 and uniformly dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a uniform cathode slurry with a solid content of 32%. The mixed cathode slurry is coated on both sides of an 8 μm aluminum foil, baked, and rolled at a pressure of 50 to 150 T (the pressure in this embodiment is 120 T) to form a cathode active material layer with a thickness of 38 μm. The electrode body 11 is obtained after cutting.

[0104] Aluminum oxide and a binder, PVDF, were uniformly mixed, and a dispersant (NMP) was added and stirred to obtain the slurry. The slurry was applied to the corresponding position on the surface of the cathode active material layer and dried to form a ceramic coating 12 with a thickness of 7.4 μm and a width of 80 mm, thereby obtaining a cathode sheet 1. The mass ratio of the components of the slurry was: aluminum oxide; binder PVDF; dispersant NMP = 2.85:92.15:5.

[0105] The parameters of the cathode are shown in Table 1.

[0106] (2) Preparation of anode sheet 2:

[0107] A silicon-carbon composite material (15% wt silicon-carbon, 85 wt% graphite), a conductive agent (conductive carbon black), SBR (styrene-butadiene rubber), and CMC (sodium carboxymethyl cellulose) are mixed uniformly in a mass ratio of 94.3:3:1:2, and uniformly dispersed in deionized water to form a uniform black slurry. The mixed slurry is coated on both sides of a copper foil, and then baked, rolled, and cut into pieces to obtain an anode sheet.

[0108] (3) Preparation of electrolyte: Ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate were prepared into a mixed solution at a volume ratio of 20:20:60, and then fully dried was dissolved in the mixed solution. Then, 10 wt% of fluoroethylene carbonate additive was added and mixed uniformly to obtain an electrolyte. The concentration of lithium salt (lithium hexafluorophosphate) was 1 mol / L. The entire operation was carried out in an argon atmosphere glove box with a water content of <10 ppm.

[0109] (4) Diaphragm: PE film with a thickness of 7 μm.

[0110] (5) Assembly of secondary batteries: The cathode and anode sheets are cut to size and the tabs are welded. The separator is placed between the positive and negative electrodes and wound using a winding needle to obtain a bare cell. The bare cell is placed in an outer package, injected with electrolyte, and encapsulated to obtain a secondary battery.

[0111] Example 2

[0112] The difference between Example 2 and Example 1 is that the compaction density ρ is adjusted to 4.25 mg / mm 3 , and adjust the coating ceramic volume V to 5mm 3 , as shown in Table 1.

[0113] Example 3

[0114] The difference between Example 3 and Example 1 is that the compaction density ρ is adjusted to 7 mg / mm 3 , and then adjust the parameters of the cathode plate 1, as shown in Table 1.

[0115] Example 4

[0116] The difference between Example 4 and Example 1 is that the compaction density ρ is adjusted to 4 mg / mm 3 , and adjust the coating ceramic volume V to 10mm 3 , as shown in Table 1.

[0117] Example 5

[0118] The difference between Example 5 and Example 1 is that the compaction density ρ is adjusted to 4.5 mg / mm 3 And adjust the coating ceramic volume V to 1mm 3 , as shown in Table 1.

[0119] Example 6

[0120] The difference between Example 6 and Example 1 is that the volume V of the coated ceramic is adjusted to 1 mm 3 , and then adjust the parameters of the cathode plate 1, as shown in Table 1.

[0121] Example 7

[0122] The difference between Example 7 and Example 1 is that the compaction density ρ is adjusted to 4.3 mg / mm 3 And adjust the coating ceramic volume V to 3.5mm 3 , as shown in Table 1.

[0123] Example 8

[0124] The difference between Example 8 and Example 1 is that the mass ratio of each component in the ceramic slurry is adjusted to aluminum oxide; binder PVDF: dispersant NMP = 94:1:5, and then the parameters of the cathode sheet 1 are adjusted, as shown in Table 1.

[0125] Example 9

[0126] The difference between Example 9 and Example 1 is that the mass ratio of each component in the ceramic slurry is adjusted to aluminum oxide; binder PVDF: dispersant NMP = 87:1:5, and then the parameters of the cathode sheet 1 are adjusted, as shown in Table 1.

[0127] Example 10

[0128] The difference between Example 10 and Example 1 is that the mass ratio of each component in the ceramic slurry is adjusted to be aluminum oxide; binder PVDF: dispersant NMP = 85:10:5, and then the parameters of the cathode sheet 1 are adjusted, as shown in Table 1.

[0129] Comparative Example 1

[0130] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 does not contain the ceramic coating 12 .

[0131] Comparative Example 2

[0132] The difference between Comparative Example 2 and Example 1 is that the volume V of the coated ceramic is adjusted to 12 mm 3 , as shown in Table 1.

[0133] Comparative Example 3

[0134] Comparative Example 3 is different from Example 1 in that the volume V of the coated ceramic is adjusted to 0.8 mm 3 , as shown in Table 1.

[0135] Table 1

[0136]

[0137] Performance Testing

[0138] Cycle retention rate: The secondary batteries of the examples and comparative examples were charged to 4.5V at a constant current of 0.5C and discharged to 3.0V at 0.2C for 800 cycles. The ratio of the remaining capacity to the initial capacity was recorded as the cycle retention rate. At the same time, the lithium deposition in the corner area was determined according to the following criteria (only slight lithium deposition was accepted; a large amount of lithium deposition was considered unqualified):

[0139] No lithium deposition: no purple spots or 1 to 3 lithium deposition spots appear in the corner area.

[0140] Mild lithium deposition: Some purple spots or 1 to 3 lithium deposition spots appear in the corner area.

[0141] Moderate lithium deposition: Continuous point-like lithium deposition occurs in the corner area for more than 3 times, and the number of flake-like lithium deposition is ≤1.

[0142] Severe lithium deposition: flaky lithium deposition occurs at the corners, with the number of folds > 1.

[0143] Table 2

[0144]

[0145]

[0146] Comparing Example 1 with Comparative Example 1, the present application can effectively improve the liquid retention capacity of the corner area 112 by providing a ceramic coating 12 on at least one surface of the corner area 112 of the electrode body 11. The ceramic coating 12 has a large porosity and can absorb and store part of the electrolyte to ensure ion transfer (the inability to transfer ions can easily lead to lithium deposition); in addition, after the ceramic coating 12 is coated on the corner area 112, the ceramic coating 12 can increase the gap between the cathode plate 1 and the diaphragm 3, increase the storage space of the electrolyte, and thus reduce the risk of lithium deposition due to insufficient electrolyte infiltration affecting ion transfer; and the space increased by the ceramic coating 12 can reserve the expansion space required for heat generation during use of the lithium-ion battery, reduce the stress on the cathode plate 1 in the corner area 112, and reduce the risk of lithium deposition.

[0147] By comparing Example 1 with Comparative Examples 2 to 3, it can be seen that controlling 0.22≤V / ρ≤2.5 can ensure that 1.05≤R1 / R2≤2.0, thereby avoiding the ceramic coating 12 being too small and resulting in insufficient liquid retention capacity, and also avoiding the ceramic coating 12 being too much and resulting in insufficient contact between the cathode sheet 1 and the anode sheet 2. It can also avoid the reduction in lithium ion conduction rate and the deterioration of lithium plating, thereby effectively improving the cycle performance of the secondary battery.

[0148] Comparing Examples 1 to 6, it can be seen that by controlling the cathode sheet to meet the following conditions: 0.81≤V / ρ≤1.61, 1.32≤R1 / R2≤1.89, the lithium plating phenomenon can be further improved, and the cycle performance of the secondary battery can be further enhanced.

[0149] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and are not intended to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A cathode sheet, characterized in that: The invention comprises a pole piece body (11) and a ceramic coating (12), wherein the pole piece body (11) has a straight area (111) and a corner area (112) alternately arranged along the length direction, and the ceramic coating (12) is located on at least one surface of the corner area (112); the cathode piece satisfies the following conditions: 0.22≤V / ρ≤2.5 and 1.05≤R1 / R2≤2.0; V mm 3 is the total volume of the ceramic coating (12); ρmg / mm 3 is the compaction density of the cathode sheet; R1 g / Ah is the liquid retention coefficient of the corner area (112); R2 g / Ah is the liquid retention coefficient of the straight area (111).

2. The cathode sheet according to claim 1, wherein: The cathode sheet satisfies: 0.81≤V / ρ≤1.61; and / or The cathode sheet satisfies: 1.32≤R1 / R2≤1.

89.

3. The cathode sheet according to claim 1, wherein: Satisfy at least one of the following (I) to (IV): (Ⅰ)1≤V≤10； (II)4≤ρ≤4.5; (Ⅲ)1.15≤R1≤2.45； (Ⅳ)1.08≤R2≤1.18。 4. The cathode sheet according to claim 1, wherein: The porosity of the ceramic coating (12) is φ, 30%≤φ≤80%, preferably, 45%≤φ≤71%; and / or The thickness of the ceramic coating (12) is d, which satisfies: 1 μm≤d≤15 μm.

5. The cathode sheet according to claim 1, wherein: The pole piece body (11) is provided with a plurality of coating areas (113) in the corner area (112), each of the coating areas (113) is arranged at intervals along the length direction of the pole piece body (11), and each of the coating areas (113) is coated with the ceramic coating (12).

6. The cathode sheet according to claim 1, wherein: The ceramic coating (12) comprises an insulating material and a binder, the mass percentage of the binder in the ceramic coating (12) is δ%, the mass percentage of the insulating material in the ceramic coating (12) is β%, and the following relationship is satisfied: 0.01≤δ / β≤0.

12.

7. The cathode sheet according to claim 6, characterized in that Meets: 1%≤δ%≤10.5%.

8. The cathode sheet according to claim 1, wherein: The pole piece body (11) comprises a cathode current collector and a cathode active material layer located on at least one surface of the cathode current collector.

9. A winding core, characterized in that: The invention comprises a cathode sheet (1), an anode sheet (2) and a diaphragm (3), wherein the cathode sheet (1), the anode sheet (2) and the diaphragm (3) are wound and arranged, and the diaphragm (3) is arranged between the cathode sheet (1) and the anode sheet (2), and the cathode sheet (1) comprises the cathode sheet (1) according to any one of claims 1 to 8.

10. A secondary battery, characterized in that: Comprising the winding core according to claim 9.

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