Secondary battery

Abstract

The invention discloses a secondary battery, and relates to the field of batteries. Comprising a positive electrode current collector and a positive electrode active material layer, the positive electrode current collector is provided with a straight area and a corner area, the surface of the positive electrode active material layer in the corner area is provided with a porous ceramic coating, the porous ceramic coating comprises a plurality of coating points arranged in a dot matrix mode, and C / P is smaller than or equal to 3200, and P is larger than or equal to 0.2 and smaller than or equal to 0.6; c is the unit volume capacity of the negative pole piece; p is the ratio of the area of the porous ceramic coating to the sum of the areas nearby the corner area. The porous ceramic coating is coated at the corner area of the positive pole piece, so that the storage of electrolyte is facilitated, meanwhile, the transmission distance of lithium ions is increased, and lithium precipitation is reduced; the transmission of lithium ions is prevented from being influenced by adopting a point coating mode; meanwhile, by limiting the relation between the coating area of the porous ceramic coating and the unit volume capacity of the negative electrode, the concentration polarization and the interface impedance are reduced, the cycle capacity retention rate is improved, and the lithium precipitation phenomenon is improved.

Description

Technical Field

[0001] The present invention relates to the field of secondary batteries, and in particular to a secondary battery. Background Art

[0002] Lithium-ion batteries are a key technology in the new energy sector. Their packaging and manufacturing processes directly impact battery performance, safety, and lifespan. Currently, lithium-ion batteries are primarily categorized into three types: soft-pack batteries, prismatic batteries, and cylindrical batteries. Soft-pack batteries use aluminum-plastic composite film as their outer shell, prismatic batteries have square or rectangular metal shells (such as aluminum or steel), and cylindrical batteries have cylindrical metal shells (such as steel). Soft-pack batteries, due to their lightweight, high energy density, and flexible design, hold a significant position in the market.

[0003] However, existing soft-pack batteries suffer from uneven stress on the sides and a mismatch in the CB value (the ratio of the negative electrode capacity to the positive electrode capacity) caused by the positive electrode covering the negative electrode. This can easily lead to lithium deposition at the corners of the battery cell. The lithium dendrites formed by lithium deposition not only increase the thickness of the battery cell but can also puncture the separator, causing internal short circuits in the battery and posing safety risks. Summary of the Invention

[0004] The present invention provides a secondary battery. By applying a porous ceramic coating with a needle arrangement on the corner area of ​​the positive electrode and defining the relationship between the porous ceramic coating and the unit volume capacity of the negative electrode, the transmission of lithium ions can be dispersed at multiple levels, thereby maximally improving the problems of lithium deposition in the corner of the negative electrode and tail fragmentation, while improving the battery's dynamic cycle capacity.

[0005] In order to solve the above technical problems, the present invention aims to provide a secondary battery, comprising a positive electrode sheet and a negative electrode sheet, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer, wherein the positive electrode current collector has a straight region and a corner region alternately arranged along its winding direction, wherein the position where the straight region and the corner region are connected is defined as an intersection line, and a porous ceramic coating is provided on the surface of the positive electrode active material layer in the corner region, wherein an end of the porous ceramic coating is located at a position within 10 mm of the corner region from the intersection line or an end of the porous ceramic coating extends to a position within 20 mm of the straight region from the intersection line;

[0006] The porous ceramic coating includes a plurality of coating points arranged in a lattice, and the secondary battery satisfies the following relationship: C / P≤3200, 0.2≤P≤0.6;

[0007] Where C is the unit volume capacity of the negative electrode, in mAh / cm 3 ; P is the ratio of the area of ​​the porous ceramic coating to the area of ​​the corner coating area and the area of ​​the positive electrode sheet located between the two ends of the porous ceramic coating.

[0008] The corner area of ​​the positive electrode plate of the present application is coated with a porous ceramic coating by dot coating. By limiting the relationship between the porous ceramic coating and the unit volume capacity of the negative electrode per unit plate area to satisfy C / P≤3200, the porous ceramic is beneficial to increasing the transmission distance of lithium ions, and can regulate the transmission of lithium ions to balance the transmission rate of lithium ions and the transmission distance of multi-level dispersed lithium ions, so that the lithium ions are transmitted and dispersed to the negative electrode surface and enter the negative electrode solid structure in an orderly manner, without accumulating on the negative electrode surface due to excessive surface lithium ions and causing lithium precipitation, thereby reducing concentration polarization and interface impedance; and the porous ceramic coating of the present application satisfies the coating area of ​​0.2≤P≤0.6, which can avoid the porous ceramic coating coating area being too large to affect the transmission of lithium ions, so as to ensure the kinetic performance of the battery, and is beneficial to storing more electrolyte, improving the liquid retention capacity, and improving the problem of lithium precipitation caused by insufficient electrolyte in the corner cycle.

[0009] At the same time, controlling the end of the porous ceramic coating within the above range can prevent the porous ceramic coating in the corner area from extending too much into the straight area, thereby avoiding increasing the thickness of the battery cell and improving the energy density of the battery cell. If the tail end of the porous ceramic coating is located too far from the intersection line in the corner area, the area of ​​the porous ceramic coating will be too small, and the problem of lithium plating during circulation cannot be effectively improved.

[0010] As a preferred embodiment, the porous ceramic coating includes a corner coating area and two tailing areas respectively connected to the two side ends of the corner coating area, and the thickness of the coating points located in the tailing areas decreases in the direction away from the corner coating area.

[0011] As a preferred embodiment, the end of the tailing area close to the corner coating area is the starting end, the thickness of the coating points of the tailing area close to the starting end is equal to the thickness of the coating points of the corner coating area, the thickness of the coating points in the N-1th row from the starting end to the tail end of the tailing area is X, and the thickness of the coating points in the Nth row is Y, and X and Y satisfy the following relationship: 0.6X≤Y≤0.95X; the length between the starting end and the tail end of the tailing area is 5-20 mm.

[0012] As a preferred solution, Y is equal to any one or any two of 0.6X, 0.65X, 0.7X, 0.75X, 0.8X, 0.85X, 0.9X, and 0.95X.

[0013] The porous ceramic coating in the trailing area of ​​the positive electrode of this application adopts a gradient reduction method, which can avoid significant thickness variations between the coated and uncoated areas of the porous ceramic coating on the positive electrode. This prevents the overlap of two layers of uncoated areas during winding, which can lead to stress concentration. Stress concentration can affect the dynamics of lithium-ion transport. If the improvement is not thorough, it can lead to cycle breakage and reduce cycle life. By controlling the thickness of the coating point in the trailing area to gradually decrease according to the above amplitude, stress concentration during winding of the battery cell can be effectively reduced, the cycle capacity retention rate can be improved, and the probability of breakage can be reduced.

[0014] As a preferred solution, the secondary battery satisfies the following relationship: 1700≤C / P≤2700.

[0015] As a preferred solution, the P value is in the range of any one or any two of 0.2, 0.3, 0.4, 0.5, and 0.6.

[0016] As a preferred solution, the thickness of the porous ceramic coating in the corner coating area is 3-10 μm.

[0017] As a preferred solution, the thickness of the porous ceramic coating in the corner coating area is in the range of any one or any two of 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, and 10 μm, preferably 6-9 μm.

[0018] The corner area of ​​the positive electrode plate of the present application is coated with a porous ceramic coating in a dot matrix to increase the transmission distance of lithium ions, so that the lithium ions are transmitted and dispersed to the surface of the negative electrode. However, if the thickness of the porous ceramic coating is too small, the transmission of lithium ions cannot be effectively dispersed, resulting in excessive lithium ions on the surface that have no time to diffuse and accumulate on the surface of the negative electrode, causing lithium precipitation. If the thickness of the porous ceramic coating is too large, it will also affect the transmission of lithium ions, resulting in a long transmission distance of lithium ions. The lithium ion transmission rate of the area coated with the porous ceramic coating is much lower than that of the uncoated area, affecting the kinetic performance and causing capacity decay.

[0019] As a preferred solution, the coating points in the corner coating area and the trailing area are independent of each other and have a spacing of 0.3-2.4 mm.

[0020] As a preferred solution, the coating point diameters of the corner coating area and the trailing area are independent and range from 0.3 to 1.2 mm.

[0021] As a preferred solution, the tail ends of the double-sided trailing regions of the positive electrode sheet are staggered by 2-15 mm.

[0022] The tail ends of the double-sided tailing areas of the positive electrode plate of the present application are set to be staggered with each other, which can further prevent stress concentration caused by the superposition of the uncoated porous ceramic coating areas in the tailing areas when the battery cell is wound, avoid affecting the lithium ion transmission dynamics, improve the battery cycle life and reduce the breakage rate.

[0023] As a preferred solution, the unit volume capacity C of the negative electrode plate is 500-1600.

[0024] As a preferred embodiment, the porous ceramic coating comprises porous ceramic, and the porous ceramic is at least one of aluminum oxide, boehmite, titanium oxide, zirconium oxide, silicon oxide, silicon carbide, titanium carbide, silicon nitride, aluminum nitride, zirconium diboride and titanium diboride.

[0025] As a preferred solution, the porous ceramic coating comprises porous ceramic and binder in a mass ratio of (98-99.5):(0.5-2.0).

[0026] As a preferred solution, the average pore size of the porous ceramic is 10-200 nm, preferably 80-150 nm.

[0027] As a preferred solution, the Dv50 particle size of the porous ceramic is 300-1200 nm, preferably 400-800 nm.

[0028] The porous ceramic coating of the present application adopts porous ceramics with the above-mentioned pore size and particle size. The pore size can effectively store electrolyte and improve the liquid retention capacity. The porous ceramics can take into account their adsorption capacity for lithium ions and their support for the electrode structure within this particle size range, while taking into account the coating process. Porous ceramics with too small a particle size are difficult to disperse evenly, while porous ceramics with too large a particle size affect the uniformity and density of the coating. Porous ceramics with smaller particle sizes can provide a higher specific surface area, thereby enhancing the absorption capacity for electrolyte and improving the migration efficiency of lithium ions, while porous ceramics with larger particle sizes are more suitable for providing structural support.

[0029] As a preferred solution, the end of the porous ceramic coating extends to a position within 20 mm from the intersection line of the straight area.

[0030] As a preferred solution, the negative electrode plate includes a negative electrode active material layer and a negative electrode current collector, and the negative electrode material includes a negative electrode active material.

[0031] As a preferred embodiment, the negative electrode active material is at least one of a carbon-based compound, a silicon-based compound, a titanium-based compound, a tin-based alloy, and a transition metal nitride.

[0032] As a preferred embodiment, the carbon-based compound is at least one of natural graphite, artificial graphite, surface-modified natural graphite, hard carbon, and soft carbon.

[0033] As a preferred embodiment, the positive electrode active material layer comprises a positive electrode active material, a positive electrode binder and a positive electrode conductor in a mass ratio of (92-99):(0.5-4):(0.5-2).

[0034] As a preferred embodiment, the positive electrode active material is at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate and lithium manganese oxide.

[0035] As a preferred embodiment, the negative electrode active material layer includes a negative electrode active material, a negative electrode binder, a negative electrode conductor and a plasticizer in a mass ratio of (92-99): (0.5-5): (0.5-1.5): (0-1).

[0036] As a preferred solution, the positive electrode binder and the negative electrode binder are each independent and are at least one of polyacrylate, polyvinylidene fluoride, polytetrafluoroethylene, and styrene-butadiene rubber.

[0037] As a preferred embodiment, the positive electrode conductive agent and the negative electrode conductive agent are each independent and are at least one of conductive carbon black, carbon nanotubes, acetylene black, and graphene.

[0038] As a preferred embodiment, the plasticizer is sodium carboxymethyl cellulose.

[0039] As a preferred solution, the secondary battery further includes a separator, and the separator is at least one of polyethylene, polypropylene, polyethylene terephthalate, polyimide, aramid, and polybutylene terephthalate.

[0040] As a preferred embodiment, the secondary battery further comprises an electrolyte, wherein the electrolyte comprises a lithium salt and a solvent in a mass ratio of (5-10):(90-95), and the solvent is at least one of ethylene carbonate, diethyl carbonate, propylene carbonate, propyl propionate and vinylene carbonate.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] 1. The corner area of ​​the positive electrode of the present application is coated with a porous ceramic coating with a dot matrix arrangement, and the relationship between the porous ceramic coating per unit electrode area and the unit volume capacity of the negative electrode is limited to satisfy C / P≤3200. The porous ceramic coating can disperse and increase the transmission distance of lithium ions, so that lithium ions enter the negative electrode solid structure in an orderly manner, reduce concentration polarization and interface impedance, and reduce lithium plating. The porous ceramic coating is dot-coated and the coating area satisfies 0.2≤P≤0.6, which can avoid affecting the transmission of lithium ions due to excessive area, ensure the dynamic performance of the battery, and at the same time be conducive to storing more electrolyte, improving the liquid retention capacity, and improving the lithium plating phenomenon while improving the cycle capacity retention rate.

[0043] 2. The thickness gradient of the porous ceramic coating on the tail area of ​​the positive electrode sheet of the present application decreases gradually, which can avoid obvious changes in the thickness of the porous ceramic coating coated area and the uncoated area on the positive electrode sheet, prevent the stress concentration caused by the superposition of the double-layer uncoated area during winding, improve the cycle capacity retention rate, reduce the probability of breakage, and increase the cycle life.

[0044] 3. The present application controls the end of the porous ceramic coating of the positive electrode to be within the above-mentioned range, which can prevent the porous ceramic coating from extending too long and exceeding the main body interface, which will increase the thickness of the battery cell, causing a serious reduction in capacity density and capacity attenuation; and avoid the end of the porous ceramic coating from extending too short, resulting in the corner area coating being unable to effectively improve the problem of cyclic lithium plating. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 : Schematic diagram of the array arrangement of the porous ceramic coating on the positive electrode sheet in an embodiment of the present invention;

[0046] Figure 2 : Schematic diagram of the position of the porous ceramic coating on the positive electrode sheet after winding in an embodiment of the present invention. DETAILED DESCRIPTION

[0047] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0048] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0049] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0050] In the description of the present invention, it should be understood that the terms "up", "down", "left", "right", "top", "bottom", etc., indicating directions or positional relationships, are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the present invention.

[0051] To further illustrate the present invention, the present invention is described in detail below with reference to the following examples, but they should not be construed as limiting the scope of the present invention. Unless otherwise specified, the sources of the raw materials used in the following examples and comparative examples of the present application are commercially available, and the same raw materials were used in parallel experiments.

[0052] Example 1

[0053] A secondary battery comprises a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. The positive electrode sheets, separator, and negative electrode sheets are stacked and wound in sequence to form a battery cell, with the outermost coil of the battery cell ending in a hollow foil segment of the positive electrode sheet. The negative electrode sheet comprises copper foil and negative electrode material. The negative electrode active material layer comprises negative electrode active material, acetylene black, styrene-butadiene rubber binder, and sodium carboxymethyl cellulose thickener in a mass ratio of 98:0.6:0.7:0.7. The negative electrode active material comprises silicon carbon and graphite in a mass ratio of 15:85. The separator is a polyethylene porous film with an alumina ceramic coating on both sides. The electrolyte comprises lithium salt LiPF6 and a non-aqueous organic solvent in a mass ratio of 8:92. The non-aqueous organic solvent comprises ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), propyl propionate (PP), and vinylene carbonate (VC) in a mass ratio of 25:25:15:31:4.

[0054] The positive electrode sheet includes an aluminum foil and a positive electrode active material layer disposed on both sides of the aluminum foil. The positive electrode active material layer comprises a lithium cobalt oxide positive electrode active material, an acetylene black (SP) conductive agent, and a polyvinylidene fluoride (PVDF) binder in a mass ratio of 98:1.2:0.8. The positive electrode sheet has straight regions and corner regions arranged alternately along its winding direction. The location where the straight region and the corner region connect is defined as the intersection line. A tailing region is provided on both sides of the straight region and / or the corner region near the intersection line. The corner region and the location between the two tailing regions are defined as the corner coating region. The corner coating region and the tailing region, as well as the surfaces of the positive electrode active material layers on both sides, are dotted with a porous ceramic coating. The porous ceramic coating in the corner coating region extends to the tailing region. The porous ceramic coating comprises a porous ceramic and a polyvinylidene fluoride (PVDF) binder in a mass ratio of 98:2. The porous ceramic has an average pore size of 120nm and a Dv50 particle size of 600nm. The porous ceramic is alumina.

[0055] In this embodiment, the tail end of the trailing region is located 15 mm from the intersection line in the straight region. Assuming that when the tail end of the trailing region is located at the intersection line, the distance between the tail end and the intersection line is 0 mm, when the tail end of the trailing region is located in the straight region, the distance between the tail end and the intersection line is a positive value, and when the tail end of the trailing region is located in the corner region, the distance between the tail end and the intersection line is a negative value, then in Example 1, the distance between the tail end of the trailing region and the intersection line is 15 mm.

[0056] Porous ceramic coatings are composed of several Figure 1 The coating dots arranged in the vertical and horizontal arrays are composed of 1 mm spacing between adjacent coating dots in the vertical and horizontal directions, and the coating dots located in the corner coating area have a thickness of 8 μm. Figure 2 As shown, the thickness of the coating points in the tailing area decreases as it moves away from the corner area. The length of the tailing area is 10 mm. The thickness of the coating points in the row near the starting end of the tailing area is the same as the thickness of the coating points in the corner coating area. The thickness of the coating points in the N-1th row from the starting end to the tail end of the tailing area is X, and the thickness of the coating points in the Nth row is Y, satisfying the following relationship: Y = 0.8X.

[0057] The secondary battery satisfies the following relationship: C / P = 2228, P = 0.4; where C is the unit volume capacity of the negative electrode, in mAh / cm 3 ; P is the ratio of the area of ​​the porous ceramic coating to the sum of the areas of the corner coating area and the tail area of ​​the positive electrode.

[0058] The unit volume capacity C value of the negative electrode sheet is calculated according to the following formula: The unit volume capacity C of the negative electrode sheet = the compaction density of the negative electrode active material × the gram capacity of the negative electrode active material. The unit volume capacity C value of the negative electrode sheet is 891 mAh / cm 3 The compacted density of the negative electrode active material is 1.65 g / cm 3 ; The gram capacity of the negative electrode active material is 540mAh / g.

[0059] The method for preparing a secondary battery in the above embodiment 1 comprises the following steps:

[0060] (1) adding porous ceramic and PVDF to N-methylpyrrolidone (NMP) in a mass ratio of 98:2 and stirring evenly to prepare a porous ceramic coating slurry, wherein the mass fraction of NMP in the porous ceramic coating slurry is 25%, and adding lithium cobalt oxide positive electrode active material, acetylene black (SP) conductive agent, and polyvinylidene fluoride (PVDF) binder in a mass ratio of 98:1.2:0.8 in an N-methylpyrrolidone solvent system and stirring and mixing evenly to prepare a positive electrode slurry with a solid content of 75%, which is then coated on aluminum foil, dried and rolled to form a positive electrode active material layer, and the porous ceramic coating slurry is spot-coated on the corner coating area and the trailing area of ​​the positive electrode sheet and on the surface of the positive electrode active material layer on both sides, and dried and stripped to obtain a positive electrode sheet;

[0061] (2) The negative electrode active material, acetylene black, styrene-butadiene rubber binder and sodium carboxymethyl cellulose thickener were thoroughly stirred and mixed in deionized water at a mass ratio of 98:0.6:0.7:0.7 to prepare a negative electrode slurry with a solid content of 40%, which was coated on a copper foil at 105°C in vacuum, dried, rolled and slit to obtain a negative electrode sheet;

[0062] (3) Stack the positive electrode sheet, separator and negative electrode sheet in order, so that the separator is placed between the positive electrode sheet and the negative electrode sheet to play a role of safety isolation, and wind them to obtain an electrode assembly, place the electrode assembly in a packaging shell, inject electrolyte, and encapsulate and form it to obtain a secondary battery.

[0063] Example 2

[0064] A secondary battery is different from Example 1 in that the average pore size of the aluminum oxide in the porous ceramic coating is 10 nm, and the DV50 particle size is 300 nm.

[0065] Example 3

[0066] A secondary battery is different from Example 1 in that the average pore size of the aluminum oxide in the porous ceramic coating is 200 nm, and the DV50 particle size is 1200 nm.

[0067] Example 4

[0068] A secondary battery is different from Example 1 in that the thickness of the coating points in the N-1th row from the starting end to the tail end of the trailing region is X, and the thickness of the coating points in the Nth row is Y, satisfying the following relationship: Y=0.6X.

[0069] Example 5

[0070] A secondary battery is different from Example 1 in that the thickness of the coating points in the N-1th row from the starting end to the tail end of the trailing region is X, and the thickness of the coating points in the Nth row is Y, satisfying the following relationship: Y=0.95X.

[0071] Example 6

[0072] A secondary battery, which is different from Example 1 in that the thickness of the coating points in the N-1th row from the starting end to the tail end of the tail area is X, and the thickness of the coating points in the Nth row is Y, satisfying the following relationship: Y=X, indicating that the thickness of the coating points in the tail area and the corner coating area are consistent.

[0073] Example 7

[0074] A secondary battery is different from Example 1 in that the coating point thickness in the corner coating area is 3 μm.

[0075] Example 8

[0076] A secondary battery is different from Example 1 in that the coating point thickness in the corner coating area is 5 μm.

[0077] Example 9

[0078] A secondary battery is different from Example 1 in that the coating point thickness in the corner coating area is 10 μm.

[0079] Example 10

[0080] A secondary battery is different from Example 1 in that the tail end of the tail region is located at a position 10 mm away from the intersection line in the corner area, and the distance between the tail end of the tail region and the intersection line is -10 mm.

[0081] Example 11

[0082] A secondary battery is different from the embodiment 1 in that the tail end of the tail region is located at the intersection line, and the distance between the tail end of the tail region and the intersection line is 0 mm.

[0083] Example 12

[0084] A secondary battery is different from Example 1 in that the tail end of the tail region is located 20 mm away from the intersection line in the straight region, and the distance between the tail end of the tail region and the intersection line is 20 mm.

[0085] Example 13

[0086] A secondary battery is different from Example 1 in that the porous ceramic in the porous ceramic coating is silicon dioxide.

[0087] Example 14

[0088] A secondary battery is different from Example 1 in that the porous ceramic in the porous ceramic coating is titanium dioxide.

[0089] Example 15

[0090] A secondary battery, which is different from Example 1 in that the negative electrode active material includes silicon carbon and graphite in a mass ratio of 5:95, and the compaction density of the negative electrode active material is 1.5 g / cm 3 The negative electrode active material gram capacity is 420mAh / g, and the negative electrode unit volume capacity C value is 630mAh / cm 3 , P value is 0.2, C / P=3150.

[0091] Example 16

[0092] A secondary battery, which is different from Example 1 in that the negative electrode active material includes silicon carbon and graphite in a mass ratio of 10:90, and the compaction density of the negative electrode active material is 1.6 g / cm 3 The negative electrode active material gram capacity is 480mAh / g, and the negative electrode unit volume capacity C value is 768mAh / cm 3 , P value is 0.3, C / P=2560.

[0093] Example 17

[0094] A secondary battery, which is different from Example 1 in that the negative electrode active material includes silicon carbon and graphite in a mass ratio of 20:80, and the compaction density of the negative electrode active material is 1.65 g / cm 3 The negative electrode active material gram capacity is 600mAh / g, and the negative electrode unit volume capacity C value is 990mAh / cm 3 , P value is 0.5, C / P=1980.

[0095] Example 18

[0096] A secondary battery, which is different from Example 1 in that the negative electrode active material includes silicon carbon and graphite in a mass ratio of 25:75, and the compaction density of the negative electrode active material is 1.65 g / cm 3 The negative electrode active material gram capacity is 660mAh / g, and the negative electrode unit volume capacity C value is 1089mAh / cm 3 , P value is 0.6, C / P=1815.

[0097] Example 19

[0098] A secondary battery, which is different from Example 1 in that the negative electrode active material includes silicon carbon and graphite in a mass ratio of 50:50, and the compaction density of the negative electrode active material is 1.65 g / cm 3 The negative electrode active material gram capacity is 960mAh / g, and the negative electrode unit volume capacity C value is 1584mAh / cm 3 , P value is 0.6, C / P=2640.

[0099] Example 20

[0100] A secondary battery is different from the embodiment 1 in that the P value is 0.3 and C / P=2970.

[0101] Example 21

[0102] A secondary battery is different from the embodiment 1 in that the P value is 0.5, and C / P=1782.

[0103] Example 22

[0104] A secondary battery is different from Example 1 in that the coating point diameter of the porous ceramic coating is 0.8 mm, and the spacing between the coating points can be calculated based on the P value and the coating point diameter.

[0105] Example 23

[0106] A secondary battery, which differs from Example 1 in that the tail ends of the double-sided tail areas of the positive electrode plate are staggered by 10 mm from each other, the tail end of the tail area located on the inner arc surface of the corner area after winding is located in the straight area and is 10 mm away from the intersection line, and the tail end of the tail area located on the outer arc surface of the corner area after winding is located in the straight area and is 20 mm away from the intersection line.

[0107] Comparative Example 1

[0108] A secondary battery is different from Example 1 in that the corner coating area and the tail area and the surfaces of the positive electrode active material layer on both sides are not dotted with porous ceramic coating, the thickness of the corner coating is 0 μm, P=0, and C / P=0.

[0109] Comparative Example 2

[0110] A secondary battery is different from the embodiment 1 in that the P value is 0.2 and C / P=4455.

[0111] Comparative Example 3

[0112] A secondary battery is different from the embodiment 1 in that the P value is 0.7 and C / P=1272.

[0113] Comparative Example 4

[0114] A secondary battery, which is different from Example 1 in that the negative electrode active material includes silicon carbon and graphite in a mass ratio of 50:50, and the compaction density of the negative electrode active material is 1.65 g / cm 3 The negative electrode active material gram capacity is 960mAh / g, and the negative electrode unit volume capacity C value is 1584mAh / cm 3 , P value is 0.7, C / P=2262.

[0115] Comparative Example 5

[0116] A secondary battery is different from the embodiment 1 in that the P value is 0.1 and C / P=8910.

[0117] Comparative Example 6

[0118] A secondary battery, which is different from Example 1 in that the negative electrode active material is graphite, and the compaction density of the negative electrode active material is 1.45 g / cm 3 The negative electrode active material gram capacity is 360mAh / g, and the negative electrode unit volume capacity C value is 522mAh / cm 3 , P value is 0.1, C / P=5220.

[0119] Comparative Example 7

[0120] A secondary battery is different from Example 1 in that the P value is 1, P=1 indicates that the porous ceramic coating in the corner coating area and the tail area is fully coated, C / P=891.

[0121] Comparative Example 8

[0122] A secondary battery is different from Example 1 in that the tail end of the tail region is located at a position 15 mm away from the intersection line in the corner area, and the distance between the tail end of the tail region and the intersection line is -15 mm.

[0123] Comparative Example 9

[0124] A secondary battery is different from Example 1 in that the tail end of the tail region is located 25 mm away from the intersection line in the straight region, and the distance between the tail end of the tail region and the intersection line is 25 mm.

[0125] Comparative Example 10

[0126] A secondary battery, which is different from Example 1 in that a porous ceramic coating is applied to the surface of the positive electrode active material layer in the corner coating area and the tail area and located on one side; in step (1), porous ceramic and PVDF are added to N-methylpyrrolidine (NMP) in a mass ratio of 98:2 and stirred evenly to prepare a porous ceramic coating slurry, the mass fraction of NMP in the porous ceramic coating slurry is 25%, lithium cobalt oxide positive electrode active material, acetylene black (SP) conductive agent, and polyvinylidene fluoride (PVDF) binder are fully stirred and mixed in an N-methylpyrrolidone solvent system in a mass ratio of 98:1.2:0.8 to prepare a positive electrode slurry with a solid content of 75%, which is then coated on aluminum foil, dried and rolled to form a positive electrode active material layer, and the porous ceramic coating slurry is applied to the surface of the positive electrode active material layer in the corner coating area and the tail area of ​​the positive electrode sheet and located on one side, and dried and stripped to obtain a positive electrode sheet.

[0127] In the secondary batteries prepared in the above embodiments and comparative examples, the porous ceramic composition, the average pore size of the porous ceramic, the Dv50 particle size of the porous ceramic, the coating point thickness of the corner coating area, the relationship between the Y and X values, the negative electrode unit volume capacity C, the ratio P of the porous ceramic coating area to the sum of the areas of the corner coating area and the tail area of ​​the positive electrode sheet, the C / P ratio, and the distance between the tail end of the tail area and the intersection line are all shown in Table 1.

[0128] Table 1 - Parameter values ​​of secondary batteries in Examples and Comparative Examples

[0129]

[0130]

[0131]

[0132] Performance testing

[0133] 1. Capacity retention: The secondary batteries prepared in the above embodiments and comparative examples were subjected to charge and discharge cycle tests at room temperature and 45°C, respectively. The battery was charged to 4.53V at a constant current of 0.5C, charged to a cut-off current of 0.05C at a constant voltage, and discharged to 3.0V at a constant current of 0.5C. This one-step charge and discharge was recorded as one cycle. The number of cycles at which the capacity retention rate reached 80% was recorded. The lithium plating in the negative electrode material area was observed after 1000 cycles at room temperature and 600 cycles at 45°C. The lithium plating level determination method is shown in Table 2. At the same time, the electrode fragment breakage rates after 1200 cycles at room temperature and 700 cycles at 45°C were observed and counted. The test results are shown in Table 3 below.

[0134] Table 2 - Determination method of lithium plating level at negative electrode interface

[0135]

[0136] Table 3 - Performance test results of secondary batteries prepared in the examples of the present application and the comparative examples

[0137]

[0138]

[0139] As shown in Table 3, the corner area of ​​the positive electrode in Example 1 of the present application is coated with a porous ceramic coating. The relationship between the porous ceramic coating per unit area of ​​the electrode and the negative electrode unit volume capacity satisfies C / P≤3200. The porous ceramic can increase the transmission distance of lithium ions, disperse lithium ions to enter the negative electrode structure in an orderly manner, avoid the accumulation of lithium ions on the negative electrode surface and cause lithium precipitation, and the porous structure of the coating stores electrolyte; the porous ceramic coating is applied in a spot coating manner, and the coating area satisfies 0.2≤P≤0.6, which can avoid affecting the dynamic performance of the battery cell, improve the capacity retention rate while improving the lithium precipitation effect, and effectively reduce the battery breakage rate. In Comparative Example 1, the corner area of ​​the positive electrode is not coated with a porous ceramic coating, the battery's liquid retention capacity is reduced, and the lithium ion transmission distance is shorter. More lithium ions accumulate on the negative electrode surface, resulting in serious lithium precipitation in the corner area of ​​the negative electrode, affecting the battery's cycle performance.

[0140] Compared to Example 1, the coating area P value of the porous ceramic coating in the positive electrode of Comparative Example 2 is 0.2. The coating area P value of the negative electrode is too small when the unit volume capacity is 891, resulting in a C / P value exceeding 3200. Lithium ion transport cannot be effectively dispersed, resulting in severe lithium deposition on the negative electrode surface, an increased fragmentation rate, and affecting the cycle performance of the battery. The coating area P value of the porous ceramic coating in the positive electrode of Comparative Example 3 is 0.7. The porous ceramic coating of the positive electrode of Comparative Example 5 is fully coated, and the coating area is too large, thereby affecting the transmission of lithium ions and causing a decrease in the dynamic performance of the battery. The cycle capacity retention rate of Comparative Examples 3 and 5 is significantly reduced, and lithium deposition occurs.

[0141] In Examples 1 and 15-19, the C values ​​of the unit volume capacity of the negative electrode plates are different, and the P values ​​of the porous ceramic coating area of ​​the positive electrode plates are also different, but the C / P ratio is between 1815-3150. The dispersion effect of the porous ceramic coating on lithium ion transmission can ensure that lithium ions enter the negative electrode structure in an orderly manner, reducing the lithium plating phenomenon; and as the C / P ratio decreases, the improvement effect of the negative electrode lithium plating phenomenon becomes more obvious; while the C / P ratios of the batteries in Comparative Example 2 all exceed 3200, indicating that the area P value of the porous ceramic coating is too small, and it cannot effectively disperse the lithium ion transmission, resulting in the negative electrode lithium plating phenomenon.

[0142] Compared with Example 1, the tail end of the tail area of ​​the positive electrode sheet of Comparative Example 8 is located in the corner area 15 mm away from the intersection line, resulting in the corner coating area being too short and the area being too small, unable to effectively disperse the lithium ion transport, resulting in lithium deposition on the negative electrode surface; and the tail end of the tail area of ​​the positive electrode sheet of Comparative Example 9 is located in the straight area 25 mm away from the intersection line, resulting in the corner coating area and the tail area extending too much into the straight area, thereby increasing the thickness of the battery, greatly increasing the breakage rate, resulting in a decrease in capacity density, and affecting the battery's cycle capacity.

[0143] Compared with Example 1, the coating point thickness of the tail area of ​​the positive electrode plate of Example 6 is consistent with the coating point thickness of the corner coating area, and the coating points in the tail area are not gradually decreased, resulting in stress concentration in the area of ​​the plate not coated with the porous ceramic coating during winding, thereby increasing the breakage rate and reducing the battery's cycle capacity retention rate.

[0144] The specific embodiments described above further illustrate the objectives, technical solutions, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. In particular, it should be noted that any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included within the scope of protection of the present invention for those skilled in the art.

Claims

1. A secondary battery, characterized in that: The invention comprises a positive electrode sheet and a negative electrode sheet, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer, wherein the positive electrode current collector has a straight region and a corner region alternately arranged along its winding direction, wherein the position where the straight region and the corner region are connected is defined as an intersection line, and a porous ceramic coating is provided on the surface of the positive electrode active material layer in the corner region, wherein an end of the porous ceramic coating is located within 10 mm of the intersection line in the corner region or an end of the porous ceramic coating extends to a position within 20 mm of the intersection line in the straight region; The porous ceramic coating includes a plurality of coating points arranged in a lattice, and the secondary battery satisfies the following relationship: C / P≤3200, 0.2≤P≤0.6; Where C is the unit volume capacity of the negative electrode, in mAh / cm 3 ; P is the ratio of the area of ​​the porous ceramic coating to the area of ​​the region of the positive electrode sheet located between the two ends of the porous ceramic coating.

2. The secondary battery according to claim 1, wherein The porous ceramic coating includes a corner coating area and two tailing areas respectively connected to both ends of the corner coating area. The thickness of the coating points located in the tailing areas decreases in a direction away from the corner coating area.

3. The secondary battery according to claim 2, wherein The coating points in the tailing area are arranged vertically and horizontally, the end of the tailing area close to the corner coating area is the starting end, the thickness of the coating points in the tailing area close to the starting end is equal to the thickness of the coating points in the corner coating area, the thickness of the coating points in the N-1th row from the starting end to the tail end of the tailing area is X, and the thickness of the coating points in the Nth row is Y, and X and Y satisfy the following relationship: 0.6X≤Y≤0.95X; the length between the starting end and the tail end of the tailing area is 5-20 mm.

4. The secondary battery according to claim 2, wherein The thickness of the porous ceramic coating in the corner coating area is 3-10 μm; and / or, the coating point spacings in the corner coating area and the trailing area are independent and range from 0.3 to 2.4 mm; and / or, the coating point diameters of the corner coating area and the trailing area are independent and range from 0.3 to 1.2 mm; And / or, the tail ends of the trailing regions on both sides of the positive electrode sheet are staggered by 2-15 mm.

5. The secondary battery according to claim 1, wherein The secondary battery satisfies the following relationship: 1700≤C / P≤2700.

6. The secondary battery according to claim 1, wherein The unit volume capacity C of the negative electrode plate is 500-1600.

7. The secondary battery according to claim 1, wherein The porous ceramic coating comprises a porous ceramic, wherein the porous ceramic is at least one of aluminum oxide, boehmite, titanium oxide, zirconium oxide, silicon oxide, silicon carbide, titanium carbide, silicon nitride, aluminum nitride, zirconium diboride and titanium diboride; And / or, the porous ceramic coating comprises porous ceramic and binder in a mass ratio of (98-99.5):(0.5-2.0).

8. The secondary battery according to claim 7, wherein The average pore size of the porous ceramic is 10-200 nm; And / or, the Dv50 particle size of the porous ceramic is 300-1200 nm.

9. The secondary battery according to claim 6, wherein The negative electrode plate includes a negative electrode active material layer and a negative electrode current collector, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material is at least one of a carbon-based compound, a silicon-based compound, a titanium-based compound, a tin-based alloy, and a transition metal nitride; And / or, the negative electrode active material layer includes a negative electrode active material, a negative electrode binder, a negative electrode conductor, and a plasticizer in a mass ratio of (92-99):(0.5-5):(0.5-1.5):(0-1).

10. The secondary battery according to claim 1, wherein The positive electrode active material layer comprises a positive electrode active material, a positive electrode binder, and a positive electrode conductor in a mass ratio of (92-99): (0.5-4): (0.5-2); the positive electrode active material is at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate, and lithium manganese oxide; And / or, the secondary battery further comprises a separator, wherein the separator is at least one of polyethylene, polypropylene, polyethylene terephthalate, polyimide, aramid, and polybutylene terephthalate; And / or, the secondary battery further comprises an electrolyte, the electrolyte comprising a lithium salt and a solvent in a mass ratio of (5-10):(90-95), the solvent being at least one of ethylene carbonate, diethyl carbonate, propylene carbonate, propyl propionate and vinylene carbonate.

Images