Jelly roll and battery
By optimizing the core structure and controlling the geometric parameters of the core and the composition of the negative electrode sheet, the problem of folding on one side of the negative electrode head in lithium-ion batteries has been solved, thus improving the safety and reliability of the battery.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- SPRINGPOWER TECHNOLOGY (SHENZHEN) CO LTD
- Filing Date
- 2025-12-30
- Publication Date
- 2026-07-09
Smart Images
Figure CN2025147019_09072026_PF_FP_ABST
Abstract
Description
[Amended according to Rule 26, 2026] A winding core and a battery
[0001] This application claims priority to Chinese Patent Application No. 202510008428.9, filed on January 3, 2025, entitled "A Winding Core and Battery", the entire contents of which are incorporated herein by reference. Technical Field
[0002] This invention relates to the field of battery technology, specifically to a winding core and a battery. Background Technology
[0003] Lithium-ion batteries have advantages such as high energy density, high operating voltage, customizable size, and no memory effect, and are widely used in various consumer battery fields.
[0004] In pursuit of higher energy density, thin copper foil and high negative electrode compaction are becoming increasingly common. However, the varying dimensions of different consumer battery compartments can lead to various process defects during battery manufacturing. For instance, the negative electrode head of current lithium-ion batteries contains two single-sided areas during winding (see Figure 1). Due to the different forces on both sides of these areas, residual stress from previous winding processes is released during winding, causing folding in the single-sided area of the negative electrode head. This folding results in poor interface contact, negatively impacting long-term reliability. Therefore, overcoming these technical problems and defects is a key issue that needs to be addressed. Summary of the Invention
[0005] To address the problem that existing batteries have two single-sided areas at the negative electrode head, which folds during winding, this invention provides a winding core and a battery.
[0006] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:
[0007] The first aspect of the present invention provides a wound core, comprising a positive electrode sheet, a separator, and a negative electrode sheet, wherein the positive electrode sheet, the separator, and the negative electrode sheet are stacked in sequence and wound along the direction from the starting end to the ending end to form the wound core;
[0008] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on the surface of the negative electrode current collector;
[0009] The negative electrode sheet includes an empty foil area, a single-sheet material area, and a double-sheet material area connected in sequence.
[0010] The negative electrode active material layer is not provided on both sides of the empty foil area; the negative electrode active material layer is not provided on the side of the single-sheet area away from the positive electrode sheet; the negative electrode active material layer is provided on both sides of the double-sheet area; the empty foil area and the single-sheet area are located at the starting end of the negative electrode sheet;
[0011] The starting end of the positive electrode sheet is stacked on one side of the single-layer fabric area;
[0012] The wound core and the negative electrode sheet satisfy the following relationship: 0 ≤ (a+b)*ab+(cd) 2 ≤2.2;
[0013] Where, a = W / h1 / 18; b = 1.2 * W / L; c = 5 / h2; d = x / 1.73;
[0014] W is the width of the core, in mm; h1 is the thickness of the core, in mm; L is the length of the core, in mm; h2 is the thickness of the negative electrode current collector, in μm; x is the compaction density of the negative electrode active material layer, in g / cm³. 3 .
[0015] Optionally, the value of 'a' can be in the range of 0.2 to 2.0.
[0016] Optionally, the value of 'a' can be in the range of 0.2 to 0.8.
[0017] Optionally, the value of b ranges from 0.2 to 2.0.
[0018] Optionally, the value of b ranges from 0.3 to 1.5.
[0019] Optionally, the thickness h2 of the negative electrode current collector can range from 3 to 9 μm.
[0020] Optionally, the thickness h2 of the negative electrode current collector is in the range of 4 to 6 μm.
[0021] Optionally, the compaction density x of the negative electrode active material layer is in the range of 1.0 g / cm³. 3 ~2.0g / cm 3 .
[0022] Optionally, the compaction density x of the negative electrode active material layer is in the range of 1.4 g / cm³. 3 ~1.9g / cm 3 .
[0023] Optionally, the core is a square core, the core including a straight area in the middle and arc areas on both sides; the empty foil area is located in the straight area and the arc area of the first fold of the negative electrode sheet; the single fabric area is located in the straight area and the arc area of the second and third folds of the negative electrode sheet.
[0024] A second aspect of the present invention provides a battery comprising a battery housing and the aforementioned winding core, wherein the winding core is disposed within the housing.
[0025] According to the core provided by the present invention, by limiting the length, width and thickness of the core, the thickness of the negative electrode current collector, and the compaction density of the negative electrode active material layer, the following conditions are met: 0 ≤ (a+b)*ab+(cd). 2 When the value is ≤2.2, the single-sheet area of the negative electrode sheet is less prone to folding during the winding production of the core 100, thereby improving the safe performance of the battery. Attached Figure Description
[0026] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0027] Figure 1 is a schematic diagram of a winding core provided in an embodiment of the present invention;
[0028] Figure 2 is a schematic diagram showing the first to third folds of a core provided in an embodiment of the present invention;
[0029] Figure 3 is a schematic diagram of the labeling of the negative electrode sheet in a winding core provided in an embodiment of the present invention;
[0030] Figure 4 is a schematic diagram of one side of the negative electrode sheet provided in an embodiment of the present invention;
[0031] Figure 5 is a schematic diagram of the other side of the negative electrode sheet provided in an embodiment of the present invention;
[0032] Figure 6 is a schematic diagram of the structure of a negative electrode sheet provided in an embodiment of the present invention;
[0033] The reference numerals in the accompanying drawings are as follows: 100-core; 101-straight area; 102-arc area; 103-first fold; 104-second fold; 105-third fold; 1-negative electrode sheet; 11-negative electrode current collector; 12-negative electrode active material layer; 13-empty foil area; 14-single fabric area; 15-double fabric area; 2-positive electrode sheet; 21-positive electrode current collector; 22-positive electrode active material layer; 3-separator. Detailed Implementation
[0034] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
[0035] In the description of this invention, it should be understood that the terms "longitudinal," "radial," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.
[0036] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.
[0037] As shown in Figures 1-6, in one embodiment, the first aspect of the present invention provides a core 100, including a positive electrode 2, a separator 3 and a negative electrode 1, wherein the positive electrode 2, the separator 3 and the negative electrode 1 are stacked in sequence and wound along the direction from the starting end to the ending end to form the core 100.
[0038] The negative electrode sheet 1 includes a negative electrode current collector 11 and a negative electrode active material layer 12 coated on the surface of the negative electrode current collector 11;
[0039] The negative electrode 1 includes an empty foil area 13, a single-layer fabric area 14, and a double-layer fabric area 15 connected in sequence.
[0040] The negative electrode active material layer 12 is not provided on both sides of the empty foil area 13; the negative electrode active material layer 12 is not provided on the side of the single-sheet area 14 away from the positive electrode sheet 2; the negative electrode active material layer 12 is provided on both sides of the double-sheet area 15; the empty foil area 13 and the single-sheet area 14 are located at the starting end of the negative electrode sheet 1.
[0041] The starting end of the positive electrode 2 is stacked on one side of the single-layer fabric area 14;
[0042] The wound core 100 and the negative electrode 1 satisfy the following relationship: 0 ≤ (a+b)*ab+(cd) 2 ≤2.2;
[0043] Where, a = W / h1 / 18; b = 1.2 * W / L; c = 5 / h2; d = x / 1.73;
[0044] W is the width of the core 100 in mm; h1 is the thickness of the core 100 in mm; L is the length of the core 100 in mm; h2 is the thickness of the negative electrode current collector 11 in μm; x is the compaction density of the negative electrode active material layer 12 in g / cm³. 3 .
[0045] Specifically, (a+b)*ab+(cd) 2 The value is any single value or a range of any two values selected from 0, 0.2, 0.4, 0.6, 0.8, 1, 1.2, 1.4, 1.6, 1.8, 2, or 2.2. In a preferred embodiment, 0 ≤ (a+b)*ab+(cd) 2 ≤1.2.
[0046] The length, width, and thickness of the core 100, the thickness of the negative electrode current collector 11, and the compaction density of the negative electrode active material layer 12 satisfy 0 ≤ (a + b) * ab + (cd). 2 When the value is ≤2.2, during the winding production of the core 100, the single-sheet area 14 of the negative electrode sheet 1 is less likely to fold, thereby improving the safe performance of the battery.
[0047] The length, width, and thickness of the core 100, the thickness of the negative electrode current collector 11, and the compaction density of the negative electrode active material layer 12 satisfy (a+b)*ab+(cd). 2 When the value is greater than 2.2, during the winding process of the core 100, the single fabric area 14 of the negative electrode sheet 1 is prone to folding, which leads to poor interface contact of the negative electrode sheet 1 and has a negative impact on the reliability of long-term use.
[0048] As shown in Figures 1-6, in one embodiment, the value of 'a' ranges from 0.2 to 2.0.
[0049] Specifically, the value of 'a' is any one value or a range of any two values from 0.2, 0.4, 0.6, 0.8, 1, 1.2, 1.4, 1.6, 1.8, or 2.
[0050] When the value of a is in the range of 0.2 to 2.0, the single-layer fabric area 14 of the negative electrode 1 is less prone to folding, thereby improving the safe use performance of the battery. When the value of a is greater than 2.0, since a = W / h1 / 18, the width of the core 100 is larger, and the corresponding width of the winding needle is larger. When the negative electrode 1 passes the corner in the inner circle during winding, the tension is prone to be too large. Subsequently, when the core 100 is hot-pressed after the winding needle is peeled off, the single-layer fabric area 14 of the negative electrode 1 is prone to folding, resulting in poor interface contact of the negative electrode 1, which has a negative effect on the reliability of long-term use. When the value of a is less than 0.2, it will be difficult to remove the winding needle after winding, which will easily cause the electrode inside the core 100 to shift or fold, reduce the coating effect of the inner layer of the core 100, and cause folding problems.
[0051] As shown in Figures 1-6, in a preferred embodiment, the value of 'a' ranges from 0.2 to 0.8.
[0052] As shown in Figures 1-6, in one embodiment, the value of b ranges from 0.2 to 2.0.
[0053] Specifically, the value of b is any one point value or any two point values from 0.2, 0.4, 0.6, 0.8, 1, 1.2, 1.4, 1.6, 1.8 or 2.
[0054] When the value of b is in the range of 0.2 to 2.0, it can prevent the single-sheet area 14 at the beginning of the negative electrode sheet 1 from folding and also take into account the energy density of the product. When the value of b is less than 0.2, since b = 1.2 * W / L, the length of the core 100 is more than 6 times the width of the core 100, which makes the inner ring of the core 100 easy to slip after winding. It also has an adverse effect on the folding of the single-sheet area 14 during hot pressing. When the value of b is greater than 2, the width of the core 100 will be more than 1.66 times the length. The tension of the arc area 102 is not easy to control during winding, which can easily cause the inner ring of the battery to fold due to excessive tension in the inner arc area 102. At the same time, the proportion of the top seal of the cell increases, which is not conducive to improving the energy density of the product.
[0055] As shown in Figures 1-6, in a preferred embodiment, the value of b ranges from 0.3 to 1.5.
[0056] As shown in Figures 1-6, in one embodiment, the thickness h2 of the negative electrode current collector 11 ranges from 3 to 9 μm.
[0057] Specifically, the thickness h2 of the negative electrode current collector 11 is a range of any one value or any two values from 3um, 4um, 5um, 6um, 7um, 8um or 9um.
[0058] The thickness h2 of the negative electrode current collector 11 ranges from 3 to 9 μm, which balances the energy density of the product and the folding and breakage of the negative electrode sheet 1 during production. When the thickness h2 of the negative electrode current collector 11 is less than 3 μm, since c = 5 / h2, c > 5 / 3, which will lead to a decrease in the strength of the negative electrode current collector 11. During production, the electrode roll is prone to breakage, and the single fabric area 14 at the starting end of the negative electrode sheet 1 is prone to folding. When the thickness h2 of the negative electrode current collector 11 is greater than 9 μm, it will lead to a loss of product energy density.
[0059] As shown in Figures 1-6, in a preferred embodiment, the thickness h2 of the negative electrode current collector 11 ranges from 4 to 6 μm.
[0060] As shown in Figures 1-6, in one embodiment, the compaction density x of the negative electrode active material layer 12 ranges from 1.0 g / cm³. 3 ~2.0g / cm 3 .
[0061] Specifically, the compaction density x of the negative electrode active material layer 12 ranges from 1 g / cm³. 3 1.1g / cm 3 1.2g / cm 3 1.3g / cm 3 1.4g / cm 3 1.5g / cm 3 1.6g / cm 3 1.7g / cm 3 1.8g / cm 3 1.9g / cm 3 or 2g / cm 3 The range of values consisting of any one point value or any two point values.
[0062] When the compaction density x of the negative electrode active material layer 12 is in the range of 1.0 g / cm³ 3 ~2.0g / cm 3 It has the function of balancing product energy density and internal stress control during the rolling process of negative electrode 1; when the compaction density x of the negative electrode active material layer 12 is less than 1.0 g / cm³. 3 This will lead to a loss of product energy density. The lower the compaction density, the worse the electron contact between material particles will be, which will affect the capacity retention rate during cycling. When the compaction density x of the negative electrode active material layer 12 is greater than 2.0 g / cm³, it will cause a loss of product energy density. 3Since d = x / 1.73, d > 1.156 at this time. During the rolling process, the single fabric area 14 is prone to accumulating large stress. During the unwinding process, due to the release of winding tension, the single fabric area 14 is also prone to folding, especially when using copper foil with weak mechanical strength to pursue high energy density.
[0063] As shown in Figures 1-6, in a preferred embodiment, the compaction density x of the negative electrode active material layer 12 ranges from 1.4 g / cm³. 3 ~1.9g / cm 3 .
[0064] As shown in Figures 1-6, in one embodiment, the core 100 is a square core 100, which includes a straight area 101 in the middle and arc areas 102 on both sides; the empty foil area 13 is located in the straight area 101 and the arc area 102 of the first fold 103 of the negative electrode sheet 1; the single fabric area 14 is located in the straight area 101 and the arc area 102 of the second fold 104 and the third fold 105 of the negative electrode sheet 1.
[0065] Setting an empty foil area 13 in the straight area 101 and the arc area 102 of the first fold 103 of the negative electrode sheet 1 can avoid the problem of powder shedding from the negative electrode active material layer 12; placing the single fabric area 14 in the straight area 101 and the arc area 102 of the second fold 104 and the third fold 105 of the negative electrode sheet 1 has the technical effect of reducing the thickness of the core 100 and increasing the energy density of the product.
[0066] As shown in Figures 1-6, in one embodiment, the second aspect of the present invention provides a battery including a battery housing and the aforementioned winding core 100, wherein the winding core 100 is disposed within the housing.
[0067] In one embodiment, the negative electrode active material layer includes a negative electrode active material, a conductive agent, a binder, and a thickener.
[0068] In one embodiment, the negative electrode 1 includes a negative electrode active material, which includes one or more of the following: graphite negative electrode material, silicon-oxygen negative electrode material, silicon-carbon negative electrode material, silicon negative electrode material, tin negative electrode material, tin oxide negative electrode material, tin alloy negative electrode material (Sn-Fe, Sn-Co, Sn-Cu, etc.), lithium metal negative electrode material, lithium alloy negative electrode material (Li-Ag, Li-Al, Li-Sn, Li-Mg, Li-Zn, Li-In, Li-Ga, etc.), and lithium-free negative electrode material.
[0069] In one embodiment, the negative electrode conductive agent includes one or more of graphite, superconducting carbon, acetylene black, carbon black, carbon nanotubes, graphene, carbon nanofibers, metal powder, metal fibers, and polyphenylene derivatives.
[0070] In one embodiment, the negative electrode binder includes one or more of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, and polymethacrylic acid.
[0071] In one embodiment, the thickener includes one or more of sodium alginate, sodium carboxymethyl cellulose, and carboxymethyl chitosan.
[0072] In one embodiment, the mass percentage of each component in the negative electrode active material layer is: 96%-98.2% negative electrode active material, 0.1%-1.0% conductive agent, 0.8%-1.2% binder and 0.5%-1.2% thickener.
[0073] In one embodiment, the negative electrode current collector 11 is selected from a metallic material that can conduct electrons. Preferably, the negative electrode current collector 11 includes one or more of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the negative electrode current collector 11 is selected from copper foil.
[0074] In one embodiment, the negative electrode sheet 1 can be prepared according to conventional methods in the art. For example, the negative electrode active material layer is typically formed by coating a negative electrode slurry, consisting of a negative electrode active material, a negative electrode conductive agent, a negative electrode binder, and any other components, onto the negative electrode current collector 11, followed by drying and cold pressing. The solvent can be an aqueous solvent, but is not limited thereto.
[0075] In one embodiment, the positive electrode 2 includes a positive current collector 21 and a positive active material layer 22 coated on the surface of the positive current collector 21;
[0076] In one embodiment, the positive electrode active material layer includes a positive electrode active material, a conductive agent, and a binder; the positive electrode active material includes one or more of lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), lithium cobalt oxide (LCO), lithium manganese oxide (LMO), lithium nickel oxide (LNO), ternary materials (NCM, NCA), lithium-rich manganese-based (LMR), lithium nickel manganese oxide (LNMO), and lithium vanadium oxide phosphate (Li3V2(PO4)3, LiVOPO4).
[0077] In one embodiment, the positive electrode conductive agent includes one or more of graphite, superconducting carbon, acetylene black, carbon black, carbon nanotubes, graphene, carbon nanofibers, metal powder, metal fibers, and polyphenylene derivatives.
[0078] In one embodiment, the positive electrode binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.
[0079] In one embodiment, the mass percentage of each component in the positive electrode active material layer is: 96-98.5 wt% positive electrode active material, 0.5-1.5 wt% conductive agent, and 1.0-1.8 wt% binder.
[0080] If the mass percentage of the positive electrode active material in the positive electrode active material layer is within the above range, the positive electrode sheet 2 can have a higher lithium delithiation and lithium insertion capacity, thus enabling the battery to have a higher capacity.
[0081] In one embodiment, the positive current collector 21 is selected from a metallic material that can conduct electrons. Preferably, the positive current collector 21 includes one or more of copper, nickel, tin, copper, and stainless steel. In a more preferred embodiment, the positive current collector 21 is selected from aluminum foil.
[0082] In one embodiment, the diaphragm 3 may be selected from one or more materials such as polypropylene (PP), polyethylene (PE), PP / PE / PP composite membrane, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ceramic diaphragm 3, ceramic polyamide (PI), aramid (AF), and nonwoven fabric.
[0083] In one embodiment, the battery manufacturing process includes the following steps:
[0084] The positive electrode 2, the separator 3, and the negative electrode 1 are stacked in sequence, with the separator 3 positioned between the positive electrode 2 and the negative electrode 1 to provide isolation. Then, the separator is wound along the direction from the starting end to the ending end to form the core 100. The starting end of the negative electrode 1 is located at the innermost circle of the core 100, and the starting end of the positive electrode 2 is located on the outer periphery of the starting end of the negative electrode 1.
[0085] The wound core 100 is placed into the punched and formed battery casing, and the electrolyte is injected into the baked and dried cell. After vacuum sealing, standing, formation and other processes, the battery is obtained.
[0086] The beneficial effects of the present invention will be further illustrated below with reference to the embodiments.
[0087] To make the inventive objectives, technical solutions, and beneficial effects of this invention clearer, the invention is further described in detail below with reference to embodiments. However, it should be understood that the embodiments of this invention are merely for illustrative purposes and not for limiting the invention, and the embodiments are not limited to those given in the specification. Materials not specified in the embodiments were prepared under conventional conditions or according to the conditions recommended by the material supplier.
[0088] Furthermore, it should be understood that the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, does not preclude the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, unless otherwise stated. It should also be understood that the combined connection relationship between one or more devices / apparatus mentioned in this invention does not preclude the existence of other devices / apparatus before or after the combined devices / apparatus, or the insertion of other devices / apparatus between these explicitly mentioned devices / apparatus, unless otherwise stated. Moreover, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not for limiting the order of the method steps or limiting the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.
[0089] In the following embodiments, the reagents, materials and instruments used, unless otherwise specified, are commercially available or can be obtained through synthesis methods known in the art.
[0090] Table 1 shows the design parameters of the core and negative electrode sheet in Examples 1-13 and Comparative Examples 1-7;
[0091] Example 1
[0092] This embodiment illustrates the winding core and battery disclosed in this invention; it includes the following operational steps:
[0093] Preparation of negative electrode sheet:
[0094] Graphite, CMC additive, conductive carbon black SP, and binder SBR were mixed in a ratio of 97:1.1:0.8:1.1 to prepare a slurry. This slurry was then coated onto a 5µm thick copper foil for the negative electrode current collector using a coating machine. After drying, rolling, and pressing, the compacted density of the negative electrode active material layer was 1.40 g / cm³. 3 After processes such as die-cutting, a negative electrode sheet that meets the requirements is obtained.
[0095] Preparation of the positive electrode sheet:
[0096] Lithium cobalt oxide, single-walled carbon nanotubes, conductive carbon black SP, and binder PVDF are mixed in a ratio of 97.3:0.5:1.0:1.2 to prepare a positive electrode slurry. The positive electrode slurry is then coated onto the surface of the positive electrode current collector on a coating machine. After drying, rolling, die-cutting, and other processes, a positive electrode sheet that meets the requirements is obtained.
[0097] Electrolyte preparation:
[0098] Lithium hexafluorophosphate (LiPF6) was dissolved in a mixed solvent consisting of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a mass ratio of 1:2:1 to obtain an electrolyte with a concentration of 1 mol / L.
[0099] Preparation of the diaphragm:
[0100] PE porous polymer film is used as the membrane substrate;
[0101] Battery manufacturing:
[0102] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. Then, the electrode is wound from the starting end to the ending end to form a core. The core is 80mm long, 30mm wide, and 8.3mm thick.
[0103] The starting end of the negative electrode is located at the innermost circle of the winding core, and the starting end of the positive electrode is located on the outer periphery of the starting end of the negative electrode.
[0104] The wound core 100 is placed into the punched and formed battery casing, and the electrolyte is injected into the baked and dried cell. After vacuum sealing, standing, formation and other processes, the battery is obtained.
[0105] Example 2-13
[0106] Examples 2-13 illustrate the winding core and battery disclosed in this invention, including most of the operating steps in Example 1, with the following differences:
[0107] The parameters of the core and negative electrode sheet shown in Table 1 are used.
[0108] Comparative Examples 1-7
[0109] Comparative Examples 1-7 are used to illustrate the winding core and battery disclosed in this invention, including most of the operating steps in Example 1, the difference being:
[0110] The parameters of the core and negative electrode sheet shown in Table 1 are used.
[0111] Performance testing
[0112] The following performance tests were performed on the batteries prepared in Examples 1-13 and Comparative Examples 1-7:
[0113] 1. Battery life test: Room temperature cycle test: The battery is placed at 25℃ and charged and discharged at a current of 1.2C within a charge-discharge voltage range of 3.0-4.51V. The initial capacity is recorded as Q, and the capacity after 500 cycles is selected as Q1. The capacity retention rate of the battery after 500 cycles at room temperature is calculated using the following formula:
[0114] Capacity retention rate (%) = Q1 / Q × 100;
[0115] The test results are shown in Table 2.
[0116] Table 2 Battery Electrochemical Performance
[0117] As shown in Table 2, comparing Examples 1-13 with Comparative Examples 2 and 4, it can be seen that when the core and the negative electrode sheet satisfy the relationship: 0≤(a+b)*ab+(cd) 2 When the value is ≤2.2, the single-layer fabric area of the negative electrode sheet is less prone to folding during the winding process of the core. (a+b)*ab+(cd) 2 When the value is greater than 2.2, the single fabric area of the negative electrode sheet is prone to folding during the winding process of the core.
[0118] Comparing Examples 1-4 and Comparative Examples 1-2, it can be seen that when the value of 'a' is in the range of 0.2 to 2.0, the single-layer fabric area of the negative electrode sheet is less prone to folding, thereby improving the safe use performance of the battery. When the value of 'a' is greater than 2.0, since 'a' = W / h1 / 18, the width of the core is larger, and the corresponding width of the winding needle is larger. When the negative electrode sheet 1 passes the corner in the inner circle during winding, the tension is prone to be too large. Subsequently, when the winding needle is peeled off and the core is hot-pressed, the single-layer fabric area of the negative electrode sheet is prone to folding, resulting in poor contact at the interface of the negative electrode sheet, which has a negative effect on the reliability of long-term use. When the value of 'a' is less than 0.2, it will be difficult to remove the winding needle after winding, which will easily cause the electrode sheet inside the core to shift or fold, reduce the coating effect of the inner layer of the core, and cause folding problems.
[0119] Comparing Examples 5-8 and Comparative Examples 3-4, it can be seen that when the value of b is in the range of 0.2 to 2.0, it can prevent the single-sheet material area at the beginning of the negative electrode sheet from folding while taking into account the energy density of the product. When the value of b is less than 0.2, since b = 1.2 * W / L, the length of the core is more than 6 times the width of the core, which makes the inner ring of the core after winding prone to slippage, and also has an adverse effect on the folding of the single-sheet material area during hot pressing. When the value of b is greater than 2, the width of the core will be more than 1.66 times the length, and the tension of the arc area during winding will be difficult to control, which can easily cause the inner ring of the battery to fold due to excessive tension in the inner arc area. At the same time, the proportion of the top seal of the cell increases, which is not conducive to improving the energy density of the product.
[0120] Comparing Examples 9-11 and Comparative Example 5, it can be seen that the thickness h2 of the negative electrode current collector is in the range of 3 to 9 μm, which has the effect of balancing the energy density of the product and the folding and breakage of the negative electrode sheet during the production process. Currently, the thickness h2 of the negative electrode current collector is almost never less than 3 μm, so it will not be discussed here. When the thickness h2 of the negative electrode current collector is greater than 9 μm, it will lead to a loss of product energy density.
[0121] Comparing Examples 3, 12-13, and 6-7, it can be seen that when the compaction density x of the negative electrode active material layer is in the range of 1.0 g / cm³, 3 ~2.0g / cm 3 It has the function of balancing product energy density and internal stress control during the rolling process of the negative electrode sheet; when the compaction density x of the negative electrode active material layer is less than 1.0 g / cm³. 3 This will lead to a loss of product energy density. The lower the compaction density, the worse the electron contact between material particles will be, which will affect the capacity retention rate during cycling. When the compaction density x of the negative electrode active material layer is greater than 2.0 g / cm³, it will cause a loss of product energy density. 3 Since d = x / 1.73, d > 1.156. During the rolling process, the single-layer fabric area is prone to accumulating large stress. During the unwinding process, due to the release of winding tension, the single-layer fabric area is also prone to folding, especially when using copper foil with weak mechanical strength to pursue high energy density.
[0122] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A winding core, characterized in that: The core includes a positive electrode, a separator, and a negative electrode. The positive electrode, the separator, and the negative electrode are stacked in sequence and then wound along the direction from the starting end to the ending end. The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on the surface of the negative electrode current collector; The negative electrode sheet includes an empty foil area, a single-sheet material area, and a double-sheet material area connected in sequence. The negative electrode active material layer is not provided on both sides of the empty foil area; the negative electrode active material layer is not provided on the side of the single-sheet area away from the positive electrode sheet; the negative electrode active material layer is provided on both sides of the double-sheet area; the empty foil area and the single-sheet area are located at the starting end of the negative electrode sheet; The starting end of the positive electrode sheet is stacked on one side of the single-layer fabric area; The wound core and the negative electrode sheet satisfy the following relationship: 0 ≤ (a+b)*ab+(cd) 2 ≤2.2; Where, a = W / h1 / 18; b = 1.2 * W / L; c = 5 / h2; d = x / 1.73; W is the width of the core, in mm; h1 is the thickness of the core, in mm; L is the length of the core, in mm; h2 is the thickness of the negative electrode current collector, in μm; x is the compaction density of the negative electrode active material layer, in g / cm³. 3 .
2. The winding core according to claim 1, characterized in that: The value of 'a' ranges from 0.2 to 2.
0.
3. The winding core according to claim 2, characterized in that: The value of 'a' ranges from 0.2 to 0.
8.
4. The winding core according to claim 1, characterized in that: The value of b ranges from 0.2 to 2.
0.
5. The winding core according to claim 4, characterized in that: The value of b ranges from 0.3 to 1.
5.
6. The winding core according to claim 1, characterized in that: The thickness h2 of the negative electrode current collector ranges from 3 to 9 μm.
7. The winding core according to claim 6, characterized in that: The thickness h2 of the negative electrode current collector ranges from 4 to 6 μm.
8. The winding core according to claim 1, characterized in that: The compaction density x of the negative electrode active material layer ranges from 1.0 g / cm³. 3 ~2.0g / cm 3 .
9. The winding core according to claim 8, characterized in that: The compaction density x of the negative electrode active material layer ranges from 1.4 g / cm³. 3 ~1.9g / cm 3 .
10. The winding core according to any one of claims 1-9, characterized in that: The core is a square core, which includes a straight area in the middle and arc areas on both sides; the empty foil area is located in the straight area and the arc area of the first fold of the negative electrode sheet; the single fabric area is located in the straight area and the arc area of the second and third folds of the negative electrode sheet.
11. A battery, characterized in that: It includes a battery housing and a winding core as described in any one of claims 1-10, wherein the winding core is disposed within the housing.