A winding core and a battery

Abstract

The present invention provides a winding core, comprising a positive electrode sheet, a separator and a negative electrode sheet, which are stacked in sequence and then wound in a direction from a starting end to a tail end to form a winding core; the negative electrode sheet comprises 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 comprises a hollow foil area, a single-surface area and a double-surface area connected in sequence; no negative electrode active material layer is provided on both sides of the hollow foil area; no negative electrode active material layer is provided on the side of the single-surface area facing away from the positive electrode sheet; negative electrode active material layers are provided on both sides of the double-surface area; the hollow foil area and the single-surface 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-surface area; the winding core and the negative electrode sheet satisfy the 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; the core of the present invention satisfies 0≤(a+b)*ab+(cd) 2 When the coefficient of resistance is ≤2.2, the single surface area of the negative electrode sheet is less likely to be folded during the winding production of the core, thereby improving the safe use performance of the battery.

Description

Technical Field

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

[0002] Lithium-ion batteries have the advantages of high energy density, high operating platform voltage, customizable size, and no memory, and are widely used in various consumer battery fields.

[0003] In order to pursue product energy density, thin copper foil and high negative electrode compaction are increasingly used. At the same time, the different sizes and designs of various consumer battery compartments will lead to various process defects in the battery preparation process. For example, the negative electrode head of the lithium-ion battery contains two single-sided areas during winding (see attached). Figure 1 Due to the different forces on each side of the single-sided area, the residual stress generated in the pre-winding process is released during winding, causing the negative electrode head area to buckle during winding. This buckling leads to poor interfacial contact and negatively affects reliability in subsequent long-term use. Therefore, overcoming these technical problems and defects has become a key issue that needs to be addressed. Summary of the Invention

[0004] Aiming at the problem that the negative electrode head of an existing battery contains two single-sided areas and the single-sided areas of the negative electrode head are folded during winding, the present invention provides a winding core and a battery.

[0005] The technical solutions adopted by the present invention to solve the above technical problems are as follows:

[0006] A first aspect of the present invention provides a winding 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 from a starting end to an ending end to form the winding core;

[0007] 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;

[0008] The negative electrode sheet comprises a hollow foil area, a single-foil area and a double-foil area connected in sequence;

[0009] 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-faced fabric area facing away from the positive electrode sheet; the negative electrode active material layer is provided on both sides of the double-faced fabric area; the empty foil area and the single-faced fabric area are located at the starting end of the negative electrode sheet;

[0010] The starting end of the positive electrode sheet is stacked on one side of the single fabric area;

[0011] The winding core and the negative electrode sheet satisfy the relationship: 0≤(a+b)*ab+(cd) 2 ≤2.2;

[0012] Where, a=W / h1 / 18; b=1.2*W / L; c=5 / h2; d=x / 1.73;

[0013] W is the width of the winding core, in mm; h1 is the thickness of the winding core, in mm; L is the length of the winding core, in mm; h2 is the thickness of the negative electrode current collector, in μm; x is the compacted density of the negative electrode active material layer, in g / cm 3 .

[0014] Optionally, the value range of a is 0.2~2.0.

[0015] Optionally, the value range of a is 0.2~0.8.

[0016] Optionally, the value range of b is 0.2~2.0.

[0017] Optionally, the value range of b is 0.3~1.5.

[0018] Optionally, the thickness h2 of the negative electrode current collector ranges from 3 to 9 μm.

[0019] Optionally, the thickness h2 of the negative electrode current collector ranges from 4 to 6 μm.

[0020] Optionally, the compaction density x of the negative electrode active material layer is in the range of 1.0 g / cm 3 ~2.0g / cm 3 .

[0021] Optionally, the compaction density x of the negative electrode active material layer is in the range of 1.4 g / cm 3 ~1.9g / cm 3 .

[0022] Optionally, the winding core is a square winding 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.

[0023] A second aspect of the present invention provides a battery, comprising a battery housing and the winding core described above, wherein the winding core is disposed in the housing.

[0024] According to the winding core provided by the present invention, the length, width and thickness of the winding core, the thickness of the negative electrode current collector, and the compaction density of the negative electrode active material layer are limited so as to satisfy 0≤(a+b)*ab+(cd) 2When the coefficient of thermal conductivity is ≤2.2, the single surface area of the negative electrode sheet is less likely to be folded during the winding production of the winding core 100, thereby improving the safe use performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0026] Figure 1 is a schematic diagram of a winding core provided by one embodiment of the present invention;

[0027] Figure 2 1 is a schematic diagram of the first fold to the third fold of the roll core provided by one embodiment of the present invention;

[0028] Figure 3 1 is a schematic diagram of the negative electrode sheet in the winding core provided by one embodiment of the present invention;

[0029] Figure 4 is a schematic diagram of one side of a negative electrode sheet provided by one embodiment of the present invention;

[0030] Figure 5 is a schematic diagram of the other side of the negative electrode sheet provided by one embodiment of the present invention;

[0031] Figure 6 1 is a schematic structural diagram of a negative electrode sheet provided by one embodiment of the present invention;

[0032] The reference numerals in the drawings of the specification are as follows:

[0033] 100-winding 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-face area; 15-double-face area; 2-positive electrode sheet; 21-positive electrode current collector; 22-positive electrode active material layer; 3-diaphragm. DETAILED DESCRIPTION

[0034] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0035] In the description of the present invention, it should be understood that the terms "longitudinal", "radial", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended only to facilitate the description of the present invention and simplify the description. They do not indicate or imply that the devices or elements referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore should not be understood as limiting the present invention. In the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0036] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0037] like Figures 1-6 As shown, in one embodiment, the first aspect of the present invention provides a winding core 100, comprising a positive electrode sheet 2, a separator 3, and a negative electrode sheet 1. The positive electrode sheet 2, the separator 3, and the negative electrode sheet 1 are stacked in sequence and wound from a starting end to an ending end to form the winding 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 sheet 1 comprises a hollow foil area 13, a single-faced fabric area 14 and a double-faced 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-faced fabric area 14 facing away from the positive electrode sheet 2; the negative electrode active material layer 12 is provided on both sides of the double-faced fabric area 15; the empty foil area 13 and the single-faced fabric area 14 are located at the starting end of the negative electrode sheet 1;

[0041] The starting end of the positive electrode sheet 2 is stacked on one side of the single fabric area 14;

[0042] The winding core 100 and the negative electrode sheet 1 satisfy the 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 winding core 100, in mm; h1 is the thickness of the winding core 100, in mm; L is the length of the winding 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 / cm 3 .

[0045] Specifically, (a+b)*ab+(cd) 2 The value of is any one of 0, 0.2, 0.4, 0.6, 0.8, 1, 1.2, 1.4, 1.6, 1.8, 2 or 2.2 or a range of any two values. In a preferred embodiment, 0≤(a+b)*ab+(cd) 2 ≤1.2.

[0046] When the length, width and thickness of the winding 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 coefficient of thermal conductivity is ≤2.2, the single surface area 14 of the negative electrode sheet 1 is less likely to be folded during the winding production of the winding core 100, thereby improving the safe use performance of the battery.

[0047] When the length, width and thickness of the winding 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 thickness is greater than 2.2, the single material area 14 of the negative electrode sheet 1 is prone to folding during the winding production of the winding core 100, resulting in poor interface contact of the negative electrode sheet 1, which has a negative effect on the reliability of subsequent long-term use.

[0048] like Figures 1-6 As shown, in one embodiment, the value range of a is 0.2~2.0.

[0049] Specifically, the value range of a is any point value among 0.2, 0.4, 0.6, 0.8, 1, 1.2, 1.4, 1.6, 1.8 or 2, or a range value consisting of any two point values.

[0050] When the value range of a is 0.2~2.0, the single fabric area 14 of the negative electrode sheet 1 is not prone to folding, thereby improving the safe use performance of the battery. When the a value is greater than 2.0, since a=W / h1 / 18; at this time, the width of the core 100 is large, and the corresponding winding needle width is large. When winding, the tension of the negative electrode sheet 1 is likely to be too large when it passes the corner in the inner circle. Subsequently, when the winding needle is peeled off and the core 100 is hot-pressed, the single fabric area 14 of the negative electrode sheet 1 is likely to be folded, resulting in poor interface contact of the negative electrode sheet 1, which has a negative effect on the reliability of subsequent long-term use; when the a value is less than 0.2, it will make it difficult to remove the winding needle after winding is completed, and it is easy to cause the internal electrode sheet of the core 100 to shift or fold, reducing the coating effect of the inner layer of the core 100 to cause folding problems.

[0051] like Figures 1-6 As shown, in a preferred embodiment, the value range of a is 0.2~0.8.

[0052] like Figures 1-6 As shown, in one embodiment, the value range of b is 0.2~2.0.

[0053] Specifically, the value range of b is any point value among 0.2, 0.4, 0.6, 0.8, 1, 1.2, 1.4, 1.6, 1.8 or 2, or a range value consisting of any two point values.

[0054] When the value range of b is 0.2~2.0, it has the function of preventing the single fabric area 14 at the starting end of the negative electrode sheet 1 from being folded and 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; at this time, the length of the core 100 is more than 6 times the width of the core 100, which causes the inner circle of the core 100 after winding to easily slip, and also has an adverse effect on the folding of the single fabric area 14 during hot pressing; when the value of b is greater than 2, it will cause the width of the core 100 to be more than 1.66 times the length, and the tension of the arc area 102 is difficult to control during winding, which can easily cause the tension of the inner arc area 102 to be too large, causing the inner circle of the battery to be folded, and at the same time, the proportion of the top seal of the battery cell becomes larger, which is not conducive to the improvement of the energy density of the product.

[0055] like Figures 1-6 As shown, in a preferred embodiment, the value range of b is 0.3~1.5.

[0056] like Figures 1-6 As shown, 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 in the range of any one value among 3um, 4um, 5um, 6um, 7um, 8um and 9um, or a range consisting of any two values.

[0058] The thickness h2 of the negative electrode current collector 11 is in the range of 3~9um, which has the effect of taking into account the energy density of the product and balancing the folding and breaking of the negative electrode sheet 1 during the production process; when the thickness h2 of the negative electrode current collector 11 is less than 3um, since c=5 / h2, at this time c>5 / 3, the strength of the negative electrode current collector 11 will be reduced, the electrode roll will easily break during the production process, and the single fabric area 14 at the starting end of the negative electrode sheet 1 will easily be folded during winding; when the thickness h2 of the negative electrode current collector 11 is greater than 9um, the energy density of the product will be lost.

[0059] like Figures 1-6 As shown, in a preferred embodiment, the thickness h2 of the negative electrode current collector 11 ranges from 4 to 6 μm.

[0060] like Figures 1-6 As shown, in one embodiment, the compaction density x of the negative electrode active material layer 12 is in the range of 1.0 g / cm 3 ~2.0g / cm 3 .

[0061] Specifically, the compaction density x of the negative electrode active material layer 12 is in the range of 1 g / cm 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 Any point value or any range of two point values in .

[0062] When the compaction density x of the negative electrode active material layer 12 is in the range of 1.0 g / cm 3 ~2.0g / cm 3 , which has the effect of taking into account both the product energy density and the internal stress control during the rolling process of the negative electrode sheet 1; when the compaction density x of the negative electrode active material layer 12 is less than 1.0g / cm 3, which will lead to a loss of product energy density. The smaller the compaction density, the worse the electronic contact between the material particles will be, which will affect the capacity retention rate during the cycle. When the compaction density x of the negative electrode active material layer 12 is greater than 2.0 g / cm 3 Since d=x / 1.73, d>1.156 at this time, the single fabric area 14 is prone to accumulate large stress during the rolling process. During the unwinding process, due to the release of the winding tension, the single fabric area 14 is also prone to folding problems, especially when using copper foil with weaker mechanical strength when pursuing high energy density.

[0063] like Figures 1-6 As shown, in a preferred embodiment, the compaction density x of the negative electrode active material layer 12 is in the range of 1.4 g / cm 3 ~1.9g / cm 3 .

[0064] like Figures 1-6 As shown, in one embodiment, the winding core 100 is a square winding core 100, and the winding core 100 includes a straight area 101 located in the middle and arc areas 102 located 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] Providing 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 falling of the negative electrode active material layer 12; locating 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 improving the energy density of the product.

[0066] like Figures 1-6 As shown, 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 in 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 sheet 1 includes a negative electrode active material, and the negative electrode active material includes one or more of a graphite negative electrode material, a silicon-oxygen negative electrode material, a silicon-carbon negative electrode material, a silicon negative electrode material, a tin negative electrode material, a tin oxide negative electrode material, a tin alloy negative electrode material (Sn-Fe, Sn-Co, Sn-Cu, etc.), a lithium metal negative electrode material, a lithium alloy negative electrode material (Li-Ag, Li-Al, Li-Sn, Li-Mg, Li-Zn, Li-In, Li-Ga, etc.), and a 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 percentages of the components in the negative electrode active material layer are: 96%-98.2% of the negative electrode active material, 0.1%-1.0% of the conductive agent, 0.8%-1.2% of the binder, and 0.5%-1.2% of the thickener.

[0073] In one embodiment, the negative electrode current collector 11 is selected from a metal 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 comprising the 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, but is not limited to, an aqueous solvent.

[0075] In one embodiment, the positive electrode sheet 2 includes a positive electrode current collector 21 and a positive electrode active material layer 22 coated on the surface of the positive electrode 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 manganese-rich base (LMR), lithium nickel manganese oxide (LNMO), and lithium vanadium oxyphosphate (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 fluorine-containing acrylic resin.

[0079] In one embodiment, the mass percentages of the components in the positive electrode active material layer are: 96-98.5 wt % of the positive electrode active material, 0.5-1.5 wt % of the conductive agent, and 1.0-1.8 wt % of the binder.

[0080] When the mass ratio 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 removal and lithium insertion capacity, and the battery can have a higher capacity.

[0081] In one embodiment, the positive electrode current collector 21 is selected from a metal material that can conduct electrons. Preferably, the positive electrode current collector 21 includes one or more of copper, nickel, tin, copper, and stainless steel. In a more preferred embodiment, the positive electrode current collector 21 is selected from aluminum foil.

[0082] In one embodiment, the diaphragm 3 can be selected from one or more materials such as polypropylene (PP), polyethylene (PE), PP / PE / PP composite film, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ceramic diaphragm 3, ceramic polyamide (PI), aramid (AF), non-woven fabric, etc.

[0083] In one embodiment, the production of the battery includes the following steps:

[0084] The positive electrode sheet 2, the separator 3 and the negative electrode sheet 1 are stacked in sequence, with the separator 3 located between the positive electrode sheet 2 and the negative electrode sheet 1 to serve as an isolation, and then wound in the direction from the starting end to the ending end to form the winding core 100; the starting end of the negative electrode sheet 1 is located at the innermost circle of the winding core 100, and the starting end of the positive electrode sheet 2 is arranged on the periphery of the starting end of the negative electrode sheet 1.

[0085] The wound core 100 is placed in a battery shell that has been punched and formed, and the electrolyte is injected into the baked and dried battery cell. After vacuum packaging, standing, and formation processes, a battery is obtained.

[0086] The beneficial effects of the present invention are further illustrated below with reference to the examples.

[0087] In order to make the invention objectives, technical solutions and beneficial technical effects of the present invention clearer, the present invention is further described in detail below with reference to the examples. However, it should be understood that the examples of the present invention are only for the purpose of explaining the present invention and are not intended to limit the present invention, and the examples of the present invention are not limited to the examples given in the specification. In the examples, where specific experimental conditions or operating conditions are not specified, the preparations were made under conventional conditions or under the conditions recommended by the material supplier.

[0088] Furthermore, it should be understood that the one or more method steps mentioned in the present invention do not exclude the presence of other method steps before or after the combination step, or the insertion of other method steps between these explicitly mentioned steps, unless otherwise specified. It should also be understood that the combination connection relationship between one or more devices / apparatuses mentioned in the present invention does not exclude the presence of other devices / apparatuses before or after the combination device / apparatus, or the insertion of other devices / apparatuses between two explicitly mentioned devices / apparatuses, unless otherwise specified. Furthermore, unless otherwise specified, the numbering of each method step is merely a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or to define the scope of the present invention. Changes or adjustments to their relative relationships, without substantially changing the technical content, should also be considered within the scope of the present invention.

[0089] In the following examples, the reagents, materials and instruments used, unless otherwise specified, can be purchased commercially or obtained through synthetic methods known in the art.

[0090] Table 1 Design of winding core and negative electrode sheet parameters for Examples 1-13 and Comparative Examples 1-7;

[0091]

[0092] Example 1

[0093] This embodiment is used to illustrate the winding core and battery disclosed in the present invention and includes the following steps:

[0094] Preparation of negative electrode sheet:

[0095] 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. The slurry was coated on a 5um thick negative electrode current collector copper foil on a coater. After drying, rolling and rolling, the compaction density of the negative electrode active material layer was 1.40g / cm 3 After processes such as die cutting, the negative electrode sheet that meets the requirements is obtained.

[0096] Preparation of positive electrode:

[0097] 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, which is then coated onto the surface of the positive electrode current collector on a coating machine. After drying, rolling, die-cutting and other processes, the positive electrode sheet that meets the requirements is obtained.

[0098] Preparation of electrolyte:

[0099] Lithium hexafluorophosphate (LiPF6) was dissolved in a mixed solvent consisting of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) (the mass ratio of the three was 1:2:1) to obtain an electrolyte with a concentration of 1 mol / L.

[0100] Preparation of diaphragm:

[0101] PE porous polymer film is used as the separator substrate;

[0102] Preparation of the battery:

[0103] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrodes to act as a separator. The core is then wound from the starting end to the end to form a core; the core is 80 mm long, 30 mm wide, and 8.3 mm thick.

[0104] The starting end of the negative electrode sheet is located at the innermost circle of the winding core, and the starting end of the positive electrode sheet is arranged on the periphery of the starting end of the negative electrode sheet.

[0105] The wound core 100 is placed in a battery shell that has been punched and formed, and the electrolyte is injected into the baked and dried battery cell. After vacuum packaging, standing, and formation processes, a battery is obtained.

[0106] Example 2-13

[0107] Examples 2-13 are used to illustrate the winding core and battery disclosed in the present invention, and include most of the operating steps of Example 1, except that:

[0108] The parameters of the winding core and negative electrode sheet shown in Table 1 were used.

[0109] Comparative Examples 1-7

[0110] Comparative Examples 1-7 are used to illustrate the winding core and battery disclosed in the present invention, and include most of the operating steps in Example 1, except that:

[0111] The parameters of the winding core and negative electrode sheet shown in Table 1 were used.

[0112] Performance Testing

[0113] The following performance tests were performed on the batteries prepared in Examples 1 to 13 and Comparative Examples 1 to 7:

[0114] 1. Battery life test: Normal temperature cycle test: The battery is placed at 25°C and charged and discharged at a current of 1.2C in the charge and 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 normal temperature is calculated using the following formula:

[0115] Capacity retention rate (%) = Q1 / Q × 100;

[0116] The test results are shown in Table 2.

[0117] Table 2 Battery electrochemical performance

[0118]

[0119] As shown in Table 2, by comparing Examples 1-13 with Comparative Examples 2 and 4, when the winding core and the negative electrode sheet satisfy the relationship: 0≤(a+b)*ab+(cd) 2 When ≤2.2, the negative electrode sheet’s single surface area is not prone to folding during winding. 2 When the core is >2.2, the negative electrode sheet's single surface area is prone to folding during winding.

[0120] By comparing Examples 1-4 and Comparative Examples 1-2, it can be seen that when the value range of a is 0.2~2.0, the single-surface area of the negative electrode sheet is not prone to folding, thereby improving the safe use performance of the battery. When the a value is greater than 2.0, since a=W / h1 / 18; at this time, the width of the core is larger, and the corresponding winding needle width is larger. When winding, the tension of the negative electrode sheet 1 is likely to be too large when it passes the corner in the inner circle. Subsequently, when the winding needle is peeled off and the core is hot-pressed, the single-surface area of the negative electrode sheet is prone to folding, resulting in poor interface contact of the negative electrode sheet, which has a negative effect on the reliability of subsequent long-term use. When the a value is less than 0.2, it will make it difficult to remove the winding needle after winding is completed, which can easily cause the electrode sheet inside the core to shift or fold, reducing the coating effect of the inner layer of the core and causing folding problems.

[0121] By comparing Examples 5-8 and Comparative Examples 3-4, it can be seen that when the value range of b is 0.2~2.0, it has the effect of preventing the single fabric area at the starting end of the negative electrode sheet from being folded and 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; at this time, the length of the core is more than 6 times the width of the core, which causes the inner circle of the core after winding to easily slip, and also has an adverse effect on the folding of the single fabric 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 in the arc area will be difficult to control during winding, which will easily cause the tension in the inner arc area to be too large, causing the inner circle of the battery to be folded. At the same time, the proportion of the top seal of the battery cell will increase, which is not conducive to improving the energy density of the product.

[0122] By comparing Examples 9-11 and Comparative Example 5, it can be seen that the thickness h2 of the negative electrode current collector ranges from 3 to 9 μm, which has the effect of taking into account both the energy density of the product and the folding and breaking of the negative electrode sheet during the balanced production process; currently, the thickness h2 of the negative electrode current collector almost does not have a range of values less than 3 μm, which will not be discussed here; when the thickness h2 of the negative electrode current collector ranges from greater than 9 μm, it will lead to a loss of product energy density.

[0123] Comparison of Example 3 with Examples 12-13 and Comparative Examples 6-7 shows that when the compaction density x of the negative electrode active material layer is in the range of 1.0 g / cm 3 ~2.0g / cm 3 , which has the effect of taking into account both the product energy density and the internal stress control during the negative electrode sheet rolling process; when the compaction density x of the negative electrode active material layer is less than 1.0g / cm 3 , which will lead to a loss of product energy density. The smaller the compaction density, the worse the electronic contact between the material particles will be, which will affect the capacity retention rate during the cycle. When the compaction density x of the negative electrode active material layer is greater than 2.0 g / cm 3 Since d=x / 1.73, d>1.156 at this time, the single fabric area is prone to accumulate large stress during the rolling process. During the unwinding process, due to the release of the winding tension, the single fabric area is also prone to folding problems, especially when using copper foil with weaker mechanical strength when pursuing high energy density.

[0124] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A winding core, characterized in that: The positive electrode sheet, the separator and the negative electrode sheet are stacked in sequence and then wound from the starting end to the ending end to form the winding core; 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 comprises a hollow foil area, a single-foil area and a double-foil 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-faced fabric area facing away from the positive electrode sheet; the negative electrode active material layer is provided on both sides of the double-faced fabric area; the empty foil area and the single-faced fabric 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 fabric area; The winding core and the negative electrode sheet satisfy the 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; Wmm is the width of the core in the winding direction; h1mm is the thickness of the core; Lmm is the length of the core in the winding axis; h2um is the thickness of the negative electrode collector; xg / cm 3 is the compaction density of the negative electrode active material layer; The value range of b is 0.2~2.0; The compaction density x of the negative electrode active material layer is in the range of 1.0 g / cm 3 ~2.0g / cm 3 ; The winding core is a square winding core, and the winding core includes a straight area in the middle and arc areas on both sides.

2. The winding core according to claim 1, characterized in that: The value range of a is 0.2~2.

0.

3. The winding core according to claim 2, wherein: The value range of a is 0.2~0.

8.

4. The winding core according to claim 1, wherein: The value range of b is 0.3~1.

5.

5. The winding core according to claim 1, wherein: The thickness h2 of the negative electrode current collector ranges from 3 to 9 μm.

6. The winding core according to claim 5, characterized in that: The thickness h2 of the negative electrode current collector ranges from 4 to 6 μm.

7. The winding core according to claim 1, characterized in that: The compaction density x of the negative electrode active material layer is in the range of 1.4 g / cm 3 ~1.9g / cm 3 .

8. The winding core according to any one of claims 1 to 7, characterized in that: 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.

9. A battery, characterized in that: The invention comprises a battery housing and a winding core according to any one of claims 1 to 8, wherein the winding core is arranged in the housing.

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