Roll core and battery

Abstract

The invention provides a roll core which comprises a positive plate, a diaphragm and a negative plate, and the positive plate, the diaphragm and the negative plate are sequentially stacked and then wound in the direction from the starting end to the ending end to form the roll core; the negative plate comprises a negative current collector and a negative active material layer coated on the surface of the negative current collector; the negative plate comprises an empty foil area, a single-fabric area and a double-fabric area which are connected in sequence; negative electrode active material layers are not arranged on the two sides of the empty foil area; one side, deviating from the positive plate, of the single fabric area is not provided with a negative active material layer; negative electrode active material layers are arranged on the two sides of the double-fabric area; the empty foil area and the single fabric area are positioned at the starting end of the negative plate; the starting end of the positive plate is overlapped on one side of the single fabric area; the roll core and the negative plate meet the relational expression that (a + b) * ab + (cd) < 2 > is greater than or equal to 0 and less than or equal to 2.2; wherein a = W / h1 / 18; b = 1.2 * W / L; c = 5 / h2; d is equal to x / 1.73; when the roll core meets the condition that (a + b) * ab + (cd) < 2 > is greater than or equal to 0 and less than or equal to 2.2, the single fabric area of the negative plate is not easy to fold when the roll core is subjected to winding production, so that the safe use performance of the battery is improved.

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 working 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 size design of various consumer battery compartments is different, which 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 both sides of the single-sided area, the residual stress generated in the pre-winding process is released during winding, resulting in the folding of the single-sided area of ​​the negative electrode head during battery winding. The folding problem leads to poor interface contact and has a negative effect on the reliability of subsequent long-term use. Therefore, how to overcome the above-mentioned technical problems and defects has become a key issue that needs to be solved. Summary of the invention

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

[0005] The technical solution adopted by the present invention to solve the above technical problems is as follows: 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 then wound from a starting end to a tail end to form the 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-faced foil area and a double-faced 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 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; Among them, a=W / h1 / 18; b=1.2*W / L; c=5 / h2; d=x / 1.73; 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 um; x is the compaction density of the negative electrode active material layer, in g / cm 3 .

[0006] Optionally, the value range of a is 0.2~2.0.

[0007] Optionally, the value range of a is 0.2~0.8.

[0008] Optionally, the value range of b is 0.2~2.0.

[0009] Optionally, the value range of b is 0.3~1.5.

[0010] Optionally, the thickness h2 of the negative electrode current collector ranges from 3 to 9 um.

[0011] Optionally, the thickness h2 of the negative electrode current collector ranges from 4 to 6 um.

[0012] 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 .

[0013] 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 .

[0014] Optionally, the winding core is a square winding core, comprising 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.

[0015] 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.

[0016] 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) 2 When 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

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings in the following description 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.

[0018] Figure 1 is a schematic diagram of a winding core provided by an embodiment of the present invention; Figure 2 It is a schematic diagram of the first fold to the third fold of the roll core provided by one embodiment of the present invention; Figure 3 is a schematic diagram of a negative electrode sheet in a winding core provided by an embodiment of the present invention; Figure 4 is a schematic diagram of one side of a negative electrode sheet provided by an embodiment of the present invention; Figure 5 is a schematic diagram of the other side of a negative electrode sheet provided by an embodiment of the present invention; Figure 6 is a schematic structural diagram of a negative electrode sheet provided by an embodiment of the present invention; The reference numerals in the drawings of the specification are as follows: 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

[0019] 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 in conjunction with 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 used to limit the present invention.

[0020] 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" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0021] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0022] like Figure 1-Figure 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, wherein 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 a tail end to form the winding core 100; 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; The negative electrode sheet 1 comprises a hollow foil area 13, a single-foil area 14 and a double-foil area 15 connected in sequence; 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-face area 14 away from the positive electrode sheet 2; the negative electrode active material layer 12 is provided on both sides of the double-face area 15; the empty foil area 13 and the single-face area 14 are located at the starting end of the negative electrode sheet 1; The starting end of the positive electrode sheet 2 is stacked on one side of the single surface area 14; The winding core 100 and the negative electrode sheet 1 satisfy the relationship: 0≤(a+b)*ab+(cd) 2 ≤2.2; Among them, a=W / h1 / 18; b=1.2*W / L; c=5 / h2; d=x / 1.73; 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 um; x is the compaction density of the negative electrode active material layer 12, in g / cm 3 .

[0023] Specifically, (a+b)*ab+(cd) 2 The value of is any point value among 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 values ​​consisting of any two point values. In a preferred embodiment, 0≤(a+b)*ab+(cd) 2 ≤1.2.

[0024] 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 not prone to bend during the winding production of the winding core 100, thereby improving the safe use performance of the battery.

[0025] 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-surface area 14 of the negative electrode sheet 1 is prone to bend 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.

[0026] like Figure 1-Figure 6 As shown, in one embodiment, the value range of a is 0.2~2.0.

[0027] 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.

[0028] When the value range of a is 0.2~2.0, the single-surface 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 relatively large, and the corresponding winding needle width is relatively 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. When the winding needle is subsequently peeled off and the core 100 is hot-pressed, the single-surface 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 the winding is completed, and it is easy to cause the electrode sheet inside the core 100 to shift or fold, reducing the coating effect of the inner layer of the core 100 to cause folding problems.

[0029] like Figure 1-Figure 6 As shown, in a preferred embodiment, the value range of a is 0.2~0.8.

[0030] like Figure 1-Figure 6 As shown, in one embodiment, the value range of b is 0.2~2.0.

[0031] 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.

[0032] When the value range of b is 0.2~2.0, it can prevent the single-surface area 14 at the starting end of the negative electrode sheet 1 from being folded and 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; 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-surface 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.

[0033] like Figure 1-Figure 6 As shown, in a preferred embodiment, the value range of b is 0.3~1.5.

[0034] like Figure 1-Figure 6 As shown, in one embodiment, the thickness h2 of the negative electrode current collector 11 ranges from 3 to 9 um.

[0035] Specifically, the thickness h2 of the negative electrode current collector 11 is in the range of any point value among 3um, 4um, 5um, 6um, 7um, 8um or 9um, or a range consisting of any two point values.

[0036] The thickness h2 of the negative electrode current collector 11 is in the range of 3 to 9 um, which has the effect of taking into account both the product energy density and 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 3 um, since c=5 / h2, at this time c>5 / 3, the strength of the negative electrode current collector 11 will decrease, the electrode roll will easily break during the production process, and the single-surface area 14 at the starting end of the negative electrode sheet 1 will easily fold during winding; when the thickness h2 of the negative electrode current collector 11 is greater than 9 um, the product energy density will be lost.

[0037] like Figure 1-Figure 6 As shown, in a preferred embodiment, the thickness h2 of the negative electrode current collector 11 ranges from 4 to 6 um.

[0038] like Figure 1-Figure 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 .

[0039] 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 a range of values ​​consisting of any two point values ​​in .

[0040] 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 function 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 1.0 g / cm 3 , which will lead to a loss in product energy density. The smaller the compaction density, the worse the electronic contact between 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 easy to accumulate large stress during the rolling process, and the single fabric area 14 is also easy to bend due to the release of winding tension during unwinding in the winding process, especially when using copper foil with weaker mechanical strength when pursuing high energy density.

[0041] like Figure 1-Figure 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 .

[0042] like Figure 1-Figure 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.

[0043] 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-material 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.

[0044] like Figure 1-Figure 6 As shown, in one embodiment, the second aspect of the present invention provides a battery, including a battery housing and the winding core 100 described above, wherein the winding core 100 is disposed in the housing.

[0045] In one embodiment, the negative electrode active material layer includes a negative electrode active material, a conductive agent, a binder, and a thickener.

[0046] 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.

[0047] 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 powders, metal fibers, and polyphenylene derivatives.

[0048] 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.

[0049] In one embodiment, the thickener includes one or more of sodium alginate, sodium carboxymethyl cellulose and carboxymethyl chitosan.

[0050] 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.

[0051] 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.

[0052] 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 usually prepared by coating a negative electrode slurry made of a negative electrode active material, a negative electrode conductive agent, a negative electrode binder and any other components on the negative electrode current collector 11, and then drying and cold pressing. The solvent can be an aqueous solvent, but is not limited thereto.

[0053] 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; 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 iron manganese 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 phosphate (Li3V2(PO4)3, LiVOPO4).

[0054] 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 powders, metal fibers, and polyphenylene derivatives.

[0055] 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.

[0056] In one embodiment, the mass percentage of each component in the positive electrode active material layer is: 96-98.5wt% of positive electrode active material, 0.5-1.5wt% of conductive agent, and 1.0-1.8wt% of binder.

[0057] 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 insertion capacity, and the battery can have a higher capacity.

[0058] 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.

[0059] 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.

[0060] In one embodiment, the manufacturing of the battery includes the following steps: The positive electrode sheet 2, the separator 3 and the negative electrode sheet 1 are stacked in sequence, with the separator 3 being located between the positive electrode sheet 2 and the negative electrode sheet 1 to play an isolating role, and then wound in a 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.

[0061] The wound winding 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, formation and other processes, a battery is obtained.

[0062] The beneficial effects of the present invention are further illustrated below in conjunction with embodiments.

[0063] In order to make the invention purpose, technical scheme and beneficial technical effect of the present invention clearer, the present invention is further described in detail below in conjunction with examples. However, it should be understood that the examples of the present invention are only for explaining the present invention, not for limiting the present invention, and the examples of the present invention are not limited to the examples given in the specification. The specific experimental conditions or operating conditions not specified in the examples are prepared under conventional conditions, or prepared under the conditions recommended by the material supplier.

[0064] In addition, it should be understood that one or more method steps mentioned in the present invention do not exclude the existence 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 existence of other devices / apparatuses before or after the combination device / apparatus or the insertion of other devices / apparatuses between these explicitly mentioned two devices / apparatuses, unless otherwise specified. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or the scope of the present invention. Changes or adjustments in their relative relationships should also be regarded as the scope of the present invention without substantially changing the technical content.

[0065] In the following examples, the reagents, materials and instruments used, unless otherwise specified, can be purchased commercially or obtained by synthetic methods known in the art.

[0066] Table 1 Design of winding core and negative electrode sheet parameters of Examples 1-13 and Comparative Examples 1-7;

[0067] Example 1 This embodiment is used to illustrate the winding core and battery disclosed in the present invention; it includes the following steps: Preparation of negative electrode sheet: 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, which was coated on a 5um thick negative electrode current collector copper foil on a coating machine. 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.

[0068] Preparation of positive electrode: 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 on the surface of the positive electrode collector on a coating machine. After drying, rolling, die-cutting and other processes, a positive electrode sheet that meets the requirements is obtained.

[0069] Preparation of electrolyte: Lithium hexafluorophosphate (LiPF6) is dissolved in a mixed solvent consisting of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) (the mass ratio of the three is 1:2:1) to obtain an electrolyte with a concentration of 1 mol / L.

[0070] Preparation of diaphragm: PE porous polymer film is used as the diaphragm substrate; Preparation of the battery: The positive electrode sheet, the separator and the negative electrode sheet are stacked in order, so that the separator is in the middle of the positive and negative electrodes to play a role of isolation, and then wound from the starting end to the end to form a winding core; the winding core is 80mm long, 30mm wide and 8.3mm thick; 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 at the periphery of the starting end of the negative electrode sheet.

[0071] The wound winding 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, formation and other processes, a battery is obtained.

[0072] Example 2-13 Examples 2-13 are used to illustrate the winding core and battery disclosed in the present invention, and include most of the operation steps in Example 1, except that: The parameters of the winding core and the negative electrode sheet shown in Table 1 were used.

[0073] Comparative Examples 1-7 Comparative Examples 1-7 are used to illustrate the winding core and battery disclosed in the present invention, and include most of the operation steps in Example 1, except that: The parameters of the winding core and the negative electrode sheet shown in Table 1 were used.

[0074] Performance Testing The following performance tests were performed on the batteries prepared in the above Examples 1 to 13 and Comparative Examples 1 to 7: 1. Battery life test: Normal temperature cycle test: The battery is placed at 25°C, and the charge and discharge cycle is performed using a 1.2C current 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 by the following formula: Capacity retention rate (%) = Q1 / Q × 100; The test results are shown in Table 2.

[0075] Table 2 Battery electrochemical performance

[0076] 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 ≤2.2, the single surface area of ​​the negative electrode sheet is not prone to folding during winding. 2 When the core is wound, the single surface area of ​​the negative electrode sheet is prone to folding when the core is wound. 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 relatively large, and the corresponding winding needle width is relatively 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. When the winding needle is subsequently 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 the winding is completed, which may 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.

[0077] 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 function of preventing the single-surface 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-surface 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 zone will be difficult to control during winding, which can easily cause the tension in the inner arc zone 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 becomes larger, which is not conducive to the improvement of the energy density of the product.

[0078] 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 um, which has the effect of taking into account both the product energy density 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 value range of less than 3 um, which is not discussed here; when the thickness h2 of the negative electrode current collector ranges from more than 9 um, it will lead to a loss of product energy density.

[0079] By comparing Example 3 with Examples 12-13 and Comparative Examples 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 / cm 3 ~2.0g / cm 3 , which has the function 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 in product energy density. The smaller the compaction density, the worse the electronic contact between 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-surface area is prone to accumulate large stress during the rolling process, and the single-surface area is also prone to folding due to the release of winding tension during unwinding in the winding process, especially when using copper foil with weaker mechanical strength when pursuing high energy density.

[0080] 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 protection scope of the present invention.

Claims

1. A winding core, characterized in that: It comprises 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 then wound along the direction from the starting end to the ending end to form the 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-faced foil area and a double-faced 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 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; Among them, a=W / h1 / 18; b=1.2*W / L; c=5 / h2; d=x / 1.73; 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 um; x is the compaction density of the negative electrode active material layer, in g / cm 3 .

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, characterized in that: The value range of a is 0.2~0.

8.

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

0.

5. The winding core according to claim 4, characterized in that: The value range of b is 0.3~1.

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 um.

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 um.

8. 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 1.0 g / cm 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 is in the range of 1.4 g / cm 3 ~1.9g / cm 3 .

10. The winding core according to any one of claims 1 to 9, characterized in that: The winding core is a square winding core, and the winding core includes a straight area located in the middle and arc areas located 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 comprises a battery housing and a winding core as claimed in any one of claims 1 to 10, wherein the winding core is arranged in the housing.

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