Electrode sheets, winding cores and batteries

Abstract

The present invention provides an electrode sheet, a winding core, and a battery. The electrode sheet is applied to the winding core and includes: a current collector, the current collector including a first side surface and a second side surface disposed opposite each other; a protective coating layer including a conductive powder, a conductive agent, and an adhesive, the protective coating layer including a target side surface, the target side surface disposed away from the current collector; an active material coating layer including an active material; when the first side surface is not coated with the protective coating layer, and the second side surface is coated with the protective coating layer, the active material coating layer is coated on the target side surface and the second side surface; when both the first side surface and the second side surface are coated with the protective coating layer, the active material coating layer is coated on the target side surface; a whitening coating layer is coated on the target side surface, and the whitening coating layer is provided on the area not coated with the active material coating layer, and the grayscale value difference A between the whitening coating layer and the winding core's finishing adhesive layer is 40 to 80. The present invention solves the problems of difficult identification of finishing adhesive layer in lithium-ion batteries and easy air expansion at high temperatures.

Description

Technical Field

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

[0002] Lithium-ion batteries are widely used in various electronic devices due to their advantages such as high platform voltage, high energy density, no memory effect, and long life. In the event of a puncture in a lithium-ion battery, the positive electrode, negative electrode, and separator are partially broken.

[0003] If a lithium-ion battery is punctured and the active material coating on the positive electrode sheet falls off, the aluminum foil will be directly exposed and come into contact with the negative electrode sheet, increasing the risk of thermal runaway of the lithium-ion battery. Therefore, the safety of lithium-ion batteries in the existing technology is relatively low in the event of mechanical damage such as puncture. Summary of the Invention

[0004] The present invention provides an electrode sheet, a winding core and a battery, so as to solve the problems of difficulty in identifying the finishing glue in lithium-ion batteries and easy inflation of lithium-ion batteries at high temperatures.

[0005] In a first aspect, the present invention provides an electrode sheet applied to a winding core, comprising:

[0006] a current collector, the current collector comprising a first side surface and a second side surface disposed opposite to each other;

[0007] a protective coating, the protective coating including a target side, the target side being disposed away from the current collector;

[0008] an active material coating, the active material coating comprising an active material;

[0009] wherein, in a case where the first side is not coated with the protective coating and the second side is coated with the protective coating, the active material coating is coated on the target side and the second side;

[0010] In the case where both the first side and the second side are coated with the protective coating, the active material coating is coated on the target side;

[0011] A whitening coating is applied on the target side, and the area not coated with the active material coating is provided with the whitening coating, and the difference A between the grayscale value of the whitening coating and the finishing glue of the core is 40 to 80.

[0012] In one example, the difference B between the grayscale values ​​of the protective coating and the finishing adhesive of the core is 10 to 30, then A>B;

[0013] And / or, the target side is provided with a first region and a second region, the second region is provided close to an end of the current collector, the active material coating is coated on the first region, and the whitening coating is coated on the second region.

[0014] In one example, the length of the second region ranges from 50 mm to 200 mm, and the length direction of the second region is parallel to the length direction of the current collector.

[0015] In one example, the whitening coating has a thickness of 2 μm to 20 μm, preferably 5 μm to 10 μm.

[0016] In one embodiment, A is 50 to 80;

[0017] and / or, B is 10 to 20;

[0018] And / or, AB is 30 to 70.

[0019] In one example, on the same target side, the coating area of ​​the whitening coating is smaller than the coating area of ​​the active material coating;

[0020] And / or, the sum of the coating area of ​​the whitening coating and the coating area of ​​the active material coating is not less than the area of ​​the target side of the protective coating.

[0021] In a second aspect, the present invention further provides a winding core comprising the electrode sheet as described in the first aspect.

[0022] In one example, in the electrode sheet, the second regions of the protective coating on both sides are coated with a whitening coating.

[0023] In one example, in the electrode sheet, a second region of the protective coating on one side is coated with a whitening coating, and the whitening coating is located in the second region away from the center of the winding core.

[0024] In a third aspect, the present invention further provides a battery comprising the winding core as described in the second aspect.

[0025] In the present invention, the electrode sheet is applied to the core, comprising: a current collector, a protective coating and an active material coating, the current collector comprising a first side surface and a second side surface disposed opposite to each other; the protective coating is coated on the first side surface and / or the second side surface. By providing the protective coating, an extra layer of protection is provided for the current collector, reducing the risk of current collector exposure, reducing the possibility of contact with the negative electrode active layer, and improving the safety of the battery. At the same time, by providing the whitening coating, the difference A in the grayscale value between the whitening coating and the end glue of the core is limited to 40 to 80, thereby increasing the grayscale value of the whitening coating and the end glue of the core. When the end glue is positioned using a CCD device, the whitening coating and the end glue can be distinguished more clearly and conveniently, thereby increasing recognition and improving the accuracy and convenience of positioning the end glue. In addition, the whitening coating is coated on the target side, and the area not coated with the active material coating is provided with the whitening coating to avoid contact between the protective coating and the electrolyte, thereby reducing the side reaction between the protective coating and the electrolyte, improving high-temperature aeration, and reducing the expansion rate of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] 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 describing 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 paying any creative labor.

[0027] Figure 1 This is one of the cross-sectional schematic diagrams of the electrode sheet provided by an embodiment of the present invention;

[0028] Figure 2 This is a second cross-sectional schematic diagram of an electrode sheet provided by an embodiment of the present invention;

[0029] Figure 3 This is the third cross-sectional schematic diagram of the electrode sheet provided by an embodiment of the present invention;

[0030] Figure 4 This is the fourth cross-sectional schematic diagram of the electrode sheet provided by an embodiment of the present invention;

[0031] Figure 5 This is the fifth cross-sectional schematic diagram of the electrode sheet provided by the embodiment of the present invention;

[0032] Figure 6 This is the sixth cross-sectional schematic diagram of the electrode sheet provided by the embodiment of the present invention;

[0033] Figure 7 This is one of the structural schematic diagrams of the winding core provided by an embodiment of the present invention;

[0034] Figure 8 This is the second structural schematic diagram of the winding core provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0035] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0036] Unless otherwise defined, the technical or scientific terms used in the present invention should have the ordinary meaning understood by people with ordinary skills in the field to which the present invention belongs. The words "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship also changes accordingly. In this article, unless otherwise specified, the data range includes the endpoints.

[0037] like Figures 1-6 As shown, the present invention provides an electrode sheet applied to a winding core, comprising:

[0038] A current collector 10, wherein the current collector 10 includes a first side surface and a second side surface disposed opposite to each other;

[0039] a protective coating 20 , the protective coating including a target side surface, the target side surface being disposed away from the current collector 10 ;

[0040] an active material coating 30 , wherein the active material coating 30 includes an active material;

[0041] Wherein, in the case where the first side is not coated with the protective coating 20 and the second side is coated with the protective coating 20, the active material coating 30 is coated on the target side and the second side;

[0042] In the case where both the first side and the second side are coated with the protective coating 20, the active material coating 30 is coated on the target side;

[0043] A whitening coating 40 is applied to the target side, and the area not coated with the active material coating is provided with the whitening coating, and the difference A between the grayscale value of the whitening coating (40) and the end glue of the winding core is 40 to 80 (for example, 40, 45, 50, 55, 60, 65, 70, 75, 80).

[0044] The grayscale value can be obtained through a CCD visual detection system.

[0045] In one embodiment, A is 50 to 80.

[0046] See Figure 1 In one embodiment, the protective coating 20 is coated on the first and second sides of the current collector 10, and the active material coating 30 is coated on the target side (the side of the protective coating 20 facing away from the current collector 10). Specifically, the active material coating 30 is coated on the target side of the protective coating 20 on both sides.

[0047] See Figure 2 In another case, the protective coating 20 is only coated on the first side of the current collector 10 , and the active material coating 30 is coated on the target side of the protective coating 20 and the second side of the current collector 10 .

[0048] It should be noted that the first side and the second side are only used to distinguish the two opposite sides of the current collector 10. The situation where the protective coating 20 is only coated on the second side of the current collector 10 can be referred to the situation where the protective coating 20 is only coated on the first side of the current collector 10. In order to avoid repetition, they will not be elaborated here.

[0049] It should be understood that the specific structure of the current collector 10 is not limited herein. For example, in one embodiment, the current collector 10 is aluminum foil.

[0050] It should be understood that the active material included in the active material coating 30 is not limited herein. In a specific implementation, the active material coating 30 can be made of active materials commonly used in related technologies. For example, in one embodiment, the active material coating 30 includes lithium cobalt oxide, acetylene black, and polyvinylidene fluoride.

[0051] The protective coating 20 comprises a conductive powder, a conductive agent, and an adhesive. The specific ratios of the conductive powder, conductive agent, and adhesive are not limited herein. The inclusion of the conductive powder and conductive agent in the protective coating provides excellent electrical conductivity, thereby enhancing the electrical performance of the electrode sheet. Furthermore, the inclusion of the adhesive in the protective coating improves the adhesion between the protective coating and the current collector, reducing the likelihood of the protective coating detaching from mechanical abuse.

[0052] It should be understood that the specific structure of the conductive powder is not limited here, and the conductive powder can be understood as a powder with conductivity. In this embodiment, the protective coating 20 uses conductive powder as the main material, which can make the protective coating 20 have better conductivity and thus make the lithium-ion battery have better electrical performance.

[0053] Optionally, in one embodiment, the conductive powder includes inorganic particles and a conductive coating layer, and the conductive coating layer wraps the inorganic particles.

[0054] In one embodiment, the conductive powder can be understood as a composite conductive material with inorganic particles as a core and a conductive coating layer as a shell.

[0055] Optionally, in one embodiment, the conductive coating layer is a metal oxide, or a metal oxide doped with an impurity element. The metal oxide can be any metal oxide, and the impurity element doped in the metal oxide can also be any element. For example, in one embodiment, the conductive coating layer is tin oxide (SnO2) doped with antimony (Sb), or antimony doped tin oxide (ATO). In another embodiment, the conductive coating layer is SnO2 doped with fluorine (F), or TCO conductive glass (FTO). The conductive coating layer is indium oxide (In2O3) doped with tin (Sn), or indium tin oxide (ITO).

[0056] Alternatively, in one embodiment, the inorganic particles included in the conductive powder may be any inorganic particles. For example, in one embodiment, the inorganic particles included in the conductive powder include at least one of the following: titanium dioxide, zinc oxide, mica powder, quartz powder, barite, aluminum oxide, boehmite, magnesium oxide, and silicon oxide.

[0057] Optionally, in one embodiment, the Dv50 of the conductive powder is less than 5 μm (e.g., 5 μm, 4.5 μm, 4 μm, 3.5 μm, 3 μm, 2.5 μm, 2 μm, 1.5 μm, 1 μm, 0.5 μm, 0.1 μm). Furthermore, in one embodiment, the Dv50 of the conductive powder is less than 4 μm. Optionally, in another embodiment, the Dv50 of the conductive powder is less than 1 μm.

[0058] It should be understood that Dv50 can be understood as the particle size corresponding to the 50% cumulative volume particle size distribution percentage of a sample. Its physical meaning is that 50% of the particles are larger than this value, and 50% of the particles are smaller than this value. Therefore, Dv50 is also called the median diameter or median particle size.

[0059] It should be noted that the Dv50 of the active material included in the active material coating 30 is typically 15 μm. In one embodiment, the Dv50 of the conductive powder is much smaller than the Dv50 of the active material included in the active material coating 30. Therefore, the D50 of the material included in the protective coating 20 is even smaller. Therefore, if mechanical abuse causes the active material coating 30 to break, the probability of the protective coating 20 breaking is reduced, thereby reducing the probability of the current collector 10 being exposed and improving battery safety.

[0060] In one example, the difference B between the grayscale values ​​of the protective coating 20 and the finishing adhesive of the core is 10 to 30 (eg, 10, 12, 15, 17, 20, 22, 25, 27, 30), and A>B.

[0061] In one embodiment, B is 10 to 20.

[0062] In one example, AB is 30 to 70 (e.g., 30, 35, 40, 45, 50, 55, 60, 65, 70).

[0063] The target side is provided with a first area and a second area, the second area is arranged near the end of the current collector 10, and in the core, the end is the tail of the core away from the center of the core, the active material coating 30 is coated on the first area, and the whitening coating 40 is coated on the second area.

[0064] In this embodiment, the electrode sheet further includes a whitening coating 40. For example, in one embodiment, the whitening coating 40 includes inorganic particles. Furthermore, in another embodiment, the inorganic particles included in the whitening coating 40 include at least one of the following: aluminum oxide, boehmite, magnesium oxide, titanium oxide, zinc oxide, and silicon oxide.

[0065] See Figure 3 In one embodiment, the protective coating 20 is applied to both the first and second sides of the current collector 10, while the whitening coating 40 and the active material coating 30 are applied to the target side. Specifically, the active material coating 30 is applied to the first region of the protective coating 20 on both sides, and the whitening coating 40 is applied to the second region of the protective coating 20 on both sides. In this case, the protective coating is completely covered by the whitening coating and the active material coating, preventing direct contact between the protective coating and the electrolyte. This reduces the problem of gas generation caused by side reactions between the protective coating and the electrolyte, thereby reducing the battery expansion rate.

[0066] Of course, if Figure 4 As shown, in one embodiment, only the second area of ​​the protective coating 20 on one side may be coated with the whitening coating 40 .

[0067] In such Figure 4 In the illustrated embodiment, only the second region of the protective coating 20 on one side is coated with a whitening coating 40, located in the second region away from the center of the winding core. This whitening coating can reduce the risk of short circuits in the event of mechanical damage such as battery puncture, for example, where the positive electrode current collector contacts the negative electrode active material coating, or vice versa, thereby improving battery safety.

[0068] In another embodiment, if Figure 5 As shown, the protective coating 20 not coated with the whitening coating 40 does not completely cover the current collector 10. Figure 7 As shown, when the core is wound, the area of ​​the current collector 10 not covered by the protective coating 20 faces the inside of the core. It is difficult for this area to short-circuit with the nail during puncture, and the positive electrode is in contact with it. The probability of short-circuiting with the negative electrode is also low, and the safety risk is small.

[0069] See Figure 6 In another embodiment, the protective coating 20 is only coated on the first side of the current collector 10, and the active material coating 30 and the whitening coating 40 are coated on the target side. Specifically, the active material coating 30 is coated on the first area of ​​the protective coating 20, and the whitening coating 40 is coated on the second area of ​​the protective coating 20. The whitening coating 40 is located in the second area away from the center of the core.

[0070] It should be noted that Figures 1-6 The electrode sheet schematic diagram shown in the figure is only used to illustrate the relative positions between the current collector 10, the protective coating 20, the active material coating 30 and the whitening coating 40. The width and length of each of the above coatings are only for illustration and do not represent the information or correspondence between the length or width of the current collector 10, the protective coating 20, the active material coating 30 and the whitening coating 40.

[0071] It should be noted that the electrode sheet provided by the present invention is applied to the winding core. The specific process of preparing the winding core based on the electrode sheet can be referred to the description in the related art. In order to avoid repetition, it will not be described here. For the sake of ease of understanding, only the finishing glue is briefly described below.

[0072] When preparing a winding core based on an electrode sheet, the electrode sheet needs to be wound and adhesive tape is applied to the end of the winding core. Therefore, the adhesive tape is located at the end of the winding core and adheres to the outermost surface of the winding core, away from the center of the winding core.

[0073] In one embodiment, the second region is located near the end of the current collector 10, and the whitening coating 40 is applied to the second region. Therefore, it can be understood that the whitening coating 40 is provided on the outermost surface of the core away from the center of the core, and the whitening coating 40 is located at the end of the core. When the end glue is adhered to the end of the core, the end glue 50 will connect with the whitening coating 40 and cover part of the whitening coating 40. See Figure 8 .

[0074] In a specific implementation, the protective coating 20 includes conductive powder, conductive agent and adhesive. The difference in grayscale value between the protective coating 20 and the finishing glue is usually small. Therefore, when using a charge coupled device (CCD) to locate the finishing glue, it is difficult to distinguish between the protective coating 20 and the finishing glue.

[0075] The provision of the whitening coating 40 in the present invention increases the grayscale value of the whitening coating 40 and the end-of-roll adhesive. This allows for a more clear and convenient distinction between the whitening coating 40 and the end-of-roll adhesive when locating the end-of-roll adhesive using a CCD device, thereby improving the accuracy and convenience of end-of-roll adhesive positioning. Furthermore, the whitening coating 40 does not cover the active material coating 30, reducing interference with the active material coating 30 and ensuring that the performance of the electrode sheet (e.g., energy density) is not affected.

[0076] Optionally, in one embodiment, the length of the second region ranges from 50 mm to 200 mm (for example, 50 mm, 70 mm, 100 mm, 120 mm, 150 mm, 170 mm, 200 mm), and the length direction of the second region is parallel to the length direction of the current collector 10 .

[0077] It should be understood that the length direction of the second region is parallel to the length direction of the current collector 10. Figure 1 Taking the rectangular coordinate system shown in as an example, the length direction of the second area is Figure 1 The direction of the x-axis is shown in .

[0078] It should be understood that the length direction of the current collector 10 should be understood as the length direction of the current collector 10 when the electrode sheet is in a flat state before being wound.

[0079] In one embodiment, the length of the second region ranges from 50 mm to 200 mm. Because the length of the second region ranges from 50 mm to 200 mm, the area of ​​the whitening coating 40 is much smaller than the area of ​​the active material coating 30 (i.e., on the same target side, the coating area of ​​the whitening coating is smaller than the coating area of ​​the active material coating). This reduces the impact of the whitening coating 40 on the function of the active material coating 30, ensuring that the performance of the electrode sheet (e.g., the energy density of the battery) is not affected, and the battery has a higher energy density while maintaining its safety performance.

[0080] Optionally, in one embodiment, the sum of the coating area of ​​the whitening coating and the coating area of ​​the active material coating is larger than the area of ​​the target side of the protective coating. This prevents direct contact between the protective coating and the electrolyte, reduces the risk of gassing, and thus reduces the high-temperature expansion rate of the battery.

[0081] Optionally, in one embodiment, the resistivity of the conductive powder ranges from 0.01Ω·m to 10Ω·m (for example, 0.01Ω·m, 0.05Ω·m, 0.1Ω·m, 0.15Ω·m, 0.2Ω·m, 0.25Ω·m, 0.3Ω·m, 0.35Ω·m, 0.4Ω·m, 0.45Ω·m, 0.5Ω·m, 0.55Ω·m, 0.6Ω·m, 0.65Ω·m, 0.7Ω·m, 0.75Ω·m, 0.8Ω·m, 0.85Ω·m, 0.9Ω·m, 0.95Ω·m, 1Ω·m, 2Ω·m, 3Ω·m, 4Ω·m, 5Ω·m, 6Ω·m, 7Ω·m, 8Ω·m, 9Ω·m, 10Ω·m). Optionally, in another embodiment, the resistivity of the conductive powder is in the range of 0.1Ω·cm to 1Ω·m.

[0082] In one embodiment, the resistivity of the conductive powder ranges from 0.01 Ω·m to 10 Ω·m, or preferably, from 0.1 Ω·cm to 1 Ω·m. This configuration allows the protective coating 20 to have good electrical conductivity, thereby enabling the lithium-ion battery to have better electrical performance.

[0083] It should be understood that the specific material of the conductive agent is not limited herein. For example, in one embodiment, the conductive agent includes at least one of the following: conductive carbon black, acetylene black, graphite, graphene, carbon nanotubes, and carbon nanofibers.

[0084] It should be understood that the specific material of the binder is not limited herein. For example, in one embodiment, the binder includes at least one of the following: polyvinylidene difluoride (PVDF), acrylic acid-modified PVDF, polyacrylate polymer, polyimide, styrene-butadiene rubber, and styrene-acrylic rubber.

[0085] Optionally, in one embodiment, the proportion of the binder in the protective coating 20 is greater than the proportion of the adhesive included in the active material coating 30, thereby further improving the bonding force between the protective coating 20 and the current collector 10 and reducing the risk of the protective coating 20 falling off when subjected to external force.

[0086] In one embodiment, an electrode sheet, applied to a winding core, includes: a current collector 10, a protective coating 20 and an active material coating 30, the current collector 10 includes a first side surface and a second side surface disposed opposite to each other; the protective coating 20 is coated on the first side surface and / or the second side surface, and the protective coating 20 includes a conductive powder, a conductive agent and an adhesive. By providing the protective coating 20, an extra layer of protection is provided for the current collector 10, reducing the risk of exposure of the current collector 10. Since the protective coating 20 includes a conductive powder and a conductive agent, the protective coating 20 has better conductive properties, thereby enabling the electrode sheet to have better electrical properties. At the same time, since the protective coating 20 includes an adhesive, the bonding performance between the protective coating 20 and the current collector 10 is improved, reducing the probability of the protective coating 20 falling off during mechanical abuse.

[0087] The present invention also provides a winding core comprising the aforementioned electrode sheet. In one embodiment, the electrode sheet is the electrode sheet described in the aforementioned embodiment. The specific structure can be referred to in the description of the aforementioned embodiment and will not be further described here. Because the present invention utilizes the electrode sheet described in the aforementioned embodiment, the winding core provided by the present invention has all the beneficial effects of the electrode sheet described in the aforementioned embodiment.

[0088] It should be noted that, during mechanical abuse, the risk of thermal runaway caused by the contact between the current collector 10 of the positive electrode sheet and the negative electrode sheet is relatively high. Therefore, in one embodiment, the above-mentioned electrode sheet is used as the positive electrode sheet. Specifically, in one embodiment, the winding core includes the electrode sheet, separator and negative electrode sheet in the above-mentioned embodiment. The electrode sheet, separator and negative electrode sheet in the above-mentioned embodiment are stacked in sequence and wound to form a winding core. In this embodiment, a protective coating 20 is provided on the current collector 10 of the positive electrode sheet to avoid short circuit between the current collector 10 of the positive electrode sheet and the negative electrode sheet during mechanical abuse, thereby improving the safety of the battery.

[0089] In one example, in the electrode sheet, the second regions of the protective coating 20 on both sides are coated with the whitening coating 40 .

[0090] In one example, in the electrode sheet, the second region of the protective coating 20 on one side is coated with the whitening coating 40 , and the whitening coating 40 is located in the second region away from the center of the winding core.

[0091] The present invention further provides a battery comprising the aforementioned winding core. It should be noted that the battery provided by the present invention includes all the technical features of the aforementioned winding core embodiment and can achieve the same technical effects. To avoid repetition, they will not be described here.

[0092] It should be noted that the battery provided by the present invention can be applied to electronic devices, or used as a power battery to provide power for electric vehicles, electric trains, electric bicycles, golf carts and other power vehicles.

[0093] Among them, the electronic device can be a terminal-side device such as a mobile phone, a tablet personal computer, a laptop computer or a notebook computer, a personal digital assistant (PDA), a handheld computer, a netbook, an ultra-mobile personal computer (UMPC), a mobile Internet device (MID), a wearable device (Wearable Device) or a vehicle user equipment (VUE), a pedestrian user equipment (PUE), etc. Wearable devices include: smart watches, bracelets, headphones, glasses, etc. It should be noted that the specific types of the above-mentioned electronic devices are not limited in the embodiments of the present application.

[0094] For ease of understanding, the following uses specific embodiments as examples to illustrate the structure, preparation process, and effects of the electrode sheet, winding core, and battery provided by the present invention. First, the preparation process of the electrode sheet, winding core, and battery is introduced.

[0095] Example 1

[0096] A protective coating 20 slurry was prepared. Specifically, 90% by weight of conductive titanium dioxide (ATO-coated TiO2), 2% by weight of carbon black, 1% by weight of carbon nanoparticles, and 7% by weight of PVDF were mixed, and a certain amount of N-methylpyrrolidone (NMP) was added. The solid content of the slurry was adjusted to 40%, and the mixture was stirred to prepare the protective coating 20 slurry.

[0097] The whitening coating 40 slurry was prepared by mixing 90% by mass of boehmite and 10% by mass of PVDF, adding a certain amount of NMP, adjusting the solid content of the slurry to 40%, and stirring to prepare the whitening coating 40 slurry.

[0098] Prepare the active material coating 30 slurry for the positive electrode sheet. The active material coating 30 for the positive electrode sheet can be prepared using a formulation known in the related art. Specifically, in this embodiment, 96% by weight of lithium cobalt oxide, 1% by weight of carbon black, 1% by weight of carbon nanotubes, and 2% by weight of PVDF are mixed. A certain amount of NMP is added to adjust the solids content of the slurry to 70%. The mixture is stirred to prepare the active material coating 30 slurry for the positive electrode sheet.

[0099] Prepare the slurry for the active material coating 30 of the negative electrode sheet. The active material coating 30 of the negative electrode sheet can be prepared using a formulation known in the related art. Specifically, in this embodiment, 96% by weight of artificial graphite, 1% by weight of carbon black, 1.5% by weight of styrene-butadiene rubber, and 1.5% by weight of sodium carboxymethyl cellulose are mixed, deionized water is added, and the solids content of the slurry is adjusted to 40%. The mixture is stirred to prepare the slurry for the active material coating 30 of the negative electrode sheet.

[0100] Positive electrode sheet preparation. Specifically, the prepared protective coating 20 slurry is applied to opposite sides of the positive electrode current collector 10. The prepared whitening coating 40 slurry is then applied to the second region of the protective coating 20. The active material coating 30 slurry for the positive electrode sheet is then applied to the second region of the protective coating 20. After drying, the positive electrode sheet is obtained. See Table 1 for details.

[0101] Preparation of negative electrode sheet: Specifically, the prepared active material coating 30 slurry of the negative electrode sheet is coated on the negative electrode current collector 10 by an extrusion coating process to obtain the negative electrode sheet.

[0102] Use a roller press to roll the positive and negative electrode sheets to the designed thickness respectively, and use a slitting machine to cut the positive and negative electrode sheets to the designed width, then weld the tabs on the electrode sheets and apply protective tape.

[0103] Place the diaphragm between the positive and negative electrodes and wind or stack them to obtain a core or stack, which is then fixed with adhesive tape.

[0104] Use a punching mold to punch out the aluminum-plastic film, then use the punched aluminum-plastic film to encapsulate the roll core or stacked core to obtain the battery cell, bake it until the moisture content is qualified, and inject the electrolyte.

[0105] Use lithium-ion battery formation equipment to charge and discharge the battery cells, harden the battery cells, and sort out the battery cell capacity.

[0106] The battery cell is sealed for the second time and folded to form the basic shape of the battery cell.

[0107] Example 2 group

[0108] Example 2a

[0109] The same procedure is carried out as in Example 1, except that a whitening coating is applied to the second area of ​​the protective coating on one side and the whitening coating is located in the second area away from the center of the winding core. See Table 1 for details.

[0110] Example 2b

[0111] The same procedure is carried out as in Example 1, except that a whitening coating is applied to the second area of ​​the protective coating on one side, and the whitening coating is located in the second area close to the center of the winding core. For details, see Table 1.

[0112] Example 3 group

[0113] This set of examples is used to illustrate the impact when AB changes.

[0114] This embodiment group was carried out with reference to the embodiment 1, except that AB was changed by adjusting A and / or B, as shown in Table 1 for details.

[0115] Example 4 Group

[0116] This set of examples is used to illustrate the effects produced when the thickness of the whitening coating is changed.

[0117] This example group was carried out with reference to Example 1, except that the thickness of the whitening coating was changed. See Table 1 for details.

[0118] Example 5

[0119] This example is carried out with reference to Example 1, except that the sum of the coating area of ​​the whitening coating and the coating area of ​​the active material coating is smaller than the area of ​​the target side of the protective coating, see Table 1 for details.

[0120] Example 6

[0121] This embodiment is carried out with reference to embodiment 1, except that the coating area of ​​the whitening coating and the coating area of ​​the active material coating are changed, wherein the sum of the coating area of ​​the whitening coating and the coating area of ​​the active material coating is equal to the area of ​​the target side of the protective coating, see Table 1 for details.

[0122] Comparative Example 1

[0123] The same procedure was followed as in Example 1, except that the two back sides of the current collector 10 of the positive electrode sheet were not coated with the protective coating 20 , that is, the battery in Comparative Example 1 did not include the protective coating 20 .

[0124] Comparative Example 2

[0125] The same process is carried out as in Example 1, except that the positive electrode sheet is not protected by the whitening coating.

[0126] Comparative Example 3

[0127] The same procedure is carried out as in Example 1, except that A is 20 and B is 20, i.e., A=B.

[0128] Table 1

[0129]

[0130]

[0131] * indicates the same as Example 1;

[0132] - means it does not exist.

[0133] Test Case

[0134] In order to test the performance of the battery prepared in the embodiment and the performance of the battery prepared in the comparative example, the open circuit voltage (OCV) test was performed on the battery prepared in the embodiment and the battery prepared in the comparative example, and the K value of the battery was tested, and the products with qualified K value were selected.

[0135] (1) Acupuncture test

[0136] The batteries prepared in the examples and the comparative examples were subjected to a needle penetration test. Specifically, the lithium-ion batteries were fully charged (100% SOC) and then placed on the test bench of the needle penetration test equipment. A tungsten steel needle with a diameter of 3 mm and a tip length of 3.62 mm was inserted through the center of the battery at a speed of 100 mm / s. The battery passed the test if it did not catch fire or explode. The needle penetration pass rate a / b was used to indicate that in any b needle penetration tests, the number of test results was a.

[0137] (2) Recognition rate test

[0138] A certain number of batteries are manufactured in batches, such as M. The CCD visual inspection system and manual full inspection are used to inspect M batteries to determine whether the adhesive position of the finishing tape is qualified. Among the qualified products determined by the CCD visual inspection system, the number of unqualified products determined by the manual full inspection is A, and among the unqualified products determined by the CCD visual inspection system, the number of qualified products determined by the manual full inspection is B. The recognition rate is [1-(A+B) / M]*100%.

[0139] (3) Energy density test

[0140] After the battery is fully charged, it is discharged to the lowest voltage (usually 3.0V). The discharge energy is recorded as E, and the energy density is E / (L*W*H), where L is the length of the battery, W is the width of the battery, and H is the height of the battery.

[0141] (4) Expansion rate test

[0142] The battery is stored at a high temperature of 60°C for 30 days. The initial thickness is recorded as D1, the thickness after storage is recorded as D2, and the expansion rate is [(D2-D1) / D1]*100%.

[0143] The performance test results of the batteries prepared in the examples and the batteries prepared in the comparative examples are shown in Table 2.

[0144] Table 2

[0145]

[0146]

[0147] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. An electrode sheet, applied to a winding core, characterized in that: include: A current collector (10), the current collector (10) comprising a first side surface and a second side surface disposed opposite to each other; a protective coating (20), the protective coating comprising a target side, the target side being disposed away from the current collector (10); an active material coating (30), wherein the active material coating (30) comprises an active material; wherein, in a case where the first side is not coated with the protective coating (20) and the second side is coated with the protective coating (20), the active material coating (30) is coated on the target side and the second side; In the case where both the first side and the second side are coated with the protective coating (20), the active material coating (30) is coated on the target side; A whitening coating (40) is applied to the target side, and the whitening coating is provided on the area not coated with the active material coating, and the grayscale value difference A between the whitening coating (40) and the end glue of the winding core is 40 to 80; the target side is provided with a first area and a second area, the second area is provided near the end of the current collector (10), the active material coating (30) is applied to the first area, and the whitening coating (40) is applied to the second area; the length of the second area ranges from 50 mm to 200 mm, and the length direction of the second area is parallel to the length direction of the current collector (10), the protective coating (20) includes a conductive powder, a conductive agent and an adhesive, the conductive powder includes inorganic particles and a conductive coating layer, the conductive coating layer wraps the inorganic particles, the whitening coating (40) includes inorganic particles, and the inorganic particles included in the whitening coating (40) include at least one of the following: aluminum oxide, boehmite, magnesium oxide, titanium oxide, zinc oxide and silicon oxide.

2. The electrode sheet according to claim 1, characterized in that The difference B between the grayscale values ​​of the protective coating (20) and the finishing adhesive of the core is 10 to 30, then A>B.

3. The electrode sheet according to claim 1, characterized in that The thickness of the whitening coating is 2 μm to 20 μm.

4. The electrode sheet according to claim 3, characterized in that The thickness of the whitening coating is 5 μm to 10 μm.

5. The electrode sheet according to claim 1, characterized in that A is 50 to 80; and / or, B is 10 to 20; And / or, AB is 30 to 70.

6. The electrode sheet according to any one of claims 1 to 5, characterized in that: On the same target side, the coating area of ​​the whitening coating is smaller than the coating area of ​​the active material coating; And / or, the sum of the coating area of ​​the whitening coating and the coating area of ​​the active material coating is greater than or equal to the area of ​​the target side of the protective coating.

7. A winding core, characterized in that: The invention comprises the electrode sheet according to any one of claims 1 to 6.

8. The winding core according to claim 7, characterized in that In the electrode sheet, the second regions of the protective coating (20) on both sides are coated with a whitening coating (40).

9. The winding core according to claim 7, characterized in that In the electrode sheet, a second region of the protective coating (20) on one side is coated with a whitening coating (40), and the whitening coating (40) is located in the second region away from the center of the winding core.

10. A battery, characterized in that: Comprising the winding core according to any one of claims 7 to 9.

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