A wound battery cell and an electrochemical device comprising the wound battery cell

Abstract

The present application relates to the field of battery materials, and specifically to a wound battery cell and an electrochemical device including the wound battery cell, comprising a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator located between the positive electrode sheet and the negative electrode sheet, wherein the separator comprises a base film and a composite layer located on one side of the base film, the ratio of the mass content of the first element of the composite layer on the surface of the arc area to the mass content of the first element of the composite layer on the surface of the plane area is a, the thickness difference between the aqueous polymer coating in the arc area and the aqueous polymer coating in the plane area is H μm, the thickness of the oily coating is T μm, and the relationship between H, a and T satisfies: 0.5≤T×(H / a)≤4. The wound battery cell provided by the present application can not only effectively reduce the K value but also improve the high-temperature cycle performance of the battery by controlling the relationship between H, a and T T×(H / a) within the above range.

Description

Technical Field

[0001] The present application relates to the field of battery materials, and in particular to a wound battery cell and an electrochemical device comprising the wound battery cell. Background Art

[0002] In the consumer 3C field, lithium-ion batteries have been widely used in mobile phones, laptops, drones, smart wearables and other products due to their advantages such as high voltage stability, high energy density and long cycle life.

[0003] As an important component of lithium-ion batteries, the diaphragm is placed between the positive and negative electrodes and plays a key role in isolating electrons and conducting ions. At present, the market mainly adopts the form of winding packaging, which has efficient process and relatively low cost. However, wound lithium batteries have flat areas and arc areas. With the increase in high energy density, the arc area is prone to electrolyte deficiency and lithium deposition in thick electrode systems. The existing technology mainly improves the electrolyte wettability of the arc area by creating a gap height in the arc area through the use of diaphragm coating, thereby improving cyclic lithium deposition. However, the difference between the flat area and the arc area of ​​the diaphragm is prone to cause uneven stress, resulting in an increased risk of local micro-short circuits, which increases the K value of the battery process. Summary of the Invention

[0004] The present application provides a wound battery cell and an electrochemical device comprising the wound battery cell, aiming to improve the problem of increased K value in the battery process by winding the battery cell while taking into account the long cycle performance requirements.

[0005] In a first aspect, the present application provides a wound battery cell, comprising a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator located between the positive electrode sheet and the negative electrode sheet, wherein the separator comprises a base film and a composite layer located on one side of the base film, the composite layer comprising a heat-resistant layer and a water-based polymer coating located on a side of the heat-resistant layer facing away from the base film, and an oily coating is provided on a side of the base film facing away from the composite layer; the oily coating is in contact with the negative electrode sheet, and the water-based polymer coating is in contact with the positive electrode sheet;

[0006] The composite layer contains a first element, which is one or more of Al, Ba, Mg, Si, Sn, Ti, and N. The ratio of the mass content of the first element on the surface of the composite layer in the arc area to the mass content of the first element on the surface of the composite layer in the plane area is a. The thickness difference between the water-based polymer coating in the arc area and the water-based polymer coating in the plane area is H μm, the thickness of the oily coating is T μm, and the relationship between H, a, and T satisfies: 0.5≤T×(H / a)≤4.

[0007] In an optional embodiment, the positive electrode plate includes a positive electrode current collector and a positive electrode active material layer arranged on at least one side surface of the current collector, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes a lithium nickel cobalt manganese oxide material.

[0008] In an optional embodiment, based on the total mass of the positive electrode active material layer, the mass content of the lithium nickel cobalt manganese oxide material is 40%-100%.

[0009] In an optional embodiment, the positive electrode active material further includes one or more of lithium manganese oxide, lithium cobalt oxide, lithium iron phosphate, and lithium nickel cobalt aluminum oxide.

[0010] In an optional embodiment, based on the mass of the positive electrode active material layer, the mass content of the Mn element is b%, 5≤b≤30; and a and b satisfy the following relationship: 7≤b / a≤30.

[0011] In an optional embodiment, the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes a silicon-carbon composite material.

[0012] In an optional embodiment, based on the total mass of the negative electrode active material, the mass content of the silicon-carbon composite material is W%, the mass content of the first element on the surface of the oily coating is P%, and P and W satisfy the following relationship: 0.5≤W / P≤15.

[0013] In an optional embodiment, the mass content of the silicon-carbon composite material is 3%-50% based on the total mass of the negative electrode active material.

[0014] In an optional embodiment, the mass content of the first element on the surface of the oily coating is 3%-10%.

[0015] In an optional embodiment, the electrolyte comprises LiPF6 and an unsaturated nitrile additive, and the mass content of the LiPF6 is c based on the total mass of the electrolyte;

[0016] Based on the total mass of the electrolyte, the mass content of the unsaturated nitrile additive is e;

[0017] The heat-resistant layer includes heat-resistant particles, and the Dv10 of the heat-resistant particles is d;

[0018] c, e, and d satisfy 0.5c≤d≤10e.

[0019] In an optional embodiment, the electrolyte includes LiPF6, and the mass content of LiPF6 is 10%-20% based on the total mass of the electrolyte.

[0020] In an optional embodiment, the electrolyte includes an unsaturated nitrile additive, and the mass content of the unsaturated nitrile additive is 0.1%-5% based on the total mass of the electrolyte.

[0021] In an optional embodiment, the heat-resistant layer includes heat-resistant particles, and the Dv10 of the heat-resistant particles is 0.05 μm-0.3 μm.

[0022] In an optional embodiment, the unsaturated nitrile additive includes one or more of acrylonitrile, methacrylonitrile, ethacrylonitrile, chloroacrylonitrile, fluoroacrylonitrile, and phenylacrylonitrile.

[0023] In an optional embodiment, the Dv10 of the heat-resistant particles is 0.1 μm-0.15 μm.

[0024] In an optional embodiment, the Dv90 of the heat-resistant particles is 1.8 μm-5 μm.

[0025] In an optional embodiment, the components of the heat-resistant particles are selected from one or more of boehmite, aluminum oxide, barium sulfate, magnesium oxide, magnesium hydroxide, silicon dioxide, tin dioxide, titanium oxide, barium titanate, melamine cyanurate, 1,3,5-triazine-2,4,6-triamine, and melamine thiocyanate.

[0026] In an optional embodiment, 1 <a≤1.5。

[0027] In an optional embodiment, 0.8≤H≤4.

[0028] In an optional embodiment, 0.5≤T≤2.

[0029] In an optional embodiment, the base film has a thickness of 3 μm-12 μm.

[0030] In an optional embodiment, the porosity of the base film is 25%-55%.

[0031] In an optional embodiment, the aqueous polymer coating includes a blank portion and a coating portion, and the coating portion includes polymer particles A.

[0032] In an optional embodiment, the oily coating comprises filler particles and polymer B, and the polymer B is non-granular.

[0033] In an optional embodiment, 1.1≤a≤1.5.

[0034] In an optional embodiment, based on the total area of ​​the surface of one side of the heat-resistant layer, the projected area of ​​the coating portion on the heat-resistant layer accounts for 15%-60%.

[0035] In an optional embodiment, the coating portion has a thickness of 0.5 μm-5 μm.

[0036] In an optional embodiment, the mass content of polymer B in the oily coating is 20%-70%.

[0037] In an optional embodiment, the polymer particles A include primary particles, and the average particle size of the primary particles is 150 nm to 500 nm.

[0038] In an optional embodiment, the polymer particles A include secondary particles, and the average particle size of the secondary particles is 3 μm-12 μm.

[0039] In an optional embodiment, the filler particles have a Dv90 of 1.8 μm to 5 μm.

[0040] In an optional embodiment, the filler particles are composed of one or more selected from boehmite, aluminum oxide, barium sulfate, magnesium oxide, magnesium hydroxide, silicon dioxide, tin dioxide, titanium oxide, barium titanate, melamine cyanurate, 1,3,5-triazine-2,4,6-triamine, and melamine thiocyanate.

[0041] In an optional embodiment, the polymer particles A include a first polymer, which includes a polymer copolymerized with one or more monomers selected from the group consisting of methyl methacrylate, acrylonitrile, butyl acrylate, isooctyl acrylate, octadecyl acrylate, ethyl acrylate, styrene, ethylene, and butadiene.

[0042] In an optional embodiment, the polymer B includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl fluoride, vinyl fluoride-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, and tetrafluoroethylene-hexafluoropropylene copolymer.

[0043] In a second aspect, the present application provides an electrochemical device comprising the wound battery cell as described in any one of the first aspects of the present application.

[0044] The technical solution of this application has the following advantages:

[0045] The wound battery cell provided in the present application includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator located between the positive electrode sheet and the negative electrode sheet, the separator includes a base film and a composite layer located on one side of the base film, the composite layer includes a heat-resistant layer and a water-based polymer coating located on the side of the heat-resistant layer away from the base film, and the base film is provided with an oily coating on the side away from the composite layer; the oily coating is in contact with the negative electrode sheet, and the water-based polymer coating is in contact with the positive electrode sheet; the composite layer contains a first element, the first element is one or more of Al, Ba, Mg, Si, Sn, Ti, and N, the ratio of the mass content of the first element of the composite layer on the surface of the arc area to the mass content of the first element of the composite layer on the surface of the plane area is a, the thickness difference between the water-based polymer coating in the arc area and the water-based polymer coating in the plane area is H μm, the thickness of the oily coating is T μm, and the relationship between H, a and T satisfies: 0.5≤T×(H / a)≤4. When the above relationship is met, on the one hand, the difference in stress intensity between the arc area and the plane area separator can be improved, the uniformity of stress distribution can be improved, the proportion of micro-short circuits caused by local lithium dendrites piercing the separator can be reduced, and the problem of increased K value can be effectively reduced; on the other hand, the substance containing the first element (such as Al element) on the surface of the arc area separator in contact with the electrode can absorb HF generated by the electrolyte to a certain extent at high temperature, and the first element (such as Al element) in the product after reaction with HF can stabilize the structure of the positive electrode active particles, reduce the dissolution of transition metal ions at the positive end, improve the stability of the CEI film, reduce the difference in interface impedance between the plane area and the arc area, and improve the high-temperature cycle performance of the battery.

[0046] Additional aspects and advantages of the embodiments of the present application will be described and shown in part in the subsequent description, or explained through the implementation of the embodiments of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the specific implementation methods or the description of the prior art. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0048] Figure 1 This is a schematic diagram of the structure of a battery cell in this application.

[0049] Figure 2 It is a structural diagram of another battery cell of the present application;

[0050] Among them, the figure numbers are explained as follows: 110, base film, 120, water-based polymer coating, 130, oily coating, 140, positive electrode plate, 150, negative electrode plate, 160, heat-resistant layer, 121, blank part, 122, coating part, 1, arc area, 2, plane area. DETAILED DESCRIPTION

[0051] The following examples are provided to further better understand the present application, but are not limited to the best implementation mode described herein, and do not limit the content and protection scope of the present application. Any product identical or similar to the present application obtained by anyone under the inspiration of the present application or by combining the features of the present application with other prior arts shall fall within the scope of protection of the present application.

[0052] In the description of this application, it should be noted that the terms "inner" and "outer" and the like, indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate the description of this application and simplify the description. They are not intended to indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0053] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in this field can be used. If the manufacturer of the reagents or instruments is not specified, they are all commercially available conventional reagents.

[0054] In addition, the technical features involved in the different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0055] This application provides a wound battery cell and an electrochemical device including the wound battery cell, which can improve the uneven stress distribution of the separator in the arc and flat areas of the battery cell, reduce the risk of dendrites on the electrode surface piercing the separator and causing micro-short circuits, and improve the battery process K value and high-temperature external short-circuit performance while also ensuring long-cycle performance. The technical solution adopted in this application is described below.

[0056] In the first aspect, the wound battery cell provided by the present application includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator located between the positive electrode sheet and the negative electrode sheet, the separator includes a base film and a composite layer located on one side of the base film, the composite layer includes a heat-resistant layer and a water-based polymer coating located on the side of the heat-resistant layer away from the base film, and the base film is provided with an oily coating on the side away from the composite layer; the oily coating is in contact with the negative electrode sheet, and the water-based polymer coating is in contact with the positive electrode sheet; the composite layer contains a first element, and the first element is one or more of Al, Ba, Mg, Si, Sn, Ti, and N. The ratio of the mass content of the first element of the composite layer on the surface of the arc area to the mass content of the first element of the composite layer on the surface of the plane area is a, the thickness difference between the water-based polymer coating in the arc area and the water-based polymer coating in the plane area is H μm, the thickness of the oily coating is T μm, and the relationship between H, a and T satisfies: 0.5≤T×(H / a)≤4.

[0057] Those skilled in the art will understand that, for a diaphragm with different water and oil surfaces, there is a height difference between the aqueous polymer coating in the arc area and the flat area. Although it can improve the wettability of the electrolyte in the arc area, enhance the cycle stability, and reduce lithium precipitation caused by lack of liquid in the arc area. However, the thickness of the diaphragm in the arc area and the flat area is inconsistent. On the one hand, it is easy to cause uneven stress distribution of the diaphragm as a whole, and the stress concentration will increase the local current density, which will lead to the growth of local lithium dendrites and excessive self-discharge K value. On the other hand, the thicker arc area of ​​the diaphragm leads to loose fitting with the electrode, which easily leads to insufficient contact sites between the diaphragm and the electrode, and easily leads to continuous rupture and regeneration of the CEI film of the positive active particles during the cycle, increasing the interface impedance of the arc area. In order to solve the problems of uneven stress distribution of the diaphragm and excessive interface impedance of the arc area, the wound battery cell provided in the present application satisfies the relationship between H, a and T by: 0.5 When T×(H / a)≤4, the strength difference between the arc-shaped and flat-surface separators can be improved, improving the uniformity of stress distribution, reducing the proportion of micro-shorts caused by local lithium dendrites piercing the separator, effectively lowering the K value and thus improving safety. Furthermore, the first element-containing material (e.g., Al) on the arc-shaped separator surface in contact with the electrode can absorb HF generated by the electrolyte to a certain extent at high temperatures. The first element (e.g., Al) in the product of the reaction with HF stabilizes the structure of the positive electrode active particles, reduces the dissolution of transition metal ions at the positive electrode, improves the stability of the CEI film, reduces interfacial impedance, and enhances the battery's high-temperature cycling performance. When T×(H / a)>4, the gap height of the water-based polymer coating is insufficient, resulting in poor stress distribution uniformity in the battery cell, affecting the K value yield of the process. When T×(H / a) < 0.5, the separator's strength improves stress distribution uniformity. However, due to the influence of the coating thickness on both sides, electrolyte concentration polarization increases, affecting the ion transfer rate during charging. This can lead to insufficient lithium insertion and the formation of lithium deposits on the negative electrode surface, which not only increases the battery's K value but also affects high-temperature cycling stability. For example, T×(H / a) can be 0.5, 1, 2, 3, 3.5, or any two of these values.

[0058] The term "mass content of the first element" refers to the percentage of the mass of the first element exposed on the surface of the coating to the total mass of all elements exposed on the surface of the coating.

[0059] The term "the ratio of the mass content of the first element of the composite layer on the surface of the arc area to the mass content of the first element of the composite layer on the surface of the plane area" refers to the ratio of the mass content of the first element exposed on the surface of the composite layer corresponding to the arc area of ​​the wound battery cell to the mass content of the first element exposed on the surface of the composite layer corresponding to the plane area of ​​the wound battery cell.

[0060] The term "mass content of the first element on the surface of the oil-based coating" refers to the percentage of the mass of the first element exposed on the surface of the oil-based coating in the total mass of all elements exposed on the surface of the coating. When the oil-based coating contains macropores, the elements exposed on the coating surface should also include the elements exposed through the pores of the coating. In this case, both the mass of the first element and the total mass of all elements are counted. This enables the element content exposed on the coating surface to reflect the overall comprehensive performance of the coating and the interfacial performance between the separator and the electrode.

[0061] The test method for the mass content of the first element on the coating surface is as follows: Electron microscope EDS energy spectrum analysis, surface scanning of the composite layer or the oil-based coating surface at a magnification of 500X, repeating the above operation 5 times, counting the element mass content, and taking the average value. The mass content of the first element on the surface of the composite layer in the arc region and the mass content of the first element on the surface of the composite layer in the flat region are respectively tested by taking the arc region and the flat region of the separator after disassembling the lithium-ion battery to test the element mass content on the surface of the composite layer.

[0062] The term "thickness difference between the aqueous polymer coating in the arc region and the aqueous polymer coating in the flat region" refers to the difference between the thickness of the aqueous polymer coating in the arc region and the thickness of the aqueous polymer coating in the flat region. The calculation formula is as follows: Thickness difference between the aqueous polymer coating in the arc region and the aqueous polymer coating in the flat region = Thickness of the aqueous polymer coating in the arc region - Thickness of the aqueous polymer coating in the flat region. H can be achieved due to the inconsistent compression degree of polymer particles A in the flat region and the arc region caused by the hot pressing process during battery manufacturing, or due to the inconsistent thickness of the aqueous polymer coatings coated in the arc region and the flat region, or the inconsistent particle size of polymer particles A.

[0063] In an optional embodiment, 1 < a ≤ 1.5; at this time, the strength of the separator is moderate, which can further improve the uniformity of the internal stress distribution of the battery and reduce the proportion of micro-shorts. For example, a can be > 1.0, 1.02, 1.1, 1.2, 1. Four, 1.5 or within the range composed of any two of the above values. a can be achieved by adjusting one or more of the particle size of the heat-resistant particles, the content of the heat-resistant particles, the proportion of the projected area of the coated part in the aqueous polymer coating on the heat-resistant layer, the particle size of polymer particles A, the molecular weight of the first polymer, and the proportion of the monomer containing an ester group in the first polymer.

[0064] In an optional embodiment, 0.8≤H≤4; controlling the thickness difference within the above range can further improve the electrolyte wettability in the width direction of the aqueous polymer coating side, enhance the ion transmission efficiency, and at the same time buffer the extrusion caused by the expansion of the electrode, thereby reducing the phenomenon of lithium deposition caused by local current unevenness; for example, H can be 0.8, 1, 2, 3, 4 or within the range formed by any two of the above values.

[0065] In an optional embodiment, 0.5≤T≤2, at which time the thickness of the oily coating is moderate, which can further regulate the electrolyte concentration polarization on both sides of the diaphragm, and can improve the efficiency of lithium ion transmission and embedding into the negative electrode; for example, T can be 0.5, 1, 2 or within the range of any two of the above values.

[0066] In an optional embodiment, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the current collector. The positive active material layer includes a positive active material, and the positive active material includes a lithium nickel cobalt manganese oxide material. The use of the lithium nickel cobalt manganese oxide material can further improve the cycling stability of the battery cell.

[0067] In a specific embodiment, the wound battery cell provided in the present application includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator located between the positive electrode sheet and the negative electrode sheet, the separator includes a base film and a composite layer located on one side of the base film, the composite layer includes a heat-resistant layer and a water-based polymer coating located on the side of the heat-resistant layer away from the base film, and the base film is provided with an oily coating on the side away from the composite layer; the oily coating is in contact with the negative electrode sheet, and the water-based polymer coating is in contact with the positive electrode sheet; the composite layer contains a first element, the first element is Al (the heat-resistant layer includes heat-resistant particles, and the components of the heat-resistant particles are selected from one or more of boehmite and alumina), the ratio of the mass content of the first element of the composite layer on the surface of the arc area to the mass content of the first element of the composite layer on the surface of the plane area is a, the thickness difference between the water-based polymer coating in the arc area and the water-based polymer coating in the plane area is H μm, and the thickness of the oily coating is T μm, the relationship between H, a and T satisfies: 0.5≤T×(H / a)≤4; the positive electrode plate includes a positive electrode current collector and a positive electrode active material layer provided on at least one side surface of the current collector, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes a lithium nickel cobalt manganese oxide material.

[0068] In an optional embodiment, the mass content of the lithium nickel cobalt manganese oxide material is 40%-100% based on the total mass of the positive electrode active material layer. For example, the mass content of the lithium nickel cobalt manganese oxide material can be 40%, 50%, 60%, 70%, 80%, 90%, 100%, or a range formed by any two of the above values.

[0069] In an optional embodiment, based on the mass of the positive electrode active material layer, the mass content of Mn is b%, 5≤b≤30; and a and b satisfy the following relationship: 7≤b / a≤30. When a and b satisfy this relationship, the first element (e.g., Al) acting on the positive electrode active particles is matched to the Mn content. The first element-containing material on the arc-shaped separator surface in contact with the electrode plate can absorb HF generated by the electrolyte to a certain extent at high temperatures, reducing the risk of HF-induced Mn dissolution in the ternary material. Furthermore, the first element in the product of the reaction with HF stabilizes the structure of the positive electrode active particles, improves the stability of the CEI film, further reduces interfacial impedance, and mitigates the expansion of the positive electrode material during cycling, further improving the high-temperature cycling performance of the battery. For example, b can be 5, 10, 15, 20, 25, 30, or any range thereof. b / a can be 7, 10, 15, 20, 25, 30, or any range thereof. The method for testing the mass content of the Mn element in the positive electrode active material layer is as follows: scrape about 0.1g of sample from the surface of the positive electrode active material layer, and then use the ICP-OES method to test to obtain the mass content of the Mn element.

[0070] In an optional embodiment, the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material comprises a silicon-carbon composite material. The use of the silicon-carbon composite material can further increase the energy density of the battery, while reducing the thickness of the plate and improving the lithium insertion efficiency.

[0071] In an optional embodiment, the mass content of the first element on the surface of the oily coating is P%, and the mass content of the silicon-carbon composite material is W% based on the total mass of the negative electrode active material, and P and W satisfy the following relationship: 0.5≤W / P≤15. When P and W satisfy the aforementioned relationship, the flexibility of the oil-based coating layer can be matched with the water-based electrode, and the interface performance between the silicon negative electrode and the diaphragm during the expansion process can be improved, and the interface impedance can be prevented from increasing due to silicon expansion, thereby improving the uniformity of the interface stress and reducing the risk of lithium deposition due to local stress concentration on the negative electrode surface during cyclic charging, while taking into account long cycle performance. For example, W / P can be 0.5, 1, 1.5, 2, 5, 6, 8, 10, 15, or within the range of any two of the above values.

[0072] In an optional embodiment, based on the total mass of the negative electrode active material, the mass content of the silicon-carbon composite material is 3%-50% (i.e., 3≤W≤50); and / or the mass content of the first element on the surface of the oily coating is 3%-10% (i.e., 3≤P≤10). For example, P can be 3, 5, 6, 8, 10, or within a range formed by any two of the above values. W can be 3, 5, 6, 8, 10, 15, 20, 30, 50, or within a range formed by any two of the above values.

[0073] In an optional embodiment, the electrolyte includes LiPF6 and an unsaturated nitrile additive, wherein the mass content of LiPF6, based on the total mass of the electrolyte, is c; the mass content of the unsaturated nitrile additive, based on the total mass of the electrolyte, is e; the heat-resistant layer includes heat-resistant particles, wherein the Dv10 of the heat-resistant particles is d; and c, e, and d satisfy 0.5c≤d≤10e. When c, e, and d satisfy this relationship, the stabilizing effect of the first element in the arc region on the positive electrode active particles can be promoted without affecting the structural stability of the heat-resistant layer, thereby further suppressing high-temperature gassing of the battery and improving high-temperature cycling performance. For example, the unsaturated nitrile additive includes one or more of 1,4-dicyano-2-butene, acrylonitrile, crotononitrile, trans-butenedinitrile, and trans-hexenedinitrile.

[0074] In an optional embodiment, the heat-resistant particles contain a first element. For example, the components of the heat-resistant particles are selected from one or more of boehmite (γ-AlOOH), aluminum oxide (Al2O3), barium sulfate (BaSO4), magnesium oxide (MgO), magnesium hydroxide (Mg(OH)2), silicon dioxide (SiO2), tin dioxide (SnO2), titanium oxide (TiO2), barium titanate (BaTiO3), melamine cyanurate, 1,3,5-triazine-2,4,6-triamine, and melamine thiocyanate.

[0075] In an optional embodiment, the electrolyte includes a cyclic carbonate and a linear carbonate, the weight ratio of the linear carbonate to the cyclic carbonate is 0.2-0.8, the weight content of the cyclic carbonate is 5%-30%, and the weight content of the linear carbonate is 5%-20%. When the weight content and ratio of the cyclic carbonate and the linear carbonate in the electrolyte, as well as c, e, and d, simultaneously meet the above relationship, the polarization of the battery at low temperature and high rate can be further reduced, thereby improving the low-temperature performance of the battery.

[0076] In an optional embodiment, the electrolyte includes LiPF6, and the mass content of the LiPF6 is 10%-20% based on the total mass of the electrolyte; for example, the mass content of the LiPF6 can be 10%, 12%, 15%, 18%, 20% or within the range of any two of the above values.

[0077] In an optional embodiment, the electrolyte includes an unsaturated nitrile additive, and the mass content of the unsaturated nitrile additive is 0.1%-5% based on the total mass of the electrolyte; for example, the mass content of the unsaturated nitrile additive can be 0.1%, 0.3%, 1%, 3%, 5% or within the range of any two of the above values.

[0078] In an optional embodiment, the Dv10 of the heat-resistant particles is 0.05 μm-0.3 μm. For example, the Dv10 of the heat-resistant particles is 0.05 μm, 0.08 μm, 0.1 μm, 0.2 μm, 0.3 μm, or a range formed by any two of the above values.

[0079] In an optional embodiment, the Dv90 of the heat-resistant particles is 1.8 μm-5 μm. By controlling the particle size Dv90 and / or particle size Dv10 of the heat-resistant particles within the above range, the stabilization effect of the first element in the arc region on the positive electrode active particles is facilitated without affecting the structural stability of the heat-resistant layer. For example, the Dv90 of the heat-resistant particles is 1.8 μm, 2 μm, 3 μm, 4 μm, 5 μm, or within a range consisting of any two of the above values.

[0080] Particle sizes Dv10 and Dv90 represent the particle sizes corresponding to the cumulative volume distribution percentages of the corresponding materials reaching 10% and 90%, respectively; they are measured by a laser particle size analyzer.

[0081] In a specific embodiment, the positive electrode plate includes a positive electrode collector and a positive electrode active material layer arranged on at least one side surface of the current collector, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes a lithium nickel cobalt manganese oxide material; the electrolyte includes LiPF6 and an unsaturated nitrile additive, and the mass content of the LiPF6 is c based on the total mass of the electrolyte; the mass content of the unsaturated nitrile additive is e based on the total mass of the electrolyte; the heat-resistant layer includes heat-resistant particles, and the Dv10 of the heat-resistant particles is d; c, e and d satisfy 0.5c≤d≤10e.

[0082] In an optional embodiment, the thickness of the base film is 3μm-12μm; and / or the porosity of the base film is 25%-55%; and / or the average pore size of the base film is 28nm-45nm; by adopting a base film of such thickness, porosity, and average pore size, it not only helps to maintain the tensile strength of the diaphragm and improve the safety of the battery cell, but also helps to obtain good liquid retention capacity, thereby delaying capacity decay. For example, the thickness of the base film can be 3μm, 4μm, 5μm, 8μm, 12μm or within the range of any two of the above values, the porosity can be 25%, 30%, 40%, 50%, 55% or within the range of any two of the above values, and the average pore size can be 28nm, 35nm, 40nm, 45nm or within the range of any two of the above values. For example, the component of the base film is selected from polypropylene and / or polyethylene.

[0083] In an optional embodiment, the aqueous polymer coating includes a blank portion and a coating portion, and the coating portion includes polymer particles A; for example, the polymer particles A include a first polymer, and the first polymer includes a polymer copolymerized with one or more monomers selected from methyl methacrylate, acrylonitrile, butyl acrylate, isooctyl acrylate, octadecyl acrylate, ethyl acrylate, styrene, ethylene, and butadiene.

[0084] In an optional embodiment, the molecular weight of the first polymer is 15,000-200,000.

[0085] In an optional embodiment, based on the total mass of the first polymer, the mass proportion of the monomer containing an ester group in the first polymer is 50%-100%.

[0086] In an optional embodiment, the polymer particles A include primary particles, and the average particle size of the primary particles is 150nm-500nm; and / or, the first polymer includes secondary particles, and the average particle size of the secondary particles is 3μm-12μm. Wherein, primary particles refer to single particles, and secondary particles refer to large particles formed by agglomeration of two or more primary particles. When the particle size of the secondary particles is too large, the wettability of the electrolyte is better, but the large thickness leads to a large loss of energy density. When the particle size is too small, the wetting improvement effect is poor, and it is easy to form the risk of adhesion and pore blocking. The present application controls the particle size of the secondary particles within the above range to ensure that the electrolyte has a good wetting effect while avoiding the loss of energy density. Controlling the primary particles within the above range is conducive to the formation of secondary particle agglomerates with uniform particle size during centrifugal drying. For example, the average particle size of the primary particles of the polymer particles A is 150nm, 200nm, 300nm, 500nm or within the range composed of any two of the above values. The average particle size of the secondary particles of the polymer particles A is 3 μm, 5 μm, 10 μm, 12 μm, or within a range formed by any two of the above values.

[0087] In an optional embodiment, the oily coating includes filler particles and polymer B, and the polymer B is non-granular. For example, the polymer B includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyhexafluoropropylene, a copolymer of vinylidene fluoride and chlorotrifluoroethylene, a vinylidene fluoride and hexafluoropropylene polymer, and a copolymer of vinylidene fluoride and trichloroethylene. For example, the components of the filler particles are selected from one or more of boehmite (γ-AlOOH), aluminum oxide (Al2O3), barium sulfate (BaSO4), magnesium oxide (MgO), magnesium hydroxide (Mg(OH)2), silicon dioxide (SiO2), tin dioxide (SnO2), titanium oxide (TiO2), barium titanate (BaTiO3), melamine cyanurate, 1,3,5-triazine-2,4,6-triamine, and melamine thiocyanate.

[0088] In an optional embodiment, the filler particles have a Dv90 value of 1.8 μm to 5 μm. Controlling the filler particle size Dv90 within this range not only facilitates obtaining a separator with an appropriate porosity, thereby improving lithium ion migration efficiency, but also improves the heat resistance of the separator, thereby improving battery thermal safety. For example, the filler particles have a Dv90 value of 1.8 μm, 2 μm, 3 μm, 4 μm, 5 μm, or a range consisting of any two of these values.

[0089] In an optional embodiment, the coating portion of the adhesive layer further includes a first polymer binder. For example, the first polymer binder is selected from one or more of polyacrylate, polyvinyl alcohol, and styrene-butadiene rubber.

[0090] In an optional embodiment, based on the total mass of the coated portion of the aqueous polymer coating, the mass content of the polymer particles A is 95%-99%; the mass content of the first polymer binder is 1%-5%. By controlling the mass content of the polymer particles A and the first polymer binder within the above ranges, the adhesion between the polymer particles A and the heat-resistant layer is improved without affecting lithium ion transmission. For example, the mass content of the polymer particles A is 95%, 97%, 99%, or within a range consisting of any two of the above values. The mass content of the first polymer binder is 5%, 3%, 1%, or within a range consisting of any two of the above values.

[0091] In an optional embodiment, the heat-resistant layer further comprises a second polymer binder, a thickener, and a wetting agent. For example, the second polymer binder is selected from one or more of polyacrylate, polyvinyl alcohol, and styrene-butadiene rubber; the thickener is selected from one or more of sodium carboxymethyl cellulose, alginic acid, or gelatin; the wetting agent is selected from one or more of alkylnaphthalene sulfonates, alkylbenzene sulfonates, or polyoxyethylene fatty alcohol ethers; wherein the alkylnaphthalene sulfonate is selected from one or more of sodium butylnaphthalene sulfonate, sodium dodecylnaphthalene sulfonate, potassium butylnaphthalene sulfonate, and potassium dodecylnaphthalene sulfonate; and the alkylbenzene sulfonate is selected from one or more of sodium hexadecylbenzene sulfonate, sodium dodecylbenzene sulfonate, potassium hexadecylbenzene sulfonate, and potassium dodecylbenzene sulfonate.

[0092] In one optional embodiment, the projected area of ​​the coating portion on the heat-resistant layer (hereinafter referred to as the coating portion area ratio or coating portion coverage) is 15%-60% of the total surface area of ​​one side of the heat-resistant layer. When the coating portion accounts for >60%, the separator's wetting effect on the electrolyte is poor. When the coating portion area is too small, the adhesion between the separator and the electrode is insufficient, which can easily cause the coating to peel and fall off during cycling. In this application, controlling the coating portion area within this range can achieve both good electrolyte wetting and good interfacial adhesion, thereby improving the cycling performance and safety of the battery cell. The method for determining the area of ​​the coated portion is as follows: In the present invention, the coverage of the coated portion can be calculated using SEM (scanning electron microscope) images. Specifically, the following steps may be included: Under a 1000x magnification SEM field of view, randomly select an area of ​​100 μm × 100 μm on the surface of the separator, divide this area into 400 uniform squares of 5 μm × 5 μm, and calculate the total number of squares occupied by the first polymer particles, X (Note: When the first polymer particles occupy ≥ 50% of the square area, it is considered occupied; otherwise, it is considered unoccupied). The coverage ratio = X / 400 × 100%. To increase data accuracy, 5 points are randomly selected for area division calculation, and the above operation is repeated 5 times, and the average value is taken. For example, based on the total area of ​​the water-based polymer coating, the area coverage of the coated portion is 15%, 30%, 50%, 60%, or within a range consisting of any two of the above values.

[0093] In an optional embodiment, the content of polymer B in the oily coating is 20%-70%; when the content of polymer B is too high, the surface polarity of the coating is large, the interface adhesion ability is strong, which is not conducive to the infiltration of the electrolyte, and the static electricity of the diaphragm is large, and it is easy to adsorb dust impurities during the production of the battery cell, causing local micro-short circuits. When the content is too low, the interface adhesion is weak, and the coating is prone to peeling and falling off during the cycle. The present application controls the mass content of polymer B within the above range to ensure good infiltration of the electrolyte while preventing the coating from peeling or falling off during the cycle, thereby improving the cycle performance of the battery cell while ensuring its safety. For example, the content of polymer B in the oily coating is 20%, 40%, 50%, 60%, 70% or within the range composed of any two of the above values.

[0094] In an optional embodiment, the thickness of the coated portion of the water-based polymer coating is 0.5 μm-5 μm. A water-based polymer coating with such a thickness range can effectively improve the adhesion between the diaphragm and the electrode, avoid short circuits caused by contact between the positive and negative electrodes, and improve battery safety. For example, the thickness of the coated portion of the water-based polymer coating is 0.5 μm, 1 μm, 2 μm, 5 μm, or within a range consisting of any two of the above values. The thickness of the oil-based coating is 0.5 μm, 1 μm, 2 μm, or within a range consisting of any two of the above values.

[0095] The content of the negative electrode active material is ≥ 96% based on the mass of the negative electrode active material layer. For example, the content of the negative electrode active material is 96%, 97%, 98%, 99%, or within a range formed by any two of the above values.

[0096] In some embodiments, the positive electrode active material layer or the negative electrode active layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), styrene-butadiene rubber, polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin. In some embodiments, the binder may optionally account for 0.5% to 3% of the total weight of the positive electrode active material layer. Alternatively, the binder may account for 0.5% to 3% of the total weight of the negative electrode active material layer.

[0097] In some embodiments, the positive electrode active material layer or the negative electrode active layer may further include a conductive agent. For example, the conductive agent may include at least one of carbon nanotubes, acetylene black, carbon black, Ketjen black, graphene, and carbon nanofibers.

[0098] In some embodiments, optionally, the conductive agent accounts for 0.5%-5% of the total weight of the positive electrode active material layer.

[0099] In some embodiments, the positive electrode active material layer or the negative electrode active layer may further include a thickener. As an example, the conductive agent may include sodium carboxymethyl cellulose.

[0100] In some embodiments, optionally, the thickener accounts for 0.1%-2% of the total weight of the positive electrode active material layer.

[0101] The electrolyte used in the battery of the present application may include any electrolyte disclosed in the prior art.

[0102] In a second aspect, the present application provides an electrochemical device comprising the battery cell described in any one of the first aspects.

[0103] The present application is further described in detail below with reference to specific examples, which should not be construed as limiting the scope of protection claimed in the present application. In all examples and comparative examples of the present application, the unit wt% represents the percentage by mass.

[0104] In the following embodiments of the present application, corresponding technical solutions and technical effects are described based on lithium-ion secondary batteries as an example, but the solutions described in the present application can still be applied to other feasible battery systems.

[0105] Example 1

[0106] This embodiment provides a wound battery cell, such as Figure 1 and 2 The structure shown in the figure shows the wound lithium-ion battery described in this application, which includes a base film 110 and a composite layer and an oily coating 130 located on both sides of the base film 110. The composite layer includes a heat-resistant layer 160 and an aqueous polymer coating 120 located on the side of the heat-resistant layer 160 facing away from the base film. The aqueous polymer coating 120 includes a blank portion 121 and a coated portion 122. The oily coating 130 contacts the negative electrode sheet 150, and the aqueous polymer coating 120 contacts the positive electrode sheet 140. The wound lithium-ion battery includes a flat area 2 and an arc area 1.

[0107] The preparation method is as follows:

[0108] (1) Preparation of positive electrode sheet

[0109] According to the weight ratio of 96.5:1.5:2, lithium nickel cobalt manganese oxide (molecular formula: LiNi 0.6 Co 0.1 Mn 0.3 The cathode slurry is then coated on 9μm thick aluminum foil and dried in a 120°C vacuum oven for 6 hours. The resulting cathode sheets are then rolled and slit to obtain the desired cathode.

[0110] (2) Preparation of negative electrode sheet

[0111] The negative electrode active material (composed of 15wt% silicon-carbon composite material and 85wt% graphite), the thickener sodium carboxymethyl cellulose (CMC), the binder styrene-butadiene rubber, and the conductive agent (conductive carbon black Super P: carbon nanotubes at a mass ratio of 1:1) were mixed in an aqueous solvent at a weight ratio of 97.2:0.6:1.2:1. The mixture was continuously stirred in a blender to form a uniform, fluid negative electrode slurry. The slurry was then coated on the surface of a 6μm-thick current collector copper foil and dried in a 120°C vacuum oven for 6 hours. The resulting negative electrode sheets were then rolled and slit.

[0112] (3) Preparation of electrolyte

[0113] In an argon-filled glove box (moisture <1ppm, oxygen <1ppm), ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, and propyl propionate were mixed in a mass ratio of 3:3:1:3:20 to form a uniform solvent. LiPF6 was slowly added to the mixed solvent so that the mass content of LiPF6 accounted for 15% of the total mass of the electrolyte. After stirring evenly, the desired basic lithium-ion battery electrolyte was obtained.

[0114] (4) Preparation of diaphragm

[0115] 1. Preparation of the Oily Coating: Polymer B and the organic solvent DMAC (dimethylacetamide) were blended and thoroughly stirred to dissolve. Filler particles were then added and dispersed uniformly to obtain a mixed slurry with an 8% solids content. The mass ratio of PVDF to filler particles was 4:6, with the slurry containing 100% solids. The mixed slurry was then coated onto the first surface of a porous base membrane (PE, 5μm thick, 40% porosity, and an average pore size of 41nm) using a gravure roller. The organic solvent was extracted in a water tank to create pores, and the coating was then dried in a multi-section oven at 60°C to form a 1μm thick oily coating. Polymer B was PVDF, using Arkema's LBG. The filler particles were conventional alumina with a particle size Dv10 of 0.11μm and a particle size Dv90 of 1.8μm.

[0116] 2. Preparation of the heat-resistant layer: Heat-resistant particles, a second polymer binder, a thickener, a wetting agent, and deionized water were blended to form a ceramic slurry with a solid content of 35%. The mass ratio of heat-resistant particles: second polymer binder: thickener: wetting agent was 94.5:5:0.4:0.1, calculated based on 100% solids. After thorough stirring and dispersion, the slurry was coated onto the second surface of the porous base membrane using a gravure roll and dried in a multi-section oven at 60°C to form a heat-resistant layer with a thickness of 1 μm. The heat-resistant particles used were aluminum oxide with a particle size Dv10 of 0.11 μm and a particle size Dv90 of 1.8 μm. The second polymer binder was polyacrylate, the thickener was CMC, and the wetting agent was sodium dodecylbenzene sulfonate.

[0117] 3. Preparation of the Water-Based Polymer Coating: Polymer particles A, a first polymer binder, and deionized water were blended to form a mixed slurry with a solids content of 5%. The mass ratio of polymer particles A to the first polymer binder, calculated as 100% solids, was 95:5. After thorough stirring and dispersion, the slurry was coated onto the surface of the heat-resistant layer using a gravure roller and dried in a multi-section oven at 60°C to form a water-based polymer coating comprising a blank portion and a coated portion, thereby obtaining the separator described in the invention application. The coated portion of the water-based polymer coating had a thickness of 3 μm, the blank portion had a thickness of 0 μm, and the coated portion accounted for 26.5% of the total area. The first polymer binder was polyacrylate. The average primary particle size of polymer particles A was 300 nm, and the average secondary particle size was 6.5 μm. The monomers were styrene, isooctyl acrylate, and methyl methacrylate, copolymerized in a ratio of 60:9:31. Polymer particles A were provided by Shenzhen Bairou New Materials Technology Co., Ltd., model DWP4201A.

[0118] (5) Preparation of lithium-ion batteries

[0119] The positive electrode sheet, separator and negative electrode sheet prepared above are wound to prepare a bare cell; then the bare cell is placed in an aluminum-plastic film, and the prepared electrolyte is injected into the dried bare cell. After vacuum packaging, room temperature standing, hot pressing and other processes, the required lithium-ion battery is obtained.

[0120] The preparation methods for the battery cells in Examples 2 to 5 were essentially the same as those in Example 1, differing only in that the coating area of ​​the water-based polymer coating, i.e., the area ratio of the coated portion, was adjusted to vary H and a, as shown in Table 1. In Example 3, the average particle size of the secondary particle agglomerates of polymer particles A was adjusted to 7.3 μm. In Example 5, the average particle size of the secondary particle agglomerates of polymer particles A was adjusted to 8 μm.

[0121] The preparation methods of the battery cells in Examples 6 to 9 are basically the same as those in Example 1, with the only difference being that the thickness T of the oily coating is different, as shown in Table 1.

[0122] The preparation method of the battery cell in Example 10 is basically the same as that in Example 1, except that lithium nickel cobalt manganese oxide (molecular formula: LiNi 0.6 Co 0.2 Mn 0.2 O2) instead of lithium nickel cobalt manganese oxide (molecular formula: LiNi 0.6 Co 0.1 Mn 0.3 O2).

[0123] The preparation method of the battery cell in Example 11 is basically the same as that in Example 1, except that lithium cobalt oxide and lithium nickel cobalt manganese oxide (molecular formula: LiNi) are used in a mass ratio of 50%:50%. 0.6 Co 0.1 Mn 0.3 O2) instead of "lithium nickel cobalt manganese oxide (molecular formula: LiNi 0.6 Co 0.1 Mn 0.3 O2)".

[0124] The preparation method of the battery cell in Example 12 is basically the same as that in Example 1, except that lithium cobalt oxide and lithium nickel cobalt manganese oxide (molecular formula: LiNi) are used in a mass ratio of 50%:50%. 0.6 Co 0.2 Mn 0.2 O2) instead of "lithium nickel cobalt manganese oxide (molecular formula: LiNi 0.6 Co 0.1 Mn 0.3 O2)".

[0125] The preparation method of the battery cell in Example 13 is basically the same as that in Example 1, except that lithium nickel cobalt manganese oxide (molecular formula: LiNi 0.2 Co 0.2 Mn 0.6 O2) instead of lithium nickel cobalt manganese oxide (molecular formula: LiNi 0.6 Co 0.1 Mn 0.3 O2).

[0126] The preparation method of the battery cell in Example 14 is basically the same as that in Example 1, except that the mass ratio of PVDF to filler particles is adjusted to 2:8, resulting in a different P value.

[0127] The preparation method of the battery cells in Examples 15-16 is basically the same as that in Example 1, except that the mass contents of the silicon-carbon composite material and graphite used in the negative electrode active material are adjusted.

[0128] The preparation method of the battery cell in Example 17 is basically the same as that in Example 15, except that the mass ratio of PVDF to filler particles is adjusted to 6:4, resulting in a different P value.

[0129] The preparation method of the battery cell in Example 18 is basically the same as that in Example 16, except that the mass ratio of PVDF to filler particles is adjusted to 2:8, resulting in a different P value.

[0130] The preparation method of the battery cell in Example 19 is essentially the same as that in Example 1, differing only in the preparation method of the separator. In this example, the same mass of boehmite (γ-AlOOH) was used as filler particles instead of alumina during the preparation of the oily coating, and the same mass of boehmite (γ-AlOOH) was used as heat-resistant particles during the preparation of the heat-resistant layer. The boehmite (γ-AlOOH) had a particle size Dv90 of 1.8 μm.

[0131] The preparation method of the battery cell in Example 20 is essentially the same as that in Example 1, differing only in the preparation method of the separator. In this example, melamine cyanurate of the same mass is used as filler particles instead of alumina during the preparation of the oily coating, and melamine cyanurate of the same mass is used as heat-resistant particles during the preparation of the heat-resistant layer. The particle size Dv90 of the melamine cyanurate is 1.8 μm.

[0132] The preparation method of the battery cell in Example 21 is basically the same as that in Example 1, except that the preparation method of the separator is different, and the coating area of ​​the water-based polymer coating, that is, the area ratio of the coating part, is adjusted to make H and a different, as shown in Table 1. At the same time, when preparing the positive electrode sheet, lithium nickel cobalt manganese oxide (molecular formula: LiNi 0.2 Co 0.2 Mn 0.6 O2) instead of lithium nickel cobalt manganese oxide (molecular formula: LiNi 0.6 Co 0.1 Mn 0.3 O2).

[0133] The preparation method of the battery cell in Example 22 is basically the same as that in Example 1, the only difference is that the preparation method of the electrolyte is different. The preparation method of the electrolyte in this embodiment is: in a glove box filled with argon (water <1ppm, oxygen <1ppm), ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, and propyl propionate solvents are mixed in a mass ratio of 3:3:1:3:20 to form a uniform solvent to obtain a mixed solvent, and LiPF6 is slowly added to the mixed solvent so that the mass content of LiPF6 accounts for 15% of the total mass of the electrolyte, and 1,4-dicyano-2-butene is slowly added to the mixed solvent so that the mass content of 1,4-dicyano-2-butene accounts for 2% of the total mass of the electrolyte, and stirred evenly to obtain the required basic lithium-ion battery electrolyte.

[0134] The preparation method of the battery cells in Examples 23-27 is basically the same as that in Example 22, with the only difference being that the particle size of the heat-resistant particles is adjusted. The value of the particle size Dv10 is shown in Table 2. In addition, Examples 25-26 also adjust the content of LiPF6 in the electrolyte, and Examples 24-26 also adjust the content of 1,4-dicyano-2-butene in the electrode solution.

[0135] Comparative Example 1 is basically the same as Example 7, except that the coating area of ​​the water-based polymer coating is adjusted so that T×(H / a) is different, as shown in Table 1.

[0136] Comparative Example 2 is basically the same as Example 6, except that the coating area of ​​the water-based polymer coating is adjusted so that T×(H / a) is different, as shown in Table 1.

[0137] Table 1 Physical parameters of positive electrode sheet, negative electrode sheet, electrolyte and separator

[0138]

[0139] Table 2 Physical parameters of heat-resistant layer and electrolyte

[0140]

[0141] Test Case

[0142] The lithium-ion batteries prepared in the examples and comparative examples were tested as follows:

[0143] 1. Cycle performance:

[0144] At 45°C ± 2°C, charge the battery to 4.3V at 0.7C constant current and constant voltage, cut off at 0.05C, and record the initial thickness P0. Then discharge the battery to 3.0V at 0.2C constant current, and record the initial discharge capacity as C0. After 10 minutes of rest, the battery is cycled as follows: charge the battery to 3.9V at 1.2C constant current and constant voltage, then charge the battery to 4.3V at 0.7C constant current and constant voltage, cut off at 0.05C, and rest for 5 minutes. Then discharge the battery to 3.0V at 0.7C. After 700 cycles, charge the battery to 4.3V at 0.7C constant current and constant voltage, cut off at 0.05C, and record the final thickness P1. Then discharge the battery to 3.0V at 0.2C constant current, and record the discharge capacity after 700 cycles as C1.

[0145] Capacity retention rate: C=C1 / C0*100%, thickness expansion rate: P=(P1-P0) / P0*100%.

[0146] 2. K value test

[0147] In an environment of 25℃±2℃, charge to 50% SOC at 0.5C constant current and constant voltage, then place the lithium-ion battery in a 45℃±2℃ oven at high temperature for 48 hours. After high-temperature standing, take the battery out of the oven and place it in a room temperature environment. After 24 hours, test the voltage, recorded as OCV1, then continue to stand at room temperature for 48 hours, and then test the voltage again, recorded as OCV2. Each batch of batteries is not less than 50pcs, and the average K value is calculated. The smaller the K value, the lower the self-discharge of the battery and the better the performance stability.

[0148] K value = (OCV1-OCV2) / 48, unit: mV / h.

[0149] 3. High temperature gas production

[0150] At 60°C, the battery was charged to 4.45V at a 1C rate, discharged to 3.0V at a 1C rate, and cycled for 20 cycles. A battery gas production test device was used to detect the gas production after the battery cycle, in μL.

[0151] Please see Table 3 for the test results above.

[0152] Table 3 Performance test results

[0153]

[0154] It can be seen from the results in the above table that, compared with Comparative Examples 1 and 2, the embodiments of the present application can not only effectively reduce the K value, but also improve the high-temperature cycle performance of the battery and reduce the high-temperature gas production.

[0155] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of this application.

Claims

1. A wound battery cell, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator located between the positive electrode sheet and the negative electrode sheet, wherein the separator comprises a base film and a composite layer located on one side of the base film, the composite layer comprises a heat-resistant layer and a water-based polymer coating located on a side of the heat-resistant layer away from the base film, the water-based polymer coating comprises a blank portion and a coating portion, and an oily coating is provided on a side of the base film away from the composite layer; The oily coating is in contact with the negative electrode plate, and the water-based polymer coating is in contact with the positive electrode plate; The heat-resistant layer comprises heat-resistant particles, the heat-resistant particles comprise a first element, the first element is one or more of Al, Ba, Mg, Si, Sn, Ti, and N, the ratio of the mass content of the first element on the surface of the composite layer in the arc region to the mass content of the first element on the surface of the composite layer in the plane region is a, the thickness difference between the water-based polymer coating in the arc region and the water-based polymer coating in the plane region is H μm, the thickness of the oily coating is T μm, and the relationship between H, a, and T satisfies: 0.5≤T×(H / a)≤4; wherein, 1 <a≤1.5,0.8≤H≤4,0.5≤T≤2; The mass content of the first element refers to the percentage of the mass of the first element exposed on the surface of the coating to the total mass of all elements exposed on the surface of the coating; the ratio of the mass content of the first element on the surface of the composite layer in the arc area to the mass content of the first element on the surface of the composite layer in the plane area refers to the ratio of the mass content of the first element exposed on the surface of the composite layer corresponding to the arc area of ​​the wound battery cell to the mass content of the first element exposed on the surface of the composite layer corresponding to the plane area of ​​the wound battery cell; The difference in thickness between the water-based polymer coating in the arc region and the water-based polymer coating in the plane region=the thickness of the water-based polymer coating in the arc region-the thickness of the water-based polymer coating in the plane region.

2. The wound battery cell according to claim 1, characterized in that The positive electrode plate includes a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the current collector. The positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes a lithium nickel cobalt manganese oxide material.

3. The wound battery cell according to claim 2, characterized in that: The positive electrode plate satisfies one or more of the following requirements: A. Based on the total mass of the positive electrode active material layer, the mass content of the lithium nickel cobalt manganese oxide material is 40%-100%; B. The positive electrode active material further comprises one or more of lithium manganese oxide, lithium cobalt oxide, lithium iron phosphate, and lithium nickel cobalt aluminum oxide; C. Based on the mass of the positive electrode active material layer, the mass content of the Mn element is b%, 5≤b≤30; and a and b satisfy the following relationship: 7≤b / a≤30.

4. The wound battery cell according to claim 1, characterized in that The negative electrode plate includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes a silicon-carbon composite material.

5. The wound battery cell according to claim 4, characterized in that: Based on the total mass of the negative electrode active material, the mass content of the silicon-carbon composite material is W%, the mass content of the first element on the surface of the oily coating is P%, and P and W satisfy the following relationship: 0.5≤ W / P ≤15; the mass content of the first element on the surface of the oily coating refers to the percentage of the mass of the first element exposed on the surface of the oily coating to the total mass of all elements exposed on the surface of the coating; wherein W is 3-50 and P is 3-10.

6. The wound battery cell according to claim 4, characterized in that: Based on the total mass of the negative electrode active material, the mass content of the silicon-carbon composite material is 3%-50%.

7. The wound battery cell according to claim 1, characterized in that: The mass content of the first element on the surface of the oily coating is 3%-10%; the mass content of the first element on the surface of the oily coating refers to the percentage of the mass of the first element exposed on the surface of the oily coating to the total mass of all elements exposed on the surface of the coating.

8. The wound battery cell according to claim 1, characterized in that: The electrolyte comprises LiPF6 and an unsaturated nitrile additive, wherein the mass content of the LiPF6 is c based on the total mass of the electrolyte; Based on the total mass of the electrolyte, the mass content of the unsaturated nitrile additive is e; The particle size Dv10 of the heat-resistant particles is d, in μm; c, e and d satisfy 0.5c≤d≤10e; among them, c is 10%-20%; e is 0.1%-5%, and d is 0.05-0.

3.

9. The wound battery cell according to claim 1, characterized in that: The electrolyte includes LiPF6, and the mass content of the LiPF6 is 10%-20% based on the total mass of the electrolyte.

10. The wound battery cell according to claim 1, characterized in that: The electrolyte includes an unsaturated nitrile additive, and the mass content of the unsaturated nitrile additive is 0.1%-5% based on the total mass of the electrolyte.

11. The wound battery cell according to claim 1, characterized in that: The Dv10 of the heat-resistant particles is 0.05 μm-0.3 μm.

12. The wound battery cell according to claim 8, characterized in that: The unsaturated nitrile additive includes one or more of 1,4-dicyano-2-butene, acrylonitrile, crotononitrile, trans-butenedinitrile, and trans-hexenedinitrile.

13. The wound battery cell according to claim 1, characterized in that: The Dv10 of the heat-resistant particles is 0.1 μm-0.15 μm; and / or, the Dv90 of the heat-resistant particles is 1.8 μm-5 μm; And / or, the components of the heat-resistant particles are selected from one or more of boehmite, aluminum oxide, barium sulfate, magnesium oxide, magnesium hydroxide, silicon dioxide, tin dioxide, titanium oxide, barium titanate, melamine cyanurate, 1,3,5-triazine-2,4,6-triamine, and melamine thiocyanate.

14. The wound battery cell according to any one of claims 1 to 13, characterized in that: The thickness of the base film is 3 μm-12 μm; and / or, the porosity of the base film is 25%-55%; and / or, the average pore size of the basement membrane is 28 nm to 45 nm; and / or, the coating portion comprises polymer particles A; and / or, the oily coating comprises filler particles and polymer B, and the polymer B is non-granular; and / or, 1.1≤a≤1.5; And / or, based on the total area of ​​one side of the heat-resistant layer, the projected area of ​​the coating portion on the heat-resistant layer accounts for 15%-60%; And / or, the coating portion has a thickness of 0.5 μm to 5 μm.

15. The wound battery cell according to claim 14, characterized in that: And / or, the mass content of polymer B in the oily coating is 20%-70%; And / or, the polymer particles A include primary particles, and the average particle size of the primary particles is 150 nm to 500 nm; And / or, the polymer particles A include secondary particles, and the average particle size of the secondary particles is 3 μm-12 μm; and / or, the filler particles are selected from one or more of boehmite, alumina, barium sulfate, magnesium oxide, magnesium hydroxide, silicon dioxide, tin dioxide, titanium oxide, barium titanate, melamine cyanurate, 1,3,5-triazine-2,4,6-triamine, and melamine thiocyanate; And / or, the polymer particles A include a first polymer, wherein the first polymer includes a copolymer of one or more monomers selected from the group consisting of methyl methacrylate, acrylonitrile, butyl acrylate, isooctyl acrylate, octadecyl acrylate, ethyl acrylate, styrene, ethylene, and butadiene; And / or, the polymer B includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl fluoride, vinyl fluoride-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, and tetrafluoroethylene-hexafluoropropylene copolymer.

16. An electrochemical device, characterized in that The invention comprises the wound battery cell according to any one of claims 1 to 15.

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