Winding battery cell and electrochemical device comprising winding battery cell

Abstract

The invention relates to the field of battery materials, in particular to a wound battery cell and an electrochemical device comprising the wound battery cell, the wound battery cell comprises a positive pole piece, a negative pole piece, electrolyte and a diaphragm located between the positive pole piece and the negative pole piece, the diaphragm comprises a base membrane and a composite layer located on one side of the base membrane, 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 [mu] m, and the thickness of the oily coating is T [mu] m, the relation of H, a and T satisfies 0.5 < = T * (H / a) < = 4. According to the winding battery cell provided by the invention, the relation T * (H / a) among H, a and T is controlled in the range, so that the K value can be effectively reduced, and the high-temperature cycle performance of the battery can be improved.

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 pole pieces 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 plane areas and arc areas. With the increase of high energy density, the arc area is prone to electrolyte deficiency and lithium precipitation in thick pole piece systems. The existing technology mainly improves the electrolyte wettability of the arc area by using a diaphragm coating to create a gap height in the arc area, thereby improving the cyclic lithium precipitation. However, the difference between the plane area and the arc area of the diaphragm is prone to cause uneven stress problems, 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 including 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 requirements for long cycle performance.

[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 comprises a heat-resistant layer and an aqueous polymer coating located on a side of the heat-resistant layer away from the base film, 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 sheet, and the aqueous 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 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.

[0006] In an alternative embodiment, the positive electrode plate includes a positive electrode current collector and a positive electrode active material layer provided on at least one 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.

[0007] In an alternative 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%.

[0008] In an alternative embodiment, the positive electrode active material further includes one or more of lithium manganate, lithium cobaltate, lithium iron phosphate, and lithium nickel cobalt aluminate.

[0009] In an alternative embodiment, based on the mass of the positive electrode active material layer, the mass content of Mn element is b%, 5 ≤ b ≤ 30; a and b satisfy the following relationship: 7 ≤ b / a ≤ 30.

[0010] In an alternative embodiment, the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, and the negative electrode active material contains a silicon-carbon composite material.

[0011] In an alternative embodiment, based on the total mass of the negative electrode active material, the mass content of the silicon-carbon composite material is W%, and the mass content of the first element on the surface of the oily coating is P%. P and W satisfy the following relationship: 0.5 ≤ W / P ≤ 15.

[0012] In an alternative embodiment, based on the total mass of the negative electrode active material, the mass content of the silicon-carbon composite material is 3% - 50%.

[0013] In an alternative embodiment, the mass content of the first element on the surface of the oily coating is 3% - 10%.

[0014] In an alternative embodiment, the electrolyte includes LiPF6 and an unsaturated nitrile additive. Based on the total mass of the electrolyte, the mass content of LiPF6 is c; Based on the total mass of the electrolyte, the mass content of the unsaturated nitrile additive is e; 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.

[0015] In an alternative embodiment, the electrolyte includes LiPF6. Based on the total mass of the electrolyte, the mass content of LiPF6 is 10% - 20%.

[0016] In an alternative embodiment, the electrolyte includes an unsaturated nitrile additive, and based on the total mass of the electrolyte, the mass content of the unsaturated nitrile additive is 0.1% - 5%.

[0017] In an alternative embodiment, the heat-resistant layer includes heat-resistant particles, and the Dv10 of the heat-resistant particles is 0.05 μm - 0.3 μm.

[0018] In an alternative embodiment, the unsaturated nitrile additive includes one or more of acrylonitrile, methacrylonitrile, ethyl acrylonitrile, chloroacrylonitrile, fluoroacrylonitrile, and phenylacrylonitrile.

[0019] In an alternative embodiment, the Dv10 of the heat-resistant particles is 0.1 μm - 0.15 μm.

[0020] In an alternative embodiment, the Dv90 of the heat-resistant particles is 1.8 μm - 5 μm.

[0021] In an alternative embodiment, the composition of the heat-resistant particles is 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 trithiocyanate.

[0022] In an alternative embodiment, 1 < a ≤ 1.5.

[0023] In an alternative embodiment, 0.8 ≤ H ≤ 4.

[0024] In an alternative embodiment, 0.5 ≤ T ≤ 2.

[0025] In an alternative embodiment, the thickness of the base film is 3 μm - 12 μm.

[0026] In an alternative embodiment, the porosity of the base film is 25% - 55%.

[0027] In an alternative embodiment, the aqueous polymer coating includes a blank part and a coated part, and the coated part includes polymer particles A.

[0028] In an alternative embodiment, the oily coating includes filler particles and polymer B, and polymer B is non-granular.

[0029] In an alternative embodiment, 1.1 ≤ a ≤ 1.5.

[0030] In an alternative embodiment, based on the total area of one side surface of the heat-resistant layer, the proportion of the projected area of the coated portion on the heat-resistant layer is 15% - 60%.

[0031] In an alternative embodiment, the thickness of the coated portion is 0.5 μm - 5 μm.

[0032] In an alternative embodiment, the mass content of polymer B in the oily coating is 20% - 70%.

[0033] In an alternative embodiment, the polymer particle A includes primary particles, and the average particle size of the primary particles is 150 nm - 500 nm.

[0034] In an alternative embodiment, the polymer particle A includes secondary particles, and the average particle size of the secondary particles is 3 μm - 12 μm.

[0035] In an alternative embodiment, the Dv90 of the filler particles is 1.8 μm - 5 μm.

[0036] In an alternative embodiment, the composition of the filler particles is 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 trithiocyanate.

[0037] In an alternative embodiment, the polymer particle A includes a first polymer, and the first polymer includes a polymer copolymerized from one or more monomers selected from methyl methacrylate, acrylonitrile, butyl acrylate, isooctyl acrylate, octadecyl acrylate, ethyl acrylate, styrene, ethylene, and butadiene.

[0038] In an alternative 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.

[0039] In a second aspect, the present application provides an electrochemical device including the wound battery cell according to any one of the first aspects of the present application.

[0040] The technical solution of the present application has the following advantages: The wound 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 an aqueous polymer coating located on the side of the heat-resistant layer facing away from the base film. An oil-based coating is provided on the side of the base film facing away from the composite layer; the oil-based coating is in contact with the negative electrode sheet, and the aqueous 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 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 planar region is a. The thickness difference between the aqueous polymer coating in the arc region and the aqueous polymer coating in the planar region is H μm, and the thickness of the oil-based coating is T μm. The relationship among H, a, and T satisfies: 0.5 ≤ T×(H / a) ≤ 4. When the foregoing relationship is satisfied, on the one hand, the difference in the stress intensity received by the separator in the arc region and the planar region can be improved, the uniformity of the stress distribution can be enhanced, the proportion of micro-shorts caused by local lithium dendrite piercing the separator can be reduced, and the problem of an increase in the K value can be effectively reduced; on the other hand, the substance containing the first element (such as Al element) in contact with the electrode sheet on the surface of the separator in the arc region can absorb HF generated by the electrolyte to a certain extent at high temperatures, and the first element (such as Al element) in the product after reacting with HF can stabilize the structure of the positive active particles, reduce the dissolution of transition metal ions at the positive electrode end, enhance the stability of the CEI film, reduce the difference in the interfacial impedance between the planar region and the arc region, and improve the high-temperature cycle performance of the battery.

[0041] Additional aspects and advantages of embodiments of the present application will be described and shown in part in the subsequent description, or will be explained through the implementation of embodiments of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0043] Figure 1 is a schematic structural diagram of a cell of the present application, Figure 2 is a schematic structural diagram of another cell of the present application; Among them, the reference numerals are explained as follows: 110, base film; 120, aqueous polymer coating; 130, oil-based coating; 140, positive electrode sheet; 150, negative electrode sheet; 160, heat-resistant layer; 121, blank part; 122, coated part; 1, arc area; 2, flat area. Detailed implementation manners

[0044] The following embodiments are provided to better understand the present application further. They are not limited to the best implementation manners, and do not constitute a limitation to 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 those of other prior arts falls within the protection scope of the present application.

[0045] In the description of the present application, it should be noted that the orientation or positional relationship indicated by terms such as "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be construed as a limitation to the present application. In addition, the terms "first", "second", "third" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0046] For those steps or conditions not specified in the embodiments, the operations or conditions of the conventional experimental steps described in the literature in this field can be followed. For the reagents or instruments whose manufacturers are not specified, they are all conventional reagent products that can be obtained through commercial purchase.

[0047] In addition, the technical features involved in different implementation manners of the present application described below can be combined with each other as long as they do not conflict with each other.

[0048] The present application provides a wound battery cell and an electrochemical device including the wound battery cell, which can improve the problem of uneven stress distribution of the separator in the arc area and the flat area of the battery cell, reduce the risk of micro short circuit caused by dendrite piercing the separator on the surface of the electrode sheet, improve the K value of the battery manufacturing process and the high-temperature external short circuit performance, and take into account the long cycle performance. The technical solutions adopted in the present application are as follows.

[0049] In a first aspect, the wound battery cell provided by the present application 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, the separator comprising a base film and a composite layer located on one side of the base film, the composite layer comprising a heat-resistant layer and an aqueous 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 aqueous polymer coating is in contact with the positive electrode sheet; the composite layer comprises 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 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.

[0050] Those skilled in the art can understand that for a diaphragm with water and oil on different planes, there is a height difference in the aqueous polymer coatings in the arc region and the planar region. Although it can improve the wettability of the electrolyte in the arc region, enhance the cycle stability, and reduce the lithium plating caused by the lack of liquid in the arc region. However, the thickness of the diaphragm in the arc region and the planar region is inconsistent. On the one hand, it is easy to cause uneven stress distribution in the overall diaphragm, and the stress concentration area will increase the local current density, which will in turn lead to local lithium dendrite growth and an excessive self-discharge K value. On the other hand, in the arc region where the diaphragm is thicker, it is not closely attached to the electrode sheet, which easily leads to insufficient contact sites between the diaphragm and the electrode sheet, and easily causes the CEI film of the positive active particles to continuously break and regenerate during the cycle, increasing the interfacial impedance in the arc region. To solve the problems of uneven stress distribution of the diaphragm and excessive interfacial impedance in the arc region, the wound battery cell provided in this application satisfies the relationship between H, a, and T: when 0.5 ≤ T×(H / a) ≤ 4, on the one hand, it can improve the strength difference between the diaphragms in the arc region and the planar region, enhance the uniformity of stress distribution, reduce the proportion of micro-shorts caused by local lithium dendrites piercing the diaphragm, effectively reduce the K value, and thus improve safety. On the other hand, the substance containing the first element (such as Al element) on the surface of the diaphragm in the arc region in contact with the electrode sheet can absorb HF generated by the electrolyte to a certain extent at high temperatures, and the first element (such as Al element) in the product after reacting with HF can stabilize the structure of the positive active particles, reduce the dissolution of transition metal ions at the positive electrode end, enhance the stability of the CEI film, reduce the interfacial impedance, and improve the high-temperature cycle performance of the battery. When T×(H / a) > 4, the height of the gap in the aqueous polymer coating is insufficient at this time, resulting in poor stress distribution uniformity of the battery cell and affecting the yield of the process K value. When T×(H / a) < 0.5, the strength of the diaphragm improves the stress distribution uniformity to a certain extent at this time, but affected by the coating thickness on both sides, the concentration polarization of the electrolyte increases, affecting the ion transport rate during charging, and easily causing insufficient lithium intercalation and lithium deposition on the negative electrode surface, which not only increases the battery K value but also affects the high-temperature cycle stability. For example, T×(H / a) can be 0.5, 1, 2, 3, 3.5 or within the range composed of any two of the above values.

[0051] 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 in the total mass of all elements exposed on the surface of the coating.

[0052] The term "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 planar region" refers to the ratio of the mass content of the first element exposed on the surface of the composite layer corresponding to the arc region of the wound battery cell to the mass content of the first element exposed on the surface of the composite layer corresponding to the planar region of the wound battery cell.

[0053] 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, whether counting the mass of the first element or the total mass of all elements, they are both included in the statistics. Thus, the element content exposed on the coating surface can reflect the overall comprehensive performance of the coating and the interfacial performance between the separator and the electrode.

[0054] The test method for the mass content of the first element on the coating surface is as follows: Electron microscope EDS energy spectrum analysis. Perform area scanning on the surface of the composite layer or the oil-based coating at a magnification of 500X, repeat the above operation 5 times, count the element mass content, and take 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 disassembling the lithium-ion battery and taking the arc region and the flat region of the separator to test the element mass content on the surface of the composite layer.

[0055] 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.

[0056] In an alternative 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, 1.4, 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 following factors: the particle size of the heat-resistant particles, the content of the heat-resistant particles, the proportion of the projection 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 monomers containing ester groups in the first polymer.

[0057] In an alternative 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 transport efficiency, and at the same time form a buffer against the extrusion caused by the expansion of the electrode sheet, reducing the phenomenon of lithium deposition caused by uneven local current; for example, H can be 0.8, 1, 2, 3, 4 or within the range composed of any two of the above values.

[0058] In an alternative embodiment, 0.5 ≤ T ≤ 2. At this time, the thickness of the oily coating is appropriate, which can further regulate the concentration polarization of the electrolyte on both sides of the separator and improve the efficiency of lithium ion transport and insertion into the negative electrode; for example, T can be 0.5, 1, 2 or within the range composed of any two of the above values.

[0059] In an alternative embodiment, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer provided on at least one 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 use of the lithium nickel cobalt manganese oxide material can further improve the cycle stability of the battery cell.

[0060] 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 on one side of the base film. The composite layer includes a heat-resistant layer and an aqueous polymer coating on the side of the heat-resistant layer facing away from the base film. The base film is provided with an oily coating on the side facing away from the composite layer; the oily coating is in contact with the negative electrode sheet, and the aqueous polymer coating is in contact with the positive electrode sheet; the composite layer contains a first element, and the first element is Al (the heat-resistant layer includes heat-resistant particles, and the composition of the heat-resistant particles is selected from one or more of boehmite and alumina). 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 planar region is a. The thickness difference between the aqueous polymer coating in the arc region and the aqueous polymer coating in the planar region is H μm, and the thickness of the oily coating is T μm. The relationship among H, a, and T satisfies: 0.5 ≤ T×(H / a) ≤ 4; the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer provided on at least one 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.

[0061] In an alternative embodiment, based on the total mass of the positive electrode active material layer, the mass content of the lithium nickel cobalt manganate material is 40% - 100%. For example, the mass content of the lithium nickel cobalt manganate material can be 40%, 50%, 60%, 70%, 80%, 90%, 100% or within the range composed of any two of the above values.

[0062] In an alternative embodiment, based on the mass of the positive electrode active material layer, the mass content of Mn element is b%, 5 ≤ b ≤ 30; a and b satisfy the following relationship: 7 ≤ b / a ≤ 30. When a and b satisfy the above relationship, the first element (such as Al element) acting on the positive electrode active particles can be matched with the Mn content. The substance containing the first element in contact with the electrode sheet on the surface of the arc-shaped area separator can absorb HF generated by the electrolyte to a certain extent at high temperature, which can reduce the risk of Mn dissolution in the ternary material caused by HF. And the first element in the product after reacting with HF can stabilize the structure of the positive electrode active particles, improve the stability of the CEI film, further reduce the interfacial impedance, and slow down the expansion of the positive electrode material during the cycling process, further improving the high-temperature cycling performance of the battery. For example, b can be 5, 10, 15, 20, 25, 30 or within the range composed of any two of the above values. b / a can be 7, 10, 15, 20, 25, 30 or within the range composed of any two of the above values. The testing method for the mass content of Mn element in the positive electrode active material layer is as follows: scrape about 0.1 g of sample from the surface of the positive electrode sheet active material layer, and then use the ICP-OES method to test to obtain the mass content of Mn element.

[0063] In an alternative embodiment, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, and the negative electrode active material contains a silicon-carbon composite material. By using the silicon-carbon composite material, the energy density of the battery can be further improved, while reducing the thickness of the electrode sheet and improving the lithium intercalation efficiency.

[0064] In an alternative embodiment, the mass content of the first element on the surface of the oily coating is P%, and based on the total mass of the negative electrode active material, the mass content of the silicon-carbon composite material is W%. P and W satisfy the following relationship: 0.5 ≤ W / P ≤ 15. When P and W satisfy the foregoing relationship, the flexibility of the oil-based coating layer can be matched with the water-based electrode, improving the interfacial performance between the silicon negative electrode and the separator during the swelling process, preventing the increase in interfacial impedance caused by silicon swelling, enhancing the interfacial stress uniformity, reducing the risk of lithium plating caused by local stress concentration on the negative electrode surface during cyclic charging, and taking into account the long cycle performance. For example, W / P can be 0.5, 1, 1.5, 2, 5, 6, 8, 10, 15 or within the range composed of any two of the above values.

[0065] In an alternative 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 the range composed of any two of the above values. W can be 3, 5, 6, 8, 10, 15, 20, 30, 50 or within the range composed of any two of the above values.

[0066] In an alternative embodiment, the electrolyte includes LiPF6 and an unsaturated nitrile additive. Based on the total mass of the electrolyte, the mass content of LiPF6 is c; based on the total mass of the electrolyte, the mass content of the unsaturated nitrile additive is e; 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. When c, e, and d satisfy the above relationship, it can promote the stabilizing effect of the first element in the arc region on the positive electrode active particles and does not affect the structural stability of the heat-resistant layer, thereby further suppressing the high-temperature gas generation of the battery and improving the high-temperature cycle performance. For example, the unsaturated nitrile additive includes one or more of 1,4-dicyano-2-butene, acrylonitrile, crotonitrile, trans-butenedinitrile, and trans-hexenedinitrile.

[0067] In an alternative 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), alumina (Al2O3), barium sulfate (BaSO4), magnesium oxide (MgO), magnesium hydroxide (Mg(OH)2), silicon dioxide (SiO2), tin dioxide (SnO2), titanium dioxide (TiO2), barium titanate (BaTiO3), melamine cyanurate, 1,3,5-triazine-2,4,6-triamine, and melamine trithiocyanate.

[0068] In an alternative embodiment, the electrolyte includes cyclic carbonates and linear carbonates. The weight content 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, ratio, and c, e and d of the cyclic carbonate and linear carbonate in the electrolyte simultaneously satisfy the above relationships, the polarization of the battery at low temperature and high rate can be further reduced, and the low temperature performance of the battery can be improved.

[0069] In an alternative embodiment, the electrolyte includes LiPF6. Based on the total mass of the electrolyte, the mass content of LiPF6 is 10% - 20%; for example, the mass content of LiPF6 can be 10%, 12%, 15%, 18%, 20% or within the range composed of any two of the above values.

[0070] In an alternative embodiment, the electrolyte includes unsaturated nitrile additives. Based on the total mass of the electrolyte, the mass content of the unsaturated nitrile additives is 0.1% - 5%; for example, the mass content of the unsaturated nitrile additives can be 0.1%, 0.3%, 1%, 3%, 5% or within the range composed of any two of the above values.

[0071] In an alternative 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 within the range composed of any two of the above values.

[0072] In an alternative 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, it is beneficial to the stabilizing effect of the first element in the arc area on the positive active particles and does not affect 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 the range composed of any two of the above values.

[0073] The particle sizes Dv10 and Dv90 respectively represent the particle sizes corresponding to when the cumulative volume distribution percentage of the corresponding material reaches 10% and 90%; measured by a laser particle size analyzer.

[0074] In a specific embodiment, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one 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. Based on the total mass of the electrolyte, the mass content of LiPF6 is c; based on the total mass of the electrolyte, the mass content of the unsaturated nitrile additive is e; 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.

[0075] In an alternative embodiment, 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 diameter of the base film is 28 nm - 45 nm; By using a base film with such thickness, porosity, and average pore diameter, it not only helps to maintain the tensile strength of the separator and improve the safety of the battery cell, but also is beneficial to obtaining good liquid retention ability, thereby delaying capacity decay. For example, the thickness of the base film can be 3 μm, 4 μm, 5 μm, 8 μm, 12 μm or within the range composed of any two of the above values, the porosity can be 25%, 30%, 40%, 50%, 55% or within the range composed of any two of the above values, and the average pore diameter can be 28 nm, 35 nm, 40 nm, 45 nm or within the range composed of any two of the above values. For example, the composition of the base film is selected from polypropylene and / or polyethylene.

[0076] In an alternative embodiment, the aqueous polymer coating includes a blank part and a coated part, and the coated part includes polymer particles A; For example, the polymer particles A include a first polymer, and the first polymer includes a polymer copolymerized from one or more monomers selected from methyl methacrylate, acrylonitrile, butyl acrylate, isooctyl acrylate, octadecyl acrylate, ethyl acrylate, styrene, ethylene, and butadiene.

[0077] In an alternative embodiment, the molecular weight of the first polymer is 15,000 - 200,000.

[0078] In an alternative embodiment, based on the total mass of the first polymer, the mass proportion of the monomers containing ester groups in the first polymer is 50% - 100%.

[0079] In an alternative embodiment, the polymer particle A comprises primary particles with an average particle size of 150 nm - 500 nm; and / or, the first polymer comprises secondary particles with an average particle size of 3 μm - 12 μm. Herein, the primary particle refers to a single particle, and the secondary particle refers to a large particle formed by agglomeration and combination of two or more primary particles. When the particle size of the secondary particle is too large, the wettability effect of the electrolyte is better, but the thickness is relatively large, resulting in more energy density loss. When the particle size is too small, the wetting improvement effect is poor, and at the same time, there is a risk of adhesion and pore blockage. In this application, by controlling the particle size of the secondary particle within the above range, while ensuring good wetting effect of the electrolyte, the loss of energy density is avoided. And controlling the primary particle within the above range is beneficial to forming secondary particle aggregates with uniform particle size during centrifugal drying. For example, the average particle size of the primary particles of the polymer particle A is 150 nm, 200 nm, 300 nm, 500 nm or within the range composed of any two of the above values. The average particle size of the secondary particles of the polymer particle A is 3 μm, 5 μm, 10 μm, 12 μm or within the range composed of any two of the above values.

[0080] In an alternative embodiment, the oily coating comprises filler particles and polymer B, and the polymer B is non-granular. For example, the polymer B comprises one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyhexafluoropropylene, copolymers of vinylidene fluoride - trichloroethylene, vinylidene fluoride - hexafluoropropylene polymers, copolymers of vinylidene fluoride - trichloroethylene. For example, the composition of the filler particles is selected from one or more of boehmite (γ - AlOOH), alumina (Al2O3), barium sulfate (BaSO4), magnesium oxide (MgO), magnesium hydroxide (Mg(OH)2), silicon dioxide (SiO2), tin dioxide (SnO2), titanium dioxide (TiO2), barium titanate (BaTiO3), melamine cyanurate, 1,3,5 - triazine - 2,4,6 - triamine, melamine trithiocyanate.

[0081] In an alternative embodiment, the Dv90 of the filler particles is 1.8 μm - 5 μm; by controlling the particle size Dv90 of the filler particles within the above range, it is not only beneficial to control the diaphragm with a suitable porosity range, thereby improving the migration efficiency of lithium ions, but also beneficial to improving the heat resistance of the diaphragm, thereby improving the thermal safety of the battery. For example, the Dv90 of the filler particles is 1.8 μm, 2 μm, 3 μm, 4 μm, 5 μm or within the range composed of any two of the above values.

[0082] In an alternative embodiment, the coated portion of the glue coating layer further includes a first polymer binder. By way of example, the first polymer binder is selected from one or more of polyacrylate, polyvinyl alcohol, and styrene-butadiene rubber.

[0083] In an alternative 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 contents 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 can be improved without affecting lithium ion transport. By way of example, the mass content of the polymer particles A is 95%, 97%, 99% or within the range composed of any two of the above values. The mass content of the first polymer binder is 5%, 3%, 1% or within the range composed of any two of the above values.

[0084] In an alternative embodiment, the heat-resistant layer further includes a second polymer binder, a thickener, and a wetting agent. By way of 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, and gelatin; the wetting agent is selected from one or more of alkyl naphthalene sulfonates, alkyl benzene sulfonates, and polyoxyethylene fatty alcohol ethers; wherein, the alkyl naphthalene sulfonates are selected from one or more of sodium butyl naphthalene sulfonate, sodium dodecyl naphthalene sulfonate, potassium butyl naphthalene sulfonate, and potassium dodecyl naphthalene sulfonate; the alkyl benzene sulfonates are selected from one or more of sodium hexadecyl benzene sulfonate, sodium dodecyl benzene sulfonate, potassium hexadecyl benzene sulfonate, and potassium dodecyl benzene sulfonate.

[0085] In an alternative embodiment, based on the total area of one surface of the heat-resistant layer, the proportion of the projected area of the coated portion on the heat-resistant layer (hereinafter referred to as the area proportion or coverage rate of the coated portion) is 15%-60%; when the area proportion of the coated portion > 60%, the wetting effect of the separator on the electrolyte is poor, and when the area of the coated portion is too small, the adhesion between the separator and the electrode sheet is insufficient, and coating peeling and shedding are likely to occur during the cycling process. By controlling the area of the coated portion within the above range in this application, good electrolyte infiltration and good interfacial bonding effects can be balanced, thereby improving the cycling performance and safety performance of the battery cell. The method for measuring the area of the coated portion is as follows: In the present invention, the coverage rate of the coated portion can be calculated through SEM (scanning electron microscope) images, which specifically includes the following steps: On the surface of the separator under a 1000-fold magnification SEM view, an area of 100 μm × 100 μm is randomly selected, and this area is divided into 400 uniform grids of 5 μm × 5 μm. Calculate the total number X of grids occupied by the first polymer particles (note: when the first polymer particle occupies an area of the grid ≥ 50%, it is considered occupied; otherwise, it is considered unoccupied), then the coverage rate = X / 400 × 100%. To increase the accuracy of the data, 5 points are randomly selected for area division calculation, and the above operation is repeated, and the average value of 5 times is taken. For example, based on the total area of the aqueous polymer coating, the area proportion of the coated portion is 15%, 30%, 50%, 60% or within the range composed of any two of the above values.

[0086] In an alternative 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 interfacial bonding ability is strong, which is not conducive to electrolyte infiltration, and at the same time, the static electricity of the separator is large, and it is easy to adsorb dust impurities during the battery cell manufacturing process, causing local micro-short circuits. When the content is too low, the interfacial bonding is weak, and coating peeling and shedding are likely to occur during the cycling process. By controlling the mass content of polymer B within the above range in this application, while ensuring good infiltration of the electrolyte, it can also prevent coating peeling or shedding during the cycling process, improving the cycling 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.

[0087] In an alternative embodiment, the thickness of the coated portion of the aqueous polymer coating is 0.5 μm - 5 μm; an aqueous polymer coating with such a thickness range can well improve the adhesion between the separator and the electrode sheet, avoid short circuits caused by the contact between the positive and negative electrodes, and improve the battery safety. For example, the thickness of the coated portion of the aqueous polymer coating is 0.5 μm, 1 μm, 2 μm, 5 μm or within the range composed of any two of the above values. The thickness of the oily coating is 0.5 μm, 1 μm, 2 μm or within the range composed of any two of the above values.

[0088] Based on the mass of the negative electrode active material layer, the content of the negative electrode active material ≥ 96%. For example, the content of the negative electrode active material is 96%, 97%, 98%, 99% or within the range composed of any two of the above values.

[0089] 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), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin. In some embodiments, optionally, the binder accounts for 0.5% - 3% of the total weight of the positive electrode active material layer. Optionally, the binder accounts for 0.5% - 3% of the total weight of the negative electrode active material layer.

[0090] In some embodiments, the positive electrode active material layer or the negative electrode active layer may further optionally include a conductive agent. As an example, the conductive agent may include at least one of carbon nanotubes, acetylene black, carbon black, Ketjen black, graphene, and carbon nanofibers.

[0091] In some embodiments, optionally, the conductive agent accounts for 0.5% - 5% of the total weight of the positive electrode active material layer.

[0092] In some embodiments, the positive electrode active material layer or the negative electrode active layer may further optionally include a thickening agent. As an example, the conductive agent may include sodium carboxymethyl cellulose.

[0093] In some embodiments, optionally, the thickening agent accounts for 0.1% - 2% of the total weight of the positive electrode active material layer.

[0094] The electrolyte used in the battery of the present application may include any technology disclosed in the prior art.

[0095] In a second aspect, the present application provides an electrochemical device, including the battery cell according to any one of the first aspect.

[0096] The present application is further described in detail below in conjunction with 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 mass percentage content.

[0097] 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.

[0098] Example 1 This embodiment provides a wound battery cell, such as Figure 1 and 2 The structure shown in the figure, the wound lithium-ion battery of the present application comprises a base film 110 and a composite layer and an oily coating 130 respectively located on both sides of the base film 110, the composite layer comprises a heat-resistant layer 160 and an aqueous polymer coating 120 located on the side of the heat-resistant layer 160 away from the base film, the aqueous polymer coating 120 comprises a blank portion 121 and a coating 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 comprises a plane area 2 and an arc area 1.

[0099] The preparation method is as follows: (1) Preparation of positive electrode 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 O2), binder polyvinylidene fluoride (PVDF 500), and conductive agent (conductive carbon black Super P: carbon nanotube mass ratio is 1:2) are mixed in N-methylpyrrolidone (NMP) solvent and continuously stirred into a uniform and flowing positive electrode slurry under the action of a stirrer. Subsequently, the positive electrode slurry is coated on an aluminum foil with a thickness of 9μm, sent to a 120℃ vacuum oven for drying for 6h, and then rolled and cut to obtain the required positive electrode sheet.

[0100] (2) Preparation of negative electrode sheet The negative electrode active material (the negative electrode active material consists of 15wt% silicon-carbon composite material and 85wt% graphite), thickener sodium carboxymethyl cellulose (CMC), binder styrene-butadiene rubber, and conductive agent (the mass ratio of conductive carbon black Super P: carbon nanotube is 1:1) are mixed in a water solvent at a weight ratio of 97.2:0.6:1.2:1, and continuously stirred into a uniform and flowing negative electrode slurry under the action of a stirrer. Subsequently, the slurry is coated on the surface of a current collector copper foil with a thickness of 6μm, sent to a 120℃ vacuum oven for drying for 6h, and then rolled and cut to obtain the desired negative electrode sheet.

[0101] (3) Preparation of electrolyte In a glove box filled with argon (moisture < 1 ppm, oxygen content < 1 ppm), ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, and propyl propionate solvents were mixed in a mass ratio of 3:3:1:3:20 to form a homogeneous solvent, obtaining a mixed solvent. LiPF6 was slowly added to the mixed solvent according to 15% of the mass content of LiPF6 in the total mass of the electrolyte. After stirring evenly, the required basic lithium-ion battery electrolyte was obtained.

[0102] (4) Preparation of separator 1. Preparation of oil-based coating: Polymer B and organic solvent DMAC (dimethylacetamide) were blended. After fully stirring and dissolving, filler particles were added, and after stirring and dispersing evenly, a mixed slurry with a solid content of 8% was obtained. Based on the 100% solid mass ratio of the slurry, the mass ratio of PVDF to filler particles was 4:6. The mixed slurry was coated on the first surface of a porous base film (specific type: PE, thickness 5 μm, porosity 40%, average pore diameter 41 nm) through a gravure roll. After extracting the organic solvent through a water bath for pore formation, it was then dried in a multi-stage oven at 60 °C to form an oil-based coating with a thickness of 1 μm. The polymer B is PVDF, LBG from Arkema was selected, and the filler particles are conventional alumina with a Dv10 particle size of 0.11 μm and a Dv90 particle size of 1.8 μm.

[0103] 2. Preparation of heat-resistant layer: Heat-resistant particles, a second polymer binder, a thickener, a wetting agent, and deionized water were blended to obtain a ceramic slurry with a solid content of 35%. Based on 100% solid mass calculation, the mass ratio of heat-resistant particles: second polymer binder: thickener: wetting agent is 94.5:5:0.4:0.1. After fully stirring and dispersing, the slurry was coated on the second surface of the porous base film through a gravure roll and dried in a multi-stage oven at 60 °C to form a heat-resistant layer with a thickness of 1 μm. The heat-resistant particles used are alumina with a Dv10 particle size of 0.11 μm and a Dv90 particle size of 1.8 μm, the second polymer binder is polyacrylate, the thickener is CMC, and the wetting agent is sodium dodecylbenzenesulfonate.

[0104] 3. Preparation of aqueous polymer coating: Polymer particles A, the first polymer binder and deionized water were blended to obtain a mixed slurry with a solid content of 5%. Based on 100% solid mass, the mass ratio of polymer particles A to the first polymer binder was 95:5. After sufficient stirring and dispersion, the slurry was coated on the surface of the heat-resistant layer by gravure roll coating, and dried in a multi-section oven at 60 °C to form an aqueous polymer coating including a blank part and a coated part, obtaining the separator described in the invention application. The thickness of the coated part in the aqueous polymer coating was 3 μm, the thickness of the blank part was 0 μm, and the area ratio of the coated part was 26.5%. The first polymer binder was polyacrylate. The average primary particle size of polymer particles A was 300 nm, and the average secondary particle aggregate size was 6.5 μm. The polymer monomer was composed of styrene, isooctyl acrylate and methyl methacrylate, and the copolymerization ratio was 60:9:31. Polymer particles A were provided by Shenzhen Bairou New Material Technology Co., Ltd., with the model DWP4201A.

[0105] (5)Preparation of lithium-ion battery The positive electrode sheet, separator and negative electrode sheet prepared above were wound to prepare a bare battery cell; subsequently, the bare battery cell was placed in an aluminum-plastic film, and the prepared electrolyte was injected into the dried bare battery cell. After processes such as vacuum packaging, normal temperature standing, and hot pressing forming, the required lithium-ion battery was obtained.

[0106] The preparation methods of the battery cells in Examples 2 to 5 were basically the same as those in Example 1, except that the coating area of the aqueous polymer coating, that is, the area ratio of the coated part, was adjusted to make H and a different, as shown in Table 1. In Example 3, the average secondary particle aggregate size of polymer particles A was also adjusted to 7.3 μm. In Example 5, the average secondary particle aggregate size of polymer particles A was also adjusted to 8 μm.

[0107] The preparation methods of the battery cells in Examples 6 to 9 were basically the same as those in Example 1, except that the thickness T of the oily coating was different, as shown in Table 1.

[0108] The preparation method of the battery cell in Example 10 was 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) was used instead of lithium nickel cobalt manganese oxide (molecular formula: LiNi 0.6 Co 0.1 Mn 0.3 O2).

[0109] The preparation method of the battery cell in Example 11 was basically the same as that in Example 1, except that lithium cobalt oxide and lithium nickel cobalt manganese oxide (molecular formula: LiNi0.6 Co 0.1 Mn 0.3 O2) mixture is used to replace "lithium nickel cobalt manganate (molecular formula: LiNi 0.6 Co 0.1 Mn 0.3 O2)".

[0110] The preparation method of the battery cell in Example 12 is basically the same as that in Example 1, except that lithium cobaltate and lithium nickel cobalt manganate (molecular formula: LiNi 0.6 Co 0.2 Mn 0.2 O2) mixture with the same mass and a mass ratio of 50%:50% is used to replace "lithium nickel cobalt manganate (molecular formula: LiNi 0.6 Co 0.1 Mn 0.3 O2)".

[0111] The preparation method of the battery cell in Example 13 is basically the same as that in Example 1, except that lithium nickel cobalt manganate (molecular formula: LiNi 0.2 Co 0.2 Mn 0.6 O2) is used to replace lithium nickel cobalt manganate (molecular formula: LiNi 0.6 Co 0.1 Mn 0.3 O2).

[0112] 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 to make the P value different.

[0113] The preparation methods of the battery cells in Examples 15 - 16 are basically the same as that in Example 1, except that the mass contents of the silicon-carbon composite material and graphite used as the anode active material are adjusted.

[0114] 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 to make the P value different.

[0115] 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 to make the P value different.

[0116] The preparation method of the battery cell in Example 19 is basically the same as that in Example 1, except that the preparation method of the separator is different. In the preparation process of the oily coating in this example, boehmite (γ-AlOOH) with the same mass is used instead of alumina as the filler particles, and in the preparation process of the heat-resistant layer, boehmite (γ-AlOOH) with the same mass is used as the heat-resistant particles. The Dv90 of boehmite (γ-AlOOH) is 1.8 μm.

[0117] The preparation method of the battery cell in Example 20 is basically the same as that in Example 1, except that the preparation method of the separator is different. In the preparation process of the oily coating in this example, melamine cyanurate with the same mass is used instead of alumina as the filler particles, and in the preparation process of the heat-resistant layer, melamine cyanurate with the same mass is used as the heat-resistant particles. The Dv90 of melamine cyanurate is 1.8 μm.

[0118] 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. Adjust the coating area of the water-based polymer coating, that is, the area ratio of the coated part, so that H and a are different, as shown in Table 1. At the same time, when preparing the positive electrode sheet, lithium nickel cobalt manganate (molecular formula: LiNi 0.2 Co 0.2 Mn 0.6 O2) is used instead of lithium nickel cobalt manganate (molecular formula: LiNi 0.6 Co 0.1 Mn 0.3 O2).

[0119] The preparation method of the battery cell in Example 22 is basically the same as that in Example 1, except that the preparation method of the electrolyte is different. The preparation method of the electrolyte in this example is as follows: in a glove box filled with argon (water content < 1 ppm, oxygen content < 1 ppm), ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, and propyl propionate solvents are mixed into a homogeneous solvent in a mass ratio of 3:3:1:3:20 to obtain a mixed solvent. LiPF6 is slowly added to the mixed solvent according to 15% of the total mass of the electrolyte, and 1,4-dicyano-2-butene is slowly added to the mixed solvent according to 2% of the total mass of the electrolyte, and then stirred evenly to obtain the required basic lithium-ion battery electrolyte.

[0120] The preparation methods of the battery cells in Examples 23-27 are basically the same as those in Example 22, except that the particle size of the heat-resistant particles is adjusted. The values of Dv10 are shown in Table 2. In addition, the content of LiPF6 in the electrolyte is adjusted in Examples 25-26, and the content of 1,4-dicyano-2-butene in the electrode solution is adjusted in Examples 24-26.

[0121] Comparative Example 1 is basically the same as Example 7, except that the coating area of the aqueous polymer coating is adjusted to make T×(H / a) different, as specifically shown in Table 1.

[0122] Comparative Example 2 is basically the same as Example 6, except that the coating area of the aqueous polymer coating is adjusted to make T×(H / a) different, as specifically shown in Table 1.

[0123] Table 1 Physical Parameters of the Positive Electrode Sheet, Negative Electrode Sheet, Electrolyte and Separator

[0124] Table 2 Physical Parameters of the Heat-resistant Layer and the Electrolyte

[0125] Test Example The lithium-ion batteries prepared in each example and comparative example were taken for the following tests: 1. Cycling performance: Under the environment of 45°C ± 2°C, it was charged at a constant current and constant voltage of 0.7C to 4.3V, cut off at 0.05C, and the initial thickness P0 was recorded. Then it was discharged at a constant current of 0.2C to 3.0V, and the initial discharge capacity was recorded as C0. After standing for 10 minutes, the cycling mode was: charged at a constant current and constant voltage of 1.2C to 3.9V, then switched to charged at a constant current and constant voltage of 0.7C to 4.3V, cut off at 0.05C, stood for 5 minutes, and discharged at 0.7C to 3.0V. After 700 cycles, it was charged at a constant current and constant voltage of 0.7C to 4.3V, cut off at 0.05C, and the final thickness P1 was recorded. Then it was discharged at a constant current of 0.2C to 3.0V, and the discharge capacity after 700 cycles was recorded as C1.

[0126] Capacity retention rate: C = C1 / C0 * 100%, thickness expansion rate: P = (P1 - P0) / P0 * 100%.

[0127] 2. K value test Under the environment of 25°C ± 2°C, it was charged at a constant current and constant voltage of 0.5C to 50% SOC. Then the lithium-ion battery was placed in an oven at 45°C ± 2°C for high-temperature standing for 48H. After high-temperature standing, the battery was taken out of the oven and placed in a normal-temperature environment. After 24H, the voltage was measured and recorded as OCV1. Then it was continuously stood in the normal-temperature environment for 48H, and the voltage was measured again and recorded as OCV2. Each batch of batteries was not less than 50 pcs, and the average value of the K value was calculated. The smaller the K value, the lower the self-discharge of the battery and the better the performance stability.

[0128] K value = (OCV1 - OCV2) / 48, unit mV / h.

[0129] 3. High-temperature gas generation At 60 °C, the battery is charged at a rate of 1C to 4.45V and discharged at a rate of 1C to 3.0V for 20 cycles. The gas production of the battery after cycling is detected using a battery gas production test device, with the unit being μL.

[0130] Please refer to Table 3 for the test results of the above items.

[0131] Table 3 Performance Test Results

[0132] From the results of the above table, it can be seen that compared with Comparative Example 1 and Comparative Example 2, each embodiment 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.

[0133] Obviously, the above embodiments are only examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present application.

Claims

1. A wound battery cell, characterized in that, It includes a positive electrode plate, a negative electrode plate, an electrolyte, and a separator located between the positive electrode plate and the negative electrode plate. The separator includes a base film and a composite layer on one side of the base film. The composite layer includes a heat-resistant layer and an aqueous polymer coating on the side of the heat-resistant layer facing away from the base film. An oil-based coating is provided on the side of the base film facing away from the composite layer; the oil-based coating is in contact with the negative electrode plate, and the aqueous polymer coating is in contact with the positive electrode plate; The composite layer contains a first element, which is one or more of Al, Ba, Mg, Si, Sn, Ti, N. The ratio of the mass content of the first element on the surface of the arc region of the composite layer to the mass content of the first element on the surface of the planar region of the composite layer is a. The thickness difference between the aqueous polymer coating in the arc region and the aqueous polymer coating in the planar region is H μm, and the thickness of the oil-based coating is T μm. The relationship among H, a, and T satisfies: 0.5 ≤ T×(H / a) ≤ 4.

2. The wound cell according to claim 1, wherein The positive electrode plate includes a positive current collector and a positive active material layer provided 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.

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

4. The wound cell according to claim 1, wherein The negative electrode plate includes a negative current collector and a negative active material layer provided on at least one surface of the negative current collector. The negative active material layer includes a negative active material, and the negative active material contains a silicon-carbon composite material.

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

6. The wound cell according to claim 1, wherein The electrolyte includes LiPF6 and an unsaturated nitrile additive. Based on the total mass of the electrolyte, the mass content of LiPF6 is c; Based on the total mass of the electrolyte, the mass content of the unsaturated nitrile additive is e; 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; and / or, the electrolyte includes LiPF6. Based on the total mass of the electrolyte, the mass content of LiPF6 is 10% - 20%; And / or, the electrolyte includes an unsaturated nitrile additive, and based on the total mass of the electrolyte, the mass content of the unsaturated nitrile additive is 0.1% - 5%; And / or, the heat-resistant layer includes heat-resistant particles, and the Dv10 of the heat-resistant particles is 0.05 μm - 0.3 μm.

7. The wound cell according to claim 6, wherein The unsaturated nitrile additive includes one or more of 1,4-dicyano-2-butene, acrylonitrile, crotonitrile, trans-butenedinitrile, and trans-hexenedinitrile; And / or, 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, alumina, barium sulfate, magnesia, magnesium hydroxide, silica, stannic oxide, titanium oxide, barium titanate, melamine cyanurate, 1,3,5-triazine-2,4,6-triamine, and melamine trithiocyanate; 8. The wound battery cell according to any one of claims 1-7, characterized in that, 1<a≤1.5； And / or, 0.8 ≤ H ≤ 4; And / or, 0.5 ≤ T ≤ 2; And / or, 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 base film is 28 nm - 45 nm; And / or, the aqueous polymer coating includes a blank part and a coated part, and the coated part includes polymer particles A; And / or, the oily coating includes filler particles and polymer B, and polymer B is non-granular.

9. The wound cell according to claim 8, wherein 1.1≤a≤1.5； And / or, based on the total surface area of one side surface of the heat-resistant layer, the projected area ratio of the coated part on the heat-resistant layer is 15% - 60%; And / or, the thickness of the coated part is 0.5 μm - 5 μm; 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 - 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, magnesia, magnesium hydroxide, silica, stannic oxide, titanium oxide, barium titanate, melamine cyanurate, 1,3,5-triazine-2,4,6-triamine, and melamine trithiocyanate; And / or, the polymer particles A include a first polymer, and the first polymer includes a polymer copolymerized from one or more monomers 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.

10. An electrochemical device, characterized in that, Including the wound battery cell according to any one of claims 1 - 9.

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