Electrode assemblies, secondary batteries, and power consumption devices

Abstract

This application relates to the field of battery technology, and more specifically to electrode assemblies, secondary batteries, and power consumption devices. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator. The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer located on at least one surface of the positive electrode current collector. The positive electrode film layer according to this application includes a nickel compound and a binder. Let Y be the molar percentage content of nickel relative to the total molar amount of transition elements in the nickel compound, and X be the mass percentage content of the binder in the positive electrode film layer, satisfying Y / X < 53. The electrode assembly designed in this application can improve the safety of lithium-ion batteries.

Description

[Technical Field]

[0001] Cross-reference of related applications This application claims priority to the Chinese patent application filed on 19 October 2023, application number 202311355800.0, titled "Electrode Assembly, Secondary Battery and Power Consumption Device," the entirety of which is incorporated herein by reference.

[0002] This application relates to the field of batteries, and more specifically to electrode assemblies, secondary batteries, and power consumption devices. [Background technology]

[0003] In recent years, secondary batteries have made remarkable progress, and the rapid development of pure electric new energy vehicles that use secondary batteries, particularly lithium-ion batteries, as their power unit has attracted particular attention.

[0004] As the range of applications for rechargeable batteries expands, the requirements for battery performance and the energy density of rechargeable batteries are becoming increasingly stringent. Consequently, safety issues are becoming particularly prominent. Currently, there is a need for further improvements in the safety of rechargeable batteries, particularly lithium-ion batteries. [Overview of the project]

[0005] In view of the above issues, this application provides an electrode assembly, a secondary battery, and a power consumption device that are advantageous for improving the safety of lithium-ion batteries.

[0006] According to a first aspect, the present application provides an electrode assembly, which is: A positive electrode sheet comprising a positive electrode current collector and a positive electrode film layer located on at least one surface of the positive electrode current collector, Negative electrode sheet and Includes a separator, The positive electrode film layer contains a nickel compound and a binder. Let the molar percentage content of nickel element relative to the total molar amount of transition elements in the nickel compound be Y, and the mass percentage content of the binder in the positive electrode film layer be X, satisfying Y / X < 53.

[0007] The binder contained in the positive electrode film layer according to the present application can improve the adhesion with the current collector. For example, in the cutting process of the positive electrode and the negative electrode, the probability of contact between the conductive layer and the negative electrode is reduced by the peeling of the positive electrode active material from the current collector, and further, the peeling amount of the active material in the cutting process of the positive electrode and the negative electrode is suppressed. On the other hand, when the content of the binder and the molar percentage content of the nickel element in the nickel compound satisfy the above relationship, the compatibility between the binder and the nickel-containing compound is enhanced, the resistance of the positive electrode film layer is increased, and finally, the resistance value at the time of short circuit due to contact is improved to reduce the failure probability of the battery. In summary, the electrode assembly designed in the present application can improve the safety of the lithium-ion battery while ensuring the energy density of the lithium-ion battery.

[0008] In some embodiments of the present application, the molar percentage content Y of the nickel element in the nickel compound and the mass percentage content X of the binder in the positive electrode film layer satisfy 3 ≤ Y / X < 53.

[0009] In some embodiments of the present application, the molar percentage content Y of the nickel element satisfies 30% ≤ Y ≤ 100%.

[0010] In some embodiments of the present application, the mass percentage content X of the binder in the positive electrode film layer satisfies 1% ≤ X ≤ 10%.

[0011] In some embodiments of the present application, the positive electrode film layer (1.1) When 80% ≤ Y ≤ 100%, it satisfies 8 ≤ Y / X ≤ 40, and (1.2) When 50% < Y < 80%, it satisfies 5 < Y / X < 53, and When 30% ≤ Y ≤ 50%, it satisfies any one of the following: 3 ≤ Y / X ≤ 50.

[0012] In some embodiments of the present application, the positive electrode film layer (2.1) When 80% ≤ Y ≤ 100%, 2.5% ≤ X ≤ 10%, (2.2) When 50% < Y < 80%, 1.5% ≤ X ≤ 10%, (2.3) When 30% ≤ Y ≤ 50%, 1% ≤ X ≤ 10%, and it satisfies any one of the above.

[0013] In some embodiments of the present application, when the tap density of the positive electrode sheet is 3.5 g / cm 3 In the case of (3.1) When 80% ≤ Y ≤ 100%, the resistance of the positive electrode sheet ≥ 1.81 mΩ, (3.2) When 50% < Y < 80%, the resistance of the positive electrode sheet ≥ 0.40 mΩ, (3.3) When 30% ≤ Y ≤ 50%, the resistance of the positive electrode sheet ≥ 0.30 mΩ, and it satisfies any one of the above.

[0014] In some embodiments of the present application, the negative electrode sheet includes a negative electrode current collector, and the positive electrode current collector and / or the negative electrode current collector is a composite current collector. The composite current collector includes a support layer and a conductive layer provided on at least one surface of the support layer, and the thickness of the conductive layer is not more than the thickness of the support layer.

[0015] In the electrode assembly according to the present application, the thickness of the support layer is not less than the thickness of the conductive layer, and the support layer is used to effectively support the conductive layer. Furthermore, the composite current collector composed of the support layer and the conductive layer can reduce the amount of burrs generated in the cutting process of the positive electrode and the negative electrode compared with the conventional metal current collector, and can reduce the short-circuit area.

[0016] In some embodiments of the present application, the thickness of the support layer and the molar percentage content of nickel element in the nickel compound Satisfy D1 ≥ Y × 10 + 2, D1 is the thickness of the support layer, and its unit is μm. Y represents the molar percentage content of nickel element in the nickel compound, expressed in %.

[0017] In some embodiments of the present application, the thickness of the support layer satisfies 2 μm ≤ D1 ≤ 30 μm, preferably 5 μm ≤ D1 ≤ 20 μm.

[0018] In some embodiments of this application, the thickness of the conductive layer is D2, satisfying D2 ≤ 3 μm, preferably 30 nm ≤ D2 ≤ 3 μm.

[0019] In some embodiments of the present application, the composite current collector further includes a protective layer located on at least one surface of the conductive layer.

[0020] In some embodiments of the present application, the thickness of the protective layer is D4, and the thickness of the conductive layer D2 satisfies the condition D4 ≤ 0.1 × D2. Preferably, satisfy 1nm ≤ D4 ≤ 200nm, More preferably, the conditions are met: 20nm ≤ D4 ≤ 150nm.

[0021] In some embodiments of the present application, the thickness of the positive electrode film layer is D3, and the relationship between D3 and the thickness of the support layer D1 satisfies 1 ≤ D3 / D1 ≤ 300.

[0022] In some embodiments of the present application, the thickness D3 of the positive electrode film layer satisfies 10 μm ≤ D3 ≤ 300 μm, and preferably 80 μm ≤ D3 ≤ 200 μm.

[0023] In some embodiments of the present application, the shrinkage rate of the separator at 130°C includes the MD shrinkage rate and the TD shrinkage rate. The MD shrinkage rate and / or TD shrinkage rate ≤ (13 - Y × 10) / 100, Y is the molar percentage content of the element nickel in the nickel compound, expressed as %, The MD shrinkage rate is the thermal shrinkage rate measured along the length of the separator. TD shrinkage rate is the thermal shrinkage rate measured along the width direction of the separator.

[0024] In some embodiments of the present application, the separator includes a base film and a coating layer provided on at least one surface of the base film. Preferably, the coating layer contains organic polymer fibers, and the organic polymer fibers include one or more combinations of aramid fibers, polyacrylonitrile fibers, polyimide fibers, polycarbonate fibers, polyphenylene sulfide fibers, polyetheretherketone fibers, polysulfone fibers, and polyarylate fibers.

[0025] In some embodiments of the present application, the nickel compound includes one or more combinations of lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and modified compounds thereof.

[0026] In some embodiments of the present application, the binder comprises a fluorine-containing polymer, the fluorine-containing polymer comprising one or more of the following: polyvinylidene fluoride, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, and fluorine-containing acrylate resin.

[0027] A second aspect of the present application provides a secondary battery including the electrode assembly described in the first aspect.

[0028] A third aspect of the present application provides a power consumption device including the electrode assembly described in the first aspect or the secondary battery described in the second aspect.

[0029] The above description is merely an outline of the technical solution of this application. In order to understand the technical solution of this application more clearly, and to enable a clearer understanding of the above and other objectives, features, and advantages of this application, specific embodiments of this application are given below, which can be implemented in accordance with the contents of the specification. [Brief explanation of the drawing]

[0030] For those skilled in the art, various other advantages and effects will become clear by reading the detailed description of the preferred embodiments below. The drawings are intended to illustrate preferred embodiments and should not be considered limiting to the present application. In all drawings, the same components are referred to by the same reference numerals. The drawings are as follows:

[0031] [Figure 1] This is a schematic diagram of a lithium-ion battery according to some embodiments of the present invention. [Figure 2] This is a schematic diagram of the disassembled structure of a lithium-ion battery according to some embodiments of the present invention. [Figure 3] This is a schematic diagram of a positive electrode sheet according to several embodiments of the present application. [Figure 4] This is a schematic diagram of a positive electrode sheet according to several embodiments of the present application. [Figure 5] This is a schematic diagram of a positive electrode sheet according to several embodiments of the present application. [Figure 6] This is a schematic diagram of a negative electrode sheet according to some embodiments of the present application. [Figure 7] This is a schematic diagram of a resistance test of a positive electrode film layer according to several embodiments of the present application. (Explanation of symbols)

[0032] 5. Lithium-ion battery 51. Housing 52. Electrode Assembly 53. Cover plate 100, Positive electrode sheet 110, positive electrode current collector 120, Positive electrode film layer 111, 1st support layer 112, First conductive layer 113, 1st protective layer 200, negative electrode sheet 210, negative electrode current collector 220, Negative electrode film layer 211, second support layer 212, Second conductive layer Coordinate axis x direction: direction of the negative electrode current collector Coordinate axis y direction: direction of the thickness of the negative electrode current collector [Modes for carrying out the invention]

[0033] The embodiments of the electrode assembly, secondary battery, and power consumption device specifically disclosed herein will be described in detail below, with appropriate reference to the drawings. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters or redundant descriptions of substantially identical structures may be omitted. This is to avoid unnecessarily verbose descriptions and to facilitate understanding for those skilled in the art. Furthermore, the drawings and the following descriptions are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter described in the claims.

[0034] The “range” disclosed herein is defined in the form of a lower and upper limit, and a given range is defined by selecting one lower limit and one upper limit, the selected lower and upper limits defining the boundaries of a particular range. Ranges defined in this manner may or may not include the values ​​at both ends and can be combined in any way, that is, any lower limit can be combined with any upper limit to form a range. For example, if the ranges 60-120 and 80-110 are listed for a particular parameter, it is understood that the ranges 60-110 and 80-120 are also expected. Similarly, if the minimum range values ​​1 and 2 are listed, and the maximum range values ​​3, 4 and 5 are listed, the ranges 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5 are all intended. In this application, unless otherwise specified, the numerical range “a-b” means an abbreviated expression for any combination of real numbers between a and b, where both a and b are real numbers. For example, the numerical range "0 to 5" means that all real numbers between "0 to 5" are listed in this specification, and "0 to 5" is merely an abbreviated expression for combinations of these numbers. Also, when a parameter is described as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0035] All embodiments and optional embodiments of this application can be combined to form new technical solutions unless otherwise specified.

[0036] All of the technical features and selectable technical features of this application can be combined to form new technical solutions, unless otherwise specified.

[0037] All steps of the present application may be performed sequentially or randomly unless otherwise specified, preferably in order. For example, if the method includes steps (a) and (b), it indicates that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, if the method mentioned above may further include step (c), it indicates that step (c) may be added to the method in any order, for example, that the method may include steps (a), (b), and (c), or steps (a), (c), and (b), or steps (c), (a), and (b).

[0038] As used herein, “includes” and “inclusive” refer to both open and closed forms unless otherwise specified. For example, “includes” and “inclusive” may include or include other components not listed, or may include or include only the listed components.

[0039] In this application, unless otherwise specified, the term “or” is inclusive. For example, the phrase “A or B” means “A, B, or both A and B.” More specifically, the condition “A or B” is satisfied by either A being true (or existing) and B being false (or not existing), A being false (or not existing) and B being true (or existing), or both A and B being true (or existing).

[0040] Unless otherwise specified, terms such as "first," "second," etc., in this application are merely used to distinguish different subjects and should not be understood as implicitly indicating the quantity, specific order, or hierarchical relationship of technical features that show, suggest, or demonstrate relative importance.

[0041] Unless otherwise specified, in this application the term "multiple" refers to two or more (including two), similarly "multiple sets" refers to two or more sets (including two sets), and "multiple sheets" refers to two or more sheets (including two sheets).

[0042] Unless otherwise specified, the directions or positional relationships indicated by terms such as "center," "vertical direction," "horizontal direction," "length," "width," "thickness," "top," "bottom," "front," "back," "left," "right," "vertical," "horizontal," "upper part," "bottom," "inside," "outside," "clockwise," "counterclockwise," "axial direction," "radial direction," and "circumferential direction" in this application are merely for the purpose of simplifying the explanation and making it easier to describe the embodiments of this application, based on the directions or positional relationships shown in the drawings. They do not indicate or imply that the device or element in question has a specific direction, or that it should be composed of and operated in a specific direction, and therefore should not be understood as limiting the embodiments of this application.

[0043] Unless otherwise specified and explicitly defined, terms such as “attached,” “connected,” “bonded,” and “fixed” should be understood in a broad sense. For example, they may be fixed connections, detachable connections, or integral connections. They may be mechanical connections or electrical connections. They may be directly connected, indirectly connected via an intermediate medium, or be internal communication between two elements or an interaction relationship between two components. Those skilled in the art will be able to understand the specific meaning of the above terms in the embodiments of this application, depending on the specific circumstances.

[0044] As the range of applications for secondary batteries expands, the requirements for battery performance and the energy density of secondary batteries are also increasing. Consequently, safety issues are becoming particularly prominent. Taking lithium-ion batteries as an example, there are numerous factors that affect their safety risks. In general, these factors mainly consist of three types: mechanical abuse, electrical abuse, and thermal abuse. These manifest mainly as abnormal currents and side reactions occurring inside the battery due to mechanical and electrical abuse, causing abnormal temperature increases inside, and ultimately leading to thermal runaway, explosion, or fire.

[0045] Research has shown that in lithium-ion batteries containing nickel compounds in the positive electrode material, cations (Li) are released during the actual charge and discharge process. 2+ / Ni3+ It has become clear that the presence of these impurities is likely to occur, affecting the structural stability of the material. Furthermore, this phenomenon becomes more pronounced as the nickel content increases, and the safety issues associated with improved conductivity become even more serious.

[0046] Conventional technologies primarily improve battery safety through improvements to the materials themselves or battery components, but such improvements usually take a long time.

[0047] The causes of lithium-ion battery failure are nothing more than internal short circuits, high temperatures, and overvoltage. Focusing on the causes of failure is advantageous in improving the safety of lithium-ion batteries.

[0048] Based on the above, in order to solve the problem of current lithium-ion batteries, which have high energy density but cannot achieve safety, we conducted experimental studies based on the above design philosophy and obtained an electrode assembly, a secondary battery, and a power consumption device.

[0049] First, the present invention provides an electrode assembly comprising a positive electrode sheet, a negative electrode sheet, and a separator, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer located on at least one surface of the positive electrode current collector, and the positive electrode film layer according to the present invention comprises a nickel compound and a binder, wherein Y is the molar percentage content of nickel element relative to the total molar amount of transition elements in the nickel compound, and X is the mass percentage content of the binder in the positive electrode film layer, satisfying Y / X < 53.

[0050] The binder contained in the positive electrode film layer according to this application can improve adhesion to the current collector, for example, reducing the probability of contact between the conductive layer and the negative electrode due to the peeling of the positive electrode active material from the current collector during the cutting process of the positive and negative electrodes, and further suppressing the amount of peeling of the positive electrode active material during the cutting process of the positive and negative electrodes. On the other hand, the binder content and the molar percentage content of nickel element in the nickel compound satisfy the above relationship, and by appropriately combining the binder content and the nickel compound content based on this relationship, the resistance of the positive electrode film layer can be increased, and as the resistance value increases, the probability of battery failure can be reduced even if the positive and negative electrodes come into contact. In summary, the electrode assembly designed in this application can improve the safety of the lithium-ion battery while ensuring the energy density of the lithium-ion battery.

[0051] The electrode assembly provided in this application has not only a certain energy density but also a certain safety factor, and the electrode assembly is manufactured into a secondary battery. The secondary battery may include an outer casing. The outer casing is used to enclose the electrode assembly and electrolyte. The outer casing of the secondary battery may be a hard case such as a rigid plastic case, an aluminum case, or a steel case. The outer casing of the secondary battery may also be a soft pack such as a pouch-type soft pack. The material of the soft pack may be plastic, and examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0052] This invention does not particularly limit the shape of the secondary battery, and it may be cylindrical, prismatic, or any other shape. For example, Figure 1 shows a prismatic lithium-ion battery 5 as an example.

[0053] In some embodiments relating to the present invention, referring to Figure 2, the exterior material may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, forming a housing cavity enclosed by the bottom plate and side plates. The housing 51 has an opening that communicates with the housing cavity, and the cover plate 53 can be placed over the opening to seal the housing cavity. The positive electrode sheet, negative electrode sheet and separator can form an electrode assembly 52 via a winding process or a lamination process. The electrode assembly 52 is sealed within the housing cavity. The electrolyte is impregnated into the electrode assembly 52. ​​The number of electrode assemblies 52 included in the lithium-ion battery 5 may be one or more, and a person skilled in the art can select according to the specific practical requirements.

[0054] In some embodiments relating to the present invention, secondary batteries are applied to power consumption devices. These secondary batteries are applied to power consumption devices such as vehicles, ships, or aircraft, but are not limited to these. Furthermore, by applying these power consumption devices to a power supply system, the technical objective of improving safety can be achieved.

[0055] The embodiment of the present invention provides a power consumption device that uses a secondary battery as a power source. The power consumption device includes, but is not limited to, mobile phones, tablets, laptop computers, electric toys, power tools, battery cars, electric vehicles, ships, spacecraft, etc. Electric toys may include stationary or mobile electric toys such as game consoles, electric car toys, electric boat toys, and electric aircraft toys, and spacecraft may include aircraft, rockets, space shuttles, and spacecraft, etc.

[0056] Electrode assembly This application provides an electrode assembly comprising a positive electrode sheet, a negative electrode sheet, and a separator, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer located on at least one surface of the positive electrode current collector, and the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer. The positive electrode film layer comprises a nickel compound and a binder, where Y is the molar percentage content of nickel element relative to the total molar amount of transition elements in the nickel compound, and X is the mass percentage content of the binder in the positive electrode film layer, satisfying Y / X < 53.

[0057] The positive electrode film layer according to this application contains a binder and a nickel compound. The nickel compound, as the main positive electrode active material, has the effect of increasing the energy density of the battery as the nickel content increases. However, with the improvement of internal conductivity, cations (Li) are produced during the charge and discharge process. 2+ / Ni 3+ The probability of the mixture of ) increases, and the probability of battery failure also increases. In this application, "failure" includes ignition, explosion, etc., due to factors such as short circuits. The binder contained in the positive electrode film layer can improve adhesion to the current collector, for example, in the cutting process of the positive and negative electrodes, it reduces the probability of the conductive layer and the negative electrode coming into contact due to the peeling of the positive electrode active material from the current collector, and further suppresses the amount of peeling of the positive electrode active material in the cutting process of the positive and negative electrodes.

[0058] In this application, the molar percentage content of nickel in a nickel compound is calculated based on the total molar amount of transition elements in the nickel compound. For example, the molar percentage content of nickel in NCM811 is 80%. Also, for example, the molar percentage content of nickel in LiNiO2 is 100%.

[0059] As an option in this application, the binder content and the molar percentage content of nickel element in the nickel compound satisfy the above relationship. By appropriately combining the binder content and the nickel compound content based on this relationship, the resistance of the positive electrode film layer can be increased, and as the resistance value increases, the probability of battery failure can be reduced even when the positive and negative electrodes are in contact. In summary, the electrode assembly designed in this application can improve the safety of lithium-ion batteries while ensuring the energy density of the lithium-ion battery.

[0060] According to some embodiments of the present invention, the molar percentage content Y of the nickel element and the mass percentage content X of the binder in the positive electrode film layer satisfy 3 ≤ Y / X < 53.

[0061] In this application, since the safety requirements for nickel compounds differ for each electrode assembly, the requirements for binder content and type also differ according to the safety requirements. Furthermore, the type and content of the binder affect other performance aspects of the electrode assembly, such as energy density. In this application, by controlling the molar percentage content Y of the nickel element and the mass percentage content X of the binder in the positive electrode film layer to satisfy 3 ≤ Y / X < 53, it is possible to effectively improve the safety of the lithium-ion battery while ensuring the energy density of the lithium-ion battery.

[0062] Positive electrode film layer According to some embodiments of the present invention, the positive electrode film layer in the electrode assembly according to the present invention contains a nickel compound, where the molar percentage content Y of the nickel element in the nickel compound satisfies 30% ≤ Y ≤ 100%.

[0063] In this invention, nickel compounds, as the main positive electrode active material, have the effect of increasing the energy density of the battery as the nickel content increases. However, with the improvement of internal conductivity, cations (Li) are produced during the charge and discharge process. 1+ / Ni 3+) is likely to occur, increasing the probability of battery failure. Therefore, in this application, the safety of the electrode assembly with the molar percentage content of nickel element in the range of 30% to 100% was mainly considered.

[0064] According to some embodiments of the present application, the nickel compound contained in the positive electrode film layer includes one or a combination of two or more of lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide and its modified compounds.

[0065] The modified compounds according to the present application include any modifications such as physical modifications and chemical modifications commonly performed in this field, and the modifications commonly performed in this field include doping and the like.

[0066] In the present application, lithium nickel oxide includes but is not limited to LiNiO2, lithium nickel cobalt oxide includes but is not limited to LiNi 0.8 Co 0.2 O2, lithium nickel manganese oxide includes but is not limited to LiNi 0.5 Mn 0.5 O2, lithium nickel cobalt manganese oxide includes but is not limited to LiNi x Co y Mn z O2 (x = 0.3 to 0.92, y = 0.03 to 0.4, z = 0.05 to 0.4), and specifically, for example, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), LiNi[[ID=5l]] 0.9 Co 0.05 Mn 0.05It contains one or more types of O2, and lithium nickel cobalt aluminum oxide is LiNi x Co y Al z O2 (x=0.3~0.92, y=0.03~0.4, z=0.05~0.4):LiNi 1 / 3 Co 1 / 3 Al 1 / 3 O2(NCA333), LiNi 0.5 Co 0.2 Al 0.3 O2 (NCA523), LiNi 0.6 Co 0.2 Al 0.2 O2 (NCA622), LiNi 0.8 Co 0.1 Al 0.1 O2 (NCA811), LiNi 0.9 Co 0.05 Al 0.05 It contains, but is not limited to, at least one of the O2 species.

[0067] The nickel compounds related to this invention, as the main positive electrode active material, have the effect of increasing the energy density of the battery as the nickel content increases. However, while increasing the nickel content brings the advantage of improved electrode conductivity, it also increases the probability of the two electrodes coming into contact and causing a short circuit during the cutting process of the positive and negative electrodes. In this invention, these various factors are comprehensively considered and the type of nickel compound is rationally optimized and selected.

[0068] According to some embodiments of the present application, the mass percentage content X of the binder in the positive electrode film layer satisfies 1% ≤ X ≤ 10%. In some embodiments of the present application, the mass percentage content X of the binder in the positive electrode film layer may be any one of 1%, 2%, 3%, 4%, 4.5%, 5%, 6%, 7%, 8%, 9%, or 10%, or it may satisfy any of the range values ​​or a specific numerical value.

[0069] In some embodiments of the present application, the binder includes a fluorine-containing polymer, and the fluorine-containing polymer includes one or a combination of two or more of polyvinylidene fluoride, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, and fluorine-containing acrylate resin.

[0070] In the present application, a fluorine-containing polymer is selected as the binder. The fluorine-containing polymer can improve the adhesion to the current collector. On the other hand, there is a correlation between the conductivity of the fluorine-containing polymer and its content. In the present application, the influence on the resistance of the positive electrode film layer when using polyvinylidene fluoride as the fluorine-containing polymer was mainly investigated. For example, by combining a certain amount of polyvinylidene fluoride with specific types of nickel compounds, the resistance of the polar sheet can be increased, and the resistance of the contact short circuit can be increased, thereby reducing the failure probability. In addition, one or two or more of vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, and fluorine-containing acrylate resin can also meet the requirements for the fluorine-containing polymer of the present application.

[0071] In the present application, by selecting an appropriate type of nickel compound and combining it with the usage amount of the binder, the resistance of the positive electrode film layer is appropriately increased, and the resistance during contact short circuit in the cutting process of the positive electrode and the negative electrode is improved.

[0072] According to some embodiments of the present application, the positive electrode film layer satisfies any one of the following.

[0073] (1.1) When the molar percentage content of nickel element in the nickel compound is 80% ≤ Y ≤ 100%, 8 ≤ Y / X ≤ 40 is satisfied.

[0074] (1.2) When the molar percentage content of nickel element in the nickel compound is 50% < Y < 80%, 5 < Y / X < 53 is satisfied.

[0075] When the molar percentage content of nickel element in the nickel compound is 30% ≤ Y ≤ 50%, 3 ≤ Y / X ≤ 50 is satisfied.

[0076] In the present application, since the influence on the resistance value of the positive electrode film layer varies depending on the type of nickel compound, the requirements for the content of the binder also differ accordingly. In the present application, the change range of the molar percentage content of nickel element is divided into three steps in descending order, and different intervals of Y / X ratio are corresponding to each step. Considering the molar percentage content of nickel element in the nickel compound, it is possible to select an optimal binder content according to an appropriate Y / X ratio, and by matching the content of the binder with the molar percentage content of nickel element in the nickel compound, the resistance of the positive electrode film layer can be increased, and finally the resistance at the time of contact short circuit can be increased to reduce the failure probability of the battery.

[0077] According to some embodiments of the present application, the positive electrode film layer satisfies any one of the following.

[0078] When the molar percentage content of nickel element in the nickel compound is 80% ≤ Y ≤ 100%, the mass percentage content of the binder in the positive electrode film layer satisfies 2.5% ≤ X ≤ 10%.

[0079] When the molar percentage content of nickel element in the nickel compound is 50% < Y < 80%, the mass percentage content of the binder in the positive electrode film layer satisfies 1.5% ≤ X ≤ 10%.

[0080] When the molar percentage content of nickel element in the nickel compound is 30% ≤ Y ≤ 50%, the mass percentage content of the binder in the positive electrode film layer satisfies 1% ≤ X ≤ 10%.

[0081] In this application, the main purposes of limiting the amount of binder used are twofold: 1. To increase the resistance of the film in the positive electrode sheet. 2. To improve the adhesion between the positive electrode active material and other materials. Since each material has a different particle size, there are significant differences in thermal stability. Therefore, the amount of binder used to achieve both high resistance and excellent adhesion will differ, and PVDF-based binders were considered as additives for the positive electrode sheet.

[0082] The powder resistivity of positive electrode active materials varies depending on the material; for example, in NCM systems, the higher the Ni content, the lower the short-circuit resistance. Therefore, to improve short-circuit resistance, it is necessary to increase the non-conductive binder content in the positive electrode sheet, which can increase the failure resistance during a contact short circuit.

[0083] In this invention, since the effect on the resistance value of the positive electrode film layer differs depending on the type of nickel compound, the requirements for the binder also differ accordingly. In this invention, by combining an appropriate type of nickel compound with an appropriate binder content, the resistance of the polar sheet is increased, the resistance during a contact short circuit is increased, and thereby the probability of failure is reduced.

[0084] According to some embodiments of the present invention, the sum of the mass of the fluorine-containing polymer and the mass of the nickel compound is 90% or more of the total weight of the positive electrode film layer.

[0085] According to some embodiments of the present application, the positive electrode film layer further includes a conductive agent and a dispersant. The conductive agent includes, but is not limited to, one or more combinations of graphite, superconducting carbon, carbon black (e.g., acetylene black, Ketjen black, Super P, etc.), carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The dispersant includes cellulose and its salts, specifically methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, sodium carboxymethylcellulose, lithium carboxymethylcellulose, etc.

[0086] Negative electrode film layer According to some embodiments of the present invention, the negative electrode film layer in the negative electrode sheet includes a negative electrode active material, a binder, a conductive agent, and a dispersant, and the negative electrode active material includes a carbon-based material, and the carbon-based material includes one or more combinations of artificial graphite, natural graphite, soft carbon, and hard carbon. Artificial graphite, natural graphite, soft carbon, hard carbon, etc., include any form of material commonly used in the art, and include any manufacturer and model number commonly supplied in the art. The negative electrode active material may also include a silicon-based material, and the silicon-based material includes one or two types of silicon oxide material or silicon-carbon material. In addition, the negative electrode active material may further include silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, and TiO2-Li4Ti5O 12 This may include Li-Al alloys. However, the present invention is not limited to these materials, and other conventional materials usable as negative electrode active materials for lithium-ion batteries may be used. These negative electrode active materials may be used individually or in combination of two or more types. The types of binder, conductive agent, and dispersant in the negative electrode sheet may be the same as those in the positive electrode sheet.

[0087] Current collector According to some embodiments of the present invention, in an electrode assembly provided by the present invention, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer located on at least one surface of the positive electrode current collector, and the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector. The positive electrode current collector and / or negative electrode current collector is a composite current collector, the composite current collector includes a support layer and a conductive layer provided on at least one surface of the support layer, the positive electrode film layer is located on one surface of the conductive layer away from the support layer, and the thickness of the support layer is equal to or greater than the thickness of the conductive layer.

[0088] In this application, "and / or" means that at least one of the positive electrode current collector and the negative electrode current collector is a composite current collector, and "composite" means that the current collector has a structure of two or more layers, and each layer is integrated by any composite method commonly used in the art, such as bonding, coating, or deposition. Compared to conventional metal current collectors (e.g., aluminum foil or copper foil), composite current collectors have lower thermal conductivity, and when cutting a composite current collector, the amount of burrs generated on the positive and negative electrodes during the cutting process can be reduced, which is advantageous in reducing the short-circuit area and improving the safety of the electrode assembly.

[0089] According to some embodiments of the present application, the present application provides an electrode assembly comprising a positive electrode sheet, a negative electrode sheet, and a separator, and as shown in Figure 3, the positive electrode sheet 100 comprises a positive electrode current collector 110 and a positive electrode film layer 120 located on at least one surface of the positive electrode current collector 110, and "at least one surface" includes one surface, both surfaces or more. Figure 3 of the present application shows a schematic of one side. As shown in Figure 4, the positive electrode current collector 110 comprises a first support layer 111 and a first conductive layer 112 provided on at least one surface of the first support layer 111, and similarly, "at least one surface" includes one surface, both surfaces or more. Figure 4 of the present application shows a schematic of one side. Furthermore, the positive electrode film layer 120 is located on one surface of the first conductive layer 112 that is away from the first support layer 111.

[0090] According to some embodiments of the present invention, as shown in Figure 5, the positive electrode current collector 110 further includes a first protective layer 113, the first protective layer 113 located on one side of the surface of the first conductive layer 112.

[0091] As shown in Figure 6, the negative electrode sheet 200 includes a negative electrode current collector 210 and a negative electrode film layer 220. The negative electrode current collector 210 includes a second support layer 211 and a second conductive layer 212 provided on at least one surface of the second support layer 211. Similarly, "at least one surface" includes one surface, both surfaces or more. Figure 6 in this application shows a schematic of one side. The negative electrode current collector 210 may further include a second protective layer, which is located on one surface of the second conductive layer and is not shown in this application.

[0092] In this application, the thickness of each layer of the composite current collector refers to the distance from one end face to the opposite end face along the thickness direction of the current collector (the y-direction of the coordinate axis in Figures 3 to 6). The specific numerical value can be obtained by measurement. For example, it can be obtained by measuring the thickness in the front-to-back direction using a micrometer and then calculating the difference between the front and back. Alternatively, it can be obtained by photographing a cross-sectional sample cut in the thickness direction of the current collector using a scanning electron microscope and measuring on the resulting image.

[0093] In this invention, the support layer in the composite current collector can perform a support function as the current collector body itself, which is advantageous in ensuring the overall strength of the composite current collector. The support layer may be a single-layer structure or a composite layer structure of two or more layers. The support layer includes an organic support layer, and by using an organic material for the organic support layer, the thermal conductivity of the composite current collector is reduced.

[0094] The conductive layer relating to this application is used to achieve the purposes of conductivity and current collection.

[0095] The thickness of the support layer in this invention is greater than or equal to the thickness of the conductive layer, and the support layer is used to effectively support the conductive layer. Furthermore, compared to conventional metal current collectors, the composite current collector consisting of the support layer and the conductive layer can reduce the amount of burrs generated in the cutting process of the positive and negative electrodes, thereby reducing the short-circuit area.

[0096] According to several embodiments of the present invention, the positive electrode current collector is a composite current collector, and the negative electrode current collector is a general metal foil. Compared to conventional secondary batteries in which the positive electrode current collector is metal foil, the safety is improved.

[0097] According to several embodiments of this application, both the positive electrode current collector and the negative electrode current collector are composite current collectors. The safety of the secondary battery is further improved.

[0098] According to some embodiments of the present invention, the thickness of the support layer is greater than that of conventional metal current collectors such as aluminum foil or copper foil, and the probability of the positive electrode and negative electrode coming into contact during the cutting process and causing a short circuit can be effectively reduced.

[0099] According to some embodiments of the present invention, the thickness of the support layer and the molar percentage content of nickel element in the nickel compound satisfy a certain mathematical relationship. For example, D1≧Y×10+2 Formula (X) D1 is the thickness of the support layer, and its unit is μm. Y represents the molar percentage content of nickel element in the nickel compound, expressed in %.

[0100] Figure 5 shows the thickness D1 of the support layer according to the present invention. In this invention, the lower limit of the support layer thickness can be selected based on the molar percentage content of nickel element in the nickel compound. If the thickness is greater than or equal to this lower limit, the probability of the positive electrode and negative electrode coming into contact during the cutting process and causing a short circuit can be effectively reduced.

[0101] In some embodiments of the present application, the specific values ​​of the thickness of the support layer for the positive electrode film layer are mainly examined, and similarly, the thickness of the support layer for the negative electrode film layer also satisfies the same relationship and value.

[0102] According to some embodiments of the present application, the thickness of the support layer satisfies 2 μm ≤ D1 ≤ 30 μm.

[0103] According to some embodiments of the present application, the thickness of the support layer satisfies 5 μm ≤ D1 ≤ 20 μm.

[0104] According to some embodiments of the present invention, the thickness of the conductive layer is thinner than that of conventional metal current collectors such as aluminum foil or copper foil, which reduces the amount of burrs generated in the cutting process of the positive and negative electrodes and reduces the short-circuit area.

[0105] According to some embodiments of the present application, the thickness of the conductive layer is D2, and D2 ≤ 3 μm is satisfied.

[0106] Figure 5 shows the thickness D2 of the conductive layer in this application.

[0107] According to some embodiments of the present application, the thickness D2 of the conductive layer satisfies 30 nm ≤ D2 ≤ 3 μm.

[0108] In this application, the thickness of the conductive layer can be any one of 30 nm, 50 nm, 80 nm, 100 nm, 200 nm, 500 nm, 1 μm, 2 μm, or 3 μm, any range within this range, or any specific value. By using a conductive layer thickness within this range, the amount of burrs generated during the cutting process of the positive and negative electrodes can be reduced, thereby reducing the short-circuit area.

[0109] In some embodiments of the present invention, the thickness of the support layer is less than or equal to the thickness of the positive electrode film layer. In this invention, particular attention was paid to ensuring that the thickness of the first support layer in the positive electrode current collector is less than or equal to the thickness of the positive electrode film layer. In this invention, by selecting that the thickness of the first support layer is less than or equal to the thickness of the positive electrode film layer, the first support layer performs its support function without affecting the normal operation of the positive electrode film layer, and is also advantageous in improving the safety and energy density of the battery.

[0110] According to some embodiments of the present invention, the thickness of the first support layer (support layer) is D1, the thickness of the positive electrode film layer is D3, and the equation (XI) 1 ≤ D3 / D1 ≤ 300 is satisfied.

[0111] Figure 5 shows the thickness D3 of the positive electrode film layer in this application.

[0112] In this application, the relationship between the thickness of the first support layer and the thickness of the positive electrode film layer is specifically defined. When this relationship is satisfied, it does not affect the normal operation of the positive electrode film layer and is also advantageous in improving the safety and energy density of the battery.

[0113] According to some embodiments of the present application, the thickness D1 of the first support layer satisfies 2 μm ≤ D1 ≤ 30 μm.

[0114] According to some embodiments of the present application, the thickness D1 of the first support layer satisfies 5 μm ≤ D1 ≤ 20 μm.

[0115] In this application, the thickness of the first support layer can be any one of 2 μm, 5 μm, 8 μm, 10 μm, 15 μm, 20 μm, or 30 μm, any range within that range, or any specific value. The thickness of the support layer within this range can effectively reduce the probability of the positive and negative electrodes coming into contact during the cutting process and causing a short circuit.

[0116] In this application, the thickness of the second support layer is also within the range of 2 μm to 30 μm, for example, the thickness of the second support layer is made equal to the thickness of the first support layer.

[0117] According to some embodiments of the present application, the thickness D3 of the positive electrode film layer satisfies 10 μm ≤ D3 ≤ 300 μm.

[0118] According to some embodiments of the present application, the thickness D3 of the positive electrode film layer satisfies 80 μm ≤ D3 ≤ 200 μm.

[0119] In this application, the thickness of the positive electrode film layer can be any one of 10 μm, 20 μm, 30 μm, 50 μm, 80 μm, 100 μm, 200 μm, or 300 μm, any range within that range, or any specific value. A positive electrode film layer within this range is advantageous for improving the safety and energy density of the battery.

[0120] According to some embodiments of the present invention, the positive electrode current collector further includes a first protective layer, the first protective layer is located between the positive electrode film layer and the conductive layer, and the thickness of the first protective layer is D4.

[0121] Figure 5 shows the thickness D4 of the first protective layer relating to this application.

[0122] In this application, the first protective layer reduces the degree of damage the conductive layer sustains during the cutting process and further reduces the short-circuit area.

[0123] According to some embodiments of the present invention, the thickness D4 of the first protective layer and the thickness D2 of the conductive layer satisfy equation (XII) D4 ≤ 0.1 × D2.

[0124] The thickness of the first protective layer in this application satisfying the said relation is advantageous for protecting the conductive layer.

[0125] According to some embodiments of the present application, the thickness D4 of the first protective layer satisfies the condition 1 nm ≤ D4 ≤ 200 nm.

[0126] According to some embodiments of the present application, the thickness D4 of the first protective layer satisfies the condition 20 nm ≤ D4 ≤ 150 nm.

[0127] The thickness of the first protective layer in this application can be any one of 1 nm, 5 nm, 10 nm, 20 nm, 50 nm, 100 nm, 150 nm, or 200 nm, any range within that range, or any specific value. A thickness of the first protective layer within this range is advantageous for protecting the conductive layer.

[0128] The negative electrode current collector relating to this application may also include a second protective layer, and the thickness of the second protective layer is within the range of 1 nm to 200 nm. For example, the thickness of the second protective layer may be equal to the thickness of the first protective layer.

[0129] In this invention, the support layer in the composite current collector can perform a support function as the current collector body itself, which is advantageous in ensuring the overall strength of the composite current collector. The support layer may be a single-layer structure or a composite layer structure of two or more layers. The support layer includes an organic support layer, and by using an organic material for the organic support layer, the thermal conductivity of the composite current collector is reduced. The material of the organic support layer includes one or two types of polymer materials and polymer-based composite materials, wherein the polymer material includes one or more types from among polyamide, polyimide, polyethylene terephthalate, polybutylene terephthalate, polynaphthalenedicarboxylate ethylene glycol ester, polycarbonate, polyethylene, polypropylene, polybutene, acrylonitrile-butadiene-styrene copolymer, polyvinyl alcohol, polystyrene, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, sodium polystyrene sulfonate, polyethylene block, silicone rubber, polyacetal, polyphenylene ether, polyphenylene sulfide, polyethylene glycol, sulfur nitrogen polymer, polyphenylene, polypyrrole, polyaniline, polythiophene, polypyridine, cellulose, starch, protein, epoxy resin, phenolic resin, and their derivatives, crosslinks, and copolymers. The polymer-based composite material includes the above polymer material and additives, wherein the additives include one or more types from among metallic materials and inorganic nonmetallic materials. Metallic materials include one or more of the following: aluminum, aluminum alloys, copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, iron, iron alloys, silver, and silver alloys. Inorganic nonmetallic materials include one or more of the following: carbon-based materials, aluminum oxide, silicon dioxide, silicon nitride, silicon carbide, boron nitride, silicates, iron oxides, glass materials, ceramic materials, and ceramic composite materials. Carbon-based materials include one or more of the following: graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. As the above additives, carbon-based materials coated with metallic materials may also be used, for example, one or more of the following: nickel-coated graphite powder or nickel-coated carbon fibers.

[0130] The conductive layer according to this application is used to achieve the purposes of conductivity and current collection. The conductive layer includes one or more types of materials selected from metallic materials, carbon-based conductive materials, and conductive polymer materials. Metallic materials may include one or more types selected from aluminum, aluminum alloys, copper, copper alloys, nickel, nickel alloys, iron, iron alloys, titanium, titanium alloys, silver, and silver alloys. Carbon-based conductive materials may include one or more types selected from graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. Conductive polymer materials may include one or more types selected from polysulfide nitrogen-based compounds, aliphatic conjugated polymers, aromatic ring conjugated polymers, and aromatic heteroring conjugated polymers. As an example, conductive polymer materials may include one or more types selected from polyphenylene, polypyrrole, polyacetylene, polystyrene rubber, polythiophene, and polypyridine. Furthermore, conductivity can be improved by increasing the electron delocalization of the conductive polymer material through doping.

[0131] In this application, the protective layer is primarily used to reduce the probability of chemical corrosion or mechanical damage to the conductive layer. The protective layer includes one or more of the following: metal, metal oxide, and conductive carbon. The metal includes, for example, one or more of the following: nickel, chromium, nickel-based alloy, and copper-based alloy. The nickel-based alloy is an alloy composed of pure nickel as a base with the addition of one or more other elements, and is preferably a nickel-chromium alloy. The nickel-chromium alloy is an alloy composed of metallic nickel and metallic chromium, and optionally, the weight ratio of nickel to chromium in the nickel-chromium alloy can be 1:99 to 99:1 (e.g., 9:1). The copper-based alloy is an alloy composed of pure copper as a base with the addition of one or more other elements, and is preferably a nickel-copper alloy. Optionally, the weight ratio of nickel to copper in the nickel-copper alloy can be 1:99 to 99:1 (e.g., 9:1). The metal oxide is, for example, one or more of the following: aluminum oxide, cobalt oxide, chromium oxide, and nickel oxide. The conductive carbon mentioned above is, for example, one or more of the following: graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers, and furthermore, one or more of the following: carbon black, carbon nanotubes, and graphene.

[0132] Separator According to several embodiments of the present invention, heat is generated during the cutting process of the positive and negative electrodes, and this heat affects the shrinkage of the separator. The smaller the effect on the shrinkage rate of the separator, the smaller the short-circuit contact area between the positive and negative electrodes caused by the shrinkage of the separator during the cutting process. Since heat correlates with the positive electrode active material, the present invention establishes a mathematical relationship between the shrinkage rate of the separator and the molar percentage content of nickel element in the nickel compound.

[0133] MD shrinkage rate and / or TD shrinkage rate ≤ (13 - Y × 10) / 100 Equation (XIII) Here, the shrinkage rate of the separator at 130°C includes the MD shrinkage rate and the TD shrinkage rate. Y is the molar percentage content of the element nickel in the nickel compound, expressed as %, The MD shrinkage rate is the thermal shrinkage rate measured along the length of the separator. TD shrinkage rate is the thermal shrinkage rate measured along the width direction of the separator.

[0134] The shrinkage rate of the separator according to this application at 130°C can be obtained by direct measurement and calculation.

[0135] The separator of the present invention is advantageous in reducing the shrinkage rate after heating and reducing the short-circuit contact area between the positive and negative electrodes caused by the shrinkage of the separator during the cutting process.

[0136] According to some embodiments of the present invention, the separator includes a base film and a coating layer provided on at least one surface of the base film.

[0137] According to some embodiments of the present application, the base film includes, but is not limited to, one of the following: polyethylene film, polypropylene film, polypropylene / polyethylene / polypropylene composite film, polyvinylidene fluoride film, polyethylene / polyvinylidene fluoride composite film, polypropylene / polyvinylidene fluoride composite film, aramid film, or polyimide film.

[0138] According to some embodiments of the present application, the thickness of the base film can be 3 μm to 16 μm, for example, any one of 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or 16 μm, any range within this range, or any specific value.

[0139] According to some embodiments of the present application, the coating layer includes high-temperature resistant organic polymer fibers, and the organic polymer fibers include one or more of the following: aramid fibers, polyacrylonitrile fibers, polyimide fibers, polycarbonate fibers, polyphenylene sulfide fibers, polyether ether ketone fibers, polysulfone fibers, and polyarylate fibers.

[0140] According to some embodiments of the present application, the thickness of the coating layer is 1 μm to 10 μm, and can be any one of 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm, any range within that range, or any specific value.

[0141] According to some embodiments of the present invention, the shrinkage rate of the separator along the length direction (TD) at 130°C is ≤ 8%.

[0142] According to some embodiments of the present invention, the shrinkage rate of the separator along the width direction (MD) at 130°C is ≤ 8%.

[0143] The separator according to this application reduces the probability of a short circuit occurring between the positive and negative electrodes when the circuit is broken, and even if a short circuit does occur, the separator will not shrink or break significantly due to the heat generated inside, thereby suppressing further expansion of the short-circuit area.

[0144] According to some embodiments of the present invention, the needle puncture strength of the separator is ≥ 400 gf.

[0145] The separator of this invention has a certain level of puncture resistance, and can effectively reduce the probability that burrs generated during the cutting process will penetrate the separator and cause contact between the positive and negative electrodes.

[0146] electrolyte The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. This application does not particularly limit the type of electrolyte and can be selected as needed. For example, the electrolyte may be a liquid, a gel, or a solid. The electrolyte solution comprises an electrolyte salt and a solvent, and the electrolyte salt may be selected from one or more of the following: lithium hexafluoride phosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoride arsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluoro(oxalato)borate (LiDFOB), lithium bisoxalobis(borate) (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalophosphate (LiDFOP), and lithium tetrafluoro(oxalato)phosphate (LiTFOP). The concentration of the electrolyte salt is generally 0.5 mol / L to 5 mol / L. The solvents are fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), diisopropyl carbonate (EPC), butylene carbonate (BC), methyl formate (MF), methyl acetate (MA), and ethyl methyl carbonate. The electrolyte can be selected from one or more of the following: propyl acetate (EA), n-propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), n-propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), tetramethylene sulfone (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE). The electrolyte may further optionally contain additives.For example, the additives may include a negative electrode film-forming additive and a positive electrode film-forming additive, and may also include additives that can improve specific characteristics of the battery, such as an additive that improves the overcharge characteristics of the battery or an additive that improves the high-temperature or low-temperature characteristics of the battery.

[0147] Manufacturing of current collectors A conductive layer is formed by depositing aluminum on one surface of the support layer (polycarbonate), and a protective layer is formed by depositing a nickel-chromium alloy on the surface of the conductive layer. The thickness D4 of the protective layer and the thickness D2 of the conductive layer satisfy the condition D4 ≤ 0.1 × D2.

[0148] In the embodiment of the present application, the thickness of the conductive layer is ≤ 3 μm, and the thickness of the protective layer is 1 nm ≤ D4 ≤ 200 nm.

[0149] In the specific embodiment of this application, the thickness of the protective layer satisfies the above relation and range.

[0150] The resulting current collector is then used as both a positive electrode current collector and a negative electrode current collector.

[0151] Manufacturing of positive electrode sheets A nickel compound, polyvinylidene fluoride as a binder, superconducting carbon as a conductive agent, and carboxymethylcellulose as a dispersant were mixed in a mass ratio of (99-x):x:0.8:0.2. N-methylpyrrolidone (NMP) was added as a solvent, and the mixture was stirred in a vacuum stirrer until it was stable and homogeneous to obtain a positive electrode paste. The obtained paste was uniformly applied to an aluminum foil, which served as the positive electrode current collector, with a coating weight of 0.275 g / 1540 mm². 2 The material was adjusted to achieve the following characteristics. After drying, cold pressing, and slitting, a typical positive electrode sheet was obtained. The compaction density of the obtained positive electrode sheet was 3.5 g / cm³. 3 The thickness of the positive electrode film layer in the positive electrode sheet is 125 μm.

[0152] Manufacturing of negative electrode sheets Graphite as the negative electrode active material, acetylene black as the conductive agent, CMC as the thickener, and SBR as the binder were mixed in a mass ratio of 97:1:1:1. Deionized water was added as the solvent, and the mixture was stirred in a vacuum stirrer until it was stable and homogeneous to obtain a negative electrode paste. The obtained paste was uniformly applied to a negative electrode current collector, and a general negative electrode sheet was obtained by drying and cold pressing. The compaction density of the negative electrode sheet thus obtained was 1.7 g / cm³ 3 That is the case.

[0153] Manufacturing of separators A coating layer was applied to both surfaces of the polyethylene film, and the thickness of the polyethylene film and the coating layer, as well as the type of coating layer, were adjusted to select a separator that met the following requirements.

[0154] The shrinkage rate of the separator along the length direction (TD) at 130°C is ≤8%. The shrinkage rate of the separator along the width direction (MD) at 130°C is ≤8%. The needle puncture strength of the separator is ≥ 400 gf.

[0155] Manufacturing of electrolyte To a solution of ethylene carbonate and ethyl methyl carbonate mixed in a volume ratio of 5:5, lithium hexafluoride phosphate was added as an electrolyte salt at a concentration of 2 mol / L.

[0156] Manufacturing of lithium-ion rechargeable batteries After obtaining a cell by winding a positive electrode sheet, a negative electrode sheet, and a separator, the cell was placed in an outer case, an electrolyte was injected and sealed, and a lithium-ion secondary battery was obtained through processes such as standing, compaction, chemical formation, and exhaust.

[0157] Examples 1 to 5 are current collectors, positive electrode film layers, and separators obtained according to the above manufacturing method.

[0158] Measurement conditions: (1) Measurement of the resistance of the positive electrode film layer Under 5% humidity and room temperature conditions, one positive electrode sheet, cut to a size of 100 mm x 100 mm and immersed in the electrolyte solution, was removed and folded in half (for polar sheets with a positive electrode film layer formed by coating both sides, it was folded as is; for polar sheets with a coating on one side, it was folded with the positive electrode film layer facing outwards). Next, the folded positive electrode sheet was placed between the probes of a film resistance measuring device (see Figure 7), and the test was performed to measure the resistance of the positive electrode film layer of the polar sheet. This was done for five samples, and the average of the obtained resistance values ​​was taken to determine the resistance of the positive electrode film layer.

[0159] (2) Measurement of MD shrinkage rate and TD shrinkage rate of separator A separator with appropriate length and width was used as a sample. It was placed on a stainless steel plate in a convection-type constant-temperature dryer, which was positioned in the center of the dryer. After heating at 90°C for 1 hour, the sample was removed, cooled to the test environment temperature, its dimensions were measured, and the shrinkage rate of the separator was calculated according to the following formula.

[0160] T = (L1 - L2) / L2 × 100% Here, T is the thermal shrinkage rate of the separator, expressed in %, L1 is the length before heating, in mm, and L2 is the length after heating, in mm.

[0161] The thermal shrinkage rate measured in the length direction of the separator sample is defined as the TD shrinkage rate, and the thermal shrinkage rate measured in the width direction is defined as the MD shrinkage rate.

[0162] (3) Measurement of needle puncture strength of separator An electronic universal testing machine was used. The separator was cut into strips with a cutter knife, and the width of the strip separator must be greater than 100 mm. A test piece with a width of 100 mm was attached to the sample film fixing clamping ring, and a steel pin with a diameter of 1.0 mm and a tip radius of 0.5 mm was used to pierce the test piece (width 100 mm) at a speed of 50 ± 5 mm / min, and the maximum load when the pin penetrated the test piece was measured. For the same test piece, tests were conducted at three or more locations, and for the same type of separator, measurements were made using five or more test pieces. The arithmetic mean value of a plurality of data obtained from tests on the same type of separator was taken as the piercing strength of the separator. The piercing strength of the separator used in the examples of this application satisfies ≧400 gf.

[0163] (4) Cutting test of secondary battery The secondary battery was charged to the upper cut-off voltage with a current of 0.3 C at 25 °C, and then fixed with a compression device. The cutting machine was started and cut linearly along the length (width) direction or the height direction to be completely separated. The cutting position was avoided from the pole terminals, and it was observed whether any abnormalities such as smoking, ignition, or explosion occurred during cutting. And the cutting test of this application is not limited to the model numbers of the compression device and the cutting machine. The purpose of this application is to evaluate the safety of the electrode assembly according to this application through a severe cutting test.

[0164] The design principles of this application are shown in Table 1.

[0165]

Table 1

[0166] Here, in the ternary system described in Table 1, when "5 < x < 8", it satisfies 5 < Y / X < 53, and "qualified" described in Table 1 indicates that there is no ignition, smoking, or explosion during the cutting process.

[0167] Table 1 indicates that when the conditions of the list are satisfied simultaneously, there is no ignition, smoking, or explosion of the cell during the cutting process.

[0168] Specific examples are shown in Table 2.

[0169] [Table 2A] [Table 2B] [Table 2C]

[0170] Furthermore, adjusting the compaction density of the positive electrode sheet or the thickness of the positive electrode film layer in this application affects the resistance value of the film, and consequently, the safety requirements of the battery also change. In the above embodiment of this application, the compaction density of the positive electrode sheet is 3.5 g / cm³. 3 The study focused on the actual battery state when the positive electrode film layer thickness was 125 μm, but in reality, the positive electrode film layer thickness ranged from 10 μm to 300 μm, and the compaction density of the positive electrode sheet was 2.0 to 4.0 g / cm³. 3 These fall within the scope of protection of this application.

[0171] Table 2 shows that the secondary battery designed in Comparative Example 2-2 of the present invention did not simultaneously satisfy the parameter requirements listed in Table 1 and rapidly ignited during the cutting test. The secondary batteries designed in Comparative Examples 2-1, 4-1, and 5-1 of the present invention did not satisfy the requirement to rationally control the relationship between the amount of binder used and the molar percentage content of nickel in the nickel-containing compound, and first emitted smoke and then ignited during the cutting test. In other examples, by rationally controlling the amount of binder used and corresponding it to the molar percentage content of nickel element in the nickel compound, and further selecting a composite current collector of appropriate thickness and utilizing the heat insulating capacity of the separator, the manufactured electrode assemblies and secondary batteries were able to pass the rigorous cutting test. This further demonstrates that the electrode assembly designed in the present invention can improve safety while ensuring the energy density of lithium-ion batteries.

[0172] Finally, it should be noted that the above embodiments are merely for illustrating, and not limiting, the technical solutions of the present application. While the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that it is still possible to modify the technical solutions described in the above embodiments, or to substitute some or all of their technical features, and such modifications or substitutions do not cause the substance of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application, and they should all be included within the scope of the claims and specification of the present application. In particular, the technical features mentioned in each embodiment can all be combined in any way, provided there is no structural inconsistency. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions included in the claims. [Explanation of symbols]

[0173] 5. Lithium-ion battery 51. Housing 52. Electrode Assembly 53. Cover plate 100, Positive electrode sheet 110, positive electrode current collector 120, Positive electrode film layer 111, 1st support layer 112, First conductive layer 113, 1st protective layer 200, negative electrode sheet 210, negative electrode current collector 220, Negative electrode film layer 211, second support layer 212, Second conductive layer Coordinate axis x direction: direction of the negative electrode current collector Coordinate axis y direction: direction of the thickness of the negative electrode current collector

Claims

1. A positive electrode sheet comprising a positive electrode current collector and a positive electrode film layer located on at least one surface of the positive electrode current collector, Negative electrode sheet and Includes a separator, The positive electrode film layer comprises a nickel compound and a binder, and the molar percentage content of the nickel element is Y relative to the total molar amount of transition elements in the nickel compound. Let X be the mass percentage content of the binder in the positive electrode film layer. An electrode assembly characterized by satisfying Y / X < 53.

2. The electrode assembly according to claim 1, characterized in that it satisfies 3 ≤ Y / X < 53.

3. The electrode assembly according to claim 1, characterized in that the molar percentage content Y of the nickel element satisfies 30% ≤ Y ≤ 100%.

4. The electrode assembly according to claim 1, characterized in that the mass percentage content X of the binder in the positive electrode film layer satisfies 1% ≤ X ≤ 10%.

5. The positive electrode film layer is (1.1) If 80% ≤ Y ≤ 100%, then 8 ≤ Y / X ≤ 40 must be satisfied, (1.2) If 50% < Y < 80%, then 5 < Y / X < 53 must be satisfied. (1.3) The electrode assembly according to claim 1, characterized in that it satisfies either of the following conditions: when 30% ≤ Y ≤ 50%, 3 ≤ Y / X ≤ 50.

6. The positive electrode film layer is (2.1) When 80% ≤ Y ≤ 100%, then 2.5% ≤ X ≤ 10%, (2.2) When 50% < Y < 80%, then 1.5% ≤ X ≤ 10%, (2.3) The electrode assembly according to claim 1, characterized in that it satisfies either of the following conditions: 30% ≤ Y ≤ 50%, and 1% ≤ X ≤ 10%.

7. The compacted powder density of the aforementioned positive electrode sheet is 3.5 g / cm³. ３ If that is the case, (3.1) When 80% ≤ Y ≤ 100%, the resistance of the positive electrode sheet is ≥ 1.81 mΩ, (3.2) When 50% < Y < 80%, the resistance of the positive electrode sheet is ≥ 0.40 mΩ, (3.3) The electrode assembly according to claim 1, characterized in that it satisfies one of the following conditions: (3.3) When 30% ≤ Y ≤ 50%, the resistance of the positive electrode sheet is ≥ 0.30 mΩ.

8. The electrode assembly according to claim 1, characterized in that the negative electrode sheet includes a negative electrode current collector, the positive electrode current collector and / or the negative electrode current collector is a composite current collector, the composite current collector includes a support layer and a conductive layer provided on at least one surface of the support layer, and the thickness of the conductive layer is less than or equal to the thickness of the support layer.

9. The thickness of the support layer and the molar percentage content of nickel element in the nickel compound are, D1 ≥ Y × 10 + 2 satisfies, D1 is the thickness of the support layer, and its unit is μm. The electrode assembly according to claim 8, characterized in that Y is the molar percentage content of nickel element in the nickel compound, expressed as %.

10. The electrode assembly according to claim 8, characterized in that the thickness of the support layer satisfies 2 μm ≤ D1 ≤ 30 μm, and preferably 5 μm ≤ D1 ≤ 20 μm.

11. The electrode assembly according to claim 8, characterized in that the thickness of the conductive layer is D2, satisfying D2 ≤ 3 μm, and preferably satisfying 30 nm ≤ D2 ≤ 3 μm.

12. The electrode assembly according to claim 8, characterized in that the composite current collector further includes a protective layer located on at least one surface of the conductive layer.

13. Let the thickness of the protective layer be D4, and the thickness of the conductive layer D2 satisfies the condition D4 ≤ 0.1 × D2. Preferably, satisfying 1 nm ≤ D4 ≤ 200 nm, More preferably, the electrode assembly according to claim 12, characterized in that 20 nm ≤ D4 ≤ 150 nm.

14. The electrode assembly according to claim 1, characterized in that the thickness of the positive electrode film layer is D3, and the relationship between D3 and the thickness D1 of the support layer satisfies 1 ≤ D3 / D1 ≤ 300.

15. The electrode assembly according to claim 14, characterized in that the thickness D3 of the positive electrode film layer satisfies 10 μm ≤ D3 ≤ 300 μm, and preferably 80 μm ≤ D3 ≤ 200 μm.

16. The shrinkage rate of the separator at 130°C includes the MD shrinkage rate and the TD shrinkage rate. The aforementioned MD shrinkage rate and / or TD shrinkage rate ≤ (13 - Y × 10) / 100, Y is the molar percentage content of nickel element in the nickel compound, expressed as %, The MD shrinkage rate is the thermal shrinkage rate along the length direction of the separator. The electrode assembly according to claim 1, characterized in that the TD shrinkage rate is the thermal shrinkage rate along the width direction of the separator.

17. The separator includes a base film and a coating layer provided on at least one surface of the base film. Preferably, the electrode assembly according to claim 16, wherein the coating layer includes organic polymer fibers, and the organic polymer fibers include one or more types selected from aramid fibers, polyacrylonitrile fibers, polyimide fibers, polycarbonate fibers, polyphenylene sulfide fibers, polyetheretherketone fibers, polysulfone fibers, and polyarylate fibers.

18. The electrode assembly according to claim 1, characterized in that the nickel compound includes one or more combinations of lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and modified compounds thereof.

19. The electrode assembly according to claim 1, characterized in that the binder comprises a fluorine-containing polymer, and the fluorine-containing polymer comprises one or more of the following: polyvinylidene fluoride, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, and fluorine-containing acrylate resin.

20. A secondary battery comprising the electrode assembly described in claim 1.

21. A power consumption device characterized by including the electrode assembly described in claim 1 or the secondary battery described in claim 20.

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