Electrode assembly, secondary battery, and electric device

Abstract

The invention belongs to the technical field of batteries, and particularly relates to an electrode assembly, a secondary battery and an electric device. The electrode assembly comprises a positive pole piece, a negative pole piece and an isolating membrane, the positive pole piece comprises a positive current collector and a positive membrane layer located on the surface of at least one side of the positive current collector, the positive membrane layer comprises a nickel-containing compound and a binder, based on the total molar weight of transition elements in the nickel-containing compound, the molar percentage content of the nickel element is Y, the mass percent content of the binder in the positive electrode film layer is X; y / X is less than 53. The electrode assembly designed by the invention is beneficial to improving the safety of the lithium ion battery.

Description

Technical Field

[0001] The present application relates to the field of batteries, and in particular to an electrode assembly, a secondary battery and an electrical device. Background Art

[0002] In recent years, secondary batteries have made great progress, especially the rapid development of pure electric new energy vehicles using secondary batteries represented by lithium-ion batteries as power units has attracted much attention.

[0003] As the application scope of secondary batteries becomes wider and wider, the requirements for battery performance are getting higher and higher, the energy density of secondary batteries is also getting higher and higher, and the safety hazards associated with it are becoming particularly prominent. At present, the safety of secondary batteries represented by lithium-ion batteries still needs to be improved. Summary of the invention

[0004] In view of the above problems, the present application provides an electrode assembly, a secondary battery and an electrical device, which are beneficial to improving the safety of lithium-ion batteries.

[0005] In a first aspect, the present application provides an electrode assembly, comprising:

[0006] Positive electrode sheet: comprising a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector;

[0007] Negative electrode;

[0008] Isolation film;

[0009] The positive electrode film layer comprises a nickel-containing compound and a binder, wherein the molar percentage content of nickel element in the nickel-containing compound based on the total molar amount of transition elements is Y; the mass percentage content of the binder in the positive electrode film layer is X; and the condition is satisfied: Y / X<53.

[0010] The adhesive in the positive electrode film layer of the present application can improve its bonding ability with the current collector, for example, during the positive and negative electrode cutting process, it can reduce the probability of overlap between the conductive layer and the negative electrode caused by the positive electrode active material falling off the current collector, and even reduce the amount of active material falling off during the positive and negative electrode cutting process. On the other hand, the content of the adhesive and the molar percentage content of the nickel element in the nickel-containing compound satisfy the above relationship to improve the matching degree between the adhesive and the nickel-containing compound and thus increase the resistance of the positive electrode film, and ultimately increase the resistance value when a short circuit occurs to reduce the probability of battery failure. In short, the electrode assembly designed in the present application can improve the safety of lithium-ion batteries while ensuring the energy density of lithium-ion batteries.

[0011] In some embodiments of the present application, the molar percentage content Y of the nickel element in the nickel-containing compound and the mass percentage content X of the binder in the positive electrode film layer satisfy: 3≤Y / X<53.

[0012] In some embodiments of the present application, the molar percentage content Y of the nickel element satisfies: 30%≤Y≤100%.

[0013] 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%.

[0014] In some embodiments of the present application, the positive electrode film layer satisfies any of the following:

[0015] (1.1) When 80%≤Y≤100%, 8≤Y / X≤40 is satisfied;

[0016] (1.2) When 50%<Y<80%, 5<Y / X<53;

[0017] (1.3) When 30%≤Y≤50%, 3≤Y / X≤50 is satisfied.

[0018] In some embodiments of the present application, the positive electrode film layer satisfies any of the following:

[0019] (2.1) When 80%≤Y≤100%, 2.5%≤X≤10%;

[0020] (2.2) When 50%<Y<80%, 1.5%≤X≤10%;

[0021] (2.3)When 30%≤Y≤50%, 1%≤X≤10%.

[0022] In some embodiments of the present application, the compaction density of the positive electrode sheet is 3.5 g / cm 3 When any of the following is satisfied:

[0023] (3.1) When 80%≤Y≤100%, the positive electrode sheet resistance is ≥1.81mΩ;

[0024] (3.2) When 50%<Y<80%, the positive electrode sheet resistance is ≥0.40mΩ;

[0025] (3.3) When 30%≤Y≤50%, the positive electrode sheet resistance is ≥0.30mΩ.

[0026] In some embodiments of the present application, the negative electrode plate 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 arranged on at least one side surface of the support layer; the thickness of the conductive layer is not greater than the thickness of the support layer.

[0027] The thickness of the support layer in the electrode assembly of the present application is not less than the thickness of the conductive layer. The support layer is used to provide effective support for the conductive layer. The composite current collector formed by the support layer and the conductive layer can reduce the number of burrs generated during the cutting process of the positive and negative electrodes compared to conventional metal current collectors, thereby reducing the short-circuit area.

[0028] In some embodiments of the present application, the thickness of the support layer and the molar percentage content of the nickel element in the nickel-containing compound satisfy:

[0029] D1≥Y×10+2;

[0030] D1, thickness of the support layer, in μm;

[0031] Y, the molar percentage content of nickel element in the nickel-containing compound, %.

[0032] 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.

[0033] In some embodiments of the present application, the thickness of the conductive layer is D2, satisfying: D2≤3 μm; preferably, 30 nm≤D2≤3 μm.

[0034] In some embodiments of the present application, the composite current collector further comprises a protective layer located on at least one surface of the conductive layer.

[0035] In some embodiments of the present application, the thickness of the protective layer is D4, and the thickness of D4 and the thickness of the conductive layer D2 satisfy: D4≤0.1×D2;

[0036] Preferably, 1nm≤D4≤200nm;

[0037] More preferably, 20nm≤D4≤150nm.

[0038] In some embodiments of the present application, the thickness of the positive electrode film layer is D3, and D3 and the thickness D1 of the support layer satisfy: 1≤D3 / D1≤300.

[0039] In some embodiments of the present application, the thickness D3 of the positive electrode film layer satisfies: 10 μm≤D3≤300 μm, preferably 80 μm≤D3≤200 μm.

[0040] In some embodiments of the present application, the shrinkage rate of the isolation film at 130° C. includes MD shrinkage rate and TD shrinkage rate;

[0041] MD shrinkage and / or TD shrinkage ≤ (13-Y×10) / 100;

[0042] Y, molar percentage content of nickel element in nickel-containing compound, %;

[0043] MD shrinkage, the thermal shrinkage measured along the length direction of the separator;

[0044] TD shrinkage is the thermal shrinkage measured along the width direction of the separator.

[0045] In some embodiments of the present application, the isolation film comprises a base film and a coating disposed on at least one side of the base film;

[0046] Preferably, the coating comprises organic polymer fibers, and the organic polymer fibers include one or a combination of two or more of aramid fibers, polyacrylonitrile fibers, polyimide fibers, polycarbonate fibers, polyphenylene sulfide fibers, polyetheretherketone fibers, polysulfone fibers, and polyarylate fibers.

[0047] In some embodiments of the present application, the nickel-containing compound 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 modified compounds thereof.

[0048] In some embodiments of the present application, the adhesive comprises a fluorine-containing polymer, and the fluorine-containing polymer comprises 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.

[0049] A second aspect of the present application is to provide a secondary battery comprising the electrode assembly described in the first aspect.

[0050] The third aspect of the present application is to provide an electrical device comprising the electrode assembly described in the first aspect or the secondary battery described in the second aspect.

[0051] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present application. Moreover, the same reference numerals are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

[0053] Figure 1 Schematic diagram of a lithium-ion battery according to some embodiments of the present application.

[0054] Figure 2Schematic diagram of the exploded structure of a lithium-ion battery according to some embodiments of the present application.

[0055] Figure 3 Schematic diagram of the positive electrode sheet of some embodiments of the present application.

[0056] Figure 4 Schematic diagram of the positive electrode sheet of some embodiments of the present application.

[0057] Figure 5 Schematic diagram of the positive electrode sheet of some embodiments of the present application.

[0058] Figure 6 Schematic diagram of the negative electrode sheet of some embodiments of the present application.

[0059] Figure 7 Schematic diagram of resistance testing of a positive electrode film layer according to some embodiments of the present application.

[0060] The reference numerals in the specific implementation manner are as follows:

[0061] 5. lithium-ion battery; 51. housing; 52. electrode assembly; 53. cover plate.

[0062] 100, positive electrode plate; 110, positive electrode current collector; 120, positive electrode film layer; 111, first support layer; 112, first conductive layer; 113, first protective layer;

[0063] 200, negative electrode plate; 210, negative electrode current collector; 220, negative electrode film layer; 211, second supporting layer; 212, second conductive layer.

[0064] Coordinate axis x direction: length direction of negative electrode current collector;

[0065] Coordinate axis y direction: thickness direction of negative electrode current collector. DETAILED DESCRIPTION

[0066] Below, the embodiments of the electrode assembly, secondary battery and electrical device of the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0067] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. The range defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a particular parameter, it is understood that a range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0068] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0069] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0070] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0071] If there is no special explanation, the "include" and "comprising" mentioned in this application represent open-ended or closed-ended expressions. For example, the "include" and "comprising" may represent that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0072] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0073] If not otherwise specified, in this application, the terms "first", "second", etc. are only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity, specific order or primary and secondary relationship of the indicated technical features.

[0074] Unless otherwise specified, in this application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple sheets" refers to more than two sheets (including two sheets).

[0075] Unless otherwise specified, the orientations or positional relationships indicated by technical terms such as "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", and "circumferential" are based on the orientations or positional relationships shown in the accompanying drawings and are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the embodiments of the present application.

[0076] If there is no special explanation, unless otherwise clearly specified and limited, technical terms such as "install", "connect", "connect", "fix" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0077] As the application scope of secondary batteries becomes wider and wider, the requirements for battery performance are getting higher and higher, the energy density of secondary batteries is also getting higher and higher, and the safety hazards that come with it have become particularly prominent. Taking lithium-ion batteries as an example, there are many factors that affect their safety risks. In general, the factors mainly include mechanical abuse, electrical abuse and thermal abuse. The main manifestations are that mechanical abuse and electrical abuse cause abnormal current or side reactions inside the battery, which leads to abnormal internal temperature rise, and ultimately thermal runaway, explosion or even fire.

[0078] The research found that for lithium-ion batteries whose cathode materials contain nickel compounds, cations (Li 2+ / Ni 3+ ) will affect the structural stability of the material, and with the increase of nickel content, this phenomenon will become more obvious, that is, the safety problem caused by the increase in conductivity will become more prominent.

[0079] Existing technologies mostly improve battery safety by improving the materials themselves or battery components, but this type of improvement usually takes a long time.

[0080] The reasons for the failure of lithium-ion batteries include internal short circuit, high temperature, overvoltage, etc. If we can start from the reasons for the failure, it will be beneficial to improve the safety of lithium-ion batteries.

[0081] Based on the above considerations, in order to solve the problem that existing lithium-ion batteries have high energy density but cannot take into account safety, an electrode assembly, a secondary battery and an electrical device are obtained according to the above design concept and experimental research.

[0082] First, the present application provides an electrode assembly, which includes a positive electrode plate, a negative electrode plate and a separator, the positive electrode plate includes a positive electrode collector and a positive electrode film layer located on at least one side of the positive electrode collector, the positive electrode film layer of the present application includes a nickel-containing compound and a binder, the molar percentage content of the nickel element in the nickel-containing compound based on the total molar amount of transition elements is Y; the mass percentage content of the binder in the positive electrode film layer is X; and it satisfies: Y / X<53.

[0083] The adhesive in the positive electrode film layer of the present application can improve its bonding ability with the current collector, such as reducing the probability of overlap between the conductive layer and the negative electrode caused by the positive electrode active material falling off the current collector during the positive and negative electrode cutting process, and even reducing the number of positive electrode active materials falling off during the positive and negative electrode cutting process. On the other hand, the content of the adhesive and the molar percentage content of the nickel element in the nickel-containing compound satisfy the above relationship. Under this relationship, the content of the adhesive and the content of the nickel-containing compound are reasonably matched to increase the resistance of the positive electrode film. As the resistance value increases, even if the positive and negative electrodes overlap, the probability of battery failure can be reduced. In short, the electrode assembly designed in the present application can improve the safety of lithium-ion batteries while ensuring the energy density of lithium-ion batteries.

[0084] The electrode assembly provided in the present application has both a certain energy density and a certain safety factor, and the electrode assembly is made into a secondary battery. The secondary battery may include an outer packaging. The outer packaging can be used to encapsulate the above-mentioned electrode assembly and electrolyte. The outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, and as plastic, polypropylene, polybutylene terephthalate, and polybutylene succinate can be listed.

[0085] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. Figure 1 A lithium-ion battery 5 having a square structure is used as an example.

[0086] According to some embodiments of the present application, Figure 2 , the outer package may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the lithium-ion battery 5 can be one or more, and those skilled in the art can choose according to specific actual needs.

[0087] According to some embodiments of the present application, the secondary battery is used in an electrical device. The secondary battery can be applied to, but not limited to, electrical devices such as vehicles, ships, or aircraft; the electrical device is further applied to a power supply system to achieve the technical purpose of improving safety.

[0088] The embodiment of the present application provides an electric device using a secondary battery as a power source. The electric device may include, but is not limited to, a mobile phone, a tablet, a laptop, an electric toy, an electric tool, a battery car, an electric car, a ship, a spacecraft, and the like. Among them, the electric toy may include a fixed or mobile electric toy, for example, a game console, an electric car toy, an electric ship toy, and an electric airplane toy, and the spacecraft may include an airplane, a rocket, a space shuttle, and a spacecraft, and the like.

[0089] Electrode assembly

[0090] The present application provides an electrode assembly, which includes a positive electrode sheet, a negative electrode sheet and a separator, wherein the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector, and the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer. The positive electrode film layer includes a nickel-containing compound and a binder, wherein the molar percentage content of the nickel element in the nickel-containing compound based on the total molar amount of the transition element is Y; the mass percentage content of the binder in the positive electrode film layer is X; and the following is satisfied: Y / X<53.

[0091] The positive electrode film layer in this application includes a binder and a nickel-containing compound. Among them, the nickel-containing compound is the main positive electrode active material. As the nickel content increases, it is beneficial to increase the energy density of the battery. However, due to the increase in internal conductivity and the generation of cations (Li 2+ / Ni 3+ ) The probability of mixing increases, and the probability of battery failure increases. "Failure" in this application includes fire, explosion, etc. caused by short circuit and other factors. The adhesive in the positive electrode film layer can improve its bonding ability with the current collector. For example, during the positive and negative electrode cutting process, it reduces the probability of the conductive layer and the negative electrode overlapping caused by the positive electrode active material falling off from the current collector, and even reduces the amount of positive electrode active material falling off during the positive and negative electrode cutting process.

[0092] In the present application, the molar percentage content of nickel in the nickel-containing compound is calculated based on the total molar amount of transition elements in the nickel-containing compound. For example, for NCM811, the molar percentage content of nickel is 80%. For another example, for LiNiO2, the molar percentage content of nickel is 100%.

[0093] The present application selects the above relationship between the content of the adhesive and the molar percentage content of the nickel element in the nickel-containing compound. Under this relationship, the content of the adhesive and the content of the nickel-containing compound are reasonably matched to increase the resistance of the positive electrode film. As the resistance value increases, even if the positive and negative electrodes overlap, the probability of battery failure can be reduced. In short, the electrode assembly designed in the present application can improve the safety of lithium-ion batteries while ensuring the energy density of lithium-ion batteries.

[0094] According to some embodiments of the present application, 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.

[0095] In this application, since the electrode assemblies with different nickel-containing compounds have different safety requirements, the requirements for the content and type of the adhesive are also inconsistent. At the same time, the type and content of the adhesive also affect other properties of the electrode assembly, such as energy density. This application controls: the molar percentage content Y of the nickel element and the mass percentage content X of the binder in the positive electrode film layer meet: 3≤Y / X<53, which can not only ensure the energy density of the lithium-ion battery, but also effectively improve the safety of the lithium-ion battery.

[0096] Positive electrode film

[0097] According to some embodiments of the present application, the positive electrode film layer in the electrode assembly of the present application comprises a nickel-containing compound, wherein the molar percentage content Y of the nickel element in the nickel-containing compound satisfies: and 30%≤Y≤100%.

[0098] In this application, nickel-containing compounds are used as the main positive electrode active material. As the nickel content increases, it is beneficial to improve the energy density of the battery. However, due to the increase in internal conductivity and the generation of cations (Li 2+ / Ni 3+ ) The probability of mixing increases, and the probability of battery failure also increases. Therefore, this application mainly explores the safety of electrode assemblies with a molar percentage content of nickel between 30% and 100%.

[0099] According to some embodiments of the present application, the nickel-containing compound 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 modified compounds thereof.

[0100] The modified compounds in the present application include any modification conventional in the art, such as physical modification or chemical modification, etc., and conventional modifications in the art include doping, etc.

[0101] In the present application, lithium nickel oxide includes but is not limited to LiNiO2, and lithium nickel cobalt oxide includes but is not limited to LiNi 0.8 Co 0.2 O2, lithium nickel manganese oxide including but not limited to LiNi 0.5 Mn 0.5 O2, lithium nickel cobalt manganese oxide including but not limited to LiNi x Co y Mn z O2 (x = 0.3 ~ 0.92, y = 0.03 ~ 0.4, z = 0.05 ~ 0.4), such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3O2(NCM333),LiNi 0.5 Co0.2 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 0.9 Co 0.05 Mn 0.05 O2, lithium nickel cobalt aluminum oxide including but not limited to 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 At least one of O2.

[0102] The nickel-containing compound in this application is the main positive electrode active material. As the nickel content increases, it is beneficial to improve the energy density of the battery. However, the increase in nickel content also brings the advantage of increased electrode conductivity and the probability of overlapping short circuits between the positive and negative electrodes during the cutting process of the positive and negative electrodes. This application comprehensively considers various factors and makes a reasonable optimization and selection of the types of nickel-containing compounds.

[0103] 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 can be any one of 1%, 2%, 3%, 4%, 4.5%, 5%, 6%, 7%, 8%, 9%, 10%, or any range or specific value in the range value.

[0104] At the same time, in some embodiments of the present application, the adhesive 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.

[0105] In this application, a fluorinated polymer is selected as an adhesive, wherein the fluorinated polymer is beneficial to improve the bonding ability between the fluorinated polymer and the current collector. On the other hand, the conductivity of the fluorinated polymer is correlated with its content. This application focuses on the effect of the fluorinated polymer on the resistance of the positive electrode film layer when it is polyvinylidene fluoride. For example, by means of a certain amount of polyvinylidene fluoride and a specific type of nickel-containing compound, the electrode resistance can be increased and the resistance when a lap short circuit occurs can be increased to reduce the probability of failure. At the same time, one or more of vinylidene fluoride tetrafluoroethylene propylene terpolymer, vinylidene fluoride hexafluoropropylene tetrafluoroethylene terpolymer, and fluorinated acrylate resin can also meet the requirements of this application for fluorinated polymers.

[0106] The present application selects a reasonable type of nickel-containing compound and combines it with the amount of adhesive used to appropriately increase the resistance of the positive electrode film layer to improve the short-circuit resistance of the overlap that occurs during the cutting process of the positive and negative electrodes.

[0107] According to some embodiments of the present application, the positive electrode film layer satisfies any of the following conditions:

[0108] (1.1) When the molar percentage content of nickel element in the nickel-containing compound is 80%≤Y≤100%, it satisfies: 8≤Y / X≤40;

[0109] (1.2) When the molar percentage content of nickel in the nickel-containing compound is 50%<Y<80%, 5<Y / X<53;

[0110] (1.3) When the molar percentage content of nickel element in the nickel-containing compound is 30%≤Y≤50%, 3≤Y / X≤50.

[0111] In this application, different nickel-containing compounds have different effects on the resistance value of the positive electrode film layer, so the requirements for the content of the adhesive are also different. This application divides the molar percentage content of the nickel element from high to low into three levels, and each level corresponds to a different Y / X ratio range. Combined with the molar percentage content of the nickel element in the nickel-containing compound, according to the appropriate Y / X ratio, the appropriate content of the adhesive can be selected, and the content of the adhesive matches the molar percentage content of the nickel element in the nickel-containing compound to increase the resistance of the positive electrode film, and finally increase the resistance when a lap short circuit occurs to reduce the probability of battery failure.

[0112] According to some embodiments of the present application, the positive electrode film layer satisfies any of the following conditions:

[0113] (2.1) When the molar percentage content of nickel element in the nickel-containing compound is 80%≤Y≤100%, the mass percentage content of the binder in the positive electrode film layer satisfies: 2.5%≤X≤10%;

[0114] (2.2) The molar percentage content of nickel element in the nickel-containing compound is 50%<Y<80%, and the mass percentage content of the binder in the positive electrode film layer satisfies: 1.5%≤X≤10%;

[0115] (2.3) When the molar percentage content of nickel element in the nickel-containing compound is 30%≤Y≤50%, the mass percentage content of the binder in the positive electrode film layer satisfies: 1%≤X≤10%.

[0116] In this application, the amount of binder is limited for two main purposes: 1. Increase the film resistance of the positive electrode sheet; 2. Enhance the adhesion between the positive electrode active material and other materials. Due to the different particle sizes and significant differences in thermal stability of different materials, the amount of binder used to achieve high resistance and high adhesion is different. PVDF-type binders are used as additives for positive electrode sheets for research.

[0117] There are differences in the powder resistivity of different positive electrode active materials. For example, in the NCM system, the higher the Ni content, the lower the short-circuit resistance. Therefore, in order to improve the short-circuit resistance, it is necessary to increase the content of non-conductive binder in the positive electrode sheet, thereby increasing the failure short-circuit resistance during overlap.

[0118] Different nickel-containing compounds in this application have different effects on the resistance value of the positive electrode film layer, so the requirements for the adhesive are also different. This application selects a suitable type of nickel-containing compound and a suitable content of adhesive to increase the electrode resistance and thereby increase the resistance when a bridging short circuit occurs to reduce the probability of failure.

[0119] According to some embodiments of the present application, based on the total weight of the positive electrode film layer, the sum of the mass of the fluorine-containing polymer and the mass of the nickel-containing compound is greater than 90%.

[0120] According to some embodiments of the present application, the positive electrode film layer further includes a conductive agent and a dispersant, and the conductive agent includes but is not limited to one or more combinations of graphite, superconducting carbon, carbon black (such as acetylene black, Ketjen black, Super P, etc.), carbon dots, carbon nanotubes, graphene and carbon nanofibers. The dispersant includes cellulose and its salts, specifically including but not limited to methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, etc.

[0121] Negative electrode film

[0122] According to some embodiments of the present application, the negative electrode film layer in the negative electrode plate includes a negative electrode active material, a binder, a conductive agent and a dispersant, etc. The negative electrode active material includes a carbonaceous material, and the carbonaceous material includes one or a combination of two or more of artificial graphite, natural graphite, soft carbon, and hard carbon. Among them, artificial graphite, natural graphite, soft carbon, hard carbon, etc. include materials of any form conventional in the art, and include any conventional manufacturers and models in the art. At the same time, the negative electrode active material may also include a silicon-based material, and the silicon-based material includes one or two of a silicon-oxygen material or a silicon-carbon material. In addition, the negative electrode active material may also include a silicon-carbon composite, a Li-Sn alloy, a Li-Sn-O alloy, Sn, SnO, SnO2, TiO2-Li4Ti5O 12 , Li-Al alloy. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for lithium-ion batteries can also be used. These negative electrode active materials can be used alone or in combination of two or more. The types of binder, conductive agent and dispersant in the negative electrode sheet can be the same as those of the positive electrode sheet.

[0123] current collector

[0124] In some embodiments of the present application, in the electrode assembly provided by the present application, the positive electrode plate comprises a positive electrode current collector and a positive electrode film layer located on at least one side surface of the positive electrode current collector, and the negative electrode plate comprises a negative electrode current collector and a positive electrode film layer located on at least one side surface of the positive electrode current collector. The positive electrode current collector and / or the negative electrode current collector is a composite current collector, the composite current collector comprises a support layer and a conductive layer disposed on at least one side surface of the support layer, the positive electrode film layer is located on one side surface of the conductive layer away from the support layer, wherein the thickness of the support layer is not less than the thickness of the conductive layer.

[0125] The "and / or" in this application includes that at least one of the positive electrode current collector and the negative electrode current collector is a composite current collector, and "composite" includes that the current collector has a structure of more than two layers, and the layers are formed together by any conventional composite method in the art, such as bonding, coating, deposition, etc. The thermal conductivity of the composite current collector is worse than that of conventional metal current collectors, such as aluminum foil and copper foil, and when cutting the composite current collector, the number of burrs generated by the positive and negative electrodes during the cutting process can be reduced, thereby reducing the short-circuit area, which is beneficial to improving the safety of the electrode assembly.

[0126] According to some embodiments of the present application, the present application provides an electrode assembly, which includes a positive electrode sheet, a negative electrode sheet and a separator, such as Figure 3 As shown, the positive electrode sheet 100 includes a positive electrode current collector 110 and a positive electrode film layer 120 located on at least one side surface of the positive electrode current collector 110; "at least one side surface" includes one side surface, two side surfaces, and more. Figure 3 A schematic diagram of one side is given. Figure 4As shown, the positive electrode current collector 110 includes a first support layer 111 and a first conductive layer 112 disposed on at least one side surface of the first support layer 111. Similarly, "at least one side surface" includes one side surface, two side surfaces, and more. Figure 4 In addition, the positive electrode film layer 120 is located on a surface of the first conductive layer 112 that is away from the first support layer 111 .

[0127] According to some embodiments of the present application, Figure 5 As shown, the positive electrode current collector 110 further includes a first protective layer 113 , and the first protective layer 113 is located on one side surface of the first conductive layer 112 .

[0128] like Figure 6 As shown, 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 disposed on at least one side surface of the second support layer 211. Similarly, "at least one side surface" includes one side surface, two side surfaces and more. Figure 6 Meanwhile, the negative electrode current collector 210 may further include a second protective layer, which is located on one side surface of the second conductive layer, but is not directly shown in the drawings.

[0129] The thickness of each layer of the composite current collector in this application is the thickness of each layer along the current collector ( Figures 3 to 6 The specific value of the distance between one end face on the y direction of the coordinate axis of the current collector and the other end face opposite to it can be obtained by measurement, such as measuring the thickness before and after with a micrometer and then calculating the difference. It can also be obtained by taking a picture of a slice sample in the thickness direction of the current collector with a scanning electron microscope and measuring the image obtained with the scanning electron microscope.

[0130] The support layer in the composite current collector in the present application can serve as a support for the current collector body, which is beneficial to ensure the overall strength of the composite current collector. The support layer can be a single-layer structure or a composite layer structure of more than two layers. The support layer includes an organic support layer, and the organic support layer uses organic materials to reduce the thermal conductivity of the composite current collector.

[0131] The conductive layer in the present application is used to achieve the purpose of conducting electricity and collecting current.

[0132] The thickness of the support layer in the present application is not less than the thickness of the conductive layer. The support layer is used to provide effective support for the conductive layer. The composite current collector formed by the support layer and the conductive layer can reduce the number of burrs generated during the cutting process of the positive and negative electrodes compared to conventional metal current collectors, thereby reducing the short-circuit area.

[0133] According to some embodiments of the present application, the positive electrode current collector is a composite current collector, and the negative electrode current collector is a conventional metal foil. Compared with a conventional secondary battery in which the positive electrode current collector is also a metal foil, the safety is improved.

[0134] According to some embodiments of the present 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.

[0135] According to some embodiments of the present application, the thickness of the support layer is thicker than that of conventional metal current collectors, such as aluminum foil and copper foil, which can effectively reduce the probability of overlapping short circuits between the positive and negative electrodes during the cutting process.

[0136] According to some embodiments of the present application, the thickness of the support layer and the molar percentage content of the nickel element in the nickel-containing compound satisfy a certain mathematical relationship, such as:

[0137] D1≥Y×10+2; formula (X);

[0138] D1, thickness of the support layer, in μm;

[0139] Y, the molar percentage content of nickel element in the nickel-containing compound, %.

[0140] The thickness D1 of the support layer of the present application is as follows Figure 5 It is shown that the present application can select a lower limit value of the thickness of the support layer according to the molar percentage content of the nickel element in the nickel-containing compound. Above this lower limit value, the probability of overlapping short circuits between the positive and negative electrodes during the cutting process can be effectively reduced.

[0141] According to some embodiments of the present application, the present application mainly discusses the specific value of the support layer thickness of the positive electrode film layer in these embodiments. Similarly, the support layer thickness of the negative electrode film layer also satisfies the relationship and value.

[0142] According to some embodiments of the present application, the thickness of the support layer satisfies: 2 μm≤D1≤30 μm.

[0143] According to some embodiments of the present application, the thickness of the support layer satisfies: 5 μm≤D1≤20 μm.

[0144] According to some embodiments of the present application, the thickness of the conductive layer is thinner than that of conventional metal current collectors, such as aluminum foil and copper foil, which can reduce the number of burrs generated during the cutting process of the positive and negative electrodes, thereby reducing the short circuit area.

[0145] According to some embodiments of the present application, the thickness of the conductive layer is D2, satisfying: D2≤3 μm.

[0146] The thickness D2 of the conductive layer of the present application is as follows Figure 5 Hint.

[0147] According to some embodiments of the present application, the thickness D2 of the conductive layer satisfies: 30 nm≤D2≤3 μm.

[0148] The thickness of the conductive layer in the present application can be any one of 30nm, 50nm, 80nm, 100nm, 200nm, 500nm, 1μm, 2μm, 3μm, or any range or any specific value in the range value. The thickness of the conductive layer within the range value can reduce the number of burrs generated during the cutting process of the positive and negative electrodes, thereby reducing the short circuit area.

[0149] According to some embodiments of the present application, the thickness of the support layer is not greater than the thickness of the positive electrode film layer. The present application focuses on exploring that the thickness of the first support layer in the positive electrode current collector is not greater than the thickness of the positive electrode film layer. In the present application, the thickness of the first support layer is selected to be not greater than the thickness of the positive electrode film layer. Under the premise of ensuring that the first support layer plays a supporting role, it does not affect the normal operation of the positive electrode film layer, and at the same time, it is conducive to improving battery safety and energy density.

[0150] According to some embodiments of the present application, the thickness of the first support layer (support layer) is D1, and the thickness of the positive electrode film layer is D3, satisfying: 1≤D3 / D1≤300 formula (XI).

[0151] The thickness D3 of the positive electrode film layer of the present application is as follows Figure 5 Hint.

[0152] The present application specifically defines the relationship between the thickness of the first support layer and the thickness of the positive electrode film layer. When the relationship is satisfied, the normal operation of the positive electrode film layer is not affected and the battery safety and energy density are improved.

[0153] According to some embodiments of the present application, a thickness D1 of the first supporting layer satisfies: 2 μm≤D1≤30 μm.

[0154] According to some embodiments of the present application, a thickness D1 of the first supporting layer satisfies: 5 μm≤D1≤20 μm.

[0155] In the present 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, 30 μm, or any range or any specific value in the range value. The thickness of the support layer within the range value can effectively reduce the probability of overlap short circuit of the positive and negative electrodes during the cutting process.

[0156] In the present application, the thickness of the second supporting layer also meets the range of 2 μm to 30 μm. For example, the thickness of the second supporting layer is equal to the thickness of the first supporting layer.

[0157] According to some embodiments of the present application, the thickness D3 of the positive electrode film layer satisfies: 10 μm≤D3≤300 μm.

[0158] According to some embodiments of the present application, the thickness D3 of the positive electrode film layer satisfies: 80 μm≤D3≤200 μm.

[0159] The thickness of the positive electrode film layer in the present application can be any one of 10 μm, 20 μm, 30 μm, 50 μm, 80 μm, 100 μm, 200 μm, 300 μm, or any range or any specific value in the range value. The positive electrode film layer within the range value is conducive to improving battery safety and energy density.

[0160] According to some embodiments of the present application, 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.

[0161] The thickness D4 of the first protective layer of the present application is as follows Figure 5 Hint.

[0162] In the present application, the first protective layer can reduce the degree of damage to the conductive layer during the cutting process and further reduce the short circuit area.

[0163] According to some embodiments of the present application, the thickness D4 of the first protective layer and the thickness D2 of the conductive layer satisfy: D4≤0.1×D2 formula (XII).

[0164] The thickness of the first protective layer in the present application satisfies the relationship, which is beneficial to the protection of the conductive layer.

[0165] According to some embodiments of the present application, a thickness D4 of the first protective layer satisfies: 1 nm≤D4≤200 nm.

[0166] According to some embodiments of the present application, a thickness D4 of the first protective layer satisfies: 20 nm ≤ D4 ≤ 150 nm.

[0167] The thickness of the first protective layer in the present application can be any one of 1nm, 5nm, 10nm, 20nm, 50nm, 100nm, 150nm, 200nm or any range or any specific value in the range value. The thickness of the first protective layer within the range value is beneficial to the protection of the conductive layer.

[0168] The negative electrode current collector in the present application may also include a second protective layer, and the thickness of the second protective layer also satisfies the range of 1 nm to 200 nm. For example, the thickness of the second protective layer is equal to the thickness of the first protective layer.

[0169] The support layer in the composite current collector in the present application can serve as a support for the current collector body, which is beneficial to ensure the overall strength of the composite current collector. The support layer can be a single-layer structure or a composite layer structure of more than two layers. The support layer includes an organic support layer, and the organic support layer uses organic materials to reduce the thermal conductivity of the composite current collector. The material of the organic support layer includes one or two of polymer materials and polymer-based composite materials, wherein the polymer materials include one or more of polyamide, polyimide, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycarbonate, polyethylene, polypropylene, polypropylene, acrylonitrile-butadiene-styrene copolymer, polyvinyl alcohol, polystyrene, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, sodium polystyrene sulfonate, polyethylene, silicone rubber, polyoxymethylene, polyphenylene oxide, polyphenylene sulfide, polyethylene glycol, polysulfur nitride, polyphenylene, polypyrrole, polyaniline, polythiophene, polypyridine, cellulose, starch, protein, epoxy resin, phenolic resin, their derivatives, their crosslinked products and their copolymers. The polymer-based composite material includes the above-mentioned polymer materials and additives, and the additives include one or more of metal materials and inorganic non-metallic materials. Metal materials include one or more of aluminum, aluminum alloys, copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, iron, iron alloys, silver and silver alloys. Inorganic non-metallic materials include one or more of 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 graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers. As the above-mentioned additives, it can also be a carbon-based material coated with a metal material, such as one or more of nickel-coated graphite powder and nickel-coated carbon fiber.

[0170] The conductive layer in the present application is used to achieve the purpose of conducting electricity and collecting current. The conductive layer includes one or more of metal materials, carbon-based conductive materials and conductive polymer materials. The metal material may include one or more of aluminum, aluminum alloy, copper, copper alloy, nickel, nickel alloy, iron, iron alloy, titanium, titanium alloy, silver and silver alloy. The carbon-based conductive material includes one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers. The conductive polymer material includes one or more of polysulfur nitride, aliphatic conjugated polymer, aromatic ring conjugated polymer and aromatic heterocyclic conjugated polymer. As an example, the conductive polymer material may include one or more of polyethylene, polyphenylene, polypyrrole, polyethylene, polyphenylene glue, polythiophene and polypyridine. In addition, the electron delocalization of the conductive polymer material can be increased by doping to improve the conductivity.

[0171] The protective layer in the present application is mainly used to reduce the probability of chemical corrosion or mechanical damage to the conductive layer. The protective layer includes one or more of metals, metal oxides and conductive carbon, and the metal is, for example, one or more of nickel, chromium, nickel-based alloys and copper-based alloys. The aforementioned nickel-based alloy is an alloy composed of pure nickel as a matrix and one or more other elements, preferably a nickel-chromium alloy. Nickel-chromium alloy is an alloy formed by metallic nickel and metallic chromium. Optionally, the weight ratio of nickel to chromium in the nickel-chromium alloy is 1:99 to 99:1, such as 9:1. The aforementioned copper-based alloy is an alloy composed of pure copper as a matrix and one or more other elements, preferably a nickel-copper alloy. Optionally, the weight ratio of nickel to copper in the nickel-copper alloy is 1:99 to 99:1, such as 9:1. The above-mentioned metal oxides are, for example, one or more of aluminum oxide, cobalt oxide, chromium oxide and nickel oxide. The conductive carbon mentioned above is, for example, one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers, and further one or more of carbon black, carbon nanotubes and graphene.

[0172] Isolation film

[0173] According to some embodiments of the present application, since heat is generated during the cutting process of the positive and negative electrodes, this part of the heat will affect the shrinkage of the separator. If the shrinkage rate of the separator is affected to a small extent, the positive and negative short-circuit overlap area caused by the shrinkage of the separator during the cutting process can be reduced. Since heat is related to the positive electrode active material, the present application establishes a mathematical relationship between the shrinkage rate of the separator and the molar percentage content of the nickel element in the nickel-containing compound:

[0174] MD shrinkage and / or TD shrinkage ≤ (13-Y×10) / 100; formula (XIII);

[0175] The shrinkage rate of the isolation film at 130°C includes the MD shrinkage rate and the TD shrinkage rate;

[0176] Y, molar percentage content of nickel element in nickel-containing compound, %;

[0177] MD shrinkage, the thermal shrinkage measured along the length direction of the separator;

[0178] TD shrinkage is the thermal shrinkage measured along the width direction of the separator.

[0179] The shrinkage rate of the isolation film in the present application at 130° C. can be obtained by direct measurement and calculation.

[0180] The isolation film in the present application is beneficial to reducing its shrinkage rate after heating, by reducing the short-circuit overlap area of ​​the positive and negative electrodes caused by the shrinkage of the isolation film during the cutting process.

[0181] According to some embodiments of the present application, the isolation film includes a base film and a coating disposed on at least one surface of the base film.

[0182] According to some embodiments of the present application, the base film includes but is not limited to one of a polyethylene film, a polypropylene film, a polypropylene / polyethylene / polypropylene composite film, a polyvinylidene fluoride film, a polyethylene / polyvinylidene fluoride composite film, a polypropylene / polyvinylidene fluoride composite film, an aramid film and a polyimide film.

[0183] According to some embodiments of the present application, the thickness of the base film can be 3μm to 16μm, such as any one of 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, and 16μm, or any range or any specific value in the range value.

[0184] According to some embodiments of the present application, the coating contains high temperature resistant organic polymer fibers, and the organic polymer fibers include one or more of aramid fibers, polyacrylonitrile fibers, polyimide fibers, polycarbonate fibers, polyphenylene sulfide fibers, polyetheretherketone fibers, polysulfone fibers, and polyarylate fibers.

[0185] According to some embodiments of the present application, the thickness of the coating is 1μm to 10μm, such as any one of 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, or any range or any specific value in the range value.

[0186] According to some embodiments of the present application, the shrinkage rate of the isolation film along the length direction (TD) at 130° C. is ≤8%.

[0187] According to some embodiments of the present application, the shrinkage rate of the isolation film along the width direction (MD) at 130° C. is ≤8%.

[0188] The isolation film in the present application can reduce the probability of short circuit between the positive and negative electrodes when sawed. Even if a short circuit occurs, the heat generated inside will not cause serious shrinkage and damage to the isolation film, thereby reducing the further increase of the short circuit area.

[0189] According to some embodiments of the present application, the puncture strength of the isolation film is ≥400 gf.

[0190] The isolation membrane in the present application has a certain puncture resistance, which can effectively avoid the probability of burrs piercing the membrane during the cutting process and causing overlap of the positive and negative electrodes.

[0191] Electrolytes

[0192] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to demand. For example, the electrolyte can be liquid, gel or all-solid. The electrolyte includes an electrolyte salt and a solvent, and the electrolyte salt can be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalate phosphate) (LiDFOP) and lithium tetrafluorooxalate phosphate (LiTFOP). The concentration of the electrolyte salt is generally 0.5 mol / L to 5 mol / L. The solvent may be selected from one or more of 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), ethyl propyl carbonate (EPC), butylene carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), cyclopentane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl sulfone (ESE). The electrolyte may also optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain properties of the battery, such as additives that improve the overcharge performance of the battery, additives that improve the high or low temperature performance of the battery, etc.

[0193] Preparation of current collector

[0194] Aluminum is deposited on one surface of the support layer (polycarbonate) to form a conductive layer, and a nickel-chromium alloy is deposited on the surface of the conductive layer to form a protective layer. The thickness D4 of the protective layer and the thickness D2 of the conductive layer satisfy: D4≤0.1×D2.

[0195] 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.

[0196] In the specific embodiments of the present application, the thickness of the protective layer satisfies the above relationship and range.

[0197] The prepared current collector is used for both positive electrode current collector and negative electrode current collector.

[0198] Preparation of positive electrode

[0199] The nickel-containing compound, the binder polyvinylidene fluoride, the conductive agent superconducting carbon, and the dispersant carboxymethyl cellulose were mixed in a mass ratio of (99-x): x: 0.8: 0.2, and the solvent N-methylpyrrolidone (NMP) was added, and the mixture was stirred in a vacuum mixer until it was stable and uniform to obtain a positive electrode slurry. The positive electrode slurry was evenly coated on the positive electrode current collector aluminum foil, and the coating weight was 0.275 g / 1540 mm 2 After drying, cold pressing and slitting, a conventional positive electrode sheet is obtained, and the compaction density of the positive electrode sheet is 3.5g / cm 3 The thickness of the positive electrode film layer in the positive electrode sheet is 125μm.

[0200] Preparation of negative electrode

[0201] The negative electrode active material graphite, the conductive agent acetylene black, the thickener CMC, and the binder SBR were mixed in a mass ratio of 97:1:1:1, and the solvent deionized water was added, and the mixture was stirred in a vacuum mixer until it was stable and uniform to obtain a negative electrode slurry. The negative electrode slurry was evenly coated on the negative electrode collector, and after drying and cold pressing, a conventional negative electrode sheet was obtained. The compaction density of the negative electrode sheet was 1.7 g / cm 3 .

[0202] Preparation of isolation film

[0203] Coating is applied on both sides of the polyethylene film. By adjusting the polyethylene film, the thickness of the coating, and the type of coating, the isolation film is selected to meet the following requirements:

[0204] The shrinkage of the isolation film along the length direction (TD) at 130°C is ≤8%;

[0205] The shrinkage of the isolation film along the width direction (MD) at 130°C is ≤8%;

[0206] The puncture strength of the isolation film is ≥400gf.

[0207] Preparation of electrolyte

[0208] Lithium hexafluorophosphate electrolyte salt was added to a mixture of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 5:5 at a concentration of 2 mol / L.

[0209] Preparation of lithium-ion secondary batteries

[0210] The positive electrode sheet, the negative electrode sheet and the isolation film are wound to obtain a battery cell, and after the battery cell is placed in a packaging shell, an electrolyte is injected and the shell is sealed. After standing, compacting, forming, exhausting and other processes, a lithium-ion secondary battery is obtained.

[0211] Among them, Examples 1 to 5 are current collectors, positive electrode films and separators obtained according to the above preparation method.

[0212] Test conditions:

[0213] (1) Determination of positive electrode film resistance:

[0214] Under 5% humidity and room temperature, take a 100mm×100mm positive electrode sheet soaked in the above electrolyte, fold it in the middle (here, the double-sided coated positive electrode sheet is used as an example, for the single-sided coated electrode sheet, the positive electrode sheet is folded outwards) and place it in the middle of the film resistance meter probe (such as Figure 7 As shown), the test is then carried out to obtain the positive electrode film resistance of the electrode being tested. After testing 5 samples, the average value is obtained, which is the resistance of the positive electrode film layer.

[0215] (2) MD shrinkage and TD shrinkage test of isolation film:

[0216] Take a suitable length and width of the isolation film, make a sample, and then place the sample on a stainless steel plate in a blast-type constant temperature oven. The stainless steel plate is located in the middle of the constant temperature oven. The heating temperature is 90°C. After heating for 1 hour, take out the sample, cool it to the test environment temperature, measure the sample size, and calculate the shrinkage rate of the isolation film according to the following formula:

[0217] T = (L1 - L2) / L2 x 100%.

[0218] Wherein T is the thermal shrinkage rate of the isolation film, %; L1 is the length before heating, in mm; L2 is the length after heating, in mm.

[0219] The heat shrinkage rate measured in the length direction of the separator sample is the TD shrinkage rate, and the heat shrinkage rate measured in the width direction of the separator sample is the MD shrinkage rate.

[0220] (3) Test of the needle puncture strength of the isolation film:

[0221] An electronic universal testing machine is used. Use a utility knife to cut the diaphragm into strips, where the width of the strip diaphragm must be greater than 100mm. Install a test piece with a width of 100mm on the sample film fixing clamp ring, and then use a steel needle with a diameter of 1.0mm and a radius of 0.5mm at the top of the diameter to puncture the test piece with a width of 100mm at a speed of (50±5)mm / min, and read the maximum load of the steel needle penetrating the test piece. The same test piece is selected from 3 or more points for testing, and 5 or more test pieces of the same isolation membrane are selected for measurement. The arithmetic mean of multiple data collected from the test of the same isolation membrane is taken as the pinpoint strength of the isolation membrane. The puncture strength of the isolation membrane used in the embodiment of the present application meets ≥400gf.

[0222] (4) Cutting test of secondary batteries:

[0223] Charge the secondary battery at 0.33C current at 25°C to the upper cut-off voltage, then fix it with a clamping device, start the cutting machine to cut in a straight line along the length (width) direction or the height direction until it is cut off, and the cutting position cannot be at the pole position. Observe whether there is smoke, fire, explosion, etc. during the cutting process. The cutting test of this application is not limited by the model of the clamping device or the cutting machine. This application hopes to judge the safety of the electrode assembly of this application through rigorous cutting tests.

[0224] The design principles of this application are shown in Table 1.

[0225] Table 1 List of design principles

[0226]

[0227] Among them, when "5<x<8" in the ternary system of Table 1, 5<Y / X<53 is satisfied; "pass" in Table 1 means that there is no fire, no smoke and no explosion during the sawing process.

[0228] Table 1 shows that the listed conditions are met at the same time, and the battery cell does not catch fire, smoke or explode during the sawing process.

[0229] The specific implementation example is shown in Table 2;

[0230] Table 2 List of Examples and Comparative Examples

[0231]

[0232]

[0233] In addition, in this application, if the compaction density of the positive electrode sheet or the thickness of the positive electrode film layer is adjusted, the film resistance value will be affected, and the corresponding battery safety conditions will also change. In the above embodiment, this application focuses on exploring the compaction density of the positive electrode sheet of 3.5g / cm 3 The thickness of the positive electrode film is 125 microns. In fact, the thickness of the positive electrode film is 10μm~300μm, and the compaction density of the positive electrode sheet is 2.0~4.0g / cm 3 All are within the protection scope of this application.

[0234] Combined with Table 2, it can be seen that the secondary battery designed in Comparative Example 2-2 of the present application does not meet the requirements of each parameter listed in Table 1 at the same time, and it quickly catches fire during the cutting process. The secondary batteries designed in Comparative Examples 2-1, Comparative Example 4-1, and Comparative Example 5-1 of the present application do not meet the requirements of reasonably controlling the relationship between the amount of adhesive used and the molar percentage content of the nickel element in the nickel-containing compound, and will first smoke and then catch fire during the cutting process. Other embodiments reasonably control the amount of adhesive used and match it with the molar percentage content of the nickel element in the nickel-containing compound. At the same time, a composite current collector with a suitable thickness is further selected, and with the help of the heat insulation ability of the isolation film, the prepared electrode assembly, secondary battery, etc. can pass the rigorous cutting test, which once again proves that the electrode assembly designed in this application can improve the safety of lithium-ion batteries while ensuring the energy density of lithium-ion batteries.

[0235] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. An electrode assembly, characterized in that: include: Positive electrode sheet: comprising a positive electrode current collector and a positive electrode film layer located on at least one side surface of the positive electrode current collector; Negative electrode; Isolation film; The positive electrode film layer comprises a nickel-containing compound and a binder, wherein the molar percentage content of the nickel element in the nickel-containing compound based on the total molar amount of transition elements is Y; The mass percentage content of the binder in the positive electrode film layer is X; Satisfies: Y / X<53.

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

3. The electrode assembly according to any one of claims 1 to 2, characterized in that: The molar percentage content Y of the nickel element satisfies: 30%≤Y≤100%.

4. The electrode assembly according to any one of claims 1 to 2, characterized in that: The mass percentage content X of the binder in the positive electrode film layer satisfies: 1%≤X≤10%.

5. The electrode assembly according to any one of claims 1 to 4, characterized in that: The positive electrode film layer satisfies any of the following conditions: (1.1) When 80%≤Y≤100%, 8≤Y / X≤40 is satisfied; (1.2) When 50%<Y<80%, 5<Y / X<53; (1.3) When 30%≤Y≤50%, 3≤Y / X≤50 is satisfied.

6. The electrode assembly according to any one of claims 1 to 5, characterized in that: The positive electrode film layer satisfies any of the following conditions: (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%.

7. The electrode assembly according to any one of claims 1 to 6, characterized in that: The compaction density of the positive electrode sheet is 3.5 g / cm 3 When any of the following is satisfied: (3.1) When 80%≤Y≤100%, the positive electrode sheet resistance is ≥1.81mΩ; (3.2) When 50%<Y<80%, the positive electrode sheet resistance is ≥0.40mΩ; (3.3) When 30%≤Y≤50%, the positive electrode sheet resistance is ≥0.30mΩ.

8. The electrode assembly according to any one of claims 1 to 7, characterized in that: The negative electrode plate includes a negative electrode current collector, the positive electrode current collector and / or the negative electrode current collector is a composite current collector, and the composite current collector includes a support layer and a conductive layer arranged on at least one side surface of the support layer; the thickness of the conductive layer is not greater than the thickness of the support layer.

9. The electrode assembly according to claim 8, characterized in that: The thickness of the support layer and the molar percentage content of the nickel element in the nickel-containing compound satisfy: D1≥Y×10+2; D1, thickness of the support layer, in μm; Y, the molar percentage content of nickel element in the nickel-containing compound, %.

10. The electrode assembly according to claim 8 or 9, characterized in that: The thickness of the support layer satisfies: 2 μm≤D1≤30 μm, preferably 5 μm≤D1≤20 μm.

11. The electrode assembly according to any one of claims 8 to 10, characterized in that: The thickness of the conductive layer is D2, satisfying: D2≤3 μm; preferably, 30 nm≤D2≤3 μm.

12. The electrode assembly according to any one of claims 8 to 11, characterized in that: The composite current collector further comprises a protective layer located on at least one side surface of the conductive layer.

13. The electrode assembly according to claim 12, characterized in that: The thickness of the protective layer is D4, and D4 and the thickness of the conductive layer D2 satisfy: D4≤0.1×D2; Preferably, 1nm≤D4≤200nm; More preferably, 20nm≤D4≤150nm.

14. The electrode assembly according to any one of claims 1 to 13, characterized in that: The thickness of the positive electrode film layer is D3, and the thickness D3 and the thickness D1 of the support layer satisfy: 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, preferably 80 μm≤D3≤200 μm.

16. The electrode assembly according to any one of claims 1 to 15, characterized in that: The shrinkage rate of the isolation film at 130° C. includes MD shrinkage rate and TD shrinkage rate; The MD shrinkage and / or TD shrinkage is ≤ (13-Y×10) / 100; Y, molar percentage content of nickel element in nickel-containing compound, %; MD shrinkage, thermal shrinkage along the length direction of the separator; TD shrinkage, thermal shrinkage along the width direction of the separator.

17. The electrode assembly according to claim 16, characterized in that: The isolation film comprises a base film and a coating disposed on at least one side of the base film; Preferably, the coating comprises organic polymer fibers, and the organic polymer fibers include one or a combination of two or more of aramid fibers, polyacrylonitrile fibers, polyimide fibers, polycarbonate fibers, polyphenylene sulfide fibers, polyetheretherketone fibers, polysulfone fibers, and polyarylate fibers.

18. The electrode assembly according to any one of claims 1 to 17, characterized in that: The nickel-containing compound 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 modified compounds thereof.

19. The electrode assembly according to any one of claims 1 to 17, characterized in that: The adhesive comprises a fluorine-containing polymer, and the fluorine-containing polymer comprises one or a combination of two or more of polyvinylidene fluoride, a vinylidene fluoride tetrafluoroethylene propylene terpolymer, a vinylidene fluoride hexafluoropropylene tetrafluoroethylene terpolymer, and a fluorine-containing acrylate resin.

20. A secondary battery, characterized in that: An electrode assembly comprising any one of claims 1 to 19.

21. An electrical device, characterized in that: An electrode assembly according to any one of claims 1 to 19 or a secondary battery according to claim 20.

Images