Binder for secondary battery and manufacturing method thereof, secondary battery and power consumption device

Abstract

This application relates to the field of secondary battery technology, and particularly to a binder for secondary batteries, a method for manufacturing the same, secondary batteries, and power consumption devices. The binder includes a core layer structure and a shell layer structure provided on the surface of the core layer structure. The shell layer structure includes an acrylate copolymer, the core layer structure includes a high-rigidity polymer, and the range value of the crystallinity of the high-rigidity polymer is 32% to 94%. The core-shell structured binder includes a core layer structure of a high-rigidity polymer. In the process of cold pressing the cell, the high-rigidity polymer stabilizes the particle structure of the binder as a support, that is, the high-rigidity polymer plays a supporting role, improves the overall rigidity of the binder, and improves the size stability of the binder during cold pressing of the cell, without being completely deformed, and improves the adhesion during cold pressing of the cell, thereby improving the hardness of the cell.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to a Chinese patent application with application number 202310447245.8, filed on April 24, 2023, the entire contents of which are incorporated herein by reference.

[0002] The present application relates to the technical field of secondary batteries, and more particularly to a binder for secondary batteries and a method for manufacturing the same, a secondary battery, and a power consuming device. [Background technology]

[0003] With the rapid growth of portable electronic devices, electric vehicles, etc., the demand for power batteries is also increasing, and the electrical and chemical properties of batteries are attracting increasing attention.

[0004] Currently, battery cells have a problem of opening, that is, gaps are easily formed between the polar sheet and the separator, which deteriorates the cycle characteristics of the battery. Summary of the Invention

[0005] The primary objective of this application is to provide a binder that improves adhesion between the polar sheet and the separator, thereby improving battery performance.

[0006] To achieve the above object, the present application provides a binder for a secondary battery, the binder comprising a core layer structure and a shell layer structure provided on the surface of the core layer structure, the shell layer structure comprising an acrylic ester copolymer, the core layer structure comprising a high-rigidity polymer, and the range of crystallinity of the high-rigidity polymer being 32% to 94%.

[0007] The acrylic acid ester copolymer has good adhesive properties, and the use of the acrylic acid ester copolymer can further improve the adhesiveness between the separator and the polar sheet after cold pressing.

[0008] Regarding the high stiffness polymer, the range of the crystallinity of the high stiffness polymer is 32% to 94%, and it has the properties of high strength, impact resistance, heat resistance, hardness and deterioration resistance. During the cold pressing process of the cell, the high stiffness polymer is not easily deformed, and as can be understood, during the cold pressing process, the high stiffness polymer is not deformed or only deforms slightly.

[0009] The core-shell binder has a core layer structure of a high-rigidity polymer, and during the cold-pressing process of the cells, the high-rigidity polymer acts as a support to stabilize the particle structure of the binder, i.e., the high-rigidity polymer plays a supporting role and improves the overall rigidity of the binder, improving the dimensional stability of the binder during cold-pressing of the cells and preventing complete deformation, thereby improving the adhesive strength of the cold-pressed cells and improving the hardness of the cells.

[0010] As can be seen, if the core layer does not have a high-rigidity polymer support, the binder is more likely to be crushed, and in the process of crushing the binder, the voids between the binders are compressed and blocked, which is detrimental to the penetration of the electrolyte and the transmission of ions.

[0011] Because the high-rigidity polymer is difficult to deform, the binder can maintain a certain shape during the cold pressing process, which solves the problem of the voids between the binder particles being blocked due to the deformation of the binder during the process of crushing the binder.

[0012] Because the binder of the present invention has the support of a highly rigid polymer, complete deformation of the binder particles is unlikely to occur during cold pressing, and the voids between the binder particles are not blocked. The unblocked voids serve as paths for electrolyte impregnation, which is favorable for ion transmission. At the same time, the hardness of the cell can be further improved, the dynamic properties of the secondary battery can be improved, the electrical and chemical impedance can be reduced, and the cycle characteristics of the secondary battery can be improved.

[0013] It can be seen that during the cold pressing of the cells, the core layer structure of the binder is not deformed or is deformed only slightly, reducing the probability of the binder particles being crushed; the shell layer structure contains an acrylic ester copolymer, which can provide good viscosity and improve the adhesive strength of the cold pressing of the cells; it can be seen that during the cold pressing, the acrylic ester copolymer of the shell layer structure is deformed under the extrusion force, allowing the shell layer structure to be inserted into the gaps between the separator and the polar sheet, improving the adhesive strength.

[0014] Optionally, the crystallinity of the high stiffness polymer ranges from 40% to 80%.

[0015] In order to improve the hardness of the high stiffness polymer, the crystallinity of the high stiffness polymer is preferably 40% or more. At the same time, considering that if the crystallinity is too high, it is difficult to realize the process, the crystallinity of the high stiffness polymer is preferably 80% or less.

[0016] Optionally, the high stiffness polymer comprises at least one of polyethylene, polypropylene, polystyrene, polymethyl methacrylate, polyamide.

[0017] High-rigidity polymers include common engineering plastics, which are industrial plastics used for industrial parts or outer casing materials and have good strength, impact resistance, heat resistance, hardness, and degradation resistance. For example, they include at least one of polyethylene, polypropylene, polystyrene, polymethyl methacrylate, and polyamide. The high-rigidity polymers of the present application can be selected from the high-rigidity polymers listed above, but of course, other high-rigidity polymers besides those listed herein can also be selected. The crystallinity of engineering plastics is relatively high, typically 32% to 94%. Using the above high-rigidity polymers as the core layer structure is advantageous in improving the cold press performance of the binder.

[0018] Optionally, the shape of the binder comprises a sphere.

[0019] The spherical shape is advantageous for uniform dispersion during the paste stirring process and helps in uniform application.

[0020] Alternatively, the binder has a volumetric particle size distribution Dv50 of 1 μm to 15 μm, and preferably, the binder has a volumetric particle size distribution Dv50 of 1 μm to 12 μm.

[0021] In order to improve the permeability of lithium ions (lithium ion batteries are used as an example, but other types of secondary batteries may also be used) on the separator and the energy density of the battery, the volume-based particle size distribution Dv50 of the binder is 1 μm to 15 μm, and preferably 1 μm to 12 μm.

[0022] Optionally, the ratio of the volume-based particle size distribution Dv50 of the acrylic acid ester copolymer to the volume-based particle size distribution Dv50 of the high-rigidity polymer is 1:(1 to 50).

[0023] In order to effectively adsorb the acrylate copolymer onto the surface of the core layer structure and form a core-shell structure, the volumetric particle size distribution Dv50 of the acrylate copolymer is smaller than the volumetric particle size distribution Dv50 of the high rigidity polymer; specifically, the ratio of the volumetric particle size distribution Dv50 of the acrylate copolymer to the volumetric particle size distribution Dv50 of the high rigidity polymer is 1:(1 to 50).

[0024] Alternatively, the volume-based particle size distribution Dv50 of the high rigidity polymer is 0.1 μm to 5 μm, and preferably, the volume-based particle size distribution Dv50 of the high rigidity polymer is 0.5 μm to 2 μm; And / or, the volumetric particle size distribution Dv50 of the acrylic acid ester copolymer is 100 nm to 200 nm, preferably 130 nm to 180 nm. As will be understood, in order to obtain a binder with a core-shell structure and further to improve the adhesiveness of the binder, the volumetric particle size distribution Dv50 of the high-rigidity polymer is 0.1 μm to 5 μm, preferably 0.5 μm to 2 μm, and the volumetric particle size distribution Dv50 of the acrylic acid ester copolymer is 100 nm to 200 nm, preferably 130 nm to 180 nm.

[0025] As will be understood, in the binder of the core-shell structure, the shell layer structure may completely cover the core layer structure, or the shell layer structure may not completely cover the shell layer structure.

[0026] Optionally, the ratio of the mass of the shell layer structure to the mass of the core layer structure is 1:(0.1 to 10), and preferably, the ratio of the mass of the shell layer structure to the mass of the core layer structure is 1:(0.1 to 5).

[0027] In order to alleviate the problem that the adhesive performance of the binder is reduced when the mass of the high-rigidity polymer is too large, and to alleviate the problem that the overall hardness of the binder is reduced when the mass of the high-rigidity polymer is too small, which affects the performance of the subsequent cell, the ratio of the mass of the shell layer structure to the mass of the core layer structure is 1: (0.1 to 10), and preferably the ratio of the mass of the shell layer structure to the mass of the core layer structure is 1: (0.1 to 5).

[0028] Optionally, the constituent monomers of the acrylic acid ester copolymer include at least two of an acrylic acid ester monomer, an acrylonitrile monomer, and an acrylamide monomer.

[0029] The acrylic acid ester copolymer has good adhesive properties, and the use of the acrylic acid ester copolymer can further improve the adhesiveness between the separator and the polar sheet after cold pressing.

[0030] As can be seen, the acrylic ester monomer can improve the swelling resistance of the polymer and, as a flexible monomer segment in the molecular segment, can adjust the glass transition temperature of the polymer, improving the toughness during binder application and providing good adhesive properties. The acrylonitrile monomer has a highly polar cyano group, which helps improve ionic conductivity. The acrylamide monomer plays a role in adjusting the molecular weight.

[0031] When the constituent monomers of an acrylic acid ester copolymer contain two of an acrylic acid ester monomer, an acrylonitrile monomer, and an acrylamide monomer, the adhesive performance is excellent, and when the constituent monomers contain the above three monomers simultaneously, the performance is even better.

[0032] Alternatively, the acrylic acid ester monomer may include at least one of methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, n-propyl acrylate, cyclohexyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, isobornyl methacrylate, lauryl methacrylate, 2-hydroxyethyl methacrylate, and 2-hydroxypropyl methacrylate; and / or the acrylonitrile-based monomer comprises at least one of acrylonitrile or methacrylonitrile; And / or, the acrylamide-based monomer includes at least one of acrylamide, N-methylolacrylamide, and N-butoxymethylacrylamide.

[0033] The use of one or more of the above acrylic ester monomers can adjust the glass transition temperature of the polymer and improve the swelling resistance of the polymer. The above is a list of acrylic ester monomers, and the acrylic ester monomer used in the present application may be one of the above listed substances or an acrylic ester monomer other than that of the present application.

[0034] The ionic conductivity of the binder can be improved by using one or more of the above acrylonitrile-based monomers. The above is a list of acrylonitrile-based monomers, and the acrylonitrile-based monomer used in the present application may be one of the above listed substances or an acrylonitrile-based monomer other than that of the present application.

[0035] The use of one or more of the above acrylamide-based monomers can adjust the molecular weight, and is used to adjust the molecular weight of the polymer, thereby helping to improve adhesion within a certain range of the molecular weight of the binder. The above is a list of acrylamide-based monomers, and the acrylamide-based monomer used in the present application may be one of the above-listed substances or may be an acrylamide-based monomer other than that of the present application.

[0036] Alternatively, the constituent monomers of the acrylic ester copolymer include an acrylic ester monomer, an acrylonitrile monomer, and an acrylamide monomer, and the mass ratio of the acrylic ester monomer to the acrylonitrile monomer to the acrylamide monomer is 1:(0.01-0.8):(0.01-0.15), and preferably the mass ratio of the acrylic ester monomer to the acrylonitrile monomer to the acrylamide monomer is 1:(0.1-0.6):(0.06-0.12).

[0037] By controlling the mass ratio of the above three monomers within the above range, the molecular weight and glass transition temperature of the polymer can be controlled, thereby improving the adhesive performance of the binder.

[0038] The present application further provides: preparing an acrylic ester copolymer emulsion; and mixing the acrylic acid ester copolymer emulsion with a high-rigidity polymer, followed by spray drying to obtain a binder having a core-shell structure.

[0039] An acrylic ester copolymer emulsion is prepared by emulsion polymerization, and the acrylic ester copolymer emulsion is mixed with a high-rigidity polymer, followed by spray drying to obtain a binder with a core-shell structure.

[0040] During spray drying, the acrylic acid ester copolymer, which has a small particle size and viscosity, is adsorbed onto the surface of non-viscous, highly rigid particles and coated thereon, thereby forming a core-shell structure.

[0041] In the step of forming the core-shell structure binder, spray drying is more effective than emulsion polymerization in coating the high-rigidity particles with the acrylate copolymer. At the same time, since the emulsion polymerization process makes it difficult to control the polymerization step, the core-shell structure binder is prepared by the spray drying process, and the resulting binder has better adhesion.

[0042] During the spray drying process, the shell layer structure is formed by the accumulation of spherical particles on the surface of the core layer structure, and the spherical particles are in point contact with each other, forming channels and voids in the shell layer, which is conducive to the impregnation of the electrolyte. The support of the core layer structure reduces the probability of the binder particles being crushed during the cold pressing process, that is, reduces the possibility of the channels and voids in the shell layer being crushed, improves the porosity of the adhesive layer, and allows the electrolyte to penetrate into the binder through the voids between the acrylate copolymer particles.

[0043] At the same time, some high-rigidity polymer materials have abundant functional groups on their surfaces, which can improve the impregnation of the electrolyte, accelerate the ion transmission rate, and improve the electrical and chemical properties of the battery. For example, high-rigidity polymers made of polymethyl methacrylate have ester groups, which can improve the impregnation of the solvent in the electrolyte, such as ethylene carbonate, propylene carbonate, methyl ethyl carbonate, etc.

[0044] Optionally, the step of preparing the acrylic ester-based copolymer emulsion includes: a step of emulsifying water, an emulsifier, and constituent monomers of an acrylic acid ester copolymer by stirring to obtain a preliminary emulsion of the monomers; and a step of emulsifying the emulsifier and water by stirring, adding the pre-emulsion and initiator under heating conditions, and raising the temperature to obtain an acrylic acid ester copolymer emulsion.

[0045] In the preparation of the acrylate copolymer emulsion, the monomers are mixed more uniformly by first pre-emulsifying and then polymerizing, so that the resulting acrylate copolymer has more uniform particles and more stable performance.

[0046] The present application further provides a separator including a base film and an adhesive layer provided on at least one side of the base film, the adhesive layer including the binder for a secondary battery; Alternatively, the adhesive layer may include a binder manufactured by the method for manufacturing a binder for a secondary battery.

[0047] The present application further provides a secondary battery including the separator.

[0048] The present application further provides a power consuming device including the secondary battery. [Brief explanation of the drawings]

[0049] In order to more clearly describe the embodiments of the present application or the technical solutions in the prior art, the drawings necessary for describing the embodiments or the prior art are briefly described below. The drawings shown below are only some embodiments of the present application, and it is obvious that a person skilled in the art can obtain other drawings based on the structures shown in these drawings without any creative efforts.

[0050] [Figure 1] 1 is a scanning electron microscope image of a binder according to Example 1 of the present application. [Figure 2] 1 is a flowchart of a method for producing a binder according to an embodiment of the present application. [Figure 3] 1 is a schematic diagram of a secondary battery according to an embodiment of the present application. [Figure 4] FIG. 4 is an exploded view of the secondary battery according to the embodiment of the present invention shown in FIG. [Figure 5] 1 is a schematic diagram of a battery module according to an embodiment of the present application; [Figure 6] 1 is a schematic diagram of a battery pack according to an embodiment of the present application. [Figure 7] FIG. 7 is an exploded view of the battery pack according to the embodiment of the present invention shown in FIG. [Figure 8] 1 is a schematic diagram of a power consumption device that uses a secondary battery according to an embodiment of the present application as a power source. [Explanation of symbols]

[0051] 1 battery pack 2 Upper case 3 Lower housing 4 Battery Module 5 Secondary battery 51 Housing 52 Electrode Assembly 53 Top cover assembly

[0052] The realization of the object, features and advantages of the function of the present invention will be further explained in combination with the embodiments and with reference to the drawings. DETAILED DESCRIPTION OF THE INVENTION

[0053] The technical solutions in the embodiments of the present application will be described below clearly and completely with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only some of the embodiments of the present application, not all of the embodiments, and all other embodiments obtained by those skilled in the art based on the embodiments of the present application without any creative efforts fall within the scope of protection of the present application.

[0054] Hereinafter, embodiments of the binder and its manufacturing method, as well as separators, electrode assemblies, battery cells, batteries, and power consuming devices containing the binder, according to the present application, will be described in detail with reference to the accompanying drawings as appropriate. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and redundant descriptions of substantially identical structures may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate understanding by those skilled in the art. Furthermore, the drawings and the following description are provided to enable those skilled in the art to fully understand the present application, and are not intended to limit the subject matter described in the claims.

[0055] The "ranges" disclosed herein are defined in terms of lower and upper limits. A given range is defined by selecting one lower limit and one upper limit, and the selected lower and upper limits define the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive of the endpoints and may be arbitrarily combined, i.e., any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are recited for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also contemplated. Also, if minimum range values ​​of 1 and 2 are recited and maximum range values ​​of 3, 4, and 5 are recited, then the ranges of 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5 are all contemplated. Unless otherwise specified, the numerical range "a to b" herein is a shorthand notation for any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0 to 5" means that all real numbers between "0 and 5" are recited herein, and "0 to 5" is merely a shorthand notation for combinations of these numbers. Furthermore, expressing a parameter as an integer ≧2 is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0056] All embodiments and alternative embodiments of the present application can be combined with each other to form new technical solutions, unless otherwise specified.

[0057] All technical features and optional technical features in the present application can be combined with each other to form new technical solutions unless otherwise stated.

[0058] All steps in this application can be performed in order or randomly, and are preferably performed in order, unless otherwise specified. For example, when the method includes steps (a) and (b), this means that the method may include steps (a) and (b) performed in order, or may include steps (b) and (a) performed in order. For example, when the method may further include step (c), this means that step (c) may be added to the method in any order, such as 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.

[0059] The battery cell has an opening problem, that is, gaps are easily formed between the polar sheet and the separator, which deteriorates the cycle performance of the battery.

[0060] For example, polyvinylidene fluoride (PVF), the most common binder, is widely used in separators. However, at present, PVF is expensive. Polyvinylidene fluoride polymers can be applied to the surface of secondary battery separators to partially solve the separator's high-temperature shrinkage problem. Cold pressing is performed on wound cells, but typical PVF is a homopolymer with a crystallinity of approximately 50%, which results in insufficient adhesion to the positive and negative electrode sheets, resulting in frequent cell openings. This does not meet the separator coating performance requirements for power secondary batteries.

[0061] Specifically, polyvinylidene fluoride polymer is applied to the surface of a battery separator, partially resolving the separator's high-temperature shrinkage problem. The wound cell is cold-pressed, but typical polyvinylidene fluoride is a homopolymer with a crystallinity of approximately 50%, resulting in insufficient adhesion to the positive and negative electrode sheets, which often leads to cell openings. Cell openings form gaps between the polar sheets and the separator, loosening the overall cell structure and reducing the cell's hardness, affecting the cell's cycle performance.

[0062] A cell is formed by bonding a positive electrode sheet, a negative electrode sheet, and a separator, and the cell has a certain hardness. That is, the bonded positive electrode sheet, negative electrode sheet, and separator are bonded together and supported by each other, forming a structure with a certain thickness. A structure with a certain thickness has a certain hardness. However, the negative electrode expands during charging and discharging. If the adhesive strength is weak, gaps will form between the positive electrode sheet or negative electrode sheet and the separator, and the positive and negative electrode sheets and the separator will not be bonded to each other and will not be able to support each other. This will cause the cell to become loose and its hardness will decrease. At this time, the power characteristics of the cell will deteriorate, such as the rate characteristics and cycle characteristics will also deteriorate. For example, in an electric vehicle, loose battery cells will slow down the battery's charging speed and at the same time, the battery's cycle characteristics will deteriorate, directly leading to a shortened battery life, requiring frequent battery replacement in the electric vehicle, and increasing the costs for electric vehicle consumers.

[0063] Based on this, the present application provides a binder for a secondary battery, the binder comprising a core layer structure and a shell layer structure provided on the surface of the core layer structure, the shell layer structure comprising an acrylic acid ester copolymer, the core layer structure comprising a high-rigidity polymer, and the range of crystallinity of the high-rigidity polymer being 32% to 94%.

[0064] A binder is a material that has adhesive properties and is used to bond different substances together.

[0065] The core-shell structure refers to a structure consisting of a central core and a shell covering the outer layer.

[0066] The core layer structure is a structure located inside the core-shell structure and covered with the outer shell.

[0067] The shell layer structure is a structure located outside the core-shell structure and covering the surface of the core layer structure.

[0068] The core-shell structure can be observed using a transmission electron microscope. Specifically, because the materials of the core-shell structure are different, a difference in brightness (weight-thickness contrast) occurs between the core layer structure and the shell layer structure in the transmission electron microscope image. The weight-thickness contrast is caused by differences in thickness and mass in different areas of the sample surface, and the contrast is brought about by differences in the electron scattering ability of each part of the sample, and the number of transmitted electrons that pass through the objective lens also differs. Therefore, there is a difference in the intensity of the electron beam, and areas with strong scattering and few transmitted electrons will have a dark image, and vice versa will have a bright image.

[0069] Regarding the acrylic acid ester copolymer, the acrylic acid ester copolymer is a general term for polymers produced by copolymerizing an acrylic acid ester monomer with another comonomer.

[0070] The structure of the acrylic acid ester monomer has an acrylic acid ester group, and examples thereof include methyl acrylate, ethyl acrylate, and n-butyl acrylate.

[0071] The acrylic acid ester copolymer has good adhesive properties, and the use of the acrylic acid ester copolymer can further improve the adhesiveness between the separator and the polar sheet after cold pressing.

[0072] Regarding crystallinity, crystallinity is used to express the proportion of crystalline regions in a polymer, where crystals are regular arrangements of molecular chains.

[0073] Crystallinity can be measured using DSC (differential scanning calorimetry). For example, the crystallinity of polypropylene can be measured as follows: The DSC method is used to determine crystallinity, and the heat of fusion ΔH0 of a completely crystalline polymer is a standardized value, reducing the influence of the sample on the measurement results. The specific procedure is as follows: Under nitrogen gas protection at a flow rate of 20 mL / min, a 5 mg sample is placed in a DSC (differential scanning calorimetry (DSC) instrument: SDT2960, TA, USA). The temperature is increased from room temperature to 210°C at a rate of 15°C / min, and the sample is allowed to cool at a constant temperature for 5 minutes. The cooling process is then recorded and the crystallinity is calculated.

[0074] Regarding high-rigidity polymers, the crystallinity range of high-rigidity polymers is 32% to 94%, and they have high strength, impact resistance, heat resistance, hardness, and resistance to deterioration. Examples include polyethylene and polypropylene. High-rigidity polymers have a lower specific gravity than inorganic particles, which can improve battery energy density.

[0075] During the cold pressing of the cell, the high stiffness polymer is less likely to deform, and as can be seen, no or only small deformation occurs in the high stiffness polymer during the cold pressing process. As can be seen, the cold pressing force range during the cold pressing process is 1 MPa to 10 MPa, and within this range, no or only small deformation occurs in the high stiffness polymer.

[0076] The core-shell binder has a core layer structure of a high-rigidity polymer, and during the cold-pressing process of the cells, the high-rigidity polymer acts as a support to stabilize the particle structure of the binder, i.e., the high-rigidity polymer plays a supporting role and improves the overall rigidity of the binder, improving the dimensional stability of the binder during cold-pressing of the cells and preventing complete deformation, thereby improving the adhesive strength of the cold-pressed cells and improving the hardness of the cells.

[0077] As can be seen, if the core layer does not have a high-rigidity polymer support, the binder is more likely to be crushed, and in the process of crushing the binder, the voids between the binders are compressed and blocked, which is detrimental to the penetration of the electrolyte and the transmission of ions.

[0078] Because the high-rigidity polymer is difficult to deform, the binder can maintain a certain shape during the cold pressing process, which solves the problem of the voids between the binder particles being blocked due to the deformation of the binder during the process of crushing the binder.

[0079] Because the binder of the present invention has the support of a highly rigid polymer, complete deformation of the binder particles is unlikely to occur during cold pressing, and the voids between the binder particles are not blocked. The unblocked voids serve as paths for electrolyte impregnation, which is favorable for ion transmission. At the same time, the hardness of the cell can be further improved, the dynamic properties of the secondary battery can be improved, the electrical and chemical impedance can be reduced, and the cycle characteristics of the secondary battery can be improved.

[0080] As can be seen, during the cold pressing of the cells, the core layer structure of the binder is not deformed or is deformed only slightly, reducing the probability of the binder particles being crushed, and the shell layer structure includes an acrylic ester copolymer, which can provide good viscosity and improve the adhesive strength of the cold pressing of the cells.

[0081] In the above range of 32% to 94%, values ​​include the minimum and maximum values ​​of the range, and each value between this minimum and maximum value. Specific examples include, but are not limited to, the endpoint values ​​in the examples and 32%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 94%, etc., and range values ​​between any two of the above endpoint values.

[0082] In one embodiment, the range of crystallinity values ​​for the high stiffness polymer includes 40% to 80%.

[0083] In order to improve the hardness of the high stiffness polymer, the crystallinity of the high stiffness polymer is preferably 40% or more. At the same time, considering that if the crystallinity is too high, it is difficult to realize the process, the crystallinity of the high stiffness polymer is preferably 80% or less.

[0084] In the above range of 40% to 80%, the values ​​include the minimum and maximum values ​​of the range, and each value between the minimum and maximum values. Specific examples include, but are not limited to, the endpoint values ​​in the examples and 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, etc., and range values ​​between any two of the endpoint values.

[0085] In one embodiment, the high stiffness polymer comprises at least one of polyethylene, polypropylene, polystyrene, polymethyl methacrylate, and polyamide.

[0086] High-rigidity polymers include common engineering plastics, which are industrial plastics used for industrial parts or outer casing materials and have good strength, impact resistance, heat resistance, hardness, and degradation resistance. For example, they include at least one of polyethylene, polypropylene, polystyrene, polymethyl methacrylate, and polyamide. The high-rigidity polymers of the present application can be selected from the high-rigidity polymers listed above, but of course, other high-rigidity polymers besides those listed herein can also be selected. The crystallinity of engineering plastics is relatively high, typically 32% to 94%. Using the above high-rigidity polymers as the core layer structure is advantageous in improving the cold press performance of the binder.

[0087] In one embodiment, the shape of the binder comprises a sphere.

[0088] The spherical shape is advantageous for uniform dispersion during the paste stirring process and helps in uniform application.

[0089] In one embodiment, the volume-based particle size distribution Dv50 of the binder is 1 μm to 15 μm, and preferably, the volume-based particle size distribution Dv50 of the binder is 1 μm to 12 μm.

[0090] Regarding Dv50, in the sample particles, the particle size of particles that make up 50% of the total volume is larger than this value, and the particle size of particles that make up the other 50% of the total volume is smaller than this value, and Dv50 represents the particle size value in the sample.

[0091] The volumetric particle size distribution Dv50 of the binder can be measured using methods known in the art, for example, GB / T 19077-2016, and characterization tests can be performed using a Malvern laser granulometer, such as a Malvern Mastersizer-3000.

[0092] In order to improve the permeability of lithium ions (lithium ion batteries are used as an example, but other types of secondary batteries may also be used) on the separator and the energy density of the battery, the volume-based particle size distribution Dv50 of the binder is 1 μm to 15 μm, and preferably 1 μm to 12 μm.

[0093] In the above range of 1 μm to 15 μm, the values ​​include the minimum and maximum values ​​of the range, and each value between this minimum and maximum value. Specific examples include, but are not limited to, the endpoint values ​​in the examples and 1 μm, 2 μm, 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, etc., and range values ​​between any two of the endpoint values.

[0094] In the above range of 1 μm to 15 μm, the values ​​include the minimum and maximum values ​​of the range, and each value between the minimum and maximum values. Specific examples include, but are not limited to, the endpoint values ​​in the examples and 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, etc., and range values ​​between any two of the endpoint values.

[0095] Theoretically, the volumetric particle size distribution Dv50 of the acrylic acid ester copolymer and the volumetric particle size distribution Dv50 of the high-rigidity polymer in the binder can be obtained after measurement with a transmission electron microscope and a scanning electron microscope.

[0096] The size of the core layer structure can be measured from the binder image obtained by transmission electron microscopy, and the size of the shell layer particles can be measured from the image obtained by scanning electron microscopy.

[0097] In one embodiment, the ratio of the volume-based particle size distribution Dv50 of the acrylic acid ester copolymer to the volume-based particle size distribution Dv50 of the high rigidity polymer is 1:(1 to 50).

[0098] In order to effectively adsorb the acrylate copolymer onto the surface of the core layer structure and form a core-shell structure, the volumetric particle size distribution Dv50 of the acrylate copolymer is smaller than the volumetric particle size distribution Dv50 of the high rigidity polymer; specifically, the ratio of the volumetric particle size distribution Dv50 of the acrylate copolymer to the volumetric particle size distribution Dv50 of the high rigidity polymer is 1:(1 to 50).

[0099] In the above 1: (1 to 50), the values ​​include the minimum and maximum values ​​of the range, and each value between the minimum and maximum values. Specific examples include, but are not limited to, the endpoint values ​​in the examples and 1:1, 1:5, 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, 1:50, etc., and range values ​​between any two of the endpoint values.

[0100] In one embodiment, the volumetric particle size distribution Dv50 of the high rigidity polymer is 0.1 μm to 5 μm, preferably 0.5 μm to 2 μm, and / or the volumetric particle size distribution Dv50 of the acrylic acid ester copolymer is 100 nm to 200 nm, preferably 130 nm to 180 nm.

[0101] As can be seen, in order to obtain a binder with a core-shell structure and further to improve the adhesiveness of the binder, the volumetric particle size distribution Dv50 of the high-rigidity polymer is 0.1 μm to 5 μm, preferably 0.5 μm to 2 μm, and the volumetric particle size distribution Dv50 of the acrylic acid ester copolymer is 100 nm to 200 nm, preferably 130 nm to 180 nm.

[0102] In the above range of 0.1 μm to 5 μm, the values ​​include the minimum and maximum values ​​of the range, and each value between the minimum and maximum values. Specific examples include, but are not limited to, the endpoint values ​​in the examples and 0.1 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, etc., and range values ​​between any two of the endpoint values.

[0103] In the above range of 0.5 μm to 2 μm, the values ​​include the minimum and maximum values ​​of the range, and each value between the minimum and maximum values. Specific examples include, but are not limited to, the endpoint values ​​in the examples and 0.5 μm, 0.7 μm, 0.9 μm, 1 μm, 1.2 μm, 1.4 μm, 1.5 μm, 1.7 μm, 1.9 μm, 2 μm, etc., and range values ​​between any two of the endpoint values.

[0104] In the above range of 100 nm to 200 nm, the values ​​include the minimum and maximum values ​​of the range, and each value between the minimum and maximum values. Specific examples include, but are not limited to, the endpoint values ​​in the examples and 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 18 nm, 190 nm, 200 nm, etc., and range values ​​between any two of the endpoint values.

[0105] In the above range of 130 nm to 180 nm, the values ​​include the minimum and maximum values ​​of the range, and each value between the minimum and maximum values. Specific examples include, but are not limited to, the endpoint values ​​in the examples and range values ​​between any two of the endpoint values, such as 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 18 nm, etc.

[0106] As will be understood, the binder of the core-shell structure may be such that the shell layer structure completely covers the core layer structure, or the shell layer structure may not completely cover the shell layer structure, and is not specifically limited.

[0107] In one embodiment, the ratio of the mass of the shell layer structure to the mass of the core layer structure is 1:(0.1-10), and preferably the ratio of the mass of the shell layer structure to the mass of the core layer structure is 1:(0.1-5).

[0108] Regarding the method for measuring the mass ratio, when the mass of the high-rigidity polymer for producing the core layer structure added in the binder production process is recorded as m and the mass of the acrylic acid ester copolymer for producing the shell layer structure is recorded as n, the mass ratio of the core layer structure to the shell layer structure is m:n.

[0109] In order to alleviate the problem that the adhesive performance of the binder is reduced when the mass of the high-rigidity polymer is too large, and to alleviate the problem that the overall hardness of the binder is reduced when the mass of the high-rigidity polymer is too small, which affects the performance of the subsequent cells, the ratio of the mass of the shell layer structure to the mass of the core layer structure is 1: (0.1 to 10), preferably 1: (0.1 to 5).

[0110] In the above 1: (0.1 to 10), the values ​​include the minimum and maximum values ​​of the range, and each value between this minimum and maximum value. Specific examples include, but are not limited to, the endpoint values ​​in the examples and 1:0.1, 1:0.5, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, etc., and range values ​​between any two of the above endpoint values. In the above 1: (0.1 to 5), the values ​​include the minimum and maximum values ​​of the range, and each value between this minimum and maximum value. Specific examples include, but are not limited to, the endpoint values ​​in the examples and 1:0.1, 1:1, 1:2, 1:3, 1:4, 1:5, etc., and range values ​​between any two of the endpoint values.

[0111] In one embodiment, the constituent monomers of the acrylic ester copolymer include at least two of an acrylic ester monomer, an acrylonitrile monomer, and an acrylamide monomer.

[0112] The acrylic ester monomer contains an acrylic ester group in the structure of the acrylic ester monomer, and the structural formula thereof is, for example: JPEG0007815280000001.jpg20170, where R1 comprises a hydrogen atom or an alkyl group having 1 to 12 carbon atoms, and R2 comprises an alkyl group having 1 to 12 carbon atoms. In one embodiment, the acrylic ester monomer includes methyl acrylate, ethyl acrylate, n-butyl acrylate, etc.

[0113] The acrylonitrile-based monomer contains an unsaturated cyano group in the structure of the acrylonitrile-based monomer, and its structural formula is, for example: JPEG0007815280000002.jpg17170, where R3 comprises a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. In one embodiment, the acrylonitrile-based monomer comprises acrylonitrile, methacrylonitrile, etc.

[0114] The acrylamide monomer contains an unsaturated amide group in the structure of the acrylamide monomer, for example, the structural formula JPEG0007815280000003.jpg22170, where R4 comprises a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and R5 comprises a hydrogen atom, an alkyl group having 1 to 6 carbon atoms substituted with a hydroxyl group, or an alkoxy group having 1 to 6 carbon atoms. In one embodiment, the acrylamide-based monomer includes acrylamide, N-methylolacrylamide, and N-butoxymethylacrylamide.

[0115] As can be seen, the acrylic acid ester monomer can improve the swelling resistance of the polymer, and can adjust the glass transition temperature of the polymer as a flexible monomer segment in the molecular segment, which helps improve the toughness of the binder during coating and exhibit good adhesive properties.

[0116] The acrylonitrile monomer has a cyano group with strong polarity, which helps to improve ionic conductivity.

[0117] The acrylamide monomer serves to adjust the molecular weight.

[0118] When the constituent monomers of the acrylic ester copolymer include two of an acrylic ester monomer, an acrylonitrile monomer, and an acrylamide monomer, for example, when the copolymer includes an acrylic ester monomer and an acrylonitrile monomer, and when the copolymer includes an acrylic ester monomer and an acrylamide monomer, the copolymer exhibits excellent adhesive performance, and when the copolymer includes the above three monomers simultaneously, the performance is even better.

[0119] In one embodiment, the acrylic ester monomer includes at least one of methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, n-propyl acrylate, cyclohexyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, isobornyl methacrylate, lauryl methacrylate, 2-hydroxyethyl methacrylate, and 2-hydroxypropyl methacrylate; and / or the acrylonitrile monomer includes at least one of acrylonitrile or methacrylonitrile; and / or the acrylamide monomer includes at least one of acrylamide, N-methylolacrylamide, and N-butoxymethylacrylamide.

[0120] The use of one or more of the above acrylic ester monomers can adjust the glass transition temperature of the polymer and improve the swelling resistance of the polymer. The above is a list of acrylic ester monomers, and the acrylic ester monomer used in the present application may be one of the above listed substances or an acrylic ester monomer other than that of the present application.

[0121] The ionic conductivity of the binder can be improved by using one or more of the above acrylonitrile-based monomers. The above is a list of acrylonitrile-based monomers, and the acrylonitrile-based monomer used in the present application may be one of the above listed substances or an acrylonitrile-based monomer other than that of the present application.

[0122] The use of one or more of the above acrylamide-based monomers can adjust the molecular weight, and is used to adjust the molecular weight of the polymer, thereby helping to improve adhesion within a certain range of the molecular weight of the binder. The above is a list of acrylamide-based monomers, and the acrylamide-based monomer used in the present application may be one of the above-listed substances or may be an acrylamide-based monomer other than that of the present application.

[0123] In one embodiment, the constituent monomers of the acrylic ester copolymer include an acrylic ester monomer, an acrylonitrile monomer, and an acrylamide monomer, and the mass ratio of the acrylic ester monomer to the acrylonitrile monomer to the acrylamide monomer is 1:(0.01-0.8):(0.01-0.15), and preferably the mass ratio of the acrylic ester monomer to the acrylonitrile monomer to the acrylamide monomer is 1:(0.1-0.6):(0.06-0.12).

[0124] By controlling the mass ratio of the above three monomers within the above range, the molecular weight and glass transition temperature of the polymer can be controlled, thereby improving the adhesive performance of the binder.

[0125] In the above 1:(0.01-0.8):(0.01-0.15), the values ​​include the minimum and maximum values ​​of the range, and each value between the minimum and maximum values. Specific examples include the endpoint values ​​in the examples and 1:0.01:0.01, 1:0.1:0.01, 1:0.4:0.01, 1:0.8:0.01, 1:0.01:0.05, 1:0.01: Including, but not limited to, 0.1, 1:0.01:0.15, 1:0.1:0.01, 1:0.1:0.05, 1:0.1:0.15, 1:0.4:0.01, 1:0.4:0.05, 1:0.4:0.15, 1:0.8:0.01, 1:0.8:0.05, 1:0.8:0.15, etc., and range values ​​between any two of the above endpoints.

[0126] In the above 1:(0.1-0.6):(0.06-0.12), the values ​​include the minimum and maximum values ​​of the range, and each value between this minimum and maximum value. Specific examples include, but are not limited to, the endpoint values ​​in the examples and range values ​​between any two of the endpoint values, such as 1:0.1:0.06, 1:0.4:0.06, 1:0.6:0.06, 1:0.1:0.1, 1:0.1:0.12, etc.

[0127] In one embodiment, the present application provides a method for producing a binder for a secondary battery, further comprising the steps of: preparing an acrylic ester-based copolymer emulsion; and mixing the acrylic ester-based copolymer emulsion with a high-rigidity polymer and spray-drying the mixture to obtain a binder having a core-shell structure.

[0128] Spray drying is a process in which the material to be dried (a mixture of acrylic ester copolymer emulsion and high-rigidity polymer) is dispersed into very fine mist-like particles by mechanical action, and then brought into contact with hot air (which increases the evaporation surface area of ​​the water and accelerates the drying process), instantly removing most of the water and drying the solid substances in the material into powder.

[0129] The core-shell structure binder is obtained by the process of spray drying.

[0130] During spray drying, the acrylic acid ester copolymer, which has a small particle size and viscosity, is adsorbed onto the surface of non-viscous, highly rigid particles and coated thereon, thereby forming a core-shell structure.

[0131] In the step of forming the core-shell structure binder, spray drying is more effective than emulsion polymerization in coating the high-rigidity particles with the acrylate copolymer. At the same time, since the emulsion polymerization process makes it difficult to control the polymerization step, the core-shell structure binder is prepared by the spray drying process, and the resulting binder has better adhesion.

[0132] During the spray drying process, the shell layer structure is formed by the accumulation of spherical particles on the surface of the core layer structure, and the spherical particles are in point contact with each other, forming channels and voids in the shell layer, which is conducive to the impregnation of the electrolyte. The support of the core layer structure reduces the probability of the binder particles being crushed during the cold pressing process, that is, reduces the possibility of the channels and voids in the shell layer being crushed, improves the porosity of the adhesive layer, and allows the electrolyte to penetrate into the binder through the voids between the acrylate copolymer particles.

[0133] As is well known, most separators in conventional secondary batteries are polyolefin separators. Multilayer separators have the function of closing pores at high temperatures to block ion transmission, ensuring battery safety. The PP (polypropylene) layer on the separator surface further improves the separator's antioxidant ability. Such multilayer polyolefin composite separators provide some improvement in battery cycle performance and safety compared to conventional single-layer separators. However, polyolefin separators still have poor electrolyte impregnation and low thermal decomposition temperatures, making it increasingly difficult for the performance of multilayer polyolefin separators to meet the ever-increasing needs of society.

[0134] The high-rigidity polymers of the present application have low density and excellent thermal and chemical stability. At the same time, the surface of some high-rigidity polymer materials has abundant functional groups, which can improve the impregnation of the electrolyte, accelerate the ion transmission rate, and improve the electrical and chemical properties of the battery. For example, high-rigidity polymers composed of polymethyl methacrylate have ester groups, which can improve the impregnation of the solvent in the electrolyte, such as ethylene carbonate, propylene carbonate, methyl ethyl carbonate, etc.

[0135] In one embodiment, the step of preparing the acrylate copolymer emulsion includes the steps of emulsifying water, an emulsifier, and constituent monomers of the acrylate copolymer by stirring to obtain a preliminary emulsion of the monomers, and emulsifying the emulsifier and water by stirring, adding the preliminary emulsion and an initiator under heating conditions, and then raising the temperature to obtain the acrylate copolymer emulsion.

[0136] The pre-emulsified liquid is a solution obtained by pre-emulsifying the monomers. Emulsification is the process of uniformly dispersing one liquid into another liquid in the form of very small droplets that are not soluble in each other. Water, an emulsifier, and the constituent monomers of the acrylic acid ester copolymer are mixed and stirred, and the constituent monomers of the acrylic acid ester copolymer are dispersed in water under the action of the emulsifier.

[0137] Regarding emulsion polymerization, emulsion polymerization is a method in which a monomer is dispersed in water with an emulsifier and mechanical stirring to form an emulsion, and then an initiator is added to start the polymerization of the monomer.

[0138] Regarding emulsifiers, they are substances that convert insoluble oil and water into emulsions that are difficult to separate. Emulsifiers are generally surfactants that combine the properties of both hydrophilic polar groups and hydrophobic (lipophilic) non-polar groups.

[0139] Regarding initiators, initiators are substances that can initiate the polymerization reaction of monomers. For example, radical initiators refer to compounds that can easily decompose under heat to form radicals (i.e., primary radicals), and can be used to initiate the radical polymerization and copolymerization of olefin and diene monomers.

[0140] In the preparation of the acrylate copolymer emulsion, the monomers are mixed more uniformly by first pre-emulsifying and then polymerizing, so that the resulting acrylate copolymer has more uniform particles and more stable performance, which helps the acrylate copolymer particles to be effectively arranged on the core layer structure during the spray drying process.

[0141] As can be seen, in a specific operating process, the test operation can be carried out using two vessels, and water, an emulsifier, and the constituent monomers of the acrylate copolymer are added to the first vessel and emulsified by stirring to obtain a preliminary emulsion of the monomers. An emulsifier and water are further added to the second vessel and emulsified by stirring, and the preliminary emulsion and initiator solution are added under heating conditions, and the temperature is raised to obtain an acrylate copolymer emulsion.

[0142] For example, in one embodiment, the volumetric particle size distribution Dv50 of the acrylate copolymer obtained by emulsion polymerization is between 0.1 μm and 0.11 μm, with a relatively uniform particle size, while the volumetric particle size distribution Dv50 of the high rigidity polymer is in the range of about 1 μm ± 0.2 μm. The spray drying process allows the acrylate copolymer to be effectively adhered to the surface of the high rigidity polymer.

[0143] An embodiment of the present application further provides a separator including a base film and an adhesive layer provided on at least one side of the base film, wherein the adhesive layer includes the binder for a secondary battery, or the adhesive layer includes a binder manufactured by the method for manufacturing a binder for a secondary battery.

[0144] An embodiment of the present application further provides a secondary battery including the separator.

[0145] The secondary battery includes forms such as a battery module, a battery cell, a battery pack, etc. When the secondary battery is a battery cell, the battery cell includes the separator, when the secondary battery is a battery module, the battery module includes the separator, and when the secondary battery is a battery pack, the battery pack includes the separator.

[0146] An embodiment of the present application further provides a power consuming device including the secondary battery.

[0147] The electrode assembly, battery cell, battery, and power consuming device of the present application will be described below with reference to the drawings as appropriate.

[0148] In one embodiment of the present application, an electrode assembly is provided.

[0149] Generally, an electrode assembly includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charge and discharge process of a battery, active ions are inserted and removed between the positive electrode sheet and the negative electrode sheet. The electrolyte serves to conduct ions between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet and serves to prevent short-circuiting between the positive and negative electrodes while allowing ions to pass through. The separator is the improved separator described above.

[0150] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector.

[0151] As an example, the positive electrode current collector has two surfaces facing each other in the thickness direction thereof, and the positive electrode film layer is provided on one or both of the two facing surfaces of the positive electrode current collector.

[0152] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. The metal foil can be, for example, aluminum foil. The composite current collector can include a polymer substrate layer and a metal layer formed on at least one surface of the polymer substrate layer. The composite current collector can be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, or silver alloy) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE)).

[0153] In some embodiments, when the electrode assembly is a lithium-ion battery, the positive electrode active material can be a known positive electrode active material for batteries. As an example, the positive electrode active material may include at least one of a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and a modified compound thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include lithium cobalt oxide (e.g., LiCoO), lithium nickel oxide (e.g., LiNiO), lithium manganese oxide (e.g., LiMnO, LiMnO), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide (e.g., LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (abbreviated as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (abbreviated as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (abbreviated as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (abbreviated as NCM622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (abbreviated as NCM 811 )), lithium nickel cobalt aluminum oxide (e.g., LiNi 0.85 Co 0.15 Al 0.05 O2) and modified compounds thereof, etc. The lithium-containing phosphate having an olivine structure may include, but is not limited to, for example, at least one of lithium iron phosphate (e.g., LiFePO4 (abbreviated as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (e.g., LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon.

[0154] In some embodiments, the positive electrode film layer may further include a binder, such as at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0155] In some embodiments, the positive electrode film layer may further include an optional conductive agent, such as at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0156] In some embodiments, the positive electrode sheet can be manufactured by the following method: Components for manufacturing the positive electrode sheet, such as a positive electrode active material, a conductive agent, a binder, and any other components, are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode paste, which is then applied to a positive electrode current collector, followed by steps such as drying and cold pressing, to obtain a positive electrode sheet.

[0157] The negative electrode sheet includes a negative electrode active material and includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector.

[0158] As an example, the negative electrode current collector has two surfaces facing each other in the thickness direction thereof, and the negative electrode film layer is provided on one or both of the two facing surfaces of the negative electrode current collector.

[0159] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. The metal foil can be, for example, a copper foil. The composite current collector can include a polymer substrate layer and a metal layer formed on at least one surface of the polymer substrate. The composite current collector can be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, or silver alloy) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE)).

[0160] In some embodiments, the negative electrode active material may be a known battery negative electrode active material. For example, the negative electrode active material may include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of silicon elemental, silicon oxide, silicon carbon composite, silicon nitrogen composite, and silicon alloy. The tin-based material may be selected from at least one of tin elemental, tin oxide, and tin alloy. However, the present application is not limited to these materials, and other conventional materials usable as negative electrode active materials in batteries may also be used. These negative electrode active materials may be used alone or in combination.

[0161] In some embodiments, the negative electrode film layer may further include a binder, which may be selected from at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0162] In some embodiments, the negative electrode film layer may optionally further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0163] In some embodiments, the negative electrode film layer optionally further comprises other auxiliary agents, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0164] In some embodiments, the negative electrode sheet can be manufactured in the following manner: Components for manufacturing the negative electrode sheet, such as a negative electrode active material, a conductive agent, a binder, and any other components, are dispersed in a solvent (e.g., deionized water) to form a negative electrode paste, which is then applied to a negative electrode current collector, and the negative electrode sheet can be obtained through steps such as drying and cold pressing.

[0165] The electrolyte serves to conduct ions between the positive electrode sheet and the negative electrode sheet. The present application does not particularly limit the type of electrolyte, and it can be selected as needed.

[0166] In some embodiments, the electrolyte uses an electrolyte solution, which includes an electrolyte salt and a solvent.

[0167] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bistrifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium bisoxalate borate, lithium difluorooxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0168] In some embodiments, the solvent can be chosen from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0169] In some embodiments, the electrolyte solution optionally further contains additives. For example, the additives may include a negative electrode film-forming additive, a positive electrode film-forming additive, and / or an additive capable of improving specific battery characteristics, 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.

[0170] In some embodiments, the electrode assembly further includes a separator. The present application does not particularly limit the type of separator, and any known porous separator having good chemical and mechanical stability can be selected.

[0171] In some embodiments, the separator may be made of at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, and is not particularly limited. When the separator is a multi-layer composite film, the materials of the layers may be the same or different, and are not particularly limited.

[0172] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be fabricated into an electrode assembly via a winding or lamination process.

[0173] In some embodiments, the electrode assembly can include a sheath, which is used to encapsulate the electrode assembly and electrolyte.

[0174] In some embodiments, the housing of the electrode assembly may be a hard case such as a hard plastic case, an aluminum case, or a steel case. The housing of the electrode assembly may be a soft pack such as a pouch-type soft pack. The soft pack may be made of plastic, such as polypropylene, polybutylene terephthalate, or polybutylene succinate.

[0175] The present application does not particularly limit the shape of the electrode assembly, and it may be cylindrical, rectangular, or any other shape. For example, Figure 3 shows an example of a secondary battery 5 with a rectangular structure.

[0176] In some embodiments, referring to Fig. 4, the exterior material may include a housing 51 and a cover plate 53. The housing 51 includes a bottom plate and a side plate connected to the bottom plate, and a receiving cavity surrounded by the bottom plate and the side plate is formed. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can cover the opening to seal the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator are wound or stacked through a process. Electrode Assembly 52 can be formed. Electrode Assembly 52 is sealed in the receiving cavity. Electrode Assembly 52 is impregnated in the secondary battery 5. Electrode Assembly The number of 52 may be one or more, and those skilled in the art can select it according to specific actual requirements.

[0177] In some embodiments, the electrode assemblies can be assembled into a battery module, and the number of electrode assemblies included in the battery module can be one or more, and the specific number can be selected by those skilled in the art depending on the application and capacity of the battery module.

[0178] FIG. 5 shows an example of a battery module 4. Referring to FIG. 5, in the battery module 4, a plurality of secondary batteries 5 can be arranged in order along the length of the battery module 4. Of course, any other arrangement may be used. The plurality of secondary batteries 5 can also be fixed by fasteners.

[0179] Optionally, the battery module 4 may further include an outer case having an accommodating space for accommodating a plurality of secondary batteries 5.

[0180] In some embodiments, the battery modules can be further assembled into a battery pack, and the number of battery modules included in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0181] 6 and 7 show an example of a battery pack 1. Referring to FIGS. 6 and 7, the battery pack 1 may include a battery case and a plurality of battery modules 4 installed in the battery case. The battery case includes an upper housing 2 and a lower housing 3, and the upper housing 2 can be fitted over the lower housing 3 to form a sealed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the battery case in any manner.

[0182] The present application also provides a power consuming device including at least one of the electrode assembly, battery module, or battery pack according to the present application. The electrode assembly, battery module, or battery pack may be used as a power source for the power consuming device or as an energy storage element for the power consuming device. The power consuming device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), trains, ships, satellites, energy storage systems, etc.

[0183] As the power consuming device, an electrode assembly, a battery module or a battery pack can be selected according to the requirements of its use.

[0184] 8 shows an example of a power consuming device, such as a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the electrode assembly of the power consuming device, a battery pack or a battery module can be used.

[0185] Another example of the device may be a mobile phone, a tablet computer, a laptop, etc. Such devices are generally required to be lightweight and thin, and may use an electrode assembly as a power source.

[0186] Example The following examples are provided for the present application. The examples described below are illustrative and are intended to illustrate the present application only and should not be construed as limiting the present application. If specific techniques or conditions are not specified in the examples, they are carried out according to the techniques or conditions described in the literature in this field or according to the product instructions. If the manufacturer of the reagents or equipment used is not specified, they are all commercially available general products.

[0187] Example 1 Manufacture of acrylic ester copolymers Manufacturing Example 1 (1) Add 150g of deionized water and 3.6g of sodium dodecyl sulfate to a 500ml three-neck flask, and emulsify by thoroughly stirring for 15 minutes. Then, add 91.74g of acrylic acid ester monomer ethyl acrylate, 0.92g of acrylonitrile monomer acrylonitrile, and 7.34g of acrylamide monomer N-methylol acrylamide in a mass ratio of 1:0.01:0.08, in that order, so that the total amount of monomers is 100g. Stir thoroughly for 60 minutes to obtain a preliminary emulsion of the monomers, which is then removed and prepared for use.

[0188] (2) Add 100ml of deionized water and 0.15g of sodium dodecylbenzenesulfonate to a 500ml three-neck flask, heat to 75°C, and emulsify for 15 minutes at 2000 r / min. After the system is fully emulsified, slowly add the preliminary emulsion prepared in the previous step and the initiator solution (0.2g of initiator potassium persulfate dissolved in 30g of deionized water to form a solution). After the addition is complete, increase the temperature to 90°C and keep the reaction temperature for 0.5 hours. Cool to 40°C, adjust the pH to 7 with aqueous ammonia, stop stirring, filter, and discharge to obtain an acrylate copolymer emulsion. The volumetric particle size distribution Dv50 of the acrylate copolymer is 0.1μm±0.01μm (the volumetric particle size distribution Dv50 of the shell layer structure polymer in each example is 0.1μm±0.01μm).

[0189] Manufacturing Examples 2 to 10 Based on Production Example 1, Production Examples 2 to 10 are obtained by changing the types and mass ratios of the monomers added.

[0190] Binder manufacturing Example 1 The acrylate copolymer emulsion (containing 100 g of the acrylate copolymer) from Production Example 1 and 100 g of polypropylene particles with a volumetric particle size distribution Dv50 of 1 μm were dispersed at high speed for 60 minutes, stirred uniformly, and then spray-dried to obtain a core-shell binder. The spray-drying parameters were an intake air temperature of 110°C and an exhaust air temperature of 50°C.

[0191] Examples 2 to 31 Based on Example 1, Examples 2 to 31 are obtained by adjusting the types and mass ratios of polymers in the core layer structure and shell layer structure, the volumetric particle size distribution Dv50 of the core layer structure, and the volumetric particle size distribution Dv50 of the binder.

[0192] Comparative Example 1 Based on Example 1, the mass ratio of the shell layer structure to the core layer structure is adjusted to 1:0, that is, there is no core layer structure, to obtain Comparative Example 1.

[0193] Cell manufacturing and battery manufacturing 1. Separator manufacturing A commercially available PE microporous film (obtained from Zhuogao Electronics Technology Co., Ltd.) with a thickness of 7 μm and an average pore size of 80 nm was used as the substrate. The binder prepared by the above method was uniformly mixed in deionized water by stirring to obtain a paste (solid content 20%). The paste was uniformly applied to both sides of the substrate and dried to remove the solvent, resulting in a coating density of 1.5 g / m2 on the substrate. 2 and obtain the separator.

[0194] 2. Manufacturing the positive electrode sheet A positive electrode paste was prepared by thoroughly stirring and homogeneously mixing polyvinylidene fluoride (PVDF), lithium iron phosphate (LFP), conductive carbon black, and N-methylpyrrolidone (NMP) in a mass ratio of 1.2:58.38:0.42:40. The positive electrode paste was then applied to a 200 g / m 2 The coated aluminum foil is then dried, cold pressed, and cut to obtain a positive electrode sheet.

[0195] 3. Manufacturing of negative electrode sheet Artificial graphite, acetylene black as a conductive agent, styrene butadiene rubber (SBR) as a binder, and sodium carboxymethyl cellulose (CMC-Na) as a thickener were added to deionized water in a mass ratio of 96.2:1.0:1.6:1.2, and the mixture was thoroughly stirred to homogeneously mix, producing a negative electrode paste (solid content 63%). 2 After coating the copper foil of the negative electrode current collector with the amount of the support, the negative electrode sheet is obtained by drying, cold pressing, and cutting.

[0196] 4. Electrolyte Production At 25°C, ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain a mixed solvent, and then LiPF6 was dissolved in the mixed solvent to obtain an electrolyte solution with a LiPF6 concentration of 1 mol / L.

[0197] 5. Secondary battery manufacturing The positive electrode sheet, separator, and negative electrode sheet are laminated and wound in this order, and cold press molding is performed (during which the separator and polar sheet are bonded together) to obtain a cell. The cell is then placed in an exterior material, the above-prepared electrolyte solution is added, and a secondary battery is obtained through processes such as sealing, leaving it to stand, chemical conversion, and aging.

[0198] Performance Test 1. Cold press bonding: The battery's negative electrode sheet and separator were placed on top of each other in a heat press. The heat press parameters were set to 25°C, 10T, and 30 seconds, and a bonded separator / positive electrode sheet sample was obtained by applying pressure. The separator / negative electrode sheet sample was then cut into a 150mm x 20mm rectangular strip. One side of the polar sheet of the rectangular strip was attached to a steel plate with double-sided tape, and the separator and polar sheet were separated at one end of the rectangular strip by a length of 2cm along the length to create a test sample.

[0199] The steel plate was held horizontally and fixed in the lower clamp of a universal testing machine (Xieqiang Instrument Manufacturing (Shanghai) Co., Ltd., model CTM2100), and the peeled end of the separator was fixed in the upper clamp of the universal testing machine and connected to a tensile machine. The measurement conditions were set to a tensile speed of 20 mm / min and a horizontal tensile strength of 10 cm. After the tensile force stabilized, the tensile force value was recorded, and the ratio of the tensile force value to the sample width was used to determine the adhesive strength between the separator and the polar sheet.

[0200] 2. Cell hardness: The cell is placed on a table with both ends horizontal, the width of the hollow part in the center is fixed to 12 cm, the cell is placed naturally flat, and the width by which the center position of the cell deviates from the horizontal reference line is measured, and the hardness of the cell is evaluated based on this.

[0201] 3. EIS data: Using Shanghai Chenhua's CHI660D electrochemical workstation, a small-amplitude sinusoidal voltage signal with a frequency of W1 is applied to the battery system, and the system generates a sinusoidal current response with a frequency of W2. The change in the ratio of the excitation voltage to the response current is the impedance spectrum of the electrochemical system. In AC impedance measurement, the measurement frequency range is 10mHz to 100kHz, and the amplitude is 5mV. Through the measurement, information such as the real and imaginary parts of the impedance at different frequencies can be obtained.

[0202] 4. Cycle characteristics of lithium-ion batteries: Using a LAND battery measurement system, the resulting battery was charged at 25°C at a constant current of 1 / 3C to 3.65V, then further charged at a constant voltage of 3.65V until the current reached 0.05C, allowed to stand for 5 minutes, and then discharged at 1 / 3C to 2.5V. The resulting discharge capacity was designated as the initial capacity C0. The same battery was then subjected to the same steps, and the discharge capacity Cn after 500 cycles was recorded. The battery capacity retention rate Pn after each cycle was calculated as Pn = (Cn / C0) × 100%. Differences in cycle characteristics can be expressed as the battery capacity retention rate at a specific number of cycles.

[0203] Acrylic ester copolymer emulsion manufacturing parameter table [Table 1]

[0204] Binder manufacturing parameter table [Table 2-1] Binder manufacturing parameter table [Table 2-2] Binder manufacturing parameter table [Table 2-3]

[0205] As can be seen from the above data, binders comprising an acrylic ester copolymer shell layer structure and a high-rigidity polymer core layer structure can be applied to batteries, improving the cell hardness while improving the adhesion of the cold-pressed cell, and at the same time helping to reduce electrical and chemical impedance and improving the cycle characteristics of secondary batteries.

[0206] The above is merely a preferred embodiment of the present application and does not limit the scope of the patent of the present application. Any equivalent structural transformation made using the contents of the specification and drawings of the present application under the application concept of the present application, or any direct or indirect application to other related technical fields, is included in the scope of protection of the patent of the present application.

Claims

1. A binder for a secondary battery, comprising: a core layer structure; and a shell layer structure provided on a surface of the core layer structure, wherein the shell layer structure comprises an acrylic acid ester copolymer; and the core layer structure comprises a high-rigidity polymer, the high-rigidity polymer having a crystallinity ranging from 32% to 94%, and the high-rigidity polymer comprising at least one of polyethylene, polypropylene, polystyrene, polymethyl methacrylate, and polyamide.

2. 2. The binder for a secondary battery according to claim 1, wherein the high-rigidity polymer has a crystallinity ranging from 40% to 80%.

3. The binder for a secondary battery according to claim 1 or 2, wherein the shape of the binder includes a spherical shape.

4. 3. The binder for a secondary battery according to claim 1, wherein the binder has a Dv50 of 1 μm to 15 μm.

5. 3. The binder for a secondary battery according to claim 1, wherein the ratio of Dv50 of said acrylic acid ester copolymer to Dv50 of said high rigidity polymer is 1:(1 to 50).

6. The high rigidity polymer has a Dv50 of 0.1 μm to 5 μm, And / or, the acrylic acid ester copolymer has a Dv50 of 100 nm to 200 nm.

7. 3. The binder for a secondary battery according to claim 1, wherein the ratio of the mass of the shell layer structure to the mass of the core layer structure is 1:(0.1 to 10).

8. 3. The binder for a secondary battery according to claim 1, wherein constituent monomers of the acrylic ester copolymer include at least two of an acrylic ester monomer, an acrylonitrile monomer, and an acrylamide monomer.

9. The acrylic acid ester monomer includes at least one of methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, n-propyl acrylate, cyclohexyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, isobornyl methacrylate, lauryl methacrylate, 2-hydroxyethyl methacrylate, and 2-hydroxypropyl methacrylate; and / or the acrylonitrile-based monomer includes at least one of acrylonitrile or methacrylonitrile; and / or the acrylamide-based monomer includes at least one of acrylamide, N-methylolacrylamide, and N-butoxymethylacrylamide.

10. A binder for a secondary battery comprising: a core layer structure and a shell layer structure provided on a surface of the core layer structure, wherein the shell layer structure comprises an acrylate ester copolymer, and the core layer structure comprises a high-rigidity polymer, the high-rigidity polymer having a degree of crystallinity in the range of 32% to 94%, and wherein constituent monomers of the acrylate ester copolymer include an acrylate ester monomer, an acrylonitrile monomer, and an acrylamide monomer, and the mass ratio of the acrylate ester monomer to the acrylonitrile monomer to the acrylamide monomer is 1:(0.01-0.8):(0.01-0.15).

11. A method for producing a binder for a secondary battery, comprising: a core layer structure; and a shell layer structure provided on a surface of the core layer structure, the shell layer structure comprising an acrylic acid ester copolymer; the core layer structure comprising a high-rigidity polymer; and a range value of the crystallinity of the high-rigidity polymer being 32% to 94%, preparing an acrylic ester copolymer emulsion; and mixing the acrylic acid ester copolymer emulsion with a high-rigidity polymer, followed by spray drying to obtain a binder having a core-shell structure.

12. The step of preparing an acrylic ester copolymer emulsion includes: a step of emulsifying water, an emulsifier, and constituent monomers of an acrylic acid ester copolymer by stirring to obtain a preliminary emulsion of the monomers; a step of emulsifying the emulsifier and water by stirring, adding the preliminary emulsion and the initiator under heating conditions, and raising the temperature to obtain an acrylic acid ester-based copolymer emulsion.

13. A separator comprising a base film and an adhesive layer provided on at least one side of the base film, the adhesive layer comprising a binder for a secondary battery including a core layer structure and a shell layer structure provided on a surface of the core layer structure, wherein the shell layer structure comprises an acrylic acid ester copolymer, the core layer structure comprises a high-rigidity polymer, and the range of crystallinity of the high-rigidity polymer is 32% to 94%.

14. A secondary battery comprising the separator according to claim 13.

15. A power consuming device comprising the secondary battery of claim 14.

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