Binder for secondary battery, method for preparing the same, secondary battery, and electric device

Abstract

The present application relates to the technical field of secondary batteries, and particularly relates to a kind of binder for secondary battery and its preparation method, secondary battery and electric device.The binder includes core layer structure and shell layer structure arranged on the surface of core layer structure, the shell layer structure includes acrylate copolymer, the core layer structure includes rigid polymer, and the crystallinity range value of rigid polymer is 32% to 94%.The binder of core-shell structure includes the core layer structure of rigid polymer, and in the process of cell cold pressing, rigid polymer is supported to make that binder particle structure is stable, that is, rigid polymer plays the role of support, the rigidity of binder is improved as a whole, when cell cold pressing, the dimensional stability of binder is improved, not to be completely deformed, in the case where the adhesion of cell cold pressing is improved, the hardness of cell is improved.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, and in particular to a binder for secondary batteries, its preparation method, a secondary battery, and an electrical device. Background Technology

[0002] With the rapid growth of portable electronic devices, electric vehicles, and other technologies, the demand for power batteries is also constantly increasing. Among these, the electrochemical performance of batteries is receiving increasing attention.

[0003] Currently, battery cells have an issue with openings, meaning that gaps can easily form between the electrodes and the separator, leading to poor battery cycle performance. Summary of the Invention

[0004] The main objective of this invention is to provide an adhesive that improves the adhesion between the electrode and the separator, thereby enhancing battery performance.

[0005] To achieve the above objectives, the present invention provides an adhesive for secondary batteries, the adhesive comprising a core layer structure and a shell layer structure disposed on the surface of the core layer structure, the shell layer structure comprising an acrylate copolymer, and the core layer structure comprising a rigid polymer, the rigid polymer having a crystallinity ranging from 32% to 94%.

[0006] Acrylic copolymers have good adhesion, and using acrylic copolymers results in better adhesion between the diaphragm and the electrode after cold pressing.

[0007] Rigid polymers, with a crystallinity ranging from 32% to 94%, possess characteristics such as high strength, impact resistance, heat resistance, hardness, and aging resistance. During the cold pressing process of the battery cell, rigid polymers are difficult to deform; understandably, they undergo little or no deformation during cold pressing.

[0008] The core-shell structured binder includes a core layer structure of rigid polymer. During the cold pressing of the battery cell, the rigid polymer acts as a support to stabilize the binder particle structure. In other words, the rigid polymer plays a supporting role, and the overall rigidity of the binder is improved. During the cold pressing of the battery cell, the dimensional stability of the binder is improved, preventing complete deformation. While improving the bonding force of the battery cell during cold pressing, the hardness of the battery cell is also improved.

[0009] Understandably, without the rigid polymer core layer as support, the probability of the adhesive being flattened increases. During the flattening process, the pores between the adhesives are compressed and blocked, which is not conducive to the penetration of electrolyte and the transport of ions.

[0010] Because rigid polymers are difficult to deform, the binder can maintain a certain shape during cold pressing, which improves the problem of the binder clogging the pores between binder particles due to deformation during the flattening process.

[0011] Because the binder of this application has the support of a rigid polymer, the binder particles are difficult to completely deform during cold pressing, so as not to block the pores between the binder particles. These unblocked pores become channels for electrolyte wetting, which is conducive to ion transport. At the same time, it also improves the hardness of the cell, improves the dynamic performance of the secondary battery, reduces electrochemical impedance, and can improve the cycle performance of the secondary battery.

[0012] Understandably, during the cold pressing process of the battery cell, the core layer structure of the binder does not deform or undergoes only minor deformation, reducing the probability of the binder particles being flattened. The shell structure includes acrylate copolymers, which provide good adhesion and improve the cold pressing adhesion of the battery cell. Understandably, during the cold pressing process, the acrylate copolymers in the shell structure deform under extrusion pressure, allowing the shell structure to be inserted into the gaps of the separator and electrode, thereby improving the adhesion.

[0013] Optionally, the crystallinity of the rigid polymer ranges from 40% to 80%.

[0014] To improve the hardness of rigid polymers, preferably, the crystallinity of the rigid polymer is greater than or equal to 40%. However, considering that excessive crystallinity makes the process difficult to implement, preferably, the crystallinity of the rigid polymer is less than or equal to 80%.

[0015] Optionally, the rigid polymer includes at least one of polyethylene, polypropylene, polystyrene, polymethyl methacrylate, and polyamide.

[0016] Rigid polymers include commonly used engineering plastics, which are industrial plastics used as materials for industrial parts or housings, possessing good strength, impact resistance, heat resistance, hardness, and aging resistance. Examples include at least one of polyethylene, polypropylene, polystyrene, polymethyl methacrylate, and polyamide. The rigid polymer used in this application can be one of the rigid polymers listed above, or other rigid polymers not listed herein. Engineering plastics have a relatively high crystallinity, generally between 32% and 94%. Using the aforementioned rigid polymer as the core layer structure is beneficial for improving the cold-pressing performance of the binder.

[0017] Optionally, the adhesive may be spherical in shape.

[0018] The spherical shape facilitates uniform dispersion during the mixing process, which is beneficial for even coating.

[0019] Optionally, the volumetric particle size distribution Dv50 of the adhesive is from 1 μm to 15 μm, and preferably, the volumetric particle size distribution Dv50 of the adhesive is from 1 μm to 12 μm.

[0020] In order to improve the permeability of lithium ions (taking lithium-ion batteries as an example, but other types of secondary batteries are also possible) on the separator and to improve the energy density of the battery, the volumetric particle size distribution Dv50 of the binder is 1 μm to 15 μm, preferably 1 μm to 12 μm.

[0021] Optionally, the ratio of the volumetric particle size distribution Dv50 of the acrylate copolymer to the volumetric particle size distribution Dv50 of the rigid polymer is 1:(1-50).

[0022] In order to effectively set the acrylate copolymer on 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 that of the rigid polymer. Specifically, the ratio of the volumetric particle size distribution Dv50 of the acrylate copolymer to that of the rigid polymer is 1:(1~50).

[0023] Optionally, the volumetric particle size distribution Dv50 of the rigid polymer is from 0.1 μm to 5 μm, and preferably, the volumetric particle size distribution Dv50 of the rigid polymer is from 0.5 μm to 2 μm.

[0024] And / or, the volumetric particle size distribution Dv50 of the acrylate copolymer is 100 nm to 200 nm, preferably 130 nm to 180 nm. It is understood that, in order to obtain a core-shell structured binder and improve the adhesiveness of the binder, the rigid polymer has a volumetric particle size distribution Dv50 of 0.1 μm to 5 μm, preferably 0.5 μm to 2 μm, and the acrylate copolymer has a volumetric particle size distribution Dv50 of 100 nm to 200 nm, preferably 130 nm to 180 nm.

[0025] It is understandable that the binder of the core-shell structure can be either a shell structure that completely covers the core structure, or a shell structure that does not completely cover the core structure.

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

[0027] To address the issue of reduced adhesive bonding performance caused by excessive rigid polymer mass, and to mitigate the problem of reduced overall hardness of the adhesive due to insufficient rigid polymer mass, which affects subsequent cell performance, a shell structure mass to core structure mass ratio of 1:(0.1-10) is adopted. Preferably, the shell structure mass to core structure mass ratio of 1:(0.1-5) is adopted.

[0028] Optionally, the monomers constituting the acrylate copolymer include at least two of acrylate monomers, acrylonitrile monomers, and acrylamide monomers.

[0029] Acrylic copolymers have good adhesion, and using acrylic copolymers results in better adhesion between the diaphragm and the electrode after cold pressing.

[0030] Understandably, acrylate monomers can improve the polymer's resistance to swelling, and as flexible monomer segments in the molecular chain, they can regulate the polymer's glass transition temperature, improve the adhesive's toughness during application, and contribute to good bonding. Acrylonitrile monomers, with their highly polar cyano groups, help improve ionic conductivity. Acrylamide monomers play a role in regulating molecular weight.

[0031] Acrylic copolymers exhibit better bonding properties when the constituent monomers include two of the following: acrylate monomers, acrylonitrile monomers, and acrylamide monomers. The properties are even better when all three monomers are included.

[0032] Optionally, the acrylate monomers 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.

[0033] And / or, the acrylonitrile monomer includes at least one of acrylonitrile or methacrylonitrile;

[0034] And / or, the acrylamide monomers include at least one of acrylamide, N-hydroxymethylacrylamide and N-butoxymethylacrylamide.

[0035] By using any one or more of the above-mentioned acrylate monomers, the glass transition temperature of the polymer can be adjusted, thereby improving the polymer's resistance to swelling. The above are examples of acrylate monomers; the acrylate monomers used in this application can be substances listed above, or other acrylate monomers not specified in this application.

[0036] Using any one or more of the above-mentioned acrylonitrile monomers can improve the ionic conductivity of the binder. The above is an example of acrylonitrile monomers; the acrylonitrile monomers used in this application can be substances listed above, or other acrylonitrile monomers not listed in this application.

[0037] Using any one or more of the above-mentioned acrylamide monomers can help adjust the molecular weight of the polymer, thereby improving the adhesion of the binder within a certain range. The above are examples of acrylamide monomers; the acrylamide monomers used in this application can be substances listed above, or other acrylamide monomers not included in this application.

[0038] Optionally, the monomers constituting the acrylate copolymer include acrylate monomers, acrylonitrile monomers, and acrylamide monomers, wherein the mass ratio of the acrylate monomers, acrylonitrile monomers, and acrylamide monomers is 1:(0.01-0.8):(0.01-0.15). Preferably, the mass ratio of the acrylate monomers, acrylonitrile monomers, and acrylamide monomers is 1:(0.1-0.6):(0.06-0.12).

[0039] By controlling the mass ratio of the three monomers within the aforementioned range, the molecular weight and glass transition temperature of the polymer can be controlled, thereby improving the adhesive properties of the binder.

[0040] This application also provides a method for preparing a binder for secondary batteries, comprising:

[0041] Preparation of acrylate copolymer emulsions;

[0042] The acrylate copolymer emulsion was blended with a rigid polymer and then spray-dried to obtain a core-shell structured binder.

[0043] An acrylate copolymer emulsion was prepared by emulsion polymerization, and then blended with a rigid polymer and spray-dried to obtain a core-shell structured binder.

[0044] During spray drying, the small particle size and stickiness of acrylate copolymers cause them to adsorb onto the surface of rigid particles that have no stickiness, thus forming a core-shell structure.

[0045] In the process of forming core-shell structured binders, spray drying, compared to emulsion polymerization, results in better coating of rigid particles by acrylate copolymers. Furthermore, the polymerization steps in emulsion polymerization are difficult to control; therefore, using spray drying to prepare core-shell structured binders leads to binders with superior bonding properties.

[0046] During spray drying, the shell structure is formed by the accumulation of spherical particles on the surface of the core structure. The spherical particles are in point contact, creating channels and voids in the shell, which facilitates electrolyte wetting. Due to the support of the core structure, the probability of binder particles being flattened during cold pressing is reduced. This decreases the likelihood of the channels and voids in the shell being compressed and blocked, increasing the porosity of the binder layer and allowing the electrolyte to penetrate into the binder through the gaps between the acrylate copolymer particles.

[0047] Meanwhile, some rigid polymer materials also possess abundant functional groups on their surfaces, which can improve electrolyte wettability, accelerate ion transport, and enhance the electrochemical performance of the battery. For example, rigid polymers composed of polymethyl methacrylate (PMMA) have ester groups, which can improve the wettability of solvents in the electrolyte, such as ethylene carbonate, propylene carbonate, and ethyl methyl carbonate.

[0048] Optionally, the step of preparing the acrylate copolymer emulsion includes:

[0049] Water, emulsifier, and monomers constituting the acrylate copolymer are stirred and emulsified to obtain a pre-emulsion of the monomers;

[0050] The emulsifier and water are stirred and emulsified. The pre-emulsion and initiator are added under heating conditions, and the temperature is increased to obtain an acrylate copolymer emulsion.

[0051] In the preparation of acrylate copolymer emulsions, a pre-emulsification followed by polymerization is adopted to make the monomers more uniformly mixed, resulting in more uniform acrylate copolymer particles and more stable performance.

[0052] This application also provides a separator, the separator comprising a base membrane and an adhesive layer disposed on at least one side of the base membrane, the adhesive layer comprising an adhesive for secondary batteries as described above;

[0053] Alternatively, the adhesive layer may comprise an adhesive prepared by the method described above for preparing adhesives for secondary batteries.

[0054] This application also provides a secondary battery, which includes the separator as described above.

[0055] This application also provides an electrical device, which includes a secondary battery as described above. Attached Figure Description

[0056] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0057] Figure 1 A scanning electron microscope image of the adhesive provided in Embodiment 1 of this application;

[0058] Figure 2 A schematic flowchart illustrating a method for preparing an adhesive provided in an embodiment of this application;

[0059] Figure 3 This is a schematic diagram of a secondary battery provided in an embodiment of this application;

[0060] Figure 4 yes Figure 3 The diagram shown is an exploded view of the secondary battery provided in the embodiment of this application.

[0061] Figure 5 This is a schematic diagram of the battery module provided in an embodiment of this application;

[0062] Figure 6 This is a schematic diagram of the battery pack provided in an embodiment of this application;

[0063] Figure 7 yes Figure 6 The diagram shown is an exploded view of the battery pack provided in the embodiment of this application;

[0064] Figure 8 This is a schematic diagram of an electrical device using a secondary battery as a power source, as provided in an embodiment of this application.

[0065] Explanation of icon numbers:

[0066]

[0067]

[0068] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0069] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0070] The following detailed description, with appropriate reference to the accompanying drawings, discloses the binder of this application and its preparation method, as well as embodiments of the separator, electrode assembly, battery cell, battery, and power device comprising the binder. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0071] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0072] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0073] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0074] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0075] The battery cell has an opening problem, that is, gaps can easily form between the electrode and the separator, which leads to poor battery cycle performance.

[0076] For example, polyvinylidene fluoride (PVDF) is widely used as a binder in separators, but its cost is currently high. Coating the surface of the secondary battery separator with PVDF polymer can partially solve the problem of high-temperature shrinkage. After the battery cell is wound, it is cold-pressed, but conventional PVDF is a homopolymer with a crystallinity of about 50%, which results in insufficient adhesion to the positive and negative electrode sheets, often causing cell opening problems and failing to meet the performance requirements of the coated separator for power secondary batteries.

[0077] In other words, coating the surface of the battery separator with polyvinylidene fluoride polymer can partially solve the problem of high-temperature shrinkage of the separator. After the battery cell is wound, it is cold-pressed, but conventional polyvinylidene fluoride is a homopolymer with a crystallinity of about 50%, which leads to insufficient adhesion to the positive and negative electrode plates, often resulting in cell openings. The openings in the battery cell cause gaps to form between the electrode plates and the separator, resulting in a loose overall cell structure, reduced cell hardness, and poor cycle performance.

[0078] A battery cell is formed by bonding positive and negative electrode plates and a separator. The cell has a certain degree of rigidity; that is, because the bonded positive and negative electrode plates and separator adhere and support each other, they form a structure of a certain thickness. This thickness provides a certain level of rigidity. During charging and discharging, the negative electrode expands. If the bonding force is weak, gaps will form between the positive and negative electrode plates and the separator, preventing them from adhering and supporting each other. This results in a loose cell with reduced rigidity. Consequently, the cell's power performance deteriorates, for example, its rate capability decreases, and its cycle performance worsens. For instance, in electric vehicles, loose battery cells lead to slower charging speeds and poorer cycle performance, directly shortening battery life. This necessitates frequent battery replacements, increasing costs for consumers.

[0079] Based on this, this application proposes an adhesive for secondary batteries, the adhesive comprising a core structure and a shell structure disposed on the surface of the core structure, the shell structure comprising an acrylate copolymer, and the core structure comprising a rigid polymer, the rigid polymer having a crystallinity range of 32% to 94%.

[0080] Adhesives are materials with adhesive properties used to bond different substances together.

[0081] A core-shell structure is a structure consisting of a central core and an outer shell.

[0082] In a core-shell structure, the structure located inside the shell and enclosed by an outer shell is called a core-shell structure.

[0083] In a core-shell structure, the outermost layer, covering the surface of the core layer, is called the shell structure.

[0084] The core-shell structure can be observed using a transmission electron microscope (TEM). Specifically, due to the different materials of the core and shell structures, there will be a difference in brightness (mass-thickness contrast) between the core and shell structures in the TEM image. This mass-thickness contrast is the difference in contrast caused by the difference in thickness and mass of different regions of the sample surface. Since different parts of the sample have different electron scattering capabilities, the number of electrons transmitted through the objective lens will also be different, resulting in differences in electron beam intensity. Regions with strong scattering and fewer transmitted electrons will appear dark, while those with strong scattering and fewer transmitted electrons will appear bright.

[0085] Acrylic ester copolymers are a general term for polymers produced by copolymerization of acrylate monomers and other comonomers.

[0086] Acrylic monomers have acrylate groups in their structure, such as methyl acrylate, ethyl acrylate, and n-butyl acrylate.

[0087] Acrylic copolymers have good adhesion, and using acrylic copolymers results in better adhesion between the diaphragm and the electrode after cold pressing.

[0088] Crystallinity is used to represent the proportion of crystalline regions in a polymer. Crystallization is an ordered arrangement of molecular chains.

[0089] Crystallinity can be tested using DSC (Differential Scanning Calorimetry). For example, the crystallinity test method for polypropylene is as follows: Crystallinity is determined using DSC. The heat of fusion ΔH0 of fully crystalline polymers is used as a uniform value to reduce the influence on the sample test results. The specific procedure is as follows: Under nitrogen protection at a flow rate of 20 mL / min, 5 mg of sample is placed in a DSC instrument (Differential Scanning Calorimetry (DSC) instrument: SDT2960, TA Instruments, USA). The temperature is increased from room temperature to 210°C at a rate of 15°C / min, held at this temperature for 5 min to eliminate thermal history, and then cooled to room temperature at a constant rate of 5°C / min. The process is recorded and the crystallinity is calculated.

[0090] Rigid polymers, with a crystallinity ranging from 32% to 94%, possess properties such as high strength, impact resistance, heat resistance, hardness, and aging resistance. Examples include polyethylene and polypropylene. Rigid polymers are lighter than inorganic particles, which can improve battery energy density.

[0091] During the cold pressing process of the battery cell, rigid polymers are difficult to deform. It is understood that rigid polymers do not deform or undergo only minor deformation during cold pressing. It is understood that the cold pressure range during the cold pressing process is 1MPa to 10MPa, within which rigid polymers do not deform or undergo only minor deformation.

[0092] The core-shell structured binder includes a core layer structure of rigid polymer. During the cold pressing of the battery cell, the rigid polymer acts as a support to stabilize the binder particle structure. In other words, the rigid polymer plays a supporting role, and the overall rigidity of the binder is improved. During the cold pressing of the battery cell, the dimensional stability of the binder is improved, preventing complete deformation. While improving the bonding force of the battery cell during cold pressing, the hardness of the battery cell is also improved.

[0093] Understandably, without the rigid polymer core layer as support, the probability of the adhesive being flattened increases. During the flattening process, the pores between the adhesives are compressed and blocked, which is not conducive to the penetration of electrolyte and the transport of ions.

[0094] Because rigid polymers are difficult to deform, the binder can maintain a certain shape during cold pressing, which improves the problem of the binder clogging the pores between binder particles due to deformation during the flattening process.

[0095] Because the binder of this application has the support of a rigid polymer, the binder particles are difficult to completely deform during cold pressing, so as not to block the pores between the binder particles. These unblocked pores become channels for electrolyte wetting, which is conducive to ion transport. At the same time, it also improves the hardness of the cell, improves the dynamic performance of the secondary battery, reduces electrochemical impedance, and can improve the cycle performance of the secondary battery.

[0096] Understandably, during the cold pressing process of the battery cell, the core layer structure of the binder does not deform or undergoes only minor deformation, reducing the probability of the binder particles being flattened. The shell structure includes acrylate copolymers, which can provide better adhesion and improve the cold pressing adhesion of the battery cell.

[0097] The values ​​in the range of 32% to 94% include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, and 32%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 94%, etc., as well as the range values ​​between any two of the above point values.

[0098] In one embodiment, the crystallinity range of the rigid polymer includes 40% to 80%.

[0099] To improve the hardness of rigid polymers, preferably, the crystallinity of the rigid polymer is greater than or equal to 40%. However, considering that excessive crystallinity makes the process difficult to implement, preferably, the crystallinity of the rigid polymer is less than or equal to 80%.

[0100] The values ​​in the range of 40% to 80% include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, etc., as well as the range values ​​between any two of the above point values.

[0101] In one embodiment, the rigid polymer includes at least one of polyethylene, polypropylene, polystyrene, polymethyl methacrylate, and polyamide.

[0102] Rigid polymers include commonly used engineering plastics, which are industrial plastics used as materials for industrial parts or housings, possessing good strength, impact resistance, heat resistance, hardness, and aging resistance. Examples include at least one of polyethylene, polypropylene, polystyrene, polymethyl methacrylate, and polyamide. The rigid polymer used in this application can be one of the rigid polymers listed above, or other rigid polymers not listed herein. Engineering plastics have a relatively high crystallinity, generally between 32% and 94%. Using the aforementioned rigid polymer as the core layer structure is beneficial for improving the cold-pressing performance of the binder.

[0103] In one embodiment, the adhesive may be spherical in shape.

[0104] The spherical shape facilitates uniform dispersion during the mixing process, which is beneficial for even coating.

[0105] In one embodiment, the volumetric particle size distribution Dv50 of the adhesive is from 1 μm to 15 μm, preferably from 1 μm to 12 μm.

[0106] Dv50 represents the median particle size of a sample, where 50% of the total volume of particles have a diameter greater than this value, and another 50% of the total volume of particles have a diameter less than this value.

[0107] The volumetric particle size distribution (Dv50) of the binder can be tested using methods known in the art. For example, it can be characterized using a Malvern laser particle size analyzer, such as the Malvern Mastersizer-3000, in accordance with GB / T 19077-2016.

[0108] In order to improve the permeability of lithium ions (taking lithium-ion batteries as an example, but other types of secondary batteries are also possible) on the separator and to improve the energy density of the battery, the volumetric particle size distribution Dv50 of the binder is 1 μm to 15 μm, preferably 1 μm to 12 μm.

[0109] The values ​​in the range of 1μm to 15μm include the minimum and maximum values ​​of this range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, and 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, etc., as well as the range values ​​between any two of the above point values.

[0110] The values ​​in the range of 1μm to 15μm include the minimum and maximum values ​​of this range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, and 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, etc., as well as the range values ​​between any two of the above point values.

[0111] In theory, the volumetric particle size distribution Dv50 of acrylate copolymers in adhesives and the volumetric particle size distribution Dv50 of rigid polymers can be obtained by measuring with transmission electron microscopy and scanning electron microscopy.

[0112] The size of the core structure can be measured by images of the binder obtained by transmission electron microscopy, while the size of the shell particles can be measured by images obtained by scanning electron microscopy.

[0113] In one embodiment, the ratio of the volumetric particle size distribution Dv50 of the acrylate copolymer to the volumetric particle size distribution Dv50 of the rigid polymer is 1:(1-50).

[0114] In order to effectively set the acrylate copolymer on 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 that of the rigid polymer. Specifically, the ratio of the volumetric particle size distribution Dv50 of the acrylate copolymer to that of the rigid polymer is 1:(1~50).

[0115] In the above 1: (1~50), the values ​​include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and 1:1, 1:5, 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, 1:50, etc., as well as the range values ​​between any two of the above point values.

[0116] In one embodiment, the volumetric particle size distribution Dv50 of the rigid 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 acrylate copolymer is 100 nm to 200 nm, preferably 130 nm to 180 nm.

[0117] It is understood that, in order to obtain a core-shell structured binder and improve the adhesiveness of the binder, the volumetric particle size distribution Dv50 of the rigid polymer is 0.1 μm to 5 μm, preferably 0.5 μm to 2 μm, and the volumetric particle size distribution Dv50 of the acrylate copolymer is 100 nm to 200 nm, preferably 130 nm to 180 nm.

[0118] The values ​​in the range of 0.1μm to 5μm include the minimum and maximum values ​​of this range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, and 0.1μm, 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, etc., as well as the range values ​​between any two of the above point values.

[0119] The values ​​in the range of 0.5μm to 2μm include the minimum and maximum values ​​of this range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, and 0.5μm, 0.7μm, 0.9μm, 1μm, 1.2μm, 1.4μm, 1.5μm, 1.7μm, 1.9μm, 2μm, etc., as well as the range values ​​between any two of the above point values.

[0120] The values ​​in the range of 100nm to 200nm include the minimum and maximum values ​​of this range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, and 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 18nm, 190nm, 200nm, etc., as well as the range values ​​between any two of the above point values.

[0121] The values ​​in the range of 130nm to 180nm include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, as well as 130nm, 140nm, 150nm, 160nm, 170nm, 18nm, etc., and the range values ​​between any two of the above point values.

[0122] It is understandable that the binder for the core-shell structure can be either a shell structure that completely covers the core structure or a shell structure that does not completely cover the core structure; there is no specific limitation.

[0123] In one embodiment, the mass ratio of the shell structure to the core structure is 1:(0.1 to 10), and preferably, the mass ratio of the shell structure to the core structure is 1:(0.1 to 5).

[0124] The mass ratio test method involves recording the mass of the rigid polymer used to prepare the core layer structure as m and the mass of the acrylate copolymer used to prepare the shell layer structure as n during the preparation process of the adhesive. The mass ratio of the core layer structure to the shell structure is then m:n.

[0125] To address the issue of reduced adhesive bonding performance caused by excessive rigid polymer mass, and to mitigate the problem of reduced overall hardness of the adhesive due to insufficient rigid polymer mass, which affects subsequent cell performance, a shell structure mass to core structure mass ratio of 1:(0.1-10), preferably 1:(0.1-5), is adopted.

[0126] In the above 1:(0.1~10), the values ​​include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, 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., as well as the range values ​​between any two of the above point values.

[0127] In the above 1:(0.1~5), the values ​​include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and 1:0.1, 1:1, 1:2, 1:3, 1:4, 1:5, etc., as well as the range values ​​between any two of the above point values.

[0128] In one embodiment, the constituent monomers of the acrylate copolymer include at least two of acrylate monomers, acrylonitrile monomers, and acrylamide monomers.

[0129] Acrylate monomers, whose structures include acrylate groups, for example, have the following structural formula: Wherein, R1 comprises a hydrogen atom or an alkyl group with 1-12 carbon atoms, and R2 comprises an alkyl group with 1-12 carbon atoms. In one embodiment, the acrylate monomers include methyl acrylate, ethyl acrylate, n-butyl acrylate, etc.

[0130] Acrylonitrile monomers, which contain unsaturated cyano groups in their structure, for example, have the following structural formula: R3 includes a hydrogen atom or an alkyl group with 1-6 carbon atoms. In one embodiment, the acrylonitrile monomer includes acrylonitrile, methacrylonitrile, etc.

[0131] Acrylamide monomers, whose structures include unsaturated amide groups, for example, have the following structural formula: Wherein, R4 comprises a hydrogen atom or an alkyl group of 1-6 carbon atoms, and R5 comprises a hydrogen atom, a hydroxyl-substituted alkyl group of 1-6 carbon atoms, or an alkoxy group of 1-6 carbon atoms. In one embodiment, the acrylamide monomer includes acrylamide, N-hydroxymethylacrylamide, and N-butoxymethylacrylamide, etc.

[0132] It is understandable that acrylate monomers can improve the polymer's resistance to swelling, and as flexible monomer segments in the molecular chain, they can regulate the polymer's glass transition temperature, improve the toughness of the adhesive during application, and help to exert a good bonding effect.

[0133] Acrylonitrile monomers, with their highly polar cyano groups, contribute to improved ionic conductivity.

[0134] Acrylamide monomers play a role in regulating molecular weight.

[0135] When the constituent monomers of acrylate copolymers include two of the following: acrylate monomers, acrylonitrile monomers, and acrylamide monomers, such as acrylate monomers and acrylonitrile monomers, or acrylate monomers and acrylamide monomers, the bonding performance is better. When all three monomers are included, the performance is even better.

[0136] In one embodiment, the acrylate monomers 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 monomers include at least one of acrylonitrile or methacrylonitrile; and / or, the acrylamide monomers include at least one of acrylamide, N-hydroxymethylacrylamide, and N-butoxymethylacrylamide.

[0137] By using any one or more of the above-mentioned acrylate monomers, the glass transition temperature of the polymer can be adjusted, thereby improving the polymer's resistance to swelling. The above are examples of acrylate monomers; the acrylate monomers used in this application can be substances listed above, or other acrylate monomers not specified in this application.

[0138] Using any one or more of the above-mentioned acrylonitrile monomers can improve the ionic conductivity of the binder. The above is an example of acrylonitrile monomers; the acrylonitrile monomers used in this application can be substances listed above, or other acrylonitrile monomers not listed in this application.

[0139] Using any one or more of the above-mentioned acrylamide monomers can help adjust the molecular weight of the polymer, thereby improving the adhesion of the binder within a certain range. The above are examples of acrylamide monomers; the acrylamide monomers used in this application can be substances listed above, or other acrylamide monomers not included in this application.

[0140] In one embodiment, the constituent monomers of the acrylate copolymer include acrylate monomers, acrylonitrile monomers, and acrylamide monomers, and the mass ratio of acrylate monomers, acrylonitrile monomers, and acrylamide monomers is 1:(0.01-0.8):(0.01-0.15). Preferably, the mass ratio of acrylate monomers, acrylonitrile monomers, and acrylamide monomers is 1:(0.1-0.6):(0.06-0.12).

[0141] By controlling the mass ratio of the three monomers within the aforementioned range, the molecular weight and glass transition temperature of the polymer can be controlled, thereby improving the adhesive properties of the binder.

[0142] In the above 1:(0.01~0.8):(0.01~0.15), the values ​​include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, 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, 1:0.01:0.1, 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., as well as the range values ​​between any two of the above point values.

[0143] In the above 1:(0.1~0.6):(0.06~0.12), the values ​​include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, and 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., as well as the range values ​​between any two of the above point values.

[0144] In one embodiment, this application also provides a method for preparing an adhesive for secondary batteries, comprising: preparing an acrylate copolymer emulsion; blending the acrylate copolymer emulsion with a rigid polymer and spray drying it to obtain a core-shell structured adhesive.

[0145] Spray drying uses mechanical action to disperse the material to be dried (a mixture of acrylate copolymer emulsion and rigid polymer) into very fine, mist-like particles (increasing the surface area for water evaporation and accelerating the drying process). These particles then come into contact with hot air, instantly removing most of the moisture and drying the solid matter in the material into powder.

[0146] The core-shell structure binder is obtained through a spray drying process.

[0147] During spray drying, the small particle size and stickiness of acrylate copolymers cause them to adsorb onto the surface of rigid particles that have no stickiness, thus forming a core-shell structure.

[0148] In the process of forming core-shell structured binders, spray drying, compared to emulsion polymerization, results in better coating of rigid particles by acrylate copolymers. Furthermore, the polymerization steps in emulsion polymerization are difficult to control; therefore, using spray drying to prepare core-shell structured binders leads to binders with superior bonding properties.

[0149] During spray drying, the shell structure is formed by the accumulation of spherical particles on the surface of the core structure. The spherical particles are in point contact, creating channels and voids in the shell, which facilitates electrolyte wetting. Due to the support of the core structure, the probability of binder particles being flattened during cold pressing is reduced. This decreases the likelihood of the channels and voids in the shell being compressed and blocked, increasing the porosity of the binder layer and allowing the electrolyte to penetrate into the binder through the gaps between the acrylate copolymer particles.

[0150] Understandably, traditional secondary battery separators are mostly polyolefin separators. Multilayer separators have the function of blocking ion transport by closing pores at high temperatures, ensuring battery safety; the PP (polypropylene) layer on the surface of the separator further improves the separator's oxidation resistance. Compared with traditional single-layer separators, these multilayer polyolefin composite separators improve the battery's cycle performance and safety to a certain extent. However, the characteristics of polyolefin separators, such as poor electrolyte wettability and low thermal decomposition temperature, still exist, and the performance of multilayer polyolefin separators is gradually becoming unable to meet the growing social demands.

[0151] The rigid polymers of this application possess low density, excellent thermal stability, and chemical stability. Furthermore, some rigid polymer materials have abundant functional groups on their surface, which can improve electrolyte wettability, accelerate ion transport, and enhance the electrochemical performance of the battery. For example, rigid polymers composed of polymethyl methacrylate (PMMA) have ester groups, which can improve the wettability of solvents in the electrolyte, such as ethylene carbonate, propylene carbonate, and ethyl methyl carbonate.

[0152] In one embodiment, the step of preparing the acrylate copolymer emulsion includes: stirring and emulsifying water, emulsifier, and monomers constituting the acrylate copolymer to obtain a pre-emulsion of the monomers; stirring and emulsifying the emulsifier and water; adding the pre-emulsion and initiator under heating conditions; and raising the temperature to obtain the acrylate copolymer emulsion.

[0153] Pre-emulsion is a solution obtained by pre-emulsifying monomers. Emulsification is the process of uniformly dispersing a liquid into another immiscible liquid as extremely small droplets. Water, emulsifier, and the constituent monomers of acrylate copolymers are mixed and stirred so that the constituent monomers of acrylate copolymers are dispersed in water under the action of emulsifier.

[0154] Emulsion polymerization is a process in which monomers are dispersed in water to form an emulsion using emulsifiers and mechanical stirring, and then an initiator is added to initiate the polymerization of the monomers.

[0155] Emulsifiers are substances that can transform immiscible oils and water into emulsions that are difficult to separate. Emulsifiers are usually surfactants that combine the properties of both hydrophilic polar groups and hydrophobic (lipophilic) nonpolar groups.

[0156] An initiator is a substance that can initiate a polymerization reaction of monomers. For example, a free radical initiator refers to a class of compounds that easily decompose into free radicals (i.e., primary free radicals) when heated, and can be used to initiate free radical polymerization and copolymerization reactions of alkene and diene monomers.

[0157] In the preparation of acrylate copolymer emulsions, a pre-emulsification followed by polymerization is employed to ensure more uniform monomer mixing, resulting in more homogeneous and stable acrylate copolymer particles. This facilitates the effective placement of acrylate copolymer particles on the core layer structure during spray drying.

[0158] Understandably, in the specific operation process, two containers can be used for experimental operation. Water, emulsifier, and monomers constituting the acrylate copolymer are added to the first container and stirred and emulsified to obtain a pre-emulsion of the monomers. Emulsifier and water are added to the second container again and stirred and emulsified. Under heating conditions, the above-mentioned pre-emulsion and initiator solution are added, and the temperature is raised to obtain the acrylate copolymer emulsion.

[0159] For example, in one embodiment, the acrylate copolymer obtained by emulsion polymerization has a volumetric particle size distribution (Dv50) between 0.1 μm and 0.11 μm, exhibiting relatively uniform particle size, while the rigid polymer has a volumetric particle size distribution (Dv50) in the range of approximately 1 μm ± 0.2 μm. The acrylate copolymer can be effectively bonded to the surface of the rigid polymer via a spray drying process.

[0160] Embodiments of this application also provide a separator, the separator comprising a base membrane and an adhesive layer disposed on at least one side of the base membrane, the adhesive layer comprising an adhesive for secondary batteries as described above; or, the adhesive layer comprising an adhesive prepared by the method for preparing adhesive for secondary batteries as described above.

[0161] Embodiments of this application also provide a secondary battery, which includes the separator as described above.

[0162] Secondary batteries include battery modules, battery cells, and battery packs. When a secondary battery is a battery cell, the battery cell includes the separator as described above; when a secondary battery is a battery module, the battery module includes the separator as described above; when a secondary battery is a battery pack, the battery pack includes the separator as described above.

[0163] An embodiment of this application also provides an electrical device, which includes the aforementioned secondary battery.

[0164] In addition, the electrode assembly, battery cell, battery and power device of this application will be described below with appropriate reference to the accompanying drawings.

[0165] In one embodiment of this application, an electrode assembly is provided.

[0166] Typically, an electrode assembly includes a positive electrode, a negative electrode, an electrolyte, and a separator. During battery charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through. The separator described above is the improved separator of this application.

[0167] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector.

[0168] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0169] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0170] In some embodiments, when the electrode assembly is a lithium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials 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, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0171] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0172] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0173] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0174] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0175] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0176] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0177] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0178] In some embodiments, the negative electrode film layer may optionally include a binder. The binder 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).

[0179] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0180] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0181] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0182] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not specify any particular type of electrolyte; it can be selected according to requirements.

[0183] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0184] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0185] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl 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.

[0186] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0187] In some embodiments, the electrode assembly also includes a diaphragm. This application does not impose any particular limitation on the type of diaphragm; any known porous diaphragm with good chemical and mechanical stability can be selected.

[0188] In some embodiments, the diaphragm material can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The diaphragm can be a single-layer film or a multi-layer composite film, without particular limitation. When the diaphragm is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0189] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0190] In some embodiments, the electrode assembly may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and the electrolyte.

[0191] In some embodiments, the outer packaging of the electrode assembly can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the electrode assembly can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0192] This application does not impose any particular limitation on the shape of the electrode assembly; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 3 This is an example of a square-structured secondary battery 5.

[0193] In some implementations, refer to Figure 4 The outer packaging may include a shell 51 and a cover 53. The shell 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The shell 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator can be formed into a secondary battery 52 through a winding process or a stacking process. The secondary battery 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the secondary battery 52. ​​The secondary battery 52 may contain one or more secondary batteries, which can be selected by those skilled in the art according to specific practical needs.

[0194] In some embodiments, the electrode assemblies can be assembled into a battery module, and the number of electrode assemblies contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0195] Figure 5 This is battery module 4, used as an example. (See reference...) Figure 5 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0196] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0197] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0198] Figure 6 and Figure 7 This is battery pack 1 as an example. (See reference...) Figure 6 and Figure 7 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0199] In addition, this application also provides an electrical device, which includes at least one of the electrode assembly, battery module, or battery pack provided in this application. The electrode assembly, battery module, or battery pack can be the power source of the electrical device or the energy storage unit of the electrical device. The electrical 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.), electric trains, ships and satellites, energy storage systems, etc.

[0200] As an electrical device, electrode components, battery modules, or battery packs can be selected according to their usage requirements.

[0201] Figure 8 This is an example of an electrical device. The device could be 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 components, a battery pack or battery module can be used.

[0202] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a thin and light design and may use electrode components as a power source.

[0203] Example

[0204] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0205] Example 1

[0206] Preparation of acrylate copolymers

[0207] Preparation Example 1

[0208] (1) Add 150g of deionized water and 3.6g of sodium dodecyl sulfonate to a 500ml three-necked flask and stir thoroughly for 15min to emulsify. Then, add 91.74g of ethyl acrylate, 0.92g of acrylonitrile, and 7.34g of N-hydroxymethylacrylamide in a mass ratio of 1:0.01:0.08, for a total of 100g of monomers. Stir thoroughly for 60min to obtain a pre-emulsion of monomers, and set it aside for later use.

[0209] (2) Add 100ml of deionized water and 0.15g of sodium dodecylbenzenesulfonate to a 500ml three-necked flask, heat to 75℃, and emulsify at 2000r / min for 15min to ensure complete emulsification. Then slowly add the pre-emulsion and initiator solution prepared in the previous step (dissolve 0.2g of potassium persulfate in 30g of deionized water to form a solution). After the addition is complete, raise the temperature to 90℃ and keep it at that temperature for 0.5h. Cool to 40℃. Adjust the pH to 7 with 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 structure polymer in each example is 0.1μm±0.01μm).

[0210] Preparation Examples 2 to 10

[0211] Based on Preparation Example 1, the types and mass ratios of the monomers used were changed to obtain Preparation Examples 2 to 10.

[0212] Preparation of adhesive

[0213] Example 1

[0214] The acrylate copolymer emulsion (containing 100g of acrylate copolymer) from Preparation Example 1 was dispersed at high speed for 60min with 100g of polypropylene particles with a volume particle size distribution Dv50 of 1μm. After stirring until homogeneous, the mixture was spray-dried to obtain a core-shell structured binder. The spray-drying parameters were: inlet air temperature 110℃ and outlet air temperature 50℃.

[0215] Examples 2 to 31

[0216] Based on Example 1, the types and mass ratios of polymers in the core and shell structures, the volumetric particle size distribution Dv50 of the core structure, and the volumetric particle size distribution Dv50 of the binder were adjusted to obtain Examples 2 to 31.

[0217] Comparative Example 1

[0218] Based on Example 1, the mass ratio of the shell structure to the core structure was adjusted to 1:0, i.e., without a core structure, to obtain Comparative Example 1.

[0219] Cell fabrication and battery fabrication

[0220] 1. Preparation of the separating membrane

[0221] A commercially available PE microporous film with a thickness of 7 μm and an average pore size of 80 nm (from Zogo Electronics Technology Co., Ltd.) was used as the substrate. The adhesive prepared above was stirred and mixed evenly in deionized water to obtain a slurry (solid content of 20%). The slurry was uniformly coated on both surfaces of the substrate, dried to remove the solvent, and the coating density of the coating composition on the substrate was 1.5 g / m². 2 An isolation membrane is obtained.

[0222] 2. Preparation of the positive electrode sheet

[0223] A positive electrode slurry was prepared by thoroughly mixing polyvinylidene fluoride (PVDF), lithium iron phosphate (LFP), conductive agent carbon black, and N-methylpyrrolidone (NMP) at a mass ratio of 1.2:58.38:0.42:40. The positive electrode slurry was then subjected to a 200 g / m³ concentration. 2 The loading is uniformly coated on the positive current collector aluminum foil, and then dried, cold-pressed and cut to obtain the positive electrode sheet.

[0224] 3. Preparation of negative electrode sheet

[0225] Artificial graphite, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) were added to deionized water at a mass ratio of 96.2:1.0:1.6:1.2 and thoroughly mixed to prepare a negative electrode slurry (solid content 63%). This negative electrode slurry was then subjected to a concentration of 98 g / m³. 2 The loading amount is coated on the negative electrode current collector copper foil, and then dried, cold pressed and slit to obtain the negative electrode sheet.

[0226] 4. Preparation of electrolyte

[0227] At 25°C, ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain a mixed solvent. LiPF6 is then dissolved in the mixed solvent to obtain an electrolyte, wherein the concentration of LiPF6 is 1 mol / L.

[0228] 5. Preparation of secondary batteries

[0229] The positive electrode, separator, and negative electrode are stacked, wound, and cold-pressed in sequence to obtain a battery cell (during which the separator is bonded to the electrode). The battery cell is placed in an outer package, the electrolyte prepared above is added, and after processes such as encapsulation, standing, formation, and aging, a secondary battery is obtained.

[0230] Performance testing

[0231] 1. Cold pressing bonding:

[0232] The negative electrode sheet and the separator were overlapped and placed on a hot press. The hot press parameters were set as follows: temperature 25℃, pressure 10t, and time 30s. The pressure was applied to obtain a bonded separator / positive electrode sheet sample. The separator / negative electrode sheet sample was cut into rectangular strips of 150mm × 20mm. The electrode side of the rectangular strips was glued to a steel plate with double-sided adhesive. At one end of the rectangular strip, the separator and the electrode sheet were separated by 2cm along the length direction to obtain the test sample.

[0233] Keep the steel plate horizontal and fix it with the lower clamp of the universal testing machine (Xieqiang Instrument Manufacturing (Shanghai) Co., Ltd., model CTM2100). Fix the peeled end of the separator as described above with the upper clamp of the universal testing machine and connect it to a tensile testing machine. Set the test conditions to a tensile rate of 20 mm / min and a horizontal pull of 10 cm. After the tensile force stabilizes, record the tensile force value. The adhesion force between the separator and the electrode is obtained by the ratio of the tensile force value to the sample width.

[0234] 2. Cell hardness:

[0235] Place the battery cell on a platform with both ends level, fix the middle hollow part with a width of 12cm, let the battery cell lie flat naturally, and measure the deviation of the center position of the battery cell from the horizontal baseline to evaluate the hardness of the battery cell.

[0236] 3. EIS data:

[0237] Using a CHI660D electrochemical workstation from Shanghai Chenhua Company, a small-amplitude sinusoidal voltage signal with a frequency of W1 was applied to the battery system. The system generated a sinusoidal current response with a frequency of W2. The change in the ratio of the excitation voltage to the response current constitutes the impedance spectrum of the electrochemical system. In the AC impedance test, the frequency range was from 10 mHz to 100 kHz, and the amplitude was 5 mV. The test yielded information such as the real and imaginary parts of the impedance at different frequencies.

[0238] 4. Cycle performance of lithium-ion batteries:

[0239] Using the LAND battery testing system, the prepared battery was charged at 25°C with a constant current of 1 / 3C to 3.65V, then charged with a constant voltage of 3.65V to a current of 0.05C, rested for 5 minutes, and then discharged at 1 / 3C to 2.5V. The resulting discharge capacity was recorded as the initial capacity C0. The above steps were repeated for the same battery, and the discharge capacity Cn of the battery after the 500th cycle was recorded. The battery capacity retention rate after each cycle is Pn = (Cn / C0) × 100%. The difference in cycle performance can be reflected by the battery capacity retention rate after a specific number of cycles.

[0240] Table 1. Parameters for the Preparation of Acrylate Copolymer Emulsions

[0241]

[0242] Table 2. Parameters for Adhesive Preparation

[0243]

[0244]

[0245]

[0246] The data above shows that applying binders containing shell structures of acrylate copolymers and core structures of rigid polymers to batteries improves cell hardness while enhancing cold-pressing adhesion, and also helps reduce electrochemical impedance and improve the cycle performance of secondary batteries.

[0247] The above are merely preferred embodiments of the present invention and do not limit the scope of the patent. Any equivalent structural transformations made using the contents of the specification and drawings of the present invention under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the scope of patent protection of the present invention.

Claims

1. An adhesive for secondary batteries, characterized in that, The adhesive includes a core structure and a shell structure disposed on the surface of the core structure. The shell structure includes an acrylate copolymer, and the core structure includes a rigid polymer. The crystallinity of the rigid polymer ranges from 32% to 94%, and the rigid polymer includes at least one of polyethylene, polypropylene, polystyrene, polymethyl methacrylate, and polyamide. The monomers constituting the acrylate copolymer include acrylate monomers, acrylonitrile monomers, and acrylamide monomers, wherein the mass ratio of the acrylate monomers, the acrylonitrile monomers, and the acrylamide monomers is 1:(0.01~0.8):(0.01~0.15). The mass ratio of the shell structure to the core structure is 1:(0.1~10).

2. The adhesive for secondary batteries as described in claim 1, characterized in that, The crystallinity of the rigid polymer ranges from 40% to 80%.

3. The adhesive for secondary batteries as described in claim 1 or 2, characterized in that, The adhesive may be spherical.

4. The adhesive for secondary batteries as described in any one of claims 1 to 3, characterized in that, The volumetric particle size distribution Dv50 of the binder is from 1 μm to 15 μm.

5. The adhesive for secondary batteries as described in claim 4, characterized in that, The volumetric particle size distribution Dv50 of the binder is from 1 μm to 12 μm.

6. The adhesive for secondary batteries as described in any one of claims 1 to 5, characterized in that, The ratio of the volumetric particle size distribution Dv50 of the acrylate copolymer to that of the rigid polymer is 1:(1~50).

7. The adhesive for secondary batteries as described in claim 6, characterized in that, The rigid polymer has a volumetric particle size distribution Dv50 of 0.1 μm to 5 μm; And / or, the volumetric particle size distribution Dv50 of the acrylate copolymer is 100 nm to 200 nm.

8. The adhesive for secondary batteries as described in claim 7, characterized in that, The rigid polymer has a volumetric particle size distribution Dv50 of 0.5 μm to 2 μm; And / or, the volumetric particle size distribution Dv50 of the acrylate copolymer is 130 nm to 180 nm.

9. The adhesive for secondary batteries as described in any one of claims 1 to 8, characterized in that, The mass ratio of the shell structure to the core structure is 1:(0.1~5).

10. The adhesive for secondary batteries according to any one of claims 1 to 9, characterized in that, The acrylate monomers include at least one of the following: 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 monomers include at least one of acrylamide, N-hydroxymethylacrylamide and N-butoxymethylacrylamide.

11. The adhesive for secondary batteries according to any one of claims 1 to 10, characterized in that, The mass ratio of the acrylate monomer, the acrylonitrile monomer, and the acrylamide monomer is 1:(0.1-0.6):(0.06-0.12).

12. A method for preparing a binder for secondary batteries as described in any one of claims 1 to 11, characterized in that, include: Preparation of acrylate copolymer emulsions; The acrylate copolymer emulsion was blended with a rigid polymer and then spray-dried to obtain a core-shell structured binder.

13. The method for preparing the binder for secondary batteries as described in claim 12, characterized in that, The steps in preparing acrylate copolymer emulsions include: Water, emulsifier, and monomers constituting the acrylate copolymer are stirred and emulsified to obtain a pre-emulsion of the monomers; The emulsifier and water are stirred and emulsified. The pre-emulsion and initiator are added under heating conditions, and the temperature is increased to obtain an acrylate copolymer emulsion.

14. A diaphragm, characterized in that, The separator includes a base membrane and an adhesive layer disposed on at least one side of the base membrane, the adhesive layer including an adhesive for secondary batteries as described in any one of claims 1 to 11; Alternatively, the adhesive layer may comprise an adhesive prepared by the method for preparing an adhesive for secondary batteries as described in claim 12 or 13.

15. A secondary battery, characterized in that, The secondary battery includes the separator as described in claim 14.

16. An electrical appliance, characterized in that, The electrical device includes the secondary battery as described in claim 15.

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