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

Abstract

The application provides a binder, comprising modified polybutadiene and / or modified polystyrene butadiene copolymer, a main chain of the modified polybutadiene comprising butadiene repeating units and modified butadiene repeating units; a main chain of the modified polystyrene butadiene copolymer comprising styrene repeating units, butadiene repeating units and modified butadiene repeating units, the modified butadiene repeating units being at least one functional side group grafted to a main chain of butadiene, the functional side group having a fluorescent effect. The application also provides a preparation method of the binder, a negative electrode sheet, a secondary battery and an electric device. The binder provided by the application can directly characterize, in situ, the distribution of the negative electrode binder in the negative electrode sheet by fluorescence microscopy, whether the negative electrode binder has the phenomenon of floating and the like, and then analyze the failure of the secondary battery.

Description

Adhesives and their preparation methods, negative electrode sheets, secondary batteries and electrical devices Technical Field

[0001] This application relates to the field of battery technology, and in particular to a binder and its preparation method, a negative electrode sheet, a secondary battery, and an electrical device. Background Technology

[0002] Rechargeable batteries enhance battery life, significantly improve the economic efficiency of energy storage, and promote the upgrading and transformation of consumer electronics, thus having a profound impact on human life. A rechargeable battery mainly consists of a positive electrode, a negative electrode, a separator, and an electrolyte. The electrodes typically include active materials, conductive agents, binders, and solvents. The binder plays a crucial role in bonding the active materials to the current collector, between active materials themselves, and between the active materials and the conductive agent. Although the amount of binder used is small, it has a significant impact on improving the energy density of lithium-ion batteries, reducing internal resistance, and the overall cycle life of the rechargeable battery. The distribution of the binder in the electrode material directly affects the strength of its adhesion to the active materials, conductive agents, and current collectors.

[0003] However, existing negative electrode binders are difficult to characterize to obtain information on the distribution of the binder in the negative electrode material, making it impossible to judge the quality of the negative electrode binder dispersion process or to perform secondary battery failure analysis.

[0004] The above statements are for the purpose of providing background information in relation to this application only and do not necessarily constitute prior art. Summary of the Invention

[0005] In view of the above problems, this application provides an adhesive and its preparation method, a negative electrode sheet, a secondary battery and an electrical device to solve the above-mentioned technical problems existing in secondary batteries.

[0006] In a first aspect, this application provides an adhesive comprising modified polybutadiene and / or modified polystyrene-butadiene copolymer, wherein the main chain of the modified polybutadiene comprises butadiene repeating units and modified butadiene repeating units; the main chain of the polystyrene-butadiene copolymer comprises styrene repeating units, butadiene repeating units and modified butadiene repeating units, wherein the modified butadiene repeating units are at least one functional side group branched onto the main chain of the butadiene, and the functional side group has a fluorescent effect.

[0007] In the technical solution of this application embodiment, by using at least one functional side group with a fluorescent effect in the main linking branch of the butadiene repeating unit, when ultraviolet light or visible light with a shorter wavelength is irradiated to the functional side group, the binder will emit visible light of various colors and intensities, and when the light source stops irradiating, this light disappears. Therefore, in the negative electrode sheet of this application embodiment, when the ultraviolet light source of the fluorescence microscope irradiates the negative electrode sheet, the binder in the negative electrode sheet emits fluorescence. The distribution of the binder in the negative electrode sheet can be directly observed under the fluorescence microscope, and the distribution of the negative electrode binder in the negative electrode sheet can be directly characterized in situ by fluorescence microscopy, and whether the negative electrode binder floats or other phenomena can be observed, thereby performing secondary battery failure analysis.

[0008] In some embodiments of this application, the functional side base includes a large π bond.

[0009] In the technical solution of this application embodiment, the functional side group includes a large π bond. The large π bond can generate π-π conjugation with negative electrode materials such as graphite negative electrode and silicon-based negative electrode, which can increase the interaction between the negative electrode binder and the negative electrode material and improve the adhesion of the negative electrode binder. Moreover, it can also improve the dispersion performance of negative electrode materials such as graphite negative electrode and silicon-based negative electrode, so that the negative electrode material is more uniformly dispersed in the negative electrode binder, and thus the negative electrode material is more uniformly dispersed in the negative electrode sheet.

[0010] In some embodiments of this application, the functional side group includes at least one of fused ring aromatic hydrocarbon radical, fused ring aromatic hydrocarbon derivative radical, naphthalene dicarboximide radical, naphthalene dicarboximide derivative radical, triphenylamine radical, or triphenylamine derivative radical.

[0011] In the technical solutions of this application embodiment, fused-ring aromatic hydrocarbon free radicals, fused-ring aromatic hydrocarbon derivative free radicals, naphthalene dicarboximide free radicals, naphthalene dicarboximide derivative free radicals, triphenylamine free radicals, or triphenylamine derivative free radicals all exhibit good fluorescence effects. Therefore, in the negative electrode sheet of this application embodiment, when the ultraviolet light source of the fluorescence microscope irradiates the negative electrode sheet, the binder in the negative electrode sheet can rapidly emit fluorescence. The distribution of the binder in the negative electrode sheet can be directly observed under the fluorescence microscope, thereby characterizing the distribution of the negative electrode binder in the negative electrode sheet in situ.

[0012] Moreover, fused ring aromatic hydrocarbon radicals, fused ring aromatic hydrocarbon derivative radicals, naphthalene dicarboximide radicals, naphthalene dicarboximide derivative radicals, triphenylamine radicals, or triphenylamine derivative radicals all contain benzene rings, thus the functional side groups have high stability and rigidity, thereby improving the mechanical properties of the binder.

[0013] In some embodiments of this application, the functional side base includes At least one of the free radicals.

[0014] In the technical solution of the embodiments of this application, The free radicals all have good fluorescence effects, and the distribution of the binder in the negative electrode sheet can be directly observed under a fluorescence microscope, thus enabling in-situ characterization of the distribution of the negative electrode binder in the negative electrode sheet.

[0015] and, The free radicals all contain multiple benzene rings, and the benzene rings are relatively large. Therefore, the groups containing multiple benzene rings are also relatively large, which can effectively improve the mechanical strength of the binder. At the same time, the large benzene rings can reduce the aggregation of binder molecules, resulting in less swelling in the electrolyte, stronger adhesion, and improved cycle stability of the secondary battery. Furthermore, Free radicals are relatively easy to obtain, thus reducing costs.

[0016] In some embodiments of this application, the functional side group is formed by a functional molecule including a thiol group, wherein the sulfur atom in the thiol group is connected to the carbon atom in the modified butadiene repeating unit, and the hydrogen atom in the thiol group is substituted.

[0017] In the technical solution of this application embodiment, the functional molecule includes a thiol group, which can undergo a click reaction with the butadiene chain segment in the main chain. The click reaction has the advantages of high efficiency, mild reaction conditions, easy product purification, and simple post-processing, thereby enabling the functional side group to be rapidly grafted onto the butadiene main chain.

[0018] In some embodiments of this application, the general formula for functional side bases is: R includes at least one of alkyl groups, and R' includes at least one of fused-ring aromatic hydrocarbon radicals, fused-ring aromatic hydrocarbon derivative radicals, naphthalene dicarboximide radicals, naphthalene dicarboximide derivative radicals, triphenylamine radicals, or triphenylamine derivative radicals.

[0019] In the technical solutions of this application, the fused-ring aromatic hydrocarbon free radicals, fused-ring aromatic hydrocarbon derivative free radicals, naphthalene dicarboximide free radicals, naphthalene dicarboximide derivative free radicals, triphenylamine free radicals, or triphenylamine derivative free radicals all contain benzene rings. Therefore, the functional side groups have high stability and rigidity, thereby improving the mechanical properties of the binder. Moreover, the fused-ring aromatic hydrocarbon free radicals, fused-ring aromatic hydrocarbon derivative free radicals, naphthalene dicarboximide free radicals, naphthalene dicarboximide derivative free radicals, triphenylamine free radicals, or triphenylamine derivative free radicals have excellent fluorescence properties, allowing direct observation of the distribution of the negative electrode binder in the negative electrode sheet using a fluorescence microscope.

[0020] In some embodiments of this application, R includes x is greater than or equal to 1 and less than or equal to 9.

[0021] For straight-chain side chains, within a certain range, as the side chain length increases, the polymer's flexibility increases, which is beneficial for polymer diffusion and surface wetting, thus promoting adhesion. However, if the side chain is too long, it can lead to intermolecular entanglement, which is detrimental to cohesion and reduces the polymer's flexibility and adhesive properties.

[0022] In the technical solution of this application embodiment, by controlling x to be greater than or equal to 1 and less than or equal to 9, the side chains in the modified polybutadiene or modified polystyrene-butadiene copolymer are within a reasonable length range, thereby improving the flexibility and bonding performance of the adhesive.

[0023] In some embodiments of this application, R' includes At least one of the free radicals.

[0024] In the technical solution of the embodiments of this application, The free radicals contain multiple benzene rings, which are relatively large. Therefore, the groups containing multiple benzene rings are also relatively large, which can effectively improve the mechanical strength of the binder. At the same time, the large-volume benzene rings can reduce the aggregation of binder molecules, resulting in less swelling in the electrolyte, stronger bonding, and improved cycle stability of the secondary battery.

[0025] In some embodiments of this application, the modified polystyrene-butadiene copolymer is a block copolymer or a random copolymer.

[0026] In the technical solutions of this application embodiment, styrene-butadiene random copolymer and styrene-butadiene block copolymer have excellent tensile strength, elasticity and electrical properties, small permanent deformation, good flexural and resilience, etc., which can improve the mechanical strength and flexibility of the adhesive.

[0027] In some embodiments of this application, the number-average molecular weight of the modified polybutadiene is 10,000 to 1,000,000, and the number-average molecular weight of the modified polystyrene-butadiene copolymer is 10,000 to 1,000,000.

[0028] If the number-average molecular weight of the modified polybutadiene and modified polystyrene-butadiene copolymer is too low, for example, less than 10,000, the mechanical properties of the binder are poor and it is prone to breakage. If the molecular weight of the modified polybutadiene and modified polystyrene-butadiene copolymer is too high, for example, greater than 1 million, the flexibility of the binder is reduced, and it is not conducive to the dispersion of the binder. The binder cannot quickly diffuse into the interior of the negative electrode active material, and the negative electrode active material cannot be fully bonded together. Moreover, a high molecular weight will also affect the wettability of the electrolyte.

[0029] In the technical solution of this application embodiment, by controlling the number average molecular weight of modified polybutadiene to be 10,000-1,000,000 and the number average molecular weight of modified polystyrene-butadiene copolymer to be 10,000-1,000,000, the mechanical properties of the adhesive are improved while ensuring the flexibility, dispersibility and electrolyte wettability of the adhesive.

[0030] In some embodiments of this application, the modified polybutadiene includes modified cis-1,4-polybutadiene.

[0031] In the technical solution of this application embodiment, the distance between the molecular chains in cis-1,4-polybutadiene is relatively large, making it easier to modify. Moreover, the modified cis-1,4-polybutadiene has the characteristics of high elasticity and low hysteresis, high tensile strength and wear resistance, thereby improving the performance of the binder.

[0032] Secondly, this application provides a method for preparing the adhesive in any of the above embodiments, comprising:

[0033] The functional molecule is mixed with polybutadiene and / or polystyrene-butadiene copolymer, the functional molecule reacts with the polybutadiene and / or polystyrene-butadiene copolymer, and the functional molecule is grafted onto the main chain of the butadiene repeating unit in the polybutadiene and / or the polystyrene-butadiene copolymer to form a functional side group.

[0034] The reaction products of the above reaction are extracted to obtain the adhesive.

[0035] In the technical solution of this application embodiment, by mixing functional molecules with polybutadiene and / or polystyrene-butadiene copolymer, at least one functional side group with a fluorescent effect is added to the main linking branch of the butadiene repeating unit. This allows for direct in-situ characterization of the distribution of the negative electrode binder in the negative electrode sheet using a fluorescence microscope, as well as whether the negative electrode binder has floated to the surface, thereby enabling secondary battery failure analysis. Moreover, the preparation method is simple and rapid.

[0036] In some embodiments of this application, the method for preparing the adhesive includes:

[0037] The functional molecules are added to a solvent and mixed to obtain a mixture;

[0038] The mixture is photoinitiated or thermally initiated so that the functional molecules react with polybutadiene and / or polystyrene-butadiene copolymer;

[0039] Add a precipitant to extract the reaction products of the above reaction to obtain the binder.

[0040] In the technical solution of this application embodiment, functional molecules and polybutadiene and / or polystyrene-butadiene copolymer are added to the solvent, so that the functional molecules and polybutadiene and / or polystyrene-butadiene copolymer are mixed more evenly, which is more conducive to the reaction. The functional molecules and polybutadiene and / or polystyrene-butadiene copolymer react rapidly through photoinitiation or thermal initiation, and the reaction product is purified by adding a precipitant. The method is simple, the product is easy to purify, and the cost is low.

[0041] In some embodiments of this application, the functional molecule includes a thiol group, which undergoes a click reaction with polybutadiene and / or polystyrene-butadiene copolymer.

[0042] In the technical solution of this application embodiment, the functional molecule includes a thiol group. Under photo-initiation or thermal initiation, the thiol group can undergo a click reaction with the double bond in the butadiene repeating unit. The click reaction is highly efficient, which allows the functional side group to be quickly grafted onto the side chain of the butadiene segment. Moreover, the click reaction conditions are mild, the product is easy to purify, and the post-processing is simple.

[0043] In some embodiments of this application, the molar ratio of polybutadiene and / or polystyrene-butadiene copolymer to functional molecules is greater than or equal to 2:1 and less than or equal to 3:1.

[0044] If the molar ratio of polybutadiene and / or polystyrene-butadiene copolymer to functional side groups is too small, for example, less than 2:1, it easily results in too many functional side groups, leading to insufficient flexibility of the adhesive. If the molar ratio of polybutadiene and / or polystyrene-butadiene copolymer to functional side groups is too large, for example, greater than 3:1, it results in too few functional side groups, weak fluorescence effect, and low mechanical properties of the adhesive. In the technical solution of this application embodiment, controlling the molar ratio of polybutadiene and / or polystyrene-butadiene copolymer to functional side groups to be greater than or equal to 2:1 and less than or equal to 3:1 results in good adhesion, flexibility, and mechanical properties of the adhesive, and a significant fluorescence effect.

[0045] In some embodiments of this application, the solvent includes at least one of chloroform, cyclohexane, and benzene.

[0046] In the technical solutions of this application embodiment, chloroform, cyclohexane and benzene have good solubility, and functional molecules, polybutadiene and polystyrene-butadiene copolymer can be quickly dissolved in the above solvents, and the cost of the above solvents is low.

[0047] In some embodiments of this application, the precipitant includes at least one of methanol, water, and acetone.

[0048] In the technical solution of this application embodiment, the above-mentioned precipitant can quickly form a precipitate with the reaction product of functional molecules and polybutadiene and / or polystyrene-butadiene copolymer, thereby extracting the reaction product.

[0049] In some embodiments of this application, after adding a precipitant to extract the reaction product of the above reaction, the extracted reaction product is further freeze-dried.

[0050] In the technical solution of this application embodiment, freeze drying can quickly remove the solvent and has little impact on the performance of the reaction product.

[0051] Thirdly, this application provides a negative electrode sheet, including the binder of any of the above embodiments or the binder prepared by the preparation method of the binder of any of the above embodiments.

[0052] Fourthly, this application provides a secondary battery, including the negative electrode sheet of any of the above embodiments.

[0053] Fifthly, this application provides an electrical device including a secondary battery from any of the above embodiments.

[0054] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0055] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0056] Figure 1 is a schematic diagram of the structure of an electrical device according to some embodiments of this application;

[0057] Figure 2 is an exploded structural diagram of a battery according to some embodiments of this application;

[0058] Figure 3 is an exploded structural diagram of a battery cell according to some embodiments of this application;

[0059] Figure 4 is a flowchart of the preparation method of the adhesive according to some embodiments of this application;

[0060] Figure 5 is a flowchart of the preparation method of the adhesive according to some embodiments of this application.

[0061] The accompanying drawings are not drawn to scale.

[0062] Marking description: Electrical device 1000;

[0063] Battery 100, controller 200, motor 300;

[0064] Box 10, Part 11, Part 2 12;

[0065] Battery cell 20, end cap 21, electrode terminal 21a, housing 22, cell assembly 23, tab 23a. Detailed Implementation

[0066] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0067] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0068] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0069] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0070] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0071] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0072] Existing negative electrode binders are difficult to characterize to obtain information on their distribution in the negative electrode material, making it impossible to determine the quality of the negative electrode binder dispersion process or to perform secondary battery failure analysis.

[0073] To address the aforementioned technical problems of secondary batteries, this invention designs a binder comprising modified polybutadiene and / or modified polystyrene-butadiene copolymer. By using at least one functional side group with a fluorescent effect as the main linking branch of the butadiene repeating unit, the distribution of the negative electrode binder in the negative electrode sheet can be directly characterized in situ using a fluorescence microscope. This allows for the determination of whether the binder floats on the negative electrode sheet, the assessment of the quality of the negative electrode binder dispersion process, and the analysis of secondary battery failure.

[0074] Based on the above considerations, in order to solve the problems of existing negative electrode binders making it difficult to obtain the distribution information of the binder in the negative electrode material through characterization methods, making it impossible to judge the quality of the negative electrode binder dispersion process, and to perform secondary battery failure analysis, a binder was designed, including modified polybutadiene and / or modified polystyrene-butadiene copolymer. The main chain of the modified polybutadiene includes butadiene repeating units and modified butadiene repeating units; the main chain of the polystyrene-butadiene copolymer includes styrene repeating units, butadiene repeating units and modified butadiene repeating units. The modified butadiene repeating unit is a butadiene main chain with at least one functional side group branched on it. The functional side group has a fluorescent effect.

[0075] By using at least one functional side group with fluorescence effect in the main linking branch of the butadiene repeating unit, the distribution of the negative electrode binder in the negative electrode sheet can be directly characterized in situ by fluorescence microscopy, and phenomena such as whether the negative electrode binder floats can be determined. This allows for the assessment of the quality of the negative electrode binder dispersion process and the analysis of secondary battery failure.

[0076] The adhesive disclosed in this application can be applied to battery cells, which can be used in electrical devices that use batteries as a power source or in various energy storage systems that use batteries as energy storage elements. Electrical devices can be, but are not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0077] For ease of explanation, the following embodiments will be described using a vehicle as an example of an electrical device 1000 according to an embodiment of this application.

[0078] Please refer to Figure 1, which is a schematic diagram of the structure of an electrical device 1000 provided in some embodiments of this application. The electrical device 1000 can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. A battery 100 is internally installed in the electrical device 1000, and the battery 100 can be located at the bottom, head, or tail of the electrical device 1000. The battery 100 can be used to power the electrical device 1000; for example, the battery 100 can serve as the operating power source for the electrical device 1000. The electrical device 1000 may also include a controller 200 and a motor 300. The controller 200 is used to control the battery 100 to supply power to the motor 300, for example, to meet the power needs of the electrical device 1000 during startup, navigation, and driving.

[0079] In some embodiments of this application, the battery 100 can not only serve as the operating power source for the electrical device 1000, but also as the driving power source for the electrical device 1000, replacing or partially replacing fuel oil or natural gas to provide driving power for the electrical device 1000.

[0080] Please refer to Figure 2, which is an exploded structural diagram of a battery 100 provided in some embodiments of this application. The battery 100 includes a housing 10 and a battery cell 20, with the battery cell 20 housed within the housing 10. The housing 10 provides a space for the battery cell 20 and can adopt various structures. In some embodiments, the housing 10 may include a first portion 11 and a second portion 12, which overlap each other, jointly defining a space for accommodating the battery cell 20. The second portion 12 may be a hollow structure with one open end, and the first portion 11 may be a plate-like structure, covering the open side of the second portion 12 so that the first portion 11 and the second portion 12 jointly define the space. Alternatively, the first portion 11 and the second portion 12 may both be hollow structures with one open side, with the open side of the first portion 11 covering the open side of the second portion 12. Of course, the housing 10 formed by the first portion 11 and the second portion 12 can be of various shapes, such as a cylinder, a cuboid, etc.

[0081] In battery 100, there can be multiple battery cells 20, which can be connected in series, parallel, or in a mixed manner. A mixed connection means that multiple battery cells 20 are connected in both series and parallel configurations. Multiple battery cells 20 can be directly connected in series, parallel, or in a mixed manner, and then the entire assembly of the multiple battery cells 20 is housed within the housing 10. Alternatively, battery 100 can also be composed of multiple battery cells 20 first connected in series, parallel, or in a mixed manner to form a battery module, and then multiple battery modules are connected in series, parallel, or in a mixed manner to form a whole, which is also housed within the housing 10. Battery 100 may also include other structures; for example, it may include a busbar component for electrical connection between the multiple battery cells 20.

[0082] Each battery cell 20 can be a rechargeable battery; it can be a lithium-sulfur battery, a lithium-ion battery, or a lithium metal battery, but is not limited to these. The battery cell 20 can be cylindrical, flat, cuboid, or other shapes.

[0083] Please refer to Figure 3, which is an exploded structural diagram of a battery cell 20 provided in some embodiments of this application. A battery cell 20 refers to the smallest unit that makes up a battery. As shown in Figure 3, the battery cell 20 includes an end cap 21, a housing 22, a cell assembly 23, and other functional components.

[0084] End cap 21 refers to a component that covers the opening of housing 22 to isolate the internal environment of battery cell 20 from the external environment. The shape of end cap 21 can be adapted to the shape of housing 22 to fit it. End cap 21 can be made of a material with certain hardness and strength (such as aluminum alloy), so that end cap 21 is not easily deformed under pressure and impact, allowing battery cell 20 to have higher structural strength and improved safety performance. Functional components such as electrode terminals 21a can be provided on end cap 21. Electrode terminals 21a can be used for electrical connection with cell assembly 23 to output or input electrical energy to battery cell 20. In some embodiments, end cap 21 can also be provided with a pressure relief mechanism for releasing internal pressure when the internal pressure or temperature of battery cell 20 reaches a threshold. The material of end cap 21 can also be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and this application embodiment does not impose any special limitations on this. In some embodiments, an insulating element may be provided on the inner side of the end cap 21. The insulating element can be used to isolate the electrical connection components within the housing 22 from the end cap 21 to reduce the risk of short circuits. For example, the insulating element may be made of plastic, rubber, etc.

[0085] The housing 22 is a component used to cooperate with the end cap 21 to form the internal environment of the battery cell 20. This internal environment can accommodate the cell assembly 23, electrolyte, and other components. The housing 22 and the end cap 21 can be independent components. An opening can be provided on the housing 22, and the end cap 21 can be used to close the opening to form the internal environment of the battery cell 20. Alternatively, the end cap 21 and the housing 22 can be integrated. Specifically, the end cap 21 and the housing 22 can form a common connecting surface before other components are inserted into the housing. When it is necessary to encapsulate the interior of the housing 22, the end cap 21 closes the housing 22. The housing 22 can be of various shapes and sizes, such as cuboid, cylindrical, hexagonal prism, etc. Specifically, the shape of the housing 22 can be determined according to the specific shape and size of the cell assembly 23. The material of the housing 22 can be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc. This application embodiment does not impose any special limitations on this.

[0086] The cell assembly 23 is the component in the battery cell 100 where the electrochemical reaction occurs. The casing 22 may contain one or more cell assemblies 23. The cell assembly 23 is mainly formed by winding or stacking cathode and anode plates, and typically a separator is provided between the cathode and anode plates. The portions of the cathode and anode plates containing active material constitute the main body of the cell assembly, while the portions of the cathode and anode plates without active material each constitute a tab 23a. The cathode tab and anode tab may be located together at one end of the main body or separately at both ends of the main body. During the charging and discharging process of the battery, the cathode active material and the anode active material react with the electrolyte, and the tab 23a connects to the electrode terminals to form a current loop.

[0087] According to some embodiments of this application, this application provides an adhesive comprising modified polybutadiene and / or modified polystyrene-butadiene copolymer, wherein the main chain of the modified polybutadiene comprises butadiene repeating units and modified butadiene repeating units; the main chain of the polystyrene-butadiene copolymer comprises styrene repeating units, butadiene repeating units and modified butadiene repeating units, wherein the modified butadiene repeating unit is a butadiene main chain with at least one functional side group, and the functional side group has a fluorescent effect.

[0088] The fluorescence effect of functional side groups refers to the emission of visible light of various colors and intensities by the functional side groups of a compound when ultraviolet light or visible light with shorter wavelengths is irradiated. When the light source stops irradiating, this light disappears.

[0089] In some embodiments, the binder comprises only modified polybutadiene. In some embodiments, the binder comprises only modified polystyrene-butadiene copolymer. In some embodiments, the binder comprises a mixture of modified polybutadiene and modified polystyrene-butadiene copolymer.

[0090] As an example, the structural formula of the adhesive may be, but is not limited to, represented as: When k equals 0, it is modified polybutadiene; when k is greater than 0, it is modified polystyrene-butadiene copolymer. The functional side groups are not limited to those in the above example formulas. It can also be other functional side groups with fluorescent effects.

[0091] By using at least one fluorescent functional side group as the main linking branch of the butadiene repeating unit, the binder emits visible light of various colors and intensities when irradiated by ultraviolet light or shorter wavelength visible light. This light disappears when the light source stops irradiating. Therefore, in the embodiments of this application, the negative electrode sheet is irradiated by the ultraviolet light source of the fluorescence microscope, causing the binder in the negative electrode sheet to fluoresce. The distribution of the binder in the negative electrode sheet can be directly observed under the fluorescence microscope. This allows for direct in-situ characterization of the distribution of the negative electrode binder in the negative electrode sheet, determining whether the negative electrode binder floats, judging the quality of the negative electrode binder dispersion process, and performing secondary battery failure analysis.

[0092] Moreover, butadiene repeating units are flexible segments, which are easy to process and can form flexible negative electrode sheets with negative electrode materials.

[0093] According to some embodiments of this application, the functional side base includes a large π bond.

[0094] In polyatomic molecules, if there are parallel p orbitals, they overlap together to form a whole. The p electrons move between multiple atoms to form π-type chemical bonds. This π bond, which is not limited to two atoms, is called a delocalized π bond, or a conjugated large π bond, or simply a large π bond. It can form π-π conjugation with molecules containing π bonds.

[0095] The large π bonds in the functional side groups of this application embodiment can generate π-π conjugation with negative electrode materials such as graphite negative electrodes and silicon-based negative electrodes, increasing the interaction between the negative electrode binder and the negative electrode material and improving the adhesion of the negative electrode binder; moreover, it can also improve the dispersion performance of negative electrode materials such as graphite negative electrodes and silicon-based negative electrodes, making the dispersion of the negative electrode material in the negative electrode sheet more uniform. This solves the technical problem of existing binders having low adhesion to negative electrode materials such as graphite negative electrodes and silicon-based negative electrodes, and poor dispersion performance of these materials.

[0096] Moreover, since the adhesive has both flexible segments (segments of polybutadiene) and rigid segments (including functional side groups with large π bonds), the adhesive of this application can adjust the degree of adhesion and mechanical properties as needed.

[0097] According to some embodiments of this application, the functional side group includes at least one of fused ring aromatic hydrocarbon radical, fused ring aromatic hydrocarbon derivative radical, naphthalene dicarboximide radical, naphthalene dicarboximide derivative radical, triphenylamine radical, or triphenylamine derivative radical.

[0098] Fused ring aromatic hydrocarbon radicals, fused ring aromatic hydrocarbon derivative radicals, naphthalene dicarboximide radicals, naphthalene dicarboximide derivative radicals, triphenylamine radicals, or triphenylamine derivative radicals all exhibit good fluorescence effects. Therefore, in the embodiments of this application, when the negative electrode sheet is irradiated by the ultraviolet light source of the fluorescence microscope, the binder in the negative electrode sheet can quickly emit fluorescence. The distribution of the binder in the negative electrode sheet can be directly observed under the fluorescence microscope, thereby characterizing the distribution of the negative electrode binder in the negative electrode sheet in situ.

[0099] Moreover, fused ring aromatic hydrocarbon radicals, fused ring aromatic hydrocarbon derivative radicals, naphthalene dicarboximide radicals, naphthalene dicarboximide derivative radicals, triphenylamine radicals, or triphenylamine derivative radicals all contain benzene rings, thus the functional side groups have high stability and rigidity, thereby improving the mechanical properties of the binder.

[0100] According to some embodiments of this application, the functional side base includes At least one of the free radicals.

[0101] The free radicals exhibit good fluorescence effects, allowing direct observation of the binder distribution within the negative electrode sheet under a fluorescence microscope, thus enabling in-situ characterization of the negative electrode binder distribution.

[0102] and, The free radicals all contain multiple benzene rings, and the benzene rings are relatively large. Therefore, the groups containing multiple benzene rings are also relatively large, which can effectively improve the mechanical strength of the binder. At the same time, the large benzene rings can reduce the aggregation of binder molecules, resulting in less swelling in the electrolyte, stronger adhesion, and improved cycle stability of the secondary battery. Furthermore, Free radicals are relatively easy to obtain, thus reducing costs.

[0103] According to some embodiments of this application, functional side groups are formed by functional molecules, including thiol groups, wherein the sulfur atom in the thiol group is connected to the carbon atom in the modified butadiene repeating unit, and the hydrogen atom in the thiol group is substituted.

[0104] Functional side groups are formed through functional molecules including thiol groups. The thiol groups can undergo click reactions with butadiene segments in the main chain. Click reactions have advantages such as high efficiency, mild reaction conditions, easy product purification, and simple post-processing, thereby enabling functional side groups to be rapidly grafted onto the butadiene main chain.

[0105] In some alternative embodiments, the functional side group includes a thiol group, wherein the sulfur atom in the thiol group is directly connected to the carbon atom in the modified butadiene repeating unit.

[0106] According to some embodiments of this application, the general formula of the functional side base is: R includes at least one of alkyl groups, and R' includes at least one of fused-ring aromatic hydrocarbon radicals, fused-ring aromatic hydrocarbon derivatives, naphthalene dicarboximide radicals, naphthalene dicarboximide derivative radicals, triphenylamine radicals, or triphenylamine derivative radicals.

[0107] Fused ring aromatic hydrocarbon radicals, fused ring aromatic hydrocarbon derivative radicals, naphthalene dicarboximide radicals, naphthalene dicarboximide derivative radicals, triphenylamine radicals, or triphenylamine derivative radicals all contain a benzene ring. The benzene ring has a large volume and high stability, thus the functional side groups have high stability and rigidity, thereby improving the mechanical properties of the binder. Furthermore, fused ring aromatic hydrocarbon radicals, fused ring aromatic hydrocarbon derivative radicals, naphthalene dicarboximide radicals, naphthalene dicarboximide derivative radicals, triphenylamine radicals, or triphenylamine derivative radicals all exhibit excellent fluorescence effects, allowing direct observation of the distribution of the negative electrode binder within the negative electrode sheet using a fluorescence microscope.

[0108] The type and amount of alkyl groups can be selected according to implementation needs; for example, alkyl groups can be, but are not limited to, methyl, ethyl, propyl, etc. Optionally, according to some embodiments of this application, R includes... x is greater than or equal to 1 and less than or equal to 9.

[0109] For straight-chain side chains, within a certain range, as the side chain length increases, the polymer's flexibility increases, which is beneficial for polymer diffusion and surface wetting, thus promoting adhesion. However, if the side chain is too long, it can lead to intermolecular entanglement, which is detrimental to cohesion and reduces the polymer's flexibility and adhesive properties.

[0110] Some embodiments of this application improve the flexibility and bonding performance of the adhesive by controlling x to be greater than or equal to 1 and less than or equal to 9, so that the side chains in the modified polybutadiene or modified polystyrene-butadiene copolymer are within a reasonable length range.

[0111] Optionally, according to some embodiments of this application, R' includes At least one of the free radicals.

[0112] The free radicals contain multiple benzene rings, which are relatively large. Therefore, these groups containing multiple benzene rings can effectively improve the mechanical strength of the binder, reduce binder molecule aggregation, reduce swelling in the electrolyte, strengthen adhesion, and improve the cycle stability of the secondary battery. Furthermore... The free radicals have excellent fluorescence properties, and the distribution of the negative electrode binder in the negative electrode sheet can be directly observed using a fluorescence microscope.

[0113] In some optional embodiments, the general formula for the functional side base is: R' is Free radicals.

[0114] According to some embodiments of this application, the number of butadiene repeating units in the main chain of modified polybutadiene is m, the number of modified butadiene repeating units is n, and the ratio of m to n is in the range of (1:100)-(100:1).

[0115] As an example, the ratio of m to n can be 1, 5, 10, 10.5, 20, 27, 33.5, 40, 45.5, 50, 60.5, 70, 90, 99.9, 100, etc. The ratio of m to n can also be 1-5, 5-10, 10-10.5, 10.5-20, 20-27, 27-33.5, 33.5-40, 40-45.5, 45.5-50, 50-60.5, 60.5-70, 70-90, 90-99.5, 99.5-100, etc. The ratio of m to n only needs to satisfy the range of (1:100)-(100:1).

[0116] By adjusting the content of functional side groups, the adhesion and mechanical properties of the adhesive can be easily adjusted to meet customized needs.

[0117] According to some embodiments of this application, the number of styrene repeating units in the main chain of the polystyrene-butadiene copolymer is k, the number of butadiene repeating units is m, the number of modified butadiene repeating units is n, the ratio of m to n is in the range of (1:100)-(100:1), and the ratio of k to m is greater than 0 and less than or equal to (100:1).

[0118] As an example, the ratio of m to n can be 1, 5, 10, 10.5, 20, 27, 33.5, 40, 45.5, 50, 60.5, 70, 90, 99.5, 100, etc. The ratio of m to n can also be 1-5, 5-10, 10-10.5, 10.5-20, 20-27, 27-33.5, 33.5-40, 40-45.5, 45.5-50, 50-60.5, 60.5-70, 70-90, 90-99.5, 99.5-100, etc. It can be adjusted according to actual needs, as long as it meets the range of (1:100)-(100:1).

[0119] As an example, the ratio of k to m can be 0.1, 1, 5, 10, 15.5, 20, 30.5, 40, 50.5, 70, 80, 90, 99.5, 100, etc. The ratio of k to m can also be 0.1-1, 1-5, 5-10, 10-15.5, 15.5-20, 20-30.5, 30.5-40, 40-50.5, 50.5-70, 70-80, 80-90, 90-99.5, 99.5-100, etc., which can be adjusted according to actual needs, as long as the ratio is greater than 0 and less than or equal to (100:1).

[0120] By adjusting the ratio of styrene repeating units to butadiene repeating units, as well as the content of functional side groups, the adhesion, elasticity, and mechanical properties of the adhesive can be easily adjusted to meet specific needs.

[0121] According to some embodiments of this application, the modified polystyrene-butadiene copolymer is a block copolymer or a random copolymer.

[0122] Styrene-butadiene random copolymers and styrene-butadiene block copolymers have excellent tensile strength, elasticity and electrical properties, small permanent deformation, good flexural strength and resilience, which can improve the mechanical strength and flexibility of the adhesive.

[0123] According to some embodiments of this application, the number average molecular weight of the modified polybutadiene is 10,000 to 1,000,000, and the number average molecular weight of the modified polystyrene-butadiene copolymer is 10,000 to 1,000,000.

[0124] As an example, the number-average molecular weight of modified polybutadiene can be 10,000, 50,000, 100,000, 250,000, 360,000, 480,000, 600,000, 750,000, 900,000, 990,000, 1,000,000, etc., or it can be 10,000-50,000, 50,000-100,000, 100,000-250,000, 250,000-360,000, 360,000-480,000, 480,000-600,000, 600,000-750,000, 750,000-900,000, 900,000-990,000, 990,000-1,000,000, etc., which can be adjusted according to actual needs, as long as the number-average molecular weight of modified polybutadiene is between 10,000 and 1,000,000.

[0125] The number-average molecular weight of the modified polystyrene-butadiene copolymer can be 10,000, 50,000, 100,000, 250,000, 360,000, 480,000, 600,000, 750,000, 900,000, 990,000, 1,000,000, etc., or it can be 10,000-50,000, 50,000-100,000, 100,000-250,000, 250,000-360,000, 360,000-480,000, 480,000-600,000, 600,000-750,000, 750,000-900,000, 900,000-990,000, 990,000-1,000,000, etc., which can be adjusted according to actual needs, as long as the number-average molecular weight of the modified polystyrene-butadiene copolymer is between 10,000 and 1,000,000.

[0126] If the number-average molecular weight of the modified polybutadiene or modified polystyrene-butadiene copolymer is too small, for example, less than 10,000, the polymer backbone has low flexibility, poor mechanical strength, and low viscosity, which in turn results in low flexibility, mechanical properties, and viscosity of the binder. If the number-average molecular weight of the modified polybutadiene or modified polystyrene-butadiene copolymer is too large, for example, greater than 1 million, the polymer molecular chains are prone to entanglement, reducing polymer flexibility and fluidity, which is not conducive to binder dispersion. The binder cannot quickly diffuse into the interior of the negative electrode active material, and the negative electrode active materials cannot be fully bonded together. Moreover, a large molecular weight will also affect the wettability of the electrolyte.

[0127] In the technical solution of this application embodiment, by controlling the number average molecular weight of modified polybutadiene to be 10,000-1,000,000 and the number average molecular weight of modified polystyrene-butadiene copolymer to be 10,000-1,000,000, the adhesive simultaneously possesses good flexibility, dispersibility, adhesion, and mechanical properties.

[0128] According to some embodiments of this application, the modified polybutadiene includes modified cis-1,4-polybutadiene.

[0129] The molecular chains of cis-1,4-polybutadiene are relatively far apart, making them easier to modify. Furthermore, modified cis-1,4-polybutadiene exhibits high elasticity, low hysteresis, high tensile strength, and wear resistance, thereby improving the performance of adhesives.

[0130] It is understood that the modified polybutadiene of this application is not limited to modified cis-1,4-polybutadiene. In other embodiments, the modified polybutadiene may also include modified trans-1,4-polybutadiene, modified 1,3-polybutadiene, and / or modified 1,2-polybutadiene.

[0131] Please refer to Figure 4. According to some embodiments of this application, this application also provides a method for preparing the adhesive of any of the above embodiments, including the following steps:

[0132] The functional molecule is mixed with polybutadiene and / or polystyrene-butadiene copolymer, the functional molecule reacts with the polybutadiene and / or polystyrene-butadiene copolymer, and the functional molecule is grafted onto the main chain of the butadiene repeating unit in the polybutadiene and / or the polystyrene-butadiene copolymer to form a functional side group.

[0133] The reaction products of the above reaction are extracted to obtain the adhesive.

[0134] Polybutadiene corresponds to the modified polybutadiene described above, and polystyrene-butadiene copolymer corresponds to the modified polystyrene-butadiene copolymer described above, and will not be described again here.

[0135] Functional molecules refer to the functional side groups in the adhesive before they form free radicals.

[0136] In some embodiments, the general formula of the functional molecule can be: R includes at least one alkyl group, and R' includes at least one of a fused-ring aromatic hydrocarbon, a fused-ring aromatic hydrocarbon derivative, a naphthalene dicarboximide, a naphthalene dicarboximide derivative, triphenylamine, or a triphenylamine derivative.

[0137] In some alternative embodiments, R includes x is greater than or equal to 1 and less than or equal to 9.

[0138] In some alternative embodiments, R' includes At least one of them.

[0139] Please refer to Figure 5. According to some embodiments of this application, the preparation method of the adhesive in any of the above embodiments includes: adding functional molecules and polybutadiene and / or polystyrene-butadiene copolymer to a solvent for mixing to obtain a mixture; subjecting the mixture to photoinitiation or thermal initiation, so that the functional molecules react with polybutadiene and / or polystyrene-butadiene copolymer; adding a precipitant to extract the reaction product of the above reaction to obtain the adhesive.

[0140] The order in which functional molecules and polybutadiene and / or polystyrene-butadiene copolymers are added to the solvent is not limited.

[0141] In some optional embodiments, the mixture is irradiated with ultraviolet light to allow the functional molecules to react with polybutadiene and / or polystyrene-butadiene copolymer. The irradiation time can be adjusted according to actual needs; optionally, the mixture is irradiated with ultraviolet light for 4-12 hours. Shorter irradiation times, such as less than 4 hours, result in weak fluorescence and poor observation of the binder distribution; longer irradiation times, such as more than 12 hours, can degrade the binder's performance. Irradiating the mixture with ultraviolet light for 4-12 hours ensures good binder performance while allowing for better observation of the binder's distribution.

[0142] The wavelength of ultraviolet light can be set according to actual needs. For example, in some optional embodiments, ultraviolet light irradiation is used without adding a photoinitiator, and the wavelength of the ultraviolet light can be, but is not limited to, 254 nm. In other optional embodiments, ultraviolet light irradiation is used with the addition of the photoinitiator benzophenone, and the wavelength of the ultraviolet light can be, but is not limited to, 254 nm or 365 nm.

[0143] In some alternative embodiments, the mixture is irradiated with white light to cause the functional molecules to react with polybutadiene and / or polystyrene-butadiene copolymer. In some alternative embodiments, the mixture is thermally initiated to cause the functional molecules to react with the polybutadiene and / or polystyrene-butadiene copolymer. The initiator used for thermal initiation can be, but is not limited to, azo initiators such as azobisisobutyronitrile (AIBN), and the initiation temperature can be selected from 55°C to 75°C. In some alternative embodiments, the thermal initiation temperature is 70°C, at which point the bond-breaking rate of the initiator is suitable.

[0144] In some embodiments of this application, the ultraviolet irradiation can be carried out by, but is not limited to, ultraviolet lamps or other instruments capable of emitting ultraviolet light, and can be selected according to actual needs.

[0145] According to some embodiments of this application, the functional molecule includes a thiol group, which undergoes a click reaction with polybutadiene and / or polystyrene-butadiene copolymer.

[0146] It is very difficult to graft benzene ring-containing groups onto the main chain of butadiene using existing technologies; the methods are extremely complex.

[0147] In the embodiments of this application, under ultraviolet light irradiation, the mercapto group can undergo a click reaction with the double bond in the butadiene repeating unit. The click reaction is highly efficient, enabling functional molecules, especially those including benzene rings, to be rapidly grafted onto the side chain of the butadiene segment. Moreover, the click reaction conditions are mild, the product is easy to purify, and the post-processing is simple.

[0148] The molar ratio of polybutadiene and / or polystyrene-butadiene copolymer to functional molecules can be adjusted according to actual needs. According to some embodiments of this application, the molar ratio of polybutadiene and / or polystyrene-butadiene copolymer to functional molecules is greater than or equal to 2:1 and less than or equal to 3:1.

[0149] If the molar ratio of polybutadiene and / or polystyrene-butadiene copolymer to functional molecules is too small, for example, less than 2:1, it easily results in too many functional side groups, leading to insufficient flexibility of the adhesive. If the molar ratio of polybutadiene and / or polystyrene-butadiene copolymer to functional molecules is too large, for example, greater than 3:1, it results in too few functional side groups, weak fluorescence effect, and low mechanical properties of the adhesive. Therefore, when the molar ratio of polybutadiene and / or polystyrene-butadiene copolymer to functional molecules is greater than or equal to 2:1 and less than or equal to 3:1, the adhesive exhibits good adhesion, flexibility, and mechanical properties, and a significant fluorescence effect.

[0150] According to some embodiments of this application, the solvent includes at least one of chloroform, cyclohexane, and benzene.

[0151] Chloroform, cyclohexane, and benzene all have good solubility. Functional molecules, polybutadiene, and polystyrene-butadiene copolymers can all be quickly dissolved in these solvents, and these solvents are also inexpensive.

[0152] According to some embodiments of this application, the precipitant includes at least one of methanol, water, and acetone.

[0153] The aforementioned precipitant can rapidly form a precipitate with the reaction products of functional molecules reacting with polybutadiene and / or polystyrene-butadiene copolymers, thereby extracting the reaction products.

[0154] According to some embodiments of this application, after adding a precipitant to extract the reaction product, the extracted reaction product is further freeze-dried.

[0155] The freeze-drying temperature and time can be selected according to actual needs. In some optional embodiments, the freeze-drying temperature is greater than or equal to -40°C, and the freezing time does not exceed 24 hours.

[0156] Freeze-drying can quickly remove solvents and has little impact on the properties of the reaction products.

[0157] According to some embodiments of this application, this application provides a negative electrode sheet, including the binder of any of the preceding embodiments or the binder prepared by the preparation method of the binder of any of the preceding embodiments.

[0158] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The negative electrode film layer is formed by coating a negative electrode slurry onto at least one side of the negative current collector and then drying it. The negative electrode slurry includes at least a negative electrode active material and a binder prepared by a method for preparing the binder as described in any of the preceding embodiments.

[0159] In some embodiments, the negative electrode current collector may be a negative electrode current collector known in the art for use in secondary batteries. For example, copper foil, aluminum foil, etc.

[0160] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in secondary 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. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material 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.

[0161] In some embodiments, the negative electrode slurry 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.

[0162] In some embodiments, the negative electrode slurry may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0163] In some embodiments, the negative electrode slurry may optionally include a solvent, such as deionized water.

[0164] In some alternative embodiments, the binder has a mass percentage of 1%wt-3%wt in the negative electrode slurry.

[0165] As an example, the mass percentage of the binder in the negative electrode slurry can be 1%wt, 1.2%wt, 1.5%wt, 2.0%wt, 2.3%wt, 2.6%wt, 3%wt, etc., or it can be 1%-1.2%wt, 1.2%wt-1.5%wt, 1.5%wt-2.0%wt, 2.0%wt-2.3%wt, 2.3%wt-2.6%wt, 2.6%wt-3%wt. It can be selected according to actual needs, as long as the mass percentage of the binder in the negative electrode slurry is 1%wt-3%wt.

[0166] If the mass percentage of the binder in the negative electrode slurry is too small, for example, less than 1% wt, the bonding effect will be poor; if the mass percentage of the binder in the negative electrode slurry is too large, for example, greater than 3% wt, it will have a significant impact on the conductivity of the negative electrode sheet. The embodiments of this application achieve a good bonding effect and have minimal impact on the conductivity of the negative electrode sheet by controlling the mass percentage of the binder in the negative electrode slurry between 1% wt and 3% wt.

[0167] According to some embodiments of this application, this application provides a secondary battery, including a positive electrode, a negative electrode, and a separator, wherein the separator is disposed between the positive electrode and the negative electrode, and the negative electrode is the negative electrode as described in any of the embodiments above. The secondary battery can be the battery 100 or the battery cell 20 as described above.

[0168] According to some embodiments of this application, this application provides an electrical device including a secondary battery as described in any of the preceding embodiments, and the secondary battery is used to provide electrical energy to the electrical device.

[0169] The electrical device can be any of the aforementioned devices or systems that use secondary batteries.

[0170] The preparation process and test data are described below:

[0171] Example 1:

[0172] Preparation of adhesive:

[0173] cis-1,4-polybutadiene with a number-average molecular weight of 150,000 was combined with functional molecules Add the mixture to toluene solvent at a molar ratio of 2:1 and stir thoroughly to obtain a mixture.

[0174] The mixture was irradiated under a UV lamp for 8 hours, so that... It reacts with cis-1,4-polybutadiene;

[0175] Methanol is added as a precipitant to extract the reaction products of the above reaction, yielding the binder.

[0176] Preparation of negative electrode sheet:

[0177] 2% wt of the binder from Example 1 was mixed with 95 wt% of the negative electrode active material (micron-sized silicon), 1.0 wt% of the conductive agent (conductive carbon black), and 2.0 wt% of the thickener (sodium carboxymethyl cellulose (CMC)). Deionized water was added and stirred to disperse the mixture into a negative electrode slurry. The negative electrode slurry was then coated onto a Cu foil. After coating both sides, the foil was dried, cold-pressed, slit, and sheeted to obtain the negative electrode sheet.

[0178] Preparation of the positive electrode sheet:

[0179] 96 wt% of positive electrode active material (lithium iron phosphate), 1.0 wt% of conductive agent (conductive carbon black), 2.5 wt% of binder (polyvinylidene fluoride), and 0.5 wt% of dispersant were mixed, and then N-methylpyrrolidone was added and stirred to disperse the mixture, thus preparing a positive electrode slurry. The slurry was then coated on both sides, dried, cold-pressed, and slit to obtain the positive electrode sheet.

[0180] Preparation of lithium-ion batteries:

[0181] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The bare cell is placed in the outer packaging, and the prepared electrolyte is injected. The process includes encapsulation, electrolyte injection, formation, and venting to obtain a lithium-ion battery.

[0182] Example 2:

[0183] This embodiment 2 is basically the same as embodiment 1, the only difference being that the functional molecule is...

[0184] Example 3:

[0185] This embodiment 3 is basically the same as embodiment 1, the only difference being that the functional molecule is...

[0186] Example 4:

[0187] Example 4 is essentially the same as Example 1, except that the polymer involved in the blending is a polystyrene-butadiene copolymer (SBR) with a number-average molecular weight of 150,000, wherein the molar ratio of double bonds to side phenyl groups in the SBR main chain is 2:1; and the polystyrene-butadiene copolymer and functional molecules... Add the mixture to toluene solvent at a molar ratio of 3:1 and stir thoroughly to obtain a mixture.

[0188] Example 5:

[0189] This embodiment 5 is basically the same as embodiment 4, the only difference being that the functional molecule is... Polystyrene butadiene copolymer and Add the mixture to toluene solvent at a molar ratio of 3:1 and stir thoroughly to obtain a mixture.

[0190] Example 6:

[0191] This embodiment 5 is basically the same as embodiment 4, the only difference being that the functional molecule is... Polystyrene butadiene copolymer and Add the mixture to toluene solvent at a molar ratio of 3:1 and stir thoroughly to obtain a mixture.

[0192] Example 7:

[0193] Example 7 is essentially the same as Example 1, except that the polymers involved in the blending are polystyrene-butadiene copolymer (SBR) with a number average molecular weight of 150,000 and cis-1,4-polybutadiene with a number average molecular weight of 150,000. The SBR and cis-1,4-polybutadiene are thoroughly mixed in a molar ratio of 1:1 to form a mixed polymer, wherein the molar ratio of the double bonds to the side phenyl groups in the SBR main chain is 2:1. The mixed polymer is then blended according to the functional molecules... The mixture was added to the solvent toluene at a molar ratio of 3:1 and stirred thoroughly to obtain a mixture.

[0194] Example 8:

[0195] Example 8 is basically the same as Example 1, except that the preparation method of the binder is different. Functional molecules... 1,3-Butadiene and alkyllithium were mixed evenly in toluene at a molar ratio of 1:1, and copolymerized using alkyllithium as an initiator to produce a copolymer with a number average molecular weight of 150,000. Methanol was added as a precipitant to extract the reaction product, yielding the binder.

[0196] Example 9:

[0197] Example 9 is essentially the same as Example 1, except for the preparation method of the adhesive. Cis-1,4-polybutadiene with a number-average molecular weight of 150,000 is combined with functional molecules... The mixture was added to toluene at a molar ratio of 2:1 and stirred thoroughly to obtain a solution. Under acid catalysis, the hydroxyl groups on the functional molecules underwent an addition reaction with the double bonds on the polymer backbone.

[0198] Methanol is added as a precipitant to extract the reaction products of the above reaction, yielding the binder.

[0199] Comparative Example 1:

[0200] The only difference from Example 4 is that the adhesive was not modified with functional side groups. The adhesive used was a polystyrene-butadiene copolymer (SBR) with a number average molecular weight of 150,000, in which the molar ratio of double bonds in the main chain to phenyl side groups was 2:1.

[0201] Comparative Example 2:

[0202] The only difference from Example 1 is that the binder was not modified with functional side groups; the binder is cis-1,4-polybutadiene with a number average molecular weight of 150,000.

[0203] Comparative Example 3:

[0204] The only difference from Example 7 is that the adhesive was not modified with functional side groups. The adhesive was made by fully mixing polystyrene-butadiene copolymer (SBR) with a number average molecular weight of 150,000 and cis-1,4-polybutadiene with a number average molecular weight of 150,000 in a molar ratio of 1:1, wherein the molar ratio of double bonds and side group phenyl groups in the SBR main chain is 2:1.

[0205] Negative electrode sheets and lithium-ion batteries using binders from Examples 1-9 and Comparative Examples 1-3, respectively, were subjected to electrode peel strength tests, binder distribution characterization tests, and cycle stability tests. The test methods are as follows:

[0206] Negative electrode sheet peel strength test:

[0207] Equipment Model: AG-X Electronic Universal Material Testing Machine (Made in Japan) Specific Testing Procedure: Cut the negative electrode sheet into 25mm×100mm samples. Fix the side of the sample coated with negative electrode slurry to the stainless steel plate of the peel strength tester with double-sided tape. Peel off one end of the sample and fix it to the tensile probe. Peel off 180° at a constant speed of 300mm / min. Test the magnitude of the peel force during the peeling process.

[0208] Adhesive distribution characterization test:

[0209] The negative electrode sheets prepared in Examples 1-9 and Comparative Examples 1-3 were placed in a dark room and irradiated with a handheld ultraviolet analyzer (Spectroline UV lamp EA-1610) to observe the distribution of the binder on the surface of the negative electrode sheet with the naked eye.

[0210] Cyclic stability test:

[0211] The lithium-ion battery was left to stand at 25°C for 30 minutes; then charged at a constant current of 0.05C to 3.65V; left to stand at 25°C for 10 minutes; then discharged at a constant current of 0.33C to 2.5V, and then discharged at a constant current of 0.05C to 2.5V; then charged at a constant current of 0.1C to 3.65V at 25°C; left to stand at 25°C for 10 minutes; then discharged at a constant current of 0.1C to 2.5V at 25°C; left to stand at 25°C for 10 minutes; the above charging and discharging steps were repeated until the capacity value reached 80% of the initial value, at which point the test was completed.

[0212] Table 1: Performance parameters of negative electrode sheets and lithium-ion batteries of Examples 1-9 and Comparative Examples 1-3

[0213]

[0214]

[0215] The comparison of the results of Examples 1-9 and Comparative Examples 1-3 in Table 1 shows that the binders modified with functional side groups in the embodiments of this application can all characterize the distribution of the binder on the surface of the negative electrode sheet, while the binders not modified with functional side groups cannot characterize the distribution of the binder on the surface of the negative electrode sheet. Moreover, compared with the binders of Examples 1-9, the binders of Comparative Examples 1-3 have relatively poor adhesion and cycle stability of the lithium-ion batteries.

[0216] The comparison of the results of Examples 1-3 and 9 with Comparative Example 2 shows that by introducing functional side groups into the main link of cis-1,4-polybutadiene, not only can the adhesion of the cis-1,4-polybutadiene binder and the cycle stability of the lithium-ion battery using the binder be improved, but also the distribution of the binder can be characterized by introducing fluorescent groups into the binder.

[0217] The comparison of the results of Examples 4-6 with Comparative Example 1 shows that by branching functional side groups onto the main link of the polystyrene-butadiene copolymer, not only can the adhesion of the polystyrene-butadiene copolymer binder and the cycle stability of lithium-ion batteries using the binder be improved, but also the distribution of the binder can be characterized by introducing fluorescent groups into the binder.

[0218] The comparison between the results of Example 7 and Comparative Example 3 shows that by using the main linking functional side groups of the copolymer formed by cis-1,4-polybutadiene and polystyrene-butadiene copolymer, it is possible not only to improve the adhesion of the copolymer binder and the cycle stability of lithium-ion batteries using this binder, but also to make it possible to characterize the distribution of the binder by introducing fluorescent groups into the binder.

[0219] A comparison of the results from Examples 1-3 and Examples 4-6 shows that when the functional molecule is At this time, the adhesive force of the binder is the greatest, and the lithium-ion battery using the binder has the best cycle stability.

[0220] In the technical solution of this application embodiment, by using at least one functional side group with a fluorescent effect in the main linking branch of the butadiene repeating unit, the distribution of the negative electrode binder in the negative electrode sheet can be directly characterized in situ using a fluorescence microscope, and phenomena such as the floating of the negative electrode binder can be observed, thereby enabling secondary battery failure analysis. Furthermore, the functional side groups of the binder in this application embodiment include large π bonds, which can generate π-π conjugation with negative electrode materials such as graphite negative electrodes and silicon-based negative electrodes, increasing the interaction between the negative electrode binder and the negative electrode material, and improving the adhesion of the negative electrode binder; it can also improve the dispersion performance of negative electrode materials such as graphite negative electrodes and silicon-based negative electrodes, making the dispersion of the negative electrode material in the negative electrode sheet more uniform, thereby improving the cycle stability of the lithium-ion battery.

[0221] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. An adhesive, characterized in that, The invention comprises modified polybutadiene and / or modified polystyrene-butadiene copolymers, wherein the main chain of the modified polybutadiene includes butadiene repeating units and modified butadiene repeating units; the main chain of the modified polystyrene-butadiene copolymer includes styrene repeating units, butadiene repeating units, and modified butadiene repeating units, wherein the modified butadiene repeating units are obtained by grafting at least one functional side group onto the main chain of butadiene, and the functional side group has a fluorescent effect; the functional side group includes a large π bond; the functional side group is grafted onto the main chain of the butadiene through a click reaction between a functional molecule including a thiol group and the polybutadiene and / or polystyrene-butadiene copolymer, and after grafting, the sulfur atom in the thiol group is connected to the carbon atom on the main chain of the butadiene.

2. The adhesive according to claim 1, characterized in that, The functional side group includes at least one of a fused ring aromatic hydrocarbon group, a naphthalene dicarboximide group, and a triphenylamine group.

3. The adhesive according to claim 1 or 2, characterized in that, The functional side bases include 、 、 、 、 or At least one of them.

4. The adhesive according to claim 1, characterized in that, The general formula for the functional side base is: or R includes at least one of alkylene groups, and R' includes at least one of fused-ring aromatic hydrocarbon groups, naphthalene dicarboximide groups, and triphenylamine groups.

5. The adhesive according to claim 4, characterized in that, The R includes x is greater than or equal to 1 and less than or equal to 9.

6. The adhesive according to claim 4 or 5, characterized in that, The R' includes 、 、 、 、 or At least one of them.

7. The adhesive according to claim 1, characterized in that, The modified polystyrene-butadiene copolymer is a block copolymer or a random copolymer.

8. The adhesive according to claim 1, characterized in that, The number-average molecular weight of the modified polybutadiene is 10,000 to 1,000,000, and the number-average molecular weight of the modified polystyrene-butadiene copolymer is 10,000 to 1,000,000.

9. The adhesive according to claim 1, characterized in that, The modified polybutadiene includes modified cis-1,4-polybutadiene.

10. A method for preparing the adhesive according to any one of claims 1-9, characterized in that, include: A functional molecule including a thiol group is mixed with polybutadiene and / or a polystyrene-butadiene copolymer, and the functional molecule undergoes a click reaction with the polybutadiene and / or the polystyrene-butadiene copolymer; the reaction product of the above reaction is extracted to obtain the adhesive.

11. The method for preparing the adhesive according to claim 10, characterized in that, include: The functional molecule is added to the polybutadiene and / or the polystyrene-butadiene copolymer and mixed in a solvent to obtain a mixture; The mixture is subjected to photoinitiation or thermal initiation to cause the functional molecules to react with the polybutadiene and / or the polystyrene-butadiene copolymer; a precipitant is added to extract the reaction products of the above reaction to obtain the binder.

12. The method for preparing the adhesive according to claim 10, characterized in that, The molar ratio of the polybutadiene and / or the polystyrene-butadiene copolymer to the functional molecule is greater than or equal to 2:1 and less than or equal to 3:

1.

13. The method for preparing the adhesive according to claim 11, characterized in that, The solvent includes at least one of chloroform, cyclohexane, and benzene.

14. The method for preparing the adhesive according to claim 11, characterized in that, The precipitant includes at least one of methanol, water, and acetone.

15. The method for preparing the adhesive according to claim 10, characterized in that, After extracting the reaction products from the above reaction, the extracted reaction products were further freeze-dried.

16. A negative electrode sheet, characterized in that, This includes adhesives prepared by any one of the methods described in claims 1-9 or 10-15.

17. A secondary battery, characterized in that, Includes the negative electrode sheet as described in claim 16.

18. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 17.

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