Polyimide binder, electrode sheet, battery, battery pack, and electric device

Abstract

A polyimide binder, an electrode sheet, a battery, a battery pack, and an electric device. The polyimide binder comprises an aromatic hard segment and a polyester soft segment, wherein the mass percentage content of the polyester soft segment in the polyimide binder is 30-90%. The present application can improve the properties of adhesiveness, flexibility, etc., of a bonding material, improve the bonding strength between an electrode coating and an electrode current collector in an electrode sheet, and avoid the problems of peeling, etc., of the electrode sheet, thereby improving the stability of the electrode sheet, and improving the performance of the cycle capacity, etc., of the battery.

Description

A polyimide adhesive, electrode sheet, battery, battery pack and electrical device

[0001] This application claims priority to Chinese Patent Application No. 202510500239.3, filed on April 18, 2025, entitled "A Polyimide Adhesive, Electrode Sheet, Battery, Battery Pack and Electrical Equipment", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application belongs to the field of battery technology and relates to a polyimide binder, electrode sheet, battery, battery pack and electrical equipment. Background Technology

[0003] Batteries are common electrochemical devices with wide applications. Electrode sheets are a crucial component of batteries, affecting their cycle capacity and other performance characteristics. Electrode sheets typically consist of an electrode current collector and an electrode coating. The electrode coating is mainly composed of electrode active materials, conductive agents, and binders. The binder is primarily used to bind the electrode active materials and conductive agents within the electrode coating, and to bond the electrode coating to the electrode current collector. Therefore, it plays a vital role in maintaining the stability and electrochemical performance of the electrode sheet.

[0004] For example, polyvinylidene fluoride (PVDF) is commonly used as a binder in the positive electrode of batteries such as lithium-ion batteries. However, PVDF contains fluorine (F) and is not easily degraded. The production process of PVDF (which usually uses fluorinated emulsifiers), its use, and its decomposition and recycling after disposal all face significant challenges. This results in a large environmental pressure throughout its entire life cycle, which is not conducive to the industrialization requirements of green environmental protection and sustainability. Replacing PVDF with hydrogenated nitrile butadiene rubber (NBR) and modified acrylonitrile can overcome environmental problems to some extent. However, these existing binders still generally have some issues that limit the cycle performance of the battery. For example, the positive electrode sheet using hydrogenated NBR as a binder has a large internal resistance, affecting the battery's rate capability and cycle performance. As for modified acrylonitrile, it is difficult to balance the electrolyte's ability to wet and coat the electrode active materials with the modified acrylonitrile's own anti-swelling ability and chemical stability. Specifically, when the acrylonitrile content is high, the binder's excessive crystallinity makes it difficult to have sufficient dispersion ability for the main material, while when the acrylonitrile content is low, the binder is unable to perform its own anti-swelling and chemical stability properties.

[0005] Polyimide adhesives possess good thermal and electrochemical stability, effectively overcoming the problems associated with PVDF, hydrogenated nitrile rubber, and modified acrylonitrile adhesives, and are gradually gaining widespread attention and application.

[0006] However, due to the poor adhesion, poor flexibility, and poor processability of existing polyimide binders when used in electrode sheet preparation (e.g., the poor stability of the electrode slurry formed when preparing electrode sheets by coating), electrode sheets generally suffer from problems such as low bonding strength between the electrode coating and the electrode current collector, and easy peeling of the electrode coating, which affect the cycle capacity and other performance of the battery. Summary of the Invention

[0007] This application provides a polyimide binder, electrode sheet, battery, battery pack, and electrical device, which can improve the adhesion, flexibility, and processability of the binder material during electrode sheet preparation, enhance the bonding strength between the electrode coating and the electrode current collector in the electrode sheet, avoid problems such as electrode coating peeling, thereby improving the stability of the electrode sheet and increasing the cycle capacity and other performance of the battery.

[0008] In one aspect, this application provides a polyimide adhesive comprising aromatic hard segments and polyester soft segments, wherein the polyester soft segments in the polyimide adhesive comprise 30% to 90% by mass.

[0009] According to one embodiment of this application, the mass percentage of the polyester soft segment in the polyimide adhesive is 60% to 70%.

[0010] According to one embodiment of this application, the aromatic hard segment has the structure shown in Formula I.

[0011] R1 is selected from substituted or unsubstituted aryl groups, or substituted or unsubstituted biaryl groups;

[0012] Preferably, the substituted or unsubstituted biaryl group has the structure shown in formula V:

[0013] R7 and R8 each independently represent a monosubstituted to the maximum permissible substituent, and R7 and R8 each independently are selected from hydrogen, substituted or unsubstituted alkyl, or carboxyl, and L2 is selected from one or more of single bond, substituted or unsubstituted alkyl, carbonyl, ester, oxygen, sulfone, and amide.

[0014] According to one embodiment of this application, the aromatic hard segment is selected from the structures shown in Formulas I-1 to I-9 as follows:

[0015] According to one embodiment of this application, the polyester soft segment comprises the structure shown in Formula II and / or Formula III as follows:

[0016] R3 is selected from straight-chain alkyl groups having 1 to 18 carbon atoms or branched alkyl groups, and x is an integer from 5 to 5000; preferably, R3 is selected from straight-chain alkyl groups having 4 to 8 carbon atoms or branched alkyl groups; preferably, x is an integer from 5 to 100.

[0017] R4 and R5 are each independently selected from straight-chain alkyl groups having 1 to 12 carbon atoms or branched alkyl groups, and y is an integer from 5 to 5000; preferably, R4 and R5 are each independently selected from straight-chain alkyl groups having 1 to 5 carbon atoms or branched alkyl groups, and preferably y is an integer from 5 to 100.

[0018] According to one embodiment of this application, the polyimide adhesive includes a connecting segment, the connecting segment comprising the structure shown in Formula IV:

[0019] L1 is selected from substituted or unsubstituted aryl, substituted or unsubstituted biaryl, or substituted or unsubstituted alkyl. The symbol represents the connection site between Formula IV and the polymeric segment of the polyester soft segment, and * represents the connection site between Formula IV and the aromatic hard segment.

[0020] According to one embodiment of this application, the number average molecular weight of the polyimide adhesive is 10kDa-10000kDa, preferably 75kDa-95kDa; and / or, the ratio of the weight average molecular weight to the number average molecular weight of the polyimide adhesive is 1-10, preferably 2.3-2.8.

[0021] Another aspect of this application provides a method for preparing the above-mentioned polyimide adhesive, comprising the following steps: subjecting an ester monomer to a first polymerization reaction to obtain a polyester precursor; subjecting the polyester precursor, diisocyanate, and an anhydride monomer to a second polymerization reaction to obtain the polyimide adhesive; wherein at least one of the diisocyanate and the anhydride monomer contains an aryl group.

[0022] According to one embodiment of this application, the ester monomer includes a cyclic ester monomer, preferably the cyclic ester monomer includes lactone monomers and / or lactone monomers; and / or, the anhydride monomer includes a dianhydride monomer, preferably the dianhydride monomer may include a dianhydride monomer having the structure shown in Formula X; and / or, the molar ratio of the anhydride monomer to the ester monomer is (0.07~1.32):1; and / or, the diisocyanate has the structure shown in Formula IA; and / or, the mass ratio of the diisocyanate to the ester monomer is (0.01~0.3):1; and / or, the temperature of the first polymerization reaction is 40~120℃, preferably 40~100℃, and the time is 3h~12h, preferably 3h~10h.

[0023] In formula X, R1 is selected from substituted or unsubstituted aryl groups or substituted or unsubstituted biaryl groups.

[0024] OCN-L1-NCO Formula IA

[0025] In the formula IA, L1 is selected from substituted or unsubstituted aryl, substituted or unsubstituted biaryl, or substituted or unsubstituted alkyl.

[0026] According to one embodiment of this application, the ester monomer undergoes the first polymerization reaction under the action of an initiator, satisfying the following: the initiator includes at least one of a small molecule diol initiator and a small molecule diamine initiator; and / or, the molar ratio of the ester monomer to the initiator is (5-5000):1, preferably (5-100):1.

[0027] According to one embodiment of this application, the process of carrying out a second polymerization reaction of the polyester precursor, diisocyanate and anhydride monomer includes: carrying out an addition reaction of the polyester precursor and the diisocyanate, then adding the anhydride monomer thereto, and then carrying out the second polymerization reaction to obtain the polyimide binder; preferably, the temperature of the addition reaction is 70-90°C and the time is 2-20 min.

[0028] According to one embodiment of this application, the temperature of the second polymerization reaction is 100-180°C and the time is 1-15 hours.

[0029] In another aspect of this application, an electrode sheet is provided, comprising an electrode coating, the electrode coating comprising the above-described polyimide binder, or a polyimide binder prepared according to the above-described method for preparing the polyimide binder.

[0030] According to one embodiment of this application, the electrode sheet includes a positive electrode sheet.

[0031] In another aspect of this application, a battery is provided, including the aforementioned electrode sheet.

[0032] Another aspect of this application provides a battery pack comprising at least two of the aforementioned batteries connected to each other.

[0033] Another aspect of this application provides an electrical device including the aforementioned battery or battery pack.

[0034] The bonding material provided in this application includes a polyimide binder. By combining aromatic hard segments and polyester soft segments, and controlling the mass percentage of polyester soft segments in the polyimide binder within the range of 30% to 90%, the adhesion of the polyimide binder can be improved, giving it both good mechanical properties and flexibility. Simultaneously, it improves the processing performance of the polyimide binder when used in electrode sheet preparation. For example, it can improve the stability of the electrode slurry formed when preparing electrode sheets by coating, thereby enhancing the bonding force (or electrode sheet peel force) between the electrode coating and the electrode sheet, and giving the electrode sheet good flexibility. This avoids problems such as electrode coating peeling (e.g., electrode coating peeling from the electrode current collector, electrode coating cracking, and powder shedding), while also improving the processing performance of the electrode sheet and ensuring its structural stability, thereby improving the battery's safety, cycle stability, and cycle capacity. Attached Figure Description

[0035] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0036] Figure 1 is a schematic diagram of the preparation process of the polyimide adhesive provided in this application;

[0037] Figure 2 is a schematic diagram of the preparation process of the polyimide adhesive provided in Example 1 of this application;

[0038] Figure 3 is the 1H NMR spectrum of the polyimide binder provided in Example 1 of this application.

[0039] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0040] To enable those skilled in the art to better understand the solutions of this application, a further detailed description of this application is provided below. The specific embodiments listed below are merely descriptions of the principles and features of this application; the examples are only for explaining this application and are not intended to limit its scope. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application. When the following description relates to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements.

[0041] Based on the inventors' long-term research, polyimide binders have poor adhesion, resulting in weak bonding forces (adhesive forces) between the electrode active materials and conductive agents in the electrode coating, as well as between the electrode coating and the electrode current collector, leading to poor electrode stability. Furthermore, polyimide binders are primarily rigid skeletons with poor flexibility. When used as electrode binders, they cause the electrode coating to have high hardness and brittleness, easily leading to peeling, cracking, and material loss. Additionally, polyimide binders have poor processability; for example, in the process of preparing electrode sheets by coating methods... During the process, due to the highly cross-linked and rigid molecular structure of polyimide, it is difficult to dissolve in solvents (such as common organic solvents like N-methylpyrrolidone (NMP)). After forming the electrode slurry using polyimide binders, electrode active materials, conductive agents, and solvents, the polyimide binder is difficult to disperse uniformly in the electrode slurry. The uniformity and stability of the electrode slurry are poor, and problems such as dry material are prone to occur. This results in many surface defects and poor appearance of the prepared electrode sheet, which is also an important factor affecting the electrochemical performance of the electrode sheet, and thus affecting the cycle capacity and other performance of the battery.

[0042] Therefore, due to the poor adhesion and flexibility of polyimide binders, electrode sheets generally suffer from problems such as low bonding strength between the electrode coating and the electrode current collector, and easy powder shedding from the electrode sheets, which affect the battery's cycle capacity and other performance characteristics.

[0043] In view of this, embodiments of this application provide a polyimide adhesive comprising aromatic hard segments and polyester soft segments, wherein the mass percentage of the polyester soft segments in the polyimide adhesive is 30% to 90%.

[0044] According to the inventors' research, by introducing aromatic hard segments and polyester soft segments into the polyimide binder and controlling the mass percentage of polyester soft segments in the polyimide binder within the range of 30% to 90%, the adhesion, flexibility, and processability of the polyimide binder during electrode sheet preparation can be improved. This enhances the bonding strength between the electrode coating and the electrode current collector in the electrode sheet, avoids problems such as electrode sheet peeling (e.g., electrode coating peeling off from the electrode current collector, electrode coating cracking, and powder shedding), thereby improving the stability and flexibility of the electrode sheet and increasing the cycle life of the battery.

[0045] The reason for this is that, within the aforementioned polyimide binder composition system, the polyimide binder exhibits excellent adhesion, enhancing the bonding force between the electrode active material and conductive agent components in the electrode coating, as well as the bonding force between the electrode coating and the electrode current collector. This improves the structural stability of the electrode sheet, enhances its stability during battery cycling, and increases the battery cycle capacity. Simultaneously, by introducing aromatic hard segments and polyester soft segments into the polyimide binder, and controlling the mass percentage of polyester soft segments within the range of 30% to 90%, the mechanical properties of the polyimide are maintained based on the hardness characteristics of the aromatic hard segments, while the flexibility of the polyimide binder is improved based on the flexibility of the polyester soft segments, thereby improving the electrode's performance. The flexibility of the electrode sheet avoids problems such as electrode coating peeling caused by excessive hardness and rigidity (e.g., electrode coating peeling off from the electrode current collector, electrode coating cracking, and powdering). At the same time, the polyimide binder has good processing performance. For example, in the process of preparing the electrode sheet by coating method, the polyimide binder is easy to dissolve in solvents (e.g., organic solvents such as N-methylpyrrolidone (NMP)). After forming the electrode slurry with the polyimide binder, electrode active material, conductive agent, and solvent, the polyimide binder is more uniformly dispersed in the electrode slurry, improving the uniformity and stability of the electrode slurry, avoiding problems such as dry material, thereby reducing surface defects of the electrode sheet and improving the electrochemical performance of the electrode sheet. Therefore, the embodiments of this application can improve the adhesion, flexibility and processability of the bonding material when used in electrode sheet preparation, enhance the bonding strength between the electrode coating and the electrode current collector in the electrode sheet, and avoid problems such as electrode sheet peeling (e.g., electrode coating peeling off from the electrode current collector, electrode coating cracking and powder shedding), thereby improving the stability and flexibility of the electrode sheet and improving the cycle capacity of the battery.

[0046] In the aforementioned polyimide binder system, if the mass percentage of polyester soft segments is too small (<30%), the polyimide binder exhibits poor flexibility, failing to effectively improve the flexibility and other properties of the electrode sheet, thus affecting its stability. Conversely, if the mass percentage of polyester soft segments is too large (>90%), the polyimide binder contains too many soft segments and too few hard segments, resulting in poor mechanical properties, such as reduced resistance to swelling, which also affects the stability of the electrode sheet. Therefore, by controlling the mass percentage of polyester soft segments in the polyimide binder within the range of 30% to 90%, the polyimide binder can possess both good flexibility and mechanical properties, as well as excellent adhesion, thereby improving the structural stability of the electrode sheet, preventing electrode coating peeling, and ultimately enhancing the battery's cycle life and other performance characteristics.

[0047] For example, the mass percentage of polyester soft segments in the polyimide adhesive is, for example, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or any combination thereof.

[0048] In some embodiments, the polyester soft segment in the polyimide binder has a mass percentage of 60% to 70%, which helps to further balance the mechanical properties and flexibility of the polyimide binder, and further improve the adhesion, flexibility and processability of the polyimide binder when used in electrode sheet preparation. This, in turn, improves the stability of the electrode slurry used to form the electrode sheet, the flexibility of the electrode sheet, the peel strength of the electrode coating and current collector, and enhances the cycle capacity and other properties of the battery.

[0049] In addition, the mass percentage of aromatic hard segments in polyimide adhesives can be 10% to 70%, for example, 10%, 20%, 30%, 40%, 50%, 60%, 70%, or any combination thereof.

[0050] The mass percentage of polyester soft segments and aromatic hard segments in the polyimide adhesive of this application embodiment can be determined by conventional methods in the art, such as nuclear magnetic resonance (NMR) and thermogravimetric analysis (TGA). For example, the thermal decomposition temperatures of aromatic hard segments and polyester soft segments are different (the thermal decomposition temperature of aromatic hard segments is higher than that of polyester soft segments), therefore, the content of polyester soft segments and aromatic hard segments in the polyimide adhesive can be determined by thermogravimetric analysis. The thermal decomposition temperature of the polyester soft segment is between 200℃ and 300℃. During thermogravimetric analysis, the initial mass of the polyimide binder (i.e., the mass before heating) is recorded as m3. Then, the polyimide binder is heated to 300℃ and held at 300℃ for 10 minutes. The mass of the product after holding at 300℃ is recorded as m4. The mass of the polyester soft segment is basically equal to the difference between m3 and m4. (m3-m4) / m3 is the mass percentage of the polyester soft segment in the polyimide binder. The mass percentage of the aromatic hard segment in the polyimide binder is basically equal to 100% - (m3-m4) / m3.

[0051] In practice, the battery can be completely discharged and then disassembled to separate the electrode plates. The electrode active material layer (electrode coating) can be scraped off the electrode plates, crushed into powder, and dispersed in a solvent. After filtration and centrifugation, the solvent is allowed to evaporate completely, and the collected product is the polyimide adhesive. The polyimide adhesive is then subjected to tests such as nuclear magnetic resonance and thermogravimetric analysis to determine its characteristics, such as the mass percentage of polyester soft segments. The solvent used can be a conventional solvent, as long as it can dissolve the polyimide and facilitate the separation of the polyimide adhesive from the electrode active material powder. In practice, the solvent used may include N-methylpyrrolidone (NMP).

[0052] In the polyimide binder of this application embodiment, the polyester soft segment is composed of repeating units connected by ester bonds (-COO-). These units are connected by flexible carbon chains. Compared with the aromatic ring structure, this flexible segment provides more free rotation angles and increases the overall flexibility of the molecular chain. Therefore, by introducing the polyester soft segment into the polyimide, the rigidity of the polyimide can be reduced and the flexibility of the molecular chain can be increased. This allows the polyimide binder to better adapt to the volume changes of material particles such as electrode active materials in the electrode coating during charging and discharging, reducing stress concentration in the electrode coating and the resulting cracking and peeling of the electrode coating, thereby extending the battery's service life.

[0053] In the embodiments of this application, the polyester soft segment may include the structure shown in Formula II and / or Formula III, which is more conducive to improving the adhesion, flexibility and processability of the polyimide binder when used in electrode sheet preparation, improving the stability and flexibility of the electrode sheet, and increasing the cycle life of the battery.

[0054] In Formula II, R3 is selected from alkyl groups, specifically straight-chain alkyl groups or branched alkyl groups.

[0055] Specifically, R3 can be selected from alkyl groups having 1 to 18 carbon atoms, that is, R3 can be selected from straight-chain alkyl groups having C1 to C18 carbon atoms or branched alkyl groups (i.e., R3 is selected from straight-chain alkyl groups having 1 to 18 carbon atoms or branched alkyl groups having 1 to 18 carbon atoms). The number of carbon atoms in R3 is, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17 or 18. Preferably, R3 is a straight-chain alkyl group having 4 to 8 carbon atoms or a branched alkyl group.

[0056] For example, when R3 is a straight-chain alkyl group, it includes, but is not limited to, methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, etc.; when R3 is a branched alkyl group, it includes, but is not limited to, isopropyl, tert-butyl, isobutyl, sec-butyl, neopentyl, isopentyl, tert-pentyl, 3-methylbutyl, 2-methylbutyl, 2,2-dimethylpropyl, 2-methylpentyl, 3-methylpentyl, 2,2-dimethylbutyl, 2,3-dimethylbutyl, 2,2,3-trimethylbutyl, 2,2,4-trimethylpentyl, 2,4-dimethylpentyl, 3,3-dimethylbutyl, 3-methylhexyl, 2-methylhexyl, 2,3-dimethylpentyl, 2,4-dimethylhexyl, 2,2,5-trimethylhexyl, 2,2,4-trimethylpentyl, etc.

[0057] In Equation II, x represents the repeated unit in Equation II. The quantity (x is a positive integer greater than 1), specifically x can be an integer from 5 to 5000, for example, 5, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 30, 40, 50, 60, 70, 80, 90, 100, 500, 1000, 2000, 3000, 4000, 5000, or any range thereof. In some embodiments, x can specifically be an integer from 5 to 100.

[0058] In detail, the structure shown in Formula II is formed by the ring-opening polymerization of a lactone (such as the lactone monomer shown in Formula VII-1 below) (as described in the first polymerization reaction below). During the ring-opening polymerization of the lactone, the carbon-oxygen single bond (CO) in the ester bond breaks, resulting in the ring opening of the lactone. The broken ester bond then forms a linear polymer chain with another broken ester bond through chain polymerization, i.e., the repeating unit is formed by this chain. The polymeric chain segment (Formula II) is composed of lactones, which is more conducive to the preparation of polyimide binders and also facilitates the control of the molecular weight of polyimide binders, resulting in polyimide binders with a narrower molecular weight distribution, and further improving the adhesion and flexibility of polyimide binders.

[0059] R4 and R5 are each independently selected from alkyl groups, specifically from straight-chain alkyl groups having 1 to 12 carbon atoms or branched alkyl groups (i.e., R4 and R5 are each independently selected from straight-chain alkyl groups having 1 to 12 carbon atoms or branched alkyl groups having 1 to 12 carbon atoms); y represents the repeating unit in Formula III. The quantity (y is a positive integer greater than 1), specifically y can be an integer from 5 to 5000, for example, 5, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 30, 40, 50, 60, 70, 80, 90, 100, 500, 1000, 2000, 3000, 4000, 5000, or any range between two of these. In some embodiments, y can specifically be an integer from 5 to 100.

[0060] Specifically, R4 is selected from alkyl groups, specifically straight-chain alkyl groups or branched alkyl groups. More specifically, R4 can be selected from straight-chain alkyl groups or branched alkyl groups having 1 to 12 carbon atoms, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 carbon atoms. Preferably, R4 is a straight-chain alkyl group or a branched alkyl group having 1 to 5 carbon atoms.

[0061] For example, when R4 is a straight-chain alkyl group, it includes, but is not limited to, methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, etc.; when R4 is a branched alkyl group, it includes, but is not limited to, isopropyl, tert-butyl, isobutyl, sec-butyl, neopentyl, isopentyl, tert-pentyl, 3-methylbutyl, 2-methylbutyl, 2,2-dimethylpropyl, 2-methylpentyl, 3-methylpentyl, 2,2-dimethylbutyl, 2,3-dimethylbutyl, 2,2,3-trimethylbutyl, 2,2,4-trimethylpentyl, 2,4-dimethylpentyl, 3,3-dimethylbutyl, 3-methylhexyl, 2-methylhexyl, 2,3-dimethylpentyl, 2,4-dimethylhexyl, 2,2,5-trimethylhexyl, 2,2,4-trimethylpentyl, etc.

[0062] R5 is selected from alkyl groups, specifically straight-chain alkyl groups or branched alkyl groups. Specifically, R5 is a straight-chain alkyl group or a branched alkyl group having 1 to 12 carbon atoms, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12 carbon atoms. Preferably, R5 is a straight-chain alkyl group or a branched alkyl group having 1 to 5 carbon atoms. For example, when R5 is a straight-chain alkyl group, it includes, but is not limited to, methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, etc.; when R5 is a branched alkyl group, it includes, but is not limited to, isopropyl, tert-butyl, isobutyl, sec-butyl, neopentyl, isopentyl, tert-pentyl, 3-methylbutyl, 2-methylbutyl, 2,2-dimethylpropyl, 2-methylpentyl, 3-methylpentyl, 2,2-dimethylbutyl, 2,3-dimethylbutyl, 2,2,3-trimethylbutyl, 2,2,4-trimethylpentyl, 2,4-dimethylpentyl, 3,3-dimethylbutyl, 3-methylhexyl, 2-methylhexyl, 2,3-dimethylpentyl, 2,4-dimethylhexyl, 2,2,5-trimethylhexyl, 2,2,4-trimethylpentyl, etc.

[0063] The structure shown in Formula III is formed by the ring-opening polymerization of lactones (such as the lactone monomers shown in Formula VII-2 below) (as described in the first polymerization reaction below). In the ring-opening polymerization process of the lactones in the embodiments of this application, the carbon-oxygen single bond (CO) in the ester bond is broken, resulting in the ring opening of the lactone. The broken ester bond and another broken ester bond form a linear polymer chain through chain polymerization, that is, the repeating unit is formed by this repeating unit. The polymeric chain segment (Formula III) is composed of lactones. Using lactones is more conducive to the preparation of polyimide binders, and it is also conducive to controlling the molecular weight of polyimide binders, resulting in polyimide binders with a narrower molecular weight distribution, further improving the adhesion and flexibility of polyimide binders.

[0064] In the embodiments of this application, x in Formula II and y in Formula III can be controlled by conventional methods of controlling the number of repeating units in polymer segments or polymers. For example, the number of repeating units (i.e., x) of the ester groups in the polyester soft segment of the formed polyimide adhesive can be controlled by controlling conditions such as the molar ratio of the monomer (such as the lactone monomer below) used to form the structure shown in Formula II to the initiator. The number of repeating units (i.e., y) of the ester groups in the polyester soft segment of the formed polyimide adhesive can be controlled by controlling conditions such as the molar ratio of the monomer (such as the lactone monomer below) used to form the structure shown in Formula III to the initiator.

[0065] Furthermore, in the embodiments of this application, x in Formula II and y in Formula III can be determined by conventional testing methods for the number of repeating units in polymer segments or polymers. For example, after obtaining the polyimide binder, the polyimide binder is degraded to obtain various monomers, initiators, and other components used to form the polyimide binder, and x in Formula II or y in Formula III is determined by high performance gas chromatography. The test results are basically consistent with the results calculated based on the molar ratio of ester monomers to initiators during the preparation of the polyimide binder. For example, when lactone monomers are used to form the polymer segment shown in Formula II, x in Formula II is basically equal to the molar ratio of lactone monomers to initiators. When lactone monomers are used to form the polymer segment shown in Formula III, y in Formula III is basically equal to the molar ratio of lactone monomers to initiators.

[0066] For example, the polyester soft segment can be selected from the following structures:

[0067] In this context, m and b are each independently the number of methylene groups in the polyester soft segment, and m and b are each integers from 1 to 12, such as 1, 2, 3, 4, 5, 10, 12, etc.; a is the number of methylene groups on the side chains in the polyester soft segment, and a takes the value of an integer from 1 to 12, such as 1, 2, 3, 4, 5, 10, 12, etc.; x and y are each independently the number of repeating units in the polyester soft segment. m, a, and b can all be measured using conventional testing methods for the number of repeating units, such as NMR spectroscopy.

[0068] As mentioned above, the polyimide binder in the embodiments of this application includes aromatic hard segments, which may have the structure shown in Formula I:

[0069] R1 is selected from substituted or unsubstituted aryl groups, or substituted or unsubstituted biaryl groups.

[0070] Specifically, the aryl group can be selected from phenyl or naphthyl, and the substituted or unsubstituted biaryl group can have one or more of the structures shown in Formula V below:

[0071] R7 and R8 each independently represent a monosubstituted to the maximum permissible substituent (i.e., in Formula V, R7 and R8 can each independently be attached to one or more attachment sites on their respective benzene rings, for example, 1, 2, 3, or 4), and R7 and R8 can each independently be selected from hydrogen, substituted or unsubstituted alkyl groups, or carboxyl groups. Exemplarily, R7 and R8 are each independently hydrogen, and a biaryl group having the structure shown in Formula V can have the structure shown in Formula V-1:

[0072] L2 is selected from one or more of the following groups: single bond, substituted or unsubstituted alkyl, carbonyl, ester, oxygen, sulfone, and amide.

[0073] Specifically, L2 can be selected from one or more of the following: alkyl group (C1-C12), carbonyl group (C1-C12), ester group (C1-C12), oxygen group, sulfone group, and amide group (C1-C12).

[0074] For example, when L2 is selected from C1 to C12 alkyl groups, the alkyl group can be a straight-chain alkyl group or a branched alkyl group, and the number of carbon atoms in L2 can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12; when L2 is selected from C1 to C12 carbonyl groups, the number of carbon atoms in L2 can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12; when L2 is selected from C1 to C12 ester groups, the number of carbon atoms in L2 can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12; when L2 is selected from C1 to C12 amide groups, the number of carbon atoms in L2 can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12.

[0075] For example, when L2 is an alkyl group, it includes, but is not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, neopentyl, and n-hexyl; when L2 is a carbonyl group, it includes, but is not limited to, aldehyde and ketone groups; when L2 is an ester group, it includes, but is not limited to, methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, and butoxycarbonyl; when L2 is a sulfone group, it includes, but is not limited to, dimethyl sulfone, diethyl sulfone, and methyl ethyl sulfone; when L2 is an amide group, it includes, but is not limited to, carbamoyl, acetamido, N-methylcarbamoyl, and N,N-dimethylcarbamoyl. Furthermore, any hydrogen atom in L2 can be replaced by a halogen atom, such as a fluorine atom.

[0076] This application embodiment uses an aromatic hard segment with the structure shown in Formula I above as the hard segment of the polyimide adhesive, which makes the polyimide adhesive have better thermal stability and mechanical strength, thereby further improving its mechanical properties while maintaining good bonding effect.

[0077] Furthermore, when the aromatic hard segment is selected from the structures shown in Formulas I-1 to I-9, it is beneficial to further improve the thermal stability and mechanical strength of the adhesive while simultaneously improving the adhesion, flexibility, and processing performance of the polyimide binder.

[0078] In some embodiments, the polyimide adhesive further includes a connecting segment, the connecting segment comprising the structure shown in Formula IV:

[0079] L1 is selected from substituted or unsubstituted aryl groups, substituted or unsubstituted biaryl groups, or substituted or unsubstituted alkyl groups. Specifically, it can be selected from aryl groups with 4 to 24 carbon atoms, biaryl groups with 12 to 48 carbon atoms, or straight-chain alkyl groups or branched alkyl groups with 1 to 12 carbon atoms (i.e., straight-chain alkyl groups with 1 to 12 carbon atoms or branched alkyl groups with 1 to 12 carbon atoms). The symbol represents the connection site between Formula IV and the polymeric segment of the polyester soft segment (such as the polymeric segment shown in Formula II or the polymeric segment shown in Formula III), and * represents the connection site between Formula IV and the aromatic hard segment (such as the aromatic hard segment shown in Formula I).

[0080] For example, the number of carbon atoms in an aryl group having 4 to 24 carbon atoms can be 4, 5, 6, 7, 8, 9, 10, 11, or 12. The number of carbon atoms in a straight-chain alkyl group having 1 to 12 carbon atoms or a branched alkyl group can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12. For example, L1 can be an aryl group having 6 carbon atoms (such as phenyl), or L1 can be a straight-chain alkyl group having 1 to 6 carbon atoms or a branched alkyl group.

[0081] For example, when L1 is aryl, it includes, but is not limited to, phenyl, tolyl, xylyl, naphthyl, anthracene, phenanthryl, pyrene, biphenyl, terphenyl, tetrahydronaphthyl, indene, fluorenyl, acenaphthene, xanthyl, thiophene, furanyl, pyridyl, quinolinyl, isoquinolinyl, indolyl, carbazole, pyrrole, imidazolyl, thiazolyl, oxazolyl, benzothiophene, benzofuranyl, benzimidazolyl, benzothiazolyl, and benzoxazolyl, etc.; when L1 is a straight-chain alkyl group, it includes, but is not limited to, methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, and n-dodecane. L1 is a branched alkyl group, including but not limited to isopropyl, tert-butyl, isobutyl, sec-butyl, neopentyl, isopentyl, tert-pentyl, 3-methylbutyl, 2-methylbutyl, 2,2-dimethylpropyl, 2-methylpentyl, 3-methylpentyl, 2,2-dimethylbutyl, 2,3-dimethylbutyl, 2,2,3-trimethylbutyl, 2,2,4-trimethylpentyl, 2,4-dimethylpentyl, 3,3-dimethylbutyl, 3-methylhexyl, 2-methylhexyl, 2,3-dimethylpentyl, 2,4-dimethylhexyl, 2,2,5-trimethylhexyl, 2,2,4-trimethylpentyl, etc.

[0082] In some specific embodiments, the connecting chain segment may have the structure shown in Formula IV-1 or Formula IV-2 as follows:

[0083] In Formula VI-2, w represents the number of alkyl (methylene) groups, which can be an integer from 1 to 12. It is important to clarify that one end (ester group) of the aforementioned connecting segment is connected to the polymeric segment of the polyester soft segment, while the other end (alkyl group in Formula IV-1 or phenyl group in Formula IV-2) is connected to the aromatic hard segment. This makes the polyimide binder a polymer system with both soft and hard segment structures, giving it both good flexibility and suitable mechanical properties, which is beneficial for maintaining the integrity of the electrode active material layer during battery operation.

[0084] Specifically, the polyimide adhesive can have repeating units with the structure shown in Formula Y-1:

[0085] In formula Y-1, R6 represents the polymeric segment of the polyester soft segment (e.g., formula II or formula III). For example, when R6 is formula II, the repeating unit of the structure shown in formula YI has the structure shown in formula Y-I1:

[0086] It is understandable that when L1 is an aromatic group (e.g., aryl or biaryl), it can belong to the aromatic hard segment, while the remaining non-aromatic groups in the linking segment shown in Formula IV belong to the polyester soft segment; when L1 is an alkyl group, the linking segment containing L1 can belong to the polyester soft segment. In polyimide, L1 is only a group in the linking segment, accounting for a small proportion, and basically does not affect the characteristics such as the mass percentage of polyester soft segment and aromatic hard segment in polyimide as measured by thermogravimetric analysis.

[0087] Specifically, polyimide adhesives can have the structure shown in Formula VI:

[0088] In Equation VI, R2 is an aromatic hard segment, comprising polymeric segments of polyester soft segments and connecting segments between the polymeric segments and the aromatic hard segments. n is the degree of polymerization of the polyimide binder, i.e., n is the repeating unit of the polyimide binder. The quantity.

[0089] R1 in Formula VI is the same as R1 in Formula I. As mentioned above, R1 can be selected from one or more of the aryl group or the group shown in Formula V, which will not be repeated here.

[0090] Specifically, both ends of the polymeric segments of the polyester soft segment are connected to connecting segments. For example, R2 (the polyester soft segment with connecting segments) in Formula VI can have a structure as shown in Formula VI-1 or Formula VI-2:

[0091] R3 in Formula VI-1 is the same as R3 in Formula II, R4 in Formula VI-2 is the same as R4 in Formula III, R5 in Formula VI-2 is the same as R5 in Formula III, and L1 in Formula VI-1 and Formula VI-2 is the same as L1 in Formula IV. These will not be elaborated further here.

[0092] For example, the polyimide adhesive may have the structure shown in Formula VI-11 or Formula VI-12:

[0093] In some embodiments, the number average molecular weight of the polyimide binder is between 10 kDa and 10,000 kDa. For example, the number average molecular weight of the polyimide binder may be within the range of 10 kDa, 30 kDa, 50 kDa, 70 kDa, 75 kDa, 80 kDa, 85 kDa, 90 kDa, 95 kDa, 100 kDa, 500 kDa, 1000 kDa, 5000 kDa, 10000 kDa, or any combination thereof. When the number average molecular weight of the polyimide binder is within the above range, it is beneficial to further improve the bonding performance, flexibility, and processability of the polyimide binder, thereby improving the cycle stability and lifespan of the battery. According to the inventors' research, when the number average molecular weight of the polyimide binder is between 75kDa and 95kDa, the polyimide binder has a more suitable molecular weight window, which further improves the adhesion, flexibility and processability of the polyimide binder, thereby improving the flexibility and peel strength of the electrode sheet and improving the cycle performance of the battery.

[0094] In one specific embodiment, the molecular weight distribution of the polyimide binder (i.e., the ratio of the weight-average molecular weight to the number-average molecular weight of the polyimide binder) is 1 to 10, for example, a range consisting of 1, 2, 2.3, 2.5, 2.8, 3, 4, 5, 6, 7, 8, 9, 10, or any two of these ranges. The ratio of the weight-average molecular weight to the number-average molecular weight of the polyimide binder is also known as the polydispersity index (PDI), which measures the width of the molecular weight distribution of the polymer sample. When the ratio of the weight-average molecular weight to the number-average molecular weight of the polyimide binder is within the above range, the length difference of the soft segment polymer molecular chains in the polyimide binder is smaller. Using the binder material in the preparation of battery electrodes results in better processing and mechanical properties. In particular, when the ratio of the weight-average molecular weight to the number-average molecular weight of the polyimide binder is 2.3 to 2.8, it is beneficial to further improve the stability and other properties of the electrode slurry used to prepare the electrode sheet, thereby further improving the preparation efficiency and performance of the electrode sheet.

[0095] This application provides a method for preparing a polyimide adhesive, comprising the following steps: performing a first polymerization reaction on an ester monomer to obtain a polyester precursor; performing a second polymerization reaction on the polyester precursor, diisocyanate, and an anhydride monomer to obtain the above-mentioned polyimide adhesive; wherein at least one of the diisocyanate and the anhydride monomer contains an aryl group.

[0096] In the preparation of the polyester precursor in this application, the ester monomer may include cyclic ester monomers, specifically lactones and / or lactides. That is, the ester monomer may be only a lactone monomer, or only a lactide monomer, or it may simultaneously include both lactone and lactide monomers. During the first polymerization reaction, only lactone monomers, only lactide monomers, or both lactone and lactide monomers may be used simultaneously. When using both lactone and lactide monomers simultaneously in the first polymerization reaction, this application does not impose any special limitation on their molar ratio; it can be selected according to the actual situation.

[0097] Specifically, the lactone monomer in the embodiments of this application may have the structure shown in formula VII-1:

[0098] Specifically, R3 in Formula VII-1 is the same as R3 in Formula II. As mentioned above, R3 can be selected from alkyl groups, specifically from straight-chain alkyl groups or branched alkyl groups with 1 to 18 carbon atoms, which will not be elaborated further.

[0099] In contrast, when R3 in Formula VII-1 is selected from alkyl groups with C4 to C8 carbon atoms, it is beneficial to further improve the adhesion, flexibility and processability of polyimide binders. At the same time, such lactone monomers also have lower costs and are easier to prepare.

[0100] The lactone monomers in the embodiments of this application may have the structure shown in formula VII-2: 2.

[0101] Specifically, R4 in Formula VII-2 is the same as R4 in Formula III, and R5 in Formula VII-2 is the same as R5 in Formula III. As mentioned above, R4 and R5 can be independently selected from alkyl groups, specifically from straight-chain alkyl groups or branched alkyl groups with 1 to 12 carbon atoms, which will not be elaborated further.

[0102] Specifically, R4 and R5 can have the same or different number of carbon atoms.

[0103] In contrast, when the number of carbon atoms in R4 and R5 in Formula VII-2 is independently 1 to 5, it is advantageous to further improve the adhesion, flexibility, and processability of the polyimide adhesive. At the same time, such lactone monomers also have lower costs and are easier to prepare. In some embodiments, the sum of the number of carbon atoms in R4 and R5 is 3 to 10, for example, 4 to 8.

[0104] For example, lactone monomers can have the structure shown in Formula VIII-1:

[0105] In formula VIII-1, a, b, and c represent the number of methylene groups at the corresponding positions of the monomers, with a being an integer from 0 to 11; b being an integer from 0 to 12; and c being an integer from 0 to 12.

[0106] For example, lactone monomers can have a structure as shown in Formula VIII-2:

[0107] In formula VIII-2, a and b are the number of methylene groups at the corresponding positions of the monomer, where a is an integer from 1 to 10 and b is an integer from 1 to 10.

[0108] For example, the lactone monomers in the embodiments of this application include, but are not limited to, one or more of caprolactone (i.e., R3 in formula VII-1 is a straight-chain hexane (as shown in Figure 2), pentyl lactone, butyl lactone, nonyl lactone (γ-nonyl lactone); the lactide monomers in the embodiments of this application include, but are not limited to, one or more of lactide (lactide (R4 and R5 in formula VII-2 each have 3 carbon atoms independently)), glycolide, and di-n-butyl glycolide.

[0109] Generally, the esters in polyimide adhesives are formed by the condensation polymerization of diacid and glycol monomers. This stepwise approach makes it difficult to control the polymer's molecular weight and results in a wide molecular weight distribution. Consequently, the modified polyimide adhesive exhibits high fluctuations in process performance and battery electrical properties, poor repeatability, and low industrial economics. However, in the embodiments of this application, by using the aforementioned ester monomers, the polymerization reaction is carried out in a chain polymerization manner. The reaction process is more uniform, which is beneficial for controlling the polymer's molecular weight and molecular weight distribution, thereby facilitating the preparation of polyimide adhesives with better processability.

[0110] Specifically, polyester soft segments synthesized by ring-opening polymerization of cyclic ester monomers exhibit a more uniform molecular weight and distribution. This is because, compared to ester compounds synthesized by stepwise polymerization of diacid and glycol monomers, the synthesis of polyester soft segments using cyclic ester monomers such as lactones or lactides through ring-opening polymerization exhibits distinct chain polymerization characteristics. In this process, the growing polyester soft segment continuously adds monomer units through active centers, with each monomer added to the polymer chain (i.e., the aforementioned polyester soft segment) almost simultaneously and at the same rate, resulting in a polymer with a narrow molecular weight distribution. Furthermore, the high consistency of active centers and the continuity of monomer addition during chain polymerization effectively reduce side reactions and make the resulting polymer chain length more uniform. Therefore, chain polymerization can achieve higher uniformity and more controllable molecular weight distribution than stepwise polymerization, resulting in a more concentrated polymer molecular weight distribution and reducing the occurrence of extreme cases where the molecular weight is too long or too short.

[0111] In the above preparation process, the ester monomer can undergo a first polymerization reaction under the action of an initiator, which is beneficial for initiating the first polymerization reaction and generating a polyester segment precursor. Taking a cyclic ester monomer as an example, under the action of an initiator, the cyclic ester monomer undergoes ring opening and a first polymerization reaction to generate a polyester segment precursor with hydroxyl groups at the end.

[0112] In some embodiments, the initiator includes at least one of a diol initiator and a diamine initiator. Generally, regardless of whether a diol initiator or a diamine initiator is used, the resulting polyester precursor with hydroxyl end groups will have hydroxyl end groups.

[0113] For example, the initiator may have the structure shown in EZE, wherein E is selected from hydroxyl (-OH) or amino, and Z may be selected from alkyl, for example from alkyl groups having 1 to 8 carbon atoms. Wherein, when E is hydroxyl, the initiator is a diol initiator; when E is amino, the initiator is a diamine initiator.

[0114] In one specific embodiment, the initiator includes at least one of a small molecule diol initiator and a small molecule diamine initiator. For example, the small molecule diol initiator includes, but is not limited to, one or more of ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, triethylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, cyclohexanediol, and glycerol. In a specific implementation, ethylene glycol can be used as the small molecule diol initiator.

[0115] Small molecule diamine initiators include, but are not limited to, one or more of the following: ethylenediamine, propylenediamine, butyldiamine (1,4-butyldiamine), pentanediamine (1,5-pentanediamine), hexanediamine (1,6-hexanediamine), isophorone diamine (IPDA), phenyl dimethyl diamine (such as m-phenylenediamine and p-phenylenediamine), cyclohexane diamine (such as 1,2-cyclohexanediamine and 1,4-cyclohexanediamine), diethyltoluene diamine (DETDA), and dimethylthiotoluene diamine (DMTDA).

[0116] Specifically, the ester monomer undergoes a first polymerization reaction in a solvent, which can be carried out in the presence of an initiator. This application does not impose specific limitations on the type and amount of solvent; the solvent can be selected based on the subsequent preparation of the electrode paste. For example, the solvent includes at least one of N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc), tetramethylurea, 1,3-dimethyl-2-imidazolone acetone, butanone (MEK), tetrahydrofuran (THF), ethanol, isopropanol, ethylene glycol monomethyl ether, diethylene glycol dimethyl ether, ethylene carbonate, and propylene carbonate. In specific implementations, N-methylpyrrolidone (NMP) can be selected as the solvent.

[0117] In addition, the mass percentage of the ester monomer in the solvent can be 1% to 10%, such as 1%, 3%, 5%, 7%, or 10%.

[0118] In the embodiments of this application, at least one of the diisocyanate and the anhydride monomer contains an aryl group to introduce aromatic hard segments into the polyimide binder.

[0119] Specifically, the acid anhydride monomer may include a diacid anhydride monomer, and the resulting aromatic hard segment has the structure shown in Formula I.

[0120] Specifically, the dianhydride monomer may include a dianhydride monomer having the structure shown in Formula X:

[0121] In some specific embodiments, the dianhydride monomer may include one or more of the compounds represented by formulas X-1 to X-9.

[0122] In the above preparation process, after the ester monomer undergoes the first polymerization reaction, the resulting polyester segment precursor is an ester segment, which can specifically be a hydroxyl-terminated ester segment. Specifically, as mentioned above, the ester monomer can include cyclic ester monomers, such as lactone monomers and / or lactide monomers. During the first polymerization reaction, the cyclic ester monomer undergoes ring opening and polymerization to form a hydroxyl-terminated ester segment (i.e., the polyester segment precursor).

[0123] In addition, diisocyanate can undergo addition with polyester segment precursor to form a soft segment precursor with isocyanate group (-NCO) end capping. In the second polymerization reaction, the N element in the isocyanate group replaces the oxygen element between the two carbon groups in the anhydride monomer (each substitution site will correspondingly remove one molecule of carbon dioxide (CO2)), causing the soft segment precursor to polymerize with the anhydride monomer to generate polyimide binder.

[0124] In this embodiment, an addition reaction is carried out between a polyester precursor and a diisocyanate to form an isocyanate group (-NCO) end-capping structure in the polyester precursor. This facilitates the reaction of the isocyanate group with the anhydride monomer during the second polymerization reaction to generate a polyimide binder. It also helps to control the molecular weight and distribution of the polymer, making the molecular weight distribution of the polyimide binder more concentrated and improving the stability and other properties of the polyimide binder.

[0125] In some embodiments, the process of carrying out a second polymerization reaction of the polyester precursor, diisocyanate, and ester anhydride monomer includes: after the polyester precursor undergoes an addition reaction with diisocyanate, an anhydride monomer is added thereto, and then a second polymerization reaction is carried out to generate a polyimide binder. This method is more conducive to the addition reaction of the polyester precursor with isocyanate, followed by polymerization with the anhydride monomer, thereby improving the preparation efficiency and performance of the polyimide binder.

[0126] The temperature at which the polyester precursor reacts with the diisocyanate during the addition reaction can be 70–90°C, for example 80°C, and the reaction time can be 2–20 min, for example 10 min.

[0127] Taking the lactone monomer of Formula VII-1 and the dianhydride monomer as an example, the reaction process for preparing the polyimide binder is shown in Figure 1. Specifically, the initiator can be mixed with the lactone monomer of Formula VIII-1 and heated to induce a chemical reaction (i.e., the first polymerization reaction) to obtain a polyester segment precursor (hydroxyl-terminated ester segments). Then, diisocyanate is added to it in situ, and the diisocyanate undergoes addition with the polyester segment precursor to obtain a soft segment precursor. Next, a hard segment dianhydride monomer (i.e., dianhydride monomer) is added to the above reaction system including the soft segment precursor in situ, mixed and heated, and after a chemical reaction (i.e., the second polymerization reaction), the soft segment precursor and the dianhydride monomer polymerize, removing carbon dioxide to generate the polyimide binder.

[0128] In the preparation process of the above-mentioned polyimide adhesive, in order to make the first polymerization reaction and the second polymerization reaction more complete, the reaction system can be mixed, such as by using a stirrer.

[0129] In some embodiments of this application, the polyester segment precursor has a structure as shown in Formula IX:

[0130] HO-R6-OH Formula IX

[0131] Accordingly, the soft segment precursor has the structure shown in Equation IIX:

[0132] For example, the precursor of the structure shown in Formula IX has the structure shown in Formula IX-1, and the soft segment of the structure shown in Formula IIX can have the structure shown in Formula IIX-1:

[0133] For example, the precursor of the structure shown in Formula IX has the structure shown in Formula IX-2, and the soft segment of the structure shown in Formula IIX can have the structure shown in Formula IIX-2:

[0134] The specific choices for L1, R3, R4, and R5 are as described above and will not be repeated here.

[0135] Specifically, diisocyanates are compounds containing two isocyanate groups, and can have the structure shown in formula IA:

[0136] O=C=N-L1-N=C=O (i.e., OCN-L1-NCO) IA

[0137] L1 in Equation A is the same as L1 in Equation IV, and will not be repeated here.

[0138] Specifically, the diisocyanate can be a small molecule diisocyanate compound. In some embodiments, the diisocyanate may include, but is not limited to, one or more of toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), naphthalene diisocyanate (NDI), p-phenyl diisocyanate (PPDI), n-hexyl diisocyanate, and cyclohexane diisocyanate (CHDI).

[0139] In the embodiments of this application, the ester monomers, diisocyanates, initiators, anhydride monomers and other materials used can all be obtained by conventional methods, such as commercial purchases, or self-made by conventional methods in the art.

[0140] In this embodiment, the mass percentage of polyester soft segments in the polyimide binder can be controlled by the mass percentage of the ester monomer in the total mass of raw materials added during the synthesis of the polyimide binder, including the ester monomer, diisocyanate, dianhydride monomer, and initiator. That is, the mass percentage of polyester soft segments in the obtained polyimide binder is essentially equal to the proportion of the mass of the ester monomer to the total mass of raw materials added during the synthesis of the polyimide binder. The mass percentage of polyester soft segments in the polyimide binder calculated by this method is essentially consistent with the mass percentage of polyester soft segments in the polyimide measured by methods such as thermogravimetric analysis. For example, in the synthesis of polyimide, the ester monomer undergoes a first polymerization reaction under the action of an initiator, and then the resulting polyester segment precursor, diisocyanate, and dianhydride monomer undergo a second polymerization reaction to generate the polyimide binder. The mass percentage of polyester soft segments in the obtained polyimide binder = mass of ester monomer / (mass of ester monomer + mass of dianhydride monomer + mass of initiator + mass of initiator).

[0141] Furthermore, the mass percentage of aromatic hard segments in polyimide binders can also be controlled by the mass percentage of anhydride monomers in the total mass of raw materials added during the synthesis of polyimide binders. That is, the mass percentage of polyester soft segments in the obtained polyimide binders is basically equal to the proportion of the mass of anhydride monomers in the total mass of raw materials added during the synthesis of polyimide binders (this proportion is basically equal to the difference between 100% and the mass percentage of polyester soft segments). The mass percentage of aromatic hard segments in polyimide binders can be calculated according to aromatic hard segments = 100% - mass percentage of polyester soft segments, or it can be calculated according to the mass percentage of anhydride monomers in the total mass of raw materials added during the synthesis of polyimide binders. For example, in the synthesis of polyimide, an ester monomer undergoes a first polymerization reaction under the action of an initiator. Then, the resulting polyester precursor, diisocyanate, and anhydride monomer undergo a second polymerization reaction to generate a polyimide binder. The mass percentage of aromatic hard segments in the resulting polyimide binder is calculated as: mass of anhydride monomer / (mass of ester monomer + mass of anhydride monomer + mass of initiator). The mass percentage of aromatic hard segments in the polyimide binder calculated using this method is essentially consistent with the mass percentage of aromatic soft segments in the polyimide determined by methods such as thermogravimetric analysis.

[0142] Furthermore, in the embodiments of this application, the number of repeating units of ester groups in the polyester soft segment (e.g., x in Formula II, y in Formula III) and other characteristics can be controlled by adjusting conditions such as the molar ratio of the initiator to the ester monomer.

[0143] In some embodiments, the molar ratio of ester monomer to initiator is (5 to 5000):1, for example, 5, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 30, 40, 50, 60, 70, 80, 90, 100, 500, 1000, 2000, 3000, 4000, 5000 or a range between any two of these, specifically (5 to 100):1.

[0144] In some embodiments, the molar ratio of the anhydride monomer to the ester monomer is (0.07 to 1.32):1, for example, a range consisting of 0.07, 0.1, 0.3, 0.5, 0.8, 1, 1.2, 1.32, or any two of these.

[0145] In some embodiments, the mass ratio of diisocyanate to ester monomer is (0.01 to 0.3):1, for example, 0.01:1, 0.03:1, 0.05:1, 0.08:1, 0.1:1, 0.13:1, 0.15:1, 0.18:1, 0.2:1, 0.23:1, 0.25:1, 0.28:1, 0.3:1, or any combination thereof.

[0146] In some embodiments, the molar ratio of diisocyanate to initiator can be less than or equal to 2:1, specifically 2:(1-1.1), for example 2:1, which facilitates a more complete reaction of the monomer raw materials, avoids residual monomers in the polyimide binder, and thus further improves the performance of the prepared polyimide binder.

[0147] In some embodiments, the molar ratio of dianhydride monomer to diisocyanate can be (0.9–1.1):1, for example, 1:1.

[0148] Furthermore, in the above-mentioned method for preparing the adhesive material, the temperature of the first polymerization reaction can be 40 to 120°C, for example, 40, 60, 80, 100 or any combination thereof, and the time can be 3 to 12 hours (h), for example, 3h, 5h, 9h, 12h.

[0149] In addition, the temperature of the second polymerization reaction can be 100 to 180°C, for example 150°C, and the time can be 1 hour to 15 hours, for example 10 hours.

[0150] This application further limits the feeding ratio of raw materials (ester monomer, initiator, diisocyanate, acid anhydride monomer) and reaction conditions in the preparation method of polyimide adhesive, which is beneficial to synthesizing polyimide adhesive with uniform molecular weight and distribution, and further improves the adhesive flexibility and mechanical strength of the obtained polyimide adhesive.

[0151] In the embodiments of this application, the ester monomers, acid anhydride monomers, diisocyanates and other raw materials used can all be obtained by conventional methods, such as commercial purchases or preparation by conventional methods of these compounds, and there is no particular limitation thereto.

[0152] In this embodiment, the bonding material includes a polyimide binder. The polyimide binder in this embodiment can also be used in combination with other conventional components, such as adding antioxidants and buffers to further improve the performance of the bonding material; the choice can be made according to the actual situation. Specifically, the prepared polyimide binder can be directly applied to the electrode paste for preparing the electrode sheet, or it can be purified by precipitation in solvents such as water, ethanol, or methanol before being applied to the preparation of the electrode paste.

[0153] This application provides an electrode sheet including an electrode coating. The electrode coating includes the aforementioned polyimide binder, or a polyimide binder prepared according to the aforementioned method for preparing the polyimide binder. This electrode sheet has advantages corresponding to the aforementioned polyimide binder, which will not be elaborated further.

[0154] The electrode sheet provided in this application embodiment is prepared by using the above-mentioned polyimide binder, which can reduce the occurrence of peeling, cracking and powdering of the electrode active material layer in the electrode sheet, so that the electrode sheet can maintain its integrity structure even when the battery is working for a long time, which greatly improves the safety, cycle stability and service life of the battery.

[0155] In this embodiment, the polyimide binder can be used only in the positive electrode of the battery, only in the negative electrode, or in both the positive and negative electrodes. In specific implementations, the polyimide binder can be used in the positive electrode of the battery. The binder can better adapt to the volume changes of the positive electrode during charge-discharge cycles, and is compatible with the positive electrode slurry system used to prepare the positive electrode. This solves the problem of poor dispersibility of conventional polyimides in organic solvents such as NMP, thereby improving the uniformity and stability of the positive electrode slurry and enhancing the electrochemical performance of the positive electrode.

[0156] It should be clarified that the aforementioned polyimide binder can be used alone in the battery electrode sheet, or it can be used in combination with other binders conventionally used in the art in the battery electrode sheet.

[0157] The electrode sheet includes an electrode current collector and an electrode active material layer located on at least one side of the electrode current collector. Specifically, the electrode active material layer may be located on only one side of the electrode current collector, or the electrode active material layer may be provided on both sides of the electrode current collector.

[0158] Furthermore, the embodiments of this application do not impose any special limitation on the areal density of the electrode sheet; for example, the areal density of the electrode sheet can be 50–700 g / m³. 2 For example, 50g / m 2 100g / m 2 150g / m 2 200g / m 2 250g / m 2 300g / m 2 350g / m 2 400g / m 2 450g / m 2 500g / m 2 550g / m 2 600g / m 2 650g / m 2 700g / m 2 or a range consisting of any two of them.

[0159] In this embodiment, the test process for the areal density of the electrode coating is as follows: Take an electrode sheet (positive electrode sheet or negative electrode sheet) sample (specifically, a cutter can be used to cut the negative electrode sheet to obtain a negative electrode sheet sample of suitable size), test the total mass m1 of the electrode sheet sample, the total thickness T1 of the electrode sheet sample (T1 = total thickness of the electrode active material layer + thickness of the electrode current collector; when the electrode active material layer is provided on both the positive and negative surfaces of the electrode current collector, the total thickness of the electrode active material layer = thickness of the electrode active material layer on one side of the electrode current collector + thickness of the electrode active material layer on the other side of the electrode current collector), and the surface area S of one side of the electrode sheet sample in the thickness direction; then scrape off the electrode active material layer on the electrode sheet sample, test the mass m2 of the obtained electrode current collector, and the thickness T2 of the electrode current collector, then the total thickness of the electrode active material layer = T1 - T2, and the areal density of the electrode active material layer = (m1 - m2) / S.

[0160] In detail, when the electrode sheet is a positive electrode sheet, the electrode current collector is a positive electrode current collector, and the electrode active material layer is a positive electrode active material layer (or positive electrode active layer). Specifically, the positive electrode active layer can be provided on one side of the surface in the thickness direction of the positive electrode current collector, or the positive electrode active layer can be provided on both sides of the opposite surface in the thickness direction of the positive electrode current collector.

[0161] The positive electrode active material layer may include positive electrode active material, conductive agent and binder. In the positive electrode coating, the mass percentage of positive electrode active material may be 70% to 99%, for example, 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99% or any combination thereof. The mass fraction of binder may be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15% or any combination thereof.

[0162] The binder for the positive electrode active material layer can be the polyimide binder provided in the embodiments of this application, or it can be a composite of one or more of the following: polyvinylidene fluoride (PVDF), polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, etc., used as the binder for the positive electrode active material layer.

[0163] In some embodiments, the positive electrode active material may include LiCoO2, LiNiO2, or LiCo. x Ni 1-x O2 (0≤x≤1), LiCo x Ni 1-x-y Al y O2(0≤x≤1,0≤y≤1), LiMn2O4, LiFe x Mn y M z O4 (M is one or more of Al, Mg, Ga, Cr, Co, Ni, Cu, Zn or Mo, 0≤x≤1, 0≤y≤1, 0≤z≤1, x+y+z=1), Li 1+x L 1－y－z M y N z O2 (L, M, N are one or more of Li, Co, Mn, Ni, Fe, Al, Mg, Ga, Ti, Cr, Cu, Zn, Mo, F, I, S, B, -0.1≤x≤0.2, 0≤y≤1, 0≤z≤1, 0≤y+z≤1), LiFePO4, Li3V2(PO4)3, Li3V3(PO4)3, LiVPO4F, Li2CuO2, Li5FeO4, and metal sulfides and oxides (such as TiS2, V2S3, FeS, FeS2, LiMS) x (M is at least one of the transition metal elements such as Ti, Fe, Ni, Cu, Mo, etc., 1≤x≤2.5), TiO2, Cr3O8, V2O5, MnO2, etc.

[0164] The embodiments of this application may employ conventional positive current collectors in the art, for example, positive current collectors may include aluminum foil.

[0165] In this embodiment, the positive electrode sheet can be prepared by conventional methods in the art, such as by coating. Specifically, the positive electrode active material, conductive agent, binder, and other components used to form the positive electrode active layer can be dispersed in a solvent, such as N-methylpyrrolidone (NMP), to prepare a positive electrode slurry. This slurry is then coated onto the surface of the positive electrode current collector, and after drying, rolling, and other processes, the positive electrode sheet is obtained. The coating, drying, and rolling processes involved are conventional operations for preparing positive electrode sheets using the coating method, and are not particularly limited thereto.

[0166] In one specific embodiment, when the electrode sheet is a negative electrode sheet, the electrode current collector is a negative electrode current collector. A negative electrode active material layer can be provided on one side surface of the negative electrode current collector in the thickness direction, or negative electrode active material layers can be provided on both opposite sides surface in the thickness direction of the negative electrode current collector.

[0167] In this embodiment, the binder in the negative electrode active material layer can be the polyimide binder provided in this embodiment, or it can be used in combination with any binder suitable for negative electrodes known in the art. For example, at least one of polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), tetrafluoroethylene and its copolymers, polyvinylidene fluoride and its copolymers, polyolefins and their copolymers (e.g., polyethylene-polyethylene glycol block copolymers), polyethers and their copolymers (e.g., polyethylene oxide), polyphenylene ethers and their copolymers, polysiloxanes and their copolymers (e.g., polydimethylsiloxane, poly(dimethylsiloxane-co-alkylmethylsiloxane)), polyesters and their copolymers (e.g., polyethylene ester, polyvinyl acetate, polyacrylate, etc.), carboxymethyl cellulose, styrene-butadiene latex, nitrile rubber, and polyacrylic acid (PAA) can be used together with the polyimide binder provided in this embodiment to prepare the negative electrode active material layer.

[0168] Specifically, polyolefins include one or more of polyethylene, polypropylene, ethylene / propylene copolymer, ethylene / vinylidene fluoride copolymer, and propylene / vinylidene fluoride copolymer; polytetrafluoroethylene and its copolymers may be at least one of tetrafluoroethylene / ethylene copolymer, tetrafluoroethylene / propylene copolymer, tetrafluoroethylene / vinylidene fluoride copolymer, tetrafluoroethylene / ether copolymer, tetrafluoroethylene / branched polyether copolymer, tetrafluoroethylene / vinyl ether copolymer, tetrafluoroethylene / branched polyether / vinyl ether copolymer, and tetrafluoroethylene / siloxane copolymer.

[0169] In addition, the negative electrode active material layer also includes a negative electrode active material and a conductive agent. Specifically, the negative electrode active material may include graphite, and the conductive agent may include one or more of conductive carbon black, carbon nanotubes (CNTs), acetylene black, graphene, Ketjen black, and carbon fiber. Generally, the mass percentage of the negative electrode active material in the negative electrode active material layer can be 80% to 100%, and the mass percentage of the negative electrode active material in the negative electrode active material layer can be, for example, 80%, 82%, 85%, 88%, 90%, 92%, 95%, 98%, 100%, or any combination thereof.

[0170] The embodiments of this application may employ conventional negative electrode current collectors in the art, for example, negative electrode current collectors may include copper foil.

[0171] In the embodiments of this application, the negative electrode sheet can be prepared by a dry process (i.e., rolling the material used to form the negative electrode active layer into a film and then combining it with the negative electrode current collector to obtain the negative electrode sheet), or by a wet process (coating method) (i.e., coating the negative electrode slurry used to form the negative electrode active layer onto the surface of the negative electrode current collector, and then drying, rolling and other processes to form the negative electrode active layer on the surface of the negative electrode sheet to obtain the negative electrode sheet).

[0172] This application provides a battery including the electrode sheets described above. This battery has advantages over the aforementioned polyimide binder, which will not be elaborated further.

[0173] Generally, a battery includes an electrolyte, a battery cell, and a casing for encapsulating the battery cell. The electrolyte is injected into the battery cell within the casing. The battery cell includes electrode plates (including positive and negative electrode plates) and a separator located between the positive and negative electrode plates. The battery cell can be a stacked cell, meaning it is composed of positive electrode plates, a separator, and negative electrode plates stacked alternately; or it can be a wound cell, meaning it is composed of positive electrode plates, a separator, and negative electrode plates stacked and then wound together. In practice, a stacked cell can be formed by alternating layers of positive electrode plates, a separator, and negative electrode plates, and then the cell is encapsulated using an aluminum-plastic film.

[0174] The electrolyte in this application embodiment can be a conventional electrolyte in the art. For example, the electrolyte is a non-aqueous electrolyte, which may specifically include organic solvents, additives and electrolyte salts. Organic solvents include one or more of ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC) and propylene carbonate (PC). Additives include, for example, fluoroethylene carbonate (FEC) and vinylene carbonate (VC). Electrolyte salts may include lithium salts, such as lithium hexafluorophosphate (LiPF6), but are not limited thereto.

[0175] In this embodiment, the separator is used to separate the positive electrode and the negative electrode to prevent the positive electrode and the negative electrode from short-circuiting due to contact. Conventional separators in the art can be used in this embodiment, and there are no special restrictions.

[0176] In this embodiment, the battery cell can be packaged using conventional housing materials in the art, such as flexible packaging materials like aluminum-plastic film, but is not limited to these.

[0177] The embodiments of this application can assemble components such as positive electrode, separator and negative electrode into a battery using conventional methods in the art. For example, positive electrode, separator and negative electrode can be stacked alternately to obtain a stacked cell (or wound into a wound cell); then the cell is placed in a casing (outer packaging) and after conventional processes such as electrolyte injection, encapsulation, formation and capacity testing, a battery is obtained.

[0178] Furthermore, this application does not specifically limit the type of battery; the battery may be a lithium-ion battery or a sodium-ion battery.

[0179] When the battery is a sodium-ion battery, the positive electrode active material includes, but is not limited to, one or a combination of several of the following: transition metal oxides, polyanionic compounds, organic polymers, Prussian blue materials, etc.

[0180] This application provides a battery pack comprising at least two of the aforementioned batteries. This battery pack has advantages corresponding to the aforementioned polyimide binder, which will not be elaborated further.

[0181] Generally, a battery pack includes multiple batteries as individual cells, which are connected to form the battery pack. These batteries can be electrically connected using methods conventional in the art, such as series connection, parallel connection, or a combination of these connection methods, without any particular limitation.

[0182] This application also provides an electrical device including the aforementioned battery or battery pack. This electrical device has advantages over the aforementioned polyimide adhesive, which will not be elaborated further.

[0183] The electrical equipment provided in this application can be conventional electrical equipment in the field, such as power equipment (e.g., electric vehicles), electrical equipment (e.g., mobile phones, tablets, laptops, digital cameras, etc.), wearable devices (e.g., watches, bracelets, VR glasses, etc.), energy storage power stations, etc., without any particular limitation.

[0184] The technical solution of this application will be further described below with reference to specific embodiments.

[0185] Example 1

[0186] The preparation process of the adhesive material in this embodiment is as follows (Figure 2 shows the reaction formula of the polyimide adhesive preparation process):

[0187] 1) Add 62g of ethylene glycol initiator and 1.14kg of caprolactone monomer to 1000mL of N-methylpyrrolidone (NMP) solvent, mix well, heat to 100℃, and carry out the first polymerization reaction for 3 hours to obtain the polyester precursor.

[0188] 2) Mix the above polyester precursor with 160g of p-phenyl diisocyanate evenly, heat to 80℃, and keep warm for 10min.

[0189] 3) Add 1.1 kg of terephthalic anhydride (formula X-1) monomer to the above system and heat to 150 °C to carry out the second polymerization reaction for 10 hours. At the same time, carbon dioxide is removed from the system to obtain polyimide binder (the 1H NMR spectrum of the obtained polyimide binder is shown in Figure 3).

[0190] The preparation process of the positive electrode sheet in this embodiment is as follows:

[0191] 1) Mix lithium iron phosphate, carbon black, the above-mentioned polyimide binder, and NMP in a mass ratio of 100:2.0:1.0:52 and stir for 1 hour to obtain the positive electrode slurry.

[0192] 2) The above-mentioned positive electrode slurry is coated onto the surface of aluminum foil, and then dried, rolled, and slit to obtain a positive electrode sheet. Both sides of the positive electrode sheet are provided with a positive electrode active material layer; the areal density of the positive electrode active material layer is 200 g / m³. 2 .

[0193] The battery manufacturing process in this embodiment is as follows:

[0194] The above-mentioned positive electrode sheet, polypropylene separator, and graphite negative electrode sheet are stacked, packaged in an aluminum-plastic film, and then injected with electrolyte (1M LiPF6-EC / DMC (1:1 vol%)). After sealing and formation, it is ready for use. The electrolyte composition is as follows: the organic solvent of the electrolyte is composed of EC and DMC mixed in a 1:1 volume ratio, and the concentration of LiPF6 in the electrolyte is 1 mol / L.

[0195] Example 2: This example is basically the same as Example 1, except that 0.57 kg of caprolactone monomer is added in this example to meet the ratio of each component in Table 1.

[0196] Example 3: This example is basically the same as Example 1, except that 2.28 kg of caprolactone monomer is added in this example to meet the ratio of each component in Table 1.

[0197] Example 4: This example is basically the same as Example 1, except that 3.42 kg of caprolactone monomer is added in this example to meet the ratio of each component in Table 1.

[0198] Example 5: This example is basically the same as Example 1, except that 4.56 kg of caprolactone monomer is added in this example to meet the ratio of each component in Table 1.

[0199] Example 6: This example is basically the same as Example 1, except that 11.4 kg of caprolactone monomer is added in this example to meet the ratio of each component in Table 1.

[0200] Examples 7 to 11: The difference from Example 1 is that the ester monomers used are different, as shown in Table 2. The other conditions are basically the same.

[0201] Example 12: This example is basically the same as Example 1, except that the diisocyanate used in this example is n-hexyl diisocyanate.

[0202] Examples 13 to 20: The difference from Example 1 is that the dianhydride monomers used are different, as shown in Table 2. The other conditions are basically the same.

[0203] Comparative Example 1: This comparative example is basically the same as Example 1, except that 0.44 kg of caprolactone monomer was added to satisfy the ratio of each component to the ester monomer recorded in Table 1.

[0204] Comparative Example 2: This comparative example is basically the same as Example 1, except that 15.2 kg of caprolactone monomer was added to satisfy the ratio of each component to the ester monomer recorded in Table 1.

[0205] The mass percentages of polyester soft segments, aromatic hard segments, number-average molecular weight, weight-average molecular weight to number-average molecular weight ratio, molar ratio of initiator to ester monomer, mass ratio of diisocyanate to ester monomer, and molar ratio of dianhydride monomer to ester monomer in the polyimide binders prepared in each embodiment and comparative example are summarized in Tables 1 and 2. The mass percentages of polyester soft segments and aromatic hard segments in the polyimide binder are calculated as follows: Mass percentage of polyester soft segments = mass of ester monomer / (mass of ester monomer + mass of initiator + mass of diisocyanate + mass of dianhydride monomer); Mass percentage of aromatic hard segments = 100% - mass percentage of polyester soft segments.

[0206] Test case

[0207] Determination of the number-average molecular weight and molecular weight distribution of polyimide adhesive: A 2 mg / mL N-methylpyrrolidone solution was prepared using polyimide adhesive, and a sample was injected into a gel permeation chromatograph (Agilent PL-GPC 220, test temperature 50℃) using N-methylpyrrolidone as the mobile phase. The obtained curve was calibrated with polystyrene of known molecular weight to obtain the molecular weight and distribution of the polyimide adhesive (the ratio of the weight-average molecular weight to the number-average molecular weight of the polyimide adhesive). The test results are shown in Table 2.

[0208] Melting point determination of polyimide adhesive: Differential scanning calorimetry (DSC) was used. A 5 mg sample (polyimide adhesive) was cyclically heated from -100℃ to 250℃ at a rate of 5℃ / min for two cycles (the first cycle involved heating from -100℃ to 250℃ at a rate of 5℃ / min, followed by cooling back to -100℃ at a rate of 5℃ / min; the second cycle involved heating from -100℃ to 250℃ again at a rate of 5℃ / min). The temperature corresponding to the melting point endothermic peak in the second cycle's heating curve was taken as the melting point of the polyimide adhesive. The test results are shown in Table 3.

[0209] Slurry stability determination: After the positive electrode slurry is prepared, its stability is measured by a rheometer over 1 second. -1 The viscosity of the cathode slurry was recorded as J1. After standing for 24 hours, the viscosity of the cathode slurry was measured and recorded again as J2. Slurry stability = J2 / J1. The larger this value, the more unstable the slurry. The test results are shown in Table 3.

[0210] Electrode flexibility: The rolled positive electrode sheet was cut into 100mm*20mm pieces, folded in half along the long side, and then pressed down with a 50g weight at the edge of the long side. The weight was pushed towards the folded side until the electrode sheet broke, and the displacement of the weight was recorded. The test results are shown in Table 3.

[0211] Electrode peel strength: Unrolled positive electrode precursors (i.e., the precursors after coating and drying during the positive electrode preparation process) were cut into 40*100mm pieces. Adhesive tape was applied to the surface, and the precursors were rolled three times using a roller press at speeds of 1200r / min to 1450r / min. A tensile testing machine was used to test the peel strength (the peel force between the positive electrode active material layer and the aluminum foil in the positive electrode). The machine speed was 50mm / min. Each sample was tested three times. After each peel, the peel force trend remained constant, and the peel force at this point was recorded. The average of the three tests was taken as the electrode peel strength test result. The test results are shown in Table 3.

[0212] Battery cycle capacity retention test: After assembling the battery, constant current charge and discharge was performed at room temperature at a 1C / 1C charge / discharge rate within a voltage window of 2.0–3.8V. After 200 cycles, the ratio of the battery discharge capacity to the initial capacity was recorded (i.e., the capacity retention rate of the battery after 200 cycles). The test results are shown in Table 3.

[0213] Table 1

[0214] Table 2

[0215] Table 3

[0216] As can be seen from Table 3, compared with Comparative Example 1 and Comparative Example 2, Examples 1 to 20, by controlling the mass percentage of polyester soft segments in the polyimide binder within the range of 30% to 90%, achieve a balance between the soft and hard segments of the polyimide binder, which can significantly improve the stability of the slurry (slurry stability less than 300%), improve the processing performance of the polyimide binder when applied to electrode sheet preparation, and at the same time give the electrode sheet good flexibility, while also improving the electrode sheet peeling force and enhancing the battery cycle capacity retention rate.

[0217] Finally, it should be noted that other embodiments of this application will readily conceive of by those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and alterations may be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

1. A polyimide adhesive, wherein, The polyimide binder comprises aromatic hard segments and polyester soft segments, wherein the polyester soft segments in the polyimide binder comprise 30% to 90% by mass.

2. The polyimide adhesive according to claim 1, wherein, The polyester soft segment in the polyimide adhesive has a mass percentage content of 60% to 70%.

3. The polyimide adhesive according to claim 1 or 2, wherein, The aromatic hard segment has the structure shown in Formula I: R1 is selected from substituted or unsubstituted aryl groups, or substituted or unsubstituted biaryl groups; Preferably, the substituted or unsubstituted biaryl group has the structure shown in formula V: R7 and R8 each independently represent a monosubstituted to the maximum permissible substituent, and R7 and R8 each independently are selected from hydrogen, substituted or unsubstituted alkyl, or carboxyl, and L2 is selected from one or more of single bond, substituted or unsubstituted alkyl, carbonyl, ester, oxygen, sulfone, and amide.

4. The polyimide adhesive according to claim 3, wherein, The aromatic hard segment is selected from the structures shown in Formulas I-1 to I-9 below:

5. The polyimide adhesive according to any one of claims 1-4, wherein, The polyester soft segment comprises the structure shown in Formula II and / or Formula III as follows: R3 is selected from straight-chain alkyl groups having 1 to 18 carbon atoms or branched alkyl groups, and x is an integer from 5 to 5000; preferably, R3 is selected from straight-chain alkyl groups having 4 to 8 carbon atoms or branched alkyl groups; preferably, x is an integer from 5 to 100. R4 and R5 are each independently selected from straight-chain alkyl groups having 1 to 12 carbon atoms or branched alkyl groups, and y is an integer from 5 to 5000; preferably, R4 and R5 are each independently selected from straight-chain alkyl groups having 1 to 5 carbon atoms or branched alkyl groups; preferably, y is an integer from 5 to 100.

6. The polyimide adhesive according to any one of claims 1-5, wherein, The polyimide adhesive includes connecting segments, which have the structure shown in Formula IV: L1 is selected from substituted or unsubstituted aryl, substituted or unsubstituted biaryl, or substituted or unsubstituted alkyl. The symbol represents the connection site between Formula IV and the polymeric segment of the polyester soft segment, and * represents the connection site between Formula IV and the aromatic hard segment.

7. The polyimide adhesive according to any one of claims 1-6, wherein, The number average molecular weight of the polyimide binder is 10kDa-10000kDa, preferably 75kDa-95kDa; And / or, the ratio of the weight-average molecular weight to the number-average molecular weight of the polyimide adhesive is 1 to 10, preferably 2.3 to 2.

8.

8. A method for preparing the polyimide adhesive according to any one of claims 1-7, wherein, Includes the following steps: The ester monomer is subjected to a first polymerization reaction to obtain a polyester precursor; the polyester precursor, diisocyanate and anhydride monomer are subjected to a second polymerization reaction to obtain the polyimide binder; wherein at least one of the diisocyanate and the anhydride monomer contains an aryl group.

9. The method for preparing the polyimide adhesive according to claim 8, wherein, The ester monomers include cyclic ester monomers, and preferably the cyclic ester monomers include lactone monomers and / or lactone monomers; And / or, the anhydride monomer comprises a dianhydride monomer, preferably, the dianhydride monomer comprises a dianhydride monomer having the structure shown in Formula X: In formula X, R1 is selected from substituted or unsubstituted aryl groups or substituted or unsubstituted biaryl groups; And / or, the molar ratio of the anhydride monomer to the ester monomer is (0.07–1.32):1; And / or, the diisocyanate has the structure shown in Formula IA: OCN-L1-NCO Formula IA In the formula IA, L1 is selected from substituted or unsubstituted aryl, substituted or unsubstituted biaryl, or substituted or unsubstituted alkyl. And / or, the mass ratio of the diisocyanate to the ester monomer is (0.01–0.3):1; And / or, the temperature of the first polymerization reaction is 40 to 120°C, preferably 40 to 100°C, and the time is 3 to 12 hours, preferably 3 to 10 hours.

10. The method for preparing the polyimide adhesive according to claim 8 or 9, wherein, The ester monomer undergoes the first polymerization reaction under the action of an initiator, satisfying the following: The initiator includes at least one of a small molecule diol initiator and a small molecule diamine initiator; And / or, the molar ratio of the ester monomer to the initiator is (5-5000):1, preferably (5-100):

1.

11. The method for preparing the polyimide adhesive according to any one of claims 8-10, wherein, The process of carrying out the second polymerization reaction of the polyester precursor, diisocyanate and anhydride monomer includes: adding the polyester precursor and the diisocyanate to the diisocyanate, then adding the anhydride monomer, and then carrying out the second polymerization reaction to obtain the polyimide binder; preferably, the temperature of the addition reaction is 70-90°C and the time is 2-20 min.

12. The method for preparing the polyimide adhesive according to any one of claims 8-11, wherein, The second polymerization reaction is carried out at a temperature of 100–180°C for 1–15 hours.

13. An electrode sheet, wherein, The electrode coating includes the polyimide binder according to any one of claims 1-7, or the polyimide binder prepared according to the preparation method of the polyimide binder according to any one of claims 8-12.

14. The electrode sheet according to claim 13, wherein, The electrode sheet includes a positive electrode sheet.

15. A battery, wherein, Includes the electrode sheet as described in claim 13 or 14.

16. A battery pack, wherein, It includes at least two batteries as described in claim 15 that are interconnected.

17. An electrical appliance, wherein, Includes the battery of claim 15 or the battery pack of claim 16.

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