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 a polyimide binder, and the polyimide binder comprises an aromatic hard segment, a polyamide soft segment and a multi-branched soft segment. The present application can improve the properties of adhesiveness, flexibility, swelling, long-term stability, etc., of the polyimide binder, improve the bonding strength between an electrode coating and an electrode current collector in an electrode sheet, and avoid the problems of peeling, material falling, etc., of the electrode sheet, thereby improving the stability of the electrode sheet, and improving the performance of the cycle life, etc., of a battery.

Description

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

[0001] This application claims priority to Chinese Patent Application No. 202510495550.3, filed on April 18, 2025, entitled “A polyimide adhesive, electrode sheet, battery, battery pack and electrical device”, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of battery technology, and in particular 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 life 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 (HNBR) and modified acrylonitrile can overcome environmental issues to some extent. However, these existing binders still generally have some problems that limit the cycle performance of the battery. For example, the positive electrode sheet using HNBR 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 is too crystallized and cannot disperse the main material sufficiently. When the acrylonitrile content is low, the binder cannot 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 limitations of existing polyimide binders, such as poor adhesion, poor flexibility, high swelling rate, poor long-term stability, and poor processability when used in electrode sheet preparation (e.g., poor stability of the electrode slurry formed when preparing electrode sheets by coating method), electrode sheets generally suffer from problems such as low bonding strength between the electrode coating and the electrode current collector, easy peeling of the electrode coating, and material shedding, which affect the cycle life 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 polyimide binder during electrode sheet preparation and reduce the swelling of the polyimide binder. It can also enhance the bonding strength between the electrode coating and the electrode current collector in the electrode sheet, avoid problems such as electrode coating peeling and material shedding, thereby improving the stability of the electrode sheet and increasing the cycle life and other performance of the battery.

[0008] In one aspect, this application provides a polyimide adhesive comprising aromatic hard segments, polyamide soft segments, and multibranched soft segments.

[0009] According to one embodiment of this application, the multibranched soft segment includes the structure shown in Formula XIII-1; and / or, the total number of carbon atoms in the multibranched soft segment is 6 to 72, preferably 32 to 36.

[0010] According to one embodiment of this application, the polyamide soft segment includes the structure shown in Formula II and / or Formula III.

[0011] According to one embodiment of this application, the aromatic hard segment includes a first aromatic hard segment having the structure shown in Formula I; preferably, the first substituted or unsubstituted aryl group is selected from phenyl or naphthyl; preferably, the first substituted or unsubstituted biaryl group includes a first substituted or unsubstituted biphenyl group; preferably, the first substituted or unsubstituted biphenyl group has one or more of the groups shown in Formula V.

[0012] According to one embodiment of this application, the first aromatic hard segment is selected from the structures shown in Formulas I-1 to I-9.

[0013] According to one embodiment of this application, the polyimide adhesive includes a first connecting segment, the first connecting segment having a structure shown in Formula IY.

[0014] According to one embodiment of this application, the polyimide adhesive includes a second connecting segment, the second connecting segment having a structure as shown in Formula IV.

[0015] According to one embodiment of this application, the aromatic hard segment further includes a second aromatic hard segment, the second aromatic hard segment being selected from a second substituted or unsubstituted aryl group or a second substituted or unsubstituted biaryl group; preferably, the second substituted or unsubstituted arylphenyl, naphthyl, benzoic acid group, naphtholic acid group or one or more of these groups; preferably, the second substituted or unsubstituted biaryl group includes a second substituted or unsubstituted biphenyl group; preferably, the second substituted or unsubstituted biphenyl group has one or more of the groups shown in Formula XI.

[0016] According to one embodiment of this application, the second aromatic hard segment is selected from the structures shown in Formulas XI-1 to XI-16.

[0017] According to one embodiment of this application, the sum of the mass of the polyamide soft segments and the multibranched soft segments accounts for 20% to 80% of the mass of the polyimide adhesive, preferably 25% to 45%; and / or, the mass percentage of the polyamide soft segments in the polyimide adhesive is 10% to 70%, preferably 20% to 40%; and / or, the mass percentage of the multibranched soft segments in the polyimide adhesive is 10% to 70%, preferably 10% to 40%.

[0018] 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 1.5-5, more preferably 2.3-2.8.

[0019] According to one embodiment of this application, the proton NMR spectrum of the polyimide adhesive includes absorption peaks in the chemical shift range of 2.5 ppm to 3.52 ppm, absorption peaks in the chemical shift range of 6.0 ppm to 9.0 ppm, and absorption peaks in the chemical shift range of 0.8 ppm to 1.2 ppm.

[0020] Another aspect of this application provides a method for preparing the above-mentioned polyimide adhesive, comprising the following steps: subjecting an amide monomer to a first polymerization reaction to obtain a polyamide precursor; subjecting the polyamide precursor, a multibranched monomer, a 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.

[0021] According to one embodiment of this application, the diisocyanate includes a first diisocyanate and a second diisocyanate, the first diisocyanate having the structure shown in Formula IA, and the second diisocyanate having the structure shown in Formula IB; the process of carrying out a second polymerization reaction of the polyamide segment precursor, the multibranched monomer, the diisocyanate, and the anhydride monomer includes: carrying out an addition reaction of the polyamide segment precursor and the multibranched monomer with the first diisocyanate to obtain a polyamide soft segment precursor and a multibranched soft segment precursor; carrying out a second polymerization reaction of the polyamide soft segment precursor, the multibranched soft segment precursor, the second diisocyanate, and the anhydride monomer to obtain the polyimide binder; preferably, the temperature of the addition reaction is 70-90°C, and the time is 2-20 min.

[0022] According to one embodiment of this application, the first diisocyanate is the same as the second diisocyanate, and the process of carrying out the second polymerization reaction of the polyamide segment precursor, the multibranched monomer, the diisocyanate and the anhydride monomer includes: carrying out an addition reaction of the polyamide segment precursor, the multibranched monomer and the diisocyanate to obtain a polyamide soft segment precursor and a multibranched soft segment precursor; and then adding the anhydride monomer thereto to carry out the second polymerization reaction to obtain the polyimide binder.

[0023] According to one embodiment of this application, the amide monomer includes a cyclic amide monomer, preferably a lactam and / or a lamide; and / or, the multibranched monomer includes an aliphatic diamine; and / or, the anhydride monomer includes a dianhydride monomer; and / or, the temperature of the first polymerization reaction is 40–120°C and the time is 3–12 h; and / or, the temperature of the second polymerization reaction is 100–180°C and the time is 1–15 h.

[0024] According to one embodiment of this application, the amide monomer undergoes the first polymerization reaction under the action of an initiator, satisfying the following conditions: 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 diisocyanate to the initiator is (1-100):1; and / or, the molar ratio of the amide monomer to the initiator is (5-5000):1, preferably (5-40):1; and / or, the molar ratio of the branched monomer to the initiator is (5-40):1; and / or, the molar ratio of the anhydride monomer to the initiator is (1-20):1.

[0025] 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.

[0026] According to one embodiment of this application, the electrode sheet includes a positive electrode sheet.

[0027] In another aspect of this application, a battery is provided, including the aforementioned electrode sheet.

[0028] Another aspect of this application provides a battery pack comprising at least two of the aforementioned batteries connected to each other.

[0029] Another aspect of this application provides an electrical device including the aforementioned battery or battery pack.

[0030] The polyimide binder provided in this application includes a polyimide binder comprising aromatic hard segments, polyamide soft segments, and multi-branched soft segments. By using the interlocking structure of aromatic hard segments, polyamide soft segments, and multi-branched soft segments, 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 applied to 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, avoiding problems such as electrode coating peeling (e.g., electrode coating peeling from the electrode current collector, electrode coating cracking, and powder shedding). It also improves the processing performance of the electrode sheet, ensuring the structural stability of the electrode sheet, thereby improving the battery's safety, cycle stability, and cycle life. Simultaneously, it can also improve the long-term stability of the polyimide binder, ensuring that the polyimide binder maintains the stability and integrity of the electrode during battery operation and preventing electrode material shedding. Therefore, this application can simultaneously improve the adhesion, flexibility, long-term stability, and processability of the polyimide binder during electrode sheet preparation, enhancing the bonding strength between the electrode coating and the electrode current collector in the electrode sheet, preventing problems such as electrode coating peeling and material shedding, thereby improving the stability of the electrode sheet and increasing the battery's cycle capacity and other performance characteristics. Attached Figure Description

[0031] Figure 1 is a schematic diagram of the preparation process of a polyimide adhesive according to an embodiment of this application;

[0032] Figure 2 is a schematic diagram of the preparation process of a polyimide adhesive according to another embodiment of this application;

[0033] Figure 3 is a schematic diagram of the first polymerization reaction during the preparation process of the polyimide adhesive of Example 1 of this application;

[0034] Figure 4 is a schematic diagram of the addition reaction during the preparation of the polyimide adhesive of Example 1 of this application;

[0035] Figure 5 is a schematic diagram of the second polymerization reaction during the preparation process of the polyimide adhesive in Example 1 of this application;

[0036] Figure 6 is a schematic diagram of the structure of the polyimide adhesive of Example 1 of this application. Detailed Implementation

[0037] To enable those skilled in the art to better understand the solutions of this application, the application is further described in detail 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 protection scope of this application. When the following description involves accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements.

[0038] Electrode sheets typically consist of an electrode current collector and an electrode coating. The electrode coating is mainly composed of components such as electrode active materials, conductive agents, and binders. The binder is mainly used to bind the electrode active materials and conductive agents in the electrode coating, as well as to bond the electrode coating to the electrode current collector. Therefore, it plays an important role in maintaining the stability and electrochemical performance of the electrode sheet.

[0039] However, according to 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 preparation of 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 binder, electrode active material, conductive agent, and solvent, 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 life and other performance of the battery.

[0040] 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.

[0041] According to the inventors' research, introducing polyester soft segments into polyimide can improve the rigidity of the polyimide bonding skeleton, thereby improving its flexibility to a certain extent. However, the introduction of polyester soft segments will reduce the long-term stability of polyimide bonding. For example, it will degrade in acidic electrolytes after long-term immersion, causing the electrode sheets to fall off, which will also have a significant impact on the cycle life of the battery.

[0042] In view of this, embodiments of this application provide a polyimide adhesive, the polyimide adhesive comprising a first aromatic hard segment, a polyamide soft segment, and a multibranched soft segment.

[0043] According to the inventors' research, by introducing a first aromatic hard segment, a polyamide soft segment, and a multi-branched soft segment structure into the polyimide binder, the long-term stability of the polyimide binder is improved, effectively preventing the degradation of the polyimide binder caused by long-term immersion in the electrolyte. This prevents the electrode sheet from shedding material during battery operation. At the same time, it can also improve the adhesion, flexibility, and processability of the polyimide binder 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). This improves the stability and flexibility of the electrode sheet and enhances the cycle life of the battery.

[0044] 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 extends battery cycle life. Simultaneously, the introduction of a first aromatic hard segment, a polyamide soft segment, and a multi-branched soft segment into the polyimide binder maintains the mechanical properties of the polyimide based on the hardness characteristics of the first aromatic hard segment. Furthermore, the flexibility of the polyimide binder is improved based on the flexibility of the polyamide soft segment and the multi-branched soft segment, thereby improving the flexibility of the electrode sheet and preventing problems such as electrode coating peeling due to excessive hardness and rigidity (e.g., the electrode coating detaching from the electrode current collector). This process avoids issues such as peeling, electrode coating cracking, and powder shedding. Furthermore, the polyamide soft segments give the polyimide binder good long-term stability, allowing the electrode coating to maintain its structural integrity for a longer period, thus improving battery cycle life and other performance characteristics. Simultaneously, the polyimide binder exhibits excellent processing properties. For example, during the preparation of electrode sheets via coating, the polyimide binder dissolves readily in solvents (such as organic solvents like N-methylpyrrolidone (NMP)). When the polyimide binder, electrode active materials, conductive agents, and solvents are used to form the electrode slurry, the polyimide binder is more uniformly dispersed in the slurry, improving the uniformity and stability of the electrode slurry, avoiding problems such as dry material formation, thereby reducing surface defects on the electrode sheet and improving its electrochemical performance.

[0045] Therefore, the embodiments of this application can improve the adhesion, flexibility, long-term stability and processability of polyimide binders 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 further improving the stability and flexibility of the electrode sheet and improving the cycle life of the battery.

[0046] Specifically, the polyimide adhesive of this application embodiment includes soft segments and hard segments. The soft segments include polyamide soft segments and multi-branched soft segments, and the hard segments include aromatic hard segments (such as the first aromatic hard segment and / or the second aromatic hard segment described below).

[0047] Specifically, the multi-branched segment soft segment can be a soft segment mainly composed of multi-branched alkyl chains, which can include the structure shown in Formula XIII below. This is more conducive to improving the adhesion, flexibility, and processability of polyimide binders when used in electrode sheet preparation, improving the stability and flexibility of electrode sheets, and increasing the cycle capacity of batteries.

[0048] Among them, R7, R8, R9, R 10 R 11 R 12 Each is independently selected from straight-chain alkyl groups or branched alkyl groups having 1 to 18 carbon atoms.

[0049] In some specific embodiments, the multibranched soft segment may include alkylamine soft segments, which may specifically include the structure shown in XIII-1 below:

[0050] In some embodiments of this application, the total number of carbon atoms in the multibranched soft segments is 6 to 72, preferably 32 to 36.

[0051] In detail, the branched soft segments in this application embodiment are aliphatic alkyl chains, and the branched soft segments include highly branched aliphatic alkyl chains in the structure shown in Formula XII. By introducing the branched soft segments of Formula XII into the polyimide binder, this application embodiment can effectively break the regularity of the polymer backbone and reduce crystallinity, thereby making the molecular chain segments easier to slip and rearrange under external force, thus improving the ductility and elongation at break of the material. The branched soft segments can also weaken intermolecular forces, such as hydrogen bonds and van der Waals forces, reducing the close contact between rigid parts in the polyimide binder, so that the polyimide binder exhibits better flexibility and impact resistance while maintaining sufficient strength. In addition, the presence of branched soft segments can further improve the solubility and processing performance of the polyimide binder, which helps to form a more uniform film or coating and further enhances the mechanical properties of the electrode coating.

[0052] In some embodiments, R7, R8, R9, R 10 R 11 R 12 Each is independently selected from straight-chain alkyl groups or branched alkyl groups having 1 to 18 carbon atoms. Specifically, R7, R8, R9, R... 10 R 11 R 12 The number of carbon atoms can be the same or different. R7, R8, R9, R 10 R 11 R 12 The number of carbon atoms is, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17 and 18.

[0053] For example, when R7 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 (lauryl), n-tridecyl, n-tetradecyl (myristyl), n-pentadecanyl, n-hexadecyl (palmityl), n-heptadecyl, and n-octadecyl (stearyl). R8, R9, R 10 R 11 R 12 Each can be independently selected from the above-mentioned straight-chain alkyl groups.

[0054] When R7 is a straight-chain alkyl group, it includes, but is not limited to, isopropyl, isobutyl, sec-butyl, tert-butyl, neopentyl, isopentyl, tert-pentyl, 2-methylhexyl, 3-methylhexyl, isooctyl, 2-ethylhexyl, 2,2-dimethylhexyl, 2-methyloctyl, 3-methyloctyl, 2,4-dimethylheptyl, isodel, 2-propylheptyl, 2-methyldecyl, 3,7-dimethyloctyl, 2-butylnonyl, 2-methyltridecyl, 2-pentyldecyl, 2-hexyldodecyl, 2-heptyltridecyl, and 2-octyltetradecyl. R8, R9, R 10 R 11 R 12 Each can be independently selected from the above-mentioned branched alkyl groups.

[0055] In some embodiments, the total number of carbon atoms in the multi-branched soft segments is 6 to 72, preferably 32 to 36. By using multi-branched soft segments with the above-mentioned total number of carbon atoms, the embodiments of this application can further improve the solubility and processing performance of the polyimide binder, which helps to form a more uniform film or coating and further enhances the mechanical properties of the electrode coating.

[0056] The polyamide soft segment of this application embodiment includes the structure shown in Formula II and / or Formula III as follows: Formula II; in Formula II, R3 is selected from alkyl groups, specifically straight-chain alkyl groups or branched alkyl groups.

[0057] 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.

[0058] 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.

[0059] In Equation II, x represents the repeated unit in Equation II. The quantity of x (x is generally a positive integer greater than 1); x can be 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 combination thereof. In some embodiments, x can specifically be an integer from 5 to 100, for example, an integer from 10 to 25.

[0060] In detail, the structure shown in Formula II is formed by the ring-opening polymerization of a lactam (such as the lactam monomer shown in Formula VII-1 below) (as described in the first polymerization reaction below). During the ring-opening polymerization of the lactam, the carbon-nitrogen single bond (CN) in the amide bond breaks, leading to ring opening of the lactam. The broken amide bond then forms a linear polymer chain with another broken amide bond through chain polymerization, i.e., consisting of repeating units. The polymeric chain segment (Formula II) is composed of lactams, 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 properties of polyimide binders.

[0061] R4 and R5 are each independently selected from alkyl groups, specifically, each can be a straight-chain alkyl group having 1 to 12 carbon atoms or a branched alkyl group (i.e., R4 and R5 are each independently selected from a straight-chain alkyl group having 1 to 12 carbon atoms or a branched alkyl group having 1 to 12 carbon atoms), preferably R4 and R5 are each independently selected from a straight-chain alkyl group having 1 to 3 carbon atoms or a branched alkyl group, where y represents the repeating unit in Formula III. The quantity (y is a positive integer greater than 1) can be an integer from 5 to 5000, preferably an integer from 10 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 is specifically an integer from 5 to 100, for example, an integer from 10 to 25.

[0062] 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 3 carbon atoms.

[0063] 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.

[0064] 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 3 carbon atoms.

[0065] 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.

[0066] The structure shown in Formula III is formed by the ring-opening polymerization of a lactam (such as the lactam monomer shown in Formula VII-2 below) (as described in the first polymerization reaction below). In the ring-opening polymerization process of the lactam in the embodiments of this application, the carbon-nitrogen single bond (CN) in the amide bond is broken, resulting in the ring opening of the lactam. The broken amide bond and another broken amide bond form a linear polymer chain by chain polymerization, that is, a chain consisting of repeating units. The polymeric chain segment (Formula III) is composed of lignin-based substances, 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, further improving the adhesion and flexibility properties of polyimide binders.

[0067] 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 amide groups in the polyamide soft segment of the polyimide binder formed by controlling conditions such as the molar ratio of the monomer (such as the lactam monomer below) used to form the structure shown in Formula II to the initiator can be controlled, and the number of repeating units (i.e., y) of the amide groups in the polyamide soft segment of the polyimide binder formed by controlling conditions such as the molar ratio of the monomer (such as the leptamide monomer below) used to form the structure shown in Formula III to the initiator can be controlled.

[0068] 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 amide monomers to initiators during the preparation of the polyimide binder. For example, when lactam monomers are used to form the polymer segment shown in Formula II, x in Formula II is basically equal to the molar ratio of lactam monomers to initiators. When laminamide monomers are used to form the polymer segment shown in Formula III, y in Formula III is basically equal to the molar ratio of laminamide monomers to initiators.

[0069] This application embodiment, by introducing polyamide soft segments of Formula II or Formula III into the polyimide binder, can improve the bonding strength between the electrode coating and the electrode current collector in the electrode sheet, further reducing the probability of problems such as electrode sheet peeling (e.g., electrode coating peeling 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. Simultaneously, introducing polyamide soft segments of Formula II or Formula III into the polyimide binder can also improve the long-term stability of the polyimide binder, allowing it to exist more stably in the electrolyte. This further enables the electrode to maintain its structural integrity for a longer period, which is beneficial for improving the cycle life of the battery. The reason for this is that the amide groups in the polyimide soft segments can enhance intermolecular interactions, such as hydrogen bonds. These stronger interactions help form a more stable three-dimensional network structure, thereby effectively improving the overall mechanical strength and stability of the material. Furthermore, the presence of the amide structure can improve the interfacial compatibility of polyimide, enabling it to form a tighter and more uniform contact with active materials and conductive additives. This reduces the performance degradation caused by electrode material shedding and volume changes during cycling. The nitrogen and oxygen atoms in the amide group also provide additional electron density, which helps stabilize the electrode surface, resist electrolyte erosion, and further protect the electrode from chemical degradation and physical damage that may be encountered during long-term cycling. This ensures that the electrode can maintain good structural integrity and efficient electrochemical performance after multiple charge-discharge cycles, thereby significantly extending the battery's lifespan.

[0070] For example, the polyamide soft segment can be selected from the following structures:

[0071] Where m represents the number of methylene groups in the polyamide soft segment, and m is an integer from 1 to 12, such as 1, 2, 3, 4, 5, 10, 12, etc.; a represents the number of methylene groups on the side chains in the polyamide 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 polyamide soft segment. Both m and a can be tested using conventional techniques in this field, such as NMR spectroscopy.

[0072] In this embodiment, the aromatic hard segment in the polyimide adhesive may include a first aromatic hard segment, which has the structure shown in Formula I:

[0073] R1 is selected from a first substituted or unsubstituted aryl group or a first substituted or unsubstituted biaryl group. Specifically, the first substituted or unsubstituted aryl group may be selected from phenyl or naphthyl, and the first substituted or unsubstituted biaryl group may have one or more of the structures shown in Formula V below.

[0074] R 13 and R 14 Each independently represents a monosubstituted substituent up to the maximum permissible substituent (i.e., in equation V, R). 13 and R 14 Each can independently connect to one or more connectable sites on its respective benzene ring (e.g., 1, 2, 3, or 4), and R 13 and R 14 Each group is independently selected from hydrogen, substituted or unsubstituted alkyl groups, or carboxyl groups. For example, R... 13 and R 14 Each of the individual hydrogen atoms, and the biaryl group having the structure shown in Formula V, can have the structure shown in Formula V-1:

[0075] L2 is selected from one or more of the following groups: single bond, substituted or unsubstituted alkyl, carbonyl, ester, oxygen, sulfone, and amide. Specifically, L2 may be selected from one or more of the following groups: alkyl with C1 to C12 carbon atoms, carbonyl with C1 to C12 carbon atoms, ester with C1 to C12 carbon atoms, oxygen, sulfone, and amide with C1 to C12 carbon atoms.

[0076] 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.

[0077] 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.

[0078] The embodiments of this application introduce a first aromatic hard segment with the above-mentioned structure into the polyimide adhesive, which is more conducive to the compatibility of the first aromatic hard segment with the multi-branched soft segment and polyester soft segment groups in the polyimide adhesive, so that the polyimide adhesive has better thermal stability and mechanical strength, and further improves the adhesion, flexibility and swelling resistance of the polyimide adhesive.

[0079] Furthermore, when the first 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, swelling resistance, and processing performance of the polyimide binder.

[0080] In some embodiments, the polyimide binder may further include a second aromatic hard segment selected from a second substituted or unsubstituted aryl group or a second substituted or unsubstituted biaryl group.

[0081] Specifically, the second substituted or unsubstituted aryl group can be selected from one or more of phenyl, naphthyl, benzoic acid, and naphtholic acid groups, which is more conducive to the compatibility of the second aromatic hard segment with the multi-branched soft segment and polyester soft segment groups in the polyimide adhesive, and further improves the adhesion, flexibility and swelling resistance of the polyimide adhesive.

[0082] Specifically, the second substituted or unsubstituted biaryl group may include the second substituted or unsubstituted biphenyl group. The second substituted or unsubstituted biphenyl group may specifically include biphenyl group having the structure shown in Formula XI. This facilitates the compatibility of the second aromatic hard segment with the multi-branched soft segment and polyester soft segment groups in the polyimide adhesive, further improving the adhesion, flexibility and swelling resistance of the polyimide adhesive.

[0083] R 15 and R 16 Each independently represents a monosubstituted substituent up to the maximum permissible substituent (i.e., in equation XI, R). 15 and R 16 Each can independently connect to one or more connectable sites on its respective benzene ring (e.g., 1, 2, 3, or 4), and R 15 and R 16 Each group is independently selected from hydrogen, substituted or unsubstituted alkyl groups, or carboxyl groups. For example, R... 15 and R 16 Each of the biaryl groups, being hydrogen in its own right, and having the structure shown in formula V, can also have the structure shown in formula XI-101:

[0084] L3 is selected from one or more of single bonds, substituted or unsubstituted alkyl, carbonyl, ester, oxygen, sulfone, and amide groups, specifically from one or more of C1-C12 alkyl, C1-C12 carbonyl, C1-C12 ester, oxygen, sulfone, and C1-C12 amide groups.

[0085] 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.

[0086] For example, when L3 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 L3 is a carbonyl group, it includes, but is not limited to, aldehyde and ketone groups; when L3 is an ester group, it includes, but is not limited to, methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, and butoxycarbonyl; when L3 is a sulfone group, it includes, but is not limited to, dimethyl sulfone, diethyl sulfone, and methyl ethyl sulfone; when L3 is an amide group, it includes, but is not limited to, carbamoyl, acetamido, N-methylcarbamoyl, and N,N-dimethylcarbamoyl. Furthermore, any hydrogen atom in L3 can be replaced by a halogen atom, such as a fluorine atom.

[0087] Introducing a second aromatic hard segment into the polyimide composition system of this application embodiment can further enhance the mechanical properties of the polyimide binder while improving adhesion and flexibility. This ensures that the electrode maintains its integrity and stability during battery operation, preventing material shedding and peeling. Furthermore, the second aromatic hard segment can further improve the anti-swelling properties of the polyimide binder, which is beneficial for further enhancing the structural integrity of the electrode during long-term battery operation, thereby improving the battery's cycle life.

[0088] In some embodiments, the second aromatic hard segment is selected from the structures shown in Formulas XI-1 to XI-16, which helps to further improve the adhesion, flexibility and swelling resistance of the polyimide adhesive.

[0089] For example, equation XI-1 can be the structure shown in equation XI-11 below:

[0090] Equation XI-2 can be a structure as shown in Equation XI-21 below:

[0091] In some embodiments, the polyimide adhesive includes a first connecting segment, the first connecting segment comprising the structure shown in Formula IY:

[0092] In formula IY, The symbol IY represents the connection site between the branched soft segment and the symbol * represents the connection site between the symbol IY and the first aromatic hard segment.

[0093] In some embodiments, the polyimide adhesive includes a second connecting segment, the second connecting segment comprising the structure shown in Formula IV:

[0094] In Equation IV, The symbol represents the connection site between Formula IV and the polyamide soft segment, and * represents the connection site between Formula IV and the first aromatic hard segment (as shown in Formula I).

[0095] In the above-mentioned connecting segments (in Formula IY and Formula IV), L1 is selected from a third-substituted or unsubstituted aryl group, a third-substituted or unsubstituted biaryl group, or a substituted or unsubstituted alkyl group. Specifically, it can be selected from an aryl group with 4 to 24 carbon atoms, or a straight-chain alkyl group with 1 to 12 carbon atoms, or a branched alkyl group (i.e., a straight-chain alkyl group with 1 to 12 carbon atoms or a branched alkyl group with 1 to 12 carbon atoms).

[0096] 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 biaryl group having 12 to 48 carbon atoms can be 12, 18, 24, 30, 36, 40, or 48; and 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.

[0097] 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.

[0098] For example, the second connecting segment can be a structure as shown in formula IV-1 or IV-2:

[0099] In Formula VI-2, n represents the number of alkyl (methylene) groups, which can be an integer from 1 to 12.

[0100] It should be clarified that one end of the first connecting segment (the urea end) is connected to the multi-branched soft segment, and the other end is connected to the first aromatic hard segment. One end of the second connecting segment (the urea end) is connected to the polyamide soft segment, and the other end (the alkyl group of formula IV-1 or the phenyl group of formula IV-2) is connected to the first aromatic hard segment. * indicates the connection site between formula IV and the first aromatic hard segment. This makes the polyimide binder a polymer system with a soft and hard segment structure, which gives it both good flexibility and suitable mechanical properties, which is beneficial for maintaining the integrity of the electrode active material layer during battery operation.

[0101] In some embodiments, L1 in the connecting segments (Formula IY, Formula IV) can be the same as the second aromatic hard segment; for example, L1 can have the structure shown in Formula XI. This facilitates further improvement of the adhesion, flexibility, and swelling resistance of the polyimide adhesive, while also facilitating the preparation of the polyimide adhesive.

[0102] Specifically, as shown in Figure 1, the polyimide adhesive can be synthesized via the following pathway: after the amide monomer undergoes a first polymerization reaction, a polyamide segment precursor is obtained; the polyamide segment precursor undergoes an addition reaction with a first diisocyanate (diisocyanate A in Figure 1) to obtain a polyamide soft segment precursor with isocyanate group (-NCO) end-capped; simultaneously, the multibranched monomer undergoes an addition reaction with the first diisocyanate to generate a multibranched soft segment precursor with isocyanate group end-capped; the polyamide soft segment precursor, the multibranched soft segment precursor, the second diisocyanate (diisocyanate B in Figure 1), and the anhydride monomer undergo a second polymerization reaction to obtain the polyimide adhesive. The first diisocyanate contains L1 (the first diisocyanate has the structure shown in formula IA below), which is used to achieve chemical bonding between the soft segment precursor and the anhydride monomer to form a linking segment in the polyimide binder (after the multibranched alkylamine monomer is chemically bonded to the anhydride monomer through the first diisocyanate, a first linking segment is formed in the polyimide binder; the polyamide segment precursor is chemically bonded to the anhydride monomer through the first diisocyanate to form a second linking segment in the polyimide binder); after the second polymerization reaction, the anhydride monomer reacts with the isocyanate groups in the soft segment precursor and the second diisocyanate to form a first aromatic hard segment, and the second diisocyanate contains a second aromatic hard segment (the second diisocyanate has the structure shown in formula IB below, where L4 represents the second aromatic hard segment), which is used to introduce the second aromatic hard segment into the polyimide binder.

[0103] OCN-L4-NCO type IB

[0104] In Formula IB, L4 represents the second aromatic hard segment, which, as mentioned above, can be selected from a second substituted or unsubstituted aryl group or a second substituted or unsubstituted biaryl group, and will not be elaborated further. Specifically, the first diisocyanate and the second diisocyanate can be the same or different. When the first diisocyanate and the second diisocyanate are the same, that is, L1 and L4 are the same, that is, L1 in the linking segment (Formula IY, Formula IV) of the polyimide adhesive is the same as the second aromatic hard segment. In this case, using a diisocyanate is beneficial to improving the adhesion, flexibility and anti-swelling properties of the polyimide adhesive, while also facilitating the preparation of the polyimide adhesive.

[0105] OCN-L1-NCO type IA

[0106] Specifically, the polyimide adhesive may have one or more of the following: a first repeating unit with the structure shown in W1, a second repeating unit with the structure shown in W2, and a third repeating unit with the structure shown in W3.

[0107] In W2, Q represents an alkyl segment of a multi-branched soft segment (such as formula XIII).

[0108] For example, a polyimide adhesive may have the structure shown in Formula VI:

[0109] Among them, W 11 Includes polymeric segments of polyester soft satin and a second connecting segment (W) connecting the polymeric segments and the first aromatic hard segment. 11 (For polyester soft segments with a second connecting segment); W 21 Includes a multi-branched soft segment and a first connecting chain segment (W) connecting the multi-branched soft segment and the first aromatic hard segment. 11 (For a multi-branched soft segment with a first connecting link segment); W 31 This indicates the second aromatic hard segment.

[0110] Specifically, each end of the polymeric segment in the polyamide soft segment W1 is connected to a second connecting segment. For example, W... 11 (The polyamide soft segment with connecting chain segments) can have a structure as shown in Formula VI-1 or Formula VI-2:

[0111] 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.

[0112] For example, the polyimide adhesive has a structure as shown in Formula VI-11 or Formula VI-12:

[0113] W1-W2-W3 type VI-12

[0114] In some embodiments of this application, the sum of the mass of the polyamide soft segments and the multi-branched soft segments accounts for 20% to 80% of the mass of the polyimide binder, for example, 20%, 25%, 30%, 40%, 50%, 60%, 70%, 80%, or any combination thereof, specifically 25% to 45%. By controlling the mass ratio of the sum of the mass of the polyamide soft segments and the multi-branched soft segments to the mass of the polyimide binder within the above-mentioned range, this application's embodiments are beneficial to further improve the long-term stability of the polyimide binder, while also improving the flexibility and anti-swelling properties of the polyimide binder, avoiding problems such as electrode sheet peeling (e.g., electrode coating peeling 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.

[0115] As mentioned above, based on considerations of improving the long-term stability of polyimide, in some embodiments, the mass percentage of polyamide soft segments in the polyimide binder is 10% to 70%, for example, 10%, 30%, 40%, 50%, 60%, 70%, or any combination thereof, specifically 20% to 40%. By controlling the mass percentage of polyamide soft segments in the polyimide binder within the above range, the polyimide binder can possess both better long-term stability and better mechanical properties, while also exhibiting good adhesion performance. This improves the structural stability of the electrode sheet, avoids problems such as electrode coating peeling, and ultimately enhances the cycle life and other performance characteristics of the battery.

[0116] In one specific embodiment, the mass percentage of the multibranched soft segments in the polyimide binder is 10% to 70%, for example, a range of 10%, 30%, 40%, 50%, 60%, 70%, or any combination thereof, specifically 10% to 40%, which is beneficial to improve the flexibility of the polyimide binder, thereby further improving the flexibility of the electrode sheet and improving the cycle life and other performance of the battery.

[0117] In addition, the mass percentage of aromatic hard segments in polyimide adhesives can be 20% to 80%, for example, 20%, 25%, 30%, 40%, 50%, 60%, 70%, 80%, or any combination thereof, which is beneficial for further improving the flexibility and swelling resistance of polyimide adhesives.

[0118] In this embodiment, the mass percentage of aromatic hard segments (20% to 80%) refers to the sum of the mass percentages of all aromatic hard segments in the polyimide binder. For example, if the aromatic hard segments in the polyimide binder are the first aromatic hard segment and the second aromatic hard segment, then the mass percentage of aromatic hard segments (20% to 80%) refers to the sum of the mass percentages of the first aromatic hard segment and the second aromatic hard segment.

[0119] In some embodiments, the mass percentage of the second aromatic hard segment is 10% to 70%, for example, a range of 10%, 30%, 40%, 50%, 60%, 70%, or any two thereof, specifically 20% to 50%.

[0120] In this embodiment, the polyamide soft segments, multibranched soft segments, and aromatic hard segments in the polyimide binder can be measured using conventional testing methods such as NMR. The mass percentages of the polyamide soft segments, multibranched soft segments, aromatic hard segments, and each aromatic hard segment in the polyimide binder can also be measured using conventional methods in the art, such as NMR and thermogravimetric analysis. For example, NMR can be used to test the characteristics of two aromatic hard segments (the first aromatic hard segment and the second aromatic hard segment) and their mass percentages in the polyimide binder, while thermogravimetric analysis can be used to determine the mass percentage of soft segments in the polyimide binder (the sum of the masses of the polyamide soft segments and the multibranched soft segments).

[0121] For example, the thermal decomposition temperatures of soft segments (polyamide soft segments, multi-branched soft segments) and hard segments (first aromatic hard segments, second aromatic hard segments) are different (the thermal decomposition temperature of hard segments is higher than that of soft segments). Therefore, the content of soft segments in polyimide binders can be determined by thermogravimetric analysis (TGA). The thermal decomposition temperature of soft segments is between 300℃ and 350℃. In TGA, 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 is recorded as m4. The mass of the soft segments is approximately equal to the difference between m3 and m4. (m3-m4) / m3 is the mass percentage of soft segments in the polyimide binder.

[0122] In practice, the battery can be disassembled after being fully discharged, the electrode plates can be separated, and the electrode active material layer (electrode coating) can be scraped off from the electrode plates. The electrode active material layer can be crushed into powder, dissolved in a solvent, filtered, centrifuged, and the filtrate can be dried. The collected product is the polyimide adhesive. The polyimide adhesive can then be tested using nuclear magnetic resonance (NMR) and thermogravimetric analysis (TGA) to determine the mass percentage of polyamide soft segments and multibranched soft segments in the polyimide adhesive. 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 layer powder. In practice, the solvent used may include N-methylpyrrolidone (NMP).

[0123] To further improve the bonding performance, flexibility, swelling resistance, and processability of the polyimide binder, 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, 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 ensures that the polyimide binder has good solubility and processability while also providing sufficient mechanical strength and heat resistance for the battery electrodes, 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, swelling resistance and processability of the polyimide binder, thereby improving the flexibility and peel strength of the electrode sheet.

[0124] 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) is 1 to 10, for example, a range of 1, 1.5, 2, 2.3, 2.5, 2.8, 3, 4, 5, 6, 7, 8, 9, 10, or any two of these ranges, specifically 1.5 to 5. 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), used to measure 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 polymer molecular chains in the polyimide binder is small, resulting in better processing and mechanical properties when using the polyimide binder to prepare battery electrodes. 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 bonding performance, flexibility, and anti-swelling properties of the polyimide binder.

[0125] In one specific embodiment, the proton nuclear magnetic resonance spectrum of the polyimide adhesive (NMR spectrum) 1 The ¹H NMR spectrum includes absorption peaks in the chemical shift range of 2.5 ppm to 3.52 ppm, 6.0 ppm to 9.0 ppm, and 0.8 ppm to 1.2 ppm. Specifically, the absorption peak in the 2.5 ppm to 3.52 ppm range is generally associated with methylene hydrogen (-CH₂-) attached to an electronegative atom (such as oxygen or nitrogen) or hydrogen directly attached to a heteroatom (such as O, N). In this embodiment, the α-hydrogen of the polyamide soft segment produces an absorption peak in this chemical shift range. The absorption peak in the 6.0 ppm to 9.0 ppm range is attributed to aromatic hydrogen and olefinic hydrogen signals. In this embodiment, the aromatic hydrogen in the first and second aromatic hard segments produces an absorption peak in this chemical shift range. The absorption peak in the 0.8 ppm to 1.2 ppm range is caused by methyl hydrogen (-CH₃) at the alkyl chain terminus. In this embodiment, the methyl hydrogen in the multibranched soft segment produces an absorption peak in this chemical shift range. In this embodiment, the polyimide binder that generates signals in the three chemical shift ranges of the proton nuclear magnetic resonance spectrum has better adhesion, flexibility and long-term stability. This is beneficial to further reduce the degradation of the polyimide binder caused by long-term immersion in the electrolyte, thereby further reducing the problem of material shedding from the electrode sheet during battery operation, and thus further improving the cycle life and other characteristics of the battery.

[0126] This application also provides a method for preparing a polyimide adhesive, comprising the following steps: subjecting an amide monomer to a first polymerization reaction to obtain a polyamide precursor; subjecting the polyamide precursor, a multibranched monomer, a diisocyanate, and an anhydride monomer to a second polymerization reaction to obtain a polyimide adhesive; wherein at least one of the diisocyanate and the anhydride monomer contains an aryl group.

[0127] In the preparation of the polyamide precursor in this application, the amide monomer may include cyclic amide monomers, specifically lactams and / or laminecides. That is, the amide monomer may be only a lactam monomer, or only a laminec monomer, or it may simultaneously include both lactam and laminec monomers. During the first polymerization reaction, only lactam monomers, only laminecides, or both lactam and laminec monomers may be used simultaneously. When using both lactam and laminec monomers simultaneously, this application does not impose any special limitation on their molar ratio; it can be selected according to the actual situation.

[0128] In the above preparation process, after the amide monomer undergoes the first polymerization reaction, the resulting polyamide segment precursor is an amide segment, which can specifically be an amino-terminated amide segment. Specifically, the amide monomer can include cyclic amide monomers, such as lactam monomers and / or laminecides. During the first polymerization reaction, the cyclic amide monomer undergoes ring-opening and polymerization to form an amino-terminated amide segment.

[0129] Specifically, the lactam monomers in the embodiments of this application have the structure shown in Formula VII-1:

[0130] 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.

[0131] In contrast, when R3 in Formula VII-1 is selected from alkyl groups with C4 to C6 carbon atoms, it is beneficial to further improve the adhesion, flexibility and processability of polyimide adhesives. At the same time, such lactone monomers also have lower costs and are easier to prepare.

[0132] The lactam monomer in the embodiments of this application can have the structure shown in formula VII-2:

[0133] 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.

[0134] For example, lactam monomers can have the structure shown in Formula VIII-1:

[0135] 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.

[0136] For example, the lactam monomer has a structure as shown in Formula VIII-2:

[0137] Where a is the number of methylene groups at the site shown in Formula VIII-2, and the value of a is an integer from 1 to 18; b is the number of methylene groups at the site shown in Formula VIII-2, and the value of b is an integer from 1 to 18.

[0138] For example, the lactam monomers in the embodiments of this application include, but are not limited to, one or more of caprolactam (i.e., R3 in formula VII-1 is a linear hexylene (as shown in Figure 2, the N-methylcaprolactam structure)), propiolactam, laurolactam, and butyrolactam; the lactam monomers in the embodiments of this application include, but are not limited to, one or more of glycolamide and propiolactam.

[0139] In some embodiments, a lactam having the following formula VIII-21 may also be used as the amide monomer:

[0140] Accordingly, the lactam having formula VIII-21 in polyimide has the structure shown in formula VIII-22:

[0141] Specifically, the amide monomer undergoes a first polymerization reaction in a solvent. This application does not specifically limit 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, and the mass percentage of the amide monomer in NMP is 20% to 80%.

[0142] In the above preparation process, during the first polymerization reaction of the amide monomer, the amide monomer undergoes a ring-opening polymerization reaction to generate polyamide segments with amino groups as end groups (i.e., polyamide segment precursors). Specifically, the amide monomer can undergo the first polymerization reaction under the action of an initiator, which facilitates the initiation of the first polymerization reaction and the generation of polyamide segment precursors. Taking a cyclic amide monomer as an example, under the action of an initiator, the cyclic amide monomer undergoes ring-opening and the first polymerization reaction to generate polyamide segment precursors.

[0143] Generally, the esters in polyimide adhesives are formed by the condensation of diacid and glycol monomers. This stepwise process makes it difficult to control the polymer molecular weight and results in a wide molecular weight distribution. Consequently, the modified polyimide adhesives produced exhibit high fluctuations in process and battery electrical performance, poor repeatability, and low industrial economics.

[0144] In the embodiments of this application, by using the above-mentioned amide monomer, the polymerization reaction is carried out in a chain polymerization manner, the reaction process is more uniform, which is conducive to controlling the molecular weight and molecular weight distribution of the polymer, and thus conducive to preparing a polyimide binder with good stability and processability.

[0145] The reason for this is that polyimides formed by the condensation polymerization of diacid and glycol monomers have ester groups. Although ester segments have good flexibility, their long-term stability is poor. Replacing ester segments with polyamide soft segments can avoid the problem of poor long-term stability of ester groups in polyester soft segments. At the same time, the multi-branched soft segments have a high degree of branching, which can avoid the problem of reduced electrode flexibility caused by the introduction of polyamide soft segments. Therefore, compared with existing polyimide binders formed by the condensation polymerization of diacid and glycol monomers, the embodiments of this application use amide monomers, multi-branched monomers, diisocyanates and anhydride monomers to synthesize polyimide binders. Introducing aromatic hard segments, polyamide soft segments and multi-branched soft segments into polyimide binders can simultaneously improve the adhesion, flexibility, and anti-swelling properties of polyimide binders.

[0146] Furthermore, compared to typical ester compounds synthesized by stepwise polymerization of diacid and glycol monomers, the embodiments of this application use cyclic amide monomers such as lactams or lamides to synthesize polyamide soft segments, exhibiting distinct chain polymerization characteristics. Specifically, the growing polyamide soft segments continuously add monomer units through active centers, with each monomer added to the polymer chain (i.e., the aforementioned polyamide soft segments) almost simultaneously and at the same rate, thereby generating a polymer with a narrow molecular weight distribution. Moreover, due to the high consistency of active centers and the continuity of monomer addition during chain polymerization, side reactions are effectively reduced, and the resulting polymer chain length is ensured to be more uniform. Therefore, the chain polymerization method used in the embodiments of this application achieves higher uniformity and a more controllable molecular weight distribution than stepwise polymerization.

[0147] The polyamide soft segments formed by ring-opening polymerization of cyclic amide monomers have relatively uniform molecular weight and distribution. After the first polymerization reaction is completed, the above-mentioned polyamide segment precursor with amino end groups is subjected to a second polymerization reaction with diisocyanate and multibranched monomers to obtain polyimide binder.

[0148] Specifically, branched monomers may include branched alkylamine monomers, specifically aliphatic diamines.

[0149] In some embodiments, the aliphatic diamine has a structure as shown in Formula XIV: In equation XIV, R7, R8, R9, and R 10 R 11 R 12 With R7, R8, R9, R in equation XIII10 R 11 R 12 The same applies, so I will not elaborate further here.

[0150] In one specific embodiment, the aliphatic diamine has a structure as shown in Formula XIV-1:

[0151] Accordingly, the aliphatic diamine represented by formula XIV-1 has the structure represented by formula XIV-11 in the polyimide binder:

[0152] The embodiments of this application utilize the aforementioned aliphatic diamine to perform a second polymerization reaction, thereby obtaining multi-branched soft segments with good flexibility, which is beneficial for improving the flexibility of the electrode sheet and enhancing the cycle life and other performance characteristics of the battery.

[0153] In the above preparation process, the diisocyanate includes a first diisocyanate, which, as mentioned above, may have the structure shown in Formula IA:

[0154] O=C=N-L1-N=C=O (i.e., OCN-L1-NCO) IA

[0155] In addition, the first diisocyanate amide compound undergoes an addition reaction with polyamide segment precursors, aliphatic diamines, and other branched monomers to form polyamide segments (polyamide soft segment precursors) capped with isocyanate groups (-NCO) and branched segments (branched soft segment precursors) capped with isocyanate groups (-NCO). During the second polymerization reaction, the nitrogen element in the isocyanate amide group replaces the oxygen element between the two carbon groups in the anhydride monomer (each substitution site will correspondingly remove one mole of carbon dioxide (CO2)), causing the polyamide soft segment precursor, the branched soft segment precursor, and the anhydride monomer to polymerize and generate polyimide binders.

[0156] In this embodiment, an addition reaction is performed between the polyamide precursor and the first diisocyanate amide to form an isocyanate group (-NCO) end-capping structure in the polyamide precursor. This facilitates the reaction of the isocyanate amide group with the dianhydride 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.

[0157] In some embodiments, the process of performing a second polymerization reaction on the polyamide segment precursor, the multibranched monomer, the diisocyanate, and the anhydride monomer includes: performing an addition reaction between the polyamide segment precursor, the multibranched monomer, and the first diisocyanate to obtain a polyamide soft segment precursor and a multibranched soft segment precursor; and performing a second polymerization reaction between the polyamide soft segment precursor, the multibranched soft segment precursor, the second diisocyanate, and the anhydride monomer to obtain a polyimide binder. The temperature of the addition reaction can be 70–90°C, such as 80°C, and the reaction time can be 2–20 min, such as 10 min.

[0158] Specifically, the first diisocyanate and the second diisocyanate may be the same or different.

[0159] In practice, the polyamide precursor, multibranched monomer, and diisocyanate (first diisocyanate and second diisocyanate) can be mixed and subjected to an addition reaction. Then, an anhydride monomer can be added to carry out a second polymerization reaction to obtain a polyimide binder.

[0160] In some specific embodiments, the first diisocyanate is the same as the second diisocyanate. The process of carrying out a second polymerization reaction of the polyamide segment precursor, the multibranched monomer, the diisocyanate and the anhydride monomer includes: carrying out an addition reaction of the polyamide segment precursor, the multibranched monomer and the diisocyanate to obtain a polyamide soft segment precursor and a multibranched soft segment precursor; and then adding the anhydride monomer thereto to carry out a second polymerization reaction to obtain a polyimide binder.

[0161] Taking the amide monomer as formula VI-1 and the initiator as a small molecule diamine initiator as an example, the reaction process for preparing polyimide binders is shown in Figure 1. The small molecule diamine initiator is mixed with the lactam monomer shown in formula VI-1 and heated to carry out the first polymerization reaction to obtain the polyamide segment precursor. Then, diisocyanate and multibranched monomer are added in situ to carry out the addition reaction to obtain the polyamide soft segment precursor and the multibranched soft segment precursor, respectively. Next, an anhydride monomer is added to the above reaction system in situ, mixed and heated, and after a chemical reaction (i.e., the second polymerization reaction), the soft segment precursor and the anhydride monomer polymerize, remove carbon dioxide, and generate polyimide binders.

[0162] 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.

[0163] In some embodiments of this application, the polyamide segment precursor has a structure as shown in Formula IX: H2N-R6-NH2 Formula IX

[0164] Accordingly, the isocyanate-terminated polyamide has the structure shown in Formula IIX:

[0165] In some embodiments of this application, 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:

[0166] 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:

[0167] The specific choices for L1, R3, R4, and R5 are as described above and will not be repeated here.

[0168] Specifically, a diisocyanate is a compound containing two isocyanate groups, and it can be a small molecule diisocyanate. In some embodiments, the diisocyanate includes, 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), p-biphenyl diisocyanate, n-hexyl diisocyanate, and cyclohexane diisocyanate (CHDI). The structures of p-phenyl diisocyanate (PPDI) and n-hexyl diisocyanate are shown below:

[0169] Specifically, the first diisocyanate may include one or more of toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), naphthalene diisocyanate (NDI), p-phenyl diisocyanate (PPDI), p-biphenyl diisocyanate, n-hexyl diisocyanate, and cyclohexane diisocyanate (CHDI).

[0170] In addition, the second diisocyanate may include, but is not limited to, one or more of toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), naphthalene diisocyanate (NDI), p-phenyl diisocyanate (PPDI), and p-biphenyl diisocyanate.

[0171] In some embodiments, the first diisocyanate and the second diisocyanate may each be independently selected from structures of formulas XII-1 to XII-16:

[0172] In some embodiments, the first diisocyanate and the second diisocyanate may each independently comprise one or more of the diisocyanate compounds with the structures shown in formulas XII-11, XII-21, XII-41, XII-71, XII-91, XII-111, XII-131, and XII-132:

[0173] For example, the polyamide soft segment precursor may have a structure as shown in Formula IX-1 and / or Formula IX-2:

[0174] R3 in Equation IX-1 is the same as R3 in Equation II, R4 in Equation IX-2 is the same as R4 in Equation III, R5 in Equation IX-2 is the same as R5 in Equation III, and L1 in Equation IX-1 and Equation IX-2 is the same as L1 in Equation IV. These will not be elaborated further here.

[0175] For example, the second connecting segment can be a structure as shown in formula IV-1 or IV-2:

[0176] For example, formula IX-3 can have the structure shown in formula IX-31:

[0177] In the embodiments of this application, the amide monomers, diisocyanates, initiators, aliphatic diamines, acid 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.

[0178] In this embodiment, the sum of the mass percentages of polyamide soft segments and multibranched soft segments, the mass percentage of aromatic hard segments, and the mass percentages of each soft segment and each aromatic hard segment in the polyimide binder can be controlled by the mass percentage of the raw materials used to introduce the segment into the polyimide in the total mass of the raw materials added during the synthesis of the polyimide binder. Taking the mass percentage of polyamide soft segments in the polyimide binder as an example, it can be controlled by the mass percentage of the amide monomer in the total mass of the raw materials added during the synthesis of the polyimide binder, such as the amide monomer, diisocyanate, anhydride monomer, initiator, and multibranched monomer. That is, the mass percentage of polyamide soft segments in the obtained polyimide binder is basically equal to the proportion of the mass of the amide monomer to the total mass of the raw materials added during the synthesis of the polyimide binder. The mass percentage of polyamide soft segments in the polyimide binder calculated by this method is basically consistent with the mass percentage of polyamide soft segments in the polyimide measured by methods such as NMR. For example, in the synthesis of polyimide, amide monomers undergo a first polymerization reaction under the action of an initiator, and then the resulting polyamide precursor, diisocyanate, multibranched monomer, and acid anhydride monomer undergo a second polymerization reaction to produce a polyimide binder. The mass percentage of polyamide soft segments in the obtained polyimide binder = mass of amide monomer / (mass of amide monomer + mass of acid anhydride monomer + mass of diisocyanate + mass of initiator).

[0179] In addition, the mass percentage of aromatic hard segments in polyimide binders (the sum of the mass percentages of all aromatic hard segments) can be calculated based on aromatic hard segments = 100% - mass percentage of soft segments (the sum of the mass percentages of polyamide soft segments and multibranched soft segments), or it can be calculated based on the mass percentage of the total mass of raw materials introduced into each aromatic hard segment in the total mass of raw materials added during the synthesis of polyimide binders.

[0180] In this embodiment, the polyimide binder includes a polyimide binder. Other components, such as antioxidants and buffers, can be added to the polyimide binder in this embodiment to improve its performance; the choice can be made according to actual conditions. Specifically, the prepared polyimide binder can be directly applied to the preparation of electrode slurry, or it can be purified by precipitation in solvents such as water, ethanol, or methanol before being applied to the preparation of electrode slurry.

[0181] In some embodiments, the molar ratio of diisocyanate to initiator is greater than 2:1 (the molar ratio of diisocyanate to initiator is basically equal to the molar ratio of diisocyanate to polyamide precursor), that is, the ratio of the sum of the amounts of the first diisocyanate and the second diisocyanate to the amount of the initiator is greater than 2:1, for example (3 to 50):1, such as 3:1, 5:1, 10:1, 20:1, 30:1, 40:1, 50:1 or any combination thereof, specifically (3 to 10):1, which is beneficial to obtaining polyimide binders with better adhesion, flexibility and long-term stability, and is beneficial to improving the cycle life and other performance of the battery.

[0182] In this embodiment, the anhydride monomer may include a diacid anhydride monomer, and the first aromatic hard segment formed specifically has the structure shown in Formula I.

[0183] Specifically, the dianhydride monomer may include a dianhydride monomer having the structure shown in Formula X:

[0184] In some specific implementations, the dianhydride monomer includes, but is not limited to, one or more compounds represented by formulas X-1 to X-9.

[0185] In one specific embodiment, the dianhydride monomer may include p-biphenyl dicarboxylic anhydride having a structure as shown in Formula X-10:

[0186] In this embodiment, the anhydride monomer provides a first aromatic hard segment structure for the polyimide binder, which gives the polyimide binder better mechanical properties, thereby giving the electrode sheet better mechanical properties. This allows the electrode sheet to maintain structural integrity during battery operation, which is beneficial for improving the battery's cycle life and other performance characteristics.

[0187] In the above method for preparing the polyimide adhesive, the temperature of the first polymerization reaction is 40–120°C, and the time is 3–12 h. For example, the temperature of the first polymerization reaction is, for example, a range of 40°C, 60°C, 80°C, 100°C, 120°C, or any combination thereof; the time of the first polymerization reaction is, for example, a range of 3 h, 6 h, 9 h, 12 h, or any combination thereof.

[0188] In some embodiments, the process of a second polymerization reaction between the polyamide precursor and the multibranched monomer and the anhydride monomer includes: reacting the polyamide precursor with diisocyanate and the multibranched monomer, then adding the anhydride monomer, and then carrying out the second polymerization reaction to generate a polyimide binder. The embodiments of this application can prepare a polyimide binder with better mechanical properties and anti-swelling properties through the above preparation process, which is beneficial for further improving the cycle life and other performance characteristics of the battery.

[0189] In one specific embodiment, the temperature of the second polymerization reaction is 100–180°C, and the time is 1–15 h. For example, the temperature of the second polymerization reaction is, for example, a range of 100°C, 120°C, 140°C, 160°C, 180°C, or any combination thereof; the time of the second polymerization reaction is, for example, a range of 1 h, 3 h, 6 h, 9 h, 12 h, 15 h, or any combination thereof.

[0190] In some embodiments, the initiator includes at least one of a glycol initiator and a diamine initiator. It should be noted that regardless of whether a glycol initiator or a diamine initiator is used, the resulting polyamide precursor with amino-terminated segments will have amino groups as end groups.

[0191] 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.

[0192] 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.

[0193] 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).

[0194] In some embodiments, the molar ratio of diisocyanate to initiator is (1 to 100):1, and the molar ratio of diisocyanate to initiator is, for example, 1:1, 2:1, 10:1, 20:1, 30:1, 40:1, 60:1, 80:1, 100:1 or any combination thereof.

[0195] In one specific embodiment, the molar ratio of amide monomer to initiator is (5-5000):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 between any two of these ranges, specifically (5-40):1.

[0196] In one specific embodiment, the molar ratio of the branched monomer to the initiator is (5 to 40):1. For example, the molar ratio of the branched monomer to the initiator is, for example, a range of 5:1, 10:1, 20:1, 30:1, 40:1, or any two of these.

[0197] In one specific embodiment, the molar ratio of the anhydride monomer to the initiator is (1 to 20):1. For example, the molar ratio of the anhydride monomer to the initiator is, for example, 1:1, 5:1, 2:1, 15:1, 20:1, or any combination thereof.

[0198] Furthermore, in the embodiments of this application, the number of repeating units of amide groups in the polyamide soft segment (e.g., x in Formula II, y in Formula III) can be controlled by adjusting conditions such as the molar ratio of the initiator to the amide monomer.

[0199] 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.

[0200] 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.

[0201] 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.

[0202] 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.

[0203] 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.

[0204] 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.

[0205] 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.

[0206] In detail, when the electrode sheet is a positive electrode sheet, the electrode current collector is a positive electrode current collector, and the electrode coating (electrode active layer) is a positive electrode active material layer (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.

[0207] The positive electrode active material layer may include a positive electrode active material (positive electrode active material), a conductive agent, and a binder. In the positive electrode active layer, the mass percentage of the positive electrode active material can be 70% to 99%, for example, 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99%, or any combination thereof. The mass fraction of the binder can 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.

[0208] The binder for the positive electrode active 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 as the binder for the positive electrode active material layer: 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.

[0209] 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-yAl 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.

[0210] The embodiments of this application may employ conventional positive current collectors in the art, for example, positive current collectors may include aluminum foil.

[0211] 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.

[0212] 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.

[0213] In this embodiment, the binder in the negative electrode active material layer can be either the polyimide binder provided in this embodiment or a combination of any binder suitable for negative electrodes known in the art. For example, at least one of the following can be used together with the polyimide binder in the preparation of the negative electrode active material layer: 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), carboxymethyl cellulose, styrene-butadiene latex, nitrile rubber, and polyacrylic acid (PAA).

[0214] 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.

[0215] In addition, the negative electrode active material layer also includes a negative electrode active material. 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%, for example, 80%, 82%, 85%, 88%, 90%, 92%, 95%, 98%, 100%, or any combination thereof.

[0216] 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.

[0217] In the embodiments of this application, the negative electrode sheet can be prepared by a dry process (i.e., the material used to form the negative electrode active layer is rolled into a film and then combined with the negative electrode current collector to obtain the negative electrode sheet), or by a wet process (coating method) (i.e., the negative electrode slurry used to form the negative electrode active layer is coated on the surface of the negative electrode current collector, and then dried, rolled and other processes are performed to form the negative electrode active layer on the surface of the negative electrode sheet to obtain the negative electrode sheet).

[0218] This application provides a battery including the electrode sheet provided in the third aspect of this application. This battery has advantages corresponding to the polyimide binder described above, which will not be elaborated further.

[0219] 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.

[0220] 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.

[0221] 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.

[0222] 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.

[0223] 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.

[0224] Furthermore, this application does not specifically limit the type of battery. In some embodiments, the battery may be a lithium-ion battery or a sodium-ion battery.

[0225] When the battery is a sodium-ion battery, the positive electrode active material includes, but is not limited to, one or a combination of transition metal oxides, polyanionic compounds, organic polymers, and Prussian blue materials.

[0226] 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.

[0227] Generally, a battery pack comprises multiple batteries as described above, which are connected as individual cells 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.

[0228] 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.

[0229] 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.

[0230] The technical solution of this application will be further described below with reference to specific embodiments.

[0231] Example 1

[0232] As shown in Figure 1, the preparation process of the polyimide adhesive in this embodiment is as follows (Figures 2, 3, 4, and 5 show the preparation process of the polyimide adhesive).

[0233] The diisocyanate was mixed evenly and heated to 80℃ for 8 hours to obtain isocyanate-terminated polyamide and isocyanate-terminated multibranched soft segment. After addition reaction, a polyimide binder precursor was obtained.

[0234] 3) Add 1.5 mol of terephthalic anhydride monomer to the above system and heat to 50°C to carry out the second polymerization reaction for 9 hours. At the same time, carbon dioxide is removed from the system to obtain polyimide binder, which is then used as polyimide binder for later use.

[0235] In Figure 1, R6 is a polymer formed by the ring-opening polymerization of N-methylcaprolactam. After the first polymerization reaction, this polymer forms a polyamide precursor with amino-terminated segments. z is the number of repeating units of R6.

[0236] The structural formula of the polyimide adhesive prepared in this embodiment is shown in Figure 6.

[0237] The preparation process of the positive electrode sheet in this embodiment is as follows:

[0238] 1) Lithium iron phosphate, carbon black, the above-mentioned polyimide binder, and NMP are mixed in a mass ratio of 100:2.0:1.0:52 and stirred for 1 hour to obtain a positive electrode slurry. 2) The above positive electrode slurry is coated onto the surface of aluminum foil, 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 surface density of the positive electrode active material layer on one side is 200 g / m³. 2 .

[0239] The battery manufacturing process in this embodiment is as follows:

[0240] 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, they are ready for use.

[0241] Example 2: This example is basically the same as Example 1, except that the amount of N-methylcaprolactam monomer added in this example is 1 mol, the amount of aliphatic diamine is 0.1 mol, the amount of p-phenyl diisocyanate is 0.5 mol, and the amount of terephthalic anhydride monomer is 0.5 mol.

[0242] Example 3: This example is basically the same as Example 1, except that the amount of N-methylcaprolactam monomer added in this example is 1.5 mol, aliphatic diamine is 0.05 mol, p-phenyl diisocyanate is 0.5 mol, and terephthalic anhydride monomer is 0.5 mol.

[0243] Example 4: This example is basically the same as Example 1, except that the amount of N-methylcaprolactam monomer added in this example is 60 mol, aliphatic diamine is 0.2 mol, p-phenyl diisocyanate is 3 mol, and terephthalic anhydride monomer is 3 mol.

[0244] Example 5: This example is basically the same as Example 1, except that the amount of N-methylcaprolactam monomer added in this example is 0.2 mol, aliphatic diamine is 0.5 mol, p-phenyl diisocyanate is 0.5 mol, and terephthalic anhydride monomer is 0.5 mol.

[0245] Example 6: This example is basically the same as Example 1, except that the amount of N-methylcaprolactam monomer added in this example is 5 mol, the amount of aliphatic diamine is 2 mol, the amount of p-phenyl diisocyanate is 1.5 mol, and the amount of terephthalic anhydride monomer is 1.5 mol.

[0246] Example 7: This example is basically the same as Example 1, except that the aliphatic diamine added in this example has the structural formula of n-octadecanediamine.

[0247] Example 8: This example is basically the same as Example 1, except that the diisocyanate used in this example is n-hexyl diisocyanate.

[0248] Example 9: This example is basically the same as Example 1, except that the diisocyanate used in this example is 1,2-cyclohexyl diisocyanate.

[0249] Examples 10 to 17: 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.

[0250] Example 18: This example is basically the same as Example 1, except that the structural formula of the amide monomer used in this example is:

[0251] Example 19: This example is basically the same as Example 1, except that the amount of N-methylcaprolactam monomer added in this example is 0.7 mol.

[0252] Example 20: This example is basically the same as Example 1, except that the amount of N-methylcaprolactam monomer added in this example is 60 mol.

[0253] Example 21: This example is basically the same as Example 1, except that the amount of N-methylcaprolactam monomer added in this example is 4 mol, and the amount of aliphatic diamine added is 12.5 mol.

[0254] Example 22: This example is basically the same as Example 1, except that the amount of terephthalic anhydride monomer added in this example is 1 mol, and the amount of aliphatic diamine added is 13 mol.

[0255] Example 23: This example is basically the same as Example 1, except that the aliphatic diamine added in this example is 30 mol.

[0256] Example 24: This example is basically the same as Example 1, except that the acid anhydride monomer added in this example is p-biphenyl dicarboxylic anhydride, and the diisocyanate added is p-biphenyl diisocyanate.

[0257] Comparative Example 1

[0258] Preparation of ester-modified polyimide adhesive:

[0259] 1) Add 62g of ethylene glycol initiator and 1.14kg of caprolactone monomer to 1000mL of N-methylpyrrolidone (NMP) solvent, mix thoroughly, and heat to 100℃ to obtain a hydroxyl-terminated polyamide precursor. 2) Mix the above hydroxyl-terminated polyester precursor with 480g of p-phenyl diisocyanate and heat to 80℃. 3) Add 660g of terephthalic anhydride monomer to the above system and heat to 50℃. Remove carbon dioxide from the system to obtain an ester-modified polyimide binder with a polyester content of 50wt%.

[0260] The cathode preparation process and battery assembly process are the same as in Example 1.

[0261] Comparative Example 2: The difference between this comparative example and Example 1 is that polyimide without introducing multi-branched soft segments is used as the polyimide binder for the positive electrode during the preparation of the positive electrode.

[0262] Comparative Example 3: The difference between this comparative example and Example 1 is that polyimide without polyamide soft segments is used as the polyimide binder for the positive electrode during the preparation of the positive electrode.

[0263] The molar ratios of initiator to amide monomer, diisocyanate to amide monomer, dianhydride monomer to amide monomer, aliphatic diamine to amide monomer, mass percentage of the first aromatic hard segment in polyimide (hereinafter referred to as the mass percentage of the first aromatic hard segment in Table 1), and mass percentage of the second aromatic hard segment in polyimide (hereinafter referred to as the mass percentage of the second aromatic hard segment in Table 1) for each embodiment and comparative example are shown in Table 1; the mass percentage of the polyamide soft segment in polyimide (hereinafter referred to as the mass percentage of the polyamide soft segment in Table 2), and the mass percentage of the polyamide soft segment in polyimide are also shown in Table 2. The mass percentage of branched soft segments in polyimide (referred to as the mass percentage of multi-branched soft segments in Table 2), the total mass of polyamide soft segments and multi-branched soft segments as a percentage of the mass of polyimide binder (referred to as the mass percentage of soft segments in Table 2), the number average molecular weight of the polyamide binder, the ratio of the weight average molecular weight to the number average molecular weight of the polyamide binder, and the area of ​​the NMR characteristic peak of the alkyl soft chain are shown in Table 2. The anhydride monomers, amide monomers, aliphatic diamines, diisocyanates, x values ​​in Formula II or y values ​​in Formula III used in each example and comparative example are shown in Table 3.

[0264] The mass percentage of polyamide soft segments in polyimide binders is calculated as follows: Mass percentage of polyamide soft segments = Mass of amide monomer / (Mass of amide monomer + Mass of initiator + Mass of diisocyanate + Mass of anhydride monomer + Mass of aliphatic diamine); The mass percentage of the first aromatic hard segment is calculated as follows: Mass percentage of the first aromatic hard segment = Mass of anhydride monomer / (Mass of amide monomer + Mass of initiator + Mass of diisocyanate + Mass of anhydride monomer + Mass of aliphatic diamine); The mass percentage of the second aromatic hard segment is calculated as follows: Mass percentage of the second aromatic hard segment = Mass of diisocyanate / (Mass of amide monomer + Mass of initiator + Mass of diisocyanate + Mass of anhydride monomer + Mass of aliphatic diamine); The mass percentage of the multibranched soft segments is calculated as follows: Mass percentage of the multibranched soft segments = Mass of aliphatic diamine / (Mass of amide monomer + Mass of initiator + Mass of diisocyanate + Mass of anhydride monomer + Mass of aliphatic diamine).

[0265] Test case

[0266] Number-average molecular weight determination 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) using N-methylpyrrolidone as the mobile phase. The test temperature was 50℃. The obtained curve was calibrated with polystyrene of known molecular weight to obtain the corresponding molecular weight and its distribution (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.

[0267] Electrode flexibility: The rolled positive electrode sheet was cut into 30mm*100mm 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 4.

[0268] Electrode peel strength: Unrolled positive electrode sheets were cut into 40*100mm pieces, and adhesive tape was applied to the surface before rolling them three times with a roller mill at a speed 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 sheet). The machine speed was 50mm / min. Each sample was tested three times. After each peel, the peel force trend remained unchanged, 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 4.

[0269] Battery cycle capacity retention test: After assembling the battery, constant current charge and discharge was performed at room temperature at a charge / discharge rate of 1C / 1C within a voltage window of 2.0 to 3.8V: (1) Following this cycle process, 200 cycles were performed. The ratio of the battery discharge capacity after 200 cycles to the initial capacity is the battery capacity retention rate after 200 cycles; (2) Following this cycle process, 500 cycles were performed. The ratio of the battery discharge capacity after 500 cycles to the initial capacity is the battery capacity retention rate after 500 cycles. The test results are shown in Table 4.

[0270] 1H NMR spectrum: Take 5mg of solid sample (polyimide binder), dissolve it in 1ml of deuterated dimethyl sulfoxide, and test the 600M 1H NMR spectrum at room temperature.

[0271] As can be seen from the 1H NMR spectrum, the polyimide adhesive in the embodiments of this application has absorption peaks in the chemical shift range of 2.5ppm to 3.52ppm, 6.0ppm to 9.0ppm, and 0.8ppm to 1.2ppm.

[0272] Positive electrode swelling rate test:

[0273] 1. Sample preparation

[0274] Sampling: Cut the positive electrode to be tested into a circular piece with a diameter of 3cm.

[0275] Initial thickness measurement: Use a micrometer or thickness gauge to measure the initial thickness of the positive electrode (circular sheet). Take measurements at at least 3 different locations and take the average value to obtain the initial thickness H0.

[0276] 2. Soaking in electrolyte

[0277] Completely immerse the positive electrode (circular plate) in the electrolyte (1M LiPF6-EC / DMC (1:1 vol%)) (avoiding air bubbles) and soak at 60°C for 3 days. During the soaking process, use a sealed container to prevent the electrolyte from evaporating.

[0278] 3. Post-processing and measurement

[0279] After soaking, remove the positive electrode (circular plate) with tweezers, quickly blot away any residual electrolyte on the surface with filter paper, and immediately measure the thickness of the positive electrode (circular plate) after swelling. Take the average value from multiple locations to obtain the thickness H1 after swelling. Therefore, the swelling ratio of the positive electrode is H0 / H1.

[0280] Table 1

[0281] Table 2

[0282] Table 3

[0283] Table 4

[0284] As shown in the table, compared with Comparative Examples 1-3, Examples 1 to 24, by simultaneously introducing aromatic hardness, polyamide soft segments and multi-branched soft segments into the polyimide binder, can simultaneously improve the adhesion, flexibility, swelling resistance and processability of the polyimide binder when used in electrode sheet preparation, thereby improving the cycle life of the battery.

Claims

1. A polyimide binder, wherein, The polyimide binder includes aromatic hard segments, polyamide soft segments, and multibranched soft segments.

2. The polyimide adhesive according to claim 1, wherein, The multi-branched soft segment comprises a structure as shown in the following formula XIII-1: Among them, R7, R8, R9, R 10 R 11 R 12 Each is independently selected from straight-chain alkyl groups or branched alkyl groups having 1 to 18 carbon atoms; And / or, the total number of carbon atoms in the multibranched soft segments is 6 to 72, preferably 32 to 36.

3. The polyimide adhesive according to claim 1 or 2, wherein, The polyamide soft segments comprise structures according to formula II and / or formula III 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 3 carbon atoms or branched alkyl groups; preferably, y is an integer from 5 to 100.

4. The polyimide adhesive according to any one of claims 1-3, wherein, The aromatic hard segment includes a first aromatic hard segment, which has the structure shown in Formula I: R1 is selected from aryl groups with or without first substitution or biaryl groups with or without first substitution; Preferably, the first substituted or unsubstituted aryl group is selected from phenyl or naphthyl; Preferably, the first substituted or unsubstituted biaryl group comprises a first substituted or unsubstituted biphenyl group; more preferably, the first substituted or unsubstituted biphenyl group has one or more of the groups represented by Formula V: R 13 and R 14 Each independently represents a monosubstituted to the maximum permissible substituent, and R 13 and R 14 Each is independently selected from hydrogen, substituted or unsubstituted alkyl, or carboxyl; L2 is selected from one or more of single bond, substituted or unsubstituted alkyl, carbonyl, ester, oxygen, sulfone, and amide.

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

6. The polyimide adhesive according to claim 4 or 5, wherein, The polyimide adhesive includes a first connecting segment, which has a structure as shown in Formula IY: L1 is selected from aryl groups that are third-substituted or unsubstituted, biaryl groups that are third-substituted or unsubstituted, or alkyl groups that are substituted or unsubstituted. The * represents the connection site between formula IY and the multibranched soft segment, and the * represents the connection site between formula IY and the first aromatic hard segment.

7. The polyimide adhesive according to claim 4 or 5, wherein, The polyimide adhesive includes a second connecting segment, which has the structure shown in Formula IV: L1 is selected from aryl groups that are third-substituted or unsubstituted, biaryl groups that are third-substituted or unsubstituted, or alkyl groups that are substituted or unsubstituted. The symbol represents the connection site between Formula IV and the polymeric segment of the polyamide soft segment, and * represents the connection site between Formula IV and the first aromatic hard segment.

8. The polyimide adhesive according to any one of claims 1-7, wherein, The aromatic hard segment further includes a second aromatic hard segment, the second aromatic hard segment being selected from a second substituted or unsubstituted aryl group or a second substituted or unsubstituted biaryl group; Preferably, the second substituted or unsubstituted arylphenyl, naphthyl, benzoic acid, naphtholic acid is one or more of these groups; Preferably, the second substituted or unsubstituted biaryl group comprises a second substituted or unsubstituted biphenyl group; preferably, the second substituted or unsubstituted biphenyl group has one or more of the groups shown in Formula XI: R 15 and R 16 Each independently represents a monosubstituted to the maximum permissible substituent, and R 15 and R 16 Each group is independently selected from hydrogen, substituted or unsubstituted alkyl groups, or carboxyl groups; L3 is selected from one or more of single bonds, substituted or unsubstituted alkyl groups, carbonyl groups, ester groups, oxygen groups, sulfone groups, and amide groups.

9. The polyimide adhesive according to claim 8, wherein, The second aromatic hard segment is selected from the structures shown in formulas XI-1 to XI-16 below:

10. The polyimide adhesive according to any one of claims 1-9, wherein, The sum of the mass of the polyamide soft segments and the multibranched soft segments accounts for 20% to 80% of the mass of the polyimide adhesive, preferably 25% to 45%. And / or, the polyamide soft segment in the polyimide binder has a mass percentage of 10% to 70%, preferably 20% to 40%; And / or, the multibranched soft segments in the polyimide adhesive have a mass percentage of 10% to 70%, preferably 10% to 40%.

11. The polyimide adhesive according to any one of claims 1-10, 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 1.5 to 5, more preferably 2.3 to 2.

8.

12. The adhesive according to any one of claims 1-10, wherein, The proton NMR spectrum of the polyimide adhesive includes absorption peaks in the chemical shift range of 2.5 ppm to 3.52 ppm, 6.0 ppm to 9.0 ppm, and 0.8 ppm to 1.2 ppm.

13. A method for preparing the polyimide adhesive according to any one of claims 1-12, wherein, Includes the following steps: The amide monomer is subjected to a first polymerization reaction to obtain a polyamide precursor; The polyamide precursor, multibranched monomer, 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.

14. The method for preparing the polyimide adhesive according to claim 13, wherein, The diisocyanate comprises a first diisocyanate and a second diisocyanate, the first diisocyanate having the structure shown in Formula IA: OCN-L1-NCO Formula IA In the formula IA, L1 is selected from a third-substituted or unsubstituted aryl group, a third-substituted or unsubstituted biaryl group, or a substituted or unsubstituted alkyl group; The second diisocyanate has the structure shown in Formula IB: OCN-L4-NCO type IB In the formula IB, L4 is selected from a second substituted or unsubstituted aryl group or a second substituted or unsubstituted biaryl group; The process of carrying out a second polymerization reaction of the polyamide segment precursor, the multibranched monomer, the diisocyanate and the anhydride monomer includes: performing an addition reaction between the polyamide segment precursor, the multibranched monomer and the first diisocyanate to obtain a polyamide soft segment precursor and a multibranched soft segment precursor. The polyamide soft segment precursor, the multibranched soft segment precursor, the second diisocyanate, and the anhydride monomer are subjected to the second polymerization reaction to obtain the polyimide binder; preferably, the addition reaction is carried out at a temperature of 70-90°C for a time of 2-20 min.

15. The method for preparing the polyimide adhesive according to claim 14, wherein, The first diisocyanate is the same as the second diisocyanate. The process of carrying out the second polymerization reaction of the polyamide segment precursor, the multibranched monomer, the diisocyanate and the anhydride monomer includes: carrying out an addition reaction of the polyamide segment precursor, the multibranched monomer and the diisocyanate to obtain a polyamide soft segment precursor and a multibranched soft segment precursor; and then adding the anhydride monomer thereto to carry out the second polymerization reaction to obtain the polyimide binder.

16. The method for preparing the polyimide adhesive according to any one of claims 13-15, wherein, The amide monomer includes a cyclic amide monomer, preferably a lactam and / or a cycloamide; And / or, the multibranched monomer includes an aliphatic diamine; And / or, the anhydride monomer includes a dianhydride monomer; And / or, the temperature of the first polymerization reaction is 40–120°C, and the time is 3–12 h; And / or, the temperature of the second polymerization reaction is 100–180°C, and the time is 1–15 h.

17. The method for preparing the polyimide adhesive according to any one of claims 13-16, wherein, The amide 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 diisocyanate to the initiator is (1-100):1; And / or, the molar ratio of the amide monomer to the initiator is (5-5000):1, preferably (5-40):1; And / or, the molar ratio of the multibranched monomer to the initiator is (5-40):1; And / or, the molar ratio of the anhydride monomer to the initiator is (1-20):

1.

18. An electrode sheet, wherein, The electrode coating includes the polyimide binder according to any one of claims 1-12, or the polyimide binder prepared according to the preparation method of the polyimide binder according to any one of claims 13-17.

19. The electrode sheet according to claim 18, wherein, The electrode sheet includes a positive electrode sheet.

20. A battery, wherein, Includes the electrode sheet as described in claim 18 or 19.

21. A battery pack, wherein, It includes at least two batteries as described in claim 20 that are interconnected.

22. An electrical appliance, wherein, Includes the battery of claim 20 or the battery pack of claim 21.

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