A polyimide binder and its preparation method, electrode sheet, battery and electrical device thereof

Abstract

This application provides a polyimide binder and its preparation method, electrode sheet, battery, and electrical device. The polyimide binder includes polyacrylonitrile soft segments and aromatic hard segments. This polyimide binder not only overcomes the problems of poor environmental friendliness and poor electrode flexibility caused by traditional binders, but also solves the problem of poor binder stability caused by ester groups as functional groups of binders by introducing polyacrylonitrile soft segments. This effectively improves the electrochemical and chemical stability of polyimide binders, thereby enabling the battery to maintain stable performance during long-term cycling.

Description

Technical Field

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

[0002] Electrode sheets, as key components in batteries, are divided into positive and negative electrodes, mainly composed of current collectors and coatings. During electrode fabrication, binders are typically introduced. Their main functions include stabilizing the electrode structure, preventing active material shedding, and optimizing characteristics such as electrode peel strength and slurry stability, thereby improving the overall battery performance, such as rate performance and safety.

[0003] Traditional binders (such as PVDF) have good bonding properties, but they suffer from poor environmental performance and insufficient flexibility, leading to electrode brittleness and severely affecting battery life. Currently, introducing ester segments into polyimide not only overcomes the environmental problems of traditional binders but also effectively improves their flexibility.

[0004] However, due to the insufficient electrochemical and chemical stability of the ester groups in this type of binder, the cycle performance of the battery still falls short of expectations. Summary of the Invention

[0005] This application provides a polyimide binder that, through its special structural composition, effectively improves the cycle performance of the battery while ensuring the environmental friendliness of the binder and the flexibility of the electrode sheet.

[0006] This application also provides a method for preparing a polyimide adhesive, used to prepare the above-mentioned polyimide adhesive.

[0007] This application also provides an electrode sheet comprising the above-mentioned polyimide binder, which has the advantages of good flexibility and high stability, and can effectively improve the cycle performance of the battery.

[0008] This application also provides a battery comprising the aforementioned polyimide binder, thus having the advantage of stable cycle performance.

[0009] This application also provides an electrical device including the aforementioned battery, which thus has the advantage of a long standby time.

[0010] This application provides a polyimide adhesive comprising a polyacrylonitrile soft segments and aromatic hard segments.

[0011] The polyimide adhesive described above, wherein the polyacrylonitrile soft segment comprises the structure shown in Formula I and / or Formula II:

[0012] Formula I Formula II

[0013] In Formula I and Formula II, * denotes the connection site between the shown structure and the aromatic hard segment; in Formula I, m is the number of cyano-substituted -(CH2)2- in the polyacrylonitrile soft segment, and n is the number of -(CH2)2-; in Formula II, p, n, and q are each independently the number of methylene groups, o is the number of methine groups, and m is the number of methine groups substituted with cyano groups; in Formula I and Formula II, m is selected from integers between 1 and 50, n is selected from integers between 0 and 100, and o, p, and q are each independently selected from integers between 0 and 50.

[0014] The polyimide adhesive described above has a polyacrylonitrile soft segment content of 10% to 90% by mass, preferably 25% to 70%.

[0015] The polyimide adhesive described above, wherein the aromatic hard segment includes a first aromatic hard segment having the structure shown in Formula III:

[0016] Formula III

[0017] R1 is selected from aryl groups with or without first substitution or biaryl groups with or without first substitution;

[0018] Preferably, the first substituted or unsubstituted aryl group is selected from phenyl or naphthyl;

[0019] 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 the structure shown in Formula IV:

[0020] Formula IV

[0021] 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.

[0022] In the polyimide adhesive described above, the first aromatic hard segment is selected from the structures shown in Formulas I-1 to I-9:

[0023] .

[0024] The polyimide adhesive described above includes a first connecting segment comprising a structure shown in Formula IY:

[0025] Formula IY

[0026] In the formula IY, 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, and L5 is selected from one of an oxygen atom, a nitrogen atom, a sulfur atom, and an ester group. The symbol IY represents the connection site between the polyacrylonitrile soft segment and the symbol * represents the connection site between the polyacrylonitrile soft segment and the first aromatic hard segment.

[0027] The polyimide binder described above further includes a second aromatic hard segment, wherein the second aromatic hard segment is selected from a second substituted or unsubstituted aryl group or a second substituted or unsubstituted biaryl group; preferably, the second substituted or unsubstituted aryl group is selected from one or more of phenyl, naphthyl, benzoic acid, and naphtholic acid; preferably, the second substituted or unsubstituted biaryl group comprises a second substituted or unsubstituted biphenyl; preferably, the second substituted or unsubstituted biphenyl has the structure shown in Formula XI:

[0028] Formula XI

[0029] 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.

[0030] In the polyimide adhesive described above, the second aromatic hard segment is selected from the structures shown in Formulas XI-1 to XI-16 below:

[0031] .

[0032] The polyimide adhesive described above has a weight-average molecular weight of 10 kDa to 1000 kDa, preferably 100 kDa to 600 kDa; and / or, the Fourier transform infrared spectrum of the polyimide adhesive is in the range of 3000 to 3700 cm⁻¹. -1 It contains the first characteristic peak, located at 2200–2300 cm⁻¹. -1 The first characteristic peak has a second characteristic peak, and the ratio of the peak area of ​​the first characteristic peak to the second characteristic peak is 0.3 to 4; and / or, the 1H NMR spectrum of the polyimide adhesive has a third characteristic peak in the range of 6.0 to 10.0 ppm and a fourth characteristic peak in the range of 2.2 to 4.5 ppm, and the ratio of the peak area of ​​the third characteristic peak to the fourth characteristic peak is 0.1 to 5.

[0033] This application also provides a method for preparing the polyimide adhesive according to any one of the above claims, comprising the following steps: polymerizing a polyacrylonitrile precursor with a diisocyanate and an anhydride monomer to obtain the polyimide adhesive; wherein at least one of the diisocyanate and the anhydride monomer contains an aryl group.

[0034] The preparation method described above, 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, wherein 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: The polymerization reaction is of formula IB, wherein L4 is selected from a second substituted or unsubstituted aryl group or a second substituted or unsubstituted biaryl group; and / or, the polyacrylonitrile precursor comprises a nitrile compound containing a capping group, wherein the capping group comprises at least one of a hydroxyl, amino, mercapto, and carboxyl group; and / or, the anhydride monomer comprises a diacid anhydride monomer; and / or, the polymerization reaction is carried out at a temperature of 100°C to 180°C for a time of 1 h to 24 h.

[0035] The preparation method described above includes the following steps: performing an addition reaction between the polyacrylonitrile precursor and the first diisocyanate to obtain a polyacrylonitrile soft segment precursor; and then performing the polymerization reaction between the polyacrylonitrile soft segment precursor, the second diisocyanate, and the anhydride monomer to obtain the polyimide binder.

[0036] This application also provides an electrode sheet, including an electrode coating, the electrode coating comprising the polyimide binder described in any one of the preceding claims, or the polyimide binder obtained according to the preparation method described in any one of the preceding claims.

[0037] This application also provides a battery including the electrode sheets described above.

[0038] This application also provides an electrical device, including the battery described above.

[0039] The polyimide binder provided in this application, by combining polyacrylonitrile soft segments and aromatic hard segments, not only overcomes the problems of poor environmental friendliness and poor electrode flexibility of traditional binders, but also solves the problem of poor binder stability caused by ester groups as functional groups of binders by introducing polyacrylonitrile soft segments. This effectively improves the electrochemical and chemical stability of polyimide binders, thereby enabling the battery to maintain stable performance during long-term cycling. Attached Figure Description

[0040] Figure 1This is a schematic diagram illustrating the preparation process of the polyimide adhesive provided in this application. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0042] In the description of this application, unless otherwise expressly specified and limited, terms such as "first" and "second" are used for descriptive purposes only, such as distinguishing components to more clearly illustrate / explain the technical solution, and should not be construed as indicating or implying the number of technical features indicated or the order of features of substantial significance.

[0043] Although polyimide itself possesses high stability and environmental friendliness, its rigid skeletal structure makes it difficult to meet practical requirements for the processing performance and adhesion of electrode sheets. Currently, introducing polyester segments can alleviate these problems to some extent and enhance the flexibility of the electrode sheets. However, this improvement also introduces new problems: the ester groups in the polyester segments are chemically reactive and may cause changes in electrode potential, thereby inducing material degradation and increased battery impedance, ultimately affecting the battery's cycle performance and making it difficult to achieve the expected lifespan.

[0044] After analysis, the inventors concluded that, compared to ester groups, cyano groups possess stronger chemical stability and the advantage of promoting salt dissociation. Introducing them into the polyimide structure can effectively improve the stability of the binder. Therefore, the inventors attempted to improve the cycle performance of the battery by introducing cyano groups into the polyimide structure.

[0045] Based on this, this application provides a polyimide adhesive comprising a polyacrylonitrile soft segments and aromatic hard segments.

[0046] In detail, the aromatic hard segment comprises aromatic groups and forms a rigid structure in the polyimide binder, while the polyacrylonitrile soft segment comprises multiple cyano groups and forms a flexible structure in the polyimide binder. The synergistic matching of these two components allows the polyimide binder to balance rigidity and flexibility, enabling the electrode to maintain high flexibility during battery cycling, improving the binder's resistance to swelling, and thus better adapting to volume changes in the electrolyte and active material particles.

[0047] On the other hand, the cyano group, with its strong polarity and high electronegativity, exhibits significant advantages in battery applications. Firstly, its strong dipole interaction helps form a stable interfacial layer, enabling the material to maintain excellent structural integrity and electrochemical stability during long-term cycling, and giving the battery good weather resistance. The cyano group can also effectively weaken the Coulomb force between metal salt cations and anions through coordination, thereby promoting salt dissociation, increasing the concentration of freely moving metal ions in the system, and thus improving the metal ion conductivity, effectively reducing the battery's interfacial impedance.

[0048] Therefore, introducing polyacrylonitrile soft segments and aromatic hard segments into polyimide can not only maintain the advantages of environmental friendliness and high flexibility, but also further improve the cycle performance of the battery.

[0049] In one specific embodiment, the polyacrylonitrile soft segment may include the structure shown in Formula I and / or Formula II, which is beneficial to further balance the flexibility, electrochemical stability and battery impedance of the polyimide binder, and further improve the cycle performance of the battery.

[0050] Formula I Formula II

[0051] In Formulas I and II, * indicates the connection site between the structure shown and the aromatic hard segment;

[0052] In Formula I, m is the number of -(CH2)2- substituents with cyano groups in the polyacrylonitrile soft segment, and n is the number of -(CH2)2- substituents; in Formula II, p, n, and q are each independently the number of methylene groups, o is the number of methine groups, and m is the number of methine groups substituted with cyano groups.

[0053] In Equations I and II, m is selected from integers between 1 and 50, n is selected from integers between 0 and 100, and o, p, and q are each independently selected from integers between 0 and 50.

[0054] In Equations I and II, m is selected from integers between 1 and 50, n is selected from integers between 0 and 100, and o, p, and q are each independently selected from integers between 0 and 50.

[0055] The value of m also determines the number of cyano groups in the polyacrylonitrile soft segment. When m is controlled within the above range, it is also beneficial to introduce suitable cyano groups into the polyimide binder, thereby effectively reducing the risk of reduced electrode peel force caused by excessive cyano groups and further improving the cycle stability of the electrode.

[0056] In the embodiments of this application, m can be one of 1, 3, 6, 12, n can be one of 1, 10, 50, o can be one of 0, 12, 50, p can be one of 0, 3, 5, and q can be one of 0, 1, 3.

[0057] Furthermore, when the mass percentage of polyacrylonitrile soft segments is 10% to 90%, it is beneficial to further improve the flexibility, electrochemical stability, and battery impedance of the imide binder. Preferably, the mass percentage of polyacrylonitrile soft segments in the polyimide binder is 25% to 70%.

[0058] In one specific embodiment, the aromatic hard segment includes a first aromatic hard segment having the structure shown in Formula III, which is beneficial to further improve the compatibility with the polyacrylonitrile soft segment, thereby further improving the mechanical properties and processing properties of the polyimide binder.

[0059] Formula III

[0060] R1 is selected from aryl groups with or without first substitution or biaryl groups with or without first substitution;

[0061] Specifically, the first substituted or unsubstituted aryl group is selected from phenyl or naphthyl, and the first substituted or unsubstituted biaryl group includes the first substituted or unsubstituted biphenyl group; preferably, the first substituted or unsubstituted biphenyl group has the structure shown in Formula IV:

[0062] Formula IV

[0063] 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.

[0064] In detail, monosubstitution to the maximum permissible substituent refers to R in formula IV. 13 and R 14 Each can be independently attached to one or more attachment sites on its respective benzene ring, such as 1, 2, 3 or 4.

[0065] 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, n-hexyl, etc.; when L2 is a carbonyl group, it includes, but is not limited to, aldehyde and ketone groups, etc.; when L2 is an ester group, it includes, but is not limited to, methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, etc.; when L2 is a sulfone group, it includes, but is not limited to, dimethylsulfone, diethylsulfone, methylethylsulfone, etc.; when L2 is an amide group, it includes, but is not limited to, carbamoyl, acetamido, N-methylcarbamoyl, N,N-dimethylcarbamoyl, etc. Furthermore, any one or more hydrogen atoms in L2 can be replaced by halogen atoms, such as fluorine atoms. For example, when L2 is a substituted alkyl group, it can specifically be an isopropyl group in which both hydrogen atoms of the methyl group are replaced by fluorine atoms.

[0066] Furthermore, when the first aromatic hard segment is selected from the structures shown in Formulas I-1 to I-9, the mechanical and processing properties of the polyimide binder are further improved.

[0067] .

[0068] Furthermore, the polyimide adhesive includes a first connecting segment, which comprises the structure shown in Formula IY:

[0069] Formula IY

[0070] In formula IY, 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, and L5 is selected from one of an oxygen atom, a nitrogen atom, a sulfur atom, and an ester group. The symbol represents the connection site between formula IY and the polyacrylonitrile soft segment, and * represents the connection site between formula IY and the first aromatic hard segment.

[0071] In detail, the structural stability at the junction of the polyacrylonitrile soft segment and the aromatic hard segment affects the overall chemical stability of the polyimide adhesive. Specifically, the first connecting segment can be located between the polyacrylonitrile soft segment and the first aromatic hard segment to make the three compatible with each other. When the first segment includes the structure shown in IY, it can further facilitate the preparation of the polyimide adhesive while maintaining the original properties of the polyimide adhesive.

[0072] Specifically, the polyimide binder is prepared from raw materials including a polyacrylonitrile precursor, for example... Figure 1 As shown, the polyimide binder can be prepared by reacting a capped polyacrylonitrile precursor with a diisocyanate via an addition reaction to generate an isocyanate-terminated (-CNO) polyacrylonitrile soft segment precursor. The polyacrylonitrile soft segment precursor is then reacted with an anhydride monomer via the isocyanate group to obtain the polyimide binder. Specifically, the reaction of the isocyanate group with the anhydride monomer forms a linking chain between the polyacrylonitrile soft segment and the first aromatic hard segment.

[0073] 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.

[0074] In one specific embodiment, the aromatic hard segment further includes a second aromatic hard segment, which is selected from a second substituted or unsubstituted aryl group or a second substituted or unsubstituted biaryl group. By introducing the second aromatic hard segment into the polyimide binder, it is more advantageous for the second aromatic hard segment to be compatible with the polyacrylonitrile soft segment in the polyimide binder, thereby further improving the flexibility and anti-swelling properties of the polyimide binder.

[0075] The second aromatic hard segment differs from the first aromatic hard segment in that it does not contain amide groups. Introducing these two aromatic hard segments into the polyimide binder allows for the formation of a more suitable rigid structure based on their combined effect, thereby further improving the adhesion, flexibility, and swelling resistance of the polyimide binder.

[0076] Furthermore, when the second substituted or unsubstituted aryl group is selected from one or more of phenyl, naphthyl, benzoic acid, and naphtholic acid, the second aromatic hard segment is more compatible with the polyacrylonitrile soft segment, further improving the flexibility and adhesion of the polyimide adhesive.

[0077] Furthermore, when the second substituted or unsubstituted biaryl group includes a second substituted or unsubstituted biphenyl group, and the second substituted or unsubstituted biphenyl group has the structure shown in Formula XI, the improvement effect on the flexibility and anti-swelling properties of the polyimide adhesive is further enhanced.

[0078] Formula XI

[0079] 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.

[0080] In detail, monosubstitution up to the maximum permissible substituent refers to R in formula XI. 15 and R 16 Each can be independently attached to one or more attachment sites on its respective benzene ring, such as 1, 2, 3 or 4.

[0081] 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, n-hexyl, etc.; when L3 is a carbonyl group, it includes, but is not limited to, aldehyde and ketone groups, etc.; when L3 is an ester group, it includes, but is not limited to, methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, etc.; when L3 is a sulfone group, it includes, but is not limited to, dimethyl sulfone, diethyl sulfone, methyl ethyl sulfone, etc.; when L3 is an amide group, it includes, but is not limited to, carbamoyl, acetamido, N-methylcarbamoyl, N,N-dimethylcarbamoyl, etc. Furthermore, any one or more hydrogen atoms in L3 can be replaced by halogen atoms, such as fluorine atoms. For example, when L3 is a substituted alkyl group, it can specifically be an isopropyl group in which both hydrogen atoms of the methyl group are replaced by fluorine atoms.

[0082] In one specific embodiment, when the second aromatic hard segment is selected from the structures shown in Formulas XI-1 to XI-16, the effect of improving the flexibility and structural stability of the polyimide binder is further enhanced.

[0083] .

[0084] For example, equation XI-1 can be the structure shown in equation XI-11 below, and equation XI-2 can be the structure shown in equation XI-21 below:

[0085] Type XI-11 Type XI-21

[0086] In one specific embodiment, the polyimide adhesive structure includes a first copolymer block of A1 and A2, and a second copolymer block of A1 and A3. A1 is a first aromatic hard segment, A2 is a polyacrylonitrile soft segment, and A3 is a second aromatic hard segment.

[0087] The ratio of the degree of polymerization of the first copolymer block to the second copolymer block is 1:1-10.

[0088] In one specific embodiment, the weight-average molecular weight of the polyimide binder is 10 kDa to 1000 kDa.

[0089] When the weight-average molecular weight of the polyimide binder is within the above range, the adhesion and flexibility of the polyimide binder are further improved, thereby effectively improving the cycle stability and service life of the battery. Preferably, the weight-average molecular weight of the polyimide binder is 100kDa~600kDa.

[0090] In one specific embodiment, the Fourier transform infrared spectrum of the polyimide adhesive is in the range of 3000~3700 cm⁻¹. -1 It contains the first characteristic peak, located at 2200–2300 cm⁻¹. -1 It contains a second characteristic peak, and the ratio of the peak area of ​​the first characteristic peak to the peak area of ​​the second characteristic peak is 0.3 to 4.

[0091] In detail, the first characteristic peak is an infrared characteristic absorption peak including the first connecting segment, and the second characteristic peak is an infrared characteristic absorption peak including the cyano group. When the peak area ratio of the two is within the above range, the polyacrylonitrile soft segment and the first connecting segment are more matched, which further optimizes the stability of the polyimide binder during battery cycling.

[0092] In one specific embodiment, the 1H NMR spectrum of the polyimide adhesive has a third characteristic peak in the range of 6.0 to 10.0 ppm and a fourth characteristic peak in the range of 2.2 to 4.5 ppm, with the peak area ratio of the third characteristic peak to the fourth characteristic peak being 0.1 to 5.

[0093] In detail, the solvent for the 1H NMR spectrum of this application is deuterated DMSO. The third characteristic peak is the characteristic absorption peak of hydrogen atoms in the aromatic hard segment, and the fourth characteristic peak is the characteristic absorption peak of hydrogen atoms in the polyacrylonitrile soft segment. When the peak area ratio of the two is within the above range, the aromatic hard segment and the polyacrylonitrile soft segment are more matched, which further optimizes the stability of the polyimide binder during battery cycling.

[0094] The parameters mentioned above in this application can be measured using conventional methods in the art, such as infrared spectroscopy, nuclear magnetic resonance, and thermogravimetric analysis. When measuring the binder in the battery, the battery can be disassembled after being fully discharged, the electrode sheets separated, and the electrode coating scraped off. The electrode coating is then crushed into powder, dispersed in a solvent, filtered, and centrifuged until the solvent evaporates completely. The collected product is the polyimide binder, which is then measured using the aforementioned conventional methods. The solvent used can be a conventional solvent, as long as it can dissolve the polyimide binder and facilitate its separation from the electrode coating powder. In specific implementations, the solvent may include N-methylpyrrolidone (NMP).

[0095] This application also provides a method for preparing the aforementioned polyimide adhesive, comprising the following steps:

[0096] A polyacrylonitrile precursor is polymerized with a diisocyanate and an anhydride monomer to obtain a polyimide binder; wherein at least one of the diisocyanate and the anhydride monomer contains an aryl group.

[0097] In detail, diisocyanate is a compound containing two isocyanate groups. Isocyanate-terminated groups can be introduced into polyacrylonitrile precursors. At least one of the diisocyanate and the anhydride monomer contains an aryl group, thereby introducing an aromatic hard segment into the polyimide binder. Through polymerization, the oxygen atom in the carbonyl group of the anhydride monomer is replaced by the nitrogen atom in the cyano group, removing carbon dioxide and generating the polyimide binder.

[0098] In one specific embodiment, 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, where 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;

[0099] The second diisocyanate has the structure shown in formula IB: OCN-L4-NCO formula IB, where L4 is selected from a second substituted or unsubstituted aryl group or a second substituted or unsubstituted biaryl group.

[0100] In detail, the first diisocyanate can introduce isocyanate-terminated groups into the polyacrylonitrile precursor, thereby satisfying the conditions for reaction with the acid anhydride monomer, while the second diisocyanate can react directly with the acid anhydride monomer.

[0101] Furthermore, the first diisocyanate and the second diisocyanate can be the same or different. When they are the same, that is, L1 and L4 are the same, it is more beneficial to use the same diisocyanate to prepare the polyimide binder. The first diisocyanate and the second diisocyanate can contain aryl or not contain aryl. When at least one of them contains aryl, a second aromatic hard segment can be introduced into the polyimide binder.

[0102] Specifically, the first diisocyanate may include at least one 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).

[0103] The second diisocyanate may include, but is not limited to, at least one of toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), naphthalene diisocyanate (NDI), p-phenyl diisocyanate (PPDI), and p-biphenyl diisocyanate.

[0104] In some embodiments, the diisocyanate (first diisocyanate, second diisocyanate) may comprise one or more of the diisocyanate compounds with the structures shown in formulas XII-1 to XII-16:

[0105]

[0106] In one specific embodiment, the polyacrylonitrile precursor comprises a nitrile compound containing end-capping groups, the end-capping groups including at least one of hydroxyl, amino, mercapto, and carboxyl groups.

[0107] In detail, the aforementioned nitrile compounds are polymers containing cyano groups. The end capping groups are used to control their molecular weight. The molecular weight of the polynitrile soft segment is basically equal to the molecular weight of the polynitrile precursor. Polynitrile soft segments of corresponding molecular weight can be introduced by using polynitrile precursors of corresponding molecular weight. Different end capping groups will introduce different L5 first linking segments. For example, if the end capping group is hydroxyl, then L5 is an oxygen atom.

[0108] In some embodiments, the polyacrylonitrile precursor may include one or more structures as shown in Formulas IX-I to IX-VI.

[0109] Formula IX-I Formula IX-II

[0110] Formula IX-III Formula IX-Ⅳ

[0111] Formula IX-V IX-VI

[0112] In one specific embodiment, the anhydride monomer includes a diacid anhydride monomer.

[0113] In detail, a dianhydride monomer refers to a monomeric compound containing two anhydride structures. The dianhydride monomer can have the structure shown in Formula X, and the first aromatic hard segment formed has the structure shown in Formula III.

[0114] Formula X.

[0115] In some specific embodiments, the dianhydride monomer may include one or more of the compounds shown in Formula X-1 to Formula X-9.

[0116]

[0117] Specifically, the polymerization reaction can be carried out at a temperature of 100℃ to 180℃ for a time of 1 hour to 24 hours.

[0118] The polyimide binder of this application embodiment can also be used in combination with other conventional components, such as adding antioxidants, buffers, etc., to further improve the performance of the binder material. The choice can be made according to the actual situation. In specific implementation, the prepared polyimide binder can be directly applied to the electrode slurry for preparing the electrode sheet, or the prepared polyimide binder can be purified by precipitation in solvents such as water, ethanol, or methanol before being applied to the preparation of the electrode slurry, thereby obtaining the electrode sheet.

[0119] In one specific embodiment, the first diisocyanate is different from the second diisocyanate, and the polymerization process includes: performing an addition reaction between the polyacrylonitrile precursor and the first diisocyanate to obtain a polyacrylonitrile soft segment precursor; and then performing a polymerization reaction between the polyacrylonitrile soft segment precursor, the second diisocyanate, and the anhydride monomer to obtain a polyimide binder.

[0120] In detail, such as Figure 1 As shown, the first diisocyanate undergoes addition with the polyacrylonitrile precursor to form a polyacrylonitrile soft segment precursor with isocyanate group end capping. During the polymerization reaction, the N element in the isocyanate group replaces the oxygen element in the anhydride monomer that is connected between two carbon groups. Each substitution site will correspondingly remove one molecule of carbon dioxide to generate a polyimide binder.

[0121] In another specific embodiment, the first diisocyanate is the same as the second diisocyanate, and the polymerization process includes: performing an addition reaction between the polyacrylonitrile precursor and the diisocyanate to obtain a polyacrylonitrile soft segment precursor; and then adding an anhydride monomer thereto to perform a polymerization reaction to obtain a polyimide binder.

[0122] In one specific embodiment, the temperature of the addition reaction can be 70°C to 90°C, and the reaction time can be 2 min to 20 min.

[0123] Specifically, the above reactions (addition reactions, polymerization reactions) can be carried out in a solvent, which may include organic solvents, specifically one or more of ketone solvents, amide solvents, urea solvents, furan solvents, alcohol solvents, ether solvents, and ester solvents. Ketone solvents may include N-methylpyrrolidone (NMP) and / or butanone (MEK), amide solvents may include dimethylformamide (DMF) and / or dimethylacetamide (DMAc), urea solvents may include tetramethylurea and / or 1,3-dimethyl-2-imidazolinone, furan solvents may include tetrahydrofuran (THF), alcohol solvents may include ethanol and / or isopropanol, ether solvents may include ethylene glycol monomethyl ether and / or diethylene glycol dimethyl ether, and ester solvents may include ethylene carbonate and / or propylene carbonate.

[0124] This application also provides an electrode sheet including an electrode coating, the electrode coating comprising the aforementioned polyimide binder, or a polyimide binder obtained according to the aforementioned preparation method. This electrode sheet has advantages corresponding to the aforementioned polyimide binder, which will not be elaborated further here.

[0125] The electrode sheet in this application can be either a positive electrode sheet or a negative electrode sheet. Relatively speaking, the aforementioned polyimide binder is more suitable for positive electrode systems. When applied to the positive electrode sheet of a battery, it can adapt to the volume changes that occur during charge-discharge cycles. At the same time, it is compatible with the positive electrode slurry system used to prepare the positive electrode sheet, solving problems such as poor dispersibility of conventional polyimide binders in organic solvents such as NMP. This improves the uniformity and stability of the positive electrode slurry and enhances the electrochemical performance of the positive electrode sheet.

[0126] 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, without any particular limitation.

[0127] Generally, an electrode sheet includes an electrode current collector and an electrode coating (or electrode active layer) located on at least one side of the electrode current collector. Specifically, the electrode coating may be located on only one side of the electrode current collector, or the electrode coating may be provided on both opposite sides of the electrode current collector (i.e., on both the front and back surfaces of the electrode current collector).

[0128] Generally, the electrode coating also includes electrode active material and conductive agent. In the electrode coating, the mass percentage of electrode active material can be 70% to 99%, for example, 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99% or any two of these ranges. The mass percentage of 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 two of these ranges. The mass percentage of conductive agent 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 two of these ranges.

[0129] Specifically, when the electrode sheet is a positive electrode sheet, the electrode current collector is a positive electrode current collector, the electrode coating is a positive electrode coating (or positive electrode active layer), and the electrode active material is a positive electrode active material.

[0130] The binder in the positive electrode coating can be the polyimide binder provided in the embodiments of this application, or it can be combined with other conventional binders as the binder for the positive electrode coating. Other conventional binders include one or more of the following: polyvinylidene fluoride (PVDF), polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, etc.

[0131] The positive electrode active material can be a conventional positive electrode active material in the art. For example, the positive electrode active material can include a lithium-containing active material capable of lithium ion intercalation and deintercalation. It can be a lithium-containing active material commonly used in lithium-ion batteries, such as one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, ternary materials, etc. The ternary material can include lithium nickel cobalt manganese oxide (NCM) and / or lithium nickel cobalt aluminum oxide (NCA), but is not limited thereto. In other embodiments, the positive electrode active material can also be a sodium battery positive electrode material capable of sodium ion intercalation and deintercalation. It can be a positive electrode active material commonly used in sodium-ion batteries, such as one or more of transition metal oxide sodium battery positive electrode materials and / or Prussian blue sodium battery positive electrode materials.

[0132] The embodiments of this application may employ conventional positive current collectors in the art, for example, positive current collectors may include aluminum foil.

[0133] 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.

[0134] When the electrode sheet is a negative electrode sheet, the electrode current collector is a negative electrode current collector, the electrode coating is a negative electrode coating (or negative electrode active layer), and the electrode active material is a negative electrode active material.

[0135] In this embodiment, the binder in the negative electrode coating can be the polyimide binder provided in this embodiment, or any binder known in the art suitable for the negative electrode can be used or combined. For example, the binder in the negative electrode coating may include at least one of polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), tetrafluoroethylene and its copolymers, polyvinylidene fluoride and its copolymers, polyolefins and their copolymers (e.g., polyethylene, polypropylene, polyethylene-polyethylene glycol block copolymers, etc.), polyvinyl alcohol, polyurethane, polyvinyl chloride, polyvinylpyrrolidone, nitrile rubber, polyacrylic acid (PAA), and polyacrylates (such as sodium polyacrylate).

[0136] Furthermore, the negative electrode active material can be a conventional negative electrode active material in the art; for example, the negative electrode active material may include graphite, but is not limited thereto. Embodiments of this application may employ conventional negative electrode current collectors in the art; for example, the negative electrode current collector includes copper foil.

[0137] In this embodiment, the negative electrode sheet can be prepared by conventional methods in the art, such as by coating. Specifically, the components used to form the negative electrode active layer, such as the negative electrode active material, conductive agent, and binder, can be dispersed in a solvent, such as water, specifically deionized water, to prepare a negative electrode slurry. This slurry is then coated onto the surface of the negative electrode current collector, and after drying, rolling, and other processes, the negative electrode sheet is obtained. The coating, drying, and rolling processes involved are conventional operations for preparing negative electrode sheets using the coating method, and are not particularly limited thereto.

[0138] In addition, the conductive agent in the electrode coating (positive electrode coating, negative electrode coating) can be a conventional conductive material in the art. For example, the conductive agent may include one or more of carbon black, carbon nanotubes (CNT), acetylene black, graphene, Ketjen black, and carbon fiber.

[0139] In addition, the areal density of the electrode sheet can be 50 g / m². 2 ~700g / m2 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, but not limited to this.

[0140] In this embodiment, the areal density of the electrode coating can be measured by the following process: 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 and the surface area of ​​one side of the electrode sheet sample in the thickness direction (i.e., the single-sided area of ​​the electrode sheet) S; then scrape off the electrode coating on the electrode sheet sample, and test the mass m2 of the obtained electrode current collector. Then the areal density of the electrode coating = (m1-m2) / S.

[0141] This application also provides a battery including the aforementioned electrode sheet, which has advantages corresponding to the aforementioned polyimide binder, which will not be elaborated further here.

[0142] It is worth mentioning that the battery provided in this application includes at least one of a single cell, a battery pack, and a battery module. In the embodiments of this application, the battery can be a liquid battery, specifically a lithium-ion secondary battery. The battery of this application can include the aforementioned positive electrode, or the aforementioned negative electrode, or both the aforementioned positive electrode and negative electrode.

[0143] Generally, a single battery cell 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 a positive electrode, a negative electrode, and a separator located between the positive and negative electrode. The battery cell can be a stacked cell, meaning it is composed of alternating layers of positive electrode, separator, and negative electrode; or it can be a wound cell, meaning it is composed of stacked positive electrode, separator, and negative electrode, which are then wound together.

[0144] 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.

[0145] 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, such as polypropylene membranes, and there is no particular limitation.

[0146] 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.

[0147] 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 using conventional winding process); then the cell is packaged (i.e., the cell is placed in the casing), and after conventional processes such as electrolyte injection, sealing, formation and capacity testing, a single cell is obtained.

[0148] The battery pack includes at least two of the aforementioned individual cells. Generally, a battery pack may include multiple of the aforementioned individual cells, connected together to form the battery pack. These individual cells can be electrically connected using methods conventional in the art, such as series connection, parallel connection, or a hybrid connection including both of these methods, without particular limitation.

[0149] The battery pack includes at least two of the aforementioned battery packs. Generally, the battery pack may include a combination of multiple of the aforementioned battery packs. These battery packs can be combined by series or parallel electrical connections and are usually equipped with corresponding components, such as a battery management system (BMS), thermal management device or mechanical structural components, without any particular limitation.

[0150] This application also provides an electrical device including the aforementioned battery. This electrical device has advantages corresponding to the aforementioned polyimide adhesive, which will not be elaborated further.

[0151] The electrical equipment provided in this application can be conventional electrical equipment in the field, such as power equipment (e.g., electric vehicles, electric cars), electronic 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.

[0152] The polyimide adhesive provided in this application will be described in detail below through specific embodiments.

[0153] Unless otherwise specified, the reagents, materials and instruments used in the following examples are all conventional reagents, materials and instruments in the art, and can be obtained commercially. The reagents involved can also be synthesized by conventional methods in the art.

[0154] Example 1

[0155] 1. Preparation of polyimide adhesive:

[0156] 1) Add polyacrylonitrile precursor (1,26-dihydroxyhexadecane-1,3,5-trimethylnitrile) and diisocyanate (p-phenyl diisocyanate) to N-methylpyrrolidone (NMP, solvent), mix well, and then perform an addition reaction at 80°C for 20 min.

[0157] 2) Add dianhydride monomer (pyromellitic dianhydride) to the above system, and polymerize at 120°C for 8 h to remove carbon dioxide, thereby obtaining polyimide binder.

[0158] 2. Preparation of the positive electrode:

[0159] (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 h to obtain positive electrode slurry.

[0160] (2) The above-mentioned positive electrode slurry is coated on both sides of the aluminum foil, dried and rolled to form a positive electrode coating, and then slit to obtain positive electrode sheets; wherein the areal density of the positive electrode coating is 200 g / m³. 2 .

[0161] 3. Battery manufacturing

[0162] The above-mentioned positive electrode sheet, polypropylene separator, and graphite negative electrode sheet are stacked to form a stacked battery cell. Then, after being packaged (aluminum-plastic film) and injected with electrolyte, a lithium-ion battery is obtained through sealing, formation and other processes. The electrolyte (1 M LiPF6-EC / DMC (1:1 vol%)) has the following composition: the organic solvent of the electrolyte is composed of EC and DMC mixed in a volume ratio of 1:1, and the concentration of LiPF6 in the electrolyte is 1 mol / L.

[0163] Examples 2 to 16: The difference from Example 1 is that the types of polyacrylonitrile precursors, diisocyanates, anhydride monomers, the ratios of raw materials, reaction times, and other conditions are different. Please refer to Table 1 for details. Except for the differences shown in Table 1, the other steps and conditions are the same as in Example 1.

[0164] Comparative Example 1

[0165] The binder used in this comparative example is polyvinylidene fluoride (PVDF) binder.

[0166] Comparative Example 2

[0167] The difference between this comparative example and Example 1 is that the polyimide adhesive does not contain polyacrylonitrile soft segments. The preparation process is as follows: terephthalic anhydride monomer (pyromellitic dianhydride) is added to p-phenyl diisocyanate, and after mixing, the mixture is polymerized at 150°C for 9 hours to obtain the polyimide adhesive.

[0168] Comparative Example 3

[0169] The difference between this comparative example and Example 1 is that the polyimide adhesive contains polyester soft segments but not polyacrylonitrile soft segments, and the preparation process is as follows:

[0170] (1) Add 62 g of ethylene glycol and 1.14 kg of caprolactone to N-methylpyrrolidone (solvent), mix well, and then polymerize at 100 °C for 3 h to obtain the polyester precursor;

[0171] (2) Add 640 g of 1,6-hexyl diisocyanate to the above polyester precursor system, mix well, and then perform an addition reaction at 80°C for 10 min.

[0172] (3) Add 880 g of terephthalic anhydride monomer to the above system and polymerize at 150°C for 9 h to obtain polyimide binder.

[0173] The molecular weight and distribution of the polyimide binder in each embodiment and comparative example, as well as the performance of the positive electrode and battery, were tested using the following methods. The results are shown in Tables 1 and 2.

[0174] 1. Determination of the molecular weight of polyimide binder: Polyimide binder and N-methylpyrrolidone were mixed to prepare a 2 mg / mL N-methylpyrrolidone solution. A sample was then taken and injected into a gel permeation chromatograph (Agilent PL-GPC 220) using N-methylpyrrolidone as the mobile phase at 50°C. The resulting curve was calibrated against polystyrene of known molecular weight to determine the molecular weight and distribution of the polyimide binder.

[0175] 2. Mass percentage of polyacrylonitrile soft segment: Thermogravimetric analysis of polyimide adhesive was performed, and the thermogravimetric curve showed two thermogravimetric processes. The process with the lower thermogravimetric temperature is the thermal decomposition process of polyacrylonitrile soft segment. The mass percentage of polyacrylonitrile soft segment can be determined by calculating the mass loss percentage of this stage.

[0176] 3. Ratio of the first characteristic peak to the second characteristic peak: Take 5 mg of polyimide adhesive sample, dissolve it in 1 mL of deuterated dimethyl sulfoxide, and test the 600 M 1H NMR spectrum at room temperature.

[0177] 4. Ratio of the third to the fourth characteristic peak: A 10% (w / w) N-methylpyrrolidone adhesive solution of polyimide binder was dried to a film approximately 200 μm thick. The spectral range was set to 4000-400 cm⁻¹. -1 The signal-to-noise ratio is 2 cm⁻¹ -1 The scan was performed 16 times, and Fourier transform infrared spectroscopy was conducted.

[0178] 5. Positive electrode sheet flexibility: Cut the rolled positive electrode sheet into 300mm*100mm pieces, fold it in half along the long side, press it down with a 50g weight at the edge of the long side, push the weight towards the folded side until the positive electrode sheet breaks, and record the displacement of the weight.

[0179] 6. Positive electrode peel strength: Cut the unrolled positive electrode sheet into 40*100mm sizes to obtain positive electrode sheet samples; after attaching adhesive tape to the surface of the positive electrode sheet sample, roll it three times using a roller press with a roller speed between 1200r / min and 1450r / min. Then, use a tensile testing machine to test the peel strength to test the peel force between the positive electrode coating and the aluminum foil in the positive electrode sheet. During the test, the peeling machine speed is 50mm / min. Each sample is tested three times. After each peeling force trend remains unchanged, record the peel force when the trend remains unchanged. Take the average of the three tests as the peel force test result of the electrode sheet.

[0180] 7. Battery impedance: After assembling the battery, discharge it at 1.5C for 30s at 25℃, and record the voltage difference at the beginning of the discharge, i.e., the voltage drop, to evaluate the battery impedance.

[0181] 8. Battery Cycle Capacity Retention Rate Test: After assembling the battery, constant current charge and discharge is performed at 60℃ with a 1C / 1C charge and discharge rate within a voltage window of 2.0~3.8V. The battery is cycled 500 times. The ratio of the battery's discharge capacity to its initial capacity after 500 cycles is the battery's capacity retention rate after 500 cycles.

[0182] Table 1

[0183]

[0184] Table 2

[0185]

[0186] As can be seen from Tables 1 and 2, the polyimide binder of this application can effectively improve the problem of decreased battery cycle performance caused by ester chain segments.

[0187] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A polyimide adhesive, characterized in that, It includes polyacrylonitrile soft segments and aromatic hard segments.

2. The polyimide adhesive according to claim 1, characterized in that, The polyacrylonitrile soft segment comprises the structure shown in Formula I and / or Formula II as follows: Formula I Formula II In Formulas I and II, * indicates the connection site between the structure shown and the aromatic hard segment; In Formula I, m is the number of -(CH2)2- substituents with cyano groups in the polyacrylonitrile soft segment, and n is the number of -(CH2)2- substituents; in Formula II, p, n, and q are each independently the number of methylene groups, o is the number of methine groups, and m is the number of methine groups substituted with cyano groups. In Equations I and II, m is selected from integers between 1 and 50, n is selected from integers between 0 and 100, and o, p, and q are each independently selected from integers between 0 and 50.

3. The polyimide adhesive according to claim 1 or 2, characterized in that, The mass percentage of the polyacrylonitrile soft segment is 10% to 90%, preferably 25% to 70%.

4. The polyimide adhesive according to any one of claims 1-3, characterized in that, The aromatic hard segment includes a first aromatic hard segment, which has the structure shown in Formula III: Formula III 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 the structure shown in Formula IV: Formula IV 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, characterized in that, 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, characterized in that, The polyimide adhesive includes a first connecting segment, which has a structure as shown in Formula IY: Formula IY In the formula IY, 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, and L5 is selected from one of an oxygen atom, a nitrogen atom, a sulfur atom, and an ester group. The symbol IY represents the connection site between the polyacrylonitrile soft segment and the symbol * represents the connection site between the polyacrylonitrile soft segment and the first aromatic hard segment.

7. The polyimide adhesive according to any one of claims 1-6, characterized in that, 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 aryl group is selected from one or more of phenyl, naphthyl, benzoic acid, and naphtholic acid; 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 the structure shown in Formula XI: 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.

8. The polyimide adhesive according to claim 7, characterized in that, The second aromatic hard segment is selected from the structures shown in formulas XI-1 to XI-16 below: 。 9. The polyimide adhesive according to any one of claims 1-8, characterized in that, The polyimide binder has a weight-average molecular weight of 10 kDa to 1000 kDa, preferably 100 kDa to 600 kDa; and / or, The Fourier transform infrared spectrum of the polyimide adhesive is in the range of 3000–3700 cm⁻¹. -1 It contains the first characteristic peak, located at 2200–2300 cm⁻¹. -1 It contains a second characteristic peak, and the ratio of the peak area of ​​the first characteristic peak to the peak area of ​​the second characteristic peak is 0.3~4; and / or, The polyimide binder has a third characteristic peak in the range of 6.0 to 10.0 ppm and a fourth characteristic peak in the range of 2.2 to 4.5 ppm, and the ratio of the peak area of ​​the third characteristic peak to the peak area of ​​the fourth characteristic peak is 0.1 to 5.

10. A method for preparing the polyimide adhesive according to any one of claims 1-9, characterized in that, Includes the following steps: The polyacrylonitrile precursor is polymerized with diisocyanate and anhydride monomer to obtain the polyimide binder; wherein at least one of the diisocyanate and the anhydride monomer contains an aryl group.

11. The preparation method according to claim 10, characterized in that, 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, wherein 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 formula IB, wherein L4 is selected from a second substituted or unsubstituted aryl group, or a second substituted or unsubstituted biaryl group; and / or, The polyacrylonitrile precursor comprises a nitrile compound containing end-capped groups, wherein the end-capped groups include at least one selected from hydroxyl, amino, mercapto, and carboxyl groups; and / or, The anhydride monomer includes a diacid anhydride monomer; and / or, The polymerization reaction is carried out at a temperature of 100℃ to 180℃ for a time of 1h to 24h.

12. The preparation method according to claim 11, characterized in that, The polymerization process includes: performing an addition reaction between the polyacrylonitrile precursor and the first diisocyanate to obtain a polyacrylonitrile soft segment precursor; and then performing the polymerization reaction between the polyacrylonitrile soft segment precursor, the second diisocyanate, and the anhydride monomer to obtain the polyimide binder.

13. An electrode sheet, characterized in that, The electrode coating includes the polyimide binder according to any one of claims 1-9, or the polyimide binder obtained according to the preparation method according to any one of claims 10-12.

14. A battery, characterized in that, Includes the electrode sheet as described in claim 13.

15. An electrical appliance, characterized in that, Includes the battery as described in claim 14.

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