An adhesive, a positive electrode, a lithium-ion battery, and an electrical device.

Abstract

This application relates to the field of new energy materials technology, specifically to a binder, a positive electrode, a lithium-ion battery, and electrical equipment. The binder provided in this application involves the directional grafting of sulfur- and nitrogen-containing polar functional groups as ion-conducting functional groups onto the side groups of the PAA main chain, while simultaneously introducing oxygen-containing polar functional groups as highly efficient bonding polar functional groups. The PAA main chain is then bridged through crosslinking groups. This allows for the construction of a three-dimensional crosslinked network within the molecular chain when subsequently applied to the electrode, achieving an integrated design of ion-conducting sites, bonding sites, a rigid framework, and a crosslinked network. Through this molecular structure design, ion conduction, strong bonding, resistance to electrolyte swelling, and high mechanical properties are achieved, with a synergistic effect among these properties rather than a single-dimensional improvement.

Description

Technical Field

[0001] This application relates to the field of new energy materials technology, specifically to a binder, a positive electrode sheet, a lithium-ion battery, and an electrical device. Background Technology

[0002] As the application scenarios of new energy power batteries and energy storage batteries continue to expand, the market demand for battery energy density continues to rise. Increasing the loading of positive electrode active materials is one of the core paths to break through the bottleneck of battery energy density. Its core logic is to increase the proportion of active materials in the electrode per unit area, reduce the dilution effect of inactive components such as current collectors and binders on battery energy density, and thus simultaneously improve the volumetric energy density and gravimetric energy density of the battery.

[0003] Currently, polyvinylidene fluoride (PVDF) is widely used as a binder in commercial battery cathodes. It needs to be dissolved in N-methylpyrrolidone (NMP) solvent to bond the active material, conductive agent, and current collector, ensuring the integrity of the electrode structure and stability during cycling. However, PVDF binders have inherent defects that severely restrict the improvement of cathode loading: First, PVDF has limited bonding strength. To avoid cracking and peeling during charge-discharge cycles and roll forming, its usage in traditional processes needs to account for 3%-5% of the total cathode mass. Excessive binder not only occupies effective reaction sites of the active material but also hinders electrolyte ion penetration and electron conduction, forming a performance bottleneck. Second, PVDF is prone to swelling in the electrolyte, and its bonding performance decays after long-term cycling, resulting in a loose electrode structure that cannot meet the structural requirements of thick electrodes with high loading. Third, PVDF has weak high-temperature and high-pressure resistance and poor compatibility with high-energy-density cathode materials such as high-nickel ternary (NCM811, NCM955, etc.) and lithium-rich manganese-based materials, further limiting the implementation of high-loading technology.

[0004] In summary, how to simultaneously optimize the structural stability, ion conduction efficiency, bonding performance, electrolyte swelling resistance, high temperature resistance, and mechanical properties of electrodes under high load conditions with relatively low binder usage has become an urgent problem to be solved in this field, and is also a key direction to break through the energy density bottleneck of existing batteries. Summary of the Invention

[0005] This application provides an adhesive, a positive electrode sheet, a lithium-ion battery, and an electrical device to solve the problems in the prior art where adhesives cannot simultaneously optimize the structural stability, ion conduction efficiency, bonding performance, electrolyte swelling resistance, high temperature resistance, and mechanical properties of electrodes under high load conditions with low dosage.

[0006] In a first aspect, this application provides an adhesive comprising a polyamic acid backbone, wherein R1 groups and R2 groups are grafted onto the backbone, and the backbones are bridged by crosslinking groups; Wherein, the R1 group is a sulfur-nitrogen polar functional group; the R2 group is an oxygen-nitrogen polar functional group; The crosslinking groups include at least one of the following: aliphatic urethane bridging groups, aliphatic amide bridging groups, aromatic urethane bridging groups, aromatic amide bridging groups, aromatic imine bridging groups, epoxy ring-opening ether bridging groups, epoxy ring-opening ester bridging groups, aromatic ester bridging groups, and aromatic imine bridging groups. In the infrared spectrum of the adhesive, at 1640 cm⁻¹ -1 -1650cm -1 The characteristic peak intensity at the wavenumber is 0.2-0.4.

[0007] In one optional embodiment, the grafting rates of the R1 group and the R2 group are ≥90% respectively; optionally, the grafting rates of the R1 group and the R2 group are independently 90%-98%. And / or, the molar ratio of the R1 group to the R2 group is 0.8-1.2:1; And / or, the R1 group is a lithium sulfonamide group; the R2 group is a hydroxyl and / or a carboxyl group.

[0008] In one optional embodiment, the grafting rate of the crosslinking group is ≥90%, optionally 90%-98%.

[0009] In one optional embodiment, the polyamic acid backbone is an aromatic polyamic acid backbone or an aliphatic polyamic acid backbone; And / or, the polyamic acid backbone is formed by the polymerization reaction of dianhydride and diamine; Optionally, the dianhydride includes at least one of aromatic dianhydride and aliphatic dianhydride; further optionally, the aromatic dianhydride includes at least one of pyromellitic dianhydride, diphenyl ether dianhydride, biphenyl dianhydride, benzophenone dianhydride, bisphenol A type diether dianhydride, 3,3,4,4-diphenyl sulfone tetracarboxylic acid dianhydride, and 1,4,5,8-naphthalene tetracarboxylic acid dianhydride; the aliphatic dianhydride includes at least one of cyclobutane tetracarboxylic acid dianhydride, cyclohexane tetracarboxylic acid dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic acid dianhydride, hydrogenated pyromellitic dianhydride, and 1,2,3,4-butane tetracarboxylic acid dianhydride; Optionally, the diamine includes at least one of aromatic diamines and aliphatic diamines; more preferably, the aromatic diamine includes at least one of 4,4'-diaminodiphenyl ether, p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfone, 2,2'-dimethyl-4,4'-diaminobiphenyl, 2,2'-di(trifluoromethyl)diaminobiphenyl, and 1,5-naphthyldiamine; the aliphatic diamine includes at least one of 1,4-cyclohexanediamine, isophoronediamine, 1,3-cyclohexanedimethylamine, ethylenediamine, 1,6-hexanediamine, and piperazine.

[0010] In one optional embodiment, the number-average molecular weight of the adhesive is 8 × 10⁻⁶. 4 -3×10 5 ; And / or, the adhesive has an ionic conductivity of 10 at 25°C. -6 -10 -5 S / cm; And / or, the adhesive has a tensile strength of 120-160 MPa and an elongation at break of 8%-12%; And / or, the electrolyte swelling resistance of the adhesive is ≤5%.

[0011] Secondly, this application provides a positive electrode sheet, the positive electrode sheet comprising a current collector and a positive electrode active layer located on at least one side surface of the current collector; the positive electrode active layer comprises a positive electrode active material and the aforementioned binder; in the infrared spectrum of the positive electrode sheet, at 1640 cm⁻¹... -1 -1650cm -1 The characteristic peak intensity at the wavenumber is 0.6-0.8.

[0012] In one optional embodiment, the binder comprises 0.5%-2.5% by mass of the total mass of the positive electrode active layer; optionally, it comprises 1%-2%. And / or, the areal density of the positive electrode active layer is 180-200 g / m³. 2 ; And / or, the thickness of the positive electrode active layer is 100-250 μm and the porosity is 35%-45%.

[0013] In one optional embodiment, the interfacial peel strength between the positive electrode active layer and the current collector is 1.2-1.5 N / cm; And / or, the thermogravimetric analysis is performed in an N2 atmosphere, with a heating rate of 10℃ / min and a test range of room temperature to 800℃. The initial weight loss temperature (T5%) of the positive electrode is ≥380℃, and the residual carbon rate at 800℃ is 10%-16%.

[0014] Thirdly, this application provides a lithium-ion battery, including the aforementioned positive electrode.

[0015] Fourthly, an electrical device comprising the aforementioned lithium-ion battery.

[0016] The technical solution of this application has the following advantages: The binder provided in this application involves the directional grafting of sulfur- and nitrogen-containing polar functional groups (such as -SO2NLiSO2-, R1 group) onto the side groups of the polyamic acid (PAA) backbone as ion-conducting functional groups. At the same time, oxygen-containing polar functional groups (such as hydroxyl (-OH) and / or carboxyl (-COOH), R2 group) are introduced as highly efficient bonding polar functional groups. The PAA backbone is then bridged through crosslinking groups. This allows for the construction of a three-dimensional crosslinking network between PAA molecular chains when subsequently applied to batteries, achieving an integrated design of ion-conducting sites, bonding sites, rigid framework, and crosslinking network. Through the above molecular structure design, multiple optimizations are achieved, including ion conduction, strong bonding, resistance to electrolyte swelling, and high mechanical properties. A synergistic effect mechanism is formed among these properties, rather than a single-dimensional improvement.

[0017] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Detailed Implementation

[0018] The following embodiments are provided to better understand this application. However, the following embodiments do not constitute a limitation on the content and scope of protection of this application. Any product that is the same as or similar to this application, derived by anyone under the guidance of this application or by combining the features of this application with other prior art, falls within the scope of protection of this application.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having” and any variations thereof in the text of this application are intended to cover non-exclusive inclusion.

[0020] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0021] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers from a to b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed herein, and "0-5" is merely a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥ 2, it is equivalent to disclosing that the parameter can be, for example, integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0022] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0023] In the description of the embodiments of this application, the term "at least one" refers to one or more (including two).

[0024] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, but sequentially is preferred.

[0025] Unless otherwise specified, the experimental steps or conditions in the examples were performed in accordance with conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0026] As described in the background section, PVDF, as a widely used binder for commercial battery cathodes, suffers from inherent defects such as limited bonding strength, easy swelling in electrolytes, weak high-temperature and high-voltage resistance, and poor compatibility with high energy density. Polyimide (PI), as a high-performance polymer with an aromatic ring backbone, is known to possess mechanical strength far exceeding that of PVDF (PI's tensile strength can reach 100-150 MPa, 2-3 times that of PVDF), excellent chemical stability, and high-temperature resistance. Although some existing technologies have attempted to use PI in the field of battery binders to overcome the inherent defects of PVDF binders mentioned in the prior art, PI also has significant technical limitations: firstly, in most solutions, the amount of PI used is comparable to or even higher than that of PVDF, failing to demonstrate the advantage of low-dosage usage; secondly, ordinary PI binders are typical insulating polymers with an ionic conductivity of only 10.-8 -10 -7 S / cm, much lower than PVDF (10 -6 When PI binder is used to directly replace PVDF for high-load thick electrodes (S / cm), it is prone to severe degradation of rate performance due to the extension of ion transport path and excessive impedance, which cannot meet the high-rate charge and discharge requirements of power batteries. Thirdly, PI binder exists in the form of linear molecular chains, and the interfacial bonding depends on the intermolecular van der Waals forces. It is difficult to balance the bonding strength at low dosage with the structural stability of high-load electrodes in rolling and charge-discharge cycles, which can easily lead to problems such as film cracking and peeling.

[0027] How to simultaneously optimize the structural stability, ion conduction efficiency, bonding performance, electrolyte swelling resistance, high temperature resistance, and mechanical properties of high-load thick electrodes with relatively low binder usage has become an urgent problem to be solved in this field and a key direction to break through the energy density bottleneck of existing batteries.

[0028] Therefore, this application provides the following technical solution: In a first aspect, this application provides an adhesive comprising a polyamic acid (PAA) backbone, wherein R1 groups and R2 groups are grafted onto the backbone, and the backbones are bridged by crosslinking groups; Wherein, the R1 group is a sulfur-nitrogen polar functional group; the R2 group is an oxygen-nitrogen polar functional group; The crosslinking groups include at least one of the following: aliphatic urethane bridging groups, aliphatic amide bridging groups, aromatic urethane bridging groups, aromatic amide bridging groups, aromatic imine bridging groups, epoxy ring-opening ether bridging groups, epoxy ring-opening ester bridging groups, aromatic ester bridging groups, and aromatic imine bridging groups. In the infrared spectrum of the adhesive, at 1640 cm⁻¹ -1 -1650cm -1 The characteristic peak intensity at the wavenumber is 0.2-0.4.

[0029] As an example, in the infrared spectrum of the adhesive, at 1640 cm⁻¹ -1 -1650cm -1 The characteristic peak intensity at the wavenumber can be 0.2, 0.22, 0.25, 0.27, 0.3, 0.33, 0.35, 0.38, 0.4, or within any of the above values.

[0030] As an example, the binder provided in this application has sulfur- and nitrogen-containing polar functional groups (such as lithium sulfonylimide group -SO2NLiSO2-, R1 group) orientedly grafted onto the side groups of the PAA main chain as ion-conducting functional groups. At the same time, oxygen-containing polar functional groups (hydroxyl (-OH) and / or carboxyl (-COOH), R2 group) are introduced as highly efficient bonding polar functional groups. The PAA main chain is bridged through crosslinking groups. In this way, when applied to batteries, a three-dimensional crosslinking network can be constructed between the PAA molecular chains to achieve the integrated design of ion-conducting sites, bonding sites, rigid framework, and crosslinking network. Through the above molecular structure design, the optimization of ion conduction, strong bonding, resistance to electrolyte swelling, and high mechanical properties is achieved, forming a synergistic effect mechanism among various properties, rather than a single-dimensional improvement. Specifically, the sulfur- and nitrogen-containing polar functional groups, acting as ion-conducting functional groups, achieve ion conduction without disrupting the chemisorption between the oxygen-containing polar functional groups (-OH / -COOH) and the active material / current collector; the rigid PI framework formed after PAA cyclization provides the structural basis for ion conduction, adhesion, and resistance to electrolyte swelling; the binder at 1640 cm⁻¹... -1 -1640cm -1 The intensity of the characteristic peak (imide characteristic peak) at the wavenumber is limited to 0.2-0.4, ensuring that a three-dimensional cross-linked network does not form in the binder. This prevents the formation of a three-dimensional cross-linked network during subsequent application to the battery, improving the mechanical properties and swelling resistance of the binder while providing a continuous channel for lithium-ion transport. If a three-dimensional cross-linked network forms in the binder stage, it will lead to decreased solubility of PAA segments and a reduction in active sites, hindering effective bonding of the conductive agent and active material during electrode preparation and affecting the adhesive strength between the active layer and the current collector. By grafting functional groups onto the PAA main chain, rather than inserting functional groups into the main chain, damage to the main chain structure is avoided, thus preserving the rigid framework and preventing deterioration of high-temperature resistance and mechanical properties.

[0031] In this application, the intensity of the characteristic peak is obtained by the following method: the sample is tested using a Fourier transform infrared spectrometer (FTIR) to obtain the corresponding spectrum, and the peak height value or the integral area value of the characteristic peak is used as the intensity of the characteristic peak (in the embodiments of this application, the peak height value is used as the intensity of the characteristic peak). In one alternative embodiment, the grafting rates of the R1 group and the R2 group are ≥90% respectively. Optionally, the grafting rates of the R1 group and the R2 group are independently 90%-98%. As an example, the grafting rates of the R1 group and the R2 group are independently 90%, 92%, 94%, 95%, 96%, 98%, or within any of the above values.

[0032] This application, by limiting the grafting ratio, ensures a reasonable number of grafts of R1, R2 functional groups and crosslinking groups, balancing the processability and functionality of the binder. This allows PAA to stably form a PI crosslinking network during subsequent cyclization, guaranteeing electrode bonding strength, ion conduction efficiency, and battery cycle performance. A reasonable grafting ratio solves the problem of mutual constraints between binder adhesion and ion conduction in existing technologies. A reasonable grafting ratio optimizes the bonding force between the binder and the active material and current collector, improves electrode structural stability, reduces ion transport impedance, and ensures electrode coating processability. If the grafting ratio is too low, it will lead to insufficient ion conduction, insufficient bonding strength, and the inability to stably form a crosslinking network, thus affecting battery cycle performance.

[0033] It should be noted that the grafting rate test method in this application can be quantitative nuclear magnetic resonance (NMR), specifically including the following steps: 1. Sample preparation: Take the dried adhesive sample, dissolve it in a suitable solvent, and prepare a homogeneous test solution; 2. Testing: Nuclear magnetic resonance (NMR) was used. 1 H-NMR), the nuclear magnetic resonance spectrum of the test sample, the characteristic peak area corresponding to the aromatic ring of the integrated main chain, and the characteristic peak area corresponding to the R1 and R2 groups; 3. Calculation: Based on the integral area ratio of the main chain characteristic peak and the side-linked branched functional group characteristic peak, and combined with the repeating unit structure, the grafting rate is calculated.

[0034] In one alternative embodiment, the molar ratio of the R1 group to the R2 group is 0.8-1.2:1. As an example, the molar ratio of the R1 group to the R2 group can be 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, or within any range of the above values.

[0035] Based on the aforementioned technical methods, directional grafting of R1 groups onto the side groups of the PAA main chain can improve ion conduction performance, while grafting of R2 groups can improve adhesion performance. By limiting the molar ratio of these two groups, a better balance between ion conduction and adhesion performance can be achieved. If the molar ratio of R1 to R2 groups is below the specified range (i.e., R1 is too low and R2 is too high), it will lead to a decrease in ion conduction performance, preventing the formation of continuous ion transport channels within the electrode and hindering ion migration during battery charging and discharging. If the proportion of R2 groups is too high, although it can improve adhesion, it will lead to increased rigidity and decreased flexibility of the binder, making it prone to brittleness after subsequent cyclization, failing to meet the dual requirements of ion conduction and adhesion. If the molar ratio is above the specified range (i.e., R1 is too high and R2 is too low), it will lead to weakened intermolecular forces in the binder, resulting in insufficient adhesion strength after the electrode is dried and formed. Insufficient R2 groups will prevent good interfacial bonding, and excessive R1 will increase the hydrophilicity of the binder, leading to incomplete cyclization reaction and affecting the overall structural stability.

[0036] In this application, the molar ratio of the two can be determined using quantitative nuclear magnetic resonance (NMR). 1 H 13 Determined by C NMR or elemental analysis.

[0037] In one alternative embodiment, the R1 group is a lithium sulfonamide group; the R2 group is a hydroxyl and / or carboxyl group.

[0038] In one alternative embodiment, the grafting rate of the crosslinking group is ≥90%, optionally 90%-98%. As an example, the grafting rate of the crosslinking group can be 90%, 92%, 94%, 95%, 96%, 98%, or within any range of the above values.

[0039] By limiting the grafting rate, this application ensures that a sufficient number of crosslinking groups are grafted onto the PAA main chain, providing ample reaction sites for the formation of a stable PI three-dimensional crosslinking network during the subsequent high-temperature cyclization of the electrode. At the same time, it takes into account the processability of the PAA binder, avoiding the impact of insufficient or excessive grafting of crosslinking groups on the binder performance, and ultimately achieving excellent structural stability, bonding strength and long cycle performance of the battery. Before coating the electrode, the binder must maintain good solubility and coatability, with a grafting rate limited to ≥90%. This avoids insufficient grafting leading to a lack of crosslinking sites, while also preventing excessive grafting (above 98%) from causing PAA molecular chain entanglement, which affects slurry dispersion and coating effect. Sufficient crosslinking groups can form a complete and stable PI three-dimensional crosslinking network between PAA molecular chains during the high-temperature cyclization process of the electrode, effectively inhibiting PI molecular chain peristalsis, improving electrode structural stability, and reducing electrode volume expansion during charge and discharge. A high grafting rate ensures a uniform and dense crosslinking network, which can further improve the interfacial bonding force between the binder and the active material and current collector, preventing electrode powder shedding and delamination. If the crosslinking group grafting rate is too low (below 90%), there are insufficient reaction sites during the high-temperature cyclization process, making it impossible to form a complete and stable PI three-dimensional crosslinking network. This results in poor electrode structural stability and insufficient bonding strength, affecting the cycle life and safety of the battery.

[0040] It should be noted that the grafting rate test method in this application can be achieved by using X-ray photoelectron spectroscopy (XPS) coupled with inductively coupled plasma optical emission spectroscopy (ICP-OES) to quantitatively or semi-quantitatively determine the grafting rate of lithium sulfonylimide groups in the binder. The specific steps are as follows: Sample pretreatment: Take the finished positive electrode sheet, cut it to a suitable size, and dry it under vacuum to remove residual electrolyte and moisture for later use; XPS test: Elemental and chemical bonding state analysis was performed on the electrode surface to confirm that the S element exists in the lithium sulfonylimide structure and to obtain the molar ratio of S, N, Li and other elements on the surface. ICP-OES test: The active layer material of the electrode was scraped off, digested, and the total S and total Li content of the system was determined. Grafting rate calculation: Based on the theoretical molar ratio of the repeating unit in the PAA main chain to the sulfur element in the lithium sulfonamide group, the grafting rate of the lithium sulfonamide functional group was calculated.

[0041] In one optional embodiment, the polyamic acid backbone is an aromatic polyamic acid backbone or an aliphatic polyamic acid backbone; And / or, the polyamic acid backbone is formed by the polymerization reaction of dianhydride and diamine; Optionally, the dianhydride includes at least one of aromatic dianhydride and aliphatic dianhydride; further optionally, the aromatic dianhydride includes at least one of pyromellitic dianhydride, diphenyl ether dianhydride, biphenyl dianhydride, benzophenone dianhydride, bisphenol A type diether dianhydride, 3,3,4,4-diphenyl sulfone tetracarboxylic dianhydride (CAS: 2540-99-0), and 1,4,5,8-naphthalene tetracarboxylic dianhydride (CAS: 81-30-1); the aliphatic dianhydride includes at least one of cyclobutane tetracarboxylic dianhydride, cyclohexane tetracarboxylic dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (CAS: 1719-83-1), hydrogenated pyromellitic dianhydride, and 1,2,3,4-butane tetracarboxylic dianhydride (CAS: 4534-73-0); Optionally, the diamine includes at least one of aromatic diamines and aliphatic diamines; more preferably, the aromatic diamine includes at least one of 4,4'-diaminodiphenyl ether, p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfone, 2,2'-dimethyl-4,4'-diaminobiphenyl (CAS: 84-67-3), 2,2'-di(trifluoromethyl)diaminobiphenyl (CAS: 341-58-2), and 1,5-naphthyldiamine; the aliphatic diamine includes at least one of 1,4-cyclohexanediamine, isophoronediamine, 1,3-cyclohexanedimethylamine, ethylenediamine, 1,6-hexanediamine, and piperazine.

[0042] In this application, the polyamic acid backbone is preferably an aromatic polyamic acid backbone. Compared with the aliphatic polyamic acid backbone, the aromatic backbone has higher thermal stability, mechanical strength and structural rigidity. It is not easy to decompose or deform during the high-temperature baking and cyclization process of the electrode, which can ensure that the PI crosslinking network formed later is more dense and stable. At the same time, the aromatic ring conjugated structure can further improve the resistance to electrolyte swelling, suppress electrode expansion and structural damage during charging and discharging, and thus improve the battery cycle life.

[0043] In one optional embodiment, the number-average molecular weight of the binder in the positive electrode sheet is 8 × 10⁻⁶. 4 -3×10 5 As an example, the number-average molecular weight of the binder in the positive electrode sheet can be 8 × 10⁻⁶. 4 9×10 4 1×10 5 1.5×10 5 2×10 5 2.5×10 5 3×10 5 , or within the range of any of the above values.

[0044] By controlling the number-average molecular weight of the binder in the positive electrode within the aforementioned range using the above-mentioned techniques, an optimal balance can be achieved between the binder's processability, adhesive strength, film-forming properties, and ion transport. If the number-average molecular weight is lower than 8 × 10⁻⁶, the optimal balance is achieved. 4 Short molecular chains lead to decreased entanglement and bonding strength, resulting in poorer cycle stability. Furthermore, short-chain structures struggle to form continuous and effective ion conduction pathways, leading to increased internal resistance and decreased rate performance. If the number-average molecular weight exceeds 3 × 10⁻⁶... 5 Excessively long molecular chains can lead to entanglement, excessively high slurry viscosity, uneven dispersion of active materials and conductive agents, and poor electrode coating quality. Furthermore, excessively long molecular chains can hinder ion transport, increase interfacial impedance, and easily leave solvent residues during high-temperature cyclization, affecting the uniformity of the PI network structure and hindering the overall performance of the battery.

[0045] The method for testing the number-average molecular weight in this application involves preparing a binder-cured membrane and then performing the test using gel permeation chromatography (GPC), under the following specific conditions: I. Method for preparing adhesive-cured film Sample preparation: Take the adhesive sample to be tested and dissolve it in N,N-dimethylformamide (DMF) at a mass ratio of 1:8-12 (adhesive:solvent). Stir well to obtain a homogeneous adhesive solution. Film preparation: The above adhesive solution is evenly coated into a clean polytetrafluoroethylene mold, and the coating thickness is controlled at 0.1-0.2 mm; Curing: Place the coated mold into a vacuum drying oven, set the temperature to 70-90℃ and the vacuum degree to -0.07~-0.095MPa, and dry for 1-3 hours to remove the solvent; then raise the temperature to 110-150℃ and keep it at that temperature for 0.5-2 hours to complete the curing and obtain the adhesive cured film. Sampling and testing: After the cured film cools to room temperature, it is peeled off from the mold and cut into appropriate sizes for subsequent molecular weight and related performance tests.

[0046] II. Number-average molecular weight test method The gel permeation chromatography (GPC) method was used for testing, and the specific steps are as follows: Sample preparation: Take the adhesive-cured film prepared above, crush it, add an appropriate amount of DMF solvent, stir until completely dissolved, prepare a test solution with a concentration of 1-2 mg / mL, filter it through a 0.22 μm filter membrane to remove insoluble impurities; Test conditions: DMF was used as the mobile phase, the flow rate was 1.0 mL / min, the column temperature was 30℃, and the detector was a differential refractive index detector; Standard curve preparation: Using polystyrene as a standard, a molecular weight standard curve is prepared, and the number-average molecular weight and weight-average molecular weight of the sample are calculated by the retention time of the chromatographic peaks.

[0047] In one alternative embodiment, the adhesive has an ionic conductivity of 10 at 25°C. -6 -10 -5 S / cm; as an example, the ionic conductivity of the adhesive at 25°C is 10. -6 S / cm, 2×10 -6 S / cm, 4×10 -6 S / cm, 5×10 -6 S / cm, 7×10 -6 S / cm, 9×10 -6 S / cm, 10 -5 S / cm, or within any of the above values.

[0048] It should be noted that, relying on the exclusive lithium-ion transport sites R1 groups grafted onto the PAA main chain, the bottleneck of intrinsic insulation of polyimide (PI) is overcome. The activation energy for lithium-ion transport in the binder phase is ≤0.35eV, which is much lower than that of ordinary PI (≥0.8eV), thus improving ion conductivity and limiting its ion conductivity coefficient at 25℃ to 10. -6 -10 -5A conductivity coefficient of S / cm ensures rapid and uniform lithium-ion transport in high-load thick-film electrodes, effectively preventing aggravated electrode polarization and meeting the application requirements of high-load thick-film electrodes. High-load thick-film electrodes have greater electrode thickness and higher active material content, demanding higher lithium-ion transport efficiency. This range of ionic conductivity ensures rapid lithium-ion migration in the binder phase, compensating for the long ion transport path of thick-film electrodes and preventing uneven lithium-ion distribution due to insufficient transport rate, effectively suppressing electrode polarization and ensuring battery stability during charge and discharge. This range of ionic conductivity allows lithium-ions to quickly shuttle between the active material and current collector during charge and discharge, especially at high rates, effectively reducing lithium-ion transport hysteresis, lowering interface impedance, and preventing capacity decay due to aggravated polarization. Simultaneously, stable ion transport efficiency reduces irreversible loss of active materials, extends battery cycle life, and meets the application requirements of high-rate, long-cycle rechargeable batteries. If the ionic conductivity coefficient is below 10... -6 S / cm: Slower lithium-ion transport rate in the binder phase leads to lithium-ion transport lag, especially during high-rate charge / discharge, resulting in capacity decay and voltage instability. Simultaneously, excessively slow ion transport reduces the utilization rate of active materials, preventing the battery energy density from reaching expectations. If the ion conductivity is higher than 10... -5 S / cm: Although it can further improve the ion transport rate, it requires a significant increase in the amount of R1 groups grafted. This will disrupt the regularity of the PAA main chain, leading to a decrease in the bonding strength of the binder. At the same time, excessive R1 groups will increase the hydrophilicity of the binder, resulting in insufficient subsequent high-temperature cyclization reaction. The resulting PI crosslinking network is loose, and the electrode's resistance to electrolyte swelling and structural stability deteriorates, which in turn reduces the cycle stability and safety of the battery.

[0049] The method for testing the ionic conductivity coefficient in this application is as follows: a cured film is prepared according to the above method, and a circular sample with a diameter of 12-14 mm is cut for later use (ensuring that the sample is undamaged, wrinkle-free, and has a smooth surface). The ionic conductivity coefficient σ (unit: S / cm) is obtained by using the electrochemical impedance spectroscopy (EIS) method on an electrochemical workstation.

[0050] In one alternative embodiment, the adhesive has a tensile strength of 120-160 MPa and an elongation at break of 8%-12%; as an example, the tensile strength of the adhesive can be 120 MPa, 130 MPa, 140 MPa, 150 MPa, 160 MPa, or within any range of the above values; the elongation at break of the adhesive can be 8%, 9%, 10%, 11%, 12%, or within any range of the above values.

[0051] It should be noted that the binder provided in this application can form a three-dimensional cross-linked network, organically combining the rigidity of the PI main chain with the flexibility of the grafted side chain functional groups. This allows the pure rubber to achieve a tensile strength of 120~160MPa and an elongation at break of 8%~12%. Positive electrode sheets prepared using this binder exhibit no delamination, cracking, or powder shedding under high-load, thick film layers (positive electrode active layer thickness 100-250μm), meeting the mechanical requirements for power battery winding and assembly. High-load, thick film electrode sheets will withstand certain tensile and compressive stresses during winding, assembly, and charging / discharging. The tensile strength of 120~160MPa ensures that the binder can firmly fix the active material, preventing damage to the positive electrode sheet during processing and use. The 8%~12% elongation at break imparts a certain degree of flexibility to offset stress changes in the thick film layer, preventing brittleness due to excessive rigidity, perfectly matching the mechanical requirements for power battery winding and assembly. If the tensile strength is below 120 MPa, it indicates that the three-dimensional cross-linked network of the binder is not dense enough, the intermolecular bonding force is insufficient, and it cannot effectively fix the positive electrode active material, affecting the cycle stability and safety of the battery. If the tensile strength is above 160 MPa, it indicates that the cross-linking of the binder is too high and the molecular chains are too dense, which will lead to a significant decrease in its flexibility, and the elongation at break will be less than 8%. At this time, the binder will become brittle and hard, unable to offset the volume expansion stress of the high-load thick film positive electrode during charge and discharge. If the elongation at break is above 12%, it indicates that the side chain flexibility of the binder is too high, the degree of cross-linking is insufficient, and the intermolecular bonding force is weakened, which will lead to a decrease in bonding strength, making it impossible to firmly fix the active material. At the same time, it is difficult to form a stable three-dimensional cross-linked network during high-temperature cyclization, affecting the structural stability of the positive electrode.

[0052] The test methods for tensile strength and elongation at break in this application are as follows: Prepare an adhesive curing film according to the above method, and cut it into dumbbell-shaped specimens according to a standard cutter. The specimen dimensions are: total length 115mm, gauge length 30mm, gauge width 10mm, and end width 25mm. After cutting, remove burrs from the edge of the specimen to ensure that the specimen is undamaged, wrinkle-free, and has a flat surface, and set it aside for later use.

[0053] The test was conducted using an electronic universal testing machine. The ambient temperature was controlled at 25±2℃, the relative humidity at 50±5%, and the test speed was set to 5mm / min. The prepared dumbbell-shaped specimen was clamped at both ends in the upper and lower clamps of the electronic universal testing machine. The testing machine was started to perform a tensile test until the specimen broke. The maximum tensile force (in N) displayed by the testing machine was recorded, and the tensile strength (in MPa) was obtained.

[0054] Using the same dumbbell-shaped specimen as the tensile strength test, mark the gauge length lines at both ends of the specimen gauge length with a marker pen, accurately measure and record the initial gauge length L0 (in mm); clamp both ends of the specimen in the upper and lower clamps of the electronic universal testing machine; start the testing machine and stretch at a speed of 5 mm / min until the specimen breaks, record the final gauge length L1 (in mm) when the specimen breaks, and calculate the elongation at break (in %).

[0055] In one alternative embodiment, the electrolyte swelling resistance of the adhesive is ≤5%. As an example, the electrolyte swelling resistance of the adhesive can be 0.5%, 1%, 2%, 3%, 4%, 5%, or within any range of the above values.

[0056] It should be noted that the binder of this application, after being immersed in a carbonate electrolyte (EC / DMC / EMC=1:1:1, containing 1 mol / L LiPF6) for 72 hours, exhibits an electrolyte swelling rate of ≤5%, far lower than that of ordinary PI (≥10%), and shows no dissolution. It maintains structural and performance stability over a wide temperature range of -40 to 200℃, meeting the requirements of high and low temperature operating scenarios for power batteries. During power battery operation, the electrode is immersed in the electrolyte for extended periods. Controlling the swelling rate to ≤5% avoids excessive swelling of the binder, which could lead to structural loosening and network damage. This stabilizes the positive electrode material without hindering lithium-ion transport, synergizing with ion conductivity to ensure stable electrode structure and transport efficiency.

[0057] The swelling rate test method in this application involves preparing an adhesive-cured film according to the above method, cutting the cured film into a 2cm×2cm square sample, measuring the sample thickness with a micrometer screw gauge, and accurately weighing it (recorded as m0). The adhesive-cured film sample is then completely immersed in the above electrolyte. After immersion, excess electrolyte on the sample surface is absorbed with filter paper, and the sample is immediately and accurately weighed (recorded as m1). The swelling rate is calculated based on the mass change before and after immersion.

[0058] It should be noted that in this application, the role of the crosslinking agent is to "bridge the PAA molecular chain". After it undergoes a covalent reaction with the active groups (-OH, -COOH) on the PAA main chain, the crosslinking structural units (i.e. crosslinking groups) remaining between the PI molecular chains are described below. The names and general formulas of the crosslinking groups formed by each crosslinking agent are described below. All of them are group structures that exist stably after the crosslinking reaction.

[0059] (1) Aliphatic diisocyanate crosslinking agents (such as hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), HMDI, etc.) Crosslinking reaction principle: The two -NCO groups of aliphatic diisocyanate (O=C=NRN=C=O) react with -OH / -COOH on the two PAA molecular chains respectively to form urethane bonds (-O-CO-NH-) or amide bonds (-CO-NH-), thus achieving molecular chain bridging.

[0060] Name of the residual group after crosslinking: aliphatic urethane bridging group (or aliphatic amide bridging group).

[0061] General structural formula: -(O-CO-NH-R-NH-CO-O)- (reacts with -OH to form an urethane bond for bridging). -(CO-NH-R-NH-CO)- (reacts with -COOH to form an amide bond for bridging). Wherein, R is an aliphatic group in aliphatic diisocyanates (e.g., R is -(CH2)6- in HDI, R is an isophorone-structured aliphatic group in IPDI, and R is -(CH2)2-C6H in 4,4'-dicyclohexylmethane diisocyanate (HMDI). 10 -(CH2)2-).

[0062] (2) Aromatic diisocyanate crosslinking agents (such as diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI), etc.) Crosslinking reaction principle: The two -NCO groups of aromatic diisocyanate (O=C=N-Ar-N=C=O) react with the -OH / -COOH groups on the two PAA molecular chains respectively to form urethane bonds or amide bonds for bridging.

[0063] Name of the residual group after crosslinking: aromatic urethane bridging group (or aromatic amide bridging group).

[0064] General structural formula: -(O-CO-NH-Ar-NH-CO-O)- (reacts with -OH to form an urethane bond for bridging). -(CO-NH-Ar-NH-CO)- (reacts with -COOH to form an amide bond for bridging). Ar is an aromatic group in aromatic diisocyanates (e.g., Ar in MDI is a diphenylmethane structural group (-C6H4-CH2-C4H6-), and Ar in TDI is a tolyl group).

[0065] (3) Benzodicarbonaldehyde and aromatic dialdehyde crosslinking agents (such as terephthalaldehyde, isophthalaldehyde, etc.) Crosslinking reaction principle: The two aldehyde groups (-CHO) of the aromatic dialdehyde (OCH-Ar-CHO) undergo a condensation reaction with the -NH- on the PAA main chain (introduced by PAA cyclization residue or modification) to form an imine bond (-CH=N-), thus achieving molecular chain bridging.

[0066] Name of the residual group after crosslinking: Aromatic imine bridging group.

[0067] General structural formula: -(NH-CH=N-Ar-N=CH-NH)-; Ar represents the aromatic group in aromatic dialdehydes.

[0068] (4) Difunctional epoxy crosslinking agents (such as polyethylene glycol diglycidyl ether, bisphenol A diglycidyl ether, etc.) Crosslinking reaction principle: The two epoxy groups in the difunctional epoxy compound undergo ring-opening reactions with the -OH / -COOH groups on the two PAA molecular chains respectively, forming ether bonds (-O-) or ester bonds (-CO-O-), thus achieving molecular chain bridging.

[0069] Name of the residual group after crosslinking: epoxy ring-opening ether bond bridging group (or epoxy ring-opening ester bond bridging group).

[0070] General structural formula: -(O-CH2-CH(OH)-CH2-ORO-CH2-CH(OH)-CH2-O)- (reacts with -OH to form an ether bond); -(CO-O-CH2-CH(OH)-CH2-ORO-CH2-CH(OH)-CH2-O-CO)- (reacts with -COOH to form an ester bond); Where R is a linking group in a difunctional epoxy compound (e.g., R is -(CH2CH2O) in polyethylene glycol diglycidyl ether). n - In bisphenol A diglycidyl ether, R is a bisphenol A structural group.

[0071] (5) Aromatic dicarboxylic acid anhydride crosslinking agents (such as pyromellitic dianhydride (PMDA), 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA), 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride (BTDA), etc.) Crosslinking reaction principle: The two anhydride groups of the aromatic dicarboxylic acid anhydride (-CO-O-CO-Ar-CO-O-CO-) react with the -OH groups on the two PAA molecular chains respectively to open the ring and form ester bonds (-CO-O-), thus achieving molecular chain bridging; or react with -NH- to form imide bonds, further strengthening the crosslinking network.

[0072] Name of the residual group after crosslinking: Aromatic ester bond bridging group (or aromatic imide bridging group).

[0073] General structural formula: -(O-CO-Ar-CO-O)- (reacts with -OH to form an ester bond bridge). -(NH-CO-Ar-CO-NH)- (reacts with -NH- to form an imide bond for bridging); Ar is an aromatic group in aromatic dicarboxylic acid anhydrides (e.g., Ar in PMDA is a pyromellitic ring group, Ar in BPDA is a biphenyl ring group, and Ar in BTDA is a benzophenone ring group).

[0074] Secondly, this application provides a positive electrode sheet, the positive electrode sheet comprising a current collector and a positive electrode active layer located on at least one side surface of the current collector; the positive electrode active layer comprises a positive electrode active material and the aforementioned binder; in the infrared spectrum of the positive electrode sheet, at 1640 cm⁻¹... -1 -1650cm -1 The characteristic peak intensity at the wavenumber is 0.6-0.8.

[0075] As an example, in the infrared spectrum of the positive electrode, at 1640 cm⁻¹... -1 -1650cm -1 The characteristic peak intensity at the wavenumber is 0.6, 0.65, 0.7, 0.75, 0.8, or within any of the above values.

[0076] According to the above-mentioned technical means, the binder provided in this application is used. The binder directionally grafts sulfur- and nitrogen-containing polar functional groups (such as lithium sulfonylimide group -SO2NLiSO2-, R1 group) ion-conducting functional groups onto the side groups of the PAA main chain. Simultaneously, oxygen-containing polar functional groups (hydroxyl (-OH) and / or carboxyl (-COOH), R2 group) are introduced as highly efficient bonding polar functional groups. The PAA main chain is bridged through crosslinking groups. This allows for the construction of a three-dimensional crosslinking network in the molecular chain when subsequently applied to the electrode, achieving an integrated design of ion-conducting sites, bonding sites, a rigid framework, and a crosslinking network. Through this molecular structure design, comprehensive optimization of ion conduction, strong adhesion, environmental resistance (such as resistance to electrolyte swelling), and high mechanical properties is achieved. The positive electrode is at 1640 cm⁻¹. -1 -1650cm -1 The characteristic peak intensity at the wavenumber is 0.6-0.8. This characteristic peak corresponds to the characteristic structure formed after the crosslinking groups react with the molecular chains, proving that the three-dimensional crosslinked network has been stably formed during the preparation of the positive electrode. If the characteristic peak intensity is low, it indicates that a three-dimensional crosslinked network structure has not been formed in the electrode, which will directly affect the mechanical properties and swelling resistance of the binder, and lithium-ion transport will also be affected.

[0077] In this application, the characteristic peak intensity of the positive electrode is obtained by Fourier transform infrared spectroscopy (FT-IR). The specific sample preparation method and characteristic peak intensity acquisition method are as follows: I. Sample Preparation Method Cut a 1cm×1cm sample from the non-edge area of ​​the positive electrode and prepare 3 parallel samples. Dry the sample under vacuum at 80-90℃ and -0.08~-0.09MPa for 1-2 hours to remove moisture, electrolyte and impurities. Place the dried sample flat on a KBr salt sheet, and use a blank KBr salt sheet as a blank control.

[0078] II. Methods for Obtaining Characteristic Peak Intensity The binder sample was mixed evenly with dry KBr powder in a certain proportion, pressed into a pellet, and then tested on an infrared spectrometer. The test range was 4000-4000 cm⁻¹. -1 The peak height is used as the characteristic peak intensity.

[0079] In one alternative embodiment, the mass percentage of the binder is 0.5%-2.5% based on the total mass of the positive electrode active layer; alternatively, it is 1%-2%; as an example, the mass percentage of the binder can be 0.5%, 1%, 1.5%, 1.7%, 1.9%, 2%, 2.2%, 2.4%, 2.5%, or within any range of the above values.

[0080] In one optional embodiment, the areal density of the positive electrode active layer is 180-200 mg / cm³. 2 As an example, the areal density of the positive electrode active layer is 180 mg / cm³. 2 185mg / cm 2 190mg / cm 2 195mg / cm 2 200mg / cm 2 , or within the range of any of the above values.

[0081] Based on the aforementioned technical methods, the selected binder achieves a three-in-one functional improvement in "ion conduction, strong adhesion, and environmental resistance," allowing for a reduction in binder dosage to the aforementioned range. At this low dosage, the proportion of active material can be increased to 90%-96%, laying the foundation for high areal density and high energy density in the positive electrode, and supporting an active material areal loading of 45-85 mg / cm³. 2The efficiency is significantly higher than that of traditional PVDF electrodes, without sacrificing the structural stability and electrochemical performance of the electrode. The mass percentage of binder is limited to 0.5%-2.5% (preferably 1%-2%). If the amount is lower or higher than this limit, it will have a significant adverse effect on the structural stability, electrochemical performance, and energy density of the positive electrode. If the amount of binder is too low, the bonding performance is insufficient, the ion-conducting network is discontinuous, affecting the electrochemical performance. At the same time, the conductive agent cannot be effectively fixed, and agglomeration is prone to occur, increasing the interfacial impedance and leading to a decrease in battery rate performance and cycle stability. If the amount of binder is higher than 2.5%, although the structural stability of the electrode can be improved, the proportion of active material decreases, and the energy density decreases. Excessive binder will form an excessively thick coating layer on the surface of the active material and conductive agent, blocking the lithium-ion transport channels and hindering the rapid migration of lithium ions between the active material and the current collector, resulting in a decrease in ion conduction efficiency.

[0082] In one optional embodiment, the thickness of the positive electrode active layer is 100-250 μm, and the porosity is 35%-45%. As an example, the thickness of the positive electrode active layer can be 100 μm, 130 μm, 50 μm, 180 μm, 200 μm, 230 μm, 250 μm, or within any range of the above values; the porosity can be 35%, 38%, 40%, 42%, 44%, 45%, or within any range of the above values.

[0083] In this application, the thickness of the positive electrode active layer is set to 100-250 μm, which maximizes the loading of active material within a limited space and improves energy density. The binder in this application has high bonding strength, high ion conductivity, and excellent resistance to electrolyte swelling, which can stably support the 100-250 μm thick film structure and solve the problems of weak bonding, poor ion transport, and easy structural failure of traditional thick electrode sheets.

[0084] This application, by limiting the porosity of the active layer, ensures unobstructed electrolyte permeation channels while avoiding a decrease in volumetric energy density due to excessive porosity. Batteries using this cathode exhibit a 20%-35% increase in volumetric energy density, with high-nickel ternary systems reaching 800-900 Wh / L and lithium iron phosphate systems reaching 700-750 Wh / L, far exceeding the levels of existing traditional batteries. If the porosity of the cathode active layer is below 35%, the electrolyte permeation channels become blocked, ion transport is hindered, and excessively low porosity leads to an overly dense internal structure of the electrode, failing to buffer the stress generated by volume changes during charge and discharge, affecting the stability of the electrode structure. Furthermore, the electrode's heat dissipation performance decreases, increasing the risk of localized overheating. If the porosity is above 45%, the volumetric energy density decreases; excessively high porosity also results in a loose internal structure of the electrode, where the three-dimensional cross-linked network formed by the binder cannot effectively support the electrode structure. During charge and discharge cycles, active materials easily detach from the pores and aggregate, leading to battery capacity decay and shortened cycle life.

[0085] In one alternative embodiment, the interfacial peel strength between the positive electrode active layer and the current collector is 1.2-1.5 N / cm; as an example, the interfacial peel strength between the positive electrode active layer and the current collector is 1.2 N / cm, 1.3 N / cm, 1.4 N / cm, 1.5 N / cm, or within any of the above values.

[0086] It should be noted that the R2 groups of the PAA main linking branches of the binder used in the positive electrode sheet can form a dual chemical adsorption of hydrogen bonds and coordination bonds with the metal oxygen bonds on the surface of the positive electrode active material (high nickel ternary / lithium iron phosphate (LFP) etc.) and the alumina layer on the surface of the current collector aluminum foil. Combined with the "anchoring effect" of the three-dimensional cross-linking network on the active material / conductive agent, the 180° interface peel strength of the electrode sheet still reaches 1.2-1.5 N / cm, even with the binder amount being only 1.5%-2.5% of the total mass of the positive electrode active layer. This achieves "half the amount and the stronger bonding strength", breaking through the inherent understanding in the existing technology that "the amount of binder is positively correlated with the bonding strength".

[0087] In one optional embodiment, a thermogravimetric analysis (TGA) test is conducted using an N2 atmosphere, a heating rate of 10°C / min, and a test range of room temperature to 800°C. The initial weight loss temperature (T5%) of the positive electrode is ≥380°C, and the residual carbon rate at 800°C is 10%-16%. As an example, the residual carbon rate of the positive electrode at 800°C can be 10%, 11%, 12%, 13%, 4%, 15%, 16%, or within any range of the above values.

[0088] Based on the above technical methods, the high-temperature resistance of the positive electrode is guaranteed. An initial weight loss temperature (T5%) ≥ 380℃ indicates that the positive electrode experiences almost no significant mass loss below 380℃, far exceeding the normal operating temperature (-40~60℃) and the maximum temperature under extreme conditions (≤200℃) of the power battery. This ensures that the positive electrode will not suffer structural damage or performance degradation due to thermal decomposition during long-term use and in extreme high-temperature scenarios, thus guaranteeing battery safety. The residual carbon rate at 800℃ is limited to 10%-16%. The residual carbon mainly originates from the rigid PI framework and cross-linked network formed after the binder cyclization. This residual carbon rate range indicates that the three-dimensional cross-linked network structure of the binder is dense and has excellent thermal stability. Even at the extreme high temperature of 800℃, it can still retain a certain framework structure, effectively fixing the active material.

[0089] The preparation and curing mechanism of the adhesive in this application are described below: This adhesive is prepared via a polyamic acid precursor route. First, the basic monomer is dissolved in NMP solvent and polymerized under controlled temperature and stirring to synthesize a precursor to the target molecular weight. Then, based on the -COOH / -CONH- active sites on the main chain, modifiers containing epoxy groups / isocyanate groups / anhydride groups and high-temperature resistant crosslinking agents (decomposition temperature 200~280℃) are added stepwise. Through covalent grafting reactions such as esterification, ring-opening esterification, and ring-opening amidation, sulfur- and nitrogen-containing polar functional groups are grafted onto the adhesive. The polyamic acid precursor molecular chain is directionally introduced with functional groups (lithium sulfonylimide ion-conducting polar functional groups), oxygen-containing polar functional groups (-OH / -COOH binding polar functional groups), and crosslinking groups to form a uniformly grafted adhesive without premature crosslinking. This adhesive is then used in the preparation of positive electrode sheets. After coating, the material undergoes high-temperature heat treatment at 200-250℃, causing the PAA molecules to undergo dehydration and cyclization to form a rigid PI structure. Simultaneously, the crosslinking agent triggers intermolecular covalent crosslinking reactions at the directionally introduced crosslinking sites, ultimately forming a dense three-dimensional crosslinked network structure. This network structure not only locks the functional sites of the modified functional groups (R1 and R2 groups) but also strengthens the adhesion through intermolecular chemical bonds, effectively preventing structural loosening of the high areal density electrode during rolling and charge-discharge cycles. This is the core reason why it can maintain high structural stability even with half the amount used. In summary, this ion-conducting PAA binder, through molecular structure modification and preparation process optimization, not only overcomes the inherent defects of ordinary PI binders—strong insulation and weak interfacial bonding—but also provides core support for the synergistic achievement of "half the dosage, high areal density, and superior performance." Its three-dimensional cross-linked network structure effectively resists the mechanical stress of high-load thick electrodes during rolling and the volume expansion during charge-discharge cycles, completely solving the technical challenges of cracking and peeling of high-load thick electrodes.

[0090] Specifically, the preparation method of the binder and positive electrode sheet in this application may include the following steps: (1) Preparation of ion-conducting PAA adhesive solution: Based on aliphatic / aromatic dianhydrides and diamines, the monomers are dissolved in N-methylpyrrolidone (NMP) solvent and reacted at 30-40℃ for 1.5-2.5 hours under a nitrogen atmosphere to synthesize polyamic acid (PAA) precursor; then, polar functional group modifiers (lithium sulfonylimide modifiers (such as lithium bis(trifluoromethanesulfonylimide), hydroxyphthalic anhydride modifiers (such as 4-hydroxyphthalic anhydride), carboxyphthalic anhydride modifiers (such as trimellitic anhydride)) and crosslinking agents (aliphatic diisocyanate, aromatic diisocyanate, phthalaldehyde, aromatic dialdehyde, difunctional epoxide) are added. The precursor contains one or more of the following: aromatic diacid anhydrides. The modifier is used at 5%-10% of the precursor mass (of which, lithium sulfonylimide modifiers account for 30%-50 wt%, and hydroxyphthalic anhydride or carboxyphthalic anhydride modifiers account for 50%-70 wt%), and the crosslinking agent is used at 3%-5% of the precursor mass. The mixture is heated to 60-80℃ and stirred for 2-3 hours to graft the modifier onto the precursor molecular chain. Simultaneously, the crosslinking agent covalently bridges the precursor molecular chains. The mixture is then ultrasonically dispersed for 30-60 minutes to remove air bubbles from the solution. The solid content is adjusted to 8%-12%, and the viscosity to 1000-2000 mPa·s. The solution is then sealed for later use. Strict control of the reaction temperature and time is required during this process to prevent premature cyclization of the PAA precursor and to ensure a grafting rate of modified functional groups ≥90%.

[0091] 2) Preparation of positive electrode slurry: Add the active material and conductive agent to a double planetary mixer according to the ratio, and dry mix at 500-800 r / min for 20-30 minutes to ensure that the conductive agent is uniformly coated on the surface of the active material and forms a preliminary conductive network; then slowly add the above binder solution, and at the same time add an appropriate amount of NMP solvent to adjust the slurry viscosity to 3000-8000 mPa·s. First stir at 1000-1500 r / min for 30-45 minutes, and then disperse at 2000-2500 r / min for 60-90 minutes to ensure that all components are uniformly mixed and obtain a positive electrode slurry with excellent dispersibility; the effective mass percentage of binder (based on the solid content of the solution to measure the amount of binder added, which can be determined by drying to constant weight) is 1.5%-2.5% based on the total mass of active material, conductive agent, and binder, and the mass percentage of conductive agent is 1.5-3.5%.

[0092] 3) Coating and gradient drying: The positive electrode slurry is uniformly coated onto the pretreated current collector surface using a scraper at a speed of 0.5-1.5 m / min. Then, it is sent to a drying oven for gradient drying, passing through 70-85℃ (0.5-1.5 hours), 90-105℃ (0.5-1.5 hours), and 110-130℃ (0.3-1 hours) in sequence to gradually remove the NMP solvent in the slurry. This avoids rapid solvent evaporation, which could lead to pinholes and cracks in the membrane layer, resulting in a wet membrane layer with a moisture content of ≤0.5%. 4) Curing and Precision Rolling: The dried electrode is placed in a high-temperature oven protected by an inert gas (nitrogen or argon) and heated to 200-250°C at a heating rate of 5°C / min. It is then held at this temperature for 2-4 hours to allow the PAA precursor to fully dehydrate and cyclize to form a PI three-dimensional cross-linked structure. After cooling to room temperature, the electrode is removed. A two-roll mill is used for precise rolling, with the rolling pressure controlled at 5-10 MPa and the rolling speed at 0.3-0.8 m / min. The final thickness of the positive electrode active layer is controlled to be 100-250 μm to ensure the film density and structural integrity, thereby obtaining the target high areal density battery positive electrode.

[0093] Thirdly, this application provides a lithium-ion battery, including the aforementioned positive electrode.

[0094] Specifically, the lithium-ion battery of this application includes the aforementioned high areal density battery positive electrode, negative electrode, separator, electrolyte, and casing, forming a complete electrochemical system. The negative electrode, satisfying the requirements of a high areal density positive electrode, is a high-capacity negative electrode selected from graphite, silicon-based negative electrode (silicon content 10%-30%), hard carbon, or soft carbon. Its areal capacity (referring to the amount of electricity that can be held per unit area of ​​electrode, typically measured in mAh / cm²) is... 2The matching degree between the positive electrode surface capacity and the positive electrode surface capacity is controlled at 1.05-1.2:1, which can effectively avoid the risk of lithium deposition during battery charging and discharging; the separator is a single-layer polypropylene (PP), polyethylene (PE) membrane or PP / PE / PP composite separator, with a thickness of 12-20μm, a porosity of 40%-50%, and a ceramic coating (alumina or zirconium oxide) modified on the surface to improve the high temperature resistance and mechanical strength of the separator, meeting the safety requirements of high surface density batteries; the electrolyte is a carbonate mixed solvent (ethylene carbonate EC, dimethyl carbonate DMC, ethyl methyl carbonate EMC). The system is composed of a mixture of lithium salt and lithium salt in a volume ratio of (0.8-1.2):(0.8-1.2):(0.8-1.2). The lithium salt is selected from one or more of LiPF6, LiFSI or LiTFSI, and the total lithium salt concentration is 1.0-1.2 mol / L. Appropriate additives (such as fluoroethylene carbonate FEC, vinylene carbonate VC) can be added according to the specific battery system to improve the interfacial stability between the electrode and the electrolyte. The outer shell is an aluminum-plastic film (suitable for soft-pack batteries) or a steel shell or aluminum shell (suitable for cylindrical / square batteries) to meet the packaging requirements of different application scenarios.

[0095] The binder provided in this application exhibits film-forming properties and compatibility with electrode preparation processes consistent with traditional PVDF. It can directly replace existing PVDF binders without altering industrial processes such as electrode coating, drying, and rolling, resulting in zero modification costs and good industrialization performance. Furthermore, it can achieve an active material content of 90%-96% at low dosages, laying the foundation for high areal density and high energy density in the positive electrode, and supporting an active material areal density of 180-200 mg / cm³. 2 It is far superior to traditional PVDF electrodes, while not sacrificing the structural stability and electrochemical performance of the electrode.

[0096] Fourthly, this application provides an electrical device including the aforementioned lithium-ion battery.

[0097] Those skilled in the art will understand that the lithium-ion battery provided in this application, in addition to the electrolyte described above, also includes structural components such as a positive electrode, a negative electrode, a separator, and a casing. During the charging and discharging process, lithium ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor between the positive and negative electrodes, and the separator, disposed between the positive and negative electrodes, primarily serves to prevent short circuits between the positive and negative electrodes while allowing lithium ions to pass through.

[0098] As an example, the positive electrode sheet includes a positive current collector and a positive active layer. The positive current collector has two opposing surfaces in its own thickness direction, and the positive active layer is disposed on either or both of the opposing surfaces of the positive current collector. The materials, composition, and manufacturing methods of the positive electrode sheet used in the lithium-ion battery of this application may include any techniques disclosed in the prior art.

[0099] As an example, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer. The negative electrode current collector has two opposing surfaces in its own thickness direction, and the negative electrode active layer is disposed on either or both of the opposing surfaces of the negative electrode current collector. The materials, composition, and manufacturing methods of the negative electrode sheet used in the lithium-ion battery of this application may include any techniques disclosed in the prior art.

[0100] The materials and shapes of the separators used in the lithium-ion batteries of this application are not particularly limited, and may include any techniques disclosed in the prior art.

[0101] Those skilled in the art will understand that the electrolyte plays a role in conducting ions between the positive and negative electrodes, and the electrolyte used in the lithium-ion battery of this application can include any technology disclosed in the prior art. As an example, the electrolyte may include lithium salts, solvents, etc. In some embodiments, the electrolyte may also optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0102] This application does not specify a particular method for preparing lithium-ion batteries; conventional methods in the art can be used to prepare lithium-ion batteries. For example, a positive electrode, a separator, and a negative electrode can be stacked sequentially, with the separator positioned between the positive and negative electrodes. A cell can be obtained through a stacking or winding process, followed by baking, electrolyte injection, formation, and encapsulation to obtain the lithium-ion battery of this application.

[0103] It is understood that in the electrical equipment provided in this application, the lithium-ion battery can be used as a power source for the electrical equipment, or as an energy storage unit for the electrical equipment. The electrical equipment may be, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0104] The electrical equipment provided in this application has the same advantages as the lithium-ion battery mentioned above because it uses the lithium-ion battery provided in this application, which will not be repeated here.

[0105] The present application will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present application in any way.

[0106] [Adhesive Examples and Comparative Examples] Example 1 This embodiment provides an adhesive, the composition of which and its preparation method are as follows: (1) Using pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) as basic monomers, they were added at a molar ratio of 1:1 and dissolved in N-methylpyrrolidone (NMP) solvent. The reaction was carried out under a nitrogen atmosphere at 35°C for 2 hours to synthesize a polyamic acid (PAA) precursor; (2) Subsequently, a polar functional group modifier (lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), 4-hydroxyphthalic anhydride or trimellitic anhydride (TMA)) and a crosslinking agent terephthalaldehyde were added, wherein the amount of modifier was equal to the amount of precursor. The amount of the pure substance (i.e., the mass excluding the solvent) is 8% (3wt% lithium sulfonylimide modifier, 2wt% hydroxyphthalic anhydride modifier, and 3wt% carboxyphthalic anhydride modifier), and the amount of crosslinking agent is 4% of the pure substance mass of the precursor. The mixture is heated to 70℃ and stirred for 2.5 hours to graft the modifier onto the precursor molecular chain. At the same time, the crosslinking agent covalently bridges the precursor molecular chains. The mixture is ultrasonically dispersed for 45 minutes to break the air bubbles inside the adhesive. The solid content is adjusted to 10% and the viscosity to 1500 mPa·s. The mixture is then sealed for later use.

[0107] Example 2 This embodiment provides an adhesive, the composition of which and its preparation method are as follows: (1) Using pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) as basic monomers, they were added at a molar ratio of 1:1 and dissolved in N-methylpyrrolidone (NMP) solvent. The reaction was carried out under a nitrogen atmosphere at 30°C for 2 hours to synthesize polyamic acid (PAA) precursor. (2) Then add polar functional group modifiers (lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), 4-hydroxyphthalic anhydride, trimellitic anhydride (TMA)) and crosslinking agent terephthalaldehyde, wherein the amount of modifier is 5% of the pure substance mass of the precursor (lithium sulfonylimide modifier accounts for 2wt%, hydroxyphthalic anhydride modifier accounts for 1wt%, and carboxyphthalic anhydride modifier accounts for 2wt%), and the amount of crosslinking agent is 3% of the pure substance mass of the precursor. Heat to 60℃ and stir for 2 hours to graft the modifier onto the precursor molecular chain. At the same time, the crosslinking agent covalently bridges the precursor molecular chains. Disperse ultrasonically for 30 minutes to break the bubbles inside the glue. Adjust the solid content to 8% and the viscosity to 1000 mPa·s. Seal and store for later use.

[0108] Example 3 This embodiment provides an adhesive, the composition of which and its preparation method are as follows: (1) Using pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) as basic monomers, they were added at a molar ratio of 1:1 and dissolved in N-methylpyrrolidone (NMP) solvent. The reaction was carried out under a nitrogen atmosphere at 40°C for 2 hours to synthesize polyamic acid (PAA) precursor. (2) Then add polar functional group modifiers (lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), 4-hydroxyphthalic anhydride, trimellitic anhydride (TMA)) and crosslinking agent terephthalaldehyde. The amount of modifier is 10% of the pure substance mass of the precursor (lithium sulfonylimide modifier accounts for 4wt%, hydroxyphthalic anhydride modifier accounts for 3wt%, and carboxyphthalic anhydride modifier accounts for 3wt%), and the amount of crosslinking agent is 5% of the pure substance mass of the precursor. Heat to 80℃ and stir for 3 hours to graft the modifier onto the precursor molecular chain. At the same time, the crosslinking agent covalently bridges the precursor molecular chains. Disperse ultrasonically for 60 minutes to break the bubbles inside the glue. Adjust the solid content to 12% and the viscosity to 2000 mPa·s. Seal and store for later use.

[0109] Example 4 This embodiment provides an adhesive, the composition of which and its preparation method are as follows: (1) Using pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) as basic monomers, they were added at a molar ratio of 1:1 and dissolved in N-methylpyrrolidone (NMP) solvent. The reaction was carried out under a nitrogen atmosphere at 38°C for 2 hours to synthesize polyamic acid (PAA) precursor. (2) Subsequently, polar functional group modifiers (lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), 4-hydroxyphthalic anhydride, trimellitic anhydride (TMA)) and crosslinking agent terephthalaldehyde were added. The amount of modifier was 9% of the precursor mass (lithium sulfonylimide modifier accounted for 4wt%, hydroxyphthalic anhydride modifier accounted for 3wt%, and carboxyphthalic anhydride modifier accounted for 2wt%), and the amount of crosslinking agent was 4.5% of the precursor mass. The mixture was heated to 78°C and stirred for 2.8 hours to graft the modifier onto the precursor molecular chain. At the same time, the crosslinking agent covalently bridged the precursor molecular chains. The mixture was ultrasonically dispersed for 55 minutes to break the air bubbles inside the adhesive. The solid content was adjusted to 11% and the viscosity to 1800 mPa·s. The mixture was then sealed for later use.

[0110] Example 5 This embodiment provides an adhesive, the composition of which and its preparation method are as follows: (1) Using pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) as basic monomers, they were added at a molar ratio of 1:1 and dissolved in N-methylpyrrolidone (NMP) solvent. The reaction was carried out under a nitrogen atmosphere at 32°C for 2 hours to synthesize polyamic acid (PAA) precursor. (2) Subsequently, polar functional group modifiers (lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), 4-hydroxyphthalic anhydride, trimellitic anhydride (TMA)) and crosslinking agent terephthalaldehyde were added. The amount of modifier was 6% of the pure substance mass of the precursor (lithium sulfonylimide modifier accounted for 2.5wt%, hydroxyphthalic anhydride modifier accounted for 1.5wt%, and carboxyphthalic anhydride modifier accounted for 2wt%), and the amount of crosslinking agent was 3.5% of the pure substance mass of the precursor. The mixture was heated to 65°C and stirred for 2.2 hours to graft the modifier onto the precursor molecular chain. At the same time, the crosslinking agent covalently bridged the precursor molecular chains. The mixture was ultrasonically dispersed for 35 minutes to break the air bubbles inside the adhesive. The solid content was adjusted to 9% and the viscosity to 1200 mPa·s. The mixture was then sealed for later use.

[0111] Example 6 This embodiment provides an adhesive with different monomer selection compared to Example 1: an equal amount of aliphatic dianhydride cyclobutanetetracarboxylic dianhydride is used instead of aromatic dianhydride, and an equal amount of aliphatic diamine 1,4-cyclohexanediamine is used instead of aromatic diamine.

[0112] Example 7 This embodiment provides an adhesive that differs from Embodiment 5 in that the composition of the modifier is different. In the modifier, lithium sulfonylimide modifier accounts for 1.8 wt%, hydroxyphthalic anhydride modifier accounts for 2.2 wt%, and carboxyphthalic anhydride modifier accounts for 2 wt%.

[0113] Example 8 This embodiment provides an adhesive that differs from Embodiment 4 in that the composition of the modifier is different. In the modifier, lithium sulfonylimide modifier accounts for 4.8 wt%, hydroxyphthalic anhydride modifier accounts for 2.2 wt%, and carboxyphthalic anhydride modifier accounts for 2 wt%.

[0114] Example 9 This embodiment provides an adhesive, the composition of which and its preparation method are as follows: (1) Using pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) as basic monomers, they were added at a molar ratio of 1:1 and dissolved in N-methylpyrrolidone (NMP) solvent. The reaction was carried out under a nitrogen atmosphere at 30°C for 2 hours to synthesize polyamic acid (PAA) precursor. (2) Then add polar functional group modifiers (lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), 4-hydroxyphthalic anhydride, trimellitic anhydride (TMA)) and crosslinking agent terephthalaldehyde. The amount of modifier is 5% of the pure substance mass of the precursor (lithium sulfonylimide modifier accounts for 2wt%, hydroxyphthalic anhydride modifier accounts for 1.5wt%, and carboxyphthalic anhydride modifier accounts for 1.5wt%), and the amount of crosslinking agent is 3% of the pure substance mass of the precursor. Heat to 60℃ and stir for 2 hours to graft the modifier onto the precursor molecular chain. At the same time, the crosslinking agent covalently bridges the precursor molecular chains. Disperse ultrasonically for 30 minutes to break the bubbles inside the glue. Adjust the solid content to 8% and the viscosity to 1000 mPa·s. Seal and store for later use.

[0115] Example 10 This embodiment provides an adhesive, the composition of which and its preparation method are as follows: (1) Using pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) as basic monomers, they were added at a molar ratio of 1:1 and dissolved in N-methylpyrrolidone (NMP) solvent. The reaction was carried out under a nitrogen atmosphere at 38°C for 2 hours to synthesize polyamic acid (PAA) precursor. (2) Then add polar functional group modifiers (lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), 4-hydroxyphthalic anhydride, trimellitic anhydride (TMA)) and crosslinking agent terephthalaldehyde. The amount of modifier is 8% of the pure substance mass of the precursor (lithium sulfonylimide modifier accounts for 3.2wt%, hydroxyphthalic anhydride modifier accounts for 2.4wt%, and carboxyphthalic anhydride modifier accounts for 2.4wt%), and the amount of crosslinking agent is 4% of the pure substance mass of the precursor. Heat to 75℃ and stir for 3 hours to graft the modifier onto the precursor molecular chain. At the same time, the crosslinking agent covalently bridges the precursor molecular chains. Disperse ultrasonically for 40 minutes to break the bubbles inside the glue. Adjust the solid content to 10% and the viscosity to 1500 mPa·s. Seal and set aside for later use.

[0116] Example 11 This embodiment provides an adhesive, which differs from Example 1 in the specific selection of each raw material: in this embodiment, the dianhydride is benzophenone tetracarboxylic dianhydride; the diamine is p-phenylenediamine; the modifier is lithium bis(fluorosulfonyl)imide (LiFSI), 3-hydroxyphthalic anhydride, and pyromellitic dianhydride (PMDA, auxiliary modifier); and the crosslinking agent is diphenylmethane diisocyanate.

[0117] Example 12 This embodiment provides an adhesive, which differs from Embodiment 1 in the specific selection of each raw material: in this embodiment, the dianhydride is diphenyl ether tetracarboxylic dianhydride; the diamine is 4,4'-diaminodiphenylmethane; the modifier is sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), 5-hydroxyphthalic anhydride, and phenyltrimonium anhydride (TMA, auxiliary modifier); and the crosslinking agent is toluene diisocyanate.

[0118] Comparative Example 1 This comparative example provides an adhesive that differs from Example 1 in that it uses an equal amount of lithium sulfonylimide modifier instead of hydroxyphthalic anhydride modifier and carboxyphthalic anhydride modifier.

[0119] Comparative Example 2 This comparative example provides an adhesive that differs from Example 1 in that it uses an equal amount of hydroxyphthalic anhydride modifier instead of lithium sulfonylimide modifier.

[0120] Comparative Example 3 This comparative example provides an adhesive, the composition of which and its preparation method are as follows: (1) Using pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether (ODA) as basic monomers, they were added at a molar ratio of 1:1 and dissolved in N-methylpyrrolidone (NMP) solvent. The reaction was carried out at 35°C under a nitrogen atmosphere for 2 hours to synthesize polyamic acid (PAA) precursor. (2) Then add polar functional group modifiers (lithium bis(trifluoromethanesulfonyl)imide, 4-hydroxyphthalic anhydride, trimellitic anhydride) and crosslinking agent dipentaerythritol pentaacrylate, wherein the amount of modifier is 10% of the pure substance mass of the precursor (lithium sulfonylimide modifier accounts for 6wt%, hydroxyphthalic anhydride modifier accounts for 2wt%, and carboxyphthalic anhydride modifier accounts for 2wt%), and the amount of crosslinking agent is 4% of the pure substance mass of the precursor. Heat to 80℃ and stir for 3 hours to graft the modifier onto the precursor molecular chain. At the same time, the crosslinking agent covalently bridges the precursor molecular chains. Disperse ultrasonically for 45 minutes to break the bubbles inside the glue. Adjust the solid content to 10% and the viscosity to 1500 mPa·s. Seal and store for later use.

[0121] Comparative Example 4 This comparative example provides an adhesive that differs from Example 1 in that no crosslinking agent is added during the preparation process.

[0122] Comparative Example 5 This comparative example uses TAD-800 type conventional PI adhesive manufactured by TEDA Electronic Materials Co., Ltd.

[0123] Comparative Example 6 This comparative example uses Kynar® HSV 900 conventional PVDF adhesive manufactured by Arkema, France.

[0124] Experimental Example 1 The adhesives provided in the above embodiments and comparative examples were subjected to various performance tests. The specific test items and methods are as follows: (1) Infrared spectral structural characterization (FTIR): Referring to the aforementioned test methods, Fourier transform infrared spectroscopy was used for testing in either ATR total reflection mode or KBr pellet method (KBr pellet method in this test example), with a wavenumber range of 4000-400 cm⁻¹. -1 4cm resolution -1 32 scans were performed. A 1640cm sample was obtained. -1 -1650cm -1 The peak height of the characteristic peak at the wavenumber is used as the characteristic peak intensity.

[0125] (2) Referring to the description of the relevant test methods mentioned above, the grafting rates of R1 group and R2 group were determined by... 1 Quantitative nuclear magnetic resonance (NMR) was performed using H-NMR; the molar ratio of R1 group to R2 group was determined by elemental analysis; and the grafting rate of crosslinking groups was determined by a combination of X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma optical emission spectroscopy (ICP-OES).

[0126] (3) Number-average molecular weight Referring to the description of the relevant test methods above, the number-average molecular weight was tested using gel permeation chromatography (GPC).

[0127] (4) Ion conductivity coefficient Referring to the description of the relevant test methods above, the test was performed using the electrochemical impedance spectroscopy (EIS) method on an electrochemical workstation.

[0128] (5) Tensile strength and elongation at break Referring to the description of the relevant test methods mentioned above and GB / T 1040.1-2006, a universal tensile testing machine was used to stretch the material at a speed of 5 mm / min at room temperature, and the stress-strain curve was recorded to obtain the tensile strength and elongation at break.

[0129] (6) Swelling rate Referring to the aforementioned test method description, the film dried to constant weight was weighed and recorded as m0. It was then immersed in a 1 mol / L LiPF6 / EC:DMC:EMC = 1:1:1 electrolyte at 25°C for 72 hours. After removing and drying the surface electrolyte, it was weighed again as m1. The swelling rate was calculated using the formula: Swelling rate (%) = (m1 / m0) * (m0 ... m0) / m0×100%.

[0130] The specific test results are shown in the table below: Table 1

[0131] [Examples and Comparative Examples of Positive Electrode Plates] Example 13 This embodiment provides a positive electrode sheet, the specific composition and preparation method of which are as follows: Preparation of the positive electrode: A 13μm thick aluminum foil was used as the positive electrode current collector; lithium manganese oxide composite material (manufacturer: Hunan Bangpu Recycling Technology Co., Ltd., model: BPM-LMO-01), conductive carbon black, and the binder from Example 1 were thoroughly mixed in an appropriate amount of NMP solvent at a weight ratio of 97.7:1.3:1.0 (binder usage 1.0%, low usage design) to form a uniform positive electrode slurry; the positive electrode slurry was uniformly coated on the surface of the aluminum foil of the positive electrode current collector and dried (passed through 80℃ sequentially). The NMP solvent in the slurry was gradually removed by heating at 100℃ (1 hour), 100℃ (1 hour), and 120℃ (0.5 hours) to prevent rapid solvent evaporation from causing pinholes and cracks in the film. The dried electrode was then placed in a high-temperature oven under inert gas (nitrogen or argon) protection, heated to 220℃ at a rate of 5℃ / min, held at that temperature for 3 hours, and cooled to room temperature before being removed. Precise rolling was then performed using a two-roll mill, with the rolling pressure controlled at 8MPa and the rolling speed at 0.5m / min (compacted density 2.7g / cm³). 3 After satisfying the strong bonding characteristics of the PI binder, the positive electrode sheet is obtained; the active layer density of the positive electrode sheet is 190 g / m². 2 The porosity is 40%, and the thickness of the positive electrode active layer is 180μm.

[0132] To conduct electrical performance testing, the above-mentioned positive electrode sheet was fabricated into a battery cell. The specific fabrication method is as follows: Preparation of the negative electrode: An 8μm thick copper foil was used as the negative electrode current collector. The negative electrode active material (graphite), binder (styrene-butadiene rubber (SBR), thickener (sodium carboxymethyl cellulose (CMC-Na), and conductive agent (SuperP)) were thoroughly mixed in an appropriate amount of deionized water at a weight ratio of 96.2:1.8:1.2:0.8 to form a uniform negative electrode slurry. The negative electrode slurry was uniformly coated onto the surface of the copper foil, and then dried and cold-pressed (compacted density 1.55 g / cm³). 3 After that, a negative electrode sheet was obtained; the areal density of the negative electrode sheet was 88 g / m³. 2 .

[0133] Separating membrane: A porous polyethylene (PE) membrane with a thickness of 12μm and a porosity of 40% is used as the separating membrane.

[0134] Preparation of electrolyte: Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried LiPF6 was dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L. 0.8 wt% fluoroethylene carbonate (FEC) additive was added.

[0135] Preparation of the secondary battery: The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. Then, the electrode assembly is wound to obtain the electrode assembly. The electrode assembly is placed in an outer packaging shell of model 18650 (outer diameter 18mm, height 65mm), and the electrolyte prepared above is injected. After vacuum sealing, standing, formation, aging and other processes, the secondary battery is obtained. The cell design capacity is 2300mAh.

[0136] Examples 14-24 This embodiment provides a positive electrode sheet, which, compared with Embodiment 13, uses the binders provided in Embodiments 2-12 respectively.

[0137] Examples 25-28 This embodiment provides a positive electrode sheet. Compared with embodiment 13, the amount of binder is different, namely 0.5%, 1.5%, 2%, and 2.5%. Positive electrode active material is used to compensate for the change in binder content. For example, in embodiment 25, the binder content is 0.5%, which is 0.5% less than that in embodiment 13. Therefore, the content of positive electrode active material in this embodiment is increased by 0.5% accordingly.

[0138] Examples 29-34 This embodiment provides a positive electrode sheet. Compared with embodiment 13, the areal density, active layer thickness, and active layer porosity of the positive electrode active layer are different, as detailed in the table below.

[0139] Table 2

[0140] Comparative Examples 7-12 This comparative example provides a positive electrode sheet, which, compared with Example 13, uses the binders provided by Comparative Examples 1-6 respectively.

[0141] Experimental Example 2 The positive electrode and battery cell provided in the above embodiments and comparative examples were subjected to various performance tests. The specific test items and test methods are as follows: (1) Infrared spectral structural characterization (FTIR): Referring to the aforementioned test methods, Fourier transform infrared spectrometers were used for testing, with a wavenumber range of 4000-400 cm⁻¹.-1 4cm resolution -1 32 scans were performed. A 1640cm sample was obtained. -1 -1650cm -1 The peak height of the characteristic peak at the wavenumber is used as the characteristic peak intensity.

[0142] (2) Interfacial peel strength The positive electrode sheet was cut into 15mm×100mm electrode strips and subjected to a 180° peel test using a universal tensile testing machine at a peel speed of 50mm / min. The stable peel force was recorded and the peel strength was calculated.

[0143] (3) Porosity test The porosity test uses the helium displacement method to determine the true density of the electrode coating material, the weighing method combined with a thickness gauge to measure the compaction density of the electrode, and then the electrode porosity ε is calculated according to the formula. ε=(1 (Compacted density / True density) × 100%.

[0144] (4) Thermal decomposition test Thermogravimetric (TG) tests were conducted at the electrode end using an N2 atmosphere, a heating rate of 10℃ / min, and a test range from room temperature to 800℃ to obtain the test curve, initial thermal decomposition temperature, and residual carbon rate at 800℃.

[0145] (5) Normal temperature circulation Under normal temperature (25±2℃) conditions, the battery cells provided in the above embodiments and comparative examples are charged to 4.3V at 0.33C, and then charged at 4.3V at a constant voltage until the current is less than or equal to 0.05mA. After standing for 5 minutes, they are discharged to 3.0V at 0.33C. The capacity C0 at this time is recorded. The above charge and discharge cycle process is repeated. The discharge capacity is recorded after each cycle until the discharge capacity is reduced to 80% of the initial capacity C0. The total number of cycles at this time is recorded.

[0146] (6) 45℃ high temperature cycling Under constant temperature of 45℃, the battery cells provided in the above embodiments and comparative examples are charged to 4.3V at 0.33C, and then charged at 4.3V at constant voltage until the current is less than or equal to 0.05mA. After standing for 5 minutes, they are discharged to 3.0V at 0.33C. The capacity C1 at this time is recorded. The above charge and discharge cycle process is repeated, and the constant temperature of 45℃ is maintained throughout. The discharge capacity is recorded after each cycle until the discharge capacity is reduced to 80% of the initial capacity C1. The total number of cycles at this time is recorded.

[0147] (7) 3C ratio retention rate Under normal temperature (25±2℃) conditions, the battery cells provided in the above embodiments and comparative examples were charged to 4.3V at 0.33C, and then charged at 4.3V at a constant voltage until the current was less than or equal to 0.05mA. After standing for 5 minutes, the batteries were discharged to 3.0V at 0.5C and 3C rates respectively. After each discharge rate, the batteries were left to stand for 10 minutes before the next rate test was performed. The discharge capacity at the 3C rate was recorded, and the ratio of its capacity to the capacity at the 0.5C rate was calculated, which is the 3C rate capacity retention rate.

[0148] (8) Positive electrode expansion rate Before the cycle test, select the positive electrode sheet and use a thickness gauge to measure the thickness at different positions (5 points are selected evenly) and take the average value. Record the initial thickness d1. After the cell completes the above 100 room temperature cycles, disassemble the battery and take out the positive and negative electrodes. Wipe the electrolyte on the surface with lint-free paper and measure the thickness at the same 5 positions and take the average value. Record the thickness d2 after the cycle. Calculate the electrode thickness expansion rate according to the formula: Thickness expansion rate (%) = (thickness after cycle - initial thickness) / initial thickness × 100%.

[0149] (9) Volumetric energy density The volumetric energy density of the battery was tested as follows: at 25±2℃, the length, width and thickness of the individual battery cells were measured using digital vernier calipers, and the apparent volume of the battery was calculated; the actual discharge energy of the battery was tested using a 0.2C constant current charge and discharge regime (3.0V-4.3V), and the volumetric energy density was calculated as the ratio of battery energy to apparent volume, with the unit being Wh / L.

[0150] The specific test results are shown in the table below: Table 3

[0151] The test results above show that the binder provided in this application embodiment has sulfur- and nitrogen-containing polar functional groups directionally grafted onto the side groups of the PAA main chain as ion-conducting functional groups, and oxygen-containing polar functional groups introduced as highly efficient bonding polar functional groups. The PAA main chain is then bridged by crosslinking groups. This allows for the construction of a three-dimensional crosslinking network in the molecular chain when applied to the electrode, achieving an integrated design of ion-conducting sites, bonding sites, rigid framework, and crosslinking network. Through the above molecular structure design, multi-dimensional improvements in ion conduction, strong bonding, resistance to electrolyte swelling, and high mechanical properties are achieved, with a good balance among various properties.

[0152] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. An adhesive, characterized in that, It includes a polyamic acid backbone, on which R1 groups and R2 groups are grafted, and the backbones are bridged by crosslinking groups. Wherein, the R1 group is a sulfur-nitrogen polar functional group; the R2 group is an oxygen-nitrogen polar functional group; The crosslinking groups include at least one of the following: aliphatic urethane bridging groups, aliphatic amide bridging groups, aromatic urethane bridging groups, aromatic amide bridging groups, aromatic imine bridging groups, epoxy ring-opening ether bridging groups, epoxy ring-opening ester bridging groups, aromatic ester bridging groups, and aromatic imine bridging groups. In the infrared spectrum of the adhesive, at 1640 cm⁻¹ -1 -1650cm -1 The characteristic peak intensity at the wavenumber is 0.2-0.

4.

2. The adhesive according to claim 1, characterized in that, The grafting rates of the R1 group and the R2 group are ≥90% respectively. Optionally, the grafting rates of the R1 group and the R2 group are independently 90%-98%. And / or, the molar ratio of the R1 group to the R2 group is 0.8-1.2:1; And / or, the R1 group is a lithium sulfonamide group; the R2 group is a hydroxyl and / or a carboxyl group.

3. The adhesive according to claim 1, characterized in that, The grafting rate of the crosslinking group is ≥90%, optionally 90%-98%.

4. The adhesive according to claim 1, characterized in that, The polyamic acid backbone is an aromatic polyamic acid backbone or an aliphatic polyamic acid backbone; And / or, the polyamic acid backbone is formed by the polymerization reaction of dianhydride and diamine; Optionally, the dianhydride includes at least one of aromatic dianhydride and aliphatic dianhydride; further optionally, the aromatic dianhydride includes at least one of pyromellitic dianhydride, diphenyl ether dianhydride, biphenyl dianhydride, benzophenone dianhydride, bisphenol A type diether dianhydride, 3,3,4,4-diphenyl sulfone tetracarboxylic acid dianhydride, and 1,4,5,8-naphthalene tetracarboxylic acid dianhydride; the aliphatic dianhydride includes at least one of cyclobutane tetracarboxylic acid dianhydride, cyclohexane tetracarboxylic acid dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic acid dianhydride, hydrogenated pyromellitic dianhydride, and 1,2,3,4-butane tetracarboxylic acid dianhydride; Optionally, the diamine includes at least one of aromatic diamines and aliphatic diamines; more preferably, the aromatic diamine includes at least one of 4,4'-diaminodiphenyl ether, p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfone, 2,2'-dimethyl-4,4'-diaminobiphenyl, 2,2'-di(trifluoromethyl)diaminobiphenyl, and 1,5-naphthyldiamine; the aliphatic diamine includes at least one of 1,4-cyclohexanediamine, isophoronediamine, 1,3-cyclohexanedimethylamine, ethylenediamine, 1,6-hexanediamine, and piperazine.

5. The adhesive according to claim 1, characterized in that, The number average molecular weight of the adhesive is 8 × 10⁻⁶. 4 -3×10 5 ; And / or, the adhesive has an ionic conductivity of 10 at 25°C. -6 -10 -5 S / cm; And / or, the adhesive has a tensile strength of 120-160 MPa and an elongation at break of 8%-12%; And / or, the electrolyte swelling resistance of the adhesive is ≤5%.

6. A positive electrode, the positive electrode comprising a current collector and a positive electrode active layer located on at least one surface of the current collector; characterized in that, The positive electrode active layer includes a positive electrode active material and the binder according to any one of claims 1-5. In the infrared spectrum of the positive electrode sheet, at 1640 cm⁻¹... -1 -1650cm -1 The characteristic peak intensity at the wavenumber is 0.6-0.

8.

7. The positive electrode sheet according to claim 6, characterized in that, The binder comprises 0.5%-2.5% by mass of the total mass of the positive electrode active layer; optionally, it comprises 1%-2%. And / or, the areal density of the positive electrode active layer is 180-200 g / m³. 2 ; And / or, the thickness of the positive electrode active layer is 100-250 μm and the porosity is 35%-45%.

8. The positive electrode sheet according to claim 7, characterized in that, The interfacial peel strength between the positive electrode active layer and the current collector is 1.2-1.5 N / cm; And / or, the thermogravimetric analysis is performed in an N2 atmosphere, with a heating rate of 10℃ / min and a test range of room temperature to 800℃. The initial weight loss temperature (T5%) of the positive electrode is ≥380℃, and the residual carbon rate at 800℃ is 10%-16%.

9. A lithium-ion battery, characterized in that, Includes the positive electrode sheet as described in any one of claims 6-8.

10. An electrical appliance, characterized in that, Including the lithium-ion battery as described in claim 9.

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