Polyimide binder for positive electrode of lithium-ion battery and preparation method for polyimide binder

Abstract

Disclosed in the present invention are a polyimide binder for a positive electrode of a lithium-ion battery and a preparation method for the polyimide binder. The polyimide binder comprises cyclodextrin and a sulfonic acid group. The method comprises: dissolving cyclodextrin, sulfonated diamine, and triethylamine in an organic solvent, stirring these materials until same are fully dissolved, and then adding a dianhydride to obtain a sulfonated polyamic acid solution included in cyclodextrin; and then adding benzoic acid and a catalyst to the sulfonated polyamic acid solution, imidizing and cooling the mixture, adding a washing solvent to form a precipitate, and filtering the precipitate to obtain the polyimide binder. The polyimide binder of the present invention has excellent thermal stability and relatively strong mechanical properties. In addition, a relatively high bonding strength effectively inhibits the separation of the binder from active material particles and aluminum foil. An electrode sheet prepared using the obtained polyimide binder, when used in a lithium-ion battery, effectively improves the electrochemical performance of the lithium-ion battery.

Description

A polyimide binder for lithium-ion battery cathode and its preparation method Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a polyimide binder for the positive electrode of a lithium-ion battery and its preparation method. Background Technology

[0002] Lithium-ion batteries, as a new generation of green energy storage system, possess advantages such as high specific energy, high energy density, high coulombic efficiency, high operating voltage, long cycle life, and wide operating temperature range. Therefore, lithium-ion batteries are widely used in portable electronic products, electric vehicles, and other fields. However, their application in these fields still faces challenges related to energy density, cost, and safety. Developing lithium-ion batteries with high energy density, low cost, and high safety remains a key focus of current research.

[0003] Lithium-ion batteries consist of components such as a positive electrode, a separator, an electrolyte, and a negative electrode. The positive and negative electrodes are composed of powdered active materials (such as lithium metal oxides or carbon anode materials), conductive agents, electrode current collectors, and binders. The binder's role is to bond the active materials, conductive agents, and current collectors together. For an ideal electrode, each active particle should be properly shaped, dispersed, and connected to the current collector and electrolyte, possessing low resistance and continuous internal channels.

[0004] For a long time, in the large-scale production of lithium-ion batteries, polyvinylidene fluoride (PVDF) has been mainly used as a binder and organic solvents such as N-methylpyrrolidone (NMP) as dispersants. However, PVDF has its own drawbacks, such as poor flexibility and bonding properties, and it swells in the electrolyte. Furthermore, it reacts with metallic lithium and lithium... x C6 undergoes an exothermic reaction at high temperatures, posing a significant safety hazard.

[0005] Therefore, to address the aforementioned problems, this invention provides a polyimide binder for lithium-ion battery cathodes and its preparation method. Cyclodextrins have multiple hydroxyl groups (-OH) in their molecular structure, which can form hydrogen bonds and other physicochemical interactions with the electrode material surface, thus providing excellent adhesion. The molecular structure of cyclodextrins is hydrophilic inside and hydrophobic outside, which can promote electrolyte penetration and ion migration through its internal porous structure. This characteristic helps to improve the conduction speed and efficiency of lithium ions in the electrode material during charging and discharging, thereby improving the rate performance and energy density of the battery. The sulfonate groups can dissociate into negatively charged sulfonate ions, increasing the ionic conductivity in the electrode and improving the transport efficiency of lithium ions in the electrode, thereby improving the overall electrochemical performance of the battery. Polyimide materials possess characteristics such as structural diversity, good thermal stability, stable chemical structure, and excellent mechanical properties. As a binder in lithium-ion battery cathodes, it is of great significance for developing polyimides with high capacity, stable cycle performance, and good safety performance. Summary of the Invention

[0006] The purpose of this invention is to provide a polyimide binder for lithium-ion battery cathodes and its preparation method. This binder has advantages such as excellent thermal stability, stable chemical structure, and strong adhesion. By incorporating cyclodextrin and introducing groups such as sulfonate, this binder improves the conduction speed and efficiency of lithium ions in the electrode material, enhances the rate performance and energy density of the battery, reduces electrode impedance, increases the flexibility of the electrode sheet, and ensures the cycle stability of the lithium-ion battery.

[0007] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0008] A polyimide binder for the positive electrode of a lithium-ion battery, the polyimide binder comprising a polyimide containing cyclodextrin and sulfonic acid groups, the polyimide having the structural formula shown in Structural Formula 1:

[0009] Where m is any integer from 100 to 1000, and the weight-average molecular weight is greater than 20,000. Preferably, the A group in structural formula 1 is selected from any one of the following structural formulas:

[0010] Preferably, the B group in structural formula 1 is selected from any one of the following structural formulas:

[0011] This application also claims a method for preparing a polyimide binder for the positive electrode of a lithium-ion battery, comprising the following steps:

[0012] (1) Under nitrogen protection, cyclodextrin, sulfonated diamine and triethylamine are dissolved in an organic solvent and stirred until fully dissolved. Then, diacid anhydride is added and the mixture is stirred at 60-100℃ for 6-12 hours to obtain a sulfonated polyamic acid solution containing cyclodextrin.

[0013] (2) Add benzoic acid and catalyst to the sulfonated polyamic acid solution containing cyclodextrin obtained in step (1), heat to 180-220℃, react at a constant temperature for 10-18h to carry out imidization, cool to room temperature, add washing solvent to precipitate, filter, and obtain the polyimide binder for lithium-ion battery cathode.

[0014] Preferably, in step (1), the molar ratio of the cyclodextrin to the sulfonated diamine is 1:0.5-1.5; and the molar ratio of the sulfonic acid group in the sulfonated diamine to the triethylamine is 1:0.9-1.1.

[0015] The cyclodextrin is selected from one of α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin;

[0016] The organic solvent is selected from one or more of m-cresol, N-methylpyrrolidone, dimethylacetamide, N,N-dimethylformamide, and p-chlorophenol;

[0017] The solid content of the sulfonated polyamic acid solution is 10-25 wt%.

[0018] Preferably, in step (2), the washing solvent is selected from one or more of ethyl acetate, methanol, ethanol, isopropanol, ethylene glycol, 2-butanol or cyclopentanol;

[0019] The catalyst is selected from one of quinoline, isoquinoline, or tertiary amine.

[0020] The method for preparing the lithium-ion battery positive electrode sheet using polyimide binder as described above includes the following steps:

[0021] S1. Take polyimide binder and stir it to dissolve it in solvent to obtain binder solution. Grind and mix the positive electrode active material and conductive agent evenly and add them to binder solution. Adjust the viscosity of the mixture to 2000-10000 mPa·s by adding solvent to obtain black slurry.

[0022] S2. The black slurry obtained in step S1 is uniformly coated onto aluminum foil, dried, and then compacted to obtain the positive electrode sheet of a lithium-ion battery.

[0023] Preferably, in step S1, the solvent is selected from one of N,N-dimethylformamide, N,N-dimethylacetamide, or N-methylpyrrolidone;

[0024] The positive electrode active material is selected from one or more of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, or ternary positive electrode material lithium nickel cobalt manganese oxide.

[0025] The conductive agent is selected from one or more of acetylene black, superconducting carbon black (SuperP), carbon nanotubes, graphene, and Ketjen black.

[0026] Preferably, in step S1, the mass concentration of the adhesive solution is 5%-20%; in step S2, the drying is vacuum drying at 80℃-120℃.

[0027] Preferably, in step S1, the content of the positive electrode active material is 2 mg·cm³. -2 -4mg·cm -2 In step S2, the positive electrode sheet of the lithium-ion battery is composed of an active material layer and an aluminum foil; the active material layer is composed of a positive electrode active material, a conductive agent, and a polyimide binder; the mass content of the binder in the active material layer is 1%-15%; the mass content of the conductive agent in the active material layer is 2%-25%.

[0028] Due to the application of the above technical solution, the present invention has the following beneficial effects compared with the prior art:

[0029] 1. The polyimide binder for lithium-ion battery cathode of the present invention uses polyimide as a skeleton, which has excellent thermal stability and strong mechanical properties, improves the bonding strength of the binder, and effectively inhibits the separation between the binder and the active material particles and aluminum foil.

[0030] 2. In the lithium-ion battery positive electrode of the present invention, cyclodextrin is encapsulated on the polyimide backbone chain by a polyimide binder. The cyclodextrin has multiple hydroxyl groups in its molecular structure. These hydroxyl groups can form hydrogen bonds and other interactions with the surface of the electrode material, providing good adhesion. The internal pore structure of cyclodextrin can also promote electrolyte penetration and ion migration, thereby improving cycle performance.

[0031] 3. The lithium-ion battery positive electrode of the present invention uses polyimide binder to introduce sulfonate and other groups, which can dissociate negatively charged sulfonate ions, increase the ionic conductivity in the electrode, and improve the transport efficiency of lithium ions in the electrode.

[0032] 4. The electrode sheet prepared by the polyimide binder obtained in this invention is used in lithium-ion batteries, which effectively enhances the electrochemical performance of lithium-ion batteries. Attached Figure Description

[0033] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, some of the drawings in the following description are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0034] Figure 1 is a schematic diagram of the battery assembly process in Embodiment 1 of the present invention;

[0035] Figure 2 is a schematic diagram of the structure of the electrode sheet for preparing the positive electrode of the battery in Example 1 of the present invention;

[0036] Figure 3 is an initial morphology SEM image of the electrode sheet of the battery positive electrode prepared in Comparative Example 1 of the present invention, with a magnification of 1000x;

[0037] Figure 4 is an initial morphology SEM image of the electrode sheet of the battery positive electrode prepared in Example 1 of the present invention, with a magnification of 500x;

[0038] Figure 5 is a graph showing the bonding strength of the electrode sheets of the battery positive electrode prepared in Example 1 and Comparative Example 1 of the present invention;

[0039] Figure 6 shows the initial impedance diagram and the impedance diagram after 100 cycles of the assembled battery of Comparative Example 1 of the present invention.

[0040] Figure 7 shows the cycle performance of the assembled batteries of Embodiment 1, Comparative Example 1, and Comparative Example 2 of the present invention. Detailed Implementation

[0041] To provide a clearer understanding of the technical features, objectives, and effects of this invention, specific implementation schemes are now described in detail.

[0042] The present invention will be further described below with reference to embodiments, but the present invention is not limited to the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to different requirements of specific use, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in the various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0043] Example 1

[0044] Referring to Figures 1, 2, 4, 5, and 7, this embodiment provides a polyimide binder for lithium-ion battery cathodes and its preparation method, including the following steps:

[0045] (1) Under nitrogen protection, 1.794 g of 4,4'-bis(4-aminophenoxy)-[1,1'-biphenyl]-3-sulfonic acid, 4.54 g of β-cyclodextrin and 0.85 g of triethylamine were dissolved in 20 ml of m-cresol and stirred until fully dissolved. Then, 1.2533 g of 4,4'-oxydiphthalic anhydride was added and stirred at 80 °C for 8 h to obtain a sulfonated polyamic acid solution containing cyclodextrin.

[0046] (2) Add 0.0844 g isoquinoline and 0.7327 g benzoic acid to the sulfonated polyamic acid solution containing cyclodextrin obtained in step (1), heat to 180°C, and react at a constant temperature for 18 h to carry out imidization. After the reaction is completed, cool to room temperature, drop the polyimide solution into ethyl acetate to precipitate the precipitate, filter, and obtain the polyimide binder for the positive electrode of the lithium-ion battery.

[0047] The method for preparing the lithium-ion battery positive electrode sheet using polyimide binder as described above includes the following steps:

[0048] S1. Dissolve 0.1g of the binder in 1.5ml of N-methylpyrrolidone to obtain a binder solution. Grind and mix 0.8g of lithium cobalt oxide (LiCoO2) positive electrode active material and 0.1g of conductive agent SuperP thoroughly. Add them to the binder solution in batches and stir to mix them evenly to obtain a black slurry.

[0049] S2. Using a four-sided coating apparatus, the black slurry obtained in step S1 is uniformly coated onto a clean aluminum foil and vacuum dried at 120°C for 12 hours to obtain the positive electrode sheet of LiCoO2 lithium-ion battery.

[0050] Example 2

[0051] This embodiment provides a polyimide binder for lithium-ion battery cathodes and its preparation method, including the following steps:

[0052] (1) Under nitrogen protection, 1.794 g of 4,4'-bis(4-aminophenoxy)-[1,1'-biphenyl]-3-sulfonic acid, 4.54 g of β-cyclodextrin and 0.85 g of triethylamine were dissolved in 20 ml of m-cresol and stirred until fully dissolved. Then, 1.3018 g of 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride was added and stirred at 80 °C for 8 h to obtain a solution containing sulfonated polyamic acid encapsulated by cyclodextrin.

[0053] (2) Add 0.0849 g isoquinoline and 0.7327 g benzoic acid to the sulfonated polyamic acid solution containing cyclodextrin obtained in step (1), heat to 180 °C, and react at a constant temperature for 18 h to carry out imidization. After the reaction is completed, cool to room temperature, drop the polyimide solution into ethyl acetate to precipitate the precipitate, filter, and obtain the polyimide binder for the positive electrode of the lithium-ion battery.

[0054] The method for preparing the lithium-ion battery positive electrode sheet using polyimide binder as described above includes the following steps:

[0055] S1. Dissolve 0.1g of the binder in 1.5ml of N-methylpyrrolidone to obtain a binder solution. Grind and mix 0.8g of lithium cobalt oxide (LiCoO2) positive electrode active material and 0.1g of conductive agent SuperP thoroughly. Add them to the binder solution in batches and stir to mix them evenly to obtain a black slurry.

[0056] S2. Using a four-sided coating apparatus, the black slurry obtained in step S1 is uniformly coated onto a clean aluminum foil and vacuum dried at 120°C for 12 hours to obtain the positive electrode sheet of LiCoO2 lithium-ion battery.

[0057] Example 3

[0058] This embodiment provides a polyimide binder for lithium-ion battery cathodes and its preparation method, including the following steps:

[0059] (1) Under nitrogen protection, 1.794 g of 4,4'-bis(4-aminophenoxy)-[1,1'-biphenyl]-3-sulfonic acid, 4.54 g of β-cyclodextrin and 0.85 g of triethylamine were dissolved in 20 ml of m-cresol and stirred until completely dissolved. Then, 2.1028 g of bisphenol A type diether dianhydride was added and stirred at 80 °C for 8 h to obtain a sulfonated polyamic acid solution containing cyclodextrin.

[0060] (2) Add 0.0929 g isoquinoline and 0.7327 g benzoic acid to the sulfonated polyamic acid solution containing cyclodextrin obtained in step (1), heat to 180 °C, and react at a constant temperature for 18 h to carry out imidization. After the reaction is completed, cool to room temperature, drop the polyimide solution into ethyl acetate to precipitate the precipitate, filter, and obtain the polyimide binder for the positive electrode of the lithium-ion battery.

[0061] The method for preparing the lithium-ion battery positive electrode sheet using polyimide binder as described above includes the following steps:

[0062] S1. Dissolve 0.1g of the binder in 1.5ml of N-methylpyrrolidone to obtain a binder solution. Grind and mix 0.8g of lithium cobalt oxide (LiCoO2) positive electrode active material and 0.1g of conductive agent SuperP thoroughly. Add them to the binder solution in batches and stir to mix them evenly to obtain a black slurry.

[0063] S2. Using a four-sided coating apparatus, the black slurry obtained in step S1 is uniformly coated onto a clean aluminum foil and vacuum dried at 120°C for 12 hours to obtain the positive electrode sheet of LiCoO2 lithium-ion battery.

[0064] Example 4

[0065] This embodiment provides a polyimide binder for lithium-ion battery cathodes and its preparation method, including the following steps:

[0066] (1) Under nitrogen protection, 2.1142 g of 4,4'-bis(4-aminophenoxy)-[1,1'-biphenyl]-3,3'-disulfonic acid, 4.54 g of β-cyclodextrin and 0.85 g of triethylamine were dissolved in 20 ml of m-cresol and stirred until completely dissolved. Then, 1.2533 g of 4,4'-oxydiphthalic anhydride was added and stirred at 80 °C for 8 h to obtain a sulfonated polyamic acid solution containing cyclodextrin-encapsulated polyamic acid.

[0067] (2) Add 0.0876 g isoquinoline and 0.7327 g benzoic acid to the sulfonated polyamic acid solution containing cyclodextrin obtained in step (1), heat to 180°C, and react at a constant temperature for 18 h to carry out imidization. After the reaction is completed, cool to room temperature, drop the polyimide solution into ethyl acetate to precipitate the precipitate, filter, and obtain the polyimide binder for the positive electrode of the lithium-ion battery.

[0068] The method for preparing the lithium-ion battery positive electrode sheet using polyimide binder as described above includes the following steps:

[0069] S1. Dissolve 0.1g of the binder in 1.5ml of N-methylpyrrolidone to obtain a binder solution. Grind and mix 0.8g of lithium cobalt oxide (LiCoO2) positive electrode active material and 0.1g of conductive agent SuperP thoroughly. Add them to the binder solution in batches and stir to mix them evenly to obtain a black slurry.

[0070] S2. Using a four-sided coating apparatus, the black slurry obtained in step S1 is uniformly coated onto a clean aluminum foil and vacuum dried at 120°C for 12 hours to obtain the positive electrode sheet of LiCoO2 lithium-ion battery.

[0071] Example 5

[0072] This embodiment provides a polyimide binder for lithium-ion battery cathodes and its preparation method, including the following steps:

[0073] (1) Under nitrogen protection, 2.1142 g of 4,4'-bis(4-aminophenoxy)-[1,1'-biphenyl]-3,3'-disulfonic acid, 4.54 g of β-cyclodextrin and 0.85 g of triethylamine were dissolved in 20 ml of m-cresol and stirred until completely dissolved. Then, 1.3018 g of 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride was added and stirred at 80 °C for 8 h to obtain a solution containing sulfonated polyamic acid encapsulated by cyclodextrin.

[0074] (2) Add 0.0881 g isoquinoline and 0.7327 g benzoic acid to the sulfonated polyamic acid solution containing cyclodextrin obtained in step (1), heat to 180°C, and react at a constant temperature for 18 h to carry out imidization. After the reaction is completed, cool to room temperature, drop the polyimide solution into ethyl acetate to precipitate the precipitate, filter, and obtain the polyimide binder for the positive electrode of the lithium-ion battery.

[0075] The method for preparing the lithium-ion battery positive electrode sheet using polyimide binder as described above includes the following steps:

[0076] S1. Dissolve 0.1g of the binder in 1.5ml of N-methylpyrrolidone to obtain a binder solution. Grind and mix 0.8g of lithium cobalt oxide (LiCoO2) positive electrode active material and 0.1g of conductive agent SuperP thoroughly. Add them to the binder solution in batches and stir to mix them evenly to obtain a black slurry.

[0077] S2. Using a four-sided coating apparatus, the black slurry obtained in step S1 is uniformly coated onto a clean aluminum foil and vacuum dried at 120°C for 12 hours to obtain the positive electrode sheet of LiCoO2 lithium-ion battery.

[0078] Example 6

[0079] This embodiment provides a polyimide binder for lithium-ion battery cathodes and its preparation method, including the following steps:

[0080] (1) Under nitrogen protection, 2.1142 g of 4,4'-bis(4-aminophenoxy)-[1,1'-biphenyl]-3,3'-disulfonic acid, 4.54 g of β-cyclodextrin and 0.85 g of triethylamine were dissolved in 20 ml of m-cresol and stirred until completely dissolved. Then, 2.1028 g of bisphenol A type diether dianhydride was added and stirred at 80 °C for 8 h to obtain a sulfonated polyamic acid solution containing cyclodextrin.

[0081] (2) Add 0.0961 g isoquinoline and 0.7327 g benzoic acid to the sulfonated polyamic acid solution containing cyclodextrin obtained in step (1), heat to 180°C, and react at a constant temperature for 18 h to carry out imidization. After the reaction is completed, cool to room temperature, drop the polyimide solution into ethyl acetate to precipitate the precipitate, filter, and obtain the polyimide binder for the positive electrode of the lithium-ion battery.

[0082] The method for preparing the lithium-ion battery positive electrode sheet using polyimide binder as described above includes the following steps:

[0083] S1. Dissolve 0.1g of the binder in 1.5ml of N-methylpyrrolidone to obtain a binder solution. Grind and mix 0.8g of lithium cobalt oxide (LiCoO2) positive electrode active material and 0.1g of conductive agent SuperP thoroughly. Add them to the binder solution in batches and stir to mix them evenly to obtain a black slurry.

[0084] S2. Using a four-sided coating apparatus, the black slurry obtained in step S1 is uniformly coated onto a clean aluminum foil and vacuum dried at 120°C for 12 hours to obtain the positive electrode sheet of LiCoO2 lithium-ion battery.

[0085] Comparative Example 1

[0086] Referring to Figures 3, 5, 6, and 7, this embodiment provides a method for preparing a positive electrode sheet for a lithium-ion battery, comprising the following steps:

[0087] S1. Dissolve 0.1g of polyvinylidene fluoride (PVDF) in 2.0ml of N-methylpyrrolidone to obtain a binder solution. Grind and mix 0.8g of lithium cobalt oxide (LiCoO2) positive electrode active material and 0.1g of conductive agent SuperP thoroughly, then add them to the binder solution in batches and stir to mix them evenly to obtain a black slurry.

[0088] S2. Using a four-sided coating apparatus, the black slurry obtained in step S1 is uniformly coated onto a clean aluminum foil and vacuum dried at 120°C for 12 hours to obtain the positive electrode sheet of LiCoO2 lithium-ion battery.

[0089] Comparative Example 2

[0090] Referring to Figure 7, this embodiment provides a polyimide binder for lithium-ion battery cathodes and its preparation method, including the following steps:

[0091] (1) Under nitrogen protection, 1.794 g of 4,4'-bis(4-aminophenoxy)-[1,1'-biphenyl]-3-sulfonic acid and 0.85 g of triethylamine were dissolved in 20 ml of m-cresol and stirred until completely dissolved. Then, 1.2533 g of 4,4'-oxobisphthalic anhydride was added and stirred at 80 °C for 8 h to obtain a sulfonated polyamic acid solution containing cyclodextrin.

[0092] (2) Add 0.039 g isoquinoline and 0.7327 g benzoic acid to the sulfonated polyamic acid solution containing cyclodextrin obtained in step (1), heat to 180 °C, and react at a constant temperature for 18 h to carry out imidization. After the reaction is completed, cool to room temperature, drop the polyimide solution into ethyl acetate to precipitate the precipitate, filter, and obtain the polyimide binder for the positive electrode of the lithium-ion battery.

[0093] The method for preparing the lithium-ion battery positive electrode sheet using polyimide binder as described above includes the following steps:

[0094] S1. Dissolve 0.1g of the binder in 1.5ml of N-methylpyrrolidone to obtain a binder solution. Grind and mix 0.8g of lithium cobalt oxide (LiCoO2) positive electrode active material and 0.1g of conductive agent SuperP thoroughly. Add them to the binder solution in batches and stir to mix them evenly to obtain a black slurry.

[0095] S2. Using a four-sided coating apparatus, the black slurry obtained in step S1 is uniformly coated onto a clean aluminum foil and vacuum dried at 120°C for 12 hours to obtain the positive electrode sheet of LiCoO2 lithium-ion battery.

[0096] The lithium-ion battery positive electrode sheets obtained in the above embodiments and comparative examples were cut into circular sheets with a diameter of 14 mm, rolled, weighed, and tested. The test results are shown in Table 1.

[0097] The lithium-ion battery positive electrode sheets obtained in the above embodiments and comparative examples were tested according to the following method:

[0098] After drying and weighing the positive electrode sheet, place it in a glove box and assemble the coin cell using a 2032 type coin cell casing: place the positive electrode casing, positive electrode sheet, separator, lithium sheet, gasket, and spring in sequence, add 60μL of electrolyte, cover with the positive electrode casing, and seal the coin cell on a sealing machine; this electrode preparation and battery assembly method is applicable to all embodiments and comparative examples;

[0099] Electrochemical long-cycle test: The battery cycle performance was tested at room temperature (25℃) using the battery testing system of Landian Electronics Co., Ltd. First, it was cycled 3 times, and then a long-cycle test was conducted at a current density of 0.5C. The test voltage range was 2.5-4.5V.

[0100] AC impedance test: Battery test conditions, amplitude 1mV, frequency range 10 -2 -10 6 Hz, to test the initial interface impedance of the battery and the interface impedance after 100 cycles;

[0101] Adhesion strength test: Cut the prepared and completely dried positive electrode sheet into strips 25mm wide and 150mm long; then stick one side of 3M double-sided tape to a clean aluminum plate, smooth it out, and ensure that the double-sided tape adheres tightly to the aluminum plate. Peel off the double-sided tape and stick the electrode sheet with the slurry applied to the tape strip, ensuring that the electrode sheet and the double-sided tape are perfectly matched and adhered; insert the aluminum plate with the electrode sheet already attached into the lower clamp and fix it vertically; insert the electrode sheet without adhesive into the upper clamp and fix it, so that the electrode sheet attached to the double-sided tape is at 180° with the electrode sheet fixed in the upper clamp. After fixing the test sample, first calibrate and zero it, peel speed 100mm / min, and then start the test to obtain the peel strength curve and average value.

[0102] Table 1

[0103] As shown in Table 1, the average bonding strength of Examples 1-6 is higher than that of Comparative Example 1. This indicates that the polyimide binder used in this invention has a strong bonding force with the electrode sheet, and there is a strong interaction between the polyimide and the positive electrode component, which effectively inhibits the detachment of the binder from the active material particles and the aluminum foil. In contrast, the molecular chain of Comparative Example 1 (PVDF) is simple, and the interaction with the active material is mainly through the weak van der Waals forces formed by F and H atoms, making it very easy to detach from the electrode sheet. As can be seen from Examples 1 and Comparative Example 2, the sulfonated polyimide binder containing cyclodextrin has a stronger bonding ability. This is because the molecular structure of cyclodextrin contains multiple hydroxyl groups, which can form hydrogen bonds and other interactions with the surface of the electrode material, providing good bonding force.

[0104] As can be seen from Table 1, the impedance values ​​of Examples 1-3 are generally larger than those of Examples 4-6. This is because the sulfonated diamine monomers in Examples 1-3 have fewer sulfonic acid groups. The sulfonic acid groups can dissociate into negatively charged sulfonate ions, which increases the ionic conductivity in the electrode and reduces the electrode impedance.

[0105] As can be seen from Table 1, the initial discharge specific capacity and capacity retention of Examples 1-6 are higher than those of Comparative Example 1, indicating that the electrochemical performance of the polyimide binder used in this invention is superior to that of commercial polyvinylidene fluoride.

[0106] As can be seen from Figures 3 and 4, in Example 1, the polyimide adhesive uniformly coats the positive electrode active material lithium cobalt oxide and conductive carbon black, and the positive electrode components are tightly connected to form a complete and tight conductive structure. The positive electrode components have very strong adhesion properties, and the coating and bonding effects are good. In contrast, the active material of the electrode sheet made with the polyvinylidene fluoride adhesive in Comparative Example 1 is basically exposed on the surface. This is because the polyvinylidene fluoride adhesive and the active material rely only on van der Waals forces, resulting in poor adhesion.

[0107] The positive electrode sheets prepared in Example 1, Comparative Example 1, and Comparative Example 2 were assembled into coin cells and subjected to charge-discharge cycle tests. The test results are shown in Figure 7. After 200 cycles, the discharge specific capacity of the coin cell assembled in Example 1 remained almost unchanged, with a capacity retention rate of 99%. After 200 cycles, the capacity of Comparative Example 1 and Comparative Example 2 decreased rapidly. The discharge specific capacity of Comparative Example 2 dropped to half of its original value, and the discharge specific capacity of Comparative Example 1 was only 30% of its original value. This shows that the electrode sheets prepared by the polyimide binder of this invention can effectively improve the electrochemical performance of lithium-ion batteries.

[0108] In summary, the polyimide binder for lithium-ion battery cathodes of this invention uses polyimide as a backbone, exhibiting excellent thermal stability and strong mechanical properties, thus improving the binder's bonding strength and effectively suppressing detachment between the binder and active material particles and aluminum foil. The polyimide binder for lithium-ion battery cathodes of this invention encapsulates cyclodextrin onto the polyimide backbone chain. The cyclodextrin's molecular structure contains multiple hydroxyl groups, which can form hydrogen bonds and other interactions with the electrode material surface, providing excellent adhesion. The internal porous structure of cyclodextrin also promotes electrolyte penetration and ion migration, thereby improving cycle performance. The polyimide binder for lithium-ion battery cathodes of this invention introduces sulfonate and other groups, enabling the dissociation of negatively charged sulfonate ions, increasing the ionic conductivity in the electrode, and improving the lithium-ion transport efficiency in the electrode. The electrode sheets prepared using the obtained polyimide binder of this invention, when used in lithium-ion batteries, effectively enhance the electrochemical performance of lithium-ion batteries.

[0109] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A polyimide binder for the positive electrode of a lithium-ion battery, characterized in that, The polyimide binder for the positive electrode of the lithium-ion battery includes a polyimide containing cyclodextrin and sulfonic acid groups, and the polyimide structure is shown in structural formula 1: Where m is any integer from 100 to 1000, and the weight-average molecular weight is greater than 20000.

2. The polyimide binder for the positive electrode of a lithium-ion battery according to claim 1, characterized in that, In structural formula 1, group A is selected from any of the following structural formulas:

3. The polyimide binder for the positive electrode of a lithium-ion battery according to claim 1, characterized in that, In structural formula 1, the B group is selected from any of the following structural formulas:

4. A method for preparing a polyimide binder for the positive electrode of a lithium-ion battery, characterized in that, Includes the following steps: (1) Under nitrogen protection, cyclodextrin, sulfonated diamine and triethylamine are dissolved in an organic solvent and stirred until fully dissolved. Then, diacid anhydride is added and the mixture is stirred at 60-100℃ for 6-12 hours to obtain a sulfonated polyamic acid solution containing cyclodextrin. (2) Add benzoic acid and catalyst to the sulfonated polyamic acid solution containing cyclodextrin obtained in step (1), heat to 180-220℃, react at a constant temperature for 10-18h to carry out imidization, cool to room temperature, add washing solvent to precipitate, filter, and obtain the polyimide binder for lithium-ion battery cathode.

5. The method for preparing the polyimide binder for the positive electrode of a lithium-ion battery according to claim 4, characterized in that, In step (1), the molar ratio of the cyclodextrin to the sulfonated diamine is 1:0.5-1.5; the molar ratio of the sulfonic acid group in the sulfonated diamine to the triethylamine is 1:0.9-1.

1. The cyclodextrin is selected from one of α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin; The organic solvent is selected from one or more of m-cresol, N-methylpyrrolidone, dimethylacetamide, N,N-dimethylformamide, and p-chlorophenol; The solid content of the sulfonated polyamic acid solution is 10-25 wt%.

6. The method for preparing the polyimide binder for the positive electrode of a lithium-ion battery according to claim 4, characterized in that, In step (2), the washing solvent is selected from one or more of ethyl acetate, methanol, ethanol, isopropanol, ethylene glycol, 2-butanol or cyclopentanol; The catalyst is selected from one of quinoline, isoquinoline, or tertiary amine.

7. The polyimide binder for the positive electrode of a lithium-ion battery according to claim 1, characterized in that, The method for preparing the lithium-ion battery positive electrode sheet using polyimide binder includes the following steps: S1. Take polyimide binder and stir it to dissolve it in solvent to obtain binder solution. Grind and mix the positive electrode active material and conductive agent evenly and add them to binder solution. Adjust the viscosity of the mixture to 2000-10000 mPa·s by adding solvent to obtain black slurry. S2. The black slurry obtained in step S1 is uniformly coated onto aluminum foil, dried, and then compacted to obtain the positive electrode sheet of a lithium-ion battery.

8. The polyimide binder for the positive electrode of a lithium-ion battery according to claim 7, characterized in that, In step S1, the solvent is selected from one of N,N-dimethylformamide, N,N-dimethylacetamide, or N-methylpyrrolidone; The positive electrode active material is selected from one or more of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, or ternary positive electrode material lithium nickel cobalt manganese oxide. The conductive agent is selected from one or more of acetylene black, superconducting carbon black (Super P), carbon nanotubes, graphene, and Ketjen black.

9. The polyimide binder for the positive electrode of a lithium-ion battery according to claim 7, characterized in that, In step S1, the mass concentration of the adhesive solution is 5%-20%; in step S2, the drying is vacuum drying at 80℃-120℃.

10. The polyimide binder for the positive electrode of a lithium-ion battery according to claim 7, characterized in that, In step S1, the content of the positive electrode active material is 2 mg·cm³. -2 -4mg·cm -2 In step S2, the positive electrode sheet of the lithium-ion battery is composed of an active material layer and an aluminum foil; the active material layer is composed of a positive electrode active material, a conductive agent, and a polyimide binder; the mass content of the binder in the active material layer is 1%-15%; the mass content of the conductive agent in the active material layer is 2%-25%.

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