Hyperbranched ionic liquid, preparation method and application thereof, diaphragm and lithium ion battery

Abstract

The invention discloses hyperbranched ionic liquid and a preparation method and application thereof, a diaphragm and a lithium ion battery, the hyperbranched ionic liquid comprises a main chain and at least one branch chain, the main chain is a hyperbranched polymer containing quaternary ammonium cations, one end of the branch chain is connected with the quaternary ammonium cations through chemical bonds, and the other end of the branch chain is connected with the quaternary ammonium cations through chemical bonds. The other end of the branched chain comprises carboxyl anions or sulfonic anions, and the chemical bond is selected from at least one of an ester bond, an amido bond, an ether bond and a carbon-nitrogen bond. When the hyperbranched ionic liquid modified cellulose is used for preparing a diaphragm and the diaphragm is used for preparing a lithium ion battery, the battery performance can be effectively improved.

Description

Technical Field

[0001] The present application relates to the field of polymer technology, and in particular to a hyperbranched ionic liquid, a preparation method and use thereof, a diaphragm, and a lithium-ion battery. Background Art

[0002] The development and conversion of clean energy, as well as the research and development of energy storage devices, have become a hot topic for scholars both domestically and internationally. As a storage medium for clean, renewable energy, lithium-ion batteries offer advantages such as high specific energy, high voltage, and environmental friendliness, and are currently widely used in many fields. The separator, one of the most important structures in lithium-ion batteries, primarily separates the cathode and anode, preventing short circuits and providing channels for ion transport.

[0003] Currently, the commonly used lithium battery separator materials include polyolefin composite separators, fluoropolymer separators and cellulose-based separators. Due to the high production cost of traditional synthetic polymer separators (the cost of the separator accounts for about 20% of the total battery cost). In addition, traditional lithium-ion battery separators, such as polyethylene, polyvinylidene fluoride and glass microfiber membranes, have very obvious shortcomings, such as poor thermal stability at high operating temperatures, limited electrolyte wettability, and weak mechanical strength. Polyolefin-based separators have poor mechanical stability / dimensional stability and are prone to failure in relatively harsh operating environments, causing internal short circuit problems in the battery. Paper-based cellulose separators contain a large number of hydroxyl functional groups, and the strong intermolecular forces they generate reduce the pore size of the separator, thereby hindering the transport of lithium ions in the pores, and thus affecting battery performance. Summary of the Invention

[0004] The purpose of the present application is to provide a hyperbranched ionic liquid, which can be used to prepare a diaphragm, and when the diaphragm is used in a lithium ion battery, it can effectively improve the battery performance.

[0005] To achieve the above-mentioned objectives, the first aspect of the present application provides a hyperbranched ionic liquid comprising a main chain and at least one branch chain, wherein the main chain is a hyperbranched polymer comprising a quaternary ammonium cation, one end of the branch chain is connected to the quaternary ammonium cation via a chemical bond, and the other end of the branch chain comprises a carboxyl anion or a sulfonic acid anion, and the chemical bond is selected from at least one of an ester bond, an amide bond, an ether bond and a carbon-nitrogen bond.

[0006] In some embodiments of the first aspect, the structural formula of the hyperbranched ionic liquid is selected from Formula 1 to Formula 3.

[0007] The second aspect of the present application provides a method for preparing a hyperbranched ionic liquid, which is obtained by ionizing a hyperbranched polymer containing an amino group and a multifunctional monomer containing a carboxyl group and / or a sulfonic acid group in a solvent.

[0008] In some embodiments of the second aspect, the amino-containing hyperbranched polymer is selected from at least one of polyethyleneimine, ethylenediamine core dendritic polyamidoamine, 1,4-butanediamine core dendritic polyamidoamine, cystamine core dendritic polyamidoamine, hyperbranched polyamide, and hyperbranched polyamidoamine; and / or the multifunctional monomer containing a carboxyl group and / or a sulfonic acid group is selected from succinic acid, sebacic acid, adipic acid, azelaic acid, malonic acid, suberic acid, phthalic anhydride, malic acid, itaconic acid, glutaric acid, itaconic anhydride, phenylmalonic acid, maleic acid, butylene ... At least one of 1,2-dimethylsuccinic anhydride, 1,4-butane sultone, 1,3-propane sultone, 1,8-naphthalene sultone, trimellitic anhydride, maleic anhydride, succinic anhydride, glutaric anhydride, citraconic anhydride, biphenyl anhydride, methylsuccinic anhydride, pyromellitic dianhydride, 3-methylglutaric anhydride, 1,2-cyclohexane dianhydride, 2,2-dimethylsuccinic anhydride, propylene carbonate, 4-hydroxyacetoacetic acid lactone, and isocitrate lactone.

[0009] In some embodiments of the second aspect, the solvent is selected from at least one of deionized water, methanol, ethanol, toluene, xylene, acetonitrile, pyridine, cyclohexane, petroleum ether, n-hexane, ethyl ether, acetone, butanone, ethyl acetate, butyl acetate, dichloromethane, tetrahydrofuran, dimethyl sulfoxide, N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0010] In some embodiments of the second aspect, the reaction conditions satisfy at least one of the following: (1) the molar ratio of the amino-containing hyperbranched polymer to the carboxyl and / or sulfonic acid-containing multifunctional monomer is 1:1 to 1:50; (2) the reaction temperature is 30°C to 100°C, and the reaction time is 1 hour to 40 hours.

[0011] The third aspect of the present application provides use of the aforementioned hyperbranched ionic liquid for preparing a diaphragm.

[0012] The fourth aspect of the present application provides a membrane comprising: a cellulose matrix and the aforementioned hyperbranched ionic liquid, wherein the cellulose matrix and the hyperbranched ionic liquid are combined by intermolecular forces and / or molecular chain entanglement.

[0013] In some embodiments of the fourth aspect, the mass of the hyperbranched ionic liquid accounts for 0.1% to 10% of the total mass of the membrane.

[0014] A fifth aspect of the present application provides a lithium-ion battery, comprising: a positive electrode sheet, a negative electrode sheet, and the above-mentioned separator, wherein the separator is located between the positive electrode sheet and the negative electrode sheet.

[0015] Compared with the prior art, the technical solution of this application has the following beneficial effects:

[0016] The hyperbranched ionic liquid of the present application uses a hyperbranched polymer containing a quaternary ammonium cation as a main chain, connects one end of a side chain at the quaternary ammonium cation, and the other end of the side chain contains a carboxyl anion or a sulfonic acid anion. When preparing a diaphragm by modifying cellulose with this hyperbranched ionic liquid, the hyperbranched ionic liquid can weaken the obstruction of ion transmission by polar functional groups on the cellulose molecular chain, and also opens up a "hole chain" dual path for ion transmission. When assembling a lithium-ion battery with this diaphragm, the transmission of lithium ions is more uniform, and a higher specific capacity can be maintained under different currents, with performance advantages such as high battery capacity and good battery stability.

[0017] This application uses commercially available amino-containing hyperbranched polymers and multifunctional monomers containing carboxyl and / or sulfonic acid groups as raw materials to directly prepare a hyperbranched ionic liquid through a primary ionization reaction. Simultaneously, when using this hyperbranched ionic liquid to prepare a diaphragm, the cellulose substrate can be directly immersed in a solution of the hyperbranched ionic liquid. Therefore, both the preparation of the hyperbranched ionic liquid and the preparation of the diaphragm have the advantages of readily available raw materials, simple reaction equipment and production process, and a short reaction cycle, making them suitable for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The following figures describe in detail exemplary embodiments disclosed in this application. Identical reference numerals denote similar structures in several views of the drawings. Those skilled in the art will appreciate that these embodiments are non-limiting, exemplary embodiments, and that the drawings are for illustration and description purposes only and are not intended to limit the scope of this application. Other embodiments may also achieve the same inventive intent as described in this application. It should be understood that the drawings are not drawn to scale. Among them:

[0019] Figure 1 Schematic diagram of the structure of the hyperbranched ionic liquid of the embodiment of the present application;

[0020] Figure 2 The charge and discharge cycle test results of the lithium-ion battery of Comparative Example 1 of this application at a current of 1C are shown;

[0021] Figure 3 The charge and discharge cycle test results of the lithium-ion battery of Example 6 of the present application at a current of 1C;

[0022] Figure 4 The charge and discharge cycle test results of the lithium-ion battery of Example 7 of the present application at a current of 1C are shown;

[0023] Figure 5The charge and discharge cycle test results of the lithium-ion batteries of Examples 6 to 7 and Comparative Example 1 of the present application at currents of 0.1C, 0.2C, 1C, 2C, and 3C are shown;

[0024] Figure 6 These are the mechanical property test results of the diaphragm prepared in Example 4 of the present application and a commercial PP diaphragm. DETAILED DESCRIPTION

[0025] The following description provides specific application scenarios and requirements of the present application, with the purpose of enabling those skilled in the art to make and use the content of this application. Various local modifications to the disclosed embodiments will be apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of this application. Therefore, this application is not limited to the embodiments shown, but is intended to be of the widest scope consistent with the claims.

[0026] Cellulose is a natural, environmentally friendly polymer found widely in plants and microorganisms. The unique properties of cellulose and its derivatives, such as numerous chiral sites, excellent thermal stability, and biodegradability, make them promising materials for battery separators. However, direct use of natural cellulose in battery separators presents challenges. The high concentration of hydroxyl groups in the fibers results in strong intermolecular forces, resulting in a small pore size in the separator, hindering lithium ion transport.

[0027] To solve this problem, the inventors of this application improved the ion transport characteristics of the battery by changing the composition and structure of the lithium-ion battery. One way is to use the hydroxyl sites with strong surface activity of cellulose to graft polar groups (carbonyl, carboxyl, amino, etc.) onto cellulose fibers, thereby weakening the intermolecular forces of the fibers. However, this also sacrifices the overall mechanical strength of the diaphragm. In addition, the complexity and randomness of the grafting process also have more stringent requirements for production and processing technology. Therefore, this method is not suitable for the industrial production of cellulose diaphragms.

[0028] In addition, attempts have been made to improve the ion transport properties of natural cellulose-based membranes by introducing nanoparticle coatings (inorganic particles, polymer particles, etc.). Although nanoparticle coatings can improve the electrolyte wettability of composite membranes to a certain extent due to their good affinity with electrolytes, excessive aggregation of nanoparticles may block some ion transport channels, rendering the overall modification ineffective, thereby reducing the coating effect and the lifespan of the membrane.

[0029] Furthermore, the inventors of the present application conducted in-depth research on the modification method of cellulose and found that the diaphragm can be modified using hyperbranched ionic liquids. Suitable hyperbranched ionic liquids can not only reduce the obstruction of polar functional groups on the diaphragm to ion transport, but also provide molecular chain transmission paths in addition to pore transmission paths, thereby opening up a "pore-chain" dual path for ion transmission, thereby greatly improving the ion transmission efficiency and enhancing the performance of lithium-ion batteries.

[0030] Specifically, the present invention provides a hyperbranched ionic liquid having the following characteristics: Figure 1 The structure shown in FIG. 2 shows a hyperbranched ionic liquid comprising a main chain and a side chain, wherein the main chain is a hyperbranched polymer, and the hyperbranched polymer comprises a quaternary ammonium cation, and the number of the quaternary ammonium cations can be one or more. One end of the side chain is connected to the quaternary ammonium cation by a chemical bond. The chemical bond connecting the quaternary ammonium cation and one end of the side chain can be at least one of an ester bond, an amide bond, an ether bond, and a carbon-nitrogen bond. The other end of the side chain is a free end (also known as an end group), and comprises a carboxyl anion and / or a sulfonic acid anion. The number of the side chains is one or more, and the specific structures of the multiple side chains connected to the same main chain can be the same or different. The specific structure of the side chain comprises the main structure and the end group of the side chain. The same specific structure of the side chain means that the main structure and the end group of the side chain are the same. The different specific structures of the side chain means that at least one of the main structure and the end group is different. The carboxyl anions and / or sulfonic acid anions grafted onto the main chain can play a role in transporting lithium ions, and compared with the method of adding counter anions (such as chloride ions) free from the main chain, the effect of transporting lithium ions is better.

[0031] In some embodiments, the hyperbranched ionic liquid is obtained by grafting a multifunctional monomer having carboxyl and / or sulfonic acid groups onto a hyperbranched polymer having one or more amino groups at its end groups. In some embodiments, the hyperbranched polymer having multiple amino groups at its end groups is selected from polyethyleneimine (Mn can be 300, 600, 1200, 1800, 10,000, 25,000, 60,000, 70,000, etc.), ethylenediamine core dendritic polyamidoamine (generation G can be 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, etc.), 1,4-butanediamine core dendritic polyamidoamine (generation G can be 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, etc.), cystamine core dendritic polyamidoamine (generation G can be 1.0, 2.0, 3.0, 4.0, 5.0, etc.), hyperbranched polyamide, or any one or a mixture of two or more of these.

[0032] In some embodiments, the multifunctional monomer having a carboxyl group and / or a sulfonic acid group is selected from any one of succinic acid, sebacic acid, adipic acid, azelaic acid, malonic acid, suberic acid, phthalic anhydride, malic acid, itaconic acid, glutaric acid, itaconic anhydride, phenylmalonic acid, maleic acid, undecanedioic acid, hexadecanedioic acid, dodecanedioic acid, methylmalonic acid, phenylsuccinic acid, citric acid, 1,4-butanesultone, 1,3-propanesultone, 1,8-naphthalenesultone, trimellitic anhydride, maleic anhydride, succinic anhydride, glutaric anhydride, citraconic anhydride, biphenyl anhydride, methylsuccinic anhydride, pyromellitic dianhydride, 3-methylglutaric anhydride, 1,2-cyclohexanedicarboxylic anhydride, 2,2-dimethylsuccinic anhydride, propylene carbonate, 4-hydroxyacetoacetic acid lactone, and isocitrate lactone, or a mixture of two or more thereof.

[0033] In some embodiments, the structural formula of the hyperbranched ionic liquid is selected from the group consisting of:

[0034]

[0035] The number average molecular weight (Mn) of the hyperbranched ionic liquids shown in Formulas 1 and 2 is 350 to 80,000. For example, the number average molecular weight of the hyperbranched ionic liquids shown in Formulas 1 and 2 can be 350, 600, 1200, 1800, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 10,000, 15,000, 20,000, 25,000, 30,000, 35,000, 40,000, 45,000, 50,000, 55,000, 60,000, 65,000, 70,000, 75,000, 80,000, and any other value within this range. It will be understood that, given a given structural formula and number average molecular weight, the degrees of polymerization n1 and n2 in the structural formula can be calculated according to a known method.

[0036] The present application embodiment also provides a method for preparing a hyperbranched ionic liquid, which can be prepared by reacting an amino-containing hyperbranched polymer with a carboxyl and / or sulfonic acid-containing multifunctional monomer in a solvent for ionization reaction. After the reaction is completed, the carboxyl and / or sulfonic acid-containing multifunctional monomer is grafted onto the amino-containing hyperbranched polymer. Specifically, the amino-containing hyperbranched polymer serves as the main chain, and the carboxyl or sulfonic acid group of the multifunctional monomer reacts with the amino group on the main chain to form at least one chemical bond among an ester bond, an amide bond, an ether bond, and a carbon-nitrogen bond, so that the multifunctional monomer is grafted onto the main chain to form a side chain, and the other end of the side chain is a free end and contains a carboxyl or sulfonic acid group. When the prepared hyperbranched ionic liquid is dissolved in a solvent, ionization forms a quaternary ammonium cation, a carboxyl anion, or a sulfonic acid anion.

[0037] In some embodiments, the amino-containing hyperbranched polymer is selected from polyethyleneimine, ethylenediamine core dendritic polyamidoamine, 1,4-butanediamine core dendritic polyamidoamine, cystamine core dendritic polyamidoamine, hyperbranched polyamide, and a mixture of two or more thereof.

[0038] In some embodiments, the multifunctional monomer containing a carboxyl group and / or a sulfonic acid group is selected from one or a mixture of two or more of succinic acid, sebacic acid, adipic acid, azelaic acid, malonic acid, suberic acid, phthalic anhydride, malic acid, itaconic acid, glutaric acid, itaconic anhydride, phenylmalonic acid, maleic acid, undecanedioic acid, hexadecanedioic acid, dodecanedioic acid, methylmalonic acid, phenylsuccinic acid, citric acid, 1,4-butanesultone, 1,3-propanesultone, 1,8-naphthalenesultone, trimellitic anhydride, maleic anhydride, succinic anhydride, glutaric anhydride, citraconic anhydride, biphenyl anhydride, methylsuccinic anhydride, pyromellitic dianhydride, 3-methylglutaric anhydride, 1,2-cyclohexanedicarboxylic anhydride, 2,2-dimethylsuccinic anhydride, propylene carbonate, 4-hydroxyacetoacetic acid lactone, and isocitrate lactone.

[0039] In some embodiments, the solvent is selected from one or a mixture of two or more of deionized water, methanol, ethanol, toluene, xylene, acetonitrile, pyridine, cyclohexane, petroleum ether, n-hexane, ethyl ether, acetone, butanone, ethyl acetate, butyl acetate, dichloromethane, tetrahydrofuran, dimethyl sulfoxide, N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0040] In the above examples, the amino-containing hyperbranched polymer, carboxyl- and / or sulfonic-group-containing multifunctional monomer, and solvent are preferred raw materials for the above-mentioned ionization reaction. It is understood that the raw materials that can be used in this application are not limited to those listed above, and other raw materials known in the art can also be used. As long as they can comply with the above-mentioned reaction mechanism, those skilled in the art can use them in substitution.

[0041] In some embodiments, the molar ratio of the amino-containing hyperbranched polymer to the carboxyl and / or sulfonic acid-containing multifunctional monomer is 1:1 to 1:50. For example, the molar ratio can be 1:1, 1:2, 1:3, 1:4, 1:5, 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, 1:50, or any ratio within the ranges of the aforementioned ratios. Limiting the molar ratio within the aforementioned range can effectively promote the reaction to produce the hyperbranched ionic liquid of the present application.

[0042] In some embodiments, the reaction temperature of the amino-containing hyperbranched polymer and the carboxyl- and / or sulfonic-group-containing multifunctional monomer is 30° C. to 100° C., and the reaction time is 1 to 40 hours. Preferably, the reaction time is 1 to 24 hours. Such reaction temperature and reaction time may be conducive to the formation of the product, wherein the reaction temperature may also be 40° C., 60° C., 80° C., 100° C., 120° C., 140° C., 160° C., etc., as well as 200° C., 220° C., 240° C., etc., and any other point value within this range, and the reaction time may also be 2, 3, 4, 5, 6, 8, 10, 12, 13, 14, 15, 16, 18, 20 hours, etc., and those skilled in the art may adjust according to the actual reaction conditions.

[0043] In the above embodiments, commercially available amino-containing hyperbranched polymers are mainly used to undergo ionization reactions with multifunctional monomers containing carboxyl and / or sulfonic acid groups to directly obtain hyperbranched ionic liquids. The preparation method is simple and mature, and can be effectively used in the industrial production and preparation of hyperbranched ionic liquids.

[0044] Based on the defects of the current lithium-ion battery diaphragms, the embodiments of the present application apply the above-mentioned hyperbranched ionic liquid to the preparation of the diaphragm. In the embodiments of the present application, the cellulose matrix is ​​modified by the hyperbranched ionic liquid to prepare the diaphragm. Specifically, the hyperbranched ionic liquid can be dissolved in a solvent (such as ethanol) to form a solution, and the cellulose is immersed in the solution and then dried to obtain the diaphragm. The diaphragm includes: a cellulose matrix and a hyperbranched ionic liquid grafted onto the hydroxyl sites of the cellulose matrix, wherein the mass of the hyperbranched ionic liquid can be 0.1% to 10% of the total mass of the diaphragm. For example, the mass percentage of the hyperbranched ionic liquid can be 0.1%, 0.2%, 0.3%, 0.5%, 0.7%, 1.0%, 1.2%, 1.3%, 1.5%, 1.7%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, 9.0%, 9.5%, 10.0%, etc. and any other point value within this range.

[0045] An embodiment of the present application further provides a lithium-ion battery, comprising: a positive electrode sheet, a negative electrode sheet, and the above-mentioned separator, wherein the separator is located between the positive electrode sheet and the negative electrode sheet.

[0046] Because the hyperbranched ionic liquid molecular chains of the embodiments of the present application contain zwitterions, they have strong ion conductivity. When the hyperbranched ionic liquid is adsorbed onto the molecular chains of cellulose, it can effectively weaken the obstruction of ion transmission by the polar functional groups on the cellulose matrix, increase the pores of the cellulose diaphragm, and form a pore transmission path. At the same time, the carboxyl anions or sulfonic acid anions on the hyperbranched ionic liquid molecular chains can play a role in transmitting lithium ions, forming a molecular chain transmission path. This forms a "pore chain" dual path for lithium ion transmission, greatly improving the ion transmission efficiency, thereby optimizing the charge and discharge rate, efficiency and cycle performance of the lithium ion battery.

[0047] The following examples will be used to clearly and completely describe the technical solutions of the present application. Unless otherwise specified, all reagents and raw materials used can be purchased from commercial sources. The experimental methods in the following examples, where specific conditions are not specified, were performed according to conventional methods and conditions, or selected according to the product specifications.

[0048] Example 1

[0049] 5 g of polyethyleneimine PEI (Mn=1200) was dissolved in 50 mL of ethanol, and 2 g of succinic anhydride was added at 30° C. to react for 24 hours. After the reaction, the ethanol was removed at 60° C., and the mixture was washed twice with dichloromethane and dried in a spin-drying machine to obtain a hyperbranched ionic liquid 1 with a number average molecular weight of 1670 and the following structural formula:

[0050]

[0051] The H of the hyperbranched ionic liquid 1 prepared in this example 1 -NMR characterization data are as follows:

[0052] H 1 -NMR(DMSO): δ(ppm)=8.01-7.94(2H); 1.55-1.44(7H); 3.46-3.30(12H);

[0053] 3.14-3.01(14H); 2.89-2.64(20H); 2.53-2.39(18H).

[0054] Example 2

[0055] 5 g of polyethyleneimine PEI (Mn=3500) was dissolved in 50 mL of butanone, and 1 g of 1,8-naphthalenesulfonate was added at 40°C for 16 hours. After the reaction, butanone was removed at 40°C, and the mixture was washed twice with ethyl acetate and dried to obtain a hyperbranched ionic liquid 2 with a number average molecular weight of 4320. The structural formula is as follows:

[0056]

[0057] The H of the hyperbranched ionic liquid 2 prepared in this example 1 -NMR characterization data are as follows:

[0058] H 1 -NMR(DMSO): δ(ppm)=9.48-9.35(3H); 8.37-8.10(16H); 7.54-7.45(4H);

[0059] 7.34-7.20(4H); 3.58-3.45(10H); 2.33-2.20(34H); 1.54-1.48(7H).

[0060] Example 3

[0061] 5 g of ethylenediamine core dendritic polyamidoamine (G=2.0) was dissolved in 50 mL of methanol, and 2 g of propylene carbonate was added at 30° C. to react for 24 hours. After the reaction, the methanol was removed at 60° C., and the mixture was washed twice with ethyl acetate and dried to obtain a hyperbranched ionic liquid 3 with a number average molecular weight of 4580 and the structural formula is as follows:

[0062]

[0063] The H of the hyperbranched ionic liquid 3 prepared in this example 1 -NMR characterization data are as follows:

[0064] H 1 -NMR(DMSO): δ(ppm)=8.10-7.99(30H); 6.70-6.55(14H); 5.47-5.30(14H);

[0065] 4.41-4.35(14H); 4.28-4.19(28H); 3.66-3.52(32H); 3.49-3.29(84H); 3.14-3.02(24H); 2.69-2.50(68H); 2.48-2.36(24H); 1.31-1.22(42H).

[0066] Example 4

[0067] Hyperbranched ionic liquid 2 was dissolved in ethanol to a 10 mg / mL solution, and a cellulose-based filter paper was immersed in the solution at 60°C for 1 hour. The cellulose-based filter paper was removed and vacuum-dried at 60°C for 24 hours to obtain a membrane 1, in which the hyperbranched ionic liquid accounted for 5.2% of the total membrane mass.

[0068] Example 5

[0069] Hyperbranched ionic liquid 2 was dissolved in ethanol to a 20 mg / mL solution, and a cellulose-based filter paper was immersed in the solution at 60°C for 1 hour. The cellulose-based filter paper was removed and vacuum-dried at 60°C for 24 hours to obtain a membrane 2, in which the hyperbranched ionic liquid accounted for 9.8% of the total membrane mass.

[0070] Example 6

[0071] A lithium-ion battery is assembled with lithium iron phosphate as the positive electrode, a metal lithium sheet as the negative electrode, LiPF6 as the electrolyte, and a separator 1.

[0072] Example 7

[0073] A lithium-ion battery is assembled with lithium iron phosphate as the positive electrode, metal lithium sheet as the negative electrode, LiPF6 as the electrolyte, and a separator 2.

[0074] Comparative Example 1

[0075] A lithium-ion battery was assembled with lithium iron phosphate as the positive electrode, metallic lithium sheet as the negative electrode, LiPF6 as the electrolyte, and a commercial PP separator (celgard2500, Zhengzhou Jinghong New Energy Technology Co., Ltd.).

[0076] The lithium-ion batteries of Examples 6-7 and Comparative Example 1 were subjected to electrical performance testing using the following method: Using a low-current button-type cell tester (CT-4000), the batteries were assembled with lithium iron phosphate as the positive electrode, a lithium metal sheet as the negative electrode, and LiPF6 as the electrolyte. The batteries were then subjected to charge-discharge cycle testing at a current of 1C. The batteries were then subjected to charge-discharge cycle testing at currents of 0.1C, 0.2C, 1C, 2C, and 3C, respectively.

[0077] The separator 1 prepared in Example 4 and the commercial PP separator samples were cut into 1×3 cm strips, and the mechanical properties of the strips were tested using an electronic universal material testing machine (Model Instron 3365) at a tensile rate of 5 mm / min.

[0078] Figure 2 The charge and discharge cycle test results of the lithium-ion battery of Comparative Example 1 at 1C current are shown. Figure 3 The charge and discharge cycle test results of the lithium-ion battery of Example 6 at 1C current are shown. Figure 4 The charge and discharge cycle test results of the lithium-ion battery of Example 7 at 1C current are shown. Figure 5 The charge and discharge cycle tests of the lithium ion batteries of Examples 6 to 7 and Comparative Example 1 at currents of 0.1C, 0.2C, 1C, 2C, and 3C are shown.

[0079] refer to Figures 2 to 4, the lithium-ion batteries of Examples 6-7 experienced little capacity attenuation during 300 charge-discharge cycles, and the battery charge-discharge efficiency was close to 100%. At the same time, the capacity retention rate of the lithium-ion battery of Comparative Example 1 was 91%, while the capacity retention rates of the lithium-ion batteries of Examples 6-7 were significantly higher than that of Comparative Example 1, at 93% and 99%, respectively. It can be seen that when the mass of active material is the same, when the lithium-ion battery prepared using the diaphragm of the embodiment of the present application can have a higher capacity retention rate while maintaining the same coulombic efficiency as a commercial diaphragm battery.

[0080] refer to Figure 5 During charge and discharge at different currents, the specific capacity of lithium-ion batteries assembled with separators 1 and 2 was maintained better than that of commercial separators. In particular, the specific capacity of the lithium-ion battery assembled with separator 1 was higher at low currents, demonstrating that hyperbranched ionic liquids can regulate the movement of lithium ions, making lithium ion transmission more uniform.

[0081] Figure 6 The mechanical properties of membrane 1 and commercial PP membrane are shown. The mechanical properties of the membrane prepared by using hyperbranched ionic liquid modified cellulose are better than those of the commercial PP membrane.

[0082] In summary, modification of cellulose-based membranes by hyperbranched ionic liquids can improve the mechanical properties of membrane materials and the electrical properties of lithium-ion batteries.

[0083] The above description of the embodiments is intended to facilitate understanding and application of the present application by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without expending any creative effort. Therefore, the present application is not limited to the embodiments described herein, and improvements and modifications made by those skilled in the art based on the disclosure of this application without departing from the scope and spirit of this application are within the scope of this application.

Claims

1. A hyperbranched ionic liquid, characterized in that The invention comprises a main chain and at least one branch chain, wherein the main chain is a hyperbranched polymer containing a quaternary ammonium cation, one end of the branch chain is connected to the quaternary ammonium cation through a chemical bond, and the other end of the branch chain contains a carboxyl anion or a sulfonic acid anion, and the chemical bond is selected from at least one of an ester bond, an amide bond, an ether bond and a carbon-nitrogen bond.

2. The hyperbranched ionic liquid according to claim 1, wherein The structural formula of the hyperbranched ionic liquid is selected from the following group: The number average molecular weight of the hyperbranched ionic liquids represented by Formula 1 and Formula 2 is 350 to 80,000.

3. A method for preparing a hyperbranched ionic liquid, characterized in that: The polymer is obtained by ionization reaction of a hyperbranched polymer containing amino groups and a multifunctional monomer containing carboxyl groups and / or sulfonic acid groups in a solvent.

4. The method for preparing a hyperbranched ionic liquid according to claim 3, wherein The amino-containing hyperbranched polymer is selected from at least one of polyethyleneimine, ethylenediamine core dendritic polyamidoamine, 1,4-butanediamine core dendritic polyamidoamine, cystamine core dendritic polyamidoamine, hyperbranched polyamide, and hyperbranched polyamidoamine; And / or, the multifunctional monomer containing a carboxyl group and / or a sulfonic acid group is selected from at least one of succinic acid, sebacic acid, adipic acid, azelaic acid, malonic acid, suberic acid, phthalic anhydride, malic acid, itaconic acid, glutaric acid, itaconic anhydride, phenylmalonic acid, maleic acid, undecanedioic acid, hexadecanedioic acid, dodecanedioic acid, methylmalonic acid, phenylsuccinic acid, citric acid, 1,4-butanesultone, 1,3-propanesultone, 1,8-naphthalenesultone, trimellitic anhydride, maleic anhydride, succinic anhydride, glutaric anhydride, citraconic anhydride, biphenyl anhydride, methylsuccinic anhydride, pyromellitic dianhydride, 3-methylglutaric anhydride, 1,2-cyclohexanedicarboxylic anhydride, 2,2-dimethylsuccinic anhydride, propylene carbonate, 4-hydroxyacetoacetic acid lactone, and isocitrate lactone.

5. The method for preparing a hyperbranched ionic liquid according to claim 3, wherein The solvent is selected from at least one of deionized water, methanol, ethanol, toluene, xylene, acetonitrile, pyridine, cyclohexane, petroleum ether, n-hexane, ethyl ether, acetone, butanone, ethyl acetate, butyl acetate, dichloromethane, tetrahydrofuran, dimethyl sulfoxide, N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide.

6. The method for preparing a hyperbranched ionic liquid according to claim 3, wherein The reaction conditions meet at least one of the following: (1) The molar ratio of the amino-containing hyperbranched polymer to the carboxyl and / or sulfonic acid-containing multifunctional monomer is 1:1 to 1:50; (2) The reaction temperature is 30°C to 100°C, and the reaction time is 1 hour to 40 hours.

7. Use of the hyperbranched ionic liquid according to claim 1 or 2 for preparing a diaphragm.

8. A diaphragm, characterized in that: include: A cellulose matrix and the hyperbranched ionic liquid according to claim 1 or 2, wherein the cellulose matrix and the hyperbranched ionic liquid are combined by intermolecular forces and / or molecular chain entanglement.

9. The diaphragm according to claim 8, characterized in that The mass of the hyperbranched ionic liquid accounts for 0.1% to 10% of the total mass of the diaphragm.

10. A lithium ion battery, characterized in that: include: A positive electrode sheet, a negative electrode sheet, and the separator according to claim 8 or 9, wherein the separator is located between the positive electrode sheet and the negative electrode sheet.

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