Preparation and application of in-situ initiated hyperbranched polymer electrolyte by diaphragm

Abstract

The application provides a preparation of a hyperbranched polymer electrolyte in-situ initiated by a diaphragm and application thereof. The diaphragm is first grafted with bromo-isobutyric acid ester through acylation reaction by using the abundant hydroxyl groups on the surface of the cellulose diaphragm; then a precursor solution is obtained by mixing a polymer monomer A, a branching initiation monomer B, a catalyst, a ligand and a lithium salt electrolyte; finally, the grafted cellulose diaphragm is soaked in the precursor solution to make the grafted cellulose diaphragm swell fully, and the hyperbranched polymer electrolyte in-situ initiated by the diaphragm is obtained after in-situ thermal polymerization of the battery. The hyperbranched polymer electrolyte in-situ initiated by the diaphragm prepared by the method has the advantages of high safety, high room temperature ionic conductivity and excellent interface stability, and the hyperbranched polymer electrolyte also has the diaphragm function, thereby providing a new research idea and method for preparing a high-performance polymer electrolyte.

Description

Technical Field

[0001] This invention relates to the field of polymer electrolyte technology, and in particular to the preparation and application of a membrane-initiated hyperbranched polymer electrolyte. Background Technology

[0002] Lithium-ion batteries have attracted widespread attention in electric vehicles, portable electronic devices, and large-scale energy storage systems due to their high energy density, long cycle life, and good safety. The electrolyte, as a crucial component of lithium-ion batteries, plays a vital role in their safety and stability. Currently, lithium-ion batteries commonly use liquid electrolytes. While liquid electrolytes possess high ionic conductivity, their inherent volatility, flammability, and the corrosive effects of organic solvents on electrode materials lead to safety hazards such as thermal runaway and leakage. Therefore, there is an urgent need to find novel electrolyte systems to replace liquid electrolytes.

[0003] To overcome the safety bottlenecks of liquid electrolytes, solid-state electrolyte systems have become a research hotspot. Among the many solid-state electrolyte systems, polymer-based solid-state electrolytes have attracted much attention due to their good mechanical flexibility and formability. However, traditional polymer-based solid-state electrolytes generally have low room-temperature ionic conductivity (most are below 10). -8 S / cm to 10 -4 Within the range of S / cm, the conductivity level required for lithium secondary batteries cannot be achieved at room temperature. Furthermore, traditional polymer-based solid electrolytes exhibit poor interfacial stability at the lithium metal anode interface, readily undergoing side reactions with lithium metal to form an unstable interfacial layer. This leads to increased interfacial impedance and a rapid decline in battery cycle stability.

[0004] Therefore, developing novel electrolyte systems with high safety, high room temperature ionic conductivity, and excellent interfacial stability is an urgent problem to be solved. Summary of the Invention

[0005] This invention provides a method for preparing a membrane-initiated hyperbranched polymer electrolyte. This method can generate hyperbranched polymers in situ on a cellulose membrane grafted with bromide isobutyrate, successfully preparing a membrane-initiated hyperbranched polymer electrolyte (hereinafter referred to as hyperbranched polymer electrolyte). The hyperbranched polymer electrolyte is gel-like and has the advantages of high safety, high room temperature ionic conductivity and excellent interfacial stability. In addition, the hyperbranched polymer electrolyte also has a membrane function.

[0006] The present invention also provides a membrane-initiated hyperbranched polymer electrolyte prepared by the above preparation method. The hyperbranched polymer electrolyte is gel-like and has the advantages of high safety, high room temperature ionic conductivity and excellent interface stability.

[0007] The present invention also provides a lithium secondary battery comprising a membrane-initiated hyperbranched polymer electrolyte prepared by the above preparation method. Using the hyperbranched polymer electrolyte can enhance the interfacial contact between the electrolyte and the electrode, reduce the interfacial impedance of the battery, reduce battery polarization, and improve the cycle stability of the lithium secondary battery.

[0008] The first aspect of the present invention provides a method for preparing a membrane-initiated hyperbranched polymer electrolyte, comprising the following steps:

[0009] S1. A cellulose membrane, 4-dimethylaminopyridine, an organic solvent and an acid-binding agent are mixed and the cellulose membrane is fully swollen under anhydrous, oxygen-free and inert gas protection. Then, 2-bromoisobutyryl bromide is added to carry out an acylation reaction to obtain a cellulose membrane grafted with bromoisobutyrate.

[0010] S2. Mix monomer A, branching initiator B, catalyst, ligand, and lithium salt electrolyte to obtain precursor solution;

[0011] S3. Immerse the bromoisobutyrate-grafted cellulose membrane in the precursor solution to fully swell the bromoisobutyrate-grafted cellulose membrane, thereby obtaining a bromoisobutyrate-grafted cellulose membrane containing the precursor solution.

[0012] S4. After assembling the cellulose membrane grafted with the bromoisobutyrate containing the precursor solution into a battery, place it at 60℃-80℃ for in-situ polymerization reaction for 24h-72h. Hyperbranched polymer is generated in-situ on the cellulose membrane grafted with bromoisobutyrate, thus obtaining the membrane in-situ initiated hyperbranched polymer electrolyte.

[0013] The preparation method of the diaphragm-initiated hyperbranched polymer electrolyte as described above, wherein the hyperbranched polymer electrolyte is a gel electrolyte.

[0014] The method for preparing a membrane-initiated hyperbranched polymer electrolyte as described above, wherein the organic solvent includes N,N-dimethylformamide;

[0015] And / or, the acid-binding agent includes triethylamine;

[0016] And / or, the polymerizable monomer A is an average M n 550 g / mol of polyethylene glycol dimethacrylate, average M n It is at least one of polyethylene glycol diacrylates at a concentration of 528 g / mol;

[0017] And / or, the branching-initiating monomer B is 2-bromo-3,3,3-trifluoropropene;

[0018] And / or, the catalyst comprises cobalt(II) bromide;

[0019] And / or, the ligand comprises tris[2-(dimethylamino)ethyl]amine.

[0020] In the above-described method for preparing a membrane-initiated hyperbranched polymer electrolyte, the mass of the polymer monomer A is 10%-30% of the total mass of the precursor solution.

[0021] In the above-described method for preparing a membrane-initiated hyperbranched polymer electrolyte, the amount of the branching initiator monomer B is 8%-16% of the amount of the polymer monomer A; and the amount of the catalyst is 1%-2% of the amount of the polymer monomer A.

[0022] In the above-described method for preparing a membrane-initiated hyperbranched polymer electrolyte, the amount of the ligand is 1 to 5 times the amount of the catalyst.

[0023] The method for preparing a membrane-initiated hyperbranched polymer electrolyte as described above, wherein the lithium salt electrolyte comprises a lithium salt and a solvent;

[0024] The lithium salt is at least one of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonyl)imide, lithium difluorooxalate borate, and lithium nitrate, and the solvent is at least one of ethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and 1,3-dioxane.

[0025] In the above-described method for preparing a membrane-initiated hyperbranched polymer electrolyte, the concentration of the lithium salt in the lithium salt electrolyte is 0.1 mol / L to 4 mol / L.

[0026] A second aspect of the present invention provides a membrane-initiated hyperbranched polymer electrolyte, which is prepared by the aforementioned preparation method.

[0027] A third aspect of the present invention provides a lithium secondary battery comprising a membrane-initiated hyperbranched polymer electrolyte or the membrane-initiated hyperbranched polymer electrolyte prepared by the preparation method described above.

[0028] The solution of the present invention has at least the following effects:

[0029] The present invention provides a method for preparing a membrane-initiated hyperbranched polymer electrolyte. First, utilizing the abundant hydroxyl groups on the surface of a cellulose membrane, an initiator (2-bromoisobutyryl bromide) containing ATRP-initiating active sites is grafted onto the cellulose membrane via an acylation reaction. Then, polymeric monomer A, branching monomer B, a catalyst, ligands, and lithium salt electrolyte are mixed to obtain a precursor solution. Finally, the grafted cellulose membrane is immersed in the precursor solution to allow it to fully swell. After assembling the battery, in-situ thermal polymerization is performed, generating a hyperbranched polymer on the bromoisobutyryl ester-grafted cellulose membrane, successfully preparing the membrane-initiated hyperbranched polymer electrolyte. When the branching monomer B participates in the chain growth reaction as a comonomer, it forms new chain growth initiation sites on the polymer chain under the action of a catalyst, allowing polymeric monomer A to further undergo chain growth at these sites, thereby further expanding the branched structure of the polymer chain and forming a hyperbranched polymer network. The hyperbranched polymer electrolyte prepared by the method of the present invention is in gel form and has the advantages of high safety, high room temperature ionic conductivity and excellent interfacial stability. In addition, the hyperbranched polymer electrolyte also has a membrane function, providing a new research idea and method for preparing high-performance polymer electrolytes.

[0030] The in-situ initiated hyperbranched polymer electrolyte provided by this invention has a hyperbranched polymer network, which can provide more lithium-ion transport sites, reduce the energy barrier for lithium-ion diffusion, improve lithium-ion transport performance, and help improve the room temperature ionic conductivity of the electrolyte. This hyperbranched polymer electrolyte functions as both an electrolyte and a separator. Using this hyperbranched polymer electrolyte can enhance the interfacial contact between the electrolyte and the electrode, reduce the interfacial impedance of the battery, reduce battery polarization, and help improve the cycle stability of the battery. This hyperbranched polymer electrolyte also acts as a separator, effectively replacing the electrolyte in liquid lithium secondary batteries as a gel electrolyte, offering higher safety compared to liquid electrolytes. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a schematic diagram illustrating the preparation of the hyperbranched polymer electrolyte according to the present invention; wherein, Figure 1 (a) is a schematic diagram of the preparation of a bromoisobutyrate-grafted cellulose membrane. Figure 1(b) is a schematic diagram of the preparation of hyperbranched polymers; in the figure, n and m represent the degree of polymerization;

[0033] Figure 2 These are the infrared spectroscopy and nuclear magnetic resonance test results of this invention; wherein, Figure 2 (a) is the infrared spectrum of the cellulose membrane (membrane), grafted cellulose membrane (grafted membrane), polyethylene glycol dimethacrylate (polymer monomer A) and membrane in-situ initiated hyperbranched polymer electrolyte (hyperbranched polymer) in Example 1. Figure 2 (b) is the solid-state carbon NMR spectrum of the cellulose diaphragm (diaphragm) and the grafted cellulose diaphragm (grafted diaphragm) in Example 1; Figure 2 (c) are solid-state NMR fluorine spectra of the membrane-initiated hyperbranched polymer electrolyte (hyperbranched) in Example 1 and the membrane-initiated polymer electrolyte (unbranched) in Comparative Example 1.

[0034] Figure 3 The images show SEM images of the grafted cellulose membrane and the membrane-in-situ hyperbranched polymer electrolyte (hyperbranched polymer electrolyte) in Example 1 of this invention, and the membrane-in-situ hyperbranched polymer electrolyte in Comparative Example 6; wherein, Figure 3 (a) is a SEM image of the grafted cellulose diaphragm in Example 1; Figure 3 (b) is a SEM image of the hyperbranched polymer electrolyte (hyperbranched polymer electrolyte) initiated in situ by the diaphragm in Example 1; Figure 3 (c) is a SEM image of the hyperbranched polymer electrolyte induced in situ by the diaphragm in Comparative Example 6.

[0035] Figure 4 The results of room temperature ionic conductivity tests of the diaphragm-initiated hyperbranched polymer electrolyte (hyperbranched polymer electrolyte) in Examples 1-4 of this invention are shown.

[0036] Figure 5 The room temperature ionic conductivity test results are as follows: in Example 1, Comparative Examples 2-4, the membrane-initiated hyperbranched polymer electrolyte (hyperbranched polymer electrolyte) and in Comparative Example 1, the membrane-initiated polymer electrolyte (unbranched polymer electrolyte).

[0037] Figure 6 The results show the ionic conductivity of the in-situ diaphragm-induced hyperbranched polymer electrolyte (hereinafter referred to as hyperbranched) in Example 1 of the present invention and the in-situ diaphragm-induced polymer electrolyte (hereinafter referred to as unbranched) in Comparative Example 1 at different temperatures.

[0038] Figure 7 The results of cycling tests at different current densities are as follows: in Example 1, the diaphragm-initiated hyperbranched polymer electrolyte (hereinafter referred to as hyperbranched) and in Comparative Example 1, the diaphragm-initiated polymer electrolyte (hereinafter referred to as unbranched);

[0039] Figure 8 The in-situ initiation of hyperbranched polymer electrolyte (hereinafter referred to as hyperbranched) in Example 1 of the present invention and the in-situ initiation of unbranched polymer electrolyte (hereinafter referred to as unbranched) in Comparative Example 1 were carried out at 0.2 mA cm⁻¹. -2 Impedance plot after 50 cycles at a given current density. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this art or in accordance with the product instructions. Reagents or instruments used without specified manufacturers are all conventional products that can be obtained commercially.

[0041] In the following description, the term "and / or" is used to describe the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, B exists alone, and A and B exist simultaneously. A and B can be singular or plural.

[0042] In the following description, the terms "including," "containing," and "containing" are open-ended terms, meaning that they include but are not limited to.

[0043] Those skilled in the art should understand that, in the following description of the embodiments of the present invention, the sequence of numbers does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0044] Those skilled in the art will understand that the numerical ranges in the embodiments of the present invention should be understood to specifically disclose each intermediate value between the upper and lower limits of the range. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0045] Unless otherwise stated, the technical / scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art to which this invention pertains. While only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0046] Figure 1 This is a schematic diagram of the preparation of hyperbranched polymer electrolytes according to the present invention, as shown below. Figure 1 As shown, the first aspect of the present invention provides a method for preparing a membrane-initiated hyperbranched polymer electrolyte, comprising the following steps:

[0047] S1. A cellulose membrane, 4-dimethylaminopyridine, an organic solvent and an acid-binding agent are mixed and the cellulose membrane is fully swollen under anhydrous, oxygen-free and inert gas protection. Then, 2-bromoisobutyryl bromide is added to carry out an acylation reaction to obtain a cellulose membrane grafted with bromoisobutyrate.

[0048] S2. Mix monomer A, branching initiator B, catalyst, ligand, and lithium salt electrolyte to obtain precursor solution;

[0049] S3. Immerse the bromoisobutyrate-grafted cellulose membrane in the precursor solution to fully swell the bromoisobutyrate-grafted cellulose membrane, thereby obtaining a bromoisobutyrate-grafted cellulose membrane containing the precursor solution.

[0050] S4. After assembling the cellulose membrane grafted with the bromoisobutyrate containing the precursor solution into a battery, place it at 60℃-80℃ for in-situ polymerization reaction for 24h-72h. Hyperbranched polymer is generated in-situ on the cellulose membrane grafted with bromoisobutyrate, thus obtaining the membrane in-situ initiated hyperbranched polymer electrolyte.

[0051] In step S1, 4-dimethylaminopyridine is used as a catalyst.

[0052] In step S1, fully swelling the cellulose membrane is to separate the stacked macromolecular chains of the cellulose membrane, exposing more hydroxyl groups on the cellulose membrane to facilitate a full reaction with 2-bromoisobutyryl bromide. The cellulose membrane surface is rich in hydroxyl groups, and 2-bromoisobutyryl bromide is an initiator containing ATRP reaction initiation sites. This invention grafts 2-bromoisobutyryl bromide onto the cellulose membrane via an acylation reaction, enabling the cellulose membrane to act as both a supporting framework for the polymer electrolyte and a macromolecular initiator to initiate in-situ polymerization within the battery.

[0053] In step S3, the purpose of fully swelling the bromoisobutyrate-grafted cellulose membrane is to fully expose the bromoisobutyrate groups grafted onto the bromoisobutyrate-grafted cellulose membrane, so as to facilitate sufficient contact with the precursor solution in the subsequent process.

[0054] The mechanism of the in-situ polymerization reaction in step S4 of the present invention is explained as follows: In the cellulose membrane grafted with bromoisobutyrate containing the precursor solution, the branching monomer B participates in the chain growth reaction as a comonomer. Under the action of a catalyst and under thermal initiation conditions, it forms new chain growth initiation sites on the polymer chain, causing the polymer monomer A to undergo further chain growth reaction at these sites, further expanding the branching structure of the polymer chain. A hyperbranched polymer with a hyperbranched polymer network is formed in situ on the bromoisobutyrate grafted cellulose membrane, thereby obtaining the membrane-initiated hyperbranched polymer electrolyte.

[0055] In this invention, the inert gas is argon.

[0056] In this invention, the acylation reaction is carried out with stirring at room temperature. The specific stirring time is not particularly limited, as long as the cellulose membrane is fully swollen; the specific stirring time depends on the quality of the cellulose membrane and the liquid components in contact with it.

[0057] The hyperbranched polymer electrolyte prepared by the method of the present invention is in gel form and has the advantages of high safety, high room temperature ionic conductivity and excellent interfacial stability. In addition, the hyperbranched polymer electrolyte also has a membrane function, providing a new research idea and method for preparing high-performance polymer electrolytes.

[0058] In one specific embodiment, the hyperbranched polymer electrolyte is a gel electrolyte. Therefore, this hyperbranched polymer electrolyte has higher safety compared to an electrolyte solution.

[0059] In one specific embodiment, the organic solvent includes N,N-dimethylformamide.

[0060] In one specific embodiment, the acid-binding agent includes triethylamine.

[0061] In one specific embodiment, the polymeric monomer A is an average M n The content of polyethylene glycol dimethacrylate is 550 g / mol, with an average M n It is at least one of polyethylene glycol diacrylates in a concentration of 528 g / mol.

[0062] In this invention, the average M n This represents the average number-average molecular weight.

[0063] In one specific embodiment, the branching-initiating monomer B is 2-bromo-3,3,3-trifluoropropylene.

[0064] Using 2-bromo-3,3,3-trifluoropropene as monomer B to initiate branching, trifluoromethyl groups can be introduced into the hyperbranched polymer backbone while initiating branching, thereby further improving the oxidative stability of the hyperbranched polymer backbone.

[0065] In one specific embodiment, the catalyst comprises cobalt(II) bromide.

[0066] In one specific embodiment, the ligand comprises tris[2-(dimethylamino)ethyl]amine.

[0067] In one specific embodiment, the mass of the polymeric monomer A is 10%-30% of the total mass of the precursor liquid.

[0068] In one specific embodiment, the amount of the branching-initiating monomer B is 8%-16% of the amount of the polymerizing monomer A.

[0069] This invention controls the amount of the branching-initiating monomer B to be 8%-16% of the amount of the polymerizing monomer A, ensuring gel formation while achieving good ion transport performance. If the amount of the branching-initiating monomer B is too high (e.g., the amount of the branching-initiating monomer B is 20% of the amount of the polymerizing monomer A), gel formation may be impossible; if the amount of the branching-initiating monomer B is too low (e.g., the amount of the branching-initiating monomer B is 5% of the amount of the polymerizing monomer A), the room temperature ionic conductivity of the final hyperbranched polymer electrolyte may be low.

[0070] In one specific embodiment, the amount of the catalyst is 1%-2% of the amount of the polymeric monomer A.

[0071] In one specific embodiment, the amount of the ligand is 1 to 5 times the amount of the catalyst.

[0072] In one specific embodiment, the lithium salt electrolyte comprises a lithium salt and a solvent; wherein the lithium salt is at least one of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonyl)imide, lithium difluorooxalate borate, and lithium nitrate, and the solvent is at least one of ethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and 1,3-dioxane.

[0073] In one specific embodiment, the concentration of the lithium salt in the lithium salt electrolyte is 0.1 mol / L to 4 mol / L.

[0074] In one specific embodiment, the mass-volume ratio of the cellulose membrane, the 4-dimethylaminopyridine, the organic solvent, and the acid-binding agent is 1g:(0.1g-0.2g):(20mL-30mL):(1mL-4mL).

[0075] In one specific embodiment, before immersing the bromoisobutyrate-grafted cellulose membrane in the precursor solution, the bromoisobutyrate-grafted cellulose membrane is further subjected to washing and drying treatment.

[0076] A second aspect of the present invention provides a membrane-initiated hyperbranched polymer electrolyte, prepared by the aforementioned method. This membrane-initiated hyperbranched polymer electrolyte possesses a hyperbranched polymer network, providing more lithium-ion transport sites, lowering the energy barrier for lithium-ion diffusion, and improving lithium-ion transport performance, thus enhancing the room-temperature ionic conductivity of the electrolyte. This hyperbranched polymer electrolyte functions as both an electrolyte and a membrane. Using this hyperbranched polymer electrolyte enhances the interfacial contact between the electrolyte and the electrode, reduces the interfacial impedance of the battery, reduces battery polarization, and improves the cycle stability of the battery. This hyperbranched polymer electrolyte also functions as a membrane, effectively replacing the electrolyte in liquid lithium secondary batteries, offering higher safety compared to liquid electrolytes.

[0077] A third aspect of the present invention provides a lithium secondary battery comprising a membrane-initiated hyperbranched polymer electrolyte or the membrane-initiated hyperbranched polymer electrolyte prepared by the preparation method described above.

[0078] The present invention will be further described below through specific embodiments.

[0079] In the following examples, the cellulose membrane was purchased from Suzhou Duoduo Chemical Technology Co., Ltd.; 2-bromoisobutyryl bromide was purchased from Anaiji; and polyethylene glycol dimethacrylate (average) was used. M n (550 g / mol) purchased from Aladdin; polyethylene glycol diacrylate (average) M n (528 g / mol) was purchased from Aladdin; 2-bromo-3,3,3-trifluoropropene was purchased from TCI.

[0080] Example 1

[0081] This embodiment provides a method for preparing a membrane-initiated hyperbranched polymer electrolyte, comprising the following steps:

[0082] (1) Preparation of bromoisobutyrate-grafted cellulose membrane:

[0083] 5g of cellulose diaphragm (5×5cm)2 Add 0.5g of 4-dimethylaminopyridine and 120mL of ultra-dry N,N-dimethylformamide to a round-bottom flask. Seal the round-bottom flask and perform anhydrous and oxygen-free treatment under argon protection. Then add 10mL of anhydrous triethylamine. Stir at room temperature for 1 hour under anhydrous, oxygen-free and argon protection to allow the cellulose membrane to fully swell, and obtain the swollen cellulose membrane.

[0084] Under ice-water bath protection, 4 mL of 2-bromoisobutyryl bromide was added dropwise to the swollen cellulose membrane to obtain a reaction system; then the reaction system was placed in a room temperature environment and allowed to rise naturally to room temperature, and stirred at room temperature for 24 h to obtain a bromoisobutyrate-grafted cellulose membrane.

[0085] The bromoisobutyrate-grafted cellulose membrane was washed sequentially with deionized water, N,N-dimethylformamide, and tetrahydrofuran, and then dried in a vacuum oven at 100°C for 12 hours. It was then cut into discs with a diameter of 16 mm and vacuum dried in a vacuum oven at 100°C for 8 hours to finally obtain the dried bromoisobutyrate-grafted cellulose membrane (also known as grafted cellulose membrane).

[0086] (2) Preparation of precursor solution:

[0087] Lithium bis(trifluoromethanesulfonyl)imide was dissolved in a mixed solvent prepared by ethylene glycol dimethyl ether and 1,3-dioxane in a volume ratio of 1:1 to obtain a lithium salt electrolyte; the concentration of lithium bis(trifluoromethanesulfonyl)imide in the lithium salt electrolyte was 1 mol / L.

[0088] 1.375g of polyethylene glycol dimethacrylate (average) M n The precursor solution was obtained by mixing 550 g / mol of 2-bromo-3,3,3-trifluoropropene, 5.5 mg of cobalt bromide, 5.8 mg of tris[2-(dimethylamino)ethyl]amine, and 5.5 g of the lithium salt electrolyte.

[0089] (3) Preparation of membrane-initiated hyperbranched polymer electrolyte:

[0090] The dried bromoisobutyrate-grafted cellulose membrane was immersed in the precursor solution for 6 hours to allow the dried bromoisobutyrate-grafted cellulose membrane to fully swell, thereby obtaining a bromoisobutyrate-grafted cellulose membrane containing the precursor solution.

[0091] After assembling the cellulose membrane grafted with the bromoisobutyrate containing the precursor solution with two lithium sheets into a battery, it is placed in an oven at 80°C for in-situ polymerization for 72 hours. Hyperbranched polymers, namely membrane-initiated hyperbranched polymer electrolytes, are generated in situ on the bromoisobutyrate grafted cellulose membrane, resulting in a battery containing membrane-initiated hyperbranched polymer electrolytes. The membrane-initiated hyperbranched polymer electrolytes are then removed from the battery to obtain the membrane-initiated hyperbranched polymer electrolyte (also known as hyperbranched polymer electrolyte).

[0092] Example 2

[0093] The preparation method of the membrane-initiated hyperbranched polymer electrolyte provided in this embodiment is basically the same as that in Example 1, except that:

[0094] In step (2), lithium bis(trifluoromethanesulfonyl)imide is replaced with lithium bis(fluorosulfonyl)imide, lithium difluorooxalate borate and lithium nitrate; in the lithium salt electrolyte, the concentration of lithium bis(fluorosulfonyl)imide is 3 mol / L, the concentration of lithium difluorooxalate borate is 0.1 mol / L and the concentration of lithium nitrate is 0.1 mol / L.

[0095] Example 3

[0096] The preparation method of the membrane-initiated hyperbranched polymer electrolyte provided in this embodiment is basically the same as that in Example 1, except that:

[0097] In step (2), 1.375g of polyethylene glycol dimethacrylate (average) was added. M n The 550 g / mol was replaced with 1.375 g of polyethylene glycol diacrylate (average). M n (528 g / mol).

[0098] Example 4

[0099] The preparation method of the membrane-initiated hyperbranched polymer electrolyte provided in this embodiment is basically the same as that in Example 1, except that:

[0100] In step (2), the mixed solvent prepared by ethylene glycol dimethyl ether and 1,3-dioxane in a volume ratio of 1:1 is replaced with tetraethylene glycol dimethyl ether; the concentration of lithium bis(trifluoromethanesulfonyl)imide in the lithium salt electrolyte is 3 mol / L.

[0101] Comparative Example 1

[0102] The preparation method of the in-situ initiated polymer electrolyte by the diaphragm provided in this comparative example is basically the same as that in Example 1, except that:

[0103] In step (2), 2-bromo-3,3,3-trifluoropropene was not added.

[0104] In step (3), an unbranched polymer electrolyte, namely the membrane in-situ initiated polymer electrolyte, is generated in situ on the cellulose membrane grafted with bromoisobutyrate, to obtain a battery containing the membrane in-situ initiated polymer electrolyte; the membrane in-situ initiated polymer electrolyte is removed from the battery to obtain the membrane in-situ initiated polymer electrolyte (also known as unbranched polymer electrolyte).

[0105] Comparative Example 2

[0106] The preparation method of the in-situ initiated hyperbranched polymer electrolyte with a diaphragm provided in this comparative example is basically the same as that in Example 1, except that:

[0107] In step (2), 1.375g of polyethylene glycol dimethacrylate (average) was added. M n The 550 g / mol was replaced with 1.737 g of polyethylene glycol dimethacrylate (average). M n (550 g / mol), replace 5.5 mg cobalt bromide with 9.1 mg cuprous bromide, and replace 5.8 mg tris[2-(dimethylamino)ethyl]amine with 43.6 mg 1,1,4,7,10,10-hexamethyltriethylenetetramine.

[0108] Comparative Example 3

[0109] The preparation method of the in-situ initiated hyperbranched polymer electrolyte with a diaphragm provided in this comparative example is basically the same as that in Example 1, except that:

[0110] In step (2), 1.375g of polyethylene glycol dimethacrylate (average) was added. M n The 550 g / mol was replaced with 2.313 g of polyethylene glycol dimethacrylate (average). M n (550 g / mol), replace 5.5 mg cobalt bromide with 12.0 mg cuprous bromide, and replace 5.8 mg tris[2-(dimethylamino)ethyl]amine with 58.1 mg 1,1,4,7,10,10-hexamethyltriethylenetetramine.

[0111] Comparative Example 4

[0112] The preparation method of the in-situ initiated hyperbranched polymer electrolyte provided in this comparative example is basically the same as that in Example 1, except that:

[0113] In step (2), 43.7 mg of 2-bromo-3,3,3-trifluoropropene is replaced with 21.8 mg of 2-bromo-3,3,3-trifluoropropene.

[0114] Comparative Example 5

[0115] The preparation method of the in-situ initiated hyperbranched polymer electrolyte provided in this comparative example is basically the same as that in Example 1, except that:

[0116] In step (2), 43.7 mg of 2-bromo-3,3,3-trifluoropropene is replaced with 87.4 mg of 2-bromo-3,3,3-trifluoropropene.

[0117] During the preparation of the in-situ hyperbranched polymer electrolyte in this comparative example, the inventors discovered that the cellulose membrane grafted with bromoisobutyrate containing a precursor solution in this comparative example could not form a gel, and subsequent performance tests were not conducted.

[0118] Comparative Example 6

[0119] The preparation method of the in-situ initiated hyperbranched polymer electrolyte provided in this comparative example is basically the same as that in Example 1, except that:

[0120] In step (2), 1.375g of polyethylene glycol dimethacrylate (average) was added. M n The 550 g / mol was replaced with 865.7 mg of polyethylene glycol dimethacrylate (average). M n (550 g / mol), replace 5.5 mg cobalt bromide with 4.5 mg cuprous bromide, and replace 5.8 mg tris[2-(dimethylamino)ethyl]amine with 21.7 mg 1,1,4,7,10,10-hexamethyltriethylenetetramine.

[0121] In the process of preparing the membrane-initiated hyperbranched polymer electrolyte in this comparative example, the inventors found that the membrane-initiated hyperbranched polymer electrolyte prepared using the cellulose membrane grafted with bromoisobutyrate containing the precursor solution in this comparative example did not form a good gel morphology. Figure 3 (c) No further performance testing will be conducted.

[0122] Performance testing

[0123] 1. The cellulose membrane (hereinafter referred to as membrane), grafted cellulose membrane (hereinafter referred to as grafted membrane), polyethylene glycol dimethacrylate (hereinafter referred to as monomer A), and membrane-initiated hyperbranched polymer electrolyte (hereinafter referred to as hyperbranched polymer) in Example 1 of the present invention, as well as the membrane-initiated polymer electrolyte (hereinafter referred to as unbranched polymer) in Comparative Example 1, were characterized respectively, and the results are as follows: Figure 2 As shown. Figure 2 These are the infrared spectroscopy and nuclear magnetic resonance test results of this invention; wherein, Figure 2 (a) is the infrared spectrum of the cellulose membrane (membrane), grafted cellulose membrane (grafted membrane), polyethylene glycol dimethacrylate (polymer monomer A) and membrane in-situ initiated hyperbranched polymer electrolyte (hyperbranched polymer) in Example 1. Figure 2 (b) is the solid-state carbon NMR spectrum of the cellulose diaphragm (diaphragm) and the grafted cellulose diaphragm (grafted diaphragm) in Example 1; Figure 2 (c) is the solid-state NMR fluorine spectrum of the membrane-initiated hyperbranched polymer electrolyte (hyperbranched) in Example 1 and the membrane-initiated polymer electrolyte (unbranched) in Comparative Example 1.

[0124] Figure 2 (a) shows that the grafted cellulose septum (grafted septum) is at 1728 cm⁻¹. -1 The presence of a -C=O vibrational absorption peak indicates the successful introduction of the ester group.

[0125] Figure 2 (b) shows that the grafted cellulose membrane (grafted membrane) exhibits new characteristic peaks at 31.5 ppm and 171.3 ppm, corresponding to the peak positions of C in the C-Br bond and C in -OC=O, respectively, indicating that the bromoisobutyrate was successfully grafted onto the cellulose membrane.

[0126] Figure 2 (a) shows polyethylene glycol dimethacrylate (polymer monomer A) at 1637 cm⁻¹ -1 The characteristic vibrational peak of -C=C at this point disappears after the formation of hyperbranched polymers. Figure 2 (c) shows that the in-situ initiated hyperbranched polymer electrolyte (hyperbranching) has a significant signal peak at -73.16 ppm, which corresponds to the characteristic peak of -CF3 after the polymerization of the branching monomer B, proving the successful preparation of the hyperbranched polymer.

[0127] 2. Scanning electron microscopy (SEM) was performed on the grafted cellulose diaphragm and the diaphragm-initiated hyperbranched polymer electrolyte (hyperbranched polymer electrolyte) in Example 1 of the present invention, as well as the diaphragm-initiated hyperbranched polymer electrolyte in Comparative Example 6. The results are as follows: Figure 3 As shown. Figure 3 The images show SEM images of the grafted cellulose membrane and the membrane-in-situ hyperbranched polymer electrolyte (hyperbranched polymer electrolyte) in Example 1 of this invention, and the membrane-in-situ hyperbranched polymer electrolyte in Comparative Example 6; wherein, Figure 3 (a) is a SEM image of the grafted cellulose diaphragm in Example 1; Figure 3(b) is a SEM image of the hyperbranched polymer electrolyte (hyperbranched polymer electrolyte) initiated in situ by the diaphragm in Example 1; Figure 3 (c) is a SEM image of the hyperbranched polymer electrolyte induced in situ by the diaphragm in Comparative Example 6.

[0128] Depend on Figure 3 As shown in (a)-(b), after the in-situ polymerization reaction is completed, the pores in the grafted cellulose membrane are filled and it is gel-like, indicating that the hyperbranched polymer electrolyte is gel-like.

[0129] Depend on Figure 3 As can be seen from (c), the pores in the grafted cellulose membrane were not completely filled, and the fiber structure still existed in some areas, resulting in poor gel formation or incomplete gel formation. The inventors analyzed that the reason might be due to insufficient amount of polyethylene glycol dimethacrylate.

[0130] 3. The room temperature ionic conductivity of the in-situ diaphragm-induced hyperbranched polymer electrolytes in Examples 1-4, Comparative Example 1, and Comparative Examples 2-4 was tested, and the test results are summarized in Table 1. Figure 4 The results of room temperature ionic conductivity tests of the diaphragm-initiated hyperbranched polymer electrolyte (hyperbranched polymer electrolyte) in Examples 1-4 of this invention are shown. Figure 5 The results show the room temperature ionic conductivity of the in-situ diaphragm-induced hyperbranched polymer electrolyte (hyperbranched polymer electrolyte) in Example 1 and Comparative Examples 2-4 of this invention, and the in-situ diaphragm-induced polymer electrolyte (unbranched polymer electrolyte) in Comparative Example 1.

[0131] Room temperature ionic conductivity: A coin cell with a stainless steel / polymer electrolyte / stainless steel system, constructed using a blocking battery, was measured using an electrochemical workstation (Vionic, Metrohm China Ltd.), employing AC impedance spectroscopy, with a bias voltage of 10mV and a frequency range of 0.1Hz-10Hz. 5 Hz, ionic conductivity was tested at room temperature.

[0132] Table 1. Room temperature ionic conductivity test results of Examples 1-4 and Comparative Examples 1-5

[0133]

[0134] Depend on Figures 4-5 As shown in Table 1, the hyperbranched polymer electrolyte (0.37 mS cm⁻¹) in Example 1... -1 ) and the unbranched polymer electrolyte (0.17 mS cm) in Comparative Example 1 -1Compared to other methods, the hyperbranched polymer electrolytes exhibit higher room-temperature ionic conductivity, demonstrating the enhancement of ion transport performance through hyperbranching. The room-temperature ionic conductivity of the hyperbranched polymer electrolytes in Examples 1-4 all reached 0.2 mS / cm. -1 The above demonstrates that hyperbranched polymer electrolytes prepared using different monomers A and different electrolyte systems all exhibit good ion transport performance, proving the good applicability of hyperbranched electrolytes to different systems.

[0135] 4. The ionic conductivity of the in-situ membrane-initiated hyperbranched polymer electrolyte (hyperbranched polymer electrolyte) in Example 1 and the in-situ membrane-initiated polymer electrolyte (unbranched polymer electrolyte) in Comparative Example 1 were tested at different temperatures. The results are as follows: Figure 6 As shown. Figure 6 The results show the ionic conductivity of the in-situ diaphragm-induced hyperbranched polymer electrolyte (hereinafter referred to as hyperbranched) in Example 1 and the in-situ diaphragm-induced polymer electrolyte (hereinafter referred to as unbranched) in Comparative Example 1 at different temperatures.

[0136] Depend on Figure 6 It can be seen that hyperbranched polymer electrolytes have higher ionic conductivity compared to unbranched polymer electrolytes. Furthermore, the ion migration activation energies of hyperbranched and unbranched polymer electrolytes were calculated using the Arrhenius equation. The activation energy of hyperbranched polymer electrolytes was 0.133 eV, while that of unbranched polymer electrolytes was 0.173 eV. This indicates that hyperbranched polymer electrolytes have lower activation energies and lower ion diffusion barriers, which are more conducive to ion transport.

[0137] 5. Cyclic tests were conducted at different current densities on the in-situ diaphragm-induced hyperbranched polymer electrolyte (hyperbranched polymer electrolyte) in Example 1 and the in-situ diaphragm-induced polymer electrolyte (unbranched polymer electrolyte) in Comparative Example 1. The results are as follows: Figure 7 As shown. Figure 7 The results are the cycle test results of the in-situ diaphragm-induced hyperbranched polymer electrolyte (hereinafter referred to as hyperbranched) in Example 1 of the present invention and the in-situ diaphragm-induced polymer electrolyte (hereinafter referred to as unbranched) in Comparative Example 1 at different current densities.

[0138] Depend on Figure 7 It can be seen that, compared with unbranched polymer electrolytes, hyperbranched polymer electrolytes have smaller polarization voltages at different current densities.

[0139] 6. The in-situ membrane-initiated hyperbranched polymer electrolyte (hyperbranched polymer electrolyte) from Example 1 and the in-situ membrane-initiated polymer electrolyte (unbranched polymer electrolyte) from Comparative Example 1 were respectively subjected to a temperature of 0.2 mA cm⁻¹.-2 Impedance testing was performed after 50 cycles at a current density, and the results are as follows: Figure 8 As shown. Figure 8 The in-situ initiation of hyperbranched polymer electrolyte (hereinafter referred to as hyperbranched) in Example 1 of the present invention and the in-situ initiation of unbranched polymer electrolyte (hereinafter referred to as unbranched) in Comparative Example 1 were carried out at 0.2 mA cm⁻¹. -2 Impedance plot after 50 cycles at a given current density.

[0140] Depend on Figure 8 It can be seen that hyperbranched polymer electrolytes have lower interfacial impedance compared to unbranched polymer electrolytes, proving that hyperbranched polymer electrolytes have better interfacial stability.

[0141] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a membrane-initiated hyperbranched polymer electrolyte, characterized in that, Includes the following steps: S1. A cellulose membrane, 4-dimethylaminopyridine, an organic solvent and an acid-binding agent are mixed and the cellulose membrane is fully swollen under anhydrous, oxygen-free and inert gas protection. Then, 2-bromoisobutyryl bromide is added to carry out an acylation reaction to obtain a cellulose membrane grafted with bromoisobutyrate. S2. Mix monomer A, branching initiator B, catalyst, ligand, and lithium salt electrolyte to obtain precursor solution; S3. Immerse the bromoisobutyrate-grafted cellulose membrane in the precursor solution to fully swell the bromoisobutyrate-grafted cellulose membrane, thereby obtaining a bromoisobutyrate-grafted cellulose membrane containing the precursor solution. S4. After assembling the cellulose membrane grafted with bromoisobutyrate containing the precursor solution into a battery, place it at 60℃-80℃ for in-situ polymerization reaction for 24h-72h to generate hyperbranched polymer in situ on the cellulose membrane grafted with bromoisobutyrate, thus obtaining the membrane in-situ initiated hyperbranched polymer electrolyte. Wherein, the polymeric monomer A is the average M n The content of polyethylene glycol dimethacrylate is 550 g / mol, with an average M n It is at least one of polyethylene glycol diacrylate at a concentration of 528 g / mol; the branching initiator monomer B is 2-bromo-3,3,3-trifluoropropylene.

2. The method for preparing a membrane-initiated hyperbranched polymer electrolyte according to claim 1, characterized in that, The hyperbranched polymer electrolyte is a gel electrolyte.

3. The method for preparing a membrane-initiated hyperbranched polymer electrolyte according to claim 1, characterized in that, The organic solvent includes N,N-dimethylformamide; And / or, the acid-binding agent includes triethylamine; And / or, the catalyst comprises cobalt(II) bromide; And / or, the ligand comprises tris[2-(dimethylamino)ethyl]amine.

4. The method for preparing a membrane-initiated hyperbranched polymer electrolyte according to claim 1, characterized in that, The mass of the polymer monomer A is 10%-30% of the total mass of the precursor solution.

5. The method for preparing a membrane-initiated hyperbranched polymer electrolyte according to claim 1, characterized in that, The amount of the branching-initiating monomer B is 8%-16% of the amount of the polymerizing monomer A; the amount of the catalyst is 1%-2% of the amount of the polymerizing monomer A.

6. The method for preparing a membrane-initiated hyperbranched polymer electrolyte according to claim 1, characterized in that, The amount of the ligand is 1 to 5 times the amount of the catalyst.

7. The method for preparing a membrane-initiated hyperbranched polymer electrolyte according to claim 1, characterized in that, The lithium salt electrolyte comprises a lithium salt and a solvent; The lithium salt is at least one of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonyl)imide, lithium difluorooxalate borate, and lithium nitrate, and the solvent is at least one of ethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and 1,3-dioxane.

8. The method for preparing a membrane-initiated hyperbranched polymer electrolyte according to claim 7, characterized in that, In the lithium salt electrolyte, the concentration of the lithium salt is 0.1 mol / L to 4 mol / L.

9. A membrane-initiated hyperbranched polymer electrolyte, characterized in that, It is prepared by the preparation method described in any one of claims 1-8.

10. A lithium secondary battery, characterized in that, This includes the membrane-initiated hyperbranched polymer electrolyte prepared by the preparation method according to any one of claims 1-8 or the membrane-initiated hyperbranched polymer electrolyte according to claim 9.

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