A gel electrolyte membrane and its preparation method and application

Abstract

The present invention discloses a gel electrolyte membrane and its preparation method and application, wherein the preparation method of the gel electrolyte membrane comprises the following steps: dissolving a branched polymer containing a hydroxyl group or a carboxyl group in a first solvent, ultrasonically dispersing it under ice bath conditions, and then stirring at a constant temperature to obtain a solution of the branched polymer; dissolving polyvinylidene fluoride-hexafluoropropylene in a second solvent, adding polyethylene oxide, heating and stirring, and obtaining a mixed solution; mixing the branched polymer solution with the mixed solution, heating and stirring, and obtaining a polymer electrolyte slurry; curing the polymer electrolyte slurry into a shape, and then immersing it in an electrolyte in an inert gas atmosphere for activation to obtain a gel electrolyte membrane. The gel electrolyte membrane obtained by this method has a three-dimensional porous network structure that conducts lithium ions rapidly. The gel electrolyte membrane with this structure is assembled into a battery with high ion conductivity and cycle stability.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and more particularly to a gel electrolyte membrane, a preparation method thereof, and applications thereof. Background Art

[0002] Lithium-ion batteries are the representatives of modern high-performance batteries, and their main components include positive electrode materials, negative electrode materials and electrolytes. Among them, the electrolyte must not only be able to provide suitable ionic conductivity within a wide range of ambient temperature and electrochemical windows, but also be able to maintain good chemical stability and good compatibility with electrode materials. The electrolytes used in commercial lithium-ion batteries are all liquid organic electrolytes, which limits the application of high energy density and high power density materials, and is accompanied by safety hazards of spontaneous combustion and explosion. Although solid electrolytes have higher safety, their ionic conductivity is still not ideal, and there is still a long way to go in industrial applications. Gel electrolytes form gel electrolytes by solidifying organic electrolytes through polymers, which improves the electrolyte-electrode interface contact. In theory, it can have both the good ionic conductivity of liquid electrolytes (10 -4 ~10 -3 Scm -1 ) and the high safety of solid-state electrolytes, but in practical applications, the ionic conductivity of gel electrolytes still needs to be further improved. Summary of the Invention

[0003] In view of the above problems, the present invention is proposed to provide a gel electrolyte membrane and a preparation method and application thereof that overcome the above problems or at least partially solve the above problems.

[0004] As one aspect of the present invention, a method for preparing a gel electrolyte membrane is provided, comprising: dissolving a branched polymer containing a hydroxyl group or a carboxyl group in a first solvent, ultrasonically dispersing the polymer in an ice bath, and then stirring the polymer at a constant temperature to obtain a solution of the branched polymer; dissolving polyvinylidene fluoride-hexafluoropropylene in a second solvent, adding polyethylene oxide, heating and stirring the solution, and obtaining a mixed solution; mixing the branched polymer solution with the mixed solution, heating and stirring the solution, and obtaining a polymer electrolyte slurry; solidifying the polymer electrolyte slurry into a shape, and then immersing the polymer electrolyte slurry in an inert gas atmosphere for activation to obtain a gel electrolyte membrane.

[0005] Optionally, in the preparation method of the gel electrolyte membrane of the present invention, the branched polymer containing hydroxyl or carboxyl groups is one or a combination of any two of polyvinyl alcohol, polyethylene glycol, polyethylene glycol dicarboxylic acid, polyethylene glycol diacrylate, hydroxy-polyethylene glycol-hydroxy, polyacrylic acid, polyacrylamide, and polyethyl acrylate.

[0006] Optionally, in the method for preparing the gel electrolyte membrane of the present invention, the mass fraction of polyethylene oxide in the mixed solution is 5 wt % to 20 wt %.

[0007] Optionally, in the method for preparing the gel electrolyte membrane of the present invention, in the polymer electrolyte slurry, the mass ratio of the branched polymer, polyethylene oxide, and polyvinylidene fluoride-hexafluoropropylene is 0.01-0.1:0.01-0.1:1.

[0008] Optionally, in the preparation method of the gel electrolyte membrane of the present invention, the first solvent is one of deionized water, ethanol, ethylene glycol, propylene glycol, isopropanol, acetone, N-methylpyrrolidone, N,N-dimethylformamide, or a combination of any several of them.

[0009] Optionally, in the method for preparing the gel electrolyte membrane of the present invention, the second solvent is one of NMP, DMF, ethanol, acetonitrile, isopropanol, and acetone, or any combination thereof.

[0010] Optionally, in the preparation method of the gel electrolyte membrane of the present invention, the ultrasonic dispersion under ice bath conditions is performed in an ice bath ultrasonic low temperature tank with an ultrasonic power of 450 W and an ultrasonic frequency of 50 kHz to 60 kHz for 1 h to 3 h.

[0011] Optionally, in the preparation method of the gel electrolyte membrane of the present invention, the constant temperature stirring is carried out at 20° C. to 50° C. and a rotation speed of 300 rpm to 500 rpm for 8 h to 12 h.

[0012] Optionally, in the method for preparing the gel electrolyte membrane of the present invention, the heating and stirring is carried out at 50° C. to 80° C. and a rotation speed of 300 rpm to 500 rpm for 1 to 2 hours.

[0013] Optionally, in the method for preparing the gel electrolyte membrane of the present invention, the activation time is 1 hour to 8 hours.

[0014] Optionally, in the preparation method of the gel electrolyte membrane of the present invention, the solute of the electrolyte is one or a combination of any two of lithium bis(oxalatoborate), lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonylimide), lithium bis(fluorosulfonylimide), lithium hexafluorophosphate, lithium perchlorate and lithium difluorooxalatoborate.

[0015] Optionally, in the method for preparing the gel electrolyte membrane of the present invention, the curing and molding comprises: casting the polymer electrolyte slurry into a mold, followed by vacuum drying.

[0016] Optionally, in the method for preparing the gel electrolyte membrane of the present invention, the vacuum drying is carried out at 60° C. to 100° C. for 12 h to 24 h.

[0017] Optionally, in the preparation method of the gel electrolyte membrane of the present invention, the relative molecular mass of polyvinylidene fluoride-hexafluoropropylene is 3×10 5 ~6×10 5 .

[0018] Optionally, in the preparation method of the gel electrolyte membrane of the present invention, the relative molecular mass of polyethylene oxide is 6×10 5 ~1×10 6 .

[0019] Optionally, in the method for preparing the gel electrolyte membrane of the present invention, the thickness of the gel electrolyte membrane is 40 μm to 60 μm.

[0020] According to another aspect of the present invention, a gel electrolyte membrane is provided, which is prepared by the above preparation method.

[0021] According to another aspect of the present invention, a lithium ion battery is provided, comprising a positive electrode, a negative electrode, and the above-mentioned gel electrolyte membrane, wherein the gel electrolyte membrane is located between the positive electrode and the negative electrode.

[0022] As in the solution of the present invention, by selecting a branched polymer rich in hydroxyl or carboxyl groups, ultrasonically treating and stirring at a constant temperature to disperse it in a solvent for later use, polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) is used as a polymer electrolyte matrix and dissolved in an organic solvent, a certain mass fraction of polyethylene oxide (PEO) is added to obtain a mixed solution, the branched polymer dispersion is added to the mixed solution according to a certain solid content ratio, heated and stirred to obtain a uniform polymer electrolyte slurry, the uniform slurry is cast into a mold, and vacuum dried to obtain a polymer film. The polymer film is punched into a circular sheet, placed in a glove box with an Ar atmosphere, and immersed in an electrolyte for activation to obtain a gel polymer electrolyte membrane. The branched polymer rich in hydroxyl or carboxyl groups can form intermolecular hydrogen bonds with polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) and polyethylene oxide (PEO), bonding to construct a three-dimensional porous network with rapid lithium ion conduction, increasing the gel electrolyte's liquid absorption rate and liquid retention rate to the electrolyte, and improving ionic conductivity.

[0023] The preparation method of the gel electrolyte membrane of the present invention has the advantages of low cost, simple process and strong controllability.

[0024] The gel electrolyte membrane prepared by the solution of the present invention has a three-dimensional porous network structure that quickly conducts lithium ions. This structure not only has good flexibility, but also the assembled lithium ion battery has high ion conductivity and cycle stability, making it a good choice to replace traditional lithium ion battery electrolytes.

[0025] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are specifically listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present invention. The same reference symbols are used throughout the drawings to represent the same components. In the drawings:

[0027] Figure 1 1 is a schematic flow chart of a method 100 for preparing a gel electrolyte membrane according to an embodiment of the present invention;

[0028] Figure 2 shows a scanning electron microscope image of a gel electrolyte membrane prepared according to one embodiment of the present invention;

[0029] Figure 3 The EIS graphs of the gel electrolyte membranes prepared in Example 1 and Comparative Examples 1-4 according to one embodiment of the present invention are shown. DETAILED DESCRIPTION

[0030] Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0031] Figure 1 FIG. 1 is a schematic flow chart of a method 100 for preparing a gel electrolyte membrane according to an embodiment of the present invention.

[0032] like Figure 1 As shown, the purpose of this method is to prepare a three-dimensional porous network structure with fast lithium ion conduction, which not only has good flexibility, but also has a gel electrolyte membrane for assembled lithium-ion batteries with high ion conductivity and cycle stability.

[0033] Method 100 begins with step 102. In step 102, a branched polymer containing hydroxyl or carboxyl groups is dissolved in a first solvent, ultrasonically dispersed in an ice bath, and then stirred at a constant temperature to obtain a branched polymer solution. The ultrasonic dispersion in the ice bath is performed in an ice bath ultrasonic low-temperature tank at an ultrasonic power of 450 W and an ultrasonic frequency of 50 kHz to 60 kHz for 1 to 3 hours. The constant temperature stirring is performed at a temperature of 20° C. to 50° C. and a rotation speed of 300 rpm to 500 rpm for 8 to 12 hours.

[0034] In some embodiments, the branched polymer containing hydroxyl or carboxyl groups is one or a combination of polyvinyl alcohol, polyethylene glycol, polyethylene glycol dicarboxylic acid, polyethylene glycol diacrylate, hydroxy-polyethylene glycol-hydroxy, polyacrylic acid, polyacrylamide, and polyethyl acrylate. The first solvent is one or a combination of deionized water, ethanol, ethylene glycol, propylene glycol, isopropyl alcohol, acetone, N-methylpyrrolidone, and N,N-dimethylformamide.

[0035] Then, step 104 is performed to dissolve polyvinylidene fluoride-hexafluoropropylene in a second solvent, add polyethylene oxide, and heat and stir to obtain a mixed solution. The relative molecular mass of polyvinylidene fluoride-hexafluoropropylene is 3×10 5 ~6×10 5 The second solvent is one of NMP, DMF, ethanol, acetonitrile, isopropanol, and acetone, or any combination thereof.

[0036] The relative molecular mass of the added polyethylene oxide (PEO) is 6×10 5 ~1×10 6 , and its mass fraction in the mixed solution is 5wt% to 20wt%.

[0037] Subsequently, in step 106, the branched polymer solution is mixed with the mixed solution and heated and stirred to obtain a polymer electrolyte slurry. The heating and stirring is performed at 50°C to 80°C and a rotation speed of 300 to 500 rpm for 1 to 2 hours. The resulting polymer electrolyte slurry has a mass ratio of branched polymer, polyethylene oxide, and polyvinylidene fluoride-hexafluoropropylene of 0.01 to 0.1:0.01 to 0.1:1.

[0038] Finally, in step 108, the polymer electrolyte slurry is solidified and then immersed in an electrolyte in an inert gas atmosphere for activation to obtain Figure 2 The gel electrolyte membrane shown. Figure 2As shown, the gel electrolyte membrane prepared by the preparation method provided in this embodiment has a rich three-dimensional network porous structure, and the thickness of the gel electrolyte membrane can be maintained at 40 μm to 60 μm (the scale bar in the figure is 5 μm).

[0039] The curing step includes: casting the polymer electrolyte slurry into a mold, and then vacuum drying the slurry at 60° C. to 100° C. for 12 to 24 hours.

[0040] Preferably, the inert gas atmosphere can be realized in a glove box with an Ar atmosphere. The solute of the electrolyte is selected from one or a combination of lithium bis(oxalatoborate), lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonylimide), lithium bis(fluorosulfonylimide), lithium hexafluorophosphate, lithium perchlorate and lithium difluorooxalatoborate.

[0041] In some embodiments, the activation time is 1 h to 8 h.

[0042] In summary, the preparation method 100 provided by the present invention is to select a branched polymer rich in hydroxyl or carboxyl groups, ultrasonically treat and stir at a constant temperature to disperse it in a solvent for standby use, dissolve polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) as a polymer electrolyte matrix in an organic solvent, add a certain mass fraction of polyethylene oxide (PEO) to obtain a mixed solution, add the branched polymer dispersion to the mixed solution according to a certain solid content ratio, heat and stir to obtain a uniform polymer electrolyte slurry, cast the uniform slurry into a mold, and vacuum dry to obtain a polymer film. The polymer film is punched into a circular sheet, placed in an Ar atmosphere glove box, and immersed in an electrolyte for activation to obtain a gel polymer electrolyte membrane. The branched polymer rich in hydroxyl or carboxyl groups can form intermolecular hydrogen bonds with polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) and polyethylene oxide (PEO), forming a three-dimensional porous network with fast lithium ion conduction, increasing the liquid absorption rate and liquid retention of the gel electrolyte to the electrolyte, and improving the ionic conductivity.

[0043] The gel electrolyte membrane and the preparation method thereof of the present invention are described below by means of specific examples. This description is only intended to help those skilled in the art better understand the present invention, but does not limit the present invention in any way.

[0044] Example 1

[0045] (1) Dissolve 1.0060 g of polyethylene glycol dicarboxylic acid (PEGCE) powder in 100.6000 mL of deionized water and stir in a thermostatic stirrer at 500 rpm and 25°C for 12 h to prepare a 10 mg / mL polyethylene glycol dicarboxylic acid dispersion.

[0046] (2) 1.0130 g of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) with a molecular weight of 455,000 was dissolved in 14.0000 mL of acetone and stirred in a thermostatic stirrer at 500 rpm and 60°C for 1 h to obtain a uniform polymer matrix solution;

[0047] (3) 0.0507 g of polyethylene oxide (PEO) with a molecular weight of 600,000 was dissolved in the polymer matrix solution of step (2) and stirred in a thermostatic stirrer at a speed of 500 rpm and a temperature of 60° C. for 2 h to obtain a mixed solution;

[0048] (4) The 10 mg / mL polyethylene glycol dicarboxylic acid dispersion prepared in step (1) was mixed with the mixed solution obtained in step (3) and stirred to form a stable polymer slurry with a solid content of (PVDF-HFP:PEO:PEGCE=100:5:5);

[0049] (5) The polymer slurry prepared in step (4) was cast into a mold, dried under vacuum at 60°C for 24 h, and cured to obtain a polymer film with a thickness of 50 μm;

[0050] (6) The prepared polymer membrane was punched into thin sheets, placed in a glove box with Ar atmosphere, and immersed in 1M lithium hexafluorophosphate (LiPF6) (EC:DMC:EMC=1:1:1Vol%) electrolyte for activation for 2h to obtain a gel polymer electrolyte membrane (denoted as PVDF-HFP@PEO@PEGCE).

[0051] Example 2

[0052] (1) Dissolve 1.0080 g of polyethylene glycol (PEG) in 100.8000 mL of deionized water and stir in a thermostatic stirrer at 500 rpm and 25°C for 12 h to prepare a 10 mg / mL polyethylene glycol dispersion.

[0053] (2) 1.0160 g of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) with a molecular weight of 455,000 was dissolved in 14.1000 mL of acetone and stirred in a thermostatic stirrer at 500 rpm and 60°C for 1 h to obtain a uniform polymer matrix solution;

[0054] (3) 0.0508 g of polyethylene oxide (PEO) with a molecular weight of 600,000 was dissolved in the polymer matrix solution of step (2) and stirred in a thermostatic stirrer at a speed of 500 rpm and a temperature of 60° C. for 2 h to obtain a mixed solution;

[0055] (4) The 10 mg / mL polyethylene glycol dispersion prepared in step (1) was mixed with the mixed solution obtained in step (3) and stirred to form a stable polymer slurry with a solid content of (PVDF-HFP:PEO:PEG=100:5:5);

[0056] (5) The polymer slurry prepared in step (4) was cast into a mold, dried under vacuum at 60°C for 24 h, and cured to obtain a polymer film with a thickness of 30 μm;

[0057] (6) The prepared polymer membrane was punched into thin sheets, placed in a glove box with an Ar atmosphere, and immersed in a 1MLiPF6 (EC:DMC:EMC=1:1:1Vol%) electrolyte for activation for 2h to obtain a gel polymer electrolyte membrane.

[0058] Example 3

[0059] (1) Dissolve 1.0020 g of hydroxy-PEG-hydroxy (OH-PEG-OG) in 100.2000 mL of deionized water and stir in a thermostatic stirrer at 500 rpm and 25°C for 12 h to prepare a 10 mg / mL OH-PEG-OG dispersion.

[0060] (2) 1.0080 g of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) with a molecular weight of 455,000 was dissolved in 13.8000 mL of acetone and stirred in a thermostatic stirrer at 500 rpm and 60°C for 1 h to obtain a uniform polymer matrix solution;

[0061] (3) 0.1080 g of polyethylene oxide (PEO) with a molecular weight of 600,000 was dissolved in the polymer matrix solution of step (2), and stirred in a thermostatic stirrer at a speed of 500 rpm and a temperature of 60° C. for 2 h to obtain a mixed solution;

[0062] (4) The 10 mg / mL OH-PEG-OG dispersion prepared in step (1) was mixed with the mixed solution obtained in step (3) and stirred to form a stable polymer slurry with a solid content of (PVDF-HFP:PEO:OH-PEG-OG=100:5:5);

[0063] (5) The polymer slurry prepared in step (4) was cast into a mold, dried under vacuum at 60°C for 24 h, and cured to obtain a polymer film with a thickness of 26 μm;

[0064] (6) The prepared polymer membrane was punched into thin sheets, placed in a glove box with an Ar atmosphere, and immersed in a 1MLiPF6 (EC:DMC:EMC=1:1:1Vol%) electrolyte for activation for 2 h to obtain a gel polymer electrolyte membrane.

[0065] Example 4

[0066] (1) Dissolve 1.0150 g of polyacrylic acid (PAA) powder in 101.5000 mL of deionized water and stir in a thermostatic stirrer at 500 rpm and 25°C for 12 h to prepare a 10 mg / mL PAA dispersion.

[0067] (2) 0.9980 g of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) with a molecular weight of 455,000 was dissolved in 13.5000 mL of acetone and stirred in a thermostatic stirrer at 500 rpm and 60°C for 1 h to obtain a uniform polymer matrix solution;

[0068] (3) 0.0499 g of polyethylene oxide (PEO) with a molecular weight of 600,000 was dissolved in the polymer matrix solution of step (2) and stirred in a thermostatic stirrer at a speed of 500 rpm and a temperature of 60° C. for 2 h to obtain a mixed solution;

[0069] (4) The 10 mg / mL polyacrylic acid dispersion prepared in step (1) was mixed with the mixed solution obtained in step (3) and stirred to form a stable polymer slurry with a solid content of (PVDF-HFP:PEO:PAA=100:5:5);

[0070] (5) The polymer slurry prepared in step (4) was cast into a mold, dried under vacuum at 60°C for 24 h, and cured to obtain a polymer film with a thickness of 33 μm;

[0071] (6) The prepared polymer membrane was punched into thin sheets, placed in a glove box with an Ar atmosphere, and immersed in a 1MLiPF6 (EC:DMC:EMC=1:1:1Vol%) electrolyte for activation for 2 h to obtain a gel polymer electrolyte membrane.

[0072] Example 5

[0073] (1) Dissolve 1.0030 g of polyvinyl alcohol (PVA) powder in 100.3000 mL of deionized water and stir in a thermostatic stirrer at 500 rpm and 25°C for 12 h to prepare a 10 mg / mL polyvinyl alcohol dispersion.

[0074] (2) 1.080 g of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) with a molecular weight of 455,000 was dissolved in 13.8000 mL of acetone and stirred in a thermostatic stirrer at 500 rpm and 60°C for 1 h to obtain a uniform polymer matrix solution;

[0075] (3) 0.0540 g of polyethylene oxide (PEO) with a molecular weight of 600,000 was dissolved in the polymer matrix solution of step (2), and stirred in a thermostatic stirrer at a speed of 500 rpm and a temperature of 60° C. for 2 h to obtain a mixed solution;

[0076] (4) The 10 mg / mL polyvinyl alcohol dispersion prepared in step (1) was mixed with the mixed solution obtained in step (3) and stirred to form a stable polymer slurry with a solid content of (PVDF-HFP:PEO:PVA=100:5:5);

[0077] (5) The polymer slurry prepared in step (4) was cast into a mold, dried under vacuum at 60°C for 24 h, and cured to obtain a polymer film with a thickness of 32 μm;

[0078] (6) The prepared polymer membrane was punched into thin sheets, placed in a glove box with an Ar atmosphere, and immersed in a 1MLiPF6 (EC:DMC:EMC=1:1:1Vol%) electrolyte for activation for 2 h to obtain a gel polymer electrolyte membrane.

[0079] Comparative Example 1

[0080] (1) 1.0050 g of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) with a molecular weight of 455,000 was dissolved in 13.2000 mL of acetone and stirred in a thermostatic stirrer at 500 rpm and 60°C for 1 h to obtain a uniform polymer matrix solution;

[0081] (2) The polymer slurry prepared in step (1) was cast into a mold, dried under vacuum at 60°C for 24 hours, and cured to obtain a polymer film with a thickness of 15 μm;

[0082] (3) The prepared polymer membrane was punched into thin sheets, placed in a glove box with Ar atmosphere, and immersed in 1MLiPF6 (EC:DMC:EMC=1:1:1Vol%) electrolyte for activation for 2h to obtain a gel polymer electrolyte membrane (denoted as PVDF-HFP).

[0083] Comparative Example 2

[0084] (1) 1.0100 g of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) with a molecular weight of 455,000 was dissolved in 13.5000 mL of acetone and stirred in a thermostatic stirrer at 500 rpm and 60°C for 1 h to obtain a uniform polymer matrix solution;

[0085] (2) 0.0505 g of polyethylene oxide (PEO) with a molecular weight of 600,000 was dissolved in the polymer matrix solution of step (2) and stirred in a thermostatic stirrer at a speed of 500 rpm and a temperature of 60° C. for 2 h to obtain a stable polymer slurry with a solid content of (PVDF-HFP:PEO=100:5);

[0086] (3) The polymer slurry prepared in step (2) was cast into a mold, dried under vacuum at 60°C for 24 h, and cured to obtain a polymer film with a thickness of 25 μm;

[0087] (5) The prepared polymer membrane was punched into thin sheets, placed in a glove box with Ar atmosphere, and immersed in 1MLiPF6 (EC:DMC:EMC=1:1:1Vol%) electrolyte for activation for 2h to obtain a gel polymer electrolyte membrane (denoted as PVDF-HFP@PEO).

[0088] Comparative Example 3

[0089] (1) Dissolve 0.9970 g of polyethylene glycol dicarboxylic acid (PEGCE) powder in 99.7000 mL of anhydrous ethanol and stir in a thermostatic stirrer at 500 rpm and 25°C for 12 h to prepare a 10 mg / mL polyethylene glycol dicarboxylic acid dispersion.

[0090] (2) 1.0080 g of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) with a molecular weight of 455,000 was dissolved in 13.3000 mL of acetone and stirred in a thermostatic stirrer at 500 rpm and 60°C for 1 h to obtain a uniform polymer matrix solution;

[0091] (3) 9.9800 ml of the 10 mg / mL polyethylene glycol dicarboxylic acid dispersion prepared in step (1) was mixed with the polymer matrix solution obtained in step (2) to form a stable polymer slurry with a solid content of (PVDF-HFP:PEGCE=100:5);

[0092] (4) The polymer slurry prepared in step (3) was cast into a mold, dried under vacuum at 60°C for 24 h, and cured to obtain a polymer film with a thickness of 40 μm;

[0093] (5) The prepared polymer membrane was punched into thin sheets, placed in a glove box with Ar atmosphere, and immersed in 1MLiPF6 (EC:DMC:EMC=1:1:1Vol%) electrolyte for activation for 2h to obtain a gel polymer electrolyte membrane (denoted as PVDF-HFP@PEGCE).

[0094] Comparative Example 4

[0095] (1) A commercial PP separator was punched into thin sheets, placed in a glove box with an Ar atmosphere, and immersed in a 1M LiPF6 (EC:DMC:EMC=1:1:1 Vol%) electrolyte for activation for 2 h.

[0096] Test Case

[0097] Comparative Example 1 and Comparative Examples 1-4 prepared gel electrolyte membrane EIS results are shown in Figure 3 , Figure 3 The ionic conductivity of the gel electrolyte membrane prepared in Example 1 is as high as 5×10 -4 S cm -1 Compared with the gel electrolyte membrane obtained by unmodified or single use of PEO or PEGCE, it has better ion conductivity, and the ion conductivity almost reaches the level of liquid electrolyte.

[0098] The branched polymers containing hydroxyl groups or carboxyl groups, polyvinylidene fluoride-hexafluoropropylene and polyethylene oxide used in the above examples or comparative examples were purchased from Aladdin Chemical Reagent Network.

[0099] In summary, the present invention uses a small amount of branched polymers rich in hydroxyl or carboxyl groups to modify the polymer electrolyte matrix polyvinylidene fluoride-hexafluoropropylene and polyethylene oxide. The three form intermolecular hydrogen bonds and bond to construct a three-dimensional porous network with rapid lithium ion conduction. This structure can improve the ionic conductivity of the gel electrolyte membrane, thereby making the lithium-ion battery have more excellent electrochemical performance.

[0100] A9. The method as described in A1, wherein the heating and stirring is carried out at 50°C to 80°C and a rotation speed of 300rpm to 500rpm for 1h to 2h. A10. The method as described in A1, wherein the activation time is 1h to 8h. A11. The method as described in A1, wherein the solute of the electrolyte is one or a combination of any of the following: lithium bis(oxalatoborate), lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonylimide), lithium bis(fluorosulfonylimide), lithium hexafluorophosphate, lithium perchlorate and lithium difluorooxalatoborate. A12. The method as described in A1, wherein the curing molding comprises: casting the polymer electrolyte slurry into a mold, followed by vacuum drying. A13. The method as described in A12, wherein the vacuum drying is carried out at 60°C to 100°C for 12h to 24h. A14. The method as described in A1, wherein the relative molecular mass of the polyvinylidene fluoride-hexafluoropropylene is 3×10 5 ~6×10 5 A15. The method as described in A1, wherein the relative molecular mass of the polyethylene oxide is 6×10 5 ~1×10 6A16. The method according to A1, wherein the thickness of the gel electrolyte membrane is 40 μm to 60 μm.

[0101] In the description of this specification, unless otherwise expressly specified or limited, the terms "connected", "fixed", etc. should be understood in a broad sense. In addition, the terms "upper", "lower", "inner", "outer", "top", "bottom", etc. indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings and are only used to facilitate the description of the present invention and simplify the description. They do not indicate or imply that the devices or units referred to must have a specific direction, be constructed and operate in a specific orientation. Therefore, they should not be understood as limiting the present invention.

[0102] Throughout this specification, terms such as "one embodiment," "some embodiments," and "specific embodiments" mean that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0103] In the description provided herein, a large number of specific details are described. However, it is understood that embodiments of the present invention can be practiced without these specific details. In some instances, well-known methods, structures, and techniques are not shown in detail so as not to obscure the understanding of this description.

[0104] Similarly, it should be understood that in order to streamline the present disclosure and aid understanding of one or more of the various inventive aspects, in the above description of exemplary embodiments of the present invention, various features of the present invention are sometimes grouped together into a single embodiment, figure, or description thereof. However, this method of disclosure should not be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Accordingly, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of the present invention.

[0105] Furthermore, those skilled in the art will appreciate that although some embodiments described herein include certain features and not other features included in other embodiments, the combination of features from different embodiments is intended to be within the scope of the invention and to form different embodiments.

[0106] Although the present invention has been described as having a limited number of embodiments, it will be apparent to those skilled in the art, having the benefit of the foregoing description, that other embodiments are contemplated within the scope of the invention thus described. Furthermore, it should be noted that the language used in this specification has been selected primarily for readability and didactic purposes, and not for the purpose of explaining or limiting the subject matter of the invention. Accordingly, many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the appended claims. The disclosure of the present invention is intended to be illustrative and not restrictive of the scope of the invention, which is defined by the appended claims.

Claims

1. A method for preparing a gel electrolyte membrane, comprising: Dissolving a branched polymer containing a hydroxyl group or a carboxyl group in a first solvent, performing ultrasonic dispersion under ice bath conditions, and then stirring at a constant temperature to obtain a branched polymer solution, wherein the branched polymer containing a hydroxyl group or a carboxyl group is one or a combination of any of polyvinyl alcohol, polyethylene glycol, polyethylene glycol dicarboxylic acid, polyethylene glycol diacrylate, hydroxy-polyethylene glycol-hydroxy, polyacrylic acid, polyacrylamide, and polyethyl acrylate; Dissolve polyvinylidene fluoride-hexafluoropropylene in a second solvent, add polyethylene oxide, and heat and stir to obtain a mixed solution, wherein the mass fraction of polyethylene oxide in the mixed solution is 5wt%~20wt%, and the relative molecular mass of the polyvinylidene fluoride-hexafluoropropylene is 3×10 5 ~6×10 5 The relative molecular mass of the polyethylene oxide is 6×10 5 ~1×10 6 ; The branched polymer solution is mixed with the mixed solution, and the mixture is heated and stirred to obtain a polymer electrolyte slurry, wherein the mass ratio of the branched polymer, polyethylene oxide and polyvinylidene fluoride-hexafluoropropylene in the polymer electrolyte slurry is 0.01-0.1:0.01-0.1:1; The polymer electrolyte slurry is solidified and formed, and then immersed in an electrolyte in an inert gas atmosphere for activation to obtain the gel electrolyte membrane. The activation time is 1 hour to 8 hours, and the thickness of the gel electrolyte membrane is 40 μm to 60 μm.

2. The method according to claim 1, wherein The first solvent is one of deionized water, ethanol, ethylene glycol, propylene glycol, isopropyl alcohol, acetone, N-methylpyrrolidone, N,N-dimethylformamide, or a combination of any of them.

3. The method according to claim 1, wherein The second solvent is one of NMP, DMF, ethanol, acetonitrile, isopropanol, and acetone, or a combination of any of them.

4. The preparation method according to claim 1, wherein Ultrasonic dispersion under ice bath conditions is carried out in an ice bath ultrasonic low temperature tank with an ultrasonic power of 450W and an ultrasonic frequency of 50kHz~60kHz for 1h~3h.

5. The method according to claim 1, wherein The constant temperature stirring is carried out at 20°C to 50°C and a rotation speed of 300rpm to 500rpm for 8h to 12h.

6. The method of claim 1, wherein: The heating and stirring are carried out at 50°C to 80°C and a rotation speed of 300 rpm to 500 rpm for 1 hour to 2 hours.

7. The method of claim 1, wherein: The solute of the electrolyte is one or a combination of any of lithium bis(oxalatoborate), lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonylimide), lithium bis(fluorosulfonylimide), lithium hexafluorophosphate, lithium perchlorate and lithium difluorooxalatoborate.

8. The method of claim 1, wherein: The curing molding comprises: casting the polymer electrolyte slurry into a mold, and then vacuum drying.

9. The method of claim 8, wherein: The vacuum drying is carried out at a temperature of 60° C. to 100° C. for 12 h to 24 h.

10. A gel electrolyte membrane, prepared by the preparation method according to any one of claims 1 to 9.

11. A lithium-ion battery comprising a positive electrode, a negative electrode, and the gel electrolyte membrane according to claim 10 or the gel electrolyte membrane prepared by the preparation method according to any one of claims 1 to 9, wherein the gel electrolyte membrane is located between the positive electrode and the negative electrode.

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