A method for preparing a gradient fiber structure composite gel polymer electrolyte for lithium batteries

Abstract

A method for preparing a gradient fiber structure composite gel polymer electrolyte for lithium batteries belongs to the technical field of lithium battery polymer electrolytes. An organic-inorganic composite fiber membrane with a gradient structure is prepared by electrospinning technology, wherein a high-voltage resistant polymer fiber layer matching the high-voltage positive electrode material is selected for the positive electrode side, an inorganic nanofiber layer with high mechanical strength and thermal stability is selected for the middle layer, and a polymer fiber layer with good interface compatibility with the negative electrode material is selected for the negative electrode side. A composite gel polymer electrolyte is formed by introducing a liquid electrolyte. The gradient fiber structure composite gel polymer electrolyte has high ionic conductivity, excellent mechanical strength, high safety, good high-voltage resistance and interface compatibility, which significantly improves the cycle life of the lithium battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium battery polymer electrolytes, and in particular relates to a method for preparing a gradient fiber structure composite gel polymer electrolyte for lithium batteries. Background Art

[0002] With the rapid development of portable electronic devices and the rapid expansion of the electric vehicle market, the demand for efficient, reliable, and environmentally friendly energy storage systems is becoming increasingly urgent. The operation of these devices and vehicles relies on battery systems that can provide continuous and stable energy output. The performance of batteries depends largely on their core component: the electrolyte. The volatility and flammability of liquid electrolytes make them prone to thermal runaway under high temperature and overcharge conditions, leading to battery fires and even explosions. Furthermore, liquid electrolytes may gradually decompose over long-term use, producing harmful byproducts that affect battery stability and lifespan. Gel polymer electrolytes combine the safety of solid electrolytes with the high conductivity of liquid electrolytes. They also possess good flexibility, can be used in battery designs of various shapes and sizes, and are easy to process and integrate into battery systems. Further incorporating inorganic nanofillers into polymer electrolytes to construct organic-inorganic composite polymer electrolytes can effectively reduce polymer crystallinity, improve strong electrolyte stability, and enhance ion transport performance.

[0003] However, despite the advantages of composite polymer electrolytes, they still face challenges in practical applications. Inorganic nanofillers have a large specific surface area, high surface energy, and are prone to agglomeration. Existing gel polymer electrolytes are generally insufficient in mechanical strength, which limits their reliability when subjected to mechanical stress. In addition, interfacial compatibility issues between gel polymer electrolytes and electrode materials may lead to increased interfacial resistance, affecting the overall performance and life of the battery. Most polymers cannot match high-voltage positive electrodes, making the electrolyte prone to degradation or failure under high-voltage working environments, limiting the energy density and operating voltage range of the battery. Summary of the Invention

[0004] The present invention aims to address the problem of poor compatibility between gel polymer electrolytes and electrode materials by providing a method for preparing a gradient fiber structure composite gel polymer electrolyte for lithium batteries. This method utilizes a high-voltage-resistant polymer fiber layer, an inorganic nanofiber layer with high mechanical strength and thermal stability, and a polymer fiber layer with excellent interfacial compatibility on the positive electrode side, the intermediate layer, and the negative electrode side, respectively. Electrospinning is then used to prepare a gradient fiber structure composite membrane with varying properties from the positive electrode side to the negative electrode side. Liquid electrolyte is then introduced onto this structure to produce a composite gel polymer electrolyte with high ionic conductivity, high mechanical strength, good interfacial compatibility, and high-voltage resistance.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing a gradient fiber structure composite gel polymer electrolyte for a lithium battery, the method comprising the following steps:

[0007] Step 1: dissolving an inorganic filler precursor and polyvinyl pyrrolidone (PVP) or polyvinyl alcohol (PVA) in a mixed solution of ethanol and acetic acid to prepare an intermediate layer spinning solution;

[0008] Step 2: The middle layer spinning solution is electrospun. During the spinning process, the internal temperature of the body is 40°C, the internal humidity is 40%, the applied working voltage is 18kV, the propulsion pump propulsion rate is 0.8mL / h, and the receiving distance from the needle to the receiver is 18cm. The obtained spinning membrane is heat-treated to obtain an inorganic nanofiber membrane with high mechanical strength (tensile strength>5Mpa);

[0009] Step 3: Select a polymer with high voltage resistance (electrochemical window ≥ 4.3V) and dissolve it in a mixed solution of N, N-dimethylformamide and acetone to prepare a positive electrode side spinning solution;

[0010] Step 4: Select a polymer with excellent interfacial compatibility and dissolve it in a mixed solution of N,N-dimethylformamide and acetone to prepare a negative electrode side spinning solution;

[0011] Step 5: Electrospinning the positive electrode side spinning solution on one side of the inorganic nanofiber membrane and electrospinning the negative electrode side spinning solution on the other side of the inorganic nanofiber membrane to obtain a gradient fiber composite membrane; the specific parameters of the electrospinning on the positive electrode side and the negative electrode side are the same as those of the middle layer;

[0012] Step 6: drying the obtained gradient fiber composite membrane to remove the solvent;

[0013] Step 7: Add a certain amount of liquid electrolyte to the composite membrane and wait for it to swell to obtain a composite gel polymer electrolyte.

[0014] Furthermore, in step 1, the inorganic filler precursor is one or more of ethyl orthosilicate, aluminum nitrate, zirconium n-butoxide, and titanium tetrachloride. The corresponding inorganic nanofiber membrane is one or more of silicon dioxide (SiO2), aluminum oxide (Al2O3), zirconium dioxide (ZrO2), and titanium dioxide (TiO2).

[0015] Furthermore, in step 1, the mass ratio of the inorganic filler precursor: PVP: ethanol: acetic acid is 0.5-2: 0.1: 1: 0.02-0.05.

[0016] Furthermore, in step 2, the heat treatment temperature is 500-1200° C., preferably 700-1000° C., and the time is 0.5-6 h, preferably 2-4 h.

[0017] Furthermore, in step three, the polymer is one or more of polyacrylonitrile (PAN), polypropylene carbonate (PPC), polyvinyl carbonate (PEC), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polychlorotrifluoroethylene (PCTFE), poly(ethylene-co-hexafluoropropylene) (ETFE) or monomers of the above polymers.

[0018] Furthermore, in step 4, the polymer includes one or more of polyoxyethylene (PEO), polyoxypropylene (PPO), polymethyl methacrylate (PMMA), polybutadiene (PBD), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyethylene glycol dimethyl ether (PEGDME), polyacrylate (PAA) or monomers of the above polymers.

[0019] The gradient fiber structure positive / negative electrode side polymer layer (composite membrane) is formed by blending or copolymerizing polymer raw materials, and the polymer raw materials are selected from polymer monomers and / or polymers, and the polymers are, for example, polymer monomer copolymers, polymer blends, and copolymers of polymers and polymer monomers.

[0020] Furthermore, in steps 3 and 4, the volume ratio of N,N-dimethylformamide and acetone is 3:1 to 7:1, for example, 3:1, 4:1, 5:1, 6:1, or 7:1, and the mass concentration of the polymer raw material in the mixed solution is 0.03 g / ml to 0.4 g / ml, preferably 0.05 g / ml to 0.35 g / ml.

[0021] Furthermore, in step six, the total thickness of the composite membrane after drying is 1 to 250 μm, preferably, the thickness of the composite membrane is 10 to 150 μm, and more preferably, the thickness of the composite membrane is 20 to 100 μm; wherein the thickness ratio of the positive electrode side: the intermediate layer: the negative electrode side is 1 to 3: 1 to 5: 1 to 3.

[0022] Furthermore, in step six, the pore size of the micro-nano pore structure on the composite membrane is 20 nm to 5 μm, preferably, the pore size is 100 nm to 4 μm, and more preferably, the pore size is 1 μm to 3 μm.

[0023] Furthermore, in step 7, the liquid electrolyte includes one of a liquid ether electrolyte or a liquid ester electrolyte, for example, LiTFSI-DME / DOL (1:1), LiTFSI-DME / DOL (1:1) + 1% LiNO3, or LiPF6-EC / DEC / DMC (1:1:1), LiPF6-EC / DEC / DMC (1:1:1) + 1% FEC, or LiPF6-EC / DEC (1:1) + 5% FEC. The ratios are by volume and the percentages are by mass.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The preparation of gradient fiber composite membrane structure by electrospinning method can effectively control the thickness and porosity, promote electrolyte infiltration, form a fast ion transmission path, accelerate the migration rate of lithium ions in the electrolyte, and significantly improve the ionic conductivity and lithium ion migration number of the electrolyte.

[0026] (2) The use of high-voltage resistant polymer materials on the positive electrode side allows the electrolyte to remain stable under high voltage conditions and is not prone to decomposition or degradation, thereby broadening the operating voltage range of the battery and improving the energy density and safety of the battery.

[0027] (3) By introducing inorganic nanofibers with high mechanical strength and toughness into the intermediate layer, the tensile and compressive properties of the overall electrolyte can be significantly improved, thereby enhancing the structural stability of the battery, effectively inhibiting the growth and volume change of lithium dendrites on the negative electrode side during charging and discharging, and avoiding structural damage caused by mechanical stress. Inorganic nanofibers have good chemical stability and can resist chemical corrosion during battery charging and discharging, thereby increasing the service life of the electrolyte. They also have excellent thermal stability, which improves the flame retardant properties of the electrolyte, allowing it to remain stable in high temperature environments and not easily subject to thermal decomposition and thermal runaway, further improving the safety of the battery.

[0028] (4) Inorganic nanofibers are uniform in thickness and have high porosity, which can provide more ion transmission channels and improve the ion transmission rate of the electrolyte. The Lewis acid groups on their surface can effectively adsorb anions, promote the dissociation of lithium salts, and increase the lithium ion migration number.

[0029] (5) The negative electrode side uses a polymer material with good interface compatibility with the negative electrode material, which reduces the interface impedance between the electrolyte and the electrode, improves the interface contact between the electrode and the electrolyte, and is conducive to accelerating ion transport at the interface.

[0030] (6) The advantages of different polymers are brought together through gradient polymerization to obtain a gel polymer electrolyte with high ionic conductivity, excellent mechanical strength, high safety, good high-voltage resistance and interface compatibility.

[0031] (7) The gradient fiber structure composite gel polymer electrolyte prepared by the present invention has a simple process, convenient operation, and is easy to achieve large-scale production, and has high practicality and economic value. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the gradient fiber structure composite membrane prepared in Example 1;

[0033] Figure 2 This is an SEM image of the positive electrode side composite membrane PAN-PVDF prepared in Example 2;

[0034] Figure 3 This is an SEM image of the intermediate layer composite film SiO2-ZrO2 prepared in Example 2;

[0035] Figure 4 This is the SEM image of the negative electrode side composite membrane PEO-PVDF prepared in Example 2.

[0036] Figure 5 This is an SEM image of the cathode side composite membrane PPC-PVDF prepared in Example 3;

[0037] Figure 6 This is an SEM image of the intermediate layer composite film ZrO2 prepared in Example 3;

[0038] Figure 7 This is an SEM image of the negative electrode side composite membrane PEO-PMMA prepared in Example 3;

[0039] Figure 8 Lithium prepared in Example 4 || LiNi 0.8 Co 0.1 Mn 0.1 Battery cycle performance diagram. DETAILED DESCRIPTION

[0040] The technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and Examples. Obviously, the described embodiments are only a part of the embodiments of the invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0041] The present invention provides a method for preparing a gradient fiber structure composite gel polymer electrolyte, comprising the following steps: preparing a spinning solution by dissolving an inorganic filler precursor and polyvinylpyrrolidone (PVP) in a mixed solution of ethanol and acetic acid, performing electrospinning, and heat treating to obtain an inorganic nanofiber layer. Separately, different polymer raw materials are dissolved in an organic solvent to obtain spinning solutions for the positive electrode side polymer fiber layer and the negative electrode side polymer fiber layer. The two spinning solutions are gradient spun and dried on both sides of the inorganic nanofiber layer to obtain a gradient composite polymer film. A liquid electrolyte is added to the porous polymer film to obtain a composite structure gel polymer electrolyte.

[0042] Example 1

[0043] A certain amount of tetraethyl orthosilicate and polyvinylpyrrolidone (PVP) was dissolved in a mixed solution of ethanol and acetic acid, stirred at 60°C for 12 hours, and allowed to stand for 1 hour to remove bubbles generated during the stirring process to obtain a uniform intermediate layer spinning solution. The mass ratio of tetraethyl orthosilicate: PVP: ethanol: acetic acid was 1:0.1:1:0.02. The resulting spinning solution was electrospun at an internal temperature of 40°C, a humidity of 40%, an applied operating voltage of 18kV, a propulsion pump rate of 0.8mL / h, and a receiving distance of 18cm from the needle tip to the receiver. The spinning membrane was then heat treated at 800°C for 2 hours to produce the inorganic nanofiber layer.

[0044] Dissolve 0.3g of polyacrylonitrile in a mixed solvent of 3ml of dimethylformamide and 1ml of acetone at room temperature; dissolve 0.15g of polyethylene oxide in a mixed solvent of 3ml of dimethylformamide and 1ml of acetone at room temperature. Stir the mixed solvents at 60°C for 12 hours and let them stand for 1 hour to remove bubbles generated during the stirring process to obtain uniform positive electrode side spinning solution and negative electrode side spinning solution. The two spinning solutions were spun on both sides of the inorganic nanofiber layer and the solvent was dried at 60°C to produce a film material with a micro-nano fiber structure. Figure 1 Schematic diagram. The specific electrospinning parameters for the positive and negative electrodes are the same as those for the intermediate layer. Under an argon atmosphere, a liquid ester electrolyte consisting of 1M LiPF6-EC / DEC / DMC (1:1:1) + 1% FEC was added to the gradient fiber membrane and allowed to stand for 12 hours to produce a gradient fiber-structured composite gel polymer electrolyte.

[0045] Example 2

[0046] A certain amount of tetraethyl orthosilicate, zirconium n-butoxide, and polyvinylpyrrolidone (PVP) were dissolved in a mixture of ethanol and acetic acid, stirred at 60°C for 12 hours, and allowed to stand for 1 hour to remove bubbles generated during the stirring process, thereby obtaining a uniform intermediate layer spinning solution. The mass ratio of tetraethyl orthosilicate: zirconium n-butoxide: PVP: ethanol: acetic acid was 0.5:0.5:0.1:1:0.02. The resulting spinning solution was electrospun at an internal temperature of 40°C, a humidity of 40%, an applied voltage of 18 kV, a propulsion pump rate of 0.8 mL / h, and a receiving distance of 18 cm from the needle tip to the receiver. The spinning membrane was then heat-treated at 800°C for 2 hours to produce the inorganic nanofiber layer.

[0047] Dissolve 0.2g of polyacrylonitrile and 0.6g of polyvinylidene fluoride in a mixed solvent of 3ml of dimethylformamide and 1ml of acetone at room temperature; dissolve 0.1g of polyethylene oxide and 0.6g of polyvinylidene fluoride-hexafluoropropylene in a mixed solvent of 3ml of dimethylformamide and 1ml of acetone at room temperature. Stir the above mixed solvents at 60°C for 12h, let it stand for 1h to remove the bubbles generated during the stirring process to obtain uniform positive electrode side spinning solution and negative electrode side spinning solution. The two spinning solutions obtained are spun on both sides of the inorganic nanofiber layer respectively and the solvents are dried at 60°C to prepare a thin film material with a micro-nano fiber structure. The specific parameters of electrospinning on the positive and negative sides are the same as those of the middle layer; under an argon atmosphere, a liquid ester electrolyte of 1M LiPF6-EC / DEC / DMC (1:1:1) + 1% FEC is added to the gradient fiber membrane and allowed to stand for 12h to obtain a gradient fiber structure composite gel polymer electrolyte. See Figure 2-4 As shown in the SEM photos, the gradient fiber membrane prepared in this embodiment has a uniform pore size distribution and a large porosity, which is conducive to the transmission of lithium ions.

[0048] Example 3

[0049] A certain amount of zirconium n-butoxide and polyvinylpyrrolidone (PVP) were dissolved in a mixed solution of ethanol and acetic acid, stirred at 60°C for 12 hours, and allowed to stand for 1 hour to remove bubbles generated during the stirring process to obtain a uniform intermediate layer spinning solution. The mass ratio of zirconium n-butoxide: PVP: ethanol: acetic acid is 1:0.1:1:0.02. The obtained spinning solution was subjected to electrospinning. During the spinning process, the internal temperature of the body was 40°C, the internal humidity was 40%, the applied working voltage was 18kV, the propulsion pump propulsion rate was 0.8mL / h, and the receiving distance from the needle to the receiver was 18cm. The spinning membrane was then heat-treated at 800°C for 2 hours to obtain an inorganic nanofiber layer. Figure 5-7 As shown in the SEM photos, the gradient fiber membrane prepared in this embodiment has a uniform pore size distribution and a large porosity, which is conducive to the transmission of lithium ions.

[0050] 0.2g of poly(ethylene carbonate) and 0.6g of poly(vinylidene fluoride) were dissolved in a mixture of 2ml of dimethylformamide and 2ml of acetone at room temperature. 0.1g of polyethylene oxide and 0.6g of poly(methyl methacrylate) were dissolved in a mixture of 3ml of dimethylformamide and 1ml of acetone at room temperature. The mixed solvents were stirred at 60°C for 12 hours and allowed to stand for 1 hour to remove bubbles generated during stirring, thereby obtaining uniform positive and negative electrode spinning solutions. The two spinning solutions were then spun onto both sides of the inorganic nanofiber layer and dried at 60°C to produce a thin film material with a micro-nanofiber structure. The specific electrospinning parameters for the positive and negative electrodes were the same as for the intermediate layer. A liquid ester electrolyte solution of 1M LiPF6-EC / DEC / DMC (1:1:1) + 1% FEC was added to the gradient fiber membrane under an argon atmosphere and allowed to stand for 12 hours to produce a gradient fiber composite gel polymer electrolyte.

[0051] Example 4

[0052] A certain amount of tetraethyl orthosilicate, zirconium n-butoxide, and polyvinylpyrrolidone (PVP) were dissolved in a mixture of ethanol and acetic acid, stirred at 60°C for 12 hours, and allowed to stand for 1 hour to remove bubbles generated during the stirring process, thereby obtaining a uniform intermediate layer spinning solution. The mass ratio of tetraethyl orthosilicate: zirconium n-butoxide: PVP: ethanol: acetic acid was 0.5:0.5:0.1:1:0.02. The resulting spinning solution was electrospun at an internal temperature of 40°C, a humidity of 40%, an applied voltage of 18 kV, a propulsion pump rate of 0.8 mL / h, and a receiving distance of 18 cm from the needle tip to the receiver. The spinning membrane was then heat-treated at 1000°C for 2 hours to produce the inorganic nanofiber layer.

[0053] 0.2g polyacrylonitrile and 0.6g polyvinylidene fluoride were dissolved in a mixed solvent of 3ml dimethylformamide and 1ml acetone at room temperature; 0.1g polyethylene oxide and 0.6g polyvinylidene fluoride-hexafluoropropylene were dissolved in a mixed solvent of 3ml dimethylformamide and 1ml acetone at room temperature. The mixed solvents were stirred at 60°C for 12h and allowed to stand for 1h to remove the bubbles generated during the stirring process to obtain uniform positive electrode side spinning solution and negative electrode side spinning solution. The two spinning solutions were spun on both sides of the inorganic nanofiber layer and the solvents were dried at 60°C to prepare a thin film material with a micro-nano fiber structure. The specific parameters of the electrospinning on the positive and negative sides were the same as those of the middle layer; under an argon atmosphere, a liquid ester electrolyte of 1MLiPF6-EC / DEC / DMC (1:1:1) + 1% FEC was added to the gradient fiber membrane and allowed to stand for 12h to obtain a gradient fiber structure composite gel polymer electrolyte. The lithium sheet was used as the negative electrode and the ternary material LiNi 0.8Co 0.1 Mn 0.1 As the positive electrode, assemble lithium||LiNi 0.8 Co 0.1 Mn 0.1 Battery, cycle performance such as Figure 8 shown.

[0054] Example 5

[0055] A certain amount of titanium tetrachloride and polyvinylpyrrolidone (PVP) was dissolved in a mixed solution of ethanol and acetic acid, stirred at 60°C for 12 hours, and allowed to stand for 1 hour to remove bubbles generated during the stirring process to obtain a uniform intermediate layer spinning solution. The mass ratio of titanium tetrachloride:PVP:ethanol:acetic acid was 1:0.1:1:0.02. The resulting spinning solution was electrospun at an internal temperature of 40°C, a humidity of 40%, an applied operating voltage of 18kV, a propulsion pump rate of 0.8mL / h, and a receiving distance of 18cm from the needle tip to the receiver. The spinning membrane was then heat treated at 800°C for 2 hours to produce the inorganic nanofiber layer.

[0056] 0.2g of polyacrylonitrile and 0.6g of polyvinylidene fluoride-hexafluoropropylene were dissolved in a mixture of 2ml of dimethylformamide and 2ml of acetone at room temperature. 0.1g of polyethylene oxide and 0.6g of polyvinylidene fluoride-hexafluoropropylene were dissolved in a mixture of 3ml of dimethylformamide and 1ml of acetone at room temperature. The mixed solvents were stirred at 60°C for 12 hours and allowed to stand for 1 hour to remove bubbles generated during stirring, thereby obtaining uniform positive and negative electrode spinning solutions. The two spinning solutions were spun onto both sides of the inorganic nanofiber layer and dried at 60°C to produce a thin film material with a micro-nanofiber structure. The specific electrospinning parameters for the positive and negative electrodes were the same as for the intermediate layer. Under an argon atmosphere, a liquid ether electrolyte solution of 1M LiTFSI-DME / DOL (1:1) + 1% LiNO3 was added to the gradient fiber membrane and allowed to stand for 12 hours to obtain a gradient fiber composite gel polymer electrolyte.

[0057] Example 6

[0058] A certain amount of aluminum nitrate and polyvinylpyrrolidone (PVP) was dissolved in a mixed solution of ethanol and acetic acid, stirred at 60°C for 12 hours, and allowed to stand for 1 hour to remove bubbles generated during the stirring process to obtain a uniform intermediate layer spinning solution. The mass ratio of aluminum nitrate: PVP: ethanol: acetic acid was 1:0.1:1:0.02. The resulting spinning solution was electrospun during the spinning process. During the spinning process, the internal temperature of the body was 40°C, the internal humidity was 40%, the applied working voltage was 18kV, the propulsion pump propulsion rate was 0.8mL / h, and the receiving distance from the needle to the receiver was 18cm. The spinning membrane was then heat treated at 800°C for 2 hours to obtain the inorganic nanofiber layer.

[0059] 0.2g of polyacrylonitrile and 0.6g of polyvinylidene fluoride were dissolved in a mixture of 2ml of dimethylformamide and 2ml of acetone at room temperature. 0.1g of polyethylene oxide and 0.6g of polyvinylidene fluoride were dissolved in a mixture of 3ml of dimethylformamide and 1ml of acetone at room temperature. The mixed solvents were stirred at 60°C for 12 hours and allowed to stand for 1 hour to remove bubbles generated during stirring, thereby obtaining uniform positive and negative electrode spinning solutions. The two spinning solutions were spun onto both sides of the inorganic nanofiber layer, and the solvents were dried at 60°C to produce a thin film material with a micro-nanofiber structure. The specific electrospinning parameters for the positive and negative electrodes were the same as those for the intermediate layer. Under an argon atmosphere, a liquid ether electrolyte solution of 1M LiTFSI-DME / DOL (1:1) + 1% LiNO3 was added to the gradient fiber membrane and allowed to stand for 12 hours to obtain a gradient fiber structure composite gel polymer electrolyte.

[0060] The above-mentioned embodiments of the present invention were assembled into CR2032 button batteries in an argon glove box and tested. 0.8 Co 0.1 Mn 0.1 Battery: LiNi 0.8 Co 0.1 Mn 0.1The positive electrode material is the active material, which is mixed with the conductive agent Super P and the binder polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1. N-methylpyrrolidone (NMP) is used as the solvent, and the mixture is placed in a weighing bottle and stirred for 12 hours to obtain a slurry. The slurry is coated on the current collector aluminum foil using an applicator, transferred to a vacuum drying oven at 120°C and dried for 12 hours. The sheet is punched into a 14mm diameter electrode and the electrode mass is accurately weighed. A button cell is assembled using a metal lithium sheet as the negative electrode and the gel polymer electrolyte of the above embodiment. The button cell is charged and discharged in the voltage range of 3.0-4.3V. Before the cycle test, it is first activated three times with a small current density of 40mA / g (0.2C), and then cycled at a 1C rate within the same voltage range. All electrochemical performance tests are carried out at room temperature. Lithium||lithium symmetric battery: A symmetric cell is assembled using metal lithium sheets as the positive and negative electrodes and the gel polymer electrolyte of the above embodiment. The lithium ion migration number of the lithium||lithium symmetrical battery was tested by constant potential polarization, and the initial impedance and stable impedance values were obtained by electrochemical impedance spectroscopy (EIS) test. The current time curve test time was 4000 seconds, and the external constant perturbation voltage ΔU was 10mV. Steel sheet||steel sheet symmetrical battery: stainless steel sheets were used as positive and negative electrodes, and the gel polymer electrolyte in the above embodiment was used to assemble a symmetrical battery for ion conductivity test. The conductivity value was obtained by gradient fiber membrane thickness / (stainless steel sheet cross-sectional area × battery internal resistance), where the battery internal resistance was obtained by EIS test. Lithium||steel sheet symmetrical battery: metal lithium sheet was used as negative electrode, stainless steel sheet was used as positive electrode, and the gel polymer electrolyte in the above embodiment was used to assemble the battery. Linear sweep voltammetry (LSV) was used to perform electrochemical window test on lithium||steel sheet battery. The scan rate was set to 1mV s -1 The test voltage range was set at 0-5.5 V. The safety of the gel polymer electrolyte was tested through an ignition test. The tensile strength of the gel polymer electrolyte membrane, cut into 5 cm x 1 cm strips, was tested through a stress test.

[0061] Table 1 Performance of lithium batteries prepared in Examples 1 to 6

[0062]

[0063]

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements 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.

[0065] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A method for preparing a gradient fiber structure composite gel polymer electrolyte for lithium batteries, characterized by: The method comprises the following steps: Step 1: dissolving an inorganic filler precursor and polyvinyl pyrrolidone or polyvinyl alcohol in a mixed solution of ethanol and acetic acid to prepare an intermediate layer spinning solution; Step 2: electrospinning the intermediate layer spinning solution. During the spinning process, the internal temperature of the machine body is 40°C, the internal humidity is 40%, the applied working voltage is 18kV, the propulsion pump propulsion rate is 0.8mL / h, and the receiving distance from the needle to the receiver is 18cm. The obtained spinning membrane is heat-treated to obtain an inorganic nanofiber membrane; Step 3: Select a polymer with high-voltage resistance and dissolve it in a mixed solution of N,N-dimethylformamide and acetone to prepare a positive electrode side spinning solution; in step 3, the polymer is one or more of polyacrylonitrile, polypropylene carbonate, polyethylene carbonate, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polychlorotrifluoroethylene, or poly(ethylene-co-hexafluoropropylene); Step 4: Select a polymer with excellent interfacial compatibility and dissolve it in a mixed solution of N,N-dimethylformamide and acetone to prepare a negative electrode side spinning solution; in step 4, the polymer includes one or more of polyoxyethylene, polyoxypropylene, polymethyl methacrylate, polybutadiene, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene glycol dimethyl ether or polyacrylate; Step 5: Electrospinning the positive electrode side spinning solution on one side of the inorganic nanofiber membrane and electrospinning the negative electrode side spinning solution on the other side of the inorganic nanofiber membrane to obtain a gradient fiber composite membrane; the specific parameters of the electrospinning on the positive electrode side and the negative electrode side are the same as those of the middle layer; Step 6: drying the obtained gradient fiber composite membrane to remove the solvent; Step 7: Add a certain amount of liquid electrolyte to the composite membrane and wait for it to swell to obtain a composite gel polymer electrolyte.

2. The method for preparing a gradient fiber structure composite gel polymer electrolyte for lithium batteries according to claim 1, characterized in that: In step 1, the inorganic filler precursor is one or more of tetraethyl orthosilicate, aluminum nitrate, zirconium n-butoxide, and titanium tetrachloride.

3. The method for preparing a gradient fiber structure composite gel polymer electrolyte for lithium batteries according to claim 1, characterized in that: In step 1, the mass ratio of the inorganic filler precursor: PVP: ethanol: acetic acid is 0.5-2: 0.1: 1: 0.02-0.

05.

4. The method for preparing a gradient fiber structure composite gel polymer electrolyte for lithium batteries according to claim 1, characterized in that: In step 2, the heat treatment temperature is 500-1200° C., and the time is 0.5-6 hours.

5. The method for preparing a gradient fiber structure composite gel polymer electrolyte for lithium batteries according to claim 1, characterized in that: In steps 3 and 4, the volume ratio of N,N-dimethylformamide to acetone is 3:1 to 7:1, and the mass concentration of the polymer raw material in the mixed solution is 0.03 g / ml to 0.4 g / ml.

6. The method for preparing a gradient fiber structure composite gel polymer electrolyte for lithium batteries according to claim 1, characterized in that: In step 6, the total thickness of the composite film is 1-250 μm; The thickness ratio of the positive electrode side: the intermediate layer: the negative electrode side is 1~3:1~5:1~3.

7. The method for preparing a gradient fiber structure composite gel polymer electrolyte for lithium batteries according to claim 1 or 6, characterized in that: In step six, the pore size of the micro-nano pore structure on the composite membrane is 20 nm to 5 μm.

8. The method for preparing a gradient fiber structure composite gel polymer electrolyte for lithium batteries according to claim 1, characterized in that: In step seven, the liquid electrolyte includes one of a liquid ether electrolyte and a liquid ester electrolyte.

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