阅读说明：本技术 用于金属二次电池的纤维素基复合隔膜及其制备方法 (Cellulose-based composite diaphragm for metal secondary battery and preparation method thereof ) 是由 朱玉松 傅梗桂 秦赛男 王雨琦 安莹 曾志连 于 2021-07-01 设计创作，主要内容包括：本发明属于高分子材料和电池领域,具体涉及用于金属二次电池的隔膜及其制备方法。此类隔膜涉及由静电纺丝法、热压法、辊压法、冷冻干燥法、原位聚合法、相转化法、流延法、膜支撑法等方法制得。涉及的高分子材料包括天然纤维素、纤维素改性物或纤维素衍生物的一种或多种,还包括聚腈、聚酯、聚醚、含氟聚烯烃、聚碳酸酯、聚胺、天然多糖及其衍生物的一种或多种与天然纤维素、纤维素改性物或纤维素衍生物一种或多种的共混或共聚物。制得的隔膜不仅具有优异的电化学性：高离子电导率、高离子迁移数、宽电化学窗口、出色的倍率性能和长循环稳定性等性能,而且还制作工艺简单,生产成本低,电池安全环保,易实现商业化。(The invention belongs to the field of high polymer materials and batteries, and particularly relates to a diaphragm for a metal secondary battery and a preparation method thereof. The diaphragm is prepared by electrostatic spinning, hot pressing, rolling, freeze drying, in-situ polymerization, phase inversion, casting, membrane supporting and other methods. The high molecular material comprises one or more of natural cellulose, cellulose modification substances or cellulose derivatives, and also comprises one or more of polynitrile, polyester, polyether, fluorine-containing polyolefin, polycarbonate, polyamine, natural polysaccharide and derivatives thereof, and one or more of natural cellulose, cellulose modification substances or cellulose derivatives. The prepared separator has excellent electrochemistry: high ionic conductivity, high ion migration number, wide electrochemical window, excellent rate performance, long cycle stability and other performances, simple manufacturing process, low production cost, safe and environment-friendly battery and easy realization of commercialization.)

1. A cellulose-based composite separator for a metal secondary battery, characterized in that: the polymer matrix high molecular material or the homopolymer, copolymer or blend of the high molecular material and the inorganic filler mixture is compounded by various preparation methods to prepare the polymer electrolyte diaphragm, and the diaphragm absorbs a certain electrolyte to obtain the gel polymer electrolyte or the solid polymer electrolyte which is applied to the metal secondary battery.

2. The cellulose-based composite separator for a metal secondary battery according to claim 1, wherein: the preparation method includes but is not limited to an electrostatic spinning method, a coaxial electrostatic spinning method, a multi-axis electrostatic spinning method, a hot pressing method, a rolling method, a freeze-drying method, an in-situ polymerization method, a phase inversion method, a casting method or a membrane supporting method.

3. The cellulose-based composite separator for a metal secondary battery according to claim 1, wherein: the polymer material comprises one or more of natural cellulose, cellulose modification substances or cellulose derivatives, and also comprises one or more of polynitrile, polyester, polyether, fluorine-containing polyolefin, polycarbonate, polyamine, natural polysaccharide and derivatives thereof, and one or more of natural cellulose, cellulose modification substances or cellulose derivatives; the inorganic filler includes, but is not limited to, inorganic fillers which are not intrinsically ion conductive, metal organic frameworks and clay minerals and inorganic fillers which are ion conductive; the metal secondary battery includes, but is not limited to, a zinc battery, a lithium battery, a sodium battery, a potassium battery, a magnesium battery, or an aluminum battery.

4. A method for preparing a separator for a metal secondary battery, characterized by the steps of:

(1) dissolving a high molecular material or a mixture of the high molecular material and an inorganic filler and the filler in a solvent to obtain a uniform solution;

(2) preparing the diaphragm by an electrostatic spinning method, a coaxial electrostatic spinning method, a multi-axis electrostatic spinning method, a hot pressing method, a rolling method, a freeze drying method, an in-situ polymerization method, a phase inversion method, a casting method or a membrane supporting method;

(3) placing the diaphragm obtained in the step (2) in a vacuum drying oven, drying at the temperature of 20-120 ℃, and removing trace solvent or water;

(4) and (3) soaking the dried membrane obtained in the step (3) in an electrolyte for 1 minute to 24 hours to obtain a polymer electrolyte, or directly using the solid electrolyte diaphragm in a metal secondary battery.

5. The method according to claim 4, wherein the solvent in step (1) is a non-toxic or low-toxic solvent capable of dissolving the polymer material, and includes but is not limited to one or more of ultrapure water, acetone, formic acid, acetic acid, N-dimethylformamide, N-dimethylacetamide, N-methylpyrrolidone, carbonate, and dimethylsulfoxide.

6. The method according to claim 4, wherein in step (2), all electrospun membranes are produced on an electrospinning machine at a voltage ranging from-500 KV to +500KV, freeze-dried membranes are produced by a freeze-dryer, and the roll-pressing method is carried out by a roll-pressing machine.

7. The method according to claim 4, wherein in the step (2), the thickness of the separator is 5 to 500 μm;

in the step (3), the diaphragms are all placed in a vacuum drying oven to be dried for more than 12 hours before being used; the anhydrous and oxygen-free environment in the step (4) refers to that the water oxygen content is less than 0.1ppm and the atmosphere is argon.

8. The method of claim 4, wherein the electrolyte of step (4) comprises an aqueous solution containing an electrolyteAnd an organic electrolyte solution prepared by dissolving an electrolyte salt in a carbonate or ether organic solvent, wherein the concentration of the electrolyte salt is 0.5mol L^-1-30mol L^-1In the meantime.

9. The method of claim 8, wherein said electrolyte salt solution of step (4) is formed from electrolyte salts including but not limited to LiCl, LiNO, and mixtures thereof₃、Li₂SO₄、LiAc、LiClO₄、LiTFSI、AlCl₃、Al(NO₃)₃、Al₂(SO₄)₃、Al(Ac)₃、ZnSO₄、ZnCl₂、Zn(NO₃)₂、Zn(Ac)₂Dissolved in deionized water to form a solution with the concentration of 0.5mol L^-1-30mol L^-1In the meantime.

10. The method of claim 8, wherein said organic electrolyte of step (4) is formed from a metal salt including but not limited to LiClO₄、LiBF₄、LiAsF₆、LiPF₆、LiTFSI、LiFSI、LiBOB、LiODFB、LiTDI、NaClO₄、NaBF₄、NaAsF₆、NaPF₆、NaTFSI、NaFSI、NaBOB、NaODFB、NaTDI、KClO₄、KBF₄、KAsF₆、KPF₆KTFSI, KFSI, KBOB, KODFB, KTDI dissolved in a carbonate or ether solvent at a concentration of 0.5mol L^-1-30mol L^-1In the meantime.

Technical Field

The invention belongs to the technical field of electrochemistry, and particularly relates to a diaphragm for a metal (lithium, sodium, zinc, potassium, magnesium aluminum and other metals) secondary battery and a preparation method thereof, and also relates to application of a solid electrolyte.

Background

The lithium ion battery has the characteristics of high energy density and output voltage, long cycle life, environmental friendliness, no memory effect and the like, and becomes an ideal choice for future energy storage systems. Besides having considerable application prospect in energy storage, the lithium ion battery occupies an absolute leading position in the field of portable electronic products, and mobile phones, notebook computers, intelligent robots and unmanned planes can not be supported by the lithium ion battery. This is because lithium ion batteries have relatively high energy density and power density, long service life, low self-discharge, and no memory effect, compared to other secondary batteries. At present, the theoretical capacity density of commercial lithium ion batteries is only 372mAh g due to the use of graphite as a negative electrode^-1Theoretical energy density is only 390Wh kg^-1. The ceiling with energy density limits the endurance time of electronic products, energy storage systems and electric automobiles, the development of lithium ion batteries is hindered, and the development of a cathode material with higher specific capacity is one of important measures for solving the endurance problem of the lithium ion batteries. According to theoretical calculation, the capacity of the current commercial battery is improved by more than 50 percent by replacing the prior carbon material negative electrode with zinc or alkali metal without changing the prior positive electrode material. The metal cathode has the advantages that the metal cathode can provide a metal source required by the ion battery, so that the cathode material has more choices, and the use of metal-free materials such as sulfur, oxygen, carbon dioxide and the like with higher specific capacity as the cathode is possible.

Conventional metal secondary batteries use a non-aqueous electrolyte and contain a large amount of flammable organic carbonate solvent, thereby possibly causing a risk of electrolyte leakage, causing thermal runaway or a fire hazard. While the metallic negative electrode in contact with the liquid electrolyte grows uncontrollably during cycling and penetrates the separator, causing short-circuiting and even explosion of the battery. Irregular electrodeposition of the metal negative electrode causes the SEI film to be broken and form 'dead lithium'/'dead zinc' and the like, and also causes the coulombic efficiency of the battery to be reduced and the service life of the battery to be shortened. Which limits their use in metal secondary batteries. And the metal has high activity, and is easy to generate side reaction, metal corrosion and the like with the electrolyte. These two problems are present in both metal organic batteries and metal aqueous batteries, and are the main culminations of the commercialization of metal secondary batteries.

Disclosure of Invention

The present invention is directed to a separator for a metal secondary battery, which is manufactured by using a hot press method, a roll pressing method, a phase inversion method, an in-situ polymerization method, a casting method, a freeze-drying method, a film support method, an electrostatic spinning method, and the like. The prepared separator has excellent electrochemistry: high ionic conductivity, high ion migration number, wide electrochemical window, excellent rate performance, long cycle stability and other performances, simple manufacturing process, low production cost, safe and environment-friendly battery and easy realization of commercialization.

The invention also aims to provide a protective effect of the prepared diaphragm on a metal negative electrode, strong adhesion with an electrode material of an electrochemical energy storage system, and effective function of inhibiting dendritic crystal production and application thereof in a metal secondary battery.

In order to achieve the purpose, the invention provides the following technical scheme: a cellulose-based composite separator for a metal secondary battery, characterized in that: the polymer matrix high molecular material or the homopolymer, copolymer or blend of the high molecular material and the inorganic filler mixture is compounded by various preparation methods to prepare the polymer electrolyte diaphragm, and the diaphragm absorbs a certain electrolyte to obtain the gel polymer electrolyte or the solid polymer electrolyte which is applied to the metal secondary battery.

The preparation method includes but is not limited to an electrostatic spinning method, a coaxial electrostatic spinning method, a multi-axis electrostatic spinning method, a hot pressing method, a rolling method, a freeze-drying method, an in-situ polymerization method, a phase inversion method, a casting method or a membrane supporting method.

The polymer material comprises one or more of natural cellulose, cellulose modification substances or cellulose derivatives, and also comprises one or more of polynitrile, polyester, polyether, fluorine-containing polyolefin, polycarbonate, polyamine, natural polysaccharide and derivatives thereof, and one or more of natural cellulose, cellulose modification substances or cellulose derivatives; the inorganic filler includes, but is not limited to, inorganic fillers which are not intrinsically ion conductive, metal organic frameworks and clay minerals and inorganic fillers which are ion conductive; the metal secondary battery includes, but is not limited to, a zinc battery, a lithium battery, a sodium battery, a potassium battery, a magnesium battery, or an aluminum battery.

A method for preparing a separator for a metal secondary battery, characterized by the steps of:

(1) dissolving a high molecular material or a mixture of the high molecular material and an inorganic filler and the filler in a solvent to obtain a uniform solution;

(2) preparing the diaphragm by an electrostatic spinning method, a coaxial electrostatic spinning method, a multi-axis electrostatic spinning method, a hot pressing method, a rolling method, a freeze drying method, an in-situ polymerization method, a phase inversion method, a casting method or a membrane supporting method;

(3) placing the diaphragm obtained in the step (2) in a vacuum drying oven, drying at the temperature of 20-120 ℃, and removing trace solvent or water;

(4) and (3) soaking the dried membrane obtained in the step (3) in an electrolyte for 1 minute to 24 hours to obtain a polymer electrolyte, or directly using the solid electrolyte diaphragm in a metal secondary battery.

The solvent in the step (1) is a nontoxic or low-toxic solvent capable of dissolving the polymer material, and includes but is not limited to one or more of ultrapure water, acetone, formic acid, acetic acid, N-dimethylformamide, N-dimethylacetamide, N-methylpyrrolidone, carbonate and dimethyl sulfoxide.

In the step (2), all the electrospinning films are prepared on an electrospinning machine, the voltage range is-500 KV to +500KV, the freeze-dried films are prepared by using a freeze dryer, and the rolling method is prepared by using a rolling machine.

In the step (2), the thickness of the diaphragm is 5-500 μm;

in the step (3), the diaphragms are all placed in a vacuum drying oven to be dried for more than 12 hours before being used; the anhydrous and oxygen-free environment in the step (4) refers to that the water oxygen content is less than 0.1ppm and the atmosphere is argon.

The electrolyte in the step (4) is an organic electrolyte formed by dissolving an aqueous solution containing electrolyte and electrolyte salt in a carbonate or ether organic solvent, and the concentration of the organic electrolyte is 0.5mol L^-1-30mol L^-1In the meantime.

The electrolyte salt solution in the step (4) is prepared from electrolyte salts including but not limited to LiCl and LiNO₃、Li₂SO₄、LiAc、LiClO₄、LiTFSI、AlCl₃、Al(NO₃)₃、Al₂(SO₄)₃、Al(Ac)₃、ZnSO₄、ZnCl₂、Zn(NO₃)₂、Zn(Ac)₂Dissolved in deionized water to form a solution with the concentration of 0.5mol L^-1-30mol L^-1In the meantime.

The organic electrolyte in the step (4) is composed of metal salt including but not limited to LiClO₄、LiBF₄、LiAsF₆、LiPF₆、LiTFSI、LiFSI、LiBOB、LiODFB、LiTDI、NaClO₄、NaBF₄、NaAsF₆、NaPF₆、NaTFSI、NaFSI、NaBOB、NaODFB、NaTDI、KClO₄、KBF₄、KAsF₆、KPF₆KTFSI, KFSI, KBOB, KODFB, KTDI dissolved in a carbonate or ether solvent at a concentration of 0.5mol L^-1-30mol L^-1In the meantime.

The gel polymer electrolyte diaphragm and the solid electrolyte diaphragm prepared by the invention not only well solve the safety problems of electrolyte leakage, flammability and explosiveness of commercial batteries, but also have high ionic conductivity, wide electrochemical window, excellent cycle performance and rate capability and well inhibit the growth of dendrite, and can be used for metal secondary batteries with large capacity, high power and high energy density. In addition, the manufacturing cost of the electrolyte diaphragm is low, and most of the selected high polymer materials are environment-friendly, degradable and renewable environment-friendly materials.

Drawings

FIG. 1a is a scanning electron microscope image of the surface of the CA/PVDF electrospun membrane obtained in example 1 of the invention at a scale bar of 20 μm; FIG. 1b is a scanning electron microscope image of the surface of the CA/PVDF electrospun membrane obtained in example 1 of the invention at a scale bar of 5 μm; FIG. 1c is a scanning electron micrograph of a cross-section of a CA/PVDF electrospun membrane obtained in example 1 of the present invention; FIG. 1d is a surface scanning electron micrograph of Celgard 2400 of comparative example 1 of the present invention.

FIG. 2 is a graph comparing the tensile force-stress curves of the CA/PVDF electrospun membrane obtained in example 1 of the invention and the Celgard 2400 membrane used in comparative example 1.

FIG. 3 is a graph showing thermal shrinkage tests of a CA/PVDF electrospun membrane obtained in example 1 of the present invention and a Celgard 2400 membrane used in comparative example 1, which are photographs showing three-dimensional changes in a two-hour heat-retention at 25 deg.C (a), 150 deg.C (b), and 180 deg.C (c), respectively.

FIG. 4 CA/PVDF-GPE obtained in example 1 of the invention and 1mol L used in comparative example 1^-1LiPF₆Ionic conductivity at different temperatures of electrolyte saturated Celgard 2400 separator is compared to arrhenius equation curves.

FIG. 5 CA/PVDF-GPE obtained in example 1 of the invention and 1mol L used in comparative example 1^-1LiPF₆Comparative graph of lithium ion transport number test of Celgard 2400 diaphragm saturated with electrolyte.

FIG. 6 CA/PVDF-GPE obtained in example 1 of the invention and 1mol L used in comparative example 1^-1LiPF₆Comparative plot of electrochemical window test for electrolyte saturation of Celgard 2400.

FIG. 7Li | CA/PVDF-GPE | Li and Li | Celgard 2400-liquid electrolyte | Li symmetric cell electrochemical performance. (a) Two symmetric cell lithium ion deposition/dissolution voltage curves; detail drawings for 10-20 h; detail diagrams of 320-330 h; (b) SEM image of fresh lithium electrode surface; (c) SEM images of lithium electrode surfaces after 300 hour cycling for Li | Celgard 2400-liquid electrolyte | Li battery and (d) Li | CA/PVDF-GPE | Li battery.

FIGS. 8a and 8b CA/PVDF-GPE obtained in example 1 of the invention and 1mol L used in comparative example 1^-1LiPF₆Electrolyte saturated Celgard 2400Comparative plots of charge and discharge curves for (a)1C and (a)5C at different current densities by LiFePO 4/gel film or separator/Li battery systems.

FIG. 9 CA/PVDF-GPE obtained in example 1 of the invention and 1mol L used in comparative example 1^-1LiPF₆Rate performance comparison plots for electrolyte saturated Celgard 2400 evaluated by LiFePO 4/gel film or separator/Li battery systems.

Detailed Description

The invention is further described below with reference to the accompanying drawings.

Example 1

(1) Cellulose Acetate (CA) and PVDF were dissolved in a 2:1 mass ratio in a mixed solvent of acetone and DMAc at room temperature to form a solution with a total polymer concentration of 10 wt%, and magnetically stirred overnight to form a homogeneous clear solution.

(2) And (3) electrospinning the CA-PVDF blended solution by using an electrostatic spinning machine, and covering an aluminum foil on a rotary drum collector to conveniently take down the electrostatic spinning film. Applying 50kV high voltage between a spinning nozzle and a current collector, wherein the liquid inlet speed of a needle is 1mL h^-1. In addition, the range of the syringe, the translation distance of the needle, the receiving distance, the working temperature and the relative humidity conditions of the electrospinning process were 5mL, ± 2cm, 20cm, 25 ℃ and 60%, respectively.

(3) And (3) drying the electro-spinning aluminum foil for 12 hours in a vacuum drying oven at 80 ℃ to evaporate the solvent, and finally completely removing the electro-spinning aluminum foil to obtain the CA-PVDF electro-spinning composite membrane with the thickness of 45 microns.

(4) The dried electrospun membrane was cut to an appropriate size and transferred into a glove box. The membrane was immersed in 1.0mol l^{- 1}LiPF₆And (3) obtaining CA/PVDF 2 after 8 hours in the electrolyte: 1 gel electrolyte.

Example 2

(1) Cellulose Acetate (CA) and PVDF were dissolved in a mixed solvent of acetone and DMAc at 5:1 mass ratio at room temperature to form a solution with a total polymer concentration of 20 wt%, and magnetically stirred overnight to form a homogeneous clear solution.

(2) Electrospinning the CA-PVDF blended solution by an electrostatic spinning machine, and covering an aluminum foil on a rotary drum collectorSo as to conveniently take down the electrostatic spinning membrane. Applying 100kV high voltage between the spinning nozzle and the current collector, and setting the liquid inlet speed of the needle at 5mL h^-1. In addition, the range of the syringe, the translation distance of the needle, the receiving distance, the working temperature and the relative humidity conditions of the electrospinning process were 5mL, ± 2cm, 20cm, 25 ℃ and 60%, respectively.

(3) And (3) drying the electro-spinning aluminum foil in a vacuum drying oven at 80 ℃ for 12 hours to evaporate the solvent, and finally completely removing the electro-spinning aluminum foil from the aluminum foil to obtain the CA-PVDF electro-spinning composite membrane with the thickness of 24 microns.

(4) The dried electrospun membrane was cut to an appropriate size and transferred into a glove box. The membrane was immersed in 1.0mol l^{- 1}LiPF₆And (3) obtaining CA/PVDF 5 after 8 hours in the electrolyte: 1 glue electrolyte.

Example 3

(1) CA is dissolved in a mixed solvent of DMAc and acetone to 30 wt%, PVDF is dissolved in DMF to 30 wt%, and the mixture is magnetically stirred overnight to form a uniform clear solution.

(2) The spinning was carried out in an electrospinning machine using coaxial needles, the CA solution and the PVDF solution were fed through concentrically arranged needles having an outer diameter and an inner diameter of 1.01 and 0.41mm, respectively, to feed the inner tube to eject the PVDF filaments, and the outer tube to eject the CA filaments. Applying 30KV high pressure between the spinning nozzle and the collector, and fixing the liquid inlet speed of the needle at 1.5mL h^-1And carrying out coaxial electrospinning. In addition, the range of the syringe, the translation distance of the needle, the receiving distance, the working temperature and the relative humidity of the electrospinning process were 5mL, ± 1.5cm, 20cm, 30 ℃ and 50%, respectively.

(3) And (3) drying the electro-spinning aluminum foil in a vacuum drying oven at 80 ℃ for 12 hours to evaporate the solvent, and finally completely removing the electro-spinning aluminum foil from the aluminum foil to obtain the CA-PVDF coaxial electro-spinning composite membrane with the thickness of 120 mu m.

(4) Drying the obtained electro-spinning aluminum foil for 12 hours in a vacuum drying oven at 80 ℃ after electro-spinning is finished to evaporate the solvent, finally completely uncovering the aluminum foil to obtain a CA/PVDF coaxial electro-spinning membrane, soaking the CA/PVDF coaxial electro-spinning membrane in 5M NaOH ethanol solution for hydrolysis to obtain a Hy-CA/PVDF membrane, repeatedly rinsing the Hy-CA/PVDF membrane in deionized water for 3 times, and placing the Hy-CA/PVDF membrane in the vacuum drying oven at 60 ℃ for drying for 12 hours.

(5) Cutting Hy-CA/PVDF composite membrane into appropriate size, soaking in 1mol L^-1ZnSO₄Obtaining the Hy-CA/PVDF gel electrolyte membrane after 8 hours in the aqueous solution, and applying the Hy-CA/PVDF gel electrolyte membrane to a zinc metal secondary battery.

Comparative example 1

After cutting a commercial septum (Celgard 2400, PP) to a suitable size, it was placed in a vacuum oven at 80 ℃ for vacuum drying for 24 hours and vacuum cooled to room temperature and transferred into a glove box. Before electrochemical tests were carried out, Celgard 2400 membranes were soaked in 1mol l^-1LiPF₆And (4) the electrolyte is immersed for 8 hours.

The CA/PVDF composite membrane obtained by the method of example 1 and the Celgard 2400 diaphragm in the comparative example are subjected to physical characterization such as: scanning electron microscope SEM, thermogravimetric analysis, thermal difference analysis, liquid absorption rate, porosity and mechanical property; for gel polymer electrolyte and 1mol^-1The Celgard 2400 diaphragm saturated with LiPF6 electrolyte was subjected to TG, ionic conductivity at different temperatures, ionic transport number, charge-discharge cycle and rate performance tests. The test results are shown in the figure.

Porosity (Porosity) refers to the percentage of the internal pore volume of a separator as a function of its total volume. After soaking the weighed dry electrospun membrane or commercial separator in n-butanol (ethanol is used for aqueous zinc electrolyte) for 12 hours, the mass was measured again after wiping excess liquid on the surface with filter paper. The porosity (P) can be calculated by the formula (1):

P＝(W_t–W₀)/ρV×100％ (1)

wherein, W₀And W_tThe quality of the electrostatic spinning film or the commercial diaphragm before and after soaking in n-butyl alcohol (or ethanol) for saturation. ρ is the density of n-butanol (or ethanol), V is the volume of the dried electrospun membrane or commercial separator (V ═ Sd, S is the bottom area of the membrane, d is the thickness of the membrane). The porosity of the CA/PVDF electrospun membrane obtained by the method of example 1 is 76.9%, and the porosity of the Celgard 2400 membrane in comparative example 1 is 45.2%

Liquid uptake (Liquid uptake) refers to the ratio of the mass of the separator after the entire gelling process (i.e. absorption of electrolyte) to the mass of the dried electrospun film or commercial separator. The liquid absorption rate (. eta.) is calculated by the formula (2):

η＝(W_t–W₀)/W₀×100％ (2)

wherein, W₀And W_tRespectively representing the mass of the dry film and the mass of the electrolyte after being fully absorbed. The liquid absorption rate of the CA/PVDF electrospun membrane obtained by the method of example 1 is 97.1 percent, and the liquid absorption rate of the Celgard 2400 diaphragm in the comparative example 1 is 78.1 percent

The ionic conductivity was calculated from equation (3):

σ＝l/(R_bA) (3)

wherein σ is the ionic conductivity in S cm^-1；R_bIs the bulk resistance, in units of Ω; l is the thickness of the film in cm; a is the contact area of the stainless steel electrode and the membrane, and the unit is cm². The conductivity at room temperature of the CA/PVDF gel film obtained by the method of example 1 reaches 1.82mS cm^-1Comparative example 1mol L^-1LiPF₆The room temperature conductivity of the electrolyte-saturated Celgard 2400 separator was 0.61mS cm^-1。

The ion transport number (t) is calculated from equation (4):

wherein, I₀For timing the initial current in the current curve, I_SThe unit is mA for the steady-state current in the timing current curve; Δ V is the step potential in mV; r₀And R_SThe unit is omega, and the AC impedance of the battery before and after polarization is respectively. The room temperature lithium ion transference number of the CA/PVDF gel membrane obtained by the method of example 1 is 0.506, 1mol L^-1LiPF₆The room temperature lithium ion transport number of the electrolyte saturated Celgard 2400 separator was 0.336.

From the comparison of the comparative example and the example, the gel polymer electrolyte of the lithium metal secondary battery based on the cellulose and PVDF materials has the characteristics of high safety, high electrochemical performance and low production cost, and can meet the requirements of the lithium metal secondary battery with high power, high efficiency and high energy density. The invention provides a novel strategy for preparing the gel electrolyte of the lithium metal secondary battery with high thermal stability, good electrochemical performance, long cycle life and low cost by the electrostatic spinning technology.