WO2016095771A1

WO2016095771A1 - Composite nanofiber separator with thermal shutdown function, preparation method therefor and energy storage components

Info

Publication number: WO2016095771A1
Application number: PCT/CN2015/097248
Authority: WO
Inventors: 宣萱; 解明
Original assignee: 宁波艾特米克锂电科技有限公司
Priority date: 2014-12-19
Filing date: 2015-12-14
Publication date: 2016-06-23
Also published as: CN104485437A; CN104485437B

Abstract

The present invention provides a composite nanofiber separator with a thermal shutdown function, a preparation method therefor and energy storage components, and relates to lithium-ion batteries, lithium-sulphur batteries, supercapacitors, lead-acid batteries, alkaline batteries, zinc-air batteries, sodium-ion batteries and fiber separators thereof. The composite nanofiber separator with a thermal shutdown function is of a non-woven fabric structure and is formed by cross-linking a fibrillated cellulose nanofiber and at least one low-melting-point polymer nanofiber, the low-melting-point polymer nanofiber being a polyolefin- and polyester-containing nanofiber. The thickness of the composite nanofiber separator with a thermal shutdown function may range from 10 μm to 80 μm, and the shutdown temperature ranges from 130°C to 170°C. The nanofiber separator does not shrink after shutdown, and the heat shrinkage rate is less than 2％ after heating at 200°C for 30 min. The composite nanofiber separator can achieve a thermal shutdown function, thereby preventing the direct contact between the positive and negative electrodes of a battery due to thermal inertia and significantly improving the safety of the aforementioned energy storage components.

Description

Composite nanofiber membrane with heat closed pore function, preparation method and energy storage device

Technical field

The invention belongs to the technical field of batteries, and the battery comprises a lithium ion battery, a lithium sulfur battery, a super capacitor, a lead acid battery, an alkaline battery, a zinc air battery and a sodium ion battery. The invention relates to a composite nanofiber membrane with closed pore function and a preparation method thereof. The invention also relates to the production of such membranes and the use of such membranes as battery separators.

Background technique

The composite nanofiber membrane can be used as a separator for batteries such as lithium ion batteries, lithium sulfur batteries, super capacitors, lead acid batteries, zinc air batteries, and sodium ion batteries. At present, lithium-ion batteries have been widely used in portable electronic products such as mobile phones, notebook computers, and cameras because of their high energy density, long cycle life, fast charge and discharge, no pollution, and no memory effect. The required rechargeable batteries are also gradually expanding into electric vehicles, aerospace, energy storage and other fields.

Battery separator is a key component related to battery safety performance. Its main function is to isolate the positive and negative electrodes and prevent electrons from passing freely. At the same time, the ions can pass freely. The performance determines the interface structure and internal resistance of the battery. The overall performance of the lithium battery. In the case where the lithium battery is isolated from the positive and negative poles, battery overcharging or short circuit occurs, or incorrect connection occurs, abnormal current is generated, and when the power is large and the capacity is high, the temperature inside the battery is sharply increased, and the battery separator should be There is sufficient temperature resistance; due to the increase of battery temperature, the diaphragm aperture is reduced, lithium ions can not pass normally, resulting in the battery temperature rising, reaching the melting point of lithium or the ignition point of the electrolyte, which will cause the burning and explosion of the battery. occur.

Lithium battery safety is a very urgent problem, especially power lithium-ion batteries, which have entered many fields such as automobiles, robots, power tools, aerospace, etc. Power lithium batteries are more likely to be exposed to high temperatures due to large current consumption. High, its security has received much attention. So the diaphragm The full performance should mention a higher level (when the battery temperature is too high, the diaphragm can block the conduction of current through the closed hole, prevent explosion, and the diaphragm size is stable after the closed hole does not shrink).

At present, the mainstream products of lithium ion battery separators are polypropylene and polyethylene porous membranes and composite membranes thereof with porous ceramic coatings. The outstanding problems are poor wettability, weak liquid absorption ability, difficulty in achieving high rate charge and discharge, easy formation of dendrites under high temperature cycling conditions, and large deformation due to heat, and there are serious safety hazards.

In order to improve the heat resistance of the separator, the researchers mainly adopt the following methods: First, the heat resistance of the nanofiber membrane is improved by in situ formation or addition of nanoparticles by sol-gel or coating of a solution containing nanoparticles. Such as CN200810244343.7, CN201110434221.6, these methods are complicated in preparation process, generally require coating process, hot pressing treatment or extraction process, and the membrane shrinks with closed volume, the membrane area shrinks, and the diaphragm loses positive and negative electrodes. Inter-segmentation, causing unsafe hidden dangers; second, electrospinning using a highly heat-resistant polymer solution, such as CN201210486465.3, CN201210425855.X, CN201010166400.1, and CN201210169182.6, the fiber membrane function prepared by the method It is single and the preparation process is cumbersome and costly. Third, the use of non-woven membranes of nanofiber materials in the field of lithium ion battery separators is one of the important topics in the development of high-end lithium-ion battery separators. The nano-based battery separator can significantly improve the wettability of the separator material and effectively improve the heat resistance and ion conductivity of the separator. The patent of CN103688387A of Dreamweave Company of the United States discloses a microporous polymer battery separator, which combines polymer nanometers into a matrix of polymer microfibers by high shear treatment to form a nanofiber web with good pore size effect, in heat resistance, Dimensional stability and good liquid absorption, wettability, etc. Similarly, there are patents CN103270639 A, CN103943806 A, etc., but still can not meet the excellent thermal dimensional stability and good self-closing performance of the diaphragm material, which may cause potential damage to the battery such as burning and explosion.

Summary of the invention

The technical problem to be solved by the present invention is to provide a manufacturing process that is simple, A composite nanofiber separator with low cost and excellent performance and a preparation method thereof.

In order to solve the above technical problems, the present invention firstly provides a nanofiber separator having a heat sealing function, the raw material of which comprises fibrillated cellulose nanofibers and low melting point polymer nanofibers, between the fibrillated cellulose nanofibers The fibrillated cellulose nanofibers and the low melting point polymer nanofibers are combined by long-chain molecular cross-linking mainly by hydrogen bonding and intermolecular force; the composite nanofiber membrane has The pores allow electrolyte ions to pass through and prevent electrons from passing through; in a temperature environment of 130 to 170 ° C, the composite nanofiber membrane pores are closed to prevent excessive and undesired ions from passing through the battery after damage.

When the composite nanofiber membrane has a closed pore state, the composite nanofiber membrane has a stable size, and is heated within a temperature of 200 ° C for 30 minutes, and the heat shrinkage rate is less than 2%.

The composite nanofiber membrane having a closed cell function has a thickness of 10 to 80 μm.

The invention discloses a method for preparing a composite nanofiber membrane having a closed cell function, which is prepared by using a fibrillated cellulose nanofiber and a low melting point polymer nanofiber with a mass ratio of 1:9 to 9:1 as a raw material.

The preparation method of the composite nanofiber membrane having the closed cell function comprises the following specific steps:

I. The fibrillated cellulose nanofibers and the at least one low-melting polymer nanofibers are respectively dispersed in a solvent at a mass ratio of 1:9 to 9:1, and rapidly stirred to form a slurry;

II. Adding a binder to the slurry of step I; adding a binder can increase the mechanical strength thereof, and the binder can be selected in a wide range, such as polyethylene glycol, polyvinyl alcohol, butadiene and styrene. Polymer, acrylonitrile polymer, polyvinylidene fluoride and epoxy resin.

III, the slurry after step II is diluted to a concentration of 0.01% to 0.05%;

IV. The diluted slurry is subjected to dehydration molding, pressing, drying and hot rolling forming on the Internet to obtain the composite nanofiber separator having a closed cell function.

Preferably, the fibrillated cellulose nanofibers have a diameter of 10 to 1000 nm and a length of 10 to 3000 μm.

The fibrillated cellulose nanofibers include cellulose nanofibers separated from nanosized wood materials, seaweed cellulose nanofibers, and bacterial cellulose nanofibers obtained by culturing strains.

Preferably, the low melting point polymer nanofibers have a diameter of 10 to 1000 nm.

The low melting point polymer nanofibers are polymethyl methacrylate, vinylidene fluoride polymer, polyurethane, polyvinyl chloride, polyolefin, polyethylene-vinyl acetate copolymer, polybutylene succinate One or more combinations of esters.

The solvent is a low molecular weight alcohol, deionized water, or a mixture of a low molecular weight alcohol and deionized water.

Another aspect of the present invention is to provide an energy storage device prepared by using the composite nanofiber membrane having the closed cell function, including a lithium ion battery, a lithium sulfur battery, an alkaline battery, a super capacitor, a lead acid battery, and zinc air. Battery, sodium ion battery.

The preparation method of the invention has low cost, simple production process, convenient transfer and is suitable for large-scale production.

The closed-cell functional composite nanofiber membrane prepared by the invention exhibits excellent physical properties including: closed cell, heat resistance, dimensional stability, gas permeability, good wettability with respect to electrolyte and high liquid absorption Rate and other characteristics. The closed cell temperature is 130-170 ° C. After the closed cell, the fiber membrane does not shrink, and the heat shrinkage rate is less than 2% when heated at 200 ° C for 30 min.

DRAWINGS

Figure 1 is a SEM photograph of a polyolefin-based separator of a comparative example;

2 is a SEM photograph of the closed-cell functional composite nanofiber membrane of Example 5;

3 is a SEM photograph of the closed-cell functional composite nanofiber membrane of Example 5 after heat treatment at 200 ° C for 2 hours;

4 is a photograph of the heat shrinkability of the comparative example and the closed-cell functional composite nanofiber membrane of Example 3 at 150 ° C and 200 ° C;

5 is a comparative example and the closed-cell functional composite nanofiber membrane electrolyte infiltration of the comparative example 3 sheet.

detailed description

The present invention is further described in detail with reference to the accompanying drawings, but the invention is not limited to the embodiments discussed below, and may be implemented in various forms. The following examples are intended to illustrate and practice the invention by those skilled in the art.

Preparation of a closed cell functional composite nanofiber membrane using fibrillated cellulose nanofibers and low melting polymer nanofibers in accordance with an embodiment of the present invention.

The separator is prepared using a fibrillated fibrillated cellulose nanofiber and a low melting polymer nanofiber slurry. Here, the fibrillated cellulose nanofibers may have a diameter of 10 to 1000 nm.

When the diameter of the fibrillated cellulose nanofibers is less than 10 nm, it is very difficult to form fibrillated cellulose nanofibers, but when the diameter of the fibrillated cellulose nanofibers exceeds 1000 nm, the separator has a rough surface, which makes the electrodes Not in good contact with the diaphragm.

Also, when the diameter of the fibrillated cellulose nanofibers exceeds 200 nm, pores are not uniformly formed. Therefore, the value diameter of the fibrillated cellulose nanofibers is more preferably between 10 and 200 nm.

The separator is prepared using a fibrillated fibrillated cellulose nanofiber and a low melting polymer nanofiber slurry. Here, the low melting point polymer nanofibers may have a diameter of 10 to 1000 nm.

The fibrillated cellulose nanofibers may be selected from the group consisting of fibrillated cellulose nanofibers separated from nanosized wood materials, algae fibrillated cellulose nanofibers, and bacterial fibrillated cellulose nanometers obtained by culturing strains. At least one of the fibers.

The type of the low-melting polymer nanofiber can be used all without limitation, as long as it is a nanofiber having a low melting point, and includes a slurry in which the low-melting polymer nanofiber in the slurry can be uniformly mixed with the fibril The cellulose nanofibers are mixed and are not soluble during the preparation of the slurry.

The low melting point polymer nanofiber is selected from the group consisting of: low melting point polymer nanofibers, polymethyl methacrylate, vinylidene fluoride polymer, polyurethane, polyvinyl chloride, polyolefin, polyethylene-vinyl acetate copolymer One or more combinations of polyethylene succinate.

A solvent in which fibrillated cellulose nanofibers and low melting point polymer nanofibers are stably dispersed can be used as a solvent. For example, deionized water, a low molecular weight alcohol, and a mixture of a low molecular weight alcohol and deionized water can be selected as the solvent.

Compared with the fibrillated cellulose nanofibers in the preparation method, when the mixing ratio of the fibrillated cellulose nanofibers and the low melting point polymer nanofibers is less than 1:9, the separator does not reach the closed pores due to heat. On the other hand, when the mixing ratio of the fibrillated cellulose nanofibers to the low melting point polymer nanofibers exceeds 9:1, the heat resistance and dimensional stability of the separator are seriously affected and it is difficult to transfer.

A solution containing fibrillated cellulose nanofibers and low-melting polymer nanofibers was prepared by high-speed stirring, and the slurry was subjected to a papermaking method to prepare a separator of the present invention.

In this case, according to an embodiment of the present invention, a method of preparing a separator, for example, a conventional method of preparing paper, is used to prepare a fibrillated cellulose nanofiber into a nonwoven fabric. However, all methods of preparing the separator can be used to prepare a separator for a lithium ion battery.

The thickness of the separator can be in the range of approximately 10-80 μm. When the thickness of the separator exceeds 80 μm, the charge and discharge efficiency of the battery will be seriously affected. When the thickness of the separator is less than 10 μm, the self-discharge and short-circuit rate of the battery are greatly improved.

The advantage of fibrillated cellulose nanofibers is that when a binder is used in the preparation of the separator, the -OH group present in the functional group is reduced, which is due to an increase in hydrogen bonding, when fibrillated cellulose nanofibers When used for a lithium secondary battery separator, the reaction between Li ions and -OH groups in the fibrillated cellulose nanofibers does not occur anymore, which leads to an increase in stability.

Because the end of the binder has an -OH group. Therefore, the binder can be uniformly mixed with the fibrillated cellulose nanofibers.

Those skilled in the art can understand that the energy storage device prepared by using the above composite nanofiber membrane with closed cell function includes lithium ion battery, lithium sulfur battery, alkaline battery, super capacitor, lead acid battery, zinc air battery, sodium ion. The battery must effectively improve the safety and reliability of the energy storage device.

Example 1

Cellulose nanofibers and low melting point polymer nanofibers (polymethyl methacrylate and polysuccinic acid) separated from nanosized wood materials by fibrillated cellulose nanofibers: low melting polymer nanofibers = 9:1 The glycol ester) is dispersed in a solvent, and then the slurry is uniformly homogenized by high-speed mechanical stirring to prepare a slurry. The solvent is diluted to 0.01% by adding a solvent, and the diluted slurry is dehydrated by the net; pressed and dried; hot-rolled at a molding temperature of 100 ° C and a line pressure of 100 kg/cm, and then rolled, Rewinding, slitting and packaging to produce a battery separator.

The above closed-cell composite separator exhibits excellent characteristics, for example, a porosity of 56% and 55% before and after heat treatment at 200 ° C for 2 hours, a heat shrinkage rate of almost 0 at 30 ° C for 30 minutes, and an absorbance of 31% at 200 ° C; The Gutley value (s/100 cc) before and after the 2 h heat treatment was 23 and 23.

Example 2

Dispersing fibrillated cellulose nanofibers: low melting point polymer nanofibers = 7:3 algae cellulose nanofibers and low melting polymer nanofibers (vinylidene fluoride polymer) in a solvent, and then passing high speed machinery The slurry was prepared by stirring to bring the solution to an overall uniformity. The solvent is diluted to 0.01% by adding a solvent, and the diluted slurry is dehydrated by the net; pressed and dried; hot-rolled at a molding temperature of 100 ° C and a line pressure of 100 kg/cm, and then rolled, Rewinding, slitting and packaging to produce a battery separator.

The above closed-cell composite separator exhibits excellent characteristics, for example, a porosity of 56% and 30% before and after heat treatment at 200 ° C for 2 hours, and a heat shrinkage rate of almost 1% at 200 ° C for 30 minutes; The Gutley value (s/100 cc) before and after heat treatment at 200 ° C for 2 h was 23 and 800.

Example 3

Dispersing bacterial cellulose nanofibers and low melting polymer nanofibers (polyurethane, polyvinyl chloride and polyolefin) obtained by culturing strains of fibrillated cellulose nanofibers: low melting polymer nanofibers = 5:5 in a solvent Medium and then through a high-speed mechanical agitation to achieve a uniform solution A slurry was prepared. The solvent is diluted to 0.01% by adding a solvent, and the diluted slurry is dehydrated by the net; pressed and dried; hot-rolled at a molding temperature of 100 ° C and a line pressure of 100 kg/cm, and then rolled, Rewinding, slitting and packaging to produce a battery separator.

The above closed-cell composite membrane exhibits excellent characteristics, for example, a porosity of 54% and 18% before and after heat treatment at 200 ° C for 2 hours, a heat shrinkage of 1.4% at 200 ° C, 30 minutes, and a percentage of absorbance of 285%; The Gurley value (s/100 cc) before and after the heat treatment at °C for 2 h was 23 and 2020.

Example 4

Dispersing fibrillated cellulose nanofibers: low melting point polymer nanofibers = 3:7 algae cellulose nanofibers and low melting polymer nanofibers (polyethylene-vinyl acetate copolymer) in a solvent, and then passing The slurry is prepared by high-speed mechanical agitation to achieve uniformity of the solution. The solvent is diluted to 0.01% by adding a solvent, and the diluted slurry is dehydrated by the net; pressed and dried; hot-rolled at a molding temperature of 100 ° C and a line pressure of 100 kg/cm, and then rolled, Rewinding, slitting and packaging to produce a battery separator.

The above closed-cell composite membrane exhibits excellent closed cell characteristics, for example, 200 ° C, and a porosity of 58% and 5% before and after heat treatment for 2 hours, and a heat shrinkage rate of 5% at 200 ° C, 30 minutes; The Gurley value (s/100 cc) before and after heat treatment at 200 ° C for 2 h was 25 and 3867.

Example 5

Cellulose nanofibers and low melting point polymer nanofibers (polyurethane) separated from nanosized wood materials of fibrillated cellulose nanofibers: low melting point polymer nanofibers 1:9 are dispersed in a solvent, and then passed through a high speed The slurry is prepared by mechanical agitation to achieve uniformity of the solution. The solvent is diluted to 0.01% by adding a solvent, and the diluted slurry is dehydrated by the net; pressed and dried; hot-rolled at a molding temperature of 100 ° C and a line pressure of 100 kg/cm, and then rolled, Rewinding, slitting and packaging to produce a battery separator.

The above closed-cell composite membrane exhibits excellent characteristics, for example, 200 ° C, 2 h heat treatment before and after the hole The gap ratios were 57% and 1%, respectively; at 20 °C, 18% heat shrinkage at 30 min; 235% absorbance percentage; 200 °C, Gurley value (s/100 cc) before and after 2 h heat treatment was 23 and substantially no aeration.

According to the present invention, the method of preparing a composite nanofiber membrane having a closed cell function has an advantage in that it is suitable for mass production due to its competitive price due to its simple preparation process and preparation cost.

Also, a separator having excellent physical characteristics such as closed cell properties, gas permeability, thermal stability, dimensional stability, thickness adjustable, and impregnation properties can be prepared.

While the invention has been illustrated and described with respect to the specific embodiments the embodiments of the invention

Comparative example:

Commercial PE diaphragms are tested directly without any treatment.

The parameters of the comparative membrane are shown in Table 1.

The mechanical properties of the closed-cell nanofiber composite separator prepared in the examples were tested below. The test method is as follows:

Structural characterization

The surface of Comparative Example 1 and Comparative Example 1 were examined by scanning electron microscopy at 200 ° C for 2 h. The SEM images are shown in Figures 1, 2 and 3.

2. Porosity test

The weighed separator (Wd) was immersed in n-butanol for 2 hours, and then the liquid on the surface was gently blotted with a filter paper. After weighing (Ww), the mass of n-butanol absorbed by the separator was obtained. Wb=Ww-Wd. The pore volume of the membrane can be obtained by dividing the mass of n-butanol (Wb) by the density of n-butanol (ρb), the ratio of this volume to the volume of the dry membrane (Vp) and the porosity of the membrane. The calculation formula is:

Where Wd is the mass of the membrane, Ww is the mass of the membrane after soaking, and Wb is the absorption of the membrane The mass of the alcohol, Vp is the volume of the dry membrane, and ρb is the density of n-butanol.

3. Air permeability (expressed by Gurley value)

At room temperature, under a static pressure of 1.22 KPa, the Gurley densitometer measures the time (sec) required for 100 mL of air through a sample with an effective test area of 1.0 Sqinch (0.01, 0.25 Sqinch optional) as the gas permeability value of the film (at least 5 parallels) test).

4. Heat shrinkage

The closed-cell composite separator obtained in the examples was heat-treated at 200 ° C for 0.5 h, and the dimensional change of the statistical separator was observed (at least 5 parallel tests).

5. Diaphragm lyophilic testing

The composite separator obtained in the examples was placed in an electrolyte solution (1.0 M LiPF6 electrolyte of vinyl carbonate (EC) and dimethyl carbonate (DMC) (v/v = 1:1)) for 1 h, and quickly taken out. Excess electrolyte solution was washed out with filter paper, the mass change before and after adsorption of the composite membrane was tested, and the percentage of liquid absorption was calculated. The calculation formula is as follows:

Structural analysis:

Comparative Example 1, the separator of Example 5 was compared at 200 ° C for 2 h before and after the SEM photograph of the surface, and Figure 1 is a SEM photograph of the PE separator of the comparative example, the pore structure of which is a uniformly distributed pore formed by stretching. . Figure 2 is a SEM photograph of the closed-cell composite membrane before it is heated. It can be seen that the cross-linking between the nanofibers exhibits a three-dimensional pore structure. Fig. 3 is a SEM photograph of the closed-cell membrane after heating at 200 ° C for 2 h, substantially no visible pore structure exists, and the pores formed by cross-linking between the fibers are closed.

The properties of the closed cell nanofiber composite separator prepared in the examples of Table 1 and the comparative examples

4 is a photograph of a comparative example olefin-based separator and the porous separator of Example 3 taken before the separator was exposed to high temperature, and after exposure to 150 ° C and 30 ° C at 30 ° C.

Since the olefin-based separator of the comparative example had a lower melting point, when the olefin-based separator was exposed to a temperature of 200 ° C, the frame of the olefin-based separator was completely lost. Therefore, when the olefin-based separator of Comparative Example 1 was used as a separator of a lithium ion battery, its safety was not secured.

Meanwhile, since the thermal stability of the porous separator of Example 3 was continued to 250 ° C, it was found that the closed-cell nanocomposite separator is suitable as a separator for a lithium secondary battery in terms of dimensional stability and heat shrinkage.

Measurement of lyophilicity of the porous membrane of the present invention.

In order to determine the wetting characteristics of the electrolyte of the porous separator according to the present invention, the comparative example and the separator of Example 3 were prepared, and the electrolyte was dropped into the comparative example and the separator of Example 3 with a micro-adjusting syringe, and the results were obtained after 2 s and 15 minutes. As shown in Figure 5.

Propylene carbonate was not impregnated at all to the separator in the comparative example. However, the electrolyte was impregnated onto the separator of Example 3 immediately after it was dropped into the separator.

It is assumed that the cell infiltration property of the closed cell function composite nanofiber separator of the lithium secondary battery has a large influence on the cell yield and efficiency, and the closed cell nanocomposite in Example 3 can be seen to be suitable for the separator of a lithium secondary battery.

The above-mentioned embodiments are merely illustrative of the present invention, and are not intended to limit the scope of the present invention, and various ratios and parameters made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention. Changes, modifications, substitutions, combinations, simplifications, and equivalent substitutions are intended to fall within the scope of the invention as defined by the appended claims.

Claims

A composite nanofiber membrane having a closed cell function, characterized in that the raw material comprises fibrillated cellulose nanofibers and low melting point polymer nanofibers, and the fibrillated cellulose nanofibers mainly pass hydrogen bonding, Intermolecular force bonding, the fibrillated cellulose nanofibers and the low melting point polymer nanofibers are combined by long-term molecular cross-linking; the composite nanofiber membrane has pores for electrolyte ions Passing through and preventing electrons from passing through; the composite nanofiber membrane pores are closed at a temperature of 130 to 170 ° C to prevent excessive and undesired ions from passing through the battery after damage.
The composite nanofiber membrane having a closed cell function according to claim 1, wherein the composite nanofiber membrane has a pore size closed state, and the composite nanofiber membrane has a stable size and is heated within a temperature of 200 ° C for 30 minutes. The heat shrinkage rate is less than 2%.
The composite nanofiber membrane having a closed cell function according to claim 1, wherein the composite nanofiber membrane having a closed cell function has a thickness of 10 to 80 μm.
A method for preparing a composite nanofiber membrane having a closed cell function according to claim 1, wherein the fibrillated cellulose nanofiber and the low melting polymer nanofiber are used in a mass ratio of 1:9 to 9:1. As a raw material, it is prepared by a papermaking process.
The method for preparing a composite nanofiber membrane having a closed cell function according to claim 4, comprising the following specific steps:

I. The fibrillated cellulose nanofibers and the at least one low-melting polymer nanofibers are respectively dispersed in a solvent at a mass ratio of 1:9 to 9:1, and rapidly stirred to form a slurry;

II. adding a binder to the slurry of step I;

III, the slurry after step II is diluted to a concentration of 0.01% to 0.05%;

IV. The diluted slurry is subjected to dehydration molding, pressing, drying and hot rolling forming on the Internet to obtain the composite nanofiber separator having a closed cell function.
The method for preparing a composite nanofiber membrane having a closed cell function according to claim 4, wherein the fibrillated cellulose nanofiber has a diameter of 10 to 1000 nm and a length of 10-3000 μm.
The method for preparing a composite nanofiber membrane having a closed cell function according to claim 4, 5 or 6, wherein the fibrillated cellulose nanofiber comprises cellulose nanofibers separated from a nanometer size wood material, Algae cellulose nanofibers, and bacterial cellulose nanofibers obtained by culturing strains.
The method for preparing a composite nanofiber membrane having a closed cell function according to claim 4, wherein the low melting point polymer nanofiber has a diameter of 10 to 1000 nm.
The method for preparing a composite nanofiber membrane having a closed cell function according to claim 4, 5 or 8, wherein the low melting point polymer nanofiber is polymethyl methacrylate and a vinylidene fluoride polymerization. One or more combinations of polyurethane, polyvinyl chloride, polyolefin, polyethylene-vinyl acetate copolymer, polyethylene succinate.
An energy storage device prepared by using the composite nanofiber membrane with closed cell function according to one of claims 1 to 3, including a lithium ion battery, a lithium sulfur battery, an alkaline battery, a super capacitor, a lead acid battery, and a zinc air battery. , sodium ion battery.