CN107742688B - A kind of polyolefin lithium battery separator and preparation method thereof - Google Patents

Abstract

The invention discloses a polyolefin lithium battery separator, which uses a porous polyolefin separator as a matrix. The polyolefin separator is electrospun on one side or both sides and is coated with modified polyethylene terephthalate (PET) fibers. layer, the modified polyethylene terephthalate fiber is a composite fiber of inorganic oxide nanoparticles and polyethylene terephthalate. Aiming at the problems of low high temperature integrity of the existing polypropylene or polyethylene porous diaphragm, and the problems of uneven pore structure or composite structure existing in the existing electrospinning diaphragm, the invention provides a polyolefin lithium battery diaphragm, which can withstand temperature It can reach 250-260 °C, effectively avoiding the problem of material melting and closing pores under the extreme conditions of battery abuse, and has good high-temperature integrity, which can greatly improve the thermal safety of the battery.

Description

A kind of polyolefin lithium battery separator and preparation method thereof

technical field

The invention belongs to the field of new energy materials, and particularly relates to a polyolefin lithium battery diaphragm and a preparation method thereof.

Background technique

The separator is the most critical material that determines the safety of lithium batteries. It is generally prepared from polypropylene or polyethylene by dry single drawing, dry double drawing or wet method. Under the extreme conditions of overcharge/overdischarge or other improper use, the temperature inside the lithium battery will rapidly rise above the melting point of polyolefin, causing the separator to fuse, the positive and negative electrodes to directly contact in local areas and short-circuit, the battery catches fire or explode.

At present, the method to improve the lithium battery separator is mainly to coat the surface of the separator with an inert polymer binder (mainly polyvinylidene fluoride PVDF, vinylidene fluoride-hexafluoropropylene copolymer PVD-HFP) bonded nano-inorganic oxide particle coating. In the melting temperature range of polypropylene or polyethylene base film, such as 120 ~ 160 ℃, the inorganic oxide has good dimensional stability. The specific method is: under the action of water dispersion, the binder and inorganic oxide are fully It is dispersed into slurry, and then coated on the diaphragm to form a ceramic coating after drying. For example, patent CN201110048688 discloses a kind of water-based dispersion of polyvinylidene fluoride and other polymer binders and inorganic particles such as alumina in polyethylene glycol. With the aid of a thickener such as carboxymethyl cellulose, it is dispersed in an aqueous solution to prepare an inorganic coating method; patent CN201310017708 discloses a method of using vinylidene fluoride to hexafluoropropylene copolymer to bond with the aid of thickeners such as carboxymethyl cellulose. A method for preparing a diaphragm ceramic coating by mixing the agent and zeolite; the patent CN201510706160.2 discloses a lithium battery diaphragm containing a lithium ion conductive porous inorganic oxide and a preparation method thereof. The lithium ion conductive polymer and the inorganic oxide precursor are used in Under the action of surfactant, it is first compounded, and then crystallized under hydrothermal conditions to form a porous inorganic oxide that can conduct lithium ions, and then mixed with binder, stabilizer, and alkyl chain UV cross-linking agent to prepare slurry, Finally, it is coated on the surface of the lithium ion battery separator, irradiated with ultraviolet rays and dried to obtain a coated separator. However, the thermal stability temperature of the polymer binder in the coating also has a great influence on the thermal stability of the coating. After the binder softens, it loses its cohesive force and falls off; in addition, the coating cannot be independent after the separator body is softened. There is, the melting of the larger area of the separator body will lead to the pulverization of the coating, which makes it difficult to play the role of blocking the positive and negative electrodes in extreme cases.

Electrospinning (electrospinning) technology can use polymers with better melting temperature as raw materials to obtain high-porosity separators or coatings. For example, patent CN201510849210.2 discloses the preparation method of electrospinning composite diaphragm. Electrospinning technology is used to combine polyvinylidene fluoride and another polymer precursor solution A, polyvinylidene fluoride and inorganic nanomaterials. The precursor solution B is prepared into a porous mesh composite fiber membrane; the patent CN201610747668.1 adopts a coaxial electrospinning technology to prepare a composite fiber membrane with a core/shell structure. The core and shell layers of the composite fiber membrane are concentric. The core layer is composed of polyarylethersulfone ketone nanofibers with high melting point, and the shell layer is composed of polyvinylidene fluoride nanofibers with low melting point. However, there are two problems with the electrospinning film directly used as a battery separator. One is that the porosity of the separator is very high, with a typical value reaching 60-80%, which leads to a low electronic isolation capability of the separator and serious battery self-discharge. The silk separator has not undergone directional stretching, and its general strength is only 5-20 MPa, which is much lower than the 100 MPa of the traditional stretched separator, which is difficult to meet the needs of battery manufacturing process and mechanical safety.

CN201510069176.7 discloses a composite lithium-ion battery separator, comprising a non-woven substrate layer, an electrospinning layer and a polymer porous coating, specifically using non-woven fabric as the substrate to ensure high porosity of the separator and heat resistance; the electrospinning layer is arranged on the upper and lower surfaces of the non-woven substrate, which reduces the pore size of the non-woven fabric and makes the pore size uniform; the patent CN201510069135.8 adopts a similar process to prepare electrospinning with environmentally friendly water-soluble polymers. filament layer, but the problems of self-discharge and strength of electrospun membranes remain unsolved. Patent CN201210128618.7 discloses a three-layer nanofiber composite lithium-ion battery film and its preparation technology. The battery film includes a non-woven or nanofiber film located in the middle layer and a first outer layer and a second outer layer located on both sides of the middle layer. For the second outer layer, the first outer layer and the second outer layer are prepared by electrospinning technology, and then combined with the middle layer by hot pressing to obtain a composite structure. In addition, the hot-pressing composite requires a large thickness of the single-layer film, which is not in line with the current trend of thin-layer diaphragms.

Patent CN201710142596.2 discloses a polymer composite lithium battery separator and a preparation method thereof. The polymer composite lithium battery separator includes a base film and an inorganic particle coating coated on one or both sides of the base film, and the inorganic particle coating The surface of the film is coated with at least one layer of high temperature resin, and the coating is transferred to the base film by one of dip coating, gravure printing, spray coating, extrusion coating, electrospinning and transfer coating, but , In this structure, the inorganic oxide is added in a physical way, and it is difficult to disperse.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a polyolefin lithium battery separator, which has good high temperature integrity, can withstand temperatures up to 240-260°C, and can greatly improve the thermal safety of the battery. .

The technical scheme adopted by the present invention to solve the above-mentioned problems is:

A polyolefin lithium battery separator, which uses a porous polyolefin separator as a matrix, one side or both sides of the polyolefin separator is coated with a modified polyethylene terephthalate (PET) fiber coating, and the The modified polyethylene terephthalate (PET) fiber is a fiber composed of inorganic oxide nanoparticles and polyethylene terephthalate.

According to the above scheme, the porous polyolefin separator has a thickness of 6-50 μm and a porosity of 35-50 vol%; the thickness of the modified polyethylene terephthalate (PET) fiber coating is 2-10 μm .

According to the above scheme, the porous polyolefin membrane base material is mainly selected from any one of dry-process single-stretch polypropylene, dry-process double-stretch polypropylene or wet-process polyethylene lithium battery membrane.

According to the above scheme, the coating mainly adopts electrospinning (electrospinning).

According to the above scheme, the inorganic oxide is mainly selected from silicon dioxide, aluminum oxide, titanium dioxide and the like.

The present invention also provides the preparation method of the above-mentioned polyolefin lithium battery separator, the main process is:

In the first step, in the mixed solution of terephthalic acid and ethylene glycol, the inorganic oxide precursors use electrostatic self-assembly to synthesize inorganic oxide nanoparticles to obtain a dispersion liquid of inorganic oxide nanoparticles, that is, the dispersion liquid Using terephthalic acid and ethylene glycol as solvent and inorganic oxide nanoparticles as solute;

In the second step, the dispersion liquid of the inorganic oxide nanoparticles obtained in the first step is heated to make the ethylene glycol and terephthalic acid in it undergo esterification and polycondensation reaction, so as to obtain the polyterephthalic acid compounded by the inorganic oxide nanoparticles Ethylene glycol ester (PET) dispersion;

In the third step, the PET dispersion liquid compounded by the inorganic oxide nanoparticles obtained in the second step is diluted and used as a spinning slurry; and then the spinning slurry is electrospun on one or both sides of the porous polyolefin membrane to obtain a Modified polyethylene terephthalate (PET) fiber composite polyolefin lithium battery separator.

According to the above scheme, in the first step, the weight ratio of terephthalic acid, inorganic oxide precursor and ethylene glycol is 1:0.01-0.1:2-5.

According to the above scheme, in the first step, the inorganic oxide precursor is selected from any one of ethyl orthosilicate, tetraethoxysilane, ethyl titanate, aluminum isopropoxide, and the like.

According to the above scheme, in the first step, the reaction conditions of electrostatic self-assembly are as follows: inorganic acid is used as hydrolysis catalyst, pH is 0.1-2, pH of reaction system is controlled at 0.1-2, and reaction time is 1-4h.

According to the above scheme, in the first step, the preferred concentration of the inorganic acid is an aqueous solution of 10-30 wt%, for example: any one of an aqueous nitric acid solution, an aqueous hydrochloric acid solution, and the like.

According to the above scheme, in the first step, the step of synthesizing inorganic oxide nanoparticles further includes the step of removing acid and water, specifically: heating under stirring condition to remove free inorganic acid and low-boiling water solvent by distillation. Here, the heating temperature is 180 to 193°C.

According to the above scheme, in the second step, the conditions for the esterification and polycondensation reaction are heating to 220-240° C. and keeping the temperature for 30-40 min. Among them, the temperature increase rate during heating is preferably 2 to 5°C/min.

According to the above scheme, in the third step, dilute to a viscosity between 1000 and 3000 mPa.S, preferably isopropanol as the diluent.

According to the above scheme, in the third step, the ambient temperature of the electrospinning is controlled to be 10-30°C, and the humidity is controlled to be 50-70RH%; The thickness is controlled to be 2 to 10 μm.

Further, the present invention also provides a more specific preparation method of the polyolefin lithium battery separator, and the detailed process is:

1) The terephthalic acid and inorganic oxide precursor are dispersed in ethylene glycol, and the weight ratio of terephthalic acid, inorganic oxide precursor and ethylene glycol is 1:0.01~0.1:2~5, after mixing Stir for 0.5 to 2 hours; then, slowly add a mineral acid aqueous solution with a concentration of 10 to 30 wt% as a hydrolysis catalyst under stirring, and control the addition speed of the acid to keep the pH value of the solution system between 0.1 to 2, and continue to stir for 1 to 4h is fully hydrolyzed; after the hydrolysis is completed, the solution system is heated under stirring until the solution temperature rises to 180-193 ° C, to remove free inorganic acid and low-boiling water solvent by distillation, and then cooled to room temperature to obtain inorganic oxide nanoparticles. Dispersions;

2) heating the dispersion liquid of the inorganic oxide nanoparticles obtained in the first step to 220-240° C. at 2-5° C./min, and maintaining the temperature for 30-40 min to cause esterification and polycondensation of ethylene glycol and terephthalic acid to obtain inorganic oxide. Oxide nanoparticle composite PET dispersion;

3) After diluting the inorganic oxide nanoparticle composite PET dispersion liquid obtained in the second step to a viscosity between 1000 and 3000 mPa.S, it is used as a spinning slurry; Surface or double-sided electrospinning, the spinning environment temperature is controlled at 10-30°C, and the humidity is controlled at 50-70RH%; the spinning positive voltage is 30-50kV, the negative voltage is -30--10kV, and the spinning layer thickness is controlled at 2 to 10 μm; after the spinning is completed and dried, a polyolefin lithium battery separator is obtained.

Compared with the prior art, the beneficial effects of the present invention are:

First, the present invention provides a polyolefin lithium battery diaphragm for the problems of low high temperature integrity of the existing polypropylene or polyethylene porous diaphragm, and the problem of uneven pore structure or composite structure existing in the existing electrospinning diaphragm. Since the modified PET fiber of inorganic oxide nanoparticles forms a stable single-layer structure, the temperature can reach 240-260 °C, which effectively avoids the problem of material melting and closing pores under the extreme conditions of battery abuse. High temperature integrity can greatly improve the thermal safety of the battery.

Second, the present invention adopts the method of in-situ compounding to compound inorganic oxide nanoparticles in the PET fiber, and the functional groups on the surface of the inorganic oxide are closer to the polarity of the electrolyte, which can improve the toughness and resistance of the PET fiber coating. The wettability of the electrolyte is beneficial to improve the performance of the composite diaphragm.

Description of drawings

Fig. 1 is the cross-sectional scanning electron microscope picture of composite diaphragm in embodiment 1;

FIG. 2 is an ion-thinning high-resolution transmission electron microscope photograph of the composite separator fiber coating in Example 1. FIG.

Detailed ways

In order to better understand the present invention, the content of the present invention is further illustrated below in conjunction with the embodiments, but the content of the present invention is not limited to the following embodiments.

Example 1

A polyolefin lithium battery separator is based on a dry single-draw polypropylene lithium battery separator (20 μm, porosity 42 vol%), and the polyolefin separator is electrospun on both sides with modified polyethylene terephthalate. (PET) fiber coating, the thickness of the modified polyethylene terephthalate (PET) fiber coating is 2 μm; the modified polyethylene terephthalate (PET) fiber is Fibers made of silica nanoparticles and polyethylene terephthalate.

The preparation method of the above-mentioned polyolefin lithium battery separator, the concrete steps are as follows:

1) Disperse terephthalic acid and ethyl orthosilicate in ethylene glycol and stir for 0.5h, and the weight ratio of terephthalic acid, ethyl orthosilicate and ethylene glycol is 1:0.05:2; Continue to slowly add a 10wt% nitric acid aqueous solution as a hydrolysis catalyst under stirring, control the addition speed to keep the pH of the solution system between 0.1 and 0.3, and continue stirring for 1 h to fully hydrolyze; after the hydrolysis is completed, heat the solution system under stirring conditions When the solution temperature rises to 180°C, free inorganic acid and low-boiling water solvent are distilled off, and then cooled to room temperature to obtain a dispersion of silica nanoparticles;

2) adding the dispersion of the silicon dioxide nanoparticles obtained in step 1) into the reactor, heating up to 220°C at 2°C/min, and keeping the temperature for 30min to make ethylene glycol and terephthalic acid esterification and polycondensation reaction, to obtain dioxide dioxide. Silicon nanoparticle composite PET dispersion;

3) adding isopropyl alcohol to the PET dispersion liquid compounded by the silica nanoparticles obtained in step 2) to dilute and adjust to a viscosity of 2800-3000 mPa.S, as spinning slurry, wherein the addition amount of isopropyl alcohol is step 1 ) 5 times the weight of phthalic acid; then the spinning slurry was subjected to double-sided electrospinning on a dry single-draw polypropylene lithium battery separator (20 μm, porosity 42 vol%) through a nanofiber spinning machine, spinning The ambient temperature was controlled at 10°C, the humidity was controlled at 50RH%, the positive spinning voltage was 30kV, the negative voltage was -10kV, and the thickness of the spinning layer was controlled at 2 μm; after the spinning was completed, the obtained film was placed in a 90°C oven to dry for 10 hours , to obtain a modified PET fiber composite polyolefin lithium battery separator.

The SEM photo of the cross-section of the polyolefin lithium battery separator obtained in this example is shown in Figure 1. It can be seen that the electrospun fiber coating and the polypropylene matrix are closely combined, the interface is uniform, and the modification of the inorganic silica nanoparticles The PET fiber forms a film with a thickness of several microns on the surface of the substrate. The appearance structure can be seen from the scanning electron microscope that it is a stable structure formed by weaving. It is inferred that it is a single-layer structure that can exist stably. The modified PET fiber itself forms a stable single-layer structure; and the ion-thinning high-resolution transmission electron microscope photo of the fiber coating of the obtained polyolefin lithium battery separator is shown in Figure 2, and it can be seen that the silica nanoparticles are uniformly distributed. in PET fibers.

In Example 1 and the following other examples, the coating peeling force, breaking strength and puncture strength of the lithium battery diaphragm were measured by a universal material stretching machine; the porosity was measured by a Gurley air permeability tester; powdered lithium iron phosphate was used as the positive electrode material, A button battery was assembled with artificial graphite as the negative electrode, and the temperature was increased at a rate of 0.1 °C/min in an environmental test chamber, and an electrochemical workstation was used to measure the temperature when a short circuit occurred. Various performance indicators of the polyolefin lithium battery separator obtained in Example 1 are shown in Table 1, and Table 1 also includes various performance indicators of the matrix itself used in this example.

Table 1

Example 2

A polyolefin lithium battery separator is based on a dry double-drawn polypropylene lithium battery separator (50 μm, 39 vol% porosity), and the polyolefin separator is electrospun on both sides with modified polyethylene terephthalate. (PET) fiber coating, the thickness of the modified polyethylene terephthalate (PET) fiber coating is 5 μm; the modified polyethylene terephthalate (PET) fiber is Fibers made of silica nanoparticles and polyethylene terephthalate.

The preparation method of the above-mentioned polyolefin lithium battery separator, the concrete steps are as follows:

1) Disperse terephthalic acid and tetraethoxysilane in ethylene glycol and stir for 1 h. The weight ratio of terephthalic acid, tetraethoxysilane and ethylene glycol is 1:0.01:3; Continue to slowly add the aqueous hydrochloric acid solution with a concentration of 20wt% as a hydrolysis catalyst in the state, control the adding speed to keep the pH of the solution system between 0.5 and 0.7, and continue to stir for 3h to fully hydrolyze; after the hydrolysis is completed, heat the solution system under stirring conditions to The temperature of the solution was raised to 190°C, the free inorganic acid and the low-boiling water solvent were distilled off, and then cooled to room temperature to obtain a dispersion of silica nanoparticles;

2) adding the dispersion of the silicon dioxide nanoparticles obtained in step 1) into the reactor, heating up to 230°C at 4°C/min, and keeping the temperature for 35min to make ethylene glycol and terephthalic acid esterification and polycondensation reaction, to obtain dioxide dioxide. Silicon nanoparticle composite PET dispersion;

3) adding isopropanol to the PET dispersion liquid compounded by the silica nanoparticles obtained in step 2) to dilute and adjust to a viscosity of 2100-2200 mPa.S, as spinning slurry, wherein the addition amount of isopropanol is step 1 ) 8 times the weight of phthalic acid; then the spinning slurry was subjected to double-sided electrospinning on a dry double-drawn polypropylene lithium battery separator (50 μm, porosity 39 vol%) through a nanofiber spinning machine, spinning The ambient temperature was controlled at 25°C, the humidity was controlled at 60RH%, the positive voltage for spinning was 40kV, the negative voltage was -20kV, and the thickness of the spinning layer was controlled at 5 μm; after the spinning was completed, the obtained film was placed in a 95°C oven to dry for 8 hours , to obtain a modified PET fiber composite polyolefin lithium battery separator.

The performance indicators of various aspects of the polyolefin lithium battery separator obtained in Example 2 are shown in Table 2. Meanwhile, various performance indicators of the matrix itself used in this example are also attached in Table 2.

Table 2

Performance Example 2 gained lithium battery separator matrix Porosity% 45 39 Air permeability s/100mL 533 517 Puncture strength, gf 807 792 Longitudinal tensile strength, MPa 146 153 Coating peel force Nm^-1 37.4 / Short circuit temperature °C 252 173

Example 3

A polyolefin lithium battery separator, using a wet-process polyethylene lithium battery separator (12 μm, 46 vol%) as a matrix, and one side of the polyolefin separator is electrospun with modified polyethylene terephthalate (PET) fibers The coating, the thickness of the modified polyethylene terephthalate (PET) fiber coating is 10 μm; the modified polyethylene terephthalate (PET) fiber is titanium dioxide nanoparticles and Fiber made from polyethylene terephthalate.

The preparation method of the above-mentioned polyolefin lithium battery separator, the concrete steps are as follows:

1) Disperse terephthalic acid and ethyl titanate in ethylene glycol and stir for 2h, the weight ratio of terephthalic acid, ethyl titanate and ethylene glycol is 1:0.1:5; then, under stirring Continue to slowly add aqueous hydrochloric acid solution with a concentration of 30wt% as a hydrolysis catalyst, control the addition speed to keep the pH of the solution system between 1.6 and 2, and continue to stir for 4h to fully hydrolyze; after the hydrolysis is completed, heat the solution system to the solution temperature under stirring conditions. Raised to 193°C, distilled to remove free inorganic acid and low-boiling water solvent, and then cooled to room temperature to obtain a dispersion of silica nanoparticles;

2) adding the dispersion liquid of the silica nanoparticles obtained in step 1) into the reactor, heating up to 240°C at 5°C/min, and maintaining the temperature for 40min to make ethylene glycol and terephthalic acid esterification and polycondensation reaction, to obtain dioxide dioxide. Silicon nanoparticle composite PET dispersion;

3) adding isopropanol to the PET dispersion liquid compounded by silica nanoparticles obtained in step 2) to dilute and adjust to a viscosity of 1000-1200 mPa.S, as spinning slurry, wherein the addition amount of isopropanol is step 1 ) 10 times the weight of phthalic acid; then the spinning slurry was subjected to single-sided electrospinning on a wet-process polyethylene lithium battery separator (12 μm, 46 vol%) through a nanofiber spinning machine, and the spinning environment temperature was controlled as 30°C, the humidity is controlled to 70RH%, the positive voltage of spinning is 50kV, the negative voltage is -30kV, and the thickness of the spinning layer is controlled to be 10 μm; after the spinning is completed, the obtained film is placed in a 100°C oven to dry for 10 hours to obtain the modified film. PET fiber composite polyolefin lithium battery separator.

The performance indicators of various aspects of the polyolefin lithium battery separator obtained in Example 3 are shown in Table 3. Meanwhile, various performance indicators of the matrix itself used in this example are also attached in Table 3.

table 3

Performance Example 3 gained lithium battery separator matrix Porosity% 52 46 Air permeability s/100mL 174 167 Puncture strength, gf 335 326 Longitudinal tensile strength, MPa 146 153 Coating peel force Nm^-1 42.5 / Short circuit temperature °C 246 135

Example 4

A polyolefin lithium battery separator, which uses a dry single-draw polypropylene lithium battery separator (15 μm, 46 vol%) as a matrix, and one side of the polyolefin separator is electrospun with modified polyethylene terephthalate (PET). ) fiber coating, the thickness of the modified polyethylene terephthalate (PET) fiber coating is 3 μm; the modified polyethylene terephthalate (PET) fiber is a carbon dioxide Fiber made of aluminum nanoparticles and polyethylene terephthalate.

The preparation method of the above-mentioned polyolefin lithium battery separator, the concrete steps are as follows:

The preparation method of the above-mentioned polyolefin lithium battery separator, the concrete steps are as follows:

1) Disperse terephthalic acid and aluminum isopropoxide in ethylene glycol and stir for 1 h, and the weight ratio of terephthalic acid, aluminum isopropoxide and ethylene glycol is 1:0.03:4; then, under stirring Continue to slowly add an aqueous solution of nitric acid with a concentration of 30wt% as a hydrolysis catalyst, control the addition speed to keep the pH of the solution system between 0.1 and 0.12, and continue to stir for 3h to fully hydrolyze; after the hydrolysis is completed, heat the solution system to the solution temperature under stirring conditions Raised to 190°C, distilled to remove free inorganic acid and low-boiling water solvent, and then cooled to room temperature to obtain a dispersion of silica nanoparticles;

2) adding the dispersion liquid of the silica nanoparticles obtained in step 1) into the reaction kettle, warming up to 222°C at 3°C/min, and maintaining the temperature for 40min to make ethylene glycol and terephthalic acid esterification and polycondensation reaction, to obtain dioxide dioxide. Silicon nanoparticle composite PET dispersion;

3) adding isopropanol to the PET dispersion liquid compounded by the silica nanoparticles obtained in step 2) to dilute and adjust to a viscosity of 2200-2400 mPa.S, as spinning slurry, wherein the addition amount of isopropanol is step 1 ) 7 times the weight of phthalic acid; then the spinning slurry was subjected to single-sided electrospinning on a dry single-draw polypropylene lithium battery separator (15 μm, 46 vol%) through a nanofiber spinning machine, and the spinning ambient temperature Controlled at 20°C, humidity was controlled at 70RH%, positive spinning voltage was 50kV, negative voltage was -30kV, and the thickness of the spinning layer was controlled at 3 μm; after spinning, the resulting film was placed in a 100°C oven to dry for 7 hours to obtain Modified PET fiber composite polyolefin lithium battery separator.

The performance indicators of various aspects of the polyolefin lithium battery separator obtained in Example 4 are shown in Table 4. Meanwhile, various performance indicators of the matrix itself used in this example are also attached in Table 4.

Table 4

Performance Example 4 gained lithium battery separator matrix Porosity% 51 46 Air permeability s/100mL 193 185 Puncture strength, gf 342 336 Longitudinal tensile strength, MPa 141 146 Coating peel force Nm^-1 38.4 / Short circuit temperature °C 247 165

As shown in Tables 1-4, the polyolefin lithium battery separator prepared by the present invention has high porosity, good air permeability, suitable puncture strength, longitudinal tensile strength and shrinkage rate, and the short-circuit temperature is 243-252°C, and has good high temperature integrity. It can greatly improve the thermal safety of the battery. Among them, relative to the respective matrix, the high porosity of the electrospun fiber layer has no obvious influence on the porosity and air permeability of the separator.

The above are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, some improvements and transformations can be made without departing from the inventive concept of the present invention, which all belong to the present invention. scope of protection.

Claims (10)

1. A polyolefin lithium battery diaphragm takes a porous polyolefin diaphragm as a matrix, and is characterized in that one side or two sides of the polyolefin diaphragm are coated with a modified polyethylene glycol terephthalate fiber coating, and the modified polyethylene glycol terephthalate fiber is a fiber formed by compounding inorganic oxide nanoparticles and polyethylene glycol terephthalate;

the preparation method of the polyolefin lithium battery diaphragm mainly comprises the following steps:

firstly, synthesizing inorganic oxide nanoparticles from an inorganic oxide precursor in a mixed solution of terephthalic acid and ethylene glycol by adopting an electrostatic self-assembly method to obtain a dispersion liquid of the inorganic oxide nanoparticles, wherein the dispersion liquid takes the terephthalic acid and the ethylene glycol as solvents and the inorganic oxide nanoparticles as solutes;

secondly, heating the dispersion liquid of the inorganic oxide nano particles obtained in the first step to enable ethylene glycol and terephthalic acid in the dispersion liquid to have esterification and polycondensation reactions so as to obtain polyethylene terephthalate dispersion liquid compounded by the inorganic oxide nano particles;

thirdly, diluting the inorganic oxide nano-particle composite polyethylene glycol terephthalate dispersion liquid obtained in the second step to obtain spinning slurry; and then, carrying out single-side or double-side electrostatic spinning on the spinning slurry on the porous polyolefin diaphragm to obtain the modified polyethylene glycol terephthalate fiber compounded polyolefin lithium battery diaphragm.

2. The polyolefin lithium battery separator according to claim 1, wherein the porous polyolefin separator has a thickness of 6 to 50 μm and a porosity of 35 to 50 vol%; the thickness of the modified polyethylene terephthalate fiber coating is 2-10 mu m.

3. The polyolefin lithium battery separator according to claim 1, wherein the porous polyolefin separator substrate is selected from any one of a dry-process mono-drawn polypropylene, a dry-process bi-drawn polypropylene or a wet-process polyethylene lithium battery separator; the inorganic oxide is selected from silicon dioxide, aluminum oxide and titanium dioxide.

4. The preparation method of the polyolefin lithium battery diaphragm is characterized by comprising the following main processes:

firstly, synthesizing inorganic oxide nanoparticles from an inorganic oxide precursor in a mixed solution of terephthalic acid and ethylene glycol by adopting an electrostatic self-assembly method to obtain a dispersion liquid of the inorganic oxide nanoparticles, wherein the dispersion liquid takes the terephthalic acid and the ethylene glycol as solvents and the inorganic oxide nanoparticles as solutes;

secondly, heating the dispersion liquid of the inorganic oxide nano particles obtained in the first step to enable ethylene glycol and terephthalic acid in the dispersion liquid to have esterification and polycondensation reactions so as to obtain polyethylene terephthalate dispersion liquid compounded by the inorganic oxide nano particles;

thirdly, diluting the inorganic oxide nano-particle composite polyethylene glycol terephthalate dispersion liquid obtained in the second step to obtain spinning slurry; and then, carrying out single-side or double-side electrostatic spinning on the spinning slurry on the porous polyolefin diaphragm to obtain the modified polyethylene glycol terephthalate fiber compounded polyolefin lithium battery diaphragm.

5. The preparation method of the polyolefin lithium battery separator according to claim 4, wherein in the first step, the weight ratio of terephthalic acid, inorganic oxide precursor and ethylene glycol is 1: 0.01-0.1: 2 to 5.

6. The preparation method of the polyolefin lithium battery separator according to claim 4, wherein in the first step, the reaction conditions of electrostatic self-assembly are as follows: inorganic acid is used as a hydrolysis catalyst, the pH value is 0.1-2, the pH value of a reaction system is controlled to be 0.1-2, and the reaction time is 1-4 h.

7. The method for preparing a polyolefin lithium battery separator according to claim 4, wherein the step of synthesizing inorganic oxide nanoparticles in the first step further comprises a step of removing acid and water.

8. The method for preparing a polyolefin lithium battery separator as claimed in claim 4, wherein the esterification and polycondensation reaction conditions in the second step are heating to 240 ℃ and maintaining the temperature for 30-40 min.

9. The preparation method of the polyolefin lithium battery separator according to claim 4, wherein in the third step, the polyolefin lithium battery separator is diluted to have a viscosity of 1000-3000 mPa.S, and isopropanol is used as a diluent.

10. The preparation method of the polyolefin lithium battery separator according to claim 4, wherein in the third step, the environmental temperature of electrostatic spinning is controlled to be 10-30 ℃, and the humidity is controlled to be 50-70 RH%; the positive voltage of spinning is 30-50 kV, the negative voltage is-30 to-10 kV, and the thickness of the spinning layer is controlled to be 2-10 mu m.

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