WO2018095093A1

WO2018095093A1 - Battery separator film and method for fabrication thereof

Info

Publication number: WO2018095093A1
Application number: PCT/CN2017/099371
Authority: WO
Inventors: 程跃; 熊磊; 邓洪贵; 何方波; 王伟强
Original assignee: 上海恩捷新材料科技股份有限公司
Priority date: 2016-11-25
Filing date: 2017-08-29
Publication date: 2018-05-31
Also published as: CN106486632A

Abstract

Provided are a battery separator film and method for fabrication thereof; in said method, a battery separator film is obtained by means of extruding mixed raw materials, cooling and forming, extracting, drawing, and heat-setting; said raw materials comprise ultra-high molecular weight polyethylene having a molecular weight of 1.0×10⁶-10.0×10⁶, high-density polyethylene having a molecular weight within the range of 0.940-0.976g/cm ³, an antioxidant, and a pore-forming agent; said method comprises crosslinking.

Description

Battery separator and preparation method thereof

Technical field

The invention relates to the field of electrochemistry, and in particular to a method for preparing a battery separator.

Background technique

Lithium-ion batteries are usually composed mainly of a positive electrode, a negative electrode, a separator, an electrolyte, and a battery casing. In lithium-ion battery construction, the diaphragm is one of the key inner layer components. The main function of the separator is to separate the positive and negative electrodes of the battery to prevent direct contact between the positive and negative electrodes and short circuit. At the same time, the electrolyte ions can pass smoothly during the charging and discharging process of the battery to form a current, and the battery operating temperature is abnormal. When rising, the electrolyte ion migration channel is turned off, and the current is cut off to ensure battery safety. It can be seen that the performance of the diaphragm determines the interface structure and internal resistance of the battery, which directly affects the capacity, cycle and safety performance of the battery. The separator with excellent performance plays an important role in improving the overall performance of the battery. Currently, commercially available lithium ion battery separators generally employ a polyolefin porous membrane.

The main performance parameters of the battery separator include thickness, porosity, pore size, pore size distribution, strength, heat shrinkage, closed cell temperature and membrane rupture temperature. In order to reduce the internal resistance of the battery, the electrode area must be as large as possible, so the thickness of the diaphragm is required to be as thin as possible. Although the battery separator itself is not electrically conductive, the conductive ions need to migrate through the diaphragm. This requires that the diaphragm itself needs a certain number of pores, that is, porosity, but the porosity is too high, which will cause the strength of the diaphragm to decrease, affecting the overall reliability of the battery. In addition, the wettability of the electrolyte on the separator directly affects the resistance of ion migration. The better the wettability, the smaller the resistance of ions to migrate through the separator, and the smaller the internal resistance of the battery. Generally, in the case where the pore diameter is not very large, the more uniform the pore size distribution, the better the wettability of the electrolyte. The battery assembly needs to pull the diaphragm during its production and assembly process. After the assembly is completed, it is also necessary to ensure that the diaphragm is not pierced by the electrode material, so the diaphragm not only needs sufficient tensile strength but also requires a certain piercing strength. The polymer separator will undergo heat shrinkage under certain heating conditions. In order to avoid internal short circuit caused by direct contact between the positive and negative electrodes caused by heat shrinkage, the heat shrinkage rate of the separator is also required. Under abnormal conditions, such as when a short circuit occurs on an external line, the internal temperature of the battery rises sharply due to excessive current, which requires the diaphragm to close the migration path of the conductive ions in time. Therefore, the temperature at which the micropores of the battery separator are melt-closed is referred to as a closed-cell temperature. When the temperature continues to rise, the isolation film is broken and the fracture temperature is called the film breaking temperature. From the perspective of the safety of lithium-ion batteries, the closed-cell temperature and the membrane-breaking temperature of the diaphragm must have a certain temperature difference. It is ensured that even if the temperature continues to rise after the diaphragm is closed, the diaphragm will not break enough between the buffers.

In order to improve the safety of the lithium ion battery separator, the most common method is to apply a ceramic slurry coating treatment to the polyolefin porous film. Although the coating treatment can significantly increase the membrane rupture temperature of the polyolefin porous membrane, it cannot simultaneously The diaphragm closed-cell temperature is lowered, and the coating process is highly demanding for the ceramic slurry, and the overall raw material and process cost are relatively high.

Therefore, there is an urgent need in the art to provide a significant improvement in the film-breaking temperature and the closed cell temperature difference as well as the heat shrinkage rate, while at the same time having a good strength, average pore size and pore size distribution of a conventional polymer separator, thereby ensuring excellent battery performance. Based on a battery separator that improves battery reliability and safety.

Summary of the invention

The present invention aims to provide a battery separator which is superior in performance.

In a first aspect of the invention, there is provided a method of preparing a battery separator, which comprises obtaining a battery separator by extruding, cooling forming, extracting, drawing and heat setting the mixed raw materials, the method comprising The cross-linking is radiation cross-linking or chemical cross-linking; the raw material contains a co-crosslinking agent.

In another preferred embodiment, the co-crosslinking agent is selected from one or a mixture of two or more of the following: mercaptobenzothiazole, benzothiazole disulfide, N-cyclohexylbenzothiazole sulfenamide, oxygen Divinylbenzothiazole sulfenamide, tetramethylthiuram monosulfide, tetramethylthiuram disulfide, zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, diphenyl Bismuth, di-o-toluene, ethylene thiourea, N, N'-diethyl thiourea, hexamethylenetetramine, zinc isopropyl xanthate, trimethylolpropane trimethacrylate, Trimethylolpropane triacrylate, tripropylene cyanurate and triallyl isocyanurate; more preferably triallyl isocyanurate.

In another preferred embodiment, the irradiation crosslinking is selected from the group consisting of high energy gamma ray irradiation crosslinking, high energy electron beam irradiation crosslinking, or photoinitiated crosslinking; the irradiation dose ranges from 5 to 1000 kGy; preferably 10-500 kGy; more preferably 50-400 kGy; most preferably 100-300 kGy; the high-energy gamma ray is derived from an artificial or natural radioisotope selected from the group consisting of cobalt (60 Co) element, cerium (137 Cs) element, zinc (65 Zn) element, mercury (203 Hg) element, yttrium (141 Ce) element, ytterbium (124 Sb) element, or yttrium (192 Ir) element; the high energy electron beam has an energy range of 0.1-10 MeV, beam range 1- 100 mA electron beam; more preferably an electron beam with an energy range of 1-10 MeV and a beam range of 1-30 mA; most preferably an energy range of 2-5 MeV, An electron beam having a beam current range of 3-15 mA; the photoinitiator comprises a photoinitiator in the raw material; the initiating light source is ultraviolet light having a wavelength range of 250-420 nm or visible light of 400-800 nm, and the illumination time is 5- 60 min; preferably an illumination time of 5-50 min; more preferably an illumination time of 10-40 min; most preferably an illumination time of 20-30 min.

In another preferred embodiment, the photoinitiator is selected from one or a mixture of two or more of the following: benzoin, benzoin dimethyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin butyl ether, diphenyl ethyl ketone , α,α-dimethoxy-α-phenylacetophenone, α,α-diethoxyacetophenone, α-hydroxyalkylphenone, α-aminoalkylphenone, aroylphosphine oxide , bisbenzoylphenylphosphine oxide, benzophenone, 2,4-dihydroxybenzophenone, Michler's ketone, thiopropoxy thioxanthone, isopropyl thioxanthone, two An aryl iodonium salt, a triaryl iodonium salt, an alkyl iodonium salt, and isopropyl boroferrocene hexafluorophosphate.

In another preferred embodiment, when the chemical crosslinking is performed, the raw material includes a peroxide crosslinking agent and/or a silane crosslinking agent.

In another preferred embodiment, the peroxide crosslinking agent is selected from the group consisting of dicumyl peroxide, di-tert-butylperoxydiisopropylbenzene, 1,1-di-tert-peroxy-3,3 , 5-trimethylcyclohexane or tert-butyl cumyl peroxide; the silane crosslinker is selected from the group consisting of methyltriacetoxysilane, methyltrimethoxysilane or methyltributyrone mercaptosilane .

In another preferred embodiment, the raw material comprises ultrahigh molecular weight polyethylene having a molecular weight of 1.0×10 ^{6 to} 10.0×10 ⁶ , high density polyethylene having a density in the range of 0.940-0.976 g/cm ³ , an antioxidant, a pore former, and a co-crosslinking agent; the weight ratio of the ultrahigh molecular weight polyethylene to the high density polyethylene in the raw material is 1:1-20; more preferably 1:2-10; most preferably 1:5-10 ;

The porogen is contained in an amount of 500 to 2000 parts by weight, more preferably 700 to 1800 parts by weight; most preferably 800 to 1600 parts by weight, based on 100 parts by weight of the mixture of the ultrahigh molecular weight polyethylene and the high density polyethylene;

Having 0.5-20 parts of an antioxidant, more preferably 1.5-16 parts by weight; most preferably 2-12 parts by weight, based on 100 parts by weight of the mixture of the ultrahigh molecular weight polyethylene and the high density polyethylene;

The mixture contains 0.1 to 10 parts by weight of the crosslinking agent, more preferably 0.5 to 5 parts by weight, most preferably 0.5 to 3 parts by weight, based on 100 parts by weight of the mixture of the ultrahigh molecular weight polyethylene and the high density polyethylene.

In another preferred embodiment, the mixture of the ultrahigh molecular weight polyethylene and the high density polyethylene is contained in an amount of 0.1 to 10 parts by weight based on 100 parts by weight; more preferably 0.5 to 5 parts by weight; most preferably 0.5- 3 parts by weight.

In another preferred embodiment, according to the mixture of the ultrahigh molecular weight polyethylene and the high density polyethylene The weight is 100 parts, and contains 0.1 to 10 parts of a peroxide crosslinking agent and/or a silane crosslinking agent; more preferably 0.5 to 5 parts by weight; most preferably 0.5 to 3 parts by weight.

In another preferred embodiment, the ultrahigh molecular weight polyethylene has a molecular weight of 2.0×10 ^{6 to} 8.0×10 ⁶ ; more preferably 3.5×10 ^{6 to} 5.0×10 ⁶ ; and the density of the high density polyethylene is 0.940. -0.960 g/cm ³ ; more preferably 0.950-0.960 g/cm ³ .

In another preferred embodiment, the pore forming agent is selected from one or a mixture of two or more of the following: natural mineral oil, C _6-15 alkane, C _8-15 aliphatic carboxylic acid, C _8-15 fat a carboxylic acid C _1-4 alkyl ester and a C _2-6 halogenated alkane.

In another preferred embodiment, the antioxidant is selected from one or a mixture of two or more of the following: 4,4-thiobis(6-tert-butylm-cresol), dibutylhydroxytoluene, sub- Phosphate ester, tert-butyl hydroquinone, β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid n-octadecyl carbonate, 1,1,3-tris(2-methyl-) 4-hydroxy-5-tert-butylphenyl)butane, 2-tert-butyl-6-methylphenol, N,N'-di-β-naphthyl p-phenylenediamine, dilauryl thiodipropionate, Tris(nonylphenyl) phosphite and triphenyl phosphite.

In a second aspect of the invention, there is provided a preparation provided by the invention as described above The battery separator obtained by the method; the separator has a thickness of 9-35 μm, a pore diameter of 0.3-0.65 μm, a porosity of 40-50%, and a difference between a closed-cell temperature and a membrane-breaking temperature of 65-90 ° C, heat The shrinkage rate is as low as 0.7%.

In a third aspect of the invention, there is provided an application of the battery separator provided by the invention as described above.

Accordingly, the present invention provides a significant improvement in the film-breaking temperature and the closed cell temperature difference as well as the heat shrinkage rate, while at the same time having the good strength, average pore size and pore size distribution of the conventional polymer separator, thereby ensuring excellent battery performance. Based on a battery separator that improves battery reliability and safety.

detailed description

The inventors have found through extensive and in-depth research that the method of preparing a battery separator by cross-linking can effectively solve the problem that the difference between the film-breaking temperature and the closed-cell temperature difference and the heat shrinkage rate of the present separator is not ideal. Further, the inventors have found that the effect of irradiation cross-linking is good, and particularly in the case where a co-crosslinking agent is used in the raw material, unexpectedly excellent effects occur. On the basis of this, the present invention has been completed.

Preparation

There are some conventional steps in the preparation of the battery separator in the art, such as, but not limited to, including mixing of raw materials, extruding the mixture from a twin-screw extruder, and then extruding through a slit die to a casting chill roll to form a ribbon, The ribbon is subjected to extraction and washing to obtain a film. However, the method for producing a battery separator of the present invention differs from the prior art in that it further includes a step of crosslinking, and the raw material contains a co-crosslinking agent. The crosslinking may be irradiation crosslinking or chemical crosslinking, preferably irradiation crosslinking. The co-crosslinking agent may be mercaptobenzothiazole, benzothiazole disulfide, N-cyclohexylbenzothiazole sulfenamide, oxydivinylbenzothiazole sulfenamide, tetramethylthiuram monosulfide, Tetramethylthiuram disulfide, zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, diphenylguanidine, di-o-tolylhydrazine, ethylenethiourea, N,N'-di Ethyl thiourea, hexamethylenetetramine, zinc isopropyl xanthate, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, tripropylene cyanurate, and three One or more compositions of allyl isocyanurate; preferably triallyl isocyanurate.

If the irradiation cross-linking is carried out, the obtained film is heat-set and wound by a conventional method in the art to obtain an uncrosslinked battery separator, and then the obtained uncrosslinked battery separator is subjected to the obtained uncrosslinked battery separator. Irradiation treatment, thereby obtaining a battery separator containing a crosslinked polymer provided by the present invention.

The irradiation treatment is selected from high energy gamma ray irradiation crosslinking, high energy electron beam irradiation crosslinking, or photoinitiated crosslinking; the irradiation dose range of high energy γ ray irradiation crosslinking or high energy electron beam irradiation crosslinking is 5-1000 kGy; preferably 10-500 kGy; more preferably 50-400 kGy; most preferably 100-300 kGy.

The high-energy gamma ray is derived from an artificial or natural radioisotope and is selected from the group consisting of cobalt (60 Co) element, cerium (137 Cs) element, zinc (65 Zn) element, mercury (203 Hg) element, and cerium (141 Ce) element.锑 (124 Sb) element, or 铱 (192 Ir) element.

The high-energy electron beam is an electron beam having an energy range of 0.1-10 MeV and a beam current range of 1-100 mA; preferably an energy range of 1-10 MeV, an electron beam having a beam range of 1-30 mA; and most preferably an energy range of 2-5 MeV, a beam range 3-15 mA electron beam.

Photoinitiating cross-linking for irradiation treatment, the raw material further contains a photoinitiator; the photoinitiator may be benzoin, benzoin dimethyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin butyl ether, diphenyl ethyl ketone , α,α-dimethoxy-α-phenylacetophenone, α,α-diethoxyacetophenone, α-hydroxyalkylphenone, α-aminoalkylphenone, aroylphosphine oxidation , bisbenzoylphenylphosphine oxide, benzophenone, 2,4-dihydroxybenzophenone, Michler's ketone, thiopropoxy thioxanthone, isopropyl thioxanthone, One or more compositions of an aryl iodonium salt, a triaryl iodonium salt, an alkyl iodonium salt, and isopropyl benzoferrocene hexafluorophosphate. The initiation source used for the photoinitiated crosslinking is ultraviolet light having a wavelength in the range of 250-420 nm or visible light in the range of 400-800 nm, and the illumination time is 5-60 min; preferably, the illumination time is 5-50 min; more preferably, the illumination time is 10-40 min. Most preferably, the illumination time is 20-30 min.

If chemical cross-linking is carried out, the raw material also contains a peroxide cross-linking agent and/or a silane cross-linking agent, and through some conventional steps, such as, but not limited to, mixing of raw materials, the mixture is extruded from a twin-screw extruder and passed through a slit. The die is extruded into a casting chill roll to form a ribbon, the ribbon is extracted, and the film is obtained by washing, and the obtained film is heat-set and wound to obtain a battery separator containing the crosslinked polymer provided by the present invention. membrane. The cross-linking agent for peroxide crosslinking may be dicumyl peroxide, di-tert-butylperoxydiisopropylbenzene, 1,1-di-tert-butylperoxy-3,3,5- One of trimethylcyclohexane, tert-butyl cumyl peroxide. The crosslinking agent used for the crosslinking of the silane may be one of methyltriacetoxysilane, methyltrimethoxysilane, and methyltributylketopoxime.

In addition to the above-mentioned co-crosslinking agent, photoinitiator, peroxide cross-linking agent, silane cross-linking agent for the crosslinking step peculiar to the present invention, the present invention of course requires some conventional raw materials for forming a battery separator, such as but not Limited to mixtures of ultra high molecular weight polyethylene and high density polyethylene, pore formers, and antioxidants.

In a preferred embodiment of the present invention, the ultrahigh molecular weight polyethylene has a molecular weight of 1.0 × 10 ^{6 -} 10.0 × 10 ⁶ , more preferably 2.0 × 10 ^{6 -} 8.0 × 10 ⁶ , most preferably 3.5 × 10 ⁶ -5.0×10 ⁶ .

In a preferred embodiment of the invention, the high density polyethylene has a density of from 0.940 to 0.976 g/cm ³ , more preferably from 0.940 to 0.960 g/cm ³ , most preferably from 0.950 to 0.960 g/cm ³ .

In a preferred embodiment of the invention, the weight ratio of the ultrahigh molecular weight polyethylene to the high density polyethylene is 1:1-20, more preferably 1:2-10, most preferably 1:5-10 .

In a preferred embodiment of the invention, the pore former may be a natural mineral oil, a C _6-15 alkane, a C _8-15 aliphatic carboxylic acid, a C _8-15 aliphatic carboxylic acid C _1-4 alkane. One or more mixtures of esters and C _2-6 haloalkanes. The porogen content is from 500 to 2000 parts by weight, more preferably from 700 to 1800 parts by weight, most preferably from 800 to 1600 parts by weight, based on 100 parts by weight of the mixture of ultrahigh molecular weight polyethylene and high density polyethylene.

In a preferred embodiment of the present invention, the antioxidant may be 4,4-thiobis(6-tert-butylm-cresol), dibutylhydroxytoluene, phosphite, tert-butyl-p-benzene. Diphenol, β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid n-octadecyl carbonate, 1,1,3-tris(2-methyl-4hydroxy-5-tert-butylbenzene Butane, 2-tert-butyl-6-methylphenol, N,N'-di-β-naphthyl p-phenylenediamine, dilauryl thiodipropionate, tris(nonylphenyl) phosphite And one or more of the esters, triphenyl phosphite. The antioxidant content is from 0.5 to 20 parts by weight, more preferably from 1.5 to 16 parts by weight, most preferably from 2 to 12 parts by weight, based on 100 parts by weight of the mixture of the ultrahigh molecular weight polyethylene and the high density polyethylene.

In a preferred embodiment of the present invention, the co-crosslinking agent is contained in an amount of from 0.1 to 10 parts by weight, more preferably from 0.5 to 5 parts by weight based on 100 parts by weight of the mixture of the ultrahigh molecular weight polyethylene and the high density polyethylene. The portion is most preferably from 0.5 to 3 parts by weight.

In a preferred embodiment of the present invention, the initiator is contained in an amount of 0.1 to 10 parts by weight, more preferably 0.5 to 5 parts by weight, based on 100 parts by weight of the mixture of the ultrahigh molecular weight polyethylene and the high density polyethylene. Most preferably it is 0.5 to 3 parts by weight.

In a preferred embodiment of the present invention, the peroxide crosslinking agent and/or the silane crosslinking agent is 0.1 to 10 parts by weight based on 100 parts by weight of the mixture of the ultrahigh molecular weight polyethylene and the high density polyethylene. It is more preferably 0.5 to 5 parts by weight, and most preferably 0.5 to 3 parts by weight.

Battery separator

The battery separator obtained by the above preparation method provided by the present invention is a battery separator containing a crosslinked polymer component, having a thickness of 9 to 35 μm, a pore diameter of 0.3 to 0.65 μm, and a porosity. 40-50%, the difference between the closed cell temperature and the membrane breakage temperature is 65-90 ° C, and the heat shrinkage rate is as low as 0.7%.

The battery separator provided by the invention can be used for a lithium ion battery, especially a power lithium ion battery.

The above-mentioned features mentioned in the present invention, or the features mentioned in the embodiments, may be arbitrarily combined. All of the features disclosed in the present specification can be used in combination with any of the compositions, and the various features disclosed in the specification can be substituted for any alternative feature that provides the same, equal or similar purpose. Therefore, unless otherwise stated, the disclosed features are only general examples of equal or similar features.

The main advantages of the invention are:

1. The present invention obtains a battery separator, in particular, a lithium ion battery separator, by a cross-linking method for the first time.

2. The battery separator provided by the present invention has excellent comprehensive properties such as lower average pore diameter, uniform pore size distribution, good porosity and film strength, especially lower closed cell temperature and higher film rupture temperature. , lower heat shrinkage rate.

The invention is further illustrated below in conjunction with specific embodiments. It is to be understood that the examples are not intended to limit the scope of the invention. The experimental methods in the following examples which do not specify the specific conditions are usually carried out according to conventional conditions or according to the conditions recommended by the manufacturer. All percentages, ratios, ratios, or parts are by weight unless otherwise indicated. The units in the weight percent by volume in the present invention are well known to those skilled in the art and, for example, refer to the weight of the solute in a 100 ml solution. Unless otherwise defined, all professional and scientific terms used herein have the same meaning as those skilled in the art. In addition, any methods and materials similar or equivalent to those described may be employed in the methods of the invention. The preferred embodiments and materials described herein are for illustrative purposes only.

The materials used in the following examples are as follows:

The antioxidant is: β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid n-octadecyl carbonate,

The co-crosslinking agent is: triallyl isocyanurate,

Photoinitiator: benzophenone,

Peroxide crosslinker: dicumyl peroxide

Silane crosslinker: methyltriacetoxysilane

Mineral oil: natural mineral oil (CAS8020-83-5, purchased from Lanzhou Petrochemical Company)

Example 1

220 g of high density polyethylene with a density of 0.956 g/cm ³ , 100 g of ultrahigh molecular weight polyethylene having a molecular weight of 5.0×10 ⁶ , 6.4 g of antioxidant, 3.2 g of co-crosslinking agent, 2200 g of mineral oil were added continuously. In the batching charging kettle, the mixture was stirred at a rate of 50 rpm, and the raw materials were uniformly mixed.

The mixture is continuously added to a twin-screw extruder, and the ultrahigh molecular weight polyethylene, high density polyethylene, antioxidant and co-crosslinking agent are continuously dissolved in mineral oil in a twin-screw extruder at 180 ° C. Then, the twin-screw extruder continuously extrudes at a speed of 200 rpm, the mixture continuously enters into the slit die, and the mixture is extruded through a slit die to a casting cooling roll, and is cast at 80 ° C. Ribbon.

The obtained ribbon was placed in an extraction tank containing dichloromethane for extraction to remove mineral oil from the ribbon. Thereafter, the extracted ribbon was continuously fed into a biaxial stretching machine at 120 ° C to be stretched into a film, and then the obtained film material was subjected to secondary extraction with dichloromethane, and the resulting film was washed with deionized water. The film was heat-set at 120 ° C for 15 minutes, and the film was wound up at a speed of 20 m / min to obtain an uncrosslinked battery separator. Cobalt (60 Co) element was selected as the γ-ray source, the irradiation dose was 50kGy, 100kGy, 200kGy, 300kGy, and the uncrosslinked separator was irradiated to obtain a separator containing cross-linked polymer. The specific performance parameters have been tested as shown in the following table:

Example 2

The obtained ribbon was placed in an extraction tank containing dichloromethane for extraction to remove mineral oil from the ribbon. Thereafter, the extracted ribbon was continuously fed into a biaxial stretching machine at 120 ° C to be stretched into a film, and then the obtained film material was subjected to secondary extraction with dichloromethane, and the resulting film was washed with deionized water. The film was heat-set at 120 ° C for 15 minutes, and the film was wound up at a speed of 20 m / min to obtain an uncrosslinked battery separator. The 5MeV electron accelerator and 8mA current were selected as the irradiation source, and the irradiation doses were 50kGy, 100kGy, 200kGy, 300kGy, respectively, and the uncrosslinked separator was irradiated to obtain a separator containing a crosslinked polymer. The specific performance parameters have been tested as shown in the following table:

Example 3

220 g of high density polyethylene having a density of 0.956 g/cm ³ , 100 g of ultrahigh molecular weight polyethylene having a molecular weight of 5.0×10 ⁶ , 6.4 g of an antioxidant, 3.2 g of a photoinitiator, 3.2 g of a co-crosslinking agent, 2200 g of mineral oil was added to the continuous batching charging kettle, and stirred at a speed of 50 rpm to uniformly mix the raw materials.

The mixture is continuously added to a twin-screw extruder, and the ultrahigh molecular weight polyethylene, high density polyethylene, antioxidant, photoinitiator and co-crosslinking agent are continuously dissolved in a twin-screw extruder at 180 ° C. In mineral oil, the product was continuously extruded at a speed of 200 rpm by a twin-screw extruder, the mixture was continuously introduced into a slit die, and the mixture was extruded through a slit die to a casting chill roll at 80 ° C. Cast into a ribbon under conditions.

The obtained ribbon was placed in an extraction tank containing dichloromethane for extraction to remove mineral oil from the ribbon. Thereafter, the extracted ribbon was continuously fed into a biaxial stretching machine at 120 ° C to be stretched into a film, and then the obtained film material was subjected to secondary extraction with dichloromethane, and the resulting film was washed with deionized water. The film was heat-set at 120 ° C for 15 minutes, and the film was wound up at a speed of 20 m / min to obtain an uncrosslinked battery separator. The uncrosslinked separator was irradiated with ultraviolet light with a wavelength range of 250-420 nm, and the irradiation time was 10 min, 15 min, 20 min, and 30 min, respectively. Finally, a separator containing a crosslinked polymer was obtained, and the specific performance parameters were obtained. The test is shown in the following table:

Example 4

220 g of high density polyethylene with a density of 0.956 g/cm ³ , 100 g of ultra high molecular weight polyethylene having a molecular weight of 5.0×10 ⁶ , 6.4 g of antioxidant, 4.8 g of peroxide crosslinker, 3.2 g of auxiliary The joint agent, 2200 g of mineral oil was added to the continuous batching charging kettle, and stirred at a speed of 50 rpm to uniformly mix the raw materials.

The mixture is continuously fed to a twin-screw extruder at 180 ° C, the ultra-high molecular weight polyethylene, high-density polyethylene, antioxidant, peroxide cross-linking agent and co-crosslinking agent in a twin-screw extruder The mixture was continuously dissolved in mineral oil, and continuously extruded by a twin-screw extruder at a speed of 200 rpm. The mixture was continuously introduced into the slit die, and the mixture was extruded through a slit die to a casting chill roll. Cast into a ribbon at 80 °C.

The obtained ribbon was placed in an extraction tank containing dichloromethane for extraction to remove mineral oil from the ribbon. Thereafter, the extracted ribbon was continuously fed into a biaxial stretching machine at 120 ° C to be stretched into a film, and then the obtained film material was subjected to secondary extraction with dichloromethane, and the resulting film was washed with deionized water. The film was heat-set at 120 ° C for 30 minutes, and the film was wound at a speed of 20 m / min to directly obtain a battery separator containing a crosslinked polymer. The specific performance parameters have been tested as shown in the following table:

Example 5

220 g of high density polyethylene with a density of 0.956 g/cm ³ , 100 g of ultra high molecular weight polyethylene having a molecular weight of 5.0×10 ⁶ , 6.4 g of antioxidant, 4.8 g of peroxide crosslinker, 4.8 g of silane The crosslinking agent, 3.2 g of the co-crosslinking agent, 2200 g of mineral oil was added to the continuous compounding charging kettle, and stirred at a speed of 50 rpm to uniformly mix the raw materials.

The mixture is continuously fed to a twin-screw extruder at 180 ° C, the ultra high molecular weight polyethylene, high density polyethylene, antioxidant, peroxide crosslinking agent, silane crosslinking agent and co-crosslinking agent The twin-screw extruder was continuously dissolved in mineral oil, and then continuously extruded by a twin-screw extruder at a speed of 200 rpm. The mixture continuously entered the slit die, and the mixture was extruded through a slit die. The chill roll was cast and cast into a ribbon at 80 °C.

The obtained ribbon was placed in an extraction tank containing dichloromethane for extraction to remove mineral oil from the ribbon. Then, the extracted ribbon was continuously fed into a biaxial stretching machine at 120 ° C to be stretched into a film, and then the obtained film material was subjected to secondary extraction with dichloromethane, and the obtained film was placed in deionized water at 95 ° C repeatedly. Wash for 15 min. The film was heat-set at 120 ° C for 15 minutes, and the film was wound at a speed of 20 m / min to directly obtain a battery separator containing a crosslinked polymer. The specific performance parameters have been tested as shown in the following table:

Comparative example 1

220 g of high density polyethylene with a density of 0.956 g/cm ³ , 100 g of ultrahigh molecular weight polyethylene having a molecular weight of 5.0×10 ⁶ , 6.4 g of antioxidant, 2200 g of mineral oil were added to the continuous dosing kettle to 50 Stir at a speed of rpm, and mix the raw materials evenly.

The obtained ribbon was placed in an extraction tank containing dichloromethane for extraction to remove mineral oil from the ribbon. Thereafter, the extracted ribbon was continuously fed into a biaxial stretching machine at 120 ° C to be stretched into a film, and then the obtained film material was subjected to secondary extraction with dichloromethane, and the resulting film was washed with deionized water. The film was heat-set at 120 ° C for 15 minutes, and the film was wound up at a speed of 20 m / min to obtain an uncrosslinked battery separator. The specific performance parameters have been tested as shown in the following table:

Comparative example 2

Comparative example 3

The results show that regardless of the cross-linking method, the temperature difference between the film-breaking temperature and the closed-cell temperature of the cross-linked polymer separator is increased from 55 °C to 65-90 °C before the cross-linking. The heat shrinkage rate after the joint is also significantly reduced, and the safety and reliability of the separator are greatly improved. Other properties, such as resistance, transmittance, open porosity, and pore size, did not deteriorate, and thus did not affect the normal use of the separator. Further comparison can also be found that the improvement effect of heat resistance obtained by different crosslinking methods is different, especially the comprehensive improvement effect of radiation crosslinking is relatively good, and the example with the addition of a crosslinking agent has heat resistance. With further improvement.

The above is only the preferred embodiment of the present invention, and is not intended to limit the scope of the technical scope of the present invention. The technical content of the present invention is broadly defined in the scope of the claims of the application, and any technical entity completed by others. The method or method, if it is identical to the scope of the claims, or equivalents, is considered to be within the scope of the claims.

Claims

A method of preparing a battery separator, which comprises obtaining a battery separator by extruding, cooling, forming, drawing, and heat-setting a mixed material, wherein the method comprises crosslinking.
The preparation method according to claim 1, wherein the crosslinking is irradiation crosslinking or chemical crosslinking; and the raw material contains a co-crosslinking agent.
The method according to claim 2, wherein the irradiation crosslinking is selected from the group consisting of high energy gamma ray irradiation crosslinking, high energy electron beam irradiation crosslinking, or photoinduced crosslinking.
The preparation method according to claim 3, wherein the irradiation dose ranges from 5 to 1000 kGy; preferably from 10 to 500 kGy; more preferably from 50 to 400 kGy; most preferably from 100 to 300 kGy.
The preparation method according to claim 3 or 4, wherein the high-energy electron beam is an electron beam having an energy range of 0.1 to 10 MeV and a beam current ranging from 1 to 100 mA; preferably an energy range of 1 to 10 MeV, and a beam current range of 1 to 3 30 mA electron beam; most preferred is an electron beam with an energy range of 2-5 MeV and a beam range of 3-15 mA.
The preparation method according to claim 3, wherein the photoinitiator comprises a photoinitiator in the raw material; the initiating light source is ultraviolet light having a wavelength in the range of 250 to 420 nm or visible light in the range of 400 to 800 nm, and the illumination time is 5-60 min; preferably illumination time 5-50 min; more preferably illumination time 10-40 min; most preferably illumination time 20-30 min.
The method according to claim 2, wherein in the chemical crosslinking, the raw material comprises a peroxide crosslinking agent and/or a silane crosslinking agent.
The process according to claim 1 or 2, wherein the raw material comprises an ultrahigh molecular weight polyethylene having a molecular weight of from 1.0 × 10 6 to 10.0 × 10 6 and having a density in the range of from 0.940 to 0.976 g/cm 3 . High density polyethylene, antioxidants, pore formers, and co-crosslinkers;

The weight ratio of the ultrahigh molecular weight polyethylene and the high density polyethylene in the raw material is 1:1-20; preferably 1:2-10; more preferably 1:5-10;

Having 500-2000 parts by weight of a pore forming agent, preferably 700-1800 parts by weight; more preferably 800-1600 parts by weight, based on 100 parts by weight of the mixture of the ultrahigh molecular weight polyethylene and the high density polyethylene;

And containing 0.5-20 parts of an antioxidant; preferably 1.5-16 parts by weight; more preferably 2-12 parts by weight, based on 100 parts by weight of the mixture of the ultrahigh molecular weight polyethylene and the high density polyethylene;

It is contained in an amount of 0.1 to 10 parts by weight of the crosslinking agent, preferably 0.5 to 5 parts by weight; more preferably 0.5 to 3 parts by weight, based on 100 parts by weight of the mixture of the ultrahigh molecular weight polyethylene and the high density polyethylene.
A battery separator obtained by the production method according to any one of claims 1 to 8; the separator has a thickness of 9 to 35 μm, a pore diameter of 0.3 to 0.65 μm, and a porosity of 40 to 50%. The difference between the closed cell temperature and the membrane breakage temperature is 65-90 ° C, and the heat shrinkage rate is as low as 0.7%.
An application of the battery separator of claim 9.