CN116207440A - Cross-linked lithium ion battery diaphragm and preparation method thereof - Google Patents
Cross-linked lithium ion battery diaphragm and preparation method thereof Download PDFInfo
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- CN116207440A CN116207440A CN202310498838.7A CN202310498838A CN116207440A CN 116207440 A CN116207440 A CN 116207440A CN 202310498838 A CN202310498838 A CN 202310498838A CN 116207440 A CN116207440 A CN 116207440A
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/411—Organic material
- H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
- H01M50/417—Polyolefins
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/403—Manufacturing processes of separators, membranes or diaphragms
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/446—Composite material consisting of a mixture of organic and inorganic materials
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
The application relates to the technical field of battery diaphragms, in particular to a cross-linked lithium ion battery diaphragm and a preparation method thereof. The invention discloses a cross-linked lithium ion battery diaphragm, which comprises the following raw material components in parts by weight: 25 parts of ultra-high molecular weight polyethylene with the weight average molecular weight of 40-150 ten thousand, 1-10 parts of high-density polyethylene, 63-73 parts of diluent, 1.4 parts of silane cross-linking agent, 0.2-0.3 part of free radical initiator, 0.1-0.3 part of water absorbent and 0.1-0.3 part of antioxidant 1010. The density of the high-density polyethylene is more than 0.93g/cm 3 The melt index was 0.3g/10min. Through the specific addition of the heat-resistant high-density polyethylene and the water absorbent, the crosslinking degree of the lithium ion battery diaphragm is improved, the heat shrinkage rate is reduced, and meanwhile, the preparation process is high in crosslinking speed and low in energy consumption.
Description
Technical Field
The application relates to the technical field of battery diaphragms, in particular to a cross-linked lithium ion battery diaphragm and a preparation method thereof.
Background
With the increase of the energy density of lithium ion batteries, the safety performance of the batteries becomes particularly important. In general, when the temperature of the battery rises above 80 ℃, the exothermic chemical reaction rate inside the battery accelerates and heats the battery core further, leading to positive temperature feedback until the separator melts to cause thermal runaway phenomenon, resulting in combustion and explosion of the battery. Typically, ultra-high molecular weight polyethylene separators have a melting point of not more than 140 ℃ at the highest, and the separators shrink and deform at high temperatures above the melting point in practical use, and in some cases, the positive and negative electrodes may contact each other, causing internal short circuits and thermal runaway, even in the event of fire.
Based on this, there have been many proposals to solve the problem of insufficient heat resistance of ultra high molecular weight polyethylene separators. For example, CN105576172a discloses a crosslinked polyethylene membrane and a manufacturing method thereof, and a porous membrane with high membrane rupture temperature is obtained, but the preparation process is complex, a crosslinking process under a 24h high-temperature and high-humidity environment is added on the basis of the original wet membrane process, the energy consumption is high, the membrane is easy to deform, and the industrialization difficulty is high. Meanwhile, CN108198986A discloses a silane crosslinked polymer isolating membrane and a preparation method thereof, wherein the preparation process is carried out after two extractions are carried out in a wet diaphragm process, the method is complex, and the membrane is inconvenient to clean.
Disclosure of Invention
The invention aims to provide a cross-linked lithium ion battery diaphragm and a preparation method thereof, wherein the cross-linked lithium ion battery diaphragm is prepared by adding high-density polyethylene (density is more than 0.93 g/cm) 3 Melt index of 0.3g/10 min) and water absorbent, and performing self-crosslinking treatment under normal temperature conditions, thereby solving the problems that the prior art needs to crosslink under a high-temperature and high-humidity environment for 24 hours, the energy consumption is high, the film is easy to deform, and the industrialization difficulty is high; meanwhile, the problem of cleaning the semi-finished film is not required.
In order to solve the technical problems, the invention adopts the following scheme:
the cross-linked lithium ion battery diaphragm comprises the following raw material components in parts by weight: 25 parts of ultra-high molecular weight polyethylene with the weight average molecular weight of 40-150 ten thousand, 1-10 parts of high-density polyethylene, 63-73 parts of diluent, 1.4 parts of silane cross-linking agent, 0.2-0.3 part of free radical initiator, 0.1-0.3 part of water absorbent and 0.1-0.3 part of antioxidant 1010.
Further, there are two chemical crosslinking modes of ultra high molecular weight polyethylene (UHMW-PE), namely hydroperoxide crosslinking and coupling agent crosslinking, respectively. The chemical crosslinking mode adopted by the invention is coupling agent crosslinking, at least one of vinyl trimethoxy silane, vinyl triethoxy silane or vinyl methoxyethoxy silane is usually adopted, and peroxide is generally used for initiation. The process of forming silane cross-linked superhigh molecular weight polyethylene includes heating peroxide to decompose into free radicals with high chemical activity, abstracting hydrogen atom from polymer molecule to change polymer main chain into active free radical, grafting with silane, and hydrolyzing and condensing the grafted superhigh molecular weight polyethylene under the action of water and silanol condensation catalyst to form cross-linking bond.
However, because only methylene exists on the molecular chain of the ultra-high molecular weight polyethylene, the silane grafting difficulty is high, and the heat-resistant high-density polyethylene (PE-RT) is introduced, the high-density polyethylene is provided with long-chain branches, the molecular branching degree is high, hydrogen on the main chain is very easy to be extracted by an initiator, so that polyethylene free radicals are generated, and the silane grafting rate and the crosslinking degree of a final product can be improved. The high-density polyethylene and the ultra-high molecular weight polyethylene can realize thermodynamic compatibility, and more lacing molecules can be formed by a copolymerization monomer of the high-density polyethylene, so that the high temperature resistance of the material is improved; while enabling a reduction in the thermal shrinkage rate of the separator below the melting point.
The water absorbent has the main function of absorbing moisture in air at normal temperature, so that silane groups are hydrolyzed to form silanol, condensation crosslinking reaction is further carried out, and the silane crosslinking reaction can only be carried out under the environment of high temperature and high humidity without the prior art. By adding the water absorbent, the production of the lithium-ion battery separator with high crosslinking degree and low thermal shrinkage rate is realized under the conditions of no equipment transformation, no energy consumption increase and no influence on productivity.
Preferably, 5-10 parts of high-density polyethylene, 63-68 parts of diluent, 0.2 part of free radical initiator, 0.3 part of water absorbent and 0.1 part of antioxidant 1010.
Preferably, the high-density polyethylene is copolymerized from ethylene and octene, the density of the high-density polyethylene is greater than 0.93g/cm3, and the melt index is 0.3g/10min.
Preferably, the diluent is at least one of paraffin oil, mineral oil, soybean oil, phthalate and fatty acid ester.
Preferably, the silane cross-linking agent is at least one of vinyltrimethoxysilane, vinyltriethoxysilane, or vinylmethoxyethoxysilane.
Preferably, the free radical initiator is at least one of 1, 1-di-tert-butylperoxycyclohexane, 2, 5-dimethyl-2, 5-di-tert-butylperoxy-3-hexyne, 1-di-tert-butylperoxy-3, 5-trimethylcyclohexane and benzoyl peroxide.
Preferably, the water absorbing agent is at least one of magnesium chloride, calcium chloride and aluminum chloride.
Preferably, the thickness of the battery separator is 9.0-9.2 mu m, the crosslinking degree is 75% -83%, the longitudinal heat shrinkage rate is 3.2-4.7%, and the transverse heat shrinkage rate is 1.1-2.3%.
The preparation method of the cross-linked lithium ion battery diaphragm comprises the following steps:
s1: uniformly mixing ultrahigh molecular weight polyethylene, high density polyethylene, a diluent, a silane cross-linking agent, a free radical initiator, a water absorbent and an antioxidant 1010 according to parts by weight, adding the mixture into a double-screw extruder, and carrying out tape casting to obtain a base film;
s2: carrying out synchronous or asynchronous longitudinal stretching and primary transverse stretching on the base film to obtain a film;
s3: extracting the film by using methylene dichloride as an extracting agent to obtain a microporous film;
s4: performing secondary transverse stretching on the extracted film to obtain a first semi-finished film;
s5: performing heat setting on the first semi-finished film to obtain a second semi-finished film;
s6: and (3) placing the second semi-finished membrane under normal temperature, and performing normal temperature self-crosslinking treatment for 24 hours to obtain the crosslinked lithium ion battery diaphragm.
Specifically, the room temperature condition in this step is a self-crosslinking treatment performed without heating and humidifying conditions in a natural state of room temperature and humidity. The invention optimizes the preparation process on the premise of improving the formula. The improvement of the formula is obtained by several experiments, the high-density polyethylene and the water absorbent are specifically introduced, under the mutual cooperation of the two, the preparation process of the battery diaphragm does not need to prepare under the conditions of high temperature and high humidity, and meanwhile, the battery diaphragm does not need to be cleaned after the secondary extraction, so that the whole film preparation process is optimized, and the production of the lithium-ion battery diaphragm with high crosslinking degree and low heat shrinkage rate is realized under the conditions of no equipment transformation, no energy consumption increase and no influence on productivity.
Preferably, in the step S1, the extrusion temperature is 185 to 230 ℃;
in the step S2, the stretching temperature of longitudinal stretching is 80-115 ℃, the stretching multiplying power is 6 times, the stretching temperature of primary transverse stretching is 95-120 ℃, and the stretching multiplying power is 8 times;
in the step S4, the stretching temperature of the secondary transverse stretching is 125-135 ℃, and the stretching multiplying power is 1.8 times.
The beneficial effects of the invention are as follows:
1. because the molecular chain of the ultra-high molecular weight polyethylene (UHMW-PE) has only methylene, the silane grafting difficulty is high, and the heat-resistant high-density polyethylene (PE-RT) is introduced, and because the polyethylene has long-chain branches, the polyethylene is easy to be subjected to hydrogen abstraction by free radicals to generate free radicals, so that the silane grafting rate and the crosslinking degree of a final product are improved;
2. by introducing heat-resistant high density polyethylene (PE-RT), the thermal shrinkage of the separator below the melting point can be reduced;
3. the water absorbent is introduced and combined with a wet process production line of the lithium battery diaphragm, and on the basis of adding heat-resistant high-density polyethylene (PE-RT), the production of the high-crosslinking-degree polyethylene diaphragm is realized without equipment modification, energy consumption increase and capacity influence, and the crosslinking speed is high.
Drawings
Fig. 1 is a process flow diagram of a method for preparing a crosslinked lithium ion battery separator according to the present invention.
Detailed Description
In order to more clearly demonstrate the objects, technical solutions and advantages of the present invention, the present application will be further described with reference to examples.
Example 1
The raw material components of the embodiment 1 of the invention are as follows in parts by weight: weight average molecular weight 40X 10 4 25 parts of Ultra High Molecular Weight Polyethylene (UHMWPE); 5 parts of high-density polyethylene (PE-RT) with the melt index of 0.3g/10 min; selecting white oil as a diluent, and 68 parts; vinyl trimethoxy silane, 1.4 parts; 0.2 part of 2, 5-dimethyl-2, 5-di-tert-butyl peroxy-3-hexyne; 0.3 parts of calcium chloride; 1010,0.1 parts of an antioxidant.
The preparation method comprises the following steps, as shown in figure 1:
(1) Uniformly mixing the raw material components in parts by weight, adding the raw material components into a double-screw extruder for melt mixing, extruding at 185-215 ℃, forming through a T-type die, and carrying out tape casting to obtain a base film;
(2) Synchronously or asynchronously carrying out longitudinal stretching and primary transverse stretching on the base film, wherein the stretching multiplying power is 6 times, and the stretching temperature is 80-105 ℃; when the film is subjected to primary transverse stretching, the stretching multiplying power is 8 times, and the stretching temperature is 95-115 ℃ to obtain the film;
(3) Extracting the film stretched synchronously or asynchronously by using dichloromethane as an extracting agent, and removing a diluent in the film to form holes to obtain a microporous film;
(4) Carrying out secondary transverse stretching on the extracted microporous membrane, wherein the stretching temperature is 125-135 ℃, and the stretching multiplying power is 1.8 times, so as to obtain a first semi-finished membrane;
(5) Performing heat setting treatment on the first semi-finished film to obtain a second semi-finished film;
(6) And (3) placing the second semi-finished membrane under normal temperature, and performing normal temperature self-crosslinking treatment for 24 hours to obtain the crosslinked lithium ion battery diaphragm.
Example 2
The invention is thatThe raw material components of the embodiment 2 of the invention are as follows in parts by weight: weight average molecular weight 80X 10 4 25 parts of Ultra High Molecular Weight Polyethylene (UHMWPE); 10 parts of high-density polyethylene (PE-RT) with the melt index of 0.3g/10 min; selecting white oil as a diluent, and 63 parts; vinyl trimethoxy silane, 1.4 parts; 0.2 part of 2, 5-dimethyl-2, 5-di-tert-butyl peroxy-3-hexyne; 0.3 parts of calcium chloride; 1010,0.1 parts of an antioxidant.
The preparation method comprises the following steps:
(1) Uniformly mixing the raw material components in parts by weight, adding the raw material components into a double-screw extruder for melt mixing, extruding at 190-220 ℃, forming through a T-type die, and carrying out tape casting to obtain a base film;
(2) Synchronously or asynchronously carrying out longitudinal stretching and primary transverse stretching on the base film, wherein the stretching multiplying power is 6 times when the base film is subjected to longitudinal stretching, and the stretching temperature is 95-115 ℃; when the film is subjected to primary transverse stretching, the stretching multiplying power is 8 times, and the stretching temperature is 100-120 ℃ to obtain the film;
(3) Extracting the film stretched synchronously or asynchronously by using dichloromethane as an extracting agent, and removing a diluent in the film to form holes to obtain a microporous film;
(4) Carrying out secondary transverse stretching on the extracted microporous membrane, wherein the stretching temperature is 125-135 ℃, and the stretching multiplying power is 1.8 times, so as to obtain a semi-finished membrane;
(5) Performing heat setting treatment on the first semi-finished film to obtain a second semi-finished film;
(6) And (3) placing the second semi-finished membrane under normal temperature, and performing normal temperature self-crosslinking treatment for 24 hours to obtain the crosslinked lithium ion battery diaphragm.
Example 3
The raw material components of the embodiment 3 of the invention are as follows in parts by weight: weight average molecular weight of 150X 10 4 25 parts of Ultra High Molecular Weight Polyethylene (UHMWPE); 5 parts of high-density polyethylene (PE-RT) with the melt index of 0.3g/10 min; selecting white oil as a diluent, and 68 parts; vinyl trimethoxy silane, 1.4 parts; 0.2 part of 2, 5-dimethyl-2, 5-di-tert-butyl peroxy-3-hexyne; 0.3 parts of calcium chloride; 1010,0.1 parts of an antioxidant.
The preparation method comprises the following steps:
(1) Uniformly mixing the raw material components in parts by weight, adding the raw material components into a double-screw extruder for melt mixing, extruding at 190-230 ℃, forming through a T-type die, and carrying out tape casting to obtain a base film;
(2) Synchronously or asynchronously carrying out longitudinal stretching and primary transverse stretching on the base film, wherein the stretching multiplying power is 6 times when the base film is subjected to longitudinal stretching, and the stretching temperature is 95-115 ℃; when the film is subjected to primary transverse stretching, the stretching multiplying power is 8 times, and the stretching temperature is 100-115 ℃ to obtain the film;
(3) Extracting the film stretched synchronously or asynchronously by using dichloromethane as an extracting agent, and removing a diluent in the film to form holes to obtain a microporous film;
(4) Carrying out secondary transverse stretching on the extracted microporous membrane, wherein the stretching temperature is 125-135 ℃, and the stretching multiplying power is 1.8 times, so as to obtain a semi-finished membrane;
(5) Performing heat setting treatment on the first semi-finished film to obtain a second semi-finished film;
(6) And (3) placing the second semi-finished membrane under normal temperature, and performing normal temperature self-crosslinking treatment for 24 hours to obtain the crosslinked lithium ion battery diaphragm.
Comparative example 1
The raw material components of the comparative example 1 of the invention are as follows in parts by weight: weight average molecular weight 40X 10 4 25 parts of Ultra High Molecular Weight Polyethylene (UHMWPE); 5 parts of high-density polyethylene (PE-RT) with the melt index of 0.3g/10 min; selecting white oil as a diluent, and 68 parts; vinyl trimethoxy silane, 1.4 parts; 0.3 part of 2, 5-dimethyl-2, 5-di-tert-butyl peroxy-3-hexyne; 0 parts of calcium chloride; 1010,0.3 parts of an antioxidant.
The preparation method of comparative example 1 according to the present invention is substantially the same as that of example 1, except that comparative example 1 is calcium chloride to which the water-absorbing agent is not added.
Comparative example 2
The raw material components of the comparative example 2 of the invention are as follows in parts by weight: weight average molecular weight 40X 10 4 25 parts of Ultra High Molecular Weight Polyethylene (UHMWPE); 0 parts of high density polyethylene (PE-RT) with a melt index of 0.3g/10 min; selectingSelecting white oil as a diluent, and 73 parts; vinyl trimethoxy silane, 1.4 parts; 0.2 part of 2, 5-dimethyl-2, 5-di-tert-butyl peroxy-3-hexyne; 0.3 parts of calcium chloride; 1010,0.1 parts of an antioxidant.
The preparation method of comparative example 2 according to the present invention is substantially the same as that of example 1, except that comparative example 2 is a polyethylene (PE-RT) having no high density added thereto
Comparative example 3
The raw material components of the comparative example 3 of the invention are as follows in parts by weight: weight average molecular weight 80X 10 4 25 parts of Ultra High Molecular Weight Polyethylene (UHMWPE); 10 parts of high-density polyethylene (PE-RT) with the melt index of 0.3g/10 min; selecting white oil as a diluent, and 63 parts; vinyl trimethoxy silane, 1.4 parts; 0.3 part of 2, 5-dimethyl-2, 5-di-tert-butyl peroxy-3-hexyne; 0 parts of calcium chloride; 1010,0.3 parts of an antioxidant.
The preparation method of comparative example 3 according to the present invention is substantially the same as that of example 2, except that the water-absorbing agent calcium chloride was not added to comparative example 3.
Comparative example 4
The raw material components of the comparative example 4 of the invention are as follows in parts by weight: weight average molecular weight 80X 10 4 25 parts of Ultra High Molecular Weight Polyethylene (UHMWPE); 0 parts of high density polyethylene (PE-RT) with a melt index of 0.3g/10 min; selecting white oil as a diluent, and 73 parts; vinyl trimethoxy silane, 1.4 parts; 0.2 part of 2, 5-dimethyl-2, 5-di-tert-butyl peroxy-3-hexyne; 0.3 parts of calcium chloride; 1010,0.1 parts of an antioxidant.
The preparation method of comparative example 4 according to the present invention is substantially the same as that of example 2, except that no high density polyethylene (PE-RT) was added to comparative example 4.
Comparative example 5
The raw material components of the comparative example 5 of the invention are as follows in parts by weight: weight average molecular weight of 150X 10 4 25 parts of Ultra High Molecular Weight Polyethylene (UHMWPE); 5 parts of high-density polyethylene (PE-RT) with the melt index of 0.3g/10 min; selecting white oil as a diluent, and 68 parts; vinyl trimethoxy silane, 1.4 parts; 0.3 part of 2, 5-dimethyl-2, 5-di-tert-butyl peroxy-3-hexyne; 0 parts of calcium chloride; antioxidant 1010,0.3Parts by weight.
The preparation method of comparative example 5 according to the present invention is substantially the same as that of example 3, except that the water-absorbing agent calcium chloride was not added to comparative example 5.
Comparative example 6
The raw material components of the comparative example 6 of the invention are as follows in parts by weight: weight average molecular weight of 150X 10 4 25 parts of Ultra High Molecular Weight Polyethylene (UHMWPE); 0 parts of high density polyethylene (PE-RT) with a melt index of 0.3g/10 min; selecting white oil as a diluent, and 73 parts; vinyl trimethoxy silane, 1.4 parts; 0.2 part of 2, 5-dimethyl-2, 5-di-tert-butyl peroxy-3-hexyne; 0.3 parts of calcium chloride; 1010,0.1 parts of an antioxidant.
The preparation method of comparative example 6 according to the present invention is substantially the same as that of example 3, except that no high density polyethylene (PE-RT) was added to comparative example 6.
Table 1 various performance index tables of example 1 to comparative example 6
As shown in table 1, example 1 was substantially the same as the preparation methods of comparative example 1 and comparative example 2, comparative example 1 was not added with a water absorbing agent, and comparative example 2 was not added with high density polyethylene; example 1 differs from example 2 in that the high density polyethylene and white oil are added in different parts by weight, and the rest is the same. By comparison, the degree of crosslinking in example 1 was found to be significantly higher than that in comparative example 1 (no water-absorbing agent added) and comparative example 2 (no high-density polyethylene added); the heat shrinkage in the machine direction and the transverse direction was significantly lower than those of comparative examples 1 and 2; meanwhile, the crosslinking degree of comparative example 1 (no water absorbent added, high density polyethylene added) was lower than that of comparative example 2 (no water absorbent added, high density polyethylene not added); the heat shrinkage of comparative example 1 was lower than that of comparative example 2. Similarly, example 2 is compared with comparative examples 3 to 4, and example 3 is compared with comparative examples 5 to 6 to obtain the same result, further proving that the water absorbing agent promotes the improvement of the crosslinking degree; high density polyethylene promotes an increase in the degree of crosslinking and reduces the heat shrinkage in the machine and transverse directions.
Further, the heat shrinkage rates of examples 1 to 3 in the transverse and longitudinal directions are significantly lower than those of comparative examples 1 to 6 by using ultra-high molecular weight polyethylene (PE-RT) with weight average molecular weight of 40 ten thousand, 80 ten thousand and 150 ten thousand and water absorbent with melt index of 0.3g/10min respectively, and it is further confirmed that the addition of heat-resistant high density polyethylene and water absorbent can improve the crosslinking degree of ultra-high molecular weight polyethylene and reduce the heat shrinkage rates in the longitudinal and transverse directions; meanwhile, the high rupture temperature of the membrane can avoid shrinkage and deformation of the membrane due to overhigh temperature, so that short circuit is generated. Furthermore, the invention is based on the raw material components, does not need to carry out secondary extraction and cleaning for crosslinking under the conditions of high temperature and high humidity, and only needs to place the second semi-finished film after heat setting under the natural conditions of normal temperature and normal humidity for self-crosslinking for 24 hours. The method does not need to carry out crosslinking under the conditions of high temperature and high humidity, does not need to carry out equipment transformation, and has the advantages of high crosslinking speed and low energy consumption, and the prepared finished film has high crosslinking degree and low thermal shrinkage.
The foregoing description of the preferred embodiment of the invention is not intended to limit the invention in any way, but rather to cover all modifications, equivalents, improvements and alternatives falling within the spirit and principles of the invention.
Claims (10)
1. The cross-linked lithium ion battery diaphragm is characterized by comprising the following raw material components in parts by weight: 25 parts of ultra-high molecular weight polyethylene with the weight average molecular weight of 40-150 ten thousand, 1-10 parts of high-density polyethylene, 63-73 parts of diluent, 1.4 parts of silane cross-linking agent, 0.2-0.3 part of free radical initiator, 0.1-0.3 part of water absorbent and 0.1-0.3 part of antioxidant 1010.
2. The cross-linked lithium ion battery separator according to claim 1, wherein the high-density polyethylene is 5-10 parts, the diluent is 63-68 parts, the free radical initiator is 0.2 part, the water absorbent is 0.3 part, and the antioxidant 1010 is 0.1 part.
3. The cross-linked lithium ion battery separator of claim 1, wherein the high-density polyethylene is copolymerized from ethylene and octene, and the density of the high-density polyethylene is greater than 0.93g/cm 3 The melt index was 0.3g/10min.
4. The crosslinked lithium ion battery separator of claim 1 wherein the diluent is at least one of paraffin oil, mineral oil, soybean oil, phthalate, fatty acid ester.
5. The crosslinked lithium ion battery separator of claim 1 wherein the silane crosslinking agent is at least one of vinyltrimethoxysilane, vinyltriethoxysilane, or vinylmethoxyethoxysilane.
6. The crosslinked lithium ion battery separator of claim 1 wherein the free radical initiator is at least one of 1, 1-di-t-butylperoxy cyclohexane, 2, 5-dimethyl-2, 5-di-t-butylperoxy-3-hexyne, 1-di-t-butylperoxy-3, 5-trimethylcyclohexane, benzoyl peroxide.
7. The cross-linked lithium ion battery separator according to claim 1, wherein the water absorbing agent is at least one of magnesium chloride, calcium chloride and aluminum chloride.
8. The cross-linked lithium ion battery separator according to claim 1, wherein the thickness of the battery separator is 9.0-9.2 μm, the cross-linking degree is 75% -83%, the longitudinal heat shrinkage rate is 3.2-4.7%, and the transverse heat shrinkage rate is 1.1-2.3%.
9. The preparation method of the cross-linked lithium ion battery diaphragm is characterized by comprising the following steps of:
s1: uniformly mixing ultrahigh molecular weight polyethylene, high density polyethylene, a diluent, a silane cross-linking agent, a free radical initiator, a water absorbent and an antioxidant 1010 according to parts by weight, adding the mixture into a double-screw extruder, and carrying out tape casting to obtain a base film;
s2: carrying out synchronous or asynchronous longitudinal stretching and primary transverse stretching on the base film to obtain a film;
s3: extracting the film by using methylene dichloride as an extracting agent to obtain a microporous film;
s4: performing secondary transverse stretching on the extracted film to obtain a first semi-finished film;
s5: performing heat setting treatment on the first semi-finished film to obtain a second semi-finished film;
s6: and (3) placing the second semi-finished membrane under normal temperature, and performing normal temperature self-crosslinking treatment for 24 hours to obtain the crosslinked lithium ion battery diaphragm.
10. The method for preparing a cross-linked lithium ion battery separator according to claim 9, wherein in the step S1, the extrusion temperature is 185-230 ℃;
in the step S2, the stretching temperature of longitudinal stretching is 80-115 ℃, the stretching multiplying power is 6 times, the stretching temperature of primary transverse stretching is 95-120 ℃, and the stretching multiplying power is 8 times;
in the step S4, the stretching temperature of the secondary transverse stretching is 125-135 ℃, and the stretching multiplying power is 1.8 times.
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