CN110945681A - Lithium battery diaphragm and preparation method thereof - Google Patents
Lithium battery diaphragm and preparation method thereof Download PDFInfo
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- CN110945681A CN110945681A CN201880000917.8A CN201880000917A CN110945681A CN 110945681 A CN110945681 A CN 110945681A CN 201880000917 A CN201880000917 A CN 201880000917A CN 110945681 A CN110945681 A CN 110945681A
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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
- H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
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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
- H01M50/443—Particulate material
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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
- H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
- H01M50/491—Porosity
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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
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Abstract
The lithium battery diaphragm comprises a base film and polyolefin films laminated on one side or two sides of the base film, wherein the base film comprises 5-25% of polyethylene and 75-95% of pore-forming agent by weight percent, and the molecular weight of the polyethylene is more than 200 ten thousand. The lithium battery diaphragm provided by the disclosure has good dimensional stability and form retention capacity, so that the diaphragm breaking temperature and the mechanical strength of the diaphragm are effectively improved, and the safety performance of the diaphragm in the application of a lithium battery is improved.
Description
The disclosure relates to the field of lithium ion batteries, in particular to a lithium battery diaphragm and a preparation method thereof.
The lithium ion battery is a preferred power supplier of the new energy automobile, and along with the rapid development of the new energy automobile, the performance requirement on the lithium ion battery matching material is higher and higher. The traditional PP and PE polyolefin diaphragms used by the lithium ion battery cannot meet the performance requirements of high safety, quick charge, high energy density, high cyclicity and the like of power easily. At present, the main improvement measures adopted for the lithium ion battery diaphragm are as follows: firstly, coating modification is carried out on a polyolefin diaphragm, so that the interface performance of the diaphragm and a battery pole piece and the heat resistance and hydrophilicity of the diaphragm are improved, an additional coating process is required, the cost is increased, micropores of the prepared diaphragm are easy to block, so that the air permeability is reduced, and the problems of failure of the coating adhesion force, falling off and the like can occur in the long-time use process; and secondly, adding a functional component in the polyolefin diaphragm forming process by adopting a blending process, wherein the mode is limited by the process (dispersibility, compatibility of the functional component and matrix resin), the adding amount of the functional component is small, and the adding component is single, so that the improvement effect is limited, and even other performances of the diaphragm can be sacrificed.
Therefore, there is a need for a separator for a lithium battery that is easy to prepare, has good stability, shape-retaining ability, mechanical strength, and safety, and is easy to process.
Disclosure of Invention
In order to overcome at least one of the above disadvantages, the present disclosure provides a lithium battery separator having high structural strength, high film breaking temperature, and good safety.
The disclosure also provides a preparation method of the lithium battery diaphragm, which is simple and suitable for large-scale production.
The object of the present disclosure is achieved mainly by the following technical measures.
A lithium battery diaphragm comprises a base film and a polyolefin film laminated on one side or two sides of the base film, wherein the base film comprises 5-25% of polyethylene and 75-95% of pore-forming agent by weight percent, and the molecular weight of the polyethylene is more than 200 ten thousand.
In a preferable mode, the thickness of the base film is 2 to 25 μm; preferably, the thickness of the base film is 3 to 15 μm; more preferably, the porosity of the base film is 35 to 55%; more preferably, the porosity of the base film is 40 to 45%.
As a preferable mode, the thickness of the polyolefin film is 1 to 5 μm; preferably, the polyolefin film has a thickness of 2 to 3 μm; more preferably, the polyolefin film has a porosity of 30 to 60%; more preferably, the polyolefin film has a porosity of 40 to 50%.
In a preferred embodiment, the polyolefin film is selected from the group consisting of polyethylene film, polypropylene and polyethylene composite base film, polyimide base film, and polyvinylidene fluoride base film.
As a preferred mode, the pore-forming agent is one selected from the group consisting of paraffin oil, saturated fatty acid, alcohol, ester, and ether.
As a preferable mode, the base film further includes a polymer in an amount of 10 to 25% by mass thereof.
In a preferred embodiment, the polymer is at least one selected from the group consisting of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, a copolymer of polyvinylidene fluoride and vinylidene chloride, polystyrene, polypropylene copolymer, poly (n-butyl acrylate), polymethyl methacrylate, polyethyl methacrylate, poly (t-butyl acrylate), polyvinyl acetate, polyacrylonitrile, and polyvinyl acetate.
Preferably, the base film further comprises 5-15% by mass of a nanoparticle material.
As a preferable mode, the nanoparticle material is at least one selected from the group consisting of silicon nitride, aluminum nitride, boron nitride, and titanium nitride; more preferably, the particle size of the nano-ionic material is 30-120 nm.
A preparation method of a lithium battery diaphragm comprises the following steps:
stirring and blending polyethylene with the molecular weight of more than 200 ten thousand and a pore-forming agent to obtain a mixed solution;
stirring the mixed solution and plasticizing at low temperature to obtain a pre-swelling body;
respectively plasticizing the pre-swelling body and the polyolefin by using a screw extruder, blending, extruding, and then carrying out tape casting, stretching and shaping by using a die head to obtain the diaphragm.
As a preferable mode, the polyethylene and the pore-forming agent are stirred and blended at the temperature of 60-120 ℃; preferably, the stirring speed is 60-150r/min, and the stirring time is 20-60 min.
As a preferable mode, the mixed solution is stirred in a screw extruder and plasticized at low temperature to obtain a pre-swelling body; the rotating speed of stirring low-temperature plasticization is 40-90r/min, the time of stirring low-temperature plasticization is 7-15min, and the temperature of stirring low-temperature plasticization is 135-170 ℃.
As a preferred mode, the extrusion temperature during extrusion is 190-230 ℃, and the extrusion rotation speed is 80-150 r/min.
As a preferable mode, before stirring and plasticizing the mixed solution at low temperature to obtain a pre-swelling body, adding a polymer into the mixed solution and uniformly stirring; preferably, the stirring is performed at 160r/min and 120-.
As a preferred mode, before the mixed solution is stirred and plasticized at low temperature to obtain a pre-swelling body, the nano particle material is added into the mixed solution and uniformly mixed; preferably, the mixing is carried out uniformly by stirring for 15-30min at 30-90 r/min.
Compared with the prior art, the advantages and the beneficial effects of the disclosure at least comprise:
1. the lithium battery diaphragm provided by the disclosure adopts the ultra-high molecular weight polyethylene with the molecular weight of more than 200 ten thousand as the diaphragm intermediate layer material, and has good dimensional stability and form retention capacity, so that the diaphragm breaking temperature and the mechanical strength of the diaphragm are effectively improved, and the safety performance of the diaphragm in the application of the lithium battery is improved.
2. The pore-forming agent is adopted to carry out two-stage pretreatment on the ultrahigh molecular weight polyethylene with the molecular weight of more than 200 ten thousand, which is used as the material of the diaphragm intermediate layer, so that the fluidity of the ultrahigh molecular weight polyethylene can be improved, the consistency of a melt is improved, and the processing difficulty is reduced.
3. The polymer and/or nanoparticle material is adopted to treat the ultrahigh molecular weight polyethylene interlayer with the molecular weight of more than 200 ten thousand, so that a synergistic effect can be generated, the structural strength and the rupture temperature of the diaphragm are improved under the condition of improving the lithium ion conductivity, and the safety performance is enhanced.
The technical solutions of the present disclosure will be clearly and completely described below with reference to the accompanying drawings and the detailed description, but those skilled in the art will understand that the following described embodiments are some, not all, of the embodiments of the present disclosure, and are only used for illustrating the present disclosure, and should not be construed as limiting the scope of the present disclosure. All other embodiments, which can be derived by a person skilled in the art from the embodiments disclosed herein without making any creative effort, shall fall within the protection scope of the present disclosure. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
The present disclosure provides a lithium battery separator including a base film and a polyolefin film laminated on one or both sides of the base film, wherein the base film includes 5-25% by weight of polyethylene and 75-95% by weight of a pore-forming agent, and the molecular weight of the polyethylene is 200 ten thousand or more.
The lithium battery diaphragm provided by the disclosure adopts the ultra-high molecular weight polyethylene with the molecular weight of more than 200 ten thousand as the middle layer material to ensure the comprehensive performance of the diaphragm, remarkably improves the mechanical strength of the diaphragm, improves the film breaking temperature and the safety performance of the diaphragm, and simultaneously uses the polyolefin as the surface layer material to control the appearance and the basic physical properties of the diaphragm, wherein the ultra-high molecular weight polyethylene with the molecular weight of more than 200 ten thousand has low flowability to cause processing difficulty, so that the special pore-forming agent is used for processing, thereby effectively improving the flowability of the material to facilitate extrusion processing operation on one hand, effectively improving the dispersion and mixing effects of the ultra-high molecular weight polyethylene and the pore-forming agent on the other hand, improving the consistency of a melt and improving the uniformity of micropores.
Optionally, the thickness of the base film is 2-25 μm; preferably, the thickness of the base film is 3 to 15 μm; more preferably, the porosity of the base film is 35 to 55%; more preferably, the porosity of the base film is 40 to 45%. The thickness and the porosity of the base film can be controlled to ensure that the base film prepared from the polyethylene material with the ultrahigh molecular weight has certain structural strength and excellent electrochemical performance, and the base film has high porosity to improve the lithium ion conductivity.
Optionally, the polyolefin film has a thickness of 1-5 μm; preferably, the polyolefin film has a thickness of 2 to 3 μm; more preferably, the polyolefin film has a porosity of 30 to 60%; more preferably, the polyolefin film has a porosity of 40 to 50%. The polyolefin film can be effectively protected by the intermediate layer and has high porosity so as to improve the lithium ion conductivity by controlling the thickness and the porosity of the polyolefin film.
Optionally, the polyolefin film is selected from one of the group consisting of polyethylene film, polypropylene and polyethylene composite base film, polyimide-based film, and polyvinylidene fluoride base film. The polyethylene film, the polypropylene and polyethylene composite base film, the polyimide base film and the polyvinylidene fluoride base film are used as the middle layer prepared from the ultra-high molecular weight polyethylene with the protective molecular weight of more than 200 ten thousand, so that the structural strength and the electrochemical performance of the diaphragm can be effectively improved, and the diaphragm breaking temperature and the safety performance of the diaphragm are improved.
Optionally, the pore former is selected from one of the group consisting of paraffin oil, saturated fatty acid, alcohol, ester, ether. Among them, preferably, the saturated fatty acid is selected from one of the group consisting of lauric acid, stearic acid, capric acid; the alcohol is selected from one of the combination of ethanol and propanol; the ester is selected from one of ethyl acetate, glyceride and isoamyl acetate; the ether is selected from one of the combination of diethyl ether and phenyl ether. The method adopts paraffin oil, saturated fatty acid, alcohol, ester, ether and the like as pore-forming agents to carry out two-stage pretreatment on the ultrahigh molecular weight polyethylene with the molecular weight of more than 200 ten thousand, can improve the fluidity of the ultrahigh molecular weight polyethylene, further improves the melting property of the ultrahigh molecular weight polyethylene and reduces the processing difficulty.
On the basis of the technical scheme, the base film also comprises a polymer with the mass of 10-25 percent; preferably, the polymer is at least one selected from the group consisting of polyvinylidene fluoride, polyvinylidene fluoride and hexafluoropropylene copolymer, polyvinylidene fluoride and vinylidene chloride copolymer, polystyrene, co-polypropylene, poly-n-butyl acrylate, polymethyl methacrylate, polyethyl methacrylate, poly-t-butyl acrylate, polyvinyl acetate, polyacrylonitrile, polyvinyl acetate. The lithium battery diaphragm provided by the disclosure can further add polymers in the base film, and the polymers can further improve the mechanical and heat-resistant properties of the diaphragm and effectively improve the diaphragm breaking temperature of the diaphragm, thereby improving the safety performance of the diaphragm.
On the basis of the technical scheme, the base film also comprises a nano particle material with the mass of 5-15 percent; preferably, the nanoparticle material is selected from at least one of the group consisting of silicon nitride, aluminum nitride, boron nitride and titanium nitride; more preferably, the particle size of the nano-ionic material is 30-120 nm. The lithium battery diaphragm that this disclosure provided can also be further add nano particle material in the base film to improve the structural strength and the high temperature resistance of the base film in intermediate level through nano particle material, thereby the effectual broken membrane temperature who improves the diaphragm improves the security performance of diaphragm.
The present disclosure also provides a method for preparing a lithium battery separator, which includes the following steps:
stirring and blending polyethylene with the molecular weight of more than 200 ten thousand and a pore-forming agent to obtain a mixed solution; optionally, the polyethylene and the pore-forming agent are stirred and blended at the temperature of 60-120 ℃; preferably, the stirring speed is 60-150r/min, and the stirring time is 20-60 min.
Stirring the mixed solution and plasticizing at low temperature to obtain a pre-swelling body; optionally, stirring the mixed solution in a screw extruder, and plasticizing at low temperature to obtain a pre-swelling body; preferably, the rotating speed of stirring low-temperature plasticization is 40-90r/min, and the time of stirring low-temperature plasticization is 7-15 min; more preferably, the temperature for stirring low-temperature plasticization is 135-170 ℃.
Respectively plasticizing, blending and extruding the pre-swelling body and the polyolefin by using a double-screw extruder, and then carrying out tape casting, stretching and shaping by using a die head to obtain a diaphragm; preferably, the extrusion temperature during extrusion is 190-230 ℃, and the extrusion rotation speed is 80-150 r/min.
The preparation method of the lithium battery diaphragm comprises the steps of mixing and stirring a pore-forming agent and a polyethylene material with the molecular weight of more than 200 ten thousand for one-time mixing treatment to obtain a mixed solution, then carrying out secondary low-temperature plasticizing treatment on the mixed solution to obtain a pre-swelling body, then respectively plasticizing the prepared pre-swelling body and polyolefin by using a screw extruder, blending, extruding, casting, stretching and shaping by using a die head to obtain the diaphragm.
Optionally, before the mixed solution is stirred and plasticized at a low temperature to obtain a pre-swelling body, adding a polymer into the mixed solution and uniformly stirring; preferably, the stirring is performed at 160r/min and 120-. Optionally, before the mixed solution is stirred and plasticized at a low temperature to obtain a pre-swelling body, adding the nano particle material into the mixed solution and uniformly mixing; preferably, the mixing is carried out uniformly by stirring for 15-30min at 30-90 r/min.
On the basis of the technical scheme, the polymer or the nano particles can be further added into the mixed solution to carry out modified crosslinking treatment on the polyethylene material with the ultrahigh molecular weight, so that the structural strength of the obtained interlayer base film is improved, the film breaking temperature is increased, and the safety performance of the diaphragm is improved.
The above-described scheme is further illustrated below with reference to specific examples and comparative examples.
Example 1
The embodiment provides a lithium battery diaphragm applied to a lithium battery, which is prepared according to the following process steps:
s11, 2kg of polyethylene with the average molecular weight of 220 ten thousand and 3kg of paraffin oil are sequentially put into a stirring tank and stirred for 40min at the stirring speed of 90r/min under the environment of 120 ℃ to obtain a mixed solution.
S12, putting the mixed solution into a double-screw extruder from a stirring tank by using an oil injection pump, and performing low-temperature plasticizing treatment for 30min at the temperature of 150 ℃ and at the speed of 120r/min to obtain a pre-swelling body.
S13, respectively putting the pre-swelling body and polyethylene with the average molecular weight of 30 ten thousand into a double-screw extruder, wherein the pre-swelling body is extruded at 220 ℃ and 120r/min to obtain uniform melts, the polyethylene with the average molecular weight of 30 ten thousand is extruded at 210 ℃ and 200r/min to obtain uniform melts, the two uniform melts are respectively put into a three-layer die head by using a melt pump, and the three-layer lithium battery diaphragm with the middle layer being a high molecular weight polyethylene layer and the upper and lower surface layers being low molecular weight polyethylene layers is obtained through casting, stretching and sizing.
The lithium battery diaphragm is detected, the thickness of the high molecular weight polyethylene layer of the basal membrane is 12 μm, and the thickness of the low molecular weight polyethylene layer of the surface layers at the two sides of the basal membrane is 3 μm.
Example 2
The embodiment provides a lithium battery diaphragm applied to a lithium battery, which is prepared according to the following process steps:
s21, 1.8kg of polyethylene with average molecular weight of 220 ten thousand and 3.5kg of lauric acid are sequentially put into a stirring tank and stirred for 50min at the stirring speed of 120r/min under the environment of 100 ℃ to obtain a mixed solution.
And S22, putting the mixed solution into a double-screw extruder from a stirring tank by using an oil injection pump, and performing low-temperature plasticizing treatment for 25min at the temperature of 160 ℃ and at the speed of 180r/min to obtain a pre-swelling body.
S23, respectively putting the pre-swelling body and polyethylene with the average molecular weight of 40 ten thousand into a double-screw extruder, wherein the pre-swelling body is extruded at 190 ℃ and 80r/min to obtain uniform melts, the polyethylene with the average molecular weight of 40 ten thousand is extruded at 200 ℃ and 90r/min to obtain uniform melts, the two uniform melts are respectively put into a three-layer die head by using a melt pump, and the three-layer lithium battery diaphragm with the middle layer being a high molecular weight polyethylene layer and the upper and lower surface layers being low molecular weight polyethylene layers is obtained through casting, stretching and sizing.
The lithium battery diaphragm is detected, the thickness of the high molecular weight polyethylene layer of the basal membrane is 15 μm, and the thickness of the low molecular weight polyethylene layer of the surface layers at the two sides of the basal membrane is 2 μm.
Example 3
The embodiment provides a lithium battery diaphragm applied to a lithium battery, which is prepared according to the following process steps:
s31, 2.5kg of polyethylene with average molecular weight of 220 ten thousand and 5kg of propanol are sequentially put into a stirring tank and stirred for 30min at the stirring speed of 70r/min under the environment of 80 ℃ to obtain a mixed solution.
S32, putting the mixed solution into a double-screw extruder from a stirring tank by using an oil injection pump, and performing low-temperature plasticizing treatment for 20min at the temperature of 130 ℃ and at the speed of 150r/min to obtain a pre-swelling body.
S33, respectively putting the pre-swelling body and polyethylene with the average molecular weight of 35 ten thousand into a double-screw extruder, wherein the pre-swelling body is extruded at 230 ℃ and 150r/min to obtain uniform melts, the polyethylene with the average molecular weight of 35 ten thousand is extruded at 200 ℃ and 140r/min to obtain uniform melts, the two uniform melts are respectively put into a three-layer die head by using a melt pump, and the three-layer lithium battery diaphragm with the middle layer being a high molecular weight polyethylene layer and the upper and lower surface layers being low molecular weight polyethylene layers is obtained through casting, stretching and sizing.
The lithium battery diaphragm is detected, the thickness of the high molecular weight polyethylene layer of the basal membrane is 10 μm, and the thickness of the low molecular weight polyethylene layer of the surface layers at the two sides of the basal membrane is 2 μm.
Example 4
The embodiment provides a lithium battery diaphragm applied to a lithium battery, which is prepared according to the following process steps:
s41, sequentially putting 2kg of polyethylene with average molecular weight of 220 ten thousand and 4kg of ethyl acetate into a stirring tank, and stirring at a stirring speed of 150r/min for 60min under the environment of 80 ℃ to obtain a mixed solution.
And S42, putting the mixed solution into a double-screw extruder from a stirring tank by using an oil injection pump, and performing low-temperature plasticizing treatment for 35min at the temperature of 120 ℃ and at the speed of 170r/min to obtain a pre-swelling body.
S43, respectively putting the pre-swelling body and polyethylene with the average molecular weight of 45 ten thousand into a double-screw extruder, wherein the pre-swelling body is extruded at 210 ℃ and 110r/min to obtain uniform melts, the polyethylene with the average molecular weight of 45 ten thousand is extruded at 200 ℃ and 150r/min to obtain uniform melts, the two uniform melts are respectively put into a three-layer die head by using a melt pump, and casting, stretching and shaping are carried out to obtain the three-layer lithium battery diaphragm with the middle layer being a high molecular weight polyethylene layer and the upper and lower surface layers being low molecular weight polyethylene.
The lithium battery diaphragm is detected, the thickness of the high molecular weight polyethylene layer of the basal membrane is 15 μm, and the thickness of the low molecular weight polyethylene layer of the surface layers at the two sides of the basal membrane is 3 μm.
Example 5
The embodiment provides a lithium battery diaphragm applied to a lithium battery, which is prepared according to the following process steps:
s51, sequentially putting 2kg of polyethylene with average molecular weight of 220 ten thousand and 3kg of diethyl ether into a stirring tank, and stirring at a stirring speed of 60r/min at the temperature of 60 ℃ for 60min to obtain a mixed solution.
And S52, putting the mixed solution into a double-screw extruder from a stirring tank by using an oil injection pump, and performing low-temperature plasticizing treatment for 20min at the temperature of 120 ℃ and at the speed of 90r/min to obtain a pre-swelling body.
S53, respectively putting the pre-swelling body and polyethylene with the molecular weight of 40 ten thousand into a double-screw extruder, wherein the pre-swelling body is extruded at 220 ℃ and 120r/min to obtain uniform melts, the polyethylene with the molecular weight of 40 ten thousand is extruded at 210 ℃ and 100r/min to obtain uniform melts, the two uniform melts are respectively put into a three-layer die head by using a melt pump, and the three-layer lithium battery diaphragm with the middle layer of a high molecular weight polyethylene layer and the upper and lower surface layers of low molecular weight polyethylene is obtained through casting, stretching and sizing.
The lithium battery diaphragm is detected, the thickness of the high molecular weight polyethylene layer of the basal membrane is 14 μm, and the thickness of the low molecular weight polyethylene layer of the surface layers at the two sides of the basal membrane is 2 μm.
Example 6
The embodiment provides a lithium battery diaphragm applied to a lithium battery, which is prepared according to the following process steps:
s61, 2kg of polyethylene with the average molecular weight of 220 ten thousand and 3kg of paraffin oil are sequentially put into a stirring tank and stirred for 40min at the stirring speed of 120r/min under the environment of 120 ℃ to obtain a mixed solution.
S62, adding 1kg of copolymer into the mixed solution, and stirring uniformly for 30min at the speed of 150r/min, wherein the copolymer is prepared by mixing polyvinylidene fluoride, poly (n-butyl acrylate) and polyvinyl acetate according to the weight ratio of 1: 1: 2 in a mass ratio;
and S63, putting the mixed solution into a double-screw extruder from a stirring tank by using an oil injection pump, and performing low-temperature plasticizing treatment for 30min at the temperature of 120 ℃ and at the speed of 90r/min to obtain a pre-swelling body.
S64, respectively putting the pre-swelling body and polyethylene with the molecular weight of 45 ten thousand into a double-screw extruder, wherein the pre-swelling body is extruded at 230 ℃ and 130r/min to obtain uniform melts, the polyethylene with the molecular weight of 45 ten thousand is extruded at 190 ℃ and 150r/min to obtain uniform melts, the two uniform melts are respectively put into a three-layer die head by using a melt pump, and casting, stretching and shaping are carried out to obtain the three-layer lithium battery diaphragm with the middle layer being a high molecular weight polyethylene layer and the upper and lower surface layers being low molecular weight polyethylene.
The lithium battery diaphragm is detected, the thickness of the high molecular weight polyethylene layer of the basal membrane is 12 μm, and the thickness of the low molecular weight polyethylene layer of the surface layers at the two sides of the basal membrane is 2 μm.
Example 7
The embodiment provides a lithium battery diaphragm applied to a lithium battery, which is prepared according to the following process steps:
s71, 2kg of polyethylene with the average molecular weight of 220 ten thousand and 3kg of paraffin oil are sequentially put into a stirring tank and stirred for 40min at the stirring speed of 120r/min under the environment of 120 ℃ to obtain a mixed solution.
S72, adding 0.8kg of copolymer into the mixed solution, stirring at 150r/min for 30min, and uniformly stirring, wherein the copolymer is prepared by mixing polyvinylidene fluoride and hexafluoropropylene copolymer, polypropylene copolymer, polyacrylonitrile and polyvinyl acetate according to the weight ratio of 1: 1: 2: 2 in a mass ratio;
and S73, putting the mixed solution into a double-screw extruder from a stirring tank by using an oil injection pump, and performing low-temperature plasticizing treatment for 30min at the temperature of 120 ℃ and at the speed of 90r/min to obtain a pre-swelling body.
S74, respectively putting the pre-swelling body and polyethylene with the molecular weight of 30 ten thousand into a double-screw extruder, wherein the pre-swelling body is extruded at 230 ℃ and 130r/min to obtain uniform melts, the polyethylene with the molecular weight of 30 ten thousand is extruded at 210 ℃ and 90r/min to obtain uniform melts, the two uniform melts are respectively put into a three-layer die head by using a melt pump, and casting, stretching and shaping are carried out to obtain the three-layer lithium battery diaphragm with the middle layer being a high molecular weight polyethylene layer and the upper and lower surface layers being low molecular weight polyethylene.
The lithium battery diaphragm is detected, the thickness of the high molecular weight polyethylene layer of the basal membrane is 10 μm, and the thickness of the low molecular weight polyethylene layer of the surface layers at the two sides of the basal membrane is 3 μm.
Example 8
The embodiment provides a lithium battery diaphragm applied to a lithium battery, which is prepared according to the following process steps:
s81, sequentially putting 2kg of polyethylene with average molecular weight of 220 ten thousand and 3kg of paraffin oil into a stirring tank, and stirring for 60min at a stirring speed of 60r/min under the environment of 60 ℃ to obtain a mixed solution.
S82, adding 0.25kg of silicon nitride into the mixed solution, stirring at 50r/min for 20min, and uniformly stirring, wherein the average particle size of the silicon nitride is 1 mu m;
and S83, putting the mixed solution into a double-screw extruder from a stirring tank by using an oil injection pump, and performing low-temperature plasticizing treatment for 30min at the temperature of 120 ℃ and at the speed of 90r/min to obtain a pre-swelling body.
S84, respectively putting the pre-swelling body and polyethylene with the molecular weight of 35 ten thousand into a double-screw extruder, wherein the pre-swelling body is extruded at 210 ℃ and 130r/min to obtain uniform melts, the polyethylene with the molecular weight of 35 ten thousand is extruded at 190 ℃ and 110r/min to obtain uniform melts, the two uniform melts are respectively put into a three-layer die head by using a melt pump, and casting, stretching and shaping are carried out to obtain the three-layer lithium battery diaphragm with the middle layer being a high molecular weight polyethylene layer and the upper and lower surface layers being low molecular weight polyethylene.
The lithium battery diaphragm is detected, the thickness of the high molecular weight polyethylene layer of the basal membrane is 12 μm, and the thickness of the low molecular weight polyethylene layer of the surface layers at the two sides of the basal membrane is 1 μm.
Example 9
The embodiment provides a lithium battery diaphragm applied to a lithium battery, which is prepared according to the following process steps:
s91, sequentially putting 2kg of polyethylene with average molecular weight of 220 ten thousand and 3kg of paraffin oil into a stirring tank, and stirring for 60min at a stirring speed of 60r/min under the environment of 60 ℃ to obtain a mixed solution.
S92, adding 0.15kg of silicon nitride and 0.15kg of boron nitride into the mixed solution, stirring at 150r/min for 30min, and uniformly stirring, wherein the average grain sizes of the silicon nitride and the boron nitride are both 0.75 mu m;
and S93, putting the mixed solution into a double-screw extruder from a stirring tank by using an oil injection pump, and performing low-temperature plasticizing treatment for 30min at the temperature of 120 ℃ and at the speed of 90r/min to obtain a pre-swelling body.
S94, respectively putting the pre-swelling body and polyethylene with the molecular weight of 55 ten thousand into a double-screw extruder, wherein the pre-swelling body is extruded at 220 ℃ and 140r/min to obtain uniform melts, the polyethylene with the molecular weight of 55 ten thousand is extruded at 200 ℃ and 110r/min to obtain uniform melts, the two uniform melts are respectively put into a three-layer die head by using a melt pump, and casting, stretching and shaping are carried out to obtain the three-layer lithium battery diaphragm with the middle layer being a high molecular weight polyethylene layer and the upper and lower surface layers being low molecular weight polyethylene.
The lithium battery diaphragm is detected, the thickness of the high molecular weight polyethylene layer of the basal membrane is 15 μm, and the thickness of the low molecular weight polyethylene layer of the surface layers at the two sides of the basal membrane is 2 μm.
Example 10
The embodiment provides a lithium battery diaphragm applied to a lithium battery, which is prepared according to the following process steps:
s101, sequentially putting 2kg of polyethylene with the average molecular weight of 220 ten thousand and 3kg of paraffin oil into a stirring tank, and stirring at a stirring speed of 60r/min for 60min at the temperature of 60 ℃ to obtain a mixed solution.
S102, adding 0.8kg of copolymer into the mixed solution, and stirring the mixture for 30min at the speed of 150r/min to be uniformly stirred, wherein the copolymer is prepared by mixing polyvinylidene fluoride and dichloroethylene copolymer, poly (n-butyl acrylate), polymethyl methacrylate, polyethyl methacrylate and poly (tert-butyl acrylate) according to the weight ratio of 2: 1: 2: 1: 2, then further adding 0.15kg of aluminum nitride and 0.15kg of titanium nitride into the mixed solution, stirring at 150r/min for 30min, and uniformly stirring, wherein the average grain sizes of silicon nitride and boron nitride are both 0.75 mu m;
s103, putting the mixed solution into a double-screw extruder from a stirring tank by using an oil injection pump, and performing low-temperature plasticizing treatment for 30min at the temperature of 120 ℃ and at the speed of 90r/min to obtain a pre-swelling body.
S104, respectively putting the pre-swelling body and polyethylene with the molecular weight of 60 ten thousand into a double-screw extruder, wherein the pre-swelling body is extruded at 190 ℃ and 90r/min to obtain uniform melts, the polyethylene with the molecular weight of 60 ten thousand is extruded at 210 ℃ and 110r/min to obtain uniform melts, the two uniform melts are respectively put into a three-layer die head by using a melt pump, and casting, stretching and shaping are carried out to obtain the three-layer lithium battery diaphragm with the middle layer being a high-molecular-weight polyethylene layer and the upper and lower surface layers being low-molecular-weight polyethylene.
The lithium battery diaphragm is detected, the thickness of the high molecular weight polyethylene layer of the basal membrane is 13 μm, and the thickness of the low molecular weight polyethylene layer of the surface layers at the two sides of the basal membrane is 2 μm.
Comparative example 1
Comparative example 1 provides a lithium battery separator applied to a lithium battery, which is prepared according to the following process steps:
s111, sequentially putting 2kg of polyethylene with the average molecular weight of 50 ten thousand and 3kg of paraffin oil into a stirring tank, and stirring at a stirring speed of 120r/min for 40min at 90 ℃ to obtain a mixed solution;
and S112, putting the mixed solution into a double-screw extruder from a stirring tank by using an oil injection pump, and performing low-temperature plasticizing treatment for 30min at the temperature of 120 ℃ and at the speed of 90r/min to obtain a pre-swelling body.
S113, respectively putting the pre-swelling body and polyethylene with the molecular weight of 50 ten thousand into a double-screw extruder, wherein the pre-swelling body is extruded at 200 ℃ and 140r/min to obtain uniform melts, the polyethylene with the molecular weight of 50 ten thousand is extruded at 190 ℃ and 110r/min to obtain uniform melts, the two uniform melts are put into a three-layer die head by using a melt pump, and casting, stretching and shaping are carried out to obtain the three-layer lithium battery diaphragm with the middle layer being a high-molecular-weight polyethylene layer and the upper and lower surface layers being low-molecular-weight polyethylene.
The lithium battery diaphragm is detected, the thickness of the high molecular weight polyethylene layer of the basal membrane is 15 μm, and the thickness of the low molecular weight polyethylene layer of the surface layer on both sides of the basal membrane is 2 μm.
The puncture strength and the rupture temperature of the lithium battery separators prepared in the above examples 1 to 10 and comparative example 1 were measured, respectively, and the results are shown in the following table 1:
table 1 test data structures of lithium battery separators provided in examples of the present invention and comparative examples
As can be seen from table 1 above, the lithium battery separator prepared according to the preparation method disclosed by the present disclosure has the advantages of high puncture strength, high film breaking temperature, and small high-temperature heat shrinkage, and each index is obviously superior to that of the lithium battery separator prepared according to the conventional technical scheme in comparative example 1.
While particular embodiments of the present disclosure have been illustrated and described, it will be appreciated that the above embodiments are merely illustrative of the technical solutions of the present disclosure and are not limiting thereof; those of ordinary skill in the art will understand that: modifications may be made to the above-described embodiments, or equivalents may be substituted for some or all of the features thereof without departing from the spirit and scope of the present disclosure; the modifications or the substitutions do not cause the essence of the corresponding technical solutions to depart from the scope of the technical solutions of the embodiments of the present disclosure; accordingly, it is intended to cover in the appended claims all such alternatives and modifications that are within the scope of the disclosure.
The lithium battery diaphragm provided by the disclosure adopts ultra-high molecular weight polyethylene with the molecular weight more than 200 ten thousand as the diaphragm intermediate layer material, and has good dimensional stability and form retention capacity, so that the diaphragm breaking temperature and the mechanical strength of the diaphragm are effectively improved, and the safety performance of the diaphragm in the application of a lithium battery is improved. The preparation method of the lithium battery diaphragm provided by the disclosure is simple in process, convenient to operate and suitable for large-scale production and manufacturing.
Claims (15)
- A lithium battery separator characterized by: the polyolefin film comprises a base film and a polyolefin film laminated on one side or two sides of the base film, wherein the base film comprises 5-25% of polyethylene and 75-95% of pore-forming agent by weight, and the molecular weight of the polyethylene is more than 200 ten thousand.
- The lithium battery separator according to claim 1, wherein: the thickness of the base film is 2-25 μm; preferably, the thickness of the base film is 3 to 15 μm; more preferably, the porosity of the base film is 35 to 55%; further preferably, the porosity of the base film is 40 to 45%.
- The lithium battery separator according to claim 1 or 2, characterized in that: the thickness of the polyolefin film is 1-5 μm; preferably, the polyolefin film has a thickness of 2 to 3 μm; more preferably, the polyolefin film has a porosity of 30 to 60%; further preferably, the polyolefin film has a porosity of 40 to 50%.
- The lithium battery separator according to any one of claims 1 to 3, wherein: the polyolefin film is selected from one of the group consisting of polyethylene film, polypropylene and polyethylene composite base film, polyimide base film and polyvinylidene fluoride base film.
- The lithium battery separator according to any one of claims 1 to 4, wherein: the pore-forming agent is one selected from the group consisting of paraffin oil, saturated fatty acid, alcohol, ester and ether.
- The lithium battery separator according to any one of claims 1 to 5, wherein: the base film also includes a polymer in an amount of 10 to 25% by mass thereof.
- The lithium battery separator according to claim 6, wherein: the polymer is selected from at least one of polyvinylidene fluoride, polyvinylidene fluoride and hexafluoropropylene copolymer, polyvinylidene fluoride and dichloroethylene copolymer, polystyrene, co-polypropylene, poly (n-butyl acrylate), polymethyl methacrylate, polyethyl methacrylate, poly (tert-butyl acrylate), polyvinyl acetate, polyacrylonitrile and polyvinyl acetate.
- The lithium battery separator according to any one of claims 1 to 7, wherein: the base film also comprises 5-15% by mass of a nanoparticle material.
- The lithium battery separator according to claim 8, wherein: the nano particle material is selected from at least one of the group consisting of silicon nitride, aluminum nitride, boron nitride and titanium nitride; more preferably, the particle size of the nano ionic material is 30-120 nm.
- The method for preparing a lithium battery separator as claimed in any one of claims 1 to 5, comprising the steps of:stirring and blending polyethylene with the molecular weight of more than 200 ten thousand and a pore-forming agent to obtain a mixed solution;stirring the mixed solution and plasticizing at low temperature to obtain a pre-swelling body;and respectively plasticizing, blending and extruding the pre-swelling body and the polyolefin by using a screw extruder, and then carrying out tape casting, stretching and shaping by using a die head to obtain the diaphragm.
- The method for preparing a lithium battery separator as claimed in claim 10, wherein the polyethylene and the pore-forming agent are blended with stirring at 60 to 120 ℃; preferably, the stirring speed is 60-150r/min, and the stirring time is 20-60 min.
- The method for producing a lithium battery separator according to claim 10 or 11, wherein the mixed solution is stirred in a screw extruder and plasticized at a low temperature to obtain the pre-swollen body; the rotating speed of stirring low-temperature plasticization is 40-90r/min, the time of stirring low-temperature plasticization is 7-15min, and the temperature of stirring low-temperature plasticization is 135-170 ℃.
- The method for preparing the lithium battery separator as claimed in any one of claims 10 to 12, wherein the extrusion temperature during the extrusion is 190 ℃ and 230 ℃, and the extrusion rotation speed is 80 to 150 r/min.
- The method for manufacturing a lithium battery separator according to any one of claims 10 to 13, wherein a polymer is added to the mixed solution and uniformly stirred before the mixed solution is stirred and plasticized at a low temperature to obtain a pre-swollen body; preferably, the stirring is performed at 160r/min and 120-.
- The method for manufacturing a lithium battery separator according to any one of claims 10 to 14, wherein the nanoparticle material is added to the mixed solution and mixed uniformly before the mixed solution is stirred and plasticized at a low temperature to obtain a pre-swollen body; preferably, the mixing is carried out uniformly by stirring for 15-30min at 30-90 r/min.
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| PCT/CN2018/097066 WO2020019203A1 (en) | 2018-07-25 | 2018-07-25 | Lithium battery separator and preparation method therefor |
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Cited By (2)
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| CN115764159A (en) * | 2023-01-09 | 2023-03-07 | 星源材质(南通)新材料科技有限公司 | Three-layer lithium battery diaphragm and preparation method thereof |
| CN117175141A (en) * | 2023-07-31 | 2023-12-05 | 中国科学院大连化学物理研究所 | Lithium battery diaphragm and preparation method and application thereof |
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