CN110718650B - Lithium battery inner layer composite membrane with super-strong corrosion resistance and preparation method thereof - Google Patents
Lithium battery inner layer composite membrane with super-strong corrosion resistance and preparation method thereof Download PDFInfo
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- CN110718650B CN110718650B CN201910984194.6A CN201910984194A CN110718650B CN 110718650 B CN110718650 B CN 110718650B CN 201910984194 A CN201910984194 A CN 201910984194A CN 110718650 B CN110718650 B CN 110718650B
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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
- H01M50/10—Primary casings, jackets or wrappings of a single cell or a single battery
- H01M50/116—Primary casings, jackets or wrappings of a single cell or a single battery characterised by the 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
- H01M50/10—Primary casings, jackets or wrappings of a single cell or a single battery
- H01M50/116—Primary casings, jackets or wrappings of a single cell or a single battery characterised by the material
- H01M50/124—Primary casings, jackets or wrappings of a single cell or a single battery characterised by the material having a layered structure
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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 invention discloses a lithium battery inner layer composite membrane with super-strong corrosion resistance and a preparation method thereof, wherein the lithium battery inner layer composite membrane is obtained by sequentially coating polyethylene glycol terephthalate and polyvinyl butyral on the upper surface and the lower surface of an inner layer base membrane and then compounding the inner layer base membrane and the polyethylene glycol terephthalate and the polyvinyl butyral by an extrusion compounding method; the inner-layer base film is prepared from 18.5-51.7 parts of terpolymer polypropylene, 28.4-52.8 parts of homopolymerized polypropylene, 17.6-55.6 parts of mixed polypropylene, 1.3-15.5 parts of graphene, 0.52-9 parts of crosslinking monomer, 0.28-9.4 parts of initiator and 4.3-10.6 parts of nylon by weight, and solves the problems of puncture resistance, electrolyte resistance, high barrier, high insulation and poor high heat seal strength of the inner-layer base film.
Description
Technical Field
The invention belongs to the technical field of production of inner-layer composite membranes of lithium batteries, and particularly relates to an inner-layer composite membrane of a lithium battery with super-strong corrosion resistance and a preparation method thereof.
Background
The electrolyte of the lithium battery contains various organic solvents, the organic solvents usually swell, dissolve and absorb flexible packaging materials, and in addition, the organic solvents can dissolve the adhesive of the composite film, so that the bonding effect between the composite layers is damaged, the concentration of each component in the electrolyte is changed, the electrical property of the battery is further influenced, and the inner film of the lithium battery needs to have electrolyte resistance.
The periphery of the lithium ion battery core is provided with burrs of the copper net and the aluminum net, when the package is vacuumized, the flexible package film shrinks, the burrs can fiercely pierce the inner film, if the inner film is pierced to the aluminum layer, hydrofluoric acid in the battery core is directly led to the aluminum foil to cause punctiform corrosion, and the battery is scrapped, so that the inner layer composite film of the lithium battery has puncture resistance.
The utmost point ear of battery core will carry out the heat-seal through two-layer plastic-aluminum complex film, will guarantee utmost point ear and packaging material not short circuit and the interior electrolyte of battery is long-time not outwards leaked to require that the packaging material inlayer heat sealability is good.
The electrolyte of the lithium battery contains lithium salt which can rapidly generate strong corrosive hydrofluoric acid when meeting water, so that the defects of gas expansion and the like are caused, and the inner-layer composite film is required to have extremely high water vapor barrier property.
In the structure of the lithium battery, a flexible packaging film is positioned between a positive electrode and a negative electrode and mainly used for separating positive and negative active substances and preventing the two electrodes from short circuit caused by contact, so that the flexible packaging film of the lithium battery is required to have high insulation.
However, the existing lithium battery flexible packaging film in the market at present does not have the characteristics of puncture resistance, electrolyte resistance, high barrier property, high insulation, high heat sealing strength and the like.
Disclosure of Invention
The invention aims to provide a lithium battery inner layer composite film with super-strong corrosion resistance and a preparation method thereof, and aims to solve the problems of puncture resistance, electrolyte resistance, high barrier property, high insulation and high heat seal strength of a flexible packaging film inner layer of a power lithium battery in the background.
The technical problems to be solved by the invention are as follows:
1. how to prepare the inner base film.
2. How to determine a reasonable inner-layer composite membrane structure.
3. How to select the material for making the inner base film.
In order to achieve the purpose, the invention provides the following technical scheme:
the lithium battery inner layer composite membrane with super-strong corrosion resistance is obtained by sequentially coating polyethylene glycol terephthalate and polyvinyl butyral on the upper surface and the lower surface of an inner layer base membrane and then compounding the inner layer base membrane and the polyethylene glycol terephthalate and the polyvinyl butyral by an extrusion compounding method;
the inner-layer base film is prepared from 18.5-51.7 parts of terpolymer polypropylene, 28.4-52.8 parts of homopolymerized polypropylene, 17.6-55.6 parts of mixed polypropylene, 1.3-15.5 parts of graphene, 0.52-9 parts of crosslinking monomer, 0.28-9.4 parts of initiator and 4.3-10.6 parts of nylon by weight;
the preparation steps of the inner base film are as follows:
1) 18.5-51.7 parts of ternary copolymer polypropylene, 0.5-5 parts of graphene, 0.2-3 parts of pentaerythritol tetraacrylate and 0.1-3 parts of dicumyl peroxide are mixed to obtain a first mixture;
2) 28.4-52.8 parts of homopolymerized polypropylene, 0.5-5 parts of graphene, 0.2-3 parts of pentaerythritol tetraacrylate and 0.1-3 parts of dicumyl peroxide are mixed to obtain a second mixture;
3) 17.6-55.6 parts of mixed polypropylene, 0.5-5 parts of graphene, 0.2-3 parts of pentaerythritol tetraacrylate and 0.1-3 parts of dicumyl peroxide are mixed to obtain a third mixture;
4) placing the first mixture, the second mixture and the third mixture into a feed port of a double-screw extruder;
5) carrying out micro-crosslinking reaction on the first mixture, the second mixture and the third mixture in a double-screw extruder to obtain a polypropylene product in a micro-crosslinking state; the micro-crosslinking reaction enables the ternary copolymer polypropylene, the homo-polypropylene and the mixed polypropylene to be linked into a net-shaped high-molecular mechanism in a covalent bond mode, and the layer-to-layer compounding is achieved under the condition that no adhesive is used, so that the internal resistance of the battery is reduced, the internal consumption of the battery is reduced, and the performance of the battery is improved.
6) Extruding the polypropylene product in a micro-crosslinking state and 4.3-10.6 parts by weight of nylon into a T-shaped die head through a double-screw extruder, casting the polypropylene product in a sheet shape to the roll surface of a casting roller which rotates stably through casting equipment after the polypropylene product is extruded out of the T-shaped die head, and cooling and shaping the casting roller to obtain an inner-layer base film; the casting equipment comprises the following steps: firstly, adjusting the position of a rotating shaft in a sliding groove in the precision plate according to a positioning plate, screwing a nut, fixing a casting roller between the two precision plates, opening a first motor, a second motor, a corona motor and a fan, and carrying out casting corona on a film through the casting roller and the corona roller to obtain an inner-layer base film.
Preferably, the mixed polypropylene is a mixture of polypropylene and polyethylene according to the mass fraction of 4: 1, mixing to obtain; the thickness of the inner base film is 37-65 μm, and the number of layers is four; the thicknesses of the ternary copolymer polypropylene, the homopolymerized polypropylene, the mixed polypropylene and the nylon are as follows in sequence: 10-20 μm, 15-20 μm, 10-20 μm, 2-5 μm.
Preferably, the crosslinking monomer is one of pentaerythritol tetraacrylate, glycerol triacrylate, divinylbenzene or triacrylate isocyanurate.
Preferably, the initiator is dicumyl peroxide or 2, 5-dimethyl-2, 5-di (t-butylperoxy) hexane.
Preferably, the temperature of the compression section of the double-screw extruder is 100-170 ℃, the temperature of the homogenization section is 200 ℃, the temperature of the head and the die section is 175-210 ℃, and the rotating speed of the screw is 35-45 r/min.
Preferably, the casting equipment comprises a fixed base, fixed plates and support bases, wherein a plurality of support bases are uniformly welded at the bottom of the fixed base, the fixed plates are welded at two sides of the surface of the fixed base, the two fixed plates are both provided with fixed frames, a fan fixed plate is welded between the two fixed frames, and a fan is arranged at the bottom of the fan fixed plate;
the bottom parts of the two fixing frames are fixedly welded with precision plates, sliding grooves are formed in the two precision plates, scales are arranged on two sides of each sliding groove, positioning plates are mounted on one sides of the two precision plates, the precision plates are perpendicular to and movably connected with the positioning plates, the other ends of the two positioning plates are movably mounted on the surfaces of the fixing frames, a casting roller is mounted between the two precision plates, a rotating shaft penetrates through the sliding grooves, the casting roller and the positioning plates and is fixed between the two precision plates through nuts, L-shaped fixing plates are fixedly welded below the two positioning plates, a corona roller is mounted between the two L-shaped fixing plates and is connected with a corona motor mounted in the fixing base through a wire, and the rotating shaft penetrates through the corona roller and movably fixes the corona roller between the two L-shaped fixing plates through the nuts;
a first motor is installed on one side of the fixing plate, a second rotating wheel is installed on the first motor, a second driven wheel is installed at one end of the casting roller on the same side of the first motor, the second rotating wheel and the second driven wheel are connected through a rotating belt, a second motor is installed below the first motor, a first rotating wheel is installed on the second motor, a first driven wheel is installed at one end of the corona roller on the same side of the second motor, and the first rotating wheel is connected with the first driven wheel through the rotating belt;
the casting heat sealing temperature is 230-250 ℃, the casting roller temperature is 30 ℃, the air flow is increased in the cooling process, and the tightening tension is 38-42 dyn/cm.
Preferably, the preparation method of the lithium battery inner layer composite membrane comprises the following steps:
firstly, coating polyethylene glycol terephthalate on the upper surface and the lower surface of the obtained inner-layer base film in a coating machine to obtain a first product of an inner-layer composite film; then coating polyvinyl butyral on the upper and lower surfaces of the inner-layer base film to obtain a second product of the inner-layer composite film;
compounding the second product of the inner layer composite film by an extrusion compounding method to obtain an inner layer composite film, wherein the extrusion compounding temperature of the extrusion compounding machine is 210-240 ℃, and ethylene acrylic acid copolymer with the thickness of 3-4 mu m is selected as extrusion resin; the AC agent is selected from isocyanate or carbamate, and the coating weight is 0.2-0.8g/m2The method adopts the extrusion compounding method to compound, thereby avoiding the defect that the cross-linking agent in the common compounding is not resistant to electrolyte solvents.
Preferably, in the first step, the polyethylene terephthalate is coated with 2 layers and has a thickness of 0.02-0.04mm, and the polyvinyl butyral is coated with 1 layer and has a thickness of 0.02-0.04 mm.
The invention has the beneficial effects that:
(1) the inner-layer composite membrane is prepared by adopting a multi-layer co-extrusion method, the terpolymer polypropylene is taken as the innermost layer, the homopolymer polypropylene, the mixed polypropylene and the nylon sequentially form other layers, a small amount of reactive monomer with 3 or more functional groups of pentaerythritol tetraacrylate is added into the raw materials of each polypropylene layer, peroxide (such as dicumyl peroxide) is taken as an initiator, micro-crosslinking of each polypropylene layer is realized in the extrusion processing process, the polypropylene in a micro-crosslinking state is enabled to be connected into a net structure by sequentially passing through covalent bonds, and the polypropylene in the micro-crosslinking state has good fluidity and elasticity, so that the characteristics of puncture resistance, high barrier property and the like of the base membrane of the inner layer are improved.
(2) In addition, in the process of preparing the polypropylene in a micro-crosslinking state, barrier graphene is added, so that the requirements of the inner layer of the lithium battery flexible packaging film on puncture resistance, high insulation, high barrier and high heat sealing strength are met; according to the casting equipment, the film is clicked by the corona roller to be subjected to corona modification while the cylinder surface of the casting roller is cooled, so that the surface of the inner-layer base film is clean, the inner-layer base film can be coated conveniently in the rear direction, the coating is more uniformly coated on the surface of the inner-layer base film to a certain extent, and the coating quality of the inner-layer base film is ensured.
(3) The polyethylene terephthalate has excellent mechanical properties, the long-term use temperature can reach 120 ℃, the electrical insulation property is excellent, and the polyethylene terephthalate has excellent gas barrier and water resistance; the polyvinyl butyral has the excellent characteristics of higher corrosion resistance, cold resistance, impact resistance and ultraviolet irradiation resistance, so that the polyethylene glycol terephthalate is firstly coated on the inner layer base film, then the polyvinyl butyral is coated, and the extrusion compounding method is adopted for compounding, thereby avoiding the defect that the cross-linking agent in the common compounding is not resistant to an electrolyte solvent, and meeting the requirements of the inner layer on electrolyte resistance, high insulation and puncture resistance.
Drawings
FIG. 1 is a schematic view of a main structure of a casting apparatus;
FIG. 2 is a schematic left view of the casting apparatus;
FIG. 3 is a schematic view of a right side of the casting apparatus;
in the figure: 1. a fixing plate; 2. a fixed mount; 3. a fan fixing plate; 4. a fan; 5. a first motor; 6. a rotating shaft; 7. a second motor; 8. a fixed base; 9. a corona motor; 10. an L-shaped fixing plate; 11. a corona roller; 12. a casting roll; 13. a support base; 14. a precision plate; 15. positioning a plate; 16. a first rotating wheel; 17. a second rotating wheel; 18. a first driven wheel; 19. a second driven wheel.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1:
referring to fig. 1 to 3, an inner layer composite film of a lithium battery having superior corrosion resistance is obtained by sequentially coating polyethylene terephthalate and polyvinyl butyral on the upper and lower surfaces of an inner layer base film, and then laminating the inner layer composite film by an extrusion method;
the inner base film is prepared by the following preparation steps:
1) mixing 20 parts of ternary copolymer polypropylene, 0.5 part of graphene, 0.2 part of pentaerythritol tetraacrylate and 0.2 part of dicumyl peroxide to obtain a first mixture; the graphene is mixed with the ternary copolymer polypropylene to achieve the purpose of mixing modification;
2) 30 parts of homopolymerized polypropylene, 0.5 part of graphene, 0.2 part of pentaerythritol tetraacrylate and 0.2 part of dicumyl peroxide are mixed to obtain a second mixture;
3) firstly, mixing polypropylene and polyethylene according to the mass fraction of 4: 1, mixing to obtain mixed polypropylene, and then mixing 20 parts of the mixed polypropylene, 0.5 part of graphene, 0.2 part of pentaerythritol tetraacrylate and 0.2 part of dicumyl peroxide to obtain a third mixture;
4) placing the first mixture, the second mixture and the third mixture into a feed port of a double-screw extruder;
5) setting the rotating speed of the double-screw extruder at 35r/min, the temperature of a compression section at 140 ℃, the temperature of a homogenization section at 200 ℃ and the temperature of a machine head and a mouth mold section at 195 ℃;
6) and under the condition of 5), carrying out micro-crosslinking reaction on the first mixture, the second mixture and the third mixture in a double-screw extruder to obtain a polypropylene product in a micro-crosslinked state;
7) extruding the polypropylene product in a micro-crosslinking state and 5 parts of nylon into a T-shaped die head together through a double-screw extruder, casting the polypropylene product in a sheet shape to the roll surface of a stably rotating casting roller through casting equipment after the polypropylene product and the nylon are extruded out through the T-shaped die head, and cooling and shaping a diaphragm on the casting roller to obtain an inner-layer base film with a four-layer structure; the casting equipment comprises the following steps: first, the position of the rotating shaft 6 in the sliding groove inside the precision plate 14 is adjusted according to the positioning plate 15, the nut is tightened, the casting roller 12 is fixed between the two precision plates 14, the first motor 5, the second motor 7, the corona motor 9 and the fan 4 are opened, and the film is subjected to corona casting through the casting roller 12 and the corona roller 11 to obtain an inner base film.
The inner base film uses ternary polymerization polypropylene as the innermost layer, and consists of other layers of homopolymerization polypropylene, mixed polypropylene and nylon in sequence, and the thicknesses of the layers are as follows in sequence: 10 μm, 15 μm, 10 μm, 2 μm, and the thickness of the inner base film is 37 μm;
the casting equipment comprises a fixed base 8, fixed plates 1 and supporting bases 13, wherein the supporting bases 13 are uniformly welded at the bottom of the fixed base 8, the fixed plates 1 are welded at two sides of the surface of the fixed base 8, the fixed frames 2 are respectively installed on the two fixed plates 1, a fan fixed plate 3 is welded between the two fixed frames 2, and a fan 4 is arranged at the bottom of the fan fixed plate 3;
a first motor 5 is installed on one side of the fixed plate 1, a second rotating wheel 17 is installed on the first motor 5, a second driven wheel 19 is installed at one end of the casting roller 12 on the same side of the first motor 5, the second rotating wheel 17 and the second driven wheel 19 are connected through a rotating belt, a second motor 7 is installed below the first motor 5, a first rotating wheel 16 is installed on the second motor 7, a first driven wheel 18 is installed at one end of the corona roller 11 on the same side of the second motor 7, and the first rotating wheel 16 is connected with the first driven wheel 18 through the rotating belt;
the casting equipment conditions are respectively as follows: the casting heat sealing temperature is 230 ℃, the casting roller temperature is 30 ℃, the air flow is increased in the cooling process, and the tightening tension is 38 dyn/cm;
the preparation method of the lithium battery inner layer composite membrane comprises the following steps:
step one, putting the inner-layer base film obtained in the step 7) into a coating machine, and finishing the coating work of 2 layers of polyethylene terephthalate on the upper surface and the lower surface of the inner-layer base film in the coating machine by using a narrow-slit extrusion coating method, wherein the coating thickness is 0.02mm, so as to obtain a first product of the inner-layer composite film.
And step two, coating 1 layer of polyvinyl butyral with the thickness of 0.02mm on the upper surface and the lower surface of the first product of the inner-layer composite film in the step one to obtain a second product of the inner-layer composite film.
Step three, compounding the second product of the inner layer composite film by an extrusion compounding method to obtain the inner layer composite film, wherein the extrusion compounding temperature is 210 ℃, the extrusion compounding resin is ethylene acrylic acid copolymer, the thickness of the resin is 4 mu m, the coating weight of the AC agent is 0.3g/m2。
The performance test of the inner-layer composite membrane comprises the following specific steps:
firstly, performing an inner layer composite film puncture resistance test: using an electronic tensile testing machine to test the puncture strength of the membrane, firstly mounting a test piece with the diameter of 100mm on a sample membrane fixing clamping ring, then using a steel needle with the diameter of 1.0mm and the diameter top end radius of 0.5mm to take a top prick at the speed of (50 +/-5) mm/min, reading the maximum load of the steel needle penetrating through the test piece, and taking the arithmetic average value of the test pieces, wherein the number of the test pieces is more than 5;
secondly, carrying out electrolyte resistance test on the inner layer composite membrane: immersing the inner-layer composite membrane with certain mass and size in electrolyte at 50 ℃ for 5h, then taking out the inner-layer composite membrane, weighing and measuring the size again after cleaning and drying, and comparing the change of the mass and size of the inner-layer composite membrane before and after soaking;
next, an inner layer composite film high barrier test was performed: placing the inner-layer composite membrane in an air permeability detector, and allowing air with a certain volume to penetrate through the inner-layer composite membrane with a specified area under a certain pressure for a certain time; placing the inner-layer composite membrane into a water vapor transmission rate tester, wherein nitrogen with stable relative humidity flows at one side of the inner-layer composite membrane, dry nitrogen flows at the other side of the inner-layer composite membrane, water vapor can penetrate through the inner-layer composite membrane from a high-humidity side to diffuse to low humidity due to the existence of a humidity gradient, and parameters such as water vapor transmission rate and the like are obtained through analysis and calculation of a low-humidity side sensor;
subsequently, an inner layer composite film high insulation test is carried out: the probe is inserted into any edge sealing of the soft package lithium battery, so that the probe is contacted with the aluminum-plastic layer, the probe and the positive electrode lug or the negative electrode lug of the lithium battery are respectively connected with two poles of a voltage-adjustable direct-current power supply through a lead, the power supply is started, and whether the edge sealing of the battery has the phenomena of liquid leakage, breakdown or smoking is observed;
subsequently, the inner layer composite film high heat seal strength test was performed: the electronic tension testing machine is used for clamping the inner-layer composite film between two chucks of the clamp, the two chucks move relatively, and force value change and displacement change in the experimental process are collected through a force value sensor located on the chuck and a displacement sensor arranged in the machine, so that the heat sealing strength of the inner-layer composite film is calculated.
Example 2:
referring to fig. 1 to 3, an inner composite film of a lithium battery having superior corrosion resistance is obtained by sequentially coating polyethylene terephthalate and polyvinyl butyral on the upper and lower surfaces of an inner base film, and then laminating the inner composite film by an extrusion method;
the inner base film is prepared by the following preparation steps:
1) 30 parts of ternary copolymer polypropylene, 0.7 part of graphene, 0.4 part of glycerol triacrylate and 0.3 part of 2, 5-dimethyl-2, 5-di (tert-butylperoxy) hexane are mixed to obtain a first mixture;
2) 50 parts of homopolymerized polypropylene, 0.6 part of graphene, 0.3 part of glycerol triacrylate and 0.3 part of 2, 5-dimethyl-2, 5-di (tert-butylperoxy) hexane are mixed to obtain a second mixture;
3) and mixing polypropylene and polyethylene according to the mass fraction of 4: 1 mixing to obtain mixed polypropylene; mixing 40 parts of polypropylene, 0.8 part of graphene, 0.3 part of glycerol triacrylate and 0.3 part of 2, 5-dimethyl-2, 5-di (tert-butylperoxy) hexane to obtain a third mixture;
4) placing the first mixture, the second mixture and the third mixture into a feed port of a double-screw extruder;
5) setting the rotation speed of the double-screw extruder at 40r/min, the temperature of the compression section at 145 ℃, the temperature of the homogenization section at 200 ℃ and the temperature of the head and the neck mold section at 195 ℃.
6) And under the condition of 5), carrying out micro-crosslinking reaction on the first mixture, the second mixture and the third mixture in a double-screw extruder to obtain a polypropylene product in a micro-crosslinked state;
7) extruding the polypropylene product in a micro-crosslinking state and 7 parts of nylon into a T-shaped die head together through a double-screw extruder, casting the polypropylene product in a sheet shape to the roll surface of a stably rotating casting roller through casting equipment after the polypropylene product and the nylon are extruded out through the T-shaped die head, and cooling and shaping a diaphragm on the casting roller to obtain an inner-layer base film with a four-layer structure;
the inner base film uses ternary polymerization polypropylene as the innermost layer, and consists of other layers of homopolymerization polypropylene, mixed polypropylene and nylon in sequence, and the thicknesses of the layers are as follows in sequence: 15 μm, 20 μm, 17 μm, 3 μm, and the thickness of the inner base film is 55 μm;
the casting equipment conditions are respectively as follows: the casting heat sealing temperature is 250 ℃, the casting roller temperature is 30 ℃, the air flow is increased in the cooling process, and the tightening tension is 40 dyn/cm.
The preparation method of the lithium battery inner layer composite membrane comprises the following steps:
step one, putting the inner-layer base film obtained in the step 7) into a coating machine, and finishing the coating work of 2 layers of polyethylene terephthalate on the upper surface and the lower surface of the inner-layer base film in the coating machine by using a narrow-slit extrusion coating method, wherein the coating thickness is 0.03mm, so as to obtain a first product of the inner-layer composite film.
And step two, coating 1 layer of polyvinyl butyral with the thickness of 0.04mm on the upper surface and the lower surface of the first product of the inner-layer composite film in the step one to obtain a second product of the inner-layer composite film.
Step three, compounding the second product of the inner layer composite film by an extrusion coating method to obtain the inner layer composite film, wherein the extrusion coating temperature is 220 ℃, the extrusion coating resin is ethylene acrylic acid copolymer, the thickness of the resin is 3 mu m, the AC agent is isocyanate, and the coating weight of the AC agent is 0.6g/m2。
Other conditions and process methods and performance test procedures were the same as in example 1.
Example 3:
referring to fig. 1 to 3, an inner composite film of a lithium battery having superior corrosion resistance is obtained by sequentially coating polyethylene terephthalate and polyvinyl butyral on the upper and lower surfaces of an inner base film, and then laminating the inner composite film by an extrusion method;
the inner base film is prepared by the following preparation steps:
1) 50 parts of ternary copolymer polypropylene, 1.1 parts of graphene, 0.55 part of triacrylate isocyanurate and 0.75 part of 2, 5-dimethyl-2, 5-di (tert-butylperoxy) hexane are mixed to obtain a first mixture;
2) 50 parts of homopolymerized polypropylene, 1.5 parts of graphene, 0.62 part of triacrylate isocyanurate and 0.68 part of 2, 5-dimethyl-2, 5-di (tert-butylperoxy) hexane are mixed to obtain a second mixture;
3) firstly, mixing polypropylene and polyethylene according to the mass fraction of 4: 1 to obtain mixed polypropylene, and then mixing 20 parts of the mixed polypropylene, 0.8 part of graphene, 0.78 part of triacrylate isocyanurate and 0.73 part of 2, 5-dimethyl-2, 5-di (t-butylperoxy) hexane to obtain a third mixture;
4) placing the first mixture, the second mixture and the third mixture into a feed port of a double-screw extruder;
5) setting the rotation speed of the double-screw extruder at 45r/min, the temperature of a compression section at 170 ℃, the temperature of a homogenization section at 200 ℃ and the temperature of a machine head and a die section at 210 ℃.
6) And under the condition of 5), carrying out micro-crosslinking reaction on the first mixture, the second mixture and the third mixture in a double-screw extruder to obtain a polypropylene product in a micro-crosslinked state;
7) extruding the polypropylene product in a micro-crosslinking state and 10 parts of nylon into a T-shaped die head together through a double-screw extruder, casting the polypropylene product in a sheet shape to the roll surface of a stably rotating casting roller through casting equipment after the polypropylene product and the nylon are extruded out through the T-shaped die head, and cooling and shaping a diaphragm on the casting roller to obtain an inner-layer base film with a four-layer structure;
the inner base film is composed of ternary copolymer polypropylene, homopolymerized polypropylene, mixed polypropylene and nylon in sequence, and the thicknesses of the three components are as follows: 20 μm, 5 μm, and the thickness of the inner base film is 65 μm;
the casting equipment conditions are respectively as follows: the casting heat sealing temperature is 230 ℃, the casting roller temperature is 30 ℃, the air flow is increased in the cooling process, and the tightening tension is 42 dyn/cm.
The preparation method of the lithium battery inner layer composite membrane comprises the following steps:
step one, putting the inner-layer base film obtained in the step 7) into a coating machine, and finishing the coating work of 2 layers of polyethylene terephthalate on the upper surface and the lower surface of the inner-layer base film in the coating machine by using a narrow-slit extrusion coating method, wherein the coating thickness is 0.04mm, and the inner-layer composite film is a first product.
And step two, coating 1 layer of polyvinyl butyral with the thickness of 0.03mm on the upper surface and the lower surface of the first product of the inner-layer composite film in the step one to obtain a second product of the inner-layer composite film.
Step three, compounding the second product of the inner layer composite film by an extrusion compounding method to obtain the inner layer composite film, wherein the extrusion compounding temperature is 240 ℃, the extrusion compounding resin is ethylene acrylic acid copolymer, the thickness of the resin is 3 mu m, the AC agent is selected from carbamate, and the coating weight of the AC agent is 0.2g/m2。
Other conditions and process methods and performance test procedures were the same as in example 1.
Comparative example 1:
no graphene was added during the preparation of the inner base film, the remainder being identical to example 1.
Comparative example 2:
the inner base film was not coated with polyethylene terephthalate, and the rest was in accordance with example 2.
Comparative example 3:
the inner base film was not coated with polyvinyl butyral, the remainder remaining in accordance with example 3.
The lithium battery inner layer composite membrane produced by the above example has the following test results according to the items of puncture resistance, electrolyte resistance, high barrier, high insulation and high heat sealing strength:
1. compared with the example 1, the inner-layer composite film produced by the process has the advantages that the inner-layer base film is not added in the preparation process of the inner-layer base film, and the puncture resistance, high insulation property and high heat seal strength of the inner-layer composite film produced by the process are inferior to those of the inner-layer composite film produced by the process of the example 1.
2. Comparative example 2 compared with example 2, the inner layer base film was not coated with polyethylene terephthalate, and the high barrier property and high insulation property of the inner layer composite film produced by the process were inferior to those of the inner layer composite film produced by the process of example 2.
3. Comparative example 3 compared with example 3, the inner layer base film was not coated with polyvinyl butyral, and the puncture resistance and electrolyte resistance of the inner layer composite film produced by the process were not the same as those of the inner layer composite film produced by the process of example 3.
The following conclusions were made: the inner-layer composite film is prepared by a multi-layer co-extrusion method, the inner-layer base film is prepared by adding graphene into polypropylene, and the surface treatment is carried out on the inner-layer base film, namely polyethylene terephthalate and polyvinyl butyral materials are coated, so that the characteristics of puncture resistance, electrolyte resistance, high barrier property, high insulation and high heat seal of the inner-layer composite film are improved to a great extent.
The foregoing is merely exemplary and illustrative of the principles of the present invention and various modifications, additions and substitutions of the specific embodiments described herein may be made by those skilled in the art without departing from the principles of the present invention or exceeding the scope of the claims set forth herein.
Claims (8)
1. The utility model provides a lithium cell inlayer complex film with superstrong corrosion resistance which characterized in that: the inner layer composite film of the lithium battery is obtained by sequentially coating polyethylene glycol terephthalate and polyvinyl butyral on the upper surface and the lower surface of an inner layer base film and then compounding the layers by an extrusion compounding method;
the inner-layer base film is prepared from 18.5-51.7 parts of terpolymer polypropylene, 28.4-52.8 parts of homopolymerized polypropylene, 17.6-55.6 parts of mixed polypropylene, 1.3-15.5 parts of graphene, 0.52-9 parts of crosslinking monomer, 0.28-9.4 parts of initiator and 4.3-10.6 parts of nylon by weight;
the preparation steps of the inner base film are as follows:
1) 18.5-51.7 parts of ternary copolymer polypropylene, 0.5-5 parts of graphene, 0.2-3 parts of pentaerythritol tetraacrylate and 0.1-3 parts of dicumyl peroxide are mixed to obtain a first mixture;
2) 28.4-52.8 parts of homopolymerized polypropylene, 0.5-5 parts of graphene, 0.2-3 parts of pentaerythritol tetraacrylate and 0.1-3 parts of dicumyl peroxide are mixed to obtain a second mixture;
3) 17.6-55.6 parts of mixed polypropylene, 0.5-5 parts of graphene, 0.2-3 parts of pentaerythritol tetraacrylate and 0.1-3 parts of dicumyl peroxide are mixed to obtain a third mixture;
4) placing the first mixture, the second mixture and the third mixture into a feed port of a double-screw extruder;
5) carrying out micro-crosslinking reaction on the first mixture, the second mixture and the third mixture in a double-screw extruder to obtain a polypropylene product in a micro-crosslinking state;
6) extruding the polypropylene product in a micro-crosslinking state and 4.3-10.6 parts by weight of nylon into a T-shaped die head through a double-screw extruder, casting the polypropylene product in a sheet shape to the roll surface of a casting roller which rotates stably through casting equipment after the polypropylene product is extruded out of the T-shaped die head, and cooling and shaping the casting roller to obtain an inner-layer base film; the casting equipment comprises the following steps: firstly, adjusting the position of a rotating shaft (6) in a sliding groove in the precision plate (14) according to a positioning plate (15), screwing a nut, fixing a casting roller (12) between the two precision plates (14), opening a first motor (5), a second motor (7), a corona motor (9) and a fan (4), and casting a corona film by the casting roller (12) and a corona roller (11) to obtain an inner base film; taking ternary copolymer polypropylene as the innermost layer, and forming other layers by homo-polypropylene, mixed polypropylene and nylon in sequence.
2. The lithium battery inner layer composite film with ultra-strong corrosion resistance as claimed in claim 1, wherein: the mixed polypropylene is prepared from polypropylene and polyethylene according to the mass fraction of 4: 1, mixing to obtain; the thickness of the inner base film is 37-65 μm, and the number of layers is four; the thicknesses of the ternary copolymer polypropylene, the homopolymerized polypropylene, the mixed polypropylene and the nylon are as follows in sequence: 10-20 μm, 15-20 μm, 10-20 μm, 2-5 μm.
3. The lithium battery inner layer composite film with ultra-strong corrosion resistance as claimed in claim 1, wherein: the crosslinking monomer is one of pentaerythritol tetraacrylate, glycerol triacrylate, divinylbenzene or triacrylate isocyanurate.
4. The lithium battery inner-layer composite film with super corrosion resistance according to claim 1, wherein: the initiator is dicumyl peroxide or 2, 5-dimethyl-2, 5-di (tert-butylperoxy) hexane.
5. The lithium battery inner-layer composite film with super corrosion resistance according to claim 1, wherein: the temperature of the compression section of the double-screw extruder is 100-170 ℃, the temperature of the homogenization section is 200 ℃, the temperature of the head and the neck mold section is 175-210 ℃, and the rotating speed of the screw is 35-45 r/min.
6. The lithium battery inner-layer composite film with super corrosion resistance according to claim 1, wherein: the casting equipment comprises fixed bases (8), fixed plates (1) and supporting bases (13), wherein the supporting bases (13) are uniformly welded at the bottoms of the fixed bases (8), the fixed plates (1) are welded at two sides of the surface of the fixed bases (8), the fixed plates (2) are arranged on the two fixed plates (1), a fan fixed plate (3) is welded between the two fixed plates (2), and a fan (4) is arranged at the bottom of the fan fixed plate (3);
two all welded fastening has precision board (14) bottom mount (2), two precision board (14) inside is provided with the sliding tray, and the sliding tray both sides are provided with the scale, and locating plate (15) are all installed to two precision board (14) one side, and precision board (14) and locating plate (15) mutually perpendicular and swing joint, two locating plate (15) other end movable mounting is on fixed plate (1) surface, installs curtain coating roller (12) between two precision board (14), and axis of rotation (6) pass sliding tray, curtain coating roller (12) and locating plate (15) through the nut fix two between precision board (14), two all welded fastening has L type fixed plate (10) below of locating plate (15), installs corona roller (11) between two L type fixed plate (10), corona roller (11) link to each other through wire and install corona motor (9) inside unable adjustment base (8), the rotating shaft (6) penetrates through the corona roller (11) and movably fixes the corona roller (11) between the two L-shaped fixing plates (10) through nuts;
a first motor (5) is installed on one side of a fixing plate (1), a second rotating wheel (17) is installed on the first motor (5), a second driven wheel (19) is installed at one end of a casting roller (12) on the same side of the first motor (5), the second rotating wheel (17) is connected with the second driven wheel (19) through a rotating belt, a second motor (7) is installed below the first motor (5), a first rotating wheel (16) is installed on the second motor (7), a first driven wheel (18) is installed at one end of a corona roller (11) on the same side of the second motor (7), and the first rotating wheel (16) is connected with the first driven wheel (18) through the rotating belt;
the casting heat sealing temperature is 230-250 ℃, the casting roller temperature is 30 ℃, the air flow is increased in the cooling process, and the tightening tension is 38-42 dyn/cm.
7. A preparation method of a lithium battery inner layer composite membrane with super-strong corrosion resistance is characterized by comprising the following steps: the preparation method of the lithium battery inner layer composite membrane comprises the following steps:
firstly, coating polyethylene glycol terephthalate on the upper surface and the lower surface of the obtained inner-layer base film in a coating machine to obtain a first product of an inner-layer composite film; then coating polyvinyl butyral on the upper and lower surfaces of the inner-layer base film to obtain a second product of the inner-layer composite film;
step two, compounding the second product of the inner layer composite film by an extrusion compounding method to obtain the inner layer composite film, wherein the extrusion compounding temperature of the extrusion compounding machine is 210-240 ℃, ethylene acrylic acid copolymer is selected as extrusion resin, and the thickness is 3-4 μm; the AC agent is selected from isocyanate or carbamate, and the coating weight is 0.2-0.8g/m2。
8. The method for preparing the lithium battery inner layer composite membrane with super corrosion resistance according to claim 7, wherein the method comprises the following steps: in the first step, 2 layers of polyethylene terephthalate are coated, the thickness of the polyethylene terephthalate is 0.02-0.04mm, and 1 layer of polyvinyl butyral is coated, the thickness of the polyvinyl butyral is 0.02-0.04 mm.
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| CN111715461B (en) * | 2020-06-30 | 2021-06-15 | 长江师范学院 | Universal electrode coating system for lithium/sodium ion battery |
| CN112652844B (en) * | 2020-12-24 | 2022-04-29 | 界首市天鸿新材料股份有限公司 | Power lithium battery flexible packaging film |
| CN112721402B (en) * | 2020-12-24 | 2023-06-27 | 界首市天鸿新材料股份有限公司 | Preparation process of flexible packaging film of power lithium battery |
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