Basalt fiber reinforced polyethylene separator, preparation method and application thereof in lithium battery

Abstract

The application provides basalt fiber reinforced polyethylene diaphragm, a preparation method and application thereof in lithium batteries, and relates to the technical field of lithium batteries. The method comprises the following steps: 1) performing melt treatment and granulation treatment on basalt fibers, polyethylene resin and paraffin oil to obtain basalt fiber reinforced resin particles; and 2) performing hydrophilic modification treatment on the basalt fiber reinforced resin particles to obtain basalt fiber reinforced polyethylene diaphragm. The heat resistance of the diaphragm prepared by the method is improved compared with that of a traditional diaphragm material.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium batteries, in particular, the present application relates to a basalt fiber reinforced polyethylene separator, a preparation method and its application in lithium batteries. BACKGROUND

[0002] With the progress of science and technology and the development of society, lithium ion battery as a new energy storage method, its application range is more and more widely. With the gradual expansion of the market of new energy vehicles, the field of new energy vehicles also puts forward higher requirements for lithium ion battery. Lithium ion battery is mainly composed of positive and negative electrode materials, electrolyte and separator. As one of the four main materials of lithium ion battery, the rich microporous structure of the separator not only has the function of providing lithium ion to pass through, but also has the function of isolating the positive and negative electrodes of the battery, preventing the positive and negative electrodes from contacting to cause short circuit. The structure and morphology of the separator determine the size of the electrolyte retention rate, so the separator not only plays an important role in the rate performance and cycle performance of lithium battery, but also relates to the safety performance of the battery.

[0003] The performance of the separator directly affects the cycle capacity, usability and safety of the lithium ion battery. At present, the commercial lithium ion battery separator is mainly polyethylene (PE) and polypropylene / polyethylene (PP / PE) separator, which mainly benefits from its excellent mechanical properties and electrochemical stability, but at the same time, due to the low melting point of the polymer, the polyolefin separator has poor high temperature resistance, mainly manifested in its poor thermal shrinkage in electrolyte environment, large shrinkage rate, which easily leads to battery high temperature thermal failure, further causes internal short circuit of the battery and fire, causing safety hazards. Therefore, it is an urgent need of the industry to develop lithium ion battery separator which is easy to produce, resistant to high temperature and suitable for large current charging and discharging long cycle.

[0004] In order to improve the heat resistance of the separator material itself, polytetrafluoroethylene material can be used as lithium battery separator, for example: patent CN201010291126.0 designs a sandwich polytetrafluoroethylene / polyethylene / polytetrafluoroethylene structure lithium battery separator, but due to the low surface energy of the polytetrafluoroethylene layer, the molecules are not modified for hydrophilicity, the affinity between the separator and the electrolyte is poor, which will seriously affect the cycle performance of the lithium battery; Patent CN104022249A discloses a three-layer lithium battery separator and a preparation method thereof, which adopts a three-layer co-extrusion process to prepare a PP / PE / PP composite separator structure, which improves the temperature difference between the closed pore temperature and the broken membrane temperature of the separator. Patent CN202010774162.6 reports a scheme of coating oxide ceramic particles and lithium compound particles on both sides of the base film at the same time, but there are still limitations of the polyolefin separator itself on the thermal stability of the material and the inevitable problem of ceramic coating falling off.

[0005] Therefore, how to improve the high safety of the separator is a technical problem to be solved in the field. SUMMARY

[0006] To improve the heat resistance of lithium ion battery separators under high temperature conditions, the present application provides a method for preparing a basalt fiber reinforced polyethylene separator. The basalt fiber is dried, immersed and added to the double screw extruder with the super high molecular weight polyethylene modified by silane coupling agent for melting and granulation. After the re-granulated basalt fiber reinforced resin particles are melted in the double screw extruder, they are stretched in two directions, extracted, dried after hydrophilic modification, and the basalt fiber reinforced polyethylene separator is prepared. Due to the excellent structure and chemical stability of the polyethylene and basalt fiber mixed material, the heat resistance of this type of separator is improved compared with traditional separator materials.

[0007] In one aspect of the present application, a method for preparing a basalt fiber reinforced polyethylene separator is provided. According to embodiments of the present application, the method comprises:

[0008] 1) melt treating and granulating basalt fiber, polyethylene resin and paraffin oil to obtain basalt fiber reinforced resin particles;

[0009] 2) hydrophilic modification of the basalt fiber reinforced resin particles to obtain a basalt fiber reinforced polyethylene separator. Due to the excellent structure and chemical stability of the polyethylene and basalt fiber mixed material, the heat resistance of the separator prepared according to embodiments of the present application is improved compared with traditional separator materials.

[0010] According to embodiments of the present application, the above method can further comprise at least one of the following accessory technical features:

[0011] According to embodiments of the present application, the basalt fiber is pre-treated by drying and immersion.

[0012] According to embodiments of the present application, the thickness of the basalt fiber is 3 μm.

[0013] According to embodiments of the present application, the drying treatment further comprises immersing the basalt fiber in acetone solution for 30 min before the drying treatment.

[0014] According to embodiments of the present application, the immersion treatment is immersing the basalt fiber after the drying treatment in an aqueous solution containing polyoxyethylene-polyoxypropylene ether, N-methyl diethanol, KH055 coupling agent and methyl pyrrolidone.

[0015] According to embodiments of the present application, the mass ratio of polyoxyethylene-polyoxypropylene ether, N-methyl diethanol, KH055 coupling agent and methyl pyrrolidone is 1:6:1:0.5.

[0016] According to embodiments of the present application, the immersion treatment time is 30 min.

[0017] According to an embodiment of the present application, the polyethylene resin is used in an amount of 30% to 40%, and the paraffin oil is used in an amount of 55% to 65%.

[0018] According to an embodiment of the present application, the step 1) further comprises an antioxidant.

[0019] According to an embodiment of the present application, the antioxidant is used in an amount of 0% to 5%.

[0020] According to an embodiment of the present application, the antioxidant is antioxidant 1010 or antioxidant 168.

[0021] According to an embodiment of the present application, the total mass of the polyethylene resin, the paraffin oil and the antioxidant is (70 to 90) : (10 to 30) with respect to the mass of the basalt fiber.

[0022] According to an embodiment of the present application, the polyethylene resin has a viscosity average molecular weight of 500000 to 1500000.

[0023] According to an embodiment of the present application, the melt processing is performed in an extruder.

[0024] According to an embodiment of the present application, the basalt fiber is fed in a side feed port.

[0025] According to an embodiment of the present application, the polyethylene resin, the paraffin oil and the antioxidant are fed in a main feed port.

[0026] According to an embodiment of the present application, the melt processing is performed at a temperature of 180°C to 220°C.

[0027] According to an embodiment of the present application, the extruder has a stirring speed of 90 to 120 rpm.

[0028] According to an embodiment of the present application, the basalt fiber reinforced resin particles further comprise a first biaxial stretching process, an extraction process, a drying process, a second biaxial stretching process and a setting process before the hydrophilic modification process.

[0029] According to an embodiment of the present application, the first biaxial stretching process is performed at a temperature of 110°C to 125°C.

[0030] According to an embodiment of the present application, the first biaxial stretching process is performed at a stretching ratio of 6 to 10 times.

[0031] According to an embodiment of the present application, the extraction process uses dichloromethane as a solvent.

[0032] According to an embodiment of the present application, the extraction process is performed at room temperature.

[0033] According to an embodiment of the present application, the temperature of the drying treatment is 40℃.

[0034] According to an embodiment of the present application, the stretching temperature of the second biaxial stretching treatment is 110℃-125℃.

[0035] According to an embodiment of the present application, the stretching ratio of the second biaxial stretching treatment is 5-10 times.

[0036] According to an embodiment of the present application, the temperature of the setting treatment is 130-150℃.

[0037] According to an embodiment of the present application, the hydrophilic modification treatment is performed by immersing the basalt fiber reinforced resin particles in a silane coupling agent KH055 solution.

[0038] According to an embodiment of the present application, the concentration of the silane coupling agent KH055 is 1%-3%.

[0039] According to an embodiment of the present application, the time of the immersing is 30min.

[0040] According to an embodiment of the present application, a drying treatment is performed after the immersing.

[0041] In another aspect of the present application, the present application further provides a basalt fiber reinforced polyethylene separator. According to an embodiment of the present application, the basalt fiber reinforced polyethylene separator is prepared according to the method described above.

[0042] In still another aspect of the present application, the present application further provides a lithium battery. According to an embodiment of the present application, the lithium battery comprises the basalt fiber reinforced polyethylene separator prepared according to the method described above or the basalt fiber reinforced polyethylene separator described above.

[0043] In still another aspect of the present application, the present application further provides a method for preparing a basalt fiber reinforced polyethylene separator.

[0044] According to an embodiment of the present application, the method comprises:

[0045] 1. 3μm chopped basalt fibers are immersed in an acetone solution for 30min and dried, and then immersed in an aqueous solution of polyoxyethylene-polyoxypropylene ether: N-methyl diethanol: KH055 coupling agent: methyl pyrrolidone = 1:6:1:0.5 for 30min and dried;

[0046] 2. 30%~40% polyethylene resin, 55~65% paraffin oil, 0~5% antioxidant 1010 or 168 are mixed and then put into the extruder through the main feeding port, basalt fibers in step 1 are added to the side feeding port, wherein the mass ratio of the main feeding port feeding to the side feeding port feeding is 70~90%:10~30%, melt blending is carried out, and the mixed temperature T=180~220°C, the stirring speed n=90~120rpm; the viscosity average molecular weight of the polyethylene resin is 500000~1500000;

[0047] 3. The basalt fiber reinforced composite particles are obtained after the material in step 2 is extruded, granulated and cooled;

[0048] 4. The sheet in step 3 is bidirectionally stretched, the stretching temperature is 110~125°C, and the stretching ratio is 6~10 times;

[0049] 5. The material in step 4 is immersed in dichloromethane for extraction, and then dried after extraction; the extraction temperature is room temperature, and the drying temperature is 40°C;

[0050] 6. The material in step 5 is bidirectionally stretched and shaped, the stretching temperature is 110~125°C, the stretching ratio is 5~10 times, and the shaping temperature is 130~150°C;

[0051] 7. The material in step 6 is immersed in 1%~3% silane coupling agent KH055 for modification, the soaking time is 30min, and the material is dried after soaking;

[0052] 8. The material in step 7 is wound.

[0053] According to the embodiment of the present application, the basalt fiber reinforced polyethylene diaphragm has the characteristics of high tensile strength, good heat resistance and good acid and alkali resistance, and the heat resistance of the diaphragm of this type is obviously improved through the compounding of ultrahigh molecular weight polyethylene, and the tensile and puncture resistance of the diaphragm is also improved, so that the overall strength of the diaphragm is higher and safer. BRIEF DESCRIPTION OF DRAWINGS

[0054] The above and / or additional aspects and advantages of the present application will become apparent and be readily understood from the following description, taken in conjunction with the following drawings, in which:

[0055] Figure 1 Figure 4 is an electron microscope image of the basalt fiber reinforced polyethylene diaphragm of Example 1. DETAILED DESCRIPTION

[0056] The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present application, and cannot be understood as a limitation of the present application.

[0057] Furthermore, the terms "first", "second", "third", etc. are used herein for descriptive purposes only and should not be construed as indicating or implying relative importance or an ordered sequence. Thus, features referring to "first", "second" etc. can include at least one of the features, explicitly or implicitly.

[0058] The application will be described with respect to the following specific examples, which are merely illustrative, and are not to be construed as limiting the application in any way.

[0059] Example 1

[0060] 1. 3 μm chopped basalt fiber was immersed in acetone solution for 30 min and dried, then immersed in water solution of polyoxyethylene-polyoxypropylene ether: N-methyl diethanol: KH055 coupling agent: methyl pyrrolidone = 1:6:1:0.5 for 30 min and dried.

[0061] 2. 30%~40% polyethylene resin, 55~65% paraffin oil, 0~5% antioxidant 1010 or 168 were mixed and fed into the extruder through the main feed port, and the basalt fiber of step 1 was fed into the side feed port, wherein the mass ratio of the main feed port feed to the side feed port feed was 97%:3%, and melt blending was performed, and the mixture was extruded through a die. The mixing temperature T = 180~220°C, and the stirring speed n = 90~120 rpm. The viscosity average molecular weight of the polyethylene resin was 500000~1500000.

[0062] 3. The material of step 2 was extruded, granulated, and cooled to obtain basalt fiber reinforced composite granules.

[0063] 4. The sheet of step 3 was bidirectionally stretched, and the stretching temperature was 110~125°C, and the stretching ratio was 6~10 times.

[0064] 5. The material of step 4 was immersed in dichloromethane for extraction, and then dried. The extraction temperature was room temperature, and the drying temperature was 40°C.

[0065] 6. The material of step 5 was bidirectionally stretched and set, and the stretching temperature was 110~125°C, the stretching ratio was 5~10 times, and the setting temperature was 130~150°C.

[0066] 7. The material of step 6 was immersed in a solution containing 1%~3% silane coupling agent KH055 for modification, and the immersion time was 30 min, and the material was dried after immersion.

[0067] 8. The material of step 7 was wound.

[0068] Example 2

[0069] 1. 3 μm chopped basalt fiber is immersed in acetone solution for 30 min and dried, and then immersed in an aqueous solution of polyoxyethylene-polyoxypropylene ether: N-methyl diethanol: KH055 coupling agent: methyl pyrrolidone = 1:6:1:0.5 for 30 min and dried.

[0070] 2. 30% to 40% polyethylene resin, 55% to 65% paraffin oil, and 0% to 5% antioxidant 1010 or 168 are mixed and fed into an extruder through a main feed port, and the basalt fiber of step 1 is fed into a side feed port, wherein the mass ratio of the main feed port feed to the side feed port feed is 90%:10%, and melt blending is performed, and then extruded through a die. The mixing temperature T is 180°C to 220°C, and the stirring speed n is 90 to 120 rpm. The polyethylene resin has a viscosity average molecular weight of 500000 to 1500000.

[0071] 3. The material of step 2 is extruded, pelletized, and cooled to obtain basalt fiber reinforced composite pellets.

[0072] 4. The sheet of step 3 is biaxially stretched at a stretching temperature of 110°C to 125°C and a stretching ratio of 6 to 10 times.

[0073] 5. The material of step 4 is immersed in dichloromethane for extraction, and then dried after extraction. The extraction temperature is room temperature, and the drying temperature is 40°C.

[0074] 6. The material of step 5 is biaxially stretched and set at a stretching temperature of 110°C to 125°C and a stretching ratio of 5 to 10 times, and a setting temperature of 130 to 150°C.

[0075] 7. The material of step 6 is immersed in a solution containing 1% to 3% silane coupling agent KH055 for modification, and the immersion time is 30 min, and then dried after immersion.

[0076] 8. The material of step 7 is wound.

[0077] Example 3

[0078] 1. 3 μm chopped basalt fiber is immersed in acetone solution for 30 min and dried, and then immersed in an aqueous solution of polyoxyethylene-polyoxypropylene ether: N-methyl diethanol: KH055 coupling agent: methyl pyrrolidone = 1:6:1:0.5 for 30 min and dried.

[0079] 2. 30%~40% polyethylene resin, 55~65% paraffin oil, 0~5% antioxidant 1010 or 168 are mixed and fed into the extruder through the main feed port, basalt fibers in step 1 are added to the side feed port, the mass ratio of the main feed port to the side feed port is 85%:15%, melt blending is carried out, and extrusion is carried out through the die. The mixing temperature T=180~220℃, the stirring speed n=90~120rpm. The viscosity average molecular weight of the polyethylene resin is 500000~1500000.

[0080] 3. The material in step 2 is extruded, granulated, and cooled to obtain basalt fiber reinforced composite granules.

[0081] 4. The sheet in step 3 is bidirectionally stretched, the stretching temperature is 110~125℃, and the stretching ratio is 6~10 times.

[0082] 5. The material in step 4 is immersed in dichloromethane for extraction, and then dried. The extraction temperature is room temperature, and the drying temperature is 40℃.

[0083] 6. The material in step 5 is bidirectionally stretched and shaped, the stretching temperature is 110~125℃, the stretching ratio is 5~10 times, and the shaping temperature is 130~150℃.

[0084] 7. The material in step 6 is immersed in 1%~3% silane coupling agent KH055 for modification, the soaking time is 30min, and then dried after soaking.

[0085] 8. The material in step 7 is wound.

[0086] Comparative Example 1

[0087] 1. 25% polyethylene resin, 5% aluminum oxide (Al2O3), and 70% paraffin oil are mixed and fed into the extruder for melt blending, and then extruded through the die. The mixing temperature T=320℃, the stirring speed n=90rpm. The viscosity average molecular weight of the polyethylene resin is 900000.

[0088] 2. The sheet in step 1 is bidirectionally stretched, the stretching temperature is 1500℃, and the stretching ratio is 6 times.

[0089] 3. The material in step 2 is immersed in dichloromethane for extraction, and then dried. The extraction temperature is room temperature, and the drying temperature is 40℃.

[0090] 4. The material in step 3 is bidirectionally stretched and shaped, the stretching temperature is 180℃, the stretching ratio is 8 times, and the shaping temperature is 120℃.

[0091] 5. The coating slurry is prepared: 30% nano-SiO2, 0.2% polyacrylamide, 0.2% polyvinyl butyral, and 69.6% pure water

[0092] 6. The slurry in step 5 is coated onto the sheet in step 4 by gravure roll, and dried.

[0093] 7. The material in step 8 is wound up.

[0094] Comparative Example 2

[0095] 1. 40% polyethylene resin, 60% paraffin oil are mixed and fed into an extruder for melt blending. The mixed melt is Melt A. The mixing temperature T = 340°C, and the stirring speed n = 100 rpm. The viscosity average molecular weight of the polyethylene resin is 1,650,000.

[0096] 2. 30% polyethylene resin, 70% paraffin oil are mixed and fed into an extruder for melt blending. The mixed melt is Melt B. The mixing temperature T = 190°C, and the stirring speed n = 75 rpm. The viscosity average molecular weight of the polyethylene resin is 1,200,000.

[0097] 3. Melt A and Melt B are extruded through a three-cavity co-extrusion die to form a sheet with A / B / A structure. The composite temperature is 190°C.

[0098] 4. The sheet in step 3 is biaxially stretched. The stretching temperature is 200°C, and the stretching ratio is 8 times.

[0099] 5. The material in step 4 is immersed in dichloromethane for extraction, and then dried. The extraction temperature is room temperature, and the drying temperature is 40°C.

[0100] 6. The material in step 5 is immersed in silane coupling agent KH550 containing 2% vinyl acetate for modification. The immersion time is 5 min, and the material is dried after immersion.

[0101] 7. The material in step 6 is dried.

[0102] 8. The material in step 7 is biaxially stretched and set. The stretching temperature is 180°C, the stretching ratio is 10 times, and the setting temperature is 120.

[0103] 9. The material in step 8 is wound up.

[0104] Table 1 Performance Comparison of Examples and Comparative Examples

[0105]

[0106] From Table 1, it can be found by comparing the tensile strength and film breaking temperature of Examples 1, 2, 3 and Comparative Examples 1, 2 that the tensile strength of the separator is obviously improved due to the high tensile modulus of basalt fiber, and the film breaking temperature of the basalt fiber reinforced local ethylene separator is obviously higher than that of other separators, which makes the separator perform better in heat resistance in lithium batteries, thereby further improving the overall safety of lithium batteries. Moreover, the basalt fiber reinforced polyethylene separator is superior to nano-SiO2 filled separator and PE composite separator in tensile strength, needle penetration strength, heat shrinkage and film breaking temperature, and the improvement is obvious.

[0107] In the description of the present specification, the description referring to the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. Furthermore, the different embodiments or examples described in the present specification and the features of the different embodiments or examples can be combined and combined by those skilled in the art without contradiction.

[0108] Although the embodiments of the present application have been shown and described above, it is understood that the above-described embodiments are exemplary and are not to be construed as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above-described embodiments within the scope of the present application.

Claims

1. A method for preparing basalt fiber reinforced polyethylene membrane, characterized in that, include: (1) After immersing 3μm short-cut basalt fibers in acetone solution for 30 min and drying them, they were then immersed in an aqueous solution with a mass ratio of polyoxyethylene-polyoxypropylene ether: N-methyldiethanolamine: KH550 coupling agent: methylpyrrolidone = 1:6:1:0.5 and dried for 30 min. (2) 30% to 40% polyethylene resin, 55% to 65% paraffin oil, and 0% to 5% antioxidant 1010 or 168 are mixed and fed into an extruder through the main feed port. The basalt fiber from step (1) is added to the side feed port. The mass ratio of the feed from the main feed port to the feed from the side feed port is 70% to 90%: 10% to 30%. The mixture is melt-blended and extruded through a die. The mixing temperature is T = 180℃ to 220℃, the stirring speed is n = 90 to 120 rpm, and the viscosity-average molecular weight of the polyethylene resin is 500,000 to 1,500,000. (3) The material in step (2) is extruded, pelletized and cooled to obtain basalt fiber reinforced composite particles; (4) The sheet in step (3) is subjected to biaxial stretching at a stretching temperature of 110℃~125℃ and a stretching ratio of 6~10 times. (5) Immerse the material in step (4) in dichloromethane for extraction, and dry it after extraction. The extraction temperature is room temperature and the drying temperature is 40℃. (6) The material in step (5) is subjected to biaxial stretching and shaping at a stretching temperature of 110℃~125℃, a stretching ratio of 5~10 times, and a shaping temperature of 130~150℃. (7) Immerse the material from step (6) in a solution containing 1% to 3% silane coupling agent KH550 for 30 minutes and dry it after immersion. (8) Roll up the material from step (7).

2. A basalt fiber reinforced polyethylene diaphragm, characterized in that, The basalt fiber reinforced polyethylene diaphragm is prepared according to the method described in claim 1.

3. A lithium battery, characterized in that, The lithium battery comprises a basalt fiber reinforced polyethylene separator prepared by the method according to claim 1 or the basalt fiber reinforced polyethylene separator according to claim 2.

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