CN114883746A - Novel polyimide microsphere slurry and coating diaphragm thereof - Google Patents
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Abstract
The invention discloses a novel polyimide microsphere slurry and a coating diaphragm thereof, which are used in the field of lithium ion batteries. The slurry consists of polyimide microspheres, inorganic particles, a binder, a surfactant, a dispersant and a solvent. The coating diaphragm is obtained by coating the slurry on at least one side surface of a porous base membrane in a micro-concave coating, extrusion coating, transfer coating, dipping coating or wire rod coating mode and then drying, and the coating diaphragm has excellent lithium dendrite puncture resistance and the function of preventing short circuit in a battery by high-temperature closed pores. Compared with the common ceramic diaphragm, the novel polyimide microsphere slurry coating diaphragm has more excellent cohesiveness and thermal shrinkage resistance. The novel polyimide coated separator has a lower areal density than the ceramic coated separator, and will significantly increase the energy density of the lithium ion battery. The slurry and the diaphragm are suitable for the existing mature diaphragm coating process, and have great application prospects.
Description
Technical Field
The invention belongs to the technical field of lithium ion battery diaphragms, and particularly relates to novel polyimide microsphere slurry and a coating diaphragm thereof.
Background
The lithium ion battery has the outstanding advantages of small volume, light weight, high power density, long service life, environmental friendliness and the like, is mainly applied to 3C products at first, and is widely developed in recent years in the fields of new energy automobiles, electric tools and energy storage. At present, lithium ion batteries are developing towards high capacity and high specific energy, and meanwhile, the safety of the lithium ion batteries is receiving more and more extensive attention. The traditional polyolefin diaphragm has poor thermal performance and electrolyte infiltration performance and cannot meet the requirements of a lithium ion battery. Therefore, the development of a novel lithium ion battery diaphragm with high mechanical strength, high temperature resistance and high wettability has great significance for producing a high-performance lithium ion battery.
Based on the above problems, the industry has developed a ceramic-coated polyolefin composite diaphragm on the basis of a polyolefin diaphragm, that is, ceramic particles, a binder, a solvent and other additives are prepared into ceramic slurry, and an inorganic ceramic layer is prepared on one side or both sides of a polyolefin base film by means of dimple coating, extrusion coating, wire rod coating and the like, so that the high temperature resistance and the wettability of the diaphragm to an electrolyte can be remarkably improved, and the excellent mechanical properties of the polyolefin diaphragm can be maintained, thereby being widely applied. However, the inorganic ceramic-coated modified polyolefin separator still has many problems. For example, the inorganic ceramic layer has poor interface compatibility with the polyolefin base film, the binding force is weak, and ceramic particles are easy to fall off; in addition, the inorganic ceramic layer has high density, which causes the increase of the surface density of the ceramic-coated polyolefin diaphragm and is not beneficial to the improvement of the specific energy of the lithium ion battery. The high-temperature-resistant polymer is adopted for coating, so that the problems of high density, insufficient cohesiveness and easy powder falling of the ceramic coating can be effectively solved. The polymers used in many cases include polyvinylidene fluoride (PVDF), Polyacrylonitrile (PAN), Polyimide (PI), aramid, and the like. For example, patent CN 104993089a discloses a lithium ion battery separator, which is composed of a base film and an aramid fiber coating layer coated on one or both sides of the base film, wherein the presence of the aramid fiber coating layer improves the temperature resistance of the modified separator, but this method requires dissolving the aramid fiber in advance, and then preparing the coating layer by a coagulation bath pore-forming technique, which leads to a serious decrease in production efficiency.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a polyimide microsphere slurry coated porous composite diaphragm and a preparation method thereof. The composite diaphragm keeps the excellent mechanical property of the porous diaphragm, has the function of high-temperature hole closing, and can play a role in preventing short circuit in the battery. Meanwhile, the polyimide microsphere/ceramic nanoparticle mixed coating obviously improves the heat shrinkage resistance of the porous base membrane. Importantly, the polyimide microsphere slurry coated diaphragm has lower surface density compared with a pure ceramic coated diaphragm, and is beneficial to improving the mass energy density of the lithium ion battery; and the polyimide microspheres have better compatibility with the organic base film and higher bonding strength, and the polyimide microspheres are not easy to fall off. The slurry provided by the invention can be used for large-scale production through the existing mature coating technology, such as dimple coating, extrusion coating, wire rod coating and the like, so as to prepare the composite diaphragm, and the production efficiency is high, and the process is simple.
The invention provides novel polyimide microsphere slurry which is characterized by comprising 5-59 parts of polyimide microspheres, 0.1-10 parts of binder, 0.01-3 parts of surfactant, 0.01-8 parts of dispersant and 40-95 parts of solvent, wherein the mass ratio of the polyimide microspheres to the inorganic particles is (100-10): (0-90).
Furthermore, the particle size range of the polyimide microspheres in the novel polyimide microsphere slurry is 0.02-10 μm.
Further, the inorganic nanoparticles are one or a combination of two or more of silicon dioxide, aluminum oxide, boehmite, zirconium dioxide, magnesium hydroxide, zinc oxide and titanium dioxide.
Further, the particle diameter of the inorganic particles is 0.01 to 2 μm.
Further, the binder is one or a combination of two or more of polyvinyl alcohol, polytetrafluoroethylene, sodium carboxymethylcellulose, polyurethane, styrene-butadiene rubber, fluorinated rubber, styrene-butadiene polymer, polyvinylidene fluoride-hexafluoropropylene, polyacrylic acid, polymethacrylic acid, polyacrylate, polymethyl methacrylate and polyacrylonitrile.
The solvent is an organic solvent or an aqueous solvent, the organic solvent is one or a combination of two or more of N-methyl pyrrolidone, dimethyl sulfoxide, N-dimethylformamide, N-dimethylacetamide and acetone, and the aqueous solvent is pure water or a combination of water and one or two or more of ethanol, ethylene glycol, propanol, glycerol, isopropanol and butanol.
Further, the surfactant is a fluorocarbon surfactant, such as perfluoroalkyl ether ethanolamine salt, perfluoroalkyl ether quaternary ammonium salt; nonionic surfactants such as polyethylene glycol type, polyhydric alcohol type, block copolyether; cationic surfactants such as cetyltrimethylammonium bromide, dodecyltrimethylammonium bromide, dodecylpyridinium bromide; anionic surfactants such as one or a combination of two or more of fatty acid salts, sulfonates, phosphates and sulfate salts, preferably fluorocarbon surfactants and nonionic surfactants.
The dispersant is a cellulose ether dispersant such as hydroxypropyl methylcellulose, hydroxyethyl cellulose, a cellulose alkyl ether or a cellulose hydroxyalkyl ether, or one or a combination of two or more of polyvinyl alcohol, polyethylene glycol, polyvinyl pyrrolidone, polyacrylamide, and sodium polyacrylate, and preferably hydroxypropyl methylcellulose and polyacrylamide.
The novel polyimide microsphere slurry coating diaphragm is characterized by comprising a porous base film and a polyimide microsphere coating layer or a mixed coating layer of polyimide microspheres and inorganic particles, wherein the polyimide microsphere coating layer or the mixed coating layer of polyimide microspheres and inorganic particles is coated on at least one side surface of the porous base film.
Further, the porous base membrane is one of a polyolefin membrane, a cellulose membrane, a polyester membrane, a nanofiber non-woven membrane and an aramid membrane; preferably, the porous separator is a polyolefin separator.
The novel polyimide microsphere coating diaphragm coating mode is one of micro-concave coating, extrusion coating, transfer coating, dipping coating or wire rod coating, and the single-side coating thickness of the dried coating layer is 0.1-5 mu m.
An article comprising the novel polyimide microspheres or a mixture of polyimide microspheres and inorganic particles coated with a separator.
Compared with the prior art, the invention has the following excellent effects:
(1) compared with ceramic particles, the polyimide microspheres have lower density, can obviously reduce the surface density of the coated diaphragm, and are beneficial to improving the mass energy density of the battery.
(2) The polyimide microspheres are used as a high molecular material, have better compatibility with common polymer base films, and compared with a ceramic coating diaphragm, the polyimide microspheres have better cohesiveness between a coating and the base film, are not easy to shed powder and have higher peel strength.
(3) The polyimide microsphere/ceramic mixed coating formed after coating has better cohesiveness with a base film on the basis of keeping coating compactness, thereby having better heat shrinkage resistance.
(4) Compared with other existing polymer coated composite diaphragms, the polyimide microsphere slurry provided by the invention has high matching degree with the existing coating process, has extremely high production efficiency, and is beneficial to large-scale application.
Description of the drawings:
FIG. 1 is a scanning electron micrograph of a ceramic coated polyolefin separator provided in comparative example 1 of the present invention;
FIG. 2 is a scanning electron micrograph of a polyimide microsphere coated olefin separator provided in example 1 of the present invention;
FIG. 3 is a scanning electron micrograph of a polyimide microsphere/ceramic hybrid coated polyolefin membrane provided in example 2 of the present invention;
the specific implementation mode is as follows:
the invention will be further illustrated by reference to the following specific examples. It should be noted that: the following examples are only for illustrating the present invention and are not intended to limit the technical solutions described in the present invention. Thus, while the present invention has been described in detail with reference to the following examples, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted; all such modifications and variations are intended to be included herein within the scope of this disclosure and the present invention and protected by the following claims.
Example 1
A polyolefin diaphragm coated with pure polyimide microspheres is prepared by coating the polyimide microspheres on the surface of a PE diaphragm by a wet method by using a dimple coating process. The preparation method of the polyimide microsphere coated PE diaphragm comprises the following steps:
(1) preparing polyimide microspheres: according to the mol ratio of 1: 1, weighing monomer pyromellitic dianhydride (PMDA) and monomer 4, 4' -diaminodiphenyl ether (ODA), taking N, N-Dimethylformamide (DMF) as a solvent, mixing and stirring, and controlling reaction conditions to prepare the polyamic acid solution with the solid content of 15 percent and the apparent viscosity of 80 cp. Preparing polyamide acid microspheres in an electric field with the electric field intensity of 1kV/cm by adopting an electrostatic spraying mode, then putting the polyamide acid microspheres in a high-temperature heating furnace for imidization, and naturally cooling the polyamide acid microspheres to room temperature to obtain the polyimide microspheres.
(2) Preparing polyimide microsphere slurry: first, 200g of polyimide microspheres were weighed and poured into a mixed solvent of 395g of water and 5g of ethanol to obtain a polyimide microsphere dispersion. Then 2g of hexadecyl trimethyl ammonium bromide powder, 4g of sodium carboxymethyl cellulose and 20g of acrylate adhesive with the solid content of 25 percent are weighed and added into the polyimide microsphere dispersion liquid in sequence, a high-speed homogenizer is used for stirring, the rotating speed is set to be 8000r/min, and the stirring time is 60 min.
(3) Coating a diaphragm: and (3) placing the polyimide microsphere slurry obtained in the step (2) into a vacuum oven for 1 hour for defoaming treatment. Then uniformly coating the slurry on one or two surfaces of a polyolefin diaphragm with the thickness of 7 mu m by using a micro-concave coating mode, and controlling the thickness to obtain two kinds of coated diaphragms;
(4) drying a diaphragm: and (3) drying the coated diaphragm in a constant-temperature oven at the drying temperature of 60 ℃ for 15 min. The resulting single-coated separator was labeled 7+4P and the double-coated separator was labeled 2P +7+2P, where the numbers "4" and "2" represent the coating thickness. The morphology of the obtained polyimide microsphere coated polyolefin membrane is shown in figure 2.
Example 2
A polyimide microsphere/ceramic mixed coating polyolefin diaphragm uses a dimple coating process to coat polyimide microsphere slurry on the surface of a wet-process PE diaphragm, and the slurry simultaneously contains ceramic nanoparticles in a certain proportion. The preparation method of the polyimide microsphere/ceramic mixed coating polyolefin diaphragm comprises the following steps:
(1) preparing polyimide microspheres: according to the mol ratio of 1: 1, weighing monomer pyromellitic dianhydride (PMDA) and monomer 4, 4' -diaminodiphenyl ether (ODA), taking N, N-Dimethylformamide (DMF) as a solvent, mixing and stirring, and controlling reaction conditions to prepare the polyamic acid solution with the solid content of 15 percent and the apparent viscosity of 80 cp. Preparing polyamide acid microspheres in an electric field with the electric field intensity of 1kV/cm by adopting an electrostatic spraying mode, then putting the polyamide acid microspheres in a high-temperature heating furnace for imidization, and naturally cooling the polyamide acid microspheres to room temperature to obtain the polyimide microspheres.
(2) Preparing polyimide microsphere slurry: firstly, 150g of polyimide microsphere and 100g of nano alumina powder are weighed and poured into a mixed solvent of 395g of water and 5g of ethanol to obtain a primary polyimide microsphere/ceramic dispersion liquid. Then 0.8g of disodium laureth sulfosuccinate, 1.5g of cetyltrimethylammonium bromide, 5g of sodium carboxymethylcellulose and 20g of acrylate adhesive with the solid content of 25% are weighed and added into the polyimide microsphere/ceramic dispersion liquid in sequence, and a high-speed homogenizer is used for stirring, wherein the rotating speed is set to 8000r/min, and the stirring time is 60 min.
(3) Coating a diaphragm: and (3) placing the stirred polyimide microsphere slurry into a vacuum oven for 1 hour for defoaming treatment. Then uniformly coating the slurry on one or two surfaces of a polyolefin diaphragm with the thickness of 7 mu m by using a micro-concave coating mode, and controlling the thickness to obtain two kinds of coated diaphragms;
(4) drying a diaphragm: and (3) drying the coated diaphragm in a constant-temperature oven at the drying temperature of 60 ℃ for 15 min. The resulting single-coated membrane was labeled 7+4CP and the double-coated membrane was labeled 2CP +7+2CP, where the numbers "4" and "2" represent the coating thickness. The morphology of the obtained polyimide microsphere/ceramic mixed coating polyolefin membrane is shown in figure 3.
The 7+4C, 2C +7+2C, 7+4P, 2P +7+2P, 7+4CP, 2CP +7+2CP separator and 7 μm PE base film obtained by the above coating were cut into separators of 5cm × 5cm size, and the peel strength, areal density and heat shrinkage properties were tested. The thermal shrinkage test adopts heat preservation at 150 ℃ for 30min, and the shrinkage rate is tested. The results obtained are shown in table 1 below.
Comparative example 1
A polyolefin diaphragm coated with ceramic is prepared through coating nano ceramic particles on the surface of PE diaphragm by wet method. The preparation method of the ceramic coating PE diaphragm comprises the following steps:
(1) preparing ceramic coating slurry: 430g of nano alumina powder is weighed, poured into 650g of water, and stirred to obtain a primary ceramic particle dispersion liquid. Then 3g of disodium laureth sulfosuccinate, 5g of sodium carboxymethylcellulose and 20g of acrylate adhesive with the solid content of 25 percent are weighed and added into the ceramic particle dispersion liquid in sequence, and a high-speed homogenizer is used for stirring, wherein the rotating speed is set to 8000r/min, and the stirring time is 60 min.
(2) Coating a diaphragm: and (4) putting the stirred ceramic slurry into a vacuum oven for 1 hour for defoaming treatment. Then uniformly coating the slurry on one or two surfaces of a 7-micron wet-process PE diaphragm by using a micro-concave coating mode, and controlling the thickness to obtain two kinds of coated diaphragms;
(3) drying a diaphragm: and (3) drying the coated diaphragm in a constant-temperature oven at the drying temperature of 60 ℃ for 15 min. The resulting single-sided ceramic coated membrane is labeled 7+4C and the double-sided ceramic coated membrane is labeled 2C +7+2C, where the numbers "4" and "2" represent the coating thickness. The morphology of the resulting ceramic coated polyolefin separator is shown in figure 1.
TABLE 1 comparison of polyolefin based membranes and coated membranes
| Examples | Diaphragm specification | Peel strength (N/m) | Areal density (g/m) 2 ) | Heat shrinkage at 150 deg.C |
| Comparative example 1 | 7+4C | 67 | 11.82 | 8.9％ |
| Example 2 | 7+4P | 138 | 7.59 | 3.2％ |
| Example 3 | 7+4CP | 106 | 8.63 | 2.8％ |
| Comparative example 1 | 2C+7+2C | 66 | 11.79 | 4.3％ |
| Example 2 | 2P+7+2P | 136 | 7.45 | 1.5％ |
| Example 3 | 2CP+7+2CP | 95 | 8.91 | 0.9％ |
As can be seen from the data in table 1, the areal density of the polyimide microsphere coated membranes and polyimide microsphere/ceramic hybrid coated membranes is significantly lower than the ceramic coated membranes, whether single or double coated. It can be reasonably speculated from the above data that the battery adopting the polyimide microsphere or the polyimide microsphere/ceramic mixed coating membrane has higher mass energy density than the battery adopting the ceramic coated membrane under the same specification. Meanwhile, based on better compatibility between the PI microspheres and the polyolefin base film, the peel strength of the polyimide microsphere coated diaphragm and the polyimide microsphere/ceramic mixed coated diaphragm is obviously higher than that of the ceramic coated diaphragm, so that powder falling is not easy to occur in actual production. Both sides of the double coated separator did not substantially shrink as a result of heat shrinking at 150 ℃. In the single-side coated diaphragm, although the compactness of the diaphragm coated by the pure polyimide microspheres is lower than that of the diaphragm coated by the ceramic from an electron microscope picture, the adhesion force between the diaphragm coated by the pure polyimide microspheres and the base film is obviously stronger, so that the contraction degree of the diaphragm coated by the pure polyimide microspheres is equivalent to that of the diaphragm coated by the ceramic after the diaphragm is kept at 150 ℃ for 30 min. The polyimide microsphere/ceramic mixed coating membrane has obviously lower thermal shrinkage because the compactness of the mixed coating is close to that of the ceramic coating, and the adhesion force with the base membrane is obviously higher than that of the ceramic coating.
Claims (10)
1. The novel polyimide microsphere slurry is characterized by comprising 5-59 parts by mass of polyimide microspheres, 0.1-10 parts by mass of binder, 0.01-3 parts by mass of surfactant, 0.01-8 parts by mass of dispersant and 40-95 parts by mass of solvent, wherein the mass ratio of the polyimide microspheres to the inorganic particles is (100-10): (0-90).
2. The novel polyimide microsphere slurry according to claim 1, wherein the particle size of the polyimide microspheres is 0.02 μm to 10 μm.
3. The novel polyimide microsphere slurry according to claim 1, wherein the inorganic particles are one or a combination of two or more of silica, alumina, boehmite, zirconia, magnesium hydroxide, zinc oxide and titania, and the particle size of the inorganic particles is in the range of 0.01 μm to 2 μm.
4. The novel polyimide microsphere slurry according to claim 1, wherein the binder is one or a combination of two or more selected from the group consisting of polyvinyl alcohol, polytetrafluoroethylene, sodium carboxymethylcellulose, polyurethane, styrene-butadiene rubber, fluorinated rubber, styrene-butadiene polymer, polyvinylidene fluoride-hexafluoropropylene, polyacrylic acid, polymethacrylic acid, polyacrylate, polymethyl methacrylate, and polyacrylonitrile.
5. The novel polyimide microsphere slurry according to claim 1, wherein the solvent is an organic solvent or an aqueous solvent, the organic solvent is one or a combination of two or more of N-methylpyrrolidone, dimethyl sulfoxide, N-dimethylformamide, N-dimethylacetamide and acetone, and the aqueous solvent is pure water or a combination of one or two or more of water, ethanol, ethylene glycol, propanol, glycerol, isopropanol and butanol.
6. The novel polyimide microsphere slurry according to claim 1, characterized in that the surfactant is a fluorocarbon surfactant such as perfluoroalkyl ether ethanolamine salt, perfluoroalkyl ether quaternary ammonium salt; nonionic surfactants such as polyethylene glycol type, polyhydric alcohol type, block copolyether; cationic surfactants such as cetyltrimethylammonium bromide, dodecyltrimethylammonium bromide, dodecylpyridinium bromide; anionic surfactants such as one or a combination of two or more of fatty acid salts, sulfonates, phosphates and sulfate salts, preferably fluorocarbon surfactants and nonionic surfactants.
7. The novel polyimide microsphere slurry according to claim 1, wherein the dispersant is one or a combination of two or more selected from the group consisting of cellulose ether dispersants such as hydroxypropyl methylcellulose, hydroxyethyl cellulose, cellulose alkyl ether and cellulose hydroxyalkyl ether, polyvinyl alcohol, polyethylene glycol, polyvinyl pyrrolidone, polyacrylamide and sodium polyacrylate, preferably hydroxypropyl methylcellulose and polyacrylamide.
8. The novel polyimide microsphere coated diaphragm is characterized by comprising a porous base film and a polyimide microsphere coating layer or a mixed coating layer of polyimide microspheres and inorganic particles, wherein the polyimide microsphere coating layer or the mixed coating layer of polyimide microspheres and inorganic particles is coated on at least one side surface of the porous base film.
9. The novel polyimide microsphere coated membrane according to claim 8, wherein the porous base membrane is one of a polyolefin membrane, a cellulose membrane, a polyester membrane, a nanofiber non-woven membrane and an aramid membrane; preferably, the porous separator is a polyolefin separator.
10. The novel polyimide microsphere coated membrane as claimed in claim 8, wherein the coated membrane is obtained by coating the surface of a porous base membrane by a method of micro-gravure coating, extrusion coating, transfer coating, dip coating or wire rod coating and then drying, and the single-side coating thickness of the dried coating layer is 0.1-5 μm.
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| CN116315447A (en) * | 2023-05-04 | 2023-06-23 | 合肥长阳新能源科技有限公司 | Polyimide porous microsphere coated diaphragm for lithium battery and preparation method thereof |
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| CN103078077A (en) * | 2013-01-17 | 2013-05-01 | 中国科学院金属研究所 | Lithium ion battery diaphragm with special structure and preparation method thereof |
| CN109103397A (en) * | 2018-09-28 | 2018-12-28 | 河南福森新能源科技有限公司 | A kind of preparation method of lithium ion battery ceramic coating membrane |
| CN109817870A (en) * | 2018-12-29 | 2019-05-28 | 东莞东阳光科研发有限公司 | Polyimide microsphere slurry, composite diaphragm and lithium ion battery |
| WO2020150886A1 (en) * | 2019-01-22 | 2020-07-30 | 东莞东阳光科研发有限公司 | Polyimide microsphere slurry, composite separator, and lithium-ion battery |
| CN113169418A (en) * | 2019-01-22 | 2021-07-23 | 东莞东阳光科研发有限公司 | Polyimide microsphere slurry, composite diaphragm and lithium ion battery |
| CN113969006A (en) * | 2021-10-21 | 2022-01-25 | 北京宇程科技有限公司 | Polyimide coating modified polyolefin composite diaphragm and preparation method thereof |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116315447A (en) * | 2023-05-04 | 2023-06-23 | 合肥长阳新能源科技有限公司 | Polyimide porous microsphere coated diaphragm for lithium battery and preparation method thereof |
| CN116315447B (en) * | 2023-05-04 | 2023-08-01 | 合肥长阳新能源科技有限公司 | Polyimide porous microsphere coated diaphragm for lithium battery and preparation method thereof |
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