Nanometer coating liquid, preparation method thereof and nanometer coating diaphragm

Abstract

The invention relates to the technical field of diaphragms for lithium ion batteries, in particular to nano coating liquid, a preparation method of the nano coating liquid and a nano coating diaphragm. The nano coating liquid provided by the invention is prepared from the following components in parts by mass: 20 to 95 parts of large-particle inorganic powder, 5 to 80 parts of small-particle inorganic powder, 5 to 30 parts of nano cellulose, 1 to 5 parts of a solution type binder, 1 to 5 parts of an emulsion type binder, 0 to 1 part of a wetting agent and 200 to 800 parts of a polar solvent, the D50 of the large-particle inorganic powder is 0.1 to 3 [mu] m; and the D50 of the small-particle inorganic powder is 10 to 150 nm. The diaphragm prepared from the nano coating liquid provided by the invention has good heat resistance on the premise of keeping good liquid absorption capacity and air permeability.

Description

Technical Field

[0001] The present invention relates to the technical field of diaphragms for lithium - ion batteries, and particularly to a nano - coating liquid, a preparation method thereof, and a nano - coated diaphragm. Background Art

[0002] In lithium - ion batteries, the diaphragm has two main functions: First, since the diaphragm is an electronically insulating polymer functional material, it can separate the positive and negative electrodes of the battery to prevent direct contact between the two electrodes and cause a short - circuit; Second, the diaphragm has a large number of tortuous and through - hole micropores, which can allow lithium ions in the electrolyte to freely pass through the micropores, migrate between the positive and negative electrodes to form a circuit, while electrons form an electric current through the external circuit and are provided for use by electrical equipment.

[0003] Existing lithium - ion battery diaphragms, such as polyolefin microporous membranes and polyethylene microporous membranes, have poor high - temperature stability and poor wettability to electrolytes. In order to improve the high - temperature stability of lithium - ion battery diaphragms and their wettability to electrolytes, the main solution at present is to coat alumina ceramic particle materials on the surface of microporous diaphragms. Although the heat resistance of the diaphragm has been improved to a certain extent after coating with alumina ceramic particles, when the coating thickness exceeds 3μm, its heat - resistance upper limit does not exceed 150°C (generally, the thicker the thickness, the better the heat - resistance), which is difficult to meet the actual requirements. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a nano - coating liquid, a preparation method thereof, and a nano - coated diaphragm. The diaphragm formed by the nano - coating liquid provided by the present invention has good heat - resistance performance on the premise of maintaining good liquid absorption capacity and air permeability.

[0005] To achieve the above - mentioned invention purpose, the present invention provides the following technical solutions:

[0006] The present invention provides a nano - coating liquid, which, by mass fraction, includes: 20 - 95 parts of large - particle inorganic powder, 5 - 80 parts of small - particle inorganic powder, 5 - 30 parts of nano - cellulose, 1 - 5 parts of solution - type binder, 1 - 5 parts of emulsion - type binder, 0 - 1 part of wetting agent, and 200 - 800 parts of polar solvent;

[0007] The D50 of the large - particle inorganic powder is 0.1 - 3μm;

[0008] The D50 of the small - particle inorganic powder is 10 - 150nm.

[0009] Preferably, the large - particle inorganic powder includes one or more of alumina, boehmite, titanium dioxide, silicon dioxide, cerium oxide, magnesium aluminate spinel, zirconium oxide, and lithium phosphate.

[0010] Preferably, the alumina includes porous alumina and / or non-porous alumina; the large-particle inorganic powder includes porous alumina and / or non-porous alumina.

[0011] Preferably, the pore diameter of the porous alumina is 2-60 nm.

[0012] Preferably, the solid content of the nano-coating liquid is 10-40%.

[0013] Preferably, the small-particle inorganic powder includes one or more of fumed alumina, boehmite, titanium dioxide, silicon dioxide, and lithium-based compounds.

[0014] Preferably, the nano-cellulose includes one or more of cellulose nanofibers, cellulose nanocrystals, bacterial nanocellulose, and microfibrillated cellulose.

[0015] Preferably, the solution-type binder includes one or more of polyvinylidene fluoride, polyacrylic acid, acrylate-acrylonitrile copolymer, polyacrylate, and acrylic derivative multi-component copolymer;

[0016] The emulsion-type binder includes one or more of styrene-butadiene rubber emulsion, polystyrene emulsion, styrene-acrylic emulsion, and polyvinyl acetate emulsion.

[0017] Preferably, the polar solvent includes one or more of water, N-methylpyrrolidone, dimethylacetamide, and acetone.

[0018] The present invention provides a method for preparing the nano-coating liquid described in the above scheme, including the following steps: dispersing nano-cellulose, large-particle inorganic powder, and small-particle inorganic powder into a polar solvent, and adding a solution-type binder, an emulsion-type binder, and a wetting agent to the obtained dispersion to obtain the nano-coating liquid.

[0019] The present invention provides a nano-coated separator formed by coating the nano-coating liquid described in the above scheme or the nano-coating liquid prepared by the preparation method described in the above scheme on a lithium-ion battery separator.

[0020] The present invention provides a nano - coating liquid, which, by mass fraction, comprises: 20 - 95 parts of large - particle inorganic powder, 5 - 80 parts of small - particle inorganic powder, 5 - 30 parts of nano - cellulose, 1 - 5 parts of solution - type binder, 1 - 5 parts of emulsion - type binder, 0 - 1 part of wetting agent, and 200 - 800 parts of polar solvent; the D50 of the large - particle inorganic powder is 0.1 - 3 μm; the D50 of the small - particle inorganic powder is 10 - 150 nm. The nano - coating liquid provided by the present invention contains nano - cellulose. The nano - cellulose contains a large number of lipophilic - CH2 groups, which can significantly improve the liquid absorption rate and wettability of the battery separator; the addition of the small - particle inorganic powder can form more voids in the separator, improving the air permeability of the separator. The large - particle inorganic powder serves as the skeleton of the separator and can resist the internal force of the separator during heat - induced stretching by its own gravity. The nano - cellulose can form a film by itself. It interpenetrates between the large - particle inorganic powder and the small - particle inorganic powder to form a net - like structure with high stability. At the same time, the mechanical strength of the nano - cellulose is very high, so it can effectively resist the internal force of the separator during heating above 180 °C, achieving a good heat - resistant shrinkage effect. In addition, the nano - coating liquid provided by the present invention contains both a solution - type binder and an emulsion - type binder, having better heat - resistant performance than a single - type binder.

[0021] Further, the large - particle - sized alumina of the present invention can be porous alumina. Due to the porous nature of the porous alumina itself, a higher liquid absorption rate can be achieved compared to non - porous alumina (also known as conventional alumina). Brief Description of the Drawings

[0022] Figure 1 Photograph of the separator after single - side coating with the coating liquid of Example 1 at 180 °C / h;

[0023] Figure 2 Photograph of the separator after double - side coating (1#) with the coating liquid of Example 1 at 200 °C / h. Detailed Description of the Invention

[0024] The present invention provides a nano - coating liquid, which, by mass fraction, comprises: 20 - 95 parts of large - particle inorganic powder, 5 - 80 parts of small - particle inorganic powder, 5 - 30 parts of nano - cellulose, 1 - 5 parts of solution - type binder, 1 - 5 parts of emulsion - type binder, 0 - 1 part of wetting agent, and 200 - 800 parts of polar solvent;

[0025] The D50 of the large - particle inorganic powder is 0.1 - 3 μm;

[0026] The D50 of the small - particle inorganic powder is 10 - 150 nm.

[0027] In the present invention, unless otherwise specified, the raw materials used are well - known commercially available products in the art.

[0028] In terms of parts by mass, the nano - coating liquid provided by the present invention comprises 20 - 95 parts of large - particle inorganic powder. In specific embodiments, it can be 20 parts, 30 parts, 40 parts, 50 parts, 60 parts, 70 parts, 80 parts, 90 parts or 95 parts. In the present invention, the D50 of the large - particle inorganic powder is 0.1 - 3 μm. In specific embodiments, it can be 0.1 μm, 0.2 μm, 0.4 μm, 0.6 μm, 0.8 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm or 3 μm, and most preferably 0.2 - 0.6 μm. In the present invention, the large - particle inorganic powder is preferably one or more of alumina, boehmite (AlOOH), titanium dioxide, silicon dioxide, cerium - magnesium - aluminum spinel (MgAl2O4), zirconia and lithium phosphate. Among them, in terms of crystal form, the alumina is preferably at least one of α - alumina, θ - alumina, δ - alumina, γ - alumina; in terms of pore structure, the alumina preferably comprises porous alumina and / or non - porous alumina, and more preferably porous alumina. When the large - particle inorganic powder is porous alumina, due to the porous characteristics of the porous alumina itself, a higher liquid absorption rate can be achieved compared with conventional alumina. In the present invention, the pore diameter of the porous alumina is preferably 2 - 60 nm. In specific embodiments, it can be 2 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 40 nm, 50 nm, 55 nm or 60 nm. In the present invention, the large - particle inorganic powder serves as the skeleton of the nano - coated separator, and can resist the internal force of the separator during heat - induced stretching by its own gravity, thereby improving the heat resistance of the separator.

[0029] Based on the unit mass parts of the large - particle inorganic powder, the nano - coating liquid provided by the present invention comprises 5 - 80 parts of small - particle inorganic powder. In specific embodiments, it can be 5 parts, 10 parts, 20 parts, 30 parts, 40 parts, 50 parts, 60 parts, 70 parts or 80 parts. In the present invention, the D50 of the small - particle inorganic powder is 10 - 150 nm. In specific embodiments, it can be 10 nm, 20 nm, 30 nm, 50 nm, 60 nm, 80 nm, 100 nm, 120 nm, 140 nm or 150 nm; the small - particle inorganic powder preferably comprises one or more of fumed alumina, boehmite, titanium dioxide, silicon dioxide and lithium - based compounds. The lithium - based compounds are preferably one or more of lithium phosphate, lithium fluoride, lithium titanium aluminum phosphate, lithium zirconium phosphate, lithium titanium phosphate, lithium germanium phosphate, lithium lanthanum titanate, lithium sulfide phosphate, lithium sulfide phosphate germanium and lithium lanthanum zirconium oxide. In the present invention, the function of the small - particle inorganic powder is to form more voids in the separator, thereby improving the air permeability of the nano - coated separator.

[0030] Based on the unit mass fraction of the large-particle inorganic powder, the nano-coating liquid provided by the present invention comprises 5 to 30 parts of nano-cellulose, which can be 5 parts, 10 parts, 15 parts, 20 parts, 25 parts or 30 parts in specific embodiments. In the present invention, the nano-cellulose preferably comprises one or more of cellulose nanofibers, cellulose nanocrystals, bacterial nano-cellulose and microfibrillated cellulose. From the perspective of whether it is modified, the nano-cellulose can be unmodified nano-cellulose, sulfonated modified nano-cellulose, carboxylated modified nano-cellulose, carboxymethylated modified nano-cellulose, esterified modified nano-cellulose, etherified modified nano-cellulose, silanized modified nano-cellulose. In specific embodiments, it is sulfonated modified cellulose nanocrystals, carboxylated modified cellulose nanocrystals; more preferably sulfonated modified cellulose nanocrystals, carboxylated modified cellulose nanocrystals. In the present invention, the nano-cellulose contains a large number of lipophilic -CH2 groups, which can greatly improve the liquid absorption rate and wettability of the battery separator; in addition, the nano-cellulose can form a film by itself. It interpenetrates between the large-particle inorganic powder and the small-particle inorganic powder to form a network-like structure, which has high stability. At the same time, the mechanical strength of the nano-cellulose is very high, and it can effectively resist the internal force of the separator heated above 180°C, achieving a good heat shrinkage effect.

[0031] Based on the unit mass fraction of the large-particle inorganic powder, the nano-coating liquid provided by the present invention comprises 1 to 5 parts of a solution-type binder, which can be 1 part, 2 parts, 3 parts, 4 parts or 5 parts in specific embodiments. In the present invention, the solution-type binder preferably comprises one or more of polyvinylidene fluoride, polyacrylic acid, acrylate-acrylonitrile copolymer, polyacrylate and acrylic derivative multi-copolymer; the specific polyacrylates can be acrylate, n-butyl acrylate, and the specific acrylic derivative multi-copolymers can be acrylic acid-acrylate copolymer, acrylonitrile multi-copolymer, sodium polyacrylate grafted carboxymethyl cellulose, polyacrylic acid-polyaspartic acid-poly(N-isopropylacrylamide) block copolymer.

[0032] Based on the unit mass fraction of the large-particle inorganic powder, the nano-coating liquid provided by the present invention comprises 1 to 5 parts of an emulsion-type binder, which can be 1 part, 2 parts, 3 parts, 4 parts or 5 parts in specific embodiments. In the present invention, the emulsion-type binder preferably comprises one or more of styrene-butadiene rubber emulsion, polystyrene emulsion, styrene-acrylic emulsion and polyvinyl acetate emulsion. In the present invention, the functions of the solution-type binder and the emulsion-type binder are to improve the adhesion between the large-particle inorganic powder, the small-particle inorganic powder, the nano-cellulose and the lithium-ion battery separator. The present invention simultaneously uses a solution-type binder and an emulsion-type binder, and has better heat resistance than a single type of binder.

[0033] Based on the unit mass fraction of the large-particle inorganic powder, the nano-coating liquid provided by the present invention includes 0 to 1 part of a wetting agent, which can be 0 part, 0.1 part, 0.3 part, 0.5 part, 0.7 part, 0.8 part or 1 part in specific embodiments. In the present invention, the wetting agent preferably includes one or more of polyether-modified polysiloxane copolymer, sodium dodecylsulfonate, perfluoroalkyl ethoxy ether alcohol, polyether-modified siloxane, and sodium hydroxyethylsulfonate. In the present invention, the function of the wetting agent is to improve the wettability of the nano-coated separator.

[0034] Based on the unit mass fraction of the large-particle inorganic powder, the nano-coating liquid provided by the present invention includes 200 to 800 parts of a polar solvent, which can be 200 parts, 300 parts, 400 parts, 500 parts, 600 parts, 700 parts or 800 parts in specific embodiments. In the present invention, the polar solvent preferably includes one or more of water, N-methylpyrrolidone, dimethylacetamide, and acetone.

[0035] In the present invention, the solid content of the nano-coating liquid is preferably 10 to 40%, which can be 10%, 15%, 20%, 25%, 30%, 35% or 40% in specific embodiments.

[0036] The present invention provides a preparation method of the nano-coating liquid described in the above scheme, including the following steps: dispersing nano-cellulose, large-particle inorganic powder and small-particle inorganic powder into a polar solvent, and adding a solution-type binder, an emulsion-type binder and a wetting agent to the obtained dispersion liquid to obtain the nano-coating liquid.

[0037] The present invention has no special requirements for the dispersion process of the nano-cellulose, large-particle inorganic powder and small-particle inorganic powder, and it is only necessary to disperse each component evenly. In the embodiments of the present invention, specifically, the nano-cellulose, large-particle inorganic powder and small-particle inorganic powder are added to a polar organic solvent and stirred evenly.

[0038] In the present invention, the solution-type binder, emulsion-type binder and wetting agent are preferably added separately, and more preferably, the solution-type binder or emulsion-type binder is added first and stirred evenly, then the other binder is added and stirred evenly, and finally the wetting agent is added and stirred evenly.

[0039] In the present invention, after all components are stirred evenly, the present invention preferably passes through a 200-700 mesh filter screen to obtain the nano-coating liquid. In specific embodiments, it can pass through a 200-mesh, 300-mesh, 400-mesh, 500-mesh, 600-mesh or 700-mesh filter screen.

[0040] The nano-coating liquid provided by the present invention has the advantages of good dispersibility, excellent processability and easy industrial production.

[0041] The present invention provides a nano-coated separator, which is formed by coating the above-mentioned nano-coating liquid on a lithium-ion battery separator.

[0042] In the present invention, the lithium-ion battery separator preferably includes a polyolefin separator, a non-woven fabric separator or a polymethylpentene separator. The polyolefin separator is preferably a polyethylene microporous membrane, a polypropylene microporous membrane, or a two-layer or multi-layer composite membrane composed of a polyethylene microporous membrane and a polypropylene microporous membrane.

[0043] In the present invention, the coating is preferably single-sided coating or double-sided coating. The coating thickness of each side is independently preferably 0.5 - 4 μm, and in specific embodiments, it can be 0.5 μm, 1 μm, 2 μm, 3 μm or 4 μm.

[0044] The present invention has no special requirements for the coating method, and any coating method well-known in the art can be used, such as knife coating, dip coating, spraying, roll coating or extrusion coating.

[0045] Compared with the existing ordinary alumina coating liquid, the nano-coating liquid provided by the present invention has simple preparation raw materials and processes; at the same time, compared with the existing ordinary alumina separator, the nano-coated separator provided by the present invention has a higher liquid absorption rate, a higher heat resistance temperature, and is more helpful to improve the safety performance of the battery.

[0046] The following examples are used to illustrate in detail the nano-coating liquid provided by the present invention, its preparation method, and the nano-coated separator, but they should not be construed as limiting the protection scope of the present invention.

[0047] In the following examples and comparative examples, the D50 of the porous alumina is 0.4 μm, the pore diameter is 20 nm, and the D50 of the fumed alumina is 45 nm.

[0048] The following carboxylated cellulose nanowhiskers used in the examples and comparative examples are of the model C-CNC, purchased from Guilin Qihong Technology Co., Ltd.; the sulfonated modified cellulose nanowhiskers are of the model CNC-C, purchased from Guilin Qihong Technology Co., Ltd.; the cellulose nanofibers are of the model CNF-C, purchased from Guilin Qihong Technology Co., Ltd.; the polyacrylate binder is of the model LA132, purchased from Dongguan Donglin High Polymer Materials Co., Ltd.; the polystyrene emulsion binder is of the model SN-307R, purchased from Shanghai Waidian International Trade Co., Ltd.

[0049] Example 1

[0050] Disperse 10 parts of carboxylated cellulose nanowhiskers, 40 parts of porous alumina, and 45 parts of fumed alumina in 400 parts of deionized water and stir evenly; then add 2.5 parts of polyacrylate binder to the evenly stirred mixed liquid and stir evenly; add 2.5 parts of polystyrene emulsion to the mixed liquid again and stir evenly; finally, add 0.1 part of polyether-modified silicone and stir evenly. After filtering through a 300-mesh filter screen, a nano-coating liquid can be obtained with a solid content of 20%. Coating one side of the polyethylene microporous membrane by roll coating can obtain the nano-coated separator.

[0051] Example 2

[0052] Disperse 10 parts of carboxylated cellulose nanowhiskers, 20 parts of porous alumina, and 65 parts of fumed alumina in 400 parts of deionized water and stir evenly; then add 2.5 parts of polyacrylate binder to the evenly stirred mixed liquid and stir evenly; add 2.5 parts of polystyrene emulsion to the mixed liquid again and stir evenly; finally, add 0.1 part of polyether-modified silicone and stir evenly. After filtering through a 300-mesh filter screen, a nano-coating liquid can be obtained with a solid content of 20%. Coating one side of the polyethylene microporous membrane by roll coating can obtain the nano-coated separator.

[0053] Example 3

[0054] Disperse 10 parts of carboxylated cellulose nanowhiskers, 60 parts of porous alumina, and 25 parts of fumed alumina in 400 parts of deionized water and stir evenly; then add 2.5 parts of polyacrylate binder to the evenly stirred mixed liquid and stir evenly; add 2.5 parts of polystyrene emulsion to the mixed liquid again and stir evenly; finally, add 0.1 part of perfluoroalkyl ethoxy ether alcohol and stir evenly. After filtering through a 300-mesh filter screen, a nano-coating liquid can be obtained with a solid content of 20%. Coating one side of the polyethylene microporous membrane by roll coating can obtain the nano-coated separator.

[0055] Example 4

[0056] Disperse 15 parts of carboxylated cellulose nanowhiskers, 70 parts of porous alumina, and 10 parts of fumed alumina in 400 parts of deionized water and stir evenly; then add 2 parts of polyacrylate binder to the evenly stirred mixed liquid and stir evenly; add 3 parts of polystyrene emulsion to the mixed liquid again and stir evenly; finally, add 0.1 part of polyether-modified silicone and stir evenly. After filtering through a 300-mesh filter screen, a nano-coating liquid can be obtained with a solid content of 20%. Coating one side of the polyethylene microporous membrane by roll coating can obtain the nano-coated separator.

[0057] Example 5

[0058] Disperse 20 parts of carboxylated cellulose nanowhiskers, 35 parts of porous alumina, and 40 parts of fumed alumina in 400 parts of deionized water and stir evenly; then add 2 parts of polyacrylate binder to the evenly stirred mixed liquid and stir evenly; add 3 parts of polystyrene emulsion to the mixed liquid again and stir evenly; finally, add 0.3 part of sodium hydroxyethyl sulfonate and stir evenly. After suction filtration through a 300-mesh filter screen, a nano-coating liquid can be obtained, and the solid content is 20%. Coating one side of the polyethylene microporous membrane by roll coating can obtain a nano-coated separator.

[0059] Example 6

[0060] Disperse 25 parts of carboxylated cellulose nanowhiskers, 35 parts of porous alumina, and 35 parts of fumed alumina in 500 parts of deionized water and stir evenly; then add 2 parts of polyacrylate binder to the evenly stirred mixed liquid and stir evenly; add 3 parts of polystyrene emulsion to the mixed liquid again and stir evenly; finally, add 0.3 part of sodium dodecyl sulfonate and stir evenly. After suction filtration through a 300-mesh filter screen, a nano-coating liquid can be obtained, and the solid content is 16.7%. Coating one side of the polyethylene microporous membrane by roll coating can obtain a nano-coated separator.

[0061] Example 7

[0062] Disperse 10 parts of carboxylated cellulose nanowhiskers, 40 parts of conventional alumina (D50 is 400 nm), and 45 parts of fumed alumina in 400 parts of deionized water and stir evenly; then add 2.5 parts of polyacrylate binder to the evenly stirred mixed liquid and stir evenly; finally, add 2.5 parts of polystyrene emulsion to the mixed liquid and stir evenly. After suction filtration through a 300-mesh filter screen, a nano-coating liquid can be obtained, and the solid content is 20%. Coating one side of the polyethylene microporous membrane by roll coating can obtain a nano-coated separator.

[0063] Example 8

[0064] Disperse 10 parts of carboxylated cellulose nanowhiskers, 40 parts of boehmite (D50 is 400 nm), and 45 parts of titanium dioxide (D50 is 50 nm) in 400 parts of deionized water and stir evenly; then add 2.5 parts of acrylate-acrylonitrile copolymer binder to the evenly stirred mixed liquid and stir evenly; add 2.5 parts of polystyrene emulsion to the mixed liquid again and stir evenly; finally, add 0.1 part of polyether-modified silicone and stir evenly. After suction filtration through a 300-mesh filter screen, a nano-coating liquid can be obtained, and the solid content is 20%. Coating one side of the polyethylene microporous membrane by roll coating can obtain a nano-coated separator.

[0065] Example 9

[0066] Disperse 8 parts of sulfonated modified cellulose nanowhiskers, 42 parts of titanium dioxide (D50 is 400 nm), and 45 parts of lithium phosphate (D50 is 45 nm) in 450 parts of deionized water and stir evenly; then add 2.5 parts of acrylonitrile copolymer binder to the evenly stirred mixed liquid and stir evenly; add 2.5 parts of styrene-butadiene rubber latex to the mixed liquid again and stir evenly; finally, add 0.1 part of polyether-modified silicone and stir evenly. Subsequently, after suction filtration through a 300-mesh filter screen, a nano-coating liquid can be obtained. The solid content is 18.2%. Coating one side of the polyethylene microporous membrane by roll coating can obtain a nano-coated separator.

[0067] Example 10

[0068] Disperse 8 parts of sulfonated modified cellulose nanowhiskers, 42 parts of silicon dioxide (D50 is 400 nm), and 45 parts of lithium titanium aluminum phosphate (D50 is 50 nm) in 450 parts of deionized water and stir evenly; then add 2.5 parts of polyacrylate binder to the evenly stirred mixed liquid and stir evenly; add 2.5 parts of polystyrene latex to the mixed liquid again and stir evenly; finally, add 0.1 part of polyether-modified silicone and stir evenly. Subsequently, after suction filtration through a 300-mesh filter screen, a nano-coating liquid can be obtained. The solid content is 18.2%. Coating one side of the polyethylene microporous membrane by roll coating can obtain a nano-coated separator.

[0069] Example 11

[0070] Disperse 10 parts of carboxylated cellulose nanowhiskers, 40 parts of cerium oxide (D50 is 400 nm), and 45 parts of lithium germanium sulfide phosphide (D50 is 50 nm) in 400 parts of deionized water and stir evenly; then add 2.5 parts of polyacrylate binder to the evenly stirred mixed liquid and stir evenly; add 2.5 parts of polystyrene latex to the mixed liquid again and stir evenly; finally, add 0.1 part of polyether-modified silicone and stir evenly. Subsequently, after suction filtration through a 300-mesh filter screen, a nano-coating liquid can be obtained. The solid content is 20%. Coating one side of the polyethylene microporous membrane by roll coating can obtain a nano-coated separator.

[0071] Example 12

[0072] Disperse 7 parts of cellulose nanofibers, 43 parts of magnesium aluminate spinel (D50 is 400 nm), and 45 parts of lithium lanthanum zirconium oxide (D50 is 50 nm) in 400 parts of deionized water and stir evenly; then add 2.5 parts of polyacrylate binder to the evenly stirred mixed liquid and stir evenly; add 2.5 parts of polystyrene emulsion to the mixed liquid again and stir evenly; finally, add 0.1 part of polyether-modified silicone and stir evenly. Subsequently, after suction filtration through a 300-mesh filter screen, a nano-coating liquid can be obtained with a solid content of 20%. Coating one side of a polyethylene microporous membrane by roll coating can obtain a nano-coated separator.

[0073] Example 13

[0074] Disperse 7 parts of cellulose nanofibers, 43 parts of zirconia (D50 is 400 nm), and 45 parts of lithium lanthanum titanate (D50 is 55 nm) in 400 parts of deionized water and stir evenly; then add 2.5 parts of polyacrylate binder to the evenly stirred mixed liquid and stir evenly; add 2.5 parts of polystyrene emulsion to the mixed liquid again and stir evenly; finally, add 0.1 part of polyether-modified silicone and stir evenly. Subsequently, after suction filtration through a 300-mesh filter screen, a nano-coating liquid can be obtained with a solid content of 20%. Coating one side of a polyethylene microporous membrane by roll coating can obtain a nano-coated separator.

[0075] Perform performance tests on each example and the polyethylene microporous membrane (base membrane). Among them, use a thickness tester to measure the thickness of the battery separator, measure at 5 arbitrary points on the separator, and calculate the average value; the thermal shrinkage rate test is detected according to the method in reference GB / T 12027-2004; the liquid absorption rate test method is as follows: weigh the battery separator, then immerse it in a conventional electrolyte for 10 min, take out the battery separator, dry the surface electrolyte with filter paper, weigh the mass again, calculate the percentage increase in mass after immersion in the electrolyte, measure 3 times respectively, and the average value is the liquid absorption rate; the peel strength test is carried out according to the test method in reference GB / T 2792-1998. The test results are shown in Table 1 and Table 2.

[0076] Table 1 Performance of Examples 1-7 and the Base Membrane

[0077]

[0078]

[0079] Table 2 Performance of Examples 8-13 and the Base Membrane

[0080]

[0081] Note: The thickness in each embodiment is the base film thickness + coating thickness. The difference between 1# and Example 1 is that Example 1 is single-sided coating and 1# is double-sided coating. The smaller the air permeability increase value, the better, which represents more pores and is more beneficial to the fast charging performance; the lower the basis weight, the better, which is more beneficial to the lightweight of the battery; MD represents the machine direction, TD represents the transverse direction, and the smaller the thermal shrinkage, the better the heat resistance performance.

[0082] Figure 1 It is a photo of the separator after single-sided coating with the coating liquid of Example 1 at 180 °C / h for testing; Figure 2 It is a photo of the separator after double-sided coating (1#) with the coating liquid of Example 1 at 200 °C / h for testing. From Figure 1 and Figure 2 it can be seen that the separator formed by the coating liquid provided by the present invention has good heat resistance and still maintains good dimensional stability after undergoing a high-temperature test at 200 °C.

[0083] Comparative Example 1

[0084] Keeping the solid content unchanged as in Example 1, nano-cellulose and small particle inorganic powder are omitted. Specifically:

[0085] 95 parts of porous alumina are dispersed in 400 parts of deionized water and stirred evenly; then 2.5 parts of polyacrylate binder are added to the evenly stirred mixed liquid and stirred evenly; again, 2.5 parts of polystyrene emulsion are added to the mixed liquid and stirred evenly; finally, 0.1 part of polyether-modified silicone is added and stirred evenly. Then, after filtration through a 300-mesh filter screen, the porous alumina coating liquid can be obtained. By means of roll coating on one side of the polyethylene microporous membrane, the nano-coated separator for lithium-ion batteries can be obtained.

[0086] Comparative Example 2

[0087] Based on Example 1, nano-cellulose is omitted. Specifically:

[0088] 45 parts of fumed alumina and 40 parts of porous alumina are dispersed in 360 parts of deionized water and stirred evenly; then 2.5 parts of polyacrylate binder are added to the evenly stirred mixed liquid and stirred evenly; again, 2.5 parts of polystyrene emulsion are added to the mixed liquid and stirred evenly; finally, 0.1 part of polyether-modified silicone is added and stirred evenly. Then, after filtration through a 300-mesh filter screen, the porous alumina coating liquid can be obtained with a solid content of 20%. By means of roll coating on one side of the polyethylene microporous membrane, the nano-coated separator for lithium-ion batteries can be obtained.

[0089] Comparative Example 3

[0090] The difference from Example 1 is only that a single binder is used. Specifically:

[0091] Disperse 10 parts of carboxylated cellulose nanowhiskers, 40 parts of porous alumina, and 45 parts of fumed alumina in 400 parts of deionized water and stir evenly; finally, add 5 parts of polystyrene emulsion to the mixed liquid and stir evenly. Then add 0.1 part of polyether-modified silicone and stir evenly; subsequently, filter through a 300-mesh filter screen to obtain a porous alumina nano-coating solution with a solid content of 20%. Coating one side of the polyethylene microporous membrane by roll coating can obtain a nano-coated separator for lithium-ion batteries.

[0092] Comparative Example 4

[0093] Based on Example 7, omit the nanocellulose. Specifically:

[0094] Disperse 40 parts of conventional alumina (D50 is 400 nm) and 45 parts of fumed alumina in 360 parts of deionized water and stir evenly; then add 2.5 parts of polyacrylate binder to the evenly stirred mixed liquid and stir evenly; add 2.5 parts of polystyrene emulsion to the mixed liquid again and stir evenly; subsequently, filter through a 300-mesh filter screen to obtain a conventional alumina coating solution with a solid content of 20%. Coating one side of the polyethylene microporous membrane by roll coating can obtain a nano-coated separator for lithium-ion batteries.

[0095] Comparative Example 5

[0096] Replace the small particle inorganic powder in Example 1 with porous alumina. Specifically:

[0097] Disperse 10 parts of carboxylated cellulose nanowhiskers and 85 parts of porous alumina in 400 parts of deionized water and stir evenly; then add 2.5 parts of polyacrylate binder to the evenly stirred mixed liquid and stir evenly; add 2.5 parts of polystyrene emulsion to the mixed liquid again and stir evenly; finally, add 0.1 part of polyether-modified silicone and stir evenly. Subsequently, filter through a 300-mesh filter screen to obtain a porous alumina coating solution with a solid content of 20%. Coating one side of the polyethylene microporous membrane by roll coating can obtain a nano-coated separator for lithium-ion batteries.

[0098] Table 3 Performance of Comparative Examples

[0099]

[0100]

[0101] Data analysis:

[0102] By analyzing the data of the examples in Tables 1-2 above and the comparative examples in Table 3, it can be seen that Example 1 is the optimal solution. The heat resistance of the single-sided coating of the Example 1 formulation reaches 180 °C / h, and the heat resistance of the double-sided coating (1#) reaches 200 °C / h. At the same time, there are significant improvements in air permeability, puncture strength, and liquid absorption rate. Comparing the performance test results of the examples and the comparative examples, the addition of nanocellulose can effectively improve the heat resistance of the separator and the liquid absorption rate of the electrolyte. This is because nanocellulose contains a large number of lipophilic -CH2 groups, and combined with the porous structure of porous alumina itself, the combination of the two can greatly improve the liquid absorption rate of the electrolyte; in improving heat resistance, due to the long and small size of nanocellulose, it can squeeze into the gaps between alumina and alumina, building a network structure of nanocellulose, effectively resisting the internal force of the base film thermal shrinkage. In the comparative example without the addition of nanocellulose, it does not have the effect of this network structure. When the base film undergoes thermal shrinkage, it can only rely on its own gravity to resist the internal force of the base film thermal shrinkage, and it is difficult to improve the heat resistance of the battery separator by pure ceramic coating.

[0103] The above are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A nano-coating liquid, characterized in that, By mass fraction, it includes: 20 - 95 parts of large - particle inorganic powder, 5 - 80 parts of small - particle inorganic powder, 5 - 30 parts of nanocellulose, 1 - 5 parts of solution - type binder, 1 - 5 parts of emulsion - type binder, 0 - 1 part of wetting agent, and 200 - 800 parts of polar solvent; The D50 of the large - particle inorganic powder is 0.1 - 3 μm; The D50 of the small - particle inorganic powder is 10 - 150 nm.

2. The nano-coating liquid according to claim 1, wherein, The large - particle inorganic powder includes one or more of alumina, boehmite, titanium dioxide, silicon dioxide, cerium oxide, magnesium aluminate spinel, zirconia, and lithium phosphate.

3. The nano-coating liquid according to claim 2, characterized in that, The alumina includes porous alumina and / or non - porous alumina; the pore size of the porous alumina is 2 - 60 nm.

4. The nano-coating liquid according to claim 1, wherein The solid content of the nano - coating liquid is 10 - 40%.

5. The nano-coating liquid according to claim 1, characterized in that, The small - particle inorganic powder includes one or more of fumed alumina, boehmite, titanium dioxide, silicon dioxide, and lithium - based compounds.

6. The nano-coating liquid according to claim 1, wherein The nanocellulose includes one or more of cellulose nanofibers, cellulose nanocrystals, bacterial nanocellulose, and microfibrillated cellulose.

7. The nano coating liquid according to claim 1, characterized in that, The solution - type binder includes one or more of polyvinylidene fluoride, polyacrylic acid, acrylate - acrylonitrile copolymer, polyacrylate, and acrylic - derivative multi - copolymer; The emulsion - type binder includes one or more of styrene - butadiene rubber emulsion, polystyrene emulsion, styrene - acrylic emulsion, and polyvinyl acetate emulsion.

8. The nano-coating liquid according to claim 1, characterized in that, The polar solvent includes one or more of water, N - methylpyrrolidone, dimethylacetamide, and acetone.

9. The preparation method of the nano-coating liquid according to any one of claims 1 to 8, comprising the following steps: Disperse the nanocellulose, large - particle inorganic powder, and small - particle inorganic powder into the polar solvent, and add the solution - type binder, emulsion - type binder, and wetting agent to the obtained dispersion to obtain the nano - coating liquid.

10. A nano - coated separator is formed by coating the nano - coating liquid according to any one of claims 1 - 8 or the nano - coating liquid prepared by the preparation method of claim 9 on a lithium - ion battery separator.

Images