Aqueous coated aramid modified separator, and preparation method and application thereof

Abstract

A water-based coated aramid-modified separator, its preparation method, and its application are disclosed, relating to the field of battery separator technology. This invention solves the problem of complex coating processes in existing aramid-modified separators. The water-based coated aramid-modified separator comprises a polyolefin separator and a nano-aramid fiber coating applied to the surface of the polyolefin separator; the nano-aramid fibers are nano-meta-aramid precipitated fibers, nano-para-aramid pulp, or a combination of both; the specific surface area of ​​the nano-aramid fibers is 200 m² / g. 2 / g~300m 2 / g. Initial aramid fibers are fully dispersed in pure water, first coarsely ground using a conical refiner, then finely ground using a horizontal sand mill, and finally precision ground using a nano-sand mill. The finely ground fibers are then fully disintegrated using a high-frequency de-fiber machine to obtain a nano-aramid fiber pure aqueous solution. This nano-aramid fiber pure aqueous solution is then precisely coated onto the surface of a polyolefin separator, and finally dried and wound up. This invention can be applied to the field of lithium batteries.

Description

Technical Field

[0001] This invention relates to the field of battery separator technology, specifically to an aqueous coated aramid modified separator, its preparation method, and its application. Background Technology

[0002] In the structure of lithium-ion batteries, the separator is one of the key internal components and also one of the high-value-added materials with the highest technological barriers. It plays a crucial role in the battery's safety and electrochemical performance, accounting for approximately 20% to 30% of the cost of lithium-ion batteries. However, currently commercially available mainstream polyolefin separators such as PE and PP have poor heat resistance and hydrophilicity, and are prone to shrinkage under high temperatures or high current densities, leading to battery short circuits and posing significant safety risks. Therefore, researching and developing novel high-performance battery separator materials to meet practical needs is of great significance.

[0003] Currently, a common modification method for polyolefin separators is to modify the surface of the polyolefin separator by coating it with nano-inorganic fillers (such as ceramics). For example, Chinese patent document CN109830632A discloses an aramid-coated lithium-ion battery separator, including a base film and a slurry adhered to one or both sides of the base film. This slurry is a coating slurry containing aramid 1313 and aramid 1414, and the base film is a PP separator, PE separator, or non-woven fabric containing 0.1wt.% to 5wt.% SiO2 or Al2O3. This method solves the problem that the high-temperature resistance, heat shrinkage rate, and strength of coated separators in the prior art cannot meet the requirements under certain temperature conditions. Inorganic filler coating has good high-temperature resistance, but it is prone to moisture absorption, has poor wettability, is heavy, and is prone to powder shedding.

[0004] Aramid fibers possess superior flexibility, resistance to high and low temperatures, acid and alkali resistance, abrasion resistance, voltage resistance, insulation, and flame retardancy. Their lightweight nature is particularly advantageous, a characteristic not found in inorganic materials. Aramid-coated separators exhibit significantly enhanced liquid absorption, retention, and ionic conductivity. The application of lightweight aramid-coated separators also improves battery energy density. These excellent overall properties make aramid separators suitable for use in power batteries. Compared to traditional nano-ceramic coatings, aramid-coated separators offer advantages such as lighter coating weight, stronger adhesion, and resistance to oxidation, acids and alkalis, flame retardancy, abrasion, and tearing. With a rupture temperature exceeding 260℃, they are an ideal ultra-durable lithium-ion battery separator, significantly improving battery safety and energy density. Currently developed aramid membrane coating processes are all solvent-based. For example, CN115663394A discloses a dissolution system for para-aramid and its application, an aramid membrane and its preparation method, and an aramid-ceramic composite membrane and its preparation method. The para-aramid dissolution system includes a proton donor, a solvent, and a co-solvent. The main component of the solvent is a non-proton, strongly polar solvent, and the co-solvent includes a strong base. The aramid coating process uses a large amount of organic solvent to dissolve or disperse the aramid fibers, making the coating process cumbersome and complex. On the one hand, the use of expensive solvents such as NMP and DMSO leads to high costs; on the other hand, the solvents are flammable and pollute the environment, and the recovery process is complex and cumbersome, requiring a large initial investment in solvent recovery equipment. These problems have prevented aramid membranes from being put into large-scale production and application.

[0005] Given that current solvent-based coating processes are technically challenging and require significant investment, and that mature technologies are mainly concentrated in the hands of foreign companies, it is necessary to develop an environmentally friendly, high-performance, and more cost-competitive water-based coated aramid-modified membrane. Summary of the Invention

[0006] To address the problem of complex coating processes in existing aramid-modified separators, this invention proposes an aqueous coated aramid-modified separator, its preparation method, and its applications.

[0007] The technical solution of the present invention is as follows:

[0008] A water-based coated aramid-modified separator includes a polyolefin separator and a nano-aramid fiber coating coated on the surface of the polyolefin separator.

[0009] The nano-aramid fiber is nano-meta-aramid precipitated fiber, nano-para-aramid pulp, or a combination of the two.

[0010] The specific surface area of ​​the nano-aramid fiber is 200 m². 2 / g~300m 2 / g.

[0011] Preferably, the thickness of the nano-aramid fiber coating is 0.5 μm to 15 μm.

[0012] Preferably, the polyolefin separator is a PE separator, a PP separator, a PE / PP composite separator, or a PP / PE / PP composite separator.

[0013] Preferably, the thickness of the polyolefin membrane is 9 μm to 32 μm.

[0014] The present invention also provides a method for preparing the water-based coated aramid modified separator as described above, comprising the following steps:

[0015] S1. The initial aramid fibers are fully dispersed in pure water, first coarsely ground by a conical refiner, then finely ground by a horizontal sand mill, and then finely ground by a nano sand mill. The finely ground fibers are then fully disintegrated by a high-frequency disintegrator to obtain a pure aqueous solution of nano aramid fibers.

[0016] S2. A pure aqueous solution of nano-aramid fiber is precisely coated onto the surface of a polyolefin separator, and then dried and wound up.

[0017] Preferably, the initial aramid fiber in step S1 is a meta-aramid precipitated fiber or para-aramid pulp or a combination of both with an initial length of 1.1 mm.

[0018] Preferably, in step S1, the slurry concentration of the coarse grinding is 3%–10%, and the fiber length after coarse grinding is no more than 300 μm; the grinding concentration of the fine grinding is 3%–10%, and the fiber length after fine grinding is no more than 50 μm; the grinding concentration of the fine grinding is 1%–5%, and the fiber length after fine grinding is 50 nm–800 nm, more preferably 100 nm–500 nm; the defragmentation concentration is 0.5%–3%, and the specific surface area of ​​the fiber after defragmentation is 200 m². 2 / g~300m 2 / g.

[0019] Preferably, the precision coating in step S2 is performed by roller coating.

[0020] Preferably, the roller coating method in step S2 uses a micro-grooving head for coating, and the coating speed is 1m / min to 10m / min.

[0021] Preferably, the drying process in step S2 is infrared drying, the drying temperature is 100℃~300℃, and the drying time is 0.5min~10min.

[0022] The present invention also provides an application of the above-mentioned water-based coated aramid modified separator in lithium-ion batteries, for use as a separator for lithium-ion batteries.

[0023] Compared with the prior art, the specific beneficial effects of the present invention are as follows:

[0024] 1. The raw materials of this invention are readily available, and no organic solvents or co-solvents are used. The operation is simple, and no coagulation and washing processes are required. Strong acids or strong alkalis are not used, and no solvent recovery or acid-base treatment devices are needed. The intermediate medium is pure water, which is very friendly to operation and environment. It has a significant cost advantage compared to other aramid membranes.

[0025] 2. The present invention adopts a three-stage grinding process of coarse grinding, fine grinding and fine grinding, which greatly speeds up the grinding efficiency. The fibers after high-frequency disintegration have an ultra-high specific surface area, strong adhesion to polyolefin membranes, and superior heat resistance and liquid absorption performance compared to polyolefin membranes. The overall performance is better than commercially available samples. Detailed Implementation

[0026] To make the technical solutions of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. It should be noted that the following embodiments are only used to better understand the technical solutions of the present invention and should not be construed as limiting the present invention.

[0027] Example 1.

[0028] S1. Take meta-aramid precipitated fibers with an initial length of 1.1 mm, fully disperse them in pure water, and first coarsely grind them using a conical refiner with a refinement concentration of 5%, adjusting the coarse grinding time to control the fiber length at 280 μm; then finely grind them using a horizontal sand mill with a grinding concentration of 5%, resulting in a fiber length of 38 μm; further finely grind them using a nano-sand mill with a grinding concentration of 3%, resulting in a fiber length of 350 nm; finally, fully loosen the ground fibers using a high-frequency delamination machine with a delamination concentration of 1%, keeping them in a fully extended state for subsequent processes, with a specific surface area of ​​224 m². 2 / g.

[0029] S2. The pure aqueous solution of nano-meta-aramid fiber prepared above is coated onto a PE membrane on one side through a micro-grooving coating head. The thickness of the PE membrane is 9μm, the thickness of the nano-aramid fiber coating is 3μm, and the coating speed is 8m / min.

[0030] S3. The above-coated modified diaphragm is dried by infrared heating at a temperature of 200°C for 6 minutes, and then wound up to obtain the water-based coated aramid modified diaphragm.

[0031] Example 2.

[0032] S1: Take para-aramid pulp with an initial length of 0.9 mm, fully disperse it in pure water, and first coarsely grind it using a conical refiner with a pulp concentration of 8%, adjusting the coarse grinding time to control the fiber length at 220 μm; then finely grind it using a horizontal sand mill with a grinding concentration of 8%, resulting in a fiber length of 29 μm; further finely grind it using a nano-sand mill with a grinding concentration of 5%, resulting in a fiber length of 500 nm; finally, fully loosen the ground fibers using a high-frequency delamination machine with a delamination concentration of 3%, keeping them in a fully extended state for subsequent processes, with a specific surface area of ​​208 m². 2 / g.

[0033] S2: The pure aqueous solution of nano-para-aramid pulp prepared above is coated on one side of the PP membrane through a micro-grooving coating head. The thickness of the PP membrane is 12μm, the thickness of the nano-aramid fiber coating is 5μm, and the coating speed is 5m / min.

[0034] S3: The above-coated modified diaphragm is dried by infrared heating at a temperature of 250°C for 5 minutes, and then wound up to obtain the water-based coated aramid modified diaphragm.

[0035] Example 3.

[0036] S1: Take para-aramid pulp with an initial length of 0.9 mm, fully disperse it in pure water, and first coarsely grind it using a conical refiner with a pulp concentration of 8%, adjusting the coarse grinding time to control the fiber length at 220 μm; then finely grind it using a horizontal sand mill with a grinding concentration of 8%, resulting in a fiber length of 29 μm; further finely grind it using a nano-sand mill with a grinding concentration of 5%, resulting in a fiber length of 500 nm; finally, fully loosen the ground fibers using a high-frequency delamination machine with a delamination concentration of 3%, keeping them in a fully extended state for subsequent processes, with a specific surface area of ​​208 m². 2 / g.

[0037] S2: The pure aqueous solution of nano-para-aramid pulp prepared above is coated on both sides of a PP / PE / PP three-layer composite membrane through a micro-grooving coating head. The composite membrane thickness is 20μm, the single-sided nano-aramid fiber coating thickness is 2.5μm, the double-sided coating thickness is 5μm, and the coating speed is 10m / min.

[0038] S3: The above-coated modified diaphragm is dried by infrared heating at a temperature of 300°C for 8 minutes, and then wound up to obtain the water-based coated aramid modified diaphragm.

[0039] Example of results.

[0040] The thickness, contact angle, thermal shrinkage rate, membrane rupture temperature, and air permeability of commercially available PE-based films, PP-based films, single-sided coated aramid membranes, double-sided coated aramid membranes, and the water-based coated aramid modified membranes prepared in Examples 1-3 above were tested. The test results are shown in the table below:

[0041]

[0042]

[0043] The test data above show that the water-based coated aramid-modified separator prepared by the method of this application has a lower contact angle and heat shrinkage rate, and exhibits superior heat resistance and liquid absorption properties compared to polyolefin separators. Its overall performance is superior to commercially available samples. Furthermore, the raw materials used in this invention are readily available, the operation is simple, it is environmentally friendly, requires no coagulation or washing processes, and has high production efficiency, offering a significant cost advantage compared to other aramid separators.

[0044] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing an aqueous coated aramid-modified separator, characterized in that, The water-based coated aramid-modified separator includes a polyolefin separator and a nano-aramid fiber coating coated on the surface of the polyolefin separator. The nano-aramid fiber is nano-meta-aramid precipitated fiber, nano-para-aramid pulp, or a combination of the two. The specific surface area of ​​the nano-aramid fiber is 200 m². 2 / g~300m 2 / g; The preparation method includes the following steps: S1. The initial aramid fibers are fully dispersed in pure water, first coarsely ground by a conical refiner, then finely ground by a horizontal sand mill, and then finely ground by a nano sand mill. The finely ground fibers are then fully disintegrated by a high-frequency disintegrator to obtain a pure aqueous solution of nano aramid fibers. The initial aramid fiber is meta-aramid precipitated fiber or para-aramid pulp or a combination of the two. S2. A pure aqueous solution of nano-aramid fiber is precisely coated onto the surface of a polyolefin separator, and then dried and wound up. The coarse grinding has a slurry concentration of 3% to 10%, and the fiber length after coarse grinding is no more than 300 μm; the fine grinding has a slurry concentration of 3% to 10%, and the fiber length after fine grinding is no more than 50 μm; the precision grinding has a slurry concentration of 1% to 5%, and the fiber length after precision grinding is 50 nm to 800 nm; the defragmentation has a defragmentation concentration of 0.5% to 3%, and the specific surface area of ​​the defragmented fiber is 200 m². 2 / g~300m 2 / g; The precision coating is performed by roller coating using a micro-grooving coating head, and the coating speed is 1m / min to 10m / min.

2. The method for preparing the water-based coated aramid-modified separator according to claim 1, characterized in that, The thickness of the nano-aramid fiber coating is 0.5μm~15μm, and the thickness of the polyolefin separator is 9μm~32μm.

3. The method for preparing the water-based coated aramid-modified separator according to claim 1, characterized in that, The polyolefin separator is a PE separator, a PP separator, a PE / PP composite separator, or a PP / PE / PP composite separator.

4. The method for preparing the water-based coated aramid-modified separator according to claim 1, characterized in that, The initial aramid fiber in step S1 has a length of 0.6 mm to 1.3 mm.

5. The method for preparing the water-based coated aramid-modified separator according to claim 1, characterized in that, The drying in step S2 is infrared drying, the drying temperature is 100℃~300℃, and the drying time is 0.5min~10min.

6. The application of an aqueous coated aramid-modified separator prepared by any one of claims 1 to 5 in a lithium-ion battery, characterized in that, Used as a separator for lithium-ion batteries.

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