A high-performance lithium-ion battery separator with low pore-closure temperature and its preparation method

Abstract

This invention relates to the field of battery separator technology, specifically to a high-performance lithium-ion battery separator with a low pore-closure temperature and its preparation method. The high-performance lithium-ion battery separator provided by this invention exhibits a low pore-closure temperature, good thermal stability, minimal electrolyte swelling, and high electrochemical stability. This invention also provides applications for the aforementioned high-performance low pore-closure temperature lithium-ion battery separator, specifically for use in coin-type lithium-ion batteries.

Description

Technical Field

[0001] This invention relates to the field of battery separator technology, specifically to a high-performance lithium battery separator with low pore-closing temperature and its preparation method. Background Technology

[0002] Product safety is a crucial aspect of the industrialization of high-performance lithium-ion batteries. Whether it's small lithium-ion batteries used in portable electronic products or those for automotive or energy storage, battery safety is a paramount concern for both manufacturers and users. The separator is an indispensable component of lithium-ion batteries, and its presence is critical to their safety. In many safety incidents, internal short circuits are considered a major cause of thermal runaway in lithium-ion batteries. CN118486999A discloses a method for preparing a high-strength lithium-ion battery separator with a low pore-closure temperature, characterized by a high pore-closure temperature and complex process. Generally, a low pore-closure temperature in a lithium-ion battery separator can interrupt ion transport during periods of rapid internal heating, thus ensuring battery safety. Furthermore, the separator should possess good thermal stability; a low thermal shrinkage rate or a high rupture temperature prevents melting or rupture at high temperatures, which could lead to large-area short circuits. Therefore, reducing the pore-closure temperature of the separator while simultaneously improving its thermal stability is of great significance for the application of lithium-ion batteries. Summary of the Invention

[0003] In view of the problems existing in the prior art and to overcome the shortcomings of the prior art, the technical problem to be solved by the present invention is to provide a high-performance low-closure-temperature lithium battery separator with low pore temperature, good thermal stability, small swelling of electrolyte and high electrochemical stability, and the preparation method thereof.

[0004] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: A high-performance lithium-ion battery separator with low pore-closure temperature includes a separator substrate. An organic-inorganic composite coating of a mixture of polyolefin and nano-ceramic material is coated on at least one surface of the separator substrate. The coating thickness of the organic-inorganic composite coating on the one surface is 1-3 μm. The separator substrate is selected from wet-process polyethylene separators, with a substrate thickness of 5-12 μm. The polyolefin is selected from polyethylene wax emulsion, with a melting point of 110-120℃ and an emulsion particle size of 0.4-1.0 μm. The nano-ceramic material is selected from alumina and boehmite, with a particle size of 0.4-0.7 μm.

[0005] A high-performance lithium-ion battery separator with low pore-closure temperature includes a separator substrate. First, a nano-ceramic material coating is applied to one surface of the separator substrate. Then, a polyolefin coating is applied to the ceramic material coating or a polyolefin coating is applied to the other side of the separator substrate. The coating thickness of both the polyolefin coating and the ceramic material coating is 1-3 μm. The separator substrate is selected from wet-process polyethylene separators, with a substrate thickness of 5-12 μm. The polyolefin is selected from polyethylene wax emulsions, with a melting point of 110-120℃ and an emulsion particle size of 0.4-1.0 μm. The nano-ceramic material is selected from alumina and boehmite, with a particle size of 0.4-0.7 μm.

[0006] Preferably, the organic-inorganic composite coating of polyolefin and nano-ceramic material is obtained by coating with an organic-inorganic mixed coating slurry, which includes water, dispersant, nano-ceramic material, polyethylene wax emulsion, thickener, binder and wetting agent, and the total solids content of the organic-inorganic mixed coating slurry is 35%-42%.

[0007] Preferably, in the lithium battery separator, the nano-ceramic material coating is obtained by coating with a ceramic coating slurry, which includes water, dispersant, nano-ceramic material, thickener, binder, and wetting agent, and the total solid content of the ceramic coating slurry is 25%-35%; the polyolefin coating is obtained by coating with a polyethylene wax coating slurry, which includes water, dispersant, polyethylene wax emulsion, thickener, binder, and wetting agent, and the total solid content of the polyethylene wax coating slurry is 18%-25%.

[0008] In this invention, if there is a conflict between the Chinese name and the structural formula of a compound, the structural formula shall prevail, unless the structural formula is obviously incorrect.

[0009] The beneficial effects of this invention are as follows: The lithium-ion battery separator of the present invention contains polyethylene wax in the coating material applied to the separator substrate. Polyethylene wax is a low-melting-point polymer, which can reduce the pore-closing temperature of the separator, keeping it at 110-120°C. When the internal temperature of the lithium-ion battery reaches the pore-closing temperature, the separator coating can melt rapidly, which can hinder the conduction of lithium ions at the first moment, thereby stopping the lithium battery from operating and protecting the lithium-ion battery. The coating of the lithium-ion battery separator of the present invention contains heat-resistant nano-ceramic materials, ensuring that the thermal shrinkage rate of the separator is less than 3% after baking at 130°C for 1 hour. This indicates that the separator has little deformation and no cracking at high temperatures, effectively preventing short circuits caused by large-area contact of lithium-ion battery electrodes.

[0010] 3) The polyethylene wax emulsion has a microsphere structure. This material has low swelling to electrolyte and the diaphragm has good stability at a voltage of 1-5V. Detailed Implementation

[0011] The present invention is illustrated below with reference to examples, but is not intended to limit the invention. Any simple substitutions or modifications made to the present invention by those skilled in the art are within the scope of the technical solutions protected by this invention. Example 1:

[0012] (1) 32% Al2O3 particles with a median particle size of 0.6 μm and 0.13% PAA-Na were premixed in 58% ultrapure water for 50 min at a stirring speed of 600 rpm; 8% polyethylene wax emulsion with a median particle size of 0.7 μm (Shanghai Shunya Chemical Co., Ltd.) was added and stirred for 30 min, followed by the addition of 0.6% PVP and 1.9% PAA; the stirring speed was reduced to 400 rpm and a mixture of 0.15% ethoxylated alcohol and ethynylene glycol (mass ratio 1:1) was added and stirred for 30 min to obtain an organic-inorganic composite coating slurry; (2) The coating slurry from step (1) is coated onto the two surfaces of the 9μm PE separator using a wire rod. The separator is then dried at 60°C for 60s to obtain a high-performance lithium battery separator with low pore temperature.

[0013] (3) Assemble the low pore temperature lithium battery separator from step (2) into a coin cell and test the electrochemical linear sweep voltammetry (LSV) curve of the cell. Example 2:

[0014] 30% Al2O3 particles with a median particle size of 0.5 μm and 0.15% PAA-Na were premixed in 68% ultrapure water for 50 min with a stirring speed of 600 rpm. Then, 0.4% CMC-Na and 1.6% PAA were added sequentially. After reducing the stirring speed to 400 rpm, a mixture of 0.12% ethoxylated alcohol and ethynylene glycol (mass ratio 1:1) was added and stirred for 30 min to obtain a nano-ceramic coating slurry. 18% polyethylene wax emulsion with a median particle size of 0.7 μm and 0.1% PAA-Na were stirred for 30 min at a stirring speed of 600 rpm. Then, 0.5% PVP and 1.0% PAA were added sequentially. After reducing the stirring speed to 400 rpm, a mixture of 0.15% ethoxylated alcohol and ethynylene glycol was added. The water content in the slurry was 80%. The mixture was stirred for 30 min to obtain the polyethylene wax coating slurry. Using a wire rod, the coating slurry from step (1) is coated onto one surface of a 9μm PE separator to obtain a ceramic-coated film. After drying, the coating slurry from step (2) is coated onto the ceramic coating. The separator is then dried at 60°C for 60 seconds to obtain a high-performance lithium battery separator with low pore temperature.

[0015] (4) Assemble the low pore temperature lithium battery separator from step (3) into a coin cell and test the electrochemical linear sweep voltammetry (LSV) curve of the cell. Example 3:

[0016] (1) 28% Al2O3 particles with a median particle size of 0.5 μm and 0.14% PAA-Na were premixed in 70% ultrapure water for 50 min with a stirring speed of 600 rpm. Then, 0.32% CMC-Na and 1.4% PAA were added in sequence. After the stirring speed was reduced to 400 rpm, a mixture of 0.11% ethoxylated alcohol and ethynylene glycol (mass ratio 1:1) was added and stirred for 30 min to obtain nano-ceramic coating slurry. (2) Stir 18% polyethylene wax emulsion with a median particle size of 0.7 μm and 0.1% PAA-Na for 30 min at a stirring speed of 600 rpm, then add 0.4% CMC-Na and 1.0% PAA in sequence; after reducing the stirring speed to 400 rpm, add a mixture of 0.15% ethoxylated alcohol and ethynylene glycol. The water content in the slurry is 80%. Stir for 30 min to obtain polyethylene wax coating slurry. (3) Use a wire rod to coat the coating slurry in step (1) onto one surface of a 9μm PE separator to obtain a ceramic coating film. After drying, coat the coating slurry in step (2) onto the PE surface of the ceramic coating film. Dry the separator at 60°C for 60s to obtain a high-performance low-closed-pore temperature lithium battery separator.

[0017] (4) Assemble the low pore temperature lithium battery separator from step (3) into a coin cell and test the electrochemical linear sweep voltammetry (LSV) curve of the cell. Example 4 The experimental method was the same as in Example 1, with the PE membrane thickness being 7 μm.

[0018] Comparative Example 1 (1) 18% polyethylene wax emulsion with a median particle size of 0.7 μm and 0.1% PAA-Na were stirred for 30 min at a stirring speed of 600 rpm. 0.5% PVP and 1.2% PAA were added in sequence. After the stirring speed was reduced to 400 rpm, a mixture of 0.15% ethoxylated alcohol and ethynylene glycol (mass ratio 1:1) was added. The water content in the slurry was 80%. After stirring for 30 min, a polyethylene wax coating slurry was obtained. (2) The coating slurry from step (1) is coated onto one surface of a 9μm PE separator using a wire rod. The separator is then dried at 60°C for 60s to obtain a low-closure-temperature lithium battery separator.

[0019] Comparative Example 2 Except for not applying polyethylene wax coating paste to the ceramic coating, the rest is the same as in Example 2.

[0020] Comparative Example 3 The experimental method was the same as in Example 1, except that the polyethylene wax emulsion was replaced with polymethyl methacrylate.

[0021] Performance testing The low pore-closure temperature lithium battery separators prepared in Examples 1-4 and Comparative Examples 1-3 of this invention were tested, and the results are shown in the table below:

[0022] As shown in Table 1, the closed-cell temperature of the coated separator prepared in Example 14 is more than 20°C lower than that of the polyethylene separator, and its electrochemical stability window is more than 1V higher, meaning that the coated separator can maintain chemical and structural stability over a wider voltage range. The thermal shrinkage rate of the coated separator prepared in Example 14 is less than that of the coated separators in Comparative Examples 1 and 2, and the polyethylene separator, indicating that this high-performance, low-closed-cell-temperature battery separator has good dimensional stability at high temperatures. Under the premise that the difference in coating areal density and coating thickness between the two coated separators is small, compared with Comparative Example 3, the closed-cell temperature of the coated separator prepared in Example 1 is slightly lower, the thermal shrinkage rates of the two films are similar, while the electrolyte swelling and electrochemical stability of the coated separator in Example 1 are better.

[0023] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A high-performance lithium battery separator with low pore-closure temperature, characterized in that, The diaphragm substrate includes an organic-inorganic composite coating of a mixture of polyolefin and nano-ceramic material coated on at least one surface of the diaphragm substrate, wherein the coating thickness of the organic-inorganic composite coating on the one surface is 1-3 μm; the diaphragm substrate is a wet-process polyethylene diaphragm with a substrate thickness of 5-12 μm; the polyolefin is selected from polyethylene wax emulsion with a melting point of 110-120℃ and an emulsion particle size of 0.4-1.0 μm; the nano-ceramic material is selected from alumina and boehmite with a particle size of 0.4-0.7 μm.

2. The lithium battery separator according to claim 1, characterized in that, The organic-inorganic composite coating, which is a mixture of polyolefin and nano-ceramic materials, is obtained by coating with an organic-inorganic mixed coating slurry. The organic-inorganic mixed coating slurry includes water, dispersant, nano-ceramic materials, polyethylene wax emulsion, thickener, binder and wetting agent, and the total solids content of the organic-inorganic mixed coating slurry is 35%-42%.

3. The lithium battery separator according to claim 2, characterized in that, The water constitutes 58%-65% of the organic-inorganic mixed coating slurry by mass; the nano-ceramic material constitutes 23%-32% of the organic-inorganic mixed coating slurry by mass; the polyethylene wax emulsion constitutes 8%-13% of the organic-inorganic mixed coating slurry by mass; the dispersant is sodium polyacrylate, which constitutes 0.1%-0.15% of the organic-inorganic mixed coating slurry by mass; the thickener is one of polyvinylpyrrolidone and sodium carboxymethyl cellulose, which constitutes 0.3%-1.0% of the organic-inorganic mixed coating slurry by mass; the binder is polyacrylic acid, which constitutes 1.0%-2.0% of the organic-inorganic mixed coating slurry by mass; and the wetting agent is a mixture of ethoxylated alcohol and ethynylene glycol, which constitutes 0.10%-0.18% of the organic-inorganic mixed coating slurry by mass.

4. The method for preparing the lithium battery separator according to claim 3, characterized in that, Includes the following steps: Step 1: Mix pure water, dispersant, nano-ceramic material, and polyethylene wax emulsion to obtain a mixture; add thickener, binder, and wetting agent to the above mixture in sequence to prepare an organic-inorganic mixed coating slurry; Step 2: The organic-inorganic mixed coating slurry obtained in Step 1 is coated onto both surfaces of the polyethylene membrane using a wire rod to obtain a coated film; Step 3: Dry the coating film obtained in Step 2 to obtain a high-performance lithium battery separator with low pore temperature.

5. A high-performance lithium battery separator with low pore-closure temperature, characterized in that, The diaphragm substrate is first coated with a nano-ceramic material coating on one surface of the diaphragm substrate, and then coated with a polyolefin coating on the ceramic material coating or coated with a polyolefin coating on the other side of the diaphragm substrate. The coating thickness of both the polyolefin coating and the ceramic material coating is 1-3 μm. The diaphragm substrate is selected from 9 μm polyethylene diaphragms, and the polyolefin is selected from polyethylene wax emulsion with a melting point of 110-120℃ and a particle size of 0.4-1.0 μm. The nano-ceramic material is selected from alumina and boehmite, with a particle size of 0.4-0.7 μm.

6. The lithium battery separator according to claim 5, characterized in that, The nano-ceramic material coating is obtained by coating with a ceramic coating slurry, which includes water, dispersant, nano-ceramic material, thickener, binder, and wetting agent, and the total solid content of the ceramic coating slurry is 25%-35%; the polyolefin coating is obtained by coating with a polyethylene wax coating slurry, which includes water, dispersant, polyethylene wax emulsion, thickener, binder, and wetting agent, and the total solid content of the polyethylene wax coating slurry is 18%-25%.

7. The lithium battery separator according to claim 6, characterized in that, The water content of the ceramic coating slurry is 60%-70% of the slurry's mass, and the ceramic content is 27%-38% of the slurry's mass. The dispersant is sodium polyacrylate, accounting for 0.1%-0.15% of the slurry's mass. The thickener is either polyvinylpyrrolidone or sodium carboxymethyl cellulose, accounting for 0.3%-1.0% of the slurry's mass. The binder is polyacrylic acid, accounting for 1.0%-2.0% of the slurry's mass. The wetting agent is a mixture of ethoxylated alcohol and ethynyl glycol, accounting for 0.10%-0.18% of the slurry's mass. The polyethylene wax coating... The water content of the slurry is 68%-82% of the mass percentage of the polyethylene wax coating slurry, and the amount of polyethylene wax emulsion used is 16%-30% of the mass percentage of the polyethylene wax coating slurry. The dispersant is sodium polyacrylate, and the dispersant accounts for 0.1%-0.15% of the mass percentage of the polyethylene wax coating slurry. The thickener is one of polyvinylpyrrolidone and sodium carboxymethyl cellulose, and the thickener accounts for 0.3%-1.0% of the mass percentage of the polyethylene wax coating slurry. The binder is polyacrylic acid, and the binder accounts for 1.0%-2.0% of the mass percentage of the polyethylene wax coating slurry. The wetting agent is a mixture of ethoxylated alcohol and acetylene glycol, and the wetting agent accounts for 0.10%-0.18% of the mass percentage of the polyethylene wax coating slurry.

8. The method for preparing the lithium battery separator according to claim 7, characterized in that, Includes the following steps: Step 1: Stir pure water, dispersant and nano-ceramic material to obtain a dispersion; add thickener, binder and wetting agent to the above dispersion in sequence to prepare ceramic coating slurry; Step 2: Stir pure water, dispersant and polyethylene wax emulsion to obtain a dispersion; add thickener, binder and wetting agent to the above dispersion in sequence to prepare polyethylene wax coating slurry; Step 3: Apply the ceramic slurry obtained in Step 1 to any surface of the polyethylene membrane using a wire rod, and dry it to obtain a ceramic-coated membrane. Step 4: Apply the polyethylene wax coating slurry prepared in Step 2 to the ceramic coating surface of the ceramic-coated diaphragm described in Step 3 or to the polyethylene diaphragm surface on the other side using a wire rod to obtain a coated film; Step 5: Dry the coating film obtained in Step 4 to obtain a high-performance lithium battery separator with low pore temperature.

9. A lithium battery, characterized in that, Includes the lithium battery separator as described in any one of claims 1-4.

10. A lithium battery, characterized in that, Includes the lithium battery separator as described in any one of claims 5-8.

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