Separator for lithium-ion batteries and modification method

Abstract

A separator for lithium-ion batteries and a modification method. The modification method comprises: using anisole as a solvent, octakis(chloropropyl)silsesquioxane as an initiator, methyl methacrylate as a monomer, cuprous chloride as a catalyst, and pentamethyldiethylenetriamine as a ligand, and synthesizing polymethacrylate-polyhedral oligomeric silsesquioxane by means of an atom transfer radical polymerization method; preparing a modified slurry from the polymethacrylate-polyhedral oligomeric silsesquioxane; and coating a surface of a base film of a separator with the modified slurry and drying same, so as to obtain a separator coated with polymethacrylate-polyhedral oligomeric silsesquioxane. The improved technique not only achieves significant effects in terms of improving the mechanical properties and thermal stability of a separator, but also realizes the optimization of cost efficiency and supply stability while maintaining good electrolyte wettability and reducing the internal resistance of a battery cell, thereby exhibiting potential in a wide range of applications.

Description

Lithium ion battery separator and modification method TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion battery separator modification, and particularly relates to a lithium ion battery separator and a modification method. BACKGROUND

[0002] The separator is a functional film material with a microporous structure and is one of components of a lithium ion battery. Currently, commercially available separator materials are mainly polyolefin separators, including polyethylene (PE), polypropylene (PP) and multi-layer composite separators. However, the polyolefin has problems such as poor wettability with electrolyte and poor interface compatibility with electrodes. In order to improve and solve these problems, a commonly used method is to coat the surface of the polyolefin separator with inorganic nanoparticles such as silica (SiO2), alumina (Al2O3) and boehmite (AlOOH) coating, which is usually used to improve mechanical properties and thermal stability, and polyvinylidene fluoride (PVDF) coating, which is usually used to improve the adhesion between the separator and the electrode sheet and improve the wettability of the electrolyte to the separator. However, PVDF has a high price and a production bottleneck, which increases the uncertainty of supply and the cost of the battery.

[0003] Poly (methyl methacrylate) (PMMA) is also called acrylic, which has a low price and is easy to process and has good chemical stability and is easily wetted by electrolyte, and has great potential in replacing the PVDF separator coating. However, compared with PVDF, PMMA has a large production and a lower price, but has a low mechanical strength and is easy to scratch, and the lithium dendrites generated during long-term use of the lithium battery can easily pierce the coated separator, thereby causing internal short circuit of the battery. In addition, PMMA is easy to swell in electrolyte, which blocks the pores of the separator and hinders the transfer of lithium ions, thereby increasing the internal resistance of the battery. SUMMARY

[0004] (I) Technical problems to be solved

[0005] The present application is mainly aimed at the above problems, and provides a lithium ion battery separator and a modification method, which aims to solve the problems of poor wettability of the polyolefin separator with electrolyte and poor interface compatibility with electrodes in the existing lithium ion battery, and the problems of high price and limited production of polyvinylidene fluoride (PVDF) as a coating material, which can improve the above problems but increases the cost and supply uncertainty.

[0006] (II) Technical solutions

[0007] To achieve the above purpose, the first aspect of the present application provides a modification method of a lithium ion battery separator, which comprises:

[0008] Synthesizing poly-methyl methacrylate cage polysilsesquioxane by atom transfer radical polymerization method, using anisole as solvent, octachloropropyl silyl silicate as initiator, methyl methacrylate as monomer, cuprous chloride as catalyst, and pentamethyl diethylenetriamine as ligand;

[0009] Preparation of modified slurry containing poly-methyl methacrylate cage polysilsesquioxane from the synthesized poly-methyl methacrylate cage polysilsesquioxane;

[0010] Coating the modified slurry on the surface of the separator base film and drying to obtain poly-methyl methacrylate cage polysilsesquioxane coated separator.

[0011] Further, the preparation method of poly-methyl methacrylate cage polysilsesquioxane comprises: gradually adding anisole, octachloropropyl silyl silicate, pentamethyl diethylenetriamine, cuprous chloride, and MMA into a flask, then placing the flask with a stopper into liquid nitrogen, removing oxygen and water vapor in the flask by using a vacuum pump to extract air in the flask and filling high-purity nitrogen, thawing and refreezing, repeating three times, reacting at 80℃ for 6-12h, precipitating, filtering, and extracting the product.

[0012] Further, the preparation of the modified slurry comprises: adding deionized water, dispersant, poly-methyl methacrylate cage polysilsesquioxane powder, binder, thickening agent, and wetting agent in a mass ratio, and mixing and stirring.

[0013] Further, 100 parts of anisole, 1-8 parts of octachloropropyl silyl silicate, 1-3 parts of pentamethyl diethylenetriamine, 0.5-2 parts of cuprous chloride, and 89-96 parts of MMA are gradually added into a flask, then the flask with a stopper is placed into liquid nitrogen, oxygen and water vapor in the flask are removed by using a vacuum pump to extract air in the flask and filling high-purity nitrogen, thawing and refreezing are repeated three times, reaction is carried out at 80℃ for 6-12h, precipitation is carried out, the product is filtered and extracted.

[0014] Further, 0.3-1 parts of dispersant are added in 30-90 parts of deionized water, and stirring and dispersing are carried out at a rotation speed of 800-1200rpm for 5-20 minutes;

[0015] 10-40 parts of poly-methyl methacrylate cage polysilsesquioxane powder are added, and stirring and dispersing are carried out at a rotation speed of 800-1500rpm for 40-80 minutes;

[0016] 0.2-2 parts of binder are added, and stirring and dispersing are carried out at a rotation speed of 700-1000rpm for 15-35 minutes;

[0017] 0.05-0.5 parts of thickening agent are added, and stirring and dispersing are carried out at a rotation speed of 800-1200rpm for 10-30 minutes;

[0018] Add 0.0001-0.01 parts wetting agent and stir and disperse at 700-900 rpm for 25-50 minutes;

[0019] A modified slurry containing polymethacrylic acid-cage polysilsesquioxane was obtained.

[0020] Furthermore, it also includes transferring the obtained modified slurry into a finished product container and maintaining low-speed stirring.

[0021] Furthermore, the modified slurry is coated onto the surface of the diaphragm base membrane using a gravure method or a spraying method, and the moisture is dried in an oven to obtain a polymethacrylic acid-cage polysilsesquioxane coated diaphragm.

[0022] Furthermore, in the preparation process of the polymethacrylate-cage polysilsesquioxane powder, the molecular weight of the obtained polymethacrylate-cage polysilsesquioxane is adjusted by adjusting the ratio of octachloropropylsilsesquioxane to methyl methacrylate.

[0023] To achieve the above objectives, the first aspect of the present invention provides a lithium-ion battery separator, which is made by the aforementioned modification method and includes a polymethacrylate-cage-polysilsesquioxane coating and a separator base film layer. The polymethacrylate-cage-polysilsesquioxane coating is formed by coating a modified slurry containing polymethacrylate-cage-polysilsesquioxane onto the surface of the separator base film.

[0024] Furthermore, the diaphragm base membrane is selected from polyethylene, polypropylene, or a multilayer composite diaphragm.

[0025] (III) Beneficial Effects

[0026] Compared with the prior art, the present invention provides a lithium-ion battery separator and a modification method. The present invention uses polymethyl methacrylate (PMMA) modified with cage-type polysilsesquioxane (POSS), namely POSS-(PMMA)8, as the coating material for the lithium-ion battery separator, thus solving several problems of the prior art separators, specifically as follows:

[0027] 1. Improved Mechanical Properties: The inorganic framework of POSS molecules provides excellent mechanical properties and thermal stability. When these molecules are introduced into PMMA, they act as reinforcing agents, improving the overall mechanical strength of the coating. This is because the inorganic core of POSS can act as stress dispersion points, more effectively dispersing and bearing stress under mechanical forces, thereby reducing the possibility of material damage and scratches. This is particularly important for preventing lithium dendrites from penetrating the separator.

[0028] 2. Enhancement of thermal stability: The inorganic component of POSS also provides higher thermal stability. This property can prevent thermal degradation of the separator material under high temperature conditions, thereby reducing the safety risk of lithium-ion batteries when overheating. In addition, higher thermal stability is also beneficial for maintaining the performance of the battery over a wide temperature range.

[0029] 3. Improvement of electrolyte wettability: PMMA itself has good electrolyte wettability, which means that the electrolyte can more easily penetrate the separator, ensuring efficient transport of lithium ions. The use of POSS-(PMMA)8 further optimizes this property by increasing the hydrophilic or lipophilic side chains of the material, thereby improving the wettability of the electrolyte and ensuring good lithium ion transport efficiency.

[0030] 4. Reduction of cell internal resistance: Improved electrolyte wettability and optimized pore structure help reduce the resistance of lithium ions in the electrolyte, thereby reducing the internal resistance of the entire cell. Lower internal resistance means less energy loss during charging and discharging, improving the energy utilization efficiency and charging and discharging performance of the battery.

[0031] 5. Cost and supply advantages: Compared with traditional coating materials such as PVDF, the use of POSS-(PMMA)8 provides cost-effective and stable supply advantages, as PMMA is a commonly used and low-cost material, and its modified product can reduce production costs and market supply risks without sacrificing performance.

[0032] In summary, through the modification method of the present application, the modified PMMA-coated separator technology of the present application not only achieves significant results in improving the mechanical properties and thermal stability of the separator, but also maintains good electrolyte wettability and reduces the internal resistance of the cell while optimizing cost-effectiveness and stable supply, showing wide application potential. DETAILED DESCRIPTION

[0033] The specific embodiments of the present application will be further described in detail below in conjunction with examples. The following examples are used to illustrate the present application, but are not intended to limit the scope of the present application.

[0034] Cage-type polyhedral oligomeric silsesquioxane (POSS) has the chemical formula (RSiO3 / 2) n is an organic-inorganic hybrid material with Si-O-Si as the structural backbone and functionalized organic side chains, composed of organic and inorganic parts.

[0035] Inorganic part: The main chain composed of Si-O-Si provides good mechanical properties and thermal stability. This part constitutes the framework or backbone of the POSS molecule and is the source of its stability and mechanical strength.

[0036] Organic moieties: are functionalized organic side chains attached to the inorganic framework. These organic side chains impart more functionality and design potential to POSS, including its amphiphilic nature. Depending on the number of R side chains on the POSS, it is further classified into T6, T8, T12, etc. The T8 hexagonal cage-shaped polyhedral oligomeric silsesquioxane structure has good symmetry, and is easier to synthesize.

[0037] Specific to poly-methacrylic acid-based-cage-shaped polyhedral oligomeric silsesquioxane (POSS-(PMMA)8), the PMMA moiety, i.e. polymethyl methacrylate, as a side chain, is the organic part of the material. The side chain is connected to the inorganic backbone through a chemical bond, providing possible interface compatibility improvement, hydrophobic or hydrophilic property adjustment, etc.

[0038] A lithium ion battery separator of the present application comprises a poly-methacrylic acid-based-cage-shaped polyhedral oligomeric silsesquioxane coating and a separator base film layer, wherein the poly-methacrylic acid-based-cage-shaped polyhedral oligomeric silsesquioxane coating is formed by coating a modified slurry containing poly-methacrylic acid-based-cage-shaped polyhedral oligomeric silsesquioxane on the surface of the separator base film.

[0039] As a preferred method of the present embodiment, the separator base film is selected from one of polyethylene, polypropylene or a multi-layer composite separator.

[0040] Therefore, the modification method of the lithium ion battery separator comprises three parts, the first step is to prepare poly-methacrylic acid-based-cage-shaped polyhedral oligomeric silsesquioxane (POSS-(PMMA)8), the second step is to prepare a modified slurry; the third step is to coat the modified slurry. The preparation method of each part is as follows:

[0041] First step, preparation of poly-methacrylic acid-based-cage-shaped polyhedral oligomeric silsesquioxane (POSS-(PMMA)8):

[0042] POSS-(PMMA)8 is synthesized by ATRP method (atom transfer radical polymerization) with C7H8O (anisole) as solvent, POSS-(C3H6Cl)8 (octachloropropylsilsesquioxane) as initiator, MMA (methyl methacrylate) as monomer, CuCl (cuprous chloride) as catalyst, and PMDETA (pentamethyldiethylenetriamine) as ligand. In the specific implementation process, 100 parts of C7H8O, 1-8 parts of POSS-(C3H6Cl)8, 1-3 parts of PMDETA, 0.5-2 parts of CuCl, and 89-96 parts of MMA are gradually added to the flask, then the flask with a stopper is placed in liquid nitrogen, the oxygen and water vapor in the flask are removed by using a vacuum pump to pump out the air in the flask and fill in high-purity nitrogen, and the flask is thawed and refrozen for three times. The product is extracted by precipitation and filtration, and the molecular weight of the obtained POSS-(PMMA)8 is adjusted by adjusting the ratio of POSS-(C3H6Cl)8 and MMA.

[0043] Second step, preparation of modified slurry:

[0044] In 30-90 parts of deionized water, add (0.3-1 parts) dispersant by mass ratio, stir and disperse at 800-1200 rpm for 5-20 min; add 10-40 parts of POSS-(PMMA)8 powder, stir and disperse at 800-1500 rpm for 40-80 min; add 0.2-2 parts of binder, stir and disperse at 700-1000 rpm for 15-35 min; add 0.05-0.5 parts of thickening agent, stir and disperse at 800-1200 rpm for 10-30 min; add 0.0001-0.01 parts of wetting agent, stir and disperse at 700-900 rpm for 25-50 min; get uniformly dispersed POSS-(PMMA)8 slurry, transfer the slurry to the finished product container and keep low speed stirring to prevent the slurry from settling.

[0045] Third step, coating of modified slurry:

[0046] Using gravure method, spraying method and other methods, the modified slurry prepared in the second step is coated on the surface of the separator base film, the moisture is dried by oven, and the POSS-(PMMA)8 coated separator is obtained.

[0047] The present application solves the technical problem by introducing a new modified material, cage-shaped polyhedral oligomeric silsesquioxane (POSS) modified PMMA (POSS-(PMMA)8), as a coating material for the separator. By utilizing the excellent mechanical properties and thermal stability of POSS and the good electrolyte wettability and processability of PMMA, the two are combined through the above chemical synthesis method to obtain a separator material with improved mechanical strength, thermal stability and electrolyte wettability. This modification method not only improves the comprehensive performance of the separator, reduces the internal resistance of the battery, increases the hardness and safety performance of the battery, but also overcomes the problems of high cost and uncertain supply of the original PVDF coating material. By adjusting the concentration and molecular weight of POSS-(PMMA)8, the performance of the coated separator is further optimized, making it more suitable for the requirements of high-performance lithium ion batteries, showing great application potential. This method provides a cost-effective and excellent performance lithium ion battery separator modification technology, which helps to promote the progress and application of lithium ion battery technology.

[0048] The technical solutions of the present application will be described in detail below in combination with examples and comparative examples.

[0049] Example one

[0050] Preparation of POSS-(PMMA)8

[0051] At room temperature, 100 parts of C7H8O, 1 part of POSS-(C3H6Cl)8, 96 parts of MMA, 2 parts of PMDETA, and 1 part of CuCl were gradually added into a flask in a molar ratio, a magnetic rotor was added, the flask with a stopper was cooled in liquid nitrogen, oxygen and water vapor in the flask were removed by using a vacuum pump to pump out the air in the flask and filling high-purity nitrogen, and the process was repeated three times. After being thawed and refrozen, magnetic stirring was performed at 80°C for 12 hours. The precipitate was filtered, dried, and the product was extracted to obtain a modified POSS-(PMMA)8 powder.

[0052] Preparation of coating slurry

[0053] In 65 parts of deionized water, 0.6 parts of vinyl bis-stearamide was added in a mass ratio and dispersed at a stirring speed of 800 rpm for 10 min. 30 parts of POSS-(PMMA)8 powder was added into the container and stirred and dispersed at a stirring speed of 1000 rpm for 60 min. 1.5 parts of polyvinyl alcohol was added and stirred and dispersed at a stirring speed of 800 rpm for 30 min. 0.1 parts of carboxymethyl cellulose was added and stirred and dispersed at a stirring speed of 900 rpm for 25 min. 0.0001 parts of sodium dodecyl sulfate was added and stirred and dispersed at a stirring speed of 900 rpm for 25 min. A uniformly dispersed POSS-(PMMA)8 slurry was obtained, and the slurry was transferred to a finished product container and kept stirring at a low speed to prevent the slurry from precipitating.

[0054] Preparation of coated separator

[0055] The slurry prepared in the previous step was coated on a polyethylene separator with a thickness of 12 μm by micro-gravure method, and the coating thickness was 2 μm. The water was dried by using an oven to obtain a POSS-(PMMA)8 coated separator.

[0056] Example Two

[0057] At room temperature, 100 parts of C7H8O, 3 parts of POSS-(C3H6Cl)8, 94 parts of MMA, 2 parts of PMDETA, and 1 part of CuCl were gradually added into a flask in a mass ratio, a magnetic rotor was added, the flask with a stopper was cooled in liquid nitrogen, oxygen and water vapor in the flask were removed by using a vacuum pump to pump out the air in the flask and filling high-purity nitrogen, and the process was repeated three times. After being thawed and refrozen, magnetic stirring was performed at 80°C for 12 hours. The precipitate was filtered, dried, and the product was extracted to obtain a modified POSS-(PMMA)8 powder.

[0058] Preparation of coating slurry

[0059] In 65 parts of deionized water, 0.5 parts of vinyl bis stearamide was added by mass ratio and stirred and dispersed at 800 rpm for 10 min; 30 parts of POSS-(PMMA)8 powder was added into the container and stirred and dispersed at 1000 rpm for 60 min; 1.5 parts of polyvinyl alcohol was added and stirred and dispersed at 800 rpm for 30 min; 0.15 parts of carboxymethyl cellulose was added and stirred and dispersed at 900 rpm for 25 min; 0.0001 parts of sodium dodecyl sulfate was added and stirred and dispersed at 900 rpm for 20 min; a uniformly dispersed POSS-(PMMA)8 slurry was obtained, and the slurry was transferred to a finished product container and kept stirring at low speed to prevent the slurry from settling.

[0060] Preparation of coated separator

[0061] The slurry prepared in the previous step was coated on a polyethylene separator with a thickness of 12 μm by micro-gravure method, and the coating thickness was 2 μm. The water was dried using an oven to obtain a POSS-(PMMA)8 coated separator.

[0062] Example Three

[0063] At room temperature, 100 parts of C7H8O, 5 parts of POSS-(C3H6Cl)8, 92 parts of MMA, 2 parts of PMDETA and 1 part of CuCl were gradually added into a flask according to the mass ratio, a magnetic rotor was added, the flask with a stopper was cooled in liquid nitrogen, the oxygen and water vapor in the flask were removed by using a vacuum pump to extract high-purity nitrogen, and the process was repeated three times. The flask was thawed and refrozen, and stirred at 80°C for 12 h. The product was obtained by precipitation, filtration and drying. Modified POSS-(PMMA)8 powder was obtained.

[0064] Preparation of coating slurry

[0065] In 65 parts of deionized water, 0.4 parts of vinyl bis stearamide was added by mass ratio and stirred and dispersed at 800 rpm for 10 min; 30 parts of POSS-(PMMA)8 powder was added into the container and stirred and dispersed at 1000 rpm for 60 min; 1.5 parts of polyvinyl alcohol was added and stirred and dispersed at 800 rpm for 30 min; 0.2 parts of carboxymethyl cellulose was added and stirred and dispersed at 900 rpm for 25 min; 0.0001 parts of sodium dodecyl sulfate was added and stirred and dispersed at 900 rpm for 20 min; a uniformly dispersed POSS-(PMMA)8 slurry was obtained, and the slurry was transferred to a finished product container and kept stirring at low speed to prevent the slurry from settling.

[0066] Preparation of coated separator

[0067] The slurry prepared in the previous step was coated on a polyethylene separator with a thickness of 12 μm by micro gravure method, and the coating thickness was 2 μm. The water was dried by using an oven to obtain a POSS-(PMMA)8coated separator.

[0068] Example Four

[0069] At room temperature, 100 parts of C7H8O, 8 parts of POSS-(C3H6Cl)8, 89 parts of MMA, 2 parts of PMDETA and 1 part of CuCl were added into a flask in a mass ratio. A magnetic rotor was added, the flask with a stopper was cooled in liquid nitrogen, and the oxygen and water vapor in the flask were removed by using a vacuum pump to extract high-purity nitrogen. The flask was thawed and refrozen, and the process was repeated three times. The flask was magnetically stirred at 80°C for 10 hours, and the product was obtained by precipitation, filtration and drying.

[0070] Preparation of coating slurry

[0071] In 65 parts of deionized water, 0.3 parts of vinyl bis stearyl amide was added in a mass ratio and stirred at a speed of 800 rpm for 10 min. 30 parts of POSS-(PMMA)8powder was added into the container, and stirred and dispersed at a speed of 1000 rpm for 60 min. 1.5 parts of polyvinyl alcohol was added, and stirred and dispersed at a speed of 800 rpm for 30 min. 0.3 parts of carboxymethyl cellulose was added, and stirred and dispersed at a speed of 900 rpm for 25 min. 0.0001 parts of sodium dodecyl sulfate was added, and stirred and dispersed at a speed of 900 rpm for 20 min. A uniformly dispersed POSS-(PMMA)8slurry was obtained, and the slurry was transferred to a finished product container and kept stirring at a low speed to prevent the slurry from settling.

[0072] Preparation of coated separator

[0073] The slurry prepared in the previous step was coated on a polyethylene separator with a thickness of 12 μm by micro gravure method, and the coating thickness was 2 μm. The water was dried by using an oven to obtain a POSS-(PMMA)8coated separator.

[0074] Comparative Example

[0075] Preparation of coating slurry

[0076] In 65 parts of deionized water, 0.5 parts of vinyl bis-stearamide was added by mass ratio and stirred and dispersed at 800 rpm for 10 min; 30 parts of commercial PMMA powder was added in the container, and stirred and dispersed at 1000 rpm for 60 min; 1.5 parts of polyvinyl alcohol was added, and stirred and dispersed at 800 rpm for 30 min; 0.15 parts of carboxymethyl cellulose was added, and stirred and dispersed at 900 rpm for 25 min; 0.0001 parts of sodium dodecyl sulfate was added, and stirred and dispersed at 900 rpm for 20 min; a uniformly dispersed PMMA slurry was obtained, and the slurry was transferred to a finished product container and kept under low speed stirring to prevent the slurry from settling.

[0077] Preparation of coated separator

[0078] The slurry prepared in the previous step was coated on a polyethylene separator with a thickness of 12 μm by micro-gravure method, and the coating thickness was 2 μm. The water was dried by using an oven, and a POSS-(PMMA)8coated separator was obtained.

[0079] The coated separators obtained in Examples 1 to 4 and Comparative Examples were tested, and the specific test methods were as follows:

[0080] 1. Thickness test:

[0081] A thickness gauge provided by Mahr Company was used to test the thickness of the lithium battery separator according to the standard of GB / T6672-2001.

[0082] 2. Area density test:

[0083] A weighing method device for area density measurement provided by Mettler Toledo Company was used. The area density of the lithium battery separator was tested according to the international standard of ASTM D792-13.

[0084] 3. Air permeability test:

[0085] A test device of Gurley air permeability meter provided by Gurley Company was used. The air permeability of the lithium battery separator prepared in the examples was tested according to the international standard of ASTM D7264-16. Specifically, the sample was clamped between two annular clamps, a differential pressure was applied, and the air flow was quantitatively analyzed to determine the air permeability of the sample.

[0086] 4. 120℃*1h heat shrinkage test method:

[0087] The separator sample was cut into a size of 10 cm x 10 cm, and the sample surface was ensured to be flat.

[0088] Place the sample in a TYL-6C series digital heat shrinkage instrument manufactured by Weihai Tianyuan Precision Machinery Co., Ltd., set the temperature to 120°C, and select the constant temperature mode to keep the sample stable at 120°C.

[0089] Record the initial size (length, width) under constant temperature conditions.

[0090] Heat the sample at 120°C for 1 h to reach thermal shrinkage equilibrium.

[0091] After completing the heat shrinkage, measure the size (length, width) of the sample again.

[0092] Calculate the MD heat shrinkage rate and TD heat shrinkage rate (MD is the longitudinal direction, i.e. the continuous film forming direction of the diaphragm during stretching, and TD is the transverse direction, i.e. perpendicular to the MD direction):

[0093] MD heat shrinkage rate = [(initial length - heat shrinkage length) / initial length] x 100%

[0094] TD heat shrinkage rate = [(initial width - heat shrinkage width) / initial width] x 100%

[0095] 5. Tensile strength and elongation at break test:

[0096] Use the AGS-X electronic universal testing machine produced by SHIMADZU company to test the tensile strength and TD and MD elongation at break of the diaphragm according to the provisions of GB / T1040.3-2006 standard.

[0097] 6. Puncture strength

[0098] Use the AGS-X electronic universal testing machine produced by SHIMADZU company to test the diaphragm. Clamping the sample on the instrument, using a needle with a spherical end and a diameter of 1.0 mm, applying a force at a speed of 2.0 mm / s until the diaphragm is punctured. Record the maximum force value to reach the puncture as the puncture strength

[0099] The experimental results are shown in the following table:

[0100] As can be seen from the above table, compared with the coated separator made of ordinary PMMA microparticles without modification, the coated separator made of modified PMMA in the examples has better mechanical properties, and the stress and heat energy transmission and release can be better achieved by using POSS as a hard segment, so that the tensile strength and heat shrinkage performance are obviously improved. At the same time, due to the increase in the overall size of the molecular chain and the addition of the hard segment, the dimensional stability of PMMA is increased, and the membrane pore diameter is not easy to block, so that the air permeability is better. By comparing the four examples, the performance of the separator obtained in example three is better than that in examples one, two and four, and it can be seen that the amount of initiator POSS-(C3H6Cl)8 is not the more the better, and too much initiator will cause the performance of the prepared POSS-(PMMA)8 to decrease, thereby causing the performance of the coated separator to decrease.

[0101] In summary, the modified PMMA microparticles and the coated separator prepared by the present application have better mechanical properties and thermal stability compared with the conventional PMMA coated separator, and the increase in the overall size of the molecular chain and the addition of the hard segment make it less likely to block the membrane pore diameter, improve the air permeability, and theoretically reduce the internal resistance, which has great application potential.

[0102] The above examples are only used to illustrate the technical solutions of the present application and not to limit it, although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A method of modifying a lithium battery separator, characterized by, The modification method comprises the following steps: The poly-methacrylic acid cage polysilsesquioxane is prepared into modified slurry containing the poly-methacrylic acid cage polysilsesquioxane; The modified slurry is coated on the surface of the diaphragm base film and dried to obtain the poly-methacrylic acid cage polysilsesquioxane coated diaphragm. The preparation method of the poly-methacrylic acid cage polysilsesquioxane comprises the following steps: 100 parts of anisole, 1-8 parts of octachloropropyl silsesquioxane, 1-3 parts of pentamethyl diethylene triamine, 0.5-2 parts of cuprous chloride and 89-96 parts of MMA are gradually added into a flask, then the flask with a stopper is placed in liquid nitrogen, the oxygen and water vapor in the flask are removed by using a vacuum pump to extract the air in the flask and filling high-purity nitrogen, and the process of thawing and refreezing is repeated three times, and the reaction is carried out at 80 DEG C for 6-12 hours, and the product is precipitated, filtered and extracted.

2. The modification method according to claim 1, characterized by, The preparation of the modified slurry comprises the following steps: deionized water, a dispersing agent, poly-methacrylic acid cage polysilsesquioxane powder, a binder, a thickening agent and a wetting agent are added in a mass ratio, and mixing and stirring are carried out.

3. The modification method of claim 1, wherein, The addition amount of the deionized water is 30-90 parts, the addition amount of the dispersing agent is 0.3-1 part, the addition amount of the poly-methacrylic acid cage polysilsesquioxane powder is 10-40 parts, the addition amount of the binder is 0.2-2 parts, the addition amount of the thickening agent is 0.05-0.5 parts, and the addition amount of the wetting agent is 0.0001-0.01 parts.

4. The modification method according to claim 3, characterized in that, 0.3-1 parts of the dispersing agent are added in 30-90 parts of deionized water, and stirring and dispersion are carried out at a speed of 800-1200 rpm for 5-20 minutes; 5. The modification method according to claim 3, wherein 10-40 parts of the poly-methacrylic acid cage polysilsesquioxane powder are added, and stirring and dispersion are carried out at a speed of 800-1500 rpm for 40-80 minutes; 0.2-2 parts of the binder are added, and stirring and dispersion are carried out at a speed of 700-1000 rpm for 15-35 minutes; 0.05-0.5 parts of the thickening agent are added, and stirring and dispersion are carried out at a speed of 800-1200 rpm for 10-30 minutes; 0.0001-0.01 parts of the wetting agent are added, and stirring and dispersion are carried out at a speed of 700-900 rpm for 25-50 minutes; The modified slurry containing the poly-methacrylic acid cage polysilsesquioxane is obtained. The obtained modified slurry is transferred into a finished product container and kept under low-speed stirring.

6. The modification method according to claim 5, wherein The modified slurry is coated on the surface of the diaphragm base film by using the gravure method or the spraying method, and the moisture is dried by using an oven to obtain the poly-methacrylic acid cage polysilsesquioxane coated diaphragm.

7. The modification method of claim 1, wherein In the preparation process of the poly-methacrylic acid cage polysilsesquioxane powder, the molecular weight of the obtained poly-methacrylic acid cage polysilsesquioxane is adjusted by adjusting the ratio of octachloropropyl silsesquioxane to methyl methacrylate.

8. The modification method of claim 1, wherein, ​ 9. A lithium-ion battery separator, characterized by, A modified membrane made by the modifying method of any one of claims 1-8, comprising a polymethacrylic acid-based-caged polysilsesquioxane coating layer and a separator-based membrane layer, the polymethacrylic acid-based-caged polysilsesquioxane coating layer formed by coating a modified slurry containing a polymethacrylic acid-based-caged polysilsesquioxane on a surface of the separator-based membrane.

10. The separator for lithium ion batteries according to claim 9, wherein The separator-based membrane is selected from one of a polyethylene, a polypropylene, or a multi-layer composite separator.

Images