WO2016201757A1 - High dielectric constant nano-composite coating separator and manufacturing method thereof - Google Patents

Abstract

The present invention provides a high dielectric constant nano-composite coating separator having a high ionic conductivity and excellent battery performance and manufacturing method thereof. The nano-composite coating prepared by inorganic-organic polymer composite particles formed by compounding 50-90 parts by weight of gel polymer and 10-50 parts by weight of nano inorganic ceramic particles, has a dielectric constant significantly higher than that of the prior art and enhanced safety. The present invention utilizes a cooperative effect of the characteristic of the high dielectric constant inorganic nano-particles and the polymer of low molecular weight to obtain the inorganic-organic polymer composite particles for preparing the nano-composite coating separator having the characteristics of high-efficiency absorption and gelation of an electrolyte and excellent battery performance. The processes of synthesis and slurry preparation adopted by the present invention produce no other byproducts, and all solid components function effectively in the battery, thus being highly efficient, low-cost, and environmentally friendly.

Description

Nano-composite coating separator with high dielectric constant and preparation method thereof Technical field

The invention relates to the field of lithium ion batteries, in particular to a nano composite coating membrane with a high dielectric constant coating layer and a preparation method thereof.

Background technique

In recent years, with the development of lithium-ion battery technology, higher requirements have been placed on the function of lithium battery separators. As an important part of traditional lithium-ion batteries, the separator has the basic functions of isolating the positive and negative electrodes, preventing short circuits, and providing lithium ion conduction holes. The traditional ion battery separator adopts a single layer or a plurality of porous membranes of polyolefin. The pure polyolefin porous membrane only has the basic functions of a lithium battery separator, and it is difficult to meet the technical requirements of a new generation of lithium ion batteries.

In order to improve the performance of polyolefin separators and meet the technical requirements of a new generation of lithium batteries, such as safety, long life, and diverse battery structure, ceramic coated diaphragms and polymer coated diaphragms were born. The ceramic coated separator can improve the thermal stability, wettability, and liquid absorption of the polyolefin separator, thereby improving the safety and cycle life of the lithium ion battery. However, lithium-ion batteries using ceramic-coated separators cannot escape the concept of liquid lithium batteries, and the shortcomings of liquid lithium batteries have not been completely overcome, such as safety problems caused by liquid leakage. Although the polymer coated diaphragm imparts the function of absorbing the electrolyte gel, the lithium battery no longer causes safety problems due to leakage, but the battery internal resistance is too large, which affects the battery performance, and the rate and cycle life are reduced. In addition, there are composite coated separators obtained by blending polymers and ceramic powders, but all of them affect the performance of the battery due to poor interfacial properties of the composite coating.

At present, a commercially available composite coated separator usually uses a ceramic powder having a low dielectric constant such as alumina, silica or barium sulfate, and the obtained composite separator has poor ion conductivity. In view of this, it is necessary to provide a functionalized nanocomposite coated separator having a high dielectric constant coating layer and a method of preparing the same.

Summary of the invention

In view of the performance deficiencies of the currently commercialized composite coated lithium ion battery separator, the present invention provides a high dielectric constant nanocomposite coating separator having high ionic conductivity and excellent battery performance and a preparation method thereof. Here, the parts described in the present invention are all parts by weight unless otherwise specified.

A nano composite coating separator comprising a polyolefin porous film and a nano composite coating on one side or both sides of the polyolefin porous film, wherein the nano composite coating is an inorganic-organic polymer composite particle. The inorganic-organic polymer composite particles contain a gel polymer and nano ceramic particles, and the parts by weight are:

50 to 90 parts of gel polymer,

Nano ceramic particles 10 to 50 parts.

The lithium ion battery separator provided by the invention has the inorganic-organic polymer composite particles compounded by the gel polymer and the nano ceramic particles, and has the characteristics of high dielectric constant due to the presence of the inorganic-organic polymer composite particles, and can be fully Prevent the diaphragm from being broken down by voltage and short-circuit the battery. Therefore, not only is the safety better, but the service life is longer and so on. In particular, the inorganic-organic polymer composite particles obtained by combining 50 to 90 parts by weight of the gel polymer and 10 to 50 parts by weight of the nano ceramic particles of the present invention have a high dielectric constant which is much higher than that of the existing composite coating. Technology, better security.

The nanocomposite coating layer preferably has a thickness of 1 to 4 μm. When the nanocomposite coating is less than 1 μm, the dielectric constant is small, which does not meet the need for improving safety. When the nanocomposite coating is larger than 4μm, the dielectric constant is improved, but the excessive thickness of the nanocomposite coating affects the isolation effect of lithium ions.

As a preferred embodiment, the inorganic-organic polymer composite particles, wherein the gel polymer monomer comprises acrylonitrile, methyl methacrylate, butyl acrylate, butyl acrylate, methacrylic acid, acrylic acid, styrene One or a mixture of two or more. The high dielectric constant nano ceramic particles are one or a mixture of two or more of rutile type nano titanium dioxide, nano barium titanate, and nano CaCu ₃ Ti ₄ O ₁₂ .

As a preferred embodiment, the aqueous coating slurry used in the nano composite coating layer contains a composition and an aqueous solvent; wherein the composition is in parts by weight, and the inorganic-organic polymer composite particles are 90 to 95 parts, 1 to 5 parts of the wet agent and 3 to 10 parts of the adhesive.

As a preferred mode, the wetting agent is a fluoroalkyl methoxy ether alcohol, a fluoroalkyl ethoxy ether alcohol, an alkyl phenol ethoxylate, a fatty alcohol polyoxyethylene ether, a fatty acid polyoxygen One or more of vinyl ethers.

In a preferred embodiment, the adhesive is one or more of polyethylene glycol, styrene-butadiene latex, and polyvinyl acetate.

In a preferred embodiment, the aqueous solvent includes one or two or more kinds of water-miscible alcohol solvents such as deionized water, ethanol, methanol, and ethylene glycol.

As a preferred embodiment, the inorganic-organic polymer composite particles are surface-treated with a graft polymer, and the surface treatment coupling agent mainly uses a silane coupling agent with a double bond, and the silane coupling agent includes vinyl triethyl hydride. One or two or more of oxysilane, vinyltrimethoxysilane, vinyltris(β-methoxyethoxy)silane, and γ-methacryloxypropyl-trimethoxysilane.

After the inorganic-organic polymer composite particles are surface-treated with a graft polymer, the dielectric constant thereof is further improved, and the safety performance is remarkably improved.

As a preferred embodiment, the polyolefin separator is a polyethylene separator, a polypropylene separator, a polypropylene/polyethylene/polypropylene separator, and has a thickness of 5 to 40 μm and a porosity of 30% to 60%.

The invention also discloses a preparation method of a nano composite coating membrane, comprising the following steps:

(1) Add 10 to 50 parts of nano ceramic particles to an aqueous solvent, add 0.1 to 1 part of a silane coupling agent, adjust the acid-base pH of the system to 3 to 9, and use a nano-ball mill for high-speed ball milling, ball milling time 1-4 Hour, during ball milling, dispersion The temperature of the system reaches 50-80 ° C, and a surface-treated and uniformly dispersed nano-powder dispersion is obtained;

(2) Transfer the dispersion into a polymerization vessel, adding 50 to 90 parts of polymer monomer, 0.1 to 0.5 parts of initiator, 1 to 5 parts of emulsifier, 1 to 5 parts of wetting agent, and 3 to 10 parts of adhesive. At the same time, it is protected by nitrogen or an inert gas; a coating slurry of inorganic-organic polymer composite particles having a high dielectric constant is obtained by a method of seed emulsion polymerization;

(3) Applying the coating slurry to one side or both sides of the polyolefin film, and drying to obtain a nanocomposite separator having a high dielectric constant coating layer.

Since the polymer layer in the inorganic-organic polymer composite particles prepared by the method has a low molecular weight and generally has a molecular weight of less than 10,000, it is easy to gel with the electrolyte in a lithium battery, so the nanocomposite coating membrane absorbs the electrolyte gel. The internal state of the battery is dry, which can improve the safety and hardness of the lithium battery. The inorganic nanoparticles with high dielectric constant are dispersed on the surface and inside of the coating layer, and the surface nanoparticles can effectively reduce the transfer of lithium ions from the electrode to the electrolyte. The energy barrier of the process serves to reduce the interface resistance of the lithium battery and improve the performance of the battery rate. At the same time, the entire coating system increases the wettability and liquid absorption of the separator, which effectively improves the cycle performance of the battery.

Compared with the prior art, the advantages and benefits of the present invention are:

(1) The present invention utilizes the synergistic effect of the high dielectric constant of the inorganic nanoparticles and the low molecular weight polymer to obtain an inorganic-organic polymer composite particle for preparing a nanocomposite coating separator, which has an efficient absorption of the electrolyte and condensation. The properties of the glue are excellent in the performance of the nanocomposite coated separator battery.

(2) The invention adopts synthesis and slurry preparation process without other by-products, and various solid components can exert their functions in the battery, and the efficiency is high, the cost is low, and the environment is environmentally friendly.

DRAWINGS

Figure 1 is a high dielectric constant nanocomposite coating diaphragm electron micrograph

detailed description

The content of the present invention is further described below in conjunction with specific embodiments, but the scope of the present invention is not limited to the contents described in the embodiments.

Example 1

A high dielectric constant nanocomposite coated separator comprising a polypropylene based film and a nanocomposite coating applied to one side of the polypropylene film. The polypropylene porous film has a thickness of 16 μm, a porosity of 42%, and a coating thickness of 2 μm. The nanocomposite coating is mainly composed of rutile-type nano-titanium dioxide and polymethyl methacrylate oligomer, wherein rutile titanium dioxide The dielectric constant is 180 and the particle size is 5-10 nm. The mass ratio of polymethyl methacrylate to nano titanium dioxide is controlled at 2:1, The coating slurry used deionized water and ethanol as a mixed solvent, and the volume ratio was controlled at 9:1. The slurry configuration includes 95 parts of high dielectric constant inorganic-organic nanocomposite particles, 2 parts of a wetting agent, and 3 parts of an adhesive calculated in parts by weight.

Preparing a rutile nano TiO ₂ functionalized composite membrane having a high dielectric constant, comprising the steps of:

(1) taking a certain amount of rutile-type nano-TiO ₂ into a mixed solvent of water and ethanol, while adding a silane coupling agent vinyl triethoxysilane, stirring at high speed to obtain a mixed solution I;

(2) Injecting the mixed solution I into a high-speed nano-sand mill, adjusting the pH=3 to 5, and circulating the mixture in a ball mill for 2 hours to obtain a stable dispersion;

(3) The dispersion is transferred into the polymerization vessel, while adding a certain amount of methyl methacrylate monomer, the initiator potassium persulfate and the emulsifier OP-10, protected by nitrogen, the polymerization stability is controlled at 60-80 ° C;

(4) adding a certain amount of adhesive polyethylene glycol to the polymerization emulsion, the wetting agent is fluoroalkyl methoxy ether alcohol, stirring at a high speed, filtering with a 400 mesh screen to obtain a coating slurry, and obtaining a coating Overlay.

(5) The coating slurry was applied to one side of the polypropylene base film by a precision coater, and dried to obtain a nanocomposite separator having a high dielectric constant coating layer.

Example 2

A high dielectric constant nanocomposite coated separator comprising a polyethylene porous film and a mixed coating applied on both sides of a polyethylene porous film, wherein the polyethylene porous film has a thickness of 9 μm and a porosity of 48% on both sides The thickness of the coating is 2μm. The nanocomposite coating is mainly composed of nano-barium titanate and polymethyl methacrylate oligomer. The nano-barium titanate has a dielectric constant of 380 and an average particle diameter of 20 nm. The mass ratio of methyl acrylate to nano titanium dioxide was controlled at 4:1, and the coating slurry was treated with deionized water and ethylene glycol as a mixed solvent, and the volume ratio was controlled at 4:1. The slurry configuration included 93 parts of high dielectric constant inorganic-organic nanocomposite particles, 2 parts of a wetting agent, and 5 parts of an adhesive calculated in parts by weight.

Preparing a nanocomposite functionalized composite separator having a high dielectric constant, comprising the steps of:

(1) A certain amount of nano-barium titanate is added to a mixed solvent of water and ethylene glycol, and a silane coupling agent γ-methacryloxypropyl-trimethoxysilane is added thereto, and the mixture is stirred at a high speed to obtain a mixed solution. I;

(2) Injecting the mixed solution I into a high-speed nano-sand mill, the mixed liquid is circulated and ball-milled, the ball milling time is 2 hours, and the pH is adjusted to 3 to 5 by using nitric acid to obtain a stable dispersion;

(3) Transfer the dispersion into the polymerization tank, and add a certain amount of methyl methacrylate monomer, the initiator potassium persulfate and the emulsifier Triton-100, protected by nitrogen, and the polymerization stability is controlled at 60-80 °C. ;

(4) adding a certain amount of a water-based adhesive styrene-butadiene latex to the polymerization emulsion, the wetting agent is a fluoroalkyl methoxy ether alcohol, stirring at a high speed, and filtering with a 400-mesh sieve to obtain a coating slurry;

(5) The coating slurry was applied to both sides of the polyethylene wet base film by a precision coater, and dried to obtain a nanocomposite separator having a high dielectric constant coating layer.

Example 3

A high dielectric constant nanocomposite coated separator comprising a polypropylene/polyethylene/polypropylene porous membrane and a mixed coating applied on both sides of a polyethylene porous membrane, wherein the base film has a thickness of 25 μm and a porosity of 38 %, both sides of the coating thickness are 2μm, the nanocomposite coating is mainly composed of nano-titanium titanate surface modified nano-barium titanate particles and polyacrylonitrile oligomer, wherein the coated inorganic nanoparticles have a dielectric constant of 248 The average particle size is 25 nm, the mass ratio of polyacrylonitrile to nano titanium dioxide is controlled at 5:2, and the coating slurry is treated with deionized water and ethylene glycol as a mixed solvent, and the volume ratio is controlled at 5:1. The slurry configuration includes 90 parts of high dielectric constant inorganic-organic nanocomposite particles, 1 part of a wetting agent, and 10 parts of an adhesive, calculated by parts by weight.

Preparing a nano-sized composite membrane having a high dielectric constant nano-titanium dioxide-barium titanate, comprising the following steps:

(1) A certain amount of nano-titanium dioxide-coated barium titanate is added to a mixed solvent of water and methanol, and a silane coupling agent γ-methacryloxypropyl-trimethoxysilane is added thereto, and stirred at a high speed to obtain Mixed solution I;

(2) Injecting the mixed solution I into a high-speed nano-sand mill, the mixed liquid is circulated and ball-milled, the ball milling time is 2 hours, and the pH is adjusted to 8-9 with ammonia water to obtain a stable dispersion;

(3) The dispersion is transferred into the polymerization vessel, while adding a certain amount of acrylonitrile monomer, the initiator potassium persulfate and the emulsifier Triton-100, protected by nitrogen, the polymerization stability is controlled at 60-80 ° C;

(4) A certain amount of a water-based adhesive polyvinyl acetate was added to the polymerization emulsion, and the wetting agent was a fatty alcohol polyoxyethylene ether, which was stirred at a high speed and filtered through a 400-mesh sieve to obtain a coating slurry.

(5) The coating slurry was applied to both sides of the base film by a precision coater and dried to obtain a nanocomposite separator having a high dielectric constant coating layer.

Comparative example 1

This comparative example provides an alumina ceramic coated lithium ion battery separator comprising a porous polypropylene membrane and an alumina coating applied to one side of the porous membrane of polypropylene, wherein the porous polypropylene membrane has a thickness of 16 μm and a porosity. 42%, the alumina coating thickness is 4 μm.

Comparative example 2

This comparative example provides a polymer coated lithium ion battery separator comprising a polypropylene porous membrane and a cohesive polymer coating applied to one side of the polypropylene porous membrane, wherein the polypropylene porous membrane has a thickness of 16 μm, pores The rate was 42% and the polymer coating thickness was 1 μm.

Comparative example 3

The present comparative example provides a polymer coated lithium ion battery separator comprising a polypropylene porous membrane and a cohesive polymer-ceramic hybrid coating applied to one side of the polypropylene porous membrane, wherein the polypropylene porous membrane has a thickness of 16 μm, porosity is 42%, and polymer coating thickness is 2 μm.

Comparative example 4

This comparative example used a porous film having a thickness of 16 μm and a porosity of 42%, and was not subjected to any coating treatment.

Example 4

The particle conductivity test was carried out on the lithium ion battery separators of Examples 1 to 3 and Comparative Examples 1-4, and the diaphragm was assembled into a steel/steel sheet analog battery, and the particle conductivity of the separator was tested by using an alternating current impedance. In Table 1.

Table 1 Diaphragm ionic conductivity

It can be seen from Table 1 that coating a polyolefin with a high dielectric constant nanocomposite coating facilitates the migration efficiency of lithium ions in the separator and increases the ionic conductivity. At the same time, because the high dielectric constant nanocomposite coating is composed of high dielectric constant nano-inorganic particles and oligomers, it has a strong absorption of electrolyte gel, which can be used in lithium batteries to obtain internal apparent dryness. State structure, the battery does not leak, and the safety performance of the battery is correspondingly improved.

Example 5

A lithium ion battery separator was prepared by using Example 1, wherein the gel polymer and the nano inorganic ceramic particles were parts by weight, and the test results are shown in Table 2.

Table 2

Serial number	Gel polymer (parts)	Nano inorganic ceramic particles (parts)	Ionic conductivity S/cm
				1	30	70	1.23×10 -3
2	40	60	1.73×10 -3
				3	50	50	2.61×10 -3
4	60	40	2.82×10 -3
				5	70	30	2.87×10 -3
6	80	20	2.77×10 -3
				7	90	10	2.63×10 -3
8	100	1	1.81×10 -3

As can be seen from Table 2, the preferred technical parameters of the present invention, the separator prepared by 50 to 90 parts of the gel polymer and 10 to 50 parts of the nano inorganic ceramic particles, have stable ionic conductivity.

Example 6

A lithium ion battery separator was prepared by using Example 1, wherein the thickness of the nanocomposite coating and the test results are shown in Table 3.

table 3

It can be seen from Table 3 that the preferred technical parameters of the present invention, the thickness of the nanocomposite coating is 1-4 μm, the ionic conductivity is stable, and the useful life effect is particularly remarkable.

The above embodiments may be modified and modified as appropriate by those skilled in the art in light of the above disclosure. Therefore, the invention is not limited to the specific embodiments described above, and equivalent changes or modifications may be included within the scope of the appended claims. In addition, although specific terms are used in the specification, these terms are merely for convenience of description and do not limit the invention.

Claims (10)

1. A nano composite coating separator comprising a polyolefin porous film and a nano composite coating on one side or both sides of the polyolefin porous film, wherein the nano composite coating is an inorganic-organic polymer composite particle. The inorganic-organic polymer composite particles contain a gel polymer and nano ceramic particles, and the parts by weight are:

   50 to 90 parts of gel polymer,

   Nano ceramic particles 10 to 50 parts.
2. The nanocomposite coating separator according to claim 1, wherein the nanocomposite coating layer has a thickness of preferably 1 to 4 μm.
3. The nanocomposite coated separator according to claim 1 or 2, wherein the gel polymer has monomers including acrylonitrile, methyl methacrylate, butyl acrylate, butyl acrylate, methacrylic acid, One or a mixture of two or more of acrylic acid and styrene.
4. The nanocomposite coating separator according to claim 1 or 2, wherein the nano ceramic particles are one or a mixture of two or more of rutile-type nano-titanium dioxide, nano-barium titanate, and nano-CaCu ₃ Ti ₄ O ₁₂ .
5. The nanocomposite coating separator according to claim 1 or 2, wherein the nanocomposite coating is prepared from an aqueous coating slurry containing a composition and an aqueous solvent; The parts by weight of the composition are 90 to 95 parts of the inorganic-organic polymer composite particles, 1 to 5 parts of the wetting agent, and 3 to 10 parts of the adhesive.
6. The nanocomposite coated separator according to claim 5, wherein the wetting agent is a fluoroalkyl methoxyether alcohol, a fluoroalkyl ethoxy ether alcohol, an alkylphenol ethoxylate, One or more of a fatty alcohol polyoxyethylene ether and a fatty acid polyoxyethylene ether.
7. The nanocomposite coated separator according to claim 5, wherein the adhesive is one or more of polyethylene glycol, styrene-butadiene latex, and polyvinyl acetate.
8. The nanocomposite coating separator according to claim 5, wherein the aqueous solvent comprises one or two or more kinds of water-miscible alcohol solvents such as deionized water, ethanol, methanol, and ethylene glycol.
9. The nano composite coating separator according to any one of claims 1 to 3, wherein the inorganic-organic polymer composite particles are surface-treated with a graft polymer, and the surface treatment coupling agent is mainly a silane having a double bond. a coupling agent, the silane coupling agent comprising vinyltriethoxysilane, vinyltrimethoxysilane, vinyltris(β-methoxyethoxy)silane, γ-methacryloyloxy One or more of propyl-trimethoxysilane.
10. A method for preparing a nano composite coating membrane, comprising the steps of:

    (1) Add 10 to 50 parts of nano ceramic particles to an aqueous solvent, add 0.1 to 1 part of a silane coupling agent, adjust the acid-base pH of the system to 3 to 9, and use a nano-ball mill for high-speed ball milling, ball milling time 1-4 In the hour, during the ball milling process, the temperature of the dispersion system reaches 50-80 ° C, and a surface-treated and uniformly dispersed nano-powder dispersion liquid is obtained;

    (2) Transfer the dispersion into a polymerization vessel, adding 50 to 90 parts of polymer monomer, 0.1 to 0.5 parts of initiator, 1 to 5 parts of emulsifier, 1 to 5 parts of wetting agent, and 3 to 10 parts of adhesive. At the same time, it is protected by nitrogen or an inert gas; a coating slurry of inorganic-organic polymer composite particles having a high dielectric constant is obtained by a method of seed emulsion polymerization;

    (3) Applying the coating slurry to one side or both sides of the polyolefin film, and drying to obtain a nanocomposite separator having a high dielectric constant coating layer.

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