KR101318728B1 - A separator having anion-receptive and heat-resistant coating layer and electrochemical device containing the same - Google Patents

Abstract

The present invention relates to a separator having a functional coating layer including an anion fixing material and a heat resistant polymer, and an electrochemical device including the same. More specifically, the present invention provides a novel separator and an electrochemical device including the same, wherein the cation conductivity and voltage stability of the anion stabilizer are improved, and the thermal stability of the separator is improved according to the introduction of heat-resistant polymer.

Description

Separator having a functional coating layer containing anion stabilizer and heat-resistant polymer and an electrochemical device comprising the same {A separator having anion-receptive and heat-resistant coating layer and electrochemical device containing the same}

The present invention relates to a separator provided with a functional coating layer and an electrochemical device comprising the same, and more particularly, to a functional separator coated with an anion stabilizer and a heat resistant polymer, and an electrochemical device including the same.

The interest in electrochemical devices, a key component, is rapidly increasing due to expectations for the continuous expansion of the portable electronic device market and the explosive growth of the electric vehicle and energy storage devices markets. The most widely used device among electrochemical devices is a secondary battery, and lithium secondary batteries are leading the market in terms of operating voltage, energy, and power density. Lithium secondary batteries have better performance than conventional secondary batteries such as lead acid batteries using Ni-Cd, Ni-MH, etc., but they are difficult to ignite and explode due to the use of non-aqueous electrolytes, and the manufacturing process is difficult. There is this. In addition, there are many problems to be solved, such as high temperature reliability, low temperature characteristics, and unit price, for the use of electric vehicles and energy storage devices.

 One important issue in the design of electrochemical devices for non-aqueous electrolytes is the use of thin-film separators to overcome the low ionic conductivity of non-aqueous electrolytes. To this end, a microporous polyolefin-based separator having a thickness of several tens of micrometers rather than a non-woven fabric having a thickness of several hundred micrometers used in an electrochemical device for an aqueous electrolyte solution has been applied. Microporous separators exhibit extreme heat shrinkage at temperatures of 100 or more due to the material properties of polyolefins and the manufacturing process properties, including stretching. At this time, the battery ignites and explodes due to internal short circuits of the positive electrode and the negative electrode.

In order to solve the high temperature safety problem of the electrochemical device, the inorganic particles and the binder on at least one surface of the porous substrate having a plurality of pores in Korean Patent Publication Nos. 10-2006-72065, 10-2007-231, etc. A separator is proposed in which a porous coating layer of a mixture of polymers is formed. In such a separator, the inorganic particles in the porous coating layer formed on the porous substrate serve as a kind of spacer capable of maintaining the physical form of the porous coating layer. This suppresses thermal shrinkage of the porous substrate when the electrochemical device is overheated, and prevents the positive electrode and the negative electrode from directly contacting even when the porous substrate is damaged.

As described above, various solutions have been proposed for improving the safety of the electrochemical device, but it is not easy to stably maintain the binding of the nano-inorganic particles at a high temperature with the conventionally proposed binder polymer material. Therefore, the development of a heat-resistant binder polymer material that is easy to apply to the coating layer introduction process is continuously required.

In addition, due to the increase in the resistance of the electrolyte region due to the introduction of the coating layer and the recent increase in the voltage of the positive electrode material, the need for development of a functional separator as well as a new nonaqueous electrolyte is greatly increased. According to Korean Patent Publication No. 10-2007-80149, etc., a functional separator is proposed in which a polymer type anionic polymer material is introduced on a surface of a separator to improve the cation conductivity, voltage stability, and the like of an electrolyte.

As described above, various solutions for improving the safety and performance of the separator for electrochemical devices have been proposed, but it is necessary to develop a new functional separator that can improve not only the thermal stability but also the performance of the separator.

Accordingly, the present invention is to solve the problems of the prior art as described above, and provides a separator and an electrochemical device comprising a functional coating layer containing a heat-resistant polymer that can bind the anion-fixing material and high temperature well. I would like to.

In order to achieve the above object, the separator of the present invention is coated on at least one surface of the porous substrate and the porous substrate having a plurality of pores, characterized in that it is provided with a coating layer containing the anion stabilizer and heat-resistant polymer at the same time.

In the separator of the present invention, the anion-immobilizing material may be used as long as it is an inorganic material containing a group IIIA element and a substance capable of interacting with an anion and Lewis acid-Lewis base in a non-aqueous electrolyte.

In addition, in the separator of the present invention, the anion-immobilizing material includes inorganic substances such as boron oxide (B ₂ O ₃ ), aluminum oxide (Al ₂ O ₃ ), aluminum fluoride (AlF ₃ ), aluminum chloride (AlCl ₃ ), and the like. Can be used.

In the separator of the present invention, the heat-resistant polymer used for improving the thermal stability of the separator should have a melting temperature of 200 or more and be soluble in the coating solvent. Non-limiting examples of such heat-resistant polymer materials are polyimide, polyethyleneterephthalate, polybutyleneterephthalate, polyester, polyacetal, polyamide, Polycarbonate, polyetheretherketon, polysthersulfone, polyphenyleneoxide, polyphenylenesylfidro, polyethylenenaphthalene or mixtures thereof And other heat-resistant engineering polymers can be used without limitation.

Such a separator may be interposed between the positive electrode and the negative electrode to be used in an electrochemical device such as a lithium secondary battery or a capacitor device.

According to the present invention, a separator having a functional coating layer including an anion stabilizer and a heat resistant polymer is improved in the cationic conductivity and voltage stability of the anion stabilizer, and thermal stability of the inorganic material and the heat resistant polymer is improved. In addition, in the case of an electrochemical device including the same, the high temperature performance and battery safety are greatly improved.

1 is a cross-sectional view schematically showing a separator according to an embodiment of the present invention.
2 is a cross-sectional view schematically showing a separator proposed differently in the present invention.
3 is a diagram showing the high temperature numerical stability of the separator prepared according to the embodiment of the present invention and the separator prepared according to the comparative example.

In order to fully understand the present invention, operational advantages of the present invention, and objects achieved by the practice of the present invention, reference should be made to the accompanying drawings and the accompanying drawings which illustrate preferred embodiments of the present invention.

Hereinafter, the present invention will be described in detail with reference to the preferred embodiments of the present invention with reference to the accompanying drawings. However, the present invention can be implemented in various different forms, and is not limited to the embodiments described. In order to clearly describe the present invention, parts that are not related to the description are omitted, and the same reference numerals in the drawings denote the same members.

Throughout the specification, when an element is referred to as "including" an element, it does not exclude other elements unless specifically stated to the contrary. In addition, the submersible pump and water treatment apparatus used in the present invention is based on the pump and the composite metal catalyst, and includes any and all elements including wires.

Hereinafter, the present invention will be described in detail, but the scope of the present invention is not limited thereto.

The separator of the present invention includes a porous substrate having a plurality of pores and a functional coating layer coated on at least one surface of the porous substrate and including an anion stabilizer and a heat resistant polymer at the same time. By including the anion-immobilized material in the functional coating layer, the dissociation degree of the lithium salt in the electrolyte and the cationic conductivity and electrochemical stability due to the anion immobilization effect are improved. In addition, the anion-immobilized material is not only an inorganic material having excellent thermal stability but also heat-resistant polymer is used as a binder to improve the high temperature numerical stability of the separator, thereby contributing to the high temperature safety of the electrochemical device.

In the separator of the present invention, the anion-immobilizing material of the functional coating layer may be used as long as it is an inorganic material containing group IIIA elements and a material capable of interacting with anions and Lewis acid-Lewis base in a non-aqueous electrolyte. As specific anion fixing materials, inorganic materials such as boron oxide (B ₂ O ₃ ), aluminum oxide (Al ₂ O ₃ ), aluminum fluoride (AlF ₃ ), and aluminum chloride (AlCl ₃ ) may be used alone or in combination of two or more thereof. Use it. The anion stabilizer can greatly improve the cation conductivity, which is the mobility of the cation necessary for the electrochemical reaction of the electrode by increasing the dissociation degree of the salt and inhibiting the movement of the anion through strong interaction with the anion of the salt in the non-aqueous electrolyte. This is the basis for greatly improving the high rate characteristics of the electrochemical device. In addition, by suppressing the electrochemical oxidative decomposition reaction of the anion to improve the voltage stability of the non-aqueous electrolyte, it can be applied to the electrochemical device requiring high voltage driving.

In the separator of the present invention, the heat-resistant polymer used for improving the thermal stability of the separator should have a melting temperature of 200 or more and be soluble in the coating solvent. Non-limiting examples of heat-resistant polymers having a weight average molecular weight of 100,000 to 1,000,000 are polyimide, polyethyleneterephthalate, polybutyleneterephthalate, polyester, polyacetal , Polyamide, polycarbonate, polyetheretherketon, polysthersulfone, polyphenyleneoxide, polyphenylenesylfidro, polyethylenenaphthalene Or mixtures thereof, and other heat resistant engineering polymers may be used without limitation.

In the separator of the present invention, the particle size of the anion stabilizer of the functional coating layer is not limited, but in order to form a coating layer with a uniform thickness and an appropriate porosity, the particle size is preferably in the range of 0.01 to 10. If it is less than 0.01, the dispersibility is lowered, so it is not easy to control the properties of the separator. If it is more than 10, the thickness of the functional coating layer may be increased, and the mechanical properties may be deteriorated. The probability of an internal short circuit is increased.

The composition ratio of the anion stabilizer and the heat resistant polymer of the functional coating layer coated on the separator according to the present invention is preferably in the range of 10:90 to 99: 1, more preferably 50:50 to 95: 5. The thickness of the functional coating layer composed of the anion-immobilizing material and the heat-resistant polymer binder is not particularly limited, but is preferably in the range of 0.01 to 20. In addition, pore size and porosity is also not particularly limited, pore size is preferably in the range of 0.01 to 10, porosity is preferably in the range of 5 to 90%.

In addition to the above-mentioned anion stabilizer particles and heat-resistant polymers as the functional coating layer component of the separator of the present invention, other additives may be further included.

In addition, in the separator of the present invention, any porous substrate commonly used in an electrochemical device may be used as the porous substrate on which the functional coating layer is formed.

Referring to FIG. 1, the separator 1a of the present invention uses a polyolefin-based porous membrane 2 as a porous substrate, and has a porosity formed of anion-immobilizing material 3 and a heat-resistant polymer binder 4 on one or both surfaces thereof. A coating layer can be formed. The polyolefin-based porous membrane is formed of, for example, polyolefin-based polymers such as polyethylene, polypropylene, polybutylene, and polypentene, such as high density polyethylene, linear low density polyethylene, low density polyethylene, and ultra high molecular weight polyethylene, alone or in combination thereof. One membrane may be mentioned.

In addition, referring to FIG. 2, the separator 1b of the present invention may be formed of a porous coating layer made of a non-woven fabric as a porous substrate and formed of anion-immobilizing material 3 and a heat-resistant polymer binder 4 on one or both surfaces thereof. have. The nonwoven fabric is, for example, polyimide or polyethylene terephthalate in addition to the above-described polyolefin nonwoven fabric.

(polyethyleneterephthalate), polybutyleneterephthalate, polyester, polyacetal, polyamide, polycarbonate, polyetheretherketon, polyethersulfone ), Polyphenylene oxide, polyphenylenesylfidro, polyethylenenaphthalene, and the like, or a nonwoven fabric formed of a polymer obtained by mixing them alone. The structure of the nonwoven fabric is preferably a spunbond nonwoven or melt blown nonwoven composed of long fibers.

The thickness of the porous substrate is not particularly limited, but is preferably 5 to 50, and the pore size and pore present in the porous substrate are also not particularly limited, but are preferably 0.01 to 50 and 10 to 95%, respectively.

According to the present invention, a preferred manufacturing method of the separator coated with the functional coating layer is exemplified below, but is not limited thereto.

First, 1) a polymer solution is prepared by dissolving the heat-resistant polymer in an appropriate solvent.

The solvent used when mixing the heat-resistant polymer is preferably a low boiling point (boling point). This is because mixing can be made uniform, and then the solvent can be easily removed. Non-limiting examples of solvents include acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (N- methyl-2-pyrrolidone, NMP), cyclohexane, water, or a mixture thereof.

2) Inorganic particles and polymer mixtures are prepared by adding and dispersing anion-immobilizing materials to the prepared polymer solution.

After adding an anion fixer to a polymer solution, it is preferable to carry out crushing of anion fixer particle | grains. In this case, the crushing time is suitably 1 to 20 hours, and the particle size of the crushed anion-fixing particles is preferably 0.001 to 10 groups as mentioned above. As the crushing method, a conventional method can be used, and a ball mill method is particularly preferable.

The composition of the mixture consisting of the anion stabilizer and the heat resistant polymer is not particularly limited, and thus, the thickness, pore size, and porosity of the separator equipped with the functional coating layer including the final anion stabilizer and the heat resistant polymer can be controlled. .

3) By coating the prepared mixture of the anion stabilizer and the heat-resistant polymer on the prepared polyolefin-based separator substrate and then dried, it is possible to obtain a separator with a functional coating layer containing the anion-immobilized material and heat-resistant polymer of the present invention.

At this time, the method of coating the mixture of the anion-immobilizing material and the heat-resistant polymer on the polyolefin-based separator substrate may use a conventional coating method known in the art, for example dip coating, die coating Various methods such as roll coating, comma coating, or a mixture thereof may be used. In addition, when the mixture of the anion-immobilizing material and the heat-resistant polymer is coated on the polyolefin-based separator substrate, it can be carried out on both sides of the separator substrate and can be selectively carried out only on one side.

The separator having a functional coating layer including the anion-immobilized material and the heat-resistant polymer prepared as described above may be used as an electrochemical device, preferably a separator of a lithium secondary battery. In particular, when a gelable polymer is used when the liquid electrolyte solution is impregnated as a coating layer component, the electrolyte and the polymer may react by injecting a water electrolyte solution in which a battery is assembled using the separator to form a gel-type organic / inorganic composite electrolyte.

In addition, the present invention provides an electrochemical device including a separator and an electrolyte having a positive electrode, a negative electrode, a functional coating layer including the anion-fixing material and heat-resistant polymer of the present invention interposed between the positive electrode and the negative electrode.

The electrochemical device includes all devices that undergo an electrochemical reaction, and specific examples thereof include all kinds of primary, secondary cells, fuel cells, solar cells, or capacitors. In particular, a lithium secondary battery is preferable among secondary batteries, and non-limiting examples thereof include a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

The electrochemical device may be manufactured according to a conventional method known in the art. For example, the electrochemical device may be assembled by interposing the electrode and the separator and then injecting the electrolyte into the assembly.

Electrolyte that may be used in the present invention is A ⁺ B ^- consists of a salt and a solvent in the structure, such as. As a salt, A ⁺ is Li ^+, Na ^+, K ⁺ comprises an alkaline metal cation or an ion composed of a combination thereof, such as, and B ^- is _{^{PF 6 -, BF 4 -,}} Cl -, Br -, I -, ClO _{^{4 -, AsF 6 -, CH}} 3 CO 2 -, CF 3 SO 3 -, N (CF 3 SO 2) 2 -, C (CF 2 SO 2) 3 - and include such anions or an ion composed of a combination of Salts are propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, Some dissolved or dissociated in an organic solvent consisting of tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethylmethylcarbonate (EMC), gamma butyrolactone (-butyrolactone), or mixtures thereof, It is not limited only to this.

Hereinafter, the present invention will be described in more detail with reference to Examples and drawings. The following embodiments are provided by way of example so that those skilled in the art can fully understand the spirit of the present invention. Therefore, the scope of the present invention is not limited thereto.

Example 1 (manufacture of separator with a functional coating layer)

The porosity was 40%, and the thickness of the polyethylene porous substrate 20 was washed with acetone and dried in a vacuum oven of 60 or more for 6 hours. As the coating solution, B ₂ O ₃ having an average particle diameter of 500 nm and polyimide having a weight average molecular weight of 150,000 were used. B ₂ O ₃ / polyimide = 70/30 (% by weight) was added 80mL of acetone and dispersed by a ball mill (ball mill) method for more than 12 hours.

 The coating solution thus prepared was adjusted to about 3 coating thicknesses using a dip coating method. The porosity and porosity in the active layer impregnated and coated on the polyethylene porous substrate were about 0.5 and about 50%, respectively, as measured by a porosimeter.

Example 2 (manufacture of separator with a functional coating layer)

Except that B ₂ O ₃ / polyimide = 90/10 (% by weight) was carried out in the same manner as in Example 1. As measured by the porosity measuring device, the pore size and porosity were about 0.4 and 55%, respectively.

Example 3 (manufacture of lithium secondary battery)

Anode manufacturing

N-methyl-2 as a solvent in 92 wt% of lithium cobalt oxide (LiCoO ₂ ) as a positive electrode active material, 4 wt% of carbon black as a conductive material, and 4 wt% of polyvinylidene fluoride (PVdF) as a binder. Pyrrolidone (NMP) was added at twice the weight ratio of the active material, the conductive material and the binder to prepare a positive electrode mixture slurry . The positive electrode mixture slurry was coated and dried on an aluminum (Al) thin film, which is a positive electrode current collector having a thickness of about 15, to prepare a positive electrode, and then roll press was performed.

Cathode manufacturing

N-methyl-2 pyrrolidone (NMP) as a solvent was added to 85% by weight of carbon powder as a negative electrode active material, 8% by weight of carbon black as a conductive material, and 7% by weight of polyvinylidene fluoride (PVdF) as a binder. Addition to prepare a negative electrode mixture slurry. The negative electrode mixture slurry was coated and dried on a copper thin film having a thickness of 20, which is a negative electrode current collector, to prepare a negative electrode, and then roll press was performed.

Battery manufacturing

The unit cell was assembled by stacking the separator including the upper electrode, the anode, and the functional coating layer including the anion-immobilized materials and the heat-resistant polymers prepared in Examples 1 to 2. A lithium secondary battery was prepared by injecting an ethylene carbonate / dimethyl carbonate (EC / DEC = 1: 2, volume ratio) electrolyte in which hexafluorophosphate (LiPF ₆ ) was dissolved.

Comparative Example 1

A polyethylene porous substrate having a porosity of 40% and a thickness of 20 was used as a comparative group when evaluating the performance of the separator with the functional coating layer.

Comparative Example 2

It was prepared in the same manner as in Example 1 except that SiO ₂ having an average particle diameter of 450 nm was used instead of the anion fixing material.

Experimental Example 1 (ion conductivity, cation yield measurement)

The separators prepared in Examples 1, 2 and Comparative Example 1 were transferred into an argon atmosphere glove box, and ethylene carbonate / dimethyl carbonate (EC / DEC = 1: 2) in which 1 M lithium hexafluorophosphate (LiPF ₆ ) was dissolved. After impregnation with a volume-based electrolyte solution, it was adhered between two stainless steel electrodes and sealed with an aluminum packaging material coated with polyethylene, and then ion conductivity was measured. As a result, when the membrane of the present invention is used in cation yield and cation conductivity, it showed very good performance.

Table 1.

Experimental Example 2 (voltage stability)

Separator (Examples 1 and 2) with a functional coating layer containing anionic stabilizer and heat-resistant polymer and ethylene carbonate / dimethyl carbonate in which 1M lithium hexafluorophosphate (LiPF ₆ ) was dissolved After impregnating the (EC / DEC = 1: 2, volume ratio) -based electrolyte solution, an SUS / lithium battery was made to evaluate electrochemical stability. As a reference electrode, a lithium electrode was selected as a working electrode, and SUS was selected, and a voltage was applied at a rate of 2 mV / sec from 0V to 7V to show a result. The battery having the separator of the present invention showed very excellent voltage stability.

Table 2.

Experimental Example 3 (thermal safety)

The separators of Example 1, Example 2 and Comparative Examples 1 and 2, which were prepared with a functional coating layer containing anion-immobilizing material and heat-resistant polymer, were cut into 3 × 3 cm ² having a constant size and then placed in a 140 oven for 30 minutes. After the heat shrinkage was observed. As a result, it was confirmed that the thermal contraction rate of the separator according to the present invention is significantly reduced.

Experimental Example 4 (Performance Evaluation of Lithium Secondary Battery)

In order to evaluate the rate-specific characteristics of the lithium secondary battery including a separator provided with a functional coating layer containing anion-immobilized material and heat-resistant polymer prepared in the present invention, it was performed as follows. The separator provided with the functional coating layer containing the anion-immobilizing material and the heat-resistant polymer prepared in Examples 1 and 2 and the separator of Comparative Examples 1 and 2 were made of a unit cell having a battery capacity of 3mAh. The charging rate was fixed at 0.2C, and each of the batteries was cycled at a discharge rate of 0.5C, 5C, and 10C, and their discharge capacities are shown in Table 1 by the rate-specific characteristics. As a result, the battery using the separator according to the present invention showed a very good capacity retention rate.

Table 3

Claims (10)

A porous substrate; And polyimide, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide and polyethylene on at least one side of the porous substrate. Lithium secondary battery separator having a coating layer containing at least one heat-resistant polymer selected from naphthalene and boron oxide in a weight ratio of 10:90 ~ 99: 1.
delete delete delete The method of claim 1,
The pore size and porosity of the coating layer is a separator of 0.01 to 10㎛ and 5 to 95%, respectively.
The method of claim 1,
The thickness of the coating layer is a separator of 1 to 20㎛.
delete delete The method of claim 1,
The particle size of the boron oxide is a separator of 0.01 to 10㎛.
In the electrochemical device comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode,
The electrochemical device of claim 1, wherein the separator is a separator of any one of claims 1, 5, 6, and 9.

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