KR101490883B1 - A composited nonwoven separator and method of production thereof for secondary battery - Google Patents

Abstract

The method for producing a separation membrane for a secondary battery includes the steps of forming a nanofiber nonwoven fabric by using a solution of a polymer dissolved in the polymer, and coating the functional material on the nanofiber nonwoven fabric. The polymer may be selected from the group consisting of 1) a polymer containing a hydroxyl group (-OH group) in a molecular structure such as a cellulose derivative, chitin, chitosan, alginate and polyvinyl alcohol (PVA) having a polymerization degree of 1,000 or less, 2) a poly sulfone (PSU) ether imide, or 3) polyvinylidene fluoride (PVDF), poly acrylonitrile (PVDF), poly ethylene oxide (PEO), poly ethylene (PE) ), Poly (ethylene terephthalate) (PET), or a mixture thereof. The functional material may be at least one selected from the group consisting of PVA, PVA, water-soluble or water-dispersible polyester-polyol, polyacrylonitrile, methyl methacrylate), or a mixture thereof.

Description

TECHNICAL FIELD [0001] The present invention relates to a composite nonwoven fabric separator for secondary batteries,

The present invention relates to a separation membrane for a secondary battery and a manufacturing method thereof.

Lithium secondary batteries are widely used in mobile devices and IT devices due to their high energy density. Recently, researches have been made to apply lithium secondary batteries to large-capacity high power applications such as HEV, PHEV, EV, Development is progressing all over the world. However, the lithium secondary battery is constantly incurred in safety related accidents such as ignition explosion, thus causing doubts about safety in application of a large capacity high power field, and efforts are being made to dramatically improve the safety.

Conventionally, polyolefin-based separator membranes are widely used, and it is necessary to secure a high-performance membrane element technology that can replace the polyolefin-based separator membrane, which has poor thermal stability at high temperatures and chemical stability when used for a long period of time. Since the mechanical and thermal stability of the separation membrane physically separating the positive electrode and the negative electrode is improved, heat generation and ignition explosion due to short-circuiting of the battery can be prevented in advance. Therefore, the separation membrane is a core part having close relation with the safety improvement of the lithium secondary battery to be.

The polyolefin-based separator which is currently in commercial use exhibits extreme heat shrinkage at a temperature of 150 ° C or higher, and its mechanical strength is lowered, which is pointed out as the biggest problem related to the safety accident of the battery. Therefore, the development of a new separation membrane material and nano-ceramic coating technology to improve the fundamental thermal stability and mechanical stability of the polyolefin-based separation membrane are being studied.

LG Chem, a domestic company, has developed a composite membrane coated with ceramic particles on a polyolefin-based membrane, and is currently being applied to a lithium secondary battery mounted on an Avante LPI hybrid vehicle developed by Hyundai Motor. Motorola USA filed a number of patents in the field of using a porous membrane as a support, and a representative example is US Pat. No. 5,681,357. In this patent, a cell is prepared by coating with a poly (vinylidene fluoride) solution on a polyethylene-based separator well known as a Celgard, and then an electrolyte is injected and gelated at a high temperature to form lithium A method of manufacturing a secondary battery is proposed.

As described above, a technique of coating a functional material such as ceramic particles or polyvinylidene fluoride on a conventional polyolefin-based separation membrane to improve thermal shrinkage and mechanical strength at a temperature of 150 ° C or higher is effective in reducing the adhesion force of the coating material, And has the same problem. Conventional polyolefin-based membranes are hydrophobic and have a very smooth surface, so that the adhesion strength of the coating material is low, so that the selection and coating of the coating material is very difficult. In the process of assembling the secondary battery or in contact with the electrolyte in the secondary battery There is a possibility that the function is lost. In addition, conventional polyolefin type membranes have a pore size of less than 0.5 μm and a porosity of about 40%, so that as the amount of the coating increases, the pore size and porosity decrease, and the membrane function is lost.

When heat-resistant nonwoven fabric is used as a separator, thermal stability and porosity of 60% or more are excellent. However, in the case of a nonwoven fabric having a thickness of about 20 탆, the pore size is about several tens of 탆 larger than that of the polyolefin-based separator, and therefore, the nonwoven fabric has a limit to be applied as a separator for a lithium secondary battery. Techniques for controlling the pore size, which is a disadvantage of the nonwoven fabric separator, have been introduced at home and abroad by coating functional materials such as ceramic particles and polyvinylidene fluoride on the nonwoven fabric.

Evonics, Germany, has developed a composite membrane that is coated with ceramic particles on polyethylene terephthalate (PET) nonwoven fabric, and is currently in production of prototype products. However, there are no examples applied to lithium secondary batteries. Mitsubishi Chemical of Japan is developing products coated with ceramic particles on a nonwoven fabric made of aramid fibers. However, there are no commercialized products to date, and Asahi, Tonen in Japan and Celgard in the US are also developing high-safety separators have.

The present invention has been made to solve the above problems, and it is an object of the present invention to provide a separation membrane for a secondary battery having a desired pore size, porosity, tensile strength, permeability, .

The method for manufacturing a separation membrane for a secondary battery according to an embodiment of the present invention includes forming a nanofiber nonwoven fabric by using a solution of a polymer dissolved in a polymer, and coating a functional material on the nanofiber nonwoven fabric. The polymer may be selected from the group consisting of 1) a polymer containing a hydroxyl group (-OH group) in a molecular structure such as a cellulose derivative, chitin, chitosan, alginate and polyvinyl alcohol (PVA) having a degree of polymerization of 1,000 or less, 2) ether imide, or 3) polyvinylidene fluoride (PVDF), polyacrylonitrile (PVDF), poly ethylene oxide (PEO), polyethylene (PE), polypropylene terephthalate, or a mixture thereof. The functional material may be a PVA-based, water-soluble or water-dispersible polyester-polyol (polyurethane, thermoplastic polyurethane), PAN (polyacrylonitrile), PMMA (poly methyl methacrylate) .

The method for manufacturing a separation membrane for a secondary battery according to another embodiment of the present invention may further include pressing the nanofiber nonwoven fabric to control physical properties of the nanofiber nonwoven fabric, May be performed after the step of coating.

The method for manufacturing a separation membrane for a secondary battery according to another embodiment of the present invention may further include pressing the nanofiber nonwoven fabric to control physical properties of the nanofiber nonwoven fabric, May be performed prior to coating.

The method for manufacturing a separation membrane for a secondary battery according to another embodiment of the present invention may further include pressing the nanofiber nonwoven fabric to control physical properties of the nanofiber nonwoven fabric, May be performed before and after the coating step, respectively.

The nanofiber nonwoven fabric may be produced by using the polymer solution such as electro-spinning, melt spinning, electro-blowing, melt-blowing (composite spinning, Spun-bonded, air laid, or? Can be prepared by a wet laid process.

The nanofiber nonwoven fabric may have a thickness of 10 to 100 μm, and the nanofibers constituting the nanofiber nonwoven fabric may have a diameter of 100 to 3000 nm.

The PVA system may comprise fully hydrolyzed PVA (polyvinyl alcohol) having a degree of saponification of 98 to 99% or partially hydrolyzed PVA having a saponification degree of 85 to 89% have.

The separation membrane for a secondary battery according to an embodiment of the present invention is formed by coating a functional material on a nanofiber nonwoven fabric formed by using a solution of a polymer dissolved in a polymer. The polymer may be selected from the group consisting of 1) a polymer containing a hydroxyl group (-OH group) in a molecular structure such as a cellulose derivative, chitin, chitosan, alginate and polyvinyl alcohol (PVA) having a degree of polymerization of 1,000 or less, 2) ether imide), 3) polyvinylidene fluoride (PVDF), polyacrylonitrile (PVDF), poly ethylene oxide (PEO), polyethylene (PE), polypropylene (PP), poly ethylene terephthalate ), Or a mixture thereof. The functional material may be a PVA-based, water-soluble or water-dispersible polyester-polyol (polyurethane), a polyacrylonitrile (PAN), a poly methyl methacrylate (PMMA) to be.

The nanofiber nonwoven fabric may be pressed to adjust its physical properties.

The nanofiber nonwoven fabric may be produced by using the polymer solution such as electro-spinning, melt spinning, electro-blowing, melt-blowing (composite spinning, Spun-bonded, air laid, or? Can be prepared by a wet laid process.

The nanofiber nonwoven fabric may have a thickness of 10 to 100 μm, and the nanofibers constituting the nanofiber nonwoven fabric may have a diameter of 100 to 3000 nm.

The PVA system may comprise fully hydrolyzed PVA (polyvinyl alcohol) having a saponification degree of 98 to 99% or partially hydrolyzed PVA having a saponification degree of 85 to 89%.

According to the embodiment of the present invention, a functional material can be coated on the polymer nanofiber nonwoven fabric to prevent a voltage delay phenomenon. Also, the coated functional material plays a role of adjusting the tensile strength, pore size, porosity, permeability, heat shrinkage, and nonwoven fabric thickness of the nonwoven fabric and can increase the ion conductivity of the lithium ion battery in the conventional lithium secondary battery electrolyte.

Further, by pressing the polymer nanofiber nonwoven fabric, desired tensile strength, pore size, porosity, permeability, heat shrinkage, and nonwoven fabric thickness can be controlled.

In the present invention, PVA polymer having excellent heat resistance and chemical resistance is applied to nonwoven fabrication step and functional material coating step according to degree of saponification and degree of polymerization, respectively. In the case of PVA having a degree of polymerization of more than 1,000 regardless of degree of saponification, It was confirmed that there is no problem in the secondary battery separator material even if it is applied regardless of the coating step of the functional material.

It is possible to manufacture separation membranes which are excellent in cost efficiency and low cost as a secondary battery separator material of water-soluble PVA having a polymerization degree of more than 1,000, and provide environmentally friendly secondary battery separator and manufacturing technology by using water as a solvent in the manufacturing step or coating step of nonwoven fabric This is possible.

Further, the method may further include pressing the nanofiber nonwoven fabric so that physical properties of the nanofiber nonwoven fabric are controlled. The pressing of the nanofiber nonwoven fabric may be performed before or after the step of coating the functional material, The nonwoven fabric separator obtained by the combination of the coating and pressing processes has a significantly increased stability due to no voltage delay phenomenon in the lithium secondary battery as compared with the untreated nonwoven fabric separator, The tensile strength can be increased, and the heat resistance and permeability can be improved as compared with conventional polyolefin-based membranes.

FIG. 1 and FIG. 2 are views showing the results of measurement of the thickness and tensile strength of the separator according to the coating amount of the composite nonwoven fabric separator prepared by combining the nonwoven fabric with the coating step and the pressing step.
FIG. 3 is a view showing a result of a coin cell evaluation showing a voltage delay phenomenon, FIG. 4 is a view showing a result of a coin cell evaluation showing a state of a normal charge / discharge characteristic, Fig. 6 is a view showing a result of a coin cell evaluation.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The composite nonwoven fabric separator for a secondary battery according to an embodiment of the present invention can be used as a separator for a secondary battery such as a lithium secondary battery. Hereinafter, a method for manufacturing a composite nonwoven fabric separator for a secondary battery according to an embodiment of the present invention, The battery composite nonwoven fabric separator will be described.

The method for fabricating a composite nonwoven fabric separator for a secondary battery according to an embodiment of the present invention includes forming a nanofiber nonwoven fabric by using a solution of a polymer dissolved in the polymer, and coating a functional material on the formed nanofiber nonwoven fabric. It is possible to obtain an effect of preventing the voltage delay of the separation membrane by coating the functional material.

Meanwhile, the method for fabricating a composite nonwoven fabric separator for a secondary battery according to another embodiment of the present invention may further include pressing the nanofiber nonwoven fabric. In the step of pressing the nanofiber nonwoven fabric, Or may be performed before the step of coating the functional material. According to another embodiment of the present invention, the step of pressing the nanofiber nonwoven fabric may be performed before and after the step of coating the functional material, respectively. By pressing the nanofiber nonwoven fabric, the properties of the nanofiber nonwoven fabric can be controlled so that the separator has desired properties.

The polymer forming the nanofiber nonwoven fabric may include various polymers that can be formed into nanofibers. Examples of the polymer include cellulose derivatives (e.g., cellulose, cellulose acetate, etc.), chitin, chitosan, alginate, poly 2) PSU (poly sulfone) and PEI (polyether imide); 3) PVA, PI (polyimide) and poly (vinylidene chloride) Those belonging to polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), poly ethylene oxide (PEO), poly ethylene (PE), polypropylene (PP) and poly ethylene terephthalate (PET) have.

A nanofiber nonwoven fabric is formed by using the polymer solution obtained by dissolving the above-mentioned polymer.

The nanofiber nonwoven fabric may be formed by electro-spinning the above polymer solution, and may be formed by melt spinning, electro-blowing, melt-blowing, Spun-bonded, air laid, or? Or may be formed through wet laid or the like.

According to an embodiment of the present invention, the nanofiber nonwoven fabric may have a thickness of 10 to 100 mu m, and the polymer nanofibers constituting the nanofiber nonwoven fabric may have a diameter of 100 to 3000 nm.

On the other hand, the functional material coated on the nanofiber nonwoven fabric may be a polymer or a polymer or a blend thereof having heat resistance, stability against organic electrolytic solution, mechanical properties, high lithium ion conductivity, etc. For example, (PVA), water-soluble polyolefin (PEO), water-soluble or water-dispersible polyester-polyol, polyacrylonitrile (PAN), poly methyl methacrylate ≪ / RTI >

For example, the functional material may be coated on the nanofiber nonwoven fabric by a method of spraying the functional material comprising the polymer solution onto the nanofiber nonwoven fabric, or a method of impregnating the nanofiber nonwoven fabric with the polymer solution.

Meanwhile, the method for manufacturing a separation membrane for a secondary battery according to an embodiment of the present invention may include pressing the nanofiber nonwoven fabric, and the properties of the nanofiber nonwoven fabric can be controlled by pressing the nonwoven fabric, .

For example, pressing of the nanofiber nonwoven fabric can be performed by pressing a polymer nanofiber nonwoven fabric or a polymer nanofiber nonwoven fabric coated with a functional material using a high-pressure press machine. At this time, the pressing can be performed at a pressing pressure of 245 kgf / cm (line pressure) or less and a pressing temperature of 70 DEG C or less.

The composite nonwoven fabric separator comprising the nanofiber nonwoven fabric obtained by the coating of the polymer nanofiber nonwoven fabric or the combination of coating and pressing as described above can be produced. Thus, the composite nonwoven fabric separator obtained by the combination of the coating and pressing processes has a higher voltage stability than the untreated nonwoven fabric separator, and thus the stability is significantly increased, and the thickness and the pore size can be reduced And the tensile strength can be increased, and the heat resistance and permeability can be improved as compared with the conventional polyolefin-based separator.

Hereinafter, experimental examples according to embodiments of the present invention will be described.

Experimental Example 1 : Cellulose Composite nonwoven fabric  Preparation of Membrane and Evaluation Results of Secondary Battery Cell Using the Membrane

Nonwoven fabric membranes were prepared by combining PVDF or PVA based coating liquid on the cellulose nonwoven fabric and pressing step, and evaluated the lithium secondary battery cell by applying it as a separator. The cellulose nonwoven fabric was manufactured by a wet-laid method from a paper manufacturer.

Properties of Cellulose Composite Nonwoven Membrane Prepared by PVDF Coating and Pressing Process and Evaluation Results of Lithium Secondary Cell Non-woven coating Pressing Basis weight
(g / m ² ) thickness
(μm) The tensile strength
(Kgf / cm ² ) Specularity
(sec / 100 ml) Heat shrinkage
(%, 150 degrees / 1 hr) 전압 지연 Cellulose PVDF Line pressure (Kgf / cm) at 30 ° C, 5 m / min X X 8 24 280 8 0 O O X 19 43 - 11 0 X O O (94) 19 24 310 40 0 X O O (245) 19 21 360 86 0 O

Properties of Cellulose Composite Nonwoven Membrane Prepared by PVDF Coating and Pressing Process and Evaluation Results of Lithium Secondary Cell Non-woven Pressing coating Basis weight
(g / m ² ) thickness
(μm) The tensile strength
(Kgf / cm ² ) Specularity
(sec / 100 ml) Heat shrinkage
(%, 150 degrees / 1 hr) 전압 지연 Cellulose Line pressure (245 Kgf / cm) at 30 ° C, 5 m / min PVDF O X 8 14 - 17 0 O O 13 19 330 41 0 O O 17 23 350 490 0 X

In the first cellulosic nonwoven fabric, a voltage delay phenomenon was observed in the evaluation of a lithium secondary battery cell. However, when the sample was coated at a pressure of 94 Kgf / cm or less after coating with a sample coated with PVDF The voltage delay phenomenon disappears and the normal charge / discharge characteristic behavior is exhibited.

Thickness, tensile strength and air permeability values except heat shrinkage rate could be controlled by coating and pressing step. After the coating process, the basis weight was increased, but the thickness was less than 24 ㎛ and the tensile strength and porosity were increased as compared with the initial cellulose nonwoven fabric. When coated with the same coating amount, the maximum thickness and maximum tensile strength were obtained when the maximum linear pressure used in this study was 245 Kgf / cm. However, there was a problem in using as a separator due to the voltage delay phenomenon.

The results are shown in Table 2, when the samples were subjected to the pressing step after 245 Kgf / cm 2 of pressurization, the values were higher than the basis weight of the first cellulose nonwoven fabric, but the thickness decreased and tensile strength and permeability increased. Also, as the amount of coating increased, the values of thickness, tensile strength and permeability increased. In the case of pressed cellulose nonwoven fabric, the voltage delay phenomenon was observed like the first cellulose nonwoven fabric, and when the coating was coated with a certain level of coating amount, the voltage delay phenomenon disappears and a normal charge / discharge characteristic curve could be obtained.

FIG. 1 and FIG. 2 are views showing the results of measurement of the thickness and tensile strength of the separator according to the coating amount of the composite nonwoven fabric separator prepared by combining the nonwoven fabric with the coating step and the pressing step. As shown in FIG. 1 and FIG. 2, as the amount of coating increases, the thickness and tensile strength increase. In the case of applying the same amount of coating, the case of the pressed sample after coating is the thinnest and the thinner High tensile strength.

Taking all the above results into consideration, it is possible to eliminate the voltage delay phenomenon, to maintain or lower the thickness of the initially used cellulose nonwoven fabric, to produce a composite nonwoven fabric membrane having the maximum tensile strength and heat shrinkage at 150 ° C., It was possible to manufacture when the coating step after pressing was performed. The amount of the appropriate coating and the pressing pressure depend on the amount of coating, the kind of coating liquid, the material of the nonwoven fabric, the thickness, and the degree of pelletization (or pore size).

Properties of Cellulose Composite Nonwoven Membranes Prepared by PVA Coating and Pressing Process and Evaluation Results of Lithium Secondary Cells Non-woven coating Pressing Basis weight
(g / m ² ) thickness
(μm) The tensile strength
(Kgf / cm ² ) Specularity
(sec / 100 ml) Heat shrinkage
(%, 150 degrees / 1 hr) 전압 지연 Cellulose PVA
(Polymerization degree, saponification degree) Line pressure (Kgf / cm) at 30 ° C, 5 m / min X X 13 36 270 0 0 O 500,
98 to 99% X - - - - 0 O 500,
85 to 89% X - - - - 0 O 1000, 98-99% X - - - - 0 O 1000, 85-89% X - - - - 0 O 1700, 98-99% X - - - - 0 X O (94) - - - - 0 X O (245) - - - - 0 O 1700, 85-89% X 20 72 - 0.4 0 X O (94) 20 46 400 0.4 0 X O (245) 20 30 465 0.4 0 O

Properties of Cellulose Composite Nonwoven Membranes Prepared by PVA Coating and Pressing Process and Evaluation Results of Lithium Secondary Cells Non-woven Pressing coating Basis weight
(g / m ² ) thickness
(μm) The tensile strength
(Kgf / cm ² ) Specularity
(sec / 100 ml) Heat shrinkage
(%, 150 degrees / 1 hr) 전압 지연 Cellulose Line pressure (245 Kgf / cm) at 30 ° C, 5 m / min PVA O X 13 28 330 0 0 O O 17.5 51 320 1.1 0 O O 22.5 56 270 1.3 0 X

Tables 3 and 4 show experimental results of the cellulose nonwoven fabric membrane obtained by combining the coating step and the pressing step using PVA having different coating degree and degree of polymerization. PVA was purchased from Aldrich and Kuraray, and PVA with a degree of polymerization between 1,000 and 1,700 was not available.

Regardless of the degree of saponification, the voltage-delay phenomenon was still observed in PVA-coated cellulose nonwoven membranes with a degree of polymerization of 500 and 1,000. When PVA with a degree of polymerization of 1,700 was applied regardless of saponification degree, the voltage delay phenomenon disappeared and the normal charge- . The cellulosic nonwoven fabric coated with PVA having a degree of polymerization of 1,700 having the above normal charge and discharge characteristic curve was subjected to a subsequent pressing step, and a voltage delay was again observed in the sample pressed at a linear pressure of 245 Kgf / cm.

Similar to the results shown in Table 1 and Table 2, when the cellulosic nonwoven fabric pressed at a linear pressure of 245 Kgf / cm 2 was coated with PVA having a degree of polymerization of 1,700 by coating amount, a voltage delay phenomenon was observed in the case of the pressed cellulose nonwoven fabric as in the case of the first cellulose nonwoven fabric In case of coating with a certain amount of coating, the voltage delay phenomenon disappears and a normal charging / discharging characteristic curve can be obtained.

In Table 3 and Table 4, the thickness, tensile strength, and air permeability of the cellulose nonwoven fabric were controllable by the combination of the PVA coating step and the pressing step in the same manner as in the results of FIGS. 1 and 2. The cellulosic non- Non-woven fabric separator with a maximum tensile strength and no heat shrinkage at 150 ° C while maintaining or reducing the thickness of the nonwoven fabric is coated with an appropriate amount of coating using PVA having a degree of polymerization of more than 1,000 regardless of degree of saponification, It was possible to manufacture in the case of the coating step. The amount of the appropriate coating and the pressing pressure depend on the amount of coating, the kind of coating liquid used, the material of the nonwoven fabric, the thickness, the degree of pelletization (or pore size), and the like.

FIG. 3 is a view showing a result of a coin cell evaluation showing a voltage delay phenomenon, FIG. 4 is a view showing a result of a coin cell evaluation showing a state of a normal charge / discharge characteristic, Fig. 7 is a view showing a result of a coin cell evaluation showing a state of a coin cell.

The above results show that if the initial nonwoven fabric has a voltage delay, it can solve the voltage delay problem by coating with PVDF or a PVA coating solution having a degree of polymerization of more than 1,000 by using an appropriate coating amount. However, if the coating amount is too low, the voltage delay phenomenon does not disappear, and if the coating amount is excessively large, a result of the capacity shortage characteristic is obtained (see FIG. 3 to FIG. 5). The optimum amount of coating can be determined depending on the material, thickness, and purity (or pore size) of the nonwoven fabric to be used together with the coating material used.

In order to minimize the thickness of the membrane to be produced and maximize the tensile strength, it is necessary to carry out a pressing step under a high linear pressure condition. In order to obtain a normal charging / discharging characteristic curve, the coating material, The proper pressing pressure can be determined according to the material, thickness, and air permeability (or pore size) of the nonwoven fabric.

The following Example 2 can overcome the limitations of the coating amount and the pressing pressure mentioned above. If the nonwoven fabric in the original state is made of an electrochemically stable material in the secondary battery cell and the risk of voltage delay disappears, The pressing pressure can be fixed to the maximum to easily determine the coating conditions (such as the amount of coating) that can minimize the thickness of the paper and maximize the tensile strength.

Experimental Example  2. PVDF Composite nonwoven fabric  Preparation of Membrane and Evaluation Results of Secondary Battery Cell Using the Membrane

A composite nonwoven fabric separator was prepared by combining the PVDF nonwoven fabric with the PVA coating liquid having a degree of polymerization of 1,700 as described in Experimental Example 1 and a pressing step, and was applied as a separator to evaluate the lithium secondary battery cell.

Physical Properties and Evaluation of Lithium Secondary Battery Cells of PVDF Composite Nonwoven Membranes Prepared by PVA Coating and Pressing Process Non-woven coating Pressing Basis weight
(g / m ² ) thickness
(μm) The tensile strength
(Kgf / cm ² ) Specularity
(sec / 100 ml) Heat shrinkage
(%, 150 degrees / 1 hr) 전압 지연 PVDF PVA
(Degree of polymerization: 1,700) (245 Kgf / cm) at 30 < 0 > C, 5 m / min X X 10 21 155 One 36 X X O 10 15 - 11 24 X O O 12.5 13 210 87 16 X O O 15 17 240 - 6 X

Table 5 shows PVDF composite nonwoven fabric membranes prepared by a coating process using a coating solution obtained by dissolving PVA having a degree of polymerization of 1,700 in distilled water and a pressing step (under a linear pressure of 245 Kgf / cm) in a nonwoven fabric obtained by electrospinning PVDF, And evaluation results of a lithium secondary battery cell.

In the case of the PVDF nonwoven fabric and the pressed nonwoven fabric, no voltage delay phenomenon was observed unlike the cellulose nonwoven fabric of Experimental Example 1. However, the thermal shrinkage at 150 ° C is not less than 20%, and the problem of thermal stability and mechanical stability at a temperature of 150 ° C or more, like conventional polyolefin-based separators, has not been solved.

For the purpose of solving this problem, PVDF composite nonwoven fabric membranes were prepared by using PVA with excellent heat resistance, chemical resistance, mechanical strength and low cost. An optimal lithium secondary battery separator having no voltage delay phenomenon could be manufactured while improving the tensile strength. In addition, no voltage delay was observed regardless of the amount of PVA coating, and no voltage delay was observed in the samples pressed at the best linear pressure (245 Kgf / cm) used in this study.

As a result of the above results, unlike the result of Experimental Example 1, there is no restriction on the coating amount and the pressing pressure when the nonwoven fabric having no initial voltage delay phenomenon is used. As shown in FIGS. 1 and 2, It is possible to manufacture a composite nonwoven fabric separator for a secondary battery having a minimum thickness and a maximum tensile strength and having an improved heat shrinkage and no voltage delay.

Experimental Example  3. PVA Composite nonwoven fabric  Preparation of Membrane and Evaluation Results of Secondary Battery Cell Using the Membrane

In the case of the PVA composite nonwoven fabric membrane prepared through the coating step using the coating liquid obtained by dissolving PVDF in a nonwoven fabric obtained by electrospinning of PVA having a degree of polymerization of 1,700 as described in Experimental Examples 1 and 2 and the step of pressing (a linear pressure of 245 Kgf / cm) As in the case of Experimental Example 2, the PVA nonwoven fabric initially used had no voltage delay phenomenon as in the case of PVDF nonwoven fabric, and there was no restriction on the coating amount and the pressing pressure. As shown in FIGS. 1 and 2, after the coating was subjected to a preliminary pressure of 245 Kgf / cm The heat shrinkage was reduced and a composite nonwoven fabric membrane for a secondary battery having a minimum thickness and a maximum tensile strength without voltage delay was fabricated.

Table 6 and Table 7 show the results of the previous patent and the results of coating the PVDF on the nonwoven fabric obtained by electrospinning using PVA having a degree of polymerization of 500 and the physical properties and cell evaluation results of the samples prepared through the pressing step. As in the case of the cellulose nonwoven fabric of Experimental Example 1, a voltage delay was observed in the first PVA nonwoven fabric and the pressed PVA nonwoven fabric. In the pressed sample after the coating, It is possible to manufacture a separation membrane without delay.

Properties of composite nonwoven fabric membranes prepared by PVDF coating and pressing process on PVA nonwoven fabric having a degree of polymerization of 500 and evaluation results of lithium secondary battery cells Non-woven coating Pressing Basis weight
(g / m ² ) thickness
(μm) The tensile strength
(Kgf / cm ² ) Specularity
(sec / 100 ml) Heat shrinkage
(%, 150 degrees / 1 hr) 전압 지연 PVA
(Degree of polymerization: 500) PVDF Line pressure (Kgf / cm) at 30 ° C, 5 m / min X X 8 29 70 0.4 13 O O X 12 30 120 1.5 8 X O O (94) 13 25 140 2.4 8 X O O (245) 13.6 20 180 4.4 5 O

Properties of composite nonwoven fabric membranes prepared by PVDF coating and pressing process on PVA nonwoven fabric having a degree of polymerization of 500 and evaluation results of lithium secondary battery cells Non-woven Pressing coating Basis weight
(g / m ² ) thickness
(μm) The tensile strength
(Kgf / cm ² ) Specularity
(sec / 100 ml) Heat shrinkage
(%, 150 degrees / 1 hr) 전압 지연 PVA
(Degree of polymerization: 500) Line pressure (245 Kgf / cm) at 30 ° C, 5 m / min PVDF O X 8 29 70 0.4 13 O X 8 23 135 1.0 13 O O 10 23 130 3.7 8 O O 12 25 170 10.4 5 X

As a result of the above results, it can be seen that the electrolytic solution of lithium secondary battery (a carbonate-based organic solvent such as ethylene carbonate or propylene carbonate containing lithium salt), such as cellulose used in this experiment or polyvinyl alcohol having a degree of polymerization of 1,000 or less, When used as a lithium secondary battery separator, there are those containing a hydroxyl group (-OH group) in a molecular structure such as a cellulose derivative such as cellulose acetate, chitin, chitosan or alginate, which causes a voltage delay phenomenon. These polymers have a high melting temperature of 200 ° C or higher and are cheap enough to overcome the disadvantages of existing polyolefin-based separators because of their low cost. However, they can not be applied directly to lithium secondary battery separators due to voltage delays. In addition, since the amount of coating and the pressing pressure are limited, it is necessary to determine an appropriate coating amount and a pressing pressure according to physical properties of the nonwoven fabric such as the material and thickness of the coating material and the nonwoven fabric to be used and the degree of pelletization (or pore size) There is a hassle to be able to manufacture.

In the case of PSU (poly sulfone) and PEI (polyether imide), the material and thickness of the coating material and the nonwoven fabric used in the same manner as in the case of the PVA nonwoven fabric or the cellulose nonwoven fabric having a polymerization degree of 1,000 or less, (Or pore size) of the non-woven fabric, it is necessary to determine the proper amount of coating and the pressing pressure to manufacture the separation membrane having no voltage delay phenomenon.

In the case of nonwoven fabric made of PI (polyimide), PVDF, PAN, PEO, polyethylene (PE), polypropylene (PP) or polyethylene terephthalate (PET) If a nonwoven fabric having a thickness of 20 to 25 占 퐉 and a pore size of several 占 퐉 or less is used by using a material having no heat resistance and voltage delay (electrochemically stable in a lithium secondary battery cell), the water- It is possible to manufacture the best secondary battery separator having a tensile strength improved and a voltage retardation phenomenon while maintaining a heat shrinkage of 0% and a thickness of 20 to 25 탆 at 150 ° C through a coating step and a pressing step using a PVA coating solution .

In general, a conventional polyolefin-based membrane has a tensile strength of 1,000 Kgf / cm 2 or more, but it is not easy to have a tensile strength of 300 Kgf / cm ² or more in the case of a nonwoven fabric having a thickness of 20 to 25 μm (pore size of several μm or less) . This difference in mechanical strength is not immediately applicable to the lithium secondary battery mass production line at present and a solution for improving the tensile strength of the nonwoven fabric separator can be obtained through the coating step and the pressing step using the aqueous PVA coating solution of this patent.

While the present invention has been particularly shown and described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, And all changes and modifications to the scope of the invention.

Claims (12)

A step of forming a nanofiber nonwoven fabric by using a polymer solution in which a polymer is dissolved,
Pressing the nanofiber nonwoven fabric so that physical properties of the nanofiber nonwoven fabric are controlled, and
And coating a functional material on the nanofiber nonwoven fabric,
The polymer may be selected from the group consisting of 1) a polymer containing a hydroxyl group (-OH group) in a molecular structure such as cellulose derivatives, chitin, chitosan, alginate, and polyvinyl alcohol having a degree of polymerization of 1,000 or less, 2) poly sulfone (PSU) ether imide, or 3) polyvinylidene fluoride (PVDF), polyacrylonitrile (PVDF), poly ethylene oxide (PEO), polyethylene (PE), polypropylene terephthalate, or a mixture thereof,
The functional material may be a PVA-based, water-soluble or water-dispersible polyester-polyol (polyurethane), a polyacrylonitrile (PAN), a poly methyl methacrylate (PMMA) The separation membrane for secondary battery. The method of claim 1,
Wherein the step of pressing the nanofiber nonwoven fabric is performed after the step of coating the functional material. The method of claim 1,
Wherein the step of pressing the nanofiber nonwoven fabric is performed prior to the step of coating the functional material. The method of claim 1,
Wherein the pressing of the nanofiber nonwoven fabric is performed before and after the step of coating the functional material, respectively. 5. The method according to any one of claims 1 to 4,
The nanofiber nonwoven fabric may be produced by using the polymer solution such as electro-spinning, melt spinning, electro-blowing, melt-blowing (composite spinning, Spun-bonded, air laid, or? A method for producing a separation membrane for a secondary battery, which is manufactured by a wet laid method. 5. The method according to any one of claims 1 to 4,
Wherein the nanofiber nonwoven fabric has a thickness of 10 to 100 mu m, and the nanofibers constituting the nanofiber nonwoven fabric have a diameter of 100 to 3000 nm. 5. The method according to any one of claims 1 to 4,
Wherein the PVA system comprises fully hydrolyzed PVA (polyvinyl alcohol) having a saponification degree of 98 to 99% or partially hydrolyzed PVA having a saponification degree of 85 to 89%. The non-woven fabric is formed by coating a functional material on a nanofiber nonwoven fabric formed by using a solution of a polymer dissolved in a polymer,
The nanofiber nonwoven fabric is pressed to adjust the physical properties,
The polymer may be selected from the group consisting of 1) a first group containing a polymer containing a hydroxyl group (-OH group) in a molecular structure such as cellulose derivatives, chitin, chitosan, alginate, and polyvinyl alcohol (PVA) (PVDF), poly (acrylonitrile), poly (ethylene oxide), poly (ethylene oxide), PE (poly ethylene) , Polypropylene (PP), polyethylene terephthalate (PET), or a mixture thereof.
The functional material may be a PVA-based, water-soluble or water-dispersible polyester-polyol (polyurethane), a polyacrylonitrile (PAN), a poly methyl methacrylate (PMMA) Separator for a secondary battery. delete 9. The method of claim 8,
The nanofiber nonwoven fabric may be produced by using the polymer solution such as electro-spinning, melt spinning, electro-blowing, melt-blowing (composite spinning, Spun-bonded, air laid, or? A separator for a secondary battery produced by a wet laid process. The method according to claim 8 or 10,
Wherein the nanofiber nonwoven fabric has a thickness of 10 to 100 mu m and the nanofiber nonwoven fabric has a diameter of 100 to 3000 nm. The method according to claim 8 or 10,
The PVA system comprises fully hydrolyzed PVA (polyvinyl alcohol) having a degree of saponification of 98 to 99% or partially hydrolyzed PVA having a saponification degree of 85 to 89%.

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