KR101915328B1 - Nanocomposite membrane for separator of lithium secondary battery and preparation method thereof - Google Patents

Abstract

The present invention relates to a process for producing a thermally-converting poly (benzoxazole-imide) nanocomposite film by forming a nanoparticle coating layer of the same material as the nonwoven fabric obtained by the reprecipitation method on a hydroxy group-containing polyimide copolymer nonwoven film, And is applied to a separator of a lithium secondary battery.
The nanocomposite membrane for a lithium secondary battery separator comprising the heat-converted poly (benzoxazole-imide) copolymer nanoparticle coating layer produced according to the present invention is excellent in thermal, mechanical and chemical properties and has a high porosity, It has excellent wettability and can be suitably applied to various electrochemical devices due to improved stability at high temperature and high pressure.

Description

TECHNICAL FIELD The present invention relates to a nanocomposite membrane separator for lithium secondary battery separator,

The present invention relates to a nanocomposite membrane for a lithium secondary battery separator and a method of manufacturing the same, and more particularly, to a nanocomposite membrane having the same material as the nonwoven fabric obtained by the reprecipitation method on a polyimide copolymer non- (Benzoxazole-imide) nanocomposite membrane by heat-treating it and applying it to a separator of a lithium secondary battery.

Recently, as the interest in energy storage technology has increased, a large power module device including a small power module device included in portable devices such as a portable multimedia player, a notebook computer, a mobile phone, and a camcorder, a large power module requiring a medium and large power source such as a hybrid electric vehicle, Research on devices has been actively conducted. Among them, a lithium ion secondary battery manufactured by using a material capable of intercalating / deintercalating lithium ions as a cathode and an anode, providing a porous separator as a separator between two electrodes, and injecting an electrolyte, has advantages of high operating voltage and high energy density It is in the spotlight.

Particularly, the separator of the lithium secondary battery should have the property that the separator of the lithium secondary battery should prevent electric short circuit between the positive electrode and the negative electrode, allow the lithium ions to freely move due to the porous pores, and not pass the particles other than lithium ions. In addition, the wettability to the electrolyte and the compatibility with the electrolytic solution should be good. A polyolefin-based polymer such as polyethylene or polypropylene is mainly used as a material of a separator that is currently in commercial use. A polyolefin-based separator has micro-sized porous pores in a simple manufacturing process. On the other hand, Which may cause internal short circuit.

Therefore, in order to improve the thermal stability and mechanical properties of the separator, techniques for coating ceramic particles on a conventional porous polymer substrate such as a polyolefin-based polymer have been developed, but the porosity of the ceramic particles is low and an adhesive is used Documents 1 and 2).

On the other hand, attempts have been made to apply rigid glassy wholly aromatic organic polymers such as polybenzoxazole, polybenzimidazole, or polybenzthiazole, which have excellent thermal, mechanical and chemical properties, as a separator. These organic polymers are mostly organic solvents It is difficult to produce a film by a simple and practical solvent casting method. Therefore, a blend film of a polyimide and a poly (styrenesulfonic acid) having a hydroxyl group at orthosilox sites is thermally converted at 300 to 650 DEG C to form a polybenzoxazole A method of imidizing a hydroxy group-containing polyimide that can be a precursor for producing a polybenzoxazole film ultimately has not been specifically disclosed, and the prepared separation membrane is also limited to gas separation 3).

Further, the polybenzimidazole membrane is prepared by thermal conversion of a polyimide having a hydroxy group at an ortho position, so that the permeability of carbon dioxide is 10 to 100 times higher than that of a conventional polybenzoxazole membrane produced by the solvent casting method The results have been reported (Non-Patent Document 1).

However, the polybenzoxazole membranes or the heat-converted polybenzoxazole membranes described in the above prior art documents are all limited to gas separation and can be applied to the separator of a lithium secondary battery, It is not disclosed or implied in technical literatures.

Accordingly, the inventors of the present invention have found that a thermally-converting poly (benzoxazole-imide) copolymer film is excellent in thermal, mechanical, and chemical properties and can be manufactured as a porous separator, and thus can be applied to a separator of a lithium secondary battery. And has reached the completion of the invention.

Patent Document 1 Korean Patent Laid-Open No. 10-2013-0093977 Patent Document 2 US Patent No. 8,372,475 Patent Document 3 Japanese Patent Application Laid-Open No. 2013-505822

Non-Patent Document 1 Y.M. Lee et al., Science 318, 254-258 (2007)

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is an object of the present invention to provide a method of manufacturing a semiconductor device having excellent thermal, mechanical and chemical characteristics, high porosity, excellent wettability to an electrolyte, A nanocomposite film for a lithium secondary battery separator including a poly (benzoxazole-imide) copolymer nanoparticle coating layer, and a method of manufacturing the same.

In order to accomplish the above object, the present invention provides a nonwoven fabric comprising: (a) a hydroxy group-containing polyimide copolymer nonwoven film; And (b) a heat-converted poly (benzoxazole-imide) copolymer nanoparticle coating layer on the nonwoven fabric film.

The heat-converted poly (benzoxazole-imide) copolymer is characterized by having a repeating unit represented by the following formula (1).

≪ Formula 1 >

In the above formula (1)

Ar ₁ is an aromatic ring group selected from a substituted or unsubstituted quadrivalent arylene group having 6 to 24 carbon atoms and a substituted or unsubstituted quadrivalent heterocyclic group having 4 to 24 carbon atoms and the aromatic ring group is present alone; Two or more of them form a condensed ring with each other; Two or more single bond, O, S, CO, SO 2, Si (CH 3) 2, (CH 2) p (1≤p≤10), (CF 2) q (1≤q≤10), C (CH _{3) 2,} and is connected to a C (CF _{3) 2} or CO-NH,

Ar ₂ is an aromatic ring group selected from a substituted or unsubstituted divalent arylene group having 6 to 24 carbon atoms and a substituted or unsubstituted divalent heterocyclic group having 4 to 24 carbon atoms and the aromatic ring group is present alone; Two or more of them form a condensed ring with each other; Two or more single bond, O, S, CO, SO 2, Si (CH 3) 2, (CH 2) p (1≤p≤10), (CF 2) q (1≤q≤10), C _{(CH 3) 2, C (} CF 3) is connected to ₂ or CO-NH,

Q is a single bond; _{O, S, CO, SO 2} , Si (CH 3) 2, (CH 2) p (1≤p≤10), (CF 2) q (1≤q≤10), C (CH 3) 2, C _{(CF 3) 2, CO-} NH, C (CH 3) (CF 3), or a substituted or unsubstituted phenylene ring, x, y is 0.1≤x≤0.9, 0.1≤y≤ a molar fraction within each repeating unit 0.9, and x + y = 1.

In the above formula (1), Ar ₁ is any one selected from the following formula (1).

<Structure 1>

In the above formula 1,

X ₁ , X ₂ , X ₃ and X ₄ are the same or different from each other and each independently represents O, S, CO, SO ₂ , Si (CH ₃ ) ₂ , (CH ₂ ) _p (CF ₂ ) _q ( ₁ ? _Q ? 10), C (CH ₃ ) ₂ , C (CF ₃ ) ₂ or CO-NH, W ₁ and W ₂ are the same or different and independently O, S , Or CO and Z ₁ is O, S, CR ₁ R ₂ or NR ₃ wherein R ₁ , R ₂ and R ₃ are the same or different and each independently is hydrogen or an alkyl group having 1 to 5 carbon atoms and Z ₂ and Z ₃ are the same or different and are each independently N or CR ₄ (R ₄ is hydrogen or an alkyl group having 1 to 5 carbon atoms) or is not CR ₄ at the same time.

And Ar < ₁ > is any one selected from the following Structural Formulas (2).

&Lt; Formula 2 >

In the above formula (1), Ar ₂ is any one selected from the following formula (3).

<Formula 3>

In the above formula 3,

X ₁ , X ₂ , X ₃ and X ₄ are the same or different from each other and each independently represents O, S, CO, SO ₂ , Si (CH ₃ ) ₂ , (CH ₂ ) _p (CF ₂ ) _q ( ₁ ? _Q ? 10), C (CH ₃ ) ₂ , C (CF ₃ ) ₂ or CO-NH, W ₁ and W ₂ are the same or different and independently O, S , Or CO and Z ₁ is O, S, CR ₁ R ₂ or NR ₃ wherein R ₁ , R ₂ and R ₃ are the same or different and each independently is hydrogen or an alkyl group having 1 to 5 carbon atoms and Z ₂ and Z ₃ are the same or different and are each independently N or CR ₄ (R ₄ is hydrogen or an alkyl group having 1 to 5 carbon atoms) or is not CR ₄ at the same time.

And Ar < ₂ > is any one selected from the following Structural Formula (4).

<Formula 4>

The present invention also provides a lithium secondary battery comprising the nanocomposite film.

The present invention also provides a method for preparing a polyimide precursor solution, comprising the steps of: i) reacting an acid dianhydride, ortho-hydroxydiamine and an aromatic diamine to obtain a polyamic acid solution, and then synthesizing a hydroxyl group-containing polyimide copolymer by an azeotropic thermal imidization method;

ii) electrospinning a polymer solution obtained by dissolving the hydroxy group-containing polyimide copolymer of step i) in an organic solvent to obtain a hydroxy group-containing polyimide copolymer nonwoven film; And

and iii) coating the non-woven fabric film of the step ii) with hydroxy group-containing polyimide copolymer nano-particles previously obtained according to the reprecipitation method, followed by heat treatment, to provide a method for producing a nano composite membrane for a lithium secondary battery separator .

The acid dianhydride in the step i) is represented by the following formula (2).

(2)

In the above formula (2), Ar ₁ is as defined in the above formula (1).

The ortho-hydroxydiamine of the step i) is represented by the following formula (3).

(3)

In the above formula (3), Q is as defined in the above formula (1).

The aromatic diamine in the step i) is represented by the following formula (4).

&Lt; Formula 4 >

In the formula 4, Ar ₂ is the same as defined in the formula 1.

In the azeotropic thermal imidization of step i), toluene or xylene is added to the polyamic acid solution, and the mixture is stirred to perform imidization reaction at 180 to 200 ° C for 6 to 12 hours.

The reprecipitation method is characterized by using 2 to 5% by weight of polyvinylpyrrolidone (PVP) or polyvinyl alcohol (PVA) as a stabilizer.

The coating of step iii) is carried out by a spray method.

The heat treatment in step iii) is performed by raising the temperature to 350 to 450 DEG C at a rate of 1 to 20 DEG C / min in an inert gas atmosphere of high purity, and then maintaining an isothermal state for 0.1 to 3 hours.

The nanocomposite membrane for a lithium secondary battery separator comprising the heat-converted poly (benzoxazole-imide) copolymer nanoparticle coating layer produced according to the present invention is excellent in thermal, mechanical and chemical properties and has a high porosity, It is excellent in wettability and can be suitably applied to various electrochemical devices due to improved stability at high temperature and high voltage.

1 is an ATR-IR spectrum of a thermally-converting poly (benzoxazole-imide) nanocomposite membrane prepared according to Examples 1-9.
FIG. 2 is a scanning electron microscope (SEM) photograph of the surface (a) of the nanocomposite membrane coated with the film surface (a) before the coating layer according to Example 8 is formed and then heat-treated.
FIG. 3 is a graph showing the results of ODPA-HAB ₅ -ODA ₅ (A) and (b) scanning electron microscopy (SEM) photographs of the nanocomposite membranes coated with the nonwoven fabric after heat treatment.
FIG. 4 is a graph showing the results of ODPA-HAB ₅ -ODA ₅ (A) and (b) scanning electron microscopy (SEM) photographs of the nanocomposite membranes coated with the nonwoven fabric after heat treatment.
FIG. 5 is a thermogravimetric-mass spectrometry (TG-MS) graph showing the thermogravimetric reduction characteristics of the thermally-converting poly (benzoxazole-imide) nanocomposite membrane according to Example 1 during thermal conversion.
6 is a graph showing the cycle characteristics (30 DEG C) at 1C of a lithium secondary battery using the thermally-converting poly (benzoxazole-imide) nanocomposite membrane produced according to Example 8 and Example 17 and the commercialized separator (Celgard 2400) .
7 shows the cycle characteristics (55 ° C) at 1 C of the lithium secondary battery using the thermally-converting poly (benzoxazole-imide) nanocomposite membrane produced according to Example 8 and Example 17 and the commercialized separator (Celgard 2400) .
8 is a graph showing the relationship between the electrochemical impedance of the first charge-discharge cycle of a lithium secondary battery using the thermally-converting poly (benzoxazole-imide) nanocomposite film prepared according to Example 8 and Example 17 and the commercialized separator (Celgard 2400) Analysis (EIS) results.
9 is a graph showing the relationship between the electrochemical impedance after charging and discharging for 10 cycles of the lithium secondary battery using the thermally-converting poly (benzoxazole-imide) nanocomposite membrane produced according to Example 8 and Example 17 and the commercialized separator (Celgard 2400) Analysis (EIS) results.

The present invention relates to (a) a hydroxy group-containing polyimide copolymer nonwoven film; And (b) a heat-converted poly (benzoxazole-imide) copolymer nanoparticle coating layer on the nonwoven fabric film.

The nano composite membrane for a lithium secondary battery separator, which is the object of the present invention, uses a hydroxy group-containing polyimide copolymer nonwoven film as a support or substrate for introducing a polybenzoxazole group having excellent thermal, mechanical and chemical properties. Then, the same material as that of the nonwoven fabric layer is coated on the nonwoven fabric layer, and the resultant structure is heat-treated to change the structure of the polyoxyethylene group-containing polyimide to polybenzoxazole to form a heat conversion poly (benzoxazole-imide) copolymer nanoparticle coating layer Thus, a nanocomposite membrane in which the nonwoven fabric layer and the nanoparticle coating layer are completely connected to each other is obtained. In particular, since the same material as the nonwoven fabric film is used for the coating, the polymer particles can be coated and fixed without a binder, so that the cost can be reduced.

The heat-converted poly (benzoxazole-imide) copolymer according to the present invention has a repeating unit represented by the following formula (1).

&Lt; Formula 1 >

In the above formula (1)

Ar ₁ is an aromatic ring group selected from a substituted or unsubstituted quadrivalent arylene group having 6 to 24 carbon atoms and a substituted or unsubstituted quadrivalent heterocyclic group having 4 to 24 carbon atoms and the aromatic ring group is present alone; Two or more of them form a condensed ring with each other; Two or more single bond, O, S, CO, SO 2, Si (CH 3) 2, (CH 2) p (1≤p≤10), (CF 2) q (1≤q≤10), C (CH _{3) 2,} and is connected to a C (CF _{3) 2} or CO-NH,

Ar ₂ is an aromatic ring group selected from a substituted or unsubstituted divalent arylene group having 6 to 24 carbon atoms and a substituted or unsubstituted divalent heterocyclic group having 4 to 24 carbon atoms and the aromatic ring group is present alone; Two or more of them form a condensed ring with each other; Two or more single bond, O, S, CO, SO 2, Si (CH 3) 2, (CH 2) p (1≤p≤10), (CF 2) q (1≤q≤10), C _{(CH 3) 2, C (} CF 3) is connected to ₂ or CO-NH,

Q is a single bond; _{O, S, CO, SO 2} , Si (CH 3) 2, (CH 2) p (1≤p≤10), (CF 2) q (1≤q≤10), C (CH 3) 2, C _{(CF 3) 2, CO-} NH, C (CH 3) (CF 3), or a substituted or unsubstituted phenylene ring, x, y is 0.1≤x≤0.9, 0.1≤y≤ a molar fraction within each repeating unit 0.9, and x + y = 1.

In the above formula (1), Ar ₁ may be any one selected from the following formula (1).

<Structure 1>

In the above formula 1,

X ₁ , X ₂ , X ₃ and X ₄ are the same or different from each other and each independently represents O, S, CO, SO ₂ , Si (CH ₃ ) ₂ , (CH ₂ ) _p (CF ₂ ) _q ( ₁ ? _Q ? 10), C (CH ₃ ) ₂ , C (CF ₃ ) ₂ or CO-NH, W ₁ and W ₂ are the same or different and independently O, S , Or CO and Z ₁ is O, S, CR ₁ R ₂ or NR ₃ wherein R ₁ , R ₂ and R ₃ are the same or different and each independently is hydrogen or an alkyl group having 1 to 5 carbon atoms and Z ₂ and Z ₃ are the same or different and are each independently N or CR ₄ (R ₄ is hydrogen or an alkyl group having 1 to 5 carbon atoms) or is not CR ₄ at the same time.

Specific examples of the above-mentioned Ar ₁ include those represented by the following structural formula (2).

&Lt; Formula 2 >

In the above formula (1), Ar ₂ may be any one selected from the following formula (3).

<Formula 3>

In the above formula 3,

X ₁ , X ₂ , X ₃ and X ₄ are the same or different from each other and each independently represents O, S, CO, SO ₂ , Si (CH ₃ ) ₂ , (CH ₂ ) _p (CF ₂ ) _q ( ₁ ? _Q ? 10), C (CH ₃ ) ₂ , C (CF ₃ ) ₂ or CO-NH, W ₁ and W ₂ are the same or different and independently O, S , Or CO and Z ₁ is O, S, CR ₁ R ₂ or NR ₃ wherein R ₁ , R ₂ and R ₃ are the same or different and each independently is hydrogen or an alkyl group having 1 to 5 carbon atoms and Z ₂ and Z ₃ are the same or different and are each independently N or CR ₄ (R ₄ is hydrogen or an alkyl group having 1 to 5 carbon atoms) or is not CR ₄ at the same time.

Specific examples of the above-mentioned Ar ₂ include those represented by the following structural formula (4).

<Formula 4>

Since the nanocomposite membrane according to the present invention has improved thermal stability and stability at high temperature and high voltage due to the introduction of the thermally-converting poly (benzoxazole-imide) copolymer structure, the electrochemical characteristics are improved, .

The structure of the poly (benzoxazole-imide) copolymer represented by the formula (1) is based on the synthesis of a polyimide prepared by imidizing a polyamic acid obtained by reacting an acid dianhydride with a diamine. In addition, the thermally-modified polybenzoxazole can be prepared by a method in which a functional group such as a hydroxyl group in the ortho-position of the aromatic imido linkage attacks an imine ring carbonyl group to form an intermediate of the carboxy- benzoxazole structure, In the present invention, a nanocomposite membrane for a lithium secondary battery separator is prepared including the following steps.

That is, in the present invention, i) a step of synthesizing a hydroxy group-containing polyimide copolymer by an azeotropic thermal imidization method after reacting an acid anhydride, ortho-hydroxydiamine and an aromatic diamine to obtain a polyamic acid solution;

ii) electrospinning a polymer solution obtained by dissolving the hydroxy group-containing polyimide copolymer of step i) in an organic solvent to obtain a hydroxy group-containing polyimide copolymer nonwoven film; And

and iii) coating the non-woven fabric film of the step ii) with hydroxy group-containing polyimide copolymer nano-particles previously obtained according to the reprecipitation method, followed by heat treatment, to provide a method for producing a nano composite membrane for a lithium secondary battery separator .

In order to synthesize a polyimide, a polyamic acid must first be obtained by reacting an acid dianhydride with a diamine. In the present invention, a compound represented by the following formula (2) is used as an acid anhydride.

(2)

In the above formula (2), Ar ₁ is as defined in the above formula (1).

As the monomers for synthesizing the polyimide, any of the acid dianhydrides may be used as long as they are as defined in the above formula (2). However, considering that the thermal and chemical properties of the polyimide to be synthesized can be further improved, fluorine Hexafluoroisopropylidenephthalic acid dianhydride (6FDA), or 4,4'-oxydiphthalic acid dianhydride (ODPA) having a group represented by the following formula

In addition, since the present invention ultimately has a poly (benzoxazole-imide) copolymer structure, attention has been paid to the fact that polybenzoxazole units can be introduced by thermal conversion of ortho-hydroxypolyimide, As the ortho-hydroxy diamine, a compound represented by the following formula (3) is used to synthesize the hydroxy polyimide.

(3)

In the above formula (3), Q is as defined in the above formula (1).

As the ortho-hydroxydiamine, there can be used any of those as defined in the above formula (3). However, considering that the thermal and chemical properties of the polyimide to be synthesized can be further improved, (3-amino-4-hydroxyphenyl) hexafluoropropane (APAF) or 3,3'-diamino-4,4'-dihydroxybiphenyl (HAB) desirable.

In the present invention, an aromatic diamine represented by the following formula (4) is used as a comonomer to react with an acid anhydride of the formula (2) and an ortho-hydroxy diamine of the formula (3) The coalescence can be synthesized.

&Lt; Formula 4 >

In the formula 4, Ar ₂ is the same as defined in the formula 1.

The aromatic diamine may be any of those as defined in the above formula (4), but it is preferable to use 4,4'-oxydianiline (ODA) or 2,4,6-trimethylphenylenediamine (DAM) Can be used.

That is, in step i), an acid dianhydride of formula 2, an ortho-hydroxydearmin of formula 3 and an aromatic diamine of formula 4 are dissolved in an organic solvent such as N-methylpyrrolidone (NMP) After dissolving and stirring to obtain a polyamic acid solution, a hydroxy group-containing polyimide-polyimide copolymer represented by the following general formula (1) is synthesized by azeotropic thermal imidization.

&Lt; General Formula 1 &

Ar ₁ , Ar ₂ , Q, x and y in the general formula (1) are the same as defined in the general formula (1).

At this time, in the azeotropic thermal imidization method, toluene or xylene is added to the polyamic acid solution and the mixture is stirred to perform imidization reaction at 180 to 200 ° C for 6 to 12 hours. During this period, Is separated as an azeotropic mixture of toluene or xylene.

Next, a polymer solution obtained by dissolving the hydroxy group-containing polyimide copolymer of the above step i) represented by the general formula (1) in an organic solvent such as N-methylpyrrolidone (NMP) is electrospun to form a hydroxy group-containing polyimide To obtain a copolymer nonwoven film.

Next, the hydroxy group-containing polyimide copolymer nanoparticles previously obtained according to the reprecipitation method are coated on the nonwoven fabric layer in the step ii) and then heat-treated to obtain a heat-converted polyimide copolymer Oxazole-imide) copolymer nanoparticle coating layer is formed. At this time, the hydroxy group-containing polyimide copolymer nanoparticles are prepared by controlling the particle size to nanosize through a known repulping process in which a hydroxy group-containing polyimide copolymer is dissolved in an organic solvent such as NMP, can do. Particularly, in order to control the porosity, polyvinylpyrrolidone (PVP) or polyvinyl alcohol (PVA) of 2 to 5% by weight is more preferably used as a stabilizer in the polymer solution, and polyvinylpyrrolidone (PVP) Can be used.

In addition, in order to form the coating layer on the hydroxy group-containing polyimide copolymer nonwoven fabric film, various known coating methods can be used, but the spray method is more preferable in view of the uniformity and convenience of the coating.

Finally, a nanocomposite film having a heat-converted poly (benzoxazole-imide) copolymer nanoparticle coating layer formed on a support or a hydroxy group-containing polyimide copolymer nonwoven film containing a substrate as a substrate is prepared. A uniform nanoparticle coating layer is completed by thermal conversion, and at the same time, the hydroxy group-containing polyimide copolymer nonwoven film and the coating layer are completely connected to each other.

The heat treatment is performed by raising the temperature to 350 to 450 DEG C at a heating rate of 1 to 20 DEG C / min in an inert gas atmosphere of high purity, and then maintaining an isothermal state for 0.1 to 3 hours.

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

[ Synthetic example  1] Synthesis of hydroxy group-containing polyimide copolymer

2.0 mmol of 2,2-bis (3-amino-4-hydroxyphenyl) hexafluoropropane (APAF) and 8.0 mmol of 4,4'-oxydianiline (ODA) were dissolved in 10 ml of anhydrous NMP, After cooling, 10 mmol of 4,4'-hexafluoroisopropylidene phthalic anhydride (6FDA) dissolved in 10 ml of anhydrous NMP was added thereto. The reaction mixture was stirred at 0 占 폚 for 15 minutes, then allowed to warm to room temperature and allowed to stand overnight to obtain a polyamic acid viscous solution. Next, 20 ml of ortho-xylene was added to the polyamic acid solution, and the mixture was vigorously stirred and heated to perform imidization at 180 ° C for 6 hours. In this process, the water released by the formation of the imide ring was isolated as the xylene azeotropic mixture. The thus-obtained brown solution was cooled to room temperature, immersed in distilled water, washed several times with hot water, and dried in a convection oven at 120 ° C for 12 hours to synthesize a hydroxy group-containing polyimide copolymer represented by the following formula , And named it 6FDA-APAF ₂ -ODA ₈ .

&Lt; Formula 5 >

In the above formula (5), x and y are mole fractions in the repeating unit, and x = 0.2 and y = 0.8.

It was confirmed by ¹ H-NMR and FT-IR data that the hydroxy group-containing polyimide copolymer represented by the formula (5) was synthesized from the above Synthesis Example 1 as follows.

^{1 H-NMR (300 MHz,} DMSO- d 6, ppm): 10.41 (s, -OH), 8.10 (d, H ar, J = 8.0Hz), 7.92 (d, H ar, J = 8.0Hz), _{7.85 (s, H ar),} 7.80 (s, H ar), 7.71 (s, H ar), 7.47 (s, H ar), 7.20 (d, H ar, J = 8.3Hz), 7.04 (d, H _ar , J = 8.3 Hz). FT-IR (film): ν (OH) at 3400 cm ^-1 , ν (C═O) at 1786 and 1705 cm ^-1 , Ar (CC) at 1619, 1519 cm ^-1 , imide ν (CN) at 1377 cm ^-1 , (CF) at 1299-1135 cm ^-1 , imide (CNC) at 1102 and 720 cm ^-1 .

[ Synthetic example  2-9] Synthesis of hydroxy group-containing polyimide copolymer

A hydroxy group-containing polyimide copolymer was synthesized in the same manner as in Synthesis Example 1 except that various acid dianhydrides, ortho-hydroxydiamine and aromatic diamines shown in the following [Table 1] were used as reactants, 1.

Synthetic example Sample name Mole fraction Synthesis Example 2 6FDA-APAF ₅ -ODA ₅ x = 0.5, y = 0.5 Synthesis Example 3 6FDA-APAF ₈ -ODA ₂ x = 0.8, y = 0.2 Synthesis Example 4 6FDA-APAF ₅ -DAM ₅ x = 0.5, y = 0.5 Synthesis Example 5 6FDA-HAB ₅ -ODA ₅ x = 0.5, y = 0.5 Synthesis Example 6 6FDA-HAB ₈ -ODA ₂ x = 0.8, y = 0.2 Synthesis Example 7 6FDA-HAB ₅ -DAM ₅ x = 0.5, y = 0.5 Synthesis Example 8 ODPA-HAB ₅ -ODA ₅ x = 0.5, y = 0.5 Synthesis Example 9 ODPA-HAB ₈ -ODA ₂ x = 0.8, y = 0.2

HAB (3,3'-diamino-4,4'-dihydroxybiphenyl)

DAM (2,4,6-trimethylphenylenediamine)

[ Example  One] Thermal Conversion Poly ( Benzoxazole - Imide ) Nano Composite membrane  Produce

6FDA-APAF ₂ -ODA ₈ obtained from Synthesis Example 1 was dissolved in dimethylacetamide (DMAc) to prepare a 10 wt% solution. 6 ml of the polymer solution was filled in a 10 ml syringe equipped with a 23 G needle and then mounted on a syringe pump of an electrospinning device (ES-robot, NanoNC, Korea) and electrospun according to normal electrospinning conditions to obtain a nonwoven film . The nanoparticles of 6FDA-APAF ₂ -ODA ₈ copolymer according to Synthesis Example 1 having an average particle diameter of 700 nm previously obtained by a known reprecipitation method using 2% by weight of polyvinylpyrrolidone (PVP) as a stabilizer were added to ethanol A solution dispersed at a concentration of 1 wt% was spray coated onto the nonwoven fabric film. Then, the spray-coated nonwoven fabric film was placed between the alumina plate and the carbon cloth, and the temperature was raised to 400 DEG C at a rate of 3 DEG C / min in a high purity argon gas atmosphere. Thereafter, the isotropic state was maintained at 400 DEG C for 2 hours, (Benzoxazole-imide) nanocomposite membrane represented by Formula 6 was prepared (x and y are as defined in Formula 5).

(6)

[ Example  2 to 9] Thermal Conversion Poly ( Benzoxazole - Imide ) Nano Composite membrane  Produce

Heat-converted poly (benzoxazole-imide) nanocomposite membranes were prepared in the same manner as in Example 1, using the samples obtained in Synthesis Examples 2 to 9.

[ Example  10 to 18] Thermal Conversion Poly ( Benzoxazole - Imide ) Nano Composite membrane  Produce

Except that the nanoparticles of the copolymers according to Synthesis Examples 1 to 9 having an average particle size of 900 nm were obtained in advance by a known reprecipitation method using 5% by weight of polyvinylpyrrolidone (PVP) as a stabilizer, (Benzoxazole-imide) nanocomposite membrane was prepared in the same manner as in Example 9.

[ Experimental Example ] The lithium secondary battery Charging and discharging  Characterization

Electrodes were fabricated according to a conventional method using LiCoO ₂ (Wellcos, Japan) as the positive electrode material and graphite (Wellcos, Japan) as the negative electrode material. Using the nanocomposite membrane according to Examples 1 to 19 as the separator, , And an electrolyte solution in which 1 M of lithium hexafluorophosphate (LiPF ₆ ) was dissolved in a mixed solvent of ethylene carbonate: diethyl carbonate (1: 1, volume ratio) was injected to prepare a lithium secondary battery. The charge / discharge characteristics of the lithium secondary battery thus fabricated were measured. As a comparative example, the charge / discharge characteristics of a lithium secondary battery using a commercially available separator (Celgard 2400, microporous polypropylene single membrane) as a separator were measured.

FIG. 1 shows the ATR-IR spectra of the heat-converted poly (benzoxazole-imide) nanocomposite films prepared according to Examples 1 to 9. OH stretching peak appearing at around 3400 cm ^-1 disappears and a peak due to a typical benzoxazole ring is observed at around 1054 cm ^-1 . As a result, a benzoxazole ring was formed in the heat treatment process. In addition, since the inherent absorption band of the imide is also found around 1784 cm ^-1 and 1717 cm ^-1 , the thermal stability of the aromatic imide linkage can be confirmed even at the heat conversion temperature reaching 400 ° C., Benzoxazole-imide) composite membrane was stably produced.

2 shows a scanning electron microscope (SEM) photograph of the surface (a) of the composite membrane according to Example 8 and the surface (b) of the composite membrane obtained by forming the coating layer and heat- 2 (b), a uniform nanoparticle coating layer is completed by the final thermal conversion, and at the same time, the hydroxy group-containing polyimide copolymer nonwoven fabric layer by electrospinning and the coating layer are completely connected to each other, - imide) nanocomposite membrane was fabricated.

3 shows TEM images of the ODPA-HAB ₅ -ODA ₅ copolymer nanoparticles according to Example 8 (FIG. 3 (a)) and the nanocomposite films coated with the heat-treated nanoparticles An electron microscope (SEM) photograph (Fig. 3 (b)) is shown. 4 is a transmission electron microscope (TEM) photograph of the ODPA-HAB ₅ -ODA ₅ copolymer nanoparticles according to Example 17 (FIG. 4 (a)), 4 (a) and 4 (b) show a low porosity and a high porosity from Figs. 4 (a) and 4 (b) It is known that the porosity can be controlled by controlling the concentration of polyvinylpyrrolidone (PVP) used as a stabilizer in the range of 2 to 5 wt% in the preparation of nanoparticles by the reprecipitation method, A nanocomposite membrane having high porosity can be more preferably used as a separator of a lithium ion battery.

In addition, the weight reduction by decarboxylation in the course of thermal conversion of the thermally-converting poly (benzoxazole-imide) nanocomposite membrane according to Example 1 was tested with a thermogravimetric analyzer (TGA) The results are shown

Figure can be seen a marked weight loss peak in the typical decomposition temperature of 500 to 600 ℃ previous 300 to 470 ℃ in the polymer chain in the 5, and during this first weight loss step is that the CO ₂ emission evidenced by the mass spectrometer, Which means that a thermal conversion process is involved.

In order to comparatively evaluate the charge-discharge characteristics of the lithium secondary battery using the heat-converted poly (benzoxazole-imide) nanocomposite membrane according to the present invention as a separator, the heat conversion poly (Benzoxazole-imide) nanocomposite membrane and a commercially available separator (Celgard 2400) are shown in Fig. 6 and Fig. 7, respectively, at 30 캜 and 55 캜 in 1 C of the lithium secondary battery.

As shown in FIGS. 6 and 7, a lithium secondary battery using a thermally-converting poly (benzoxazole-imide) nanocomposite membrane according to the present invention as a separator rather than a commercialized separator (Celgard 2400) And exhibits excellent electrochemical characteristics. In particular, at 55 ° C, which is a relatively high temperature, there are more differences, indicating that the heat-converted poly (benzoxazole-imide) nanocomposite film has superior electrochemical properties due to its excellent thermal stability.

8 and 9 show the first charge / discharge cycles of a lithium secondary battery using the thermally-converting poly (benzoxazole-imide) nanocomposite film produced by Example 8 and Example 17 and the commercialized separator (Celgard 2400) The electrochemical impedance analysis (EIS) results of the cycle (FIG. 8) and the electrochemical impedance analysis (EIS) results after 10 cycles of charging and discharging (FIG. 9) are shown. As shown in FIGS. 8 and 9, a lithium secondary battery using a thermally-converted poly (benzoxazole-imide) nanocomposite membrane according to the present invention as a separator rather than a commercially available separator (Celgard 2400) has a lower impedance resistance value , Which is a result of the excellent wettability and high porosity of the heat conversion poly (benzoxazole-imide) nanocomposite membrane according to the present invention.

Accordingly, the thermally-converted poly (benzoxazole-imide) nanocomposite membrane according to the present invention is excellent in thermal, mechanical and chemical properties, has high porosity, has excellent wettability with respect to electrolytes, and has improved stability at high temperatures and high pressures , It can be used as a separator to provide a lithium secondary battery excellent in electrochemical characteristics and can be suitably applied to various electrochemical devices.

Claims (15)

(a) a hydroxy group-containing polyimide copolymer nonwoven fabric film having a repeating unit represented by the following general formula (1); And
(b) a heat-converted poly (benzoxazole-imide) copolymer nanoparticle coating layer having a repeating unit represented by the following formula (1) formed on the nonwoven fabric film.
&Lt; General Formula 1 &

&Lt; Formula 1 >

In the above-mentioned general formulas 1 and 2,
Ar ₁ is an aromatic ring group selected from a substituted or unsubstituted quadrivalent arylene group having 6 to 24 carbon atoms and a substituted or unsubstituted quadrivalent heterocyclic group having 4 to 24 carbon atoms and the aromatic ring group is present alone; Two or more of them form a condensed ring with each other; Two or more single bond, O, S, CO, SO 2, Si (CH 3) 2, (CH 2) p (1≤p≤10), (CF 2) q (1≤q≤10), C (CH _{3) 2,} and is connected to a C (CF _{3) 2} or CO-NH,
Ar ₂ is an aromatic ring group selected from a substituted or unsubstituted divalent arylene group having 6 to 24 carbon atoms and a substituted or unsubstituted divalent heterocyclic group having 4 to 24 carbon atoms and the aromatic ring group is present alone; Two or more of them form a condensed ring with each other; Two or more single bond, O, S, CO, SO 2, Si (CH 3) 2, (CH 2) p (1≤p≤10), (CF 2) q (1≤q≤10), C _{(CH 3) 2, C (} CF 3) is connected to ₂ or CO-NH,
Q is a single bond; _{O, S, CO, SO 2} , Si (CH 3) 2, (CH 2) p (1≤p≤10), (CF 2) q (1≤q≤10), C (CH 3) 2, C _{(CF 3) 2, CO-} NH, C (CH 3) (CF 3), or a substituted or unsubstituted phenylene ring, x, y is 0.1≤x≤0.9, 0.1≤y≤ a molar fraction within each repeating unit 0.9, and x + y = 1. delete The method according to claim 1,
Wherein Ar _< 1 > is any one selected from the following structural formula (1): < EMI ID =
<Structure 1>

In the above formula 1,
X ₁ , X ₂ , X ₃ and X ₄ are the same or different from each other and each independently represents O, S, CO, SO ₂ , Si (CH ₃ ) ₂ , (CH ₂ ) _p (CF ₂ ) _q ( ₁ ? _Q ? 10), C (CH ₃ ) ₂ , C (CF ₃ ) ₂ or CO-NH, W ₁ and W ₂ are the same or different and independently O, S , Or CO and Z ₁ is O, S, CR ₁ R ₂ or NR ₃ wherein R ₁ , R ₂ and R ₃ are the same or different and each independently is hydrogen or an alkyl group having 1 to 5 carbon atoms and Z ₂ and Z ₃ are the same or different and are each independently N or CR ₄ (R ₄ is hydrogen or an alkyl group having 1 to 5 carbon atoms) or is not CR ₄ at the same time. The method of claim 3,
Wherein Ar < ₁ > is any one selected from the following Structural Formulas 2:
&Lt; Formula 2 >

The method according to claim 1,
Wherein Ar < _{2 >} is any one selected from the following Structural Formula 3:
<Formula 3>

In the above formula 3,
X ₁ , X ₂ , X ₃ and X ₄ are the same or different from each other and each independently represents O, S, CO, SO ₂ , Si (CH ₃ ) ₂ , (CH ₂ ) _p (CF ₂ ) _q ( ₁ ? _Q ? 10), C (CH ₃ ) ₂ , C (CF ₃ ) ₂ or CO-NH, W ₁ and W ₂ are the same or different and independently O, S , Or CO and Z ₁ is O, S, CR ₁ R ₂ or NR ₃ wherein R ₁ , R ₂ and R ₃ are the same or different and each independently is hydrogen or an alkyl group having 1 to 5 carbon atoms and Z ₂ and Z ₃ are the same or different and are each independently N or CR ₄ (R ₄ is hydrogen or an alkyl group having 1 to 5 carbon atoms) or is not CR ₄ at the same time. 6. The method of claim 5,
Wherein Ar < ₂ > is any one selected from the following structural formula (4): < EMI ID =
<Formula 4>

A lithium secondary battery comprising the nanocomposite membrane according to any one of claims 1 to 6. i) reacting an acid dianhydride represented by the following general formula (2), ortho-hydroxydiamine represented by the following general formula (3) and an aromatic diamine represented by the general formula (4) to obtain a polyamic acid solution, Synthesizing a hydroxy group-containing polyimide copolymer represented by Formula 1;
ii) electrospinning a polymer solution obtained by dissolving the hydroxy group-containing polyimide copolymer represented by the following general formula 1 in an organic solvent to obtain a hydroxy group-containing polyimide copolymer nonwoven film; And
iii) coating the nonwoven fabric film obtained in the step ii) with the hydroxyl group-containing polyimide copolymer nanoparticles represented by the following general formula 1 previously obtained in the above step i) according to the reprecipitation method and then heat- And a step of forming a heat-converted poly (benzoxazole-imide) copolymer nanoparticle coating layer having a repeating unit having a repeating unit represented by the following formula (1).
&Lt; Formula 1 >

In the above formula (1)
Ar ₁ is an aromatic ring group selected from a substituted or unsubstituted quadrivalent arylene group having 6 to 24 carbon atoms and a substituted or unsubstituted quadrivalent heterocyclic group having 4 to 24 carbon atoms and the aromatic ring group is present alone; Two or more of them form a condensed ring with each other; Two or more single bond, O, S, CO, SO 2, Si (CH 3) 2, (CH 2) p (1≤p≤10), (CF 2) q (1≤q≤10), C (CH _{3) 2,} and is connected to a C (CF _{3) 2} or CO-NH,
Ar ₂ is an aromatic ring group selected from a substituted or unsubstituted divalent arylene group having 6 to 24 carbon atoms and a substituted or unsubstituted divalent heterocyclic group having 4 to 24 carbon atoms and the aromatic ring group is present alone; Two or more of them form a condensed ring with each other; Two or more single bond, O, S, CO, SO 2, Si (CH 3) 2, (CH 2) p (1≤p≤10), (CF 2) q (1≤q≤10), C _{(CH 3) 2, C (} CF 3) is connected to ₂ or CO-NH,
Q is a single bond; _{O, S, CO, SO 2} , Si (CH 3) 2, (CH 2) p (1≤p≤10), (CF 2) q (1≤q≤10), C (CH 3) 2, C _{(CF 3) 2, CO-} NH, C (CH 3) (CF 3), or a substituted or unsubstituted phenylene ring, x, y is 0.1≤x≤0.9, 0.1≤y≤ a molar fraction within each repeating unit 0.9, and x + y = 1.
(2)

In the above formula (2), Ar ₁ is as defined in the above formula (1).
(3)

In the above formula (3), Q is as defined in the above formula (1).
&Lt; Formula 4 >

In the formula 4, Ar ₂ is the same as defined in the formula 1.
&Lt; General Formula 1 &

In the general formula (1), Ar ₁ , Ar ₂ , Q, x and y are the same as defined in the general formula (1). delete delete delete 9. The method of claim 8,
The azeotropic thermal imidization method of step i) is characterized in that toluene or xylene is added to the polyamic acid solution, and the imidation reaction is carried out at 180 to 200 ° C for 6 to 12 hours with stirring. A method for producing a composite membrane. 9. The method of claim 8,
Wherein the reprecipitation method comprises using 2 to 5% by weight of polyvinylpyrrolidone (PVP) or polyvinyl alcohol (PVA) as a stabilizer. 9. The method of claim 8,
Wherein the coating of step iii) is carried out by spraying. &Lt; RTI ID = 0.0 &gt; 15. &lt; / RTI &gt; 9. The method of claim 8,
Wherein the heat treatment in step iii) is performed by raising the temperature to 350 to 450 DEG C at a rate of 1 to 20 DEG C / min in an inert gas atmosphere of high purity, and then maintaining an isothermal state for 0.1 to 3 hours. (Method for producing a nanocomposite membrane for separator).

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