KR20160007366A - Binder for rechargeable lithium battery, separator for rechargeable lithium battery and rechargeable lithium battery - Google Patents

Abstract

Provided are: a binder for a lithium secondary battery, comprising a main chain containing polyvinylidene fluoride, and polyhedral oligomeric silsesquioxane derivatives bonded to the main chain; a separator for a lithium secondary battery; and a lithium secondary battery. Provided are: a binder for a lithium secondary battery having excellent heat resistance and strong adhesion force; and the lithium secondary battery with excellent cycle properties.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a binder for a lithium secondary battery, a separator for a lithium secondary battery, and a lithium secondary battery. BACKGROUND OF THE INVENTION 1. Field of the Invention [0001]

A binder for a lithium secondary battery, a separator for a lithium secondary battery, and a lithium secondary battery.

Lithium ion secondary batteries have advantages such as high voltage, long lifetime and high energy density. As a result, active research on lithium secondary batteries has been conducted, and lithium secondary batteries have been put to practical use as power sources for various electronic apparatuses.

The characteristics of the lithium secondary battery largely depend on the characteristics of the components of the lithium secondary battery, for example, the electrodes and the like. Particularly, the separator of the lithium secondary battery affects the cycle characteristics of the lithium secondary battery.

Specifically, a slurry containing inorganic particles and a binder may be applied to a porous substrate to prepare a separator. Such a separator is also called a coating separator because a coating layer composed of inorganic particles and a binder is formed on a porous substrate. The binder serves to bind inorganic particles to a polyethylene film as a porous substrate. When a lithium secondary battery is manufactured using such a separator, the cycle characteristics of the lithium secondary battery may depend on characteristics of the porous polyethylene film, inorganic particles, and binder.

For example, as a method for improving the cycle characteristics of a lithium secondary battery, there has been proposed a method of using high heat-resisting ceramic particles as a kind of inorganic particles. In order for such high-heat-resistant ceramic particles to fully exhibit their properties, the binder must ensure that the high-heat-resistant ceramic particles are stably held in the separator during charging and discharging of the lithium secondary battery. Further, it is necessary that the binder firmly bonds the separator and each electrode. Therefore, strong adhesion to the binder is required, and high heat resistance is also required.

There are not many examples of the binder used in such a coating separator. In many cases, a binder for an electrode is often applied as a binder for a coating separator. Specifically, polyvinylidene fluoride (PVDF) binder, which is a typical binder for an electrode, is widely used as a binder for a coating separator.

However, since the PVDF binder does not have sufficient adhesive strength, the PVDF binder can not stably maintain the inorganic particles in the separator. In other words, the structure stability of the separator layer was not sufficient. As a method for solving this problem, a method of using a large amount of PVDF binder in a separator can be considered, but this method may cause a problem of thickening of the separator. Furthermore, even when a large amount of PVDF binder was introduced into the separator, the PVDF binder still had insufficient adhesion.

On the other hand, Japanese Laid-Open Patent Publication Nos. 2012-221824 and 2011-6585 disclose a technique of including an organosilicon compound in a separator. However, the adhesion of these compounds was still not sufficient. As a result, a binder having high heat resistance and strong adhesive strength is required.

One embodiment is to provide a binder for a lithium secondary battery having excellent heat resistance and strong adhesion.

Another embodiment is to provide a separator for a lithium secondary battery comprising the binder for the lithium secondary battery.

Another embodiment is to provide a lithium secondary battery including the separator for a lithium secondary battery.

One embodiment includes a main chain comprising polyvinylidene fluoride; And a polyhedral oligomeric silsesquioxane derivative bonded to the main chain. The present invention also provides a binder for a lithium secondary battery.

The polyhedral oligomeric silsesquioxane derivative may be bound to the main chain by graft polymerization.

The binder for the lithium secondary battery may be a compound containing a structural unit represented by the following general formula (1).

[Chemical Formula 1]

(In the formula 1,

n, m, l and q are arbitrary natural numbers,

A is a hydrogen atom or a methyl group,

X is a chlorine atom or a fluorine atom,

Each R is independently a functional group selected from a C1 to C8 alkyl group, a cyclohexyl group, a phenyl group, and a C1 to C8 perfluoroalkyl group.

Another embodiment provides a separator for a lithium secondary battery comprising the binder.

The separator may further include inorganic particles.

Another embodiment provides a lithium secondary battery comprising the separator.

The details of other embodiments are included in the detailed description below.

Since a binder for a lithium secondary battery having excellent heat resistance and strong adhesive force is provided, a lithium secondary battery having excellent cycle characteristics can be realized.

1 is a side sectional view showing a schematic configuration of a lithium secondary battery according to one embodiment.
Figure 2 shows the IR spectra according to Synthesis Examples 1 to 6 and PVDF-CTFE.
3 shows a 19 F NMR spectrum according to Synthesis Examples 1 to 6 and PVDF-CTFE.

Hereinafter, embodiments of the present invention will be described in detail. However, it should be understood that the present invention is not limited thereto, and the present invention is only defined by the scope of the following claims.

It is to be understood that where a layer, film, region, plate, or the like is referred to as being "on" another portion, unless stated otherwise in this specification, .

Hereinafter, a lithium secondary battery according to one embodiment will be described with reference to FIG.

1 is a side sectional view showing a schematic configuration of a lithium secondary battery according to one embodiment.

1, the lithium secondary battery 10 may include a positive electrode 20, a negative electrode 30, a separator 40, and a non-aqueous electrolyte.

Li / Li ⁺ ) and 5.0 V or less, specifically 4.5 V or more and 5.0 V or less, for example, in the lithium secondary battery 10.

The shape of the lithium secondary battery 10 is not particularly limited, and may be cylindrical, angular, laminate, button, or the like.

The anode 20 may include a current collector 21 and a cathode active material layer 22 formed on the current collector.

The current collector 21 may be formed of any conductive material, for example, aluminum, stainless steel, nickel coated steel, or the like.

The cathode active material layer 22 includes a cathode active material, and may further include a conductive material and a binder.

The cathode active material is, for example, a solid solution oxide containing lithium, but is not particularly limited as long as it is a material capable of occluding and releasing lithium ions electrochemically.

The solid solution oxides include Li _a Mn _x Co _y Ni _z O ₂ (1.150? A? 1.430, 0.45? _X? 0.6, 0.10? Y? 0.15, 0.20? Z? 0.28), LiMn _x Co _y Ni _z O ₂ (0.3? X? 0.85, 0.10? Y? 0.3, 0.10? Z? 0.3), LiMn _1.5 Ni _0.5 O ₄ and the like.

The conductive material may be, for example, carbon black such as Ketjen black or acetylene black, natural graphite, artificial graphite or the like, but is not particularly limited as long as it enhances the conductivity of the anode.

The binder may be, for example, polyvinylidene fluoride, ethylene-propylene-diene terpolymer, styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, a polyvinyl acetate, a polymethyl methacrylate, a polyethylene, a nitrocellulose and the like can be cited. However, when the positive electrode active material and the conductive material are placed on the current collector 21 And is not particularly limited as long as it is capable of binding.

The cathode active material layer 22 can be produced, for example, in the following manner. First, a positive electrode active material, a conductive material and a binder are dry-mixed to prepare a positive electrode composite material. Then, the positive electrode active material layer may be prepared by dispersing the positive electrode mixture material in an appropriate organic solvent to prepare a positive electrode slurry, coating the positive electrode material slurry on the current collector 21, and drying and rolling.

The cathode 30 may include a current collector 31 and a negative electrode active material layer 32 formed on the current collector 31.

The current collector 31 may be any conductive material, for example, copper (Cu), nickel (Ni), or the like.

The negative electrode active material layer 32 may be any material as long as it is used as a negative electrode active material layer of a lithium secondary battery. For example, the negative electrode active material layer 32 includes a negative electrode active material, and may further include a binder.

The negative electrode active material may be a carbon-based material, a silicon-based material, a tin-based material, a lithium metal oxide, a metal lithium, or the like, or a mixture of two or more thereof. The carbon-based material may be, for example, graphite based materials such as artificial graphite, natural graphite, a mixture of artificial graphite and natural graphite, and natural graphite coated with artificial graphite. The silicon-based material may be, for example, silicon, a silicon oxide, a silicon-containing alloy, or a mixture of these with a graphite-based material. The silicon oxide may be represented by SiO _x (0 < x? 2). The silicon-containing alloy is an alloy in which the content of silicon is the greatest among all the metal elements with respect to the total amount of the alloy, and examples thereof include Si-Al-Fe alloys. The tin-based material may be, for example, tin, tin oxide, a tin-containing alloy, a mixture thereof with a graphite-based material, or the like. The lithium metal oxide includes, for example, a titanium oxide-based compound such as Li ₄ Ti ₅ O ₁₂ . According to one embodiment, when the graphite is used, the cycle life characteristics of the lithium secondary battery can be further improved.

The binder may be of the same kind as the binder constituting the positive electrode active material layer 22.

The weight ratio of the active material to the binder is not particularly limited and may be applied in a weight ratio used in conventional lithium secondary batteries.

The negative electrode active material layer 32 can be produced, for example, by the following method. First, a negative electrode active material and a binder are dry mixed to produce a negative electrode composite. The negative electrode material mixture slurry is dispersed in a suitable solvent to prepare a negative electrode material slurry and then the negative electrode material slurry is coated on the current collector 31 and dried and rolled to produce the negative electrode active material layer 32.

The separator 40 may include a substrate 40a and a coating layer 40b formed on at least one side of the substrate.

The base material 40a is not particularly limited, and any material can be used as long as it is used as a separator of a lithium secondary battery. For example, a porous film or nonwoven fabric exhibiting excellent high rate discharge performance can be used singly or in combination.

Examples of the resin constituting the base material 40a include polyolefin resin, polyester resin, polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride Vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride- Vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride- Copolymer, a vinylidene fluoride-ethylene-tetrafluoroethylene copolymer, and the like. There. Examples of the polyolefin-based resin include polyethylene and polypropylene. Examples of the polyester-based resin include polyethylene terephthalate and polybutylene terephthalate.

The coating layer 40b may include inorganic particles and a binder.

The inorganic particles include, for example, inorganic particles having high heat resistance. Examples of the inorganic particles include oxides of silicon, aluminum, magnesium, and titanium, and hydroxides thereof. By including inorganic particles having high heat resistance in the separator 40, the cycle characteristics of the lithium secondary battery 10 can be improved. The particle size of the inorganic particles is not particularly limited and is not particularly limited as long as it is the particle size of the inorganic particles used in the lithium secondary battery 10.

The binder serves to hold the inorganic particles in the coating layer 40b, that is, in the separator 40. [

The binder according to one embodiment may include a main chain comprising polyvinylidene fluoride (PVdF) and a polyhedral oligomeric silsesquioxane (POSS) derivative coupled to the main chain.

The main chain comprising the polyvinylidene fluoride means a main chain comprising polyvinyl fluoride (-CH ₂ CHF) _n -.

The main chain may be composed of polyvinylidene fluoride (PVdF) alone, or may be a copolymer of PVdF and another polymer. Examples of such a copolymer include a copolymer (PVDF-CTFE) of PVDF with polychlorotrifluoroethylene (CTFE), a copolymer of PVDF and polytetrafluoroethylene (PTFE) (PVDF-PTFE) .

The polyhedral oligomeric silsesquioxane (POSS) derivative may be one in which POSS has a functional group for main chain bonding. POSS can also be referred to as basket-like silsesquioxane. Examples of the functional groups for main chain bonding include acryloxy groups and the like.

Examples of the POSS derivatives include acryloisobutyl POSS (registered trademark), methacryloisobutyl POSS (registered trademark), and the like.

The POSS derivative may be bonded to the main chain, for example, by graft polymerization to the main chain.

The binder may be, for example, a compound containing a structural unit represented by the following formula (1).

[Chemical Formula 1]

(In the formula 1,

n, m, l and q are arbitrary natural numbers,

A is a hydrogen atom or a methyl group,

X is a chlorine atom or a fluorine atom,

Each R is independently a functional group selected from a C1 to C8 alkyl group, a cyclohexyl group, a phenyl group, and a C1 to C8 perfluoroalkyl group.

When the main chain is PVDF-CTFE, X in the above formula (1) may be a chlorine atom.

When the POSS derivative is acryloisobutyl POSS, l in the formula (1) may be 3, A may be a hydrogen atom, and R may be an isobutyl group.

Also, when the POSS derivative is methacryloyl isobutyl POSS, l in the above formula (1) may be 3, A may be a methyl group, and R may be an isobutyl group.

The graft ratio of the POSS derivative may be 50% or less, for example, 7% to 30%. The graft ratio can be calculated by the following equation (1).

[Equation 1]

x = [(y-z) / y] X 100

(Where x is the graft rate of the POSS derivative, y is the weight of the resulting binder, and z is the weight of the raw material of the main chain).

When the graft ratio is within the above range, the binder is well dissolved in the solvent and the slurry can be uniformly applied, thereby improving the adhesion of the binder and further improving the cycle characteristics of the lithium secondary battery. Further, the adhesive strength and cycle characteristics can be improved as compared with the case of using a PVdF binder.

The separator 40 may be manufactured, for example, in the following manner.

First, an inorganic particle dispersion and a binder solution are prepared. The solvent of the inorganic particle dispersion liquid is not particularly limited as long as it can disperse the inorganic particles. The solvent of the inorganic particle dispersion may be the same as the solvent of the binder solution. The solvent of the binder solution is not particularly limited as long as it can dissolve the binder. Examples of such a solvent include N-methylpyrrolidone (NMP) and the like.

Subsequently, the inorganic particle dispersion and the binder solution are mixed to prepare a slurry. The slurry may optionally be added with a solvent such as a solvent of the binder solution to adjust the concentration of the inorganic particles and the binder. Further, another kind of binder such as a PVdF binder (a binder containing PVDF as a main chain) may be further added to the slurry.

Then, the slurry is applied onto the substrate 40a and dried to form the coating layer 40b. Substrate 40a may be immersed in the slurry.

By these processes, the separator 40 can be manufactured.

Although the coating layer 40b is formed only on the surface of the base material 40a in Fig. 1, the coating layer 40b may also be formed in the micropores of the base material 40a.

The nonaqueous electrolyte solution may be any nonaqueous electrolytic solution which can be used in conventional lithium secondary batteries without any particular limitation.

The non-aqueous electrolyte may have a composition containing an electrolyte salt in a non-aqueous solvent.

Examples of the non-aqueous solvent include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate and vinylene carbonate; Chain carbonates such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate; cyclic esters such as? -butyrolactone and? -valerolactone; Chain esters such as methyl formate, methyl acetate and butyric acid methyl; Tetrahydrofuran or a derivative thereof; Ethers such as 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxyethane, 1,4-dibutoxyethane and methyl diglyme; Nitriles such as acetonitrile and benzonitrile; Dioxolane or derivatives thereof; Ethylene sulfide, sulfolane, sultone or a derivative thereof may be used alone or as a mixture of two or more thereof, but is not limited thereto.

The electrolyte salt may be, for _{example, LiClO 4, LiBF 4, LiAsF} 6, LiPF 6, LiPF 6-x (CnF 2n + 1) x (1 <x <6, n = 1 or 2), LiSCN, LiBr, LiI, Li ₂ SO _4, Li ₂ B ₁₀ Cl _10, NaClO _4, NaI, NaSCN, NaBr, KClO _4, an inorganic ion salt containing lithium, sodium or potassium, such as one type of KSCN; _{LiCF 3 SO 3, LiN (CF} 3 SO 2) 2, LiN (C 2 F 5 SO 2) 2, LiN (CF 3 SO 2) (C 4 F 9 SO 2), LiC (CF 3 SO 2) 3, _{LiC (C 2 F 5 SO 2} ) 3, (CH 3) 4 NBF 4, (CH 3) 4 NBr, (C 2 H 5) 4 NClO 4, (C 2 H 5) 4 NI, (C 3 H 7 _{) 4 NBr, (nC 4 H} 9) 4 NClO 4, (nC 4 H 9) 4 NI, (C 2 H 5) 4 N- _{maleate, (C 2 H 5) 4} N- benzoate, (C ₂ H ₅ ) ₄ N-phthalate, lithium stearylsulfonate, lithium octylsulfonate, and lithium dodecylbenzenesulfonate. These ionic compounds may be used singly or in combination of two or more.

The concentration of the electrolyte salt is not particularly limited and may be, for example, 0.8 to 1.5 mol / L.

Various additives may be added to the nonaqueous electrolyte solution. Examples of the additive include an anode active additive, an anode active additive, an ester additive, a carbonate ester additive, a sulfate ester additive, a phosphate ester additive, a borate ester additive, an acid anhydride additive, And the like. Any one of them may be used, or two or more of them may be used in combination.

Hereinafter, a method for producing a lithium secondary battery will be described.

The anode 20 can be manufactured as follows. First, a mixture obtained by mixing a cathode active material, a conductive material and a binder is dispersed in a solvent, for example, N-methyl-2-pyrrolidone to prepare a slurry. Then, the slurry is coated on the current collector 21 and dried to form the positive electrode active material layer 22. The coating method is not particularly limited, and examples thereof include a knife coater method and a gravure coater method. The following application process can be carried out in the same way. Then, the cathode 20 can be manufactured by pressing the cathode active material layer 22 by a press machine.

The cathode (3) can be manufactured in the same manner as the anode (20). For example, a slurry is prepared by first dispersing a mixture of a negative electrode active material and a binder in a solvent such as N-methyl-2-pyrrolidone, water and the like. Then, the slurry is coated on the current collector 31 and dried to form the negative electrode active material layer 32. Subsequently, the negative electrode 30 can be produced by pressing the negative electrode active material layer 32 by a press machine.

The separator 40 can be manufactured, for example, by the following method. First, an inorganic particle dispersion and a binder solution are prepared. Subsequently, the inorganic particle dispersion and the binder solution are mixed to prepare a slurry. The slurry may optionally be added with a solvent such as a solvent of the binder solution to adjust the concentration of the inorganic particles and the binder. Then, the slurry is coated on the substrate 40a and dried to form the coating layer 40b. Substrate 40a may be immersed in the slurry. By these processes, the separator 40 can be manufactured.

Next, the separator 40 is disposed between the anode 20 and the cathode 30 to produce an electrode structure. Next, the electrode structure is processed into a desired shape, for example, a cylindrical shape, a square shape, a laminate shape, a button shape, or the like, and inserted into the container of the above-described shape. Subsequently, an electrolyte solution having the above composition is injected into the container, and the electrolyte solution is impregnated into each pore in the separator. This process produces a lithium secondary battery.

Hereinafter, specific embodiments of the present invention will be described. However, the embodiments described below are only intended to illustrate or explain the present invention, and thus the present invention should not be limited thereto. In addition, contents not described here can be inferred sufficiently technically if they are skilled in the art, and a description thereof will be omitted.

(Binder synthesis)

Synthesis Example 1: PVdF-CTFE-graft-acryloisobutyl POSS synthesis

In a 300 ml three-necked flask equipped with a stirring bar, a thermometer and a cooling tube, 100 g of a 10% by weight N-mefylpyrrolidone solution of PVdF-CTFE (KFM Polymer # 7500, (N-mespyrrolidone solution containing 10% by weight of PVDF-CTFE based on the weight), 39.6 g (42.6 mmol) of acryloisobutyl POSS, 29.96 g (191.8 mmol) of bipyridyl, 6.33 g (63.9 mmol) of triphenylphosphine, 0.86 g (6.4 mmol) of copper (II) chloride and 100 g of N-methylpyrrolidone.

Subsequently, the inner pressure was reduced to 10 mmHg with a diaphragm pump, and the operation of returning the inner pressure to normal pressure using nitrogen was repeated three times. Subsequently, the mixed solution obtained in the oil bath was heated to 140 캜 and stirred for 24 hours. In this process, PVDF-CTFE was graft polymerized with acryloisobutyl POSS.

The obtained reaction solution was cooled to room temperature, and then added to 2000 ml of water with stirring to re-precipitate the polymer as a reaction product. The solution containing the polymer was then transferred to a mixer and the polymer was pulverized. As a result, the color of the solution changed from reddish brown to green. The pulverized polymer was collected by filtration, and washed with water, ethanol and ethyl acetate. Subsequently, the obtained polymer was blow-dried at 80 占 폚 for 3 hours.

The dried polymer was redissolved in 100 g of N-methylpyrrolidone and then added with stirring in 2000 ml of water again to reprecipitate the polymer. Subsequently, the solution containing the polymer was transferred to a mixer, and the polymer was pulverized. Thereafter, the polymer was collected by filtration, and washed with water, ethanol, and ethyl acetate. Subsequently, the polymer was vacuum-dried at 80 DEG C for 6 hours to obtain 10.8 g of PVdF-CTFE-graft-acryloyl isobutyl POSS (hereinafter referred to as "first POSS binder").

As a result of calculating the graft ratio according to the above-mentioned formula (1), the graft ratio was found to be [(10.8-10) /10.8] X 100 = 7.4%.

Further, 90 g of N-methylpyrrolidone was added to 10 g of the obtained first POSS binder, and the mixture was heated to 140 占 폚 so that the first POSS binder was a first POSS binder N-methyl A pyrrolidone solution was prepared. Subsequently, the first POSS binder N-methylpyrrolidone solution was cooled to room temperature to prepare 100 g of a 10 wt% N-methylpyrrolidone solution of a first POSS binder.

Synthesis Example 2: PVdF-CTFE-graft-acryloyl isobutyl POSS synthesis

Except that the reaction time (graft polymerization time) between PVdF-CTFE and acryloisobutyl POSS was changed to 72 hours. Thus, 11.5 g of PVdF-CTFE-graft-acryloyl isobutyl POSS (graft ratio 13.0%) (hereinafter referred to as "second POSS binder") was obtained. Further, 100 g of a 10 wt% N-methylpyrrolidone solution of the second POSS binder was obtained.

Synthesis Example 3: PVdF-CTFE-graft-acryloisobutyl POSS synthesis

The procedure of Synthesis Example 1 was repeated except that the amount of acryloylbutyl POSS was changed to 178.3 g (190.0 mmol) and a 1000 ml three-necked flask was used as a reaction vessel. Thus, 13.8 g of PVdF-CTFE-graft-acryloisobutyl POSS (graft ratio 27.5%) (hereinafter referred to as "third POSS binder") was obtained. Further, 100 g of a 10 wt% N-methylpyrrolidone solution of the third POSS binder was obtained.

Synthesis Example 4: PVdF-CTFE-graft-acryloyl isobutyl POSS synthesis

The procedure of Synthesis Example 3 was repeated except that the reaction time (graft polymerization time) of PVdF-CTFE and acryloisobutyl POSS was changed to 120 hours. Thus, 20.4 g of PVdF-CTFE-graft-acryloisobutyl POSS (graft ratio: 51.0%) (hereinafter referred to as "fourth POSS binder") was obtained.

After adding 90 g of N-methylpyrrolidone to 10 g of the obtained fourth POSS binder, the mixture was heated to 140 DEG C, and the fourth POSS binder was added to the fourth POSS binder N-methyl A pyrrolidone solution was prepared. Then, the fourth POSS binder N-methylpyrrolidone solution was cooled to room temperature to obtain 100 g of a 10 wt% N-methylpyrrolidone solution of the fourth POSS binder.

In the N-methylpyrrolidone solution of the fourth POSS binder, turbidity (cloudiness) occurred over time. As a result, the N-methylpyrrolidone solution became a suspension. A portion of the suspension was obtained and diluted 2-fold with N-methylpyrrolidone. Thereafter, the diluted solution was heated to 140 캜, resulting in a uniform solution. However, when the N-methylpyrrolidone solution was cooled to room temperature, turbidity (cloudiness) occurred again. As a result, the N-methylpyrrolidone solution became a suspension.

Synthesis Example 5: Synthesis of PVdF-CTFE-graft-methacryloylbutyl POSS

Except that 181.0 g (190.0 mmol) of methacryloyl isobutyl POSS instead of acryloyl isobutyl POSS was added, and a 1000 ml three-necked flask was used in the reaction vessel. As a result, 10.6 g of PVdF-CTFE-graft-methacryloyl isobutyl POSS (graft ratio: 5.7%) (hereinafter referred to as "fifth POSS binder") was obtained. Further, 100 g of a 10 wt% N-methylpyrrolidone solution of the fifth POSS binder was obtained.

Synthesis Example 6: PVdF-CTFE-graft-acryloyl isobutyl POSS synthesis

The procedure of Synthesis Example 3 was repeated except that the reaction time (graft polymerization time) of PVdF-CTFE and acryloyl isobutyl POSS was changed to 72 hours. Thus, 18.2 g of PVdF-CTFE-graft-acryloyl isobutyl POSS (graft ratio: 43.0%) (hereinafter referred to as "sixth POSS binder") was obtained. Further, 100 g of a 10 wt% N-methylpyrrolidone solution of the sixth POSS binder was obtained.

Evaluation 1: IR spectrum of the binder and ¹⁹ F NMR spectrum

And wherein the first POSS binder to sixth measuring the IR spectrum and the ¹⁹ F NMR spectrum of POSS binder (Synthesis Example 1-6), in Figure 2 the IR spectrum, ¹⁹ F NMR were respectively indicate the spectrum in Fig.

Fig. 2 shows the IR spectra according to Synthesis Examples 1 to 6 and PVDF-CTFE, and Fig. 3 shows ¹⁹ F NMR spectra according to Synthesis Examples 1 to 6 and PVDF-CTFE.

Referring to FIG. 2, in the IR spectra of the first to sixth POSS binders, acryloisobutyl POSS and carbonyl peak derived from methacryloyl isobutyl POSS can be identified at around 1720 cm ^-1 .

3, in the ¹⁹ F NMR spectrum of the first to sixth POSS binders, a peak near -120 ppm (a peak derived from F bound to Cl bonded to carbon in CTFE) observed in PVdF-CTFE Disappear, and the appearance of a new peak near -198 ppm can be confirmed. From these observation results, it can be predicted that the graft reaction proceeds from the carbon moiety in which Cl is bonded to CTFE, and the graft chain derived from acryloyl isobutyl POSS and methacryloyl isobutyl POSS is bonded to the carbon moiety.

Also, according to the results of the above IR spectrum and ¹⁹ F NMR spectrum, the first to sixth POSS binders were not blended polymers of PVdF-CTFE and polyacryloyl isobutyl POSS or polymethacryloyl isobutyl POSS but PVdF-CTFE Polyacryl isobutyl POSS or polymethacryloyl isobutyl POSS are chemically bonded graft polymers.

(Manufactured by separator)

Production Example 1

70 g (solid content concentration: 30% by weight) of N-methylpyrrolidone was added to 30 g of alumina (SUMITOMO CHEMICAL Co., Ltd., Sumiko Random AA03), and the mixed solution was treated in an ultrasonic disperser for 15 minutes to obtain N-methylpyrrolidone To prepare a dispersion.

Then, 22.6 g (alumina / binder = 93/7 by weight) of a 10 wt% N-methylpyrrolidone solution of the first POSS binder and 6.4 g of N-methylpyrrolidone were added to the dispersion. The resulting mixed solution was stirred in a distiller for 30 minutes to prepare a slurry (alumina / binder mixed solution (solid concentration 25% by weight)).

Subsequently, a gap of a dip coater was prepared so that the film thickness after drying was 12 占 퐉. The above slurry was applied to a polyethylene microporous membrane (Toray BSF, E07BLS) having a thickness of 7 占 퐉 by using the above dip coater. Subsequently, the polyethylene microporous membrane having completed the slurry application was immersed in a water bath. Thereafter, the microporous membrane was dried to obtain a coated separator.

Production Example 2

A coating separator was obtained in the same manner as in Preparation Example 1 except that a 10 wt% N-methylpyrrolidone solution of the second POSS binder was used.

Production Example 3

A coating separator was obtained in the same manner as in Preparation Example 1 except that a 10 wt% N-methylpyrrolidone solution of the third POSS binder was used.

Production Example 4

A coating separator was obtained in the same manner as in Preparation Example 1 except that a 10 wt% N-methylpyrrolidone solution of the fourth POSS binder was used.

Production Example 5

A coating separator was obtained in the same manner as in Preparation Example 1 except that a 10 wt% N-methylpyrrolidone solution of the fifth POSS binder was used.

Production Example 6

A coating separator was obtained in the same manner as in Preparation Example 1 except that a 10 wt% N-methylpyrrolidone solution of the sixth POSS binder was used.

Production Example 7

A coating separator was obtained in the same manner as in Preparation Example 1 except that a 10 wt% N-methylpyrrolidone solution of PVdF-CTFE was used.

Evaluation 2: Evaluation of coating layer adhesion

The coating separator prepared in the above Production Examples 1 to 7 was fixed on a stainless steel plate and attached to a fixed coating separator was Cell Tape (registered trademark) No. 405 manufactured by Nichiban Co., Ltd.) having a width of 1.5 cm. Subsequently, peel strength was measured by peeling at 180 ° using a peeling tester (SHIMAZU EZ-S, manufactured by Shimadzu). The results of the adhesion evaluation are shown in Table 1 below.

Evaluation 3: Evaluation of heat shrinkage

The coated separators prepared according to Preparation Examples 1 to 7 were cut in a transverse direction X MD (machine direction, length) = 60 mm X 80 mm. Using a nonius in the TD / MD direction, . The separator was sandwiched between aluminum foils folded once and allowed to stand in a thermostatic chamber at 150 占 폚 for 15 minutes. After the separator was taken out, the display interval of each of the TD / MD was read by Nogus and the heat shrinkage rate was calculated according to the following formula (2). The results of the heat shrinkage rate are shown in Table 1 below.

&Quot; (2) &quot;

Shrinkage percentage (%) = [(50 - interval after heating) / 50] X 100

In the above equation (2), a distance in the TD direction is used as an interval after heating.

bookbinder Coated Separator Peel strength (mN / mm) Shrinkage (%) Synthesis Example 1 Production Example 1 9.2 19 Synthesis Example 2 Production Example 2 15.8 18 Synthesis Example 3 Production Example 3 19.3 16 Synthesis Example 4 Production Example 4 7.5 20 Synthesis Example 5 Production Example 5 7.2 18 Synthesis Example 6 Production Example 6 16.5 15 PVdF-CTFE Production Example 7 2.2 24

It can be seen from Table 1 that the binders according to Synthesis Examples 1 to 6, i.e., the first to sixth POSS binders have excellent heat resistance and adhesion.

(Production of lithium secondary battery)

Example 1

The mixture was mixed with 96% by weight of artificial graphite, 2% by weight of acetylene black, 1% by weight of a styrene-butadiene rubber (SBR) binder and 1% by weight of carboxymethylcellulose (CMC) To prepare a negative electrode slurry. The nonvolatile component in the negative electrode slurry was 48% by weight based on the total weight of the slurry. Subsequently, the gap of the bar coater was adjusted so that the coating amount (area density) after drying was 9.55 mg / cm ² , and the negative electrode composite slurry was uniformly coated on the copper foil (thickness 10 μm) by the bar coater. Subsequently, the negative electrode slurry was dried for 15 minutes in a blower dryer set at 80 占 폚. Subsequently, the negative electrode mixture after drying was pressed by a roll press machine so that the compound density became 1.65 g / cm &lt; ^{3 &} gt ;. Subsequently, the negative electrode mixture was vacuum-dried at 150 占 폚 for 6 hours to prepare a sheet-like negative electrode comprising a collector and a negative electrode active material layer.

Solid solution oxide Li _1.20 Mn _0.55 Co _0.10 Ni _0.15 O ₂ 96% by weight, Ketjenblack 2% by weight and polyvinylidene fluoride 2% by weight were dispersed in N-methyl-2-pyrrolidone to prepare a positive electrode slurry. The nonvolatile component in the positive electrode composite slurry was 50% by weight based on the total weight of the slurry. Subsequently, the gap of the bar coater was adjusted so that the application amount (area density) after drying was 22.7 mg / cm ² , and the positive electrode slurry slurry was coated on the aluminum current collecting foil as the current collector by using the bar coater. Subsequently, the positive electrode composite slurry was dried for 15 minutes in a blower dryer set at 80 DEG C, and the dried positive electrode composite material was pressed by a roll press machine so as to have a compound density of 3.9 g / cm &lt; ^{3 &} gt ;. Subsequently, the positive electrode mixture was vacuum-dried at 80 占 폚 for 6 hours to prepare a sheet-like positive electrode comprising a current collector and a positive electrode active material layer.

The prepared negative electrode was cut into a circle having a diameter of 1.55 cm, and the prepared positive electrode was cut into a circle having a diameter of 1.3 cm. Then, the coated separator according to Preparation Example 1 was cut into a circle 1.8 cm in diameter.

In a stainless steel coin type external container having a diameter of 2.0 cm, a positive electrode cut into a circle having a diameter of 1.3 cm, a coating separator cut into a circle having a diameter of 1.8 cm, a negative electrode cut into a circle having a diameter of 1.55 cm, And copper foil having a thickness of 200 mu m cut into a circle of 1.5 cm was laminated in this order.

Subsequently, 150 쨉 l of an electrolyte solution containing 1.4M of LiPF ₆ dissolved in a solvent mixed with ethylene carbonate / diethyl carbonate / fluoroethylene carbonate at a volume ratio of 10/70/20 was added.

Subsequently, a cap made of stainless steel was put on the container through a packing made of polypropylene, and the container was sealed with an adapter for making a coin cell. Thus, a lithium secondary battery of a coin cell was produced.

Examples 2 to 6 and Comparative Example 1

A lithium secondary battery was produced in the same manner as in Example 1 except that the separator according to Production Examples 2 to 7 was used instead of the separator according to Production Example 1 as shown in Table 2 below.

Evaluation 4: Evaluation of cycle life

The lithium secondary batteries of Examples 1 to 6 and Comparative Example 1 were charged and discharged once at 0.2C. Thereafter, the charge / discharge cycle for charging / discharging the lithium secondary battery at 1.0 C was repeated 300 times. Each charge and discharge was performed at 25 ° C. The discharge capacity retention rate (percentage) was calculated by dividing the discharge capacity at 300 cycles (300th cycle in a 1.0C charge / discharge cycle) by the discharge capacity at the time of one cycle (1.0C charge / discharge cycle first time) The results are shown in Table 2 below.

Separator Capacity retention rate (%) Example 1 Production Example 1 68 Example 2 Production Example 2 67 Example 3 Production Example 3 68 Example 4 Production Example 4 66 Example 5 Production Example 5 65 Example 6 Production Example 6 65 Comparative Example 1 Production Example 7 61

It can be seen from Table 2 that the cycle characteristics of the lithium secondary battery according to one embodiment are improved. Further, when the graft ratio is within the range of 7% to 30%, the cycle characteristics are further improved.

As described above, the binder according to one embodiment has excellent heat resistance and strong adhesive force. Therefore, the separator can be manufactured using the binder according to one embodiment, and the lithium secondary battery can be manufactured using the separator to improve the cycle characteristics. Further, since the heat shrinkage of the separator is also suppressed, thermal runaway of the lithium secondary battery can be suppressed, and the safety of the lithium secondary battery can be further improved.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, And falls within the scope of the invention.

1 Lithium secondary battery
20 anode
30 cathode
40 Separator
40a
40b coating layer

Claims (6)

A main chain comprising polyvinylidene fluoride; And
The polyhedral oligomeric silsesquioxane derivative bound to the main chain
And a binder for a lithium secondary battery. The method of claim 1,
Wherein the polyhedral oligomeric silsesquioxane derivative is bonded to the main chain by graft polymerization. The method of claim 1,
Wherein the binder for the lithium secondary battery is a compound containing a structural unit represented by the following formula (1).
[Chemical Formula 1]

(In the formula 1,
n, m, l and q are arbitrary natural numbers,
A is a hydrogen atom or a methyl group,
X is a chlorine atom or a fluorine atom,
Each R is independently a functional group selected from a C1 to C8 alkyl group, a cyclohexyl group, a phenyl group, and a C1 to C8 perfluoroalkyl group. A separator for a lithium secondary battery, comprising the binder according to any one of claims 1 to 3. 5. The method of claim 4,
A separator for a lithium secondary battery further comprising inorganic particles. A lithium secondary battery comprising the separator of claim 4.

Images