KR20150037276A - Binder Composition for Secondary Battery, and Lithium Secondary Battery Comprising The Same - Google Patents

Abstract

The present invention relates to a binder composition for a second battery, the binder composition containing: conjugated dienes latex particle (A) whose amount is 50 wt % or more based on the total weight of solid contents; and acryl-acid ester-based latex particle (B) whose glass transition temperature (Tg) differs by 5°C or less in comparison with the latex particle (A). Also, the present invention relates to the binder composition for the second battery containing an aggregated material having a snow-man form of latex particle (A) and latex particle (B.)

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a binder composition for a secondary battery and a lithium secondary battery comprising the binder composition.

The present invention relates to a binder composition for a secondary battery and a lithium secondary battery comprising the binder composition.

Due to the rapid increase in the use of fossil fuels, the demand for the use of alternative energy or clean energy is increasing. As a part of this, the most active field of research is electric power generation and storage.

At present, a typical example of an electrochemical device utilizing such electrochemical energy is a secondary battery, and the use area thereof is gradually increasing.

2. Description of the Related Art [0002] Recently, as technology development and demand for portable devices such as portable computers, portable phones, and cameras have increased, the demand for secondary batteries as energy sources has increased sharply. Among such secondary batteries, they exhibit high energy density and operating potential, Many studies have been made on a lithium secondary battery having a long self discharge rate, and it has been commercialized and widely used.

In addition, as the interest in environmental issues grows, researches on electric vehicles and hybrid electric vehicles that can replace fossil fuel-based vehicles such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution, , Lithium secondary batteries are also used as power sources for such electric vehicles and hybrid electric vehicles.

Generally, in a lithium secondary battery, charging and discharging proceed while repeating the process in which lithium ions in the positive electrode are inserted into the negative electrode and desorbed. Such insertion and desorption of lithium ions repeatedly progresses, so that the bond between the electrode active material or the conductive material is loosened and the contact resistance between the particles is increased. As a result, the resistance of the electrode increases and the battery characteristics may deteriorate. Therefore, the binder is preferably a polymer having elasticity, since it is required to be capable of buffering against the expansion and contraction of the electrode active material due to insertion and desorption of lithium ions in the electrode.

Further, the binder is required to have an adhesive strength enough to maintain the binding force between the electrode active material and the current collector during the drying process of the electrode plate. Particularly, in order to increase the discharge capacity, when a material such as silicon, tin, silicon-tin alloy having a large discharging capacity is mixed with natural graphite having a theoretical discharge capacity of 372 mAh / g is used, The volume expansion of the negative electrode material significantly increases. As a result, deterioration of the negative electrode material occurs. As a result, the capacity of the battery may be drastically deteriorated as a repetitive cycle progresses.

In order to maximize the capacity and the energy density, it is desirable to increase the content of the electrode active material and reduce the content of the binder as low as possible.

Representative binders currently commercialized include polyvinylidene fluoride (PVdF), styrene-butadiene rubber (SBR), carboxy methyl cellulose (CMC), and the like. In the case of a negative electrode having a large volume expansion, SBR / CMC, which has a smaller amount of use and has a better binding force than PVdF, is used.

<List of Prior Art Documents>

Prior Art 1: United States Patent No. 5468571

Prior Art 2: JP-A-1992-342966

The prior art document 1 discloses a polyvinylidene fluoride binder. However, the polyvinylidene fluoride binder has a problem that the electrode active material falls from the current collector during repeated charge and discharge.

The prior art document 2 discloses a binder in which carboxymethylcellulose is mixed or dissolved in a latex in which styrene-butadiene rubber is suspended in water. However, since carboxymethylcellulose lowers the flexibility of the electrode, the balance with the binding persistence of the rubber latex is disrupted, and sufficient performance is not obtained.

Disclosure of Invention Technical Problem [8] Accordingly, the present invention has been made to solve the above-mentioned problems of the prior art and the technical problems required from the past, and to provide a binder composition excellent in adhesion and binding durability and a lithium secondary battery comprising the binder composition.

A binder composition for a secondary battery according to a non-limiting example of the present invention,

Conjugated dienes latex particles (A) having a content of 50% by weight or more based on the total mass of solids; And latex particles (B) of acrylic ester type having a difference in glass transition temperature (Tg) from the latex particle (A) to less than 5 占 폚.

The latex particles (A) having a relatively high glass transition temperature can exert an excellent adhesive force between the current collector, the electrode active material, and the electrode active material. In addition, the latex particles (B) having a relatively low glass transition temperature can exhibit excellent binding persistence even when the volume of the electrode active material varies due to repeated charge and discharge.

The inventors of the present application have found that the excellent binding persistence of the latex particles (A) and the excellent adhesion strength of the latex particles (B) are such that the content of the latex particles (A) is at least 50% And a synergistic effect could be exhibited when the temperature was less than 5 占 폚.

At this time, the binder composition according to a non-limiting example of the present invention may include composite latex particles having a two-phase structure in which physical properties are distinguished, and the latex particles (A) and the latex particles (B) May be a single particle that is bound to each other by chemical bonding. Specifically, the latex particles (A) and the latex particles (B) may be combined or aggregated to form snow-like composite latex particles.

In a non-limiting example of the present invention, the latex particles (A) may range from 50 wt% to 95 wt% based on the total mass of solids. When the content of the latex particles (A) is less than 50% by weight, the electrode active material may be detached from the current collector during repeated charge and discharge, thereby deteriorating life characteristics of the battery. Therefore, the content of the latex particles (A) is preferably 50% by weight or more.

The content of the latex particles (B) may be in the range of 5 wt% or more to 50 wt% or less based on the total mass of solid matter. When the content of the latex particles (B) is less than 5% by weight, there is a problem that the adhesive force between the current collector and the electrode active material and the electrode active material decreases and the resistance increases. Therefore, the content of the latex particles (B) is preferably 5% by weight or more.

The latex particles (A) may be prepared by polymerizing (i) at least one compound selected from the group consisting of an aromatic vinyl compound and a vinyl cyan compound, (ii) an unsaturated monocarboxylic acid compound, and (iii) a polymeric compound of a conjugated diene compound .

In a non-limiting example of the present invention, the conjugated diene compound is contained in an amount of from 30% by weight to 70% by weight, and at least one compound selected from the group consisting of the aromatic vinyl compound and the vinyl cyan compound The content of the unsaturated monocarboxylic acid compound may be in the range of not less than 29 wt% to not more than 70 wt%, and the content of the unsaturated monocarboxylic acid compound may be in the range of not less than 0.1 wt% and not more than 5 wt%.

In a non-limiting example of the present invention, the conjugated diene-based compound may be at least one compound selected from the group consisting of 1,3-butadiene, isoprene, chloroprene, and pyridene. However, the present invention is not limited thereto.

(I) at least one compound selected from the group consisting of an aromatic vinyl compound, a vinyl cyan compound, and a (meth) acrylamide compound, (ii) an unsaturated monocarboxylic acid compound, and (iii) ) (Meth) acrylic acid ester compound.

In a non-limiting example of the present invention, the (meth) acrylic acid ester compound is contained in an amount of not less than 39% by weight and not more than 80% by weight and has an aromatic vinyl compound, a vinyl cyan compound, The content of the unsaturated monocarboxylic acid compound is in the range of 1 wt% or more to 15 wt% or less within the range of 1 wt% or more to 15 wt% or less, and the content of the at least one compound selected from the group consisting of .

In a non-limiting embodiment of the present invention, the (meth) acrylate-based compounds, C ₁ -C (meth) with ₁₄ alkyl group may be acrylic acid ester compound, the C ₁ -C a (meth) acrylic acid with ₁₄ alkyl group The ester compound may be at least one selected from the group consisting of methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-amyl acrylate, isoamyl acrylate, Methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-butyl methacrylate, -Methyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, n-ethylhexyl methacrylate, 2-ethylhexyl methacrylate, hydroxyethyl It may include other methacrylate, and hydroxypropyl methacrylate.

In a non-limiting example of the present invention, the aromatic vinyl compound may include styrene,? -Methylstyrene,? -Methylstyrene, p-methylstyrene, pt-butylstyrene, vinyltoluene.

The vinyl cyan compound may include acrylonitrile, methacrylonitrile, and a monomer having a cyan functional group.

The (meth) acrylamide-based compound may include acrylamide, n-methylol acrylamide, n-butoxymethylacrylamide, n-methylol methacrylamide and n-butoxymethylmethacrylamide.

The unsaturated monocarboxylic acid compound may include crotonic acid, isocrotonic acid, maleic anhydride, fumaric acid, itaconic acid, acrylic acid, and methacrylic acid.

The method for producing the latex particles (A) and the latex particles (B) is not particularly limited and may be carried out by a known suspension polymerization method, emulsion polymerization method, seed polymerization method or the like using a polymerization initiator, a crosslinking agent, .

The latex particles (A) and the latex particles (B) may be prepared by emulsion polymerization. In this case, the latex particles (A) and the latex particles (B) Can be controlled by the amount of the emulsifier. Generally, as the amount of the emulsifier increases, the particle size decreases. As the amount of the emulsifier decreases, the particle size tends to increase. The desired average particle diameter can be realized by adjusting the amount of the emulsifier used in consideration of the desired particle size, reaction time, and reaction stability.

The polymerization temperature and the polymerization time may be appropriately determined according to the type of polymerization initiator and the like. For example, the polymerization temperature may be from 50 캜 to 200 캜, and the polymerization time may be from 1 to 20 hours.

The polymerization initiator may be an inorganic or organic peroxide. For example, a water-soluble initiator including potassium persulfate, sodium persulfate, ammonium persulfate and the like and an oil-soluble initiator including cumene hydroperoxide, benzoyl peroxide, Can be used.

The polymerization initiator may further include an activating agent to promote the initiating reaction of the peroxide with the polymerization initiator. Examples of the activating agent include sodium formaldehyde sulfoxylate, sodium ethylenediamine tetraacetate, ferrous sulfate and dextrose One or more selected from the group consisting of

The crosslinking agent may be, for example, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, 1,3-butanediol dimethacrylate, 1,6-hexanediol dimethacrylate Trimethylolpropane trimethacrylate, trimethylolmethane triacrylate, aryl methacrylate (AMA), and the like are used. As the grafting agent, aryl methacrylate (AMA), triarylisocyanurate (TAIC), triarylamine (TAA), diarylamine (DAA) and the like are used.

Examples of the molecular weight regulator include mercaptans or terpines such as terbinol, dipentene and t-terpine; halogenated hydrocarbons such as chloroform and carbon tetrachloride; and the like.

The emulsifier is a substance having both a hydrophilic group and a hydrophobic group. For example, fatty acid salts such as oleic acid, stearic acid, lauric acid, sodium or potassium salts of mixed fatty acids, and general anionic emulsifiers such as sulfate, sulfonate, phosphate and sulfosuccinate can be used .

Meanwhile, antioxidants and preservatives may be added during the preparation of the binder solution. Particularly, when the conjugated diene polymer is used in the binder solution, deterioration of physical properties is likely to occur due to softening or gelation during the operation of the battery, so that the lifetime of the battery may be shortened. Can be preferably used.

In addition, a non-limiting example of the present invention can provide a secondary battery including the above-described binder composition and an electrode active material capable of intercalating and deintercalating lithium, and a battery pack including the secondary battery.

The secondary battery may be a lithium secondary battery, and the lithium secondary battery may be a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery. The lithium secondary battery includes an electrode laminate having a structure in which a separator is interposed between an anode and a cathode, at least one anode, at least one cathode, and at least one separator, a non-aqueous electrolyte, And includes a battery case which is built in and sealed.

The electrode may be a positive electrode or a negative electrode, and may be manufactured by a manufacturing method including the following processes.

In the electrode manufacturing method,

Dispersing or dissolving the binder in a solvent to prepare a binder solution; Preparing an electrode slurry by mixing the binder solution, the electrode active material, and the conductive material; Coating the electrode slurry on a current collector; Drying the electrode; And compressing the electrode to a constant thickness. In some cases, the rolled electrode may further be dried.

The binder solution preparation process is a process of dispersing or dissolving the binder in a solvent to prepare a binder solution. The solvent can be selectively used depending on the type of the binder. For example, organic solvents such as isopropyl alcohol, N-methylpyrrolidone (NMP), and acetone and water can be used.

An electrode active material and a conductive material may be mixed / dispersed in the binder solution to prepare an electrode slurry. The electrode slurry thus prepared can be transferred to a storage tank and stored until the coating process. In order to prevent the electrode slurry from hardening in the storage tank, the electrode slurry can be agitated continuously. The electrode active material may be a positive electrode active material or a negative electrode active material.

Specifically, the cathode active material may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium manganese oxides such as Li _{1 + y} Mn _2-y O ₄ (where y is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ and LiMnO ₂ ; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; Formula _{LiNi 1-y M y O 2} ( where, the M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, y = 0.01 ~ 0.3 Im) Ni site type lithium nickel oxide which is represented by; Formula _{LiMn 2-y M y O 2} ( where, M = Co, Ni, Fe , Cr, and Zn, or Ta, y = 0.01 ~ 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, Ni, Cu, or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like. However, the present invention is not limited to these.

The negative electrode active material may include, for example, carbon such as non-graphitized carbon or graphite carbon; _{Li x Fe 2 O 3 (0≤x≤1} ), Li x WO 2 (0≤x≤1), Sn x Me 1-x Me 'y O z (Me: Mn, Fe, Pb, Ge; Me' : Metal complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, Halogen, 0 &lt; x &lt; Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{SnO, SnO 2, PbO, PbO} 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4, Bi ₂ O ₅ and the like; Li-Co-Ni-based material, and the like.

The conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, graphite such as natural graphite or artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

A viscosity modifier and a filler may be optionally added to the electrode slurry, if necessary. The viscosity adjusting agent is a component that adjusts the viscosity of the electrode mixture so that the mixing process of the electrode mixture and the coating process on the current collector can be easily performed. Examples of such a viscosity adjusting agent include carboxymethylcellulose, polyacrylic acid, However, the present invention is not limited to these. The filler is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery, and examples thereof include olefin-based polymerizers such as polyethylene and polypropylene; Fibrous materials such as glass fiber, carbon fiber and the like can be used.

The process of coating the electrode slurry on the current collector is a process in which the electrode slurry is passed through a coater head to coat the current collector with a predetermined pattern and a constant thickness. The method of coating the electrode slurry on the current collector includes a method of uniformly dispersing the electrode slurry on a current collector using a doctor blade or the like, a method of die casting, comma coating coating, screen printing, and the like. Alternatively, the electrode slurry may be bonded to the current collector by molding on a separate substrate, followed by pressing or lamination.

The current collector is not particularly limited as long as it has high conductivity without causing a chemical change in the battery. For example, the current collector may be made of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, a surface of copper or stainless steel A surface treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. Specifically, the cathode current collector may be a metal current collector including aluminum, and the anode current collector may be a metal current collector including copper. The electrode current collector may be a metal foil, and may be an aluminum foil or a copper foil.

The drying process is a process of removing the solvent and moisture in the slurry to dry the slurry coated on the metal current collector. In a specific example, the drying process is performed within one day in a vacuum oven at 50 to 200 ° C. After the drying process, a cooling process may be further included.

In order to increase the capacity density of the coated electrode and increase the adhesion between the current collector and the active materials, an electrode can be passed between two rolls heated at a high temperature and compressed to a desired thickness. This process is called the rolling process.

The electrode can be preheated before passing the electrode between two heated, heated rolls. The preheating process is a process of preheating the electrode before it is introduced into the roll to increase the compression effect of the electrode.

The electrode having completed the rolling process as described above can be dried within one day in a vacuum oven at 50 to 200 DEG C in a range satisfying a temperature equal to or higher than the melting point of the binder. The rolled electrode may be cut to a certain length and then dried. After the drying process, a cooling process may be further included.

In the case where a solid electrolyte such as a polymer is used as the electrolyte, the separation membrane may also serve as a separation membrane. The separator is made of an insulating thin film having high ion permeability and mechanical strength. The pore diameter of the separator is generally 0.01 to 10 mu m and the thickness is generally 5 to 300 mu m. Such separation membranes include, for example, olefinic polymers such as polypropylene, which are chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like; Kraft paper and the like are used. Representative examples currently on the market include the Celgard ^R 2400, 2300 (from Hoechest Celanese Corp.), polypropylene separator (from Ube Industries Ltd. or Pall RAI), and polyethylene series (from Tonen or Entek).

In some cases, a gel polymer electrolyte may be coated on the separation membrane to increase the stability of the cell. Representative examples of such a gel polymer include polyethylene oxide, polyvinylidene fluoride, and polyacrylonitrile.

As the non-aqueous electrolyte, a non-aqueous electrolyte, an organic solid electrolyte, an inorganic solid electrolyte, or the like is used. Examples of the nonaqueous electrolyte include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate , Gamma -butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, Diethyl ether, formamide, dimethyl formamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane A non-protonic organic solvent such as an ether, a methyl pyrophosphate, or an ethyl propionate is used as the solvent, a sulfone, a methyl sulfolane, a 1,3-dimethyl-2-imidazolidinone, a propylene carbonate derivative, a tetrahydrofuran derivative, .

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, Polymers containing ionic dissociation groups, and the like can be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides and sulfates of Li such as Li ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be used.

The lithium salt is a material that is readily soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO 4, LiBF 4, LiB 10 Cl 10, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, CF 3 SO 3 Li, LiSCN, LiC (CF 3 SO 2) 3, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, 4-phenylborate, imide, and the like can be used.

For the purpose of improving the charge / discharge characteristics and the flame retardancy, the electrolytic solution is preferably mixed with an organic solvent such as pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, . In some cases, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further added to impart nonflammability. In order to improve the high-temperature storage characteristics, carbon dioxide gas may be further added. FEC (fluoro-ethylene carbonate, PRS (propene sultone), FPC (fluoro-propylene carbonate), and the like.

As described above, when the binder composition according to a non-limiting example of the present invention is applied, the battery can maintain a good bonding force between the electrode materials that undergo volume change during charging and discharging, and between the electrode active material and the current collector . As a result, it is possible to provide a secondary battery exhibiting an initial capacity and excellent lifespan characteristics.

In the following Examples, Comparative Examples and Experimental Examples, the contents of the present invention will be described in more detail, but the present invention is not limited thereto.

[Example 1]

&Lt; Production of 1-1 latex particles (B)

Monomers were prepared by adding butyl acrylate (60 g), styrene (35 g), acrylic acid (5 g), sodium polyoxyethylene lauryl ether sulfate (0.7 g) and NaHCO ₃ (0.4 g) do. The mixture was heated to 75 캜, and then ammonium persulfate was added as a polymerization initiator to initiate polymerization. And the mixture was reacted for about 4 hours while maintaining the temperature at 75 캜 to prepare latex particles.

&Lt; Preparation of 1-2 latex particles (A-B)

100 g of the latex particles (B) prepared in <1-1> were added to the reactor in an amount of 100 g based on the solid content, and the mixture was heated to 70 ° C., and the mixed monomer corresponding to the latex particles (A) Lt; RTI ID = 0.0 &gt; 70 C &lt; / RTI &gt; for a period of time to obtain a binder composition (AB). In this case, the monomer corresponding to the latex particle (A) was obtained by mixing 40 g of 1,3-butadiene, 59 g of styrene, 1 g of acrylic acid, 0.4 g of NaHCO ₃ as a buffer, Ethylene lauryl ether sulfate (0.4 g), and dodecyl mercaptan (0.9 g) as a molecular weight regulator.

&Lt; Preparation of 1-3 binder composition >

The shape of the latex particles was analyzed by TEM (Transmission Electron Microscopy) to confirm the combination of the snowman shape.

<1-4 Preparation of electrode slurry and electrode>

The negative electrode was prepared by mixing 96.9 g of natural graphite, 0.4 g of Super P, 1.5 g of the binder for the secondary battery prepared above, and 1.2 g of carboxymethylcellulose as a thickener on the basis of 100 g of the total solid content, And a slurry for a negative electrode was prepared to have a total solid content of 50% by weight and applied to a copper foil, followed by drying and pressing to prepare a negative electrode.

The anode was prepared by mixing LiCoO ₂ (96 g), Super P (2 g) and PVDF binder (2 g) as active materials with NMP (N-methyl-2-pyrrolidone) Dried, and then pressed to produce a positive electrode.

&Lt; 1-5 Preparation of lithium secondary battery >

The prepared negative electrode plate was drilled at a surface area of 13.33 cm ² , and the positive electrode plate was drilled at a surface area of 12.60 cm ² to prepare a single cell (mono-cell). A tab was attached to the upper part of the anode and the upper part of the cathode. The resultant was placed on the aluminum pouch with a separator made of a polyolefin microporous membrane between the cathode and the anode, and 500 mg of the electrolyte was injected into the pouch.

The electrolyte solution was prepared by dissolving LiPF ₆ at a concentration of 1 M using a mixed solvent of EC (Ethyl carbonate): DEC (dimethyl carbonate): EMC (Ethyl-methyl carbonate) = 4: 3: 3 (volume ratio). Thereafter, the pouch is sealed using a vacuum packing machine, and the pouch is maintained at room temperature for 12 hours, and then subjected to a constant voltage charging process in which a constant current is charged at a rate of about 0.05 degree and a voltage is maintained until the voltage becomes about 1/6 of a current. At this time, since gas is generated in the cell, a degassing process and a resealing process were performed to complete the lithium secondary battery.

[Example 2]

A lithium secondary battery was produced in the same manner as in Example 1, except that a binder composition was prepared by controlling the amount of the latex particles (A): latex particles (B) = 95: 5 in terms of solid mass ratio .

[Comparative Example 1]

A lithium secondary battery was produced in the same manner as in Example 1 except that the binder composition was prepared by polymerizing latex particles (A): latex particles (B) = 40:60 in terms of solid content by mass.

[Comparative Example 2] - When Tg is 5 ° C or more

A lithium secondary battery was produced in the same manner as in Example 1, except that butyl acrylate (70 g) was substituted for butyl acrylate (60 g) in the latex particles (B) and styrene (20 g) Respectively.

<Experimental Example 1>

&Lt; Glass transition temperature (Tg) >

In order to confirm the difference in Tg between the particles (A) and (B), the particles (A) and the particles (B) were polymerized singly and then the Tg was measured using DSC.

(A) the Tg of the particles (B) Tg of the particles Difference in Tg between (A) particle and (B) particle Example 1 4.5 1.3 3.2 Example 2 4.5 1.3 3.2 Comparative Example 1 4.5 1.3 3.2 Comparative Example 2 4.5 -10.3 14.8

<Experimental Example 2>

&Lt; Electrolyte Impregnation Experiment &

The electrolytic solution impregnation test of the binders of Examples 1 and 2 and Comparative Examples 1 and 2 was carried out. The binder was applied on PET film to a certain thickness and dried, and the binder film was cut to 1 cm x 4 cm to prepare test pieces. The degree of swelling of the electrolytic solution was measured by measuring the elongated volume after impregnating the electrolytic solution containing ethylene carbonate (EC): propylene carbonate (PC): diethylene carbonate (DEC) = 3: 2: 5 for 2 days.

Electrolyte swelling (%) Example 1 76 Example 2 42 Comparative Example 1 102 Comparative Example 2 91

<Experimental Example 3>

&Lt; Adhesion Test &

Experiments were conducted to measure the adhesive force between the negative electrode composition and the current collector when the binder according to Examples 1 and 2 and Comparative Examples 1 and 2 was used for the negative electrode. The negative electrode plate prepared in Examples 1 and 2 and Comparative Examples 1 and 2 was cut into a predetermined size and fixed to a slide glass. The current collector was peeled off and the 180 ° peel strength was measured. The results are shown in Table 3 below. The evaluation was made by measuring the peel strengths of 5 or more and calculating the average value.

<Experimental Example 4>

<Battery Test>

Charging and discharging tests of the batteries prepared in Examples 1 and 2 and Comparative Examples 1 and 2 were carried out. First, charge and discharge tests were carried out twice at a charge / discharge current density of 0.2C, a charge end voltage of 4.2V (Li / Li +) and a discharge end voltage of 3V (Li / Li +). Charging and discharging tests were carried out 48 times with charging / discharging current density of 1C, end-of-charge voltage of 4.2V (Li / Li +) and end-of-discharge voltage of 3V (Li / Li +). All charging was performed at constant current / constant voltage, and the end current of constant voltage charging was 0.05C. After completing a total of 50 cycles, the charge / discharge efficiency (initial efficiency and 50 cycle capacity retention rate) of the first cycle was obtained. Then, the capacity ratio (50 ^th / 1 ^st ) of dividing the charge capacity of 50 cycles by the charge capacity of the first cycle was calculated and regarded as the capacity retention rate. The results are shown in Table 3 below.

Adhesion (gf / cm) Initial efficiency (%) 50 Cycle Capacity Maintenance (%) Example 1 16.6 94.2 97.5 Example 2 18.0 94.1 98.1 Comparative Example 1 11.1 93.5 94.3 Comparative Example 2 12.3 93.7 92.7

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. will be.

Claims (16)

As a binder composition for a secondary battery,
Conjugated dienes latex particles (A) having a content of 50% by weight or more based on the total mass of solids; And
Acrylate-based latex particles (B) having a difference in glass transition temperature (Tg) from the latex particles (A) to less than 5 占 폚;
&Lt; / RTI &gt; The method according to claim 1,
Wherein the latex particles (A) have a content in the range of from 50% by weight or more to 95% by weight or less based on the total mass of solid matter. The method according to claim 1,
The latex particles (A) are prepared by polymerizing (i) at least one compound selected from the group consisting of an aromatic vinyl compound and a vinyl cyan compound, (ii) an unsaturated monocarboxylic acid compound, and (iii) a conjugated diene compound &Lt; / RTI &gt; The method of claim 3,
Wherein the content of the conjugated diene compound is in the range of 30% by weight or more and 70% by weight or less, and the content of the at least one compound selected from the group consisting of aromatic vinyl compound and vinyl cyan compound is 29% And the unsaturated monocarboxylic acid compound has a content within a range of 0.1 wt% or more to 5 wt% or less. The method of claim 3,
Wherein the conjugated diene compound is at least one compound selected from the group consisting of 1,3-butadiene, isoprene, chloroprene, and pyridene. The method according to claim 1,
(I) at least one compound selected from the group consisting of an aromatic vinyl compound, a vinyl cyan compound, and a (meth) acrylamide compound, (ii) an unsaturated monocarboxylic acid compound, and (iii) (Meth) acrylic acid ester compound. The method according to claim 6,
Wherein the (meth) acrylic ester compound is a (meth) acrylic acid ester compound having a C ₁ -C ₁₄ alkyl group. 8. The method of claim 7,
The (meth) acrylic acid ester compound having a C ₁ -C ₁₄ alkyl group may be at least _{one selected from the} group consisting of methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, Ethyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n -Butyl methacrylate, isobutyl methacrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, n-ethylhexyl methacrylate, 2-ethylhexyl methacrylate, Methyl methacrylate, ethyl methacrylate, and hydroxypropyl methacrylate. 8. The method of claim 7,
Wherein the aromatic vinyl compound comprises at least one member selected from the group consisting of styrene,? -Methylstyrene,? -Methylstyrene, p-methylstyrene, pt-butylstyrene and vinyltoluene. The method according to claim 6,
Wherein the vinyl cyan compound comprises at least one member selected from the group consisting of acrylonitrile, methacrylonitrile, and monomers having a cyan functional group. The method according to claim 6,
The (meth) acrylamide-based compound is preferably selected from the group consisting of acrylamide, n-methylol acrylamide, n-butoxymethylacrylamide, methacrylate, n-methylolmethacrylamide and n-butoxymethylmethacrylamide Lt; RTI ID = 0.0 &gt; 1, &lt; / RTI &gt; The method according to claim 6,
Wherein the unsaturated monocarboxylic acid compound comprises at least one member selected from the group consisting of crotonic acid, isocrotonic acid, maleic anhydride, fumaric acid, itaconic acid, acrylic acid and methacrylic acid. The method according to claim 6,
The content of the (meth) acrylic acid ester compound (a) is in the range of not less than 39% by weight and not more than 80% by weight,
At least one compound selected from the group consisting of an aromatic vinyl compound, a vinyl cyan compound, and a (meth) acrylamide compound is contained in an amount of 10 wt% or more to 60 wt% or less,
Wherein the content of the unsaturated monocarboxylic acid compound is in the range of 1% by weight or more and 15% by weight or less. As a binder composition for a secondary battery,
Characterized in that it comprises a snowman shaped combination or aggregate of conjugated dienes latex particles (A) and acrylic ester based latex particles (B). 15. A secondary battery comprising: the binder composition according to any one of claims 1 to 14; and an electrode active material capable of intercalating and deintercalating lithium. A battery pack comprising a secondary battery according to claim 15.