KR101120434B1 - Binder for Secondary Battery Containing Copolymer of Polyester Acrylate-based Compound - Google Patents

Abstract

The present invention provides a secondary battery comprising an electrode prepared by using a binder for a secondary battery comprising a copolymer comprising a polyester acrylate monomer or oligomer and an electrode mixture containing the same.

Since the binder of the present invention has excellent affinity between the dispersion medium and the binder particles, the adhesion and coating properties can be greatly improved, and further, the electrode adhesion can be structurally improved when cured by a photocuring reaction. The present invention provides a secondary battery having excellent overall performance.

Description

Binder for Secondary Battery Containing Copolymer of Polyester Acrylate Compound {Binder for Secondary Battery Containing Copolymer of Polyester Acrylate-based Compound}

The present invention relates to a binder for a secondary battery comprising a copolymer of a polyester acrylate compound, by controlling the volume change of the electrode active material generated during repeated charge and discharge of the battery by excellent adhesion and coating properties, and discharge capacity versus charge The present invention relates to a secondary battery binder capable of improving efficiency, particularly cycle characteristics of a battery by improving efficiency, an electrode manufactured using a slurry for electrodes containing the same, and a secondary battery having the electrode.

As technology development and demand for mobile devices increase, the demand for secondary batteries as energy sources is rapidly increasing, and lithium secondary batteries having high energy density and voltage are commercially used in such secondary batteries.

Such lithium secondary batteries generally use graphite as a negative electrode active material, and are repeatedly charged and discharged while repeating a process of intercalating and deintercalating lithium ions of the positive electrode. The theoretical capacity of the battery is different depending on the type of the electrode active material, but as the cycle progresses, the charge and discharge capacity is generally lowered. This phenomenon is the biggest cause of the separation between the electrode active material or between the electrode active material and the current collector due to the volume change of the electrode generated as the charge and discharge of the battery proceeds, the active material does not perform its function. In addition, during the insertion and desorption process, lithium ions inserted into the negative electrode do not escape properly, thereby reducing the active point of the negative electrode. As a result, the charge and discharge capacity and life characteristics of the battery may decrease as the cycle progresses.

In particular, in order to increase the discharge capacity, when using a combination of materials such as silicon, tin, silicon-tin alloy with a high discharge capacity to natural graphite having a theoretical discharge capacity of 372mAh / g, charge and discharge As this progresses, the volume expansion of the material is remarkably increased. As a result, the separation of the negative electrode material from the electrode material occurs, which causes a problem in that the capacity of the battery is drastically reduced when several cycles are performed.

In this regard, Japanese Patent Application Laid-Open No. 1997-321977 discloses a binder containing a fluorine-based resin containing from 0.1 to 20% by weight of an acrylic polymer composed mainly of at least one monomer selected from acrylic esters or methacrylic esters. It is starting. However, the technique is based on the fluorine-based resin, there is a limit in preventing the bonding force between the current collector and the bonding force between the active materials due to the volume change of the silicon-based negative electrode active material. In addition, US Patent No. 5780184 includes a polymer having a hydrophilic group and a hydrophobic group at the same time, the polymer is selected from acrylic homopolymers, copolymers, and terpolymers, unsaturated organic acid copolymers and unsaturated acid anhydride copolymers A technique relating to a binder is disclosed. However, the above technique is a negative electrode binder of an alkaline battery, and the alkaline battery is difficult to be used as it is in a lithium secondary battery due to the difference in the mechanism of action as a primary battery, and is also different in practical applications.

In addition, even by the above techniques, the desired adhesion and coating properties are not obtained, and thus the problem of deterioration of physical properties is not solved.

Accordingly, there is a very high need for a technology capable of controlling the volume expansion of the electrode active material generated during repeated charging and discharging, thereby improving structural stability of the electrode and thereby improving battery performance.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problems of the prior art and the technical problems required from the past.

After extensive research and various experiments, the inventors of the present application use a polyester acrylate monomer having a hydrophilic group and a hydrophobic group at the same time, or a copolymer including an oligomer thereof, as a component of a binder for a secondary battery. In addition, even when the binder particles are uniformly dispersed on the dispersion medium and the slurry for the electrode, the cycle characteristics of the battery are greatly improved because they are not easily detached due to excellent binding strength and coating properties between the active materials or between the active materials and the current collector. It confirmed and completed this invention.

Therefore, the binder for secondary battery manufacture according to the present invention has a hydrophobic group and a hydrophilic group at the same time, a monomer based on an ester structure and an acrylate structure or an oligomer thereof (compound (A)), and a (meth) acrylic acid ester monomer or its Comprising copolymers of one or more monomers or oligomers thereof (compound (B)) selected from the group consisting of oligomers, vinyl monomers or oligomers thereof, conjugated diene monomers or oligomers thereof and nitrile group-containing compounds It consists of.

According to the experimental results carried out by the inventors of the present application, when including a copolymer of the compound (A) and the compound (B) as a binder, it shows that the adhesive and coating properties significantly improved compared to the conventional binder Could. This fact can be confirmed more clearly in the following Examples, Examples, and the like.

Therefore, when the binder composition comprising the copolymer according to the present invention is applied to the electrode mixture and the secondary battery, it is possible to maintain excellent bonding between the active materials and the electrode active material and the current collector, which undergo a volume change during charging and discharging. In the case of preparing a copolymer by photocuring the monomers with each other, since the electrode adhesion is further improved by processing the paste between the active materials and between the active materials and the current collector, battery characteristics such as coating characteristics and cycle characteristics can be improved. .

Here, "oligomer" means a monomer having two or more low-polymerization linear polymers having a viscosity that can be handled in the form of a liquid, and generally a material in which about 2 to 25 monomers are polymerized, for example, a low degree of polymerization Or low viscosity linear polymers, crosslinked polymers and the like.

The compound (A) is a polyester acrylate-based compound, and has a hydrophilic group and a hydrophobic group at the same time, thereby improving the dispersibility in the dispersion medium, so that the binder particles can be evenly distributed between the electrode active material, thereby inter-active material particles And / or improve adhesion between the electrode active material and the current collector, and implement excellent coating properties.

The kind of the compound (A) is not particularly limited as long as it has both a hydrophobic group and a hydrophilic group and is based on an ester structure and an acrylate structure, and representative examples thereof include a polymer of Formula 1 below.

(1)

(One)

Wherein R is lower alkyl having 1 to 10 carbon atoms.

The compound (A) is preferably a multifunctional ester acrylate, ester acrylate (ester acrylate), ester diacrylate (ester diacrylate), ester meta acrylate (ester metaacrylate), ester pentatritriol tree With acrylate (ester pentaerithritol triacrylate), ester pentaerithritol tetraacrylate, ester pentaerithritol pentaacrylate, ester pentaerithritol hexaacrylate It may be one or more selected from the group consisting of.

In the present invention, the compound (B) is selected from the group consisting of a (meth) acrylic acid ester monomer or an oligomer thereof, a vinyl monomer or an oligomer thereof, a conjugated diene monomer or an oligomer thereof and a nitrile group-containing compound. One or more monomers or oligomers thereof.

The acrylic ester monomer is preferably methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n- amyl acrylate, iso amyl acrylate, n One or more selected from the group consisting of hexyl acrylate, 2-ethylhexyl acrylate, and 2-hydroxyethyl acrylate may be used, but is not limited thereto.

The methacrylic acid ester monomer is preferably methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-amyl methacrylate. From the group consisting of methacrylate, isoamyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, allyl methacrylate or mixtures thereof One or more selected may be mentioned, but is not limited thereto.

The vinyl monomer may preferably be at least one selected from the group consisting of styrene, α-methylstyrene, β-methylstyrene, pt -butylstyrene, divinylbenzene, mixtures thereof, and the like.

The conjugated diene monomer is preferably a styrene-butadiene copolymer, an acrylonitrile-butadiene copolymer, a styrene-isoprene copolymer, an acrylate-butadiene rubber, an acrylonitrile-butadiene-styrene rubber, an ethylene-propylene-diene Systemic polymers or polymers in which these polymers are partially hydrogenated, epoxidized, brominated and mixtures thereof may be used, more preferably 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene and 1 It may be one or more selected from the group consisting of, 3-pentadiene.

As the nitrile group-containing compound, for example, succinonitrile, sebaconitrile, fluorinated nitrile, nitrile chloride, and the like can be used, and preferably selected from the group consisting of acrylonitrile, methacrylonitrile or mixtures thereof. It may be one or more.

One or more monomers of the monomers may be used as the binder polymer constituent, and the type and content of the monomers may be appropriately changed according to the properties of the monomers and the required physical properties.

The polyester acrylate compound, which is the compound (A), may be included in an amount of 0.1 to 95 parts by weight, and preferably 1 to 50 parts by weight, based on 100 parts by weight of the binder polymer. When the content of the polyester acrylate-based polymer is less than 0.1 parts by weight, the adhesion and coating properties of the binder may be significantly lowered. On the contrary, when the content of the polyester acrylate polymer is greater than 95 parts by weight, it is difficult to manufacture the binder due to a decrease in stability in the manufacturing process of the binder. .

The content of the compound (B) can be appropriately adjusted within the conventional range known in the art, but preferably 1 to 95 parts by weight based on 100 parts by weight of the binder polymer of the present invention.

In one preferred embodiment, one or more monomers selected from the group consisting of (meth) acrylamide monomers and unsaturated monocarboxylic acid monomers may be further added to the copolymer.

The (meth) acrylamide monomer may preferably be acrylamide, n-methylol acrylamide, n-butoxymethylacrylamide, methacrylamide, or a mixture thereof, and the unsaturated monocarboxylic acid monomer may be Preferably it may be acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, metaconic acid, glutamic acid, tetrahydrophthalic acid, crotonic acid, isocrotonic acid nadic acid, or mixtures thereof, but It is not limited.

Since the polymerization of the binder may be difficult when the added monomer is contained in an excessive amount, preferably 2 to 15 parts by weight based on 100 parts by weight of the binder polymer.

In one preferred example, the glass transition temperature (Tg) of the copolymer particles may be -10 to 30 ℃, gel content may range from 10 to 100%. If the glass transition temperature is less than -10 ° C, the copolymer interferes with the movement of the electrode active material, causing an increase in internal resistance, and if the glass transition temperature exceeds 30 ° C, the flexibility and bonding strength of the binder become weak, which is not preferable.

In addition to the monomer or oligomer components, the binder of the present invention may use a molecular weight regulator and a crosslinking agent as a polymerization additive. In particular, the gel content of the binder particles can be controlled by adjusting the amount of the molecular weight regulator and the crosslinking agent.

As the molecular weight modifier, for example, t-dodecyl mercaptan, n-dodecyl mercaptan, n-octyl mercaptan and the like can be used, and as a crosslinking agent, 1,3-butanediol diacrylate and 1,3-butanediol Dimethacrylate, 1,4-butanediol diacrylate, 1,4-butanediol dimethacrylate, aryl acrylate, aryl methacrylate, trimethylolpropane triacrylate, tetraethylene glycol diacrylate, tetraethylene glycol Dimethacrylate or divinylbenzene may be used, but the present invention is not limited thereto.

The method of polymerizing the monomers according to the present invention is not particularly limited, and may be polymerized by a known polymerization method, for example, by bulk polymerization, suspension polymerization, solution polymerization, emulsion polymerization, photopolymerization, and the like. The polymerization temperature and the polymerization time may be appropriately selected depending on the polymerization method or the kind of polymerization initiator to be used. For example, the polymerization temperature may be about 50 to 200 ° C., and the polymerization time may be 0.5 to 20 hours. Photocuring reaction using a light source is also possible.

In the polymerization process, the monomers or oligomers may be administered at one time to proceed with polymerization, or may be sequentially administered according to the properties and desired physical properties of the monomers or oligomers.

At this time, the acrylate monomer is preferably administered in the second half of the polymerization. Here, the latter half of the polymerization may be, for example, a state in which the polymerization conversion rate is 80 to 90%, preferably in a state of progressing at least 85%.

The polymerization initiator may be used any compound that can cause radical generation, for example, ammonium persulfate, potassium persulfate, sodium persulfate, ammonium peroxide, benzoyl peroxide, butyl hydroperoxide, cumene hydroper Oxide or azo bis butyronitrile, etc. can be used, Among these, a polymerization initiator by a water-soluble or redox reaction is preferable.

The present invention also provides a slurry for electrodes comprising the binder and an electrode active material capable of occluding and releasing lithium.

The electrode active material is a material that plays an important role in determining the capacity of the battery.

Among them, examples of the active material for a positive electrode include a compound substituted with a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or one or more transition metals; Li _{1 + x} Mn _{2 - x} O ₄ (Where x is 0 to 0.33), lithium manganese oxides such as 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 , Cu ₂ V ₂ O ₇ and the like; Chemical Formula LiNi _{1 - x} MxO ₂ Ni-site type lithium nickel oxide represented by (wherein M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3); Formula LiMn _2-x M _x O ₂ , wherein M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 to 0.1, or Li ₂ Mn ₃ MO ₈ , where M = Fe, Co, Lithium manganese composite oxide represented by Ni, Cu, or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with alkaline earth metal ions; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like. However, the present invention is not limited to these.

Examples of the negative electrode active material include carbon and graphite materials such as natural graphite, artificial graphite, expanded graphite, carbon fiber, non-graphitizable carbon, carbon black, carbon nanotube, fullerene, and activated carbon; Metals such as Al, Si, Sn, Ag, Bi, Mg, Zn, In, Ge, Pb, Pd, Pt and Ti which can be alloyed with lithium and compounds containing these elements; Complexes of metals and their compounds and carbon and graphite materials; Lithium-containing nitrides, and the like. Among them, carbon-based active materials, silicon-based active materials, tin-based active materials, and silicon-carbon-based active materials are more preferable, and these may be used alone or in combination of two or more.

The form of the graphite is not particularly limited, and may be amorphous, flat, flake, granular or the like. The average particle diameter of graphite is 0.1-100 micrometers, Preferably it is 1-40 micrometers, More preferably, it is 2-30 micrometers. In addition, a silicon-graphite composite active material or a tin-graphite composite active material may be used by mixing, pulverizing and firing silicon or tin with the graphite. At this time, the size of the silicon or tin particles is 0.1 to 5 ㎛, preferably 0.1 to 2 ㎛, more preferably about 0.1 to 1 ㎛.

The silicon or tin-based negative active material is meant to include silicon (Si) particles, tin (Sn) particles, silicon-tin alloys, their respective alloy particles, composites, and the like. Typical examples of the alloy include, but are not limited to, solid solutions such as aluminum (Al), manganese (Mn), iron (Fe), titanium (Ti), intermetallic compounds, eutectic alloys, and the like. . The composite can be used as a preferred example, a silicone / graphite composite according to the applicant's international patent application WO 2005/011030, the contents of which are incorporated by reference in the context of the present invention.

In addition to the electrode active material and the binder, the electrode slurry according to the present invention may further include other components, such as a dispersion medium, a conductive material, a viscosity regulator, a filler, a coupling agent, an adhesion promoter, or a combination of two or more thereof.

The dispersion medium is not particularly limited, and in particular, the binder according to the present invention may be dispersed in water as well as an organic solvent. It is preferable that it is a liquid at normal temperature and normal pressure which can maintain the shape of a polymer particle when the slurry for battery electrodes of this invention is apply | coated and dried to an electrical power collector. For example, water; Alcohols such as methanol, ethanol, propanol, isopropanol, butanol, isobutanol, s-butanol, t-butanol, pentanol, isopentanol and hexanol; Ketones such as acetone, methyl ethyl ketone, methyl propyl ketone, ethyl propyl ketone, cyclopentanone, cyclohexanone and cycloheptanone; Methyl ethyl ether, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, diisobutyl ether, din-amyl ether, diisoamyl ether, methylpropyl ether, methyl isopropyl ether, methyl butyl ether, Ethers such as ethyl propyl ether, ethyl isobutyl ether, ethyl n-amyl ether, ethyl isoamyl ether and tetrahydrofuran; lactones such as γ-butyrolactone and δ-butyrolactone; lactams such as β-lactams; Cyclic aliphatic compounds such as cyclopentane, cyclohexane and cycloheptane; Aromatic hydrocarbons such as benzene, toluene, o-xylene, m-xylene, p-xylene, ethylbenzene, propylbenzene, isopropylbenzene, butylbenzene, isobutylbenzene, n-amylbenzene; Aliphatic hydrocarbons such as heptane, octane, nonane and decane; Linear and cyclic amides such as dimethylformamide and N-methylpyrrolidone; Esters such as methyl lactate, ethyl lactate, propyl lactate, butyl lactate, and methyl benzoate; Although the liquid substance which comprises the solvent of the electrolyte solution mentioned later is mentioned, It is not limited only to these, You may use it, mixing about 2-5 types of said dispersion mediums.

It is preferable in the process of electrode preparation that a boiling point uses a dispersion medium of 80 degreeC or more, Preferably it is 85 degreeC or more as said dispersion medium.

The conductive material is a component for further improving the conductivity of the electrode active material, and may be added in an amount of 1 to 20 wt% based on the total weight of the electrode mixture. Such a conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery, and examples thereof include graphite such as natural graphite and artificial graphite; Carbon blacks 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 powder, aluminum powder and nickel powder; Conductive whiskeys 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.

The viscosity modifier is a component for adjusting the viscosity of the electrode mixture so that the mixing process of the electrode mixture and the coating process on the current collector thereof can be easily added, up to 30% by weight based on the total weight of the electrode mixture. Examples of such viscosity modifiers include water-soluble polymers such as carboxymethyl cellulose, carboxyethyl cellulose, ethyl cellulose, hydroxymethyl cellulose, hydroxypropyl cellulose, carboxyethyl methyl cellulose, polyethylene oxide, and ethylene glycol. It is not limited only. In some cases, the above-described solvent may play a role as a viscosity modifier, and a solvent such as N-methylpyrrolidone (NMP) may be used in an amount of 0 to 30% by weight based on 100% by weight of the electrode slurry. In case of using it, drying process should be carried out before or after polymerization or curing.

The filler is an auxiliary component that suppresses the expansion of the electrode, and is not particularly limited as long as it is a fibrous material without causing chemical changes in the battery. Examples of the filler include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The coupling agent is an auxiliary component for increasing the adhesion between the electrode active material and the binder, characterized in that it has two or more functional groups, it can be used up to 30% by weight based on the weight of the binder. Such coupling agents include, for example, one functional group reacting with a hydroxyl group or a carboxyl group on the surface of a silicon, tin, or graphite-based active material to form a chemical bond, and the other functional group is chemically bonded through a reaction with a polymer binder. It may be a material forming a. Specific examples of the coupling agent include triethoxysilylpropyl tetrasulfide, mercaptopropyl triethoxysilane, aminopropyl triethoxysilane, and chloropropyl triethoxysilane ( chloropropyl triethoxysilane, vinyl triethoxysilane, methacryloxypropyl triethoxysilane, glycidoxypropyl triethoxysilane, isocyanatopropyl triethoxysilane, cyan Although silane coupling agents, such as atopropyl triethoxysilane, are mentioned, It is not limited only to these.

The adhesion promoter may be added in an amount of 10% by weight or less based on the binder, for example, oxalic acid, adipic acid, Formic acid, acrylic acid derivatives, itaconic acid derivatives, and the like.

The present invention also provides an electrode for secondary batteries in which a slurry including the binder and the electrode active material is coated on a current collector.

The secondary battery electrode can be manufactured by a known method, and is generally manufactured by coating an electrode mixture in which an electrode active material, a binder, and optionally a conductive material, a filler, and the like are mixed on a current collector. For example, the slurry may be prepared by applying a slurry on a current collector such as a metal foil, followed by drying and pressing.

In the electrode according to the present invention, the current collector is a site where electrons move in the electrochemical reaction of the active material, and a negative electrode current collector and a positive electrode current collector exist according to the type of electrode.

The negative electrode collector is generally made to have a thickness of 3 to 500 mu m. Such an anode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and may be formed of a material such as copper, stainless steel, aluminum, nickel, titanium, fired carbon, 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.

The cathode current collector generally has a thickness of 3 to 500 mu m. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, the surface of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel Surface treated with carbon, nickel, titanium, silver or the like can be used.

These current collectors may form fine concavities and convexities on the surface thereof to enhance the bonding strength of the electrode active material, and may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

This invention also provides the manufacturing method of the electrode for secondary batteries comprised by mixing said compound (A) and compound (B) with an electrode active material, apply | coating to an electrical power collector, and then photocuring.

The secondary battery electrode manufactured by the above method is coated with the electrode active material and the like with a reaction material of a photopolymer containing a polyester acrylate compound as a binder, and then polymerized by light, between the electrode active material or between the active material and the current collector By greatly increasing the binding force, despite the large volume change of the negative electrode active material during charge and discharge, the interface change between the active materials is small, the increase in resistance is small and not easily detached, thereby providing a very good charge and discharge cycle characteristics. Moreover, since the polymerization reaction is induced by light irradiation, the process can be carried out within a short time under severe conditions.

Since a reactant such as a polyester acrylate compound forming such a photopolymer is a substance which may cause a chain extension reaction, a crosslinking reaction, or the like by photopolymerization, the photocuring reaction in the present invention may be carried out between the active materials and each other by solidification of the materials. / Or means a reaction that can cause a bonding force with the current collector, it is a concept that includes both polymerization, crosslinking, and the like.

In the case of photopolymerization according to the above method, a photoinitiator may be further included as a catalyst. As photoinitiators, radical photoinitiators that generate radicals and cationic photoinitiators that generate cations may be used. Examples of such radical photoinitiators include dialkoxyacetophenone, benzilketal, and hydroxyalkylphenylketones. hydroxyalkylphenyl ketone, benzoyl oxime ester, amino ketone and the like, but are not limited thereto. Onium salts may be used as cationic photoinitiators, and typical oni salts include dialkyliodonium salts and triarylsulfonium salts. It is not limited only. Specific examples of the photoinitiator include mixed triaryl sulfonium hexafluoroantimonate salts, 1-hydroxy cyclohexyl phenyl ketone and benzophenone ( benzophenone), and the like.

The photoinitiator may be used alone or a mixture of various initiators may be used, and a photosensitizer may be further used to further increase efficiency. Examples of the photosensitizer include thioxanthone and amines, but are not limited thereto.

Examples of the light source used to decompose the photoinitiator include ultraviolet rays, visible rays, electron beams, X-rays, gamma rays, lasers, and the like.

The present invention also provides a lithium secondary battery comprising the electrode. The lithium secondary battery has a structure in which a lithium salt-containing non-aqueous electrolyte is impregnated into an electrode assembly having a separator interposed between a positive electrode and a negative electrode.

When the binder according to the present invention is used only for the negative electrode or the positive electrode, a general binder known in the art may be used for the remaining electrodes. Examples of such binders include polyvinylidene fluoride, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene -Propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers and the like can be used.

The separator is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally from 0.01 to 10 ㎛ ㎛, thickness is generally 5 ~ 300 ㎛. As such a separator, for example, olefin polymers such as chemical resistance and hydrophobic polypropylene; Sheets or non-woven fabrics made of glass fibers or polyethylene are used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

A lithium salt containing non-aqueous electrolyte consists of a non-aqueous electrolyte solution and a lithium salt. As the non-aqueous electrolyte, a non-aqueous organic solvent, a solid electrolyte, an inorganic solid electrolyte, and the like are used.

As the non-aqueous organic solvent, for example, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butylo lactone, 1,2- Dimethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolon, formamide, dimethylformamide, dioxorone, acetonitrile, nitromethane , Methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxorone derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative Aprotic organic solvents such as ether, methyl pyroionate and ethyl propionate can be used.

Examples of the organic solid electrolyte include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyedgetion lysine, polyester sulfides, polyvinyl alcohols, polyvinylidene fluorides, Polymers containing ionic dissociating groups and the like can be used. As the inorganic solid electrolyte, for example, 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, sulfates, and the like of Li, such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS _2, 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, sulfates and the like of Li, such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ , and the like, may 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, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide have.

In addition, for the purpose of improving charge / discharge characteristics, flame retardancy, etc., the non-aqueous electrolyte solution includes, for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, and hexaphosphate triamide. Nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxy ethanol, aluminum trichloride, etc. It may be. In some cases, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further added to impart nonflammability, or a carbon dioxide gas may be further added to improve high-temperature storage characteristics.

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

Example 1

1-1. Preparation of Binder Composition

250 g of ion-exchanged water was administered inside the reactor and the temperature was raised to 75 ° C. When the temperature of ion-exchanged water reached 75 degreeC, 25 g of butylacrylates, 15 g of styrene, 10 g of polyester acrylate oligomers, 0.25 g of allyl methacrylate, and 1 g of sodium lauryl sulfate were administered. 0.6 g of potassium persulfate was dissolved in 25 g of ion-exchanged water while maintaining the temperature of the reactor at 75 ° C., and then the reaction was allowed to proceed for 4 hours. Then, a binder composition was prepared by adjusting the pH to 7 using potassium hydroxide in the prepared polymer.

1-2. Electrode active material Slurry  Produce

Using water as a dispersion medium, 85 g of the silicon graphite composite active material, 10 g of the binder composition prepared in Example 1-1, and 5 g of carboxymethyl cellulose as a water-soluble polymer were mixed with a thickener, and the total solid content was 30%. A negative electrode active material slurry was prepared.

The slurry for the positive electrode was prepared by using NMP (N-methyl-2-pyrrolidone) as a dispersion medium, and mixing 94 g of an active material LiCoO ₂ , 1.0 g of a conductive polymer, and 5.0 g of a PVDF binder to obtain a solid content of 45%.

1-3. Preparation of the electrode

The negative electrode active material slurry and the positive electrode active material slurry prepared in Example 1-2 were coated with a doctor blade to a copper foil and a positive electrode to aluminum foil at a thickness of 200 μm, respectively, and then placed in a dry oven at 90 ° C. The electrode was prepared by drying for 20 minutes and rolling to an appropriate thickness.

1-4. Fabrication of Lithium Secondary Battery

A coin-type battery was manufactured by interposing a separator made of a polyolefin microporous membrane between the negative electrode and the positive electrode prepared in Example 1-3. Thereafter, using an EC (Ethyl Carbonate): EMC (Ethyl Methyl Carbonate) = 1: 2 (volume ratio) mixed solvent, the electrolyte solution in which the LiPF ₆ electrolyte was dissolved at a concentration of 1 mol / liter was administered.

[Example 2]

A lithium secondary battery was manufactured in the same manner as in Example 1, except that 10 g of polyester diacrylate oligomer was administered instead of 10 g of polyester acrylate oligomer.

Example 3

A lithium secondary battery was manufactured in the same manner as in Example 1, except that butyl acrylate and styrene were not used and 10 g of polyester acrylate monomer and 40 g of 2-hydroxyethyl acrylate were administered.

Example 4

A lithium secondary battery was manufactured in the same manner as in Example 1, except that butyl acrylate and styrene were not used and 10 g of polyester diacrylate oligomer and 40 g of 2-hydroxyethyl acrylate were administered.

Example 5

5-1. Preparation of the electrode

As a negative electrode active material, 85 g of a silicon graphite composite active material, an oligomer of polyester acrylate, and 5 g of hydroxy ethyl acrylate oligomer were mixed to prepare a negative electrode mixture, which was 200 μm thick on copper foil using a doctor blade. After the coating, a metal halide lamp was used to supply UV at an intensity of 5 J / cm ² and coated at a rate of 0.5 m / min to prepare a negative electrode.

A positive electrode mixture was prepared by mixing 94 g of LiCoO ₂ as a positive electrode active material, polyvinylidene fluoride (PVdF) as a binder, and 3% carbon black powder as a conductive material. Added. The mixture was stirred for about 30 minutes to prepare a slurry for the positive electrode, which was applied to an aluminum foil at a thickness of 200 μm, placed in a dry oven at 90 ° C., dried for 20 minutes, and rolled to an appropriate thickness to prepare a positive electrode.

5-2. Fabrication of Lithium Secondary Battery

A coin-type battery was manufactured by interposing a separator made of a polyolefin microporous membrane between the negative electrode and the positive electrode prepared in Example 5-1. Thereafter, using an EC (Ethyl Carbonate): EMC (Ethyl Methyl Carbonate) = 1: 2 (volume ratio) mixed solvent, the electrolyte solution in which the LiPF ₆ electrolyte was dissolved at a concentration of 1 mol / liter was administered.

[Example 6]

A lithium secondary battery was manufactured in the same manner as in Example 5, except that 10 g of polyester diacrylate oligomer was administered to the negative electrode mixture instead of 10 g of polyester acrylate oligomer.

Example 7

A lithium secondary battery was prepared in the same manner as in Example 5, except that 20 g of NMP (n-methyl pyrrolidone) was administered to the negative electrode mixture, and thus a heat drying process was performed.

Example 8

20 g of N-methyl pyrrolidone (NMP) was administered to the negative electrode mixture, followed by a heat drying step, except that 10 g of polyester diacrylate oligomer was administered instead of 10 g of polyester acrylate oligomer. A lithium secondary battery was manufactured in the same manner as in Example 5.

Comparative Example 1

A lithium secondary battery was manufactured in the same manner as in Example 1, except that no polyester acrylate oligomer was used.

Comparative Example 2

85 g of a silicon graphite composite active material and 15 g of PVdF (polyvinylidene fluoride) as a binder were dispersed and dispersed by using NMP (N-methyl-2-pyrrolidone) as a dispersion medium to prepare a negative electrode using an anode active material slurry having a solid content of about 45%. Except that, a lithium secondary battery was prepared in the same manner as in Example 1.

Experimental Example 1 Evaluation of Characteristics of Binder and Lithium Secondary Battery Using the Same

In order to evaluate the properties of the binder prepared according to the present invention, for example, adhesion and coating properties, and the properties of the lithium secondary battery using the binder composition, the following experiment was performed.

As a sample, a binder prepared in Examples 1 to 8, an electrode using the same, and a lithium secondary battery provided with the electrode were used, and the binder composition prepared in Comparative Examples 1 and 2 and the binder of Comparative Examples 1 and 2 were used as a control. Electrodes of Comparative Examples 1 and 2 and a lithium secondary battery provided with the same were used.

1-1. Adhesion Evaluation

In order to measure the adhesive force between the electrode active material and the current collector, the surface of the prepared electrode was cut to a fixed size and fixed to a slide glass, and then the current collector was peeled off. Peel strength was measured. Evaluation was made as an average value by measuring 5 or more peeling strengths. The experimental results are shown in Table 1 below.

1-2. Coating property evaluation

In order to evaluate the coating properties, the solid content was increased from the existing 30% to 40% to prepare a slurry, and likewise, the applied state was applied to the current collector with a thickness of 200 μm to evaluate the applied state as O and X. The experimental results are shown in Table 1 below (O: when the slurry completely applied the current collector, X: when an uncoated current collector surface appeared).

1-3. Battery performance evaluation

In order to evaluate battery characteristics, the batteries were repeatedly charged and discharged at 3 cycles and 30 cycles by 0.1 C constant current / constant voltage method, and their initial capacity, initial efficiency, capacity after 3 cycles, and capacity after 30 cycles were compared, respectively. Evaluation was made into the average value after evaluating five or more coin type batteries about the same binder composition. These results are shown in Table 1 below.

TABLE 1

As shown in Table 1, the binder of Examples 1 to 8 prepared using the copolymer according to the present invention is significantly improved compared to Comparative Example 1 to which a conventional SBR binder is applied or Comparative Example 2 to which a conventional PVdF binder is applied. It can be seen that the adhesion and coating properties.

Moreover, the adhesion and coating properties were further improved in Examples 3 to 8, which copolymerized or photocured polyester acrylate and hydroxyethyl acrylate, whereby the hydrophilic groups of the polyester acrylate were It can be assumed that it contributes greatly to showing an even distribution.

In particular, when the photocuring (Examples 5 and 6) shows the best results, this is due to the structure that the binder contributes to the electrode adhesion. That is, in a general polymerization reaction, the binder is in a point contact with the active material to exert adhesion between the active material and the active material and the current collector, whereas curing between the active material and the polyester acrylate polymer when preparing the electrode by photocuring Since the electrode itself is hardly formed due to the reaction, it is presumed that an extremely high electrode adhesion force appears.

In addition, as a result of evaluating the performance of the lithium secondary battery, the lithium secondary batteries of Examples 1 to 8 were compared with Comparative Example 1 and in terms of the initial capacity, initial efficiency, capacity after 3 cycles, and capacity after 30 cycles of the battery. It can be seen that the performance is significantly improved compared to the two batteries. In particular, the batteries prepared by the photocuring reactions of Examples 5 to 8 exhibit very excellent battery characteristics, and by using a binder that gives excellent electrode adhesion and coating properties, even if charge and discharge are repeated, between the active materials and the active material and the collection Since structural stability between all is ensured, it is guessed that it is because the performance of a battery is maintained stably.

As described above, the binder of the copolymer comprising a polyester acrylate oligomer having both a hydrophobic group and a hydrophilic group according to the present invention greatly improves coating properties and adhesion by imparting affinity between the dispersion medium and the binder particles. In the case of curing by the photocuring reaction, since the electrode adhesive force can be structurally improved, a secondary battery having excellent overall performance such as charge and discharge capacity and cycle characteristics can be manufactured.

Those skilled in the art to which the present invention pertains will be able to perform various applications and modifications within the scope of the present invention based on the above contents.

Claims (13)

Monomers or oligomers thereof (compound (A)) and (meth) acrylic acid ester monomers or oligomers thereof, vinyl monomers or oligomers thereof, conjugated dienes which have both hydrophobic and hydrophilic groups and are based on ester and acrylate structures It is composed of one or more copolymers (compound (B)) selected from the group consisting of a monomer or an oligomer and a nitrile group-containing compound thereof, The compound (A) is a multifunctional polyester acrylate, ester acrylate, ester diacrylate, ester meta acrylate, ester pentaerytriol triacrylate, ester pentaerytriol tetraacrylate, ester pentaetitri One or more selected from the group consisting of all pentaacrylate, ester pentaethtriol hexaacrylate; The (meth) acrylic acid ester monomer is methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n- amyl acrylate, iso amyl acrylate, n- Hexyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate With acrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate and allyl methacrylate A secondary battery binder, characterized in that one or more selected from the group consisting of. delete delete The binder of claim 1, wherein the vinyl monomer is one or more selected from the group consisting of styrene, α-methylstyrene, β-methylstyrene, p-t-butylstyrene, and divinylbenzene. The method of claim 1, wherein the conjugated diene monomer is one or more selected from the group consisting of 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene and 1,3-pentadiene A secondary battery binder. The secondary battery binder according to claim 1, wherein the nitrile group-containing compound is one or more selected from the group consisting of acrylonitrile and methacrylonitrile. According to claim 1, wherein the compound A is a secondary battery binder, characterized in that contained in 0.1 to 95 parts by weight with respect to 100 parts by weight of the binder polymer. The secondary battery of claim 1, wherein the copolymer further comprises one or more monomers or oligomers thereof selected from the group consisting of (meth) acrylamide monomers and unsaturated monocarboxylic acid monomers. bookbinder. The method according to claim 8, wherein the (meth) acrylamide monomer or oligomer thereof is one or more selected from the group consisting of acrylamide, n-methylolacrylamide, n-butoxymethylacrylamide and methacrylamide The unsaturated monocarboxylic acid monomer is a group consisting of acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, metaconic acid, glutamic acid, tetrahydrophthalic acid, crotonic acid, isocrotonic acid and nadic acid. The secondary battery binder, characterized in that one or more selected from. (a) a binder according to any one of claims 1 and 4 to 9; And (b) an electrode active material capable of occluding and releasing lithium Slurry for electrodes comprising a. The electrode for secondary batteries in which the slurry of Claim 10 is apply | coated to the electrical power collector. The method of claim 1, wherein the compound (A) and the compound (B) according to claim 1 are mixed with an electrode active material and coated on a current collector, followed by photocuring to produce a secondary battery electrode. A secondary battery comprising a positive electrode, a negative electrode, a separator and an electrolyte interposed between the positive electrode and the negative electrode, wherein the positive electrode, the negative electrode, or both electrodes are the electrode of claim 12.