KR100993129B1 - Binder for Secondary Battery with Improved Thermal Stability - Google Patents

Abstract

The present invention provides an electrode prepared by using a binder for a secondary battery comprising an antioxidant in a binder polymer and a slurry for an electrode containing the same, and a secondary battery having the electrode.

When the binder of the present invention does not decompose the binder component even when exposed to high temperature, it is possible to increase the mechanical stability, this effect is further improved when the binder composition contains a monomer having excellent heat resistance, the drying process of the electrode, The performance of the binder can be stably maintained during battery manufacturing and charging / discharging.

Description

Binder for Secondary Battery with Improved Thermal Stability}

The present invention relates to an electrode prepared using a binder for secondary battery production comprising an antioxidant in a binder polymer and 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 lithium transition metal oxides as positive electrode active materials and graphite-based materials as negative electrode active materials.

The negative electrode made of graphite-based material has a disadvantage in that the theoretical maximum capacity is 372 mAh / g (844 mAh / cc), which limits the capacity increase. In addition, although lithium metal, which has been examined as a negative electrode material, has a very high energy density and can realize a high capacity, there are problems of safety due to dendrite growth and short cycle life during repeated charging and discharging. In addition, attempts have been made to use carbon nanotubes as negative electrode active materials, but problems such as low productivity, high price, and low initial efficiency of 50% or less have been pointed out.

As another cathode material, it has been known that silicon, tin, or alloys thereof can reversibly occlude and release a large amount of lithium through a compound formation reaction with lithium. Is going on. For example, silicon is promising as a high capacity cathode material because the theoretical maximum capacity is about 4020 mAh / g (9800 mAh / cc, specific gravity 2.23), which is much larger than graphite-based materials. However, the negative electrode material has a disadvantage that the volume change during charge and discharge is very large.

Meanwhile, in the lithium secondary battery, charging and discharging proceed while repeating a process of intercalation and deintercalation of lithium ions of a positive electrode. When such charge and discharge are repeated, the theoretical capacity of the battery differs depending on the type of electrode active material, but the charge and discharge capacity generally decreases as the cycle progresses.

This is because the electrode active material or the electrode active material and the current collector are detached due to the volume change of the electrode as the charge and discharge are repeated, thereby preventing the electrode active material from functioning. In addition, since the lithium ions inserted into the negative electrode do not move properly during the insertion and desorption of lithium ions, the charge / discharge capacity and the lifespan characteristics of the battery may be reduced.

This problem becomes more serious when the function of the binder is impaired by exposing the electrode to high temperature during drying of the electrode.

In this regard, Japanese Patent No. 3721727 mixes (meth) acrylic acid esters, conjugated dienes, aromatic vinyl groups, and ethylenically unsaturated carboxylic acid monomers in a predetermined ratio in order to secure current collecting properties of electrode active materials. As one copolymer, a binder containing an aqueous dispersion of a copolymer having a glass transition point of -15 to 150 ° C is disclosed. In addition, Korean Patent Application Publication No. 2004-104400 discloses aromatic vinyl monomers, conjugated diene monomers, (meth) acrylic acid ester monomers, nitrile monomers, and unsaturated carboxylic acid monomers in order to improve the dispersion characteristics of the binder polymer slurry. Disclosed is a technique for a binder comprising a binder polymer made of at least one monomer selected from the group consisting of and a dispersant chemically bonded to the surface of the binder polymer.

However, the above techniques are techniques for securing a bonding force between electrode active materials or between an electrode active material and a current collector, including a predetermined binder polymer, and even when the above techniques are used, deterioration of physical properties that may occur when a binder is exposed to high temperature Does not solve the problem.

Therefore, there is a great need for a technology that can fundamentally solve the problem of deterioration of physical properties when the binder is exposed to high temperatures during the electrode manufacturing process (particularly, during the drying process), the battery manufacturing process, and the battery charging and discharging. .

The present invention aims to solve the problems of the prior art as described above and the technical problems that have been requested from the past.

After extensive research and various experiments, the inventors of the present application have excellent thermal stability when using a binder comprising a binder polymer and an antioxidant, and thus may be caused by exposure of the binder to high temperature during drying of the electrode. It was confirmed that the cycle characteristics of the battery were greatly improved by preventing the deterioration of physical properties, and by being excellent in the bonding strength between the active materials or between the active materials and the current collector and not being easily detached, thus completing the present invention.

Therefore, the binder for secondary battery manufacture which concerns on this invention is comprised by including a binder polymer and antioxidant.

As described above, the performance of the binder is degraded by exposing the electrode to high temperatures in the process of heating and drying the electrode, manufacturing the battery, and charging and discharging, and thus free radicals unstable by the mechanical shear force generated in the process This is because the double bond of the binder polymer is broken by these free radicals.

Therefore, since the binder according to the present invention contains an antioxidant and prevents a decrease in physical properties even when exposed to high temperature, it is possible to suppress a sudden volume change of the electrode active material during charging and discharging, so that the secondary battery including the binder is charged. The discharge capacity and cycle characteristics are very excellent. This effect is further enhanced when a polymer having excellent heat resistance is used as the binder polymer, as will be described later.

The antioxidants are largely divided into primary antioxidants and secondary antioxidants, which differ in their mechanism of action. The primary antioxidant acts as a hydrogen donor or radical scavenger to stabilize the unstable radicals produced by oxidation in the electrode mixture including the binder into a stable form. On the other hand, the secondary antioxidant is a hydrogen peroxide decomposer in order to prevent the unstable free radicals are combined with oxygen to form a hydrogen peroxide, and the hydrogen peroxide produced by the oxidation process again to another kind of free radicals hydroperoxide decomposer).

The antioxidant according to the present invention, preferably, a phenolic antioxidant that is a primary antioxidant, a phosphite antioxidant that is a secondary antioxidant, or both may be used.

Preferred examples of the phenol-based antioxidants are N, N'-di-2-butyl-1,4-phenylenediamine, 2,6-di-tert-butyl-4-methylphenol, 2,4-dimethyl-6-tert -butylphenol, 2,6-di-tert-butyl phenol, 2,2'-Ethylidenebis [4,6-di-t-butylphenol], 2,2'-Methylenebis (6-t-butyl-4-methylphenol), 4,4'-Butylidenebis (2-t-buty-5-methyl phenol), Polymeric sterically hindered phenol, 4,4'-Thiobis (2-t-butyl-5-methylphenol), Tetrakis [methylene-3 (3, 5-di-t-butyl-4-hydroxyphenyl) propionate] methane, Octadecyl 3- (3 ', 5'-di-t-butyl-4'-hydroxyphenyl) propionate, and the like; Preferred examples include, but are not limited to, phenyl phospite, Bis (2,4-di-t-butylphenyl) pentaerythritol diphosphite, or Tris (2,4-di-t-butylphenyl) phosphate. .

The antioxidant may be added in an amount of preferably 0.1 to 30 parts by weight based on 100 parts by weight of the binder polymer. If the amount of the antioxidant is too small, the effect of the addition is not obtained, on the contrary, if too much, the excess electrolyte due to high affinity with the electrolyte is absorbed and swelled, which is not preferable because it may cause detachment of the electrode from the current collector. .

Such an antioxidant may be added during the preparation of the binder polymer, but may be added after the preparation of the binder polymer because it may affect the polymerization reaction of the polymer.

On the other hand, the binder polymer is not particularly limited as long as it is a polymer that can be used as a binder for secondary batteries, and known materials may be used as it is.

In one preferred embodiment, the binder polymer is at least one monomer (a) selected from the group consisting of (meth) acrylic acid ester monomers, conjugated diene monomers and nitrile group-containing compounds and an aromatic group-containing vinyl monomer having excellent heat resistance ( may be a copolymer of b).

The (meth) acrylic acid ester monomer is preferably methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-amyl acrylate, isoamyl acryl. One or more selected from the group consisting of latex, n-hexyl acrylate, 2-ethylhexyl acrylate, hydroxyethyl methacrylate and hydroxypropyl methacrylate may be used, but is not limited thereto.

The conjugated diene monomer is not particularly limited, and for example, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, styrene-isoprene copolymer, acrylate-butadiene rubber, acrylonitrile-butadiene-styrene rubber, Ethylene-propylene-diene-based polymers or polymers in which these polymers are partially hydrogenated, epoxidized, brominated and mixtures thereof can be used, preferably 1,3-butadiene, isoprene, 2,3-dimethyl-1,3 It may be one or more selected from the group consisting of -butadiene and 1,3-pentadiene.

The nitrile group-containing compound may be, for example, succinonitrile, sebaconitrile, fluorinated nitrile, nitrile chloride, or the like, and preferably at least one selected from the group consisting of acrylonitrile and methacrylonitrile. have.

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 vinyl monomer (b) is not particularly limited as long as it contains an aromatic group having excellent heat resistance. For example, the vinyl monomer (b) may have a structure in which another chemical structure is introduced into the styrene monomer, and preferably, alpha-methylstyrene, pt At least one selected from the group consisting of -butyl styrene, vinyl toluene, and chloro styrene. These monomers have an improved rigidity (rigidity) compared to styrene, so the mobility of the monomer is significantly lowered, the glass transition temperature is higher, so that the heat resistance of the binder can be significantly increased.

Therefore, since the performance of the binder can be stably maintained even at high temperatures, the binding force between the electrode active material particles or between the electrode active material and the current collector can be maintained to suppress a sudden volume change of the electrode active material during charge and discharge, thereby improving overall performance of the battery. Can improve with you.

The vinyl monomer (b) may be included in an amount of 0.1 to 95 parts by weight, preferably 1 to 50 parts by weight, and more preferably 1 to 10 parts by weight, based on 100 parts by weight of the binder polymer. When the content of the vinyl monomer (b) is too small, sufficient heat resistance cannot be exhibited and the strength is weak. On the contrary, when too much, the binder becomes too hard, which may lower the charge / discharge characteristics. It is not preferable because it falls.

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 is preferably acrylamide, n-methylol acrylamide, n-butoxymethylacrylamide or methacrylamide or mixtures thereof, and the unsaturated monocarboxylic acid monomer is preferably 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 is not limited thereto. It doesn't happen.

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

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.

The polymerization of the copolymer may be initiated or promoted by a polymerization initiator. Examples of such polymerization initiators include ammonium peroxide, ammonium persulfate, potassium persulfate, sodium persulfate, benzoyl peroxide, and butyl hydroperoxide. , Cumene hydroperoxide, azo bis butyronitrile, and the like. Preferably, a polymerization initiator by water-soluble or redox reaction may be used.

In addition to the monomer components, the binder polymer may further include a molecular weight regulator and a crosslinking agent as a polymerization additive, and the gel content of the binder particles may be adjusted by controlling the content of the polymerization additive.

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, divinylbenzene, and the like 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, emulsion polymerization, suspension polymerization, dispersion polymerization, seed polymerization, or the like. However, the polymerization method may be selected, and the polymerization temperature and the polymerization time may be appropriately selected depending on the polymerization method, the kind of polymerization initiator to be used, and the like. For example, the polymerization temperature may be about 50 to 200 ° C, and the polymerization time may be May be from 0.5 to 20 hours.

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

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%.

Therefore, the acrylate monomer is located on the surface of the binder, it is possible to improve the dispersibility of the final binder particles due to the long chain of the acrylate monomer. In addition, when the acrylate-based monomer contains a hydrophilic substituent and / or stretchability imparting substituent may further improve the dispersibility of the binder and the durability of the binder may also be increased.

The present invention also provides the binder (A); And an electrode active material (B) capable of occluding and releasing lithium.

The electrode active material (B) 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; Lithium manganese oxides such as Li _{1 + x} Mn _2-x O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO _2, and the like; 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; Ni-site type lithium nickel oxide represented by the formula LiNi _1-x MxO ₂ , 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; Lactone, such as (gamma)-butyrolactone and (delta)-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 adjusting agent may be added up to 30% by weight based on the total weight of the electrode mixture, so as to control the viscosity of the electrode mixture so that the mixing process of the electrode mixture and the coating process on the collector may be easy. Examples of such viscosity modifiers include carboxymethylcellulose, polyvinylidene fluoride and the like, but are not limited thereto. In some cases, the solvent described above can serve as a viscosity modifier.

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; Fiber-like substances 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 is an auxiliary component added to improve adhesion of the active material to the current collector, and may be added in an amount of 10 wt% or less, 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 is 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 with 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 current collector is generally made to a thickness of 3 to 500 ㎛. 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 binding force of the electrode active material, and may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

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.

The lithium salt-containing non-aqueous electrolyte consists of a non-aqueous electrolyte and lithium. 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. 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.

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

225 g of ion-exchanged water was administered inside the reactor and the temperature was raised to 75 ° C. When the temperature of ion-exchange water reached 75 degreeC, 35 g of butylacrylates, 15 g of styrene, 0.25 g of aryl methacrylates, 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. 0.25 g of 2,6-di-tert-butyl phenol was administered as a phenolic antioxidant to the binder composition prepared above.

1-2. Electrode active material Slurry  Produce

90 g of natural graphite using water as a dispersion medium, 5 g of the binder composition prepared in Example 1-1, and 5 g of carboxymethyl cellulose, which is a water-soluble polymer, were mixed with a thickener, and the total solid content was 30% by weight. An active material slurry was prepared.

In the positive electrode active material slurry, NMP (N-methyl-2-pyrrolidone) was used as a dispersion medium, and 94 g of LiCoO ₂ , 1.0 g of conductive polymer, and 5.0 g of PVDF binder were mixed to obtain a solid content of 45 wt%. .

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 at a thickness of 200 μm on the copper foil and the positive electrode on the aluminum foil, respectively, and then placed in a dry oven at 90 ° C. It was dried for 20 minutes and rolled to an appropriate thickness to complete the electrode production.

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 cathode and the anode completed in Example 1-3. Thereafter, an electrolytic solution in which a LiPF ₆ electrolyte was dissolved at a concentration of 1 mol / liter was completed using an EC (Ethyl Carbonate): EMC (Ethyl Methyl Carbonate) = 1: 2 (volume ratio) mixed solvent.

[Example 2]

A lithium secondary battery was manufactured in the same manner as in Example 1, except that 0.25 g of 2,6-di-tert-butyl-4-methyl phenol was administered after binder polymerization.

Example 3

A lithium secondary battery was manufactured in the same manner as in Example 1, except that 0.25 g of 2,4-dimethyl-6-tert-butyl phenol was administered after binder polymerization.

Example 4

A lithium secondary battery was manufactured in the same manner as in Example 1, except that 0.25 g of polymeric sterically hindered phenol was administered after binder polymerization.

Example 5

A lithium secondary battery was manufactured in the same manner as in Example 1, except that 15 g of alpha methyl styrene was used instead of 15 g of styrene.

Example 6

A lithium secondary battery was manufactured in the same manner as in Example 5, except that 0.5 g of 2,6-di-tert-butyl phenol was administered after binder polymerization.

Example 7

A lithium secondary battery was manufactured in the same manner as in Example 2, except that 15 g of alpha methyl styrene was used instead of 15 g of styrene.

Example 8

A lithium secondary battery was manufactured in the same manner as in Example 7, except that 0.5 g of 2,6-di-tert-butyl-4-methyl phenol was administered after binder polymerization.

Example 9

A lithium secondary battery was manufactured in the same manner as in Example 3, except that 15 g of alpha methyl styrene was used instead of 15 g of styrene.

Example 10

A lithium secondary battery was manufactured in the same manner as in Example 9, except that 0.5 g of 2,4-dimethyl-6-tert-butyl phenol was administered after binder polymerization.

Example 11

A lithium secondary battery was manufactured in the same manner as in Example 4, except that 15 g of alpha methyl styrene was used instead of 15 g of styrene.

Example 12

A lithium secondary battery was manufactured in the same manner as in Example 11, except that 0.5 g of polymeric sterically hindered phenol was administered after binder polymerization.

Comparative Example 1

A lithium secondary battery was manufactured in the same manner as in Example 5, except that the phenolic antioxidant was not administered after the binder polymerization.

Experimental Example 1 Measurement of Thermal Stability of Binder

In order to measure the intrinsic physical properties of the binder prepared according to the present invention, the following experiment was performed.

As the binder, each binder composition prepared in Examples 1 to 12 and Comparative Example 1 was dried and used in a gel state.

The thermal stability of the binder was measured by TGA (Thermal gravimetric analysis) to measure the temperature when the mass of the binder gel decreased to 2%, 5% and 10%, respectively, while the temperature was raised to 600 ° C at a heating rate of 20 ° C / min. . The experimental results are shown in Table 1 below.

TABLE 1

상기 표 1에서 보는 바와 같이, 산화방지제를 첨가한 실시예 1 내지 4의 바인더 조성물은 비교예 1의 바인더 조성물에 비해 더 높은 온도에서 동일한 질량 감소율은 나타내므로, 열안정성이 향상되었음을 알 수 있고, 특히, 바인더 중합체에 우수한 내열성의 방향족기 함유 비닐계 단량체를 투여한 실시예 5 내지 12의 바인더는 실시예 1 내지 4 및 비교예 1에 비하여 훨씬 더 높은 온도에서 질량 감소가 일어남으로써 열안정성이 현저히 우수함을 알 수 있다. 또한, 열안정성의 정도는 산화방지제의 종류 및 함량에 따라 차이가 있으며, 2,6-di-tert-butyl-4-methyl phenol를 0.5 g 첨가한 실시예 8의 바인더는 바인더의 질량이 각각 2%, 5% 감소했을 때, 비교예 1의 바인더 보다 대략 110℃ 이상 높은 온도에서 동일한 질량 감소가 일어나므로 열안정성이 가장 우수한 것으로 나타났다.

As shown in Table 1, the binder composition of Examples 1 to 4 to which the antioxidant is added shows the same mass reduction rate at higher temperature than the binder composition of Comparative Example 1, it can be seen that the thermal stability is improved, In particular, the binders of Examples 5 to 12 in which the binder polymer was administered with an excellent heat-resistant aromatic group-containing vinyl monomer were significantly reduced in thermal stability due to mass loss at a much higher temperature than Examples 1 to 4 and Comparative Example 1. It can be seen that excellent. In addition, the degree of thermal stability is different depending on the type and content of the antioxidant, the binder of Example 8 to which 0.5 g of 2,6-di-tert-butyl-4-methyl phenol is added, the mass of the binder is 2 When the% and 5% decrease, the same mass loss occurs at a temperature of about 110 ° C. or more higher than that of the binder of Comparative Example 1, indicating that the thermal stability is the best.

Experimental Example 2 Characterization of Binder and Lithium Secondary Battery Using the Same

Properties of the binders prepared according to the invention, such as adhesion and coating properties; And to evaluate the characteristics of the lithium secondary battery using the binder composition, the following experiment was performed.

As a sample, a binder composition prepared in Examples 1 to 12, an electrode using the same, and a lithium secondary battery provided with the electrode were used, and the binder composition prepared in Comparative Example 1 and a binder of Comparative Example 1 were prepared as a control. An electrode and a lithium secondary battery having the same were used.

2-1. Adhesion Evaluation

In order to measure the adhesion between the electrode active material and the current collector, the surface of the prepared electrode was cut to a certain 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 2 below.

2-2. 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 2 (O: when the slurry completely applied the current collector, X: when an uncoated current collector surface appeared).

2-3. Battery performance evaluation

In order to evaluate the 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 by evaluating five or more coin-type batteries for the same binder composition, and then set the average value. Experimental results are shown in Table 2 below.

TABLE 2

As shown in Table 2, it can be seen that the electrode adhesion of Examples 1 to 12 was significantly improved by more than twice the adhesion of Comparative Example 1, and also in the battery experiments, the initial capacity and efficiency were similar, but three cycles, 30 It can be seen that as the charge / discharge cycle proceeds, the administration of the antioxidant maintains more stable battery performance. As a result, it can be seen that the mechanical thermal stability is ensured during the drying of the electrode, the battery manufacturing process, and the charging / discharging process by administering the antioxidant.

As described above, it is assumed that the antioxidant prevents the generation of radicals due to heat and mechanical properties in the process of applying heat to the electrode to dry, manufacturing the battery, and charging and discharging to maintain the physical properties of the binder. do.

In particular, in the binders of Examples 5 to 12 to which the aromatic group-containing vinyl monomers having excellent heat resistance were added, the battery cycle characteristics were excellent compared to those of Examples 1 to 4 to which only the antioxidant was administered. Was further improved. This is presumably because the mobility of the monomer is significantly lowered as the monomer having improved rigidity compared to styrene, and the glass transition temperature is increased, thereby minimizing the decrease in physical properties of the binder due to the temperature rise.

While the content of the present invention has been described with reference to some specific examples, 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.

As described above, the binder comprising the binder polymer and the antioxidant according to the present invention, the electrode mixture comprising the same, and the lithium secondary battery is very excellent in thermal stability, especially when the binder polymer comprises a heat-resistant monomer Since the binder is not deformed by high temperature and exhibits stable performance, the secondary battery not only improves the adhesive force between the active material on the electrode and the current collector, but also has excellent charge and discharge capacity and cycle characteristics.

Claims (16)

Consisting of a binder polymer and an antioxidant, The binder polymer is a copolymer of at least one monomer (a) selected from the group consisting of a (meth) acrylic acid ester monomer, a conjugated diene monomer and a nitrile group-containing compound and an excellent heat resistance aromatic group-containing vinyl monomer (b). A secondary battery manufacturing binder, characterized in that configured. The binder of claim 1, wherein the antioxidant is at least one selected from the group consisting of phenolic antioxidants and phosphite antioxidants. The method of claim 2, wherein the phenolic antioxidant is N, N'-di-2 butyl-1,4-phenylenediamine, 2,6-di-tert-butyl-4-methylphenol, 2,4-dimethyl-6- tert-butylphenol, 2,6-di-tert-butyl phenol, 2,2'-Ethylidenebis [4,6-di-t-butylphenol], 2,2'-Methylenebis (6-t-butyl-4-methylphenol) , 4,4'-Butylidenebis (2-t-buty-5-methyl phenol), Polymeric sterically hindered phenol, 4,4'-Thiobis (2-t-butyl-5-methylphenol), Tetrakis [methylene-3 (3 , 5-di-t-butyl-4-hydroxyphenyl) propionate] methane and Octadecyl 3- (3 ', 5'-di-t-butyl-4'-hydroxyphenyl) propionate; The phosphite-based antioxidant is at least one member selected from the group consisting of phenyl phospite, Bis (2,4-di-t-butylphenyl) pentaerythritol diphosphite, and Tris (2,4-di-t-butylphenyl) phosphite Binder. The binder of claim 1, wherein the antioxidant is added in an amount of 0.1 to 30 parts by weight per 100 parts by weight of the binder polymer. delete The binder according to claim 1, wherein the monomer (b) is at least one member selected from the group consisting of alpha-methyl styrene, p-t-butyl styrene, vinyl toluene, and chloro styrene. The method of claim 1, wherein the (meth) acrylic acid ester monomer is methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n- amyl acrylate, iso A binder characterized by one or more selected from the group consisting of amyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, hydroxyethyl methacrylate and hydroxypropyl methacrylate. The method of claim 1, wherein the conjugated diene monomer is at least one member selected from the group consisting of 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene and 1,3-pentadiene. Binder. The binder according to claim 1, wherein the nitrile group-containing compound is at least one member selected from the group consisting of acrylonitrile and methacrylonitrile. The binder according to claim 1, wherein at least one monomer selected from the group consisting of (meth) acrylamide monomers and unsaturated monocarboxylic acid monomers is further added to the binder polymer. The method according to claim 10, wherein the (meth) acrylamide monomer is acrylamide, n-methylolacrylamide, n-butoxymethylacrylamide or methacrylamide; The unsaturated monocarboxylic acid monomer is a binder, characterized in that acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, metaconic acid, glutamic acid, tetrahydrophthalic acid, crotonic acid, isocrotonic acid or nadic acid. . 11. The binder according to claim 10, wherein the added monomer is added in the range of 2 to 15 parts by weight per 100 parts by weight of the copolymer. The binder according to claim 1, wherein the binder polymer particles have a glass transition temperature (Tg) of −10 to 30 ° C. and a gel content of 10 to 100%. (a) a binder according to any one of claims 1 to 4 and 6 to 13; And (b) an electrode active material capable of occluding and releasing lithium; Slurry for electrodes comprising a. The electrode in which the slurry of Claim 14 was apply | coated to the electrical power collector. 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 the positive electrode is the electrode of claim 15.