KR20090008085A - Electrolyte assembly with improved thermal stability and secondary battery employed with the same - Google Patents

Abstract

An electrode assembly is provided to prevent the deterioration or oxidation of a polymer compound within an electrode assembly and to ensure excellent durability and cycleability, and good storage and lifetime property at the high temperature. An electrode assembly is manufactured by laminating a plurality of electrodes in a state where a separation film is interposed, and cross-coupling them through heating/pressurization. The coupling of a separation film and electrode is achieved by heating/pressurizing an adhesive layer formed on the separation film and an electrode which are facing each other. The adhesive layer comprises the microcapsules supported with a thermal stabilizer prior to the heating/pressurization. In a heating/pressurizing process, the shell of microcapsule bursts and is flowed out into the adhesive layer.

Description

Electrode assembly with excellent thermal stability and secondary battery comprising same {Electrolyte Assembly with Improved Thermal Stability and Secondary Battery Employed with the Same}

The present invention relates to an electrode assembly having excellent thermal stability and a secondary battery including the same, and more particularly, to an electrode assembly having a structure in which a plurality of electrodes are laminated with a separator interposed therebetween and then bonded to each other by heating / pressurization. Coupling of the electrode and the separator is achieved by heating / pressurizing the adhesive layer formed on the separator and the electrode in a mutually facing state, and the adhesive layer includes a microcapsule supporting a heat stabilizer in a state before heating / pressurization. The present invention relates to an electrode assembly, in which a shell of a microcapsule is ruptured during pressurization, and a supported thermal stabilizer flows out to an adhesive layer, or an aggregate formed by agglomerating the thermal stabilizer by physical bonding.

As the technology development and demand for mobile devices increase, the demand for this secondary battery as an energy source is rapidly increasing. Among such secondary batteries, lithium secondary batteries having high energy density and voltage have been commercialized and widely used. Such lithium secondary batteries generally use lithium transition metal oxides as positive electrode active materials and graphite-based materials as negative electrode active materials.

In the lithium secondary battery, charging and discharging proceed while repeating a process of intercalation and deintercalation of lithium ions of a positive electrode into a negative 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.

As one of the causes, the charge and discharge capacity and the lifespan characteristics of the battery may be reduced because lithium ions inserted into the negative electrode may not move properly during the insertion and desorption of lithium ions. Moreover, the problem that the transition metal in the lithium transition metal oxide which comprises a positive electrode elutes in an electrolyte, and precipitates in a negative electrode is mentioned.

In a specific example, when lithium cobalt oxide is used for the positive electrode, it is known that cobalt ions elute at a high potential of 4.2 V or higher. As a result, the crystal structure of the lithium cobalt oxide is destroyed and the battery capacity is lowered. Therefore, since cobalt itself is a strong oxidizing agent, there is a problem of causing deterioration of the separator. Deterioration of mechanical strength due to such deterioration of the separator causes internal short circuits and battery performance deterioration. In addition, the eluted cobalt ions are precipitated in the cathode to cause dendritic growth, there is a problem that an internal short circuit occurs. Moreover, cobalt precipitated at the negative electrode acts as a catalyst for promoting decomposition of the electrolyte to generate gas inside the cell. This problem is exacerbated when the cell is exposed to high temperatures above 45 ° C.

In this regard, Japanese Patent Application Laid-Open No. 1998-67211 discloses a technique of including an antioxidant in a positive electrode, and Korean Patent Application Laid-Open No. 2002-020699 and Japanese Patent Application Laid-open No. 1998-247517 are disclosed in an electrolyte solution. Techniques for adding oxidative additives or antioxidants are disclosed.

However, when such an antioxidant or the like is included in the electrode or the electrolyte solution, it was confirmed that there is a problem that the battery performance is reduced by causing various side reactions in the battery (see Japanese Patent Application Laid-Open No. 2000-30685).

Therefore, some prior arts disclose a technique of adding an antioxidant to a separator (see Japanese Patent Application Laid-Open No. 2000-204174 and Korean Patent Application Laid-Open No. 2004-0062441). However, according to the above techniques, since an antioxidant is added in a process of manufacturing a melt-extruded separator, a plurality of antioxidants are consumed in a high temperature process of melt extrusion. On the other hand, in the case of coating on the surface of the separator, there is a problem that the rate characteristic is lowered because the mobility of lithium is penetrated into the porous structure of the separator.

U.S. Patent Application Publication No. 2004-166415 also discloses a technique for interposing an oxidative barrier between a separator and an anode. According to the above technique, as an oxidative barrier, a polymer coating layer of halocarbon, metal oxide, etc., such as polypropylene, polyvinylidene fluoride (PVDF), and the like is disclosed, and antioxidants can be added thereto. However, it has been confirmed that the above technique is not able to achieve the desired effect due to the considerable consumption of antioxidants during the heating and pressing process of the electrode and the separator for the preparation of the electrode assembly. In order to solve this problem, it is necessary to add a relatively large amount of antioxidant, in this case, there is a problem that the operating performance of the battery is lowered, the manufacturing cost is increased, and the bonding force between the electrode and the separator is weakened.

Therefore, there is a very high need for a technology capable of exerting a maximum effect in a minimum amount while adding a material for preventing the oxidation or deterioration of the polymer component present in the electrode assembly due to the high temperature.

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.

Specifically, the first object of the present invention is to form an adhesive layer containing a microcapsule carrying a heat stabilizer on the separator, and the shell of the microcapsule is ruptured by heating / pressurizing in a state where the electrode is facing. It is to provide an electrode assembly, characterized in that the heat stabilization flows out to the adhesive layer.

A second object of the present invention is to form an electrode assembly, characterized in that the heat stabilizer is formed by forming an adhesive layer containing the aggregate formed by agglomeration by physical bonding force on the separator, and heating / pressurizing the electrode in a facing state. To provide.

Accordingly, the electrode assembly according to the present invention is an electrode assembly having a structure in which a plurality of electrodes are laminated in a state where a separator is interposed therebetween and then bonded to each other by heating / pressurization. It is achieved by heating / pressing in the state where the electrodes face each other, and the adhesive layer includes a microcapsule carrying a heat stabilizer in a state before heating / pressurizing, and the shell of the microcapsule ruptures during the heating / pressing process. And the supported heat stabilizer flows out into the adhesive layer.

In another preferred embodiment, the heat stabilizer may be included in the adhesive layer in the form of aggregates formed by aggregation by physical bonding.

These thermal stabilizers act to capture unstable free radicals generated when the cell is exposed to high temperatures during charge and discharge. As a result, deterioration such as oxidization or double bonding (polyene) and boiling of the polymer components in the battery such as a binder, an adhesive layer, and a separator by the free radicals, and the deterioration of the battery operation performance can be prevented.

Therefore, by preventing the weakening of the mechanical strength of the separator or the like or the lowering of the adhesive strength of the binder component or the adhesive layer, the durability of the battery can be improved, and the deterioration of the charge / discharge capacity can be prevented, in particular, the cycle characteristics and the storage and life characteristics at high temperatures. This is improved. In addition, unlike the case in which the heat stabilizer is included in the electrolyte or the separator, waste of the heat stabilizer may be minimized during the heating and pressurization process for manufacturing the electrode assembly, and thus, there is an advantage of high operational reliability and efficiency.

In the first embodiment of the present invention, the heat stabilizer is included in the adhesive layer on the surface of the separator in a state of being supported in a microcapsule, and flows out to the adhesive layer while the shell ruptures in the heating / pressing process of the electrode assembly.

As described above, when the heat stabilizer is included in the membrane itself, which is a polymer material, a considerable amount thereof is consumed at a high temperature of the melt extrusion process for manufacturing the separator, and as a result, there is a problem in that the final cell does not have a desired effect. there was. In addition, when the heat stabilizer is directly included in the adhesive layer of the separator, a significant amount of the heat stabilizer is also consumed under high temperature conditions in the process of heating / pressurizing the separator and the electrode. On the other hand, when the heat stabilizer is added to the adhesive layer of the separator in a state in which the heat stabilizer is supported in the microcapsules, a process of destroying the shell of the microcapsules occurs in the heating / pressing process, thus reducing unnecessary consumption of the heat stabilizer. It can be minimized.

The shell of the microcapsules may be melted or decomposed at a temperature of 70 to 100 ° C. or broken under a pressure of 3 to 10 kg / cm ² so that the shell of the microcapsules may be ruptured in the heating / pressurization process of the electrode assembly. The shell of the microcapsules may themselves be inert in the cell's internal environment or decompose at this temperature. On the other hand, the conditions in which the shell itself melts or ruptures can be appropriately controlled by the physical properties or molecular size of the material itself.

The material of the shell is not particularly limited as long as it is insoluble in the electrolyte and exhibits inertness in the internal environment of the battery, and may be melted or ruptured under the conditions described above, and may be various kinds of polymers. For example, one or more selected from the group consisting of polyolefins such as polyethylene and polypropylene, polyvinyl alcohol (PVA), polyvinyl chloride (PVC), and combinations thereof, but is not limited thereto.

The method for producing the microcapsules is not particularly limited as long as it is a technique for preparing a capsule on which a heat stabilizer is loaded as in the present invention. For example, the phase change material may be prepared by dispersing in an aqueous solution through an emulsification process and polymerizing a polymer on the surface of its oil phase. In this case, as the polymerization method, interfacial polymerization, in-situ polymerization, coacervation method, or the like may be used.

The size of the microcapsule preferably has a particle size of approximately 1 to 50 ㎛. The larger the size of the microcapsules, the easier it may be to rupture due to pressure, but in terms of uniform distribution of the heat stabilizer, a small particle size having a large surface area per unit weight is preferable. However, capsule particles of too small a particle size may be difficult to prepare themselves and may not be destroyed in the heating / pressing process, and thus may be appropriately determined in the above range.

In a second embodiment of the present invention, the heat stabilizer may be included in the adhesive layer in the form of aggregates formed by aggregation by physical bonding. In this case, it is possible to reduce the consumption in the heating / pressing process compared to the case where the heat stabilizer is widely distributed in the adhesive layer in units of compounds.

In one preferred example, the aggregate may be a mixture of thermal stabilizers in the form of primary particles having a relatively small particle diameter are aggregated by mutual physical bonding to form secondary particles. Such aggregates may be widely dispersed in the adhesive layer while being primary granulated in the heating / pressing process.

In another preferred example, the aggregate may be formed by combining a heat stabilizer having a relatively small particle diameter by a predetermined binder. Such a binder may be the same as or different from the adhesive component of the separator adhesive layer.

As a result, the heat stabilizer included in the membrane adhesive layer in the form of agglomerates can minimize the consumption due to the high heat during the heating / pressurization process due to the relatively small surface area, and the agglomeration is loosened or the small particle size By disintegrating the particles, it is possible to maximize the amount of heat stabilizer effective in the final electrode assembly.

The heat stabilizer is largely classified into a primary heat stabilizer and a secondary heat stabilizer, and these have a different mechanism of action. The primary heat stabilizer acts as a hydrogen donor or a radical scavenger to stabilize the unstable radicals produced by oxidation in the cell into a stable form. On the other hand, the secondary heat stabilizer 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. plays the role of a hydroperoxide decomposer.

The heat stabilizer according to the present invention, for example, phenolic compound, cyclic amine compound, semicarbazide (Semicarbazide), amine compound, nitro compound, phosphite compound, unsaturated hydrocarbon compound And it may be selected from the group consisting of thio compounds. More preferably, phenolic heat stabilizers as primary heat stabilizers, phosphite heat stabilizers as secondary heat stabilizers, or both may be used.

Preferred examples of the phenol-based heat stabilizer are 2,2-di (4'-hydroxyphenyl) propane, hydroquinone, p-methoxyphenol, t-butylhydroxy-anisole, n-octadecyl-3- (4-hydroxy-3,5- di-t-butyl-phenyl) propionate, n-octadecyl-3- (4-hydroxy-3,5-di-t-butylphenyl) propionate, pentaerythritol tetrakis- [3- (3,5-di-t-butyl- 4-hydroxyphenyl) propionate], 1,2-propylene glycol bis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], stearamido N, N-bis- [ethylene 3- (3, 5-di-t-butyl-4-hydroxyphenyl) propionate], 2,5-di-t-butylhydroquinone, 4,4'-butylidenebis (3-methyl-6-t-butylphenol), 3,5-di-t -butyl-4-hydroxytoluene, 2,2'-methylene-bis (4-ethyl-6-t-butylphenol), triethyleneglycol-bis- [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate ], pentaerythritoltetrakis [3- (3,5-di-t-butyl-4-hydroxy-phenyl) propionate], 2,6-di-t-butyl-4-methylphenol, t-butylcatechol, 4,4-thiobis ( 6-t-butyl-m-cresol), tocopherol, and nordihydroguaiaretic acid, but are not limited thereto. Particularly preferred n-octadecyl-3- (4-hydroxy-3,5-di-t-butylphenyl) propionate may be used among the phenolic heat stabilizers.

Examples of the cyclic amine thermal stabilizer include phenylnaphthylamine, N, N'-diphenyl-p-phenylenediamine, and 4,4'-bis (dimethylbenzyl) diphenylamine. Examples of the semicarbazide thermal stabilizer include: Hydrofluoride, hydrochloride, nitrate, acid sulfate, sulfate, chlorate, formate, acid oxalate, acid maleate, and maleate of semicarbazide; derivatives of semicarbazide such as 1-acetylsemicarbazide, 1-chloroacetylsemicarbazide, 1-dichloroacetyl-semicarbazide, 1-benzoylsemicarbazide, and semicarbazone.

The amine heat stabilizer may be, for example, carbohydrazide, thiosemicarbazide, thiosemicarbazone derivative, thiocarbazide, and thiocarbazide derivative, and the like, and the nitro-based stabilizer may include nitroanisole, N-nitrosodiphenylamine, nitroaniline, and N-nitrosophenylhydroxylamine aluminum salt. .

The unsaturated hydrocarbon-based heat stabilizer is not particularly limited, and may be, for example, styrene, 1,3-hexadiene, and methyl styrene, and the thio-based heat stabilizer may be dilauryl thiodipropionate, dimyristylthiopropionate, distearylthiodipropionate, dodecylmercaptan, 1,3 -diphenyl-2-thiourea, etc. are mentioned.

The phosphite thermal stabilizer is, for example, triphenyl phosphite, diphenylisodecyl phosphite, phenyldiisodecyl phosphite, 4,4'-butylidene-bis (3-methyl-6-t-butylphenyl-di-tri-decyl) phosphate, cyclic neopentanetetrayl-bis (octa-decyl) phosphite, tris (nonylphenyl) phosphite, and tris (dinonyl) phosphite. dioctadecyl-3,5-di-t-butyl-4-hydroxybenzylphosphonate, di-n-octadecyl-1- (3,5-di-t-butyl-4-hydroxy-phenyl) -ethanephosphonate, and the like. It is not limited only.

The total content of the heat stabilizer may be included in an amount of preferably 0.01 to 1% by weight based on the total weight of the membrane adhesive layer. If the content of the thermal stabilizer is too small, the effect of the addition may not be obtained. On the contrary, if the content of the thermal stabilizer is too high, an excessive amount of the electrolyte may be absorbed and swelled due to high affinity with the electrolyte, thereby weakening the binding force between the electrode and the separator. This is undesirable because it can cause various side reactions.

The adhesive layer may be formed on any one or both sides of the separator, the thickness thereof is preferably 0.5 to 10 ㎛. If the thickness of the adhesive layer is too thin, it is difficult to provide a predetermined bonding force and, on the contrary, too thick, it may interfere with the movement of lithium ions, causing an increase in the internal resistance of the battery and a decrease in the rate characteristic.

The adhesive layer or adhesive material is not particularly limited as long as it does not cause an electrochemical reaction in the electrode assembly, and well-known adhesive materials may be used as it is, for example, acrylic, silicone or epoxy based materials, rubber based, cellulose It may be a series polymer material.

In one preferred example, the adhesive layer or adhesive material may be the same as the binder component for bonding between the electrode active material and the current collector. Examples of such adhesive layer components or adhesives include polyvinylidene fluoride (PVdF), 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. Especially preferably, PVdF can be used.

The electrode assembly according to the present invention has a structure in which a plurality of electrodes of a positive electrode and a negative electrode are stacked in a state where a separator is interposed.

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; A sheet or a nonwoven fabric made of glass fiber or polyethylene may be used, and preferably, a polyolefin resin porous membrane. In particular, polypropylene resin may be more preferable when applied to the present invention because it is a material that is relatively easy to oxidize. On the other hand, when a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

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.

The positive electrode is prepared by, for example, applying a mixture of a positive electrode active material, a conductive material, and a binder to a positive electrode current collector, followed by drying, and optionally, a filler is further added to the mixture.

The positive electrode current collector is generally made to a thickness of 3 to 500 μm. 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. The current collector may form fine irregularities on its surface to increase the adhesion of the positive electrode active material, and may be in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; 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 , 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 M _x O 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 (wherein 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, but are not limited to these.

The conductive material is typically added in an amount of 1 to 50% by weight based on the total weight of the mixture including the positive electrode active material. 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 fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder and nickel powder; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used. In some cases, since the conductive second coating layer is added to the positive electrode active material, the addition of the conductive material may be omitted.

The binder is a component that assists in bonding the active material and the conductive material to the current collector, and is generally added in an amount of 1 to 50 wt% based on the total weight of the mixture including the positive electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers and the like.

As such, a high molecular material such as polyvinylidene fluoride is generally used as the binder component. When the battery is exposed to high temperature, it is solvated by having a low molecular weight while being double bonded. In this case, deterioration of the battery may occur seriously while the bonding strength between the electrode active materials and the current collector is lowered. On the other hand, since the electrode assembly according to the present invention includes a heat stabilizer to prevent the double bond of the binder component can be improved battery capacity and cycle characteristics.

The filler is optionally used as a component for inhibiting expansion of the positive electrode, and is not particularly limited as long as it is a fibrous material without causing chemical change in the battery. Examples of the filler include olefinic polymers such as polyethylene and polypropylene; Fibrous materials, such as glass fiber and carbon fiber, are used.

The negative electrode is manufactured by applying and drying a negative electrode material on the negative electrode current collector, and if necessary, the components as described above may be further included.

The negative electrode current collector is generally made to a thickness of 3 to 500 ㎛. Such a negative electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, the surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel Surface-treated with carbon, nickel, titanium, silver, and the like, aluminum-cadmium alloy, and the like can be used. In addition, like the positive electrode current collector, fine concavities and convexities may be formed on the surface to enhance the bonding strength of the negative electrode active material, and may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The negative electrode material may be, for example, carbon such as hardly graphitized carbon or graphite carbon; Li _x Fe ₂ O ₃ (0 ≦ _x ≦ 1), Li _x WO ₂ (0 ≦ _x ≦ 1), Sn _x Me _{1 - x} Me ' _y O _z (Me: Mn, Fe, Pb, Ge; Me' Metal complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen, 0 <x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8); Lithium metal; Lithium alloys; Silicon-based alloys; Tin-based alloys; SnO, SnO ₂ , PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , GeO, GeO ₂ , Bi ₂ O ₃ , Bi ₂ O ₄ , and oxides such as Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

The present invention also provides a lithium secondary battery having a structure in which a lithium salt-containing non-aqueous electrolyte solution is impregnated into the electrode assembly.

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

Examples of the non-aqueous electrolyte include N-methyl-2-pyrrolidinone, propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), Gamma-butyl lactone, 1,2-dimethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxolon, formamide, dimethylformamide, dioxo Run, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxy methane, dioxorone derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate Aprotic organic solvents such as derivatives, tetrahydrofuran derivatives, ethers, methyl pyroionate and ethyl propionate can be used.

In one preferred embodiment, the non-aqueous electrolyte may be EC, DEC, DMC, EMC and mixed solvents thereof, which are aprotic organic solvents, more preferably, a mixed solvent of EC / DEC, a mixture of EC / EMC Solvents or mixed solvents of EC / EMC / DMC can be used. Particularly, in the case of DMC, since the ion conductivity is high, the charge / discharge cycle characteristics are improved, but there is a problem in that a large amount of gas is generated during high temperature storage. However, when the heat stabilizer is included in the adhesive layer as in the present invention, Since the film on the cathode is stabilized, there is an advantage that it is possible to effectively suppress the generation of gas during high temperature storage.

The lithium salt is a material that is easy to dissolve 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, in order to impart nonflammability, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further included, and carbon dioxide gas may be further included to improve high temperature storage characteristics.

The present invention also provides a method of manufacturing the electrode assembly according to the first embodiment and the second embodiment.

The electrode assembly according to the first embodiment,

(i) dissolving the adhesive layer component in an organic solvent, and then dispersing the microcapsules loaded with a heat stabilizer to prepare a coating solution;

(ii) coating the coating solution prepared in step (i) on both or one side of the separator to form an adhesive layer; And

(iii) interposing a separator formed with the adhesive layer between an anode and a cathode and performing a heating / pressing process;

It may be configured to include.

In addition, the electrode assembly according to the second embodiment,

(i) dissolving the heat stabilizer in an organic solvent and then adding a flocculant or an adhesive to prepare agglomerates of the heat stabilizer;

(ii) dissolving the adhesive layer component in an organic solvent, and then dispersing the aggregate prepared in step (i) to prepare a coating solution;

(iii) forming an adhesive layer by coating the coating solution prepared in step (ii) on both or one side of the separator; And

(iv) interposing a separator formed with the adhesive layer between an anode and a cathode and performing a heating / pressing process;

It may be configured to include.

In the preparation of the electrode assembly according to the present invention, the heat stabilizer is dispersed in a coating solution for forming a separator adhesive layer in the form of a capsule or in the form of agglomerates of a heat stabilizer, and after dissolving the adhesive layer component in an organic solvent, the final manufacturing step of the coating solution. Since it is added at, the form can be sufficiently maintained in the previous state of the heating / pressurization process. Accordingly, the consumption in the heating / pressing process can be minimized as compared with the case where the heat stabilizer is itself widely distributed in the adhesive layer. Therefore, since the effective amount capable of capturing the radicals generated from the polymer component included in the electrode assembly in the relatively high temperature state of the battery can be maintained high, the operation reliability is high.

Examples of the organic solvent for dissolving the adhesive layer component or the heat stabilizer include N-methyl-2-pyrrolidone (NMP), N, N-dimethylformamide, tetrahydrofuran, dimethylacetamide, and dimethyl sulfoxide. Seeds, hexamethylsulfonamides, tetramethylurea, acetone, methylethylketone, and the like can be used, and these may be used alone or in the form of two or more mixed solvents. Especially preferably, NMP can be used.

The coating method of the coating liquid is not particularly limited, and for example, a doctor bleed coating method, a spray coating method, a screen printing method, or the like may be used.

The heating / pressing process is preferably performed for 1 to 10 minutes at a temperature of 70 to 100 ° C. and a pressure of 3 to 10 kg / cm ² so as to achieve sufficient bonding strength between the separator and the electrode. It may be carried out for 3 to 5 minutes at a temperature of 80 to 90 ℃, a pressure of 4 to 6 kg / cm ² .

In the heating / pressing process, if the temperature is too high, deterioration of the electrode or the separator may occur, and if the pressure or the treatment time is too high or long, the electrode assembly may be deformed, which is not preferable. In the opposite case, there is a problem because sufficient bonding force between the separator and the electrode cannot be exerted.

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

Example 1

One. Heat stabilizer Supported  Preparation of microcapsules and coating liquid containing same

Polystyrene (PS) was dissolved in dichloromethane (DCM) to prepare 25 ml of a dispersion (a). In addition, 250 ml of an aqueous solution (b) containing 0.1 wt% of n-octadecyl-3- (4-hydroxy-3,5-di-t-butyl phenyl) propionate was prepared. The dispersion (a) was added to the aqueous solution (b) to form an oil / water emulsion. Then, DCM was evaporated to remove, thereby obtaining a PS capsule of approximately 30 μm size. This was washed several times in distilled water to prepare a final capsule.

Meanwhile, 3% by weight of PVdF was dissolved in NMP and stirred. Then, the prepared capsules were dispersed to prepare a coating solution.

2. Manufacture of batteries

The negative electrode is N-methyl-2-pyrrolidone (93% by weight of a carbon active material (MCMB10-28 from Osaka Gas) and 7% by weight of polyvinylidene difluoride (PVDF, Kynar 761 from Elf Atochem) NMP) was added and mixed in a mixer (mixer manufactured by Ika) for 2 hours, and then coated on a copper foil current collector and dried at 130 ° C.

The positive electrode was prepared by mixing 91% by weight of LiCoO ₂ , 3% by weight of PVDF (Kynar 761) and 6% by weight of conductive carbon (KS-6 from Lonza) in a solvent, N-methyl-2-pyrrolidone (NMP). After mixing for 2 hours in a mixer (mixer manufactured by Ika), it was coated on an aluminum foil current collector, and dried at 130 ° C to prepare.

Polypropylene-based separator (Celgard ^TM 2400) was used as a bare film of the separator, and the coating solution was coated on both sides by a spray coating method with a thickness of approximately 5 μm, and then left at room temperature for 12 hours and dried to form an adhesive layer. This coated separator was prepared.

Then, the coated separator is laminated between the prepared negative electrode and the positive electrode, and then the electrode assembly is bonded by combining the electrode and the separator by a heating / pressing process for 5 minutes under a temperature of 85 ° C. and a pressure of 5 kg / cm ² . Prepared. The prepared electrode assembly was accommodated in a pouch-type case, an electrolyte solution was injected, and heat-sealed to prepare a pouch-type lithium secondary battery. 1 M LiPF ₆ EC / DMC solution was used as the electrolyte.

Example 2

A battery was prepared in the same manner as in Example 1, except that a solution of 1 M LiPF ₆ EC / EMC / DMC was used as the electrolyte.

Comparative Example 1

A battery was manufactured in the same manner as in Example 1, except that the separator was not coated.

Comparative Example 2

Instead of the coating solution containing the microcapsules, 3% by weight of PVdF and 1% by weight of n-octadecyl-3- (4-hydroxy-3,5-di-t-butyl phenyl) propionate were dissolved in NMP to prepare a coating solution. The battery was manufactured in the same manner as in Example 1, except that the coating solution was coated on a surface of the separator facing the positive electrode.

[Experimental Example] Life characteristic evaluation experiment

After charging and discharging the battery prepared in Examples 1 and 2 and Comparative Examples 1 and 2 at 0.5 C at 200 ° C. 200 times, the discharge capacity retention rate of 100 times and 200 times compared to the one time discharge capacity was calculated. Shown in

TABLE 1

As shown in Table 1, Comparative Example 1 and the heat stabilizer was added directly to the adhesive layer without the addition of n-octadecyl-3- (4-hydroxy-3,5-di-t-butyl phenyl) propionate as a heat stabilizer Compared with the battery of Comparative Example 2, the cells of Examples 1 and 2 in which the n-octadecyl-3- (4-hydroxy-3,5-di-t-butyl phenyl) propionate supporting capsule were added to the electrolyte and the negative electrode, respectively, were higher. Dose retention was shown. This can be seen that more than 200 times more significant discharge.

From the results of the above life characteristics, as shown in Examples 1 and 2, when the heat stabilized supporting capsule is added to the adhesive layer and then heated / pressed, the shell of the capsule is destroyed during the heating / pressing process, and the heat stabilizer is converted into the adhesive layer. Since it flows out, it can be seen that a problem in which a considerable amount of the heat stabilizer is consumed when the heat stabilizer is added after the heat stabilizer is directly added to the adhesive layer as in Comparative Example 2 is performed.

In addition, the effective amount of the heat stabilizer is included in the adhesive layer between the electrode and the separator, thereby preventing deterioration of the polymer material in the battery as compared with Comparative Examples 1 and 2, improving battery durability, battery capacity and high temperature cycle characteristics, and heating. It can be seen that the operating performance and efficiency are excellent by minimizing the consumption of the heat stabilizer in the / pressurization process.

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

As described above, in the electrode assembly according to the present invention, after the heat stabilizer is added to the separator adhesive layer in the form of a capsule or in the form of agglomerates, the heat stabilizer flows out to the adhesive layer in the heating / pressurization process for manufacturing the electrode assembly. Therefore, the effective amount of the heat stabilizer in the final electrode assembly can be increased. Therefore, the lithium secondary battery including such a heat stabilizer is improved in durability and can be prevented from lowering in charge and discharge capacity, and particularly excellent in cycle characteristics and storage and life characteristics at high temperatures. In addition, there is an advantage that the operation reliability and efficiency is high by minimizing the waste of the heat stabilizer that can be caused during the heating, pressurization process, etc. for the production of the electrode assembly.

Claims (19)

An electrode assembly having a structure in which a plurality of electrodes are laminated in a state in which a separator is interposed and then bonded to each other by heating / pressing, wherein the bonding of the electrode and the separator is performed by heating / pressing the adhesive layer formed on the separator and the electrodes facing each other. It is achieved by the, the adhesive layer includes a microcapsule loaded with a heat stabilizer in the state before heating / pressing, the shell of the microcapsules during the heating / pressing process (rupture of the shell (shell) of the microcapsules are leaked to the adhesive layer) Electrode assembly, characterized in that. The electrode assembly of claim 1, wherein the shell of the microcapsules is melted at a temperature of 70 to 100 ° C or ruptured under a pressure of 3 to 10 kg / cm ² . The electrode assembly of claim 2, wherein the shell of the microcapsules is made of polyolefin. The electrode assembly of claim 1, wherein the microcapsules have a particle size of about 1 to 50 μm. An electrode assembly having a structure in which a plurality of electrodes are laminated in a state in which a separator is interposed and then mutually bonded by heating / pressurization, wherein the bonding of the electrode and the separator is performed by heating and / or facing the electrode and the adhesive layer formed on the separator. The electrode assembly, which is achieved by pressurization, wherein the adhesive layer includes agglomerates formed by agglomeration of heat stabilizers by physical bonding. The electrode assembly according to claim 5, wherein the aggregate has a structure in which thermal stabilizers in the form of primary particles having a relatively small particle diameter are aggregated by mutual physical bonding to form secondary particles. The electrode assembly according to claim 5, wherein the aggregate has a structure in which a heat stabilizer is bonded by a predetermined binder. 8. The electrode assembly of claim 7, wherein the binder is PVdF. The heat stabilizer according to claim 1 or 5, wherein the heat stabilizer is a phenolic compound, a cyclic amine compound, a semicarbazide, an amine compound, a nitro compound, a phosphorus compound, an unsaturated hydrocarbon compound, and a thio compound. Electrode assembly, characterized in that selected from the group consisting of a compound. The method of claim 9, wherein the phenolic compound is 2,2-di (4'-hydroxyphenyl) propane, hydroquinone, p-methoxyphenol, t-butylhydroxy-anisole, n-octadecyl-3- (4-hydroxy-3,5 -di-t-butyl-phenyl) propionate, pentaerythritol tetrakis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], 1,2-propylene glycol bis- [3- (3,5 -di-t-butyl-4-hydroxyphenyl) propionate], stearamido N, N-bis- [ethylene 3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], 2,5-di-t -butylhydroquinone, 4,4'-butylidenebis (3-methyl-6-t-butylphenol), 3,5-di-t-butyl-4-hydroxytoluene, 2,2'-methylene-bis (4-ethyl-6- t-butylphenol), triethyleneglycol-bis- [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate], pentaerythritoltetrakis [3- (3,5-di-t-butyl-4-hydroxy-phenyl ) propionate], 2,6-di-t-butyl-4-methylphenol, t-butylcatechol, 4,4-thiobis (6-t-butyl-m-cresol), tocopherol, and nordihydroguaiaretic acid Electrode assembly, characterized in that. The electrode assembly of claim 10, wherein the phenolic compound is n-octadecyl-3- (4-hydroxy-3,5-di-t-butylphenyl) propionate. The electrode assembly of claim 1 or 5, wherein the total amount of the heat stabilizer is included in an amount of 0.01 to 1 wt% based on the total weight of the membrane adhesive layer. The electrode assembly of claim 1 or 5, wherein the separator adhesive layer has a thickness of 0.5 to 10 µm. The electrode assembly according to claim 1 or 5, wherein the separator is a polyolefin-based porous separator. A lithium secondary battery comprising a lithium salt-containing non-aqueous electrolyte solution in an electrode assembly according to claim 1 or 5. (i) dissolving the adhesive layer component in an organic solvent, and then dispersing the microcapsules loaded with a heat stabilizer to prepare a coating solution; (ii) coating the coating solution prepared in step (i) on both or one side of the separator to form an adhesive layer; And (iii) interposing a separator formed with the adhesive layer between an anode and a cathode and performing a heating / pressing process; Method of manufacturing an electrode assembly according to claim 1 comprising a. (i) dissolving the heat stabilizer in an organic solvent and then adding a flocculant or an adhesive to prepare agglomerates of the heat stabilizer; (ii) dissolving the adhesive layer component in an organic solvent, and then dispersing the aggregate prepared in step (i) to prepare a coating solution; (iii) forming an adhesive layer by coating the coating solution prepared in step (ii) on both or one side of the separator; And (iv) interposing a separator formed with the adhesive layer between an anode and a cathode and performing a heating / pressing process; Method of manufacturing an electrode assembly according to claim 5 comprising a. 18. The method of claim 16 or 17, wherein the organic solvent is NMP. 18. The method of claim 16 or 17, wherein the heating / pressing process is performed for 1 to 10 minutes at a temperature of 70 to 100 ° C. and a pressure of 3 to 10 kg / cm ² .