KR20090008086A - Secondary battery with improved thermal stability - Google Patents

Abstract

A secondary battery is provided to prevent the water permeation from the outside and the leakage of electrolyte due to the crack generated in heat sealing and the degradation of sealability, and to improve durability and safety of a battery and high temperature cycle characteristics. A secondary battery includes an electrode assembly(500) of an anode/separation film/cathode structure built in a battery case(100) of laminated sheet containing a resin layer and metal layer. The laminated sheet comprises an inner resin layer, a metal layer and an outer resin layer. A thermal stabilizer is added to a part or the whole of the inner resin layer of the battery case. The case peripheral part mutually connected with the inner resin layer forms a sealing through heat sealing in a state of being added with the thermal stabilizer.

Description

Secondary Battery with Improved Thermal Stability}

The present invention is a secondary battery having improved thermal stability, and more particularly, a secondary battery in which an electrode assembly having a cathode / separation membrane / cathode structure is built in a battery case of a laminate sheet including a resin layer and a metal layer. A resin layer, a barrier metal layer, and an outer resin layer are formed. A heat stabilizer is added to all or a part of the inner resin layer of the battery case. It relates to a secondary battery characterized in that the sealing portion is coupled to each other by heat fusion in the added state.

As the development and demand for mobile devices increases, the demand for secondary batteries as energy sources is increasing rapidly. Among them, many researches have been conducted and commercialized and widely used for lithium secondary batteries with high energy density and discharge voltage. It is used.

Representatively, there is a high demand for square and pouch type secondary batteries that can be applied to products such as mobile phones with a thin thickness in terms of shape of batteries, and high energy density, discharge voltage, and output stability in terms of materials. There is a high demand for lithium secondary batteries such as lithium ion batteries, lithium ion polymer batteries and the like.

In addition, secondary batteries are classified according to the structure of the electrode assembly having a cathode / separation membrane / cathode structure. Representatively, a jelly having a structure in which long sheet-shaped anodes and cathodes are wound with a separator interposed therebetween -Roll (electrode) electrode assembly, a stack (stacked) electrode assembly in which a plurality of positive and negative electrodes cut in units of a predetermined size are sequentially stacked with a separator, and the positive and negative electrodes of a predetermined unit are separated through a separator And a stacked / folding electrode assembly having a structure in which a bi-cell or full cells stacked in a state are wound.

Recently, a pouch-type battery having a structure in which a stack type or a stack / fold type electrode assembly is incorporated into a pouch type battery case of an aluminum laminate sheet has attracted much attention due to its low manufacturing cost, small weight, and easy shape deformation. Its usage is also gradually increasing.

In general, a pouch type secondary battery has, for example, a structure in which an electrode assembly is incorporated in a housing portion of a pouch type battery case made of an aluminum laminate sheet. That is, the pouch-type secondary battery forms an accommodating part for mounting the electrode assembly on a laminate sheet, and heat-seals a separate sheet which is separated from the sheet or a sheet extending therefrom while the electrode assembly is mounted on the accommodating part. It is produced by sealing.

1 schematically illustrates a cross-sectional structure of a laminate sheet generally used in a pouch-type battery, and FIG. 2 schematically illustrates an exploded perspective view of a pouch-type secondary battery including a battery case made of the laminate sheet of FIG. 1. Is shown as an example.

First, referring to FIG. 1, the laminate sheet 10 includes an outermost outer coating layer 11 that forms an outermost shell, a barrier layer 12 that prevents penetration of a material, an adhesive layer 14, and an inner resin layer 13 for sealing. It consists of.

Since the outer coating layer 11 serves to protect the battery from the outside, excellent tensile strength and weather resistance to the thickness are required, and ONy (stretched nylon film) is frequently used. The barrier layer 12 serves to prevent air, moisture, and the like from flowing into the battery, and mainly aluminum (Al) is used. The inner resin layer 13 serves to provide heat sealing by mutual heat fusion by applied heat and pressure in a state in which the electrode assembly is embedded, and mainly consists of CPP (non-stretched polypropylene film). The adhesive layer 14 serves to complement the low adhesion of the CPP inner resin layer 13 to the barrier layer 12.

2, the battery case 15 is integrated with the main body 20 and the main body 20 in which the accommodating part 21 for mounting the electrode assembly 50 is formed, and the accommodating part 21. It consists of a cover 30 of the form capable of sealing.

Therefore, in the pouch type secondary battery, the electrode assembly is mounted on the accommodating portion 21 of the battery case 15, and then bent at the connection portion between the main body 20 and the lid 30, and the accommodating portion 21 is pushed. It is manufactured by heat-sealing three surfaces of the sealing portion 22 and the cover 30 of the main body 20 except for the bent portion for sealing.

That is, when heat is applied to the sealing portion of the main body 20 and the lid 30 which the inner resin layers corresponding to the innermost layer face each other, the inner resin layer is melted and the main body 20 and the lid 30 are fused together. Are joined and sealed by.

However, free radicals may be generated in the internal resin layer constituting the battery case 10 by the high temperature heat applied in the thermal fusion process. Accordingly, deterioration such as oxidation of the internal resin layer or generation of fine cracks may occur. In this case, since the sealing property of the battery is reduced, a problem may occur in that the electrolyte may leak to the outside or external moisture may penetrate into the battery, which may shorten the life of the battery and cause serious problems in the safety of the battery. Can be. In particular, a secondary battery used in a medium-large battery pack as a power source of an electric vehicle, a hybrid vehicle, etc. needs a long lifespan, and it is very important to secure safety due to the fact that many battery cells are concentrated.

Nevertheless, since there is almost no recognition of such a problem, there is no technology capable of solving the problem of oxidation or deterioration of the internal resin layer due to thermal fusion. Accordingly, the present invention proposes a technique of adding a heat stabilizer to the inner surface of the pouch-type battery case in order to solve the above problems.

In this regard, some techniques for adding antioxidants and the like exist in the battery as a method for improving the high temperature stability of the conventional battery. For example, Japanese Patent Application Laid-Open No. 1998-67211 discloses a technique of incorporating an antioxidant into a positive electrode, and Korean Patent Application Publication No. 2002-020699 and Japanese Patent Application Publication No. 1998-247517 are disclosed in an electrolyte solution. Techniques for adding oxidative additives or antioxidants are disclosed.

However, when such an antioxidant is included in the electrode or the electrolyte, there is a problem that battery performance is deteriorated by causing various side reactions in the battery, such as a decrease in battery capacity, a decrease in mobility of lithium ions, and a decrease in rate characteristics. (See Japanese Patent Application Laid-Open No. 2000-30685).

Therefore, there is a need for a technology that fundamentally prevents a problem of deterioration of battery performance such as cracking in the battery case due to oxidation or deterioration of the internal resin layer that may be caused during thermal fusion, and to secure battery stability. This is high.

The present invention is a secondary battery in which an electrode assembly having a positive electrode / separation membrane / cathode structure is built in a battery case of a laminate sheet including a resin layer and a metal layer, wherein the laminate sheet includes an inner resin layer, a barrier metal layer, and an outer resin layer. In the structure of the battery case, a heat stabilizer is added to all or part of the inner resin layer of the battery case, the outer peripheral portion of the case in which the inner resin layer is in contact with each other by heat bonding in a state in which the heat stabilizer is added to the sealing It is characterized by forming a part.

These thermal stabilizers act to capture unstable free radicals generated when the cell is exposed to high temperatures during charge and discharge. Accordingly, the polymer material constituting the internal resin layer may be prevented from being oxidized or double-bonded (polyene) and boiled by free radicals, and thus, deterioration of battery operation performance. Therefore, durability and sealing property of the battery can be improved to prevent water penetration into the battery and leakage of electrolyte solution, and the life and safety of the battery can be improved.

In addition, the thermal stabilizer is effective even when the battery is exposed to high temperature in the charge and discharge process, it is possible to prevent the polymer components in the battery such as binders, adhesive layers, separators, etc. to be oxidized or deteriorated excellent temperature cycle characteristics. In addition, various side reactions that may occur when the heat stabilizer is directly added to the electrode assembly, the electrolyte, and the like, a decrease in battery performance, and a decrease in battery capacity may be prevented.

In the present invention, the heat stabilizer may be added to all or part of the inner resin layer located on the inner surface of the battery case, as defined above. This is because high temperature heat applied to the battery case at the time of heat fusion is conducted to the entire battery case, thereby affecting the whole or part of the internal resin layer located on the inner surface of the battery case.

Since heat is directly applied to the outer circumference of the case during thermal fusion, in one preferred example for the effective addition of a heat stabilizer, the heat stabilizer is a case outer circumference, that is, a sealing example, which is a portion to which heat is directly applied during the thermal fusion process. Can only be added to the government. As a result, the finally manufactured secondary battery has a structure in which a heat stabilizer is included in the sealing part, and the heat stabilizer may partially lose its efficacy due to high temperature and high pressure in the process of forming the sealing part. . Hereinafter, for convenience of description, the 'case outer periphery' and the 'sealing part' to be heated and pressurized for sealing may be abbreviated as 'sealing part'.

In a specific example, the heat stabilizer may be added to the three-sided sealing portion of the three-sided sealing secondary battery or the four-sided sealing portion of the four-sided sealing secondary battery. Here, the three-sided sealing secondary battery and the four-sided sealing secondary battery distinguish the secondary battery equipped with the pouch-type battery case according to the manufacturing method. The three-sided sealing is mainly performed in a secondary battery of one unit member in which an accommodating part and a cover are integrated. On the other hand, the four-sided sealing method is a method using two independent sheets that will constitute the upper and lower surfaces, respectively, the outer peripheral surface of the two sheets are both heat dissipation to all four sides in the secondary battery of the two-unit member discontinuous The sealing is carried out, thereby producing a battery.

In the secondary battery according to the present invention, the laminate sheet has a structure including an inner resin layer, a barrier metal layer, and an outer resin layer as defined above.

Since the outer resin layer should have excellent resistance from the external environment, it is necessary to have a tensile strength and weather resistance of a predetermined or more. In such aspect, polyethylene terephthalate (PET) and a stretched nylon film may be preferably used as the polymer resin of the outer resin layer.

The barrier metal layer is preferably aluminum may be used to exhibit a function of improving the strength of the battery case in addition to the function of preventing the inflow or leakage of foreign substances such as gas, moisture.

As the polymer resin of the internal resin layer, a polyolefin-based resin having heat fusion (heat adhesion), low hygroscopicity to suppress the invasion of the electrolyte, and which is not expanded or eroded by the electrolyte is preferably used. More preferably unstretched polypropylene (CPP) may be used.

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 free radical scavenger to make unstable free radicals produced by oxidation in a 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. 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-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, but are not limited thereto. Particularly preferred among the phenolic heat stabilizers is n-Octadecyl-3- (4-hydroxy-3,5-di-t-butyl phenyl) propionate which is used to act as a hydrogen donor or free radical acceptor for oxidation. And free radicals can be removed by reduction.

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-benzoylsemicar and semicarbazone.

The amine-based 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 is 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 heat stabilizer may be preferably added in an amount of 0.01 to 5 wt% based on the total weight of the battery case. If the amount of the heat stabilizer is too small, the desired effect of addition cannot be obtained. On the contrary, if the content of the heat stabilizer is too high, heat sealing is not easy, and thus the sealing property may be impaired.

The method of adding the heat stabilizer to one surface of the laminate sheet member or the inner surface of the battery case is not particularly limited, and preferably may be added by coating on an inner resin layer located on the inner surface of the battery case.

The coating method may be, for example, a doctor bleed coating method, a spray coating method, a screen printing method, a flow coating method, a spin coating method, a dip coating method, a bar coating method, or the like. As a specific example, the laminate sheet member or the battery case may be immersed in a solution in which the heat stabilizer is dispersed, or the dispersion of the heat stabilizer may be coated by a spray coating method. In addition, a method of vaporizing a heat stabilizer and depositing on one surface of the laminate sheet member or the inner surface of the battery case is also possible. In order to increase the binding strength of the hydrophobic material to the surface of the separator in such a coating process, a predetermined binding aid may be added. For example, a fluorine-based polymer such as PVdF and PTFE, PVdF as a binding mineralizer to a solvent such as NMP, etc. Coating may be performed by applying a coating solution containing a system copolymer polymer, PMMA, PAN, PEO, SBR, and the like to a separator.

The heat stabilizer may be added to the inner resin layer of the laminate sheet before the battery case is formed, and after the laminate sheet member is manufactured into a pouch type battery case by a known method such as deep drawing, the battery case You can also do this.

The present invention also provides a battery case for a secondary battery manufactured by using a laminate sheet to which a heat stabilizer is added to the internal resin layer as described above. The site | part to which a heat stabilizer is added may be a part of internal resin layer including at least a sealing part, or the whole internal resin layer may be sufficient as it.

The battery case according to the present invention may have various forms, and preferably, may include a form in which the electrode assembly is formed in a pouch form. That is, a pouch-type battery case may be formed by forming an accommodating part in which an electrode assembly may be seated by drawing processing on one side of the laminate sheet and bending the other side in the form of a cover. Since this is well known in the art, a detailed description thereof will be omitted.

The present invention also provides a method of manufacturing the secondary battery. Secondary battery according to the present invention

(i) dissolving the heat stabilizer in an organic solvent and then dispersing to prepare a coating solution;

(ii) coating the coating solution prepared in step (i) on the inner resin layer of the laminate sheet constituting the battery case; And

(iii) heating / pressurizing the outer circumference of the case coated with the heat stabilizer to form a sealing portion;

It may be prepared to include.

By coating the inner surface of the laminate sheet or case, heating / pressurization of the battery case without concern such as causing various side reactions and reduction of battery performance which may occur when the heat stabilizer is directly added to the electrode assembly, the electrolyte, and the like. It is possible to prevent deterioration and oxidation of the battery according to the process. In addition, it is possible to prevent the generation of cracks in the battery case by removing the free radicals generated during thermal fusion, ultimately to minimize the effect of the heating / pressurization process during the thermal fusion to the battery, and improve the safety of the battery have.

As the organic solvent for dissolving the heat stabilizer, for example, N-methyl-2-pyrrolidone (NMP), N, N-dimethylformamide, tetrahydrofuran, dimethylacetamide, dimethyl sulfoxide, hexamethyl Sulfonamide, tetramethyl urea, acetone, methyl ethyl ketone and the like may 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 heating / pressing process may be performed, for example, by applying a high temperature and a high pressure through the die to allow the inner resin layers to melt and bond at the outer periphery of the case where the sheets face each other.

The secondary battery according to the present invention may preferably be a lithium secondary battery having a structure in which a lithium salt-containing non-aqueous electrolyte is impregnated.

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

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

In one preferred embodiment, the non-aqueous organic solvent may be EC, DEC, DMC, EMC and mixed solvents thereof, which are aprotic organic solvents, more preferably, a mixed solvent of EC / DEC, EC / EMC Mixed solvents, or mixed solvents of EC / EMC / DMC 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 good material to be dissolved 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 secondary battery including the battery case. In particular, the battery according to the present invention may be a pouch type battery in which an electrode assembly is embedded in a pouch type battery case of a laminate sheet including a metal layer and a resin layer, specifically, an aluminum laminate sheet.

The electrode assembly is composed of a positive electrode and a negative electrode to enable charge and discharge, for example, a structure in which the positive electrode and the negative electrode is laminated with a separator therebetween, a folding type (gel-roll) type, a stacked type, or a stack. / Folded type. The positive electrode and the negative electrode of the electrode assembly may have a form in which electrode tabs thereof protrude directly to the outside of the battery, or the electrode tabs may be connected to separate leads and protrude out of the battery.

The secondary battery has a structure in which an electrolyte solution is impregnated into an electrode assembly having a separator interposed between a positive electrode and a negative electrode.

For example, the positive electrode may be manufactured by coating and drying a positive electrode active material on a positive electrode current collector, and may further include a binder and a conductive material and, as necessary, components described above with respect to the structure of the positive electrode.

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. In addition, the positive electrode current collector may increase the adhesion of the positive electrode active material by forming fine unevenness on its surface, 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 negative electrode is manufactured by coating, drying, and compressing a negative electrode material including a negative electrode active material and a binder on a current collector, and optionally, components such as a conductive material and a filler may be further included.

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 metal oxides such as Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

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. As in the positive electrode current collector, fine concavities and convexities may be formed on the surface thereof to increase the adhesion of the negative electrode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric may be possible.

Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), cellulose, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose Rhodes, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers, high polymer poly Vinyl alcohol, and the like.

The conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery. Examples of the conductive material 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 metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used. Specific examples of commercially available conductive materials include Chevron Chemical Company, Denka Singapore Private Limited, Gulf Oil Company, Ketjenblack and EC, which are acetylene black series. Family (Armak Company), Vulcan XC-72 (manufactured by Cabot Company) and Super (manufactured by Super P, Timcal).

In some cases, a filler may be optionally added as a component that suppresses expansion of the electrode. Such a filler 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.

In addition, other components, such as viscosity modifiers, adhesion promoters, and the like may optionally be further included or in combination of two or more.

The viscosity modifier is a component that adjusts the viscosity of the electrode mixture so that the mixing process of the electrode mixture and the coating process on the current collector thereof can be easily added, up to 5% by weight based on the total weight of the electrode mixture. Examples of such viscosity modifiers include, but are not limited to, carboxymethyl cellulose, polyvinylidene fluoride, and the like. In some cases, the solvent described above can serve as a viscosity modifier.

The adhesion promoter is an auxiliary component added to improve the adhesion of the active material to the current collector, it may be added in less than 10% by weight compared to the binder, for example, oxalic acid (oxalic acid), adipic acid (adipic acid), Formic acid, acrylic acid derivatives, itaconic acid derivatives, and the like.

The binder, the conductive material and the filler added as necessary are the same as those described for the positive electrode.

The separator is interposed between the anode and the cathode, 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, a sheet, a nonwoven fabric, or the like made of an olefin polymer such as polypropylene having chemical resistance and hydrophobicity, glass fiber or polyethylene, or the like is used.

In some cases, a gel polymer electrolyte may be coated on the separator to increase battery stability. Representative of such gel polymers are polyethylene oxide, polyvinylidene fluoride, polyacrylonitrile and the like. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

Hereinafter, although described with reference to the drawings according to an embodiment of the present invention, this is for easier understanding of the present invention, the scope of the present invention is not limited thereto.

3 is an exploded perspective view schematically illustrating a secondary battery in which a heat stabilizer is added to an inner surface sealing portion of a battery case according to one embodiment of the present invention.

Referring to FIG. 3, the battery case 100 is composed of a single unit member in which a main body 200 in which an accommodating part 210 for mounting an electrode assembly 500 is formed, and a cover 300 are integrated. . The battery case is formed of a laminate sheet composed of an outermost layer, a metal barrier layer, and an innermost layer, and an inner resin layer of a heat sealable that can be sealed by heat sealing is positioned as an innermost layer. The heat stabilizer is added to the outer surface 220 of the three-sided case of the main body 200 and the cover 300 to which high temperature heat is directly applied during thermal fusion.

After the electrode assembly 500 is mounted on the accommodating part 210, the two case outer parts are heated and heat-sealed, and the electrolyte is injected through the other one case outer part, and then the cover 300 is heated and heated. By fusion, a secondary battery is produced. At this time, a heat stabilizer is coated on the case outer circumferential portion 220, so that the internal resin layer (sealant layer) can be prevented from being deteriorated or oxidized by the high temperature heat applied to the case outer circumferential portion 220, thereby ensuring durability and sealing of the battery. The power is improved. Therefore, the cycle characteristics and stability of the battery are excellent. In addition, since the thermal stabilizer is not directly added to the electrode assembly 500 or the electrolyte, the high temperature cycle characteristics may be improved while preventing the performance of the battery.

As described above, the secondary battery according to the present invention has a heat stabilizer added to all or a part of the internal resin layer located on the inner surface of the battery case, due to cracks or deterioration in sealability that may occur during thermal fusion. Excellent durability and safety of battery by preventing external moisture penetration and electrolyte leakage. In addition, since a heat stabilizer is added to the inner surface of the battery case, side reactions generated when the battery is added to a part directly related to the operation of the battery, such as an electrode assembly or an electrolyte, and the performance of the battery is not deteriorated.

1 is a schematic diagram of a cross-sectional structure of a laminate sheet generally used in a pouch type battery;

2 is an exploded perspective view of a pouch type secondary battery including a battery case made of the laminate sheet according to FIG. 1;

3 is an exploded perspective view of a rechargeable battery according to an exemplary embodiment of the present invention.

Claims (12)

A secondary battery in which an electrode assembly having a cathode / separation membrane / cathode structure is built in a battery case of a laminate sheet including a resin layer and a metal layer, wherein the laminate sheet has a structure including an inner resin layer, a barrier metal layer, and an outer resin layer. And a heat stabilizer is added to all or a part of the inner resin layer of the battery case, and the outer circumferences of the case where the inner resin layers are in contact with each other are bonded to each other by heat fusion in the state where the heat stabilizer is added to form a sealing portion. Secondary battery, characterized in that. The secondary battery according to claim 1, wherein the heat stabilizer is added only to the outer periphery of the case. The method of claim 1, wherein the heat stabilizer is a phenolic compound, a cyclic amine compound, a semicarbazide (Semicarbazide), an amine compound, a nitro compound, a phosphorus compound, an unsaturated hydrocarbon compound, and a thio compound Secondary battery, characterized in that selected from the group. The method of claim 3, wherein the phenolic heat stabilizer is 2,2-di (4'-hydroxyphenyl) propane, hydroquinone, p-methoxyphenol, t-butylhydroxy-anisole, n-octadecyl-3- (4-hydroxy-3, 5-di-t-butylphenyl) propionate, 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 a secondary battery, characterized in that selected from the group consisting of nordihydroguaiaretic acid. The secondary battery of claim 4, wherein the phenolic heat stabilizer is n-Octadecyl-3- (4-hydroxy-3,5-di-t-butyl phenyl) propionate. The secondary battery of claim 1, wherein the thermal stabilizer is added in an amount of about 0.01 wt% to about 5 wt% based on the total weight of the battery case. The secondary battery of claim 1, wherein the heat stabilizer is added by coating on an inner resin layer. The secondary battery according to any one of claims 1 to 7, wherein the secondary battery is a lithium secondary battery impregnated with a lithium salt-containing non-aqueous electrolyte. A battery case for a secondary battery manufacture, comprising a laminate sheet comprising a resin layer and a metal layer, wherein a heat stabilizer is added to the internal resin layer. The battery case for a secondary battery manufacturing according to claim 9, wherein a portion to which the heat stabilizer is added is part of an inner resin layer or an entire inner resin layer including a case outer peripheral portion to form a sealing portion by heating and pressing. (i) dissolving the heat stabilizer in an organic solvent and then dispersing to prepare a coating solution; (ii) coating the coating solution prepared in step (i) on the inner surface of the laminate sheet or case; And (iii) forming a sealing part by heating / pressing the outer peripheral part of the case in which the heat stabilizer is coated; Method of manufacturing a secondary battery according to claim 1 comprising a. The method of claim 11, wherein the organic solvent is NMP.

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