KR20150056944A - Pouch-type Secondary Battery Having pH indicator - Google Patents

Abstract

The present invention relates to a secondary battery where an electrode assembly in the structure of a positive electrode/a separation film/a negative electrode is sealed with an electrolyte inside a pouch type battery case. In order to detect the penetration of moisture to the inside of the battery or the leakage of the electrolyte from the battery, provided is the secondary battery where a pH indicator, changing a color in accordance with pH, is added to the battery case in the state of not being in contact with the sealed electrolyte.

Description

[0001] The present invention relates to a pouch-type secondary battery having a pH indicator,

The present invention relates to a pouch type secondary battery including a pH indicator

As technology development and demand for mobile devices are increasing, the demand for batteries as energy sources is rapidly increasing, and accordingly, a lot of researches on batteries capable of meeting various demands have been conducted.

Typically, in terms of the shape of a battery, there is a high demand for a prismatic secondary battery and a pouch-type secondary battery which can be applied to products such as mobile phones with a small thickness, and has advantages such as high energy density, discharge voltage, There is a high demand for lithium secondary batteries such as lithium ion batteries and lithium ion polymer batteries.

Also, the secondary battery is classified according to how the electrode assembly having the anode / separator / cathode structure is formed. Typically, the long battery-shaped anodes and cathodes are jelly- A stacked (stacked) electrode assembly in which a plurality of positive electrodes and negative electrodes cut in units of a predetermined size are sequentially stacked with a separator interposed therebetween, a stacked (stacked) electrode assembly in which a predetermined unit of positive and negative electrodes are stacked, A stack / folding type electrode assembly in which a Bi-cell or a full cell stacked in a single state is wound up as a separation film can be given.

Recently, a pouch-shaped battery having a structure in which a stacked or stacked / folded electrode assembly is embedded in a pouch-shaped battery case of an aluminum laminate sheet is attracting much attention due to low manufacturing cost, small weight, Its usage is also gradually increasing.

In this regard, FIG. 1 schematically shows a general structure of a conventional pouch-type secondary battery.

1, the battery case 100 includes a main body 103 having a storage portion 101 for mounting an electrode assembly (not shown) and a main body 103, And a lid 102 of a type that can be used.

Therefore, after the electrode assembly is attached to the housing portion 101 of the battery case 100, the pouch type secondary battery is bent at the connection portion between the main body 103 and the lid 102 to seal the housing portion 101 The lid 102 and the three sealing portions of the main body 103 except for the bent portion are thermally fused.

2 is a cross-sectional view of a laminate sheet for forming a battery case 101 in the secondary battery of FIG.

Referring to FIG. 2, the laminate sheet includes an outer coating layer 203 forming an outermost layer, a metal barrier layer 202 preventing penetration of a material, and an inner sealant layer 201 for sealing.

The inner sealant layer 201 serves to provide sealing property by mutually heat-sealing by heat and pressure applied while the electrode assembly is embedded, and is mainly composed of CPP (unleaded polypropylene film).

The barrier layer 202 may be made of aluminum (Al) or an aluminum alloy so as to exhibit a function of preventing foreign matter from entering or leaking.

In the case of applying heat to the sealing portions of the main body 103 and the lid 102 in which the inner sealant layer 201 corresponding to the innermost layer face each other in the thermal fusion process, the inner sealant layer 201 is melted The main body 103 and the lid 102 are joined and sealed by fusion.

However, during the manufacturing process of the battery, in the deep-drawing process for forming the electrode assembly accommodating portion 101 in the battery case 100 or the heat-sealing process for forming the outer circumferential sealing portion of the battery case, Or excessive thermal fusion may be performed to expose the metal barrier layer 202 while the outer coating layer and / or the inner sealant layer 201 are partially broken.

In this case, since the sealing property of the battery is lowered, there is a problem that the electrolytic solution leaks to the outside or moisture from the outside can penetrate into the battery. When the exposed aluminum layer comes into contact with the electrolytic solution or the electrode tab, Is destroyed.

At this time, aluminum as a barrier layer has a large difference in electromotive force from nickel as an electrode lead and a connecting member. Therefore, when the secondary battery is charged and discharged in the above-described electrically connected state, corrosion of aluminum proceeds.

As a result, the water introduced through the outer coating layer having no moisture barrier property flows into the battery case through the fine cracks formed in the aluminum layer, causing swelling of the battery. As a result, safety of the lithium secondary battery, Or diffused moisture may cause adverse effects such as swelling of the battery, deterioration of lifetime characteristics, deterioration of long-term storage characteristics, and reduction of insulation resistance. Therefore, it is very important to seal the lithium ion secondary battery after injecting the electrolyte solution.

Therefore, it is necessary to form the battery so that the electrolyte does not leak first. However, once the electrolyte is leaked, it is necessary to quickly find the cell and remove or replace it so as not to damage the electric / electronic device. When a large amount of electrolytic solution flows out and the outside of the cell shows damage, it is possible to easily determine the leakage of the electrolytic solution. However, it can be very difficult to detect, replace, or remove electrolyte leakage if it is continuously drained from the battery in small quantities through some vulnerable parts.

In particular, a secondary battery used in a middle- or large-sized battery pack as a power source for an electric vehicle or a hybrid automobile requires a long-term service life, and it is very important to secure safety because of the characteristics of a large number of battery cells.

Therefore, there is a high need for a technology that can fundamentally solve these problems.

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

The present inventors have found that when an indicator layer causing color change depending on pH is formed in a certain layer constituting a battery case, it is possible to easily perceive the penetration of moisture into the naked eye or leakage of the electrolyte due to the color change of the indicator And finally completed the present invention.

It is still another object of the present invention to provide a battery which can easily distinguish a defective battery or a battery that has reached the end of its life from a normal yield battery and can prevent damage to the apparatus due to moisture permeation or leakage of the electrolyte and heavy metal poisoning of the human body from heavy metals contained in the electrolyte .

To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a pouch-shaped battery case according to the present invention is a secondary battery in which an electrode assembly having a positive electrode / separator / negative electrode structure is sealed inside a pouch- A pH indicator that causes a color change depending on pH is added to the battery case in a state in which the pH indicator is not in contact with the sealed electrolyte so that leakage of the electrolyte solution from the battery can be detected.

Therefore, in the pouch-shaped battery case according to the present invention, in addition to the conventional pouch-shaped battery case, a pH indicator for causing a color change depending on pH is further added, so that the reaction product of lithium salt and water contained in the electrolytic solution It is possible to easily visually observe the penetration of water or leakage of the electrolytic solution due to the color change of the pH indicator according to the pH of the reaction product or the leakage electrolyte, It is possible to prevent the performance degradation and the damage of the apparatus itself.

Further, since the damaged battery can be easily distinguished from the normal battery, it is possible to prevent damage to the apparatus due to moisture infiltration or leakage of the electrolyte, and secondary damage caused by the leak.

The secondary battery according to the present invention may be composed of a laminate sheet including a resin layer and a metal layer.

Since the resin layer protects the battery from the outside, the resin layer must have excellent resistance to the external environment, so that it is required to have excellent tensile strength and weather resistance against the thickness. For example, polyethylene terephthalate (PET), polybutylene terephthalate A polyolefin resin such as polyethylene (PE) or polypropylene (PP), a polystyrene resin such as polystyrene, a polyvinyl chloride resin (polyvinyl chloride resin) such as polyvinylidene fluoride , A polyvinylidene chloride-based resin, and the like can be used. These materials can be used alone or in combination of two or more, and ONy (stretched nylon film) is widely used.

The metal layer may be made of aluminum (Al) or an aluminum alloy so as to exhibit a function of improving the strength of the battery case in addition to a function of preventing foreign matter such as gas and moisture from leaking or leaking. As the aluminum alloy, Alloy Nos. 8079, 1N30, 8021, 3003, 3004, 3005, 3104, 3105, etc. These may be used singly or in combination of two or more.

The electrolyte solution containing a lithium salt is composed of an electrolyte solution and a lithium salt. As the electrolyte solution, non-aqueous organic solvents, organic solid electrolytes, inorganic solid electrolytes, and the like are used.

Examples of the non-aqueous organic solvent include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), N-methyl-2-pyrrolidinone, gamma-butylolactone, 1,2-dimethoxyethane, tetrahydroxyfurans, 2-methyltetrahydrofuran, Dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethyl formamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, An aprotic organic solvent such as propane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl pyrophosphate and ethyl propionate may be used, But is not limited thereto.

In order to further prevent aging and / or deterioration of the negative electrode due to decomposition of the electrolytic solution, the non-aqueous liquid electrolyte of the present invention may contain an ester compound (for example, vinylene carbonate) having a cyclic molecular structure and a C═C unsaturated bond in the ring Small amounts can be added.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, A polymer containing an ionic dissociation group 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 and sulfates of Li such as Li ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be used.

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

For the purpose of improving the charge / discharge characteristics and the flame retardancy, the electrolytic solution is preferably mixed with an organic solvent such as pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, . In some cases, 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 a preferred _{embodiment, LiPF 6, LiClO 4, LiBF} 4, LiN (SO 2 CF 3) 2 , such as a lithium salt, a highly dielectric solvent of DEC, DMC or EMC Fig solvent cyclic carbonate and a low viscosity of the EC or PC of And then adding it to a mixed solvent of linear carbonate to prepare a lithium salt-containing non-aqueous electrolyte.

The present invention provides a lithium secondary battery in which the non-aqueous liquid electrolyte is added to an electrode assembly of an anode, a cathode, and a separator.

In the secondary battery according to the present invention, the pH indicator may change color in an acid condition, and in one specific example, the color may be changed at a pH of 6.6 or less, more specifically, The color may change under the conditions of 5.6.

The pH indicator may be selected from the group consisting of Alizarin Blue, Methyl Violet, O-Cresol Red, Crystal Violet, Erythrosin, Thymol Blue, m - m -Cresol Red, Methyl Violet 6B, Aminoazobenzene, Alizarin Yellow R, β-Dinitrophenol (2,6-Dinitrophenol) ), methyl orange (methyl orange), Congo Red (Congo Red), p - ethyl orange (p -Ethyl orange), naphthyl red (naphthyl Red), methyl red (methyl Red), carboxylic acid (Carminic acid), and Chlorophenol Red, and the like, and the type of the electrolytic solution or the lithium salt is discolored according to the acidity (pH) of the acid generated by the reaction with moisture.

The pH range at which specific color change occurs for each pH indicator and the hue at each range are shown in FIG.

The battery case of the secondary battery according to the present invention includes a pH indicator or a coating layer formed of a pH indicator on the outer surface of the battery case. Therefore, in the process of manufacturing the battery and the battery pack, It is possible to visually confirm the penetration of moisture or leakage of the electrolyte due to the change.

In addition, it is possible to clarify whether the electrolyte is missing or not, thereby securing the performance and safety of the secondary battery in the production and discharge of the battery. That is, by applying the present invention, it is possible to prevent leakage of a battery in which an electrolyte is missing during the manufacturing process.

In one specific example, the coating layer may be a litmus paper having a litmus pigment. Therefore, the color of the litmus pigment may change according to the acidity of the electrolyte, thereby allowing the user to detect the leakage of the electrolyte.

The litmus paper is one of test papers for determining whether the sample solution is acidic or alkaline, and is made using a pigment obtained from moss named litmus. Litmus paper has red and blue colors. Each litmus alcohol solution is added with a small amount of hydrochloric acid or ammonia to make a red or blue color, which is then impregnated with a filter paper and dried. The color change zone of litmus paper is pH 5.0 to 8.0, it turns red when put in acid solution, and becomes blue when put into basic solution.

Further, for example, the coating layer may be an oil paper having physical properties capable of wetting the electrolyte solution, but is not limited thereto.

The fat may be a natural pulp nonwoven fabric. The oil seeps into the leaked electrolytic solution. The electrolytic solution retaining neutrality inside the case contacts with the air to become acidified, and the color of the sustainable color may change. At this time, it is needless to say that the indicator may be arranged on the rim of the coating layer which is in contact with the air, particularly as a piece of small oil.

The battery case of the secondary battery according to the present invention may have a structure in which the outer circumferential surface is sealed by heat sealing while the electrode assembly and the electrolyte are embedded.

In one specific example, a pH indicator may be added on the outer circumferential sealing portion of the battery case to facilitate detection in a portion where the risk of electrolyte leakage is large. Therefore, the penetration of water or leakage of the electrolytic solution can be promptly confirmed, and the effect of replacing the battery or reducing the damage of the device can be obtained.

In one specific example, the end of the outer surface sealing portion may be wrapped by a film, and in particular the film may comprise a pH indicator or may comprise a pH indicator.

Therefore, by applying the film to only the end portion of the sealing portion, it is possible to easily confirm moisture infiltration or leakage of the electrolyte solution, and also an effect of reducing manufacturing cost can be obtained.

6, a pH indicator is provided on a central portion of the battery case lid or on the outer surface of the lower storage portion, and a pH indicator is provided on a portion of a portion of the battery case other than the sealing portion. Can be added. Therefore, compared with the case where the pH indicator is added only on the outer circumferential sealing portion of the battery case, it is easier to check the penetration of moisture or the leakage of the electrolyte, so that the battery can be replaced more quickly.

The present invention also provides a positive electrode for a lithium secondary battery, wherein the positive electrode active material as described above is applied to a current collector. A specific method for producing the positive electrode including the positive electrode active material according to the present invention will be described below.

First, the cathode active material of the present invention, the binder and the conductive agent are added to the dispersion in an amount of 1 to 20% by weight with respect to the cathode active material and stirred to prepare a paste, which is then applied to a metal plate for current collector, And dried to produce a laminate-shaped electrode.

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 change in the battery, and may be formed of a material such as stainless steel, aluminum, nickel, titanium, sintered carbon, or a surface of aluminum or stainless steel Treated with carbon, nickel, titanium, silver or the like may be used. The current collector may have fine irregularities on the surface thereof to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), cellulose, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene, butylene, rubber, fluorocarbon rubber, various copolymers and the like. .

The conductive agent is not particularly limited as long as it has electrical conductivity without causing any chemical change in the battery, and examples thereof include graphite such as natural graphite and artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used. Concrete examples of commercially available conductive agents include acetylene black series such as Chevron Chemical Company, Denka Singapore Private Limited, Gulf Oil Company, etc., Ketjenblack, , EC series (Armak Company), Vulcan XC-72 (Cabot Company), and Super P (Timcal).

The filler is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery, and examples thereof include an olefin polymer such as polyethylene and polypropylene ; Fibrous materials such as glass fibers and carbon fibers are used.

Typical examples of the dispersion include isopropyl alcohol, N-methyl pyrrolidone (NMP), and acetone.

The method of applying the paste of the electrode material to the metal material in a uniform manner can be selected from known methods in consideration of the characteristics of the material and the like or can be carried out by a new suitable method. For example, the paste can be uniformly dispersed by using a doctor blade or the like after being distributed on the current collector. In some cases, a method of performing the distribution and dispersion processes in a single process may be used. In addition, a die casting method, a comma coating method, a screen printing method, or the like may be used. Alternatively, the resin may be formed on a separate substrate, and then pressed or laminated by a pressing or laminating method. .

Drying of the paste applied on the metal plate is preferably performed in a vacuum oven at 50 to 200 DEG C for 1 to 3 days.

The present invention also provides a lithium secondary battery comprising an electrode assembly in which the positive electrode faces the negative electrode with a separating film sandwiched therebetween, and a non-aqueous electrolyte containing a lithium salt.

The negative electrode may be formed by coating a negative electrode active material on a negative electrode collector and drying the negative electrode active material. If necessary, the negative electrode may further include components such as a conductive agent, a binder, and a filler as described above.

The negative electrode collector is generally made to have a thickness of 3 to 500 mu m. Such an anode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and may be formed of a material such as copper, stainless steel, aluminum, nickel, titanium, fired carbon, surface of copper or stainless steel A surface treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

The negative electrode active material may include, for example, carbon such as non-graphitized carbon or graphite carbon; Li _x Fe ₂ O ₃ (0 _x 1), Li _x WO ₂ (0 _x 1), Sn _x M4 _1-x M5 _y O _z (M4: Mn, Fe, Pb, , B, P, Si, Group 1, Group 2 and Group 3 elements of the periodic table, Halogen, 0 <x <1> 1 <y> 3, 1 <z <8); Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{SnO, SnO 2, PbO, PbO} 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4, Bi ₂ O ₅ and the like; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

The separation membrane 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 0.01 to 10 mu m and the thickness is generally 5 to 300 mu m. Such separation membranes include, for example, olefinic polymers such as polypropylene, which are chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like; Kraft paper and the like are used. Representative examples currently on the market include the Celgard ^R 2400, 2300 (from Hoechest Celanese Corp.), polypropylene separator (from Ube Industries Ltd. or Pall RAI), and polyethylene series (from Tonen or Entek).

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

When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

The present invention also provides a battery pack including the lithium secondary battery as a unit battery and a device including the battery pack as a power source.

Specifically, the battery pack may be used as a power source for devices requiring high temperature safety, long cycle characteristics, and high rate characteristics. Examples of such devices include mobile electronic devices, power tools that are powered by a battery- a power tool; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and the like; An electric motorcycle including an electric bike (E-bike) and an electric scooter (E-scooter); An electric golf cart; And a power storage system, but the present invention is not limited thereto.

The middle- or large-sized battery module is configured to include a plurality of battery cells, and accordingly, the cost of the members used for manufacturing the battery cell greatly affects the manufacturing cost of the entire battery module. Therefore, It can be particularly preferably applied to a battery module.

The structure of these devices and their fabrication methods are well known in the art, and a detailed description thereof will be omitted herein.

As described above, the secondary battery according to the present invention has a pH indicator, which causes a color change depending on pH, to be added to the battery case in a state not in contact with the sealed electrolyte, The leakage of the electrolytic solution can be visually confirmed easily.

Further, by constituting the pH indicator, it is possible to prevent degradation of performance of the battery itself or damage of the device due to electrolyte leakage and heavy metal poisoning of the human body.

1 is an exploded perspective view of a general structure of a conventional pouch type secondary battery;
2 is a schematic view of a cross-sectional structure of a conventional laminate sheet;
3 is a schematic view of a cross-sectional structure of a laminate sheet according to one embodiment of the present invention;
4 is a schematic view of a pouch-shaped battery case according to an embodiment of the present invention;
5 is a schematic view of a pouch-shaped battery case according to an embodiment of the present invention;
6 is a schematic view of a pouch-shaped battery case according to an embodiment of the present invention; And
7 is a color change chart according to the pH of the pH indicator of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings, but the present invention is not limited by the scope of the present invention.

3 is a schematic view showing a cross-sectional structure of a laminated sheet according to an embodiment of the present invention.

Referring to this figure, the laminate sheet constituting the battery case is laminated in this order from the inner side to the inner sealant layer 301, the metal barrier layer 302, the outer cover layer 303, and the indicator layer 304 .

2, which is a conventional laminate sheet, an indicator layer is further laminated on the outer layer of the outer coating layer 203, so that it is possible to prevent the leakage of water into the battery or leakage of the electrolyte from the battery, It can be easily confirmed with the naked eye.

4 to 6 are schematic views of a pouch-shaped battery case according to an embodiment of the present invention.

4 shows a pouch-type battery case manufactured by using a laminate sheet including a pH indicator or a coating layer 401 made of a pH indicator on the entire outer surface of the battery case as one embodiment of the present invention have.

5 shows a structure in which a pH indicator is added 501 on the outer circumferential sealing portion of the battery case according to another embodiment of the present invention. In FIG. 6, as another embodiment of the present invention, A pH indicator is added (601) on a part of the part excluding the part of the battery case, that is, the central part of the lid of the battery case or the outer surface of the lower storage part.

Specifically, the laminate sheet may be provided with a pH indicator on the outer circumferential sealing portion where the inner sealant layer is broken due to high-temperature heat or the like in the outer circumferential surface of the battery case, and the electrolyte is liable to leak to the outside, The end of the outer surface sealing part may include a pH indicator or may be surrounded by a film 401 comprising a pH indicator.

More specifically, the film 401 may be formed so as to enclose only three sealing portions 501 of the main body 103 except the bending portion in order to seal the receiving portion 101 of the battery case 100.

FIG. 7 shows a color change table according to the pH of the pH indicator of the present invention.

The pH indicator is a reagent for determining whether a solution is acidic or basic and the indicator itself has a weak acid or base and changes to a unique color as shown in FIG. 7 depending on the acidity of the solution.

For example, when water penetrates into the battery, LiPF ₆ reacts with moisture in the electrolyte to generate HF. When the HF reacts with the pH indicator constituting the outer surface of the battery case, a color change occurs.

As another example, when the electrolyte is leaked, since EC, EMC, etc. constituting the electrolyte solvent are acidic, when the electrolyte solution flowing out of the battery case reacts with the pH indicator constituting the outer surface of the battery case, The color changes depending on the pH of the solution.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments.

Claims (16)

A secondary battery in which an electrode assembly having a positive electrode / separator / negative electrode structure is sealed inside a pouch-shaped battery case together with an electrolyte. The secondary battery has a color change according to the pH to allow moisture penetration into the battery or leakage of electrolyte from the battery. Is added to the battery case in a state in which the pH indicator is not in contact with the sealed electrolyte. The secondary battery according to claim 1, wherein the battery case comprises a laminate sheet including a resin layer and a metal layer. The secondary battery according to claim 1, wherein the pH indicator changes color in an acid condition. The secondary battery according to claim 3, wherein the pH indicator is changed in color at a pH of 6.6 or less. The secondary battery according to claim 3, wherein the pH indicator is changed in color from pH 0.1 to pH 5.6. The pH indicator of claim 1, wherein the pH indicator is selected from the group consisting of Alizarin Blue, Methyl Violet, O-Cresol Red, Crystal Violet, Erythrosin, blue (Thymol blue), m - cresol red (m -Cresol Red), methyl violet 6B (methyl Violet 6B), amino-azobenzene (Aminoazobenzene), alizarin yellow R (alizarin yellow R), β- dinitrophenol (β-dinitrophenol (2,6-Dinitrophenol)), methyl orange (methyl orange), Congo Red (Congo Red), p - ethyl orange (p -Ethyl orange), naphthyl red (naphthyl Red), methyl red (methyl Red), carboxylic Wherein the secondary battery is at least one selected from the group consisting of carminic acid, and chlorophenol red. The secondary battery according to claim 1, wherein a coating layer comprising a pH indicator or a pH indicator is provided on the outer surface of the battery case. The secondary battery according to claim 7, wherein the coating layer is composed of litmus paper or oil paper. The secondary battery according to claim 1, wherein the battery case has a structure in which an outer circumferential surface of the battery case is thermally fused and sealed with the electrode assembly and the electrolyte contained therein. The secondary battery according to claim 9, wherein a pH indicator is provided on the outer circumferential sealing portion of the battery case. The secondary battery according to claim 10, wherein an end of the outer circumferential sealing portion is wrapped by a film. The secondary battery according to claim 11, wherein the film comprises a pH indicator or a pH indicator. The secondary battery according to claim 9, wherein a pH indicator is added to a portion of the battery case excluding the sealing portion. A battery pack comprising a secondary battery according to any one of claims 1 to 13 as a unit cell. A device comprising the battery pack according to claim 14 as a power source. 16. The device of claim 15, wherein the device is a mobile electronic device, an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a power storage device.

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