JP4747583B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a conductive polymer film applied thereto and an anion contained in the non-aqueous electrolyte.

  Non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries with high energy density have been widely used as power sources used in the field of portable devices such as personal computers, mobile phones, digital cameras, and camcorders. In addition, development of non-aqueous electrolyte secondary batteries with high energy density is also in progress as a drive power source for electric vehicles that are required in the near future due to environmental problems and resource problems.

  In general, non-aqueous electrolytes used in today's non-aqueous electrolyte secondary batteries contain a flammable non-aqueous solvent. Further, a metal oxide such as lithium cobaltate is used for the positive electrode active material, and a carbon material such as graphite is used for the negative electrode active material. Therefore, when the temperature of the non-aqueous electrolyte secondary battery rises abnormally for some reason, the positive electrode active material decomposes and generates oxygen. When the oxygen oxidizes the negative electrode active material and the non-aqueous solvent, the battery bursts. There is a risk of thermal runaway. The abnormal temperature rise of the non-aqueous electrolyte secondary battery includes an overall temperature rise of the battery due to overcharging and a local temperature rise of the battery due to an internal short circuit. If both occur at the same time, the risk becomes even higher. Therefore, in order to improve the safety of the battery, it is required to prevent overcharging and to prevent an internal short circuit at a location where the positive electrode active material, the negative electrode active material, and the nonaqueous solvent coexist.

  As a conventional technique for preventing overcharging of a battery, a conductive material that exhibits conductivity by doping ions is present between the positive electrode and the negative electrode, so that when the battery is overcharged, There is a technique for preventing overcharging by short-circuiting (see, for example, Patent Document 1 and Patent Document 2).

In Patent Document 1, an internal short circuit is formed between the positive electrode and the negative electrode during overcharge by interposing a separator including a polymer that develops conductivity by doping ions between the positive electrode and the negative electrode. A technique for generating and preventing further overcharge is disclosed. In addition, Patent Document 2 discloses that a conductive additive generated in the electrolyte causes an internal short circuit between the positive electrode and the negative electrode by adding a monomer additive that generates a conductive polymer by polymerization at an overcharge voltage. Discloses a technique for preventing overcharge.
JP-A-2-199769 JP-A-10-32258

  However, in the above-described conventional technology, the internal short circuit generated by the conductive polymer is where the positive electrode active material, the negative electrode active material, and the nonaqueous solvent coexist between the positive and negative electrodes. When the battery is overcharged and the decomposition temperature of the positive electrode active material is low, when the positive electrode and the negative electrode are short-circuited at the location where the positive electrode active material exists, Joule heat is generated at the short-circuit location due to the short-circuit current. Therefore, the local temperature further rises, and the positive electrode active material is easily decomposed to generate oxygen. Therefore, the risk that the internal pressure of the battery rises and the battery bursts increases. Furthermore, when the local temperature exceeds the ignition temperature of the non-aqueous solvent or the oxidation reaction temperature of the negative electrode active material, oxygen produced from the positive electrode active material burns them, and the risk of the battery running out of heat increases.

  Therefore, the present invention provides a technique for preventing overcharging and preventing an internal short circuit at a location where the positive electrode active material, the negative electrode active material, and the nonaqueous solvent coexist, and the nonaqueous solution that is extremely excellent in safety by the technique. Providing an electrolyte secondary battery is a problem to be solved.

In order to solve the above problems, the non-aqueous electrolyte secondary battery of the present invention includes a positive electrode in which a layer containing a positive electrode active material is formed on a positive electrode current collector, and a negative electrode active material on the negative electrode current collector. A non-aqueous electrolyte secondary battery in which an electrode body having a wound structure in which a negative electrode formed with a containing layer is wound via a separator is accommodated in a battery case and a non-aqueous electrolyte is injected. The exposed portion of the positive electrode current collector and the exposed portion of the negative electrode current collector of the wound structure electrode body are opposed to each other through a conductive polymer film, and the conductive polymer film has a battery voltage of 4 It is characterized by having an insulating property at .2V or less and conductivity when the battery voltage exceeds 4.2V . That is, a portion where the active material does not exist is provided in a part of the positive electrode and the negative electrode inside the battery, and a general separator is used when the battery voltage is 4.2 V or less in a normal use state, instead of the separator between both electrodes of the part. By placing a conductive polymer film that is electrically insulating and has an overcharged state of 4.2 V , an anion contained in the non-aqueous electrolyte is doped to express conductivity, and at the time of overcharge The positive electrode and the negative electrode are short-circuited to prevent further overcharge from proceeding. And since a short circuit generate | occur | produces in the location where a positive electrode active material and a negative electrode active material do not exist, generation | occurrence | production of oxygen from a positive electrode active material can be suppressed. Therefore, the battery can be prevented from bursting without increasing the internal pressure of the battery, and further, the negative electrode active material and the electrolyte can be prevented from burning.

Then, before Kishirube conductive polymer film polythiophene, polyfuran, it is preferably at least one selected from the group consisting of polyparaphenylene and derivatives thereof. Using a conductive material with a battery voltage of 4.2 V or less in normal use will discharge during storage of the battery, and the battery capacity will decrease as the conductivity increases. A material that is not conductive as much as possible is desired. In addition, as the battery voltage increases in an overcharged state exceeding 4.2 V, the positive electrode active material becomes unstable and easily decomposes, so that the battery is discharged with a low overcharge voltage. In order to efficiently perform the short-circuit discharge, a material having high conductivity is desired. The above material group is a preferable material that satisfies these requirements.

The anion contained in the non-aqueous electrolyte is preferably at least one of PF ₆ ⁻ and BF ₄ ⁻ . A general non-aqueous electrolyte is composed of at least a non-aqueous solvent and an electrolyte. If a compound containing these anions, such as LiPF ₆ or LiBF ₄ , is selected as the electrolyte, these electrolytes are dissolved in the non-aqueous solvent. The above-mentioned anions generated in the above can be included in the battery. Since the conductive polymer doped with these anions has high conductivity, short-circuit discharge during overcharge can be efficiently performed.

  According to the present invention, the battery can be prevented from being overcharged, and an internal short circuit can be prevented at a location where the positive electrode active material, the negative electrode active material, and the nonaqueous solvent coexist. A liquid secondary battery can be provided.

As described above, the present invention provides a positive electrode formed by forming a layer containing a positive electrode active material on a positive electrode current collector, and a negative electrode formed by forming a layer containing a negative electrode active material on a negative electrode current collector. The positive electrode current collector in the wound electrode body of a non-aqueous electrolyte secondary battery in which a non-aqueous electrolyte secondary battery in which a non-aqueous electrolyte solution is injected is accommodated in a battery case. The exposed portion of the negative electrode current collector and the exposed portion of the negative electrode current collector face each other through a conductive polymer film, and the conductive polymer film has an insulating property when the battery voltage is 4.2 V or less, and the battery voltage is 4. It has been found that, when the voltage exceeds 2 V , an anion contained in the non-aqueous electrolyte is doped to form a film that exhibits conductivity, thereby providing a non-aqueous electrolyte secondary battery that is extremely excellent in safety. Further, the material of the conductive polymer film polythiophene, polyfuran, preferably when selected from the group consisting of polyparaphenylene and derivatives thereof, anion contained in the non-aqueous electrolyte, PF ₆ ^-, BF ₄ ^- at least one It has been found that it is still more preferable.

  Hereinafter, the nonaqueous electrolyte secondary battery of the present invention will be described in detail based on embodiments. In the present embodiment, a non-aqueous electrolyte secondary battery will be described based on a lithium ion secondary battery.

(Conductive polymer)
The conductive polymer of the present invention is a film that has an insulating property when the battery voltage is 4.2 V or less, and exhibits conductivity when the battery voltage exceeds 4.2 V and is doped with an anion contained in the non-aqueous electrolyte. It is.

  There are various polymer materials in the conductive polymer, and some of them are known to be doped with anions or cations to increase the electronic conductivity at a constant potential. Examples thereof include polyacetylene, polypyrrole, polyparaphenylene, polyparaphenylene vinylene, polythiophene, polyfuran, polyaniline, and derivatives thereof. These conductive polymer materials can be synthesized by chemically and electrochemically polymerizing the corresponding monomers of acetylene, pyrrole, benzene, biphenyl, thiophene, furan, aniline and derivatives thereof. In particular, a film-like conductive polymer can be easily prepared by electrochemically polymerizing on a flat plate electrode.

The potential at which these conductive polymers are doped with anions or cations varies depending on the combination of the conductive polymer and ions. For example, the potential Li ⁺ cations are doped polyacetylene is ^{0.4V (Li / Li +),} PF 6 polyacetylene ^- potential anion is doped is 3.2V (Li / Li ^+). The conductivity of the conductive polymer varies depending on the type and concentration of ions to be doped. For example, the conductivity of polyacetylene that is not doped with ions is as low as 10 ⁻⁶ Ω ⁻¹ cm ⁻¹ and can be regarded as an insulator, but when doped with 1% PF ₆ ⁻ anion, it is 1 Ω ⁻¹ cm ^{−. 1,} 3% or more PF ₆ ^- anions exhibits high conductivity of about metal and the 10 ² Ω ^-1 cm ^-1 is doped. However, the polyacetylene exemplified here is not suitable for the conductive polymer of the present invention. This is because, PF ₆ polyacetylene as described previously ^- for potential anion is doped is ^{3.7V (Li / Li +),} 4.2V below the lithium ion secondary battery is a voltage used in the normal This is because the battery is discharged with high conductivity. The inventors searched for a conductive polymer that exhibits conductivity at a battery voltage exceeding 4.2 V, and as a result of various investigations, have found that polythiophene, polyfuran, polyparaphenylene, and derivatives thereof are preferable. When thiophene and furan are polymerized, they are bonded at the 2nd and 5th positions, so that the derivatives of thiophene and furan at the 3rd and 4th positions are desirable. Since polyparaphenylene, which is a polymer of benzene, is bonded at the 1-position and 4-position, the derivatives are preferably 2-, 3-, 5- and 6-position substituted derivatives. Also when polyparaphenylene is polymerized from biphenyl, a biphenyl derivative corresponding to the dimer of the benzene derivative is desirable. More specifically, alkyl group, acetyl group, hydroxyl group, aldehyde group, sulfo group, nitro group, amino group, carboxyl group, carbonyl group, imino group, cyano group, aryl group, thiol group, sulfo group, phenyl group And functional groups such as allyl group, azo group, naphthyl group and carbonitrile group, and substituted derivatives with halogen such as fluorine, chlorine, bromine and sulfur. Among them, the electron-withdrawing group and the halogen-substituted derivative polymer are doped with anions, and the potential to develop conductivity is high, and the electron-donating group substituted derivative polymer is doped with anions to develop conductivity. The potential tends to be low, and the potential at which conductivity is exhibited can be controlled by selecting the type and number of substituents. As for the polythiophene derivative and the polyfuran derivative, a derivative in which only one of the 3-position and the 4-position is substituted is more preferable because the conductivity is higher than that of the derivative in which both the 3-position and 4-position are substituted.

(Non-aqueous electrolyte secondary battery)
In the nonaqueous electrolyte secondary battery of the present invention, known battery structures such as a cylindrical type, a square type, and a sheet type can be adopted. Regardless of the shape, a positive electrode and a negative electrode are wound in a battery case, and the positive electrode and the negative electrode current collector are connected to the outside. After connecting between the terminal and the negative electrode terminal using a current collecting lead or the like, a non-aqueous electrolyte is injected and sealed.

The positive electrode is made by mixing a conductive material and a binder with a positive electrode active material capable of inserting and extracting lithium ions, and adding a suitable solvent to form a paste-like positive electrode mixture of a metal foil such as aluminum. It is formed by applying and drying on the surface of the current collector and forming a layer containing the active material by subsequent rolling. In order to provide a portion where the active material-containing layer is not formed on a part of the positive electrode, when the positive electrode mixture is applied to the current collector surface in the above process, it is not partially applied, or After coating, the layer containing the active material is partially peeled from the current collector. As the positive electrode active material, a known positive electrode active material such as a lithium transition metal composite oxide or a transition metal polyanion compound can be used. Lithium transition metal composite oxides include lithium cobalt oxide (LiCoO ₂ ), modified lithium cobaltate, lithium nickelate (LiNiO ₂ ), modified lithium nickelate, lithium manganate (LiMn ₂ O ₂ ), manganic acid Modified lithium, a part of Co, Ni or Mn of these oxides is substituted with other transition metal elements, typical metals such as aluminum, and alkaline earth metals such as magnesium. The transition metal polyanion compound is a phosphoric acid compound or sulfuric acid compound such as manganese, iron, cobalt, or nickel having a NASICON structure or an olivine structure. When these lithium transition metal composite oxides and transition metal polyanion compounds are used as the positive electrode active material, they can be used alone or in combination. The conductive material is for ensuring the electrical conductivity of the layer containing the active material of the positive electrode, and is a combination of one or more carbon materials such as carbon black, acetylene black, ketjen black, and graphite. Things can be used. The binder is used to bind the active material and the conductive material and bind to the surface of the current collector. Polytetrafluoroethylene (PTFE), a modified PTFE, polyvinylidene fluoride (PVDF), PVDF Modified bodies, fluorine-containing resins such as fluoro rubber, thermoplastic resins such as polypropylene and polyethylene, and modified acrylonitrile rubber particles (such as “BM-500B (trade name)” manufactured by Nippon Zeon Co., Ltd.) can be used. PTFE and BM-500B can be used in combination with carboxymethylcellulose (CMC), polyethylene oxide (PEO), modified acrylonitrile rubber ("BM-720H (trade name)" manufactured by Nippon Zeon Co., Ltd.) as a thickener. preferable. As a solvent for dispersing these active material, conductive material, and binder, an organic solvent such as N-methyl-2-pyrrolidone, water, or the like can be used. At this time, it is also effective to add an additive such as a surfactant in order to improve the temporal stability and dispersibility of the paste-like positive electrode mixture. As the current collector, a metal foil stable at the positive electrode potential such as aluminum, a film in which a metal stable at the positive electrode potential such as aluminum is arranged on the surface layer, or the like can be used. In addition, in order to improve the current collecting property of the current collector, the surface can be provided with irregularities or can be perforated. The conductive polymer film only needs to have electrical continuity with a current collector portion in which a layer containing an active material is not formed on a part of the positive electrode. In addition, when the film is attached by pressure bonding, it is preferable to heat the film at a temperature lower than the alteration temperature of the conductive polymer because not only the film can be firmly attached but also the interface resistance is reduced. When the conductive polymer is soluble in a solvent, the solution can be applied to a current collector and dried to form a conductive polymer film. Although the film thickness is not limited, a thin film is preferable because the film resistance is small, but the mechanical strength is also small and the risk of film breakage increases. On the contrary, when it is thick, the mechanical strength is increased, which is preferable. However, since the film resistance is increased, efficient short-circuit discharge becomes difficult. Therefore, the thickness of the conductive polymer film is preferably in the range of 0.5 to 500 μm. In the case where a conductive polymer film is formed on a current collector portion where a layer containing an active material on the negative electrode side is not formed, it is not always necessary to form a conductive polymer film on the positive electrode side.

  A negative electrode active material capable of occluding and releasing lithium ions is mixed with a binder, and an appropriate solvent is added to form a paste-like negative electrode mixture. It is formed by applying and drying on the surface and forming a layer containing the active material by subsequent rolling. In order to provide a part where the layer containing the active material is not formed in a part of the negative electrode, when the negative electrode mixture is applied to the current collector surface in the above process, it is not partially applied, or After coating, the layer containing the active material is partially peeled from the current collector. Negative electrode active materials include various natural graphites, various artificial graphites, petroleum coke, carbon fibers, organic polymer fired products, carbon materials such as carbon nanotubes and carbon nanohorns, oxides, silicon such as silicide, tin-containing composite materials, various types A known active material such as a metal or alloy material can be used. The binder is not particularly limited, but rubber particles are preferable from the viewpoint of exhibiting binding properties in a small amount, and those containing styrene units and butadiene units are particularly preferable. For example, a styrene-butadiene copolymer (SBR), a modified SBR, or the like can be used. When rubber particles are used as the negative electrode binder, it is desirable to use a thickener composed of a water-soluble polymer. As the water-soluble polymer, a cellulose resin is preferable, and CMC is particularly preferable. In addition, PVDF, a modified form of PVDF, and the like can also be used as the binder. As the current collector, a metal foil that is stable under a negative electrode potential such as copper, or a film in which a metal that is stable under a negative electrode potential such as copper is disposed on the surface layer can be used. In addition, in order to improve the current collecting property of the current collector, the surface can be provided with irregularities or can be perforated. The conductive polymer film only needs to have electrical continuity with a current collector portion in which a layer containing an active material is not formed in a part of the negative electrode. In addition, when the film is attached by pressure bonding, it is preferable to heat the film at a temperature lower than the alteration temperature of the conductive polymer because not only the film can be firmly attached but also the interface resistance is reduced. When the conductive polymer is soluble in a solvent, the solution can be applied to a current collector and dried to form a conductive polymer film. The film thickness is not limited, but is preferably in the range of 0.5 to 500 μm for the same reason as in the case of the positive electrode. In the case where the conductive polymer film is formed on the current collector portion where the positive electrode side active material-containing layer is not formed, it is not always necessary to form the conductive polymer film on the negative electrode side.

  The separator is not particularly limited as long as the separator is a material that can withstand the use environment of the battery, and is not particularly limited as long as it is a microporous film or a non-woven fabric that permeates ions of the electrolytic solution and insulates between the positive and negative electrodes. Is generally used. As the polyolefin resin, polyethylene, polypropylene, or the like is used. The microporous film may be a single layer film made of one kind of resin, a multilayer film made of two or more kinds of resins, or a multilayer film made of an inorganic material such as resin and alumina.

  The case is not particularly limited and can be made of a known material and form. Generally, aluminum alloy, nickel-plated iron alloy, a laminate of various resins and metals, and the like are used as the material. The form is a cylindrical or square bottomed can or bag shape depending on the shape of the battery to be created.

The nonaqueous electrolytic solution is obtained by dissolving an electrolyte in an organic solvent. The organic solvent is not particularly limited as long as it is an organic solvent used in ordinary non-aqueous electrolyte secondary batteries. For example, carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, lactones An oxolane compound or the like can be used. In particular, a mixed solvent of a high dielectric constant solvent such as ethylene carbonate (EC) or propylene carbonate (PC) and a low viscosity solvent such as dimethyl carbonate (DMC), diethyl carbonate (DEC), or ethyl methyl carbonate (EMC) is preferable. . In addition, dimethoxyethane (DME), tetrahydrofuran (THF), γ-butyrolactone (GBL), or the like may be used as a co-solvent. Various additives may be used for the purpose of improving battery characteristics such as storage characteristics, cycle characteristics, and safety. In particular, it is preferable to add vinylene carbonate (VC), cyclohexylbenzene (CHB), and derivatives thereof to the nonaqueous electrolytic solution. The electrolyte is an inorganic salt selected from LiPF ₆ , LiBF ₄ , LiClO ₄ and LiAsF ₆ , a derivative of the inorganic salt, LiSO ₃ CF ₃ , LiC (SO ₃ CF ₃ ) ₂ , LiN (SO ₃ CF ₃ ) ₂ , LiN Organic salts selected from (SO ₂ C ₂ F ₅ ) ₂ and LiN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ ), and derivatives of the organic salts can be used. Among these, the use of LiPF _6, LiBF _4, as described above, the anion generated from these conductivity of doped conductive polymer is increased, performs the short-circuit discharge during overcharge efficiently This is particularly preferable in the present invention. The concentration of the electrolyte is not particularly limited, but is usually used in the range of 0.5 to 2.0 mol / l.

  Hereinafter, the nonaqueous electrolyte battery of the present invention will be described based on lithium ion secondary batteries of Examples.

(Conductive polymer film)
All of the conductive polymer films of this example were manufactured by Rieke Metals, Inc., USA. The following were manufactured and had a thickness of 30 to 50 μm.

  Conductive polymer film 1 Polyparaphenylene, conductive polymer film 2 Poly (2-methylparaphenylene), conductive polymer film 3 Poly (2,3-dimethylparaphenylene), conductive polymer film 4 Poly (2,5- Dimethylparaphenylene), conductive polymer film 5 poly (2,6-dimethylparaphenylene), conductive polymer film 6 poly (2-bromoparaphenylene), conductive polymer film 7 poly (2-carbonitrileparaphenylene), Conductive polymer film 8 Poly (2-methoxyparaphenylene), conductive polymer film 9 Poly (2-ethoxyparaphenylene), conductive polymer film 10 Polythiophene, conductive polymer film 11 Poly (3-methylthiophene), conductive Polymer film 12 Poly (3-ethylthiophene), Conductive polymer film 13 Poly (3 Propylthiophene), conductive polymer film 14 poly (3-butylthiophene), conductive polymer film 15 poly (3-pentylthiophene), conductive polymer film 16 poly (3-hexylthiophene), conductive polymer film 17 poly ( 3-octylthiophene), conductive polymer film 18 poly (3-decylthiophene), conductive polymer film 19 poly (3-dodecylthiophene), conductive polymer film 20 poly (3-phenylthiophene), conductive polymer film 21 Poly (3-carbonitrilethiophene), conductive polymer film 22 poly (3- (ethyl-5-pentanoate) thiophene), conductive polymer film 23 poly (3- (ethyl-6-hexanoate) thiophene), conductive polymer Membrane 24 Poly (3- (ethyl-7-heptanoate) thio Phen), conductive polymer film 25 polyfuran, conductive polymer film 26 poly (3-methylfuran), conductive polymer film 27 poly (3-ethylfuran), conductive polymer film 28 poly (3-propylfuran), conductive Conductive polymer film 29 Poly (3-butylfuran), Conductive polymer film 30 Poly (3-pentylfuran), Conductive polymer film 31 Poly (3-hexylfuran), Conductive polymer film 32 Poly (3-octylfuran) , Conductive polymer film 33 poly (3-decylfuran), conductive polymer film 34 poly (3-dodecylfuran), conductive polymer film 35 poly (3-phenylfuran), conductive polymer film 36 poly (3-carbonitrile Furan), conductive polymer film 37 poly (3- (ethyl-5-pentanoate) furan), conductive poly Over membrane 38 of poly (3- (ethyl-6-hexanoate) furan), a conductive polymer film 39 poly (3- (ethyl-7-heptanoate) furan).

(Lithium ion secondary battery)
The lithium ion secondary battery of this example is a lithium ion secondary battery using lithium cobaltate represented by the composition formula LiCoO ₂ as a positive electrode active material and graphite as a negative electrode active material.

a) Preparation of positive electrode 3 kg of lithium cobaltate as a positive electrode active material, 1 kg of “# 1320 (trade name)” (NMP solution containing 12% by weight of PVDF) manufactured by Kureha Chemical Co., Ltd. as a positive electrode binder, and a conductive agent As a mixture, 90 g of acetylene black and an appropriate amount of NMP were stirred with a double-arm kneader to prepare a paste-like positive electrode mixture. The positive electrode mixture was applied to both surfaces of a 15 μm thick aluminum foil as a positive electrode current collector, excluding the connection portion of the positive electrode lead and the conductive polymer film, and the dried coating film was rolled with a roller. Then, a layer containing an active material having an active material layer density (active material weight / mixture layer volume) of 3.3 g / cm ³ was formed. Under the present circumstances, the thickness of the electrode plate which consists of a layer containing an aluminum foil and an active material was controlled to 160 micrometers. Thereafter, the electrode plate was slit to a width that could be inserted into a battery can of a cylindrical battery (Part No. 18650) to obtain a positive electrode hoop.

b) Preparation of Negative Electrode 3 kg of artificial graphite as the negative electrode active material and 40% by weight of “BM-400B (trade name)” (modified styrene-butadiene copolymer) manufactured by Nippon Zeon Co., Ltd. as the negative electrode binder. (Aqueous dispersion) 75 g, 30 g of CMC as a thickener, and an appropriate amount of water were stirred with a double-arm kneader to prepare a paste-like negative electrode mixture. This negative electrode mixture was applied to both sides of a 10 μm thick copper foil as a negative electrode current collector, excluding the junction between the negative electrode lead connection portion and the conductive polymer film, and the dried coating film was rolled with a roller. Then, a layer containing an active material having an active material layer density (active material weight / mixture layer volume) of 1.4 g / cm ³ was formed. Under the present circumstances, the thickness of the electrode plate which consists of a layer containing copper foil and an active material was controlled to 180 micrometers. Thereafter, the electrode plate was slit to a width that could be inserted into a battery can of a cylindrical battery (Part No. 18650) to obtain a negative electrode hoop.

c) Preparation of non-aqueous electrolyte A non-aqueous electrolyte was prepared by dissolving an electrolyte at a concentration of 1 mol / l in a non-aqueous solvent mixture containing EC, DMC, and EMC at a volume ratio of 2: 3: 3. Further, 3 parts by weight of VC was added per 100 parts by weight of the non-aqueous electrolyte. An electrolyte solution using LiPF ₆ as an electrolyte, an electrolyte solution B using LiBF ₄ as an electrolyte, an electrolyte solution C using LiClO ₄ as an electrolyte, and an electrolyte solution using LiAsF ₆ as an electrolyte Called D.

d) Production of Battery A cylindrical battery having a product number of 18650 was produced in the following manner using the conductive polymer film, the positive electrode, the negative electrode, and the nonaqueous electrolytic solution. First, the positive electrode and the negative electrode were each cut to a predetermined length. One end of the positive electrode lead was connected to the positive electrode lead connection portion, and one end of the negative electrode lead was connected to the negative electrode lead connection portion. The conductive polymer film was pressure-bonded to the joint of the positive electrode so as to have the same width as the positive electrode and a length of 5 cm in the winding direction. FIG. 1 shows a diagram of these positive and negative electrodes. After that, the portion where the conductive polymer film of the positive electrode is joined and the current collector portion without the layer containing the active material of the negative electrode are matched so that the layer containing the active material of the positive electrode and the negative electrode faces each other Was wound through a separator made of a microporous film made of polyethylene resin having a thickness of 15 μm to constitute a cylindrical electrode body. No separator is interposed at the joint between the positive and negative electrode conductive polymer films. The outer surface of the electrode body was interposed with a separator. This electrode body was accommodated in the battery can in a state sandwiched between the upper insulating ring and the lower insulating ring. Next, 5 g of the above non-aqueous electrolyte was weighed, poured into a battery can, and impregnated into the electrode plate group by reducing the pressure to 133 Pa.

  The other end of the positive electrode lead was welded to the back surface of the battery lid, and the other end of the negative electrode lead was welded to the inner bottom surface of the battery can. Finally, the opening of the battery can was closed with a battery lid with insulating packing on the periphery. Thus, a cylindrical lithium ion secondary battery having a design capacity of 2 Ah was produced. After that, each battery was charged and discharged for 2 cycles at a constant current of 400 mA between 3 V and 4.2 V to complete the battery.

(Lithium ion secondary batteries of Examples 1 to 156)
In the production of the battery, the lithium ion secondary batteries of Examples 1 to 156 in which the conductive polymer films 1 to 39 and the electrolytes A to D are combined are distinguished from each other, and the implementation batteries 1A and 1B to 1 are implemented. It is referred to as 39D. For example, the implementation battery 1A is a lithium ion secondary battery implemented using the conductive polymer film 1, that is, polyparaphenylene and the electrolyte A, that is, the nonaqueous electrolyte using LiPF ₆ as the electrolyte.

(Lithium ion secondary batteries of Comparative Examples 1 to 4)
The lithium ion secondary battery of this comparative example does not use a conductive polymer in the preparation of the above-described battery, and the microporous material made of polyethylene resin also in the current collector portion that does not have a layer containing the active material of the positive electrode and the negative electrode The configuration and manufacturing method are the same as those of the lithium ion secondary battery of the example except that the film is wound through a separator made of a film. The lithium ion secondary batteries of the electrolytic solutions A to D used here are distinguished from one another and referred to as comparative batteries A to D.

(Lithium ion secondary batteries of Comparative Examples 5 to 7)
In the lithium ion secondary battery of this comparative example, the composite material was applied except for the lead connection part in the preparation of the positive electrode and the preparation of the negative electrode, and the conductive polymer film was activated in the positive electrode and the negative electrode in the preparation of the battery. It is a lithium ion secondary battery in which an electrode body is configured by being disposed between a positive electrode and a negative electrode having a layer containing a substance. That is, it is configured such that a short circuit due to the conductive polymer during overcharge occurs in a portion where the layer containing the active material of the positive electrode and the negative electrode is present. In any case, the electrolytic solution A was used as the nonaqueous electrolytic solution. Here, three kinds of conductive polymers of polythiophene, polyfuran, and polyparaphenylene were used.

(Overcharge test)
The battery terminal voltage and thermocouple were charged while charging the lithium ion secondary batteries of the examples and comparative examples at an environmental temperature of 20 ° C. for 2 hours at a constant current of 4 A at a rate of 0.5 hours with respect to the design capacity. Was used to measure the surface temperature.

(result)
A typical result of the overcharge test is shown in FIG. FIG. 2 is a graph in which the horizontal axis indicates the elapsed time since the start of constant current charging at 4 A, the left vertical axis indicates the battery voltage, and the right vertical axis indicates the surface temperature of the battery.

  Both the lithium ion secondary batteries of the example and the comparative example increased the battery voltage and the surface temperature by charging.

  In the lithium ion secondary batteries of Comparative Examples 1 to 4, the battery voltage suddenly increased around 45 minutes. This is because the internal resistance of the battery has increased due to the progress of overcharge. Along with this, the battery temperature suddenly increased, leading to thermal runaway.

  Since the battery voltage of the lithium ion secondary batteries of Comparative Examples 5 to 7 once flattened in about 50 minutes, the conductive polymer film was doped with anions to develop conductivity and short-circuited. Inferred. However, the surface temperature continued to rise during this period, and thermal runaway occurred around 70 minutes. Along with this, it is considered that the internal resistance of the battery increased and the battery voltage increased rapidly.

  On the other hand, in the lithium ion secondary battery of the example, the battery voltage started to decrease from around 50 minutes and then gradually decreased. Therefore, the charging rate was higher than the charged current of 4A. It is thought that internal short circuit discharge occurred. Although the temperature continued to rise slowly, thermal runaway did not occur until the end of the test. The difference in behavior between this example and Comparative Examples 5 to 7 can be considered as follows.

  The batteries of the examples and comparative examples 5 to 7 are both manufactured, and when the battery voltage exceeds 4.2 V, the conductive polymer film is doped with anions contained in the non-aqueous electrolyte so as to exhibit conductivity and short circuit. Waking up is the same. However, since the conductive polymer films of Comparative Examples 5 to 7 were provided between the layers containing the positive electrode and the negative electrode active material, the short-circuited layer was a layer containing the positive electrode active material and the layer containing the negative electrode active material. Occurs between. In general, the electric resistance of the layer containing the active material of the positive electrode is larger than the electric resistance of the layer containing the negative electrode and the electric resistance of the current collector. Therefore, the electrical resistance of the path through which the short-circuit current flows is increased, and not only high rate discharge cannot be performed, but also Joule heat generation is increased. Therefore, when the overcharge current is large, not only is it difficult to suppress the progress of overcharge, but large Joule heat generation in the layer containing the active material having a large electrical resistance causes the positive electrode to decompose and dissociate. It is considered that the oxidized oxygen oxidizes the nearby negative electrode active material and the electrolytic solution and leads to thermal runaway. On the other hand, since the conductive polymer film of the example is interposed between the positive and negative electrode active material-containing portions, that is, between the positive and negative electrode current collectors, the electrical resistance of the path through which the short-circuit current flows Is small. Therefore, high-rate short-circuit discharge is possible, and not only the progress of overcharge can be prevented even when the charging current is large, but it is also possible to discharge to the extent that the charging depth is lowered, making the battery more thermally stable. It can be in a state. Moreover, although the short circuit current of an Example is larger than the short circuit current of Comparative Examples 5-7, since the electrical resistance of the path | route through which a short circuit current flows is small, a Joule heat generation amount can be decreased below equivalent. And there is no layer containing the positive electrode active material in the path through which the short-circuit current flows. Therefore, since the positive electrode active material is decomposed to dissociate oxygen, which can eliminate the cause of thermal runaway that oxidizes the negative electrode active material and the electrolytic solution, to provide a non-aqueous electrolyte secondary battery that is extremely excellent in safety Can do.

  In FIG. 2, the result of the overcharge test is shown in a typical graph, but in order to clarify the difference in the results of many examples, the results are shown in Table 1 as numerical values. Table 1 shows the name of each battery, the type of the conductive polymer and the non-aqueous electrolyte, and the short-circuit voltage in the overcharge test (that is, the conductive polymer is doped with the anion contained in the non-aqueous electrolyte). The short circuit voltage due to the development of conductivity) and the maximum temperature reached by the battery were shown.

In any of the examples, the battery exhibited extremely excellent safety without thermal runaway. The short circuit occurred in the range of 4.23 to 4.97 V, and the maximum temperature was 85.5 ° C. at the highest. When compared with the types of conductive polymers, the short-circuit voltage of polythiophene and its derivatives tended to be low, and the short-circuit voltage of polyparaphenylene and its derivatives tended to be high, but all showed good safety. Compared with the types of non-aqueous electrolytes, the short-circuit voltage between electrolyte A and electrolyte B tends to be low and the maximum temperature tends to be low, and the short-circuit voltage between electrolyte C and electrolyte D is high and the maximum temperature tends to be high. Indicated. Therefore, PF ₆ ⁻ and BF ₄ ⁻ tended to be preferable as anions contained in the non-aqueous electrolyte.

  Thus, the short circuit current varies depending on the material of the conductive polymer film used. Therefore, even if the charging voltage of the future lithium ion secondary battery becomes higher than the present 4.2V, it is the same as that of the present invention by selecting an appropriate short-circuit voltage from the materials described in this embodiment. It will be clear that an effect is obtained.

As described above, the non-aqueous electrolyte secondary battery according to the present invention includes a positive electrode formed by forming a layer containing a positive electrode active material on the positive electrode current collector, and a negative electrode active material on the negative electrode current collector. A non-aqueous electrolyte secondary battery in which an electrode body having a wound structure in which a negative electrode formed with a layer is wound via a separator is accommodated in a battery case and then a non-aqueous electrolyte is injected. The exposed portion of the positive electrode current collector and the exposed portion of the negative electrode current collector of the wound structure electrode body are opposed to each other through a conductive polymer film, and the conductive polymer film has a battery voltage of 4 .2V or less has an insulating property, and when the battery voltage exceeds 4.2V , an anion contained in the non-aqueous electrolyte is doped to prevent the battery from being overcharged. In addition, within the place where the positive electrode active material, the negative electrode active material, and the non-aqueous solvent coexist. Short and extremely excellent in safety since it is possible to prevent, useful for non-aqueous electrolyte secondary batteries in general.

Schematic diagram showing the structure of the positive and negative electrodes in this example The figure which shows the relationship between the charging time in this example, battery voltage, and battery temperature.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode active material 2 Conductive polymer film 3 Positive electrode lead 4 Negative electrode active material 5 Negative electrode core material 6 Negative electrode lead

Claims (3)

A winding in which a positive electrode formed by forming a layer containing a positive electrode active material on a positive electrode current collector and a negative electrode formed by forming a layer containing a negative electrode active material on a negative electrode current collector via a separator A non-aqueous electrolyte secondary battery in which an electrode body having a structure is accommodated in a battery case and injecting a non-aqueous electrolyte, wherein the exposed portion of the positive electrode current collector and the negative electrode in the wound electrode body The exposed portions of the current collector face each other through the conductive polymer film, and the conductive polymer film is insulative when the battery voltage is 4.2 V or less, and is conductive when the battery voltage exceeds 4.2 V. A non-aqueous electrolyte secondary battery comprising: The non-aqueous electrolyte secondary battery according to claim 1, wherein the material of the conductive polymer film is at least one selected from the group consisting of polythiophene, polyfuran, polyparaphenylene, and derivatives thereof. Non-aqueous anion contained in the electrolytic solution, PF ₆ ^-, BF ₄ ^- Non-aqueous electrolyte secondary battery according to claim 1 or 2 is at least one.

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