JP2006286496A - Polymer cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent abrupt heat generation of a cell under abnormal conditions such as a voltage drop inside the cell or an internal short-circuit. <P>SOLUTION: A collector-exposed-part of a positive electrode and that of a negative electrode are provided at respective winding ends of the positive electrode and the negative electrode, at which the positive electrode and the negative electrode are non-coated with a positive electrode active material or negative electrode active material, the collector-exposed-parts having such a width as to cover the outermost periphery of a cell element to an extent of one or more turns. A coating material is applied to at least one of the collector-exposed-part of the positive electrode and that of the negative electrode. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a polymer battery having a polymer electrolyte layer such as a gel electrolyte or a polymer solid electrolyte.

  In recent years, electronic devices such as mobile phones and notebook computers have become cordless and portable, and thin, small, and lightweight portable electronic devices have been developed one after another. In addition, the amount of electric power used is increasing due to diversification of devices and functions, and there is an increasing demand for higher capacity of batteries, particularly secondary batteries, which are energy sources for these electronic devices.

  Conventional secondary batteries include lead-acid batteries and nickel-cadmium (Ni-Cd) batteries, and new secondary batteries include nickel-hydrogen (Ni-MH) batteries and lithium-ion (Li-ion) batteries. Batteries are in practical use.

  In addition, stainless steel (SUS) tubes and aluminum (Al) cans were conventionally used as battery exteriors, but in recent years, by using gel electrolytes or polymer solid electrolytes, commercialization of batteries with laminate films as exteriors has been made. Became possible. Lithium polymer secondary batteries using this laminate film, unlike batteries using liquid electrolytes (electrolytes), do not have to worry about leakage and are small, light, thin, and have a high energy density. It has become possible.

  A lithium ion secondary battery is a battery element in which a belt-like positive electrode having a positive electrode active material layer formed on both sides and a belt-like negative electrode having a negative electrode active material layer formed on both sides are wound through a separator. Is housed in an exterior material to form a battery. In the case of the lithium polymer battery as described above, a polymer electrolyte layer is formed on both surfaces of the positive electrode and the negative electrode, flattened after winding to form a battery element, and this is packaged with a laminate film to form a battery.

  In these batteries, measures are taken to prevent an internal short circuit by preventing overcharging with a protection circuit or the like. Moreover, it is designed so that the battery only generates heat in a normal internal short circuit and does not lead to thermal runaway. However, it has been found that when the battery is crushed by pressure from the outside of the battery or pierced with a nail, abnormal heat is generated inside the battery, resulting in lack of safety.

Therefore, in Patent Document 1 below, in each of the strip-shaped positive electrode and the strip-shaped negative electrode, the positive electrode current collector exposed portion and the negative electrode current collector exposed in which the current collector is exposed on both ends at one end in the length direction of the electrode. A configuration in which the positive electrode current collector exposed portion and the negative electrode current collector exposed portion cover the outer peripheral portion of the battery one or more times through a separator is described.
JP-A-11-233149

  In general, when the resistance of the short-circuited part is sufficiently small, the current that flows is larger than Joule's law, but the amount of heat generation is small. In the battery system, the resistance at the short-circuit portion is large due to the short circuit via the positive and negative active materials, and the resistance is small due to the short circuit between the positive and negative current collectors. Therefore, if the short-circuit between the positive electrode current collector and the negative electrode current collector having a small resistance can be surely caused, the safety of the battery is ensured without abnormal heat generation.

  The site where the current collectors can face each other is the outermost or innermost circumference, which is the application end of the active material. Assuming that damage occurs from the outside, it is necessary to take this structure on the outermost periphery. When the positive electrode current collector and the negative electrode current collector are opposed to each other on the outermost periphery, a separator is disposed between the current collectors in order to ensure insulation between the positive and negative electrodes.

  In the battery configuration of Patent Document 1, when pressure is applied from the outside, the positive electrode current collector exposed portion and the negative electrode current collector exposed portion at the outermost peripheral portion of the battery are short-circuited, and heat is diffused to minimize damage inside the battery. To the limit.

  However, as described above, in the electrode structure in which the current collector exposed portion is provided at the electrode end portion, and the battery element structure in which the polymer electrolyte is applied only to the reaction portion coated with the active material and wound, the polymer When the electrolyte is applied, the electrolyte may scatter and adhere to the current collector exposed portion. The attached portion of the electrolyte that is not connected to the polymer electrolyte applied on the active material layer behaves as a local battery after the positive and negative electrodes are stacked via the separator, and copper ions dissolved from the negative electrode current collector are deposited. For this reason, a voltage drop due to self-discharge occurs, and the battery characteristics deteriorate. In addition, the deposited copper ions break through the separator and come into contact with the positive electrode current collector to cause a short circuit.

  Therefore, in view of the above problems, an object of the present invention is to provide a polymer battery having high battery performance and safety.

  In order to solve the above problems, in the polymer battery according to the present invention, the positive electrode current collector exposed portion and the negative electrode current collector exposed portion of the outermost circumference of the battery element are provided at the winding end portions of the positive electrode and the negative electrode, It is set as the structure by which the coating material was provided in at least one of the positive electrode collector exposed part and the said negative electrode collector exposed part.

  Specifically, a method of applying a polymer electrolyte to each of the positive electrode current collector exposed portion and the negative electrode current collector exposed portion, one of the positive electrode current collector exposed portion and the negative electrode current collector exposed portion with a polymer film or a protective film The method of coating is mentioned.

  According to the present invention, it is possible to prevent the battery voltage from being lowered and to prevent rapid battery heat generation even in the event of an abnormality such as an internal short circuit.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a configuration of a nonaqueous electrolyte battery manufactured by applying the present invention. As shown in detail in FIG. 2, the battery 1 is produced by sealing the periphery of the battery element 10 with the battery element 10 housed in a recess formed in the laminate film 4. . Hereinafter, the configuration of the battery element 10 will be described.

  FIG. 3 shows the structure of the battery element 10 accommodated in the laminate film 4. This battery element 10 is formed by sequentially laminating a strip-like positive electrode 11, a separator 13a, a strip-like negative electrode 12 disposed opposite to the positive electrode 11, and a separator 13b, and is wound in the longitudinal direction. A polymer electrolyte 14 is applied to both surfaces of the negative electrode 12. A positive electrode terminal 2a connected to the positive electrode 11 and a negative electrode terminal 2b connected to the negative electrode 12 are led out from the battery element 10 (hereinafter referred to as an electrode terminal 2 when not referring to a specific terminal). 2a and negative electrode terminal 2b are coated with sealant 3a and 3b (hereinafter referred to as sealant 3 as appropriate when a specific sealant is not shown) to improve the adhesion to laminate film 4 to be packaged later. Has been.

[Positive electrode]
In the positive electrode, a positive electrode active material layer containing a positive electrode active material is formed on both surfaces of a positive electrode current collector. The positive electrode current collector is made of, for example, a metal foil such as an aluminum (Al) foil, a nickel (Ni) foil, or a stainless steel foil.

  The positive electrode active material layer includes, for example, a positive electrode active material, a conductive agent, and a binder. Here, the positive electrode active material, the conductive agent, the binder, and the solvent only have to be uniformly dispersed, and the mixing ratio is not limited.

As the positive electrode active material, a metal oxide, a metal sulfide, or a specific polymer can be used depending on the type of the target battery. For example, in the case of constituting a lithium ion battery, Li _x MO ₂ (wherein M represents one or more transition metals, and x varies depending on the charge / discharge state of the battery, and is usually 0.05 or more and 1.10 or less. ) And a composite oxide of lithium and transition metal. As the transition metal constituting the lithium composite oxide, cobalt (Co), Ni, manganese (Mn) or the like is used.

Specific examples of such a lithium composite oxide include LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiNi _y Co _1-y O ₂ (0 <y <1). A solid solution in which a part of the transition metal element is substituted with another element can also be used. Examples thereof include LiNi _0.5 Co _0.5 O ₂ and LiNi _0.8 Co _0.2 O ₂ . These lithium composite oxides can generate a high voltage and have an excellent energy density. _{Furthermore, TiS 2, MoS 2, NbSe} 2, V 2 O no lithium metal sulfides such as ₅ or may be used an oxide as the positive electrode active material. These positive electrode active materials may be used alone or in combination of two or more.

  As the conductive agent, for example, a carbon material such as carbon black or graphite is used. As the binder, for example, polyvinylidene fluoride, polytetrafluoroethylene, polyvinylidene fluoride, or the like is used. Moreover, as a solvent, N-methyl-2-pyrrolidone (NMP) etc. are used, for example.

  The above-described positive electrode active material, binder, and conductive agent are uniformly mixed to form a positive electrode mixture, and this positive electrode mixture is dispersed in a solvent to form a slurry. Next, this slurry is uniformly applied on the positive electrode current collector by a doctor blade method or the like.

  At this time, as shown in FIG. 4, in the positive electrode 11 before winding, an uncoated portion of the positive electrode mixture (hereinafter, appropriately referred to as a positive electrode current collector exposed portion) 15 a is formed on a part of both surfaces of the positive electrode current collector 11 a. Provide. In FIG. 4, when the A side is the winding start end portion of the wound body and the B side is the winding end portion, the positive electrode mixture is applied so that the positive electrode current collector exposed portion 15a is formed at the winding end portion. Is done. The positive electrode current collector exposed portion 15a is formed so that the positive electrode current collector exposed portion 15a covers the outermost peripheral portion one or more times in the battery element 10 which is laminated and wound together with the negative electrode 12 and the separator 13.

  For this purpose, one surface of the positive electrode 11 is provided with one or more positive electrode current collector exposed portions 15 a, and the other surface is further increased by one round and the positive electrode current collector of two or more rounds. An exposed portion 15a is provided. Thereby, in the battery element 10 after being wound, the opposing portions of the positive electrode current collector exposed portion 15a and the negative electrode current collector exposed portion 15b are formed for one or more rounds.

  Thus, after apply | coating a positive mix so that the positive electrode collector exposed part 15a may be provided, it is made to dry at high temperature and a positive electrode active material layer is formed by flying a solvent.

  The positive electrode 11 has a positive electrode terminal 2a connected to one end of the positive electrode current collector 11a by spot welding or ultrasonic welding. The positive electrode terminal is preferably a metal foil or a mesh-like one, but there is no problem even if it is not a metal as long as it is electrochemically and chemically stable and can conduct electricity. Examples of the material for the positive electrode terminal include Al.

[Negative electrode]
In the negative electrode, a negative electrode active material layer containing a negative electrode active material is formed on both surfaces of a negative electrode current collector. The negative electrode current collector is made of a metal foil such as a copper (Cu) foil, a Ni foil, or a stainless steel foil.

  The negative electrode active material layer includes, for example, a negative electrode active material, a conductive agent if necessary, and a binder. These are uniformly mixed to form a negative electrode mixture, and this negative electrode mixture is dispersed in a solvent to form a slurry. Next, this slurry is uniformly applied on the negative electrode current collector by a doctor blade method or the like, dried at a high temperature, and the solvent is blown off. Here, the mixing ratio of the negative electrode active material, the conductive agent, the binder, and the solvent is not limited as in the positive electrode active material.

As the negative electrode active material, lithium metal, a lithium alloy, a carbon material that can be doped / undoped with lithium, or a composite material of a metal material and a carbon material is used. Specific examples of the carbon material that can be doped / undoped with lithium include graphite, non-graphitizable carbon, and graphitizable carbon. More specifically, pyrolytic carbons, cokes (pitch coke, needle coke, petroleum coke), graphites, glassy carbons, organic polymer compound fired bodies (phenolic resin, furan resin, etc.) at an appropriate temperature. Carbon materials such as those obtained by firing and carbonization), carbon fibers, activated carbon, and the like can be used. Furthermore, as a material capable of doping and dedoping lithium, a polymer such as polyacetylene or polypyrrole or an oxide such as SnO ₂ can be used.

  In addition, various types of metals can be used as materials capable of alloying lithium, but tin (Sn), cobalt (Co), indium (In), Al, silicon (Si), and alloys thereof can be used. Often used. When metal lithium is used, it is not always necessary to use powder as a coating film with a binder, and a method of pressing a rolled Li metal foil to a current collector may be used.

  As the binder, for example, polyvinylidene fluoride, styrene butadiene rubber or the like is used. Examples of the solvent include N-methyl-2-pyrrolidone and methyl ethyl ketone.

  The negative electrode active material, binder, and conductive agent described above are uniformly mixed to form a negative electrode mixture, dispersed in a solvent to form a slurry, and then uniformly applied on the negative electrode current collector in the same manner as the positive electrode To do.

  At this time, similarly to the case of the positive electrode 11 shown in FIG. 4, a negative electrode mixture uncoated portion (hereinafter, appropriately referred to as a negative electrode current collector exposed portion) 15 b is provided on a part of both surfaces of the negative electrode current collector 12 a. The negative electrode current collector exposed portion 15b is formed so as to cover one or more rounds of the outermost peripheral portion of the wound battery element 10.

  Similarly to the positive electrode 11, the negative electrode 12 has a negative electrode terminal 2b connected to one end of the current collector by spot welding or ultrasonic welding, and this negative electrode terminal 2b is electrochemically and chemically stable. There is no problem even if it is not metal as long as it can conduct electricity. Examples of the material for the negative electrode terminal include copper and Ni.

  In addition, although it is preferable that the positive electrode terminal 2a and the negative electrode terminal 2b are derived | led-out from the same direction, if a short circuit etc. do not occur and there is no problem in battery performance, it is satisfactory even if it derive | leads out from which direction. Moreover, the connection location of the positive electrode terminal 2a and the negative electrode terminal 2b is not limited to the above example as long as electrical contact is established, and the method of attachment is not limited to the above example.

[Polymer electrolyte]
As the polymer electrolyte, a polymer solid electrolyte or a gel electrolyte can be used. Hereinafter, the electrolyte will be described in detail.

  For the solid electrolyte or gel electrolyte laminated on the positive electrode active material layer or the negative electrode active material layer, a solution composed of a polymer compound, an electrolyte salt, and a solvent (or a plasticizer in the case of a gel electrolyte) is used as the positive electrode active material. A layer or a negative electrode active material layer is impregnated, and the solvent is removed to solidify or gel. Part of the solid electrolyte or gel electrolyte laminated on the positive electrode active material layer or the negative electrode active material layer is impregnated into the positive electrode active material layer or the negative electrode active material layer to be solidified or gelled. In the case of a crosslinked system, it is then solidified by crosslinking with light or heat.

  The gel electrolyte is obtained by adding an electrolyte salt to a plasticizer, mixing 2% by weight to 30% by weight of a matrix polymer and a solvent, applying the mixture to an electrode, and removing the solvent.

  As the plasticizer used for the gel electrolyte, esters, ethers, and carbonates may be used alone, or a plurality of types may be mixed with a predetermined composition. Specific examples include ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, and ethyl propyl carbonate.

Moreover, as lithium salt, it is possible to use the material used for normal battery electrolyte solution. Specifically, LiCl, LiBr, LiI, LiClO ₃ , LiClO ₄ , LiBF ₄ , LiPF ₆ , LiNO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiAsF ₆ , LiCF ₃ SO ₃ , LiC (SO ₂ CF ₃ ) ₃ , LiAlCl ₄ , LiSiF _{6 and the} like can be mentioned, but LiPF ₆ and LiBF ₄ are preferable from the viewpoint of oxidation stability. These lithium salts may be used alone or in combination of two or more. Although it can implement by 0.1-3.0 mol in a plasticizer as a density | concentration which melt | dissolves lithium salt, Preferably it can use at 0.5-2.0 mol / l.

  In preparing the gel electrolyte, various polymers used for constituting the gel electrolyte can be used as the matrix polymer for gelling such a plasticizer. Among these, from the viewpoint of redox stability, it is desirable to use a fluorine-based polymer such as polyvinylidene fluoride or a copolymer of polyvinylidene fluoride and hexafluoropropylene.

  Further, as the solvent, a low boiling point solvent which is easy to volatilize is desirable. Specific examples include dimethyl carbonate and ethyl methyl carbonate.

  The polymer solid electrolyte is composed of a lithium salt and a polymer compound that dissolves the lithium salt. Examples of the polymer compound include ether polymers such as poly (ethylene oxide) and cross-linked polymers, poly (methacrylate) esters, and acrylates. , Fluorine-based polymers such as poly (vinylidene fluoride) and poly (vinylidene fluoride-co-hexafluoropropylene) can be used alone or in combination. It is desirable to use a fluorine-based polymer such as vinylidene or a copolymer of polyvinylidene fluoride and hexafluoropropylene.

  As the lithium salt, the same material as that used in the gel electrolyte can be used.

[Separator]
The separator is composed of, for example, a porous film made of a polyolefin-based material such as polypropylene (PP) or polyethylene (PE), or a porous film made of an inorganic material such as a ceramic nonwoven fabric. A structure in which a porous film is laminated may be used. Among these, polyethylene and polypropylene porous films are the most effective.

  In general, the thickness of the separator is preferably 5 to 50 μm, more preferably 7 to 30 μm. If the separator is too thick, the amount of the active material filled decreases, the battery capacity decreases, and the ionic conductivity decreases and the current characteristics deteriorate. On the other hand, if the film is too thin, the mechanical strength of the film decreases.

[Production of battery element]
The polymer electrolyte solution prepared as described above is uniformly applied to the positive electrode 11 and the negative electrode 12 and impregnated in the positive electrode active material layer and the negative electrode active material layer, and then stored at room temperature or a polymer electrolyte through a drying process. Layer 14 is formed. At this time, as shown in FIG. 5, the polymer electrolyte layer 14 is continuously formed from the positive electrode active material layer 11b so as to cover all ends of the positive electrode current collector exposed portion 15a. The polymer electrolyte may be applied only on one side facing the negative electrode 12 so that the positive electrode current collector exposed portion 15a is entirely covered. Further, since the other surface is the facing portion between the battery element 10 and the laminate film 4 wound around the outermost circumference, the polymer electrolyte 14 does not have to be applied to the portion facing the laminate film 4. Further, unlike the positive electrode 11, the negative electrode 12 may be formed by applying the polymer electrolyte 14 only on the negative electrode active material layer 12 b as shown in FIG. 6.

  As described above, the application part of the polymer electrolyte 14 was changed between the positive electrode 11 and the negative electrode 12 because the polymer electrolyte 14 was continuously applied from the active material application part to prevent local battery formation and suppress copper deposition. For this reason, since the polymer electrolyte layer 14 is in close contact with each of the positive electrode 11 and the negative electrode 12 by laminating the positive electrode 11 and the negative electrode 12, the polymer electrolyte 14 may be applied to one of the electrodes. In this battery, since the positive electrode 11 is longer than the negative electrode 12 at the winding end portion, the polymer electrolyte 14 is applied to the positive electrode current collector exposed portion 15a.

  Next, using the positive electrode 11 and the negative electrode 12 on which the polymer electrolyte layer 14 is formed, the positive electrode 12, the separator 13a, the negative electrode 12, and the separator 13b are stacked and wound in this order to obtain a battery element 10 as shown in FIG. At this time, the positive electrode current collector exposed portion 15a and the negative electrode current collector exposed portion 15b are arranged to face each other and cover the outer peripheral portion of the battery element 10 one or more times.

  Such a battery element 10 is accommodated in a laminate film 4 which is an exterior material, and the periphery of the battery element 10 is sealed by heat welding or the like to obtain a battery. The laminate film 4 is made of a multilayer film having moisture resistance and insulation in which both surfaces of a metal foil are covered with an insulating resin material.

  In addition to improving the strength of the exterior material, the metal foil plays the most important role of protecting the contents by preventing the ingress of moisture, oxygen, and light. It is appropriate to use stainless steel or nickel-plated iron as the material as appropriate. However, aluminum (Al) is the most suitable because of its lightness, extensibility, price, and ease of processing.

  In addition, the resin layer located inside the battery is a part that melts and fuses with heat or ultrasonic waves. Other than polyethylene (PE), non-axially stretched polypropylene (CPP), polyethylene terephthalate (PET), nylon (Ny) Low density polyethylene (LDPE), high density polyethylene (HDPE), and linear low density polyethylene (LLDPE) can be used, and a plurality of types can be selected and used.

  Further, nylon (Ny), polyethylene terephthalate (PET), or polyethylene (PE) is used for the resin layer located outside the battery because of its beautiful appearance, toughness, and flexibility. It is also possible to select and use the type.

  Thus, a polymer battery having an appearance as shown in FIG. 1 is produced. In this battery, local battery formation can be prevented, and precipitation of copper can be suppressed by the negative electrode collector exposed portion 15b. When this method is used, the problem can be solved only by applying the polymer electrolyte 14, which is very suitable from the viewpoint of manufacturing cost and production tact.

  In addition, as a second embodiment, there is a method in which the copper foil as the negative electrode current collector 12 and the polymer electrolyte 14 are prevented from being contacted to suppress copper precipitation.

  In this method, as in the first embodiment, the winding end portions on the positive electrode current collector 11a and the negative electrode current collector 12a are made to be the positive electrode current collector exposed portion 15a and the negative electrode current collector exposed portion 15b. The positive electrode active material layer 11b and the negative electrode active material layer 12b are provided, and the polymer film 20 is formed on the positive electrode current collector exposed portion 15a.

  A fluorine-based polymer is mixed with a solvent such as NMP (N-methyl-2-pyrrolidone) at a concentration of about 1 to 5%, and this mixed solution is applied to the positive electrode current collector exposed portion 15 a provided on both surfaces of the positive electrode 11. Apply. Thereafter, by drying at a high temperature of about 120 ° C., the polymer film 20 is formed on the positive electrode current collector exposed portion 15a as shown in FIG.

  At this time, the polymer film 20 is formed so as to be placed on the end portion of the positive electrode active material layer 11b so that there is no gap near the end portion of the positive electrode active material layer 11b. Moreover, it is made longer than the edge part of the negative electrode 12 at the time of winding, and it comprises so that the positive electrode 11 and the negative electrode 12 may not contact.

  As the fluorine-based polymer, polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyvinyl fluoride, or the like can be used.

  Moreover, in order to improve adhesiveness with copper foil, it is also possible to mix a modified substance with the above-mentioned fluoropolymer. Specific examples of the modifying substance include ethylene, styrene, butadiene, vinyl chloride, vinyl acetate, acrylic acid, methyl acrylate, methyl vinyl ketone, acrylamide, acrylonitrile, vinylidene chloride, methacrylic acid, methyl methacrylate, monomethyl maleate, Alternatively, isoprene or the like can be used.

  The polymer electrolyte solution is applied to each of the negative electrode 12 and the positive electrode 11 thus manufactured, and then stored at room temperature, or the polymer electrolyte layer 14 is formed through a drying process. The polymer electrolyte solution may be formed on the positive electrode active material 11b and the negative electrode active material 12b.

  Subsequently, the positive electrode 11, the separator 13a, the negative electrode 12, and the separator 13b are laminated | stacked in order and wound, and it is set as the battery element 10 as shown in FIG. Furthermore, this battery element 10 was covered with a laminate film, and the periphery was sealed to obtain a battery.

  Thus, self-discharge inside the battery can be prevented by suppressing contact between the positive electrode and the negative electrode. In this method, since the fluoropolymer mixed solution is dried after application, a very thin film of about 2 to 8 μm can be formed, and the volume efficiency of the battery is improved.

  Furthermore, as a third embodiment, as shown in FIG. 10, there is a method in which the positive electrode current collector exposed portion 15a is covered with a protective film 21 to prevent contact between the copper foil and the polymer electrolyte. As the protective film 21, an adhesive tape can be used, and any material can be used as long as it uses a material that is not easily damaged by the polymer electrolyte 14. Specifically, an adhesive tape made of polypropylene (PP) or polyethylene (PE) is suitable.

  Although these embodiments can be used alone, a voltage drop occurs more by using the first embodiment and the second embodiment or the combination of the first embodiment and the third embodiment. It is difficult to obtain a highly safe battery.

  Hereinafter, the present invention will be specifically described by way of examples. First, a test battery is produced as follows.

<Example 1>
[Production of positive electrode]
A positive electrode is produced using LiCoO ₂ as the positive electrode active material. First, in order to obtain LiCoO ₂ , lithium carbonate and cobalt carbonate were mixed at a ratio of 0.5 mol: 1 mol and fired in air at 900 ° C. for 5 hours. Next, 91 parts by weight of LiCoO ₂ obtained, 6 parts by weight of graphite as a conductive agent, and 10 parts by weight of a copolymer of polyvinylidene fluoride and hexafluoropropylene as a binder are mixed to prepare a positive electrode mixture. Further, this was dispersed in N-methyl-2-pyrrolidone to form a slurry.

  Next, this slurry was uniformly applied to both surfaces of a 20 μm-thick strip-shaped aluminum foil as a positive electrode current collector. At this time, a positive electrode current collector exposed portion for one round of the outermost periphery of the battery element was provided on both surfaces of one end of the positive electrode current collector. Next, after a drying process, compression molding was performed with a roll press to obtain a positive electrode.

[Production of negative electrode]
90 parts by weight of the pulverized artificial graphite powder and 10 parts by weight of a copolymer of polyvinylidene fluoride and hexafluoropropylene as a binder are mixed to prepare a negative electrode mixture, and this is further mixed with N-methyl-2- Dispersed in pyrrolidone to form a slurry.

  Next, this slurry was uniformly applied to both surfaces of a 10 μm-thick strip-shaped copper foil as a negative electrode current collector. At this time, a negative electrode current collector exposed portion corresponding to one round of the outermost periphery of the battery element was formed on both surfaces of one end of the negative electrode current collector. Then, after passing through a drying process, it was compression molded with a roll press to obtain a negative electrode.

[Gel electrolyte]
After mixing 50 parts by weight of ethylene carbonate (EC) and 50 parts by weight of propylene carbonate (PC) and dissolving 0.7 mol / kg of LiPF ₆ as an electrolyte salt, polyvinylidene fluoride having a weight average molecular weight of 600,000 and 10 parts by weight of a copolymer with hexafluoropropylene was mixed. Furthermore, dimethyl carbonate was mixed and dissolved to prepare an electrolyte solution.

  This electrolyte solution was uniformly applied to the surfaces of the positive electrode and the negative electrode, and impregnated into the positive electrode active material layer and the negative electrode active material layer. At this time, the electrolyte solution was applied to the positive electrode so that the positive electrode active material layer and the positive electrode current collector exposed portion were continuously covered. Moreover, the negative electrode applied the electrolyte solution only on the negative electrode active material layer. Subsequently, it was left at room temperature for 8 hours, and dimethyl carbonate was vaporized and removed to obtain a gel electrolyte membrane.

  Next, the positive electrode and the negative electrode on which the gel electrolyte membrane was formed were laminated via a separator and wound to produce a battery element. This battery element was covered with an aluminum laminate film having a thickness of 100 μm, and after the positive electrode terminal and the negative electrode terminal were led out from the aluminum laminate film, the periphery of the battery element was sealed to produce a test battery as shown in FIG. . Note that the cross-sectional views of the test battery shown in FIG. 7 and subsequent figures are shown with a smaller number of turns than the actual number of turns, and actually, for example, those wound about 10 to 20 times are used.

<Example 2>
After producing a positive electrode and a negative electrode in the same manner as in Example 1, a polymer film is formed on the positive electrode current collector exposed portions on both sides of the positive electrode. The polymer film was formed by applying a solution in which 97 parts by weight of N-methyl-2-pyrrolidone and 3 parts by weight of polyvinylidene fluoride were applied to the exposed part of the positive electrode current collector and then drying in an atmosphere of 120 ° C.

  After forming a polymer film on the exposed portion of the positive electrode current collector, a polymer electrolyte was applied on the positive electrode active material layer and the negative electrode active material layer, and the positive electrode and the negative electrode were stacked and wound via a separator to prepare a battery element. Thereafter, the battery element was covered with a laminate film to obtain a test battery as shown in FIG.

<Example 3>
After producing a positive electrode and a negative electrode in the same manner as in Example 1, the protective film was coated on the positive electrode current collector exposed portions on both sides of the positive electrode. As the protective film, an adhesive tape made of polypropylene and having a thickness of 20 μm was used. Next, a polymer electrolyte was applied on the positive electrode active material layer and the negative electrode active material layer, and then the positive electrode and the negative electrode were stacked and wound via a separator to produce a battery element. Thereafter, the battery element was packaged with a laminate film to obtain a test battery as shown in FIG.

<Comparative Example 1>
After producing a positive electrode and a negative electrode in the same manner as in Example 1, a polymer electrolyte layer is formed only on the active material layer portion of both the positive and negative electrodes, laminated and wound through a separator to form a battery element, and then packaged with a laminate film. Thus, a test battery as shown in FIG. 11 was obtained. This battery is a battery in which only a separator is present at a portion facing the outermost positive electrode current collector exposed portion and the negative electrode current collector exposed portion.

<Comparative example 2>
Using the same material as in Example 1, a positive electrode and a negative electrode were prepared in which the positive electrode current collector exposed portion and the negative electrode current collector exposed portion were not provided. The polymer electrolyte was applied on the positive electrode active material layer and the negative electrode active material layer, laminated and wound through a separator to form a battery element, and then packaged with a laminate film to obtain a test battery as shown in FIG.

(1) Nail penetration safety test Using 10 batteries for each test, a nail penetration safety test was conducted in an atmosphere at 25 ° C. In this test, each test battery was charged at a constant current up to 4.5 V at a current of 1 C, and then charged at a constant voltage of 4.5 V for a total of 3 hours. Next, an iron nail was passed through each test battery at 6000 mm / sec, and the subsequent heat generation state of the battery was observed.

  The nail penetration test is severe enough to find a lack of safety that cannot be generated under normal use conditions because the short circuit area is smaller and the current is concentrated than when crushing or external short circuit, and the current concentrates. It is a safety test. Therefore, if safety can be confirmed by a nail penetration test, it is considered that safety is sufficiently ensured even during abnormal use.

  Table 1 below shows the test results of the nail penetration safety test. For each test battery, a battery having an exothermic temperature of less than 150 ° C. was regarded as a non-defective product from the viewpoint of practical use, and the number of batteries having reached 150 ° C. or more was measured.

  From the above results, it can be seen that a battery having a structure in which the positive electrode current collector exposed portion and the negative electrode current collector exposed portion are opposed to the outermost periphery of the battery element does not show a rapid temperature rise and has high safety.

(2) Measurement of internal short-circuit rate 100 test batteries were used, and the internal short-circuit rate was determined from the number of short-circuits. The criteria for determining internal short-circuiting were that each test battery was charged at a constant current up to 4.2 V at a current of 1 C, and then constant voltage charging at 4.2 V was performed for a total of 3 hours. Thereafter, the sample was stored in an atmosphere at 25 ° C. for one week, and when the battery voltage decreased to 4.10 V or less, it was considered that a short circuit occurred and the internal short circuit rate was measured.

  Table 2 below shows the measurement results of the internal short-circuit rate.

  From the above results, the battery in which only the separator exists in the facing portion of the positive electrode current collector and the negative electrode current collector on the outermost periphery of the battery element causes an internal short circuit, whereas the positive electrode current collector and the negative electrode current collector face each other. In the battery in which the polymer electrolyte layer, the polymer film, the adhesive tape, and the positive and negative electrode active material layers were formed on the part, no internal short circuit was observed.

  From the above nail penetration safety test and measurement results of the internal short-circuit rate, a positive electrode current collector exposed portion and a negative electrode current collector exposed portion are provided on the outermost periphery of the battery element, and a covering material is used for the negative electrode current collector exposed portion. Accordingly, it is possible to prevent the battery voltage from being lowered and to prevent the battery from rapidly generating heat even when there is an abnormality such as an internal short circuit.

  As mentioned above, although embodiment of this invention was described concretely, this invention is not limited to the above-mentioned embodiment, The various deformation | transformation based on the technical idea of this invention is possible.

  For example, the numerical values given in the above embodiment are merely examples, and different numerical values may be used as necessary.

  Moreover, you may provide the part which made the positive electrode collector exposed part and the negative electrode collector exposed part oppose in the battery element innermost peripheral part. Also in this case, by covering the positive electrode current collector exposed portion and the negative electrode current collector exposed portion by the methods of the first, second, and third embodiments, a battery that is unlikely to cause a voltage drop is obtained.

  Moreover, it is good also as a battery structure which does not use a separator. Further, the battery element can be applied not only to a laminate film but also to a case where it is packaged with a battery can.

  In addition, the coating material is not necessarily formed on the positive electrode current collector exposed portion, and may be configured so that the negative electrode current collector exposed portion can be completely covered.

It is a schematic diagram which shows an example of the external appearance of the nonaqueous electrolyte battery produced by applying this invention. It is a schematic diagram which shows in detail the structure of the nonaqueous electrolyte battery produced by applying this invention. It is a schematic diagram which shows the structure of the battery element accommodated in a laminate film exterior material. It is a schematic diagram which shows the structure of the positive electrode to which this invention is applied. It is a schematic diagram which shows the mode of the positive electrode in 1st Embodiment. It is a schematic diagram which shows the mode of the negative electrode in 1st Embodiment. It is sectional drawing which shows the structure of the battery element in 1st Embodiment. It is a schematic diagram which shows the mode of the positive electrode in 2nd Embodiment. It is sectional drawing which shows the structure of the battery element in 2nd Embodiment. It is sectional drawing which shows the structure of the battery element in 3rd Embodiment. 6 is a cross-sectional view showing the structure of a battery element in Comparative Example 1. FIG. 6 is a cross-sectional view showing the structure of a battery element in Comparative Example 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Battery 2 ... Electrode terminal 2a ... Positive electrode terminal 2b ... Negative electrode terminal 3a, 3b ... Sealant 4 ... Laminate film 10 ... Battery element 11 ... Positive electrode 11a ... -Positive electrode current collector 11b ... Positive electrode active material layer 12 ... Negative electrode 12a ... Negative electrode current collector 12b ... Negative electrode active material layer 13, 13a, 13b ... Separator 14 ... Polymer electrolyte 15a ... Positive electrode current collector exposed portion 15b ... Negative electrode current collector exposed portion 20 ... Polymer film 21 ... Adhesive tape

Claims (5)

In a polymer battery having a battery element produced by laminating and winding a positive electrode and a negative electrode with a polymer electrolyte formed on the surface,
The winding end of the positive electrode and the negative electrode has a positive electrode current collector exposed portion and a negative electrode current collector exposed portion of one or more outer circumferences of the battery element,
A polymer battery, wherein a coating material is provided on at least one of the positive electrode current collector exposed portion and the negative electrode current collector exposed portion.   The positive electrode current collector exposed portion and the negative electrode current collector exposed portion are each coated with the polymer electrolyte, and the polymer electrolyte is continuous with the positive electrode active material and the polymer electrolyte applied on the negative electrode active material. The polymer battery according to claim 1.   2. The polymer battery according to claim 1, wherein one of the positive electrode current collector exposed portion and the negative electrode current collector exposed portion is covered with a film containing a fluorine-based polymer.   The polymer battery according to claim 3, wherein the fluorine-based polymer contains a modifying substance.     The polymer battery according to claim 1, wherein one of the positive electrode current collector exposed portion and the negative electrode current collector exposed portion is covered with a protective film.

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