JP2006079960A - Flat nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flat nonaqueous electrolyte secondary battery capable of enhancing a charge and discharge cycle life while avoiding rupture caused by a gas generated when it is overcharged. <P>SOLUTION: This flat nonaqueous electrolyte secondary battery is equipped with a group of electrodes 4 housed in a sealed vessel with a circular main surface and formed by rolling the positive electrode 5 and the negative electrode 6 in a flat shape through a separator 7, and a nonaqueous electrolyte housed in the sealed vessel so as to have a nominal capacity of 3.5 mg or more per 1mAh. The positive electrode 5 contains a positive electrode active material layer 5b carried by a positive electrode collector 5a, and at least one side of its rolling start part is the collector exposed surface carrying no positive electrode active material. The negative electrode 6 contains a negative electrode active material layer 6b carried by a negative electrode collector 6a, and at least one side of its rolling start part is the exposed collector surface carrying no negative electrode active material layer. The exposed collector surface of the rolling start part 8 of the positive electrode 5 faces the exposed collector surface of the rolling start part 9 of the negative electrode 6 through 1-6 layers of the separator 7. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a flat nonaqueous electrolyte secondary battery.

A metal oxide such as MnO ₂ or V ₂ O ₂ , an inorganic compound such as fluorinated graphite, or an organic compound such as polyaniline or a polyacene structure is used as the positive electrode active material, and metal lithium, lithium alloy, or polyacene is used as the negative electrode. An organic compound such as a structure, a carbonaceous material capable of occluding and releasing lithium, or an oxide such as lithium titanate or lithium-containing silicon oxide, and propylene carbonate, ethylene carbonate, butylene carbonate, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ ) in a non-aqueous solvent such as diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, dimethoxyethane, and γ-butyl lactone a supporting salt such as F ₅ SO _{2) 2} Coin-shaped and button-shaped flat non-aqueous electrolyte secondary batteries using the above-mentioned ones have already been commercialized, and backup of SRAMs and RTCs that discharge at light loads with a discharge current of several to several tens of μA It is applied to applications such as power supplies for mains and main power supplies for watches that do not require battery replacement.

  These conventional flat non-aqueous electrolyte secondary batteries have a simple structure and can be miniaturized, and are excellent in mass productivity, long-term reliability, and safety. However, on the other hand, the electrode area is limited. Therefore, it is not suitable for medium to heavy load discharge. Therefore, it could not be adopted as a main power source for small information terminals and portable devices.

  In contrast, flat nonaqueous electrolyte secondary batteries capable of heavy load discharge have been developed and provided by increasing the electrode area without changing the battery shape (for example, Patent Documents 1 and 2). ).

  In Patent Documents 1 and 2, when a cross section in a direction perpendicular to the flat surface of the flat nonaqueous electrolyte secondary battery is viewed, at least three positive and negative electrode facing surfaces in which the positive electrode and the negative electrode face each other with a separator interposed therebetween The heavy load characteristic is remarkably improved by using the existing electrode group and increasing the total sum of the positive and negative electrode facing areas in the electrode group. Further, in Patent Documents 1 and 2, a positive electrode plate in which a positive electrode active material is applied to a current collector made of a metal thin film and a metal thin film in order to accommodate an electrode group having a large positive / negative electrode area in a small case. The negative electrode current collector plate and the negative electrode plate coated with the negative electrode active material are wound and laminated through a separator to form an electrode group, impregnated with a liquid non-aqueous electrolyte, and encased in this electrode group Sealing is performed by caulking and fixing a positive electrode case made of metal and a negative electrode case made of metal via a gasket.

  In a flat type nonaqueous electrolyte secondary battery using such a wound electrode group, the positive electrode and the negative electrode are repeatedly expanded and contracted by charging and discharging, so that the distribution of the nonaqueous electrolyte is likely to be uneven. Increasing the amount of non-aqueous electrolyte added is being investigated.

  As a method for efficiently impregnating the electrode group with the nonaqueous electrolyte, Patent Document 3 describes a method of heating the nonaqueous electrolyte to 30 to 50 ° C. Patent Document 4 discloses that a nonaqueous electrolyte retention amount is increased by inserting a mesh piece as a spacer between the facing surfaces of the positive electrode and the separator or between the facing surfaces of the negative electrode and the separator.

  When the non-aqueous electrolyte is heated as in Patent Document 3, the viscosity of the non-aqueous electrolyte is lowered and impregnation into the electrode group is promoted, but the low boiling point solvent contained in the non-aqueous electrolyte is volatilized and the non-aqueous electrolyte is dissolved. The composition may change. On the other hand, when a spacer is inserted between the positive electrode or the negative electrode and the separator as in Patent Document 4, the distance between the positive electrode and the negative electrode increases, resulting in a decrease in heavy load discharge characteristics.

Furthermore, an increase in the amount of retained nonaqueous electrolyte is preferable for improving the charge / discharge cycle life, but an increase in the amount of gas generated at the time of overcharging is caused, so there is no safety valve mechanism for releasing gas when the internal pressure increases. The flat nonaqueous electrolyte secondary battery also has a problem of increasing the risk of rupture.
JP 2001-68160 A JP 2001-68143 A JP-A-10-284121 JP 2002-110216 A

  An object of the present invention is to provide a flat nonaqueous electrolyte secondary battery capable of improving the charge / discharge cycle life while avoiding rupture due to gas generation during overcharge.

A first flat nonaqueous electrolyte secondary battery according to the present invention includes a sealed container having a circular main surface;
An electrode group housed in the sealed container, the positive electrode and the negative electrode wound in a flat shape via a separator;
A non-aqueous electrolyte housed in the sealed container at a nominal capacity of 3.5 mg or more per 1 mAh,
The positive electrode includes a positive electrode current collector and a positive electrode active material-containing layer supported on the positive electrode current collector, and at least one surface of the winding start portion has a positive electrode active material-containing layer unsupported current collector exposed surface And
The negative electrode includes a negative electrode current collector and a negative electrode active material-containing layer supported on the negative electrode current collector, and at least one surface of the winding start portion has a negative electrode active material-containing layer not supported And
The current collector exposed surface of the winding start portion of the positive electrode and the current collector exposed surface of the winding start portion of the negative electrode are opposed to each other with 1 to 6 layers of the separator. Is.

A second flat nonaqueous electrolyte secondary battery according to the present invention includes a sealed container having a circular main surface;
An electrode group housed in the sealed container, the positive electrode and the negative electrode wound in a flat shape via a separator;
A non-aqueous electrolyte housed in the sealed container at a nominal capacity of 3.5 mg or more per 1 mAh,
The negative electrode includes a negative electrode current collector and a negative electrode active material-containing layer supported on the negative electrode current collector, and at least one surface of the winding start portion has a negative electrode active material-containing layer not supported And
The winding start portion of the negative electrode is wound so as to surround the separator having 1 to 6 layers with the current collector surface facing inward.

  According to the present invention, it is possible to provide a flat nonaqueous electrolyte secondary battery in which rupture due to gas generation during overcharge is avoided and charge / discharge cycle life is improved.

  In a flat nonaqueous electrolyte secondary battery in which an electrode group in which a main surface is circular and a positive electrode and a negative electrode are wound in a flat shape via a separator is accommodated, the outer shape (circular) of the container and the electrode group Due to the different outer shapes (squares), there is a relatively large dead space in the container, and it is necessary to inject an amount more than necessary to impregnate the nonaqueous electrolytic mass required for the electrode group. There is.

  In a flat type non-aqueous electrolyte secondary battery with increased non-aqueous electrolysis mass, the amount of gas generation during overcharge is considered to be due to the causes described below.

  In the flat non-aqueous electrolyte secondary battery as described above, the excess non-aqueous electrolyte injected to ensure the non-aqueous electrolyte mass necessary for the electrode group is present in the dead space in the container. On the other hand, at the time of overcharge, a large amount of nonaqueous electrolyte is lost in the positive electrode due to oxidative decomposition of the nonaqueous electrolyte, so that the free nonaqueous electrolyte is replenished to the positive electrode by a phenomenon similar to capillary action. The non-aqueous electrolyte present in the dead space penetrates into the electrode group through the separator exposed on the winding end surface of the electrode group, and this is considered to promote the oxidative decomposition reaction and increase the amount of gas generated. The

  As in the present invention, a current collector exposed surface on which no active material-containing layer is formed is provided at the winding start portion of the positive electrode and the negative electrode, and the current collector exposed surfaces are opposed to each other via 1 to 6 layers of separators. By this, this separator can be functioned as a reservoir for holding a surplus when the nonaqueous electrolytic mass is 3.5 mg or more per nominal capacity of 1 mAh, and free nonaqueous electrolyte can be reduced. Since there is no active material in this reservoir location, oxidative decomposition of the non-aqueous electrolyte does not occur even if overcharge occurs. Furthermore, the nonaqueous electrolyte retained in the reservoir separator diffuses to the surrounding positive electrode as the overcharge reaction proceeds, but gradually progresses because it is diffused in the radial direction through the negative electrode and other separators. In addition, the promotion of oxidative decomposition can be avoided. This makes it possible to improve the charge / discharge cycle life while avoiding rupture due to gas generation during overcharge.

  Also, a current collector surface on which the active material-containing layer is not formed is provided at the winding start portion of the negative electrode, and 1 to 6 layers of separators are provided at the winding start portion of the negative electrode with the current collector exposed surface inside. Even if enclosed, this separator can function as a reservoir for holding a surplus when the nonaqueous electrolytic mass is 3.5 mg or more per nominal capacity of 1 mAh. Since there is no active material in this reservoir location, oxidative decomposition of the non-aqueous electrolyte does not occur even if overcharge occurs. Furthermore, since only the negative electrode is in contact with the reservoir separator, the diffusion of the non-aqueous electrolyte to the positive electrode during overcharging can be further slowed, and the consumption of the non-aqueous electrolyte due to oxidative decomposition can be further reduced. it can. Therefore, not only the amount of gas generated during overcharge can be further reduced, but the charge / discharge cycle life can be further improved.

  The number of reservoir separator layers is preferably two or more in order to obtain a sufficient effect, and if the number of separator layers is too large, a high energy density may not be obtained. It is more preferable to make it below the layer.

  Hereinafter, the positive electrode, the negative electrode, the separator, and the nonaqueous electrolyte will be described.

There is no particular limitation on the positive electrode active material, for _{example, MnO 2, V 2 O 5} , Nb 2 O 5, LiTi 2 O 4, Li 4 Ti 5 O 12, LiFe 2 O 4, lithium cobaltate, lithium nickelate, metal oxides such as lithium manganate, or fluorinated graphite, inorganic compounds such as FeS _2, or an organic compound such as polyaniline or polyacene structure thereof. However, lithium-containing oxides in which lithium cobaltate, lithium nickelate, lithium manganate, mixtures thereof, or some of these elements are substituted with other metal elements are high in terms of operating potential and excellent cycle characteristics. Lithium cobaltate is a flat type non-aqueous electrolyte secondary battery that is more preferable and may be used for a long period of time because it is chemically stable with a high capacity and low reactivity with electrolyte and moisture. Is more preferable.

  As the positive electrode current collector, for example, a metal foil such as an aluminum foil or an aluminum alloy foil can be used.

Although it does not limit about a negative electrode active material, For example, lithium, such as metallic lithium or Li-Al, Li-In, Li-Sn, Li-Si, Li-Ge, Li-Bi, Li-Pb Alloys, organic compounds such as polyacene structures, carbonaceous materials capable of occluding and releasing lithium, or oxides such as Nb ₂ O ₅ , LiTi ₂ O ₄ , Li ₄ Ti ₅ O ₁₂ and Li-containing silicon oxides Etc. Among them, a carbonaceous material that can occlude and release Li is preferable because of its excellent cycle characteristics, low operating potential, and high capacity, and natural graphite and artificial materials are particularly low in that the operating voltage of the battery is low even at the end of discharge. graphite, expanded graphite, mesophase pitch fired, carbonaceous material surface spacing is less graphite structure 0.338nm a developed d _002, such as mesophase pitch fiber sintered body is more preferable.

  As the negative electrode current collector, for example, a metal foil such as a copper foil, an aluminum foil, or an aluminum alloy foil can be used.

  Next, the electrode is preferably a slurry obtained by applying a slurry mixture to the current collector and drying it because it is easy to produce a thin electrode for both the positive and negative electrodes, and a rolled product can also be used.

  In addition, it is possible to use an electrode in which an active material-containing layer is formed only on one side of the current collector as an electrode. In addition, it is desirable that active material-containing layers are formed on both sides of the current collector. For example, the energization portion may be formed by not forming the active material-containing layer from the beginning, or by forming the active material-containing layer once on both surfaces and then removing the active material-containing layer only from the corresponding portion.

  As a separator, a porous film or a nonwoven fabric can be used, for example. The porous sheet is preferably made of at least one material selected from, for example, polyolefin and cellulose. Examples of the polyolefin include polyethylene and polypropylene.

  The thickness of the separator is desirably 12 μm or more and 30 μm or less.

  As the nonaqueous electrolyte, a liquid or gel-like one can be used. The liquid nonaqueous electrolyte is prepared, for example, by dissolving a lithium salt in a nonaqueous solvent.

  Although it does not specifically limit as a non-aqueous solvent, For example, propylene carbonate (PC), ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), diethoxyethane (DEE), γ-butyrolactone (γ-BL), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), 1,3-dioxolane, 1,3-dimethoxypropane and the like. The type of the non-aqueous solvent can be one type or two or more types.

The lithium salt is not particularly limited. For example, lithium perchlorate (LiClO ₄ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluoroarsenide (LiAsF ₆ ), lithium hexafluorophosphate Examples thereof include lithium salts such as (LiPF ₆ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), and lithium aluminum tetrachloride. The type of electrolyte can be one type or two or more types. The amount of the electrolyte dissolved in the non-aqueous solvent is preferably in the range of 0.5 to 1.5 mol / L.

  The amount of nonaqueous electrolyte retained is 3.5 mg or more per nominal capacity 1 mAh from the viewpoint of improving the charge / discharge cycle life, but if the amount exceeds 6 mg per nominal capacity 1 mAh, a sufficient effect cannot be expected. There is a risk that explosion during overcharging cannot be prevented. Therefore, the retained amount of the nonaqueous electrolyte is preferably 3.5 mg or more and 5.5 mg or less per nominal capacity of 1 mAh.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

  The sealed container is composed of an outer can 1 and a sealed can 2. The outer can 1 having a bottomed cylindrical shape also serves as one electrode (for example, positive electrode) terminal. The outer end of the outer can 1 is bent inward by caulking. On the other hand, the sealing can 2 having a bottomed cylindrical shape also serves as the other electrode (for example, negative electrode) terminal. The opening end of the sealing can 2 is folded back in a U shape toward the outside. The sealing can 2 has a folded portion 2 a inserted into a folded portion at the opening end of the outer can 1 and is caulked to the outer can 1 via an insulating gasket 3 disposed between the folded portion 2 a and the inner wall of the outer can 1. It is fixed.

  The electrode group 4 has a structure in which a positive electrode 5 and a negative electrode 6 are wound in a flat shape with a separator 7 therebetween. The outer shape of the electrode group 4 is substantially square. Here, examples of the square (square) include a rectangle and a square.

  As shown in FIG. 2, the positive electrode 5 includes a positive electrode current collector 5a and a positive electrode active material-containing layer 5b supported on the positive electrode current collector 5a. The winding start portion 8 of the positive electrode 5 is a current collector surface on which both sides of the active material-containing layer are not supported. The positive electrode 5 is supported on one side because a surface facing the winding start portion 8 and a single surface of a winding end portion (not shown) serving as a current-carrying portion is a current collector surface, but is basically a positive electrode current collector. Positive electrode active material-containing layers 5b are formed on both surfaces of 5a. On the other hand, the negative electrode 6 includes a negative electrode current collector 6a and a negative electrode active material-containing layer 6b supported on the negative electrode current collector 6a. The winding start portion 9 of the negative electrode 6 is a current collector exposed surface having no active material-containing layer on both sides. The negative electrode 6 is supported on one side because one side of the portion facing the winding start portion 9 and the winding end portion (not shown) serving as a current-carrying portion is a current collector exposed surface, but is basically a negative electrode current collector. Negative electrode active material-containing layers 6b are formed on both surfaces of 6a.

  The separator 7 is disposed between the two flat cores 10 a and 10 b, the winding start portion 8 of the positive electrode 5 is sandwiched between the core 10 a and the separator 7, and the negative electrode is interposed between the core 10 b and the separator 7. 6 winding start portion 9 is sandwiched. When the winding cores 10a and 10b are wound in the direction indicated by the arrow in FIG. 2, the result is as shown in FIG. That is, the single-layer separator 7 is interposed between the current collector exposed surface of the winding start portion 8 of the positive electrode 5 and the current collector exposed surface of the winding start portion 9 of the negative electrode 6.

  When the winding is further performed, the electrode group 4 shown in FIG. 1 is obtained. One outermost layer of the electrode group 4 is a positive electrode current collector 5a. The other outermost layer of the electrode group 4 is a negative electrode current collector 6a. In addition, the winding end end part of the electrode group 4 is fixed with a winding stopper tape (not shown).

  Such an electrode group 4 is accommodated in a liquid-tight space formed by the outer can 1 and the sealing can 2. Further, in the electrode group 4, the surface on which the positive electrode current collector 5a is the outermost layer is in contact with the bottom inner surface of the outer can 1, and the surface on which the negative electrode current collector 6a is the outermost layer is in contact with the bottom inner surface of the sealing can 2. Yes.

  A positive electrode conductive layer (not shown) made of, for example, a metal porous plate may be disposed between the outermost positive electrode current collector 5a and the inner surface of the bottom of the outer can 1 to improve the conduction. Is possible. In addition, a negative electrode conductive layer (not shown) made of, for example, a metal porous plate is also disposed between the outermost negative electrode current collector 6a and the inner surface of the bottom of the sealing can 2 in order to improve the conduction. Is possible.

  When the number of stacked separators 7 is three, for example, a configuration as shown in FIG. 4 can be used. The positive electrode 5 contains a positive electrode active material on both sides of the positive electrode current collector 5a except that one side of the winding start portion 8 and one side of a winding end portion (not shown) serving as a current-carrying portion are current collector exposed surfaces. Layer 5b is formed. On the other hand, as the negative electrode 6, the negative electrode current collector 6a has both sides of the negative electrode current collector 6a except that one side of the winding start portion 9 and one side of a winding end portion (not shown) serving as a current-carrying portion are current collector exposed surfaces. A substance-containing layer 6b is formed. The separator 7 is sandwiched between the winding cores 10a and 10b, one end is drawn around the winding core 10a, and the other end is drawn around the winding core 10b. The separator 7 is formed in an S shape around the winding cores 10a and 10b. To place. After the winding cores 10 a and 10 b are rotated in the direction of the arrow, the winding start portion 9 of the negative electrode 6 is interposed between the two layers of the separator 7 stacked on the winding core 10 a with the current collector surface through the separator 7. Then, it is inserted so as to face the winding core 10a. At the same time, the winding start portion 8 of the positive electrode 5 is inserted between the two layers of separators 7 stacked on the winding core 10 b so that the current collector exposed surface faces the winding core 10 b through the separator 7. When these are further wound, an electrode group is obtained in which the current collector exposed surface of the winding start portion 8 of the positive electrode 5 and the current collector exposed surface of the winding start portion 9 of the negative electrode 6 are opposed via the three-layer separator 7. .

  When the number of stacked separators 7 is five, for example, a configuration as shown in FIG. First, after the separator 7 is arranged in an S shape around the cores 10a and 10b in the same manner as described with reference to FIG. 4, the cores 10a and 10b are wound in the direction indicated by the arrow in FIG. . Next, the winding start portion 9 of the negative electrode 6 is disposed between the second and third separators 7 of the three-layer separator 7 stacked on the winding core 10a, and the current-carrying surface of the current collector is the second-layer separator 7 And insert so that it faces. At the same time, the winding start portion 8 of the positive electrode 5 is placed between the second layer and the third layer separator 7 of the three-layer separator 7 stacked on the winding core 10b, and the current collector surface is the second layer separator 7. And insert so that it faces. When these are further wound, an electrode group is obtained in which the current collector exposed surface of the winding start portion 8 of the positive electrode 5 and the current collector exposed surface of the winding start portion 9 of the negative electrode 6 are opposed via the five-layer separator 7. .

  Next, an electrode group having a configuration in which the separator 7 is surrounded by the current collector surface of the winding start portion 9 of the negative electrode 6 will be described. First, the case where the number of stacked separators 7 is two will be described with reference to FIGS. The positive electrode 5 is one that supports both sides of the active material-containing layer 5b except that one side of a winding end portion (not shown) serving as a current-carrying portion is a current collector exposed surface. The winding start portion 9 of the negative electrode 6 is a current collector surface on one side of which no active material-containing layer is carried. The negative electrode 6 is supported on one side because one side of the winding start portion 9 and a winding end portion (not shown) serving as a current-carrying portion is a current collector exposed surface, but basically both sides of the negative electrode current collector 6a. A negative electrode active material-containing layer 6b is formed on the substrate.

  After sandwiching the separator 7 between the winding core 10a and the winding core 10b, one end is routed around the winding core 10a, and the other end is routed around the winding core 10b. As shown in FIG. The separator 7 is arranged in an S shape around 10b. Between the winding core 10b and the separator 7, the winding start portion 9 of the negative electrode 6 is disposed so that the current collector exposed surface 6a faces the winding core 10b. After winding the winding cores 10a and 10b 180 ° in the direction of the arrow, as shown in FIG. 7, the winding start portion of the positive electrode 5 is inserted between the separators 7 and the winding start portion 9 of the negative electrode 6 and the separator 7 are interposed. Make them face each other. By further winding these, an electrode group having a configuration in which the winding start portion 9 of the negative electrode 6 surrounds the two layers of separators 7 with the current collector exposed surface 6a inside.

  In the case where the number of stacked separators 7 is four, for example, the configuration shown in FIG. As the positive electrode 5, one having the same configuration as described in the case where the number of stacked separators is two can be used. On the other hand, the negative electrode 6 contains a negative electrode active material on both sides of the negative electrode current collector 6a, except that one side of the winding start portion and one side of the winding end portion (not shown) are supported on one side by the current collector exposed surface. What formed the layer 6b can be used. First, the separator 7 is arranged in an S shape around the cores 10a and 10b in the same manner as described above with reference to FIG. 6, and then both the separators 7 are pulled out in the same direction. Surrounds about half the circumference. And the circumference | surroundings are surrounded by the winding start part of the negative electrode 6 with the collector surface exposed inside. When the winding start portion of the positive electrode 5 is inserted between the two separators 7 and wound in the direction indicated by the arrow in FIG. 8, the winding start portion of the negative electrode 6 has four layers with the current collector exposed surface 6a inside. An electrode group having a configuration surrounding the separator 7 is obtained.

  When the number of stacked separators 7 is six, for example, the configuration shown in FIG. 9 can be used. As the positive electrode 5 and the negative electrode 6, those having the same configuration as described in the case where the number of stacked separators is four can be used.

  First, the separator 7 is arranged in an S shape around the cores 10a and 10b in the same manner as described above with reference to FIG. 6, and then both the separators 7 are pulled out in the same direction. Surround the surrounding area by one lap. Then, the winding start portion of the negative electrode 6 is inserted between the two separators 7 with the current collector exposed surface facing inward, and the separator 7 in contact with the active material-containing layer 6b of the negative electrode 6 is positioned further outside. When the winding start portion of the positive electrode 5 is inserted between the separator 7 to be wound and wound in the direction indicated by the arrow in FIG. 9, the winding start portion of the negative electrode 6 is separated into six layers with the current collector exposed surface 6a inside. 7 is obtained.

[Example]
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings described above.
Example 1
<Preparation of positive electrode>
Add 5 parts by mass of acetylene black and 5 parts by mass of graphite powder as a conductive agent to 100 parts by mass of LiCoO ₂ , add 5 parts by mass of polyvinylidene fluoride as a binder, dilute and mix with N-methylpyrrolidone, A positive electrode mixture was obtained. Next, a positive electrode active material-containing layer was formed by applying and drying a positive electrode mixture on both surfaces of a 0.02 mm thick aluminum foil as a positive electrode current collector by a doctor blade method. Thereafter, coating and drying were repeated until the coating thickness of the positive electrode active material-containing layer became 0.15 mm on both sides, to produce a double-sided coated positive electrode.

  Next, the portion of the positive electrode active material containing layer in contact with the outer can which is the positive electrode case was removed from one end of the positive electrode, and the aluminum layer was exposed to form an energization portion. In addition, the positive electrode active material-containing layer at the winding start portion and the portion facing the winding start portion is removed from the end opposite to the energizing portion, and the aluminum layer is exposed, and the length is 12 mm long, 120 mm long, and 0.15 mm thick A positive electrode cut out was prepared.

<Production of negative electrode>
2.5 parts by mass of styrene butadiene rubber (SBR) and carboxymethyl cellulose (CMC) as binders are added to 100 parts by mass of graphitized mesophase pitch carbon fiber powder, diluted and mixed with ion-exchanged water, and a slurry-like negative electrode A mixture was obtained. The obtained negative electrode mixture was repeatedly coated and dried in the same manner as in the case of the positive electrode so that the thickness of the negative electrode active material-containing layer was 0.15 mm on a 0.02 mm thick copper foil as a negative electrode current collector. A negative electrode coated on both sides was prepared.

  Next, the portion of the negative electrode active material-containing layer in contact with the sealing can as the negative electrode case was removed from one end of the negative electrode, and the copper layer was exposed to form a current-carrying portion. A portion of the negative electrode active material containing layer that is opposite to the winding start portion of the positive electrode is removed from the end located on the opposite side of the current-carrying portion, and the copper layer is exposed to a width of 13 mm, a length of 130 mm, and a thickness of 0.15 mm A negative electrode cut into a length was prepared.

<Battery assembly>
Using the obtained positive electrode, negative electrode, and separator made of a polyethylene microporous film having a thickness of 30 μm, as described with reference to FIGS. An electrode group having a configuration in which a single-layer separator 7 was interposed between the current collector surface of the winding start portion 9 of the negative electrode 6 was produced.

  The cores 10a and 10b were pulled out from the obtained electrode group, then subjected to compression treatment, and further dried at 85 ° C. for 12 hours.

Subsequently, the outermost negative electrode current collector 6a of the electrode group is brought into contact with the bottom inner surface of the negative electrode case 2 in which the insulating gasket 3 is integrated, and a solvent in which ethylene carbonate and methyl ethyl carbonate are mixed at a volume ratio of 1: 1. 5 mg of a liquid non-aqueous electrolyte in which LiPF ₆ was dissolved as a supporting salt at a rate of 1 mol / L was injected into the negative electrode case 2 per nominal capacity of 1 mAh, and the positive electrode current collector 5a as the outermost layer of the electrode group The positive electrode case 1 is fitted so as to be in contact with the inner surface of the bottom portion of the case 1, and after being turned upside down, the positive electrode case 1 is subjected to caulking, and has the structure shown in FIG. 1, and has a diameter of 24 mm and a thickness of 3.2 mm. A flat nonaqueous electrolyte secondary battery was manufactured.

  The nominal capacity is the discharge capacity discharged at a current value corresponding to the designed discharge capacity of 0.2 CmA.

(Example 2)
As described above with reference to FIG. 4, the three-layer separator 7 is interposed between the current collector exposed surface of the winding start portion 8 of the positive electrode 5 and the current collector exposed surface of the winding start portion 9 of the negative electrode 6. A flat nonaqueous electrolyte secondary battery was manufactured in the same manner as described in Example 1 except that the electrode group having the above-described configuration was manufactured.

(Example 3)
In the same manner as described above with reference to FIG. 5, the five-layer separator 7 is interposed between the current collector exposed surface of the winding start portion 8 of the positive electrode 5 and the current collector exposed surface of the winding start portion 9 of the negative electrode 6. A flat nonaqueous electrolyte secondary battery was manufactured in the same manner as described in Example 1 except that the electrode group having the above-described configuration was manufactured.

Example 4
In the same manner as described above with reference to FIGS. 6 and 7, except that an electrode group having a configuration in which the winding start portion of the negative electrode 6 surrounds the two layers of separators 7 with the current collector surface facing inward, A flat nonaqueous electrolyte secondary battery was produced in the same manner as described in Example 1 above.

(Example 5)
In the same manner as described with reference to FIG. 8 described above, except that an electrode group having a configuration in which the winding start portion of the negative electrode 6 surrounds the four layers of separators 7 with the current collector surface facing inward is described above. A flat nonaqueous electrolyte secondary battery was manufactured in the same manner as described in Example 1.

(Example 6)
In the same manner as described with reference to FIG. 9 described above, except that an electrode group having a configuration in which the winding start portion of the negative electrode 6 surrounds the six-layer separator 7 with the current collector exposed surface inside is described above. A flat nonaqueous electrolyte secondary battery was manufactured in the same manner as described in Example 1.

(Comparative Example 1)
As shown in FIG. 10, the active material-containing layer at the winding start portion of the positive electrode and the negative electrode is left between the positive electrode active material-containing layer 5 b at the winding start portion of the positive electrode 5 and the negative electrode active material-containing layer 6 b at the winding start portion of the negative electrode 6. A flat nonaqueous electrolyte secondary battery was manufactured in the same manner as described in Example 1 except that an electrode group in which one layer of separator 7 was interposed was prepared.

(Comparative Example 2)
The active material containing layer at the beginning of winding of the positive and negative electrodes is left, and as shown in FIG. 11, between the positive electrode active material containing layer 5 b at the beginning of winding of the positive electrode 5 and the negative electrode active material containing layer 6 b at the beginning of winding of the negative electrode 6. A flat nonaqueous electrolyte secondary battery was manufactured in the same manner as described in Example 1 except that an electrode group in which three layers of separators 7 were interposed was manufactured.

(Comparative Example 3)
The active material containing layer at the beginning of winding of the positive and negative electrodes is left, and five layers of separators 7 are interposed between the positive electrode active material containing layer 5b at the beginning of winding of the positive electrode 5 and the negative electrode active material containing layer 6b at the beginning of winding of the negative electrode 6. A flat nonaqueous electrolyte secondary battery was produced in the same manner as described in Example 1 except that the intervening electrode group was produced.

(Comparative Example 4)
12. An electrode group having a configuration in which the active material-containing layer at the start of winding of the positive and negative electrodes is left and the winding start of the negative electrode 6 surrounds the two separators 7 with the negative electrode active material-containing layer 6a inside as shown in FIG. A flat non-aqueous electrolyte secondary battery was manufactured in the same manner as described in Example 1 above, except that was manufactured.

(Comparative Example 5)
Except for producing an electrode group having a configuration in which the active material-containing layer at the winding start portion of the positive and negative electrodes is left and the winding start portion of the negative electrode 6 surrounds the four-layer separator 7 with the negative electrode active material-containing layer 6a inside. A flat nonaqueous electrolyte secondary battery was produced in the same manner as described in Example 1 above.

(Comparative Example 6)
Except for producing an electrode group having a configuration in which the active material containing layer at the beginning of winding of the positive and negative electrodes is left and the winding start of the negative electrode 6 surrounds the six layers of separators 7 with the negative electrode active material containing layer 6a inside. A flat nonaqueous electrolyte secondary battery was produced in the same manner as described in Example 1 above.

(Comparative Example 7)
As described above, except that a positive electrode active material-containing layer 5b at the beginning of winding of the positive electrode 5 and a negative electrode active material-containing layer 6b at the beginning of winding of the negative electrode 6 are used to produce an electrode group in which seven layers of separators 7 are interposed. A flat nonaqueous electrolyte secondary battery was manufactured in the same manner as described in Example 1.

(Comparative Example 8)
Except for producing an electrode group in which the winding start portion of the negative electrode 6 has a configuration in which the negative electrode active material-containing layer 6a is disposed inside and surrounds the eight layers of the separator 7, the flattening is performed in the same manner as described in the first embodiment. A non-aqueous electrolyte secondary battery was manufactured.

  50 pieces of each of the obtained batteries of Examples 1 to 6 and Comparative Examples 1 to 8 were prepared.

  With respect to the electrode groups of Examples 1 to 6 and Comparative Examples 1 to 8, the electrode group weights were previously measured and 5 electrode groups were immersed in a non-aqueous electrolyte while maintaining the shape, and the excess was not able to penetrate. After the nonaqueous electrolyte was wiped off, the weight was measured. The weight of the electrode group after immersion with respect to the weight of the electrode group before immersion is expressed as a percentage, and the results are shown in Table 1 below as the liquid retention rate.

  In the batteries of Comparative Examples 7 and 8, the battery thickness after battery production exceeded 3.2 mm, and the dimensions as designed could not be achieved. This is probably because the electrode group after injection was swollen because the portion holding the non-aqueous electrolyte was excessive at the center of the electrode group, and the battery thickness was increased.

  The batteries prepared in Examples 1 to 6 and Comparative Examples 1 to 6 were allowed to stand in a 20 ° C. atmosphere for 2 days, and then charged with a constant current and a constant voltage of 5 mA and 4.2 V for 24 hours. Furthermore, after leaving still for 3 days, discharge was performed in a 20 ° C atmosphere at a constant current of 10 mA until the closed circuit voltage became 3.0 V.

  In each of 10 batteries, charging / discharging was repeated 500 times under the above charging conditions and discharging conditions. Table 1 shows the ratio of the 500th discharge capacity to the first discharge capacity at that time.

Further, an overcharge test was performed on 10 batteries each, in which application of 10 mA and 12 V was continued for 50 hours. The presence or absence of battery rupture at that time was confirmed. The results are shown in Table 1.

  As shown in Table 1, in the batteries of Examples 1 to 6, since the non-aqueous electrolyte is sufficiently held in the electrode group, the discharge capacity maintenance rate when the charge / discharge cycle is repeated is maintained at 80% or more. The battery characteristics were good. This is because the non-aqueous electrolyte is held in the part not involved in the electrode reaction, so that even when the non-aqueous electrolyte moves due to the expansion or contraction of the positive electrode or the negative electrode due to charge / discharge, It is considered that the battery characteristics could be prevented from being lowered because the non-aqueous electrolyte held in the battery could move.

  Moreover, in the overcharge test in the batteries of Examples 1 to 6, there was no battery burst and there was no problem with respect to safety. This is because the surplus nonaqueous electrolyte retained in the electrode group is not in contact with the positive and negative electrode active material-containing layer causing the decomposition reaction, so the surplus nonaqueous electrolyte retained is not decomposed, Furthermore, since the nonaqueous electrolyte gradually diffuses radially from the winding center, the gas generation rate during overcharging becomes slow, and it is considered that the battery was not ruptured.

  In addition, the secondary batteries of Examples 4 to 6 having a configuration in which the separator is surrounded by the current collector exposed surface of the negative electrode winding start portion tend to have a higher charge / discharge cycle maintenance rate than Examples 1 to 3. It has been.

  On the other hand, in Comparative Examples 1 to 3, the non-aqueous electrolyte retained in the electrode group is in contact with the positive and negative electrode active material-containing layers, and the surplus with respect to the charge / discharge reaction compared to Examples 1 to 6 Therefore, when the charge / discharge cycle was performed, the discharge capacity retention rate was lower than in Examples 1 to 6. Moreover, in the overcharge test in the batteries of Comparative Examples 1 to 3, since the nonaqueous electrolyte serving as the surplus is in contact with the positive and negative electrode active material-containing layer, the surplus nonaqueous electrolyte is decomposed, It is thought that the battery internal pressure was raised and the battery burst.

  In Comparative Examples 4 to 6, since the negative electrode active material-containing layer in the winding center portion does not face the positive electrode active material-containing layer, an excess negative electrode active material-containing layer exists, Lithium extraction reaction due to charging occurred excessively, and the discharge capacity retention rate was lower than in Examples 1-6. Moreover, in the overcharge test in the batteries of Comparative Examples 4 to 6, since the nonaqueous electrolyte that is excessive with respect to the charge / discharge reaction is in contact with the negative electrode active material-containing layer, the excessive nonaqueous electrolyte is decomposed. This is considered to have caused the battery internal pressure to rise and the battery to rupture.

  In addition, although the Example of this invention was demonstrated using the flat type nonaqueous electrolyte secondary battery which used the nonaqueous solvent for the nonaqueous electrolyte, this invention is the polymer secondary using the polymer electrolyte for the nonaqueous electrolyte. The battery shape can be applied, and the battery shape has been described based on a flat nonaqueous electrolyte secondary battery that is sealed by caulking of the positive electrode case, but the positive and negative electrodes are replaced and sealed by caulking. It is also possible. Furthermore, the electrode group shape does not need to be rectangular, and the same effect can be obtained even in a flat nonaqueous electrolyte secondary battery having a special shape such as an oval shape or a polygonal shape.

  As described above, according to the present invention, battery safety can be improved without deteriorating battery characteristics. Therefore, its industrial value is very large.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

Sectional drawing which shows one Embodiment of the flat type nonaqueous electrolyte secondary battery which concerns on this invention. Sectional drawing which showed typically the state of the winding start in the electrode group preparation process of the flat type nonaqueous electrolyte secondary battery of Example 1. FIG. Sectional drawing which showed typically the state of the 1st round in the electrode group preparation process of the flat nonaqueous electrolyte secondary battery of Example 1. FIG. Sectional drawing which showed typically the electrode group production process of the flat type nonaqueous electrolyte secondary battery of Example 2. FIG. Sectional drawing which showed typically the electrode group production process of the flat type nonaqueous electrolyte secondary battery of Example 3. FIG. Sectional drawing which showed typically the state of the winding start in the electrode group preparation process of the flat type nonaqueous electrolyte secondary battery of Example 4. Sectional drawing which showed typically the state of the 2nd round in the electrode group preparation process of the flat type nonaqueous electrolyte secondary battery of Example 4. FIG. Sectional drawing which showed typically the electrode group production process of the flat type nonaqueous electrolyte secondary battery of Example 5. FIG. Sectional drawing which showed typically the electrode group production process of the flat nonaqueous electrolyte secondary battery of Example 6. FIG. Sectional drawing which showed typically the electrode group production process of the flat type nonaqueous electrolyte secondary battery of the comparative example 1. FIG. Sectional drawing which showed typically the electrode group production process of the flat type nonaqueous electrolyte secondary battery of the comparative example 2. FIG. Sectional drawing which showed typically the electrode group production process of the flat type nonaqueous electrolyte secondary battery of the comparative example 4. FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Outer can, 2 ... Sealing can, 2a ... Folding part, 3 ... Insulating gasket, 4 ... Electrode group, 5 ... Positive electrode, 5a ... Positive electrode collector, 5b ... Positive electrode active material containing layer, 6 ... Negative electrode, 6a ... Negative electrode current collector, 6b ... negative electrode active material-containing layer, 7 ... separator, 8 ... positive electrode winding start portion, 9 ... negative electrode winding start portion, 10a, 10b ... winding core.

Claims (2)

A sealed container with a circular main surface;
An electrode group housed in the sealed container, the positive electrode and the negative electrode wound in a flat shape via a separator;
A non-aqueous electrolyte housed in the sealed container at a nominal capacity of 3.5 mg or more per 1 mAh,
The positive electrode includes a positive electrode current collector and a positive electrode active material-containing layer supported on the positive electrode current collector, and at least one surface of the winding start portion has a positive electrode active material-containing layer unsupported current collector exposed surface And
The negative electrode includes a negative electrode current collector and a negative electrode active material-containing layer supported on the negative electrode current collector, and at least one surface of the winding start portion has a negative electrode active material-containing layer not supported And
The current collector exposed surface of the winding start portion of the positive electrode and the current collector exposed surface of the winding start portion of the negative electrode are opposed to each other with 1 to 6 layers of the separator. Flat nonaqueous electrolyte secondary battery. A sealed container with a circular main surface;
An electrode group housed in the sealed container, the positive electrode and the negative electrode wound in a flat shape via a separator;
A non-aqueous electrolyte housed in the sealed container at a nominal capacity of 3.5 mg or more per 1 mAh,
The negative electrode includes a negative electrode current collector and a negative electrode active material-containing layer supported on the negative electrode current collector, and at least one surface of the winding start portion has a negative electrode active material-containing layer not supported And
The flat non-aqueous electrolyte secondary battery is characterized in that the winding start portion of the negative electrode is wound so as to surround the separator having 1 to 6 layers with the current collector surface facing inward.

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