JP2007141482A - Nonaqueous electrolyte winding type secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte winding type secondary battery with excellent productivity capable of suppressing material cost and increase of the number of processes through prevention of internal short circuit at the time of trickle charging or the like caused by adhesion of conductive particles such as fallen-off active materials to a site where an active material non-coated part of a cathode and an anode mixture coated part of an anode are opposed in the nonaqueous electrolyte secondary battery. <P>SOLUTION: The cathode has a cathode mixture non-coated part where a cathode mixture is not coated on a metal collector foil. A part of a separator 15 where the separator 15 interposes between the cathode mixture non-coated part and an anode mixture coated part of the anode is to be a non-porous separator part which has become substantially non-porous through thermal treatment 22 above a fusion contraction temperature. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte wound secondary battery, and more particularly to a non-aqueous electrolyte wound secondary battery using a separator having a suitable configuration.

  Various structures are known as a wound type secondary battery, but with the recent miniaturization of electronic devices, secondary batteries as power source batteries are also required to have high capacity and high density. For this reason, a nickel secondary battery or nickel metal hydride battery, which is a conventional aqueous electrolyte secondary battery, is being replaced by a lithium secondary battery, which is a nonaqueous electrolyte secondary battery. In this lithium secondary battery, the lithium ion secondary battery generally has the following structure. A group of electrode plates is formed by spirally winding a separator between a positive electrode plate and a negative electrode plate. The electrode plate group is housed in a battery case, the electrode plate group is impregnated with a non-aqueous electrolyte, and the opening of the battery case is sealed with a sealing plate.

  However, in the production of such a wound electrode group, conductive particles on the active material uncoated portion of the positive electrode, that is, on the current collector exposed portion, due to falling off of the active material or wear of the manufacturing apparatus in the manufacturing process. When the conductive particles crush and mold the wound electrode plate group, or the electrode plate expands due to battery charging / discharging, the negative electrode and the positive electrode are electrically connected through the conductive particles. Conduction forms a short circuit. This short circuit occurs at a very high rate in the part where the active material uncoated part of the positive electrode and the negative electrode mixture coated part of the negative electrode are facing each other. This short circuit causes the battery to generate abnormal heat during its use. In addition, the capacity is reduced and the battery life is shortened.

An insulating tape is applied to a portion where the positive electrode mixture of the positive electrode is not coated on the metal current collector foil and is opposite to the negative electrode mixture coated portion of the negative electrode through the separator. By sticking, the part where the positive electrode mixture uncoated part of the positive electrode and the negative electrode mixture coated part of the negative electrode are facing each other is covered with an insulating layer. It has been proposed that an internal short circuit can be prevented even if the conductive particles adhere and break through the separator. (For example, see Patent Document 1)
JP-A-10-241737

  In a non-aqueous electrolyte secondary battery typified by a lithium ion secondary battery, the negative electrode mixture layer must be coated with a positive electrode mixture in order to smoothly absorb lithium ions released from the positive electrode active material during charging into the negative electrode active material. Therefore, the negative electrode mixture application part always has a larger area than the positive electrode mixture application part, and therefore the non-aqueous electrolyte secondary battery has the above-described positive electrode active material. There are many portions where the uncoated portion and the negative electrode mixture coated portion of the negative electrode face each other. There is an urgent need to take measures against an internal short circuit that is caused by the adhering of the active material that has fallen into this portion or conductive particles generated by wear of the manufacturing apparatus.

  However, insulating adhesive tapes that have been used to prevent short circuits have been frequently stopped and cleaned because the adhesive adheres to the manufacturing equipment in the battery manufacturing process, such as the tape cutting process and the tape application process to the electrodes. There is a problem that productivity is reduced.

Therefore, the object of the present invention is to solve such a conventional problem, it is difficult to cause an internal short circuit between the electrodes, has high reliability, and can reduce the frequency of cleaning and stopping of the battery manufacturing process. Therefore, it is to provide a nonaqueous electrolyte wound secondary battery with improved manufacturing efficiency.

  In order to solve the conventional problem, a nonaqueous electrolyte wound secondary battery according to claim 1 of the present invention includes a positive electrode active material that occludes and releases lithium ions on a metal current collector foil. Between a positive electrode coated with a mixture and a negative electrode coated with a negative electrode mixture containing a negative electrode active material that occludes and releases lithium ions on a metal current collector foil, through a porous separator having a melting shrinkage temperature In a nonaqueous electrolyte wound secondary battery having a spirally wound electrode plate group, the positive electrode mixture is not applied on the metal current collector foil on the positive electrode. A portion of the separator that is interposed between the positive electrode mixture unapplied portion and the negative electrode mixture application portion in the negative electrode is substantially heat-treated at a temperature equal to or higher than the melt shrinkage temperature. Non-porous separator part that has become non-porous It is an feature.

  This non-porous separator becomes non-porous by being heat-treated at a melting temperature or higher, and becomes a resin sheet having substantially no ionic conductivity.

  An internal short circuit can be prevented even when conductive particles generated due to the active material dropped due to the above configuration or wear of the manufacturing apparatus adhere.

  Moreover, the nonaqueous electrolyte wound secondary battery according to claim 2 of the present invention is the nonaqueous electrolyte wound secondary battery according to claim 1, wherein the nonporous separator part is nonporous. The separator that has become is folded once or more.

  This configuration prevents internal short-circuiting when the non-porous part created by heat treatment of the separator is thicker against internal short-circuits where attached conductive particles break through the separator. This is preferable.

  According to the present invention, it is possible to provide a non-aqueous electrolyte wound secondary battery excellent in productivity that suppresses an increase in material cost and the number of processes and can prevent an internal short circuit.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings, but these do not limit the present invention in any way.

  Here, the embodiment of the present invention will be described by taking the prismatic lithium ion secondary battery shown in FIG. 1 as an example.

  As shown in FIG. 1, the prismatic lithium ion secondary battery includes a bottomed prismatic battery case 11 in which an electrode plate group in which a positive electrode plate 14 and a negative electrode plate 16 are wound in an elliptical shape with a separator 15 interposed therebetween. And is electrically connected to the internal terminal of the sealing plate 12, and after laser welding the sealing plate 12 and the battery case 11, from a liquid injection hole (not shown) provided in the sealing plate 12. After injecting a non-aqueous electrolyte, an injection stopper (not shown) is sealed with a laser.

  The positive electrode plate 14 is, for example, a paste in which a positive electrode active material, a binder, and a conductive agent are kneaded and dispersed in one or both sides of a current collector 13 made of an aluminum foil, a lathed or etched foil, or the like. Can be produced by coating, drying and rolling. And it is preferable that the positive electrode plate 14 is 110 micrometers-200 micrometers in thickness, and has a softness | flexibility.

As the positive electrode active material, for example, a lithium-containing transition metal compound that can accept lithium ions as a guest is used. For example, as a lithium-containing transition metal compound, a composite metal oxide of at least one metal selected from cobalt, manganese, nickel, chromium, iron and vanadium and lithium, lithium cobaltate (hereinafter abbreviated as LiCoO ₂ ), LiMnO ₂ , LiNiO ₂ , LiCo _x Ni _(1-x) O ₂ (0 <x <1), LiCrO ₂ , αLiFeO ₂ , and LiVO ₂ are preferable.

  The binder is not particularly limited as long as it can be kneaded and dispersed in a dispersion medium. For example, a fluorine-based binder, acrylic rubber, modified acrylic rubber, styrene-butadiene rubber (hereinafter abbreviated as SBR). ), An acrylic polymer, a vinyl polymer or the like can be used alone or as a mixture or copolymer of two or more. As the fluorine-based binder, for example, polyvinylidene fluoride, a copolymer of vinylidene fluoride and propylene hexafluoride, and a dispersion of polytetrafluoroethylene resin are preferable.

  As the conductive agent, acetylene black, graphite, carbon fiber or the like is used alone or a mixture of two or more kinds is preferable. Moreover, a thickener can be added as needed, and as a thickener, ethylene-vinyl alcohol copolymer, carboxymethylcellulose, methylcellulose, etc. are preferable.

  As the dispersion medium, a solvent in which the binder can be dissolved is suitable. In the case of organic binders, organic solvents such as N-methyl-2-pyrrolidone, N, N-dimethylformamide, tetrahydrofuran, dimethylacetamide, dimethyl sulfoxide, hexamethylsulfuramide, tetramethylurea, acetone, and methyl ethyl ketone Are preferably used alone or a mixed solvent in which these are mixed. In the case of an aqueous binder, water or warm water is preferred.

  In addition, various dispersants, surfactants, stabilizers, and the like can be added as necessary when the paste is kneaded and dispersed.

  The coating and drying is not particularly limited. The slurry-like mixture kneaded and dispersed as in the above paste can be easily applied using, for example, a slit die coater, reverse roll coater, lip coater, blade coater, knife coater, gravure coater, dip coater, etc. can do. Moreover, although natural drying is preferable for drying, considering productivity, it is preferable to dry for 5 hours-10 minutes at the temperature of 70 to 200 degreeC.

  It is preferable that the rolling is performed several times with a roll press until a predetermined thickness is achieved, or the pressing pressure is changed.

  The negative electrode plate 16 may be prepared by applying, drying, and rolling a paste obtained by kneading and dispersing a negative electrode active material, a binder, and, if necessary, a conductive agent in a solvent on one side or both sides of the current collector 17. it can. The negative electrode plate preferably has a thickness of 110 μm to 210 μm and is flexible like the positive electrode plate.

  The negative electrode current collector 17 is preferably a copper foil or a copper alloy foil, but is not particularly limited. Examples of those foils include rolled foil and electrolytic foil. The shape of the foil may be foil, perforated foil, expanded material, lath material, or the like.

  As the negative electrode active material, for example, a material containing graphite having a graphite type crystal structure capable of reversibly inserting and extracting lithium ions is preferable. As a material containing graphite having a graphite-type crystal structure, for example, natural graphite, spherical / fibrous artificial graphite, non-graphitizable carbon (hard carbon), graphitizable carbon (soft carbon) and the like are preferable.

  As the binder, the dispersion medium, the conductive agent that can be added as necessary, and the thickener, the same materials as those for the positive electrode can be used.

  As a material for the separator 15, a single layer of a microporous polyolefin resin such as polyethylene resin or polypropylene resin, or a laminate of polypropylene resin on both sides of the polyethylene resin is preferable. The thickness of the separator 15 is preferably 10 to 30 μm.

  The battery case 11 is a bottomed rectangular case having an open upper end. The material is preferably an aluminum alloy containing a very small amount of metal such as manganese or copper, or a steel plate plated with nickel, from the viewpoint of pressure strength.

  The electrolyte is adjusted by dissolving the electrolyte in a non-aqueous solvent. Examples of the non-aqueous solvent include ethylene carbonate (hereinafter abbreviated as EC), propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, 1,2-dichloroethane, 1,3. -Dimethoxypropane, 4-methyl-2-pentanone, 1,4-dioxane, acetonitrile, propionitrile, butyronitrile, valeronitrile, benzonitrile, sulfolane, 3-methyl-sulfolane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethylformamide, Dimethyl sulfoxide, dimethylformamide, trimethyl phosphate, triethyl phosphate, and the like can be used. These nonaqueous solvents can be used alone or as a mixed solvent of two or more kinds.

As the electrolyte, for example, a lithium salt having a strong electron withdrawing property can be used. For example, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiC (SO ₂ CF ₃ ) _3, etc. Can be mentioned. These electrolytes may be used alone or in combination of two or more. These electrolytes are preferably dissolved at a concentration of 0.5 to 1.5M in the nonaqueous solvent.

  A positive electrode 14 coated with a positive electrode mixture containing a positive electrode active material that occludes and releases lithium ions on a metal current collector foil, and a negative electrode composite containing a negative electrode active material that occludes and releases lithium ions on a metal current collector foil A positive electrode mixture in which the positive electrode mixture of the positive electrode is not applied on the metal current collector foil, the electrode plate group being wound in a spiral shape with a separator 15 between the negative electrode 16 coated with the agent. The separator in the portion where the agent is not applied and facing the negative electrode mixture application portion in the negative electrode is manufactured to be substantially non-porous by heat treatment at a temperature equal to or higher than the melt shrinkage temperature.

  Specific examples will be described in detail below.

  The prismatic lithium ion secondary battery of the present invention is produced as follows.

Example 1
The positive electrode plate 14 was prepared by adding 100 parts by weight of LiCoO ₂ as a positive electrode active material, ₂ parts by weight of acetylene black as a conductive agent, and 3 parts by weight of a polyvinylidene fluoride resin as a binder, and adding N-methyl-2- A paste was prepared by kneading and dispersing pyrrolidone as a solvent. This paste was continuously intermittently applied to a current collector 13 made of a strip-shaped aluminum foil having a thickness of 15 μm, dried, and then rolled three times.

The positive electrode lead 21 made of aluminum was welded by spot welding. In order to prevent an internal short circuit, an insulating adhesive made of polypropylene resin was attached so as to sandwich the positive electrode lead 21. In this way, a positive electrode plate 14 having a width dimension of 42 mm, a length of 300 mm, and a thickness of 0.14 mm was produced.

  The negative electrode plate 16 has 100 parts by weight of scaly graphite capable of occluding and releasing lithium as a negative electrode active material, 1 part by weight of a water-soluble SBR dispersion as a binder, and carboxymethyl cellulose as a thickener. 1 part by weight of water as a solvent was added and kneaded and dispersed to prepare a paste. This paste was continuously and intermittently applied to a current collector 17 made of a strip-shaped copper foil having a thickness of 10 μm, dried at 110 ° C. for 30 minutes, and then rolled.

  Then, the negative electrode lead 20 made of nickel was welded by spot welding. In order to prevent an internal short circuit, an insulating adhesive made of polypropylene resin (not shown) was attached so as to sandwich the negative electrode lead 20. Thus, the negative electrode plate 16 having a width dimension of 43 mm, a length of 400 mm, and a thickness of 0.14 mm was produced.

  When the positive electrode plate 14 and the negative electrode plate 16 manufactured in this way are wound in an elliptical shape through a microporous separator 15 made of polyethylene resin having a thickness of 20 μm, the electrode plate group shown in FIG. Heat treatment is performed at 130 ° C. on the separator 15 in the portion where the positive electrode mixture of the plate 14 is not applied to the current collector 13 and the portion of the negative electrode plate 14 facing the negative electrode mixture application portion. And after forming the part 22 which lost the porosity of the separator, the electrode plate group was created, and the electrode plate group was made flat by pressing the long side surface.

  The electrode plate group was housed in a bottomed rectangular battery case 11. The bottomed rectangular battery case 11 is a 3000 series aluminum alloy containing a trace amount of metals such as manganese and copper, has a thickness of 0.25 mm, a width dimension of 6.3 mm, a length dimension of 34.0 mm, and a total height of 50. 0.0 mm.

  Next, the positive electrode lead 21 welded to the positive electrode plate 14 and the negative electrode lead 20 welded to the negative electrode plate 16 were welded to the respective polar terminals of the sealing plate 12. After drying in such a state and finishing the predetermined drying, the moisture content of the electrode plate group was measured with a Karl Fischer moisture meter. It was confirmed that the moisture content of the electrode plate group was not more than a predetermined moisture content.

Further, the sealing plate 12 and the battery case 11 were welded by laser welding. A nonaqueous electrolytic solution was prepared by dissolving LiPF ₆ as an electrolyte at a concentration of 1.0 M in a mixed solvent in which EC and ethyl methyl carbonate were mixed at a ratio of 2: 1. This nonaqueous electrolytic solution was injected from a liquid injection hole (not shown) provided in the sealing plate 12. Thereafter, a liquid injection stopper (not shown) was sealed by laser welding. The prismatic lithium ion secondary battery produced in this way had a battery capacity design value of 1000 mAh. This prismatic lithium ion secondary battery was designated as battery A.

(Example 2)
When preparing the electrode plate group, the positive electrode mixture of the positive electrode plate 14 is a portion where the positive electrode mixture is not applied to the current collector 13, and only the portion of the negative electrode plate 16 facing the negative electrode mixture application portion. The separator 15 was folded back as shown in FIG. 3 and then heat-treated at 130 ° C. to prepare an electrode plate group. Otherwise, a rectangular lithium ion secondary battery was produced in the same manner as in Example 1, and a battery B was obtained.

(Comparative Example 1)
When preparing the electrode plate group, the positive electrode mixture of the positive electrode plate 14 is a portion where the positive electrode mixture is not applied to the current collector 13 and is opposite to the negative electrode mixture application portion of the negative electrode plate 16. An insulating tape with a paste material made of polypropylene (thickness: 30 μm) was attached to prepare an electrode plate group. Otherwise, a rectangular lithium ion secondary battery was produced in the same manner as in Example 1, and a battery C was obtained.

(Comparative Example 2)
When producing the electrode plate group, the positive electrode mixture of the positive electrode plate 14 is a portion where the positive electrode mixture is not applied to the current collector 13, and the portion of the negative electrode plate 16 facing the negative electrode mixture application portion A prismatic lithium ion secondary battery was fabricated in the same manner as in Example 1 except that no heat treatment was applied to the separator 15 and the electrode plate group was wound in the same manner as the other portions of the separator, and the battery was wound. D.

(Battery evaluation)
In order to confirm the effect of the present invention, the batteries A to D thus produced were subjected to trickle continuous charge tests for 100 months at 60 ° C. for one month, two months, and three months. The presence or absence of a short circuit was confirmed. In the trickle continuous charging method, the battery is charged at a constant current of 1000 mA (1 CmA) until the battery voltage reaches 4.2 V, and then the current is attenuated and the constant voltage (4.2 V) is charged. The total charging period is one month. It set so that it might become.

  The results are shown in Table 1.

From the results in Table 1, the following can be understood. From the result of the battery D, it was found that an internal short circuit occurs with a considerable probability when the insulating material is not applied to the portion of the negative electrode plate where the negative electrode mixture is applied, which is not applied to the negative electrode mixture. .

On the other hand, the battery A and the battery B of the present invention had an effect of preventing an internal short circuit, and the battery B with the separator turned back did not cause an internal short circuit even in 3 months, and the effect was remarkable.
This is presumed to be due to the fact that the thickness of the separator made non-porous by folding the separator is three times the thickness of the separator made non-porous in battery A, which further increases the insulation. The

  Moreover, in the pasting method of the insulation tape shown as the battery C, although an internal short circuit was able to be prevented effectively, it is an adhesive in battery manufacturing processes, such as a tape cutting process and the tape affixing process to an electrode. However, when the batteries A and B of the present invention were prepared, the separator was continuously set before winding the electrode plate group. It was not necessary to stop and clean the apparatus as in the battery C in order to heat-treat this part.

  In the above-described embodiments, the case of a prismatic lithium ion secondary battery has been described. However, the present invention is not limited to a prismatic lithium ion secondary battery, but can be applied to a nickel-cadmium battery and a nickel metal hydride battery. It is. Further, the battery shape is not particularly limited, and can be applied to secondary batteries having various shapes such as a flat type and a cylindrical type.

  According to the present invention, a battery having excellent reliability against internal short circuit can be obtained, which is useful as a power source for small electronic devices.

Sectional drawing of the lithium secondary battery which shows one Embodiment of this invention Enlarged schematic view of separator heat treatment part of the present invention Enlarged schematic view of the separator folding heat treatment portion of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Battery case 12 Sealing plate 13 Positive electrode collector 14 Positive electrode plate 15 Separator 16 Negative electrode plate 17 Negative electrode collector 20 Negative electrode lead 21 Positive electrode lead 22 Separator heat treatment part

Claims (2)

A positive electrode in which a positive electrode mixture containing a positive electrode active material that occludes and releases lithium ions is applied on a metal current collector foil, and a negative electrode mixture that contains a negative electrode active material that occludes and releases lithium ions in a metal current collector foil In a non-aqueous electrolyte wound secondary battery having a group of electrodes wound spirally through a porous separator having a melting shrinkage temperature between the negative electrode coated with
The positive electrode has a positive electrode mixture non-applied portion where the positive electrode mixture is not applied on the metal current collector foil, and a negative electrode mixture in the positive electrode mixture non-applied portion and the negative electrode of the separator. The portion intervening in the place where the coating portion is opposed is a non-porous separator portion that has become substantially non-porous by heat treatment at a temperature equal to or higher than the melting shrinkage temperature. Rechargeable secondary battery. 2. The non-aqueous electrolyte wound secondary battery according to claim 1, wherein the non-porous separator portion has a non-porous separator folded back once or more.