JP4875868B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly, a non-aqueous electrolyte secondary battery in which a battery lid is caulked and fixed on one side of a battery container made of metal and coated with an insoluble metal plating in the non-aqueous electrolyte. It relates to batteries.

  Conventionally, in the field of a rechargeable secondary battery, a battery using an aqueous electrolyte such as a lead battery, a nickel-cadmium battery, or a nickel-hydrogen battery has been mainstream. However, as electric devices have become smaller and lighter, batteries using non-aqueous electrolytes with high energy density have attracted attention, and research, development, and commercialization have progressed, and now for mobile phones and laptop computers. Non-aqueous electrolyte secondary batteries are widely used for small consumer use. In addition, for example, large nonaqueous electrolyte secondary batteries for electric vehicles and assembled batteries in which a plurality of nonaqueous electrolyte secondary batteries are connected have also been put into practical use.

  In a non-aqueous electrolyte secondary battery, a battery container made of a metal such as steel mainly containing iron and having an opening formed on one side (upper side) is generally used. The battery container accommodates an electrode group obtained by winding or laminating positive and negative electrodes, and after the nonaqueous electrolytic solution is injected, the battery lid is caulked and fixed in the opening. That is, after accommodating the electrode group in the battery container, the battery container is subjected to a stepping process for forming a stepped portion for placing the battery lid on the inner surface side of the battery container above the electrode group. Thereafter, the battery cover is fixed by caulking above the stepped portion.

  In such a metal battery container, the metal (base metal) of the battery container may be dissolved in the non-aqueous electrolyte and metal ions may be eluted. Since the eluted metal ions precipitate and grow on the negative electrode surface as a metal when the battery is charged / discharged, a micro short circuit occurs between the positive and negative electrodes through the separator separating the positive and negative electrodes, and when a micro short circuit occurs, the battery The voltage will be reduced. In order to avoid this, it is necessary to prevent dissolution of the metal in the battery container. For this reason, it is preferable not to use a metal such as iron that dissolves in the non-aqueous electrolyte in the battery container. However, when the battery container is used with a negative polarity connected to the negative electrode, a non-aqueous electrolyte secondary battery is used. After the battery is charged, the battery container is reduced due to electrical influence, so that metals such as iron are difficult to dissolve. Therefore, metal such as iron is used as the material of the battery container in consideration of cost.

  However, before charging the non-aqueous electrolyte secondary battery, that is, from the time when the electrode group is accommodated in the battery container and the non-aqueous electrolyte is injected to the time of charging, the metal of the battery container is dissolved. Depending on the area of the positive and negative electrodes, the method of injecting the nonaqueous electrolyte, etc., the period from injecting the nonaqueous electrolyte to charging is the initial stage by spreading the nonaqueous electrolyte over the entire surface of the positive and negative electrodes. In order to stabilize the charge / discharge characteristics, it is preferable to have several days. As a technique for suppressing the dissolution of the metal in the battery container, there is a method of coating the battery container with a metal or resin that is difficult to dissolve (insoluble or hardly soluble) in the non-aqueous electrolyte. For example, a technique using an aluminum alloy coated with a synthetic resin on a battery container is disclosed (see Patent Document 1). In addition, a technique for forming a nickel plating layer containing a fine powder of fluororesin having excellent corrosion resistance on the surface of an iron battery container is disclosed (for example, see Patent Document 2).

JP-A-8-167401 JP 2002-231195 A

  However, in the techniques of Patent Document 1 and Patent Document 2, since the battery container is deformed when the battery container is stepped or when the battery lid is caulked and fixed, the battery container is covered with the stepped part and the caulking fixing part. Cracks occur frequently in the synthetic resin and nickel plating layer. In the cracked part of the synthetic resin or nickel plating layer, the metal of the battery container, that is, the aluminum alloy or iron comes into contact with the non-aqueous electrolyte. Elutes. Since the above-described minute short circuit between the positive and negative electrodes occurs due to metal ions eluted from the metal, there is a problem that the battery voltage is lowered.

  This invention makes it a subject to provide the nonaqueous electrolyte secondary battery which can suppress the fall of the battery voltage by melt | dissolution of metal battery containers in view of the said matter.

In order to solve the above problems, the present invention provides a nonaqueous electrolyte secondary battery in which a battery lid is caulked and fixed on one side of a battery container that is made of metal and is coated with a metal plating that is insoluble in the nonaqueous electrolyte. the battery case has a negative polarity by being connected to the electrode, and a feature that the coating material covering the metal plating on the inner surface of a portion at least the battery lid was fixed by caulking is distribution To do.

In the present invention, since the battery container in which the metal plating insoluble in the nonaqueous electrolyte solution made of metal has been performed, the coating material for coating the metal plating on the inner surface of a portion at least the battery lid is fixed by caulking is distribution, Even when the battery lid is crimped and fixed to the battery container, even if the metal plating cracks due to deformation of the battery container, the coating material covers the inner surface of the battery container, so that the nonaqueous electrolyte contacts the base metal of the battery container. Therefore, dissolution of the metal can be prevented. Therefore, since a minute short circuit between the positive and negative electrodes is suppressed, a decrease in battery voltage can be suppressed.

In this case, if it is distributing the coating material on the inner surface to the inner bottom surface near the battery container from one side end, even if cracks in the metal plating by an external force when the battery is used to prevent dissolution of the base metal of the battery container be able to. The coating material is preferably insoluble in the nonaqueous electrolytic solution. Furthermore, the coating material may be an organic compound. At this time, the organic compound may be asphalt. Moreover, it is preferable that a coating material has insulation. At this time, if it is coordinating further coating material to the outer surface and the end surface of one side of the bottom surface near the one end of the battery container, the battery container of negative polarity to the battery pack manufacturing or the like, positive polarity of adjacent cell The occurrence of a short circuit due to contact with the battery lid can be suppressed.

According to the present invention, the battery container, since the coating material for coating the metal plating on the inner surface of the caulking portion at least battery cover is high, even if cracks in the metal plating by deformation of the battery container, Since the coating material covers the inner surface of the battery container, the non-aqueous electrolyte does not come into contact with the base metal of the battery container, so that the base metal can be prevented from dissolving and the decrease in battery voltage can be suppressed. Can be obtained.

  Embodiments of a cylindrical lithium ion secondary battery to which the present invention is applied will be described below with reference to the drawings.

(Constitution)
As shown in FIG. 1, a cylindrical lithium ion secondary battery 20 of this embodiment includes a battery container 7 whose bottom is cylindrical and whose upper side is sealed with a battery lid, and a strip-shaped positive and negative electrode plate having a cross-sectional spiral through a separator. The electrode group 6 is wound in a shape.

  Iron is used as the material of the battery container 7, and nickel plating that is insoluble in the non-aqueous electrolyte is applied to the entire inner and outer surfaces. As shown in FIG. 2, a coating 25 is formed on the surface of the battery container 7 by coating with a flexible coating material. For the coating material, for example, an organic compound such as blown asphalt that is insoluble in the non-aqueous electrolyte and has electrical insulation is used. The coating 25 may be at least a portion for caulking and fixing the battery lid and may be formed on the inner surface of the battery container 7. In this example, the coating 25 extends from the upper end of the battery container 7 to a position corresponding to the lower end surface of the electrode group 6. It is formed on the inner and outer surfaces and the upper end surface of the battery container 7. The coating 25 is not formed on the inner and outer surfaces of the bottom of the battery container 7, and the nickel plating is exposed.

  As shown in FIG. 1, on the upper side of the electrode group 6, an aluminum positive electrode current collecting ring 4 for collecting the electric potential from the positive electrode plate is disposed on a substantially extension line of the shaft core 1. The positive electrode current collecting ring 4 is fixed to the upper end portion of the shaft core 1. The edge part of the positive electrode lead piece 2 led out from the positive electrode plate is joined by ultrasonic welding to the peripheral edge of the flange part integrally protruding from the periphery of the positive electrode current collecting ring 4. A disc-shaped battery lid serving as a positive electrode external terminal is disposed above the positive electrode current collecting ring 4. The battery lid includes an aluminum lid case 12, a lid cap 13, a valve retainer 14 that keeps airtightness, and a cleavage valve 11 that is cleaved by an increase in internal pressure, and these are laminated to form a peripheral edge of the lid case 12. It is assembled by caulking and fixing. One end of two positive electrode leads 9 formed by superposing a plurality of aluminum ribbons is fixed to the upper portion of the positive electrode current collecting ring 4, and another one is fixed to the lower surface of the lid case 12. One end is welded. The other ends of the two positive electrode leads 9 are joined by welding.

  On the other hand, a copper negative electrode current collecting ring 5 for collecting a potential from the negative electrode plate is disposed below the electrode group 6. The outer peripheral surface of the lower end portion of the shaft core 1 is fixed to the inner peripheral surface of the negative electrode current collecting ring 5. The end of the negative electrode lead piece 3 led out from the negative electrode plate is joined to the outer peripheral edge of the negative electrode current collecting ring 5 by welding. A copper negative electrode lead plate 8 for electrical conduction is welded to the lower part of the negative electrode current collecting ring 5, and the negative electrode lead plate 8 is joined to the inner bottom surface of the battery container 7 by welding. In this example, the dimensions of the battery container 7 are set to a height of 113.5 mm, an outer diameter of 40 mm, and an inner diameter of 39 mm.

The battery lid is caulked and fixed to the upper side of the battery container 7 via an insulating and heat resistant EPDM resin gasket 10. For this reason, the inside of the lithium ion secondary battery 20 is sealed, the battery container 7 also serves as the negative electrode external terminal, and the battery lid also serves as the positive electrode external terminal. In addition, a non-aqueous electrolyte is injected into the battery container 7. As the non-aqueous electrolyte, a solution obtained by dissolving 1 mol / liter of lithium hexafluorophosphate (LiPF ₆ ) as a lithium salt in a mixed solvent of ethylene carbonate and dimethyl carbonate in a volume ratio of 1: 1 is used. .

  In the electrode group 6, the positive electrode plate and the negative electrode plate are wound around the outer periphery (outside) of the shaft core 1 through a separator so that the two electrode plates do not directly contact each other. In this example, a porous polyethylene film having a width of 90.5 mm and a thickness of 40 μm is used as the separator. The positive electrode lead piece 2 and the negative electrode lead piece 3 are disposed on both end surfaces of the electrode group 6 opposite to each other. Insulation coating is applied to the entire circumference of the collar surface of the electrode group 6 and the positive electrode current collector ring 4. For the insulation coating, an adhesive tape in which a hexamethacrylate adhesive is applied to one side of a polyimide base material is used. The pressure-sensitive adhesive tape is wound one or more times from the collar surface to the outer circumferential surface of the electrode group 6. By adjusting the lengths of the positive electrode plate, the negative electrode plate, and the separator, the diameter of the electrode group 6 is set to 38 ± 0.1 mm.

  The negative electrode plate constituting the electrode group 6 has a rolled copper foil having a thickness of 10 μm as a negative electrode current collector. A negative electrode mixture containing amorphous carbon powder capable of occluding and releasing lithium ions as a negative electrode active material is coated on both surfaces of the rolled copper foil. In the negative electrode mixture, for example, 10 parts by weight of polyvinylidene fluoride (hereinafter abbreviated as PVDF) as a binder (binder) is blended with 90 parts by weight of amorphous carbon powder. When applying the negative electrode mixture to the rolled copper foil, a dispersion solvent N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP) is used. An uncoated portion of a negative electrode mixture having a width of 30 mm is formed on the side edge on one side in the longitudinal direction of the rolled copper foil. The uncoated part is notched in a comb shape, and the negative electrode lead piece 3 is formed in the notch remaining part. The interval between the adjacent negative electrode lead pieces 3 is set to 50 mm, and the width of the negative electrode lead piece 3 is set to 5 mm. The negative electrode plate is pressed with a heatable roll press so as to have a thickness of 70 μm after being dried, and is cut into a width of 88 mm.

  On the other hand, the positive electrode plate has an aluminum foil having a thickness of 20 μm as a positive electrode current collector. A positive electrode mixture containing a lithium transition metal double oxide as a positive electrode active material is applied to both surfaces of the aluminum foil. In the positive electrode mixture, for example, 10 parts by weight of flaky graphite as a conductive material and 5 parts by weight of PVDF as a binder are blended with 100 parts by weight of lithium transition metal double oxide. When applying the positive electrode mixture to the aluminum foil, a dispersion solvent NMP is used. An uncoated portion of a positive electrode mixture with a width of 30 mm is formed on the side edge on one side in the longitudinal direction of the aluminum foil, and a positive electrode lead piece 2 is formed. The interval between the adjacent positive electrode lead pieces 2 is set to 50 mm, and the width of the positive electrode lead piece 2 is set to 5 mm. The positive electrode plate, after drying, is pressed in the same manner as the negative electrode plate so as to have a thickness of 90 μm, and is cut into a width of 84 mm.

(Battery assembly)
The lithium ion secondary battery 20 is assembled in the following procedure. First, a coating material is coated on the surface of the battery container 7 to form a coating film 25 (see FIG. 2). At this time, a dip coating method is used in which the upper end of the battery container 7 in which the opening is formed is on the lower side, and a range of 100 mm from the upper end is immersed in the liquid of the coating material and then dried. Drying is performed in a vacuum state at 25 ° C. for 1 day. The coating 25 is formed up to a position corresponding to the lower end surface of the electrode group 6 by coating in a range of 100 mm from the upper end. On the other hand, the positive and negative electrode plates are wound around the shaft core 1 with a winding device through a separator to produce the electrode group 6, and the positive electrode lead piece 2 and the negative electrode lead piece 3 respectively led out from both end faces of the electrode group 6. Are welded to the positive electrode current collector ring 4 and the negative electrode current collector ring 5, respectively. As shown in FIG. 3, the electrode group 6 is inserted into the battery container 7 on which the coating film 25 is formed, and the negative electrode lead plate 8 previously welded to the negative electrode current collecting ring 5 is welded to the inner bottom surface of the battery container 7. . A stepping process for forming a stepped portion 28 for placing the battery lid is performed inside a position 9 mm below the upper end of the battery container 7. After connecting the positive electrode current collecting ring 4 and the battery lid with the positive electrode lead plate 9, a nonaqueous electrolyte is injected into the battery container 7 from the hollow portion of the shaft core 1 to infiltrate the electrode group 6 into the nonaqueous electrolyte. . After the positive electrode lead plate 9 is folded and accommodated in the battery container 7 and the battery lid is placed on the stepped portion 28, the battery lid is caulked and fixed above the stepped portion 28 via the gasket 10, The assembly of the lithium ion secondary battery 20 is completed.

  Next, the operation and the like of the lithium ion secondary battery 20 of the present embodiment will be described.

  In the lithium ion secondary battery 20 of the present embodiment, the coating 25 is formed on the inner surface from the upper end of the nickel-plated battery container 7 to the position corresponding to the lower end surface of the electrode group 6. The coating 25 is made of a blown asphalt made of an organic compound that is insoluble in the non-aqueous electrolyte and has flexibility. Therefore, when the stepped portion 28 is formed in the battery container 7 or when the battery lid is caulked and fixed, the coating 25 is cracked even if the nickel plating is cracked due to deformation of the battery container 7. Without deformation, the inner surface of the battery container 7 is covered. As a result, the contact between the non-aqueous electrolyte and the bare metal of the battery container 7 is hindered by the coating 25 at the portion where the nickel plating is cracked. Elution into the water electrolyte can be prevented. Further, since the coating 25 is insoluble in the non-aqueous electrolyte, the inner surface of the battery container 7 can be stably coated for a long period of time. Therefore, even if the lithium ion secondary battery 20 is charged and discharged, a minute short circuit between the positive and negative electrodes due to the deposition of iron is not formed, and a decrease in battery voltage can be suppressed.

  Further, since the coating 25 is formed up to the position corresponding to the lower end surface of the electrode group 6, the nickel plating of the battery container 7 is cracked by an external force from the side surface of the lithium ion secondary battery 20 when the battery is used. Can also prevent the dissolution of iron in the metal. Thereby, even when the deformation | transformation on the external appearance by external force is not recognized, the micro short circuit accompanying iron precipitation can be prevented and the fall of a battery voltage can be suppressed.

  Furthermore, in the lithium ion secondary battery 20 of the present embodiment, the coating 25 is also formed on the outer surface from the upper end of the battery container 7 to the position corresponding to the lower end surface of the electrode group 6. Since the coating 25 also has electrical insulation, for example, when producing an assembled battery, a battery lid that also serves as the positive electrode external terminal of one of the two adjacent lithium ion secondary batteries 20, Even if the side surface of the battery container 7 that also serves as the negative electrode external terminal of the other battery approaches, the coating 25 is interposed, so that the occurrence of a short circuit can be prevented. Thereby, since generation | occurrence | production of a defective battery reduces, the yield of assembled battery production can be improved.

  Furthermore, in the lithium ion secondary battery 20 of the present embodiment, the coating 25 is also formed on the upper end surface of the battery container 7. For this reason, since the coating 25 is interposed in addition to the gasket 10 between the battery lid and the upper end portion of the battery container 7 to which the battery lid is fixed by caulking, the metal contacts the upper surface of the lithium ion secondary battery 20. Even so, a short circuit between the positive and negative electrodes can be prevented.

  In conventional lithium ion secondary batteries, in order to prevent metals such as iron used for battery containers from dissolving in non-aqueous electrolyte, the surface of the battery container is plated with nickel that is insoluble in non-aqueous electrolyte. . However, since the battery container is deformed, for example, when the battery lid is caulked and fixed to the battery container, cracks occur in the plating of nickel or the like. Since the metal such as iron in contact with the non-aqueous electrolyte dissolves in the cracked portion, metal ions such as iron are eluted. The eluted metal ions are deposited as a metal on the negative electrode surface as the battery is charged and discharged and grow to form dendrites, causing a short circuit between the positive and negative electrodes through the separator, leading to a decrease in battery voltage. Moreover, in the case of a large-sized lithium ion secondary battery, since it is sold as an assembled battery in which a plurality of lithium ion secondary batteries are connected, insulation treatment is performed after the assembled battery is manufactured. In this case, in the lithium ion secondary battery in which the battery container also serves as the negative electrode external terminal, since the battery container occupies most of the battery surface, the battery lid that also serves as the positive electrode external terminal and the battery container may approach each other. For this reason, there is a possibility that a trouble may occur that an individual non-aqueous electrolyte secondary battery comes into contact with another non-aqueous electrolyte secondary battery, metal, or the like during a battery assembly and short-circuits. The present embodiment is a lithium ion secondary battery that solves these problems.

  In the present embodiment, the coating material for forming the coating 25 is exemplified by blown asphalt of an organic compound that is insoluble in the non-aqueous electrolyte and has flexibility, but the present invention is not limited thereto, What is necessary is just to have flexibility. Examples of the coating material that can be used other than the present embodiment include asphalt such as straight asphalt and olefin resin such as polypropylene. If a material insoluble in the non-aqueous electrolyte is used for the coating material, the effect of preventing the elution of metal ions from the battery container can be maintained for a long period of time. Moreover, if an organic compound is used for the coating material, the coating 25 having flexibility and insolubility with respect to the nonaqueous electrolytic solution can be easily obtained. Furthermore, if the coating material has an insulating property, it is possible to prevent an unexpected (inadvertent) short circuit from occurring due to contact between batteries or contact with metal.

  In the present embodiment, the coating 25 is formed on the inner surface and the outer surface from the upper end of the battery container 7 to the position corresponding to the lower end surface of the electrode group 6 and on the upper end surface of the battery container 7. The invention is not limited to this. It suffices if the coating 25 is formed at least on the inner surface of the portion where the battery cover is fixed by caulking, and by this, it is possible to prevent the dissolution of the metal due to the cracking of the nickel plating at the time of stepping or caulking. If the coating 25 is formed from the upper end of the inner surface of the battery container 7 to the vicinity of the inner bottom surface, dissolution of the metal of the battery container 7 can be prevented even with an external force when the battery is used. Further, if the coating 25 is formed from the upper end of the outer surface of the battery container 7 to the vicinity of the bottom surface, the occurrence of a short circuit due to contact between the batteries can be prevented, and if the film 25 is formed on the upper end surface of the battery container 7, the battery It is possible to prevent the occurrence of a short circuit due to the metal contacting the upper surface.

  Furthermore, in this embodiment, the example which uses the iron which gave nickel plating to the battery container 7 was shown, but this invention is not limited to this, The metal plating which is insoluble in a nonaqueous electrolyte solution is made of metal. The applied battery container can be used. Examples of the base metal of the battery container that can be used other than the present embodiment include carbon steel containing iron and carbon, and special steel containing nickel and chromium. Examples of the metal plating include nickel alloy plating.

  Furthermore, in the present embodiment, the dip coating method in which the inner surface and the outer surface are simultaneously coated with the same coating material by immersing the battery container 7 in the coating material liquid for the formation of the coating film 25 is exemplified. Is not limited to this. For example, a spray method or the like may be used, and any method that can form a coating material on the battery container 7 in a film shape may be used. Further, for example, the inner surface and the outer surface of the battery container 7 may be separately coated with different coating materials.

  Furthermore, in the present embodiment, the cylindrical lithium ion secondary battery 20 is exemplified, but the present invention is not limited to this, and any secondary battery using a non-aqueous electrolyte can be applied. . Moreover, there is no restriction | limiting also about a battery shape, For example, a square shape and a polygon may be sufficient. Furthermore, you may use the electrode group laminated | stacked other than the electrode group 6 by which the positive electrode and the negative electrode were wound through the separator.

  Next, examples of the lithium ion secondary battery 20 manufactured according to the present embodiment will be described. In addition, it describes together about the lithium ion secondary battery of the comparative example produced for the comparison.

Example 1
In Example 1, a battery was fabricated using a battery container 7 made of iron with nickel plating and coated with blown asphalt on the inner and outer surfaces to form a coating 25. The coat was in a range of 100 mm from the upper end of the battery container 7. The lower end of the film 25 is a position corresponding to the lower end surface of the electrode group 6.

(Comparative Example 1)
Comparative Example 1 was the same as Example 1 except that the nickel-plated iron battery container was used as it was without coating. Therefore, the battery of Comparative Example 1 is a conventional lithium ion secondary battery.

(Comparative Example 2)
In Comparative Example 2, a battery was fabricated using a battery container made of nickel-plated iron and coated with silica on the inner and outer surfaces to form a silica coating. The coating range was set to 100 mm from the upper end of the battery container as in Example 1.

(Comparative Example 3)
In Comparative Example 3, a battery was fabricated using a battery container made of nickel-plated iron and coated on the inner and outer surfaces with vegetable oil to form a vegetable oil film. The coating range was set to 100 mm from the upper end of the battery container as in Example 1.

<Test and evaluation>
1. Measurement of iron ion elution amount For each battery of Examples and Comparative Examples, after leaving for one week without charging, a hole was made using a titanium rod in the aluminum part of the battery lid, and the non-aqueous electrolyte was taken out. The iron ion concentration in the non-aqueous electrolyte was measured by ICP (Inductively Coupled Plasma) emission analysis. The iron ion concentration in the non-aqueous electrolyte before pouring into the battery container is 0.1 ppm or less, and since the material containing iron other than the battery container is not used inside the battery, the measured iron ion concentration Corresponds to the amount of iron ions eluted from the battery container. The measurement results of the iron ion concentration are shown in Table 1 below.

  As shown in Table 1, in the lithium ion secondary battery of Comparative Example 1 using an uncoated battery container, the nickel plating covered the entire surface inside and outside the battery container, but the nickel plating metal was used. Some iron is dissolved and iron ions are eluted. When the battery was disassembled and investigated, a portion where the battery cover was fixed by crimping (hereinafter referred to as a crimping fixing portion) and a portion of the nickel plating near the portion were cracked. For this reason, it is considered that the non-aqueous electrolyte contacted the iron of the metal at the part where the nickel plating was broken, and the iron ions were eluted. Further, in the lithium ion secondary battery of Comparative Example 2 using the battery container on which the silica coating is formed, the elution of iron ions is slightly suppressed as compared with Comparative Example 1, but the silica coating prevents the elution of iron ions. No significant effect was confirmed. When the battery was disassembled and investigated, a part of the silica coating was cracked along with the nickel plating in the vicinity of the caulking fixing portion. From this fact, it is considered that the elution of iron ions cannot be prevented because the silica coating is broken even when coated with silica having poor flexibility. Further, in the lithium ion secondary battery of Comparative Example 3 using the battery container in which the vegetable oil film is formed, the elution of iron ions is slightly suppressed as compared with Comparative Example 1, but the vegetable oil film prevents the elution of iron ions. No significant effect was confirmed. When the battery was disassembled, there was no vegetable oil film on the inner surface of the battery container. From this, even if it coats with vegetable oil which is easily soluble in nonaqueous electrolyte, since vegetable oil will dissolve in nonaqueous electrolyte, it is thought that iron ion eluted from the part which nickel plating broke.

  For these comparative examples, elution of iron ions was not confirmed in the lithium ion secondary battery 20 of Example 1 using the battery container 7 coated with blown asphalt and formed with the coating 25. Even if nickel plating is cracked due to deformation of the battery container 7 during stepping or caulking, the blown asphalt coating 25 is insoluble in non-aqueous electrolyte and flexible on the nickel plating (inner surface). This is considered to be because the contact between the non-aqueous electrolyte and the base metal of the battery container 7 was prevented.

2. Measurement of battery voltage drop amount For each of the 10 batteries of the examples and comparative examples, the nonaqueous electrolyte was poured and sealed, left for 1 week, and then charged to 4.1 V with a current of 0.3 C → 1 C The battery was discharged to 2.7 V at a current of 1 to 3.7 V with a current of 1 C. Then, it was left at a temperature of 22.5 ° C., and the 14th day voltage and the 21st day voltage were measured. The voltage drop amount was calculated by subtracting the 21st day voltage from the measured 14th day voltage, and the average value of 10 batteries was calculated. The measurement results of the voltage drop amount are shown in Table 2 below.

  As shown in Tables 1 and 2, it was found that the voltage drop amount was larger for the battery with a larger amount of iron ion elution. After the measurement of the voltage drop amount was completed, the battery was disassembled, and the separator was taken out and observed. As a result, the battery with a larger iron ion elution amount was discolored black. As a result of the compositional analysis of the black-colored portion, iron element was observed. From this, it is considered that the difference in the amount of voltage drop was caused by the difference (number of occurrences) of the short circuit caused by the formation (growth) of dendrite. Therefore, by coating the inner and outer surfaces of the nickel-plated iron battery container with blown asphalt from the upper end to the position corresponding to the lower end surface of the electrode group 6, it is possible to reduce micro short-circuits and suppress a decrease in battery voltage. found.

3. Battery short circuit test For each battery of the example and the comparative example, the positive terminal (battery cover) of the battery and the battery container part adjacent to the gasket are brought into contact with a copper plate having an electric resistance of 1 mΩ or less, and a short circuit occurs. I investigated. The battery voltage was 3.7 V, and the short circuit was performed by pressing strongly against the copper plate. The results of the short circuit test are shown in Table 3 below.

  As shown in Table 3, the lithium ion secondary battery of Comparative Example 1 was severely short-circuited by bringing the battery lid and battery container into contact with the copper plate. When the copper plate was removed and the short-circuited portion was observed, short-circuit traces remained. On the other hand, in the lithium ion secondary battery 20 of Example 1 and the lithium ion secondary batteries of Comparative Examples 2 and 3, no short circuit occurred. This is because the surface of the nickel-plated battery container is coated with an insulating coating material (there is a film), so that the battery container and the battery lid are not in direct contact and are electrically insulated. Conceivable. Therefore, when the battery lid is crimped and fixed, an insulating film is formed on the battery container portion assumed to be located near the positive terminal, and the battery lid is crimped and fixed to the battery container to prevent a short circuit. Turned out to be possible.

  The present invention provides a non-aqueous electrolyte secondary battery that can suppress a decrease in battery voltage due to dissolution of a metal battery container, and therefore contributes to the manufacture and sale of non-aqueous electrolyte secondary batteries. With the availability of

It is sectional drawing which shows the cylindrical lithium ion secondary battery of embodiment to which this invention is applied. It is sectional drawing which shows the battery container which coated the coating material which has flexibility. It is sectional drawing which shows the battery container which formed the step part after coating the coating material which has flexibility, and inserting the electrode group.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 Negative electrode lead piece 5 Negative electrode current collection ring 6 Electrode group 7 Battery container 20 Cylindrical lithium ion secondary battery 25 Coating 28 Stepped part

Claims (7)

In a non-aqueous electrolyte secondary battery in which a battery lid is caulked and fixed on one side of a battery container that is made of metal and is coated with a metal plating that is insoluble in the non-aqueous electrolyte, the battery container is connected to an electrode. It has a negative polarity, and at least the battery cover is non-aqueous electrolyte secondary battery, wherein a coating material covering the metal plating on the inner surface of the caulking portion is distribution. The battery container, a non-aqueous electrolyte secondary battery according to claim 1, wherein the coating material is distribution on the inner surface to the inner bottom surface near from the one end.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the coating material is insoluble in the non-aqueous electrolyte.   The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the coating material is an organic compound.   The non-aqueous electrolyte secondary battery according to claim 4, wherein the organic compound is asphalt.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the coating material has an insulating property. The battery container, a non-aqueous electrolyte secondary battery according to claim 6, characterized in that it is further said coating material distribution on the outer surface and the end surface of the one side from the one side end to the vicinity of the bottom surface.

Images