JP2012190756A - Sealed battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a constitution where a battery case can be prevented from being corroded even when an exterior cover made of polyethylene terephthalate is used, in a sealed battery including a metal battery case which houses an electrode body therein and is installed under a highly corrosive environment.SOLUTION: A sealed battery (1) includes: a metal battery case (1a) housing an electrode body (30) therein; and an exterior cover (40) covering the outside surface of the battery case (1a) and made of polyethylene terephthalate. A protective layer (60) for preventing the battery case (1a) from being corroded is formed on the outside surface of the exterior cover (40) and the outside surface of the battery case (1a) which is not covered with the exterior cover (40).

Description

  The present invention relates to a sealed battery installed in an environment in which a battery case that houses an electrode body is susceptible to corrosion.

  Conventionally, a sealed battery installed in an environment in which a battery case that houses an electrode body is easily corroded is known. In such a sealed battery, as disclosed in Patent Document 1, for example, an electrode body is enclosed in a battery case made of metal such as iron or stainless steel.

JP 2008-192524 A

  By the way, when the battery case is made of metal as in Patent Document 1 described above, the outer surface of the battery case is generally made of a resin such as polyethylene terephthalate so as not to get an electric shock when the user contacts the battery case. Covered with an exterior cover.

  On the other hand, when the battery case is made of metal as in Patent Document 1 described above, corrosion is likely to occur in the battery case in an environment such as outdoors where condensation is likely to occur. Therefore, in such an environment, even when the outer surface of the battery case is covered with an outer cover made of polyethylene terephthalate, moisture passes through the outer cover, or moisture passes through the gap between the outer cover and the battery case. May invade and corrode the battery case.

  In the present invention, in a sealed battery installed in an environment where the metal battery case that houses the electrode body is susceptible to corrosion, the battery case can be prevented from corroding even when an exterior cover made of polyethylene terephthalate is used. There is to get.

  A sealed battery according to an embodiment of the present invention includes a metal battery case in which an electrode body is housed, and an outer cover made of polyethylene terephthalate that covers an outer surface of the battery case. A protective layer for preventing corrosion of the battery case is formed on the outer surface and on the outer surface of the battery case that is not covered by the exterior cover (first configuration).

  With this configuration, even when the outer surface of the metal battery case is covered with an outer cover made of polyethylene terephthalate, corrosion of the outer surface of the battery case can be prevented. In other words, polyethylene terephthalate has higher moisture permeability than other resin materials such as polyvinyl chloride, but as described above, by covering the outer cover made of polyethylene terephthalate with a protective layer, it can reach the outer surface of the battery case. Can prevent moisture from reaching.

  In addition, since polyethylene terephthalate is less susceptible to thermal shrinkage than other resin materials and is not easily deformed along the battery case, a gap is likely to occur between the outer cover made of polyethylene terephthalate and the battery case. On the other hand, since the gap between the battery case and the outer cover can be covered with the protective layer by forming the protective layer on the outer surfaces of the battery case and the outer cover as in the above-described configuration, the gap Can prevent moisture from entering. Therefore, with the above-described configuration, even when a polyethylene terephthalate exterior cover is used, corrosion can be prevented from occurring on the outer surface of the battery case.

  In the first configuration, the protective layer is made of a polyolefin resin (second configuration). Thereby, since the polyolefin resin has a small change with time and less deterioration due to heat compared to the polyurethane resin, the outer surface of the battery case can be more reliably protected. In addition, since the polyolefin resin has a lower viscosity than the polyurethane resin, the surface of the battery having small gaps and irregularities can be covered more reliably. Furthermore, since the solvent used in the case of polyolefin resin is a low polarity solvent such as methylcyclohexane, the resin outer cover disposed on the outer periphery of the battery case is dissolved, or characters printed on the outer cover are removed. It will not be erased.

  In the first or second configuration, the battery case further includes a lead terminal attached to and fixed to one end side of the battery case, and the protective layer is also formed on one end side of the lead terminal (third configuration). ).

  Thereby, it becomes possible to take out electric power from a battery via a lead-out terminal. In addition, since a protective layer is formed on one end side of the lead terminal that is attached and fixed to the battery case, it is possible to prevent corrosion from occurring at the attachment portion with the battery case. In addition, since the protective layer is formed only on one end side of the lead terminal attached and fixed to the battery case, the other end side of the lead terminal can be electrically connected to a terminal of the device.

  In any one of the first to third configurations, an insulating member for electrically insulating the battery case and the lead terminal is disposed on the battery case, and the insulation The member is fixed on the battery case by partially covering the member with the exterior cover (fourth configuration).

  By doing so, the battery case and the lead terminal can be electrically insulated by the insulating member. Here, since the insulating member is fixed on the battery case by being partly covered by the outer cover, between the battery case and the insulating member, between the insulating member and the outer cover, A gap is likely to occur. Also in such a configuration, by forming the protective layer as in the first configuration described above, the gap can be filled with the protective layer, and moisture can be prevented from entering through the gap. Therefore, corrosion can be prevented from occurring on the outer surface of the battery case even with the above-described configuration.

  In any one of the first to fourth configurations, the battery case is formed in a substantially columnar shape extending in the axial direction, and the lead terminal intersects the axis of the battery case. It is attached and fixed to the battery case so as to extend in the direction (fifth configuration).

  Thereby, when forming a protective layer on the outer surface of a battery case and an exterior cover, it becomes possible to dip a battery case in the liquid which comprises this protective layer, hold | gripping a lead terminal. Therefore, the protective layer can be easily and more reliably formed on the outer surfaces of the battery case and the outer cover.

  According to the sealed battery according to the embodiment of the present invention, the outer surface of the battery case is covered with the outer cover made of polyethylene terephthalate, and the protective layer is formed on the battery case and the outer cover. Thereby, even when a polyethylene terephthalate exterior cover is used, corrosion can be prevented from occurring on the outer surface of the battery case.

FIG. 1 is a cross-sectional view showing a schematic configuration of a sealed battery according to an embodiment of the present invention. FIG. 2 is a perspective view showing an outline of the appearance of the sealed battery. FIG. 3 is a diagram schematically showing a state in which the sealed battery is immersed in the mixed liquid in the container.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The same or corresponding parts in the drawings are denoted by the same reference numerals and description thereof will not be repeated.

(overall structure)
FIG. 1 is a diagram showing a schematic configuration of a sealed battery 1 according to an embodiment of the present invention. The sealed battery 1 has a sealing body 20 attached to the opening side of a bottomed cylindrical outer can 10 in which an electrode body 30 is housed. That is, the sealed battery 1 includes an outer can 10, a sealing body 20, and an electrode body 30 housed in a space formed by the outer can 10 and the sealing body 20. The outer can 10 and the sealing body 20 constitute a substantially cylindrical battery case 1a extending in the axial direction. In addition to the electrode body 30, a non-aqueous electrolyte (not shown) is also enclosed in the space formed in the battery case 1a.

  The outer can 10 is an iron member formed into a bottomed cylindrical shape by press molding. That is, the outer can 10 is formed by integrally forming a circular bottom portion 11 and a cylindrical peripheral wall portion 12. An outermost peripheral portion of an electrode body 30 described later is in contact with the peripheral wall portion 12 of the outer can 10 over the entire circumferential direction of the inner peripheral surface of the peripheral wall portion 12. As will be described in detail later, since the negative electrode is located on the outermost peripheral portion of the electrode body 30, the outer can 10 has the potential of the negative electrode.

  The lead terminal 2 is fixed to the bottom 11 of the outer can 10 by welding. The lead terminal 2 is a flat plate member made of a metal material such as stainless steel, and includes a terminal body 2a connected and fixed to the bottom 11 of the outer can 10 and a connection 2b connected to an external wiring or the like. ing. That is, the lead terminal 2 is attached to the substantially cylindrical battery case 1a extending in the axial direction so as to extend in a direction intersecting with the axial line.

  The connection portion 2b of the lead terminal 2 is formed so that the width thereof is smaller than the width of the terminal body portion 2a (see FIG. 2). As shown in FIG. 1, the terminal body 2 a is formed so that the connection portion with the bottom 11 of the outer can 10 bulges in the thickness direction of the lead terminal 2 and toward the bottom 11 of the outer can 10. .

  The sealing body 20 includes a cover plate 21 fixed to the opening end of the peripheral wall portion 12 of the outer can 10, and an insulating packing 24 made of rubber in an opening provided in the center portion of the cover plate 21 in a plan view. And an insulator 23 disposed on the battery inner side of the terminal 22. The insulator 23 is formed in a bottomed cylindrical shape, and a gas vent 23a is provided at the center of the bottom. The cover plate 21 is fixed to the opening end portion of the peripheral wall portion 12 of the outer can 10 by laser welding or the like while being supported by the opening end portion of the insulator 23. The lid plate 21 is fixed to the peripheral wall portion 12 of the outer can 10 so as to form a step with respect to the opening end of the outer can 10. As will be described later, an insulating plate 25 is disposed in the space created by this step.

  The terminal 22 has a shaft portion 22a and flange portions 22b and 22c located at both ends thereof. The terminal 22 is engaged with the opening peripheral edge portion of the lid plate 21 by these flange portions 22b and 22c. The flange portion 22c located on the battery inner side of the terminal 22 is formed by crushing and flattening the tip portion of the shaft portion 22a. That is, the terminal 22 is formed by crushing the tip end portion of the shaft portion 22a in a state where the insulating packing 24 is disposed on the opening peripheral portion of the cover plate 21 and the shaft portion 22a is inserted into the opening of the cover plate. The cover plate 21 is engaged with the peripheral edge of the opening. As a result, the insulating packing 24 is sandwiched between the shaft portion 22 a of the terminal 22 and the lid plate 21. Therefore, the insulating packing 24 electrically insulates the terminal 22 and the cover plate 21 and seals between the terminal 22 and the cover plate 21.

  As with the bottom portion 11 of the outer can 10, the lead terminal 3 connected to an external wiring or the like is fixed to the flange portion 22b on the battery outer side of the terminal 22 by welding. The lead terminal 3 is a flat plate member made of metal such as stainless steel, and includes a terminal main body portion 3a connected to the terminal 22 of the sealed battery 1 and a connection portion 3b connected to an external wiring or the like. Yes. That is, the lead terminal 3 is also attached to the substantially cylindrical battery case 1a extending in the axial direction so as to extend in a direction intersecting with the axial line.

  Similar to the connection portion 2b of the lead terminal 2, the connection portion 3b of the lead terminal 3 is formed to have a width smaller than the width of the terminal main body portion 3a. Similarly to the terminal main body 2 a of the above-described lead terminal 2, the terminal main body 3 a of the lead terminal 3 has a connection portion with the terminal 22 of the sealed battery 1 on the terminal 22 side in the thickness direction of the lead terminal 3. It is formed to bulge.

  An insulating plate 25 (insulating member) formed in a substantially donut shape is disposed on the lid plate 21. The insulating plate 25 is disposed on the lid plate 21 so as to fill a step formed between the open end of the outer can 10 and the lid plate 21. That is, the insulating plate 25 has a thickness equivalent to the height of the step formed between the open end of the outer can 10 and the lid plate 21. For example, the insulating plate 25 has a thickness of 0.3 mm.

  By disposing the insulating plate 25 as described above on the lid plate 21, the lid plate 21, the terminal 22, and the lead terminal 3 can be electrically insulated by the insulating plate 25. That is, in this embodiment, the cover plate 21 is connected to the outer can 10 and the outer can 10 has a negative potential as described later. Therefore, the cover plate 21 has a negative potential. On the other hand, since the terminal 22 and the lead-out terminal 3 are electrically connected to the positive electrode 31 via the positive electrode lead 15 as described later, they have a positive electrode potential. The lid plate 21, the terminal 22 and the lead terminal 3 having different potentials can be electrically insulated by the insulating plate 25 described above.

  Moreover, the outer peripheral side part of the insulating plate 25 is covered with the exterior cover 40 mentioned later. Thereby, a part of the insulating plate 25 is sandwiched between the outer cover 40 and the lid plate 21 and fixed on the lid plate 21.

  Although not particularly illustrated, a vent that is cleaved when the internal pressure of the sealed battery 1 rises is provided on either the cover plate 21 of the sealing body 20 or the bottom 11 of the outer can 10. The vent is formed to be thin so as to be cleaved when the internal pressure of the sealed battery 1 rises, and is configured to discharge the gas in the sealed battery 1 to the outside by being cleaved.

  Although not particularly shown, the electrode body 30 is a spirally wound sheet in which a sheet-like positive electrode 31 and a negative electrode 36 are stacked in a thickness direction with a separator 35 interposed therebetween. In the electrode body 30, the positive electrode 31 has a positive electrode active material, and the negative electrode 36 has a negative electrode active material.

  The positive electrode 31 includes a strip-shaped positive electrode current collector 32 and two strip-shaped positive electrode sheets 33 which are provided so as to sandwich the positive electrode current collector 32 and have the same thickness dimension. The positive electrode sheet 33 constitutes a positive electrode active material layer. For example, a positive electrode mixture formed by adding a conductive additive or a binder to the positive electrode active material and adding water or the like as necessary is rolled with a roll or the like. It is obtained by drying and grinding this, rolling it again and forming it into a sheet. Examples of the positive electrode active material include manganese dioxide, carbon fluoride, lithium cobalt composite oxide, spinel type lithium composite oxide, and the like. Moreover, as a conductive support agent, the 1 type, or 2 or more types of composite selected from graphite, carbon black, acetylene black, ketjen black, etc. can be mentioned. Further, as the binder, polytetrafluoroethylene (PTFE) or a rubber-based binder can be used. As the positive electrode current collector 32, a plain woven wire mesh made of stainless steel, expanded metal, lath steel, punching metal, metal foil, or the like can be used.

  The positive electrode sheet 33 is formed such that the width dimension (longitudinal direction of the sealed battery 1 in FIG. 1) is larger than the width dimension of the positive electrode current collector 32. As shown in FIG. 1, the positive electrode 31 of the electrode body 30 and the lower surface of the terminal 22 are connected by a positive electrode lead 15. As a result, the terminal 22 and the lead terminal 3 fixed to the terminal 22 by welding have a positive potential.

  The negative electrode 36 includes a strip-shaped negative electrode current collector 37 and two strip-shaped negative electrode sheets 38 which are provided so as to sandwich the negative electrode current collector 37 and have the same thickness dimension. The negative electrode sheet 38 is formed by forming metallic lithium into a sheet shape. As the negative electrode current collector 37, a metal foil made of copper, nickel, iron, stainless steel, or the like can be used.

  The negative electrode current collector 37 is formed such that the width dimension (longitudinal direction of the sealed battery 1 in FIG. 1) is larger than the width dimension of the negative electrode sheet 38.

  As shown in FIG. 1, the electrode body 30 is wound with the positive electrode 31 and the negative electrode 36 overlapped so that the negative electrode current collector 37 of the negative electrode 36 is exposed to the outside. As a result, the peripheral wall portion 12 of the outer can 10 in contact with the outermost peripheral surface of the electrode body 30 is electrically connected to the negative electrode current collector 37 of the negative electrode 36 to become a negative electrode. Therefore, the lead-out terminal 2 welded and fixed to the bottom 11 of the outer can 10 has a negative potential.

  In the electrode body 30, a separator 35 is disposed between both end portions in the axial direction and between the positive electrode 31 and the negative electrode 36. Although detailed description is omitted, the separator 35 is configured by overlapping a nonwoven fabric and a microporous film.

(Protective layer)
In the sealed battery 1 having the above-described configuration, an exterior cover 40 made of polyethylene terephthalate (PET) is attached on the outer surface of the battery case 1a as shown in FIGS. Characters 41 such as a model number of the sealed battery 1 are printed on the exterior cover 40. The exterior cover 40 is not provided in the vicinity of the center portion where the extraction terminal 2 is attached at the bottom 11 of the exterior can 10 and the terminal 22 where the extraction terminal 3 of the sealing body 20 is attached. That is, the bottom portion 11 and the sealing body 20 of the outer can 10 are in a state where the central portions are exposed.

  Here, the attachment of the exterior cover 40 onto the outer surface of the battery case 1a is performed using the thermal shrinkage of polyethylene terephthalate. Specifically, a cylindrical member made of polyethylene terephthalate is placed on the battery case 1a, and heat is applied in this state to thermally contract the cylindrical member, thereby closely attaching the outer cover 40 to the outer surface of the battery case 1a. .

  A protective layer 60 is formed on the outer surface of the outer cover 40 to protect the sealed battery 1 from moisture generated by condensation or the like. That is, the protective layer 60 is formed on the outer cover 40 provided on the peripheral wall portion 12 of the outer can 10 as shown by a thick line on the outer surface of the sealed battery 1 in FIG. It is formed so as to cover the bottom 11 of the can 10, the outer surface of the sealing body 20, and part of the attachment terminals 2 and 3. Specifically, the protective layer 60 is formed on the entire outer surface of the sealed battery 1 except for the tip portions of the connection portions 2 b and 3 b of the attachment terminals 2 and 3. Since the tip portions of the connection portions 2b and 3b of the attachment terminals 2 and 3 are connected to external wiring or the like, the protective layer 60 is not formed on the tip portions.

  The protective layer 60 is configured using a polyolefin-based elastomer. Specifically, for example, the protective layer 60 is configured using a thermoplastic elastomer in which EPDM (ethylene-propylene-diene rubber) or EPM (ethylene-propylene rubber) is finely dispersed in polypropylene. The protective layer 60 may be a resin other than the above-described resin as long as it is a polyolefin-based resin.

  Thus, by using a polyolefin-type elastomer for the protective layer 60, as described later, a low polarity solvent such as methylcyclohexane or ethylcyclohexane can be used. As a result, since a highly polar solvent such as rutile acetate is not used, the outer cover 40 made of polyethylene terephthalate covering the outer surface of the battery case 1a is melted or the character 41 printed on the outer cover 40 disappears. Can be prevented.

  Further, since the use of a polyolefin-based elastomer for the protective layer 60 makes it difficult for moisture to permeate compared to the case where a urethane-based resin is used, even if the exterior cover 40 is configured with polyethylene terephthalate as in this embodiment, the battery Corrosion of the case 1a can be suppressed. That is, the polyethylene terephthalate used in the present embodiment has higher moisture permeability than other resins such as polyvinyl chloride (PVC), but by forming the protective layer 60 with a polyolefin-based elastomer as described above, Permeation can be suppressed and corrosion of the battery case 1a can be prevented.

  Further, by using a polyolefin-based elastomer for the protective layer 60, the flexibility in a liquid state before curing is higher than that of a urethane-based resin, so that the protective layer 60 can easily enter a gap or the like. Therefore, even when the exterior cover 40 is made of polyethylene terephthalate that hardly heat shrinks and hardly deforms as in the present embodiment, when the protective layer 60 is formed, the polyolefin-based elastomer enters the gaps, so that moisture can enter. It can be prevented more reliably. Therefore, by using the polyolefin-based elastomer for the protective layer 60, it is possible to make the battery case 1a less susceptible to corrosion.

  Further, the protective layer 60 includes a fluorescent paint 61 (determination paint) for confirming whether the protective layer 60 is formed on the outer surface of the sealed battery 1. For the fluorescent paint 61, for example, a material containing barium or strontium as a fluorescent pigment is used. The fluorescent paint 61 is transparent, but emits light when irradiated with ultraviolet rays having a predetermined wavelength (wavelength 380 nm to 450 nm).

  By using the fluorescent paint 61 made of the material as described above, the fluorescent paint 61 does not emit light when not irradiated with ultraviolet rays, and the protective layer 60 is transparent. Thereby, it can prevent that the character 41 printed on the exterior cover 40 of the sealed battery 1 becomes difficult to be visually recognized by the fluorescent paint 61 of the protective layer 60.

  Then, by including the fluorescent paint 61 in the protective layer 60, it is possible to confirm whether the protective layer 60 is formed on the outer surface of the sealed battery 1. That is, by confirming the light emission of the fluorescent paint 61, it can be easily confirmed whether or not the protective layer 60 is formed on the entire outer surface of the sealed battery 1. In particular, the protective layer 60 is formed on the portion of the sealed battery 1 where the metal is exposed (the lead terminals 2 and 3, the sealing body 20 of the sealed battery 1, and the bottom 11 of the outer can 10) with the above-described configuration. Therefore, it is possible to more reliably prevent the portion from being corroded by moisture or the like.

  Next, a method for forming the protective layer 60 will be described.

  First, a solvent such as methylcyclohexane or ethylcyclohexane is mixed with the above-described polyolefin-based elastomer, and the fluorescent paint 61 is also mixed. At this time, the polyolefin-based elastomer is mixed with the solvent so that the weight ratio is about 50%. In the present embodiment, a solvent obtained by mixing ethylcyclohexane with methylcyclohexane is used as the solvent. However, the present invention is not limited to this, and 100% methylcyclohexane may be used as a solvent.

  Then, as shown in FIG. 3, the sealed battery 1 in which only the tip portions of the connecting portions 2b and 3b of the lead terminals 2 and 3 are masked is formed as described above while holding the tip portion. It is immersed in the liquid mixture 62. Thereby, the liquid mixture 62 is adhered on the outer surface of the sealed battery 1. Thus, by masking the tip portions of the connecting portions 2b and 3b of the lead terminals 2 and 3, it is possible to more reliably prevent the protective layer from being formed on the tip portion connected to an external wiring or the like. In FIG. 3, reference numeral 45 denotes a mask portion covering the tip portions of the connecting portions 2b and 3b of the lead terminals 2 and 3, reference numeral 62 denotes the above-mentioned mixed liquid, and reference numeral 63 denotes a container.

  In the present embodiment, a mask portion 45 is provided at the tip of the connecting portions 2b and 3b of the lead terminals 2 and 3. However, the present invention is not limited thereto, and the mask portion 45 may not be provided, and the tip portion may not be immersed in the liquid mixture 62 while the tip portion is gripped.

  Thereafter, the above-mentioned protective layer 60 is formed by drying the liquid mixture 62 adhering to the outer peripheral surface of the sealed battery 1 for a predetermined time (for example, about 3 hours at room temperature) and evaporating the solvent in the liquid mixture 62. To do. Thus, the protective layer 60 can be uniformly formed on the outer surface of the sealed battery 1 by immersing the sealed battery 1 in the mixed liquid 62.

  At this time, the thickness of the protective layer 60 is greatly influenced by the viscosity of the mixed liquid 62. That is, if the viscosity of the liquid mixture 62 is large, the liquid mixture 62 adhering to the outer surface of the sealed battery 1 increases, and the thickness of the protective layer 60 formed on the outer surface of the sealed battery 1 correspondingly increases. Also grows. The viscosity of the mixed liquid 62 is determined by the mixing ratio of the polyolefin-based elastomer to the solvent (weight ratio of the elastomer to the solvent).

  Inventors conducted the following tests in order to investigate the influence of the mixing ratio of the liquid mixture 62 adhered to the outer surface of the sealed battery 1. In the following description, the film thickness of the protective layer 60 formed on the outer surface of the sealed battery 1 is calculated based on the weight change of the sealed battery 1. Specifically, the film thickness of the protective layer 60 is calculated from the measurement result of the weight change before and after the formation of the protective layer 60 in the sealed battery 1 using the surface area of the sealed battery 1 and the specific gravity of the resin.

  First, the inventors made two types (10%, 25%) of mixed liquids with different mixing ratios, immersed the sealed battery 1 in each mixed liquid, and then dried the two types of mixed liquids. A sealed battery was manufactured. In addition, when the protective layer formed on the outer surface of the sealed battery is calculated from the weight difference of the sealed battery before and after application of the mixed liquid (before application and 22 hours after application), the mixture ratio is 10%. When the film thickness was less than 1 μm and the mixing ratio was 25%, the film thickness was about 5 μm.

Each sealed battery produced as described above was soaked in water to check whether rust was generated. The test results are shown in Table 1.

  As can be seen from Table 1, in a sealed battery in which a protective layer was formed using a mixed solution having a mixing ratio of 10%, rust was generated in about one week. On the other hand, in a sealed battery in which a protective layer was formed using a mixed solution having a mixing ratio of 25%, rust did not occur even when immersed in water for about one week. Therefore, the mixing ratio of the mixed solution is preferably 20% or more, and more preferably 25% or more from the viewpoint of the film thickness of the protective layer and moldability. Note that, even if the viscosity of the mixed solution is too high, the mixed solution is only unnecessarily deposited on the outer surface of the sealed battery. Therefore, the mixing ratio of the mixed solution is preferably 100% or less.

  Moreover, as a film thickness of a protective layer, 1 micrometer or more is preferable from the above-mentioned result. In order to more reliably form the protective layer on the outer surface of the sealed battery, it is more preferable to set the film thickness to 5 μm or more. On the other hand, the thickness of the protective layer is preferably 30 μm or less because it is meaningless even if it is excessively thick.

Next, in order to confirm the difference in effect due to the difference in the thickness of the protective layer, a sealed battery having a protective layer with a thickness of 20 μm and a sealed battery having a protective layer with a thickness of 10 μm were manufactured. . These batteries were soaked in water, and the presence or absence of rust generation and a decrease in OCV (Open Circuit Voltage) were confirmed. Table 2 shows the results. The rated voltage of the sealed battery is 3V for all. Further, the protective layer having a thickness of 10 μm was formed using a mixed solution having a half concentration compared to the mixed solution used when forming the protective layer having a thickness of 20 μm.

  As can be seen from Table 2, rust was generated after 45 days regardless of the thickness of the protective layer. However, when the film thickness is 10 μm, the decrease in OCV is 32 mV, whereas when the film thickness is 20 μm, the decrease in OCV is 3 mV. From this, the one where the film thickness of a protective layer is large has high environmental resistance, and can suppress the performance fall of a sealed battery more.

Moreover, in order to confirm the effect of a protective layer, the sealed type battery of the stainless steel outer can in which the protective layer was not formed was also manufactured. A sealed battery of this stainless steel outer can (Comparative Example 1) and a sealed battery of this embodiment (Example 1) in which a protective layer having a film thickness of 5 μm was formed using a mixed solution having a mixing ratio of 25%. Each was soaked in water to confirm the occurrence of rust and the decrease in OCV. Table 3 shows the results. The sealed battery of the stainless steel outer can is in a state where the outer cover is not formed on the outer surface and the outer can is exposed on the surface.

  As can be seen from Table 3, in the sealed battery of the stainless steel outer can (Comparative Example 1), rust was generated in about 2 weeks, and the decrease in OCV was 39 mV. On the other hand, in the sealed battery (Example 1) of the present embodiment in which the protective layer was formed, rust was generated in about 2 weeks, but the decrease in OCV was 5 mV. As can be seen from these results, the sealed battery (Example 1) of this embodiment in which the protective layer is formed has higher environmental resistance than the stainless steel outer can. The rated voltage of the sealed battery is 3V for all.

Furthermore, in order to confirm the effect of the protective layer 60 in the exterior cover 40 made of polyethylene terephthalate (PET), a sealed battery in which the protective layer 60 was not formed was also manufactured. For reference, a sealed battery having an outer cover made of polyvinyl chloride (PVC) and having no protective layer was also manufactured. These sealed batteries were placed in a furnace having a temperature of 85 ° C. and a humidity of 90%, and the presence or absence of rust was visually confirmed. Table 4 shows the results. In Example 2 in Table 4, the thickness of the protective layer was about 10 μm. The thickness of the outer cover made of polyethylene terephthalate (PET) is 0.08 mm, and the thickness of the outer cover made of polyvinyl chloride (PVC) is 0.04 mm.

  As can be seen from Table 4, in a sealed battery (Comparative Example 2) having an outer cover made of polyethylene terephthalate (PET) in which a protective layer is not formed, rust has already occurred in 5 days, In the sealed battery (Example 2) in which the protective layer was formed, rust did not occur even after 20 days. Further, in the sealed battery (Comparative Example 3) having an outer cover made of polyvinyl chloride (PVC), rust is not generated until 10 days have passed. From this, it can be seen that the outer cover made of polyethylene terephthalate (PET) is more permeable to moisture than the outer cover made of polyvinyl chloride (PVC), and rust is likely to occur in the battery case 1a. From the above results, it can be seen that corrosion of the battery case 1a can be effectively prevented by providing a protective layer as in this embodiment on an exterior cover made of polyethylene terephthalate (PET) that easily allows moisture to permeate.

(Effect of embodiment)
With the above configuration, the outer cover 40 made of polyethylene terephthalate is provided on the outer surface of the battery case 1a, and the sealed battery 1 is protected from moisture generated by condensation on the surfaces of the battery case 1a and the outer cover 40. The protective layer 60 was provided. Thereby, it can suppress that the sealed battery 1 corrodes by dew condensation. That is, even when the exterior cover 40 is made of polyethylene terephthalate that easily permeates moisture, the battery case 1a can be prevented from corroding by providing the protective layer 60. In addition, since polyethylene terephthalate is a material that is relatively resistant to heat shrinkage and is difficult to deform, if the exterior cover 40 is made of polyethylene terephthalate, a gap is likely to be generated between the exterior cover 40 and the battery case 1a. On the other hand, by providing the protective layer 60 as described above, the gap formed between the outer cover 40 and the battery case 1a can be closed by the protective layer 60, and corrosion of the battery case 1a can be prevented. Generation can be effectively prevented.

  Moreover, even when the above-described protective layer 60 is made of a polyolefin elastomer having low moisture permeability and high flexibility, even when the exterior cover 40 made of polyethylene terephthalate is used as described above, moisture can reach the surface of the battery case 1a. Intrusion can be effectively prevented. Thereby, even when the exterior cover 40 made of polyethylene terephthalate is used, corrosion of the sealed battery 1 can be prevented.

  Furthermore, by forming the protective layer 60 from a polyolefin-based elastomer, a low polarity solvent such as methylcyclohexane or ethylcyclohexane can be used. Thereby, it can prevent that the resin-made exterior cover 40 which covers the side surface of the sealed battery 1 is melt | dissolved with a solvent, or the character 41 printed on this exterior cover 40 disappears.

  Further, by attaching the lead terminals 2 and 3 to the substantially cylindrical battery case 1a extending in the axial direction as a whole so as to extend in the direction intersecting the axis, the battery terminals 1 and 3 are sealed in a gripped state. The battery 1 can be immersed in the liquid mixture 62. Thereby, the protective layer 60 can be formed on the entire surface of the sealed battery 1. In addition, since the protective layer 60 can be formed at the connection portion between the lead terminals 2 and 3 and the bottom 11 and the terminal 22 of the outer can 11, corrosion of the sealed battery 1 can be more reliably prevented.

  Further, the insulating plate 25 is disposed on the cover plate 21 and the outer peripheral side thereof is covered with the exterior cover 40, so that the end portion of the cylindrical sealed battery 1 is formed in comparison with the case where the insulating portion is integrally formed on the cover plate. Thus, the configuration can be simplified and made compact. Moreover, in the configuration in which the insulating plate 25 is fixed on the lid plate 21 by the exterior cover 40 as described above, gaps are generated between the insulating plate 25 and the lid plate 21 and between the insulating plate 25 and the exterior cover 40, respectively. However, by providing the protective layer 60 described above, the gap between them can be filled. Thereby, it can prevent that corrosion arises in the battery case 1a also in such a structure.

  Moreover, it is possible to easily detect whether or not the protective layer 60 is formed on the entire outer surface of the sealed battery 1 by putting the fluorescent paint 61 in the protective layer 60. Thereby, the battery case 1a can be more reliably protected by the protective layer 60.

  Therefore, even if the outer can 10 of the sealed battery 1 is made of iron instead of stainless steel, corrosion of the outer can 10 can be suppressed. Therefore, the manufacturing cost of the sealed battery 1 can be reduced.

  The fluorescent paint 61 contained in the protective layer 60 is colorless and transparent, and emits light when irradiated with ultraviolet rays. As described above, by using the transparent fluorescent paint 61 when ultraviolet rays are not irradiated, it is possible to prevent the characters 41 and the like printed on the exterior cover 40 on the side surface of the sealed battery 1 from being easily recognized.

(Other embodiments)
While the embodiments of the present invention have been described above, the above-described embodiments are merely examples for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and can be implemented by appropriately modifying the above-described embodiment without departing from the spirit thereof.

  In the embodiment, the protective layer 60 is formed on the outer surface of the sealed battery 1 provided with the lead terminals 2 and 3 at both ends. However, a protective layer may be formed on the outer surface of a battery having another configuration such as a battery in which the lead terminals 2 and 3 are not provided.

  In the embodiment, the protective layer 60 includes the fluorescent paint 61 that emits light when irradiated with ultraviolet rays. However, any coating material can be used as long as it can be detected that the protective layer 60 is formed on the outer surface of the sealed battery 1, such as a fluorescent coating that emits light of other wavelengths. You may go out. Further, the protective layer 60 may not include such a paint.

  In the embodiment, the sealed battery 1 is configured such that the terminal 22 of the sealing body 20 has a positive potential while the outer can 10 has a negative potential. However, the sealed battery may be configured such that the terminal of the sealing body has a negative potential and the outer can has a positive potential.

  In the embodiment, the outer can 10 is made of iron. However, the present invention is not limited to this, and any other metal material can be used as long as the electrode body 30 and the lead terminal 2 can be electrically connected by the bottom 11. It may be configured.

  The sealed battery according to the present invention can be used for a sealed battery installed in a place where condensation is likely to occur such as outdoors.

1: sealed battery, 1a: battery case, 2, 3: drawer terminal, 10: exterior can, 20: sealing body, 21: lid plate, 25: insulating plate (insulating member), 30: electrode body, 40: exterior Cover, 60: protective layer

Claims (5)

A metal battery case in which the electrode body is stored;
An exterior cover made of polyethylene terephthalate covering the outer surface of the battery case;
A sealed battery in which a protective layer for preventing corrosion of the battery case is formed on the outer surface of the outer cover and on the outer surface of the battery case not covered with the outer cover. The sealed battery according to claim 1,
The said protective layer is a sealed battery comprised with polyolefin resin. The sealed battery according to claim 1 or 2,
The battery case further includes a lead terminal attached and fixed to one end side of the battery case,
A sealed battery in which the protective layer is also formed on one end side of the lead terminal. The sealed battery according to any one of claims 1 to 3,
On the battery case, an insulating member for electrically insulating the battery case and the lead terminal is disposed,
The insulating member is a sealed battery, wherein a part of the insulating member is fixed on the battery case by being covered with the exterior cover. The sealed battery according to any one of claims 1 to 4,
The battery case is formed in a substantially cylindrical shape extending in the axial direction,
The sealed battery is attached and fixed to the battery case so as to extend in a direction intersecting the axis of the battery case.

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