JP4664614B2 - Sealed battery - Google Patents

Description

  The present invention relates to a sealed battery, and more particularly to a sealed battery in which a power generation element is housed in a drawn part of a drawn metal laminated resin film outer package, and then a peripheral part of the outer package is sealed. The present invention relates to a sealed battery in which defects such as pinholes are less likely to occur during the drawing of a film exterior material, the amount of injected electrolyte penetrates, the capacity of the battery is increased, and productivity can be improved.

  In recent years, there have been remarkable developments in technologies aimed at rapid performance enhancement, multifunctionalization, weight reduction, and miniaturization in portable electronic devices such as video cameras, headphone stereos, and portable terminals. Technical demands for higher energy and higher capacity of secondary batteries, which serve as drive power sources for time operation, are further increasing.

  In order to meet these technical demands, the development of non-aqueous electrolyte secondary batteries using materials that can occlude and release lithium, such as lithium metal, lithium alloys, or carbonaceous materials, is actively promoted. It became so. Among these non-aqueous electrolyte secondary batteries, from the technical point of view that reducing the volume occupied by elements other than the power generation element of the battery is advantageous for increasing the energy and size of the battery, it has been conventionally used as a battery exterior material. Instead of the metal cans made of iron or aluminum, a sealed battery using a metal laminate resin film that can be made thinner as an exterior material has been attracting attention.

  The metal laminate resin film is formed by laminating and laminating a soft metal film such as an aluminum foil capable of preventing permeation of electrolyte solution, moisture and gas, and a plastic film such as nylon, polyethylene, and polypropylene. . When this metal laminate resin film is used as a battery exterior material, a structure in which the outer periphery of the exterior material is sealed by thermal fusion in a state where the power generation element is accommodated is generally employed.

  When adopting the above sealing structure, the form of the metal laminate resin film is roughly divided into two types, and as one conventional form, a laminated sheet metal laminate resin film is formed as a bag as it is, A configuration is adopted in which a power generation element (battery body) is housed inside (see, for example, Patent Document 1).

Another form is a form in which the metal laminate resin film is subjected to a drawing process, and the power generation element is housed in the drawing part. In this case, in the latter form, since the drawn portion that matches the shape of the power generation element to be accommodated is formed, the ratio of the power generation element to the entire battery volume compared to the former bag-shaped exterior material There is an advantage that the battery capacity can be increased.
Japanese Patent Laid-Open No. 11-40114 (page 1-3, FIG. 3)

  As described above, in order to realize a high capacity of the sealed battery, it is effective to set the volume ratio of the power generation element occupying the limited battery volume to the maximum, and the metal subjected to the draw forming Even in a sealed battery using a laminate resin film, the ratio of the power generation element to the inner volume of the drawn portion is increased to almost the limit. Furthermore, in order to increase the adhesion amount per unit volume of the positive and negative electrode active materials attached to the positive electrode plate and the negative electrode plate, the positive and negative electrode active materials are preliminarily pressed at a high pressure to be consolidated. With the introduction, positive and negative electrodes are becoming more densely formed.

  However, problems related to the electrolyte injection process are being raised in the process of increasing the capacity by increasing the volume of the power generation element in the battery volume and increasing the density of the positive and negative electrode active materials. In other words, as the amount of positive and negative electrode active material in the battery increases, the amount of electrolyte required to smoothly promote the battery reaction by the active material does not necessarily increase. It will not be obtained.

  However, the space for filling and holding the electrolyte in the battery is also reduced, making it difficult to inject the electrolyte. At the same time, since the positive and negative electrode active materials are also formed at a high density, the electrolyte solution is less likely to penetrate into the active material layer itself. As a result, battery performance degradation due to insufficient penetration of the electrolytic solution and productivity degradation due to the prolonged time of the electrolytic solution pouring process are highlighted as problems to be solved.

  On the other hand, the metal laminate resin film exterior material to be drawn has a disadvantage in that it cannot accommodate all sizes required in the market because of the limited drawing depth. In addition, when the exterior material is molded in the deep drawing region close to the limit of the drawing depth, a small hole called a pinhole is opened in the soft metal layer of the metal laminate resin film. In such a case, there has been a problem that the moisture-proof property of the exterior material is lost and moisture enters the battery to inhibit the battery reaction. For this reason, in a sealed battery that uses a metal-laminated resin film that has been subjected to drawing molding as an exterior material, it should be devised so that drawing can be deeper and more stable without causing defects such as pinholes. However, in reality, if pinholes are prevented from being generated and formability is given priority, there is a problem that problems such as deterioration of the filling properties of the electrolyte and deterioration of battery characteristics occur.

  The present invention has been made to solve the above-mentioned conventional problems, and after the power generation element is housed in the drawn portion of the drawn metal laminated resin film outer package, the peripheral portion of the outer package is sealed. It is a sealed battery, and there are few defects such as pinholes when drawing metal laminate resin film exterior materials, increasing the amount of electrolyte penetration, increasing battery capacity, and improving productivity. It is an object of the present invention to provide a sealed battery that can be used.

  In order to achieve the above object, the inventors of the present invention, when drawing a metal laminate resin film exterior material, the shape of the mold for forming each part of the draw molding portion, the moldability of the exterior material, The following findings were obtained as a result of comparative examination of various effects on the presence / absence of pinholes and the effect on electrolyte penetration.

  That is, as a method for carrying out the drawing process of the exterior material, in a state where the metal laminate resin film is sandwiched between a die formed of a die and a punch formed in a shape corresponding to the shape of the target drawing part. In general, the punching is performed by pressing the punch in the die direction. In this case, in order to carry out the drawing in a more stable state, the slipperiness between the metal laminate resin film and the mold is extremely important, and the curvature radius of the side or corner that forms the mold action part is very important. It was found that the moldability was completely different depending on the size. In other words, in a portion where the radius of curvature is small, a large slip resistance is generated at the time of molding, and the metal laminate resin film is not sufficiently slid into the narrowed portion, resulting in an increase in the probability of occurrence of pinholes. confirmed. Therefore, it is desirable that the radius of curvature of the sides and corners forming the mold is large only from the viewpoint of preventing the generation of pinholes and improving the moldability.

  On the other hand, when the radius of curvature of all sides and corners forming the draw-formed part is increased to achieve stable formability as described above, the internal volume of the draw-formed part changes in a decreasing direction. In addition, since the side surface parallel to the winding axis of the power generation element and the side inner surface of the exterior material having a large curvature radius are in close contact with each other, the electrolyte solution is held between them or the electrolyte solution penetrates into the power generation element. It becomes difficult.

  Therefore, while increasing the curvature radius of the inner surface at the corner (corner portion) where the molding amount of the exterior material increases during molding, the moldability of the exterior material is maintained well, while the side center portion where the molding amount becomes relatively small By forming a space that can accommodate and hold the electrolyte between the exterior material and the power generation element by reducing the curvature radius of the inner surface of the battery, it is possible to increase the formability of the exterior material, increase the capacity of the battery, and improve the productivity of the liquid injection process As a result, it was found that a sealed battery satisfying both the electrolyte and the electrolyte pouring property can be obtained for the first time. The present invention has been completed based on the above findings.

That is, the sealed battery according to the present invention has a peripheral edge of the outer packaging material after the power generation element is housed in the drawing molded portion of the metal laminate resin film outer packaging material formed so as to protrude from the drawn molding portion having a substantially rectangular cross section. In a sealed battery with a sealed portion, the radius of curvature of the inner surface of the central portion of the side that is the boundary from the side surface of the protruding drawn portion to the end surface is smaller than the radius of curvature of the inner surface near the corner of the side. To do.

  That is, in the present invention, the radius of curvature of the inner surface of the central portion of each side forming the convex surface of the rectangular drawn portion formed by the drawing method on the metal laminate resin film used as the exterior material is set on the inner surface of the corner portion. By making it relatively smaller than the radius of curvature, the volume in the drawn portion can be increased without lowering the drawability, and the productivity of the liquid injection process can be improved.

  In the present invention, the “near the corner” of the side that is a boundary that moves from the side surface to the end surface of the protruding drawing portion is two sides in the planar direction and one side in the height direction of the protruding rectangular drawing portion. Meaning the area within 10mm from the intersecting point (corner, corner), while "center" means the area excluding the length of the corner from the total length of each of the four sides of the rectangle To do.

  In the sealed battery, in order to realize a stable draw forming in which no pinhole defect or the like is formed, the curvature radius of the inner surface near the corner of the exterior material is preferably 1 mm or more, and more preferably 2.5 mm. It is the above range. When the radius of curvature of the inner surface near the corner is 1 mm or more, the slip resistance at the corner portion does not become excessive at the time of molding, and the exterior material can be molded in a stable state without causing defects such as pinholes.

  On the other hand, the radius of curvature at the inner surface of each central part of the four sides defining the convex surface (end surface) of the protruding drawn part is set as small as possible within the range where drawing can be performed in order to increase the injection space for the electrolyte. Specifically, a range of 0.5 mm to 1.5 mm is desirable. By making the curvature radius at the inner surface of the central portion of each side smaller than the curvature radius of the inner surface of the corner portion as described above, a space capable of accommodating and holding the electrolytic solution can be formed between the exterior material and the power generation element, It is possible to increase the space capacity, and it is possible to obtain a sealed battery that simultaneously satisfies a high capacity of the battery, an improvement in productivity of the liquid injection process, and a liquid injection property of the electrolytic solution.

  Further, in the above sealed battery, as a power generation element housed in the metal laminate resin film exterior material, a laminate in which a positive electrode plate and a negative electrode plate are combined via a separator is wound into a long cylindrical shape and then flattened. It is preferable to store the power generation element formed in the above.

  Between the side surface of the power generation element formed in the above flat shape and the inner surface of the central part of both sides of the draw forming part formed with a small radius of curvature, a space that can accommodate and hold the electrolyte between the draw forming part and the power generation element It becomes possible to increase the space capacity in the battery.

  Further, in the sealed battery, when the peripheral portion of the metal laminate resin film exterior material containing the power generation element in the drawing portion is sealed by thermal fusion, the metal laminate resin film exterior material is formed. It is preferable that the inside of the drawn portion is sealed in a state where the pressure is reduced.

  As described above, by performing sealing work in a reduced pressure environment and sealing the inside of the drawn-formed part formed on the exterior material in a pre-reduced state, the useless space inside the battery can be reduced as much as possible. The effects of gas components and the like remaining in the battery from the battery manufacturing stage can be effectively avoided, and in particular, the effect of effectively preventing the deformation of the battery due to the increase in internal pressure accompanying the aging of the battery can be obtained.

  According to the sealed battery of the present invention, since the radius of curvature of the inner surface at the corner (corner portion) where the molding amount of the exterior material becomes large at the time of drawing, the formability of the exterior material can be maintained well. On the other hand, since the radius of curvature of the inner surface of the side central portion where the molding amount is relatively small is made small, it is possible to form a space that can accommodate and hold the electrolytic solution between the exterior material and the power generation element. As a result, a sealed battery that satisfies both the moldability of the outer packaging material, the high capacity of the battery, the improvement of the productivity of the injection process and the injection of the electrolyte can be obtained for the first time, and the stable quality with high productivity can be achieved. A sealed battery can be obtained.

  Hereinafter, an example of an embodiment of a sealed battery according to the present invention will be described more specifically with reference to the accompanying drawings.

  FIG. 1 is an exploded perspective view showing a state where a power generation element 1 and an exterior material 4 constituting a sealed battery to which the present invention is applied are assembled. The power generation element 1 includes a negative electrode plate in which a negative electrode material is held on a negative electrode current collector that is a support, a positive electrode plate in which a positive electrode active material is held on a positive electrode current collector that is a support, and the negative electrode The separator is interposed between the plate and the positive electrode plate to hold the electrolytic solution and prevent a short circuit between the two electrodes. The negative electrode plate, the positive electrode plate, and the separator are all formed into a thin sheet shape or foil shape, and these laminated bodies are pressed around a predetermined winding axis and then pressed into a flat long cylindrical shape. Formed. The power generation element 1 is provided with a negative electrode lead 2 electrically connected to the negative electrode and a positive electrode lead 3 electrically connected to the positive electrode, both of which generate the power generation in a direction parallel to the winding axis. It extends from element 1.

  As the exterior material 4 that houses the power generation element 1, a metal laminate resin film that has been subjected to a drawing process is used. The metal laminate resin film is formed by bonding a thermoplastic metal film such as polyethylene, polypropylene, nylon, etc., for heat-sealing after housing the power generating element 1 to a soft metal thin film such as aluminum.

  As shown in FIG. 1, the method of housing the power generating element 1 in the metal laminate resin film exterior material 4 is to fold one side of the exterior material 4 on which the rectangular drawn portion 7 is formed, The power generation element 1 is housed so that the negative electrode lead 2 and the positive electrode lead 3 are pulled out from the opposite side to the opposite side, and the peripheral portions of the three sides other than the valley-folded side are thermally fused. It was set as the method of sealing automatically.

  In the above-described three-side fusion process, first, a side (top seal portion) from which the positive and negative electrode leads 2 and 3 are drawn and one side (side seal portion) of the two sides parallel to the positive and negative electrode leads 2 and 3 are used. At the stage of heat sealing, the electrolyte is injected from the remaining one side (side seal part) side where heat sealing is not performed. Furthermore, when performing the thermal fusion of the unfused side (side seal part) after the electrolyte injection, the inside of the battery is brought into a decompressed state by adopting a method such as thermal fusion in a reduced pressure environment. The useless space inside the battery was reduced as much as possible.

  In a battery using a metal laminate resin film as an exterior material, the negative electrode terminal 2 and the positive electrode terminal 3 are pulled out to the outside via a heat-sealed portion (top seal portion) of the exterior material 4 as shown in FIG. It serves as an external terminal. Since the fused portion of the negative electrode terminal 2 and the positive electrode terminal 3 has a weak joint structure in which a metal and a resin are fused, sealing performance is improved as compared with a strong joint structure portion in which the resin of the exterior material is fused. Inferior. For this reason, it is desirable to seal the side from which the external terminal is drawn out before injecting the electrolyte.

  Next, a drawing forming method applied to form the drawing portion 7 on the exterior material 4 will be described with reference to FIG. In the drawing process, the metal laminate resin film is sandwiched between the punch 13 and the die 12, and at the same time, the punch 11 is pressed into the concave portion of the die 12 for processing. At this time, the shape of the tip pressing portion of the punch 11 determines the shape of the inner surface of the drawing portion 7 of the exterior material 4. The shape of the concave portion of the die 12 used in combination with the punch 11 determines the shape of the rising portion of the drawing portion 7. That is, the radius of curvature of the inner surface of the four sides 5 forming the rectangle of the protruding end surface of the drawing portion (convex portion) 7 formed on the outer packaging material 4 is directly equal to the radius of curvature of the side 6 of the ridge portion of the punch 11. It is reflected in.

  Therefore, in the present invention, the radius of curvature of the inner surface of the central portion of the side 5 forming the drawn portion (convex portion) 7 of the metal laminate resin film used as the exterior material 4 is made smaller than the radius of curvature around the corner. However, the operation of changing the radius of curvature specifically in each part of the drawing portion 7 in each embodiment or the like is adjusted and executed by changing the radius of curvature of the side 6 of the ridge portion of the punch 11 to which the drawing processing is performed. Specifically, this is realized by making the central part of the side smaller than the radius of curvature around the corner.

  Next, embodiments to which the present invention is applied will be described more specifically with reference to the following examples and comparative examples.

[Example 1]
As a metal laminate resin film used as an exterior material, an aluminum laminate film composed of a nylon layer having a thickness of 25 μm, a soft aluminum layer having a thickness of 40 μm, and a polypropylene layer having a thickness of 30 μm was prepared. Next, a drawing machine comprising a punch 11 and a die 12 as shown in FIG. 5 was used to draw the exterior material so that the nylon layer was on the outside. A punch 11 having a size of 60 mm in length and 40 mm in width was prepared as the punch 11 subjected to the drawing process. The radius of curvature of the side 6 of the edge of the punch 11 is 3 mm in the range X1 of 8 mm from the apex of the four corners, the range X2 of 18 mm and the side of 40 mm length on both sides from the midpoint of the side of 60 mm The range X3 of 8mm on each side from the middle point is 1mm, and the curvature radius of the part connecting X1 and X2 with different curvature radii and the part of X4 connecting X1 and X3 changes smoothly from 3mm to 1mm The shape was The other curvature radii of the sides and corners of the punch 11 were all 3 mm. Moreover, about the depth of the drawing forming part, it shape | molded so that the inner dimension in which an electric power generation element is accommodated might be 6 mm.

  As shown in FIG. 1, the side 5 of the drawn portion (convex portion) 7 of the exterior material 4 drawn by the punch 11 reflects the radius of curvature of the side 6 of the punch ridge, and is near the corner. Y1 has a radius of curvature of 3 mm, while Y2 and Y3 near the center of side 5 have a radius of 1 mm.

[Comparative Example 1]
Except for using the punch 11 in which the radii of curvature of the ridges (sides) of the punch 11 to be used are all 3 mm over the entire side, the same exterior material as that of the first embodiment is used, and is substantially the same as the first embodiment. The exterior material provided with the drawing forming part which has the same external dimension was prepared.

[Comparative Example 2]
Except for using the punch 11 in which the radii of curvature (edges) of the punch 11 to be used are all 1 mm over the entire side, the same exterior material as that in Example 1 is used, and it is abbreviated as Example 1. The exterior material provided with the drawing forming part which has the same external dimension was prepared.

  About 100 exterior materials for examples and comparative examples prepared by drawing as described above, the occurrence of pinholes by drawing was confirmed, and the results shown in Table 1 were obtained.

  In addition, after the power generation element 1 is accommodated in the drawing portion 7 of the exterior material for the example in which no pinhole was generated, the outer peripheral edge (3 sides) of the exterior material 4 is heat-sealed as shown in FIG. did. In the fusion process on the three sides, first, two sides (side seal portions) parallel to the positive and negative electrode leads 2 and 3 are thermally fused at atmospheric pressure, and then the exterior material is placed in a decompression chamber whose pressure is adjusted to 100 Torr. By transferring and injecting about 4 cc of electrolyte from the remaining one side that has not been heat-sealed, and by heat-sealing the unfused side (top seal portion) after the electrolyte is injected A sealed battery according to Example 1 was produced.

  On the other hand, after using the outer packaging material for Comparative Examples 1 and 2 in which the drawn portions were formed using the punches having different shapes of the pressing portions as described above, the power generation element 1 was accommodated in the drawn portions, A sealed battery according to each of Comparative Examples 1 and 2 was produced by injecting an electrolytic solution under atmospheric pressure and processing under the same conditions as in the Examples except that the outer peripheral edge of the outer packaging material 4 was thermally fused. .

The results shown in Table 1 below were measured while measuring the injection time required for injecting only 4 cc of the electrolyte into the sealed batteries according to the examples and comparative examples prepared as described above, and measuring the space volume in the battery. Got. In addition, the average value of the injection time of the electrolytic solution and the average value of the space volume in the battery were relatively displayed with Comparative Example 1 as a reference value (100).

  In the case where the exterior material is subjected to the drawing by the drawing method as described above, the portion where the pinhole is generated is around the corner of the drawing portion (convex portion). In addition, slip resistance at the time of molding increases around the corner, and the amount of material wraparound decreases, so that the vicinity of the corner tends to be thinner than other portions.

  Therefore, in the exterior material for the example in which the drawn portion was formed using the punch having a larger curvature radius near the corner, the metal laminate resin film easily slipped into the corner portion of the drawn portion. As is clear from the results, even when 100 exterior members each having a 6 mm deep drawn part were formed, no pinholes were generated, and excellent formability was obtained.

  In addition, in the examples, since the injection of the electrolytic solution and the thermal fusion of the sealing portion are performed in a reduced pressure environment, the injection operation of the electrolytic solution proceeds quickly, and the productivity in the injection process is improved. As a result, the gas component remaining inside the battery is reduced, and a useless space inside the battery can be reduced as much as possible, and the internal volume of the battery can be increased by about 5% compared to the battery of the comparative example 1 of the related art. Met.

  On the other hand, even in the case of the exterior material of Comparative Example 1 that was drawn and formed using punches in which the radius of curvature of the side of the punch ridge part was set to 3 mm including the vicinity of the corner, there was no occurrence of pinholes. Met. However, the power generation element and the both edges of the exterior material are in close contact with each other, and the battery internal volume is relatively reduced as compared with the example.

  On the other hand, in the battery outer packaging material according to Comparative Example 2 in which the draw-molded portion is formed using punch punches in which the radii of curvature of the ridges (sides) are all set to 1 mm, out of 100 draw-molded outer packaging materials, 37 Pinholes were generated in the outer packaging material, and a significant decrease in formability was reconfirmed, demonstrating that the production yield dropped sharply.

  As is clear from the above comparison, according to the sealed battery according to the present example, when the radius of curvature near the corner of the drawn portion (convex portion) is increased, the radius of curvature at the center of the side is reduced. It has also been demonstrated that stable deep-drawing is possible.

In addition, in the sealed battery according to the example, the radius of curvature of the inner surface of the exterior material in the region of the central part 36 mm of the side with the length of 60 mm of the drawn portion and the region of the central part 16 mm of the side with the length of 40 mm is Since the thickness is 1 mm, the calculation is performed assuming that each exterior material is a rigid body, and the internal volume is increased by about 200 mm ³ compared to the battery of Comparative Example 1. In a sealed battery of this size, about 4 cc of electrolyte is injected, and this volume increase is equivalent to about 5% of the amount of electrolyte, and the volume of electrolyte corresponding to the volume can be increased. It becomes possible. In addition, since the space for holding the electrolytic solution in the battery becomes large, it is obvious that it also works to improve the productivity in the liquid injection process accompanying the increase in capacity.

  As described above, according to the sealed battery according to the present embodiment, since the radius of curvature of the inner surface of the corner portion (corner portion) where the molding amount of the outer packaging material 4 becomes large at the time of drawing molding is increased, the molding of the outer packaging material 4 is performed. Since the curvature radius of the inner surface of the side central portion where the molding amount is relatively small can be reduced while maintaining good performance, a space in which the electrolytic solution can be accommodated between the exterior material 4 and the power generation element 1 is provided. It becomes possible to form. As a result, for the first time, a sealed battery satisfying both the moldability of the outer packaging 4, the high capacity of the battery, the productivity improvement of the liquid injection process, and the liquid injection property of the electrolytic solution can be obtained. A sealed battery having the following can be obtained.

The disassembled perspective view which shows the state which assembled the electric power generation element and exterior material which comprise the sealed battery to which this invention is applied. The perspective view which shows roughly the external structure of the sealed battery to which this invention is applied. The III-III arrow partial sectional view in the draw forming part of the exterior material shown in FIG. FIG. 4 is a partial cross-sectional view taken along the arrow IV-IV in the drawing portion of the exterior material shown in FIG. 1. The perspective exploded view which shows the example of a structure of the drawing machine which consists of a die | dye and a punch, and the state which draw-molds an exterior material using this drawing machine.

Explanation of symbols

1 Power generation element 2 Negative electrode lead (negative electrode terminal)
3 Positive lead (positive terminal)
4 Exterior material (metal laminate resin film)
5 Sides of the draw forming convex part 6 Sides of the punch ridge 7 Drawing part 11 Punch 13

Claims (6)

In a sealed battery in which a power generation element is housed in the drawing part of the metal laminate resin film exterior member formed so as to protrude from the drawing part having a substantially rectangular cross section, and the peripheral part of the exterior member is sealed, A sealed battery characterized in that the radius of curvature of the inner surface of the central portion of the side, which is a boundary from the side surface of the projecting drawn portion to the end surface, is smaller than the radius of curvature of the inner surface near the corner of the side . As a power generation element housed in the metal laminate resin film exterior material, a power generation element formed into a flat shape after winding a laminated body in which a positive electrode plate and a negative electrode plate are combined through a separator is housed. The sealed battery according to claim 1. When the periphery of the metal laminate resin film exterior material containing the power generation element in the draw molding portion is sealed by heat sealing, the inside of the draw molding portion formed in the metal laminate resin film exterior material is decompressed The sealed battery according to claim 1, wherein the sealed battery is sealed with. 2. The sealed battery according to claim 1, wherein the radius of curvature of the inner surface near the corner of the drawn portion is 1 mm or more. 2. The sealed battery according to claim 1, wherein the radius of curvature of the inner surface of the central portion of the side that is a boundary that moves from the side surface to the end surface of the drawn portion is in the range of 0.5 to 1.5 mm. 2. The sealed battery according to claim 1, wherein the curvature radius of the portion connecting the inner surface of the central portion and the inner surface near the corner of the sides having different curvature radii changes smoothly.

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