JP2018166040A - Square secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a square secondary battery which is capable of preventing a cathode or an anode from being short-circuited with a square outer package and improves an insertion property of an electrode body covered by an insulation sheet into the square outer package during manufacture.SOLUTION: A square secondary battery comprises: an opened box-like square outer package; a sealing plate which seals the opening; a wound electrode body which is accommodated in the square outer package; and an insulation sheet between the wound electrode body and the square outer package. The square outer package includes a bottom surface, a pair of opposite first sidewalls and a pair of opposite second sidewalls having a larger area than the first sidewalls. The insulation sheet includes: a bottom region that is disposed between the wound electrode body and the bottom surface of the square outer package; and a first region which extends from the bottom region to the sealing plate and is disposed between the first sidewalls and the wound electrode body. In both ends of a borderline between the bottom region and the first region, an easily foldable part is formed from at least either a portion reduced in thickness compared to the periphery or a portion that is cut at least partially. In a center of the borderline, the easily foldable part is not formed.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a prismatic secondary battery.

  As power sources for hybrid electric vehicles (HEV, PHEV) and electric vehicles (EV), non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries and secondary batteries such as nickel hydride secondary batteries are used.

  These secondary batteries have a higher need for prismatic batteries than cylindrical ones, particularly when space efficiency is required. Furthermore, when physical strength is required, a metal case is generally employed as the battery outer package.

  For example, a prismatic nonaqueous electrolyte secondary battery is manufactured as follows. That is, a negative electrode active material mixture containing a negative electrode active material is applied to both surfaces of a negative electrode core (current collector) made of a strip-shaped copper foil or the like to produce a negative electrode plate. In addition, a positive electrode plate is prepared by applying a positive electrode active material mixture containing a positive electrode active material to both surfaces of a positive electrode core made of a strip-shaped aluminum foil or the like.

  Next, the negative electrode plate and the positive electrode plate are overlapped with a separator made of a microporous polyethylene film or the like interposed therebetween, and a cylindrical core is formed with the negative electrode plate and the positive electrode plate insulated from each other by the separator. Are wound in a spiral shape to produce a cylindrical wound electrode body.

  Next, the cylindrical wound electrode body is crushed with a press and formed into a flat wound electrode body that can be inserted into a rectangular battery outer body. A rectangular non-aqueous electrolyte secondary battery is obtained by sealing the opening of the battery exterior body except the liquid injection hole, injecting the electrolytic solution, and finally closing the injection hole for the electrolytic solution.

  In addition to the above, when a metal case is adopted as the exterior body, in addition to the above, for insulation between the metal case (hereinafter referred to as “exterior can”) as the exterior body and the electrode body, electrical insulation is provided. A rectangular non-aqueous electrolyte secondary battery having an outer can is manufactured by previously wrapping the flat wound electrode body with a member having a shape and then storing the electrode body in the outer can (see Patent Documents 1 to 3).

JP 2009-170137 A JP 2009-277443 A International Publication WO2013 / 035668

  Even in the case of a rectangular secondary battery in which an insulating sheet is disposed between a flat wound electrode body and a rectangular outer casing in order to insulate the flat wound electrode body and the rectangular outer casing, The inventors of the present application have found that there is a possibility that the positive electrode or the negative electrode may be short-circuited with the rectangular outer casing depending on the use conditions of the secondary battery. It has been found that this short circuit may occur in the vicinity of the boundary between the side surface and the bottom surface of the rectangular outer casing facing the positive electrode core exposed portion of the positive electrode or the negative electrode core exposed portion of the negative electrode. Such a phenomenon is a phenomenon that is not described in Patent Documents 1 to 3 and other documents.

  The present invention has been made in view of such points, and its main purpose is excellent in the insertion property of a flat wound electrode body covered with an insulating sheet into a rectangular exterior body, and a positive electrode or a negative electrode is provided. An object of the present invention is to provide a prismatic secondary battery capable of preventing a short circuit with a prismatic exterior body.

  A rectangular secondary battery according to an embodiment of the present invention includes a box-shaped metal rectangular exterior body having one open surface, a sealing plate that seals the opening, and a positive electrode and a negative electrode wound with a separator interposed therebetween. A wound electrode body accommodated in the rectangular exterior body, and an insulating sheet disposed between the wound electrode body and the rectangular exterior body, wherein the rectangular exterior body faces the opening. A bottom surface, a pair of first side walls opposed to each other, and a pair of second side walls opposed to each other having a larger area than the area of the first side wall; A positive electrode core exposed portion wound around one end in the rotational axis direction, a negative electrode core exposed portion wound around the other end in the winding axis direction, and a winding The rotation axis is accommodated in the rectangular exterior body parallel to the bottom surface of the rectangular exterior body, and the positive electrode core body The protruding portion is disposed on one side of the pair of first side walls, the negative electrode core exposed portion is disposed on the other side of the pair of first side walls, and the insulating sheet is wound on the winding A bottom region disposed between the mold electrode body and the bottom surface of the rectangular exterior body, and extends from the bottom region toward the sealing plate and disposed between the first side wall and the wound electrode body. At least one of a part where the thickness is reduced and at least a part where the part is cut at both ends of the boundary line between the bottom region and the first region. An easy-to-bend part is formed, and the easy-to-bend part is not formed at the center of the boundary line.

  In the above-described prismatic secondary battery, an easy-to-bend portion is provided at both ends of the boundary line between the bottom region and the first region of the insulating sheet so that the boundary line can be easily bent. For this reason, an insulating sheet becomes a desired shape and the insertability to the square exterior body of the winding type electrode body covered with the insulating sheet improves. Further, in the above-described prismatic secondary battery, the easy-to-bend portion is not provided at the central portion of the boundary line between the bottom region of the insulating sheet and the first region where the positive electrode core exposed portion or the negative electrode core exposed portion may pierce. . For this reason, it can be ensured that the positive electrode or the negative electrode is short-circuited with the rectangular outer casing. In addition, according to the above-described prismatic secondary battery, since the insertability of the wound electrode body covered with the insulating sheet into the prismatic exterior body is improved, the occurrence of damage to the rectangular exterior body or the insulating sheet is suppressed. And a highly reliable prismatic secondary battery.

  The length of the region where the easy-to-bend portion provided at the center of the boundary line is not formed is preferably 40% or more and 95% or less with respect to the thickness of the wound electrode body, and 45% It is more preferably 85% or less and further preferably 50% or more and 80% or less.

  It is preferable that the bendable part is at least one of a cut line, a thin part, and a perforation.

  The easy-to-bend portion is a thin portion, and the thin portion is preferably formed by denting a surface of the insulating sheet that faces the wound electrode body.

  A rectangular secondary battery according to an embodiment of the present invention includes a box-shaped metal rectangular exterior body having one open surface, a sealing plate that seals the opening, and a positive electrode and a negative electrode wound with a separator interposed therebetween. A wound electrode body accommodated in the rectangular exterior body, and an insulating sheet disposed between the wound electrode body and the rectangular exterior body, wherein the rectangular exterior body faces the opening. A bottom surface, a pair of first side walls opposed to each other, and a pair of second side walls opposed to each other having a larger area than the area of the first side wall; A positive electrode core exposed portion wound around one end in the rotational axis direction, a negative electrode core exposed portion wound around the other end in the winding axis direction, and a winding The rotation axis is accommodated in the rectangular exterior body parallel to the bottom surface of the rectangular exterior body, and the positive electrode core body The protruding portion is disposed on one side of the pair of first side walls, the negative electrode core exposed portion is disposed on the other side of the pair of first side walls, and the insulating sheet is wound on the winding A bottom region disposed between the mold electrode body and the bottom surface of the rectangular exterior body, and extends from the bottom region toward the sealing plate and disposed between the first side wall and the wound electrode body. The first region is formed, and at both ends of the boundary line between the bottom region and the first region, easy-bending portions each having a smaller thickness than the periphery are formed, and the boundary line The thickness of the central part is larger than the thickness of the easy-to-bend part.

  In the above-described prismatic secondary battery, easy-to-bend portions are provided at both ends of the boundary line between the bottom region and the first region of the insulating sheet so that the boundary line can be easily bent. For this reason, an insulating sheet becomes a desired shape and the insertability to the square exterior body of the winding type electrode body covered with the insulating sheet improves. Further, in the above-described prismatic secondary battery, the thickness of the center part of the boundary line between the bottom region of the insulating sheet and the first region where the positive electrode core exposed portion or the negative electrode core exposed portion may pierce is set to It is larger than the thickness. For this reason, it can be ensured that the positive electrode or the negative electrode is short-circuited with the rectangular outer casing. In addition, according to the above-described prismatic secondary battery, since the insertability of the wound electrode body covered with the insulating sheet into the prismatic exterior body is improved, the occurrence of damage to the rectangular exterior body or the insulating sheet is suppressed. And a highly reliable prismatic secondary battery.

  It is possible to provide a prismatic secondary battery that is excellent in insertability of a wound electrode body covered with an insulating sheet into a prismatic exterior body and in which a positive electrode or a negative electrode is prevented from being short-circuited with the prismatic exterior body.

It is the front view which represented the square secondary battery of this embodiment by seeing through the square exterior body and the insulating sheet. It is sectional drawing along the II-II line of FIG. It is an expanded view of the insulating sheet used with the square secondary battery of this embodiment. It is a perspective view for demonstrating the combined structure of the flat electrode body and an insulating sheet in the square secondary battery of this embodiment. It is the elements on larger scale of an insulating sheet. It is the schematic diagram which observed the winding type electrode body along the winding axis direction. It is an expanded view which shows the 1st modification of an insulating sheet. It is an expanded view which shows the 2nd modification of an insulating sheet. It is an expansion schematic diagram of the bend easy part vicinity of another embodiment. FIG. 10 is a sectional view taken along line B-B ′ of FIG. 9. It is an expansion schematic diagram of the bendable part vicinity of other embodiment. FIG. 12 is a sectional view taken along line C-C ′ of FIG. 11. FIG. 12 is a sectional view taken along line D-D ′ of FIG. 11. FIG. 12 is a sectional view taken along line E-E ′ of FIG. 11. It is an expansion schematic diagram of the bendable part vicinity of another embodiment. FIG. 16 is a cross-sectional view taken along line F-F ′ in FIG. 15. FIG. 16 is a sectional view taken along line G-G ′ of FIG. 15. FIG. 16 is a cross-sectional view taken along line H-H ′ of FIG. 15.

  Before describing the embodiment, the background to the present invention will be described.

  A sheet of insulating sheet is bent into a box shape with a bottom, and a rectangular secondary battery in which a flat wound electrode body is arranged is manufactured. The rectangular secondary battery is exposed to intense vibration. When used for a long time in the environment, it has been found that a phenomenon in which the positive electrode or the negative electrode is short-circuited with the metal rectangular outer casing occurs rarely. As a result of examining the cause, the boundary portion between the side surface and the bottom surface of the insulating sheet, where the core exposed portion of the positive electrode or the negative electrode is opposed, is broken through by the metal foil that is the core of the positive electrode or the negative electrode, It was found that the core body and the square exterior body were in contact.

  In the prismatic secondary battery described above, a perforation or a thin-walled portion is provided at the boundary between the side surface and the bottom portion in order to bend the insulating sheet into a bottomed box shape. Then, in the insulating sheet, the tip portion of the curved portion is broken through the wound positive electrode core exposed portion or the wound negative electrode core exposed portion in the portion where the perforation or thin wall portion is formed, and the positive electrode core body It was found that the exposed portion or the negative electrode core exposed portion and the square exterior body contact each other. Therefore, when a perforation or a thin portion is not provided at the boundary between the side surface and the bottom surface, the vicinity of the boundary between the side surface and the bottom surface of the insulating sheet is unlikely to have a desired shape, and the wound electrode accommodated in the insulating sheet It becomes difficult to insert the body into the rectangular exterior body. For example, there is a possibility that the wound electrode body housed in the insulating sheet is not disposed at a predetermined position in the rectangular exterior body. Or there exists a possibility that an insulation sheet thru | or a rectangular exterior body may be damaged. The inventors of the present invention have come up with the present invention as a result of intensive studies to solve such a situation.

(Embodiment 1)
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following description of the preferred embodiments is merely exemplary in nature and is not intended to limit the invention, its application, or its use. In the following drawings, components having substantially the same function are denoted by the same reference numerals for the sake of brevity.

  First, a prismatic secondary battery using the nonaqueous electrolyte according to the present embodiment will be described with reference to FIGS. 1 and 2. The rectangular secondary battery 10 is formed by covering a flat wound electrode body 11 in which a positive electrode plate and a negative electrode plate are wound via a separator (both not shown) with an insulating sheet 301, The rectangular outer package 12 is housed inside a box-shaped rectangular outer package 12 and the rectangular outer package 12 is hermetically sealed by a sealing plate 13. In addition, in FIG.1 and FIG.2, illustration of the insulating sheet 301 is abbreviate | omitted.

  The rectangular exterior body 12 has a bottom surface 12c facing the opening sealed by the sealing plate 13, a pair of first side walls 12a and 12a facing each other, and an area larger than the first side walls 12a and 12a and facing each other. And a pair of second side walls 12b, 12b.

  The positive electrode plate is coated with a positive electrode active material mixture so that a positive electrode core exposed portion 14 in which a strip-shaped aluminum foil is exposed is formed on both surfaces of an aluminum foil as a positive electrode core, and is rolled after being dried. It is made by doing. The negative electrode plate is coated with a negative electrode active material mixture and dried so that the negative electrode core exposed portion 15 in which the strip-shaped copper foil is exposed is formed on both sides of the copper foil as the negative electrode core. It is produced by rolling later. The wound electrode body 11 is configured such that the positive electrode plate and the negative electrode plate are not overlapped with the active material mixture coating portion of the electrode facing the positive electrode core exposed portion 14 and the negative electrode core exposed portion 15. The positive electrode core exposed portion 14 is positioned at one end in the winding axis direction, and the negative electrode core exposed portion 15 is positioned at the other end, for example, made of polyethylene. After being wound through a porous separator (not shown), it is produced by being formed into a flat shape.

  Among these, the positive electrode core exposed portion 14 is connected to the positive electrode terminal 17 via the positive electrode current collector 16, and the negative electrode core exposed portion 15 is connected to the negative electrode terminal 19 via the negative electrode current collector 181. The positive electrode current collector 16 has a main body portion 16a and a rib 16b bent substantially perpendicularly from the main body portion 16a. The main body portion 16a includes a positive electrode current collector receiving part (not shown) and a positive electrode core body exposed portion. 14 and resistance welding. Similarly, the negative electrode current collector 181 has a main body portion 181a and a rib 181b bent substantially vertically from the main body portion 181a, and the negative electrode current collector receiving part 182 is bent substantially vertically from the main body portion 182a and the main body portion 182a. The main body part 181a of the negative electrode current collector 181 is resistance-welded with the main body part 182a of the negative electrode current collector receiving part 182 and the negative electrode core body exposed part 15 interposed therebetween. In addition, the broken-line circle | round | yen part in FIG. 1 is a resistance welding location.

  The wound electrode body 11 is accommodated in the rectangular exterior body 12 with the winding axis parallel to the bottom surface 12 c of the rectangular exterior body 12. The positive electrode core exposed portion 14 is disposed so as to face one side of the pair of first side walls 12a and 12a, and the negative electrode core exposed portion 15 of the pair of first side walls 12a and 12a. It is arranged to face the other side.

  The positive terminal 17 and the negative terminal 19 are fixed to the sealing plate 13 via insulating members 20 and 21, respectively. In this prismatic secondary battery 10, after the wound electrode body 11 is inserted into a metal rectangular sheath 12, the sealing plate 13 is laser welded to the opening of the rectangular sheath 12, and then an electrolyte injection hole A non-aqueous electrolyte is injected from (not shown) and the electrolyte injection hole is sealed.

  Here, a specific configuration of the wound electrode body 11 and the insulating sheet 301 and a method of covering the wound electrode body 11 with the insulating sheet 301 in the rectangular secondary battery 10 of the present embodiment will be described.

[Preparation of positive electrode plate]
The positive electrode plate was produced as follows. First, a binder composed of 94% by mass of lithium cobaltate (LiCoO ₂ ) powder as a positive electrode active material, 3% by mass of carbon-based powder such as acetylene black or graphite as a conductive agent, and polyvinylidene fluoride (PVdF). 3% by mass was mixed, and an organic solvent composed of N-methyl-2-pyrrolidone (NMP) was added to the obtained mixture and kneaded to prepare a positive electrode active material mixture slurry. Next, a positive electrode core body made of aluminum foil (for example, having a thickness of 20 μm) is prepared, and the positive electrode active material mixture slurry prepared as described above is uniformly applied to both surfaces of the positive electrode core body. An active material mixture layer was applied. At this time, on one side of the positive electrode active material mixture layer, a non-coated portion (positive electrode core exposed portion 14) having a predetermined width (12 mm in this case) to which the positive electrode active material mixture slurry is not applied is a positive electrode core. It was applied to form along the edge of the body. Thereafter, the positive electrode core body on which the positive electrode active material mixture layer was formed was passed through a drier to remove NMP necessary for slurry preparation and dry. After drying, it was rolled with a roll press until the thickness became 0.06 mm to produce a positive electrode plate. The positive electrode plate thus produced was cut into a strip shape having a width of 95 mm, and a positive electrode plate provided with a positive electrode core exposed portion 14 made of strip-shaped aluminum having a width of 10 mm was obtained.

[Production of negative electrode plate]
The negative electrode plate was produced as follows. First, 98% by mass of natural graphite powder as a negative electrode active material and 1% by mass of carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) as a binder are mixed, and water is added to knead to prepare a negative electrode. An active material mixture slurry was prepared. Next, a negative electrode core made of copper foil (for example, having a thickness of 12 μm) is prepared, and the negative electrode active material mixture slurry prepared as described above is uniformly applied to both surfaces of the negative electrode core to form a negative electrode An active material mixture layer was formed. In this case, on one side of the negative electrode active material mixture layer, a non-coated portion (negative electrode core exposed portion 15) having a predetermined width (here, 10 mm) where the negative electrode active material mixture slurry is not applied is a negative electrode. It applied so that it might form along the edge of a core. Thereafter, the negative electrode core body on which the negative electrode active material mixture layer was formed was passed through a dryer and dried. After drying, a negative electrode plate was produced by rolling with a roll press until the thickness became 0.05 mm. The negative electrode plate thus produced was cut into a strip shape having a width of 100 mm, and a negative electrode plate provided with a strip-shaped negative electrode core exposed portion 15 having a width of 8 mm was obtained.

[Production of wound electrode body]
The positive electrode core exposed portion 14 of the positive electrode plate obtained as described above and the negative electrode core exposed portion 15 of the negative electrode plate are shifted so as not to overlap with the active material mixture layer of the opposing electrode, respectively. The wound electrode body 11 was produced by winding through a manufactured porous separator (thickness of 0.022 mm and width of 100 mm). At that time, the outermost peripheral side of the wound electrode body was covered with the porous separator.

  Next, after the wound electrode body is pressed into a flat shape, an aluminum positive electrode current collector 16 and a positive electrode current collector receiving part (not shown) are placed on the positive electrode core exposed portion 14. The wound electrode body 11 of the embodiment was manufactured by attaching a copper negative electrode current collector 181 and a negative electrode current collector receiving component 182 to the body exposed portion 15 by resistance welding, respectively. The dimensions of the wound electrode body 11 are such that the width (the length from the end on the positive electrode core exposed portion side to the end on the negative electrode core exposed portion side) is 107 mm and the thickness (positive electrode active of the positive electrode plate). The thickness of the portion where the material mixture layer was formed and the portion where the negative electrode active material mixture layer of the negative electrode plate was laminated via the separator was 11.6 mm.

  Here, the width of the wound electrode body 11 (the length from the end on the positive electrode core exposed portion side to the end on the negative electrode core exposed portion side) is opposed to the side surface on the large area side of the insulating sheet. Corresponds to the width of the body. Further, the thickness of the wound electrode body 11 (the portion where the positive electrode active material mixture layer of the positive electrode plate is formed and the portion of the negative electrode plate where the negative electrode active material mixture layer is formed are laminated via a separator. Is equivalent to the width of the electrode body facing the side surface on the small area side of the insulating sheet.

[Preparation of insulation sheet]
As a material for the insulating sheet 301 used in the prismatic secondary battery 10 of the present embodiment, a polypropylene sheet having a thickness of 150 μm was used. As shown in FIG. 3, the sheet is made up of a front portion 30a, a back portion 30b, a bottom portion (bottom region) 30c, a pair of side portions 30d, a pair of first folded portions 30e, and a pair of small tongue pieces. It cut out into the shape provided with the 2nd folding | turning part (1st area | region) 30f. In order to bend the portion indicated by the two-dot chain line, the insulating sheet 301 was formed by forming perforations in the portion of the portion to be folded, excluding the boundary between the bottom surface portion 30c and the second folded portion 30f.

  As shown in FIG. 5, the boundary between the bottom surface portion 30 c and the second folded portion 30 f is provided at the center portion sandwiched between both ends by providing cuts 40, 40 (foldable portions) at both ends. It is not done. That is, the center part of the boundary line is in the state of a non-processed polypropylene sheet like the bottom surface part 30c and the second folded part 30f on both sides of the boundary line. The length L of each cut 40, 40 at both ends is 0.2 as compared with the length W of the boundary line.

[Coating of wound electrode body]
After the insulating sheet 301 is creased by mountain folds along the perforations and cuts 40, the wound electrode body 11 is placed in the space formed by the insulating sheet 301 as shown in FIG. The electrode body 11 is inserted so that the winding axis direction of the electrode body 11 is horizontal and the positive electrode current collector (not shown) and the negative electrode current collector (not shown) face the side surface portion 30d of the insulating sheet 301, respectively. Then, the winding electrode body 11 was covered with the insulating sheet 301 formed in a box shape by bonding the overlapping portion of the first folded portion 30e and the front portion 30a by heat welding.

  When the overlapping portion between the first folded portion 30e and the front portion 30a is bonded by thermal welding, a portion of the second folded portion 30f except for the second folded portion 30f is opened, and the second folded portion 30f It protrudes from the box shape as a small tongue piece in a slightly open state. In other words, since the boundary between the bottom surface portion 30c and the second folded portion 30f is provided with cuts 40, 40 at both ends, the second folded portion 30f becomes a pair of side surface portions when the boundary line is creased. The angle between 30d becomes an acute angle and the wings are widened.

  Thereafter, when the wound electrode body 11 covered with the insulating sheet 301 is inserted into the rectangular exterior body 12, a crease is formed at the boundary between the bottom surface portion 30c and the second folded portion 30f. The resistance between the second folded portion 30f and the inner surface of the rectangular exterior body 12 is reduced, and the insertion is extremely easy. Therefore, the assembling process can be performed in a short time, and since no great force is applied to the boundary between the bottom surface portion 30c and the second folded portion 30f, the boundary is not damaged.

  In order to secure the ease of insertion as described above, the length L of each of the cuts 40, 40 at both ends of the boundary portion is 0.025 compared with the length W of the boundary line. ≦ L / W ≦ 0.3 is preferable, 0.075 ≦ L / W ≦ 0.275 is more preferable, and 0.1 ≦ L / W ≦ 0.25 is further more preferable.

  As shown in FIG. 4, among the exposed portions of the positive electrode core body (metal foil), the positive electrode core body exposed lower portion 14 a disposed on the bottom surface portion 30 c side of the box-shaped insulating sheet 301 has a side surface portion 30 d (square shape). In the cross section parallel to the first side wall 12a of the exterior body, the lowermost part is in a semicircular state. That is, there is a possibility that the positive electrode core body may come into contact with the central portion of the boundary line between the bottom surface portion 30c and the side surface portion 30d of the box-shaped insulating sheet 301, but it is difficult to contact both end portions of the boundary line. ing.

  When a very strong impact or vibration is applied to the prismatic secondary battery, particularly when an impact or vibration in a direction perpendicular to the pair of first side walls 12a and 12a of the rectangular exterior body is applied, the positive electrode current collector 16 and the negative electrode current collector are provided. The electric body 181 is deformed, and the positive electrode core exposed lower portion 14a or the negative electrode core exposed portion 15a may collide with the central portion of the boundary line of the insulating sheet 301. At this time, if there is a cut, thin wall portion or perforation at the center of the boundary line, these are inferior in strength to the surrounding unprocessed sheet. There is a possibility that the portion is cut and the positive electrode core body jumps out of the insulating sheet 301 and comes into contact with the rectangular exterior body. However, in this embodiment, there are no cuts, thin portions, or perforations in the center portion of the boundary line, and there is no possibility of being cut by the positive electrode core. Since it is the same structure also on the negative electrode side, there is no possibility that the central part of the boundary line is cut by the negative electrode core. Therefore, the square secondary battery of the present embodiment can prevent a short circuit between the positive electrode or the negative electrode and the square outer casing caused by vibration or the like.

  On the other hand, both end portions of the boundary line do not come into contact with the positive electrode core body or the negative electrode core body due to very strong impact, vibration, or the like. The body or the negative electrode core does not jump out of the insulating sheet 301.

  Note that, in the boundary between the bottom surface portion 30c of the insulating sheet 301 and the second folded portion 30f, the region of the central portion where nothing is provided between the cuts 40, 40 which are the foldable portions at both ends is flat. It has been found that an appropriate length exists in relation to the thickness of the cylindrical wound electrode body 11 (more specifically, the positive electrode core exposed portion 14 and the negative electrode core exposed portion 15 which are the end portions). Hereinafter, description will be made with reference to FIG.

  FIG. 6 is a schematic view in which a wound electrode body (positive electrode core exposed portion 14 or negative electrode core exposed portion 15) is observed along the winding axis, and a portion close to the bottom surface of the insulating sheet 301 is enlarged. . In order to facilitate the explanation, only the positive electrode core exposed portion 14 or the negative electrode core exposed portion 15 and the bottom surface of the insulating sheet 30 are displayed. Here, the thickness (the length in the direction parallel to the bottom surface 12c in the plane perpendicular to the winding axis) of the wound electrode body (the positive electrode core exposed portion 14 or the negative electrode core exposed portion 15) is 2r. Here, the thickness 2r of the wound electrode body is the thickness of the thickest portion. The lower end of the wound electrode body (positive electrode core exposed portion 14 or negative electrode core exposed portion 15) is semicircular, and its diameter is 2r. Also, let A be the distance between the wound electrode body (positive electrode core exposed portion 14 or negative electrode core exposed portion 15) and the bottom surface of the insulating sheet 301.

In this case, at the boundary between the bottom surface portion 30c of the insulating sheet 301 and the second folded portion 30f, the length of the central region where nothing is provided between the cuts 40, 40 which are the foldable portions at both ends. The ^length is preferably larger than {r ² − (r−A) ² } ^1/2 . This is a range in which the positive electrode core body or the negative electrode core body does not jump out of the insulating sheet 301 even by a very strong impact or vibration obtained by repeating the experiment.

(Modification)
The shape of the insulating sheet is not limited to the shape shown in FIG. For example, shapes such as the insulating sheets 302 and 303 shown in FIGS. 7 and 8 can be cited as a first modification and a second modification, respectively.

  In the first modification shown in FIG. 7, the insulating sheet 302 in FIG. 3 is different from the insulating sheet 301 in FIG. 3 in that the front portion 30 a of the insulating sheet 302 is also provided with a pair of side surface portions 30 g and a pair of first folded portions 30 h. It is different, but otherwise it is the same. Therefore, also in the first modified example, the boundary line between the bottom surface part 30c and the second folded part 30f is provided with a cut that is a foldable part at both ends, and the central part has no foldable part and is adjacent to the boundary line. The sheet has the same structure as the part to be performed.

  In the second modification shown in FIG. 8, the second folded portion 30f is changed to a pair of side surface portions 30d, and first folded portions 30e, 30g are provided on both sides of the pair of side surface portions 30d. . Therefore, in the second modified example, the boundary line between the bottom surface part 30c and the pair of side surface parts 30d is provided with a cut that is a foldable part at both ends, and the central part has no foldable part and is adjacent to the boundary line. The seat has the same structure as the part.

  Also in the 1st and 2nd modification, there exists an effect similar to the insulating sheet of FIG.

(Embodiment 2)
The second embodiment is different from the first embodiment in that the bendable portion is a perforation, and the other points are the same as those in the first embodiment. Therefore, the differences from the first embodiment will be described below.

  As shown in FIGS. 9 and 10, perforations 41 are formed in the insulating sheet 304 of the present embodiment as easy-to-bend portions. The present embodiment has the same effects as those of the first embodiment, and the mechanical strength of the easy-to-bend portion is larger than that of the first embodiment.

(Embodiment 3)
The third embodiment is different from the first embodiment in that the easy-to-bend portion is a thin-walled portion, and the other points are the same as those in the first embodiment. Therefore, the differences from the first embodiment will be described below.

  As shown in FIGS. 11, 12, 13, and 14, the insulating sheet 305 of the present embodiment is formed with a thin portion 42 as an easily bendable portion. The thin portion 42 is a portion where the thickness of the insulating sheet 305 is smaller than the surroundings. The present embodiment has the same effects as those of the first embodiment, and the mechanical strength of the easy-to-bend portion is larger than that of the first embodiment.

(Embodiment 4)
The fourth embodiment is different from the third embodiment in that a thin portion is formed in the central region, and the other points are the same as those in the third embodiment. Therefore, differences from the first embodiment will be described below.

  As shown in FIGS. 15, 16, 17, and 18, the insulating sheet 306 of the present embodiment has a first thin portion 43 formed as a foldable portion, and the second thin wall also in the central region to be folded. Part 50 is formed. The second thin portion 50 is formed to be thicker than the first thin portion 43. This embodiment has the same effect as the first embodiment, has a higher mechanical strength than the first embodiment, and can prevent a break in the central region, and further has a second thin portion 50. Therefore, it is easier to bend.

(Other embodiments)
The above-described embodiment is an exemplification of the present invention, and the present invention is not limited to these examples, and these examples may be combined or partially replaced with known techniques, common techniques, and known techniques. Also, modified inventions easily conceived by those skilled in the art are included in the present invention.

  In the above embodiment, the cuts are provided as the easy-to-bend parts at both ends of the boundary between the side surface and the bottom surface of the insulating sheet, but may be perforated or thin-walled instead of the cut. A plurality of these types may be used. It can be said that the perforation is a series of small cuts. In the case of forming the thin wall portion, it is preferable to form a thin wall portion by denting the surface facing the wound electrode body, since it can be prevented from being caught by the rectangular exterior body when being bent and inserted into the rectangular exterior body.

  In the above-described embodiment, an example in which the small folded piece-like second folded portion (first region) 30f is disposed outside the side surface portion 30d has been described. However, the small folded piece-shaped second folded portion (first region) is illustrated. ) 30f can also be arranged inside the side portion 30d. When the small tongue-like second folded portion (first region) 30f is arranged outside the side surface portion 30d, the wound electrode body 11 covered with the insulating sheet 301 is inserted into the rectangular exterior body 12. It is preferable because the lower end portion of the side surface portion 30d can be prevented from being caught by the opening of the rectangular exterior body 12.

  The prismatic secondary battery according to the present invention is a conventional prismatic battery except that a foldable portion is provided at both ends of the boundary between the bottom region and the first region of the insulating sheet, and a foldable portion is not provided at the center portion. It can be manufactured by the same method as the secondary battery.

  In the above-described embodiment, a single polypropylene sheet having a thickness of 150 μm is used as the insulating sheet by cutting it into a specific dimension, but any material having flexibility and insulating properties is used as the insulating sheet. Any molding method can be employed. For example, a resin molded into a box shape can be used, and not only polypropylene but also those made of polyethylene, polyphenylene sulfide, polyether ether ketone, nylon, etc. can be used. .

  In addition, it is preferable that the thickness of an insulating sheet is 100 micrometers-500 micrometers, It is more preferable that it is 100 micrometers-300 micrometers, It is further more preferable that they are 100 micrometers-200 micrometers.

  When providing a thin part as an easily bendable part, it is preferable that the thickness of a thin part is 80 micrometers or less, and it is more preferable that it is 75 micrometers or less.

  When the thin portion is used, the thickness of the thin portion is preferably 75% or less, more preferably 50% or less of the thickness of the portion where the thin portion is not formed.

  Moreover, it is preferable that the density of a thin part is higher than the density of another part. In order to form such a thin portion, it is preferable to form the thin portion on the insulating sheet by pressing the insulating sheet. By such a method, the part which becomes a thin part is compressed by press work, and becomes higher density than another part. With such a configuration, the insulating sheet can be prevented from being broken.

  The rectangular exterior body 12 and the sealing plate 13 are made of metal, and are preferably made of, for example, aluminum, aluminum alloy, iron, or iron alloy.

In the boundary between the bottom surface portion of the insulating sheet and the second folded portion, which is described from FIG. 6, the region of the central portion that is sandwiched between the bendable portions at both ends is the second, third embodiment. Even when the easy-to-bend portion is a perforation or a thin-walled portion, or when a thin-walled portion is also provided in the central portion of the fourth embodiment, it is larger than {r ² − (r−A) ² } ^1/2 It is preferable.

  In the prismatic secondary battery, the boundary between the bottom region and the first region exists at two locations on the positive electrode core exposed portion side and the negative electrode core exposed portion side. The present invention may be applied to at least one of the two locations. However, it is preferable that the present invention is applied to both.

DESCRIPTION OF SYMBOLS 10: Square secondary battery 11: Winding type electrode body 12: Square exterior body 12a: 1st side wall 12b: 2nd side wall 12c: Bottom surface 13: Sealing plate 14: Positive electrode core body exposed part 14a: Positive electrode core body exposed lower part 15 : Negative electrode core exposed part 16: Positive electrode current collector 16a: Main body part 16b: Rib 17: Positive electrode terminal 181: Negative electrode current collector 181a: Main body part 181b: Rib 182: Negative electrode current collector receiving part 182a: Main body part 182b: Rib 19: Negative electrode terminal 20, 21: Insulating member 30c: Bottom portion (bottom region)
30f: Second folded portion (first region)
40: Cut (easy to bend)
41: perforation (foldable part)
42: Thin part (foldable part)
43: 1st thin part (folding easy part)
50: 2nd thin part 301-303: Insulation sheet 304-306: Insulation sheet

Claims (7)

A box-shaped metal square exterior body having one open surface;
A sealing plate for sealing the opening;
A wound electrode body in which a positive electrode and a negative electrode are wound through a separator, and is accommodated in the rectangular exterior body,
An insulating sheet disposed between the wound electrode body and the rectangular exterior body,
The rectangular exterior body includes a bottom surface that faces the opening, a pair of first side walls that face each other, and a pair of second side walls that have an area larger than the area of the first side wall and face each other. And
The wound electrode body has a positive electrode core exposed portion wound around one end in the winding axis direction, and a negative electrode core exposed around the other end in the winding axis direction. And a winding axis is accommodated in the rectangular exterior body in parallel with the bottom surface of the rectangular exterior body,
The positive electrode core exposed portion is disposed on one side of the pair of first side walls,
The negative electrode core exposed portion is disposed on the other side of the pair of first side walls,
The insulating sheet includes a bottom region disposed between the wound electrode body and the bottom surface of the rectangular exterior body, and extends from the bottom region toward the sealing plate and the first side wall and the winding. A first region disposed between the mold electrode body and
At both ends of the boundary line between the bottom region and the first region, a bendable portion composed of at least one of a portion having a smaller thickness than the periphery and a portion at least partially cutting is formed,
A prismatic secondary battery in which the foldable portion is not formed at the center of the boundary line.   The length of the area | region where the said bendable part provided in the center part of the said boundary line is not formed is 40% or more and 95% or less with respect to the thickness of the said winding type electrode body. Square rechargeable battery.   The prismatic secondary battery according to claim 1, wherein the bendable part is at least one of a cut line, a thin part, and a perforation. The bendable part is a thin part,
4. The prismatic secondary battery according to claim 1, wherein the thin portion is formed by recessing a surface of the insulating sheet that faces the wound electrode body. 5. A box-shaped metal square exterior body having one open surface;
A sealing plate for sealing the opening;
A wound electrode body in which a positive electrode and a negative electrode are wound through a separator, and is accommodated in the rectangular exterior body,
An insulating sheet disposed between the wound electrode body and the rectangular exterior body,
The rectangular exterior body includes a bottom surface that faces the opening, a pair of first side walls that face each other, and a pair of second side walls that have an area larger than the area of the first side wall and face each other. And
The wound electrode body has a positive electrode core exposed portion wound around one end in the winding axis direction, and a negative electrode core exposed around the other end in the winding axis direction. And a winding axis is accommodated in the rectangular exterior body in parallel with the bottom surface of the rectangular exterior body,
The positive electrode core exposed portion is disposed on one side of the pair of first side walls,
The negative electrode core exposed portion is disposed on the other side of the pair of first side walls,
The insulating sheet includes a bottom region disposed between the wound electrode body and the bottom surface of the rectangular exterior body, and extends from the bottom region toward the sealing plate and the first side wall and the winding. A first region disposed between the mold electrode body and
At both ends of the boundary line between the bottom region and the first region, a bendable portion composed of a portion having a smaller thickness than the periphery is formed,
A square secondary battery in which a thickness of a central portion of the boundary line is larger than a thickness of the easily bendable portion.   The length of the part which has thickness larger than the thickness of the said bendable part in the center part of the said boundary line is 40% or more and 95% or less with respect to the thickness of the said winding type electrode body. Square rechargeable battery.   The prismatic secondary battery according to claim 6, wherein a thickness of the easily bendable portion is 75% or less with respect to a thickness of a central portion of the boundary line.