JP2018049708A - Power storage device and method of manufacturing power storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power storage device with excellent cycle performance.SOLUTION: A power storage device according to the present invention comprises: a wound electrode group around which a positive electrode and a negative electrode are wound; a case which houses the wound electrode group; and a pressing member which presses the case. The wound electrode group has: two curved surfaces located at the ends on both sides; and a pair of wide surfaces arranged between the two curved surfaces. The cell case has a pair of cell case surfaces which face the pair of wide surfaces. At least one of the pair of cell case surfaces has, at its center, a protrusion protruding toward the wound electrode group. A pressing portion of the pressing member is located on both sides of the protrusion on the cell case surface.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a power storage device and a method for manufacturing the power storage device.

  Power storage devices such as lithium ion secondary batteries are widely used in electronic devices such as personal computers and communication terminals, automobiles, and the like because of their high energy density.

  As the power storage device, a positive electrode is connected via a separator in order to absorb the twist generated between the electrodes of the power generation element and suppress an increase in battery thickness and to exhibit excellent battery characteristics by reducing the gap between the electrodes. In a non-aqueous secondary battery in which a power generation element wound in a spiral shape in a state of being laminated with a negative electrode is housed in a rectangular flat outer can, the outer can is made of an aluminum Al alloy and is housed in the outer can A non-aqueous prismatic secondary battery is known in which protrusions that press the generated power generation element are integrally formed on the inner side of a pair of opposed long side surfaces of the outer can (Japanese Patent Application Laid-Open (JP-A)). 2005-243274).

JP 2005-243274 A

  However, as a result of intensive studies by the present inventors, there are some in which protrusions that press the power generation element stored in the outer can are integrally formed on the inner side of a pair of opposed long side surfaces of the outer can. It was found that the cycle performance was not improved sufficiently.

  The present invention has been made based on the above circumstances, and an object thereof is to provide a power storage device having excellent cycle performance and a method for manufacturing the power storage device.

  The invention made to solve the above problems comprises a wound electrode group in which the positive electrode and the negative electrode are wound, a case for housing the wound electrode group, and a pressing member for pressing the case, The wound electrode group has two curved surface portions located at both end portions and a pair of wide surface portions between the two curved surface portions, and the cell case is a pair facing the pair of wide surface portions. The cell case surface, at least one of the pair of cell case surfaces has a convex portion in the center that protrudes toward the wound electrode group side, and the pressing portion of the pressing member is the cell case surface. It is the both side part of the said convex part.

Another invention made in order to solve the above-described problem includes a wound electrode group in which a positive electrode and a negative electrode are wound, and a case that accommodates the wound electrode group, and the wound electrode group includes: , Having two curved surface portions located at both ends and a pair of wide surface portions between the two curved surface portions, and the cell case has a pair of cell case surfaces opposed to the pair of wide surface portions Preparing an electrode group housing case in which at least one of the pair of cell case surfaces has a convex portion protruding in the center toward the wound electrode group side, and both sides of the convex portion of the electrode group housing case It is a manufacturing method of the electrical storage apparatus which has a part pressed to the said winding type electrode group side with a press member.

  The power storage device of the present invention and the power storage device manufactured by the manufacturing method of the present invention are excellent in cycle performance.

FIG. 1 is a longitudinal sectional view schematically showing an internal configuration of a power storage device according to an embodiment of the present invention. FIG. 2 is a perspective view schematically showing a wound electrode group in the power storage device of FIG. FIG. 3 is a side view schematically showing a wound electrode group in the power storage device of FIG. 1. FIG. 4 is a front view schematically showing a wound electrode group in the power storage device of FIG. 1. FIG. 5 is a front view schematically showing the power storage device of FIG. 1. FIG. 6 is a longitudinal sectional view schematically showing one stage of the manufacturing process in the method for manufacturing the power storage device of FIG. FIG. 7 is a longitudinal sectional view schematically showing one stage of the manufacturing process in the method for manufacturing the power storage device of FIG. 1. 6 is a longitudinal sectional view schematically showing a power storage device of Comparative Example 1. FIG.

  A power storage device according to one embodiment of the present invention includes a wound electrode group in which a positive electrode and a negative electrode are wound, a case that houses the wound electrode group, and a pressing member that presses the case. The circular electrode group has two curved surface portions located at both end portions and a pair of wide surface portions between the two curved surface portions, and the cell case is opposed to the pair of wide surface portions. Having a case surface, at least one of the pair of cell case surfaces has a convex portion in the center protruding toward the wound electrode group side, and the pressing portion of the pressing member is the surface of the cell case surface It is the both side part of a convex part. In addition, that the cell case surface has a convex portion in the center means that the convex portion is formed at a position where the convex portion comes into contact with the wide surface portion of the wound electrode group. The both side parts of the convex part of the cell case surface mean the part of the cell case surface that is located on both side ends from the center where the convex part is formed and has no convex part.

  The power storage device is excellent in that the wide surface portion of the wound electrode group is pressed by the convex portion of the cell case, and further, both side portions of the convex portion of the cell case are pressed by the pressing member toward the wound electrode group side. Cycle performance. The cause of this is not always clear, but the wide surface portion of the wound electrode group is pressed by the convex portion of the cell case, so that initial gas accumulation and distortion of the electrode plate are reduced, and the convex portion of the cell case is reduced by the pressing member. It is considered that the partial internal pressure variation inside the cell with the progress of the cycle test is suppressed by pressing both side portions of the electrode toward the wound electrode group. This suppresses uneven salt concentration in the electrode surface due to variations in internal pressure, and provides excellent cycle performance.

  In the power storage device, the pair of cell case surfaces preferably have the convex portions, and the pair of wide surface portions of the wound electrode group are pressed by the convex portions, whereby the cycle performance of the power storage device is improved. Improvement is achieved.

  The convex portion may press a portion of the wide surface portion corresponding to the winding axis side of the innermost pair of turn portions of the wound electrode group, thereby further suppressing variation in internal pressure. Thus, the cycle performance of the power storage device can be improved. The innermost turn portion of the wound electrode group means a portion of the positive electrode and the negative electrode that are wound and is located on the innermost periphery and folded back for winding.

  The protrusion amount of the convex part is preferably 0.02 times or more of the distance between the pair of cell case surfaces, whereby the variation in internal pressure can be further suppressed, and the cycle performance of the power storage device can be improved. Figured. In addition, the protrusion amount of the said convex part means the sum total of the maximum protrusion amount of the said convex part, when a pair of cell case surface has the said convex part which each opposes, and other than that (For example, one side) In the case where only the cell case surface has the convex portion), it means the maximum protrusion amount of one convex portion.

  A method for manufacturing a power storage device according to one embodiment of the present invention includes a wound electrode group in which a positive electrode and a negative electrode are wound, and a case that houses the wound electrode group, and the wound electrode group includes: Two curved surface portions located at both end portions and a pair of wide surface portions between the two curved surface portions, the cell case has a pair of cell case surfaces facing the pair of wide surface portions, Preparing an electrode group housing case in which at least one of the pair of cell case surfaces has a convex portion protruding in the center toward the wound electrode group side, and both side portions of the convex portion of the electrode group housing case Is pressed against the wound electrode group side by a pressing member.

  In the power storage device manufactured by this manufacturing method, the wide surface portion of the wound electrode group is pressed by the convex portion of the cell case, and both side portions of the convex portion of the cell case are pressed by the pressing member toward the wound electrode group side. As a result, excellent cycle performance is achieved.

[Power storage device]
Hereinafter, embodiments of a power storage device according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a power storage device according to an embodiment of the present invention. The power storage device of this embodiment includes a wound electrode group 1, a cell case 8 that houses the wound electrode group 1, and a pressing member 12 that presses the cell case 8. As shown in FIG. 2, the wound electrode group 1 has a positive electrode 2 a and a negative electrode 2 b wound, and a pair of wide surface portions between the two curved surface portions 5 located at both end portions and the two curved surface portions 5. 6. The cell case 8 has a pair of cell case surfaces 9 opposed to the pair of wide surface portions 6, and at least one of the pair of cell case surfaces 9 protrudes toward the wound electrode group 1 side. It has part 9a in the center. The pressing member 12 presses both side portions 9b of the convex portion 9a of the cell case surface 9 toward the wound electrode group 1 side. In the power storage device of this embodiment, the wide surface portion 6 of the wound electrode group 1 is pressed by the convex portion 9a of the cell case 8, and both side portions 9b of the convex portion 9a of the cell case 8 are wound by the pressing member 12. By being pressed to the electrode group 1 side, excellent cycle performance is achieved. In addition, the electrical storage apparatus of this embodiment is storage batteries, such as a nonaqueous electrolyte secondary battery, for example.

<Winded electrode group>
The wound electrode group 1 is configured by winding a sheet body 2. The sheet body 2 includes the positive electrode 2a, the separator 2c, and the negative electrode 2b (see FIG. 2), and the positive electrode 2a, the separator 2c, and the negative electrode 2b are stacked in this order.

  The wound electrode group 1 has two curved surface portions 5 located at both end portions and a pair of wide surface portions 6 between the two curved surface portions 5. The curved surface portion 5 is a surface formed by the turn portion of the sheet body 2 that is wound as described above. Specifically, the sheet body 2 is folded from one wide surface portion 6 to the other wide surface portion 6. It is a surface formed by being bent. A pair of said wide surface part 6 is a surface which respectively opposes the cell case surface 9 mentioned later, and is pressed by the convex part 9a mentioned later. More specifically, each of the pair of wide surface portions 6 is substantially the same as the flat surface 3a on the innermost circumference of the wound electrode group 1, that is, the wide surface portion 6 on the winding axis side of the wound electrode group 1. They are arranged in parallel. Note that “substantially parallel” means that the angle difference in the normal direction of each part is less than 10 °.

  The wide surface portion 6 has a square shape as shown in FIG. 4 when viewed from the normal direction of the wide surface portion 6. In FIG. 4, a symbol B is a boundary between the wide surface portion 6 and the curved surface portion 7. The wide surface portion 6 is perpendicular to the winding axis direction (Y direction in FIG. 4 (positioned in the wide surface portion 6) rather than the length (L1) of the sheet body 2 in the winding axis direction (X direction in FIG. 4). The length (L2) of the longitudinal direction of the sheet body 2)) is large. Here, the ratio (aspect ratio) of the length (L2) in the longitudinal direction to the length (L1) in the short direction in the wide surface portion 6 is not particularly limited, but is 1.0 or more and 1.5, for example. The following can be done.

  In addition, when winding the sheet body 2, a core material (not shown) is used, and as this core material, a conventionally known one can be adopted, but in other words, the innermost circumference of the wound sheet body 2, in other words, As shown in FIG. 3, both end edges 3b of one flat surface 3a and both end edges 3b of the other flat surface 3a are connected to a portion that contacts the outer periphery of the core member when the sheet body 2 is wound. The side surface 3c (turn part) is comprised from the curved surface in the example of illustration.

<Cell case>
As shown in FIG. 1, the cell case 8 has a pair of cell case surfaces 9 opposed to the pair of wide surface portions 6. Specifically, the cell case 8 has a pair of cell case surfaces 9 facing each other with a predetermined gap, and a pair of side wall surfaces 10 arranged to connect both ends of the pair of cell case surfaces 9. (Refer FIG.1 and FIG.5), for example, it has a rectangular parallelepiped box shape as a whole. As described above, the wound electrode group is configured so that the pair of wide surface portions 6 face the cell case 8 and the pair of side wall surfaces 10 face the pair of curved surface portions 5 as described above. 1 is housed. The cell case 8 has a lid portion 8a for closing the upper opening after the wound electrode group 1 is accommodated.

  The material of the cell case 8 is not particularly limited. For example, a plastically deformable material such as a metal such as stainless steel may be used. In the present embodiment, the convex portion 9a is configured such that the cell case surface 9 is pressed and deformed to the other cell case surface 9 side.

  The thicknesses of the cell case surface 9 and the side wall surface 10 are not particularly limited, but may be, for example, 0.2 mm or more and 1.5 mm or less. In addition, the space | interval of a pair of cell case surface 9 means the space | interval of the inner surfaces of the part (the said both-sides part 9b) pressed by the said pressing member 12. FIG. In other words, the interval between the pair of cell case surfaces 9 means the interval between the inner surfaces of the pair of cell case surfaces 9 before the formation of the convex portions 9a.

  As described above, the pair of cell case surfaces 9 have the convex portions 9a protruding toward the wound electrode group 1 in the center. The convex portion 9 a abuts on one wide surface portion 6 of the wound electrode group 1 and presses the one wide surface portion 6 toward the other wide surface portion 6. In addition, the said center means the location contact | abutted to the said wide surface part 6. FIG. Moreover, the convex part 9a formed in a pair of cell case surface 9 protrudes so that it may mutually oppose, and is formed in the surface symmetrical shape.

  As shown in FIG. 1, the protrusion 9 a gradually increases in the amount of protrusion according to the center in the longitudinal direction of the wide surface portion 6. That is, in the convex portion 9a, the projection amount (L4) at the center in the longitudinal direction of the wide surface portion 6 is larger than the projection amount on the outside in the longitudinal direction. Further, the protruding portion 9a gradually increases in the protruding amount along the center of the wide surface portion 6 in the short direction. That is, the protruding portion 9a has a protruding amount at the center in the short direction of the wide surface portion 6 larger than the protruding amount on the outside in the short direction. That is, in this embodiment, the protrusion amount of the site | part facing the center of the wide surface part 6 of the said convex part 9a is larger than another site | part.

  The ratio of the total maximum protrusion amount (L4) of the pair of convex portions 9a to the distance (L3) between the pair of cell case surfaces 9 is preferably 0.02 or more and 0.05 or less. The lower limit of this ratio is more preferably 0.03. The upper limit of this ratio is more preferably 0.04. When the ratio is equal to or higher than the lower limit, excellent cycle performance can be obtained. On the other hand, when the ratio is equal to or less than the upper limit, it is possible to prevent the wound electrode group 1 from being overloaded. Note that the maximum protrusion amount L4 of the pair of convex portions 9a is substantially the same. Note that “substantially the same” means that the difference between them is 5% or less of the median value of both.

  The ratio of the maximum protrusion amount (L4) of the one convex portion 9a to the distance (L3) between the pair of cell case surfaces 9 is preferably 0.01 or more and 0.025 or less. The lower limit of this ratio is more preferably 0.015. The upper limit of this ratio is more preferably 0.02. When the ratio is equal to or higher than the lower limit, excellent cycle performance can be obtained. On the other hand, when the ratio is equal to or less than the upper limit, it is possible to prevent the wound electrode group 1 from being overloaded.

  The convex portion forming region A is disposed in the central region of the wide surface portion 6 as shown in FIG. Specifically, it is preferable that the convex portion 9a is formed within 80% in the longitudinal direction with reference to the center of the wide surface portion 6 in the longitudinal direction (Y direction). The upper limit of the projection forming area A in the longitudinal direction is more preferably 75%. The lower limit of the projection forming area A in the longitudinal direction is preferably 40%. Excellent cycle performance is obtained when the convex portion forming region A in the longitudinal direction is within the above range.

  In other words, the convex portion is within a range of 0.1 times the longitudinal length (L2) of the wide surface portion 6 on the other side from one of the pair of boundaries B between the wide surface portion 6 and the curved surface portion 5. It is preferable that 9a is not formed, that is, the lower limit of the convex portion non-forming region is 0.1 times the length (L2) of the wide surface portion 6 in the longitudinal direction. As for the minimum of the said convex part non-formation area | region in this longitudinal direction, 0.125 time of the said length (L2) is more preferable. The upper limit of the convex part non-forming region in the longitudinal direction is preferably 0.30 times the length (L2). Excellent cycle performance can be obtained when the protrusion-free region in the longitudinal direction is within the above range. In addition, it cannot be overemphasized that the convex-shaped part which does not press the said winding type electrode group 1 may be provided in the said convex part non-formation area | region.

  It is preferable that the convex portion 9a is formed in a region of 70% or less in the short direction with respect to the short direction of the wide surface portion 6 (X direction in FIG. 4). The upper limit of the convex portion forming area A in the short direction is more preferably 65%. The lower limit of the convex portion forming region A in the short direction is preferably 35%. Excellent cycle performance is obtained when the convex portion forming region in the short direction is within the above range.

  In other words, the convex portion 9a is not formed within a range within 0.15 times the length (L1) in the short direction of the wide surface portion 6 from one of the upper end and the lower end of the wide surface portion 6 to the other side. That is, it is preferable that the lower limit of the convex portion non-forming region is 0.15 times the length (L1) of the wide surface portion 6 in the short direction. The lower limit of the convex portion non-forming region in the short direction is more preferably 0.175 times the length (L1). The upper limit of the convex portion non-forming region in the short direction is preferably 0.325 times the length (L1). Excellent cycle performance is obtained when the convex part non-forming region in the short direction is within the above range.

  The convex portion formation region A has a shape having a major axis in the longitudinal direction (Y direction) of the wide surface portion 6 when viewed from the normal direction of the cell case surface 9 (front view), specifically, As shown in FIG. 4, it has a square shape.

  Further, the convex portion 9 a presses a portion of the wide surface portion 6 that is closer to the winding axis than the innermost turn portion of the wound electrode group 1. Specifically, as shown in FIG. 4, the convex portion forming region A is located on the center side (winding shaft side) with respect to the edge 3b of the flat surface 3a.

  The cell case 8 is provided with a terminal (not shown) that is connected to a positive electrode current collector (not shown) or a negative electrode current collector (not shown) and energizes the outside. Further, the cell case 8 is filled with an electrolytic solution.

<Pressing member>
The pressing member 12 presses both side portions 9b of the convex portion 9a of the cell case surface 9 as described above. Both side portions 9 b of the convex portion 9 a are the convex portion non-forming regions of the cell case surface 9.

  In the present embodiment, the pressing member 12 includes a pair of plate-like members 13 arranged so as to sandwich the cell case 8. Although the material of this plate-shaped member 13 is not specifically limited, For example, it is comprised from metals, such as stainless steel. As shown in FIG. 5, the plate member 13 is provided wider than the cell case surface 9. That is, the length of the plate member 13 in the Y direction (direction substantially orthogonal to the winding axis direction of the sheet body 2) is shorter than the length of the cell case surface 9 in the Y direction. Specifically, the plate member 13 is provided so as not to contact the lid portion 8 a of the cell case 8.

  The pressing member 12 has a fastening member for applying a pressing force to the cell case surface 9. As shown in FIG. 1, the fastening member includes a bolt 14 that passes through the pair of plate-like members 13 and a nut 15 that is screwed to the bolt 14, and the nut 15 is fastened to the bolt 14. As a result, the cell case 8 is held between the pair of plate-like members 13, and a predetermined pressing force is applied to the cell case surface 9. Note that a plurality of pairs of the bolts 14 and nuts 15 are provided, and the plurality of pairs of bolts 14 and nuts 15 are equally arranged as viewed from the normal direction of the cell case surface 9.

The pressing force applied to the cell case surface 9 by the pressing member 12 may be, for example, 5 N / cm ² or more and 100 N / cm ² or less. The lower limit of this pressing force is preferably 10 N / cm ² . The upper limit of this pressing force is preferably 30 N / cm ² . When the pressing force is within the above range, the cell case surface 9 can be accurately pressed by the pressing member 12, and the cycle performance of the power storage device of the present embodiment can be improved.

[Method for Manufacturing Power Storage Device]
The power storage device of the embodiment is manufactured by, for example, a manufacturing method described below. In the method for manufacturing the power storage device of this embodiment, a predetermined electrode group housing case 11 is prepared, and both side portions 9b of the convex portion 9a of the electrode group housing case 11 are Pressing to the group 1 side. In the description of the manufacturing method of the present embodiment, the description of the same parts as the description of the power storage device of the above embodiment may be omitted.

(Preparation of a predetermined battery group housing case)
The predetermined electrode group housing case 11 includes a wound electrode group 1 in which the positive electrode 2a and the negative electrode 2b are wound, and a case 8 in which the wound electrode group 1 is housed. The electrode group 1 has two curved surface portions 5 located at both end portions and a pair of wide surface portions 6 between the two curved surface portions 5, and the cell case 8 faces the pair of wide surface portions 6. An electrode group housing case 11 having a pair of cell case surfaces 9 and at least one of the pair of cell case surfaces 9 projecting toward the wound electrode group 1 side in the center is prepared. Is made by The electrode group housing case 11 is filled with an electrolytic solution.

  Preparation of the predetermined electrode group housing case 11 is performed, for example, by housing the wound electrode group 1 in the cell case 8 (see FIG. 6), and after housing the wound electrode group 1 in the cell case 8, The center of at least one cell case surface 9 of the pair of cell case surfaces 9 can be deformed to the wound electrode group 1 side so as to press the wide surface portion 6 (see FIG. 7).

  Pressing toward the wound electrode group 1 by the pressing member 12 presses both side portions 9b of the convex portion 9a of the electrode group housing case 11 toward the wound electrode group 1 with the pressing member 12. (See FIG. 1). Thereby, the electrical storage apparatus of this embodiment provided with the wound electrode group 1, the cell case 8, and the pressing member 12 is manufactured.

[advantage]
In the power storage device of this embodiment, the wide surface portion 6 of the wound electrode group 1 is pressed by the convex portion 9a of the cell case 8, and both side portions 9b of the convex portion 9a of the cell case 8 are wound by the pressing member 12. By being pressed to the electrode group 1 side, excellent cycle performance is achieved. The cause of this is not necessarily clear, but in the case where the wound electrode group 1 is simply pressed by the convex portion 9a of the cell case 8 (electrode group housing case 11 shown in FIG. 7), a gas pool or electrode plate is formed immediately after manufacture. Distortion is reduced, but the internal pressure increases due to the increase in partial internal pressure variation due to multiple use, and the internal resistance increases due to the increased salt concentration in the electrode surface. . On the other hand, by applying a pressing force to the cell case surface 9 of the electrode group housing case 11 with the pressing member 12 as shown in FIG. 1, partial variations in internal pressure due to multiple use are reduced. Therefore, it is considered that the cycle performance is excellent.

  Moreover, since the convex part 9a between the both-sides part 9b pressed by the pressing member 12 presses the center area | region of the wide surface part 6 of the winding type electrode group 1 as above-mentioned in the electrical storage apparatus of this embodiment. The gas remaining between the positive electrode 2a and the negative electrode 2b of the mold electrode group 1 can be easily removed, whereby the unreacted portions of the positive electrode 2a and the negative electrode 2b can be reduced. Further, since the portion of the wound electrode group 1 that is easily affected by the swelling is pressed by the convex portion 9a, the positive electrode 2a or the negative electrode 2b is hardly distorted, and an increase in the thickness of the wound electrode group 1 is suppressed. In addition, the increase in the thickness of the power storage device and the variation in the thickness of the wound electrode group 1 can be reduced, and the swollenness of the wound electrode group 1 can be accurately suppressed during continuous use.

  Furthermore, since the power storage device of the present embodiment is provided with the convex portions 9a on the pair of cell case surfaces 9, the pressing force acting on the wound electrode group 1 can be made uniform, and the positive electrode 2a and By bringing the opposing surfaces of the negative electrode 2b close to each other, better cycle performance can be ensured.

  The convex portion 9a presses a portion of the wide surface portion 6 that is closer to the winding axis than the innermost turn portion of the wound electrode group 1, so that the sheet body 2 of the wound electrode group 1 is pressed. Since the innermost turn portion is not pressed, excessive stress concentration on the wound electrode group 1 due to the pressing force of the convex portion 9a can be suppressed, and the cycle performance of the power storage device of this embodiment can be improved. It is done.

[Other Embodiments]
The electricity storage device of the present invention is not limited to the above embodiment. In the embodiment described above, the case where each of the pair of cell case surfaces has the convex portion has been described. However, only one of the cell case surfaces may have the convex portion.

  In the above embodiment, the convex portion is formed by plastically deforming the cell case surface. However, the convex portion is configured by separately attaching a member constituting the convex portion to the inner surface of the cell case. May be.

  In the said embodiment, although the said press member demonstrated what has a pair of plate-shaped member, the specific structure of a press member is not limited to the thing of the said embodiment.

  Although the power storage device of the above embodiment has been described as having only one cell case, the present invention may have a plurality of the cell cases. Specifically, for example, a plurality of cell cases may be stacked such that the cell case surfaces face each other, and a stacked body in which the plurality of cell cases are stacked may be sandwiched between pressing members. Moreover, when it has a some cell case, it is also possible to electrically connect the winding type electrode group in each cell case, and to make an assembled battery.

[Example]
The following examples of the present invention will be described, but the following examples do not limit the scope of the present invention.

Example 1
In Example 1, the wound electrode group 1 was produced by winding the positive electrode 2a and the negative electrode 2b with the separator 2c interposed between the positive electrode 2a and the negative electrode 2b. Then, the wound electrode group 1 is accommodated in the cell case 8 through the opening of the cell case 8, the positive electrode plate lead is bonded to the battery lid, the negative electrode plate lead is bonded to the negative electrode terminal, and then the lid portion 8a is attached. A secondary battery in an uninjected state in which the nonaqueous electrolyte is not injected into the cell case is produced by fitting the cell case 8 and the lid 8a by laser welding by fitting into the opening of the cell case 8. did. Then, after injecting the nonaqueous electrolyte into the cell case 8 from the injection port provided on the side surface of the cell case 8, the injection port is sealed with a stopper, whereby a 4.15V nonaqueous electrolyte secondary battery is provided. (Electrode group accommodation case 11) was produced. In addition, the space | interval (space | interval between inner surfaces) of a pair of cell case surface 9 of this cell case 8 was 5.08 mm.

And the electrode group accommodation case 11 which each has the said convex part 9a in the center of a pair of cell case surface 9 was formed by deform | transforming this pair of cell case surface 9 (refer FIG. 7). In this case, a torque wrench was used, and the maximum protrusion amount of the protrusion 9a was 0.085 mm, and the total maximum protrusion amount of the pair of protrusions 9a was 0.17 mm. Further, the convex portion 9a is formed in a region of 52% in the short direction with respect to the longitudinal direction of the wide surface portion 6 and in a region of 45% or less in the short direction with respect to the short direction of the wide surface portion 6. did. The electrode group housing case 11 was sandwiched between a pair of stainless steel plates 13 having a thickness of 3 mm as shown in FIG. 1, thereby applying a pressing force to both side portions 9 b of the convex portion 9 a of the cell case surface 9. This pressing force was 22 N / cm ² .

(Comparative Examples 1-3)
The power storage device of Comparative Example 1 was the same as that of Example 1 except that the cell case did not have a convex portion on the cell case surface. In the power storage device of Comparative Example 1, as shown in FIG. 8, the wound electrode group 101 is accommodated in the cell case 108, and the cell case 108 is pressed by the pressing member 108.

  The power storage device of Comparative Example 2 was the same as that of Example 1 except that no pressing member was used. That is, the power storage device of Comparative Example 2 has a convex portion as shown in FIG.

  The power storage device of Comparative Example 3 was the same as that of Example 1 except that the cell case had no protrusion on the cell case surface and no pressing member was used. That is, the power storage device of Comparative Example 3 is in a state where the wound electrode body is simply housed in the cell case as shown in FIG.

(test)
About the electrical storage apparatus of Example 1 and Comparative Examples 1-3, the charge / discharge cycle test was done on 25 degreeC conditions, and the change of the capacity | capacitance retention in 150 cycles was measured. The capacity retention rate is a percentage of the discharge capacity after each cycle with respect to the initial (0 cycle) discharge capacity, and the capacity retention rate after 150 cycles is 95.7 in Example 1. %, Comparative Example 1 was 66.6%, Comparative Example 2 was 86.1%, and Comparative Example 3 was 92.1%.

(Evaluation)
As is clear from the test results, the power storage device of Example 1 in which the above-described convex portions are provided on the cell case surface and both side portions of the convex portions are pressed by pressing members is the power storage device of Comparative Examples 1-3. Excellent cycle performance is demonstrated compared to the equipment.

  As described above, since the power storage device according to the present invention is excellent in cycle performance, it is suitably used, for example, as various lithium ion secondary batteries.

DESCRIPTION OF SYMBOLS 1 Winding type electrode group 2 Sheet | seat body 3a Flat surface 3b Edge 3c of a flat surface Side surface 5 Curved surface part 6 Wide surface part 8 Cell case 9 Cell case surface 9a Convex part 9b Both side part 10 Side wall surface 11 Electrode group accommodation case 12 Press member 13 Plate-like member 14 Bolt 15 Nut A Convex-forming portion B Boundary between the curved surface portion and the wide surface portion (at the outermost periphery of the electrode group)

Claims (5)

A wound electrode group in which the positive electrode and the negative electrode are wound, a case that accommodates the wound electrode group, and a pressing member that presses the case,
The wound electrode group has two curved surface portions located at both end portions and a pair of wide surface portions between the two curved surface portions,
The cell case has a pair of cell case surfaces facing the pair of wide surface portions,
At least one of the pair of cell case surfaces has a convex portion at the center that protrudes toward the wound electrode group side,
The power storage device, wherein the pressing portion of the pressing member is both side portions of the convex portion of the cell case surface.   The power storage device according to claim 1, wherein each of the pair of cell case surfaces has the convex portion.   3. The power storage device according to claim 1, wherein the convex portion presses a portion of the wide surface portion corresponding to the winding axis side of the innermost pair of turn portions of the wound electrode group.   4. The power storage device according to claim 1, wherein an amount of protrusion of the convex portion is 0.02 times or more of an interval between the pair of cell case surfaces. A wound electrode group in which a positive electrode and a negative electrode are wound, and a case that accommodates the wound electrode group, wherein the wound electrode group includes two curved surface portions located at both end portions and the 2 A pair of wide surface portions between the two curved surface portions, the cell case has a pair of cell case surfaces opposed to the pair of wide surface portions, and at least one of the pair of cell case surfaces is the above Preparing an electrode group housing case having a convex portion projecting toward the wound electrode group side in the center; and both side portions of the convex portion of the electrode group housing case are placed on the wound electrode group side by a pressing member. The manufacturing method of the electrical storage apparatus which has pressing.

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