JPWO2012004886A1 - Secondary battery and method of manufacturing flat wound electrode group - Google Patents

Abstract

In the secondary battery, the shaft core 30 has a thickness TB0 at the center portion larger than the thickness TA0 at both end portions in the width direction. At the time of winding, the positive electrode 1, the negative electrode 2, and the separators 3a and 3b are given tensions A and A ′ in the length direction. With the tensions A and A ′, An inward tightening force B directed toward the shaft core 30 acts on the positive electrode 1, the negative electrode 2, and the separators 3a and 3b. The positive electrode 1, the negative electrode 2, and the separators 3 a and 3 b have elastic force spreading in the outer peripheral direction, but the positive force 1, the negative electrode 2, and the separators 3 a and 3 b are tightly tightened while the tightening force B resists this elastic force. . As a result, no gap is generated between the positive electrode 1 and the negative electrode 2, and the density of the flat wound electrode group 4 is increased, and the capacity of the secondary battery can be increased.

Description

  The present invention relates to a secondary battery mounted on a vehicle or the like and a method of manufacturing a flat wound electrode group used for the secondary battery.

Technical background

  In response to social trends in global environmental protection, there is an urgent need for the practical use and popularization of secondary batteries for driving vehicles such as hybrid cars and electric cars. The structure of the secondary battery for driving a vehicle is that a positive and negative electrode sheet (positive and negative electrode plate), a separator for insulation between the positive and negative electrode plates, and an electrolyte solution are made of metal or resin. A device provided with an external terminal that is housed in an airtight container and joined to both electrodes of the power generation element is widely known.

  Most secondary batteries that have been put to practical use have a cylindrical outer shape. However, secondary batteries for driving vehicles require high output and large capacity. Therefore, an assembled battery in which more than 100 secondary batteries are combined is required. Therefore, in order to improve the mounting density, prismatic secondary batteries have been actively put into practical use, and the shape of the electrode group used in the prismatic secondary battery is flat.

  In the secondary battery described in Patent Document 1, as a method of forming a flat wound electrode group, a plate-shaped core material is arranged at the center of the electrode group, and a positive electrode plate, a negative electrode plate, and a gap between them are arranged. The separator is disposed by interposing and arranging.

JP 2008-47304 A

  In the secondary battery of Patent Document 1, both ends of the positive and negative electrode plates can be closely contacted between the electrodes, but in the flat portion, since the positive and negative electrode plates are not restrained in the radial direction, there is no gap between the positive and negative electrode plates. As a result, the density is lowered and the capacity may be reduced.

A secondary battery according to the first aspect of the present invention is a secondary battery comprising a flat wound electrode group formed by winding a positive electrode and a negative electrode around a shaft while being insulated with a separator, the positive electrode, the negative electrode, The separator laminate is wound on the front and back surfaces of the shaft core with an upward gradient from one end portion in the winding direction to the central portion and with a downward gradient from the central portion to the other end portion in the winding direction. In this secondary battery, the laminated body generates a tightening force at the central portion of the shaft core by an internal force generated in the longitudinal direction of the laminated body by winding.
The shaft core can be formed with an inclined surface that is inclined downward from the center of the front and back surfaces toward both ends in the winding direction. It is preferable that the inclined surface extends as a gentle arc surface from the center to both ends. For example, the cross-sectional shape of the shaft core is a flat elliptical shape or a substantially elliptical shape. Both end portions of the shaft core are preferably arcuate surfaces or flat surfaces.
The shaft core may have a substantially rectangular cross-section at the center, and an inclined surface from the center toward both ends may be a flat surface or a gentle arc surface. In this example, the inclined surface may extend as a flat surface from the central portion to both end portions. Also in this example, it is preferable that both end portions of the shaft core are arc surfaces or flat surfaces. Further, the cross-sectional shape of the shaft core may be substantially rhombus.
As described above, it is preferable to reduce the weight by providing a hollow in the shaft core of various forms.
The second aspect of the present invention is a method for manufacturing a wound electrode group of a secondary battery. The wound electrode group is wound while the long positive electrode and the negative electrode are laminated on the shaft core while being insulated with a separator, and the front and back surfaces of the shaft core are inclined downward from the center to both ends. A winding surface inclined at is formed. In such a method of manufacturing a wound electrode group, one end of the innermost separator is welded to the winding surface, and the shaft core is rotated while applying tension while alternately laminating positive and negative electrodes between the separators. And turn around.
When rotating the shaft core while applying tension to the laminate of the positive electrode, the negative electrode and the separator, an internal force is applied to the laminate extending between one end portion of the shaft core and the central portion in one longitudinal direction thereof, The laminated body is preferably wound by rotating the shaft core so that an internal force is applied to the laminated body extending from the central portion of the shaft core to the other end in the other direction of the longitudinal direction.

  According to the present invention, the density of the flat wound electrode group can be increased.

The perspective view which shows the external appearance of the secondary battery by 1st Embodiment. The disassembled perspective view of the secondary battery of FIG. The perspective view which shows the structure of the flat wound electrode group of FIG. FIG. 2 is a perspective view showing the flat wound electrode group of FIG. The perspective view which shows the axial center of the secondary battery of FIG. The perspective view which shows the state which has arrange | positioned the positive / negative electrode and the separator to the axial center of FIG. (A) is sectional drawing which shows the state when winding a positive / negative electrode and a separator around the axial center of FIG. 5, (b) is a cross-sectional schematic diagram explaining the virtual inclined surface of an axial center. Sectional drawing which shows the state which advanced winding rather than the state of Fig.7 (a). Sectional drawing which shows the axial center in 2nd Embodiment of the secondary battery by this invention. Sectional drawing which shows the axial center in 3rd Embodiment of the secondary battery by this invention. Sectional drawing which shows the axial center in 4th Embodiment of the secondary battery by this invention. Sectional drawing which shows the axial center in 5th Embodiment of the secondary battery by this invention. Sectional drawing which shows the axial center in 6th Embodiment of the secondary battery by this invention. Sectional drawing which shows the axial center in 7th Embodiment of the secondary battery by this invention. Sectional drawing which shows the axial center in 8th Embodiment of the secondary battery by this invention. The perspective view which shows the axial center in 9th Embodiment of the secondary battery by this invention. The perspective view which shows the axial center in 10th Embodiment of the secondary battery by this invention. Sectional drawing which shows the modification of the secondary battery by this invention. Sectional drawing which shows the modification of the secondary battery by this invention.

[First embodiment]
A first embodiment in which the present invention is applied to a flat rectangular lithium ion secondary battery will be described with reference to FIGS.

[Overall configuration of prismatic battery]
1 to 4, a rectangular battery 20 is configured by housing a flat wound electrode group 4 in a battery container 13 via an insulating sheet 12. The rectangular opening of the battery container 13 is sealed by laser welding a rectangular battery lid 9 to the battery container 13. The battery lid 9 is provided with a positive external terminal 7 and a negative external terminal 8. Electric power is supplied to the external load via the external terminals 7 and 8, or external generated power is charged to the wound electrode group 4 via the external terminals 7 and 8.

  As shown in FIG. 2, a positive electrode connection member 5 is connected to the positive electrode lead 1a of the wound electrode group 4 by ultrasonic welding, and the positive electrode connection member 5 is connected to the positive electrode external terminal 7 of the flat lithium ion secondary battery. It is connected to the. On the other hand, a negative electrode connection member 6 is connected to the negative electrode lead 2a of the wound electrode group 4 by ultrasonic welding, and the negative electrode connection member 6 is connected to the negative electrode external terminal 8 of the flat lithium ion secondary battery.

  The connection members 5 and 6 and the external terminals 7 and 8 are electrically insulated from the battery lid 9 by an insulating material (not shown). In addition, a sealing material (not shown) is provided in the through hole of the battery lid 9 to prevent liquid leakage from the battery container.

  The battery lid 9 is provided with a liquid injection port 11 for injecting an electrolytic solution into the battery container 13, and the liquid injection port 11 is sealed with a liquid injection plug after the injection of the electrolytic solution. The battery cover 9 is also provided with a gas discharge valve 10. When the pressure in the battery container rises, the gas discharge valve 10 opens to discharge gas from the inside, and the pressure in the battery container is reduced.

  Both the battery container 13 and the battery lid 9 are made of an aluminum alloy. The positive side connecting member 5 and the external terminal 7 are made of an aluminum alloy, and the negative side connecting member 6 and the external terminal 8 are made of a copper alloy.

[Entire configuration of wound electrode group]
As shown in FIGS. 3 and 4, the wound electrode group 4 is configured by winding the positive and negative electrodes 1 and 2 in a flat shape in an insulated state while interposing separators 3 a and 3 b around an axis 30. . As shown in FIG. 5, the shaft core 30 has a substantially flat elliptical cross section. Details of the shaft core 30 will be described later.

  As shown in FIG. 3, the positive and negative electrodes 1 and 2 have electrode layers 1b and 2b obtained by applying an active material mixture on a sheet-like positive and negative electrode current collector foil, and the width direction (winding direction) of each electrode foil The positive and negative electrode leads 1a and 2a to which no active material mixture is applied are provided at one end in the direction perpendicular to each other. Accordingly, the positive and negative electrode leads 1a and 2a are formed at positions opposite to each other in the width direction (axial center extending direction) of the wound electrode group 4. As described above with reference to FIG. 2, the positive electrode connecting member 5 is connected to the positive electrode lead 1a of the wound electrode group 4 by ultrasonic welding, and the positive electrode connecting member 5 is connected to the positive electrode external terminal of the flat lithium ion secondary battery. 7 is connected. On the other hand, a negative electrode connection member 6 is connected to the negative electrode lead 2a of the wound electrode group 4 by ultrasonic welding, and the negative electrode connection member 6 is connected to the negative electrode external terminal 8 of the flat lithium ion secondary battery.

In the production of the positive electrode 1, a lithium-containing double oxide powder as a positive electrode active material, scaly graphite as a conductive material, and polyvinylidene fluoride (PVDF) as a binder are mixed at a weight ratio of 85: 10: 5, A slurry kneaded with N-methylpyrrolidone (NMP) as a dispersion solvent is applied to both sides of an aluminum foil having a thickness of 20 μm. Thereafter, drying, pressing, and cutting were performed to obtain a positive electrode 1 having a width of 80 mm, a thickness of 130 μm, and a length of 4 m at a portion where the active material mixture layer was disposed.
In addition, it has the part by which the active material mixture layer formed continuously was not distribute | arranged in the one end side extended in the longitudinal direction of aluminum foil, and let this part be the positive electrode lead 1a.

  In producing the negative electrode 2, amorphous carbon powder as a negative electrode active material, PVDF as a binder, and NMP as a dispersion solvent are added and kneaded slurry on both sides of a rolled copper foil having a thickness of 10 μm. Applied. Thereafter, the negative electrode 2 having a width of 84 mm, a length of 4.4 m, a predetermined thickness, and a predetermined adhesion strength at a portion where the active material mixture layer was disposed was obtained by dry pressing and cutting.

  The thickness of one side of the active material synthesis layer of the negative electrode 2 is desirably 60 μm or more and 100 μm or less. When the thickness is less than 60 μm, the capacity of the battery is insufficient. When the thickness is 100 μm or more, the active material mixture layer at the corner of the innermost electrode may be peeled off and dropped off.

The adhesion strength between the active material mixture layer of the negative electrode 2 and the negative electrode metal foil is preferably 0.05 N / mm or more and 1.00 N / mm. If it is less than 0.05 N / mm, the active material mixture layer at the corner portion of the innermost peripheral electrode may be peeled off and dropped off. In order to set it to 1.00 N / mm or more, since it is necessary to mix the quantity of a binder excessively, the performance of a battery cannot fully be exhibited.
In addition, it has the part by which the active material mixture layer formed continuously was not distribute | arranged to the one end side extended in the longitudinal direction of rolled copper foil, and let this part be the negative electrode lead 2a.

The positive electrode connection member 5 and the negative electrode connection member 6 are connected to the positive electrode 1 and the negative electrode 2, respectively, whereby the flat wound electrode group 4 is connected to the positive electrode external terminal 7 and the negative electrode external terminal 8. When connecting the positive electrode 1 and the positive electrode connecting member 5, the positive electrode lead 1 a was deformed and brought into contact with the positive electrode connecting member 5, and then the positive electrode lead 1 a and the positive electrode connecting member 5 were ultrasonically welded. The connection process between the negative electrode 2 and the negative electrode connection member 6 is the same.
By such a connection process, the flat wound electrode group 4 is attached to the battery lid assembly including the positive and negative electrode connecting members 5 and 6, the battery lid 9 and the positive and negative electrode external terminals 7 and 8.

  When the flat wound electrode group 4 is stored in the battery case, the flat wound electrode group 4 is inserted into the battery case 13 after being put in the insulating bag 12. Thereafter, the battery lid 9 is joined to the battery case 13 by welding or the like.

  In the present specification, the positive and negative electrodes 1 and 2 are long materials made of sheet metal foil, and are also referred to as a positive electrode sheet, a negative electrode sheet, a positive electrode body, or a negative electrode plate.

[Axis core configuration and winding method]
The winding method of winding the shape of the shaft core 30 and the positive and negative electrodes 1 and 2 around the shaft core 30 will be described with reference to FIGS. 7A and 8 exaggerate the thickness of the separator 3a, the negative electrode 2, the separator 3b, and the positive electrode 1 so as to be clear.

  As shown in FIG. 5, the shaft core 30 having a substantially flat oval cross section includes a pair of wide surfaces 30W that are gently (gradually) curved in the winding direction, and a chamfered portion that connects the wide surfaces 30W. 30R. The wide surface 30W and the chamfered portion 30R are formed on the outer peripheral surface of the shaft core 30, and the wide surface 30W is a surface on which the positive and negative electrodes 1 and 2 are wound closely. That is, winding surfaces 30 </ b> W are formed on the front and back surfaces of the shaft core 30 around which the positive electrode 1, the negative electrode 2, and the separators 3 a and 3 b are wound, so as to incline with a downward gradient from the central portion toward both ends. . In the secondary battery of the first embodiment, the winding surface 30W is an arc surface that spreads at a downward gradient from at least the central part of the shaft core to both ends.

  A hole 31 that engages with a rotation shaft (not shown) of a winding device (not shown) is formed at one end face (a portion indicated by arrow C) in the axial direction of the shaft 30 at a position away from the rotation center. ing.

  The shaft core 30 is made of an insulating material such as polypropylene, but may be made of a metal material if a structure that insulates the positive and negative electrodes 1 and 2 from each other is adopted.

6 and 7 are views showing a state in which the positive and negative electrodes 1 and 2 and the separators 3a and 3b are started to be wound around the shaft core 30. FIG. 7 is a cross-sectional view taken along line VII-VII in FIG.
As shown in FIGS. 6 and 7, when winding the positive and negative electrodes 1 and 2 and the separators 3 a and 3 b around the shaft core 30, the end portion 3 E of the separator 3 is placed at the center in the width direction of one wide surface 30 W. Heat-welded and fixed, and the separator 3a, the negative electrode 2, the separator 3b, and the positive electrode 1 are stacked in this order from the inside. At the time of lamination, the end of the negative electrode 2 is disposed on the separator 3a in a state slightly shifted from the end of the separator 3a. A separator 3b is disposed on the negative electrode 2 so as to cover an end of the negative electrode 2, and a positive electrode 1 is disposed on the separator 3b.

  In this laminated state, the shaft core 30 is rotated in the T direction about the rotation axis, and the positive electrode 1, the negative electrode 2, and the separators 3a and 3b are wound in a spiral while applying tension, thereby obtaining a flat wound electrode group 4. It is done. The laminate of the positive electrode 1, the negative electrode 2, and the separators 3 a and 3 b has a rising gradient from one end portion in the winding direction to the central portion on the front and back surfaces of the shaft core 30, and from the central portion to the other end portion in the winding direction. It is wound on a downward slope.

  As shown in FIG. 5, the length of the axis 30 in the rotation axis direction is L1, and the length in the width direction (winding direction) is L2 (<L1). Further, as shown in FIG. 7A, the thickness of the central portion of the shaft core 30 is TB0, and the thickness of both end portions in the width direction is TA0 (<TB0). Referring to FIG. 7B, an imaginary line connecting a point P1 on the outer periphery of the shaft that defines the maximum thickness TB0 of the wide surface 30W and a point P2 on the outer surface of the shaft that defines the thickness TA0 of both ends. The inclination angle θ1 of VL is a factor that affects the tightening force of the positive and negative electrodes 1 and 2. In FIG. 7B, L3 is the distance between the points P2 on both ends of the shaft core.

As shown in FIG. 8, at the time of winding, the positive electrode 1, the negative electrode 2, and the separators 3a and 3b are given tensions A and A 'in the longitudinal direction. In the wide surface 30W, an inward tightening force B directed toward the shaft core 30 acts on the stacked body of the positive electrode 1, the negative electrode 2, and the separators 3a and 3b. The tightening force B is expressed by equation (1).
Tightening force B = Asin θ1 or A′sin θ1 Formula (1)

  The laminate of the positive electrode 1, the negative electrode 2, and the separators 3a and 3b has an elastic force that spreads in the outer peripheral direction, but the clamping force B expressed by the equation (1) resists this elastic force, while the positive electrode 1, the negative electrode, 2. Tighten the separators 3a and 3b tightly. That is, when the shaft core 30 is rotated while tension is applied to the laminated body, an internal force A is applied to the laminated body between one end portion and the central portion of the shaft core 30 in one direction in the longitudinal direction. The laminated body between the center portion and the other end of the core 30 is rotated by rotating the shaft core 30 so that the internal force A ′ is applied in the other direction of the longitudinal direction.

  Thus, the positive and negative electrodes 1 and 2 stacked on the front and back surfaces of the shaft core 30 are tightened toward the center portion of the shaft core 30 by the internal forces A and A ′ acting in the longitudinal direction (biasing force). ) B is generated. As a result, no gap is generated between the positive electrode 1 and the negative electrode 2, and the density of the flat wound electrode group 4 is increased, and the capacity of the secondary battery can be increased. The tightening force B can be increased as the inclination angle θ1 is increased.

  In order for the positive and negative electrodes 1 and 2 along the wide surface 30W to have the tightening force B accompanying the internal forces A and A ′ generated by the tension during winding, the virtual line VL shown in FIG. The wall thickness TB0 at the central portion of the shaft core may be made larger than the wall thickness TA0 at both end portions so that it is inclined toward the both end portions of the shaft core 30 at the inclination angle θ1.

  The axial core 30 of the flat wound electrode group 4 of the first embodiment described above has both ends from the center to the front and back surfaces on which the laminate of the positive electrode 1, the negative electrode 2, and the separators 3a and 3b is wound. A winding surface that is inclined downward is formed. And the manufacturing method of the said flat wound electrode group is the process which welds the edge part of the separator which is one end of a laminated body to the winding surface, and rotates the axis | shaft 30 while giving tension | tensile_strength to a laminated body, and is laminated | stacked Winding the body. When the shaft core 30 is rotated while tension is applied to the laminated body, an internal force A is applied to the laminated body between one end portion and the central portion of the shaft core 30 in one direction in the longitudinal direction. An internal force A ′ is applied to the laminated body between the center portion and the other end portion in the other direction in the longitudinal direction. The laminated body is wound around the shaft core 30 by repeatedly rotating the shaft core 30.

  The cross-sectional shape of the shaft core 30 is not limited to the first embodiment. Hereinafter, the shaft core according to the second to tenth embodiments will be described with reference to FIGS. 9 to 17. In the figure, the same or corresponding parts as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

[Second Embodiment]
As shown in FIG. 9, the cross-sectional shape of the axial core 30 of the wound electrode group 4 according to the second embodiment is substantially elliptical. When the thickness of both end portions of the shaft core 30 is TA1, and the thickness TB1 of the central portion, the tightening force B is a point P1 that defines the maximum thickness TB1 of the wide surface 30W, as shown by the equation (1). And the inclination angle θ2 of the virtual line VL connecting the point P2 that defines the thickness TA1 at both ends.

  The wound electrode group 4 according to the second embodiment has the same effects as the wound electrode group 4 according to the first embodiment. If the tilt angle θ2 of the shaft core 30 of the second embodiment is equivalent to the tilt angle θ1 of the shaft core 30 of the first embodiment, a similar tightening force B can be obtained, and if the tilt angle θ2 <θ1. The tightening force B can be reduced.

  In the wound electrode group 4 according to the second embodiment, the dimensions L1, L2, L3 of the shaft core 30 are equal to the dimensions L1, L2, L3 in the wound electrode group 4 according to the first embodiment.

[Third Embodiment]
The basic cross section of the first and second shaft cores was a flat ellipse or a substantially ellipse. As shown in FIG. 10, the axial core 30 of the wound electrode group 4 according to the third embodiment has a basic cross section that is substantially rectangular. The peripheral surface of the shaft core 30 is a pair of wide surfaces 30W that are gently curved in the winding direction, a large-diameter arc surface 30A that connects these wide surfaces, and a surface that connects the wide surface 30W and the arc surface 30A. It consists of the take part 30R.

  When the wall thickness at both ends of the shaft core 30 is TA2 and the wall thickness TB2 at the center, the tightening force B is expressed by the maximum thickness point P1 of the wide surface 30W and the both ends as shown by the equation (1). It depends on the inclination angle θ3 of the virtual line VL connecting the point P2.

  The wound electrode group 4 according to the third embodiment has the same effects as the wound electrode group 4 according to the first embodiment. If the tilt angle θ3 of the shaft core 30 of the third embodiment is equivalent to the tilt angle θ1 of the shaft core 30 of the first embodiment, a similar tightening force B can be obtained, and if the tilt angle θ2 <θ1. The tightening force B can be reduced.

[Fourth Embodiment]
As shown in FIG. 11, the axial core 30 of the wound electrode group 4 according to the fourth embodiment has a substantially rhombus cross section. The peripheral surface of the shaft 30 has a pair of mountain-shaped wide surfaces 30W that are inclined at an inclination angle θ4 from a point P1 that defines the maximum thickness of the central portion toward a point P2 that defines the thickness of both ends, and these wide surfaces. It comprises a large-diameter arc surface 30A that couples the surface 30W, and a chamfered portion 30R that couples the wide surface 30W and the arc surface 30A. The wide surface 30 </ b> W is a flat surface that is inclined from the center portion of the shaft core to the front and back surfaces of both ends.

  The wall thickness at both ends of the shaft core 30 is TA3, and the wall thickness at the center is TB3. The wide surface 30W is an inclined plane having a relatively steep angle θ4 in both end directions, and the angle θ4 is larger than the inclination angle θ1 of the wound electrode group 4 according to the first embodiment. The peak P1 of the chevron of the wide surface 30W is chamfered so that the friction between the positive and negative electrodes 1 and 2 and the shaft core 30 is reduced when the positive and negative electrodes 1 and 2 are wound.

  Since the inclination angle θ4 of the wound electrode group 4 according to the fourth embodiment is larger than the inclination angle θ1 of the wound electrode group 4 according to the first embodiment, as can be seen from the equation (1), according to the fourth embodiment. The wound electrode group 4 has a larger clamping force B than the wound electrode group 4 according to the first embodiment.

[Fifth Embodiment]
As shown in FIG. 12, the shaft core 30 has a substantially octagonal shape with a flat cross section. The outer peripheral surface includes a flat surface 30W1 having a constant thickness TB4 extending in the central region L4 of the shaft core 30, arc surfaces 30W2 extending from both sides of the flat surface 30W1 to both ends of the shaft core, and these arc surfaces extending from the front and back of the shaft core. It has a large-diameter arc surface 30A that connects 30W2 and a chamfered portion 30R that connects the arc surface 30W2 and the arc surface 30A. The inclination angle θ5 of the virtual inclined surface VL that connects the point P2 that defines the thickness TA4 at both ends from the connecting point P1 between the flat surface 30W1 and the arcuate surface 30W2 is as shown in the figure, and the tightening force B is the magnitude of the inclination angle θ5. Depends on the size.

The wall thickness at both ends of the shaft core 30 is TA4, and the wall thickness at the center is TB4. The continuous contact between the flat surface 30W1 and the arcuate surface 30W2 is rounded to reduce friction between the positive and negative electrodes 1 and 2 and the shaft core 30 when the positive and negative electrodes 1 and 2 are wound.
The wound electrode group 4 according to the fifth embodiment has the same effects as the wound electrode group 4 according to the first embodiment.

[Sixth Embodiment]
As shown in FIG. 13, the axial core 30 of the wound electrode group 4 according to the sixth embodiment is such that the arc surface 30A of the axial core 30 of the wound electrode group 4 according to the third embodiment is a plane 30F. is there. The wound electrode group 4 according to the sixth embodiment has the same effects as the wound electrode group 4 according to the third embodiment.

[Seventh Embodiment]
As shown in FIG. 14, the axial core 30 of the wound electrode group 4 according to the seventh embodiment has a circular surface 30A in the axial core 30 of the wound electrode group 4 according to the fourth embodiment as a flat surface 30F. is there. The wound electrode group 4 according to the seventh embodiment has the same effects as the wound electrode group 4 according to the fourth embodiment.

[Eighth Embodiment]
As shown in FIG. 15, the axial core 30 of the wound electrode group 4 according to the eighth embodiment is such that the arc surface 30A of the axial core 30 of the wound electrode group 4 according to the fifth embodiment is a plane 30F. is there. The wound electrode group 4 according to the eighth embodiment has the same effects as the wound electrode group 4 according to the fifth embodiment.

[Ninth Embodiment]
As shown in FIG. 16, the axial core 30 of the wound electrode group 4 according to the ninth embodiment has the same shape and dimensions as the axial core 30 of the wound electrode group 4 according to the first embodiment, and its wide width. In the surface 30W, the lightening 101 is formed. The lightening 101 is a through hole or a recess, and the shaft core 30 is reduced in weight by this. That is, the wound electrode group 4 according to the ninth embodiment has the effect of reducing the weight of the secondary battery in addition to the effect of the wound electrode group 4 according to the first embodiment.
In addition, it is naturally possible to make a similar thinning 110 in the axial core 30 of the wound electrode group 4 according to the second to eighth embodiments, and the same effect can be obtained.

[Tenth embodiment]
As shown in FIG. 17, the axial core 30 of the wound electrode group 4 according to the tenth embodiment has the same shape and dimensions as the axial core 30 of the wound electrode group 4 according to the first embodiment, and is axially oriented. In this case, the lightening 111 is formed on both end surfaces. The lightening 111 is a through hole or a recess, and the shaft core 30 is reduced in weight by this.

That is, the wound electrode group 4 according to the tenth embodiment has the effect of reducing the weight of the secondary battery in addition to the effect of the wound electrode group 4 according to the first embodiment.
In addition, it is naturally possible to make a similar cutout 111 in the shaft core 30 of the wound electrode group 4 according to the second to eighth embodiments, and the same effect can be obtained.

  In the above embodiment, PVDF is exemplified as the binder, but polytetrafluoroethylene (PTFE), polyethylene, polystyrene, polybutadiene, butyl rubber, nitrile rubber, styrene / butadiene rubber, polysulfide rubber, nitrocellulose, cyanoethyl cellulose, various latexes Polymers such as acrylonitrile, vinyl fluoride, vinylidene fluoride, propylene fluoride, and chloroprene fluoride, and mixtures thereof may be used.

In the above embodiment, the nonaqueous electrolytic solution in which LiPF ₆ is dissolved in a mixed solution of EC, DEC, and DMC is exemplified. However, a nonaqueous electrolytic solution in which a general lithium salt is used as an electrolyte and this is dissolved in an organic solvent. The present invention is not particularly limited to the lithium salt or organic solvent used.

For example, as the electrolyte, LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, or a mixture thereof can be used. Examples of the organic solvent include propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, Diethyl ether, sulfolane, methyl sulfolane, acetonitrile, propiontonyl, etc., or a mixed solvent of two or more of these may be used, and the mixing ratio is not limited.

  In the above, 1st-10th embodiment was described about the axial center 30 in the secondary battery by this invention. However, the present invention is not limited to these embodiments. That is, in the flat wound electrode group formed by winding the positive and negative electrodes 1 and 2 while being insulated by the separators 3a and 3b, the positive and negative electrodes 1 and 2 are generated in the longitudinal direction of the laminate of the positive and negative electrodes 1, 2 and 3a and 3b. The present invention can be applied to shaft cores of any shape and size as long as the shaft core has a shape and dimensions that generate a tightening force B toward the center of the shaft core 30 due to internal force.

  For example, the shaft cores of the first to tenth embodiments are integrally formed. As shown in FIG. 18, the shaft core 300 is provided on the shaft core body 301 and the front and back surfaces of the shaft core body 301. The thickness forming member 302 may be provided, and the inclined surface RL may be formed from the central part of the axial center to both end parts. Alternatively, as shown in FIG. 19, the shaft core 300 includes a shaft core body 301 and a thickness forming member 302 provided at the front and back center portions of the shaft core body 301, and a virtual inclined surface from the shaft core center portion to both ends. A VL may be formed.

Industrial application fields

  The secondary battery according to the present invention is particularly suitable for a secondary battery having a medium to large capacity (for example, 4 to 50 Ah) such as a hybrid vehicle or an electric vehicle.

Secondary battery according to the first aspect of the present invention, the separator is fixed in welding to the axis, a flat wound Kaigata electrode group formed by winding the axial core with insulating the positive electrode and the negative electrode with the separator cell A secondary battery housed in a container, wherein a laminate of a positive electrode, a negative electrode, and a separator has an upward gradient from one end portion in the winding direction to the central portion on the front and back surfaces of the shaft, and the winding direction from the central portion The other end is wound with a downward slope. In this secondary battery, the laminated body generates a tightening force at the central portion of the shaft core by an internal force generated in the longitudinal direction of the laminated body by winding.
The shaft core can be formed with an inclined surface that is inclined downward from the center of the front and back surfaces toward both ends in the winding direction. It is preferable that the inclined surface extends as a gentle arc surface from the center to both ends. For example, the cross-sectional shape of the shaft core is a flat elliptical shape or a substantially elliptical shape. Both end portions of the shaft core are preferably arcuate surfaces or flat surfaces.
The shaft core may have a substantially rectangular cross-section at the center, and an inclined surface from the center toward both ends may be a flat surface or a gentle arc surface. In this example, the inclined surface may extend as a flat surface from the central portion to both end portions. Also in this example, it is preferable that both end portions of the shaft core are arc surfaces or flat surfaces. Further, the cross-sectional shape of the shaft core may be substantially rhombus.
As described above, it is preferable to reduce the weight by providing a hollow in the shaft core of various forms.
The second aspect of the present invention is a method for manufacturing a wound electrode group of a secondary battery. The wound electrode group is wound while the long positive electrode and the negative electrode are laminated on the shaft core while being insulated with a separator, and the front and back surfaces of the shaft core are inclined downward from the center to both ends. A winding surface inclined at is formed. In such a method of manufacturing a wound electrode group, one end of the innermost separator is welded to the winding surface, and the shaft core is rotated while applying tension while alternately laminating positive and negative electrodes between the separators. And turn around.
When rotating the shaft core while applying tension to the laminate of the positive electrode, the negative electrode and the separator, an internal force is applied to the laminate extending between one end portion of the shaft core and the central portion in one longitudinal direction thereof, The laminated body is preferably wound by rotating the shaft core so that an internal force is applied to the laminated body extending from the central portion of the shaft core to the other end in the other direction of the longitudinal direction.

Claims (13)

A secondary battery comprising a flat wound electrode group formed by winding on a shaft core while insulating a positive electrode and a negative electrode with a separator,
The laminate of the positive electrode, the negative electrode, and the separator has a rising gradient from one end portion in the winding direction to the central portion and a downward gradient from the central portion to the other end portion in the winding direction on the front and back surfaces of the shaft core. Secondary battery being turned. In the secondary battery according to claim 1,
A secondary battery in which the laminated body generates a tightening force at a central portion of an axial core by an internal force generated in a longitudinal direction of the laminated body by the winding. In the secondary battery according to claim 1,
A secondary battery in which the shaft core is formed with an inclined surface that is inclined downward from the center of the front and back surfaces toward both ends in the winding direction. The secondary battery according to claim 3,
The inclined surface is a secondary battery extending as a gentle arc surface from the central portion to the both end portions. The secondary battery according to claim 4,
The secondary battery has a circular arc surface or a flat surface at both ends. The secondary battery according to claim 4,
A secondary battery in which a cross-sectional shape of the shaft core is a flat elliptical shape or a substantially elliptical shape. The secondary battery according to claim 1,
A secondary battery in which the cross-sectional shape of the central portion of the shaft core is substantially rectangular, and the inclined surface from the central portion toward the both end portions is a flat surface or a gentle arc surface. The secondary battery according to claim 3,
The inclined surface is a secondary battery extending as a flat surface from the central portion to the both end portions. The secondary battery according to claim 8,
The secondary battery has a circular arc surface or a flat surface at both ends. The secondary battery according to claim 8,
A secondary battery in which a cross-sectional shape of the shaft core is substantially rhombus. The secondary battery according to claim 1,
A secondary battery in which a hollow is provided on the shaft core. It is an electrode group of a secondary battery, and is wound while being stacked on a shaft core while insulating a positive electrode and a negative electrode, which are long objects, with a separator. In the method of manufacturing a flat wound electrode group in which a wound surface inclined at a downward slope is formed,
Welding one end of the innermost separator to the winding surface;
A method for producing a flat wound electrode group, in which the positive electrode and the negative electrode are alternately laminated between the separators and the tension is applied while rotating the shaft core. In the manufacturing method of the flat wound electrode group according to claim 12,
When the shaft core is rotated while applying tension to the laminate of the positive electrode, the negative electrode, and the separator, the laminate extending between one end portion and the center portion of the shaft core has an internal force in one longitudinal direction. The laminate is wound by rotating the shaft core so that an internal force is applied in the other direction in the longitudinal direction to the laminate extending between the central portion and the other end of the shaft core. A method for manufacturing a flat wound electrode group.

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