JP5406733B2 - Flat rechargeable secondary battery - Google Patents

Description

  The present invention relates to a flat wound secondary battery.

  In flat wound secondary batteries, the flat part of the battery swells due to the effects of electrode expansion during battery charging / discharging, resulting in a decrease in battery capacity due to electrode facing failure and an increase in resistance due to an increase in the distance between electrodes. It becomes a problem.

  As one of the techniques for solving this problem, Patent Document 1 includes a winding body in which a positive electrode, a negative electrode, and a separator interposed therebetween are wound, and the cross section has a flat shape, A non-aqueous electrolyte secondary battery in which a plate-like core material is arranged at the center of a wound body is disclosed. According to this non-aqueous electrolyte secondary battery, since the positive electrode and the negative electrode are wound around the core material without any gaps, the core material can receive the stress caused by the expansion of the electrode, buckling, etc. It is described that the deformation of the electrode can be suppressed.

JP 2008-47304 A

  An object of the present invention is to provide a flat wound secondary battery having excellent life characteristics while suppressing deformation of a core material and a battery container due to charging / discharging of the battery.

  The flat wound secondary battery of the present invention accommodates an electrode winding group formed by winding a positive electrode, a negative electrode, and a separator sandwiched between them on a core material. And the said core material has a thin part, a notch part, or a cutout part, It is characterized by the above-mentioned.

  ADVANTAGE OF THE INVENTION According to this invention, the stress which arises in an electrode winding group with charging / discharging of a battery can be relieved, the swelling of a battery can can be suppressed, and the lifetime of a flat winding type secondary battery can be lengthened. .

It is a perspective view which shows the electrode winding group of the flat wound type secondary battery of an Example. It is an external appearance perspective view which shows the flat winding type secondary battery of an Example. It is a longitudinal cross-sectional view which shows the flat wound type secondary battery of an Example. It is a perspective view which shows the core material of the flat wound type secondary battery which is an Example. It is a perspective view which shows the core material of the flat wound type secondary battery which is an Example. It is a perspective view which shows the core material of the flat wound type secondary battery which is an Example. It is a perspective view which shows the core material of the flat wound type secondary battery which is an Example. It is a perspective view which shows the core material of the flat wound type secondary battery which is an Example. It is sectional drawing which shows the state before charge of the flat wound type secondary battery which is an Example. It is sectional drawing which shows the state after charge of the flat wound type secondary battery which is an Example. It is a graph which shows the change of the battery thickness in the charging / discharging cycle of the flat wound type secondary battery of an Example and a comparative example. It is a graph which shows the change of DC resistance in the charging / discharging cycle of the flat wound type secondary battery of an Example and a comparative example.

  The present invention relates to a flat wound secondary battery used for an electric vehicle (EV), a hybrid electric vehicle (HEV) in which a part of driving is assisted by an electric motor, or the like.

  Hereinafter, a flat wound secondary battery according to an embodiment of the present invention will be described.

(Constitution)
This embodiment is basically configured as follows.

  The flat wound secondary battery accommodates an electrode winding group formed by winding a positive electrode, a negative electrode, and a separator sandwiched between them on a core material. And a core material has a thin part, a notch part, or a cutout part.

  In the flat wound secondary battery, it is preferable that a core material is formed of a resin and has an insulating property.

  In the flat wound secondary battery, it is desirable that a thin portion, a notch portion, or a cutout portion is provided at the center of the wide portion of the core material.

  In the flat wound secondary battery, it is preferable that the thickness of the end region in the winding axis direction of the core material is the largest among the thicknesses of the core material. Here, the end region refers to a region having a certain area in the wide portion located at the end in the winding axis direction of the core material.

  Hereinafter, the present embodiment will be described with reference to the drawings.

  FIG. 1 is a perspective view showing an electrode winding group of a flat wound secondary battery according to an embodiment.

  In this figure, a belt-like positive electrode sheet 106 and a negative electrode sheet 108 are wound around a core material 11 in a roll shape so as to face each other with separators 10 a and 10 b therebetween, thereby forming an electrode winding group 5. The separators 10 a and 10 b have a thickness in the range of about 15 to 50 μm, and the width is larger than the width of the positive electrode sheet 106 and the negative electrode sheet 108.

  Here, the core material 11 is preferably made of resin and has an insulating property. As the resin used here, polypropylene (PP) or the like is desirable because heat resistance under the usage conditions of the battery is also required. Further, polypropylene or the like reinforced with glass fiber or the like is more desirable.

  The positive electrode sheet 106 is formed with a positive electrode mixture coated portion 6a coated with a positive electrode mixture and a positive electrode mixture uncoated portion 6b not coated with a positive electrode mixture. Further, the negative electrode sheet 108 is formed with a negative electrode mixture coated portion 8a coated with a negative electrode mixture and a negative electrode mixture uncoated portion 8b not coated with the negative electrode mixture.

  By cutting out the positive electrode mixture uncoated portion 6b and the negative electrode mixture uncoated portion 8b, a plurality of positive electrode current collecting tabs 7 (also referred to as positive electrode lead pieces) and negative electrode current collecting tabs 9 (also referred to as negative electrode lead pieces). ). The positive electrode current collecting tab 7 and the negative electrode current collecting tab 9 are respectively disposed on both end faces on the opposite side of the electrode winding group 5. In addition, an insulating coating is provided on the outermost periphery of the electrode winding group 5 in order to prevent electrical contact between the electrode winding group 5 and the battery can 1.

  When the positive electrode current collector tab 7 and the negative electrode current collector tab 9 are not formed in the positive electrode mixture uncoated portion 6b and the negative electrode mixture uncoated portion 8b, the electrode sheets (the positive electrode sheet 106 and the negative electrode sheet 108) are pressed (pressurized) ) Electrode mixture coating part (positive electrode mixture coating part 6a and negative electrode mixture coating part 8a) and electrode mixture uncoated part (positive electrode mixture uncoated part 6b and negative electrode mixture uncoated) Due to the difference in press pressure in the working part 8b), the electrode is distorted, which causes a winding failure.

  In the case of a lithium ion battery, the positive electrode sheet 106 constituting the electrode winding group 5 uses an aluminum foil as a positive electrode current collector. As for the thickness of aluminum foil, about 5-20 micrometers is desirable.

  On both surfaces of the aluminum foil, for example, a conductive agent such as graphite and a binder (binder) such as polyvinylidene fluoride (hereinafter abbreviated as PVDF) are blended with an active material such as a lithium composite oxide, and N- A positive electrode mixture whose viscosity is adjusted with a dispersion solvent such as methylpyrrolidone (hereinafter abbreviated as NMP) is applied.

  After coating the positive electrode mixture, it is dried and the density is adjusted by a roll press.

Although the optimum value of the density of the positive electrode mixture varies depending on the active material and the conductive agent to be used, it is preferably about 2.0 to 3.5 g / cm ³ .

  On the other hand, the negative electrode sheet 108 uses copper foil as a negative electrode current collector. As for the thickness of copper foil, 5-15 micrometers is desirable.

  On both surfaces of the copper foil, for example, a carbon-based conductive agent such as acetylene black and a binder such as PVDF are blended with an active material such as graphite, and a negative electrode mixture whose viscosity is adjusted with a dispersion solvent such as NMP is applied.

  After coating the negative electrode mixture, it is dried and the density is adjusted by a roll press.

The optimum value of the density of the negative electrode mixture varies depending on the active material used, but is preferably about 1.0 to 2.0 g / cm ³ .

  After the positive electrode sheet 106 and the negative electrode sheet 108 are wound, the positive electrode sheet 106 does not protrude from the negative electrode sheet 108 in the winding circumferential direction at the innermost peripheral part and the outermost peripheral part of the electrode winding group 5 so as not to overlap. The length of the negative electrode sheet 108 is longer than the length of the positive electrode sheet 106.

  In addition, the width of the negative electrode mixture coating portion 8a of the negative electrode sheet 108 is made wider than the width of the positive electrode mixture coating portion 6a in the winding circumferential direction of the electrode winding group 5 in consideration of dendrite precipitation and the like. It is.

  FIG. 2 is an external perspective view showing the flat wound secondary battery of the example.

  The battery 100 shown in this figure is one in which the electrode winding group 5 shown in FIG. 1 is accommodated in a flat cylindrical battery can 1 made of aluminum. Further, a positive electrode terminal 2 and a negative electrode terminal 3 are provided as external terminals, a gasket (not shown) for insulating the positive electrode terminal 2 and the negative electrode terminal 3 and the battery can 1, and a nut for fixing the electrode winding group 5. (Not shown) and a liquid injection port 4 for injecting the electrolyte into the battery 100 are provided.

  FIG. 3 is a longitudinal sectional view showing the flat wound secondary battery of the example.

  In this figure, the positive electrode current collecting tab 7 of the battery 100 is welded to the positive electrode current collecting plate 12 by ultrasonic welding. Similarly, the negative electrode current collecting tab 9 is welded to the negative electrode current collecting plate 13 by ultrasonic welding.

  In addition, although the ultrasonic welding was illustrated in a present Example, the welding method is not limited to this, Welding methods, such as laser welding, can also be applied.

  In this figure, both ends in the winding axis direction are sealed using a battery lid 16. The battery lid 16 is fixed to the battery can 1 by laser welding or the like.

  The battery cover 16 is provided with openings for taking out the positive electrode terminal 2 and the negative electrode terminal 3 as external terminals to the outside of the battery 100, and a gasket for insulating the positive electrode terminal 2 and the negative electrode terminal 3 from the battery cover 16. 14, a nut 15 for fixing the electrode winding group 5 at the portion of the positive electrode terminal 2 and the negative electrode terminal 3, and a liquid injection port 4 for injecting the electrolyte into the battery 100.

  After injecting the electrolytic solution from the liquid injection port 4, it is sealed with a blind rivet via a synthetic resin sleeve. In the case of a lithium ion battery, as an electrolyte, non-hexafluorolithium phosphate dissolved in a mixed solvent such as ethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate so as to have a concentration of 1 mol / L (mol / liter) is used. A water electrolyte is used.

  The electrode winding group 5 is wound around the core material 11 via a porous separator 10 such as polyethylene so that the positive electrode sheet 106 and the negative electrode sheet 108 do not directly contact each other.

  FIGS. 4-8 is a perspective view which shows the core material of the flat wound type secondary battery which is an Example.

  In FIG. 4, it has the structure cut out leaving the outer frame part 201 and the center part 202 of the core material 11, and has the cutout part 203 of two places. The two cutouts 203 absorb the expansion of the electrode.

  In FIG. 5, the core material 11 has a structure (notched portion 204) in which the upper end portion 211 and the lower end portion 212 in the winding axis direction and the center portion 202 are left out. The two notches 204 absorb the expansion of the electrode.

  In FIG. 6, there is a portion (thin wall portion 221) where the thickness of the core material 11 is reduced between the upper end portion 211 and the lower end portion 212 in the winding axis direction of the core material 11. The recess formed by the thin portion 221 absorbs the expansion of the electrode.

  In FIG. 7, it has the structure cut out leaving the outer frame part 201 of the core material 11, and has the cutout part 203 of one place. The one cutout 203 absorbs the expansion of the electrode.

  In FIG. 8, the outer frame portion 201 of the core material 11 is left and cut out in a circular shape, and a single cutout portion 203 is provided. The one cutout 203 absorbs the expansion of the electrode. In the case of this figure, since the cut-out portion 203 has no corners, stress concentration is less likely to occur when the core material 11 receives a force, and the strength of the core material 11 can be increased.

  4 to 8, the thickness of the constant region (end region) at the upper end portion and the lower end portion in the winding axis direction of the core material 11 is thicker than that of the thin portion 221. In other words, the thickest region of the thickness of the core material 11 is provided at the upper end portion and the lower end portion in the winding axis direction of the core material 11. Thereby, when the electrode (electrode sheet) located in the wide part of the core material 11 expands, the electrode located in the upper end part and the lower end part is supported to suppress deformation, and the electrode is located in the wide part of the core material 11. The entire electrode to be entered enters the cutout portion 204, the cutout portion 203, or the thin portion 221 and can prevent the metal foil constituting the electrode from being broken or buckled. Here, the wide portion of the core material 11 refers to a flat surface portion of the surface of the core material 11 having the widest width in the winding circumferential direction of the core material 11. The flat portion may have irregularities formed by the cutout portion 204, the cutout portion 203, the thin portion 221 or the like.

  In addition, if the effect | action which suppresses a deformation | transformation by supporting an electrode is acquired, it is sufficient to thicken any one edge part area | region among the core materials 11 located in said upper end part and lower end part.

(Battery assembly)
The assembly of the flat wound secondary battery will be described with reference to FIGS.

  First, one end (winding start portion) of the separator 10 is fixed to the core material 11 with a tape or the like.

  After winding only the separator 10 about 2-3 times at the beginning of winding, the positive electrode sheet 106 and the negative electrode sheet 108 are opposed so that the electrode width of the positive electrode sheet 106 is positioned inside the electrode width of the negative electrode sheet 108, and It winds so that the positive electrode current collection tab 7 and the negative electrode current collection tab 9 may be located in a mutually opposing direction.

  After winding the positive electrode sheet 106 and the negative electrode sheet 108, the separator 10 is wound about 2 to 3 times at the end of winding so that the electrode is not exposed at the outermost peripheral portion of the electrode winding group 5.

  Hereinafter, a description will be given with reference to FIG.

  After ultrasonic welding the positive electrode current collector tab 7 and the negative electrode current collector tab 9 provided at the end in the winding axis direction of the produced electrode winding group 5, respectively, to the positive electrode current collector plate 12 and the negative electrode current collector plate 13 The outermost peripheral portion of the electrode winding group 5 is coated to insulate the electrode winding group 5 and the battery can 1, and the electrode winding group 5 is inserted into the battery can 1.

  The battery cover 16 is fitted into the battery can 1 and fixed with a nut 15 via a gasket 14. The joint between the battery lid 16 and the battery can 1 is welded by laser welding or the like. In this state, vacuum drying is performed at 60 ° C. for 20 hours.

  After vacuum drying, an electrolytic solution is injected from the liquid injection port 4 provided in the battery lid 16. After injecting the electrolytic solution, a blind rivet is attached to the injection port 4 via a sleeve made of synthetic resin, thereby sealing the battery 100 and completing the assembly.

(Action etc.)
Hereinafter, the operation and the like of the flat wound secondary battery of the present embodiment will be described.

  As shown in FIGS. 4 to 8, in the flat wound secondary battery of this embodiment, a core material 11 having a thin portion, a cutout portion, or a cutout portion is used.

  9A is a cross-sectional view illustrating a state before charging of the electrode winding group according to the embodiment, and FIG. 9B is a cross-sectional view illustrating a state after charging of the electrode winding group according to the embodiment. Here, the core material 11 is the same as that shown in FIG.

  Before charging in FIG. 9A, the wide electrode sheet 401 (positive electrode sheet or negative electrode sheet) of the core material 11 is not deformed and is in a straight state. On the other hand, after the charging shown in FIG. For this reason, the stress to the battery can generated by the expansion of the electrode accompanying the charging / discharging of the battery can be relaxed, and the life of the battery can be extended.

  In the present embodiment, a lithium ion battery has been exemplified, but the present invention is not limited to this, and can be applied to any electrode wound secondary battery (power storage device) such as a nickel metal hydride battery, an electric double layer capacitor, or a lithium ion capacitor. Applicable. For this reason, the electrode active material, the conductive agent, the electrolytic solution, and the like used for the battery are not particularly limited to those exemplified, and any of those normally used for the above electricity storage device can be used.

  Hereinafter, examples of the flat wound secondary battery will be described. A comparative example is also shown.

  Example 1 uses the core shown in FIG.

(Comparative Example 1)
The comparative example 1 uses the flat core material which has not performed processing, such as cutting. The portions other than the core material were the same as in the example.

(Battery evaluation test)
The life characteristics of the flat wound secondary batteries of Examples and Comparative Examples were evaluated.

  The charge / discharge test is performed in a constant temperature bath at 25 ° C. with a charging end voltage of 4.2 V, a current value of 1 CA, and constant current / constant voltage charging for 1.5 hours, and a constant current discharge to 3.0 V at the same current value. This test was repeated 500 cycles. In addition, the battery thickness and DC resistance (DCR) were measured every 100 cycles.

  FIG. 10 is a graph showing changes in battery thickness in the charge / discharge cycle of the flat wound secondary battery of the example and the comparative example.

  The horizontal axis represents the number of cycles N, and the vertical axis represents the battery thickness variation.

  As shown in this figure, it can be seen that the battery thickness change amount of Example 1 is smaller than that of Comparative Example 1.

  FIG. 11 is a graph showing a change in DC resistance in the charge / discharge cycle of the flat wound secondary battery of the example and the comparative example.

  The horizontal axis represents the number of cycles N, and the vertical axis represents the DCR change.

  As shown in this figure, it can be seen that the change in DCR in Example 1 is smaller than that in Comparative Example 1.

  From the above, it was confirmed that by providing the cutout part in the core material, the battery thickness change amount and DCR change can be suppressed, and the life characteristics can be improved (long life).

  ADVANTAGE OF THE INVENTION According to this invention, the stress added to a core material and a battery can by the expansion | swelling of the electrode in charging / discharging of a battery can be reduced, and a deformation | transformation of a core material and a battery can and the buckling of an electrode can be prevented.

  Moreover, according to this invention, the mass of a core material can be reduced and it can contribute also to the weight reduction of the whole battery.

  Furthermore, according to the present invention, it is possible to provide a flat wound secondary battery having high current collection efficiency, energy density, and output density, and high reliability and productivity.

  A flat wound secondary battery can be applied to the present invention.

  1: battery can, 2: positive electrode terminal, 3: negative electrode terminal, 4: injection port, 5: electrode winding group, 7: positive electrode current collecting tab, 9: negative electrode current collecting tab, 10: separator, 11: core material , 12: positive electrode current collector plate, 13: negative electrode current collector plate, 14: gasket, 15: nut, 16: battery lid, 100: battery, 106: positive electrode sheet, 108: negative electrode sheet, 203: cut-out portion, 204: cut Notch part, 221: Thin part.

Claims (3)

A flat wound secondary battery containing an electrode winding group formed by winding a positive electrode, a negative electrode, and a separator sandwiched between them on a core material, the core material comprising a thin portion, notches or have a cut-out portion, the thin portion, the flat spirally wound secondary battery, characterized in that the notches or the cut-out portion is provided in the center portion of the wide portion of the core material.   2. The flat wound secondary battery according to claim 1, wherein the core material is formed of a resin and has an insulating property. Flat wound type secondary battery according to claim 1 or 2, characterized in that the thickness in the end region of the winding axis direction of the core material are then thickest among the thickness of the core material.

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