JP2014093149A - Power storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power storage device capable of improving a safety of a safety measure electrode unit.SOLUTION: A secondary battery 10 comprises: a case 12; an electrode assembly 20 housed in the case 12; a pair of conductive members 40A, 40B consisting of a positive electrode conductive member 40A electrically connected to a positive electrode 22A of the electrode assembly 20 and a negative electrode conductive member 40B electrically connected to a negative electrode 22B of the electrode assembly 20; and a safety measure electrode unit 30 stacked outside of the electrode assembly 20 and positioned between the electrode assembly 20 and the case 12. The safety measure electrode unit 30 has a first metal foil 32A welded to the positive electrode conductive member 40A; a second metal foil 32B welded to the negative electrode conductive member 40B; and an insulation layer 34 arranged between the first metal foil 32A and the second metal foil 32B, and at least one of the first metal foil 32A and the second metal foil 32B is a laminated metal foil in which a plurality of metal foils are laminated.

Description

  The present invention relates to a power storage device.

  Conventionally, as a secondary battery which is a kind of power storage device, for example, a lithium ion secondary battery or a nickel-hydrogen secondary battery is well known. Such a secondary battery has a configuration in which an electrode assembly which is a power storage element is accommodated in a case. In the electrode assembly, a positive electrode formed by applying a positive electrode active material to a metal foil such as an aluminum foil and a negative electrode formed by applying a negative electrode active material to a metal foil such as a copper foil are laminated via a separator. It is a thing. Further, the secondary battery includes a pair of electrode terminals for taking out electric power to the outside, the positive electrode of the electrode assembly is connected to the positive electrode terminal via a conductive member, and the negative electrode of the electrode assembly is electrically connected to the negative electrode terminal. It is connected via a member.

  In the following Patent Document 1, in the secondary battery as described above, an electrode unit having a pair of metal foils not coated with an active material on both outer sides of the electrode assembly (hereinafter referred to as a safety measure electrode unit). ), And one metal foil of the electrode unit is connected to a conductive member extending to the positive terminal, and the other metal foil is connected to a conductive member extending to the negative terminal.

  In the secondary battery disclosed in Patent Document 1, when an impact is applied from the outside of the case due to nail penetration or crushing, a pair of metal foils are provided prior to a short circuit between the positive electrode and the negative electrode of the electrode assembly. A short circuit occurs between the two electrodes to reduce the remaining battery level, so that a large current flows between the positive electrode and the negative electrode of the electrode assembly to prevent abnormal heat generation or ignition, thereby improving safety. It has been.

JP 2001-351670 A JP 2001-68156 A

  However, the conventional secondary battery described above has the following problems. That is, when a current flows through the metal foil of the safety electrode unit due to the short circuit, the metal foil generates heat, but when the metal foil is melted by the heat generation, the function of the safety electrode unit deteriorates.

  Such a problem occurs not only in the secondary battery but also in other power storage devices such as an electric double layer capacitor.

  Therefore, an object of the present invention is to provide a power storage device in which safety of the safety measure electrode unit is improved.

  In a power storage device according to the present invention, a case, a positive electrode formed by applying a positive electrode active material to a metal foil, and a negative electrode formed by applying a negative electrode active material to a metal foil are provided via a separator. A pair of conductive members comprising a laminated electrode assembly, a positive electrode conductive member electrically connected to the positive electrode of the electrode assembly, and a negative electrode conductive member electrically connected to the negative electrode of the electrode assembly And a safety electrode unit laminated on the outside of the electrode assembly and interposed between the electrode assembly and the case, the safety electrode unit being welded to the positive electrode conductive member, And a second metal foil welded to the negative electrode conductive member, and an insulating layer interposed between the first metal foil and the second metal foil, the first metal foil and the second metal foil At least one of these is a laminated metal foil in which a plurality of metal foils are laminated.

  In this power storage device, at least one of the first metal foil welded to the positive electrode conductive member and the second metal foil welded to the negative electrode conductive member of the safety measure electrode unit is a laminated metal foil. According to such a laminated metal foil, the electrical resistance is reduced as compared with the case where one metal foil is welded to each of the positive electrode conductive member and the negative electrode conductive member as in the prior art. Thereby, since the situation where a metal foil melt | dissolves by resistance heating is suppressed effectively, the high safety | security of a safety measure electrode unit is implement | achieved.

  Moreover, the aspect by which only one part metal foil of the laminated metal foil is welded to the electrically-conductive member may be sufficient. In this case, it can weld more easily than the case where all the metal foils of a laminated metal foil and a conductive member are welded.

  Further, the first metal foil and the second metal foil may be laminated metal foils. In this case, higher safety of the safety measure electrode unit is realized as compared with the case where one of the first metal foil and the second metal foil is a laminated metal foil.

  Also, a plurality of metal foils constituting the laminated metal foil are welded, and the laminated metal foil welded portion where the plurality of metal foils are welded is a region corresponding to the active material coating region of the electrode assembly. The aspect which exists in a remaining area | region may be sufficient. In this case, the laminated metal foil welded portion does not overlap the active material coating region of the electrode assembly, and the unevenness does not affect the electrode assembly.

  Further, the power storage device may be a secondary battery.

  ADVANTAGE OF THE INVENTION According to this invention, the electrical storage apparatus with which the safety improvement of the safety countermeasure electrode unit was achieved is provided.

FIG. 1 is a schematic cross-sectional view illustrating a configuration of a secondary battery according to an embodiment of the present invention. FIG. 2 is a view showing the connection between the electrode assembly of the secondary battery of FIG. 1 and the safety electrode unit, and is a cross-sectional view at a position where a positive electrode tab is present. FIG. 3 is a diagram showing a state of nail penetration in the secondary battery of FIG. FIG. 4 is a diagram showing a state of current flowing through the safety electrode unit at the time of nail penetration in FIG.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected about the same or equivalent element, and the description is abbreviate | omitted when description overlaps.

  First, a configuration of a secondary battery 10 as a power storage device according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2.

  As shown in FIG. 1, the secondary battery 10 includes a case 12. The case 12 is made of metal (for example, stainless steel or aluminum), and an insulating layer 14 is formed on the inner surface thereof.

  An electrode assembly 20 is accommodated in the case 12. The electrode assembly 20 includes a positive electrode 22A and a negative electrode 22B that are laminated in a layered structure (laminated structure) by about 10 to 100 layers, and supplies electric power stored by charging. The negative electrode 22B is covered with a bag-shaped separator (diaphragm) 27, and the positive electrode 22A and the negative electrode 22B are insulated by the separator 27. The separator 27 is not limited to a bag shape, and may be a sheet-like separator interposed between the positive electrode 22A and the negative electrode 22B.

  The positive electrode 22 </ b> A has a configuration in which a positive electrode active material 24 is coated on a positive electrode metal foil 23. The positive electrode metal foil 23 is made of an aluminum foil having a thickness of about 8 to 20 μm (for example, a thickness of 15 μm), and has a tab 231 at one end thereof. The tab 231 is an uncoated portion where the positive electrode active material is not applied, and the positive electrode metal foil 23 is overlapped on the positive electrode conductive member 40A at the tab 231 and is welded to each welding point W (that is, welding of the tab 231). Welding is performed at the location W1 and the welding location W3) of the positive electrode conductive member 40A.

  The negative electrode 22 </ b> B has a configuration in which a negative electrode active material 26 is coated on a negative electrode metal foil 25. The negative electrode metal foil 25 is made of a copper foil having a thickness of about 8 to 20 μm (for example, a thickness of 10 μm), and has a tab 251 at one end thereof, like the positive electrode metal foil 23. The tab 251 is an uncoated portion where the negative electrode active material is not applied, and the negative electrode metal foil 25 is overlaid on the negative electrode conductive member 40B on the tab 251 and welded to each welding point W (that is, welding of the tab 251). It welds in a location (not shown) and the welding location W3 of the negative electrode electrically-conductive member 40B.

  As shown in FIG. 2, in the electrode assembly 20, the region where the positive electrode active material of the positive electrode 22A is coated and the region where the negative electrode active material of the negative electrode 22B is coated are the same region. In the description, this region is referred to as an active material coating region 28.

  The case 12 houses a safety electrode unit 30 that is stacked outside the electrode assembly 20 and is interposed between the electrode assembly 20 and the case 12. The safety electrode unit 30 is provided on both surfaces of the electrode assembly 20 (that is, not only on the upper surface shown in FIG. 1 but also on the lower surface). Only the electrode unit 30 will be described.

  The safety electrode unit 30 includes a first metal foil 32A, a second metal foil 32B, and an insulating layer 34 interposed between the first metal foil 32A and the second metal foil 32B. Yes.

  The first metal foil 32A is a laminated metal foil in which three metal foils 35A, 35B, and 35C are laminated. Each of the metal foils 35A, 35B, and 35C is a metal foil made of the same type of metal as the metal foil constituting the positive electrode metal foil 23 described above, and is a metal foil (not yet coated with the positive electrode active material 24). Coating foil). These metal foils 35 </ b> A, 35 </ b> B, and 35 </ b> C are larger than the active material coating region 28 of the electrode assembly 20, and are configured by a region 38 corresponding to the active material coating region 28 and its remaining region 39. The remaining area 39 is an area protruding from the area 38 to the tab 351 side.

  In the first metal foil 32A, a laminated metal foil welded portion 36A penetrating in the laminating direction of the three metal foils 35A, 35B, and 35C is formed in the remaining region 39 by resistance welding. With this laminated metal foil welded part 36A, the three metal foils 35A, 35B, and 35C are electrically connected to each other and their relative positions are fixed. One of the three metal foils 35A, 35B, and 35C constituting the first metal foil 32A is one end of the metal foil 35A (the metal foil located on the innermost side and closest to the electrode assembly 20). Has a tab 351. This tab 351 is overlaid on the tab 231 of the positive electrode metal foil 23 and over the positive electrode conductive member 40A and is welded so as to be electrically connected to each other.

  The second metal foil 32B is a laminated metal foil in which three metal foils 37A, 37B, and 37C are laminated. Each of the metal foils 37A, 37B, and 37C is a metal foil made of the same type of metal as the metal foil that constitutes the negative electrode metal foil 25 described above, and is a metal foil that is not coated with the negative electrode active material 26 (not yet applied). Coating foil). Similarly to the metal foils 35A, 35B, and 35C, the metal foils 37A, 37B, and 37C are larger than the active material application region 28 of the electrode assembly 20, and correspond to the active material application region 28 and the remaining region 39. It consists of

  In the second metal foil 32B, a laminated metal foil welded portion 36B penetrating in the lamination direction of the three metal foils 37A, 37B, and 37C is formed in the remaining region 39 by resistance welding. With this laminated metal foil welded part 36B, the three metal foils 37A, 37B, 37C are electrically connected to each other and their relative positions are fixed. One of the three metal foils 37A, 37B, and 37C constituting the second metal foil 32B is one end of one metal foil 37A (the metal foil closest to the electrode assembly 20 located on the innermost side). Has a tab 371.

  Further, the case 12 is filled with an electrolyte (electrolytic solution) corresponding to the type of the secondary battery 10 such as a lithium ion secondary battery or a nickel hydride secondary battery.

  Next, the connection between the electrode assembly 20 of the secondary battery 10 and the safety measure electrode unit 30 will be described with reference to FIG. 2 is a cross-sectional view at the position of the tab 231 of the positive electrode 22A, the tab 251 of the negative electrode 22B is not shown.

  The safety measure electrode unit 30 is electrically connected to the electrode assembly 20 for each polarity. That is, the first metal foil 32A of the safety measure electrode unit 30 is connected to the positive electrode 22A of the electrode assembly 20, and the second metal foil 32B is connected to the negative electrode 22B of the electrode assembly 20. At this time, regarding the electrical connection of the positive electrode, a laminated metal foil is formed by laminating and welding three metal foils 35A, 35B, and 35C in advance, and then the metal foil 35A of the first metal foil 32A is formed. The tab 351 and the tab 231 of the positive electrode 22A are overlapped and resistance-welded to each other at each welding point W (that is, the welding point W2 of the tab 351 and the welding point W1 of the tab 231).

  Further, the tab 351 of the metal foil 35A of the first metal foil 32A and the tab 231 of the positive electrode 22A are superimposed on a positive electrode conductive member 40A connected to a positive electrode terminal (not shown) and resistance welded.

  Since the electrical connection of the negative electrode is the same as that of the positive electrode, the description thereof is omitted. The tab 371 (see FIG. 4) of the metal foil 37A of the second metal foil 32B and the tab 251 (see FIG. 1) of the negative electrode 22B are superimposed on a negative electrode conductive member 40B connected to a negative electrode terminal (not shown) and resistance welded. Is done.

  The resistance welding may be performed by either voltage control welding or current control welding. For example, the positive electrode may be welded by current control welding, and the negative electrode may be welded by voltage control welding. At the time of welding, a pressure of several thousand N is applied to the welding spot W having an area of about several square millimeters, and a current is passed for a time of several milliseconds to several seconds.

  As a method for welding the metal foil of the safety electrode unit 30 to the electrode assembly 20, there is a method as described below as a method different from the above. That is, first, only the metal foil 35A having the tab 351 is resistance-welded to the tab 231 of the positive electrode 22A of the electrode assembly 20, and then the remaining metal foils 35B and 35C are overlapped on the metal foil 35A to bond the metal foils together. Weld. Even with this method, the safety electrode unit 30 having the above-described configuration can be connected to the electrode assembly 20.

  Subsequently, as an example of a situation in which the secondary battery 10 receives an impact from the outside of the case, a case where the secondary battery 10 is nipped is described with reference to FIGS. 3 and 4.

  When the secondary battery 10 is pierced from the outside of the case along the thickness direction of the electrode assembly 20 and the nail 50 penetrates the positive electrode 22A and the negative electrode 22B of the electrode assembly 20, the electrode assembly 20 is short-circuited. Occurs.

  However, since the secondary battery 10 includes the safety electrode unit 30 interposed between the case 12 and the electrode assembly 20, the nail 50 is disposed before the safety electrode unit 30 reaches the electrode assembly 20. Pierce. As a result, as shown in FIG. 4, between the first metal foil 32A connected to the positive electrode conductive member 40A and the positive electrode 22A and the second metal foil 32B connected to the negative electrode conductive member 40B and the negative electrode 22B. A short circuit occurs and the remaining battery capacity of the electrode assembly 20 decreases. Therefore, even if a short circuit of the electrode assembly 20 occurs after that, a large current does not flow through the electrode assembly 20, and a situation in which abnormal heat generation or ignition occurs is suppressed.

  In particular, according to the safety measure electrode unit 30, both the first metal foil 32 </ b> A and the second metal foil 32 </ b> B are composed of laminated metal foils, compared with the case of being composed of a single metal foil. Thus, the electric resistance is low and the electricity can easily flow, thereby effectively suppressing the melting of the metal foil due to the resistance heat generation.

  Further, in the safety measure electrode unit 30, not all the metal foils constituting the first metal foil 32A and the second metal foil 32B are welded to the electrode assembly, but one metal foil 35A therein. , 37A are provided with tabs 351 and 371, and the tabs 351 and 371 are welded. By doing in this way, the heat capacity at the time of carrying out resistance welding of the 1st metal foil 32A and the 2nd metal foil 32B becomes small. Therefore, the temperature of the tabs 351 and 371 having the welding point W2 can be increased to the welding temperature in a short time, and thermal diffusion (heat escape to the tab) of the tabs 351 and 371 during welding is suppressed. Therefore, according to the safety measure electrode unit 30, it is possible to perform welding more easily than when all the metal foils constituting the first metal foil 32A and the second metal foil 32B are welded to the electrode assembly. it can.

  Further, in the safety measure electrode unit 30, the metal foils constituting the first metal foil 32A and the second metal foil 32B are resistance-welded to each other by the laminated metal foil welded portions 36A and 36B. When the metal foils are brought into surface contact with each other, the oxide film on the surface of the metal foil increases the electrical resistance. However, since the metal foils are welded together in the safety measure electrode unit 30, the oxide film The resistance between the metal foils is reduced without being affected by the increase in resistance. Thus, resistance heat generation can be suppressed by reducing the resistance between the metal foils. The number of laminated metal foil welded portions 36A and 36B is not limited to one, and a plurality of laminated metal foil welded portions 36A and 36B may be provided.

  However, the laminated metal foil welds 36A and 36B are provided in the remaining region 39 of the region 38 corresponding to the active material coating region 28 of the electrode assembly 20, that is, the laminated metal foil welds 36A and 36B are electrodes. It is preferable that it is provided so as not to overlap the active material coating region 28 of the assembly 20. This is because even if the laminated metal foil welded portions 36A and 36B have irregularities, the irregularities do not affect the pressure caused by the load applied to the electrode assembly 20.

  The number of metal foils constituting the laminated metal foil is not limited to three, and can be appropriately increased or decreased to, for example, about 2 to 30. Further, the number of metal foils connected to the electrodes of the laminated metal foil is not limited to one, and may be a plurality. Furthermore, the metal foil connected to the electrode of the laminated metal foil is not limited to the metal foil closest to the electrode assembly, but is a metal foil at other positions (for example, the center position or the position farthest from the electrode assembly). It may be.

  In addition, this invention is not limited to the said embodiment, A various deformation | transformation is possible. For example, the power storage device is not limited to a secondary battery, but may be another power storage device (for example, an electric double layer capacitor).

  DESCRIPTION OF SYMBOLS 10 ... Secondary battery, 12 ... Case, 20 ... Electrode assembly, 22A ... Positive electrode, 22B ... Negative electrode, 27 ... Separator, 30 ... Safety measure electrode unit, 32A ... 1st metal foil, 32B ... 2nd metal foil 34 ... Insulating layer, 36A, 36B ... Laminated metal foil weld, 40A, 40B ... Conductive member, 50 ... Nail.

Claims (5)

Case and
An electrode assembly housed in the case, a positive electrode formed by applying a positive electrode active material to a metal foil and a negative electrode formed by applying a negative electrode active material to a metal foil, and laminated via a separator;
A pair of conductive members composed of a positive electrode conductive member electrically connected to the positive electrode of the electrode assembly and a negative electrode conductive member electrically connected to the negative electrode of the electrode assembly;
A safety measure electrode unit laminated outside the electrode assembly and interposed between the electrode assembly and the case;
The safety measure electrode unit includes a first metal foil welded to the positive electrode conductive member, a second metal foil welded to the negative electrode conductive member, the first metal foil, and the second metal foil. And an insulating layer interposed between
The power storage device, wherein at least one of the first metal foil and the second metal foil is a laminated metal foil in which a plurality of metal foils are laminated.   The power storage device according to claim 1, wherein only a part of the laminated metal foil is welded to the conductive member.   The power storage device according to claim 1 or 2, wherein both the first metal foil and the second metal foil are laminated metal foils.   A plurality of metal foils constituting the laminated metal foil are welded to each other, and a laminated metal foil welded portion where the plurality of metal foils are welded is a region corresponding to an active material coating region of the electrode assembly. The power storage device according to claim 1, wherein the power storage device is in the remaining region.   The power storage device according to claim 1, wherein the power storage device is a secondary battery.

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