JP2018163817A - Power storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power storage device capable of suppressing breakage of an insulation sheet due to expansion of an electrode.SOLUTION: A secondary battery 10 comprises: a rectangular parallelepiped electrode assembly 12 alternately laminating a plurality of rectangular sheet-like positive electrodes and negative electrodes in a state of insulation with a separator; a rectangular parallelepiped case 11 housing the electrode assembly 12; and an insulation film 30 that is arranged between the electrode assembly 12 and the case 11, is formed in a bag-shape housing the electrode assembly 12, and insulates the electrode assembly 12 and the case 11. The piercing resistance of the insulation film 30 is set to 30 to 70 N.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a power storage device including an electrode assembly, a case that accommodates the electrode assembly, and an insulating sheet that is disposed between the electrode assembly and the case and insulates the two.

  A vehicle such as an EV (Electric Vehicle) or a PHV (Plug-in Hybrid Vehicle) is equipped with a secondary battery as a power storage device that stores power supplied to a traveling motor. The secondary battery includes an electrode assembly in which a rectangular sheet-like positive electrode and negative electrode are stacked, and a rectangular parallelepiped case that accommodates the electrode assembly. Moreover, the electrode assembly and the case are insulated by covering the electrode assembly with an insulating sheet formed in a bag shape (see Patent Document 1).

JP 2014-38736 A

  By the way, since the positive electrode and the negative electrode expand and contract during charging and discharging of the secondary battery, the insulating sheet may be sandwiched between the corners of the expanded positive electrode and negative electrode and the inner surface of the case, and the insulating sheet may be broken. There is. When the insulating sheet is broken, the electrode assembly and the case are short-circuited.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a power storage device that can suppress breakage of an insulating sheet due to expansion of an electrode.

  A power storage device for solving the above-described problems contains a rectangular parallelepiped electrode assembly in which a plurality of rectangular sheet-like positive electrodes and negative electrodes are alternately stacked in a state of being insulated by a separator, and houses the electrode assembly A rectangular parallelepiped case, and a bag-like container that is disposed between the electrode assembly and the case and accommodates the electrode assembly, and that insulates the electrode assembly from the case. The summary is that the puncture strength of the insulating sheet is 30 to 70 N.

  According to this, the positive electrode and the negative electrode expand when the power storage device is charged, the corners of the positive electrode and the negative electrode are pressed against the insulating sheet, and the pressed portions of the insulating sheet are the positive electrode and the negative electrode. Even if the insulating sheet is sandwiched between the corner portion and the inner surface of the case, the insulating sheet is hardly broken.

In the power storage device, the insulating sheet is preferably made of polypropylene having a thickness of 120 to 150 μm.
Insulating sheets made of the same material become harder to tear because the piercing strength increases as the thickness increases. On the other hand, the thicker the insulating sheet, the smaller the volume of the electrode assembly that occupies the case, and the capacity of the power storage device decreases. Therefore, when the insulating sheet is made of polypropylene, the thickness is set to 120 to 150 μm in consideration of both the piercing strength of the insulating sheet and the volume of the electrode assembly, thereby insulating without significantly reducing the capacity of the power storage device. Sheet tearing can be suppressed. Moreover, by making the insulating sheet made of polypropylene (PP), for example, the production cost of the insulating sheet can be reduced as compared with the case of making polyphenylene sulfide (PPS).

In the above power storage device, it is preferable that the negative electrode includes a current collector and an active material layer present on both surfaces or one surface of the current collector, and the active material layer includes silicon.
When the active material layer of the negative electrode includes silicon, the amount of expansion is large compared to the case where silicon is not included, and thus the load applied to the insulating sheet from the corner of the expanded negative electrode increases. For this reason, it is good to suppress a tear of an insulating sheet by employ | adopting an insulating sheet with a puncture strength of 30-70N.

  According to the present invention, it is possible to suppress the tearing of the insulating sheet due to the expansion of the electrode.

The disassembled perspective view of the secondary battery of embodiment. (A) is sectional drawing of the secondary battery of embodiment, (b) is an expanded sectional view of (a). The disassembled perspective view of the electrode assembly of embodiment.

Hereinafter, an embodiment embodying a power storage device will be described with reference to FIGS.
As shown in FIGS. 1 and 2A, the secondary battery 10 as a power storage device includes a case 11. The secondary battery 10 includes an electrode assembly 12 accommodated in a case 11. The case 11 includes a rectangular parallelepiped case main body 13 and a rectangular flat lid 14 that closes the opening 13 a of the case main body 13. Both the case main body 13 and the lid 14 constituting the case 11 are made of metal (for example, stainless steel or aluminum). Further, the secondary battery 10 of the present embodiment is a prismatic battery whose appearance is square. Further, the secondary battery 10 of the present embodiment is a lithium ion battery.

  The case main body 13 includes a bottom wall 13b (see FIG. 2A) and first to fourth wall portions 13c to 13f connected to the bottom wall 13b. The case body 13 includes a first wall portion 13c on one of the wall portions connected to the pair of long edges of the bottom wall 13b, and a second wall on the other wall portion facing the first wall portion 13c. A portion 13d is provided. The case main body 13 includes a third wall portion 13e on one of the wall portions connecting the first wall portion 13c and the second wall portion 13d and connecting to the pair of short edge portions of the bottom wall 13b. The other wall portion facing the third wall portion 13e is provided with a fourth wall portion 13f. As shown in FIG. 2, the case main body 13 has a bottom from the first to fourth wall portions 13c to 13f at a portion where the inner bottom surface of the bottom wall 13b intersects with the inner surfaces of the first to fourth wall portions 13c to 13f. It has a rounded corner 13g that faces the wall 13b. The case body 13 is manufactured by plastically deforming a metal plate by plastic working such as deep drawing or impact pressing. The corner 13g is generated during plastic processing.

  The secondary battery 10 includes a positive electrode terminal 15 and a negative electrode terminal 16 for taking out electricity from the electrode assembly 12. The positive electrode terminal 15 and the negative electrode terminal 16 are exposed to the outside of the case 11 through a pair of holes 14 a arranged in parallel with the lid 14 at a predetermined interval. Further, a ring-shaped insulating ring 17 a for insulating from the case 11 is attached to the positive terminal 15 and the negative terminal 16, respectively.

  As shown in FIG. 3, the electrode assembly 12 includes a plurality of positive electrodes 20 in the form of rectangular sheets as first electrodes, a plurality of negative electrodes 21 in the form of rectangular sheets as second electrodes, and a rectangular sheet shape. And a plurality of separators 28. The electrode assembly 12 has a structure in which a separator 28 is interposed between the positive electrode 20 and the negative electrode 21 and laminated in a state of being insulated from each other. The electrode assembly 12 has a rectangular parallelepiped shape.

  The positive electrode 20 includes a positive metal foil (for example, an aluminum foil) 22 as a rectangular sheet-shaped current collector, and a positive electrode active material layer 23 present on both surfaces of the positive metal foil 22. The positive electrode 20 includes a first edge portion 20a at one edge portion of the edge portions along the pair of long sides. The positive electrode 20 includes a positive electrode tab 24 having a shape protruding from a part of the first edge 20a. The positive electrode tab 24 is configured by the positive electrode metal foil 22 itself without the positive electrode active material layer 23.

  Further, the positive electrode 20 includes a second edge 20b on the other edge which is the opposite side of the first edge 20a among the edges along the pair of long sides. Further, the positive electrode 20 includes a third edge 20c on one edge of a pair of short edges connecting the first edge 20a and the second edge 20b, and the third edge 20c. A fourth edge portion 20d is provided on the other edge portion which is the opposite side. The positive electrode 20 includes a first corner 20e at a portion where the second edge 20b and the third edge 20c intersect, and a second corner at a portion where the second edge 20b and the fourth edge 20d intersect. 20f is provided.

  The negative electrode 21 includes a negative electrode metal foil (for example, copper foil) 25 as a rectangular sheet-shaped current collector, and negative electrode active material layers 26 present on both surfaces of the negative electrode metal foil 25. The negative electrode active material layer 26 is formed by applying an active material paste, in which an active material, a conductive additive, a solvent, and a binder are mixed, to a current collector and then drying it. The active material of this embodiment is silicon. By using silicon as the active material, for example, the capacity of the secondary battery 10 can be increased compared to the case of using carbon. On the other hand, the negative electrode active material layer 26 containing silicon has a large amount of expansion and contraction when the secondary battery 10 is charged and discharged. The negative electrode 21 includes a first edge portion 21a on one edge portion of the edge portions along the pair of long sides. The negative electrode 21 has a negative electrode tab 27 having a shape protruding from a part of the first edge 21a. The negative electrode tab 27 is configured by the negative electrode metal foil 25 itself without the negative electrode active material layer 26.

  Moreover, the negative electrode 21 is provided with the 2nd edge part 21b in the other edge part used as the opposite side of the 1st edge part 21a among the edge parts along a pair of long side. Furthermore, the negative electrode 21 includes a third edge 21c on one edge of the pair of short edges connecting the first edge 21a and the second edge 21b, and the third edge 21c. A fourth edge portion 21d is provided on the other edge portion which is the opposite side. The negative electrode 21 includes a first corner 21e at a portion where the second edge 21b and the third edge 21c intersect, and a second corner at a portion where the second edge 21b and the fourth edge 21d intersect. A portion 21f is provided. Hereinafter, a direction orthogonal to the surface of the negative electrode 21 is defined as a first direction X <b> 1 as a thickness direction of the negative electrode 21. The direction along the first and second edge portions 21a and 21b is defined as a second direction X2, and the direction along the third and fourth edge portions 21c and 21d is defined as a third direction X3.

  As shown in FIG. 1, each positive electrode 20 is stacked such that the respective positive electrode tabs 24 are arranged in a line along the stacking direction of the electrode assembly 12. Similarly, each negative electrode 21 is laminated so that the respective negative electrode tabs 27 are arranged in a line along the lamination direction of the electrode assembly 12 so as not to overlap the positive electrode tab 24. The positive electrode tabs 24 are collected in a range from one end to the other end in the stacking direction of the electrode assembly 12 to form a positive electrode tab group 24a. The positive electrode terminal 15 is electrically joined to the positive electrode tab group 24a. Similarly, the negative electrode tabs 27 are gathered in a range from one end to the other end in the stacking direction of the electrode assembly 12 to form a negative electrode tab group 27a. The negative electrode terminal 16 is electrically connected to the negative electrode tab group 27a.

  The electrode assembly 12 includes a tab-side end surface 12a in which a positive electrode tab group 24a and a negative electrode tab group 27a exist on the end surface facing the lid 14, and the bottom-side end surface 12b on the end surface facing the inner surface of the bottom wall 13b of the case body 13. Is provided. The bottom end face 12b is configured by laminating the second edges 20b and 21b of the positive electrode 20 and the negative electrode 21. In addition, the electrode assembly 12 includes a first side surface 12 c on an end surface facing the inner surface of the first wall portion 13 c of the case body 13, and a second side surface on the end surface facing the inner surface of the second wall portion 13 d of the case body 13. 12d. The electrode assembly 12 includes a third side surface 12e on the end surface facing the inner surface of the third wall portion 13e of the case body 13, and the fourth side surface 12f on the end surface facing the inner surface of the fourth wall portion 13f of the case body 13. Prepare. The third side surface 12e is configured by laminating the third edges 20c and 21c of the positive electrode 20 and the negative electrode 21, and the fourth side surface 12f is configured by the fourth edges 20d and 21d of the positive electrode 20 and the negative electrode 21. It is configured by stacking. Such an electrode assembly 12 is accommodated in an insulating film 30 as a bag-shaped insulating sheet.

Here, the positive electrode 20 and the negative electrode 21 during charging / discharging of the secondary battery 10 will be described.
When the secondary battery 10 is charged and discharged, the positive electrode active material layer 23 of the positive electrode 20 and the negative electrode active material layer 26 of the negative electrode 21 expand and contract in the second direction X2 and the third direction X3. The positive electrode active material layer 23 and the negative electrode active material layer 26 try to expand and contract in the first direction X1 as well. In general, the secondary battery 10 is charged / discharged by first holding the electrode assembly 12 with a restraining jig (not shown). Since it is performed in a state constrained in the direction X1, the amount of expansion and contraction in the first direction X1 is sufficiently small. As the positive electrode active material layer 23 and the negative electrode active material layer 26 expand, the positive electrode metal foil 22 of the positive electrode 20 and the negative electrode metal foil 25 of the negative electrode 21 also expand in the second direction X2 and the third direction X3. Thereby, a load is applied to the first portion 30a of the insulating film 30 from the first corner portions 20e and 21e of the positive electrode 20 and the negative electrode 21. Similarly, a load is applied to the second portion 30 b of the insulating film 30 from the second corner portions 20 f and 21 f of the positive electrode 20 and the negative electrode 21.

  The insulating film 30 is an insulating sheet for insulating the electrode assembly 12 from the metal case 11. The puncture strength of the insulating film 30 is set to 30 to 70N. The insulating film 30 of this embodiment is made of polypropylene (PP) having a thickness of 150 μm, and the piercing strength is 58N.

  The puncture strength is measured by the following method. First, the insulating film 30 is restrained by a restraining tool (not shown). The restraining tool includes a pair of restraining plates, a bolt that connects the pair of restraining plates, and a nut that is screwed to the bolt. Each constraining plate includes a through hole. Each constraining plate includes an annular silicon rubber on one side. The through hole communicates with the inside of the silicon rubber. Of the pair of restraining plates, one restraining plate is disposed so that the silicon rubber faces one surface of the insulating film 30, and the other restraining plate has the silicon rubber facing the other surface of the insulating film 30. Are arranged as follows. In this state, the nuts are screwed onto the bolts, so that the pair of restraining plates restrains the insulating film 30 via silicon rubber. The insulating film 30 is restrained in a stretched state (a state without wrinkles or deflection). Next, a nail (not shown) is lowered with respect to the restrained insulating film 30 at a constant speed (25 mm / min), and a load is applied to the insulating film 30. The nail has a diameter of 8 mm and has a tapered portion at the tip. The inclination angle of the tapered portion with respect to the central axis of the nail is 60 degrees. Then, the load immediately after the nail contacts the insulating film 30 and immediately before the tip of the nail penetrates the insulating film 30 is measured. The measured load is the puncture strength. That is, the piercing strength is a load applied to the insulating film 30 immediately before a hole is opened in the insulating film 30 by a nail.

  When the piercing strength of the insulating film 30 is smaller than 30N, it is not preferable because the insulating film 30 is likely to be broken due to the expansion of the positive electrode 20 and the negative electrode 21 described above. When the degree of expansion of the positive electrode 20 and the negative electrode 21 is large and the load applied to the insulating film 30 from each corner 20e, 20f, 21e, 21f of the positive electrode 20 and the negative electrode 21 exceeds 70 N, the entire electrode assembly 12 is Move toward the lid 14. Thereby, the insulating film 30 is not sandwiched between the corners 20e, 20f, 21e, 21f of the positive electrode 20 and the negative electrode 21 and the corner 13g of the case body 13, and the insulating film 30 may be broken. Is low. For this reason, the piercing strength of the insulating film 30 may be 70 N or less.

  The piercing strength of the insulating film 30 increases as the thickness of the insulating film 30 increases. On the other hand, as the insulating film 30 becomes thicker, the volume of the electrode assembly 12 occupying the case 11 becomes smaller, and the capacity of the secondary battery 10 decreases. Therefore, for example, in the case of the insulating film 30 made of polypropylene (PP), it is preferable to set the thickness to 120 to 150 μm in consideration of both the piercing strength of the insulating film 30 and the capacity of the secondary battery 10.

  The insulating film 30 of this embodiment is formed in a bag shape by folding and welding one insulating film 30. The insulating film 30 covers five surfaces (the bottom end surface 12b and the first to fourth side surfaces 12c to 12f) excluding the tab side end surface 12a of the electrode assembly 12. In the insulating film 30, a portion covering the first corner portions 20e and 21e of the positive electrode 20 and the negative electrode 21 is defined as a first portion 30a, and a portion covering the second corner portions 20f and 21f is defined as a second portion 30b. In a state where the electrode assembly 12 covered with the insulating film 30 is accommodated in the case main body 13, the first portion 30 a is located between the first corner portions 20 e and 21 e and the corner portion 13 g of the case main body 13. The two portions 30b are located between the second corner portions 20f and 21f and the corner portion 13g of the case body 13 (see FIG. 2B).

Next, the operation of this embodiment will be described.
Since the puncture strength of the insulating film 30 of the present embodiment is set to 30 to 70 N, even if the positive electrode 20 and the negative electrode 21 expand, the first part 30a and the second part 30b are not easily broken.

Next, the effect of this embodiment will be described.
(1) The puncture strength of the insulating film 30 is set to 30 to 70N. Therefore, when the secondary battery 10 is charged, the positive electrode 20 and the negative electrode 21 expand, and the first corners 20e and 21e and the second corners 20f and 21f of the positive electrode 20 and the negative electrode 21 are the first of the insulating film 30. The first portion 30a or the second portion 30b is pressed against the portion 30a or the second portion 30b, and is sandwiched between the first corner portions 20e and 21e or the second corner portions 20f and 21f and the corner portion 13g of the case body 13. However, the insulating film 30 is less likely to be broken.

  (2) The insulating film 30 is made of polypropylene (PP) having a thickness of 120 to 150 μm. Since the puncture strength increases as the thickness of the insulating film 30 increases, the tearing can be suppressed by increasing the thickness of the insulating film 30. On the other hand, as the insulating film 30 becomes thicker, the volume of the electrode assembly 12 occupying the case 11 becomes smaller, and the capacity of the secondary battery 10 decreases. Therefore, by setting both the piercing strength of the insulating film 30 and the capacity of the secondary battery 10 to set the thickness of the insulating film 30, the tearing of the insulating film 30 is suppressed without reducing the capacity of the secondary battery 10. it can. Further, by making the insulating film 30 made of polypropylene (PP), for example, the production cost of the insulating film 30 can be suppressed as compared with the case of making polyphenylene sulfide (PPS).

  (3) Since the negative electrode active material layer 26 contains silicon, the amount of expansion is larger than that of the negative electrode active material layer not containing silicon. Therefore, the load applied to the insulating film 30 from the corners 21e and 21f of the negative electrode 21 is also increased. For this reason, it is good to suppress the tearing of the insulating film 30 by employ | adopting the insulating film 30 whose puncture strength is 30-70N.

In addition, you may change the said embodiment as follows.
The current collector is not limited to the positive electrode metal foil 22 and the negative electrode metal foil 25 as long as the positive electrode active material layer 23 and the negative electrode active material layer 26 can be formed. For example, a woven or net-like sheet may be used.

  The positive electrode 20 may have a structure in which the positive electrode active material layer 23 exists on one side of the positive electrode metal foil 22. Similarly, the negative electrode 21 may have a configuration in which the negative electrode active material layer 26 exists on one surface of the negative electrode metal foil 25.

  (Circle) you may make the external shape of the electrode of one polarity of the positive electrode 20 and the negative electrode 21 larger than the external shape of the electrode of the other polarity. In this case, the insulating film 30 is sandwiched between the corner portion of the electrode having the larger outer shape and the corner portion 13 g of the case body 13.

  ○ The active material of the negative electrode active material layer 26 may be carbon, or may include both silicon and carbon. The type and ratio of the material used for the active material may be changed according to the capacity of the secondary battery 10.

O The puncture strength of the insulating film 30 of the above embodiment was 58 N, but may be appropriately changed within the range of 30 to 70 N.
The insulating film 30 of the above embodiment is made of polypropylene (PP) having a thickness of 150 μm, but the material and thickness of the insulating film 30 may be appropriately changed within a range where the puncture strength is 30 to 70N. Examples of other materials for the insulating film 30 include polyphenylene sulfide (PPS) and polyethylene (PE).

O The electrode assembly 12 may be covered by forming a plurality of insulating films 30 in a bag shape.
(Circle) the method of forming the insulating film 30 in a bag shape is not limited to welding. For example, the electrode assembly 12 is covered with a single insulating film 30. And you may affix with the tape so that the part which protruded from the electrode assembly 12 in the insulating film 30 may overlap with the part which has covered the electrode assembly 12. FIG. As another method, the electrode assembly 12 is housed in a bag-like insulating film 30 that is slightly larger than the electrode assembly 12, and then the insulating film 30 is thermally contracted, thereby the electrode assembly 12 and the insulating film. 30 may be brought into close contact with each other.

  The secondary battery 10 may be a lithium ion secondary battery or another secondary battery. In short, any ion may be used as long as ions move between the active material for the positive electrode and the active material for the negative electrode and charge is transferred.

  The power storage device can also be applied to power storage devices other than secondary batteries, such as capacitors.

  DESCRIPTION OF SYMBOLS 10 ... Secondary battery as an electrical storage device, 11 ... Case, 12 ... Electrode assembly, 20 ... Positive electrode, 21 ... Negative electrode, 25 ... Negative electrode metal foil as a collector, 26 ... Negative electrode active as an active material layer Material layer, 28 ... separator, 30 ... insulating film as an insulating sheet.

Claims (3)

A rectangular parallelepiped electrode assembly in which a plurality of rectangular sheet-like positive electrodes and negative electrodes are alternately laminated in a state insulated by a separator;
A rectangular parallelepiped case for housing the electrode assembly;
An insulating sheet that is disposed between the electrode assembly and the case and that accommodates the electrode assembly, and that insulates the electrode assembly from the case;
A power storage device comprising:
The electrical storage device, wherein the piercing strength of the insulating sheet is 30 to 70N.   The power storage device according to claim 1, wherein the insulating sheet is made of polypropylene having a thickness of 120 to 150 μm. The negative electrode has a current collector and an active material layer present on both sides or one side of the current collector,
The power storage device according to claim 1, wherein the active material layer contains silicon.