JP2018045797A - Secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery in which short-circuit can be suppressed.SOLUTION: The secondary battery includes: an electrode body 80; a battery case 50; an insulating film 20 provided between the electrode body 80 and an inner wall of the battery case 50; and a restraint member 90 for restraining the electrode body 80 while pressurizing it in a lamination direction 92 via the battery case 50 and the insulating film 20. The restraint pressure in the lamination direction 92 by the restraint member 90 is set to be in a range of 0.5 MPa to 10 MPa. When wall thickness of the battery case 50 is t1 (μm) and the wall thickness of the insulating film 20 is t2 (μm), the secondary battery satisfies relationships of 530≤t1≤1310, 80≤t2≤250, and 120000≤t1×t2≤130000.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a secondary battery. Specifically, the present invention relates to a secondary battery including an electrode body configured by laminating a positive electrode and a negative electrode via a separator.

  In recent years, lithium ion secondary batteries, nickel metal hydride batteries, and other secondary batteries (storage batteries) have become increasingly important as on-vehicle power supplies, or personal computers and portable terminals. In particular, a lithium ion secondary battery that is lightweight and obtains a high energy density is preferably used as a high-output power source mounted on a vehicle. In this type of secondary battery, a battery structure including an electrode body in which a sheet-like positive electrode and a sheet-like negative electrode are laminated via a separator is known.

  In this type of battery, an electrode body and a battery case (that is, an exterior container) may be manufactured separately, and then the electrode body may be accommodated in the battery case. In many cases, a metal package is used as the battery case. In this case, it is necessary to wrap the electrode body with an insulating film in order to insulate the metal package from the electrode body. For example, Patent Document 1 discloses a configuration of a secondary battery in which an electrode body is inserted into an insulating member formed of a polypropylene film in a bag shape, and the electrode body and a metal battery case are electrically insulated. Yes.

JP 2009-026704 A

By the way, when this type of secondary battery is mounted on a vehicle such as an automobile, an assembled battery comprising a plurality of such batteries connected in series is constructed in order to obtain high output. At that time, since it is premised on use in a state where vibration occurs in addition to limiting the mounting space, the assembled battery can be constructed in a state where a large number of batteries are arranged and restrained. At the time of such restraint, a considerable pressure (restraint pressure) is applied to each battery constituting the assembled battery. However, in a battery in which a restraint pressure is applied to the electrode body, when the insulating film described above is disposed between the electrode body and the battery case, the insulating film is broken by conductive foreign matters (for example, metal scraps) mixed in the battery, There was a case where the electrode body and the battery case were short-circuited. In addition, the foreign matter may pass through the separator and cause a short circuit between the positive and negative electrodes.
This invention is made | formed in view of this point, The main objective is to provide the reliable secondary battery which can suppress the said short circuit, even when a foreign material mixes in the inside of a battery.

  In order to solve the above problems, the secondary battery provided by the present invention includes an electrode body in which a positive electrode and a negative electrode are stacked in a stacking direction via a separator, and an aluminum battery that houses the electrode body. A polypropylene insulating film provided between a case, the electrode body and the inner wall of the battery case, and insulating the electrode body and the battery case; and disposed outside the battery case; And a restraining member that restrains the battery case and pressurizing in the stacking direction via the insulating film. The restraining pressure in the stacking direction by the restraining member is set within a range of 0.5 MPa to 10 MPa. When the thickness of the battery case is t1 (μm) and the thickness of the insulating film is t2 (μm), 530 ≦ t1 ≦ 1310, 80 ≦ t2 ≦ 250, 120,000 ≦ t1 × t2 ≦ 130000 Satisfy the relationship. According to such a configuration, a highly reliable secondary battery that can suppress a short circuit between the electrode body and the battery case and between the positive and negative electrodes even when foreign matter is mixed in the battery is provided.

FIG. 1 is a front view schematically showing a secondary battery according to an embodiment. FIG. 2 is a cross-sectional view schematically showing a secondary battery according to an embodiment. FIG. 3 is a cross-sectional view schematically showing a main part of the secondary battery according to the embodiment. FIG. 4 is a cross-sectional view schematically showing a main part of the secondary battery according to the embodiment. FIG. 5 is a cross-sectional view schematically showing a main part of a secondary battery of a comparative example. FIG. 6 is a cross-sectional view schematically showing a main part of a secondary battery of a comparative example.

  Embodiments according to the present invention will be described below with reference to the drawings. Note that the dimensional relationship (length, width, thickness, etc.) in each drawing does not reflect the actual dimensional relationship. Further, matters other than the matters specifically mentioned in the present specification and matters necessary for carrying out the present invention (for example, the configuration and manufacturing method of the electrode body including the positive electrode and the negative electrode, the shape of the battery (case), etc., General techniques related to battery construction, etc.) can be grasped as design matters of those skilled in the art based on conventional techniques in the field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field. Further, in the following drawings, members / parts having the same action are described with the same reference numerals, and overlapping descriptions may be omitted or simplified.

  Although not intended to be particularly limited, a preferred embodiment according to the secondary battery of the present invention will be described below mainly using a lithium ion secondary battery as an example. In this specification, the term “lithium ion secondary battery” refers to a secondary battery that uses lithium ions (Li ions) as electrolyte ions and is charged and discharged by the movement of charges associated with Li ions between the positive and negative electrodes. Say.

  FIG. 1 is a front view schematically showing the appearance of a lithium ion secondary battery according to an embodiment of the present invention, and FIG. 2 is a sectional view thereof. FIG. 3 is a cross-sectional view schematically showing a main part of the lithium ion secondary battery. As shown in FIGS. 1 to 3, the lithium ion secondary battery 100 according to this embodiment includes an electrode body 80 including a positive electrode 82 and a negative electrode 84, a battery case 50 that houses the electrode body 80, and an insulating film 20. And a restraining member 90.

  The battery case 50 includes a battery case main body 52 and a lid 54. The battery case main body 52 has a shape that can accommodate the electrode body 80. In this embodiment, the battery case main body 52 has a box shape that can accommodate the flat electrode body 80. The battery case main body 52 has an upper opening end 53, and is configured to accommodate the electrode body 80 via the upper opening end 53. The outer wall constituting the battery case main body 52 has wide side surfaces 52A (FIG. 1) formed at both ends in the thickness direction of the battery, and narrow side surfaces 52B (FIG. 1) formed at both ends in the battery width direction. The bottom surface 52C (FIG. 1). The lid 54 is a member that closes the upper opening end 53 of the battery case main body 52, and in this embodiment, a substantially rectangular plate-like member is suitably used. The material of the battery case main body 52 and the lid body 54 is aluminum (Al).

A safety valve 70 is provided on the upper surface of the lid 54 in the same manner as a conventional battery case. When the pressure in the battery case 50 rises abnormally, the safety valve 70 deforms a valve body (not shown) for safety, and internal gas or the like is released from a gap formed between the valve body and the lid 54. It is configured to be released. Further, a liquid injection port 62 is provided on the upper surface of the lid 54. The liquid injection port 62 can accommodate the electrolytic solution in the battery case 50 through the liquid injection port 62, and is normally sealed with a sealing plug 60. As the electrolytic solution that can be accommodated in the battery case 50, for example, a nonaqueous electrolytic solution in which an electrolyte is dissolved in a nonaqueous solvent can be used. In this embodiment, a mixed solvent of diethyl carbonate and ethylene carbonate (for example, a mass ratio of 1: 1) is used as the nonaqueous solvent, lithium hexafluorophosphate (LiPF ₆ ) is used as the electrolyte, and the concentration is It is adjusted to about 1 mol / liter.

  An electrode body 80 is accommodated in the battery case 50 together with the electrolytic solution. The electrode body 80 includes a positive electrode 82 and a negative electrode 84, and a separator 86 interposed between the positive and negative electrodes, like the electrode body of a normal lithium ion battery. The electrode body 80 is configured by laminating a positive electrode 82 and a negative electrode 84 with a separator 86 interposed therebetween. In this embodiment, the electrode body 80 is formed by laminating a positive electrode sheet 82 and a negative electrode sheet 84 together with a total of two separators 86, and further winding the positive electrode sheet 82 and the negative electrode sheet 84 with a slight shift, and then obtaining This is a flat wound electrode body 80 produced by crushing the laminating body from the side direction and causing it to be ablated.

  As a result of the winding electrode body 80 being wound with a slight shift as described above in the lateral direction with respect to the winding direction, the ends of the positive electrode sheet 82 and the negative electrode sheet 84 are respectively wound core portions 81 (that is, the positive electrode). The portion of the sheet 82 where the positive electrode active material layer is formed, the portion of the negative electrode sheet 84 where the negative electrode active material layer is formed, and the separator 86 are closely wound) protrudes outward. A positive electrode lead terminal 82B and a negative electrode lead terminal 84A are attached to such a positive electrode side protruding portion (ie, a non-forming portion of the positive electrode active material layer) 82A and a negative electrode side protruding portion (ie, a non-forming portion of the negative electrode active material layer) 84A. Are electrically connected to the positive terminal 42 and the negative terminal 44, respectively. In this embodiment, the positive electrode terminal 42 and the negative electrode terminal 44 are respectively attached to the lid body 54 of the battery case 50 via a gasket (not shown).

  The material and member itself constituting the wound electrode body 80 may be the same as the electrode body of the conventional lithium ion secondary battery, and are not particularly limited. For example, the positive electrode sheet 82 is formed by applying a positive electrode active material layer for a lithium ion secondary battery on a long positive electrode current collector (in this embodiment, an aluminum foil). On the other hand, the negative electrode sheet 84 is formed by providing a negative electrode active material layer for a lithium ion secondary battery on a long negative electrode current collector (copper foil in this embodiment). The total thickness of the negative electrode sheet 84 may be 90 μm, for example. Among them, the thickness of the negative electrode current collector can be, for example, 10 μm.

  Moreover, as a suitable separator 86 interposed between the positive / negative electrode sheets 82 and 84, what was comprised with the porous polyolefin-type resin is mentioned. For example, a porous separator made of synthetic resin (for example, made of polyolefin such as polyethylene) can be suitably used.

  Between the electrode body 80 and the inner wall of the battery case 50, the insulating film 20 that separates the electrode body 80 and the battery case 50 is disposed. The insulating film 20 is formed in a shape that surrounds (preferably encloses) the electrode body 80. Further, the insulating film 20 is configured to cover the entire wound electrode body 80. By interposing the insulating film 20 in this way, direct contact between the wound electrode body 80 that is a power generation element and the battery case 50 is avoided, and insulation between the wound electrode body 80 and the battery case 50 is ensured. Can do. The material of the insulating film 20 is polypropylene (PP).

  The restraining member 90 is a member that is disposed outside the battery case 50 and restrains the electrode body 80 while pressing the electrode body 80 in the stacking direction 92 via the battery case 50 and the insulating film 20. In this embodiment, an assembled battery is constructed in which the battery 100 is a single cell, and a plurality of the single cells are integrally held by a restraining member 90. This assembled battery is constrained in a state in which a plurality of batteries 100 are arranged in a predetermined direction (stacking direction 92) and a load is applied in the arrangement direction. Specifically, the plurality of batteries 100 are arranged so as to be inverted one by one so that the positive terminals 42 and the negative terminals 44 are alternately arranged, and the wide side surface 52A of the battery case 50 (FIG. 1). ) Are arranged in opposite directions. A restraining member 90 that restrains the plurality of batteries 100 together is provided around the arranged batteries 100. That is, a pair of restraining plates (constraining members 90) are arranged on the outer side of the battery 100 located on the outermost side in the unit cell arrangement direction. A tightening beam member is attached so as to bridge the pair of restraining plates. Then, the battery 100 can be restrained so that a predetermined load is applied in the arrangement direction by fastening and fixing the end of the beam member to the restraining plate with a screw. Restraint pressure (surface pressure) in the tightening direction (that is, the arrangement direction) is applied to the wide side surface of each battery 100 at a level corresponding to the tightening condition of the beam material. Here, the restraining pressure in the stacking direction 92 by the restraining member 90 is set in the range of 0.5 MPa to 10 MPa.

  The battery case 50 of this embodiment is made of a thin material (aluminum) that is easily distorted. Therefore, the restraining pressure applied in the arrangement direction (stacking direction 92) of the battery 100 is transmitted to the electrode body 80 via the wide side surface 52A and the insulating film 20 of the battery case 50. That is, the restraint pressure applied in the tightening direction (that is, the arrangement direction) at a level corresponding to the tightening condition of the beam material is used to reduce the restraint pressure in the stacking direction 92 set in the range of 0.5 MPa to 10 MPa in the battery case 50. It can be added to the electrode body 80.

In the technology disclosed herein, in the battery in which the binding pressure is applied to the stacking direction 92 of the electrode body 80 from the outside of the battery case 50 via the battery case 50 and the insulating film 20 as described above, When the thickness is t1 (μm) and the thickness of the insulating film 20 is t2 (μm), the following relationship:
530 ≦ t1 ≦ 1310,
80 ≦ t2 ≦ 250,
120,000 ≦ t1 × t2 ≦ 130000
Meet. Thereby, even when conductive foreign matter (for example, metal scraps) is mixed in the battery, it is possible to appropriately suppress a short circuit between the electrode body 80 and the battery case 50 and between the positive electrode 82 and the negative electrode 84.

  The reason why such an effect is obtained is not particularly limited, but may be considered as follows, for example. That is, as shown in FIG. 5, when the thicknesses t1 and t2 of both the insulating film 20 and the battery case 50 are too thin, if the conductive foreign matter 94 is mixed in the battery, the foreign matter 94 is not completely embedded in the insulating film 20. The load applied from the foreign matter 94 is directly applied to the battery case 50. At that time, since the deformation of the battery case 50 is restricted by the restraining member 90, the load further increases. As a result, the insulating film 20 is broken by the foreign matter 94 and the electrode body 80 and the battery case 50 are easily short-circuited. On the other hand, if the thicknesses t1 and t2 of both the insulating film 20 and the battery case 50 are too thick, the deformation of the insulating film 20 and the battery case 50 is limited as shown in FIG. The foreign material 94 is hardly embedded in the insulating film 20. As a result, the foreign matter 94 penetrates the separator 86 and the positive electrode 82 and the negative electrode 84 are easily short-circuited. On the other hand, in a battery in which the thickness t1 of the battery case 50 and the thickness t2 of the insulating film 20 satisfy the above relationship, the conductive foreign matter 94 mixed in the battery is moderately applied to the insulating film 20 as shown in FIG. The load applied from the foreign material 94 is relieved by being buried in. Moreover, the load is further reduced by the battery case 50 being deformed in the same manner as the insulating film 20. As a result, breakage of the insulating film 20 and the separator 86 can be suppressed. This is considered to contribute to the suppression of the short circuit.

  The product (t1 × t2) of the wall thickness t1 of the battery case 50 and the wall thickness t2 of the insulating film 20 is usually 120,000 or more, typically 122000 or more, for example, 124000 or more. Further, the product of the thickness (t1 × t2) is usually 130,000 or less, typically 128000 or less, for example 126000 or less. In a battery having a product with a thickness within a predetermined range (t1 × t2), the foreign matter 94 mixed in the battery is appropriately embedded in the insulating film 20 and the battery case 50. Therefore, the application effect of the technique disclosed herein can be appropriately exhibited.

  The thickness t1 of the battery case 50 is usually 530 μm or more. The thickness t1 of the battery case 50 is, for example, 600 μm or more, typically 700 μm or more, from the viewpoint of suppressing breakage of the insulating film 20 (and hence short-circuiting between the battery case 50 and the electrode body 80). Further, the thickness t1 of the battery case 50 can be, for example, 1310 μm or less. From the viewpoint of suppressing the breakage of the separator 86 (and hence the short circuit between the positive electrode 82 and the negative electrode 84), it is, for example, 1000 μm or less, typically 900 μm or less. For example, a battery case 50 having a wall thickness t1 of 600 μm or more and 1300 μm or less (for example, 700 μm or more and 900 μm or less) can be preferably used.

  The thickness t2 of the insulating film 20 is usually 80 μm or more. The thickness t2 of the insulating film 20 is, for example, 100 μm or more, typically 130 μm or more, from the viewpoint of suppressing breakage of the insulating film 20 (and hence short circuit between the battery case 50 and the electrode body 80). Further, the thickness t2 of the insulating film 20 is usually 250 μm or less. From the viewpoint of suppressing the breakage of the separator 86 (and hence the short circuit between the positive electrode 82 and the negative electrode 84), the thickness t2 of the insulating film 20 is, for example, 220 μm or less, typically 180 μm or less. For example, the insulating film 20 having a wall thickness t2 of 100 μm or more and 200 μm or less (for example, 130 μm or more and 180 μm or less) can be preferably used.

  Next, although the test example regarding this invention is demonstrated, it is not intending to limit this invention to what is shown to a test example.

  Here, the evaluation cell includes a wound electrode body configured by winding a positive electrode sheet and a negative electrode sheet through a separator, an aluminum battery case containing the wound electrode body, and a wound electrode body. And an insulating film made of polypropylene provided between the battery case and an inner wall of the battery case, and a restraining member that applies a restraining pressure in the stacking direction of the wound electrode body from the outside of the battery case. Here, batteries with different thicknesses t1 of the battery case, thickness t2 of the insulating film, and restraining pressure in the stacking direction applied to the electrode bodies were produced.

The positive electrode sheet is made of LiNi _1/3 Mn _1/3 Co _1/3 O ₂ powder as positive electrode active material particles contained in the positive electrode active material layer, polyvinylidene fluoride (PVDF) as a binder, and acetylene black (AB) as a conductive material. Using. Here, the mixture for forming the positive electrode active material layer includes LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , PVDF, AB, and N-methylpyrrolidone (NMP) as a dispersion solvent. Were prepared in a predetermined mass proportion. And this mixture paste was apply | coated on both surfaces of the aluminum foil as a positive electrode electrical power collector, it was made to dry, and it rolled, and formed the positive electrode sheet.

  The negative electrode sheet used graphite powder as the negative electrode active material particles contained in the negative electrode active material layer, styrene butadiene rubber (SBR) as the binder, and carboxymethyl cellulose (CMC) as the thickener. Here, a mixture paste prepared by mixing graphite, SBR, CMC, and water as a dispersion solvent in a mass ratio was prepared as a mixture for forming the negative electrode active material layer. And this mixture paste was apply | coated on both surfaces of the copper foil as a negative electrode collector, it was made to dry and it rolled, and the negative electrode sheet was formed. The thickness of the negative electrode sheet was 90 μm, and the thickness of the negative electrode current collector was 10 μm.

A polyethylene porous resin sheet was used for the separator. As the electrolytic solution, ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate were mixed at a volume ratio of 3: 4: 3, and 1.1 mol of LiPF ₆ was dissolved.

  The positive electrode sheet and the negative electrode sheet were laminated via a separator, and the laminated body was wound to produce a wound electrode body. Subsequently, the wound electrode body was accommodated in a bag-like insulating film, and this was accommodated in a box-shaped battery case together with the electrolyte solution, thereby producing an evaluation cell. Then, the restraint member restrains the wide side surface of the battery case of the obtained evaluation cell, and sets the restraint pressure by the restraint member so that a predetermined pressure is applied to the stacking direction of the electrode bodies accommodated in the battery case. did.

  The cell for evaluation of each example differs in the thickness t1 of the battery case, the thickness t2 of the insulating film, and the binding pressure. Tables 1 to 7 collectively show battery case thickness t1, insulating film thickness t2, product of thickness (t1 × t2), and restraint pressure (only Table 7) for the evaluation cells according to each example. . In addition, about the evaluation cell of Table 1-Table 6, the restraint pressure was set to 1 MPa.

<Foreign matter contamination test>
For each evaluation cell in each example, a spherical conductive foreign substance (particle size: 500 μm) is mixed between the inner wall of the wide side surface of the battery case and the insulating film, and the electricity between the battery case and the electrode body, and between the positive electrode and the negative electrode. Resistance was measured. When the electric resistance was 100Ω or less, it was determined that the battery case and the electrode body or the positive electrode and the negative electrode were short-circuited. In addition, the particle size of 500 μm of the conductive foreign matter used is the maximum particle size of the conductive foreign matter that may be mixed in the battery. The results are shown in the corresponding columns of Tables 1-7.

  As shown in Tables 1 to 6, the thickness t1 (μm) of the battery case and the thickness t2 (μm) of the insulating film are 530 ≦ t1 ≦ 1310, 80 ≦ t2 ≦ 250, and 120,000 ≦ t1 × t2. The evaluation cells of Examples 8 to 13, 26 to 32, 44 to 54, 64, 77, 78, and 94 satisfying the relationship of ≦ 130,000 were not short-circuited even after foreign matters were mixed therein, and the foreign matter resistance was good. Moreover, as shown in Table 7, it can be seen that such a short-circuit suppressing effect can be effectively exhibited when the restraining pressure by the restraining member is in the range of 0.5 MPa to 10 MPa.

  From the above, in the battery in which the constraint pressure is set within the range of 0.5 MPa to 10 MPa, the thickness t1 (μm) of the battery case and the thickness t2 (μm) of the insulating film are 530 ≦ t1 ≦ 1310, 80 ≦ By satisfying the relationship of t2 ≦ 250 and 120,000 ≦ t1 × t2 ≦ 130000, it is confirmed that short-circuiting between the electrode body and the battery case and between the positive electrode and the negative electrode can be suppressed even when foreign matter is mixed inside the battery. It was.

  Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The invention disclosed herein can include various modifications and alterations of the specific examples described above.

20 Insulating film 50 Battery case 80 Electrode body 82 Positive electrode 84 Negative electrode 86 Separator 90 Restraining member 92 Laminating direction 94 Conductive foreign matter 100 Secondary battery

Claims (1)

An electrode body configured by laminating a positive electrode and a negative electrode in a laminating direction via a separator;
An aluminum battery case containing the electrode body;
An insulating film made of polypropylene provided between the electrode body and the inner wall of the battery case, and insulating the electrode body and the battery case;
A restraining member that is disposed outside the battery case and restrains the electrode body while pressurizing the electrode body in the stacking direction via the battery case and the insulating film;
The restraining pressure in the stacking direction by the restraining member is set within a range of 0.5 MPa to 10 MPa,
When the thickness of the battery case is t1 (μm) and the thickness of the insulating film is t2 (μm), the following relationship:
530 ≦ t1 ≦ 1310,
80 ≦ t2 ≦ 250,
120,000 ≦ t1 × t2 ≦ 130000
Satisfying secondary batteries.

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