JP5780048B2 - Winding type secondary battery - Google Patents

Description

  The present invention relates to a wound secondary battery obtained by winding a strip-like positive and negative electrode plate. More specifically, the present invention relates to a wound secondary battery wound into a flat shape.

  Conventionally, for example, a wound secondary battery such as a lithium ion secondary battery has been used. In this wound type secondary battery, the positive electrode plate and the negative electrode plate are wound so as to face each other with a separator interposed therebetween. In secondary batteries, it is known that the battery temperature may be higher than during normal use due to causes such as overcharge and micro short circuit. Since the separator is usually made of resin, it may shrink or deform depending on the temperature rise.

  If the separator shrinks between the positive electrode plate and the negative electrode plate or a hole is formed by deformation, the insulation at that location may not be maintained, which is not preferable. On the other hand, for example, Patent Document 1 discloses a secondary battery in which a tape having high heat resistance is wound around the outermost periphery of a wound electrode body. Thereby, even if battery temperature rises, it is supposed that the insulation of an exterior can and an electrode body is maintained, and a short circuit is prevented. Patent Document 2 discloses a secondary battery in which a heat-resistant layer is provided on a part of the separator surface.

JP 2000-251866 A JP 2005-302634 A

  However, in the technique described in the above-described conventional patent document 1, no measures are taken for the inside of the electrode body even if insulation between the outer can and the can is ensured. In a wound type secondary battery, generally, the inner peripheral side tends to become high temperature, and it is particularly necessary to secure insulation between the positive electrode plate and the negative electrode plate in the innermost periphery. In particular, in an electrode body wound in a flat shape, a stress due to a relatively large bending deformation is applied to the electrode plate and the separator at an R portion formed between the flat surfaces. For this reason, there was a risk that the separator at this location could be deformed simply by making the separator somewhat flexible by the temperature rise.

  In the technique of Patent Document 2, since the heat-resistant layer is formed on the separator, when the separator contracts due to a temperature rise or the like, the heat-resistant layer also moves together with the separator. Therefore, when the temperature is raised, there is a possibility that there is no heat-resistant layer at a position where insulation is desired.

  The present invention has been made to solve the problems of the above-described conventional wound secondary battery. That is, an object of the present invention is to provide a wound secondary battery that can reliably ensure insulation between the positive electrode plate and the negative electrode plate even when the temperature inside the secondary battery rises.

In order to solve this problem, the wound type secondary battery of the present invention includes a wound body in which a positive electrode and a negative electrode plate are wound together with a separator in a flat shape, and an electrolyte solution enclosed in a battery case. In the wound type secondary battery, the wound body has an R portion formed between the flat portion and the flat portion, and at least the innermost circumferential side of the wound portion of the R portion. Is provided at a position between the first electrode plate and the second electrode plate, and has an insulator provided separately from the separator that allows the electrolyte to pass therethrough. It is arranged over the entire width in the winding axis direction and has a shrinkage rate of 1.5% or less when left at 150 ° C. for 10 minutes.

According to the wound secondary battery of the present invention, the insulator is provided in the R portion of the wound body. In particular, since it is located at the position between the first and second electrode plates from the innermost circumference side of the winding, the insulation state is secured at the inner circumference side where heat tends to accumulate. can do. This insulator is provided separately from the separator included in the wound body. Further, the separator may be disposed on the inner peripheral side or the outer peripheral side of the separator between the first electrode plate and the second electrode plate from the innermost peripheral side. Furthermore, since the insulator allows the electrolyte to permeate, it does not affect the performance of the secondary battery. Therefore, even when the temperature inside the secondary battery rises, it is a wound secondary battery that can reliably ensure insulation between the positive electrode plate and the negative electrode plate. In addition, since an insulator having a small shrinkage rate is used, the insulation state can be secured even when the temperature of the secondary battery rises.

Furthermore, in the present invention, it is desirable that the thickness of the insulator is in the range of 10 to 15 μm .

Furthermore, in the present invention, it is desirable that the insulators are respectively provided in the R portions on both sides so as not to overlap each other.
If it is in this way, the insulation state of R part can be ensured, without providing an insulator larger than necessary.

  According to the wound secondary battery of the present invention, it is possible to reliably ensure insulation between the positive electrode plate and the negative electrode plate even when the temperature inside the secondary battery rises.

It is a perspective view which shows the internal structure of the secondary battery of this form. It is explanatory drawing which shows a part of electrode body. It is explanatory drawing which shows a part of electrode body.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to a flat lithium ion secondary battery.

  As shown in FIG. 1, the secondary battery 10 of this embodiment is configured by enclosing an electrode body 11 wound in a flat shape in a battery case 12 together with an electrolytic solution 13. The electrode body 11 of this embodiment is a flat wound body. And the upper and lower locations in the figure of the electrode body 11 are R portions 14 having a smaller curvature than the other locations. Insulators 21 are sandwiched between the inner peripheral portions of the upper and lower R portions 14.

  As shown in FIG. 1, the insulator 21 has a width that reaches both end portions of the electrode body 11 in the winding axis direction and a length that covers the R portion 14 in the circumferential direction of the electrode body 11. The insulator 21 is U-shaped by bending a plate-like member along the shape of the R portion 14. Note that it is preferable that the width of the insulator 21 does not hit the battery case 12. It is desirable that the length of the insulator 21 (the length in the circumferential direction of the electrode body 11) be such that the two sheets on both sides do not overlap each other. For example, the length of the insulator 21 is preferably smaller than half of the innermost circumference of the electrode body 11. Further, it is desirable that the insulator 21 does not cover the flat portion of the electrode body 11 so much.

  The R portion 14 of the electrode body 11 includes a negative electrode plate 31, a positive electrode plate 32, and a separator 33 as shown in an enlarged view of a part of FIG. This figure shows a cross section of a range A indicated by a dashed line in FIG. The electrode body 11 has the same configuration with respect to another R portion 14 shown below in FIG.

  The negative electrode plate 31 is obtained by forming a negative electrode active material layer on a copper foil. The positive electrode plate 32 is obtained by forming a positive electrode active material layer on an aluminum foil. In the electrode body of this embodiment, the negative electrode plate 31 is wound from the positive electrode plate 32 to the inner peripheral side. There are actually two separators 33. One sheet is disposed in contact with the outer peripheral surface of the negative electrode plate 31 and the inner peripheral surface of the positive electrode plate 32, and the other sheet is disposed in contact with the outer peripheral surface of the positive electrode plate 32 and the inner peripheral surface of the negative electrode plate 31. .

  Then, one end portions of the two separators are overlapped and wound around the innermost periphery of the electrode body 11. The separator 33 of this embodiment has a three-layer structure of PP (polypropylene) / PE (polyethylene) / PP and has a shutdown function. The separator 33 contracts to some extent as the temperature rises.

  As shown in FIG. 2, the insulator 21 of this embodiment is disposed between the innermost peripheral portion of the negative electrode plate 31 and the separator 33 on the outer peripheral side thereof. The insulator 21 of this embodiment is an insulating film having thermoplasticity and has a shrinkage rate at 150 ° C. of 1.5% or less. Here, the shrinkage rate is the rate of decrease of the length after leaving the insulator 21 at 150 ° C. for 10 minutes from the length before leaving. Furthermore, the insulator 21 of the present embodiment has many minute holes and can transmit the electrolytic solution 13.

As the insulator 21 of this embodiment, for example, a mesh material made of PET (polyethylene terephthalate), PEN (polyethylene naphthalate), or the like is suitable. Furthermore, the thickness of the insulator 21 of this embodiment is preferably in the range of 10 to 15 μm. Further, the length of the insulator 21 in the circumferential direction of the winding of the electrode body 11 is preferably within a range of 15 to 25 mm, for example.

  The insulator 21 is made of a material that is less likely to heat shrink than the separator 33. Even in a situation where the separator 33 contracts, the degree of contraction of the insulator 21 is very small, and the insulator 21 can maintain almost the original width. Furthermore, the insulator 21 is only sandwiched between the electrode bodies 11 and is not fixed to the separator 33. Therefore, it is not pulled by the separator 33 and moved together. Therefore, even if the temperature of the secondary battery rises, the entire R portion 14 can be continuously insulated in the axial direction by the insulator 21.

The inventor has confirmed the effect of the present invention by experiments. In this experiment, various batteries were manufactured, and an overcharge test and resistance measurement were performed on each of them. The overcharge test was performed by continuously charging the secondary battery at a constant current and a constant voltage of 50A-30V in an environment of 60 ° C., and observing the state 20 minutes after the start of charging. Evaluation was as follows.
○ that there was no abnormality
X that has been confirmed abnormal

The resistance was obtained by the present inventors by discharging the batteries of each example at 120 A for 10 seconds in an environment of 25 ° C. and measuring the discharge resistance. The resistance was expressed as an index with the value of Comparative Example 1 as 100. Note that arbitrary index of resistance favored more if the 9 8 or more.

  Table 1 shows the material of the insulator used in this experiment and the results of the evaluation test. In this experiment, the materials of the insulator inserted into the R portion 14 of the electrode body in Examples 1 to 4 are as shown in the above table. Example 1 was a PET mesh material, and Example 2 was a PEN mesh material. In Example 3, an ion permeable paper separator was used. Moreover, the aramid nonwoven fabric of Example 4 used the nonwoven fabric of the aramid single-piece | unit.

The numerical values in the above table have the following meanings.
As for the arrangement, an insulator inserted into the R portion 14 separately from the separator is referred to as “R portion insertion”, and an insulator not inserted is referred to as a “separator”. Of course, all the embodiments are “R section insertion”. On the other hand, the comparative example includes both “R section insertion” and “separator”.
In the case of “inserted R part”, the material is the material of the inserted insulator, and “Separator” indicates the material of the separator.
The thickness is the thickness of the inserted insulator in the case of “R portion insertion”, and the thickness of the separator is shown in “Separator”. Note that “6 + 20” in Comparative Example 3 means that a 6 μm thick ceramic heat-resistant layer was applied to a 20 μm separator.
For the shrinkage rate, various insulators were allowed to stand at 150 ° C. for 10 minutes, and the ratio of the shrinkage before leaving was determined.

In Comparative Examples 1 to 4, the insulator was not inserted into the R portion 14.
Comparative Example 1 used a PP / PE / PP three-layer separator, and Comparative Example 4 used a PE single-layer separator.
The comparative example 2 uses the nonwoven fabric containing PE and an aramid fiber as a separator.
The separator of Comparative Example 3 is obtained by providing a ceramic heat-resistant layer on the surface of the separator of Comparative Example 1.
In Comparative Example 5, an insulator having the same material as that of Example 1 and having a shrinkage rate exceeding the range of the present invention is inserted into the R portion 14.
In the fifth embodiment, an insulator having the same material as that of the first embodiment and having a thickness exceeding a preferable range is inserted into the R portion 14.

As shown in Table 1, in Examples 1 to 4, both the result of the overcharge test and the resistance value were within an appropriate range. By inserting these materials into the R portion 14, it was confirmed that a short circuit due to thermal contraction can be prevented while maintaining battery characteristics. On the other hand, Comparative Examples 1 to 5 were not good in the result of the overcharge test. Even when a PET mesh was inserted, it was confirmed that sufficient effects could not be obtained with a material having a large shrinkage rate as in Comparative Example 5. Also obtained by inserting a PET mesh is too thick as in Example 5, Ru in the performance disadvantage der battery While overcharging test was confirmed that no problem. Thus preferably, the thickness of the insulating material, it was confirmed that good Ikoto better be up to 15μm.

  As described above in detail, according to the secondary battery 10 of this embodiment, the insulator 21 is provided between the innermost positive electrode plate and the innermost negative electrode plate in the R portion 14 of the electrode body 11. Has been inserted. Therefore, even if the separator 33 contracts due to a high temperature, the insulation in the R portion 14 is maintained. That is, even when the internal temperature rises, the secondary battery can reliably ensure insulation between the positive electrode plate and the negative electrode plate.

In addition, this form is only a mere illustration and does not limit this invention at all. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof.
As shown in FIG. 3, the insulator 21 may be disposed between the separator 33 on the outer peripheral side of the innermost negative electrode plate 31 and the innermost positive electrode plate 32. Further, the number of insulators 21 is not limited to one for each R portion 14. It may be provided not only on the innermost circumference but also between the negative electrode plate 31 and the positive electrode plate 32 on the second or third round from the innermost circumference.

DESCRIPTION OF SYMBOLS 10 Secondary battery 11 Electrode body 12 Battery case 13 Electrolytic solution 14 R part 21 Insulator 31 Negative electrode plate 32 Positive electrode plate 33 Separator

Claims (3)

In a wound secondary battery in which an electrode plate of a positive electrode and a negative electrode is wound together with a separator into a flat shape, and a wound secondary battery in which an electrolyte is enclosed in a battery case,
The wound body is
R part is formed between the flat part and the flat part,
The R portion is disposed at least at a position between the first electrode plate and the second electrode plate from the innermost circumferential side of the winding , and is provided separately from the separator that allows the electrolytic solution to pass therethrough. An insulated insulator,
The insulator is
Arranged over the entire width of the winding body in the winding axis direction;
A wound secondary battery having a shrinkage rate of 1.5% or less when left at 150 ° C. for 10 minutes. The wound secondary battery according to claim 1,
A wound secondary battery, wherein the insulator has a thickness in the range of 10 to 15 µm . The wound secondary battery according to claim 1 or 2,
The wound secondary battery according to claim 1, wherein the insulators are provided in R portions on both sides so as not to overlap each other.

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