JP2007026689A - Flat cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flat cell causing no internal short-circuit due to swelling of a positive electrode in discharge without reducing positive electrode capacity by arranging a step part on a sealing board opposite face in a gasket bottom part and housing a separator in a space formed of the gasket step part and the sealing board while bringing the circumference part of the separator into contact with the sealing board opposite face of the gasket step part in a flat cell using a hat-shaped sealing board. <P>SOLUTION: A step part is arranged on the sealing board opposite face of the gasket bottom part, and a space formed on the gasket step part and the sealing board is used as a separator housing part. When the separator is housed in the separator housing part while the circumference part of the separator is brought into contact with the sealing board opposite face in the gasket step part, the positive electrode and the sealing board are separated from each other by the separator. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a flat battery in which a power generation element is sealed with a positive electrode case, a sealing plate and a gasket, and more particularly to the shape of the gasket.

  In recent years, a flat nonaqueous electrolyte battery (hereinafter simply referred to as a “flat battery”) in which a power generation element in which a nonaqueous electrolyte is combined with an alkali metal or an alloy thereof is housed in a flat battery case is excellent. Since it has reliability and high energy density, it is suitably used as a driving power source for various small electronic devices and a memory backup power source. Up to now, this type of battery has been mainly a primary battery that cannot be recharged. However, in recent years, various rechargeable secondary batteries have been developed, and the demand is increasing as a backup power source for memory and clock functions. Recently, the demand for electronic devices such as mobile phones and digital still cameras has been increasing rapidly. However, along with the downsizing and thinning of these electronic devices, the flat and small batteries placed inside the devices are also small and thin. Is required.

  As a structure enabling thinning, as shown in Patent Document 1, a sealing plate comprising a planar central portion protruding to the outer surface side of the positive electrode case and a planar peripheral portion extending substantially parallel to the central portion ( A flat battery has been proposed in which a hat-shaped sealing plate) and a positive electrode case are used, the peripheral edge of the separator is disposed between the gasket and the hat-shaped sealing plate, and the power generation element is sealed via the gasket. However, in the battery of this structure shown in FIG. 4, when the separator 44 is pulled at the time of sealing, tension is applied to a portion that mainly contacts the corner of the pellet-like positive electrode 16, and the separator 44 is cut or torn. However, this has caused a problem of causing an internal short circuit.

In order to solve this problem, as shown in FIG. 3, a flat separator 34 is arranged between the positive electrode 16 and the negative electrode 15, and the hat-shaped sealing plate 11 and the positive electrode case 12 through the gasket 33 are used. There is a method of sealing the power generation element (for example, Patent Document 2).
US Pat. No. 5,486,431 Re-publication 00/0335033

  However, in the battery structure of FIG. 3, the inner surface of the sealing plate 11 is not completely covered with the separator 34 when viewed from the positive electrode 16 side. Therefore, when the battery is discharged, the positive electrode 16 expands and the inner surface of the sealing plate 11 Contact could cause an internal short circuit. Therefore, it is necessary to mold the positive electrode 16 so small that an internal short circuit does not occur even if the positive electrode 16 expands due to discharge, and there is a problem that the capacity cannot be increased.

  An object of the present invention is to solve such problems and to provide a flat battery having a high capacity and excellent in prevention of internal short circuit.

  To achieve the above object, the flat battery of the present invention is a flat battery in which a positive electrode, a negative electrode, an electrolyte, and a separator are sealed with a hat-shaped sealing plate and a positive electrode case via a gasket. The gasket has a stepped portion at the portion facing the sealing plate, and the peripheral portion of the separator is stored in a separator storage portion formed by the stepped portion and the sealing plate. By using the gasket of the present invention, even if the positive electrode expands during discharge, the separator is isolated from the sealing plate by the separator. Therefore, the positive electrode and the sealing plate do not contact each other, and an internal short circuit can be prevented.

  According to the present invention, it is possible to provide a flat battery that has a high capacity and does not cause an internal short circuit even if it is thin.

  A flat battery in which a positive electrode, a negative electrode, an electrolyte, and a separator are sealed with a hat-shaped sealing plate and a positive electrode case via a gasket, and a step portion is provided at a portion facing the sealing plate of the gasket. The separator housing portion formed by the stepped portion and the sealing plate has a structure in which the peripheral edge portion of the separator is accommodated, so that the separator is cut due to excessive pulling during the sealing. And tearing can be prevented. Further, by providing a structure in which a convex portion is provided at the end portion of the gasket step portion on the side facing the sealing plate, the peripheral portion of the separator is provided with a convex portion and a sealing portion provided at the end portion of the gasket step portion on the side facing the sealing plate It can be clamped by a plate and fixed more stably. In addition, even if the convex part provided in the edge part by the side of the sealing board opposing surface of a step part is formed continuously, the effect of this invention can be show | played.

  Hereinafter, a preferred embodiment of the present invention will be described with reference to the drawings, taking a non-aqueous electrolyte secondary battery as an example. The present invention is not limited to the secondary battery.

  The flat battery of the present invention is integrally formed in a hat shape using a clad material of an aluminum alloy and stainless steel that can serve as one electrode terminal, and can serve as the other electrode terminal, and can absorb and release lithium. The power generation element is sealed by the molded sealing plate 11 and the gasket 13 that insulates the positive electrode case 12 and the sealing plate 11.

  A stepped portion is provided at the sealing plate facing portion at the bottom of the gasket 13, and a separator housing portion formed by this stepped portion and the sealing plate 11 is provided on the sealing plate facing surface where the peripheral portion of the separator 14 is a stepped portion. It is characterized by being housed in a state of being in contact with. In other words, in the present embodiment, the shape of the gasket 13 has the greatest feature. By making the gasket 13 in the present invention have the above-described structure, it is possible to prevent the separator 14 from being cut or torn due to excessive pulling of the separator 14 during sealing.

  Furthermore, since the aluminum surface of the sealing plate 11 is covered with the separator 14 when viewed from the positive electrode 16 side, a state where the aluminum surface is not exposed can be created. For this reason, even when the positive electrode 16 expands due to battery discharge, the positive electrode 16 and the aluminum surface do not come into contact with each other. Accordingly, the peripheral edge of the positive electrode 16 can be enlarged to the vicinity of the inner peripheral side surface of the gasket, and the size of the positive electrode 16 can be increased as compared with the flat battery shown in FIG. Can be obtained. In particular, in the case of a small-diameter size, the collar portion of the hat-shaped sealing plate 11 is relatively large in the radial direction, and conversely, the portion that accommodates the positive electrode 16 is relatively small. In the flat battery of the invention, the capacity can be increased.

  Further, in the flat battery shown in FIG. 2, a step portion is provided at the sealing plate facing portion at the bottom of the gasket 23, and the separator 14 is formed in the separator storage portion formed by this step portion and the sealing plate 11. Is stored in the separator storage portion in a state in which the peripheral edge portion is in contact with the sealing plate facing surface of the step portion, and the separator 14 is sandwiched between the convex portion provided on the sealing plate facing surface of the step portion and the sealing plate 11. ing.

  Thereby, at the time of sealing, the separator 14 can be prevented from being cut or torn due to being pulled excessively. Further, when viewed from the positive electrode 16 side, the aluminum surface of the sealing plate 11 is the separator 14. Since it is covered, it is possible to create a state where the aluminum surface is not exposed. For this reason, even when the positive electrode expands due to battery discharge, the positive electrode 16 and the aluminum surface do not come into contact with each other. Moreover, since the peripheral part of the separator 14 is pinched | interposed by the convex part provided in the sealing board opposing surface of the gasket step part, and the sealing board 11, it can fix more stably.

  Hereinafter, preferred embodiments of the present invention will be described.

Example 1
FIG. 1 is a cross-sectional view of a flat battery of the present invention.

  As Example 1, a flat battery having a diameter of 4.8 mm and a thickness of 0.8 mm shown in FIG. 1 was produced under the following conditions. The sealing plate 11 also serves as a negative electrode terminal, and is made of a clad material of stainless steel (thickness 0.12 mm) excellent in corrosion resistance and an aluminum alloy (thickness 0.13 mm) capable of inserting and extracting lithium. . The positive electrode case 12 also serves as a positive electrode terminal and is made of stainless steel (thickness: 0.10 mm) having excellent corrosion resistance. As the separator 14 disposed between the positive electrode 16 and the lithium metal 15, polyphenylene sulfide having a thickness of 0.10 mm was used. The gasket 13 insulates the sealing plate 11 and the positive electrode case 12 and physically seals the power generation element in the battery container. Polyphenylene sulfide is used, and the innermost diameter at the bottom of the gasket 13 is 2. It was 4 mm. A step portion having a step of 0.08 mm is provided on the sealing plate facing surface of the bottom portion of the gasket 13, and the peripheral portion of the separator 14 is formed in the separator housing portion formed by the step portion and the sealing plate 11. It is stored in contact with the sealing plate facing surface of the stepped portion. A solution obtained by diluting butyl rubber with toluene was applied between the gasket 13 and the sealing plate 11 and the positive electrode case 12 and the gasket 13, and the toluene was evaporated to obtain a sealant made of a butyl rubber film.

The positive electrode 16 is composed of monoclinic niobium pentoxide (BET specific surface area 1.5 m ² / g) obtained by firing niobium hydroxide at 1000 ° C. as an active material, carbon black as a conductive agent and binder as a conductive agent. After the fluororesin powder was mixed and molded into a pellet, it was dried at 250 ° C. for 12 hours to obtain a diameter of 2.2 mm and a thickness of 0.25 mm.

On the other hand, in the negative electrode, lithium metal 15 (thickness: 0.10 mm) is pressure-bonded to the surface of the aluminum alloy existing inside the sealing plate 11, and the lithium metal 15 and aluminum are short-circuited by injecting an electrolyte during battery assembly. Thus, the lithium metal 15 is electrochemically occluded in the aluminum metal. Furthermore, as the electrolyte, a solution in which bistrifluoromethanesulfonimidolithium LiN (CF ₃ SO ₂ ) ₂ is dissolved in an equal volume mixed solvent of polypropylene carbonate and 1,2-dimethoxyethane at a rate of 1 mol / liter is used. It was.

(Example 2)
FIG. 2 is a cross-sectional view of the flat battery in this example.

  For the gasket 23, polyphenylene sulfide was used, and the innermost inner diameter of the bottom portion of the gasket 23 was 2.4 mm. A stepped portion with a step of 0.08 mm is provided on the sealing plate facing surface at the bottom of the gasket 23, and the peripheral portion of the separator 14 is formed in the separator storage portion formed by the gasket stepped portion and the sealing plate 11. The separator 14 is sandwiched between the sealing plate 11 and the 0.10 mm convex portion provided on the sealing plate facing surface of the step portion while being stored in contact with the sealing plate facing surface of the step portion. The other configuration is a flat battery having the same configuration as that of the first embodiment.

(Comparative Example 1)
FIG. 4 is a cross-sectional view of the flat battery in this comparative example.

  For the gasket 33, polyphenylene sulfide was used, and the innermost inner diameter of the bottom of the gasket 33 was 2.4 mm. No step portion is provided on the sealing plate facing surface of the bottom of the gasket 33, and the peripheral edge of the separator 44 is sandwiched between the gasket 33 and the sealing plate 11. The other configuration is a flat battery having the same configuration as that of the first embodiment.

(Comparative Example 2)
FIG. 3 is a cross-sectional view of a flat battery in a comparative example.

  For the gasket 33, polyphenylene sulfide was used, and the innermost inner diameter of the bottom of the gasket 33 was 2.4 mm. No step portion is provided on the sealing plate facing surface at the bottom of the gasket 33, and the separator 34 is flat and sandwiched between the positive electrode 16 and the lithium metal 15 (thickness 0.10 mm). A positive electrode 16 having a diameter of 2.2 mm and a thickness of 0.25 mm was used. The other structure is a flat battery having the same structure as that of the first embodiment.

(Comparative Example 3)
A positive battery 16 having a diameter of 2.0 mm and a thickness of 0.25 mm was used, and a flat battery book having the same structure as that of Comparative Example 2 was prepared.

(Comparative Example 4)
A positive electrode 16 having a diameter of 1.8 mm and a thickness of 0.25 mm was used, and a flat battery having the same configuration as that of Comparative Example 2 was prepared.

  100 batteries each of Example 1, Example 2 and Comparative Examples 1 to 4 were prepared, and the batteries that caused an internal short circuit were checked immediately after assembly. Table 1 shows the percentage of batteries that caused an internal short circuit.

  In the batteries of Example 1, Example 2 and Comparative Examples 2 to 4, the separator was not torn due to the separator being pulled at the time of sealing, so no internal short circuit occurred. On the other hand, in the battery of Comparative Example 1, the separator was torn due to the separator being pulled at the time of sealing, and the positive electrode 16 and the lithium metal 15 were in contact through the tear, thus causing an internal short circuit.

  Next, using a battery that did not cause an internal short circuit immediately after assembly, a constant resistance discharge of 300 kΩ was performed at a temperature of 20 ° C. until it reached 1.0 V, the discharge capacity was measured, and an internal short circuit occurred during the discharge. The battery was checked. Table 2 shows the ratio of the number of batteries that caused an internal short circuit during discharge and the average value of the discharge capacity of the batteries that did not cause an internal short circuit during discharge.

  In the batteries of Example 1, Example 2, and Comparative Example 1, since the aluminum surface of the sealing plate 11 is covered with the separator 14 when viewed from the positive electrode 16 side, a state in which the aluminum surface is not exposed can be created. For this reason, even when the positive electrode 16 expands due to the battery discharge, the positive electrode 16 and the aluminum surface do not come into contact with each other, and an internal short circuit does not occur. On the other hand, in the batteries of Comparative Example 2 and Comparative Example 3, the positive electrode 16 and the aluminum surface come into contact with each other due to expansion of the positive electrode 16 accompanying the discharge of the battery, causing an internal short circuit. This tendency depends on the outer diameter of the positive electrode 16, and an internal short circuit is more likely to occur as the diameter increases. The battery of Comparative Example 4 did not cause an internal short circuit during discharge, but this is because the outer diameter of the positive electrode 16 is reduced, and it is considered that the positive electrode 16 does not contact the aluminum surface even if it expands in the lateral direction.

  As described above, in the batteries of Comparative Examples 2 and 3, the outer diameter of the positive electrode 16 is as small as shown in Comparative Example 4 so as not to cause an internal short circuit even when the positive electrode 16 expands in the lateral direction. Therefore, the capacity is reduced. On the other hand, in the flat battery of the present invention, since there is no internal short circuit due to the expansion of the positive electrode 16 accompanying the discharge of the battery, the outer diameter of the positive electrode 16 can be increased.

  In this embodiment, polyphenylene sulfide is used as the separator material, but polypropylene, polyether ether ketone, perfluoroalcogin, glass fiber, or the like may be used. Further, as a gasket material, in addition to polyphenylene sulfide, polypropylene, polyether ether ketone, perfluoroalcogin and the like can be applied.

  The present invention relates to a flat battery using a hat-shaped sealing plate, having a step portion on the surface facing the sealing plate at the bottom of the gasket, and a space formed by the gasket step portion and the sealing plate as a separator housing portion, Because the part is stored in the separator storage part in contact with the sealing plate facing surface of the gasket step part, even if it is small and thin, the capacity is not significantly reduced, and high capacity prevents internal short circuits. Can be provided.

Sectional drawing of the flat battery in Example 1 of this invention Sectional drawing of the flat battery in Example 2 of this invention Sectional drawing of the flat battery in the comparative example 2-comparative example 4 of this invention Sectional drawing of the flat battery in the comparative example 1 of this invention

Explanation of symbols

11 Sealing plate 12 Positive electrode case 13, 23, 33 Gasket 14, 34, 44 Separator 15 Lithium metal 16 Positive electrode

Claims (2)

A flat battery in which a positive electrode, a negative electrode, an electrolyte, and a separator are sealed with a hat-shaped sealing plate and a positive electrode case via a gasket, and a step portion is provided at a portion facing the sealing plate of the gasket. A flat battery in which a peripheral portion of the separator is housed in a separator housing portion formed by the step portion and the sealing plate. 2. The flat battery according to claim 1, wherein a convex portion is provided at an end portion of the step portion on the side facing the sealing plate.

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