JP2005174793A - Nonaqueous secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery restraining an internal short circuit caused by the buckling of an electrode group or the breakage of a separator due to the swelling of an electrode plate caused by overcharge, not by restraining the swelling of the electrode plate but by restraining the stress of the neighboring area of the innermost periphery of the electrode group generated only in the overcharge. <P>SOLUTION: The nonaqueous secondary battery has a cylinder-shaped part 5a arranged in an electrode plate winding core space fixed to the bottom or a sealing plate of an external can, and a heat-shrinkable resin film 4a wound around the cylinder-shaped part arranged so as to contact and move together with the separator 3a at the innermost periphery of the electrode group, has a structure of heat shrinking in a winding direction when overcharged. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a non-aqueous secondary battery, and more particularly to a wound battery.

A non-aqueous secondary battery using lithium cobalt oxide (LiCoO ₂ ) for the positive electrode, a carbon material for the negative electrode, and an electrolytic solution in which a lithium salt is dissolved in a non-aqueous solvent as the electrolytic solution has high voltage and high energy density, and is portable. Widely used as a power source for equipment. In a non-aqueous secondary battery, the electrode plate expands during charging, and therefore the electrode plate group may be bent due to stress of electrode plate expansion particularly during overcharging. In the vicinity of the innermost circumference of the electrode plate group, the curvature of the electrode plate is high, so that it is difficult to absorb stress, and particularly, it tends to be buckled. Such buckling of the electrode plate group may damage the separator and cause an internal short circuit.

Conventionally, in order to prevent the electrode group from buckling, it has been practiced to suppress the expansion of the electrode plate which is the cause. As a means for suppressing the expansion of the electrode plate, it has been proposed to provide a large number of slits on the surface of the electrode plate (see, for example, Patent Document 1). Further, as means for suppressing the expansion of the electrode plate group even if the electrode plate expands, it has been proposed to thermally weld the separators protruding from the electrode plate group in the winding axis direction (for example, Patent Documents). 2).
Japanese Patent Application Laid-Open No. 07-272760 JP 2003-151615 A

  However, in the method of constantly suppressing the expansion of the electrode plates, there is a problem that other characteristics deteriorate even if the electrode plate group can be suppressed from being buckled. For example, when a large number of slits are provided on the surface of the electrode plate, the amount of active material of the electrode plate is reduced, so that the volume energy density is reduced. Furthermore, since the amount of the active material on the electrode plate becomes non-uniform, charging / discharging becomes non-uniform and lithium may be deposited on the electrode plate. In addition, when the protruding portions of the separator are welded to each other, stress due to deformation of the electrode plate group is likely to be applied to the separator, so that the possibility of an internal short circuit due to breakage of the separator is increased during overcharge.

  The present invention does not suppress the expansion of the electrode plate, but relaxes the stress applied to the vicinity of the innermost periphery of the electrode plate group only at the time of overcharge, thereby preventing deterioration of other characteristics and at the time of overcharge. An object is to suppress the internal short circuit due to the bending of the electrode plate group due to the expansion of the electrode plate and the breakage of the separator.

  In order to solve this problem, the non-aqueous secondary battery of the present invention includes an electrode plate in which a positive electrode and a negative electrode are spirally wound via a separator, a non-aqueous electrolyte solution, and a bottomed cylindrical outer can. A non-aqueous secondary battery including a sealing plate for sealing the outer can, and a cylindrical component that is installed in the electrode plate group winding space and fixed to the bottom of the outer can or the sealing plate. The heat-shrinkable resin film, which is wound and installed in contact with the innermost separator of the electrode group, has a structure that heat-shrinks in the winding direction when abnormalities such as overcharge occur. Is.

As for the installation of the heat-shrinkable resin film, any structure may be used as long as it is in contact with the innermost separator of the electrode plate group, and in particular, it is wound around a cylindrical part. The innermost end of the heat-shrinkable resin film is fixed to the cylindrical part, and the outermost end is bonded to the innermost separator of the electrode plate group. A structure in which the heat-shrinkable resin film and the separator are wound around the circumference is preferable because the effects of the present invention are remarkably exhibited.

  As the heat-shrinkable resin, polypropylene, polyethylene, crosslinked polyolefin, polyvinyl chloride, polyethylene terephthalate, or the like can be used. As the resin film to be used, one having a thickness of 20 to 45 μm and a shrinkage ratio in the vertical direction of 5 to 15% and a shrinkage ratio in the horizontal direction of 40 to 60% in a temperature range of 100 ° C. or higher is suitable.

  During overcharge, heat is generated due to decomposition of the active material and electrolyte, and the battery temperature rises abnormally. This temperature rise causes the heat-shrinkable resin film to shrink in the winding direction, and the separator in the electrode plate group that is in close contact with the film is pulled in the winding direction, so that the vicinity of the innermost circumference of the electrode plate group is loosened and overcharged Suppresses the bending of the electrode plate at time. At this time, it is preferable that the cylindrical part is fixed to the bottom of the outer can or the sealing plate because this action is ensured.

  The nonaqueous secondary battery according to the present invention has the above-described configuration, and has an excellent effect of suppressing the buckling of the electrode plate group that causes an internal short circuit during overcharge.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Embodiment 1)
As shown in FIG. 1, the non-aqueous secondary battery according to an embodiment of the present invention includes a positive electrode 1a and a negative electrode 2a wound in a spiral shape through a separator 3a. The innermost end 6a of the heat-shrinkable resin film 4a wound around the cylindrical part 5a is fixed to the cylindrical part, and the outermost end 7 is bonded to the innermost part of the separator of the electrode plate group. With a structured. Here, the cylindrical part also serves as a core for winding the electrode plate group, and is detachable from the winding machine.

When the electrode plate is wound, the winding is performed as shown in FIG. That is, a cylindrical spacer 8 having a slit in the longitudinal direction is placed on the cylindrical part 5b to which the winding start portion 6b which is the innermost end of the heat-shrinkable resin film 4b is fixed. A heat-shrinkable resin film is wound, and after the winding, the spacer is pulled out from the electrode plate group. In this way, when the heat-shrinkable resin film shrinks during overcharge, a space for the expanded electrode plate group to loosen can be created. Is suppressed.
(Embodiment 2)
As shown in FIG. 3, the nonaqueous secondary battery according to another embodiment of the present invention has a structure in which the heat-shrinkable resin film 4c and the separator 3c overlap and are wound around the innermost periphery of the electrode plate group. Have. The positive electrode 1c and the negative electrode 2c are not wound around the innermost periphery. Unlike Example 1, both ends of the heat-shrinkable resin film are not bonded to the cylindrical part and the innermost separator of the electrode plate group, but are over-charged because they are wound around the cylindrical part. Occasionally, when the film shrinks, it comes into close contact with the overlapping innermost separator of the electrode plate group, and they are pulled in the winding direction, making it possible to create a space for the expanded electrode plate group to relax. , Buckling of the electrode plate group causing internal short circuit is suppressed.

A more specific embodiment of the present invention will be described.
(Example 1)
A non-aqueous secondary battery having the configuration of FIG. 1 was prepared by the following procedure.

As the heat-shrinkable resin film, a uniaxially stretched polypropylene film having a thickness of 30 μm was used.

LiCoO ₂ classified to 100 mesh or less is used as the positive electrode active material, 10 g of acetylene black (AB) powder as a conductive agent and polytetrafluoroethylene (PTFE) dispersion as a binder with respect to 100 g of the positive electrode active material. After 6 g is sufficiently mixed, an appropriate amount of n-methyl-2-pyrrolidone (NMP) is added, mixed sufficiently to form a paste, applied to an aluminum core (film thickness 25 μm), dried and rolled to a film thickness of 200 μm. A positive electrode was obtained.

  100 g of artificial graphite powder of the negative electrode active material was mixed well with 15 g of AB powder as a conductive agent and 8 g of styrene butadiene rubber (SBR) as a binder, and a paste formed using water as a dispersion solvent was copper. Was applied to the core material, and then dried and rolled at 100 ° C. to obtain a negative electrode having a thickness of 250 μm.

A positive electrode lead made of aluminum was joined to aluminum of the positive electrode core material by ultrasonic welding, and a copper negative electrode lead was similarly joined to copper of the negative electrode core material by ultrasonic welding. A strip-shaped porous polyethylene separator having a width wider than both electrode plates was disposed between the positive electrode and the negative electrode to form an electrode plate group. One end of the heat-shrinkable resin film is fixed to the cylindrical part attached to the core part of the winding machine with an adhesive tape, and a cylindrical spacer with a slit in the longitudinal direction is placed on the heat-shrinkable resin film. Was placed so as to pass between the slits. The separator of the winding start part used as the innermost periphery of an electrode group was heat-welded with the edge of the heat-shrinkable resin film which has come out from the slit, and it wound. The cylindrical part used was the same stainless steel as the battery outer can. After the winding was completed, the entire cylindrical part was removed from the winding machine, and the spacer was pulled out from the electrode plate group. Polypropylene insulating plates were placed on the upper and lower sides of the electrode plate group, respectively, and inserted into the battery outer can, and the cylindrical part and the outer can bottom were resistance welded. As a non-aqueous electrolyte solution, an equivalent volume mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) in which 1 mol / l LiPF ₆ was dissolved was injected. Thereafter, it was impregnated with a vacuum, a sealing plate was inserted, and sealed by mechanical caulking to obtain a cylindrical battery.

  In addition, as a comparative example, a cylindrical battery having the same configuration as that of Example 1 was prepared except that the heat-shrinkable resin film was not used.

An overcharge test was performed on the prepared battery. A constant current charge was performed up to SOC 180% at a test temperature of 20 ° C. and 0.7 C, and a photograph of a cross section parallel to the bottom surface of the outer can was taken with an X-ray CT scanning device for the charged battery, and the state of the electrode plate group was examined. . In the battery of the comparative example, buckling was confirmed near the innermost periphery of the electrode plate group, whereas in the battery of Example 1 using a heat-shrinkable resin film, no electrode plate group buckling was confirmed.
(Example 2)
A non-aqueous secondary battery having the configuration of FIG. 2 was prepared by the following procedure.

  The same battery component as in Example 1 was used. When winding the electrode plate group, the heat shrinkable resin film is stacked on the separator at the winding start portion which is the innermost periphery of the electrode plate group, and then the positive electrode and the negative electrode are stacked so as to sandwich the separator. Made a round. After completion of winding, the electrode plate group was pulled out from the winding core, and a cylindrical part was inserted into the winding core space. After the electrode plate group was thus configured, a cylindrical battery was obtained in the same manner as in Example 1.

  About the created battery, the same overcharge test as Example 1 was done. In the cross-sectional photograph by CT scan, the bending of the electrode plate group was not confirmed.

  The non-aqueous secondary battery according to the present invention is useful as a power source for portable devices such as notebook PCs.

Sectional drawing which shows the structure of the cylindrical non-aqueous secondary battery in Example 1 of this invention Sectional drawing which shows the electrode group winding method in Example 1 of this invention Sectional drawing which shows the structure of the cylindrical non-aqueous secondary battery in Example 2 of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a, 1c Positive electrode 2a, 2c Negative electrode 3a, 3c Separator 4a, 4b, 4c Heat-shrinkable resin film 5a, 5b, 5c Cylindrical part 6a, 6b End of innermost side of heat-shrinkable resin film 7 Heat-shrinkable resin The outermost edge of the film 8 Spacer

Claims (3)

In a non-aqueous secondary battery comprising a positive electrode and a negative electrode spirally wound via a separator, a non-aqueous electrolyte, a bottomed cylindrical outer can, and a sealing plate that seals the outer can A heat-shrinkable resin film provided with a cylindrical part installed in the electrode group winding core space, and installed in contact with the innermost separator of the electrode group wound around the cylindrical part However, a non-aqueous secondary battery characterized by having a structure that thermally contracts in the winding direction in the event of an abnormality. The innermost end of the heat-shrinkable resin film wound around the cylindrical part is fixed to the cylindrical part, and the outermost end is bonded to the innermost separator of the electrode plate group. The non-aqueous secondary battery according to claim 1. 2. The non-aqueous secondary battery according to claim 1, wherein the heat-shrinkable resin film and the separator are wound around each other on the innermost circumference of the electrode plate group.