JP2010250985A - Secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a secondary battery capable of restraining deviation of ions used as charge carriers on a negative electrode. <P>SOLUTION: In the secondary battery having a positive electrode 10 wherein a positive electrode mixture 12 is coated on a positive electrode collector 11, the negative electrode 20 wherein a negative electrode mixture 22 is coated on a negative electrode collector 21, and a separator 30 interposed between the positive electrode 10 and the negative electrode 20, in which a coated area of the negative electrode mixture 22 is larger than a coated area of the positive electrode mixture 12, slits 23, 23 are arranged on the negative electrode mixture 22 of the negative electrode 20 from a coated surface of the negative electrode mixture 22 to the negative electrode collector 21 on the negative electrode 20, and the slits 23, 23 are arranged at a section located on an outer periphery of the positive electrode mixture 12 in the negative electrode mixture 22 while the positive electrode 10, the negative electrode 20, and the separator 30 are laminated. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a secondary battery, and more particularly to a lithium ion secondary battery having a negative electrode having a larger area than a positive electrode.

  Conventionally, as a secondary battery, there is a battery that is housed in a case in a wound state of an electrode group formed by laminating a positive electrode and a negative electrode formed in a sheet shape via a separator. In such a wound type secondary battery, there is a problem that, when the electrode is mainly wound, a gap is generated between the positive electrode and the negative electrode facing each other, and dendrite is generated during charging. In consideration of the above, a negative electrode having a larger area than the positive electrode is used (for example, see Patent Document 1).

However, as shown in FIG. 4, the secondary battery having the negative electrode 120 having a larger area than the positive electrode 110 has a positive electrode in which ions P serving as charge carriers such as lithium ions in the negative electrode 120 face the negative electrode 120. More than the area of 110, the negative electrode 120 causes ion bias.
Therefore, potential unevenness occurs in the negative electrode 120, so that a portion with a high potential has a low thermal runaway temperature and a large amount of heat generation, and as a result, the safety of each part of the negative electrode 120 varies.
Also, the SOC (State of Charge) is shifted between the positive electrode 110 and the negative electrode 120, and the SOC of the positive electrode 110 and the negative electrode 120 facing each other varies depending on the part, and accordingly, the capacity of the entire battery deteriorates. .

JP-A-8-50917

  An object of the present invention is to provide a secondary battery that suppresses unevenness of ions serving as charge carriers on a negative electrode.

  In claim 1, a positive electrode in which a positive electrode mixture is applied to a positive electrode current collector, a negative electrode in which a negative electrode mixture is applied to a negative electrode current collector, and the positive electrode and the negative electrode are interposed. A secondary battery having a coating area of the negative electrode mixture larger than a coating area of the positive electrode mixture, and the negative electrode mixture of the negative electrode includes the negative electrode In the state where the negative electrode mixture is removed from the coating surface of the negative electrode mixture in the negative electrode current collector, a first slit is provided, and the first slit is in a state where the positive electrode, the negative electrode, and the separator are laminated, It arrange | positions in the part located in the outer periphery of the said positive mix in the said negative mix.

  According to a second aspect of the present invention, the negative electrode mixture of the negative electrode is provided with a second slit outside the first slit from the coating surface of the negative electrode mixture in the negative electrode to the negative electrode current collector. .

  In Claim 3, the negative electrode mixture of the negative electrode is provided with a third slit on the inner side of the first slit from the coating surface of the negative electrode mixture in the negative electrode to the negative electrode current collector. .

  According to the present invention, it is possible to suppress the deviation of ions serving as charge carriers on the negative electrode. Therefore, potential unevenness at the negative electrode and SOC shift between the positive electrode and the negative electrode can be prevented, and the safety of the secondary battery can be improved and the battery capacity can be prevented from deteriorating.

Schematic which shows the electrode group of the secondary battery which concerns on one Embodiment of this invention. Schematic which shows another form of the secondary battery which concerns on one Embodiment of this invention. Schematic which shows another form of the secondary battery which concerns on one Embodiment of this invention. Schematic which shows the electrode group of the conventional secondary battery.

As shown in FIG. 1, a secondary battery according to an embodiment of the present invention is a secondary battery such as a lithium ion secondary battery or a nickel / hydrogen storage battery mainly composed of a positive electrode 10, a negative electrode 20, and a separator 30. It is.
Specifically, in the secondary battery, the positive electrode 10 and the negative electrode 20 are laminated with a separator 30 interposed therebetween to form an electrode group 40, and the electrode group 40 is wound to form a metal can, a metal resin composite film, or the like. After being housed in a container, it is configured by impregnating with an electrolytic solution.
In the following description, the horizontal direction in the drawing is referred to as the “width direction” of the electrode group 40, and the direction perpendicular to the “width direction” in the depth direction is described as the “winding direction” of the electrode group 40.

The positive electrode 10 is a positive electrode used for a secondary battery, and a paste-like positive electrode mixture 12 was applied to the surface of a positive electrode current collector 11 which is a metal foil using a coating device such as a die coater and dried. Thereafter, it is formed through a predetermined process such as a roll press.
The positive electrode current collector 11 is a current collector made of a metal foil such as aluminum, titanium, or stainless steel.
The positive electrode mixture 12 is a paste-like electrode mixture obtained by kneading a powdered positive electrode active material with a conductive solvent, a binder, and the like in a dispersion solvent.

The negative electrode 20 is a negative electrode used for a secondary battery, and has a larger area than the positive electrode 10. Similarly to the positive electrode 10, the negative electrode 20 was applied to the surface of the negative electrode current collector 21, which is a metal foil, using a coating device such as a die coater, dried, and then rolled. It forms through predetermined processes, such as.
The negative electrode current collector 21 is a current collector made of a metal foil such as copper, nickel, and stainless steel.
The negative electrode mixture 22 is a paste-like electrode mixture obtained by kneading a powdered negative electrode active material with a conductive solvent, a binder, and the like in a dispersion solvent.

  The separator 30 is an insulator that is interposed between the positive electrode 10 and the negative electrode 20 and separates them. The separator 30 is made of a porous material such as a polyolefin resin, and retains ionic conductivity by allowing ions P serving as charge carriers to move between the positive electrode 10 and the negative electrode 20 via the separator 30.

  In the electrode group 40, the positive electrode 10, the negative electrode 20, and the separator 30 are laminated in a state in which the coating surface of the positive electrode mixture 12 in the positive electrode 10 and the coating surface of the negative electrode mixture 22 in the negative electrode 20 face each other with the separator 30 interposed therebetween. Charge / discharge element.

  Below, the structure of the negative electrode 20 in the secondary battery which concerns on one Embodiment of this invention is demonstrated in detail.

  As shown in FIG. 1, the negative electrode 20 has a larger area than the positive electrode 10. Specifically, the coating width (the coating length in the width direction) of the negative electrode mixture 22 on the negative electrode current collector 21 in the negative electrode 20 is equal to the coating width of the positive electrode mixture 12 on the positive electrode current collector 11 in the positive electrode 10. The coating area of the negative electrode mixture 22 on the negative electrode current collector 21 is larger than the coating area of the positive electrode mixture 12 on the positive electrode current collector 11 in the positive electrode 10. ing. However, the lengths of the positive electrode mixture 12 and the negative electrode mixture 22 in the winding direction are equal.

  In the negative electrode mixture 22 of the negative electrode 20, slits 23 and 23 are provided along the winding direction, and the positive electrode mixture 12 in the negative electrode mixture 22 in the state where the positive electrode 10, the negative electrode 20, and the separator 30 are laminated. It arrange | positions at the part located in the outer periphery, ie, the part (position shown with the broken line LR in FIG. 1) located in the both ends in the width direction of the positive mix 12 respectively. In other words, the coating area of the positive electrode mixture 12 on the positive electrode 10 and the area of the portion surrounded by the slits 23, 23 of the negative electrode mixture 22 on the negative electrode 20 facing it are substantially the same. 23 is provided.

The slit 23 extends from the coating surface (surface on the separator 30 side) of the negative electrode mixture 22 in the negative electrode 20 to portions (positions indicated by broken lines L and R in FIG. 1) located at both ends in the width direction of the positive electrode mixture 12. It is a cut formed in a rectangular shape up to the negative electrode current collector 21. That is, on the negative electrode current collector 21, the negative electrode mixture 22 does not exist at the positions where the slits 23 and 23 are formed. Thus, in the negative electrode mixture 22, the passage of the ions P is blocked by the slits 23 and 23.
The slit 23 is formed by applying a negative electrode mixture 22 to the negative electrode current collector 21 and then cutting the negative electrode mixture 22 using a needle-like member, or intermittently applying the negative electrode mixture 22 to the negative electrode current collector 21. Or the like.

As described above, the slits 23 and 23 are provided in the negative electrode mixture 22 of the negative electrode 20. That is, by providing the slits 23, 23, even when the negative electrode 20 has a larger area than the positive electrode 10, the coating area of the positive electrode mixture 12 on the positive electrode 10 and the positive electrode mixture 12 of the positive electrode 10 are opposed to each other. The coating area of the negative electrode mixture 22 in the negative electrode 20 is made approximately the same.
As a result, the ions P cannot move beyond the slit 23 and do not spread beyond the coating area of the positive electrode mixture 12 on the positive electrode 10 facing the negative electrode 20, so that the bias of the ions P in the negative electrode 20 Can be suppressed.
Therefore, it is possible to prevent potential unevenness in the negative electrode 20 and shift of SOC between the positive electrode 10 and the negative electrode 20, thereby improving the safety of the secondary battery and preventing deterioration of the battery capacity. Can do.

In addition, as shown in FIG. 2, a configuration may be adopted in which slits 24 and 24 are further provided as second slits with a predetermined interval on the outer side in the width direction from the slits 23 and 23 of the negative electrode mixture 22 in the negative electrode 20.
The slit 24 is a cut formed in substantially the same manner as the slit 23, and the negative electrode mixture 22 is removed from the portion where the slit 23 is formed, and the coating surface (separator 30) of the negative electrode mixture 22 in the negative electrode 20. From the side surface) to the negative electrode current collector 21.

Thereby, for example, when the electrode group 40 is wound, even if the positive electrode 10 is displaced to one side in the width direction (the arrow direction shown in FIG. 2) with respect to the negative electrode 20, Since the slit 24 is provided on the outer side in the width direction than the slit 23 that is positioned (the displacement direction of the positive electrode 10), the diffusion of the ions P on the negative electrode 20 on the outer side in the width direction with respect to the slit 23 is caused between the slit 23 and the slit 24. The bias of the ions P can be suppressed, and the bias of the ions P in the portion of the negative electrode 20 facing the positive electrode 10 is suppressed in substantially the same manner as when the deviation of the positive electrode 10 does not occur. It becomes possible.
Further, even when the positive electrode 10 is shifted to the other side in the width direction with respect to the negative electrode 20 (opposite to the arrow direction shown in FIG. 2), the outer side in the width direction (the positive electrode 10) Since the slit 24 is provided in the direction of misalignment), the same effect as when the positive electrode 10 is misaligned in the arrow direction shown in FIG.

Furthermore, as shown in FIG. 3, it is good also as a structure which provides the slit 25 * 25 as a 3rd slit at predetermined intervals in the width direction inner side rather than the slit 23 * 23 of the negative mix 22 in the negative electrode 20. FIG. .
The slit 25 is a cut formed in substantially the same manner as the slit 23, and is formed in a rectangular shape from the coating surface (surface on the separator 30 side) of the negative electrode mixture 22 in the negative electrode 20 to the negative electrode current collector 21. .

Thereby, for example, when the electrode group 40 is wound, even if the positive electrode 10 is shifted to one side in the width direction (the arrow direction shown in FIG. 3) with respect to the negative electrode 20, Since the slit 25 is provided on the inner side in the width direction (shift direction of the positive electrode 10) than the slit 23 positioned, it is possible to suppress the bias of the ions P at the negative electrode 20 on the inner side in the width direction from the slit 23. Furthermore, the diffusion of the ions P in the portion of the negative electrode 20 facing the positive electrode 10 can be stopped between the slits 25 and 25, and the bias of the ions P can be suppressed.
Further, even when the positive electrode 10 is shifted to the other side in the width direction with respect to the negative electrode 20 (the direction opposite to the arrow direction shown in FIG. 2), the inner side in the width direction (the positive electrode 10) Since the slits 25 are provided in the direction of misalignment), the same effect as when the positive electrode 10 is misaligned in the direction of the arrow shown in FIG.

  Note that the positions of the slits 24 and 25 are set in consideration of a shift that occurs when the electrode group 40 is wound. Specifically, the slit 24 is arranged on the outer side and the slit 25 is arranged on the inner side with a gap from the slit 23 by an amount corresponding to the expected deviation between the positive electrode 10 and the negative electrode 20.

  As described above, the negative electrode mixture 22 of the negative electrode 20 is further provided with slits 24 and 24 and slits 25 and 25, that is, by forming a plurality of slits in the width direction of the negative electrode mixture 22, Even when a deviation from the negative electrode 20 occurs, the effect of the slits 23 and 23 when there is no deviation between the positive electrode 10 and the negative electrode 20 is substantially the same, and the electrode group 40 is wound. The generated deviation between the positive electrode 10 and the negative electrode 20 can be absorbed.

The length in the width direction of the slits 23, 24, and 25 is set to such an extent that the passage of the ions P can be blocked and no adverse effects such as generation of dendrites in the slits 23, 24, and 25 occur.
In addition, the slits 23, 24, and 25 are formed in a rectangular shape in this embodiment. However, the slits 23, 24, and 25 can block the passage of ions P such as a V shape or a semi-elliptical shape, and the slits 23, 24, and 25 have dendrites. The shape is not limited as long as there is no adverse effect that is generated.

  In the present embodiment, the lengths of the positive electrode mixture 12 and the negative electrode mixture 22 in the winding direction are equal, but the winding length of the negative electrode mixture 22 is longer than the length of the positive electrode mixture 12 in the winding direction. When the length in the direction is large, the slit 23 is provided over the entire circumference in a portion of the negative electrode mixture 22 located on the outer periphery of the positive electrode mixture 12 in a state where the positive electrode 10, the negative electrode 20, and the separator 30 are laminated. Then, a slit 24 is provided on the outer side and a slit 25 is provided on the inner side so as to be parallel to the slit 23 with an interval from the slit 23 corresponding to the expected deviation between the positive electrode 10 and the negative electrode 20.

P ion 10 Positive electrode 11 Positive electrode current collector 12 Positive electrode mixture 20 Negative electrode 21 Negative electrode current collector 22 Negative electrode mixture 23 Slit (first slit)
24 slit (second slit)
25 Slit (third slit)
30 separator 40 electrode group

Claims (3)

A positive electrode in which a positive electrode mixture is applied to a positive electrode current collector;
A negative electrode in which a negative electrode mixture is applied to a negative electrode current collector;
A separator interposed between the positive electrode and the negative electrode,
The coating area of the negative electrode mixture is a secondary battery larger than the coating area of the positive electrode mixture,
The negative electrode mixture of the negative electrode is provided with a first slit in which the negative electrode mixture is removed from the coating surface of the negative electrode mixture in the negative electrode to the negative electrode current collector,
The first slit is a secondary battery disposed in a portion of the negative electrode mixture positioned on the outer periphery of the positive electrode mixture in a state where the positive electrode, the negative electrode, and the separator are stacked.   2. The secondary battery according to claim 1, wherein the negative electrode mixture of the negative electrode is provided with a second slit outside the first slit from the coating surface of the negative electrode mixture in the negative electrode to the negative electrode current collector. .   The negative electrode mixture of the negative electrode is provided with a third slit inside the first slit from the coating surface of the negative electrode mixture in the negative electrode to the negative electrode current collector. Secondary battery.

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