JP2671387B2 - Cylindrical lithium secondary battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to a cylinder having an electrode body in which a negative electrode plate using metallic lithium as an active material and a positive electrode plate are spirally formed with a separator interposed between the two electrodes. The present invention relates to a lithium secondary battery.

2. Description of the Related Art Generally, an organic electrolyte lithium battery has features such as high energy density, excellent long-term reliability, and a wide operating temperature range.

In recent years, so-called lithium secondary batteries that can be recharged while taking advantage of such advantages have been actively developed. Generally, a negative electrode containing metallic lithium as the main active material and various intercalation compounds such as titanium disulfide (TiS ₂ ) are used as the positive electrode active material, and lithium perchlorate is used as an organic solvent such as propylene carbonate. An organic electrolytic solution in which the above is dissolved is used. However, due to the short life of the charge / discharge cycle of the negative electrode, it has not yet been put to practical use. Lithium as a negative electrode active material has a difficult problem such that it deforms with charge / discharge cycles to generate dendritic deposits (dendrites), which form internal short-circuit bridges. In particular, dendrites are concentrated in places with high current density,
It has the property of growing vertically from the lithium negative electrode surface, and as the charge and discharge cycle progresses, the nonuniformity of the surface due to dendrites is promoted, and eventually it falls off. The dendrite of lithium that has fallen off from the negative electrode in this way is
Since it floats in the electrolyte, there is a risk of contact with the battery case or lead that has electrical contact with the positive electrode.
If they come into contact, a so-called internal short circuit will occur,
The function as a battery is lost. Even if the dendrites do not fall off, there is a high risk that the dendrites will grow and penetrate through the holes of the separator to cause an internal short circuit.

In order to improve such a defect of the negative electrode, from the viewpoint of cycle life, although a method of adding an additive that suppresses the generation of dendrite to the electrolytic solution or a method of using an alloy with lithium has been studied, It can be said that the examination from the viewpoint of improvement of reliability, especially safety is delayed.

That is, when dendrites are generated, it is important that they do not penetrate through the separator holes and float in the electrolyte. For that purpose, it is necessary to optimize the structure of the separator so as to have high reliability and to reduce the energy density as much as possible.

However, the conventional separator of this kind of electrode body,
A nonwoven fabric having a cross-sectional shape as shown in FIG. 4 or a microporous film having a two-dimensional pore structure as shown in FIG. 5 is used. There are the following two methods of construction, and the sectional views of the constitution of each electrode body are the same as the constitution method of the existing lithium primary battery as shown in FIGS. 6 and 7. In the first method, as shown in FIG. 6, a positive electrode plate 1 formed by filling a core material such as expanded metal or a net with a mixture containing titanium disulfide as an active material and drying the active material contains lithium metal as an active material. Band separator 3 between the negative electrode plate 2 and
This is a method in which the whole is formed in a spiral shape by interposing.

In the second method, as shown in FIG. 7, the positive and negative electrode plates 1 and 2 are covered with a separator 3 to form a spiral shape.

Problems to be Solved by the Invention The conventional structure has the following problems in terms of the shape of the separator and the method of forming the separator.

First, the shape of the separator is required to have the following four characteristics.

(1) The surface shape of the separator is smooth in order to allow a uniform charge / discharge reaction to proceed.

(2) It has a pore structure that does not penetrate the pores of the separator due to the growth of dendrites.

(3) The separator has a high temperature pore-closing property capable of instantaneously interrupting the electrode reaction when an abnormality such as a battery short circuit occurs.

(4) Excellent electrolyte retention.

In contrast to the above characteristics, in the case of a non-woven fabric, since the fibrous resin is irregularly formed, the surface shape is rough and the pores are large and non-uniform, so that none of the above four characteristics can be satisfied. There is.

In the case of a microporous film having a two-dimensional pore structure,
Although the characteristics 1 and 3 described above are provided, there is a problem that the structure of the pores is poor in liquid retaining property, and when the dendrite grows, it easily penetrates the pores to cause an internal short circuit.

Next, the following two conditions are important in terms of the constitution of the separator.

(1) The structure should prevent the dendrites from floating.

(2) The energy density should not be reduced.

However, in the conventional configuration, in the case of the first method, since the upper and lower portions of the separator 3 are open, there is an extremely high risk of causing an internal short circuit due to floating dendrites or bridges. Therefore, it is necessary to mount insulating plates on the upper and lower sides of the electrode body. However, when the insulating plates are pressed against the upper and lower sides of the electrode body, the separators protruding from the upper and lower sides of the electrode body are bent unevenly, and the insulating plate is pushed up by the repulsive action of the bent separators. The adhesion of the plate was uneven and insufficient, and it was difficult to prevent internal short circuit due to dendrites. Further, when the insulating plate is pressed firmly to increase the adhesion between the electrode body and the insulating plate, there is a problem that the electrode plate may fall off to deteriorate the battery performance and prevent the internal short circuit.

Further, in the case of the second method, wrinkles of the separator occur in the shaded portion A in FIG. 8 when spirally wound.
Therefore, the outer diameter of the electrode body becomes large, and it becomes difficult to insert the electrode body into the case.

Therefore, it is necessary to deal with the electrode plate by making it thin or short, which causes a problem of reducing the discharge capacity. Further, since the electrolytic solution is difficult to uniformly penetrate into the wrinkle portion, there is a problem that the variation in charge / discharge characteristics is increased.

The present invention solves such problems and aims to improve safety and charge / discharge characteristics.

Means for Solving the Problems In order to solve these problems, the present invention configures an electrode body by the first method using a separator made of a microporous film having a three-dimensional pore structure, and further, The separator protruding from the top and bottom of the electrode body is bent in the winding core direction by hot air heating to cover the positive, negative and bipolar plates.

Action With this configuration, the electrolyte is uniformly permeated and the liquid retaining property is excellent, so that variations in charge / discharge characteristics can be reduced. Moreover, even when the dendrite grows, an internal short circuit due to the hole penetration can be prevented. Further, since it is a microporous film, the film melts due to heat generation during abnormalities such as a short circuit of the battery to block the pores, and the electrode reaction is instantaneously blocked to ensure safety.

Further, since the upper and lower parts of the electrode body can be uniformly covered, the dendrites are unlikely to fall off, and even if the dendrites fall off, they can be prevented from floating in the electrolytic solution.

EXAMPLE FIG. 1 is a sectional view of a cylindrical lithium secondary battery according to an example of the present invention, which will be described in detail below.

In FIG. 1, the positive electrode plate 1 is chromium pentaoxide (Cr ₂ O ₅ ).
Is filled in a core material made of an expanded metal made of titanium and dried. Reference numeral 4 denotes a positive electrode lead plate made of the same material as the core material, which is spot-welded to the core material. The negative electrode 2 is made of metallic lithium, and the negative electrode lead plate 5 is pressure bonded to one side surface thereof.

3 is a microporous film of a polyolefin type, for example, polypropylene, polyethylene or a copolymer thereof having a three-dimensional pore structure (sponge-like structure) as shown in FIG. 0.5 μ is preferable), and the separator is cut into a band shape wider than the positive and negative electrodes 1 and 2. In this example, a microporous film made of polypropylene was used. FIG. 3 is an enlarged schematic view of a portion 3a in FIG. 2, which has a large communication hole.

Next, the separator 3 is interposed between the positive and negative electrodes 1 and 2, and the whole is spirally wound to form an electrode body.

And while rotating the electrode body, the upper and lower end faces of the electrode body,
That is, hot air is blown to the separator protruding from the positive and negative electrodes 1 and 2 in a direction slightly obliquely above the core of the electrode body, and the protruding part of the separator is bent while contracting in the core direction to cover the electrode body. The configuration of the electrode body is completed. (The heating temperature varies depending on the material of the separator, but in the case of this embodiment, the heating temperature is 140 to 180 ° C. Further, a flat plate may be appropriately pressed against the bent portion to enhance the adhesion. Next, after forming a step on the upper part of the case 8, an electrolytic solution (in this example, a solution obtained by dissolving lithium perchlorate as a solute in a mixed solvent of propylene carbonate and 1,2-dimethoxyethane) was used. Used.) Is injected. When injecting the solution, a uniform impregnation state can be obtained in a short time by operating under reduced pressure.

Then, after the sealing plate 9 is attached, the opening end of the case 8 is caulked to complete the assembly of the battery.

Table 1 summarizes the number of voltage failures due to internal short-circuits and the maximum, minimum, and average values of the discharge capacity at the 50th cycle during the charge / discharge test of 100 products of the present invention and 100 products of the conventional product. The test conditions in this case are repeated charging and discharging at a constant current of 50 mA at 20 ° C. at a depth of 600 mAh, which is about 80% of the filling capacity of the positive electrode.

FIG. 9 shows an example of the discharge characteristics at the 200th cycle when the product of the present invention and the conventional product were subjected to a charge / discharge test under the same conditions.

As is clear from these results, since the surface shape of the separator of the present invention is smooth, the charge / discharge reaction can proceed uniformly, and the growth of dendrites can be suppressed. Further, since it has a three-dimensional pore structure, it has uniform permeation of the electrolytic solution and excellent liquid retention, so that variations in charge / discharge characteristics can be reduced. Moreover, even when the dendrite grows, an internal short circuit due to the hole penetration can be prevented. Further, since it is a microporous film, the film melts due to heat generation during abnormalities such as a short circuit of the battery to block the pores, and the electrode reaction is instantaneously blocked to ensure safety.

Further, in the separator configuration, since the electrode plate is previously covered with the bag-shaped separator to form the spiral electrode body without the wrinkles of the separator, the outer diameter of the electrode body becomes large and It is not difficult to insert. Furthermore, by heating the upper and lower end surfaces of the separator protruding above and below the electrode body with hot air, it conforms well to the irregularities on the top and bottom of the electrode body and at the same time bends in the winding direction to evenly cover the upper and lower parts of the electrode body. It is possible to prevent dendrites from falling off, and even if dendrites drop out, it is possible to prevent the dendrites from floating in the electrolyte, which is excellent in terms of preventing internal short circuits and charging / discharging characteristics. I understand.

EFFECTS OF THE INVENTION As described above, according to the present invention, it is possible to obtain the effects of suppressing internal short-circuiting due to the generation of dendrites in the negative electrode lithium and reducing or reducing the charge / discharge characteristics.

[Brief description of the drawings]

1 is a sectional view of a cylindrical lithium secondary battery according to an embodiment of the present invention, FIG. 2 is a sectional view of a separator according to an embodiment of the present invention, and FIG. 3 is an enlarged view of a portion 3a in FIG. 4 and 5 are views showing the cross-sectional shape of a conventional separator, FIGS. 6 and 7 are cross-sectional views showing the structure of a conventional spirally wound electrode body, and FIG. 8 is a conventional separator-covered electrode plate. It is a figure which shows the wrinkle generation part at the time of winding. FIG. 9 is a diagram showing discharge characteristics at the 200th cycle in the charge / discharge test. 1 ... Positive electrode, 2 ... Negative electrode, 3 ... Separator.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Zenichiro Ito 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Yukio Nishikawa 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. (72) Inventor Junichi Yamaura 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) Reference JP-A-1-122574 (JP, A) JP-A-1-143140 (JP, A)

Claims (1)

(57) [Claims] 1. A spirally wound electrode having a positive electrode, a negative electrode, and a separator made of a polyolefin-based microporous film having a three-dimensional pore structure, which is wider than the both electrode plates, and is interposed between the electrode plates. Characterized in that the positive and negative electrode plates are covered by bending the end faces of the separator protruding above and below the electrode body in the winding core direction by hot air heating. And a cylindrical lithium secondary battery.