JPH1055823A - Battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery capable of applying uniform pressure to the whole of a plate group through a simple structure, even in the case of such a type as having plates of low strength stacked in a multilayer. SOLUTION: This battery has a stacked plate group formed out of plates stacked so as to prevent the plates of different polarity from coming in contact with each other, and a pressing member 1 for pressing the stacked plate group in a stacked direction. In this case, the pressing member 1 is formed to be substantially resistant against an electrolyte. Also, one side of the pressing member 1 has convex lens type surface and the other side has flat surface. Furthermore, the flat surface of the pressing member 1 is kept in contact with the surface of the stacked plate group at least at one side, while the convex lens type surface thereof is kept in contact with the inner wall of a battery vessel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery provided with a laminated electrode group formed by laminating electrode plates having different polarities so as not to be in direct contact with each other, and to an improvement in the structure thereof.

[0002]

2. Description of the Related Art Conventionally, in the field of rechargeable secondary batteries, lead-acid batteries, nickel-cadmium batteries, nickel-
Batteries such as hydrogen batteries were the mainstream. However, with the rapid spread of mobile phones and notebook computers in recent years,
There has been a demand for smaller and higher capacity batteries. In response to such a demand, a so-called lithium ion secondary battery has been developed which uses a carbon material for the negative electrode and allows charging and discharging by inserting and removing lithium ions. Lithium ion secondary batteries have lower energy density than batteries using metallic lithium as the negative electrode material, but have the advantage of being safer and have higher energy density than conventional batteries, and have rapidly spread the market. I have. In general, a lithium ion secondary battery has a characteristic that it is difficult to obtain a high discharge capacity unless a certain pressing force is applied to the electrode plate group like other rechargeable batteries. This is because the pressing force improves the adhesion between the active material and the current collector, that is, the effect of improving the current collection. Conventional automotive lead-acid batteries are provided with a flat plate-like pressing member in the battery,
The electrode plate is constantly pressed in spite of volume changes such as expansion and contraction of the electrode plate due to the charge / discharge reaction of the battery. Also, as disclosed in Japanese Patent Application Laid-Open No. 4-62762, a thin lead-acid battery is designed so that a penetrating rod is directly passed through the electrode plate to apply a uniform pressing force to the electrode plate.

[0003]

However, it is difficult to apply a uniform pressing force to the entire stacked electrode group in the stacking direction with the conventional flat plate pressing member as a spacer. This is because, in order for the flat plate pressing member to apply a uniform pressing force to the entire stacked electrode group in the stacking direction, it is required that one flat plate pressing member has no variation in thickness. This is a problem related to the molding technique of the pressing member. For example, when a flat plate pressing member that cannot contact the respective surfaces with a uniform pressing force is disposed between the inner surface of the battery container and the pressing surface of the stacked electrode group, the stacked electrode group is only partially pressed. Can not do. The partially-pressed laminated electrode group has a portion that is not substantially pressed. In particular, when the strength of the electrode plate used is low, the difference between the pressing force of the pressed portion and the pressing force of the non-pressed portion is very large. The reason for this is that a high-strength electrode plate functions as a pressing member for an electrode plate located inside even a part where pressure is not applied, whereas a low-strength electrode plate is easily used. This is because the role of the pressure member cannot be expected in a portion that is not pressed because it is deformed. If uniform pressure is not applied to the stacked electrode group, ohmic loss of the electrode plate increases, and not only does the battery not have a predetermined capacity but also the discharge capacity particularly at a high rate is greatly reduced. .
In addition, it is difficult to apply the method to an electrode group using a low-strength electrode plate even by a method of directly passing a penetrating rod through an electrode plate and applying pressure as disclosed in JP-A-4-62762. This is because the work of passing the through rod through the electrode group using a low-strength electrode plate involves not only the risk of short-circuiting of the battery due to the falling off of the active material and the like, but also the vicinity of the through rod as described above. However, pressure is applied only to the electrode plate group, and a uniform pressing force cannot be expected over the entire electrode plate group. The problem to be solved by the present invention is to obtain a battery that can apply a pressing force uniformly to the entire electrode plate group with a simple structure, even for a battery in which low-strength electrode plates are laminated in multiple layers. Things.

[0004]

Means for Solving the Problems To solve the above-mentioned problems, a laminated electrode group according to the present invention, which is formed by laminating electrode plates having different polarities so as not to directly contact each other, is laminated. In the battery having the pressing member 1 for pressing in the direction, the pressing member 1 is electrolyte-resistant, one surface of the pressing member 1 is a convex lens shape, and the other surface is flat. The flat surface is in contact with at least one end face of the stacked electrode plate group, and the convex lens-shaped surface of the pressing member 1 is in contact with the inner wall of the battery container. By using the pressing member 1 having a convex lens shape on one side and a planar structure on the other side, the convex lens shape side comes in contact with the battery container at an arbitrary point, and the flat side has a surface in contact with the electrode plate group surface. Will be in contact with you. Therefore, even if the pressing member 1 is displaced in a state inclined with respect to the pressing surface in the battery, the convex lens-shaped side of the pressing member 1 is still in contact with the battery container at a point, and the point is used as a starting point. The pressing force can be uniformly applied to the pressing surface. In addition, since the pressing member 1 is substantially resistant to the electrolytic solution, it does not dissolve into the electrolytic solution and does not cause deformation of the pressing member 1. Also, there is no adverse effect on battery performance such as a decrease in ionic conductivity of the electrolyte. Further, the pressing member 1 is preferably made of a material that does not hold the electrolytic solution. As a material for holding the electrolytic solution, there are water-absorbing polymers and the like, which are easily deformed by holding the electrolytic solution. However, there is no problem as long as the material does not substantially deform even when the electrolyte is held, and the degree of deformation is such that the problem to be solved by the present invention can be solved.

Due to such an effect, when pressing the laminated electrode group in the laminating direction as shown in FIG. 1, it is not always necessary to arrange the pressing members 1 on both sides of the pressing surface, and one of them is sufficient. The effect is obtained. In this case, the inner surface of the battery container on which the pressing member 1 is not disposed plays a role similar to that of the pressing member. However, the pressing member 1 may be arranged on both sides of the pressing surface.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below by taking a lithium ion secondary battery as an example. (Preparation of positive electrode) 8% by weight of polyvinylidene fluoride as a binder was added to lithium cobaltate, N-methylpyrrolidone was added as a dispersion solvent, and the kneaded slurry was applied to both surfaces of a 20 μm-thick aluminum foil. A positive electrode having a thickness of 200 μm was obtained by coating, followed by drying, pressing and cutting.

(Preparation of Negative Electrode) Polyvinylidene fluoride as a binder is added to graphite at a weight ratio of 8%, N-methylpyrrolidone is added as a dispersing solvent, and the kneaded slurry is mixed with a 10 μm thick copper foil on both sides. , And then dried, pressed and cut to obtain a negative electrode having a thickness of 130 μm.

The positive electrode produced by the above method was alternately laminated with the negative electrode via a polyethylene separator. Along with this electrode plate group, a polyethylene pressing member 1 shown in FIG. 2 having a convex lens shape on one side and a flat structure on the other side was inserted into a rectangular battery container. At this time, the convex lens-shaped surface is brought into contact with the inner surface of the battery container, and the plane is brought into contact with the laminated electrode plate side. Further, at this time, a pressing force is generated at the contact point between the inner surface of the battery container and each pressing member, and as a result, the stacked electrode group is adjusted so as to be pressed in the stacking direction. Thereafter, the upper lid of the battery container was welded and sealed, and a predetermined amount of electrolyte was injected from the injection port, and the injection port was sealed to obtain a lithium ion battery. FIG. 1 shows a cross-sectional view of a stacked secondary battery according to the present invention. As the electrolytic solution, a solution prepared by dissolving lithium hexafluorophosphate at 1 mol / L in a mixed solution of ethylene carbonate and dimethyl carbonate was used.

[0009]

EXAMPLES In order to verify the effectiveness of the present invention, lithium ion secondary batteries (Examples) described in the embodiments of the invention and batteries of Conventional Examples 1 to 3 described below were produced and compared. (Preparation of Battery of Conventional Example 1) The same positive electrode and negative electrode as in the above-described embodiment of the present invention, an electrolytic solution, and a separator were used, and the positive electrode and the negative electrode were stacked alternately with the separator interposed therebetween.
Thereafter, the battery was assembled in the same manner as in the example except that the pressing member used in the example according to the present invention was not inserted. No pressure member is inserted in this battery. (Preparation of Battery of Conventional Example 2) Using the same positive electrode and negative electrode, an electrolytic solution, and a separator as in the above-described embodiment of the present invention, the positive electrode and the negative electrode were alternately stacked with the separator interposed therebetween.
Thereafter, a battery was assembled in the same manner as in the example according to the present invention, except that a pressing member having a planar structure on both sides was used. (Preparation of Battery of Conventional Example 3) Using the same positive electrode and negative electrode, an electrolytic solution, and a separator as in the above-described example according to the present invention, the positive electrode and the negative electrode were alternately laminated via the separator.
After that, a through hole is made to pass through rods through these electrode plates,
Both ends of the laminated electrode plate group were pressed down at both ends of the through-bar made of heat-shrinkable polypropylene, and then the through-bar was heated to apply pressure from both sides. Thereafter, a battery was assembled in the same manner as in the example according to the present invention. Although no pressing member is inserted in this battery, the electrode group is pressed by a penetrating rod.

(Experiment) The initial capacity and the high-rate discharge performance of the batteries of the above embodiment and conventional examples 1 to 3 were compared. In the initial capacity test, after charging at a constant current at an 8-hour rate, the battery was discharged at an 8-hour rate (１ ／ C) to a final voltage of 2.8 V. The high-rate discharge performance is as follows: after the charge / discharge efficiency is stabilized after the initial capacity test, the battery is charged at a constant current at an 8-hour rate, and the discharge is performed at an 8-hour rate (1 / 8C), a 1-hour rate (1C), and a 2-hour rate ( 2
In C), the operation was performed up to the final voltage = 2.8V.

Table 1 shows the results of the initial capacity test and the high rate discharge test. The initial capacity is shown as a ratio when the discharge capacity of the battery in the example of the present invention is set to 100%. The high-rate discharges are shown as ratios to 1 / 8C discharges.

[0012]

[Table 1]

The battery of the embodiment of the present invention is excellent in both initial capacity and high-rate discharge performance because a uniform pressing force is obtained over the entire surface to be pressed of the electrode plate group. On the other hand, Conventional Example 1, which does not use a pressing member, has very low initial capacity and high-rate discharge performance. Further, Conventional Examples 2 and 3 using other pressurizing members and the like have better characteristics than Conventional Example 1 using no pressurizing members, but do not reach much the embodiments according to the present invention. From these results, it was found that by using the pressing member used in the example of the present invention, a battery having better initial capacity and high-rate discharge performance than the conventional battery could be obtained. These results are obtained because the pressing member used in the embodiment has a structure capable of pressing the laminated electrode group more uniformly.

In this embodiment, as shown in FIG. 1, the pressing members are arranged at both ends of the laminated electrode plate group. However, even if they are arranged only on one side, the same results as in this embodiment are obtained. However, when the stacked electrode group was inserted into the battery container together with the pressing member, the work was easier when the electrodes were placed on both sides of the surface to be pressed as in the present embodiment. This is because the frictional resistance between the pressing member and the battery case is smaller than the frictional resistance between the surface of the stacked electrode plate group and the battery case. In this embodiment, lithium cobalt oxide was used as the positive electrode, graphite was used as the negative electrode, and lithium hexafluorophosphate dissolved at 1 mol / l in a mixed solution of ethylene carbonate and dimethyl carbonate was used as the electrolyte. Is not limited to the above-described material configuration, and a similar effect has been confirmed in a stacked secondary battery having another material configuration. The same effect can be obtained if the pressing member is made of a material resistant to an electrolytic solution. In the case of a lithium ion secondary battery, other materials for the pressing member include polyolefins other than polyethylene and polytetrafluoroethylene other than the polyethylene used in this embodiment.

[0015]

According to the present invention, it is possible to obtain a battery capable of uniformly applying a pressing force to the entire electrode plate group with a simple structure, even for a battery in which low-strength electrode plates are laminated in multiple layers. Was completed.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of the battery of the present invention.

FIG. 2 is a cross-sectional view illustrating an example of a pressing member according to the present invention.

[Explanation of symbols]

 1. Pressing member 2. Negative electrode 3. Positive electrode 4. Separator

Claims (3)

[Claims] 1. A battery comprising: a stacked electrode group formed by stacking electrode plates having different polarities so as not to directly contact each other; and a pressing member for pressing the stacked electrode group in a stacking direction. The member is substantially electrolyte-resistant, and one surface of the pressing member is a convex lens shape, and the other surface is flat;
A battery wherein a flat surface of the pressing member is in contact with at least one end surface of the laminated electrode plate group, and a convex lens-shaped surface of the pressing member is in contact with an inner wall of a battery container. 2. The battery according to claim 1, wherein the pressing member is made of a material that does not hold an electrolytic solution. 3. The battery according to claim 1, wherein the battery is a lithium ion secondary battery.