JPH10199493A - Secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent bulging caused by internal pressure, and enhance charge/ discharge cycle efficiency and space efficiency by forming a recess in the facing side walls, and setting the longitudinal and lateral dimensions of the recess to those of the side walls within the specified range in a battery container for housing an electrode group of a lithium secondary battery formed by stacking and winding a positive sheet and a negative sheet through a separator. SOLUTION: An electrode group formed by stacking and winding a positive sheet and a negative sheet through a separator is housed in a round square- shaped battery container 8' made of 0.5mm thick aluminum plate, a positive lead 4 and a negative lead 5 are taken out, and a secondary battery is formed. A recess is formed in the facing side walls of the battery container 8', the lateral and longitudinal dimensions a, b to the lateral and longitudinal dimensions c, d are set in the ranges of c>=a>=c/2 and d>=b>=d/2. By setting radius of curvature of the cross section of the recess in the range of 80-250mm, the strength of the battery container 8' against the internal pressure is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary battery having a high energy density and a high safety as a power source for driving an electronic device or a memory holding power source or a battery for an electric vehicle.

[0002]

2. Description of the Related Art As electronic devices have rapidly become smaller and lighter,
There is an increasing demand for the development of a secondary battery that is small, lightweight, has a high energy density, and that can be repeatedly charged and discharged with respect to the battery as the power source. As a secondary battery satisfying these requirements, an organic electrolyte secondary battery is most promising.

The positive electrode active material of an organic electrolyte secondary battery includes titanium disulfide, lithium cobalt composite oxide, lithium nickel composite oxide, spinel type lithium manganese oxide, vanadium pentoxide and molybdenum trioxide. Metal sulfides and metal oxides have been studied, and lithium alloys, carbon materials, etc., including metal lithium, have been studied as negative electrode active materials.

[0004]

In a conventional battery, an electrode group formed by spirally winding a positive electrode sheet and a negative electrode sheet via a separator is housed in a cylindrical container.
There is a drawback that many gaps, so-called dead spaces, occur when the battery is housed in an electronic device or when a battery pack is used. In recent years, as shown in JP-A-5-135780 as a battery having a small dead space, an electrode group formed by winding a positive electrode sheet and a negative electrode sheet via a separator has a round cross section in a square shape. An organic electrolyte secondary battery housed in a case has been proposed, but has a problem in that the battery swells significantly and the discharge capacity decreases due to the progress of charge / discharge cycles and storage at high temperatures.

[0005] In electronic equipment, which has been increasing in density in recent years, swelling of a battery causes destruction of peripheral parts, and in an assembled battery, there are various problems such as disconnection of connection leads between batteries and deformation of terminals connecting the leads. Cause problems. As a countermeasure against this, a method of increasing the thickness of the case was examined, but there was a problem that the energy density per weight and capacity was reduced.

[0006]

A secondary battery according to the present invention includes a battery case in which a wound electrode body is housed, and a side wall of the opposed battery case is provided with respect to an electrode body winding axis. Parallel recesses are provided, and the recesses are c ≧ a ≧ c / 2, where a is a width and b is a height, and c is a width and d is a width of a side wall provided with the recess. And d
It is characterized by satisfying the relationship of ≧ b ≧ d / 2.

A second invention according to the first invention is characterized in that the recess has an arc shape having a radius of curvature of 80 mm to 250 mm in a cross section perpendicular to the winding axis of the electrode body.

A secondary battery according to the first or second aspect of the present invention includes a battery case having a round cross section perpendicular to the winding axis of the electrode body and having a round cross section in the side wall of the battery case. Is characterized in that the concave portion is formed.

A fourth invention according to the first, second or third aspect is characterized in that the negative electrode is an organic electrolyte secondary battery including a lithium host material capable of inserting and extracting lithium ions.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION A rounded square shape having a cross section perpendicular to the winding axis of an organic electrolyte secondary battery case, particularly an electrode body of the battery case, comprising a straight portion and a curved portion (see FIG. 3)
The inventors found that the cause of the swelling was a problem peculiar to this type of battery system as described below.

Among organic electrolyte secondary batteries, batteries using a carbon material for the negative electrode, in particular, decompose the electrolyte at the negative electrode during initial charging and as the charge / discharge cycle progresses, and generate gas mainly composed of carbon dioxide gas. I do. However, this type of battery does not absorb gas by the negative electrode unlike aqueous secondary batteries such as lead batteries, nickel cadmium and nickel hydrogen batteries, and when water enters the battery, the reaction between water and the active material occurs. As a result, the battery performance is reduced, so that the battery is completely sealed.

That is, since the generated gas remains in the battery, the internal pressure of the battery increases with the progress of gas generation. In a battery having a round cross-section square shape, a linear portion having a small strength is distorted and the battery swells. Occur.

However, by forming the battery case accommodating the above-mentioned power generating element into a rounded square shape in which a concave portion having an arc-shaped cross section is provided in a linear portion of a cross-sectional shape of the battery case, the case strength against an increase in internal pressure is improved. It was revealed that the swelling of the case could be solved dramatically.

The recess has a horizontal width (horizontal length) of a
If the vertical width (height) is b, and the lateral width (horizontal length) of the side wall provided with the concave portion is c and the vertical width (height) is d, c ≧ a ≧ c / 2 and d It has been found that it is necessary to satisfy the relationship of ≧ b ≧ d / 2. That is, if the width of the concave portion is smaller than の 長 of the length of the straight portion of the rounded square shape, satisfactory strength cannot be obtained, and the length of the concave portion is also 1/1 of the vertical width (height) of the case side wall. When it was smaller than 2, similar results were obtained.

In addition, the width c of the concave portion is a (a = c) and / or the vertical width is at least the same as the electrode width, and is the case side wall portion facing the electrode, and A more favorable result was obtained by forming it on the upper end of the electrode group.

Further, the cross-sectional shape of the recess has a radius of curvature of 8
By making the shape of an arc having 0 mm to 250 mm,
It has been found that it has a very good effect.

When the present application is applied to a battery case having a square cross section, the same effect is obtained. In the case of a rectangular shape, it may be formed on the long side surface and / or the short side surface, but it is sufficient to form it on the long side surface.

Further, the rounded square shape as referred to in the present invention has a set of opposed linear portions and a set of arc-shaped curved portions opposed to each other, and both ends of the straight portion are respectively provided at each end. It refers to the shape connected to the end of the curved part. Here, the curved portion has an outwardly convex shape.

The length of the straight portion and the length of the curved portion can be set arbitrarily.

Further, the present invention has a feature of being excellent in space efficiency as in the case of the rounded square shape.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An organic electrolyte secondary battery according to one embodiment of the present invention will be described below in detail with reference to the drawings. It goes without saying that the present invention is not limited to the present embodiment without departing from the spirit and scope of the present invention.

In FIG. 1, a sheet-shaped positive electrode 1 has a thickness 2
Lithium cobalt oxide (L
iCoO ₂ ) was held using a binder together with a conductive agent, and had a thickness of 190 μm and a width of 80 mm.

The sheet-shaped negative electrode 3 is formed by holding graphite on a copper foil having a thickness of 14 μm by using a binder.
Those having a thickness of 0 μm and a width of 83 mm were used. Separator 2
Is a microporous membrane made of polyethylene and has a thickness of 25
μm and a width of 89 mm were used.

Five positive electrode leads 4 and five negative electrode leads 5 were attached to the exposed metal foils on the upper end surfaces of the positive and negative electrode sheets by ultrasonic welding. Positive electrode 1 and negative electrode 3
And an electrode body having a cylindrical cross-sectional structure using an aluminum pipe 6 as a winding core.

The outer periphery of the electrode body was fixed with a tape 7, crushed and formed as shown in FIG.

The above-mentioned electrode body is housed in a battery container 8 'having a round cross section in which a straight portion is curved in an arc shape (a plane perpendicular to the winding axis of the electrode body), and after sealing, ethylene carbonate is used. An electrolytic solution in which 1 mol of lithium hexafluorophosphate was dissolved was injected under reduced pressure into a mixed solvent of 1: 1 (volume ratio) of dimethyl carbonate and dimethyl carbonate, and a positive electrode terminal 9 and a negative electrode terminal 10 as shown in FIG. 2 having a safety valve 11
A battery having a size of 2 mm, a width of 60 mm, and a height of 100 mm was manufactured.

As shown in FIG. 4, the straight portions were respectively formed with radii of curvature of 50 mm, 80 mm, 150 mm, 250 mm, and 35 mm.
Batteries 12 recessed at 0 mm and having recesses were designated A, B, C, D and E, respectively, and battery 12 'having no recess in the linear portion was designated F. Here, when the width of the concave portion is a and the vertical width is b, and the vertical width (height) of the side wall provided with the concave portion is c and the vertical width is d, the horizontal width of the concave portion is c =
a, d = b. (See FIG. 11, c ≧ a as a reference example.
FIG. 12 shows the case where ≧ c / 2 and d ≧ b ≧ d / 2. However, when c> a ≧ c / 2 and d> b ≧ d / 2, the position of the concave portion is most preferably at the center of the linear portion in the direction perpendicular to the winding axis. The direction parallel to the winding axis is most preferably from the bottom of the case to the upper end of the electrode plate group. Then, aluminum having a thickness of 0.5 mm was used as the material of the battery case.

(Here, the curved portion is formed in a semicircular arc shape, but may be a fan arc shape, but the shape is not limited to this.) Next, the manufactured battery of the present invention is subjected to a constant current. After charging to 4.1 V at 2 A, the battery was discharged to 2.75 V at a constant current of 2 A, and the discharge capacity was measured. The test temperature was 25 ° C. Table 1 summarizes the discharge capacity and the length of the positive electrode plate that can be inserted into the battery.

[0029]

[Table 1] As is clear from Table 1, the radius of curvature of the concave portion of the straight portion is 8
When it was less than 0 mm, the discharge capacity was significantly reduced. It is considered that the cause is that when the radius of curvature is less than 80 mm, the electrode space in the battery is extremely compressed, so that the electrode length that can be inserted into the battery is shortened.

Next, the battery of the present invention was charged to 4.1 V at a constant current of 2 A and then discharged to 2.75 V at a constant current of 2 A for 500 charge / discharge cycle tests. The test temperature was 45 ° C.

FIGS. 5, 6 and 7 show changes in the discharge capacity, internal resistance, and battery thickness as the charge / discharge cycle progresses.

In the batteries B, C, and D of the present invention, the decrease in capacity and the increase in internal resistance with the progress of the cycle are small, and there is no change in battery thickness. However, it was found that the battery E and the comparative battery F had a large increase in battery thickness in addition to a decrease in capacity and an increase in internal resistance as the cycle proceeded. The cause of the shortened charge / discharge cycle life of the batteries E and F is estimated as follows.

That is, gas is generated as the charge / discharge cycle progresses, and the battery case swells due to an increase in internal pressure. It is considered that when the case swells, the distance between the electrodes increases, and the electrochemical reaction does not proceed smoothly. From the above example, the battery of the present invention in which a concave portion having a radius of curvature of 80 mm to 250 mm was formed in a straight portion having a rounded square shape,
It has been found that the battery has the same discharge capacity as the conventional elliptical battery, and the charge / discharge cycle life performance is dramatically improved.

Next, the height 50 mm, the width 130 mm, the height 2
A 10 mm battery was manufactured, and the effect of the present invention was examined.

The number of positive electrode leads and the number of negative electrode leads were each 50, and a sheet-shaped positive electrode was 171 mm wide aluminum foil, a sheet-shaped negative electrode was 172 mm wide copper base foil, and a separator was 180 mm wide. A battery was assembled in the same manner as in the above example except that the material was 1.2 mm thick aluminum.

The linear portions are each defined with a radius of curvature of 50 mm and 80 mm.
The batteries 12 recessed by mm, 150 mm, 250 mm, and 350 mm were designated G, H, I, J, and K, respectively, and the battery 12 ′ having no concave portion in the linear portion was designated L.

Next, the prepared battery of the present invention was charged at a constant current of 20 A.
And then discharged to 2.75 V at a constant current of 20 A, and the discharge capacity was measured. The test temperature was 25 ° C.
Table 2 summarizes the discharge capacity and the length of the positive electrode plate that can be inserted into the battery.

[0038]

[Table 2] As is clear from Table 2, the radius of curvature of the concave portion of the straight portion is 8
It was found that when the thickness was less than 0 mm, the discharge capacity was significantly reduced as in the example at 10 Ah. Next, after charging the produced battery to 4.1 V at a constant current of 20 A,
50 charge / discharge cycle tests to discharge to 2.75 V
0 cycles were performed. The test temperature was 45 ° C.

FIGS. 8, 9 and 10 summarize changes in the discharge capacity, internal resistance, and battery thickness as the charge / discharge cycle progresses. In the batteries H, I, and J of the present invention, a decrease in capacity and an increase in internal resistance due to the progress of the cycle are small, and no change in battery thickness is observed. However, it was found that E and Comparative Battery F had a large increase in battery thickness, in addition to a decrease in capacity and an increase in internal resistance as the cycle proceeded.

From the above examples, it was clarified that the present invention can obtain the effect of improving the battery characteristics regardless of the size of the battery.

The concave portion according to the present invention may be press-molded into a half case, may be formed later in a cylindrical case having a bottom, or may be formed simultaneously with the case by, for example, an impact molding method. May be. Needless to say, the battery lid used should conform to the shape of the case.

Further, in the example, Li was used as the positive electrode active material.
Although the case of using CoO ₂ has been described, titanium disulfide, manganese dioxide, lithium nickel composite oxide, lithium nickel cobalt composite oxide, lithium nickel cobalt manganese composite oxide, lithium cobalt aluminum composite oxide, lithium nickel cobalt Various materials such as an aluminum composite oxide, a lithium nickel cobalt manganese aluminum composite oxide, a spinel lithium manganese oxide, vanadium pentoxide, and molybdenum trioxide can be used. Although a graphite material is used for the negative electrode, various materials such as a low-crystalline carbon material, an amorphous carbon material, and an oxide can be used.

Further, the present invention can be applied to various sealed secondary batteries in which the internal pressure of the battery increases. For example,
A lead battery, a nickel cadmium battery, a nickel hydride battery and the like can be mentioned.

The concave portion according to the present invention is not limited to the cross-sectional shape of an arc, but may have a substantially trapezoidal oblique side excluding the lower base of the trapezoid, and may have a stepped shape. The shape may be a composite shape in which the upper base is an arc, and is not limited to these.

[0045]

The secondary battery according to the present invention is provided with a battery case in which a wound electrode body is housed, and a concave portion parallel to the electrode body winding axis is formed on the opposed battery case side wall. The recess is c ≧ a ≧ c / 2 and d ≧ b, where a is a width and b is a width, and c is a width and d is a height of a side wall provided with the recess. ≧ d / 2 is satisfied.

A second invention according to the first invention is characterized in that the recess has an arc shape having a radius of curvature of 80 mm to 250 mm in a cross section perpendicular to the winding axis of the electrode body.

In the secondary battery according to the first or second aspect of the present invention, a battery case having a round cross section perpendicular to the winding axis of the electrode body is provided on the side wall of the battery case having a straight cross section. Is characterized in that the concave portion is formed.

A fourth invention according to the first, second or third aspect is characterized in that the negative electrode is an organic electrolyte secondary battery including a lithium host material capable of inserting and extracting lithium ions.

According to this, it is possible to provide a battery in which swelling of the battery is effectively suppressed, and which is excellent in charge / discharge cycle life performance and space efficiency. Further, by applying a material that stores and releases lithium on the negative electrode to a battery system using a metal oxide or metal sulfide for the positive electrode, a lithium secondary electrolyte battery with a high capacity can be obtained.
Its industrial value is enormous.

[Brief description of the drawings]

FIG. 1 shows a group of electrodes wound in a cylindrical shape.

FIG. 2 shows an electrode group processed into a rounded square shape.

FIG. 3 is an external view of a conventional battery.

FIG. 4 is a cross-sectional shape of a battery case.

FIG. 5 is a diagram showing a change in discharge capacity as a charge / discharge cycle of a test battery progresses.

FIG. 6 is a diagram showing a change in internal resistance as a charge / discharge cycle of a test battery progresses.

FIG. 7 is a diagram showing a change in battery thickness as a charge / discharge cycle of a test battery progresses.

FIG. 8 is a diagram showing a change in discharge capacity as a charge / discharge cycle of a test battery progresses.

FIG. 9 is a diagram showing a change in internal resistance as a charge / discharge cycle of a test battery progresses.

FIG. 10 is a diagram showing a change in battery thickness as a charge / discharge cycle of a test battery progresses.

FIG. 11 is a view showing one embodiment of a secondary battery according to the present invention.

FIG. 12 is a view showing another embodiment of the secondary battery according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Separator 3 Negative electrode 4 Positive electrode lead 5 Negative electrode lead 6 Aluminum pipe 7 Tape 8 Conventional battery container (round cross section square shape) 8 'Battery container (it becomes this invention) 9 Positive electrode terminal 10 Negative electrode terminal 11 Safety valve 12 Battery according to the present invention

Claims (4)

[Claims] 1. A secondary battery comprising a battery case in which a wound electrode body is housed, wherein a side wall of the facing battery case is provided with a concave portion parallel to a winding axis of the electrode body. When the width of the concave portion is a and the vertical width is b, and the width of the side wall provided with the concave portion is c and the vertical width is d, c ≧ a ≧ c / 2 and d ≧ b ≧ d / 2. A secondary battery characterized by satisfying the relationship. 2. The secondary battery according to claim 1, wherein the recess has an arc shape having a radius of curvature of 80 mm to 250 mm in a cross section perpendicular to the winding axis of the electrode body. 3. A secondary battery comprising a battery case having a rounded and quadrangular cross section perpendicular to the winding axis of the electrode body, wherein the concave portion is formed in a battery case side wall having a straight cross section. The secondary battery according to claim 1, wherein: 4. The secondary battery according to claim 1, wherein the negative electrode is an organic electrolyte secondary battery including a lithium host material capable of occluding and releasing lithium ions.