JPH0955224A - Coin type lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation of defects peculiar to a battery attendant on making the shape thin in the secondary battery capable of storing large capacity as the coin type battery used as the power source of various small appliances. SOLUTION: A coin type lithium secondary battery has a cylindrical stainless steel positive electrode can 5 having prescribed thickness, hardness, height, and diameter, a positive electrode current collector 6, a negative electrode can 7 having prescribed thickness, hardness, a negative electrode current collector 8 welded to the inner surface of the negative electrode can 7, and a circular gasket 9. A negative electrode 2 and the negative electrode current collector 8 are housed in the negative electrode can 7 to which the circular gasket 9 is fit, a separator 3 is placed on the negative electrode 2, the prescribed amount of an organic electrolyte is poured, a positive electrode 1 is placed, and the positive can 5 fixed with the positive electrode current collector 6 is fit, then the positive electrode can 5 is sealed with a press die.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called coin type secondary battery which can store a large amount of electric capacity.

[0002]

2. Description of the Related Art In recent years, batteries used as a power source for various devices have tended to be thinner in shape with the miniaturization of the devices. Is required. In this respect, a lithium secondary battery having a large battery capacity is drawing attention.

By the way, since the electric capacity depends on the volume of the battery, in order to secure a constant volume with a limited thickness, the form of the battery is flat and the area of the can bottom is considerably large. I have no choice.

Also in the lithium secondary battery, a material for the positive electrode has been developed in order to further increase the electric capacity, and lithium nickel oxide (Li
Lithium-manganese composite oxides, which have a higher capacity density than NiO ₂ ) or lithium cobalt oxide (LiCoO ₂ ) are drawing attention.

Therefore, it is desired to develop a coin-type lithium secondary battery using a lithium manganese composite oxide as a thin battery having a large electric capacity.

[0006]

However, compared with lithium nickel oxide, lithium manganese composite oxide has the characteristic that the volume fluctuation during charge and discharge is large,
As a result, for example, when the can bottom area becomes 7 cm ² or more (hereinafter, this is abbreviated as X1), the flatness of this flat portion is not maintained and the outer can is deformed. In addition, in some cases, not only the deformation but also the contact with the internal active material mixture becomes insufficient, which makes charging and discharging difficult.

In particular, when it is 11 cm ² (hereinafter, abbreviated as X2) or more, this tendency becomes remarkable, and when it is 18 cm ² (hereinafter, abbreviated as X3) or more, this phenomenon cannot be ignored and remains as it is. Then it becomes a serious defect.

[0008]

Therefore, the inventors of the present invention have made various investigations to solve this problem. As a result, by devising the material of the outer can of the battery, the above problems can be prevented as much as possible. I found that I can.

That is, a positive electrode, a negative electrode, and an organic electrolytic solution containing a lithium manganese composite oxide facing each other through a separator are housed in a space composed of a positive electrode can and a negative electrode can, and the positive electrode can and the negative electrode can are In a coin-type lithium secondary battery in which a gasket is placed between and sealed, the total proof stress of both the positive and negative outer cans is 410 N / mm ² (hereinafter referred to as Y0 value), etc. 44 rather than a small value
It has come to the surprising fact that the above-mentioned problems can be completely prevented by making it 5 N / mm ² (hereinafter referred to as Y1 value) or more. Regarding this Y1 value, it is more preferable that the range is further reduced to 490 N / mm ² (hereinafter referred to as Y2 value) or more, and 590 N / mm ² (hereinafter referred to as Y3 value) or more. It was also found that this is more preferable. The above facts (hereinafter referred to as the Y value) have led to the discovery of the surprising fact that the above problems can be completely prevented.

In the coin type battery of the present invention, materials, manufacturing and assembly may be appropriately adjusted so as to satisfy the above values. Generally, lithium nickel oxide or the like is used as a positive electrode active material, and phosphorous graphite is used as an electron conduction aid in an amount of 0 to 20% by weight, and polytetrafluoroethylene or polyvinylidene fluoride (hereinafter referred to as PV) as a binder.
2 to 10% by weight may be mixed to prepare the positive electrode mixture. The positive electrode mixture may be filled in a mold and pressure-molded into a disc shape at a pressure of usually 0.5 to ² t / cm ² . Further, graphite is also used for the negative electrode, and P is used as a binder for this.
VDF is mixed at a ratio of 95 to 50% by weight to prepare a negative electrode mixture, which is filled in a mold and press-molded into a disc shape at a pressure of 0.5 to ² t / cm ² at 450 ° C. The negative electrode may be heat treated below.

The separator may be composed of a microporous polypropylene film, a microporous polyethylene film, and an electrolyte solution absorber such as polypropylene nonwoven fabric.

The shape of the positive electrode can may be determined according to the application, but is generally cylindrical. A preferred material is stainless steel. In addition, a stainless steel net, an aluminum net or a titanium net is well suited to the positive electrode can as the positive electrode collector. The negative electrode can is also preferably made of stainless steel, nickel or copper, and the surface is preferably nickel-plated.

If the negative electrode current collector is also made of stainless steel and is welded to the inner surface of the negative electrode can, highly reliable conductivity is possible. In this way, the negative electrode is successfully pressure-bonded to the negative electrode current collector made of the stainless steel net.

The material of the annular gasket is preferably polypropylene.

In the assembly of this battery, the negative electrode and the negative electrode current collector are housed in a negative electrode can covered with an annular gasket, a separator is placed and a predetermined amount of organic electrolyte is injected, and a positive electrode is further placed on the positive electrode collector. This can be easily done by combining the positive electrode cans to which the electric body is attached and sealing with a press die. The electrolyte solution 2 was prepared by adding ethylene carbonate and methyl ethyl carbonate to a mixed solvent having a volume ratio of 3: 1 to 1: 3 in a Li solvent.
It may be prepared by dissolving PF ₆ or the like.

The coin type as used herein is not limited to the one having a circular flat portion, and may have a rectangular shape. A gasket may be provided between a flat positive electrode can and a flat negative electrode can. It refers to all things that are arranged and sealed.

[0017]

EXAMPLES Next, the present invention will be specifically described with reference to actual examples. However, the present invention is not limited to those examples.

Examples 1-5, Comparative Examples 1-3, Reference Examples 1-
10 coin-type batteries of 10 types each
00 pieces were produced. However, except that the environment of the shape of the coin type battery was changed as shown in Table 1, the coin type battery was manufactured by the same procedure. LiMn ₃ O ₆ was synthesized by sufficiently pulverizing and mixing lithium nitrate (LiNO ₃ ) and electrolytic manganese dioxide (MnO ₂ ) and then heat treating. The above synthesis was performed as follows.

Lithium nitrate and electrolytic manganese dioxide are added to Li
After weighing so that the ratio of / Mn = 1/3 (molar ratio), it was mixed while being crushed in an agate mortar. This was heated in air at 350 ° C. for 20 hours to synthesize LiMn ₃ O ₆ .

Using lithium manganese oxide synthesized by heat treatment as described above as a positive electrode active material,
A scaly graphite as an electron conduction aid and polytetrafluoroethylene as a binder were mixed at a ratio of 80: 15: 5 (weight ratio) to prepare a positive electrode mixture. This positive electrode material mixture was filled in a mold, pressure-molded at 1 t / cm ² into a disc shape having a diameter of 70% of a predetermined diameter of a coin battery, and then 2
It heat-processed at 50 degreeC and it was set as the positive electrode. Using this positive electrode, FIG.
A coin-type lithium secondary battery having the structure shown in was produced.

In FIG. 1, 1 is the above positive electrode, and 2
Is a disk-shaped negative electrode pressure-molded into a disk having a diameter of 70% of the predetermined diameter of the coin-type battery. Graphite was used for this negative electrode, and PVDF was mixed as a binder at a ratio of 90:10 (weight ratio) to prepare a negative electrode mixture. Mixing is P
VDF was previously dissolved in NMP (N-methylpyrrolidone) and mixed, and then NMP was evaporated at 150 ° C. to obtain a mixture. This negative electrode mixture was filled in a mold, pressure-molded at 1 t / cm ² into a disk shape having a diameter of 80% of a predetermined diameter of a coin battery, and then heat-treated at 250 ° C. to obtain a negative electrode.

Further, a separator having a predetermined thickness, which is composed of the microporous polypropylene film 3 and the electrolyte solution absorber 4 made of polypropylene nonwoven fabric, is used.

Reference numeral 5 denotes a cylindrical positive electrode can made of stainless steel having a predetermined thickness and a predetermined hardness and a predetermined diameter, 6 is a positive electrode current collector made of a stainless steel net, and 7 is a predetermined. It is a negative electrode can made of stainless steel whose thickness is adjusted to a predetermined hardness and having a nickel-plated surface.

Reference numeral 8 is a negative electrode current collector made of stainless steel net, which is spot-welded to the inner surface of the negative electrode can 7. The negative electrode 2 is connected to the negative electrode current collector 8 made of stainless steel net. It is crimped. Reference numeral 9 is an annular gasket made of polypropylene. 10 shows the bottom of the can.

The negative electrode and the negative electrode current collector were housed in a negative electrode can covered with an annular gasket, a separator was placed thereon, and the volume ratio of ethylene carbonate and methyl ethyl carbonate was 1: 1.
A predetermined amount of an organic electrolyte solution in which 1.0 mol / l of LiPF ₆ was dissolved was mixed in the mixed solvent of, a positive electrode was further placed, and a positive electrode can equipped with a positive electrode current collector was united with it and sealed with a press die. did.

In order to confirm the difference in the environment depending on the shape of the coin-type battery thus manufactured, the coin-type battery whose Y value is out of the predetermined range and the Y-value is not particularly devised are brought into a state where the Y value is within the predetermined range. The coin-type battery devised in the above was manufactured, and the effect of the present invention was confirmed under the condition that the X value was different from X0, X1, X2, and X3, respectively. Table 1 shows the conditions and effects of the battery.

[0027]

[Table 1]

In this table, the numerical values of the effects are 4.1 to
The degree of external deformation when the battery is charged and discharged 100 times between 2.5 V (the number of batteries in which deformation of 30% or more of 1000 is recognized) is shown. In addition, for the sake of clarity, as a comprehensive evaluation, the number of defective products within 9 is ○, 10 to 19 are ×, 20 to 49 are XX, 5
Zero or more were expressed as XXX.

[0029]

As is apparent from this table, the problem discussed in the present case does not occur in the reference example 1 in which the X value as the environment of the shape is X0, and the Y value falls within the predetermined range as a device in the present invention. Even if it is within the range, as shown in Reference Example 2, there is no particular improvement in the effect. However,
Comparative example 1 when the value of X as the shape environment becomes X1 or more
As shown in ~ 3, the problem becomes remarkable. In this case, the devices in which the present invention has been devised so that the Y value falls within a predetermined range are, for example, the first to third embodiments in which Y = Y1.
As shown in, even if the value of X as the shape environment is X1 or more, especially X3 or more, the above-mentioned problem does not occur. Further, it can be seen that in Example 4 in which Y = Y2 and Example 5 in which Y = Y3, excellent effects are exhibited even in an extremely severe environment where the X value is X3. As described above, according to the present invention, a peculiar problem that occurs when the value of X as the shape environment becomes X1 or more can be solved by suppressing the Y value within a predetermined range.

[Brief description of drawings]

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator (microporous polypropylene film 4 Separator (electrolyte absorber) 5 Positive electrode can 6 Positive electrode current collector 7 Negative electrode can 8 Negative electrode current collector 9 Ring gasket 10 Can bottom

Claims (7)

[Claims] 1. A positive electrode, a negative electrode, and an organic electrolytic solution containing a lithium manganese composite oxide, which are opposed to each other with a separator interposed therebetween.
A coin-type lithium secondary battery having a can bottom area of 7 cm ² or more, which is housed in a space composed of a positive electrode can and a negative electrode can, and a gasket is placed between the positive electrode can and the negative electrode can to seal the container. The total yield strength of both the positive and negative outer cans is 445 N / m
A coin type lithium secondary battery characterized by being set to m ² or more. 2. The coin-type lithium secondary battery according to claim 1, wherein the total yield strength of both the positive and negative outer cans is 490.
A coin-type lithium secondary battery characterized by being set to N / mm ² or more. 3. The coin-type lithium secondary battery according to claim 2, wherein the total yield strength of both the positive and negative outer cans is 590.
A coin-type lithium secondary battery characterized by being set to N / mm ² or more. 4. A positive electrode, a negative electrode, and an organic electrolytic solution containing a lithium manganese composite oxide, which are opposed to each other with a separator interposed therebetween,
A coin-type lithium secondary battery, which is housed in a space composed of a positive electrode can and a negative electrode can, has a gasket between the positive electrode can and the negative electrode can, and has a bottom area of 11 cm ² or more, The total yield strength of both the positive and negative outer cans is 445 N /
A coin-type lithium secondary battery characterized by being set to mm ² or more. 5. A positive electrode, a negative electrode, and an organic electrolytic solution containing a lithium manganese composite oxide, which face each other with a separator interposed therebetween,
A coin-type lithium secondary battery having a can bottom area of 18 cm ² or more, which is housed in a space composed of a positive electrode can and a negative electrode can, and a gasket is placed between the positive electrode can and the negative electrode can to seal the container. The total yield strength of both the positive and negative outer cans is 445 N /
A coin-type lithium secondary battery characterized by being set to mm ² or more. 6. The coin-type lithium secondary battery according to claim 4, wherein the total yield strength of both the positive and negative outer cans is 490.
A coin-type lithium secondary battery characterized by being set to N / mm ² or more. 7. The coin-type lithium secondary battery according to claim 5, wherein the total yield strength of both the positive and negative outer cans is 590.
A coin-type lithium secondary battery characterized by being set to N / mm ² or more.