JPH0955229A - Coin type lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the deformation of an outer can caused by charge/ discharge and prevent decrease in electric capacity by setting specified condition in a coin type lithium secondary battery having the prescribed constitution. SOLUTION: A coin type lithium secondary battery is constituted in such a way that a positive electrode 1 containing a lithium compound, a negative electrode 2 containing a carbon material capable of inserting lithium between lattices, faced through separators 3, 4, and an organic electrolyte are housed in a space formed by a positive electrode can 5 and a negative electrode can 7, and a gasket 9 is arranged between the positive electrode can 5 and the negative electrode can 7, then they are sealed, and the area of a can bottom 10 is specified so as to have 7cm<2> or more. In the secondary battery, the sum total of proof stress of the outer cans of positive and negative electrodes 1, 2 is specified to be 445N/mm<2> or more, preferably 490N/mm<2> or more, and more preferably 590N/mm<2> or more.

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 lithium 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 negative electrode has been developed in order to further increase the electric capacity. For example, graphite has been proposed as a material capable of electrochemically taking in and out lithium ions by charging and discharging. There is.

[0005]

However, the carbon material, such as graphite, in which lithium can be inserted between the lattices, has the characteristic that the volume change with charge and discharge is inevitably large. , For example, can bottom area is 7c
When it is m ² or more (hereinafter, this is abbreviated as X1), the flatness of the flat portion is not maintained and the outer can is deformed. Further, in some cases, not only the deformation but also the contact with the active material mixture inside is not sufficient, which makes it difficult to perform the subsequent charge / discharge.

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

[0007]

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 containing a lithium compound and a negative electrode containing a carbon material capable of inserting lithium between the lattices and an organic electrolytic solution facing each other through a separator are placed in a space composed of a positive electrode can and a negative electrode can. In a coin-type lithium secondary battery that is housed and sealed by placing a gasket between the positive electrode can and the negative electrode can, the sum of the yield strengths of both the positive and negative outer cans is 410 N / mm ² ( We have come to the surprising fact that the above problems can be completely prevented by setting the value to 445 N / mm ² (hereinafter referred to as the Y1 value) or more rather than a small value such as the Y0 value below. Of. The Y1 value is more preferably 590 N / mm if the range is further reduced to 490 N / mm ² (hereinafter, referred to as Y2 value) or more.
It was also found that a value of ² (hereinafter referred to as Y3 value) or more 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.

Since the graphite of this negative electrode is a carbon material capable of inserting lithium between the lattices, lithium ions can be electrochemically taken in and out by charging and discharging.

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. Lithium oxide (Li ₂ O) and nickel oxide (I
II) (Ni ₂ O ₃ ) was heat treated to synthesize lithium nickel oxide. The above synthesis was performed as follows.

Li / N was added to lithium oxide and nickel oxide.
It was weighed so that the ratio was i = 1 / 1.05 (molar ratio), and then mixed while being crushed in an agate mortar. After preheating this at 500 ° C. for 2 hours in an oxygen (O ₂ ) stream, the temperature is raised to 700 ° C. at a heating rate of 50 ° C./hour or less,
It was fired by heating at 700 ° C. for 20 hours.

Lithium nickel oxide synthesized by heat treatment as described above is used as a positive electrode active material,
80: 15: 5 (weight ratio) of phosphorous graphite as an electron conduction aid and polytetrafluoroethylene as a binder
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 250
It heat-processed at ℃ and it was set as the positive electrode. Using this positive electrode, a coin-type lithium secondary battery having the structure shown in FIG. 1 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 80% of the predetermined diameter of the coin 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 environment depending on the shape of the coin-type battery thus manufactured, the coin-type battery which is not particularly devised when the Y value is outside the predetermined range and the state where the Y-value is within the predetermined range is set. And coin-type batteries that have been devised so that their X values are X0, X1, X2, and X3, respectively.
The effect of the present invention was confirmed under the conditions different from the above. 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 solution 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 containing a lithium compound and a negative electrode containing a carbon material capable of inserting lithium between lattices and an organic electrolytic solution, which are opposed to each other with a separator interposed therebetween, in a space composed of a positive electrode can and a negative electrode can. In a coin-type lithium secondary battery with a bottom area of 7 cm ² or more, the total yield strength of both outer cans of positive and negative electrodes was stored. A coin-type lithium secondary battery characterized by being set to 445 N / mm 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 containing a lithium compound and a negative electrode containing a carbon material into which lithium can be inserted between lattices and an organic electrolytic solution, which are opposed to each other via a separator, are placed in a space composed of a positive electrode can and a negative electrode can. In a coin-type lithium secondary battery with a bottom area of 11 cm ² or more, the total yield strength of both the outer cans of the positive and negative electrodes was stored. A coin-type lithium secondary battery characterized by being set to 445 N / mm ² or more. 5. A positive electrode containing a lithium compound facing each other through a separator and a negative electrode containing a carbon material capable of inserting lithium between lattices and an organic electrolytic solution are placed in a space composed of a positive electrode can and a negative electrode can. In a coin-type lithium secondary battery with a can bottom area of 18 cm ² or more, the total yield strength of both outer cans of positive and negative electrodes was stored. A coin-type lithium secondary battery characterized by being set to 445 N / 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.