JP2001345118A - Nonaqueous electrolyte battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte battery producing no performance deterioration or no bulge for a long time without damaging the advantages of high energy density and a low manufacturing cost of the battery using a metal-resin composite film in an armoring case. SOLUTION: Lithium oxide and/or lithium hydroxide of two times of more the number of moles of fluorine-containing lithium salt used in a nonaqueous electrolyte are/is added to the nonaqueous electrolyte.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte battery, and more particularly to a non-aqueous electrolyte lithium battery having an outer package made of a metal resin composite film.

[0002]

2. Description of the Related Art Since a lithium ion battery has a high energy density, it is widely used as a power supply for a portable terminal, and further development of a higher capacity and a thinner type is required.

[0003] The structure of this small secondary battery includes a cylindrical battery in which a wound electrode group is housed in an outer casing of a robust cylindrical metal can, and a robust rectangular case in which flat electrode plates are laminated. There is a prismatic battery housed in an exterior body. As a means for providing a cheaper and lighter small secondary battery, there has been proposed a method in which a power generation element is housed in a bag of a flexible and lightweight metal-resin composite film (aluminum laminated film) and sealed by heat welding.

In a battery using a non-aqueous electrolyte, particularly a lithium ion battery, lithium tetrafluoroborate (LiBF ₄ ) and lithium hexafluorophosphate (LiPF ₆ ) are used in order to obtain good high-rate discharge characteristics and low-temperature discharge characteristics. ), Etc., are frequently used. However, when a small amount of water is present inside the battery due to intrusion from the outside or the like, these fluorine-containing lithium salts are hydrolyzed to generate free acids such as hydrogen fluoride. Usually, the free acid is reduced and removed by the negative electrode.However, when the battery is in an overdischarged state due to, for example, a short circuit, and the potential of the negative electrode increases, the reducing ability of the negative electrode is lost, and the free acid concentration in the battery system increases. . As a result, various problems occur for the battery. That is, first, the lithium carbonate formed on the surface of the negative electrode carbon material is decomposed and disappears, the storage performance of the battery is reduced, and the decomposition of the lithium carbonate generates carbon dioxide gas. Second, decomposition of the electrolytic solution is promoted, and carbon dioxide gas is generated. In particular, when a flexible exterior body such as a metal-resin composite film is used, the generation of carbon dioxide gas leads to expansion of the battery. When the battery expands, it squeezes the peripheral device on which the battery is mounted,
There is a risk of damage. Third, when the power generation element is sealed by an outer package made of a metal-resin composite film, and the terminal is taken out through the sealing portion, modified polypropylene which is a sealing material of the metal-resin composite film Weakens the adhesion between the terminal and the terminal and leads the opening of the terminal sealing portion. Fourth, peeling occurs between the resin layer used in the metal-resin composite film and the thin metal layer, and the sealing performance of the exterior body is reduced.

As a measure for preventing the peripheral device from being damaged by the expansion of the battery, Japanese Patent Laid-Open Publication No. Hei 10-208720 discloses a needle-like projection which can break through the outer package when the battery expands. It has been proposed to be placed on the body. However, this method requires a space for providing the protrusion, and thus has a problem in that the energy density of the battery is reduced. Also, because it breaks through the exterior body,
There is a possibility that gas or electrolyte may leak from the opening, and a circuit of the electronic device may be damaged due to corrosion or the like.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and particularly impairs the advantages of high energy density and low manufacturing cost of a battery using a metal resin composite film for an outer package. It is an object of the present invention to provide a non-aqueous electrolyte battery that does not suffer from performance degradation or swelling for a long period of time.

[0007]

In order to solve the above problems, the present invention comprises a positive electrode using a lithium-containing transition metal oxide, a negative electrode using a carbon material capable of inserting and extracting lithium, and a non-aqueous electrolyte. In a non-aqueous electrolyte battery in which the generated power generating element is hermetically sealed by an outer package, the non-aqueous electrolyte contains a fluorine-containing lithium salt dissolved therein, and the power generating element includes a basic substance, Is twice or more the number of moles of the fluorine-containing anion in the nonaqueous electrolyte battery. The number of moles of the basic substance is not more than 6 times the number of moles of the fluorine-containing anion. Further, it is characterized in that the basic substance is lithium oxide and / or lithium hydroxide. Further, the invention is characterized in that the fluorine-containing lithium salt is lithium tetrafluoroborate and / or lithium hexafluorophosphate. Further, the invention is characterized in that the exterior body is a metal resin composite film.

[0008] That is, when the free acid is generated, the above problem is solved by the fact that the power generating element contains a basic substance capable of neutralizing the free acid.

The basic substance has only to be less acidic than carbon dioxide, and many metal oxides and metal hydroxides are applicable. Among them, when a salt of a metal which is more noble than lithium is used, the metal may precipitate on the negative electrode. Therefore, it is preferable to use a lithium compound such as lithium oxide or lithium hydroxide. Furthermore, when these lithium compounds are used as the basic substance, the slightly dissociated lithium ions are common to the lithium ions that are the ionic species of the electrolytic solution, and thus do not adversely affect battery performance. Is also preferred.

The use of lithium hexafluorophosphate (LiPF ₆ ) among the fluorine-containing lithium salts makes it possible to easily provide a nonaqueous electrolyte battery having particularly excellent high-rate discharge performance. It can be more effectively exerted. In addition, when lithium tetrafluoroborate (LiBF ₄ ) is used, it is possible to easily provide a battery having particularly excellent low-temperature performance, and it is hard to undergo hydrolysis and generate free acid. The effects of the invention can be exhibited more effectively. These fluorine-containing lithium salts may be used as a mixture of two or more kinds, or may be used as a mixture with a lithium salt containing no fluorine.

If one mole of lithium tetrafluoroborate is completely hydrolyzed, three moles of hydrogen fluoride and one mole of boric acid are produced. To neutralize these to an acidity that does not decompose lithium carbonate, 2 moles of lithium oxide or 4 moles of lithium hydroxide are required. Also,
If one mole of lithium hexaphosphate is completely hydrolyzed, it produces 5 moles of hydrogen fluoride and 1 mole of phosphoric acid. To neutralize these to an acidity that does not decompose lithium carbonate, 3 moles of lithium oxide or 6 moles of lithium hydroxide are required. It is preferable to include a basic substance appropriate for the calculation.

In general, it is known that lithium oxide or lithium hydroxide generated by decomposition of an electrolytic solution or the like is present as a film on the surface of metallic lithium or carbon material used for a negative electrode of a lithium battery. Is characterized in that it contains a basic substance in an amount far exceeding the amount present as the coating. Specifically, based on the above calculation, the electrolyte is characterized in that it contains a basic substance in a molar number twice or more the molar number of the lithium salt used in the electrolytic solution. Also,
According to the above calculation, the amount of the basic substance contained does not need to exceed 6 times the number of moles of the lithium salt used in the electrolytic solution. Conversely, excessive addition increases the viscosity of the electrolyte,
6 mol or less is preferable because it causes a reduction in battery discharge performance and a reduction in weight energy density of the battery.

There is no particular limitation on the site where the basic substance is contained, and a method of incorporating it in the positive electrode mixture, a method of incorporating it in the negative electrode mixture, a method of incorporating it in the electrolytic solution, and the like may be used. it can.

Further, the present invention exerts the maximum effect by applying a flexible film such as a metal-resin composite film to a battery using an outer package. That is, in the conventional lithium ion battery using a robust metal container, even when the above-mentioned free acid is generated, the internal pressure increases and the battery performance is slightly changed, and there is no significant effect. However, in a battery using a metal-resin composite film for an exterior body, if the above-mentioned free acid is generated, the above-mentioned serious adverse effects may be caused, and thus the application of the present invention is highly effective. That is, since the expansion of the battery can be prevented, it is possible to avoid a possibility that the peripheral device to which the battery is mounted is pressed and damaged. In addition, since it is possible to avoid the risk of guiding the opening of the sealing portion of the exterior body, it is possible to avoid the risk of leakage of toxic gas or electrolyte that corrodes the electronic circuit. In addition, it is possible to avoid the possibility of breaking the metal-resin composite film itself used for the exterior body.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is not limited by the following description.

The strip-shaped positive electrode was manufactured as follows. LiCoO ₂ is used as a positive electrode active material, acetylene black is used as a conductive agent, polyvinylidene fluoride is used as a binder, and the mixture is mixed at a weight ratio of 90: 5: 5.
A positive electrode slurry of the above material was prepared using -methylpyrrolidone. The obtained slurry was applied to both sides of a 20 μm aluminum foil, and N-methylpyrrolidone was removed by drying. This positive electrode plate was pressed by a roll press to obtain a belt-shaped positive electrode.

The strip-shaped negative electrode was manufactured as follows. As a negative electrode active material, graphite in which the surface of carbon particles is modified with amorphous carbon is mixed at a weight ratio of 95: 5 using polyvinylidene fluoride as a binder, and N- is used as a solvent.
A negative electrode slurry of the above material was prepared using methylpyrrolidone. Apply the obtained slurry to both sides of the electrolytic copper foil,
N-methylpyrrolidone was removed by drying. This negative electrode plate was pressed by a roll press to obtain a strip-shaped negative electrode.

The electrolyte A containing a basic substance (used in the battery of the present invention) was obtained as follows. Ethylene carbonate,
In a solvent in which dimethyl carbonate and ethyl-methyl carbonate are mixed at a volume ratio of 1: 1: 1, lithium hexafluorophosphate is dissolved at a concentration of 1 mol / liter as a lithium salt, and lithium oxide is further used as a basic substance. The mixture was added at a ratio of 4 mol per 1 liter of the solvent and stirred. The electrolyte became a white suspension.

The electrolyte B containing a basic substance (used in the battery of the present invention) was obtained as follows. Ethylene carbonate,
Propylene carbonate and γ-butyrolactone are:
Lithium tetrafluoroborate as a lithium salt is dissolved at a concentration of 2 mol / liter in a solvent mixed at a volume ratio of 1: 1. Further, as a basic substance, lithium oxide is dissolved in 4 mol per 1 liter of the solvent. And stirred. The electrolyte became a white suspension.

The electrolyte a (used for the comparative battery) was obtained as follows. Lithium hexafluorophosphate as a lithium salt was dissolved at a concentration of 1 mol / liter in a solvent in which ethylene carbonate, dimethyl carbonate and ethyl-methyl carbonate were mixed at a volume ratio of 1: 1: 1.

The electrolytic solution b (used for the comparative battery) was obtained as follows. Lithium tetrafluoroborate as a lithium salt was dissolved at a concentration of 2 mol / liter in a solvent in which ethylene carbonate, propylene carbonate and γ-butyrolactone were mixed at a volume ratio of 1: 1: 1.

Each of the positive electrode and the negative electrode has a positive terminal 3
Then, the negative electrode terminal 2 was attached and wound in a flat spiral shape, and a wound electrode group 4 was formed so that the outermost periphery was a copper foil. The heat-fusible adhesive 1 was provided on the terminal portion. FIG. 1 shows an external view of the wound electrode group 4. The above-mentioned wound type electrode group 4 was inserted into a cylindrical exterior body made of a metal-resin composite film shown in FIG. 2, and the sides having terminals were heat-welded. Under a reduced pressure atmosphere, 2.7 ml of an electrolyte was injected from the side having an opening facing the side having a terminal. Thereafter, the side having the opening was sealed by heat welding in a reduced-pressure atmosphere to obtain a nonaqueous electrolyte battery. FIG. 3 shows a plan view of the nonaqueous electrolyte battery.

(Battery 1 of the Present Invention) A non-aqueous electrolyte battery using electrolytic solution A containing a basic substance as the electrolytic solution was designated as Battery 1 of the present invention.

(Battery 2 of the Present Invention) A non-aqueous electrolyte battery using electrolytic solution B containing a basic substance as the electrolytic solution was designated as Battery 2 of the present invention.

(Comparative Battery 1) A non-aqueous electrolyte battery using the electrolytic solution a as the electrolytic solution was designated as Comparative Battery 1.

(Comparative Battery 2) A non-aqueous electrolyte battery using the electrolytic solution b as the electrolytic solution was designated as Comparative Battery 2.

(Short Circuit Test) Each of the batteries 1 and 2 of the present invention and the comparative batteries 1 and 2 was left for at least 16 hours after completion,
One cycle of initial charge and discharge was performed. The conditions for the initial charge and discharge were low current charge and discharge using a current value of 5 hours, and the upper limit voltage was 4.1 V and the lower limit voltage was 2.7 V.

Next, a repeated charge / discharge test of 50 cycles was performed. The conditions of the repetitive charge / discharge test were low current charge / discharge using a current value of 2 hour rate, and an upper limit voltage of 4.1.
V, and the lower limit voltage was 2.7 V.

Next, the weight and volume of each battery were measured.
The measurement of the volume was performed as follows. Each battery was placed in a container having a known internal volume, and at a temperature of 25 ° C., liquid paraffin was injected into the container until it was full. The volume of the injected liquid paraffin was determined from the weight, the volume of the liquid paraffin was subtracted from the volume of the container, and the volume was measured.

Next, a resistor of 100Ω was connected between the positive terminal and the negative terminal of each battery, and after leaving for 10 hours, the resistance was removed. Next, the positive electrode terminal and the negative electrode terminal were short-circuited using a lead wire, left in a constant-humidity constant temperature bath at a temperature of 60 ° C. and a relative humidity of 95% for two weeks, and then returned to room temperature.

The lead wire was removed, and the volume was measured again in the same manner as described above, and the change in volume of each battery was examined. As a result, no change in volume was observed in Battery 1 of the present invention and Battery 2 of the present invention. On the other hand, in Comparative Battery 1 and Comparative Battery 2, expansion of about 10 ml was confirmed, and breakage (opening) of the sealing was observed at a portion where the positive electrode terminal 3 crossed the sealing portion.

[0032]

As is clear from the above description, in particular, in a non-aqueous electrolyte secondary battery using a film for the outer package, it is possible to suppress the swelling of the battery even in a severe abuse test. Since the metal layer of the laminate is prevented from peeling and the durability and safety of the battery can be ensured, its industrial value is great.

[Brief description of the drawings]

FIG. 1 is an external view of a wound type pole group.

FIG. 2 is an external view of a tubular metal-resin composite film.

FIG. 3 is an external view of the battery of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heat-fusible adhesive 2 Negative electrode terminal 3 Positive electrode terminal 4 Wound electrode group 5 Metal resin composite film

Claims (5)

[Claims] A non-aqueous electrolyte in which a power generation element including a positive electrode using a lithium-containing transition metal oxide, a negative electrode using a carbon material capable of inserting and extracting lithium, and a non-aqueous electrolyte is sealed with an outer package. In the battery, the non-aqueous electrolyte contains a fluorine-containing lithium salt dissolved therein, and the power generating element contains a basic substance, and the number of moles of the basic substance is at least twice the number of moles of the fluorine-containing anion. A non-aqueous electrolyte battery characterized by the following. 2. The non-aqueous electrolyte battery according to claim 1, wherein the number of moles of the basic substance is six times or less the number of moles of the fluorine-containing anion. 3. The method according to claim 2, wherein the basic substance is lithium oxide and / or lithium oxide.
3. The non-aqueous electrolyte battery according to claim 1, which is lithium hydroxide. 4. The non-aqueous electrolyte battery according to claim 1, wherein the fluorine-containing lithium salt is lithium tetrafluoroborate and / or lithium hexafluorophosphate. 5. The non-aqueous electrolyte battery according to claim 1, wherein the exterior body is a metal resin composite film.