JP2002237333A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-aqueous electrolyte secondary battery, in which it is controlled that inner pressure goes up by carbon dioxide generated during initial electricity charging and high temperature storage, and, which safety and whose electricity-charging/discharging cycle characteristic are improved. SOLUTION: The non-aqueous electrolyte secondary battery has an airtight container 1, a positive electrode 8 contained in the above airtight container 1, a negative electrode 6 contained in the above airtight container 1, and a non-aqueous electrolyte contained in the above airtight container 1. In the above airtight container 1, a lithium compound oxide, which absorbs carbon dioxide, exists, and the above lithium compound oxide exists in a quantity of 4 mg or less per battery theoretical capacity of 1 mAh.

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 secondary battery.

[0002]

2. Description of the Related Art At present, lithium ion secondary batteries have been commercialized as non-aqueous electrolyte secondary batteries for portable devices such as mobile phones. As this battery, in a closed container, a positive electrode containing an active material such as lithium cobalt oxide (LiCoO ₂ ), a negative electrode containing a graphite material or a carbon material,
A separator interposed between the positive electrode and the negative electrode,
There is known a configuration in which a non-aqueous electrolyte containing an organic solvent in which a lithium salt is dissolved is housed.

As a solvent for the electrolytic solution, a non-aqueous solvent having a low viscosity and a low boiling point is used. Examples of such non-aqueous solvents include cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC), and chain carbonates such as methyl ethyl carbonate (MEC), diethyl carbonate (DEC), and dimethyl carbonate (DMC). It has been known. A non-aqueous electrolyte including a non-aqueous solvent containing a cyclic carbonate or a chain carbonate has an advantage that it is difficult to react with a positive electrode.

However, in a non-aqueous electrolyte secondary battery using a non-aqueous electrolyte containing a non-aqueous solvent containing a cyclic carbonate or a chain carbonate, the non-aqueous solvent decomposes when initially charged or stored at a high temperature. Carbon dioxide (CO ₂ )
Therefore, there is a problem that the internal pressure easily rises, the hermeticity decreases due to liquid leakage due to the operation of the opening valve, and a burst occurs due to a rapid increase in the internal pressure. In addition, even if the amount of generated carbon dioxide gas is such that the opening valve does not operate or burst, if the carbon dioxide gas remains in the secondary battery, the charge / discharge reaction is inhibited by the carbon dioxide gas. Therefore, a long life cannot be obtained. Further, when the thickness of the wall of the sealed container is reduced to reduce the thickness of the battery, a problem arises in that the container expands due to the generated carbon dioxide gas. The blister of the container
The battery may not fit in the electronic device, or the electronic device may malfunction. In particular, as a non-aqueous solvent, ME
When C, DEC or DMC is included, the generation of carbon dioxide gas becomes remarkable.

[0005] In order to solve the above problems,
Although various studies have been conducted on a novel non-aqueous electrolyte that does not generate carbon dioxide, an ideal non-aqueous electrolyte that does not generate carbon dioxide at all has not yet been developed.

[0006]

SUMMARY OF THE INVENTION The present invention provides a non-aqueous electrolyte secondary battery in which the internal pressure is prevented from increasing due to carbon dioxide gas generated during initial charging and high-temperature storage, and safety and charge / discharge cycle characteristics are improved. It is intended to provide a battery.

[0007]

A nonaqueous electrolyte secondary battery according to the present invention comprises a closed container, a positive electrode stored in the closed container, a negative electrode stored in the closed container, and a closed container. In a non-aqueous electrolyte secondary battery including a non-aqueous electrolyte housed therein, a lithium composite oxide absorbing carbon dioxide is present in the closed container, and the lithium composite oxide has a theoretical capacity of the battery (design It is characterized in that it is present in an amount of 4 mg or less per mAh.

[0008] A non-aqueous electrolyte secondary battery according to the present invention includes a closed container, a positive electrode stored in the closed container, a negative electrode stored in the closed container, and a non-aqueous battery stored in the closed container. A non-aqueous electrolyte secondary battery comprising a water electrolyte, wherein the non-aqueous electrolyte contains a lithium composite oxide absorbing carbon dioxide.

A non-aqueous electrolyte secondary battery according to the present invention includes a closed container, a positive electrode stored in the closed container, a negative electrode stored in the closed container, and a non-aqueous battery stored in the closed container. A non-aqueous electrolyte secondary battery comprising a water electrolyte, wherein the negative electrode contains a lithium composite oxide absorbing carbon dioxide.

A non-aqueous electrolyte secondary battery according to the present invention includes a closed container, an electrode group housed in the closed container, including a positive electrode and a negative electrode, and a non-aqueous electrolyte housed in the closed container. In the above nonaqueous electrolyte secondary battery, a carbon dioxide absorption layer containing a lithium composite oxide is present in a space between the closed container and the electrode group.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A non-aqueous electrolyte secondary battery according to the present invention contains an electrode group including a positive electrode and a negative electrode, a non-aqueous electrolyte contained in the electrode group, and the electrode group and the non-aqueous electrolyte. A non-aqueous electrolyte secondary battery comprising a sealed container, wherein a lithium composite oxide having a property of absorbing carbon dioxide gas is present in the sealed container.

The structure of the electrode group may be (a) a laminate including a positive electrode and a negative electrode, (b) a spiral type in which the laminate is spirally wound, or (c) a flat shape in which the laminate is wound. The flat type may be a turned flat type, or (d) a flat type obtained by bending the laminate one or more times. In the laminate,
A separator can be provided between the positive electrode and the negative electrode, or an electrolyte layer can be provided. Furthermore, it is also possible to arrange an electrolyte layer between the positive electrode and the separator and between the negative electrode and the separator.

As the closed container, for example, a container having an outer can and a lid, a bag-shaped container, and the like can be used.

The closed container can be formed from, for example, a film material, a metal plate, plastic, or the like.

Examples of the film material include a metal film, a resin sheet such as a thermoplastic resin, and a multilayer sheet in which one or both sides of a flexible metal layer are coated with a resin layer such as a thermoplastic resin. Can be formed. The resin sheet and the resin layer can be formed from one kind of resin or two or more kinds of resins. As the thermoplastic resin, polyethylene,
Examples include polypropylene. In particular, polypropylene having a melting point of 150 ° C. or higher is preferable because the sealing strength of the heat seal portion can be improved. Meanwhile, the metal layer can be formed from one kind of metal or two or more kinds of metals. Further, the metal layer and the metal film can be formed of, for example, aluminum, iron, stainless steel, nickel, copper, or the like. Among them, aluminum which is lightweight and has a high function of blocking moisture is preferable.

The thickness of the film material constituting the closed container is as follows:
It is preferable that the thickness be 0.3 mm or less. When the thickness of the film material is larger than 0.3 mm, the effect of thinning is small, that is, it is difficult to sufficiently increase the weight energy density and the volume energy density. The thickness of the film material is
It is preferably 0.25 mm or less, more preferably 0.2 mm or less. In addition, thickness is 0.05m
If the thickness is smaller than m, the material is likely to be deformed or damaged by a physical impact such as dropping. Therefore, the lower limit of the thickness is preferably set to 0.05 mm.

Examples of the metal plate include aluminum-based metal, iron, stainless steel and the like. As the aluminum-based metal, for example, pure aluminum, 0.0
An aluminum alloy containing 5% by weight or less of Mg and 0.2% by weight or less of Cu can be given. Examples of such an aluminum-based metal include, for example, A1050, A1100, A1200, and A3003 in JIS alloy numbers.

[0018] The shape of the metal closed container is such that the lid is attached to a cylindrical outer can with a bottom by laser welding or caulking, or the lid is laser welded or caulked to a rectangular outer can with a bottom. And so on. Further, an open valve for explosion protection can be formed in the metal hermetic container.

In the case of a metal closed container, the plate thickness is 0.5 mm
It is preferable to set the following. When the plate thickness is larger than 0.5 mm, the effect of thinning is small, that is, it is difficult to sufficiently increase the weight energy density and the volume energy density. Further, when the plate thickness is less than 0.1 mm, the strength is reduced, and it may be difficult to sufficiently protect the electrode group housed in the outer can. Therefore, the thickness is 0.1
It is preferable that the thickness be not less than 0.5 mm and not more than 0.5 mm. A more preferred range is 0.2 to 0.3 mm.

Examples of the plastic include polyethylene, nylon, ABS resin and the like.

Examples of the lithium composite oxide include lithium orthosilicate (Li ₄ SiO ₄ ), lithium metasilicate (Li ₂ SiO ₃ ), and lithium zirconate (L
i ₂ ZrO ₃ ), lithium aluminate (LiAl
O _2), may be used lithium ferrite (LiFeO ₂₎ and one or more oxides selected from the group consisting of lithium titanate (Li ₂ TiO _3). Li ₄
Lithium silicates such as SiO ₄ and Li ₂ SiO ₃ are used in a non-aqueous electrolyte secondary battery in the operating temperature range (−20 ° C. to 150 ° C.).
It can be absorbed rapidly carbon dioxide within the range) of the lithium composite oxide, Li ₄ SiO
₄ , Li ₂ SiO ₃ , or Li ₄ SiO ₄ and Li ₂ S
It is preferred to use both of iO ₃ .

Lithium orthosilicate (Li ₄ Si
O ₄ ) has a characteristic of rapidly absorbing carbon dioxide present at an extremely low concentration (concentration of carbon dioxide in the atmosphere is about 300 ppm) such as carbon dioxide in the atmosphere at room temperature. About 700 ~ per 1 ml of orthosilicate
It is possible to absorb 900 ml (standard state) of carbon dioxide gas. Li ₄ SiO ₄ uses silicon dioxide (SiO ₂ ) as a raw material, which can be expected to reduce costs, and is lightweight (for example, 20% lighter than Li ₂ ZrO _3). ), Non-conductive and chemically stable to non-aqueous electrolytes. Further, when the Li ₄ SiO ₄ absorbs carbon dioxide, as shown in the following reaction formula (1) and (2), since the lithium carbonate (Li ₂ CO ₃₎ to generate, the Li ₂ CO ₃ on the surface of the anode A contained protective film (solid electrolyte film) can be formed.

Li ₄ SiO ₄ + CO ₂ → Li ₂ SiO ₃ + Li ₂ CO ₃ (1) Li ₂ SiO ₃ + CO ₂ → SiO ₂ + Li ₂ CO ₃ (2) Lithium ferrite (LiFeO ₂ ) and lithium titanate (Li ₂ TiO) ₃ ) has electronic conductivity,
It is desirable to fill the closed container in such a manner that an internal short circuit does not occur due to the carbon dioxide gas absorbent.

It is preferable that the amount of lithium composite oxide present per mAh of theoretical battery capacity (battery design capacity) is 4 mg / mAh or less. This is due to the following reasons. When the abundance exceeds 4 mg / mAh, not only a high weight energy density cannot be obtained, but also a high charge capacity may not be obtained due to an increase in internal resistance of the battery. On the other hand, the minimum amount is preferably 0.1 μg / mAh. If the amount is less than 0.1 μg / mAh, carbon dioxide generated in the battery may not be sufficiently absorbed. Therefore, the abundance is 0.1
It is preferable that the concentration be not less than μg / mAh and not more than 4 mg / mAh. A more preferred range is 0.2 mg / mAh or more and 2 mg / mAh or less, and the most preferred range is 0.3 mg / mAh or less.
mg / mAh or more and 0.91 mg / mAh or less.

The identification of the lithium composite oxide in the closed vessel can be measured by the following method.

(1) Sampling of Samples For the positive electrode, the negative electrode, the separator, the insulating plate, the spacer, the closed container and the like, fragments thereof can be used as the sample.

With respect to the positive electrode and the negative electrode, a positive electrode mixture layer and a negative electrode mixture layer separated by a method described later (c; crucible C) can be used as a sample instead of fragments. The positive electrode mixture layer and the negative electrode mixture layer, which are samples, may be in the form of a lump or a powder.

As for the insulating plate and the closed container, a material film separated by a method described later in (d; crucible D) can be used as a sample instead of a piece. The sample material film may be in a lump or powder form.

The non-aqueous electrolyte can be sampled by two methods.

(I) When the non-aqueous electrolyte is a liquid, it is filtered,
The obtained residue is dried to obtain a sample. (II) The residue obtained by the method described below in (a; crucible A) is used as a sample.

(2) The crystal structure and composition of the lithium composite oxide contained in the sample obtained by the above-mentioned method (1) were determined using an X-ray diffractometer (XRD) and a thin-film X-ray diffractometer (TF).
-XRD). At this time, if synchrotron radiation is used as X-rays, strong X-rays can be obtained.
It is possible to analyze with a sample of about mg.

The amount of the lithium composite oxide present in the battery can be measured by the following method.

After disassembling the secondary battery, elemental analysis of the lithium composite oxide is performed according to the following procedure.

(A) A non-aqueous electrolyte secondary battery is cut with a cutter in an Ar gas atmosphere, then placed in a polytetrafluoroethylene (PTFE) beaker containing a methanol solution, and cleaned using an ultrasonic cleaner. I do. This operation is repeated three times while changing the methanol solution. By this washing operation, a mixture of the lithium composite oxide and the non-aqueous electrolyte is extracted into methanol. The methanol solution used for washing is transferred to a glass beaker, and the methanol is evaporated by heating to obtain a residue containing a lithium composite oxide and a non-aqueous electrolyte. This residue is transferred to crucible A.

(B) Transfer the separator to crucible B. When the secondary battery has an insulating plate, the insulating plate is also transferred to the crucible B.

(C) The positive electrode and the negative electrode are wetted with an n-methylpyrrolidone solvent, and the positive electrode mixture layer is peeled off from the positive electrode current collector, and the negative electrode mixture layer is peeled off from the negative electrode current collector. The obtained positive electrode mixture layer and negative electrode mixture layer are transferred to crucible C.

(D) The inner surface of the closed container (including the inner surface of the lid when the lid is provided) is wetted with an n-methylpyrrolidone solvent to peel off the material film adhering to these surfaces. The peeled product is transferred to crucible D.

An alkali agent is added to each of the crucibles A to D, and alkali melting is performed. After melting, the solution was dissolved, and the Si element was quantified by molybdenum blue absorption spectrophotometry or inductively coupled plasma emission spectrometry (ICP-AES).
e, Al, Ti, and Zr are quantified by an inductively coupled plasma emission spectrometer (ICP-AES). On the other hand, lithium is quantified by the atomic absorption method. Based on the measured amount, the amount of each constituent element of the lithium composite oxide is calculated, and the abundance of the lithium composite oxide is determined from this value.

The lithium composite oxide has the following (1) to
It can be present in a closed container by the method described in (5).

(1) It is contained in the positive electrode. (2) It is contained in the negative electrode. (3) It is contained in the separator. (4) It is contained in a non-aqueous electrolyte. (5) A carbon dioxide absorption layer containing a lithium composite oxide is present in a space existing between the closed container and the electrode group.

The above-described methods (1) to (5) may be used alone or in combination of two or more. Among them, the methods (2), (4) and (5) are preferable.

Hereinafter, each method will be described in detail.

1) Positive Electrode This positive electrode includes a positive electrode mixture layer containing a lithium composite oxide having a property of absorbing carbon dioxide gas and an active material, and a positive electrode current collector on which the positive electrode mixture layer is supported. .

For such a positive electrode, for example, an active material, a lithium composite oxide powder, a conductive agent and a binder are suspended in an appropriate solvent, and the obtained suspension is applied to a positive electrode current collector. After drying, it is produced by pressure molding. According to such a method, the lithium composite oxide can be dispersed in the positive electrode.

As the positive electrode active material, various oxides,
For example, manganese dioxide, lithium manganese composite oxide,
Lithium-containing nickel oxide, lithium-containing cobalt
Compound, lithium-containing nickel cobalt oxide, lithium
Iron oxide, vanadium oxide containing lithium,
Chalcogen compounds such as titanium sulfide and molybdenum disulfide
And the like. Among them, lithium-containing edge
Oxide (eg, LiCoO_Two), Lithium containing
Nickel cobalt oxide (eg, LiNi_0.8Co_0.2O
_Two), Lithium manganese composite oxide (eg, LiMn)_Two
O_Four, LiMnO _Two) Can provide high voltage
Preferred.

Examples of the conductive agent include acetylene black, carbon black, graphite and the like.

Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), ethylene-propylene-diene copolymer (EPDM), and styrene-butadiene rubber (SBR). Can be.

The mixing ratio of the positive electrode active material, the conductive agent and the binder is preferably in the range of 80 to 95% by weight of the positive electrode active material, 3 to 20% by weight of the conductive agent, and 2 to 7% by weight of the binder. .

As the current collector, for example, an aluminum foil, a stainless steel foil, a nickel foil, a tungsten foil or the like can be used.

2) Negative Electrode This negative electrode comprises a negative electrode mixture layer containing a lithium composite oxide having a property of absorbing carbon dioxide gas and a carbonaceous substance absorbing and releasing lithium, and a negative electrode carrying the negative electrode mixture layer. And a current collector.

The negative electrode is prepared by, for example, kneading a carbonaceous substance that absorbs and releases lithium, a lithium composite oxide powder, and a binder in the presence of a solvent, and applying the obtained suspension to a negative electrode current collector. After drying, it is produced by pressing once at a desired pressure or by multi-stage pressing 2 to 5 times. According to such a method, the lithium composite oxide can be dispersed in the negative electrode.

Examples of carbonaceous materials that occlude and release lithium include graphite materials or carbonaceous materials such as graphite, coke, carbon fiber, and spherical carbon, thermosetting resins, isotropic pitches, mesophase pitches, mesophase pitches. 500-3000 ° C. for carbon fibers such as mesophase pitch spheres (especially, mesophase pitch carbon fibers are preferable)
Graphite material or carbonaceous material obtained by performing a heat treatment on the substrate. Above all, it can be obtained by setting the temperature of the heat treatment to 2000 ° C. or higher,
2) It is preferable to use a graphitic material having graphite crystals with a plane spacing d ₀₀₂ of 0.34 nm or less. A non-aqueous electrolyte secondary battery including a negative electrode containing such a graphite material as a carbonaceous material can significantly improve battery capacity and large current characteristics. The plane spacing d ₀₀₂ is 0.336 nm
It is more preferred that:

Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), ethylene-propylene-diene copolymer (EPDM), styrene-butadiene rubber (SBR),
Carboxymethyl cellulose (CMC) or the like can be used.

The mixing ratio of the carbonaceous material and the binder is preferably 90% by weight or more and 10% by weight or less of the binder. In particular, the carbonaceous material is 50
It is preferable to set it in the range of 200 to 200 g / m ² .

As the current collector, for example, a copper foil, a stainless steel foil, a nickel foil, a tungsten foil, a molybdenum foil or the like can be used.

The present invention provides a non-aqueous electrolyte secondary battery including the above-described negative electrode containing a carbonaceous material that inserts and extracts lithium, and an anode containing a metal oxide, a metal sulfide, or a metal nitride. The present invention can be similarly applied to a non-aqueous electrolyte secondary battery including the same or a non-aqueous electrolyte secondary battery including a negative electrode made of lithium metal or a lithium alloy.

Examples of the metal oxide include tin oxide, silicon oxide, lithium titanium oxide, niobium oxide, and tungsten oxide.

Examples of the metal sulfide include tin sulfide and titanium sulfide.

Examples of the metal nitride include lithium cobalt nitride, lithium iron nitride, lithium manganese nitride and the like.

Examples of the lithium alloy include a lithium aluminum alloy, a lithium tin alloy, a lithium lead alloy, and a lithium silicon alloy.

3) Separator When a lithium composite oxide is contained in the separator, it is preferable to form a carbon dioxide absorption layer containing the lithium composite oxide on at least a part of the surface of the separator.
It is preferable that the carbon dioxide gas absorbing layer is not formed on the entire surface of the separator but is formed in a dispersed manner so as not to prevent the permeation of lithium ions and the non-aqueous electrolyte.

The carbon dioxide gas absorbing layer is formed, for example, by suspending a lithium composite oxide powder and a binder in an appropriate solvent, applying the suspension to at least a part of the surface of the separator, and drying. You. The binder is not particularly limited as long as it is stable with respect to the nonaqueous electrolyte and does not impair the carbon dioxide absorption capacity of the lithium composite oxide. For example, a binder used for the positive electrode and the negative electrode can be used. The ratio of the lithium composite oxide to the binder is preferably such that the binder is in the range of 3 to 10% by weight. A more preferable ratio of the binder is 3 to 4% by weight. As the solvent, for example, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF) and the like can be used.

It is preferable that the thickness of the carbon dioxide gas absorbing layer is 50 μm or less. Carbon dioxide absorption layer thickness is 50μm
If it exceeds, the capacity per volume may be reduced.
If the thickness of the carbon dioxide gas absorbing layer is less than 0.1 μm, the carbon dioxide gas generated by the oxidative decomposition of the non-aqueous electrolyte may not be sufficiently absorbed. Therefore,
A more preferable range of the thickness is in a range of 1 μm to 50 μm. A more preferred thickness is in the range of 10 μm to 25 μm.

The carbon dioxide gas absorbing layer preferably has a porous structure. Since the carbon dioxide gas absorbing layer having a porous structure is porous, the specific surface area can be increased, so that the carbon dioxide gas absorption amount can be increased. The carbon dioxide absorption layer having a porous structure can be formed, for example, by applying a suspension containing a lithium composite oxide and a binder to a separator and drying the suspension.

Hereinafter, a separator containing a carbon dioxide absorbent will be described.

As the separator, for example, polyethylene, polypropylene or polyvinylidene fluoride (PV
A porous film containing dF), a synthetic resin nonwoven fabric, or the like can be used. Among them, a porous film made of polyethylene, polypropylene, or both is preferable because the safety of the secondary battery can be improved.

It is preferable that the thickness of the separator be 30 μm or less. If the thickness exceeds 30 μm, the distance between the positive electrode and the negative electrode may increase, and the internal resistance may increase. The lower limit of the thickness is preferably set to 5 μm. If the thickness is less than 5 μm, the strength of the separator may be significantly reduced and an internal short circuit may easily occur. The upper limit of the thickness is more preferably 25 μm, and the lower limit is more preferably 10 μm.

The separator preferably has a heat shrinkage of 20% or less when left at 120 ° C. for one hour. More preferably, the heat shrinkage is 15% or less.

The porosity of the separator is preferably in the range of 30 to 60%. This is due to the following reasons. If the porosity is less than 30%, it may be difficult to obtain high electrolyte retention in the separator. On the other hand, if the porosity exceeds 60%, sufficient separator strength may not be obtained. A more preferred range of porosity is 35-50%.

The separator has an air permeability of 600 seconds / 1.
It is preferably not more than 00 cm ³ . Air permeability 6
If it exceeds 00 seconds / 100 cm ³ , it may be difficult to obtain high lithium ion mobility in the separator. The lower limit of the air permeability is 100 seconds / 10
Preferably, it is 0 cm ³ . If the air permeability is less than 100 seconds / 100 cm ³ , sufficient separator strength may not be obtained. The upper limit of the air permeability is more preferably 500 seconds / 100 cm ³ , and the lower limit is more preferably 150 seconds / 100 cm ³ .

It is preferable that at least one of the four sides of the separator extends from the ends of the positive electrode and the negative electrode. The extension of the separator is 0.25 from the end of the negative electrode.
mm or more is desirable. Insufficient extension tends to cause internal short-circuit. It is desirable that all four sides of the separator extend from the ends of the positive electrode and the negative electrode in order to prevent an internal short circuit.

4) Non-aqueous electrolyte The lithium composite oxide is dispersed in the non-aqueous electrolyte. Hereinafter, the non-aqueous electrolyte will be described.

Examples of the non-aqueous electrolyte include a liquid non-aqueous electrolyte, a gel non-aqueous electrolyte, and a solid polymer electrolyte.

The liquid non-aqueous electrolyte is prepared, for example, by dissolving the electrolyte in a non-aqueous solvent.

The gelled non-aqueous electrolyte can be obtained, for example, by dissolving a non-aqueous solvent and an electrolyte in a polymer material and gelling by heat treatment or the like. Examples of the polymer material include polyacrylonitrile (PAN), polyethylene oxide (PEO), and diacrylic acid (C10).

The solid non-aqueous electrolyte is obtained, for example, by dissolving the electrolyte in a polymer material and solidifying it. Examples of the polymer material include polyacrylonitrile,
Examples thereof include polyvinylidene fluoride (PVdF), polyethylene oxide (PEO), and a copolymer containing acrylonitrile, vinylidene fluoride, or ethylene oxide as a monomer.

When a gel nonaqueous electrolyte or solid nonaqueous electrolyte is used, a layer of a gel nonaqueous electrolyte or a solid nonaqueous electrolyte may be interposed between the positive electrode and the negative electrode. In such a configuration, the separator need not be used.

Hereinafter, the non-aqueous solvent and the electrolyte contained in the non-aqueous electrolyte will be described.

As the non-aqueous solvent, a known non-aqueous solvent can be used as a solvent for a lithium secondary battery, and is not particularly limited, but is selected from the group consisting of propylene carbonate (PC) and ethylene carbonate (EC). And a second solvent composed of at least one solvent having a viscosity lower than that of PC and EC and having a number of donors of 18 or less. It is preferable to use an aqueous solvent. Since the nonaqueous electrolyte containing a nonaqueous solvent mainly composed of such a mixed solvent can form a protective film on the surface of the negative electrode, the nonaqueous electrolyte solvated with lithium as lithium is inserted into the negative electrode by charging. Co-intercalation of the water solvent into the negative electrode can be suppressed.

As the second solvent, chain carbon is preferable. Among them, dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), diethyl carbonate (DEC), ethyl propionate, methyl propionate, γ-butyrolactone (γ- BL), acetonitrile (AN), ethyl acetate (EA), toluene, xylene,
Examples include methyl acetate (MA) and methyl formate (MF). Such a second solvent can be used alone or in the form of a mixture of two or more. In particular, the number of donors in the second solvent is more preferably 16.5 or less.

The viscosity of the second solvent at 28 ° C. is 28
mp or less.

The amount of the first solvent in the mixed solvent of the first solvent and the second solvent is preferably 10 to 80% by volume. A more preferable blending amount of the first solvent is 20 to 75% by volume.

Among the mixed solvents composed of the first solvent and the second solvent, more preferred are EC and MEC, EC and PC and MEC, EC and MEC and DEC, EC and MEC and DM.
C is a mixed solvent of EC, MEC, PC and DEC. It is preferable that the volume ratio of MEC in this mixed solvent is 30 to 80%. A more preferred MEC volume ratio is 4
It is in the range of 0-70%. Further, as a mixed solvent composed of the first solvent and the second solvent, a mixed solvent of EC and γ-BL is also preferable. The volume ratio of γ-BL in this mixed solvent is 3
Preferably it is 0-80%.

As the electrolyte, for example, lithium perchlorate
(LiClO_Four), Lithium hexafluorophosphate (LiP
F₆), Lithium borofluoride (LiBF_Four), Hexafluoride
Lithium (LiAsF)₆), Trifluorometasulfo
Lithium phosphate (LiCF_ThreeSO _Three), Bistrifluorome
Lithyl sulphonylimide [LiN (CF_ThreeSO_Two)
_Two] And other lithium salts. For such electrolytes
Is one or more selected from the types described above or 2
More than one lithium salt can be used. Inside
Also, LiPF₆, LiBF_FourIt is preferable to use

The amount of the electrolyte dissolved in the non-aqueous solvent is 0.1.
It is desirable to set it to 5 to 2 mol / L.

The non-aqueous electrolyte preferably contains an additive for the purpose of improving the stability of the protective film formed on the negative electrode surface. Examples of the additive include an organic solvent of at least one selected from the group consisting of vinyl ethylene carbonate (VEC), vinylene carbonate (VC), ethylene sulfite (ES) and propylene sulfite (PS). Can be mentioned. The volume ratio of the additive to the whole non-aqueous solvent is 5
% Is desirable. In particular, from the viewpoint of densely forming a film on the surface of the negative electrode, the volume ratio of the additive to the entire nonaqueous solvent is more preferably 0.01% or more and 5% or less.

The non-aqueous electrolyte can contain water. It is desirable that the amount of water added be in the range of 700 ppm to 1000 ppm. By adding water, carbon dioxide gas is generated due to a chemical reaction between the water and the film on the surface of the negative electrode, and since the carbon dioxide gas can be absorbed by the lithium composite oxide, the internal pressure rise when water is added is reduced. Can be suppressed.

The non-aqueous electrolyte preferably contains a surfactant from the viewpoint of improving the wettability of the electrodes such as the positive electrode and the negative electrode and the separator. As the surfactant,
For example, trioctyl phosphate (TOP) and the like can be mentioned.

A substance having a function of trapping hydrogen fluoride (for example, lithium carbonate) may be added to the non-aqueous electrolyte.

When a liquid non-aqueous electrolyte is used as the non-aqueous electrolyte, the amount of the liquid non-aqueous electrolyte is 100 mA per unit cell capacity.
It is preferable to set the amount to 0.2 to 0.6 g per h.

(5) A carbon dioxide absorption layer containing a lithium composite oxide is present in the space between the closed container and the electrode group. For example, (i) to (ii) described below
The configuration of i) is mentioned. It is also possible to combine two or more configurations of (i) to (iii).

(I) At least a part of the surface of the electrode group is covered with a carbon dioxide gas absorbing layer. (Ii) A carbon dioxide absorption layer is arranged around the electrode group. (Iii) A carbon dioxide gas absorbing layer is formed on the battery components other than the electrode group existing in the closed container.

In particular, according to the above (i) and (ii),
This is preferable because the carbon dioxide gas absorbing layer can be formed without significantly changing the manufacturing process of the secondary battery.

The carbon dioxide gas absorbing layer is desirably opposed to the surface of the electrode group. With such a configuration, carbon dioxide gas generated by the decomposition of the non-aqueous electrolyte can be quickly absorbed. In particular, it is preferable that the carbon dioxide gas absorbing layer faces the outermost layer of the surface of the electrode group.

The carbon dioxide gas absorbing layer is obtained, for example, by dispersing a lithium composite oxide and a binder in a solvent, applying the obtained suspension, and drying. The type, amount and solvent of the binder may be the same as those described for the separator. In addition, it is preferable to apply the carbon dioxide gas absorbing layer thicker in advance in consideration of the thinning due to the evaporation of the solvent during drying.

The carbon dioxide gas absorbing layer preferably has a porous structure. Since the carbon dioxide gas absorbing layer having a porous structure is porous, the specific surface area can be increased, so that the carbon dioxide gas absorption amount can be increased. The carbon dioxide gas absorbing layer having a porous structure can be formed, for example, by the above-described suspension coating method.

The thickness of the carbon dioxide gas absorbing layer is preferably 200 μm or less. Carbon dioxide absorption layer thickness is 200
If it exceeds μm, the capacity per volume may be reduced. If the thickness of the carbon dioxide gas absorbing layer is less than 2 μm, the carbon dioxide gas generated by oxidative decomposition of the non-aqueous electrolyte may not be sufficiently absorbed. Therefore,
A more preferred range for the thickness is in the range of 5 μm to 50 μm. A more preferred thickness is in the range of 10 μm to 25 μm.

The carbon dioxide gas absorbing layer can be held by a carrier for the purpose of reinforcing the carbon dioxide gas absorbing layer. As the carrier, for example, Japanese paper, paper, polymer gel, non-woven fabric, woven or non-woven fabric made of reinforcing fibers made of a polymer insoluble in a non-aqueous electrolyte, microporous film, and the like can be used. The carrier preferably has a porous structure.

Next, battery components other than the electrode group will be described.

As a nonaqueous electrolyte secondary battery, an outer can, an electrode group housed in the outer can and including a positive electrode and a negative electrode,
A non-aqueous electrolyte contained in the outer can, an insulating plate disposed between the inner surface of the bottom of the outer can and the electrode group, a lid attached to an opening of the outer can, When a battery is provided with a spacer disposed between the electrode group and the lid, and an explosion-proof opening valve formed on the outer can or the lid, carbon dioxide gas is absorbed by battery components other than the electrode group. The following method can be used to form the layer. Further, two or more of (A) to (D) can be combined.

(A) A carbon dioxide gas absorbing layer is formed on at least a part of the inner surface of the outer can. (B) A carbon dioxide gas absorbing layer is formed on at least a part of the inner surface of the lid. (C) A carbon dioxide gas absorbing layer is formed on at least a part of the surface of the insulating plate. (D) A carbon dioxide absorption layer is formed on at least a part of the surface of the spacer. (E) A carbon dioxide gas absorbing layer is formed on the inner surface including the opening valve forming region.

A non-aqueous electrolyte secondary battery comprising a hermetically sealed container made of film, an electrode group housed in the container and including a positive electrode and a negative electrode, and a non-aqueous electrolyte housed in the container In order to form the carbon dioxide gas absorbing layer on the battery components other than the electrode group, for example, (F) the carbon dioxide gas absorbing layer can be formed on at least a part of the inner surface of the closed container.

In (C) and (D) described above, it is preferable to form a carbon dioxide gas absorbing layer on the surface of the insulating plate and the spacer facing the electrode group, respectively. With such a configuration, carbon dioxide gas generated by the decomposition of the non-aqueous electrolyte can be quickly absorbed.

It is desirable that the lithium composite oxide contained in the carbon dioxide gas absorbing layer has non-conductivity from the viewpoint of avoiding impairing the insulating function of the insulating plate and the spacer. Among them, Li ₄ SiO ₄ and Li ₂ SiO ₃ are preferable.

In the above (F), when a carbon dioxide gas absorbing layer is formed on the inner surface of a sealed container made of a film material, a carbon dioxide gas absorbing layer is formed on a target region on one side of the film material, and the carbon dioxide gas absorbing layer is formed. It is preferable to produce a closed container by performing heat sealing with the gas absorption layer forming surface inside. The carbon dioxide gas absorbing layer is formed, for example, by suspending a lithium composite oxide and a binder in a solvent, applying the resulting suspension to a film material, and drying. The type, amount and solvent of the binder may be the same as those described for the separator. In order to increase the sealing strength of the closed container, it is desirable not to form a carbon dioxide gas absorbing layer in the heat sealing region of the film material. In this case, for example, the heat sealing region of the film material may be covered with a cover sheet, and the suspension may be applied in this state. The thickness of the cover sheet is preferably at least 10 μm thicker than the thickness of the carbon dioxide gas absorbing layer to be produced. This is for the following reasons. This is because, after the suspension is applied to the film material and dried, the carbon dioxide gas absorbing layer may become thin due to evaporation of the solvent.
Further, the width of the heat sealing region is preferably 5 mm or less, and more preferably 2 mm or less.

Incidentally, the nonaqueous electrolyte secondary battery according to the present invention may have the following configuration.

That is, the non-aqueous solvent is oxidized at the positive electrode, and the carbon dioxide gas generated from the liquid surface of the non-aqueous solvent is allowed to pass only through the ventilation holes by utilizing the capillary phenomenon, so that the carbon dioxide absorbing material having a gas-permeable layer is provided. The carbon dioxide gas may be introduced into the holding space where the carbon dioxide gas is absorbed by the carbon dioxide gas absorbent. The ventilation layer is not particularly limited as long as it can rapidly transmit and diffuse carbon dioxide gas.
Glass fiber, polypropylene fiber, or the like can be used.

In order to allow only carbon dioxide gas to permeate, a gas phase permeable membrane can be used in addition to a vent hole.
The gas-phase permeable membrane is not particularly limited as long as it selectively transmits carbon dioxide gas. For example, at least one material selected from the group consisting of polyimide, polysulfone, polyetherimide, and cellulose acetate can be used. The gas-phase permeable membrane is disposed between the lithium composite oxide and the non-aqueous electrolyte, and can reduce the contact between the lithium composite oxide and the non-aqueous electrolyte.

As described in detail above, the non-aqueous electrolyte secondary battery according to the present invention includes a closed container, a positive electrode stored in the closed container, a negative electrode stored in the closed container, And a non-aqueous electrolyte housed therein. In such a non-aqueous electrolyte secondary battery, the non-aqueous electrolyte is decomposed at the positive electrode at the time of initial charge or storage at high temperature to generate carbon dioxide gas. It has been found that a lithium composite oxide having an absorbing property is stable with respect to a nonaqueous electrolyte and absorbs carbon dioxide gas in a use temperature range (around normal temperature) of a secondary battery. Therefore, by allowing the lithium composite oxide having a property of absorbing carbon dioxide gas to be present in the closed container, it is possible to absorb the carbon dioxide gas and suppress an increase in the internal pressure without impairing the charge / discharge characteristics. As a result, rupture and liquid leakage can be avoided, so that safety can be improved and the charge / discharge cycle life can be improved. Also, when the thickness of the wall of the sealed container is reduced in order to reduce the thickness of the battery, it is possible to suppress the container from being expanded and deformed by gas pressure and to use a non-aqueous solution that is easily decomposed at the positive electrode. Solvents (eg, cyclic carbonate, chain carbonate) can be used. Therefore, it is possible to provide a thin non-aqueous electrolyte secondary battery having an excellent charge / discharge cycle life by taking advantage of the fact that it does not easily react with the negative electrode of the cyclic carbonate or chain carbonate.

In the non-aqueous electrolyte secondary battery according to the present invention, the amount of lithium composite oxide per 1 mAh of theoretical capacity of the battery is set to 4 mg or less, so that the carbon dioxide gas can be maintained while maintaining a high weight energy density and a low internal resistance. Therefore, it is possible to realize a non-aqueous electrolyte secondary battery that is low in rupture and liquid leakage, high in safety, and excellent in weight energy density and charge / discharge cycle life.

In the nonaqueous electrolyte secondary battery according to the present invention, the effective surface area of the lithium composite oxide can be increased by including the lithium composite oxide in the nonaqueous electrolyte. Most of the carbon dioxide gas generated by the oxidative decomposition of the nonaqueous electrolyte is dissolved in the nonaqueous solvent, so that the carbon dioxide gas can be rapidly absorbed. As a result, an increase in the internal pressure, particularly at the time of initial charging, can be significantly suppressed, and the amount of carbon dioxide present in the secondary battery can be reduced, so that the charge / discharge reaction is prevented from being inhibited by carbon dioxide. The charge / discharge cycle life can be improved.

In the non-aqueous electrolyte secondary battery according to the present invention,
The absorption of carbon dioxide gas causes lithium carbonate (Li_TwoCO_Three)
A lithium composite oxide (eg, Li_FourSi
O_Four, Li _TwoSiO_Three) By using the negative electrode
Li on the surface_TwoCO_ThreeContaining protective film (solid electrolyte film)
Lithium is occluded in the negative electrode
Control non-aqueous solvent co-intercalation
can do. As a result, deterioration of the negative electrode can be suppressed.
The charge-discharge cycle characteristics and high-temperature storage characteristics.
Can be improved. In particular, the absorption of carbon dioxide
Includes lithium composite oxide that generates lithium oxide in the negative electrode
The protective film can be formed sufficiently on the negative electrode surface.
Greatly improves charge / discharge cycle characteristics
be able to. However, lithium per theoretical mAh of battery capacity
If the amount of the composite oxide exceeds 4 mg,
Reduces the content of substances that occlude and release lithium
At the same time, the protective film becomes thicker, preventing lithium from being absorbed and released.
Response cycle is inhibited, resulting in excellent charge / discharge cycle characteristics
Can be difficult.

In the non-aqueous electrolyte secondary battery according to the present invention, the presence of the carbon dioxide gas-absorbing layer containing the lithium composite oxide in the space between the closed container and the electrode group allows the closed container to be closed. In this case, the position of the carbon dioxide gas absorbing layer can be fixed, so that the distribution of the lithium composite oxide in the closed container can always be maintained in a uniform state. As a result, carbon dioxide gas can be stably absorbed, particularly during high-temperature storage, so that safety during high-temperature storage can be significantly improved. Also,
Because the carbon dioxide absorption layer is arranged outside the electrode group,
It is possible to prevent the carbon dioxide gas absorbent from hindering the charge / discharge reaction, and to improve the discharge capacity and the charge / discharge cycle life.

[0114]

Embodiments of the present invention will be described below in detail with reference to the drawings.

Example 1 <Preparation of Positive Electrode> First, lithium cobalt oxide (Li _x
CoO ₂ ; where X is 0 ≦ X ≦ 1) 91% by weight of powder is 3% by weight of acetylene black, 3% by weight of graphite, and polyvinylidene fluoride (PVd) is used as a binder.
F) 3% by weight and N-methyl-2-pyrrolidone (NMP) as a solvent were added and mixed to prepare a slurry. The slurry was applied to both sides of a current collector made of an aluminum foil having a thickness of 15 μm, and then dried and pressed, whereby a positive electrode mixture layer having an electrode density of 3 g / cm ³ was supported on both sides of the current collector. A positive electrode having a structure was prepared.

<Preparation of Negative Electrode> 3000 carbonaceous materials were used.
93% by weight of a powder of mesophase pitch-based carbon fiber (fiber diameter: 8 μm, average fiber length: 20 μm, average plane spacing (d ₀₀₂ ): 0.3360 nm) heat-treated at ℃.
And polyvinylidene fluoride (PVdF) 7 as a binder
% By weight and N-methyl-2-pyrrolidone (N
MP) to prepare a slurry. The slurry was coated on both sides of a current collector made of copper foil having a thickness of 12 μm, dried, and pressed to obtain an electrode density of 1.4 g.
A negative electrode having a structure in which a negative electrode mixture layer having a thickness of / cm ³ was supported on a current collector was produced.

<Separator> Thickness of 25 μm, 120
A separator made of a polyethylene porous film having a heat shrinkage of 20% at 50 ° C. for 1 hour and a porosity of 50% was prepared.

<Preparation of Non-Aqueous Electrolyte> Lithium hexafluorophosphate (LiPF ₆ ) was mixed with a mixed solvent of ethylene carbonate (EC) and methyl ethyl carbonate (MEC) (mixing volume ratio 1: 2) at a concentration of 1M. To obtain a non-aqueous electrolyte.

<Preparation of Electrode Group> A band-shaped positive electrode lead was welded to the current collector of the positive electrode, and a band-shaped negative electrode lead was welded to the current collector of the negative electrode. To form an electrode group.

<Assembly of Battery> 97% by weight of lithium orthosilicate (Li ₄ SiO ₄ ) and 3% by weight of polyvinylidene fluoride (PVdF) as a binder are dispersed in N-methyl-2-pyrrolidone (NMP) as a solvent. To prepare a suspension. The above suspension was formed on the inner surface of an aluminum-based metal outer can having a bottomed rectangular tube shape and a plate thickness of 0.25 mm, and the lithium composite oxide abundance per 1 mAh of theoretical battery capacity was 0.36 mg / mAh. The resultant was coated as described above and dried to form a carbon dioxide gas absorbing layer. The electrode group and the electrolytic solution are respectively stored in such an outer can,
A prismatic lithium ion secondary battery having the structure shown in FIGS. 1 to 3 and having a thickness of 4.8 mm, a width of 30 mm, and a height of 40 mm and a theoretical capacity (design capacity) of 550 mAh. Was assembled.

That is, for example, as shown in a perspective view of a prismatic lithium ion secondary battery in FIG.
Has a structure in which a lid 3 made of an aluminum-based metal is air-tightly joined, for example, by laser welding to an opening of an outer can 2 having a bottomed rectangular cylindrical shape made of an aluminum alloy. The outer can 2 also serves as, for example, a positive electrode terminal, and has an insulating film 4 (for example, formed of a polyimide resin) disposed on the inner surface of the bottom. The electrode group 5 is housed in the outer can 2 of the closed container 1. The electrode group 5 includes:
For example, it is manufactured by spirally winding the negative electrode 6, the separator 7, and the positive electrode 8 such that the positive electrode 8 is located at the outermost periphery, and then press-forming the flat shape. Spacer 9 made of, for example, synthetic resin having a lead extraction hole near the center
(Insulating plate; formed of, for example, polypropylene resin) is disposed on the electrode group 5 in the outer can 2.

In the vicinity of the center of the lid 3, an extraction hole 10 for a negative electrode terminal is opened. The injection hole 11 is opened at a position of the lid 3 away from the extraction hole 10. The electrolyte is injected into the outer can 2 through the injection hole 11. The negative electrode terminal 12 is connected to the hole 1 of the lid 3.
0 is hermetically sealed via an insulating material 13 made of glass or resin. A lead 14 is connected to the lower end surface of the negative electrode terminal 12, and the other end of the lead 14 is connected to the negative electrode 6 of the electrode group 5. The sealing member 15 made of, for example, a metal disk is used to fill the injection hole 1 after the electrolyte is injected through the injection hole 11 of the lid 3.
One of the lids 3 is joined to the lid 3 by ultrasonic welding to hermetically seal the injection hole 11.

The upper insulating paper 17 covers the entire outer surface of the lid 3. A lower insulating paper 19 having a slit 18 is disposed on the bottom surface of the outer can 2. PTC (Positive Therma)
The l Coefficient element 20 has one surface interposed between the bottom surface of the outer can 2 and the lower insulating paper 19, and the other surface extending outside the insulating paper 19 through the slit 18. ing. Exterior tube 21
Are disposed so as to extend from the side surface of the outer can 2 to the periphery of the insulating papers 17 and 19 on the upper and lower surfaces, and the upper insulating paper 1
7 and the lower insulating paper 19 are fixed to the outer can 2. Due to such an arrangement of the outer tube 21, the other surface of the PTC element 20 extended to the outside is bent toward the bottom surface of the lower insulating paper 19. The positive electrode lead 22 has one end connected to the positive electrode 8 and the other end connected to the lower surface of the lid 3.

As shown in FIG. 2, an opening valve 23 is formed on the bottom surface of the outer can 2 by engraving, and is formed by a thin portion having a shape having V-shaped portions at both ends of a linear portion. When the internal pressure in the closed container 1 rises, the open valve 23 is broken by the gas pressure, and releases the gas in the closed container 1 to the outside to prevent explosion.

As shown in FIG. 3, a carbon dioxide gas absorbing layer 24 containing a lithium composite oxide is formed on the inner surface of the outer can 2. The carbon dioxide gas absorbing layer 24 faces the outermost periphery (outermost layer) of the electrode group 5.

Example 2 Instead of forming a carbon dioxide gas absorbing layer on the inner surface of an outer can, a nonaqueous electrolytic solution having a particle size of 1 to 1 was used.
A prismatic lithium ion secondary battery having the same configuration as that described in Example 1 was assembled except that 200 mg of fine particles of lithium orthosilicate (Li ₄ SiO ₄ ) of 0 μm were added.

Example 3 Instead of forming a carbon dioxide gas absorbing layer on the inner surface of an outer can, a nonaqueous electrolytic solution having a particle size of 1 to 1 was used.
A prismatic lithium ion secondary battery having the same configuration as that described in Example 1 was assembled except that 200 mg of fine particles of lithium metasilicate (Li ₂ SiO ₃ ) of 0 μm were added.

Example 4 Instead of forming a carbon dioxide gas absorbing layer on the inner surface of an outer can, the surface of the spacer 9 facing the electrode group 5 and the surface of the insulating film 4 facing the electrode group 5 were:
A prismatic lithium ion secondary battery having the same configuration as that described in Example 1 was assembled, except that the carbon dioxide absorption layer was formed by the method described below.

That is, lithium orthosilicate (L
i ₄ SiO ₄₎ 97 wt% and 3 wt% poly (vinylidene fluoride) (PVdF) is a binding agent dispersed in N- methyl-2-pyrrolidone (NMP), was prepared suspension. The obtained suspension was applied to the surface of the spacer 9 facing the electrode group 5 and the surface of the insulating film 4 facing the electrode group 5, and dried to form a carbon dioxide gas absorbing layer.

(Example 5) Instead of forming a carbon dioxide gas absorbing layer on the inner surface of the outer can, the surface of the spacer 9 facing the electrode group 5 and the surface of the insulating film 4 facing the electrode group 5 were
A prismatic lithium ion secondary battery having the same configuration as that described in Example 1 was assembled, except that the carbon dioxide absorption layer was formed by the method described below.

That is, lithium metasilicate (Li)
₂ SiO ₃₎ 97 wt% and 3 wt% poly (vinylidene fluoride) (PVdF) is a binding agent dispersed in N- methyl-2-pyrrolidone (NMP), was prepared suspension. The obtained suspension was applied to the surface of the spacer 9 facing the electrode group 5 and the surface of the insulating film 4 facing the electrode group 5, and dried to form a carbon dioxide gas absorbing layer.

Example 6 Instead of forming a carbon dioxide gas absorbing layer on the inner surface of an outer can, as shown in FIGS.
Except that the outermost periphery (outermost layer) of the flat electrode group 5 is covered with a carbon dioxide gas absorbing sheet 25 containing 90% of lithium orthosilicate (Li ₄ SiO ₄ ) and 10% of polyvinylidene fluoride (PVdF). 4 and 5 in the same manner as described in the first embodiment, the thickness is 4.8 mm, the width is 30 mm, and the height is 40.
550m theoretical capacity (design capacity) with external dimensions of mm
An Ah prismatic lithium ion secondary battery was assembled. 4 and 5, the same members as those in FIGS. 1 and 2 described above are denoted by the same reference numerals as those in FIGS.

Example 7 Instead of forming a carbon dioxide gas absorbing layer on the inner surface of an outer can, as shown in FIGS.
Except that the outermost periphery (outermost layer) of the flat electrode group 5 is covered with a carbon dioxide gas absorbing sheet 25 containing 90% of lithium metasilicate (Li ₂ SiO ₃ ) and 10% of polyvinylidene fluoride (PVdF). In the same manner as described in the first embodiment, the structure shown in FIGS.
4.8mm thick, 30mm wide, 40mm high
Theoretical capacity (design capacity) with external dimensions of 550 mAh
Was assembled.

(Example 8) Except that the negative electrode produced by the method described below is used instead of forming the carbon dioxide gas absorbing layer on the inner surface of the outer can, the same as that described in Example 1 described above is used. A similar prismatic lithium ion secondary battery was assembled.

That is, mesophase pitch-based carbon fibers heat-treated at 3000 ° C. as a carbonaceous material (having a fiber diameter of 8
93% by weight of a powder having an average fiber length of 20 μm and an average spacing (d ₀₀₂ ) of 0.3360 nm, 2% by weight of lithium orthosilicate (Li ₄ SiO ₄ ) powder, and polyvinylidene fluoride as a binder. (PVdF) was mixed with 5% by weight to prepare a slurry. The slurry was applied to both sides of a current collector made of a copper foil having a thickness of 12 μm, dried, and pressed to obtain an electrode density of 1.4 g / cm ^3.
A negative electrode having a structure in which the negative electrode material mixture layer was supported on a current collector was produced.

(Example 9) Except that a carbon dioxide absorbing layer was formed on the inner surface of an outer can, a negative electrode produced by the method described below was used. A similar prismatic lithium ion secondary battery was assembled.

That is, as a carbonaceous material, a mesophase pitch-based carbon fiber heat-treated at 3000 ° C. (having a fiber diameter of 8
93% by weight of a powder having an average fiber length of 20 μm and an average spacing (d ₀₀₂ ) of 0.3360 nm, ₂ % by weight of lithium metasilicate (Li ₂ SiO ₃ ) powder, and polyvinylidene fluoride as a binder. (PVdF) was mixed with 5% by weight to prepare a slurry. The slurry has a thickness of 1
Apply to both sides of a current collector made of 2 μm copper foil, dry,
Pressing produced a negative electrode having a structure in which a negative electrode mixture layer having an electrode density of 1.4 g / cm ³ was supported on a current collector.

Example 10 Instead of forming a carbon dioxide gas absorbing layer on the inner surface of the outer can, a carbon dioxide gas absorbing layer was formed on the inner surface of the bottom of the outer can 2 (the area including the open valve 23) by the method described below. Except for the formation, a prismatic lithium ion secondary battery similar to that described in Example 1 was assembled.

That is, 97% by weight of lithium orthosilicate (Li ₄ SiO ₄ ) and 3% by weight of polyvinylidene fluoride (PVdF) are contained on the inner surface of the bottom of the outer can 2 similar to that described in the first embodiment. A suspension in which the mixture was dispersed in N-methyl-2-pyrrolidone (NMP) was applied and dried to form a carbon dioxide gas absorbing layer.

Example 11 Instead of forming a carbon dioxide gas absorbing layer on the inner surface of an outer can, a carbon dioxide gas absorbing layer was formed on the inner surface of the bottom of the outer can 2 (the area including the open valve 23) by the method described below. Except for the formation, a prismatic lithium ion secondary battery similar to that described in Example 1 was assembled.

That is, 97 wt% of lithium metasilicate (Li ₂ SiO ₃ ) and ₃ wt% of polyvinylidene fluoride (PVdF) are contained on the inner surface of the bottom of the outer can 2 similar to that described in the first embodiment. The mixture is N-methyl-
A suspension dispersed in 2-pyrrolidone (NMP) was applied and dried to form a carbon dioxide absorption layer.

Example 12 Using a carbon dioxide gas absorbing sheet 25 containing 90% lithium zirconate (Li ₂ ZrO ₃ ) and 10% polyvinylidene fluoride (PVdF), and a lithium composite per 1 mAh of theoretical battery capacity A prismatic lithium ion secondary battery having the same configuration as that described in Example 6 above was assembled except that the amount of oxide added was changed to the value shown in Table 1 below.

Example 13 Using a carbon dioxide gas absorbing sheet 25 containing 90% of lithium aluminate (LiAlO ₂ ) and 10% of polyvinylidene fluoride (PVdF), and a lithium composite oxide per 1 mAh of theoretical capacity of the battery A prismatic lithium ion secondary battery having the same configuration as that described in Example 6 above was assembled except that the amount of addition was changed to the value shown in Table 1 below.

Example 14 Using a carbon dioxide absorption sheet 25 containing 90% lithium ferrite (LiFeO ₂ ) and 10% polyvinylidene fluoride (PVdF), and adding a lithium composite oxide per 1 mAh of theoretical capacity of the battery A prismatic lithium ion secondary battery having the same configuration as that described in Example 6 was assembled except that the amount was changed to the value shown in Table 1 below.

(Example 15) Lithium composite oxidation using a carbon dioxide gas absorbing sheet 25 containing 90% of lithium titanate (Li ₂ TiO ₃ ) and 10% of polyvinylidene fluoride (PVdF) and per 1 mAh of theoretical capacity of the battery A prismatic lithium ion secondary battery having the same configuration as that described in the above-mentioned Example 6 was assembled except that the amount of the substance added was changed to the value shown in Table 1 below.

Comparative Example 1 A prismatic lithium ion secondary battery was assembled in the same manner as described in Example 1 except that no carbon dioxide gas absorbent was used.

(Comparative Example 2) Ethylene carbonate (E
C) and γ-butyrolactone (γ-BL) in a mixed solvent (mixing volume ratio 1: 2) of lithium borofluoride (LiB
F4) is the same as that described in Example 1 except that a non-aqueous electrolyte prepared by dissolving F ₄ ) so as to have a concentration of 1.5 M is used and a carbon dioxide gas absorbent is not used. Thus, a prismatic lithium ion secondary battery was assembled.

The obtained Examples 1 to 15 and Comparative Examples 1 to
The lithium ion secondary battery of No. 2 was initially charged. 110mA (equivalent to 0.2C) in initial charging
A 4.2 V constant current / constant voltage charge was performed for 10 hours, and the state of swelling of the battery after the initial charge was examined. The results are shown in Table 1 below. Subsequently, the battery was discharged at a constant current of 110 mA, and the battery capacity was confirmed at a cutoff voltage of 3.0 V. 4.2 V at 550 mA (equivalent to 1.0 C) for these secondary batteries
After charging for 3 hours with constant current and constant voltage until 550
A charge / discharge cycle test in which a constant current discharge of 3.0 V cut at mA (equivalent to 1.0 C) was performed up to 500 cycles, and 5
The capacity retention ratio at the 00th cycle (the discharge capacity at the first cycle is defined as 100%) was determined, and the results are shown in Table 1 below. Table 1 also shows the amount of lithium composite oxide present per 1 mAh of theoretical capacity of the battery.

Examples 1 to 15 and Comparative Examples 1 and 2
After confirming the initial charge and the battery capacity of the lithium ion secondary batteries of
(Equivalent to 1.0 C) After constant-current / constant-voltage charging to 4.2 V was performed over 3 hours, 85 ° C.
The swelling state of the battery after storage for 150 hours was examined, and the results are shown in Table 1.

[0150]

[Table 1]

As is clear from Table 1, EC and MEC
The secondary batteries of Examples 1 to 15 including a non-aqueous electrolyte containing, and containing a lithium composite oxide as a carbon dioxide gas absorbent, have a small swelling of the container during initial charging and high-temperature storage, and
It can be seen that the capacity retention ratio at the time of 0 cycle is higher than Comparative Examples 1 and 2.

On the other hand, the secondary battery of Comparative Example 1 provided with a non-aqueous electrolyte containing EC and MEC and not using a carbon dioxide gas absorbent had a swelling of 1 mm after initial charging and a swelling of 5 mm after high-temperature storage. It turns out that it becomes large. On the other hand, the secondary battery of Comparative Example 2, which includes a non-aqueous electrolyte containing EC and γ-BL and does not use a carbon dioxide gas absorbent, can reduce the swelling of the container at the time of initial charging and at the time of high-temperature storage. It can be seen that the capacity retention ratio of the sample was as low as 60%.

In particular, when lithium orthosilicate (Li ₄ SiO ₄ ) is used as the lithium composite oxide, Li
_It can be seen that the secondary battery of Example 2 in which ₄ SiO ₄ was added to the non-aqueous electrolyte can reduce the swelling after the initial charge as compared to the secondary batteries of Examples 1, 4, 6, 8, and 10. When Li ₄ SiO ₄ was added to the negative electrode as in Example 8, the swelling after the initial charge was 0.4 mm, which was larger than that in Example 2. However, the capacity retention at 500 cycles was higher than that in Example 2. It turns out that it becomes high compared with.

On the other hand, when lithium orthosilicate (Li ₄ SiO ₄ ) is used as the lithium composite oxide, a carbon dioxide gas-absorbing layer containing Li ₄ SiO ₄ is present in the space between the sealed container and the electrode group. , 4, 6, and 10 indicate that the swelling during high-temperature storage is smaller than those in Examples 2 and 8.

(Examples 16 to 20) 1 m of theoretical capacity of battery
The lithium composite oxide content of the negative electrode per Ah is shown in Table 2 below.
A prismatic lithium-ion secondary battery similar to that described in Example 2 above was assembled, except for the changes as shown in FIG.

For the secondary batteries of Examples 16 to 20, swelling after initial charging, capacity retention after 500 cycles, and swelling after high-temperature storage were measured in the same manner as described above. The results are shown in Table 2 below. Shown in Table 2 also shows the results of Example 8 described above.

[0157]

[Table 2]

As is clear from Table 2, as the amount of the lithium composite oxide increases, the swelling after initial charging and after high-temperature storage decreases, and when the amount of the lithium composite oxide is small, 500 cycles. It can be seen that the capacity retention at the time is excellent. In particular, the secondary batteries of Examples 8, 17, and 18 suppress swelling after initial charging and after high-temperature storage, and
It can be seen that the capacity retention rate during the 00 cycle can be increased.

Example 21 <Preparation of Positive Electrode> First, lithium cobalt oxide (Li _x
CoO ₂ ; wherein X is 0 ≦ X ≦ 1) powder 90.5
A slurry was prepared by mixing a weight%, acetylene black 2.5 weight%, graphite 3 weight%, polyvinylidene fluoride (PVdF) 4 weight% and N-methylpyrrolidone (NMP) solution. The slurry was applied to a positive electrode current collector made of an aluminum foil having a thickness of 10 μm, dried, and pressed to obtain an electrode density of 3.0 g.
/ Cm ³ was prepared. The obtained positive electrode had a structure in which a positive electrode mixture layer having a thickness of 48 μm was supported on both surfaces of the positive electrode current collector. The total thickness of the positive electrode mixture layer was 96 μm.
m.

<Production of Negative Electrode> 3000 ° C. as carbonaceous material
A mesophase pitch-based carbon fiber heat-treated in was prepared. The carbon fibers had an average fiber diameter of 8 μm, an average fiber length of 20 μm, and an interplanar spacing (d ₀₀₂ ) of 0.336 nm. 93% by weight of the carbonaceous material powder, 7% by weight of polyvinylidene fluoride (PVdF) as a binder and NMP
A slurry was prepared by mixing the solutions. The obtained slurry was applied to both sides of a negative electrode current collector made of a copper foil having a thickness of 10 μm, dried, and pressed to produce a negative electrode having an electrode density of 1.35 g / cm ³ . The obtained negative electrode had a structure in which a negative electrode mixture layer having a thickness of 45 μm was supported on both surfaces of the negative electrode current collector. Note that the total thickness of the negative electrode mixture layer is 90 μm.

<Preparation of Non-Aqueous Electrolyte> Lithium hexafluorophosphate (LiPF ₆ ) was added to a mixed solvent of ethylene carbonate (EC) and methyl ethyl carbonate (MEC) (mixing volume ratio 1: 2) at a concentration of 1M. To obtain a non-aqueous electrolyte.

<Preparation of Electrode Group> A polyethylene separator having a thickness of 27 μm, a porosity of 50%, and an air permeability of 90 seconds / 100 cm ³ was prepared. After spirally winding the positive electrode and the negative electrode with a separator interposed therebetween,
By pressing this in the radial direction, it is formed into a flat shape,
An electrode group having a thickness of 2.7 mm, a width of 30 mm, and a height of 50 mm was produced.

<Assembly of Battery> 97% by weight of lithium orthosilicate (Li ₄ SiO ₄ ) and 3% by weight of polyvinylidene fluoride (PVdF) as a binder were mixed with N-methyl-2-
It was dispersed in pyrrolidone (NMP) to prepare a suspension.
Except for a heat-sealed part, the suspension was prepared by removing the heat-sealed part from one side of a 0.1 mm-thick laminated film having a multilayer structure in which both sides of an aluminum foil were coated with polypropylene and having a lithium composite oxide abundance of 0 mA per 1 mAh of theoretical battery capacity. .36m
g / mAh, and dried to form a carbon dioxide gas absorbing layer. The laminated film was processed into a bag shape by heat sealing so that the carbon dioxide gas absorbing layer surface was on the inside. The electrode group was housed in this, and the obtained one was sandwiched between holders so that the battery thickness became 2.75 mm.
Immediately after insertion into the holder, the pressure applied to the electrode group is 0.5 kg /
cm ² . 0.3% by weight of polyvinylidene fluoride (PVdF) as an adhesive polymer was dissolved in dimethylformamide (DMF) (boiling point: 153 ° C.) as an organic solvent. The obtained solution was injected into the electrode group in the laminate film so as to have a battery capacity of 0.6 mL, and the solution was permeated into the electrode group,
The electrode was attached to the entire surface of the electrode group.

Next, the organic solvent was evaporated by subjecting the electrode group in the laminate film to vacuum drying at 80 ° C. for 12 hours, and the adhesive polymer was held in the gaps between the positive electrode, the negative electrode and the separator. The negative electrode and the separator were integrated, and a porous adhesive portion was formed on the surface of the electrode group.

Next, the holder was released. The total time during which the electrode group was held between the holders was 120 minutes. 2 g of the non-aqueous electrolyte is injected into the electrode group in the laminate film, and has a structure shown in FIGS. 6 to 8 and has a thickness of 2.75 mm, a width of 32 mm, and a height of 55 mm. A water electrolyte secondary battery was assembled.

As shown in FIGS. 6 to 8, an electrode group 32 is housed in a sealed container 31 made of a laminated film. The electrode group 32 has a structure in which a laminate including a positive electrode, a separator, and a negative electrode is wound into a flat shape. A carbon dioxide gas absorbing layer 33 is formed on the inner surface of the sealed container 31 except for the heat seal portions 34 formed at both ends on the long side of the container 31 and at the end where the lead extends. The carbon dioxide gas absorbing layer 33 faces the outermost periphery (outermost layer) of the electrode group 32. The laminate of the electrode group 32 includes a separator 35, a positive electrode mixture layer 36, and a positive electrode current collector 3 from the lower side in FIG.
7, a positive electrode 38 including a positive electrode mixture layer 36, and a separator 3
5. Negative electrode mixture layer 39, negative electrode current collector 40, and negative electrode mixture layer 39
41, a separator 35, a positive electrode 38 having a positive electrode mixture layer 36, a positive electrode current collector 37, and a positive electrode mixture layer 36, and a negative electrode having a separator 35, a negative electrode mixture layer 39, and a negative electrode current collector 40. 41 have the structure laminated | stacked in this order. The negative electrode current collector 40 is located at the outermost periphery of the electrode group 32. One end of the strip-shaped positive electrode lead 42 is connected to the positive electrode current collector 37 of the electrode group 32, and the other end is extended from the sealed container 31. On the other hand, one end of the strip-shaped negative electrode lead 43 is connected to the negative electrode current collector 40 of the electrode group 32, and the other end is extended from the sealed container 31. When the lithium composite oxide constituting the carbon dioxide gas absorbing layer 33 has electron conductivity, the outermost layer (outermost periphery) of the electrode group 32 is preferably the separator 35 from the viewpoint of avoiding an internal short circuit.

(Example 22) A positive electrode, a separator, a negative electrode, and a separator were stacked in the same order as described in Example 21 and then spirally wound. 90 ℃
To produce an electrode group having a thickness of 2.7 mm, a width of 30 mm, and a height of 50 mm.

200 mg of lithium silicate (Li ₄ SiO ₄ ) fine particles having a particle size of 1 to 10 μm were added to the same nonaqueous electrolyte as described in Example 21 described above.

A 0.1 mm-thick laminated film having a multilayer structure in which both surfaces of an aluminum foil were covered with polypropylene was processed into a bag by heat sealing. The electrode group was housed in this and vacuum dried at 80 ° C. for 24 hours.

After injecting the non-aqueous electrolyte into the laminated film pack containing the electrode group, the laminated film pack was completely sealed by heat sealing.
2.75mm thick, 32mm wide, 55m high
m thin non-aqueous electrolyte secondary battery was assembled.

Example 23 93% by weight of a carbonaceous material powder similar to that described in Example 21, 5% by weight of polyvinylidene fluoride (PVdF) as a binder, and powder of lithium orthosilicate (Li ₄ SiO ₄ ) A slurry was prepared by mixing 2% by weight and the NMP solution. The obtained slurry was applied to both sides of a negative electrode current collector made of a copper foil having a thickness of 10 μm, dried, and pressed to produce a negative electrode having an electrode density of 1.35 g / cm ³ . The obtained negative electrode had a structure in which a negative electrode mixture layer having a thickness of 45 μm was supported on both surfaces of the negative electrode current collector. Note that the total thickness of the negative electrode mixture layer is 90 μm.

The obtained negative electrode, a positive electrode and a separator similar to those described in Example 21 described above were prepared, and the positive electrode, the separator, the negative electrode, and the separator were laminated in this order, and then spirally wound. This was heated and pressed at 90 ° C. to produce an electrode group having a thickness of 2.7 mm, a width of 30 mm, and a height of 50 mm.

A 0.1 mm-thick laminated film having a multilayer structure in which both surfaces of an aluminum foil were covered with polypropylene was processed into a bag by heat sealing. The electrode group was housed in this and vacuum dried at 80 ° C. for 24 hours.

After injecting the same nonaqueous electrolyte as described in Example 21 into the laminated film pack in which the electrode group was stored, the laminated film pack was completely sealed by heat sealing, and the thickness was reduced. Is 2.75m
m, a thin nonaqueous electrolyte secondary battery having a width of 32 mm and a height of 55 mm was assembled.

Comparative Example 3 A thin non-aqueous electrolyte secondary battery similar to that described in Example 21 was assembled except that the carbon dioxide gas absorbing layer was not formed.

Examples 21 to 23 and Comparative Example 3
Was initially charged. In initial charging, 100mA (corresponding to 0.2C)
A 4.2 V constant current / constant voltage charge was performed for 10 hours, and the state of swelling of the battery after the initial charge was examined. The results are shown in Table 3 below. Subsequently, the battery was discharged at a constant current of 100 mA, and the battery capacity was confirmed at a cutoff voltage of 3.0 V. 4.2 V at 500 mA (equivalent to 1.0 C) for these secondary batteries
After charging for 3 hours with constant current and constant voltage until 500
A charge / discharge cycle test in which a constant current discharge of 3.0 V cut at mA (equivalent to 1.0 C) is performed up to 500 cycles,
The capacity retention ratio at the 500th cycle (the discharge capacity at the first cycle is defined as 100%) was obtained, and the results are shown in Table 3 below. Table 3 also shows the amount of lithium composite oxide present per 1 mAh of theoretical capacity of the battery.

After the initial charging and the battery capacity of the lithium ion secondary batteries of Examples 21 to 23 and Comparative Example 3 were confirmed, these batteries were charged at 500 mA.
(Equivalent to 1.0 C) After constant-current / constant-voltage charging to 4.2 V was performed over 3 hours, 85 ° C.
The swelling state of the battery after storage for 150 hours was examined, and the results are shown in Table 3.

[0178]

[Table 3]

As is clear from Table 3, Examples 21 to 2
The thin secondary battery of No. 3 has a residual carbon dioxide gas amount of 1 mL or less after the high-temperature storage test, and has a smaller swelling of the container at the time of initial charging and high-temperature storage than the secondary battery of Comparative Example 3;
It can be seen that the capacity retention rate during the cycle is high.

In the first to twentieth embodiments, the opening valve 23 is formed on the bottom surface of the outer can 2.
For example, it can be formed on the side surface of the outer can 2, on the lid 3, or the like.

In Examples 1 to 20 described above, an electrode group having a structure in which a laminate including a positive electrode and a negative electrode and a separator disposed between the positive electrode and the negative electrode is wound into a flat shape is used. Although the example has been described, the shape of the electrode group is not particularly limited. For example, a spiral electrode group in which the laminate is spirally wound, and as shown in FIG. Flat electrode group obtained by bending five times while interposing a negative electrode, as shown in FIG.
And a positive electrode 8 may be used, for example, a stacked electrode group in which the separators 7 are interposed therebetween and alternately.

[0182]

As described above in detail, according to the nonaqueous electrolyte secondary battery according to the present invention, it is possible to suppress an increase in internal pressure due to carbon dioxide gas generated by a decomposition reaction of the nonaqueous electrolyte, thereby improving safety and satisfactory performance. A remarkable effect such as improvement of the discharge cycle life can be obtained.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view showing a prismatic lithium ion secondary battery of Example 1. FIG.

FIG. 2 is a perspective view showing an outer can of the prismatic lithium ion secondary battery of FIG.

FIG. 3 is a sectional view taken along the line III-III in FIG. 2;

FIG. 4 is a partially cutaway perspective view showing a prismatic lithium ion secondary battery of Example 6.

FIG. 5 is a perspective view showing an electrode group of the prismatic lithium ion secondary battery in FIG. 4;

FIG. 6 is a plan view showing a thin lithium ion secondary battery of Example 21.

FIG. 7 is a sectional view showing the thin lithium ion secondary battery of FIG. 6;

FIG. 8 is an enlarged sectional view showing a portion A in FIG. 7;

FIG. 9 is a side view showing another example of the electrode group of the nonaqueous electrolyte secondary battery according to the present invention.

FIG. 10 is a side view showing still another example of the electrode group of the nonaqueous electrolyte secondary battery according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Closed container, 2 ... Outer can, 3 ... Lid, 4 ... Insulating film, 5 ... Electrode group, 6 ... Negative electrode, 7 ... Separator, 8 ... Positive electrode, 9 ... Spacer, 23 ... Opening valve, 24 ... Carbon dioxide gas Absorption layer, 25: Carbon dioxide gas absorption sheet, 31: Closed container, 32: Electrode group, 33: Carbon dioxide gas absorption layer, 35: Separator, 38: Positive electrode, 41: Negative electrode.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Asako Sato 8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Prefecture Inside the Toshiba Yokohama Office (72) Inventor Shoji Kozuka 1-1-1, Komukai Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Inside the Toshiba R & D Center (72) Inventor Hiroshi Nakanishi 1 at Komukai Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa F-term in the Toshiba R & D Center (Reference) 5H029 AJ05 AJ12 AK02 AK03 AK05 AL01 AL02 AL04 AL06 AL07 AL12 AM00 AM02 AM03 AM04 AM05 AM07 AM16 CJ08 CJ22 CJ23 DJ02 DJ04 DJ08 DJ10 EJ03 EJ12 EJ14 HJ01 HJ19 5H050 AA07 AA15 BA17 CA02 CA08 CA09 CA11 CB01 CB02 CB04 CB07 CB08 CB12 DA15 EA12 GA10 HA22

Claims (5)

[Claims] 1. A non-aqueous electrolyte comprising a closed container, a positive electrode stored in the closed container, a negative electrode stored in the closed container, and a non-aqueous electrolyte stored in the closed container. In the secondary battery, a non-aqueous solution characterized in that a lithium composite oxide that absorbs carbon dioxide is present in the closed container, and the lithium composite oxide is present in an amount of 4 mg or less per 1 mAh of theoretical battery capacity. Electrolyte secondary battery. 2. A non-aqueous electrolyte comprising a closed container, a positive electrode stored in the closed container, a negative electrode stored in the closed container, and a non-aqueous electrolyte stored in the closed container. In a secondary battery, the nonaqueous electrolyte contains a lithium composite oxide that absorbs carbon dioxide gas. 3. A non-aqueous electrolyte comprising a closed container, a positive electrode stored in the closed container, a negative electrode stored in the closed container, and a non-aqueous electrolyte stored in the closed container. In the following battery, the non-aqueous electrolyte secondary battery is characterized in that the negative electrode contains a lithium composite oxide that absorbs carbon dioxide gas. 4. A non-aqueous electrolyte secondary battery comprising a closed container, an electrode group housed in the closed container, including a positive electrode and a negative electrode, and a non-aqueous electrolyte housed in the closed container. In the space existing between the closed container and the electrode group,
A non-aqueous electrolyte secondary battery comprising a carbon dioxide absorption layer containing a lithium composite oxide. 5. The non-aqueous electrolyte secondary battery according to claim 1, wherein the lithium composite oxide generates lithium carbonate (Li ₂ CO ₃ ) by absorbing carbon dioxide gas.