JP2002203562A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-aqueous electrolyte secondary battery whose capacity and electricity recharging/discharging cycle characteristic are improved. SOLUTION: The non-aqueous electrolyte secondary battery is provided with an active-material containing layer, a positive electrode which has a collector by which the above active material containing layer is held, a negative electrode which has a layer containing a substance that stores and discharges of lithium and the collector by which the above layer is held, and a non-aqueous electrolyte, wherein a protection layer containing at least one kind of material chosen from a precious metal, an alloy, a conductive ceramics, a semiconductor, an organic semiconductor, and a conductive polymer is formed in the surface of the collector of at least one electrode among the above positive electrode and the above negative electrode.

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. This battery comprises a positive electrode having an active material-containing layer containing a lithium-containing composite oxide such as lithium cobalt oxide (LiCoO ₂ ) and a current collector on which the active material-containing layer is supported, and a graphite material or a carbonaceous material. A negative electrode containing a carbonaceous material such as a material, and a liquid nonaqueous electrolyte made of an organic solvent in which a lithium salt is dissolved are provided. Inexpensive aluminum foil is often used for the positive electrode current collector of this lithium ion secondary battery.

As a lithium salt contained in a nonaqueous electrolyte of a lithium ion secondary battery, LiN (CF ₃ S
When an imide salt such as O ₂ ) ₂ is used, the thermal stability and chemical stability of the non-aqueous electrolyte are enhanced, and a stable protective film is formed on the surface of the negative electrode. The non-aqueous solvent is prevented from co-intercalating into the negative electrode with the insertion of. As a result, exfoliation of the carbonaceous material-containing layer of the negative electrode is suppressed, so that charging efficiency, discharge capacity, and charge / discharge cycle characteristics during rapid charging and high current density charging are improved.

However, in a lithium ion secondary battery provided with a nonaqueous electrolyte containing a lithium imide salt, the lithium ion secondary battery is formed on the surface of the positive electrode current collector within a normal operating voltage range (3 V to 4.2 V). Alumina oxide film (Al
₂ O ₃ ) is destroyed by the lithium imide salt, and the current collector is corroded by anodic oxidation. As a result, there arises a problem that the cycle characteristics and capacity of the secondary battery decrease.

When a non-aqueous electrolyte containing a lithium salt such as LiPF _{6 and} an additive {water or hydrofluoric acid (HF)} is used, improvement in the cycle characteristics of the secondary battery is recognized. However, in this non-aqueous electrolyte, hydrofluoric acid is generated by hydrolysis of a lithium salt, and hydrofluoric acid destroys an alumina oxide film present on the surface of an aluminum positive electrode current collector. Anodization occurs.

On the other hand, the surface of a current collector made of aluminum foil is coated with a thermosetting resin in which carbon powder is dispersed,
It has been proposed to form a positive electrode for a polymer lithium secondary battery by laminating an active material layer on the current collector and subjecting the obtained laminate to thermocompression bonding.

However, the thermosetting resin layer in which the carbon powder is dispersed cannot sufficiently suppress the corrosion of the positive electrode current collector by the lithium imide salt or hydrofluoric acid, and has a high capacity and a long life. It has been difficult to obtain a suitable lithium ion secondary battery.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a non-aqueous electrolyte secondary battery having improved capacity and charge / discharge cycle characteristics.

[0009]

A nonaqueous electrolyte secondary battery according to the present invention comprises a positive electrode having an active material-containing layer and a first current collector on which the active material-containing layer is supported;
A layer containing the substance to be released and a second layer on which this layer is carried
In a non-aqueous electrolyte secondary battery including a negative electrode having a current collector and a non-aqueous electrolyte, a surface of at least one of the first current collector and the second current collector is formed on a surface of the current collector. And a protective layer including at least one material selected from a precious metal, an alloy, a conductive ceramic, a semiconductor, an organic semiconductor, and a conductive polymer.

Further, a nonaqueous electrolyte secondary battery according to the present invention provides a current collector containing at least aluminum, a positive electrode having an active material-containing layer supported on the current collector, and a carbonaceous material that stores and releases lithium. In a non-aqueous electrolyte secondary battery comprising a negative electrode and a non-aqueous electrolyte, on the surface of the current collector of the positive electrode, at least one selected from noble metals, alloys, conductive ceramics, semiconductors, organic semiconductors, and conductive polymers. A protective layer containing one kind of material is formed.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION A non-aqueous electrolyte secondary battery according to the present invention comprises a first current collector, a positive electrode having an active material-containing layer supported on the first current collector, and a second current collector. Electric body and the second
And a non-aqueous electrolyte having a layer that contains a substance that absorbs and releases lithium while being supported by the current collector. The surface of at least one of the first current collector and the second current collector has at least one type selected from a noble metal, an alloy, a conductive ceramic, a semiconductor, an organic semiconductor, and a conductive polymer. A protective layer containing a material is formed.

Hereinafter, the positive electrode, the negative electrode, and the non-aqueous electrolyte will be described.

1) Positive electrode This positive electrode is prepared, for example, by suspending a positive electrode active material, a conductive agent and a binder in a suitable solvent, applying the obtained suspension to a first current collector, and drying the resultant. It is produced by applying pressure molding.

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-containing iron oxide, lithium-containing iron oxide, Containing vanadium oxide)
And chalcogen compounds such as titanium disulfide and molybdenum disulfide. Among them, lithium-containing cobalt oxide (for example, LiCoO ₂ ) and lithium-containing nickel cobalt oxide (for example, LiNi _0.8 C
o _0.2 O ₂ ), lithium manganese composite oxide (for example, L
It is preferable to use iMn ₂ O ₄ and LiMnO ₂ ) because a high voltage can be obtained.

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

As the binder, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), ethylene-propylene-diene copolymer (EPDM), styrene-butadiene rubber (SBR) and the like are used. 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, a thin plate mainly composed of aluminum such as an aluminum foil, a stainless steel foil, a nickel foil, a tungsten foil, a copper foil or the like can be used. Among them, it is preferable to use a thin plate mainly composed of aluminum. The thin plate mainly composed of aluminum may contain an aluminum alloy.

It is preferable that a protective layer containing at least one material selected from noble metals, alloys, conductive ceramics, semiconductors, organic semiconductors and conductive polymers be formed on the surface of the current collector. Among such materials, those having high conductivity to lithium ions, excellent stability to non-aqueous electrolyte, and excellent electrochemical stability within the operating potential range of the battery are preferable. Specific examples of the material having such properties will be described below.

Examples of the noble metal include gold, platinum and the like. The protective layer mainly composed of precious metals
For example, it can be formed by electroless plating, cathode sputtering, vacuum evaporation, sintering of salts, spin coating of a noble metal paint, and sintering.

Examples of the alloy include a gold-chromium alloy and a chromium-silicon alloy. The protective layer mainly composed of an alloy can be formed by, for example, a vacuum evaporation method or the like.

As the conductive ceramics, for example,
For example, silicon carbide (SiC), LaCrO _Three, MoSi_TwoEtc.
Can be mentioned. Mainly made of conductive ceramics
The protective layer is formed by, for example, a vacuum deposition method, a sputtering method, or the like.
Can be formed.

As the semiconductor, for example, titanium dioxide (TiO ₂ ), titanium oxide (TiO), tin oxide (Sn
O ₂ ) and strontium titanate (SrTiO ₃ ). The protective layer mainly composed of a semiconductor is, for example, a gas phase pyrolysis method, an anodic oxidation method, a dip coating method, a spray pyrolysis method, a method of sintering after performing screen printing of an organic paste containing titanium oxide nanosized particles. And the like.

Examples of the organic semiconductor include polycyclic aromatic compounds, polyacetylene, carotene, and heat-treated polyacrylonitrile. The protective layer mainly composed of an organic semiconductor can be formed by, for example, recrystallization, sublimation, or the like.

Examples of the conductive polymer include polyaniline, polypyrrole, polyacene, polydisulfide, polyparaphenylene and the like. The protective layer mainly composed of a conductive polymer is, for example, soluble in an organic solvent, is capable of being melted by heat, and is excellent in processability. After casting or applying a mixed solution in which a binder and dopan (aromatic sulfonic acid ester) are dissolved, the resulting solution film can be formed by a method of heating and drying. For the protective layer mainly composed of a soluble conductive polymer, for example, the current collector is immersed in a dilute solution of the soluble conductive polymer, or a dilute solution of the soluble conductive polymer is applied to the surface of the current collector. Can be formed.

Particularly preferred materials for forming the protective layer are gold, platinum, semiconductors, organic semiconductors, and conductive polymers. According to such a material, the protective layer can be formed on a low-melting current collector mainly composed of aluminum at a temperature equal to or lower than the melting point of the current collector.

The thickness of the protective layer is 50 ° or more and 100
It is preferably 0 μm or less. This is due to the following reasons. When the thickness of the protective layer is less than 50 °, it is difficult to sufficiently suppress the anodic oxidation (corrosion) of the current collector, and good conductivity may not be obtained. For this reason, there is a possibility that a nonaqueous electrolyte secondary battery having a high capacity, a long life, and a high charge capacity in rapid charging and high current density charging cannot be obtained. On the other hand, when the thickness of the protective layer exceeds 1000 μm, the weight energy density and the volume energy density of the nonaqueous electrolyte secondary battery may be insufficient. Further, when the thickness of the protective film exceeds 1000μm when using a gold paint film, a conductive polymer thin film or a semiconductor thin film as the protective layer,
There is a possibility that the internal resistance of the positive electrode increases, so that a nonaqueous electrolyte secondary battery having a high capacity, a long life, and a high charge capacity in rapid charging and high current density charging cannot be obtained. A more preferred range of the thickness of the protective layer is 60
0 ° to 10 μm.

2) Negative Electrode This negative electrode is prepared by, for example, kneading a carbonaceous substance that absorbs and releases lithium and a binder in the presence of a solvent, and applying the resulting suspension to a second current collector. After drying, 1 at the desired pressure
It is produced by one-time pressing or multi-stage pressing two to five times.

Examples of the carbonaceous material that occludes / releases lithium include, for example, graphite material or carbonaceous material such as graphite, coke, carbon fiber, spherical carbon, thermosetting resin, isotropic pitch, mesophase pitch, mesophase pitch. 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. Among them, copper foil is preferable.

It is preferable that a protective layer containing at least one material selected from noble metals, alloys, conductive ceramics, semiconductors, organic semiconductors, and conductive polymers be formed on the surface of the current collector. Among such materials, those having high conductivity to lithium ions, excellent stability to non-aqueous electrolyte, and excellent electrochemical stability within the operating potential range of the battery are preferable.

Specific examples of noble metals, alloys, conductive ceramics, semiconductors, organic semiconductors, and conductive polymers, and the method of forming a protective layer using each material are the same as those described in the above-mentioned section on the positive electrode. .

Particularly preferred materials for forming the protective layer are gold, platinum, semiconductors, organic semiconductors, and conductive polymers.

The protective layer has a thickness of 50 ° or more and 100
It is preferably 0 μm or less. This is due to the following reasons. If the thickness of the protective layer is less than 50 °, it becomes difficult to sufficiently suppress the corrosion of the current collector,
Also, good conductivity may not be obtained. For this reason,
There is a possibility that a non-aqueous electrolyte secondary battery having a high capacity, a long life, and a high charge capacity in rapid charging and high current density charging cannot be obtained. On the other hand, when the thickness of the protective layer exceeds 1000 μm, the weight energy density and the volume energy density of the nonaqueous electrolyte secondary battery may be insufficient. When a gold paint film, a conductive polymer thin film, or a semiconductor thin film is used as the protective layer and the thickness of the protective film exceeds 1000 μm, the internal resistance of the negative electrode increases, resulting in high capacity, long life, and rapid There is a possibility that a non-aqueous electrolyte secondary battery capable of obtaining a high charging capacity in charging and high current density charging cannot be obtained. A more preferred range of the thickness of the protective layer is from 600 ° to 10 μm.

The present invention relates to a non-aqueous electrolyte secondary battery having a negative electrode containing a carbonaceous material capable of inserting and extracting lithium, as well as a negative electrode 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) Non-aqueous electrolyte 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.

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 as a solvent for a lithium secondary battery can be used, 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 is 28 at 25 ° C.
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], Bisperfluoroethylsulfonylimidolithic
Um [Li (C_TwoF_FiveSO_Two)_TwoN] and other lithium salts
I can do it. Such electrolytes are selected from the types described above.
Uses one or more lithium salts or two or more lithium salts
can do. Among them, LiCF_ThreeSO_Three, LiN
(CF_ThreeSO_Two)_Two, Li (C_TwoF_FiveSO_Two)_TwoN, LiP
F₆, 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. Such additives include, for example, an organic solvent consisting of at least one selected from the group consisting of vinyl ethylene carbonate (VEC), vinylene carbonate (VC), ethylene sulfite (ES) and propylene sulfite (PS); Hydrofluoric acid (HF) and the like can be mentioned. It is desirable that the volume ratio of the additive to the entire non-aqueous solvent is 5% or less. In particular, from the viewpoint of forming a dense film on the negative electrode surface,
It is more preferable that the volume ratio of the additive to the entire non-aqueous solvent is 0.01% or more and 5% or less.

The non-aqueous electrolyte can contain water. In particular, when water is added when using at least one lithium salt of LiPF ₆ and LiBF ₄ as an electrolyte, a film-forming reaction occurring on the negative electrode surface can be promoted, so that the stability of the protective film is further increased. Can be. The added amount of water is 700 ppm to 1000 ppm
It is desirable to be within the range. If water is contained in the non-aqueous electrolyte, gas is likely to be generated by the electrolysis of water during charging. Therefore, it is preferable to perform charging with the lid of the battery opened.

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.

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.

It is desirable to arrange a separator between the positive electrode and the negative electrode. Hereinafter, the separator 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 not more than 20% 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.

The non-aqueous electrolyte secondary battery according to the present invention described above contains a positive electrode having an active material-containing layer and a current collector on which the active material-containing layer is supported, and a substance that absorbs and releases lithium. In a non-aqueous electrolyte secondary battery including a layer and a current collector on which the layer is carried, and a non-aqueous electrolyte, the surface of the current collector of at least one of the positive electrode and the negative electrode, A protective layer including at least one material selected from a noble metal, an alloy, a conductive ceramic, a semiconductor, an organic semiconductor, and a conductive polymer is formed.

The above-mentioned protective layer mainly composed of a conductive material has conductivity with respect to lithium ions, has high stability with respect to a non-aqueous electrolyte, and has electric conductivity within the operating voltage range of a non-aqueous electrolyte secondary battery. Has chemical stability. Therefore,
According to the non-aqueous electrolyte secondary battery according to the present invention, since the corrosion of the current collector included in at least one of the positive electrode and the negative electrode can be suppressed, the discharge capacity and the charge / discharge cycle characteristics are improved. Can be.

Further, the nonaqueous electrolyte secondary battery according to the present invention has a positive electrode having a current collector containing at least aluminum and an active material-containing layer supported on the current collector, and a carbonaceous material absorbing and releasing lithium. In a non-aqueous electrolyte secondary battery comprising a negative electrode and a non-aqueous electrolyte, on the surface of the current collector of the positive electrode, at least one selected from noble metals, alloys, conductive ceramics, semiconductors, organic semiconductors, and conductive polymers. A protective layer containing one kind of material is formed.

According to such a non-aqueous electrolyte secondary battery,
A non-aqueous electrolyte capable of forming a stable protective film on the negative electrode surface can be selected, and an additive capable of promoting film formation (eg, moisture, hydrofluoric acid)
Can be added to the non-aqueous electrolyte, so that not only the discharge capacity and the charge / discharge cycle characteristics can be improved, but also the charging efficiency during rapid charging and charging at a high current density can be increased.

That is, bistrifluoromethylsulfo
Nylimide lithium [LiN (CF _ThreeSO_Two)_Two],bird
Lithium fluorometasulfonic acid (LiCF_ThreeSO_Three)
And bisperfluoroethylsulfonylimide lithium
[Li (C_TwoF_FiveSO_Two)_TwoN]
Non-aqueous electrolyte containing at least one lithium imide salt
(Hereinafter referred to as non-aqueous electrolyte A) or
LiPF₆And LiBF_FourLess selected from the group consisting of
And one kind of lithium salt and an additive capable of promoting film formation
(For example, water, hydrofluoric acid)
(Hereinafter referred to as non-aqueous electrolyte B)
Can promote the protective film formation reaction occurring on the surface
Therefore, the stability of the protective film can be further improved.

However, the non-aqueous electrolyte A has a problem that the lithium imide salt destroys the alumina oxide film present on the surface of the positive electrode current collector, while the non-aqueous electrolyte B has a problem of LiPF ₆ or LiBF _6. There is a problem that HF generated by hydrolysis of a lithium salt such as ₄ due to moisture breaks an alumina oxide film present on the surface of the positive electrode current collector. Because of such a problem, it was difficult to use the non-aqueous electrolyte A and the non-aqueous electrolyte B as the non-aqueous electrolyte.

As in the present invention, by forming a protective layer containing at least one material selected from noble metals, alloys, conductive ceramics, semiconductors, organic semiconductors and conductive polymers on the surface of the positive electrode current collector, Non-aqueous electrolyte A
Also, when the non-aqueous electrolyte B is used, anodic oxidation of the positive electrode current collector can be suppressed. Therefore, since the non-aqueous electrolyte A and the non-aqueous electrolyte B can be selected as the non-aqueous electrolyte, a highly stable protective film can be formed on the negative electrode surface. As a result, the nonaqueous solvent can be prevented from being mixed into the negative electrode as Li is inserted into the negative electrode by charging, so that the structure of the carbonaceous material of the negative electrode is prevented from being destroyed by the nonaqueous solvent. And the peeling of the carbonaceous material layer on the negative electrode can be prevented. For this reason, the charging efficiency during rapid charging and charging at a high current density can be improved, and the discharge capacity and the charge / discharge cycle life can be increased.

Further, in the non-aqueous electrolyte secondary battery according to the present invention, by setting the thickness of the protective layer to be not less than 50 ° and not more than 1000 μm, corrosion of the current collector can be suppressed while the internal resistance of the secondary battery is kept low. It can be further suppressed.

[0073]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred 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 ; provided that the atomic ratio x is 0 ≦ x ≦ 1) Powder 9
1% by weight, 3% by weight of acetylene black, 3% by weight of graphite, 3% by weight of polyvinylidene fluoride (PVdF) as a binder, and N-methyl-2-solvent
A slurry was prepared by mixing with pyrrolidone (NMP).

On the other hand, a platinum protective layer having a thickness of 600 ° is formed on one surface of a current collector (first current collector) made of an aluminum foil having a thickness of 15 μm by vacuum deposition, and the other surface is formed on the other surface. A platinum protective layer having a thickness of 600 ° was formed by vacuum evaporation.

The obtained slurry is applied on a platinum protective layer of a current collector, dried and pressed to form an active material-containing layer having a density of 3 g / cm ³ on the platinum protective layer of the current collector. Was formed to obtain a positive electrode.

<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 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 an active material-containing layer having a thickness of / cm ³ was supported on a current collector was produced.

<Separator> When the thickness is 25 μm,
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 Nonaqueous Electrolyte> LiN (CF ₃ SO ₂ ) ₂ was added to a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) (mixing volume ratio: 1: 1) to a concentration of 1M. And propylene sulfite (PS) as an organic additive and trioctyl phosphate (TOP) as a surfactant were added to prepare a non-aqueous electrolyte (liquid non-aqueous electrolyte). In the obtained non-aqueous electrolyte, EC, DMC and P
The content of PS in the mixed nonaqueous solvent composed of S was set to 4% by volume, and the ratio of the surfactant to the entire nonaqueous electrolyte was set to 0.5% by volume.

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

The above-mentioned electrode group and the above-mentioned non-aqueous electrolyte were housed in stainless steel bottomed cylindrical containers, respectively, to assemble a cylindrical lithium ion secondary battery having the structure shown in FIGS. 1 and 2.

That is, a cylindrical container 1 made of stainless steel and having a bottom has an insulator 2 disposed at the bottom. The electrode group 3 is housed in the container 1. The electrode group 3 includes:
It has a structure in which a strip formed by laminating the positive electrode 4, the separator 5, the negative electrode 6, and the separator 5 is spirally wound so that the separator 5 is located outside.

The container 1 contains a non-aqueous electrolyte. The insulating paper 7 having a central opening is disposed above the electrode group 3 in the container 1. Insulating sealing plate 8
The sealing plate 8 is fixed to the container 1 by being arranged in the upper opening of the container 1 and caulking the vicinity of the upper opening inward. The positive electrode terminal 9 is fitted in the center of the insulating sealing plate 8. Positive electrode lead 1
0 has one end connected to the positive electrode 4 and the other end connected to the positive electrode terminal 9. The negative electrode 6 is connected to the container 1 as a negative electrode terminal via a negative electrode lead (not shown).

As shown in FIG. 2, the positive electrode 4 has a positive electrode current collector 11, protective layers 12 formed on both surfaces of the positive electrode current collector 11, and an active material carried on each protective layer 12. It has a substance-containing layer 13. Here, the thickness T of the protective layer 12 means the distance between the positive electrode current collector surface 11 and the surface of the active material containing layer 12.

Example 2 A coating material in which gold particles having a particle size of 10 nm or less were dispersed at a concentration of 80% was spin-coated on both surfaces of a 15 μm-thick aluminum foil current collector, and then heated at 160 ° C. for 10 minutes. After drying for 250 minutes at 250 ° C. for 40 minutes, a thickness of 30
A gold protective layer of 00Å was formed.

The positive electrode slurry prepared in the same manner as described in Example 1 was coated on the gold protective layer of the current collector, dried, and pressed to obtain a density on the gold protective layer of the current collector. Formed an active material-containing layer of ³ g / cm ³ to obtain a positive electrode.

A cylindrical lithium ion secondary battery having the same configuration as that of the above-mentioned Example 1 was assembled except that such a positive electrode was used.

Example 3 A 100 μm thick aluminum foil having a thickness of 100 μm was formed on both sides of a current collector made of aluminum foil by vacuum evaporation.
A 0 ° gold protective layer was formed.

The positive electrode slurry prepared in the same manner as described in Example 1 was applied on the gold protective layer of the current collector, dried, and pressed to obtain a density on the gold protective layer of the current collector. Formed an active material-containing layer of ³ g / cm ³ to obtain a positive electrode.

A cylindrical lithium ion secondary battery having the same structure as in Example 1 except that the above positive electrode was used was assembled.

Example 4 An organic paste containing tin oxide nano-sized particles was screen-printed on both sides of a current collector made of an aluminum foil having a thickness of 15 μm and then sintered to form a current collector. A tin oxide (SnO ₂ ) protective layer having a thickness of 3000 ° was formed on each surface.

The positive electrode slurry prepared in the same manner as described in Example 1 was applied on the tin oxide protective layer of the current collector, dried, and pressed to form the positive electrode slurry on the tin oxide protective layer of the current collector. Forming an active material-containing layer having a density of 3 g / cm ³ ,
A positive electrode was obtained.

A cylindrical lithium ion secondary battery having the same structure as that of the above-mentioned Example 1 was assembled except that the above positive electrode was used.

(Example 5) An organic paste containing titanium oxide nano-sized particles was screen-printed on both sides of a current collector made of an aluminum foil having a thickness of 15 μm and then sintered, whereby each of the current collectors was formed. 2500 thickness on the surface
A titanium dioxide (TiO ₂ ) protective layer of Å was formed.

The positive electrode slurry prepared in the same manner as described in Example 1 was applied on the titanium dioxide protective layer of the current collector, then dried and pressed to form a slurry on the titanium dioxide protective layer of the current collector. Then, an active material-containing layer having a density of 3 g / cm ³ was formed to obtain a positive electrode.

A cylindrical lithium ion secondary battery having the same structure as that of the above-mentioned Example 1 was assembled except that such a positive electrode was used.

(Example 6) A 10 μm thick aluminum foil having a thickness of 15 μm was formed on both sides of a current collector by firing at a low temperature.
m (10 ⁵ Å) of a polyparaphenylene protective layer was formed.

The positive electrode slurry prepared in the same manner as described in Example 1 was applied on the polyacetylene protective layer of the current collector, then dried and pressed to obtain a density on the polyacetylene protective layer of the current collector. Formed an active material-containing layer of ³ g / cm ³ to obtain a positive electrode.

A cylindrical lithium ion secondary battery having the same configuration as that of the above-mentioned Example 1 was assembled except that such a positive electrode was used.

(Comparative Example 1) A cylindrical lithium ion secondary battery having the same structure as in Example 1 described above except that no protective layer was formed on the surface of the positive electrode current collector was assembled.

(Comparative Example 2) An epoxy-based thermosetting resin in which 3% by weight of acetylene black powder was dispersed was coated on both sides of a 15 μm-thick aluminum foil current collector with a thickness of 3 μm.
000Å.

The positive electrode slurry prepared in the same manner as described in Example 1 was applied on the thermosetting resin layer of the current collector, dried, and pressed to obtain the thermosetting resin of the current collector. An active material-containing layer having a density of 3 g / cm ³ was formed on the layer to obtain a positive electrode.

A cylindrical lithium ion secondary battery having the same structure as that of the above-mentioned Example 1 was assembled except that such a positive electrode was used.

The obtained secondary batteries of Examples 1 to 6 and Comparative Examples 1 and 2 were initially charged at 100 mA (0.2 mA).
(Corresponding to C) at a constant current and constant voltage of 4.2 V for 10 hours. Next, a constant current discharge of 100 mA was performed (the cutoff voltage was 3.0 V), and the battery capacity was confirmed.
After that, these secondary batteries are charged with 500 mA (equivalent to 1.0 C).
After performing a constant current constant voltage charge to 4.2 V for 3 hours, a charge / discharge cycle test in which a constant current discharge of 3.0 V cut at 500 mA (equivalent to 1.0 C) is performed up to 600 cycles, and the 600th cycle (The discharge capacity at the first cycle is defined as 100%), and the results are shown in Table 1 below. FIG. 3 shows a discharge capacity curve in a charge / discharge cycle test for the secondary batteries of Example 1 and Comparative Example 1.

For the secondary batteries of Examples 1 to 6 and Comparative Examples 1 and 2, those whose initial charge and confirmation of the battery capacity have been completed are separately prepared, and are prepared at 500 mA (corresponding to 1.0 C). After performing constant-current constant-voltage charging up to 2 V for 4 hours, discharging was performed at 100 mA (corresponding to 0.2 C) in a 3.0 V cut, and the discharge capacity during rapid charging was measured. Of the obtained discharge capacities, the discharge capacities of the secondary batteries of Example 1 are defined as 100, and the discharge capacities of the other secondary batteries are represented as:
The results are shown in Table 1 below.

[0106]

[Table 1]

As is clear from Table 1, the noble metal on both sides
Examples 1 to 6 each including a positive electrode current collector on which a protective layer including at least one material selected from alloys, conductive ceramics, semiconductors, organic semiconductors, and conductive polymers was formed.
In the secondary battery, the quick charging efficiency is higher than that of the secondary batteries of Comparative Examples 1 and 2, and the number of cycles at which the capacity retention rate decreases to about 50% is about 400 cycles longer than that of Comparative Examples 1 and 2. Can be. The secondary battery of Comparative Example 1 had a capacity retention of 39% after 200 cycles, while the secondary battery of Comparative Example 2 had a capacity retention of 50% after 200 cycles.

Further, in the above-described embodiment, an example in which a metal can is used as a container for accommodating an electrode group has been described. However, a nonaqueous electrolyte secondary battery using a container formed of a laminated film including at least a resin layer is described. Can be similarly applied.

[0109]

As described in detail above, according to the present invention,
A high-capacity and long-life non-aqueous electrolyte secondary battery can be provided.

[Brief description of the drawings]

FIG. 1 is a partially cutaway sectional view showing a cylindrical lithium ion secondary battery of Example 1.

FIG. 2 is a sectional view showing a positive electrode of the cylindrical lithium ion secondary battery of FIG. 1;

FIG. 3 is a characteristic diagram showing a change in discharge capacity with an increase in the number of charge / discharge cycles in the cylindrical lithium ion secondary batteries of Example 1 and Comparative Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Container, 3 ... Electrode group, 4 ... Positive electrode, 5 ... Separator, 6 ... Negative electrode, 8 ... Sealing plate, 11 ... Positive electrode collector, 12 ... Protective layer, 13 ... Active material containing layer.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shuichi Komatsu 1 Tokoba Toshiba-cho, Koyuki-ku, Kawasaki-shi, Kanagawa Prefecture Inside the Toshiba R & D Center (72) Inventor Asako Sato 8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Address Toshiba Yokohama Office (72) Inventor Nao Shimura 8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Prefecture F-Terminator Toshiba Yokohama Office F-term (Reference) AJ03 AJ05 AK02 AK03 AK05 AL06 AL07 AL08 AM03 AM04 AM05 AM07 BJ02 BJ04 BJ14 CJ22 DJ07 DJ09 EJ01 EJ08 EJ13 HJ05

Claims (5)

[Claims] 1. A positive electrode having an active material-containing layer and a first current collector on which the active material-containing layer is carried, a layer containing a substance that absorbs and releases lithium, and a second electrode on which the layer is carried. In a non-aqueous electrolyte secondary battery including a negative electrode having a current collector and a non-aqueous electrolyte, a surface of at least one of the first current collector and the second current collector A non-aqueous electrolyte secondary battery comprising a protective layer containing at least one material selected from the group consisting of a noble metal, an alloy, a conductive ceramic, a semiconductor, an organic semiconductor, and a conductive polymer. 2. A positive electrode having a current collector containing at least aluminum and an active material-containing layer supported on the current collector, and a negative electrode containing a carbonaceous material that inserts and absorbs lithium.
In a non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte, on the surface of the current collector of the positive electrode, at least one material selected from noble metals, alloys, conductive ceramics, semiconductors, organic semiconductors, and conductive polymers A non-aqueous electrolyte secondary battery characterized by comprising a protective layer containing the same. 3. The non-aqueous electrolyte includes lithium bistrifluoromethylsulfonylimide [LiN (CF ₃ SO ₂ )].
₂ ], lithium trifluorometasulfonate (LiCF <sub>3
3. The</sub> composition according to claim 1, further comprising at least one lithium salt selected from the group consisting of SO ₃ ) and lithium bisperfluoroethylsulfonylimide [Li (C ₂ F ₅ SO ₂ ) ₂ N]. Non-aqueous electrolyte secondary battery. 4. The non-aqueous electrolyte comprises vinyl ethylene carbonate (VEC), vinylene carbonate (VC),
The non-aqueous electrolyte secondary battery according to claim 1 or 2, further comprising at least one organic solvent selected from the group consisting of ethylene sulfite (ES) and propylene sulfite (PS). 5. The protective layer has a thickness of not less than 50 ° and not more than 10 °.
3. The method according to claim 1, wherein the thickness is not more than 00 μm.
The nonaqueous electrolyte secondary battery according to the above item.